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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Repurposed dihydroorotate dehydrogenase inhibitors with efficacy against drug-resistant Acinetobacter baumannii

New antimicrobials are needed for the treatment of extensively drug-resistantAcinetobacter baumannii. The de novo pyrimidine biosynthetic enzyme dihydroorotate dehydrogenase (DHODH) is a validated drug target for malaria and human autoimmune diseases. Here, we provide genetic evidence thatA. baumanniiDHODH (AbDHODH) is essential for bacterial survival in rodent infection models. We chemically validate the target by repurposing a unique library of ~450 triazolopyrimidine/imidazopyrimidine analogs developed for our malaria DHODH program to identify 21 compounds with submicromolar activity onAbDHODH. The most potent (DSM186, DHODH IC 50 28 nM) had a minimal inhibitory concentration of ≤1 µg/ml against geographically diverseA. baumanniistrains, including meropenem-resistant isolates. A structurally related analog (DSM161) with a long in vivo half-life conferred significant protection in the neutropenic mouse thigh infection model. Encouragingly, the development of resistance to these compounds was not identified in vitro or in vivo. Lastly, the X-ray structure ofAbDHODH bound to DSM186 was solved to 1.4 Å resolution. These data support the potential ofAbDHODH as a drug target for the development of antimicrobials for the treatment ofA. baumanniiand potentially other high-risk bacterial infections.

Acinetobacter baumannii↗
DOE OSTI2023

30S subunit recognition and G1405 modification by the aminoglycoside-resistance 16S ribosomal RNA methyltransferase RmtC

Acquired ribosomal RNA (rRNA) methylation has emerged as a significant mechanism of aminoglycoside resistance in pathogenic bacterial infections. Modification of a single nucleotide in the ribosome decoding center by the aminoglycoside-resistance 16S rRNA (m 7 G1405) methyltransferases effectively blocks the action of all 4,6-deoxystreptamine ring-containing aminoglycosides, including the latest generation of drugs. To define the molecular basis of 30S subunit recognition and G1405 modification by these enzymes, we used a S-adenosyl-L-methionine analog to trap the complex in a postcatalytic state to enable determination of a global 3.0 Å cryo-electron microscopy structure of the m 7 G1405 methyltransferase RmtC bound to the mature Escherichia coli 30S ribosomal subunit. This structure, together with functional analyses of RmtC variants, identifies the RmtC N-terminal domain as critical for recognition and docking of the enzyme on a conserved 16S rRNA tertiary surface adjacent to G1405 in 16S rRNA helix 44 (h44). To access the G1405 N7 position for modification, a collection of residues across one surface of RmtC, including a loop that undergoes a disorder-to order transition upon 30S subunit binding, induces significant distortion of h44. This distortion flips G1405 into the enzyme active site where it is positioned for modification by two almost universally conserved RmtC residues. Further, these studies expand our understanding of ribosome recognition by rRNA modification enzymes and present a more complete structural basis for future development of strategies to inhibit m 7 G1405 modification to resensitize bacterial pathogens to aminoglycosides.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Temperature dependent striction effect in a single crystalline Nd 2 Fe 14 B revealed using a novel high temperature resistivity measurement technique

In this work, we studied the temperature dependence of resistivity in a single crystalline Nd 2 Fe 14 B using a newly developed high temperature probe. This novel probe employs mechanical pin connectors instead of conducting glue/paste. From warming and cooling curves, the Curie temperature was consistently measured around T c = 580 K. In addition, anomalous discrete jumps were found only in cooling curves between 400 and 500 K, but not shown in warming curves. More interestingly, when the jumps occurred during cooling, the resistivity was increased. This phenomenon could possibly be due to a temperature dependent striction effect induced by the re-orientation of magnetic domains well below the Curie temperature. Further microscopic study is needed to confirm this effect.

permanent magnet↗
DOE OSTI2023

On the relationship between the multi-region relaxed variational principle and resistive inner-layer theory

