A new approach to the evaluation of Casimir and van der Waals forces in the transition region

This paper studies the incorporation of Casimir and van der Waals forces applied to a nanostructure with parallel configuration. The focus of this study is in a transition region in which Casimir force gradually transforms into van der Waals force. It is proposed that in the transition region, a proportion of both Casimir and van der Waals forces, as the interacting nanoscale forces, can be considered based on the separation distance between upper structure and substrate during deflection. Moreover, as the separation distance descends during deflection, the nanoscale forces could transform from Casimir to a proportion of both Casimir and van der Waals forces and so as to van der Waals. This is also extended to the entire surface of the nanostructure in such a way that any point of the structure may be subjected to Casimir, van der Waals or a proportion of both of them about its separation distance from the substrate. Therefore, a mathematical model is presented which calculate the incorporation of Casimir and van der Waals forces considering transition region and their own domination area. The mechanical behavior of a circular nano-plate has been investigated as a case study to illustrate how different approaches to nanoscale forces lead to different results. For this purpose, the pull-in phenomena and frequency response in terms of magnitude have been studied based on Eringen nonlocal elasticity theory. The results are presented using different values of the nonlocal parameter and indicated in comparison with those of the classical theory. These results also amplify the idea of studying the mechanical behavior of nanostructures using the nonlocal elasticity theory.     

A facile and efficient dry transfer technique for two-dimensional Van der Waals heterostructure

Two-dimensional(2D) Van der Waals heterostructures have aroused extensive concerns in recent years. Their fabrication calls for facile and efficient transfer techniques for achieving well-defined structures. In this work, we report a simple and effective dry transfer method to fabricate 2D heterostructures with a clean interface. Using Propylene Carbonate(PC)films as stamps, we are able to pick up various 2D materials flakes from the substrates and unload them to the receiving substrates at an elevated temperature. Various multilayer heterostructures with ultra-clean interfaces were fabricated by this technique. Furthermore, the 2D materials can be pre-patterned before transfer so as to fabricate desired device structures,demonstrating a facile way to promote the development of 2D heterostructures.     

动力学压缩真空中的Van der Waals力

基于参数动力学过程产生的压缩效应,利用Millonni源理论方法研究了 动力学压缩真空中Van der Waals力的性质及其与真空压缩的关系。所得结果表明：Van der Waals力的性质依赖于真空压缩的程度;在一定的临界条件下,Van der Waals力由通常的 吸引性作用转化为排斥性作用。当压缩系数为零时,所得结果与通常文献完全一致。     

MOCVD生长GaN:Si单晶膜的研究

获得高质量的ｎ型ＧａＮ单晶膜是制作ＧａＮ基光电子器件的关键之一。采用立式ＭＯＣＶＤ系统生长ＧａＮ：Ｓｉ单晶膜,通过优化生长工艺,获得了电子载流于浓度高达２ ×１０１９ｃｍ－３,迁移率达１２０ｃｍ２／Ｖ·ｓ的ｎ型ＧａＮ：Ｓｉ单晶膜;并有效地抑制了ＧａＮ中由深能级引起的黄带发射,大大提高带边发光强度。研究结果还表明：随着Ｓ掺杂量的增大,ＧａＮ：Ｓｉ单晶膜的电子载流于浓度增加,迁移率下降,Ｘ光双晶衍射峰半高宽增大。首次报道了随掺Ｓ量增大,ＧａＮ：Ｓｉ单晶膜的生长速率显著下降的现象。     

The Van Vleck formula,Maslov theory,and phase space geometry

The Van Vleck formula is an approximate, semiclassical expression for the quantum propagator. It is the starting point for the derivation of the Gutzwiller trace formula, and through this, a variety of other expansions representing eigenvalues, wave functions, and matrix elements in terms of classical periodic orbits. These are currently among the best and most promising theoretical tools for understanding the asymptotic behavior of quantum systems whose classical analogs are chaotic. Nevertheless, there are currently several questions remaining about the meaning and validity of the Van Vleck formula, such as those involving its behavior for long times. This article surveys an important aspect of the Van Vleck formula, namely, the relationship between it and phase space geometry, as revealed by Maslov's theory of wave asymptotics. The geometrical constructions involved are developed with a minimum of mathematical formalism.     

关于Van der Corput不等式

本文给出Van der Corput一个不等式的改进:设 ,则我们有: 其中γ为Euler常数.若我们以(n+1)代替(A)中右边 ,则(A)为Van der Corput不等式,(A)的证明仍然用Van der Corput的方法。     

范德波尔振子方程的格林函数解

应用传播子方法，求解福克－普朗克方程。应用局域谐振子势近似，计算格林函数。计算范德波尔振子方程的瞬态解。     

Prediction of ultrasonic velocity and intermolecular free-length and their correlation with interaction in binary liquid mixtures

The ultrasonic velocities of binary liquid mixtures of 1,1,2,2-tetrachloroethane with benzene, toluene,p-xylene, acetone and cyclohexane have been evaluated at 298.15 and 308.15 K using Schaaff’s collision factor theory (CFT), Jacobson’s free length theory (FLT), Nomoto’s relation and Van Dael ideal mixing relation. The ideal mixing relation gives the minimum deviation for all the systems except with acetone. The intermolecular free length has also been evaluated using ultrasonic and thermodynamic methods and the limitations of both the methods have been discussed. The deviations in ultrasonic velocity and intermolecular free length are discussed in terms of weak interaction between unlike molecules.     

Influence of Van der Waals' volume of ethers,esters, carbonyls and alcohols on retention in gas chromatography stationary phases of different polyrity

Summary Equations for Retention Index (I) versus Van der Waals, volume (V_w) on squalane are studied for alcohols, carbonyls, esters and ethers. Each equation includes linear and branching substances with different positions of the functional group in the carbon chain. The study is extended to stationary phases with polarities from 4.29 to 91.54 on the Tarjan et al. scale. Variations of the slope and origin ordinate values with the polarity of the stationary phase are discussed.