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At least 1,531 records · Page 85
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Drosophila models to study causative genes for human rare intractable neurological diseases

Highlights: • Drosophila models targeting some ALS-causing genes are described. • Drosophila models targeting some CMT-causing genes are described. • Drosophila models targeting some Sotos syndrome-causing genes are described. • Genes and pathways that commonly interact with ALS- and/or CMT-causing genes are described. Drosophila is emerging as a convenient model for investigating human diseases. Functional homologues of almost 75% of human disease-related genes are found in Drosophila. Amyotrophic lateral sclerosis (ALS) is a severe neurodegenerative disease that causes defects in motoneurons. Charcot-Marie-Tooth disease (CMT) is one of the most commonly found inherited neuropathies affecting both motor and sensory neurons. No effective therapy has been established for either of these diseases. In this review, after overviewing ALS, Drosophila models targeting several ALS-causing genes, including TDP-43, FUS and Ubiquilin2, are described with their genetic interactants. Then, after overviewing CMT, examples of Drosophila models targeting several CMT-causing genes, including mitochondria-related genes and FIG 4, are also described with their genetic interactants. In addition, we introduce Sotos syndrome caused by mutations in the epigenetic regulator gene NSD1. Lastly, several genes and pathways that commonly interact with ALS- and/or CMT-causing genes are described. In the case of ALS and CMT that have many causative genes, it may be not practical to perform gene therapy for each of the many disease-causing genes. The possible uses of the common genes and pathways as novel diagnosis markers and effective therapeutic targets are discussed.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

First-Principles Analysis of Defect Thermodynamics and Ion Transport in Inorganic SEI Compounds: LiF and NaF

The formation mechanism and composition of the solid electrolyte interphase (SEI) in lithium ion batteries has been widely explored. However, relatively little is known about the function of the SEI as a transport medium. Such critical information is directly relevant to battery rate performance, power loss, and capacity fading. To partially bridge this gap in the case of inorganic SEI compounds, we report herein the results of first-principles calculations on the defect thermodynamics, the dominant diffusion carriers, and the diffusion pathways associated with crystalline LiF and NaF, which are stable components of the SEI in Li-ion and Na-ion batteries, respectively. The thermodynamics of common point defects are computed, and the dominant diffusion carriers are determined over a voltage range of 0-4 V, corresponding to conditions relevant to both anode and cathode SEI's. Our analyses reveal that for both compounds, vacancy defects are energetically more favorable, therefore form more readily than interstitials, due to the close-packed nature of the crystal structures. However, the vacancy concentrations are very small for the diffusion processes facilitated by defects. Ionic conductivities are calculated as a function of voltage, considering the diffusion carrier concentration and the diffusion barriers as determined by nudged elastic band calculations. These conductivities are more than ten orders of magnitude smaller in NaF than in LiF. As compared to the diffusivity of Li in other common inorganic SEI compounds, such as Li2CO3 and Li2O,the cation diffusivity in LiF and NaF is quite low, with at least three orders of magnitude lower ionic conductivities. The results quantify the extent to which fluorides pose rate limitations in Li and Na batteries.

Yildirim, Handan↗
DOE OSTI2013

Frontiers, Opportunities, and Challenges in Biochemical and Chemical Catalysis of CO2