We show that the variational energy principle of the multi-region relaxed magnetohydrodynamic (MRxMHD) model can be used to predict finite-pressure linear tearing instabilities. In this model, the plasma volume is sliced into sub-volumes separated by 'ideal interfaces', and in each volume the magnetic field relaxes to a Taylor state, where the pressure gradient $\nabla p = 0$. The MRxMHD model is implemented in the Stepped-Pressure Equilibrium Code (SPEC) so that the equilibrium solution in each region is computed while preserving the force balance across the interfaces. As SPEC computes the Hessian matrix (a discretized stability matrix), the stability of an MRxMHD equilibrium can also be computed with SPEC. In this article, using SPEC, we investigate the effect of local pressure gradients and the $\nabla p = 0$ in the vicinity of the resonant surface of a tearing mode. For low-beta plasma, we have been able to illustrate a relationship between the resistive singular-layer theory (Coppi et al 1966 Nucl. Fusion6 101; Glasser et al 1975 Phys. Fluids18 875–88) and the MRxMHD model. Within the singular layer, the volume-averaged magnetic helicity and the flux-averaged toroidal flux are shown to be the invariants for the linear tearing modes in SPEC simulations. Our technique to compute MRxMHD stability is first tested numerically in a cylindrical tokamak and its application in toroidal geometry is demonstrated. We demonstrate an agreement between the stability boundary obtained with SPEC simulation and the resistive inner-layer theories.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Impact of toroidal rotation on the resistive ballooning modes in ASDEX Upgrade tokamak

Abstract In this work, we investigate the behavior of instabilities appearing between type-I edge localized modes (ELMs), with increasing neutral beam injection (NBI) power concomitant increase in toroidal rotation, and compare it to the modeling result of the linear magneto-hydrodynamic (MHD) code CASTOR3D. An injection of one NBI beam, increasing toroidal rotation, results in the mode slowing down from 12 kHz to 7 kHz, and its associated radial displacement decreases from 5 mm to 3.5 mm. In addition, modes shift radially outwards towards higher q , decreasing their poloidal mode numbers. The mode velocity is measured to be close to the E × B velocity with significant uncertainties. Through a set of CASTOR3D simulations with varying profiles, resistivity has been identified as the primary contributor to the growth rates. Only a small stabilizing effect due to toroidal rotation has been observed. While experimental results show a decrease of mode frequency with rotation, the opposite trend is observed in modeling. Reasons for discrepancies between modeling and experiment are discussed. Nevertheless, a main contributor to the mode frequency has been identified to be rotation velocity. CASTOR3D classifies modes as resistive ballooning modes as they do not appear unstable in ideal MHD.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Resistive wall mode stability and resonant field amplification in MAST high beta plasma

The n=1 (n is the toroidal mode number) resistive wall mode (RWM) instability and the resonant field amplification (RFA) due to a stable RWM response are numerically investigated for a MAST high-pressure plasma scenario, utilizing the MARS-F (Liu Y.Q. et al 2000 Phys. Plasmas 7 3681) and MARS-K (Liu Y.Q. et al 2008 Phys. Plasmas 15 112503) codes, for the purpose of understanding the potential RWM behavior in MAST-U plasmas. Ideal kink stability analysis identifies a target plasma, with parameters similar to that of the reference equilibrium reconstructed from a MAST high-pressure discharge, that accesses the RWM regime. The unstable n=1 RWM for the target equilibrium is subject to strong damping by the plasma toroidal flow and/or the drift kinetic effects from thermal particles. As a result, the mode is found to be stable under the experimental flow conditions, or even without flow stabilization if drift kinetic stabilization is included. The stability prediction is robust against variation of the assumed resistive wall minor radius. Active magneto-hydrodynamic (MHD) spectroscopy modeling, using the magnetic coils designed for controlling the edge localized modes (ELMs) in MAST-U as the antenna, shows strong resonant field amplification due to a stable RWM response in the target plasma. Maximal amplification, of 6-7 times larger than the applied vacuum field within the plasma, is obtained assuming a coil phasing of 120-180 degrees between the upper and lower rows of the ELM control coils. The MHD-kinetic hybrid model predicts generally higher RFA than the fluid model, in particular near the low-field and high-field sides of the plasma boundary surface. Furthermore, the MARS-F/K modeling thus shows that the RWM in MAST-U is subject to strong flow and kinetic stabilization, but can nevertheless be detected by active MHD spectroscopy.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Itinerant G-type antiferromagnet SrCr 2 As 2 studied by magnetization, heat capacity, electrical resistivity, and NMR measurements

