An analysis of small-signal and large-signal base resistances forsubmicrometer BJT's

Small-signal and large-signal base resistances for submicrometer BJT's have been analyzed in detail by using a two-dimensional device simulator. It has been clarified that the small-signal base resistance cannot be obtained from the input impedance semicircle in the complex plane accurately due to the effect of the emitter resistance at low frequencies, and also due to the reduction of the base-emitter junction resistance and the diffusion capacitance at high frequencies. A new method for extracting an accurate value of the small-signal base resistance is proposed. The extracted small-signal base resistance not only differed from the large-signal base resistance extracted from the dc characteristics of a BJT, but also agreed with the differential resistance. It has been shown that, for a 0.6 μm emitter-width BJT, the measured value of the small-signal base resistance is less than half that of the large-signal base resistance in the bias region in which actual BJT circuits operate     

Pulmonary microcirculation during pulsatile and non pulsatile perfusion

During development of a rotary blood pump as an assist device, the efficacy of non pulsatile perfusion to the end organ has to be verified. However, there are few evaluations of two different perfusion mechanisms through the tissue microcirculation. In this study, the pulmonary microcirculation was analyzed by vital microscopic observation. Wistar rats weighing 400-500 g were anesthetized and ventilated by a respirator. After establishing right heart bypass from the right atrium to the pulmonary artery using a roller pump, the pulmonary microcirculation was observed during intravenous infusion of bovine albumin tagged with fluorescein isothiocyanate. The images were recorded on a videotape through an ultra-sensitive SIT TV camera. Initially, the pulmonary circulation was pulsatile, produced by the native heart, and the pulmonary capillary network was evenly perfused by the blood. After starting the pump, the flow became non pulsatile and the distribution of capillary perfusion was displaced to the short circuit connecting the pulmonary arterioles and venules. Flow distribution during non pulsatile perfusion was heterogeneous compared with pulsatile perfusion. This result suggests that non pulsatile flow may lead to the deterioration of function. Further investigation is necessary to evaluate the relationship between the microcirculation and organ function.     

A GIS-based risk assessment of hydrogen transport: Case study in Yokohama City

This study proposes a method of assessing the risk of hydrogen transport via road considering spatial features of a transport route, based on a geographic information system (GIS); a case study of Yokohama, Japan was considered in the assessment. The risk determined by multiplying the frequency of accidents with their consequences was estimated using road segments constituting the entire transport route. The effects of road structure, traffic volumes, and population information were reflected in the estimation of the risk for each road segment by using GIS. In the case study, the risks of transport route were assessed at an acceptable level under risk criteria. The results indicated that the risks fluctuated according to the road segments, indicating that spatial features of a transport route significantly affect the corresponding risks. Analyzing this importance indicates the transport routing to avoid high risk road segments as countermeasures.