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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
NASA NTRS1997

Measurement of Atomic Oxygen in Diffuse Aurora and Ion Density in the E-Region

An ion mass spectrometer (IMS) was refurbished, calibrated and supplied to the University of Colorado payload (Dr. Charles Barth, P.I.) which was launched from White Sands in September of 1993 as NASA 33.062. The nose cone failed to deploy and their were problems with the ACS so the mission was declared a failure. However, the door covering the IMS deployed and the instrument obtained data. The launch occurred shortly after a payload carrying solar x-ray detectors was launched. Thus a small portion of the Colorado payload science was salvaged; namely, the NO(+)/O2(+) ratio to compare with the measured x-ray flux. Figure I shows the NO(+) to O2(+) ratio vs. altitude. The behavior is typical of the E-region.

Sharp, William E.↗
DOE OSTI2020

Non-monotonic behavior of the lateral diffusivity in an adsorbate as a function of the surface coverage

Diffusion dynamics of adsorbate particles confined on a surface strongly depends on the adsorbate surface coverage. Our molecular dynamics simulation reveals that the average lateral diffusivity of the Lennard-Jones adsorbate on a flat substrate varies non-monotonically with the surface coverage. Given that the adsorbate becomes stratified into distinct layers, we propose a novel approach to analyze the lateral diffusion of the adsorbate particles in different layers, via dividing the total lateral diffusion into consecutive lateral diffusion processes, separated by the layer boundary crossing events. A new definition of the lateral diffusivity in the specific layer has been introduced, and it is revealed that the total lateral diffusivity is equal to the sum of lateral diffusivities in different layers. Furthermore, the non-monotonic behavior of the average lateral diffusivity with the surface coverage is found to result from the difference in behavior of the lateral diffusivity between the first and other layers.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Ab initio molecular dynamics (AIMD) simulations of NaCl, UCl 3 molten salts

Ab initio molecular dynamics (AIMD) simulations are used to calculate select thermophysical and thermodynamic properties of NaCl, UCl and NaCl-UCl 3 molten salts. Following established approaches, the AIMD simulations include a model for Van der Waals interactions. The Langreth & Lundqvist (vDW-DF2), DFT-D3, and density-dependent energy correction (DFT-dDsC) dispersion models are first tested for molten NaCl in order to assess their accuracy for density and heat capacity predictions across a range of temperatures. Based on the NaCl results, the vdW-DF2 and DFT-dDsC methods are extended to the UCl 3 system and compared to available experimental data. Next, mixtures of NaCl-UCl 3 are investigated and analyzed with respect to the deviation from ideal solution behavior. For the DFT-dDsC simulations, density deviates by up to 2% from an ideal mixture, with the maximum occurring close to the eutectic composition. The mixing energy also deviates from an ideal solution and exhibits a minimum of about -0.074 to eV per formula unit, again close to the eutectic composition. Finally, the compressibility and species diffusivity of the pure and mixed salt systems are calculated. The diffusivities are slightly reduced in the mixed compared to the pure systems and the compressibilities loosely follow a linear correlation as a function of the UCl 3 composition. The trends observed for mixing properties are rationalized by correlating them to the coordination chemistry, which emphasizes the importance of maintaining the extended network formed by U and Cl ions as the NaCl concentration increases. The concentration at which breakdown of the extended network occurs, roughly coincides with the minimum of both the mixing energy and the deviation from ideal solution behavior for density.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

Harnessing structural stochasticity in the computational discovery and design of microstructures

This paper presents a deep generative model-based design methodology for tailoring the structural stochasticity of microstructures. Although numerous methods have been established for designing deterministic (periodic) or stochastic microstructures, a systematic design approach that allows the unified treatment of both deterministic and stochastic microstructure design domains has yet to be created. The proposed methodology resolves this issue by learning a unified feature space that embodies diverse structural patterns with continuously varying stochasticity levels. A highly diverse microstructure database is established to incorporate various types of deterministic and stochastic microstructure patterns. A property-aware deep generative model is proposed to learn a unified feature space of the structural characteristics, as well as the relationship between structure features and properties of interest. Autoencoder (AE), Variational Autoencoder (VAE), and Adversarial Autoencoder (AAE) are compared to understand their relative merits in the property-aware learning of the unified feature space. Microstructural designs with tailorable stochasticity and properties are obtained by searching the unified feature space. Multiple design cases are presented to demonstrate the capability of designing microstructures for structural stochasticity and properties. Furthermore, the proposed method is employed to create stochastically graded structures, which manipulate the mechanical behaviors by varying the local stochasticity of the structure.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Black textile with bottom metallized surface having enhanced radiative cooling under solar irradiation

