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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 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

SR90, strontium shaped-charge critical ionization velocity experiment

In May 1986 an experiment was performed to test Alfven's critical ionization velocity (CIV) effect in free space, using the first high explosive shaped charge with a conical liner of strontium metal. The release, made at 540 km altitude at dawn twilight, was aimed at 48 deg to B. The background electron density was 1.5 x 10(exp 4) cu cm. A faint field-aligned Sr(+) ion streak with tip velocity of 2.6 km/s was observed from two optical sites. Using two calibration methods, it was calculated that between 4.5 x 10(exp 20) and 2 x 10(exp 21) ions were visible. An ionization time constant of 1920 s was calculated for Sr from the solar UV spectrum and ionization cross section which combined with a computer simulation of the injection predicts 1.7 x 10(exp 21) solar UV ions in the low-velocity part of the ion streak. Thus all the observed ions are from solar UV ionization of the slow (less than critical) velocity portion of the neutral jet. The observed neutral Sr velocity distribution and computer simulations indicate that 2 x 10(exp 21) solar UV ions would have been created from the fast (greater than critical) part of the jet. They would have been more diffuse, and were not observed. Using this fact it was estimated that any CIV ions created were less than 10(exp 21). It was concluded that future Sr CIV free space experiments should be conducted below the UV shadow height and in much larger background plasma density.

Wescott, Eugene M.↗
NASA NTRS1988

Spectral observations of the extreme ultraviolet astronomical background radiation

Observations in the FUV and soft X-ray bands suggest that the ISM contains several components of high-temperature gas (100,000-1 million K). If large volumes of local interstellar space are filled with this hot plasma, emission lines will be produced in the EUV. Diffuse EUV radiation, however, has only been detected with photometric instruments; no spectral measurements exist below 520 A. A unique grazing-incidence spectrometer to study the diffuse emission between 80 and 650 A with resolution 10-30 A was successfully flown on a sounding rocket in April 1986, and a preliminary analysis reveals several features. In addition to the expected interplanetary He I 584 A emission and the geocoronal He II 304 A emission, other features appear which may orginate in the hot ionized interstellar gas.

Labov, S.↗
NASA NTRS2012

Scientific Verification of Faraday Rotation Modulators: Detection of Diffuse Polarized Galactic Emission

The design and performance of a wide bandwidth linear polarization-modulator based on the Faraday effect is described. Faraday Rotation Modulators (FRMs) are solid-state polarization switches that are capable of modulation up to approx 10 kHz. Six FRMs were utilized during the 2006 observing season in the Background Imaging of Cosmic Extragalactic Polarization (BICEP) experiment; three FRMs were used at each of BICEP fs 100 and 150 GHz frequency bands. The technology was verified through high signal-to-noise detection of Galactic polarization using two of the six FRMs during four observing runs in 2006. The features exhibit strong agreement with BICEP fs measurements of the Galaxy using non-FRM pixels and with the Galactic polarization models. This marks the first detection of high signal-to-noise mm-wave celestial polarization using fast, active optical modulation. The performance of the FRMs during periods when they were not modulated was also analyzed and compared to results from BICEP fs 43 pixels without FRMs.

Moyerman, S.↗
DOE OSTI2020

Digitization modeling of a CGEM detector based on Garfield++ simulation

Abstract Background The Cylindrical Gas Electron Multiplier Inner Tracker (CGEM-IT) is one of the candidates for the replacement of the current BESIII inner drift chamber, which has developed serious aging effects due to beam-related backgrounds. Purpose To build a full digitization model, it is necessary to understand the electron drift behavior and signal induction. Methods A simulation study based on Garfield++ and ANSYS software has been performed. Results Parameters describing the Lorentz angle, diffusion effect, drift time, multiplication, and induction are obtained from the Garfield++ simulation. Based on these results, a preliminary digitization model is implemented in the BESIII offline software system.