Our central premise is that catalytic scientists can learn by studying how these important metabolic processes occur in nature. Complementarily, biochemists can learn by studying how catalytic scientists view these same chemical transformations promoted by synthetic catalysts. From these studies, hypotheses can be developed and tested through manipulation of enzyme structure and by synthesizing simple molecular catalysts to incorporate different structural features of the enzymes. It is hoped that these studies will lead to new and useful concepts in catalyst design for fuel production and utilization. This paper describes the results of a workshop held to explore these concepts in regard to the development of new and more efficient catalytic processes for the conversion of CO2 to a variety of carbon-based fuels. The organization of this overview/review is as follows: 1) The first section briefly explores how interactions between the catalysis and biological communities have been fruitful in developing new catalysts for the reduction of protons to hydrogen, the simplest fuel generation reaction. 2) The second section assesses the state of the art in both biological and chemical reduction of CO2 by two electrons to form either carbon monoxide (CO) or formate (HCOO-). It also attempts to identify common principles between biological and synthetic catalysts and productive areas for future research. 3) The third section explores both biological and chemical processes that result in the reduction of CO2 beyond the level of CO and formate, again seeking to identify common principles and productive areas of future research. 4) The fourth section explores the formation of carbon-carbon bonds in biological and chemical systems in the same vein as the other sections. 5) A fifth section addresses the role of non-redox reactions of CO2 in biological systems and their role in carbon metabolism, with a parallel discussion of chemical systems. 6) In section 6, the topics of electrode modification, photochemical systems, and tandem catalysis are briefly discussed. These areas may be important for developing practical systems for CO2 reduction, and they share the common theme of coupling chemical reactions. 7) Section 7 describes some of the crosscutting activities that are critical for advancing the science underpinning catalyst development. 8) The last section attempts to summarize common issues in biological and chemical catalysis and to identify challenges that must be addressed to achieve practical catalysts that are suitable for the reduction of CO2 to fuels.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2019

Episodes of Warm-Air Advection Causing Cloud-Surface Decoupling During the MARCUS

It has been understood for decades that advection of a cloud-topped marine boundary layer (CTBL) over warmer sea surface causes the stratification (or decoupling) of the CTBL via the entrainment feedback, a mechanism commonly known as “deepening-warming” decoupling that is typical in subtropics. This study focuses on the opposite direction of advection, that is, low-level warm air advection (LLWAA), and its impacts on the decoupling degree of a CTBL. Our hypothesis is that LLWAA stabilizes a CTBL, causing a decoupling of the CTBL. It is tested for three LLWAA episodes observed during the Measurements of Aerosols, Radiation, and CloUds over the Southern Ocean (MARCUS) field campaign between the Hobart (43°S, 147°E), Australia, and several Antarctic coast stations. By synthesizing the shipborne measurements of CTBL structure, Himawari-8 satellite imagery of cloud fields, and reanalysis of meteorological field, four common characteristics of CTBLs under the LLWAA are found: (1) CTBLs are highly stratified to the extent that penetrations of cumulus into main temperature inversions, which are common for subtropical decoupled CTBLs, do not exist; (2) sea surface temperature is 1–2 K lower than the near-surface air temperature; (3) clouds manifest stratiform with lifetime as long as several tens of hours; and (4) they locate in warm sectors of middle-latitude cyclones. Possible mechanisms for the maintenance of decoupled clouds under LLWAA are discussed in terms of dynamic and thermodynamic factors. Lapse rates of the decoupled CTBLs are markedly lower than those commonly used for passive satellite estimation of cloud top heights.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

Metabolic and spatio-taxonomic response of uncultivated seafloor bacteria following the Deepwater Horizon oil spill

The release of 700 million liters of oil into the Gulf of Mexico over a few months in 2010 produced dramatic changes in the microbial ecology of the water and sediment. Here in this work, we reconstructed the genomes of 57 widespread uncultivated bacteria from post-spill deep-sea sediments, and recovered their gene expression pattern across the seafloor. These genomes comprised a common collection of bacteria that were enriched in heavily affected sediments around the wellhead. Although rare in distal sediments, some members were still detectable at sites up to 60 km away. Many of these genomes exhibited phylogenetic clustering indicative of common trait selection by the environment, and within half we identified 264 genes associated with hydrocarbon degradation. Alkane degradation ability was near ubiquitous among candidate hydrocarbon degraders, whereas just three harbored elaborate gene inventories for the degradation of alkanes and aromatic and polycyclic aromatic hydrocarbons (PAHs). Differential gene expression profiles revealed a spill-promoted microbial sulfur cycle alongside gene upregulation associated with PAH degradation. Gene expression associated with alkane degradation was widespread, although active alkane degrader identities changed along the pollution gradient. Finally, analyses suggest that a broad metabolic capacity to respond to oil inputs exists across a large array of usually rare indigenous deep-sea bacteria.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2013