We discuss the cooling performance of garments can play an important role of enabling comfortable human activities under extreme environments. Imparting extra cooling performance to a garment in a passive way is extremely challenging under the sunlight which provides a huge energy influx to the garment, especially made of black colored textile. In this study, a solar-adaptive-textile (SAT) has been designed and experimentally demonstrated. Near-infrared (NIR) transmittance to the human skin from the solar irradiance has been intercepted by incorporating a nanoscale sputtered thin aluminum metal film underneath the textile layer facing the skin. The high-pressure sputtering employed allows a deep penetration of aluminum into the fabric structure for enhanced solar-energy-blocking effect and film stability. The aluminum layer effectively reduces the solar irradiance as well as the thermal radiation from the textile, which gets heated in lieu of the human skin. The outdoor, under-the-sun measurements with a simulated skin showed an outstanding 2 °C cooling effect compared to the normal textile without the metal film, while preserving most of the given textile properties such as colors, air permeability and wicking behavior.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Thermodynamic control on the decomposition of organic matter across different electron acceptors

The increasing availability of high-resolution characterization of natural organic matter (OM) data has shifted the paradigm of lumped descriptions of OM components and potential microbial activities. Our recent development of a substrate-explicit thermodynamic model uniquely enables incorporating complex OM pools to formulate biogeochemical reaction models based on their elemental compositions. While this previous work facilitates prediction of aerobic respiration of complex OM, it is equally imperative to consider the role of non-oxygenic electron acceptors in regulating OM turnover and the fate of carbon. In this study, we significantly expand our previous model by flexibly incorporating both detailed OM chemistry and electron acceptors other than oxygen. Here, our modeling analysis has revealed substantial variations in the energy status of OM molecules across different soils, which drive the co-occurrence of different electron-accepting processes. We demonstrated the effectiveness of the proposed model using a consistency check with experimental data. Through systematic evaluation of the impact of diverse chemical inputs (both electron donors and acceptors) on OM decomposition, the new model also revealed how key microbial growth parameters such as carbon use efficiency (CUE) and reaction rates vary across different electron-accepting processes. Our model provides a unified framework integrating thermodynamic and kinetic constraints on microbial metabolic activities. It complements traditional kinetic models, which are often designed solely to capture mass fluxes. We conclude that thermodynamic modeling emerges as a powerful tool for describing the mechanisms underlying the interplay between microbial growth and OM chemistry and cycling across different electron acceptors, enhancing our ability to project complex ecosystem behaviors in dynamic environments.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Simulated Aquifer Heterogeneity Leads to Enhanced Attenuation and Multiple Retention Processes of Zinc

Alluvial aquifers serve as one of the main water sources for domestic, agricultural, and industrial purposes globally. Groundwater quality, however, can be threatened by naturally occurring and anthropogenic metal contaminants. Differing hydrologic and biogeochemical conditions between predominantly coarse-grained aquifer sediments and embedded layers or lenses of fine-grained materials lead to variation in metal behavior. Here, we examine processes controlling Zn partitioning within a dual-pore domain-reconstructed alluvial aquifer. Natural coarse aquifer sediments from the Wind River-Little Wind River floodplain near Riverton, WY, were used in columns with or without fine-grained lenses to examine biogeochemical controls on Zn concentrations, retention mechanisms, and transport. Furthermore, following the introduction of Zn to the groundwater source, Zn preferentially accumulated in the fine-grained lenses, despite their small volumetric contributions. While the clay fraction dominated Zn retention in the sandy aquifer, the lenses supported additional reaction pathways of retention—the reducing conditions within the lenses resulted in ZnS precipitation, overriding the contribution of organic matter. Zinc concentration in the groundwater controlled the formation of Zn-clays and Zn-layered double hydroxides, whereas the extent of sulfide production controlled precipitation of ZnS. Our findings illustrate how both spatial and compositional heterogeneities govern the extent and mechanisms of Zn retention in intricate groundwater systems, with implications for plume behavior and groundwater quality.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Sensitivity of Grass Fires Burning in Marginal Conditions to Atmospheric Turbulence

