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At least 595 records · Page 33
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NASA NTRS1976

Validity of disk galaxy simulations

Several n-body calculations have simulated disk galaxies by means of a large number of self-gravitating particles moving on a plane, and have indicated many features in agreement with observation, but also some major disagreements. Some gaps remain in the arguments that results of these simulations represent physically valid consequences of a model in which a disk galaxy is composed entirely of stars. A new formulation of the n-body calculation was designed in polar coordinates, and results obtained with it are used to complete the arguments that the disagreement with observation represents a deficiency in the physical model. The physical process of formation of barlike or two-armed spiral structures from a variety of initial conditions is described; the mechanism is not an m = 2 instability in an initially axisymmetric configuration.

Miller, R. H.↗
NASA NTRS1976

Cloud patterns, waves and convection in the Venus atmosphere

Detailed descriptions and interpretations are provided for phenomena seen in the UV markings on Venus during the Mariner 10 encounter with that planet. The phenomena include the dark horizontal Y, circumequatorial belts, bowlike waves, the subsolar disturbance, midlatitude spiral streaks, the polar ring, and the polar region. Interpreting some of these phenomena in terms of physical processes that are familiar in earth's atmosphere, it is proposed that the large-scale brightness distribution can be most simply described in terms of a pattern with zonal wavenumber of unity which extends between about + and - 50 deg latitude and which progresses around the planet in about 4.2 days. The large-scale UV markings are interpreted as a wave phenomenon, and it is shown how the observed Y pattern could be produced by the superposition of a Rossby-Haurwitz wave dominant at middle latitudes and a Kelvin wave dominant near the equator. It is suggested that the bowlike waves may be true bow waves formed by the interaction of the rapid supercritical zonal flow with internal gravity waves of lower horizontal phase speeds generated by the subsolar disturbance.

Belton, M. J. S.↗
NASA NTRS1976

Initiation of non-tropical thunderstorms by solar activity

Correlative evidence accumulating since 1926 suggests that there must be some physical coupling mechanism between solar activity and thunderstorm occurrence in middle to high latitudes. Such a link may be provided by alteration of atmospheric electric parameters through the combined influence of high-energy solar protons and decreased cosmic ray intensities, both of which are associated with active solar events. The protons produce excess ionization near and above 20km, while the Forbush decreases a lowered conductivity and enhanced fair-weather atmospheric electric field below that altitude. Consequent effects ultimately lead to a charge distribution similar to that found in thunderclouds, and then other cloud physics processes take over to generate the intense electric fields required for lightning discharge.

Herman, J. R.↗
NASA NTRS1976

Evolution of the Solar System

The origin and evolution of the solar system are analyzed. Physical processes are first discussed, followed by experimental studies of plasma-solid reactions and chemical and mineralogical analyses of meteorites and lunar and terrestrial samples.

Alfven, H.↗
NASA NTRS1976

Probabilistic and deterministic aspects of linear estimation in geodesy

Recent advances in observational techniques related to geodetic work (VLBI, laser ranging) make it imperative that more consideration should be given to modeling problems. Uncertainties in the effect of atmospheric refraction, polar motion and precession-nutation parameters, cannot be dispensed with in the context of centimeter level geodesy. Even physical processes that have generally been previously altogether neglected (station motions) must now be taken into consideration. The problem of modeling functions of time or space, or at least their values at observation points (epochs) is explored. When the nature of the function to be modeled is unknown. The need to include a limited number of terms and to a priori decide upon a specific form may result in a representation which fails to sufficiently approximate the unknown function. An alternative approach of increasing application is the modeling of unknown functions as stochastic processes.

Dermanis, A.↗
NASA NTRS1976

Studies of the exhaust products from solid propellant rocket motors

This study was undertaken to determine the feasibility of conducting environmental chamber tests on the physical processes which occur when a solid rocket motor exhaust mixes with the ambient atmosphere. Of particular interest was the interaction between hydrogen chloride, aluminum oxide, and water vapor. The program consisted of three phases: (1) building a small rocket motor and using it to provide the exhaust species in a controlled environment; (2) evaluating instruments used to detect and measure HCl concentrations and if possible determining whether the HCl existed in the gaseous state or as an acid aerosol; (3) monitoring a series of 6.4-percent scale space shuttle motor tests and comparing the results to the environmental chamber studies. Eighteen firings were conducted in an environmental chamber with the initial ambient relative humidity set at values from 29 to 100 percent. Two additional firings were made in a large shed, and four were made on an open concrete apron. Six test firings at MSFC were monitored, and the ground level concentrations are reported. Evidence is presented which shows that the larger Al2O3 (5 to 50 micrometers) particles from the rocket motor can act as condensation nuclei. Under appropriate ambient conditions where there is sufficient water vapor this results in the formation of an acid aerosol. Droplets of this acid were detected both in the environmental chamber and in the scaled shuttle engine tests.

