Design of Switching Regulator with Combined FM and On-Off Control

The design and implementation of a switching regulator incorporating a high-frequency series-resonant converter and a combined FM and on-off feedback control is presented. The combined FM and on-off control results in a better conversion efficiency and a wider range of operational input voltage and output current. A 22.5 V, 50 W experimental regulator has been built to demonstrate the practicality of the circuit and its high efficiency, typically 92 to 96 percent, depending on the input and loading conditions.     

A review of the technical development of concorde

The technical problems encountered during the development and certification of Concorde are reviewed. The topics covered are mainly associated with aerodynamics, but other areas are discussed where they interact with the aerodynamic design or if there were conditions peculiar to supersonic transportation which had to be considered.     

Changes of contractile responses due to simulated weightlessness in rat soleus muscle.

Some contractile and electrophysiological properties of muscle fibers isolated from the slow-twitch soleus (SOL) and fast-twitch extensor digitorum longus (EDL) muscles of rats were compared with those measured in SOL muscles from suspended rats. In suspended SOL (21 days of tail-suspension) membrane potential (Em), intracellular sodium activity (aiNa) and the slope of the relationship between Em and log [K]o were typical of fast-twitch muscles. The relation between the maximal amplitude of K-contractures vs Em was steeper for control SOL than for EDL and suspended SOL muscles. After suspension, in SOL muscles the contractile threshold and the inactivation curves for K-contractures were shifted to more positive Em. Repriming of K-contractures was unaffected by suspension. The exposure of isolated fibers to perchlorate (ClO4-)-containing (6-40 mM) solutions resulted in a similar concentration-dependent shift to more negative Em of activation curves for EDL and suspended SOL muscles. On exposure to a Na-free TEA solution, SOL from control and suspended rats, in contrast to EDL muscles, generated slow contractile responses. Suspended SOL showed a reduced sensitivity to the contracture-producing effect of caffeine compared to control muscles. These results suggested that the modifications observed due to suspension could be encounted by changes in the characteristics of muscle fibers from slow to fast-twitch type.     

Phase gradient autofocus-a robust tool for high resolution SARphase correction

The phase gradient autofocus (PGA) technique for phase error correction of spotlight mode synthetic aperture radar (SAR) imagery is examined carefully in the context of four fundamental signal processing steps that constitute the algorithm. We demonstrate that excellent results over a wide variety of scene content, and phase error function structure are obtained if and only if all of these steps are included in the processing. Finally, we show that the computational demands of the fun PGA algorithm do not represent a large fraction of the total image formation problem, when mid to large size images are involved     

Multidimensional Algebraic Polynomial Approximation

A computational algorithm to approximate an n-dimensional function of the form F(x,y,z, ...) by an algebraic polynomial in the least square (LSQ) sense is described. The basis of this algorithm is that the n-dimensional function can be approximated by a set of polynomials in each one of the independent variables x,y,z, ... . This technique is illustrated by deriving the algebraic polynomial approximation in the LSQ sense for three-dimensional functions of the form F(x,y,z).     

Contactless positioning,manipulation and shaping of liquids by gas bearing for microgravity applications

Contactless positioning, manipulation and shaping of liquids using the gas bearing principle is demonstrated by ground experiments. Extensions to microgravity applications are presented also associated with solidification of molten materials.     

The optimal distribution of search effort: existence, uniquenessand the minimax solution

The detection search problem, one of distributing limited resources so as to maximize the detection probability in the single-try search for a concealed target with known probability density, is analyzed. Under fairly general assumptions, the optimal search density uniquely exists when the detection index is governed by the law of diminishing returns and another simple regularity condition. Numerical procedure based on the bisection method, which is guaranteed to converge if the solution uniquely exists, may be used to solve for the optimal search density and the associated Lagrange multiplier. When it is not possible to confidently estimate the target a priori probability density, the minimax solution guarantees a positive detection probability at the expense of degradation in performance     

Sporadic emission of ultra high energy gamma rays from crab pulsar

In a further study of sporadic emission from pulsars we find evidence for short lived intense emission from the Crab pulsar.     

Transport phenomena and crystal growth of the GeSe-Xenon system for different gravitational conditions

Previous chemical vapor transport experiments of the GeSe-GeI₄ system performed under reduced gravity conditions /1/ yielded crystals of considerably improved surface and bulk morphology. In addition, the mass transport rates observed in microgravity environment were significantly greater than predicted. A quantitative thermodynamic analysis of the solid-gas phase reactions of the GeSe-GeI₄ system revealed the multi-component, multi-reaction nature of the vapor phase /2/. Continued transport studies on ground of the GeSe-GeI₄ system in the presence of inert gases provided experimental evidence for the existence of a boundary layer /2/ and its thickness dependence on GeI₄ pressure in closed tube systems. Systematic transport rate measurements for different orientations of the density gradient relative to the gravity vector demonstrated the effects of ampoule inclination on mass flux /3/. Based on a computational model for simultaneous chemical vapor transport, sublimation, and Stefan flow /3/, the excellent agreement of predicted with ground-based experimental mass transport rates over wide pressure ranges /3/ confirmed the validity of the model and the discrepancy between observed and expected transport rates of the GeSe-GeI₄ system in microgravity.     

Comparison of GPS S/C orbits determined from GPS and SLR tracking data

The last two Global Positioning System (GPS) spacecraft launched on August 30, 1993 and March 10, 1994 carried identical laser retroreflector arrays that allow laser ranging from ground stations. Tracking of these targets is a low priority for most of the ground stations due to the present mandatory support of missions with no alternative tracking. The available data is sparse and concentrated primarily on the first of the two spacecraft, GPS-35 (PRN 5). Despite this, analysis of this data set indicates that there is great potential for engineering and scientific experiments in a synergistic application of Satellite Laser Ranging (SLR) and radiometric GPS techniques.