Standardizng Data

To enable the rational design of nanomaterials for improved efficacy and safety, it is critical to understand and exploit the physicochemical properties that drive biological behavior (Morris, 2010). Data mining and computer simulation are essential for deriving information about nanomaterial behavior; however, the datasets needed to support such studies are sparse and stored across a variety of repositories and resources. Schrurs and Lison (2012) have expressed the need for more coherence and structure in the conduct of nanotechnology research. Additionally, the lack of common reporting standards and non-uniformity of information reported have proven to be significant barriers to such data sharing and re-use. The Nanotechnology Working Group (Nano WG), of the US National Institutes of Health National Cancer Informatics Program, has been focused on addressing these barriers. The Nano WG - which includes representatives from over 20 organizations including government agencies, academia, industry, standards organizations, and alliances -has developed ISA-TAB-Nano (Thomas et al, 2013), a general framework for representing and integrating diverse types of data related to the description and characterization of nanomaterials. Recognizing that nanoparticle characterization studies have many of the same challenges as ‘omics-based assays, the Nano WG joined the ISA Commons (Sansone et al., 2012) to leverage lessons learned in ‘omics data sharing. The ISA Commons community brings together 50 collaborators at over 30 scientific organizations around the globe, including regulatory and industrial participants in an increasingly diverse set of life science domains. At the core of the ISA Commons is the ISA metadata tracking framework which forms the basis for the ISA-TAB-Nano extension. The extension of the ISA framework to nanotechnology domain illustrates the power of a synergistic approach that seeks the interoperability of data across multiple research disciplines. To increase adoption, especially in the commercial arena from vendors and manufactures, the ISA-Tab-Nano data-sharing specification has also been submitted for consideration as a standard to the American Society for Testing and Materials (ASTM). Delivering a community-driven specification is only the first phase of the process. To be useful and used, ISA-TAB-Nano must be implemented by tools and databases to assist researchers in reporting their data accordingly, shielding them from unnecessary complexity. Our next step is to extend the open source ISA Software Suite to provide user-oriented tools for the collection, curation, and storage of data compliant with the ISA-TAB-Nano specification. Future work will also focus on the application of the ISA-TAB-Nano format to support emerging standards on minimal information about nanomaterials in biological research (Ostraat et al, 2012; MinChar). ISA-TAB-Nano development is a community-driven effort and we welcome new contributions, collaborations and domain expertise. We invite researchers, software developers, vendors, and other stakeholders to work with us to implement the ISA-Tab-Nano format in their existing systems and research. Likewise, we welcome engagement of regulators, funding agencies, editors, and other policy makers to discuss how this standard can be used to facilitate the sharing and reuse of nanotechnology data across a wide range of disciplines. More information about the ISA-TAB-Nano project can be found online at https://wiki.nci.nih.gov/display/ICR/ISA-TAB-Nano.

informatics↗
DOE OSTI2021

Solar cell contacts: quantifying the impact of interfacial layers on selectivity, recombination, charge transfer, and V oc

