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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Measurements of the dielectric properties of simulated comet material as part of the KOSI 10 experiment

The dielectric constant epsilon of the snow-mineral used for the comet simulation in the German KOSI 10 experiment was measured in the radio frequency range from 2 to 4 GHz. The traditional microwave bridge method was used, but instead of using a waveguide that contains the sample material small lambda/4 antennas were used as sensors. A change in the dielectric properties indicates a change in density and/or composition, respectively. The method is presented as an analytical tool for measuring such density or composition changes during alteration snow-dust materials. The KOSI (determined from the German: Kometen Simulation) experiments, performed in the Space simulator of the DLR/Institut for Raumsimulation, during the last years revealed many processes that presumably take place on comets. So far, modifications of the internal structure could be identified only during the post-experiment inspection via hardness tests. It was the aim of the KOSI 10 and KOSI 10a experiments to emphasize on a synoptic detection of events like particle emission or crust formation. The composition of the KOSI 10 sample material was an ice-mineral mixture with about 10 percent mineral (olivine) content. An excellent method to investigate the change of the density of the probe material during its exposure to the artificial sun in situ is to do it via the measurement of the dielectric constant. The traditional method to determine epsilon, by using a microwave-bridge to measure the transmission and the reflection factor of the sample material for electromagnetic waves in the radio frequency range, was modified, since the commonly used practice to fill the sample material into a waveguide was not compatible with the need for in situ measurements during the simulation experiment.

Ulamec, S.↗
DOE OSTI2022

Nitrogen-Doped PtNi Catalysts on Polybenzimidazole-Functionalized Carbon Support for the Oxygen Reduction Reaction in Polymer Electrolyte Membrane Fuel Cells

PtM (M = 3d transition metals) alloys are known as the promising oxygen reduction reaction catalysts and have been considered as the replacement of pure Pt catalysts for the commercialization of proton exchange membrane fuel cells. Although great progress has been made in the past three decades, the performance and durability of PtM catalysts still face stringent challenges from practical applications. Functionalization of a catalyst carbon support with nitrogen-contained groups can add charges onto its surface, which can be utilized to build a more complete ionomer/catalyst interface, to reduce the catalyst particle size, and to improve particle size distribution. Nitriding of PtNi catalysts can effectively improve the catalyst activity and stability by the modification of lattice strain. Hereby, we propose a synergistic approach of combining polybenzimidazole-grafted Vulcan XC72 carbon as the catalyst carbon support and the nitriding of PtNi to develop PtNiN/XC72-polybenzimidazole catalysts. Such PtNiN/XC72-PBI catalysts exhibit the excellent performance of fuel cell membrane electrode assembly (i.e., mass activity, 440 mA mgPt –1 ; electrochemical surface area, 51 m 2 gPt –1 ; and rated power density, 836 mW cm –2 ) as well as promising catalyst stability. The developed PtNiN/XC72-PBI meets the US DOE 2020 targets of mass activity for the fuel cell catalysts. This work provides a novel approach and a promising pathway on the development of the catalyst using such a synergistic approach-modification of the catalyst structure by nitrogen doping and functionalization of carbon support by polybenzimidazole for both high performance and high durability.

25 ENERGY STORAGE↗
NASA NTRS2015

Bone Loss During Spaceflight: Available Models and Counter-Measures

There is ongoing concern for human health during spaceflights. Of particular interest is the uncoupling of bone remodeling and its resultant effect on calcium metabolism and bone loss. The calculated average loss of bone mineral density (BMD) is approximately 1-1.5% per month of spaceflight. The effect of decreased BMD on associated fractures in astronauts is not known. Currently on the International Space Station (ISS), bone loss is managed through dietary supplements and modifications and resistance exercise regimen. As the duration of space flights increases, a review of the current methods available for the prevention of bone loss is warranted. The goal of this project is to review and summarize recent studies that have focused on maintaining BMD during exposure to microgravity. Interventions were divided into physical (Table 1), nutritional (Table 2), or pharmacologic (Table 3) categories. Physical modalities included resistance exercise, low level vibration, and low intensity pulsed ultrasound. Nutritional interventions included altering protein, salt, and fat intake; and vitamin D supplementation. Pharmacologic interventions included the use of bisphosphonates and beta blockers. Studies reported outcomes based on bone density determined by DXA bone scan, micro-architecture of histology and microCT, and serum and urine markers of bone turnover. The ground analog models utilized to approximate osseous physiology in microgravity included human patients previously paralyzed or subjects confined to bedrest. Ground analog animal models include paralysis, immobilization and ovariectomies. As a result of the extensive research performed there is a multi-modality approach available for the management of BMD during spaceflight that includes resistance training, nutrition and dietary supplements. However, there is a paucity of literature describing a formalized tiered protocol to guide investigators through the progression from animal models to human patient ground analogs to experiments on the ISS. With regards to testing, further evaluation to determine the association between non-invasive tests and fracture during and after spaceflight needs to be performed.

