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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

The Study of Biomass Emissions for Defining Radiative Forcing of Climate

Accurate quantification of the amounts of trace gases and particulate matter emitted from vegetation fires and other sources of biomass burning (agricultural waste and biofuels) on a regional and global basis is required by a number of users, including scientists studying a wide range of atmospheric processes, national governments who are required to report greenhouse gas emissions, and those interested in quantifying the sources of air pollution that affect human health at regional scales. Over the past decade, improvements in the ability to detect and map fires using a number of different satellite systems have been achieved, largely through efforts coordinated through working groups organized by the IGBP Data and Information System and Global Observation of Forest Cover (GOFC) projects. In addition, significant advances and improvement in or understanding of the emissions factors for biomass burning in different biomes has resulted through efforts by the Biomass Burning Experiment (BIBEX) organized through the International Global Atmospheric Chemistry project. A number of satellite-based fire data products have been generated, and a number of new products will shortly be available. These new data products will provide the basis for estimating emissions from biomass burning on a global basis. However, a number of issues remain concerning the availability of other data sets needed to generate these estimates. Recognizing these issues, the GOFC-Fire Satellite Validation Workshop (held in Lisbon, Portugal on 9-11 July 2001), recommended that a workshop focusing on Improving Global Estimates of Atmospheric Emissions from Biomass Burning be organized. This workshop was held from 17- 19 July 2002 on the campus of the University of Maryland, College Park, Maryland. This workshop served as the annual meeting of the GOFC/GOLD-Fire Program. The overall goals of the meeting were to review the information products generated from satellite imagery and other sources that are currently available for developing emission estimates from biomass burning, evaluate areas where improved or additional products would be beneficial, and recommend products for use by the atmospheric science community.

Penner, Joyce↗
NASA NTRS1986

Is IRAS cirrus cloud emission largely fine-structure radiation?

The contribution of line emission to the diffuse 'cirrus' radiation components observed by IRAS at 60 and 100 microns, respectively, is evaluated. The cirrus radiation was observed straddling the galactic plane to latitudes of + or - 80 degrees. Comparison of the observed brightness from cirrus clouds with forbidden line emission of O I and O III at 63 and 88 microns showed that the flux levels observed by IRAS are of the same order as the fine-structure line emission predicted by Stacey et al. (1985). It is argued that the fine-structure line emission from neutral gas at 63 microns as well as the line emission from diffuse ionized clouds at 88 microns, are significant components in most clouds, in some clouds they are the prime source of cirrus radiation.

Harwit, M.↗
DOE OSTI2025

A curvature-based mechanism for the spontaneous emission of electromagnetic radiation at curved plasma–vacuum interfaces

In this work, we derive from first principles the dispersion relation for electromagnetic radiation that is spontaneously emitted at a 2D curved plasma–vacuum interface in the absence of both background and external electric and magnetic fields. This plasma geometry is motivated by plasmas generated through hypervelocity impact projectiles—an area that is of importance to satellite safety in the aerospace community, and may be of importance for the developing study of projectile impact-driven inertial confinement fusion. We find spontaneous radiation occurs when thermal surface waves propagate along the edge of a circular plasma, with a frequency lower than the plasma frequency and spatial decay proportional to 1/r. This is distinct from more well-known mechanisms of radiation, in which the radiation frequency is greater than or equal to the plasma frequency. This theory is validated against 2D, electromagnetic particle-in-cell simulations and shows reasonable agreement. Finally, we discuss the effects of plasma geometry and attribute the radiation generation mechanism to the acceleration of charged surface waves as they traverse azimuthally along a curved path.

Lau, Raymond (ORCID:0000000299318101)↗
NASA NTRS1994

Imaging spectroscopy of solar microwave radiation. 1: Flaring emission

We present observations of an impulsive microwave burst on the Sun with both high spatial and spectral resolution, made with the Solar Array at the Owens Valley Radio Observatory (OVRO). We used the measured brightness temperature spectrum to infer the emission process responsible for each microwave source, and to derive physical conditions in the source region. We confimed our predictions using soft X-ray measurements from Geostationary Operational Environmental Satellite (GOES), soft X-ray images from Yohkoh, and H-alpha flare images together with sunspots and magnetogram images from the Big Bear Solar Observatory.

Lim, Jeremy↗
NASA NTRS2002

Pulsar Polar Cap Heating and Surface Thermal X-ray Emission: Inverse Compton Radiation Pair Fronts - 2

We investigate the production of electron-positron pairs by inverse Compton scattered (ICS) photons above a pulsar polar cap (PC) and calculate surface heating by returning positrons. This paper is a continuation of our self-consistent treatment of acceleration, pair dynamics, and electric field screening above pulsar PCs. We calculate the altitude of the inverse Compton pair-formation fronts, the flux of returning positrons, and present the heating efficiencies and X-ray luminosities. We revise pulsar death lines implying cessation of pair formation, and present them in surface magnetic field-period space. We find that virtually all known radio pulsars are capable of producing pairs by resonant and nonresonant ICS photons radiated by particles accelerated above the PC in a pure star-centered dipole field, so that our ICS pair death line coincides with empirical radio pulsar death. Our calculations show that ICS pairs are able to screen the accelerating electric field only for high PC surface temperatures and magnetic fields. We argue that such screening at ICS pair fronts occurs locally, slowing but not turning off acceleration of particles until screening can occur at a curvature radiation (CR) pair front at higher altitude. In the case where no screening occurs above the PC surface, we anticipate that the pulsar gamma-ray luminosity will be a substantial fraction of its spin-down luminosity. The X-ray luminosity resulting from PC heating by ICS pair fronts is significantly lower than the PC heating luminosity from CR pair fronts, which dominates for most pulsars. PC heating from ICS pair fronts is highest in millisecond pulsars, which cannot produce CR pairs, and may account for observed thermal X-ray components in the spectra of these old pulsars.

