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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 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Unraveling Grain Boundary Instability in Dense Proton-Conducting Oxides

The long-term stability of protonic ceramic electrolysis cell (PCEC) materials under high-steam operating conditions remains a critical barrier to device commercialization. Here, we investigate the fundamental degradation mechanisms of dense BaCe 0.7 Zr 0.1 Y 0.1 Yb 0.1 O 3-δ (BCZYYb) electrolytes operated at 550 °C, 50% H 2 O in air. Over 1,000 h, the total electrolyte conductivity decreases by 11.1%, driven primarily by a >130% increase in grain-boundary resistivity. Post-mortem analyses reveal that damage is localized to near-surface grain boundaries extending ∼50 μm into the dense electrolyte pellet. This surface localization indicates that degradation is likely to be severe in thin, device-level electrolytes. Degradation is primarily attributed to chemo-mechanical grain-boundary weakening arising from hydration-induced chemical expansion, culminating in the formation of intergranular cracks oriented parallel to the pellet surface. These internal cracks subsequently react with steam and/or CO 2 , leading to the formation of nanoscale insulating phases, including Ba(OH) 2 , nanocrystalline BaCO 3 , and amorphous Ce/Zr/Y/Yb-containing oxides or hydroxycarbonates. After an initial degradation period of approximately 200 h, the overall conductivity stabilizes. Incorporating NiO sintering aids reduces grain-boundary density by an order of magnitude under identical sintering conditions. Although addition of NiO increases the initial resistivity by >160% at 550 °C, it substantially suppresses grain-boundary instability and mitigates chemical degradation. These findings underscore the urgent need for chemical and/or physical stabilization of BCZYYb electrolytes and offer design guidelines to enable durable, high-performance PCECs.

08 HYDROGEN↗
NASA NTRS1974

Termination of the solar wind in the hot, partially ionized interstellar medium

Theoretical foundations for understanding the problem of the termination of the solar wind are reexamined in the light of most recent findings concerning the states of the solar wind and the local interstellar medium. The investigation suggests that a simple extention of Parker's (1961) analytical model provides a useful approximate description of the combined solar wind, interstellar wind plasma flowfield under conditions presently thought to occur. A linear perturbation solution exhibiting both the effects of photoionization and charge exchange is obtained for the supersonic solar wind. A numerical algorithm is described for computing moments of the non-equilibrium hydrogen distribution function and associated source terms for the MHD equations. Computed using the algorithm in conjunction with the extended Parker solution to approximate the plasma flowfield, profiles of hydrogen number density are given in the solar wind along the upstream and downstream axes of flow with respect to the direction of the interstellar wind. Predictions of solar Lyman-alpha backscatter intensities to be observed at 1 a.u. have been computed, in turn, from a set of such hydrogen number density profiles varied over assumed conditions of the interstellar wind.

Lombard, C. K.↗
NASA NTRS1993

Analysis and design of an ultrahigh temperature hydrogen-fueled MHD generator

A coupled gas dynamics/radiative heat transfer analysis of partially ionized hydrogen, in local thermodynamic equilibrium, flowing through an ultrahigh temperature (10,000-20,000 K) magnetohydrodynamic (MHD) generator is performed. Gas dynamics are modeled by a set of quasi-one-dimensional, nonlinear differential equations which account for friction, convective and radiative heat transfer, and the interaction between the ionized gas and applied magnetic field. Radiative heat transfer is modeled using nongray, absorbing-emitting 2D and 3D P-1 approximations which permit an arbitrary variation of the spectral absorption coefficient with frequency. Gas dynamics and radiative heat transfer are coupled through the energy equation and through the temperature- and density-dependent absorption coefficient. The resulting nonlinear elliptic problem is solved by iterative methods. Design of such MHD generators as onboard, open-cycle, electric power supplies for a particular advanced airbreathing propulsion concept produced an efficient and compact 128-MWe generator characterized by an extraction ratio of 35.5 percent, a power density of 10,500 MWe/cu m, and a specific (extracted) energy of 324 MJe/kg of hydrogen. The maximum wall heat flux and total wall heat load were 453 MW/sq m and 62 MW, respectively.

