Table of Content

30 June 1988, Volume 6 Issue 2

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Articles

COMPLEX RAY ANALYSIS OF BEAM TRANSMISSION THROUGH GENERALLY-CURVED TWO-DIMENSIONAL RADOMES

GAO XIAOJIE

1988, 6(2):  95-102. 

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Assessment of the radiaton characteristics of certain types of radome-covered antennas poses the problem of transmission of amplitude tapered-aperture fields through a generally-curved dielectric taper. Modeling the amplitude taper by a Gaussian, the incident illumination can be generated by a source at a complex coordinate location. The radome problem is then addressed by tracing complex ray fields from the complex source point through the complex extension of the radome contiguration to the real location of the observer. The complex ray tracing takes into account multiple reflection inside the radome, and the multiple internal reflected complex ray can be combined into a "collective ray" which is weighted with a corrected transmission coefficient. The formulars developed in this study are applicable to generally-curved radomes, though parabolic shell radomes are chosen as the mathematical models for numerical computations.

THE MEASUREMENT OF CURVATURE RADⅡ OF SLIGHTLY BENT CRYSTALS BY (n^V,-n^S)DOUBLE-CRYSTAL DIFFRACTOMETRY

CHEN JINGYI, LI RUNSHEN, XU SHUNSHENG

1988, 6(2):  103-108. 

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The Dumond graphic method is employed in the analysis of crystal curvature radius measurement. A new method for measuring the curvature radius using the (n^v,-n^s) double-crystal diffractometry with Kα₁ spectrum only is proposed. This method is much more sensitive than the usually used (n^s,-n^s) double-crystal diffractometry with the Ka doublet method. The detectable limit of curvature can be improved about one order of magnitude. The curvature radius of the Si crystal after As⁺ ion implantation is measured by (n^v,-n^s) double-crystal diffractometry.

A NEW MODEL OF RAPID INITIAL OXIDATION IN DRY OXYGEN FOR SILICON

XU XINZHONG, RUAN GANG

1988, 6(2):  109-116. 

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A new model of the rapid initial oxidation in dry oxygen for silicon is presented. In this model, both the effects of the change in the interfacial reaction rate coefficient and the enhanced oxygen diffusion on the high, initial oxidation rate of silicon are considered. Using this new model, the trouble and the limitation existing in the so-called fixed positive charge model which was presented by Schafer and Lyon can be avoided. Compared with the oxidation model used in the process simulation program-SUPREM-Ⅲ, our model has a clearer physical meaning. The formula of the model takes the similar form to the linear-parabolic oxidation model, BO it is very suitable for VLSI process simulation. In addition, the model can also explain why there is no rapid initial oxidation of silicon in wet oxygen, and why the initial oxidation rate of nondoped polycrystalline silicon is even larger than that of the <111>-oriented single crystalline silicon.

A NEW IC WASHED EMITTER TRANSISTOR WITH MICRO-POWER DISSIPATION

HONG YUAN, LIU BINGGUO

1988, 6(2):  117-122. 

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A washed emitter transistor was developed, whose emitter was formed by phosphorus diffusion through a thin layer of thermally grown oxide. Studies were made on DC characteristics, current gain vs. collector current, and current gain vs. temperature. The effects of surface recombination and bandgap narrowing in the emitter on the gain were investigated. The results show that the washed emitter transistor has a uniform gain within the range of five orders of magnitude of I_C and can work at a current as low as 1 nA. Compared with the conventional transistors, the minimum working current can be reduced by a factor of 10³ and the surface recombination velocity by a factor of 50%, and an increased yield of 20% can be achieved. The gain is less temperature dependent because of lighter bandgap narrowing in the emitter. It can be expected that the power dissipation of ICs will be considerably reduced if the washed emitter transistor is adopted.

THE MECHANISM ANALYSIS FOR UNIFORM MOTION OF CHAIN WITH VARYING PITCH

YAN JINGPING

1988, 6(2):  123-131. 

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In this paper, the characteristics of the hinged mechanism of a chain with varying pitch, the meshing relation between the chain and sprocket, the regulation of changes in the chain speed, and the determination of main parameters have been studied quantitatively.

A STUDY OF SYSTOLIC STRUCTURE FOR CONVOLUTION COMPUTATION

LIU CHONGQING, YU RENKANG

1988, 6(2):  132-138. 

