Turbid Density Currents in Reservoirs

ABSTRACT

Physical features of turbid density currents in reservoirs are touched on in the first part of this paper: the plunging of the muddy fluid, the unsteadiness of the density current, the characteristics of velocity and concentration of density currents, the density current over a submerged dam and the submerged muddy lake formed by the density current upstream from the dam site.

Besides the conditions for formation of density currents, the condition for maintenance of a density current that may vent sediment from a reservoir is discussed. The outflow silt discharge by a vented density current, calculated by a suggested approximate method, agrees fairly well, on the average, with measured values in the Guanting Reservoir and Lake Mead.     

智能电网发展技术的研究

随着经济以及科学技术的发展,我国的电网也由传统电网向智能化电网的方向转变,客观上对电网工作人员的专业技术提出了更高的要求,笔者系统地分析了智能电网的主要特点,并就其中关键的技术要点与功能做出了简要的探究,以供同行参考,共同促进我国智能电网的发展进步。     

基于火焰检测系统的火焰信息与燃煤特性关联性实测研究

利用自研的火焰检测系统针对电站锅炉在燃用不同煤种时的炉膛火焰进行了检测,并对火焰图像进行数字图像处理得到表征火焰信息的特征参数,分析了特征参数与燃煤特性之间的关联性.结果表明,煤种的不同与其燃烧火焰图像之间存在一定相关性,从而可以借助于火焰信息来识别煤种,进而为燃烧调整提供帮助.     

建筑形状比对办公建筑冷(热)负荷的影响分析

基于DeST软件,利用正交试验法对办公建筑室内的冷负荷影响因素进行了分析,得出室内冷(热)负荷随着形状比变化的曲线,并应用曲线分析负荷变化趋势,找出冷(热)负荷随着形状比变化的具体关系式,可依此确定最佳建筑节能形式的方案。     

车用柴油机排气消声器的改进设计研究

本文采用传递矩阵法,基于MATLAB软件编制程序模拟计算原消声器的插入损失,通过试验证明计算模型的正确性,且结合试验测试YC4W31柴油机排气噪声频谱图得知,欲要匹配的排气消声器在100～500Hz范围内仍有较大噪声,进而通过建立模型对此提出了两种改进方案,通过模拟计算比较表明改进方案2有较好的效果.     

SaaS技术的发展和演进

分别从表现层、接口层和应用实现层分析SaaS,可以看到SaaS是一种业务模式、一种接口要求和一种软件能力;分析了电信运营商与SaaS的关联,明确了SaaS的发展方向和演进目标,以实现SaaS模式的成功。     

Mobile Vehicle-to-Vehicle Narrow-Band Channel Measurement and Characterization of the 5.9 GHz Dedicated Short Range Communication (DSRC) Frequency Band

This study presents narrow-band measurements of the mobile vehicle-to-vehicle propagation channel at 5.9 GHz, under realistic suburban driving conditions in Pittsburgh, Pennsylvania. Our system includes differential Global Positioning System (DGPS) receivers, thereby enabling dynamic measurements of how large-scale path loss, Doppler spectrum, and coherence time depend on vehicle location and separation. A Nakagami distribution is used for describing the fading statistics. The speed-separation diagram is introduced as a new tool for analyzing and understanding the vehicle-to-vehicle propagation environment. We show that this diagram can be used to model and predict channel Doppler spread and coherence time using vehicle speed and separation.     

Cooperative and opportunistic transmission for wireless ad hoc networks

Moving toward 4G, wireless ad hoc networks receive growing interest due to users' provisioning of mobility, usability of services, and seamless communications. In ad hoc networks fading environments provide the opportunity to exploit variations in channel conditions, and transmit to the user with the currently "best" channel. In this article two types of opportunistic transmission, which leverage time diversity and multi-user diversity, respectively, are studied. Considering the co-channel interference and lack of a central controller in ad hoc networks, the "cooperative and opportunistic transmission" concept is promoted. For opportunistic transmission that exploits time diversity, it is observed that the inequality in channel contention due to the hidden terminal phenomenon tends to result in energy inefficiency. Under this design philosophy, we propose a distributed cooperative rate adaptation (CRA) scheme to reduce overall system power consumption. Taking advantage of the time-varying channel among different users/receivers and being aware of the potential contention among neighboring transmissions, we propose a QoS-aware cooperative and opportunistic scheduling (COS) scheme to improve system performance while satisfying QoS requirements of individual flows. Simulation results show that by leveraging node cooperation, our proposed schemes, CRA and COS, achieve higher network throughput and provide better QoS support than existing work     

Extended Tunability in a Two-Chip VECSEL

We demonstrate a widely tunable vertical-external-cavity surface-emitting laser (VECSEL) with a W-shaped cavity, in which two VECSEL chips serve as fold mirrors and a birefringent filter is inserted at Brewster's angle. These two chips provide much higher modal gain and broader bandwidth of the gain than a single chip does, enhancing the VECSEL tuning range and reducing the variation of tunable output power with the tuned wavelength. This two-chip VECSEL configuration makes it possible to shape the modal gain spectra of the laser or to manipulate the tuning curve of the laser by two different chips with certain gain peak detuning (offset). Multiwatts high-brightness linearly polarized output with a tuning range of 33 nm is demonstrated in such a two-chip VECSEL     

Equilateral-Triangle-Resonator Injection Lasers With Directional Emission

Equilateral-triangle-resonator (ETR) lasers with an output waveguide jointed at one vertex of the resonator are fabricated on (100) GaInAsP-InP wafers using photolithography and a two-step inductively coupled plasma (ICP) etching technique. Distinct peaks with the mode spacing of longitudinal mode intervals are observed in the luminescence spectra at room temperature. Furthermore, some minor peaks appear in the middle of the main peaks, which can be attributed to the first-order transverse modes as predicted in the theoretical results. CW directional lasing emissions are achieved for ETR lasers with side lengths ranging from 15 to 30 mum up to 200 K. The temperature dependences of the threshold current and lasing wavelength are measured for an ETR laser with the side length of 20 mum from 80 to 200 K. The observed threshold current rapidly increases as temperature increases over 170 K