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NASA NTRS1984

Current carriers for the field-aligned current system

The Dynamics Explorer satellites have returned a large body of data containing high resolution magnetometer measurements and distributions of charged particles of all but thermal electrons. From these data the relations of the field aligned currents to particle precipitation structures were investigated and the charge carriers were identified. Results include the following: (1) during very quiet periods, field aligned currents exist primarily as fine structure; (2) during onset of substorms, region 1 and region 2 become clearly evident but contain significant structure; (3) as magnetic activity subsides, current regions become less distinct, and structure becomes more dominant; (4) the distribution of the upward currents derived from magnetometer data and calculated from suprathermal electron data agree remarkably well in shape but not necessarily in magnitude; (5) at all local times, 5 eV electrons seldom carry most of the upward current; (6) except for the accelerated inverted-V electrons, the dominant upward current carriers which are measured are below 500 eV and are distributed in energy; (7) dusk upward currents (region 1) are associated with the boundary plasma sheet; and (8) suprathermal electron bursts are important current carrying structures.

Hoffman, R. A.↗

NASA NTRS1985

Study of several factors affecting crew escape trajectories from the Space Shuttle Orbiter at low-subsonic speeds

Factors affecting the bailout characteristics from the space shuttle orbiter at low-subsonic speeds were investigated. In the 12-foot low-speed tunnel and the 4 by 7-meter tunnel with 0.03-scale models. The effect of crew-model exit velocity, body position, and body weight were studied with egress from the main side hatch with the orbiter upright and from the upper cabin hatch with the orbiter inverted. Crew model drag and flow field measurements around the orbiter were estimated. The high-angle-of-attack trim characteristics of the orbiter was determined by force tests in an attempt to improve bailout conditions. A computer simulation was made to evaluate the maneuver necessary to attain the high-angle-of-attack trim.

Scallion, W. I.↗

NASA NTRS1985

Geophysical Interpretation of Venus Gravity Data

The subsurface distribution of Venus was investigated through the analysis of the data from Pioneer Venus Orbiter (PVO). In particular, the Doppler tracking data were used to map the gravitational potential. These were compared to the topographic data from the PVO radar (ORAD). In order to obtain an unbiased comparison, the topography data obtained from the PVO-ORAD were filtered to introduce distortions which are the same as those of the gravity models. Both the gravity and filtered topography maps are derived by two stage processes with a common second stage. In the first stage, the topography was used to calculate a corresponding spacecraft acceleration under the assumptions that the topography has a uniform given density and no compensation. In the second stage, the acceleration measures found in the first stage were passed through a linear inverter to yield maps of gravity and topography. Because these maps are the result of the same inversion process, they contain the same distortion; a comparison between them is unbiased to first order.

Reasenberg, R. D.↗

NASA NTRS1985

Simulated Microgravity as a Probe for Understanding the Mechanisms of Early Pattern Specification

Early pattern specification (e.g., axial structure morphogenesis, doreal ventral polarity, etc.) is monitored in amphibian eggs which were subjected to microgravity simulation by constant rotation on a horizontal clinostat. In contrast to previous clinostat experiments, rotation is initiated either prior to fertilization or immediately thereafter. Large proportions of clinostated eggs developed normal axial structures. A model which employs a multiple set of signals for specifying early pattern is discussed. Effects of microgravity simulation on the earliest post fertilization pattern specification event dorsal/ventral polarization is analyzed in detail. Other models are developed and they are discussed. As a general mechanism for explaining the manner in which regional developmental patterns emerge from the initial, radially symmetrial egg, the density compartment model is described. The identification of the various zones or compartments of egg cytoplasm using inverted eggs is explained.

Neff, A. W.↗

NASA NTRS1983

Development and evaluation of a Fault-Tolerant Multiprocessor (FTMP) computer. Volume 3: FTMP test and evaluation

The experimental test and evaluation of the Fault-Tolerant Multiprocessor (FTMP) is described. Major objectives of this exercise include expanding validation envelope, building confidence in the system, revealing any weaknesses in the architectural concepts and in their execution in hardware and software, and in general, stressing the hardware and software. To this end, pin-level faults were injected into one LRU of the FTMP and the FTMP response was measured in terms of fault detection, isolation, and recovery times. A total of 21,055 stuck-at-0, stuck-at-1 and invert-signal faults were injected in the CPU, memory, bus interface circuits, Bus Guardian Units, and voters and error latches. Of these, 17,418 were detected. At least 80 percent of undetected faults are estimated to be on unused pins. The multiprocessor identified all detected faults correctly and recovered successfully in each case. Total recovery time for all faults averaged a little over one second. This can be reduced to half a second by including appropriate self-tests.