Interfacial layers (IFLs) are ubiquitous in solar cells, but their precise impact on carrier transfer rates and the relation of these rates to performance metrics and the concepts of selectivity and recombination is lacking. We report the use of a well-defined interdigitated back-contact (IBC) silicon solar cell to determine the precise role of such IFLs. We characterize the action of the common IFL spiro-OMeTAD by making it a third contact to the IBC cell. This architecture creates three solar cells within a single structure that, with numerical simulation, provide the exchange current densities (i.e., charge transfer rates) for electrons ( J 0n ) and holes ( J 0p ) and the quasi Fermi-level splitting in the absorber, which measures the balance of generation and recombination. Further, we describe the relation of V oc to contact recombination, the asymmetry in electron/hole collection rates at a single contact (contact selectivity), and the asymmetry in collection rates of the same carrier at separate contacts (carrier selectivity). Relative to bare gold, neat spiro-OMeTAD reduces J 0n and J 0p (their geometric mean ( J 0n J 0p ) 0.5 decreases by 10 4 ), decreasing contact recombination. Addition of the common dopant Li-TFSI and air increase J 0p / J 0n by 10 6 with little effect on ( J 0n J 0p ) 0.5 , increasing contact hole selectivity. The significant increase in V oc observed by introducing spiro-OMeTAD/Li-TFSI IFLs into the cells studied, however, is due to an increase in the carrier selectivity rather than the contact selectivity or recombination of the spiro-OMeTAD-modified contact. Operando measurements further show voltage-dependent changes in the J 0 s, demonstrating that spiro-OMeTAD contributes to hysteresis. Broader context : Solar cells operate by photogenerating excess charge carriers in an absorber material and, in competition with recombination, asymmetrically extracting them at so-called carrier-selective contacts, one that ideally collects only electrons and the other, only holes. Particularly in emerging photovoltaics such as perovskites, thin layers of organic semiconductors or related materials are introduced between the absorber and contact to improve power conversion efficiency. In terms of interfacial charge transfer, a prevailing view is that such interfacial layers improve performance by helping block the collection of the undesired carrier, considered a form of recombination. We use a novel platform to study the simultaneous impact of spiro-OMeTAD, a common interfacial layer, on the collection of electrons, the collection of holes, and on the recombination of electrons and holes. We quantitatively demonstrate that spiro-OMeTAD layers indeed passivate the contact toward recombination, but that larger improvements in the open-circuit voltage, a key cell metric, can come not only from this but also from increasing the asymmetry of the collection of electrons in the system. Further, operando measurements show transient changes in the properties of spiro-OMeTAD which suggest that it contributes to hysteresis phenomena commonly observed in perovskite and other solar cells.

36 MATERIALS SCIENCE↗
DOE OSTI2020

GaN‐based split phase transformer‐less PV inverter with auxiliary ZVT circuit

This paper explores performance enhancement of the common ground dynamic dc‐link (CGDL) inverter for single phase photovoltaic (PV) applications by a combination of gallium nitride (GaN) devices, split phase topology, coupled inductors, and zero voltage transition (ZVT) scheme. The CGDL inverter has the inherent advantage of minimised dc‐link capacitance and negligible leakage current due to the common ground configuration, but its reported efficiency was usually lower because of the higher dc‐link voltage used for the reduction of decoupling capacitance to a great extent. To solve the efficiency problem, in this study, a soft switching circuit is proposed for the first stage, while a coupled inductor integrated magnetics is incorporated in the second stage to reduce inductor loss, volume, and cost. Both of these topological improvements combined with the use of GaN devices facilitate in achieving high efficiency without compromising converter power density. Extensive experimental results are provided from a GaN based 1 kVA hardware prototype to demonstrate the superior performance of the CGDL inverter attaining a peak efficiency of 98.7% and a California Energy Commission efficiency of 98.5% at 75/50 kHz switching frequency.

Xia, Yinglai↗
DOE OSTI2013

Hydrodynamic simulations of long-scale-length two-plasmon-decay experiments at the Omega Laser Facility

