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At least 271 records · Page 15

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NASA NTRS1985

Black hole accretion disks - Electrodynamic coupling of accretion-disk coronae and the partitioning of soft and hard X-ray emission

It is demonstrated that the observed large ratio of hard to soft X-ray emission and the bimodel behavior of black hole accreting X-ray sources such as Cygnus X-1 can be described in terms of a magnetically structured accretion disk corona which is electrodynamically coupled to the disk turbulent motions while the disk is thermodynamically coupled to the corona as described by a feedback parameter delta. The observed ratio of hard to soft X-ray emission is independent of the disk thickness, and weakly dependent of the disk parameter alpha relating the disk viscous stresses to the total pressure. Observed values of the luminosity ratio point towards strong differences of the feedback of the low state compared to the high state, in the sense that low state means small feedback (delta less than 0.2) and high state means strong feedback delta of about 0.5.

Kuperus, M.↗

NASA NTRS1985

Current status of the dissipative thermal model for solar hard X-ray bursts

The existing dissipative thermal models for hard X-ray bursts are briefly examined, and it is shown that the model with additional acceleration is the best candidate for explaining the whole hard X-ray burst. In both phases, but especially in the thermal phase, the plasma beta approaches unity, and two-dimensional modeling of the hydrodynamics is required. Following the accelerated electrons only, without taking into account the response of the bulk of the plasma, is inadequate. It is suggested that a useful approach might be a multifluid one using approximately 15 fluids with the possibility of transfer between fluids in one and two dimensions. It is concluded that, while the model is a promising one, many details remain to be worked out.

Smith, D. F.↗

NASA NTRS1985

Influence of design variables on radiation hardness of silicon MINP solar cells

Metal-insulator-N/P silicon (MINP) solar cells were fabricated using different substrate resistivity values, different N-layer designs, and different I-layer designs. A shallow junction into an 0.3 ohm-cm substrate gave best efficiency whereas a deeper junction into a 1 to 4 ohm-cm substrate gave improved radiation hardness. I-layer design variation did little to influence radiation hardness.

Anderson, W. A.↗

NASA NTRS1985

The hard X-ray burst spectrometer event listing, 1980 - 1985

This event listing is a comprehensive reference for the hard X-ray bursts detected with the Hard X-Ray Burst Spectrometer on the Solar Maximum Mission from the time of launch on February 14, 1980 to September 1985. Over 8000 X-ray events were detected in the energy range from 30 to approx. 500 keV with the vast majority being solar flares. The listing includes the start time, peak time, duration and peak rate of each event.

Dennis, B. R.↗

NASA NTRS1985

Surface effects of corrosive media on hardness, friction, and wear of materials

Hardness, friction, and wear experiments were conducted with magnesium oxide exposed to various corrosive media and also with elemental iron and nickel exposed to water and NaOH. Chlorides such as MgCl2 and sodium containing films were formed on cleaved magnesium oxide surfaces. The MgCl2 films softened the magnesium oxide surfaces and caused high friction and great deformation. Hardness was strongly influenced by the pH value of the HCl-containing solution. The lower the pH, the lower the microhardness. Neither the pH value of nor the immersion time in NaOH containing, NaCl containing, and HNO3 containing solutions influenced the microhardness of magnesium oxide. NaOH formed a protective and low friction film on iron surfaces. The coefficient of friction and the wear for iron were low at concentrations of NaOH higher than 0.01 N. An increase in NaOH concentration resulted in a decrease in the concentration of ferric oxide on the iron surface. It took less NaOH to form a protective, low friction film on nickel than on iron.

Miyoshi, K.↗

NASA NTRS1985

Simultaneous observations of hard X-ray and microwave burst sources in a limb flare

Observations of a flare which occurred just behind the west solar limb on 1981 August 3 are reported. A hard X-ray source (20-30 keV) and a microwave source at 5 GHz were observed simultaneously using the Very Large Array and the hard X-ray telescope aboard the Hinotori spacecraft. Both sources were located in the corona, apparently near the tops of two independent coronal arcades or loops. The source may be composed of many thin filaments unresolved by the VLA observations.