Abstract Atmospheric forcing and interactions between the fire and atmosphere are primary drivers of wildland fire behavior. The atmosphere is known to be a chaotic system that, although deterministic, is very sensitive to small perturbations to initial conditions. We assume that as a result of the tight coupling between fire and atmosphere; wildland fire behavior, in turn, should also be sensitive to perturbations in atmospheric initial conditions. Observations suggest that low intensity prescribed fire, in particular, is susceptible to small perturbations in the wind field, which can significantly alter fire spread. Here, we employ a computational fluid dynamics model of coupled fire‐atmosphere interactions to answer the question: How sensitive is fire behavior to small variations in atmospheric turbulence? We perform ensemble simulations of fires in homogenous grass fuels. The only difference between ensemble members is the state of the turbulent atmosphere provided to the model throughout the simulation. The atmospheric state is a function of the initial conditions applied at the start of the simulation and boundary conditions applied throughout the simulation. We find a wide range of outcomes, with area burned ranging from 2,212 to 11,236 m 2 (>400% change), driven primarily by sensitivity to initial conditions, with nonnegligible contributions from boundary condition variability during the initial 30 s of simulation. Our results highlight the need for ensemble simulations, especially when considering fire behavior in marginal burning conditions.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Predicting and accessing metastable phases

Metastable phase formation of Ln 2 O 3 phases was explained and successfully predicted using calculated metastable phase diagrams. Irradiation experiments of Lu 2 O 3 show formation of 3 phases, confirming the prediction, showing a unique behavior.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Osmotic and phoretic competition explains chemotaxic assembly and sorting

Microscale objects responding to chemical gradients by migrating toward or away from a preferred species is a simple yet constitutive mechanism by which transport occurs in biological organisms. Synthetic chemotaxis provides key physical descriptions of simplified systems that can be used in biological models, or in the creation of advanced responsive material systems. In this article, we provide a quantitative framework for understanding synthetic chemotaxis of microparticles which involves a competition between phoresis and osmosis. We present separate quantitative measurements of phoresis and osmosis acting on individual taxing particles, finding that phoresis follows the long-predicted v ∼ 1 / r 2 scaling while the osmotic contribution depends on the geometry and details of the system, and must be solved on a case-by-case basis. Through this, we are able to develop a more accurate picture of particle transport at the single particle level. Equipped with this approach, we go on to describe how high concentrations of particles in a symmetric chemical gradient grow close-packed hives that reach a steady-state size tunable through light intensity or particle size. Last, we demonstrate that mixed particles experiencing the same chemical gradient will selectively migrate toward or away depending on the nature of the particle surface, thereby locally sorting out a particular species. We anticipate these results will be important in describing both biological and synthetic chemotaxis in phoretic systems and should bring a wealth of studies that take advantage of competing osmotic flows to illicit unexpected dynamic active behavior.

Science & Technology - Other Topics↗
DOE OSTI2024

Large magnetoresistance and first-order phase transition in antiferromagnetic single-crystalline EuAg 4 Sb 2

Here, we present the results of a thorough investigation of the physical properties of EuAg 4 Sb 2 single crystals using magnetization, heat capacity, and electrical resistivity measurements. High-quality single crystals, which crystallize in a trigonal structure with space group 𝑅⁢$\bar{3}$𝑚, were grown using a conventional flux method. Temperature-dependent magnetization measurements along different crystallographic orientations confirm two antiferromagnetic phase transitions around 𝑇 𝑁⁢1 = 10.5K and 𝑇 𝑁⁢2 = 7.5K. Isothermal magnetization data exhibit several metamagnetic transitions below these transition temperatures. Antiferromagnetic phase transitions in EuAg 4 Sb 2 are further confirmed by two sharp peaks in the temperature-dependent heat capacity data at 𝑇 𝑁⁢1 and 𝑇 𝑁⁢2 , which shift to lower temperature in the presence of an external magnetic field. Our systematic heat capacity measurements utilizing a long-pulse and single-slope analysis technique allow us to detect a first-order phase transition in EuAg 4 Sb 2 at 7.5 K. The temperature-dependent electrical resistivity data also manifest two features associated with magnetic order. The magnetoresistance exhibits a broad hump due to a field-induced metamagnetic transition. Remarkably, the magnetoresistance keeps increasing without showing any tendency to saturate as the applied magnetic field increases, and it reaches ∼20 000% at 1.6 K and 60 T. At high magnetic fields, several magnetic quantum oscillations are observed, indicating a complex Fermi surface. A large negative magnetoresistance of about −55% is also observed near 𝑇 𝑁⁢1 . Moreover, the 𝐻−𝑇 phase diagram constructed using magnetization, heat capacity, and magnetotransport data indicates complex magnetic behavior in EuAg 4 Sb 2 .