Moder, Jeffrey P.↗
NASA NTRS2000

Star Formation in the Galaxy and the Fluctuating UV Radiation Field

We examine the formation of massive stars in the Galaxy, the resultant fluctuating UV radiation field, and the effect of this Field on the star-forming interstellar medium. Following previous researchers such as Habing (1968), we calculate the average interstellar radiation field at the Solar Circle of the Galaxy. However, our new calculations follow more closely the time dependence of the field at any point. We show that there is a significant difference between the mean field and the median field, and that there are substantial fluctuations of the field (on timescales of order 100 million years) at a given point. Far Ultraviolet Radiation (FUV, photon energies of 6 eV - 13.6 eV) has been recognized as the main source of heating of the neutral interstellar gas. Given the pressure of the interstellar medium (ISM) the FUV field determines whether the thermal balance of the neutral gas results in cold (T approximately 50 - 100 K) clouds (CNM), warm (T about 10,000 K) (WNM), for a combination of the two (the two phase ISM) We present results for the time history of the FUV field for points in the local ISM of the Milky Way Galaxy. The presence of this fluctuating heating rate converts CNM to WNM and vice versa. We show how to calculate the average fractions of the gas in the CNM and WNM when the interstellar gas is subject to this fluctuating FUV field. The knowledge of how these fractions depend on the gas properties (i.e. mean density and composition) and on the FUV-sources (i.e. the star formation rate, or the IMF, or the size distribution of associations) is a basic step in building any detailed model of the large scale behavior of the ISM and the mutual relation between the ISM and the SFR.

Hollenbach, David↗
NASA NTRS2009

The Principle of Energetic Consistency

A basic result in estimation theory is that the minimum variance estimate of the dynamical state, given the observations, is the conditional mean estimate. This result holds independently of the specifics of any dynamical or observation nonlinearity or stochasticity, requiring only that the probability density function of the state, conditioned on the observations, has two moments. For nonlinear dynamics that conserve a total energy, this general result implies the principle of energetic consistency: if the dynamical variables are taken to be the natural energy variables, then the sum of the total energy of the conditional mean and the trace of the conditional covariance matrix (the total variance) is constant between observations. Ensemble Kalman filtering methods are designed to approximate the evolution of the conditional mean and covariance matrix. For them the principle of energetic consistency holds independently of ensemble size, even with covariance localization. However, full Kalman filter experiments with advection dynamics have shown that a small amount of numerical dissipation can cause a large, state-dependent loss of total variance, to the detriment of filter performance. The principle of energetic consistency offers a simple way to test whether this spurious loss of variance limits ensemble filter performance in full-blown applications. The classical second-moment closure (third-moment discard) equations also satisfy the principle of energetic consistency, independently of the rank of the conditional covariance matrix. Low-rank approximation of these equations offers an energetically consistent, computationally viable alternative to ensemble filtering. Current formulations of long-window, weak-constraint, four-dimensional variational methods are designed to approximate the conditional mode rather than the conditional mean. Thus they neglect the nonlinear bias term in the second-moment closure equation for the conditional mean. The principle of energetic consistency implies that, to precisely the extent that growing modes are important in data assimilation, this term is also important.

Cohn, Stephen E.↗
NASA NTRS1985

Vortex modeling of single and multiple dilution jet mixing in a crossflow

An analytical model for the behavior of normally injected jets in a crossflow is developed and applied to fluids of differing densities. Central to the model are the dynamics of the vortex pair structure associated with the local jet cross-section and the entrainment of crossflow by jet fluid. Two specific cases are modeled: one involving a single dilution jet in a crossflow, in which trajectories are found to scale primarily with jet-to-crossflow momentum ratio, and the other involving a series of spanwise jets injected into a crossflow, which indicates scaling with momentum ratio and with the spacing-to-orifice-diameter ratio. In the case of multiple jet penetration, however, merging of the jets into an approximately two-dimensional jet downstream of injection is observed for low spacing-to-diameter ratios.

Karagozian, A. R.↗
NASA NTRS1988

Advanced infrared astronomy

This task supports the application of infrared heterodyne and Fourier transform spectroscopy to ultra-high resolution studies of molecular constituents of planetary astomspheres and cometary comae. High spectral and spatial resolutions are especially useful for detection and study of localized, non-thermal phenomena in low temperature and low density regions, for detection of trace constituents and for measurement of winds and dynamical phenomena such as thermal tides. Measurement and analysis of individual spectial lines permits retrieval of atmospheric molecular abundances and temperatures and thus, information on local photochemical processes. Determination of absolute line positions to better than 10 to the minus eighth power permits direct measurements of gas velocity to a few meters/sec. Observations are made from ground based heterodyne spectrometers at the Kitt Peak McMath solar telescope and from the NASA infrared Telescope Facility on Mauna Kea, Hawaii. Wind velocities at 110km altitude on Venus were extracted approximately 1 m/sec from measurements of non-thermal emission cores of 10.3 micron CO2 lines. Results indicate a subsolar to antisolar circulationwith a small zonal retrograde component.