Direct-drive-ignition designs with plastic CH ablators create plasmas of long density scale lengths (L{sub n} {>=} 500 {mu}m) at the quarter-critical density (N{sub qc}) region of the driving laser. The two-plasmon-decay (TPD) instability can exceed its threshold in such long-scale-length plasmas (LSPs). To investigate the scaling of TPD-induced hot electrons to laser intensity and plasma conditions, a series of planar experiments have been conducted at the Omega Laser Facility with 2-ns square pulses at the maximum laser energies available on OMEGA and OMEGA EP. Radiation-hydrodynamic simulations have been performed for these LSP experiments using the two-dimensional hydrocode draco. The simulated hydrodynamic evolution of such long-scale-length plasmas has been validated with the time-resolved full-aperture backscattering and Thomson-scattering measurements. draco simulations for CH ablator indicate that (1) ignition-relevant long-scale-length plasmas of L{sub n} approaching {approx}400 {mu}m have been created; (2) the density scale length at N{sub qc} scales as L{sub n}({mu}m) Asymptotically-Equal-To (R{sub DPP} Multiplication-Sign I{sup 1/4}/2); and (3) the electron temperature T{sub e} at N{sub qc} scales as T{sub e}(keV) Asymptotically-Equal-To 0.95 Multiplication-Sign {radical}(I), with the incident intensity (I) measured in 10{sup 14} W/cm{sup 2} for plasmas created on both OMEGA and OMEGA EP configurations with different-sized (R{sub DPP}) distributed phase plates. These intensity scalings are in good agreement with the self-similar model predictions. The measured conversion fraction of laser energy into hot electrons f{sub hot} is found to have a similar behavior for both configurations: a rapid growth [f{sub hot} Asymptotically-Equal-To f{sub c} Multiplication-Sign (G{sub c}/4){sup 6} for G{sub c} < 4] followed by a saturation of the form, f{sub hot} Asymptotically-Equal-To f{sub c} Multiplication-Sign (G{sub c}/4){sup 1.2} for G{sub c} {>=} 4, with the common wave gain is defined as G{sub c}=3 Multiplication-Sign 10{sup -2} Multiplication-Sign I{sub qc}L{sub n}{lambda}{sub 0}/T{sub e}, where the laser intensity contributing to common-wave gain I{sub qc}, L{sub n}, T{sub e} at N{sub qc}, and the laser wavelength {lambda}{sub 0} are, respectively, measured in [10{sup 14} W/cm{sup 2}], [{mu}m], [keV], and [{mu}m]. The saturation level f{sub c} is observed to be f{sub c} Asymptotically-Equal-To 10{sup -2} at around G{sub c} Asymptotically-Equal-To 4. The hot-electron temperature scales roughly linear with G{sub c}. Furthermore, to mitigate TPD instability in long-scale-length plasmas, different ablator materials such as saran and aluminum have been investigated on OMEGA EP. Hot-electron generation has been reduced by a factor of 3-10 for saran and aluminum plasmas, compared to the CH case at the same incident laser intensity. draco simulations suggest that saran might be a better ablator for direct-drive-ignition designs as it balances TPD mitigation with an acceptable hydro-efficiency.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Arbitrarily small amounts of correlation for arbitrarily varying quantum channels

As our main result show that in order to achieve the randomness assisted message and entanglement transmission capacities of a finite arbitrarily varying quantum channel it is not necessary that sender and receiver share (asymptotically perfect) common randomness. Rather, it is sufficient that they each have access to an unlimited amount of uses of one part of a correlated bipartite source. This access might be restricted to an arbitrary small (nonzero) fraction per channel use, without changing the main result. We investigate the notion of common randomness. It turns out that this is a very costly resource – generically, it cannot be obtained just by local processing of a bipartite source. This result underlines the importance of our main result. Also, the asymptotic equivalence of the maximal- and average error criterion for classical message transmission over finite arbitrarily varying quantum channels is proven. At last, we prove a simplified symmetrizability condition for finite arbitrarily varying quantum channels.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Tunable color parallel tandem organic light emitting devices with carbon nanotube and metallic sheet interlayers

Parallel tandem organic light emitting devices (OLEDs) were fabricated with transparent multiwall carbon nanotube sheets (MWCNT) and thin metal films (Al, Ag) as interlayers. In parallel monolithic tandem architecture, the MWCNT (or metallic films) interlayers are an active electrode which injects similar charges into subunits. In the case of parallel tandems with common anode (C.A.) of this study, holes are injected into top and bottom subunits from the common interlayer electrode; whereas in the configuration of common cathode (C.C.), electrons are injected into the top and bottom subunits. Both subunits of the tandem can thus be monolithically connected functionally in an active structure in which each subunit can be electrically addressed separately. Our tandem OLEDs have a polymer as emitter in the bottom subunit and a small molecule emitter in the top subunit. We also compared the performance of the parallel tandem with that of in series and the additional advantages of the parallel architecture over the in-series were: tunable chromaticity, lower voltage operation, and higher brightness. Finally, we demonstrate that processing of the MWCNT sheets as a common anode in parallel tandems is an easy and low cost process, since their integration as electrodes in OLEDs is achieved by simple dry lamination process.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Uncertainty quantification for generalized Langevin dynamics

