New generation of hydrotreating catalysts

Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 2, pp. 2–4, February, 1991.     

New minimal-capacitor low-sensitivity RC-active synthesis procedure

A new low-sensitivity RC-active synthesis procedure is described which can be considered as an alternative to that of Antoniou in that the new method retains all the attractive features of his method. Further, this method uses the minimum number of capacitors which is frequently desirable for integrated circuits.     

The generation of point defects in GaAs by electron-hole recombination at dislocations

The degradation of GaAs heterojunction lasers results in the formation of long dislocation dipoles which grow by a climb process involving point defect concentrations of the order of 10¹⁹ cm⁻³. The driving force for this climb process is not understood and it has been suggested that the material contains a supersaturation of native interstitials which condense on the dislocation during device operation. An alternative model proposed that the driving force is related to the energy released by electron-hole recombination on the dislocation which is partially dissipated by the dislocation emitting vacancies into the surrounding lattice.Gallium arsenide substrates containing greater than 2 × 10¹⁸ tellurium atoms cm⁻³ contain interstitial concentrations of the order of 10¹⁷ cm⁻³ which condense out to form small dislocation loops during an anneal at 880°C. The presence of these loops indicates that the annealed material does not contain excess interstitials in solution. This annealed material was optically pumped and examined by transmission electron microscopy. It was found that the loops developed into dipoles typical of degraded lasers. The number of point defects involved in this climb process increased with increasing pumping power and time. These results are discussed in terms of the two mechanisms listed above and it is concluded that the energy released by electron-hole recombination at the dislocation provides the driving force for the climb process.     

The Investigation of the Behavior of Microorganisms by Computerized Television

Instrumentation is described which permits, along with simultaneous subjective observation, the rapid recording and quantification of the overt behavior of motile microorganisms under varying conditions. From a chain of standard commercially available units (with the exception of a single especially designed one) there has emerged a totality which provides unique advantages to the student of overt behavior. It consists of a primary optical system through which the organisms are televised, a standard video tape recorder, a unit which we have christened the ``bugwatcher' that processes the video signal from the tape for quantification of data by a computer, and finally, a digital computer.     

Analysis of quasioptical waveguide corners

The use of a mode-matching technique is shown to provide an accurate analysis of the oversize waveguide corner, thereby providing a means of checking the accuracy of other quasioptical approaches.     

Certain ineffective parametric interactions

The letter discusses a situation where both reactances of a resonator are pumped together in unison. It is shown that this mode of pumping does not yield a parametric excitation. This result may be of practical relevance in treating certain microwave and optical systems.     

Faraday rotation in a stratified medium

The effect on Faraday rotation caused by stratification in an ionized medium and in semiconductor samples is examined. Expressions for rotation are derived in closed form for linear, exponential, and parabolic electron density profiles, including the effects of reflection at the boundaries. An expression in the form of a series is also derived for a general polynomial type of electron concentration variation. The change in rotation due to the deviation from the equivalent homogeneous carrier distribution is then examined for some experimental conditions in semiconductors and in the ionosphere.     

Single-mode semiconductor laser optically pumped by an injection laser

Nanosecond pulses from an AlGaAs injection laser have been used to optically pump an ultrashort-cavity InP laser. Subnanosecond pulses from the InP laser exhibit a single longitudinal mode at 0.92?0.93 ?m.     

CMT-conductivity-modulated transistor

The characteristics of a conductivity-modulated transistor which can control AC current are presented. Measured characteristics of a fabricated device are shown and compared with calculated characteristics. Calculations are based on a physical, one-dimensional analytical model which has been, in part, derived from numerical analysis of the device. The proposed model gives relatively good qualitative agreement between calculated and measured characteristics. Potential applications of the device are discussed     

Design of Computer Experiments for Metamodel Generation

We review the use of statistical design and analysis of computer experiments (DACE) for the generation of parsimonious, surrogate models, also known as metamodels. Such metamodels are used to replace cpu- or memory-intensive, discretized approximations that often arise in MEMS and MOEMS. Emphasis is placed on optimal designs.