Exact and approximate Kohn-Sham potentials in ensemble density...
Office of Scientific and Technical Information (OSTI)
Title: Exact and approximate Kohn-Sham potentials in ensemble density-functional theory Authors: Yang, Zeng-hui ; Trail, John R. ; Pribram-Jones, Aurora ; Burke, Kieron ; Needs, ...
The Greatest Mathematical Discovery?
Bailey, David H.; Borwein, Jonathan M.
2010-05-12
What mathematical discovery more than 1500 years ago: (1) Is one of the greatest, if not the greatest, single discovery in the field of mathematics? (2) Involved three subtle ideas that eluded the greatest minds of antiquity, even geniuses such as Archimedes? (3) Was fiercely resisted in Europe for hundreds of years after its discovery? (4) Even today, in historical treatments of mathematics, is often dismissed with scant mention, or else is ascribed to the wrong source? Answer: Our modern system of positional decimal notation with zero, together with the basic arithmetic computational schemes, which were discovered in India about 500 CE.
Quigg, Chris; /Fermilab
2005-02-01
It is a pleasure to be part of the SLAC Summer Institute again, not simply because it is one of the great traditions in our field, but because this is a moment of great promise for particle physics. I look forward to exploring many opportunities with you over the course of our two weeks together. My first task in talking about Nature's Greatest Puzzles, the title of this year's Summer Institute, is to deconstruct the premise a little bit.
Nishikawa, Takeshi
2014-07-15
Most conventional atomic models in a plasma do not treat the effect of the plasma on the free-electron state density. Using a nearest neighbor approximation, the state densities in hydrogenic plasmas for both bound and free electrons were evaluated and the effect of the plasma on the atomic model (especially for the state density of the free electron) was studied. The model evaluates the electron-state densities using the potential distribution formed by the superposition of the Coulomb potentials of two ions. The potential from one ion perturbs the electronic state density on the other. Using this new model, one can evaluate the free-state density without making any ad-hoc assumptions. The resulting contours of the average ionization degree, given as a function of the plasma temperature and density, are shifted slightly to lower temperatures because of the effect of the increasing free-state density.
Double-hybrid density-functional theory with meta-generalized-gradient approximations
Souvi, Sidi M. O. Sharkas, Kamal; Toulouse, Julien; CNRS, UMR 7616, Laboratoire de Chimie Théorique, F-75005 Paris
2014-02-28
We extend the previously proposed one-parameter double-hybrid density-functional theory [K. Sharkas, J. Toulouse, and A. Savin, J. Chem. Phys. 134, 064113 (2011)] to meta-generalized-gradient-approximation (meta-GGA) exchange-correlation density functionals. We construct several variants of one-parameter double-hybrid approximations using the Tao-Perdew-Staroverov-Scuseria (TPSS) meta-GGA functional and test them on test sets of atomization energies and reaction barrier heights. The most accurate variant uses the uniform coordinate scaling of the density and of the kinetic energy density in the correlation functional, and improves over both standard Kohn-Sham TPSS and second-order Møller-Plesset calculations.
Two-component hybrid time-dependent density functional theory within the Tamm-Dancoff approximation
Kühn, Michael; Weigend, Florian
2015-01-21
We report the implementation of a two-component variant of time-dependent density functional theory (TDDFT) for hybrid functionals that accounts for spin-orbit effects within the Tamm-Dancoff approximation (TDA) for closed-shell systems. The influence of the admixture of Hartree-Fock exchange on excitation energies is investigated for several atoms and diatomic molecules by comparison to numbers for pure density functionals obtained previously [M. Kühn and F. Weigend, J. Chem. Theory Comput. 9, 5341 (2013)]. It is further related to changes upon switching to the local density approximation or using the full TDDFT formalism instead of TDA. Efficiency is demonstrated for a comparably large system, Ir(ppy){sub 3} (61 atoms, 1501 basis functions, lowest 10 excited states), which is a prototype molecule for organic light-emitting diodes, due to its “spin-forbidden” triplet-singlet transition.
Kraisler, Eli; Kronik, Leeor
2014-05-14
The fundamental gap is a central quantity in the electronic structure of matter. Unfortunately, the fundamental gap is not generally equal to the Kohn-Sham gap of density functional theory (DFT), even in principle. The two gaps differ precisely by the derivative discontinuity, namely, an abrupt change in slope of the exchange-correlation energy as a function of electron number, expected across an integer-electron point. Popular approximate functionals are thought to be devoid of a derivative discontinuity, strongly compromising their performance for prediction of spectroscopic properties. Here we show that, in fact, all exchange-correlation functionals possess a derivative discontinuity, which arises naturally from the application of ensemble considerations within DFT, without any empiricism. This derivative discontinuity can be expressed in closed form using only quantities obtained in the course of a standard DFT calculation of the neutral system. For small, finite systems, addition of this derivative discontinuity indeed results in a greatly improved prediction for the fundamental gap, even when based on the most simple approximate exchange-correlation density functional – the local density approximation (LDA). For solids, the same scheme is exact in principle, but when applied to LDA it results in a vanishing derivative discontinuity correction. This failure is shown to be directly related to the failure of LDA in predicting fundamental gaps from total energy differences in extended systems.
Relativistic equation of state at subnuclear densities in the Thomas-Fermi approximation
Zhang, Z. W.; Shen, H., E-mail: shennankai@gmail.com [School of Physics, Nankai University, Tianjin 300071 (China)
2014-06-20
We study the non-uniform nuclear matter using the self-consistent Thomas-Fermi approximation with a relativistic mean-field model. The non-uniform matter is assumed to be composed of a lattice of heavy nuclei surrounded by dripped nucleons. At each temperature T, proton fraction Y{sub p} , and baryon mass density ? {sub B}, we determine the thermodynamically favored state by minimizing the free energy with respect to the radius of the Wigner-Seitz cell, while the nucleon distribution in the cell can be determined self-consistently in the Thomas-Fermi approximation. A detailed comparison is made between the present results and previous calculations in the Thomas-Fermi approximation with a parameterized nucleon distribution that has been adopted in the widely used Shen equation of state.
Thermally-assisted-occupation density functional theory with generalized-gradient approximations
Chai, Jeng-Da
2014-05-14
We extend the recently proposed thermally-assisted-occupation density functional theory (TAO-DFT) [J.-D. Chai, J. Chem. Phys. 136, 154104 (2012)] to generalized-gradient approximation (GGA) exchange-correlation density functionals. Relative to our previous TAO-LDA (i.e., the local density approximation to TAO-DFT), the resulting TAO-GGAs are significantly superior for a wide range of applications, such as thermochemistry, kinetics, and reaction energies. For noncovalent interactions, TAO-GGAs with empirical dispersion corrections are shown to yield excellent performance. Due to their computational efficiency for systems with strong static correlation effects, TAO-LDA and TAO-GGAs are applied to study the electronic properties (e.g., the singlet-triplet energy gaps, vertical ionization potentials, vertical electron affinities, fundamental gaps, and symmetrized von Neumann entropy) of acenes with different number of linearly fused benzene rings (up to 100), which is very challenging for conventional electronic structure methods. The ground states of acenes are shown to be singlets for all the chain lengths studied here. With the increase of acene length, the singlet-triplet energy gaps, vertical ionization potentials, and fundamental gaps decrease monotonically, while the vertical electron affinities and symmetrized von Neumann entropy (i.e., a measure of polyradical character) increase monotonically.
Relativistic Coulomb excitation within the time dependent superfluid local density approximation
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Stetcu, I.; Bertulani, C. A.; Bulgac, A.; Magierski, P.; Roche, K. J.
2015-01-06
Within the framework of the unrestricted time-dependent density functional theory, we present for the first time an analysis of the relativistic Coulomb excitation of the heavy deformed open shell nucleus 238U. The approach is based on the superfluid local density approximation formulated on a spatial lattice that can take into account coupling to the continuum, enabling self-consistent studies of superfluid dynamics of any nuclear shape. We compute the energy deposited in the target nucleus as a function of the impact parameter, finding it to be significantly larger than the estimate using the Goldhaber-Teller model. The isovector giant dipole resonance, themoreÂ Â» dipole pygmy resonance, and giant quadrupole modes are excited during the process. As a result, the one-body dissipation of collective dipole modes is shown to lead a damping width Î“â†“â‰ˆ0.4 MeV and the number of preequilibrium neutrons emitted has been quantified.Â«Â less
Ribeiro, M.
2015-06-21
Ab initio calculations of hydrogen-passivated Si nanowires were performed using density functional theory within LDA-1/2, to account for the excited states properties. A range of diameters was calculated to draw conclusions about the ability of the method to correctly describe the main trends of bandgap, quantum confinement, and self-energy corrections versus the diameter of the nanowire. Bandgaps are predicted with excellent accuracy if compared with other theoretical results like GW, and with the experiment as well, but with a low computational cost.
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Giera, Brian; Lawrence Livermore National Lab.; Henson, Neil; Kober, Edward M.; Shell, M. Scott; Squires, Todd M.
2015-02-27
We evaluate the accuracy of local-density approximations (LDAs) using explicit molecular dynamics simulations of binary electrolytes comprised of equisized ions in an implicit solvent. The Bikerman LDA, which considers ions to occupy a lattice, poorly captures excluded volume interactions between primitive model ions. Instead, LDAs based on the Carnahanâ€“Starling (CS) hard-sphere equation of state capture simulated values of ideal and excess chemical potential profiles extremely well, as is the relationship between surface charge density and electrostatic potential. Excellent agreement between the EDL capacitances predicted by CS-LDAs and computed in molecular simulations is found even in systems where ion correlations drivemoreÂ Â» strong density and free charge oscillations within the EDL, despite the inability of LDAs to capture the oscillations in the detailed EDL profiles.Â«Â less
Mardirossian, Narbe; Head-Gordon, Martin
2015-02-21
A meta-generalized gradient approximation density functional paired with the VV10 nonlocal correlation functional is presented. The functional form is selected from more than 10{sup 10} choices carved out of a functional space of almost 10{sup 40} possibilities. Raw data come from training a vast number of candidate functional forms on a comprehensive training set of 1095 data points and testing the resulting fits on a comprehensive primary test set of 1153 data points. Functional forms are ranked based on their ability to reproduce the data in both the training and primary test sets with minimum empiricism, and filtered based on a set of physical constraints and an often-overlooked condition of satisfactory numerical precision with medium-sized integration grids. The resulting optimal functional form has 4 linear exchange parameters, 4 linear same-spin correlation parameters, and 4 linear opposite-spin correlation parameters, for a total of 12 fitted parameters. The final density functional, B97M-V, is further assessed on a secondary test set of 212 data points, applied to several large systems including the coronene dimer and water clusters, tested for the accurate prediction of intramolecular and intermolecular geometries, verified to have a readily attainable basis set limit, and checked for grid sensitivity. Compared to existing density functionals, B97M-V is remarkably accurate for non-bonded interactions and very satisfactory for thermochemical quantities such as atomization energies, but inherits the demonstrable limitations of existing local density functionals for barrier heights.
Oak Ridge Removes Laboratory's Greatest Source of Groundwater...
Broader source: Energy.gov (indexed) [DOE]
the 4,000-gallon Tank W-1A, which was ORNLs greatest source of groundwater contamination. Workers remove the 4,000-gallon Tank W-1A, which was ORNL's greatest source of ...
Xu, Zhuo Gu, Bo; Mori, Michiyasu; Maekawa, Sadamichi; Ziman, Timothy
2015-05-07
We analyze the spin Hall effect in CuIr alloys in theory by the combined approach of the density functional theory (DFT) and Hartree-Fock (HF) approximation. The spin Hall angle (SHA) is obtained to be negative without the local correlation effects. After including the local correlation effects of the 5d orbitals of Ir impurities, the SHA becomes positive with realistic correlation parameters and consistent with experiment [Niimi et al., Phys. Rev. Lett. 106, 126601 (2011)]. Moreover, our analysis shows that the DFTâ€‰+â€‰HF approach is a convenient and general method to study the influence of local correlation effects on the spin Hall effect.
What the World's Greatest Energy Managers Do Differently
Office of Energy Efficiency and Renewable Energy (EERE) Indexed Site
concentration of open source materials research Managing the billion-dollar U.S. ITER project I. DO Understand the GAME II. DO Build A Strong Coalition World's Greatest ...
Sato, Shunsuke A.; Taniguchi, Yasutaka; Shinohara, Yasushi; Yabana, Kazuhiro
2015-12-14
We develop methods to calculate electron dynamics in crystalline solids in real-time time-dependent density functional theory employing exchange-correlation potentials which reproduce band gap energies of dielectrics; a meta-generalized gradient approximation was proposed by Tran and Blaha [Phys. Rev. Lett. 102, 226401 (2009)] (TBm-BJ) and a hybrid functional was proposed by Heyd, Scuseria, and Ernzerhof [J. Chem. Phys. 118, 8207 (2003)] (HSE). In time evolution calculations employing the TB-mBJ potential, we have found it necessary to adopt the predictor-corrector step for a stable time evolution. We have developed a method to evaluate electronic excitation energy without referring to the energy functional which is unknown for the TB-mBJ potential. For the HSE functional, we have developed a method for the operation of the Fock-like term in Fourier space to facilitate efficient use of massive parallel computers equipped with graphic processing units. We compare electronic excitations in silicon and germanium induced by femtosecond laser pulses using the TB-mBJ, HSE, and a simple local density approximation (LDA). At low laser intensities, electronic excitations are found to be sensitive to the band gap energy: they are close to each other using TB-mBJ and HSE and are much smaller in LDA. At high laser intensities close to the damage threshold, electronic excitation energies do not differ much among the three cases.
Aquino, Fredy W.; Govind, Niranjan; Autschbach, Jochen
2011-10-01
Density functional theory (DFT) calculations of NMR chemical shifts and molecular g-tensors with Gaussian-type orbitals are implemented via second-order energy derivatives within the scalar relativistic zeroth order regular approximation (ZORA) framework. Nonhybrid functionals, standard (global) hybrids, and range-separated (Coulomb-attenuated, long-range corrected) hybrid functionals are tested. Origin invariance of the results is ensured by use of gauge-including atomic orbital (GIAO) basis functions. The new implementation in the NWChem quantum chemistry package is verified by calculations of nuclear shielding constants for the heavy atoms in HX (X=F, Cl, Br, I, At) and H2X (X = O, S, Se, Te, Po), and Te chemical shifts in a number of tellurium compounds. The basis set and functional dependence of g-shifts is investigated for 14 radicals with light and heavy atoms. The problem of accurately predicting F NMR shielding in UF6-nCln, n = 1 to 6, is revisited. The results are sensitive to approximations in the density functionals, indicating a delicate balance of DFT self-interaction vs. correlation. For the uranium halides, the results with the range-separated functionals are mixed.
Mizutani, U; Inukai, M; Sato, H; Zijlstra, E S; Lin, Q
2014-05-16
There are three key electronic parameters in elucidating the physics behind the Humeâ€“Rothery electron concentration rule: the square of the Fermi diameter (2kF)2, the square of the critical reciprocal lattice vector and the electron concentration parameter or the number of itinerant electrons per atom e/a. We have reliably determined these three parameters for 10 Rhombic Triacontahedron-type 2/1â€“2/1â€“2/1 (N = 680) and 1/1â€“1/1â€“1/1 (N = 160â€“162) approximants by making full use of the full-potential linearized augmented plane wave-Fourier band calculations based on all-electron density-functional theory. We revealed that the 2/1â€“2/1â€“2/1 approximants Al13Mg27Zn45 and Na27Au27Ga31 belong to two different sub-groups classified in terms of equal to 126 and 109 and could explain why they take different e/a values of 2.13 and 1.76, respectively. Among eight 1/1â€“1/1â€“1/1 approximants Al3Mg4Zn3, Al9Mg8Ag3, Al21Li13Cu6, Ga21Li13Cu6, Na26Au24Ga30, Na26Au37Ge18, Na26Au37Sn18 and Na26Cd40Pb6, the first two, the second two and the last four compounds were classified into three sub-groups with = 50, 46 and 42; and were claimed to obey the e/a = 2.30, 2.10â€“2.15 and 1.70â€“1.80 rules, respectively.
Mardirossian, Narbe; Head-Gordon, Martin
2014-05-14
The limit of accuracy for semi-empirical generalized gradient approximation (GGA) density functionals is explored by parameterizing a variety of local, global hybrid, and range-separated hybrid functionals. The training methodology employed differs from conventional approaches in 2 main ways: (1) Instead of uniformly truncating the exchange, same-spin correlation, and opposite-spin correlation functional inhomogeneity correction factors, all possible fits up to fourth order are considered, and (2) Instead of selecting the optimal functionals based solely on their training set performance, the fits are validated on an independent test set and ranked based on their overall performance on the training and test sets. The 3 different methods of accounting for exchange are trained both with and without dispersion corrections (DFT-D2 and VV10), resulting in a total of 491Â 508 candidate functionals. For each of the 9 functional classes considered, the results illustrate the trade-off between improved training set performance and diminished transferability. Since all 491Â 508 functionals are uniformly trained and tested, this methodology allows the relative strengths of each type of functional to be consistently compared and contrasted. The range-separated hybrid GGA functional paired with the VV10 nonlocal correlation functional emerges as the most accurate form for the present training and test sets, which span thermochemical energy differences, reaction barriers, and intermolecular interactions involving lighter main group elements.
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Wang, Jianwei; Zhang, Yong; Wang, Lin-Wang
2015-07-31
We propose a systematic approach that can empirically correct three major errors typically found in a density functional theory (DFT) calculation within the local density approximation (LDA) simultaneously for a set of common cation binary semiconductors, such as III-V compounds, (Ga or In)X with X = N,P,As,Sb, and II-VI compounds, (Zn or Cd)X, with X = O,S,Se,Te. By correcting (1) the binary band gaps at high-symmetry points , L, X, (2) the separation of p-and d-orbital-derived valence bands, and (3) conduction band effective masses to experimental values and doing so simultaneously for common cation binaries, the resulting DFT-LDA-based quasi-first-principles methodmoreÂ Â» can be used to predict the electronic structure of complex materials involving multiple binaries with comparable accuracy but much less computational cost than a GW level theory. This approach provides an efficient way to evaluate the electronic structures and other material properties of complex systems, much needed for material discovery and design.Â«Â less
Particle size for greatest penetration of HEPA filters - and...
Office of Scientific and Technical Information (OSTI)
Subject: 54 ENVIRONMENTAL SCIENCES; AEROSOLS; FILTRATION; FILTERS; EFFICIENCY; RADIOACTIVE AEROSOLS; AIR POLLUTION; AIR POLLUTION CONTROL; COMPARATIVE EVALUATIONS; DENSITY; ...
Question of the Week: What are Your Greatest Energy Concerns as We Approach Winter?
Broader source: Energy.gov [DOE]
We asked, you answered: What are your greatest energy concerns as we approach the winter heating season?
New Lessons Learned: Peer Exchange Call "Greatest Hits" Out Now |
Office of Energy Efficiency and Renewable Energy (EERE) Indexed Site
Department of Energy Lessons Learned: Peer Exchange Call "Greatest Hits" Out Now New Lessons Learned: Peer Exchange Call "Greatest Hits" Out Now Photo of an outreach event: a woman at a cart with an umbrella, interacting with several people standing nearby, and a sign and car on the curb. The latest in a series of Lessons Learned: Peer Exchange Call "greatest hits" summarizes top marketing and outreach takeaways from Better Buildings Residential Network members
Broader source: Energy.gov [DOE]
Excel file and dataset for Improvements in Fuel Economy for Low-MPG Vehicles Yield the Greatest Savings
Wang, Jianwei; Zhang, Yong; Wang, Lin-Wang
2015-07-31
We propose a systematic approach that can empirically correct three major errors typically found in a density functional theory (DFT) calculation within the local density approximation (LDA) simultaneously for a set of common cation binary semiconductors, such as III-V compounds, (Ga or In)X with X = N,P,As,Sb, and II-VI compounds, (Zn or Cd)X, with X = O,S,Se,Te. By correcting (1) the binary band gaps at high-symmetry points , L, X, (2) the separation of p-and d-orbital-derived valence bands, and (3) conduction band effective masses to experimental values and doing so simultaneously for common cation binaries, the resulting DFT-LDA-based quasi-first-principles method can be used to predict the electronic structure of complex materials involving multiple binaries with comparable accuracy but much less computational cost than a GW level theory. This approach provides an efficient way to evaluate the electronic structures and other material properties of complex systems, much needed for material discovery and design.
What Are Your Greatest Energy Concerns for Summer? | Department of Energy
Broader source: Energy.gov (indexed) [DOE]
Regional Partnership Overview June 2013 Briefing Overview ï‚¨ WRP Background ï‚¨ Importance of Region ï‚¨ WRP Tribal Relations Committee ï‚¨ WRP Energy Committee WRP Region's Uniqueness ï‚¨ 5 states stretching from the Great Plains to the Pacific Ocean ï‚¨ Diverse terrain ranging from desert valleys to forested mountains ï‚¨ Significant State Trust Landholdings ï‚¨ Approximately 188 Federally recognized Tribes ï‚¨ Significant amounts of Federally managed land ï‚¤ According to GSA 2004 study, WRP
Chalasani, P.; Saias, I.; Jha, S.
1996-04-08
As increasingly large volumes of sophisticated options (called derivative securities) are traded in world financial markets, determining a fair price for these options has become an important and difficult computational problem. Many valuation codes use the binomial pricing model, in which the stock price is driven by a random walk. In this model, the value of an n-period option on a stock is the expected time-discounted value of the future cash flow on an n-period stock price path. Path-dependent options are particularly difficult to value since the future cash flow depends on the entire stock price path rather than on just the final stock price. Currently such options are approximately priced by Monte carlo methods with error bounds that hold only with high probability and which are reduced by increasing the number of simulation runs. In this paper the authors show that pricing an arbitrary path-dependent option is {number_sign}-P hard. They show that certain types f path-dependent options can be valued exactly in polynomial time. Asian options are path-dependent options that are particularly hard to price, and for these they design deterministic polynomial-time approximate algorithms. They show that the value of a perpetual American put option (which can be computed in constant time) is in many cases a good approximation to the value of an otherwise identical n-period American put option. In contrast to Monte Carlo methods, the algorithms have guaranteed error bounds that are polynormally small (and in some cases exponentially small) in the maturity n. For the error analysis they derive large-deviation results for random walks that may be of independent interest.
Gedanken densities and exact constraints in density functional theory
Perdew, John P.; Department of Chemistry, Temple University, Philadelphia, Pennsylvania 19122 ; Ruzsinszky, Adrienn; Sun, Jianwei; Burke, Kieron
2014-05-14
Approximations to the exact density functional for the exchange-correlation energy of a many-electron ground state can be constructed by satisfying constraints that are universal, i.e., valid for all electron densities. Gedanken densities are designed for the purpose of this construction, but need not be realistic. The uniform electron gas is an old gedanken density. Here, we propose a spherical two-electron gedanken density in which the dimensionless density gradient can be an arbitrary positive constant wherever the density is non-zero. The Lieb-Oxford lower bound on the exchange energy can be satisfied within a generalized gradient approximation (GGA) by bounding its enhancement factor or simplest GGA exchange-energy density. This enhancement-factor bound is well known to be sufficient, but our gedanken density shows that it is also necessary. The conventional exact exchange-energy density satisfies no such local bound, but energy densities are not unique, and the simplest GGA exchange-energy density is not an approximation to it. We further derive a strongly and optimally tightened bound on the exchange enhancement factor of a two-electron density, which is satisfied by the local density approximation but is violated by all published GGA's or meta-GGAâ€™s. Finally, some consequences of the non-uniform density-scaling behavior for the asymptotics of the exchange enhancement factor of a GGA or meta-GGA are given.
Approximate circuits for increased reliability
Hamlet, Jason R.; Mayo, Jackson R.
2015-08-18
Embodiments of the invention describe a Boolean circuit having a voter circuit and a plurality of approximate circuits each based, at least in part, on a reference circuit. The approximate circuits are each to generate one or more output signals based on values of received input signals. The voter circuit is to receive the one or more output signals generated by each of the approximate circuits, and is to output one or more signals corresponding to a majority value of the received signals. At least some of the approximate circuits are to generate an output value different than the reference circuit for one or more input signal values; however, for each possible input signal value, the majority values of the one or more output signals generated by the approximate circuits and received by the voter circuit correspond to output signal result values of the reference circuit.
Approximate circuits for increased reliability
Hamlet, Jason R.; Mayo, Jackson R.
2015-12-22
Embodiments of the invention describe a Boolean circuit having a voter circuit and a plurality of approximate circuits each based, at least in part, on a reference circuit. The approximate circuits are each to generate one or more output signals based on values of received input signals. The voter circuit is to receive the one or more output signals generated by each of the approximate circuits, and is to output one or more signals corresponding to a majority value of the received signals. At least some of the approximate circuits are to generate an output value different than the reference circuit for one or more input signal values; however, for each possible input signal value, the majority values of the one or more output signals generated by the approximate circuits and received by the voter circuit correspond to output signal result values of the reference circuit.
Relativistic Random Phase Approximation At Finite Temperature
Niu, Y. F.; Paar, N.; Vretenar, D.; Meng, J.
2009-08-26
The fully self-consistent finite temperature relativistic random phase approximation (FTRRPA) has been established in the single-nucleon basis of the temperature dependent Dirac-Hartree model (FTDH) based on effective Lagrangian with density dependent meson-nucleon couplings. Illustrative calculations in the FTRRPA framework show the evolution of multipole responses of {sup 132}Sn with temperature. With increased temperature, in both monopole and dipole strength distributions additional transitions appear in the low energy region due to the new opened particle-particle and hole-hole transition channels.
Density-dependent covariant energy density functionals
Lalazissis, G. A.
2012-10-20
Relativistic nuclear energy density functionals are applied to the description of a variety of nuclear structure phenomena at and away fromstability line. Isoscalar monopole, isovector dipole and isoscalar quadrupole giant resonances are calculated using fully self-consistent relativistic quasiparticle randomphase approximation, based on the relativistic Hartree-Bogoliubovmodel. The impact of pairing correlations on the fission barriers in heavy and superheavy nuclei is examined. The role of pion in constructing desnity functionals is also investigated.
Plasma Physics Approximations in Ares
Managan, R. A.
2015-01-08
Lee & More derived analytic forms for the transport properties of a plasma. Many hydro-codes use their formulae for electrical and thermal conductivity. The coefficients are complex functions of Fermi-Dirac integrals, F_{n}( Î¼/Î¸ ), the chemical potential, Î¼ or Î¶ = ln(1+e^{ Î¼/Î¸} ), and the temperature, Î¸ = kT. Since these formulae are expensive to compute, rational function approximations were fit to them. Approximations are also used to find the chemical potential, either Î¼ or Î¶ . The fits use Î¶ as the independent variable instead of Î¼/Î¸ . New fits are provided for A^{Î±} (Î¶ ),A^{Î²} (Î¶ ), Î¶, f(Î¶ ) = (1 + e^{-Î¼/Î¸})F_{1/2}(Î¼/Î¸), F_{1/2}'/F_{1/2}, F_{c}^{Î±}, and F_{c}^{Î²}. In each case the relative error of the fit is minimized since the functions can vary by many orders of magnitude. The new fits are designed to exactly preserve the limiting values in the non-degenerate and highly degenerate limits or as Î¶â†’ 0 or âˆž. The original fits due to Lee & More and George Zimmerman are presented for comparison.
QCD in the Hartree approximation
Biro f , T. S.
1989-04-01
For QCD and expansion of the full quantum theory on a variational background forcing vanishing expectation values for colour fields is considered. This approach at low temperature (strong coupling) describes a colourless condensate of gluonic Cooper pairs. Their binding energy cancels exactly their background generated gluon mass, restoring the gauge symmetry. At high temperature (weak coupling) only a perturbative gluon plasma exists. The vacuum energy density and the phase transition temperature are related to the pairing energy. Our results scale according to asymptotic freedom. /copyright/ Academic Press, Inc. 1989
Ions in solution: Density corrected density functional theory (DC-DFT)
Kim, Min-Cheol; Sim, Eunji; Burke, Kieron
2014-05-14
Standard density functional approximations often give questionable results for odd-electron radical complexes, with the error typically attributed to self-interaction. In density corrected density functional theory (DC-DFT), certain classes of density functional theory calculations are significantly improved by using densities more accurate than the self-consistent densities. We discuss how to identify such cases, and how DC-DFT applies more generally. To illustrate, we calculate potential energy surfaces of HOÂ·Cl{sup âˆ’} and HOÂ·H{sub 2}O complexes using various common approximate functionals, with and without this density correction. Commonly used approximations yield wrongly shaped surfaces and/or incorrect minima when calculated self consistently, while yielding almost identical shapes and minima when density corrected. This improvement is retained even in the presence of implicit solvent.
An approximation technique for jet impingement flow
Najafi, Mahmoud; Fincher, Donald; Rahni, Taeibi; Javadi, KH.; Massah, H.
2015-03-10
The analytical approximate solution of a non-linear jet impingement flow model will be demonstrated. We will show that this is an improvement over the series approximation obtained via the Adomian decomposition method, which is itself, a powerful method for analysing non-linear differential equations. The results of these approximations will be compared to the Runge-Kutta approximation in order to demonstrate their validity.
Phenomenological Relativistic Energy Density Functionals
Lalazissis, G. A.; Kartzikos, S.; Niksic, T.; Paar, N.; Vretenar, D.; Ring, P.
2009-08-26
The framework of relativistic nuclear energy density functionals is applied to the description of a variety of nuclear structure phenomena, not only in spherical and deformed nuclei along the valley of beta-stability, but also in exotic systems with extreme isospin values and close to the particle drip-lines. Dynamical aspects of exotic nuclear structure is explored using the fully consistent quasiparticle random-phase approximation based on the relativistic Hartree-Bogoliubov model. Recent applications of energy density functionals with explicit density dependence of the meson-nucleon couplings are presented.
Exploring the Random Phase Approximately for materials chemistry and physics
Ruzsinsky, Adrienn
2015-03-23
This proposal focuses on improved accuracy for the delicate energy differences of interest in materials chemistry with the fully nonlocal random phase approximation (RPA) in a density functional context. Could RPA or RPA-like approaches become standard methods of first-principles electronic-structure calculation for atoms, molecules, solids, surfaces, and nano-structures? Direct RPA includes the full exact exchange energy and a nonlocal correlation energy from the occupied and unoccupied Kohn-Sham orbitals and orbital energies, with an approximate but universal description of long-range van der Waals attraction. RPA also improves upon simple pair-wise interaction potentials or vdW density functional theory. This improvement is essential to capture accurate energy differences in metals and different phases of semiconductors. The applications in this proposal are challenges for the simpler approximations of Kohn-Sham density functional theory, which are part of the current â€œstandard modelâ€ for quantum chemistry and condensed matter physics. Within this project we already applied RPA on different structural phase transitions on semiconductors, metals and molecules. Although RPA predicts accurate structural parameters, RPA has proven not equally accurate in all kinds of structural phase transitions. Therefore a correction to RPA can be necessary in many cases. We are currently implementing and testing a nonempirical, spatially nonlocal, frequency-dependent model for the exchange-correlation kernel in the adiabatic-connection fluctuation-dissipation context. This kernel predicts a nearly-exact correlation energy for the electron gas of uniform density. If RPA or RPA-like approaches prove to be reliably accurate, then expected increases in computer power may make them standard in the electronic-structure calculations of the future.
Approximate error conjugation gradient minimization methods
Kallman, Jeffrey S
2013-05-21
In one embodiment, a method includes selecting a subset of rays from a set of all rays to use in an error calculation for a constrained conjugate gradient minimization problem, calculating an approximate error using the subset of rays, and calculating a minimum in a conjugate gradient direction based on the approximate error. In another embodiment, a system includes a processor for executing logic, logic for selecting a subset of rays from a set of all rays to use in an error calculation for a constrained conjugate gradient minimization problem, logic for calculating an approximate error using the subset of rays, and logic for calculating a minimum in a conjugate gradient direction based on the approximate error. In other embodiments, computer program products, methods, and systems are described capable of using approximate error in constrained conjugate gradient minimization problems.
A Survey of Techniques for Approximate Computing
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Mittal, Sparsh
2016-03-18
Approximate computing trades off computation quality with the effort expended and as rising performance demands confront with plateauing resource budgets, approximate computing has become, not merely attractive, but even imperative. Here, we present a survey of techniques for approximate computing (AC). We discuss strategies for finding approximable program portions and monitoring output quality, techniques for using AC in different processing units (e.g., CPU, GPU and FPGA), processor components, memory technologies etc., and programming frameworks for AC. Moreover, we classify these techniques based on several key characteristics to emphasize their similarities and differences. Finally, the aim of this paper is tomoreÂ Â» provide insights to researchers into working of AC techniques and inspire more efforts in this area to make AC the mainstream computing approach in future systems.Â«Â less
Structural physical approximations of unphysical maps and generalized quantum measurements
Fiurasek, Jaromir
2002-11-01
We investigate properties of the structural physical approximation (SPA) of the partial transposition map recently introduced by Horodecki and Ekert [Phys. Rev. Lett. 89, 127902 (2002)]. We focus on the case of two-qubit states and show that in this case the map has the structure of a generalized quantum measurement followed by the preparation of a suitable output state. We also introduce SPA for a map that transforms two copies of density matrix of a single qubit onto a square of that matrix. We prove that also this map is essentially a generalized quantum measurement.
An improved proximity force approximation for electrostatics
Fosco, Cesar D.; Instituto Balseiro, Universidad Nacional de Cuyo, R8402AGP Bariloche ; Lombardo, Fernando C.; IFIBA ; Mazzitelli, Francisco D.
2012-08-15
A quite straightforward approximation for the electrostatic interaction between two perfectly conducting surfaces suggests itself when the distance between them is much smaller than the characteristic lengths associated with their shapes. Indeed, in the so called 'proximity force approximation' the electrostatic force is evaluated by first dividing each surface into a set of small flat patches, and then adding up the forces due two opposite pairs, the contributions of which are approximated as due to pairs of parallel planes. This approximation has been widely and successfully applied in different contexts, ranging from nuclear physics to Casimir effect calculations. We present here an improvement on this approximation, based on a derivative expansion for the electrostatic energy contained between the surfaces. The results obtained could be useful for discussing the geometric dependence of the electrostatic force, and also as a convenient benchmark for numerical analyses of the tip-sample electrostatic interaction in atomic force microscopes. - Highlights: Black-Right-Pointing-Pointer The proximity force approximation (PFA) has been widely used in different areas. Black-Right-Pointing-Pointer The PFA can be improved using a derivative expansion in the shape of the surfaces. Black-Right-Pointing-Pointer We use the improved PFA to compute electrostatic forces between conductors. Black-Right-Pointing-Pointer The results can be used as an analytic benchmark for numerical calculations in AFM. Black-Right-Pointing-Pointer Insight is provided for people who use the PFA to compute nuclear and Casimir forces.
Second derivatives for approximate spin projection methods
Thompson, Lee M.; Hratchian, Hrant P.
2015-02-07
The use of broken-symmetry electronic structure methods is required in order to obtain correct behavior of electronically strained open-shell systems, such as transition states, biradicals, and transition metals. This approach often has issues with spin contamination, which can lead to significant errors in predicted energies, geometries, and properties. Approximate projection schemes are able to correct for spin contamination and can often yield improved results. To fully make use of these methods and to carry out exploration of the potential energy surface, it is desirable to develop an efficient second energy derivative theory. In this paper, we formulate the analytical second derivatives for the Yamaguchi approximate projection scheme, building on recent work that has yielded an efficient implementation of the analytical first derivatives.
Semiclassical approximation to supersymmetric quantum gravity
Kiefer, Claus; Lueck, Tobias; Moniz, Paulo
2005-08-15
We develop a semiclassical approximation scheme for the constraint equations of supersymmetric canonical quantum gravity. This is achieved by a Born-Oppenheimer type of expansion, in analogy to the case of the usual Wheeler-DeWitt equation. The formalism is only consistent if the states at each order depend on the gravitino field. We recover at consecutive orders the Hamilton-Jacobi equation, the functional Schroedinger equation, and quantum gravitational correction terms to this Schroedinger equation. In particular, the following consequences are found: (i) the Hamilton-Jacobi equation and therefore the background spacetime must involve the gravitino, (ii) a (many-fingered) local time parameter has to be present on super Riem {sigma} (the space of all possible tetrad and gravitino fields) (iii) quantum supersymmetric gravitational corrections affect the evolution of the very early Universe. The physical meaning of these equations and results, in particular, the similarities to and differences from the pure bosonic case, are discussed.
Magnetic reconnection under anisotropic magnetohydrodynamic approximation
Hirabayashi, K.; Hoshino, M.
2013-11-15
We study the formation of slow-mode shocks in collisionless magnetic reconnection by using one- and two-dimensional collisionless MHD codes based on the double adiabatic approximation and the Landau closure model. We bridge the gap between the Petschek-type MHD reconnection model accompanied by a pair of slow shocks and the observational evidence of the rare occasion of in-situ slow shock observations. Our results showed that once magnetic reconnection takes place, a firehose-sense (p{sub ?}>p{sub ?}) pressure anisotropy arises in the downstream region, and the generated slow shocks are quite weak comparing with those in an isotropic MHD. In spite of the weakness of the shocks, however, the resultant reconnection rate is 10%–30% higher than that in an isotropic case. This result implies that the slow shock does not necessarily play an important role in the energy conversion in the reconnection system and is consistent with the satellite observation in the Earth's magnetosphere.
Approximate Model for Turbulent Stagnation Point Flow.
Dechant, Lawrence
2016-01-01
Here we derive an approximate turbulent self-similar model for a class of favorable pressure gradient wedge-like flows, focusing on the stagnation point limit. While the self-similar model provides a useful gross flow field estimate this approach must be combined with a near wall model is to determine skin friction and by Reynolds analogy the heat transfer coefficient. The combined approach is developed in detail for the stagnation point flow problem where turbulent skin friction and Nusselt number results are obtained. Comparison to the classical Van Driest (1958) result suggests overall reasonable agreement. Though the model is only valid near the stagnation region of cylinders and spheres it nonetheless provides a reasonable model for overall cylinder and sphere heat transfer. The enhancement effect of free stream turbulence upon the laminar flow is used to derive a similar expression which is valid for turbulent flow. Examination of free stream enhanced laminar flow suggests that the rather than enhancement of a laminar flow behavior free stream disturbance results in early transition to turbulent stagnation point behavior. Excellent agreement is shown between enhanced laminar flow and turbulent flow behavior for high levels, e.g. 5% of free stream turbulence. Finally the blunt body turbulent stagnation results are shown to provide realistic heat transfer results for turbulent jet impingement problems.
Bond selective chemistry beyond the adiabatic approximation
Butler, L.J.
1993-12-01
One of the most important challenges in chemistry is to develop predictive ability for the branching between energetically allowed chemical reaction pathways. Such predictive capability, coupled with a fundamental understanding of the important molecular interactions, is essential to the development and utilization of new fuels and the design of efficient combustion processes. Existing transition state and exact quantum theories successfully predict the branching between available product channels for systems in which each reaction coordinate can be adequately described by different paths along a single adiabatic potential energy surface. In particular, unimolecular dissociation following thermal, infrared multiphoton, or overtone excitation in the ground state yields a branching between energetically allowed product channels which can be successfully predicted by the application of statistical theories, i.e. the weakest bond breaks. (The predictions are particularly good for competing reactions in which when there is no saddle point along the reaction coordinates, as in simple bond fission reactions.) The predicted lack of bond selectivity results from the assumption of rapid internal vibrational energy redistribution and the implicit use of a single adiabatic Born-Oppenheimer potential energy surface for the reaction. However, the adiabatic approximation is not valid for the reaction of a wide variety of energetic materials and organic fuels; coupling between the electronic states of the reacting species play a a key role in determining the selectivity of the chemical reactions induced. The work described below investigated the central role played by coupling between electronic states in polyatomic molecules in determining the selective branching between energetically allowed fragmentation pathways in two key systems.
Insight into organic reactions from the direct random phase approximation and its corrections
Ruzsinszky, Adrienn; Zhang, Igor Ying; Scheffler, Matthias
2015-10-14
The performance of the random phase approximation (RPA) and beyond-RPA approximations for the treatment of electron correlation is benchmarked on three different molecular test sets. The test sets are chosen to represent three typical sources of error which can contribute to the failure of most density functional approximations in chemical reactions. The first test set (atomization and n-homodesmotic reactions) offers a gradually increasing balance of error from the chemical environment. The second test set (Diels-Alder reaction cycloaddition = DARC) reflects more the effect of weak dispersion interactions in chemical reactions. Finally, the third test set (self-interaction error 11 = SIE11) represents reactions which are exposed to noticeable self-interaction errors. This work seeks to answer whether any one of the many-body approximations considered here successfully addresses all these challenges.
Weber, J. W.; Bol, A. A. [Department of Applied Physics, Eindhoven University of Technology, Den Dolech 2, P.O. Box 513, 5600 MB Eindhoven (Netherlands); Sanden, M. C. M. van de [Department of Applied Physics, Eindhoven University of Technology, Den Dolech 2, P.O. Box 513, 5600 MB Eindhoven (Netherlands); Dutch Institute for Fundamental Energy Research (DIFFER), Nieuwegein (Netherlands)
2014-07-07
This work presents an improved thin film approximation to extract the optical conductivity from infrared transmittance in a simple yet accurate way. This approximation takes into account the incoherent reflections from the backside of the substrate. These reflections are shown to have a significant effect on the extracted optical conductivity and hence on derived parameters as carrier mobility and density. By excluding the backside reflections, the error for these parameters for typical chemical vapor deposited (CVD) graphene on a silicon substrate can be as high as 17% and 45% for the carrier mobility and density, respectively. For the mid- and near-infrared, the approximation can be simplified such that the real part of the optical conductivity is extracted without the need for a parameterization of the optical conductivity. This direct extraction is shown for Fourier transform infrared (FTIR) transmittance measurements of CVD graphene on silicon in the photon energy range of 370–7000?cm{sup ?1}. From the real part of the optical conductivity, the carrier density, mobility, and number of graphene layers are determined but also residue, originating from the graphene transfer, is detected. FTIR transmittance analyzed with the improved thin film approximation is shown to be a non-invasive, easy, and accurate measurement and analysis method for assessing the quality of graphene and can be used for other 2-D materials.
Visualization of electronic density
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Grosso, Bastien; Cooper, Valentino R.; Pine, Polina; Hashibon, Adham; Yaish, Yuval; Adler, Joan
2015-04-22
An atomâ€™s volume depends on its electronic density. Although this density can only be evaluated exactly for hydrogen-like atoms, there are many excellent numerical algorithms and packages to calculate it for other materials. 3D visualization of charge density is challenging, especially when several molecular/atomic levels are intertwined in space. We explore several approaches to 3D charge density visualization, including the extension of an anaglyphic stereo visualization application based on the AViz package to larger structures such as nanotubes. We will describe motivations and potential applications of these tools for answering interesting questions about nanotube properties.
Visualization of electronic density
Grosso, Bastien; Cooper, Valentino R.; Pine, Polina; Hashibon, Adham; Yaish, Yuval; Adler, Joan
2015-04-22
An atom’s volume depends on its electronic density. Although this density can only be evaluated exactly for hydrogen-like atoms, there are many excellent numerical algorithms and packages to calculate it for other materials. 3D visualization of charge density is challenging, especially when several molecular/atomic levels are intertwined in space. We explore several approaches to 3D charge density visualization, including the extension of an anaglyphic stereo visualization application based on the AViz package to larger structures such as nanotubes. We will describe motivations and potential applications of these tools for answering interesting questions about nanotube properties.
Aggelen, Helen van; Department of Chemistry, Duke University, Durham, North Carolina 27708 ; Yang, Yang; Yang, Weitao
2014-05-14
Despite their unmatched success for many applications, commonly used local, semi-local, and hybrid density functionals still face challenges when it comes to describing long-range interactions, static correlation, and electron delocalization. Density functionals of both the occupied and virtual orbitals are able to address these problems. The particle-hole (ph-) Random Phase Approximation (RPA), a functional of occupied and virtual orbitals, has recently known a revival within the density functional theory community. Following up on an idea introduced in our recent communication [H. van Aggelen, Y. Yang, and W. Yang, Phys. Rev. A 88, 030501 (2013)], we formulate more general adiabatic connections for the correlation energy in terms of pairing matrix fluctuations described by the particle-particle (pp-) propagator. With numerical examples of the pp-RPA, the lowest-order approximation to the pp-propagator, we illustrate the potential of density functional approximations based on pairing matrix fluctuations. The pp-RPA is size-extensive, self-interaction free, fully anti-symmetric, describes the strong static correlation limit in H{sub 2}, and eliminates delocalization errors in H{sub 2}{sup +} and other single-bond systems. It gives surprisingly good non-bonded interaction energies – competitive with the ph-RPA – with the correct R{sup ?6} asymptotic decay as a function of the separation R, which we argue is mainly attributable to its correct second-order energy term. While the pp-RPA tends to underestimate absolute correlation energies, it gives good relative energies: much better atomization energies than the ph-RPA, as it has no tendency to underbind, and reaction energies of similar quality. The adiabatic connection in terms of pairing matrix fluctuation paves the way for promising new density functional approximations.
An approximate framework for quantum transport calculation with model order reduction
Chen, Quan; Li, Jun; Yam, Chiyung; Zhang, Yu; Wong, Ngai; Chen, Guanhua
2015-04-01
A new approximate computational framework is proposed for computing the non-equilibrium charge density in the context of the non-equilibrium Green's function (NEGF) method for quantum mechanical transport problems. The framework consists of a new formulation, called the X-formulation, for single-energy density calculation based on the solution of sparse linear systems, and a projection-based nonlinear model order reduction (MOR) approach to address the large number of energy points required for large applied biases. The advantages of the new methods are confirmed by numerical experiments.
Litvinova, E.; Ring, P.; Tselyaev, V.; Langanke, K.
2009-05-15
Theoretical studies of low-lying dipole strength in even-even spherical nuclei within the relativistic quasiparticle time blocking approximation (RQTBA) are presented. The RQTBA developed recently as an extension of the self-consistent relativistic quasiparticle random-phase approximation (RQRPA) enables one to investigate the effects of the coupling of two-quasiparticle excitations to collective vibrations within a fully consistent calculation scheme based on covariant energy density functional theory. Dipole spectra of even-even {sup 130}Sn-{sup 140}Sn and {sup 68}Ni-{sup 78}Ni isotopes calculated within both RQRPA and RQTBA show two well-separated collective structures: the higher lying giant dipole resonance and the lower lying pygmy dipole resonance, which can be identified by the different behavior of the transition densities of states in these regions.
The Columbia Americas Greatest Power Stream
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Volume One Film Collection Volume Two 75th Anniversary Hydropower in the Northwest Woody Guthrie Videos Strategic Direction Branding & Logos Power of the River History Book...
The standard modelâ€™s greatest triumph
Gabrielse, Gerald
2013-12-01
The standard model predicts the electron magnetic moment to an astonishing accuracy of one part in a trillion.