Here, we present efficient finite difference estimators for goal-oriented sensitivity indices with applications to the generalized Langevin equation (GLE). In particular, we apply these estimators to analyze an extended variable formulation of the GLE where other well known sensitivity analysis techniques such as the likelihood ratio method are not applicable to key parameters of interest. These easily implemented estimators are formed by coupling the nominal and perturbed dynamics appearing in the finite difference through a common driving noise or common random path. After developing a general framework for variance reduction via coupling, we demonstrate the optimality of the common random path coupling in the sense that it produces a minimal variance surrogate for the difference estimator relative to sampling dynamics driven by independent paths. In order to build intuition for the common random path coupling, we evaluate the efficiency of the proposed estimators for a comprehensive set of examples of interest in particle dynamics. These reduced variance difference estimators are also a useful tool for performing global sensitivity analysis and for investigating non-local perturbations of parameters, such as increasing the number of Prony modes active in an extended variable GLE.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2017

Effect of HEH[EHP] impurities on the ALSEP solvent extraction process

In solvent extraction processes, organic phase impurities can negatively impact separation factors, hydrolytic performance, and overall system robustness. The resulting inconsistent performance can affect the process-level viability of a separation concept, and thus knowledge of the impurities present, their effects on the process, and how to remove them are vital. Deleterious impurities may be introduced into a system from reagent synthesis, or result from degradation via radiolysis and hydrolysis during use. In this work, the acidic extractant, 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (HEH[EHP])—proposed for application in extractive processes aimed at separating trivalent minor actinides from lanthanides and other fission products—is characterized with respect to its common impurities and their impact on Am(III) stripping in the Actinide Lanthanide SEParation (ALSEP) system. Furthermore, to control impurities in HEH[EHP], existing purification technologies commonly applied for the acidic organophosphorus reagent were assessed and a new chromatographic purification method specific to HEH[EHP] is presented.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Correction of the baseline fluctuations in the GEM-based ALICE TPC

To operate the ALICE Time Projection Chamber in continuous mode during the Run 3 and Run 4 data-taking periods of the Large Hadron Collider, the multi-wire proportional chamber-based readout was replaced with gas-electron multipliers. As expected, the detector performance is affected by the so-called common-mode effect, which leads to significant baseline fluctuations. A detailed study of the pulse shape with the new readout has revealed that it is also affected by ion tails. Since reconstruction and data compression are performed fully online, these effects must be corrected at the hardware level in the FPGA-based common readout units. The characteristics of the common-mode effect and of the ion tail, as well as the algorithms developed for their online correction, are described in this paper. The common-mode dependencies are studied using machine-learning techniques. Toy Monte Carlo simulations are performed to illustrate the importance of online corrections and to investigate the performance of the developed algorithms.

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

A new pinnotherid crab of the genus Pinnixulala Palacios Theil, Cuesta & Felder, 2016 from uncertain infaunal hosts in the northern Gulf of Mexico, with a rediagnosis and updated synonymy for the polychaete symbiont Pinnixulala retinens (Rathbun, 1918) (Decapoda: Brachyura: Pinnotheridae)

