Sample records for ga atlanta ia

  1. FUPWG Meeting Agenda - Atlanta, GA | Department of Energy

    Office of Energy Efficiency and Renewable Energy (EERE) Indexed Site

    Atlanta, GA FUPWG Meeting Agenda - Atlanta, GA Energy on My Mind FUPWG Atlanta, GA May 3-4, 2006 Hosted by: AGL Resources Logo May 3-4, 2006 Hosted by AGL Resources Atlanta,...

  2. Siemens Pittsburgh, PA Novelis Corporation Atlanta, GA

    E-Print Network [OSTI]

    McGaughey, Alan

    Industrial Design ­ Shanghai, China Eaton Corporation ­ Pittsburgh, PA CMU, CTTEC ­ PittsburghSiemens ­ Pittsburgh, PA Novelis Corporation ­ Atlanta, GA Expense

  3. Michael J. Poston Atlanta, GA 30307

    E-Print Network [OSTI]

    Orlando, Thomas

    Page | 1 Michael J. Poston Atlanta, GA 30307 Michael.Poston@gatech.edu Cell: 770.561.4756 U.S. Citizen Education PhD Candidate in Chemistry Georgia Institute of Technology, Atlanta, GA August 2007 with Application to Lunar Observations," JGR Planets, 118, 105, doi: 10.1002/jgre.20025. Poston, M. J

  4. In: Proceedings of the 1995 International environmental conference; 1995 May 7-10; Atlanta, GA. Atlanta, GA: TAPPI PRESS: 445-448; 1995.

    E-Print Network [OSTI]

    Abubakr, Said

    . Atlanta, GA: TAPPI PRESS: 445-448; 1995. ENVIRONMENTALLY SOUND ALTERNATIVES FOR UPGRADING MIXED OFFICE-value mixed office waste. Benefits of enzyme deinking include effective toner removal, improved effluent. Benefits of fiber loading include utilization of waste carbon dioxide from stack gases, extended fiber

  5. Advancing Residential Retrofits in Atlanta

    SciTech Connect (OSTI)

    Jackson, Roderick K [ORNL; Kim, Eyu-Jin [Southface Energy Institute; Roberts, Sydney [Southface Energy Institute; Stephenson, Robert [Southface Energy Institute

    2012-07-01T23:59:59.000Z

    This report will summarize the home energy improvements performed in the Atlanta, GA area. In total, nine homes were retrofitted with eight of the homes having predicted source energy savings of approximately 30% or greater based on simulated energy consumption.

  6. 2009 National Electric Transmission Congestion Study- Atlanta Workshop

    Broader source: Energy.gov [DOE]

    On July 29, 2008, DOE hosted a regional pre-study workshop in Atlanta, GA to receive input and suggestions concerning the 2009 National Electric Transmission Congestion Study. The agenda andfull...

  7. Atlanta- Sustainable Development Design Standards

    Broader source: Energy.gov [DOE]

    In December 2003, the City of Atlanta passed a green building [http://www.atlantaga.gov/modules/showdocument.aspx?documentid=547 ordinance] that applies to city-owned facilities and city-funded...

  8. IEEE Energy2030 Atlanta, GA USA

    E-Print Network [OSTI]

    Gross, George

    of an aggregation of battery vehicles for the provision of frequency regulation requiring very fast response times as distributed energy resources that can act both as supply and demand resources. We assess the deployment and energy supply for peak shaving. We also investigate the impacts of the aggregated battery vehicle

  9. atlanta: Topics by E-print Network

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    her own unique Gaucher, Eric 9 GDOT Viaduct at International Boulevard near CNN, Atlanta Engineering Websites Summary: N)TopDeflection,wt(mm) Qt Predicted O-cell top down O-cell...

  10. EECBG Success Story: Atlanta Suburb Greases the Path to Savings...

    Office of Energy Efficiency and Renewable Energy (EERE) Indexed Site

    Atlanta Suburb Greases the Path to Savings with Biodiesel EECBG Success Story: Atlanta Suburb Greases the Path to Savings with Biodiesel December 7, 2011 - 3:33pm Addthis Downtown...

  11. IEEE Energy2030 Atlanta, Georgia, USA

    E-Print Network [OSTI]

    Ratnasamy, Sylvia

    an innovative electric power architecture, rooted in lessons learned from the Internet and microgrids, whichIEEE Energy2030 Atlanta, Georgia, USA 17-18 November 2008 An Architecture for Local Energy-disruptive incremental adoption. Such a system, which we term a "LoCal" grid, is controlled by intelligent power switches

  12. atlanta georgia metropolitan: Topics by E-print Network

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    of 2004. Five notable plumes of SO2, apparently from coal-fired power plants, were Weber, Rodney 12 ACI Spring Convention Atlanta Georgia Engineering Websites Summary:...

  13. Better Buildings Challenge, Atlanta Nears Halfway Mark in Meeting...

    Office of Energy Efficiency and Renewable Energy (EERE) Indexed Site

    Addthis The Energy Department yesterday recognized Atlanta for its progress and leadership in meeting a citywide goal to improve the energy performance of its buildings by 20%...

  14. Dust around Type Ia supernovae

    E-Print Network [OSTI]

    Wang, Lifan

    2005-01-01T23:59:59.000Z

    Dust around Type Ia supernovae Lifan Wang 1,2 LawrenceIa. Subject headings: Supernovae: General, Dust, Extinctionline) bands for Type Ia supernovae. (a), upper panel, shows

  15. atlanta international airport: Topics by E-print Network

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    of Technology 2013-01-01 6 GDOT Viaduct at International Boulevard near CNN, Atlanta Engineering Websites Summary: N)TopDeflection,wt(mm) Qt Predicted O-cell top down O-cell...

  16. atlanta georgia usa: Topics by E-print Network

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    values SECURING AMERICA'S FUTURE 12;0 1Georgia Tech Research Institute Annual Report Bennett, Gisele 9 School of Biology Atlanta, Georgia 30332-0230 USA Biology and Medicine...

  17. Atlanta NAVIGATOR case study. Final report, May 1996--Jun 1997

    SciTech Connect (OSTI)

    Amodei, R.; Bard, E.; Brong, B.; Cahoon, F.; Jasper, K.

    1998-11-01T23:59:59.000Z

    The Atlanta metropolitan region was the location of one of the most ambitious Intelligent Transportation Systems (ITS) deployments in the United States. This deployment included several individual projects--a Central Transportation Management Center (TMC), six Traffic Control Centers (TCC), one Transit Information Center (TIC), the Travel Information Showcase (TIS), and the extension of the Metropolitan Atlanta Rapid Transit Authority (MARTA) rail network and the new high-occupancy vehicle (HOV) lanes on I-85 and I-75. The Atlanta Centennial Olympic Games and Paralympic Games created a focus for these projects. All of these systems were to be brought on line in time for the Olympic Games. This report presents the findings of the NAVIGATOR Case Study and documents the lessons learned from the Atlanta ITS deployment experience in order to improve other ITS deployments in the future. The Case Study focuses on the institutional, programmatic, and technical issues and opportunities from planning and implementing the ITS deployment in Atlanta. The Case Study collected data and information from interviews, observations, focus groups, and documentation reviews. It presents a series of lessons learned and recommendations for enabling successful ITS deployments nationwide.

  18. New approaches for modeling type Ia supernovae

    E-Print Network [OSTI]

    Zingale, Michael; Almgren, Ann S.; Bell, John B.; Day, Marcus S.; Rendleman, Charles A.; Woosley, Stan

    2007-01-01T23:59:59.000Z

    runaway in Type Ia supernovae: How to run away? oIgnition in Type Ia Supernovae. II. A Three- dimensionalnumber modeling of type Ia supernovae. I. hydrodynamics.

  19. Alternative Fuels Data Center: Atlanta Airport Converts Shuttles to CNG

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    AFDC Printable Version Share this resource Send a link to EERE: Alternative Fuels Data Center Home Page to someone by E-mail Share EERE: Alternative Fuels Data Center Home Page on Facebook Tweet about EERE: Alternative Fuels Data Center Home Page on Twitter Bookmark EERE: Alternative1 First Use of Energy for All Purposes (Fuel and Nonfuel), 2002; Level: National5Sales for4,645U.S. DOE Office511041cloth DocumentationProducts (VAP)MassachusettsExperimental VehicleNaturalPropaneAtlanta Airport

  20. New approaches for modeling type Ia supernovae

    E-Print Network [OSTI]

    Zingale, Michael; Almgren, Ann S.; Bell, John B.; Day, Marcus S.; Rendleman, Charles A.; Woosley, Stan

    2007-01-01T23:59:59.000Z

    ich and J. Stein. On the thermonuclear runaway in Type IaSmall-Scale Stability of Thermonuclear Flames o in Type IaS. E. Woosley. The thermonuclear explosion of chandrasekhar

  1. Community transportation : alternative transportation provision in a low-income neighborhoods in southeast Atlanta

    E-Print Network [OSTI]

    Alexander, James W., 1977-

    2004-01-01T23:59:59.000Z

    Regional transit agencies are ineffective at meeting many of the basic transportation needs of a clustered "Study Area" of low-income Atlanta neighborhoods. For transit dependant residents in the Study Area, getting to the ...

  2. Building America Case Study: Ground Source Heat Pump Research, TaC Studios Residence, Atlanta, Georigia (Fact Sheet)

    SciTech Connect (OSTI)

    Not Available

    2014-09-01T23:59:59.000Z

    As part of the NAHB Research Center Industry Partnership, Southface partnered with TaC Studios, an Atlanta based architecture firm specializing in residential and light commercial design, on the construction of a new test home in Atlanta, GA in the mixed-humid climate. This home serves as a residence and home office for the firm's owners, as well as a demonstration of their design approach to potential and current clients. Southface believes the home demonstrates current best practices for the mixed-humid climate, including a building envelope featuring advanced air sealing details and low density spray foam insulation, glazing that exceeds ENERGY STAR requirements, and a high performance heating and cooling system. Construction quality and execution was a high priority for TaC Studios and was ensured by a third party review process. Post construction testing showed that the project met stated goals for envelope performance, an air infiltration rate of 2.15 ACH50. The homeowner's wished to further validate whole house energy savings through the project's involvement with Building America and this long-term monitoring effort. As a Building America test home, this home was evaluated to detail whole house energy use, end use loads, and the efficiency and operation of the ground source heat pump and associated systems. Given that the home includes many non-typical end use loads including a home office, pool, landscape water feature, and other luxury features not accounted for in Building America modeling tools, these end uses were separately monitored to determine their impact on overall energy consumption.

  3. Secretary Moniz's Keynote at the Sam Nunn Policy Forum in Atlanta, GA --

    Office of Energy Efficiency and Renewable Energy (EERE) Indexed Site

    AFDC Printable Version Share this resource Send a link to EERE: Alternative Fuels Data Center Home Page to someone by E-mail Share EERE: Alternative Fuels Data Center Home Page on Facebook Tweet about EERE: Alternative Fuels Data Center Home Page on Twitter Bookmark EERE: Alternative Fuels Data Center Home Page on Google Bookmark EERE: Alternative Fuels Data Center Home Page onYouTube YouTube Note: Since the.pdfBreakingMay 2015ParentsMiddle SchoolPhysicsDeliveryforDepartmentAcademy ofFirstAs

  4. Secretary Moniz's Keynote at the Sam Nunn Policy Forum in Atlanta, GA --

    Office of Energy Efficiency and Renewable Energy (EERE) Indexed Site

    AFDC Printable Version Share this resource Send a link to EERE: Alternative Fuels Data Center Home Page to someone by E-mail Share EERE: Alternative Fuels Data Center Home Page on Facebook Tweet about EERE: Alternative Fuels Data Center Home Page on Twitter Bookmark EERE: Alternative Fuels Data Center Home Page on Google Bookmark EERE: Alternative Fuels DataDepartment of Energy Your Density Isn'tOriginEducationVideo »Usage »DownloadSolarSequestrationofPreparedEnergy Secretary MonizofAs

  5. Remarks by Federal Blue Ribbon Commission J. David Jameson Atlanta, GA

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    AFDC Printable Version Share this resource Send a link to EERE: Alternative Fuels Data Center Home Page to someone by E-mail Share EERE: Alternative Fuels Data Center Home Page on Facebook Tweet about EERE: Alternative Fuels Data Center Home Page on Twitter Bookmark EERE: Alternative1 First Use of Energy for All Purposes (Fuel and Nonfuel), 2002; Level:Energy: Grid Integration Redefining What's PossibleRadiation Protection Technical s o Freiberge s 3 c/) Release for Announcement Relocation

  6. Type Ia Supernova Explosion Models

    E-Print Network [OSTI]

    W. Hillebrandt; J. C. Niemeyer

    2000-06-21T23:59:59.000Z

    Because calibrated light curves of Type Ia supernovae have become a major tool to determine the local expansion rate of the Universe and also its geometrical structure, considerable attention has been given to models of these events over the past couple of years. There are good reasons to believe that perhaps most Type Ia supernovae are the explosions of white dwarfs that have approached the Chandrasekhar mass, M_ch ~ 1.39 M_sun, and are disrupted by thermonuclear fusion of carbon and oxygen. However, the mechanism whereby such accreting carbon-oxygen white dwarfs explode continues to be uncertain. Recent progress in modeling Type Ia supernovae as well as several of the still open questions are addressed in this review. Although the main emphasis will be on studies of the explosion mechanism itself and on the related physical processes, including the physics of turbulent nuclear combustion in degenerate stars, we also discuss observational constraints.

  7. Turbulence-Flame Interactions in Type Ia Supernovae

    E-Print Network [OSTI]

    Aspden, Andrew J; Lawrence Berkeley National Laboratory, 1 Cyclotron Road, MS 50A-1148, Berkeley, CA 94720 (Authors 1, 2 & 3); Department of Astronomy and Astrophysics, University of California at Santa Cruz, Santa Cruz, CA 95064 (Author 4); Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794 (Author 5)

    2008-01-01T23:59:59.000Z

    Interactions in Type Ia Supernovae A. J. Aspden 1 , J. B.involved in type Ia supernovae (SN Ia) requires the use of ?generated by RT in type Ia supernovae should obey Bolgiano-

  8. Ideal bandpasses for type Ia supernova cosmology

    E-Print Network [OSTI]

    Davis, Tamara M.; Schmidt, Brian P.; Kim, Alex G.

    2005-01-01T23:59:59.000Z

    diversity of type Ia Supernovae, in preparation. Kim, A.error in measurements of supernovae depends on a periodicABSTRACT To use type Ia supernovae as standard candles for

  9. Rates and progenitors of type Ia supernovae

    E-Print Network [OSTI]

    Wood-Vasey, William Michael

    2004-01-01T23:59:59.000Z

    Supernovae . . . . . . . . . . . . . . . . . . . .Supernovae Found 5.1 Introduction . . . . . . . . . . . .1.2 Non-Type Ia Supernovae . . . . . . . . . . . . . . . 1.3

  10. Appendix 14-Ia Coach's Employment

    E-Print Network [OSTI]

    Swaddle, John

    Appendix 14-Ia Coach's Employment Non Institutional Camp/Clinic Revised August 2010 ATHLETICS STAFF MEMBERS' EMPLOYMENT AT A NON-WILLIAM & MARY CAMP/CLINIC Coach's Name: ______ Sport) No athletics department staff member may be employed (salary or volunteer) in any capacity by a camp or clinic

  11. Type Ia Supernova Carbon Footprints

    E-Print Network [OSTI]

    Thomas, R C; Aragon, C; Antilogus, P; Bailey, S; Baltay, C; Bongard, S; Buton, C; Canto, A; Childress, M; Chotard, N; Copin, Y; Fakhouri, H K; Gangler, E; Hsiao, E Y; Kerschhaggl, M; Kowalski, M; Loken, S; Nugent, P; Paech, K; Pain, R; Pecontal, E; Pereira, R; Perlmutter, S; Rabinowitz, D; Rigault, M; Rubin, D; Runge, K; Scalzo, R; Smadja, G; Tao, C; Weaver, B A; Wu, C; Brown, P J; Milne, P A

    2011-01-01T23:59:59.000Z

    We present convincing evidence of unburned carbon at photospheric velocities in new observations of 5 Type Ia supernovae (SNe Ia) obtained by the Nearby Supernova Factory. These SNe are identified by examining 346 spectra from 124 SNe obtained before +2.5 d relative to maximum. Detections are based on the presence of relatively strong C II 6580 absorption "notches" in multiple spectra of each SN, aided by automated fitting with the SYNAPPS code. Four of the 5 SNe in question are otherwise spectroscopically unremarkable, with ions and ejection velocities typical of SNe Ia, but spectra of the fifth exhibits high-velocity (v > 20,000 km/s) Si II and Ca II features. On the other hand, the light curve properties are preferentially grouped, strongly suggesting a connection between carbon-positivity and broad band light curve/color behavior: Three of the 5 have relatively narrow light curves but also blue colors, and a fourth may be a dust-reddened member of this family. Accounting for signal-to-noise and phase, we ...

  12. The Value of Optimization in Dynamic Ride-Sharing: a Simulation Study in Metro Atlanta

    E-Print Network [OSTI]

    Erera, Alan

    of travelers per vehicle trip by effective usage of empty car seats by ride-sharing may of course enhance, and pollution. Moreover, ride-sharing allows users to share car-related expenses such as fuel costs. 1 #12;ByThe Value of Optimization in Dynamic Ride-Sharing: a Simulation Study in Metro Atlanta Niels Agatz

  13. Rates and Progenitors of Type Ia Supernovae

    E-Print Network [OSTI]

    William Michael Wood-Vasey

    2005-05-30T23:59:59.000Z

    The remarkable uniformity of Type Ia supernovae (SNe Ia) has allowed astronomers to use them as distance indicators to measure the properties and expansion history of the Universe. However, SNe Ia exhibit intrinsic variation in both their spectra and observed brightness. To reduce these systematic uncertainties, we need a deeper understanding of the observed variations in SNe Ia. Toward this end, the Nearby Supernova Factory (SNfactory) has been designed to discover hundreds of SNe Ia in a systematic and automated fashion and study them in detail. A prototype run of the SNfactory search pipeline conducted from 2002 to 2003 discovered 83 SNe at a final rate of 12 SNe/month. A large, homogeneous search of this scale offers an excellent opportunity to measure the rate of SNe Ia. This dissertation presents a new method for analyzing the true sensitivity of a multi-epoch supernova search and finds a SN Ia rate from $z\\sim0.01$--0.1 of $r_V = 4.26 (+1.39 -1.93) (+0.10 - 0.10)$ SNe Ia/yr/Mpc$^3$ from a preliminary analysis of a subsample of the SNfactory prototype search. Several unusual supernovae were found in the course of the SNfactory prototype search. One in particular, SN 2002ic, was the first SN Ia to exhibit convincing evidence for a circumstellar medium and offers valuable insight into the progenitors of SNe Ia.

  14. Low Mach Number Modeling of Type Ia Supernovae. II. Energy Evolution

    E-Print Network [OSTI]

    Almgren, Ann S.; Bell, John B.; Rendleman, Charles A.; Zingale, Mike

    2006-01-01T23:59:59.000Z

    Number Modeling of Type Ia Supernovae. II. Energy EvolutionIa. Subject headings: supernovae: general white dwarfs the ignition of Type Ia supernovae (SNe Ia) is critical to

  15. Turbulent Combustion in Type Ia Supernova Models

    E-Print Network [OSTI]

    F. K. Roepke; W. Hillebrandt

    2006-09-15T23:59:59.000Z

    We review the astrophysical modeling of type Ia supernova explosions and describe numerical methods to implement numerical simulations of these events. Some results of such simulations are discussed.

  16. Summary of Needs and Opportunities from the 2011 Residential Energy Efficiency Stakeholders Meeting: Atlanta, Georgia -- March 16-18, 2011

    SciTech Connect (OSTI)

    Not Available

    2011-05-01T23:59:59.000Z

    This summary report outlines needs and issues for increasing energy efficiency of new and existing U.S homes, as identified at the U.S Department of Energy Building America program Spring 2011 stakeholder meeting in Atlanta, Georgia.

  17. Theoretical cosmic Type Ia supernova rates

    E-Print Network [OSTI]

    R. Valiante; F. Matteucci; S. Recchi; F. Calura

    2009-03-16T23:59:59.000Z

    The aim of this work is the computation of the cosmic Type Ia supernova rates at very high redshifts (z>2). We adopt various progenitor models in order to predict the number of explosions in different scenarios for galaxy formation and to check whether it is possible to select the best delay time distribution model, on the basis of the available observations of Type Ia supernovae. We also computed the Type Ia supernova rate in typical elliptical galaxies of different initial luminous masses and the total amount of iron produced by Type Ia supernovae in each case. It emerges that: it is not easy to select the best delay time distribution scenario from the observational data and this is because the cosmic star formation rate dominates over the distribution function of the delay times; the monolithic collapse scenario predicts an increasing trend of the SN Ia rate at high redshifts whereas the predicted rate in the hierarchical scheme drops dramatically at high redshift; for the elliptical galaxies we note that the predicted maximum of the Type Ia supernova rate depends on the initial galactic mass. The maximum occurs earlier (at about 0.3 Gyr) in the most massive ellipticals, as a consequence of downsizing in star formation. We find that different delay time distributions predict different relations between the Type Ia supernova rate per unit mass at the present time and the color of the parent galaxies and that bluer ellipticals present higher supernova Type Ia rates at the present time.

  18. Atlanta Centennial Olympic Games and Paralympic Games event study, 1996. Final report, July 1996--August 1996

    SciTech Connect (OSTI)

    Amodei, R.; Bard, E.; Brong, B.; Cahoon, F.; Jasper, K.

    1998-11-01T23:59:59.000Z

    The Atlanta metropolitan region was the location of one of the most ambitious Intelligent Transportation Systems (ITS) deployments in the United States. This deployment included several individual projects--a Central Transportation Management Center (TMC), six Traffic Control Centers (TCCs), one Transit Information Center (TIC), The Travel Information Showcase (TIS), and the extension of the Metropolitan Atlanta Rapid Transit Authority (MARTA) Rail network and the new high-occupancy vehicle (HOV) lanes on I-85 and I-75. The 1996 Atlanta Centennial Olympic Games and Paralympic Games created a focus for these projects. All of these systems were to be brought on-line in time for the Olympic Games. This report presents the findings of the 1996 Olympic and Paralympic Games Events Study--a compilation of findings of system performance, the benefits realized, and the lessons learned during their operations over the event period. The study assessed the performance of the various Travel Demand Management (TDM) plans employed for Olympic Games traffic management.

  19. Supersoft Sources as SN Ia Progenitors

    E-Print Network [OSTI]

    Greiner, Jochen

    of the existence of supersoft X­ray sources. It is argued that SNe Ia are thermonuclear explosions of accreting C is that they represent thermonuclear disruptions of mass accreting white dwarfs (WDs). Thus, the basic ingredient

  20. Nucleosynthesis in Type Ia Supernovae

    E-Print Network [OSTI]

    K. Nomoto; K. Iwamoto; N. Nakasato; F. -K. Thielemann; F. Brachwitz; T. Tsujimoto; Y. Kubo; N. Kishimoto

    1997-06-03T23:59:59.000Z

    Among the major uncertainties involved in the Chandrasekhar mass models for Type Ia supernovae are the companion star of the accreting white dwarf (or the accretion rate that determines the carbon ignition density) and the flame speed after ignition. We present nucleosynthesis results from relatively slow deflagration (1.5 - 3 % of the sound speed) to constrain the rate of accretion from the companion star. Because of electron capture, a significant amount of neutron-rich species such as ^{54}Cr, ^{50}Ti, ^{58}Fe, ^{62}Ni, etc. are synthesized in the central region. To avoid the too large ratios of ^{54}Cr/^{56}Fe and ^{50}Ti/^{56}Fe, the central density of the white dwarf at thermonuclear runaway must be as low as \\ltsim 2 \\e9 \\gmc. Such a low central density can be realized by the accretion as fast as $\\dot M \\gtsim 1 \\times 10^{-7} M_\\odot yr^{-1}$. These rapidly accreting white dwarfs might correspond to the super-soft X-ray sources.

  1. Atlanta Suburb Greases the Path to Savings with Biodiesel | Department of

    Office of Energy Efficiency and Renewable Energy (EERE) Indexed Site

    AFDC Printable Version Share this resource Send a link to EERE: Alternative Fuels Data Center Home Page to someone by E-mail Share EERE: Alternative Fuels Data Center Home Page on Facebook Tweet about EERE: Alternative Fuels Data Center Home Page on Twitter Bookmark EERE: Alternative Fuels Data Center Home Page on Google Bookmark EERE: Alternative Fuels DataDepartment of Energy Your Density Isn't Your Destiny: The FutureComments from Tarasa U.S.LLCEnergyEnergy Atlanta Suburb Greases

  2. Proceedings of the ASME Aerospace Division, AD-Vol. 52, ASME Winter Annual Meeting, Atlanta, GA, Nov. 1996

    E-Print Network [OSTI]

    Giurgiutiu, Victor

    )), (Giurgiutiu, et al., 1996) is now developed to scaled up on full-scale structural elements. The concepts for large scale tagged composite inspection build on the previously developed small scale concepts, Nov. 1996 ACTIVE TAGGING NON-DESTRUCTIVE EVALUATION TECHNIQUES FOR FULL-SCALE STRUCTURAL COMPOSITE

  3. Survey gives clues to origin of Type Ia supernovae | EurekAlert! Science News

    E-Print Network [OSTI]

    ... to origin of Type Ia supernovae ... Type Ia supernovae still not understood despite their ... s behind the Type Ia supernovae they use to measure distances ...

  4. New findings show some Type Ia supernovae linked to novae | EurekAlert! Science News

    E-Print Network [OSTI]

    ... findings show some Type Ia supernovae linked to novae ... least some thermonuclear (Type Ia) supernovae come from a recurrent nova ... originators of other Type Ia supernovae . ...

  5. Verifying the Cosmological Utility of Type Ia Supernovae: Implications of a Dispersion in the Ultraviolet Spectra

    E-Print Network [OSTI]

    2008-01-01T23:59:59.000Z

    Utility of Type Ia Supernovae: Implications of a Dispersionheadings: surveys supernovae: general cosmologicalparameters Introduction Supernovae of Type Ia (SNe Ia) are

  6. Type Ia Supernova Intrinsic Magnitude Dispersion and the Fitting of Cosmological Parameters

    E-Print Network [OSTI]

    Kim, Alex G

    2011-01-01T23:59:59.000Z

    Applied to Type Ia supernovae, my strategy provides adata sets. Subject headings: Supernovae: Data Analysis andhomogeneous nature of Type Ia supernovae (SNe Ia) makes them

  7. Atlanta Survey

    Annual Energy Outlook 2013 [U.S. Energy Information Administration (EIA)]

    AFDC Printable Version Share this resource Send a link to EERE: Alternative Fuels Data Center Home Page to someone by E-mail Share EERE: Alternative Fuels Data Center Home Page on Facebook Tweet about EERE: Alternative Fuels Data Center Home Page on Twitter Bookmark EERE: Alternative1 First Use of Energy for All Purposes (Fuel and Nonfuel), 2002; Level: National5Sales for4,645 3,625 1,006 492 742 33 111 1,613 122 40Coal Stocks at CommercialDecade Year-0Proved Reserves (Billion Cubic3)/1Profile

  8. Visualizing Buoyant Burning Bubbles in Type Ia Supernovae at...

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    Burning in Supernovae Buoyant Burning Bubbles in Type Ia Supernovae bubble-s.jpeg Flame ignition in type Ia supernovae leads to isolated bubbles of burning buoyant fluid. As a...

  9. Closest Type Ia Supernova in Decades Solves a Cosmic Mystery

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    PTF 11kly as it appeared in the nearby M101 galaxy. (Images: Peter Nugent) Type Ia supernovae (SN Ia's) are the extraordinarily bright and remarkably similar "standard candles"...

  10. China Today IAS 2123.001

    E-Print Network [OSTI]

    Oklahoma, University of

    China Today IAS 2123.001 Kevin Carrico Tuesdays & Thursdays 10:30 am -11:45 am Approved for Non-Western culture credit Everyone knows that China today is a "rising superpower," but the real story of China's modern history is considerably more complex. This course looks beyond the headlines to rediscover China

  11. Probing Cosmological Isotropy With Type IA Supernovae

    E-Print Network [OSTI]

    Bengaly, C A P; Alcaniz, J S

    2015-01-01T23:59:59.000Z

    We investigate the validity of the Cosmological Principle by mapping the cosmological parameters $H_0$ and $q_0$ through the celestial sphere. In our analysis, performed in a low-redshift regime to follow a model-independent approach, we use two compilations of type Ia Supernovae (SNe Ia), namely the Union2.1 and the JLA datasets. Firstly, we show that the angular distributions for both SNe Ia datasets are statistically anisotropic at high confidence level ($p$-value $<$ 0.0001), in particular the JLA sample. Then we find that the cosmic expansion and acceleration are mainly of dipolar type, with maximal anisotropic expansion [acceleration] pointing towards $(l,b) \\simeq (326^{\\circ},12^{\\circ})$ [$(l,b) \\simeq (174^{\\circ},27^{\\circ})$], and $(l,b) \\simeq (58^{\\circ},-60^{\\circ})$ [$(l,b) \\simeq (225^{\\circ},51^{\\circ})$] for the Union2.1 and JLA data, respectively. Secondly, we use a geometrical method to test the hypothesis that the non-uniformly distributed SNe Ia events could introduce anisotropic imp...

  12. Models of Type Ia Supernova Explosions

    E-Print Network [OSTI]

    J. C. Niemeyer; M. Reinecke; W. Hillebrandt

    2002-03-21T23:59:59.000Z

    Type Ia supernovae have become an indispensable tool for studying the expansion history of the universe, yet our understanding of the explosion mechanism is still incomplete. We describe the variety of discussed scenarios, sketch the most relevant physics, and report recent advances in multidimensional simulations of Chandrasekhar mass white dwarf explosions.

  13. Models of Type Ia Supernova Explosions

    E-Print Network [OSTI]

    Niemeyer, J C; Hillebrandt, W

    2002-01-01T23:59:59.000Z

    Type Ia supernovae have become an indispensable tool for studying the expansion history of the universe, yet our understanding of the explosion mechanism is still incomplete. We describe the variety of discussed scenarios, sketch the most relevant physics, and report recent advances in multidimensional simulations of Chandrasekhar mass white dwarf explosions.

  14. The Outermost Ejecta of Type Ia Supernovae

    E-Print Network [OSTI]

    Masaomi Tanaka; Paolo A. Mazzali; Stefano Benetti; Ken'ichi Nomoto; Nancy Elias-Rosa; Rubina Kotak; Giuliano Pignata; Vallery Stanishev; Stephan Hachinger

    2007-12-17T23:59:59.000Z

    The properties of the highest velocity ejecta of normal Type Ia supernovae (SNe Ia) are studied via models of very early optical spectra of 6 SNe. At epochs earlier than 1 week before maximum, SNe with a rapidly evolving Si II 6355 line velocity (HVG) have a larger photospheric velocity than SNe with a slowly evolving Si II 6355 line velocity (LVG). Since the two groups have comparable luminosities, the temperature at the photosphere is higher in LVG SNe. This explains the different overall spectral appearance of HVG and LVG SNe. However, the variation of the Ca II and Si II absorptions at the highest velocities (v >~ 20,000 km/s) suggests that additional factors, such as asphericity or different abundances in the progenitor white dwarf, affect the outermost layers. The C II 6578 line is marginally detected in 3 LVG SNe, suggesting that LVG undergo less intense burning. The carbon mass fraction is small, only less than 0.01 near the photosphere, so that he mass of unburned C is only <~ 0.01 Msun. Radioactive 56Ni and stable Fe are detected in both LVG and HVG SNe. Different Fe-group abundances in the outer layers may be one of the reasons for spectral diversity among SNe Ia at the earliest times. The diversity among SNe Ia at the earliest phases could also indicate an intrinsic dispersion in the width-luminosity relation of the light curve.

  15. A threat-based definition of IA- and IA-enabled products.

    SciTech Connect (OSTI)

    Shakamuri, Mayuri; Schaefer, Mark A.; Campbell, Philip LaRoche

    2010-07-01T23:59:59.000Z

    This paper proposes a definition of 'IA and IA-enabled products' based on threat, as opposed to 'security services' (i.e., 'confidentiality, authentication, integrity, access control or non-repudiation of data'), as provided by Department of Defense (DoD) Instruction 8500.2, 'Information Assurance (IA) Implementation.' The DoDI 8500.2 definition is too broad, making it difficult to distinguish products that need higher protection from those that do not. As a consequence the products that need higher protection do not receive it, increasing risk. The threat-based definition proposed in this paper solves those problems by focusing attention on threats, thereby moving beyond compliance to risk management. (DoDI 8500.2 provides the definitions and controls that form the basis for IA across the DoD.) Familiarity with 8500.2 is assumed.

  16. A threat-based definition of IA and IA-enabled products.

    SciTech Connect (OSTI)

    Shakamuri, Mayuri; Schaefer, Mark A.; Campbell, Philip LaRoche

    2010-09-01T23:59:59.000Z

    This paper proposes a definition of 'IA and IA-enabled products' based on threat, as opposed to 'security services' (i.e., 'confidentiality, authentication, integrity, access control or non-repudiation of data'), as provided by Department of Defense (DoD) Instruction 8500.2, 'Information Assurance (IA) Implementation.' The DoDI 8500.2 definition is too broad, making it difficult to distinguish products that need higher protection from those that do not. As a consequence the products that need higher protection do not receive it, increasing risk. The threat-based definition proposed in this paper solves those problems by focusing attention on threats, thereby moving beyond compliance to risk management. (DoDI 8500.2 provides the definitions and controls that form the basis for IA across the DoD.) Familiarity with 8500.2 is assumed.

  17. Improved InGaN/GaN light-emitting diodes with a p-GaN/n-GaN/p-GaN/n-GaN/p-GaN current-

    E-Print Network [OSTI]

    Demir, Hilmi Volkan

    Improved InGaN/GaN light-emitting diodes with a p-GaN/n-GaN/p-GaN/n-GaN/p-GaN current- spreading experimental and theoretical studies on the InGaN/GaN light-emitting diodes (LEDs) with optical output power and external quantum efficiency (EQE) levels substantially enhanced by incorporating p-GaN/n-GaN/p-GaN/n-GaN/p-GaN

  18. ARCS Additional FirstYear PhD Student Award The Atlanta chapter of ARCS has just informed me that they will honor us with another graduate student

    E-Print Network [OSTI]

    Arnold, Jonathan

    ARCS Additional FirstYear PhD Student Award The Atlanta chapter of ARCS has just informed me meets their definition listed above. Sincerely, Harry A. Dailey, Ph.D. Professor and Director

  19. SHOCK BREAKOUT FROM TYPE Ia SUPERNOVA

    SciTech Connect (OSTI)

    Piro, Anthony L.; Chang, Philip; Weinberg, Nevin N., E-mail: tpiro@astro.berkeley.ed, E-mail: pchang@astro.berkeley.ed, E-mail: nweinberg@astro.berkeley.ed [Astronomy Department and Theoretical Astrophysics Center, University of California, Berkeley, CA 94720 (United States)

    2010-01-01T23:59:59.000Z

    The mode of explosive burning in Type Ia supernovae (SNe Ia) remains an outstanding problem. It is generally thought to begin as a subsonic deflagration, but this may transition into a supersonic detonation (the delayed detonation transition, DDT). We argue that this transition leads to a breakout shock, which would provide the first unambiguous evidence that DDTs occur. Its main features are a hard X-ray flash (approx20 keV) lasting approx10{sup -2} s with a total radiated energy of approx10{sup 40} erg, followed by a cooling tail. This creates a distinct feature in the visual light curve, which is separate from the nickel decay. This cooling tail has a maximum absolute visual magnitude of M{sub V} approx -9 to -10 at approx1 day, which depends most sensitively on the white dwarf radius at the time of the DDT. As the thermal diffusion wave moves in, the composition of these surface layers may be imprinted as spectral features, which would help to discern between SN Ia progenitor models. Since this feature should accompany every SNe Ia, future deep surveys (e.g., m = 24) will see it out to a distance of approx80 Mpc, giving a maximum rate of approx60 yr{sup -1}. Archival data sets can also be used to study the early rise dictated by the shock heating (at approx20 days before maximum B-band light). A similar and slightly brighter event may also accompany core bounce during the accretion-induced collapse to a neutron star, but with a lower occurrence rate.

  20. Type Ia Supernova Hubble Residuals and Host-Galaxy Properties

    E-Print Network [OSTI]

    Kim, A. G.

    2014-01-01T23:59:59.000Z

    magnitudes of type Ia supernovae from multi-band lightsuch an analysis on the supernovae of the Nearby Supernovaheadings: distance scale, supernovae: general 1 Physics

  1. K-corrections and spectral templates of Type Ia supernovae

    E-Print Network [OSTI]

    Hsiao, E. Y.

    2008-01-01T23:59:59.000Z

    templates of Type Ia supernovae E. Y. Hsiao 1 , A. Conleyobservations of low-redshift supernovae are less a?ected byobservations, stars: supernovae Department of Physics and

  2. Constraining Cosmic Evolution of Type Ia Supernovae

    SciTech Connect (OSTI)

    Foley, Ryan J.; Filippenko, Alexei V.; Aguilera, C.; Becker, A.C.; Blondin, S.; Challis, P.; Clocchiatti, A.; Covarrubias, R.; Davis, T.M.; Garnavich, P.M.; Jha, S.; Kirshner, R.P.; Krisciunas, K.; Leibundgut, B.; Li, W.; Matheson, T.; Miceli, A.; Miknaitis, G.; Pignata, G.; Rest, A.; Riess, A.G.; /UC, Berkeley, Astron. Dept. /Cerro-Tololo InterAmerican Obs. /Washington U., Seattle, Astron. Dept. /Harvard-Smithsonian Ctr. Astrophys. /Chile U., Catolica /Bohr Inst. /Notre Dame U. /KIPAC, Menlo Park /Texas A-M /European Southern Observ. /NOAO, Tucson /Fermilab /Chile U., Santiago /Harvard U., Phys. Dept. /Baltimore, Space Telescope Sci. /Johns Hopkins U. /Res. Sch. Astron. Astrophys., Weston Creek /Stockholm U. /Hawaii U. /Illinois U., Urbana, Astron. Dept.

    2008-02-13T23:59:59.000Z

    We present the first large-scale effort of creating composite spectra of high-redshift type Ia supernovae (SNe Ia) and comparing them to low-redshift counterparts. Through the ESSENCE project, we have obtained 107 spectra of 88 high-redshift SNe Ia with excellent light-curve information. In addition, we have obtained 397 spectra of low-redshift SNe through a multiple-decade effort at Lick and Keck Observatories, and we have used 45 ultraviolet spectra obtained by HST/IUE. The low-redshift spectra act as a control sample when comparing to the ESSENCE spectra. In all instances, the ESSENCE and Lick composite spectra appear very similar. The addition of galaxy light to the Lick composite spectra allows a nearly perfect match of the overall spectral-energy distribution with the ESSENCE composite spectra, indicating that the high-redshift SNe are more contaminated with host-galaxy light than their low-redshift counterparts. This is caused by observing objects at all redshifts with similar slit widths, which corresponds to different projected distances. After correcting for the galaxy-light contamination, subtle differences in the spectra remain. We have estimated the systematic errors when using current spectral templates for K-corrections to be {approx}0.02 mag. The variance in the composite spectra give an estimate of the intrinsic variance in low-redshift maximum-light SN spectra of {approx}3% in the optical and growing toward the ultraviolet. The difference between the maximum-light low and high-redshift spectra constrain SN evolution between our samples to be < 10% in the rest-frame optical.

  3. IA Blog Archive | Department of Energy

    Office of Energy Efficiency and Renewable Energy (EERE) Indexed Site

    AFDC Printable Version Share this resource Send a link to EERE: Alternative Fuels Data Center Home Page to someone by E-mail Share EERE: Alternative Fuels Data Center Home Page on Facebook Tweet about EERE: Alternative Fuels Data Center Home Page on Twitter Bookmark EERE: Alternative Fuels Data Center Home Page on Google Bookmark EERE: Alternative Fuels Data Center Home Page onYouTube YouTube Note: Since the.pdfBreaking of Blythe SolarContaminationCurrentHydronic71 IA Blog Archive en DOE andBlog

  4. IA News Archive | Department of Energy

    Office of Energy Efficiency and Renewable Energy (EERE) Indexed Site

    AFDC Printable Version Share this resource Send a link to EERE: Alternative Fuels Data Center Home Page to someone by E-mail Share EERE: Alternative Fuels Data Center Home Page on Facebook Tweet about EERE: Alternative Fuels Data Center Home Page on Twitter Bookmark EERE: Alternative Fuels Data Center Home Page on Google Bookmark EERE: Alternative Fuels Data Center Home Page onYouTube YouTube Note: Since the.pdfBreaking of Blythe SolarContaminationCurrentHydronic71 IA Blog Archive en DOENews

  5. Steamboat IA Geothermal Facility | Open Energy Information

    Open Energy Info (EERE)

    AFDC Printable Version Share this resource Send a link to EERE: Alternative Fuels Data Center Home Page to someone by E-mail Share EERE: Alternative Fuels Data Center Home Page on Facebook Tweet about EERE: Alternative Fuels Data Center Home Page on Twitter Bookmark EERE: Alternative Fuels Data Center Home Page onYou are now leaving Energy.gov You are now leaving Energy.gov You are beingZealand Jump to:Ezfeedflag JumpID-f < RAPID‎SolarCityInformation Glass Buttes AreaSteaI GeothermalIA

  6. Type Ia Supernova Explosion: Gravitationally Confined Detonation

    E-Print Network [OSTI]

    Tomasz Plewa; Alan Calder; Don Lamb

    2004-05-08T23:59:59.000Z

    We present a new mechanism for Type Ia supernova explosions in massive white dwarfs. The proposed scenario follows from relaxing the assumption of symmetry in the model and involves a detonation created in an unconfined environment. The explosion begins with an essentially central ignition of stellar material initiating a deflagration. This deflagration results in the formation of a buoyantly-driven bubble of hot material that reaches the stellar surface at supersonic speeds. The bubble breakout forms a strong pressure wave that laterally accelerates fuel-rich outer stellar layers. This material, confined by gravity to the white dwarf, races along the stellar surface and is focused at the location opposite to the point of the bubble breakout. These streams of nuclear fuel carry enough mass and energy to trigger a detonation just above the stellar surface. The flow conditions at that moment support a detonation that will incinerate the white dwarf and result in an energetic explosion. The stellar expansion following the deflagration redistributes stellar mass in a way that ensures production of intermediate mass and iron group elements consistent with observations. The ejecta will have a strongly layered structure with a mild amount of asymmetry following from the early deflagration phase. This asymmetry, combined with the amount of stellar expansion determined by details of the evolution (principally the energetics of deflagration, timing of detonation, and structure of the progenitor), can be expected to create a family of mildly diverse Type Ia supernova explosions.

  7. Dark matter ignition of type Ia supernovae

    E-Print Network [OSTI]

    Bramante, Joseph

    2015-01-01T23:59:59.000Z

    Recent studies of low redshift type Ia supernovae (SNIa) indicate that half explode from less than Chandrasekhar mass white dwarfs, implying ignition must proceed from something besides the canonical criticality of Chandrasekhar mass SNIa progenitors. We show that $0.1-10$ PeV mass asymmetric dark matter, with imminently detectable nucleon scattering interactions, can accumulate to the point of self-gravitation in a white dwarf and collapse, shedding gravitational potential energy by scattering off nuclei, thereby heating the white dwarf and igniting the flame front that precedes SNIa. We combine data on SNIa masses with data on the ages of SNIa-adjacent stars. This combination reveals a $ 3 \\sigma$ inverse correlation between SNIa masses and ignition ages, which could result from increased capture of dark matter in 1.4 versus 1.1 solar mass white dwarfs. Future studies of SNIa in galactic centers will provide additional tests of dark-matter-induced type Ia ignition. Remarkably, both bosonic and fermionic SNI...

  8. Plasma Redshift, Time Dilation, and Supernovas Ia

    E-Print Network [OSTI]

    Ari Brynjolfsson

    2004-07-20T23:59:59.000Z

    The measurements of the absolute magnitudes and redshifts of supernovas Ia show that conventional physics, which includes plasma redshift, fully explains the observed magnitude-redshift relation of the supernovas. The only parameter that is required is the Hubble constant, which in principle can be measured independently. The contemporary theory of the expansion of the universe (Big Bang) requires in addition to the Hubble constant several adjustable parameters, such as an initial explosion, the dark matter parameter, and a time adjustable dark energy parameter for explaining the supernova Ia data. The contemporary Big Bang theory also requires time dilation of distant events as an inherent premise. The contention is usually that the light curves of distant supernovas show or even prove the time dilation. In the present article, we challenge this assertion. We document and show that the previously reported data in fact indicate that there is no time dilation. The data reported by Riess et al. in the Astrophysical Journal in June 2004 confirm the plasma redshift, the absence of time dilation, dark matter, and dark energy.

  9. Three-dimensional numerical simulations of Rayleigh-Taylor unstable flames in type Ia supernovae

    E-Print Network [OSTI]

    Zingale, M.; Woosley, S.E.; Rendleman, C.A.; Day, M.S.; Bell, J.B.

    2005-01-01T23:59:59.000Z

    Unstable Flames in Type Ia Supernovae M. Zingale 1 , S. E.Subject headings: supernovae: general white dwarfs ame in Type Ia supernovae (SNe Ia) is well recognized (M

  10. Improving Type Ia Supernova Standard Candle Cosmology Measurements Using Observations of Early-Type Host Galaxies

    E-Print Network [OSTI]

    Meyers, Joshua Evan

    2012-01-01T23:59:59.000Z

    Host Galaxies of Type Ia Supernovae Introduction SN Ia Hosts109 C HAPTER 1 Cosmology, Type Ia Supernovae and HostGalaxies Observations of supernovae have played a role in

  11. UNU-IAS Policy Report Biofuels in Africa

    E-Print Network [OSTI]

    UNU-IAS Policy Report Biofuels in Africa Impacts on Ecosystem Services, Biodiversity and Human Well-being #12;#12;UNU-IAS Policy Report Biofuels in Africa Impacts on Ecosystem Services, Biodiversity and Human........................................................................................................... 9 1.2 Biofuel drivers, feedstocks and policies in Africa

  12. Diversity of Type Ia Supernovae Imprinted in Chemical Abundances

    E-Print Network [OSTI]

    Tsujimoto, Takuji

    2012-01-01T23:59:59.000Z

    A time delay of Type Ia supernova (SN Ia) explosions hinders the imprint of their nucleosynthesis on stellar abundances. However, some occasional cases give birth to stars that avoid enrichment of their chemical compositions by massive stars and thereby exhibit a SN Ia-like elemental feature including a very low [Mg/Fe] (~-1). We highlight the elemental feature of Fe-group elements for two low-Mg/Fe objects detected in nearby galaxies, and propose the presence of a class of SNe Ia that yield the low abundance ratios of [Cr,Mn,Ni/Fe]. Our novel models of chemical evolution reveal that our proposed class of SNe Ia (slow SNe Ia) is associated with ones exploding on a long timescale after their stellar birth, and gives a significant impact on the chemical enrichment in the Large Magellanic Cloud (LMC). In the Galaxy, on the other hand, this effect is unseen due to the overwhelming enrichment by the major class of SNe Ia that explode promptly (prompt SNe Ia) and eject a large amount of Fe-group elements. This nice...

  13. Nickel Bubble Expansion in Type Ia Supernovae: Adiabatic Solutions

    E-Print Network [OSTI]

    Chih-Yueh Wang

    2008-06-20T23:59:59.000Z

    This paper presents hydrodynamical and radiation-hydrodynamical simulations of the nickel bubble effect in Type Ia supernovae, comparison of results to self-similar solutions, and application to observations of Type Ia supernova remnants, with a particular emphasis on Tycho's SNR.

  14. Type Ia Supernova Remnants: Shaping by Iron Bullets

    E-Print Network [OSTI]

    Tsebrenko, Danny

    2015-01-01T23:59:59.000Z

    Using 2D numerical hydrodynamical simulations of type Ia supernova remnants (SNR Ia) we show that iron clumps few times denser than the rest of the SN ejecta might form protrusions in an otherwise spherical SNR. Such protrusions exist in some SNR Ia, e.g., SNR 1885 and Tycho. Iron clumps are expected to form in the deflagration to detonation explosion model. In SNR Ia where there are two opposite protrusions, termed ears, such as Kepler's SNR and SNR G1.9+0.3, our scenario implies that the dense clumps, or iron bullets, were formed along an axis. Such a preferred axis can result from a rotating white dwarf progenitor. If our claim holds, this offers an important clue to the SN Ia explosion scenario.

  15. Direct numerical simulations of type Ia supernovae flames I: The landau-darrieus instability

    E-Print Network [OSTI]

    Bell, J.B.; Day, M.S.; Rendleman, C.A.; Woosley, S.E.; Zingale, M.

    2003-01-01T23:59:59.000Z

    Simulations of Type Ia Supernovae Flames I: The Landau-Subject headings: supernovae: general white dwarfs could occur in Type Ia supernovae (Niemeyer & Woosley 1997),

  16. DIVERSITY OF TYPE Ia SUPERNOVAE IMPRINTED IN CHEMICAL ABUNDANCES

    SciTech Connect (OSTI)

    Tsujimoto, Takuji [National Astronomical Observatory of Japan, Mitaka-shi, Tokyo 181-8588 (Japan); Shigeyama, Toshikazu, E-mail: taku.tsujimoto@nao.ac.jp [Research Center for the Early Universe, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan)

    2012-12-01T23:59:59.000Z

    A time delay of Type Ia supernova (SN Ia) explosions hinders the imprint of their nucleosynthesis on stellar abundances. However, some occasional cases give birth to stars that avoid enrichment of their chemical compositions by massive stars and thereby exhibit an SN-Ia-like elemental feature including a very low [Mg/Fe] ( Almost-Equal-To - 1). We highlight the elemental feature of Fe-group elements for two low-Mg/Fe objects detected in nearby galaxies, and propose the presence of a class of SNe Ia that yield the low abundance ratios of [Cr, Mn, Ni/Fe]. Our novel models of chemical evolution reveal that our proposed class of SNe Ia (slow SNe Ia) is associated with ones exploding on a long timescale after their stellar birth and give a significant impact on the chemical enrichment in the Large Magellanic Cloud (LMC). In the Galaxy, on the other hand, this effect is unseen due to the overwhelming enrichment by the major class of SNe Ia that explode promptly (prompt SNe Ia) and eject a large amount of Fe-group elements. This nicely explains the different [Cr, Mn, Ni/Fe] features between the two galaxies as well as the puzzling feature seen in the LMC stars exhibiting very low Ca but normal Mg abundances. Furthermore, the corresponding channel of slow SN Ia is exemplified by performing detailed nucleosynthesis calculations in the scheme of SNe Ia resulting from a 0.8 + 0.6 M{sub Sun} white dwarf merger.

  17. Phases of a Type Ia supernova explosion

    E-Print Network [OSTI]

    J. C. Niemeyer

    1998-02-13T23:59:59.000Z

    In the framework of the Chandrasekhar mass white dwarf model for Type Ia supernovae, various stages of the explosion are described in terms of the burning regimes of the thermonuclear flame front. In the early flamelet regime following the ``smoldering'' phase prior to the explosion, the flame is sufficiently thin and fast to remain laminar on small scales. As the white dwarf density declines, the thermal flame structure becomes subject to penetration by turbulent eddies, and it enters the ``distributed burning'' regime. A specific control parameter for this transition is proposed. Furthermore, we outline an argument for the coincidence of the transition between burning regimes with the onset of a deflagration-detonation-transition (DDT) in the late phase of the explosion.

  18. On the effect of N-GaN/P-GaN/N-GaN/P-GaN/N-GaN built-in junctions in the n-GaN layer for

    E-Print Network [OSTI]

    Demir, Hilmi Volkan

    On the effect of N-GaN/P-GaN/N-GaN/P-GaN/N- GaN built-in junctions in the n-GaN layer for InGaN/GaN: N-GaN/P-GaN/N-GaN/P-GaN/N-GaN (NPNPN-GaN) junctions embedded between the n-GaN region and multiple the performance of InGaN/GaN light emitting diodes (LEDs) in this work. In the proposed architecture, each thin P-GaN

  19. K-corrections and spectral templates of Type Ia supernovae

    SciTech Connect (OSTI)

    Nugent, Peter E; Hsiao, E.Y.; Conley, A.; Howell, D.A.; Sullivan, M.; Pritchet, C.J.; Carlberg, R.G.; Nugent, P.E.; Phillips, M.M.

    2007-03-20T23:59:59.000Z

    With the advent of large dedicated Type Ia supernova (SN Ia) surveys, K-corrections of SNe Ia and their uncertainties have become especially important in the determination of cosmological parameters. While K-corrections are largely driven by SN Ia broadband colors, it is shown here that the diversity in spectral features of SNe Ia can also be important. For an individual observation, the statistical errors from the inhomogeneity in spectral features range from 0.01 (where the observed and rest-frame filters are aligned) to 0.04 (where the observed and rest-frame filters are misaligned). To minimize the systematic errors caused by an assumed SN Ia spectral energy distribution (SED), we outline a prescription for deriving a mean spectral template time series that incorporates a large and heterogeneous sample of observed spectra. We then remove the effects of broadband colors and measure the remaining uncertainties in the K-corrections associated with the diversity in spectral features. Finally, we present a template spectroscopic sequence near maximum light for further improvement on the K-correction estimate. A library of ~;;600 observed spectra of ~;;100 SNe Ia from heterogeneous sources is used for the analysis.

  20. Large-Signal HBT Model with Improved Collector Transit Time Formulation for GaAs and InP Technologies

    E-Print Network [OSTI]

    Asbeck, Peter M.

    mi': iaE Large-Signal HBT Model with Improved Collector Transit Time Formulation for GaAs and In large-signal HBT model which accurately accounts for the intricate hias dependence of collector delay collector delay function accounts for the variation of electron velocity with electric field

  1. Type Ia Supernova Progenitors, Environmental Effects, and Cosmic Supernova Rates

    E-Print Network [OSTI]

    Ken'ichi Nomoto; Hideyuki Umeda; Izumi Hachisu; Mariko Kato; Chiaki Kobayashi; Takuji Tsujimoto

    1999-07-27T23:59:59.000Z

    Relatively uniform light curves and spectral evolution of Type Ia supernovae (SNe Ia) have led to the use of SNe Ia as a ``standard candle'' to determine cosmological parameters, such as the Hubble constant, the density parameter, and the cosmological constant. Whether a statistically significant value of the cosmological constant can be obtained depends on whether the peak luminosities of SNe Ia are sufficiently free from the effects of cosmic and galactic evolutions. Here we first review the single degenerate scenario for the Chandrasekhar mass white dwarf (WD) models of SNe Ia. We identify the progenitor's evolution and population with two channels: (1) the WD+RG (red-giant) and (2) the WD+MS (near main-sequence He-rich star) channels. In these channels, the strong wind from accreting white dwarfs plays a key role, which yields important age and metallicity effects on the evolution. We then address the questions whether the nature of SNe Ia depends systematically on environmental properties such as metallicity and age of the progenitor system and whether significant evolutionary effects exist. We suggest that the variation of the carbon mass fraction $X$(C) in the C+O WD (or the variation of the initial WD mass) causes the diversity of the brightness of SNe Ia. This model can explain the observed dependence of SNe Ia brighness on the galaxy types. Finally, applying the metallicity effect on the evolution of SN Ia progenitors, we make a prediction of the cosmic supernova rate history as a composite of the supernova rates in different types of galaxies.

  2. Type Ia Supernovae: Progenitors and Evolution with Redshift

    E-Print Network [OSTI]

    Ken'ichi Nomoto; Hideyuki Umeda; Chiaki Kobayashi; Izumi Hachisu; Mariko Kato; Takuji Tsujimoto

    2000-03-09T23:59:59.000Z

    Relatively uniform light curves and spectral evolution of Type Ia supernovae (SNe Ia) have led to the use of SNe Ia as a ``standard candle'' to determine cosmological parameters. Whether a statistically significant value of the cosmological constant can be obtained depends on whether the peak luminosities of SNe Ia are sufficiently free from the effects of cosmic and galactic evolutions. Here we first review the single degenerate scenario for the Chandrasekhar mass white dwarf (WD) models of SNe Ia. We identify the progenitor's evolution and population with two channels: (1) the WD+RG (red-giant) and (2) the WD+MS (near main-sequence He-rich star) channels. In these channels, the strong wind from accreting WDs plays a key role, which yields important age and metallicity effects on the evolution. We then address the questions whether the nature of SNe Ia depends systematically on environmental properties such as metallicity and age of the progenitor system and whether significant evolutionary effects exist. We suggest that the variation of the carbon mass fraction $X$(C) in the C+O WD (or the variation of the initial WD mass) causes the diversity of the brightness of SNe Ia. This model can explain the observed dependences of SNe Ia brightness on the galaxy types and the distance from the galactic center. Finally, applying the metallicity effect on the evolution of SN Ia progenitors, we make a prediction of the cosmic supernova rate history as a composite of the supernova rates in different types of galaxies.

  3. Will Jets Identify the Progenitors of Type Ia Supernovae?

    E-Print Network [OSTI]

    Mario Livio; Adam Riess; William Sparks

    2002-04-26T23:59:59.000Z

    We use the fact that a Type Ia supernova has been serendipitously discovered near the jet of the active galaxy 3C 78 to examine the question of whether jets can enhance accretion onto white dwarfs. One interesting outcome of such a jet-induced accretion process is an enhanced rate of novae in the vicinity of jets. We present results of observations of the jet in M87 which appear to have indeed discovered 11 novae in close proximity to the jet. We show that a confirmation of the relation between jets and novae and Type Ia supernovae can finally identify the elusive progenitors of Type Ia supernovae.

  4. Single-Degenerate Type Ia Supernovae Are Preferentially Overluminous

    E-Print Network [OSTI]

    Fisher, Robert

    2015-01-01T23:59:59.000Z

    Recent observational and theoretical progress has favored merging and helium-accreting sub-Chandrasekhar mass white dwarfs in the double-degenerate and the double-detonation channels, respectively, as the most promising progenitors of normal Type Ia supernovae (SNe Ia). Thus the fate of rapidly-accreting Chandrasekhar mass white dwarfs in the single-degenerate channel remains more mysterious then ever. In this paper, we clarify the nature of ignition in Chandrasekhar-mass single-degenerate SNe Ia by analytically deriving the existence of a characteristic length scale which establishes a transition from central ignitions to buoyancy-driven ignitions. Using this criterion, combined with data from three-dimensional simulations of convection and ignition, we demonstrate that the overwhelming majority of ignition events within Chandrasekhar-mass white dwarfs in the single-degenerate channel are buoyancy-driven, and consequently lack a vigorous deflagration phase. We thus infer that single-degenerate SNe Ia are gen...

  5. CIRCUMSTELLAR ABSORPTION IN DOUBLE DETONATION TYPE Ia SUPERNOVAE

    SciTech Connect (OSTI)

    Shen, Ken J. [Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720 (United States); Guillochon, James [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Foley, Ryan J., E-mail: kenshen@astro.berkeley.edu [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

    2013-06-20T23:59:59.000Z

    Upon formation, degenerate He core white dwarfs are surrounded by a radiative H-rich layer primarily supported by ideal gas pressure. In this Letter, we examine the effect of this H-rich layer on mass transfer in He+C/O double white dwarf binaries that will eventually merge and possibly yield a Type Ia supernova (SN Ia) in the double detonation scenario. Because its thermal profile and equation of state differ from the underlying He core, the H-rich layer is transferred stably onto the C/O white dwarf prior to the He core's tidal disruption. We find that this material is ejected from the binary system and sweeps up the surrounding interstellar medium hundreds to thousands of years before the SN Ia. The close match between the resulting circumstellar medium profiles and values inferred from recent observations of circumstellar absorption in SNe Ia gives further credence to the resurgent double detonation scenario.