Dawbarn, R.↗
NASA NTRS1977

X-ray emission from high temperature plasmas

The physical processes occurring in plasma focus devices were investigated with particular emphasis on X-ray emission. Topics discussed include: trajectories of high energy electrons; detection of ion trajectories; spatial distribution of neutron emission; space and time resolved emission of hard X-rays from a plasma focus; the staged plasma focus as a variation of the hypocloidal pinch; formation of current sheets in a staged plasma focus; and X-ray and neutron emission from a staged plasma focus. The possibility of operating dense plasma-focus type devices in multiple arrays beyond the scaling law for a single gun is discussed.

Harries, W. L.↗
NASA NTRS1977

Recent activity in the moon; Proceedings of the Special Symposium, Houston, Tex., March 16, 1976

The papers review evidence for recent activity within the moon as manifested by lunar grid system, transient phenomena, moonquakes, and episodic emissions of radiogenic gases. Topics include a survey of lunar transient phenomena, possible causes of such phenomena, evidence that high-frequency seismic events may be shallow moonquakes, lunar seismicity and tectonics, a hypothesis on the nature of sites of lunar gas venting, and a search for sporadic gas emissions from the moon. Other contributions discuss the release of radiogenic argon-40 from the moon, radon-222 emission as an indicator of current activity on the moon, upper limits to gas emission from sites of lunar transient phenomena, physical processes that could produce transient changes on the lunar surface, critical-velocity gas-plasma interaction as a mechanism for lunar transient phenomena, and tidal triggering of moonquakes, transient phenomena, and radiogenic-gas emissions.

Runcorn, S. K.↗
NASA NTRS1977

Statistical equilibrium in cometary C2. I

Swan-band emission from the C2 molecule provides important information for a study of the physical processes occurring in comets. It is, therefore, a disturbing factor that many quantitative Swan-band observations are in clear contradiction of predictions of resonance fluorescence excitation of the Swan bands. A description is presented of an investigation involving an application of resonance fluorescence theory to C2. The investigation takes into account all important electronic transitions which determine the population distribution of the lowest energy states. It is found that the previous discrepancy for the brighter band sequences disappears.

Swamy, K. S. K.↗
NASA NTRS1976

A summary of observations of the earth's bow shock

The earth's bow shock can be regarded as a fast steady-state collisionless magnetohydrodynamic shock exhibiting a wide range of plasma parameter values or as an example of superalfvenic flow of a MHD fluid past a blunt body. This paper summarizes our knowledge of the bow shock. Satellite crossings of the shock have given some empirical data on the position and shape of the bow shock. Theoretical calculations on position and shape show the critical nature of the Alfven number. The main physical process to be explained with regard to the bow shock is the mechanism of thermalization of the upstream solar wind. Some of the main classes of shocks observed are quasi-parallel shocks, low Mach number laminar shocks, and high beta shocks.

Fairfield, D. H.↗
NASA NTRS1977

Mixing of two liquid metals on spar payload due to spin-up and spin-down

Unexpected results from SPAR experiments, directed at obtaining fine dispersions of metal systems that in a 1-g environment tend to segregate very rapidly, were considered. The physical processes occurring in fluid samples, such as the SPAR samples before solidification, were shown to be insufficient to produce a well mixed liquid by the time solidification was initiated. This would result in solidified samples with the type of segregation noted in the SPAR samples. Experimental evidence and analytical arguments are presented.

Schafer, C. F.↗
NASA NTRS1977

Automatic multiple-sample applicator and electrophoresis apparatus

An apparatus for performing electrophoresis and a multiple-sample applicator is described. Electrophoresis is a physical process in which electrically charged molecules and colloidal particles, upon the application of a dc current, migrate along a gel or a membrane that is wetted with an electrolyte. A multiple-sample applicator is provided which coacts with a novel tank cover to permit an operator either to depress a single button, thus causing multiple samples to be deposited on the gel or on the membrane simultaneously, or to depress one or more sample applicators separately by means of a separate button for each applicator.

