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  1. Production rate measurement of Tritium and other cosmogenic isotopes in Germanium with CDMSlite

    Future direct searches for low-mass dark matter particles with germanium detectors, such as SuperCDMS SNOLAB, are expected to be limited by backgrounds from radioactive isotopes activated by cosmogenic radiation inside the germanium. There are limited experimental data available to constrain production rates and a large spread of theoretical predictions. We examine the calculation of expected production rates, and analyze data from the second run of the CDMS low ionization threshold experiment (CDMSlite) to estimate the rates for several isotopes. We model the measured CDMSlite spectrum and fit for contributions from tritium and other isotopes. Using the knowledge of the detector history, these results are converted to cosmogenic production rates at sea level. The production rates in atoms/(kgmore » $$\cdot$$day) are 74$$\pm$$9 for $^3$H, 1.5$$\pm$$0.7 for $$^{55}$$Fe, 17$$\pm$$5 for $$^{65}$$Zn, and 30$$\pm$$18 for $$^{68}$$Ge.« less
  2. One-step nonlinear electrochemical synthesis of Te x S y @PANI nanorod materials for Li-Te x S y battery

    As a promising cathode material for rechargeable lithium ion batteries, tellurium has attracted a great deal of attention due to its high conductivity and high theoretical capacity. Yet, the large volume expansion (~104 vol%) during Li-Te alloying process prevents the application of Li-Te battery. Here, by using a novel one-step nonlinear electrochemical approach, we prepared a TexSy@polyaniline nanorod composites, in which elemental sulfur is successfully embedded into tellurium matrix to effectively tackle the volumetric variation problem. In situ transmission electron microscopy (TEM) of the Li-Te (de)alloying process on single TexSy@polyaniline particle demonstrated that the volumetric variation was efficiently suppressed inmore » comparison to the situation of pristine Te particles. Moreover, polyaniline binder effectively trapped Te and sulfur species in its network and guaranteed stable electric contact and fast transport of Li ions, which resulted in significant improvement of the battery performance. Interestingly, the as-obtained composites display a high initial capacity of 1141 mA h g−1 with typical Li-S battery characteristics at a low current density of 0.1 A g−1 , while it shows a good cycling stability at high current density of 5 A g−1 with Li-Te battery features.« less
  3. Timescales of energy storage needed for reducing renewable energy curtailment

    Integrating large amounts of variable generation (VG) resources such as wind and solar into a region's power grid without causing significant VG curtailment will likely require increased system flexibility via changing grid operation and deploying enabling technologies such as energy storage. This article analyzes the storage duration required to reduce VG curtailment under high-VG scenarios. The three analysis scenarios assume VG provides 55% of the electricity demand in the largely isolated Electricity Reliability Council of Texas grid system in 2050, with three different proportions of wind and solar generation. Across the three scenarios, 11%-16% of VG energy is curtailed withoutmore » storage due to system-generation constraints. When 8.5 GW of storage capacity with 4 h of duration are added, curtailment is reduced to 8%-10% of VG. Additional storage duration further reduces curtailment, but with rapidly diminishing returns. At least half the potential avoided-curtailment benefits are realized with 8 h of storage, and the first 4 h provide the largest benefit. At VG penetrations up to 55%, there appears to be little incremental benefit in deploying very-long-duration or seasonal storage.« less
  4. Balancing Performance and Portability with Containers in HPC: An OpenSHMEM Example

    There is a growing interest in using Linux containers to streamline software development and application deployment. A container enables the user to bundle the salient elements of the software stack from an application’s perspective. In this paper, we discuss initial experiences in using the Open MPI implementation of OpenSHMEM with containers on HPC resources. We provide a brief overview of two container runtimes, Docker & Singularity, highlighting elements that are of interest for HPC users. The Docker platform offers a rich set of services that are widely used in enterprise environments, whereas Singularity is an emerging container runtime that ismore » specifically written for use on HPC systems. We describe our procedure for container assembly and deployment that strives to maintain the portability of the container-based application. We show performance results for the Graph500 benchmark running along the typical continuum of development testbed up to full production supercomputer (ORNL’s Titan). The results show consistent performance between the native and Singularity (container) tests. The results also showed an unexplained drop in performance when using the Cray Gemini network with Open MPI’s OpenSHMEM, which was unrelated to the container usage.« less
  5. Dynamics of recombination via conical intersection in a semiconductor nanocrystal

    The ultrafast dynamics of nonradiative recombination at dangling bond defects is elucidated by nanoscale multireferenceab initiomolecular dynamics simulations.
  6. Dynamic modification of pore opening of SAPO-34 by adsorbed surface methoxy species during induction of catalytic methanol-to-olefins reactions

    Here, we report that the pore opening of SAPO-34 can be significantly modified by an adsorbed surface methoxy species during induction of the catalytic methanol-to-olefins process, which offers molecular sieving properties due to physical obstacle of the methoxy group and its adsorption modification to other hydrocarbons. X-ray powder diffraction and Rietveld refinement clearly reveal that the adsorbed single carbon atom as the methoxy group is dynamically created from methanol dehydration on a Brønsted acid site in close proximity to the pore windows. As a result, industrial desirable smaller olefins such as ethylene and propylene can be favourably made at themore » expenses of higher olefins. The structures and fundamental understanding in alteration in the olefins selectivity during induction may allow rational optimisation in catalytic performance under the complex fluidisation conditions.« less
  7. Catalytic upgrading of biomass pyrolysis vapors and model compounds using niobia supported Pd catalyst

