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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 1,009 records · Page 56

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NASA NTRS1979

Transient brightenings of interconnecting loops - Morphology of the sudden brightenings

Sudden brightenings of coronal loops that interconnect active regions are studied. Such brightenings often occur within one or two days after the birth of a new interconnecting loop, as well as in some old interconnections. The brightenings of young loops are obviously associated with the emergence of new magnetic flux near their footpoints, whereas some enhancements of old loops may be triggered by slowly moving disturbances propagating from other centers of activity. A few loop brightenings are associated with flares, but the loop does not brighten in consequence of the energy supply from the flare. Both the flare and the loop brightening are independent consequences of one common agent, presumably newly emerging flux. Temperatures in brightened loops are between 3 and 4 x 10 to the 6th K and densities are less than 2 x 10 to the 9th/cu cm, probably less than 5 x 10 to the 8th/cu cm in some old loops. The top part of a loop is the site of the most intense brightening in the initial phase of a loop enhancement. The most frequent lifetime of these brightenings is 6 to 7 hr.

Svestka, Z.↗

NASA NTRS1980

Assessment of zero gravity effects on space worker health and safety

One objective of the study is to assess the effects of all currently known deviations from normal of medical, physiological, and biochemical parameters which appear to be due to zero gravity (zero-g) environment and to acceleration and deceleration to be experienced, as outlined in the references Solar Power Satellites (SPS) design, by space worker. Study results include identification of possible health or safety effects on space workers either immediate or delayed due to the zero gravity environment and acceleration and deceleration; estimation of the probability that an individual will be adversely affected; description of the possible consequence to work efficiency in persons adversely affected; and description of the possible/probable consequences to immediate and future health of individuals exposed to this environment. A research plan, which addresses the uncertainties in current knowledge regarding the health and safety hazards to exposed SPS space workers, is presented. Although most adverse affects experienced during space flight soon disappeared upon return to the Earth's environment, there remains a definite concern for the long-term effects to SPS space workers who might spend as much as half their time in space during a possible five year career period. The proposed 90 day up/90 day down cycle, coupled with the fact that most of the effects of weightlessness may persist throughout the flight along with the realization that recovery may occupy much of the terrestrial stay, may keep the SPS workers in a deviant physical condition or state of flux for 60 to 100% of their five year career.

Source record↗

NASA NTRS1981

Search for colliding stellar winds in Plaskett's star (HD 47129)

High dispersion spectra of Plaskett's star (HD 47129) were obtained with the short wavelength spectrograph on IUE at five phases of the binary cycle. The unsaturated wind profiles, particularly those of Si IV lambda 1400, show complex phase dependent structure. Two interpretations for the structure are suggested, neither of which is entirely satisfactory: (1) the structure is a consequence of directed streams, and (2) the structure is a consequence of colliding winds from the primary and secondary.

Heap, S. R.↗

NASA NTRS1980

Common time in a four-dimensional symmetry framework

Following the ideas of Poincare, Reichenbach, and Grunbaum concerning the convention of setting up clock systems, clock systems and light propagation are analyzed within the framework of four-dimensional symmetry. It is possible to construct a new four-dimensional symmetry framework incorporating common time: observers in different inertial frames of reference use one and the same clock system, which is located in any one of the frames. Consequently, simultaneity has a meaning independent of position and independent of frame of reference. A further consequence is that the two-way speeds of light alone are isotropic in any frame. By the choice of clock system there will be one frame in which the one-way speed of light is isotropic. This frame can be arbitrarily chosen. The difference between one-way speeds and two-way speeds of light signals is considered in detail.

Hsu, J. P.↗

NASA NTRS1982

Numerical simulation of the interaction of the plasma sheet with the lobes of the Earth's magnetotail

Codes involving one and two spatial dimensions and three velocity dimensions were used to model the Earth's magnetotail. It was shown that the magnetotail can become inflated as a consequence of low energy plasma convection toward the neutral plane. The computer study exhibits a conversion of both magnetic field energy and of energy supplied by the convection electric field into particle energy. The numerical simulations suggest that much of the magnetotail substorm morphology may be a simple consequence of an increase, followed by a decrease, in the convection electric field, without the requirement of any magnetospheric size scale plasma instability or other disruptive processes. It is also concluded that the presence of the convection electric field and a continuing replenishment of low energy particles in the magnetotail are both necessary for maintenance of the magnetotail.

