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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 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Single-layer tensor network study of the Heisenberg model with chiral interactions on a kagome lattice

Here, we study the antiferromagnetic kagome Heisenberg model with an additional scalar-chiral interaction by using the infinite projected entangled-pair state (iPEPS) ansatz. We discuss in detail the implementation of the optimization algorithm in the framework of the single-layer tensor network based on the corner transfer matrix technique. Our benchmark based on the full-update algorithm shows that the single-layer algorithm is stable, which leads to the same level of accuracy as the double-layer ansatz but with much less computation time. We further apply this algorithm to study the nature of the kagome Heisenberg model with a scalar-chiral interaction by computing the bond dimension scaling of magnetization, bond energy difference, chiral order parameter, and correlation length. In particular, we find that for strong chiral coupling the correlation length, which is extracted from the transfer matrix, saturates to a finite value for large bond dimension, representing a gapped spin-liquid state. Further comparison with density matrix renormalization group results supports that our iPEPS faithfully represents the time-reversal symmetry breaking chiral state. Our iPEPS simulation results shed new light on constructing PEPS for describing gapped chiral topological states.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1981

GaAs shallow-homojunction solar cells

The feasibility of fabricating space resistant, high efficiency, light weight, low cost GaAs shallow homojunction solar cells for space application is investigated. The material preparation of ultrathin GaAs single crystal layers, and the fabrication of efficient GaAs solar cells on bulk GaAs substrates are discussed. Considerable progress was made in both areas, and conversion efficiency about 16% AMO was obtained using anodic oxide as a single layer antireflection coating. A computer design shows that even better cells can be obtained with double layer antireflection coating. Ultrathin, high efficiency solar cells were obtained from GaAs films prepared by the CLEFT process, with conversion efficiency as high as 17% at AMI from a 10 micrometers thick GaAs film. A organometallic CVD was designed and constructed.

Fan, J. C. C.↗
DOE OSTI2016

Contribution of dielectric screening to the total capacitance of few-layer graphene electrodes

We apply joint density functional theory (JDFT), which treats the electrode/electrolyte interface self-consistently, to an electric double-layer capacitor (EDLC) based on few-layer graphene electrodes. The JDFT approach allows us to quantify a third contribution to the total capacitance beyond quantum capacitance (C Q ) and EDL capacitance (C EDL ). This contribution arises from the dielectric screening of the electric field by the surface of the few-layer graphene electrode, and we therefore term it the dielectric capacitance (C Dielec ). We find that C Dielec becomes significant in affecting the total capacitance when the number of graphene layers in the electrode is more than three. In conclusion, our investigation sheds new light on the significance of the electrode dielectric screening on the capacitance of few-layer graphene electrodes.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Study of the composition, structure, and optical properties of a-Si{sub 1-x}C{sub x}:H Left-Pointing-Angle-Bracket Er Right-Pointing-Angle-Bracket films erbium doped from the Er(pd){sub 3} complex compound

Rutherford backscattering, IR spectroscopy, ellipsometry, and atomic-force microscopy are used to perform an integrated study of the composition, structure and optical properties of a-Si{sub 1-x}C{sub x}:H Left-Pointing-Angle-Bracket Er Right-Pointing-Angle-Bracket amorphous films. The technique employed to obtain the a-Si{sub 1-x}C{sub x}:H Left-Pointing-Angle-Bracket Er Right-Pointing-Angle-Bracket amorphous films includes the high-frequency decomposition of a mixture of gases, (SiH{sub 4}){sub a} + (CH{sub 4}){sub b}, and the simultaneous thermal evaporation of a complex compound, Er(pd){sub 3}. It is demonstrated that raising the amount of CH{sub 4} in the gas mixture results in an increase in the carbon content of the films under study and an increase in the optical gap E{sub g}{sup opt} from 1.75 to 2.2 eV. Changes in the composition of a-Si{sub 1-x}C{sub x}:H Left-Pointing-Angle-Bracket Er Right-Pointing-Angle-Bracket amorphous films, accompanied, in turn, by changes in the optical constants, are observed in the IR spectra. The ellipsometric spectra obtained are analyzed in terms of multiple-parameter models. The conclusion is made on the basis of this analysis that the experimental and calculated spectra coincide well when variation in the composition of the amorphous films with that of the gas mixture is taken into account. The existence of a thin (6-8 nm) silicon-oxide layer on the surface of the films under study and the validity of using the double-layer model in ellipsometric calculations is confirmed by the results of structural analyses by atomic-force microscopy.

