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At least 901 records · Page 50
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NASA NTRS1979

Particle acceleration by propagating interplanetary shocks

The process of charged particle acceleration in interplanetary shocks has been simulated for typical parameters. Since space probe observations of charged particle fluxes are the principle means of inferring the action of an acceleration mechanism, the simulation was designed to follow particles backwards in time from a given observing point, usually 1 AU. This allowed a full diagnosis of which observed particles had interacted with an oncoming shock, where the interacting occurred, and by how much the energy had been changed by the shock interaction. Simple assumptions about the preshock energy spectrum allow the construction of a full temporal profile of the expected intensity, anisotropy, and energy spectrum. The simulations are apparently capable of reproducing the main features of the less than 10 MeV/nuc ion flux enhancements observed at interplanetary shocks using only a laminar interplanetary magnetic field, Archimidean spiral, and a spherical oblique shock with typical speed, strength, and shock normal-magnetic field angle.

Armstrong, T. P.↗
NASA NTRS1979

Magnetospheric reconnection, substorms, and energetic particle acceleration

The steady state reconnection model of the terrestrial magnetosphere predicts a maximum potential drop of about 100 kV across the tail. During substorms particles are accelerated to energies above 1 MeV. At substorm onset, large inductive emfs may be generated by explosive tearing mode reconnection which is driven nonlinearly unstable by the solar wind and convection stresses on the tail plasma sheet. In the inner magnetosphere, energetic particles are also produced by stochastic wave turbulent acceleration and by convection driven inward radial diffusion.

Coroniti, F. V.↗
NASA NTRS1979

Implications of gamma ray observations for particle acceleration Experimental prospects

The relationship of gamma ray observations to the energetic particle acceleration phenomena is discussed. In particular the requirements for production of gamma rays by energetic particles are reviewed. The present state of observations of gamma rays is also reviewed and where there is a clear connection, the implications for particle acceleration theory is pointed out. In conclusion, a brief summary is given for instrument capabilities for the next major USA satellite experiments to be conducted in the 1980s.

Chupp, E. L.↗
NASA NTRS1981

Capillary and acceleration wave breakup of liquid jets in axial-flow airstreams

Empirical correlations of reciprocal mean drop diameter with airstream momentum were derived from capillary and acceleration wave breakup of liquid jets atomized by cross stream injection into axial flow airstreams. A scanning radiometer was used to obtain data over an airstream momentum range of 3.7 to 25.7 g/sq cm sec. Transition from capillary to acceleration wave breakup was obtained at a critical Weber-Reynolds number of 1,000,000.

Ingebo, R. D.↗
NASA NTRS1980

Dependence of vestibular reactions on frequency of action of sign-variable accelerations

It was revealed that during the tests with continuous action of sign variable Coriolis acceleration the development of kinetosis was proportionate to the time of head inclinations in the range of 1 to 4 seconds while illusions of rocking in sagittal plane was more expressed in fast inclinations. The obtained data provided the evidence of sufficient dependence of vestibulovegetative and vestibulosensory reactions on the period of repetition of sign variable Coriolis acceleration.

Lapayev, E. V.↗
NASA NTRS1981

Magnetosphere-Ionosphere coupling through the auroral acceleration region

An important form of coupling between the magnetosphere and the ionosphere occurs through acceleration mechanisms operative in the high altitude ionosphere on magnetic field lines connecting to the auroral zone. Energetic ion mass spectrometer data from within these auroral acceleration regions are presented to illustrate the characteristics of the mechanisms. Observations of ionospheric plasmas in the ring current, the distant plasma sheet, and the magnetotail lobes are shown illustrating the extent of their circulation and the importance of their contribution to the plasma in each regime. Finally the precipitating plasmas in the auroral region and the extent and peculiar effects of the 0(+) component of that precipitation on the ionosphere are illustrated.

Sharp, R. D.↗
NASA NTRS1981

Heating and acceleration of the solar wind

The dynamics of the expanding corona are discussed emphasizing the physical processes which accelerate the plasma as it flows away from the Sun. The solar wind plays a dominant role in the energy balance of the part of the corona in which it originates. The wind acceleration processes, in large part, with the mechanisms that transport energy to the corona in the first place.