The standard modelâ€™s greatest triumph
Gabrielse, Gerald
2013-12-15
The standard model predicts the electron magnetic moment to an astonishing accuracy of one part in a trillion.
Chiral dynamics and peripheral transverse densities
Granados, Carlos G.; Weiss, Christian
2014-01-01
In the partonic (or light-front) description of relativistic systems the electromagnetic form factors are expressed in terms of frame-independent charge and magnetization densities in transverse space. This formulation allows one to identify the chiral components of nucleon structure as the peripheral densities at transverse distances b = O(M{sub {pi}}{sup -1}) and compute them in a parametrically controlled manner. A dispersion relation connects the large-distance behavior of the transverse charge and magnetization densities to the spectral functions of the Dirac and Pauli form factors near the two--pion threshold at timelike t = 4 M{ sub {pi}}{sup 2}, which can be computed in relativistic chiral effective field theory. Using the leading-order approximation we (a) derive the asymptotic behavior (Yukawa tail) of the isovector transverse densities in the "chiral" region b = O(M{sub {pi}}{sup -1}) and the "molecular" region b = O(M{sub N}{sup 2}/M{sub {pi}}{sup 3}); (b) perform the heavy-baryon expansion of the transverse densities; (c) explain the relative magnitude of the peripheral charge and magnetization densities in a simple mechanical picture; (d) include Delta isobar intermediate states and study the peripheral transverse densities in the large-N{ sub c} limit of QCD; (e) quantify the region of transverse distances where the chiral components of the densities are numerically dominant; (f) calculate the chiral divergences of the b{sup 2}-weighted moments of the isovector transverse densities (charge and anomalous magnetic radii) in the limit M{sub {pi}} -> 0 and determine their spatial support. Our approach provides a concise formulation of the spatial structure of the nucleon's chiral component and offers new insights into basic properties of the chiral expansion. It relates the information extracted from low-t elastic form factors to the generalized parton distributions probed in peripheral high-energy scattering processes.
Xianlong, Gao; Polini, Marco; Tosi, M. P.; Campo, Vivaldo L. Jr.; Capelle, Klaus; Rigol, Marcos
2006-04-15
We present an extensive numerical study of the ground-state properties of confined repulsively interacting fermions in one-dimensional optical lattices. Detailed predictions for the atom-density profiles are obtained from parallel Kohn-Sham density-functional calculations and quantum Monte Carlo simulations. The density-functional calculations employ a Bethe ansatz based local-density approximation for the correlation energy that accounts for Luttinger-liquid and Mott-insulator physics. Semianalytical and fully numerical formulations of this approximation are compared with each other and with a cruder Thomas-Fermi-type local-density approximation for the total energy. Precise quantum Monte Carlo simulations are used to assess the reliability of the various local-density approximations, and in conjunction with these provide a detailed microscopic picture of the consequences of the interplay between particle-particle interactions and confinement in one-dimensional systems of strongly correlated fermions.
Density Equalizing Map Projections
Energy Science and Technology Software Center (OSTI)
1995-07-01
A geographic map is mathematically transformed so that the subareas of the map are proportional to a given quantity such as population. In other words, population density is equalized over the entire map. The transformed map can be used as a display tool, or it can be statistically analyzed. For example, cases of disease plotted on the transformed map should be uniformly distributed at random, if disease rates are everywhere equal. Geographic clusters of diseasemoreÂ Â» can be readily identified, and their statistical significance determined, on a density equalized map.Â«Â less
Charge-conjugation symmetric complete impulse approximation for...
Office of Scientific and Technical Information (OSTI)
from the spectator quark (referred to as the relativistic impulse approximation). In this study we also include the contributions from the poles of the quark which interacts with ...
How to Solve Schroedinger Problems by Approximating the Potential Function
Ledoux, Veerle; Van Daele, Marnix
2010-09-30
We give a survey over the efforts in the direction of solving the Schroedinger equation by using piecewise approximations of the potential function. Two types of approximating potentials have been considered in the literature, that is piecewise constant and piecewise linear functions. For polynomials of higher degree the approximating problem is not so easy to integrate analytically. This obstacle can be circumvented by using a perturbative approach to construct the solution of the approximating problem, leading to the so-called piecewise perturbation methods (PPM). We discuss the construction of a PPM in its most convenient form for applications and show that different PPM versions (CPM,LPM) are in fact equivalent.
Quasiparticle random-phase approximation with interactions from...
Office of Scientific and Technical Information (OSTI)
Quasiparticle random-phase approximation with interactions from the Similarity Renormalization Group Citation Details In-Document Search Title: Quasiparticle random-phase ...
A Multithreaded Algorithm for Network Alignment Via Approximate...
Office of Scientific and Technical Information (OSTI)
The best current approaches are entirely heuristic, and are iterative in nature. They generate real-valued heuristic approximations that must be rounded to find integer solutions. ...
ANALOG QUANTUM NEURON FOR FUNCTIONS APPROXIMATION A. EZHOV; A...
Office of Scientific and Technical Information (OSTI)
FOR FUNCTIONS APPROXIMATION A. EZHOV; A. KHROMOV; G. BERMAN 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; IMPLEMENTATION; NERVE CELLS; WAVEGUIDES We describe a system able...
Multiple density layered insulator
Alger, Terry W.
1994-01-01
A multiple density layered insulator for use with a laser is disclosed wh provides at least two different insulation materials for a laser discharge tube, where the two insulation materials have different thermoconductivities. The multiple layer insulation materials provide for improved thermoconductivity capability for improved laser operation.
Vranjes, J.; Kono, M.
2015-01-15
Inhomogeneous plasmas and fluids contain energy stored in inhomogeneity and they naturally tend to relax into lower energy states by developing instabilities or by diffusion. But the actual amount of energy in such inhomogeneities has remained unknown. In the present work, the amount of energy stored in a density gradient is calculated for several specific density profiles in a cylindrical configuration. This is of practical importance for drift wave instability in various plasmas, and, in particular, in its application in models dealing with the heating of solar corona because the instability is accompanied with stochastic heating, so the energy contained in inhomogeneity is effectively transformed into heat. It is shown that even for a rather moderate increase of the density at the axis in magnetic structures in the corona by a factor 1.5 or 3, the amount of excess energy per unit volume stored in such a density gradient becomes several orders of magnitude greater than the amount of total energy losses per unit volume (per second) in quiet regions in the corona. Consequently, within the life-time of a magnetic structure such energy losses can easily be compensated by the stochastic drift wave heating.
Multiple density layered insulator
Alger, T.W.
1994-09-06
A multiple density layered insulator for use with a laser is disclosed which provides at least two different insulation materials for a laser discharge tube, where the two insulation materials have different thermoconductivities. The multiple layer insulation materials provide for improved thermoconductivity capability for improved laser operation. 4 figs.
The problem of the universal density functional and the density matrix functional theory
Bobrov, V. B. Trigger, S. A.
2013-04-15
The analysis in this paper shows that the Hohenberg-Kohn theorem is the constellation of two statements: (i) the mathematically rigorous Hohenberg-Kohn lemma, which demonstrates that the same ground-state density cannot correspond to two different potentials of an external field, and (ii) the hypothesis of the existence of the universal density functional. Based on the obtained explicit expression for the nonrel-ativistic particle energy in a local external field, we prove that the energy of the system of more than two non-interacting electrons cannot be a functional of the inhomogeneous density. This result is generalized to the system of interacting electrons. It means that the Hohenberg-Kohn lemma cannot provide justification of the universal density functional for fermions. At the same time, statements of the density functional theory remain valid when considering any number of noninteracting ground-state bosons due to the Bose condensation effect. In the framework of the density matrix functional theory, the hypothesis of the existence of the universal density matrix functional corresponds to the cases of noninteracting particles and to interaction in the Hartree-Fock approximation.
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Density Log Jump to: navigation, search GEOTHERMAL ENERGYGeothermal Home Exploration Technique: Density Log Details Activities (7) Areas (6) Regions (0) NEPA(0) Exploration...
Rock Density | Open Energy Information
Density Jump to: navigation, search GEOTHERMAL ENERGYGeothermal Home Exploration Technique: Rock Density Details Activities (2) Areas (2) Regions (0) NEPA(0) Exploration Technique...
Properties of the Boltzmann equation in the classical approximation
Tanji, Naoto; Epelbaum, Thomas; Gelis, Francois; Wu, Bin
2014-12-30
We study the Boltzmann equation with elastic point-like scalar interactions in two different versions of the the classical approximation. Although solving numerically the Boltzmann equation with the unapproximated collision term poses no problem, this allows one to study the effect of the ultraviolet cutoff in these approximations. This cutoff dependence in the classical approximations of the Boltzmann equation is closely related to the non-renormalizability of the classical statistical approximation of the underlying quantum field theory. The kinetic theory setup that we consider here allows one to study in a much simpler way the dependence on the ultraviolet cutoff, since one has also access to the non-approximated result for comparison.
Properties of the Boltzmann equation in the classical approximation
Epelbaum, Thomas; Gelis, FranÃ§ois; Tanji, Naoto; Wu, Bin
2014-12-30
We examine the Boltzmann equation with elastic point-like scalar interactions in two different versions of the the classical approximation. Although solving numerically the Boltzmann equation with the unapproximated collision term poses no problem, this allows one to study the effect of the ultraviolet cutoff in these approximations. This cutoff dependence in the classical approximations of the Boltzmann equation is closely related to the non-renormalizability of the classical statistical approximation of the underlying quantum field theory. The kinetic theory setup that we consider here allows one to study in a much simpler way the dependence on the ultraviolet cutoff, since one has also access to the non-approximated result for comparison.
Properties of the Boltzmann equation in the classical approximation
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Epelbaum, Thomas; Gelis, FranÃ§ois; Tanji, Naoto; Wu, Bin
2014-12-30
We examine the Boltzmann equation with elastic point-like scalar interactions in two different versions of the the classical approximation. Although solving numerically the Boltzmann equation with the unapproximated collision term poses no problem, this allows one to study the effect of the ultraviolet cutoff in these approximations. This cutoff dependence in the classical approximations of the Boltzmann equation is closely related to the non-renormalizability of the classical statistical approximation of the underlying quantum field theory. The kinetic theory setup that we consider here allows one to study in a much simpler way the dependence on the ultraviolet cutoff, since onemoreÂ Â» has also access to the non-approximated result for comparison.Â«Â less
Higher-degree linear approximations of nonlinear systems
Karahan, S.
1989-01-01
In this dissertation, the author develops a new method for obtaining higher degree linear approximations of nonlinear control systems. The standard approach in the analysis and synthesis of nonlinear systems is a first order approximation by a linear model. This is usually performed by obtaining a series expansion of the system at some nominal operating point and retaining only the first degree terms in the series. The accuracy of this approximation depends on how far the system moves away from the normal point, and on the relative magnitudes of the higher degree terms in the series expansion. The approximation is achieved by finding an appropriate nonlinear coordinate transformation-feedback pair to perform the higher degree linearization. With the proposed method, one can improve the accuracy of the approximation up to arbitrarily higher degrees, provided certain solvability conditions are satisfied. The Hunt-Su linearizability theorem makes these conditions precise. This approach is similar to Poincare's Normal Form Theorem in formulation, but different in its solution method. After some mathematical background the author derives a set of equations (called the Homological Equations). A solution to this system of linear equations is equivalent to the solution to the problem of approximate linearization. However, it is generally not possible to solve the system of equations exactly. He outlines a method for systematically finding approximate solutions to these equations using singular value decomposition, while minimizing an error with respect to some defined norm.
Communication: Improved pair approximations in local coupled-cluster methods
Schwilk, Max; Werner, Hans-Joachim; Usvyat, Denis
2015-03-28
In local coupled cluster treatments the electron pairs can be classified according to the magnitude of their energy contributions or distances into strong, close, weak, and distant pairs. Different approximations are introduced for the latter three classes. In this communication, an improved simplified treatment of close and weak pairs is proposed, which is based on long-range cancellations of individually slowly decaying contributions in the amplitude equations. Benchmark calculations for correlation, reaction, and activation energies demonstrate that these approximations work extremely well, while pair approximations based on local second-order MÃ¸ller-Plesset theory can lead to errors that are 1-2 orders of magnitude larger.
Improved approximate formulas for flux from cylindrical and rectangular sources
Wallace, O.J.; Bokharee, S.A.
1993-03-01
This report provides two new approximate formulas for the flux at detector points outside the radial and axial extensions of a homogeneous cylindrical source and improved approximate formulas for the flux at points opposite rectangular surface sources. These formulas extend the range of geometries for which analytic approximations may be used by shield design engineers to make rapid scoping studies and check more extensive calculations for reasonableness. These formulas can be used to support skeptical, independent evaluations and are also valuable teaching tools for introducing shield designers to complex shield analyses.
Smith, Kyle K. G.; Poulsen, Jens Aage Nyman, Gunnar; Rossky, Peter J.
2015-06-28
We develop two classes of quasi-classical dynamics that are shown to conserve the initial quantum ensemble when used in combination with the Feynman-Kleinert approximation of the density operator. These dynamics are used to improve the Feynman-Kleinert implementation of the classical Wigner approximation for the evaluation of quantum time correlation functions known as Feynman-Kleinert linearized path-integral. As shown, both classes of dynamics are able to recover the exact classical and high temperature limits of the quantum time correlation function, while a subset is able to recover the exact harmonic limit. A comparison of the approximate quantum time correlation functions obtained from both classes of dynamics is made with the exact results for the challenging model problems of the quartic and double-well potentials. It is found that these dynamics provide a great improvement over the classical Wigner approximation, in which purely classical dynamics are used. In a special case, our first method becomes identical to centroid molecular dynamics.
Study of multiband disordered systems using the typical medium dynamical cluster approximation
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Zhang, Yi; Terletska, Hanna; Moore, C.; Ekuma, Chinedu; Tam, Ka-Ming; Berlijn, Tom; Ku, Wei; Moreno, Juana; Jarrell, Mark
2015-11-06
We generalize the typical medium dynamical cluster approximation to multiband disordered systems. Using our extended formalism, we perform a systematic study of the nonlocal correlation effects induced by disorder on the density of states and the mobility edge of the three-dimensional two-band Anderson model. We include interband and intraband hopping and an intraband disorder potential. Our results are consistent with those obtained by the transfer matrix and the kernel polynomial methods. We also apply the method to KxFe2-ySe2 with Fe vacancies. Despite the strong vacancy disorder and anisotropy, we find the material is not an Anderson insulator. Moreover our resultsmoreÂ Â» demonstrate the application of the typical medium dynamical cluster approximation method to study Anderson localization in real materials.Â«Â less
Study of multiband disordered systems using the typical medium dynamical cluster approximation
Zhang, Yi; Terletska, Hanna; Moore, C.; Ekuma, Chinedu; Tam, Ka-Ming; Berlijn, Tom; Ku, Wei; Moreno, Juana; Jarrell, Mark
2015-11-06
We generalize the typical medium dynamical cluster approximation to multiband disordered systems. Using our extended formalism, we perform a systematic study of the nonlocal correlation effects induced by disorder on the density of states and the mobility edge of the three-dimensional two-band Anderson model. We include interband and intraband hopping and an intraband disorder potential. Our results are consistent with those obtained by the transfer matrix and the kernel polynomial methods. We also apply the method to K_{x}Fe_{2-y}Se_{2} with Fe vacancies. Despite the strong vacancy disorder and anisotropy, we find the material is not an Anderson insulator. Moreover our results demonstrate the application of the typical medium dynamical cluster approximation method to study Anderson localization in real materials.
Integral approximations to classical diffusion and smoothed particle hydrodynamics
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Du, Qiang; Lehoucq, R. B.; Tartakovsky, A. M.
2014-12-31
The contribution of the paper is the approximation of a classical diffusion operator by an integral equation with a volume constraint. A particular focus is on classical diffusion problems associated with Neumann boundary conditions. By exploiting this approximation, we can also approximate other quantities such as the flux out of a domain. Our analysis of the model equation on the continuum level is closely related to the recent work on nonlocal diffusion and peridynamic mechanics. In particular, we elucidate the role of a volumetric constraint as an approximation to a classical Neumann boundary condition in the presence of physical boundary.moreÂ Â» The volume-constrained integral equation then provides the basis for accurate and robust discretization methods. As a result, an immediate application is to the understanding and improvement of the Smoothed Particle Hydrodynamics (SPH) method.Â«Â less
Second post-Newtonian approximation of Einstein-aether theory
Xie Yi; Huang Tianyi
2008-06-15
In this paper, second post-Newtonian approximation of Einstein-aether theory is obtained by Chandrasekhar's approach. Five parametrized post-Newtonian parameters in first post-Newtonian approximation are presented after a time transformation and they are identical with previous works, in which {gamma}=1, {beta}=1, and two preferred-frame parameters remain. Meanwhile, in second post-Newtonian approximation, a parameter, which represents third order nonlinearity for gravity, is zero--the same as in general relativity. For an application for future deep space laser ranging missions, we reduce the metric coefficients for light propagation in a case of N point masses as a simplified model of the Solar System. The resulting light deflection angle in second post-Newtonian approximation poses another constraint on the Einstein-aether theory.
Molecular Solid EOS based on Quasi-Harmonic Oscillator approximation for phonons
Menikoff, Ralph
2014-09-02
A complete equation of state (EOS) for a molecular solid is derived utilizing a Helmholtz free energy. Assuming that the solid is nonconducting, phonon excitations dominate the specific heat. Phonons are approximated as independent quasi-harmonic oscillators with vibrational frequencies depending on the specific volume. The model is suitable for calibrating an EOS based on isothermal compression data and infrared/Raman spectroscopy data from high pressure measurements utilizing a diamond anvil cell. In contrast to a Mie-Gr Ìˆuneisen EOS developed for an atomic solid, the specific heat and Gr Ìˆuneisen coefficient depend on both density and temperature.
High Energy Density Capacitors
2010-07-01
BEEST Project: Recapping is developing a capacitor that could rival the energy storage potential and price of today’s best EV batteries. When power is needed, the capacitor rapidly releases its stored energy, similar to lightning being discharged from a cloud. Capacitors are an ideal substitute for batteries if their energy storage capacity can be improved. Recapping is addressing storage capacity by experimenting with the material that separates the positive and negative electrodes of its capacitors. These separators could significantly improve the energy density of electrochemical devices.
Berkel, M. van; Hogeweij, G. M. D.; Tamura, N.; Ida, K.; Zwart, H. J.; Inagaki, S.; Baar, M. R. de
2014-11-15
In this paper, a number of new explicit approximations are introduced to estimate the perturbative diffusivity (Ï‡), convectivity (V), and damping (Ï„) in a cylindrical geometry. For this purpose, the harmonic components of heat waves induced by localized deposition of modulated power are used. The approximations are based upon the heat equation in a semi-infinite cylindrical domain. The approximations are based upon continued fractions, asymptotic expansions, and multiple harmonics. The relative error for the different derived approximations is presented for different values of frequency, transport coefficients, and dimensionless radius. Moreover, it is shown how combinations of different explicit formulas can yield good approximations over a wide parameter space for different cases, such as no convection and damping, only damping, and both convection and damping. This paper is the second part (Part II) of a series of three papers. In Part I, the semi-infinite slab approximations have been treated. In Part III, cylindrical approximations are treated for heat waves traveling towards the center of the plasma.
Ou, Qi; Fatehi, Shervin; Alguire, Ethan; Subotnik, Joseph E.; Shao, Yihan
2014-07-14
Working within the Tamm-Dancoff approximation, we calculate the derivative couplings between time-dependent density-functional theory excited states by assuming that the Kohn-Sham superposition of singly excited determinants represents a true electronic wavefunction. All Pulay terms are included in our derivative coupling expression. The reasonability of our approach can be established by noting that, for closely separated electronic states in the infinite basis limit, our final expression agrees exactly with the Chernyak-Mukamel expression (with transition densities from response theory). Finally, we also validate our approach empirically by analyzing the behavior of the derivative couplings around the T{sub 1}/T{sub 2} conical intersection of benzaldehyde.
Berkel, M. van; Zwart, H. J.; Tamura, N.; Ida, K.; Hogeweij, G. M. D.; Inagaki, S.; Baar, M. R. de
2014-11-15
In this paper, a number of new approximations are introduced to estimate the perturbative diffusivity (Ï‡), convectivity (V), and damping (Ï„) in cylindrical geometry. For this purpose, the harmonic components of heat waves induced by localized deposition of modulated power are used. The approximations are based on semi-infinite slab approximations of the heat equation. The main result is the approximation of Ï‡ under the influence of V and Ï„ based on the phase of two harmonics making the estimate less sensitive to calibration errors. To understand why the slab approximations can estimate Ï‡ well in cylindrical geometry, the relationships between heat transport models in slab and cylindrical geometry are studied. In addition, the relationship between amplitude and phase with respect to their derivatives, used to estimate Ï‡, is discussed. The results are presented in terms of the relative error for the different derived approximations for different values of frequency, transport coefficients, and dimensionless radius. The approximations show a significant region in which Ï‡, V, and Ï„ can be estimated well, but also regions in which the error is large. Also, it is shown that some compensation is necessary to estimate V and Ï„ in a cylindrical geometry. On the other hand, errors resulting from the simplified assumptions are also discussed showing that estimating realistic values for V and Ï„ based on infinite domains will be difficult in practice. This paper is the first part (Part I) of a series of three papers. In Part II and Part III, cylindrical approximations based directly on semi-infinite cylindrical domain (outward propagating heat pulses) and inward propagating heat pulses in a cylindrical domain, respectively, will be treated.
Low density microcellular foams
LeMay, J.D.
1991-11-19
Disclosed is a process of producing microcellular foam which comprises the steps of: (a) selecting a multifunctional epoxy oligomer resin; (b) mixing said epoxy resin with a non-reactive diluent to form a resin-diluent mixture; (c) forming a diluent containing cross-linked epoxy gel from said resin-diluent mixture; (d) replacing said diluent with a solvent therefore; (e) replacing said solvent with liquid carbon dioxide; and (f) vaporizing off said liquid carbon dioxide under supercritical conditions, whereby a foam having a density in the range of 35-150 mg/cc and cell diameters less than about 1 [mu]m is produced. Also disclosed are the foams produced by the process. 8 figures.
Low density microcellular foams
LeMay, James D.
1992-01-01
Disclosed is a process of producing microcellular from which comprises the steps of: (a) selecting a multifunctional epoxy oligomer resin; (b) mixing said epoxy resin with a non-reactive diluent to form a resin-diluent mixture; (c) forming a diluent containing cross-linked epoxy gel from said resin-diluent mixture; (d) replacing said diluent with a solvent therefore; (e) replacing said solvent with liquid carbon dioxide; and (f) vaporizing off said liquid carbon dioxide under supercritical conditions, whereby a foam having a density in the range of 35-150 mg/cc and cell diameters less than about 1 .mu.m is produced. Also disclosed are the foams produced by the process.
Low density microcellular foams
LeMay, James D.
1991-01-01
Disclosed is a process of producing microcellular foam which comprises the steps of: (a) selecting a multifunctional epoxy oligomer resin; (b) mixing said epoxy resin with a non-reactive diluent to form a resin-diluent mixture; (c) forming a diluent containing cross-linked epoxy gel from said resin-diluent mixture; (d) replacing said diluent with a solvent therefore; (e) replacing said solvent with liquid carbon dioxide; and (f) vaporizing off said liquid carbon dioxide under supercritical conditions, whereby a foam having a density in the range of 35-150 mg/cc and cell diameters less than about 1 .mu.m is produced. Also disclosed are the foams produced by the process.
Low density microcellular foams
Aubert, James H.; Clough, Roger L.; Curro, John G.; Quintana, Carlos A.; Russick, Edward M.; Shaw, Montgomery T.
1987-01-01
Low density, microporous polymer foams are provided by a process which comprises forming a solution of polymer and a suitable solvent followed by rapid cooling of the solution to form a phase-separated system and freeze the phase-separated system. The phase-separated system comprises a polymer phase and a solvent phase, each of which is substantially continuous within the other. The morphology of the polymer phase prior to and subsequent to freezing determine the morphology of the resultant foam. Both isotropic and anisotropic foams can be produced. If isotropic foams are produced, the polymer and solvent are tailored such that the solution spontaneously phase-separates prior to the point at which any component freezes. The morphology of the resultant polymer phase determines the morphology of the resultant foam and the morphology of the polymer phase is retained by cooling the system at a rate sufficient to freeze one or both components of the system before a change in morphology can occur. Anisotropic foams are produced by forming a solution of polymer and solvent that will not phase separate prior to freezing of one or both components of the solution. In such a process, the solvent typically freezes before phase separation occurs. The morphology of the resultant frozen two-phase system determines the morphology of the resultant foam. The process involves subjecting the solution to essentially one-dimensional cooling. Means for subjecting such a solvent to one-dimensional cooling are also provided. Foams having a density of less than 0.1 g/cc and a uniform cell size of less than 10 .mu.m and a volume such that the foams have a length greater than 1 cm are provided.
Low density microcellular foams
Aubert, J.H.; Clough, R.L.; Curro, J.G.; Quintana, C.A.; Russick, E.M.; Shaw, M.T.
1985-10-02
Low density, microporous polymer foams are provided by a process which comprises forming a solution of polymer and a suitable solvent followed by rapid cooling of the solution to form a phase-separated system and freeze the phase-separated system. The phase-separated system comprises a polymer phase and a solvent phase, each of which is substantially continuous within the other. The morphology of the polymer phase prior to and subsequent to freezing determine the morphology of the resultant foam. Both isotropic and anisotropic foams can be produced. If isotropic foams are produced, the polymer and solvent are tailored such that the solution spontaneously phase-separates prior to the point at which any component freezes. The morphology of the resultant polymer phase determines the morphology of the reusltant foam and the morphology of the polymer phase is retained by cooling the system at a rate sufficient to freeze one or both components of the system before a change in morphology can occur. Anisotropic foams are produced by forming a solution of polymer and solvent that will not phase separate prior to freezing of one or both components of the solution. In such a process, the solvent typically freezes before phase separation occurs. The morphology of the resultant frozen two-phase system determines the morphology of the resultant foam. The process involves subjecting the solution to essentially one-dimensional cooling. Foams having a density of less than 0.1 g/cc and a uniform cell size of less than 10 ..mu..m and a volume such that the foams have a length greater than 1 cm are provided.
Variational principles with Padé approximants for tearing mode analysis
Cole, Andrew J.; Finn, John M.
2014-03-15
Tearing modes occur in several distinct physical regimes, and it is often important to compute the inner layer response for these modes with various effects. There is a need for an approximate and efficient method of solving the inner layer equations in all these regimes. In this paper, we introduce a method of solving the inner layer equations based on using a variational principle with Padé approximants. For all the regimes considered, the main layer equations to be solved are inhomogeneous, and Padé approximants give a convenient and efficient method of satisfying the correct asymptotic behavior at the edge of the layer. Results using this variational principle—Padé approximant method in three of these regimes is presented. These regimes are the constant-? resistive-inertial (RI) regime, the constant-? viscoresistive regime, and the non-constant-? inviscid tearing regime. The last regime includes the constant-? RI regime and the inertial regime. The results show that reasonable accuracy can be obtained very efficiently with Padé approximants having a small number of parameters.
SHOCK EMERGENCE IN SUPERNOVAE: LIMITING CASES AND ACCURATE APPROXIMATIONS
Ro, Stephen; Matzner, Christopher D.
2013-08-10
We examine the dynamics of accelerating normal shocks in stratified planar atmospheres, providing accurate fitting formulae for the scaling index relating shock velocity to the initial density and for the post-shock acceleration factor as functions of the polytropic and adiabatic indices which parameterize the problem. In the limit of a uniform initial atmosphere, there are analytical formulae for these quantities. In the opposite limit of a very steep density gradient, the solutions match the outcome of shock acceleration in exponential atmospheres.
Approximate Bisimulation-Based Reduction of Power System Dynamic Models
Stankovic, AM; Dukic, SD; Saric, AT
2015-05-01
In this paper we propose approximate bisimulation relations and functions for reduction of power system dynamic models in differential- algebraic (descriptor) form. The full-size dynamic model is obtained by linearization of the nonlinear transient stability model. We generalize theoretical results on approximate bisimulation relations and bisimulation functions, originally derived for a class of constrained linear systems, to linear systems in descriptor form. An algorithm for transient stability assessment is proposed and used to determine whether the power system is able to maintain the synchronism after a large disturbance. Two benchmark power systems are used to illustrate the proposed algorithm and to evaluate the applicability of approximate bisimulation relations and bisimulation functions for reduction of the power system dynamic models.
Fokker-Planck approximation of monoenergetic transport processes
Boergers, C.; Larsen, E.W.
1994-12-31
For transport problems with highly forward-peaked scattering, the transport equation is often approximated by the Fokker-Planck equation or, if large-angle scattering is deemed sufficiently important, by the Boltzmann-Fokker-Planck equation. In this paper, we state a simple, necessary, and sufficient condition for the validity of the simpler Fokker-Planck approximation for monoenergetic particle transport. We also show that for screened Rutherford scattering, the Fokker-Planck approximation is only marginally valid and is inaccurate unless the scattering is extremely forward peaked. (The same is true for more sophisticated models of elastic scattering of charged particles. In this paper, we restrict ourselves to screened Rutherford scattering for simplicity). More details on the results presented here will be given in forthcoming publications.
Trigonometric Pade approximants for functions with regularly decreasing Fourier coefficients
Labych, Yuliya A; Starovoitov, Alexander P [Gomel State University, Gomel (Belarus)
2009-08-31
Sufficient conditions describing the regular decrease of the coefficients of a Fourier series f(x)=a{sub 0}/2 + {sigma} a{sub n} cos kx are found which ensure that the trigonometric Pade approximants {pi}{sup t}{sub n,m}(x;f) converge to the function f in the uniform norm at a rate which coincides asymptotically with the highest possible one. The results obtained are applied to problems dealing with finding sharp constants for rational approximations. Bibliography: 31 titles.
On the approximation of crack shapes found during inservice inspection
Bhate, S.R.; Chawla, D.S.; Kushwaha, H.S.
1997-04-01
This paper addresses the characterization of axial internal flaw found during inservice inspection of a pipe. J-integral distribution for various flaw shapes is obtained using line spring finite, element method. The peak J-value and its distribution across the crack is found to be characteristic feature of each shape. The triangular shape yields peak J-value away from the center, the point of depth. The elliptic approximation results in large overestimate of J-value for unsymmetric flaws. Triangular approximation is recommended for such flaws so that further service can be obtained from the component.
Harsij, Zeynab Mirza, Behrouz
2014-12-15
A helicity entangled tripartite state is considered in which the degree of entanglement is preserved in non-inertial frames. It is shown that Quantum Entanglement remains observer independent. As another measure of quantum correlation, Quantum Discord has been investigated. It is explicitly shown that acceleration has no effect on the degree of quantum correlation for the bipartite and tripartite helicity entangled states. Geometric Quantum Discord as a Hilbert–Schmidt distance is computed for helicity entangled states. It is shown that living in non-inertial frames does not make any influence on this distance, either. In addition, the analysis has been extended beyond single mode approximation to show that acceleration does not have any impact on the quantum features in the limit beyond the single mode. As an interesting result, while the density matrix depends on the right and left Unruh modes, the Negativity as a measure of Quantum Entanglement remains constant. Also, Quantum Discord does not change beyond single mode approximation. - Highlights: • The helicity entangled states here are observer independent in non-inertial frames. • It is explicitly shown that Quantum Discord for these states is observer independent. • Geometric Quantum Discord is also not affected by acceleration increase. • Extending to beyond single mode does not change the degree of entanglement. • Beyond single mode approximation the degree of Quantum Discord is also preserved.
High Energy Density Microwaves
Phillips, R.M. [Stanford Linear Accelerator Center, Stanford, CA 94309 (United States)
1999-04-01
These proceedings represent papers presented at the RF98 Workshop entitled `High Energy Density Microwaves` held in California in October, 1998. The topics discussed were predominantly accelerator{minus}related. The Workshop dealt, for the most part, with the generation and control of electron beams, the amplification of RF signals, the design of mode converters, and the effect of very high RF field gradients. This Workshop was designed to address the concerns of the microwave tube industry worldwide, the plasma physicists who deal with very high beam currents and gigawatts of RF power, and researchers in accelerator centers around the world. Papers were presented on multibeam klystrons, gyrotron development, plasmas in microwave tubes, RF breakdown, and alternatives to conventional linear coliders at 1 TeV and above. The Workshop was partially sponsored by the US Department of Energy. There were 46 papers presented at the conference,out of which 19 have been abstracted for the Energy,Science and Technology database.(AIP)
Approximations of very weak solutions to boundary-value problems.
Berggren, Martin Olof
2003-03-01
Standard weak solutions to the Poisson problem on a bounded domain have square-integrable derivatives, which limits the admissible regularity of inhomogeneous data. The concept of solution may be further weakened in order to define solutions when data is rough, such as for inhomogeneous Dirichlet data that is only square-integrable over the boundary. Such very weak solutions satisfy a nonstandard variational form (u, v) = G(v). A Galerkin approximation combined with an approximation of the right-hand side G defines a finite-element approximation of the very weak solution. Applying conforming linear elements leads to a discrete solution equivalent to the text-book finite-element solution to the Poisson problem in which the boundary data is approximated by L{sub 2}-projections. The L{sub 2} convergence rate of the discrete solution is O(h{sub s}) for some s {element_of} (0,1/2) that depends on the shape of the domain, asserting a polygonal (two-dimensional) or polyhedral (three-dimensional) domain without slits and (only) square-integrable boundary data.
Thermal effects and sudden decay approximation in the curvaton scenario
Kitajima, Naoya; Takesako, Tomohiro; Yokoyama, Shuichiro; Langlois, David; Takahashi, Tomo E-mail: langlois@apc.univ-paris7.fr E-mail: takesako@icrr.u-tokyo.ac.jp
2014-10-01
We study the impact of a temperature-dependent curvaton decay rate on the primordial curvature perturbation generated in the curvaton scenario. Using the familiar sudden decay approximation, we obtain an analytical expression for the curvature perturbation after the decay of the curvaton. We then investigate numerically the evolution of the background and of the perturbations during the decay. We first show that the instantaneous transfer coefficient, related to the curvaton energy fraction at the decay, can be extended into a more general parameter, which depends on the net transfer of the curvaton energy into radiation energy or, equivalently, on the total entropy ratio after the complete curvaton decay. We then compute the curvature perturbation and compare this result with the sudden decay approximation prediction.
Data approximation using a blending type spline construction
Dalmo, Rune; Bratlie, Jostein
2014-11-18
Generalized expo-rational B-splines (GERBS) is a blending type spline construction where local functions at each knot are blended together by C{sup k}-smooth basis functions. One way of approximating discrete regular data using GERBS is by partitioning the data set into subsets and fit a local function to each subset. Partitioning and fitting strategies can be devised such that important or interesting data points are interpolated in order to preserve certain features. We present a method for fitting discrete data using a tensor product GERBS construction. The method is based on detection of feature points using differential geometry. Derivatives, which are necessary for feature point detection and used to construct local surface patches, are approximated from the discrete data using finite differences.
Doorway states in the random-phase approximation
De Pace, A.; Molinari, A.; WeidenmÃ¼ller, H.A.
2014-12-15
By coupling a doorway state to a sea of random background states, we develop the theory of doorway states in the framework of the random-phase approximation (RPA). Because of the symmetry of the RPA equations, that theory is radically different from the standard description of doorway states in the shell model. We derive the Pastur equation in the limit of large matrix dimension and show that the results agree with those of matrix diagonalization in large spaces. The complexity of the Pastur equation does not allow for an analytical approach that would approximately describe the doorway state. Our numerical results display unexpected features: The coupling of the doorway state with states of opposite energy leads to strong mutual attraction.
The Monte Carlo Independent Column Approximation Model Intercomparison
Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)
Project (McMIP) The Monte Carlo Independent Column Approximation Model Intercomparison Project (McMIP) Barker, Howard Meteorological Service of Canada Cole, Jason Meteorological Service of Canada Raisanen, Petri Finnish Meteorological Institute Pincus, Robert NOAA-CIRES Climate Diagnostics Center Morcrette, Jean-Jacques European Centre for Medium-Range Weather Forecasts Li, Jiangnan Canadian Center for Climate Modelling Stephens, Graeme Colorado State University Vaillancourt, Paul
Crossing contours in the interacting boson approximation (IBA) symmetry triangle
McCutchan, E. A.; Casten, R. F.
2006-11-15
Constant contours of basic observables are discussed in the context of the interacting boson approximation (IBA) symmetry triangle. Contours that exhibit orthogonal crossing within the triangle are presented as a method for determining a set of parameter values for a particular nucleus and trajectories for isotopic chains. A set of contours that highlights a class of nuclei that are outside the two-parameter IBA-1 Hamitonian space is also presented.
COMPLEXITY & APPROXIMABILITY OF QUANTIFIED & STOCHASTIC CONSTRAINT SATISFACTION PROBLEMS
H. B. HUNT; M. V. MARATHE; R. E. STEARNS
2001-06-01
Let D be an arbitrary (not necessarily finite) nonempty set, let C be a finite set of constant symbols denoting arbitrary elements of D, and let S and T be an arbitrary finite set of finite-arity relations on D. We denote the problem of determining the satisfiability of finite conjunctions of relations in S applied to variables (to variables and symbols in C) by SAT(S) (by SATc(S).) Here, we study simultaneously the complexity of decision, counting, maximization and approximate maximization problems, for unquantified, quantified and stochastically quantified formulas. We present simple yet general techniques to characterize simultaneously, the complexity or efficient approximability of a number of versions/variants of the problems SAT(S), Q-SAT(S), S-SAT(S),MAX-Q-SAT(S) etc., for many different such D,C,S,T. These versions/variants include decision, counting, maximization and approximate maximization problems, for unquantified, quantified and stochastically quantified formulas. Our unified approach is based on the following two basic concepts: (i) strongly-local replacements/reductions and (ii) relational/algebraic representability. Some of the results extend the earlier results in [Pa85,LMP99,CF+93,CF+94] Our techniques and results reported here also provide significant steps towards obtaining dichotomy theorems, for a number of the problems above, including the problems MAX-Q-SAT(S), and MAX-S-SAT(S). The discovery of such dichotomy theorems, for unquantified formulas, has received significant recent attention in the literature [CF+93, CF+94, Cr95, KSW97]. Keywords: NP-hardness; Approximation Algorithms; PSPACE-hardness; Quantified and Stochastic Constraint Satisfaction Problems.
Erba, A. Dovesi, R.; Shahrokhi, M.; Moradian, R.
2015-01-28
Harmonic and quasi-harmonic thermal properties of two isostructural simple oxides (periclase, MgO, and lime, CaO) are computed with ab initio periodic simulations based on the density-functional-theory (DFT). The more polarizable character of calcium with respect to magnesium cations is found to dramatically affect the validity domain of the quasi-harmonic approximation that, for thermal structural properties (such as temperature dependence of volume, V(T), bulk modulus, K(T), and thermal expansion coefficient, Î±(T)), reduces from [0 K-1000 K] for MgO to just [0 K-100 K] for CaO. On the contrary, thermodynamic properties (such as entropy, S(T), and constant-volume specific heat, C{sub V}(T)) are described reliably at least up to 2000 K and quasi-harmonic constant-pressure specific heat, C{sub P}(T), up to about 1000 K in both cases. The effect of the adopted approximation to the exchange-correlation functional of the DFT is here explicitly investigated by considering five different expressions of three different classes (local-density approximation, generalized-gradient approximation, and hybrids). Computed harmonic thermodynamic properties are found to be almost independent of the adopted functional, whereas quasi-harmonic structural properties are more affected by the choice of the functional, with differences that increase as the system becomes softer.
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COMPLEXITY&APPROXIMABILITY OF QUANTIFIED&STOCHASTIC CONSTRAINT SATISFACTION PROBLEMS
Hunt, H. B.; Marathe, M. V.; Stearns, R. E.
2001-01-01
Let D be an arbitrary (not necessarily finite) nonempty set, let C be a finite set of constant symbols denoting arbitrary elements of D, and let S and T be an arbitrary finite set of finite-arity relations on D. We denote the problem of determining the satisfiability of finite conjunctions of relations in S applied to variables (to variables and symbols in C) by SAT(S) (by SATc(S).) Here, we study simultaneously the complexity of decision, counting, maximization and approximate maximization problems, for unquantified, quantified and stochastically quantified formulas. We present simple yet general techniques to characterize simultaneously, the complexity or efficient approximability of a number of versions/variants of the problems SAT(S), Q-SAT(S), S-SAT(S),MAX-Q-SAT(S) etc., for many different such D,C ,S, T. These versions/variants include decision, counting, maximization and approximate maximization problems, for unquantified, quantified and stochastically quantified formulas. Our unified approach is based on the following two basic concepts: (i) strongly-local replacements/reductions and (ii) relational/algebraic represent ability. Some of the results extend the earlier results in [Pa85,LMP99,CF+93,CF+94O]u r techniques and results reported here also provide significant steps towards obtaining dichotomy theorems, for a number of the problems above, including the problems MAX-&-SAT( S), and MAX-S-SAT(S). The discovery of such dichotomy theorems, for unquantified formulas, has received significant recent attention in the literature [CF+93,CF+94,Cr95,KSW97
Compton scattering from positronium and validity of the impulse approximation
Kaliman, Z.; Pisk, K.; Pratt, R. H.
2011-05-15
The cross sections for Compton scattering from positronium are calculated in the range from 1 to 100 keV incident photon energy. The calculations are based on the A{sup 2} term of the photon-electron or photon-positron interaction. Unlike in hydrogen, the scattering occurs from two centers and the interference effect plays an important role for energies below 8 keV. Because of the interference, the criterion for validity of the impulse approximation for positronium is more restrictive compared to that for hydrogen.
Multigroup Free-atom Doppler-broadening Approximation. Experiment
Gray, Mark Girard
2015-11-06
The multigroup energy Doppler-broadening approximation agrees with continuous energy Dopplerbroadening generally to within ten percent for the total cross sections of ^{1}H,^{ 56}Fe, and ^{235}U at 250 lanl. Although this is probably not good enough for broadening from room temperature through the entire temperature range in production use, it is better than any interpolation scheme between temperatures proposed to date, and may be good enough for extrapolation from high temperatures. The method deserves further study since additional improvements are possible.
EMERGENCE OF THE KENNICUTT-SCHMIDT RELATION FROM THE SMALL-SCALE SFR-DENSITY RELATION
Gnedin, Nickolay Y.; Tasker, Elizabeth J.; Fujimoto, Yusuke
2014-05-20
We use simulations of isolated galaxies with a few parsec resolution to explore the connection between the small-scale star formation rate (SFR)-gas density relation and the induced large-scale correlation between the SFR surface density and the surface density of the molecular gas (the Kennicutt-Schmidt relation). We find that, in the simulations, a power-law small-scale ''star formation law'' directly translates into an identical power-law Kennicutt-Schmidt relation. If this conclusion holds in the reality as well, it implies that the observed approximately linear Kennicutt-Schmidt relation must reflect the approximately linear small-scale ''star formation law''.
Nikiforov, Alexander; Gamez, Jose A.; Thiel, Walter; Huix-Rotllant, Miquel; Filatov, Michael
2014-09-28
Quantum-chemical computational methods are benchmarked for their ability to describe conical intersections in a series of organic molecules and models of biological chromophores. Reference results for the geometries, relative energies, and branching planes of conical intersections are obtained using ab initio multireference configuration interaction with single and double excitations (MRCISD). They are compared with the results from more approximate methods, namely, the state-interaction state-averaged restricted ensemble-referenced Kohn-Sham method, spin-flip time-dependent density functional theory, and a semiempirical MRCISD approach using an orthogonalization-corrected model. It is demonstrated that these approximate methods reproduce the ab initio reference data very well, with root-mean-square deviations in the optimized geometries of the order of 0.1 Å or less and with reasonable agreement in the computed relative energies. A detailed analysis of the branching plane vectors shows that all currently applied methods yield similar nuclear displacements for escaping the strong non-adiabatic coupling region near the conical intersections. Our comparisons support the use of the tested quantum-chemical methods for modeling the photochemistry of large organic and biological systems.
Improved association in a classical density functional theory for water
Krebs, Eric J.; Schulte, Jeff B.; Roundy, David
2014-03-28
We present a modification to our recently published statistical associating fluid theory-based classical density functional theory for water. We have recently developed and tested a functional for the averaged radial distribution function at contact of the hard-sphere fluid that is dramatically more accurate at interfaces than earlier approximations. We now incorporate this improved functional into the association term of our free energy functional for water, improving its description of hydrogen bonding. We examine the effect of this improvement by studying two hard solutes (a hard hydrophobic rod and a hard sphere) and a Lennard-Jones approximation of a krypton atom solute. The improved functional leads to a moderate change in the density profile and a large decrease in the number of hydrogen bonds broken in the vicinity of the hard solutes. We find an improvement of the partial radial distribution for a krypton atom in water when compared with experiment.
Neutrinoless double-beta decay in covariant density functional theory
Ring, P.; Yao, J. M.; Song, L. S.; Hagino, K.; Meng, J.
2015-10-15
We use covariant density functional theory beyond mean field in order to describe neutrinoless double-beta decay in a fully relativistic way. The dynamic effects of particle-number and angular-momentum conservations as well as shape fluctuations of quadrupole character are taken into account within the generator coordinate method for both initial and final nuclei. The calculations are based on the full relativistic transition operator. The nuclear matrix elements (NMEâ€™s) for a large number of possible transitions are investigated. The results are compared with various non-relativistic calculations, in particular also with the density functional theory based on the Gogny force. We find that the non-relativistic approximation is justified and that the total NMEâ€™s can be well approximated by the pure axial-vector coupling term. This corresponds to a considerable reduction of the computational effort.
A multiscale two-point flux-approximation method
Møyner, Olav Lie, Knut-Andreas
2014-10-15
A large number of multiscale finite-volume methods have been developed over the past decade to compute conservative approximations to multiphase flow problems in heterogeneous porous media. In particular, several iterative and algebraic multiscale frameworks that seek to reduce the fine-scale residual towards machine precision have been presented. Common for all such methods is that they rely on a compatible primal–dual coarse partition, which makes it challenging to extend them to stratigraphic and unstructured grids. Herein, we propose a general idea for how one can formulate multiscale finite-volume methods using only a primal coarse partition. To this end, we use two key ingredients that are computed numerically: (i) elementary functions that correspond to flow solutions used in transmissibility upscaling, and (ii) partition-of-unity functions used to combine elementary functions into basis functions. We exemplify the idea by deriving a multiscale two-point flux-approximation (MsTPFA) method, which is robust with regards to strong heterogeneities in the permeability field and can easily handle general grids with unstructured fine- and coarse-scale connections. The method can easily be adapted to arbitrary levels of coarsening, and can be used both as a standalone solver and as a preconditioner. Several numerical experiments are presented to demonstrate that the MsTPFA method can be used to solve elliptic pressure problems on a wide variety of geological models in a robust and efficient manner.
Attractor comparisons based on density
Carroll, T. L.