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In this paper, a family of systolic designs for convolution computation classified into two categories, convolution arrays with and without global data communication, is proposed. Systolic architecture, which permits multiple computations for each memory access, can speed up execution of compute-bound problems without increasing I/O requirements.
A lot of compute-bound computation problems can be solved by systolic architecture systems, onvolution computation problems can be used in the study of systolic structure. The convolution computation can be implemented efficiently using the systolic architecture systems which are consisted of several single-chip processors served as processing elements.

THEORY AND METHOD FOR EVALUATION OF ROUNDNESS DEVIATION

ZHANG HEPING, ZHANG E

1988, 6(2):  139-146. 

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The problem of roundness is usually discussed in the system of pole coordinate, but the authors deal with this problem in the system of right-angled coordinate and have developed a new method for calculating roundness. The new method ha.s the advantage of high speed and accuracy, and also the program is simple. It is discussed in the paper whether the extreme value of minimum zone evaluation is unique. Some confusing opinions have been clarified, giving the basis for using direct search methods to calculate the minimum zone value of roundness.

SOME NUMERICAL RESULTS OF ONE-DIMENSIONALINVERSION FOR ACOUSTIC WAVESUSING DIFFERENCE METHOD

GU GUIDING, ZHANG GUANQUAN

1988, 6(2):  147-155. 

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In this paper, several difference schemes are considered for the calculation of one-dimensional inversion for acoustic waves, and different kinds of model of acoustic impedance are tested. For continuous acoustic impedance, all the schemes considered are suitable, but for discontinuous impedance, we have to choose a suitable scheme to calculate, when the reflection is strong. In addition, when some noise is artificially added to the multilayer model, the function of the smooth processing is examined to control the variation of acoustic impedance.

DATA EXTRAPOLATION FOR BANDLIMITED IMAGE SIGNALS

PAN JIANQIANG

1988, 6(2):  156-162. 

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The ill-posedness inherent in the bandlimited signal extrapolation problem can be treated by means of regularization parameters. In this paper, a regularized closed form of the 2-D extrapolation matrix, which is tolerant to noise, is formed by utilizing regularization parameters. Also the realization of the architecture of a two dimensional digital extrapolator is presented. A 2-D recursive Kalman filtering extrapolation algorithm is proposed.

DISCUSSION ABOUT THE EFFECTS OF CRYSTAL LATTICE ON POSITRON ANNIHILATION

HUANG XIAOWU, LIN ZIJING, WANG KELIN

1988, 6(2):  163-168. 

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In this paper, we use Green's function method to study the first-order ladder graphs which include lattice-electron and lattice-positron interaction lines. We calculate some low order Feynman graphs in taking the static limit for electron-positron effective interaction potential, and obtain the formula of partial annihilation rate of the positron for p>p_F. Furthermore, we make some numerical calculations, and discuss and compare them with the results of Hede-Carbotte's theory.

THEORY OF PHASE TRANSITION IN THE LAYERED ANTIFERRO-ELECTRIC H₂C₄O₄

ZHANG JINGBO, SUN HEBI, QIN ZIKAI

1988, 6(2):  169-174. 

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The para-and antiferro-electric phase transition of an H₂C₄O₄ crystal is studied by means of Green's function theory based upon a pseudospin model and by taking into account its layered structure. We derive a first order transition instead of a second order one as concluded by Zinenko with the same model. We also find the change of the order parameter with temperature in better conformity with measurements.

SENSING CHARACTERISTICS OF CO GAS SENSOR OF SnO₂ DOPED CeO₂

SHBN HESHENG, ZHANG HAN, QU YICAI, SHEN YUSHENG

1988, 6(2):  175-179. 

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A new type of CO gas sensor of SnO₂ doped CeO₂ has been made. The sensing characteristics of this sensor have been examined for several gases at different temperatures. The results show that the sensor achieves high sensitivity, excellent selective detection and short response time for CO at a low temperature (115℃). The results are also discussed.

A METHOD OF SIMULATION OF PICTURE WITH COMPUTER

QIU YAN

1988, 6(2):  180-184. 

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This paper gives a brief method of simulation of picture with mini-computer IBM-PC/XT and matrix printer M2024.

STABILITY AND PHASE-LEAD COMPENSATION OF THE SINGLE TUBE HEAT EXCHANGER

CAO GUANYI, H. KANOH

1988, 6(2):  185-188. 

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Single tube heat exchanger is a typical example of distributed parameter system. The mathematical modes obtained by using partial differential have some properties which do not hold for centralized parameter system, especially due to the existance of essential singular point. The effect of essential singular point on the system stability can be shown by root loci. The system dynamics can be improved by using phase-lead compensation.