Here, the physical properties of itinerant antiferromagnetic (AFM) SrCr 2 As 2 with body-centered tetragonal ThCr 2 Si 2 structure were investigated in single crystalline and polycrystalline forms by electrical resistivity ρ, heat capacity C p , magnetic susceptibility χ versus temperature T, and magnetization M versus applied magnetic field H isotherm measurements as well as 75 As and 53 Cr nuclear magnetic resonance (NMR) measurements in the wide temperature range T = 1.6–900 K. From the χ(T) and 75 As NMR measurements, the G-type AFM state below T N = 615(15) K has been determined, consistent with the previous neutron-diffraction measurements. Direct evidence of magnetic ordering of the Cr spins was shown by the observation of the 53 Cr NMR spectrum under H = 0. From the χ( T) measurements on single-crystal SrCr 2 As 2 under the two different magnetic field directions H|| ab and H || c in the AFM state, the Cr ordered moments are shown to align along the c axis in the G-type AFM state. The metallic state is directly evidenced by the ρ, C p , and NMR measurements, and the density of states at the Fermi energy $\mathscr{D}$(E F ) in the AFM state is estimated to be 7.53 states/eV f.u. for both spin directions which is almost twice the bare $\mathscr{D}$(E F ) estimated from first-principles calculations, suggesting an enhancement of the conduction-carrier mass by a factor of two in the AFM state. The $\mathscr{D}$(E F ) is found to be nearly constant below at least 100 K and is independent of H. The ρ(T) is found to show T-linear behavior above T N and exhibits positive curvature below T N where significant loss of spin-disorder scattering upon magnetic ordering is observed. The resistivity anisotropy of the compound remains moderate ρ c /ρ a ~ 9 through most of the magnetically ordered phase but shows a rapid increase below 50 K.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Two types of superconducting pairs in stripe-ordered La 2 - x Ba x CuO 4 ( x = 1 / 8 ) : Evidence from resistivity measurements

Recent angle-resolved c-axis resistivity measurements of the stripe-ordered La 2-x Ba x CuO 4 (LBCO) with x = 1/8 revealed an unexpected dependence on the direction of the in-plane magnetic field. We argue that these and other available data for the c-axis transport point to the existence of superconducting pairs of two different types in the x = 1/8 LBCO below the stripe ordering temperature. The pairs of one type carry finite momentum and are confined to the Cu-O planes; the pairs of other type (probably the conventional d wave with zero momentum) propagate along narrow conducting channels traversing the sample in the c-axis direction. The evidence for this comes from the observed exponential temperature dependence of the c-axis resistivity ρ c (T ) which we attribute to the thermally excited slips of the superconducting phase and flux flows. We present a simple theory to fit the observed π/2-periodic dependence of ρ c on the direction of the in-plane magnetic field and the other data.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Electronegative metal dopants improve switching variability in Al 2 ⁢O 3 resistive switching devices

Resistive random-access memories are promising for nonvolatile memory and brain-inspired computing applications. High variability and low yield of these devices are key drawbacks hindering reliable training of physical neural networks. In this paper, we show that doping an oxide electrolyte, Al 2 ⁢O 3 , with electronegative metals makes resistive switching significantly more reproducible, surpassing the reproducibility requirements for obtaining reliable hardware neuromorphic circuits. Based on density functional theory calculations, the underlying mechanism is hypothesized to be the ease of creating oxygen vacancies in the vicinity of electronegative dopants due to the capture of the associated electrons by dopant midgap states and the weakening of Al-O bonds. These oxygen vacancies and vacancy clusters also bind significantly to the dopant, thereby serving as preferential sites and building blocks in the formation of conducting paths. Throughout this work, we validate this theory experimentally by implanting different dopants over a range of electronegativities in devices made of multiple alternating layers of Al 2 ⁢O 3 and WN and find superior repeatability and yield with highly electronegative metals, Au, Pt, and Pd. These devices also exhibit a gradual SET transition, enabling multibit switching that is desirable for analog computing.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Differences in Printed Contacts Lead to Susceptibility of Silicon Cells to Series Resistance Degradation