2015-01-15
Recognizing a chaotic attractor can be seen as a problem in pattern recognition. Some feature vector must be extracted from the attractor and used to compare to other attractors. The field of machine learning has many methods for extracting feature vectors, including clustering methods, decision trees, support vector machines, and many others. In this work, feature vectors are created by representing the attractor as a density in phase space and creating polynomials based on this density. Density is useful in itself because it is a one dimensional function of phase space position, but representing an attractor as a density is also a way to reduce the size of a large data set before analyzing it with graph theory methods, which can be computationally intensive. The density computation in this paper is also fast to execute. In this paper, as a demonstration of the usefulness of density, the density is used directly to construct phase space polynomials for comparing attractors. Comparisons between attractors could be useful for tracking changes in an experiment when the underlying equations are too complicated for vector field modeling.
Approximate Weighted Matching On Emerging Manycore and Multithreaded Architectures
Halappanavar, Mahantesh; Feo, John T.; Villa, Oreste; Tumeo, Antonino; Pothen, Alex
2012-11-30
Graph matching is a prototypical combinatorial problem with many applications in computer science and scientific computing, but algorithms for computing optimal matchings are challenging to parallelize. Approximate matching algorithms provide an alternate route for parallelization, and in many contexts compute near-optimal matchings for large-scale graphs. We present sharedmemory parallel implementations for computing half-approximate weighted matching on state-of-the-art multicore (Intel Nehalem and AMD Magny-Cours), manycore (Nvidia Tesla and Nvidia Fermi) and massively multithreaded (Cray XMT) platforms. We provide two implementations: the first implementation uses shared work queues, and is suited to all these platforms; the second implementation is based on dataflow principles, and exploits the architectural features of the Cray XMT. Using a carefully chosen dataset that exhibits characteristics from a wide range of real-world applications, we show scalable performance across different platforms. In particular, for one instance of the input, an R-MAT graph (RMAT-G), we show speedups of: about 32 on 48 cores of an AMD Magny-Cours; 7 on 8 cores of Intel Nehalem; 3 on Nvidia Tesla and 10 on Nvidia Fermi relative to one core of Intel Nehalem; and 60 on 128 processors of Cray XMT. We demonstrate good weak and strong scaling for graphs with up to a billion edges using up to 12, 800 threads. Given the breadth of this work, we focus on simplicity and portability of software rather than excessive fine-tuning for each platform. To the best of our knowledge, this is the first such large-scale study of the half-approximate weighted matching problem on shared-memory platforms. Driven by the critical enabling role of combinatorial algorithms such as matching in scientific computing and the emergence of informatics applications, there is a growing demand to support irregular computations on current and future computing platforms. In this context, we evaluate the capability
Bonatsos, Dennis; Karampagia, S.; Casten, R. F.
2011-05-15
Using a contraction of the SU(3) algebra to the algebra of the rigid rotator in the large-boson-number limit of the interacting boson approximation (IBA) model, a line is found inside the symmetry triangle of the IBA, along which the SU(3) symmetry is preserved. The line extends from the SU(3) vertex to near the critical line of the first-order shape/phase transition separating the spherical and prolate deformed phases, and it lies within the Alhassid-Whelan arc of regularity, the unique valley of regularity connecting the SU(3) and U(5) vertices in the midst of chaotic regions. In addition to providing an explanation for the existence of the arc of regularity, the present line represents an example of an analytically determined approximate symmetry in the interior of the symmetry triangle of the IBA. The method is applicable to algebraic models possessing subalgebras amenable to contraction. This condition is equivalent to algebras in which the equilibrium ground state and its rotational band become energetically isolated from intrinsic excitations, as typified by deformed solutions to the IBA for large numbers of valence nucleons.
Surface wake in the random-phase approximation
Garcia de Abajo, F.J. ); Echenique, P.M. )
1993-11-01
The scalar-electric-potential distribution set up by an ion traveling in the vicinity of a plane solid-vacuum interface, that is, the surface-wake potential, is investigated with the specular-reflection model to describe the response of the surface and with the random-phase approximation for the dielectric function of the bulk material. This permits us to address the study of the low-velocity surface wake: the static potential is found to have a dip at the position of the ion; that dip is shifted towards the direction opposite to the velocity vector for velocities smaller than the threshold of creation of plasmons ([approx]1.3[ital v][sub [ital F
Above-threshold ionization beyond the dipole approximation
Klaiber, Michael; Hatsagortsyan, Karen Z.; Keitel, Christoph H.
2005-03-01
A generalization of the analytical theory of above-threshold ionization in the single active electron approximation is developed while taking into account leading non-dipole and relativistic corrections in the starting Hamiltonian. Special interest is placed on the high energy part of the photoelectron spectrum which consists of a plateau and a characteristic cutoff. It is shown that the correction due to the magnetic component of the laser field gives rise to a decrease of the plateau height, an increase of the maximal cutoff energy, and a drift of the emitted electrons in propagation direction of the laser field. Furthermore, the influence of the relativistic mass shift may become non-neglible by reducing the cutoff energy significantly. Spin effects or the Zitterbewegung play a comparably minor role in the investigated parameter regime of suboptical frequencies and high but not ultra-high laser intensities.
Low density carbonized composite foams
Kong, Fung-Ming
1993-01-01
A carbonized composite foam having a density less than about 50 mg/cm.sup.3 and individual cell sizes no greater than about 1 .mu.m in diameter is described, and the process of making it.
Low density carbonized composite foams
Kong, Fung-Ming
1991-01-01
A carbonized composite foam having a density less than about 50 mg/cm.sup.3 and individual cell sizes no greater than about 1 .mu.m in diameter is described, and the process of making it.
Mixed series in ultraspherical polynomials and their approximation properties
Sharapudinov, I I
2003-04-30
New (mixed) series in ultraspherical polynomials P{sub n}{sup {alpha}}{sup ,{alpha}}(x) are introduced. The basic difference between a mixed series in the polynomials P{sub n}{sup {alpha}}{sup ,{alpha}}(x) and a Fourier series in the same polynomials is as follows: a mixed series contains terms of the form (2{sup r}f{sub r,k}{sup {alpha}})/(k+2{alpha}){sup [r]}) P{sub k+r}{sup {alpha}}{sup -r,{alpha}}{sup -r}(x), where 1{<=}r is an integer and f{sub r,k}{sup {alpha}} is the kth Fourier coefficient of the derivative f{sup (r)}(x) with respect to the ultraspherical polynomials P{sub k}{sup {alpha}}{sup ,{alpha}}(x). It is shown that the partial sums Y{sub n+2r}{sup {alpha}}(f,x) of a mixed series in the polynomial P{sub k}{sup {alpha}}{sup ,{alpha}}(x) contrast favourably with Fourier sums S{sub n}{sup {alpha}}(f,x) in the same polynomials as regards their approximation properties in classes of differentiable and analytic functions, and also in classes of functions of variable smoothness. In particular, the Y{sub n+2r}{sup {alpha}}(f,x) can be used for the simultaneous approximation of a function f(x) and its derivatives of orders up to (r- 1), whereas the S{sub n}{sup {alpha}}(f,x) are not suitable for this purpose.
Low density metal hydride foams
Maienschein, Jon L.; Barry, Patrick E.
1991-01-01
Disclosed is a low density foam having a porosity of from 0 to 98% and a density less than about 0.67 gm/cc, prepared by heating a mixture of powered lithium hydride and beryllium hydride in an inert atmosphere at a temperature ranging from about 455 to about 490 K for a period of time sufficient to cause foaming of said mixture, and cooling the foam thus produced. Also disclosed is the process of making the foam.
Characterization of the homogeneous tissue mixture approximation in breast imaging dosimetry
Sechopoulos, Ioannis; Bliznakova, Kristina; Qin Xulei; Fei Baowei; Feng, Steve Si Jia
2012-08-15
Purpose: To compare the estimate of normalized glandular dose in mammography and breast CT imaging obtained using the actual glandular tissue distribution in the breast to that obtained using the homogeneous tissue mixture approximation. Methods: Twenty volumetric images of patient breasts were acquired with a dedicated breast CT prototype system and the voxels in the breast CT images were automatically classified into skin, adipose, and glandular tissue. The breasts in the classified images underwent simulated mechanical compression to mimic the conditions present during mammographic acquisition. The compressed thickness for each breast was set to that achieved during each patient's last screening cranio-caudal (CC) acquisition. The volumetric glandular density of each breast was computed using both the compressed and uncompressed classified images, and additional images were created in which all voxels representing adipose and glandular tissue were replaced by a homogeneous mixture of these two tissues in a proportion corresponding to each breast's volumetric glandular density. All four breast images (compressed and uncompressed; heterogeneous and homogeneous tissue) were input into Monte Carlo simulations to estimate the normalized glandular dose during mammography (compressed breasts) and dedicated breast CT (uncompressed breasts). For the mammography simulations the x-ray spectra used was that used during each patient's last screening CC acquisition. For the breast CT simulations, two x-ray spectra were used, corresponding to the x-ray spectra with the lowest and highest energies currently being used in dedicated breast CT prototype systems under clinical investigation. The resulting normalized glandular dose for the heterogeneous and homogeneous versions of each breast for each modality was compared. Results: For mammography, the normalized glandular dose based on the homogeneous tissue approximation was, on average, 27% higher than that estimated using the
High Density Sensor Network Development | The Ames Laboratory
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High Density Sensor Network Development
Communication: Self-interaction correction with unitary invariance in density functional theory
Pederson, Mark R.; Ruzsinszky, Adrienn; Perdew, John P.; Department of Chemistry, Temple University, Philadelphia, Pennsylvania 19122
2014-03-28
Standard spin-density functionals for the exchange-correlation energy of a many-electron ground state make serious self-interaction errors which can be corrected by the Perdew-Zunger self-interaction correction (SIC). We propose a size-extensive construction of SIC orbitals which, unlike earlier constructions, makes SIC computationally efficient, and a true spin-density functional. The SIC orbitals are constructed from a unitary transformation that is explicitly dependent on the non-interacting one-particle density matrix. When this SIC is applied to the local spin-density approximation, improvements are found for the atomization energies of molecules.
High-density fluid compositions
Sanders, D.C.
1981-09-29
Clear, high-density fluids suitable for use as well completion, packing, and perforation media comprise aqueous solutions of zinc bromide and calcium bromide having densities lying in the range of about 14.5 up to about 18.0 pounds per gallon and measured PH's lying in the range of about 3.5 up to about 6.0. Optionally, such fluids may also comprise calcium chloride and/or a soluble film-forming amine-based corrosion inhibitor. Such fluids under conditions of ordinary use exhibit low corrosion rates and have crystallization points lying well below the range of temperatures under which they are used.
Markov Jump Processes Approximating a Non-Symmetric Generalized Diffusion
Limic, Nedzad
2011-08-15
Consider a non-symmetric generalized diffusion X( Dot-Operator ) in Double-Struck-Capital-R {sup d} determined by the differential operator A(x) = -{Sigma}{sub ij} {partial_derivative}{sub i}a{sub ij}(x){partial_derivative}{sub j} + {Sigma}{sub i} b{sub i}(x){partial_derivative}{sub i}. In this paper the diffusion process is approximated by Markov jump processes X{sub n}( Dot-Operator ), in homogeneous and isotropic grids G{sub n} Subset-Of Double-Struck-Capital-R {sup d}, which converge in distribution in the Skorokhod space D([0,{infinity}), Double-Struck-Capital-R {sup d}) to the diffusion X( Dot-Operator ). The generators of X{sub n}( Dot-Operator ) are constructed explicitly. Due to the homogeneity and isotropy of grids, the proposed method for d{>=}3 can be applied to processes for which the diffusion tensor {l_brace}a{sub ij}(x){r_brace}{sub 11}{sup dd} fulfills an additional condition. The proposed construction offers a simple method for simulation of sample paths of non-symmetric generalized diffusion. Simulations are carried out in terms of jump processes X{sub n}( Dot-Operator ). For piece-wise constant functions a{sub ij} on Double-Struck-Capital-R {sup d} and piece-wise continuous functions a{sub ij} on Double-Struck-Capital-R {sup 2} the construction and principal algorithm are described enabling an easy implementation into a computer code.
Plasma digital density determining device
Sprott, Julien C.; Lovell, Thomas W.; Holly, Donald J.
1976-01-01
The density of a decaying plasma in an electrically conducting enclosure is determined by applying an excitation to the cavity formed by the enclosure and counting digitally the number of resonant frequencies traversed by the combination of the cavity and the decaying plasma.
High energy density thermal cell
Fletcher, A.N.
1980-04-29
A thermal battery is described that uses a calcium anode and a catholyte consisting of a mixture of lithium, potassium, nitrate and chloride ions. The device is operable over a temperature range of about 150 to 600/sup 0/C and produces a long lasting, high energy density output.
Statistical density modification using local pattern matching
Terwilliger, Thomas C.
2007-01-23
A computer implemented method modifies an experimental electron density map. A set of selected known experimental and model electron density maps is provided and standard templates of electron density are created from the selected experimental and model electron density maps by clustering and averaging values of electron density in a spherical region about each point in a grid that defines each selected known experimental and model electron density maps. Histograms are also created from the selected experimental and model electron density maps that relate the value of electron density at the center of each of the spherical regions to a correlation coefficient of a density surrounding each corresponding grid point in each one of the standard templates. The standard templates and the histograms are applied to grid points on the experimental electron density map to form new estimates of electron density at each grid point in the experimental electron density map.
ARM - Lesson Plans: Air Density and Temperature
Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)
Teachers' Toolbox Lesson Plans Lesson Plans: Air Density and Temperature Objective The objective of this activity is to investigate the effect of temperature on the density of air. ...
Building a Universal Nuclear Energy Density Functional
Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)
Building a Universal Nuclear Energy Density Functional Building a Universal Nuclear Energy Density Functional VaryMatrix.png Collaboration with mathematicians and computational...
Hollman, David S.; Department of Chemistry, Virginia Tech, Blacksburg, Virginia 24061 ; Schaefer, Henry F.; Valeev, Edward F.
2014-02-14
A local density fitting scheme is considered in which atomic orbital (AO) products are approximated using only auxiliary AOs located on one of the nuclei in that product. The possibility of variational collapse to an unphysical â€œattractive electronâ€ state that can affect such density fitting [P. Merlot, T. KjÃ¦rgaard, T. Helgaker, R. Lindh, F. Aquilante, S. Reine, and T. B. Pedersen, J. Comput. Chem. 34, 1486 (2013)] is alleviated by including atom-wise semidiagonal integrals exactly. Our approach leads to a significant decrease in the computational cost of density fitting for Hartreeâ€“Fock theory while still producing results with errors 2â€“5 times smaller than standard, nonlocal density fitting. Our method allows for large Hartreeâ€“Fock and density functional theory computations with exact exchange to be carried out efficiently on large molecules, which we demonstrate by benchmarking our method on 200 of the most widely used prescription drug molecules. Our new fitting scheme leads to smooth and artifact-free potential energy surfaces and the possibility of relatively simple analytic gradients.
Upgrading of biorenewables to high energy density fuels
Gordon, John C; Batista, Enrique R; Chen, Weizhong; Currier, Robert P; Dirmyer, Matthew R; John, Kevin D; Kim, Jin K; Keith, Jason; Martin, Richard L; Pierpont, Aaron W; Silks Ill, L. A. "" Pete; Smythe, Mathan C; Sutton, Andrew D; Taw, Felicia L; Trovitch, Ryan J; Vasudevan, Kalyan V; Waidmann, Christopher R; Wu, Ruilian; Baker, R. Thomas; Schlaf, Marcel
2010-12-07
According to a recent report, lignocellulose is the most abundant renewable biological resource on earth, with an annual production of {approx} 200 x 10{sup 9} tons. Conversion of lignocellulosics derived from wood, agricultural wastes, and woody grasses into liquid fuels and value-added chemical feedstocks is an active area of research that has seen an explosion of effort due to the need to replace petroleum based sources. The carbohydrates D-glucose (C{sub 6}), L-arabinose (C{sub 5}), and D-xylose (C{sub 5}) are readily obtained from the hydrolysis of lignocellulose and constitute the most abundant renewable organic carbon source on the planet. Because they are naturally produced on such a large scale, these sugars have the greatest potential to displace petrochemical derived transportation fuel. Recent efforts in our laboratories aimed towards the production of high energy density transportation fuels from carbohydrates have been structured around the parameters of selective carbohydrate carbon chain extension chemistries, low reaction temperatures, and the desired use of water or neat substrate as the solvent. Some of our efforts in this regard will be presented.
Density variations and anomalies in palladium compacts
Back, D.; Jones, T.; Ransick, M.; Walburg, T.; Werkmeister, D.
1992-05-14
Low-density compacts of palladium powder have relative densities of about 30{plus minus}10% TD. The variations in density are of concern for operations such as chemical/hydrogen pump systems because heat, mass, and momentum transport properties can be affected. Variations in density result from the inherent nature and interacting forces of UASA compaction of powder in cylinders. In addition to these expected variations, discontinuous density anomalies, such as cracks or high density ridges, are also found. An anomaly of particular concern was found to resemble a steer's head.'' it is a symmetrical region of low density located at or near the center of a compact. Typically, this region is surrounded by a band of high density, compacted palladium that sometimes exceeds the density of the surrounding compact matrix by a factor of three. This report examines these density variations and anomalies both theoretically and empirically.
Density variations and anomalies in palladium compacts
Back, D.; Jones, T.; Ransick, M.; Walburg, T.; Werkmeister, D.
1992-05-14
Low-density compacts of palladium powder have relative densities of about 30{plus_minus}10% TD. The variations in density are of concern for operations such as chemical/hydrogen pump systems because heat, mass, and momentum transport properties can be affected. Variations in density result from the inherent nature and interacting forces of UASA compaction of powder in cylinders. In addition to these expected variations, discontinuous density anomalies, such as cracks or high density ridges, are also found. An anomaly of particular concern was found to resemble a ``steer`s head.`` it is a symmetrical region of low density located at or near the center of a compact. Typically, this region is surrounded by a band of high density, compacted palladium that sometimes exceeds the density of the surrounding compact matrix by a factor of three. This report examines these density variations and anomalies both theoretically and empirically.
Sublinear scaling for time-dependent stochastic density functional theory
Gao, Yi; Neuhauser, Daniel; Baer, Roi; Rabani, Eran
2015-01-21
A stochastic approach to time-dependent density functional theory is developed for computing the absorption cross section and the random phase approximation (RPA) correlation energy. The core idea of the approach involves time-propagation of a small set of stochastic orbitals which are first projected on the occupied space and then propagated in time according to the time-dependent Kohn-Sham equations. The evolving electron density is exactly represented when the number of random orbitals is infinite, but even a small number (â‰ˆ16) of such orbitals is enough to obtain meaningful results for absorption spectrum and the RPA correlation energy per electron. We implement the approach for silicon nanocrystals using real-space grids and find that the overall scaling of the algorithm is sublinear with computational time and memory.
Probability distribution of the vacuum energy density
Duplancic, Goran; Stefancic, Hrvoje; Glavan, Drazen
2010-12-15
As the vacuum state of a quantum field is not an eigenstate of the Hamiltonian density, the vacuum energy density can be represented as a random variable. We present an analytical calculation of the probability distribution of the vacuum energy density for real and complex massless scalar fields in Minkowski space. The obtained probability distributions are broad and the vacuum expectation value of the Hamiltonian density is not fully representative of the vacuum energy density.
Marshall, J. Jr.
1961-10-24
A reactor is described in which natural-uranium bodies are located in parallel channels which extend through the graphite mass in a regular lattice. The graphite mass has additional channels that are out of the lattice and contain no uranium. These additional channels decrease in number per unit volume of graphite from the center of the reactor to the exterior and have the effect of reducing the density of the graphite more at the center than at the exterior, thereby spreading neutron activity throughout the reactor. (AEC)
Lykissa, Iliana; Li, Shu-Yi; Granqvist, Claes G.; Niklasson, Gunnar A.; Ramzan, Muhammad; Chakraborty, Sudip; Ahuja, Rajeev
2014-05-14
Thin films of V{sub 2}O{sub 5} were prepared by sputter deposition onto transparent and electrically conducting substrates and were found to be X-ray amorphous. Their electrochemical density of states was determined by chronopotentiometry and displayed a pronounced low-energy peak followed by an almost featureless contribution at higher energies. These results were compared with density functional theory calculations for amorphous V{sub 2}O{sub 5}. Significant similarities were found between measured data and computations; specifically, the experimental low-energy peak corresponds to a split-off part of the conduction band apparent in the computations. Furthermore, the calculations approximately reproduce the experimental band gap observed in optical measurements.
Investigation of physical processes limiting plasma density in H-mode on DIII-D
Maingi, R.; Mahdavi, M.A.; Jernigan, T.C.
1996-12-01
A series of experiments was conducted on the DIII-D tokamak to investigate the physical processes which limit density in high confinement mode (H-mode) discharges. The typical H-mode to low confinement mode (L-mode) transition limit at high density near the empirical Greenwald density limit was avoided by divertor pumping, which reduced divertor neutral pressure and prevented formation of a high density, intense radiation zone (MARFE) near the X-point. It was determined that the density decay time after pellet injection was independent of density relative to the Greenwald limit and increased non-linearly with the plasma current. Magnetohydrodynamic (MHD) activity in pellet-fueled plasmas was observed at all power levels, and often caused unacceptable confinement degradation, except when the neutral beam injected (NBI) power was {le} 3 MW. Formation of MARFEs on closed field lines was avoided with low safety factor (q) operation but was observed at high q, qualitatively consistent with theory. By using pellet fueling and optimizing discharge parameters to avoid each of these limits, an operational space was accessed in which density {approximately} 1.5 {times} Greenwald limit was achieved for 600 ms, and good H-mode confinement was maintained for 300 ms of the density flattop. More significantly, the density was successfully increased to the limit where a central radiative collapse was observed, the most fundamental density limit in tokamaks.
Xi Yanbin; Liu Yue [MOE Key Laboratory of Materials Modification by Laser, Electron, and Ion Beams, School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024 (China)
2012-07-15
Considering different typical electron density profiles, a multi slab approximation model is built up to study the power absorption of broadband (0.75-30 GHz) electromagnetic waves in a partially ionized nonuniform magnetized plasma layer. Based on the model, the power absorption spectra for six cases are numerically calculated and analyzed. It is shown that the absorption strongly depends on the electron density fluctuant profile, the background electron number density, and the collision frequency. A potential optimum profile is also analyzed and studied with some particular parameters.
Progress at the interface of wave-function and density-functional theories
Gidopoulos, Nikitas I.
2011-04-15
The Kohn-Sham (KS) potential of density-functional theory (DFT) emerges as the minimizing effective potential in a variational scheme that does not involve fixing the unknown single-electron density. Using Rayleigh Schroedinger (RS) perturbation theory (PT), we construct ab initio approximations for the energy difference, the minimization of which determines the KS potential directly - thereby bypassing DFT's traditional algorithm to search for the density that minimizes the total energy. From second-order RS PT, we obtain variationally stable energy differences to be minimized, solving the severe problem of variational collapse of orbital-dependent exchange-correlation functionals based on second-order RS PT.
Weck, Philippe F.; Kim, Eunja
2015-06-11
The structure, lattice dynamics and thermodynamic properties of bulk technetium were investigated within the framework of density functional theory. The phonon density of states spectrum computed with density functional perturbation theory closely matches inelastic coherent neutron scattering measurements. The thermal properties of technetium were derived from phonon frequencies calculated within the quasi-harmonic approximation (QHA), which introduces a volume dependence of phonon frequencies as a part of the anharmonic effect. As a result, the predicted thermal expansion and isobaric heat capacity of technetium are in excellent agreement with available experimental data for temperatures up to ~1600 K.
New Lessons Learned: Peer Exchange Call "Greatest Hits" Out Now...
Office of Energy Efficiency and Renewable Energy (EERE) Indexed Site
Effective marketing of multifamily upgrades depends on whether the decision maker is a tenant or building owner. Tenants are more concerned with issues, such as reduced noise, ...
Peer Exchange Calls Inspire New Lessons Learned Greatest Hits
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A new â€œLessons Learned: Peer Exchange Callsâ€ resource summarizes top takeaways shared by Better Buildings Residential Network members, from tips to collaborating with utilities to cost-effective...
Question of the Week: What are Your Greatest Energy Concerns...
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... As an alternative to defrey the cost we purchased a pellet stove now we are watching the price of pellets. Our old farm house gets plastic on the windos every winter and a major ...
Peer Exchange Calls Inspire New Lessons Learned Greatest Hits...
Office of Energy Efficiency and Renewable Energy (EERE) Indexed Site
To make collaboration with a utility easier, show how energy efficiency can solve a financial, public relations, or customer service problem for the utility. Point-based systems ...
What the World's GREATEST Energy Managers Do Differently | Department...
Office of Energy Efficiency and Renewable Energy (EERE) Indexed Site
10, 2012) (2.36 MB) More Documents & Publications Energy Management and Financing Unveiling the Implementation Guide Communicating Success, Measuring Improvements, Sharing Results
Gambacurta, D.; Catara, F.
2011-09-15
Low-energy dipole excitations are analyzed for the stable isotopes {sup 40}Ca and {sup 48}Ca in the framework of the Skyrme-second random-phase approximation. The corresponding random-phase approximation calculations provide a negligible strength distribution for both nuclei in the energy region from 5 to 10 MeV. The inclusion and the coupling of 2 particle-2 hole configurations in the second random-phase approximation lead to an appreciable dipole response at low energies for the neutron-rich nucleus {sup 48}Ca. The presence of a neutron skin in the nucleus {sup 48}Ca would suggest the interpretation of the low-lying response in terms of a pygmy excitation. The composition of the excitation modes (content of 1 particle-1 hole and 2 particle-2 hole configurations), their transition densities and their collectivity (number and coherence of the different contributions) are analyzed. This analysis indicates that, in general, these excitations cannot be clearly interpreted in terms of oscillations of the neutron skin against the core with the exception of the peak with the largest B(E1) value, which is located at 9.09 MeV. For this peak the neutron transition density dominates and the neutron and proton transition densities oscillate out of phase in the internal part of the nucleus leading to a strong mixing of isoscalar and isovector components. Therefore, this state shows some features usually associated to pygmy resonances.
Oxides having high energy densities
Ceder, Gerbrand; Kang, Kisuk
2013-09-10
Certain disclosed embodiments generally relate to oxide materials having relatively high energy and/or power densities. Various aspects of the embodiments are directed to oxide materials having a structure B.sub.i(M.sub.jY.sub.k)O.sub.2, for example, a structure Li.sub.j(Ni.sub.jY.sub.k)O.sub.2 such as Li(Ni.sub.0.5Mn.sub.0.5)O.sub.2. In this structure, Y represents one or more atoms, each independently selected from the group consisting of alkaline earth metals, transition metals, Group 14 elements, Group 15, or Group 16 elements. In some embodiments, such an oxide material may have an O3 crystal structure, and/or a layered structure such that the oxide comprises a plurality of first, repeating atomic planes comprising Li, and a plurality of second, repeating atomic planes comprising Ni and/or Y.
Marushka, Viktor; Zabeida, Oleg Martinu, Ludvik
2014-11-01
The uniformity of ion density is critical for applications relying on the ion assisted deposition technique for the fabrication of the high quality thin films. The authors propose and describe here a method allowing one to calculate the ion density distribution on spherical substrate holders under stationary and rotating conditions for different positions of the ion source. The ion beam shape was approximated by a cos{sup n} function, and the ion current density was represented by a function inversely proportional to the distance from the ion source in accordance with our experimental results. As an example, a calculation of the current density distribution on the spherical cap substrate was performed for a broad beam ion source operated with an anode current of 3?A. The authors propose an approach for process optimization with respect to the ion source position and its inclination, in terms of uniformity and absolute value of the ion current density.
Vazquez-Mayagoitia, Alvaro; Sherrill, David; Apra, Edoardo; Sumpter, Bobby G
2010-01-01
A recently proposed double-hybrid functional called XYG3 and a semilocal GGA functional (B97-D) with a semiempirical correction for van der Waals interactions have been applied to study the potential energy curves along the dissociation coordinates of weakly bound pairs of molecules governed by London dispersion and induced dipole forces. Molecules treated in this work were the parallel sandwich, T-shaped, and parallel-displaced benzene dimer, (C6H6)2; hydrogen sulfide and benzene, H2S C6H6; methane and benzene, CH4 C6H6; the methane dimer, (CH4)2; and the pyridine dimer, (C5H5N)2. We compared the potential energy curves of these functionals with previously published benchmarks at the coupled cluster singles, doubles, and perturbative triplets [CCSD(T)] complete-basis-set limit. Both functionals, XYG3 and B97-D, exhibited very good performance, reproducing accurate energies for equilibrium distances and a smooth behavior along the dissociation coordinate. Overall, we found an agreement within a few tenths of one kcal mol-1 with the CCSD(T) results across the potential energy curves.
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space, get 33%-50% power savings Implemented These Ideas in Crayon System Crayon Software Architecture Cairo is a standard, widely-used graphics API Firefox, Graphviz, Poppler, ......
Ensemble density variational methods with self- and ghost-interaction-corrected functionals
Pastorczak, Ewa; Pernal, Katarzyna
2014-05-14
Ensemble density functional theory (DFT) offers a way of predicting excited-states energies of atomic and molecular systems without referring to a density response function. Despite a significant theoretical work, practical applications of the proposed approximations have been scarce and they do not allow for a fair judgement of the potential usefulness of ensemble DFT with available functionals. In the paper, we investigate two forms of ensemble density functionals formulated within ensemble DFT framework: the Gross, Oliveira, and Kohn (GOK) functional proposed by Gross et al. [Phys. Rev. A 37, 2809 (1988)] alongside the orbital-dependent eDFT form of the functional introduced by Nagy [J. Phys. B 34, 2363 (2001)] (the acronym eDFT proposed in analogy to eHF – ensemble Hartree-Fock method). Local and semi-local ground-state density functionals are employed in both approaches. Approximate ensemble density functionals contain not only spurious self-interaction but also the so-called ghost-interaction which has no counterpart in the ground-state DFT. We propose how to correct the GOK functional for both kinds of interactions in approximations that go beyond the exact-exchange functional. Numerical applications lead to a conclusion that functionals free of the ghost-interaction by construction, i.e., eDFT, yield much more reliable results than approximate self- and ghost-interaction-corrected GOK functional. Additionally, local density functional corrected for self-interaction employed in the eDFT framework yields excitations energies of the accuracy comparable to that of the uncorrected semi-local eDFT functional.
Snow Depth and Density at End-of-Winter for NGEE Areas A, B, C and D, Barrow, Alaska, 2012-2014
DOE Data Explorer [Office of Scientific and Technical Information (OSTI)]
Anna Liljedahl; Cathy Wilson
2016-02-02
End-of-winter snow depth and average snow density from area A, B, C and D, which include 1000's of point depth measurement located between approximately 20 and 50 cm apart.
Aerodynamic Focusing Of High-Density Aerosols
Ruiz, D. E.; Fisch, Nathaniel
2014-02-24
High-density micron-sized particle aerosols might form the basis for a number of applications in which a material target with a particular shape might be quickly ionized to form a cylindrical or sheet shaped plasma. A simple experimental device was built in order to study the properties of high-density aerosol focusing for 1#22; m silica spheres. Preliminary results recover previous findings on aerodynamic focusing at low densities. At higher densities, it is demonstrated that the focusing properties change in a way which is consistent with a density dependent Stokes number.
A simple approximation for the current-voltage characteristics of high-power, relativistic diodes
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Ekdahl, Carl
2016-06-10
A simple approximation for the current-voltage characteristics of a relativistic electron diode is presented. The approximation is accurate from non-relativistic through relativistic electron energies. Although it is empirically developed, it has many of the fundamental properties of the exact diode solutions. Lastly, the approximation is simple enough to be remembered and worked on almost any pocket calculator, so it has proven to be quite useful on the laboratory floor.
The transition to the metallic state in low density hydrogen
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
McMinis, Jeremy; Morales, Miguel A.; Ceperley, David M.; Kim, Jeongnim
2015-11-18
Solid atomic hydrogen is one of the simplest systems to undergo a metal-insulator transition. Near the transition, the electronic degrees of freedom become strongly correlated and their description provides a difficult challenge for theoretical methods. As a result, the order and density of the phase transition are still subject to debate. In this work we use diffusion quantum Monte Carlo to benchmark the transition between the paramagnetic and anti-ferromagnetic phases of ground state body centered cubic atomic hydrogen. We locate the density of the transition by computing the equation of state for these two phases and identify the phase transitionmoreÂ Â» order by computing the band gap near the phase transition. These benchmark results show that the phase transition is continuous and occurs at a Wigner-Seitz radius of rs = 2.27(3)a0. As a result, we compare our results to previously reported density functional theory, Hedin s GW approximation, and dynamical mean field theory results.Â«Â less
Calibration models for density borehole logging - construction report
Engelmann, R.E.; Lewis, R.E.; Stromswold, D.C.
1995-10-01
Two machined blocks of magnesium and aluminum alloys form the basis for Hanford`s density models. The blocks provide known densities of 1.780 {plus_minus} 0.002 g/cm{sup 3} and 2.804 {plus_minus} 0.002 g/cm{sup 3} for calibrating borehole logging tools that measure density based on gamma-ray scattering from a source in the tool. Each block is approximately 33 x 58 x 91 cm (13 x 23 x 36 in.) with cylindrical grooves cut into the sides of the blocks to hold steel casings of inner diameter 15 cm (6 in.) and 20 cm (8 in.). Spacers that can be inserted between the blocks and casings can create air gaps of thickness 0.64, 1.3, 1.9, and 2.5 cm (0.25, 0.5, 0.75 and 1.0 in.), simulating air gaps that can occur in actual wells from hole enlargements behind the casing.
The transition to the metallic state in low density hydrogen
McMinis, Jeremy; Morales, Miguel A.; Ceperley, David M.; Kim, Jeongnim
2015-11-18
Solid atomic hydrogen is one of the simplest systems to undergo a metal-insulator transition. Near the transition, the electronic degrees of freedom become strongly correlated and their description provides a difficult challenge for theoretical methods. As a result, the order and density of the phase transition are still subject to debate. In this work we use diffusion quantum Monte Carlo to benchmark the transition between the paramagnetic and anti-ferromagnetic phases of ground state body centered cubic atomic hydrogen. We locate the density of the transition by computing the equation of state for these two phases and identify the phase transition order by computing the band gap near the phase transition. These benchmark results show that the phase transition is continuous and occurs at a Wigner-Seitz radius of r_{s} = 2.27(3)a_{0}. As a result, we compare our results to previously reported density functional theory, Hedin s GW approximation, and dynamical mean field theory results.
Wu, H.; Wang, R.; Liu, Y.; Zhao, E. , P.O. Box 8730, Beijing Physics Department, Suzhou University, Suzhou Institute of High Energy Physics, Academia Sinica, Beijing Institute of Theoretical Physics, Academia Sinica, Beijing )
1992-04-01
The double-charge-exchange (DCX) reaction with Ca isotopes as targets is studied by employing the interacting-boson approximation (IBA). A comparison between the IBA and the shell-model results shows that IBA is a good approximation of the shell model in describing the DCX reactions.
Quartz resonator fluid density and viscosity monitor
Martin, Stephen J.; Wiczer, James J.; Cernosek, Richard W.; Frye, Gregory C.; Gebert, Charles T.; Casaus, Leonard; Mitchell, Mary A.
1998-01-01
A pair of thickness-shear mode resonators, one smooth and one with a textured surface, allows fluid density and viscosity to be independently resolved. A textured surface, either randomly rough or regularly patterned, leads to trapping of liquid at the device surface. The synchronous motion of this trapped liquid with the oscillating device surface allows the device to weigh the liquid; this leads to an additional response that depends on liquid density. This additional response enables a pair of devices, one smooth and one textured, to independently resolve liquid density and viscosity; the difference in responses determines the density while the smooth device determines the density-viscosity product, and thus, the pair determines both density and viscosity.
High Density Fuel Development for Research Reactors
Daniel Wachs; Dennis Keiser; Mitchell Meyer; Douglas Burkes; Curtis Clark; Glenn Moore; Jan-Fong Jue; Totju Totev; Gerard Hofman; Tom Wiencek; Yeon So Kim; Jim Snelgrove
2007-09-01
An international effort to develop, qualify, and license high and very high density fuels has been underway for several years within the framework of multi-national RERTR programs. The current development status is the result of significant contributions from many laboratories, specifically CNEA in Argentina, AECL in Canada, CEA in France, TUM in Germany, KAERI in Korea, VNIIM, RDIPE, IPPE, NCCP and RIARR in Russia, INL, ANL and Y-12 in USA. These programs are mainly engaged with UMo dispersion fuels with densities from 6 to 8 gU/cm3 (high density fuel) and UMo monolithic fuel with density as high as 16 gU/cm3 (very high density fuel). This paper, mainly focused on the French & US programs, gives the status of high density UMo fuel development and perspectives on their qualification.
The Quantum Energy Density: Improved E
Krogel, Jaron; Yu, Min; Kim, Jeongnim; Ceperley, David M.
2013-01-01
We establish a physically meaningful representation of a quantum energy density for use in Quantum Monte Carlo calculations. The energy density operator, dened in terms of Hamiltonian components and density operators, returns the correct Hamiltonian when integrated over a volume containing a cluster of particles. This property is demonstrated for a helium-neon \\gas," showing that atomic energies obtained from the energy density correspond to eigenvalues of isolated systems. The formation energies of defects or interfaces are typically calculated as total energy dierences. Using a model of delta-doped silicon (where dopant atoms form a thin plane) we show how interfacial energies can be calculated more eciently with the energy density, since the region of interest is small. We also demonstrate how the energy density correctly transitions to the bulk limit away from the interface where the correct energy is obtainable from a separate total energy calculation.
Normal and abnormal evolution of argon metastable density in high-density plasmas
Seo, B. H.; Kim, J. H.; You, S. J.
2015-05-15
A controversial problem on the evolution of Ar metastable density as a function of electron density (increasing trend versus decreasing trend) was resolved by discovering the anomalous evolution of the argon metastable density with increasing electron density (discharge power), including both trends of the metastable density [Daltrini et al., Appl. Phys. Lett. 92, 061504 (2008)]. Later, by virtue of an adequate physical explanation based on a simple global model, both evolutions of the metastable density were comprehensively understood as part of the abnormal evolution occurring at low- and high-density regimes, respectively, and thus the physics behind the metastable evolution has seemed to be clearly disclosed. In this study, however, a remarkable result for the metastable density behavior with increasing electron density was observed: even in the same electron density regime, there are both normal and abnormal evolutions of metastable-state density with electron density depending on the measurement position: The metastable density increases with increasing electron density at a position far from the inductively coupled plasma antenna but decreases at a position close to the antenna. The effect of electron temperature, which is spatially nonuniform in the plasma, on the electron population and depopulation processes of Argon metastable atoms with increasing electron density is a clue to understanding the results. The calculated results of the global model, including multistep ionization for the argon metastable state and measured electron temperature, are in a good agreement with the experimental results.
Momentum and energy approximations for elementary squeeze-film damper flows
Crandall, S.H.; El-shafei, A.
1993-09-01
To provide understanding of the effects of inertia on squeeze-film damper performance, two elementary flow patterns are studied. These elementary flows each depend on a single generalized motion coordinate whereas general planar motions of a damper are described by two independent generalized coordinates. Momentum and energy approximations for the elementary flows are compared with exact solutions. It is shown that the energy approximation, not previously applied to squeeze films, is superior to the momentum approximation in that at low Reynolds number the energy approximations agree with the exact solutions to first order in the Reynolds number whereas there are 20 percent errors in the first-order terms of the momentum approximations. 17 refs.
Method of synthesizing a low density material
Lorensen, L.E.; Monaco, S.B.
1987-02-27
A novel method of synthesizing a polymeric material of low density of the order of 50mg/cc or less. Such a low density material has applications in many areas including laser target fabrication. The method comprises preparing a polymer blend of two incompatible polymers as a major and a minor phase by mixing them and extruding the mixture, and then selectively extracting the major component, to yield a fine, low density structure.
Power balance in a high-density field reversed configuration plasma
Renneke, R. M.; Intrator, T. P.; Hsu, S. C.; Wurden, G. A.; Waganaar, W. J.; Ruden, E. L.; Grabowski, T. C.
2008-06-15
A global power balance analysis has been performed for the Field Reversed Experiment with Liner high density (>5x10{sup 22} m{sup -3}) field reversed configuration (FRC) plasma. The analysis was based on a zero-dimensional power balance model [D. J. Rey and M. Tuszewski, Phys. Fluids 27, 1514 (1984)]. The key findings are as follows. First, the percentage of radiative losses relative to total loss is an order of magnitude lower than previous lower density FRC experiments. Second, Ohmic heating was found to correlate with the poloidal flux trapping at FRC formation, suggesting that poloidal flux dissipation is primarily responsible for plasma heating. Third, high density FRCs analyzed in this work reinforce the low-density adiabatic scaling, which shows that particle confinement time and flux confinement time are approximately equal.
Building a Universal Nuclear Energy Density Functional
Bertulani, Carlos A.
2014-09-10
This grant had two components: Density functional theory and pairing and Nuclear reactions. This final report summarizes the activities for this SciDAC-2 project.
3-D capacitance density imaging system
Fasching, G.E.
1988-03-18
A three-dimensional capacitance density imaging of a gasified bed or the like in a containment vessel is achieved using a plurality of electrodes provided circumferentially about the bed in levels and along the bed in channels. The electrodes are individually and selectively excited electrically at each level to produce a plurality of current flux field patterns generated in the bed at each level. The current flux field patterns are suitably sensed and a density pattern of the bed at each level determined. By combining the determined density patterns at each level, a three-dimensional density image of the bed is achieved. 7 figs.
Calculating Atomic Number Densities for Uranium
Energy Science and Technology Software Center (OSTI)
1993-01-01
Provides method to calculate atomic number densities of selected uranium compounds and hydrogenous moderators for use in nuclear criticality safety analyses at gaseous diffusion uranium enrichment facilities.
Screening potential in high density plasmas
Amari, M.; Arranz, J. P.; Butaux, J.; Nguyen, H.
1997-01-05
On the basis of a two-ion center model, an accurate closed form of the screening potential is suggested for intermediate and high density plasmas.
Universal Nuclear Energy Density Functional (Technical Report...
Office of Scientific and Technical Information (OSTI)
Country of Publication: United States Language: English Subject: 73 NUCLEAR PHYSICS AND RADIATION PHYSICS Nuclear structure; nuclear energy density functional Word Cloud ...
Mini-review of Electron Density Visualization
Adler, Joan; Adler, Omri; Kreif, Meytal; Cohen, Or; Grosso, Bastien; Hashibon, Adham; Cooper, Valentino R
2015-01-01
We describe both educational and research oriented examples of electronic density visualization with AViz. Several detailed cases are presented and the procedures for their preparation are described.
Uncertainty Quantification for Nuclear Density Functional Theory...
Office of Scientific and Technical Information (OSTI)
Uncertainty Quantification for Nuclear Density Functional Theory and Information Content of New Measurements Citation Details In-Document Search This content will become publicly...
Chiral dynamics and peripheral transverse densities Granados...
Office of Scientific and Technical Information (OSTI)
dynamics and peripheral transverse densities Granados, Carlos G. Uppsala University (Sweden); Weiss, Christian JLAB, Newport News, VA (United States) 72 PHYSICS OF ELEMENTARY...
High Energy Density Ultracapacitors | Department of Energy
Broader source: Energy.gov (indexed) [DOE]
and Vehicle Technologies Program Annual Merit Review and Peer Evaluation es038smith2011p.pdf (1.95 MB) More Documents & Publications High Energy Density Ultracapacitors ...
Density gradient free electron collisionally excited x-ray laser
Campbell, E.M.; Rosen, M.D.
1984-11-29
An operational x-ray laser is provided that amplifies 3p-3s transition x-ray radiation along an approximately linear path. The x-ray laser is driven by a high power optical laser. The driving line focused optical laser beam illuminates a free-standing thin foil that may be associated with a substrate for improved structural integrity. This illumination produces a generally cylindrically shaped plasma having an essentially uniform electron density and temperature, that exists over a long period of time, and provides the x-ray laser gain medium. The x-ray laser may be driven by more than one optical laser beam. The x-ray laser has been successfully demonstrated to function in a series of experimental tests.
Density gradient free electron collisionally excited X-ray laser
Campbell, Edward M.; Rosen, Mordecai D.
1989-01-01
An operational X-ray laser (30) is provided that amplifies 3p-3s transition X-ray radiation along an approximately linear path. The X-ray laser (30) is driven by a high power optical laser. The driving line focused optical laser beam (32) illuminates a free-standing thin foil (34) that may be associated with a substrate (36) for improved structural integrity. This illumination produces a generally cylindrically shaped plasma having an essentially uniform electron density and temperature, that exists over a long period of time, and provides the X-ray laser gain medium. The X-ray laser (30) may be driven by more than one optical laser beam (32, 44). The X-ray laser (30) has been successfully demonstrated to function in a series of experimental tests.
Towards time-dependent current-density-functional theory in the non-linear regime
Escartín, J. M.; Vincendon, M.; Dinh, P. M.; Suraud, E.; Romaniello, P.; Reinhard, P.-G.
2015-02-28
Time-Dependent Density-Functional Theory (TDDFT) is a well-established theoretical approach to describe and understand irradiation processes in clusters and molecules. However, within the so-called adiabatic local density approximation (ALDA) to the exchange-correlation (xc) potential, TDDFT can show insufficiencies, particularly in violently dynamical processes. This is because within ALDA the xc potential is instantaneous and is a local functional of the density, which means that this approximation neglects memory effects and long-range effects. A way to go beyond ALDA is to use Time-Dependent Current-Density-Functional Theory (TDCDFT), in which the basic quantity is the current density rather than the density as in TDDFT. This has been shown to offer an adequate account of dissipation in the linear domain when the Vignale-Kohn (VK) functional is used. Here, we go beyond the linear regime and we explore this formulation in the time domain. In this case, the equations become very involved making the computation out of reach; we hence propose an approximation to the VK functional which allows us to calculate the dynamics in real time and at the same time to keep most of the physics described by the VK functional. We apply this formulation to the calculation of the time-dependent dipole moment of Ca, Mg and Na{sub 2}. Our results show trends similar to what was previously observed in model systems or within linear response. In the non-linear domain, our results show that relaxation times do not decrease with increasing deposited excitation energy, which sets some limitations to the practical use of TDCDFT in such a domain of excitations.
Convergence properties of polynomial chaos approximations for L2 random variables.