Kostiuk, T.↗
NASA NTRS1994

The morningside low-latitude boundary layer as determined from electric and magnetic field measurements on Geotail

On October 17, 1992, the Geotail satellite crossed the dawnside magnetopause approximately 41 times. At the majority of these crossings, the magnetic field and the normal component of the electric field were larger and the plasma density was smaller in a low-latitude boundary layer than they were in either the nearby magnetosheath or in the magnetosphere. These results are intepreted in terms of the Kelvin-Helmholtz instability associated with velocity shear at the magnetopause. Consistent with this interpretation, it is shown that the low-latitude boundary layer was the region where the flow decreased from its magnetosheath to magnetospheric value. Evidence is presented that the magnetopause was locally oriented within less than 20 deg of its nominal geometry on these crossings and that it moved with an amplitude of 1500-6000 kilometers. The thickness of the low-latitude boundary layer averaged 800 kilometers and the electric potential across it averaged 4 kilovolts with a spread of a factor of 2. Thus, the viscous interaction and similar processes are not significant contributors to magnetospheric convection.

Mozer, F. S.↗
DOE OSTI2022

Mapping 3D grain and precipitate structure during in situ mechanical testing of open-cell metal foam using micro-computed tomography and high-energy X-ray diffraction microscopy

Open-cell metal foams are ultra-low-density cellular metals with complex hierarchical structures that span bulk, cell, ligament, and sub-ligament scales and give rise to desirable properties such as high strength-to-weight ratio and excellent energy absorption. Although literature suggests that intrinsic material structures at sub-ligament length scales (e.g., grains and precipitates) play an important role in mechanical behavior of open-cell metal foams, there are very few experimental measurements of such structures in three dimensions and for meaningful volumes of foam. This study seeks to map and track the three-dimensional (3D) grain and precipitate structures of an intact volume of open-cell aluminum foam by advancing microstructural characterization techniques that leverage X-ray micro-computed tomography (μCT) and far-field high-energy X-ray diffraction microscopy (FF-HEDM). A 6%-relative-density aluminum foam sample was mechanically tested in compression while μCT and FF-HEDM measurements were collected at interrupted loading states at beamline 1-ID of the Advanced Photon Source. Further, a new scanning strategy and reconstruction algorithm were established to enable characterization of a foam volume with diameter approximately four times wider than the nominal width of the X-ray beam. The result is a set of maps that detail both the 3D grain and precipitate structures throughout the foam volume at successive strain steps. A novel grain tracking procedure was developed to track individual grains within the foam volume by accounting for the large rigid-body motions that individual ligaments can undergo during mechanical loading. The ability to track grains and precipitate structures in three dimensions throughout large bulk deformation of ultra-low-density polycrystalline materials enables new possibilities for validating numerical models and investigating local failure mechanisms. Furthermore, the methods and procedures developed in this study could be applied to other ultra-low-density structures, such as additively manufactured lattices.

36 MATERIALS SCIENCE↗
DOE OSTI2024

ELM-free H-mode phase and decoupling of peeling–ballooning stability boundary in the MAST Upgrade tokamak

A linear magnetohydrodynamic (MHD) peeling–ballooning stability analysis of the edge-localized mode (ELM)-free phase of a MAST Upgrade (MAST-U) H-mode plasma is presented. In contrast to other similar discharges, #47018 is found to have a significantly higher and wider pedestal during its ELM-free H-mode phase that lasts for approximately 80 ms; this is made possible by the reduced core MHD mode activity on the q = 2 surface. During this period, there is sustained decoupling of peeling and ballooning branches of the stability boundary on J–α space, opening an access channel to the second stability regime with higher peaks in pedestal current density $J_{\mathrm{N,ped}}$ and pressure gradient (α). Such decoupling of the stability boundary has not previously been observed in MAST-U H-modes, and if such a condition can be readily reproduced, it opens a wide range of opportunities for MAST-U to explore low-collisionality peeling-limited pedestal regimes as well as advanced scenarios such as quiescent H-modes that are relevant to future reactors such as STEP and ITER.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Strong Correlation DMRG and DFT

This project developed new ways to improve computer simulations of materials where electrons interact strongly with each other, a challenge for today’s most widely used method, density functional theory (DFT). We used an exact numerical method, the density matrix renormalization group (DMRG), to create highly accurate reference results for simple model systems, and used these to test DFT, prove when it will converge, and even train machine-learned functionals. We also invented new kinds of localized basis functions (“gausslets” and “multi-sliced gausslets”) and a “sliced-basis” approach that make high-accuracy simulations faster and more practical. These methods were applied to extended hydrogen systems, enabling the direct derivation of accurate low-energy models from first-principles calculations. We also introduced a new formalism, Conditional-Probability DFT, which could bypass traditional approximations. The tools and results from this work, including open-source software releases, will help scientists design and understand complex quantum materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1990