Abstract A new infaunal pinnotherid crab, Pinnixulala heardin. sp., is described from muddy substrates of the middle to inner continental shelf of the northern Gulf of Mexico. Molecular genetic analysis supports its separation from P. retinens (Rathbun, 1918), the only other western Atlantic member of the genus and a species most commonly found living as a symbiont of large polychaete worms. Both western Atlantic species are clearly separated from several described and undescribed populations of congeners occurring along shorelines of the eastern Pacific. We herein include a rediagnosis of P. retinens to facilitate morphological comparisons with P. heardin. sp. Unlike P. retinens, which is more common in shallow inshore waters and reaches larger sizes, the new species lacks development of a strong distally directed spine on the fourth pereopod ischium and has chelae that are at least as heavily developed as the second and third pereopods. In addition, the mature male first gonopods in P. heardin. sp. are tapered over their terminal one-third and directed distally, rather than being curved in their terminal one-third with the tips directed mesially, as they are in P. retinens. The new species is invariably collected from samples including infaunal worms and other invertebrates, but the specific hosts remain to be determined

Marine & Freshwater Biology↗
DOE OSTI2023

Assessment of exchange-correlation functionals on oxygen vacancy formation energies of metal oxides

Oxygen vacancies are a common defect in oxides and play vital roles in many technological applications such as oxygen separation, catalytic reactors, solid oxide fuel cells, and solar thermochemical water splitting. The oxygen vacancy formation energy is directly related to the oxide reduction enthalpy and the vacancy concentration and, therefore, is a key quantity underlying these applications. The complexity of measuring oxygen vacancy formation energies experimentally suggests the utility of calculations based on density functional theory (DFT). However, the calculated results are strongly dependent on the exchange-correlation functionals and other parameters such as the Hubbard U . In this work, we compare the performance of the meta-GGA strongly constrained and appropriately normed (SCAN) functional and the commonly used semilocal generalized gradient approximation (GGA) functionals with experimental values of structural parameters, band gaps, magnetic structures, and oxygen vacancy formation energies for six representative oxides, i.e., CaMnO 3 , SrMnO 3 , LaMnO 3 , YMnO 3 , LaFeO 3 , and CeO 2 . Further, our results show that SCAN usually has better agreement with the experimental lattice constants and band gaps and larger magnetic moments than the commonly used GGA functionals. Although SCAN overestimates the oxygen vacancy formation energies of transition metal oxides and therefore requires unusually large Hubbard U values to reproduce the experimental reduction enthalpies, it does predict the correct oxygen vacancy formation energy of CeO 2 , which challenges the commonly used GGA and hybrid functionals. Our results underscore the challenges that exist in describing these complex oxides by DFT and may shed light on developing more accurate exchange-correlation functionals for oxygen vacancy formation energy calculations.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Determination of Series Resistance in CdSeTe/CdTe Solar Cells by the Jsc–Voc Method

While commonly used in Si solar cell characterization, the Suns–Voc method of determining series resistance (Rs) is rarely used for CdTe and its alloys. However, it is advantageous relative to the slope method—commonly used in the CdTe community—because it measures series resistance at the maximum power point, at which a solar cell operates. Using the self-consistent predecessor to Suns–Voc, Jsc –Voc, , we determine Rs of two different CdSeTe/CdTe solar cell structures to be 0.96 and 2.72 Ωcm2, with repeated measurements showing little deviation

13 HYDRO ENERGY↗
DOE OSTI2019

Modeling Load Dynamics to Support Resiliency-based Operations in Low-Inertia Microgrids

Microgrids have repeatedly demonstrated the ability to provide uninterrupted service to critical end-use loads during normal outages, severe weather events, and natural disasters. While their ability to provide critical services is well documented, microgrids present a more dynamic operational environment than grid-connected distribution systems. The dynamics of a microgrid are commonly driven by the high inertia of rotating generators, which are common in many microgrids. In such high-inertia systems, the impact of end-use load dynamics are often not examined. However, with the increased penetration of inverter-based generation with little or no inertia, it is necessary to consider the impact that the dynamics of the end-use loads have on the operations of microgrids, particularly for a resiliency-based operation. These operations include, but are not limited to, switching operations, loss of generating units, and the starting of induction motors. This paper examines the importance of including dynamic models of the end-use load when evaluating the operations of low inertia microgrids, and shows that by properly representing their behavior, it is possible to cost effectively size equipment while supporting resilient operations of critical end-use loads.

Tuffner, Francis K.↗