Zhao, Jing-Yi (ORCID:0000000220287286)↗
DOE OSTI2021

A consistent and conservative model and its scheme for N -phase- M -component incompressible flows

Here, we propose a consistent and conservative model for multiphase and multicomponent incompressible flows, where there can be arbitrary numbers of phases and components. Each phase has a background fluid called the pure phase, each pair of phases is immiscible, and components are dissolvable in some specific phases. The model is developed based on the multiphase Phase-Field model including the contact angle boundary condition, the diffuse domain approach, and the analyses on the proposed consistency conditions for multiphase and multicomponent flows. The model conserves the mass of individual pure phases, the amount of each component in its dissolvable region, and thus the mass of the fluid mixture, and the momentum of the flow. It ensures that no fictitious phases or components can be generated and that the summation of the volume fractions from the Phase-Field model is unity everywhere so that there is no local void or overfilling. It satisfies a physical energy law and it is Galilean invariant. A corresponding numerical scheme is developed for the proposed model, whose formal accuracy is 2nd-order in both time and space. It is shown to be consistent and conservative and its solution is demonstrated to preserve the Galilean invariance and energy law. Numerical tests indicate that the proposed model and scheme are effective and robust to study various challenging multiphase and multicomponent flows.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

High-dimensional and permutation invariant anomaly detection

Methods for anomaly detection of new physics processes are often limited to low-dimensional spaces due to the difficulty of learning high-dimensional probability densities. Particularly at the constituent level, incorporating desirable properties such as permutation invariance and variable-length inputs becomes difficult within popular density estimation methods. In this work, we introduce a permutation-invariant density estimator for particle physics data based on diffusion models, specifically designed to handle variable-length inputs. We demonstrate the efficacy of our methodology by utilizing the learned density as a permutation-invariant anomaly detection score, effectively identifying jets with low likelihood under the background-only hypothesis. To validate our density estimation method, we investigate the ratio of learned densities and compare to those obtained by a supervised classification algorithm.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1985

Effects of breaking gravity waves on the chemical composition of the mesosphere and lower thermosphere

Eddy diffusion and momentum forcing in the mesosphere and lower thermosphere arise principally from the effects of breaking gravity and waves. The propagation and dissipation of gravity waves depend strongly on season and latitude because of its relationship to the background zonal wind. These processes have significant effects on the transport of chemical species in that region, so that observations of variations in chemical constituents provide useful tracers for dynamical theory. A parameterization of gravity wave propagation and dissipation was incorporated in the coupled dynamical-chemical model to study these effects. Several easily observable airglow features of the mesosphere-thermosphere region are shown to provide sensitive indications of gravity wave influence. In particular, theoretical predictions of large seasonal and latitudinal variations in the atomic oxygen green line, the Meinal bands of excited OH, and the O3 densities inferred from O2 (delta supra 1 sub g) emission at altitudes from 75 to 90 km are shown to be in remarkably good agreement with observations. Implications of these sensitive chemical tracers for the dynamics of the mesosphere-lower thermosphere region and its relationship to gravity waves are discussed.

Solomon, S.↗
NASA NTRS1987

Application of CARS to scramjet combustion

A coherent anti-Stokes Raman spectroscopic (CARS) instrument has been developed for measuring simultaneously temperature and N2 - O2 species concentration in hostile flame environments. A folded BOXCARS arrangement was employed to obtain high spatial resolution. Polarization discrimination against the nonresonant background decreased the lower limits of O2 detectivity. The instrument has been primarily employed for validation of computational fluid-dynamics computer-model codes. Comparisons have been made to both the CHARNAL and TEACH codes on a hydrogen diffusion flame with good results.

Antcliff, R. R.↗
NASA NTRS1989

The Nuclear Astrophysics Explorer

The Nuclear Astrophysics Explorer was proposed in 1986 for NASA's Explorer Concept Study Program by an international collaboration of 25 scientists from nine institutions. The one-year feasibility study began in June 1988. The Nuclear Astrophysics Explorer would obtain high resolution observations of gamma-ray lines, E/Delta E about 1000, at a sensitivity of about 0.000003 ph/sq cm s, in order to study fundamental problems in astrophysics such as nucleosynthesis, supernovae, neutron star and black-hole physics, and particle acceleration and interactions. The instrument would operate from 15 keV to 10 Mev and use a heavily shielded array of nine cooled Ge spectrometers in a very low background configuration. Its 10 deg FWHM field of view would contain a versatile coded mask system which would provide two-dimensional imaging with 4 deg resolution, one-dimensional imaging with 2 deg resolution, and efficiendt measurements of diffuse emission. An unshielded Ge spectrometer would obtain wide-field measurements of transient gamma-ray sources. The earliest possible mission would begin in 1995.