Field, Richard V., Jr. (.,; .); Grigoriu, Mircea (Cornell University, Ithaca, NY)
2007-03-01
Polynomial chaos (PC) representations for non-Gaussian random variables are infinite series of Hermite polynomials of standard Gaussian random variables with deterministic coefficients. For calculations, the PC representations are truncated, creating what are herein referred to as PC approximations. We study some convergence properties of PC approximations for L{sub 2} random variables. The well-known property of mean-square convergence is reviewed. Mathematical proof is then provided to show that higher-order moments (i.e., greater than two) of PC approximations may or may not converge as the number of terms retained in the series, denoted by n, grows large. In particular, it is shown that the third absolute moment of the PC approximation for a lognormal random variable does converge, while moments of order four and higher of PC approximations for uniform random variables do not converge. It has been previously demonstrated through numerical study that this lack of convergence in the higher-order moments can have a profound effect on the rate of convergence of the tails of the distribution of the PC approximation. As a result, reliability estimates based on PC approximations can exhibit large errors, even when n is large. The purpose of this report is not to criticize the use of polynomial chaos for probabilistic analysis but, rather, to motivate the need for further study of the efficacy of the method.
Tao, Jianmin; Perdew, John P; Staroverov, Viktor N; Scuseria, Gustavo E
2008-01-01
We construct a nonlocal density functional approximation with full exact exchange, while preserving the constraint-satisfaction approach and justified error cancellations of simpler semilocal functionals. This is achieved by interpolating between different approximations suitable for two extreme regions of the electron density. In a 'normal' region, the exact exchange-correlation hole density around an electron is semilocal because its spatial range is reduced by correlation and because it integrates over a narrow range to -1. These regions are well described by popular semilocal approximations (many of which have been constructed nonempirically), because of proper accuracy for a slowly-varying density or because of error cancellation between exchange and correlation. 'Abnormal' regions, where non locality is unveiled, include those in which exchange can dominate correlation (one-electron, nonuniform high-density, and rapidly-varying limits), and those open subsystems of fluctuating electron number over which the exact exchange-correlation hole integrates to a value greater than -1. Regions between these extremes are described by a hybrid functional mixing exact and semi local exchange energy densities locally (i.e., with a mixing fraction that is a function of position r and a functional of the density). Because our mixing fraction tends to 1 in the high-density limit, we employ full exact exchange according to the rigorous definition of the exchange component of any exchange-correlation energy functional. Use of full exact exchange permits the satisfaction of many exact constraints, but the nonlocality of exchange also requires balanced nonlocality of correlation. We find that this nonlocality can demand at least five empirical parameters (corresponding roughly to the four kinds of abnormal regions). Our local hybrid functional is perhaps the first accurate size-consistent density functional with full exact exchange. It satisfies other known exact constraints
Eich, F. G.; Hellgren, Maria
2014-12-14
We investigate fundamental properties of meta-generalized-gradient approximations (meta-GGAs) to the exchange-correlation energy functional, which have an implicit density dependence via the Kohn-Sham kinetic-energy density. To this purpose, we construct the most simple meta-GGA by expressing the local exchange-correlation energy per particle as a function of a fictitious density, which is obtained by inverting the Thomas-Fermi kinetic-energy functional. This simple functional considerably improves the total energy of atoms as compared to the standard local density approximation. The corresponding exchange-correlation potentials are then determined exactly through a solution of the optimized effective potential equation. These potentials support an additional bound state and exhibit a derivative discontinuity at integer particle numbers. We further demonstrate that through the kinetic-energy density any meta-GGA incorporates a derivative discontinuity. However, we also find that for commonly used meta-GGAs the discontinuity is largely underestimated and in some cases even negative.
High bandwidth vapor density diagnostic system
Globig, Michael A.; Story, Thomas W.
1992-01-01
A high bandwidth vapor density diagnostic system for measuring the density of an atomic vapor during one or more photoionization events. The system translates the measurements from a low frequency region to a high frequency, relatively noise-free region in the spectrum to provide improved signal to noise ratio.
High density laser-driven target
Lindl, John D.
1981-01-01
A high density target for implosion by laser energy composed of a central quantity of fuel surrounded by a high-Z pusher shell with a low-Z ablator-pusher shell spaced therefrom forming a region filled with low-density material.
Enhancing critical current density of cuprate superconductors
Chaudhari, Praveen
2015-06-16
The present invention concerns the enhancement of critical current densities in cuprate superconductors. Such enhancement of critical current densities include using wave function symmetry and restricting movement of Abrikosov (A) vortices, Josephson (J) vortices, or Abrikosov-Josephson (A-J) vortices by using the half integer vortices associated with d-wave symmetry present in the grain boundary.
First and second order approximations to stage numbers in multicomponent enrichment cascades
Scopatz, A.
2013-07-01
This paper describes closed form, Taylor series approximations to the number product stages in a multicomponent enrichment cascade. Such closed form approximations are required when a symbolic, rather than a numeric, algorithm is used to compute the optimal cascade state. Both first and second order approximations were implemented. The first order solution was found to be grossly incorrect, having the wrong functional form over the entire domain. On the other hand, the second order solution shows excellent agreement with the 'true' solution over the domain of interest. An implementation of the symbolic, second order solver is available in the free and open source PyNE library. (authors)
Density functional theory for carbon dioxide crystal
Chang, Yiwen; Mi, Jianguo Zhong, Chongli
2014-05-28
We present a density functional approach to describe the solid?liquid phase transition, interfacial and crystal structure, and properties of polyatomic CO{sub 2}. Unlike previous phase field crystal model or density functional theory, which are derived from the second order direct correlation function, the present density functional approach is based on the fundamental measure theory for hard-sphere repulsion in solid. More importantly, the contributions of enthalpic interactions due to the dispersive attractions and of entropic interactions arising from the molecular architecture are integrated in the density functional model. Using the theoretical model, the predicted liquid and solid densities of CO{sub 2} at equilibrium triple point are in good agreement with the experimental values. Based on the structure of crystal-liquid interfaces in different planes, the corresponding interfacial tensions are predicted. Their respective accuracies need to be tested.
Neutral depletion and the helicon density limit
Magee, R. M.; Galante, M. E.; Carr, J. Jr.; Lusk, G.; McCarren, D. W.; Scime, E. E.
2013-12-15
It is straightforward to create fully ionized plasmas with modest rf power in a helicon. It is difficult, however, to create plasmas with density >10{sup 20} m{sup ?3}, because neutral depletion leads to a lack of fuel. In order to address this density limit, we present fast (1 MHz), time-resolved measurements of the neutral density at and downstream from the rf antenna in krypton helicon plasmas. At the start of the discharge, the neutral density underneath the antenna is reduced to 1% of its initial value in 15 ?s. The ionization rate inferred from these data implies that the electron temperature near the antenna is much higher than the electron temperature measured downstream. Neutral density measurements made downstream from the antenna show much slower depletion, requiring 14 ms to decrease by a factor of 1/e. Furthermore, the downstream depletion appears to be due to neutral pumping rather than ionization.
Core density turbulence in the HSX Stellarator
Deng, C. B.; Brower, D. L.; Anderson, D. T.; Anderson, F. S. B.; Briesemeister, Alexis R.; Likin, K. M.
2015-10-23
Broadband turbulent density fluctuations are explored in the helically symmetric stellarator experiment (HSX) by investigating changes related to plasma heating power and location. No fluctuation response is observed to occur with large changes in electron temperature and its gradient, thereby eliminating temperature gradient as a driving mechanism. Instead, measurements reveal that density turbulence varies inversely with electron density scale length. This response is consistent with density gradient drive as one might expect for trapped electron mode (TEM) turbulence. In general, the plasma stored energy and particle confinement are higher for discharges with reduced fluctuations in the plasma core. When the density fluctuation amplitude is reduced, increased plasma rotation is also evident suggesting a role is being played by intrinsic plasma flow.
Far-Field Approximation in the Generalized Geometry Holdup (GGH) Model
Oberer, R. B.; Gunn, C. A.; Chiang, L.G.
2006-09-07
Quantitative gamma spectrometry measurements of uranium frequently require corrections for attenuation by an equipment or container layer and by the uranium bearing material itself. It is common to correct for attenuation using the ''far-field approximation''. Under this approximation, the minimum thickness of equipment or material is used for the correction rather than an average thickness over the detector field-of-view. In reality this aspect of the far-field approximation is really a narrow field-of-view approximation. The price of this simplification is the introduction of a bias. This bias will be investigated in this paper. In addition, there is a distance dependence of the radial response of a detector. This dependence will also be investigated.
Horowitz, Jordan M.
2015-07-28
The stochastic thermodynamics of a dilute, well-stirred mixture of chemically reacting species is built on the stochastic trajectories of reaction events obtained from the chemical master equation. However, when the molecular populations are large, the discrete chemical master equation can be approximated with a continuous diffusion process, like the chemical Langevin equation or low noise approximation. In this paper, we investigate to what extent these diffusion approximations inherit the stochastic thermodynamics of the chemical master equation. We find that a stochastic-thermodynamic description is only valid at a detailed-balanced, equilibrium steady state. Away from equilibrium, where there is no consistent stochastic thermodynamics, we show that one can still use the diffusive solutions to approximate the underlying thermodynamics of the chemical master equation.
Gambacurta, D.; Grasso, M.; Catara, F.
2012-10-20
The low-lying dipole strength distributions of {sup 40}CaCa and {sup 48}Ca, in the energy region between 5 and 10 MeV, are studied within the second random phase approximation (RPA) with Skyrme interaction. Standard RPA models do not usually predict any presence of strength in this energy region, while experimentally a significant amount of strength is found. The inclusion of the 2 particle -2 hole configurations allows to obtain a description in a rather good agreement with the experimental data. The properties of the most collective state are analyzed in terms of its 1 particle -1 hole nature and its transition densities.
Density functional theory for d- and f-electron materials and compounds
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Mattson, Ann E.; Wills, John M.
2016-02-12
Here, the fundamental requirements for a computationally tractable Density Functional Theory-based method for relativistic f- and (nonrelativistic) d-electron materials and compounds are presented. The need for basing the Kohnâ€“Sham equations on the Dirac equation is discussed. The full Dirac scheme needs exchange-correlation functionals in terms of four-currents, but ordinary functionals, using charge density and spin-magnetization, can be used in an approximate Dirac treatment. The construction of a functional that includes the additional confinement physics needed for these materials is illustrated using the subsystem-functional scheme. If future studies show that a full Dirac, four-current based, exchange-correlation functional is needed, the subsystemmoreÂ Â» functional scheme is one of the few schemes that can still be used for constructing functional approximations.Â«Â less
Phonon and magnetic structure in Î´-plutonium from density-functional theory
SÃ¶derlind, Per; Zhou, F.; Landa, A.; Klepeis, J. E.
2015-10-30
We present phonon properties of plutonium metal obtained from a combination of density-functional-theory (DFT) electronic structure and the recently developed compressive sensing lattice dynamics (CSLD). The CSLD model is here trained on DFT total energies of several hundreds of quasi-random atomic configurations for best possible accuracy of the phonon properties. The calculated phonon dispersions compare better with experiment than earlier results obtained from dynamical mean-field theory. The density-functional model of the electronic structure consists of disordered magnetic moments with all relativistic effects and explicit orbital-orbital correlations. The magnetic disorder is approximated in two ways: (i) a special quasi-random structure and (ii) the disordered-local-moment (DLM) method within the coherent potential approximation. Magnetism in plutonium has been debated intensely, However, the present magnetic approach for plutonium is validated by the close agreement between the predicted magnetic form factor and that of recent neutron-scattering experiments.
Orbital relaxation effects on Kohnâ€“Sham frontier orbital energies in density functional theory
Zhang, DaDi; Zheng, Xiao; Li, Chen; Yang, Weitao
2015-04-21
We explore effects of orbital relaxation on Kohnâ€“Sham frontier orbital energies in density functional theory by using a nonempirical scaling correction approach developed in Zheng et al. [J. Chem. Phys. 138, 174105 (2013)]. Relaxation of Kohnâ€“Sham orbitals upon addition/removal of a fractional number of electrons to/from a finite system is determined by a systematic perturbative treatment. The information of orbital relaxation is then used to improve the accuracy of predicted Kohnâ€“Sham frontier orbital energies by Hartreeâ€“Fock, local density approximation, and generalized gradient approximation methods. The results clearly highlight the significance of capturing the orbital relaxation effects. Moreover, the proposed scaling correction approach provides a useful way of computing derivative gaps and Fukui quantities of N-electron finite systems (N is an integer), without the need to perform self-consistent-field calculations for (N Â± 1)-electron systems.
Time-dependent density functional theory quantum transport simulation in non-orthogonal basis
Kwok, Yan Ho; Xie, Hang; Yam, Chi Yung; Chen, Guan Hua; Zheng, Xiao
2013-12-14
Basing on the earlier works on the hierarchical equations of motion for quantum transport, we present in this paper a first principles scheme for time-dependent quantum transport by combining time-dependent density functional theory (TDDFT) and Keldysh's non-equilibrium Green's function formalism. This scheme is beyond the wide band limit approximation and is directly applicable to the case of non-orthogonal basis without the need of basis transformation. The overlap between the basis in the lead and the device region is treated properly by including it in the self-energy and it can be shown that this approach is equivalent to a lead-device orthogonalization. This scheme has been implemented at both TDDFT and density functional tight-binding level. Simulation results are presented to demonstrate our method and comparison with wide band limit approximation is made. Finally, the sparsity of the matrices and computational complexity of this method are analyzed.
DOE Seeks to Invest Approximately $1.3 Billion to Commercialize CCS
Office of Energy Efficiency and Renewable Energy (EERE) Indexed Site
Technology | Department of Energy Approximately $1.3 Billion to Commercialize CCS Technology DOE Seeks to Invest Approximately $1.3 Billion to Commercialize CCS Technology June 24, 2008 - 2:15pm Addthis Funding Opportunity Announcement Solicits Applications for Restructured FutureGen Program WASHINGTON, DC - The U.S. Department of Energy (DOE) today issued a Funding Opportunity Announcement (FOA) to invest in multiple commercial-scale Integrated Gasification Combined Cycle (IGCC) or other
Pusa, M.; Leppaenen, J.
2012-07-01
The Chebyshev Rational Approximation Method (CRAM) has been recently introduced by the authors for solving the burnup equations with excellent results. This method has been shown to be capable of simultaneously solving an entire burnup system with thousands of nuclides both accurately and efficiently. The method was prompted by an analysis of the spectral properties of burnup matrices and it can be characterized as the best rational approximation on the negative real axis. The coefficients of the rational approximation are fixed and have been reported for various approximation orders. In addition to these coefficients, implementing the method only requires a linear solver. This paper describes an efficient method for solving the linear systems associated with the CRAM approximation. The introduced direct method is based on sparse Gaussian elimination where the sparsity pattern of the resulting upper triangular matrix is determined before the numerical elimination phase. The stability of the proposed Gaussian elimination method is discussed based on considering the numerical properties of burnup matrices. Suitable algorithms are presented for computing the symbolic factorization and numerical elimination in order to facilitate the implementation of CRAM and its adoption into routine use. The accuracy and efficiency of the described technique are demonstrated by computing the CRAM approximations for a large test case with over 1600 nuclides. (authors)
Periodic subsystem density-functional theory
Genova, Alessandro; Pavanello, Michele; Ceresoli, Davide
2014-11-07
By partitioning the electron density into subsystem contributions, the Frozen Density Embedding (FDE) formulation of subsystem Density Functional Theory (DFT) has recently emerged as a powerful tool for reducing the computational scaling of Kohnâ€“Sham DFT. To date, however, FDE has been employed to molecular systems only. Periodic systems, such as metals, semiconductors, and other crystalline solids have been outside the applicability of FDE, mostly because of the lack of a periodic FDE implementation. To fill this gap, in this work we aim at extending FDE to treat subsystems of molecular and periodic character. This goal is achieved by a dual approach. On one side, the development of a theoretical framework for periodic subsystem DFT. On the other, the realization of the method into a parallel computer code. We find that periodic FDE is capable of reproducing total electron densities and (to a lesser extent) also interaction energies of molecular systems weakly interacting with metallic surfaces. In the pilot calculations considered, we find that FDE fails in those cases where there is appreciable density overlap between the subsystems. Conversely, we find FDE to be in semiquantitative agreement with Kohnâ€“Sham DFT when the inter-subsystem density overlap is low. We also conclude that to make FDE a suitable method for describing molecular adsorption at surfaces, kinetic energy density functionals that go beyond the GGA level must be employed.
Vignolo, Patrizia; Minguzzi, Anna
2003-05-01
We develop a Green's function method to evaluate the exact equilibrium particle-density profiles of noninteracting Fermi gases in external harmonic confinement in any spatial dimension and for arbitrary trap anisotropy. While in a spherically symmetric configuration the shell effects are negligible in the case of a large number of particles, we find that for very anisotropic traps the quantum effects due to single-level occupancy and the deviations from the Thomas-Fermi approximation are also visible for mesoscopic clouds.
Low density, resorcinol-formaldehyde aerogels
Pekala, Richard W.
1991-01-01
The polycondensation of resorcinol with formaldehyde under alkaline conditions results in the formation of surface functionalized polymer "Clusters". The covalent crosslinking of these "clusters" produces gels which when processed under supercritical conditions, produce low density, organic aerogels (density.ltoreq.100 mg/cc; cell size .ltoreq.0.1 microns). The aerogels are transparent, dark red in color and consist of interconnected colloidal-like particles with diameters of about 100.circle.. These aerogels may be further carbonized to form low density carbon foams with cell size of about 0.1 micron.
Low density, resorcinol-formaldehyde aerogels
Pekala, Richard W.
1989-01-01
The polycondensation of resorcinol with formaldehyde under alkaline conditions results in the formation of surface functionalized polymer "clusters". The covalent crosslinking of these "clusters" produces gels which when processed under supercritical conditions, produce low density, organic aerogels (density .ltoreq.100 mg/cc; cell size .ltoreq.0.1 microns). The aerogels are transparent, dark red in color and consist of interconnected colloidal-like particles with diameters of about 100 .ANG.. These aerogels may be further carbonized to form low density carbon foams with cell size of about 0.1 micron.
Low density, resorcinol-formaldehyde aerogels
Pekala, R.W.
1989-10-10
The polycondensation of resorcinol with formaldehyde under alkaline conditions results in the formation of surface functionalized polymer clusters. The covalent crosslinking of these clusters produces gels which when processed under supercritical conditions, produce low density, organic aerogels (density [<=]100 mg/cc; cell size [<=]0.1 microns). The aerogels are transparent, dark red in color and consist of interconnected colloidal-like particles with diameters of about 100 [angstrom]. These aerogels may be further carbonized to form low density carbon foams with cell size of about 0.1 micron.
Low density, resorcinol-formaldehyde aerogels
Pekala, R.W.
1988-05-26
The polycondensation of resorcinol with formaldehyde under alkaline conditions results in the formation of surface functionalized polymer ''clusters''. The covalent crosslinking of these ''clusters'' produces gels which when processed under supercritical conditions, produce low density, organic aerogels (density less than or equal to100 mg/cc; cell size less than or equal to0.1 microns). The aerogels are transparent,dark red in color and consist of interconnected colloidal-like particles with diameters of about 100 A/degree/. These aerogels may be further carbonized to form low density carbon foams with cell size of about 0.1 micron. 1 fig., 1 tab.
Density controlled carbon nanotube array electrodes
Ren, Zhifeng F.; Tu, Yi
2008-12-16
CNT materials comprising aligned carbon nanotubes (CNTs) with pre-determined site densities, catalyst substrate materials for obtaining them and methods for forming aligned CNTs with controllable densities on such catalyst substrate materials are described. The fabrication of films comprising site-density controlled vertically aligned CNT arrays of the invention with variable field emission characteristics, whereby the field emission properties of the films are controlled by independently varying the length of CNTs in the aligned array within the film or by independently varying inter-tubule spacing of the CNTs within the array (site density) are disclosed. The fabrication of microelectrode arrays (MEAs) formed utilizing the carbon nanotube material of the invention is also described.
Separation of carbon nanotubes in density gradients
Hersam, Mark C.; Stupp, Samuel I.; Arnold, Michael S.
2012-02-07
The separation of single-walled carbon nanotubes (SWNTs), by chirality and/or diameter, using centrifugation of compositions of SWNTs in and surface active components in density gradient media.
Separation of carbon nanotubes in density gradients
Hersam, Mark C.; Stupp, Samuel I.; Arnold, Michael S.
2010-02-16
The separation of single-walled carbon nanotubes (SWNTs), by chirality and/or diameter, using centrifugation of compositions of SWNTs in and surface active components in density gradient media.
High density load bearing insulation peg
Nowobilski, Jeffert J.; Owens, William J.
1985-01-01
A high density peg which can support a large load and exhibits excellent thermal resistance produced by a method wherein the peg is made in compliance with specified conditions of time, temperature and pressure.
High density load bearing insulation peg
Nowobilski, J.J.; Owens, W.J.
1985-01-29
A high density peg is disclosed which can support a large load and exhibits excellent thermal resistance produced by a method wherein the peg is made in compliance with specified conditions of time, temperature and pressure. 4 figs.
Spacetime Average Density (SAD) cosmological measures
Page, Don N.
2014-11-01
The measure problem of cosmology is how to obtain normalized probabilities of observations from the quantum state of the universe. This is particularly a problem when eternal inflation leads to a universe of unbounded size so that there are apparently infinitely many realizations or occurrences of observations of each of many different kinds or types, making the ratios ambiguous. There is also the danger of domination by Boltzmann Brains. Here two new Spacetime Average Density (SAD) measures are proposed, Maximal Average Density (MAD) and Biased Average Density (BAD), for getting a finite number of observation occurrences by using properties of the Spacetime Average Density (SAD) of observation occurrences to restrict to finite regions of spacetimes that have a preferred beginning or bounce hypersurface. These measures avoid Boltzmann brain domination and appear to give results consistent with other observations that are problematic for other widely used measures, such as the observation of a positive cosmological constant.
Chiral dynamics and peripheral transverse densities (Journal...
Office of Scientific and Technical Information (OSTI)
Journal Article: Chiral dynamics and peripheral transverse densities Citation Details ... Report Number(s): JLAB-THY--13-1763; DOEOR--23177-2641 Journal ID: ISSN 1029-8479; TRN: ...
Shock compression of low-density foams
Holmes, N.C.
1993-07-01
Shock compression of very low density micro-cellular materials allows entirely new regimes of hot fluid states to be investigated experimentally. Using a two-stage light-gas gun to generate strong shocks, temperatures of several eV are readily achieved at densities of roughly 0.5--1 g/cm{sup 3} in large, uniform volumes. The conditions in these hot, expanded fluids are readily found using the Hugoniot jump conditions. We will briefly describe the basic methodology for sample preparation and experimental measurement of shock velocities. We present data for several materials over a range of initial densities. This paper will explore the applications of these methods for investigations of equations of state and phase diagrams, spectroscopy, and plasma physics. Finally, we discus the need for future work on these and related low-density materials.
Communication: Embedded fragment stochastic density functional theory
Neuhauser, Daniel; Baer, Roi; Rabani, Eran
2014-07-28
We develop a method in which the electronic densities of small fragments determined by Kohn-Sham density functional theory (DFT) are embedded using stochastic DFT to form the exact density of the full system. The new method preserves the scaling and the simplicity of the stochastic DFT but cures the slow convergence that occurs when weakly coupled subsystems are treated. It overcomes the spurious charge fluctuations that impair the applications of the original stochastic DFT approach. We demonstrate the new approach on a fullerene dimer and on clusters of water molecules and show that the density of states and the total energy can be accurately described with a relatively small number of stochastic orbitals.
Breast Density and Cancer | GE Global Research
Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)
Breast Cancer Awareness Series: Understanding Breast Density Click to email this to a friend (Opens in new window) Share on Facebook (Opens in new window) Click to share (Opens in ...
High Energy Density Ultracapacitors | Department of Energy
Broader source: Energy.gov (indexed) [DOE]
Merit Review and Peer Evaluation Meeting, May 18-22, 2009 -- Washington D.C. esp22smith.pdf (1.09 MB) More Documents & Publications High Energy Density Ultracapacitors High ...
High-Energy-Density Plasmas, Fluids
Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)
High-Energy-Density Plasmas, Fluids High-Energy-Density Plasmas, Fluids National security depends on science and technology. The United States relies on Los Alamos National Laboratory for the best of both. No place on Earth pursues a broader array of world-class scientific endeavors. TRIDENT target chamber Sasi Palaniyappan, right, and Rahul Shah left inside a target chamber where the TRIDENT short pulse laser is aimed at a very thin diamond- foil target, a fraction of a micrometer thick. The
de Stadler, M; Chand, K
2007-11-12
Gas centrifuges exhibit very complex flows. Within the centrifuge there is a rarefied region, a transition region, and a region with an extreme density gradient. The flow moves at hypersonic speeds and shock waves are present. However, the flow is subsonic in the axisymmetric plane. The analysis may be simplified by treating the flow as a perturbation of wheel flow. Wheel flow implies that the fluid is moving as a solid body. With the very large pressure gradient, the majority of the fluid is located very close to the rotor wall and moves at an azimuthal velocity proportional to its distance from the rotor wall; there is no slipping in the azimuthal plane. The fluid can be modeled as incompressible and subsonic in the axisymmetric plane. By treating the centrifuge as long, end effects can be appropriately modeled without performing a detailed boundary layer analysis. Onsager's pancake approximation is used to construct a simulation to model fluid flow in a gas centrifuge. The governing 6th order partial differential equation is broken down into an equivalent coupled system of three equations and then solved numerically. In addition to a discussion on the baseline solution, known problems and future work possibilities are presented.
L. Whinnery; S. Goods; B. Even
2000-08-01
This study was initiated to produce a low-density centering medium for use in experiments investigating the response of materials to shock-loading. While the main drivers for material selection were homogeneity, dimensional stability, performance and cost, other secondary requirements included fine cell size, the ability to manufacture 5--10 cm-sized parts and an extremely compressed development time. The authors chose a non-traditional methodology using a hollow, expandable, polymeric microballoon material system called Expancel{reg_sign}. These microballoons are made from a copolymer of polyacrylonitrile (PAN) and polymethacrylonitrile (PMAN) and use iso-pentane as the blowing agent. The average diameter (by volume) of the unexpanded powder is approximately 13 {micro}m, while the average of the expanded powder is 35--55 {micro}m, with a few large microballoons approaching 150--200 p.m. A processing method was developed that established a pre-mixed combination of unexpanded and expanded Expancel at a ratio such that the tap (or vibration) density of the mixed powders was the same as that desired of the final part. Upon heating above the tack temperature of the polymer, this zero-rise approach allowed only expansion of the unexpanded powder to fill the interstices between the pre-expanded balloons. The mechanical action of the expanding powder combined with the elevated processing temperature yielded flee-standing and mechanically robust parts. Although mechanical properties of these foams were not a key performance requirement, the data allowed for the determination of the best temperature to heat the samples. Processing the foam at higher temperatures enhanced both modulus and strength. The maximum allowable temperature was limited by dimensional stability and shrinkback considerations. Tomographic analysis of foam billets revealed very flat density profiles. Parts of any density between the low density expanded powder (approximately 0.013 g/cm{sup 3}) and the
Brett, Tobias Galla, Tobias
2014-03-28
We present a heuristic derivation of Gaussian approximations for stochastic chemical reaction systems with distributed delay. In particular, we derive the corresponding chemical Langevin equation. Due to the non-Markovian character of the underlying dynamics, these equations are integro-differential equations, and the noise in the Gaussian approximation is coloured. Following on from the chemical Langevin equation, a further reduction leads to the linear-noise approximation. We apply the formalism to a delay variant of the celebrated Brusselator model, and show how it can be used to characterise noise-driven quasi-cycles, as well as noise-triggered spiking. We find surprisingly intricate dependence of the typical frequency of quasi-cycles on the delay period.
Jin, Jinshuang; Li, Jun; Liu, Yu; Li, Xin-Qi; Yan, YiJing
2014-06-28
Beyond the second-order Born approximation, we propose an improved master equation approach to quantum transport under self-consistent Born approximation. The basic idea is to replace the free Green's function in the tunneling self-energy diagram by an effective reduced propagator under the Born approximation. This simple modification has remarkable consequences. It not only recovers the exact results for quantum transport through noninteracting systems under arbitrary voltages, but also predicts the challenging nonequilibrium Kondo effect. Compared to the nonequilibrium Green's function technique that formulates the calculation of specific correlation functions, the master equation approach contains richer dynamical information to allow more efficient studies for such as the shot noise and full counting statistics.
Simulating higher-dimensional geometries in GADRAS using approximate one-dimensional solutions.
Thoreson, Gregory G.; Mitchell, Dean James; Harding, Lee T.
2013-02-01
The Gamma Detector Response and Analysis Software (GADRAS) software package is capable of simulating the radiation transport physics for one-dimensional models. Spherical shells are naturally one-dimensional, and have been the focus of development and benchmarking. However, some objects are not spherical in shape, such as cylinders and boxes. These are not one-dimensional. Simulating the radiation transport in two or three dimensions is unattractive because of the extra computation time required. To maintain computational efficiency, higher-dimensional geometries require approximations to simulate them in one-dimension. This report summarizes the theory behind these approximations, tests the theory against other simulations, and compares the results to experimental data. Based on the results, it is recommended that GADRAS users always attempt to approximate reality using spherical shells. However, if fissile material is present, it is imperative that the shape of the one-dimensional model matches the fissile material, including the use of slab and cylinder geometry.
Density fitting for three-electron integrals in explicitly correlated electronic structure theory
Womack, James C.; Manby, Frederick R.
2014-01-28
The principal challenge in using explicitly correlated wavefunctions for molecules is the evaluation of nonfactorizable integrals over the coordinates of three or more electrons. Immense progress was made in tackling this problem through the introduction of a single-particle resolution of the identity. Decompositions of sufficient accuracy can be achieved, but only with large auxiliary basis sets. Density fitting is an alternative integral approximation scheme, which has proven to be very reliable for two-electron integrals. Here, we extend density fitting to the treatment of all three-electron integrals that appear at the MP2-F12/3*A level of theory. We demonstrate that the convergence of energies with respect to auxiliary basis size is much more rapid with density fitting than with the traditional resolution-of-the-identity approach.
Hierarchy of beam plasma instabilities up to high beam densities for fast ignition scenario
Bret, A.; Deutsch, C.
2005-08-15
The hierarchy of electromagnetic instabilities suffered by a relativistic electron beam passing through a plasma is investigated. The fluid approximation is used and beam densities up to the plasma one are considered. The hierarchy between instabilities is established in terms of two parameters only: the beam relativistic factor and the ratio n{sub b}/n{sub p} of the beam density to the plasma one. It is found that for n{sub b}/n{sub p} < or approx. 0.53, the most unstable modes are a mix between filamentation and two-stream instabilities. Beyond this limit, filamentation instability may dominate, depending on the beam relativistic factor. The largest growth rates are found for a beam density slightly smaller than the plasma one.
Bret, A.; Deutsch, C.
2005-10-01
The integrated growth rate of various relativistic beam/plasma instabilities in a weakly varying plasma density gradient is calculated using a WKB-like approximation. It is proven that such an assumption can be made in fast ignition scenario conditions. The formalism is applied to the two-stream, the filamentation, and the two-stream/filamentation instabilities, the latter instability being a mixture of the former two, and is the fastest growing one. The results are restricted to collisionless plasmas and nonrelativistic beam and plasma temperatures. Filamentation instability is reduced by the density gradient and eventually does not develop in the core, whereas two-stream and two-stream/filamentation instabilities should saturate even before they feel the gradient. Various effects connected to the density gradient are discussed. It is found they should be negligible as long as these later instabilities remain in their respective linear regime.
Alekseev, A E; Potapov, V T
2013-10-31
Spectral characteristics of the noise intensity fluctuations at the output of a scattered-light interferometer, caused by phase fluctuations of semiconductor laser radiation are considered. This kind of noise is one of the main factors limiting sensitivity of interferometric sensors. For the first time, to our knowledge, the expression is obtained for the average noise power spectral density at the interferometer output versus the degree of a light source coherence and length of the scattering segment. Also, the approximate expressions are considered which determine the power spectral density in the low-frequency range (up to 200 kHz) and in the limiting case of extended scattering segments. The expression obtained for the noise power spectral density agrees with experimental normalised power spectra with a high accuracy. (interferometry of radiation)
Approximate local magnetic-to-electric surface operators for time-harmonic Maxwell's equations
El Bouajaji, M.
2014-12-15
The aim of this paper is to propose new local and accurate approximate magnetic-to-electric surface boundary operators for the three-dimensional time-harmonic Maxwell's equations. After their construction where their accuracy is improved through a regularization process, a localization of these operators and a full finite element approximation is introduced. Next, their numerical efficiency and accuracy is investigated in detail for different scatterers when these operators are used in the extreme situation of On-Surface Radiation Conditions methods.
On the approximations of the distribution function of fusion alpha particles
Bilato, R. Brambilla, M.; Poli, E.
2014-10-15
The solution of the drift-kinetic equation for fusion-born alpha particles is derived in the limit of dominant parallel streaming, and it is related to the usual slowing-down distribution function. The typical approximations of the fast tail of fusion-born alpha particles are briefly compared and discussed. In particular, approximating the distribution function of fast-alpha particles with an “equivalent” Maxwellian is inaccurate to describe absorption of radio-frequency waves in the ion-cyclotron range of frequencies.
Liu, Fang; Lin, Lin; Vigil-Fowler, Derek; Lischner, Johannes; Kemper, Alexander F.; Sharifzadeh, Sahar; Jornada, Felipe H. da; Deslippe, Jack; Yang, Chao; and others
2015-04-01
We present a numerical integration scheme for evaluating the convolution of a Green's function with a screened Coulomb potential on the real axis in the GW approximation of the self energy. Our scheme takes the zero broadening limit in Green's function first, replaces the numerator of the integrand with a piecewise polynomial approximation, and performs principal value integration on subintervals analytically. We give the error bound of our numerical integration scheme and show by numerical examples that it is more reliable and accurate than the standard quadrature rules such as the composite trapezoidal rule. We also discuss the benefit of using different self energy expressions to perform the numerical convolution at different frequencies.
Orbital-optimized density cumulant functional theory
Sokolov, Alexander Yu. Schaefer, Henry F.
2013-11-28
In density cumulant functional theory (DCFT) the electronic energy is evaluated from the one-particle density matrix and two-particle density cumulant, circumventing the computation of the wavefunction. To achieve this, the one-particle density matrix is decomposed exactly into the mean-field (idempotent) and correlation components. While the latter can be entirely derived from the density cumulant, the former must be obtained by choosing a specific set of orbitals. In the original DCFT formulation [W. Kutzelnigg, J. Chem. Phys. 125, 171101 (2006)] the orbitals were determined by diagonalizing the effective Fock operator, which introduces partial orbital relaxation. Here we present a new orbital-optimized formulation of DCFT where the energy is variationally minimized with respect to orbital rotations. This introduces important energy contributions and significantly improves the description of the dynamic correlation. In addition, it greatly simplifies the computation of analytic gradients, for which expressions are also presented. We offer a perturbative analysis of the new orbital stationarity conditions and benchmark their performance for a variety of chemical systems.
Gorham, Caroline S.; Gaskins, John T.; Hopkins, Patrick E.; Parsons, Gregory N.; Losego, Mark D.
2014-06-23
We report on the thermal conductivity of atomic layer deposition-grown amorphous alumina thin films as a function of atomic density. Using time domain thermoreflectance, we measure the thermal conductivity of the thin alumina films at room temperature. The thermal conductivities vary ?35% for a nearly 15% change in atomic density and are substrate independent. No density dependence of the longitudinal sound speeds is observed with picosecond acoustics. The density dependence of the thermal conductivity agrees well with a minimum limit to thermal conductivity model that is modified with a differential effective-medium approximation.
Statistical approach to nuclear level density
Sen'kov, R. A.; Horoi, M.; Zelevinsky, V. G.
2014-10-15
We discuss the level density in a finite many-body system with strong interaction between the constituents. Our primary object of applications is the atomic nucleus but the same techniques can be applied to other mesoscopic systems. We calculate and compare nuclear level densities for given quantum numbers obtained by different methods, such as nuclear shell model (the most successful microscopic approach), our main instrument - moments method (statistical approach), and Fermi-gas model; the calculation with the moments method can use any shell-model Hamiltonian excluding the spurious states of the center-of-mass motion. Our goal is to investigate statistical properties of nuclear level density, define its phenomenological parameters, and offer an affordable and reliable way of calculation.
High power density solid oxide fuel cells
Pham, Ai Quoc; Glass, Robert S.
2004-10-12
A method for producing ultra-high power density solid oxide fuel cells (SOFCs). The method involves the formation of a multilayer structure cells wherein a buffer layer of doped-ceria is deposited intermediate a zirconia electrolyte and a cobalt iron based electrode using a colloidal spray deposition (CSD) technique. For example, a cobalt iron based cathode composed of (La,Sr)(Co,Fe)O (LSCF) may be deposited on a zirconia electrolyte via a buffer layer of doped-ceria deposited by the CSD technique. The thus formed SOFC have a power density of 1400 mW/cm.sup.2 at 600.degree. C. and 900 mW/cm.sup.2 at 700.degree. C. which constitutes a 2-3 times increased in power density over conventionally produced SOFCs.
Fabrication of low density ceramic material
Meek, T.T.; Blake, R.D.; Sheinberg, H.
1985-01-01
A precursor mixture and a method of making a low-density ceramic structural material are disclosed. The precursor mixture includes hollow microballoons, typically made of glass, together with a cementing agent capable of being cured by microwave irradiation. A preferred cementing agent is liquid hydrated potassium silicate, which is mixed with the glass microballoons to form a slurry. Upon irradiation the potassium silicate is dehydrated to form a solid porous matrix in which the microballoons are evenly distributed. Ground glass or other filling agents may be included in the slurry to enhance the properties of the final product. Low-density structural ceramics having densities on the order of 0.1 to 0.3 are obtained.
Hydrogen atom excitation in intense attosecond laser field: Gauge dependence of dipole approximation
Aldarmaa, Ch. E-mail: l-xemee@yahoo.com; Khenmedekh, L. E-mail: l-xemee@yahoo.com; Lkhagva, O.
2014-03-24
It is assumed that, the atomic excitations probability can be calculated using first order perturbation theory and dipole approximations. The validity of the dipole approximations had been examined by comparing the results with the results obtained by exact calculations within the first order perturbation theory[2]. Figure 1 shows the time dependence of the transition probability in the dipole approximation. From these plots it is obvious that, the probabilities obtained in the length gauge are higher than that in the velocity gauge, in the interaction period (??/2
A New 2D-Transport, 1D-Diffusion Approximation of the Boltzmann Transport equation
Larsen, Edward
2013-06-17
The work performed in this project consisted of the derivation, implementation, and testing of a new, computationally advantageous approximation to the 3D Boltz- mann transport equation. The solution of the Boltzmann equation is the neutron flux in nuclear reactor cores and shields, but solving this equation is difficult and costly. The new â€œ2D/1Dâ€ approximation takes advantage of a special geometric feature of typical 3D reactors to approximate the neutron transport physics in a specific (ax- ial) direction, but not in the other two (radial) directions. The resulting equation is much less expensive to solve computationally, and its solutions are expected to be sufficiently accurate for many practical problems. In this project we formulated the new equation, discretized it using standard methods, developed a stable itera- tion scheme for solving the equation, implemented the new numerical scheme in the MPACT code, and tested the method on several realistic problems. All the hoped- for features of this new approximation were seen. For large, difficult problems, the resulting 2D/1D solution is highly accurate, and is calculated about 100 times faster than a 3D discrete ordinates simulation.
Zhou, Zhennan
2014-09-01
In this paper, we approximate the semi-classical Schrödinger equation in the presence of electromagnetic field by the Hagedorn wave packets approach. By operator splitting, the Hamiltonian is divided into the modified part and the residual part. The modified Hamiltonian, which is the main new idea of this paper, is chosen by the fact that Hagedorn wave packets are localized both in space and momentum so that a crucial correction term is added to the truncated Hamiltonian, and is treated by evolving the parameters associated with the Hagedorn wave packets. The residual part is treated by a Galerkin approximation. We prove that, with the modified Hamiltonian only, the Hagedorn wave packets dynamics give the asymptotic solution with error O(?{sup 1/2}), where ? is the scaled Planck constant. We also prove that, the Galerkin approximation for the residual Hamiltonian can reduce the approximation error to O(?{sup k/2}), where k depends on the number of Hagedorn wave packets added to the dynamics. This approach is easy to implement, and can be naturally extended to the multidimensional cases. Unlike the high order Gaussian beam method, in which the non-constant cut-off function is necessary and some extra error is introduced, the Hagedorn wave packets approach gives a practical way to improve accuracy even when ? is not very small.
NEUTRON DENSITY CONTROL IN A NEUTRONIC REACTOR
Young, G.J.
1959-06-30
The method and means for controlling the neutron density in a nuclear reactor is described. It describes the method and means for flattening the neutron density distribution curve across the reactor by spacing the absorbing control members to varying depths in the central region closer to the center than to the periphery of the active portion of the reactor to provide a smaller neutron reproduction ratio in the region wherein the members are inserted, than in the remainder of the reactor thereby increasing the over-all potential power output.
Low density, microcellular foams, preparation, and articles
Young, Ainslie T.; Marsters, Robert G.; Moreno, Dawn K.
1984-01-01
A microcellular low density foam of poly(4-methyl-1-pentene) which is particularly useful for forming targets for inertial confinement fusion has been developed. Articles made from the foam have been machined to tolerances of 0.0001 inch, although the densities of the fragile foam are low (about 10 to about 100 mg/cc) and the cell sizes are small (about 10 to about 30 .mu.m). Methods for forming the foam and articles are given; and the yield strength of the foam of the invention is higher than was obtained in other structures of this same material.
Low density, microcellular foams, preparation, and articles
Young, A.T.
1982-03-03
A microcellular low-density foam of poly(4-methyl-1-pentene) particularly useful for forming targets for inertial confinement fusion has been developed. Articles made from the foam have been machined to tolerances of 0.0001 inch, although the densities of the fragile foam are low (about 10 to about 100 mg/cc) and the cell sizes are small (about 10 to about 30 ..mu..m). Methods for forming the foam and articles are given. The yield strength of the foam of the invention is higher than was obtained in other structures of this same material.
Size-dependent error of the density functional theory ionization potential in vacuum and solution
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Sosa Vazquez, Xochitl A.; Isborn, Christine M.
2015-12-22
Density functional theory is often the method of choice for modeling the energetics of large molecules and including explicit solvation effects. It is preferable to use a method that treats systems of different sizes and with different amounts of explicit solvent on equal footing. However, recent work suggests that approximate density functional theory has a size-dependent error in the computation of the ionization potential. We here investigate the lack of size-intensivity of the ionization potential computed with approximate density functionals in vacuum and solution. We show that local and semi-local approximations to exchange do not yield a constant ionization potentialmoreÂ Â» for an increasing number of identical isolated molecules in vacuum. Instead, as the number of molecules increases, the total energy required to ionize the system decreases. Rather surprisingly, we find that this is still the case in solution, whether using a polarizable continuum model or with explicit solvent that breaks the degeneracy of each solute, and we find that explicit solvent in the calculation can exacerbate the size-dependent delocalization error. We demonstrate that increasing the amount of exact exchange changes the character of the polarization of the solvent molecules; for small amounts of exact exchange the solvent molecules contribute a fraction of their electron density to the ionized electron, but for larger amounts of exact exchange they properly polarize in response to the cationic solute. As a result, in vacuum and explicit solvent, the ionization potential can be made size-intensive by optimally tuning a long-range corrected hybrid functional.Â«Â less
Size-dependent error of the density functional theory ionization potential in vacuum and solution
Sosa Vazquez, Xochitl A.; Isborn, Christine M.
2015-12-28
Density functional theory is often the method of choice for modeling the energetics of large molecules and including explicit solvation effects. It is preferable to use a method that treats systems of different sizes and with different amounts of explicit solvent on equal footing. However, recent work suggests that approximate density functional theory has a size-dependent error in the computation of the ionization potential. We here investigate the lack of size-intensivity of the ionization potential computed with approximate density functionals in vacuum and solution. We show that local and semi-local approximations to exchange do not yield a constant ionization potential for an increasing number of identical isolated molecules in vacuum. Instead, as the number of molecules increases, the total energy required to ionize the system decreases. Rather surprisingly, we find that this is still the case in solution, whether using a polarizable continuum model or with explicit solvent that breaks the degeneracy of each solute, and we find that explicit solvent in the calculation can exacerbate the size-dependent delocalization error. We demonstrate that increasing the amount of exact exchange changes the character of the polarization of the solvent molecules; for small amounts of exact exchange the solvent molecules contribute a fraction of their electron density to the ionized electron, but for larger amounts of exact exchange they properly polarize in response to the cationic solute. In vacuum and explicit solvent, the ionization potential can be made size-intensive by optimally tuning a long-range corrected hybrid functional.
Size-dependent error of the density functional theory ionization potential in vacuum and solution
Sosa Vazquez, Xochitl A.; Isborn, Christine M.
2015-12-22
Density functional theory is often the method of choice for modeling the energetics of large molecules and including explicit solvation effects. It is preferable to use a method that treats systems of different sizes and with different amounts of explicit solvent on equal footing. However, recent work suggests that approximate density functional theory has a size-dependent error in the computation of the ionization potential. We here investigate the lack of size-intensivity of the ionization potential computed with approximate density functionals in vacuum and solution. We show that local and semi-local approximations to exchange do not yield a constant ionization potential for an increasing number of identical isolated molecules in vacuum. Instead, as the number of molecules increases, the total energy required to ionize the system decreases. Rather surprisingly, we find that this is still the case in solution, whether using a polarizable continuum model or with explicit solvent that breaks the degeneracy of each solute, and we find that explicit solvent in the calculation can exacerbate the size-dependent delocalization error. We demonstrate that increasing the amount of exact exchange changes the character of the polarization of the solvent molecules; for small amounts of exact exchange the solvent molecules contribute a fraction of their electron density to the ionized electron, but for larger amounts of exact exchange they properly polarize in response to the cationic solute. As a result, in vacuum and explicit solvent, the ionization potential can be made size-intensive by optimally tuning a long-range corrected hybrid functional.
Approximate simulation of CO[sub 2] and H[sub 2]S absorption into aqueous alkanolamines
Glasscock, D.A.; Rochelle, G.T. . Dept. of Chemical Engineering)
1993-08-01
Rigorous and approximate methods are compared for the simulation of CO[sub 2] absorption into aqueous alkanolamine mixtures of methyldiethanolamine and diethanolamine. In addition, data for the mixtures containing monoethanolamine and the simultaneous absorption of CO[sub 2] and H[sub 2]S are presented. For the rigorous approach, the simplified eddy diffusivity theory is used to simulate the liquid-phase hydrodynamic characteristics. The approximation methods examined are the pseudo-first-order approximation, the interpolation approximation of Wellek et al. (1978), the algebraic combined flux (ACFLUX) approximation and the modified combined flux (MCFLUX) approximation. The latter approximation utilizes the reaction zone concept to determine the kinetic preference of the absorbing gas at the gas-liquid interface. Under the range of conditions studied, the MCFLUX approximation predicts very accurately the CO[sub 2] and H[sub 2]S flux rates in mixed amine systems, as compared with the rigorous solution of the differential equations.
Martini, M.; Peru, S.; Dupuis, M.