Swift, D. W.↗

NASA NTRS1980

High-power microwave optics for flexible power transmission systems

A large concave microwave mirror near the transmitter can magnify the apparent size of the Earth as seen from a phased array, and vice versa, permitting a small phased array to be coupled to a small rectenna while preserving the transmission efficiency (the reflection loss is slight) and peak power densities characteristic of the reference system. This augmentation of the phased array aperture with a large mirror gives the system greater resolution (in the optical sense), and opens new degrees of freedom in SPS design. The consequences of such an approach for a prototype satellite were explored. Its consequences for a mature SPS are discussed.

Drexler, K. E.↗

NASA NTRS1980

Effects of the space environment on the health and safety of space workers

Large numbers of individuals are required to work in space to assemble and operate a Solar Power Satellite. The physiological and behavioral consequences for large groups of men and women who perform complex tasks in the vehicular or extravehicular environments over long periods of orbital stay time were considered. The most disturbing consequences of exposure to the null gravity environment found relate to: (1) a generalized cardiovascular deconditioning along with loss of a significant amount of body fluid volume; (2) loss of bone minerals and muscle mass; and (3) degraded performance of neutral mechanisms which govern equilibrium and spatial orientation.

Hull, W. E.↗

NASA NTRS1982

Fragmentation of interstellar clouds and star formation

The principal issues are addressed: the fragmentation of molecular clouds into units of stellar mass and the impact of star formation on molecular clouds. The observational evidence for fragmentation is summarized, and the gravitational instability described of a uniform spherical cloud collapsing from rest. The implications are considered of a finite pressure for the minimum fragment mass that is attainable in opacity-limited fragmentation. The role of magnetic fields is discussed in resolving the angular momentum problem and in making the collapse anisotropic, with notable consequences for fragmentation theory. Interactions between fragments are described, with emphasis on the effect of protostellar winds on the ambient cloud matter and on inhibiting further star formation. Such interactions are likely to have profound consequences for regulating the rate of star formation and on the energetics and dynamics of molecular clouds.

Silk, J.↗

NASA NTRS1982

Non-radial flow near the cometary surface

It is shown that, as a consequence of the non-uniform temperature distribution of the cometary nucleus, large lateral pressure gradients are set up, which in turn drive strong lateral flows. However, at small heliocentric distances the onset of turbulence within a thin boundary layer destroys these steady lateral flows and the eventual outflow of gas from within the outer boundary of this layer is expected to be more or less radial. On the other hand, at large heliocentric distances, turbulence is unlikely to set in, and the lateral flows that are set up, may persist. Consequently, it is expected that the gas flow out of the cometary nucleus at these large distances to be highly non-radial.

Marconi, M. L.↗

NASA NTRS1982

Chemical weathering and the Viking biology experiments on Mars

Since the publication of studies describing models that do not require external energy sources, new LR (labeled release) test standards module studies have been reported by Levin and Straat (1981). These studies impose important constraints on the various models, and they offer strong support for the 'frost-weathering' model. These findings are discussed here, and it is proposed that the activity of all three biology experiments can now adequately be explained as a consequence of a single active agent produced by contemporary chemical weathering. Some of the possible consequences and implications of contemporary weathering for the current state and evolution of the regolith and atmosphere are briefly discussed.

Huguenin, R. L.↗

NASA NTRS1983

Ion-beam-driven electrostatic ion cyclotron instabilities

Results are presented of a particle simulation study of the electrostatic ion-cyclotron (EIC) instability driven by a parallel ion beam. The results of this simulation study demonstrate the nonlinear consequences of nonresonant EIC waves destabilized by an ion beam parallel to the magnetic field for the case of a large beam velocity. As a consequence of the instability, it is shown that the beam ions are heated strongly in the perpendicular direction and suffer a strong anomalous friction via EIC waves which leads to the beam slowing down. Simulation results indicate that the anomalous slowing down of beam ions by EIC waves is much larger than that from the classical electron-drag, and the perpendicular collision frequency measured from perpendicular beam heating is as large as that from Bohm diffusion. It is concluded that the ion beam driven EIC wave is a viable mechanism for the transfer of ion parallel beam energy to the ion perpendicular energy.

Okuda, H.↗

NASA NTRS1983

The hydrodynamics of magnetic nonequilibrium

Because the dynamical nonequilibrium of closely packed twisted flux tubes is essentially the problem of two-dimensional MHD turbulence, the extensive literature on two-dimensional turbulence represents the hydrodynamics of magnetic nonequilibrium. Many features of the turbulence can conversely be understood as a consequence of the dynamical nonequilibrium. Attention is presently given to the dynamics of the strong fluid jets, issuing from reconnection points, that are exhibited by numerical simulations of two-dimensional turbulence. Simple examples are given which show that the uniformity of jet width observed is a consequence of the form of the pressure of the magnetic fields between which the jets are confined. The general hydrodynamics of a layer of fluid confined by steady pressures is reducible to a quadrature, so that a variety of effects may be considered, including gravitation. The dissipation of the solar corona is discussed.

