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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Ion transport and loss in the earth's quiet ring current. I - Data and standard model

A study of the transport and loss of ions in the earth's quiet time ring current, in which the standard radial diffusion model developed for the high-energy radiation belt particles is compared with the measurements of the lower-energy ring current ions, is presented. The data set provides ionic composition information in an energy range that includes the bulk of the ring current energy density, 1-300 keV/e. Protons are found to dominate the quiet time energy density at all altitudes, peaking near L of about 4 at 60 keV/cu cm, with much smaller contributions from O(+) (1-10 percent), He(+) (1-5 percent), and He(2+) (less than 1 percent). A minimization procedure is used to fit the amplitudes of the standard electric radial diffusion coefficient, yielding 5.8 x 10 exp -11 R(E-squared)/s. Fluctuation ionospheric electric fields are suggested as the source of the additional diffusion detected.

Sheldon, R. B.↗
DOE OSTI2025

Exploring the energy landscape of RBMs: reciprocal space insights into bosons, hierarchical learning and symmetry breaking

Deep generative models have become ubiquitous due to their ability to learn and sample from complex distributions. Despite the proliferation of various frameworks, the relationships among these models remain largely unexplored, a gap that hinders the development of a unified theory of AI learning. In this work, we address two central challenges: clarifying the connections between different deep generative models and deepening our understanding of their learning mechanisms. We focus on Restricted Boltzmann Machines (RBMs), a class of generative models known for their universal approximation capabilities for discrete distributions. By introducing a reciprocal space formulation for RBMs, we reveal a connection between these models, diffusion processes, and systems of coupled bosons. Our analysis shows that at initialization, the RBM operates at a saddle point, where the local curvature is determined by the singular values of the weight matrix, whose distribution follows the Marc̆enko-Pastur law and exhibits rotational symmetry. During training, this rotational symmetry is broken due to hierarchical learning, where different degrees of freedom progressively capture features at multiple levels of abstraction. This leads to a symmetry breaking in the energy landscape, reminiscent of Landau’s theory. This symmetry breaking in the energy landscape is characterized by the singular values and the weight matrix eigenvector matrix. We derive the corresponding free energy in a mean-field approximation. We show that in the limit of infinite size RBM, the reciprocal variables are Gaussian distributed. Our findings indicate that in this regime, there will be some modes for which the diffusion process will not converge to the Boltzmann distribution. To illustrate our results, we trained replicas of RBMs with different hidden layer sizes using the MNIST dataset. Our findings not only bridge the gap between disparate generative frameworks but also shed light on the fundamental processes underpinning learning in deep generative models.

97 MATHEMATICS AND COMPUTING↗
NASA NTRS1990

Ion phase space densities in the Jovian magnetosphere

The Voyager Low Energy Charged Particle ion data from the Jovian magnetosphere were analyzed to determine the phase-space densities of particles in the region between 5 and 80 Jupiter radii. Data from the Jovian current sheet crossings for locally mirroring particles were used. These are the first calculations of phase-space densities in the nondipolar field region containing the Jovian magnetodisk current sheet. The profiles are consistent with lossy inward radial transport and a source in the outer magnetosphere. The inferred loss rate in a radial diffusion model measuring how quickly particles are scattered out of the neutral sheet exceeds the usual strong diffusion loss rate.