2011-03-15
Low-energy dipole excitations in neon isotopes and N=16 isotones are calculated with a fully consistent axially-symmetric-deformed quasiparticle random phase approximation (QRPA) approach based on Hartree-Fock-Bogolyubov (HFB) states. The same Gogny D1S effective force has been used both in HFB and QRPA calculations. The microscopical structure of these low-lying resonances, as well as the behavior of proton and neutron transition densities, are investigated in order to determine the isoscalar or isovector nature of the excitations. It is found that the N=16 isotones {sup 24}O, {sup 26}Ne, {sup 28}Mg, and {sup 30}Si are characterized by a similar behavior. The occupation of the 2s{sub 1/2} neutron orbit turns out to be crucial, leading to nontrivial transition densities and to small but finite collectivity. Some low-lying dipole excitations of {sup 28}Ne and {sup 30}Ne, characterized by transitions involving the {nu}1d{sub 3/2} state, present a more collective behavior and isoscalar transition densities. A collective proton low-lying excitation is identified in the {sup 18}Ne nucleus.
Durable high-density data storage
Stutz, R.A.; Lamartine, B.C.
1996-09-01
This paper will discuss the Focus Ion Beam (FIB) milling process, media life considerations, and methods of reading the micromilled data. The FIB process for data storage provides a new non-magnetic storage method for archiving large amounts of data. The process stores data on robust materials such as steel, silicon, and gold coated silicon. The storage process was developed to provide a method to insure the long term storage life of data. We estimate the useful life of data written on silicon or gold coated silicon to be a few thousand years. The process uses an ion beam to carve material from the surface much like stone cutting. The deeper information is carved into the media the longer the expected life of the information. The process can read information in three formats: (1) binary at densities of 3.5 Gbits/cm{sup 2}, (2) alphanumeric at optical or non-optical density, and (3) graphical at optical and non-optical density. The formats can be mixed on the same media; and thus it is possible to record, in a human readable format, instructions that can be read using an optical microscope. These instructions provide guidance on reading the higher density information.
Density waves in the Calogero model - revisited
Bardek, V. Feinberg, J. Meljanac, S.
2010-03-15
The Calogero model bears, in the continuum limit, collective excitations in the form of density waves and solitary modulations of the density of particles. This sector of the spectrum of the model was investigated, mostly within the framework of collective-field theory, by several authors, over the past 15 years or so. In this work we shall concentrate on periodic solutions of the collective BPS-equation (also known as 'finite amplitude density waves'), as well as on periodic solutions of the full static variational equations which vanish periodically (also known as 'large amplitude density waves'). While these solutions are not new, we feel that our analysis and presentation add to the existing literature, as we explain in the text. In addition, we show that these solutions also occur in a certain two-family generalization of the Calogero model, at special points in parameter space. A compendium of useful identities associated with Hilbert transforms, including our own proofs of these identities, appears in Appendix A. In Appendix B we also elucidate in the present paper some fine points having to do with manipulating Hilbert-transforms, which appear ubiquitously in the collective field formalism. Finally, in order to make this paper self-contained, we briefly summarize in Appendix C basic facts about the collective field formulation of the Calogero model.
Interferometer for the measurement of plasma density
Jacobson, Abram R.
1980-01-01
An interferometer which combines the advantages of a coupled cavity interferometer requiring alignment of only one light beam, and a quadrature interferometer which has the ability to track multi-fringe phase excursions unambiguously. The device utilizes a Bragg cell for generating a signal which is electronically analyzed to unambiguously determine phase modulation which is proportional to the path integral of the plasma density.
Quantum crystallographic charge density of urea
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Wall, Michael E.
2016-07-01
Standard X-ray crystallography methods use free-atom models to calculate mean unit-cell charge densities. Real molecules, however, have shared charge that is not captured accurately using free-atom models. To address this limitation, a charge density model of crystalline urea was calculated using high-level quantum theory and was refined against publicly available ultra-high-resolution experimental Bragg data, including the effects of atomic displacement parameters. The resulting quantum crystallographic model was compared with models obtained using spherical atom or multipole methods. Despite using only the same number of free parameters as the spherical atom model, the agreement of the quantum model with the datamoreÂ Â» is comparable to the multipole model. The static, theoretical crystalline charge density of the quantum model is distinct from the multipole model, indicating the quantum model provides substantially new information. Hydrogen thermal ellipsoids in the quantum model were very similar to those obtained using neutron crystallography, indicating that quantum crystallography can increase the accuracy of the X-ray crystallographic atomic displacement parameters. Lastly, the results demonstrate the feasibility and benefits of integrating fully periodic quantum charge density calculations into ultra-high-resolution X-ray crystallographic model building and refinement.Â«Â less
?Linear Gas Jet with Tailored Density Profile"
KRISHNAN, Mahadevan
2012-12-10
Supersonic, highly collimated gas jets and gas-filled capillary discharge waveguides are two primary targets of choice for Laser Plasma Accelerators (LPA) . Present gas jets have lengths of only 2-4 mm at densities of 1-4E19 cm-3, sufficient for self trapping and electron acceleration to energies up to ~150 MeV. Capillary structures 3 cm long have been used to accelerate beams up to 1 GeV. Capillary discharges used in LPAs serve to guide the pump laser and optimize the energy gain. A wall-stabilized capillary discharge provides a transverse profile across the channel that helps guide the laser and combat diffraction. Gas injection via a fast nozzle at one end provides some longitudinal density control, to improve the coupling. Gas jets with uniform or controlled density profiles may be used to control electron bunch injection and are being integrated into capillary experiments to add tuning of density. The gas jet for electron injection has not yet been optimized. Our Ph-I results have provided the LPA community with an alternative path to realizing a 2-3GeV electron bunch using just a gas jet. For example, our slit/blade combination gives a 15-20mm long acceleration path with tunable density profile, serving as an alternative to a 20-mm long capillary discharge with gas injection at one end. In Ph-II, we will extend these results to longer nozzles, to see whether we can synthesize 30 or 40-mm long plasma channels for LPAs.
Bakosi, Jozsef; Ristorcelli, Raymond J
2010-01-01
Probability density function (PDF) methods are extended to variable-density pressure-gradient-driven turbulence. We apply the new method to compute the joint PDF of density and velocity in a non-premixed binary mixture of different-density molecularly mixing fluids under gravity. The full time-evolution of the joint PDF is captured in the highly non-equilibrium flow: starting from a quiescent state, transitioning to fully developed turbulence and finally dissipated by molecular diffusion. High-Atwood-number effects (as distinguished from the Boussinesq case) are accounted for: both hydrodynamic turbulence and material mixing are treated at arbitrary density ratios, with the specific volume, mass flux and all their correlations in closed form. An extension of the generalized Langevin model, originally developed for the Lagrangian fluid particle velocity in constant-density shear-driven turbulence, is constructed for variable-density pressure-gradient-driven flows. The persistent small-scale anisotropy, a fundamentally 'non-Kolmogorovian' feature of flows under external acceleration forces, is captured by a tensorial diffusion term based on the external body force. The material mixing model for the fluid density, an active scalar, is developed based on the beta distribution. The beta-PDF is shown to be capable of capturing the mixing asymmetry and that it can accurately represent the density through transition, in fully developed turbulence and in the decay process. The joint model for hydrodynamics and active material mixing yields a time-accurate evolution of the turbulent kinetic energy and Reynolds stress anisotropy without resorting to gradient diffusion hypotheses, and represents the mixing state by the density PDF itself, eliminating the need for dubious mixing measures. Direct numerical simulations of the homogeneous Rayleigh-Taylor instability are used for model validation.
Unequal density effect on static structure factor of coupled electron layers
Saini, L. K. Nayak, Mukesh G.
2014-04-24
In order to understand the ordered phase, if any, in a real coupled electron layers (CEL), there is a need to take into account the effect of unequal layer density. Such phase is confirmed by a strong peak in a static structure factor. With the aid of quantum/dynamical version of Singwi, Tosi, Land and SjÃ¶lander (so-called qSTLS) approximation, we have calculated the intra- and interlayer static structure factors, S{sub ll}(q) and S{sub 12}(q), over a wide range of density parameter r{sub sl} and interlayer spacing d. In our present study, the sharp peak in S{sub 22}(q) has been found at critical density with sufficiently lower interlayer spacing. Further, to find the resultant effect of unequal density on intra- and interlayer static structure factors, we have compared our results with that of the recent CEL system with equal layer density and isolated single electron layer.
Zhang, D.S.; Wei, G.W.; Kouri, D.J.; Hoffman, D.K.
1997-03-01
The distributed approximating functional method is applied to the solution of the Fokker{endash}Planck equations. The present approach is limited to the standard eigenfunction expansion method. Three typical examples, a Lorentz Fokker{endash}Planck equation, a bistable diffusion model and a Henon{endash}Heiles two-dimensional anharmonic resonating system, are considered in the present numerical testing. All results are in excellent agreement with those of established methods in the field. It is found that the distributed approximating functional method yields the accuracy of a spectral method but with a local method{close_quote}s simplicity and flexibility for the eigenvalue problems arising from the Fokker{endash}Planck equations. {copyright} {ital 1997 American Institute of Physics.}
Generalized Fokker-Planck Approximations of Particle Transport with Highly Forward-Peaked Scattering
Leakeas, Christopher L.; Larsen, Edward W.
2001-03-15
The Fokker-Planck equation is often used to approximate the description of particle transport processes with highly forward-peaked scattering. Pomraning has shown that if the physical scattering kernel is sufficiently dominated by small-angle scattering, then the Fokker-Planck equation is an asymptotic approximation to the linear Boltzmann equation. However, most physically-meaningful scattering kernels contain a sufficient amount of large-angle scattering that the asymptotic criterion is not met. Thus, in many physical problems, solutions of the Fokker-Planck equation are substantially in error. In this paper, Pomraning's asymptotic results are generalized and a new generalized Fokker-Planck (GFP) theory that robustly incorporates large-angle scattering is developed. Numerical experiments demonstrate that the resulting GFP equations are much more accurate than the standard Fokker-Planck equation.
Abdelaziz, Omar; Shrestha, Som S
2014-01-01
Refrigerants are the life-blood of vapor compression systems that are widely used in Heating, Ventilation, Air-Conditioning, and Refrigeration (HVAC&R) applications. The HVAC&R community is currently transitioning from main-stream refrigerants that have high Global Warming Potential (GWP) to alternative lower-GWP refrigerants. During this transition, it is important to account for the life cycle climate performance of alternative refrigerants since their performance will be different than that of higher-GWP refrigerants. This requires the evaluation of the system performance with the new refrigerants. Unfortunately, it is extremely difficult to predict the realistic performance of new alternative refrigerants without experimental validation. One of the main challenges in this regard is modeling the compressor performance with high fidelity due to the complex interaction of operating parameters, geometry, boundary conditions, and fluid properties. High fidelity compressor models are computationally expensive and require significant pre-processing to evaluate the performance of alternative refrigerants. This paper presents a new approach to modeling compressor performance when alternative refrigerants are used. The new modeling concept relies on using existing compressor performance to create an approximate model that captures the dependence of compressor performance on key operating parameters and fluid properties. The model can be built using a myriad of approximation techniques. This paper focuses on Kriging-based techniques to develop higher fidelity approximate compressor models. Baseline and at least one alternative refrigerant performance data are used to build the model. The model accuracy was evaluated by comparing the model results with compressor performance data using other refrigerants. Preliminary results show that the approximate model can predict the compressor mass flow rate and power consumption within 5%.
Dvirny, A. I.; Slyn'ko, V. I. E-mail: vitstab@ukr.net
2014-06-01
Inverse theorems to Lyapunov's direct method are established for quasihomogeneous systems of differential equations with impulsive action. Conditions for the existence of Lyapunov functions satisfying typical bounds for quasihomogeneous functions are obtained. Using these results, we establish conditions for an equilibrium of a nonlinear system with impulsive action to be stable, using the properties of a quasihomogeneous approximation to the system. The results are illustrated by an example of a large-scale system with homogeneous subsystems. Bibliography: 30 titles. (paper)
Accuracy considerations for Chebyshev rational approximation method (CRAM) in Burnup calculations
Pusa, M.
2013-07-01
The burnup equations can in principle be solved by computing the exponential of the burnup matrix. However, due to the difficult numerical characteristics of burnup matrices, the problem is extremely stiff and the matrix exponential solution has previously been considered infeasible for an entire burnup system containing over a thousand nuclides. It was recently discovered by the author that the eigenvalues of burnup matrices are generally located near the negative real axis, which prompted introducing the Chebyshev rational approximation method (CRAM) for solving the burnup equations. CRAM can be characterized as the best rational approximation on the negative real axis and it has been shown to be capable of simultaneously solving an entire burnup system both accurately and efficiently. In this paper, the accuracy of CRAM is further studied in the context of burnup equations. The approximation error is analyzed based on the eigenvalue decomposition of the burnup matrix. It is deduced that the relative accuracy of CRAM may be compromised if a nuclide concentration diminishes significantly during the considered time step. Numerical results are presented for two test cases, the first one representing a small burnup system with 36 nuclides and the second one a full a decay system with 1531 nuclides. (authors)
Explicit solutions of the radiative transport equation in the P{sub 3} approximation
Liemert, AndrÃ© Kienle, Alwin
2014-11-01
Purpose: Explicit solutions of the monoenergetic radiative transport equation in the P{sub 3} approximation have been derived which can be evaluated with nearly the same computational effort as needed for solving the standard diffusion equation (DE). In detail, the authors considered the important case of a semi-infinite medium which is illuminated by a collimated beam of light. Methods: A combination of the classic spherical harmonics method and the recently developed method of rotated reference frames is used for solving the P{sub 3} equations in closed form. Results: The derived solutions are illustrated and compared to exact solutions of the radiative transport equation obtained via the Monte Carlo (MC) method as well as with other approximated analytical solutions. It is shown that for the considered cases which are relevant for biomedical optics applications, the P{sub 3} approximation is close to the exact solution of the radiative transport equation. Conclusions: The authors derived exact analytical solutions of the P{sub 3} equations under consideration of boundary conditions for defining a semi-infinite medium. The good agreement to Monte Carlo simulations in the investigated domains, for example, in the steady-state and time domains, as well as the short evaluation time needed suggests that the derived equations can replace the often applied solutions of the diffusion equation for the homogeneous semi-infinite medium.
Liang, Faming; Cheng, Yichen; Lin, Guang
2014-06-13
Simulated annealing has been widely used in the solution of optimization problems. As known by many researchers, the global optima cannot be guaranteed to be located by simulated annealing unless a logarithmic cooling schedule is used. However, the logarithmic cooling schedule is so slow that no one can afford to have such a long CPU time. This paper proposes a new stochastic optimization algorithm, the so-called simulated stochastic approximation annealing algorithm, which is a combination of simulated annealing and the stochastic approximation Monte Carlo algorithm. Under the framework of stochastic approximation Markov chain Monte Carlo, it is shown that the new algorithm can work with a cooling schedule in which the temperature can decrease much faster than in the logarithmic cooling schedule, e.g., a square-root cooling schedule, while guaranteeing the global optima to be reached when the temperature tends to zero. The new algorithm has been tested on a few benchmark optimization problems, including feed-forward neural network training and protein-folding. The numerical results indicate that the new algorithm can significantly outperform simulated annealing and other competitors.
Reeves, Daniel B. Weaver, John B.
2015-06-21
Magnetic nanoparticles are promising tools for a host of therapeutic and diagnostic medical applications. The dynamics of rotating magnetic nanoparticles in applied magnetic fields depend strongly on the type and strength of the field applied. There are two possible rotation mechanisms and the decision for the dominant mechanism is often made by comparing the equilibrium relaxation times. This is a problem when particles are driven with high-amplitude fields because they are not necessarily at equilibrium at all. Instead, it is more appropriate to consider the â€œcharacteristic timescalesâ€ that arise in various applied fields. Approximate forms for the characteristic time of Brownian particle rotations do exist and we show agreement between several analytical and phenomenological-fit models to simulated data from a stochastic Langevin equation approach. We also compare several approximate models with solutions of the Fokker-Planck equation to determine their range of validity for general fields and relaxation times. The effective field model is an excellent approximation, while the linear response solution is only useful for very low fields and frequencies for realistic Brownian particle rotations.
Distribution of Radiation Density in a Homogeneous Cloudy Laye
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of Radiation Density in a Homogeneous Cloudy Layer S. V. Dvoryashin, K. A. Shukorov, A. H. ... method) allowing calculating radiation density in homogeneous and non-uniform ...
Real-Time Simultaneous Measurements of Size, Density, and Composition...
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Simultaneous Measurements of Size, Density, and Composition of Single Ultrafine Diesel Tailpipe Particles Real-Time Simultaneous Measurements of Size, Density, and Composition of ...
Density Functional Theory Approach to Nuclear Fission (Conference...
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Density Functional Theory Study of Surface Carbonate Formation...
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Ultra Low Density Amorphous Shape Memory polymer Foams. (Conference...
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Error Analysis in Nuclear Density Functional Theory (Journal...
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XUV Absorption by Solid Density Aluminum (Journal Article) |...
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Controlling the Actuation Rate of Low Density Shape Memory Polymer...
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Using Radio Waves to Control Fusion Plasma Density
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A New Mechanism of Charge Density Wave Discovered in Transition...
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8 A New Mechanism of Charge Density Wave Discovered in Transition Metal Dichalcogenides Charge density waves (CDW) are a type of coupled electronic-lattice instability found in...
Couch, Sean M.; Graziani, Carlo; Flocke, Norbert
2013-12-01
Self-gravity computation by multipole expansion is a common approach in problems such as core-collapse and Type Ia supernovae, where single large condensations of mass must be treated. The standard formulation of multipole self-gravity in arbitrary coordinate systems suffers from two significant sources of error, which we correct in the formulation presented in this article. The first source of error is due to the numerical approximation that effectively places grid cell mass at the central point of the cell, then computes the gravitational potential at that point, resulting in a convergence failure of the multipole expansion. We describe a new scheme that avoids this problem by computing gravitational potential at cell faces. The second source of error is due to sub-optimal choice of location for the expansion center, which results in angular power at high multipole l values in the gravitational field, requiring a high—and expensive—value of multipole cutoff l {sub max}. By introducing a global measure of angular power in the gravitational field, we show that the optimal coordinate for the expansion is the square-density-weighted mean location. We subject our new multipole self-gravity algorithm, implemented in the FLASH simulation framework, to two rigorous test problems: MacLaurin spheroids for which exact analytic solutions are known, and core-collapse supernovae. We show that key observables of the core-collapse simulations, particularly shock expansion, proto-neutron star motion, and momentum conservation, are extremely sensitive to the accuracy of the multipole gravity, and the accuracy of their computation is greatly improved by our reformulated solver.
How important is self-consistency for the dDsC density dependent dispersion correction?
BrÃ©mond, Ã‰ric; Corminboeuf, ClÃ©mence; Golubev, Nikolay; Department of Chemistry, M. V. Lomonosov Moscow State University, Moscow 119991 ; Steinmann, Stephan N.
2014-05-14
The treatment of dispersion interactions is ubiquitous but computationally demanding for seamless ab initio approaches. A highly popular and simple remedy consists in correcting for the missing interactions a posteriori by adding an attractive energy term summed over all atom pairs to standard density functional approximations. These corrections were originally based on atom pairwise parameters and, hence, had a strong touch of empiricism. To overcome such limitations, we recently proposed a robust system-dependent dispersion correction, dDsC, that is computed from the electron density and that provides a balanced description of both weak inter- and intramolecular interactions. From the theoretical point of view and for the sake of increasing reliability, we here verify if the self-consistent implementation of dDsC impacts ground-state properties such as interaction energies, electron density, dipole moments, geometries, and harmonic frequencies. In addition, we investigate the suitability of the a posteriori scheme for molecular dynamics simulations, for which the analysis of the energy conservation constitutes a challenging tests. Our study demonstrates that the post-SCF approach in an excellent approximation.
Self-interaction corrections in density functional theory
Tsuneda, Takao; Hirao, Kimihiko
2014-05-14
Self-interaction corrections for Kohn-Sham density functional theory are reviewed for their physical meanings, formulations, and applications. The self-interaction corrections get rid of the self-interaction error, which is the sum of the Coulomb and exchange self-interactions that remains because of the use of an approximate exchange functional. The most frequently used self-interaction correction is the Perdew-Zunger correction. However, this correction leads to instabilities in the electronic state calculations of molecules. To avoid these instabilities, several self-interaction corrections have been developed on the basis of the characteristic behaviors of self-interacting electrons, which have no two-electron interactions. These include the von WeizsÃ¤cker kinetic energy and long-range (far-from-nucleus) asymptotic correction. Applications of self-interaction corrections have shown that the self-interaction error has a serious effect on the states of core electrons, but it has a smaller than expected effect on valence electrons. This finding is supported by the fact that the distribution of self-interacting electrons indicates that they are near atomic nuclei rather than in chemical bonds.
Gillespie, Dirk
2013-10-01
An algorithm to approximately calculate the partition function (and subsequently ensemble averages) and density of states of lattice spin systems through non-Monte-Carlo random sampling is developed. This algorithm (called the sampling-the-mean algorithm) can be applied to models where the up or down spins at lattice nodes interact to change the spin states of other lattice nodes, especially non-Ising-like models with long-range interactions such as the biological model considered here. Because it is based on the Central Limit Theorem of probability, the sampling-the-mean algorithm also gives estimates of the error in the partition function, ensemble averages, and density of states. Easily implemented parallelization strategies and error minimizing sampling strategies are discussed. The sampling-the-mean method works especially well for relatively small systems, systems with a density of energy states that contains sharp spikes or oscillations, or systems with little a priori knowledge of the density of states.
Ultra-high density diffraction grating
Padmore, Howard A.; Voronov, Dmytro L.; Cambie, Rossana; Yashchuk, Valeriy V.; Gullikson, Eric M.
2012-12-11
A diffraction grating structure having ultra-high density of grooves comprises an echellette substrate having periodically repeating recessed features, and a multi-layer stack of materials disposed on the echellette substrate. The surface of the diffraction grating is planarized, such that layers of the multi-layer stack form a plurality of lines disposed on the planarized surface of the structure in a periodical fashion, wherein lines having a first property alternate with lines having a dissimilar property on the surface of the substrate. For example, in one embodiment, lines comprising high-Z and low-Z materials alternate on the planarized surface providing a structure that is suitable as a diffraction grating for EUV and soft X-rays. In some embodiments, line density of between about 10,000 lines/mm to about 100,000 lines/mm is provided.
Inductor Geometry With Improved Energy Density
Cui, H; Ngo, KDT; Moss, J; Lim, MHF; Rey, E
2014-10-01
The "constant-flux" concept is leveraged to achieve high magnetic-energy density, leading to inductor geometries with height significantly lower than that of conventional products. Techniques to shape the core and to distribute the winding turns to shape a desirable field profile are described for the two basic classes of magnetic geometries: those with the winding enclosed by the core and those with the core enclosed by the winding. A relatively constant flux distribution is advantageous not only from the density standpoint, but also from the thermal standpoint via the reduction of hot spots, and from the reliability standpoint via the suppression of flux crowding. In this journal paper on a constant-flux inductor (CFI) with enclosed winding, the foci are operating principle, dc analysis, and basic design procedure. Prototype cores and windings were routed from powder-iron disks and copper sheets, respectively. The design of CFI was validated by the assembled inductor prototype.
Global coherence of dust density waves
Killer, Carsten; Melzer, André
2014-06-15
The coherence of self-excited three-dimensional dust density waves has been experimentally investigated by comparing global and local wave properties. For that purpose, three-dimensional dust clouds have been confined in a radio frequency plasma with thermophoretic levitation. Global wave properties have been measured from the line-of-sight integrated dust density obtained from homogenous light extinction measurements. Local wave properties have been obtained from thin, two-dimensional illuminated laser slices of the cloud. By correlating the simultaneous global and local wave properties, the spatial coherence of the waves has been determined. We find that linear waves with small amplitudes tend to be fragmented, featuring an incoherent wave field. Strongly non-linear waves with large amplitudes, however, feature a strong spatial coherence throughout the dust cloud, indicating a high level of synchronization.
Current density fluctuations and ambipolarity of transport
Shen, W.; Dexter, R.N.; Prager, S.C.
1991-10-01
The fluctuation in the plasma current density is measured in the MIST reversed field pinch experiment. Such fluctuations, and the measured radial profile of the k spectrum of magnetic fluctuations, supports the view and that low frequency fluctuations (f < 30 kHz) are tearing modes and high frequency fluctuations (30 kHz < f < 250 kHz) are localized turbulence in resonance with the local equilibrium magnetic field (i.e., k {center_dot} B = 0). Correlation of current density and magnetic fluctuations (< {tilde j}{parallel}{tilde B}{sub r} >) demonstrates that radial particle transport from particle motion parallel to a fluctuating magnetic field is ambipolar over the full frequency range.
Current density fluctuations and ambipolarity of transport
Shen, W.; Dexter, R.N.; Prager, S.C.
1991-10-01
The fluctuation in the plasma current density is measured in the MIST reversed field pinch experiment. Such fluctuations, and the measured radial profile of the k spectrum of magnetic fluctuations, supports the view and that low frequency fluctuations (f < 30 kHz) are tearing modes and high frequency fluctuations (30 kHz < f < 250 kHz) are localized turbulence in resonance with the local equilibrium magnetic field (i.e., k {center dot} B = 0). Correlation of current density and magnetic fluctuations (< {tilde j}{parallel}{tilde B}{sub r} >) demonstrates that radial particle transport from particle motion parallel to a fluctuating magnetic field is ambipolar over the full frequency range.
Kudzu (Pueraria montana) community responses to herbicides, burning, and high-density loblolly pine
T.B. Harrington; L.T. Rader-Dixon; J.W. Taylor, Jr.
2003-11-01
Kudzu is an aggressive, nonnative vine that currently dominates an estimated 810,000 ha of mesic forest communities in the eastern United States. To test an integrated method of weed control, abundances of kudzu and other plant species were compared during 4 yr after six herbicide treatments (clopyralid, triclopyr, metsulfuron, picloram 1 2,4-D, tebuthiuron, and a nonsprayed check), in which loblolly pines were planted at three densities (0, 1, and 4 seedlings m22) to induce competition and potentially delay kudzu recovery. This split-plot design was replicated on each of the four kudzu-dominated sites near Aiken, SC. Relative light intensity (RLI) and soil water content (SWC) were measured periodically to identify mechanisms of interference among plant species. Two years after treatment (1999), crown coverage of kudzu averaged , 2% in herbicide plots compared with 93% in the nonsprayed check, and these differences were maintained through 2001, except in clopyralid plots where kudzu cover increased to 15%. In 2001, pine interference was associated with 33, 56, and 67% reductions in biomass of kudzu, blackberry, and herbaceous vegetation, respectively. RLI in kudzu-dominated plots (4 to 15% of full sun) generally was less than half that of herbicide-treated plots. SWC was greatest in tebuthiuron plots, where total vegetation cover averaged 26% compared with 77 to 111% in other plots. None of the treatments eradicated kudzu, but combinations of herbicides and induced pine competition delayed its recovery.
Energy flux density in a thermoacoustic couple
Cao, N.; Chen, S. |; Olson, R.; Swift, G.W.
1996-06-01
The hydro- and thermodynamical processes near and within a thermoacoustic couple are simulated and analyzed by numerical solution of the compressible Navier-Stokes, continuity, and energy equations for an ideal gas, concentrating on the time-averaged energy flux density in the gas. The numerical results show details of the heat sink at one end of the plates in the thermoacoustic couple. 15 refs., 10 figs., 1 tab.
Density fluctuations of polymers in disordered media
Deutsch, Joshua M.; Olvera de la Cruz, Monica
2011-03-02
We study self-avoiding random walks in an environment where sites are excluded randomly, in two and three dimensions. For a single polymer chain, we study the statistics of the time averaged monomer density and show that these are well described by multifractal statistics. This is true even far from the percolation transition of the disordered medium. We investigate solutions of chains in a disordered environment and show that the statistics cease to be multifractal beyond the screening length of the solution.
High-density carbon ablator ignition path with low-density gas-filled rugby hohlraum
Amendt, Peter; Ho, Darwin D.; Jones, Ogden S.
2015-04-15
A recent low gas-fill density (0.6â€‰mg/cc {sup 4}He) cylindrical hohlraum experiment on the National Ignition Facility has shown high laser-coupling efficiency (>96%), reduced phenomenological laser drive corrections, and improved high-density carbon capsule implosion symmetry [Jones et al., Bull. Am. Phys. Soc. 59(15), 66 (2014)]. In this Letter, an ignition design using a large rugby-shaped hohlraum [Amendt et al., Phys. Plasmas 21, 112703 (2014)] for high energetics efficiency and symmetry control with the same low gas-fill density (0.6â€‰mg/cc {sup 4}He) is developed as a potentially robust platform for demonstrating thermonuclear burn. The companion high-density carbon capsule for this hohlraum design is driven by an adiabat-shaped [Betti et al., Phys. Plasmas 9, 2277 (2002)] 4-shock drive profile for robust high gain (>10) 1-D ignition performance and large margin to 2-D perturbation growth.
Effects of argon gas pressure on its metastable-state density in high-density plasmas
Seo, B. H.; Kim, J. H.; You, S. J.
2015-05-15
The effect of argon gas pressure on its metastable density in inductively coupled plasmas (ICPs) is investigated by using the laser-induced fluorescence method. Our results show that the metastable-state density of argon varies with the gas pressure depending on the measurement position; the density decreases with the pressure at a position far from the ICP antenna, whereas it increases with the pressure at a position near the antenna. This contrast in the metastable-state density trend with the pressure is explained by considering the electron temperature variations at the two measurement positions. The theoretical interpretation and calculation using a global model are also addressed in detail in this paper.
Shu, Yu-Chen, E-mail: ycshu@mail.ncku.edu.tw [Department of Mathematics, National Cheng Kung University, Tainan 701, Taiwan (China); Mathematics Division, National Center for Theoretical Sciences (South), Tainan 701, Taiwan (China); Chern, I-Liang, E-mail: chern@math.ntu.edu.tw [Department of Applied Mathematics, National Chiao Tung University, Hsin Chu 300, Taiwan (China); Department of Mathematics, National Taiwan University, Taipei 106, Taiwan (China); Mathematics Division, National Center for Theoretical Sciences (Taipei Office), Taipei 106, Taiwan (China); Chang, Chien C., E-mail: mechang@iam.ntu.edu.tw [Institute of Applied Mechanics, National Taiwan University, Taipei 106, Taiwan (China); Department of Mathematics, National Taiwan University, Taipei 106, Taiwan (China)
2014-10-15
Most elliptic interface solvers become complicated for complex interface problems at those “exceptional points” where there are not enough neighboring interior points for high order interpolation. Such complication increases especially in three dimensions. Usually, the solvers are thus reduced to low order accuracy. In this paper, we classify these exceptional points and propose two recipes to maintain order of accuracy there, aiming at improving the previous coupling interface method [26]. Yet the idea is also applicable to other interface solvers. The main idea is to have at least first order approximations for second order derivatives at those exceptional points. Recipe 1 is to use the finite difference approximation for the second order derivatives at a nearby interior grid point, whenever this is possible. Recipe 2 is to flip domain signatures and introduce a ghost state so that a second-order method can be applied. This ghost state is a smooth extension of the solution at the exceptional point from the other side of the interface. The original state is recovered by a post-processing using nearby states and jump conditions. The choice of recipes is determined by a classification scheme of the exceptional points. The method renders the solution and its gradient uniformly second-order accurate in the entire computed domain. Numerical examples are provided to illustrate the second order accuracy of the presently proposed method in approximating the gradients of the original states for some complex interfaces which we had tested previous in two and three dimensions, and a real molecule ( (1D63)) which is double-helix shape and composed of hundreds of atoms.
DYNAMICAL SPIN SUSCEPTIBILITY IN THE TD-LDA AND QSGW APPROXIMATIONS
SCHILFGAARDE, MARK VAN; KOTANI, TAKAO
2012-10-15
Abstract. This project was aimed at building the transverse dynamical spin susceptibility with the TD-LDA and the recently-developed Quasparticle Self-Consisent Approximations, which determines an optimum quasiparticle picture in a self-consistent manner within the GW approximation. Our main results were published into two papers, (J. Phys. Cond. Matt. 20, 95214 (2008), and Phys. Rev. B83, 060404(R) (2011). In the first paper we present spin wave dispersions for MnO, NiO, and #11;-MnAs based on quasiparticle self-consistent GW approximation (QSGW). For MnO and NiO, QSGW results are in rather good agreement with experiments, in contrast to the LDA and LDA+U descriptions. For #11;-MnAs, we find a collinear ferromagnetic ground state in QSGW, while this phase is unstable in the LDA. In the second, we apply TD-LDA to the CaFeAs2 Ã¢Â?Â? the first attempt the first ab initio calculation of dynamical susceptibililty in a system with complex electronic structure Magnetic excitations in the striped phase of CaFe2As2 are studied as a function of local moment amplitude. We find a new kind of excitation: sharp resonances of Stoner-like (itinerant) excitations at energies comparable to the NÃ?Â´eel temperature, originating largely from a narrow band of Fe d states near the Fermi level, and coexisting with more conventional (localized) spin waves. Both kinds of excitations can show multiple branches, highlighting the inadequacy of a description based on a localized spin model.
p-barp-Annihilation processes in the tree approximation of SU(3) chiral effective theory
Tarasov, V. E.; Kudryavtsev, A. E. Romanov, A. I.; Weinberg, V. M.
2012-12-15
The p-barp-annihilation reactions p-barp {yields} {eta}{eta} {eta} and p-barp {yields} {eta}KK-bar at rest are considered in the tree approximation in the framework of SU(3) chiral effective theory at leading order. The calculated branchings are compared with the data. The results for neutral ({eta}{eta}{eta}, K{sup 0}K-bar{sup 0}{sub {eta}}) and charged (K{sup +}K{sup -}{sub {eta}}) channels are essentially different.
The extraordinary wave excitation in microwave gas breakdown in the adiabatic approximation
Ghorbanalilu, M.; Shokri, B.
2008-09-15
Making use of the electron distribution function formed in the interaction of high-frequency microwave (MW) pulsed fields with a rarefied neutral gas [M. Ghorbanalilu, Phys. Plasmas. 13, 102110 (2006)], the dielectric permittivity tensor of the produced plasma is derived under the condition that the ions are cold and nonmagnetized. According to the adiabatic approximation and using the dielectric permittivity tensor elements the dispersion relations for ordinary and extraordinary excited waves are found. The numerical solution of the dispersion relation shows that the extraordinary modes are unstable in such a nonequilibrium system. These modes are generated in a wide range of wavelengths by tuning the MW field amplitude and magnetic field strength.
Kuang, Y.R. )
1991-08-01
A theoretical method to calculate the {ital K}-shell electron-capture cross section in asymmetric collisions is developed. The correlation effect between the active and the passive electrons and the screening effect in the wave function of the active electron are all considered. Under the Oppenheimer-Brinkman-Kramers approximation, an analytical expression for the total capture cross section is obtained. The calculated results for H{sup +}--carbon, nitrogen, oxygen, neon, argon and He{sup 2+}-neon collisions, at the intermediate-energy region, show very good agreement with available experimental findings. A comparison with other theoretical results is given.
Barrios, Dolores; Lopez, Guillermo L; Martinez-Finkelshtein, A; Torrano, Emilio
1999-04-30
The approximability of the resolvent of an operator induced by a band matrix by the resolvents of its finite-dimensional sections is studied. For bounded perturbations of self-adjoint matrices a positive result is obtained. The convergence domain of the sequence of resolvents can be described in this case in terms of matrices involved in the representation. This result is applied to tridiagonal complex matrices to establish conditions for the convergence of Chebyshev continued fractions on sets in the complex domain. In the particular case of compact perturbations this result is improved and a connection between the poles of the limit function and the eigenvalues of the tridiagonal matrix is established.
Foiles, Stephen Martin
2011-10-01
The predictions of binary collision approximation (BCA) and molecular dynamics (MD) simulations of displacement cascades in GaAs are compared. There are three issues addressed in this work. The first is the optimal choice of the effective displacement threshold to use in the BCA calculations to obtain the best agreement with MD results. Second, the spatial correlations of point defects are compared. This is related to the level of clustering that occurs for different types of radiation. Finally, the size and structure of amorphous zones seen in the MD simulations is summarized. BCA simulations are not able to predict the formation of amorphous material.
Simplified approach to interacting boson approximation-2 calculations using Hamiltonian invariants
Chou, W.-T.; Zamfir, N. V.; Clark University, Worcester, Massachusetts 01610; National Institute of Physics and Nuclear Engineering, Bucharest, ; Casten, R. F.
2000-07-01
A systematic study of predictions of the interacting boson approximation (IBA)-2 model leads to the identification of two parameter invariants such that calculations with the same values of the invariants yield results that are identical in certain cases and show close similarities under a wider set of conditions. The invariants validate a much-used form of the IBA-2 Hamiltonian and provide a systematic method to simplify IBA-2 calculations by choosing a truncated Hamiltonian with the same invariant values as more general Hamiltonians. (c) 2000 The American Physical Society.
Proton-Nucleus Scattering Approximations and Implications for LHC Crystal Collimation
Noble, Robert; ,
2010-06-07
In particle accelerators, scattered protons with energies close to the incident particles may travel considerable distances with the beam before impacting on accelerator components downstream. To analyze such problems, angular deflection and energy loss of scattered particles are the main quantities to be simulated since these lead to changes in the beam's phase space distribution and particle loss. Simple approximations for nuclear scattering processes causing limited energy loss to high-energy protons traversing matter are developed which are suitable for rapid estimates and reduced-description Monte Carlo simulations. The implications for proton loss in the Large Hadron Collider due to nuclear scattering on collimation crystals are discussed.
Comparison of transition densities in the DDHMS model of pre-equilibrium emission
Brito, L.; Carlson, B. V.
2014-11-11
The DDHMS (double differential hybrid Monte Carlo simulation) model treats nucleon-induced pre-equilibrium reactions as a series of particle-particle and particle-hole interactions in the space of energy and angle. This work compares spectra obtained within the model using diferent approximations to the density of accessible states. The calculations are performed with the EMPIRE reaction model code, a modular system containing several nuclear reaction models that permits a fairly complete descritpion of the reaction, from elastic scattering and absorption through the pre-equilbrium stage to the final decay by statistical emission.
Density-functional errors in ionization potential with increasing system size
Whittleton, Sarah R.; Sosa Vazquez, Xochitl A.; Isborn, Christine M.; Johnson, Erin R.
2015-05-14
This work investigates the effects of molecular size on the accuracy of density-functional ionization potentials for a set of 28 hydrocarbons, including series of alkanes, alkenes, and oligoacenes. As the system size increases, delocalization error introduces a systematic underestimation of the ionization potential, which is rationalized by considering the fractional-charge behavior of the electronic energies. The computation of the ionization potential with many density-functional approximations is not size-extensive due to excessive delocalization of the incipient positive charge. While inclusion of exact exchange reduces the observed errors, system-specific tuning of long-range corrected functionals does not generally improve accuracy. These results emphasize that good performance of a functional for small molecules is not necessarily transferable to larger systems.
Radiography to measure the longitudinal density gradients of Pd compacts
Back, D.D.
1992-05-14
This study used radiography to detect and quantify density gradients in green compacts of Palladium powder. Ultrasonic velocity measurements had been tried previously, but they were affected by material properties, in addition to the density, so that an alternative was sought. The alternative technique used radiographic exposures of a series of standard compacts whose density is known and correlated with the radiographic film density. These correlations are used to predict the density in subsequent compacts.
Wave-function functionals for the density
Slamet, Marlina; Pan Xiaoyin; Sahni, Viraht
2011-11-15
We extend the idea of the constrained-search variational method for the construction of wave-function functionals {psi}[{chi}] of functions {chi}. The search is constrained to those functions {chi} such that {psi}[{chi}] reproduces the density {rho}(r) while simultaneously leading to an upper bound to the energy. The functionals are thereby normalized and automatically satisfy the electron-nucleus coalescence condition. The functionals {psi}[{chi}] are also constructed to satisfy the electron-electron coalescence condition. The method is applied to the ground state of the helium atom to construct functionals {psi}[{chi}] that reproduce the density as given by the Kinoshita correlated wave function. The expectation of single-particle operators W={Sigma}{sub i}r{sub i}{sup n}, n=-2,-1,1,2, W={Sigma}{sub i}{delta}(r{sub i}) are exact, as must be the case. The expectations of the kinetic energy operator W=-(1/2){Sigma}{sub i}{nabla}{sub i}{sup 2}, the two-particle operators W={Sigma}{sub n}u{sup n}, n=-2,-1,1,2, where u=|r{sub i}-r{sub j}|, and the energy are accurate. We note that the construction of such functionals {psi}[{chi}] is an application of the Levy-Lieb constrained-search definition of density functional theory. It is thereby possible to rigorously determine which functional {psi}[{chi}] is closer to the true wave function.
Approximation of functions of variable smoothness by Fourier-Legendre sums
Sharapudinov, I I
2000-06-30
Assume that 0<{mu}{<=}1, and let r{>=}1 be an integer. Let {delta}={l_brace}a{sub 1},...,a{sub l}{r_brace}, where the a{sub i} are points in the interval (-1,1). The classes S{sup r}H{sup {mu}}{sub {delta}} and S{sup r}H{sup {mu}}{sub {delta}}(B) are introduced. These consist of functions with absolutely continuous (r-1)th derivative on [-1,1] such that their rth and (r+1)th derivatives satisfy certain conditions outside the set {delta}. It is proved that for 0<{mu}<1 the Fourier-Legendre sums realize the best approximation in the classes S{sup r}H{sup {mu}}{sub {delta}}(B). Using the Fourier-Legendre expansions, polynomials Y{sub n+2r} of order n+2r are constructed that possess the following property: for 0<{mu}<1 the {nu}th derivative of the polynomial Y{sub n+2r} approximates f{sup ({nu})}(x) (f element of S{sup r}H{sup {mu}}{sub {delta}}) on [-1,1] to within O(n{sup {nu}}{sup +1-r-{mu}}), and the accuracy is of order O(n{sup {nu}}{sup -r-{mu}}) outside {delta}.
Toloczko, M.B.; Garner, F.A.; Eiholzer, C.R.
1998-03-01
Three ferritic alloys were irradiated in two fast reactors to doses of 50 dpa or more at temperatures near 400 C. One martensitic alloy, HT9, was irradiated in both the FFTF and PFR reactors. PFR is the Prototype Fast Reactor in Dourneay, Scotland, and FFTF is the Fast Flux Test Facility in Richland, WA. D57 is a developmental alloy that was irradiated in PFR only, and MA957 is a Y{sub 2}O{sub 3} dispersion-hardened ferritic alloy that was irradiated only in FFTF. These alloys exhibited little or no void swelling at {approximately}400 C. Depending on the alloy starting condition, these steels develop a variety of non-creep strains early in the irradiation that are associated with phase changes. Each of these alloys creeps at a rate that is significantly lower than that of austenitic steels irradiated in the same experiments. The creep compliance for ferritic alloys in general appears to be {approximately}0.5 {times} 10{sup {minus}6} MPa{sup {minus}1} dpa{sup {minus}1}, independent of both composition and starting state. The addition of Y{sub 2}O{sub 3} as a dispersoid does not appear to change the creep behavior.
Jouvet, Guillaume
2015-04-15
In this paper, a multilayer generalisation of the Shallow Shelf Approximation (SSA) is considered. In this recent hybrid ice flow model, the ice thickness is divided into thin layers, which can spread out, contract and slide over each other in such a way that the velocity profile is layer-wise constant. Like the SSA (1-layer model), the multilayer model can be reformulated as a minimisation problem. However, unlike the SSA, the functional to be minimised involves a new penalisation term for the interlayer jumps of the velocity, which represents the vertical shear stresses induced by interlayer sliding. Taking advantage of this reformulation, numerical solvers developed for the SSA can be naturally extended layer-wise or column-wise. Numerical results show that the column-wise extension of a Newton multigrid solver proves to be robust in the sense that its convergence is barely influenced by the number of layers and the type of ice flow. In addition, the multilayer formulation appears to be naturally better conditioned than the one of the first-order approximation to face the anisotropic conditions of the sliding-dominant ice flow of ISMIP-HOM experiments.
On the Validity of Certain Approximations Used in the Modeling of Nuclear EMP
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Farmer, William A.; Cohen, Bruce I.; Eng, Chester D.
2016-04-01
The legacy codes developed for the modeling of EMP, multiple scattering of Compton electrons has typically been modeled by the obliquity factor. A recent publication has examined this approximation in the context of the generated Compton current [W. A. Farmer and A. Friedman, IEEE Trans. Nucl. Sc. 62, 1695 (2015)]. Here, this previous analysis is extended to include the generation of the electromagnetic fields. Obliquity factor predictions are compared with Monte-Carlo models. In using a Monte-Carlo description of scattering, two distributions of scattering angles are considered: Gaussian and a Gaussian with a single-scattering tail. Additionally, legacy codes also neglect themoreÂ Â» radial derivative of the backward-traveling wave for computational efficiency. The neglect of this derivative improperly treats the backward-traveling wave. Moreover, these approximations are examined in the context of a high-altitude burst, and it is shown that in comparison to more complete models, the discrepancy between field amplitudes is roughly two to three percent and between rise-times, 10%. Finally, it is concluded that the biggest factor in determining the rise time of the signal is not the dynamics of the Compton current, but is instead the conductivity.Â«Â less
Exact and approximate fermion Green`s functions in QED and QCD
Fried, H.M. [Physics Department, Brown University, Providence, Rhode Island 02912 (United States)] [Physics Department, Brown University, Providence, Rhode Island 02912 (United States); Gabellini, Y. [Institut Non-Lineaire de Nice, 1361, Route des Lucioles, 06560 Valbonne (France)] [Institut Non-Lineaire de Nice, 1361, Route des Lucioles, 06560 Valbonne (France); McKellar, B.H.J. [School of Physics, University of Melbourne, Parkville, Victoria, 3052 (Australia)] [School of Physics, University of Melbourne, Parkville, Victoria, 3052 (Australia)
1995-06-15
That special variant of the Fradkin representation, previously defined for scalar Green`s functions {ital G}{sub {ital c}}({ital x},{ital y}{vert_bar}{ital A}) in an arbitrary potential {ital A}({ital z}), is here extended to the case of vector interactions and spinor Green`s functions of QED and QCD. An exact representation is given which may again be approximated by a finite number {ital N} of quadratures, with the order of magnitude of the errors generated specified in advance, and decreasing with increasing {ital N}. A feature appears for both exact and approximate {ital G}{sub {ital c}}[{ital A}]: the possibility of chaotic behavior of a function central to the representation, which in turn generates chaotic behavior in {ital G}{sub {ital c}}[{ital A}] for certain {ital A}({ital z}). An example is given to show how the general criterion specified here works for a known case of ``quantum chaos,`` in a potential theory context of first quantization. When the full, nonperturbative, radiative corrections of quantum field theory are included, such chaotic effects are removed.
