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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

THE SPITZER INTERACTING GALAXIES SURVEY: A MID-INFRARED ATLAS OF STAR FORMATION

The Spitzer Interacting Galaxies Survey is a sample of 103 nearby galaxies in 48 systems, selected using association likelihoods and therefore free from disturbed morphology biases. All galaxies have been observed with Infrared Array Camera and MIPS 24 μm bands from the Spitzer Space Telescope. This catalog presents the global flux densities and colors of all systems and correlations between the interacting systems and their specific star formation rate (sSFR). This sample contains a wide variety of galaxy interactions with systems ranging in mass, mass ratios, and gas-content as well as interaction strength. This study seeks to identify the process of triggering star formation in galaxy interactions, therefore, we focus on the non-active galactic nucleus spiral galaxies only. From this subset of 70 spiral galaxies we have determined that this sample has enhanced sSFR compared to a sample of non-interacting field galaxies. Through optical data we have classified each system by “interaction strength”; the strongly interacting (Stage 4) galaxies have higher sSFR values than the weakly (Stage 2) and moderately (Stage 3) interacting systems. However, the Stage 2 and 3 systems have statistically identical sSFR properties, despite the lack of optical interaction signatures exhibited by the Stage 2 galaxies. We suggest that the similarity of sSFR in these stages could be a consequence of some of these Stage 2 systems actually being post-perigalactic and having had sufficient time for their tidal features to fade to undetectable levels. This interpretation is consistent with the correlation of sSFR with separation, which we have determined to have little variation up to 100 kpc.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Morphology and Crystallinity Effects of Nanochanneled Niobium Oxide Electrodes for Na-Ion Batteries

Niobium pentoxide (Nb 2 O 5 ) is a promising negative electrode for sodium ion batteries (SIBs). By engineering the morphology and crystallinity of nanochanneled niobium oxides (NCNOs) the kinetic behavior and charge storage mechanism of Nb 2 O 5 electrodes were investigated. Amorphous and crystalline NCNO samples were made by modulating anodization conditions (20 - 40V and 140 - 180 °C) to synthesize nanostructures of differing pore sizes and wall thicknesses with identical chemical composition. The electrochemical energy storage properties of the NCNOs were studied with the amorphous samples showing better overall rate performance than the crystalline samples. The enhanced rate performance of the amorphous samples is attributed to the higher capacitive contributions and Na-ion diffusivity analyzed from cyclic voltammetry (CV) and galvanostatic intermittent titration technique (GITT). It was found that the amorphous samples with smaller wall thicknesses facilitated improved kinetics. Among samples with similar pore size and wall thickness, the difference in their power performance stems from crystallinity effect, which plays a more significant role in the resulting kinetics of the materials for Na-ion batteries.

25 ENERGY STORAGE↗
DOE OSTI2013

Cationic (V, Y)-codoped TiO{sub 2} with enhanced visible light induced photocatalytic activity: A combined experimental and theoretical study

To employ TiO{sub 2} as an efficient photocatalyst, high reactivity under visible light and improved separation of photoexcited carriers are required. An effective co-doping approach is applied to modify the photocatalytic properties of TiO{sub 2} by doping vanadium (transition metal) and yttrium (rare earth element). V and/or Y codoped TiO{sub 2} was prepared using hydrothermal method without any post calcination for crystallization. Based on density functional theory, compensated and noncompensated V, Y codoped TiO{sub 2} models were constructed and their structural, electronic, and optical properties were calculated. Through combined experimental characterization and theoretical modeling, V, Y codoped TiO{sub 2} exhibited high absorption coefficient with enhanced visible light absorption. All the prepared samples showed pure anatase phase and spherical morphology with uniform particle distribution. Electronic band structure demonstrates that V, Y codoping drastically reduced the band gap of TiO{sub 2}. It is found that both the doped V and Y exist in the form of substitutional point defects replacing Ti atom in the lattice. The photocatalytic activity, evaluated by the degradation of methyl orange, displays that the codoped TiO{sub 2} sample exhibits enhanced visible light photocatalytic activity. The synergistic effects of V and Y drastically improved the Brunauer-Emmett-Teller specific surface area, visible light absorption, and electron-hole pair's separation leading to the enhanced visible light catalytic activity.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Communication: Estimating the initial biasing potential for λ-local-elevation umbrella-sampling (λ-LEUS) simulations via slow growth