36 MATERIALS SCIENCE↗
NASA NTRS1995

Plasma gradient effets on doubel-probe measurements in the magnetosphere

The effects on double-probe electric field measurements induced by electron density and temperature gradients are investigated. We show that on some occasions such gradients may lead to marked spurious electric fields if the probes are assumed to lie at the same probe potential with repect to the plasma. The use of a proper bias current will decrease the magnitude of such an error. When the probes are near the plasma potential, the magnitude of these error signals, delta Epsilon, can vary as delta Epsilon approx. T(sub e)(Delta n(sub e)/n(sub e)) + 0.5 Delta T(sub e), where T(sub e) is the electron temperature, Delta n(sub e)/ n(sub e) the relative electron density variation between the two sensors, and Delta T(sub e) the electron temperature difference between the two sensors. This not only implies that the error signals will increase linearly with the density variations but also that such signatures grow with Delta T(sub e) i.e., such effects are 10 times larger in a 10-eV plasma than in a 1-eV plasma. This type of error is independent of the probe separation distance provided the gradient scale length is much larger than the distance. The largest errors occur when the probes are near to the plasma potential. During the crossing of a small structure (e.g, a double layer) the error signal appears as a bipolar signature. Our analysis shows that errors in double-probe measurements caused by plasma gradients are not significant at large scale (much greater than 1 km) plasma boundaries, and may only be important in cases where small-scale (less than 1 km), internal gradient structures exist. Bias currents tailored for each plasma parameter regime (i.e., variable bias current) would improve the double-probe response to gradient effects considerably.

Laakso, Harri↗
DOE OSTI2026

pH-Driven Restructuring of Hydration Layers and Cation Adsorption at the Alumina–Water Interface

Oxide−water interfaces underpin ion separations, catalysis, and electrochemical energy technologies, where the electrical double layer (EDL) controls adsorption, transport, and reactivity. However, the molecular-scale links between pHdependent surface protonation, hydration-layer structure, and counterion adsorption remain poorly defined. Here, we combine in situ crystal truncation rod (CTR) and resonant anomalous X-ray reflectivity (RAXR) with streaming potential measurements and ab initio molecular dynamics (AIMD) simulations to resolve the chemical and structural evolution of the EDL at the single-crystal alumina (012)−water interface in 10 mM Rb + over pH 3−12. CTR measurements reveal two distinct adsorbed water layers at ∼2.2 and ∼3.5 Å above the surface. Each water layer shifts toward the substrate at transition pHs near 6.5 and 10.6, respectively, reflecting changes in primary hydration layer structure in response to the deprotonation of bridging and terminal aluminol groups. RAXR shows a 10-fold increase in Rb + coverage and a decrease in mean adsorption height from ∼3.5 to ∼2.7 Å with increasing pH, indicating enhanced counterion binding accompanied by Stern layer contraction. Streaming potential measurements demonstrate that the zeta potential, i.e., the potential at the hydrodynamic shear plane, is positive at pH 3 and becomes negative at pH ≥ 3.5. The negative charge magnitude increases with increasing pH, consistent with progressive surface deprotonation at higher pH. AIMD identifies inner- and outer-sphere Rb+ complexes whose adsorption heights and coordination geometries depend sensitively on the protonation state of surface oxygens, providing atomistic support for the experimentally inferred trends. These measurements establish two discrete, site-specific pH transitions in hydration-layer structure that track aluminol (de)protonation and quantitatively link them to a pH-driven contraction of the Stern layer (increasing Rb + coverage and decreasing adsorption height). This provides a direct structural basis for connecting surface acid−base chemistry to ion binding distances at an oxide−water interface.

