Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “electron sources”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,171 records · Page 65
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Particle and wave observations of low-altitude ionospheric ion acceleration events

Two sounding rockets were launched into the expansive phases of two auroral substorms and passed through source regions of transversely accelerated ionospheric ions. Energetic ion and electron, wave, and ambient plasma observations were made. The events were observed in the 400-600 km range and resulted in the ion energization of hundreds of electron volts. In the acceleration region the ionospheric ion velocity distribution function in the direction perpendicular to the local magnetic field showed a non-Maxwellian, high-energy tail. Plasma density was lower than theoretical quiescent values. Strong thermal ion drift was observed only in the perpendicular direction. Large-amplitude, low-frequency fluctuations in plasma density were present along with a number of different wave modes. The characteristics of the ion energy spectra agreed with a model of ion cyclotron acceleration and energy loss due to ion-neutral collisions.

Yau, A. W.↗
NASA NTRS1985

Survey of probable micrometer-sized Earth-orbital debris fragments in the NASA-JSC cosmic dust sample collection

A program to collect extraterrestrial dust samples from the stratosphere using impactors mounted on NASA U-2 and WB-57F aircraft is discussed. Sample collection, preparation, and analysis techniques are described and the particle types found are reviewed. Preliminary examination of the particles indicates that they represent not only extraterrestrial material, but some fraction of terrestrial contamination from both natural and manmade sources. This examination involves a combination of optical microscopy, scanning electron microscopy (SEM) and qualitative bulk elemental analysis using an energy-dispersive X-ray spectrometer (EDS) to characterize each particle. The cosmic dust collection contains samples of at least three classes of material that may present some hazard to extended spacecraft operations in near-Earth orbit: (1) micrometeorites/cosmic dust, (2) aluminum oxide spheres, and (3) alloy spherules and fragments.

Clanton, U. S.↗
NASA NTRS1985

Temporal evolution of an energetic electron population in an inhomogeneous medium: Application to solar hard X-ray bursts

Energetic electrons accelerated during solar flares can be studied through the hard X-ray emission they produce when interacting with the solar ambient atmosphere. In the case of the non thermal hard X-ray emission, the instanteous X-ray flux emitted at one point of the atmosphere is related to the instantaneous fast electron spectrum at that point. A hard X-ray source model then requires the understanding of the evolution in space and time of the fast particle distribution. The physical processes involved here are energy losses due to Coulomb collisions and pitch angle scattering due to both collisions and magnetic field gradients.

Vilmer, N.↗
NASA NTRS1986

Transfer Casting From Ion-Beam-Textured Surfaces

Textured surfaces created on metals, ceramics, and polymers. Electron-bombardment ion thrustor used as neutralized-ion-beam source. Beam of directed, energetic ions alter surface chemistry and/or morphology of many materials. By adjusting ion energy and ion-beam current density impinging upon target, precise surface modifications obtained without risk of targetmaterial melting or bulk decomposition. Technique developed to generate precise, controllable, surface microstructures on metals, ceramics, and polymers.

Banks, B. A.↗
NASA NTRS1986

The synchrotron-self-Compton process in spherical geometries. II - Application to active galactic nuclei

Observational implications and constraints on spherical nonthermal synchrotron self-Compton models with applications to AGNs are discussed. The Compton optical depth of the source and the synchrotron optical depth are considered, and plausible electron distributions are discussed. The alpha(0x), alpha(rx), and alpha(0r) system of comparing the fluxes in different energy bands is related to the nonthermal models, and sample spectra are presented that show the spectral features the models can produce. The models are applied to radio-quiet AGNs. It is shown that the infrared and X-ray continua of the AGNs can be produced by nonthermal processes.

Band, D. L.↗
NASA NTRS1986

Median density altitude profiles of the major ions in the central nightside Venus ionosphere

Altitude profiles of median values for total ion density, constituent ion densities, and the molecular ion group of the central nightside Venus ionosphere are presently derived from the Pioneer Venus retarding potential analyzer's measurements during the first five seasonal passages of the spacecraft through the nightside hemisphere. The altitude profiles for total ion density, constituent ions and the molecular ion group are compared with previously predicted profiles derived from numerical models in which the ionization source was O(+) ions transported from the dayside ionosphere and electron impact-produced ionization. The electron impact-produced profiles for O(+) is 2 orders of magnitude smaller than that observed.