Kopp, R. A.↗
NASA NTRS1980

Neutral cometary atmospheres. III - Acceleration of cometary CN by solar radiation pressure

The acceleration of cometary CN radicals due to solar radiation pressure has been determined by fitting Monte Carlo models to nine observed sunward-tailward pairs of brightness profiles of the (0-0) band of CN at 3883 A. The profiles were determined from spectrograms of comets Bennett 1970 II and West 1976 VI. The values of the observed acceleration agree with those computed from resonance fluorescence calculations to within the expected uncertainties. This provides an independent confirmation of the identification of the observed scale lengths with the photochemical lifetimes and velocities associated with the production of observed cometary CN by the photodissociation of HCN. The ratio of the intensity of the (0-1) band of CN at 4216 A to the (0-0) band at 3883 A has been determined from spectrograms of comet West, and is compared with theoretical values.

Combi, M. R.↗
NASA NTRS1980

Stellar winds, fast rotators, and magnetic acceleration

The assumption that observed mass outflow from a star is due to a magnetically driven wind implies an upper bound on the surface magnetic field strength from regions where the wind originates. Evidence is reported that corroborates Rosendhal's observation of an abrupt change in the velocity-gradient-luminosity relationship for B8 and later supergiants. The smallest upper bounds correspond to later spectral types, for which radiation would be a relatively inefficient mechanism for driving wind; these winds may in fact be magnetically driven. Be stars are prime candidates for magnetically accelerated winds due to large rotation rates and small mass loss rates. Observed flows can be driven by 0.1-10 gauss surface fields. Intense field in fast rotators can lead to dramatic mass loss rates and large terminal velocities; sigma Ori E may be such an object. Finally, the effect of magnetic acceleration on the dispersal of solar nebula is considered. The increased velocities allow the wind to disperse a mass of 90 times the initial outflowing mass in the wind.

Nerney, S.↗
NASA NTRS1981

Anti-solar acceleration of ionospheric plasma across the Venus terminator

It is demonstrated that the horizontal ionospheric particle pressure gradient across the Venus terminator is the principal body force accelerating the plasm to the observed anti-solar velocity. The large scale horizontal electromagnetic body force is typically an order of magnitude smaller than the particle pressure gradient. The viscous body forces above 300 km - drag or acceleration - are also an order of magnitude smaller than the pressure gradient body force. In the immediate vicinity of the ionopause where the ionospheric plasma density decreases below 1000 ions/cu cm and the magnetic field strength increases, the electromagnetic body force may become significant. The electromagnetic body force may also be significant in the nightside ionosphere. The bulk of the ionospheric flow momentum is not derived from the ionosheath momentum.

Knudsen, W. C.↗
NASA NTRS1981

Very low frequency waves stimulated by an electron accelerator in the auroral ionosphere

The sounding rocket, Polar 5, carrying a 10 keV electron accelerator in a mother-daughter configuration and other diagnostic instruments, was launched into a slightly disturbed ionosphere with weak auroral activity on February 1, 1976 from Northern Norway to study VLF wave phenomena. The rocket trajectory crossed two auroral regions: one, between 86 and 111 s flight time, and a secondary region between 230 and 330 s. The daughter, carrying the accelerator, was separated axially from the mother in a forward direction at an altitude of 90 km. The VLF experiment, carried by the mother payload, recorded both electromagnetic and electrostatic waves. The receiving antenna was an electric dipole, 0.3 m tip-to-tip, oriented 90 degrees to the rocket spin axis. The onboard particle detector recorded increased electron fluxes in the two auroral regions. A double peaked structure was observed in the fluxes of 4-5 and 12-27 keV electrons within the northern auroral form. The number density of thermal plasma varied during the flight, with maximum density within the main auroral region. To the north of this aurora a slow, steady decrease in the density was observed, with no enhancement in the region of the second aurora.

