[en] Optical tomography provides a means for obtaining spatially resolved measurements from line-of-sight data. Classical flow visualization approaches such as shadowgraphy, schlieren and interferometry provide information about physical observables averaged along the path of the probe beam. Locally resolved measurements cannot be obtained from such data sets, except for axially symmetric or two-dimensional flows. Tomography has been applied to medical and industrial applications. Particularly in medicine, tomographic diagnostics are well developed. Since medical objects tend to be stationary, data acquisition times need not be very rapid and sequential acquisition of projections is sufficient. In fluid mechanics no such luxury is usually allowed, since the most interesting flows are unsteady and rapidly developing. This requires that tomographic data acquisition systems have a very short response time and all projections must be collected in such a short time that the flow is essentially frozen. A new optical architecture is described that is capable providing 36 equally spaced projections about a 180 degree arc in 300 μsec. Each projection passes through a three inch diameter, three inch high cylinder, allowing a full three-dimensional reconstruction of the flow in that region. Holographic interferometry allows direct measurement of optical phase along the pathlength. From these data, the flow may be reconstructed using any of the available reconstruction techniques. The design of the optical apparatus is described, followed by an outline of the experiment, the data reduction scheme and the results obtained with this method

[en] Wave packet methods constitute a new approach to WKB theory, and provide both a new theoretical tool and a new way of solving practical problems. They are especially useful for complex geometries in several dimensions. Their main advantage is the ease with which they deal with caustics and Maslov phase shifts, and the fact that they do not suffer from any discontinuities or divergences

[en] Solid-state devices formed from compound semiconductor materials like GaAs, GaP, SiC, and (Al, Ga)As have long been viewed as candidates for use in electronic circuits functioning at temperatures greater than 300⁰C. To address the specific needs of power semiconductor devices operating simultaneously at high currents, voltages, and high temperatures, heterojunction devices formed from combinations of GaAs and (Al,Ga)As have recently been proposed. These novel heterojunction structures display reduced resistive and voltage parasitics when compared to wide-bandgap GaP or SiC homojunction diodes without seriously compromising control of thermally generated leakage currents. In this study a prototype, low-power, (Al, Ga)As/GaAs, heterojunction bipolar transistor (HBT) is described which has demonstrated excellent electrical characteristics in the 300 to 400⁰C temperature range. At 350⁰C, the HBT has a common-emitter current gain of 14 (V/sub CE/ = 5V, I/sub C/ = 10 mA) and collector-base leakage of 6.4 x 10^-2 A/cm² (V/sub CB/ = 5 V). These studies and others imply that a heterojunction, (Al Ga)As/GaAs, power semiconductor electronics technology is feasible in the near future

[en] Recent JPL experimental and theoretical results of electron attachment to molecules at ultralow energies are discussed. Specifically, electron attachment to F₂, and temperature dependencies of attachment rate constants in CFCl₃ and CCl₄ are used to illustrate some interesting features. Extensions to several important areas involving plasma-surface interactions are outlined

[en] A new apparatus for measuring both thermal conductivity and thermal diffusivity of fluids at high temperatures is described. The technique employed is that of the transient hot wire. Measurements are made with a 12.7 μm diameter platinum wire at times of up to 1 second. The data acquisition system is controlled by a microcomputer and includes several programmable digital voltmeters. The hot wire and a shorter compensating hot wire are arranged in different arms of a Wheatstone bridge. The cell containing the core of the apparatus is designed to accommodate pressures from near zero to 70 MPa and temperatures from 0 to 500⁰C. For thermal conductivity, the precision of the new system is expected to be around 0.3% and the accuracy 1.0%. For thermal diffusivity the accuracy is estimated to be around 5%. From the two variables measured, one can obtain values of the specific heat, C/sub p/, of the fluid, provided that the density is either measured, or available through an equation of state

[en] The design and construction of a wide-range, automated film balance and a set of experiments on a well-documented material to test the instrument during its development are described. The balance can be operated in the temperature range 5-50⁰C. It can measure surface tension differences up to 50 mN m^-1 with an imprecision of +/- 0.01 mN m^-1. The measurements of the liquid-expanded (LE)-liquid-compressed (LC) and the liquid-vapor transitions in pentadecanoic acid monolayers on water to confirm recent suggestions that long-standing ideas about these two transitions might be in error and that a thorough reexamination of many classic measurements will be necessary