Adsorption↗
NASA NTRS1993

Head-on collision of drops: A numerical investigation

The head-on collision of equal sized drops is studied by full numerical simulations. The Navier-Stokes equations are solved for fluid motion both inside and outside the drops using a front tracking/finite difference technique. The drops are accelerated toward each other by a body force that is turned off before the drops collide. When the drops collide, the fluid between them is pushed outward leaving a thin later bounded by the drop surface. This layer gets progressively thinner as the drops continue to deform and in several of the calculations this double layer is artificially removed once it is thin enough, thus modeling rupture. If no rupture takes place, the drops always rebound, but if the film is ruptured the drops may coalesce permanently or coalesce temporarily and then split again.

Nobari, M. R.↗
NASA NTRS1984

On stress analysis of a crack-layer

This work considers the problem of elastic interaction of a macrocrack with an array of microcracks in the vicinity of the macrocrack tip. Using the double layer potential techniques, the solution to the problem within the framework of the plane problem of elastostatics has been obtained. Three particular problems of interest to fracture mechanics have been analyzed. It follows from analysis that microcrack array can either amplify or reduce the resulting stress field of the macrocrack-microcrack array system depending on the array's configuration. Using the obtained elastic solution the energy release rate associated with the translational motion of the macrocrack-microcrack array system has been evaluated.

Chudnovsky, A.↗
DOE OSTI2023

Long-term durability test of highly efficient membrane electrode assemblies for anion exchange membrane seawater electrolyzers

Direct seawater electrolysis faces fundamental electrochemical challenges, such as suppression of chlorine adsorption and/or evolution reactions that poison the current state-of-the-art anode catalysts and accelerate the degradation of the anion exchange membrane (AEM). The technically favored solution path for addressing these issues includes development of novel selective catalysts and implementation of limited operating conditions. Therefore, development of highly active, selective, cost-effective, and stable seawater-splitting catalysts is required for a successful commercialization of the AEM water electrolyzers (AEMWEs). In this work, we report for the first-time an extended operation for over 1000 h of advanced AEMWEs, operating directly with seawater. To fabricate the membrane electrode assemblies (MEAs), catalyst coated electrodes (CCEs) are assembled with Sustainion® X37-50 grade T anion exchange membranes. The anode CCEs are fabricated by spraying an ink prepared from nanostructured NiFe-layered double hydroxide (LDH) catalyst that are synthesized by the solvothermal method and deposited directly onto platinized titanium porous transport layers (PTLs). The cathode CCEs are prepared by spraying an ink prepared from commercial Renay-Nickel catalyst onto a nickel fiber felt. As prepared AEM electrolyzer cells operated with seawater and demonstrated better than previously reported in the literature performance of over 1000 h of operation at a constant current density of 300 mA cm –2 .

25 ENERGY STORAGE↗
DOE OSTI2014

Approach towards quasi-monoenergetic laser ion acceleration with doped target

Ion acceleration using a laser pulse irradiating a disk target that includes hydrogen and carbon is examined using three-dimensional particle-in-cell simulations. It is shown that over 200 MeV protons can be generated using a 620 TW, 5 × 10{sup 21} W/cm{sup 2} laser pulse. In a polyethylene (CH{sub 2}) target, protons and carbon ions separate and form two layers by radiation pressure acceleration. A strong Coulomb explosion in this situation and Coulomb repulsion between each layer generates high energy protons. A doped target consisting of low density hydrogen within a carbon disk becomes a double layer target that is comprised of a thin low density hydrogen disk on the surface of a high-Z atom layer. This then generates a quasi-monoenergetic proton beam.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1993

Thermocapillary convection in two immiscible liquid layers with free surface

Thermocapillary convection is studied in two immiscible liquid layers with one free surface, one liquid/liquid interface, and differential heating applied parallel to the interfaces. An analytical solution is introduced for infinite horizontal layers. The defining parameter for the flow pattern is lambda, the ratio of the temperature coefficient of the interfacial tension to that of the surface tension. Four different flow patterns exist under zero gravity conditions. 'Halt' conditions which halt the fluid motion in the lower encapsulated liquid layer have been found. A numerical experiment is carried out to study effects of vertical end walls on the double layer convection in a 2D cavity. The halt condition obtained from the analytical study is found to be valid in the limit of small Reynolds numbers. The flow in the encapsulated liquid layer can be suppressed substantially.