Parker, E. N.↗

NASA NTRS1983

Design procedures for compressor blades

The conventional methods for the design of the blades in the case of axial turbomachines are considered, taking into account difficulties concerning the determination of optimal blade profiles. These difficulties have been partly overcome as a consequence of the introduction of new numerical methods during the last few years. It is pointed out that, in the case of the subsonic range, a new procedure is now available for the determination of the form of blade profile on the basis of a given velocity distribution on the profile surface. The search for a profile form with favorable characteristics is consequently transformed into a search for a favorable velocity or pressure distribution on the blade. The distribution of velocities depends to a large degree on the characteristics of the profile boundary layers. The considered concept is not new. However, its practical implementation has only recently become possible. The employment of the new design procedure is illustrated with the aid of an example involving a concrete design problem.

Starken, H.↗

NASA NTRS1984

CAD/CAM and scientific data management at Dassault

The history of CAD/CAM and scientific data management at Dassault are presented. Emphasis is put on the targets of the now commercially available software CATIA. The links with scientific computations such as aerodynamics and structural analysis are presented. Comments are made on the principles followed within the company. The consequences of the approximative nature of scientific data are examined. Consequence of the new history function is mainly its protection against copy or alteration. Future plans at Dassault for scientific data appear to be in opposite directions compared to some general tendencies.

Bohn, P.↗

NASA NTRS1983

Meteorological and dynamical requirements for MST radar networks: Waves

Studies of wave motions using the MST radar have concentrated on single station time series analyses of gravity waves and tides. Since these radars collect high time resolution data they have the potential to become a significant tool for mesoscale research. In addition, radars are operated almost continuously unattended and, consequently, data sets are available for analyzing longer period wave motions such as tides and planetary scale waves. Although there is much to learn from single station data, the possibilities of new knowledge from a network of radars is exciting. The scales of wave motions in the atmosphere cover a broad range. Consequently the choice of a radar network depends to a large extent on the types of wave motions that are studied. There are many outstanding research problems that would benefit from observations from a MST radar network. In particular, there is a strong need for measurements of gravity wave parameters and equatorial wave motions. Some of the current problems in wave dynamics are discussed.

Avery, S. K.↗

NASA NTRS1984

Models of Rapid Solidification

Laser annealing studies provide much information on various consequences of rapid solidification, including the trapping of impurities in the crystal, the generation of vacancies and twins, and on the fundamental limits to the speed of the crystal-melt interface. Some results obtained by molecular dynamics methods of the solidification of a Lennard-Jones liquid are reviewed. An indication of the relationship of interface speed to undercooling for certain materials can be derived from this model. Ising model simulations of impurity trapping in silicon are compared with some of the laser annealing results. The consequences of interface segregation and atomic strain are discussed.

Gilmer, G. H.↗

NASA NTRS1983

Luminosity correlations in quasars

Simulations are conducted with and without flux thresholds in an investigation of quasar luminosity correlations by means of a Monte Carlo analysis, for various model distributions of quasars in X-rays and optical luminosity. For the case where the X-ray photons are primary, an anticorrelation between X-ray-to-optical luminosity ratio and optical luminosity arises as a natural consequence which resembles observations. The low optical luminosities of X-ray selected quasars can be understood as a consequence of the same effect, and similar conclusions may hold if the X-ray and optical luminosities are determined independently by a third parameter, although they do not hold if the optical photons are primary. The importance of such considerations is demonstrated through a reanalysis of the published X-ray-to-optical flux ratios for the 3CR sample.

Chanan, G. A.↗

NASA NTRS1984

The effects of gusts on the fluctuating airloads of airfoils in transonic flow

Unsteady interactions of distributed and sharp-edged gusts with a stationary airfoil have been analyzed in two-dimensional transonic flow.A simple method of introducing such disturbances has been numerically implemented within the framework of unsteady, transonic small-disturbance theory. Representative solutions for various airfoils subjected to chordwise and transverse gusts show that the strength and unsteady motion of the shock wave on the airfoil significantly affect the flowfield development and, consequently, the dynamic airloads. Also a study was made of the reductions in the unsteady airloads that can be achieved by the proper active control motion of a trailing-edge flap, and a simple gust-alleviation strategy was developed. However, the chordwise pressure distributions associated with gusts are very different from those produced by trailing-edge flap oscillations. Consequently, the fluctuating lift and the unsteady pitching moments cannot both be eliminated simultaneously.

Mccroskey, W. J.↗