Integration of high-Q GaAs varactor diodes and 0.25 μmGaAs MESFET's for multifunction millimeter-wave monolithic circuitapplications

Two technologies are demonstrated whereby high-Q, vertical-structure, abrupt-junction varactor diodes are monolithically integrated with 0.25-μm GaAs MESFETs on semi-insulating GaAs substrates for multifunction millimeter-wave monolithic circuit applications. Diodes with various anode sizes have been realized with measured capacitance swings of >2.1:1 from 0 V to -4 V and series resistances of approximately 1 Ω. Diodes having a zero bias capacitance of 0.35 pF have Q's of >19000 (50 MHz) with -4 V applied to the anode. Under power bias conditions, the MESFETs have a measured gain of >6 dB at 35 GHz with extrapolated values for f _t and f_max of 32 GHz and 78 GHz, respectively. Using these technologies, a monolithic Ka-band voltage controlled oscillator (VCO) containing a varactor diode, a 0.25-μm GaAs MESFET, and the usual MMIC passive components has been built and tested. At around 31 GHz, the circuit has demonstrated 60-mW power output with 300 MHz of tuning bandwidth     

Geometrically nonlinear analysis of rectangular mindlin plates using the finite strip method

A general finite strip method of analysis is presented for the geometrically nonlinear analysis of laterally loaded, rectangular, isotropic plates. The analysis is based on the use of Mindlin plate theory and therefore includes the effects of transverse shear deformation. The nonlinearity is introduced via the strain-displacement equations and correspondingly the analysis pertains to problems involving moderate displacements but small rotations. The principle of minimum potential energy is used in the development of the strip and the complete plate stiffness equations and the latter equations are solved using the Newton-Raphson method. In numerical applications a particular type of finite strip is used in which all five reference quantities (three displacements and two rotations) are represented by cubic polynomial interpolation across the strip whilst the ends of the strip are simply supported for bending/shearing behaviour and immovable for membrane behaviour. These applications are concerned with uniformly loaded plates of both thin and moderately-thick geometry and detailed presentation is given of both displacement- and force-type quantities.     

Monolithic integration of an InP/InGaAs four-channel transimpedance optical receiver array

Fully functional four-channel transimpedance receiver array OEICs have been fabricated on 2" diameter InP substrates. Each receiver channel has a bandwidth of 200 MHz and an average input equivalent noise current of around 6 pA/ square root (Hz). The array chip is 3.7 mm*3.2 mm in size and contains 88 components. This is believed to represent the highest level of optoelectronic integration yet reported on InP.<>     

Extracellular recordings in the colchicine-lesioned rat dentate gyrus following transplants of fetal dentate gyrus and CA1 hippocampal subfield tissue

Grafts of fetal dentate gyrus (DG) and CA1 hippocampal subfield tissue were extruded into the dentate gyri of adult male Sprague-Dawley rats, 7-10 days after lesioning the granule cells with colchicine (0.06 microliter of 7 mg/ml solution at each of 5 sites/hippocampus). Graft area-host and host-graft area connectivities were investigated 4-6 months post-transplantation by recoding extracellular evoked response in hippocampal slice preparations. Following stimulation of the host mid-molecular layer, evoked field potential responses, showing considerable variation, were recorded in both types of graft. Evoked responses in the lesioned DG without grafts were recorded in very few slices. Stimulation of the area of DG tissue grafts occasionally evoked responses in the host CA3/CA4 and there was no evidence for CA1 graft area-CA3/CA4 connectivity; stimulation of DG and CA1 graft areas occasionally evoked responses in the host CA1. Responses in the area of both DG and CA1 grafts supported short-term potentiation following stimulation of the host mid-molecular layer but only DG graft areas supported long-term potentiation of the population spike amplitude. In the area of both types of transplant a tonic bicuculline-sensitive inhibition was present and paired-pulse stimulation paradigms provided some evidence for inhibition. It is possible that responses recorded within the area of grafted tissue to stimulation of the host are attributable to host-graft connectivity and similarly, responses recorded in the host to stimulation of the area of the graft may be attributable to graft-host connectivity. Only DG graft areas received host inputs which were capable of sustaining a long-term potentiation and establishing efferent contacts with the host CA3/CA4 subfield, suggesting that these would be more likely than CA1 grafts to reinstate normal functional circuitry.     

Dendritic cells and macrophages are the first and major producers of TNF-alpha in pancreatic islets in the nonobese diabetic mouse

The nonobese diabetic (NOD) mouse spontaneously develops autoimmune insulin-dependent diabetes mellitus (IDDM) and serves as an animal model for human type I diabetes. TNF-alpha is known to be produced by islet-infiltrating mononuclear cells during insulitis and subsequent beta cell destruction and has been implicated in the pathogenesis of IDDM. Previously, T cells have been suggested as the main source of TNF-alpha in the islet infiltrate. However, on immunohistochemical analysis of TNF-alpha expression in islets, we are able to show that the staining pattern of TNF-alpha resembles that of dendritic cells (DC) and macrophages (Mphi) rather than T cells and that TNF-alpha is expressed in islets at the very early stages of insulitis when no T cells are detected. On double staining for TNF-alpha and cell surface markers, we can demonstrate that TNF-alpha staining clearly correlates with DC and Mphi, whereas there is a poor correlation with T cells. This feature was observed at both early and late stages of insulitis. TNF-alpha expression was also seen in NOD-SCID islets, in addition to a peri-islet infiltration consisting of DC and Mphi, indicating that T cells are not required for the early DC and Mphi infiltration and TNF-alpha expression in islets. In conclusion, our results show that DC and Mphi are the major, early source of TNF-alpha in the NOD islet infiltrate and that TNF-alpha can be expressed independently of T cells, indicating that the early DC and Mphi infiltration and expression of TNF-alpha are crucial in initiation of diabetes.     

冷弯型钢桁架的强度和性能研究

对13个冷弯C型钢制成的全尺桁架构件进行了试验,分析了多种不同的加固方法以分析其对此截面性能提高的效果。采用集中点荷载给构件加载,模拟屋顶桁架的真实受力条件。结果显示:邻近踵板的上弦杆的局部屈曲是结构的主要破坏模式。板的畸变或蠕变会发生在没有充分加固的踵板处。研究还发现螺距的增加也会使得截面承载力增强。对连接踵板的上弦杆,踵板加劲肋和浅肋加劲板之间的踵连接的加固,能很明显地提高桁架的性能。同时采用了交互式设计公式和CSAS136-07中推荐的直接强度法对上弦杆进行了梁柱分析。