Raghunathan, Shesha; Brun, Todd A.; Goan, Hsi-Sheng
2010-11-15
A promising technique for measuring single electron spins is magnetic resonance force microscopy (MRFM), in which a microcantilever with a permanent magnetic tip is resonantly driven by a single oscillating spin. The most effective experimental technique is the oscillating cantilever-driven adiabatic reversals (OSCAR) protocol, in which the signal takes the form of a frequency shift. If the quality factor of the cantilever is high enough, this signal will be amplified over time to the point where it can be detected by optical or other techniques. An important requirement, however, is that this measurement process occurs on a time scale that is short compared to any noise which disturbs the orientation of the measured spin. We describe a model of spin noise for the MRFM system and show how this noise is transformed to become time dependent in going to the usual rotating frame. We simplify the description of the cantilever-spin system by approximating the cantilever wave function as a Gaussian wave packet and show that the resulting approximation closely matches the full quantum behavior. We then examine the problem of detecting the signal for a cantilever with thermal noise and spin with spin noise, deriving a condition for this to be a useful measurement.
Identification of cell density signal molecule
Schwarz, Richard I.
1998-01-01
Disclosed herein is a novel proteinaceous cell density signal molecule (CDS) between 25 and 35 kD, which is secreted by fibroblastic primary avian tendon cells in culture, and causes the cells to self-regulate their proliferation and the expression of differentiated function. It effects an increase of procollagen production in avian tendon cell cultures of ten fold while proliferation rates are decreased. CDS, and the antibodies which recognize them, are important for the development of diagnostics and treatments for injuries and diseases involving connective tissues, particularly tendon. Also disclosed are methods of production and use.
Identification of cell density signal molecule
Schwarz, R.I.
1998-04-21
Disclosed herein is a novel proteinaceous cell density signal molecule (CDS) between 25 and 35 kD, which is secreted by fibroblastic primary avian tendon cells in culture, and causes the cells to self-regulate their proliferation and the expression of differentiated function. It effects an increase of procollagen production in avian tendon cell cultures of ten fold while proliferation rates are decreased. CDS, and the antibodies which recognize them, are important for the development of diagnostics and treatments for injuries and diseases involving connective tissues, particularly tendon. Also disclosed are methods of production and use. 2 figs.
Method of high-density foil fabrication
Blue, Craig A.; Sikka, Vinod K.; Ohriner, Evan K.
2003-12-16
A method for preparing flat foils having a high density includes the steps of mixing a powdered material with a binder to form a green sheet. The green sheet is exposed to a high intensity radiative source adapted to emit radiation of wavelengths corresponding to an absorption spectrum of the powdered material. The surface of the green sheet is heated while a lower sub-surface temperature is maintained. An apparatus for preparing a foil from a green sheet using a radiation source is also disclosed.
MULTIPLE THICKNESS TIMES DENSITY GAMMA GAGE
Cherry, N.H.
1962-07-24
A device was developed for measuring simultaneously the thicknesses of two dissimilar materials superimposed on each other, such as coating of one material on another. The apparatus utilizes a double gamma radiation source producing radiation in two narrow band energy levels. The different materials attenuate the two bands of energy unequally with the result that a composite signal is received which can be analyzed to separate out the components due to the differing materials and indicate the thickness or densities of the two layers. (AEC)
Experimental profile evolution of a high-density field-reversed configuration
Ruden, E. L.; Zhang, Shouyin; Intrator, T. P.; Wurden, G. A.
2006-12-15
A field-reversed configuration (FRC) gains angular momentum over time, eventually resulting in an n=2 rotational instability (invariant under rotation by {pi}) terminating confinement. To study this, a laser interferometer probes the time history of line integrated plasma density along eight chords of the high-density ({approx}10{sup 17} cm{sup -3}) field-reversed configuration experiment with a liner. Abel and tomographic inversions provide density profiles during the FRC's azimuthally symmetric phase, and over a period when the rotational mode has saturated and rotates with a roughly fixed profile, respectively. During the latter part of the symmetric phase, the FRC approximates a magnetohydrodynamic (MHD) equilibrium, allowing the axial magnetic-field profile to be calculated from pressure balance. Basic FRC properties such as temperature and poloidal flux are then inferred. The subsequent two-dimensional n=2 density profiles provide angular momentum information needed to set bounds on prior values of the stability relevant parameter {alpha} (rotational to ion diamagnetic drift frequency ratio), in addition to a view of plasma kinematics useful for benchmarking plasma models of higher order than MHD.
Comparison of measured and modelled negative hydrogen ion densities at the ECR-discharge HOMER
Rauner, D.; Kurutz, U.; Fantz, U.
2015-04-08
As the negative hydrogen ion density n{sub H{sup âˆ’}} is a key parameter for the investigation of negative ion sources, its diagnostic quantification is essential in source development and operation as well as for fundamental research. By utilizing the photodetachment process of negative ions, generally two different diagnostic methods can be applied: via laser photodetachment, the density of negative ions is measured locally, but only relatively to the electron density. To obtain absolute densities, the electron density has to be measured additionally, which induces further uncertainties. Via cavity ring-down spectroscopy (CRDS), the absolute density of H{sup âˆ’} is measured directly, however LOS-averaged over the plasma length. At the ECR-discharge HOMER, where H{sup âˆ’} is produced in the plasma volume, laser photodetachment is applied as the standard method to measure n{sub H{sup âˆ’}}. The additional application of CRDS provides the possibility to directly obtain absolute values of n{sub H{sup âˆ’}}, thereby successfully bench-marking the laser photodetachment system as both diagnostics are in good agreement. In the investigated pressure range from 0.3 to 3â€…Pa, the measured negative hydrogen ion density shows a maximum at 1 to 1.5â€…Pa and an approximately linear response to increasing input microwave powers from 200 up to 500â€…W. Additionally, the volume production of negative ions is 0-dimensionally modelled by balancing H{sup âˆ’} production and destruction processes. The modelled densities are adapted to the absolute measurements of n{sub H{sup âˆ’}} via CRDS, allowing to identify collisions of H{sup âˆ’} with hydrogen atoms (associative and non-associative detachment) to be the dominant loss process of H{sup âˆ’} in the plasma volume at HOMER. Furthermore, the characteristic peak of n{sub H{sup âˆ’}} observed at 1 to 1.5â€…Pa is identified to be caused by a comparable behaviour of the electron density with varying pressure, as n{sub e} determines
Bonding Low-density Nanoporous Metal Foams Using Sputtered Solder
Bono, M; Cervantes, O; Akaba, C; Hamza, A; Foreman, R; Teslich, N
2007-08-21
could benefit from the bonding technology developed in this study, such as small-scale lightweight structural members, high-strength thermal insulating layers for electronics, and micro-scale mechanical dampers, to name but a few. Each of these applications requires one or more small metal foam components precisely bonded to a substrate. Several methods for bonding metal foam components have been developed by previous researchers. Macroscopic metal foam parts have been successfully bonded by laser welding to create T-sections and butt joints. Ultrasonic welding has been used to join aluminum sheet metal to aluminum foam for structural applications. These methods work well for bonding large foam components, but reducing these methods to a smaller length scale would be challenging. One method that has shown great potential for bonding layers of metal foams to substrates is a brazing process that uses a sputter-deposited interface material. Shirzadi et al.[9] have demonstrated bonds between stainless steel foam and a stainless steel substrate using a layer of copper-titanium filler metal that is sputtered onto the interface surfaces. The foam pieces that they bonded were approximately 10 mm in diameter and 10 mm thick with a cell size of approximately 200 {micro}m. After depositing the filler material, pressing the materials together, and heating them with an induction heater, bonds were achieved without causing significant damage to the foam. The current study also uses a sputter-deposited interface material to bond foam to a substrate. However, in contrast to previous work, the current study examines bonding microscale pieces of fragile nanoporous metal foam. In this study, a method is developed to bond a thin sheet of fragile, low-density nanoporous copper foam to an aluminum foil substrate of thickness 40 {micro}m. By sputter depositing an indium-silver alloy onto the foam and the substrate, a solder joint with a thickness of less than 2 {micro}m was achieved.
2010-04-01
Broad Funding Opportunity Announcement Project: FastCAP is improving the performance of an ultracapacitorâ€”a battery-like electronic device that can complement, and possibly even replace, an HEV or EV battery pack. Ultracapacitors have many advantages over conventional batteries, including long lifespans (over 1 million cycles, as compared to 10,000 for conventional batteries) and better durability. Ultracapacitors also charge more quickly than conventional batteries, and they release energy more quickly. However, ultracapacitors have fallen short of batteries in one key metric: energy densityâ€”high energy density means more energy storage. FastCAP is redesigning the ultracapacitorâ€™s internal structure to increase its energy density. Ultracapacitors traditionally use electrodes made of irregularly shaped, porous carbon. FastCAPâ€™s ultracapacitors are made of tiny, aligned carbon nanotubes. The nanotubes provide a regular path for ions moving in and out of the ultracapacitorâ€™s electrode, increasing the overall efficiency and energy density of the device.
Li, Xinya; Deng, Z. Daniel; USA, Richland Washington; Sun, Yannan; USA, Richland Washington; Martinez, Jayson J.; USA, Richland Washington; Fu, Tao; USA, Richland Washington; McMichael, Geoffrey A.; USA, Richland Washington; Carlson, Thomas J.; USA, Richland Washington
2014-11-27
Better understanding of fish behavior is vital for recovery of many endangered species including salmon. The Juvenile Salmon Acoustic Telemetry System (JSATS) was developed to observe the out-migratory behavior of juvenile salmonids tagged by surgical implantation of acoustic micro-transmitters and to estimate the survival when passing through dams on the Snake and Columbia Rivers. A robust three-dimensional solver was needed to accurately and efficiently estimate the time sequence of locations of fish tagged with JSATS acoustic transmitters, to describe in sufficient detail the information needed to assess the function of dam-passage design alternatives. An approximate maximum likelihood solver was developed using measurements of time difference of arrival from all hydrophones in receiving arrays on which a transmission was detected. Field experiments demonstrated that the developed solver performed significantly better in tracking efficiency and accuracy than other solvers described in the literature.
Korotkevich, Alexander O.; Lushnikov, Pavel M.; Rose, Harvey A.
2015-01-15
We developed a linear theory of backward stimulated Brillouin scatter (BSBS) of a spatially and temporally random laser beam relevant for laser fusion. Our analysis reveals a new collective regime of BSBS (CBSBS). Its intensity threshold is controlled by diffraction, once cT{sub c} exceeds a laser speckle length, with T{sub c} the laser coherence time. The BSBS spatial gain rate is approximately the sum of that due to CBSBS, and a part which is independent of diffraction and varies linearly with T{sub c}. The CBSBS spatial gain rate may be reduced significantly by the temporal bandwidth of KrF-based laser systems compared to the bandwidth currently available to temporally smoothed glass-based laser systems.
Sergio Alexandre Pinto, Alfred Stadler, Franz Gross
2009-05-01
We present the first calculations of the electromagnetic form factors of 3He and 3H within the framework of the Covariant Spectator Theory (CST). This first exploratory study concentrates on the sensitivity of the form factors to the strength of the scalar meson-nucleon off-shell coupling, known from previous studies to have a strong influence on the three-body binding energy. Results presented here were obtained using the complete impulse approximation (CIA), which includes contributions of relativistic origin that appear as two-body corrections in a non-relativistic framework, such as #28;Z-graphs#29;, but omits other two and three-body currents. We compare our results to non-relativistic calculations augmented by relativistic corrections of O(v/c)2.
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Li, Xinya; Deng, Z. Daniel; USA, Richland Washington; Sun, Yannan; USA, Richland Washington; Martinez, Jayson J.; USA, Richland Washington; Fu, Tao; USA, Richland Washington; McMichael, Geoffrey A.; et al
2014-11-27
Better understanding of fish behavior is vital for recovery of many endangered species including salmon. The Juvenile Salmon Acoustic Telemetry System (JSATS) was developed to observe the out-migratory behavior of juvenile salmonids tagged by surgical implantation of acoustic micro-transmitters and to estimate the survival when passing through dams on the Snake and Columbia Rivers. A robust three-dimensional solver was needed to accurately and efficiently estimate the time sequence of locations of fish tagged with JSATS acoustic transmitters, to describe in sufficient detail the information needed to assess the function of dam-passage design alternatives. An approximate maximum likelihood solver was developedmoreÂ Â» using measurements of time difference of arrival from all hydrophones in receiving arrays on which a transmission was detected. Field experiments demonstrated that the developed solver performed significantly better in tracking efficiency and accuracy than other solvers described in the literature.Â«Â less
Rayleigh approximation to ground state of the Bose and Coulomb glasses
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Ryan, S. D.; Mityushev, V.; Vinokur, V. M.; Berlyand, L.
2015-01-16
Glasses are rigid systems in which competing interactions prevent simultaneous minimization of local energies. This leads to frustration and highly degenerate ground states the nature and properties of which are still far from being thoroughly understood. We report an analytical approach based on the method of functional equations that allows us to construct the Rayleigh approximation to the ground state of a two-dimensional (2D) random Coulomb system with logarithmic interactions. We realize a model for 2D Coulomb glass as a cylindrical type II superconductor containing randomly located columnar defects (CD) which trap superconducting vortices induced by applied magnetic field. OurmoreÂ Â» findings break ground for analytical studies of glassy systems, marking an important step towards understanding their properties.Â«Â less
Low-energy parameters of neutron-neutron interaction in the effective-range approximation
Babenko, V. A.; Petrov, N. M. [National Academy of Sciences of Ukraine, Bogolyubov Institute for Theoretical Physics (Ukraine)
2013-06-15
The effect of the mass difference between the charged and neutral pions on the low-energy parameters of nucleon-nucleon interaction in the {sup 1}S{sub 0} state is studied in the effective-range approximation. On the basis of experimental values of the singlet parameters of neutron-proton scattering and the experimental value of the virtual-state energy for the neutron-neutron systemin the {sup 1}S{sub 0} state, the following values were obtained for the neutron-neutron scattering length and effective range: a{sub nn} = -16.59(117) fm and r{sub nn} = 2.83(11) fm. The calculated values agree well with present-day experimental results.
Pinto, SÃ©rgio Alexandre; Stadler, Alfred; Gross, Franz
2009-05-01
We present the first calculations of the electromagnetic form factors of ^{3}He and ^{3}H within the framework of the Covariant Spectator Theory (CST). This first exploratory study concentrates on the sensitivity of the form factors to the strength of the scalar meson-nucleon off-shell coupling, known from previous studies to have a strong influence on the three-body binding energy. Results presented here were obtained using the complete impulse approximation (CIA), which includes contributions of relativistic origin that appear as two-body corrections in a non-relativistic framework, such as "Z-graphs," but omits other two and three-body currents. Finally, we compare our results to non-relativistic calculations augmented by relativistic corrections of O(v/c)^{2}.
Pinto, Sergio Alexandre; Stadler, Alfred; Gross, Franz
2009-05-15
We present the first calculations of the electromagnetic form factors of {sup 3}He and {sup 3}H within the framework of the Covariant Spectator Theory (CST). This first exploratory study concentrates on the sensitivity of the form factors to the strength of the scalar meson-nucleon off-shell coupling, known from previous studies to have a strong influence on the three-body binding energy. Results presented here were obtained using the complete impulse approximation (CIA), which includes contributions of relativistic origin that appear as two-body corrections in a nonrelativistic framework, such as 'Z-graphs', but omits other two and three-body currents. We compare our results to nonrelativistic calculations augmented by relativistic corrections of O(v/c){sup 2}.
Alexandre Pinto, SÃ‚ ergio; Stadler, Alfred; Gross, Franz
2009-01-01
We present the first calculations of the electromagnetic form factors of 3He and 3H within the framework of the Covariant Spectator Theory (CST). This first exploratory study concentrates on the sensitivity of the form factors to the strength of the scalar meson-nucleon off-shell coupling, known from previous studies to have a strong influence on the three-body binding energy. Results presented here were obtained using the complete impulse approximation (CIA), which includes contributions of relativistic origin that appear as two-body corrections in a non-relativistic framework, such as ?Z-graphs?, but omits other two and three-body currents. We compare our results to non-relativistic calculations augmented by relativistic corrections of O(v/c)2.
Rayleigh approximation to ground state of the Bose and Coulomb glasses
Ryan, S. D.; Mityushev, V.; Vinokur, V. M.; Berlyand, L.
2015-01-16
Glasses are rigid systems in which competing interactions prevent simultaneous minimization of local energies. This leads to frustration and highly degenerate ground states the nature and properties of which are still far from being thoroughly understood. We report an analytical approach based on the method of functional equations that allows us to construct the Rayleigh approximation to the ground state of a two-dimensional (2D) random Coulomb system with logarithmic interactions. We realize a model for 2D Coulomb glass as a cylindrical type II superconductor containing randomly located columnar defects (CD) which trap superconducting vortices induced by applied magnetic field. Our findings break ground for analytical studies of glassy systems, marking an important step towards understanding their properties.
Pulse profiles from spinning neutron stars in the Hartle-Thorne approximation
Psaltis, Dimitrios; Ã–zel, Feryal E-mail: fozel@email.arizone.edu
2014-09-10
We present a new numerical algorithm for the calculation of pulse profiles from spinning neutron stars in the Hartle-Thorne approximation. Our approach allows us to formally take into account the effects of Doppler shifts and aberration, of frame dragging, as well as of the oblateness of the stellar surface and of its quadrupole moment. We confirm an earlier result that neglecting the oblateness of the neutron-star surface leads to â‰… 5%-30% errors in the calculated profiles and further show that neglecting the quadrupole moment of its spacetime leads to â‰… 1%-5% errors at a spin frequency of â‰… 600 Hz. We discuss the implications of our results for the measurements of neutron-star masses and radii with upcoming X-ray missions, such as NASA's NICER and ESA's LOFT.
Quantum Theory of (H,H{Sub 2}) Scattering: Approximate Treatments of Reactive Scattering
DOE R&D Accomplishments [OSTI]
Tang, K. T.; Karplus, M.
1970-10-01
A quantum mechanical study is made of reactive scattering in the (H, H{sub 2}) system. The problem is formulated in terms of a form of the distorted-wave Born approximation (DWBA) suitable for collisions in which all particles have finite mass. For certain incident energies, differential and total cross sections, as well as other attributes of the reactive collisions, (e.g. reaction configuration), are determined. Two limiting models in the DWBA formulation are compared; in one, the molecule is unperturbed by the incoming atom and in the other, the molecule adiabatically follows the incoming atom. For thermal incident energies and semi-empirical interaction potential employed, the adiabatic model seems to be more appropriate. Since the DWBA method is too complicated for a general study of the (H, H{sub 2}) reaction, a much simpler approximation method, the â€œlinear modelâ€ is developed. This model is very different in concept from treatments in which the three atoms are constrained to move on a line throughout the collision. The present model includes the full three-dimensional aspect of the collision and it is only the evaluation of the transition matrix element itself that is simplified. It is found that the linear model, when appropriately normalized, gives results in good agreement with that of the DWBA method. By application of this model, the energy dependence, rotational state of dependence and other properties of the total and differential reactions cross sections are determined. These results of the quantum mechanical treatment are compared with the classical calculation for the same potential surface. The most important result is that, in agreement with the classical treatment, the differential cross sections are strongly backward peaked at low energies and shifts in the forward direction as the energy increases. Finally, the implications of the present calculations for a theory of chemical kinetics are discussed.
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Jakeman, J. D.; Wildey, T.
2015-01-01
In this paper we present an algorithm for adaptive sparse grid approximations of quantities of interest computed from discretized partial differential equations. We use adjoint-based a posteriori error estimates of the interpolation error in the sparse grid to enhance the sparse grid approximation and to drive adaptivity. We show that utilizing these error estimates provides significantly more accurate functional values for random samples of the sparse grid approximation. We also demonstrate that alternative refinement strategies based upon a posteriori error estimates can lead to further increases in accuracy in the approximation over traditional hierarchical surplus based strategies. Throughout this papermoreÂ Â» we also provide and test a framework for balancing the physical discretization error with the stochastic interpolation error of the enhanced sparse grid approximation.Â«Â less
Jakeman, J.D. Wildey, T.
2015-01-01
In this paper we present an algorithm for adaptive sparse grid approximations of quantities of interest computed from discretized partial differential equations. We use adjoint-based a posteriori error estimates of the physical discretization error and the interpolation error in the sparse grid to enhance the sparse grid approximation and to drive adaptivity of the sparse grid. Utilizing these error estimates provides significantly more accurate functional values for random samples of the sparse grid approximation. We also demonstrate that alternative refinement strategies based upon a posteriori error estimates can lead to further increases in accuracy in the approximation over traditional hierarchical surplus based strategies. Throughout this paper we also provide and test a framework for balancing the physical discretization error with the stochastic interpolation error of the enhanced sparse grid approximation.
High energy density redox flow device
Chiang, Yet-Ming; Carter, W. Craig; Ho, Bryan Y; Duduta, Mihai; Limthongkul, Pimpa
2014-05-13
Redox flow devices are described in which at least one of the positive electrode or negative electrode-active materials is a semi-solid or is a condensed ion-storing electroactive material, and in which at least one of the electrode-active materials is transported to and from an assembly at which the electrochemical reaction occurs, producing electrical energy. The electronic conductivity of the semi-solid is increased by the addition of conductive particles to suspensions and/or via the surface modification of the solid in semi-solids (e.g., by coating the solid with a more electron conductive coating material to increase the power of the device). High energy density and high power redox flow devices are disclosed. The redox flow devices described herein can also include one or more inventive design features. In addition, inventive chemistries for use in redox flow devices are also described.
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Gonis, A.; Zhang, X. G.; Stocks, G. M.; Nicholson, D. M.
2015-10-23
Density functional theory for the case of general, N-representable densities is reformulated in terms of density functional derivatives of expectation values of operators evaluated with wave functions leading to a density, making no reference to the concept of potential. The developments provide a complete solution of the v-representability problem by establishing a mathematical procedure that determines whether a density is v-representable and in the case of an affirmative answer determines the potential (within an additive constant) as a derivative with respect to the density of a constrained search functional. It also establishes the existence of an energy functional of themoreÂ Â» density that, for v-representable densities, assumes its minimum value at the density describing the ground state of an interacting many-particle system. The theorems of Hohenberg and Kohn emerge as special cases of the formalism.Â«Â less
Gonis, A.; Zhang, X. G.; Stocks, G. M.; Nicholson, D. M.
2015-10-23
Density functional theory for the case of general, N-representable densities is reformulated in terms of density functional derivatives of expectation values of operators evaluated with wave functions leading to a density, making no reference to the concept of potential. The developments provide a complete solution of the v-representability problem by establishing a mathematical procedure that determines whether a density is v-representable and in the case of an affirmative answer determines the potential (within an additive constant) as a derivative with respect to the density of a constrained search functional. It also establishes the existence of an energy functional of the density that, for v-representable densities, assumes its minimum value at the density describing the ground state of an interacting many-particle system. The theorems of Hohenberg and Kohn emerge as special cases of the formalism.
Barone, Teresa L; Storey, John Morse; Prikhodko, Vitaly Y; Parks, II, James E
2011-01-01
We report the first in situ size-resolved density measurements of particles produced by premixed charge compression ignition (PCCI) and compare these with conventional diesel particles. The densities of size-classified particles were determined by measurements with a differential mobility analyzer (DMA) and an aerosol particle mass analyzer (APM). Particle masses of the different size classes were evaluated with a proposed DMA-APM response function for aggregates. Our results indicate that the effective densities of PCCI and conventional diesel particles were approximately the same for 50 and 100 nm electrical mobility diameters (0.9 and 0.6 g/cc, respectively), but the PCCI particle effective density (0.4 g/cc) was less than the conventional (0.5 g/cc) for 150 nm. The lowest effective particle densities were observed for exhaust gas recirculation (EGR) levels somewhat less than that required for PCCI operation. The inherent densities of conventional particles in the 50 and 100 nm size classes were 1.22 and 1.77 g/cc, which is in good agreement with Park et al. (2004). PCCI inherent particle densities for these same size classes were higher (1.27 and 2.10 g/cc), suggesting that there may have been additional adsorbed liquid hydrocarbons. For 150 nm particles, the inherent densities were nearly the same for PCCI and conventional particles at 2.20 g/cc. We expect that the lower effective density of PCCI particles may improve particulate emissions control with diesel particulate filters (DPFs). The presence of liquid hydrocarbons may also promote oxidation in DPFs.
Initial energy density and gluon distribution from the glasma...
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Initial energy density and gluon distribution from the glasma in heavy-ion collisions Citation Details In-Document Search Title: Initial energy density and gluon distribution from the ...
Effect of Lithium PFC Coatings on NSTX Density Control (Journal...
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Effect of Lithium PFC Coatings on NSTX Density Control Citation Details In-Document Search Title: Effect of Lithium PFC Coatings on NSTX Density Control Lithium coatings on the ...
Effect of Lithium PFC Coatings on NSTX Density Control (Journal...
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Effect of Lithium PFC Coatings on NSTX Density Control Citation Details In-Document Search Title: Effect of Lithium PFC Coatings on NSTX Density Control You are accessing a ...
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Air Density Lab.pdf Jump to: navigation, search File File history File usage Metadata File:Air Density Lab.pdf Size of this preview: 463 599 pixels. Other resolution: 464 600...
Approximate models for the ion-kinetic regime in inertial-confinement-fusion capsule implosions
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Hoffman, Nelson M.; Zimmerman, George B.; Molvig, Kim; Rinderknecht, Hans G.; Rosenberg, Michael J.; Albright, B. J.; Simakov, Andrei N.; Sio, Hong; Zylstra, Alex B.; Johnson, Maria Gatu; et al
2015-05-19
â€œReducedâ€ (i.e., simplified or approximate) ion-kinetic (RIK) models in radiation-hydrodynamic simulations permit a useful description of inertial-confinement-fusion (ICF) implosions where kinetic deviations from hydrodynamic behavior are important. For implosions in or near the kinetic regime (i.e., when ion mean free paths are comparable to the capsule size), simulations using a RIK model give a detailed picture of the time- and space-dependent structure of imploding capsules, allow an assessment of the relative importance of various kinetic processes during the implosion, enable explanations of past and current observations, and permit predictions of the results of future experiments. The RIK simulation method describedmoreÂ Â» here uses moment-based reduced kinetic models for transport of mass, momentum, and energy by long-mean-free-path ions, a model for the decrease of fusion reactivity owing to the associated modification of the ion distribution function, and a model of hydrodynamic turbulent mixing. The transport models are based on local gradient-diffusion approximations for the transport of moments of the ion distribution functions, with coefficients to impose flux limiting or account for transport modification. After calibration against a reference set of ICF implosions spanning the hydrodynamic-to-kinetic transition, the method has useful, quantifiable predictive ability over a broad range of capsule parameter space. Calibrated RIK simulations show that an important contributor to ion species separation in ICF capsule implosions is the preferential flux of longer-mean-free-path species out of the fuel and into the shell, leaving the fuel relatively enriched in species with shorter mean free paths. Also, the transport of ion thermal energy is enhanced in the kinetic regime, causing the fuel region to have a more uniform, lower ion temperature, extending over a larger volume, than implied by clean simulations. We expect that the success of our simple
Approximate models for the ion-kinetic regime in inertial-confinement-fusion capsule implosions
Hoffman, Nelson M.; Zimmerman, George B.; Molvig, Kim; Rinderknecht, Hans G.; Rosenberg, Michael J.; Albright, B. J.; Simakov, Andrei N.; Sio, Hong; Zylstra, Alex B.; Johnson, Maria Gatu; SÃ©guin, Fredrick H.; Frenje, Johan A.; Li, C. K.; Petrasso, Richard D.; Higdon, David M.; Srinivasan, Gowri; Glebov, Vladimir Yu.; Stoeckl, Christian; Seka, Wolf; Sangster, T. Craig
2015-05-19
â€œReducedâ€ (i.e., simplified or approximate) ion-kinetic (RIK) models in radiation-hydrodynamic simulations permit a useful description of inertial-confinement-fusion (ICF) implosions where kinetic deviations from hydrodynamic behavior are important. For implosions in or near the kinetic regime (i.e., when ion mean free paths are comparable to the capsule size), simulations using a RIK model give a detailed picture of the time- and space-dependent structure of imploding capsules, allow an assessment of the relative importance of various kinetic processes during the implosion, enable explanations of past and current observations, and permit predictions of the results of future experiments. The RIK simulation method described here uses moment-based reduced kinetic models for transport of mass, momentum, and energy by long-mean-free-path ions, a model for the decrease of fusion reactivity owing to the associated modification of the ion distribution function, and a model of hydrodynamic turbulent mixing. The transport models are based on local gradient-diffusion approximations for the transport of moments of the ion distribution functions, with coefficients to impose flux limiting or account for transport modification. After calibration against a reference set of ICF implosions spanning the hydrodynamic-to-kinetic transition, the method has useful, quantifiable predictive ability over a broad range of capsule parameter space. Calibrated RIK simulations show that an important contributor to ion species separation in ICF capsule implosions is the preferential flux of longer-mean-free-path species out of the fuel and into the shell, leaving the fuel relatively enriched in species with shorter mean free paths. Also, the transport of ion thermal energy is enhanced in the kinetic regime, causing the fuel region to have a more uniform, lower ion temperature, extending over a larger volume, than implied by clean simulations. We expect that the success of our simple approach
Density of sodium chloride solutions at high temperatures and...
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Subject: 37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; SEAWATER; DENSITY; SODIUM CHLORIDES; AQUEOUS SOLUTIONS; CHEMICAL COMPOSITION; CORRELATIONS; EQUATIONS; HIGH ...
Chiral dynamics and peripheral transverse densities (Journal Article) |
Office of Scientific and Technical Information (OSTI)
SciTech Connect Journal Article: Chiral dynamics and peripheral transverse densities Citation Details In-Document Search Title: Chiral dynamics and peripheral transverse densities In the partonic (or light-front) description of relativistic systems the electromagnetic form factors are expressed in terms of frame-independent charge and magnetization densities in transverse space. This formulation allows one to identify the chiral components of nucleon structure as the peripheral densities at
High current density cathode for electrorefining in molten electrolyte
Li, Shelly X.
2010-06-29
A high current density cathode for electrorefining in a molten electrolyte for the continuous production and collection of loose dendritic or powdery deposits. The high current density cathode eliminates the requirement for mechanical scraping and electrochemical stripping of the deposits from the cathode in an anode/cathode module. The high current density cathode comprises a perforated electrical insulated material coating such that the current density is up to 3 A/cm.sup.2.
Quantum coherent switch utilizing commensurate nanoelectrode and charge density periodicities
Harrison, Neil; Singleton, John; Migliori, Albert
2008-08-05
A quantum coherent switch having a substrate formed from a density wave (DW) material capable of having a periodic electron density modulation or spin density modulation, a dielectric layer formed onto a surface of the substrate that is orthogonal to an intrinsic wave vector of the DW material; and structure for applying an external spatially periodic electrostatic potential over the dielectric layer.
Radioactive waste management integrated data base: a bibliography. [Approximately 1100 references
Johnson, C.A.; Garland, P.A.
1980-09-01
The purpose of this indexed bibliography is to organize and collect the literature references on waste generation and treatment, characteristics, inventories, and costs. The references were captured into a searchable information file, and the information file was sorted, indexed, and printed for this bibliography. A completion of approximately 1100 references to nuclear waste management, the first of a series, is completed. Each reference is categorized by waste origin (commercial, defense, institutional, and foreign) and by subject area: (1) high-level wastes, (2) low-level wastes, (3) TRU wastes, (4) airborne wastes, (5) remedial action (formerly utilized sites, surplus facilities, and mill tailings), (6) isolation, (7) transportation, (8) spent fuel, (9) fuel cycle centers, and (10) a general category that covers nonspecific wastes. Five indexes are provided to assist the user in locating documents of interest: author, author affiliation (corporate authority), subject category, keyword, and permuted title. Machine (computer) searches of these indexes can be made specifying multiple constraints if so desired. This bibliography will be periodically updated as new information becomes available. In addition to being used in searches for specific data, the information file can also be used for resource document collection, names and addresses of contacts, and identification of potential sources of data.
Ramakrishnan, Raghunathan; Rauhut, Guntram
2015-04-21
Semi-quartic force fields (QFF) rely on a Taylor-expansion of the multi-dimensional Born-Oppenheimer potential energy surface (PES) and are frequently used within the calculation of anharmonic vibrational frequencies based on 2nd order vibrational perturbation theory (VPT2). As such they are usually determined by differentiation of the electronic energy with respect to the nuclear coordinates. Alternatively, potential energy surfaces can be expanded in terms of multi-mode expansions, which typically do not require any derivative techniques. The computational effort to retrieve QFF from size-reduced multi-mode expansions has been studied and has been compared with standard Taylor-expansions. As multi-mode expansions allow for the convenient introduction of subtle approximations, these will be discussed in some detail. In addition, a preliminary study about the applicability of a generalized Duschinsky transformation to QFFs is provided. This transformation allows for the efficient evaluation of VPT2 frequencies of isotopologues from the PES of the parent compound and thus avoids the recalculation of PESs in different axes systems.
Determination of recombination radius in Si for binary collision approximation codes
Vizkelethy, Gyorgy; Foiles, Stephen M.
2015-09-11
Displacement damage caused by ions or neutrons in microelectronic devices can have significant effect on the performance of these devices. Therefore, it is important to predict not only the displacement damage profile, but also its magnitude precisely. Analytical methods and binary collision approximation codes working with amorphous targets use the concept of displacement energy, the energy that a lattice atom has to receive to create a permanent replacement. It was found that this â€œdisplacement energyâ€ is direction dependent; it can range from 12 to 32 eV in silicon. Obviously, this model fails in BCA codes that work with crystalline targets, such as Marlowe. Marlowe does not use displacement energy; instead, it uses lattice binding energy only and then pairs the interstitial atoms with vacancies. Then based on the configuration of the Frenkel pairs it classifies them as close, near, or distant pairs, and considers the distant pairs the permanent replacements. Unfortunately, this separation is an ad hoc assumption, and the results do not agree with molecular dynamics calculations. After irradiation, there is a prompt recombination of interstitials and vacancies if they are nearby, within a recombination radius. In order to implement this recombination radius in Marlowe, we used the comparison of MD and Marlowe calculation in a range of ion energies in single crystal silicon target. As a result, the calculations showed that a single recombination radius of ~7.4 Ã… in Marlowe for a range of ion energies gives an excellent agreement with MD.
Particle-number conservation in static-path approximation for thermal superfluid systems
Kaneko, K.; Schiller, A.
2007-12-15
By applying particle-number projection to the static-path approximation (SPA), the heat capacity and the breakdown of pairing correlations are investigated in the thermally excited, superfluid systems {sup 172}Yb, {sup 94}Mo, and {sup 56}Fe. For the heavy nucleus {sup 172}Yb, the heat capacities in both the SPA and the number-projected SPA (NPSPA) exhibit an S shape; the difference between the SPA and NPSPA heat-capacity curves is not very large and the particle-number projection thereby enhances the S shape already seen in the SPA. The temperature at which the S-shape of heat capacity curve occurs parallels the temperature of the breakdown of pairing correlations as indicated by the effective pairing gap. However, for the comparatively lighter nuclei {sup 94}Mo and {sup 56}Fe, the SPA does not produce an S-shaped heat capacity on its own; only after particle-number projection the S shape appears in the heat-capacity curve. For {sup 94}Mo, we compare the NPSPA result with thermal odd-even mass differences, which are regarded as a direct measure of the pairing gap.
Description of thermal entanglement with the static path plus random-phase approximation
Canosa, N.; Matera, J. M.; Rossignoli, R.
2007-08-15
We discuss the application of the static path plus random-phase approximation (SPA+RPA) and the ensuing mean field+RPA treatment to the evaluation of entanglement in composite quantum systems at finite temperature. These methods involve just local diagonalizations and the determination of the generalized collective vibrational frequencies. As an illustration, we evaluate the pairwise entanglement in a fully connected XXZ chain of n spins at finite temperature in a transverse magnetic field b. It is shown that already the mean field+RPA provides an accurate analytic description of the concurrence below the mean field critical region (vertical bar b vertical bar 0 weak entanglement also arises when the ground state is separable (vertical bar b vertical bar >b{sub c}), with the limit temperature for pairwise entanglement exhibiting quite distinct regimes for vertical bar b vertical bar b{sub c}.
Investigation of approximations in thermal-hydraulic modeling of core conversions
Garner, Patrick L.; Hanan, Nelson A.
2008-07-15
Neutronics analyses for core conversions are usually fairly detailed, for example representing all 4 flats and all 4 corners of all 6 tubes of all 20 IRT-3M or -4M fuel assemblies in the core of the VVR-SM reactor in Uzbekistan. The coupled neutronics and thermal-hydraulic analysis for safety analysis transients is usually less detailed, for example modeling only a hot and an average fuel plate and the associated coolant. Several of the approximations have been studied using the RELAP5 and PARET computer codes in order to provide assurance that the lack of full detail is not important to the safety analysis. Two specific cases studied are (1) representation of a core of same- type fuel assemblies by a hot and an average assembly each having multiple channels as well as by merely a hot and average channel and (2) modeling a core containing multiple fuel types as the sum of fractional core models for each fuel type. (author)
Prioritizing the purchase of spare parts using an approximate reasoning models.
Eisenhawer, S. W.; Bott, T. F.; Jackson, J. W.
2001-01-01
The complexity of a spare parts prioritization model should be consonant with the amount and quality of data available to populate it. When production processes are new and the reliability database is sparse and represents primarily expert knowledge, an approximate reasoning (AR) based model is appropriate. AR models are designed to emulate the inferential processes used by experts in making judgments. We have designed and tested such a model for the planned component production process for nuclear weapons at Los Alamos National Laboratory. The model successfully represents the experts knowledge concerning the frequency and consequences of a part failure. The use of linguistic variables provides an adaptable format for eliciting this knowledge and providing a consistent brisis for valuing the effect on production of different parts. Ranking the parts for inclusion in a spare parts inventory is a straightforward transformation of the AR output. The basis for this ranking is directly traceable to the elicitation results. AR-based models are well-suited to prioritization problems with these characteristics.
Quasichemical analysis of the cluster-pair approximation for the thermodynamics of proton hydration
Pollard, Travis; Beck, Thomas L.
2014-06-14
A theoretical analysis of the cluster-pair approximation (CPA) is presented based on the quasichemical theory of solutions. The sought single-ion hydration free energy of the proton includes an interfacial potential contribution by definition. It is shown, however, that the CPA involves an extra-thermodynamic assumption that does not guarantee uniform convergence to a bulk free energy value with increasing cluster size. A numerical test of the CPA is performed using the classical polarizable AMOEBA force field and supporting quantum chemical calculations. The enthalpy and free energy differences are computed for the kosmotropic Na{sup +}/F{sup âˆ’} ion pair in water clusters of size n = 5, 25, 105. Additional calculations are performed for the chaotropic Rb{sup +}/I{sup âˆ’} ion pair. A small shift in the proton hydration free energy and a larger shift in the hydration enthalpy, relative to the CPA values, are predicted based on the n = 105 simulations. The shifts arise from a combination of sequential hydration and interfacial potential effects. The AMOEBA and quantum chemical results suggest an electrochemical surface potential of water in the range âˆ’0.4 to âˆ’0.5 V. The physical content of single-ion free energies and implications for ion-water force field development are also discussed.
Linear-scaling implementation of the direct random-phase approximation
Kállay, Mihály
2015-05-28
We report the linear-scaling implementation of the direct random-phase approximation (dRPA) for closed-shell molecular systems. As a bonus, linear-scaling algorithms are also presented for the second-order screened exchange extension of dRPA as well as for the second-order Møller–Plesset (MP2) method and its spin-scaled variants. Our approach is based on an incremental scheme which is an extension of our previous local correlation method [Rolik et al., J. Chem. Phys. 139, 094105 (2013)]. The approach extensively uses local natural orbitals to reduce the size of the molecular orbital basis of local correlation domains. In addition, we also demonstrate that using natural auxiliary functions [M. Kállay, J. Chem. Phys. 141, 244113 (2014)], the size of the auxiliary basis of the domains and thus that of the three-center Coulomb integral lists can be reduced by an order of magnitude, which results in significant savings in computation time. The new approach is validated by extensive test calculations for energies and energy differences. Our benchmark calculations also demonstrate that the new method enables dRPA calculations for molecules with more than 1000 atoms and 10?000 basis functions on a single processor.
Hussain, Ibrar; Qadir, Asghar; Mahomed, F. M.
2009-06-15
Since gravitational wave spacetimes are time-varying vacuum solutions of Einstein's field equations, there is no unambiguous means to define their energy content. However, Weber and Wheeler had demonstrated that they do impart energy to test particles. There have been various proposals to define the energy content, but they have not met with great success. Here we propose a definition using 'slightly broken' Noether symmetries. We check whether this definition is physically acceptable. The procedure adopted is to appeal to 'approximate symmetries' as defined in Lie analysis and use them in the limit of the exact symmetry holding. A problem is noted with the use of the proposal for plane-fronted gravitational waves. To attain a better understanding of the implications of this proposal we also use an artificially constructed time-varying nonvacuum metric and evaluate its Weyl and stress-energy tensors so as to obtain the gravitational and matter components separately and compare them with the energy content obtained by our proposal. The procedure is also used for cylindrical gravitational wave solutions. The usefulness of the definition is demonstrated by the fact that it leads to a result on whether gravitational waves suffer self-damping.
Regional Economic Accounting (REAcct). A software tool for rapidly approximating economic impacts
Ehlen, Mark Andrew; Vargas, Vanessa N.; Loose, Verne William; Starks, Shirley J.; Ellebracht, Lory A.
2011-07-01
This paper describes the Regional Economic Accounting (REAcct) analysis tool that has been in use for the last 5 years to rapidly estimate approximate economic impacts for disruptions due to natural or manmade events. It is based on and derived from the well-known and extensively documented input-output modeling technique initially presented by Leontief and more recently further developed by numerous contributors. REAcct provides county-level economic impact estimates in terms of gross domestic product (GDP) and employment for any area in the United States. The process for using REAcct incorporates geospatial computational tools and site-specific economic data, permitting the identification of geographic impact zones that allow differential magnitude and duration estimates to be specified for regions affected by a simulated or actual event. Using these data as input to REAcct, the number of employees for 39 directly affected economic sectors (including 37 industry production sectors and 2 government sectors) are calculated and aggregated to provide direct impact estimates. Indirect estimates are then calculated using Regional Input-Output Modeling System (RIMS II) multipliers. The interdependent relationships between critical infrastructures, industries, and markets are captured by the relationships embedded in the inputoutput modeling structure.
Discrete Dipole Approximation for Low-Energy Photoelectron Emission from NaCl Nanoparticles
Berg, Matthew J.; Wilson, Kevin R.; Sorensen, Chris; Chakrabarti, Amit; Ahmed, Musahid
2011-09-22
This work presents a model for the photoemission of electrons from sodium chloride nanoparticles 50-500 nm in size, illuminated by vacuum ultraviolet light with energy ranging from 9.4-10.9 eV. The discrete dipole approximation is used to calculate the electromagnetic field inside the particles, from which the two-dimensional angular distribution of emitted electrons is simulated. The emission is found to favor the particle?s geometrically illuminated side, and this asymmetry is compared to previous measurements performed at the Lawrence Berkeley National Laboratory. By modeling the nanoparticles as spheres, the Berkeley group is able to semi-quantitatively account for the observed asymmetry. Here however, the particles are modeled as cubes, which is closer to their actual shape, and the interaction of an emitted electron with the particle surface is also considered. The end result shows that the emission asymmetry for these low-energy electrons is more sensitive to the particle-surface interaction than to the specific particle shape, i.e., a sphere or cube.
Cosmic histories of star formation and reionization: an analysis with a power-law approximation
Yu, Yun-Wei; Cheng, K.S.; Chu, M.C.; Yeung, S. E-mail: hrspksc@hku.hk E-mail: terryys@gmail.com
2012-07-01
With a simple power-law approximation of high-redshift (?>3.5) star formation history, i.e., ?-dot {sub *}(z)?[(1+z)/4.5]{sup ??}, we investigate the reionization of intergalactic medium (IGM) and the consequent Thomson scattering optical depth for cosmic microwave background (CMB) photons. A constraint on the evolution index ? is derived from the CMB optical depth measured by the Wilkinson Microwave Anisotropy Probe (WMAP) experiment, which reads ? ? 2.18 lg N{sub ?}?3.89, where the free parameter N{sub ?} is the number of the escaped ionizing ultraviolet photons per baryon. At the same time, the redshift z{sub f} at which the IGM is fully ionized can also be expressed as a function of ? as well as N{sub ?}. By further taking into account the implication of the Gunn-Peterson trough observations to quasars for the full reionization redshift, i.e., 6?
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Moody, Daniela I.; Brumby, Steven P.; Rowland, Joel C.; Altmann, Garrett L.
2014-12-09
We present results from an ongoing effort to extend neuromimetic machine vision algorithms to multispectral data using adaptive signal processing combined with compressive sensing and machine learning techniques. Our goal is to develop a robust classification methodology that will allow for automated discretization of the landscape into distinct units based on attributes such as vegetation, surface hydrological properties, and topographic/geomorphic characteristics. We use a Hebbian learning rule to build spectral-textural dictionaries that are tailored for classification. We learn our dictionaries from millions of overlapping multispectral image patches and then use a pursuit search to generate classification features. Land cover labelsmoreÂ Â» are automatically generated using unsupervised clustering of sparse approximations (CoSA). We demonstrate our method on multispectral WorldView-2 data from a coastal plain ecosystem in Barrow, Alaska. We explore learning from both raw multispectral imagery and normalized band difference indices. We explore a quantitative metric to evaluate the spectral properties of the clusters in order to potentially aid in assigning land cover categories to the cluster labels. In this study, our results suggest CoSA is a promising approach to unsupervised land cover classification in high-resolution satellite imagery.Â«Â less
Current Density Scaling in Electrochemical Flow Capacitors
Hoyt, NC; Wainright, JS; Savinell, RF
2015-02-18
Electrochemical flow capacitors (EFCs) are a recently developed energy storage technology. One of the principal performance metrics of an EFC is the steady-state electrical current density that it can accept or deliver. Numerical models exist to predict this performance for specific cases, but here we present a study of how the current varies with respect to the applied cell voltage, flow rate, cell dimensions, and slurry properties using scaling laws. The scaling relationships are confirmed by numerical simulations and then subsequently by comparison to results from symmetric cell EFC experiments. This modeling approach permits the delimitation of three distinct operational regimes dependent on the values of two nondimensional combinations of the pertinent variables (specifically, a capacitive Graetz number and a conductivity ratio). Lastly, the models and nondimensional numbers are used to provide design guidance in terms of criteria for proper EFC operation. (C) The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. All rights reserved.