In a recent article [Bieler et al., J. Chem. Theory Comput. 10, 3006–3022 (2014)], we introduced a combination of the λ-dynamics (λD) approach for calculating alchemical free-energy differences and of the local-elevation umbrella-sampling (LEUS) memory-based biasing method to enhance the sampling along the alchemical coordinate. The combined scheme, referred to as λ-LEUS, was applied to the perturbation of hydroquinone to benzene in water as a test system, and found to represent an improvement over thermodynamic integration (TI) in terms of sampling efficiency at equivalent accuracy. However, the preoptimization of the biasing potential required in the λ-LEUS method requires “filling up” all the basins in the potential of mean force. This introduces a non-productive pre-sampling time that is system-dependent, and generally exceeds the corresponding equilibration time in a TI calculation. In this letter, a remedy is proposed to this problem, termed the slow growth memory guessing (SGMG) approach. Instead of initializing the biasing potential to zero at the start of the preoptimization, an approximate potential of mean force is estimated from a short slow growth calculation, and its negative used to construct the initial memory. Considering the same test system as in the preceding article, it is shown that of the application of SGMG in λ-LEUS permits to reduce the preoptimization time by about a factor of four.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Tailoring the Magnetic and Hyperthermic Properties of Biphase Iron Oxide Nanocubes through Post-Annealing

Tailoring the magnetic properties of iron oxide nanosystems is essential to expanding their biomedical applications. In this study, 34 nm iron oxide nanocubes with two phases consisting of Fe3O4 and α-Fe2O3 were annealed for 2 h in the presence of O2, N2, He, and Ar to tune the respective phase volume fractions and control their magnetic properties. X-ray diffraction and magnetic measurements were carried out post-treatment to evaluate changes in the treated samples compared to the as-prepared samples, showing an enhancement of the α-Fe2O3 phase in the samples annealed with O2 while the others indicated a Fe3O4 enhancement. Furthermore, the latter samples indicated enhancements in crystallinity and saturation magnetization, while coercivity enhancements were the most significant in samples annealed with O2, resulting in the highest specific absorption rates (of up to 1000 W/g) in all the applied fields of 800, 600, and 400 Oe in agar during magnetic hyperthermia measurements. The general enhancement of the specific absorption rate post-annealing underscores the importance of the annealing atmosphere in the enhancement of the magnetic and structural properties of nanostructures.

Crystallography↗
DOE OSTI2013

Influence of 8-Oxoguanosine on the Fine Structure of DNA Studied with Biasing-Potential Replica Exchange Simulations

Chemical modification or radiation can cause DNA damage, which plays a crucial role for mutagenesis of DNA, carcinogenesis, and aging. DNA damage can also alter the fine structure of DNA that may serve as a recognition signal for DNA repair enzymes. A new, advanced sampling replica-exchange method has been developed to specifically enhance the sampling of conformational substates in duplex DNA during molecular dynamics (MD) simulations. The approach employs specific biasing potentials acting on pairs of pseudodihedral angles of the nucleic acid backbone that are added in the replica simulations to promote transitions of the most common substates of the DNA backbone. The sampled states can exchange with a reference simulation under the control of the original force field. The application to 7,8-dihydro-8oxo-guanosine, one of the most common oxidative damage in DNA indicated better convergence of sampled states during 10 ns simulations compared to 20 times longer standard MD simulations. It is well suited to study systematically the fine structure and dynamics of large nucleic acids under realistic conditions, including explicit solvent and ions. The biasing potential-replica exchange MD simulations indicated significant differences in the population of nucleic acid backbone substates in the case of 7,8-dihydro-8oxo-guanosine compared to a regular guanosine in the same sequence context. This concerns both the ratio of the B-DNA substates BI and BII associated with the backbone dihedral angles ε and z but also coupled changes in the backbone dihedral angles a and g. Such differences may play a crucial role in the initial recognition of damaged DNA by repair enzymes.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2018

Enhanced high-harmonic generation from an all-dielectric metasurface

The recent observation of high-harmonic generation from solids creates a new possibility for engineering fundamental strong-field processes by patterning the solid target with subwavelength nanostructures. All-dielectric metasurfaces exhibit high damage thresholds and strong enhancement of the driving field, making them attractive platforms to control high harmonics and other high-field processes at the nanoscale. Here we report enhanced non-perturbative high-harmonic emission from a Fano-resonant Si metasurface that possesses a classical analogue of electromagnetically induced transparency. The harmonic emission is enhanced by more than two orders of magnitude compared to unpatterned samples. The enhanced high harmonics are highly anisotropic with respect to the excitation polarization and are selective by the excitation wavelength due to its resonant features. Furthermore, by combining nanofabrication technology and ultrafast strong-field physics, our work paves the way for the design of new compact ultrafast photonic devices that operate under high intensities and at short wavelengths.