  6. The Photometric Properties of Nearby Type Ia Supernovae

    E-Print Network [OSTI]

    Ganeshalingam, Mohan

    2012-01-01T23:59:59.000Z

    The Rise-Time Distribution of Nearby Type Ia Supernovae 3.1Highlight: The Physics of Supernovae, ed. W. Hillebrandt &1.1 Supernovae . . . . . . . . . . . . . . 1.1.1

  7. TYPE Ia SUPERNOVAE STRONGLY INTERACTING WITH THEIR CIRCUMSTELLAR MEDIUM

    SciTech Connect (OSTI)

    Silverman, Jeffrey M. [Department of Astronomy, University of Texas, Austin, TX 78712-0259 (United States); Nugent, Peter E. [Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Gal-Yam, Avishay; Arcavi, Iair; Ben-Ami, Sagi [Benoziyo Center for Astrophysics, Weizmann Institute of Science, Rehovot 76100 (Israel); Sullivan, Mark [School of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ (United Kingdom); Howell, D. Andrew; Graham, Melissa L. [Las Cumbres Observatory Global Telescope Network, Goleta, CA 93117 (United States); Filippenko, Alexei V.; Bloom, Joshua S.; Cenko, S. Bradley; Clubb, Kelsey I. [Department of Astronomy, University of California, Berkeley, CA 94720-3411 (United States); Cao, Yi; Horesh, Assaf; Kulkarni, Shrinivas R. [Cahill Center for Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States); Chornock, Ryan; Foley, Ryan J. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Coil, Alison L. [Department of Physics, University of California, San Diego, La Jolla, CA 92093 (United States); Griffith, Christopher V. [Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802 (United States); Kasliwal, Mansi M., E-mail: jsilverman@astro.as.utexas.edu [Observatories of the Carnegie Institution of Science, Pasadena, CA 91101 (United States); and others

    2013-07-01T23:59:59.000Z

    Owing to their utility for measurements of cosmic acceleration, Type Ia supernovae (SNe Ia) are perhaps the best-studied class of SNe, yet the progenitor systems of these explosions largely remain a mystery. A rare subclass of SNe Ia shows evidence of strong interaction with their circumstellar medium (CSM), and in particular, a hydrogen-rich CSM; we refer to them as SNe Ia-CSM. In the first systematic search for such systems, we have identified 16 SNe Ia-CSM, and here we present new spectra of 13 of them. Six SNe Ia-CSM have been well studied previously, three were previously known but are analyzed in depth for the first time here, and seven are new discoveries from the Palomar Transient Factory. The spectra of all SNe Ia-CSM are dominated by H{alpha} emission (with widths of {approx}2000 km s{sup -1}) and exhibit large H{alpha}/H{beta} intensity ratios (perhaps due to collisional excitation of hydrogen via the SN ejecta overtaking slower-moving CSM shells); moreover, they have an almost complete lack of He I emission. They also show possible evidence of dust formation through a decrease in the red wing of H{alpha} 75-100 days past maximum brightness, and nearly all SNe Ia-CSM exhibit strong Na I D absorption from the host galaxy. The absolute magnitudes (uncorrected for host-galaxy extinction) of SNe Ia-CSM are found to be -21.3 mag {<=} M{sub R} {<=} -19 mag, and they also seem to show ultraviolet emission at early times and strong infrared emission at late times (but no detected radio or X-ray emission). Finally, the host galaxies of SNe Ia-CSM are all late-type spirals similar to the Milky Way, or dwarf irregulars like the Large Magellanic Cloud, which implies that these objects come from a relatively young stellar population. This work represents the most detailed analysis of the SN Ia-CSM class to date.

  8. EARLY EMISSION FROM TYPE Ia SUPERNOVAE

    SciTech Connect (OSTI)

    Rabinak, Itay; Waxman, Eli [Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot 76100 (Israel); Livne, Eli, E-mail: itay.rabinak@weizmann.ac.il [Racah Institute of Physics, Hebrew University, Jerusalem (Israel)

    2012-09-20T23:59:59.000Z

    A unique feature of deflagration-to-detonation (DDT) white dwarf explosion models of supernovae of type Ia is the presence of a strong shock wave propagating through the outer envelope. We consider the early emission expected in such models, which is produced by the expanding shock-heated outer part of the ejecta and precedes the emission driven by radioactive decay. We expand on earlier analyses by considering the modification of the pre-detonation density profile by the weak shocks generated during the deflagration phase, the time evolution of the opacity, and the deviation of the post-shock equation of state from that obtained for radiation pressure domination. A simple analytic model is presented and shown to provide an acceptable approximation to the results of one-dimensional numerical DDT simulations. Our analysis predicts a {approx}10{sup 3} s long UV/optical flash with a luminosity of {approx}1 to {approx}3 Multiplication-Sign 10{sup 39} erg s{sup -1}. Lower luminosity corresponds to faster (turbulent) deflagration velocity. The luminosity of the UV flash is predicted to be strongly suppressed at t > t{sub drop} {approx} 1 hr due to the deviation from pure radiation domination.

  9. Type Ia Supernova Explosion Models: Homogeneity versus Diversity

    E-Print Network [OSTI]

    W. Hillebrandt; J. C. Niemeyer; M. Reinecke

    2000-05-30T23:59:59.000Z

    Type Ia supernovae (SN Ia) are generally believed to be the result of the thermonuclear disruption of Chandrasekhar-mass carbon-oxygen white dwarfs, mainly because such thermonuclear explosions can account for the right amount of Ni-56, which is needed to explain the light curves and the late-time spectra, and the abundances of intermediate-mass nuclei which dominate the spectra near maximum light. Because of their enormous brightness and apparent homogeneity SN Ia have become an important tool to measure cosmological parameters. In this article the present understanding of the physics of thermonuclear explosions is reviewed. In particular, we focus our attention on subsonic (``deflagration'') fronts, i.e. we investigate fronts propagating by heat diffusion and convection rather than by compression. Models based upon this mode of nuclear burning have been applied very successfully to the SN Ia problem, and are able to reproduce many of their observed features remarkably well. However, the models also indicate that SN Ia may differ considerably from each other, which is of importance if they are to be used as standard candles.

  10. Simulations of Turbulent Thermonuclear Burning in Type Ia Supernovae

    E-Print Network [OSTI]

    W. Hillebrandt; M. Reinecke; W. Schmidt; F. K. Roepke; C. Travaglio; J. C. Niemeyer

    2004-05-11T23:59:59.000Z

    Type Ia supernovae have recently received considerable attention because it appears that they can be used as "standard candles" to measure cosmic distances out to billions of light years away from us. Observations of type Ia supernovae seem to indicate that we are living in a universe that started to accelerate its expansion when it was about half its present age. These conclusions rest primarily on phenomenological models which, however, lack proper theoretical understanding, mainly because the explosion process, initiated by thermonuclear fusion of carbon and oxygen into heavier elements, is difficult to simulate even on supercomputers. Here, we investigate a new way of modeling turbulent thermonuclear deflagration fronts in white dwarfs undergoing a type Ia supernova explosion. Our approach is based on a level set method which treats the front as a mathematical discontinuity and allows for full coupling between the front geometry and the flow field. New results of the method applied to the problem of type Ia supernovae are obtained. It is shown that in 2-D with high spatial resolution and a physically motivated subgrid scale model for the nuclear flames numerically "converged" results can be obtained, but for most initial conditions the stars do not explode. In contrast, simulations in 3-D, do give the desired explosions and many of their properties, such as the explosion energies, lightcurves and nucleosynthesis products, are in very good agreement with observed type Ia supernovae.

  11. Presented at the ASHRAE Winter Meeting, Atlanta, GA, February 17-21, 1996, and published in the Proceedings. Calorimetric Measurements of Inward-Flowing Fraction

    E-Print Network [OSTI]

    ) or evaluated theoretically using an idealized heat transfer model (Farber, Smith et al. 1963). The underlying

  12. Strategic Utilization of Paper/Wood Waste for Biodiesel Fuel Art J. Ragauskas, Institute of Paper Science and Technology; Georgia Institute of Technology, Atlanta, GA.

    E-Print Network [OSTI]

    Strategic Utilization of Paper/Wood Waste for Biodiesel Fuel Art J. Ragauskas, Institute of Paper lignocellulosics to biodiesel fuel Feedstocks ABSTRACT This poster examines the potential of utilizing waste paper CelluloseHemicelluloseLigninResource Cracking and Refining of Polysaccharides Bio-Diesel Substitutes

  13. K-corrections and extinction corrections for Type Ia supernovae

    SciTech Connect (OSTI)

    Nugent, Peter; Kim, Alex; Perlmutter, Saul

    2002-05-21T23:59:59.000Z

    The measurement of the cosmological parameters from Type Ia supernovae hinges on our ability to compare nearby and distant supernovae accurately. Here we present an advance on a method for performing generalized K-corrections for Type Ia supernovae which allows us to compare these objects from the UV to near-IR over the redshift range 0 < z < 2. We discuss the errors currently associated with this method and how future data can improve upon it significantly. We also examine the effects of reddening on the K-corrections and the light curves of Type Ia supernovae. Finally, we provide a few examples of how these techniques affect our current understanding of a sample of both nearby and distant supernovae.

  14. The ignition of thermonuclear flames in Type Ia supernovae

    E-Print Network [OSTI]

    L. Iapichino; M. Brggen; W. Hillebrandt; J. C. Niemeyer

    2005-12-12T23:59:59.000Z

    In the framework of the Chandrasekhar-mass deflagration model for Type Ia supernovae (SNe Ia), a persisting free parameter is the initial morphology of the flame front, which is linked to the ignition process in the progenitor white dwarf. Previous analytical models indicate that the thermal runaway is driven by temperature perturbations (''bubbles'') that develop in the white dwarf's convective core. In order to probe the conditions at ignition (diameters, temperatures and evolutionary timescales), we have performed hydrodynamical 2D simulations of buoyant bubbles in white dwarf interiors. Our results show that fragmentation occurring during the bubble rise affects the outcome of the bubble evolution. Possible implications for the ignition process of SNe Ia are discussed.

  15. Refined numerical models for multidimensional Type Ia supernova simulations

    E-Print Network [OSTI]

    Reinecke, M; Niemeyer, J C

    2002-01-01T23:59:59.000Z

    Following up on earlier work on this topic (Reinecke et al. 1999, A&A 347, pp. 724 and 739), we present an improved set of numerical models for simulations of white dwarfs exploding as Type Ia supernovae (SNe Ia). Two-dimensional simulations were used to test the reliability and numerical robustness of these algorithms; the results indicate that integral quantities like the total energy release are insensitive to changes of the grid resolution (above a certain threshold), which was not the case for our former code. The models were further enhanced to allow fully three-dimensional simulations of SNe Ia. A direct comparison of a 2D and a 3D calculation with identical initial conditions shows that the explosion is considerably more energetic in three dimensions; this is most likely caused by the assumption of axisymmetry in 2D, which inhibits the growth of flame instabilities in the azimuthal direction and thereby decreases the flame surface.

  16. Refined numerical models for multidimensional Type Ia supernova simulations

    E-Print Network [OSTI]

    M. Reinecke; W. Hillebrandt; J. C. Niemeyer

    2001-11-26T23:59:59.000Z

    Following up on earlier work on this topic (Reinecke et al. 1999, A&A 347, pp. 724 and 739), we present an improved set of numerical models for simulations of white dwarfs exploding as Type Ia supernovae (SNe Ia). Two-dimensional simulations were used to test the reliability and numerical robustness of these algorithms; the results indicate that integral quantities like the total energy release are insensitive to changes of the grid resolution (above a certain threshold), which was not the case for our former code. The models were further enhanced to allow fully three-dimensional simulations of SNe Ia. A direct comparison of a 2D and a 3D calculation with identical initial conditions shows that the explosion is considerably more energetic in three dimensions; this is most likely caused by the assumption of axisymmetry in 2D, which inhibits the growth of flame instabilities in the azimuthal direction and thereby decreases the flame surface.

  17. The ignition of thermonuclear flames in Type Ia supernovae

    E-Print Network [OSTI]

    Iapichino, L; Hillebrandt, W; Niemeyer, J C

    2005-01-01T23:59:59.000Z

    In the framework of the Chandrasekhar-mass deflagration model for Type Ia supernovae (SNe Ia), a persisting free parameter is the initial morphology of the flame front, which is linked to the ignition process in the progenitor white dwarf. Previous analytical models indicate that the thermal runaway is driven by temperature perturbations (''bubbles'') that develop in the white dwarf's convective core. In order to probe the conditions at ignition (diameters, temperatures and evolutionary timescales), we have performed hydrodynamical 2D simulations of buoyant bubbles in white dwarf interiors. Our results show that fragmentation occurring during the bubble rise affects the outcome of the bubble evolution. Possible implications for the ignition process of SNe Ia are discussed.

  18. Strong Ultraviolet Pulse From a Newborn Type Ia Supernova

    E-Print Network [OSTI]

    Cao, Yi; Howell, D Andrew; Gal-Yam, Avishay; Kasliwal, Mansi M; Valenti, Stefano; Johansson, J; Amanullah, R; Goobar, A; Sollerman, J; Taddia, F; Horesh, Assaf; Sagiv, Ilan; Cenko, S Bradley; Nugent, Peter E; Arcavi, Iair; Surace, Jason; Wo?niak, P R; Moody, Daniela I; Rebbapragada, Umaa D; Bue, Brian D; Gehrels, Neil

    2015-01-01T23:59:59.000Z

    Type Ia supernovae are destructive explosions of carbon oxygen white dwarfs. Although they are used empirically to measure cosmological distances, the nature of their progenitors remains mysterious, One of the leading progenitor models, called the single degenerate channel, hypothesizes that a white dwarf accretes matter from a companion star and the resulting increase in its central pressure and temperature ignites thermonuclear explosion. Here we report observations of strong but declining ultraviolet emission from a Type Ia supernova within four days of its explosion. This emission is consistent with theoretical expectations of collision between material ejected by the supernova and a companion star, and therefore provides evidence that some Type Ia supernovae arise from the single degenerate channel.

  19. Diagnosing multiplicative error by lensing magnification of type Ia supernovae

    E-Print Network [OSTI]

    Zhang, Pengjie

    2015-01-01T23:59:59.000Z

    Weak lensing causes spatially coherent fluctuations in flux of type Ia supernovae (SNe Ia). This lensing magnification allows for weak lensing measurement independent of cosmic shear. It is free of shape measurement errors associated with cosmic shear and can therefore be used to diagnose and calibrate multiplicative error. Although this lensing magnification is difficult to measure accurately in auto correlation, its cross correlation with cosmic shear and galaxy distribution in overlapping area can be measured to significantly higher accuracy. Therefore these cross correlations can put useful constraint on multiplicative error, and the obtained constraint is free of cosmic variance in weak lensing field. We present two methods implementing this idea and estimate their performances. We find that, with $\\sim 1$ million SNe Ia that can be achieved by the proposed D2k survey with the LSST telescope (Zhan et al. 2008), multiplicative error of $\\sim 0.5\\%$ for source galaxies at $z_s\\sim 1$ can be detected and la...

  20. Type Ia supernovae from merging white dwarfs. I. Prompt detonations

    SciTech Connect (OSTI)

    Moll, R.; Woosley, S. E. [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Raskin, C.; Kasen, D. [Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States)

    2014-04-20T23:59:59.000Z

    Merging white dwarfs are a possible progenitor of Type Ia supernovae (SNe Ia). Numerical models suggest that a detonation might be initiated before the stars have coalesced to form a single compact object. Here we study such prompt detonations by means of numerical simulations, modeling the disruption and nucleosynthesis of the stars until the ejecta reach the coasting phase, and generating synthetic light curves and spectra. Three models are considered with primary masses 0.96 M {sub ?}, 1.06 M {sub ?}, and 1.20 M {sub ?}. Of these, the 0.96 M {sub ?} dwarf merging with a 0.81 M {sub ?} companion, with an {sup 56}Ni yield of 0.58 M {sub ?}, is the most promising candidate for reproducing common SNe Ia. The more massive mergers produce unusually luminous SNe Ia with peak luminosities approaching those attributed to 'super-Chandrasekhar' mass SNe Ia. While the synthetic light curves and spectra of some of the models resemble observed SNe Ia, the significant asymmetry of the ejecta leads to large orientation effects. The peak bolometric luminosity varies by more than a factor of two with the viewing angle, and the velocities of the spectral absorption features are lower when observed from angles where the light curve is brightest. The largest orientation effects are seen in the ultraviolet, where the flux varies by more than an order of magnitude. The set of three models roughly obeys a width-luminosity relation, with the brighter light curves declining more slowly in the B band. Spectral features due to unburned carbon from the secondary star are also seen in some cases.

  1. SPECTROSCOPY OF TYPE Ia SUPERNOVAE BY THE CARNEGIE SUPERNOVA PROJECT

    SciTech Connect (OSTI)

    Folatelli, Gaston [Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI), Todai Institutes for Advanced Study, the University of Tokyo, 277-8583 Kashiwa (Japan); Morrell, Nidia; Phillips, Mark M.; Hsiao, Eric; Campillay, Abdo; Contreras, Carlos; Castellon, Sergio; Roth, Miguel [Las Campanas Observatory, Carnegie Observatories, Casilla 601, La Serena (Chile); Hamuy, Mario; Anderson, Joseph P. [Departamento de Astronomia, Universidad de Chile, Casilla 36-D, Santiago (Chile); Krzeminski, Wojtek [N. Copernicus Astronomical Center, ul. Bartycka 18, 00-716 Warszawa (Poland); Stritzinger, Maximilian [Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C (Denmark); Burns, Christopher R.; Freedman, Wendy L.; Madore, Barry F.; Murphy, David; Persson, S. E. [Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Prieto, Jose L. [Department of Astrophysical Sciences, Princeton University, 4 Ivy Ln., Princeton, NJ 08544 (United States); Suntzeff, Nicholas B.; Krisciunas, Kevin, E-mail: gaston.folatelli@ipmu.jp [George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Department of Physics and Astronomy, Texas A and M University, College Station, TX 77843 (United States); and others

    2013-08-10T23:59:59.000Z

    This is the first release of optical spectroscopic data of low-redshift Type Ia supernovae (SNe Ia) by the Carnegie Supernova Project including 604 previously unpublished spectra of 93 SNe Ia. The observations cover a range of phases from 12 days before to over 150 days after the time of B-band maximum light. With the addition of 228 near-maximum spectra from the literature, we study the diversity among SNe Ia in a quantitative manner. For that purpose, spectroscopic parameters are employed such as expansion velocities from spectral line blueshifts and pseudo-equivalent widths (pW). The values of those parameters at maximum light are obtained for 78 objects, thus providing a characterization of SNe Ia that may help to improve our understanding of the properties of the exploding systems and the thermonuclear flame propagation. Two objects, namely, SNe 2005M and 2006is, stand out from the sample by showing peculiar Si II and S II velocities but otherwise standard velocities for the rest of the ions. We further study the correlations between spectroscopic and photometric parameters such as light-curve decline rate and color. In agreement with previous studies, we find that the pW of Si II absorption features are very good indicators of light-curve decline rate. Furthermore, we demonstrate that parameters such as pW2 (Si II 4130) and pW6 (Si II 5972) provide precise calibrations of the peak B-band luminosity with dispersions of Almost-Equal-To 0.15 mag. In the search for a secondary parameter in the calibration of peak luminosity for SNe Ia, we find a Almost-Equal-To 2{sigma}-3{sigma} correlation between B-band Hubble residuals and the velocity at maximum light of S II and Si II lines.

  2. Review of Multi-Person Exposure Calls to a Regional Poison Control Center

    E-Print Network [OSTI]

    Morgan, Brent W; Skinner, Carl G; Kleiman, Richard J; Geller, Robert J; Chang, Arthur S

    2010-01-01T23:59:59.000Z

    Exposure Calls to a Regional Poison Control Center Brent W.Medicine and the Georgia Poison Center, Atlanta, GA of Pediatrics and the Georgia Poison Center, Atlanta, GA

  3. System Effects of High Efficiency Filters in Homes

    E-Print Network [OSTI]

    Walker, Iain S.

    2014-01-01T23:59:59.000Z

    Air Flow in Residential Air Conditioning Systems. ASHRAErefrigerating and Air-conditioning Engineers, Atlanta, GA.refrigerating and Air-conditioning Engineers, Atlanta, GA.

  4. Energy Implications of In-line filtration in California Homes

    E-Print Network [OSTI]

    Walker, Iain S.

    2014-01-01T23:59:59.000Z

    Air Flow in Residential Air Conditioning Systems. ASHRAErefrigerating and Air-conditioning Engineers, Atlanta, GA.Refrigerating and Air- conditioning Engineers, Atlanta, GA.

  5. Sampling the Probability Distribution of Type Ia Supernova Lightcurve Parameters in Cosmological Analysis

    E-Print Network [OSTI]

    Dai, Mi

    2015-01-01T23:59:59.000Z

    In order to obtain robust cosmological constraints from Type Ia supernova (SN Ia) data, we have applied Markov Chain Monte Carlo (MCMC) to SN Ia lightcurve fitting. We develop a method for sampling the resultant probability density distributions (pdf) of the SN Ia lightcuve parameters in the MCMC likelihood analysis to constrain cosmological parameters. Applying this method to the Joint Lightcurve Analysis (JLA) data set of SNe Ia, we find that sampling the SN Ia lightcurve parameter pdf's leads to cosmological parameters closer to that of a flat Universe with a cosmological constant, compared to the usual practice of using only the best fit values of the SN Ia lightcurve parameters. Our method will be useful in the use of SN Ia data for precision cosmology.

  6. Spectral Observations and Analyses of Low-Redshift Type Ia Supernovae

    E-Print Network [OSTI]

    Silverman, Jeffrey Michael

    2011-01-01T23:59:59.000Z

    1.3.2 Thermonuclear Supernovae . . . . . . . . 1.4 Why WriteIa are the result of thermonuclear explosions of C/O whiteIa are the result of thermonuclear explosions of C/O white

  7. CfA3: 185 TYPE Ia SUPERNOVA LIGHT CURVES FROM THE CfA

    E-Print Network [OSTI]

    Krauss, Miriam

    We present multiband photometry of 185 type-Ia supernovae (SNe Ia), with over 11,500 observations. These were acquired between 2001 and 2008 at the F. L. Whipple Observatory of the Harvard-Smithsonian Center for Astrophysics ...

  8. Feasibility of Measuring the Cosmological Constant [LAMBDA] and Mass Density [Omega] using Type Ia Supernovae

    E-Print Network [OSTI]

    Goobar, A.

    2008-01-01T23:59:59.000Z

    at z = 1. uncertainty for supernovae at z = 1. mR Adding theMass Density .Q Using Type Ia Supernovae A. Goobar and S.Density Q Using Type Ia Supernovae Ariel Goobar l and Saul

  9. UV Spectroscopy of Type Ia Supernovae at Low- and High-Redshift

    E-Print Network [OSTI]

    Nugent, Peter

    2005-01-01T23:59:59.000Z

    Spectroscopy of Type Ia Supernovae at Low- and High-RedshiftUV properties of Type Ia Supernovae. The low-redshift studyULDA Access Guide No. 6: Supernovae, The Netherlands: ESA

  10. Nearby Supernova Factory Observations of SN 2006D: On Sporadic Carbon Signatures in Early Type Ia Supernova Spectra

    E-Print Network [OSTI]

    2006-01-01T23:59:59.000Z

    with low volume-?lling factor. Subject headings: supernovae:general supernovae: individual (SN 2006D)Introduction Type Ia supernovae (SNe Ia) make valuable

  11. Experto Universitario Java Enterprise 2012-2013 Depto. Ciencia de la Computacin e IA

    E-Print Network [OSTI]

    Escolano, Francisco

    Experto Universitario Java Enterprise 2012-2013 Depto. Ciencia de la Computacin e IA Lenguaje Lenguaje Java Avanzado 2012-2013 Depto. Ciencia de la Computacin e IA Lenguaje Java 2 ndice. Ciencia de la Computacin e IA Lenguaje Java 3 Java Java es un lenguaje OO creado por Sun Microsystems

  12. Experto Universitario Java Enterprise 2012-2013 Depto. Ciencia de la Computacin e IA

    E-Print Network [OSTI]

    Escolano, Francisco

    Experto Universitario Java Enterprise 2012-2013 Depto. Ciencia de la Computacin e IA Lenguaje Avanzado 2012-2013 Depto. Ciencia de la Computacin e IA Depuracin y logs - 2 El depurador de Eclipse Enterprise Lenguaje Java Avanzado 2012-2013 Depto. Ciencia de la Computacin e IA Depuracin y logs - 3 El

  13. Innovation Academy Change of Major Form (Out of IA) College of Agricultural and Life Sciences

    E-Print Network [OSTI]

    Jawitz, James W.

    Innovation Academy Change of Major Form (Out of IA) College of Agricultural and Life Sciences Academy Change of Major Form (Out of IA) College of Agricultural and Life Sciences SECTION 3: TO BE COMPLETED BY THE INNOVATION ACADEMY ADVISER IA Adviser's Comments/Conditions (circle

  14. Type Ia supernovae from exploding oxygen-neon white dwarfs

    E-Print Network [OSTI]

    Marquardt, Kai S; Ruiter, Ashley J; Seitenzahl, Ivo R; Ohlmann, Sebastian T; Kromer, Markus; Pakmor, Ruediger; Roepke, Friedrich K

    2015-01-01T23:59:59.000Z

    The progenitor problem of Type Ia supernovae (SNe Ia) is still unsolved. Most of these events are thought to be explosions of carbon-oxygen (CO) white dwarfs (WDs), but for many of the explosion scenarios, particularly those involving the externally triggered detonation of a sub-Chandrasekhar mass WD (sub-M Ch WD), there is also a possibility of having an oxygen-neon (ONe) WD as progenitor. We simulate detonations of ONe WDs and calculate synthetic observables from these models. The results are compared with detonations in CO WDs of similar mass and observational data of SNe Ia. We perform hydrodynamic explosion simulations of detonations in initially hydrostatic ONe WDs for a range of masses below the Chandrasekhar mass (M Ch), followed by detailed nucleosynthetic postprocessing with a 384-isotope nuclear reaction network. The results are used to calculate synthetic spectra and light curves, which are then compared with observations of SNe Ia. We also perform binary evolution calculations to determine the nu...

  15. Cosmic Supernova Rate History and Type Ia Supernova Progenitors

    E-Print Network [OSTI]

    Chiaki Kobayashi; Ken'ichi Nomoto; Takuji Tsujimoto

    2001-02-14T23:59:59.000Z

    Adopting a single degenerate scenario for Type Ia supernova progenitors with the metallicity effect, we make a prediction of the cosmic supernova rate history as a composite of the supernova rates in spiral and elliptical galaxies, and compare with the recent observational data up to z ~ 0.55.

  16. Probing the Type Ia environment with Light Echoes

    E-Print Network [OSTI]

    F. Patat

    2004-11-19T23:59:59.000Z

    In general, Light Echoes (LE) are beautiful, rather academical and therefore unavoidably useless phenomena. In some cases, however, they can give interesting information about the environment surrounding the exploding star. After giving a brief introduction to the subject, I describe its application to the case of Type Ia Supernovae and discuss the implications for progenitors and their location within the host galaxies.

  17. Weld Surfacing Edited by Dr I.A. Bucklow

    E-Print Network [OSTI]

    Cambridge, University of

    becomesconfigurationally frozen at a temperature of about 1150Cduring deposition by the manual-metal-arc welding techniqueV01.II Weld Surfacing Edited by Dr I.A. Bucklow ConferenceTechnicalDirector Organised by The Welding Institute in associationwith The Surface Engineering Society THE WELDING INSTITUTE #12;L

  18. Signatures of Explosion Models for SN ~Ia & Cosmology

    E-Print Network [OSTI]

    P. Hoeflich

    2004-09-07T23:59:59.000Z

    We give an overview of the current understanding of Type Ia supernovae relevant for their use as cosmological distance indicators. We present the physical basis to understand their homogeneity of the observed light curves and spectra and the observed correlations. SNe Ia have been well established as distance indicators on the 10 % level. However, the quest for the nature of the dark energy requires improvements in the accuracy to the 2 to 3 % level, we must understand the diversity within the SNe Ia population, and its evolution with redshift. Based on detailed models for the progenitors, explosions, light curves and spectra, we discuss signatures of thermonuclear explosions, and the implications for cosmology. We emphasize the relation between LC properties and spectra because, for local SNe~Ia, the diversity becomes apparent the combination of spectra and LCs whereas, by enlarge, we have to for high-z objects. At some examples, we show how we can actually probe the properties of the progenitor, its environment, and details of the explosion physics.

  19. Type Ia Supernova Cosmology in the Near-Infrared

    E-Print Network [OSTI]

    Stanishev, V; Amanullah, R; Bassett, B; Fantaye, Y T; Garnavich, P; Hlozek, R; Nordin, J; Okouma, P M; Ostman, L; Sako, M; Scalzo, R; Smith, M

    2015-01-01T23:59:59.000Z

    We main goal of this paper is to test whether the NIR peak magnitudes of SNe Ia could be accurately estimated with only a single observation obtained close to maximum light, provided the time of B band maximum and the optical stretch parameter are known. We obtained multi-epoch UBVRI and single-epoch J and H photometric observations of 16 SNe Ia in the redshift range z=0.037-0.183, doubling the leverage of the current SN Ia NIR Hubble diagram and the number of SNe beyond redshift 0.04. This sample was analyzed together with 102 NIR and 458 optical light curves (LCs) of normal SNe Ia from the literature. The analysis of 45 well-sampled NIR LCs shows that a single template accurately describes them if its time axis is stretched with the optical stretch parameter. This allows us to estimate the NIR peak magnitudes even with one observation obtained within 10 days from B-band maximum. We find that the NIR Hubble residuals show weak correlation with DM_15 and E(B-V), and for the first time we report a possible dep...

  20. On the Explosion Mechanism of SNe Type Ia

    E-Print Network [OSTI]

    M. Reinecke; J. C. Niemeyer; W. Hillebrandt

    2001-11-26T23:59:59.000Z

    In this article we discuss the first simulations of two- and three-dimensional Type Ia supernovae with an improved hydrodynamics code. After describing the various enhancements, the obtained results are compared to those of earlier code versions, observational data and the findings of other researchers in this field.

  1. Could there be a hole in type Ia supernovae?

    SciTech Connect (OSTI)

    Kasen, Daniel; Nugent, Peter; Thomas, R.C.; Wang, Lifan

    2004-04-23T23:59:59.000Z

    In the favored progenitor scenario, Type Ia supernovae (SNe Ia) arise from a white dwarf accreting material from a non-degenerate companion star. Soon after the white dwarf explodes, the ejected supernova material engulfs the companion star; two-dimensional hydrodynamical simulations by Marietta et al. (2001) show that, in the interaction, the companion star carves out a conical hole of opening angle 30-40 degrees in the supernova ejecta. In this paper we use multi-dimensional Monte Carlo radiative transfer calculations to explore the observable consequences of an ejecta-hole asymmetry. We calculate the variation of the spectrum, luminosity, and polarization with viewing angle for the aspherical supernova near maximum light. We find that the supernova looks normal from almost all viewing angles except when one looks almost directly down the hole. In the latter case, one sees into the deeper, hotter layers of ejecta. The supernova is relatively brighter and has a peculiar spectrum characterized by more highly ionized species, weaker absorption features, and lower absorption velocities. The spectrum viewed down the hole is comparable to the class of SN 1991T-like supernovae. We consider how the ejecta-hole asymmetry may explain the current spectropolarimetric observations of SNe Ia, and suggest a few observational signatures of the geometry. Finally, we discuss the variety currently seen in observed SNe Ia and how an ejecta-hole asymmetry may fit in as one of several possible sources of diversity.

  2. Nucleosynthesis in type Ia supernovae driven by asymmetric thermonuclear ignition

    SciTech Connect (OSTI)

    Maeda, Keiichi [Institute for the Physics and Mathematics of the Universe (IPMU), Todai Institutes for Advanced Study (TODIAS), University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8583 (Japan)

    2012-11-12T23:59:59.000Z

    Type Ia Supernovae (SNe Ia) are believed to be thermonuclear explosions of a white dwarf. They can be used as mature cosmological standardized candles, leading to the discovery of the accelerating expansion of the Universe. However, the explosion mechanism has not yet been fully clarified. In this paper, we first present nucleosynthetic features of a leading explosion scenario, namely a delayed-detonation scenario. Based on this, we propose a new and strong observational constraint on the explosion mechanism through emission lines from neutron-rich Fe-peaks. Especially, we show that an asymmetry in the explosion is likely a generic feature. We further argue that the diversity arising from various viewing angles can be an origin of observational diversities of SNe Ia seen in their spectral features (suspected possible biases in cosmology) and colors (related to the extinction estimate in cosmology). Using these new insights could open up a possibility of using SNe Ia as more precise distance indicators than currently employed.

  3. Effect of nuclear structure on Type Ia supernova nucleosynthesis

    E-Print Network [OSTI]

    D. J. Dean

    2000-12-08T23:59:59.000Z

    The relationship among nuclear structure, the weak processes in nuclei, and astrophysics becomes quite apparent in supernova explosion and nucleosynthesis studies. In this brief article, I report on progress made in the last few years on calculating electron capture and beta-decay rates in iron-group nuclei. I also report on applications of these rates to Type-Ia nucleosynthesis studies.

  4. Thermonuclear supernova models, and observations of Type Ia supernovae

    E-Print Network [OSTI]

    E. Bravo; C. Badenes; D. Garcia-Senz

    2004-12-07T23:59:59.000Z

    In this paper, we review the present state of theoretical models of thermonuclear supernovae, and compare their predicitions with the constraints derived from observations of Type Ia supernovae. The diversity of explosion mechanisms usually found in one-dimensional simulations is a direct consequence of the impossibility to resolve the flame structure under the assumption of spherical symmetry. Spherically symmetric models have been successful in explaining many of the observational features of Type Ia supernovae, but they rely on two kinds of empirical models: one that describes the behaviour of the flame on the scales unresolved by the code, and another that takes account of the evolution of the flame shape. In contrast, three-dimensional simulations are able to compute the flame shape in a self-consistent way, but they still need a model for the propagation of the flame in the scales unresolved by the code. Furthermore, in three dimensions the number of degrees of freedom of the initial configuration of the white dwarf at runaway is much larger than in one dimension. Recent simulations have shown that the sensitivity of the explosion output to the initial conditions can be extremely large. New paradigms of thermonuclear supernovae have emerged from this situation, as the Pulsating Reverse Detonation. The resolution of all these issues must rely on the predictions of observational properties of the models, and their comparison with current Type Ia supernova data, including X-ray spectra of Type Ia supernova remnants.

  5. Economic evaluation of the Annual Cycle Energy System. Volume I. Executive summary. Final report. [In Minneapolis, Atlanta, and Philadelphia

    SciTech Connect (OSTI)

    Not Available

    1980-05-01T23:59:59.000Z

    The objective of this study is to determine the energy effectiveness and the economic viability of the ACES concept. Three different classes of building are investigated, namely: single-family residence; multi-family residence; and commercial office building. The application of ACES to each of these building types is studied in three different climatic regions: Minneapolis, Atlanta, and Philadelphia. Computer programs - ACESIM for the residences and CACESS for the office building - were used, each comprised of four modules: loads; design; simulation; and economic. For each building type in each geographic location, the economic evaluation of the ACES is based on a comparison of the present worth of the ACES to the present worth of a number of conventional systems. The results of this analysis indicate that the economic viability of the ACES is very sensitive to the assumed value of the property tax, maintenace cost, and fuel-escalation rates, while it is relatively insensitive to the assumed values of other parameters. Fortunately, any conceivable change in the fuel-escalation rates would tend to increase the viability of the ACES concept. An increase in the assumed value of the maintenance cost or property tax would tend to make the ACES concept less viable; a decrease in either would tend to make the ACES concept more viable. The detailed results of this analysis are given in Section 5.4 of Volume II. 2 figures, 21 tables.

  6. Advantages of the Blue InGaN/GaN Light-Emitting Diodes with an AlGaN/GaN/AlGaN Quantum Well Structured Electron Blocking Layer

    E-Print Network [OSTI]

    Demir, Hilmi Volkan

    Advantages of the Blue InGaN/GaN Light-Emitting Diodes with an AlGaN/GaN/AlGaN Quantum Well ABSTRACT: InGaN/GaN light-emitting diodes (LEDs) with p-(AlGaN/GaN/AlGaN) quantum well structured electron. The proposed QWEBL LED structure, in which a p-GaN QW layer is inserted in the p-AlGaN electron blocking layer

  7. Micromechanical resonators fabricated from lattice-matched and etch-selective GaAs/InGaP/GaAs heterostructures

    E-Print Network [OSTI]

    Micromechanical resonators fabricated from lattice-matched and etch-selective GaAs/InGaP September 2007 Utilizing lattice-matched GaAs/InGaP/GaAs heterostructures, clean micromechanical resonators are fabricated and characterized. The nearly perfect selectivity of GaAs/InGaP is demonstrated by realizing

  8. Ga nanoparticle-enhanced photoluminescence of GaAs

    SciTech Connect (OSTI)

    Kang, M.; Al-Heji, A. A.; Jeon, S.; Wu, J. H. [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States)] [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States); Lee, J.-E.; Saucer, T. W.; Zhao, L.; Sih, V. [Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-1040 (United States)] [Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-1040 (United States); Katzenstein, A. L. [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States) [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States); Department of Physics, Eckerd College, St. Petersburg, Florida 33711-4744 (United States); Sofferman, D. L. [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States) [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States); Department of Physics, Adelphi University, Garden City, New York 11530-0701 (United States); Goldman, R. S. [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States) [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States); Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-1040 (United States)

    2013-09-02T23:59:59.000Z

    We have examined the influence of surface Ga nanoparticles (NPs) on the enhancement of GaAs photoluminescence (PL) efficiency. We have utilized off-normal focused-ion-beam irradiation of GaAs surfaces to fabricate close-packed Ga NP arrays. The enhancement in PL efficiency is inversely proportional to the Ga NP diameter. The maximum PL enhancement occurs for the Ga NP diameter predicted to maximize the incident electromagnetic (EM) field enhancement. The PL enhancement is driven by the surface plasmon resonance (SPR)-induced enhancement of the incident EM field which overwhelms the SPR-induced suppression of the light emission.

  9. Low-Metallicity Inhibition of Type Ia Supernovae and Galactic and Cosmic Chemical Evolution

    E-Print Network [OSTI]

    Chiaki Kobayashi; Takuji Tsujimoto; Ken'ich Nomoto; Izumi Hachisu; Mariko Kato

    1998-06-25T23:59:59.000Z

    We introduce a metallicity dependence of Type Ia supernova (SN Ia) rate into the Galactic and cosmic chemical evolution models. In our SN Ia progenitor scenario, the accreting white dwarf (WD) blows a strong wind to reach the Chandrasekhar mass limit. If the iron abundance of the progenitors is as low as [Fe/H] 1-2, SNe Ia can be found only in the environments where the timescale of metal enrichment is sufficiently short as in starburst galaxies and ellipticals. The low-metallicity inhibition of SNe Ia can shed new light on the following issues: 1) The limited metallicity range of the SN Ia progenitors would imply that ``evolution effects'' are relatively small for the use of high redshift SNe Ia to determine the cosmological parameters. 2) WDs of halo populations are poor producers of SNe Ia, so that the WD contribution to the halo mass is not constrained from the iron abundance in the halo. 3) The abundance patterns of globular clusters and field stars in the Galactic halo lack of SN Ia signatures in spite of their age difference of several Gyrs, which can be explained by the low-metallicity inhibition of SNe Ia. 4) It could also explain why the SN Ia contamination is not seen in the damped Ly\\alpha systems for over a wide range of redshift.

  10. An Analysis of Department of Defense Instruction 8500.2 'Information Assurance (IA) Implementation.'

    SciTech Connect (OSTI)

    Campbell, Philip LaRoche

    2012-01-01T23:59:59.000Z

    The Department of Defense (DoD) provides its standard for information assurance in its Instruction 8500.2, dated February 6, 2003. This Instruction lists 157 'IA Controls' for nine 'baseline IA levels.' Aside from distinguishing IA Controls that call for elevated levels of 'robustness' and grouping the IA Controls into eight 'subject areas' 8500.2 does not examine the nature of this set of controls, determining, for example, which controls do not vary in robustness, how this set of controls compares with other such sets, or even which controls are required for all nine baseline IA levels. This report analyzes (1) the IA Controls, (2) the subject areas, and (3) the Baseline IA levels. For example, this report notes that there are only 109 core IA Controls (which this report refers to as 'ICGs'), that 43 of these core IA Controls apply without variation to all nine baseline IA levels and that an additional 31 apply with variations. This report maps the IA Controls of 8500.2 to the controls in NIST 800-53 and ITGI's CoBIT. The result of this analysis and mapping, as shown in this report, serves as a companion to 8500.2. (An electronic spreadsheet accompanies this report.)

  11. AlGaN/GaN-based power semiconductor switches

    E-Print Network [OSTI]

    Lu, Bin, Ph. D. Massachusetts Institute of Technology

    2013-01-01T23:59:59.000Z

    AlGaN/GaN-based high-electron-mobility transistors (HEMTs) have great potential for their use as high efficiency and high speed power semiconductor switches, thanks to their high breakdown electric field, mobility and ...

  12. GaAs/InGaP/AlGaAs quantum-well infrared photodetectors

    SciTech Connect (OSTI)

    Keshagupta, P.; Radpour, F. [Univ. of Cincinnati, OH (United States)

    1994-12-31T23:59:59.000Z

    In this paper, a new quantum-well infrared photodetector (QWIP) based on bound-to-miniband transitions in a GaAs/InGaP quantum well with GaAs/AlGaAs short superlattice barriers is presented and compared with the conventional GaAs/InGaP QWIPs. Results of the theoretical calculations of the detector parameters and the preliminary fabrication results of an embedded-well to miniband (EWTMB) GaAs/InGaP/AlGaAs quantum well/superlattice detector are presented. The advantages of the proposed design include improvement of the material quality, ability to adjust the peak wavelength in 8--12 {micro}m range, and in the lower dark current.

  13. Learning from the Scatter in Type Ia Supernovae

    E-Print Network [OSTI]

    Scott Dodelson; Alberto Vallinotto

    2005-11-02T23:59:59.000Z

    Type Ia Supernovae are standard candles so their mean apparent magnitude has been exploited to learn about the redshift-distance relationship. Besides intrinsic scatter in this standard candle, additional source of scatter is caused by gravitational magnification by large scale structure. Here we probe the dependence of this dispersion on cosmological parameters and show that information about the amplitude of clustering, \\sigma_8, is contained in the scatter. In principle, it will be possible to constrain \\sigma_8 to within 5% with observations of 2000 Type Ia Supernovae. However, extracting this information requires subtlety as the distribution of magnifications is far from Gaussian. If one incorrectly assumes a Gaussian distribution, the estimate of the clustering amplitude will be biased three-\\sigma away from the true value.

  14. Multi-spot ignition in type Ia supernova models

    E-Print Network [OSTI]

    Roepke, F K; Niemeyer, J C; Woosley, S E

    2005-01-01T23:59:59.000Z

    We present a systematic survey of the capabilities of type Ia supernova explosion models starting from a number of flame seeds distributed around the center of the white dwarf star. To this end we greatly improved the resolution of the numerical simulations in the initial stages. This novel numerical approach facilitates a detailed study of multi-spot ignition scenarios with up to hundreds of ignition sparks. Two-dimensional simulations are shown to be inappropriate to study the effects of initial flame configurations. Based on a set of three-dimensional models, we conclude that multi-spot ignition scenarios may improve type Ia supernova models towards better agreement with observations. The achievable effect reaches a maximum at a limited number of flame ignition kernels as shown by the numerical models and corroborated by a simple dimensional analysis.

  15. Multi-spot ignition in type Ia supernova models

    E-Print Network [OSTI]

    F. K. Roepke; W. Hillebrandt; J. C. Niemeyer; S. E. Woosley

    2005-10-17T23:59:59.000Z

    We present a systematic survey of the capabilities of type Ia supernova explosion models starting from a number of flame seeds distributed around the center of the white dwarf star. To this end we greatly improved the resolution of the numerical simulations in the initial stages. This novel numerical approach facilitates a detailed study of multi-spot ignition scenarios with up to hundreds of ignition sparks. Two-dimensional simulations are shown to be inappropriate to study the effects of initial flame configurations. Based on a set of three-dimensional models, we conclude that multi-spot ignition scenarios may improve type Ia supernova models towards better agreement with observations. The achievable effect reaches a maximum at a limited number of flame ignition kernels as shown by the numerical models and corroborated by a simple dimensional analysis.

  16. Type Ia Supernova Spectral Line Ratios as LuminosityIndicators

    SciTech Connect (OSTI)

    Bongard, Sebastien; Baron, E.; Smadja, G.; Branch, David; Hauschildt, Peter H.

    2005-12-07T23:59:59.000Z

    Type Ia supernovae have played a crucial role in thediscovery of the dark energy, via the measurement of their light curvesand the determination of the peak brightness via fitting templates to theobserved lightcurve shape. Two spectroscopic indicators are also known tobe well correlated with peak luminosity. Since the spectroscopicluminosity indicators are obtained directly from observed spectra, theywill have different systematic errors than do measurements usingphotometry. Additionally, these spectroscopic indicators may be usefulfor studies of effects of evolution or age of the SNe~;Ia progenitorpopulation. We present several new variants of such spectroscopicindicators which are easy to automate and which minimize the effects ofnoise. We show that these spectroscopic indicators can be measured byproposed JDEM missions such as snap and JEDI.

  17. Investigating the Flame Microstructure in Type Ia Supernovae

    E-Print Network [OSTI]

    Roepke, F K; Niemeyer, J C

    2002-01-01T23:59:59.000Z

    We present a numerical model to study the behavior of thermonuclear flames in the discontinuity approximation. This model is applied to investigate the Landau-Darrieus instability under conditions found in Type Ia supernova explosions of Chandrasekhar mass white dwarfs. This is a first step to explore the flame microstructure in these events. The model reproduces Landau's linearized stability analysis in early stages of the flame evolution and the stabilization in a cellular flame structure in the nonlinear stage.

  18. Investigating the Flame Microstructure in Type Ia Supernovae

    E-Print Network [OSTI]

    F. K. Roepke; W. Hillebrandt; J. C. Niemeyer

    2002-04-02T23:59:59.000Z

    We present a numerical model to study the behavior of thermonuclear flames in the discontinuity approximation. This model is applied to investigate the Landau-Darrieus instability under conditions found in Type Ia supernova explosions of Chandrasekhar mass white dwarfs. This is a first step to explore the flame microstructure in these events. The model reproduces Landau's linearized stability analysis in early stages of the flame evolution and the stabilization in a cellular flame structure in the nonlinear stage.

  19. X- and Gamma-Ray Flashes from Type Ia Supernovae?

    E-Print Network [OSTI]

    Hoflich, Peter

    2009-01-01T23:59:59.000Z

    We investigate two potential mechanisms that will produce X-ray and gamma-ray flashes from Type Ia supernovae (SN-Ia). The mechanisms are the breakout of the thermonuclear burning front as it reaches the surface of the white dwarf and the interaction of the rapidly expanding envelope with an accretion disk. Based on the delayed-detonation scenario and detailed radiation-hydro calculation which include nuclear networks, we find that both mechanisms produce ~1 second flashes of high energy radiation with peak luminosities of 10^48 to 10^50 erg/sec with fast rises and exponential declines. The X- and gamma-ray visibility of a SN-Ia will depend strongly on self absorption within the progenitor system, specifically on the properties of the accretion disk and its orientation towards the observer. Such X-ray and gamma-ray flashes could be detected as triggered events by Gamma-Ray Burst (GRB) detectors on satellites, with events in current GRB catalogs. We have searched through the GRB catalogs (for the BATSE, HETE, ...

  20. The type Ia supernovae and the Hubble's constant

    E-Print Network [OSTI]

    Ari Brynjolfsson

    2004-07-20T23:59:59.000Z

    The Hubble's constant is usually surmised to be a constant; but the experiments show a large spread and conflicting estimates. According to the plasma-redshift theory, the Hubble's constant varies with the plasma densities along the line of sight. It varies then slightly with the direction and the distance to a supernova and a galaxy. The relation between the magnitudes of type Ia supernovae and their observed redshifts results in an Hubble's constant with an average value in intergalactic space of 59.44 km per s per Mpc. The standard deviation from this average value is only 0.6 km per s per Mpc, but the standard deviation in a single measurement is about 8.2 km per s per Mpc. These deviations do not include possible absolute calibration errors. The experiments show that the Hubble's constant varies with the intrinsic redshifts of the Milky Way galaxy and the host galaxies for type Ia supernovae, and that it varies with the galactic latitude. These findings support the plasma-redshift theory and contradict the contemporary big-bang theory. Together with the previously reported absence of time dilation in type Ia supernovae measurements, these findings have profound consequences for the standard cosmological theory.

  1. Theoretical Clues to the Ultraviolet Diversity of Type Ia Supernovae

    E-Print Network [OSTI]

    Brown, Peter J; Milne, Peter; Roming, Peter W A; Wang, Lifan

    2015-01-01T23:59:59.000Z

    The effect of metallicity on the observed light of Type Ia supernovae (SNe Ia) could lead to systematic errors as the absolute magnitudes of local and distant SNe Ia are compared to measure luminosity distances and determine cosmological parameters. The UV light may be especially sensitive to metallicity, though different modeling methods disagree as to the magnitude, wavelength dependence, and even the sign of the effect. The outer density structure, ^56 Ni, and to a lesser degree asphericity, also impact the UV. We compute synthetic photometry of various metallicity-dependent models and compare to UV/optical photometry from the Swift Ultra-Violet/Optical Telescope. We find that the scatter in the mid-UV to near-UV colors is larger than predicted by changes in metallicity alone and is not consistent with reddening. We demonstrate that a recently employed method to determine relative abundances using UV spectra can be done using UVOT photometry, but we warn that accurate results require an accurate model of t...

  2. CARBON DEFLAGRATION IN TYPE Ia SUPERNOVA. I. CENTRALLY IGNITED MODELS

    SciTech Connect (OSTI)

    Ma, H.; Woosley, S. E.; Malone, C. M. [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Almgren, A.; Bell, J. [Center for Computational Sciences and Engineering, Lawrence Berkeley National Lab, Berkeley, CA 94720 (United States)

    2013-07-01T23:59:59.000Z

    A leading model for Type Ia supernovae (SNe Ia) begins with a white dwarf near the Chandrasekhar mass that ignites a degenerate thermonuclear runaway close to its center and explodes. In a series of papers, we shall explore the consequences of ignition at several locations within such dwarfs. Here we assume central ignition, which has been explored before, but is worth revisiting, if only to validate those previous studies and to further elucidate the relevant physics for future work. A perturbed sphere of hot iron ash with a radius of {approx}100 km is initialized at the middle of the star. The subsequent explosion is followed in several simulations using a thickened flame model in which the flame speed is either fixed-within the range expected from turbulent combustion-or based on the local turbulent intensity. Global results, including the explosion energy and bulk nucleosynthesis (e.g., {sup 56}Ni of 0.48-0.56 M{sub Sun }) turn out to be insensitive to this speed. In all completed runs, the energy released by the nuclear burning is adequate to unbind the star, but not enough to give the energy and brightness of typical SNe Ia. As found previously, the chemical stratification observed in typical events is not reproduced. These models produce a large amount of unburned carbon and oxygen in central low velocity regions, which is inconsistent with spectroscopic observations, and the intermediate mass elements and iron group elements are strongly mixed during the explosion.

  3. Carrier spin relaxation in GaInNAsSb/GaNAsSb/GaAs quantum well

    SciTech Connect (OSTI)

    Asami, T.; Nosho, H.; Tackeuchi, A. [Department of Applied Physics, Waseda University, Shinjuku, Tokyo 169-8555 (Japan); Li, L. H.; Harmand, J. C. [Laboratory for Photonics and Nanostructures-CNRS, Site Alcatel de Marcoussis, Route de Nozay, 91460 Marcoussis (France); Lu, S. L. [Suzhou Institute of Nano-tech and Nano-bionics, CAS, Dushu, Lake Higher Education Town, Ruoshui Road 398, Suzhou Industrial Park, Suzhou 215125 (China)

    2011-12-23T23:59:59.000Z

    We have investigated the carrier spin relaxation in GaInNAsSb/GaNAsSb/GaAs quantum well (QW) by time-resolved photoluminescence (PL) measurement. The sample consists of an 8-nm-thick GaIn{sub 0.36}N{sub 0.006}AsSb{sub 0.015} well, 5-nm-thick GaN{sub 0.01}AsSb{sub 0.11} intermediate barriers and 100-nm-thick GaAs barriers grown by molecular beam epitaxy on a GaAs(100) substrate. The spin relaxation time and recombination lifetime at 10 K are measured to be 228 ps and 151 ps, respectively. As a reference, we have also obtained a spin relaxation time of 125 ps and a recombination lifetime of 63 ps for GaInNAs/GaNAs/GaAs QW. This result shows that crystal quality is slightly improved by adding Sb, although these short carrier lifetimes mainly originate from a nonradiative recombination. These spin relaxation times are longer than the 36 ps spin relaxation time of InGaAs/InP QWs and shorter than the 2 ns spin relaxation time of GaInNAs/GaAs QW.

  4. Compositionally-graded InGaAsInGaP alloys and GaAsSb alloys for metamorphic InP on GaAs

    E-Print Network [OSTI]

    Compositionally-graded InGaAsInGaP alloys and GaAsSb alloys for metamorphic InP on GaAs Li Yang a of tandem graded layers of InGaAs and InGaP with compositional grading of the In concentration. This tandem

  5. Attir Khalid William Singhose

    E-Print Network [OSTI]

    Singhose, William

    Department of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0405 David Frakes 4

  6. THE IMPACT OF METALLICITY ON THE RATE OF TYPE Ia SUPERNOVAE

    SciTech Connect (OSTI)

    Kistler, Matthew D. [California Institute of Technology, Mail Code 350-17, Pasadena, CA 91125 (United States); Stanek, K. Z.; Kochanek, Christopher S.; Thompson, Todd A. [Center for Cosmology and Astro-Particle Physics, Ohio State University, Columbus, OH 43210 (United States); Prieto, Jose L. [Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101 (United States)

    2013-06-20T23:59:59.000Z

    The metallicity of a star strongly affects both its evolution and the properties of the stellar remnant that results from its demise. It is generally accepted that stars with initial masses below {approx}8 M{sub Sun} leave behind white dwarfs and that some sub-population of these lead to Type Ia supernovae (SNe Ia). However, it is often tacitly assumed that metallicity has no effect on the rate of SNe Ia. We propose that a consequence of the effects of metallicity is to significantly increase the SN Ia rate in lower-metallicity galaxies, in contrast to previous expectations. This is because lower-metallicity stars leave behind higher-mass white dwarfs, which should be easier to bring to explosion. We first model SN Ia rates in relation to galaxy masses and ages alone, finding that the elevation in the rate of SNe Ia in lower-mass galaxies measured by Lick Observatory SN Search is readily explained. However, we then see that models incorporating this effect of metallicity agree just as well. Using the same parameters to estimate the cosmic SN Ia rate, we again find good agreement with data up to z Almost-Equal-To 2. We suggest that this degeneracy warrants more detailed examination of host galaxy metallicities. We discuss additional implications, including for hosts of high-z SNe Ia, the SN Ia delay time distribution, super-Chandrasekhar SNe, and cosmology.

  7. High-Redshift Type Ia Supernova Rates in Galaxy Cluster and Field Environments

    E-Print Network [OSTI]

    Barbary, Kyle Harris

    2011-01-01T23:59:59.000Z

    29 Candidates classified as supernovae . . . . . . . .1.1 Type Ia Supernovae as Standard Candles . . . . . . . .4.2.3 Supernovae . . . . . . . . . . . . . . . . 4.2.4

  8. Multi-layered Spectral Formation in SNe Ia Around Maximum Light

    E-Print Network [OSTI]

    Bongard, Sebastien

    2008-01-01T23:59:59.000Z

    stars: atmospheres supernovae DISCLAIMER This document wasIntroduction Type Ia supernov have been used as spanning the normal supernov blue magnitudes. Single Ion

  9. Timescale stretch parameterization of Type Ia supernova B-band light curves

    E-Print Network [OSTI]

    2001-01-01T23:59:59.000Z

    the light curve of Type Ia supernovae discovered by theof the high-redshift supernovae. This work was supported inobjects. Subject headings: supernovae: general cosmology:

  10. HOST GALAXY PROPERTIES AND HUBBLE RESIDUALS OF TYPE Ia SUPERNOVAE FROM THE NEARBY SUPERNOVA FACTORY

    SciTech Connect (OSTI)

    Childress, M.; Aldering, G.; Aragon, C.; Bailey, S.; Fakhouri, H. K.; Hsiao, E. Y.; Kim, A. G.; Loken, S. [Physics Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720 (United States); Antilogus, P.; Bongard, S.; Canto, A.; Cellier-Holzem, F.; Guy, J. [Laboratoire de Physique Nucleaire et des Hautes Energies, Universite Pierre et Marie Curie Paris 6, Universite Paris Diderot Paris 7, CNRS-IN2P3, 4 place Jussieu, F-75252 Paris Cedex 05 (France); Baltay, C. [Department of Physics, Yale University, New Haven, CT 06250-8121 (United States); Buton, C.; Kerschhaggl, M.; Kowalski, M. [Physikalisches Institut, Universitaet Bonn, Nussallee 12, D-53115 Bonn (Germany); Chotard, N.; Copin, Y.; Gangler, E. [Universite de Lyon, F-69622, Lyon (France); Universite de Lyon 1, Villeurbanne (France); CNRS/IN2P3, Institut de Physique Nucleaire de Lyon (France); and others

    2013-06-20T23:59:59.000Z

    We examine the relationship between Type Ia supernova (SN Ia) Hubble residuals and the properties of their host galaxies using a sample of 115 SNe Ia from the Nearby Supernova Factory. We use host galaxy stellar masses and specific star formation rates fitted from photometry for all hosts, as well as gas-phase metallicities for a subset of 69 star-forming (non-active galactic nucleus) hosts, to show that the SN Ia Hubble residuals correlate with each of these host properties. With these data we find new evidence for a correlation between SN Ia intrinsic color and host metallicity. When we combine our data with those of other published SN Ia surveys, we find the difference between mean SN Ia brightnesses in low- and high-mass hosts is 0.077 {+-} 0.014 mag. When viewed in narrow (0.2 dex) bins of host stellar mass, the data reveal apparent plateaus of Hubble residuals at high and low host masses with a rapid transition over a short mass range (9.8 {<=} log (M{sub *}/M{sub Sun }) {<=} 10.4). Although metallicity has been a favored interpretation for the origin of the Hubble residual trend with host mass, we illustrate how dust in star-forming galaxies and mean SN Ia progenitor age both evolve along the galaxy mass sequence, thereby presenting equally viable explanations for some or all of the observed SN Ia host bias.

  11. Direct numerical simulations of type Ia supernovae flames II: The rayleigh-taylor instability

    E-Print Network [OSTI]

    Bell, J.B.; Day, M.S.; Rendleman, C.A.; Woosley, S.E.; Zingale, M.

    2004-01-01T23:59:59.000Z

    Weaver, T. A. 1994, in Supernovae, Les Houches, Session LIV,Simulations of Type Ia Supernovae Flames II: The Rayleigh-Subject headings: supernovae: general white dwarfs

  12. Reflections on Reflexions: I. Light Echoes in Type Ia Supernovae

    E-Print Network [OSTI]

    F. Patat

    2004-09-28T23:59:59.000Z

    In the last ten years, observational evidences about a possible connection between Type Ia Supernovae (SNe) properties and the environment where they explode have been steadily growing. In this paper I discuss, from a theoretical point of view but with an observer's perspective, the usage of light echoes (LEs) to probe the CSM around SNe of Type Ia since, in principle, they give us a unique opportunity of getting a three-dimensional description of the SN environment. In turn, this can be used to check the often suggested association of some Ia's with dusty/star forming regions, which would point to a young population for the progenitors. After giving a brief introduction to the LE phenomenon in single scattering approximation, I derive analytical and numerical solutions for the optical light and colour curves for a few simple dust geometries. A fully 3D multiple scattering treatment has also been implemented in a Monte Carlo code, which I have used to investigate the effects of multiple scattering. In particular, I have explored in detail the LE colour dependency from time and dust distribution, since this is a promising tool to determine the dust density and derive the effective presence of multiple scattering from the observed properties. Finally, again by means of Monte Carlo simulations, I have studied the effects of multiple scattering on the LE linear polarization, analyzing the dependencies from the dust parameters and geometry. Both the analytical formalism and MC codes described in this paper can be used for any LE for which the light curve of the central source is known.