Takakura, T.↗

NASA NTRS1985

Quantitative analysis of hard X-ray 'footpoint' flares observed by the solar maximum mission

Amplifier gain and collimator hole size variations across the field of view, amplifier/filter efficiency, variations in effective collimator hole size and angular response with photon energy, dead-time, and hard X-ray plate transmission, are among the factors for which instrumental corrections have to be incorporated to effect reliable correction and deconvolution of images from the SMM satellite's Hard X-ray Imaging Spectrometer (HXIS). Attention is given to the substantial Poisson noise in these energy bands. The maximum entropy deconvolution/correction routine developed for establishing the spatial structure reliably inferrable from HXIS data is presented, together with the results of the application of this routine to the three impulsive flares reported by Duijemian et al. (1982) from April 10, May 21, and November 5, 1980.

Mackinnon, A. L.↗

NASA NTRS1987

Hard Suit With Adjustable Torso Length

Torso sizing rings allow single suit to fit variety of people. Sizing rings inserted between coupling rings of torso portion of hard suit. Number of rings chosen to fit torso length of suit to that of wearer. Rings mate with, and seal to, coupling rings and to each other. New adjustable-size concept with cost-saving feature applied to other suits not entirely constructed of "hard" materials, such as chemical defense suits and suits for industrial-hazard cleanup.

Vykukal, Hubert C.↗

NASA NTRS1987

Hardness Tester for Polyur

Rubber-hardness tester modified for use on rigid polyurethane foam. Provides objective basis for evaluation of improvements in foam manufacturing and inspection. Typical acceptance criterion requires minimum hardness reading of 80 on modified tester. With adequate correlation tests, modified tester used to measure indirectly tensile and compressive strengths of foam.

Hauser, D. L.↗

NASA NTRS1986

Effect of hard particle impacts on the atomic oxygen survivability of reflector surfaces with transparent protective overcoats

Silver mirror samples with protective coatings were subjected to a stream of 27 microns alumina particles to induce pinhole defects. The protective coating consisted of a layer of aluminum dioxide over silver followed by a layer of silicon dioxide over the alumina. Samples were prepared on both graphite-epoxy composite and fused quartz substrates. After exposure to the hard particle stream, the samples were exposed to an oxygen plasma environment in a laboratory plasma asher. The effects of both the hard particles and the oxygen plasma were documented by both reflectance measurements and scanning electron microscopy. The results indicated that oxidative damage to the silver reflecting layer continues beyond that of the erosively exposed silver. Oxidative undercutting of the silver layer and graphite-epoxy substrate continues in undamaged areas through adjacent, particle damaged defect sites. This may have implications for the use of such mirrors in a space station solar dynamic power system.

Gulino, D. A.↗

NASA NTRS1986

Evidence for beamed electrons in a limb X-ray flare observed by Hard X-Ray Imaging Spectrometer (HXIS)

The limb flare of November 18, 1980, 14:51 UT, was investigated on the basis of X-ray images taken by the Hard X-ray Imaging Spectrometer (HXIS) and of X-ray spectra from the Hard X-Ray Burst Spectrometer (HXRBS) aboard the Solar Maximum Mission (SMM). The impulsive burst was also recorded at microwave frequencies between 2 and 20 GHz whereas no optical flare and no radio event at frequencies below 1 GHz were reported. The flare occurred directly at the SW limb of the solar disk. Taking advantage of the spatial resolution of HXIS images, the time evolution of the X-radiation originating from relatively small source regions can be studied. Using Monte Carlo computations of the energy distribution of energetic electrons traversing the solar plasma, the bremsstrahlung spectra produced by the electrons were derived.

Haug, Eberhard↗

NASA NTRS1986

Microwave and hard X-ray emissions during the impulsive phase of solar flares: Nonthermal electron spectrum and time delay

On the basis of the summing-up and analysis of the observations and theories about the impulsive microwave and hard X-ray bursts, the correlations between these two kinds of emissions were investigated. It is shown that it is only possible to explain the optically-thin microwave spectrum and its relations with the hard X-ray spectrum by means of the nonthermal source model. A simple nonthermal trap model in the mildly-relativistic case can consistently explain the main characteristics of the spectrum and the relative time delays.