Doi, Takao↗
DOE OSTI2023

Two-layer cathode architecture for high-energy density and high-power density solid state batteries

Solid state batteries with high-energy density and high-power density require the development of thick and energy dense cathodes. Structured cathode electrodes with a double-layer configuration were enabled using a freeze tape casting technique. A bottom dense layer was utilized to enhance the energy density whereas a top porous layer with vertically aligned walls was utilized to enhance the power density. The porous structure of the power layer was achieved by ice templating this layer on top of the densified energy layer of the cathode. This configuration was found to better utilize the active material of the cathodes and was optimized using numerical simulation and computer modeling. Cells with Li metal anode and LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622) at approximately 5 and 20 mg/cm 2 were cycled at 70 °C at different C-rates. Poly(ethylene oxide) (PEO) with lithium bis-trifluoromethanesulfonimide (LiTFSI) was used for the catholyte and the solid-state electrolyte. The structured cathodes exhibited more than double capacity values as well as better Coulombic efficiency compared to non-structured (single-layer) thick cathodes. In conclusion, synchrotron X-ray tomography and scanning electron microscopy were used to characterize the microstructure of the cathodes.

25 ENERGY STORAGE↗
DOE OSTI2014

Organo-sulfur molecules enable iron-based battery electrodes to meet the challenges of large-scale electrical energy storage

Rechargeable iron-air and nickel-iron batteries are attractive as sustainable and inexpensive solutions for large-scale electrical energy storage because of the global abundance and eco-friendliness of iron, and the robustness of iron-based batteries to extended cycling. Despite these advantages, the commercial use of iron-based batteries has been limited by their low charging efficiency. This limitation arises from the iron electrodes evolving hydrogen extensively during charging. The total suppression of hydrogen evolution has been a significant challenge. We have found that organo-sulfur compounds with various structural motifs (linear and cyclic thiols, dithiols, thioethers and aromatic thiols) when added in milli-molar concentration to the aqueous alkaline electrolyte, reduce the hydrogen evolution rate by 90%. These organo-sulfur compounds form strongly adsorbed layers on the iron electrode and block the electrochemical process of hydrogen evolution. The charge-transfer resistance and double-layer capacitance of the iron/electrolyte interface confirm that the extent of suppression of hydrogen evolution depends on the degree of surface coverage and the molecular structure of the organo-sulfur compound. An unanticipated electrochemical effect of the adsorption of organo-sulfur molecules is "de-passivation" that allows the iron electrode to be discharged at high current values. The strongly adsorbed organo-sulfur compounds were also found to resist electro-oxidation even at the positive electrode potentials at which oxygen evolution can occur. Through testing on practical rechargeable battery electrodes we have verified the substantial improvements to the efficiency during charging and the increased capability to discharge at high rates. We expect these performance advances to enable the design of efficient, inexpensive and eco-friendly iron-based batteries for large-scale electrical energy storage.

Yang, B↗
DOE OSTI2018

Characteristic Atmospheric Radiative Heating Rate Profiles in Arctic Clouds as Observed at Barrow, Alaska

Abstract A 2-yr cloud microphysical property dataset derived from ground-based remote sensors at the Atmospheric Radiation Measurement site near Barrow, Alaska, was used as input into a radiative transfer model to compute radiative heating rate (RHR) profiles in the atmosphere. Both the longwave (LW; 5–100 μm) and shortwave (SW; 0.2–5 μm) RHR profiles show significant month-to-month variability because of seasonal dependence in the vertical profiles of cloud liquid and ice water contents, with additional contributions from the seasonal dependencies of solar zenith angle, water vapor amount, and temperature. The LW and SW RHR profiles were binned to provide characteristic profiles as a function of cloud type and liquid water path (LWP). Single-layer liquid-only clouds are shown to have larger (10–30 K day−1) LW radiative cooling rates at the top of the cloud layer than single-layer mixed-phase clouds; this is due primarily to differences in the vertical distribution of liquid water between the two classes. However, differences in SW RHR profiles at the top of these two classes of clouds are less than 3 K day−1. The absolute value of the RHR in single-layer ice-only clouds is an order of magnitude smaller than in liquid-bearing clouds. Furthermore, for double-layer cloud systems, the phase and condensed water path of the upper cloud strongly modulate the radiative cooling both at the top and within the lower-level cloud. While sensitivity to cloud overlap and phase has been shown previously, the characteristic RHR profiles are markedly different between the different cloud classifications.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2014

