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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Concerning the meteoritic origin of the Puchezh-Katunki crater

Criticism of the works of Vardaniants (1961) and Goretskii (1962) regarding the origin of the Puchezh-Katunki crater, and development of a new hypothesis regarding this disturbance. Although Vardaniants defines the Puchezh-Katunki disturbance as a structure of explosive nature and assumes that the explosion originated as a consequence of accumulation of gases in the crystalline basement of the Russian platform, he lacks evidence to qualify this explosion as coming from a depth. Goretskii's tectonic-injection hypothesis attributes the formation of the disturbance to penetration of an intrusion of basic and ultrabasic rocks into the Paleozoic rocks of the platform. It is shown that, even if the intrusion were spread somewhere at depth, it could not account for the extent of the deformation in the disturbance. It is suggested that this disturbance is of meteoritic origin, since the structure and morphology of the region are similar to the sloping conical surface produced by an explosive meteor crater. The energy, mass, and size of the asteroid which could cause such a disturbance are estimated, and it is shown that the probability of the occurrence of an impact of this size is finite over geological time.

Firsov, L.↗
NASA NTRS1975

Is the four-day 'rotation' of Venus illusory

An overlooked systematic error exists in the apparent radial velocities of solar lines reflected from regions of Venus near the terminator, owing to a combination of the finite angular size of the sun and its large equatorial velocity of rotation. This error produces an apparent, but fictitious, retrograde component of planetary rotation, typically on the order of 40 m/sec. Spectroscopic, photometric, and radiometric evidence against a 4-day atmospheric rotation is reviewed. The bulk of the somewhat contradictory evidence seems to favor slow motions, on the order of 5 m/sec, in the atmosphere of Venus; the 4-day 'rotation' may be due to a traveling wavelike disturbance, not bulk motions, driven by the UV albedo differences.

Young, A. T.↗
NASA NTRS1980

Nonlinear structural analysis

Development of computer programs for nonlinear structural analyses has progressed from special application programs to large, generalized programs. AGGIE I program is moderately-sized finite-element program that was developed specifically for nonlinear structural analysis. It is based on two- and three-dimensional isoparametric solid elements. AGGIE I accounts for nonlinearities due to large displacements, large strains and non-linear material behavior.

Haisler, W. E.↗
NASA NTRS1979

The impact of Sun-weather research on forecasting

The possible impact of Sun-weather research on forecasting is examined. The type of knowledge of the effect is evaluated to determine if it is in a form that can be used for forecasting purposes. It is concluded that the present understanding of the effect does not lend itself readily to applications for forecast purposes. The limits of present predictive skill are examined and it is found that skill is most lacking for prediction of the smallest scales of atmospheric motion. However, it is not expected that Sun-weather research will have any significant impact on forecasting the smaller scales since predictability at these scales is limited by the finite grid size resolution and the time scales of turbulent diffusion. The predictability limits for the largest scales are on the order of several weeks although presently only a one week forecast is achievable.

Larsen, M. F.↗
NASA NTRS1981

Interstellar extinction by small-coated or uncoated graphite grains

Calculations have been made on the theoretical extinction of spherical graphite particles from 130 to 3500 nm. It is found that graphite particles of radius near 20 nm can have small (0.5 nm) coatings and still be responsible for the 220 nm peak in the interstellar extinction curve. New calculations also show that the effect of finite particle size is relatively unimportant in determining the extinction of graphite spheres at 220 nm.

Hecht, J.↗
NASA NTRS1981

Monte-Carlo model of pitch-angle scattering in solar cosmic ray events

Monte Carlo simulations of the propagation of solar cosmic-rays in interplanetary space are reported, including the effects of pitch-angle scattering and adiabatic focusing. Time intensity profiles agree well with the corresponding spatial diffusion approximation for models close to those used by Gombosi and Owens (1980). Monte Carlo simulations of the same model problem yield results that disagree with those of Gombosi and Owens, and the most likely possible source of error in the Monte Carlo simulation is considered to be in the region near the 90 deg pitch angle where the finite step size introduces certain inconsistencies.