Matteson, J. L.↗
NASA NTRS1989

Distortion of homogeneous turbulence by axisymmetric strain and dilatation

Rapid distortion theory is applied to study distortion of homogeneous turbulence subject to two different axisymmetric strain modes: the axisymmetric contraction (AC, nozzle-type flow), and the axisymmetric expansion (AE, diffuser-type flow). The paper explores the differences in effects of the two axisymmetric strain modes on the anisotropy of correlations and structures of turbulence; examines the effect of dilatation on the distortion of turbulence; and provides a theoretical background for turbulence model development. It is found that velocity and vorticity fluctuations are enhanced more efficiently by contraction than by expansion; contraction produces much higher anisotropy in velocity and vorticity than expansion; root-mean-square pressure is slightly reduced during contraction, whereas it increases rapidly during expansion; and vortical structures of rodlike shape develop in a contraction flow, while disklike structures develop in an expansion flow. A simple model that reflects the dependence of turbulence evolution on structural parameters such as the Reynolds-stress anisotropy and total strain is proposed, and is shown to outperform all other models for all cases examined, regardless of the mean strain rate.

Lee, Moon Joo↗
NASA NTRS1994

Exchange of nitrous oxide within the Hudson Bay lowland

The source strength of atmospheric trace gases from natural ecosystems must be quantified in order to assess the effect of such inputs on the background tropospheric chemistry. A static chamber technique and a gas exchange technique were used to determine the emissions of nitrous oxide from five sites within the Hudson Bay Lowland, as part of the Northern Wetland Study. Two mechanisms, one diffusive and the other episodic, were found likely to be responsible for the emissions of nitrous oxide. The annual diffusive flux ranged from -3.8 mg(N2O)/sq m in a treed bog to 7.9 mg(N2O)/sq m in an open fen. The addition of the episodic flux, increased this range to -2.1 mg(N2O)/sq m and 18.5 mg(N2O)/sq m respectively. These episodic emissions occurred in from 2.5% to 16.7% of the samples during the late summer peak emission period. Since the gas exchange rate could not detect the episodic emissions, it was found to be a poor method for water emission rate determination within the wetland. LANDSAT-Thermatic Mapper (TM) imagery was used to scale the emissions, from the chamber level to an integrated average over the entire Hudson Bay Lowland. The total emission rate of N2O from the Hudson Bay Lowland, was determined to be 1.2 Gg(N2O)/year, of which 80% was attributed to episodic emissions.

Schiller, C. L.↗
DOE OSTI2021

Effective field theory of stochastic diffusion from gravity

Planar black holes in AdS have long-lived quasinormal modes which capture the physics of charge and momentum diffusion in the dual field theory. How should we characterize the effective dynamics of a probe system coupled to the conserved currents of the dual field theory? Specifically, how would such a probe record the long-lived memory of the black hole and its Hawking fluctuations? We address this question by exhibiting a universal gauge invariant framework which captures the physics of stochastic diffusion in holography: a designer scalar with a gravitational coupling governed by a single parameter, the Markovianity index. We argue that the physics of gauge and gravitational perturbations of a planar Schwarzschild-AdS black hole can be efficiently captured by such designer scalars. We demonstrate that this framework allows one to decouple, at the quadratic order, the long-lived quasinormal and Hawking modes from the short-lived ones. It furthermore provides a template for analyzing fluctuating open quantum field theories with memory. In particular, we use this set-up to analyze the diffusive Hawking photons and gravitons about a planar Schwarzschild-AdS black hole and derive the quadratic effective action that governs fluctuating hydrodynamics of the dual CFT. Along the way we also derive results relevant for probes of hyperscaling violating backgrounds at finite temperature.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Optical Investigation of a Partial Fuel Stratification Strategy to Stabilize Overall Lean Operation of a DISI Engine Fueled with Gasoline and E30

This paper offers new insights into a partial fuel stratification (PFS) combustion strategy that has proven to be effective at stabilizing overall lean combustion in direct injection spark ignition engines. To this aim, high spatial and temporal resolution optical diagnostics were applied in an optically accessible engine working in PFS mode for two fuels and two different durations of pilot injection at the time of spark: 210 µs and 330 µs for E30 (gasoline blended with ethanol by 30% volume fraction) and gasoline, respectively. In both conditions, early injections during the intake stroke were used to generate a well-mixed lean background. The results were compared to rich, stoichiometric and lean well-mixed combustion with different spark timings. In the PFS combustion process, it was possible to detect a non-spherical and highly wrinkled blue flame, coupled with yellow diffusive flames due to the combustion of rich zones near the spark plug. The initial flame spread for both PFS cases was faster compared to any of the well-mixed cases (lean, stoichiometric and rich), suggesting that the flame propagation for PFS is enhanced by both enrichment and enhanced local turbulence caused by the pilot injection. Different spray evolutions for the two pilot injection durations were found to strongly influence the flame kernel inception and propagation. PFS with pilot durations of 210 µs and 330 µs showed some differences in terms of shapes of the flame front and in terms of extension of diffusive flames. Yet, both cases were highly repeatable.