36 MATERIALS SCIENCE↗
DOE OSTI2024

The insufficiency of the charge transfer model for resonant $\text{XES}$ in $\text{UF}$ 4

Recently, it was suggested that the single-electron charge transfer model (ligand 2p to Uranium 5f transition) could be used to explain the U M 4,5 Resonant X-ray Emission Spectroscopy (XES) of uranium dioxide (UO 2 ) and uranium tetrafluoride (UF 4 ). Here in this report, it is shown that this model produces results inconsistent with a joint consideration of both of the bandgaps of UO 2 and UF 4 and is thus insufficient to explain the observed behavior. An alternative Raman-based model is proposed.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Metamaterials for Mechanically Directing Cell Phenotype

Recently, abundant research has begun to reveal how microscale surface topography can influence a wide range of cell phenotypes in vitro, such as cell mobility, cell size and cell viability (Flemming et al. 1999, Nikkhah et al. 2012, Wang et al. 2016). However, while these studies shed some light on cell interactions with 2D surfaces of different length scales, cells in vivo experience their surroundings in 3D. Therefore, investigations into cell interactions with varying 3D microstructures are needed to gain biologically relevant insight into how microarchitecture and feature size influences cell behavior. Understanding this relationship between 3D microstructure and cell behavior will have a huge impact on tissue engineering and mechanobiology. Until now, the ability to fabricate complex 3D microstructures for cell behavior studies has been limited. This study harnessed LLNL’s Projection Micro-Stereolithography (PμSL) capability to probe the effects of micron-scale changes in 3D architecture on cell phenotype. Furthermore, our studies explored the application of external forces—such as cyclic loading and flow-induced shear stress—to cell-seeded 3D microstructures to further examine cell behavior.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Topology Optimization of Manufacturable Photonic Crystals With Complete Bandgaps [Dissertation]

Periodic structures consisting of dielectric material, i.e. photonic crystals, are capable of prohibiting electromagnetic waves within frequency ranges referred to as bandgaps. This principle was first demonstrated with alternating slabs of material and later demonstrated with three-dimensional (3D) structures capable of reflecting waves from any incident angle. A number of potential applications for photonic bandgap structures exist, including loss-less sharp corner waveguides, fiber optics, and radome design. Further, many optical devices could benefit from the perfect-mirror behavior of photonic crystals.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Flowability of Crumbler Rotary Shear Size-Reduced Granular Biomass: An Experiment-Informed Modeling Study on the Angle of Repose

Biomass has potential as a carbon-neutral alternative to petroleum for chemical and energy products. However, complete replacement of fossil fuel is contingent upon efficient processes to eliminate undesirable characteristics of biomass, e.g., low bulk density, variability, and storage-induced quality problems. Mechanical size reduction via comminution is a processing operation to engineer favorable biomass flowability in handling. Crumbler rotary shear mill has been empirically demonstrated to produce more uniformly shaped particles with higher flowability than hammermilled biomass. This study combines modeling and experimentation to unveil fundamental understandings of the relation between granular particle characteristics and biomass flow behavior, which elucidate underlying mechanisms and guide selection of critical processing parameters. For this purpose, the impact of critical material attributes, including particle size (2–6 mm), particle shape (briquette, chip, clumped-sphere, cube, etc.), and surface roughness, on the angle of repose (AOR) of milled pine chips were investigated using discrete element method (DEM) simulations. Forest Concepts Crumbler rotary shear system is used to produce milled pine particles within the same size range considered in DEM simulations. AOR of different sets of these particles were measured experimentally to benchmark DEM results against experimental data. Specific energy consumption for the comminution of biomass with different particle size and moisture content are measured for technoeconomic analysis. Our results show that the smaller size (2 mm) of pine particle achieves better followability (i.e., smaller AOR) while the energy cost of comminution is significantly higher and bulk density is almost the same as the 6-mm pine particles. For the 2-mm particle size, Crumbles from veneer have better flow properties than Crumbles from chips. Contrarily, no significant difference was observed between the AOR of the two materials for the 6-mm particle size. Furthermore, from DEM simulations, mechanical interlocking between particles was found as a dominant factor in determining AOR of complex-shaped particles such as milled pine, which cannot be accurately captured by using simple particle shapes (e.g., mono-sphere) with a rolling resistance model. Conversely, clumped-sphere model alleviates this limitation without increasing computational cost significantly and can be used for accurate representation of biomass granular particles when simulating free-flow behavior.

