Dynamic linewidth of amplitude-modulated single-longitudinal-mode semiconductor lasers operating at 1.5 ?m wavelength

We have measured the frequency chirp characteristics of single-longitudinal-mode semiconductor lasers operating at 1.5 ?m wavelength and subject to large signal amplitude modulation in the 50 to 800 MHz range. Measurements on cleaved-coupled-cavity (C3) and GRIN-rod external cavity lasers show that the wavelength chirp is large enough to cause a penalty in ultra-high-bit-rate long-haul optical-fibre systems.     

相干光纤PSK信号传输实验研究

本文报导我们最近进行的光频相位调制和解调的实验进展,并给出了利用光频相位调制方式进行相干光纤数字信号传输的实验原理和结果。     

Linewidth reduction of cleaved-coupled-cavity lasers by optical feedback from a single-mode polarisation-preserving fibre external cavity

Linewidth characteristics of a cleaved-coupled-cavity laser with a single-mode polarisation-preserving fibre external cavity have been investigated as a function of feedback power level and side-mode suppression ratio. The optimum power feedback ratio is near 2×10?4 for a minimum linewidth of about 30 kHz. A weak dependence of linewidth on side-mode suppression ratio is observed as long as the suppression ratio is greater than 500:1.     

硬质PVC发泡制品的挤出技术及应用

本文介绍了挤出法生产硬质PVC发泡塑料的现状 ,阐述了其原材料和助剂的选择及常用的生产工艺 ,指出今后需做的工作     

A study on the formation of liquation cracks in the weld heat-affected zone of HY-80 quenched and tempered steel

Liquation cracking of heat-affected zones (HAZs) is often encountered during the welding of HY-80 steels. To reduce the sensitivity of this defect, the content of impurities, such as P and S, must be kept as low as possible. However, in the development of HY-80 steel, HAZ grain boundary liquation is still found even at very low impurity contents. In order to clarify the cause of this defect, the Gleeble hot ductility test and electron probe X-ray microanalysis (EPMA) were carried out. From the results of EPMA, it was evident that the grain boundary liquation in the heat-affected zone of HY-80 steel was due to the low-melting-point eutectic reaction between Cr, Ni and Mn, which had been swept up by the migrating grain boundaries in the welding-heating thermal cycle, and hence enriched at the grain boundary. In addition, the Gleeble hot ductility test results revealed that the HAZ liquation cracking sensitivity of HY-80 steel could be decreased by reducing the C, Ni and Cr contents of base metal, and by decreasing the dwell time at high temperatures during the welding thermal cycle.     

Laser transmission through thin cirrus clouds

A near-infrared airborne-laser transmission model for thin cirrus clouds has been developed on the basis of the successive-order-of-scattering approach to account for multiple scattering by randomly and horizontally oriented ice crystals associated with an aircraft-target system. Direct transmission and transmission due to multiple scattering are formulated specifically for this geometric system, in which scattering and absorption associated with aerosols, water vapor, and air are accounted for. A number of sensitivity experiments have been performed for investigation of the effect of aircraft-target position, cirrus cloud optical depth, and ice crystal size on laser transmission for tactical applications. We show that transmission contributions produced by orders of scattering higher than 1 are small and can be neglected. The possibility of horizontal orientation of ice crystals can enhance transmission of laser beams in the aircraft-target geometry. Transmitted energy is strongly dependent on the horizontal distance between the aircraft and the target and on the cloud optical depth as well as on whether the cloud is above or below the aircraft.     

Microwave dielectric properties of MgAl2O4–CoAl2O4 spinel compounds prepared by reaction-sintering process

MgAl₂O₄ spinel exhibits fascinating microwave dielectric properties, but the synthesis of dense MgAl₂O₄ ceramics requires high firing temperatures. In this study, Co is introduced into MgAl₂O₄ ceramics to improve their sinterability and microwave dielectric properties. An Mg_1−xCo_xAl₂O₄ solid solution of a spinel structure was observed in the MgAl₂O₄–CoAl₂O₄ system, and dense Mg_1−xCo_xAl₂O₄ ceramics were obtained by sintering at 1475–1500 °C in air for 2–6 h. Co addition is effective in lowering the sintering temperature to 1475 °C. Q × f of Mg_1−xCo_xAl₂O₄ ceramics was increased to 49,300 GHz with an increase in Co content to 0.2, but degraded with a further increase in Co content. The temperature coefficient of resonant frequency of Mg_1−xCo_xAl₂O₄ ceramics was sustained at between −73 and −23 ppm/°C to the variation of Co content.     

Clusterin expression in the early process of pancreas regeneration in the pancreatectomized rat

We have previously reported upregulation of clusterin at the time of islet cell regeneration after beta-cell injury. This led us to speculate that clusterin might be involved in the neogenic regeneration of the pancreas. Clusterin expression was examined throughout the process of pancreatic neogenesis in pancreatectomized rats. For in vitro analysis, duct cells were isolated from the rat pancreas and clusterin cDNA was transfected for its overexpression. Clusterin and its mRNA increased significantly in the early phase of regeneration, particularly at 1-3 days after pancreatectomy. Clusterin was transiently expressed in the differentiating acinar cells but faded afterwards. Interestingly, these clusterin cells were negative for PCNA (proliferating cell nuclear antigen), whereas most epithelial cells in ductules in the regenerating tissue showed extensive proliferative activity. Clusterin expression was also detected in some endocrine cells of the regenerating tissue. Transfection of clusterin cDNA into primary cultured duct cells resulted in a 2.5-fold increase in cell proliferation and induced transformation of non-differentiated duct cells into differentiated cells displaying cytokeratin immunoreactivity. Taken together, these results suggest that clusterin may play essential roles in the neogenic regeneration of pancreatic tissue by stimulating proliferation and differentiation of duct cells.     

Human glutamate dehydrogenase is immunologically distinct from other mammalian orthologues

Five monoclonal antibodies (mAbs) that recognize human glutamate dehydrogenase (GDH) have been selected and designated as monoclonal antibodies hGDH60-6, hGDH60-8, hGDH63-10, hGDH63-11, and hGDH91-14. A total of five mAbs recognizing different epitopes of the enzyme were obtained, two of which inhibited human GDH activity. When total proteins of human homogenate separated by SDS- PAGE, were probed with mAbs, a single reactive protein band of 55 kDa, which co-migrated with purified recombinant human GDH was detected. When the purified GDH was incubated with each of the mAbs, its enzyme activity was inhibited by up to 58%. Epitope mapping analysis identified, two subgroups of mAbs recognizing different peptide fragments. Using the individual anti-GDH antibodies as probes, the cross reactivities of brain GDH obtained from human and other animal brain tissues were investigated. For the human and animal tissues tested, immunoreactive bands on Western blots appeared to have the same molecular mass of 55 kDa when hGHD60-6, hGHD60-8, or hGHD91-14 mAbs were used as probes. However, the anti-human GDH mAbs immunoreactive to bands on Western blots reacted differently on the immunoblots of the other animal brains tested, i.e., the two monoclonal antibodies hGDH63-10 and hGDH63-11 only produced positive results for human. These results suggest that human brain GDH is immunologically distinct from those of other mammalian brains. Thorough characterization of these anti-human GDH mAbs could provide potentially valuable tool as immunodiagnostic reagents for the detection, identification and characterization of the various neurological diseases related to the GDH enzyme.