Grunbaum, B. W.↗
NASA NTRS1976

The pumping mechanism for the neon-nitrogen nuclear excited laser

In order to determine the physical processes for pumping this laser, a detailed study of the afterglow system has been performed. The pumping mechanism has been found to be collisional-radiative electron-ion recombination. Microwave quenching of both the laser and spontaneous afterglow light have shown conclusively that a recombination process directly produces a nitrogen atom in either the upper laser level or, more likely, in a higher lying energy level which rapidly de-excites to the upper laser level.

Cooper, G. W.↗
NASA NTRS1978

Limb-darkening and the structure of the Jovian atmosphere

By observing the transit of various cloud features across the Jovian disk, limb-darkening curves were constructed for three regions in the 4.6 to 5.1 mu cm band. Several models currently employed in describing the radiative or dynamical properties of planetary atmospheres are here examined to understand their implications for limb-darkening. The statistical problem of fitting these models to the observed data is reviewed and methods for applying multiple regression analysis are discussed. Analysis of variance techniques are introduced to test the viability of a given physical process as a cause of the observed limb-darkening.

Newman, W. I.↗
NASA NTRS1978

Gamma-ray lines from neutron stars as probes of fundamental physics

The detection of gamma-ray lines produced at the surface of neutron stars will serve to test both the strong and gravitational interactions under conditions unavailable in terrestrial laboratories. Observation of a single redshifted gamma-ray line, combined with an estimate of the mass of the star will serve as a strong constraint on allowable equations of state of matter at supernuclear densities. Detection of two redshifted lines arising from different physical processes at the neutron star surface can provide a test of the strong principle of equivalence. Expected fluxes of nuclear gamma-ray lines from accreting neutron stars were calculated, including threshold, radiative transfer and redshift effects. The most promising probes of neutron star structure are the deuterium formation line and the positron annihilation line. Detection of sharp redshifted gamma-ray lines from X-ray sources such as Cyg X-1 would argue strongly in favor of a neutron star rather than black hole identification for the object.

Brecher, K.↗
NASA NTRS1978

Design of a transonically profiled wing

The application of well known design concepts with the combined use of thick transonic profiles to aircraft wing design was investigated. Optimization in terms of weight and operational costs was emphasized. It is shown that the usual design criteria and concepts are too restricted and do not sufficiently represent the physical processes over the wing. Suggestions are made for improving this situation, and a design example given. Compared with a wing design according to previously used criteria, the new design is found to be superior in the most important functions. It is concluded that an isobar concept adjusted to the planform in conjunction with an 'organically' designed wing will lead to the weight optimum solutions of wing profiles.

Kiekebusch, B.↗
NASA NTRS1978

The analysis of high spatial resolution UV and X-ray images by computational modeling

Very high resolution stereoscopic images of high temperature loop structures observed at UV and X-ray wavelengths in the solar corona can be used to understand physical processes in the corona. An existing computational model is described and sample results are given to demonstrate that computational modeling of coronal structures can indeed take advantage of very high resolution images. The sample results include the run of temperature and number density along a typical loop and the variation of the differential emission measure with temperature. The integration of the differential emission measure with temperature along a column commensurate with an instrument's spatial resolution is the relevant parameter obtained from UV and X-ray observations. The effects of loop geometry and energy input are examined.

Vesecky, J. F.↗
NASA NTRS1977

Orbit-orbit resonances in the solar system - Varieties and similarities

Descriptions of various orbit-orbit resonance mechanisms in the solar system are brought together in such a manner that the physical processes underlying the traditional mathematical presentations are apparent. A simple qualitative model based on the resonance between Saturn's satellites Titan and Hyperion is presented, the same resonance is analyzed quantitatively, and the small-eccentricity mechanism is examined. The following resonances are investigated in detail: Enceladus-Dione, Mimas-Tethys, Neptune-Pluto, and Rhea-Titan (secular resonance). Coupled librations of several asteroids near mean motions commensurable with Jupiter's are modeled, the Laplace relation involving Io, Europa, and Ganymede is studied, and the 1:1 resonance between the Trojan asteroids and Jupiter is discussed. Some higher-order commensurabilities involving asteroids are considered, including the 3:1 resonance between Alinda and Jupiter, the 13:5 resonance of Toro with Venus, the 8:5 resonance of Toro with earth, and the 11:28 resonance of Ivar with earth.

Greenberg, R.↗