Building a Universal Nuclear Energy Density Functional
Carlson, Joe A.; Furnstahl, Dick; Horoi, Mihai; Lust, Rusty; Nazaewicc, Witek; Ng, Esmond; Thompson, Ian; Vary, James
2012-12-30
During the period of Dec. 1 2006 â€“ Jun. 30, 2012, the UNEDF collaboration carried out a comprehensive study of all nuclei, based on the most accurate knowledge of the strong nuclear interaction, the most reliable theoretical approaches, the most advanced algorithms, and extensive computational resources, with a view towards scaling to the petaflop platforms and beyond. The long-term vision initiated with UNEDF is to arrive at a comprehensive, quantitative, and unified description of nuclei and their reactions, grounded in the fundamental interactions between the constituent nucleons. We seek to replace current phenomenological models of nuclear structure and reactions with a well-founded microscopic theory that delivers maximum predictive power with well-quantified uncertainties. Specifically, the mission of this project has been three-fold: ï‚· First, to find an optimal energy density functional (EDF) using all our knowledge of the nucleonic Hamiltonian and basic nuclear properties; ï‚· Second, to apply the EDF theory and its extensions to validate the functional using all the available relevant nuclear structure and reaction data; ï‚· Third, to apply the validated theory to properties of interest that cannot be measured, in particular the properties needed for reaction theory.
Anomalous density for Bose gases at finite temperature
Boudjemaa, A.; Benarous, M.
2011-10-15
We analyze the behavior of the anomalous density as function of the radial distance at different temperatures in a variational framework. We show that the temperature dependence of the anomalous density agrees with the Hartree-Fock-Bogoliubov (HFB) calculations. Comparisons between the normal and anomalous fractions at low temperature show that the latter remains higher and, consequently, the neglect of the anomalous density may destabilize the condensate. These results are compatible with those of Yukalov. Surprisingly, the study of the anomalous density in terms of the interaction parameter shows that the dip in the central density is destroyed for sufficiently weak interactions. We explain this effect.
State densities and spectrum fluctuations: Information propagation in complex nuclei
French, J.B.; Kota, V.K.B.
1988-01-01
At excitation energies in nuclei where the state density is unambiguously defined there is a sharp separation between the smoothed spectrum (which defines the density) and fluctuations about it which have recently been studied with a view to understanding some aspects of quantum chaos. We briefly review these two complementary subjects, paying special attention to: the role of the effective interaction in determining the density; the calculation of interacting-particle state and level densities, and of expectation values of interesting operators; the information about the effective nucleon-nucleon interaction which is carried both by the density and the fluctuations. 28 refs., 1 fig.
Maurer, Simon A.; Clin, Lucien; Ochsenfeld, Christian
2014-06-14
Our recently developed QQR-type integral screening is introduced in our Cholesky-decomposed pseudo-densities Møller-Plesset perturbation theory of second order (CDD-MP2) method. We use the resolution-of-the-identity (RI) approximation in combination with efficient integral transformations employing sparse matrix multiplications. The RI-CDD-MP2 method shows an asymptotic cubic scaling behavior with system size and a small prefactor that results in an early crossover to conventional methods for both small and large basis sets. We also explore the use of local fitting approximations which allow to further reduce the scaling behavior for very large systems. The reliability of our method is demonstrated on test sets for interaction and reaction energies of medium sized systems and on a diverse selection from our own benchmark set for total energies of larger systems. Timings on DNA systems show that fast calculations for systems with more than 500 atoms are feasible using a single processor core. Parallelization extends the range of accessible system sizes on one computing node with multiple cores to more than 1000 atoms in a double-zeta basis and more than 500 atoms in a triple-zeta basis.
Probability Density Function Method for Langevin Equations with...
Office of Scientific and Technical Information (OSTI)
Language: English Subject: PDF method, uncertainty quantification, Langevin equation, Fokker-Planck equation, colored-noise, Large-Eddy-Diffusivity approximation Word Cloud More ...
Ransom, Ray M.; Gallegos-Lopez, Gabriel; Kinoshita, Michael H.
2012-07-31
Methods, system and apparatus are provided for quickly approximating a peak summed magnitude (A) of a phase voltage (Vph) waveform in a multi-phase system that implements third harmonic injection.
Lattice vibrations in the Frenkel-Kontorova model. I. Phonon dispersion, number density, and energy
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Meng, Qingping; Wu, Lijun; Welch, David O.; Zhu, Yimei
2015-06-17
We studied the lattice vibrations of two inter-penetrating atomic sublattices via the Frenkel-Kontorova (FK) model of a linear chain of harmonically interacting atoms subjected to an on-site potential, using the technique of thermodynamic Green's functions based on quantum field-theoretical methods. General expressions were deduced for the phonon frequency-wave-vector dispersion relations, number density, and energy of the FK model system. In addition, as the application of the theory, we investigated in detail cases of linear chains with various periods of the on-site potential of the FK model. Some unusual but interesting features for different amplitudes of the on-site potential of themoreÂ Â» FK model are discussed. In the commensurate structure, the phonon spectrum always starts at a finite frequency, and the gaps of the spectrum are true ones with a zero density of modes. In the incommensurate structure, the phonon spectrum starts from zero frequency, but at a non-zero wave vector; there are some modes inside these gap regions, but their density is very low. In our approximation, the energy of a higher-order commensurate state of the one-dimensional system at a finite temperature may become indefinitely close to the energy of an incommensurate state. This finding implies that the higher-order incommensurate-commensurate transitions are continuous ones and that the phase transition may exhibit a â€œdevil's staircaseâ€ behavior at a finite temperature.Â«Â less
Variation of the matter densities of nuclei from /sup 40/Ca to /sup 68/Zn
Papanicolas, C N; Sumner, W Q; Blair, J S; Bernstein, A M
1981-01-01
Analysis is made of elastic scattering of 42 MeV ..cap alpha..-particles from 19 nuclei from /sup 40/Ca to /sup 68/Zn in terms of a folding model, allowing determination of matter densities in the nuclear surface region relative to that of /sup 40/Ca. Specifically, values are deduced for the radii at which the matter density equals 0.016 nucleon/fm/sup 3/ as well as matter RMS radii. The relative sizes vary more slowly than A/sup 1/3/ between /sup 40/Ca and /sup 54/Fe and more rapidly than A/sup 1/3/ between /sup 54/Fe and /sup 68/Zn. The overall trend gives an increase with A/sup 1/3/ but with a bowing effect. The near equality of proton and matter RMS radii indicates that the neutron-proton radii are approximately equal to within the errors of the present analysis. The results are in reasonable agreement with those obtained with other hadronic probes and with calculated Hartree-Fock Bogolyubov densities.
One-electron reduced density matrices of strongly correlated harmonium atoms
Cioslowski, Jerzy
2015-03-21
Explicit asymptotic expressions are derived for the reduced one-electron density matrices (the 1-matrices) of strongly correlated two- and three-electron harmonium atoms in the ground and first excited states. These expressions, which are valid at the limit of small confinement strength ?, yield electron densities and kinetic energies in agreement with the published values. In addition, they reveal the ?{sup 5/6} asymptotic scaling of the exchange components of the electron-electron repulsion energies that differs from the ?{sup 2/3} scaling of their Coulomb and correlation counterparts. The natural orbitals of the totally symmetric ground state of the two-electron harmonium atom are found to possess collective occupancies that follow a mixed power/Gaussian dependence on the angular momentum in variance with the simple power-law prediction of Hill’s asymptotics. Providing rigorous constraints on energies as functionals of 1-matrices, these results are expected to facilitate development of approximate implementations of the density matrix functional theory and ensure their proper description of strongly correlated systems.
Current density partitioning in time-dependent current density functional theory
Mosquera, MartÃn A.; Wasserman, Adam; Department of Physics, Purdue University, West Lafayette, Indiana 47907
2014-05-14
We adapt time-dependent current density functional theory to allow for a fragment-based solution of the many-electron problem of molecules in the presence of time-dependent electric and magnetic fields. Regarding a molecule as a set of non-interacting subsystems that individually evolve under the influence of an auxiliary external electromagnetic vector-scalar potential pair, the partition 4-potential, we show that there are one-to-one mappings between this auxiliary potential, a sharply-defined set of fragment current densities, and the total current density of the system. The partition electromagnetic (EM) 4-potential is expressed in terms of the real EM 4-potential of the system and a gluing EM 4-potential that accounts for exchange-correlation effects and mutual interaction forces between fragments that are required to yield the correct electron dynamics. We prove the zero-force theorem for the fragmented system, establish a variational formulation in terms of action functionals, and provide a simple illustration for a charged particle in a ring.
MULTI-SCALE MODELING AND APPROXIMATION ASSISTED OPTIMIZATION OF BARE TUBE HEAT EXCHANGERS
Bacellar, Daniel; Ling, Jiazhen; Aute, Vikrant; Radermacher, Reinhard; Abdelaziz, Omar
2014-01-01
Air-to-refrigerant heat exchangers are very common in air-conditioning, heat pump and refrigeration applications. In these heat exchangers, there is a great benefit in terms of size, weight, refrigerant charge and heat transfer coefficient, by moving from conventional channel sizes (~ 9mm) to smaller channel sizes (< 5mm). This work investigates new designs for air-to-refrigerant heat exchangers with tube outer diameter ranging from 0.5 to 2.0mm. The goal of this research is to develop and optimize the design of these heat exchangers and compare their performance with existing state of the art designs. The air-side performance of various tube bundle configurations are analyzed using a Parallel Parameterized CFD (PPCFD) technique. PPCFD allows for fast-parametric CFD analyses of various geometries with topology change. Approximation techniques drastically reduce the number of CFD evaluations required during optimization. Maximum Entropy Design method is used for sampling and Kriging method is used for metamodeling. Metamodels are developed for the air-side heat transfer coefficients and pressure drop as a function of tube-bundle dimensions and air velocity. The metamodels are then integrated with an air-to-refrigerant heat exchanger design code. This integration allows a multi-scale analysis of air-side performance heat exchangers including air-to-refrigerant heat transfer and phase change. Overall optimization is carried out using a multi-objective genetic algorithm. The optimal designs found can exhibit 50 percent size reduction, 75 percent decrease in air side pressure drop and doubled air heat transfer coefficients compared to a high performance compact micro channel heat exchanger with same capacity and flow rates.
0{sup +} states in the large boson number limit of the Interacting Boson Approximation model
Bonatsos, Dennis; McCutchan, E. A.; Casten, R. F.
2008-11-11
Studies of the Interacting Boson Approximation (IBA) model for large boson numbers have been triggered by the discovery of shape/phase transitions between different limiting symmetries of the model. These transitions become sharper in the large boson number limit, revealing previously unnoticed regularities, which also survive to a large extent for finite boson numbers, corresponding to valence nucleon pairs in collective nuclei. It is shown that energies of 0{sub n}{sup +} states grow linearly with their ordinal number n in all three limiting symmetries of IBA [U(5), SU(3), and O(6)]. Furthermore, it is proved that the narrow transition region separating the symmetry triangle of the IBA into a spherical and a deformed region is described quite well by the degeneracies E(0{sub 2}{sup +}) = E(6{sub 1}{sup +}, E(0{sub 3}{sup +}) = E(10{sub 1}{sup +}), E(0{sub 4}{sup +}) = E(14{sub 1}{sup +}, while the energy ratio E(6{sub 1}{sup +})/E(0{sub 2}{sup +} turns out to be a simple, empirical, easy-to-measure effective order parameter, distinguishing between first- and second-order transitions. The energies of 0{sub n}{sup +} states near the point of the first order shape/phase transition between U(5) and SU(3) are shown to grow as n(n+3), in agreement with the rule dictated by the relevant critical point symmetries resulting in the framework of special solutions of the Bohr Hamiltonian. The underlying partial dynamical symmetries and quasi-dynamical symmetries are also discussed.
Second Argonne theory institute on differentiation of computational approximations of functions.
Bischof, C.H.; Eberhard, P.; Hovland, P.D.
1998-10-09
A Theory Institute on ''Differentiation of Computational Approximations to Functions'' was held at Argonne National Laboratory on May 18--20, 1998. The institute was organized by Christian Bischof and Paul Hovland of the Mathematics and Computer Science Division at Argonne National Laboratory. The Theory Institute brought together 38 researchers from the US, Great Britain, France, and Germany. Mathematicians, computer scientists, physicists, and engineers from diverse disciplines discussed advances in automatic differentiation (AD) theory and software and described benefits from applying AD methods in application areas. These areas include fluid mechanics, structural engineering, optimization, meteorology, and computational mathematics for the solution of ordinary differential equations (ODEs) or differential algebraic equations (DAEs). This meeting was the fourth workshop dedicated to automatic differentiation. Earlier meetings were the 1991 SIAM conference in Breckenridge, Colorado; the first Argonne Theory Institute on computational differentiation in 1993; and the 1996 SIAM conference in Santa Fe, New Mexico. AD methods can be used whenever gradient information or higher-order derivative information must be computed. The problem is defined by a computer program (without gradient information) that is able to compute numerical values of some output variables for a given set of input variables. As a result of applying AD methods to this computer program, a new computer program is generated automatically to compute the derivatives of the output variables with respect to the input variables. This at first glance, astonishing fact can be easily understood by viewing the program from a compiler angle. A complicated computational sequence is split into a sequence of simple operations. Then, to compute the gradients, the chain rule of differentiation is applied successively to this sequence completely automatically. The resultant gradients are accurate up to roundoff
Determination of recombination radius in Si for binary collision approximation codes
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Vizkelethy, Gyorgy; Foiles, Stephen M.
2015-09-11
Displacement damage caused by ions or neutrons in microelectronic devices can have significant effect on the performance of these devices. Therefore, it is important to predict not only the displacement damage profile, but also its magnitude precisely. Analytical methods and binary collision approximation codes working with amorphous targets use the concept of displacement energy, the energy that a lattice atom has to receive to create a permanent replacement. It was found that this â€œdisplacement energyâ€ is direction dependent; it can range from 12 to 32 eV in silicon. Obviously, this model fails in BCA codes that work with crystalline targets,moreÂ Â» such as Marlowe. Marlowe does not use displacement energy; instead, it uses lattice binding energy only and then pairs the interstitial atoms with vacancies. Then based on the configuration of the Frenkel pairs it classifies them as close, near, or distant pairs, and considers the distant pairs the permanent replacements. Unfortunately, this separation is an ad hoc assumption, and the results do not agree with molecular dynamics calculations. After irradiation, there is a prompt recombination of interstitials and vacancies if they are nearby, within a recombination radius. In order to implement this recombination radius in Marlowe, we used the comparison of MD and Marlowe calculation in a range of ion energies in single crystal silicon target. As a result, the calculations showed that a single recombination radius of ~7.4 Ã… in Marlowe for a range of ion energies gives an excellent agreement with MD.Â«Â less
Heng, Kevin; MendonÃ§a, JoÃ£o M.; Lee, Jae-Min E-mail: joao.mendonca@csh.unibe.ch
2014-11-01
We present a comprehensive analytical study of radiative transfer using the method of moments and include the effects of non-isotropic scattering in the coherent limit. Within this unified formalism, we derive the governing equations and solutions describing two-stream radiative transfer (which approximates the passage of radiation as a pair of outgoing and incoming fluxes), flux-limited diffusion (which describes radiative transfer in the deep interior), and solutions for the temperature-pressure profiles. Generally, the problem is mathematically underdetermined unless a set of closures (Eddington coefficients) is specified. We demonstrate that the hemispheric (or hemi-isotropic) closure naturally derives from the radiative transfer equation if energy conservation is obeyed, while the Eddington closure produces spurious enhancements of both reflected light and thermal emission. We concoct recipes for implementing two-stream radiative transfer in stand-alone numerical calculations and general circulation models. We use our two-stream solutions to construct toy models of the runaway greenhouse effect. We present a new solution for temperature-pressure profiles with a non-constant optical opacity and elucidate the effects of non-isotropic scattering in the optical and infrared. We derive generalized expressions for the spherical and Bond albedos and the photon deposition depth. We demonstrate that the value of the optical depth corresponding to the photosphere is not always 2/3 (Milne's solution) and depends on a combination of stellar irradiation, internal heat, and the properties of scattering in both the optical and infrared. Finally, we derive generalized expressions for the total, net, outgoing, and incoming fluxes in the convective regime.
Alemi, Mallory; Loring, Roger F.
2015-06-07
The optimized mean-trajectory (OMT) approximation is a semiclassical method for computing vibrational response functions from action-quantized classical trajectories connected by discrete transitions that represent radiation-matter interactions. Here, we extend the OMT to include additional vibrational coherence and energy transfer processes. This generalized approximation is applied to a pair of anharmonic chromophores coupled to a bath. The resulting 2D spectra are shown to reflect coherence transfer between normal modes.
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Kilcrease, D. P.; Brookes, S.
2013-08-19
The modeling of NLTE plasmas requires the solution of population rate equations to determine the populations of the various atomic levels relevant to a particular problem. The equations require many cross sections for excitation, de-excitation, ionization and recombination. Additionally, a simple and computational fast way to calculate electron collisional excitation cross-sections for ions is by using the plane-wave Born approximation. This is essentially a high-energy approximation and the cross section suffers from the unphysical problem of going to zero near threshold. Various remedies for this problem have been employed with varying degrees of success. We present a correction procedure formoreÂ Â» the Born cross-sections that employs the Elwertâ€“Sommerfeld factor to correct for the use of plane waves instead of Coulomb waves in an attempt to produce a cross-section similar to that from using the more time consuming Coulomb Born approximation. We compare this new approximation with other, often employed correction procedures. Furthermore, we also look at some further modifications to our Born Elwert procedure and its combination with Y.K. Kim's correction of the Coulomb Born approximation for singly charged ions that more accurately approximate convergent close coupling calculations.Â«Â less
A DENSITY-INDEPENDENT FORMULATION OF SMOOTHED PARTICLE HYDRODYNAMICS
Saitoh, Takayuki R.; Makino, Junichiro
2013-05-01
The standard formulation of the smoothed particle hydrodynamics (SPH) assumes that the local density distribution is differentiable. This assumption is used to derive the spatial derivatives of other quantities. However, this assumption breaks down at the contact discontinuity. At the contact discontinuity, the density of the low-density side is overestimated while that of the high-density side is underestimated. As a result, the pressure of the low-density (high-density) side is overestimated (underestimated). Thus, unphysical repulsive force appears at the contact discontinuity, resulting in the effective surface tension. This tension suppresses fluid instabilities. In this paper, we present a new formulation of SPH, which does not require the differentiability of density. Instead of the mass density, we adopt the internal energy density (pressure) and its arbitrary function, which are smoothed quantities at the contact discontinuity, as the volume element used for the kernel integration. We call this new formulation density-independent SPH (DISPH). It handles the contact discontinuity without numerical problems. The results of standard tests such as the shock tube, Kelvin-Helmholtz and Rayleigh-Taylor instabilities, point-like explosion, and blob tests are all very favorable to DISPH. We conclude that DISPH solved most of the known difficulties of the standard SPH, without introducing additional numerical diffusion or breaking the exact force symmetry or energy conservation. Our new SPH includes the formulation proposed by Ritchie and Thomas as a special case. Our formulation can be extended to handle a non-ideal gas easily.
Deconvolution of Stark broadened spectra for multi-point density measurements in a flow Z-pinch
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Vogman, G. V.; Shumlak, U.
2011-10-13
Stark broadened emission spectra, once separated from other broadening effects, provide a convenient non-perturbing means of making plasma density measurements. A deconvolution technique has been developed to measure plasma densities in the ZaP flow Z-pinch experiment. The ZaP experiment uses sheared flow to mitigate MHD instabilities. The pinches exhibit Stark broadened emission spectra, which are captured at 20 locations using a multi-chord spectroscopic system. Spectra that are time- and chord-integrated are well approximated by a Voigt function. The proposed method simultaneously resolves plasma electron density and ion temperature by deconvolving the spectral Voigt profile into constituent functions: a Gaussian functionmoreÂ Â» associated with instrument effects and Doppler broadening by temperature; and a Lorentzian function associated with Stark broadening by electron density. The method uses analytic Fourier transforms of the constituent functions to fit the Voigt profile in the Fourier domain. The method is discussed and compared to a basic least-squares fit. The Fourier transform fitting routine requires fewer fitting parameters and shows promise in being less susceptible to instrumental noise and to contamination from neighboring spectral lines. The method is evaluated and tested using simulated lines and is applied to experimental data for the 229.69 nm C III line from multiple chords to determine plasma density and temperature across the diameter of the pinch. As a result, these measurements are used to gain a better understanding of Z-pinch equilibria.Â«Â less
Deconvolution of Stark broadened spectra for multi-point density measurements in a flow Z-pinch
Vogman, G. V.; Shumlak, U.
2011-10-13
Stark broadened emission spectra, once separated from other broadening effects, provide a convenient non-perturbing means of making plasma density measurements. A deconvolution technique has been developed to measure plasma densities in the ZaP flow Z-pinch experiment. The ZaP experiment uses sheared flow to mitigate MHD instabilities. The pinches exhibit Stark broadened emission spectra, which are captured at 20 locations using a multi-chord spectroscopic system. Spectra that are time- and chord-integrated are well approximated by a Voigt function. The proposed method simultaneously resolves plasma electron density and ion temperature by deconvolving the spectral Voigt profile into constituent functions: a Gaussian function associated with instrument effects and Doppler broadening by temperature; and a Lorentzian function associated with Stark broadening by electron density. The method uses analytic Fourier transforms of the constituent functions to fit the Voigt profile in the Fourier domain. The method is discussed and compared to a basic least-squares fit. The Fourier transform fitting routine requires fewer fitting parameters and shows promise in being less susceptible to instrumental noise and to contamination from neighboring spectral lines. The method is evaluated and tested using simulated lines and is applied to experimental data for the 229.69 nm C III line from multiple chords to determine plasma density and temperature across the diameter of the pinch. As a result, these measurements are used to gain a better understanding of Z-pinch equilibria.
Investigation of density limit processes in DIII-D
Maingi, R.; Mahdavi, M.A.; Petrie, T.W.
1999-02-01
A series of experiments has been conducted in DIII-D to investigate density-limiting processes. The authors have studied divertor detachment and MARFEs on closed field lines and find semi-quantitative agreement with theoretical calculations of onset conditions. They have shown that the critical density for MARFE onset at low edge temperature scales as I{sub p}/a{sup 2}, i.e. similar to Greenwald scaling. They have also shown that the scaling of the critical separatrix density with heating power at partial detachment onset agrees with Borass` model. Both of these processes yield high edge density limits for reactors such as ITER. By using divertor pumping and pellet fueling they have avoided these and other processes and accessed densities > 1.5{times} Greenwald limit scaling with H-mode confinement, demonstrating that the Greenwald limit is not a fundamental limit on the core density.
Textured-surface quartz resonator fluid density and viscosity monitor
Martin, Stephen J.; Wiczer, James J.; Cernosek, Richard W.; Frye, Gregory C.; Gebert, Charles T.; Casaus, Leonard; Mitchell, Mary A.
1998-08-25
A pair of thickness-shear mode resonators, one smooth and one with a textured surface, allows fluid density and viscosity to be independently resolved. A textured surface, either randomly rough or regularly patterned, leads to trapping of liquid at the device surface. The synchronous motion of this trapped liquid with the oscillating device surface allows the device to weigh the liquid; this leads to an additional response that depends on liquid density. This additional response enables a pair of devices, one smooth and one textured, to independently resolve liquid density and viscosity; the difference in responses determines the density while the smooth device determines the density-viscosity product, and thus, the pair determines both density and viscosity.
Wave induced density modification in RF sheaths and close to wave launchers
Van Eester, D.; Lu, Ling-Feng
2015-12-10
With the return to full metal walls - a necessary step towards viable fusion machines - and due to the high power densities of current-day ICRH (Ion Cyclotron Resonance Heating) or RF (radio frequency) antennas, there is ample renewed interest in exploring the reasons for wave-induced sputtering and formation of hot spots. Moreover, there is experimental evidence on various machines that RF waves influence the density profile close to the wave launchers so that waves indirectly influence their own coupling efficiency. The present study presents a return to first principles and describes the wave-particle interaction using a 2-time scale model involving the equation of motion, the continuity equation and the wave equation on each of the time scales. Through the changing density pattern, the fast time scale dynamics is affected by the slow time scale events. In turn, the slow time scale density and flows are modified by the presence of the RF waves through quasilinear terms. Although finite zero order flows are identified, the usual cold plasma dielectric tensor - ignoring such flows - is adopted as a first approximation to describe the wave response to the RF driver. The resulting set of equations is composed of linear and nonlinear equations and is tackled in 1D in the present paper. Whereas the former can be solved using standard numerical techniques, the latter require special handling. At the price of multiple iterations, a simple â€™derivative switch-onâ€™ procedure allows to reformulate the nonlinear problem as a sequence of linear problems. Analytical expressions allow a first crude assessment - revealing that the ponderomotive potential plays a role similar to that of the electrostatic potential arising from charge separation - but numerical implementation is required to get a feeling of the full dynamics. A few tentative examples are provided to illustrate the phenomena involved.
Method for solvent extraction with near-equal density solutions
Birdwell, Joseph F.; Randolph, John D.; Singh, S. Paul
2001-01-01
Disclosed is a modified centrifugal contactor for separating solutions of near equal density. The modified contactor has a pressure differential establishing means that allows the application of a pressure differential across fluid in the rotor of the contactor. The pressure differential is such that it causes the boundary between solutions of near-equal density to shift, thereby facilitating separation of the phases. Also disclosed is a method of separating solutions of near-equal density.
Development of High Power Density Driveline for Vehicles | Department of
Broader source: Energy.gov (indexed) [DOE]
Energy 1 DOE Hydrogen and Fuel Cells Program, and Vehicle Technologies Program Annual Merit Review and Peer Evaluation vss058_fenske_2011_o.pdf (352.55 KB) More Documents & Publications Development of High Power Density Driveline for Vehicles Vehicle Technologies Office Merit Review 2014: Development of High Power Density Driveline for Vehicles Vehicle Technologies Office Merit Review 2015: Development of High Power Density
Testing the density matrix expansion against ab initio calculations of
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trapped neutron drops | Argonne Leadership Computing Facility Testing the density matrix expansion against ab initio calculations of trapped neutron drops Authors: Bogner, S., Furnstahl, R.J., Hergert, H., Kortelainen, M., Maris, P., Stoitsov, M., Vary, J.P. Microscopic input to a universal nuclear energy density functional can be provided through the density matrix expansion (DME), which has recently been revived and improved. Several DME implementation strategies are tested for neutron
Method for measuring the density of lightweight materials
Snow, Samuel G.; Giacomelli, Edward J.
1980-01-01
This invention relates to a nondestructive method for measuring the density of articles composed of elements having a low atomic number such as plastic and carbon composites. The measurement is accomplished by striking the article with a collimated beam of X radiation, simultaneously monitoring the radiation scattered and the radiation transmitted by the article, then relating the ratio of the radiation scattered to the radiation transmitted with the density of the article. The above method is insensitive to all variables except density.
Anomalous magnetic moment contributions to NN bremsstrahlung in the soft-photon approximation
Gibson, B.F.; Penninga, T.D.; Timmermans, R.G.E.; Liou, M.K.
2005-05-06
The soft photon approximation (SPA), which is relativistic and based upon a fundamental theorem for photon emission, is applied to explore two separate nucleon-nucleon bremsstrahlung (NN{gamma}) processes: pp{gamma} and np{gamma}. They are examined together in an effort to understand the mechanism which governs photon emission from these basic two-nucleon systems. In this investigation we focus upon the effect of the anomalous magnetic moments of the proton ({kappa}p) and the neutron ({kappa}n). In our SPA calculation we use the standard Low amplitude M{sub {mu}}{sup Low} as derived by Nyman plus the more recently developed amplitude M{sub {mu}}{sup TuTts}, referred to as the two-u-two-t special (TuTts) amplitude. The amplitude M{sub {mu}}{sup TuTts} is identical to the amplitude M{sub {mu}}{sup Low} through order K0 in the soft-photon expansion. However, M{sub {mu}}{sup TuTts} includes an additional term M{sub {mu}}{sup (3)}(K{sup 1}; {kappa}) (plus higher order terms). The term M{sub {mu}}{sup (3)}(K{sup 1}; {kappa}) is of order K1 in the soft-photon expansion and it is a function of {kappa}p and {kappa}n. Using the amplitudes M{sub {mu}}{sup TuTts} and M{sub {mu}}{sup Low}, we have calculated pp{gamma} and np{gamma} cross sections as a function of photon angle {psi}{gamma} with and without contributions from {kappa}p and {kappa}n. Comparison with available pp{gamma} data has been made; in particular, the contribution from M{sub {mu}}{sup (3)}(K{sup 1}; {kappa}) has been investigated. Results will be presented and discussed which relate to the following: (i) The anomalous magnetic moment effect is significant in pp{gamma}; however, it is small in np{gamma}. That is, the two amplitudes M{sub {mu}}{sup TuTts} and M{sub {mu}}{sup Low} yield very similar np{gamma} cross sections, but they predict very different pp{gamma} cross sections. (ii) M{sub {mu}}{sup TuTts} appears to provide a better SPA than M{sub {mu}}{sup Low} in the case of pp{gamma}. Because {kappa
Particle Gas Target for High Density Laser Produced Plasmas Charles...
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Particle Gas Target for High Density Laser Produced Plasmas Charles H. Skinner, Nathaniel Fisch, and Ernest Valeo This invention is a novel "particle gas" cell for achieving plasma ...
Radiation-Matter Coupling for Low Density Plasmas (Conference...
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Citation Details In-Document Search Title: Radiation-Matter Coupling for Low Density ... considered when constructing transport algorithms that are intended to provide ...
Ultra Low Density and Highly Crosslinked Biocompatible Shape...
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Biocompatible Shape Memory Polyurethane Foams Citation Details In-Document Search Title: Ultra Low Density and Highly Crosslinked Biocompatible Shape Memory Polyurethane Foams ...
A density-matching approach for optimization under uncertainty...
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A density-matching approach for optimization under uncertainty Citation Details ... Journal Name: Computer Methods in Applied Mechanics and Engineering Additional Journal ...
3-D capacitance density imaging of fluidized bed
Fasching, George E.
1990-01-01
A three-dimensional capacitance density imaging of a gasified bed or the like in a containment vessel is achieved using a plurality of electrodes provided circumferentially about the bed in levels and along the bed in channels. The electrodes are individually and selectively excited electrically at each level to produce a plurality of current flux field patterns generated in the bed at each level. The current flux field patterns are suitably sensed and a density pattern of the bed at each level determined. By combining the determined density patterns at each level, a three-dimensional density image of the bed is achieved.
Near-surface Density Currents Observed in the Southeast Pacific...
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Density currents preferentially occur in regions of open cells but also occur in regions ... Country of Publication: United States Language: English Subject: marine stratocumulus ...
Laser Propagation in Nanostructured Ultra-Low-Density Materials...
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By design, the gas and aerogel targets will have identical densities and identical effective ionization states. Authors: Fournier, K. B. 1 ; Colvin, J. 1 ; Yogo, A 2 ; Kemp, ...
Combined local-density and dynamical mean field theory calculations...
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Journal Article: Combined local-density and dynamical mean ... Citation Details In-Document Search Title: Combined ... This paper reports calculations for compressed Ce (4fsup ...
Ultra Low Density Shape Memory Polymer Foams With Tunable Physicochemi...
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ThesisDissertation: Ultra Low Density Shape Memory Polymer Foams With Tunable Physicochemical Properties for Treatment of intracranial Aneurysms Citation Details In-Document ...
The Effects of Highly Structured Low Density Carbon Nanotube...
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Carbon Nanotube Networks on the Thermal Degradation Behaviour of Polysiloxanes Citation Details In-Document Search Title: The Effects of Highly Structured Low Density Carbon ...
Density functional theory and conductivity studies of boron-based...
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The receptors are also potentially beneficial to rechargeable lithium ion and lithium air batteries. We apply Density Functional Theory (DFT) to show that an oxalate-based ...
Inhomogeneity smoothing using density valley formed by ion beam...
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in an ion-beam inertial confinement fusion pellets by numerical simulation. The simulation results show that the radiation energy is confined in the density valley, and the ...
Key Parameters Governing the Energy Density of Rechargeable Li...
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of Rechargeable LiS Batteries Citation Details In-Document Search Title: Key Parameters Governing the Energy Density of Rechargeable LiS Batteries Authors: Gao, Jie ; ...
Internal field, density & temperature measurements in MTF plasmas...
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Title: Internal field, density & temperature measurements in MTF plasmas using Pulsed Polarimetry final report Authors: Smith, Roger J. Publication Date: 2014-08-11 OSTI ...
Viscosity and density tables of sodium chloride solutions (Technical...
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A file is presented containing tabulated data extracted from the scientific literature on the density and viscosity of aqueous sodium chloride solutions. Also included is a ...
Centrality evolution of the charged-particle pseudorapidity density...
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Centrality evolution of the charged-particle pseudorapidity density over a broad ... Citation Details In-Document Search Title: Centrality evolution of the charged-particle ...
Practicality of magnetic compression for plasma density control...
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control Citation Details In-Document Search This content will become publicly available on March 16, 2017 Title: Practicality of magnetic compression for plasma density control ...
Controlling the Actuation Rate of Low Density Shape Memory Polymer...
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Memory Polymer Foams in Water Citation Details In-Document Search Title: Controlling the Actuation Rate of Low Density Shape Memory Polymer Foams in Water Authors: Singhal, P ; ...
High Island Densities and Long Range Repulsive Interactions:...
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long range repulsive interactions. Kinetic Monte Carlo simulations and density functional theory calculations support this conclusion. In addition to answering an outstanding...
CORRELATION BETWEEN GROUP LOCAL DENSITY AND GROUP LUMINOSITY
Deng Xinfa; Yu Guisheng
2012-11-10
In this study, we investigate the correlation between group local number density and total luminosity of groups. In four volume-limited group catalogs, we can conclude that groups with high luminosity exist preferentially in high-density regions, while groups with low luminosity are located preferentially in low-density regions, and that in a volume-limited group sample with absolute magnitude limit M{sub r} = -18, the correlation between group local number density and total luminosity of groups is the weakest. These results basically are consistent with the environmental dependence of galaxy luminosity.
Density Log At Valles Caldera - Redondo Geothermal Area (Rowley...
Jump to: navigation, search GEOTHERMAL ENERGYGeothermal Home Exploration Activity: Density Log At Valles Caldera - Redondo Geothermal Area (Rowley, Et Al., 1987) Exploration...
Rock Density At Alum Area (DOE GTP) | Open Energy Information
to: navigation, search GEOTHERMAL ENERGYGeothermal Home Exploration Activity: Rock Density At Alum Area (DOE GTP) Exploration Activity Details Location Alum Geothermal Area...
Density Log At Valles Caldera - Redondo Geothermal Area (Wilt...
Jump to: navigation, search GEOTHERMAL ENERGYGeothermal Home Exploration Activity: Density Log At Valles Caldera - Redondo Geothermal Area (Wilt & Haar, 1986) Exploration...
Palacio Mizrahi, J. H.
2014-06-15
A rigorous derivation of expressions, starting from the governing equations, for the ionization frequency, edge-to-axis ratio of plasma density, plasma density at the axis, and radially averaged plasma density in a cylindrical gas discharge has been obtained. The derived expressions are simple and involve the relevant parameters of the discharge: Cylinder radius, axial current, and neutral gas pressure. The found expressions account for ion inertia, ion temperature, and changes in plasma ion collisionality.
Multidimensional Skyrme-density-functional study of the spontaneous fission of ^{238}U
Sadhukhan, J.; Mazurek, K.; Dobaczewski, J.; Nazarewicz, W.; Sheikh, J. A.; Baran, A.
2015-01-01
We determined the spontaneous fission lifetime of ^{238}U by a minimization of the action integral in a three-dimensional space of collective variables. Apart from the mass-distribution multipole moments Q_{20} (elongation) and Q_{30} (left–right asymmetry), we also considered the pairing-fluctuation parameter ?_{2} as a collective coordinate. The collective potential was obtained self-consistently using the Skyrme energy density functional SkM*. The inertia tensor was obtained within the nonperturbative cranking approximation to the adiabatic time-dependent Hartree–Fock–Bogoliubov approach. As a result, the pairing-fluctuation parameter ?_{2} allowed us to control the pairing gap along the fission path, which significantly changed the spontaneous fission lifetime.
Investigation of the EAS Lateral Particle Density at 500 m Distance from Shower Core
Toma, G.
2008-01-24
For the experimental conditions of the KASCADE-Grande experiment, the density of EAS charged particles at the distance of about 500 m from the shower core S(500) has been shown by detailed simulation studies to be an approximate energy estimator, being nearly independent of the mass of the primary particle. This report presents some experimentally observed features of the S(500) observable registered with the KASCADE-Grande array installed at the Forschungszentrum Karlsruhe, Germany The measured energy deposits of particles in the 37 scintillation detector stations have been used to reconstruct the lateral charged particle distributions that are described by a Linsley parameterization (LDF). Among other features, the S(500) dependence from the EAS angle of incidence has been studied.
Multidimensional Skyrme-density-functional study of the spontaneous fission of 238U
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Sadhukhan, J.; Mazurek, K.; Dobaczewski, J.; Nazarewicz, W.; Sheikh, J. A.; Baran, A.
2015-01-01
We determined the spontaneous fission lifetime of 238U by a minimization of the action integral in a three-dimensional space of collective variables. Apart from the mass-distribution multipole moments Q20 (elongation) and Q30 (leftâ€“right asymmetry), we also considered the pairing-fluctuation parameter Î»2 as a collective coordinate. The collective potential was obtained self-consistently using the Skyrme energy density functional SkM*. The inertia tensor was obtained within the nonperturbative cranking approximation to the adiabatic time-dependent Hartreeâ€“Fockâ€“Bogoliubov approach. As a result, the pairing-fluctuation parameter Î»2 allowed us to control the pairing gap along the fission path, which significantly changed the spontaneous fission lifetime.
Reshak, A.H.; Khan, Saleem Ayaz
2013-11-15
Graphical abstract: - Highlights: • FPLAPW method is used for calculating the electronic and optical properties of CdGa{sub 2}X{sub 4}. • Electronic and optical properties were calculated using LDA, GGA, EVGGA and mBJ. • Band gap conformed that CdGa{sub 2}X{sub 4} are semiconductors fit for UV and visible light. • The ECD shows that change in the bond length and bond nature affect the band gap. • The dielectric tensor components and its derivatives show considerable anisotropy. - Abstract: A density functional theory (DFT) based on full potential linear augmented plane wave (FPLAPW) was used for calculating the electronic structure, charge density and optical properties of CdGa{sub 2}X{sub 4} (X = S, Se) compounds. Local density approximation (LDA), generalized gradient approximation (GGA), Engle Vasko generalized gradient approximation (EVGGA) and recently modified Becke–Johnson (mBJ) were applied to calculate the band structure, total and partial density of states. The investigation of band structures and density of states of CdGa{sub 2}X{sub 4} (X = S, Se) elucidate that mBJ potential show close agreement to the experimental results. The mBJ potential was selected for further explanation of optical properties of CdGa{sub 2}X{sub 4} (X = S, Se). The study of electronic charge density contours shows that change in the bond lengths and bond nature affect the band gap of the compounds. The two non-zero dielectric tensor components and its derivatives show considerable anisotropy between the perpendicular and parallel components. The present work provide accurate information about the combination (hybridization) of orbital, formation of bands and dispersion of non-zero tensor components of CdGa{sub 2}X{sub 4} (X = S, Se)
Symmetry Energy as a Function of Density and Mass
Danielewicz, Pawel; Lee, Jenny
2007-10-26
Energy in nuclear matter is, in practice, completely characterized at different densities and asymmetries, when the density dependencies of symmetry energy and of energy of symmetric matter are specified. The density dependence of the symmetry energy at subnormal densities produces mass dependence of nuclear symmetry coefficient and, thus, can be constrained by that latter dependence. We deduce values of the mass dependent symmetry coefficients, by using excitation energies to isobaric analog states. The coefficient systematic, for intermediate and high masses, is well described in terms of the symmetry coefficient values of a{sub a}{sup V} = (31.5-33.5) MeV for the volume coefficient and a{sub a}{sup S} = (9-12) MeV for the surface coefficient. These two further correspond to the parameter values describing density dependence of symmetry energy, of L{approx}95 MeV and K{sub sym}{approx}25 MeV.
X-ray backlighting density measurements of tungsten and aluminum wire and wire array z-pinches
Hammer, D.A.; Pikuz, S.A.; Shelkovenko, T.A.; Greenly, J.B.; Sinars, D.B.; Mingaleev, A.R.
1999-07-01
Calibrated density measurements in both the coronal plasmas and dense cores of exploding W wire and wire array Z-pinches, powered by the {approximately}450 kA, 100 ns XP-pulser at Cornell University, have been made using two-frame x-ray backlighting in conjunction with known thickness W step wedges. The backlighting images are made by Mo wire X-pinch radiation filtered by 12.5 {micro}m Ti impinging upon a sandwich of films (Micrat VR, Kodak GWL, Kodak DEF) which have different sensitivities to increase the dynamic range of the method. A W step wedge filter is placed in front of the films, giving absolute line density calibration of each exposure with estimated errors ranging from 20 to 50%. Assuming x-ray absorption by the W plasma is the same as for the solid material, the authors are able to measure W areal densities from 3.2 x 10{sup 19} to 2 x 10{sup 17}/cm{sup 2}. These can be converted to number density assuming azimuthal symmetry. For example, for an exploded 7.5 {micro}m wire with a 15--20 {micro}m diameter dense core and a 1 mm corona diameter, the implied W volume density ranges from 2x10{sup 18} to over 10{sup 22}/cm{sup 3}. Integration of the line density gives an estimate of the fraction of the wire mass in the corona and core. For example, with 100 kA peak current in a single 7.5 {micro}m W wire, {approximately}70% (>90%) of the W mass is in the corona after 53 ns (61 ns). The authors also observe that the corona has large, roughly axisymmetric axial nonuniformity both in radius and in mass density. In addition, the coronal plasma contains more of the W mass, expands faster and is more uniform when the wire is surface-cleaned by preheating. In arrays of 2--8 wires with the same 100 kA total current, detectable coronal plasma appears after 25--35 ns, and much of it is swept toward the center of the array, forming a dense channel. The portion of the initial wire mass in the coronal plasma increases with smaller wire diameter and decreases with greater
Zhang, X.C.; Xu, B.S.; Wang, H.D.; Wu, Y.X.
2005-09-01
Stoney's equation and subsequent modifications and some approximations are widely used to evaluate the macrostress within a film on a substrate, though some of these solutions are only applicable for thin films. The purpose of this paper is to review the considerable efforts devoted to the analysis of residual stresses in a single-layer film in the last century and recent years and to estimate the errors involved in using these formulas. The following are some of the important results that can be obtained. (1) The exact solution for the residual stress can be expressed in terms of Stoney's equation [Proc. R. Soc. London A82, 172 (1909)] and a correction factor (1+{sigma}{eta}{sup 3})/(1+{eta}), where {sigma},{eta} are the ratios of the elastic modulus and the thickness of the film to those of the substrate, respectively. (2) When the thickness ratio of the film and the substrate is less than 0.1, Stoney's equation and Roell's approximation [J. Appl. Phys. 47, 3224 (1976)] do not cause serious errors. (3) The approximation proposed by Vilms and Kerps [J. Appl. Phys. 53, 1536 (1982)] is an improved modification for Stoney's equation and can be applicable when {eta}{<=}0.3. (4) The approximations proposed by Brenner and Senderoff [J. Res. Natl. Bur. Stand. 42, 105 (1949)] and Teixeira [Thin Solid Films 392, 276 (2001)] can lead to serious errors and should be avoided. (5) The approximation based on the assumption of constant elastic modulus is only applicable for a ratio of {eta}{<=}0.01 and can be very misleading.
Effenberger, Frederic; Litvinenko, Yuri E.
2014-03-01
The diffusion approximation to the Fokker-Planck equation is commonly used to model the transport of solar energetic particles in interplanetary space. In this study, we present exact analytical predictions of a higher order telegraph approximation for particle transport and compare them with the corresponding predictions of the diffusion approximation and numerical solutions of the full Fokker-Planck equation. We specifically investigate the role of the adiabatic focusing effect of a spatially varying magnetic field on an evolving particle distribution. Comparison of the analytical and numerical results shows that the telegraph approximation reproduces the particle intensity profiles much more accurately than does the diffusion approximation, especially when the focusing is strong. However, the telegraph approximation appears to offer no significant advantage over the diffusion approximation for calculating the particle anisotropy. The telegraph approximation can be a useful tool for describing both diffusive and wave-like aspects of the cosmic-ray transport.
DGDFT: A massively parallel method for large scale density functional theory calculations
Hu, Wei Yang, Chao; Lin, Lin
2015-09-28
We describe a massively parallel implementation of the recently developed discontinuous Galerkin density functional theory (DGDFT) method, for efficient large-scale Kohn-Sham DFT based electronic structure calculations. The DGDFT method uses adaptive local basis (ALB) functions generated on-the-fly during the self-consistent field iteration to represent the solution to the Kohn-Sham equations. The use of the ALB set provides a systematic way to improve the accuracy of the approximation. By using the pole expansion and selected inversion technique to compute electron density, energy, and atomic forces, we can make the computational complexity of DGDFT scale at most quadratically with respect to the number of electrons for both insulating and metallic systems. We show that for the two-dimensional (2D) phosphorene systems studied here, using 37 basis functions per atom allows us to reach an accuracy level of 1.3 Ã— 10{sup âˆ’4} Hartree/atom in terms of the error of energy and 6.2 Ã— 10{sup âˆ’4} Hartree/bohr in terms of the error of atomic force, respectively. DGDFT can achieve 80% parallel efficiency on 128,000 high performance computing cores when it is used to study the electronic structure of 2D phosphorene systems with 3500-14â€‰000 atoms. This high parallel efficiency results from a two-level parallelization scheme that we will describe in detail.
Modeling the ion density distribution in collisional cooling RF multipole ion guides
Tolmachev, Aleksey V.; Udseth, Harold R.; Smith, Richard D.
2003-01-01
Collisional cooling radio frequency (RF) multipoles are widely used in mass spectrometry, as ion guides and two-dimensional (2D) ion traps. Understanding the behavior of ions in these devices is important in choosing a multipole configuration. We have developed a computer model based on ion trajectory calculations in the RF multipole electric field, taking into account ion-ion and ion-neutral interactions. The two-dimensional model for idealized infinite RF multipoles gives accurate description of the ion density distribution. We consider first a basic case of a single m/z ion cloud in the 2D RF quadrupole after equilibrium is reached. Approximate theoretical relationships for the ion cloud configuration in the 2D ion trap are tested based on simulations results. Next we proceed with a case of an ion cloud consisting of several different m/z ion species. The ion relaxation dynamics and the process of establishing the stratified ion density distribution are followed. Simulations reveal a different relaxation dynamics for the axial and radial ion kinetic energy components. The kinetic energy relaxation rate is dependent on ion population and bath gas pressure. The equilibrium distribution agrees well with the ion stratification theory, as demonstrated by simulations for RF quadrupole and octupole 2D ion traps.
Not Available
1984-03-01
The report covers the following issues concerning: highwall elimination, reclamation, and approximate original contour in surface-mining applications.