42 ENGINEERING↗
DOE OSTI2016

Effective mobility enhancement of amorphous In-Ga-Zn-O thin-film transistors by holographically generated periodic conductor

In this study, we demonstrate a mobility enhancement structure for fully transparent amorphous indium-gallium-zinc-oxide thin-film transistors (a-IGZO TFTs) by embedding a holographically generated periodic nano-conductor in the back-channel regions. The intrinsic field-effect mobility was enhanced up to 2 times compared to that of a reference sample. The enhancement originated from a decrease in the effective channel length due to the highly conductive nano-conductor region. By combining conventional and holographic lithography, the performance of the a-IGZO TFT can be effectively improved without varying the composition of the channel layer.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Effect of varying threading dislocation densities on the optical properties of InGaN/GaN quantum wells with intentionally created V-shaped pits

The effect of varying threading dislocation densities on the internal quantum efficiencies (IQEs) of InGaN quantum wells (QWs), with and without intentionally created “V-pits,” is reported here. InGaN QW samples grown on GaN-on-sapphire templates with threading dislocation densities of <1 × 108 and <1 × 109 cm−2 are compared, with and without GaN/InGaN superlattice (SL) layers incorporated to intentionally open up the threading dislocation cores and form large-size “V-pits.” The formation of “V-pits” is confirmed by cross-sectional transmission electron microscopy to initiate from threading dislocations in the SL layers. The densities of the pits are confirmed by plan-view SEM to agree with the substrate threading dislocation densities. The experimental room temperature IQEs of the “V-pit” QW samples are enhanced to 15% ± 1% compared to 6% ± 2% for conventional QW samples. Both conventional and “V-pit” samples show insensitivity to the magnitude of the dislocation densities with respect to IQE performance, while the “V-pit” samples show shifts in the peak emission wavelengths compared to the conventional samples, attributed to strain modulation. This study provides additional understanding of the causes of the observed insensitivity of the IQEs to different threading dislocation densities.

Engineering↗
DOE OSTI2025

Coalescence-Induced Spontaneous Shedding of Microdroplets on Superhydrophobic Surfaces Featuring Enclosed Micropillars with Hierarchical Roughness

This study investigated water vapor condensation on superhydrophobic surfaces (SHSs) featuring micropillars enclosed by wall lattices and having three-tier hierarchical roughness. A total of five samples were created with three (NW-J, W200-J and W400-J samples) having large micropillar depth (~6 μm) and two (NW-S and W200-S samples) having small micropillar depth (~1 μm). Two distinct condensate removal modes were observed during condensation: coalescence-induced jumping on samples with large micropillar depth and coalescence-induced shedding on samples with small micropillar depth. The results showed that the diameter of the shedding droplet on the W200-S sample having small micropillar depth could be as small as 107 μm, as compared to the theoretical critical diameter of 267 μm for gravitational shedding on the same sample. The enhanced functionality of the three-tier nanotextures on the W200-S sample could effectively suppress localized pinning of the three-phase contact line and Wenzel neck formation during the growth of condensate droplets. Consequently, during multidroplet coalescence, the released surface energy easily overcomes the solid–liquid adhesion, leading to spontaneous shedding of merged droplets. The inclusion of the wall lattice aids condensate growth by the droplet self-alignment along the walls and promoting coalescence. As a result, the W200-S sample exhibited the highest condensate collection as well. In conclusion, the proposed surface design has great potential for scaling up and implementation in heating, ventilation, and air-conditioning equipment due to the simplicity of the surface morphology and the facile spray-coating method used to achieve hierarchical roughness.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Design improvements for a recirculating reactor: Enhanced temperature measurement and sample-isolated reactivity in steady-state kinetic studies