  13. The Carnegie Supernova Project: Intrinsic colors of type Ia supernovae

    SciTech Connect (OSTI)

    Burns, Christopher R.; Persson, S. E.; Freedman, Wendy L.; Madore, Barry F. [Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Stritzinger, Maximilian; Contreras, Carlos [Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C (Denmark); Phillips, M. M.; Hsiao, E. Y.; Boldt, Luis; Campillay, Abdo; Castelln, Sergio; Morrell, Nidia; Salgado, Francisco [Carnegie Institution of Washington, Las Campanas Observatory, Colina El Pino, Casilla 601 (Chile); Folatelli, Gaston [Kavli Institute for the Physics and Mathematics of the Universe, Todai Institutes for Advanced Study, the University of Tokyo, 277-8583 Kashiwa (Japan); Suntzeff, Nicholas B. [George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Texas A and M University, Department of Physics and Astronomy, College Station, TX 77843 (United States)

    2014-07-01T23:59:59.000Z

    We present an updated analysis of the intrinsic colors of Type Ia supernova (SNe Ia) using the latest data release of the Carnegie Supernova Project. We introduce a new light-curve parameter very similar to stretch that is better suited for fast-declining events, and find that these peculiar types can be seen as extensions to the population of 'normal' SNe Ia. With a larger number of objects, an updated fit to the Lira relation is presented along with evidence for a dependence on the late-time slope of the B V light-curves with stretch and color. Using the full wavelength range from u to H band, we place constraints on the reddening law for the sample as a whole and also for individual events/hosts based solely on the observed colors. The photometric data continue to favor low values of R{sub V} , though with large variations from event to event, indicating an intrinsic distribution. We confirm the findings of other groups that there appears to be a correlation between the derived reddening law, R{sub V} , and the color excess, E(B V), such that larger E(B V) tends to favor lower R{sub V} . The intrinsic u-band colors show a relatively large scatter that cannot be explained by variations in R{sub V} or by the Goobar power-law for circumstellar dust, but rather is correlated with spectroscopic features of the supernova and is therefore likely due to metallicity effects.

  14. Low frequency noise in AlGaN/InGaN/GaN double heterostructure field effect transistors

    E-Print Network [OSTI]

    Pala, Nezih

    Torr and consisted of a 1.4 lm undoped GaN buffer layer on i-SiC substrate, * Corresponding authorLow frequency noise in AlGaN/InGaN/GaN double heterostructure field effect transistors N. Pala a November 2002 Abstract Low-frequency noise in AlGaN/InGaN/GaN double heterostructure field effect

  15. A Model for Multidimensional Delayed Detonations in SN Ia Explosions

    E-Print Network [OSTI]

    I. Golombek; J. C. Niemeyer

    2005-03-29T23:59:59.000Z

    We show that a flame tracking/capturing scheme originally developed for deflagration fronts can be used to model thermonuclear detonations in multidimensional explosion simulations of type Ia supernovae. After testing the accuracy of the front model, we present a set of two-dimensional simulations of delayed detonations with a physically motivated off-center deflagration-detonation-transition point. Furthermore, we demonstrate the ability of the front model to reproduce the full range of possible interactions of the detonation with clumps of burned material. This feature is crucial for assessing the viability of the delayed detonation scenario.

  16. Can Deflagration-Detonation-Transitions occur in Type Ia Supernovae?

    E-Print Network [OSTI]

    J. C. Niemeyer

    1999-07-19T23:59:59.000Z

    The mechanism for deflagration-detonation-transition (DDT) by turbulent preconditioning, suggested to explain the possible occurrence of delayed detonations in Type Ia supernova explosions, is argued to be conceptually inconsistent. It relies crucially on diffusive heat losses of the burned material on macroscopic scales. Regardless of the amplitude of turbulent velocity fluctuations, the typical gradient scale for temperature fluctuations is shown to be the laminar flame width or smaller, rather than the factor of thousand more required for a DDT. Furthermore, thermonuclear flames cannot be fully quenched in regions much larger than the laminar flame width as a consequence of their simple ``chemistry''. Possible alternative explosion scenarios are briefly discussed.

  17. Three-dimensional simulations of type Ia supernovae

    E-Print Network [OSTI]

    M. Reinecke; W. Hillebrandt; J. C. Niemeyer

    2002-06-26T23:59:59.000Z

    We present the results of three-dimensional hydrodynamical simulations of the subsonic thermonuclear burning phase in type Ia supernovae. The burning front model contains no adjustable parameters so that variations of the explosion outcome can be linked directly to changes in the initial conditions. In particular, we investigate the influence of the initial flame geometry on the explosion energy and find that it appears to be weaker than in 2D. Most importantly, our models predict global properties such as the produced nickel masses and ejecta velocities within their observed ranges without any fine tuning.

  18. Three-dimensional simulations of type Ia supernovae

    E-Print Network [OSTI]

    Reinecke, M; Niemeyer, J C

    2002-01-01T23:59:59.000Z

    We present the results of three-dimensional hydrodynamical simulations of the subsonic thermonuclear burning phase in type Ia supernovae. The burning front model contains no adjustable parameters so that variations of the explosion outcome can be linked directly to changes in the initial conditions. In particular, we investigate the influence of the initial flame geometry on the explosion energy and find that it appears to be weaker than in 2D. Most importantly, our models predict global properties such as the produced nickel masses and ejecta velocities within their observed ranges without any fine tuning.

  19. Marginal evidence for cosmic acceleration from Type Ia supernovae

    E-Print Network [OSTI]

    Nielsen, Jeppe Trst; Sarkar, Subir

    2015-01-01T23:59:59.000Z

    The `standard' model of cosmology is founded on the basis that the expansion rate of the universe is accelerating at present --- as was inferred originally from the Hubble diagram of Type Ia supernovae. There exists now a much bigger database of supernovae so we can perform rigorous statistical tests to check whether these `standardisable candles' indeed indicate cosmic acceleration. Taking account of the empirical procedure by which corrections are made to their absolute magnitudes to allow for the varying shape of the light curve and extinction by dust, we find, rather surprisingly, that the data are still quite consistent with a constant rate of expansion.

  20. Polarization-engineered GaN/InGaN/GaN tunnel diodes

    E-Print Network [OSTI]

    Sriram Krishnamoorthy; Digbijoy N. Nath; Fatih Akyol; Pil Sung Park; Michele Esposto; Siddharth Rajan

    2010-08-24T23:59:59.000Z

    We report on the design and demonstration of polarization-engineered GaN/InGaN/GaN tunnel junction diodes with high current density and low tunneling turn-on voltage. Wentzel-Kramers-Brillouin (WKB) calculations were used to model and design tunnel junctions with narrow bandgap InGaN-based barrier layers. N-polar p-GaN/In0.33Ga0.67N/n-GaN heterostructure tunnel diodes were grown using molecular beam epitaxy. Efficient zero bias tunneling turn-on with a high current density of 118 A/cm2 at a reverse bias of 1V, reaching a maximum current density up to 9.2 kA/cm2 were obtained. These results represent the highest current density reported in III-nitride tunnel junctions, and demonstrate the potential of III-nitride tunnel devices for a broad range of optoelectronic and electronic applications.

  1. Violet to deep-ultraviolet InGaN/GaN and GaN/AlGaN quantum structures for UV electroabsorption modulators

    E-Print Network [OSTI]

    Demir, Hilmi Volkan

    Violet to deep-ultraviolet InGaN/GaN and GaN/AlGaN quantum structures for UV electroabsorption In this paper, we present four GaN based polar quantum structures grown on c-plane embedded in p-i-n diode GaN/AlGaN quantum structures for operation in the deep-UV spectral region and the other three

  2. Grouping normal type Ia supernovae by UV to optical color differences

    SciTech Connect (OSTI)

    Milne, Peter A. [University of Arizona, Steward Observatory, 933 North Cherry Avenue, Tucson, AZ 85719 (United States); Brown, Peter J. [George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Texas A. and M. University, Department of Physics and Astronomy, 4242 TAMU, College Station, TX 77843 (United States); Roming, Peter W. A. [Space Science and Engineering Division, Southwest Research Corporation, P.O. Drawer 28510, San Antonio, TX 78228-0510 (United States); Bufano, Filomena [Universidad Andres Bello, Departmento de Cincias Fisicas, Avda. Republica 220, Santiago (Chile); Gehrels, Neil, E-mail: pbrown@physics.tamu.edu [NASA-Goddard Space Flight Center, Astrophysics Science Division, Codes 660.1 and 662, Greenbelt, MD 20771 (United States)

    2013-12-10T23:59:59.000Z

    Observations of many Type Ia supernovae (SNe Ia) for multiple epochs per object with the Swift Ultraviolet Optical Telescope instrument have revealed that there exists order to the differences in the UV-optical colors of optically normal supernovae (SNe). We examine UV-optical color curves for 23 SNe Ia, dividing the SNe into four groups, and find that roughly one-third of 'NUV-blue' SNe Ia have bluer UV-optical colors than the larger 'NUV-red' group. Two minor groups are recognized, 'MUV-blue' and 'irregular' SNe Ia. While we conclude that the latter group is a subset of the NUV-red group, containing the SNe with the broadest optical peaks, we conclude that the 'MUV-blue' group is a distinct group. Separating into the groups and accounting for the time evolution of the UV-optical colors lowers the scatter in two NUV-optical colors (e.g., u v and uvw1 v) to the level of the scatter in b v. This finding is promising for extending the cosmological utilization of SNe Ia into the NUV. We generate spectrophotometry of 33 SNe Ia and determine the correct grouping for each. We argue that there is a fundamental spectral difference in the 2900-3500 wavelength range, a region suggested to be dominated by absorption from iron-peak elements. The NUV-blue SNe Ia feature less absorption than the NUV-red SNe Ia. We show that all NUV-blue SNe Ia in this sample also show evidence of unburned carbon in optical spectra, whereas only one NUV-red SN Ia features that absorption line. Every NUV-blue event also exhibits a low gradient of the Si II ?6355 absorption feature. Many NUV-red events also exhibit a low gradient, perhaps suggestive that NUV-blue events are a subset of the larger low-velocity gradient group.

  3. Luminescence Efficiency of InGaN/GaN Quantum Wells on Bulk GaN Substrate M. Dworzak1

    E-Print Network [OSTI]

    Nabben, Reinhard

    Luminescence Efficiency of InGaN/GaN Quantum Wells on Bulk GaN Substrate M. Dworzak1 , T. Stempel1/37, 01-142 Warsaw, Poland ABSTRACT Time-integrated and time-resolved photoluminescence measurements on InGaN quantum wells grown by MOCVD on two different substrates (sapphire and GaN) show that the lumines- cence

  4. Analysis of InGaN light-emitting diodes with GaN-AlGaN and AlGaN-GaN composition-graded barriers

    SciTech Connect (OSTI)

    Yang, Yujue; Wang, Junxi; Li, Jinmin; Zeng, Yiping, E-mail: ypzeng@semi.ac.cn [Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083 (China)

    2014-06-21T23:59:59.000Z

    The effects of InGaN-based light-emitting diodes (LEDs) with Al composition increasing and decreasing GaN-AlGaN barriers along the growth direction are studied numerically. Simulation results suggest that the LEDs with GaN-AlGaN composition-decreased barriers show more significant enhancement of light-output power and internal quantum efficiency than LEDs with composition-increasing GaN-AlGaN barriers when compared with the conventional LED with GaN barriers, due to the improvement in hole injection efficiency and electron blocking capability. Moreover, the optical performance is further improved by replacing GaN-AlGaN barriers with AlGaN-GaN barriers of the same Al composition-decreasing range, which are mainly attributed to the modified band diagrams. In addition, the major causes of the different efficiency droop behaviors for all the designed structures are explained by the electron leakage current and the different increase rates of hole concentration with injection current.

  5. Design and fabrication of InGaN/GaN heterojunction bipolar transistors for microwave power amplifiers

    E-Print Network [OSTI]

    Keogh, David Martin

    2006-01-01T23:59:59.000Z

    T. Henderson, High- Speed InGaP/GaAs HBTs Using a SimpleA typical AlGaAs/GaAs HBT or InGaP/GaAs HBT has the opposite

  6. MULTIMEDIA INSTRUCTIONS IN IA-64 Ruby B. Lee, A. Murat Fiskiran and Abdulla Bubshait

    E-Print Network [OSTI]

    Lee, Ruby B.

    MULTIMEDIA INSTRUCTIONS IN IA-64 Ruby B. Lee, A. Murat Fiskiran and Abdulla Bubshait Department discuss the integer and floating-point multimedia instructions in the IA-64 instruction-set architecture (ISA). These multimedia instructions implement subword parallelism, also called packed parallelism

  7. Experto Universitario Java Enterprise 2012-2013 Depto. Ciencia de la Computacin e IA

    E-Print Network [OSTI]

    Escolano, Francisco

    Experto Universitario Java Enterprise 2012-2013 Depto. Ciencia de la Computacin e IA Lenguaje Java Avanzado Sesin 3: Tratamiento de errores #12;Lenguaje Java Avanzado 2012-2013 Depto. Ciencia de Tipos genricos #12;Lenguaje Java Avanzado 2012-2013 Depto. Ciencia de la Computacin e IA Errores - 3

  8. 2010-2011 Depto. Ciencia de la Computacin e IA Especialista Universitario Java Enterprise

    E-Print Network [OSTI]

    Escolano, Francisco

    2010-2011 Depto. Ciencia de la Computacin e IA Especialista Universitario Java Enterprise Struts Sesin 4: Introduccin a Struts 2 #12; 2010-2011 Depto. Ciencia de la Computacin e IA Especialista Taglibs Internacionalizacin Validacin Conceptos nuevos en Struts 2 #12; 2010-2011 Depto. Ciencia

  9. Investigation of the GaN-on-GaAs interface for vertical power device applications

    SciTech Connect (OSTI)

    Mreke, Janina, E-mail: janina.moereke@bristol.ac.uk; Uren, Michael J.; Kuball, Martin [H.H. Wills Physics Laboratory, Tyndall Avenue, Bristol BS8 1TL (United Kingdom); Novikov, Sergei V.; Foxon, C. Thomas [Department of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD (United Kingdom); Hosseini Vajargah, Shahrzad; Wallis, David J.; Humphreys, Colin J. [Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS (United Kingdom); Haigh, Sarah J. [Super STEM Laboratory, STFC Daresbury Campus, Keckwick Lane, Daresbury WA4 4AD (United Kingdom); School of Materials, University of Manchester, Manchester M13 9PL (United Kingdom); Al-Khalidi, Abdullah; Wasige, Edward; Thayne, Iain [School of Engineering, University of Glasgow, Rankine Bldg, Oakfield Avenue, Glasgow G12 8LT (United Kingdom)

    2014-07-07T23:59:59.000Z

    GaN layers were grown onto (111) GaAs by molecular beam epitaxy. Minimal band offset between the conduction bands for GaN and GaAs materials has been suggested in the literature raising the possibility of using GaN-on-GaAs for vertical power device applications. I-V and C-V measurements of the GaN/GaAs heterostructures however yielded a rectifying junction, even when both sides of the junction were heavily doped with an n-type dopant. Transmission electron microscopy analysis further confirmed the challenge in creating a GaN/GaAs Ohmic interface by showing a large density of dislocations in the GaN layer and suggesting roughening of the GaN/GaAs interface due to etching of the GaAs by the nitrogen plasma, diffusion of nitrogen or melting of Ga into the GaAs substrate.

  10. Type Ia supernova rate studies from the SDSS-II Supernova Study

    SciTech Connect (OSTI)

    Dilday, Benjamin; /Chicago U.

    2008-08-01T23:59:59.000Z

    The author presents new measurements of the type Ia SN rate from the SDSS-II Supernova Survey. The SDSS-II Supernova Survey was carried out during the Fall months (Sept.-Nov.) of 2005-2007 and discovered {approx} 500 spectroscopically confirmed SNe Ia with densely sampled (once every {approx} 4 days), multi-color light curves. Additionally, the SDSS-II Supernova Survey has discovered several hundred SNe Ia candidates with well-measured light curves, but without spectroscopic confirmation of type. This total, achieved in 9 months of observing, represents {approx} 15-20% of the total SNe Ia discovered worldwide since 1885. The author describes some technical details of the SN Survey observations and SN search algorithms that contributed to the extremely high-yield of discovered SNe and that are important as context for the SDSS-II Supernova Survey SN Ia rate measurements.

  11. Measurement of Omega_m, Omega_Lambda from a blind analysis of Type Ia supernovae with CMAGIC: Using color information to verify the acceleration of the Universe

    E-Print Network [OSTI]

    2006-01-01T23:59:59.000Z

    analysis of Type Ia supernovae with CMAGIC: Using colorof 21 high redshift supernovae using a new technique (lightcurves of Type Ia supernovae, ?rst introduced in Wang

  12. The Effect of Host Galaxies on Type Ia Supernovae in the SDSS-II Supernova Survey

    SciTech Connect (OSTI)

    Lampeitl, Hubert; /Portsmouth U., ICG; Smith, Mathew; /Cape Town U. /Portsmouth U., ICG; Nichol, Robert C.; /Portsmouth U., ICG; Bassett, Bruce; /South African Astron. Observ. /Cape Town U.; Cinabro, David; /Wayne State U.; Dilday, Benjamin; /Rutgers U., Piscataway; Foley, Ryan J.; /Harvard-Smithsonian Ctr. Astrophys.; Frieman, Joshua A.; /Chicago U. /Fermilab; Garnavich, Peter M.; /Notre Dame U.; Goobar, Ariel; /Stockholm U., OKC; Im, Myungshin; /Seoul Natl. U. /Rutgers U., Piscataway

    2010-05-01T23:59:59.000Z

    We present an analysis of the host galaxy dependencies of Type Ia Supernovae (SNe Ia) from the full three year sample of the SDSS-II Supernova Survey. We re-discover, to high significance, the strong correlation between host galaxy type and the width of the observed SN light curve, i.e., fainter, quickly declining SNe Ia favor passive host galaxies, while brighter, slowly declining Ia's favor star-forming galaxies. We also find evidence (at between 2 to 3{sigma}) that SNe Ia are {approx_equal} 0.1 magnitudes brighter in passive host galaxies, than in star-forming hosts, after the SN Ia light curves have been standardized using the light curve shape and color variations: This difference in brightness is present in both the SALT2 and MCLS2k2 light curve fitting methodologies. We see evidence for differences in the SN Ia color relationship between passive and star-forming host galaxies, e.g., for the MLCS2k2 technique, we see that SNe Ia in passive hosts favor a dust law of R{sub V} {approx_equal} 1, while SNe Ia in star-forming hosts require R{sub V} {approx} 2. The significance of these trends depends on the range of SN colors considered. We demonstrate that these effects can be parameterized using the stellar mass of the host galaxy (with a confidence of > 4{sigma}) and including this extra parameter provides a better statistical fit to our data. Our results suggest that future cosmological analyses of SN Ia samples should include host galaxy information.

  13. Ga NMR spectra and relaxation in wurtzite GaN M. Corti and A. Gabetta

    E-Print Network [OSTI]

    Svane, Axel Torstein

    69,71 Ga NMR spectra and relaxation in wurtzite GaN M. Corti and A. Gabetta Department of Physics properties of wurtzite GaN are studied by Ga nuclear magnetic resonance NMR in a GaN bulk crystal containing GaN is a wide band-gap semiconductor which crystallizes in the hexagonal wurtzite structure

  14. Cross-sectional Scanning Tunneling Microscopy and Spectroscopy of InGaP/GaAs Heterojunctions

    E-Print Network [OSTI]

    Feenstra, Randall

    1 Cross-sectional Scanning Tunneling Microscopy and Spectroscopy of InGaP/GaAs Heterojunctions Y Abstract Compositionally abrupt InGaP/GaAs heterojunctions grown by gas-source molecular beam epitaxy have the InGaP layer show non-uniform In and Ga distribution. About 1.5 nm of transition region

  15. Role of Electrochemical Reactions in the Degradation Mechanisms of AlGaN/GaN HEMTs

    E-Print Network [OSTI]

    del Alamo, Jess A.

    Role of Electrochemical Reactions in the Degradation Mechanisms of AlGaN/GaN HEMTs Feng Gao1, USA tpalacios@mit.edu; (617) 324-2395 Keywords: AlGaN/GaN HEMTs, reliability, moisture, electro-chemical reactions Abstract The nature of structural degradation in AlGaN/GaN high electron mobility transistors

  16. Dopant-Free GaN/AlN/AlGaN Radial Nanowire Heterostructures as High

    E-Print Network [OSTI]

    Li, Yat

    Dopant-Free GaN/AlN/AlGaN Radial Nanowire Heterostructures as High Electron Mobility Transistors, 2006 ABSTRACT We report the rational synthesis of dopant-free GaN/AlN/AlGaN radial nanowire-organic chemical vapor deposition (MOCVD). Transmission electron microscopy (TEM) studies reveal that the GaN/ AlN/AlGaN

  17. Beta decay of Ga-62

    E-Print Network [OSTI]

    Hyman, BC; Iacob, VE; Azhari, A.; Gagliardi, Carl A.; Hardy, John C.; Mayes, VE; Neilson, RG; Sanchez-Vega, M.; Tang, X.; Trache, L.; Tribble, Robert E.

    2003-01-01T23:59:59.000Z

    We report a study of the beta decay of Ga-62, whose dominant branch is a superallowed 0(+)-->0(+) transition to the ground state of Zn-62. We find the total half-life to be 115.84+/-0.25 ms. This is the first time that the Ga-62 half-life has been...

  18. Influence of GaAs surface termination on GaSb/GaAs quantum dot structure and band offsets

    SciTech Connect (OSTI)

    Zech, E. S.; Chang, A. S.; Martin, A. J.; Canniff, J. C.; Millunchick, J. M. [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States)] [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States); Lin, Y. H. [Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States)] [Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States); Goldman, R. S. [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States) [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States); Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States)

    2013-08-19T23:59:59.000Z

    We have investigated the influence of GaAs surface termination on the nanoscale structure and band offsets of GaSb/GaAs quantum dots (QDs) grown by molecular-beam epitaxy. Transmission electron microscopy reveals both coherent and semi-coherent clusters, as well as misfit dislocations, independent of surface termination. Cross-sectional scanning tunneling microscopy and spectroscopy reveal clustered GaSb QDs with type I band offsets at the GaSb/GaAs interfaces. We discuss the relative influences of strain and QD clustering on the band offsets at GaSb/GaAs interfaces.

  19. Supernova progenitor constraints from circumstellar interaction: Type Ia

    E-Print Network [OSTI]

    Peter Lundqvist; Robert J. Cumming

    1996-10-03T23:59:59.000Z

    Searching for the presence of a circumstellar medium is a direct observational way to discriminate between different types of progenitor systems for Type Ia supernovae. We have modeled whether such gas may give rise to detectable emission, especially in H-alpha, and compare the models with observations of SN 1994D. We obtain a mass loss rate less than about 2.5 10^{-5} solar masses per year for a wind speed of 10 km/s. We find that X-ray observations in the range 5-10 keV, e.g., with AXAF, provide the most useful limits on the mass loss, while high-resolution optical spectroscopy offers the only direct way of identifying circumstellar hydrogen.

  20. Polarisation spectral synthesis for Type Ia supernova explosion models

    E-Print Network [OSTI]

    Bulla, M; Kromer, M

    2015-01-01T23:59:59.000Z

    We present a Monte Carlo radiative transfer technique for calculating synthetic spectropolarimetry for multi-dimensional supernova explosion models. The approach utilises "virtual-packets" that are generated during the propagation of the Monte Carlo quanta and used to compute synthetic observables for specific observer orientations. Compared to extracting synthetic observables by direct binning of emergent Monte Carlo quanta, this virtual-packet approach leads to a substantial reduction in the Monte Carlo noise. This is vital for calculating synthetic spectropolarimetry (since the degree of polarisation is typically very small) but also useful for calculations of light curves and spectra. We first validate our approach via application of an idealised test code to simple geometries. We then describe its implementation in the Monte Carlo radiative transfer code ARTIS and present test calculations for simple models for Type Ia supernovae. Specifically, we use the well-known one-dimensional W7 model to verify tha...

  1. Type Ia supernova Hubble residuals and host-galaxy properties

    SciTech Connect (OSTI)

    Kim, A. G.; Aldering, G.; Aragon, C.; Bailey, S.; Fakhouri, H. K. [Physics Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720 (United States); Antilogus, P.; Bongard, S.; Canto, A.; Cellier-Holzem, F.; Fleury, M.; Guy, J. [Laboratoire de Physique Nuclaire et des Hautes nergies, Universit Pierre et Marie Curie Paris 6, Universit Paris Diderot Paris 7, CNRS-IN2P3, 4 place Jussieu, F-75252 Paris Cedex 05 (France); Baltay, C. [Department of Physics, Yale University, New Haven, CT 06250-8121 (United States); Buton, C.; Feindt, U.; Greskovic, P.; Kowalski, M. [Physikalisches Institut, Universitt Bonn, Nuallee 12, D-53115 Bonn (Germany); Childress, M. [Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611 (Australia); Chotard, N.; Copin, Y.; Gangler, E. [Universit de Lyon, F-69622 Lyon (France); Universit de Lyon 1, Villeurbanne (France); CNRS/IN2P3, Institut de Physique Nuclaire de Lyon (France); and others

    2014-03-20T23:59:59.000Z

    Kim et al. introduced a new methodology for determining peak-brightness absolute magnitudes of type Ia supernovae from multi-band light curves. We examine the relation between their parameterization of light curves and Hubble residuals, based on photometry synthesized from the Nearby Supernova Factory spectrophotometric time series, with global host-galaxy properties. The K13 Hubble residual step with host mass is 0.013 0.031 mag for a supernova subsample with data coverage corresponding to the K13 training; at <<1?, the step is not significant and lower than previous measurements. Relaxing the data coverage requirement of the Hubble residual step with the host mass is 0.045 0.026 mag for the larger sample; a calculation using the modes of the distributions, less sensitive to outliers, yields a step of 0.019 mag. The analysis of this article uses K13 inferred luminosities, as distinguished from previous works that use magnitude corrections as a function of SALT2 color and stretch parameters: steps at >2? significance are found in SALT2 Hubble residuals in samples split by the values of their K13 x(1) and x(2) light-curve parameters. x(1) affects the light-curve width and color around peak (similar to the ?m {sub 15} and stretch parameters), and x(2) affects colors, the near-UV light-curve width, and the light-curve decline 20-30 days after peak brightness. The novel light-curve analysis, increased parameter set, and magnitude corrections of K13 may be capturing features of SN Ia diversity arising from progenitor stellar evolution.

  2. On silicon group elements ejected by supernovae type IA

    SciTech Connect (OSTI)

    De, Soma; Timmes, F. X. [School of Earth and Space Exploration, Arizona State University, Tempe, AZ (United States); Brown, Edward F. [Joint Institute for Nuclear Astrophysics, University of Notre Dame, IN 46556 (United States); Calder, Alan C. [Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY (United States); Townsley, Dean M. [Department of Physics and Astronomy, The University of Alabama, Tuscaloosa, AL (United States); Athanassiadou, Themis [Swiss National Supercomputing Centre, Via Trevano 131, 6900 Lugano (Switzerland); Chamulak, David A. [Physics Division, Argonne National Laboratory, Argonne, IL (United States); Hawley, Wendy [Laboratoire d'Astrophysique de Marseille, Marseille cedex 13 F-13388 (France); Jack, Dennis, E-mail: somad@asu.edu [Departamento de Astronoma, Universidad de Guanajuato, Apartado Postal 144, 36000 Guanajuato (Mexico)

    2014-06-01T23:59:59.000Z

    There is evidence that the peak brightness of a Type Ia supernova is affected by the electron fraction Y {sub e} at the time of the explosion. The electron fraction is set by the aboriginal composition of the white dwarf and the reactions that occur during the pre-explosive convective burning. To date, determining the makeup of the white dwarf progenitor has relied on indirect proxies, such as the average metallicity of the host stellar population. In this paper, we present analytical calculations supporting the idea that the electron fraction of the progenitor systematically influences the nucleosynthesis of silicon group ejecta in Type Ia supernovae. In particular, we suggest the abundances generated in quasi-nuclear statistical equilibrium are preserved during the subsequent freeze-out. This allows potential recovery of Y {sub e} at explosion from the abundances recovered from an observed spectra. We show that measurement of {sup 28}Si, {sup 32}S, {sup 40}Ca, and {sup 54}Fe abundances can be used to construct Y {sub e} in the silicon-rich regions of the supernovae. If these four abundances are determined exactly, they are sufficient to recover Y {sub e} to 6%. This is because these isotopes dominate the composition of silicon-rich material and iron-rich material in quasi-nuclear statistical equilibrium. Analytical analysis shows the {sup 28}Si abundance is insensitive to Y {sub e}, the {sup 32}S abundance has a nearly linear trend with Y {sub e}, and the {sup 40}Ca abundance has a nearly quadratic trend with Y {sub e}. We verify these trends with post-processing of one-dimensional models and show that these trends are reflected in the model's synthetic spectra.

  3. Type Ia Supernovae Rates and Galaxy Clustering from the CFHT Supernova Legacy Survey

    E-Print Network [OSTI]

    M. L. Graham; C. J. Pritchet; M. Sullivan; S. D. J. Gwyn; J. D. Neill; E. Y. Hsiao; P. Astier; D. Balam; C. Balland; S. Basa; R. G. Carlberg; A. Conley; D. Fouchez; J. Guy; D. Hardin; I. M. Hook; D. A. Howell; R. Pain; K. Perrett; N. Regnault; S. Baumont; J. Le Du; C. Lidman; S. Perlmutter; P. Ripoche; N. Suzuki; E. S. Walker; T. Zhang

    2008-01-31T23:59:59.000Z

    The Canada-France-Hawaii Telescope Supernova Legacy Survey (SNLS) has created a large homogeneous database of intermediate redshift (0.2 rates, properties, and host galaxy star formation rates. The SNLS SN Ia database has now been combined with a photometric redshift galaxy catalog and an optical galaxy cluster catalog to investigate the possible influence of galaxy clustering on the SN Ia rate, over and above the expected effect due to the dependence of SFR on clustering through the morphology-density relation. We identify three cluster SNe Ia, plus three additional possible cluster SNe Ia, and find the SN Ia rate per unit mass in clusters at intermediate redshifts is consistent with the rate per unit mass in field early-type galaxies and the SN Ia cluster rate from low redshift cluster targeted surveys. We also find the number of SNe Ia in cluster environments to be within a factor of two of expectations from the two component SNIa rate model.

  4. Stellar Populations and the White Dwarf Mass Function: Connections To Supernova Ia Luminosities

    E-Print Network [OSTI]

    Ted von Hippel; G. D. Bothun; R. A. Schommer

    1997-06-11T23:59:59.000Z

    We discuss the luminosity function of SNe Ia under the assumption that recent evidence for dispersion in this standard candle is related to variations in the white dwarf mass function (WDMF) in the host galaxies. We develop a simple parameterization of the WDMF as a function of age of a stellar population and apply this to galaxies of different morphological types. We show that this simplified model is consistent with the observed WDMF of Bergeron et al. (1992) for the solar neighborhood. Our simple models predict that WDMF variations can produce a range of more than 1.8 mag in M$_B$(SN Ia), which is comparable to the observed value using the data of Phillips (1993) and van den Bergh (1996). We also predict a galaxy type dependence of M$_B$(SN Ia) under standard assumptions of the star formation history in these galaxies and show that M$_B$(SN Ia) can evolve with redshift. In principle both evolutionary and galaxy type corrections should be applied to recover the intrinsic range of M$_B$(SN Ia) from the observed values. Our current inadequate knowledge of the star formation history of galaxies coupled with poor physical understanding of the SN Ia mechanism makes the reliable estimation of these corrections both difficult and controversial. The predictions of our models combined with the observed galaxy and redshift correlations may have the power to discriminate between the Chandrasekhar and the sub-Chandrasekhar progenitor scenarios for SNe Ia.

  5. A systematic study of carbon-oxygen white dwarf mergers: mass combinations for Type Ia supernovae

    E-Print Network [OSTI]

    Sato, Yushi; Tanikawa, Ataru; Nomoto, Ken'ichi; Maeda, Keiichi; Hachisu, Izumi

    2015-01-01T23:59:59.000Z

    Mergers of two carbon-oxygen (CO) white dwarfs (WDs) have been considered as progenitors of Type Ia supernovae (SNe Ia). Based on smoothed particle hydrodynamics (SPH) simulations, previous studies claimed that mergers of CO WDs lead to an SN Ia explosion either in the dynamical merger phase or stationary rotating merger remnant phase. However, the mass range of CO WDs that lead to an SN Ia has not been clearly identified yet. In the present work, we perform systematic SPH merger simulations for the WD masses ranging from $0.5~M_{\\odot}$ to $1.1~M_{\\odot}$ with higher resolutions than the previous systematic surveys and examine whether or not carbon burning occurs dynamically or quiescently in each phase. We further study the possibility of SN Ia explosion and estimate the mass range of CO WDs that lead to an SN Ia. We found that when the both WDs are massive, i.e., in the mass range of $0.9~M_{\\odot} {\\le} M_{1,2} {\\le} 1.1~M_{\\odot}$, they can explode as an SN Ia in the merger phase. On the other hand, when...

  6. The Hubble Constant from Type Ia Supernovae in Early-Type Galaxies

    E-Print Network [OSTI]

    Tom Richtler; Georg Drenkhahn

    1999-09-07T23:59:59.000Z

    Type Ia supernovae (SNe) are the best standard candles available today in spite of an appreciable intrinsic variation of their luminosities at maximum phase, and of probably non-uniform progenitors. For an unbiased use of type Ia SNe as distance indicators it is important to know accurately how the decline rate and colour at maximum phase correlate with the peak brightness. In order to calibrate the Hubble diagram of type Ia SNe, i.e. to derive the Hubble constant, one needs to determine the absolute brightness of nearby type Ia SNe. Globular cluster systems of early type Ia host galaxies provide suitable distance indicators. We discuss how Ia SNe can be calibrated and explain the method of Globular Cluster Luminosity Functions (GCLFs). At present, the distance to the Fornax galaxy cluster is most important for deriving the Hubble constant. Our present data indicate a Hubble constant of H_0=72+-4 km/s/Mpc. As an appendix, we summarise what is known about absolute magnitudes of Ia's in late-type galaxies.

  7. HOST GALAXIES OF TYPE Ia SUPERNOVAE FROM THE NEARBY SUPERNOVA FACTORY

    SciTech Connect (OSTI)

    Childress, M.; Aldering, G.; Aragon, C.; Bailey, S.; Fakhouri, H. K.; Hsiao, E. Y.; Kim, A. G.; Loken, S. [Physics Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720 (United States); Antilogus, P.; Bongard, S.; Canto, A.; Cellier-Holzem, F.; Guy, J. [Laboratoire de Physique Nucleaire et des Hautes Energies, Universite Pierre et Marie Curie Paris 6, Universite Paris Diderot Paris 7, CNRS-IN2P3, 4 place Jussieu, F-75252 Paris Cedex 05 (France); Baltay, C. [Department of Physics, Yale University, New Haven, CT 06250-8121 (United States); Buton, C.; Kerschhaggl, M.; Kowalski, M. [Physikalisches Institut, Universitaet Bonn, Nussallee 12, D-53115 Bonn (Germany); Chotard, N.; Copin, Y.; Gangler, E. [Universite de Lyon, F-69622, Lyon (France); Universite de Lyon 1, Villeurbanne (France); CNRS/IN2P3, Institut de Physique Nucleaire de Lyon (France); and others

    2013-06-20T23:59:59.000Z

    We present photometric and spectroscopic observations of galaxies hosting Type Ia supernovae (SNe Ia) observed by the Nearby Supernova Factory. Combining Galaxy Evolution Explorer (GALEX) UV data with optical and near-infrared photometry, we employ stellar population synthesis techniques to measure SN Ia host galaxy stellar masses, star formation rates (SFRs), and reddening due to dust. We reinforce the key role of GALEX UV data in deriving accurate estimates of galaxy SFRs and dust extinction. Optical spectra of SN Ia host galaxies are fitted simultaneously for their stellar continua and emission lines fluxes, from which we derive high-precision redshifts, gas-phase metallicities, and H{alpha}-based SFRs. With these data we show that SN Ia host galaxies present tight agreement with the fiducial galaxy mass-metallicity relation from Sloan Digital Sky Survey (SDSS) for stellar masses log(M{sub *}/M{sub Sun }) > 8.5 where the relation is well defined. The star formation activity of SN Ia host galaxies is consistent with a sample of comparable SDSS field galaxies, though this comparison is limited by systematic uncertainties in SFR measurements. Our analysis indicates that SN Ia host galaxies are, on average, typical representatives of normal field galaxies.

  8. Multiple-band-edge quantum-well intermixing in the InGaAs/InGaAsP/InGaP material system

    E-Print Network [OSTI]

    Coldren, Larry A.

    Multiple-band-edge quantum-well intermixing in the InGaAs/InGaAsP/InGaP material system Erik J InGaAs/InGaAsP/InGaP material system. 2005 American Institute of Physics. DOI: 10 of achieving QWI in such active regions.3,4 However, InGaAs/InGaAsP/InGaP-based de- vices offer numerous

  9. GaInNAs laser gain

    SciTech Connect (OSTI)

    CHOW,WENG W.; JONES,ERIC D.; MODINE,NORMAND A.; KURTZ,STEVEN R.; ALLERMAN,ANDREW A.

    2000-05-23T23:59:59.000Z

    The optical gain spectra for GaInNAs/GaAs quantum wells are computed using a microscopic laser theory. From these spectra, the peak gain and carrier radiative decay rate as functions of carrier density are determined. These dependences allow the study of the lasing threshold current density of GaInNAs/GaAs quantum well structures.

  10. University Engagement and Outreach Committee Chair: PVC (IA), Prof. M Cardew-Hall

    E-Print Network [OSTI]

    Botea, Adi

    University Engagement and Outreach Committee Chair: PVC (IA), Prof. M Cardew-Hall Alternate Chair: PVC (IO), Dr. Erik Lithander Secretary: Ms. Jan O'Connor (Jan.OConnor@anu.edu.au) / Ms. Joanne Gash

  11. Structural studies of allosteric regulation in the class Ia Ribonucleotide reductase from Escherichia coli

    E-Print Network [OSTI]

    Zimanyi, Christina Marie

    2013-01-01T23:59:59.000Z

    Ribonucleotide reductase (RNR) converts ribonucleotides to deoxyribonucleotides, the building blocks for DNA replication and repair. The E. coli class Ia enzyme requires two subunits to catalyze the radical-based reduction ...

  12. Type Ia supernova rate at a redshift of ~ 0.1

    E-Print Network [OSTI]

    Blanc, G; Alard, C; Albert, J N; Aldering, G; Amadon, A; Andersen, J; Ansari, R; Aubourg, E; Balland, C; Bareyre, P; Beaulieu, J P; Charlot, X; Conley, A; Coutures, C; Dahlen, T; Derue, F; Fan, X; Ferlet, R; Folatelli, G; Fouqu, P; Garavini, G; Glicenstein, J F; Goldman, B; Goobar, A; Gould, A; Graff, D; Gros, M; Hassinski, J; Hamadache, C; Hardin, D; Hook, I M; De Kat, J; Kent, S; Kim, A; Lasserre, T; Le Guillou, Laurent; Lesquoy, E; Loup, C; Magneville, C; Marquette, J B; Maurice, E; Maury, A; Milsztajn, A; Moniez, M; Mouchet, M; Newberg, H; Nobili, S; Palanque-Delabrouille, Nathalie; Perdereau, O; Prvt, L; Rahal, Y R; Regnault, N; Rich, J; Ruiz-Lapuente, P; Spiro, M; Tisserand, P; Vidal-Madjar, A; Vigroux, L; Walton, N A; Zylberajch, S

    2004-01-01T23:59:59.000Z

    We present the type Ia rate measurement based on two EROS supernova search campaigns (in 1999 and 2000). Sixteen supernovae identified as type Ia were discovered. The measurement of the detection efficiency, using a Monte Carlo simulation, provides the type Ia supernova explosion rate at a redshift ~ 0.13. The result is $0.125^{+0.044+0.028}_{-0.034-0.028} h_{70}^2$ SNu where 1 SNu = 1 SN / $10^{10} L_{sun}^B$ / century. This value is compatible with the previous EROS measurement (Hardin et al. 2000), done with a much smaller sample, at a similar redshift. Comparison with other values at different redshifts suggests an evolution of the type Ia supernova rate.

  13. Type Ia supernova rate at a redshift of ~ 0.1

    E-Print Network [OSTI]

    G. Blanc; C. Afonso; C. Alard; J. N. Albert; G. Aldering; A. Amadon; J. Andersen; R. Ansari; E. Aubourg; C. Balland; P. Bareyre; J. P. Beaulieu; X. Charlot; A. Conley; C. Coutures; T. Dahlen; F. Derue; X. Fan; R. Ferlet; G. Folatelli; P. Fouque; G. Garavini; J. F. Glicenstein; B. Goldman; A. Goobar; A. Gould; D. Graff; M. Gros; J. Haissinski; C. Hamadache; D. Hardin; I. M. Hook; J. deKat; S. Kent; A. Kim; T. Lasserre; L. LeGuillou; E. Lesquoy; C. Loup; C. Magneville; J. B. Marquette; E. Maurice; A. Maury; A. Milsztajn; M. Moniez; M. Mouchet; H. Newberg; S. Nobili; N. Palanque-Delabrouille; O. Perdereau; L. Prevot; Y. R. Rahal; N. Regnault; J. Rich; P. Ruiz-Lapuente; M. Spiro; P. Tisserand; A. Vidal-Madjar; L. Vigroux; N. A. Walton; S. Zylberajch

    2004-05-11T23:59:59.000Z

    We present the type Ia rate measurement based on two EROS supernova search campaigns (in 1999 and 2000). Sixteen supernovae identified as type Ia were discovered. The measurement of the detection efficiency, using a Monte Carlo simulation, provides the type Ia supernova explosion rate at a redshift ~ 0.13. The result is $0.125^{+0.044+0.028}_{-0.034-0.028} h_{70}^2$ SNu where 1 SNu = 1 SN / $10^{10} L_{sun}^B$ / century. This value is compatible with the previous EROS measurement (Hardin et al. 2000), done with a much smaller sample, at a similar redshift. Comparison with other values at different redshifts suggests an evolution of the type Ia supernova rate.

  14. Hipparcos calibration of the peak brightness of four SNe Ia and the value of Ho

    E-Print Network [OSTI]

    P. Lanoix

    1997-12-10T23:59:59.000Z

    Hipparcos geometrical parallaxes allowed us to calibrate the Cepheid Period-Luminosity relation and to compute the true distance moduli of 17 galaxies. Among these 17 galaxies, we selected those which generated type Ia Supernovae (SNe Ia). We found NGC 5253, parent galaxy of 1895B and 1972E, IC 4182 and NGC 4536 parents of 1937C and 1981B, respectively. We used the available B-band photometry to determine the peak brightness of these four SNe Ia. We obtained = -19.65 \\pm 0.09. Then, we built a sample of 57 SNe Ia in order to plot the Hubble diagram and determine its zero-point. Our result (ZP_{B} = -3.16 \\pm 0.10) is in agreement with other determinations and allows us to derive the following Hubble constant : Ho = 50 \\pm 3 (internal) km.s^-1.Mpc^-1.

  15. , SEYMOUR AND MacGREGOR COGNlTlYb NEUROPSYCHOLOGY. IdyslexIa. Brain. 102. 4363.

    E-Print Network [OSTI]

    Mehler, Jacques

    .T. (1980) Word-form dyslexIa. Brain. 102. 4363. REFERENCENOTES On Reducing Language to Biology I. Holmes. J. M. (1973) Dyslexia: a lIeurolinguistic study 0/ traumatic and developmental disorders 0/ reading

  16. Imprint of modified Einstein's gravity on white dwarfs: Unifying type Ia supernovae

    E-Print Network [OSTI]

    Das, Upasana

    2015-01-01T23:59:59.000Z

    We establish the importance of modified Einstein's gravity (MG) in white dwarfs (WDs) for the first time in the literature. We show that MG leads to significantly sub- and super-Chandrasekhar limiting mass WDs, depending on a single model parameter. However, conventional WDs on approaching Chandrasekhar's limit are expected to trigger type Ia supernovae (SNeIa), a key to unravel the evolutionary history of the universe. Nevertheless, observations of several peculiar, under- and over-luminous SNeIa argue for the limiting mass widely different from Chandrasekhar's limit. Explosions of MG induced sub- and super-Chandrasekhar limiting mass WDs explain under- and over-luminous SNeIa respectively, thus unifying these two apparently disjoint sub-classes. Our discovery questions both the global validity of Einstein's gravity and the uniqueness of Chandrasekhar's limit.

  17. EVIDENCE FOR TYPE Ia SUPERNOVA DIVERSITY FROM ULTRAVIOLET OBSERVATIONS WITH THE HUBBLE SPACE TELESCOPE

    E-Print Network [OSTI]

    Lewin, Walter H. G.

    We present ultraviolet (UV) spectroscopy and photometry of four Type Ia supernovae (SNe 2004dt, 2004ef, 2005M, and 2005cf) obtained with the UV prism of the Advanced Camera for Surveys on the Hubble Space Telescope. This ...

  18. Quantitative comparison between Type Ia supernova spectra at low and high redshifts: A case study

    E-Print Network [OSTI]

    Garavini, G.; Supernova Cosmology Project

    2008-01-01T23:59:59.000Z

    Highlight - The Physics of Supernovae, ESO/MPA/MPE Workshop,Evolution in high-redshift supernovae Fig. 8 Ca ii H&KSN 1991T/SN 1999aa-like supernovae. 1. Introduction Type Ia

  19. Constructing a cosmological model-independent Hubble diagram of type Ia supernovae with cosmic chronometers

    E-Print Network [OSTI]

    Li, Zhengxiang; Yu, Hongwei; Zhu, Zong-Hong; Alcaniz, J S

    2015-01-01T23:59:59.000Z

    We apply two methods to reconstruct the Hubble parameter $H(z)$ as a function of redshift from 15 measurements of the expansion rate obtained from age estimates of passively evolving galaxies. These reconstructions enable us to derive the luminosity distance to a certain redshift $z$, calibrate the light-curve fitting parameters accounting for the (unknown) intrinsic magnitude of type Ia supernova (SNe Ia) and construct cosmological model-independent Hubble diagrams of SNe Ia. In order to test the compatibility between the reconstructed functions of $H(z)$, we perform a statistical analysis considering the latest SNe Ia sample, the so-called JLA compilation. We find that, while one of the reconstructed functions leads to a value of the local Hubble parameter $H_0$ in excellent agreement with the one reported by the Planck collaboration, the other requires a higher value of $H_0$, which is consistent with recent measurements of this quantity from Cepheids and other local distance indicators.

  20. Red emitting photonic devices using InGaP/InGaAlP material system

    E-Print Network [OSTI]

    Kangude, Yamini

    2005-01-01T23:59:59.000Z

    In this thesis, two red emitting photonic devices are presented using the InGaP/InGaAlP material system. InGaP/InGaAlP material system provides large flexibility in the band gap energy while being lattice matched to GaAs ...

  1. Measuring nickel masses in Type Ia supernovae using cobalt emission in nebular phase spectra

    E-Print Network [OSTI]

    Childress, Michael J; Seitenzahl, Ivo; Sullivan, Mark; Maguire, Kate; Taubenberger, Stefan; Scalzo, Richard; Ruiter, Ashley; Blagorodnova, Nadejda; Camacho, Yssavo; Castillo, Jayden; Elias-Rosa, Nancy; Fraser, Morgan; Gal-Yam, Avishay; Graham, Melissa; Howell, D Andrew; Inserra, Cosimo; Jha, Saurabh W; Kumar, Sahana; Mazzali, Paolo A; McCully, Curtis; Morales-Garoffolo, Antonia; Pandya, Viraj; Polshaw, Joe; Schmidt, Brian; Smartt, Stephen; Smith, Ken W; Sollerman, Jesper; Spyromilio, Jason; Tucker, Brad; Valenti, Stefano; Walton, Nicholas; Wolf, Christian; Yaron, Ofer; Young, D R; Yuan, Fang; Zhang, Bonnie

    2015-01-01T23:59:59.000Z

    The light curves of Type Ia supernovae (SNe Ia) are powered by the radioactive decay of $^{56}$Ni to $^{56}$Co at early times, and the decay of $^{56}$Co to $^{56}$Fe from ~60 days after explosion. We examine the evolution of the [Co III] 5892 A emission complex during the nebular phase for SNe Ia with multiple nebular spectra and show that the line flux follows the square of the mass of $^{56}$Co as a function of time. This result indicates both efficient local energy deposition from positrons produced in $^{56}$Co decay, and long-term stability of the ionization state of the nebula. We compile 77 nebular spectra of 25 SN Ia from the literature and present 17 new nebular spectra of 7 SNe Ia, including SN2014J. From these we measure the flux in the [Co III] 5892 A line and remove its well-behaved time dependence to infer the initial mass of $^{56}$Ni ($M_{Ni}$) produced in the explosion. We then examine $^{56}$Ni yields for different SN Ia ejected masses ($M_{ej}$ - calculated using the relation between light...

  2. Tycho Brahe's 1572 supernova as a standard type Ia explosion revealed from its light echo spectrum

    E-Print Network [OSTI]

    Oliver Krause; Masaomi Tanaka; Tomonori Usuda; Takashi Hattori; Miwa Goto; Stephan Birkmann; Ken'ichi Nomoto

    2008-10-28T23:59:59.000Z

    Type Ia supernovae (SNe Ia) are thermonuclear explosions of white dwarf stars in close binary systems. They play an important role as cosmological distance indicators and have led to the discovery of the accelerated expansion of the Universe. Among the most important unsolved questions are how the explosion actually proceeds and whether accretion occurs from a companion or via the merging of two white dwarfs. Tycho Brahe's supernova of 1572 (SN 1572) is thought to be one of the best candidates for a SN Ia in the Milky Way. The proximity of the SN 1572 remnant has allowed detailed studies, such as the possible identification of the binary companion, and provides a unique opportunity to test theories of the explosion mechanism and the nature of the progenitor. The determination of the yet unknown exact spectroscopic type of SN 1572 is crucial to relate these results to the diverse population of SNe Ia. Here we report an optical spectrum of Tycho Brahe's supernova near maximum brightness, obtained from a scattered-light echo more than four centuries after the direct light of the explosion swept past Earth. We find that SN 1572 belongs to the majority class of normal SNe Ia. The presence of a strong Ca II IR feature at velocities exceeding 20,000 km/s, which is similar to the previously observed polarized features in other SNe Ia, suggests asphericity in SN 1572.

  3. THE ABSENCE OF EX-COMPANIONS IN TYPE Ia SUPERNOVA REMNANTS

    SciTech Connect (OSTI)

    Di Stefano, R. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Kilic, Mukremin, E-mail: rd@cfa.harvard.edu, E-mail: kilic@ou.edu [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 West Brooks Street, Norman, OK 73019 (United States)

    2012-11-01T23:59:59.000Z

    Type Ia supernovae (SNe Ia) play important roles in our study of the expansion and acceleration of the universe, but because we do not know the exact nature or natures of the progenitors, there is a systematic uncertainty that must be resolved if SNe Ia are to become more precise cosmic probes. No progenitor system has ever been identified either in the pre- or post-explosion images of a Ia event. There have been recent claims for and against the detection of ex-companion stars in several SNe Ia remnants. These studies, however, usually ignore the angular momentum gain of the progenitor white dwarf (WD), which leads to a spin-up phase and a subsequent spin-down phase before explosion. For spin-down timescales greater than 10{sup 5} years, the donor star could be too dim to detect by the time of explosion. Here we revisit the current limits on ex-companion stars to SNR 0509-67.5, a 400-year-old remnant in the Large Magellanic Cloud. If the effects of possible angular momentum gain on the WD are included, a wide range of single-degenerate progenitor models are allowed for this remnant. We demonstrate that the current absence of evidence for ex-companion stars in this remnant, as well as other SNe Ia remnants, does not necessarily provide the evidence of absence for ex-companions. We discuss potential ways to identify such ex-companion stars through deep imaging observations.

  4. THE DISCOVERY OF THE MOST DISTANT KNOWN TYPE Ia SUPERNOVA AT REDSHIFT 1.914

    SciTech Connect (OSTI)

    Jones, David O.; Rodney, Steven A.; Riess, Adam G. [Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States); Mobasher, Bahram [Department of Physics and Astronomy, University of California, Riverside, CA 92521 (United States); Dahlen, Tomas; Casertano, Stefano; Koekemoer, Anton [Space Telescope Science Institute, Baltimore, MD 21218 (United States); McCully, Curtis; Keeton, Charles R.; Patel, Brandon [Department of Physics and Astronomy, Rutgers, State University of New Jersey, Piscataway, NJ 08854 (United States); Frederiksen, Teddy F.; Hjorth, Jens [Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen (Denmark); Strolger, Louis-Gregory [Department of Physics, Western Kentucky University, Bowling Green, KY 42101 (United States); Wiklind, Tommy G. [Joint ALMA Observatory, ESO, Santiago (Chile); Challis, Peter [Harvard/Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Graur, Or [School of Physics and Astronomy, Tel-Aviv University, Tel-Aviv 69978 (Israel); Hayden, Brian; Garnavich, Peter [Department of Physics, University of Notre Dame, Notre Dame, IN 46556 (United States); Weiner, Benjamin J. [Department of Astronomy, University of Arizona, Tucson, AZ 85721 (United States); Filippenko, Alexei V. [Department of Astronomy, University of California, Berkeley, CA 94720-3411 (United States); and others

    2013-05-10T23:59:59.000Z

    We present the discovery of a Type Ia supernova (SN) at redshift z = 1.914 from the CANDELS multi-cycle treasury program on the Hubble Space Telescope (HST). This SN was discovered in the infrared using the Wide-Field Camera 3, and it is the highest-redshift Type Ia SN yet observed. We classify this object as a SN Ia by comparing its light curve and spectrum with those of a large sample of Type Ia and core-collapse SNe. Its apparent magnitude is consistent with that expected from the {Lambda}CDM concordance cosmology. We discuss the use of spectral evidence for classification of z > 1.5 SNe Ia using HST grism simulations, finding that spectral data alone can frequently rule out SNe II, but distinguishing between SNe Ia and SNe Ib/c can require prohibitively long exposures. In such cases, a quantitative analysis of the light curve may be necessary for classification. Our photometric and spectroscopic classification methods can aid the determination of SN rates and cosmological parameters from the full high-redshift CANDELS SN sample.

  5. AlGaAs/InGaAs/AlGaAs Double Barrier

    E-Print Network [OSTI]

    Perera, A. G. Unil

    -state Er. Tunneling Quantum Dot Sensors for Multi-band Infrared and Terahertz Radiation Detection G radiation detection are demonstrated. In T-QDIP structures, photoabsorption takes place in InGaAs QDs (due

  6. Composition and Interface Analysis of InGaN/GaN Multiquantum...

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    Composition and Interface Analysis of InGaNGaN Multiquantum-Wells on GaN Substrates Using Atom Probe Tomography. Composition and Interface Analysis of InGaNGaN Multiquantum-Wells...

  7. GaAs, AlGaAs and InGaP Tunnel Junctions for Multi-Junction Solar Cells Under Concentration: Resistance Study

    SciTech Connect (OSTI)

    Wheeldon, Jeffrey F.; Valdivia, Christopher E.; Walker, Alex; Kolhatkar, Gitanja; Hall, Trevor J.; Hinzer, Karin [Centre for Research in Photonics, University of Ottawa, Ottawa, ON (Canada); Masson, Denis; Riel, Bruno; Fafard, Simon [Cyrium Technologies Inc., Ottawa, ON (Canada); Jaouad, Abdelatif; Turala, Artur; Ares, Richard; Aimez, Vincent [Centre de Recherche en Nanofabrication et en Nanocaracterisation CRN2, Universite de Sherbrooke, Sherbrooke, QC (Canada)

    2010-10-14T23:59:59.000Z

    The following four TJ designs, AlGaAs/AlGaAs, GaAs/GaAs, AlGaAs/InGaP and AlGaAs/GaAs are studied to determine minimum doping concentration to achieve a resistance of <10{sup -4} {omega}{center_dot}cm{sup 2} and a peak tunneling current suitable for MJ solar cells up to 1500-suns concentration (operating current of 21 A/cm{sup 2}). Experimentally calibrated numerical models are used to determine how the resistance changes as a function of doping concentration. The AlGaAs/GaAs TJ design is determined to require the least doping concentration to achieve the specified resistance and peak tunneling current, followed by the GaAs/GaAs, and AlGaAs/AlGaAs TJ designs. The AlGaAs/InGaP TJ design can only achieve resistances >5x10{sup -4} {omega}cm{sup 2}.

  8. PRESSURE DEPENDENCE OF OPTICAL TRANSITIONS IN InGaN/GaN MULTIPLE QUANTUM WELLS

    E-Print Network [OSTI]

    McCluskey, Matthew

    -m thick GaN layer deposited on a sapphire substrate, and it is capped by a 0.2-m GaN:Mg pPRESSURE DEPENDENCE OF OPTICAL TRANSITIONS IN InGaN/GaN MULTIPLE QUANTUM WELLS W. Shan,* J.W. Ager pressure on optical transitions in InGaN/GaN multiple quantum wells (MQWs) has been studied

  9. Free carrier accumulation at cubic AlGaN/GaN heterojunctions Q. Y. Wei,1

    E-Print Network [OSTI]

    As, Donat Josef

    ) substrate,7 with GaN and AlGaN layer thickness of 600 nm and 30 nm, respectively. The layer thicknessFree carrier accumulation at cubic AlGaN/GaN heterojunctions Q. Y. Wei,1 T. Li,1 J. Y. Huang,1 F. A (Received 24 February 2012; accepted 19 March 2012; published online 3 April 2012) Cubic Al0.3Ga0.7N/GaN

  10. InGaP/GaAs/InGaP double-heterojunction bipolar transistors grown by solid-source molecular-beam epitaxy with a valved phosphorus cracker

    E-Print Network [OSTI]

    Woodall, Jerry M.

    InGaP/GaAs/InGaP double-heterojunction bipolar transistors grown by solid-source molecular; accepted 17 November 1995 The growth and device characterization of an InGaP/GaAs double-quality phosphorus-containing compounds.14 The growth of high-performance InGaP/ GaAs and InGaAs/InP single

  11. InGaP/InGaAsN/GaAs NpN double-heterojunction bipolar transistor

    SciTech Connect (OSTI)

    Chang, P. C. [Sandia National Laboratories, Albuquerque, New Mexico 87123 (United States)] [Sandia National Laboratories, Albuquerque, New Mexico 87123 (United States); Baca, A. G. [Sandia National Laboratories, Albuquerque, New Mexico 87123 (United States)] [Sandia National Laboratories, Albuquerque, New Mexico 87123 (United States); Li, N. Y. [Emcore Photovoltaics, Emcore Corporation, Albuquerque, New Mexico 87123 (United States)] [Emcore Photovoltaics, Emcore Corporation, Albuquerque, New Mexico 87123 (United States); Xie, X. M. [Emcore Photovoltaics, Emcore Corporation, Albuquerque, New Mexico 87123 (United States)] [Emcore Photovoltaics, Emcore Corporation, Albuquerque, New Mexico 87123 (United States); Hou, H. Q. [Emcore Photovoltaics, Emcore Corporation, Albuquerque, New Mexico 87123 (United States)] [Emcore Photovoltaics, Emcore Corporation, Albuquerque, New Mexico 87123 (United States); Armour, E. [Emcore Corporation, Somerset, New Jersey 08873 (United States)] [Emcore Corporation, Somerset, New Jersey 08873 (United States)

    2000-04-17T23:59:59.000Z

    We have demonstrated a functional NpN double-heterojunction bipolar transistor (DHBT) using InGaAsN for the base layer. The InGaP/In{sub 0.03}Ga{sub 0.97}As{sub 0.99}N{sub 0.01}/GaAs DHBT has a low V{sub ON} of 0.81 V, which is 0.13 V lower than in a InGaP/GaAs heterojunction bipolar transistor (HBT). The lower turn-on voltage is attributed to the smaller band gap (1.20 eV) of metalorganic chemical vapor deposition-grown In{sub 0.03}Ga{sub 0.97}As{sub 0.99}N{sub 0.01} base layer. GaAs is used for the collector; thus the breakdown voltage (BV{sub CEO}) is 10 V, consistent with the BV{sub CEO} of InGaP/GaAs HBTs of comparable collector thickness and doping level. To alleviate the current blocking phenomenon caused by the larger conduction band discontinuity between InGaAsN and GaAs, a graded InGaAs layer with {delta} doping is inserted at the base-collector junction. The improved device has a peak current gain of seven with ideal current-voltage characteristics. (c) 2000 American Institute of Physics.

  12. InGaP/InGaAsN/GaAs NpN double heterojunction bipolar transistor

    SciTech Connect (OSTI)

    Chang, P.C.; Baca, A.G.; Li, N.Y.; Xie, X.M.; Sharps, P.R.; Hou, H.Q.

