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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 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Impact of Hypernova νp-process Nucleosynthesis on the Galactic Chemical Evolution of Mo and Ru

We calculate the Galactic Chemical Evolution of Mo and Ru by taking into account the contribution from νp-process nucleosynthesis. We estimate yields of p-nuclei such as 92,94 Mo and 96,98 Ru through the νp-process in various supernova progenitors based upon recent models. In particular, the νp-process in energetic hypernovae produces a large amount of p-nuclei compared to the yield in ordinary core-collapse SNe. Because of this, the abundances of 92,94 Mo and 96,98 Ru in the Galaxy are significantly enhanced at [Fe/H] = 0 by the νp-process. We find that the νp-process in hypernovae is the main contributor to the elemental abundance of 92 Mo at low metallicity [Fe/H] < −2. Our theoretical prediction of the elemental abundances in metal-poor stars becomes more consistent with observational data when the νp-process in hypernovae is taken into account.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Comprehensive Analysis of the Neutrino Process in Core-collapsing Supernovae

We investigate the neutrino flavor change effects due to neutrino self-interaction and shock wave propagation, as well as the matter effects on the neutrino process in core-collapsing supernovae (CCSNe). For the hydrodynamics, we use two models: a simple thermal bomb model and a specified hydrodynamics model for SN1987A. For the presupernova model, we take an updated model, adjusted to explain SN1987A, which employs recent developments in the (n, γ) reaction rates for nuclei near the stability line (A ~ 100). As for the neutrino luminosity, we adopt two different models: equivalent neutrino luminosity and nonequivalent luminosity models. The latter is taken from a synthetic analysis of CCSN simulation data, which quantitatively presented the results obtained by various neutrino transport models. Relevant neutrino-induced reaction rates are calculated using a shell model for light nuclei and a quasiparticle random phase approximation model for heavy nuclei. For each model, we present abundances of the light nuclei ( 7 Li, 7 Be, 11 B, and 11 C) and the heavy nuclei ( 92 Nb, 98 Tc, 138 La, and 180 Ta) produced by the neutrino process. The light nuclei abundances turn out to be sensitive to the Mikheyev–Smirnov–Wolfenstein (MSW) region around O-Ne-Mg layer while the heavy nuclei are mainly produced prior to the MSW region. Through detailed analyses, we find that neutrino self-interaction becomes a key ingredient, in addition to the MSW effect, for understanding the neutrino process and the relevant nuclear abundances. The normal mass hierarchy is shown to be more compatible with the meteorite data. The main nuclear reactions for each nucleus are also investigated in detail.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

The Origin of Star Formation in Early-type Galaxies Inferred from Spatially Resolved Spectroscopy

Abstract We investigate the origin of star formation activity in early-type galaxies with current star formation using spatially resolved spectroscopic data from the Mapping Nearby Galaxies at Apache Point Observatory in the Sloan Digital Sky Survey (SDSS). We first identify star-forming early-type galaxies from the SDSS sample, which are morphologically early-type but show current star formation activity in their optical spectra. We then construct comparison samples with different combinations of star formation activity and morphology, which include star-forming late-type galaxies, quiescent early-type galaxies, and quiescent late-type galaxies. Our analysis of the optical spectra reveals that the star-forming early-type galaxies have two distinctive episodes of star formation, which is similar to late-type galaxies but different from quiescent early-type galaxies with a single star formation episode. Star-forming early-type galaxies have properties in common with star-forming late-type galaxies, which include stellar population, gas and dust content, mass, and environment. However, the physical properties of star-forming early-type galaxies derived from spatially resolved spectroscopy differ from those of star-forming late-type galaxies in the sense that the gas in star-forming early-type galaxies is more concentrated than their stars, and is often kinematically misaligned with stars. The age gradient of star-forming early-type galaxies also differs from those of star-forming late-type galaxies. Our findings suggest that the current star formation in star-forming early-type galaxies has an external origin including galaxy mergers or accretion gas from the cosmic web.