Building upon a previous recirculating reactor design [S.A. Tenney, K. Xie, J.R. Monnier, A. Rodriguez, R.P. Galhenage, S. Audrey, D.A. Chen, Rev. Sci. Instrum. 84, 104101 (2013)], we present significant improvements that address key limitations in steady-state kinetic measurements for heterogeneous catalysis. The enhanced reactor design features direct sample heating with a focused IR lamp and temperature measurement in direct contact with the sample, enabling more accurate temperature control and improved kinetic analysis. A critical advancement is the isolation of sample reactivity from reactor wall contributions, ensuring that only the sample contributes to measured reaction rates. This was a limitation in earlier designs where the entire reactor contributed to the observed reactivity. The system incorporates a bypass flow cell for direct comparison with powder catalysts under identical conditions using a standard plug-flow reactor configuration. We demonstrate these capabilities through CO oxidation experiments on Pt(111) single crystals and graphene-passivated Pt(111), highlighting the system's ability to differentiate catalytic activity in model systems and directly compare them with high surface area powder catalysts. This reactor is particularly suited for thin films and low surface area catalysts that are not effectively evaluated in traditional flow reactors, especially for samples with low numbers of active sites or slow reaction rates.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of oxygen stoichiometry on the magnetization profiles and negative magnetization in LSMO thin films

The depth-dependent magnetization in thin film oxygen stoichiometric and oxygen-deficient La 0.7 Sr 0.3 MnO 3 is investigated by using polarized neutron reflectivity and DC bulk magnetometry. The polarized neutron reflectivity results reveal that the stoichiometric sample shows enhanced interfacial magnetization relative to the rest of the film. The oxygen-deficient sample exhibits a reduced average magnetization from the optimized recipe. Both films show regions of suppressed magnetization at the surface regardless of the growth pressure. The oxygen stoichiometric film does not show an interfacial dead layer, whereas the oxygen-deficient film exhibits a dead layer whose thickness changes with temperature. At a low applied field, we observe striking differences in the depth dependence of the magnetic ordering, with the oxygen-deficient film exhibiting exchange spring behavior, while the stoichiometric film shows a constant magnetization direction across the film. Furthermore, these results suggest that the incorporation of oxygen vacancies during growth leads to an accumulation of vacancies at the interface, which is enhanced at higher temperature due to increased oxygen mobility, creating a region of reduced magnetism that couples to the rest of the film. These results offer insight into the complex behavior and role of oxygen vacancies in the magnetism of these systems. Additionally, the study reveals further details of the negative magnetization in La 0.7 Sr 0.3 MnO 3 reported in previous studies, which are discussed here.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Structural changes induced by electric currents in a single crystal of Pr 2 CuO 4

We demonstrate an approach to the structural and electronic property modification of perovskites, focusing on Pr 2 CuO 4 , an undoped parent compound of a class of electron-doped copper-oxide superconductors. Currents were passed parallel or perpendicular to the copper oxygen layers with the voltage ramped up until a rapid drop in the resistivity was achieved, a process referred to as “flash.” The current was then further increased tenfold in current-control mode. This state was quenched by immersion into liquid nitrogen. Flash can drive many compounds into different atomic structures with new properties, whereas the quench freezes them into a long-lived state. Single-crystal neutron diffraction of as-grown and modified Pr 2 CuO 4 revealed a √10 ×√10 superlattice due to oxygen-vacancy order. The diffraction peak intensities of the superlattice of the modified sample were significantly enhanced relative to the pristine sample. Raman-active phonons in the modified sample were considerably sharper. Measurements of electrical resistivity, magnetization, and two-magnon Raman scattering indicate that the modification affected only the Pr-O layers, but not the Cu-O planes. These results point to enhanced oxygen-vacancy order in the modified samples well beyond what can be achieved without passing electrical current. Our work opens a new avenue toward electric field/quench control of structure and properties of layered perovskite oxides.

36 MATERIALS SCIENCE↗
DOE OSTI2013

NAMD - The Engine for Large-Scale Classical MD Simulations of Biomolecular Systems Based on a Polarizable Force Field (ALCF-2 Early Science Program Technical Report)

Large-scale Molecular dynamics (MD) simulation based on atomic models provide a powerful tool to understand the structure-dynamics-function relationships of important biological systems. Recent advances in computing power, especially in supercomputer, make MD simulation more and more popular in modern scientific community. However, the power of classical MD simulation has been limited mainly by the accuracy of the potential energy function and the efficiency of the dynamic algorithm enabling the adequate configurational sampling. This Early Science Project is aimed to make MD simulation method go beyond current limit using the leadership supercomputer Blue Gene/Q Mira. To address the issue of potential energy accuracy, classical Drude oscillator is developed to take into account the electronic polarizability in molecular systems. In order to develop and test the Drude polarizable force field for biomolecules, extensive MD simulations of typical polypeptides, lipids are needed. This requires efficient dynamic sampling algorithm that allows fast sampling. The sampling issue can be addressed by using advanced strategies based on multiple copies in order to enhance the sampling efficiency of brute-force MD. One such method is called replica-exchange MD (REMD).