Holtet, J. A.↗
NASA NTRS1981

A transient MHD model applicable for the source of solar cosmic ray acceleration

A two-dimensional, time-dependent magnetohydrodynamic model is used to describe the possible mechanisms for the source of solar cosmic ray acceleration following a solar flare. The hypothesis is based on the propagation of fast mode MHD shocks following a sudden release of energy. In this presentation, the effects of initial magnetic topology and strength on the formation of MHD shocks have been studied. The plasma beta (thermal pressure/magnetic pressure) is considered as a measure of the initial, relative strength of the field. During dynamic mass motion, the Alfven Mach number is the more appropriate measure of the magnetic field's ability to control the outward motion. It is suggested that this model (computed self-consistently) provides the shock waves and the disturbed mass motion behind it as likely sources for solar cosmic ray acceleration.

Dryer, M.↗
NASA NTRS1981

Statistical acceleration of electrons by lower-hybrid turbulence

The statistical acceleration of electrons along an ambient magnetic field by large-amplitude lower-hybrid turbulence is discussed. Perturbations driven by a crossfield current and propagating nearly perpendicular to the applied magnetic field are considered. It is assumed that the instability saturates rapidly and that the fluctuating electric field is predominantly electrostatic. If the turbulence is characterized by a spectrum of small parallel wavenumbers, such that the parallel phase velocity of the waves is greater than the electron thermal velocity, then the turbulence can only accelerate electrons moving with large velocities along the magnetic field. The quasi-linear diffusion equation is solved using a Green's function technique, assuming a power law spectral energy density. The time evolution of an initial Maxwellian distribution is given and the time rate of change of the mean electron energy is calculated for various cases.

Wu, C. S.↗
NASA NTRS1981

A study on task difficulty and acceleration stress

The results of two experiments which relate to task difficulty and the effects of environmental stress on tracking performance are discussed and compared to subjective evaluations. The first experiment involved five different sum of sine tracking tasks which humans tracked both in a static condition and under a 5 Gz acceleration stress condition. The second experiment involved similar environmental stress conditions but in this case the tasks were constructed from deterministic functions with specially designed velocity and acceleration profiles. Phase Plane performance analysis was conducted to study potential measures of workload or tracking difficulty.

Repperger, D. W.↗
NASA NTRS1981

On the acceleration of ions by interplanetary shock waves. 1: Single encounter considerations

The acceleration of energetic ions in interplanetary magnetosonic fast-mode shock waves was studied via analytical modeling and numerical simulations. An analytical model that combines both the shock drift and compressional acceleration mechanisms is presented. The analytical predictions of the model are shown to be in good agreement with numerical simulation results.

Pesses, M. E.↗
NASA NTRS1981

On the acceleration of ions by interplanetary shock waves. 3: High time resolution observations of CIR proton events

Observations within + or - 3 hours of corotating interaction region (CIR) shock waves of proton intensities, pitch angle distribution and crude differential energy spectra of the range of 0.6 E sub p 3.4 MeV are presented. The principle result is the evidence for the persistent flow of particles away from the shock. The observations are found to be in good agreement with the hypothesis of local interplanetary shock acceleration by the shock drift and compression mechanisms. The same set of observations strongly suggest that transit time damping does not play an important role in the acceleration of protons to 1 MeV in the immediate vicinity of CIR shocks.

Pesses, M. E.↗
NASA NTRS1982

Acceleration of convergence of vector sequences

A general approach to the construction of accelerated convergence methods for vector sequences is proposed. A simplified version of minimal polynomial extrapolation is emphasized. The convergence of this method is analyzed and it is shown that it is especially suitable for accelerating the convergence of vector sequences that are obtained when one solves linear systems of equations iteratively.

Sidi, A.↗
NASA NTRS1982

Experimental evaluation of the Battelle accelerated test design for the solar array at Mead, Nebraska

A previously developed test design for accelerated aging of photovoltaic modules was experimentally evaluated. The studies included a review of relevant field experience, environmental chamber cycling of full size modules, and electrical and physical evaluation of the effects of accelerated aging during and after the tests. The test results indicated that thermally induced fatigue of the interconnects was the primary mode of module failure as measured by normalized power output. No chemical change in the silicone encapsulant was detectable after 360 test cycles.

Frickland, P. O.↗