Knudsen, William C.↗
NASA NTRS1987

Microwave emission above steady and moving sunspots

Two-dimensional maps of radio brightness temperature and polarization, computed assuming thermal emission with free-free and gyroresonance absorption, are compared with observations of active region 2502, performed at Westerbork at lambda = 6.16 cm during a period of 3 days in June 1980. The computation is done assuming a homogeneous model in the whole field of view and a force-free extrapolation of the photospheric magnetic field observed at MSFC with a resolution of 2.34 arcsec. The mean results are the following: (1) a very good agreement is found above the large leading sunspot of the group, assuming a potential extrapolation of the magnetic field and a constant conductive flux in the transition region ranging from .2 x 10 to the 6th to 10 to the 7th erg/sq cm 5; (2) a strong radio source, associated with a new-born moving sunspot, cannot be ascribed to thermal emission. It is suggested that this source may be due to synchrotron radiation by mildly relativistic electrons accelerated by resistive instabilities occurring in the evolving magnetic configuration. An order-of-magnitude computation of the expected number of accelerated particles seems to confirm this hypothesis.

Drago, F. Chiuderi↗
NASA NTRS1988

Spectral evolution in black hole accretion powered AGN and the cosmic X-ray background

If AGN contain supermassive black holes of pregalactic origin, then the radiation emitted during their lifetime will undergo spectral evolution. For AGN black-hole-accretion disk dynamo power sources, the dynamic parameters relevant to spectral evolution are the electron crossing time in the dynamo, the electron radiative loss time, the compactness parameter, and the photon-photon pair production optical depth. It is suggested that both spectral and luminosity evolution may be required to explain the evolutionary properties of AGN.

Leiter, D.↗
NASA NTRS1989

Radiative decays of massive relic particles and the submillimeter background

The interaction of the decay photons of an unstable relic particle species with the microwave background radiation is considered. The radiative decays of these particles delay recombination and serve as an energy source for the resultant plasma. Nonrelativistic Compton scattering by these electrons couples the decay photons to the microwave background, producing submillimeter distortions. If the decay products close the universe, they must decay with a radiative branching ratio larger than 2.5 x 10 to the -5th in order to produce recently observed excess submillimeter background radiation. To be consistent with measurements of the UV background, their mass m is much greater than 114 keV and their decay redshift z is much greater than 5200.

Field, George B.↗
NASA NTRS1990

Electric potential patterns deduced for the SUNDIAL period of September 23-26, 1986

High-latitude electric potential and ionospheric conductance patterns are presented and discussed for the Northern Hemisphere during the SUNDIAL period of September 23-26, 1986 using the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) technique of Richmond and Kamide (1988). Data sources used for the model are satellite and ground magnetometers, electron precipitation instruments, incoherent scatter radars, and ionospheric coherent radars. The period was characterized by many substorms, and a wide variety of instantaneous patterns of electrodynamic parameters on a hemispheric scale are derived throughout this period, of which only a few examples are displayed. The entire set of electric potentials and conductances are being made available through the NCAR CEDAR Data Base for further analysis and utilization in simulation models.

Emery, B. A.↗
NASA NTRS1991

An electronic pan/tilt/zoom camera system

A camera system for omnidirectional image viewing applications that provides pan, tilt, zoom, and rotational orientation within a hemispherical field of view (FOV) using no moving parts was developed. The imaging device is based on the effect that from a fisheye lens, which produces a circular image of an entire hemispherical FOV, can be mathematically corrected using high speed electronic circuitry. An incoming fisheye image from any image acquisition source is captured in memory of the device, a transformation is performed for the viewing region of interest and viewing direction, and a corrected image is output as a video image signal for viewing, recording, or analysis. As a result, this device can accomplish the functions of pan, tilt, rotation, and zoom throughout a hemispherical FOV without the need for any mechanical mechanisms. A programmable transformation processor provides flexible control over viewing situations. Multiple images, each with different image magnifications and pan tilt rotation parameters, can be obtained from a single camera. The image transformation device can provide corrected images at frame rates compatible with RS-170 standard video equipment.