Harding, Alice K.↗
NASA NTRS2010

IR Thermography NDE of ISS Radiator Panels

The presentation covers an active and a passive infrared (IR) thermography for detection of delaminations in the radiator panels used for the International Space Station (ISS) program. The passive radiator IR data was taken by a NASA astronaut in an extravehicular activity (EVA) using a modified FLIR EVA hand-held camera. The IR data could be successfully analyzed to detect gross facesheet disbonds. The technique used the internal hot fluid tube as the heat source in analyzing the IR data. Some non-flight ISS radiators were inspected using an active technique of IR flash thermography to detect disbond of face sheet with honeycomb core, and debonds in facesheet overlap areas. The surface temperature and radiated heat emission from flight radiators is stable during acquisition of the IR video data. This data was analyzed to detect locations of unexpected surface temperature gradients. The flash thermography data was analyzed using derivative analysis and contrast evolutions. Results of the inspection are provided.

Koshti, Ajay↗
NASA NTRS1987

Whistler mode emissions in the Uranian radiation belts

Voyager 2 detected intense whistler mode emissions and fluxes of energetic electrons during the outbound pass through the region of auroral L shells. The observed energetic (E greater than 22 keV) electron distribution, a model warm (E less than 27.5 keV) electron distribution, and the cold plasma density profile deduced by Kurth et al. (1987) are used to calculate the ray path-integrated spatial amplification of whistlers which arrive at Voyager 2 from the magnetic equator. By matching the calculated amplification and the relative gains at different frequencies deduced from the observed whistler power spectrum, the pitch angle anisotropy parameters of the electron distributions are determined to within a fairly narrow range of values. The estimated bounce average pitch angle diffusion coefficient indicates that electrons are on strong diffusion over a wide range in energies. The electron precipitation energy flux is sufficient to produce the observed auroral light emissions.

Coroniti, F. V.↗
NASA NTRS1975

A radiative transfer model for microwave emissions from bare agricultural soils

A radiative transfer model for microwave emissions from bare, stratified agricultural soils was developed to assist in the analysis of data gathered in the joint soil moisture experiment. The predictions of the model were compared with preliminary X band (2.8 cm) microwave and ground based observations. Measured brightness temperatures at vertical and horizontal polarizations can be used to estimate the moisture content of the top centimeter of soil with + or - 1 percent accuracy. It is also shown that the Stokes parameters can be used to distinguish between moisture and surface roughness effects.

Burke, W. J.↗
NASA NTRS1985

A two-dimensional spectrum of a nonradiative shock filament in the Cygnus Loop

A two-dimensional spectrum of a nonradiative filament in the Cygnus Loop covering the spectral region 4600-7500 A is presented and discussed. Emission lines of H, He II, and forbidden O III, as well as extremely faint N II and S II forbidden lines, were detected. Small spatial differences for some of the filament's emission lines and a possible velocity gradient across the filament's western edge were also observed. Measured relative line intensities are combined with previous nonradiative data and are compared to new nonradiative shock models which treat one, two, and three postshock temperature distributions. It is found that two- and three-temperature models provide a good fit to the observed relative line intensities. The observed weak N II and S II forbidden line emissions are interpreted as due to either radiative shock emissions produced by small density fluctuations in the shocked cloud (e.g., cloud cores), or faint dust grain reflection of the remnant's bright radiative filament emission.

Fesen, R. A.↗
NASA NTRS1995

Thermal Balance in Dense Molecular Clouds: Radiative Cooling Rates and Emission-Line Luminosities

We consider the radiative cooling of fully shielded molecular astrophysical gas over a wide range of temperatures ( 10 K < T < 2500 K) and H2 densities ( 10(exp 3)/cc < n(H2) < 10(exp 10)/cc). Our model for the radiative cooling of molecular gas includes a detailed treatment of the interstellar chemistry that determines the abundances of important coolant molecules, and a detailed treatment of the excitation of the species H2, CO, H2O, HCl, O2, C, O, and their isotopic variants where important. We present results for the total radiative cooling rate and for the cooling rate due to individual coolant species, as a function of the gas temperature, density, and optical depth. We have also computed the individual millimeter, submillimeter, and far-infrared line strengths that contribute to the total radiative cooling rate, and we have obtained example spectra for the submillimeter emission expected from molecular cloud cores. Many of the important cooling lines will be detectable using the Infrared Space Observatory and the Submillimeter Wave Astronomy Satellite.

Neufeld, David A.↗
DOE OSTI2024

RadSim: Particle Transport Wrapper

RadSim is being developed to provide the capability to simulate radiation source emissions, interpolate results from radiation transport tools into a common format to prepare incident flux, and model radiation detector response. This software package includes wrapper API code which is utilized in the development of the second (transport) task of the RadSim project. This software package only contains tools to interface RadSim with radiation transport tools (GEANT4 and MCNP) and does not include any part of the transport source code itself. The users will need prior access to the transport tools (GEANT4 and MCNP), and can use this software package to interface with the transport tool of their choice. This software package takes the geometry file for a radiation transport problem and converts it into an input deck for the transport tools (GEANT4 and MCNP). Additionally, it also contains filters that convert the output of the transport tools to a common flux format.

Cheung, Hoi Sing↗