Paranicas, C. P.↗
NASA NTRS2000

Long Term Degradation of Resin for High Temperature Composites

The durability of polymer matrix composites exposed to harsh environments is a major concern. Surface degradation and damage are observed in polyimide composites used in air at 125 to 300 C. It is believed that diffusion of oxygen into the material and oxidative chemical reactions in the matrix are responsible. Previous work has characterized and modeled diffusion behavior, and thermogravimetric analyses (TGAs) have been carried out in nitrogen, air, and oxygen to provide quantitative information on thermal and oxidative reactions. However, the model developed using these data was not able to capture behavior seen in isothermal tests, especially those of long duration. A test program that focuses on lower temperatures and makes use of isothermal tests was undertaken to achieve a better understanding of the degradation reactions under use conditions. A new low-cost technique was developed to collect chemical degradation data for isothermal tests lasting over 200 hr in the temperature range 125 to 300 C. Results indicate complex behavior not captured by the previous TGA tests, including the presence of weight-adding reactions. Weight gain reactions dominated in the 125 to 225 C temperature range, while weight loss reactions dominated beyond 225 C. The data obtained from isothermal tests was used to develop a new model of the material behavior. This model was able to fully capture the behavior seen in the tests up to 275 C. Correlation of the current model with both isothermal data at 300 C and high rate TGA test data is mediocre. At 300 C and above, the reaction mechanisms appear to change. Attempts (which failed) to measure non-oxidative degradation indicate that oxidative reactions dominate the degradation at low temperatures. Based on this work, long term isothermal testing in an oxidative atmosphere is recommended for studying the degradation behavior of this class of materials.

Patekar, Kaustubh A.↗
NASA NTRS2010

The Lattice and Thermal Radiation Conductivity of Thermal Barrier Coatings: Models and Experiments

The lattice and radiation conductivity of ZrO2-Y2O3 thermal barrier coatings was evaluated using a laser heat flux approach. A diffusion model has been established to correlate the coating apparent thermal conductivity to the lattice and radiation conductivity. The radiation conductivity component can be expressed as a function of temperature, coating material scattering, and absorption properties. High temperature scattering and absorption of the coating systems can be also derived based on the testing results using the modeling approach. A comparison has been made for the gray and nongray coating models in the plasma-sprayed thermal barrier coatings. The model prediction is found to have a good agreement with experimental observations.

Zhu, Dongming↗
NASA NTRS2001

Experiments and Model Development for the Investigation of Sooting and Radiation Effects in Microgravity Droplet Combustion

Today, despite efforts to develop and utilize natural gas and renewable energy sources, nearly 97% of the energy used for transportation is derived from combustion of liquid fuels, principally derived from petroleum. While society continues to rely on liquid petroleum-based fuels as a major energy source in spite of their finite supply, it is of paramount importance to maximize the efficiency and minimize the environmental impact of the devices that burn these fuels. The development of improved energy conversion systems, having higher efficiencies and lower emissions, is central to meeting both local and regional air quality standards. This development requires improvements in computational design tools for applied energy conversion systems, which in turn requires more robust sub-model components for combustion chemistry, transport, energy transport (including radiation), and pollutant emissions (soot formation and burnout). The study of isolated droplet burning as a unidimensional, time dependent model diffusion flame system facilitates extensions of these mechanisms to include fuel molecular sizes and pollutants typical of conventional and alternative liquid fuels used in the transportation sector. Because of the simplified geometry, sub-model components from the most detailed to those reduced to sizes compatible for use in multi-dimensional, time dependent applied models can be developed, compared and validated against experimental diffusion flame processes, and tested against one another. Based on observations in microgravity experiments on droplet combustion, it appears that the formation and lingering presence of soot within the fuel-rich region of isolated droplets can modify the burning rate, flame structure and extinction, soot aerosol properties, and the effective thermophysical properties. These observations led to the belief that perhaps one of the most important outstanding contributions of microgravity droplet combustion is the observation that in the absence of asymmetrical forced and natural convection, a soot shell is formed between the droplet surface and the flame, exerting an influence on the droplet combustion response far greater than previously recognized. The effects of soot on droplet burning parameters, including burning rate, soot shell dynamics, flame structure, and extinction phenomena provide significant testing parameters for studying the structure and coupling of soot models with other sub-model components.