33 ADVANCED PROPULSION SYSTEMS↗
NASA NTRS1984

A model of the radiative properties of the El Chichon stratospheric aerosol layer

An accurate multiple-scattering model has been employed to examine the effect of an aerosol layer at 25 mb, corresponding to the El Chichon observations, on the reflection, transmission and absorption of radiation by the stratosphere as a function of latitude, optical thickness and aerosol size distribution. Results are presented and parameterized for each of two wavelength intervals in the shortwave region and 17 wavelength intervals in the longwave region for three models of the aerosol size distribution. They include one model representing the unperturbed stratospheric aerosol plus two models based on measurements of the El Chichon aerosol size distribution. In addition to models of the radiative properties of the aerosol layer, a simple model of the latitudinal distribution of aerosol optical thickness as a function of time is developed, based on diffusive transport in latitude and exponential decay in time. These parameterizations for solar and infrared radiation, together with the dispersion model, permit climate models to account for the evolution of an aerosol size distribution from post-volcanic conditions to background conditions.

King, M. D.↗
NASA NTRS1991

A measurement of the large-scale cosmic microwave background anisotropy at 1.8 millimeter wavelength

This measurement of the large-scale cosmic microwave background radiation (CMBR) anisotropy places the most stringent constraints to date on fluctuations in the CMBR on angular scales greater than about 4 deg. Using a four-channel bolometric radiometer operating at 1.8, 1.1, 0.63, and 0.44 mm, the diffuse sky brightness over half of the northern hemisphere has been mapped with an angular resolution of 3.8 deg. Analysis of the sky map at the longest wavelength for Galactic latitudes of 15 deg or more yields a 95-percent confidence level upper limit on fluctuations of the CMBR at Delta T/T of 1.6 x 10 to the -5th with a statistical power of 92 percent for Gaussian fluctuations at a correlation angle of 13 deg. Between 3 deg and 22 deg, the upper limit of fluctuations is 4.0 x 10 to the -5th . An anisotropy is detected in the map, but it cannot yet be attributed to primordial sources. The ultimate sensitivity for this experiment is 7 x 10 to the -6th over this angular range for Gaussian fluctuations.

Meyer, Stephan S.↗
NASA NTRS2003

Characterizing the X-Ray Spectrum of the Galactic Halo

The goal of this project is to determine the spectrum of the Galactic halo's soft X-ray emission. These photons are emitted by hot, diffuse gas hundreds to thousands of parsecs from the Galactic plane. Thus, the emission is weak, can be confused with locally produced photons, and must be distinguished from noise. My co-I has made significant progress on determining the background. I have been working on a complementary aspect of the project: computer simulations of the hot gas in the local and distant regions.

Source record↗
DOE OSTI2022

Contribution from TeV halos to the isotropic gamma-ray background

We report recent observations have shown that pulsars are surrounded by extended regions which emit TeV-scale gamma rays through the inverse Compton scattering of very high energy electrons and positrons. Such TeV halos are responsible for a large fraction of the Milky Way’s TeV-scale gamma-ray emission. In this paper, we calculate the gamma-ray spectrum from the population of TeV halos located within the Andromeda Galaxy, predicting a signal that is expected to be detectable by the Cherenkov Telescope Array. We also calculate the contribution from TeV halos to the isotropic gamma-ray background, finding that these sources should contribute significantly to this flux at the highest measured energies, constituting up to ~20 % of the signal observed above ~0.1TeV. We also comment on the implications of our results for the origin of the diffuse neutrino flux detected by IceCube.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1986

Magnetic field in molecular cloud cores: Limits on field strengths and linewidths

Preliminary observations by others indicate that the magnetic field strength in dense molecular cloud cores is on the order of 30 micro G, much closer to the background field strength than to the flux-freezing prediction for this density. This result implies that some process must exist to decrease the magnetic field strength in these regions to much less than its flux-frozen value, e.g., ambipolar diffusion. At these moderate field strengths, magnetohydrodynamic waves in the cores provide a good explanation of observed supra-thermal molecular linewidths.

Goodman, A. A.↗