Oxidation induced amorphous stabilization of the subsurface region in Zr-Cu metallic glass

In the present study, we demonstrate that selective surface oxidation of Zr{sub 70}Cu{sub 30} metallic glass can stabilize the amorphous structure in the subsurface region of the matrix. The oxidation proceeds by selective oxidation of Zr, forming monoclinic ZrO{sub 2} layer on the surface, and the subsurface layer becomes Cu-enriched due to back diffusion of Cu atoms from the oxide layer. Interestingly, in this system, the composition change in the subsurface region leads to enhancement of glass stability, forming of a double layered surface structure consisted of inner amorphous layer and outer monoclinic ZrO{sub 2} layer even when the remaining matrix is completely crystallized.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

Bilayer quantum Hall phase transitions and the orbifold non-Abelian fractional quantum Hall states

We study continuous quantum phase transitions that can occur in bilayer fractional quantum Hall (FQH) systems as the interlayer tunneling and interlayer repulsion are tuned. We introduce a slave-particle gauge theory description of a series of continuous transitions from the (ppq) Abelian bilayer states to a set of non-Abelian FQH states, which we dub orbifold FQH states, of which the Z{sub 4} parafermion (Read-Rezayi) state is a special case. This provides an example in which Z{sub 2} electron fractionalization leads to non-Abelian topological phases. The naive ''ideal'' wave functions and ideal Hamiltonians associated with these orbifold states do not in general correspond to incompressible phases but, instead, lie at a nearby critical point. We discuss this unusual situation from the perspective of the pattern-of-zeros/vertex algebra frameworks and discuss implications for the conceptual foundations of these approaches. Due to the proximity in the phase diagram of these non-Abelian states to the (ppq) bilayer states, they may be experimentally relevant, both as candidates for describing the plateaus in single-layer systems at filling fractions 8/3 and 12/5 and as a way to tune to non-Abelian states in double-layer or wide quantum wells.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2021

Orion Meteoroid and Debris Analysis with a Single Kevlar® Layer Enhancement to the Propulsion Tank Multi-Layer Insulation: Comparison of the Observed Data and the Adjusted Ballistic Models

In a continual mass optimization effort for the Orion vehicle by NASA and its prime contractor Lockheed Martin Space, along with the European Space Agency (ESA) and its contractors Airbus and Thales Alenia Space-Italy (TAS-I), a series of shield characterization shots have been performed to quantify the ballistic enhancement of a single-layer of Kevlar® in multi-layer insulation (MLI). This enhanced MLI is part of Orion’s propulsion subsystem, and it is planned to replace a double-layer Kevlar® configuration starting at the Artemis IV mission. This effort has included fifty-two shield characterization shots for five different shield configurations over the four Orion propellant storage vessels. These storage vessels are located in the European Service Module (ESM). This shield characterization has been managed by the Hypervelocity Impact Technology (HVIT) group in NASA Astromaterials Research and Exploration Sciences at Johnson Space Center (JSC) for the NASA Engineering and Safety Center (NESC) and the Multi-Purpose Crew Vehicle (MPCV) program office in coordination with Lockheed Martin Space and Thales Alenia Space-Italy (TAS-I). The shield characterization has used the two-stage, light-gas-gun at the Remote Hypervelocity Test Laboratory (RHTL) of NASA JSC White Sands Test Facility (WSTF) for acceleration of projectiles to representative orbital impact speeds. From this shield characterization effort, a revised ballistic limiting equation (BLE) has been developed for each of the five representative shielding configurations of the ESM pressure vessels. This document provides a brief description of the shield configurations considered for the Orion program and the shield characterization findings. These results are compared to the assumed BLE for each configuration going into the Artemis missions that utilize this version of ballistic enhanced MLI. The models are integrated into a fourteen day High Lunar Orbit (HLO) mission as a representative reliability prediction impact for Orion, and it has been found that the predicted risk of a loss-of-crew (LOC) event is actually a little less than half of the assumed value that launched this design modification opportunity.

Joshua E Miller↗