Thermal and thermosolutal convective effects in bridgman solidification: Effect of orientation relative to gravity

A concentrated binary system (Ge-Si) and a dilute one (Ge-Ga) have been solidified at 1 g, in a new vertical Bridgman furnace where radial thermal gradients have been minimized. Very different solutal boundary layer extents (δ_Ge-Si = 3 cm, δ_Ge-Ga = 2.5 mm) obtained for both systems solidified in the same thermal conditions are explained by simple analytical hydrodynamic models. It is demonstrated that :1. The convective transport of Ga in the Ge-Ga system is due to the unavoidable residual horizontal thermal gradients associated with discontinuity of thermal properties at the solid-liquid interface.2. The larger boundary layer extent observed for Ge-Si and the corresponding pure diffusive transport is the result of the stabilizing effect of the longitudinal solutal gradient in this system.Thus, in the case of dilute systems, convective effects can only be cancelled through a reduction of the gravity level. On the opposite, pure diffusive solute transport can be achieved in the vertical configuration a 1 g in the case of concentrated systems where a stabilizing solutal effect is operating.     

Analysis of Detection Probability for the Acoustooptic Receiver

A numerical method is described for analyzing the performance of an acoustooptic receiver. The method provides output waveforms, probability density functions for samples of the output, and detection probabilities for output samples. The approach is general in that input pulse envelope shapes, pulse offset frequencies, and output rilter magnitude responses are arbitrary. The basic analysis is also independent of the shape of the optical beam and of the photodiode windows.     

A Selected Bibliography on Adaptive Antenna Arrays

An adaptive antenna array is defined as an antenna array whose output is the weighted sum of the signals received at the antennas, with signal-dependent automatic adjustment of the weights to optimize some criterion. This open-literature bibliography of papers on the subject is intended to provide a brief overview of the field, and the authors involved, up to the end of 1985. Papers are listed both by subject area and by sole/primary/secondary author.     

Humane Intelligence: A Human Factors Perspective for Developing Intelligent Cockpits

A human factors perspective for creating intelligent cockpits is described and explained. A conceptualized interface among the pilots, mental models, and human information technologies is proposed wherein knowledge concerning human cognition is meshed with the capabilities and limitations of artificial intelligence (AI). Necessarily, a different way of looking at the pilot's role in the intelligent cockpit is developed.     

Radio aurora magnetic and streaming aspect sensitivities on 6 simultaneous links at 50 MHz

During August 1981, a 50 MHz c.w. radar system was operated in central Canada to measure auroral scatter amplitudes and Doppler spectra from a scattering region centered near 66° magnetic invariant latitude (L ≈ 6.0). Narrow beams from 3 transmitters, differing in frequency by 1 KHz, were directed to cover a common volume of the ionosphere over a ground location at 56.3°N, 103.5°W. The scattered signals were received on narrow beam antennas at two receiving sites, and recorded in analog form on magnetic tape under the control of an AIM65 microcomputer. The analog tapes were digitized later and FFT-processed to obtain Doppler spectra and amplitudes.The 6 transmission paths were designed to provide several magnetic aspect angles varying by 1.5°-7° from perpendicularity with the earth's field B and two streaming aspect angles differing by ～38°. The objective was to employ controlled geometric factors to study the functional dependency of signal amplitudes and Doppler shifts on magnetic and streaming aspect angles. Several hundred hours of excellent data were obtained in continuous operation during the month of August 1981. Preliminary results will be reported.     

Analysis of gravity-wave induced instabilities and turbulence viscosity parameters from optical emissions

The effects of gravity waves on OH and 5577 0I emissions have been used to investigate (1) the possible production of “secondary” waves or “ripples” by a “primary” wave; (2) the possible application of such observed optical emissions for computing atmospheric parameters such as turbulence viscosity in the mesospheric regions.     

Long term effects of low doses of 56Fe ions on the brain and retina of the mouse: ultrastructural and behavioral studies.

Eight month old male C57BL6 mice were exposed without anesthesia to whole-body irradiation in circular holders. The mice were tested for behavioral decrements after 0.5 and 50 rads of Fe particle irradiation at 6 and 12 months post irradiation to obtain long term results. A standard maze was used and the animals were timed for completion thereof. A string test also was administered to the mice, testing their ability to grasp and move along a string to safety. The results from animals exposed to 50 rads were significantly different from [correction of fron] control results to p = < .001 in both systems of testing. The hippocampus (believed to be the location of environmental interaction in the brain) and the retina were examined for ultrastructural changes. The ultrastructural changes were similar to those we found in our Cosmos 782, 936 and in our Argon experiments. The mouse data indicate that iron particles were able to induce long term changes in the central nervous system which lead to behavioral impairment.     

The transient highly excited solar flare plasma

Recent observations of the energetic particles produced in solar flares indicate that the production of electrons, with energies up to about 100 keV, is a fairly common feature of small flares. In those flares the acceleration of protons and other nuclei does not extend beyond about 1 MeV.The X-ray emission often exhibits two distinct components of which the first one is produced by non-thermal, the second by thermal electrons through bremsstrahlung collisions with the ambient ions. Along with these X rays, radio emission, in the microwave region, is observed. This radio emission is usually interpreted as due to gyrosynchrotron radiation from the same electrons.In this review a discussion is presented of the processes occurring in solar flares with special reference to the acceleration and radiation processes.     

The Calculation of Frequency-Modulation Distortion in Linear Networks

A numerical method is developed for the calculation of steady-state FM distortion in a linear passive network from the character of the FM signal input and the steady-state transfer characteristics of the network. The method of calculating FM distortion requires the solution of a finite set of linear equations which is accomplished readily by a digital computer. To illustrate the use of the method, the FM distortion introduced by a Chebyshev-response bandpass filter is calculated for a range of network and input signal parameters.     

Switchless Control Strategies for Minimum Time Frequency Transitions in Phase-Locked Loops

The problem of minimum time frequency transitions in phase-locked loops with both phase and frequency controls applied is investigated using Pontryagin's maximum principle. Typically, a type II secondorder loop with a damping ratio of 0.707 subjected to a step change in the frequency of its input signal is considered and switchless control strategies that force the transients in the loop to settle down in minimum time are obtained.