Palmer, I. D.↗
NASA NTRS1983

Scattering from a V-shaped groove in the resonance domain

Radiation scattered from a V-shaped groove in the resonance domain is measured and compared with predictions from a rigorous theory. The calculated scattering is found to accurately predict the number of peaks and the general shape of the observed scattering. Small variations in groove shape are found to alter peak heights noticeably and peak positions slightly. The finite beam size causes unavoidable discrepancies between calculated and measured scattering. The theory of Maystre provides a very good tool for determining the scattering capabilities of different shapes without having to measure them.

White, G. S.↗
NASA NTRS1984

Aeroacoustic interaction of a distributed vortex with a lifting Joukowski airfoil

A first principles computational aeroacoustics calculation of the flow and noise fields produced by the interaction of a distributed vortex with a lifting Joukowski airfoil is accomplished at the Reynolds number of 200. The case considered is that where the circulations of the vortex and the airfoil are of opposite sign, corresponding to blade vortex interaction on the retreating side of a single helicopter rotor. The results show that the flow is unsteady, even in the absence of the incoming vortex, resulting in trailing edge noise generation. After the vortex is input, it initially experiences a quite rapid apparent diffusion rate produced by stretching in the airfoil velocity gradients. Consideration of the effects of finite vortex size and viscosity causes the noise radiation during the encounter to be much less impulsive than predicted by previous analyses.

Hardin, J. C.↗
NASA NTRS1985

A leaky magnetohydrodynamic waveguide model for the acceleration of high-speed solar wind streams in coronal holes

It is now reasonably well established that there is a correlation between high-speed solar wind streams and coronal holes. It has been concluded that a significant addition of momentum and/or energy in the region of supersonic flow is needed to explain the observed particle flux and flow speed observed in the high-speed streams. The most likely source of this additional momentum appears to be magnetohydrodynamic (MHD) waves propagating up from the solar surface. The present investigation is concerned with the propagation of MHD waves in a structure of finite transverse size, taking into account the consequences for the acceleration of high-speed solar wind streams. A waveguide solution for a model coronal hole is described, giving attention to a geometric or ray analysis of the slab waveguide, a wave mode analysis, an analytic solution of the dispersion relation for high-frequency waves, and the calculation of the time-averaged wave force.

Davila, J. M.↗
NASA NTRS1984

Charging and hybridization in the finite cluster model

Cluster wavefunctions which have appropriate hybridization and polarization lead to reasonable properties for the interaction of an adsorbate with a solid surface. However, for Al clusters, it was found that the atomic change distribution is not uniform. The finite cluster size leads to changes not representative for an extended system. This effect appears to be dependent on the particular materials being studied; it does not occur in all cases.

Bauschlicher, C. W., Jr.↗
NASA NTRS1986

Experimental evaluation of the ring focus test for X-ray telescopes using AXAF's technology mirror assembly, MSFC CDDF Project No. H20

A test method particularly suited for X-ray telescopes was evaluated experimentally. The method makes use of a focused ring formed by an annular aperture when using a point source at a finite distance. This would supplement measurements of the best focus image which is blurred when the test source is at a finite distance. The telescope used was the Technology Mirror Assembly of the Advanced X-ray Astrophysis Facility (AXAF) program. Observed ring image defects could be related to the azimuthal location of their sources in the telescope even though in this case the predicted sharp ring was obscured by scattering, finite source size, and residual figure errors.

Zissa, D. E.↗
NASA NTRS1987

Observations of the 22 April 1982 stellar occultation by Uranus and the rings

The 1.5 m telescope of Teide Observatory at Teneriffe was used to observe an occultation of the stellar object KME 14 by the Uranus ring system. The telescope was equipped with a two-channel IR flux collector, with one passband centered at 4490 A and the other near 8800 A. Data processing procedures that were used are detailed. The ring profiles were analyzed with a square-well model, which accounted for diffraction and finite source size while treating each ring as sharp-edged and uniformly translucent. An emersion lightcurve was obtained and inverted to yield a temperature profile of the upper atmosphere of Uranus, which displayed a temperature maximum (at 8 microbar) near the equator.

