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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 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Thermoelectric properties of DC-sputtered filled skutterudite thin film

The Yb filled CoSb{sub 3} skutterudite thermoelectric thin films were prepared by DC magnetron sputtering. The electrical conductivity, Seebeck coefficient, thermal conductivity, and figure of merit ZT of the samples are characterized in a temperature range of 300 K to 700 K. X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy are obtained to assess the phase composition and crystallinity of thin film samples at different heat treatment temperatures. Carrier concentrations and Hall mobilities are obtained from Hall Effect measurements, which provide further insight into the electrical conductivity and Seebeck coefficient mechanisms. The thermal conductivity of thin film filled skutterudite was found to be much less compared with bulk Yb filled CoSb{sub 3} skutterudite. In this work, the 1020 K heat treatment was adopted for thin film post process due to the high degree of crystallinity as well as avoiding reverse heating effect. Thin film samples of different thicknesses were prepared with the same sputtering deposition rate and maximum ZT of 0.48 was achieved at 700 K for the 130 nm thick sample. This value was between half and one third of the bulk figure of merit which was due to the lower Hall mobility.

36 MATERIALS SCIENCE↗
DOE OSTI2019

GENE-43. Targeting GABPb1L Inhibits In Vivo Growth of TERT Promoter Mutant Glioblastoma

Understanding cancer cell immortality in primary glioblastoma (GBM) is essential for the development of more informed treatments. Multiple cancer types, including >80% of GBMs, undergo immortalization by reactivating Telomerase Reverse Transcriptase (TERT) through acquired mutations in the TERT promoter. TERT, the catalytically active and rate-limiting subunit of telomerase, functions to maintain telomeres, which cap and protect the ends of chromosomes. Our previous work has demonstrated that the transcription factor GABP - and specifically its tetramer-forming isoform GABPb1L - binds and activates the mutant TERT promoter. The generation of CRISPR-induced indels in GABPb1L results in a gradual loss of cell viability in TERT promoter mutant but not TERT promoter wild type tumor cells in vitro, but the extent to which GABPb1L function is compromised in this setting is unclear. Thus, the potential for use of GABPb1L as an effective therapeutic target for TERT promoter mutant GBM requires further investigation. Here, we use CRISPR-based strategies to demonstrate that full knockout of GABPb1L is rapidly lethal in TERT promoter mutant cells in vitro, in association with a decrease in both TERT mRNA and telomerase activity. Heterozygous deletion of GABPb1L in the context of TERT promoter mutations leads to slowed growth of orthotopic xenograft tumors in mice, and prolonged survival. Additionally, inducible RNAi-mediated inhibition of GABPb1L in growing tumors is also capable of decreasing tumor burden and increasing survival, further strongly suggesting that targeting GABPb1L in patient tumors could be a viable treatment strategy. Finally, reduced GABPb1L synergizes with temozolomide (TMZ) therapy such that TMZ treatment in the context of low GABPb1L and low TERT leads to a complete ablation of orthotopic GBM xenografts. These results highlight the potential to improve disease outcomes by targeting TERT through inhibition of GABPb1L, particularly in conjunction with TMZ treatment.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2013

Dependence on proton energy of degradation of AlGaN/GaN high electron mobility transistors

The effects of proton irradiation energy on dc, small signal, and large signal rf characteristics of AlGaN/GaN high electron mobility transistors (HEMTs) were investigated. AlGaN/GaN HEMTs were irradiated with protons at fixed fluence of 51015/cm2 and energies of 5, 10, and 15 MeV. Both dc and rf characteristics revealed more degradation at lower irradiation energy, with reductions of maximum transconductance of 11%, 22%, and 38%, and decreases in drain saturation current of 10%, 24%, and 46% for HEMTs exposed to 15, 10, and 5MeV protons, respectively. The increase in device degradation with decreasing proton energy is due to the increase in linear energy transfer and corresponding increase in nonionizing energy loss with decreasing proton energy in the active region of the HEMTs. After irradiation, both subthreshold drain leakage current and reverse gate current decreased more than 1 order of magnitude for all samples. The carrier removal rate was in the range 121 336 cm1 over the range of proton energies employed in this study