Astronomy & Astrophysics↗
DOE OSTI2020

1.2 kV, 10 A, 4H-SiC Bi-Directional Field Effect Transistor (BiDFET) with Low On-State Voltage Drop

Bidirectional power switches are used in matrix-or cyclo-converters and in multistage inverter circuits to facilitate high-frequency AC-to-AC conversion. A new 1.2 kV bidirectional MOSFET (BiDFET) with low on-resistance is achieved and demonstrated using two discrete SiC power MOSFET bare die chips, packaged within a four-terminal custom-designed module. Static and dynamic characterization has been carried out to inspect the on-state and switching behaviour of the BiDFET. Here, the BiDFET is shown to have a low forward voltage drop of 0.6 V at a current of 10 A, which is more than 2.5x smaller than previous Si IGBT and SiC MOSFET based bidirectional switch implementations.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Effect of inorganic-to-organic mass ratio on the heterogeneous OH reaction rates of erythritol: implications for atmospheric chemical stability of 2-methyltetrols

The 2-methyltetrols have been widely chosen as chemical tracers for isoprene-derived secondary organic aerosols. While they are often assumed to be relatively unreactive, a laboratory study reported that pure erythritol particles (an analog of 2-methyltetrols) can be heterogeneously oxidized by gas-phase OH radicals at a significant rate. This might question the efficacy of these compounds as tracers in aerosol source-apportionment studies. Additional uncertainty could arise as organic compounds and inorganic salts often coexist in atmospheric particles. To gain more insights into the chemical stability of 2-methyltetrols in atmospheric particles, this study investigates the heterogeneous OH oxidation of pure erythritol particles and particles containing erythritol and ammonium sulfate (AS) at different dry inorganic-to-organic mass ratios (IOR) in an aerosol flow tube reactor at a high relative humidity of 85 %. The same reaction products are formed upon heterogenous OH oxidation of erythritol and erythritol–AS particles, suggesting that the reaction pathways are not strongly affected by the presence and amount of AS. On the other hand, the effective OH uptake coefficient, $γ_{eff}$, is found to decrease by about a factor of ~20 from 0.45±0.025 to 0.02±0.001 when the relative abundance of AS increases and the IOR increases from 0.0 to 5.0. One likely explanation is the presence of dissolved ions slows down the reaction rates by decreasing the surface concentration of erythritol and reducing the frequency of collision between erythritol and gas-phase OH radicals at the particle surface. Hence, the heterogeneous OH reactivity of erythritol and likely 2-methyltetrols in atmospheric particles would be slower than previously thought when the salts are present. Given 2-methyltetrols often coexist with a significant amount of AS in many environments, where ambient IOR can vary from ~1.89 to ~250, our kinetic data would suggest that 2-methyltetrols in atmospheric particles are likely chemically stable against heterogeneous OH oxidation under humid conditions.

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

FRET-based dynamic structural biology: Challenges, perspectives and an appeal for open-science practices

Single-molecule FRET (smFRET) has become a mainstream technique for studying biomolecular structural dynamics. The rapid and wide adoption of smFRET experiments by an ever-increasing number of groups has generated significant progress in sample preparation, measurement procedures, data analysis, algorithms and documentation. Several labs that employ smFRET approaches have joined forces to inform the smFRET community about streamlining how to perform experiments and analyze results for obtaining quantitative information on biomolecular structure and dynamics. The recent efforts include blind tests to assess the accuracy and the precision of smFRET experiments among different labs using various procedures. These multi-lab studies have led to the development of smFRET procedures and documentation, which are important when submitting entries into the archiving system for integrative structure models, PDB-Dev. This position paper describes the current ‘state of the art’ from different perspectives, points to unresolved methodological issues for quantitative structural studies, provides a set of ‘soft recommendations’ about which an emerging consensus exists, and lists openly available resources for newcomers and seasoned practitioners. To make further progress, we strongly encourage ‘open science’ practices.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1988

Effects of tensile stress on the R lines of Cr(3+) in a sapphire fiber

The spectroscopic properties of a crystalline sapphire fiber unintentionally dOed with Cr(3+) are investigated. It is found that tensile stress produces blue shifts of the R lines and changes in their radiative lifetimes and integrated intensities that can be correlated to stress-induced changes of the crystal-field parameters.