09 BIOMASS FUELS↗
DOE OSTI2025

A Novel Approach to Fast Calculation of High-Order Q-Cumulants

The method of Q-cumulants has been shown as a powerful tool to study the fine details of the azimuthal anisotropies in high-energy nucleus-nucleus collisions. A new method for the fast calculation of arbitrary order Q-cumulant $v_{n}\{2k\}$ values, based on the partition of a non-negative integer l $\le$ m for calculation of the 2m-particle azimuthal correlations is presented in this paper. Unlike the standard Q-cumulants method in which the calculation of high-order multi-particle calculations is impractical, the newly proposed method enables easy calculation. The validity of the method is proven via a toy model that uses the elliptic power distribution to simulate anisotropic emission of particles. The method enables the study of fine details of the $v_{2}$ distribution, such as higher-order central moments of the $v_{2}$ distribution, as well as the hydrodynamic behavior of the Quark-Gluon Plasma.

FOS: Physical sciences↗
DOE OSTI2024

Land cover and space use influence coyote carnivory: evidence from stable-isotope analysis

For many species, the relationship between space use and diet composition is complex, with individuals adopting varying space use strategies such as territoriality to facilitate resource acquisition. Coyotes ( Canis latrans ) exhibit two disparate types of space use; defending mutually exclusive territories (residents) or moving nomadically across landscapes (transients). Resident coyotes have increased access to familiar food resources, thus improved foraging opportunities to compensate for the energetic costs of defending territories. Conversely, transients do not defend territories and are able to redirect energetic costs of territorial defense towards extensive movements in search of mates and breeding opportunities. These differences in space use attributed to different behavioral strategies likely influence foraging and ultimately diet composition, but these relationships have not been well studied. We investigated diet composition of resident and transient coyotes in the southeastern United States by pairing individual space use patterns with analysis of stable carbon (δ 13 C) and nitrogen (δ 15 N) isotope values to assess diet. During 2016–2017, we monitored 41 coyotes (26 residents, 15 transients) with GPS radio-collars along the Savannah River area in the southeastern United States. We observed a canopy effect on δ 13 C values and little anthropogenic food in coyote diets, suggesting 13 C enrichment is likely more influenced by reduced canopy cover than consumption of human foods. We also observed other land cover effects, such as agricultural cover and road density, on δ 15 N values as well as reduced space used by coyotes, suggesting that cover types and localized, resident-like space use can influence the degree of carnivory in coyotes. Finally, diets and niche space did not differ between resident and transient coyotes despite differences observed in the proportional contribution of potential food sources to their diets. Although our stable isotope mixing models detected differences between the diets of resident and transient coyotes, both relied mostly on mammalian prey (52.8%, SD = 15.9 for residents, 42.0%, SD = 15.6 for transients). Resident coyotes consumed more game birds (21.3%, SD = 11.6 vs 13.7%, SD = 8.8) and less fruit (10.5%, SD = 6.9 vs 21.3%, SD = 10.7) and insects (7.2%, SD = 4.7 vs 14.3%, SD = 8.5) than did transients. Our findings indicate that coyote populations fall on a feeding continuum of omnivory to carnivory in which variability in feeding strategies is influenced by land cover characteristics and space use behaviors.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

ANS MiNES 2023 Poster

The dynamic mechanical properties of four varieties of high purity graphite as well as the depth of penetration (DoP) of a small-scale shaped charge into these grades was experimentally determined. The grades chosen were PCEA, NBG-18, and NBG-25. These grades provide a wide range of physical properties: in density from 1.80 – 1.85 g/cc, in maximum particle size from 10s to 1000s of µm, and in porosity from 18% to 20%. The quasistatic and dynamic compressive strengths of each grade were determined and correlated to their physical properties. The split Hopkinson pressure bar experiments showed both the dynamic strength and dominant shear failure mechanisms. A small scale shaped charge was used to compare the resistance of graphite to hypervelocity jet impacts: the Teledyne RP-4. The RP-4 has a 1.01” outer diameter and 3.44 g of RDX with an RP-80 booster (86 mg PETN + 123 mg RDX). A select number of samples were analyzed using X-Ray Computed Tomography (XCT), allowing for the full characterization of the undisturbed wound channel. A selection of other samples were physically sectioned and wound channels mapped from the sections. In addition to DoP, the wound geometry was characterized in terms of total volume and diameter at different depths. The wound channel characteristics for each grade were correlated to the compressive strengths and physical properties. In several of the test samples, the wound channel diameter was smaller than the diameter of the shaped charge slug just behind where the slug had penetrated the sample. These results indicated that the wound geometry was dependent on the compressive hysteresis behavior of graphite.

36 MATERIALS SCIENCE↗