An experimental study on convective heat transfer performance of steam and air flow in V-shaped rib roughened channels

An experimental study on heat transfer characteristics of steam and air flows in a V-shaped ribbed channels was conducted. The effects of Reynolds numbers and rib angles on heat transfer of steam and air were obtained. The area-averaged Nusselt numbers of steam flow at a Reynolds number of 12,000 were 13.9%, 20.6%, 27.1%, and 27.9% higher than those of air flow for rib angles of 90°, 75°, 60°, and 45°, respectively. The correlations for Nusselt number in terms of Reynolds number and rib angle for steam and air in V-shaped ribbed channels were developed.     

自发极化强度对VFLC电光迟滞曲线影响的电路级模拟

提出了关于V字型铁电液晶(V-shaped Ferroelectric Liquid Crystal,VFLC)的等效电路模型,旨在将EDA技术引入对VFLC光电集成系统进行研究、开发和设计。该模型考虑了由铁电液晶盒多层结构和驱动电路引起的阻抗分配效应,以及极化与非极化锚定能对VFLC光电响应特性的影响。演示了电光迟滞曲线的反常迟滞、V字型及正常迟滞状态,并着重就自发极化强度对电光迟滞曲线的影响给出了模拟结果和分析。结果表明:强制电压随驱动信号频率的提高而增加,但增加速度随自发极化强度的提高而减慢;强制电压和迟滞反转频率随自发极化强度的变化均存在一个拐点,强制电压在自发极化强度为80nC/cm2时取到最小值(-0.084V),迟滞反转频率在自发极化强度为90nC/cm2时达到最大值(6.4Hz);自发极化强度小于80nC/cm2时,迟滞反转频率随自发极化强度准线性增加。模拟结果从量级和趋势上均与实验结果吻合。     

Stop band characteristics of a TESLA cavity coaxial-type HOM coupler

A TTF-type coaxial higher order modes (HOM) coupler has been used in a TESLA 9 cell cavity. It is impossible to measure the stop band characteristics of the HOM coupler with the cavity. A measurement device for the coaxial transmission line type for the HOM coupler has been designed at Peking University. Experimentally it was shown that the average voltage standing wave ratio of the coaxial transmission line is smaller than 1.08. The experimental results of the stop band characteristics of the TTF-type HOM coupler have been fitted for the simulation. This paper describes the design of the measurement device and discusses the experimental and simulation results of stop band characteristics of the HOM coupler.     

数字信号处理器红外弱小目标搜索算法

提出了一种基于数字信号处理器（DSP）的红外弱小目标搜索高速实时算法。算法主要针对天空中不规则云团在预处理过程中残留的边缘而设计,是在背景预测算法基础上改进的一种基于陷波滤波器的搜索算法。在DSP实时处理平台上实现并经实际场景试验验证,该算法能有效削弱残留边缘的影响,使最远探测距离指标上升至前向迎头26 km,实时处理速度达到75 Hz,满足系统要求。采用信噪比增益指标对算法进行了评价,结果显示,该算法能够显著提高图像信噪比,利于检测出目标。     

Study on a W-band modified V-shaped microstrip meander-line traveling-wave tube

The study on a miniaturized,low-voltage,wide-bandwidth,high-efficiency modified V-shaped microstrip meanderline slow-wave structure is presented.This structure is evolved from the original U-shaped microstrip meander-line slowwave structure,combining the advantages of a traditional microstrip and a rectangular helix.In this paper,simulations of the electromagnetic characteristics and the beam-wave interaction of this structure are carried out.Our study shows that when the design voltage and the current of a sheet electron beam are set to be 4700 V and 100 mA,respectively,this miniature millimeter-wave power amplifier is capable of delivering 160-W output power with a corresponding gain of 37.3 dB and a maximum interaction efficiency of 34% at 97 GHz.     

压电切口张开角和深度对其尖端力电损伤场的影响

基于三维各向异性压电损伤本构理论,导出了广义平面应力问题的损伤本构方程,并据此分析了压电薄板板边V形切口尖端附近的力电损伤,研究了切口张开角和深度对切口尖端力电损伤的影响规律．结果发现：和张开角对切口尖端损伤的影响相比,深度的影响更为明显;在张开角对切口尖端力损伤的影响规律方面,压电材料与一般弹塑性材料存在明显差异,原因在于压电切口尖端力电载荷比会随着深度的改变发生很大变化;不同深度下张开角与切口尖端力、电损伤关系曲线随着张开角的增大由发散逐渐会聚,不同张开角下深度与切口尖端力、电损伤关系曲线随着切口加深由会聚逐渐发散,并且电损伤曲线表现得更为明显．     

Construction of a 2D Cd（II） Coordination Polymer Based on a V-shaped Bidentate Ligand

A two-dimensional（2D）coordination polymer{[Cd（bdc）（dpb）]·H2O}n（1）has been prepared by solvothermal reaction of 1,3-dipyridyl benzene（1,3-dpb）with deprotonated1,4-benzenedicarboxylate（H2bdc）,and was characterized by elemental analysis,IR spectroscopy,and X-ray single-crystal diffraction.It crystallizes in the monoclinic system,space group C2/c with a=15.1839（12）,b=20.7585（17）,c=7.2989（6）,β=117.3450（10）°,V=2043.5（3）3,C24H18N2O5Cd,Mr=526.81,Dc=1.712 g/cm3,F（000）=1056.0,μ=1.110 mm-1and Z=4.The neighboring Cd（II）ions link the bdc2-anions and 1,3-dpb to form an infinite 2D sheet,and such two2D sheets are interlocked with each other to form a 2D→2D sheet.Two groups of interlocked sheets are further linked together by intermolecularπ···πinteraction,giving a 3D supramolecular network.In addition,the fluorescence property of 1 was also studied.     

用多凹槽滤波器控制混沌系统

提出了一种施加多个凹槽滤波器反馈控制混沌系统的方法,使混沌运动转化为规则的运动.多凹槽滤波器控制是一种具有固定参数的线性反馈控制方法,它不影响原系统的参数,截断了系统从倍周期分叉通向混沌的道路.同时,用Melnikov方法进行理论分析,给出了合适的反馈控制器的参数.将多凹槽滤波器应用于典型的混沌系统,其仿真结果表明了该控制方法的有效性与可行性 关键词： 混沌 多凹槽滤波器 Melnikov方法     

基于ANSYS的缺口和裂纹对结构应力分布影响有限元研究

缺口和裂纹都会对结构的应力分布产生影响，过去对这两个领域的研究一直平行发展，交叉领域的研究比较少。本文应用有限元软件ANSYS，分析了金属材料中缺口根部和裂纹尖端的应力分布。有限元计算结果与Taylor^[1]的理论分析一致，即在缺口和裂纹根部存在一临界距离，大于这一临界距离时，缺口和裂纹具有类似的应力值，并都易受尺寸因素的影响；临界距离内的应力与最大应力之比只同缺口半径有关，而与结构绝对尺寸无关。文中并对缺口和裂纹交叉领域以后的研究方向提出了看法。