The mass function of Seyfert 1 nuclei

The first mass function of Seyfert 1 nuclei is derived from optical spectra of the complete CfA sample of Seyfert galaxies by estimating the mass for each object from a dynamical relation. An independent estimate is also derived using a complete infrared-selected sample. The two mass functions are indistinguishable. The mean mass of Seyfert 1 nuclei is about 2 x 10 to the 7th solar masses, and the integrated mass density is about 6 x 10 to the 11th solar masses/cu Gpc. This is approximately two orders of magnitude less than the value inferred from the energetics associated with quasar counts. A careful analysis of the various parameters and assumptions involved suggests that this large difference is not due to systematic errors in the determinations. Therefore, the bulk of mass related to the accretion processes connected with past quasar activity does not reside in Seyfert 1 nuclei. Instead, the remnants of past activity must be present in a much larger number of galaxies, and a one-to-one relation between distant and local active galactic nuclei seems then to be excluded.

Padovani, P.↗
NASA NTRS1999

Analysis and Testing of High Temperature Fibrous Insulation for Reusable Launch Vehicles

Analytical models were developed to model the heat transfer through high-temperature fibrous insulation used in metallic thermal protection systems on reusable launch vehicles. The optically thick approximation was used to simulate radiation heat transfer through the insulation. Different models for gaseous conduction and solid conduction in the fibers, and for combining the various modes of heat transfer into a local, volume-averaged, thermal conductivity were considered. The governing heat transfer equations were solved numerically, and effective thermal conductivities were calculated from the steady-state results. An experimental apparatus was developed to measure the apparent thermal conductivity of insulation subjected to pressures, temperatures and temperature gradients representative of re-entry conditions for launch vehicles. The apparent thermal conductivity of an alumina fiber insulation was measured at nominal densities of 24, 48 and 96 kg/cu m. Data were obtained at environmental pressures from 10(exp 4) to 760 torr, with the insulation cold side maintained at room temperature and its hot side temperature varying up to 1000 C. The experimental results were used to evaluate the analytical models. The best analytical model resulted in effective thermal conductivity predictions that were within 8% of experimental results.

Daryabeigi, Kamran↗
DOE OSTI2023

Sparsity of the electron repulsion integral tensor using different localized virtual orbital representations in local second-order Møller–Plesset theory

Utilizing localized orbitals, local correlation theory can reduce the unphysically high system-size scaling of post-Hartree–Fock (post-HF) methods to linear scaling in insulating molecules. The sparsity of the four-index electron repulsion integral (ERI) tensor is central to achieving this reduction. For second-order Møller–Plesset theory (MP2), one of the simplest post-HF methods, only the (ia|jb) ERIs are needed, coupling occupied orbitals i, j and virtuals a, b. In this paper, we compare the numerical sparsity (called the “ragged list”) and two other approaches revealing the low-rank sparsity of the ERI. The ragged list requires only one set of (localized) virtual orbitals, and we find that the orthogonal valence virtual-hard virtual set of virtuals originally proposed by Subotnik et al. gives the sparsest ERI tensor. To further compress the ERI tensor, the pair natural orbital (PNO) type representation uses different sets of virtual orbitals for different occupied orbital pairs, while the occupied-specific virtual (OSV) approach uses different virtuals for each occupied orbital. Here, our results indicate that while the low-rank PNO representation achieves significant rank reduction, it also requires more memory than the ragged list. The OSV approach requires similar memory to that of the ragged list, but it involves greater algorithmic complexity. An approximation (called the “fixed sparsity pattern”) for solving the local MP2 equations using the numerically sparse ERI tensor is proposed and tested to be sufficiently accurate and to have highly controllable error. A low-scaling local MP2 algorithm based on the ragged list and the fixed sparsity pattern is therefore promising.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Transient mixing behavior of a supercritical fluid injected into supercritical and subcritical environments

Transient, near-field mixing of a supercritical fluid injected into supercritical and subcritical environments is investigated experimentally. Fuel (propane) from a 100 μm diameter Bosch diesel injector is injected into a high-pressure test rig with a steady flow of heated, low-velocity nitrogen to control the ambient pressure and temperature. The fuel supply pressure is approximately 190 bar, allowing short injections lasting 3–4 ms to be performed in quick succession to acquire statistically significant datasets to represent the unsteady fuel–air mixing. Two test cases with the same ambient density and injector inlet pressure and temperature were chosen in an attempt to isolate effects of mixture phase behavior. Microscopic rainbow Schlieren deflectometry (RSD) is used for visualization and quantitative data acquisition. In the case of the supercritical ambient, the injector inlet and exit and ambient conditions are all supercritical. The RSD analysis reveals a mixing process similar to the single phase fluid mixing, though condensation is also observed locally, and can be explained by the adiabatic mixing theory presented in the paper. For the subcritical ambient case, the injector inlet is supercritical, but the injector exit and ambient conditions are both subcritical. The results show a rapid expansion in the near-field promoting mixing between propane and nitrogen. At downstream locations, significant condensation is also observed as predicted by the adiabatic mixing theory. As a result, the supercritical ambient case exhibited longer and narrower jet penetration compared to the subcritical ambient case.