Density impact on performance of composite Si/graphite electrodes
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Dufek, Eric J.; Picker, Michael; Petkovic, Lucia M.
2016-01-27
The ability of alkali-substituted binders for composite Si and graphite negative electrodes to minimize capacity fade for lithium ion batteries is investigated. Polymer films and electrodes are described and characterized by FTIR following immersion in electrolyte (1:2 EC:DMC) for 24 h. FTIR analysis following electrode formation displayed similar alkali-ion dependent shifts in peak location suggesting that changes in the vibrational structure of the binder are maintained after electrode formation. The Si and graphite composite electrodes prepared using the alkali-substituted polyacrylates were also exposed to electrochemical cycling and it has been found that the performance of the Na-substituted binder is superiormoreÂ Â» to a comparable density K-substituted system. However, in comparing performance across many different electrode densities attention needs to be placed on making comparisons at similar densities, as low density electrodes tend to exhibit lower capacity fade over cycling. This is highlighted by a 6% difference between a low density K-substituted electrode and a high density Na-substituted sample. As a result, this low variance between the two systems makes it difficult to quickly make a direct evaluation of binder performance unless electrode density is tightly controlled.Â«Â less
Nanda, Vikas; Kant, Niti
2014-07-15
The effect of plasma density ramp on self-focusing of cosh-Gaussian laser beam considering ponderomotive nonlinearity is analyzed using WKB and paraxial approximation. It is noticed that cosh-Gaussian laser beam focused earlier than Gaussian beam. The focusing and de-focusing nature of the cosh-Gaussian laser beam with decentered parameter, intensity parameter, magnetic field, and relative density parameter has been studied and strong self-focusing is reported. It is investigated that decentered parameter â€œbâ€ plays a significant role for the self-focusing of the laser beam as for b=2.12, strong self-focusing is seen. Further, it is observed that extraordinary mode is more prominent toward self-focusing rather than ordinary mode of propagation. For b=2.12, with the increase in the value of magnetic field self-focusing effect, in case of extraordinary mode, becomes very strong under plasma density ramp. Present study may be very useful in the applications like the generation of inertial fusion energy driven by lasers, laser driven accelerators, and x-ray lasers. Moreover, plasma density ramp plays a vital role to enhance the self-focusing effect.
Postmortem validation of breast density using dual-energy mammography
Molloi, Sabee Ducote, Justin L.; Ding, Huanjun; Feig, Stephen A.
2014-08-15
Purpose: Mammographic density has been shown to be an indicator of breast cancer risk and also reduces the sensitivity of screening mammography. Currently, there is no accepted standard for measuring breast density. Dual energy mammography has been proposed as a technique for accurate measurement of breast density. The purpose of this study is to validate its accuracy in postmortem breasts and compare it with other existing techniques. Methods: Forty postmortem breasts were imaged using a dual energy mammography system. Glandular and adipose equivalent phantoms of uniform thickness were used to calibrate a dual energy basis decomposition algorithm. Dual energy decomposition was applied after scatter correction to calculate breast density. Breast density was also estimated using radiologist reader assessment, standard histogram thresholding and a fuzzy C-mean algorithm. Chemical analysis was used as the reference standard to assess the accuracy of different techniques to measure breast composition. Results: Breast density measurements using radiologist reader assessment, standard histogram thresholding, fuzzy C-mean algorithm, and dual energy were in good agreement with the measured fibroglandular volume fraction using chemical analysis. The standard error estimates using radiologist reader assessment, standard histogram thresholding, fuzzy C-mean, and dual energy were 9.9%, 8.6%, 7.2%, and 4.7%, respectively. Conclusions: The results indicate that dual energy mammography can be used to accurately measure breast density. The variability in breast density estimation using dual energy mammography was lower than reader assessment rankings, standard histogram thresholding, and fuzzy C-mean algorithm. Improved quantification of breast density is expected to further enhance its utility as a risk factor for breast cancer.
Wu, Yongfeng; Xiao, Weike
2014-02-01
We introduced a new two-dimensional (2D) hexagon technique for probing the topological structure of the universe in which we mapped regions of the sky with high and low galaxy densities onto a 2D lattice of hexagonal unit cells. We defined filled cells as corresponding to high-density regions and empty cells as corresponding to low-density regions. The numbers of filled cells and empty cells were kept the same by controlling the size of the cells. By analyzing the six sides of each hexagon, we could obtain and compare the statistical topological properties of high-density and low-density regions of the universe in order to have a better understanding of the evolution of the universe. We applied this hexagonal method to Two Micron All Sky Survey data and discovered significant topological differences between the high-density and low-density regions. Both regions had significant (>5?) topological shifts from both the binomial distribution and the random distribution.
Oak Ridge Removes Laboratoryâ€™s Greatest Source of Groundwater Contamination
Broader source: Energy.gov [DOE]
OAK RIDGE, Tenn. â€“ This month, Oak Ridgeâ€™s EM program bid farewell to the last shipment of waste from the Tank W-1A project.
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Biernat, Elmar P.; Gross, Franz; PeÃ±a, M. T.; Stadler, Alfred
2015-10-26
The pion form factor is calculated in the framework of the charge-conjugation invariant covariant spectator theory. This formalism is established in Minkowski space, and the calculation is set up in momentum space. In a previous calculation we included only the leading pole coming from the spectator quark (referred to as the relativistic impulse approximation). In this study we also include the contributions from the poles of the quark which interacts with the photon and average over all poles in both the upper and lower half-planes in order to preserve charge conjugation invariance (referred to as the C-symmetric complete impulse approximation).moreÂ Â» We find that for small pion mass these contributions are significant at all values of the four-momentum transfer Q2 but, surprisingly, do not alter the shape obtained from the spectator poles alone.Â«Â less
Biernat, Elmar P.; Gross, Franz; PeÃ±a, M. T.; Stadler, Alfred
2015-10-26
The pion form factor is calculated in the framework of the charge-conjugation invariant covariant spectator theory. This formalism is established in Minkowski space, and the calculation is set up in momentum space. In a previous calculation we included only the leading pole coming from the spectator quark (referred to as the relativistic impulse approximation). In this study we also include the contributions from the poles of the quark which interacts with the photon and average over all poles in both the upper and lower half-planes in order to preserve charge conjugation invariance (referred to as the C-symmetric complete impulse approximation). We find that for small pion mass these contributions are significant at all values of the four-momentum transfer Q^{2} but, surprisingly, do not alter the shape obtained from the spectator poles alone.
Controlling the Actuation Rate of Low Density Shape Memory Polymer...
Office of Scientific and Technical Information (OSTI)
Title: Controlling the Actuation Rate of Low Density Shape Memory Polymer Foams in Water Authors: Singhal, P ; Boyle, T ; Infanger, S ; Letts, S ; Small, W ; Maitland, D J ; Wilson...
Paper area density measurement from forward transmitted scattered light
Koo, Jackson C.
2001-01-01
A method whereby the average paper fiber area density (weight per unit area) can be directly calculated from the intensity of transmitted, scattered light at two different wavelengths, one being a non-absorpted wavelength. Also, the method makes it possible to derive the water percentage per fiber area density from a two-wavelength measurement. In the optical measuring technique optical transmitted intensity, for example, at 2.1 microns cellulose absorption line is measured and compared with another scattered, optical transmitted intensity reference in the nearby spectrum region, such as 1.68 microns, where there is no absorption. From the ratio of these two intensities, one can calculate the scattering absorption coefficient at 2.1 microns. This absorption coefficient at this wavelength is, then, experimentally correlated to the paper fiber area density. The water percentage per fiber area density can be derived from this two-wavelength measurement approach.
Optical Properties of the Charge-Density-Wave Polychalcogenide...
Office of Scientific and Technical Information (OSTI)
the rare-earth polychalcogenide Rsub 2Tesub 5 (R Nd, Sm and Gd) charge-density-wave (CDW) compounds by optical methods. From the absorption spectrum we extract the...
Effect of Chemical Pressure on the Charge Density Wave Transition...
Office of Scientific and Technical Information (OSTI)
The charge density wave transition is investigated in the bilayer family of rare-earth tritelluride RTesub 3 compounds (RSm, Gd, Tb, Dy, Ho, Er, and Tm) via high-resolution ...
Low density lipoprotein fraction assay for cardiac disease risk
Krauss, Ronald M.; Blanche, Patricia J.; Orr, Joseph
1999-01-01
A variable rate density gradient electrophoric gel is described which separate LDL subfractions with the precision of ultracentrifugation techniques. Also, an innovative bottom inlet mixing chamber particularly useful for producing these gels is described.
Direct experimental determination of spectral densities of molecular complexes
Pachón, Leonardo A.; Brumer, Paul
2014-11-07
Determining the spectral density of a molecular system immersed in a proteomic scaffold and in contact to a solvent is a fundamental challenge in the coarse-grained description of, e.g., electron and energy transfer dynamics. Once the spectral density is characterized, all the time scales are captured and no artificial separation between fast and slow processes need to be invoked. Based on the fluorescence Stokes shift function, we utilize a simple and robust strategy to extract the spectral density of a number of molecular complexes from available experimental data. Specifically, we show that experimental data for dye molecules in several solvents, amino acid proteins in water, and some photochemical systems (e.g., rhodopsin and green fluorescence proteins), are well described by a three-parameter family of sub-Ohmic spectral densities that are characterized by a fast initial Gaussian-like decay followed by a slow algebraic-like decay rate at long times.
COLLOQUIUM: Frontiers in Plasma Science: A High Energy Density...
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January 13, 2016, 4:15pm to 5:30pm Colloquia MBG AUDITORIUM COLLOQUIUM: Frontiers in Plasma Science: A High Energy Density Perspective Dr. Bruce A. Remington Lawrence Livermore ...
Creating, Diagnosing and Controlling High-energy-density Matter...
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October 22, 2013, 3:00pm to 4:15pm Colloquia MBG Auditorium Creating, Diagnosing and Controlling High-energy-density Matter with Lasers Dr. Yuan Ping Lawrence Livermore National ...
High power density fuel cell stack development for automotive applications
Pow, R.; Reindl, M.; Tilmetz, W.
1996-12-31
This paper describes the joint development by Daimler-Benz and Ballard Power Systems of a high power-density fuel cell stack and its demonstration in a 6-passenger Minivan.
The tokamak density limit: A thermo-resistive disruption mechanism...
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Title: The tokamak density limit: A thermo-resistive disruption mechanism Authors: Gates, D. A. 1 ; Brennan, D. P. 1 ; Delgado-Aparicio, L. 1 ; White, R. B. 1 + Show Author ...
Controlling the Actuation Rate of Low Density Shape Memory Polymer...
Office of Scientific and Technical Information (OSTI)
Memory Polymer Foams in Water Citation Details In-Document Search Title: Controlling the Actuation Rate of Low Density Shape Memory Polymer Foams in Water You are accessing a ...
Low density lipoprotein fraction assay for cardiac disease risk
Krauss, R.M.; Blanche, P.J.; Orr, J.
1999-07-20
A variable rate density gradient electrophoric gel is described which separates LDL subfractions with the precision of ultracentrifugation techniques. Also, an innovative bottom inlet mixing chamber particularly useful for producing these gels is described. 8 figs.
Plasma density diagnostic for capillary-discharge based plasma...
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Plasma density diagnostic for capillary-discharge based plasma channels Authors: Daniels, J. 1 Search SciTech Connect for author "Daniels, J." Search SciTech Connect for...
Optical Properties of the Charge-Density-Wave Polychalcogenide...
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Optical Properties of the Charge-Density-Wave Polychalcogenide Compounds R2Te5 (RNd, Sm and Gd) Citation Details In-Document Search Title: Optical Properties of the...
Probing Electron Dynamics with the Laplacian of the Momentum Density
Sukumar, N.; MacDougall, Preston J.; Levit, M. Creon
2012-09-24
This chapter in the above-titled monograph presents topological analysis of the Laplacian of the electron momentum density in organic molecules. It relates topological features in this distribution to chemical and physical properties, particularly aromaticity and electron transport.
Effect of Chemical Pressure on the Charge Density Wave Transition...
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Effect of Chemical Pressure on the Charge Density Wave Transition in Rare-Earth ... These compounds have the chemical formula RTe3, where R represents a rare earth element ...
Surface modification of low density silica and bridged polysilsesquioxane aerogels
DeFriend, K. A. (Kimberly A.); Loy, D. A. (Douglas A.); Salazar, K. V. (Kenneth V.); Wilson, K. V. (Kennard V.)
2004-01-01
Silica and bridged polysilsesquioxane aerogels are low density materials that are attractive for applications such as, thermal insulation, porous separation media or catalyst supports, adsorbents. However, aerogels are notoriously weak and brittle making it difficult to handle and machine monoliths into desired forms. This prevents the development of many applications that would otherwise benefit from the use of the low density materials. We will describe our efforts to chemically modify and mechanically enhance silica-based aerogels using chemical vapor techniques without sacrificing their characteristic low densities. Monolithic silica and organically bridged polysilsesquioxane aerogels were prepared by sol-gel polymerization of the respective methoxysilane monomers followed by supercritical carbon dioxide drying of the gels. Reactive modification of the gels with volatile silylating compounds during and after the drying process and these effects on the mechanical properties and density of the aerogels will be described.
Low density biodegradable shape memory polyurethane foams for...
Office of Scientific and Technical Information (OSTI)
Citation Details In-Document Search Title: Low density ... OSTI Identifier: 1122211 Report Number(s): LLNL-JRNL-623392 DOE Contract Number: W-7405-ENG-48 Resource Type: Journal ...
Ultra Low Density and Highly Crosslinked Biocompatible Shape...
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Citation Details In-Document Search Title: Ultra Low Density ... OSTI Identifier: 1111124 Report Number(s): LLNL-JRNL-501951 DOE Contract Number: W-7405-ENG-48 Resource Type: Journal ...
A Comprehensive Study Of Fracture Patterns And Densities In The...
specific knowledge of these in the Geysers area. (2)By locating zones of high fracture density it will be possible to reduce the cost of geothermal power development with the...
Efficient Real-Time Time-Dependent Density Functional Theory...
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Efficient Real-Time Time-Dependent Density Functional Theory Method and its Application to a Collision of an Ion with a 2D Material Title: Efficient Real-Time Time-Dependent ...
Separation of solids by varying the bulk density of a fluid separating medium
Peterson, Palmer L.; Duffy, James B.; Tokarz, Richard D.
1978-01-01
A method and apparatus for separating objects having a density greater than a selected density value from objects having a density less than said selected density value. The method typically comprises: (a) providing a separation vessel having an upper and lower portion, said vessel containing a liquid having a density exceeding said selected density value; (b) reducing the apparent density of the liquid to said selected density value by introducing solid, bubble-like bodies having a density less than that of the liquid into the lower portion of the vessel and permitting them to rise therethrough; (c) introducing the objects to be separated into the separation vessel and permitting the objects having a density greater than the apparent density of the liquid to sink to the lower portion of the vessel, while the objects having a density less than said selected density value float in the upper portion of the vessel; and (d) separately removing the higher density objects in the lower portion and the lower density objects in the upper portion from the separation vessel. The apparatus typically comprises: (a) a vessel containing a liquid having a density such that at least part of said objects having a density exceeding said selected density value will float therein; (b) means to place said objects into said vessel; (c) means to reduce the effective density of at least a portion of said liquid to said selected density value, whereby said objects having a density exceeding said selected density value sink into said liquid and said objects having a density less than said selected density value remain afloat, said means to adjust the effective density comprising solid, bubble-like bodies having a density less than said selected density value and means for introducing said bodies into said liquid; and (d) means for separately removing said objects having a density exceeding said selected density value and said objects having a density less than said selected density value
Zaslawsky, M.; Kennedy, W.N.
1992-09-30
Mathematical solutions to the problem consisting of a partially-full waste tank subjected to seismic loading, embedded in soil, is classically difficult in that one has to address: soil-structure interaction, fluid-structure interaction, non-linear behavior of material, dynamic effects. Separating the problem and applying numerous assumptions will yield approximate solutions. This paper explores methods for generating these solutions accurately.
Peru, S.; Gosselin, G.; Martini, M.; Dupuis, M.; Hilaire, S.
2011-01-15
Fully consistent axially-symmetric deformed quasiparticle random-phase approximation (QRPA) calculations have been performed, using the same Gogny D1S effective force for both the Hartree-Fock-Bogolyubov mean field and QRPA matrix. New implementation of this approach leads to the applicability of QRPA to heavy deformed nuclei. Giant resonances and low-energy collective states for monopole, dipole, quadrupole, and octupole modes are predicted for the heavy deformed nucleus {sup 238}U and compared with experimental data.
Pohle, H.
1989-03-15
We investigate lambdaphi/sup 4/ theory within the Gaussian approximation in spatially flat Robertson-Walker space in 3+1 dimensions. After having performed an adiabatic expansion for one of the ansatz functions, we find that the renormalization of the energy-momentum tensor provides two additional constraints which have to be satisfied by the bare couplings. These conditions force the theory to be trivial after renormalization.
Low density biodegradable shape memory polyurethane foams for embolic
Office of Scientific and Technical Information (OSTI)
biomedical applications (Journal Article) | SciTech Connect Low density biodegradable shape memory polyurethane foams for embolic biomedical applications Citation Details In-Document Search Title: Low density biodegradable shape memory polyurethane foams for embolic biomedical applications Authors: Singhal, P ; Small, W ; Cosgriff-Hernandez, E ; Maitland, D ; Wilson, T Publication Date: 2013-02-27 OSTI Identifier: 1122211 Report Number(s): LLNL-JRNL-623392 DOE Contract Number: W-7405-ENG-48
Density Functional Theory with Dissipation: Transport through Single Molecules
Kieron Burke
2012-04-30
A huge amount of fundamental research was performed on this grant. Most of it focussed on fundamental issues of electronic structure calculations of transport through single molecules, using density functional theory. Achievements were: (1) First density functional theory with dissipation; (2) Pseudopotential plane wave calculations with master equation; (3) Weak bias limit; (4) Long-chain conductance; and (5) Self-interaction effects in tunneling.
High Energy Density Laboratory Plasmas Program | National Nuclear Security
National Nuclear Security Administration (NNSA)
Administration | (NNSA) High Energy Density Laboratory Plasmas Program Steady advances in increasing the energy, power, and brightness of lasers and particle beams and advances in pulsed power systems have made possible the exploration of matter at extremely high energy density in the laboratory. Exciting new experimental regimes are being realized by exploiting the scientific capabilities of existing ICF Office facilities, as well as the relevant Department of Defense (DoD) and university
High Energy Density Laboratory Plasmas | National Nuclear Security
National Nuclear Security Administration (NNSA)
Administration | (NNSA) High Energy Density Laboratory Plasmas NNSA's Office of Inertial Confinement Fusion and DOE's Office of Science established a joint program in HEDLP in 2008. Initially, this program was a combination of work that was funded as part of the NNSA's Stewardship Science Academic Alliances Program in the research area of high energy density physics and the DOE Office of Science's HEDLP Program and Innovative Confinement Concepts Program. Steady advances in increasing the
Non-invasive fluid density and viscosity measurement
Sinha, Dipen N.
2012-05-01
The noninvasively measurement of the density and viscosity of static or flowing fluids in a section of pipe such that the pipe performs as the sensing apparatus, is described. Measurement of a suitable structural vibration resonance frequency of the pipe and the width of this resonance permits the density and viscosity to be determined, respectively. The viscosity may also be measured by monitoring the decay in time of a vibration resonance in the pipe.
Simulations of liquid ribidium expanded to the critical density
Ross, M; Yang, L H; Pilgrim, W
2006-05-16
Quantum molecular dynamic simulations were used to examine the change in atomic and electronic structure in liquid rubidium along its liquid-vapor coexistence curve. Starting from the liquid at the triple point, with increasing expansion we observe a continuous increase in the electron localization leading to ion clustering near the metal-nonmetal transition at about twice the critical density, in agreement with electrical measurements, and to the presence of dimers near and below the critical density.
Preface: Special Topic on Advances in Density Functional Theory
Yang, Weitao
2014-05-14
This Special Topic Issue on the Advances in Density Functional Theory, published as a celebration of the fifty years of density functional theory, contains a retrospective article, a perspective article, and a collection of original research articles that showcase recent theoretical advances in the field. It provides a timely discussion reflecting a cross section of our understanding, and the theoretical and computational developments, which have significant implications in broad areas of sciences and engineering.
Comparing the Powertrain Energy Densities of Electric and Gasoline Vehicles
Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)
| Argonne National Laboratory Comparing the Powertrain Energy Densities of Electric and Gasoline Vehicles Title Comparing the Powertrain Energy Densities of Electric and Gasoline Vehicles Publication Type Conference Paper Year of Publication 2016 Authors Vijayagopal, R, Gallagher, K, Lee, D, Rousseau, A Conference Name SAE 2016 World Congress and Exhibition Date Published 04052016 Other Numbers SAE Paper No. 2016-01-0903 Keywords batteries, electric vehicles, EVs, fuel economy, gasoline,
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Padrino-Inciarte, Juan Carlos; Ma, Xia; VanderHeyden, W. Brian; Zhang, Duan Zhong
2016-01-01
General ensemble phase averaged equations for multiphase flows have been specialized for the simulation of the steam assisted gravity drainage (SAGD) process. In the average momentum equation, fluid-solid and fluid-fluid viscous interactions are represented by separate force terms. This equation has a form similar to that of Darcyâ€™s law for multiphase flow but augmented by the fluid-fluid viscous forces. Models for these fluid-fluid interactions are suggested and implemented into the numerical code CartaBlanca. Numerical results indicate that the model captures the main features of the multiphase flow in the SAGD process, but the detailed features, such as plumes are missed.moreÂ Â» We find that viscous coupling among the fluid phases is important. Advection time scales for the different fluids differ by several orders of magnitude because of vast viscosity differences. Numerically resolving all of these time scales is time consuming. To address this problem, we introduce a steam surrogate approximation to increase the steam advection time scale, while keeping the mass and energy fluxes well approximated. This approximation leads to about a 40-fold speed-up in execution speed of the numerical calculations at the cost of a few percent error in the relevant quantities.Â«Â less
Padrino-Inciarte, Juan Carlos; Ma, Xia; VanderHeyden, W. Brian; Zhang, Duan Zhong
2016-01-01
General ensemble phase averaged equations for multiphase flows have been specialized for the simulation of the steam assisted gravity drainage (SAGD) process. In the average momentum equation, fluid-solid and fluid-fluid viscous interactions are represented by separate force terms. This equation has a form similar to that of Darcyâ€™s law for multiphase flow but augmented by the fluid-fluid viscous forces. Models for these fluid-fluid interactions are suggested and implemented into the numerical code CartaBlanca. Numerical results indicate that the model captures the main features of the multiphase flow in the SAGD process, but the detailed features, such as plumes are missed. We find that viscous coupling among the fluid phases is important. Advection time scales for the different fluids differ by several orders of magnitude because of vast viscosity differences. Numerically resolving all of these time scales is time consuming. To address this problem, we introduce a steam surrogate approximation to increase the steam advection time scale, while keeping the mass and energy fluxes well approximated. This approximation leads to about a 40-fold speed-up in execution speed of the numerical calculations at the cost of a few percent error in the relevant quantities.
Improving experimental phases for strong reflections prior to density modification
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Uervirojnangkoorn, Monarin; Hilgenfeld, Rolf; Terwilliger, Thomas C.; Read, Randy J.
2013-09-20
Experimental phasing of diffraction data from macromolecular crystals involves deriving phase probability distributions. These distributions are often bimodal, making their weighted average, the centroid phase, improbable, so that electron-density maps computed using centroid phases are often non-interpretable. Density modification brings in information about the characteristics of electron density in protein crystals. In successful cases, this allows a choice between the modes in the phase probability distributions, and the maps can cross the borderline between non-interpretable and interpretable. Based on the suggestions by Vekhter [Vekhter (2005), Acta Cryst. D61, 899â€“902], the impact of identifying optimized phases for a small number ofmoreÂ Â» strong reflections prior to the density-modification process was investigated while using the centroid phase as a starting point for the remaining reflections. A genetic algorithm was developed that optimizes the quality of such phases using the skewness of the density map as a target function. Phases optimized in this way are then used in density modification. In most of the tests, the resulting maps were of higher quality than maps generated from the original centroid phases. In one of the test cases, the new method sufficiently improved a marginal set of experimental SAD phases to enable successful map interpretation. Lastly, a computer program,SISA, has been developed to apply this method for phase improvement in macromolecular crystallography.Â«Â less
Density-shear instability in electron magneto-hydrodynamics
Wood, T. S. Hollerbach, R.; Lyutikov, M.
2014-05-15
We discuss a novel instability in inertia-less electron magneto-hydrodynamics (EMHD), which arises from a combination of electron velocity shear and electron density gradients. The unstable modes have a lengthscale longer than the transverse density scale, and a growth-rate of the order of the inverse Hall timescale. We suggest that this density-shear instability may be of importance in magnetic reconnection regions on scales smaller than the ion skin depth, and in neutron star crusts. We demonstrate that the so-called Hall drift instability, previously argued to be relevant in neutron star crusts, is a resistive tearing instability rather than an instability of the Hall term itself. We argue that the density-shear instability is of greater significance in neutron stars than the tearing instability, because it generally has a faster growth-rate and is less sensitive to geometry and boundary conditions. We prove that, for uniform electron density, EMHD is “at least as stable” as regular, incompressible MHD, in the sense that any field configuration that is stable in MHD is also stable in EMHD. We present a connection between the density-shear instability in EMHD and the magneto-buoyancy instability in anelastic MHD.
Davidson, R. L.; Earle, G. D.; Heelis, R. A.; Klenzing, J. H.
2010-08-15
Planar retarding potential analyzers (RPAs) have been utilized numerous times on high profile missions such as the Communications/Navigation Outage Forecast System and the Defense Meteorological Satellite Program to measure plasma composition, temperature, density, and the velocity component perpendicular to the plane of the instrument aperture. These instruments use biased grids to approximate ideal biased planes. These grids introduce perturbations in the electric potential distribution inside the instrument and when unaccounted for cause errors in the measured plasma parameters. Traditionally, the grids utilized in RPAs have been made of fine wires woven into a mesh. Previous studies on the errors caused by grids in RPAs have approximated woven grids with a truly flat grid. Using a commercial ion optics software package, errors in inferred parameters caused by both woven and flat grids are examined. A flat grid geometry shows the smallest temperature and density errors, while the double thick flat grid displays minimal errors for velocities over the temperature and velocity range used. Wire thickness along the dominant flow direction is found to be a critical design parameter in regard to errors in all three inferred plasma parameters. The results shown for each case provide valuable design guidelines for future RPA development.
Mirtschink, André; Gori-Giorgi, Paola; Umrigar, C. J.; Morgan, John D.
2014-05-14
Anions and radicals are important for many applications including environmental chemistry, semiconductors, and charge transfer, but are poorly described by the available approximate energy density functionals. Here we test an approximate exchange-correlation functional based on the exact strong-coupling limit of the Hohenberg-Kohn functional on the prototypical case of the He isoelectronic series with varying nuclear charge Z < 2, which includes weakly bound negative ions and a quantum phase transition at a critical value of Z, representing a big challenge for density functional theory. We use accurate wavefunction calculations to validate our results, comparing energies and Kohn-Sham potentials, thus also providing useful reference data close to and at the quantum phase transition. We show that our functional is able to bind H{sup ?} and to capture in general the physics of loosely bound anions, with a tendency to strongly overbind that can be proven mathematically. We also include corrections based on the uniform electron gas which improve the results.
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Valdivia, M. P.; Stutman, D.; Stoeckl, C.; Mileham, C.; Begishev, I.; Theobald, W.; Bromage, J.; Regan, S. P.; Klein, S. R.; Munoz-Cordoves, G.; et al
2016-04-21
Talbot-Lau X-ray Deflectometry has been developed as an electron density diagnostic for High Energy Density plasmas. The technique can deliver x-ray refraction, attenuation, elemental composition, and scatter information from a single MoirÃ© image. An 8 keV Talbot-Lau interferometer was deployed using laser and x-pinch backlighters. Grating survival and electron density mapping was demonstrated for 25-29 J, 8-30 ps laser pulses using copper foil targets. Moire pattern formation and grating survival was also observed using a copper x-pinch driven at 400 kA, ~1 kA/ns. Lastly, these results demonstrate the potential of TXD as an electron density diagnostic for HED plasmas.
Direct Measurements of Pore Fluid Density by Vibrating Tube Densimetry
Gruszkiewicz, Miroslaw {Mirek} S; Rother, Gernot; Wesolowski, David J; Cole, David R; Wallacher, Dirk
2012-01-01
The densities of pore-confined fluids were measured for the first time by means of a vibrating tube method. Isotherms of total adsorption capacity were measured directly making the method complementary to the conventional gravimetric or volumetric/piezometric adsorption techniques, which yield the excess adsorption (the Gibbsian surface excess). A custom-made high-pressure, high-temperature vibrating tube densimeter (VTD) was used to measure the densities of subcritical and supercritical propane (between 35 C and 97 C) and supercritical carbon dioxide (between 32 C and 50 C) saturating hydrophobic silica aerogel (0.2 g/cm3, 90% porosity) synthesized inside Hastelloy U-tubes. Additionally, excess adsorption isotherms for supercritical CO2 and the same porous solid were measured gravimetrically using a precise magnetically-coupled microbalance. Pore fluid densities and total adsorption isotherms increased monotonically with increasing density of the bulk fluid, in contrast to excess adsorption isotherms, which reached a maximum at a subcritical density of the bulk fluid, and then decreased towards zero or negative values at supercritical densities. Compression of the confined fluid significantly beyond the density of the bulk liquid at the same temperature was observed at subcritical temperatures. The features of the isotherms of confined fluid density are interpreted to elucidate the observed behavior of excess adsorption. The maxima of excess adsorption were found to occur below the critical density of the bulk fluid at the conditions corresponding to the beginning of the plateau of total adsorption, marking the end of the transition of pore fluid to a denser, liquid-like pore phase. The results for propane and carbon dioxide showed similarity in the sense of the principle of corresponding states. No measurable effect of pore confinement on the liquid-vapor critical point was found. Quantitative agreement was obtained between excess adsorption isotherms determined
Criticality Calculations Using the Isopiestic Density Law of Actinide Nitrates
Leclaire, Nicolas P.; Anno, Jacques A.; Courtois, Gerard; Dannus, Pascal; Poullot, Gilles; Rouyer, Veronique
2003-12-15
Up to now, criticality safety experts used density laws fitted on experimental data and applied them outside the measurement range. Depending on the case, such an approach could be wrong for nitrate solutions. Seven components are concerned: UO{sub 2}(NO{sub 3}){sub 2}, U(NO{sub 3}){sub 4}, Pu(NO{sub 3}){sub 4}, Pu(NO{sub 3}){sub 3}, Th(NO{sub 3}){sub 4}, Am(NO{sub 3}){sub 3}, and HNO{sub 3}. To obviate this problem, a new methodology based on the thermodynamic concept of mixtures of binary electrolytes solutions (one electrolyte + water) at constant water activity, a so-called 'isopiestic' solution, has been developed by the Institute de Radioprotection et de Surete Nucleaire (IRSN) to calculate the nitrate solutions density. This paper presents its qualification by using criticality experiments. The theory and the implementation are also given.Qualification results of the uranyl and plutonium nitrate solutions show that the new density law (also called the isopiestic law) is in good agreement with the benchmarks. Thus, no bias is put into evidence for the uranium solutions, and a small negative bias equal to 0.2% is found for the plutonium solutions.Moreover, the isopiestic law corrects the observed 1% overestimation of k{sub eff} due to the empirical IRSN Leroy and Jouan density law for uranium solutions and the observed 3.4% underestimation of k{sub eff} due to the ARH-600 density law for plutonium solutions.The isopiestic density law has been implemented in CIGALES V2.0, the graphical user interface of the French criticality safety package CRISTAL that calculates the atom densities of nuclides (and writes the input file for CRISTAL computations)
DIFFUSE MOLECULAR CLOUD DENSITIES FROM UV MEASUREMENTS OF CO ABSORPTION
Goldsmith, Paul F.
2013-09-10
We use UV measurements of interstellar CO toward nearby stars to calculate the density in the diffuse molecular clouds containing the molecules responsible for the observed absorption. Chemical models and recent calculations of the excitation rate coefficients indicate that the regions in which CO is found have hydrogen predominantly in molecular form and that collisional excitation is by collisions with H{sub 2} molecules. We carry out statistical equilibrium calculations using CO-H{sub 2} collision rates to solve for the H{sub 2} density in the observed sources without including effects of radiative trapping. We have assumed kinetic temperatures of 50 K and 100 K, finding this choice to make relatively little difference to the lowest transition. For the sources having T{sup ex}{sub 10} only for which we could determine upper and lower density limits, we find (n(H{sub 2})) = 49 cm{sup -3}. While we can find a consistent density range for a good fraction of the sources having either two or three values of the excitation temperature, there is a suggestion that the higher-J transitions are sampling clouds or regions within diffuse molecular cloud material that have higher densities than the material sampled by the J = 1-0 transition. The assumed kinetic temperature and derived H{sub 2} density are anticorrelated when the J = 2-1 transition data, the J = 3-2 transition data, or both are included. For sources with either two or three values of the excitation temperature, we find average values of the midpoint of the density range that is consistent with all of the observations equal to 68 cm{sup -3} for T{sup k} = 100 K and 92 cm{sup -3} for T{sup k} = 50 K. The data for this set of sources imply that diffuse molecular clouds are characterized by an average thermal pressure between 4600 and 6800 K cm{sup -3}.
Bozkaya, U?ur
2014-09-28
General analytic gradient expressions (with the frozen-core approximation) are presented for density-fitted post-HF methods. An efficient implementation of frozen-core analytic gradients for the second-order Møller–Plesset perturbation theory (MP2) with the density-fitting (DF) approximation (applying to both reference and correlation energies), which is denoted as DF-MP2, is reported. The DF-MP2 method is applied to a set of alkanes, conjugated dienes, and noncovalent interaction complexes to compare the computational cost of single point analytic gradients with MP2 with the resolution of the identity approach (RI-MP2) [F. Weigend and M. Häser, Theor. Chem. Acc. 97, 331 (1997); R. A. Distasio, R. P. Steele, Y. M. Rhee, Y. Shao, and M. Head-Gordon, J. Comput. Chem. 28, 839 (2007)]. In the RI-MP2 method, the DF approach is used only for the correlation energy. Our results demonstrate that the DF-MP2 method substantially accelerate the RI-MP2 method for analytic gradient computations due to the reduced input/output (I/O) time. Because in the DF-MP2 method the DF approach is used for both reference and correlation energies, the storage of 4-index electron repulsion integrals (ERIs) are avoided, 3-index ERI tensors are employed instead. Further, as in case of integrals, our gradient equation is completely avoid construction or storage of the 4-index two-particle density matrix (TPDM), instead we use 2- and 3-index TPDMs. Hence, the I/O bottleneck of a gradient computation is significantly overcome. Therefore, the cost of the generalized-Fock matrix (GFM), TPDM, solution of Z-vector equations, the back transformation of TPDM, and integral derivatives are substantially reduced when the DF approach is used for the entire energy expression. Further application results show that the DF approach introduce negligible errors for closed-shell reaction energies and equilibrium bond lengths.
Sereda, Yuriy V.; Ortoleva, Peter J.
2014-04-07
A closed kinetic equation for the single-particle density of a viscous simple liquid is derived using a variational method for the Liouville equation and a coarse-grained mean-field (CGMF) ansatz. The CGMF ansatz is based on the notion that during the characteristic time of deformation a given particle interacts with many others so that it experiences an average interaction. A trial function for the N-particle probability density is constructed using a multiscale perturbation method and the CGMF ansatz is applied to it. The multiscale perturbation scheme is based on the ratio of the average nearest-neighbor atom distance to the total size of the assembly. A constraint on the initial condition is discovered which guarantees that the kinetic equation is mass-conserving and closed in the single-particle density. The kinetic equation has much of the character of the Vlasov equation except that true viscous, and not Landau, damping is accounted for. The theory captures condensation kinetics and takes much of the character of the Gross-Pitaevskii equation in the weak-gradient short-range force limit.
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Tang, J. Y.
2015-09-03
The Michaelisâ€“Menten kinetics and the reverse Michaelisâ€“Menten kinetics are two popular mathematical formulations used in many land biogeochemical models to describe how microbes and plants would respond to changes in substrate abundance. However, the criteria of when to use which of the two are often ambiguous. Here I show that these two kinetics are special approximations to the Equilibrium Chemistry Approximation kinetics, which is the first order approximation to the quadratic kinetics that solves the equation of enzyme-substrate complex exactly for a single enzyme single substrate biogeochemical reaction with the law of mass action and the assumption of quasi-steady-state formoreÂ Â» the enzyme-substrate complex and that the product genesis from enzyme-substrate complex is much slower than the equilibration between enzyme-substrate complexes, substrates and enzymes. In particular, I showed that the derivation of the Michaelisâ€“Menten kinetics does not consider the mass balance constraint of the substrate, and the reverse Michaelisâ€“Menten kinetics does not consider the mass balance constraint of the enzyme, whereas both of these constraints are taken into account in the Equilibrium Chemistry Approximation kinetics. By benchmarking against predictions from the quadratic kinetics for a wide range of substrate and enzyme concentrations, the Michaelisâ€“Menten kinetics was found to persistently under-predict the normalized sensitivity âˆ‚ ln v / âˆ‚ ln k2+ of the reaction velocity v with respect to the maximum product genesis rate k2+, persistently over-predict the normalized sensitivity âˆ‚ ln v / âˆ‚ ln k1+ of v with respect to the intrinsic substrate affinity k1+, persistently over-predict the normalized sensitivity âˆ‚ ln v / âˆ‚ ln [ E ]T of v with respect the total enzyme concentration [ E ]T and persistently under-predict the normalized sensitivity âˆ‚ ln v / âˆ‚ ln [ S ]T of v with respect to the total substrate concentration [ S ]T. Meanwhile, the
Pion transverse charge density and the edge of hadrons
Carmignotto, Marco; Horn, Tanja; Miller, Gerald A.
2014-08-01
We use the world data on the pion form factor for space-like kinematics and a technique used to extract the proton transverse densities, to extract the transverse pion charge density and its uncertainty due to experimental uncertainties and incomplete knowledge of the pion form factor at large values of Q2. The pion charge density at small values of b<0.1 fm is dominated by this incompleteness error while the range between 0.1-0.3 fm is relatively well constrained. A comparison of pion and proton charge densities shows that the pion is denser than the proton for values of b<0.2 fm. The pion and proton distributions seem to be the same for values of b=0.2-0.6 fm. Future data from Jlab 12 GeV and the EIC will increase the dynamic extent of the data to higher values of Q2 and thus reduce the uncertainties in the extracted pion charge density.
Dynamics and diffusion mechanism of low-density liquid silicon
Shen, B.; Wang, Z. Y.; Dong, F.; Guo, Y. R.; Zhang, R. J.; Zheng, Y. X.; Wang, S. Y.; Wang, C. Z.; Ho, K. M.; Chen, L. Y.
2015-11-05
A first-order phase transition from a high-density liquid to a low-density liquid has been proposed to explain the various thermodynamic anomies of water. It also has been proposed that such liquidâ€“liquid phase transition would exist in supercooled silicon. Computer simulation studies show that, across the transition, the diffusivity drops roughly 2 orders of magnitude, and the structures exhibit considerable tetrahedral ordering. The resulting phase is a highly viscous, low-density liquid silicon. Investigations on the atomic diffusion of such a novel form of liquid silicon are of high interest. Here we report such diffusion results from molecular dynamics simulations using the classical Stillingerâ€“Weber (SW) potential of silicon. We show that the atomic diffusion of the low-density liquid is highly correlated with local tetrahedral geometries. We also show that atoms diffuse through hopping processes within short ranges, which gradually accumulate to an overall random motion for long ranges as in normal liquids. There is a close relationship between dynamical heterogeneity and hopping process. We point out that the above diffusion mechanism is closely related to the strong directional bonding nature of the distorted tetrahedral network. Here, our work offers new insights into the complex behavior of the highly viscous low density liquid silicon, suggesting similar diffusion behaviors in other tetrahedral coordinated liquids that exhibit liquidâ€“liquid phase transition such as carbon and germanium.
Dynamics and diffusion mechanism of low-density liquid silicon
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Shen, B.; Wang, Z. Y.; Dong, F.; Guo, Y. R.; Zhang, R. J.; Zheng, Y. X.; Wang, S. Y.; Wang, C. Z.; Ho, K. M.; Chen, L. Y.
2015-11-05
A first-order phase transition from a high-density liquid to a low-density liquid has been proposed to explain the various thermodynamic anomies of water. It also has been proposed that such liquidâ€“liquid phase transition would exist in supercooled silicon. Computer simulation studies show that, across the transition, the diffusivity drops roughly 2 orders of magnitude, and the structures exhibit considerable tetrahedral ordering. The resulting phase is a highly viscous, low-density liquid silicon. Investigations on the atomic diffusion of such a novel form of liquid silicon are of high interest. Here we report such diffusion results from molecular dynamics simulations using themoreÂ Â» classical Stillingerâ€“Weber (SW) potential of silicon. We show that the atomic diffusion of the low-density liquid is highly correlated with local tetrahedral geometries. We also show that atoms diffuse through hopping processes within short ranges, which gradually accumulate to an overall random motion for long ranges as in normal liquids. There is a close relationship between dynamical heterogeneity and hopping process. We point out that the above diffusion mechanism is closely related to the strong directional bonding nature of the distorted tetrahedral network. Here, our work offers new insights into the complex behavior of the highly viscous low density liquid silicon, suggesting similar diffusion behaviors in other tetrahedral coordinated liquids that exhibit liquidâ€“liquid phase transition such as carbon and germanium.Â«Â less
Laidman, S.; Pangilinan, J.; Guillemin, R.; Yu, S.U.; Ohrwall, G.; Lindle, D.; Hemmers, O.
2002-01-01
Understanding the electronic structure of atoms and molecules is fundamental in determining their basic properties as well as the interactions that occur with different particles such as light. One such interaction is single photoionization; a process in which a photon collides with an atom or molecule and an electron with a certain kinetic energy is emitted, leaving behind a residual ion. Theoretical models of electronic structures use the dipole approximation to simplify x-ray interactions by assuming that the electromagnetic field of the radiation, expressed as a Taylor-series expansion, can be simplified by using only the first term. It has been known for some time that the dipole approximation becomes inaccurate at high photon energies, but the threshold at which this discrepancy begins is ambiguous. In order to enhance our understanding of these limitations, we measured the electron emissions of nitrogen. Beamline 8.0.1 at the Advanced Light Source was used with an electron Time-of-Flight (TOF) end station, which measures the time required for electrons emitted to travel a fixed distance. Data were collected over a broad range of photon energies (413 - 664 eV) using five analyzers rotated to 15 chamber angles. Preliminary analysis indicates that these results confirm the breakdown of the dipole approximation at photon energies well below 1 keV and that this breakdown is greatly enhanced in molecules just above the core-level ionization threshold. As a result, new theoretical models must be made that use higher order terms that were previously truncated.
Freeze, G.A.; Larson, K.W.; Davies, P.B.
1995-10-01
Eight alternative methods for approximating salt creep and disposal room closure in a multiphase flow model of the Waste Isolation Pilot Plant (WIPP) were implemented and evaluated: Three fixed-room geometries three porosity functions and two fluid-phase-salt methods. The pressure-time-porosity line interpolation method is the method used in current WIPP Performance Assessment calculations. The room closure approximation methods were calibrated against a series of room closure simulations performed using a creep closure code, SANCHO. The fixed-room geometries did not incorporate a direct coupling between room void volume and room pressure. The two porosity function methods that utilized moles of gas as an independent parameter for closure coupling. The capillary backstress method was unable to accurately simulate conditions of re-closure of the room. Two methods were found to be accurate enough to approximate the effects of room closure; the boundary backstress method and pressure-time-porosity line interpolation. The boundary backstress method is a more reliable indicator of system behavior due to a theoretical basis for modeling salt deformation as a viscous process. It is a complex method and a detailed calibration process is required. The pressure lines method is thought to be less reliable because the results were skewed towards SANCHO results in simulations where the sequence of gas generation was significantly different from the SANCHO gas-generation rate histories used for closure calibration. This limitation in the pressure lines method is most pronounced at higher gas-generation rates and is relatively insignificant at lower gas-generation rates. Due to its relative simplicity, the pressure lines method is easier to implement in multiphase flow codes and simulations have a shorter execution time.
Peru, S.; Goutte, H.
2008-04-15
Fully consistent axially-symmetric-deformed quasiparticle random phase approximation (QRPA) calculations have been performed, in which the same Gogny D1S effective force has been used for both the Hartree-Fock-Bogolyubov mean field and the QRPA approaches. Giant resonances calculated in deformed {sup 26-28}Si and {sup 22-24}Mg nuclei as well as in the spherical {sup 30}Si and {sup 28}Mg isotopes are presented. Theoretical results for isovector-dipole and isoscalar monopole, quadrupole, and octupole responses are presented and the impact of the intrinsic nuclear deformation is discussed.
Bellomo, Bruno; De Pasquale, Antonella; Gualdi, Giulia; Marzolino, Ugo
2010-12-15
We propose a procedure to fully reconstruct the time-dependent coefficients of convolutionless non-Markovian dissipative generators via a finite number of experimental measurements. By combining a tomography-based approach with a proper data sampling, our proposal allows to relate the time-dependent coefficients governing the dissipative evolution of a quantum system to experimentally accessible quantities. The proposed scheme not only provides a way to retrieve the full information about potentially unknown dissipative coefficients, but also, most valuably, can be employed as a reliable consistency test for the approximations involved in the theoretical derivation of a given non-Markovian convolutionless master equation.
Regnier, D.; Verriere, M.; Dubray, N.; Schunck, N.
2015-11-30
In this study, we describe the software package FELIX that solves the equations of the time-dependent generator coordinate method (TDGCM) in NN-dimensions (N â‰¥ 1) under the Gaussian overlap approximation. The numerical resolution is based on the Galerkin finite element discretization of the collective space and the Crankâ€“Nicolson scheme for time integration. The TDGCM solver is implemented entirely in C++. Several additional tools written in C++, Python or bash scripting language are also included for convenience. In this paper, the solver is tested with a series of benchmarks calculations. We also demonstrate the ability of our code to handle a realistic calculation of fission dynamics.
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Nazarov, Roman; Shulenburger, Luke; Morales, Miguel A.; Hood, Randolph Q.
2016-03-28
Diffusion Monte Carlo (DMC) calculations of the spectroscopic properties of a large set of molecules were performed, assessing the effect of different approximations. In systems containing elements with large atomic numbers, we show that the errors associated with the use of nonlocal mean-field-based pseudopotentials in DMC calculations can be significant and may surpass the fixed-node error. We suggest practical guidelines for reducing these pseudopotential errors, which allow us to obtain DMC-computed spectroscopic parameters of molecules and equation of state properties of solids in excellent agreement with experiment.