Morris, Jonathan↗
DOE OSTI2023

Magnetoelastic interactions in SrCu 2 (BO 3 ) 2 studied by Raman scattering experiments and first principles calculations

Dynamic and static crystal lattice properties of SrCu 2 (BO 3 ) 2 are studied by means of Raman scattering, magnetostriction, and thermal expansion measurements in magnetic fields to 45 T. Raman experiments versus temperature reveal that some phonon modes show an unusual behavior: their frequencies soften (modes at 200 and 450 cm –1 ) while others harden (modes at 385 and 478 cm –1 ) when decreasing the temperature below 15 K. Magneto-Raman experiments show that their field dependence correlates with their respective temperature dependencies; e.g., modes that are hardened with increasing temperature also harden with applied magnetic fields and modes that become softer with temperature also soften with applied fields. We use density functional theory to successfully model and compute the energies of these modes, classifying them into two types: pantograph (modes that soften when decreasing the temperature) and nonpantograph. We conclude that the former involves the modification of the intradimer exchange interaction J and the latter the interdimer J'. Lastly, dilatometry is used to correlate field-dependent Raman modes to the closing of the spin gap as well as fractional-magnetization stripe states M = 1/4 M s and M = 1/3 M s , where M s is the saturation magnetization.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Highly efficient Pt catalyst on newly designed CeO 2 -ZrO 2 -Al 2 O 3 support for catalytic removal of pollutants from vehicle exhaust

Pt-CeO 2 catalysts have been widely studied for the vehicle emission control. Designing novel CeO 2 based supports with improved physical-chemical properties has become a research hotspot to further promote the catalytic performance and stability of Pt-CeO 2 catalysts. In this work, through utilizing a unique, two-step incipient wetness impregnation (T-IWI) method for ceria-zirconia-alumina (CZA-T) support preparation, a Pt single site catalyst (Pt/CZA-T) with excellent thermal stability was synthesized. Higher oxidation activity and Oxygen storage capacity (OSC) were achieved on activated Pt/CZA-T, comparing to Pt catalysts on regular CeO 2 /Al 2 O 3 (Pt/CA) and one-step prepared CeZrO x /Al 2 O 3 (Pt/CZA). Via the modification of hydrophilic/hydrophobic properties of γ-Al 2 O 3 by this unique T-IWI method, finer Ce 0.9 Zr 0.1 O 2 particles with higher density of surface defects were formed on CZA-T, on which a higher Pt dispersion and stronger Pt-O-Ce interaction were achieved. Upon activation, smaller, well-dispersed Pt clusters on CZA-T were generated. It was concluded that the CO oxidation performance and OSC were highly related to the size of Pt clusters on different supports that we have developed. Finally, more Pt sites located at Pt cluster-CeZrO x interfaces, which were the real active sites, were responsible for the highest OSC function and CO oxidation activity of activated Pt/CZA-T catalyst.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Insights into the thermal decomposition of plutonium(IV) oxalate – a DFT study of the intermediate structures

The thermal decomposition of plutonium oxalate to oxide is one of the most studied reactions in actinide chemistry but the intermediates have been the subject of debate for decades. Recent experimental data suggest that the decomposition of Pu(IV) oxalate in air undergoes dehydration first, then reduction to Pu(III) oxalate. The precise structural modifications that take place are unknown as experiments have not been able to fully characterize the intermediates at the microscopic level. To rectify this, we employed solid state density functional theory calculations at the PBE-D3 level with a Hubbard U correction to model the structures and energetics of potential dehydrated Pu(IV) and Pu(III) oxalate intermediate compounds. Based on the theoretical study presented here, the anhydrous analogues of the known hydrated Pu(IV) and Pu(III) oxalates are the preferred crystal structures formed through an overall exothermic reaction process. However, decomposition could proceed through the formation of a higher energy, more complicated 3D lattice structure with frustrated oxalate binding. It is expected that the intermediates presented here could be identified using spectroscopic techniques to enable further insight into the reaction mechanism.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2021