    2000-01-10T23:59:59.000Z

    The authors have demonstrated a functional NpN double heterojunction bipolar transistor (DHBT) using InGaAsN for base layer. The InGaP/In{sub 0.03}Ga{sub 0.97}As{sub 0.99}N{sub 0.01}/GaAs DHBT has a low V{sub ON} of 0.81 V, which is 0.13 V lower than in a InGaP/GaAs HBT. The lower V{sub ON} is attributed to the smaller bandgap (E{sub g}=1.20eV) of MOCVD grown In{sub 0.03}Ga{sub 0.97}As{sub 0.99}N{sub 0.01} base layer. GaAs is used for the collector; thus the BV{sub CEO} is 10 V, consistent with the BV{sub CEO} of InGaP/GaAs Hbts of comparable collector thickness and doping level. To alleviate the current blocking phenomenon caused by the larger {triangle}E{sub C} between InGaAsN and GaAs, a graded InGaAs layer with {delta}-doping is inserted at the base-collector junction. The improved device has a peak current gain of 7 with ideal IV characteristics.

  13. Intrafacet migration effects in InGaN/GaN structures grown on triangular GaN ridges studied by submicron beam x-ray diffraction

    E-Print Network [OSTI]

    Sirenko, Andrei

    Intrafacet migration effects in InGaN/GaN structures grown on triangular GaN ridges studied for x-ray diffraction and reciprocal space mapping of InGaN/GaN multiple-quantum-well MQW structures grown on the sidewalls of 10- m-wide triangular GaN ridges with 1-1.1 facets. Samples were produced

  14. GaN0.011P0.989GaP Double-Heterostructure Red Light-Emitting Diodes Directly Grown on GaP Substrates

    E-Print Network [OSTI]

    Tu, Charles W

    2000-01-01T23:59:59.000Z

    and C. W. Tu, GaN diodes on GaP substrates, 2000. [7] J. W.on a GaN directly grown on a GaP substrate was successfullyDH) directly a GaN grown on a (100) GaP substrate. Fig. 1(a)

  15. General Doppler Shift Equation and the Possibility of Systematic Error in Calculation of Z for High Redshift Type Ia Supernovae

    E-Print Network [OSTI]

    Steven M Taylor

    2007-04-10T23:59:59.000Z

    Systematic error in calculation of z for high redshift type Ia supernovae could help explain unexpected luminosity values that indicate an accelerating rate of expansion of the universe.

  16. A New Determination of the High Redshift Type Ia Supernova Rates with the Hubble Space Telescope Advanced Camera for Surveys

    E-Print Network [OSTI]

    2008-01-01T23:59:59.000Z

    Schmidt, B. P. , 2003, in Supernovae and Gamma Ray Bursts,for identifying Type Ia supernovae (although spectroscopicfor future high-statistics supernovae searches in which

  17. The type Ia supernova SNLS-03D3bb from a super-Chandrasekhar-mass white dwarf star

    E-Print Network [OSTI]

    2008-01-01T23:59:59.000Z

    magnitudes of Type IA supernovae. Astrophys. J. Lett. 413,from 42 High-Redshift Supernovae. Astrophys. J. 517, 565Observational Evidence from Supernovae for an Accelerating

  18. AlGaAs/InGaAsN/GaAs PnP double heterojunction bipolar transistor

    SciTech Connect (OSTI)

    Chang, P.C.; Baca, A.G.; Li, N.Y.; Sharps, P.R.; Hou, H.Q.; Laroche, J.R.; Ren, F.

    2000-01-11T23:59:59.000Z

    The authors have demonstrated a functional MOCVD-grown AlGaAs/InGaAsN/GaAsPnP DHBT that is lattice matched to GaAs and has a peak current gain ({beta}) of 25. Because of the smaller bandgap (E{sub g}=1.20eV)of In{sub 0.03}Ga{sub 0.97}As{sub 0.99}N{sub 0.01} used for the base layer, this device has a low V{sub ON} of 0.79 V, 0.25 V lower than in a comparable Pnp AlGaAs/GaAs HBT. The BV{sub CEO} is 12 V, consistent with its GaAs collector thickness and doping level.

  19. Asymmetric interfacial abruptness in N-polar and Ga-polar GaN/AlN/GaN heterostructures

    SciTech Connect (OSTI)

    Mazumder, B.; Hurni, C. A.; Zhang, J. Y.; Speck, J. S. [Materials Department, University of California, Santa Barbara, California 93106 (United States); Wong, M. H.; Mishra, U. K. [Department of Electrical and Computer Engineering, University of California, Santa Barbara, California 93106 (United States)

    2012-08-27T23:59:59.000Z

    In this letter, we report on the interfacial abruptness of GaN/AlN/GaN heterostructures with pulsed laser atom probe tomography (APT). The samples were grown by plasma-assisted molecular beam epitaxy (MBE) under both metal-rich and N-rich conditions on both Ga-polar (0001) GaN templates and N-polar (0001) GaN substrates. An NH{sub 3} assisted MBE technique was involved to grow similar Ga-polar and N-polar structures on GaN:Fe substrates and GaN/Al{sub 2}O{sub 3} templates, respectively, for a comparison study. We find in all cases the interface with net positive polarization charge was chemically abrupt, whereas the interface with net negative polarization charge was diffuse. We discuss the implications on device design and performance. These data validate the efficiency of APT in studying interfaces for better performance in devices.

  20. Superior radiation-resistant properties of InGaP/GaAs tandem solar cells

    SciTech Connect (OSTI)

    Yamaguchi, M.; Okuda, T.; Taylor, S.J.; Takamoto, T. [Toyota Technological Institute 2-12-1 Hisakata, Tempaku, Nagoya 468 (Japan)] [Toyota Technological Institute 2-12-1 Hisakata, Tempaku, Nagoya 468 (Japan); Ikeda, E.; Kurita, H. [Central Resource Laboratory, Japan Energy Company, Niizo-Minami, Toda, Saitama 335 (Japan)] [Central Resource Laboratory, Japan Energy Company, Niizo-Minami, Toda, Saitama 335 (Japan)

    1997-03-01T23:59:59.000Z

    The observation of minority-carrier injection-enhanced annealing of radiation damage to InGa{sub 0.5}P{sub 0.5}/GaAs tandem solar cells is reported. Radiation resistance of InGaP/GaAs tandem solar cells as is similar with GaAs-on-Ge cells have been confirmed with 1 MeV electron irradiations. Moreover, minority-carrier injection under light illumination and forward bias conditions is shown to enhance defect annealing in InGaP and to result in the recovery of InGaP/GaAs tandem solar cell properties. These results suggest that the InGaP/GaAs(/Ge) multijunction solar cells and InGaP-based devices have great potential for space applications. {copyright} {ital 1997 American Institute of Physics.}

  1. Strong near-infrared carbon in the Type Ia supernova iPTF13ebh

    E-Print Network [OSTI]

    Hsiao, E Y; Contreras, C; Hflich, P; Sand, D; Marion, G H; Phillips, M M; Stritzinger, M; Gonzlez-Gaitn, S; Mason, R E; Folatelli, G; Parent, E; Gall, C; Amanullah, R; Anupama, G C; Arcavi, I; Banerjee, D P K; Beletsky, Y; Blanc, G A; Bloom, J S; Brown, P J; Campillay, A; Cao, Y; De Cia, A; Diamond, T; Freedman, W L; Gonzalez, C; Goobar, A; Holmbo, S; Howell, D A; Johansson, J; Kasliwal, M M; Kirshner, R P; Krisciunas, K; Kulkarni, S R; Maguire, K; Milne, P A; Morrell, N; Nugent, P E; Ofek, E O; Osip, D; Palunas, P; Perley, D A; Persson, S E; Piro, A L; Rabus, M; Roth, M; Schiefelbein, J M; Srivastav, S; Sullivan, M; Suntzeff, N B; Surace, J; Wo?nia, P R; Yaron, O

    2015-01-01T23:59:59.000Z

    We present near-infrared (NIR) time-series spectroscopy, as well as complementary ultraviolet (UV), optical, and NIR data, of the Type Ia supernova (SN Ia) iPTF13ebh, which was discovered within two days from the estimated time of explosion. The first NIR spectrum was taken merely 2.3 days after explosion and may be the earliest NIR spectrum yet obtained of a SN Ia. The most striking features in the spectrum are several NIR C I lines, and the C I {\\lambda}1.0693 {\\mu}m line is the strongest ever observed in a SN Ia. Interestingly, no strong optical C II counterparts were found, even though the optical spectroscopic time series began early and is densely-cadenced. Except at the very early epochs, within a few days from the time of explosion, we show that the strong NIR C I compared to the weaker optical C II appears to be general in SNe Ia. iPTF13ebh is a fast decliner with {\\Delta}m15(B) = 1.79 $\\pm$ 0.01, and its absolute magnitude obeys the linear part of the width-luminosity relation. It is therefore categ...

  2. A Precise Distance Indicator: Type Ia Supernova Multicolor Light Curve Shapes

    E-Print Network [OSTI]

    Adam Riess; William Press; Robert Kirshner

    1996-04-24T23:59:59.000Z

    We present an empirical method that uses multicolor light curve shapes (MLCS) to estimate the luminosity, distance, and total line-of-sight extinction of Type Ia supernovae (SN Ia). The empirical correlation between the MLCS and the luminosity is derived from a ``training set'' of nine SN Ia light curves with independent distance and reddening estimates. We find that intrinsically dim SN Ia are redder and have faster light curves than the bright ones which are slow and blue. By thirty-five days after maximum the intrinsic color variations become negligable. A formal treatment of extinction employing Bayes' theorem is used to estimate the best value and its uncertainty. Applying MLCS to both light curves and to color curves provides enough information to determine which supernovae are dim because they are distant, which are intrinsically dim, and which are dim because of extinction by dust. The precision of the MLCS distances is examined by constructing a Hubble diagram with an independent set of twenty SN Ia's. The dispersion of 0.12 mag indicates a typical distance accuracy of 5 % for a single object, and the intercept yields a Hubble constant on the Cepheid distance scale (Sandage et al 1994, 1996) of H_0=65 \\pm 3 (statistical) km/s/Mpc ( \\pm 6 total error). The slope of 0.2010 pm 0.0035 mag over the distance interval 32.2 < mu < 38.3 yields the most precise confirmation of the linearity of the Hubble law.

  3. Wind-driven evolution of white dwarf binaries to type Ia supernovae

    SciTech Connect (OSTI)

    Ablimit, Iminhaji; Xu, Xiao-jie; Li, X.-D. [Department of Astronomy, Nanjing University, Nanjing 210093 (China)

    2014-01-01T23:59:59.000Z

    In the single-degenerate scenario for the progenitors of Type Ia supernovae (SNe Ia), a white dwarf rapidly accretes hydrogen- or helium-rich material from its companion star and appears as a supersoft X-ray source. This picture has been challenged by the properties of the supersoft X-ray sources with very low mass companions and the observations of several nearby SNe Ia. It has been pointed out that the X-ray radiation or the wind from the accreting white dwarf can excite winds or strip mass from the companion star, thus significantly influencing the mass transfer processes. In this paper, we perform detailed calculations of the wind-driven evolution of white dwarf binaries. We present the parameter space for the possible SN Ia progenitors and for the surviving companions after the SNe. The results show that the ex-companion stars of SNe Ia have characteristics more compatible with the observations, compared with those in the traditional single-degenerate scenario.

  4. Type Ia supernovae from merging white dwarfs. II. Post-merger detonations

    SciTech Connect (OSTI)

    Raskin, Cody; Kasen, Daniel [Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA (United States); Moll, Rainer; Woosley, Stan [Department of Physics and Department of Astronomy, University of California, Santa Cruz, CA (United States); Schwab, Josiah [Department of Physics and Department of Astronomy, University of California, Berkeley, CA (United States)

    2014-06-10T23:59:59.000Z

    Merging carbon-oxygen (CO) white dwarfs are a promising progenitor system for Type Ia supernovae (SNe Ia), but the underlying physics and timing of the detonation are still debated. If an explosion occurs after the secondary star is fully disrupted, the exploding primary will expand into a dense CO medium that may still have a disk-like structure. This interaction will decelerate and distort the ejecta. Here we carry out multidimensional simulations of 'tamped' SN Ia models, using both particle and grid-based codes to study the merger and explosion dynamics and a radiative transfer code to calculate synthetic spectra and light curves. We find that post-merger explosions exhibit an hourglass-shaped asymmetry, leading to strong variations in the light curves with viewing angle. The two most important factors affecting the outcome are the scale height of the disk, which depends sensitively on the binary mass ratio, and the total {sup 56}Ni yield, which is governed by the central density of the remnant core. The synthetic broadband light curves rise and decline very slowly, and the spectra generally look peculiar, with weak features from intermediate mass elements but relatively strong carbon absorption. We also consider the effects of the viscous evolution of the remnant and show that a longer time delay between merger and explosion probably leads to larger {sup 56}Ni yields and more symmetrical remnants. We discuss the relevance of this class of aspherical 'tamped' SN Ia for explaining the class of 'super-Chandrasekhar' SN Ia.

  5. SALT: a Spectral Adaptive Light curve Template for Type Ia Supernovae

    E-Print Network [OSTI]

    J. Guy; P. Astier; S. Nobili; N. Regnault; R. Pain

    2005-07-01T23:59:59.000Z

    We present a new method to parameterize Type Ia Supernovae (SN Ia) multi-color light curves. The method was developed in order to analyze the large number of SN Ia multi-color light curves measured in current high-redshift projects. The technique is based on empirically modeling SN Ia luminosity variations as a function of phase, wavelength, a shape parameter, and a color parameter. The model is trained with a sample of well measured nearby SN Ia and then tested with an independent set of supernovae by building an optimal luminosity distance estimator combining the supernova rest-frame luminosity, shape parameter and color reconstructed with the model. The distances we measure using B- and V-band data show a dispersion around the Hubble line comparable or lower than obtained with other methods. With this model, we are able to measure distances using U- and B-band data with a dispersion around the Hubble line of 0.16 +- 0.05.

  6. Confirmation of Hostless Type Ia Supernovae Using Hubble Space Telescope Imaging

    E-Print Network [OSTI]

    Graham, Melissa L; Zaritsky, Dennis; Pritchet, Chris J

    2015-01-01T23:59:59.000Z

    We present deep Hubble Space Telescope imaging at the locations of four, potentially hostless, long-faded Type Ia supernovae (SNe Ia) in low-redshift, rich galaxy clusters that were identified in the Multi-Epoch Nearby Cluster Survey. Assuming a steep faint-end slope for the galaxy cluster luminosity function ($\\alpha_d=-1.5$), our data includes all but $\\lesssim0.2\\%$ percent of the stellar mass in cluster galaxies ($\\lesssim0.005\\%$ with $\\alpha_d=-1.0$), a factor of 10 better than our ground-based imaging. Two of the four SNe Ia still have no possible host galaxy associated with them ($M_R>-9.2$), confirming that their progenitors belong to the intracluster stellar population. The third SNe Ia appears near a faint disk galaxy ($M_V=-12.2$) which has a relatively high probability of being a chance alignment. A faint, red, point source coincident with the fourth SN Ia's explosion position ($M_V=-8.4$) may be either a globular cluster (GC) or faint dwarf galaxy. We estimate the local surface densities of GCs ...

  7. COMPARING THE LIGHT CURVES OF SIMULATED TYPE Ia SUPERNOVAE WITH OBSERVATIONS USING DATA-DRIVEN MODELS

    SciTech Connect (OSTI)

    Diemer, Benedikt; Kessler, Richard; Graziani, Carlo; Jordan, George C. IV; Lamb, Donald Q.; Long, Min; Van Rossum, Daniel R., E-mail: bdiemer@oddjob.uchicago.edu [Flash Center for Computational Science, University of Chicago, Chicago, IL 60637 (United States)

    2013-08-20T23:59:59.000Z

    We propose a robust, quantitative method to compare the synthetic light curves of a Type Ia supernova (SN Ia) explosion model with a large set of observed SNe Ia, and derive a figure of merit for the explosion model's agreement with observations. The synthetic light curves are fit with the data-driven model SALT2 which returns values for stretch, color, and magnitude at peak brightness, as well as a goodness-of-fit parameter. Each fit is performed multiple times with different choices of filter bands and epoch range in order to quantify the systematic uncertainty on the fitted parameters. We use a parametric population model for the distribution of observed SN Ia parameters from large surveys, and extend it to represent red, dim, and bright outliers found in a low-redshift SN Ia data set. We discuss the potential uncertainties of this population model and find it to be reliable given the current uncertainties on cosmological parameters. Using our population model, we assign each set of fitted parameters a likelihood of being observed in nature, and a figure of merit based on this likelihood. We define a second figure of merit based on the quality of the light curve fit, and combine the two measures into an overall figure of merit for each explosion model. We compute figures of merit for a variety of one-, two-, and three-dimensional explosion models and show that our evaluation method allows meaningful inferences across a wide range of light curve quality and fitted parameters.

  8. Beta decay of Ga-62

    E-Print Network [OSTI]

    Hyman, BC; Iacob, VE; Azhari, A.; Gagliardi, Carl A.; Hardy, John C.; Mayes, VE; Neilson, RG; Sanchez-Vega, M.; Tang, X.; Trache, L.; Tribble, Robert E.

    2003-01-01T23:59:59.000Z

    from the ex- perimental ft value for a 01?01 b decay between analog states with the relation @3# 0556-2813/2003/68~1!/015501~6!/$20.00 68 015501- of 62Ga . Hardy, V. E. Mayes, R. G. Neilson, M. Sanchez-Vega, and R. E. Tribble y, College Station...

  9. GaN nanowires show more 3D piezoelectricity than bulk GaN

    E-Print Network [OSTI]

    Espinosa, Horacio D.

    Logo GaN nanowires show more 3D piezoelectricity than bulk GaN admin / January 11, 2012 individual gallium nitride (GaN) nanowires showing strong piezoelectric effect in 3D. This is in spite of the fact that each nanowire only measures 100nm in diameter. While GaN is ubiquitous in optoelectronic

  10. Self-aligned AlGaN/GaN transistors for sub-mm wave applications

    E-Print Network [OSTI]

    Saadat, Omair I

    2010-01-01T23:59:59.000Z

    This thesis describes work done towards realizing self-aligned AlGaN/GaN high electron mobility transistors (HEMTs). Self-aligned transistors are important for improving the frequency of AlGaN/GaN HEMTs by reducing source ...

  11. Spectral Modeling of SNe Ia Near Maximum Light: Probing the Characteristics of Hydro Models

    E-Print Network [OSTI]

    E. Baron; S. Bongard; David Branch; Peter H. Hauschildt

    2006-03-03T23:59:59.000Z

    We have performed detailed NLTE spectral synthesis modeling of 2 types of 1-D hydro models: the very highly parameterized deflagration model W7, and two delayed detonation models. We find that overall both models do about equally well at fitting well observed SNe Ia near to maximum light. However, the Si II 6150 feature of W7 is systematically too fast, whereas for the delayed detonation models it is also somewhat too fast, but significantly better than that of W7. We find that a parameterized mixed model does the best job of reproducing the Si II 6150 line near maximum light and we study the differences in the models that lead to better fits to normal SNe Ia. We discuss what is required of a hydro model to fit the spectra of observed SNe Ia near maximum light.

  12. The Late-Time Rebrightening of Type Ia SN 2005gj in the Mid-Infrared

    E-Print Network [OSTI]

    Fox, Ori D

    2013-01-01T23:59:59.000Z

    A growing number of observations reveal a subset of Type Ia supernovae undergoing circumstellar interaction (SNe Ia-CSM). We present unpublished archival Spitzer Space Telescope data on SNe Ia-CSM 2002ic and 2005gj obtained > 1300 and 500 days post-discovery, respectively. Both SNe show evidence for late-time mid-infrared (mid-IR) emission from warm dust. The dust parameters are most consistent with a pre-existing dust shell that lies beyond the forward-shock radius, most likely radiatively heated by optical and X-ray emission continuously generated by late-time CSM interaction. In the case of SN 2005gj, the mid-IR luminosity more than doubles after 1 year post-discovery. While we are not aware of any late-time optical-wavelength observations at these epochs, we attribute this rebrightening to renewed shock interaction with a dense circumstellar shell.

  13. [O I] ??6300, 6364 IN THE NEBULAR SPECTRUM OF A SUBLUMINOUS TYPE Ia SUPERNOVA

    SciTech Connect (OSTI)

    Taubenberger, S.; Kromer, M.; Hillebrandt, W. [Max-Planck-Institut fr Astrophysik, Karl-Schwarzschild-Str. 1, D-85741 Garching (Germany)] [Max-Planck-Institut fr Astrophysik, Karl-Schwarzschild-Str. 1, D-85741 Garching (Germany); Pakmor, R. [Heidelberger Institut fr Theoretische Studien, Schloss-Wolfsbrunnenweg 35, D-69118 Heidelberg (Germany)] [Heidelberger Institut fr Theoretische Studien, Schloss-Wolfsbrunnenweg 35, D-69118 Heidelberg (Germany); Pignata, G. [Departamento de Ciencias Fisicas, Universidad Andres Bello, Avda. Republica 252, Santiago (Chile)] [Departamento de Ciencias Fisicas, Universidad Andres Bello, Avda. Republica 252, Santiago (Chile); Maeda, K. [Kavli Institute for the Physics and Mathematics of the Universe (WPI), Todai Institutes for Advanced Study, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8583 (Japan)] [Kavli Institute for the Physics and Mathematics of the Universe (WPI), Todai Institutes for Advanced Study, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8583 (Japan); Hachinger, S. [Julius-Maximilians-Universitt Wrzburg, Emil-Fischer-Str. 31, D-97074 Wrzburg (Germany)] [Julius-Maximilians-Universitt Wrzburg, Emil-Fischer-Str. 31, D-97074 Wrzburg (Germany); Leibundgut, B. [European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching (Germany)] [European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching (Germany)

    2013-10-01T23:59:59.000Z

    In this Letter, a late-phase spectrum of SN 2010lp, a subluminous Type Ia supernova (SN Ia), is presented and analyzed. As in 1991bg-like SNe Ia at comparable epochs, the spectrum is characterized by relatively broad [Fe II] and [Ca II] emission lines. However, instead of narrow [Fe III] and [Co III] lines that dominate the emission from the innermost regions of 1991bg-like supernovae (SNe), SN 2010lp shows [O I] ??6300, 6364 emission, usually associated with core-collapse SNe and never previously observed in a subluminous thermonuclear explosion. The [O I] feature has a complex profile with two strong, narrow emission peaks. This suggests that oxygen is distributed in a non-spherical region close to the center of the ejecta, severely challenging most thermonuclear explosion models discussed in the literature. We conclude that, given these constraints, violent mergers are presently the most promising scenario to explain SN 2010lp.

  14. THE LATE-TIME REBRIGHTENING OF TYPE Ia SN 2005gj IN THE MID-INFRARED

    SciTech Connect (OSTI)

    Fox, Ori D.; Filippenko, Alexei V., E-mail: ofox@berkeley.edu [Department of Astronomy, University of California, Berkeley, CA 94720-3411 (United States)

    2013-07-20T23:59:59.000Z

    A growing number of observations reveal a subset of Type Ia supernovae undergoing circumstellar interaction (SNe Ia-CSM). We present unpublished archival Spitzer Space Telescope data on SNe Ia-CSM 2002ic and 2005gj obtained >1300 and 500 days post-discovery, respectively. Both SNe show evidence for late-time mid-infrared (mid-IR) emission from warm dust. The dust parameters are most consistent with a preexisting dust shell that lies beyond the forward-shock radius, most likely radiatively heated by optical and X-ray emission continuously generated by late-time CSM interaction. In the case of SN 2005gj, the mid-IR luminosity more than doubles after 1 yr post-discovery. While we are not aware of any late-time optical-wavelength observations at these epochs, we attribute this rebrightening to renewed shock interaction with a dense circumstellar shell.

  15. SALT2: using distant supernovae to improve the use of Type Ia supernovae as distance indicators

    E-Print Network [OSTI]

    J. Guy; P. Astier; S. Baumont; D. Hardin; R. Pain; N. Regnault; S. Basa; R. G. Carlberg; A. Conley; S. Fabbro; D. Fouchez; I. M. Hook; D. A. Howell; K. Perrett; C. J. Pritchet; J. Rich; M. Sullivan; P. Antilogus; E. Aubourg; G. Bazin; J. Bronder; M. Filiol; N. Palanque-Delabrouille; P. Ripoche; V. Ruhlmann-Kleider

    2007-01-29T23:59:59.000Z

    We present an empirical model of Type Ia supernovae spectro-photometric evolution with time. The model is built using a large data set including light-curves and spectra of both nearby and distant supernovae, the latter being observed by the SNLS collaboration. We derive the average spectral sequence of Type Ia supernovae and their main variability components including a color variation law. The model allows us to measure distance moduli in the spectral range 2500-8000 A with calculable uncertainties, including those arising from variability of spectral features. Thanks to the use of high-redshift SNe to model the rest-frame UV spectral energy distribution, we are able to derive improved distance estimates for SNe Ia in the redshift range 0.8supernovae.

  16. Invited Paper GaN HEMT reliability

    E-Print Network [OSTI]

    del Alamo, Jess A.

    Invited Paper GaN HEMT reliability J.A. del Alamo *, J. Joh Microsystems Technology Laboratories mechanism recently identified in GaN high-electron mobility transistors subject to electrical stress. Under high voltage, it has been found that electrically active defects are generated in the AlGaN barrier

  17. EARLY PHASE OBSERVATIONS OF EXTREMELY LUMINOUS TYPE Ia SUPERNOVA 2009dc

    SciTech Connect (OSTI)

    Yamanaka, M.; Arai, A.; Chiyonobu, S.; Fukazawa, Y.; Ikejiri, Y.; Itoh, R.; Komatsu, T.; Miyamoto, H. [Department of Physical Science, Hiroshima University, Kagamiyama 1-3-1, Higashi-Hiroshima 739-8526 (Japan); Kawabata, K. S. [Hiroshima Astrophysical Science Center, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526 (Japan); Kinugasa, K.; Hashimoto, O.; Honda, S. [Gunma Astronomical Observatory, Takayama, Gunma 377-0702 (Japan); Tanaka, M. [Department of Astronomy, School of Science, University of Tokyo, Bunkyo-ku, Tokyo 113-0033 (Japan); Imada, A.; Kuroda, D. [Okayama Astrophysical Observatory, National Astronomical Observatory of Japan, Kamogata, Asakuchi-shi, Okayama 719-0232 (Japan); Maeda, K.; Nomoto, K. [Institute for the Physics and Mathematics of the Universe, University of Tokyo, Kashiwa (Japan); Kamata, Y. [National Astronomical Observatory of Japan, Osawa, Mitaka, Tokyo 181-8588 (Japan); Kawai, N. [Department of Physics, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551 (Japan); Konishi, K., E-mail: myamanaka@hiroshima-u.ac.j [Institute for Cosmic Ray Research, University of Tokyo, 5-1-5, Kashiwanoha, Kashiwa, Chiba, 277-8582 (Japan)

    2009-12-20T23:59:59.000Z

    We present early phase observations in optical and near-infrared wavelengths for the extremely luminous Type Ia supernova (SN Ia) 2009dc. The decline rate of the light curve is DELTAm{sub 15}(B) = 0.65 +- 0.03, which is one of the slowest among SNe Ia. The peak V-band absolute magnitude is estimated to be M{sub V} = -19.90 +- 0.15 mag if no host extinction is assumed. It reaches M{sub V} = -20.19 +- 0.19 mag if we assume the host extinction of A{sub V} = 0.29 mag. SN 2009dc belongs to the most luminous class of SNe Ia, like SNe 2003fg and 2006gz. Our JHK{sub s} -band photometry shows that this SN is also one of the most luminous SNe Ia in near-infrared wavelengths. We estimate the ejected {sup 56}Ni mass of 1.2 +- 0.3 M{sub sun} for the no host extinction case (and of 1.6 +- 0.4 M{sub sun} for the host extinction of A{sub V} = 0.29 mag). The C II lambda6580 absorption line remains visible until a week after the maximum brightness, in contrast to its early disappearance in SN 2006gz. The line velocity of Si II lambda6355 is about 8000 km s{sup -1} around the maximum, being considerably slower than that of SN 2006gz. The velocity of the C II line is similar to or slightly less than that of the Si II line around the maximum. The presence of the carbon line suggests that the thick unburned C+O layer remains after the explosion. Spectropolarimetric observations by Tanaka et al. indicate that the explosion is nearly spherical. These observational facts suggest that SN 2009dc is a super-Chandrasekhar mass SN Ia.

  18. OPTICAL CROSS-CORRELATION FILTERS: AN ECONOMICAL APPROACH FOR IDENTIFYING SNe Ia AND ESTIMATING THEIR REDSHIFTS

    SciTech Connect (OSTI)

    Scolnic, Daniel M.; Riess, Adam G.; Huber, Mark E. [Department of Physics and Astronomy, Johns Hopkins University, MD 21218 (United States); Rest, Armin; Stubbs, Christoper W. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Tonry, John L. [Institute for Astronomy, University of Hawaii, Honolulu, HI 96822 (United States)

    2009-11-20T23:59:59.000Z

    Large photometric surveys of transient phenomena, such as Panoramic Survey Telescope and Rapid Response System and Large Synoptic Survey Telescope, will locate thousands to millions of Type Ia supernova (SN Ia) candidates per year, a rate prohibitive for acquiring spectroscopy to determine each candidate's type and redshift. In response, we have developed an economical approach to identifying SNe Ia and their redshifts using an uncommon type of optical filter which has multiple, discontinuous passbands on a single substrate. Observation of a supernova through a specially designed pair of these 'cross-correlation filters' measures the approximate amplitude and phase of the cross-correlation between the spectrum and a SN Ia template, a quantity typically used to determine the redshift and type of a high-redshift SN Ia. Simulating the use of these filters, we obtain a sample of SNe Ia which is approx98% pure with individual redshifts measured to sigma{sub z} = 0.01 precision. The advantages of this approach over standard broadband photometric methods are that it is insensitive to reddening, independent of the color data used for subsequent distance determinations which reduce selection or interpretation bias, and because it makes use of the spectral features its reliability is greater. A great advantage over long-slit spectroscopy comes from increased throughput, enhanced multiplexing, and reduced setup time resulting in a net gain in speed of up to approx30 times. This approach is also insensitive to host galaxy contamination. Prototype filters were built and successfully used on Magellan with LDSS-3 to characterize three SuperNova Legacy Survey candidates. We discuss how these filters can provide critical information for the upcoming photometric supernova surveys.

  19. Ultraviolet observations of Super-Chandrasekhar mass type Ia supernova candidates with swift UVOT

    SciTech Connect (OSTI)

    Brown, Peter J.; Smitka, Michael T.; Krisciunas, Kevin; Wang, Lifan [George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Texas A and M University, Department of Physics and Astronomy, 4242 TAMU, College Station, TX 77843 (United States); Kuin, Paul; De Pasquale, Massimiliano [Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking Surrey, RH5 6NT (United Kingdom); Scalzo, Richard [Research School of Astronomy and Astrophysics, The Australian National University, Mount Stromlo Observatory, Cotter Road, Weston Creek, ACT 2611 (Australia); Holland, Stephen [Space Telescope Science Center 3700 San Martin Drive, Baltimore, MD 21218 (United States); Milne, Peter, E-mail: pbrown@physics.tamu.edu [Steward Observatory, University of Arizona, Tucson, AZ 85719 (United States)

    2014-05-20T23:59:59.000Z

    Among Type Ia supernovae (SNe Ia), a class of overluminous objects exist whose ejecta mass is inferred to be larger than the canonical Chandrasekhar mass. We present and discuss the UV/optical photometric light curves, colors, absolute magnitudes, and spectra of three candidate Super-Chandrasekhar mass SNe2009dc, 2011aa, and 2012dnobserved with the Swift Ultraviolet/Optical Telescope. The light curves are at the broad end for SNe Ia, with the light curves of SN 2011aa being among the broadest ever observed. We find all three to have very blue colors which may provide a means of excluding these overluminous SNe from cosmological analysis, though there is some overlap with the bluest of 'normal' SNe Ia. All three are overluminous in their UV absolute magnitudes compared to normal and broad SNe Ia, but SNe 2011aa and 2012dn are not optically overluminous compared to normal SNe Ia. The integrated luminosity curves of SNe 2011aa and 2012dn in the UVOT range (1600-6000 ) are only half as bright as SN 2009dc, implying a smaller {sup 56}Ni yield. While it is not enough to strongly affect the bolometric flux, the early time mid-UV flux makes a significant contribution at early times. The strong spectral features in the mid-UV spectra of SNe 2009dc and 2012dn suggest a higher temperature and lower opacity to be the cause of the UV excess rather than a hot, smooth blackbody from shock interaction. Further work is needed to determine the ejecta and {sup 56}Ni masses of SNe 2011aa and 2012dn and to fully explain their high UV luminosities.

  20. New GaInP/GaAs/GaInAs, Triple-Bandgap, Tandem Solar Cell for High-Efficiency Terrestrial Concentrator Systems

    SciTech Connect (OSTI)

    Kurtz, S.; Wanlass, M.; Kramer, C.; Young, M.; Geisz, J.; Ward, S.; Duda, A.; Moriarty, T.; Carapella, J.; Ahrenkiel, P.; Emery. K.; Jones, K.; Romero, M.; Kibbler, A.; Olson, J.; Friedman, D.; McMahon, W.; Ptak, A.

    2005-11-01T23:59:59.000Z

    GaInP/GaAs/GaInAs three-junction cells are grown in an inverted configuration on GaAs, allowing high quality growth of the lattice matched GaInP and GaAs layers before a grade is used for the 1-eV GaInAs layer. Using this approach an efficiency of 37.9% was demonstrated.

  1. Constraining the Lattice Fluid Dark Energy from SNe Ia, BAO and OHD

    E-Print Network [OSTI]

    Duan, Xiaoxian; Gao, Changjun

    2011-01-01T23:59:59.000Z

    Sanchez and Lacombe have ever developed a lattice fluid theory based on a well-defined statistical mechanical model. Taking the lattice fluid as a candidate of dark energy, we investigate the cosmic evolution of this fluid. Using the combined observational data of Type Ia Supernova (SNe Ia), Baryon Acoustic Oscillations (BAO) and Observational Hubble Data (OHD), we find the best fit value of the parameter in the model, $A = -0.3_{-0.1}^{+0.1}$. Then the cosmological implications of the model are presented.

  2. Constraining the Lattice Fluid Dark Energy from SNe Ia, BAO and OHD

    E-Print Network [OSTI]

    Xiaoxian Duan; Yichao Li; Changjun Gao

    2011-11-15T23:59:59.000Z

    Sanchez and Lacombe have ever developed a lattice fluid theory based on a well-defined statistical mechanical model. Taking the lattice fluid as a candidate of dark energy, we investigate the cosmic evolution of this fluid. Using the combined observational data of Type Ia Supernova (SNe Ia), Baryon Acoustic Oscillations (BAO) and Observational Hubble Data (OHD), we find the best fit value of the parameter in the model, $A = -0.3_{-0.1}^{+0.1}$. Then the cosmological implications of the model are presented.

  3. InAs=InGaP=GaAs heterojunction power Schottky rectifiers

    E-Print Network [OSTI]

    Woodall, Jerry M.

    InAs=InGaP=GaAs heterojunction power Schottky rectifiers A. Chen, M. Young and J.M. Woodall A low-matched InGaP on GaAs, to make a high-temperature power rectifier. The LT molecular beam epitaxy technique enables the formation of an abrupt interface between InAs and InGaP. This heterojunction rectifier

  4. Monolithic Millimeter-wave Distributed Amplifiers using AlGaN/GaN HEMTs

    E-Print Network [OSTI]

    York, Robert A.

    Monolithic Millimeter-wave Distributed Amplifiers using AlGaN/GaN HEMTs Rajkumar Santhakumar, Yi have been designed and fabricated using AlGaN/GaN HEMTs. One of them uses a standard HEMT for the unit-gate distributed amplifier achieves a CW peak output power of 1W and a PAE of about 16% at 4GHz. Index Terms -- GaN

  5. Role of strain in polarization switching in semipolar InGaN/GaN quantum wells

    E-Print Network [OSTI]

    Role of strain in polarization switching in semipolar InGaN/GaN quantum wells Qimin Yan,1,a Patrick November 2010 The effect of strain on the valence-band structure of 112¯2 semipolar InGaN grown on GaN D6 is calculated for GaN and InN using density functional theory with the Heyd­Scuseria­ Ernzerhof

  6. GaN/AlGaN heterojunction infrared detector responding in 814 and 2070 m ranges

    E-Print Network [OSTI]

    Perera, A. G. Unil

    GaN/AlGaN heterojunction infrared detector responding in 814 and 2070 m ranges G. Ariyawansa, M October 2006 A GaN/AlGaN heterojunction interfacial work function internal photoemission infrared detector, the work demonstrates 54 m 5.5 THz operation of the detector based on 1s2p transition of Si donors in GaN

  7. Experto Universitario Java Enterprise Componentes de presentacin 2012-2013 Depto. Ciencia de la Computacin e IA Sesin 1

    E-Print Network [OSTI]

    Escolano, Francisco

    Experto Universitario Java Enterprise Componentes de presentacin 2012-2013 Depto. Ciencia de la Universitario Java Enterprise Componentes de presentacin 2012-2013 Depto. Ciencia de la Computacin e IA Componentes de presentacin 2012-2013 Depto. Ciencia de la Computacin e IA Sesin 1 Experto Universitario

  8. Especialista Universitario Java Enterprise Componentes de presentacin 2012-2013 Depto. Ciencia de la Computacin e IA Sesin 4

    E-Print Network [OSTI]

    Escolano, Francisco

    Especialista Universitario Java Enterprise Componentes de presentacin 2012-2013 Depto. Ciencia presentacin 2012-2013 Depto. Ciencia de la Computacin e IA Sesin 4 Experto Universitario Java Enterprise Componentes de presentacin 2012-2013 Depto. Ciencia de la Computacin e IA Sesin 4 Experto Universitario

  9. A TYPE Ia SUPERNOVA AT REDSHIFT 1.55 IN HUBBLE SPACE TELESCOPE INFRARED OBSERVATIONS FROM CANDELS

    SciTech Connect (OSTI)

    Rodney, Steven A.; Riess, Adam G.; Jones, David O. [Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States); Dahlen, Tomas; Ferguson, Henry C.; Casertano, Stefano; Grogin, Norman A. [Space Telescope Science Institute, Baltimore, MD 21218 (United States); Strolger, Louis-Gregory [Department of Physics, Western Kentucky University, Bowling Green, KY 42101 (United States); Hjorth, Jens; Frederiksen, Teddy F. [Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen (Denmark); Weiner, Benjamin J. [Department of Astronomy, University of Arizona, Tucson, AZ 85721 (United States); Mobasher, Bahram [Department of Physics and Astronomy, University of California, Riverside, CA 92521 (United States); Challis, Peter; Kirshner, Robert P. [Harvard/Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Faber, S. M. [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 92064 (United States); Filippenko, Alexei V. [Department of Astronomy, University of California, Berkeley, CA 94720-3411 (United States); Garnavich, Peter; Hayden, Brian [Department of Physics, University of Notre Dame, Notre Dame, IN 46556 (United States); Graur, Or [Department of Astrophysics, Tel Aviv University, 69978 Tel Aviv (Israel); Jha, Saurabh W. [Department of Physics and Astronomy, Rutgers, State University of New Jersey, Piscataway, NJ 08854 (United States); and others

    2012-02-10T23:59:59.000Z

    We report the discovery of a Type Ia supernova (SN Ia) at redshift z = 1.55 with the infrared detector of the Wide Field Camera 3 (WFC3-IR) on the Hubble Space Telescope (HST). This object was discovered in CANDELS imaging data of the Hubble Ultra Deep Field and followed as part of the CANDELS+CLASH Supernova project, comprising the SN search components from those two HST multi-cycle treasury programs. This is the highest redshift SN Ia with direct spectroscopic evidence for classification. It is also the first SN Ia at z > 1 found and followed in the infrared, providing a full light curve in rest-frame optical bands. The classification and redshift are securely defined from a combination of multi-band and multi-epoch photometry of the SN, ground-based spectroscopy of the host galaxy, and WFC3-IR grism spectroscopy of both the SN and host. This object is the first of a projected sample at z > 1.5 that will be discovered by the CANDELS and CLASH programs. The full CANDELS+CLASH SN Ia sample will enable unique tests for evolutionary effects that could arise due to differences in SN Ia progenitor systems as a function of redshift. This high-z sample will also allow measurement of the SN Ia rate out to z Almost-Equal-To 2, providing a complementary constraint on SN Ia progenitor models.

  10. Effect of buffer structures on AlGaN/GaN high electron mobility transistor reliability

    SciTech Connect (OSTI)

    Liu, L. [University of Florida, Gainesville; Xi, Y. Y. [University of Florida, Gainesville; Ren, F. [University of Florida; Pearton, S. J. [University of Florida; Laboutin, O. [Kopin Corporation, Taunton, MA; Cao, Yu [Kopin Corporation, Taunton, MA; Johnson, Wayne J. [Kopin Corporation, Taunton, MA; Kravchenko, Ivan I [ORNL

    2012-01-01T23:59:59.000Z

    AlGaN/GaN high electron mobility transistors (HEMTs) with three different types of buffer layers, including a GaN/AlGaN composite layer, or 1 or 2 lm GaN thick layers, were fabricated and their reliability compared. The HEMTs with the thick GaN buffer layer showed the lowest critical voltage (Vcri) during off-state drain step-stress, but this was increased by around 50% and 100% for devices with the composite AlGaN/GaN buffer layers or thinner GaN buffers, respectively. The Voff - state for HEMTs with thin GaN and composite buffers were 100 V, however, this degraded to 50 60V for devices with thick GaN buffers due to the difference in peak electric field near the gate edge. A similar trend was observed in the isolation breakdown voltage measurements, with the highest Viso achieved based on thin GaN or composite buffer designs (600 700 V), while a much smaller Viso of 200V was measured on HEMTs with the thick GaN buffer layers. These results demonstrate the strong influence of buffer structure and defect density on AlGaN/GaN HEMT performance and reliability.

  11. Multi-color light curves of type Ia supernovae on the color-magnitude diagram: A novel step toward more precise distance and extinction estimates

    E-Print Network [OSTI]

    Wang, Lifan; Goldhaber, Gerson; Aldering, Greg; Perlmutter, Saul

    2003-01-01T23:59:59.000Z

    Date is earlier than for supernovae with smaller ?m 15 . SeeLight Curves of Type Ia Supernovae on the Color-Magnituderelation of Type Ia supernovae after optical maximum can

  12. Growth of AlGaN/GaN heterojunction field effect transistors on semi-insulating GaN using an AlGaN interlayer

    SciTech Connect (OSTI)

    Chen, Z.; Denbaars, S. P. [Electrical and Computer Engineering, University of California, Santa Barbara, California 93106 (United States); Materials Department, University of California, Santa Barbara, California 93106 (United States); Pei, Y.; Newman, S.; Chu, R.; Brown, D.; Keller, S.; Mishra, U. K. [Electrical and Computer Engineering, University of California, Santa Barbara, California 93106 (United States); Chung, R.; Nakamura, S. [Materials Department, University of California, Santa Barbara, California 93106 (United States)

    2009-03-16T23:59:59.000Z

    Semi-insulating (SI) GaN layers were grown on 4H-SiC substrates by inserting an AlGaN layer between the AlN buffer and the GaN layer. Secondary ion mass spectroscopy measurements showed that the AlGaN layer prevented Si from diffusing from the substrate into the GaN layer. X-ray diffraction and atomic force microscopy analyses showed that an optimized AlGaN interlayer does not degrade the crystal quality or surface morphology of the SI GaN. The room temperature mobility of an AlGaN/GaN heterostructure using this SI GaN was 2200 cm{sup 2}/V s. High electron mobility transistors (HEMTs) with 0.65 {mu}m long gates were also fabricated on these SI GaN buffers. A power density of 19.0 W/mm with a power added efficiency of 48% was demonstrated at 10 GHz at a drain bias of 78 V. These HEMTs also exhibited sharp pinch off, low leakage, and negligible dispersion.

  13. Predicting the amount of hydrogen stripped by the SN explosion for SN 2002cx-like SNe Ia

    SciTech Connect (OSTI)

    Liu, Zheng-Wei; Chen, X. F.; Wang, B.; Han, Z. W. [Yunnan Observatories, Chinese Academy of Sciences, Kunming 650011 (China); Kromer, M. [Max-Planck-Institut fr Astrophysik, Karl-Schwarzschild-Str. 1, D-85741 Garching (Germany); Fink, M.; Rpke, F. K. [Institut fr Theoretische Physik und Astrophysik, Universitt Wrzburg, Am Hubland, D-97074 Wrzburg (Germany); Pakmor, R., E-mail: zwliu@ynao.ac.cn [Heidelberger Institut fr Theoretische Studien, Schloss-Wolfsbrunnenweg 35, D-69118 Heidelberg (Germany)

    2013-12-01T23:59:59.000Z

    The most favored progenitor scenarios for Type Ia supernovae (SNe Ia) involve the single-degenerate (SD) scenario and the double-degenerate scenario. The absence of stripped hydrogen (H) in the nebular spectra of SNe Ia challenges the SD progenitor models. Recently, it was shown that pure deflagration explosion models of Chandrasekhar-mass white dwarfs, ignited off-center, reproduce the characteristic observational features of 2002cx-like SNe Ia very well. In this work we predict, for the first time, the amount of stripped H for the off-center, pure deflagration explosions. We find that their low kinetic energies lead to inefficient H mass stripping (? 0.01 M {sub ?}), indicating that the stripped H may be hidden in (observed) late-time spectra of SN 2002cx-like SNe Ia.

  14. Strain variations in InGaAsP/InGaP superlattices studied by scanning probe microscopy

    E-Print Network [OSTI]

    Feenstra, Randall

    1 Strain variations in InGaAsP/InGaP superlattices studied by scanning probe microscopy Huajie Chen, Kista, Sweden Abstract Strain-compensated InGaAsP/InGaP superlattices are studied in cross- section. The strain compensated InGaAsP/InGaP/InP superlattices studied here have application for light sources

  15. AlGaN/GaN Metal Oxide Semiconductor Field Effect Transistors using Titanium Dioxide P. J. HANSEN

    E-Print Network [OSTI]

    York, Robert A.

    AlGaN/GaN Metal Oxide Semiconductor Field Effect Transistors using Titanium Dioxide P. J. HANSEN 1 epitaxially on AlGaN/GaN HFET structures by molecular beam epitaxy (MBE). Growth was first performed on GaN templates to establish epitaxial growth conditions. X-ray diffraction showed [001] TiO2 || [1010]GaN

  16. AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors using barium strontium titanate

    E-Print Network [OSTI]

    York, Robert A.

    AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors using barium strontium; published 13 October 2004) Use of high-k gate dielectrics in AlGaN/GaN heterostructure field transconductance and pinchoff voltage. To achieve this, AlGaN/GaN metal-oxide-semiconductor heterostructure field

  17. In this paper, an AlGaN/GaN high electron mobility transistor (HEMT) device based on a

    E-Print Network [OSTI]

    Yang, Kyounghoon

    205 Abstract In this paper, an AlGaN/GaN high electron mobility transistor (HEMT) device basedBm at 2 GHz have been demonstrated from the fabricated device. 1. Introduction In recent years, AlGaN/GaN noise amplifier and switch. Superior results have been reported in microwave power performance of AlGaN/GaN

  18. A New Architecture for AlGaN/GaN HEMT Frequency Doubler Using Active Integrated Antenna Design Approach

    E-Print Network [OSTI]

    Itoh, Tatsuo

    A New Architecture for AlGaN/GaN HEMT Frequency Doubler Using Active Integrated Antenna Design presents a new architecture for an AlGaN/GaN HEMT frequency doubler using the active integrated antenna. The antenna operates as a fundamental frequency reflector in this circuit. Using AlGaN/GaN with 1mm gate

  19. Generation-Recombination Defects In AlGaN/GaN HEMT On SiC Substrate,

    E-Print Network [OSTI]

    Boyer, Edmond

    Generation-Recombination Defects In AlGaN/GaN HEMT On SiC Substrate, Evidenced By Low Frequency Aristide Briand, 92.195 Meudon, France Abstract. Wide bandgap devices such as AlGaN/GaN High Electron of GR- bulges related respectively to AlGaN/GaN interface and quantum well are identified. Each GR

  20. Effect of dislocations on electron mobility in AlGaN/GaN and AlGaN/AlN/GaN heterostructures

    SciTech Connect (OSTI)

    Kaun, Stephen W.; Burke, Peter G.; Kyle, Erin C. H.; Speck, James S. [Materials Department, University of California, Santa Barbara, California 93106 (United States); Wong, Man Hoi; Mishra, Umesh K. [Electrical and Computer Engineering Department, University of California, Santa Barbara, California 93106 (United States)

    2012-12-24T23:59:59.000Z

    Al{sub x}Ga{sub 1-x}N/GaN (x = 0.06, 0.12, 0.24) and AlGaN/AlN/GaN heterostructures were grown on 6 H-SiC, GaN-on-sapphire, and free-standing GaN, resulting in heterostructures with threading dislocation densities of {approx}2 Multiplication-Sign 10{sup 10}, {approx}5 Multiplication-Sign 10{sup 8}, and {approx}5 Multiplication-Sign 10{sup 7} cm{sup -2}, respectively. All growths were performed under Ga-rich conditions by plasma-assisted molecular beam epitaxy. Dominant scattering mechanisms with variations in threading dislocation density and sheet concentration were indicated through temperature-dependent Hall measurements. The inclusion of an AlN interlayer was also considered. Dislocation scattering contributed to reduced mobility in these heterostructures, especially when sheet concentration was low or when an AlN interlayer was present.

  1. Type-Ia supernova rates to redshift 2.4 from clash: The cluster lensing and supernova survey with Hubble

    SciTech Connect (OSTI)

    Graur, O.; Rodney, S. A.; Riess, A. G.; Medezinski, E. [Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD 21218 (United States); Maoz, D. [School of Physics and Astronomy, Tel-Aviv University, Tel-Aviv 69978 (Israel); Jha, S. W.; Holoien, T. W.-S.; McCully, C.; Patel, B. [Department of Physics and Astronomy, Rutgers, The State University of New Jersey, Piscataway, NJ 08854 (United States); Postman, M.; Dahlen, T.; Strolger, L.-G.; Coe, D.; Bradley, L.; Koekemoer, A. [Space Telescope Science Institute, Baltimore, MD 21218 (United States); Bentez, N.; Molino, A. [Instituto de Astrofsica de Andaluca (CSIC), E-18080 Granada (Spain); Jouvel, S. [Institut de Ciencies de l'Espai, (IEEC-CSIC), E-08193 Bellaterra (Barcelona) (Spain); Nonino, M.; Balestra, I., E-mail: orgraur@jhu.edu [INAF-Osservatorio Astronomico di Trieste, I-34143 Trieste (Italy); and others

    2014-03-01T23:59:59.000Z

    We present the supernova (SN) sample and Type-Ia SN (SN Ia) rates from the Cluster Lensing And Supernova survey with Hubble (CLASH). Using the Advanced Camera for Surveys and the Wide Field Camera 3 on the Hubble Space Telescope (HST), we have imaged 25 galaxy-cluster fields and parallel fields of non-cluster galaxies. We report a sample of 27 SNe discovered in the parallel fields. Of these SNe, ?13 are classified as SN Ia candidates, including four SN Ia candidates at redshifts z > 1.2. We measure volumetric SN Ia rates to redshift 1.8 and add the first upper limit on the SN Ia rate in the range 1.8 < z < 2.4. The results are consistent with the rates measured by the HST/GOODS and Subaru Deep Field SN surveys. We model these results together with previous measurements at z < 1 from the literature. The best-fitting SN Ia delay-time distribution (DTD; the distribution of times that elapse between a short burst of star formation and subsequent SN Ia explosions) is a power law with an index of ?1.00{sub ?0.06(0.10)}{sup +0.06(0.09)} (statistical){sub ?0.08}{sup +0.12} (systematic), where the statistical uncertainty is a result of the 68% and 95% (in parentheses) statistical uncertainties reported for the various SN Ia rates (from this work and from the literature), and the systematic uncertainty reflects the range of possible cosmic star-formation histories. We also test DTD models produced by an assortment of published binary population synthesis (BPS) simulations. The shapes of all BPS double-degenerate DTDs are consistent with the volumetric SN Ia measurements, when the DTD models are scaled up by factors of 3-9. In contrast, all BPS single-degenerate DTDs are ruled out by the measurements at >99% significance level.

  2. High efficiency InGaP solar cells for InGaP/GaAs tandem cell application

    SciTech Connect (OSTI)

    Takamoto, T.; Ikeda, E.; Kurita, H.; Ohmori, M. [Japan Energy Corp., Toda, Saitama (Japan). Central Research Lab.

    1994-12-31T23:59:59.000Z

    In this paper, high conversion efficiency single junction InGaP solar cells with n-p-p{sup +} structure are presented and their application to InGaP/GaAs monolithic tandem cells is discussed. In the InGaP cells, a best conversion efficiency of 18.48% was achieved by introducing the p{sup +} peak back surface field (BSF) layer with a high carrier concentration of 2 {times} 10{sup 18} cm{sup {minus}3}, which improved both short circuit current (Isc) and open circuit voltage (Voc). However, in the case of InGaP/GaAs tandem cells, a decrease in carrier concentration of the InGaP BSF layer, which was caused by the diffusion of Zn, was found to reduce the Isc and Voc of the tandem cell. The reduction in the carrier concentration was suppressed by using a thicker BSF layer of 0.5 {micro}m, which reduced the current density in the GaAs bottom cell. An InGaP/GaAs tandem cell with 27.3% efficiency and a high Voc of 2.418 V was obtained.

  3. Relaxed, high-quality InP on GaAs by using InGaAs and InGaP graded buffers to avoid phase separation

    E-Print Network [OSTI]

    Relaxed, high-quality InP on GaAs by using InGaAs and InGaP graded buffers to avoid phaseAs was 70% of that on bulk InP at both temperatures. To achieve this, graded buffers in the InGaAs, InGaP

  4. AlGaN/GaN HEMTs grown by Molecular Beam Epitaxy on sapphire, Sic, and HVPE GaN templates

    E-Print Network [OSTI]

    Manfra, Michael J.

    PS-4 AlGaN/GaN HEMTs grown by Molecular Beam Epitaxy on sapphire, Sic, and HVPE GaN templates Nils ABSTRACT Molecular Beam Epitaxy of GaN and related alloys is becoming a rival to the more established, and HVPE SI-GaN templates on sapphire. While sapphire and SI-Sic are established substrates for the growth

  5. ZrO2 gate dielectrics produced by ultraviolet ozone oxidation for GaN and AlGaN/GaN transistors

    E-Print Network [OSTI]

    2006-01-01T23:59:59.000Z

    MOSCAP process ?ow: n-GaN substrate; Ohmic metallization andtion for a AlGaN/ GaN HEMT on a substrate which has a poorsapphire substrate, a well-passivated AlGaN/ GaN HEMT grown

  6. Green light emission by InGaN/GaN multiple-quantum-well microdisks

    SciTech Connect (OSTI)

    Hsu, Yu-Chi; Lo, Ikai, E-mail: ikailo@mail.phys.nsysu.edu.tw; Shih, Cheng-Hung; Pang, Wen-Yuan; Hu, Chia-Hsuan; Wang, Ying-Chieh; Tsai, Cheng-Da; Chou, Mitch M. C. [Department of Physics, Department of Materials and Optoelectronic Science, Center for Nanoscience and Nanotechnology, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan (China)] [Department of Physics, Department of Materials and Optoelectronic Science, Center for Nanoscience and Nanotechnology, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan (China); Hsu, Gary Z. L. [United Crystal Corporation, No. 243-3, Wenshan 36061, Miaoli, Taiwan (China)] [United Crystal Corporation, No. 243-3, Wenshan 36061, Miaoli, Taiwan (China)

    2014-03-10T23:59:59.000Z

    The high-quality In{sub x}Ga{sub 1?x}N/GaN multiple quantum wells were grown on GaN microdisks with ?-LiAlO{sub 2} substrate by using low-temperature two-step technique of plasma-assisted molecular beam epitaxy. We demonstrated that the hexagonal GaN microdisk can be used as a strain-free substrate to grow the advanced In{sub x}Ga{sub 1?x}N/GaN quantum wells for the optoelectronic applications. We showed that the green light of 566-nm wavelength (2.192?eV) emitted from the In{sub x}Ga{sub 1?x}N/GaN quantum wells was tremendously enhanced in an order of amplitude higher than the UV light of 367-nm wavelength (3.383?eV) from GaN.

  7. InGaAsN/GaAs heterojunction for multi-junction solar cells

    DOE Patents [OSTI]

    Kurtz, Steven R. (Albuquerque, NM); Allerman, Andrew A. (Albuquerque, NM); Klem, John F. (Albuquerque, NM); Jones, Eric D. (Edgewood, NM)

    2001-01-01T23:59:59.000Z

    An InGaAsN/GaAs semiconductor p-n heterojunction is disclosed for use in forming a 0.95-1.2 eV bandgap photodetector with application for use in high-efficiency multi-junction solar cells. The InGaAsN/GaAs p-n heterojunction is formed by epitaxially growing on a gallium arsenide (GaAs) or germanium (Ge) substrate an n-type indium gallium arsenide nitride (InGaAsN) layer having a semiconductor alloy composition In.sub.x Ga.sub.1-x As.sub.1-y N.sub.y with 0GaAs layer, with the InGaAsN and GaAs layers being lattice-matched to the substrate. The InGaAsN/GaAs p-n heterojunction can be epitaxially grown by either molecular beam epitaxy (MBE) or metalorganic chemical vapor deposition (MOCVD). The InGaAsN/GaAs p-n heterojunction provides a high open-circuit voltage of up to 0.62 volts and an internal quantum efficiency of >70%.

  8. BIBLIOGRAPHY Abramowitz, M. and Stegun, I.A., Handbook of Mathematical Functions, 10th ed,

    E-Print Network [OSTI]

    California at Santa Cruz, University of

    352 BIBLIOGRAPHY · Abramowitz, M. and Stegun, I.A., Handbook of Mathematical Functions, 10th ed, New York:Dover, 1972. · Akivis, M.A., Goldberg, V.V., An Introduction to Linear Algebra and Tensors. · Goodbody, A.M., Cartesian Tensors, Chichester, England:Ellis Horwood Ltd, 1982. · Hay, G.E., Vector

  9. BIBLIOGRAPHY . Abramowitz, M. and Stegun, I.A., Handbook of Mathematical Functions, 10th ed,

    E-Print Network [OSTI]

    California at Santa Cruz, University of

    352 BIBLIOGRAPHY . Abramowitz, M. and Stegun, I.A., Handbook of Mathematical Functions, 10th ed, New York:Dover, 1972. . Akivis, M.A., Goldberg, V.V., An Introduction to Linear Algebra and Tensors, A.M., Cartesian Tensors, Chichester, England:Ellis Horwood Ltd, 1982. . Hay, G.E., Vector and Tensor

  10. AN EXPLORATORY STUDY OF THE EXPOSURE DRAFT OF IAS 19 DUE

    E-Print Network [OSTI]

    Boyer, Edmond

    a strategic issue for both private and public entities. In response to the ED published in April 2010 of three questions, asked respondents to approve a common discount rate to be applied to both the defined be of interest to the accounting profession and the public at large. Key words: IAS 19, Due process, net interest

  11. IAS 3353 001 Modern Brazil Instructor: Dr. Erika Robb-Larkins

    E-Print Network [OSTI]

    Oklahoma, University of

    IAS 3353 001 Modern Brazil Instructor: Dr. Erika Robb-Larkins MW 3:00-4:15 p.m. Hester Hall, room an anthropological perspective. Beginning with a broad overview of Brazil's colonial history and emergence the course with an appreciation of the complexities of Brazil today.... and with a desire to hop on the next

  12. X-ray amplification from a Raman Free Electron Laser I.A. Andriyash,

    E-Print Network [OSTI]

    Paris-Sud XI, Universit de

    X-ray amplification from a Raman Free Electron Laser I.A. Andriyash, E. d'Humi`eres, V 5107, F33400 Talence, France We demonstrate that a mm-scale free electron laser can operate in the X and health applications. Large scale X-ray free electron laser (XFEL) projects have been launched, and start

  13. Especialista Universitario Java Enterprise 2010-2011 Depto. Ciencia de la Computacin e IA

    E-Print Network [OSTI]

    Escolano, Francisco

    Especialista Universitario Java Enterprise 2010-2011 Depto. Ciencia de la Computacin e IA Sesin 1: Introduccin a JMS #12;Servicios de Mensajes con JMS 2010-2011 Depto. Ciencia de la Computacin Una Aplicacin JMS PTP Pub/Sub #12;Servicios de Mensajes con JMS 2010-2011 Depto. Ciencia de la

  14. Tycho Brahe's 1572 supernova as a standard type Ia explosion revealed from its light echo spectrum

    E-Print Network [OSTI]

    Krause, Oliver; Usuda, Tomonori; Hattori, Takashi; Goto, Miwa; Birkmann, Stephan; Nomoto, Ken'ichi

    2008-01-01T23:59:59.000Z

    Type Ia supernovae (SNe Ia) are thermonuclear explosions of white dwarf stars in close binary systems. They play an important role as cosmological distance indicators and have led to the discovery of the accelerated expansion of the Universe. Among the most important unsolved questions are how the explosion actually proceeds and whether accretion occurs from a companion or via the merging of two white dwarfs. Tycho Brahe's supernova of 1572 (SN 1572) is thought to be one of the best candidates for a SN Ia in the Milky Way. The proximity of the SN 1572 remnant has allowed detailed studies, such as the possible identification of the binary companion, and provides a unique opportunity to test theories of the explosion mechanism and the nature of the progenitor. The determination of the yet unknown exact spectroscopic type of SN 1572 is crucial to relate these results to the diverse population of SNe Ia. Here we report an optical spectrum of Tycho Brahe's supernova near maximum brightness, obtained from a scatter...