Liu, L.↗
DOE OSTI2015

Agent-based model forecasts aging of the population of people who inject drugs in metropolitan Chicago and changing prevalence of hepatitis C infections

People who inject drugs (PWID) are at high risk for blood-borne pathogens transmitted during the sharing of contaminated injection equipment, particularly hepatitis C virus (HCV). HCV prevalence is influenced by a complex interplay of drug-use behaviors, social networks, and geography, as well as the availability of interventions, such as needle exchange programs. To adequately address this complexity in HCV epidemic forecasting, we have developed a computational model, the Agent-based Pathogen Kinetics model (APK). APK simulates the PWID population in metropolitan Chicago, including the social interactions that result in HCV infection. We used multiple empirical data sources on Chicago PWID to build a spatial distribution of an in silico PWID population and modeled networks among the PWID by considering the geography of the city and its suburbs. APK was validated against 2012 empirical data (the latest available) and shown to agree with network and epidemiological surveys to within 1%. For the period 2010–2020, APK forecasts a decline in HCV prevalence of 0.8% per year from 44(±2)% to 36(±5)%, although some sub-populations would continue to have relatively high prevalence, including Non-Hispanic Blacks, 48(±5)%. The rate of decline will be lowest in Non-Hispanic Whites and we find, in a reversal of historical trends, that incidence among non-Hispanic Whites would exceed incidence among Non-Hispanic Blacks (0.66 per 100 per years vs 0.17 per 100 person years). APK also forecasts an increase in PWID mean age from 35(±1) to 40(±2) with a corresponding increase from 59(±2)% to 80(±6)% in the proportion of the population >30 years old. Our research highlight the importance of analyzing sub-populations in disease predictions, the utility of computer simulation for analyzing demographic and health trends among PWID and serve as a tool for guiding intervention and prevention strategies in Chicago, and other major cities.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1985

A mixed pseudospectral/finite difference method for a thermally driven fluid in a nonuniform gravitational field

A numerical study of the steady, axisymmetric flow in a heated, rotating spherical shell is conducted to model the Atmospheric General Circulation Experiment (AGCE) proposed to run aboard a later shuttle mission. The AGCE will consist of concentric rotating spheres confining a dielectric fluid. By imposing a dielectric field across the fluid a radial body force will be created. The numerical solution technique is based on the incompressible Navier-Stokes equations. In the method a pseudospectral technique is based on the incompressible Navier-Stokes equations. In the method a pseudospectral technique is used in the latitudinal direction, and a second-order accurate finite difference scheme discretizes time and radial derivatives. This paper discusses the development and performance of this numerical scheme for the AGCE which has been modelled in the past only by pure FD formulations. In addition, previous models have not investigated the effect of using a dielectric force to simulate terrestrial gravity. The effect of this dielectric force on the flow field is investigated as well as a parameter study of varying rotation rates and boundary temperatures. Among the effects noted are the production of larger velocities and enhanced reversals of radial temperature gradients for a body force generated by the electric field.

Macaraeg, M. G.↗
NASA NTRS1985

A mixed pseudospectral/finite difference method for a thermally driven fluid in a nonuniform gravitational field

A numerical study of the steady, axisymmetric flow in a heated, rotating spherical shell is conducted to model the Atmospheric General Circulation Experiment (AGCE) proposed to run aboard a later Shuttle mission. The AGCE will consist of concentric rotating spheres confining a dielectric fluid. By imposing a dielectric field across the fluid a radial body force will be created. The numerical solution technique is based on the incompressible Navier-Stokes equations. In the method a pseudospectral technique is used in the latitudinal direction, and a second-order accurate finite difference scheme discretizes time and radial derivatives. This paper discusses the development and performance of this numerical scheme for the AGCE which has been modeled in the past only by pure FD formulations. In addition, previous models have not investigated the effect of using a dielectric force to simulate terrestrial gravity. The effect of this dielectric force on the flow field is investigated as well as a parameter study of varying rotation rates and boundary temperatures. Among the effects noted are the production of larger velocities and enhanced reversals of radial temperature gradients for a body force generated by the electric field.