    This work addresses the effect of the support on the performance of Pd-based catalysts for hydrodeoxygenation of different model molecules (phenol, m-cresol, anisole, guaiacol) in the vapor phase at 573?K. The activity and the selectivity to deoxygenated products strongly depended on the support, regardless the model molecule. For HDO of phenol and m-cresol, benzene and toluene were the dominant products on niobia supported catalysts, whereas cyclohexanone and methylcyclohexanone were the main compounds formed on Pd/SiO2. For HDO of anisole, demethoxylation reaction producing benzene is favored over Pd/Nb2O5 catalyst, while demethylation is the preferred route over Pd/SiO2. Phenol and methanol weremore » the main products observed for HDO of guaiacol over all catalysts but significant formation of benzene was detected over Pd/Nb2O5. The improved deoxygenation performance over the niobia supported catalysts is explained in terms of the oxophilic sites represented by Nb4+/Nb5+ cations. These catalysts were also tested for HDO of pine pyrolysis vapors. All three catalysts were effective for reducing the total yield of oxygenated products. The extent of deoxygenation was highest over the Pd/Nb2O5 and Pd/NbOPO4 catalysts. The effectiveness of Pd/Nb2O5 and Pd/NbOPO4 for deoxygenation of real feeds is in good agreement with the model compound results and suggests that these catalysts are promising materials for the upgrading of pyrolysis vapors to produce hydrocarbon fuels.« less
  8. Carrier transport through the ultrathin silicon-oxide layer in tunnel oxide passivated contact (TOPCon) c-Si solar cells

    The carrier transport through the silicon-oxide (SiOx) layer in tunnel oxide passivated contact (TOPCon) c-Si solar cells has been studied experimentally and by simulation. The current intensity versus voltage (J-V) characteristics of GaIn/n-c-Si/SiOx/n+-poly-Si/Al structures shows a linear Ohmic characteristic, while a non-Ohmic behavior is observed in the samples without the n+-poly-Si contact layer. Conductive Atomic Force Microscopy (c-AFM) images reveal some current spikes on the surface of the samples, which could be related to the transport through pinholes. The simulation results show that 1) a rectification characteristic is obtained when only the tunneling mechanism is included, 2) both the reversemore » saturation current and the forward current increase when a small amount of transport through pinholes is introduced, and 3) finally a linear Ohmic behavior is observed when the pinhole transport component reaches a certain level. Furthermore, the simulation for whole TOPCon solar cells provides some useful results. For very thin SiOx (< 1.2 nm), the tunneling provides sufficient high tunneling probability and high efficiency TOPCon solar cells can be obtained without transport through pinholes if the passivation is ensured; while for a relatively thick SiOx (> 1.2 nm) without the transport through pinholes, the TOPCon solar cell shows a poor fill factor (FF) with a high series resistance (Rs) because the tunneling does not provide a sufficient high transport channel for carrier transport, and the introduction of a small number of transports through pinholes improves the FF and reduces the Rs, hence improves the PCE. However, a high possibility for carrier going through pinholes reduces all of the performance parameters and degrades PCE for all the cases simulated. Therefore, an optimized pinhole density and size distribution is critical engineering for solar cell performance optimization. However, the establishment of an optimized method to precisely control the pinhole formation and characterization is still on the way.« less
  9. Alkaline zirconates as effective materials for hydrogen production through consecutive carbon dioxide capture and conversion in methane dry reforming

    In this work, H 2 production was evaluated using different carbonation conditions and two alkaline zirconates. For this purpose, Li 2ZrO 3 and Na 2ZrO 3 were synthesized, characterized and tested on a consecutive process composed of initial CO 2 capture, followed by methane dry reforming (MDR). Thermogravimetric results showed that under the four gas mixtures tested (diluted and saturated CO 2, CO and CO-O 2), both ceramics are able to chemisorb CO 2, with Na2ZrO3 having the highest capture with saturated CO 2. In catalytic tests, ceramics carbonated with saturated CO 2 or CO-O 2 gas flows were ablemore » to act as sorbents and catalysts, producing H 2 at T > 750 °C through the partial oxidation of methane. This reaction was produced because CO2 desorption did not occur, thus avoiding the MDR process. On the other hand, carbonated ceramics under a CO-O2 gas mixture presented an outstanding catalytic performance. Between 450 and 750 °C, H 2 was formed through the MDR process promoted by CO 2 desorption from both ceramics. This result is in line with CO 2 desorption results, where a weaker CO 2–solid interaction was observed in comparison with saturated CO 22. Afterward, both ceramics presented a similar catalytic behavior, good regeneration and cyclability after the double process proposed (CO 2 capture-MDR reaction). Lithium zirconate also presented high thermal stability during cycle tests; meanwhile, sodium zirconate showed an important H 2 production increase as a function of cycles. Finally, both materials are feasible options for producing a clean energy source in a moderate temperature range through the catalytic conversion of two greenhouse gases (CO 2 and CH 4).« less
  10. Quantification of dissolved metals in high-pressure CO2-water solutions by underwater laser-induced breakdown spectroscopy

    This paper reports quantitative measurements of dissolved metals concentrations in CO2-water solutions by using underwater laser-induced breakdown spectroscopy (underwater LIBS). The CO2 pressure was varied over the range from 10 to 400 bar. The concentrations of naturally occurring elements of environmental significance such as Mg, Ca, Sr, Ba and Mn were determined by spectral analysis. Parametric dependence for improvement of underwater LIBS sensitivity was carried out. The results successfully demonstrate that low-ppm range concentrations of Mg2+, Ca2+, Sr2+, Ba2+ and Mn2+ can be accurately measured in CO2-laden water at varied pressure conditions by using underwater LIBS.
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