Liu, Huimin↗
NASA NTRS1991

Experimental study of boundary layer transition with elevated freestream turbulence on a heated flat plate

A detailed investigation to document momentum and thermal development of boundary layers undergoing natural transition on a heated flat plate was performed. Experimental results of both overall and conditionally sampled characteristics of laminar, transitional, and low Reynolds number turbulent boundary layers are presented. Measurements were acquired in a low-speed, closed-loop wind tunnel with a freestream velocity of 100 ft/s and zero pressure gradient over a range of freestream turbulence intensities (TI) from 0.4 to 6 percent. The distributions of skin friction, heat transfer rate and Reynolds shear stress were all consistent with previously published data. Reynolds analogy factors for R(sub theta) is less than 2300 were found to be well predicted by laminar and turbulent correlations which accounted for an unheated starting length. The measured laminar value of Reynolds analogy factor was as much as 53 percent higher than the Pr(sup -2/3). A small dependence of turbulent results on TI was observed. Conditional sampling performed in the transitional boundary layer indicated the existence of a near-wall drop in intermittency, pronounced at certain low intermittencies, which is consistent with the cross-sectional shape of turbulent spots observed by others. Non-turbulent intervals were observed to possess large magnitudes of near-wall unsteadiness and turbulent intervals had peak values as much as 50 percent higher than were measured at fully turbulent stations. Non-turbulent and turbulent profiles in transitional boundary layers cannot be simply treated as Blasius and fully turbulent profiles, respectively. The boundary layer spectra indicate predicted selective amplification of T-S waves for TI is approximately 0.4 percent. However, for TI is approximately 0.8 and 1.1 percent, T-S waves are localized very near the wall and do not play a dominant role in transition process.

Sohn, Ki-Hyeon↗
NASA NTRS1989

Ellipsometric measurement of liquid film thickness

The immediate objective of this research is to measure liquid film thickness from the two equilibrium phases of a monotectic system in order to estimate the film pressure of each phase. Thus liquid film thicknesses on the inside walls of the prism cell above the liquid level have been measured elliposmetrically for the monotectic system of succinonitrile and water. The thickness varies with temperature and composition of each plane. The preliminary results from both layers at 60 deg angle of incidence show nearly uniform thickness from about 21 to 23 C. The thickness increases with temperature but near 30 C the film appears foggy and scatters the laser beam. As the temperature of the cell is raised beyond room temperature it becomes increasingly difficult to equalize the temperature inside and outside the cell. The fogging may also be an indication that solution, not pure water, is adsorbed onto the substrate. Nevertheless, preliminary results suggest that ellipsometric measurement is feasible and necessary to measure more accurately and rapidly the film thickness and to improve thermal control of the prism walls.

Chang, Ki Joon↗
NASA NTRS1992

Interactive solution-adaptive grid generation procedure

TURBO-AD is an interactive solution adaptive grid generation program under development. The program combines an interactive algebraic grid generation technique and a solution adaptive grid generation technique into a single interactive package. The control point form uses a sparse collection of control points to algebraically generate a field grid. This technique provides local grid control capability and is well suited to interactive work due to its speed and efficiency. A mapping from the physical domain to a parametric domain was used to improve difficulties encountered near outwardly concave boundaries in the control point technique. Therefore, all grid modifications are performed on the unit square in the parametric domain, and the new adapted grid is then mapped back to the physical domain. The grid adaption is achieved by adapting the control points to a numerical solution in the parametric domain using control sources obtained from the flow properties. Then a new modified grid is generated from the adapted control net. This process is efficient because the number of control points is much less than the number of grid points and the generation of the grid is an efficient algebraic process. TURBO-AD provides the user with both local and global controls.

Henderson, Todd L.↗
NASA NTRS1992

Techniques for grid manipulation and adaptation

Two approaches have been taken to provide systematic grid manipulation for improved grid quality. One is the control point form (CPF) of algebraic grid generation. It provides explicit control of the physical grid shape and grid spacing through the movement of the control points. It works well in the interactive computer graphics environment and hence can be a good candidate for integration with other emerging technologies. The other approach is grid adaptation using a numerical mapping between the physical space and a parametric space. Grid adaptation is achieved by modifying the mapping functions through the effects of grid control sources. The adaptation process can be repeated in a cyclic manner if satisfactory results are not achieved after a single application.

