CFD modeling of thermal contact resistance between solid contacting surfaces

Heat transfer has considerable applications in different industries such as designing of heat exchanger, nuclear reactor cooling, control system for spacecraft, and designing of microelectronics cooling. As the surfaces of two metals contact each other, this issue becomes so crucial. Thermal contact resistance (TCR) is one of the key physical parameters in heat transfer of mentioned surfaces. Measuring the experimental value of TCR in laboratory is highly expensive and difficult. As an alternative, numerical modeling methods could be engaged. In this study, inverse problem method solution is utilized as a proper method for estimation of TCR value. In this order, three different configurations (flat-flat, flat-cylinder, and cylinder-cylinder) were utilized in two steady and unsteady state conditions to predict the value of TCR. A comparison between the measured values and obtained values from the simulation show the errors for flat-flat, flat-cylinder, and cylinder-cylinder configuration after 10 min from starting the experiment are 4.6074%, 0.1662%, and 0.5622%, respectively. And in steady-state condition, the corresponding errors are 6.06e-3%, 1.506%, and 0.846%, respectively. In conclusion, the final results establish the fact that the inverse problem method solution can predict TCR values between contacting surfaces.     

场效应管设计

本文概述了场效应管的分类和设计。设计按常规程序考虑，特殊的ＭＯＳ管还要考虑相关许多其它因素，以及理论与实践结合后的取舍。     

矩形波导窄边倾斜缝隙天线阵的设计

介绍了一种矩形波导窄边斜缝泰勒线阵设计的方法.简要阐述了矩形波导窄边缝隙天线阵列的相关理论,并使用HFSS软件对单个缝隙结构,无限阵列环境下缝隙单元的导纳参数进行数值仿真.然后按照仿真获得的等效谐振电导曲线,运用泰勒线元法综合求出非谐振式48元波导窄边缝隙线阵,并对整个线阵进行了仿真和实测.仿真和实测结果表明,该天线阵列具有低副瓣、宽带宽、高增益等特点,并且实测结果与仿真吻合良好.     

Negative differential perpendicular velocity in GaAs/AlAs superlattices

We investigate the doping level, hydrostatic pressure, temperature and superlattice parameter dependence of the perpendicular negative differential velocity (NDV) of GaAs/AlAs superlattices. The results show that NDV is a single Γ miniband effect. A qualitative agreement is found with Esaki's negative effective mass model, although a few limitations of this model are pointed out and some improvement is suggested.     

光伏并网系统MPPT控制和实现方法的研究

太阳能电池阵列输出特性具有强烈的非线性,为了提高系统的整体效率,一个重要的途径就是实时调整光伏电池的工作点,进行最大功率点跟踪（maximum power pointtracker,MPPT）,使之始终工作在最大功率点附近。最大功率点跟踪方法是一个提高光伏组件效率的很有效的方法。     

一种改进的太阳能电池MPPT技术

为了寻找一种能更好的实现太阳能电池最大功率点跟踪的方法,文中分析了太阳能电池的数学模型和在外部环境(温度、光照强度)变化的情况下太阳能电池的输出特性。介绍了太阳能电池最大功率点跟踪技术的原理,并提出了一种自适应变步长的方法,克服了传统固定步长方法的不足。仿真结果表明,该方法能够较快地跟踪光伏极板的最大功率点,使太阳能电池工作在最大功率点。     

硅酸盐水泥导电性能的研究

通过一系列实验对影响普通水泥和粉煤灰水泥导电性能的主要因素进行了探讨。结果表明:在相同条件下,粉煤灰水泥的导电性能优于普通水泥,。在水泥中掺入一定量的石墨和金属可显著提高其导电性能。所得结果具有一定的实用意义.     

Investigation of local viscosity in polymer solutions by means of electrolytic conductivity

The local viscosity in aqueous solutions of polymers (dextran and hydroxyethl cellulose) and low-molecular weight viscogenic compounds (glycerol and d-glucose) has been studied by measuring the electrolytic conductivity of probe electrolytes. For low-molecular weight viscogenic compounds the local viscosities determined were close to the macroscopic viscosities of the solutions, whereas pronounced differences exist for polymer solutions. Of particular interest was the finding that the local viscosity for dextran was only marginally higher than the local viscosity for the corresponding monomer, d-glucose. The local viscosity for hydroxyethyl cellulose was somewhat higher than the local viscosity for dextran, indicating greater flexibility of the dextran chain.     

基于MATLAB的河道糙率计算

小麦叶片细胞间隙CO2浓度Cint全天最高值出现在早上,其日变化曲线呈"　　"型。Cint日变化在9:00后,大致呈现随施氮量增加而下降的趋势。在午前,低水处理Cint日变化较高水处理要高,午后则下降到较低的位置。各处理Cint时段变化随施氮量增加而下降,土壤水胁迫处理Cint各时期最低。小麦叶片气孔导度(Gs)在中午达到峰值,其日变化呈现"W"字型。4月20日Gs最高。Gs日变化随施氮量的增加而下降;低水叶片Gs在上午相对较高,下午则相反。Gs时段变化,低氮处理相对较高,高水与胁迫处理Gs较其它处理显著降低。