Here, in this case study, we investigate a degradation mode occurring at the cell level in fielded multi-Si modules. The modules exhibit a mix of affected and unaffected cells. Affected cells show a progressive, series-resistance-related power degradation as shown via module- and cell-level IV curves, along with electroluminescence (EL) and PL imaging at the module, cell, and cell core sample scales. Scanning electron microscopy and energy-dispersive X-ray spectroscopy reveal a difference in the oxides in the silver paste used in screen printing of the gridline contacts. The paste in the affected cells is lead rich, whereas the paste in the unaffected cells is zinc rich. This suggests that the cells were screen printed with different silver paste compositions and possibly firing conditions, and that the different composition correlates with the susceptibility to degradation. Our results indicate degradation of the contact at the oxide-silver interface, causing a severe increase in series resistance across the cell that continues to progress over time.

14 SOLAR ENERGY↗
DOE OSTI2021

Low Thermal Resistance (0.5 K/W) Ga 2 O 3 Schottky Rectifiers With Double-Side Packaging

The low thermal conductivity of Ga 2 O 3 has arguably been the most serious concern for Ga 2 O 3 power and RF devices. Despite many simulation studies, there is no experimental report on the thermal resistance of a large-area, packaged Ga 2 O 3 device. This work fills this gap by demonstrating a 15-A double-side packaged Ga 2 O 3 Schottky barrier diode (SBD) and measuring its junction-to-case thermal resistance (R θJC ) in the bottom-side- and junction-side-cooling configurations. The R θJC characterization is based on the transient dual interface method, i.e., JEDEC 51-14 standard. The R θJC of the junction- and bottom-cooled Ga 2 O 3 SBD was measured to be 0.5 K/W and 1.43 K/W, respectively, with the former R θJC lower than that of similarly-rated commercial SiC SBDs. This low R θJC is attributable to the heat extraction directly from the Schottky junction instead of through the Ga 2 O 3 chip. Here, the R θJC lower than that of commercial SiC devices proves the viability of Ga 2 O 3 devices for high-power applications and manifest the significance of proper packaging for their thermal management.

42 ENGINEERING↗
DOE OSTI2021

Differences in c-Si Solar Cell Metallization and Susceptibility to Series Resistance Degradation

In this case study, we investigate a degradation mode occurring at the cell level in fielded multi-Si modules. Affected cells in the module show a progressive, series-resistance-related power degradation observed in module- and cell-level IV curves along with EL and PL imaging at the module, cell, and cell core sample scale. SEM and elemental analysis via EDS reveal a difference in the oxides in the silver paste used in screen printing of the finger contacts. This suggests that the cells were screen printed with different silver paste compositions and possibly firing conditions. One of these combinations leads to degradation of the contact at the interface between the cell and contact finger, causing severe series resistance across the cell that continues to progress over time.