Choo, Yung K.↗
NASA NTRS1992

Analysis of the effect of initial conditions on the initial development of a turbulent jet

The effect of the initial condition at the jet exit on the downstream evolution, particularly within the potential core length, were numerically investigated as well as with available experimental data. In order to select the most dependable computational model for the present numerical experiment, a comparative study has been performed with different turbulence models at k-epsilon level, and it was found that the k-epsilon-gammma model yields superior prediction accuracy over other conventional models. The calculated results show that the potential core length and the spreading rate the initial mixing layer are dependent on the initial length scale as well as the turbulent kinetic energy at the jet exit. Such effect of the initial length scale increases with higher initial turbulence level. An empirical parameter has been devised to collapse the calculated data of the potential core length and the spreading rate with various initial conditions onto a single curve.

Kim, Soong KI↗
NASA NTRS1996

Rotordynamic Characterization of a Hybrid Superconductor Magnet Bearing

A hybrid superconductor magnet bearing uses magnetic forces between permanent magnets to provide lift and the flux pinning force between permanent magnets and superconductors to stabilize against instabilities intrinsic to the magnetic force between magnets. We have constructed a prototype kinetic energy storage system, using a hybrid superconductor magnet bearing to support a 42 lb. flywheel at the center. With five sensors on the periphery of the flywheel, we have monitored the position and attitude of the flywheel during its spin down. The results indicate low values of stiffnesses for the bearing. The implications of this and other consequences will be discussed.

Ma, Ki B.↗
NASA NTRS1995

A Natural Application for High Temperature Superconductors: a Bearing for the Azimuth Mount of a Lunar Telescope

A bearing for telescope mounts on the moon has to function in a cold dusty vacuum environment that impairs the operation of almost all traditional bearings, but it is a natural environment for bearings constructed out of magnets and high temperature superconductors. The challenge lies not so much in the weight of the telescope that has to be supported, but in the smoothness of forces required for precision positioning control over a long stretch of time without human intervention. In this paper, we present a design of hybrid superconductor magnet bearings intended for use on the azimuth mount of an altitude-azimuth telescope mount system. In addition to the general features of hybrid super conducting magnet bearings, we will address particular issues connected with the application of these bearings on a telescope mount.

Ma, Ki↗
NASA NTRS1995

High Temperature Superconducting Bearings for Lunar Telescope Mounts

A telescope to be installed on the lunar surface in the near future must work in a cold and dusty vacuum environment for long periods without on site human maintenance. To track stars, the drive mechanism must be capable of exceedingly fine steps and repeatability. Further, the use of lightweight telescopes for obvious economic benefits burdens the requirement for stable support and rotation. Conventional contact bearings and gear drives have numerous failure modes under such a restrictive and harsh environment. However, hybrid superconducting magnetic bearings (HSMB) fit in naturally. These bearings are stable, light, passive, and essentially frictionless, allowing high precision electronic positioning control. By passive levitation, the HSMB does not wear out and requires neither maintenance nor power. A prototype illustrating the feasibility of this application is presented.

Lamb, Mark↗
NASA NTRS1997

Demonstration of Wavelet Techniques in the Spectral Analysis of Bypass Transition Data

A number of wavelet-based techniques for the analysis of experimental data are developed and illustrated. A multiscale analysis based on the Mexican hat wavelet is demonstrated as a tool for acquiring physical and quantitative information not obtainable by standard signal analysis methods. Experimental data for the analysis came from simultaneous hot-wire velocity traces in a bypass transition of the boundary layer on a heated flat plate. A pair of traces (two components of velocity) at one location was excerpted. A number of ensemble and conditional statistics related to dominant time scales for energy and momentum transport were calculated. The analysis revealed a lack of energy-dominant time scales inside turbulent spots but identified transport-dominant scales inside spots that account for the largest part of the Reynolds stress. Momentum transport was much more intermittent than were energetic fluctuations. This work is the first step in a continuing study of the spatial evolution of these scale-related statistics, the goal being to apply the multiscale analysis results to improve the modeling of transitional and turbulent industrial flows.

Lewalle, Jacques↗