Inclusive heavy-flavour production at central and forward rapidity in Xe–Xe collisions at $\sqrt{s_{NN}}$ = 5.44 TeV

The first measurements of the production of muons and electrons from heavy-flavour hadron decays in Xe–Xe collisions at $\sqrt{s_{NN}}$ =5.44 TeV, using the ALICE detector at the LHC, are reported. The measurement of the nuclear modification factor R AA is performed as a function of transverse momentum p T in several centrality classes at forward rapidity (2.5 < y < 4) and midrapidity (|y| < 0.8) for muons and electrons from heavy-flavour hadron decays, respectively. A suppression by a factor up to about 2.5 compared to the binary-scaled pp reference is observed in central collisions at both central and forward rapidities. The R AA of muons from heavy-flavour hadron decays is compared to previous measurements in Pb–Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV. When the nuclear modification factors are compared in the centrality classes 0–10% for Xe–Xe collisions and 10–20% for Pb–Pb collisions, which have similar charged-particle multiplicity density, a similar suppression, with R AA ~ 0.4 in the p T interval 4 < p T < 8 GeV/c, is observed. The comparison of the measured R AA values in the two collision systems brings new insights on the properties of the quark-gluon plasma by investigating the system-size and geometry dependence of medium-induced parton energy loss. The results of muons and electrons from heavy-flavour hadron decays provide new constraints to model calculations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Smooth Modified Surfaces of Silicon for the Study of Ionic Liquid Interfaces by Neutron Reflectometry

Silicon surfaces with termination of hydrogen (H–Si), quartz, native silicon (native-Si), and chemically deposited (Au–Si) cd and sputtered gold (Au–Si) s were fabricated with roughness less than 6 Å to study the solid–liquid interface of the ionic liquid (IL) methyltrioctylammonium bis(trifluoromethylsulfonyl)imide, [N 1888 ][TFSI], by neutron reflectometry (NR). The modifications made to the silicon surface were to obtain a native positive or negative charge similar to a charged surface in electrochemical systems. The differences in scattering length density (SLD) based on mass density and composition of IL were examined. Perpendicular to the substrate surface, a distinct transition between the first ion layer and the bulk liquid is resolved out of the reflectivity data for the gold surfaces and in particular the chemically deposited Au–Si. Other interfaces are best described by a diffuse transition between regions of different SLDs. The diffuse transitions between SLDs observed here suggest that the interfacial structure of IL, while ordered, is best described by a continuous variation in composition as opposed to distinct layers of ions.

25 ENERGY STORAGE↗
DOE OSTI2024

Influence of gadolinium doping on structural, optical, and electronic properties of polymeric graphitic carbon nitride

Polymeric graphitic carbon nitride (gCN) materials have received great attention in the fields of photo and electrocatalysis due to their distinct properties in metal-free systems with high physicochemical stability. Nevertheless, the activity of undoped gCN is limited due to its relatively low specific surface area, low conductivity, and poor dispersibility. Doping Gd atoms in a gCN matrix is an efficient strategy to fine-tune its catalytic activity and its electronic structure. Herein, the influence of various wt% of gadolinium (Gd) doped in melon-type carbon nitride was systematically investigated. Gadolinium-doped graphitic carbon nitride (GdgCN) was synthesized by adding gadolinium nitrate to dicyandiamide during polymerization. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) results revealed that the crystallinity and the morphological properties are influenced by the % of Gd doping. Furthermore, X-ray photoelectron spectroscopy (XPS) studies revealed that the gadolinium ions bonded with nitrogen atoms. Complementary density functional theory (DFT) calculations illustrate possible bonding configurations of Gd ions both in bulk material and on ultrathin melon layers and provide evidence for the corresponding bandgap modifications induced by gadolinium doping.