acetic acid↗
DOE OSTI2022

New Total-Ionizing-Dose Resistant Data Storing Technique for NAND Flash Memory

This paper describes a new non-charge-based data storing technique in NAND flash memory called watermark that encodes read-only data in the form of physical properties of flash memory cells. Unlike traditional charge-based data storing method in flash memory, the proposed technique is resistant to total ionizing dose (TID) effects. To evaluate its resistance to irradiation effects, we analyze data stored in several commercial single-level-cell (SLC) flash memory chips from different vendors and technology nodes. These chips are irradiated using a Co-60 gamma-ray source array for up to 100 krad(Si) at Sandia National Laboratories. Experimental evaluation performed on a flash chip from Samsung shows that the intrinsic bit error rate (BER) of watermark increases from 0.8% for TID = 0 krad(Si) to 1% for TID = 100 krad(Si). Conversely, the BER of charge-based data stored on the same chip increases from 0% at TID = 0 krad(Si) to 1.5% at TID = 100 krad(Si). Overall, the results imply that the proposed technique may potentially offer significant improvements in data integrity relative to traditional charge-based data storage for very high radiation (TID > 100 krad(Si)) environments. These gains in data integrity relative to the charge-based data storage are useful in radiation-prone environments, but they come at the cost of increased write times and higher BERs before irradiation.

36 MATERIALS SCIENCE↗
DOE OSTI2020

A chromosome-scale reference genome of trifoliate orange ( Poncirus trifoliata ) provides insights into disease resistance, cold tolerance and genome evolution in Citrus

Trifoliate orange (Poncirus trifoliata), a deciduous close relative of evergreen Citrus, has important traits for citrus production, including tolerance/resistance to citrus greening disease (Huanglongbing, HLB) and other major diseases, and cold tolerance. It has been one of the most important rootstocks, and one of the most valuable sources of resistance and tolerance genes for citrus. Here we present a high-quality, chromosomescale genome assembly of P. trifoliata. The 264.9-Mb assembly contains nine chromosomal pseudomolecules with 25 538 protein-coding genes, covering 97.2% of the estimated gene space. Comparative analyses of P. trifoliata and nine Citrus genomes revealed 605 species-specific genes and six rapidly evolving gene families in the P. trifoliata genome. Poncirus trifoliata has evolved specific adaptation in the C-repeat/ DREB binding factor (CBF)-dependent and CBF-independent cold signaling pathways to tolerate cold. We identified candidate genes within quantitative trait loci for HLB tolerance, and at the loci for resistance to citrus tristeza virus and citrus nematode. Genetic diversity analysis of Poncirus accessions and Poncirus/ Citrus hybrids shows a narrow genetic base in the US germplasm collection, and points to the importance of collecting and preserving more natural genetic variation. Two phenotypically divergent Poncirus accessions are found to be clonally related, supporting a previous conjecture that dwarf Flying Dragon originated as a mutant of a non-dwarfing type. The high-quality genome reveals features and evolutionary insights of Poncirus, and it will serve as a valuable resource for genetic, genomic and molecular research and manipulation in citrus.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

The Role of Interfacial Thermal Resistance in Li-Ion Battery Thermal Management: Preprint

Temperature critically affects the performance, life and safety of lithium-ion batteries. Therefore, it is essential to understand heat generation and dissipation within individual battery cells and battery packs to plan a proper thermal management strategy. One of the key challenges is that interfacial heat transfer of a battery unit is difficult to quantify. The steady-state absolute method and the transient laser-flash-diffusivity method were employed to measure heat conductivities of battery layer stacks and individual battery layer separately. Results show flash diffusivity method gives higher thermal conductivity at both cross-plane and in-plane directions. The difference is primarily caused by interfacial thermal resistance so that it can be estimated by steady-state and transient measurements. To investigate the effects of interfacial thermal transport beyond individual cell level, a multiphysics battery model is used. The model is built upon a multi-scale multi-domain modeling framework for battery packs that accounts for the interplay across multiple physical phenomena. Benefits of a battery module using thermal management materials are quantified through numerical experiments. During a thermal runaway event, it is found interfacial thermal resistance can mitigate thermal runaway in a battery module by significantly reducing heat transfer between cells.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2025

Increasing the deuterated potassium dihydrogen phosphate crystal laser resistance by an additional conditioning with nanosecond pulses

Laser conditioning with 355-nm sub-nanosecond laser light is a well-known procedure to increase the bulk laser-induced damage resistance of deuterated potassium dihydrogen phosphate (DKDP) crystals. In this study, we investigate a new process to further increase the bulk damage resistance of DKDP crystals by performing additional conditioning with a 6.7-ns 355-nm laser after first conditioning with a 500-ps 355-nm laser. Here, damage tests (using both small and large beams) show that the second nanosecond conditioning raster increased the fluence required to produce the same density (large beam test) and probability (small beam test) of bulk damage by ∼30%.

