Estimation of the thickness of the lower convective layer of solar ponds

In solar ponds, the lower convective layer plays a dual role. It provides a means for the extraction of energy from the pond. It acts also as an in-built seasonal energy store. The ground beneath the pond acts as an additional energy store. To enhance the ground energy storage, a method was earlier proposed by the authors employing trapezoidal-shaped trenches at the bottom of the pond. A rigorous method is presented for the determination of the thickness of the lower convective layer in the case of a flatbottomed pond and the trench depth for a pond with trapezoidal trenches. The energy storage to be provided depends on the magnitude and the pattern of energy extraction. For a constant extraction rate, the required thickness of the lower convective layer or the trench depth increases with an increase in the rate. For a sinusoidal extraction pattern, the thickness or depth increases with an increase in the phase lag of the extraction pattern from the insolation and exhibits a minimum for the amplitude of the extraction pattern for phase lags less than about 95 days. The results also indicate that, for a given heat load (total energy extracted in a year), there exists an area for which the cost of the pond and the associated system for energy utilization is a minimum.     

SEP calculations for coherent M‐ary FSK in different fading channels with MRC diversity

In this paper, the authors derive symbol error probability (SEP) expressions for coherent M‐ary frequency shift keying (MFSK) modulation schemes in multipath fading channels. The multipath or small‐scale fading process is assumed to be slow and frequency non‐selective. In addition, the channel is also subjected to the usual degradation caused by the additive white Gaussian noise (AWGN). Different small‐scale fading statistics such as Rayleigh, Rician (Nakagami‐n), Hoyt (Nakagami‐q), and Nakagami‐m have been considered to portray diverse wireless environments. Further, to mitigate fading effects through space diversity, the receiver front‐end is assumed to be equipped with multiple antennas. Independent and identically distributed (IID) as well as uncorrelated signal replicas received through all these antennas are combined with a linear combiner before successive demodulation. As the detection is coherent in nature and thus involves phase estimation, optimum phase‐coherent combining algorithms, such as predetection maximal ratio combining (MRC), may be used without any added complexity to the receiver. In the current text, utilizing the alternate expressions for integer powers (1≤n≤4) of Gaussian Q function, SEP values of coherent MFSK are obtained through moment generating function (MGF) approach for all the fading models (with or without MRC diversity) described above. The derived end expressions are composed of finite range integrals, which can be numerically computed with ease, dispenses with the need of individual expressions for different M, and gives exact values up to M=5. When the constellation size becomes bigger (M≥6), the same SEP expressions provide a quite realistic approximation, much tighter than the bounds found in previous literatures. Error probabilities are graphically displayed for each fading model with different values of constellation size M, diversity order L, and for corresponding fading parameters (K, q, or m). To validate the proposed approximation method extensive Monte‐Carlo simulations were also performed, which show a close match with the analytical results deduced in the paper. Both these theoretical and simulation results offer valuable insight to assess the efficacy of relatively less studied coherent MFSK in the context of the optimum modulation choice in wireless communication. Copyright © 2010 John Wiley & Sons, Ltd.     

CB125摩托车噪声辐射源识别及控制研究

本文介绍了声强测试的基本原理和声强测试技术在CB25摩托车噪声控制中的应用，利用CF—6400声强测试分析系统对该摩托车进行主要噪声辐射源识别，快速、准确地找到其主要噪声源。通过有针对性地采取降噪措施，使该车行驶噪声显著降低。     

应用于3.3kV IGBT的线性渐变掺杂结终端扩展的设计与优化

本文将线性渐变掺杂结终端扩展（LG-JTE）技术用于3.3kV IGBT并进行了试验验证。和采用多次光刻和离子注入传统结终端扩展技术不同,LG-JTE只用一张注入窗口宽度随与主结的距离线性变化的掩膜版。结合仿真设计了采用LG-JTE的IGBT,并在国内工艺平台上成功流片,其测试耐压达到3.7kV,接近理想的平行平面情形的耐压。     

External cavity tunable quantum cascade lasers and their applications to trace gas monitoring

Since the first quantum cascade laser (QCL) was demonstrated approximately 16 years ago, we have witnessed an explosion of interesting developments in QCL technology and QCL-based trace gas sensors. QCLs operate in the mid-IR region (3-24?μm) and can directly access the rotational vibrational bands of most molecular species and, therefore, are ideally suited for trace gas detection with high specificity and sensitivity. These sensors have applications in a wide range of fields, including environmental monitoring, atmospheric chemistry, medical diagnostics, homeland security, detection of explosive compounds, and industrial process control, to name a few. Tunable external cavity (EC)-QCLs in particular offer narrow linewidths, wide ranges of tunability, and stable power outputs, which open up new possibilities for sensor development. These features allow for the simultaneous detection of multiple species and the study of large molecules, free radicals, ions, and reaction kinetics. In this article, we review the current status of EC-QCLs and sensor developments based on them and speculate on possible future developments.     

