烷烃二元混合物导热率的测定与预测

用实验室建立的小型液体导热率测试仪，测定常压下正庚烷－正十二烷和正十一烷－正十六烷两个二元烷烃混合物体系在３１３．１５Ｋ、３３３．１５Ｋ及３５３．１５Ｋ时的导热率数据。另外，还将流体传递性质的ｖａｎｄｅｒＷａｌｓ模型扩展，应用该模型合适的混合规则，对研究的两个烷烃二元混合物体系不同温度下的导热率进行了预测，结果令人满意。     

Accurate higher-order analytical approximate solutions to nonconservative nonlinear oscillators and application to van der Pol damped oscillators

In general, this paper deals with general nonlinear oscillations of a nonconservative and single degree-of-freedom system with odd nonlinearity and, in particular, it presents accurate higher-order analytical approximate solutions to van der Pol damped nonlinear oscillators having odd nonlinearity and the Rayleigh equation. By combining the linearization of the governing equation with harmonic balancing and the method of averaging, we establish accurate analytical approximate solutions for the general weakly damped nonlinear systems. Unlike the classical harmonic balance method, simple linear algebraic equations instead of nonlinear algebraic equations are obtained upon linearization prior to harmonic balancing. The combination of these two methods results in very accurate transient response of the periodic solution. In addition and for the first time, this paper also presents a method for deducing fourth-, fifth- and higher-order linearized governing equations from the lower-order equations without the requirement of formulating the problem from the first principle. Three examples including the van der Pol damped nonlinear oscillator are presented to illustrate the excellent agreement with approximate solution using the exact frequency.     

低温下实际与理想气体状态方程的热物性比较

在现代工程中，有关低温气体热物性的研究已经取得了很大的进展。但是，如环境温度在-100℃～25℃的低温条件下，理想气体状态方程往往就不能满足实际计算的需要，这就需要低温下能较为正确地描述气体热物性的方程。实例计算显示，温度越低，理想气体状态方程的准确性越低，一般在低温下工程上选择范德瓦尔方程进行气体性质的计算。     

基于虚拟样机技术的折叠翼厢式车液压开启系统的仿真研究

折叠翼厢式车是一种新式厢式车,给货物的装卸带来了极大的方便。本文介绍了这种厢式车的基本原理,并运用 UG建立了三维实体模型,然后导入机械动力学仿真软件ADAMS中,建立起液压与机械一体化虚拟样机模型,并进行了动 力学仿真,预见了设计方案的可行性,为物理样机的试制提供了参考。     

Unscharfe Entscheidungshilfen für die Ästung von Waldbäumen

Zusammenfassung Die Entscheidung zur Grünästung in schnellwachsenden Plantagenwäldern beruht weitgehend auf Erfahrungswissen, welches mathematisch relativ schlecht strukturiert ist und in Form einer Regel vorliegt. Es wird ein auf der Theorie unscharfer Mengen beruhendes Verfahren vorgestellt, welches eine mathematische Modellierung des Entscheidungsproblems ermöglicht und über unscharfe Aggregation bei multiattributiver Problemstruktur plausibel zur Ordnung mehrerer Ästungsalternativen genutzt werden kann.     

Influence of liquid meniscus on surface forces

The condensation of water in the gaps between members of microelecromechanical systems and precision friction units is caused by the presence of water vapors in air. The formation of liquid meniscus induces an additional force and affects considerably other surface forces. Numerical simulation was used to determine the meniscus and Van der Waals forces depending on the distance between the bodies in contact. Theoretical dependencies are used when interpreting experimental data obtained with the contact adhesion meter. Different factors that affect surface interaction and the application of the proposed approach to micro-and nanotribology are discussed.     

Dispersive forces of particle–surface interactions: direct AFM measurements and modelling

Fundamentals of particle–particle interaction are of great interest in agglomeration processes. Particle adhesion depends on dispersive forces (van der Waals force), local chemical bindings, Coulomb force and capillary attractions. Additionally, surface properties like roughness, adsorption layers and surface chemistry strongly affect adhesion forces. van der Waals interactions are poorly understood because popular ab initio force calculations for molecules like density functional theory (DFT) often do not lead to proper results. van der Waals forces are difficult to measure directly. We present direct measurements of particle–particle and particle–surface interactions in the gas phase carried out with an atomic force microscope (AFM). Special emphasis is given to a proper statistical treatment of the data. For modelling of particle adhesion, we use computer-assisted empirical potential methods. Parameters like adsorbed water and surface roughness are considered. We extract parameters for weak interactions from the Lifshitz theory and gas adsorption data. Adsorbing molecules can be used as probes to measure dispersive forces. Studying surface and particle properties combined with computer-assisted modelling is a basic requisite to reach the aim of predicting particle–particle interactions in industrial processes.     

High resistivity measurement of SiC wafers using different techniques

To establish fast, nondestructive, and inexpensive methods for resistivity measurements of SiC wafers, different resistivity-measurement techniques were tested for characterization of semi-insulating SiC wafers, namely, the four-point probe method with removable graphite contacts, the van der Pauw method with annealed metal and diffused contacts, the current-voltage (I-V) technique, and the contactless resistivity-measurement method. Comparison of different techniques is presented. The resistivity values of the semi-insulating SiC wafer measured using different techniques agree fairly well. As a result, application of removable graphite contacts is proposed for fast and nondestructive resistivity measurement of SiC wafers using the four-point probe method. High-temperature van der Pauw and room-temperature Hall characterization for the tested semi-insulating SiC wafer was also obtained and reported in this work.     

数字转播车的维护调整与改造

电视转播车是电视台制作节目的重要设备,搞好数字转播车的维护调整和设备的更新改造,不仅能减少投入,而且可持久地为录制高质量的节目提供强有力的保障.从车体和技术系统两大方面讲述数字摄像机的调整与维护.     

微区电阻测试方法及新测试仪研制

文章对国内外开展微区薄层电阻测试的方法进行了综述，特别对改进范德堡四探针技术方法的测试原理、测试过程与测试结果进行了论述与分析，对微区电阻测试方法的进一步发展提出了一种可操作的方法，并研制出新型四探针测试样机。