  15. On the thermonuclear runaway in Type Ia supernovae: How to run away

    E-Print Network [OSTI]

    P. Hflich; J. Stein

    2002-01-01T23:59:59.000Z

    Type Ia Supernovae are thought to be thermonuclear explosions of massive white dwarfs (WD). We present the first study of multi-dimensional effects during the final hours prior to the thermonuclear runaway which leads to the explosion. The calculations utilize an implicit, 2-D hydrodynamical code

  16. Turbulent Oxygen Flames in Type Ia Supernovae A. J. Aspden1

    E-Print Network [OSTI]

    Turbulent Oxygen Flames in Type Ia Supernovae A. J. Aspden1 , J. B. Bell1 , and S. E. Woosley2 oxygen flames. The two aims of the paper are to examine the response of the inductive oxygen flame to intense levels of turbulence, and to explore the possibility of transition to detonation in the oxygen

  17. Revealing progenitors of type Ia supernovae from their light curves and spectra

    E-Print Network [OSTI]

    Kutsuna, Masamichi

    2015-01-01T23:59:59.000Z

    In the single degenerate (SD) scenario of type Ia supernovae (SNe Ia), the collision of the ejecta with its companion results in stripping hydrogen rich matter from the companion star. This hydrogen rich matter might leave its trace in the light curves and/or spectra. In this paper, we perform radiation hydrodynamical simulations of this collision for three binary systems. As a result, we find that the emission from the shock-heated region is not as strong as in the previous study. This weak emission, however, may be a result of our underestimate of the coupling between the gas and radiation in the shock interaction. Therefore, though our results suggest that the observed early light curves of SNe Ia can not rule out binary systems with a short separation as the progenitor system, more elaborate numerical studies will be needed to reach a fair conclusion. Alternatively, our results indicate that the feature observed in the early phase of a recent type Ia SN 2014J might result from interaction of the ejecta wi...

  18. METALLICITY DIFFERENCES IN TYPE Ia SUPERNOVA PROGENITORS INFERRED FROM ULTRAVIOLET SPECTRA

    SciTech Connect (OSTI)

    Foley, Ryan J.; Kirshner, Robert P. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

    2013-05-20T23:59:59.000Z

    Two ''twin'' Type Ia supernovae (SNe Ia), SNe 2011by and 2011fe, have extremely similar optical light-curve shapes, colors, and spectra, yet have different ultraviolet (UV) continua as measured in Hubble Space Telescope spectra and measurably different peak luminosities. We attribute the difference in the UV continua to significantly different progenitor metallicities. This is the first robust detection of different metallicities for SN Ia progenitors. Theoretical reasoning suggests that differences in metallicity also lead to differences in luminosity. SNe Ia with higher progenitor metallicities have lower {sup 56}Ni yields and lower luminosities for the same light-curve shape. SNe 2011by and 2011fe have different peak luminosities ({Delta}M{sub V} Almost-Equal-To 0.6 mag), which correspond to different {sup 56}Ni yields: M{sub 11fe}({sup 56}Ni) / M{sub 11by}({sup 56}Ni) = 1.7{sup +0.7}{sub -0.5}. From theoretical models that account for different neutron-to-proton ratios in progenitors, the differences in {sup 56}Ni yields for SNe 2011by and 2011fe imply that their progenitor stars were above and below solar metallicity, respectively. Although we can distinguish progenitor metallicities in a qualitative way from UV data, the quantitative interpretation in terms of abundances is limited by the present state of theoretical models.

  19. ON THE LIRA LAW AND THE NATURE OF EXTINCTION TOWARD TYPE Ia SUPERNOVAE

    SciTech Connect (OSTI)

    Foerster, Francisco; Gonzalez-Gaitan, Santiago [Departamento de Astronomia, Universidad de Chile, Casilla 36-D, Santiago (Chile); Folatelli, Gaston [Kavli Institute for the Physics and Mathematics of the Universe, Todai Institutes for Advanced Study (TODIAS), University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8583 (Japan); Morrell, Nidia [Las Campanas Observatory, Carnegie Observatories, Casilla 601, La Serena (Chile)

    2013-07-20T23:59:59.000Z

    We have studied the relation between the color evolution of Type Ia supernovae (SNe Ia) from maximum light to the Lira law regime and the presence of narrow absorption features. Based on a nearby sample of 89 SNe Ia, we have found that the rate of change of B - V colors at late phases (between 35 and 80 days after maximum) varies significantly among different SNe Ia. At maximum light, faster Lira law B - V decliners have significantly higher equivalent widths of blended Na I D1 and D2 narrow absorption lines, redder colors, and lower R{sub V} reddening laws. We do not find faster Lira law B - V decliners to have a strong preference for younger galaxy environments, where higher interstellar material (ISM) column densities would be expected. We interpret these results as evidence for the presence of circumstellar material. The differences in colors and reddening laws found at maximum light are also present 55 days afterward, but unlike the colors at maximum they show a significant variation among different host galaxy morphological types. This suggests that the effect of ISM on the colors is more apparent at late times. Finally, we discuss how the transversal expansion of the ejecta in an inhomogeneous ISM could mimic some of these findings.

  20. High-Velocity Features of Calcium and Silicon in the Spectra of Type Ia Supernovae

    E-Print Network [OSTI]

    Silverman, Jeffrey M; Marion, G H; Wheeler, J Craig; Barna, Barnabas; Szalai, Tamas; Mulligan, Brian; Filippenko, Alexei V

    2015-01-01T23:59:59.000Z

    "High-velocity features" (HVFs) are spectral features in Type Ia supernovae (SNe Ia) that have minima indicating significantly higher (by greater than about 6000 km/s) velocities than typical "photospheric-velocity features" (PVFs). The PVFs are absorption features with minima indicating typical photospheric (i.e., bulk ejecta) velocities (usually ~9000-15,000 km/s near B-band maximum brightness). In this work we undertake the most in-depth study of HVFs ever performed. The dataset used herein consists of 445 low-resolution optical and near-infrared (NIR) spectra (at epochs up to 5 d past maximum brightness) of 210 low-redshift SNe Ia that follow the "Phillips relation." A series of Gaussian functions is fit to the data in order to characterise possible HVFs of Ca II H&K, Si II {\\lambda}6355, and the Ca II NIR triplet. The temporal evolution of the velocities and strengths of the PVFs and HVFs of these three spectral features is investigated, as are possible correlations with other SN Ia observables. We f...

  1. California ISO Glossary CAL I F O R N IA I S O

    E-Print Network [OSTI]

    California ISO Glossary CAL I F O R N IA I S O A watt is a measure of electricity. If you have 10 under less pressure for delivery through the straws. The ISO's job is to make sure that in the high; the ISO refers to utilities like PG&E as "load-serving entities" because that's what they do, they serve

  2. InGaP/GaAs and InGaAs mechanically-stacked triple-junction solar cells

    SciTech Connect (OSTI)

    Takamoto, T.; Ikeda, E.; Agui, T. [Japan Energy Corp., Toda, Saitama (Japan)] [and others

    1997-12-31T23:59:59.000Z

    Triple-junction cells with AM1.5 efficiencies of over 33% have been demonstrated. A planar type InGaP/GaAs monolithic dual-junction cell was fabricated on a semi-insulating FaAs substrate, which has high infra-red transparency. Then a dual-junction cell, with efficiency of 27--28%, was mechanically stacked on an InGaAs cell fabricated on an InP substrate. The bottom InGaAs cell showed an efficiency of 6.2% under the InGaP/GaAs cell, and a total efficiency of 33--34% was achieved for the four-terminal triple-junction cell.

  3. Graphene induced remote surface scattering in graphene/AlGaN/GaN heterostructures

    SciTech Connect (OSTI)

    Liu, Xiwen; Li, Dan; Wang, Bobo; Liu, Bin; Chen, Famin; Jin, Guangri; Lu, Yanwu, E-mail: ywlu@bjtu.edu.cn [Department of Physics, Beijing Jiaotong University, Beijing 100044 (China)

    2014-10-20T23:59:59.000Z

    The mobilities of single-layer graphene combined with AlGaN/GaN heterostructures on two-dimensional electron gases in graphene/AlGaN/GaN double heterojunction are calculated. The impact of electron density in single-layer graphene is also studied. Remote surface roughness (RSR) and remote interfacial charge (RIC) scatterings are introduced into this heterostructure. The mobilities limited by RSR and RIC are an order of magnitude higher than that of interface roughness and misfit dislocation. This study contributes to designing structures for generation of higher electron mobility in graphene/AlGaN/GaN double heterojunction.

  4. Experimental evidence of Ga-vacancy induced room temperature ferromagnetic behavior in GaN films

    SciTech Connect (OSTI)

    Roul, Basanta; Kumar, Mahesh [Materials Research Centre, Indian Institute of Science, Bangalore 560012 (India); Central Research Laboratory, Bharat Electronics, Bangalore 560013 (India); Rajpalke, Mohana K.; Bhat, Thirumaleshwara N.; Krupanidhi, S. B. [Materials Research Centre, Indian Institute of Science, Bangalore 560012 (India); Kalghatgi, A. T. [Central Research Laboratory, Bharat Electronics, Bangalore 560013 (India); Kumar, Nitesh; Sundaresan, A. [Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur P. O., Bangalore 560064 (India)

    2011-10-17T23:59:59.000Z

    We have grown Ga deficient GaN epitaxial films on (0001) sapphire substrate by plasma-assisted molecular beam epitaxy and report the experimental evidence of room temperature ferromagnetic behavior. The observed yellow emission peak in room temperature photoluminescence spectra and the peak positioning at 300 cm{sup -1} in Raman spectra confirms the existence of Ga vacancies. The x-ray photoelectron spectroscopic measurements further confirmed the formation of Ga vacancies; since the N/Ga is found to be >1. The ferromagnetism is believed to originate from the polarization of the unpaired 2p electrons of N surrounding the Ga vacancy.

  5. A Test for the Nature of the Type Ia Supernova Explosion Mechanism

    E-Print Network [OSTI]

    Philip A. Pinto; Ronald G. Eastman; Tamara Rogers

    2000-08-21T23:59:59.000Z

    Currently popular models for Type Ia supernovae (SNe Ia) fall into two general classes. The first comprises explosions of nearly pure carbon/oxygen (C/O) white dwarfs at the Chandrasekhar limit which ignite near their centers. The second consists of lower-mass C/O cores which are ignited by the detonation of an accreted surface helium layer. Explosions of the latter type produce copious Fe, Co and Ni K-alpha emission from 56Ni and 56Co decay in the detonated surface layers, emission which is much weaker from Chandrasekhar-mass models. The presence of this emission provides a simple and unambiguous discriminant between these two models for SNe Ia. Both mechanisms may produce 0.1-0.6 solar masses of 56Ni, making them bright gamma-ray line emitters. The time to maximum brightness of 56Ni decay lines is distinctly shorter in the sub-Chandrasekhar mass class of model (approximately 15 days) than in the Chandrasekhar mass model (approximately 30 days), making gamma-ray line evolution another direct test of the explosion mechanism. It should just be possible to detect K-shell emission from a sub-Chandrasekhar explosion from SNe Ia as far away as the Virgo cluster with the XMM Observatory. A 1 to 2 square meter X-ray telescope such as the proposed Con-X Observatory could observe K-alpha emission from sub-Chandrasekhar mass SNe Ia in the Virgo cluster, providing not just a detection, but high-accuracy flux and kinematic information.

  6. HIGH-VELOCITY LINE FORMING REGIONS IN THE TYPE Ia SUPERNOVA 2009ig

    SciTech Connect (OSTI)

    Marion, G. H.; Foley, Ryan J.; Challis, Peter; Kirshner, Robert P. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Vinko, Jozsef; Wheeler, J. Craig; Silverman, Jeffrey M. [University of Texas at Austin, 1 University Station C1400, Austin, TX 78712-0259 (United States); Hsiao, Eric Y. [Carnegie Observatories, Las Campanas Observatory, Colina El Pino, Casilla 601 (Chile); Brown, Peter J. [George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Department of Physics and Astronomy, Texas A and M University, 4242 AMU, College Station, TX 77843 (United States); Filippenko, Alexei V. [Department of Astronomy, University of California, Berkeley, CA 94720-3411 (United States); Garnavich, Peter [Department of Physics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States); Landsman, Wayne B. [Adnet Systems, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Parrent, Jerod T. [Las Cumbres Observatory Global Telescope Network, Goleta, CA 93117 (United States); Pritchard, Tyler A.; Roming, Peter W. A. [Department of Astronomy and Astrophysics, Penn State University, 525 Davey Lab, University Park, PA 16802 (United States); Wang, Xiaofeng, E-mail: gmarion@cfa.harvard.edu [Physics Department and Tsinghua Center for Astrophysics (THCA), Tsinghua University, Beijing 1,00084 (China)

    2013-11-01T23:59:59.000Z

    We report measurements and analysis of high-velocity (HVF) (>20,000 km s{sup 1}) and photospheric absorption features in a series of spectra of the Type Ia supernova (SN) 2009ig obtained between 14 days and +13 days with respect to the time of maximum B-band luminosity (B-max). We identify lines of Si II, Si III, S II, Ca II, and Fe II that produce both HVF and photospheric-velocity (PVF) absorption features. SN 2009ig is unusual for the large number of lines with detectable HVF in the spectra, but the light-curve parameters correspond to a slightly overluminous but unexceptional SN Ia (M{sub B} = 19.46 mag and ?m{sub 15}(B) = 0.90 mag). Similarly, the Si II ?6355 velocity at the time of B-max is greater than 'normal' for an SN Ia, but it is not extreme (v{sub Si} = 13,400 km s{sup 1}). The 14 days and 13 days spectra clearly resolve HVF from Si II ?6355 as separate absorptions from a detached line forming region. At these very early phases, detached HVF are prevalent in all lines. From 12 days to 6 days, HVF and PVF are detected simultaneously, and the two line forming regions maintain a constant separation of about 8000 km s{sup 1}. After 6 days all absorption features are PVF. The observations of SN 2009ig provide a complete picture of the transition from HVF to PVF. Most SNe Ia show evidence for HVF from multiple lines in spectra obtained before 10 days, and we compare the spectra of SN 2009ig to observations of other SNe. We show that each of the unusual line profiles for Si II ?6355 found in early-time spectra of SNe Ia correlate to a specific phase in a common development sequence from HVF to PVF.

  7. Ultra-Thin, Triple-Bandgap GaInP/GaAs/GaInAs Monolithic Tandem Solar Cells

    SciTech Connect (OSTI)

    Wanlass, M. W.; Ahrenkiel, S. P.; Albin, D. S.; Carapella, J. J.; Duda, A.; Emery, K.; Geisz, J. F.; Jones, K.; Kurtz, S.; Moriarty, T.; Romero, M. J.

    2007-02-01T23:59:59.000Z

    The performance of state-of-the-art, series-connected, lattice-matched (LM), triple-junction (TJ), III-V tandem solar cells could be improved substantially (10-12%) by replacing the Ge bottom subcell with a subcell having a bandgap of {approx}1 eV. For the last several years, research has been conducted by a number of organizations to develop {approx}1-eV, LM GaInAsN to provide such a subcell, but, so far, the approach has proven unsuccessful. Thus, the need for a high-performance, monolithically integrable, 1-eV subcell for TJ tandems has remained. In this paper, we present a new TJ tandem cell design that addresses the above-mentioned problem. Our approach involves inverted epitaxial growth to allow the monolithic integration of a lattice-mismatched (LMM) {approx}1-eV GaInAs/GaInP double-heterostructure (DH) bottom subcell with LM GaAs (middle) and GaInP (top) upper subcells. A transparent GaInP compositionally graded layer facilitates the integration of the LM and LMM components. Handle-mounted, ultra-thin device fabrication is a natural consequence of the inverted-structure approach, which results in a number of advantages, including robustness, potential low cost, improved thermal management, incorporation of back-surface reflectors, and possible reclamation/reuse of the parent crystalline substrate for further cost reduction. Our initial work has concerned GaInP/GaAs/GaInAs tandem cells grown on GaAs substrates. In this case, the 1-eV GaInAs experiences 2.2% compressive LMM with respect to the substrate. Specially designed GaInP graded layers are used to produce 1-eV subcells with performance parameters nearly equaling those of LM devices with the same bandgap (e.g., LM, 1-eV GaInAsP grown on InP). Previously, we reported preliminary ultra-thin tandem devices (0.237 cm{sup 2}) with NREL-confirmed efficiencies of 31.3% (global spectrum, one sun) (1), 29.7% (AM0 spectrum, one sun) (2), and 37.9% (low-AOD direct spectrum, 10.1 suns) (3), all at 25 C. Here, we include recent results of testing similar devices under the concentrated AMO spectrum, and also present the first demonstration of a high-efficiency, ultra-thin GaInP/GaAs/GaInAs tandem cell processed on a flexible kapton handle.

  8. September 16-21, 2007 Las Vegas, Nevada Gate recess technology on AlGaN/GaN HFET with InGaN as etch-stop layer

    E-Print Network [OSTI]

    Pala, Nezih

    0 2 V(V) C(pF) Before etching (material) After etching (device) G AlGaN substrate i-GaN DS AlN AlGaN substrate AlN i-GaN AlGaN S G DAlGaNAlGaN InGaNInGaN Standard gate recess InGaN stop layer gate recess InGaNICNS 7 September 16-21, 2007 Las Vegas, Nevada Gate recess technology on AlGaN/GaN HFET with InGaN

  9. A Modular Building Controls Virtual Test Bed for the Integrations of Heterogeneous Systems

    E-Print Network [OSTI]

    Wetter, Michael

    2008-01-01T23:59:59.000Z

    Marija, Michael Wetter, and Jan Hensen. 2007. Comparison ofASHRAE, Atlanta, GA. Hensen, Jan L. M. 1999. A comparison

  10. Report

    E-Print Network [OSTI]

    2015-02-04T23:59:59.000Z

    Advanced Analytics Manager, UPS, 30328 Atlanta, GA, USA, foresomenteneikona@gmail.com. Tao Wu. Advanced Analytics Department, Dow Chemical, 48642...

  11. Rutile films grown by molecular beam epitaxy on GaN and AlGaN/GaN P. J. Hansen

    E-Print Network [OSTI]

    York, Robert A.

    Rutile films grown by molecular beam epitaxy on GaN and AlGaN/GaN P. J. Hansen Materials Department March 2005 Titanium dioxide TiO2, with the rutile structure was grown on 0001 oriented GaN and 0001 Al0.33Ga0.67N/GaN heterostructure field effect transistor HFET structures by molecular beam epitaxy. X

  12. Single-Wire Light-Emitting Diodes Based on GaN Wires Containing Both Polar and Nonpolar InGaN/GaN Quantum Wells

    E-Print Network [OSTI]

    Single-Wire Light-Emitting Diodes Based on GaN Wires Containing Both Polar and Nonpolar InGaN/GaN based on radial pin multi quantum well (QW) junctions have been realized from GaN wires grown by catalyst- free metal organic vapor phase epitaxy. The Inx Ga1x N/GaN undoped QW system is coated over both

  13. High density plasma damage in InGaP/GaAs as AlGaAs/GaAs high electron mobility transistors

    SciTech Connect (OSTI)

    Lee, J.W.; Pearton, S.J. [Univ. of Florida, Gainesville, FL (United States). Dept. of Materials Science and Engineering; Ren, F.; Kopf, R.F.; Kuo, J.M. [Bell Labs., Murray Hill, NJ (United States). Lucent Technologies; Shul, R.J. [Sandia National Labs., Albuquerque, NM (United States); Constantine, C.; Johnson, D. [Plasma-Therm Inc., St. Petersburg, FL (United States)

    1998-11-01T23:59:59.000Z

    The introduction of plasma damage in InGaP/GaAs and AlGaAs/GaAs high electron mobility transistors (HEMTs) has been investigated using both inductively coupled plasma and electron cyclotron resonance Ar discharges. The saturated drain-source current is found to be decreased through introduction of compensating deep levels into the InGaP or AlGaAs donor layer. The degradation of device performance is a strong function of ion energy and ion flux, and an advantage of both high density plasma tools is that ion energy can be reduced by increasing the plasma density. Increasing process pressure and source power, and decreasing radio-frequency chuck power produce the lowest amounts of plasma damage in HEMTs.

  14. Type Ia supernova rate measurements to redshift 2.5 from CANDELS: Searching for prompt explosions in the early universe

    SciTech Connect (OSTI)

    Rodney, Steven A.; Riess, Adam G.; Graur, Or; Jones, David O. [Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD 21218 (United States); Strolger, Louis-Gregory; Dahlen, Tomas; Casertano, Stefano; Ferguson, Henry C.; Koekemoer, Anton M. [Space Telescope Science Institute, Baltimore, MD 21218 (United States); Dickinson, Mark E. [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Garnavich, Peter [Department of Physics, University of Notre Dame, Notre Dame, IN 46556 (United States); Hayden, Brian [E.O. Lawrence Berkeley National Lab, 1 Cyclotron Road, Berkeley, CA 94720 (United States); Jha, Saurabh W.; McCully, Curtis; Patel, Brandon [Department of Physics and Astronomy, Rutgers, The State University of New Jersey, Piscataway, NJ 08854 (United States); Kirshner, Robert P. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Mobasher, Bahram [Department of Physics and Astronomy, University of California, Riverside, CA 92521 (United States); Weiner, Benjamin J. [Department of Astronomy, University of Arizona, Tucson, AZ 85721 (United States); Cenko, S. Bradley [Astrophysics Science Division, NASA Goddard Space Flight Center, Mail Code 661, Greenbelt, MD 20771 (United States); Clubb, Kelsey I. [Department of Astronomy, University of California, Berkeley, CA 94720 (United States); and others

    2014-07-01T23:59:59.000Z

    The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) was a multi-cycle treasury program on the Hubble Space Telescope (HST) that surveyed a total area of ?0.25 deg{sup 2} with ?900 HST orbits spread across five fields over three years. Within these survey images we discovered 65 supernovae (SNe) of all types, out to z ? 2.5. We classify ?24 of these as Type Ia SNe (SNe Ia) based on host galaxy redshifts and SN photometry (supplemented by grism spectroscopy of six SNe). Here we present a measurement of the volumetric SN Ia rate as a function of redshift, reaching for the first time beyond z = 2 and putting new constraints on SN Ia progenitor models. Our highest redshift bin includes detections of SNe that exploded when the universe was only ?3 Gyr old and near the peak of the cosmic star formation history. This gives the CANDELS high redshift sample unique leverage for evaluating the fraction of SNe Ia that explode promptly after formation (<500 Myr). Combining the CANDELS rates with all available SN Ia rate measurements in the literature we find that this prompt SN Ia fraction is f{sub P} = 0.53{sub stat0.10}{sup 0.09}{sub sys0.26}{sup 0.10}, consistent with a delay time distribution that follows a simple t {sup 1} power law for all times t > 40 Myr. However, mild tension is apparent between ground-based low-z surveys and space-based high-z surveys. In both CANDELS and the sister HST program CLASH (Cluster Lensing And Supernova Survey with Hubble), we find a low rate of SNe Ia at z > 1. This could be a hint that prompt progenitors are in fact relatively rare, accounting for only 20% of all SN Ia explosionsthough further analysis and larger samples will be needed to examine that suggestion.

  15. Comparison of compressive and tensile relaxed composition-graded GaAsP and ,,Al...InGaP substrates

    E-Print Network [OSTI]

    Comparison of compressive and tensile relaxed composition-graded GaAsP and ,,Al...InGaP substrates, around 104 cm-2 . The structures, grown on GaP or GaAs, consist of graded In-fraction InGaP and AlInGaP. High surface roughness and branch defects in Al InGaP lead to the lowest quality virtual substrates we

  16. Carrier Dynamics in InGaN/GaN SQW Structure Probed by the Transient Grating Method

    E-Print Network [OSTI]

    Okamoto, Koichi

    Carrier Dynamics in InGaN/GaN SQW Structure Probed by the Transient Grating Method; 78.55.Cr; 78.67.De; S7.14 Carrier dynamics in GaN and InGaN/GaN SQW structures were observed by using inhomogeneity of In composition. Recently, InGaN/GaN-based light emitting diodes (LEDs) have been commercialized

  17. N-Face GaN/AlGaN HEMTs Fabricated Through Layer Transfer Technology

    E-Print Network [OSTI]

    Chung, Jinwook

    We present a new method to fabricate N-face GaN/AlGaN high electron mobility transistors (HEMTs). These devices are extremely promising for ultrahigh frequency applications where low contact resistances and excellent carrier ...

  18. Development and Industrialization of InGaN/GaN LEDs on Patterned...

    Office of Energy Efficiency and Renewable Energy (EERE) Indexed Site

    of InGaNGaN LEDs on Patterned Sapphire Substrates for Low Cost Emitter Architecture Development and Industrialization of InGaNGaN LEDs on Patterned Sapphire...

  19. Breakdown mechanism in AlGaN/GaN HEMTs on Si substrate

    E-Print Network [OSTI]

    Lu, Bin

    AlGaN/GaN high electron mobility transistors (HEMTs) grown on Si substrates have attracted a great interest for power electronics applications. Despite the low cost of the Si substrate, the breakdown voltage (V[subscript ...

  20. Sweetspot: Near-infrared observations of 13 type Ia supernovae from a new NOAO survey probing the nearby smooth Hubble flow

    SciTech Connect (OSTI)

    Weyant, Anja; Wood-Vasey, W. Michael [Pittsburgh Particle physics, Astrophysics, and Cosmology Center (PITT PACC), Physics and Astronomy Department, University of Pittsburgh, Pittsburgh, PA 15260 (United States); Allen, Lori; Joyce, Richard; Matheson, Thomas [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Garnavich, Peter M. [Department of Physics, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States); Jha, Saurabh W., E-mail: anw19@pitt.edu [Department of Physics and Astronomy, Rutgers, the State University of New Jersey, 136 Frelinghuysen Road, Piscataway, NJ 08854 (United States)

    2014-04-01T23:59:59.000Z

    We present 13 Type Ia supernovae (SNe Ia) observed in the rest-frame near-infrared (NIR) from 0.02 < z < 0.09 with the WIYN High-resolution Infrared Camera on the WIYN 3.5 m telescope. With only one to three points per light curve and a prior on the time of maximum from the spectrum used to type the object, we measure an H-band dispersion of spectroscopically normal SNe Ia of 0.164 mag. These observations continue to demonstrate the improved standard brightness of SNe Ia in an H band, even with limited data. Our sample includes two SNe Ia at z ? 0.09, which represent the most distant rest-frame NIR H-band observations published to date. This modest sample of 13 NIR SNe Ia represent the pilot sample for {sup S}weetSpot{sup }a 3 yr NOAO Survey program that will observe 144 SNe Ia in the smooth Hubble flow. By the end of the survey we will have measured the relative distance to a redshift of z ? 0.05%-1%. Nearby Type Ia supernova (SN Ia) observations such as these will test the standard nature of SNe Ia in the rest-frame NIR, allow insight into the nature of dust, and provide a critical anchor for future cosmological SN Ia surveys at higher redshift.

  1. Strain-balanced InGaN/GaN multiple quantum wells

    SciTech Connect (OSTI)

    Van Den Broeck, D. M.; Hosalli, A. M.; Bedair, S. M. [Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, North Carolina 27695 (United States); Bharrat, D.; El-Masry, N. A. [Department of Material Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695 (United States)

    2014-07-21T23:59:59.000Z

    InGaN/GaN multiple quantum well (MQW) structures suffer from a high amount of compressive strain in the InGaN wells and the accompanied piezoelectric field resulting in both a blue shift in emission and a reduction of emission intensity. We report the growth of In{sub x}Ga{sub 1?x}N/GaN strain-balanced multiple quantum wells (SBMQWs) grown on thick In{sub y}Ga{sub 1?y}N templates for x?>?y by metal organic chemical vapor deposition. SBMQWs consist of alternating layers of In{sub x}Ga{sub 1?x}N wells and GaN barriers under compressive and tensile stress, respectively, which have been lattice matched to a thick In{sub y}Ga{sub 1?y}N template. Growth of the In{sub y}Ga{sub 1?y}N template is also detailed in order to achieve thick, relaxed In{sub y}Ga{sub 1?y}N grown on GaN without the presence of V-grooves. When compared to conventional In{sub x}Ga{sub 1?x}N/GaN MQWs grown on GaN, the SBMQW structures exhibit longer wavelength emission and higher emission intensity for the same InN mole fraction due to a reduction in the well strain and piezoelectric field. By matching the average lattice constant of the MQW active region to the lattice constant of the In{sub y}Ga{sub 1?y}N template, essentially an infinite number of periods can be grown using the SBMQW growth method without relaxation-related effects. SBMQWs can be utilized to achieve longer wavelength emission in light emitting diodes without the use of excess indium and can be advantageous in addressing the green gap..

  2. High current gain InGaN=GaN HBTs with C operating temperature

    E-Print Network [OSTI]

    Asbeck, Peter M.

    with an $20 nm low-temperature (Tg 550 C) GaN buffer layer on a (0001) sapphire substrate. The layer 1018 cm3 Buffer GaN 2.5 mm Substrate Sapphire HBT device processing began by depositing a 100 nmHigh current gain InGaN=GaN HBTs with 300 C operating temperature D.M. Keogh, P.M. Asbeck, T. Chung

  3. COSMOLOGY WITH PHOTOMETRICALLY CLASSIFIED TYPE Ia SUPERNOVAE FROM THE SDSS-II SUPERNOVA SURVEY

    SciTech Connect (OSTI)

    Campbell, Heather; D'Andrea, Chris B; Nichol, Robert C.; Smith, Mathew; Lampeitl, Hubert [Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth, PO1 3FX (United Kingdom)] [Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth, PO1 3FX (United Kingdom); Sako, Masao [Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia, PA 19104 (United States)] [Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia, PA 19104 (United States); Olmstead, Matthew D.; Brown, Peter; Dawson, Kyle S. [Department of Physics and Astronomy, University of Utah, 115 South 1400 East 201, Salt Lake City, UT 84112 (United States)] [Department of Physics and Astronomy, University of Utah, 115 South 1400 East 201, Salt Lake City, UT 84112 (United States); Bassett, Bruce [Mathematics Department, University of Cape Town, Rondebosch, Cape Town (South Africa)] [Mathematics Department, University of Cape Town, Rondebosch, Cape Town (South Africa); Biswas, Rahul; Kuhlmann, Steve [Argonne National Laboratory, 9700 South Cass Avenue, Lemont, IL 60439 (United States)] [Argonne National Laboratory, 9700 South Cass Avenue, Lemont, IL 60439 (United States); Cinabro, David [Department of Physics and Astronomy, Wayne State University, Detroit, MI 48126 (United States)] [Department of Physics and Astronomy, Wayne State University, Detroit, MI 48126 (United States); Dilday, Ben [Las Cumbres Observatory Global Telescope Network, 6740 Cortona Dr., Suite 102, Goleta, CA 93117 (United States)] [Las Cumbres Observatory Global Telescope Network, 6740 Cortona Dr., Suite 102, Goleta, CA 93117 (United States); Foley, Ryan J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)] [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Frieman, Joshua A. [Department of Astronomy and Astrophysics, The University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 (United States)] [Department of Astronomy and Astrophysics, The University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 (United States); Garnavich, Peter [Department of Physics, University of Notre Dame, Notre Dame, IN 46556 (United States)] [Department of Physics, University of Notre Dame, Notre Dame, IN 46556 (United States); Hlozek, Renee [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)] [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States); Jha, Saurabh W. [Department of Physics and Astronomy, Rutgers University, 136 Frelinghuysen Road, Piscataway, NJ 08854 (United States)] [Department of Physics and Astronomy, Rutgers University, 136 Frelinghuysen Road, Piscataway, NJ 08854 (United States); Kunz, Martin, E-mail: Heather.Campbell@port.ac.uk [African Institute for Mathematical Sciences, Muizenberg, 7945, Cape Town (South Africa)] [African Institute for Mathematical Sciences, Muizenberg, 7945, Cape Town (South Africa); and others

    2013-02-15T23:59:59.000Z

    We present the cosmological analysis of 752 photometrically classified Type Ia Supernovae (SNe Ia) obtained from the full Sloan Digital Sky Survey II (SDSS-II) Supernova (SN) Survey, supplemented with host-galaxy spectroscopy from the SDSS-III Baryon Oscillation Spectroscopic Survey. Our photometric-classification method is based on the SN classification technique of Sako et al., aided by host-galaxy redshifts (0.05 < z < 0.55). SuperNova ANAlysis simulations of our methodology estimate that we have an SN Ia classification efficiency of 70.8%, with only 3.9% contamination from core-collapse (non-Ia) SNe. We demonstrate that this level of contamination has no effect on our cosmological constraints. We quantify and correct for our selection effects (e.g., Malmquist bias) using simulations. When fitting to a flat {Lambda}CDM cosmological model, we find that our photometric sample alone gives {Omega} {sub m} = 0.24{sup +0.07} {sub -0.05} (statistical errors only). If we relax the constraint on flatness, then our sample provides competitive joint statistical constraints on {Omega} {sub m} and {Omega}{sub {Lambda}}, comparable to those derived from the spectroscopically confirmed Three-year Supernova Legacy Survey (SNLS3). Using only our data, the statistics-only result favors an accelerating universe at 99.96% confidence. Assuming a constant wCDM cosmological model, and combining with H {sub 0}, cosmic microwave background, and luminous red galaxy data, we obtain w = -0.96{sup +0.10} {sub -0.10}, {Omega} {sub m} = 0.29{sup +0.02} {sub -0.02}, and {Omega} {sub k} = 0.00{sup +0.03} {sub -0.02} (statistical errors only), which is competitive with similar spectroscopically confirmed SNe Ia analyses. Overall this comparison is reassuring, considering the lower redshift leverage of the SDSS-II SN sample (z < 0.55) and the lack of spectroscopic confirmation used herein. These results demonstrate the potential of photometrically classified SN Ia samples in improving cosmological constraints.

  4. Switchable piezoelectric transduction in AlGaN/GaN MEMS resonators

    E-Print Network [OSTI]

    Weinstein, Dana

    This work presents a new switching mechanism in piezoelectric transduction of AlGaN/GaN bulk acoustic resonators. A piezoelectric transducer is formed in the AlGaN, between a top Schottky electrode and a 2D electron gas ...

  5. Spontaneous emission in GaN/InGaN photonic crystal nanopillars

    E-Print Network [OSTI]

    Boyer, Edmond

    . Sigalas, "InGaN/GaN quantum-well heterostructure light-emitting diodes employing photonic crystal, "III-nitride blue and ultraviolet photonic crystal light emitting diodes," Appl. Phys. Lett. 84, 466, and H. Benisty, "Photonic-crystal GaN light-emitting diodes with tailored guided modes distribution

  6. GaInP/GaAs/GaInAs Monolithic Tandem Cells for High-Performance Solar Concentrators

    SciTech Connect (OSTI)

    Wanlass, M. W.; Ahrenkiel, S. P.; Albin, D. S.; Carapella, J. J.; Duda, A.; Emery, K.; Geisz, J. F.; Jones, K.; Kurtz, S.; Moriarty, T.; Romero, M. J.

    2005-08-01T23:59:59.000Z

    We present a new approach for ultra-high-performance tandem solar cells that involves inverted epitaxial growth and ultra-thin device processing. The additional degree of freedom afforded by the inverted design allows the monolithic integration of high-, and medium-bandgap, lattice-matched (LM) subcell materials with lower-bandgap, lattice-mismatched (LMM) materials in a tandem structure through the use of transparent compositionally graded layers. The current work concerns an inverted, series-connected, triple-bandgap, GaInP (LM, 1.87 eV)/GaAs (LM, 1.42 eV)/GaInAs (LMM, {approx}1 eV) device structure grown on a GaAs substrate. Ultra-thin tandem devices are fabricated by mounting the epiwafers to pre-metallized Si wafer handles and selectively removing the parent GaAs substrate. The resulting handle-mounted, ultra-thin tandem cells have a number of important advantages, including improved performance and potential reclamation/reuse of the parent substrate for epitaxial growth. Additionally, realistic performance modeling calculations suggest that terrestrial concentrator efficiencies in the range of 40-45% are possible with this new tandem cell approach. A laboratory-scale (0.24 cm2), prototype GaInP/GaAs/GaInAs tandem cell with a terrestrial concentrator efficiency of 37.9% at a low concentration ratio (10.1 suns) is described, which surpasses the previous world efficiency record of 37.3%.

  7. Fine structure of Fe-Co-Ga and Fe-Cr-Ga alloys with low Ga content

    SciTech Connect (OSTI)

    Kleinerman, Nadezhda M., E-mail: kleinerman@imp.uran.ru; Serikov, Vadim V., E-mail: kleinerman@imp.uran.ru; Vershinin, Aleksandr V., E-mail: kleinerman@imp.uran.ru; Mushnikov, Nikolai V., E-mail: kleinerman@imp.uran.ru; Stashkova, Liudmila A., E-mail: kleinerman@imp.uran.ru [Institute of Metal Physics UB RAS, S. Kovalevskaya str. 18, 620990 Ekaterinburg (Russian Federation)

    2014-10-27T23:59:59.000Z

    Investigation of Ga influence on the structure of Fe-Cr and Fe-Co alloys was performed with the use of {sup 57}Fe Mssbauer spectroscopy and X-ray diffraction methods. In the alloys of the Fe-Cr system, doping with Ga handicaps the decomposition of solid solutions, observed in the binary alloys, and increases its stability. In the alloys with Co, Ga also favors the uniformity of solid solutions. The analysis of Mssbauer experiments gives some grounds to conclude that if, owing to liquation, clusterization, or initial stages of phase separation, there exist regions enriched in iron, some amount of Ga atoms prefer to enter the nearest surroundings of iron atoms, thus forming binary Fe-Ga regions (or phases)

  8. TEM Characterization of InAs/GaAs Quantum Dots Capped by a GaSb/GaAs Layer

    SciTech Connect (OSTI)

    Beltran, AM [Universidad de Cadiz, Spain; Ben, Teresa [Universidad de Cadiz, Spain; Sanchez, AM [Universidad de Cadiz, Spain; Sales Lerida, David [ORNL; Chisholm, Matthew F [ORNL; Varela del Arco, Maria [ORNL; Pennycook, Stephen J [ORNL; Galindo, Pedro [Universidad de Cadiz, Spain; Ripalda, JM [Instituto de Microelectronica de Madrid (CNM, CSIC); Molina Rubio, Sergio I [ORNL

    2008-01-01T23:59:59.000Z

    It is well known that there is intense interest in expanding the usable wavelength for electronic devices. This is one of the reasons to study new self-assembled semiconductor nanostructures. Telecommunication applications use InGaAsP/InP emitting at 1.3 and 1.55 m. Research efforts are dedicated to develop GaAs technology in order to achieve emission at the same range as InP, so GaAs could be used for optical fibre communications. Ga(As)Sb on InAs/GaAs quantum dots (QDs) is a promising nanostructure to be used in telecommunications. The introduction of antimony during or after the QDs growth is an effective solution to obtain a red shift in the emission wavelength, even at room temperature.

  9. Excitonic properties of strained wurtzite and zinc-blende GaNAlxGa1xN quantum dots

    E-Print Network [OSTI]

    Fonoberov, Vladimir

    Excitonic properties of strained wurtzite and zinc-blende GaNAlxGa1xN quantum dots Vladimir A 2003 We investigate exciton states theoretically in strained GaN/AlN quantum dots with wurtzite WZ of GaN QDs.18 Molecu- lar beam epitaxial growth in the StranskiKrastanov mode of wurtzite WZ Ga

  10. Morphological and compositional variations in strain-compensated InGaAsP/InGaP superlattices

    E-Print Network [OSTI]

    Feenstra, Randall

    Morphological and compositional variations in strain- compensated InGaAsP/InGaP superlattices R of Technology, Kista, Sweden Abstract We have investigated the properties of strain-compensated InGaAsP/In- GaP superlattices, grown by metalorganic vapor phase epitaxy, with and without InP interlayers inserted in the InGaP

  11. Operating Characteristics of GaAs/InGaP Self Aligned Stripe Lasers Benjamin J. Stevens1

    E-Print Network [OSTI]

    Operating Characteristics of GaAs/InGaP Self Aligned Stripe Lasers Benjamin J. Stevens1 , Kristian of GaAs based self-aligned lasers based upon a single overgrowth. A lattice matched n-doped InGaP layer were exposed to oxygen. True buried heterostructures devices utilising InGaP clad- ding layers have

  12. Microstructure and luminescent properties of novel InGaP alloys on relaxed GaAsP substrates

    E-Print Network [OSTI]

    Microstructure and luminescent properties of novel InGaP alloys on relaxed GaAsP substrates M. J of unconventional alloys of InGaP with In fraction of 0.20.4 grown on fully relaxed GaAsP virtual substrates demonstrate growth of extremely high quality InGaP heterostructures which hold promise for fabrication

  13. Band Offsets of InGaP/GaAs Heterojunctions by Scanning Tunneling Spectroscopy Y. Dong and R. M. Feenstra

    E-Print Network [OSTI]

    Feenstra, Randall

    1 Band Offsets of InGaP/GaAs Heterojunctions by Scanning Tunneling Spectroscopy Y. Dong and R. M Abstract Scanning tunneling microscopy and spectroscopy are used to study InGaP/GaAs heterojunctions computation of the tunnel current. Curve fitting of theory to experiment is performed. Using an InGaP band gap

  14. Negative capacitance in GaN/AlGaN heterojunction dual-band detectors L. E. Byrum,1

    E-Print Network [OSTI]

    Dietz, Nikolaus

    Negative capacitance in GaN/AlGaN heterojunction dual-band detectors L. E. Byrum,1 G. Ariyawansa,1 online 2 September 2009 A study of trap states in n+ -GaN/AlGaN heterostructures using electrical related absorption centers attributed to shallow Si-donor pinned to the AlGaN barrier , N-vacancy/ C

  15. High Power Wideband AlGaN/GaN HEMT Feedback Amplifier Module with Drain and Feedback Loop

    E-Print Network [OSTI]

    Itoh, Tatsuo

    High Power Wideband AlGaN/GaN HEMT Feedback Amplifier Module with Drain and Feedback Loop amplifier module using AlGaN/GaN high electron mobility transistor (HEMT) has been developed that covers radars and communications systems. GaN-based HEMT's for high power applications at microwave frequencies

  16. Function of the Diiron Cluster of Escherichia coli Class Ia Ribonucleotide Reductase in Proton-Coupled Electron Transfer

    E-Print Network [OSTI]

    Wrsdrfer, Bigna

    The class Ia ribonucleotide reductase (RNR) from Escherichia coli employs a free-radical mechanism, which involves bidirectional translocation of a radical equivalent or hole over a distance of ~35 from the stable ...

  17. Experto Universitario Java Enterprise Validacin e internacionalizacin 2012-2013 Depto. Ciencia de la Computacin e IA Spring

    E-Print Network [OSTI]

    Escolano, Francisco

    Experto Universitario Java Enterprise Validacin e internacionalizacin 2012-2013 Depto. Ciencia #12;Experto Universitario Java Enterprise Validacin e internacionalizacin 2012-2013 Depto. Ciencia Java Enterprise Validacin e internacionalizacin 2012-2013 Depto. Ciencia de la Computacin e IA

  18. In vivo cofactor biosynthesis and maintenance in the class Ia ribonucleotide reductase small subunit of Escherichia coli

    E-Print Network [OSTI]

    Wu, Chia-Hung, Ph. D. Massachusetts Institute of Technology

    2009-01-01T23:59:59.000Z

    The small subunit ([beta]2) of Escherichia coli class Ia ribonucleotide reductases (RNRs) contains a diferric tyrosyl radical (Y*) cofactor essential for the conversion of nucleotides to deoxynucleotides that are needed ...

  19. Restframe I-band Hubble diagram for type Ia supernovae up to redshift z ~; 0.5

    E-Print Network [OSTI]

    2005-01-01T23:59:59.000Z

    in STScI Symposium Ser. 13, Supernovae and gamma-ray bursts:Highlight: The Physics of Supernovae, ed. W. Hillebrandt &diagram for type Ia supernovae up to redshift z ? 0.5 ? S.

  20. Mechanistic studies of proton-coupled electron transfer in aminotyrosine- and fluorotyrosine- substituted class Ia Ribonucleotide reductase

    E-Print Network [OSTI]

    Minnihan, Ellen Catherine

    2012-01-01T23:59:59.000Z

    Ribonucleotide reductase (RNR) catalyzes the conversion of nucleotides to 2'- deoxynucleotides in all organisms. The class Ia RNR from Escherichia coli is active as an a2p2 complex and utilizes an unprecedented mechanism ...

  1. On the small-scale stability of thermonuclear flames in Type Ia supernovae

    E-Print Network [OSTI]

    F. K. Roepke; J. C. Niemeyer; W. Hillebrandt

    2003-05-02T23:59:59.000Z

    We present a numerical model which allows us to investigate thermonuclear flames in Type Ia supernova explosions. The model is based on a finite-volume explicit hydrodynamics solver employing PPM. Using the level-set technique combined with in-cell reconstruction and flux-splitting schemes we are able to describe the flame in the discontinuity approximation. We apply our implementation to flame propagation in Chandrasekhar-mass Type Ia supernova models. In particular we concentrate on intermediate scales between the flame width and the Gibson-scale, where the burning front is subject to the Landau-Darrieus instability. We are able to reproduce the theoretical prediction on the growth rates of perturbations in the linear regime and observe the stabilization of the flame in a cellular shape. The increase of the mean burning velocity due to the enlarged flame surface is measured. Results of our simulation are in agreement with semianalytical studies.

  2. Impact ionization in N-polar AlGaN/GaN high electron mobility transistors

    SciTech Connect (OSTI)

    Killat, N., E-mail: Nicole.Killat@bristol.ac.uk, E-mail: Martin.Kuball@bristol.ac.uk; Uren, M. J.; Kuball, M., E-mail: Nicole.Killat@bristol.ac.uk, E-mail: Martin.Kuball@bristol.ac.uk [Center for Device Thermography and Reliability (CDTR), H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL (United Kingdom); Keller, S.; Kolluri, S.; Mishra, U. K. [Department of Electrical and Computer Engineering, University of Santa Barbara California, Santa Barbara, California 93106 (United States)

    2014-08-11T23:59:59.000Z

    The existence of impact ionization as one of the open questions for GaN device reliability was studied in N-polar AlGaN/GaN high electron mobility transistors. Electroluminescence (EL) imaging and spectroscopy from underneath the device gate contact revealed the presence of hot electrons in excess of the GaN bandgap energy even at moderate on-state bias conditions, enabling impact ionization with hole currents up to several hundreds of pA/mm. The detection of high energy luminescence from hot electrons demonstrates that EL analysis is a highly sensitive tool to study degradation mechanisms in GaN devices.

  3. Tunable two-dimensional plasmon resonances in an InGaAs/InP high electron mobility transistor

    E-Print Network [OSTI]

    Peale, Robert E.

    of materials systems such as GaAs/AlGaAs,3 InGaP/InGaAs/GaAs,4 GaN/AlGaN,2,5 and Si Ref. 1 have been explored

  4. The ignition process in type Ia supernovae: numerical simulations of core temperature perturbations

    E-Print Network [OSTI]

    L. Iapichino; M. Brggen; W. Hillebrandt; J. C. Niemeyer

    2007-11-13T23:59:59.000Z

    The onset of the thermonuclear runaway in a Chandrasekhar-mass white dwarf, leading to the explosion as a type Ia supernova, is studied with hydrodynamical simulations. We investigate the evolution of temperature fluctuations (``bubbles'') in the WD's convective core by means of 2D numerical simulations. We show how the occurrence of the thermonuclear runaway depends on various bubble parameters. The relevance of the progenitor's composition for the ignition process is also discussed.

  5. The ignition process in type Ia supernovae: numerical simulations of core temperature perturbations

    E-Print Network [OSTI]

    Iapichino, L; Hillebrandt, W; Niemeyer, J C

    2007-01-01T23:59:59.000Z

    The onset of the thermonuclear runaway in a Chandrasekhar-mass white dwarf, leading to the explosion as a type Ia supernova, is studied with hydrodynamical simulations. We investigate the evolution of temperature fluctuations (``bubbles'') in the WD's convective core by means of 2D numerical simulations. We show how the occurrence of the thermonuclear runaway depends on various bubble parameters. The relevance of the progenitor's composition for the ignition process is also discussed.

  6. TIDAL TAIL EJECTION AS A SIGNATURE OF TYPE Ia SUPERNOVAE FROM WHITE DWARF MERGERS

    SciTech Connect (OSTI)

    Raskin, Cody; Kasen, Daniel [Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA (United States)

    2013-07-20T23:59:59.000Z

    The merger of two white dwarfs may be preceded by the ejection of some mass in ''tidal tails,'' creating a circumstellar medium around the system. We consider the variety of observational signatures from this material, which depend on the lag time between the start of the merger and the ultimate explosion (assuming one occurs) of the system in a Type Ia supernova (SN Ia). If the time lag is fairly short, then the interaction of the supernova ejecta with the tails could lead to detectable shock emission at radio, optical, and/or X-ray wavelengths. At somewhat later times, the tails produce relatively broad NaID absorption lines with velocity widths of the order of the white dwarf escape speed ({approx}1000 km s{sup -1}). That none of these signatures have been detected in normal SNe Ia constrains the lag time to be either very short ({approx}< 100 s) or fairly long ({approx}> 100 yr). If the tails have expanded and cooled over timescales {approx}10{sup 4} yr, then they could be observable through narrow NaID and Ca II H and K absorption lines in the spectra, which are seen in some fraction of SNe Ia. Using a combination of three-dimensional and one-dimensional hydrodynamical codes, we model the mass loss from tidal interactions in binary systems, and the subsequent interactions with the interstellar medium, which produce a slow-moving, dense shell of gas. We synthesize NaID line profiles by ray casting through this shell, and show that in some circumstances tidal tails could be responsible for narrow absorptions similar to those observed.

  7. Observational constraints from SNe Ia and Gamma-Ray Bursts on a clumpy universe

    E-Print Network [OSTI]

    Nora Bretn; Ariadna Montiel

    2013-03-06T23:59:59.000Z

    The luminosity distance describing the effect of local inhomogeneities in the propagation of light proposed by Zeldovich-Kantowski-Dyer-Roeder (ZKDR) is tested with two probes for two distinct ranges of redshifts: supernovae Ia (SNe Ia) in 0.015 gamma-ray bursts (GRBs) in 1.547 < z < 3.57. Our analysis is performed by a Markov Chain Monte Carlo (MCMC) code that allows us to constrain the matter density parameter \\Omega_m as well as the smoothness parameter $\\alpha$ that measures the inhomogeneous-homogeneous rate of the cosmic fluid in a flat \\LambdaCDM model. The obtained best fits are (\\Omega_m=0.285^{+0.019}_{-0.018}, \\alpha= 0.856^{+0.106}_{-0.176}) from SNe Ia and (\\Omega_m=0.259^{+0.028}_{-0.028}, \\alpha=0.587^{+0.201}_{-0.202}) from GRBs, while from the joint analysis the best fits are (\\Omega_m=0.284^{+0.021}_{-0.020}, \\alpha= 0.685^{+0.164}_{-0.171}) with a \\chi^2_{\\rm red}=0.975. The value of the smoothness parameter $\\alpha$ indicates a clumped universe however it does not have an impact on the amount of dark energy (cosmological constant) needed to fit observations. This result may be an indication that the Dyer-Roeder approximation does not describe in a precise form the effects of clumpiness in the expansion of the universe.

  8. Observations of Type Ia Supernova 2014J with FLITECAM/SOFIA

    E-Print Network [OSTI]

    Vacca, William D; Savage, Maureen; Shenoy, Sachindev; Becklin, E E; McLean, Ian S; Logsdon, Sarah E; Gehrz, R D; Spyromilio, J; Garnavich, P; Marion, G H; Fox, O D

    2015-01-01T23:59:59.000Z

    We present medium resolution near-infrared (NIR) spectra, covering 1.1 to 3.4 microns, of the normal Type Ia supernova (SN Ia) SN 2014J in M82 obtained with the FLITECAM instrument aboard SOFIA approximately 17-25 days after maximum B light. Our 2.8-3.4 micron spectra may be the first ~3 micron spectra of a SN Ia ever published. The spectra spanning the 1.5-2.7 micron range are characterized by a strong emission feature at ~1.77 microns with a full width at half maximum of ~11,000-13,000 km/s. We compare the observed FLITECAM spectra to the recent non-LTE delayed detonation models of Dessart et al. (2014) and find that the models agree with the spectra remarkably well in the 1.5-2.7 micron wavelength range. Based on this comparison we identify the ~1.77 micron emission peak as a blend of permitted lines of Co II. Other features seen in the 2.0 - 2.5 micron spectra are also identified as emission from permitted transitions of Co II. However, the models are not as successful at reproducing the spectra in the 1....

  9. The Cellular Burning Regime in Type Ia Supernova Explosions - I. Flame Propagation into Quiescent Fuel

    E-Print Network [OSTI]

    F. K. Roepke; W. Hillebrandt; J. C. Niemeyer

    2003-12-03T23:59:59.000Z

    We present a numerical investigation of the cellular burning regime in Type Ia supernova explosions. This regime holds at small scales (i.e. below the Gibson scale), which are unresolved in large-scale Type Ia supernova simulations. The fundamental effects that dominate the flame evolution here are the Landau-Darrieus instability and its nonlinear stabilization, leading to a stabilization of the flame in a cellular shape. The flame propagation into quiescent fuel is investigated addressing the dependence of the simulation results on the specific parameters of the numerical setup. Furthermore, we investigate the flame stability at a range of fuel densities. This is directly connected to the questions of active turbulent combustion (a mechanism of flame destabilization and subsequent self-turbulization) and a deflagration-to-detonation transition of the flame. In our simulations we find no substantial destabilization of the flame when propagating into quiescent fuels of densities down to ~10^7 g/cm^3, corroborating fundamental assumptions of large-scale SN Ia explosion models. For these models, however, we suggest an increased lower cutoff for the flame propagation velocity to take the cellular burning regime into account.

  10. Is the X-ray pulsating companion of HD 49798 a possible type Ia supernova progenitor?

    E-Print Network [OSTI]

    Liu, Dong-Dong; Wu, Cheng-Yuan; Wang, Bo

    2015-01-01T23:59:59.000Z

    HD 49798 (a hydrogen depleted subdwarf O6 star) with its massive white dwarf (WD) companion has been suggested to be a progenitor candidate of type Ia supernovae (SNe Ia). However, it is still uncertain whether the companion of HD 49798 is a carbon-oxygen (CO) WD or an oxygen-neon (ONe) WD. A CO WD will explode as an SN Ia when its mass grows approach to Chandrasekhar mass, while the outcome of an accreting ONe WD is likely to be a neutron star. We followed a series of Monte Carlo binary population synthesis approach to simulate the formation of ONe WD + He star systems. We found that there is almost no orbital period as large as HD 49798 with its WD companion in these ONe WD + He star systems based on our simulations, which means that the companion of HD 49798 might not be an ONe WD. We suggest that the companion of HD 49798 is most likely a CO WD, which can be expected to increase its mass to the Chandrasekhar mass limit by accreting He-rich material from HD 49798. Thus, HD 49798 with its companion may prod...

  11. Searching for light echoes due to CSM in SN Ia spectra

    E-Print Network [OSTI]

    Marino, Sebastin; Frster, Francisco; Folatelli, Gastn; Hamuy, Mario; Hsiao, Eric

    2015-01-01T23:59:59.000Z

    We present an analytical model for light echoes (LEs) coming from circumstellar material (CSM) around Type Ia Supernovae (SNe Ia). Using this model we find two spectral signatures at 4100 {\\AA} and 6200 {\\AA} that are useful to identify LEs during the Lira law phase (between 35 and 80 days after maximum light) coming from nearby CSM at distances of 0.01-0.25 pc. We analyze a sample of 89 SNe Ia divided in two groups according to their B-V decline rate during the Lira law phase, and search for LEs from CSM interaction in the group of SNe with steeper slopes by comparing their spectra with our LE model. We find that a model with LEs + pure extinction from interstellar material (ISM) fits better the observed spectra than a pure ISM extinction model that is constant in time, but we find that a decreasing extinction alone explains better the observations without the need of LEs, possibly implying dust sublimation due to the radiation from the SN.

  12. AlGaN/GaN heterostructure prepared on a Si (110) substrate via pulsed sputtering

    SciTech Connect (OSTI)

    Watanabe, T.; Ohta, J.; Kondo, T.; Ohashi, M.; Ueno, K.; Kobayashi, A. [Institute of Industrial Science (IIS), The University of Tokyo, 4-6-1 Komaba, Tokyo 153-8505 (Japan); Fujioka, H., E-mail: hfujioka@iis.u-tokyo.ac.jp [Institute of Industrial Science (IIS), The University of Tokyo, 4-6-1 Komaba, Tokyo 153-8505 (Japan); CREST, Japan Science and Technology Corporation (JST), 5 Sanbancho, Chiyoda-ku, Tokyo 102-0075 (Japan)

    2014-05-05T23:59:59.000Z

    GaN films were grown on Si (110) substrates using a low-temperature growth technique based on pulsed sputtering. Reduction of the growth temperature suppressed the strain in the GaN films, leading to an increase in the critical thickness for crack formation. In addition, an AlGaN/GaN heterostructure with a flat heterointerface was prepared using this technique. Furthermore, the existence of a two dimensional electron gas at the heterointerface with a mobility of 1360 cm{sup 2}/Vs and a sheet carrier density of 1.3??10{sup 13}?cm{sup ?2} was confirmed. Finally, the use of the AlGaN/GaN heterostructure in a high electron mobility transistor was demonstrated. These results indicate that low-temperature growth via pulsed sputtering is quite promising for the fabrication of GaN-based electronic devices.

  13. 56 IEEE JOURNAL OF PHOTOVOLTAICS, VOL. 2, NO. 1, JANUARY 2012 Metamorphic GaAsP and InGaP Solar Cells on GaAs

    E-Print Network [OSTI]

    Haller, Gary L.

    56 IEEE JOURNAL OF PHOTOVOLTAICS, VOL. 2, NO. 1, JANUARY 2012 Metamorphic GaAsP and InGaP Solar bandgap range. Index Terms--Epitaxy, GaAsP, InGaP, metamorphic. I. INTRODUCTION TODAY'S highest efficiency

  14. Subclasses of Type Ia Supernovae as the origin of [\\alpha/Fe] ratios in dwarf spheroidal galaxies

    E-Print Network [OSTI]

    Kobayashi, Chiaki; Hachisu, Izumi

    2015-01-01T23:59:59.000Z

    Recent extensive observations of Type Ia Supernovae (SNe Ia) have revealed the existence of a diversity of SNe Ia, including SN 2002cx-like objects (also called SN Iax). We introduce two possible channels in the single degenerate scenario: 1) double detonations in sub-Chandrasekhar (Ch) mass CO white dwarfs (WDs), where a thin He envelope is developed with relatively low accretion rates after He novae even at low metallicities, and 2) carbon deflagrations in Ch-mass possibly hybrid C+O+Ne WDs, where WD winds occur at [Fe/H] ~ -2.5 at high accretion rates. These subclasses of SNe Ia are rarer than `normal' SNe Ia and do not affect the chemical evolution in the solar neighborhood, but can be very important in metal-poor systems with stochastic star formation. In dwarf spheroidal galaxies in the Local Group, the decrease of [\\alpha/Fe] ratios at [Fe/H] ~ -2 to -1.5 can be produced depending on the star formation history. SNe Iax give high [Mn/Fe], while sub-Ch-mass SNe Ia give low [Mn/Fe], and thus a model inclu...