Macaraeg, M. G.↗
NASA NTRS1991

Two-Phase Bidirectional Heat Exchanger

Heat exchanger transfers heat from one two-phase thermal loop to another. Condenses vapor in one loop while evaporating liquid in other. Transfers heat with very small drops in temperature and pressure, and efficiently joins heat pipes thermally without mixing of their working fluids. Several such heat exchangers used to build long, complex multiloop heat-control systems. Exchanger bidirectional: transfers heat in reverse, condensing on normally evaporating side, and vice versa. Can warm equipment it normally cools, without using auxiliary heater. In reverse transfer, wicks on evaporating side supply liquid continuously by capillary action; reverse-flow pump not needed. Design modified for other working fluids and larger heat-transfer rates.

Kroliczek, Edward↗
NASA NTRS1990

The multidriver: A reliable multicast service using the Xpress Transfer Protocol

A reliable multicast facility extends traditional point-to-point virtual circuit reliability to one-to-many communication. Such services can provide more efficient use of network resources, a powerful distributed name binding capability, and reduced latency in multidestination message delivery. These benefits will be especially valuable in real-time environments where reliable multicast can enable new applications and increase the availability and the reliability of data and services. We present a unique multicast service that exploits features in the next-generation, real-time transfer layer protocol, the Xpress Transfer Protocol (XTP). In its reliable mode, the service offers error, flow, and rate-controlled multidestination delivery of arbitrary-sized messages, with provision for the coordination of reliable reverse channels. Performance measurements on a single-segment Proteon ProNET-4 4 Mbps 802.5 token ring with heterogeneous nodes are discussed.

Dempsey, Bert J.↗
NASA NTRS2012

Explaining Polarization Reversals in STEREO Wave Data

Recently Breneman et al. reported observations of large amplitude lightning and transmitter whistler mode waves from two STEREO passes through the inner radiation belt (L<2). Hodograms of the electric field in the plane transverse to the magnetic field showed that the transmitter waves underwent periodic polarization reversals. Specifically, their polarization would cycle through a pattern of right-hand to linear to left-hand polarization at a rate of roughly 200 Hz. The lightning whistlers were observed to be left-hand polarized at frequencies greater than the lower hybrid frequency and less than the transmitter frequency (21.4 kHz) and right-hand polarized otherwise. Only righthand polarized waves in the inner radiation belt should exist in the frequency range of the whistler mode and these reversals were not explained in the previous paper. We show, with a combination of observations and simulated wave superposition, that these polarization reversals are due to the beating of an incident electromagnetic whistler mode wave at 21.4 kHz and linearly polarized, symmetric lower hybrid sidebands Doppler-shifted from the incident wave by +/-200 Hz. The existence of the lower hybrid waves is consistent with the parametric decay mechanism of Lee and Kuo whereby an incident whistler mode wave decays into symmetric, short wavelength lower hybrid waves and a purely growing (zero-frequency) mode. Like the lower hybrid waves, the purely growing mode is Doppler-shifted by 200 Hz as observed on STEREO. This decay mechanism in the upper ionosphere has been previously reported at equatorial latitudes and is thought to have a direct connection with explosive spread F enhancements. As such it may represent another dissipation mechanism of VLF wave energy in the ionosphere and may help to explain a deficit of observed lightning and transmitter energy in the inner radiation belts as reported by Starks et al.

