化工重大技术装备工作"十五"的成绩与"十一五"的任务

重大技术装备的制造水平是一个国家综合实力的直接体现,因此从上个世纪八十年代初开始,历届国务院领导人均兼任国家重大技术装备领导小组组长,通过推进重大技术装备的发展,促进     

High voltage (>1kV) and high current gain (32) 4H-SiC power BJTs using Al-free ohmic contact to the base

This letter reports the design and fabrication of 4H-SiC bipolar junction transistors with both high voltage (>1kV) and high dc current gain (/spl beta/=32) at a collector current level of I/sub c/=3.83A (J/sub c/=319 A/cm/sup 2/). An Al-free base ohmic contact has been used which, when compared with BJTs fabricated with Al-based base contact, shows clearly improved blocking voltage. A specific on-resistance of 17 m/spl Omega//spl middot/cm/sup 2/ has been achieved for collector current densities up to 289 A/cm/sup 2/.     

A polymerizable photoredox initiation system for vinyl photopolymerization

A polymerizable photoredox system consisting of 4-methacryl oxbenzophenone (MABP) and N,N-dimethlaminoethyl methacrylate (DMAEMA) used for the photopolymerization of acrylonitrile (AN) was studied. It was found that the polymerization rate is proportional to the 0.93th power for the AN concentration, the 0.28th power for the MABP concentration, and the 0.25th power for the DMAEMA concentration. The overall activation energy of the polymerization obtained is 30.43 kJ/mol. The recorded ESR spectrum indicates that the excited-state MABP abstraets hydrogen mainly from the methyl group of the dimethylamino moiety. The comparison of the initiation ability of polymeric MABP or polymeric DMAEMA with their monomeric forms has also been done and the results indicate that in good solvents P (MABP) has a much higher initiation ability than that of monomeric MABP, but monomeric DMAEMA and P (DMAEMA) display almost the same initiation ability. In poor solvent, the initiation ability of P (MABP) is not so obviously higher than that in good solvents. The result of UV analysis of P (AN) initiated by the MABP–DMAEMA system indicates that both MABP and DMAEMA not only initiate the photopolymerization of AN, but also enter into P (AN) polymer chains. © 1994 John Wiley & Sons, Inc.     

STRUCTURE REPRESENTATION OF THE SPECIFIC FRACTIONS FROM PINGSHUO COAL

Basic data of four fractions, PM₁, PM₆, PM₇and PM₈, derived from Pingshuo bituminous coal were obtained by ultimate analyses, mean molecular weight measure, GC/MS, ¹³C-NM R, ¹H-NM R and FTIR technigues. A method of calculating the average molecular parameters of the fractions is introduced. Based on the calculated parameters, the molecular structure models of the fractions of PM₆, PM;and PM₈are constructed. Significant structural information about the saturated hydrocarbon and aromatic hydrocarbon with heteroatom groups is given also.     

Using thermally stimulated currents to find defective capacitors

BaTiO₃ multilayer capacitors with a nominal capacitance of 3.5nF have been carefully measured using the thermally stimulated current (TSC) technique. When a 300V polarization voltage is applied at room temperature, a new TSC peak appeared in defective sample A after it has been immersed in water. No new peak was found in good-quality sample B after a similar treatment. The accelerated life test shows that sample A hasa much shorter life than sample B in terms of insulation resistance.     

Sensitivity analysis of lossy coupled transmission lines

An analysis method, based on the numerical inversion of the Laplace transform, is described for the evaluation of the time domain sensitivity of networks that include lossy coupled transmission lines. The sensitivity can be calculated with respect to network components and parameters of the transmission lines. Sensitivity analysis is useful for waveform shaping and optimization. Examples and comparisons with sensitivity determined by perturbation are presented     

核医学成像技术中计算机的应用

由于计算机和核医学的结合,各种成像方法的计算机化医学图像层析技术正在迅速发展,并开始广泛应用。本文介绍各类成像技术中计算机的应用,特别评述其最近进展,并提出了今后的展望。     

Efficient particle filter-based processing algorithm for clutter suppression and IR point targets enhancement

A novel soft decision-based median subtraction filter is presented for clutter suppression and infrared (IR) point targets enhancement. The decision is made based on a jump Markov model and its state and parameter estimation using a particle filter. The scheme is compared with other conventional clutter background removal techniques and good results are obtained.