Roux, Benoit↗
DOE OSTI2016

Propene Metathesis over Supported Tungsten Oxide Catalysts: A Study of Active Site Formation

A detailed investigation was conducted on the factors influencing the properties of silica-supported tungsten oxide catalysts for propene metathesis. A principal goal of this work was to identify the processes involved in the formation of catalytically active sites. To probe the influence of dispersion, samples were prepared across a range of W loadings using two methods of catalyst preparation: incipient wetness impregnation of amorphous silica and ion exchange of mesoporous SBA-15. The samples were characterized by nitrogen adsorption, UV-vis, Raman, and X-ray absorption spectroscopy (XAS). Catalytic activity was observed to increase with W surface concentration up to the point where WO 3 nanoparticles formed. The catalytic performance of all samples was enhanced 2-fold by pretreatment in He, in comparison to pretreatment in air. In situ characterization of samples pretreated in He by Raman and XAS shows an increase in the relative concentration of isolated dioxo W(6+) species relative to mono-oxo W(6+) species, and in situ XAS data collected during propene metathesis indicated that a similar conversion occurs for air-pretreated samples in the presence of propene. For both air- and He-pretreated catalysts an activation period was observed, during which the activity increased and attained steady-state activity. This period was significantly longer for air-pretreated catalysts and was accompanied by the transient formation of acetone. While acetone was not observed during the much shorter transient of He-pretreated samples, in situ XAS provided evidence of reduction occurring in these samples upon contact with propene. In conclusion, it is also notable that, independent of the manner of catalyst preparation or pretreatment, the rate of propene metathesis is first order in propene and exhibits an activation energy of 200 kJ/mol. A model is proposed to explain why only a fraction of the isolated tungstate species is active for propene metathesis (~5%) and why this fraction increases with increasing concentration of W dispersed on silica.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Low temperature hopping in granular oxides La{sub 0.67}Ca{sub 0.33}MnO{sub 3} and La{sub 0.5}Sr{sub 0.5}CoO{sub 3}

We studied electrical transport in La{sub 0.67}Sr{sub 0.33}MnO{sub 3} (LCMO) and La{sub 0.5}Sr{sub 0.5}CoO{sub 3} (LSCO) nanocrystals over a temperature range of 0.4 K ≤ T ≤ 5 K. In both samples, two distinct behaviors of the conductivity are observed. For T>1 K, the variable range hopping regime is observed in LCMO sample with enhancement of the relative permittivity. In contrast, this behavior is not consistent with the extracted parameters in LSCO sample. For T<1 K, the transport is believed to occur through the metallic droplets connected to the intergranular regions where the negative magnetoresistance is due to spin-polarized tunneling phenomenon.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Importance Sampling Model-Based Diffusion for Trajectory Optimization

Trajectory optimization for robotic systems remains a challenging problem. This is especially true for robotic systems featuring nonlinear dynamics and many degrees of freedom. Data-based or model-free diffusion has recently been popularized in the fields of artificial intelligence and trajectory optimization. Model-Based Diffusion provides a data-free method of trajectory optimization, trained at runtime on a system dynamics model, suitable for high-dimensional models. This paper examines how importance sampling can enhance the performance of Model-Based Diffusion for trajectory optimization. Here, we quantify the benefits of importance sampling across three long horizon planning tasks. These results show as much as a 13x improvement in sample efficiency depending on environment and optimization parameters.

Golembeski, Seth [Georgia Institute of Technology,↗
DOE OSTI2018

Effects of Changing Hot Rolling Direction on Microstructure, Texture and Mechanical Properties of Cu-2.7Be Sheets

A hot rolling scheme (cross-rolling and unidirectional rolling) was adopted to process Cu-2.7Be sheets used as multiplier dynodes in photomultiplier. The effects of changing rolling direction on microstructure, texture and mechanical properties were studied by a combination of XRD, EBSD and TEM. It was found that higher copper-type texture and lower brass texture intensity were obtained in the ultimately cross-rolling (CR) sheet compared with the unidirectional rolling (UR) sheet.The EBSD results indicated that the grain orientation from mainly 〈101〉 for UR sample turns to random for CR sample. Great enhancements in YS and UTS after unidirectional rolling were attributed to the massive and polygonal γ precipitates. The CR sample exhibited lower anisotropy, because of the increase of S and γ precipitates with spherical and tiny shape.

36 MATERIALS SCIENCE↗