Breneman, A.↗
NASA NTRS1997

Kinetics and Thermochemistry of Reversible Adduct Formation in the Reaction of Cl((sup 2)P(sub J)) with CS2

Reversible adduct formation in the reaction of Cl((sup 2)P(sub J)) with CS2 has been observed over the temperature range 193-258 K by use of time-resolved resonance fluorescence spectroscopy to follow the decay of pulsed-laser-generated Cl((sup 2)P(sub J)) into equilbrium with CS2Cl. Rate coefficients for CS2Cl formation and decomposition have been determined as a function of temperature and pressure; hence, the equilbrium constant has been determined as a function of temperature. A second-law analysis of the temperature dependence of Kp and heat capacity corrections calculated with use of an assumed CS2Cl structure yields the following thermodynamic parameters for the association reaction: Delta-H(sub 298) = -10.5 +/- 0.5 kcal/mol, Delta-H(sub 0) = -9.5 +/- 0.7 kcal/mol, Delta-S(sub 298) = -26.8 +/- 2.4 cal/mol.deg., and Delta-H(sub f,298)(CS2Cl) = 46.4 +/- 0.6 kcal/mol. The resonance fluorescence detection scheme has been adapted to allow detection of Cl((sup 2)P(sub J)) in the presence of large concentrations of O2, thus allowing the CS2Cl + Cl + O2 reaction to be investigated. We find that the rate coefficient for CS2Cl + O2 reaction via all channels that do not generate Cl((sup 2)P(sub J)) is less than 2.5 x 10(exp-16) cu cm/(molecule.s) at 293 K and 300-Torr total pressure and that the total rate coefficient is less than 2 x 10 (exp -15) cu cm/(molecule.s) at 230 K and 30-Torr total pressure. Evidence for reversible adduct formation in the reaction of Cl((sup 2)P(sub J)) with COS was sought but not observed, even at temperatures as low as 194 K.

Nicovich, J. M.↗
DOE OSTI2026

Dynamic Nanocrystal-Ligand Boundaries: Reversible Photoinduced Ligand Detachment from Quantum Dots in Solution

The porosity of ligand shells of colloidal quantum dots (QDs) can influence the overall rate and yield of charge transfer processes occurring at their surfaces. However, the density of ligand shells on QDs can also influence their colloidal and photochemical stability. We used time-resolved infrared spectroscopy to show that photoinduced ligand detachment, the tendency for certain ligands to detach from QD surfaces when the nanocrystals are promoted to their excitonic excited states, can be used to transiently enhance the porosity of oleic acidpassivated CdSe QDs in solution. Furthermore, we synthesized CdSe QDs with varying ligand shell densities to examine the corresponding influence that van der Waals interactions among ligands have on the yield of photoinduced ligand detachment and the time scale on which ligands return to QD surfaces. We observed that oleic acid ligands on CdSe QDs with lower shell densities have a higher probability of escape for longer periods of time. Despite this, oleic acid ligands on fully passivated CdSe QDs are still able to photodetach, resulting in a transient increase of their ligand shell porosity. In contrast, QDs with multilayer ligand coronas exhibit negligible photoinduced ligand detachment because the outer molecular layers introduce a type of cage effect, preventing the escape of the interior ligands. Our findings suggest the intriguing possibility that photoinduced ligand detachment can be used to transiently decrease the density of ligand shells of QDs to facilitate charge transfer processes while still allowing them to be fully passivated between excitation events for photochemical and colloidal stability.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1987

Hyperbaric hyperoxia reversibly inhibits erythrocyte phospholipid fatty acid turnover

The effect of hyperbaric hyperoxia on the acylation of membrane phospholipid was studied by measuring the rates of activation of exogenous tritiated oleic acid to acyl thioester and of transesterification of the thioester into membrane phospholipids in intact human erythrocytes obtained 1 h after an exposure of the subjects to a hyperbaric oxygen atmosphere (3.5 h, 100 pct O2, 3 ATA). Exposure to pure oxygen was found to inhibit both the acylation and transesterification reactions by more than 30 percent, with partial recovery detected 24 h later. On the other hand, no rate changes were observed when isolated membranes from the same batches of cells were used in similar experiments. It is suggested that the decrease in the incorporation of tritiated oleic acid after hyperbaric hyperoxia may reflect an early event in the pathogenesis of oxygen-induced cellular injury and that it may be a useful index for the assessment of the tolerance of tissues to hyperoxia.