Zimmermann, Steve↗
NASA NTRS1994

Compton cooling of jets as the origin of radio-quiet quasars

We consider the Compton drag as a possible mechanism for jet deceleration in radio-quiet quasars, using an isotropic radiation field in a central region as a source of soft photons, provides an efficient means of decelerating electrons in a jet. Depending on the energy density of the radiation field, the jet may be stopped before reaching the radius at which the dynamical timescale is shorter than the Compton cooling timescale. We present preliminary results of our calculations and conclude that radio-quiet quasars may differ from radio-loud in their central radiation density.

Siemiginowska, Aneta↗
NASA NTRS1978

Chemiluminescence Study of the Autoxidation of cis-1,4-Polyisoprene

The free-radical mechanism for the autoxidation of cis-1,4-polyisoprene (natural rubber or its synthetic counterpart) has been investigated extensively. An important feature of this mechanism, and indeed also of the autoxidation of hydrocarbons generally, is that it is a chain process propagated by alkyl and peroxy radicals and terminated through bimolecular reactions involving these same radicals. In the usual oxidation situation, that is, at all oxygen pressures greater than a few torr, the alkyl radicals are rapidly converted to peroxy radicals, and the termination step proceeds almost exclusively through the latter radicals. The bimolecular decay of the peroxy radicals is accompanied by a weak emission of light or chemiluminescence. Kinetic evidence is consistent with an electronically excited ketone produced in the termination reaction as the source of the emission. The first observation of chemiluminescence from the oxidative degradation of polymers was reported by Ashby, who dealt mainly with polypropylene but made passing mention of several other polymers. Subsequently, a number of papers have appeared dealing with oxidative chemiluminescence from a variety of polymers. In this paper we report the first detailed study of the chemiluminescence emitted in the autoxidation of cis-1,4-polyisoprene. The chemiluminescence technique is extremely sensitive and can follow rates of oxidation that are too slow to be measured conveniently by other means. This work thus offered the potential of throwing new light on the autoxidation of cis-1,4-polyisoprene, especially in the very early stages or under ambient conditions where conventional spectroscopic procedures are rather insensitive.

Mendenhall, G. David↗
NASA NTRS1996

Far-Infrared Spectroscopy of Planetary Nebulae with the KAO

We present new far-infrared line observations of the planetary nebulae (PNs) NGC 7027, NGC 7009, and NGC 6210 obtained with the Kuiper Airborne Observatory (KAO). The bulk of our data are for NGC 7027 and NGC 7009, including [Ne(V)] 24 micrometers, [O(IV)] 26 micrometers, [O(III)] (52, 88) micrometers, and [N(III)] 57 micrometers. Our data for [O(III)] (52, 88) and [N(III)] 57 in NGC 7027 represent the first measurements of these lines in this source. The large [O(III)] 52/88-micrometer flux ratio implies an electron density (cubic cm) of log N(sub e)[O(III)] = 4.19, the largest Ne ever inferred from these lines. We derive N(++)/O(++) = 0.394 +/- 0.062 for NGC 7027 and 0.179 +/- 0.043 for NGC 6210. We are able to infer the O(+3)/O(++) ionic ratio from our data. As gauged by this ionic ratio, NGC 7027 is substantially higher ionization than is NGC 7009 - consistent with our observation that the former produces copious [Ne(V)] emission while the latter does not. These data help characterize the stellar ionizing radiation field. From our [O(IV)] and [O(III)] fluxes, we are able to show that O(++) is by far the dominant oxygen ion in NGC 7009. As a result, the O/H abundance inferred using these data tends to corroborate the value found from UV/optical, collisionally excited lines. We determined accurate rest wavelengths for the [Ne(V)] 2s(2)2p(2)P(sub 1) to 2s(2)2p(2)3P(sub 0) (lambda(sub rest) = 24.316 +/- 0.008 micrometers) and [O(IV)] 2s(2)2p(2)P(sup 0, sub 3/2) to 2s(2)2p(2)P(sup 0, sub 1/2) (lambda(sub rest) = 25.887 +/- 0.007 micrometers) transitions from observations of one or both of the bright PNs NGC 7027 and NGC 7009. Our [O(IV)] value, to the best of our knowledge, is the most accurate direct determination of this lambda(sub rest). These new KAO data will be beneficial for comparison with ISO observations of these PNs.