Choi, Mun Young↗
NASA NTRS1982

Ion-beam-induced topography and surface diffusion

It is pointed out that the development of surface topography along with enhanced surface and bulk diffusion processes accompanying ion bombardment have generated growing interest among users of ion beams and plasmas for thin film or material processing. Interest in these processes stems both from attempts to generate topographic changes for specific studies or applications and from the need to suppress or control undesirable changes. The present investigation provides a summary of the current status of impurity-induced texturing, with emphasis on recent developments. Particular attention is given to the texturing accompanying deposition of an impurity material onto a solid surface while simultaneously etching the surface with an ion beam. A description of experimental considerations is provided, and a thermal-diffusion model is discussed along with the development of sputter cones, and aspects of impact-enhanced surface diffusion.

Robinson, R. S.↗
NASA NTRS1984

On the linear approximation of gravity wave saturation in the mesosphere

Lindzen's model of gravity wave breaking is shown to be inconsistent with the process of convective adjustment and associated turbulent outbreak. The K-theory turbulent diffusion model used by Lindzen implies a spatially uniform turbulent field which is not in agreement with the fact that gravity wave saturation and the associated convection produce turbulence only in restricted zones. The Lindzen model may be corrected to some extent by taking the turbulent Prandtl number for a diffusion acting on the wave itself to be very large. The eddy diffusion coefficients computed by Lindzen then become a factor of 2 larger and eddy transports of heat and constituents by wave fields vanish to first order.

Chao, W. C.↗
DOE OSTI2025

Insights Into Seismicity Associated With Flexibly Operating Enhanced Geothermal System From Real‐Time Distributed Acoustic Sensing

Enhanced Geothermal Systems (EGS) have the capacity to broaden the accessible resource pool for geothermal power generation. Traditionally viewed as a “baseload” resource, their flexible operation might also enable dispatchable load‐following generation and long‐term energy storage, aligning them with the evolving landscape of decarbonized electricity systems. However, increasing permeability and extracting energy during EGS operations can induce microseismic events; for many prior EGS efforts, some associated seismicity has been observed. While energetically beneficial, the flexibility of EGS operations prompts our inquiry into whether new types of operations will yield previously unseen seismicity patterns. We demonstrate the use of distributed acoustic sensing (DAS) with real‐time edge computing to monitor seismicity during a pilot test of a cyclically operated EGS facility at the Blue Mountain geothermal field. Our focus lies in uncovering seismicity insights from the real‐time microseismic catalog, particularly during load‐following dispatchability tests simulating flexible EGS operation. Here, we find that variations in pore pressure consistently correlate with seismicity, and that controlling pressure cycles during flexible operations appears to constrain microseismic activity during subsequent cycles. The spatio‐temporal evolution of microseismic clouds recorded during cyclic injection cycles fits diffusive models over our available observation period. Additionally, seismicity elevation lags behind pore pressure increases, likely due to pressure diffusion to the fracture system boundary. Through real‐time monitoring, we offer novel insights into seismicity associated with flexibly operating EGS. Our findings suggest that leveraging DAS and edge computing can inform EGS operations and help mitigate induced seismicity.

Chamarczuk, Michal [Rice Univ., Houston, TX (Unite↗
NASA NTRS1980

Ground-based measurements of DM-2 rocket exhaust effluents using fixed-flow samplers and electrets

Electret devices were used to collect samples of rocket exhaust products. The samples were analyzed by X-ray spectroscopy. The performance of the electrets was compared with that of Thiokol fixed flow samplers during the static test firing of a solid rocket motor (SRM) demonstration model. A vertical profile of wind speed, wind direction, and air temperature, used as inputs to the multilayer diffusion model for the SRM static test is presented.

Susko, M.↗
NASA NTRS1985

Coupled low-energy - ring current plasma diffusion in the Jovian magnetosphere

The outwardly diffusing Iogenic plasma and the simultaneously inwardly diffusing ring current plasma in the Jovian magnetosphere are described using a coupled diffusion model which incorporates the effects of the pressure gradient of the ring current into the cross-L diffusion coefficient. The coupled diffusion coefficient is derived by calculating the total energy available to drive the diffusion process. The condition is imposed that the diffusion coefficient takes on a local minimum value at some point in the region L = 7-8, at which point the gradient of the Io plasma density is specified as ramp value given by Siscoe et al. (1981). The hypothesis that the pressure gradient of the ring current causes the diminution of radial plasma transport is tested, and solution profiles for the Iogenic and ring current plasma densities are obtained which imply that the Io plasma ramp is caused by a high-density, low-energy component of the ring current hitherto unobserved directly.

