Effective-index matrix analysis of distributed feedbacksemiconductor lasers

A method is developed for calculating the threshold gain in distributed feedback (DFB) semiconductor lasers consisting of a four-layer waveguide. Each corrugation region is expressed by a transfer matrix comprising the complex effective index, and the threshold calculation is reduced to the matrix multiplication. It is found that a periodic variation of the effective gain and loss induced by the modulation of the optical confinement factors gives rise to the threshold gain difference between the two adjacent modes on both sides of the Bragg frequency in standard DFB lasers without facet reflections. The absorption loss in the guiding layer increases the amplitude of the gain modulation, resulting in the increase of the threshold gain difference     

A 5-ns GaAs 16-kb SRAM

A GaAs 4 K×4-b static-Ram (SRAM) with high speed and high reliability has been developed for practical systems. By adopting a novel basic circuit technique to the peripheral circuits, the RAM operates over a wide temperature range. By using a novel memory cell, the soft-error rate is reduced to less than that of commercial silicon emitter-coupled-logic (ECL) RAMs. Furthermore, by adopting a triple-level interconnection process, the chip area is reduced to 58% of that using a double-level one. The RAM operates at a single supply voltage of 1.8 V. At an ambient temperature of between 25 and 100°C, the RAM is guaranteed a 5.0-ns access time, 2.0-W power dissipation, and ±0.1-V supply voltage tolerance     

Determination of origin of ephedrine used as precursor for illicit methamphetamine by carbon and nitrogen stable isotope ratio analysis

The sale of ephedrine, one of the precursors of methamphetamine, is strictly controlled and monitored in various countries to prevent the production of illicit methamphetamine. There are three kinds of production scheme for ephedrine manufacture, and it is very useful for precursor control to investigate the origin of ephedrine used for the synthesis of illicit methamphetamine. By means of stable isotope ratio mass spectrometry (IR-MS), we investigated the origin of ephedrine based on the delta(13)C and delta(15)N values. The various origins of ephedrine (biosynthetic, semisynthetic, or synthetic) could be discriminated clearly by using these values. The delta(15)N values of synthetic ephedrine were more negative than those of ephedrine from other sources. By the repeated distillation of methylamine in our laboratory, we confirmed that this could be due to isotope separation during distillation for the purification of methylamine used for ephedrine synthesis. The values for ephedrine used as the precursor were well-correlated with those for methamphetamine synthesized from it. This drug characterization analysis should be useful to illuminate the origin of the precursors used for clandestine methamphetamine and to trace the diversion of medicinal ephedrine for illicit manufacture of methamphetamine.     

PAF receptor antagonist in asthma therapy

Platelet-activating factor (PAF), proposed as an important inflammatory mediator in asthma, reproduces several of the features of asthma, such as micro vascular leakage, mucus secretion, broncoconstriction, and possibly increased airway responsiveness. The recognition that PAF may be a central mediator in asthma has been a relatively recent event, so that those interested in asthma research may be unfamiliar with the chemistry, biochemistry and biology of this material. It seemed appropriate therefore to assemble a group of expert investigators to make presentations and to discuss the current status of PAF research with a specific bias toward asthma. In this way, it has been possible to focus upon PAF in asthma and to provide the necessary background for consideration of the effects of existing antiasthma drugs to suppress pulmonary responses to PAF. The capacity of existing antiasthma drugs to suppress pulmonary responses to PAF implies that this will be necessary feature of many of the newer antiasthma drugs and this knowledge allows a more balanced judgment of the prospects for PAF receptor antagonists in this disease.     

弱粘煤和不粘煤的快速热解及其团聚研究

对弱粘煤和不粘煤的快速加氢热解及在快速热解情况下发生的团聚现象进行了研究．研究发现,在高温加压快速加热条件下,氢气气氛中,煤的热失重率比煤的挥发分高,而在氮气气氛中,煤的热失重率低于煤的挥发分。同时,在高温加压快速加热条件下,在氮气气氛中的热失重率远低于氢气气氛中的热失重率。大多数弱粘煤和不粘煤,在高温下快速热解,无论在氢气气氛还是在氮气气氛中都发生团聚现象,即煤热解残炭团聚为圆柱状,且有一定的强度。有些煤(如Strongman煤和兴隆煤)在氢气气氛中残炭强度大于氮气气氛中的残炭强度。     

Regulation of survival and death of mesangial cells by extracellular matrix

BACKGROUND: Cell-matrix interactions exert major effects on such phenotypic features as cell growth and differentiation. Apoptosis is an active form of cell death that is crucial for maintaining the appropriate number of cells as well as the organization of tissue. Recently, it has been suggested that apoptosis of the mesangial cells (MC) is important in glomerular remodeling after injury. The MC are surrounded by an extracellular matrix (ECM) in vivo. Since in disease conditions the mesangial matrix is altered quantitatively and qualitatively, it is of interest to determine whether cell-matrix interactions may influence apoptosis of the MC. METHODS: We first investigated the differences in the susceptibility to apoptotic stimuli of the MC cultured on various ECM components (type I collagen, fibronectin, basement membrane matrix). We then determined whether the inhibition of MC-matrix interactions would affect apoptosis. Finally, interactions between MC and matrix were disrupted by the inhibition of beta1-integrin expression with antisense oligonucleotides (ODN). RESULTS: When MC were cultured on type I collagen or fibronectin and deprived of serum for eight hours, the extracted DNA from the MC demonstrated an internucleosomal ladder pattern on gel electrophoresis that constituted the biochemical characteristic of apoptosis. However, no ladder pattern was apparent when MC were cultured on basement membrane matrix. The attachment of cells was completely inhibited when the MC were cultured on agarose-coated dishes for 24 hours. Gel electrophoresis of DNA extracted from these cells showed a ladder pattern. However, the MC attached to the substratum did not show any apoptosis. MC showed an increase in apoptotic cell death after treatment with antisense ODN against beta1-integrin molecule. CONCLUSIONS: These results indicate that normal ECM may prevent the MC from undergoing apoptosis and serve as a survival factor for MC. Signals from ECM that prevent apoptosis may be mediated by beta1-integrin molecules.     

Oxypurinol, a xanthine oxidase inhibitor and a superoxide scavenger, did not attenuate ischemic neuronal damage in gerbils

The superoxide (O2.-) scavenging activity and neuroprotective effects of oxypurinol, a xanthine oxidase inhibitor, were compared with those of alpha-phenyl-N-tert-butyl nitrone (PBN). The rate constant for the reaction of oxypurinol with O2.- at pH 7.4 was 1.71 x 10(3) M(-1) s(-1) which was more than 100-fold that of PBN (1.65 x 10 M(-1) s(-1)). Oxypurinol inhibited the release of O2.- from stimulated neutrophils better than did PBN. However, oxypurinol did not attenuate the ischemic neuronal damage in gerbils, while PBN did. These results indicate that neither xanthine oxidase inhibiting activity nor O2.- scavenging activity correlates to the therapeutic efficacy of neuroprotective agents in ischemic-reperfusion injury.