Investigations on Pd:SnO2/porous silicon structures for sensing LPG and NO2 gas

P-type porous silicon (PS) structure has been prepared by anodic electrochemical etching process under optimized conditions. Photoluminescence studies of the PS structure show emission at longer wavelengths (red) for the excitation at 365 nm. Scanning electron microscope investigations of the PS surface confirm the formation of uniform porous structure, and the pore diameter have been estimated as 25 μm. Pd:SnO₂/PS/p-Si heterojunction with top gold ohmic contact developed by conventional methods has been used as the sensor device. Sensing properties of the device towards liquefied petroleum gas (LPG) and NO₂ gas have been investigated in an indigenously developed sensor test rig. The response and recovery characteristics of the sensor device at different operating temperatures show short response time for LPG. From the studies, maximum sensitivity and optimum operating temperature of the device towards LPG and NO₂ gas sensing has been estimated as 69% at 180 °C and 52% at 220 °C, respectively. The developed sensor device shows a short response time of 25 and 57 s for sensing LPG and NO₂ gases, respectively. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006.     

Classification of Dansgaard–Oeschger climatic cycles by the application of similitude signal processing

In this work we have performed a detailed analysis, using signal processing tools, to study time series of data (temperature proxy) extracted from the GRIP ice-core records and we relate it with the evolution of atmospheric CO₂ within the last glacial period. Our method is based in considering the warm periods known as Dansgaard–Oeschger (D/O) events and posterior returns to the cold stage as a climatic cycle. After the warming phase, D/O events relax to the initial cold state in three different ways, what gives rise to three classes of cycles. Also, the Younger/Dryas–Bolling/Allerod (Y/D–B/A) cycle corresponds to one of the classes obtained. We have found that all cycles start with identical warming phases which seem completely unrelated to variations in CO₂ concentration. We discuss on the consequences for global climatology of such steady pattern of cycles.     

一种控温热管理器的传热传质分析

本文针对余热回收中控制热源温度的需求,提出了热管理器概念并研制开发了实验样机.本文建立了热管理器内部传热传质二维模型,研究其工作机理.模拟结果表明,不凝气具有有效的凝结换热阻隔作用.工况变化时,蒸汽覆盖段长度显著变化,而这一区域内饱和蒸汽温度变化很小,说明热管理器具有良好的控温性能.计算结果与实验数据吻合很好,验证了理论模型的正确性.     

萃提技术在皂素生产中的应用

天然产物的提取是一个复杂的过程。当溶剂加入到植物原料中时，在溶剂的扩散和渗透作用下，渗透至原料的内部，将原料中可溶性物质进行溶解，从而造成内部及其吸附溶剂和外部溶剂的浓度不一致，存在一定的化学势差，它付之间不断地进行交换，直至它们的化学势趋于一致，内外溶液的浓度达到一种动态平衡，此时原料、吸附溶液和外部溶液的浓度基本保持衡定，溶济提取达到最大效能［１，５］．将该溶液滤出，破坏它们之间的平衡，重新加入新的溶剂促使它们之间进行新的交换，建立一种新的平衡体系，并不断地破坏它们，从而不断地将原料中的成分…     

Signal Level Simulation Modeling for Antenna Array of Aperture Synthesis Radiometer Based on the Equivalent Complex Baseband Representations

This paper presents a signal-level simulation model for simulating the process that antenna array of Aperture Synthesis Radiometer (ASR) collecting thermal radiation and transforming thermal radiation signal into radio frequency (RF) signal. By using the equivalent complex baseband signals to represent the practical thermal radiation and RF signals, simulation efficiency is improved significantly. The statistic characteristics of simulation results are found to match the corresponding theoretical analysis well. Results of an imaging simulation experiment show that this model can be employed in ASR system-level simulator design.     

低功耗互补传输门绝热逻辑和时序电路的设计

研究了采用二相非交叠功率时钟的绝热触发器及时序电路的设计，介绍了采用二相无交叠功率时钟的互补传输门绝热逻辑（CPAL）电路，并分析了其工作原理．该电路利用nMOS管自举原理对负载进行全绝热驱动，从而减小了电路整体功耗，且CPAL能耗几乎与工作频率无关．提出了性能良好的低功耗绝热D、T和JK触发器，并与其他几种绝热触发器进行功耗比较．给出了绝热时序电路的一般设计方法，并作为实例采用应用绝热D触发器设计了十进制计数器．SPICE程序模拟表明：设计的电路具有正确的逻辑功能及低功耗的优点．     

Analysis of effective service time with age dependent interruptions and its application to optimal rollback policy for database management

A stochastic model is developed describing a service system subject to inhomogeneous Poisson interruptions with age dependent interruption periods. By studying the probabilistic flow of the underlying multivariate Markov process, the Laplace transform of the effective service time is explicitly obtained. For general renewal interruptions, only the expected effective service time is derived. As an application, an optimal checkpoint policy is examined for database management. It is shown that an optimal policy maximizing the ergodic availability of the database is to implement a checkpoint as soon as the cumulative uptime of the database reaches a prespecified constantk ^*. A computational procedure is then developed for findingk ^* and numerical results are exhibited.This work was supported in part by the National Science Foundation under Grant No. ECS-8600992 and by the IBM Program of Support for Education in the Management of Information Systems.     

以四磺基铝酞菁-牛血清白蛋白为底物的荧光恢复均相法测定胃蛋白酶

酸性介质中,红区荧光探针四磺基铝酞菁(AlS4Pc)的荧光被白蛋白显著猝灭,加入胃蛋白酶后,体系荧光明显回复。基于此现象,建立了荧光恢复均相测定胃蛋白酶的新方法。考察了各种影响因素,在最佳实验条件(pH2.5、反应温度50℃、反应时间1h)下,本方法的线性范围为0.04～4mg/L,检出限为20μg/L。用本方法测定实际样品中胃蛋白酶,取得了满意的结果。     

复合冷凝空调机组的分析

以家用分体式空调作为节能改造对象,将传统单一冷凝改进为复合冷凝,即在压缩机排气管路上串联一个水冷冷凝器,吸收部分冷凝热制备生活热水。并在此基础上建立了分析模型。模拟计算结果表明,复合冷凝空调的目的效率得到了大大的提高,当空调的蒸发温度为0℃、冷凝温度为30℃时,空调目的效率由单一冷凝时的52%上升到70%。