Crystals↗
DOE OSTI2022

Disrupting the ArcA Regulatory Network Amplifies the Fitness Cost of Tetracycline Resistance in Escherichia coli

There is an urgent need for strategies to discover secondary drugs to prevent or disrupt antimicrobial resistance (AMR), which is causing >700,000 deaths annually. Here, we demonstrate that tetracycline-resistant (Tet R ) Escherichia coli undergoes global transcriptional and metabolic remodeling, including downregulation of tricarboxylic acid cycle and disruption of redox homeostasis, to support consumption of the proton motive force for tetracycline efflux. Using a pooled genome-wide library of single-gene deletion strains, at least 308 genes, including four transcriptional regulators identified by our network analysis, were confirmed as essential for restoring the fitness of Tet R E. coli during treatment with tetracycline. Targeted knockout of ArcA, identified by network analysis as a master regulator of this new compensatory physiological state, significantly compromised fitness of Tet R E. coli during tetracycline treatment. A drug, sertraline, which generated a similar metabolome profile as the arcA knockout strain, also resensitized Tet R E. coli to tetracycline. We discovered that the potentiating effect of sertraline was eliminated upon knocking out arcA, demonstrating that the mechanism of potential synergy was through action of sertraline on the tetracycline-induced ArcA network in the Tet R strain. Our findings demonstrate that therapies that target mechanistic drivers of compensatory physiological states could resensitize AMR pathogens to lost antibiotics.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Lasofoxifene as a potential treatment for therapy-resistant ER-positive metastatic breast cancer

Background: Endocrine therapy remains the mainstay of treatment for estrogen receptor-positive (ER+) breast cancer. Constitutively active mutations in the ligand binding domain of ERα render tumors resistant to endocrine agents. Breast cancers with the two most common ERα mutations, Y537S and D538G, have low sensitivity to fulvestrant inhibition, a typical second-line endocrine therapy. Lasofoxifene is a selective estrogen receptor modulator with benefits on bone health and breast cancer prevention potential. This study investigated the anti-tumor activity of lasofoxifene in breast cancer xenografts expressing Y537S and D538G ERα mutants. The combination of lasofoxifene with palbociclib, a CDK4/6 inhibitor, was also evaluated. Methods: Luciferase-GFP tagged MCF7 cells bearing wild-type, Y537S, or D538G ERα were injected into the mammary ducts of NSG mice (MIND model), which were subsequently treated with lasofoxifene or fulvestrant as single agents or in combination with palbociclib. Tumor growth and metastasis were monitored with in vivo and ex vivo luminescence imaging, terminal tumor weight measurements, and histological analysis. Results: As a monotherapy, lasofoxifene was more effective than fulvestrant at inhibiting primary tumor growth and reducing metastases. Adding palbociclib improved the effectiveness of both lasofoxifene and fulvestrant for tumor suppression and metastasis prevention at four distal sites (lung, liver, bone, and brain), with the combination of lasofoxifene/palbociclib being generally more potent than that of fulvestrant/palbociclib. X-ray crystallography of the ERα ligand binding domain (LBD) shows that lasofoxifene stabilizes an antagonist conformation of both wild-type and Y537S LBD. The ability of lasofoxifene to promote an antagonist conformation of Y537S, combined with its long half-life and bioavailability, likely contributes to the observed potent inhibition of primary tumor growth and metastasis of MCF7 Y537S cells. Conclusions: We report for the first time the anti-tumor activity of lasofoxifene in mouse models of endocrine therapy-resistant breast cancer. The results demonstrate the potential of using lasofoxifene as an effective therapy for women with advanced or metastatic ER+ breast cancers expressing the most common constitutively active ERα mutations.

60 APPLIED LIFE SCIENCES↗