36 MATERIALS SCIENCE↗
DOE OSTI2024

The effect of plasma shaping on high density H-mode SOL profiles and fluctuations in TCV

Abstract The impact of plasma shaping on the properties of high density H-mode scrape-off layer (SOL) profiles and transport at the outer midplane has been investigated on Tokamakà configuration variable. The experimental dataset has been acquired by evolving the upper triangularity while keeping the other parameters constant. The scan comprises δ u p values between 0.0 and 0.6, excluding negative triangularity scenarios. Within this study, a transition from type-I edge localised modes to the quasi-continuous exhaust regime takes place from low to high δ u p . The modification of the upstream SOL profiles has been assessed, in terms of separatrix quantities, within the α t turbulence control parameter theoretical framework (Eich et al 2020 Nucl. Fusion 60 056016). The target parallel heat load and the upstream near-SOL density profiles have been shown to broaden significantly for increasing α t . Correspondingly, in the far SOL a density shoulder formation is observed when moving from low to high δ u p . These behaviours have been correlated with an enhancement of the SOL fluctuation level, as registered by wall-mounted Langmuir probes as well as the thermal helium beam diagnostic. Specifically, both the background and the filamentary-induced fluctuating parts of the first wall ion saturation current signal are larger at higher δ u p , with filaments being ejected more frequently into the SOL. Comparison of two pulses at the extremes of the δ u p scan range, but with otherwise same input parameters, shows that the midplane neutral pressure does not change much during the H-mode phase of the discharge. This indicates that indirect effects of the change in geometry, linked to first wall recycling sources, should not play a significant role. The total core radiation increases at high δ u p , on account of a stronger plasma–wall interaction and resulting larger carbon impurity intake from the first wall. This is likely associated to the enhanced first wall fluctuations, as well as a smaller outer gap and the close-to-double-null magnetic topology at high shaping.

Stagni, A. (ORCID:0000000180841544)↗
DOE OSTI2024

Engineering exchange bias at the interface of self-polarized ultrathin ferroelectric Ba⁢Ti⁢O 3 and ferromagnetic La 0.67⁢ Sr 0.33 ⁢Mn⁢O 3

We investigate the emergence and optimization of conventional exchange bias (EB) in ultrathin (<10 nm) ferroelectric (FE) Ba⁢Ti⁢O 3 (BTO)/ferromagnetic (FM) La 0.67 ⁢Sr 0.33⁢ Mn⁢O 3 (LSMO) epitaxial bilayers without an antiferromagnetic (AFM) material. The EB originates from the electronic orbital reconstruction at the FE-FM interface due to the ferroelectric polarization. We achieve maximum EB of approximately 42 Oe with single-domain polarization in nine-unit-cell-thick BTO, setting the BTO thickness above the critical threshold for ferroelectricity yet below the thickness of strain relaxation and multidomain breakdown. Furthermore, the LSMO layer needs to be thick enough to sustain both the FM layer and polarization-induced AFM spin configuration at the LSMO/BTO interface, yet as thin as possible to enable the EB loop shift. The temperature, training, field, and thickness dependence of the EB confirm that the LSMO/BTO interface exhibits conventional EB despite its unconventional origin. Using x-ray magnetic circular dichroism, scanning transmission electron microscopy, and density-functional-theory calculations, we confirm that the macroscopic EB effect originates from the interfacial AFM spin configuration in LSMO driven by FE-induced d-orbital modifications in interfacial Mn ions. Thus, we engineer strong interfacial EB coupling in artificial multiferroics without a conventional AFM material by controlling FE polarization, highlighting the potential for advanced spintronic applications.

exchange bias↗
DOE OSTI2020

Dynamic pulse propagation modelling for predictive femtosecond-laser-microbonding of transparent materials

A dynamic pulse propagation modeling for femtosecond laser bonding of Borofloat glass is presented. The temperature evolution and internal modifications are predicted by incorporating the nonlinear electron dynamics along with temperature dependent thermal properties. The modelling predicts the spatial and temporal distribution of absorption coefficient and plasma density that gives quantitative estimations of the heat affected zone and weld geometry. The impact of focusing condition on heat affected zone and weld geometry is investigated, which for the first time to our knowledge allows to numerically determine the desired relative position between the geometrical focus of a femtosecond-laser-pulse and the interface of the two substrates to be welded. The prediction of the modelling on the offset distance is applied to weld Borofloat glass plates having optical contact and can be applied to other dielectric solids.