  15. Optical and ultraviolet observations of the narrow-lined type Ia SN 2012fr in NGC 1365

    SciTech Connect (OSTI)

    Zhang, Ju-Jia; Bai, Jin-Ming; Wang, Bo; Liu, Zheng-Wei [Yunnan Observatories (YNAO), Chinese Academy of Sciences, Kunming 650011 (China); Wang, Xiao-Feng; Zhao, Xu-Lin; Chen, Jun-Cheng [Physics Department and Tsinghua Center for Astrophysics (THCA), Tsinghua University, Beijing 100084 (China); Zhang, Tian-Meng, E-mail: jujia@ynao.ac.cn, E-mail: baijinming@ynao.ac.cn, E-mail: wang_xf@mail.tsinghua.edu.cn [National Astronomical Observatories of China (NAOC), Chinese Academy of Sciences, Beijing 100012 (China)

    2014-07-01T23:59:59.000Z

    Extensive optical and ultraviolet (UV) observations of the type Ia supernova (SN Ia) 2012fr are presented in this paper. It has a relatively high luminosity, with an absolute B-band peak magnitude of about 19.5 mag and a smaller post-maximum decline rate than normal SNe Ia (e.g., ?m {sub 15}(B) =0.85 0.05 mag). Based on the UV and optical light curves, we derived that a {sup 56}Ni mass of about 0.88 M {sub ?} was synthesized in the explosion. The earlier spectra are characterized by noticeable high-velocity features of Si II ?6355 and Ca II with velocities in the range of ?22, 000-25, 000 km s{sup 1}. At around the maximum light, these spectral features are dominated by the photospheric components which are noticeably narrower than normal SNe Ia. The post-maximum velocity of the photosphere remains almost constant at ?12,000 km s{sup 1} for about one month, reminiscent of the behavior of some luminous SNe Ia like SN 1991T. We propose that SN 2012fr may represent a subset of the SN 1991T-like SNe Ia viewed in a direction with a clumpy or shell-like structure of ejecta, in terms of a significant level of polarization reported in Maund et al. in 2013.

  16. Constraining the Amount of Circumstellar Matter and Dust around Type Ia Supernovae through Near-Infrared Echo

    E-Print Network [OSTI]

    Maeda, Keiichi; Motohara, Kentaro

    2014-01-01T23:59:59.000Z

    Circumstellar (CS) environment is a key in understanding progenitors of type Ia supernovae (SNe Ia) as well as an origin of peculiar extinction property toward SNe Ia for cosmological application. It has been suggested that multiple em scatterings of SN photons on CS dust might explain a non-standard reddening law. In this paper, we investigate an effect of re-emissions of SN photons by CS dust in the Infrared (IR) wavelengths. We show that this effect allows observed IR light curves to be used to place a constraint on position/size and the amount of CSM dust. We apply the method to observed NIR SN Ia samples, showing that meaningful upper limits, even under conservative assumptions, on the CS dust mass can be derived. We thereby clarify a difficulty of the CS dust scattering model to be a general explanation for the peculiar reddening law, while it may still apply to a sub-sample of highly-reddened SNe Ia. For SNe Ia in general, environment at the interstellar scale should be responsible for the non-standard...

  17. Defect structures in rapidly degraded InGaAsP/InGaP double-heterostructure lasers

    SciTech Connect (OSTI)

    Ueda, O.; Wakao, K.; Yamaguchi, A.; Isozumi, S.; Komiya, S.

    1985-03-01T23:59:59.000Z

    Rapidly degraded InGaAsP/InGaP double-heterostructure lasers grown on (001)-oriented GaAs substrates by liquid phase epitaxy have been investigated by photolumi

  18. Emission properties of heterostructures with a (GaAsSb-InGaAs)/GaAs bilayer quantum well

    SciTech Connect (OSTI)

    Zvonkov, B. N.; Nekorkin, S. M.; Vikhrova, O. V.; Dikareva, N. V., E-mail: dikareva@nifti.unn.ru [Nizhni Novgorod State University, Physical-Technical Research Institute (Russian Federation)

    2013-09-15T23:59:59.000Z

    The specific features of the emission characteristics of GaAs-based heterostructures with a GaAs{sub 1-x}Sb{sub x}-In{sub y}Ga{sub 1-y}As bilayer quantum well are studied. The heterostructures are grown by metal-organic chemical vapor deposition (MOCVD). With an analysis of previously reported data on the MOCVD growth process taken into account, the temperature range (560-580 Degree-Sign C), the relation between the fluxes emitted by the sources of Group-V and -III elements ( Less-Than-Or-Equivalent-To 1), and the order of layer growth for the production of the active region of a GaAs/InGaP laser heterostructure are determined experimentally. The active region is a GaAs{sub 0.75}Sb{sub 0.25}-In{sub 0.2}Ga{sub 0.8}As bilayer quantum well. For the structure, a 1075-nm electroluminescence signal attributed to indirect transitions between the valence band of the GaAs{sub 0.75}Sb{sub 0.25} layer and the conduction band of the In{sub 0.2}Ga{sub 0.8}As layer is observed. An increase in the continuous-wave pump current yields a decrease in the 1075-nm emission intensity and initiates stable lasing at a wavelength of 1022 nm at a threshold current density of 1.4 kA cm{sup -2} at room temperature. Lasing occurs at transitions direct in coordinate space.

  19. AlGaN/GaN HFET Single-Ended Frequency Doubler Younkyu Chung and Tatsuo Itoh

    E-Print Network [OSTI]

    Itoh, Tatsuo

    AlGaN/GaN HFET Single-Ended Frequency Doubler Younkyu Chung and Tatsuo Itoh Department-mail: ykchung@ee.ucla.edu Abstract - This paper presents the first single-ended AlGaN/GaN heterojunction field, respectively. For the frequency doubler with 1mm gate periphery AlGaN/GaN HFET, conversion gain of 0.17 d

  20. Materials Science and Engineering B59 (1999) 319322 Microcalorimetric absorption spectroscopy in GaNAlGaN

    E-Print Network [OSTI]

    Nabben, Reinhard

    1999-01-01T23:59:59.000Z

    Microcalorimetric measurements of small absorption coefficients have been performed on thin GaNAlGaN quantum wells in GaNAlGaN quantum wells Axel Goldner a, *, Axel Hoffmann a , Bernard Gil b , Pierre Lefebvre b at the energy of the GaN buffer and at the energy of the thick AlGaN barrier layers, we could also readily

  1. Al fraction induced effects on the capacitance characteristics -GaN/AlxGa1-xN IR detectors

    E-Print Network [OSTI]

    Dietz, Nikolaus

    substrate. As shown in Fig. 1(a), the device structures consist of a 0.2 m n+ -GaN top contact (emitter.1117/12.828156 Proc. of SPIE Vol. 7467 74670W-1 #12;(a) Sapphire Substrate n GaN Bottom Contact AlxGa1-xN Barrier n GaNAl fraction induced effects on the capacitance characteristics of n+ -GaN/AlxGa1-xN IR detectors

  2. Improvement of breakdown voltage in InGaP/InGaAs/GaAs heterostructure MESFETs for MMICs

    SciTech Connect (OSTI)

    Koh, Inoue; Yamane, Yasuro; Shiojima, Kenji [NTT LSI Lab., Kanagawa (Japan)] [and others

    1995-12-31T23:59:59.000Z

    This paper describes the trade-off between breakdown voltage and RF performance of InGaP/InGaAs/GaAs heterostructure MESFETs for power amplifiers and oscillators in multi-function MMICs in the millimeter-wave range. The authors successfully improved both gate-drain and drain-source breakdown voltages while maintaining excellent high-frequency performance by using a double-layered gate consisting of WSiN with different nitrogen contents, and by varying epitaxial layer thickness and implantation dose.

  3. Structural and optical properties of InGaNGaN nanowire heterostructures grown by molecular beam epitaxy

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Limbach, F. [Institute of Bio- and Nanosystems (IBN-1), Research Centre Jlich GmbH and JARA-FIT Fundamentals of Future Information Technology (Germany); Gotschke, T. [Institute of Bio- and Nanosystems (IBN-1), Research Centre Jlich GmbH and JARA-FIT Fundamentals of Future Information Technology (Germany); Stoica, T. [Institute of Bio- and Nanosystems (IBN-1), Research Centre Jlich GmbH and JARA-FIT Fundamentals of Future Information Technology (Germany); Calarco, R. [Institute of Bio- and Nanosystems (IBN-1), Research Centre Jlich GmbH and JARA-FIT Fundamentals of Future Information Technology (Germany); Sutter, E. [Brookhaven National Lab., Upton, NY (United States); Ciston, J. [Brookhaven National Lab., Upton, NY (United States); Cusco, R. [Consell Superior d'Investigacions Cientifiques (CSIC), Barcelona (Spain); Artus, L. [Consell Superior d'Investigacions Cientifiques (CSIC), Barcelona (Spain); Kremling, S. [Univ. Wurzburg, Wilhelm Conrad Rontgen Research Centre Complex Matter Systems, Wurzburg (Germany); Hofling, S. [Univ. Wurzburg, Wilhelm Conrad Rontgen Research Centre Complex Matter Systems, Wurzburg (Germany); Worschech, L. [Univ. Wurzburg, Wilhelm Conrad Rontgen Research Centre Complex Matter Systems, Wurzburg (Germany); Grutzmacher, D. [Institute of Bio- and Nanosystems (IBN-1), Research Centre Jlich GmbH and JARA-FIT Fundamentals of Future Information Technology (Germany)

    2011-01-07T23:59:59.000Z

    InGaN/GaN nanowire (NW) heterostructures grown by plasma assisted molecular beam epitaxy were studied in comparison to their GaN and InGaN counterparts. The InGaN/GaN heterostructure NWs are composed of a GaN NW, a thin InGaN shell, and a multifaceted InGaN cap wrapping the top part of the GaN NW. High-resolution transmission electron microscopy (HRTEM) images taken from different parts of a InGaN/GaN NW show a wurtzite structure of the GaN core and the epitaxial InGaN shell around it, while additional crystallographic domains are observed whithin the InGaN cap region. Large changes in the lattice parameter along the wire, from pure GaN to higher In concentration demonstrate the successful growth of a complex InGaN/GaN NW heterostructure. Photoluminescence (PL) spectra of these heterostructure NW ensembles show rather broad and intense emission peak at 2.1 eV. However, ?-PL spectra measured on single NWs reveal a reduced broadening of the visible luminescence. The analysis of the longitudinal optical phonon Raman peak position and its shape reveal a variation in the In content between 20% and 30%, in agreement with the values estimated by PL and HRTEM investigations. The reported studies are important for understanding of the growth and properties of NW heterostructures suitable for applications in optoelectronics and photovoltaics.

  4. Necessity of Ga prelayers in GaAs/Ge growth using gas-source molecular beam epitaxy

    E-Print Network [OSTI]

    in a highly defective GaAs layer.as5 Recently, InGaP light-emitting diodes have been fabricated on Si using

  5. High-efficiency radiation-resistant InGaP/GaAs tandem solar cells

    SciTech Connect (OSTI)

    Takamoto, T. [Toyota Technological Inst., Tempaku, Nagoya (Japan); [Japan Energy Corp., Toda, Saitama (Japan); Yamaguchi, M.; Taylor, S.J. [Toyota Technological Inst., Tempaku, Nagoya (Japan); Ikeda, E.; Agui, T.; Kurita, H. [Japan Energy Corp., Toda, Saitama (Japan)

    1997-12-31T23:59:59.000Z

    A world-record efficiency of 26.9% (AM0, 28 C) has been obtained for InGaP/GaAs tandem solar cells fabricated by the MOCVD method. The radiation resistance of the InGaP/GaAs tandem solar cells has also been evaluated following 1 MeV electron irradiation. Degradation in the tandem cell performance has been confirmed to be mainly attributed to large degradation in the GaAs bottom cell, which features a highly doped base layer. Similar radiation-resistance with GaAs-on-Ge cells has been observed for the InGaP/GaAs tandem cell. However, some recovery of the tandem cell performance has been found due to minority-carrier injection under light illumination of forward bias, which causes defect annealing in InGaP cells. The optimal design of the InGaP base layer thickness for current matching at end of life (EOL) (after irradiation with 10{sup 15} electrons cm{sup {minus}2}) has been examined.

  6. Highly uniform, multi-stacked InGaAs/GaAs quantum dots embedded in a GaAs nanowire

    SciTech Connect (OSTI)

    Tatebayashi, J., E-mail: tatebaya@iis.u-tokyo.ac.jp; Ota, Y. [NanoQUINE, The University of Tokyo, 4-6-1, Komaba, Meguro-ku, Tokyo 153-8505 (Japan); Ishida, S.; Nishioka, M.; Iwamoto, S.; Arakawa, Y. [NanoQUINE, The University of Tokyo, 4-6-1, Komaba, Meguro-ku, Tokyo 153-8505 (Japan); Institute of Industrial Science, The University of Tokyo, 4-6-1, Komaba, Meguro-ku, Tokyo 153-8505 (Japan)

    2014-09-08T23:59:59.000Z

    We demonstrate a highly uniform, dense stack of In{sub 0.22}Ga{sub 0.78}As/GaAs quantum dot (QD) structures in a single GaAs nanowire (NW). The size (and hence emission energy) of individual QD is tuned by careful control of the growth conditions based on a diffusion model of morphological evolution of NWs and optical characterization. By carefully tailoring the emission energies of individual QD, dot-to-dot inhomogeneous broadening of QD stacks in a single NW can be as narrow as 9.3?meV. This method provides huge advantages over traditional QD stack using a strain-induced Stranski-Krastanow growth scheme. We show that it is possible to fabricate up to 200 uniform QDs in single GaAs NWs using this growth technique without degradation of the photoluminescence intensity.

  7. Strain induced variations in band offsets and built-in electric fields in InGaN/GaN multiple quantum wells

    E-Print Network [OSTI]

    Alpay, S. Pamir

    Strain induced variations in band offsets and built-in electric fields in InGaN/GaN multiple InxGa1-xN(InGaN)/GaN multilayers on the In composition and misfit strain. The results indicate that for non-polar m-plane configurations with 1210InGaN//1210GaN and 0001InGaN//0001GaN epitaxial

  8. Multi-bands photoconductive response in AlGaN/GaN multiple quantum wells

    SciTech Connect (OSTI)

    Chen, G.; Rong, X.; Xu, F. J.; Tang, N. [State Key Laboratory of Artificial Microstructure and Mesoscopic Physics, School of Physics, Peking University, Beijing 100871 (China); Wang, X. Q., E-mail: wangshi@pku.edu.cn; Shen, B., E-mail: bshen@pku.edu.cn [State Key Laboratory of Artificial Microstructure and Mesoscopic Physics, School of Physics, Peking University, Beijing 100871 (China); Collaborative Innovation Center of Quantum Matter, Beijing (China); Fu, K.; Zhang, B. S. [Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Ruoshui Road 398, 215123 Suzhou (China); Hashimoto, H.; Yoshikawa, A. [Center for SMART Green Innovation Research, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522 (Japan); Ge, W. K. [Department of Physics, Tsinghua University, Beijing 100871 (China)

    2014-04-28T23:59:59.000Z

    Based on the optical transitions among the quantum-confined electronic states in the conduction band, we have fabricated multi-bands AlGaN/GaN quantum well infrared photodetectors. Crack-free AlGaN/GaN multiple quantum wells (MQWs) with atomically sharp interfaces have been achieved by inserting an AlN interlayer, which releases most of the tensile strain in the MQWs grown on the GaN underlayer. With significant reduction of dark current by using thick AlGaN barriers, photoconductive responses are demonstrated due to intersubband transition in multiple regions with center wavelengths of 1.3, 2.3, and 4??m, which shows potential applications on near infrared detection.

  9. High-performance InGaP/GaAs pnp {delta}-doped heterojunction bipolar transistor

    SciTech Connect (OSTI)

    Tsai, J.-H. [National Kaohsiung Normal University, Department of Electronic Engineering (China)], E-mail: jhtsai@nknucc.nknu.edu.tw; Chiu, S.-Y.; Lour, W.-S. [National Taiwan Ocean University, Department of Electrical Engineering (China); Guo, D.-F. [Air Force Academy, Department of Electronic Engineering (China)

    2009-07-15T23:59:59.000Z

    In this article, a novel InGaP/GaAs pnp {delta}-doped heterojunction bipolar transistor is first demonstrated. Though the valence band discontinuity at InGaP/GaAs heterojunction is relatively large, the addition of a {delta}-doped sheet between two spacer layers at the emitter-base (E-B) junction effectively eliminates the potential spike and increases the confined barrier for electrons, simultaneously. Experimentally, a high current gain of 25 and a relatively low E-B offset voltage of 60 mV are achieved. The offset voltage is much smaller than the conventional InGaP/GaAs pnp HBT. The proposed device could be used for linear amplifiers and low-power complementary integrated circuit applications.

  10. Synthesis, morphology and optical properties of GaN and AlGaN semiconductor nanostructures

    SciTech Connect (OSTI)

    Kuppulingam, B., E-mail: drbaskar2009@gmail.com; Singh, Shubra, E-mail: drbaskar2009@gmail.com; Baskar, K., E-mail: drbaskar2009@gmail.com [Crystal Growth Centre, Anna University, Chennai-600025 (India)

    2014-04-24T23:59:59.000Z

    Hexagonal Gallium Nitride (GaN) and Aluminum Gallium Nitride (AlGaN) nanoparticles were synthesized by sol-gel method using Ethylene Diamine Tetra Acetic acid (EDTA) complex route. Powder X-ray diffraction (PXRD) analysis confirms the hexagonal wurtzite structure of GaN and Al{sub 0.25}Ga{sub 0.75}N nanoparticles. Surface morphology and elemental analysis were carried out by Scanning Electron Microscope (SEM) and Energy Dispersive X-ray spectroscopy (EDX). The room temperature Photoluminescence (PL) study shows the near band edge emission for GaN at 3.35 eV and at 3.59 eV for AlGaN nanoparticles. The Aluminum (Al) composition of 20% has been obtained from PL emission around 345 nm.

  11. Effect of polarization on intersubband transition in AlGaN/GaN multiple quantum wells

    SciTech Connect (OSTI)

    Chen, G.; Li, Z. L.; Wang, X. Q.; Huang, C. C.; Rong, X.; Xu, F. J.; Tang, N.; Qin, Z. X.; Shen, B. [State Key Laboratory of Artificial Microstructure and Mesoscopic Physics, School of Physics, Peking University, Beijing 100871 (China)] [State Key Laboratory of Artificial Microstructure and Mesoscopic Physics, School of Physics, Peking University, Beijing 100871 (China); Sang, L. W.; Sumiya, M. [Optical and Electronic Materials Unit, National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044 (Japan)] [Optical and Electronic Materials Unit, National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044 (Japan); Chen, Y. H. [Laboratory of Semiconductor Material Science, Institute of Semiconductors, CAS, Beijing 100083 (China)] [Laboratory of Semiconductor Material Science, Institute of Semiconductors, CAS, Beijing 100083 (China); Ge, W. K. [Department of Physics, Tsinghua University, Beijing 100871 (China)] [Department of Physics, Tsinghua University, Beijing 100871 (China)

    2013-05-13T23:59:59.000Z

    Intersubband transitions (ISBT) of AlGaN/GaN multiple quantum wells (MQWs) with wavelength towards atmospheric window (3-5 {mu}m) have been investigated. A Ga-excess epitaxial method is used in the molecular beam epitaxy leading to ultra-sharp interface and negligible elements inter-diffusion. The absorption peak wavelength of the ISBT was successfully tuned in the range of 3-4 {mu}m by modifying the GaN well thickness from 2.8 to 5.5 nm. It was further found that the polarization charge density of the AlGaN/GaN MQWs was about -0.034 C/m{sup 2} which gave rise to blueshift of the ISBT wavelength and thus partially compensated its redshift with increasing well thickness.

  12. InGaN/GaN single-quantum-well microdisks

    SciTech Connect (OSTI)

    Hsu, Yu-Chi; Lo, Ikai; Shih, Cheng-Hung; Pang, Wen-Yuan; Hu, Chia-Hsuan; Wang, Ying-Chieh; Chou, Mitch M. C. [Department of Physics, Department of Materials and Optoelectronic Science, Center for Nanoscience and Nanotechnology, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan (China)

    2012-06-11T23:59:59.000Z

    We have grown In{sub x}Ga{sub 1-x}N/GaN quantum wells atop GaN microdisk with {gamma}-LiAlO{sub 2} substrate by using plasma-assisted molecular beam epitaxy. The structural and optical properties of the samples were analyzed by transmission electron microscopy, x-ray diffraction, cathodoluminescence, and photoluminescence measurements. Based on the measured results, we obtained the indium concentration of the In{sub x}Ga{sub 1-x}N/GaN single quantum well to be x = 0.25 with a band-gap energy of 2.31 eV, which is consistent with the bowing effect of bulk In{sub x}Ga{sub 1-x}N: E{sub g}(x) = [3.42 - x * 2.65 - x * (1 - x) * 2.4] eV.

  13. Atomic layer deposition of GaN using GaCl3 and NH3 Oh Hyun Kim, Dojun Kim, and Tim Andersona

    E-Print Network [OSTI]

    Anderson, Timothy J.

    be grown at lower temperature than by CVD. As example, ALD growth of device quality GaAs, GaP, and InGaP

  14. Dependence of the ground-state transition energy versus optical pumping in GaAsSb/InGaAs/GaAs heterostructures

    SciTech Connect (OSTI)

    Morozov, S. V.; Kryzhkov, D. I., E-mail: krizh@ipmras.ru; Aleshkin, V. Ya. [Institute for Physics of Microstructures, RAS, 603950 Nizhny Novgorod (Russian Federation); Lobachevsky State University of Nizhny Novgorod, 603950 Nizhny Novgorod (Russian Federation); Yablonsky, A. N.; Krasilnik, Z. F. [Institute for Physics of Microstructures, RAS, 603950 Nizhny Novgorod (Russian Federation); Zvonkov, B. N.; Vikhrova, O. V. [Physical-Technical Research Institute, Lobachevsky State University of Nizhny Novgorod, 603950 Nizhny Novgorod (Russian Federation)

    2014-01-13T23:59:59.000Z

    In this work, we report on the time-resolved photoluminescence studies of a double quantum well In{sub 0.2}Ga{sub 0.8}As/GaAs{sub 0.8}Sb{sub 0.2}/GaAs heterostructure which, in contrast to the GaAsSb/GaAs structures, is expected to provide effective confinement of electrons due to additional InGaAs layer. The studies at 4.2?K have revealed a complicated nonmonotonic dependence of the ground-state transition energy on the concentration of nonequilibrium charge carriers in the quantum well. The effect observed in this work is important in terms of creating sources of radiation, including stimulated emission, on the basis of InGaAs/GaAsSb/GaAs structures.

  15. AlGaN/GaN field effect transistors for power electronicsEffect of finite GaN layer thickness on thermal characteristics

    SciTech Connect (OSTI)

    Hodges, C., E-mail: chris.hodges@bristol.ac.uk; Anaya Calvo, J.; Kuball, M. [H. H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL (United Kingdom)] [H. H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL (United Kingdom); Stoffels, S.; Marcon, D. [IMEC, Kapeldreef 75, B3001 Leuven (Belgium)] [IMEC, Kapeldreef 75, B3001 Leuven (Belgium)

    2013-11-11T23:59:59.000Z

    AlGaN/GaN heterostructure field effect transistors with a 150?nm thick GaN channel within stacked Al{sub x}Ga{sub 1?x}N layers were investigated using Raman thermography. By fitting a thermal simulation to the measured temperatures, the thermal conductivity of the GaN channel was determined to be 60?W m{sup ?1} K{sup ?1}, over 50% less than typical GaN epilayers, causing an increased peak channel temperature. This agrees with a nanoscale model. A low thermal conductivity AlGaN buffer means the GaN spreads heat; its properties are important for device thermal characteristics. When designing power devices with thin GaN layers, as well as electrical considerations, the reduced channel thermal conductivity must be considered.

  16. InGaAsP/InGaP buried heterostructure lasers at 810 nm

    SciTech Connect (OSTI)

    Wakao, K.; Isozumi, S.; Nishi, H.; Ohsaka, S.

    1984-12-01T23:59:59.000Z

    InGaAsP/InGaP buried heterostructure lasers emitting at 810 nm have been grown on GaAs substrates using two-step liquid-phase epitaxy. A threshold current of 79 mA and an external differential quantum efficiency of 26% are obtained. Fundamental transverse mode operation up to 3 mW is achieved in the laser with the active region of 3.5 ..mu..m wide.

  17. Simplified 2DEG carrier concentration model for composite barrier AlGaN/GaN HEMT

    SciTech Connect (OSTI)

    Das, Palash, E-mail: d.palash@gmail.com; Biswas, Dhrubes, E-mail: d.palash@gmail.com [Indian Institute of Technology Kharagpur, Kharagpur - 721302, West Bengal (India)

    2014-04-24T23:59:59.000Z

    The self consistent solution of Schrodinger and Poisson equations is used along with the total charge depletion model and applied with a novel approach of composite AlGaN barrier based HEMT heterostructure. The solution leaded to a completely new analytical model for Fermi energy level vs. 2DEG carrier concentration. This was eventually used to demonstrate a new analytical model for the temperature dependent 2DEG carrier concentration in AlGaN/GaN HEMT.

  18. Ohmic contacts to n-GaSb

    E-Print Network [OSTI]

    Yang, Zhengchong

    1997-01-01T23:59:59.000Z

    In recent years, the Ill-V semiconductor GaSb and its ternary alloys containing antimony have exhibited interesting electrical and optical properties for device applications which include negative resistance tunnel devices, lasers, detectors and FET...

  19. The structure of GaAs/Si(211) heteroepitaxial layers

    SciTech Connect (OSTI)

    Liliental-Weber, Z.; Weber, E.R.; Washburn, J.; Liu, T.Y.; Kroemer, H.

    1985-05-01T23:59:59.000Z

    Gallium arsenide films grown on (211)Si by molecular-beam epitaxy have been investigated using transmission electron microscopy. The main defects observed in the alloy were of misfit dislocations, stacking faults, and microtwin lamellas. Silicon surface preparation was found to play an important role on the density of defects formed at the Si/GaAs interface. Two different types of strained-layer superlattices, InGaAs/InGaP and InGaAs/GaAs, were applied either directly to the Si substrate, to a graded layer (GaP-InGaP), or to a GaAs buffer layer to stop the defect propagation into the GaAs films. Applying InGaAs/GaAs instead of InGaAs/InGaP was found to be more effective in blocking defect propagation. In all cases of strained-layer superlattices investigated, dislocation propagation was stopped primarily at the top interface between the superlattice package and GaAs. Graded layers and unstrained AlGaAs/GaAs superlattices did not significantly block dislocations propagating from the interface with Si. Growing of a 50 nm GaAs buffer layer at 505/sup 0/C followed by 10 strained-layer superlattices of InGaAs/GaAs (5 nm each) resulted in the lowest dislocation density in the GaAs layer (approx.5 x 10/sup 7//cm/sup 2/) among the structures investigated. This value is comparable to the recently reported density of dislocations in the GaAs layers grown on (100)Si substrates. Applying three sets of the same strained layers decreased the density of dislocations an additional approx.2 to 3 times.

  20. Over 30{percent} efficient InGaP/GaAs tandem solar cells

    SciTech Connect (OSTI)

    Takamoto, T.; Ikeda, E.; Kurita, H. [Central Research Laboratory, Japan Energy Corporation, 3-17-35 Niizo-Minami, Toda, Saitama 335 (Japan)] [Central Research Laboratory, Japan Energy Corporation, 3-17-35 Niizo-Minami, Toda, Saitama 335 (Japan); Ohmori, M. [Japan Energy Research Center Company, Ltd., 1-11-9 Azabudai, Minato-ku, Tokyo 106 (Japan)] [Japan Energy Research Center Company, Ltd., 1-11-9 Azabudai, Minato-ku, Tokyo 106 (Japan)

    1997-01-01T23:59:59.000Z

    A two-terminal monolithic InGaP/GaAs tandem solar cell with a new efficiency record of 30.28{percent} is realized with a practical large area of 4 cm{sup 2} under one-sun air-mass 1.5 global illumination. We report improvements of the tandem cell performance by introducing a double-hetero (hereafter DH) structure InGaP tunnel junction, in which the InGaP layers are surrounded by high band gap AlInP barriers. The DH structure by AlInP barriers increase the peak current of InGaP tunnel junction. The AlInP barrier directly below the InGaP top cell, which takes the part of a back surface field (hereafter BSF) layer, is found to be considerably effective in reflecting minority carriers in the top cell. The AlInP BSF layer does not only form a high potential barrier but also prevents the diffusion of zinc from a high doped tunnel junction toward the top cell during epitaxial growth. Furthermore, an InGaP tunnel junction reduces the absorption loss, which exists in a GaAs tunnel junction, and increases the photogenerated current in the GaAs bottom cell. {copyright} {ital 1997 American Institute of Physics.}

  1. GaTe semiconductor for radiation detection

    DOE Patents [OSTI]

    Payne, Stephen A. (Castro Valley, CA); Burger, Arnold (Nashville, TN); Mandal, Krishna C. (Ashland, MA)

    2009-06-23T23:59:59.000Z

    GaTe semiconductor is used as a room-temperature radiation detector. GaTe has useful properties for radiation detectors: ideal bandgap, favorable mobilities, low melting point (no evaporation), non-hygroscopic nature, and availability of high-purity starting materials. The detector can be used, e.g., for detection of illicit nuclear weapons and radiological dispersed devices at ports of entry, in cities, and off shore and for determination of medical isotopes present in a patient.

  2. Probing temperature gradients within the GaN buffer layer of AlGaN/GaN high electron mobility transistors with Raman thermography

    SciTech Connect (OSTI)

    Hodges, C., E-mail: chris.hodges@bristol.ac.uk; Pomeroy, J.; Kuball, M. [H. H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL (United Kingdom)

    2014-02-14T23:59:59.000Z

    We demonstrate the ability of confocal Raman thermography using a spatial filter and azimuthal polarization to probe vertical temperature gradients within the GaN buffer layer of operating AlGaN/GaN high electron mobility transistors. Temperature gradients in the GaN layer are measured by using offset focal planes to minimize the contribution from different regions of the GaN buffer. The measured temperature gradient is in good agreement with a thermal simulation treating the GaN thermal conductivity as homogeneous throughout the layer and including a low thermal conductivity nucleation layer to model the heat flow between the buffer and substrate.

  3. Hubble Residuals of Nearby SN Ia Are Correlated with Host Galaxy Masses

    SciTech Connect (OSTI)

    Kelly, Patrick L.; /KIPAC, Menlo Park /SLAC; Hicken, Malcolm; /Harvard-Smithsonian Ctr. Astrophys.; Burke, David L.; /KIPAC, Menlo Park /SLAC; Mandel, Kaisey S.; Kirshner, Robert P.; /Harvard-Smithsonian Ctr. Astrophys.

    2010-05-03T23:59:59.000Z

    From Sloan Digital Sky Survey u{prime} g{prime} r{prime} i{prime} z{prime} imaging, we estimate the stellar masses of the host galaxies of 70 low redshift SN Ia (0.015 < z < 0.08) from the hosts absolute luminosities and mass-to-light ratios. These nearby SN were discovered largely by searches targeting luminous galaxies, and we find that their host galaxies are substantially more massive than the hosts of SN discovered by the flux-limited Supernova Legacy Survey. Testing four separate light curve fitters, we detect {approx}2.5{sigma} correlations of Hubble residuals with both host galaxy size and stellar mass, such that SN Ia occurring in physically larger, more massive hosts are {approx}10% brighter after light curve correction. The Hubble residual is the deviation of the inferred distance modulus to the SN, calculated from its apparent luminosity and light curve properties, away from the expected value at the SN redshift. Marginalizing over linear trends in Hubble residuals with light curve parameters shows that the correlations cannot be attributed to a light curve-dependent calibration error. Combining 180 higher-redshift ESSENCE, SNLS, and HigherZ SN with 30 nearby SN whose host masses are less than 10{sup 10.8} M{circle_dot} n a cosmology fit yields 1 + w = 0.22{sub -0.108}{sup +0.152}, while a combination where the 30 nearby SN instead have host masses greater than 10{sup 10.8} M{circle_dot} yields 1 + w = ?0.03{sub -0.143}{sup +0.217}. Progenitor metallicity, stellar population age, and dust extinction correlate with galaxy mass and may be responsible for these systematic effects. Host galaxy measurements will yield improved distances to SN Ia.

  4. Constraints on shallow {sup 56}Ni from the early light curves of type Ia supernovae

    SciTech Connect (OSTI)

    Piro, Anthony L. [Theoretical Astrophysics, California Institute of Technology, 1200 E California Boulevard, M/C 350-17, Pasadena, CA 91125 (United States); Nakar, Ehud, E-mail: piro@caltech.edu [Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978 (Israel)

    2014-03-20T23:59:59.000Z

    Ongoing transient surveys are presenting an unprecedented account of the rising light curves of Type Ia supernovae (SNe Ia). This early emission probes the shallowest layers of the exploding white dwarf (WD), which can provide constraints on the progenitor star and the properties of the explosive burning. We use semianalytic models of radioactively powered rising light curves to analyze these observations. As we have summarized in previous work, the main limiting factor in determining the surface distribution of {sup 56}Ni is the lack of an unambiguously identified time of explosion, as would be provided by detection of shock breakout or shock-heated cooling. Without this the SN may in principle exhibit a 'dark phase' for a few hours to days, where the only emission is from shock-heated cooling that is too dim to be detected. We show that by assuming a theoretically motivated time-dependent velocity evolution, the explosion time can be better constrained, albeit with potential systematic uncertainties. This technique is used to infer the surface {sup 56}Ni distributions of three recent SNe Ia that were caught especially early in their rise. In all three we find fairly similar {sup 56}Ni distributions. Observations of SN 2011fe and SN 2012cg probe shallower depths than SN 2009ig, and in these two cases {sup 56}Ni is present merely ?10{sup 2} M {sub ?} from the WDs' surfaces. The uncertainty in this result is up to an order of magnitude given the difficulty of precisely constraining the explosion time. We also use our conclusions about the explosion times to reassess radius constraints for the progenitor of SN 2011fe, as well as discuss the roughly t {sup 2} power law that is inferred for many observed rising light curves.

  5. IS WX CEN A POSSIBLE TYPE Ia SUPERNOVA PROGENITOR WITH WIND-DRIVEN MASS TRANSFER?

    SciTech Connect (OSTI)

    Qian, S.-B.; Shi, G.; Zhu, L.-Y.; Liu, L.; Zhao, E.-G.; Li, L.-J. [Yunnan Observatories, Chinese Academy of Sciences (CAS), P.O. Box 110, 650011 Kunming (China); Fernandez Lajus, E.; Di Sisto, R. P., E-mail: qsb@ynao.ac.cn [Facultad de Ciencias Astronomicas y Geofisicas, Universidad Nacional de La Plata, 1900 La Plata, Buenos Aires (Argentina)

    2013-08-01T23:59:59.000Z

    WX Cen is one of a few compact binary supersoft X-ray sources (CBSS) in the Galaxy that is a possible Type Ia supernova (SN Ia) progenitor. The supersoft X-ray radiation is explained as hydrostatic nuclear burning on the surface of the white dwarf component that is accreting hydrogen from a stellar companion at a high rate. If the mass donor in this system has a low mass, as has been suggested in the literature, one would expect a high wind-driven mass transfer rate. In that case, the orbital period of the system should increase. To test this theoretical prediction, we have monitored the system photometrically since 2010. By using four newly determined eclipse timings together with those collected from the literature, we discovered that the orbital period is decreasing at a rate of dP/dt = -5.15 Multiplication-Sign 10{sup -7} days yr{sup -1}. The long-term decrease in the orbital period is contrary to the prediction that the system is powered by wind-driven accretion. It therefore seems plausible that the mass donor could be more massive than the white dwarf, and that the mass transfer is driven by the thermal instability of the donor star. This finding suggests that WX Cen is a key object to check the physical mechanisms of mass accretion in CBSS. The corresponding timescale of the period change is about P/P-dot {approx} 0.81 x 10{sup 6} yr, indicating that WX Cen may evolve into an SNe Ia within one million years in the Galaxy.

  6. On the Thermonuclear Runaway in Type Ia Supernovae: How to run away?

    E-Print Network [OSTI]

    P. Hoeflich; J. Stein

    2001-12-07T23:59:59.000Z

    Type Ia Supernovae are thought to be thermonuclear explosions of massive white dwarfs (WD). We present the first study of multi-dimensional effects during the final hours prior to the thermonuclear runaway which leads to the explosion. The calculations utilize an implicit, 2-D hydro code.Mixing and the ignition process are studied in detail. We find that the initial chemical structure of the WD is changed but the material is not fully homogenized. The exploding WD sustains a central region with a low C/O ratio. This implies that the explosive nuclear burning will begin in a partially C-depleted environment. The thermonuclear runaway happens in a well defined region close to the center. It is induced by compressional heat when matter is brought inwards by convective flows. We find no evidence for multiple spot or strong off-center ignition. Convective velocities are of the order of 100 km/sec which is well above the effective burning speeds in SNe Ia previously expected right after the runaway. For about 0.5 to 1 sec, the speed of the burning front will neither be determined by the laminar speed nor the Rayleigh-Taylor instabilities but by convective flows produced prior to the runaway. The consequences are discussed for our under- standing of the detailed physics of the flame propagation, the deflagration detonation transition, and the nucleosynthesis in the central layers. Our results strongly suggest the pre-conditioning of the progenitor as a key-factor for our understanding of the diversity in SNeIa.

  7. The type Ia supernova SNLS-03D3bb from a super-Chandrasekhar-masswhite dwarf star

    SciTech Connect (OSTI)

    Howell, D.Andrew; Sullivan, Mark; Nugent, Peter E.; Ellis,Richard S.; Conley, Alexander J.; Le Borgne, Damien; Carlberg, RaymondG.; Guy, Julien; Balam, David; Basa, Stephane; Fouchez, Dominique; Hook,Isobel M.; Hsiao, Eric Y.; Neill, James D.; Pain, Reynald; Perrett,Kathryn M.; Pritchet, Christopher J.

    2006-02-01T23:59:59.000Z

    The acceleration of the expansion of the universe, and theneed for Dark Energy, were inferred from the observations of Type Iasupernovae (SNe Ia) 1;2. There is consensus that SNeIa are thermonuclearexplosions that destroy carbon-oxygen white dwarf stars that accretematter from a companion star3, although the nature of this companionremains uncertain. SNe Ia are thought to be reliable distance indicatorsbecause they have a standard amount of fuel and a uniform trigger theyare predicted to explode when the mass of the white dwarf nears theChandrasekhar mass 4 - 1.4 solar masses. Here we show that the highredshift supernova SNLS-03D3bb has an exceptionally high luminosity andlow kinetic energy that both imply a super-Chandrasekhar mass progenitor.Super-Chandrasekhar mass SNeIa shouldpreferentially occur in a youngstellar population, so this may provide an explanation for the observedtrend that overluminous SNe Ia only occur in young environments5;6. Sincethis supernova does not obey the relations that allow them to becalibrated as standard candles, and since no counterparts have been foundat low redshift, future cosmology studies will have to considercontamination from such events.

  8. The p-Process in the Carbon Deflagration Model for Type Ia Supernovae and Chronology of the Solar System Formation

    SciTech Connect (OSTI)

    Kusakabe, Motohiko [Department of Astronomy, School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Iwamoto, Nobuyuki [Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan); Nomoto, Ken'ichi [Department of Astronomy, School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan)

    2006-07-12T23:59:59.000Z

    We study nucleosynthesis of p-nuclei in the carbon deflagration model for Type Ia supernovae (SNe Ia) by assuming that seed nuclei are produced by the s-process in accreting layers on a carbon-oxygen white dwarf during mass accretion from a binary companion. We find that about 50 % of the p-nuclides are synthesized in proportion to the solar abundance and that p-isotopes of Mo and Ru which are significantly underproduced in Type II supernovae (SNe II) are produced up to a level close to other p-nuclei. Comparing the yields of iron and p-nuclei in SNe Ia we find that SNe Ia can contribute to the galactic evolution of the p-nuclei. Next, we consider nucleochronology of the solar system formation by using four radioactive nuclides and apply the result of the p-process nucleosynthesis to simple galactic chemical evolution models. We find that when assumed three phases of interstellar medium are mixed by the interdiffusion with the timescale of about 40 Myr 53Mn/55Mn value in the early solar system is consistent with a meteoritic value. In addition, we put constraints to a scenario that SNe Ia induce the core collapse of the molecular cloud, which leads to the formation of the solar system.

  9. A super-Eddington wind scenario for the progenitors of type Ia supernovae: binary population synthesis calculations

    E-Print Network [OSTI]

    Wang, Bo; Liu, Dongdong; Liu, Zhengwei; Wu, Chengyuan; Zhang, Jujia; Han, Zhanwen

    2015-01-01T23:59:59.000Z

    The super-Eddington wind scenario has been proposed as an alternative way for producing type Ia supernovae (SNe Ia). The super-Eddington wind can naturally prevent the carbon--oxygen white dwarfs (CO WDs) with high mass-accretion rates from becoming red-giant-like stars. Furthermore, it works in low-metallicity environments, which may explain SNe Ia observed at high redshifts. In this article, we systematically investigated the most prominent single-degenerate WD+MS channel based on the super-Eddington wind scenario. We combined the Eggleton stellar evolution code with a rapid binary population synthesis (BPS) approach to predict SN Ia birthrates for the WD+MS channel by adopting the super-Eddington wind scenario and detailed mass-accumulation efficiencies of H-shell flashes on the WDs. Our BPS calculations found that the estimated SN Ia birthrates for the WD+MS channel are ~0.009-0.315*10^{-3}{yr}^{-1} if we adopt the Eddington accretion rate as the critical accretion rate, which are much lower than that of ...

  10. Gamma-Rays as Probes for the Multi-Dimensionality of Type Ia Supernovae

    E-Print Network [OSTI]

    P. Hoeflich

    2001-10-03T23:59:59.000Z

    We present $\\gamma $-ray spectra for a set of Type Ia supernovae models. Our study is based on a detailed Monte Carlo transport scheme for both spherical and full 3-D geometries. Classical and new challenges of the $\\gamma $ ray astronomy are addressed. We find that $\\gamma $-rays are very suitable to reveal the structure of the envelope and, thus, they allow to probe properties of the nuclear burning front and the progenitor, namely its central density and global asphericities. The potential problems are discussed for the quantitative comparison between theoretical and observed line fluxes during the first few months after the explosion.

  11. Testing the isotropy of the Universe by using the JLA compilation of type-Ia supernovae

    E-Print Network [OSTI]

    Lin, Hai-Nan; Chang, Zhe; Li, Xin

    2015-01-01T23:59:59.000Z

    We probe the possible anisotropy in the accelerated expanding Universe by using the JLA compilation of type-Ia supernovae. We constrain the amplitude and direction of anisotropy in the anisotropic cosmological models. For the dipole-modulated $\\Lambda$CDM model, the anisotropic amplitude has an upper bound $D<1.04\\times10^{-3}$ at the $68\\%$ confidence level. Similar results are found in the dipole-modulated $w$CDM and CPL models. Our studies show that there are no significant evidence for the anisotropic expansion of the Universe. Thus the Universe is still well compatible with the isotropy.

  12. On the Stability of Thermonuclear Burning Fronts in Type Ia Supernovae

    E-Print Network [OSTI]

    F. K. Roepke; W. Hillebrandt

    2004-04-26T23:59:59.000Z

    The propagation of cellularly stabilized thermonuclear flames is investigated by means of numerical simulations. In Type Ia supernova explosions the corresponding burning regime establishes at scales below the Gibson length. The cellular flame stabilization - which is a result of an interplay between the Landau-Darrieus instability and a nonlinear stabilization mechanism - is studied for the case of propagation into quiescent fuel as well as interaction with vortical fuel flows. Our simulations indicate that in thermonuclear supernova explosions stable cellular flames develop around the Gibson scale and that deflagration-to-detonation transition is unlikely to be triggered from flame evolution effects here.

  13. Thermoelectric effects in wurtzite GaN and AlxGa1-xN alloys and Alexander A. Balandin

    E-Print Network [OSTI]

    with the active thermoelectric cooling implemented on the same material system can improve the device performance, for the pro- posed cooling system should also be based on GaN. To real- ize this, the high-efficiency Ga,6 Great progress has been achieved in GaN-based microwave technology. GaN transistors with very high

  14. Journal of Crystal Growth 298 (2007) 272275 Dislocation analysis in homoepitaxial GaInN/GaN light emitting

    E-Print Network [OSTI]

    Wetzel, Christian M.

    2007-01-01T23:59:59.000Z

    of GaInN/GaN-based light emitting diodes (LED) on quasi-bulk GaN with an atomically flat polished were much improved. The optical output power of the light emitting diode increased by more than one. Cathodoluminescence; A1. Threading dislocation density; A2. Homoepitaxial growth; B1. GaInN; B3. Light emitting diode

  15. The Effect of the Thermal Boundary Resistance on Self-Heating of AlGaN/GaN HFETs

    E-Print Network [OSTI]

    The Effect of the Thermal Boundary Resistance on Self-Heating of AlGaN/GaN HFETs 1. Introduction, performance of these devices has been limited by self-heating [1] [6]. Thus, accurate modeling of heat diffusion and self-heating effects in AlGaN/GaN heterostructures and device optimization based

  16. InAsGaPInGaP high-temperature power Schottky rectifier and J. M. Woodall

    E-Print Network [OSTI]

    Woodall, Jerry M.

    C. Further improvement of the thermal stability is expected to be achieved by reducing the diffusion is thought to be due to strong covalent bonding at the InAs/GaP interface. The InAs/GaP heterointerface effectively blocks impurity diffusion. Since InGaP is superior to GaP for high-power applica- tions, as shown

  17. GaAs-based self-aligned laser incorporating InGaP opto-electronic confinement layer

    E-Print Network [OSTI]

    GaAs-based self-aligned laser incorporating InGaP opto-electronic confinement layer K.M. Groom, B fabrication, is demonstrated. An n-doped InGaP layer is utilised for both electrical and optical confinement-doped InGaP current blocking layer that also provides optical confinement. This tech- nology relies

  18. GaN/ZnO and AlGaN/ZnO heterostructure LEDs: growth, fabrication, optical and electrical characterization

    E-Print Network [OSTI]

    Wetzel, Christian M.

    GaN/ZnO and AlGaN/ZnO heterostructure LEDs: growth, fabrication, optical and electrical 12180-3590, U.S.A. ABSTRACT The wide bandgap polar semiconductors GaN and ZnO and their related alloys fields, and surface terminations. With a small lattice mismatch of ~1.8 % between GaN and Zn

  19. Direct Evidence of Nanoscale Carrier Localization in InGaN/GaN Structures Grown on Si Substrates

    E-Print Network [OSTI]

    Nabben, Reinhard

    Direct Evidence of Nanoscale Carrier Localization in InGaN/GaN Structures Grown on Si Substrates: time-resolved photoluminescence, quantum dots, InGaN, Si substrate There exists a strong continuous expensive and are limited in size. Thus, heteroepitaxial growth of GaN on silicon substrates seems

  20. Inclined dislocation-pair relaxation mechanism in homoepitaxial green GaInN/GaN light-emitting diodes

    E-Print Network [OSTI]

    Wetzel, Christian M.

    -emitting diodes LEDs on low-defect density bulk GaN substrate, but not in green LEDs on sapphire substrate an ideal substrate for homoepitaxial growth. Here we study the microstructural properties of green GaInN/GaN-Koehler force10 resulting from a macroscopic relaxation of strain. II. CRYSTAL GROWTH c plane bulk GaN substrate

  1. Junction Temperature Measurements and Thermal Modeling of GaInN/GaN Quantum Well Light-Emitting Diodes

    E-Print Network [OSTI]

    Wetzel, Christian M.

    quantum well (QW) light-emitting diodes (LEDs) grown on sapphire and bulk GaN substrate by micro efficiency in dies grown on GaN substrates with a thermal resistance of 75 K/W. For dies on sapphire of GaN-based blue and green LEDs grown on sapphire and GaN substrates using micro-Raman spectroscopy

  2. Correlation between structural properties and optical amplification in InGaN/GaN heterostructures grown by molecular beam epitaxy

    E-Print Network [OSTI]

    Nabben, Reinhard

    . The lateral homogeneity can be drastically improved using a template of GaN grown on the sapphire substrate-grown heterostructures can drastically be reduced by using a template of MOVPE-GaN on the sapphire substrate, which leadsCorrelation between structural properties and optical amplification in InGaN/GaN heterostructures

  3. Ultra-high frequency photoconductivity decay in GaAs/Ge/GaAs double heterostructure grown by molecular beam epitaxy

    SciTech Connect (OSTI)

    Hudait, M. K.; Zhu, Y. [Bradley Department of Electrical and Computer Engineering, Virginia Tech, Blacksburg, Virginia 24061 (United States)] [Bradley Department of Electrical and Computer Engineering, Virginia Tech, Blacksburg, Virginia 24061 (United States); Johnston, S. W. [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States)] [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States); Maurya, D.; Priya, S. [Center for Energy Harvesting Materials and Systems (CEHMS), Virginia Tech, Blacksburg, Virginia 24061 (United States)] [Center for Energy Harvesting Materials and Systems (CEHMS), Virginia Tech, Blacksburg, Virginia 24061 (United States); Umbel, R. [Materials Science and Engineering, Virginia Tech, Blacksburg, Virginia 24061 (United States)] [Materials Science and Engineering, Virginia Tech, Blacksburg, Virginia 24061 (United States)

    2013-03-04T23:59:59.000Z

    GaAs/Ge/GaAs double heterostructures (DHs) were grown in-situ using two separate molecular beam epitaxy chambers. High-resolution x-ray rocking curve demonstrates a high-quality GaAs/Ge/GaAs heterostructure by observing Pendelloesung oscillations. The kinetics of the carrier recombination in Ge/GaAs DHs were investigated using photoconductivity decay measurements by the incidence excitation from the front and back side of 15 nm GaAs/100 nm Ge/0.5 {mu}m GaAs/(100)GaAs substrate structure. High-minority carrier lifetimes of 1.06-1.17 {mu}s were measured when excited from the front or from the back of the Ge epitaxial layer, suggests equivalent interface quality of GaAs/Ge and Ge/GaAs. Wavelength-dependent minority carrier recombination properties are explained by the wavelength-dependent absorption coefficient of Ge.

  4. Metastable states in InGaN/GaN MQW structures doped with Sm, Eu, and Eu + Sm

    SciTech Connect (OSTI)

    Mezdrogina, M. M., E-mail: Margaret.M@mail.ioffe.ru [Russian Academy of Sciences, Ioffe Physical-Technical Institute (Russian Federation); Kozhanova, Yu. V. [St. Petersburg State Polytechnical University (Russian Federation)

    2013-04-15T23:59:59.000Z

    Measurements of the microphotoluminescence (microPL) spectra of InGaN/GaN:Sm and InGaN/GaN:Eu quantum well (QW) structures show that the action of a magnetic field gives rise to Van Vleck paramagnetism for Eu{sup 3+} and Sm{sup 3+}. The macrophotoluminescence (macroPL) spectra recorded after measuring the microPL spectra of InGaN/GaN QW structures doped with Sm or Eu + Sm at a high excitation level (>10{sup 23} photons cm{sup -2} s{sup -1}) in magnetic fields contain no QW emission lines which are present in the macroPL spectra recorded before these microPL measurements. This is indicative of the presence of photoinduced defects. Annealing of the InGaN/GaN:Sm and InGaN/GaN:(Eu + Sm) structures reduces the concentration of photoinduced defects.

  5. Gas-source molecular beam epitaxial growth and characterization of the (Al,In,Ga)NP/GaP material system and Its applications to light-emitting diodes

    E-Print Network [OSTI]

    Odnoblyudov, Vladimir

    2006-01-01T23:59:59.000Z

    on metamorphic growth of InGaP layers on GaP substrates, astemperature amber photoluminescence from InGaP QWs, grownon a metamorphic InGaP layer. References: Fred Shubert E. ,

  6. InGaN/GaN tunnel junctions for hole injection in GaN light emitting diodes

    SciTech Connect (OSTI)

    Krishnamoorthy, Sriram, E-mail: krishnamoorthy.13@osu.edu, E-mail: rajan@ece.osu.edu; Akyol, Fatih [Department of Electrical and Computer Engineering, The Ohio State University, Columbus, Ohio 43210 (United States); Rajan, Siddharth, E-mail: krishnamoorthy.13@osu.edu, E-mail: rajan@ece.osu.edu [Department of Electrical and Computer Engineering, The Ohio State University, Columbus, Ohio 43210 (United States); Department of Materials Science and Engineering, The Ohio State University, Columbus, Ohio 43210 (United States)

    2014-10-06T23:59:59.000Z

    InGaN/GaN tunnel junction contacts were grown using plasma assisted molecular beam epitaxy (MBE) on top of a metal-organic chemical vapor deposition (MOCVD)-grown InGaN/GaN blue (450?nm) light emitting diode. A voltage drop of 5.3?V at 100?mA, forward resistance of 2 10{sup ?2} ? cm{sup 2}, and a higher light output power compared to the reference light emitting diodes (LED) with semi-transparent p-contacts were measured in the tunnel junction LED (TJLED). A forward resistance of 5??10{sup ?4} ? cm{sup 2} was measured in a GaN PN junction with the identical tunnel junction contact as the TJLED, grown completely by MBE. The depletion region due to the impurities at the regrowth interface between the MBE tunnel junction and the MOCVD-grown LED was hence found to limit the forward resistance measured in the TJLED.

  7. ccsd-00000821(version1):6Nov2003 Alloy effects in Ga1-xInxN/GaN heterostructures

    E-Print Network [OSTI]

    Paris-Sud XI, Universit de

    ccsd-00000821(version1):6Nov2003 Alloy effects in Ga1-xInxN/GaN heterostructures Duc-Phuong Nguyen, France We show that the large band offsets between GaN and InN and the heavy carrier effec- tive masses preclude the use of the Virtual Crystal Approximation to describe the electronic structure of Ga1-xInxN/GaN

  8. DESIGN, GROWTH, FABRICATION AND CHARACTERIZATION OF HIGH-BAND GAP InGaN/GaN SOLAR CELLS

    E-Print Network [OSTI]

    Honsberg, Christiana

    DESIGN, GROWTH, FABRICATION AND CHARACTERIZATION OF HIGH-BAND GAP InGaN/GaN SOLAR CELLS Omkar Jani1 with a band gap of 2.4 eV or greater. InxGa1-xN is one of a few alloys that can meet this key requirement. InGaN.4 eV. InGaN has the appropriate optical properties and has been well demonstrated for light

  9. AlGaN/GaN MIS-HEMT Gate Structure Improvement Using Al2O3 Deposited by PEALD

    E-Print Network [OSTI]

    Boyer, Edmond

    AlGaN/GaN MIS-HEMT Gate Structure Improvement Using Al2O3 Deposited by PEALD R. Meunier1 , A, 38054 Grenoble Cedex 9, France 2 LAAS-CNRS, 7 Avenue du Colonel Roche, 31400 Toulouse, France AlGaN /GaN behavior. Those trapped charges can be associated to the carbon contamination of the AlGaN surface

  10. Emission mechanisms of bulk GaN and InGaN quantum wells prepared by lateral epitaxial overgrowth

    E-Print Network [OSTI]

    Bowers, John

    Emission mechanisms of bulk GaN and InGaN quantum wells prepared by lateral epitaxial overgrowth S for publication 5 January 1999 The emission mechanisms of bulk GaN and InGaN quantum wells QWs were studied suggest that TDs simply reduce the net volume of light-emitting area. This effect is less pronounced in InGaN

  11. Comparison of strong coupling regimes in bulk GaAs, GaN and ZnO semiconductor microcavities

    E-Print Network [OSTI]

    Boyer, Edmond

    , transmission and absorption spectra of bulk GaAs, GaN and ZnO microcavities, in order to compareComparison of strong coupling regimes in bulk GaAs, GaN and ZnO semiconductor microcavities SAs and GaN microcavities. PACS numbers: 78.67.-n, 71.36.+c, 78.20.Ci, 78.55.Cr, 78.55.Et Keywords: polariton

  12. Near ultraviolet emission from nonpolar cubic AlxGa1-xN/GaN quantum wells

    E-Print Network [OSTI]

    As, Donat Josef

    molecular beam epitaxy on free standing 3C-SiC 001 substrates. During growth of Al0.15Ga0.85N/GaN quantum growth of the quantum structures an 800 nm thick GaN buffer layer was deposited on the 3C-SiC substrate. The buffer and the c-AlGaN/GaN quantum wells were grown at a substrate temperature of 720 C. The layers were

  13. Nanoair-bridged lateral overgrowth of GaN on ordered nanoporous GaN template

    SciTech Connect (OSTI)

    Wang, Y.D.; Zang, K.Y.; Chua, S.J.; Tripathy, S.; Chen, P.; Fonstad, C.G. [Singapore-MIT Alliance, E4-04-10, 4 Engineering Drive 3, Singapore 117576 (Singapore) and Centre for Optoelectronics, Department of Electrical and Computer Engineering, National University of Singapore, 2 Engineering Drive 3, Singapore 117576 (Singapore); Institute of Materials Research and Engineering, 3 Research Link, Singapore 117602 (Singapore); Department of Electrical and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

    2005-12-19T23:59:59.000Z

    We report the growth of high-quality GaN epilayers on an ordered nanoporous GaN template by metalorganic chemical vapor deposition. The nanopores in GaN template were created by inductively coupled plasma etching using anodic aluminum oxide film as an etch mask. The average pore diameter and interpore distance is about 65 and 110 nm, respectively. Subsequent overgrowth of GaN first begins at the GaN crystallite surface between the pores, and then air-bridge-mediated lateral overgrowth leads to the formation of the continuous layer. Microphotoluminescence and micro-Raman measurements show improved optical properties and significant strain relaxation in the overgrown layer when compared to GaN layer of same thickness simultaneously grown on sapphire without any template. Similar to conventional epitaxial lateral overgrown GaN, such overgrown GaN on a nanopatterned surface would also serve as a template for the growth of ultraviolet-visible light-emitting III-nitride devices.

  14. AlGaN/GaN HEMT With 300-GHz fmax

    E-Print Network [OSTI]

    Chung, Jinwook W.

    We report on a gate-recessed AlGaN/GaN high-electron mobility transistor (HEMT) on a SiC substrate with a record power-gain cutoff frequency (f[subscript max]). To achieve this high f[subscript max], we combined a low-damage ...

  15. Gate-First AlGaN/GaN HEMT Technology for High-Frequency Applications

    E-Print Network [OSTI]

    Piner, Edwin L.

    This letter describes a gate-first AlGaN/GaN high-electron mobility transistor (HEMT) with a W/high-k dielectric gate stack. In this new fabrication technology, the gate stack is deposited before the ohmic contacts, and ...

  16. High Indium Concentration InGaN/GaN Grown on Sapphire Substrate by MOCVD

    E-Print Network [OSTI]

    Hartono, Haryono

    The InGaN system provides the opportunity to fabricate light emitting devices over the whole visible and ultraviolet spectrum due to band-gap energies E[subscript g] varying between 3.42 eV for GaN and 1.89 eV for InN. ...

  17. Schottky-Drain Technology for AlGaN/GaN High-Electron Mobility Transistors

    E-Print Network [OSTI]

    Lu, Bin

    In this letter, we demonstrate 27% improvement in the buffer breakdown voltage of AlGaN/GaN high-electron mobility transistors (HEMTs) grown on Si substrate by using a new Schottky-drain contact technology. Schottky-drain ...

  18. Investigation of Strain in AlGaN/GaN Multi Quantum Wells by Complementary Techniques

    SciTech Connect (OSTI)

    Devaraju, G.; Sathish, N.; Pathak, A. P. [School of Physics, University of Hyderabad, Central University (P.0), Hyderabad 500 046 (India); Dhamodaran, S. [Department of Physics, Indian Institute of Technology, IIT P O, Kanpur UP 208016 (India); Gaca, J.; Wojcik, M. [Institute of Electronic Materials Technology, 01-919 Warsaw, ul. Wolczynska 133 (Poland); Turos, A. [Institute of Electronic Materials Technology, 01-919 Warsaw, ul. Wolczynska 133 (Poland); Soltan Institute for Nuclear Studies, Swierk/Otwock, Warsaw (Poland); Arora, B. M. [Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai-400 005 (India)

    2009-03-10T23:59:59.000Z

    Al{sub 0.49}Ga{sub 0.51}N(12 nm)/GaN (13 nm) Multi Quantum Wells of 15 periods are grown on sapphire by MOCVD technique. GaN/AlN, each of thickness 200 nm and 20 nm respectively, are used as buffer layers between substrate and epilayer to incorporate the strain in epilayers. It is a well established technique to engineer the band gap in Al{sub x}Ga{sub 1-x}N by adjusting alloy composition. These samples are used in visible and UV light emitters. In the present study, we employ a photoluminescence technique to estimate the composition and luminescence peak positions of AlGaN and GaN. Crystallinity and quality of interfaces have been studied by Rocking curve scan. The Threading Dislocations formed at the GaN buffer layer travel across the entire layers to the surface to form good quality films. Photo-luminescence results show a very sharp GaN peak at 3.4 eV, as observed and reported by others, which shows that samples are free from point defects.