Summers, D.↗
NASA NTRS2000

Characteristics of Fe Ablation Trials Observed During the 1998 Leonid Meteor Shower

Eighteen Fe ablation trails were observed during the 17/18 Nov 1998 Leonid meteor shower with an airborne Fe lidar aboard the National Simulation Facility/National Center for Atmospheric Research (NSF/NCAR) Electra aircraft over Okinawa. The average altitude of the 18 trails from the high velocity (72 km/s) Leonid meteors, 95.67 +/- 0.93 km, is approximately 6.7 km higher than previously observed for slower (approx. 30 km/s) sporadic meteors. This height difference is consistent with the assumption that meteors ablate when the kinetic energy imparted to the atmosphere reaches a critical threshold. The average age of the Fe trails, determined by a diffusion model, is 10.1 min. The youngest ages were observed below 92 km and above 98 km where chemistry and diffusion dominate, respectively. The average abundance of the trails is ten percent of the abundance of the background Fe layer. Observations suggest that the 1998 Leonid shower did not have a significant impact on the abundance of the background Fe layer.

Chu, Xin-Zhao↗
NASA NTRS1972

A model for Jupiter's proton radiation belt

A model for electron and proton energy and density in Jupiter's radiation belt is proposed. It is assumed that electrons diffuse inward from the solar wind. The Davis and Chang diffusion model, in which there is a very steep L-shell dependence in density and energy, is scaled outwards from the peak of the belts at about 1.5 to 2 Jupiter radii to the magnetopause as defined by the magnetic moment. The energetic electron density is calculated to be one billionth of the density in the solar wind, and that is assumed to be the trapping ratio of Jupiter's synchrotron belts. It is further assumed that the same figures apply to protons. The flux density at 80 MHz was measured by the Culgoora ring to be identical to that at 3000 MHz, implying a constant flux density of the synchrotron source of over 20 or 30 to 1 in frequency. It is suggested that the synchrotron spectrum is flat over more than an order of magnitude of frequency. Jupiter is an enormous synchrotron source and has a strong magnetic field, causing long diffusion times for electrons in the magnetosphere.

Warwick, J.↗
NASA NTRS1973

Exhaust cloud rise and growth for Apollo Saturn engines.

Empirical and analytical results have been reduced from time-lapse photographs of exhaust clouds during the launch of Apollo 10, 14, 15, and 16 from the Kennedy Space Center. Theoretical predictions of the buoyant cloud rise and growth compare very favorably to actual measurements. The mathematical model predicts with engineering accuracy the terminal altitude and size of the clouds. A principal input to MSFC's multilayer diffusion model is top height of the exhaust cloud. It is this characteristic dimension that is the main subject of this report. An interesting occurrence during launch is the formation of bimodal exhaust cloud which is due to the north-south oriented flame trench directly beneath the base of the vehicle. This study has added considerable information on engine exhaust cloud rise and growth which is essential to the study of atmospheric dispersal in time and space.

Susko, M.↗
NASA NTRS1974

Boundary-layer analysis of subsonic inlet diffuser geometries for engines nacelles

Theoretical Mach number distributions and boundary-layer parameters are presented for subsonic nacelle inlet diffuser geometries with length to exit diameter ratios ranging from 0.4 to 1.6 and diffuser exit area to throat area ratios ranging from 1.1 to 2.0. The major portion of the study was done with a cubic diffuser contour with the inflection point at the midpoint of the diffuser, a diffuser throat Mach number of 0.6, and a free-stream Mach number of 0.12. Calculations were performed at both model (diffuser exit diameter, 30.5 cm) and full-scale (diffuser exit diameter, 183 cm) sizes. Separation limits were defined by establishing a separation boundary on plots of diffuser area ratio as a function of diffuser length to diameter ratio. The effects of diffuser contour, inlet lip geometry, and throat Mach number on the boundary-layer characteristics are illustrated. The major results of the study indicate that the separation boundary is shifted to greater area ratios by (1) increasing the diffuser length, (2) increasing the scale of the diffuser and, (3) moving the inflection point of the diffuser contour to or ahead of the midpoint of the diffuser.