Sahoo, Pankaj K. (ORCID:0000000209437319)↗
NASA NTRS1974

Electric Field Induced Spectra of H sub 2 and D sub 2

The frequencies of four Q-branch lines of H2 and five Q-branch lines of D2 were measured as a function of density, and their shifts were observed to be in the linear region. The individual slopes and extrapolated zero density frequency of each line was determined. Hydrogen was measured for polarizability using the integrated intensity of the Q1(0) and S1(1), H2 absorption line. A highly automated technique for determining the response function of the spectrometer using digitally recorded data is presented. For the Q1(0) and Q1(1) lines of H2 the halfwidths were measured as a function of electric field intensity at constant pressure, and again at several densities and compared to previously measured widths. Technical and operational details of equipment built for this experiment, and for the five-meter Littrow spectrometer used, are described. Modifications of the spectrometer optics to accept the Stark cell are discussed.

Boyd, William Joseph↗
NASA NTRS1974

Large-amplitude hydromagnetic waves

Several aspects of the theory of large-amplitude hydromagnetic waves and their behavior in the interplanetary medium are examined. The characteristic modes of the full (i.e., nonlinearized) MHD equations and their modification by collisionless and finite-frequency effects are considered. Special attention is paid to the transverse Alfven mode, which is undamped and characterized by strictly constant pressure, density, and B; this seems to be the predominant propagating fluctuation at 1 AU. It is shown that its propagation in the small-wavelength (WKB) approximation is essentially identical to that of the small-amplitude Alfven wave of linearized theory. It is also suggested that its presence at 1 AU may provide a natural explanation of the observed power anisotropy of the fluctuations. A second-order analysis is used to study fluctuations that are not characteristic modes. It is found that for a small range of propagation directions, and subject to third-order effects, a finite-amplitude wave can exist that is linearly polarized with delta B perpendicular to both B sub zero and k; such a wave can damp nonlinearly.

Barnes, A.↗
NASA NTRS1977

Laser-zone growth in a Ribbon-To-Ribbon (RTR) process silicon sheet growth development for the large area silicon sheet task of the low cost silicon solar array project

The Ribbon-to-Ribbon (RTR) approach to silicon ribbon growth was investigated. An existing RTR apparatus, RTR#1, was upgraded to allow for 5 cm wide ribbon growth with a finite stroke length of at least 15 cm. A second RTR apparatus, RTR#2, was designed, built, and operated which utilizes continuous feed mechanisms and allows continuous growth of 7.5 cm wide ribbons. RTR#2 includes development and utilization of advanced beam scanning (or shaping), high power lasers, and thermal profile modification elements to attain maximum growth velocities (with a design goal of 18 cm/min). Materials studies, process development, and thermal analyses are also described. Residual stresses and dislocation densities were minimized through theoretical and experimental efforts towards optimization of thermal profiles. Growth runs were performed on RTR#2 and solar cells were fabricated which demonstrated efficiencies greater than 10%.

Gurtler, R. W.↗
NASA NTRS1982

Airborne spectroscopy and spacecraft radiometry of Venus in the far infrared

The first spectral observations of the Venus disk in the 110 to 270 per cm spectral range are reported, made from the Kuiper Airborne Observatory in mid-March 1979, some three months following the start of the Pioneer Venus Orbiter mission. The instrumentation and its differences from earlier flight hardware is discussed. The brightness temperature was 275 K near 110/cm, dropping to 230 K near 270/cm. Radiance calculations, using temperature and cloud structure formation from the Pioneer Venus mission and including gaseous absorption by the collision-induced dipole of CO2, yield results consistently brighter than the observations. The atmospheric environment is reviewed with regard to the FIR opacity and possible particle distribution modifications are discussed. It is concluded that the most likely possibility for supplementing the FIR opacity is a population of large particles in the upper cloud with number densities less than one particle per cu cm which has remained undetected by in situ measurements.

Aumann, H. H.↗
NASA NTRS1989

On the effect of a tangential discontinuity on ions specularly reflected at an oblique shock

A study is conducted for the case of a tangential discontinuity (TD) that convects into a shock at some arbitrary angle, in order to clarify events observed in proximity to the earth's bow shock. Very different behavior is noted to result depending on the sense of ion gyration relative to the TD. The fact that particles can be injected into the TD's plane, so that they travel upstream close to the TD, implies that active current sheet (ACS) events thus far assumed to be generated by the solar wind's interaction with a large-density reflected component are actually detached from the bow shock. In other geometries, ions stay close to the shock after their TD interaction, implying that ACS events are modifications of the shock.

Burgess, D.↗