  19. Constraining the Type Ia Supernova Progenitor: The Search for Hydrogen in Nebular Spectra

    E-Print Network [OSTI]

    Douglas C. Leonard

    2007-10-16T23:59:59.000Z

    Despite intense scrutiny, the progenitor system(s) that gives rise to Type Ia supernovae remains unknown. The favored theory invokes a carbon-oxygen white dwarf accreting hydrogen-rich material from a close companion until a thermonuclear runaway ensues that incinerates the white dwarf. However, simulations resulting from this single-degenerate, binary channel demand the presence of low-velocity H-alpha emission in spectra taken during the late nebular phase, since a portion of the companion's envelope becomes entrained in the ejecta. This hydrogen has never been detected, but has only rarely been sought. Here we present results from a campaign to obtain deep, nebular-phase spectroscopy of nearby Type Ia supernovae, and include multi-epoch observations of two events: SN 2005am (slightly subluminous) and SN 2005cf (normally bright). No H-alpha emission is detected in the spectra of either object. An upper limit of 0.01 M_Sun of solar abundance material in the ejecta is established from the models of Mattila et al. which, when coupled with the mass-stripping simulations of Marietta et al. and Meng et al. effectively rules out progenitor systems for these supernovae with secondaries close enough to the white dwarf to be experiencing Roche lobe overflow at the time of explosion. Alternative explanations for the absence of H-alpha emission, along with suggestions for future investigations necessary to confidently exclude them as possibilities, are critically evaluated.

  20. First Evidence of Globular Cluster Formation from the Ejecta of Prompt Type Ia Supernovae

    E-Print Network [OSTI]

    Tsujimoto, Takuji

    2012-01-01T23:59:59.000Z

    Recent spectroscopic observations of globular clusters (GCs) in the Large Magellanic Cloud (LMC) have discovered that one of the intermediate-age GC, NGC 1718 with [Fe/H]=-0.7 has an extremely low [Mg/Fe] ratio of ~-0.9. We propose that NGC 1718 was formed from the ejecta of type Ia supernovae (SNe Ia) mixed with very metal-poor ([Fe/H] <-1.3) gas about ~ 2 Gyr ago. The proposed scenario is shown to be consistent with the observed abundances of Fe-group elements such as Cr, Mn, and Ni. In addition, compelling evidence for asymptotic giant branch stars playing a role in chemical enrichment during this GC formation is found. We suggest that the origin of the metal-poor gas is closely associated with the efficient gas-transfer from the outer gas disk of the Small Magellanic Cloud to the LMC disk. We anticipate that the outer part of the LMC disk contains field stars exhibiting significantly low [Mg/Fe] ratios, formed through the same process as NGC 1718.

  1. Inference for the dark energy equation of state using Type IA supernova data

    E-Print Network [OSTI]

    Christopher Genovese; Peter Freeman; Larry Wasserman; Robert Nichol; Christopher Miller

    2009-05-18T23:59:59.000Z

    The surprising discovery of an accelerating universe led cosmologists to posit the existence of "dark energy"--a mysterious energy field that permeates the universe. Understanding dark energy has become the central problem of modern cosmology. After describing the scientific background in depth, we formulate the task as a nonlinear inverse problem that expresses the comoving distance function in terms of the dark-energy equation of state. We present two classes of methods for making sharp statistical inferences about the equation of state from observations of Type Ia Supernovae (SNe). First, we derive a technique for testing hypotheses about the equation of state that requires no assumptions about its form and can distinguish among competing theories. Second, we present a framework for computing parametric and nonparametric estimators of the equation of state, with an associated assessment of uncertainty. Using our approach, we evaluate the strength of statistical evidence for various competing models of dark energy. Consistent with current studies, we find that with the available Type Ia SNe data, it is not possible to distinguish statistically among popular dark-energy models, and that, in particular, there is no support in the data for rejecting a cosmological constant. With much more supernova data likely to be available in coming years (e.g., from the DOE/NASA Joint Dark Energy Mission), we address the more interesting question of whether future data sets will have sufficient resolution to distinguish among competing theories.

  2. Spectroscopic Determination of the Low Redshift Type Ia Supernova Rate from the Sloan Digital Sky Survey

    SciTech Connect (OSTI)

    Krughoff, K. S. [Univ. of Washington, Seattle, WA (United States); Connolly, Andrew J. [Univ. of Washington, Seattle, WA (United States); Frieman, Joshua [Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States); SubbaRao, Mark [Univ. of Chicago, Chicago, IL (United States); Kilper, Gary [NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States); Schneider, Donald P. [Davey Laboratory, PA (United States)

    2011-04-10T23:59:59.000Z

    Supernova rates are directly coupled to high mass stellar birth and evolution. As such, they are one of the few direct measures of the history of cosmic stellar evolution. In this paper we describe an probabilistic technique for identifying supernovae within spectroscopic samples of galaxies. We present a study of 52 type Ia supernovae ranging in age from -14 days to +40 days extracted from a parent sample of \\simeq 50,000 spectra from the SDSS DR5. We find a Supernova Rate (SNR) of 0.472^{+0.048}_{-0.039}(Systematic)^{+0.081}_{-0.071}(Statistical)SNu at a redshift of = 0.1. This value is higher than other values at low redshift at the 1{\\sigma}, but is consistent at the 3{\\sigma} level. The 52 supernova candidates used in this study comprise the third largest sample of supernovae used in a type Ia rate determination to date. In this paper we demonstrate the potential for the described approach for detecting supernovae in future spectroscopic surveys.

  3. Smoothed Particle Hydrodynamics simulations of the core-degenerate scenario for Type Ia supernovae

    E-Print Network [OSTI]

    Aznar-Sigun, G; Lorn-Aguilar, P; Soker, N; Kashi, A

    2015-01-01T23:59:59.000Z

    The core-degenerate (CD) scenario for type Ia supernovae (SN Ia) involves the merger of the hot core of an asymptotic giant branch (AGB) star and a white dwarf, and might contribute a non-negligible fraction of all thermonuclear supernovae. Despite its potential interest, very few studies, and based on only crude simplifications, have been devoted to investigate this possible scenario, compared with the large efforts invested to study some other scenarios. Here we perform the first three-dimensional simulations of the merger phase, and find that this process can lead to the formation of a massive white dwarf, as required by this scenario. We consider two situations, according to the mass of the circumbinary disk formed around the system during the final stages of the common envelope phase. If the disk is massive enough, the stars merge on a highly eccentric orbit. Otherwise, the merger occurs after the circumbinary disk has been ejected and gravitational wave radiation has brought the stars close to the Roche...

  4. Consistent use of type Ia supernovae highly magnified by galaxy clusters to constrain the cosmological parameters

    SciTech Connect (OSTI)

    Zitrin, Adi [Cahill Center for Astronomy and Astrophysics, California Institute of Technology, MS 249-17, Pasadena, CA 91125 (United States); Redlich, Matthias [Universitt Heidelberg, Zentrum fr Astronomie, Institut fr Theoretische Astrophysik, Philosophenweg 12, D-69120 Heidelberg (Germany); Broadhurst, Tom, E-mail: adizitrin@gmail.com [Department of Theoretical Physics, University of Basque Country UPV/EHU, Bilbao (Spain)

    2014-07-01T23:59:59.000Z

    We discuss how Type Ia supernovae (SNe) strongly magnified by foreground galaxy clusters should be self-consistently treated when used in samples fitted for the cosmological parameters. While the cluster lens magnification of a SN can be well constrained from sets of multiple images of various background galaxies with measured redshifts, its value is typically dependent on the fiducial set of cosmological parameters used to construct the mass model. In such cases, one should not naively demagnify the observed SN luminosity by the model magnification into the expected Hubble diagram, which would create a bias, but instead take into account the cosmological parameters a priori chosen to construct the mass model. We quantify the effect and find that a systematic error of typically a few percent, up to a few dozen percent per magnified SN may be propagated onto a cosmological parameter fit unless the cosmology assumed for the mass model is taken into account (the bias can be even larger if the SN is lying very near the critical curves). We also simulate how such a bias propagates onto the cosmological parameter fit using the Union2.1 sample supplemented with strongly magnified SNe. The resulting bias on the deduced cosmological parameters is generally at the few percent level, if only few biased SNe are included, and increases with the number of lensed SNe and their redshift. Samples containing magnified Type Ia SNe, e.g., from ongoing cluster surveys, should readily account for this possible bias.

  5. The Cellular Burning Regime in Type Ia Supernova Explosions - II. Flame Propagation into Vortical Fuel

    E-Print Network [OSTI]

    F. K. Roepke; W. Hillebrandt; J. C. Niemeyer

    2003-12-08T23:59:59.000Z

    We investigate the interaction of thermonuclear flames in Type Ia supernova explosions with vortical flows by means of numerical simulations. In our study, we focus on small scales, where the flame propagation is no longer dominated by the turbulent cascade originating from large-scale effects. Here, the flame propagation proceeds in the cellular burning regime, resulting from a balance between the Landau-Darrieus instability and its nonlinear stabilization. The interaction of a cellularly stabilized flame front with a vortical fuel flow is explored applying a variety of fuel densities and strengths of the velocity fluctuations. We find that the vortical flow can break up the cellular flame structure if it is sufficiently strong. In this case the flame structure adapts to the imprinted flow field. The transition from the cellularly stabilized front to the flame structure dominated by vortices of the flow proceeds in a smooth way. The implications of the results of our simulations for Type Ia Supernova explosion models are discussed.

  6. Delayed detonations in full-star models of Type Ia supernova explosions

    E-Print Network [OSTI]

    F. K. Roepke; J. C. Niemeyer

    2007-03-14T23:59:59.000Z

    Aims: We present the first full-star three-dimensional explosion simulations of thermonuclear supernovae including parameterized deflagration-to-detonation transitions that occur once the flame enters the distributed burning regime. Methods: Treating the propagation of both the deflagration and the detonation waves in a common front-tracking approach, the detonation is prevented from crossing ash regions. Results: Our criterion triggers the detonation wave at the outer edge of the deflagration flame and consequently it has to sweep around the complex structure and to compete with expansion. Despite the impeded detonation propagation, the obtained explosions show reasonable agreement with global quantities of observed type Ia supernovae. By igniting the flame in different numbers of kernels around the center of the exploding white dwarf, we set up three different models shifting the emphasis from the deflagration phase to the detonation phase. The resulting explosion energies and iron group element productions cover a large part of the diversity of type Ia supernovae. Conclusions: Flame-driven deflagration-to-detonation transitions, if hypothetical, remain a possibility deserving further investigation.

  7. Spectroscopic Observations and Analysis of the Unusual Type Ia SN1999ac

    SciTech Connect (OSTI)

    Garavini, G.; Aldering, G.; Amadon, A.; Amanullah, R.; Astier,P.; Balland, C.; Blanc, G.; Conley, A.; Dahlen, T.; Deustua, S.E.; Ellis,R.; Fabbro, S.; Fadeyev, V.; Fan, X.; Folatelli, G.; Frye, B.; Gates,E.L.; Gibbons, R.; Goldhaber, G.; Goldman, B.; Goobar, A.; Groom, D.E.; Haissinski, J.; Hardin, D.; Hook, I.; Howell, D.A.; Kent, S.; Kim, A.G.; Knop, R.A.; Kowalski, M.; Kuznetsova, N.; Lee, B.C.; Lidman, C.; Mendez,J.; Miller, G.J.; Moniez, M.; Mouchet, M.; Mourao, A.; Newberg, H.; Nobili, S.; Nugent, P.E.; Pain, R.; Perdereau, O.; Perlmutter, S.; Quimby, R.; Regnault, N.; Rich, J.; Richards, G.T.; Ruiz-Lapuente, P.; Schaefer, B.E.; Schahmaneche, K.; Smith, E.; Spadafora, A.L.; Stanishev,V.; Thomas, R.C.; Walton, N.A.; Wang, L.; Wood-Vasey, W.M.

    2005-07-12T23:59:59.000Z

    The authors present optical spectra of the peculiar Type Ia supernova (SN Ia) 1999ac. The data extend from -15 to +42 days with respect to B-band maximum and reveal an event that is unusual in several respects. prior to B-band maximum, the spectra resemble those of SN 1999aa, a slowly declining event, but possess stronger Si II and Ca II signatures (more characteristic of a spectroscopically normal SN). Spectra after B-band maximum appear more normal. The expansion velocities inferred from the Iron lines appear to be lower than average; whereas, the expansion velocity inferred from Calcium H and K are higher than average. The expansion velocities inferred from the Iron lines appear to be lower than average; whereas, the expansion velocity inferred from Calcium H and K are higher than average. The expansion velocities inferred from Si II are among the slowest ever observed, though SN 1999ac is not particularly dim. The analysis of the parameters v{sub 10}(Si II), R(Si II), v, and {Delta}m{sub 15} further underlines the unique characteristics of SN 1999ac. They find convincing evidence of C II {lambda}6580 in the day -15 spectrum with ejection velocity v > 16,000 km s{sup -1}, but this signature disappears by day -9. This rapid evolution at early times highlights the importance of extremely early-time spectroscopy.

  8. TYCHO SN 1572: A NAKED Ia SUPERNOVA REMNANT WITHOUT AN ASSOCIATED AMBIENT MOLECULAR CLOUD

    SciTech Connect (OSTI)

    Tian, W. W. [National Astronomical Observatories, CAS, Beijing 100012 (China); Leahy, D. A., E-mail: tww@bao.ac.cn [Department of Physics and Astronomy, University of Calgary, Calgary, Alberta T2N 1N4 (Canada)

    2011-03-10T23:59:59.000Z

    The historical supernova remnant (SNR) Tycho SN 1572 originates from the explosion of a normal Type Ia supernova that is believed to have originated from a carbon-oxygen white dwarf in a binary system. We analyze the 21 cm continuum, H I, and {sup 12}CO-line data from the Canadian Galactic Plane Survey in the direction of SN 1572 and the surrounding region. We construct H I absorption spectra to SN 1572 and three nearby compact sources. We conclude that SN 1572 has no molecular cloud interaction, which argues against previous claims that a molecular cloud is interacting with the SNR. This new result does not support a recent claim that dust, newly detected by AKARI, originates from such an SNR-cloud interaction. We suggest that the SNR has a kinematic distance of 2.5-3.0 kpc based on a nonlinear rotational curve model. Very high energy {gamma}-ray emission from the remnant has been detected by the VERITAS telescope, so our result shows that its origin should not be an SNR-cloud interaction. Both radio and X-ray observations support that SN 1572 is an isolated Type Ia SNR.

  9. Variable Selection for Modeling the Absolute Magnitude at Maximum of Type Ia Supernovae

    E-Print Network [OSTI]

    Uemura, Makoto; Kawabata, S; Ikeda, Shiro; Maeda, Keiichi

    2015-01-01T23:59:59.000Z

    We discuss what is an appropriate set of explanatory variables in order to predict the absolute magnitude at the maximum of Type Ia supernovae. In order to have a good prediction, the error for future data, which is called the "generalization error," should be small. We use cross-validation in order to control the generalization error and LASSO-type estimator in order to choose the set of variables. This approach can be used even in the case that the number of samples is smaller than the number of candidate variables. We studied the Berkeley supernova database with our approach. Candidates of the explanatory variables include normalized spectral data, variables about lines, and previously proposed flux-ratios, as well as the color and light-curve widths. As a result, we confirmed the past understanding about Type Ia supernova: i) The absolute magnitude at maximum depends on the color and light-curve width. ii) The light-curve width depends on the strength of Si II. Recent studies have suggested to add more va...

  10. Gallium surface diffusion on GaAs (001) surfaces measured by crystallization dynamics of Ga droplets

    SciTech Connect (OSTI)

    Bietti, Sergio, E-mail: sergio.bietti@mater.unimib.it; Somaschini, Claudio; Esposito, Luca; Sanguinetti, Stefano [LNESS and Dipartimento di Scienza dei Materiali, Universit di Milano Bicocca, Via Cozzi 55, I20125 Milano (Italy); Fedorov, Alexey [LNESS and CNRIFN, via Anzani 42, I-22100 Como (Italy)

    2014-09-21T23:59:59.000Z

    We present accurate measurements of Ga cation surface diffusion on GaAs surfaces. The measurement method relies on atomic force microscopy measurement of the morphology of nanodisks that evolve, under group V supply, from nanoscale group III droplets, earlier deposited on the substrate surface. The dependence of the radius of such nano-droplets on crystallization conditions gives direct access to Ga diffusion length. We found an activation energy for Ga on GaAs(001) diffusion E{sub A}=1.310.15 eV, a diffusivity prefactor of D{sub 0}?=?0.53(2.11) cm{sup 2} s{sup ?1} that we compare with the values present in literature. The obtained results permit to better understand the fundamental physics governing the motion of group III adatoms on IIIV crystal surfaces and the fabrication of designable nanostructures.

  11. Lattice-matched epitaxial GaInAsSb/GaSb thermophotovoltaic devices

    SciTech Connect (OSTI)

    Wang, C.A.; Choi, H.K.; Turner, G.W.; Spears, D.L.; Manfra, M.J. [Massachusetts Inst. of Tech., Lexington, MA (United States). Lincoln Lab.; Charache, G.W. [Lockheed Martin, Inc., Schenectady, NY (United States)

    1997-05-01T23:59:59.000Z

    The materials development of Ga{sub 1{minus}x}In{sub x}As{sub y}Sb{sub 1{minus}y} alloys for lattice-matched thermophotovoltaic (TPV) devices is reported. Epilayers with cutoff wavelength 2--2.4 {micro}m at room temperature and lattice-matched to GaSb substrates were grown by both low-pressure organometallic vapor phase epitaxy and molecular beam epitaxy. These layers exhibit high optical and structural quality. For demonstrating lattice-matched thermophotovoltaic devices, p- and n-type doping studies were performed. Several TPV device structures were investigated, with variations in the base/emitter thicknesses and the incorporation of a high bandgap GaSb or AlGaAsSb window layer. Significant improvement in the external quantum efficiency is observed for devices with an AlGaAsSb window layer compared to those without one.

  12. Green cubic GaInN/GaN light-emitting diode on microstructured silicon (100)

    SciTech Connect (OSTI)

    Stark, Christoph J. M.; Detchprohm, Theeradetch; Wetzel, Christian, E-mail: wetzel@ieee.org [Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States) [Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States); Future Chips Constellation, Rensselaer Polytechnic Institute, 110 8th Street, Troy, New York 12180 (United States); Lee, S. C.; Brueck, S. R. J. [Department of Electrical and Computer Engineering and Center for High Technology Materials, University of New Mexico, 1313 Goddard SE, Albuquerque, New Mexico 87106 (United States)] [Department of Electrical and Computer Engineering and Center for High Technology Materials, University of New Mexico, 1313 Goddard SE, Albuquerque, New Mexico 87106 (United States); Jiang, Y.-B. [Department of Earth and Planetary Science, University of New Mexico, Albuquerque, New Mexico 87131 (United States)] [Department of Earth and Planetary Science, University of New Mexico, Albuquerque, New Mexico 87131 (United States)

    2013-12-02T23:59:59.000Z

    GaInN/GaN light-emitting diodes free of piezoelectric polarization were prepared on standard electronic-grade Si(100) substrates. Micro-stripes of GaN and GaInN/GaN quantum wells in the cubic crystal structure were grown on intersecting (111) planes of microscale V-grooved Si in metal-organic vapor phase epitaxy, covering over 50% of the wafer surface area. Crystal phases were identified in electron back-scattering diffraction. A cross-sectional analysis reveals a cubic structure virtually free of line defects. Electroluminescence over 20 to 100??A is found fixed at 487?nm (peak), 516?nm (dominant). Such structures therefore should allow higher efficiency, wavelength-stable light emitters throughout the visible spectrum.

  13. Large internal dipole moment in InGaN/GaN quantum dots Irina A. Ostapenko, Gerald Hnig, Christian Kindel, Sven Rodt, Andr Strittmatter et al.

    E-Print Network [OSTI]

    Nabben, Reinhard

    Large internal dipole moment in InGaN/GaN quantum dots Irina A. Ostapenko, Gerald Hnig, Christian transitions in wurtzite InGaN/GaN coupled quantum dot nanowire heterostructures with polarization internal dipole moment in InGaN/GaN quantum dots Irina A. Ostapenko,a Gerald Hnig, Christian Kindel, Sven

  14. Investigation of large Stark shifts in InGaN/GaN multiple quantum wells Guibao Xu, Guan Sun, Yujie J. Ding, Hongping Zhao, Guangyu Liu et al.

    E-Print Network [OSTI]

    Gilchrist, James F.

    Investigation of large Stark shifts in InGaN/GaN multiple quantum wells Guibao Xu, Guan Sun, Yujie overgrowth on residual strain and In incorporation in a-plane InGaN/GaN quantum wells on r- sapphire substrates J. Appl. Phys. 113, 023506 (2013) Anisotropic lattice relaxation in non-c-plane InGaN/GaN multiple

  15. Quantum confinement in GaP nanoclusters

    SciTech Connect (OSTI)

    Laurich, B.K.; Smith, D.C.; Healy, M.D.

    1994-06-01T23:59:59.000Z

    We have prepared GaP and GaAs nanoclusters from organometallic condensation reactions of E[Si(ChH{sub 3})3]3 (E = P, As) and GaCl{sub 3}. The size of the as synthesized clusters is 10 {Angstrom} to 15 {Angstrom}. Larger clusters of 20 {Angstrom} to 30 {Angstrom} size were obtained by thermal annealing of the as grown material. X-ray diffraction and transmission electron microscopy confirm the high crystalline quality. A lattice contraction of 6.7% could be seen for 10 {Angstrom} sized GaAs clusters. The clusters are nearly spherical in shape. Optical absorption spectra show a distinct line which can be assigned to the fundamental transition of the quantum confined electronic state. The measured blue shift, with respect to the GaP bulk absorption edge is 0.53 eV. As the cluster is smaller than the exciton radius, we can calculate the cluster size from this blue shift and obtain 20.2 {Angstrom}, consistent with the results from X-ray diffraction of 19.5 {Angstrom} for the same sample.

  16. Nebular spectra and abundance tomography of the type Ia supernova SN 2011fe: a normal SN Ia with a stable Fe core

    E-Print Network [OSTI]

    Mazzali, P A; Filippenko, A V; Garnavich, P M; Clubb, K I; Maguire, K; Pan, Y -C; Shappee, R; Silverman, J M; Benetti, S; Hachinger, S; Nomoto, K; Pian, E

    2015-01-01T23:59:59.000Z

    A series of optical and one near-infrared nebular spectra covering the first year of the Type Ia supernova SN 2011fe are presented and modelled. The density profile that proved best for the early optical/ultraviolet spectra, "rho-11fe", was extended to lower velocities to include the regions that emit at nebular epochs. Model rho-11fe is intermediate between the fast deflagration model W7 and a low-energy delayed-detonation. Good fits to the nebular spectra are obtained if the innermost ejecta are dominated by neutron-rich, stable Fe-group species, which contribute to cooling but not to heating. The correct thermal balance can thus be reached for the strongest [FeII] and [FeIII] lines to be reproduced with the observed ratio. The 56Ni mass thus obtained is 0.47 +/- 0.05 Mo. The bulk of 56Ni has an outermost velocity of ~8500 km/s. The mass of stable iron is 0.23 +/- 0.03 Mo. Stable Ni has low abundance, ~10^{-2} Mo. This is sufficient to reproduce an observed emission line near 7400 A. A sub-Chandrasekhar exp...

  17. A Generalized {ital K} Correction for Type Ia Supernovae: Comparing {ital R}-band Photometry Beyond {ital z=9.2} with B,V, and {ital R}-band Nearby Photometry

    E-Print Network [OSTI]

    Goodbar, Ariel

    2008-01-01T23:59:59.000Z

    spectroscopically peculiar supernovae, and to search for anyK Correction for Type Ia Supernovae: Comparing R-bandK Correction for Type Ia Supernovae: Comparing R-band

  18. UID-GaN doping1016 cm-3 2 m 5 m2 m

    E-Print Network [OSTI]

    Paris-Sud XI, Universit de

    2 m Drain Silicon UID-GaN doping1016 cm-3 1.1 m 2 m GateSource 2 m 5 m2 m AirAir Al0.25GaN doping1015 cm-3 30 nm Drain Silicon UID-GaN P-GaNSource AirAir AlxGaN Drain Silicon UID-GaN GateSource AirAir AlxGaN Gate (a) (b) (c) Drain Silicon UID-GaN P-GaNSource AirAir AlxGaN Gate (d) P-GaN P-GaN 30

  19. Carrier capture dynamics of single InGaAs/GaAs quantum-dot layers

    SciTech Connect (OSTI)

    Chauhan, K. N.; Riffe, D. M.; Everett, E. A.; Kim, D. J.; Yang, H. [Physics Department, Utah State University, Logan, Utah 84322-4415 (United States)] [Physics Department, Utah State University, Logan, Utah 84322-4415 (United States); Shen, F. K. [Center for Surface Analysis and Applications, Utah State University, Logan, Utah 84322-4415 (United States)] [Center for Surface Analysis and Applications, Utah State University, Logan, Utah 84322-4415 (United States)

    2013-05-28T23:59:59.000Z

    Using 800 nm, 25-fs pulses from a mode locked Ti:Al{sub 2}O{sub 3} laser, we have measured the ultrafast optical reflectivity of MBE-grown, single-layer In{sub 0.4}Ga{sub 0.6}As/GaAs quantum-dot (QD) samples. The QDs are formed via two-stage Stranski-Krastanov growth: following initial InGaAs deposition at a relatively low temperature, self assembly of the QDs occurs during a subsequent higher temperature anneal. The capture times for free carriers excited in the surrounding GaAs (barrier layer) are as short as 140 fs, indicating capture efficiencies for the InGaAs quantum layer approaching 1. The capture rates are positively correlated with initial InGaAs thickness and annealing temperature. With increasing excited carrier density, the capture rate decreases; this slowing of the dynamics is attributed to Pauli state blocking within the InGaAs quantum layer.

  20. Epitaxial GaN films by hyperthermal ion-beam nitridation of Ga droplets

    SciTech Connect (OSTI)

    Gerlach, J. W.; Ivanov, T.; Neumann, L.; Hoeche, Th.; Hirsch, D.; Rauschenbach, B. [Leibniz-Institut fuer Oberflaechenmodifizierung (IOM), D-04318 Leipzig (Germany)

    2012-06-01T23:59:59.000Z

    Epitaxial GaN film formation on bare 6H-SiC(0001) substrates via the process of transformation of Ga droplets into a thin GaN film by applying hyperthermal nitrogen ions is investigated. Pre-deposited Ga atoms in well defined amounts form large droplets on the substrate surface which are subsequently nitridated at a substrate temperature of 630 Degree-Sign C by a low-energy nitrogen ion beam from a constricted glow-discharge ion source. The Ga deposition and ion-beam nitridation process steps are monitored in situ by reflection high-energy electron diffraction. Ex situ characterization by x-ray diffraction and reflectivity techniques, Rutherford backscattering spectrometry, and electron microscopy shows that the thickness of the resulting GaN films depends on the various amounts of pre-deposited gallium. The films are epitaxial to the substrate, exhibit a mosaic like, smooth surface topography and consist of coalesced large domains of low defect density. Possible transport mechanisms of reactive nitrogen species during hyperthermal nitridation are discussed and the formation of GaN films by an ion-beam assisted process is explained.

  1. GaAs photoconductive semiconductor switch

    DOE Patents [OSTI]

    Loubriel, G.M.; Baca, A.G.; Zutavern, F.J.

    1998-09-08T23:59:59.000Z

    A high gain, optically triggered, photoconductive semiconductor switch (PCSS) implemented in GaAs as a reverse-biased pin structure with a passivation layer above the intrinsic GaAs substrate in the gap between the two electrodes of the device is disclosed. The reverse-biased configuration in combination with the addition of the passivation layer greatly reduces surface current leakage that has been a problem for prior PCSS devices and enables employment of the much less expensive and more reliable DC charging systems instead of the pulsed charging systems that needed to be used with prior PCSS devices. 5 figs.

  2. GaAs photoconductive semiconductor switch

    DOE Patents [OSTI]

    Loubriel, Guillermo M. (Sandia Park, NM); Baca, Albert G. (Albuquerque, NM); Zutavern, Fred J. (Albuquerque, NM)

    1998-01-01T23:59:59.000Z

    A high gain, optically triggered, photoconductive semiconductor switch (PCSS) implemented in GaAs as a reverse-biased pin structure with a passivation layer above the intrinsic GaAs substrate in the gap between the two electrodes of the device. The reverse-biased configuration in combination with the addition of the passivation layer greatly reduces surface current leakage that has been a problem for prior PCSS devices and enables employment of the much less expensive and more reliable DC charging systems instead of the pulsed charging systems that needed to be used with prior PCSS devices.

  3. GaN: Defect and Device Issues

    SciTech Connect (OSTI)

    Pearton, S.J.; Ren, F.; Shul, R.J.; Zolper, J.C.

    1998-11-09T23:59:59.000Z

    The role of extended and point defects, and key impurities such as C, O and H, on the electrical and optical properties of GaN is reviewed. Recent progress in the development of high reliability contacts, thermal processing, dry and wet etching techniques, implantation doping and isolation and gate insulator technology is detailed. Finally, the performance of GaN-based electronic and photonic devices such as field effect transistors, UV detectors, laser diodes and light-emitting diodes is covered, along with the influence of process-induced or grown-in defects and impurities on the device physics.

  4. JOURNAL OF ~IA'I'IIE~IATICAI. ANALYSIS ASD APPI.ICATIOXS 74, 456-463 (1980) Some Comments on Rota's Umbra1 Calculus

    E-Print Network [OSTI]

    Zeilberger, Doron

    's Umbra1 Calculus L>OUOS zEILRERGER* Sclzool qf Mat/mu&s, Georgia Institute of Teclrnolo~y, Atlanta, Georgia 30332 Sz+bmitted by G.-C. Rota Rota's Umbra1 Calculus is put in the context of general I.e., Q = .YD.P'. `TIus, the operator 9 is umbra1 if and on:! if .YIW 1 is a delta operator and (I), (2

  5. LATE-TIME SPECTRAL OBSERVATIONS OF THE STRONGLY INTERACTING TYPE Ia SUPERNOVA PTF11kx

    SciTech Connect (OSTI)

    Silverman, Jeffrey M. [Department of Astronomy, University of Texas, Austin, TX 78712-0259 (United States); Nugent, Peter E.; Filippenko, Alexei V.; Cenko, S. Bradley [Department of Astronomy, University of California, Berkeley, CA 94720-3411 (United States); Gal-Yam, Avishay [Benoziyo Center for Astrophysics, The Weizmann Institute of Science, Rehovot 76100 (Israel); Sullivan, Mark [School of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ (United Kingdom); Howell, D. Andrew [Las Cumbres Observatory Global Telescope Network, Goleta, CA 93117 (United States); Pan, Yen-Chen; Hook, Isobel M., E-mail: jsilverman@astro.as.utexas.edu [Department of Physics (Astrophysics), University of Oxford, Keble Road, Oxford OX1 3RH (United Kingdom)

    2013-08-01T23:59:59.000Z

    PTF11kx was a Type Ia supernova (SN Ia) that showed time-variable absorption features, including saturated Ca II H and K lines that weakened and eventually went into emission. The strength of the emission component of H{alpha} gradually increased, implying that the SN was undergoing significant interaction with its circumstellar medium (CSM). These features, and many others, were blueshifted slightly and showed a P-Cygni profile, likely indicating that the CSM was directly related to, and probably previously ejected by, the progenitor system itself. These and other observations led Dilday et al. to conclude that PTF11kx came from a symbiotic nova progenitor like RS Oph. In this work we extend the spectral coverage of PTF11kx to 124-680 rest-frame days past maximum brightness. The late-time spectra of PTF11kx are dominated by H{alpha} emission (with widths of full width at half-maximum intensity Almost-Equal-To 2000 km s{sup -1}), strong Ca II emission features ({approx}10,000 km s{sup -1} wide), and a blue 'quasi-continuum' due to many overlapping narrow lines of Fe II. Emission from oxygen, He I, and Balmer lines higher than H{alpha} is weak or completely absent at all epochs, leading to large observed H{alpha}/H{beta} intensity ratios. The H{alpha} emission appears to increase in strength with time for {approx}1 yr, but it subsequently decreases significantly along with the Ca II emission. Our latest spectrum also indicates the possibility of newly formed dust in the system as evidenced by a slight decrease in the red wing of H{alpha}. During the same epochs, multiple narrow emission features from the CSM temporally vary in strength. The weakening of the H{alpha} and Ca II emission at late times is possible evidence that the SN ejecta have overtaken the majority of the CSM and agrees with models of other strongly interacting SNe Ia. The varying narrow emission features, on the other hand, may indicate that the CSM is clumpy or consists of multiple thin shells.

  6. High-temperature molecular beam epitaxial growth of AlGaN/GaN on GaN templates with reduced interface impurity levels

    SciTech Connect (OSTI)

    Koblmueller, G. [Department of Materials, University of California, Santa Barbara, California 93106 (United States); Walter Schottky Institut, Technische Universitaet Muenchen, D-85748 Garching (Germany); Chu, R. M.; Raman, A.; Mishra, U. K. [Department of Electrical and Computer Engineering, University of California, Santa Barbara, California 93106 (United States); Speck, J. S. [Department of Materials, University of California, Santa Barbara, California 93106 (United States)

    2010-02-15T23:59:59.000Z

    We present combined in situ thermal cleaning and intentional doping strategies near the substrate regrowth interface to produce high-quality AlGaN/GaN high electron mobility transistors on semi-insulating (0001) GaN templates with low interfacial impurity concentrations and low buffer leakage. By exposing the GaN templates to an optimized thermal dissociation step in the plasma-assisted molecular beam epitaxy environment, oxygen, carbon, and, to lesser extent, Si impurities were effectively removed from the regrowth interface under preservation of good interface quality. Residual Si was further compensated by C-doped GaN via CBr{sub 4} to yield highly resistive GaN buffer layers. Improved N-rich growth conditions at high growth temperatures were then utilized for subsequent growth of the AlGaN/GaN device structure, yielding smooth surface morphologies and low residual oxygen concentration with large insensitivity to the (Al+Ga)N flux ratio. Room temperature electron mobilities of the two-dimensional electron gas at the AlGaN/GaN interface exceeded >1750 cm{sup 2}/V s and the dc drain current reached {approx}1.1 A/mm at a +1 V bias, demonstrating the effectiveness of the applied methods.

  7. Defect studies in low-temperature-grown GaAs

    SciTech Connect (OSTI)

    Bliss, D.E.

    1992-11-01T23:59:59.000Z

    High content of excess As is incorporated in GaAs grown by low-temperature molecular-beam-epitaxy (LTMBE). The excess As exists primarily as As antisite defects AsGa and a lesser extent of gallium vacancies V[sub Ga]. The neutral AsGa-related defects were measured by infrared absorption at 1[mu]m. Gallium vacancies, V[sub Ga], was investigated by slow positron annihilation. Dependence of defect contents on doping was studied by Si and Be dopants. No free carriers are generated by n-type or p-type doping up to 10[sup 19] cm[sup [minus]3] Si or Be. Raman data indicate Be occupies Ga substitutional sites but Si atom is not substitutional. Si induces more As[sub Ga] in the layer. As As[sub Ga] increases, photoquenchable As[sub Ga] decreases. Fraction of photoquenchable defects correlates to defects within 3 nearest neighbor separations disrupting the metastability. Annealing reduces neutral As[sub Ga] content around 500C, similar to irradiation damaged and plastically deformed Ga[sub As], as opposed to bulk grown GaAs in which As[sub Ga]-related defects are stable up to 1100C. The lower temperature defect removal is due to V[sub Ga] enhanced diffusion of As[sub Ga] to As precipitates. The supersaturated V[sub GA] and also decreases during annealing. Annealing kinetics for As[sub Ga]-related defects gives 2.0 [plus minus] 0.3 eV and 1.5 [plus minus] 0.3 eV migration enthalpies for the As[sub Ga] and V[sub Ga]. This represents the difference between Ga and As atoms hopping into the vacancy. The non-photoquenchable As[sub Ga]-related defects anneal with an activation energy of 1.1 [plus minus] 0.3eV. Be acceptors can be activated by 800C annealing. Temperature difference between defect annealing and Be activation formation of As[sub Ga]-Be[sub Ga] pairs. Si donors can only be partially activated.

  8. PHYSICAL REVIEW B 85, 045319 (2012) Photoluminescence from In0.5Ga0.5As/GaP quantum dots coupled to photonic crystal cavities

    E-Print Network [OSTI]

    Vuckovic, Jelena

    2012-01-01T23:59:59.000Z

    in materials systems, including InP/InGaP,69 InP/GaP,10,11 InP/AlGaInP,12,13 GaInP/GaP,14 InAs/GaP,15 and Al have been observed only in the InP/InGaP and InP/AlGaInP systems. GaP-based materials, by contrastP compared to InGaP is preferable for on-chip frequency downconversion to telecom wavelengths. Recently,17

  9. Optical spectroscopy of quantum confined states in GaAs/AlGaAs quantum well tubes

    SciTech Connect (OSTI)

    Shi, Teng; Fickenscher, Melodie; Smith, Leigh; Jackson, Howard [Department of Physics, University of Cincinnati, Cincinnati, OH 45221 (United States); Yarrison-Rice, Jan [Department of Physics, Miami University, Oxford, OH 45056 (United States); Gao, Qiang; Tan, Hoe; Jagadish, Chennupati [Department of Electronic Materials and Engineering, Australian National University, Canberra, ACT 0200 (Australia); Etheridge, Joanne [Monash Centre for Electron Microscopy, Monash University, Victoria, 3800 (Australia); Wong, Bryan M. [Materials Chemistry Department, Sandia National Laboratories, Livermore, CA 94551 (United States)

    2013-12-04T23:59:59.000Z

    We have investigated the quantum confinement of electronic states in GaAs/Al{sub x}Ga{sub 1?x}As nanowire heterostructures which contain radial GaAs quantum wells of either 4nm or 8nm. Photoluminescence and photoluminescence excitation spectroscopy are performed on single nanowires. We observed emission and excitation of electron and hole confined states. Numerical calculations of the quantum confined states using the detailed structural information on the quantum well tubes show excellent agreement with these optical results.

  10. Strain-induced fundamental optical transition in (In,Ga)As/GaP quantum dots

    SciTech Connect (OSTI)

    Robert, C., E-mail: cedric.robert@insa-rennes.fr, E-mail: cedric.robert@tyndall.ie; Pedesseau, L.; Cornet, C.; Jancu, J.-M.; Even, J.; Durand, O. [Universit Europenne de Bretagne, INSA Rennes, France and CNRS, UMR 6082 Foton, 20 Avenue des Buttes de Cosmes, 35708 Rennes (France)] [Universit Europenne de Bretagne, INSA Rennes, France and CNRS, UMR 6082 Foton, 20 Avenue des Buttes de Cosmes, 35708 Rennes (France); Nestoklon, M. O. [Ioffe Physico-Technical Institute, Russian Academy of Sciences, 194021 St. Petersburg (Russian Federation)] [Ioffe Physico-Technical Institute, Russian Academy of Sciences, 194021 St. Petersburg (Russian Federation); Pereira da Silva, K. [ICMAB-CSIC, Campus UAB, 08193 Bellaterra (Spain) [ICMAB-CSIC, Campus UAB, 08193 Bellaterra (Spain); Departamento de Fsica, Universidade Federal do Cear, P.O. Box 6030, FortalezaCE, 60455-970 (Brazil); Alonso, M. I. [ICMAB-CSIC, Campus UAB, 08193 Bellaterra (Spain)] [ICMAB-CSIC, Campus UAB, 08193 Bellaterra (Spain); Goi, A. R. [ICMAB-CSIC, Campus UAB, 08193 Bellaterra (Spain) [ICMAB-CSIC, Campus UAB, 08193 Bellaterra (Spain); ICREA, Passeig Llus Companys 23, 08010 Barcelona (Spain); Turban, P. [Equipe de Physique des Surfaces et Interfaces, Institut de Physique de Rennes UMR UR1-CNRS 6251, Universit de Rennes 1, F-35042 Rennes Cedex (France)] [Equipe de Physique des Surfaces et Interfaces, Institut de Physique de Rennes UMR UR1-CNRS 6251, Universit de Rennes 1, F-35042 Rennes Cedex (France)

    2014-01-06T23:59:59.000Z

    The nature of the ground optical transition in an (In,Ga)As/GaP quantum dot is thoroughly investigated through a million atoms supercell tight-binding simulation. Precise quantum dot morphology is deduced from previously reported scanning-tunneling-microscopy images. The strain field is calculated with the valence force field method and has a strong influence on the confinement potentials, principally, for the conduction band states. Indeed, the wavefunction of the ground electron state is spatially confined in the GaP matrix, close to the dot apex, in a large tensile strain region, having mainly Xz character. Photoluminescence experiments under hydrostatic pressure strongly support the theoretical conclusions.

  11. Midinfrared intersubband absorption in GaN/AlGaN superlattices on Si(111) templates

    SciTech Connect (OSTI)

    Kandaswamy, P. K.; Monroy, E. [CEA/CNRS group 'Nanophysique et semiconducteurs', INAC/SP2M/NPSC, CEA-Grenoble, 17 rue des Martyrs, 38054 Grenoble Cedex 9 (France); Machhadani, H.; Sakr, S.; Tchernycheva, M.; Julien, F. H. [Photis, Institut d'Electronique Fondamentale, Universite Paris-Sud, 91405 Orsay Cedex (France); Bougerol, C. [CEA/CNRS group 'Nanophysique et semiconducteurs', Institut Neel, 25 rue des Martyrs, 38042 Grenoble Cedex 9 (France)

    2009-10-05T23:59:59.000Z

    We report on the observation of midinfrared intersubband absorption in Si-doped GaN/AlGaN superlattices grown by plasma-assisted molecular-beam epitaxy on semi-insulating GaN-on-Si(111) templates. TM-polarized absorption attributed to transition between the first two electronic levels in the quantum wells peaked in the range from 2 to 9 {mu}m. The relative spectral width remains around 20% in the whole midinfrared spectral range. Doping is predicted to have a large influence on the intersubband absorption energy due to screening of polarization-induced internal electric field.

  12. Late-Time Photometry of Type Ia Supernova SN2012cg Reveals the Radioactive Decay of $^{57}$Co

    E-Print Network [OSTI]

    Graur, Or; Shara, Michael M; Riess, Adam G

    2015-01-01T23:59:59.000Z

    Seitenzahl et al. (2009) have predicted that $\\sim 3$ years after its explosion, the light we receive from a Type Ia supernova will come mostly from reprocessing of electrons and X-rays emitted by the radioactive decay chain $^{57}{\\rm Co}~\\to~^{57}{\\rm Fe}$, instead of positrons from the decay chain $^{56}{\\rm Co}~\\to~^{56}{\\rm Fe}$ that dominates the supernova light at earlier times. Using the Hubble Space Telescope, we followed the light curve of the Type Ia supernova SN2012cg out to $1055$ days after maximum light. Our measurements are consistent with the light curves predicted by the contribution of energy from the reprocessing of electrons and X-rays emitted by the decay of $^{57}$Co. This provides conclusive evidence that $^{57}$Co is produced in Type Ia supernova explosions. The ratio of luminosities produced by the decays of $^{57}$Co and $^{56}$Co, a strong constraint on any Type Ia supernova explosion model, is in the range $(0.4$ - $8.5)\\times10^{-3}$.

  13. Utilizing the Updated Gamma-Ray Bursts and Type Ia Supernovae to Constrain the Cardassian Expansion Model and Dark Energy

    E-Print Network [OSTI]

    Wei, Jun-Jie; Wu, Xue-Feng

    2015-01-01T23:59:59.000Z

    We update gamma-ray burst (GRB) luminosity relations among certain spectral and light-curve features with 139 GRBs. The distance modulus of 82 GRBs at $z>1.4$ can be calibrated with the sample at $z\\leq1.4$ by using the cubic spline interpolation method from the Union2.1 Type Ia supernovae (SNe Ia) set. We investigate the joint constraints on the Cardassian expansion model and dark energy with 580 Union2.1 SNe Ia sample ($z<1.4$) and 82 calibrated GRBs data ($1.4Ia significantly improves the constrain on $\\Omega_{m}-\\Omega_{\\Lambda}$ plane. In the Cardassian expansion model, the best fit is $\\Omega_{m}= 0.24_{-0.15}^{+0.15}$ and $n=0.16_{-0.52}^{+0.30}$ $(1\\sigma)$, which is consistent with the $\\Lambda$CDM cosmology $(n=0)$ in the $1\\sigma$ confidence region. We also discuss two dark energy models in which the equation of state $w(z)$ is parametrized as $w(z)=w_{0}$ and $w(z)=w_{0}+w_{1}z/(1+z)$, respectively. Based on o...

  14. RESULTS OF THE LICK OBSERVATORY SUPERNOVA SEARCH FOLLOW-UP PHOTOMETRY PROGRAM: BVRI LIGHT CURVES OF 165 TYPE Ia SUPERNOVAE

    SciTech Connect (OSTI)

    Ganeshalingam, Mohan; Li Weidong; Filippenko, Alexei V.; Anderson, Carmen; Foster, Griffin; Griffith, Christopher V.; Joubert, Niels; Leja, Joel; Macomber, Brent; Pritchard, Tyler; Thrasher, Patrick; Winslow, Dustin [Department of Astronomy, University of California, Berkeley, CA 94720-3411 (United States); Gates, Elinor L.; Grigsby, Bryant J.; Lowe, Thomas B. [Lick Observatory, P.O. Box 85, Mount Hamilton, CA 95140 (United States)

    2010-10-15T23:59:59.000Z

    We present BVRI light curves of 165 Type Ia supernovae (SNe Ia) from the Lick Observatory Supernova Search follow-up photometry program from 1998 through 2008. Our light curves are typically well sampled (cadence of 3-4 days) with an average of 21 photometry epochs. We describe our monitoring campaign and the photometry reduction pipeline that we have developed. Comparing our data set to that of Hicken et al., with which we have 69 overlapping supernovae (SNe), we find that as an ensemble the photometry is consistent, with only small overall systematic differences, although individual SNe may differ by as much as 0.1 mag, and occasionally even more. Such disagreement in specific cases can have significant implications for combining future large data sets. We present an analysis of our light curves which includes template fits of light-curve shape parameters useful for calibrating SNe Ia as distance indicators. Assuming the B - V color of SNe Ia at 35 days past maximum light can be presented as the convolution of an intrinsic Gaussian component and a decaying exponential attributed to host-galaxy reddening, we derive an intrinsic scatter of {sigma} = 0.076 {+-} 0.019 mag, consistent with the Lira-Phillips law. This is the first of two papers, the second of which will present a cosmological analysis of the data presented herein.

  15. CS3600 Lab Manual CyberCIEGE is an information assurance (IA) training tool that illustrates computer and

    E-Print Network [OSTI]

    CS3600 Lab Manual Lab SSL CyberCIEGE is an information assurance (IA) training tool. The CyberCIEGE SSL scenario illustrates the use of SSL to authenticate the identity of web servers. This scenario explores the following concepts: SSL is a means of authenticating a server (e.g., a web server

  16. Restframe I-band Hubble diagram for type Ia supernovae up to redshift z ~; 0.5

    E-Print Network [OSTI]

    2005-01-01T23:59:59.000Z

    up to redshift z ? 0.5 ? S. Nobili 1,2 , R. Amanullah 2 , G.up to redshift z ? 0.5 Filippenko, A.V. , Richmond, M.W. ,Ia supernovae up to redshift z ? 0.5 ported by cross-cutting

  17. Small-scale Interaction of Turbulence with Thermonuclear Flames in Type Ia Supernovae

    E-Print Network [OSTI]

    J. C. Niemeyer; W. K. Bushe; G. R. Ruetsch

    1999-05-07T23:59:59.000Z

    Microscopic turbulence-flame interactions of thermonuclear fusion flames occuring in Type Ia Supernovae were studied by means of incompressible direct numerical simulations with a highly simplified flame description. The flame is treated as a single diffusive scalar field with a nonlinear source term. It is characterized by its Prandtl number, Pr << 1, and laminar flame speed, S_L. We find that if S_L ~ u', where u' is the rms amplitude of turbulent velocity fluctuations, the local flame propagation speed does not significantly deviate from S_L even in the presence of velocity fluctuations on scales below the laminar flame thickness. This result is interpreted in the context of subgrid-scale modeling of supernova explosions and the mechanism for deflagration-detonation-transitions.

  18. Do Type-Ia Supernovae Constrain the Total Equation of State?

    E-Print Network [OSTI]

    William Komp

    2007-02-01T23:59:59.000Z

    In this paper, we consider a couple of alternative dark energy models using the total equation of state of the cosmological fluid, $\\wt$. These models are fit to the recent type-Ia supernovae data and are compared to previously considered models. The first model is based on the hyperbolic tangent and provides a good estimate of the rate of the transition to dark energy domination. The second model is a cubic spline model. This model demonstrates and quantifies the non-monotonicity in the total equation of state coming from the supernovae observations. At present, the supernovae observations indicate significance to non-monotonically decreasing dark energy. We derive constraints on the spline paramters and compare and constrast the results to the Cosmological Constant dark energy model. Both the hyperbolic and splines models indicate that a precise physical notion of dark enegy is a potentially ever more mysterious quantity?

  19. Type Ia Supernova Intrinsic Magnitude Dispersion and the Fitting of Cosmological Parameters

    SciTech Connect (OSTI)

    Kim, Alex G

    2010-12-10T23:59:59.000Z

    I present an analysis for fitting cosmological parameters from a Hubble Diagram of a standard candle with unknown intrinsic magnitude dispersion. The dispersion is determined from the data themselves, simultaneously with the cosmological parameters. This contrasts with the strategies used to date. The advantages of the presented analysis are that it is done in a single fit (it is not iterative), it provides a statistically founded and unbiased estimate of the intrinsic dispersion, and its cosmological-parameter uncertainties account for the intrinsic dispersion uncertainty. Applied to Type Ia supernovae, my strategy provides a statistical measure to test for sub-types and assess the significance of any magnitude corrections applied to the calibrated candle. Parameter bias and differences between likelihood distributions produced by the presented and currently-used fitters are negligibly small for existing and projected supernova data sets.

  20. Turbulence in a three-dimensional deflagration model for Type Ia supernovae: I. Scaling properties

    E-Print Network [OSTI]

    Ciaraldi-Schoolmann, F; Niemeyer, J C; Roepke, F K; Hillebrandt, W

    2009-01-01T23:59:59.000Z

    We analyze the statistical properties of the turbulent velocity field in the deflagration model for Type Ia supernovae. In particular, we consider the question of whether turbulence is isotropic and consistent with the Kolmogorov theory at small length scales. Using numerical data from a high-resolution simulation of a thermonuclear supernova explosion, spectra of the turbulence energy and velocity structure functions are computed. We show that the turbulent velocity field is isotropic at small length scales and follows a scaling law that is consistent with the Kolmogorov theory until most of the nuclear fuel is burned. At length scales greater than a certain characteristic scale, turbulence becomes anisotropic. Here, the radial velocity fluctuations follow the scaling law of the Rayleigh-Taylor instability, whereas the angular component still obeys Kolmogorov scaling. In the late phase of the explosion, this characteristic scale drops below the numerical resolution of the simulation. The analysis confirms th...

  1. Measurements of the Rate of Type Ia Supernovae at Redshift z < ~0.3 from the SDSS-II Supernova Survey

    SciTech Connect (OSTI)

    Dilday, Benjamin; /Rutgers U., Piscataway /Chicago U. /KICP, Chicago; Smith, Mathew; /Cape Town U., Dept. Math. /Portsmouth U.; Bassett, Bruce; /Cape Town U., Dept. Math. /South African Astron. Observ.; Becker, Andrew; /Washington U., Seattle, Astron. Dept.; Bender, Ralf; /Munich, Tech. U. /Munich U. Observ.; Castander, Francisco; /Barcelona, IEEC; Cinabro, David; /Wayne State U.; Filippenko, Alexei V.; /UC, Berkeley; Frieman, Joshua A.; /Chicago U. /Fermilab; Galbany, Lluis; /Barcelona, IFAE; Garnavich, Peter M.; /Notre Dame U. /Stockholm U., OKC /Stockholm U.

    2010-01-01T23:59:59.000Z

    We present a measurement of the volumetric Type Ia supernova (SN Ia) rate based on data from the Sloan Digital Sky Survey II (SDSS-II) Supernova Survey. The adopted sample of supernovae (SNe) includes 516 SNe Ia at redshift z {approx}< 0.3, of which 270 (52%) are spectroscopically identified as SNe Ia. The remaining 246 SNe Ia were identified through their light curves; 113 of these objects have spectroscopic redshifts from spectra of their host galaxy, and 133 have photometric redshifts estimated from the SN light curves. Based on consideration of 87 spectroscopically confirmed non-Ia SNe discovered by the SDSS-II SN Survey, we estimate that 2.04{sub -0.95}{sup +1.61}% of the photometric SNe Ia may be misidentified. The sample of SNe Ia used in this measurement represents an order of magnitude increase in the statistics for SN Ia rate measurements in the redshift range covered by the SDSS-II Supernova Survey. If we assume a SN Ia rate that is constant at low redshift (z < 0.15), then the SN observations can be used to infer a value of the SN rate of r{sub V} = (2.69{sub -0.30-0.01}{sup +0.34+0.21}) x 10{sup -5} SNe yr{sup -1} Mpc{sup -3} (H{sub 0}/(70 km s{sup -1} Mpc{sup -1})){sup 3} at a mean redshift of {approx} 0.12, based on 79 SNe Ia of which 72 are spectroscopically confirmed. However, the large sample of SNe Ia included in this study allows us to place constraints on the redshift dependence of the SN Ia rate based on the SDSS-II Supernova Survey data alone. Fitting a power-law model of the SN rate evolution, r{sub V} (z) = A{sub p} x ((1+z)/(1+z{sub 0})){sup {nu}}, over the redshift range 0.0 < z < 0.3 with z{sub 0} = 0.21, results in A{sub p} = (3.43{sub -0.15}{sup +0.15}) x 10{sup -5} SNe yr{sup -1} Mpc{sup -3} (H{sub 0}/(70 km s{sup -1} Mpc{sup -1})){sup 3} and {nu} = 2.04{sub -0.89}{sup +0.90}.

  2. Energy absorption in Ni-Mn-Ga/ polymer composites

    E-Print Network [OSTI]

    Feuchtwanger, Jorge

    2006-01-01T23:59:59.000Z

    In recent years Ni-Mn-Ga has attracted considerable attention as a new kind of actuator material. Off-stoichiometric single crystals of Ni2MnGa can regularly exhibit 6% strain in tetragonal martensites and orthorhombic ...

  3. Degradation mechanisms of GaN high electron mobility transistors

    E-Print Network [OSTI]

    Joh, Jungwoo

    2007-01-01T23:59:59.000Z

    In spite of their extraordinary performance, GaN high electron mobility transistors (HEMT) have still limited reliability. In RF power applications, GaN HEMTs operate at high voltage where good reliability is essential. ...

  4. On strongly GA-convex functions and stochastic processes

    SciTech Connect (OSTI)

    Bekar, Nurgl Okur [Department of Statistics, Giresun University, Giresun (Turkey); Akdemir, Hande Gnay; ??can, ?mdat [Department of Mathematics, Giresun University, Giresun (Turkey)

    2014-08-20T23:59:59.000Z

    In this study, we introduce strongly GA-convex functions and stochastic processes. We provide related well-known Kuhn type results and Hermite-Hadamard type inequality for strongly GA-convex functions and stochastic processes.

  5. TEM-Untersuchungen an GaN basierten Halbleiterheterostrukturen fur

    E-Print Network [OSTI]

    Schubart, Christoph

    TEM-Untersuchungen an GaN basierten Halbleiterheterostrukturen fur optoelektronische Anwendungen . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 5.1.2 Versetzungen bei Homoapitaxie auf GaN-Substraten . . . . 79 5.2 Versetzungsreduktion durch

  6. GaN Nanopore Arrays: Fabrication and Characterization

    E-Print Network [OSTI]

    Wang, Yadong

    GaN nanopore arrays with pore diameters of approximately 75 nm were fabricated by inductively coupled plasma etching (ICP) using anodic aluminum oxide (AAO) films as etch masks. Nanoporous AAO films were formed on the GaN ...

  7. DUST IN A TYPE Ia SUPERNOVA PROGENITOR: SPITZER SPECTROSCOPY OF KEPLER'S SUPERNOVA REMNANT

    SciTech Connect (OSTI)

    Williams, Brian J.; Borkowski, Kazimierz J.; Reynolds, Stephen P. [Physics Department, North Carolina State University, Raleigh, NC 27695-8202 (United States); Ghavamian, Parviz [Department of Physics, Astronomy, and Geosciences, Towson University, Towson, MD 21252 (United States); Blair, William P. [Department of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles St., Baltimore, MD 21218-2686 (United States); Long, Knox S. [STScI, 3700 San Martin Dr., Baltimore, MD 21218 (United States); Sankrit, Ravi, E-mail: brian.j.williams@nasa.gov [SOFIA/USRA, NASA Ames Research Center, M/S N211-3, Moffett Field, CA 94035 (United States)

    2012-08-10T23:59:59.000Z

    Characterization of the relatively poorly understood progenitor systems of Type Ia supernovae is of great importance in astrophysics, particularly given the important cosmological role that these supernovae play. Kepler's supernova remnant, the result of a Type Ia supernova, shows evidence for an interaction with a dense circumstellar medium (CSM), suggesting a single-degenerate progenitor system. We present 7.5-38 {mu}m infrared (IR) spectra of the remnant, obtained with the Spitzer Space Telescope, dominated by emission from warm dust. Broad spectral features at 10 and 18 {mu}m, consistent with various silicate particles, are seen throughout. These silicates were likely formed in the stellar outflow from the progenitor system during the asymptotic giant branch stage of evolution, and imply an oxygen-rich chemistry. In addition to silicate dust, a second component, possibly carbonaceous dust, is necessary to account for the short-wavelength Infrared Spectrograph and Infrared Array Camera data. This could imply a mixed chemistry in the atmosphere of the progenitor system. However, non-spherical metallic iron inclusions within silicate grains provide an alternative solution. Models of collisionally heated dust emission from fast shocks (>1000 km s{sup -1}) propagating into the CSM can reproduce the majority of the emission associated with non-radiative filaments, where dust temperatures are {approx}80-100 K, but fail to account for the highest temperatures detected, in excess of 150 K. We find that slower shocks (a few hundred km s{sup -1}) into moderate density material (n{sub 0} {approx} 50-250 cm{sup -3}) are the only viable source of heating for this hottest dust. We confirm the finding of an overall density gradient, with densities in the north being an order of magnitude greater than those in the south.

  8. Initiation of the detonation in the gravitationally confined detonation model of type Ia supernovae.

    SciTech Connect (OSTI)

    Seitenzahl, I. R.; Meakin, C. A.; Lamb, D. Q.; Truran, J. W. (Physics); (Univ. of Chicago); (Max-Planck-Inst. for Astrophysics); (Univ. of Arizona)

    2009-07-20T23:59:59.000Z

    We study the initiation of the detonation in the gravitationally confined detonation (GCD) model of Type Ia supernovae (SNe Ia). In this model, ignition occurs at one or several off-center points, resulting in a burning bubble of hot ash that rises rapidly, breaks through the surface of the star, and collides at a point on the stellar surface opposite the breakout, producing a high-velocity inwardly directed flow. Initiation of the detonation occurs spontaneously in a region where the length scale of the temperature gradient extending from the flow (in which carbon burning is already occurring) into unburned fuel is commensurate to the range of critical length scales which have been derived from one-dimensional simulations that resolve the initiation of a detonation. By increasing the maximum resolution in a truncated cone that encompasses this region, beginning somewhat before initiation of the detonation occurs, we successfully simulate in situ the first gradient-initiated detonation in a whole-star simulation. The detonation emerges when a compression wave overruns a pocket of fuel situated in a Kelvin-Helmholtz cusp at the leading edge of the inwardly directed jet of burning carbon. The compression wave preconditions the temperature in the fuel in such a way that the Zel'dovich gradient mechanism can operate and a detonation ensues. We explore the dependence of the length scale of the temperature gradient on spatial resolution and discuss the implications for the robustness of this detonation mechanism. We find that the time and the location at which initiation of the detonation occurs varies with resolution. In particular, initiation of a detonation had not yet occurred in our highest resolution simulation by the time we ended the simulation because of the computational demand it required. However, it may detonate later. We suggest that the turbulent shear layer surrounding the inwardly directed jet provides the most favorable physical conditions, and therefore the most likely location, for initiation of a detonation in the GCD model.