Lala, J. H.↗

NASA NTRS1985

Binning of satellite magnetic anomalies

Crustal magnetic anomaly signals over satellite orbits were simulated to investigate numerical averaging as an anomaly estimator. Averaging as an anomaly estimator involves significant problems concerning spatial and amplitude smoothing of the satellite magnetic observations. The results of simulations suggest that the error of numerical averaging constitutes a small and relatively minor component of the total error-budget of higher orbital anomaly estimates, whereas for lower orbital estimates numerical averaging error increases substantially. As an alternative to numerical averaging, least-squares collocation was investigated and observed to produce substantially more accurate anomaly estimates, particularly as the orbital elevation of prediction was decreased towards the crustal sources. In contrast to averaging, collocation is a significantly more resource-intensive procedure to apply because of the practical, but surmountable problems related to establishing and inverting the covariance matrix for accurate anomaly prediction. However, collocation may be much more effectively used to exploit the anomaly details contained in the lower orbital satellite magnetic data for geologic analysis.

Goyal, H. K.↗

NASA NTRS1985

Geophysical interpretation of Venus gravity data

The investigation of the subsurface mass distribution of Venus through the analysis of the data from Pioneer Venus Orbiter (PVO) is presented. The Doppler tracking data was used to map the gravitational potential, which was compared to the topographic data from the PVO radar (ORAD). In order to obtain an unbiased comparison, the topography obtained from the PVO-ORAD was filtered to introduce distortions which are the same as those of our gravity models. The last major software package that was required in order to determine the spectral admittance Z (lambda) was used. This package solves the forward problem: given the topography and its density, and assuming no compensation, find the resulting spacecraft acceleration along a given nominal trajectory. The filtered topography is obtained by processing these accelerations in the same way (i.e., with the same geophysical inverter) as the Doppler-rate data that we use to estimate the gravity maps.

Reasenberg, R. D.↗

NASA NTRS1985

Evaluation of semiconductor devices for Electric and Hybrid Vehicle (EHV) ac-drive applications, volume 1

The results of evaluation of power semiconductor devices for electric hybrid vehicle ac drive applications are summarized. Three types of power devices are evaluated in the effort: high power bipolar or Darlington transistors, power MOSFETs, and asymmetric silicon control rectifiers (ASCR). The Bipolar transistors, including discrete device and Darlington devices, range from 100 A to 400 A and from 400 V to 900 V. These devices are currently used as key switching elements inverters for ac motor drive applications. Power MOSFETs, on the other hand, are much smaller in current rating. For the 400 V device, the current rating is limited to 25 A. For the main drive of an electric vehicle, device paralleling is normally needed to achieve practical power level. For other electric vehicle (EV) related applications such as battery charger circuit, however, MOSFET is advantageous to other devices because of drive circuit simplicity and high frequency capability. Asymmetrical SCR is basically a SCR device and needs commutation circuit for turn off. However, the device poses several advantages, i.e., low conduction drop and low cost.

Lee, F. C.↗

NASA NTRS1984

Anisotropic models of the upper mantle

Long period Rayleigh wave and Love wave dispersion data, particularly for oceanic areas, were not simultaneously satisfied by an isotropic structure. Available phase and group velocity data are inverted by a procedure which includes the effects of transverse anisotropy, an elastic dispersion, sphericity, and gravity. The resulting models, for the average earth, average ocean and oceanic regions divided according to the age of the ocean floor, are quite different from previous results which ignore the above effects. The models show a low velocity zone with age dependent anisotropy and velocities higher than derived in previous surface wave studies. The correspondence between the anisotropy variation with age and a physical model based on flow aligned olivine is suggested.

Regan, J.↗

NASA NTRS1983

External control of planetary radio emission

Recent studies using data from Voyagers 1 and 2 to correlate variations in the Saturn kilometric radiation (SKR) with changes in solar-wind properties are summarized and illustrated with graphs. Best SKR correlations have been obtained with the solar-wind ram pressure and the related kinetic energy flux. It is pointed out that the related phenomenon on earth, the auroral kilometric radiation, occurs mainly in the nightside auroral region (as opposed to the dayside cleft region for SKR) and is best correlated with solar-wind velocity and inverted-V electron-precipitation events, implying a different stimulation process. The evidence for solar-wind control of the non-Io-related decametric radiation of Jupiter is also reviewed.

Rucker, H. O.↗

NASA NTRS1984

Total-dose and dose-rate dependence of proton damage in MOS devices during and after irradiation

Rad-hard CMOS/bulk inverters with input gates high and low were irradiated by protons with a nominal energy of 8 MeV in an effort to determine the total-dose and dose-rate dependence of threshold voltage shifts, both during and immediately after irradiation and over extended periods of time thereafter. It is shown that the effects in rad-hard MOS devices which are produced by specific proton and electron energies in the space environment could be simulated by cobalt-60 induced effects through careful and proper selection of total does and dose rates. This selection must be based on an experimentally established relationship of Co-60 to electron or proton damage. It is demonstrated that the simulation can be accomplished both during and after irradiation, in the long-term postirradiation period, as well as in the damage state immediately after bombardment.