Investigation of phase transition behaviors of the nitrogen-doped Sb-rich Si-Sb-Te films for phase-change memory

The phase transformation properties of the nitrogen-doped Sb-rich Si-Sb-Te films were investigated in detail. It was found that the addition of N atoms into the Si-Sb-Te films increases the temperature for phase transition from the amorphous phase to a stable hexagonal structure and enhances the sheet resistance of the films following grain refinement. The surface topography of the crystalline films was improved by doping nitrogen atoms. The activation energy for crystallization of the films was increased from 1.84 to 2.89 eV with the increased nitrogen content from 0 to 21 at.%, which promises an improved thermal stability. A prolonged data lifetime up to 10 years at 149.4 °C was realized. From the device performance point of view, the N-doped Si-Sb-Te film with a moderate nitrogen content was preferable for the phase-change memory applications due to its advantage of higher reliability.     

蒙皮效应在低层轻型钢结构住宅中的应用研究

采用有限元软件SAP 2000,考虑蒙皮效应,对轻钢结构住宅的抗震性能进行模态分析.采用2种不同的方法,即底部剪力法和模态分析法,同时考虑应力蒙皮效应,对某典型实例在地震作用下的反应进行计算,得到了一些结论,包括节点位移、剪力和该类结构的地震反应特点.     

铝蜂窝板在济康住院大楼幕墙工程中的应用

十堰市太和医院济康住院大楼平面造型为梭形,幕墙板设计为弧形,结合大楼对幕墙板的要求和铝蜂窝板的性能特点,经对比分析,最后选择铝蜂窝板作为幕墙板。深入介绍了铝蜂窝板材质、表面处理、外观质量以及其装配和生产、技术装备要求,详细介绍了铝蜂窝板幕墙的安装工艺,总结了主要质量控制措施。实践表明,铝蜂窝板幕墙满足了大楼整体外墙大分块光滑平整、抗风和大尺寸内外对缝的要求,整体效果良好。     

Global sensitivity analysis of unreinforced masonry structure using high dimensional model representation

Sensitivity Analysis (SA) has very important implications in terms of model assessment. It is an important part of reliability studies as well. This paper presents global SA using High Dimensional Model Representation (HDMR) on a mesoscale model of unreinforced masonry shear wall. The mesoscale model contains both geometric as well as material nonlinearity. Prior to performing global SA: (a) mesh sensitivity study in order to determine the optimum mesh size; and (b) experimental validation of the finite element simulation using the data available in the literature, are conducted. The ability of two major variations of HDMR, namely RS (Random Sampling)-HDMR and Cut-HDMR, for conducting global SA is explored, first by solving analytical problem and later by analyzing the mesoscale model of unreinforced shear wall. From the study, recommendations are made to obtain the sensitive parameters of an unreinforced masonry structure with minimal computational effort.     

A limit state design (LSD) approach for comparing relative drying performance of wood-frame envelope systems with full-scale lab testing

The capacity of drying out moisture accumulated within stud cavities, especially moisture due to rain penetration, is an important characteristic affecting the performance and durability of building envelope systems. This paper introduces a new approach for evaluating such drying performance based on the concepts and procedures of Limit State Design (LSD) used in structural engineering. For a well performing envelope, the moisture load must be less than the drying capacity of the system. The drying capacities are obtained through full-scale experiments that utilize moisture loading derived from a moisture source (water tray) placed at the bottom of the stud cavity. In moving out of the cavity, part of the moisture will be absorbed by the materials surrounding the stud cavity. When any part of the wall specimen reaches 20% MC, the cumulative evaporation from the water tray is termed as the ICEA (in-cavity evaporation allowance) of that wall system. The ICEA value is dependent on the envelope configuration and is a good indicator of the drying performance of that wall system. By comparing ICEA values of wall systems with their respective moisture loads, those envelopes having ICEA values higher than the amount of rain penetration calculated from prevailing driving rain and faults in the envelope are deemed to have adequate drying capacity.