  9. INITIATION OF THE DETONATION IN THE GRAVITATIONALLY CONFINED DETONATION MODEL OF TYPE Ia SUPERNOVAE

    SciTech Connect (OSTI)

    Seitenzahl, Ivo R. [Department of Physics, University of Chicago, Chicago, IL 60637 (United States); Meakin, Casey A.; Truran, James W. [Joint Institute for Nuclear Astrophysics, University of Chicago, Chicago, IL 60637 (United States); Lamb, Don Q. [Center for Astrophysical Thermonuclear Flashes, University of Chicago, Chicago, IL 60637 (United States)

    2009-07-20T23:59:59.000Z

    We study the initiation of the detonation in the gravitationally confined detonation (GCD) model of Type Ia supernovae (SNe Ia). In this model, ignition occurs at one or several off-center points, resulting in a burning bubble of hot ash that rises rapidly, breaks through the surface of the star, and collides at a point on the stellar surface opposite the breakout, producing a high-velocity inwardly directed flow. Initiation of the detonation occurs spontaneously in a region where the length scale of the temperature gradient extending from the flow (in which carbon burning is already occurring) into unburned fuel is commensurate to the range of critical length scales which have been derived from one-dimensional simulations that resolve the initiation of a detonation. By increasing the maximum resolution in a truncated cone that encompasses this region, beginning somewhat before initiation of the detonation occurs, we successfully simulate in situ the first gradient-initiated detonation in a whole-star simulation. The detonation emerges when a compression wave overruns a pocket of fuel situated in a Kelvin-Helmholtz cusp at the leading edge of the inwardly directed jet of burning carbon. The compression wave preconditions the temperature in the fuel in such a way that the Zel'dovich gradient mechanism can operate and a detonation ensues. We explore the dependence of the length scale of the temperature gradient on spatial resolution and discuss the implications for the robustness of this detonation mechanism. We find that the time and the location at which initiation of the detonation occurs varies with resolution. In particular, initiation of a detonation had not yet occurred in our highest resolution simulation by the time we ended the simulation because of the computational demand it required. However, it may detonate later. We suggest that the turbulent shear layer surrounding the inwardly directed jet provides the most favorable physical conditions, and therefore the most likely location, for initiation of a detonation in the GCD model.

  10. Study of the detonation phase in the gravitationally confined detonation model of type Ia supernovae.

    SciTech Connect (OSTI)

    Meakin, C. A.; Seitenzahl, I.; Jordan, G. C.; Truran,, J.; Lamb, D.; Physics; Univ. of Chicago; Univ. of Arizona

    2009-07-20T23:59:59.000Z

    We study the initiation of the detonation in the gravitationally confined detonation (GCD) model of Type Ia supernovae (SNe Ia). In this model, ignition occurs at one or several off-center points, resulting in a burning bubble of hot ash that rises rapidly, breaks through the surface of the star, and collides at a point on the stellar surface opposite the breakout, producing a high-velocity inwardly directed flow. Initiation of the detonation occurs spontaneously in a region where the length scale of the temperature gradient extending from the flow (in which carbon burning is already occurring) into unburned fuel is commensurate to the range of critical length scales which have been derived from one-dimensional simulations that resolve the initiation of a detonation. By increasing the maximum resolution in a truncated cone that encompasses this region, beginning somewhat before initiation of the detonation occurs, we successfully simulate in situ the first gradient-initiated detonation in a whole-star simulation. The detonation emerges when a compression wave overruns a pocket of fuel situated in a Kelvin-Helmholtz cusp at the leading edge of the inwardly directed jet of burning carbon. The compression wave preconditions the temperature in the fuel in such a way that the Zeldovich gradient mechanism can operate and a detonation ensues. We explore the dependence of the length scale of the temperature gradient on spatial resolution and discuss the implications for the robustness of this detonation mechanism. We find that the time and the location at which initiation of the detonation occurs varies with resolution. In particular, initiation of a detonation had not yet occurred in our highest resolution simulation by the time we ended the simulation because of the computational demand it required. However, it may detonate later. We suggest that the turbulent shear layer surrounding the inwardly directed jet provides the most favorable physical conditions, and therefore the most likely location, for initiation of a detonation in the GCD model.

  11. Incompatibility of a comoving Ly-alpha forest with supernova-Ia luminosity distances

    E-Print Network [OSTI]

    Jens Thomas; Hartmut Schulz

    2001-03-18T23:59:59.000Z

    Recently Perlmutter et al. suggested a positive value of Einstein's cosmological constant Lambda on the basis of luminosity distances from type-Ia supernovae. However, Lambda world models had earlier been proposed by Hoell & Priester and Liebscher et al. on the basis of quasar absorption-line data. Employing more general repulsive fluids ("dark energy") encompassing the Lambda component we quantitatively compare both approaches with each other. Fitting the SN-data by a minimum-component model consisting of dark energy + dust yields a closed universe with a large amount of dust exceeding the baryonic content constrained by big-bang nucleosynthesis. The nature of the dark energy is hardly constrained. Only when enforcing a flat universe there is a clear tendency to a dark-energy Lambda fluid and the `canonical' value Omega_M = 0.3 for dust. Conversely, fitting the quasar-data by a minimum-component model yields a sharply defined, slightly closed model with a low dust density ruling out significant pressureless dark matter. The dark-energy component obtains an equation-of-state P = -0.96 epsilon close to that of a Lambda-fluid. Omega_M = 0.3 or a precisely flat spatial geometry are inconsistent with minimum-component models. It is found that quasar and supernova data sets cannot be reconciled with each other via (repulsive ideal fluid+dust+radiation)-world models. Compatibility could be reached by drastic expansion of the parameter space with at least two exotic fluids added to dust and radiation as world constituents. If considering such solutions as far-fetched one has to conclude that the quasar absorption line and the SN-Ia constraints are incompatible.

  12. Sensitivity study of explosive nucleosynthesis in Type Ia supernovae: I. Modification of individual thermonuclear reaction rates

    E-Print Network [OSTI]

    Eduardo Bravo; Gabriel Martnez-Pinedo

    2012-04-09T23:59:59.000Z

    We explore the sensitivity of the nucleosynthesis due to type Ia supernovae with respect to uncertainties in nuclear reaction rates. We have adopted a standard one-dimensional delayed detonation model of the explosion of a Chandrasekhar-mass white dwarf, and have post-processed the thermodynamic trajectories of every mass-shell with a nucleosynthetic code, with increases (decreases) by a factor of ten on the rates of 1196 nuclear reactions. We have computed as well hydrodynamic models for different rates of the fusion reactions of 12C and of 16O. For selected reactions, we have recomputed the nucleosynthesis with alternative prescriptions for their rates taken from the JINA REACLIB database, and have analyzed the temperature ranges where modifications of their rates have the strongest effect on nucleosynthesis. The nucleosynthesis resulting from the Type Ia supernova models is quite robust with respect to variations of nuclear reaction rates, with the exception of the reaction of fusion of 12C nuclei. The energy of the explosion changes by less than \\sim4%. The changes in the nucleosynthesis due to the modification of the rates of fusion reactions are as well quite modest, for instance no species with a mass fraction larger than 0.02 experiences a variation of its yield larger than a factor of two. We provide the sensitivity of the yields of the most abundant species with respect to the rates of the most intense reactions with protons, neutrons, and alphas. In general, the yields of Fe-group nuclei are more robust than the yields of intermediate-mass elements. Among the charged particle reactions, the most influential on supernova nucleosynthesis are 30Si + p \\rightleftarrows 31P + {\\gamma}, 20Ne + {\\alpha} \\rightleftarrows 24Mg + {\\gamma}, and 24Mg + {\\alpha} \\rightleftarrows 27Al + p. The temperatures at which a modification of their rate has a larger impact are in the range 2 < T < 4 GK. (abridged)

  13. EVOLUTION OF POST-IMPACT REMNANT HELIUM STARS IN TYPE Ia SUPERNOVA REMNANTS WITHIN THE SINGLE-DEGENERATE SCENARIO

    SciTech Connect (OSTI)

    Pan, Kuo-Chuan; Ricker, Paul M. [Department of Astronomy, University of Illinois at Urbana-Champaign, 1002 West Green Street, Urbana, IL 61801 (United States); Taam, Ronald E., E-mail: kpan2@illinois.edu, E-mail: pmricker@illinois.edu, E-mail: r-taam@northwestern.edu [Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208 (United States)

    2013-08-10T23:59:59.000Z

    The progenitor systems of Type Ia supernovae (SNe Ia) are still under debate. Based on recent hydrodynamics simulations, non-degenerate companions in the single-degenerate scenario (SDS) should survive the supernova (SN) impact. One way to distinguish between the SDS and the double-degenerate scenario is to search for the post-impact remnant stars (PIRSs) in SN Ia remnants. Using a technique that combines multi-dimensional hydrodynamics simulations with one-dimensional stellar evolution simulations, we have examined the post-impact evolution of helium-rich binary companions in the SDS. It is found that these helium-rich PIRSs (He PIRSs) dramatically expand and evolve to a luminous phase (L {approx} 10{sup 4} L{sub Sun }) about 10 yr after an SN explosion. Subsequently, they contract and evolve to become hot blue-subdwarf-like (sdO-like) stars by releasing gravitational energy, persisting as sdO-like stars for several million years before evolving to the helium red-giant phase. We therefore predict that a luminous OB-like star should be detectable within {approx}30 yr after the SN explosion. Thereafter, it will shrink and become an sdO-like star in the central regions of SN Ia remnants within star-forming regions for SN Ia progenitors evolved via the helium-star channel in the SDS. These He PIRSs are predicted to be rapidly rotating (v{sub rot} {approx}> 50 km s{sup -1}) and to have high spatial velocities (v{sub linear} {approx}> 500 km s{sup -1}). Furthermore, if SN remnants have diffused away and are not recognizable at a later stage, He PIRSs could be an additional source of single sdO stars and/or hypervelocity stars.

  14. HELIUM-IGNITED VIOLENT MERGERS AS A UNIFIED MODEL FOR NORMAL AND RAPIDLY DECLINING TYPE Ia SUPERNOVAE

    SciTech Connect (OSTI)

    Pakmor, R.; Springel, V. [Heidelberger Institut fuer Theoretische Studien, Schloss-Wolfsbrunnenweg 35, D-69118 Heidelberg (Germany); Kromer, M. [Kavli Institute for the Physics and Mathematics of the Universe, University of Tokyo, Kashiwa, Chiba 277-8583 (Japan); Taubenberger, S. [Max-Planck-Institut fuer Astrophysik, Karl-Schwarzschild-Str. 1, D-85748 Garching (Germany)

    2013-06-10T23:59:59.000Z

    The progenitors of Type Ia supernovae (SNe Ia) are still unknown, despite significant progress during the past several years in theory and observations. Violent mergers of two carbon-oxygen (CO) white dwarfs (WDs) are a candidate scenario suggested to be responsible for at least a significant fraction of normal SNe Ia. Here, we simulate the merger of two CO WDs using a moving-mesh code that allows for the inclusion of thin helium (He) shells (0.01 M{sub Sun }) on top of the WDs at an unprecedented numerical resolution. The accretion of He onto the primary WD leads to the formation of a detonation in its He shell. This detonation propagates around the CO WD and sends a converging shock wave into its core, known to robustly trigger a second detonation, as in the well-known double-detonation scenario for He-accreting CO WDs. However, in contrast to that scenario where a massive He shell is required to form a detonation through thermal instability, here the He detonation is ignited dynamically. Accordingly the required He-shell mass is significantly smaller, and hence its burning products are unlikely to affect the optical display of the explosion. We show that this scenario, which works for CO primary WDs with CO- as well as He-WD companions, has the potential to explain the different brightness distributions, delay times, and relative rates of normal and fast declining SNe Ia. Finally, we discuss extensions to our unified merger model needed to obtain a comprehensive picture of the full observed diversity of SNe Ia.

  15. Height stabilization of GaSb/GaAs quantum dots by Al-rich capping

    SciTech Connect (OSTI)

    Smakman, E. P., E-mail: e.p.smakman@tue.nl; Koenraad, P. M. [Department of Applied Physics, Eindhoven University of Technology, Den Dolech 2, 5612 AZ Eindhoven (Netherlands); DeJarld, M.; Martin, A. J.; Millunchick, J. [Department of Material Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109 (United States); Luengo-Kovac, M.; Sih, V. [Department of Physics, University of Michigan, Ann Arbor, Michigan 48109 (United States)

    2014-09-01T23:59:59.000Z

    GaSb quantum dots (QDs) in a GaAs matrix are investigated with cross-sectional scanning tunneling microscopy (X-STM) and photoluminescence (PL). We observe that Al-rich capping materials prevent destabilization of the nanostructures during the capping stage of the molecular beam epitaxy (MBE) growth process and thus preserves the QD height. However, the strain induced by the absence of destabilization causes many structural defects to appear around the preserved QDs. These defects originate from misfit dislocations near the GaSb/GaAs interface and extend into the capping layer as stacking faults. The lack of a red shift in the QD PL suggests that the preserved dots do not contribute to the emission spectra. We suggest that a better control over the emission wavelength and an increase of the PL intensity is attainable by growing smaller QDs with an Al-rich overgrowth.

  16. 2DEG electrodes for piezoelectric transduction of AlGaN/GaN MEMS resonators

    E-Print Network [OSTI]

    Weinstein, Dana

    A 2D electron gas (2DEG) interdigitated transducer (IDT) in Gallium Nitride (GaN) resonators is introduced and demonstrated. This metal-free transduction does not suffer from the loss mechanisms associated with more commonly ...

  17. High-field quasi-ballistic transport in AlGaN/GaN heterostructures

    SciTech Connect (OSTI)

    Danilchenko, B. A.; Tripachko, N. A. [Institute of Physics, NASU, Pr. Nauki 46, Kiev 03028 (Ukraine); Belyaev, A. E. [Institute of Semiconductor Physics, NASU, Pr. Nauki 45, Kiev 03028 (Ukraine); Vitusevich, S. A., E-mail: s.vitusevich@fz-juelich.de; Hardtdegen, H.; Lth, H. [Peter Grnberg Institute (PGI-8,PGI-9), Forschungszentrum Jlich, Jlich D-52425 (Germany)

    2014-02-17T23:59:59.000Z

    Mechanisms of electron transport formation in 2D conducting channels of AlGaN/GaN heterostructures in extremely high electric fields at 4.2?K have been studied. Devices with a narrow constriction for the current flow demonstrate high-speed electron transport with an electron velocity of 6.8??10{sup 7}?cm/s. Such a velocity is more than two times higher than values reported for conventional semiconductors and about 15% smaller than the limit value predicted for GaN. Superior velocity is attained in the channel with considerable carrier reduction. The effect is related to a carrier runaway phenomenon. The results are in good agreement with theoretical predictions for GaN-based materials.

  18. AlGaN/GaN High-Electron-Mobility Transistor Employing an Additional Gate for High-Voltage Switching Applications

    E-Print Network [OSTI]

    Seo, Kwang Seok

    AlGaN/GaN High-Electron-Mobility Transistor Employing an Additional Gate for High-Voltage Switching 16, 2004; accepted May 10, 2005; published September 8, 2005) We have proposed and fabricated an AlGaN/GaN: GaN, AlGaN, HEMT, switch 1. Introduction GaN has attracted attention for high-power and high

  19. Cubic AlGaN/GaN Hetero-Junction Field-Effect Transistors with Normally-on and Normally-off

    E-Print Network [OSTI]

    As, Donat Josef

    Cubic AlGaN/GaN Hetero-Junction Field-Effect Transistors with Normally-on and Normally-effect transistors (HFETs) in GaN technology. HFET structures were fabricated of non-polar cubic AlGaN/GaN hetero insulation of 3C-SiC was realized by Ar+ implantation before c-AlGaN/GaN growth. HFETs with normally

  20. A 3-10 GHZLCR-matched Power Amplifier using Flip-Chip Mounted AlGaN/GaN HEMTs

    E-Print Network [OSTI]

    York, Robert A.

    WE4A-5 A 3-10 GHZLCR-matched Power Amplifier using Flip-Chip Mounted AlGaN/GaN HEMTs Jane J a GaN-based broadband power amplifier using AlGaN/GaN-HEMTs, grown on sapphire substrates amplifier using GaN- HEMTs-on-Sapphire. I INTRODUCTION GaN HEMTs have enormous potential for realizing high

  1. IPAP Conference Series 1: IWN2000, Nov., 2000 1 Morphology Dependent Growth Kinetics of Ga-polar GaN(0001)

    E-Print Network [OSTI]

    Cohen, Philip I.

    IPAP Conference Series 1: IWN2000, Nov., 2000 1 Morphology Dependent Growth Kinetics of Ga-polar GaN, cohen@ece.umn.edu GaN grown on Ga polar GaN templates prepared by metal-organic vapor deposition shows to equilibrium models of the growth. The results indicate that Ga-polar GaN(0001) has a step energy of the order

  2. Engineering of AlGaN-Delta-GaN Quantum-Well Gain Media for Mid-and Deep-Ultraviolet Lasers

    E-Print Network [OSTI]

    Gilchrist, James F.

    Engineering of AlGaN-Delta-GaN Quantum-Well Gain Media for Mid- and Deep-Ultraviolet Lasers Volume.1109/JPHOT.2013.2248705 1943-0655/$31.00 2013 IEEE #12;Engineering of AlGaN-Delta-GaN Quantum-Well Gain@Lehigh.Edu). Abstract: The gain characteristics of AlGaN-delta-GaN quantum wells (QWs) with varying delta-GaN positions

  3. Recent progress in InGaAsSb/GaSb TPV devices

    SciTech Connect (OSTI)

    Shellenbarger, Z.A.; Mauk, M.G.; DiNetta, L.C. [AstroPower, Inc., Newark, DE (United States); Charache, G.W. [Lockheed Martin Corp., Schenectady, NY (United States)

    1996-05-01T23:59:59.000Z

    AstroPower is developing InGaAsSb thermophotovoltaic (TPV) devices. This photovoltaic cell is a two-layer epitaxial InGaAsSb structure formed by liquid-phase epitaxy on a GaSb substrate. The (direct) bandgap of the In{sub 1{minus}x}Ga{sub x}As{sub 1{minus}y}Sb{sub y} alloy is 0.50 to 0.55 eV, depending on its exact alloy composition (x,y); and is closely lattice-matched to the GaSb substrate. The use of the quaternary alloy, as opposed to a ternary alloy--such as, for example InGaAs/InP--permits low bandgap devices optimized for 1,000 to 1,500 C thermal sources with, at the same time, near-exact lattice matching to the GaSb substrate. Lattice matching is important since even a small degree of lattice mismatch degrades device performance and reliability and increases processing complexity. Internal quantum efficiencies as high as 95% have been measured at a wavelength of 2 microns. At 1 micron wavelengths, internal quantum efficiencies of 55% have been observed. The open-circuit voltage at currents of 0.3 A/cm{sup 2} is 0.220 volts and 0.280 V for current densities of 2 A/cm{sup 2}. Fill factors of 56% have been measured at 60 mA/cm{sup 2}. However, as current density increases there is some decrease in fill factor. The results to date show that the GaSb-based quaternary compounds provide a viable and high performance energy conversion solution for thermophotovoltaic systems operating with 1,000 to 1,500 C source temperatures.

  4. AlGaAs/GaAs photovoltaic converters for high power narrowband radiation

    SciTech Connect (OSTI)

    Khvostikov, Vladimir; Kalyuzhnyy, Nikolay; Mintairov, Sergey; Potapovich, Nataliia; Shvarts, Maxim; Sorokina, Svetlana; Andreev, Viacheslav [Ioffe Physical-Technical Institute, 26 Polytechnicheskaya, St. Petersburg, 194021 (Russian Federation); Luque, Antonio [Ioffe Physical-Technical Institute, 26 Polytechnicheskaya, St. Petersburg, 194021, Russia and Instituto de Energia Solar, Universidad Politecnica de Madrid, Madrid (Spain)

    2014-09-26T23:59:59.000Z

    AlGaAs/GaAs-based laser power PV converters intended for operation with high-power (up to 100 W/cm{sup 2}) radiation were fabricated by LPE and MOCVD techniques. Monochromatic (? = 809 nm) conversion efficiency up to 60% was measured at cells with back surface field and low (x = 0.2) Al concentration 'window'. Modules with a voltage of 4 V and the efficiency of 56% were designed and fabricated.

  5. Sheet resistance under Ohmic contacts to AlGaN/GaN heterostructures

    SciTech Connect (OSTI)

    Haj?asz, M., E-mail: m.hajlasz@m2i.nl [Materials innovation institute (M2i), Mekelweg 2, 2628 CD, Delft (Netherlands); MESA Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE, Enschede (Netherlands); Donkers, J. J. T. M.; Sque, S. J.; Heil, S. B. S. [NXP Semiconductors Research, High Tech Campus 46, 5656 AE, Eindhoven (Netherlands); Gravesteijn, D. J. [NXP Semiconductors Research, High Tech Campus 46, 5656 AE, Eindhoven (Netherlands); MESA Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE, Enschede (Netherlands); Rietveld, F. J. R. [NXP Semiconductors, Gerstweg 2, 6534 AE, Nijmegen (Netherlands); Schmitz, J. [MESA Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE, Enschede (Netherlands)

    2014-06-16T23:59:59.000Z

    For the determination of specific contact resistance in semiconductor devices, it is usually assumed that the sheet resistance under the contact is identical to that between the contacts. This generally does not hold for contacts to AlGaN/GaN structures, where an effective doping under the contact is thought to come from reactions between the contact metals and the AlGaN/GaN. As a consequence, conventional extraction of the specific contact resistance and transfer length leads to erroneous results. In this Letter, the sheet resistance under gold-free Ti/Al-based Ohmic contacts to AlGaN/GaN heterostructures on Si substrates has been investigated by means of electrical measurements, transmission electron microscopy, and technology computer-aided design simulations. It was found to be significantly lower than that outside of the contact area; temperature-dependent electrical characterization showed that it exhibits semiconductor-like behavior. The increase in conduction is attributed to n-type activity of nitrogen vacancies in the AlGaN. They are thought to form during rapid thermal annealing of the metal stack when Ti extracts nitrogen from the underlying semiconductor. The high n-type doping in the region between the metal and the 2-dimensional electron gas pulls the conduction band towards the Fermi level and enhances horizontal electron transport in the AlGaN. Using this improved understanding of the properties of the material underneath the contact, accurate values of transfer length and specific contact resistance have been extracted.

  6. TEM and HRXRD Analysis of LP MOVPE Grown InGaP/GaAs epilayers

    SciTech Connect (OSTI)

    Pelosi, Claudio; Bosi, Matteo; Attolini, Giovanni; Germini, Fabrizio; Frigeri, Cesare [CNR-IMEM Institute, Parco Area delle Scienze 37a, Loc Fontanini 43010 Parma (Italy); Prutskij, Tatiana [Instituto de Ciencias, BUAP, Privada 17 Norte, no. 3417, colSanMiguel Hueyotlipan, 72050 Puebla, Pue. (Mexico)

    2007-04-10T23:59:59.000Z

    The diffusion phenomena at interfaces between GaAs/InGaP layers grown by low pressure MOVPE have been studied by dark field (DF) transmission Electron Microscopy (TEM) and High resolution X-ray Diffractometry (HRXRD). By comparing the results of the two techniques a mismatched layer containing P or P and In has been evidenced. The causes of this behavior are briefly discussed.

  7. Guided Neuronal Growth on Arrays of Biofunctionalized GaAs/InGaAs Semiconductor Microtubes

    E-Print Network [OSTI]

    Cornelius S. Bausch; Aune Koitme; Eric Stava; Amanda Price; Pedro J. Resto; Yu Huang; David Sonnenberg; Yuliya Stark; Christian Heyn; Justin C. Williams; Erik W. Dent; Robert H. Blick

    2013-05-06T23:59:59.000Z

    We demonstrate embedded growth of cortical mouse neurons in dense arrays of semiconductor microtubes. The microtubes, fabricated from a strained GaAs/InGaAs heterostructure, guide axon growth through them and enable electrical and optical probing of propagating action potentials. The coaxial nature of the microtubes -- similar to myelin -- is expected to enhance the signal transduction along the axon. We present a technique of suppressing arsenic toxicity and prove the success of this technique by overgrowing neuronal mouse cells.

  8. InGaN/GaN quantum wells for polariton laser diodes: Role of inhomogeneous broadening

    SciTech Connect (OSTI)

    Glauser, Marlene; Mounir, Christian; Rossbach, Georg; Feltin, Eric; Carlin, Jean-Franois; Butt, Raphal; Grandjean, Nicolas [cole Polytechnique Fdrale de Lausanne (EPFL), Institute of Condensed Matter Physics, CH-1015 Lausanne (Switzerland)

    2014-06-21T23:59:59.000Z

    Contrary to the case of III-nitride based visible light-emitting diodes for which the inhomogeneous linewidth broadening characteristic of InGaN-based multiple quantum well (MQW) heterostructures does not appear as a detrimental parameter, such a broadening issue can prevent a microcavity (MC) system entering into the strong light-matter coupling regime (SCR). The impact of excitonic disorder in low indium content (x???0.1) In{sub x}Ga{sub 1x}N/GaN MQW active regions is therefore investigated for the subsequent realization of polariton laser diodes by considering both simulations and optical characterizations. It allows deriving the requirements for such MQWs in terms of absorption, emission linewidth, and Stokes shift. Systematic absorption-like and photoluminescence (PL) spectroscopy experiments are performed on single and multiple In{sub 0.1}Ga{sub 0.9}N/GaN quantum wells (QWs). Micro-PL mappings reveal a low temperature PL linewidth of ?30?meV, compatible with SCR requirements, for single QWs for which the microscopic origin responsible for this broadening is qualitatively discussed. When stacking several InGaN/GaN QWs, a departure from such a narrow linewidth value and an increase in the Stokes shift are observed. Various possible reasons for this degradation such as inhomogeneous built-in field distribution among the QWs are then identified. An alternative solution for the MC design to achieve the SCR with the InGaN alloy is briefly discussed.

  9. Rapid Communications Strong piezoelectricity in individual GaN nanowires

    E-Print Network [OSTI]

    Espinosa, Horacio D.

    Rapid Communications Strong piezoelectricity in individual GaN nanowires Majid Minary@northwestern.edu (Received 12 July 2011; accepted 15 September 2011) Abstract GaN nanowires are promising building blocks piezoelectricity in individual single-crystal GaN nanowires revealed by direct measurement of the piezoelectric

  10. GaN Radiation Detectors for Particle Physics and

    E-Print Network [OSTI]

    Glasgow, University of

    GaN Radiation Detectors for Particle Physics and Synchrotron Applications James Paul Grant and monitoring applications. Gallium nitride (GaN) was investigated as a radiation hard particle detector diameter on three epitaxial GaN wafers grown on a sapphire sub- strate. Two of the wafers were obtained

  11. New Faces of GaN: Growth, Doping and Devices

    E-Print Network [OSTI]

    California at Santa Barbara, University of

    New Faces of GaN: Growth, Doping and Devices James S. Speck Materials Department University of California Santa Barbara, CA LEO of a-GaN from circular opening Engineering Insights 2006 #12;#12;Personnel. Wraback (ARL) $$$ JST ERATO UCSB SSLDC AFOSR ONR #12;Reversed direction of polarization Bulk GaN

  12. Analysis of the AlGaN/GaN vertical bulk current on Si, sapphire, and free-standing GaN substrates

    SciTech Connect (OSTI)

    Perez-Tomas, A.; Fontsere, A.; Llobet, J. [IMB-CNM-CSIC, Campus UAB, 08193 Bellaterra, Barcelona, CAT (Spain); Placidi, M. [IREC, Jardins Dones de Negre 1, 08930 Sant Adria de Besos, Barcelona (Spain); Rennesson, S.; Chenot, S.; Moreno, J. C.; Cordier, Y. [CRHEA-CNRS, Rue Bernard Gregory, Sophia Antipolis, 06560 Valbonne (France); Baron, N. [CRHEA-CNRS, Rue Bernard Gregory, Sophia Antipolis, 06560 Valbonne (France); PICOGIGA International, Pl M. Rebuffat, Courtaboeuf 7, 91140 Villejust (France)

    2013-05-07T23:59:59.000Z

    The vertical bulk (drain-bulk) current (I{sub db}) properties of analogous AlGaN/GaN hetero-structures molecular beam epitaxially grown on silicon, sapphire, and free-standing GaN (FS-GaN) have been evaluated in this paper. The experimental I{sub db} (25-300 Degree-Sign C) have been well reproduced with physical models based on a combination of Poole-Frenkel (trap assisted) and hopping (resistive) conduction mechanisms. The thermal activation energies (E{sub a}), the (soft or destructive) vertical breakdown voltage (V{sub B}), and the effect of inverting the drain-bulk polarity have also been comparatively investigated. GaN-on-FS-GaN appears to adhere to the resistive mechanism (E{sub a} = 0.35 eV at T = 25-300 Degree-Sign C; V{sub B} = 840 V), GaN-on-sapphire follows the trap assisted mechanism (E{sub a} = 2.5 eV at T > 265 Degree-Sign C; V{sub B} > 1100 V), and the GaN-on-Si is well reproduced with a combination of the two mechanisms (E{sub a} = 0.35 eV at T > 150 Degree-Sign C; V{sub B} = 420 V). Finally, the relationship between the vertical bulk current and the lateral AlGaN/GaN transistor leakage current is explored.

  13. A New Combustion Synthesis Method for GaN:Eu3+ and Ga2O3 :Eu3+

    E-Print Network [OSTI]

    McKittrick, Joanna

    A New Combustion Synthesis Method for GaN:Eu3+ and Ga2O3 :Eu3+ Luminescent Powders G. A. Hirata1 between the precursors. The preparation of Eu-doped Ga2O3 powders was achieved using a new combustion)3 and Ga(NO3)3 as the precursors and hydrazine as (non-carbonaceous) fuel. A spontaneous combustion

  14. Electron mobility enhancement in AlN/GaN/AlN heterostructures with InGaN nanogrooves

    E-Print Network [OSTI]

    improve the room-temperature carrier mobility in wurtzite AlN/GaN/AlN heterostructures, which is limited consider a narrow groove made of InxGa1-xN with small In content x inside a wurtzite AlN/GaN/AlN heteroN 2 nm /GaN 3 nm /AlN 3 nm . A well-known feature of wurtzite heterostructures is a strong buit

  15. Growth of GaN on porous SiC and GaN substrates C. K. Inoki1

    E-Print Network [OSTI]

    Feenstra, Randall

    1 Growth of GaN on porous SiC and GaN substrates C. K. Inoki1 , T. S. Kuan1 , Ashutosh Sagar2 , C, Albuquerque, NM 87185 4 Beckman Institute, University of Illinois, Urbana, IL 61801 GaN films were grown on porous SiC and GaN templates using both plasma-assisted molecular beam epitaxy (PAMBE) and metal

  16. Structural, morphological, and optical properties of AlGaN/GaN heterostructures with AlN buffer and interlayer

    E-Print Network [OSTI]

    Ozbay, Ekmel

    N buffer layer BL grown on an Al2O3 substrate and an AlN IL grown under the AlGaN ternary layer TL. In the present study, we investigate the effects of an AlN BL on an Al2O3 substrate and an AlN IL between an AlGaNStructural, morphological, and optical properties of AlGaN/GaN heterostructures with AlN buffer

  17. From Schottky to Ohmic graphene contacts to AlGaN/GaN heterostructures: Role of the AlGaN layer microstructure

    SciTech Connect (OSTI)

    Fisichella, G. [CNR-IMM, Strada VIII, 5, 95121 Catania (Italy); Department of Electronic Engineering, University of Catania, 95124 Catania (Italy); Greco, G.; Roccaforte, F.; Giannazzo, F. [CNR-IMM, Strada VIII, 5, 95121 Catania (Italy)

    2014-08-11T23:59:59.000Z

    The electrical behaviour of graphene (Gr) contacts to Al{sub x}Ga{sub 1?x}N/GaN heterostructures has been investigated, focusing, in particular, on the impact of the AlGaN microstructure on the current transport at Gr/AlGaN interface. Two Al{sub 0.25}Ga{sub 0.75}N/GaN heterostructures with very different quality in terms of surface roughness and defectivity, as evaluated by atomic force microscopy (AFM) and transmission electron microscopy, were compared in this study, i.e., a uniform and defect-free sample and a sample with a high density of typical V-defects, which locally cause a reduction of the AlGaN thickness. Nanoscale resolution current voltage (I-V) measurements by an Au coated conductive AFM tip were carried out at several positions both on the bare and Gr-coated AlGaN surfaces. Rectifying contacts were found onto both bare AlGaN surfaces, but with a more inhomogeneous and lower Schottky barrier height (?{sub B}???0.6?eV) for AlGaN with V-defects, with respect to the case of the uniform AlGaN (?{sub B}???0.9?eV). Instead, very different electrical behaviours were observed in the presence of the Gr interlayer between the Au tip and AlGaN, i.e., a Schottky contact with reduced barrier height (?{sub B} ? 0.4?eV) for the uniform AlGaN and an Ohmic contact for the AlGaN with V-defects. Interestingly, excellent lateral uniformity of the local I-V characteristics was found in both cases and can be ascribed to an averaging effect of the Gr electrode over the AlGaN interfacial inhomogeneities. Due to the locally reduced AlGaN layer thickness, V defect act as preferential current paths from Gr to the 2DEG and can account for the peculiar Ohmic behaviour of Gr contacts on defective AlGaN.

  18. Lattice-Mismatched GaAs/InGaAs Two-Junction Solar Cells by Direct Wafer Bonding

    SciTech Connect (OSTI)

    Tanabe, K.; Aiken, D. J.; Wanlass, M. W.; Morral, A. F.; Atwater, H. A.

    2006-01-01T23:59:59.000Z

    Direct bonded interconnect between subcells of a lattice-mismatched III-V compound multijunction cell would enable dislocation-free active regions by confining the defect network needed for lattice mismatch accommodation to tunnel junction interfaces, while metamorphic growth inevitably results in less design flexibility and lower material quality than is desirable. The first direct-bond interconnected multijunction solar cell, a two-terminal monolithic GaAs/InGaAs two-junction solar cell, is reported and demonstrates viability of direct wafer bonding for solar cell applications. The tandem cell open-circuit voltage was approximately the sum of the subcell open-circuit voltages. This achievement shows direct bonding enables us to construct lattice-mismatched III-V multijunction solar cells and is extensible to an ultrahigh efficiency InGaP/GaAs/InGaAsP/InGaAs four-junction cell by bonding a GaAs-based lattice-matched InGaP/GaAs subcell and an InP-based lattice-matched InGaAsP/InGaAs subcell. The interfacial resistance experimentally obtained for bonded GaAs/InP smaller than 0.10 Ohm-cm{sup 2} would result in a negligible decrease in overall cell efficiency of {approx}0.02%, under 1-sun illumination.

  19. X-ray diffraction analysis of InGaP/GaAs heterointerfaces grown by metalorganic chemical vapor deposition

    SciTech Connect (OSTI)

    Nittono, T.; Hyuga, F. [NTT System Electronics Laboratories 3-1, Morinosato Wakamiya, Atsugi-shi, Kanagawa, 243-01 (Japan)] [NTT System Electronics Laboratories 3-1, Morinosato Wakamiya, Atsugi-shi, Kanagawa, 243-01 (Japan)

    1997-03-01T23:59:59.000Z

    InGaP/GaAs heterointerfaces grown by metalorganic chemical vapor deposition have been characterized by a high-resolution x-ray diffraction analysis of multiple quantum well structures. The flow of AsH{sub 3} to InGaP surface produces an InGaAs-like interfacial layer at the GaAs-on-InGaP interface, indicating P atoms of the InGaP surface are easily replaced by As atoms. The flow of PH{sub 3} to GaAs surface, on the other hand, does not make any detectable interfacial layer, indicating that almost no As atoms of the GaAs surface are replaced by P atoms. It is also found that the flow of trimethylgallium (TMG) to the InGaP surface produces a GaP-like interfacial layer. This interfacial layer is probably formed by the reaction between TMG and excessive P atoms on the InGaP surface or residual PH{sub 3} in the growth chamber. {copyright} {ital 1997 American Institute of Physics.}

  20. Physica B 376377 (2006) 486490 Preferential substitution of Fe on physically equivalent Ga sites in GaN

    E-Print Network [OSTI]

    Nabben, Reinhard

    2006-01-01T23:59:59.000Z

    in GaN W. Gehlhoff, D. Azamat1 , U. Haboeck, A. Hoffmann Institute for Solid State Physics, Technical freestanding hydride vapor phase grown GaN have been studied in the X- and Q-band. A complex resonance pattern with C3v symmetry in the wurtzite structure of GaN. Aside from the displacement of their magnetic axis

  1. Superluminescence in Green Emission GaInN/GaN Quantum Well Structures under Pulsed Laser Excitation

    E-Print Network [OSTI]

    Wetzel, Christian M.

    and bulk GaN substrates, respectively. Under intense pulsed photo excitation, we observed strong the same excitation conditions, the blue shift for the m-axis grown structure on bulk GaN substrate is less-plane sapphire substrate and along the non-polar m-axis on m-plane bulk GaN substrate. The frequently used

  2. Composition and Interface Analysis of InGaN/GaN Multiquantum-Wells on GaN Substrates Using Atom Probe Tomography

    SciTech Connect (OSTI)

    Liu, Fang; Huang, Li; Davis, Robert F.; Porter, Lisa M.; Schreiber, Daniel K.; Kuchibhatla, S. V. N. T.; Shutthanandan, V.; Thevuthasan, Suntharampillai; Preble, Edward; Paskova, Tanya; Evans, K. R.

    2014-09-04T23:59:59.000Z

    In0.20Ga0.80N/GaN multi-quantum wells grown on [0001]-oriented GaN substrates with and without an InGaN buffer layer were characterized using three-dimensional atom probe tomography. In all samples, the upper interfaces of the QWs were slightly more diffuse than the lower interfaces. The buffer layers did not affect the roughness of the interfaces within the quantum well structure, a result attributed to planarization of the surface of the 1st GaN barrier layer which had an average root-mean-square roughness of 0.177 nm. The In and Ga distributions within the MQWs followed the expected distributions for a random alloy with no indications of In clustering.

  3. Point defect balance in epitaxial GaSb

    SciTech Connect (OSTI)

    Segercrantz, N., E-mail: natalie.segercrantz@aalto.fi; Slotte, J.; Makkonen, I.; Kujala, J.; Tuomisto, F. [Department of Applied Physics, Aalto University, P.O. Box 14100, FIN-00076 Aalto Espoo (Finland); Song, Y.; Wang, S. [Department of Microtechnology and Nanoscience, Chalmers University of Technology, 41296 Gteborg (Sweden); State Key Laboratory of Functional Materials for Informatics Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences 865 Changning Road, Shanghai 200050 (China)

    2014-08-25T23:59:59.000Z

    Positron annihilation spectroscopy in both conventional and coincidence Doppler broadening mode is used for studying the effect of growth conditions on the point defect balance in GaSb:Bi epitaxial layers grown by molecular beam epitaxy. Positron annihilation characteristics in GaSb are also calculated using density functional theory and compared to experimental results. We conclude that while the main positron trapping defect in bulk samples is the Ga antisite, the Ga vacancy is the most prominent trap in the samples grown by molecular beam epitaxy. The results suggest that the ptype conductivity is caused by different defects in GaSb grown with different methods.

  4. Room-temperature cw operation of InGaAsP/InGaP lasers at 727 nm grown on GaAs substrates by liquid phase epitaxy

    SciTech Connect (OSTI)

    Wakao, K.; Nishi, H.; Kusunoki, T.; Isozumi, S.; Ohsaka, S.

    1984-06-01T23:59:59.000Z

    InGaAsP/InGaP lasers emitting at 724--727 nm have been fabricated on GaAs substrates using liquid phase epitaxy. The threshold current is reduced to 8 kA/cm/sup 2/ by thinning the active layer. Room-temperature cw operation is achieved for the first time in the lasing wavelength range below 760 nm in this quaternary system.

  5. EVALUATING SYSTEMATIC DEPENDENCIES OF TYPE Ia SUPERNOVAE: THE INFLUENCE OF PROGENITOR {sup 22}Ne CONTENT ON DYNAMICS

    SciTech Connect (OSTI)

    Townsley, Dean M. [Department of Astronomy/Steward Observatory, University of Arizona, Tucson, AZ (United States); Jackson, Aaron P.; Calder, Alan C. [Department of Physics and Astronomy, State University of New York - Stony Brook, Stony Brook, NY (United States); Chamulak, David A.; Brown, Edward F. [Department of Physics and Astronomy, Michigan State University, East Lansing, MI (United States); Timmes, F. X. [Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, MI 48824 (United States)], E-mail: townsley@as.arizona.edu

    2009-08-20T23:59:59.000Z

    We present a theoretical framework for formal study of systematic effects in supernovae Type Ia (SNe Ia) that utilizes two-dimensional simulations to implement a form of the deflagration-detonation transition (DDT) explosion scenario. The framework is developed from a randomized initial condition that leads to a sample of simulated SNe Ia whose {sup 56}Ni masses have a similar average and range to those observed, and have many other modestly realistic features such as the velocity extent of intermediate-mass elements. The intended purpose is to enable statistically well defined studies of both physical and theoretical parameters of the SNe Ia explosion simulation. We present here a thorough description of the outcome of the SNe Ia explosions produced by our current simulations. A first application of this framework is utilized to study the dependence of the SNe Ia on the {sup 22}Ne content, which is known to be directly influenced by the progenitor stellar population's metallicity. Our study is very specifically tailored to measure how the {sup 22}Ne content influences the competition between the rise of plumes of burned material and the expansion of the star before these plumes reach DDT conditions. This influence arises from the dependence of the energy release, progenitor structure, and laminar flame speed on {sup 22}Ne content. For this study, we explore these three effects for a fixed carbon content and DDT density. By setting the density at which nucleosynthesis takes place during the detonation phase of the explosion, the competition between plume rise and stellar expansion controls the amount of material in nuclear statistical equilibrium (NSE) and therefore {sup 56}Ni produced. Of particular interest is how this influence of {sup 22}Ne content compares to the direct modification of the {sup 56}Ni mass via the inherent neutron excess as discussed by Timmes et al. Although the outcome following from any particular ignition condition can change dramatically with {sup 22}Ne content, with a sample of 20 ignition conditions we find that the systematic change in the expansion of the star prior to detonation is not large enough to compete with the dependence discussed by Timmes et al. In fact, our results show no statistically significant dependence of the predetonation expansion on {sup 22}Ne content, pointing to the morphology of the ignition condition as being the dominant dynamical driver of the {sup 56}Ni yield of the explosion. However, variations in the DDT density, which were specifically excluded here, are also expected to be important and to depend systematically on {sup 22}Ne content.

  6. Self-assembled In0.5Ga0.5As quantum dots on GaP Yuncheng Song,a

    E-Print Network [OSTI]

    Haller, Gary L.

    SAQDs . Several groups have investigated the growth of both InP and In-rich InGaP SAQDs on GaP.712 Most temperature operation of vis- ible light emitting diodes LEDs using InP/GaP and InGaP/ GaP SAQDs, respectively

  7. Current crowding in GaInN / GaN LEDs grown on insulating substrates X. Guo, E. F. Schubert and J. Jahns

    E-Print Network [OSTI]

    Jahns, Jrgen

    Current crowding in GaInN / GaN LEDs grown on insulating substrates X. Guo, E. F. Schubert and J spreading in a mesa-structure GaN-based LED grown on an insulating or semi-insulating substrate. (b. Jahns Current crowding in mesa-structure GaInN/GaN light-emitting diodes (LEDs) grown on insulating

  8. Gas-source molecular beam epitaxial growth and characterization of the (Al,In,Ga)NP/GaP material system and Its applications to light-emitting diodes

    E-Print Network [OSTI]

    Odnoblyudov, Vladimir

    2006-01-01T23:59:59.000Z

    ? G, Kcal/mol GaP GaN AlN o Substrate temperature, C Figurenm-thick GaN 0.006 P 0.994 layer on substrate temperature.substrate temperature for Reactions formation of AlP, GaP, GaN and

  9. IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 51, NO. 2, FEBRUARY 2003 653 AlGaN/GaN HFET Power Amplifier Integrated With

    E-Print Network [OSTI]

    Itoh, Tatsuo

    the first demonstration of a GaN-based HFET was done on a sapphire substrate in 1993 [1][3]. This is due crystal quality compared to that of the sapphire substrate. Thanks to steadfast progress in AlGaN/GaN HFETIEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 51, NO. 2, FEBRUARY 2003 653 AlGaN/GaN

  10. Tunable THz plasmon resonances in InGaAs/InP HEMT R. E. Peale*a

    E-Print Network [OSTI]

    Peale, Robert E.

    , high ns, and small m*. A variety of materials systems such as GaAs/AlGaAs [3], InGaP/InGaAs/GaAs [4

  11. Prospective emission efficiency and in-plane light polarization of nonpolar m-plane InxGa1-xN/GaN blue light emitting diodes fabricated on freestanding GaN substrates

    E-Print Network [OSTI]

    2006-01-01T23:59:59.000Z

    fabricated on freestanding GaN substrates T. Koyama and T.on freestanding m-plane GaN substrates. Although the ? inton the freestanding GaN substrate. cause the current was

  12. Reactive codoping of GaAlInP compound semiconductors

    DOE Patents [OSTI]

    Hanna, Mark Cooper (Boulder, CO); Reedy, Robert (Golden, CO)

    2008-02-12T23:59:59.000Z

    A GaAlInP compound semiconductor and a method of producing a GaAlInP compound semiconductor are provided. The apparatus and method comprises a GaAs crystal substrate in a metal organic vapor deposition reactor. Al, Ga, In vapors are prepared by thermally decomposing organometallic compounds. P vapors are prepared by thermally decomposing phospine gas, group II vapors are prepared by thermally decomposing an organometallic group IIA or IIB compound. Group VIB vapors are prepared by thermally decomposing a gaseous compound of group VIB. The Al, Ga, In, P, group II, and group VIB vapors grow a GaAlInP crystal doped with group IIA or IIB and group VIB elements on the substrate wherein the group IIA or IIB and a group VIB vapors produced a codoped GaAlInP compound semiconductor with a group IIA or IIB element serving as a p-type dopant having low group II atomic diffusion.

  13. Influence of Ga content on the structure and anomalous Hall effect of Fe{sub 1?x}Ga{sub x} thin films on GaSb(100)

    SciTech Connect (OSTI)

    Anh Tuan, Duong; Shin, Yooleemi; Viet Cuong, Tran; Cho, Sunglae, E-mail: slcho@ulsan.ac.kr [Department of Physics and Energy Harvest-Storage Research Center, University of Ulsan, Ulsan 680-749 (Korea, Republic of); Phan, The-Long [Department of Physics, Chungbuk National University, Cheongju 361-763 (Korea, Republic of)

    2014-05-07T23:59:59.000Z

    The Fe{sub 1?x}Ga{sub x} thin films (x?=?0.4, 0.5) have been grown on GaSb(100) substrate using molecular beam epitaxy. An epitaxial film with bcc ?-Fe crystal structure (A2) is observed in Fe{sub 0.6}Ga{sub 0.4} film, while an impure Fe{sub 3}Ga phase with DO{sub 3} structure is appeared in Fe{sub 0.5}Ga{sub 0.5} film. The saturated magnetizations at room temperature are observed to be 570?emu/cm{sup 3} and 180?emu/cm{sup 3} and the coercivities to be 170 and 364?Oe for Fe{sub 0.6}Ga{sub 0.4} and Fe{sub 0.5}Ga{sub 0.5}, respectively. A hysteresis trend in Hall resistance vs. magnetic field is observed for Fe{sub 0.5}Ga{sub 0.5} film. However, there is a weak hysteresis noticed in Fe{sub 0.4}Ga{sub 0.6} thin film.

  14. Catastrophic degradation of InGaAsP/InGaP double-heterostructure lasers grown on (001) GaAs substrates by liquid-phase epitaxy

    SciTech Connect (OSTI)

    Ueda, O.; Wakao, K.; Komiya, S.; Yamaguchi, A.; Isozumi, S.; Umebu, I.

    1985-12-01T23:59:59.000Z

    Catastrophically degraded InGaAsP/InGaP double-heterostructure lasers grown on (001) GaAs substrates by liquid-phase epitaxy, emitting at 727 and 810 nm are investigated by photoluminescence topography, scanning electron microscopy, transmission electron microscopy, and energy dispersive x-ray spectroscopy. The degradation is mainly due to catastrophic optical damage at the facet, i.e., development of <110> dark-line defects from the facet, and rarely due to catastrophic optical damage at some defects, i.e., development of <110> dark-line defects from the defects inside the stripe region. These <110> dark-line defects correspond to complicated dislocation networks connected with dark knots, and are quite similar to those observed in catastrophically degraded GaAlAs/GaAs double-heterostructure lasers. The degradation characteristics of the InGaAsP/InGaP double-heterostructure lasers are rather similar to those in GaAlAs/GaAs double-heterostructure lasers concerning the catastrophic degradation.

  15. Dynamics of thermalization in GaInN/GaN quantum wells grown on ammonothermal GaN

    SciTech Connect (OSTI)

    Binder, J.; Korona, K. P.; Wysmo?ek, A.; Kami?ska, M. [Faculty of Physics, University of Warsaw, ul. Hoza 69, 00-681 Warsaw (Poland); Khler, K.; Kirste, L.; Ambacher, O. [Fraunhofer Institute for Applied Solid State Physics, Tullastr. 72, 79108 Freiburg (Germany); Zaj?c, M.; Dwili?ski, R. [AMMONO SA, Czerwonego Krzy?a 2/31, 00-377 Warsaw (Poland)

    2013-12-14T23:59:59.000Z

    In this work, we present measurements of the dynamics of photoexcited carriers in GaInN/GaN quantum wells (QWs) grown on ammonothermal GaN, especially thermalization and recombination rates. Emission properties were measured by time-resolved photoluminescence (PL) and electroluminescence spectroscopy. Due to the use of high quality homoepitaxial material, we were able to obtain very valuable data on carrier thermalization. The temperature dependence of the QW energy observed in PL shows characteristic S-shape with a step of about 10?meV. Such a behavior (related to thermalization and localization at potential fluctuations) is often reported for QWs; but in our samples, the effect is smaller than in heteroepitaxial InGaN/GaN QWs due to lower potential fluctuation in our material. Absorption properties were studied by photocurrent spectroscopy measurements. A comparison of emission and absorption spectra revealed a shift in energy of about 60?meV. Contrary to PL, the QW energy observed in absorption decreases monotonically with temperature, which can be described by a Bose-like dependence E(T)?=?E(0) ? ?/(exp(?/T) ? 1), with parameters ??=?(0.11??0.01) eV, ??=?(355??20)?K, or by a Varshni dependence with coefficients ??=?(10??3) 10{sup ?4}?eV/K and ??=?(1500??500) K. Taking into account absorption and emission, the fluctuation amplitude (according to Eliseev theory) was ??=?14?meV. The time resolved PL revealed that in a short period (<1?ns) after excitation, the PL peaks were broadened because of the thermal distribution of carriers. We interpreted this distribution in terms of quasi-temperature (T{sub q}) of the carriers. The initial T{sub q} was of the order of 500?K. The thermalization led to a fast decrease of T{sub q}. The obtained cooling time in the QW was ?{sub C}?=?0.3?ns, which was faster than the observed recombination time ?{sub R}?=?2.2?ns (at 4?K)

  16. Manipulation of emission energy in GaAs/AlGaAs core-shell nanowires with radial heterostructure

    SciTech Connect (OSTI)

    Barbosa, B. G.; Arakaki, H.; Souza, C. A. de; Pusep, Yu. A. [Instituto de Fisica de So Carlos, Universidade de So Paulo, 13560-970 Sao Carlos, SP (Brazil)

    2014-03-21T23:59:59.000Z

    Photoluminescence was studied in GaAs/AlGaAs nanowires (NWs) with different radial heterostructures. We demonstrated that manipulation of the emission energy may be achieved by appropriate choice of the shell structure. The emission at highest energy is generated in the NWs with tunneling thin AlGaAs inner shell and thin GaAs outer shell due to recombination of the photoexcited electrons confined in the outer shell with the holes in the core. Lower energy emission was shown to occur in the NWs with thick outer shell grown in the form of a short-period GaAs/AlGaAs multiple quantum well structure. In this case, the tunneling probability through the multiple quantum wells controls the energy emitted by the NWs. The doping of core results in dominated low energy emission from the GaAs core.

  17. The Sloan Digital Sky Survey-II: Photometry and Supernova Ia Light Curves from the 2005 Data

    SciTech Connect (OSTI)

    Holtzman, Jon A.; /New Mexico State U.; Marriner, John; /Fermilab; Kessler, Richard; /KICP, Chicago /Chicago U., EFI; Sako, Masao; /KIPAC, Menlo Park /Pennsylvania U.; Dilday, Ben; /KICP, Chicago /Chicago U.; Frieman, Joshua A.; /Fermilab /KICP, Chicago /Chicago U., Astron. Astrophys. Ctr.; Schneider, Donald P.; /Penn State U., Astron. Astrophys.; Bassett, Bruce; /Cape Town U., Dept. Math. /South African Astron. Observ.; Becker, Andrew; /Washington U., Seattle, Astron. Dept.; Cinabro, David; /Wayne State U.; DeJongh, Fritz; /KICP, Chicago; Depoy, Darren L.; /Ohio State U., Dept. Astron.; Doi, Mamoru; /Tokyo U., Inst. Astron.; Garnavich, Peter M.; /Notre Dame U.; Hogan, Craig J.; /Washington U., Seattle, Astron. Dept.; Jha, Saurabh; /KIPAC, Menlo Park /Rutgers U., Piscataway; Konishi, Kohki; /Tokyo U., ICRR; Lampeitl, Hubert; /Baltimore, Space Telescope Sci. /Portsmouth U., ICG; Marshall, Jennifer L.; /Ohio State U., Dept. Astron.; McGinnis, David; Miknaitis, Gajus; /KICP, Chicago /Portsmouth U., ICG /Ohio State U., Dept. Astron. /Baltimore, Space Telescope Sci. /Johns Hopkins U. /Rochester Inst. Tech. /KIPAC, Menlo Park /Portsmouth U., ICG /Tokyo U., Inst. Astron. /South African Astron. Observ. /Cape Town U. /Tokyo U., ICRR /KIPAC, Menlo Park

    2010-08-26T23:59:59.000Z

    We present ugriz light curves for 146 spectroscopically confirmed or spectroscopically probable Type Ia supernovae from the 2005 season of the SDSS-II Supernova survey. The light curves have been constructed using a photometric technique that we call scene modeling, which is described in detail here; the major feature is that supernova brightnesses are extracted from a stack of images without spatial resampling or convolution of the image data. This procedure produces accurate photometry along with accurate estimates of the statistical uncertainty, and can be used to derive photometry taken with multiple telescopes. We discuss various tests of this technique that demonstrate its capabilities. We also describe the methodology used for the calibration of the photometry, and present calibrated magnitudes and fluxes for all of the spectroscopic SNe Ia from the 2005 season.

  18. Is the central binary system of the planetary nebula Henize 2-428 a Type Ia supernova progenitor?

    E-Print Network [OSTI]

    Garcia-Berro, Enrique; Althaus, Leandro G

    2015-01-01T23:59:59.000Z

    We account for recent observations of the binary system at the center of the bipolar planetary nebula Henize 2-428 by the presence of one degenerate core with a low-mass main sequence companion, rather than by two degenerate objects. We argue that the variability of the He II 5412A spectral line can be accounted for by a time-varying broad absorption line from the central star on top of which there is a time-varying narrow emission line from the compact nebula. The two (almost) symmetric broad minima in the light curve are attributed to tidal distortion caused by a companion. We find problems in the recently proposed and competing explanation of two equal-mass degenerate objects that supposedly will eventually merge, possibly leading to a SN Ia. We conclude that Henize 2-428 cannot be claimed yet to support the double-degenerate scenario for Type Ia supernovae.

  19. 0.7-eV GaInAs Junction for a GaInP/GaAs/GaInAs(1eV)/GaInAs(0.7eV) Four-Junction Solar Cell

    SciTech Connect (OSTI)

    Friedman, D. J.; Geisz, J. F.; Norman, A. G.; Wanlass, M. W.; Kurtz, S. R.

    2006-01-01T23:59:59.000Z

    We discuss recent developments in III-V multijunction solar cells, focusing on adding a fourth junction to the Ga{sub 0.5}In{sub 0.5} P/GaAs/Ga{sub 0.75}In{sub 0.25}As inverted three-junction cell. This cell, grown inverted on GaAs so that the lattice-mismatched Ga{sub 0.75}In{sub 0.25}As third junction is the last one grown, has demonstrated 38% efficiency, and 40% is likely in the near future. To achieve still further gains, a lower-bandgap Ga{sub x}In{sub 1-x}As fourth junction could be added to the three-junction structure for a four-junction cell whose efficiency could exceed 45% under concentration. Here, we present the initial development of the Ga{sub x}In{sub 1-x}As fourth junction. Junctions of various bandgaps ranging from 0.88 to 0.73 eV were grown, in order to study the effect of the different amounts of lattice mismatch. At a bandgap of 0.88 eV, junctions were obtained with very encouraging {approx}80% quantum efficiency, 57% fill factor, and 0.36 eV open-circuit voltage. The device performance degrades with decreasing bandgap (i.e., increasing lattice mismatch). We model the four-junction device efficiency vs. fourth junction bandgap to show that an 0.7-eV fourth-junction bandgap, while optimal if it could be achieved in practice, is not necessary; an 0.9-eV bandgap would still permit significant gains in multijunction cell efficiency while being easier to achieve than the lower-bandgap junction.

  20. THE IMPACT OF TYPE Ia SUPERNOVA EXPLOSIONS ON HELIUM COMPANIONS IN THE CHANDRASEKHAR-MASS EXPLOSION SCENARIO

    SciTech Connect (OSTI)

    Liu Zhengwei; Wang, B.; Han, Z. W. [Yunnan Observatories, Chinese Academy of Sciences, Kunming 650011 (China); Pakmor, R. [Heidelberger Institut fuer Theoretische Studien, Schloss-Wolfsbrunnenweg 35, D-69118 Heidelberg (Germany); Seitenzahl, I. R.; Hillebrandt, W.; Kromer, M.; Edelmann, P.; Taubenberger, S. [Max-Planck-Institut fuer Astrophysik, Karl-Schwarzschild-Str. 1, D-85741 Garching (Germany); Roepke, F. K. [Institut fuer Theoretische Physik und Astrophysik, Universitaet Wuerzburg, Am Hubland, D-97074 Wuerzburg (Germany); Maeda, K., E-mail: zwliu@ynao.ac.cn [Kavli Institute for the Physics and Mathematics of the Universe (Kavli-IPMU), Todai Institutes for Advanced Study (TODIAS), University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8583 (Japan)

    2013-09-01T23:59:59.000Z

    In the version of the single-degenerate scenario of Type Ia supernovae (SNe Ia) studied here, a carbon-oxygen white dwarf explodes close to the Chandrasekhar limit after accreting material from a non-degenerate helium (He) companion star. In the present study, we employ the STELLAR GADGET code to perform three-dimensional hydrodynamical simulations of the interaction of the SN Ia ejecta with the He companion star taking into account its orbital motion and spin. It is found that only 2%-5% of the initial companion mass is stripped off from the outer layers of He companion stars due to the supernova (SN) impact. The dependence of the unbound mass (or the kick velocity) on the orbital separation can be fitted to a good approximation by a power law for a given companion model. After the SN impact, the outer layers of a He donor star are significantly enriched with heavy elements from the low-expansion-velocity tail of SN Ia ejecta. The total mass of accumulated SN-ejecta material on the companion surface reaches about {approx}> 10{sup -3} M{sub Sun} for different companion models. This enrichment with heavy elements provides a potential way to observationally identify the surviving companion star in SN remnants. Finally, by artificially adjusting the explosion energy of the W7 explosion model, we find that the total accumulation of SN ejecta on the companion surface is also dependent on the explosion energy with a power-law relation to a good approximation.