Dise, Craig A.↗
DOE OSTI2019

Hysteresis as a probe of turbulent bifurcation in intrinsic rotation reversals on Alcator C-Mod

Analysis and modeling of a new set of rotation reversal hysteresis experiments unambiguously show that changes in turbulence are responsible for the intrinsic rotation reversal and the linear to saturated ohmic confinement (LOC/SOC) transition on Alcator C-Mod. Plasmas on either side of the reversal exhibit different toroidal rotation profiles and therefore different turbulence characteristics despite profiles of density and temperature that are indistinguishable within measurement uncertainty. The deactivation of subdominant (in linear growth rate and heat transport) ion-temperature gradient and trapped electron mode-like instabilities in a mixedmode state is identified as the only possible change in turbulence within a quasilinear transport approximation across the reversal which is consistent with the measured profiles and the inferred heat and particle fluxes. This indicates an explanation for the LOC/SOC transition that provides a mechanism for hysteresis through the dynamics of subdominant modes and changes in their relative populations, and does not involve a change in most (linearly) unstable ion-scale drift-wave instability.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Mechanism and Kinetics of Propane Dehydrogenation and Cracking over Ga/H-MFI Prepared via Vapor-Phase Exchange of H-MFI with GaCl 3

In this study, the mechanism and kinetics of C 3 H 8 dehydrogenation and cracking are examined over Ga/H-MFI catalysts prepared via vapor-phase exchange of H-MFI with GaCl 3 . The present study demonstrates that [GaH] 2+ cations are the active centers for C 3 H 8 dehydrogenation and cracking, independent of the Ga/Al ratio. For identical reaction conditions, [GaH] 2+ cations in Ga/H-MFI exhibit a turnover frequency for C 3 H 8 dehydrogenation that is 2 orders of magnitude higher and for C 3 H 8 cracking, that is 1 order of magnitude higher than the corresponding turnover frequencies over H-MFI. C 3 H 8 dehydrogenation and cracking exhibit first-order kinetics with respect to C 3 H 8 over H-MFI, but both reactions exhibit first-order kinetics over Ga/H-MFI only at very low C 3 H 8 partial pressures and zero-order kinetics at higher C 3 H 8 partial pressures. H 2 inhibits both reactions over Ga/H-MFI. It is also found that the ratio of the rate of dehydrogenation to the rate of cracking over Ga/H-MFI is independent of C 3 H 8 and H 2 partial pressures but weakly dependent on temperature. Measured activation enthalpies together with theoretical analysis are consistent with a mechanism in which both the dehydrogenation and cracking of C 3 H 8 proceed over Ga/H-MFI via reversible, heterolytic dissociation of C 3 H 8 at [GaH] 2+ sites to form [C 3 H 7 -GaH] + -H + cation pairs. The rate-determining step for dehydrogenation is the β-hydride elimination of C 3 H 6 and H 2 from the C 3 H 7 fragment. The rate-determining step for cracking is C-C bond attack of the same propyl fragment by the proximal Brønsted acid O-H group. H 2 inhibits both dehydrogenation and cracking over Ga/H-MFI via reaction with [GaH] 2+ cations to form [GaH 2 ] + -H + cation pairs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

High Energy-Density and Reversibility of Iron Fluoride Cathode Enabled Via an Intercalation-Extrusion Reaction

Iron fluoride, an intercalation-conversion cathode for lithium ion batteries, promises a high theoretical energy density of 1922 Wh Kg –1 . However, poor electrochemical reversibility due to repeated breaking/reformation of metal-fluoride bonds poses a grand challenge for its practical application. Here we report that both a high reversibility over 1000 cycles and a high capacity of 420 mAh g –1 can be realized by concerted doping of cobalt and oxygen into iron fluoride. In the doped nanorods, an energy density of ~1000 Wh Kg –1 with a decay rate of 0.03% per cycle is achieved. The anion and cation’s co-substitutions thermodynamically reduce conversion-reaction potential and shift the reaction from less reversible intercalation-conversion reaction in iron fluoride to a highly reversible intercalation-extrusion reaction in doped material. Furthermore, the co-substitution strategy to tune the thermodynamic features of the reactions could be extended to other high energy conversion materials for improved performance.