Gu, Ye-Ming↗

NASA NTRS1986

Rapid spectral and flux time variations in a solar burst observed at various dm-mm wavelengths and at hard X-rays

A solar burst was observed with high sensitivity and time resolution at cm-mm wavelengths by two different radio observatories (Itapetinga and Algonquin), with high spectral time resolution at dm-mm wavelengths by patrol instruments (Sagamore Hill), and at hard X-rays (HXM Hinotori). At the onset of the major burst time structure there was a rapid rise in the spectral turnover frequency (from 5 to 15 GHz), in about 10s, coincident to a reduction of the spectral index in the optically thin part of the spectrum. The burst maxima were not time coincident at the optically thin radio frequencies and at the different hard X-ray energy ranges. The profiles at higher radio frequencies exhibited better time coincidence to the high energy X-rays. The hardest X-ray spectrum (-3) coincided with peak radio emission at the higher frequency (44 GHz). The event appeared to be built up by a first major injection of softer particles followed by other injections of harder particles. Ultrafast time structures were identified as superimposed on the burst emission at the cm-mm high sensitivity data at X-rays, with predominant repetition rates ranging from 2.0 to 3.5 Hz.

Zodivaz, A. M.↗

NASA NTRS1986

OV and hard X-rays, observations and model calculations

An amalgamation of two published works that discuss the observation and theoretical calculations of OV (T approx. 250,000K) and Hard X-rays (30 to 100keV) emitted during flares are presented. The papers are by Poland et al (1984) and Mariska and Poland (1985). The observations of Hard X-rays and OV show that the excitation processes for each type of emission are closely coupled. Except for small differences the two types of emission rise and fall together during a flare. Model calculations are able to reproduce this behavior to a large extent, only when conductive processes do not dominate the energy transport processes.

Poland, A. I.↗

NASA NTRS1986

The effect of beam-driven return current instability on solar hard X-ray bursts

The problem of electrostatic wave generation by a return current driven by a small area electron beam during solar hard X-ray bursts is discussed. The marginal stability method is used to solve numerically the electron and ion heating equations for a prescribed beam current evolution. When ion-acoustic waves are considered, the method appears satisfactory and, following an initial phase of Coulomb resistivity in which T sub e/T sub i rise, predicts a rapid heating of substantial plasma volumes by anomalous ohmic dissipation. This hot plasma emits so much thermal bremsstrahlung that, contrary to previous expectations, the unstable beam-plasma system actually emits more hard X-rays than does the beam in the purely collisional thick target regime relevant to larger injection areas. Inclusion of ion-cyclotron waves results in ion-acoustic wave onset at lower T sub e/T sub i and a marginal stability treatment yields unphysical results.

Cromwell, D.↗

NASA NTRS1986

Energy of microwave-emitting electrons and hard x-ray/microwave source model in solar flares

Based on the rate of increse of the microwave flux relative to the hard X-ray flux at various energies from the onset to the peak of a flare, the mean energy of microwave-emitting electrons is estimated for 22 flares observed simultaneously in hard X-rays and microwaves. The energy of electrons varying in proportion to the 17 GHz emission is found to concentrate below 100 keV, and the mean energy or eletrons emitting 70 keV x-rays is less than about 130 keV for thin-target and less than about 180 keV for thick-target emission models, suggesting that the 17 GHz emission derives from electrons with energy of less than a few hundred keV. The magnetic field strength in the microwave source is found to be 500-1000 G for the thick-target and 1000-2000 G for the thin-target case, and 16 of the 22 events examined can be successfully explained by the thick-target model. Of the six events which cannot be explained by the thick-target model, two events give L of less than about 300 km.

Nitta, N.↗

NASA NTRS1987

Effect of hard particle impacts on the atomic oxygen survivability of reflector surfaces with transparent protective overcoats

Gulino, Daniel A.↗

NASA NTRS1987

Gas scintillation drift chambers with wave shifter read-out for hard X-ray astronomy

A major improvement in hard X-ray and gamma ray astrophysics could be provided by high pressure xenon time projection chambers where gas scintillation is used both for the measurement of the time of interaction and for the detection of the extracted electrons. This allows three dimensional imaging of naturally complex events (photoelectric interaction with escape photon, Compton scatter, and pair production). A novel read-out system based on wave shifter fibers, which is well suited to the high pressures and large areas required of a hard X-ray telescope is proposed. Expected performances are computed, potential problems are outlined, and the experimental effort to solve these problems are described.

Sadoulet, Bernard↗