Millis, Robert L.↗
NASA NTRS1988

Error-Tolerant Quasi-Paraboloidal Solar Concentrator

Scalloping reflector surface reduces sensitivity to manufacturing and aiming errors. Contrary to intuition, most effective shape of concentrating reflector for solar heat engine is not perfect paraboloid. According to design studies for Space Station solar concentrator, scalloped, nonimaging approximation to perfect paraboloid offers better overall performance in view of finite apparent size of Sun, imperfections of real equipment, and cost of accommodating these complexities. Scalloped-reflector concept also applied to improve performance while reducing cost of manufacturing and operation of terrestrial solar concentrator.

Wagner, Howard A.↗
NASA NTRS1988

Interleaver design for trellis-coded differential 8-PSK modulation with non-coherent detection

The effect of finite interleaver size on bit error rate (BER) performance of coded 8-DPSK is determined by means of computer simulations. The losses evaluated in this way include the SNR degradation due to the timing and frequency errors of the symbol synchronizer and the automatic frequency control (AFC) of the receiver. BER measurements are presented using a conventional 2/3 rate convolutional 8-state trellis-code for typical Rayleigh and Rician fading channels. It is shown that for a Rician channel with a Rician parameter of 7 dB, a Doppler spread of 100 Hz and a data rate of 2400 bps, an interleaver with size 16 x 16 symbols performs nearly as well as a very large interleaver. It is also shown that for very fast Rayleigh channels, the BER-curves flatten out at large SNR.

Edbauer, Franz↗
NASA NTRS1988

Measurement of micro-roughness and effects of detector bandwidth and finite width

Surface micro-roughness of grazing incidence optics has long been recognized as a critical parameter in the control of the scattered X-ray intensity and its effects on the point spread function half-energy width. Accurate knowledge of the amplitude of surface micro-roughness is vital to assess optic predicted performance during the final stages of fabrication. This requires not only a knowledge of the spatial bandwidth over which surface features must be measured, but also knowledge of the bandwidth of the measurement instrument. We show that the standard assumption that instruments respond up to their Nyquist limit is an oversimplification which neglects the finite detector size and its bandwidth limiting effects when sampling a real (i.e., two-dimensional) surface.

Reid, P. B.↗
NASA NTRS1988

Interstellar scattering of the radio source 2013+370

Results are reported from a six-station 1663-MHz VLBI observation of the radio source 2013+370. The image of this source is dominated by interstellar scattering and is observed to be elliptical, with a major axis (FWHM) of 17 marcsec and an axial ratio of of 0.70. A fit of the observations to a model visibility function yields a value for alpha, the spectral index of the power-law density irregularity spectrum, of alpha=3.79 + or - 0.05. Corrections for the finite angular size of the source would probably produce a downward revision of alpha. The present observations are consistent with the interstellar density spectrum being close to Kolmogoroff for those scales which determine the angular broadening.

Spangler, Steven R.↗
NASA NTRS1989

Angular cross-relations of Abell clusters in different distance classes

The angular autocorrelation and cross-correlation functions of the D = 1 ... 4, D = 5, and D = 6 distance class Abell clusters are estimated. There is a strong anticorrelation between the most distant D = 6 and the closest D = 1 ... 4 subsamples. It is suggested that an artifact of the cluster identification process presumably due to the finite angular size of the cluster. This anticorrelation seems to contradict some recent estimations of projection contaminations in the Abell catalog. The angular proximity of a foreground cluster may have caused a background cluster not to be counted as it was thought to be a subcluster or it was erroneously assigned to a nearer distance class.

Szalay, A. S.↗
NASA NTRS1989

Parity retransmission hybrid ARQ using rate 1/2 convolutional codes on a nonstationary channel

A parity retransmission hybrid automatic repeat request (ARQ) scheme is proposed which uses rate 1/2 convolutional codes and Viterbi decoding. A protocol is described which is capable of achieving higher throughputs than previously proposed parity retransmission schemes. The performance analysis is based on a two-state Markov model of a nonstationary channel. This model constitutes a first approximation to a nonstationary channel. The two-state channel model is used to analyze the throughput and undetected error probability of the protocol presented when the receiver has both an infinite and a finite buffer size. It is shown that the throughput improves as the channel becomes more bursty.

Lugand, Laurent R.↗