25 ENERGY STORAGE↗
DOE OSTI2017

Reinvigorating Reverse-Osmosis Membrane Technology to Stabilize the V 2 O 5 Lithium-Ion Battery Cathode

V 2 O 5 is deemed as one of the most promising cathode materials for next-generation high-capacity lithium-ion batteries (LIBs). It possesses a theoretical capacity of 294 mAh g -1 , which is much higher than conventional cathodes. But, there are many issues to be solved before its practical use, including poor cycle life and unsatisfactory rate performance, mainly owing to its low electronic conductivity and ionic diffusivity, as well as structural instability. Our work reports three types of V 2 O 5 asymmetric membranes synthesized by using an adapted reverse-osmosis membrane technology combined with sol-gel chemistry, aiming to stabilize the cyclability and improve the rate performance. V 2 O 5 asymmetric membrane cathodes prepared using graphene as the conductive additives have a specific capacity of approximately 160 mAh g -1 at a current density of 100 mA g -1 with no capacity degradation after 380 cycles. It is also found that the annealing temperature and the choice of conductive additives can affect the morphology of V 2 O 5 nanoparticles and the overall electrode cyclability. Furthermore, we find that a lower annealing temperature (300 vs. 400 °C) and the addition of graphene are beneficial to long-term cycling performance.

25 ENERGY STORAGE↗
DOE OSTI2023

Reversible Electrochemical Lithium Cycling in a Vanadium(IV)- and Niobium(V)-Based Wadsley–Roth Phase

Fast charging remains one of the greatest safety challenges in Li-ion batteries due to Li-dendrite growth occurring on graphite anodes if they are lithiated too quickly. The search for high-rate anodes has highlighted materials in the Wadsley–Roth (WR) shear phase family. The relative abundance of V compared with traditional WR compositions of Nb and W makes V-based phases attractive. However, the high voltage and poor reversibility typically associated with V redox have made V-rich WR phases less studied than Nb- and W-rich phases. Here, we show that a new V-rich Wadsley–Roth phase, V 7 Nb 6 O 29 , achieves excellent rate capability and 80% capacity retention after 228 cycles with a relatively low average voltage of 1.76 V vs Li/Li + compared with other V-rich WR phases. Single-crystal X-ray diffraction reveals a P4/m space group with repeating 2 × 2 × ∞ and 3 × 3 × ∞ blocks of V 4+ and Nb 5+ octahedra. Finally, combined neutron pair distribution function analysis, X-ray absorption spectroscopy, and density functional theory calculations show that V redox is the primary source of capacity and that cycling stability is provided by the stable octahedral coordination adopted by V 4+ in the material.

25 ENERGY STORAGE↗
NASA NTRS2022

Reversible Colorimetric Sensing of Volatile Analytes By Wicking in Close Proximity to A Photonic Film

Isolation of volatile analytes from environmental or biological fluids is a rate-determining step that can delay the response time for continuous sensing. In this paper, we demonstrate a colorimetric sensing system that enables the rapid detection of gas-phase analytes released from a flowing micro-volume fluid sample. The sensor platform is an analyte-responsive metal-insulator-metal (MIM) thin-film structure integrated with a large area quartz micropillar array. This allows precise planar alignment and microscale separation (310 μm) of the optical and fluidic structures. This configuration offers rapid and homogeneous color changes over large areas that permits detection by low-resolution optics or eye, which is well-suited to portable/wearable devices. For our proof-of-principle demonstration, we utilized a poly(methyl methacrylate) (PMMA) spacer and evaluated the sensor's response (color change) to ethanol vapor. We show that the RGB color value is quantitatively linked to the spacer swelling, which is reversible and repeatable. The optofluidic platform reduces the sensor response time from minutes to seconds compared with experiments using a conventional chamber. The sensor's concentration-dependent response was examined, confirming the potential of the reported sensing platform for continuous, compact, and quantitative colorimetric analysis of volatile analytes in low-volume samples, such as biofluids.

Timothy J. Palinski↗