02 PETROLEUM↗
NASA NTRS1982

The spectrum of the Jovian Aurora 1150-1700 A

A series of observations of the northern hemisphere of Jupiter was made in January 1981 using the International Ultraviolet Explorer short-wavelength spectrograph. Exposures of 15 minutes each were made at regular intervals of about 45 minutes around the time when Jupiter's north magnetic pole was tilted toward the earth. The auroral emissions of H Lyman-alpha, and the H2 Lyman- and Werner-bands are seen to emanate from a localized region near the north pole. Their intensity increases and decreases in a periodic way as the planet rotates with the maximum occurring at lambda sub III approximately equal to 185 deg. Using the three observations nearest the observed maximum, a composite spectrum of the aurora is obtained with about 8 A resolution and high signal-to-noise ratio, and many of the H2 Lyman- and Werner-bands in this spectral region (1150-1700 A) are identified. This spectrum is compared with a laboratory H2 spectrum and with photoabsorption cross sections for CH4 and C2H6. An upper limit to the slant column density of these hydrocarbons above the auroral emissions is found to be approximately 2 x 10 to the 17th/sq cm.

Durrance, S. T.↗
NASA NTRS1992

The ultraviolet absorption spectrum of the quasar H1821+643 (z = 0.297)

High resolution UV observations of the nearby luminous quasar H1821+643 are reported. A complete sample of 38 absorption lines has been constructed. There are five strong extragalactic Ly-alpha absorption lines in the spectrum, all with observed equivalent widths greater than 0.45 A. The local number density of Ly-alpha systems with rest equivalent widths larger than 0.32 A is estimated to be 13 +/- 5 Ly-alpha lines per unit redshift. Some of the Ly-alpha systems with redshifts significantly different from the quasar appear to be associated with galaxies or with clusters of galaxies. Two of the Ly-alpha lines have the same redshift within 400 km/s as that of an emission-line galaxy located at a projected separation from the quasar of about 90 kpc. One of the Ly-alpha systems in H1821+643 occurs at an a absorption redshift approximately equal to the emission-line redshift of the quasar and is accompanied by absorption from the C IV and of VI doublets; this is an example of associated absorption for large-redshift quasars.

Bahcall, John N.↗
NASA NTRS1994

Mechanism of Headward Fluid Shift During Exposure To Microgravity

A prominent feature of early cardiovascular adaptation to the microgravity of space flight is a shift of blood and tissue fluid from the lower body to the upper body. Symptoms of this fluid shift include facial edema, nasal congestion, and headache. Normally on Earth, the human body is exposed to hydrostatic (gravitational) blood pressure gradients during upright posture. In this posture, mean arterial pressures at head, heart, and foot levels are approximately 70, 100, and 200 mm Hg, respectively. Theoretically, all hydrostatic pressures within arteries and veins are lost during exposure to microgravity so that mean arterial pressure in all regions of the body is uniform and approximately equal to that at heart level (100 mm Hg). Acute studies of 60 head-down tilt (simulated microgravity on Earth) indicate that facial edema is caused by: 1) elevation of capillary blood pressure from 28 to 34 mm Hg, 2) reduction of blood colloid osmotic pressure 22 to 18 mm Hg, and 3) 50% increase of blood perfusion in tissues of the head. Furthermore, as compared to microvasculature in the feet, microvessels of the head have a low capacity to constrict and diminish local perfusion. Elevation of blood and tissue fluid pressures/flow in the head may also explain the higher headward bone density associated with long-term head-down tilt. These mechanistic studies of head-down tilt, along with a better understanding of the relative stresses involved with upright posture and lower body negative pressure, have facilitated development of physiologic countermeasures to maintain astronaut health during microgravity. Presently no exercise hardware is available to provide a blood pressure gradient from head to feet in space. However, recent studies in our laboratory suggest that treadmill exercise within lower body negative pressure provides equivalent or greater physiologic stress as compared to similar upright exercise on Earth.

Hargens, Alan R.↗