Rubin, Robert H.↗
NASA NTRS1976

Breast Cancer Detection

NASA's Jet Propulsion Laboratory has come up with a technique to decrease exposure to harmful x-rays in mammographies or breast radiography. Usually, physicians make more than one exposure to arrive at an x-ray film of acceptable density. Now the same solar cells used to convert sunlight into electricity on space satellites can make a single exposure sufficient. When solar cell sensor is positioned directly beneath x-ray film, it can determine exactly when film has received sufficient radiation and has been exposed to optimum density. At that point associated electronic equipment sends signal to cut off x-ray source. Reduction of mammography to single exposures not only reduced x-ray hazard significantly, but doubled the number of patient examinations handled by one machine. The NASA laboratory used this control system at the Huntington Memorial Hospital with overwhelming success.

Source record↗
NASA NTRS2004

Instrumentation for Studies of Electron Emission and Charging From Insulators

Making measurements of electron emission properties of insulators is difficult since insulators can charge either negatively or positively under charge particle bombardment. In addition, high incident energies or high fluences can result in modification of a material s conductivity, bulk and surface charge profile, structural makeup through bond breaking and defect creation, and emission properties. We discuss here some of the charging difficulties associated with making insulator-yield measurements and review the methods used in previous studies of electron emission from insulators. We present work undertaken by our group to make consistent and accurate measurements of the electron/ion yield properties for numerous thin-film and thick insulator materials using innovative instrumentation and techniques. We also summarize some of the necessary instrumentation developed for this purpose including fast response, low-noise, high-sensitivity ammeters; signal isolation and interface to standard computer data acquisition apparatus using opto-isolation, sample-and-hold, and boxcar integration techniques; computer control, automation and timing using Labview software; a multiple sample carousel; a pulsed, compact, low-energy, charge neutralization electron flood gun; and pulsed visible and UV light neutralization sources. This work is supported through funding from the NASA Space Environments and Effects Program and the NASA Graduate Research Fellowship Program.

Thomson, C. D.↗
NASA NTRS1998

Electron Beam Welder Used to Braze Sapphire to Platinum

A new use for electron beam brazing was recently developed by NASA Lewis Research Center's Manufacturing Engineering Division. This work was done to fabricate a fiberoptic probe (developed by Sentec Corporation) that could measure high temperatures less than 600 deg C of vibrating machinery, such as in jet engine combustion research. Under normal circumstances, a sapphire fiber would be attached to platinum by a ceramic epoxy. However, no epoxies can adhere ceramic fibers to platinum under such high temperatures and vibration. Also, since sapphire and platinum have different thermal properties, the epoxy bond is subjected to creep over time. Therefore, a new method had to be developed that would permanently and reliably attach a sapphire fiber to platinum. Brazing a sapphire fiber to a platinum shell. The fiber-optic probe assembly consists of a 0.015-in.-diameter sapphire fiber attached to a 0.25-in.-long, 0.059-in.-diameter platinum shell. Because of the small size of this assembly, electron beam brazing was chosen instead of conventional vacuum brazing. The advantage of the electron beam is that it can generate a localized heat source in a vacuum. Gold reactive braze was used to join the sapphire fiber and the platinum. Consequently, the sapphire fiber was not affected by the total heat needed to braze the components together.

Forsgren, Roger C.↗
NASA NTRS2003

1400-1900 GHz local oscillators for the Herschel Space Observatory

JPL continues to develop robust planar, all solid-state sources to cover the 1414 to 1908 GHz band. These sources will be used as local oscillators to drive hot electron bolometer (HEB) heterodyne mixers on the Herschel Space Observatory to observe high resolution spectra in the interstellar medium. We report our current progress and present recent results.

Schottky diode frequency multiplier THz local osci↗