Albers, J. A.↗
NASA NTRS1977

Spatial distribution of Compton-produced X-ray flux from rich and regular clusters of galaxies

The spatial distribution of radio and X-ray fluxes from rich and regular clusters of galaxies is discussed. A diffusion model is investigated in which high-energy electrons are ejected from a point source at the center of the cluster. While diffusing out, the electrons lose energy by Compton scattering with the universal blackbody photons, thus producing the X-ray emission. Traversing intracluster magnetic fields, the electrons emit synchrotron radio emission. For the Coma cluster of galaxies good agreement is found between the observed and predicted X-ray counting-rate distribution for the Compton model. From the observed radio data a value of about 3 by 10 to the -8th power gauss is deduced for the average magnetic-field strength in the central region of Coma.

Rephaeli, Y.↗
DOE OSTI2025

Integrating Ultra-Coarse-Grained Protein Models into Accessible Workflows for Multiscale Molecular Dynamics

To capture protein conformational transitions using molecular dynamics (MD), several simulation resolutions covering different spatial and temporal scales are typically needed. All-atom (AA) simulations provide fine resolution, but are computationally infeasible for large systems over longer durations. Coarse-grained (CG) and ultra-coarse-grained (UCG) models have a lower resolution and computational cost while still being able to conserve essential protein features. Prior work on a Multiscale Machinelearned Modeling Infrastructure (MuMMI) combined both AA and CG simulations to study RAS-RAF protein interactions, leveraging CG models for longer time scales and using AA to investigate unusual conformations in greater detail. However, MuMMI is still resource-intensive, and this study aims to maximize exploration of the protein conformational space while reducing computational cost. In this paper, we build on prior work that integrates UCG models based on heterogeneous elastic network modeling (hENM) into the MuMMI workflow. We demonstrate that UCG models enable accurate sampling of protein conformations, focusing on simulating RAS-RAF protein interactions. Using higher-resolution CG Martini simulation data, we can automatically refine intramolecular interactions in UCG models. We present a scalable Python package that uses fluctuations observed in higher-resolution CG Martini simulations to estimate bond coefficients of the UCG model. We built novel machine learning-based backmapping methods to recover more detailed CG Martini structures from UCG structures, using diffusion models to learn the mapping between scales. Finally, we present UCG-mini-MuMMI, an accessible and less compute-intensive version of MuMMI as a resource for the scientific community. Incorporating UCG models into MD studies is applicable to a broad range of systems and proteins, and our study offers insights into the advantages and limitations of these methods.

Chemical structure↗
NASA NTRS1991

Numerical and experimental investigations of rarefied nozzle and plume flows of nitrogen

Numerical and experimental investigations are performed for the rarefied flow of nitrogen through a small nozzle which is expanded into near-vacuum conditions. Two different numerical studies are undertaken: the first employs a continuum approach in solving the Navier-Stokes equations, and the second employs a particle approach through use of the direct simulation Monte Carlo method (DSMC). The experimental investigation concerns the measurement of pressure, using a Pitot tube, in the nozzle exit plane and near-field of the plume. Comparison of the experimental and numerical data at the nozzle exit reveals that the DSMC technique provides the more accurate description of the expanding flow. It is discovered that the DSMC solutions are quite sensitive to the model employed to simulate the interaction between the gas and the nozzle wall surface. It is concluded that the simplistic fully diffuse model is quite satisfactory for the present application.

Boyd, Iain D.↗