Stassinopoulos, E. G.↗

NASA NTRS1985

A numerical simulation of auroral ionospheric electrodynamics

A computer simulation of auroral ionospheric electrodynamics in the altitude range 80 to 250 km has been developed. The routine will either simulate typical electron precipitation profiles or accept observed data. Using a model background ionosphere, ion production rates are calculated from which equilibrium electron densities and the Hall and Pedersen conductivities may be determined. With the specification of suitable boundary conditions, the entire three-dimensional current system and electric field may be calculated within the simulation region. The results of the application of the routine to a typical inverted-V precipitation profile are demonstrated. The routine is used to explore the observed anticorrelation between electric field magnitude and peak energy in the precipitating electron spectrum of an auroral arc.

Mallinckrodt, A. J.↗

NASA NTRS1984

Some features of auroral electric fields as seen in 2D numerical simulations

Results of 2D plasma simulations are presented and related to auroral observations. The formation of V-shaped potentials is studied with a 2 1/2 dimensional electrostatic particle-in-cell code for a magnetized plasma. It is shown that amplitudes for perpendicular electric fields are larger than for parallel electric fields, and for Te less than 100 eV, the amplitudes are comparable to the electric fields associated with the electrostatic shocks observed from the S3-3 satellite. The excitation of electrostatic ion-cyclotron EIC waves which occurs in the region below the parallel potential drop is discussed. In auroral plasmas EIC waves are observed above the V-shaped double layers in association with ion beams and field-aligned currents. The results also show that oppositely directed electric fields in the center and at the edges of the simulation region produce oppositely directed currents. Precipitating auroral ions in association with electron inverted-V events are seen by the DMSP-F6 satellite.

Thiemann, H.↗

NASA NTRS1984

On the origin of power-law X-ray spectra of active galactic nuclei

In the present analytical model for a power law X-ray continuum production in active galactic nuclei, the dissipation of turbulent energy flux above the accretion disk forms an optically thin transition layer with an inverted temperature gradient. The emitted thermal radiation has a power law spectrum in the 0.1-100 keV range, with a photon energy spectral index gamma of about 0.4-1.0. Thermal X-ray contribution from the layer is 5-10 percent of the total disk luminosity. The gamma value of 0.75 is suggested as a 'natural' power law index for Seyfert galaxies and QSOs.

Schlosman, I.↗

NASA NTRS1985

Cosmological density fluctuations and large-scale structure From N-point correlation functions to the probability distribution

Knowledge of N-point correlation functions for all N allows one to invert and obtain the probability distribution of mass fluctuations in a fixed volume. The hierarchical sequence of higher order is applied to correlations with dimensionless amplitudes suggested by the BBGKY equations. The resulting distribution is significantly non-Gaussian, even for quite small mean square fluctuations. The qualitative and to some degree quantitative results are to a large degree independent of the exact sequence of amplitudes. An ensemble of such models compared with N-body simulations fails in detail to account for the low-density frequency distribution.

Fry, J. N.↗

NASA NTRS1985

An estimation of continental crust magnetization and susceptibility from Magsat data for the conterminous United States

The Magsat-derived magnetic anomaly field over the United States was inverted to magnetization in a seismically determined variable-thickness lower crust. The results are quite similar to those obtained from a previous inversion of POGO data. The average magnetization is 3.45 + or - 1.0 A/m, which gives a bulk magnetic susceptibility of 8.7 + or - 2.4 x 10 to the -2nd (SI units) for the lower crustal layer consistent with a mafic composition. These values are also consistent with previous estimates of lower crustal magnetization from aeromagnetic data and with laboratory measurements of mafic rock susceptibilities.

Schnetzler, C. C.↗

NASA NTRS1985

Bremsstrahlung spectra from thick-target electron beams with noncollisional energy losses

A generalization of the Brown's (1971) formulation of the relationship between bremsstrahlung spectrum and mean electron spectrum (electrons in the range 10-100 keV) is presented with an objective of demonstrating the information content of bremsstrahlung spectra from a thick target. It is shown that the observed photon spectrum can be inverted to yield an integral functional of the electron spectrum and the effective energy loss rate. Furthermore, if observational or theoretical electron injection spectrum is known, an effective 'phenomenological' energy loss function can be obtained.

Brown, J. C.↗

NASA NTRS1984

The scattering of ultrasonic third sound from substrate surface defects

The interaction of third sound with isolated surface defects is examined. Phase-inverted reflections are observed to occur at surface defects even when the wavelength of the third sound is much greater than the dimensions of the defect. The origin of the scattering mechanism is believed to be due to the change in the helium film thickness in the vicinity of the topological variations introduced by the presence of the surface defects. Data are obtained for ultrasonic frequencies in the 20-200 kHz range.

Generazio, E. R.↗