Discrete element crowd model for pedestrian evacuation through an exit

A series of accidents caused by crowds within the last decades evoked a lot of scientific interest in modeling the movement of pedestrian crowds. Based on the discrete element method, a granular dynamic model, in which the human body is simplified as a self-driven sphere, is proposed to simulate the characteristics of crowd flow through an exit. In this model, the repulsive force among people is considered to have an anisotropic feature, and the physical contact force due to body deformation is quantified by the Hertz contact model. The movement of the human body is simulated by applying the second Newton's law. The crowd flow through an exit at different desired velocities is studied and simulation results indicated that crowd flow exhibits three distinct states, i.e., smooth state, transition state and phase separation state. In the simulation, the clogging phenomenon occurs more easily when the desired velocity is high and the exit may as a result be totally blocked at a desired velocity of 1.6 m/s or above, leading to faster-to-frozen effect.     

Contact resistance asymmetry of amorphous indium–gallium–zinc–oxide thin-film transistors by scanning Kelvin probe microscopy

In this work, a method based on scanning Kelvin probe microscopy is proposed to separately extract source/drain(S/D) series resistance in operating amorphous indium–gallium–zinc–oxide(a-IGZO) thin-film transistors. The asymmetry behavior of S/D contact resistance is deduced and the underlying physics is discussed. The present results suggest that the asymmetry of S/D contact resistance is caused by the difference in bias conditions of the Schottky-like junction at the contact interface induced by the parasitic reaction between contact metal and a-IGZO. The overall contact resistance should be determined by both the bulk channel resistance of the contact region and the interface properties of the metalsemiconductor junction.     

Mechanism of contact angle saturation and an energy-based model for electrowetting

Electrowetting, as a well-known approach to increasing droplet wettability on a solid surface by electrical bias, has broad applications. However, it is limited by contact angle saturation at large voltage. Although several debated hypotheses have been proposed to describe it, the physical origin of contact angle saturation still remains obscure. In this work, the physical factors responsible for the onset of contact angle saturation are explored, and the correlated theoretical models are established to characterize electrowetting behavior. Combination of the proper 3-phase system employed succeeds in dropping the saturating contact angle below 25°, and validates that the contact angle saturation is not a result of device-related imperfection.     

Normalization of the stress concentrations at the rounded edges of an interference fit between a solid shaft subjected to bending and a hub

The elastic stress concentrations are addressed that are developed from the keyless frictionless press fit of a shaft subjected to bending into a hub with rounded bore edges. Derived from a formal modeling of the title problem in terms of an integral equation, a set of normalized parameters is proposed that accounts for the combined effects on the hub stress concentration of the fillet radius, the shaft radius, the hub outer radius, the hub axial length, the interference, the Young's modulus, and the bending couple. A numerical validation of the normalized parameters is presented. With the aid of Finite Elements, various design charts are compiled that (a) forecast the bending couple initiating the detachment between the shaft and the hub, and (b) report the elastic stress concentrations within the hub versus the proposed normalized parameters in the absence of shaft–hub detachment. Such charts assist the designer in dimensioning an interference fit in the presence of a bending couple.     

水中钢板爆破水介质对装药量的影响

为分析水介质对水中钢板爆破装药量的影响,理论推导了钢板背衬水介质条件下,钢板爆破最小装药量与空气中钢板爆破最小装药量的倍数关系:最小倍数关系为3.76。数值计算了钢板背衬空气介质和背衬水介质情形下钢板爆破的最小装药量,其倍数关系在3.5左右,与理论结果相近,表明钢板背衬水介质或空气介质是决定装药量大小的关键因素。数值计算了装药在空气介质中及水介质中钢板爆破爆轰产物对钢板的冲量大小,结果接近,表明水介质对炸药爆轰产物的约束作用是影响水中钢板装药量的次要因素。     

基于FEM和RSM的深穴圆柱滚子优化设计

为消除圆柱滚子端部的应力集中现象,提高滚动轴承的疲劳寿命,对圆柱滚子内修形-深穴结构的形状控制参数(深穴开口度k、深穴长度l、深穴锥角α)进行了分析,建立了滚子接触有限元(FEM)模型。基于响应曲面法(RSM),建立了以滚子端部与中间接触应力差最小为优化目标,以k,l和α为设计变量的优化数学模型,并对响应面模型进行了求解,得到一组最优解,通过对比分析表明深穴滚子可以有效地降低滚子端部的应力集中现象,优化后深穴滚子应力分布更为均匀,避免了因局部应力过大而过早发生疲劳失效;采用FEM与RSM相结合的优化方法操作简单、效率高,可将其应用于其他机械零部件的优化设计。     

Cd基化合物纳米晶-有机聚合物杂化太阳能电池研究进展

有机-无机杂化太阳能电池因其结合了有机材料和无机材料各自的优势而引起了人们的广泛关注和研究. Cd基化合物纳米晶因其具有制备方法简单、尺寸及形貌可控、载流子迁移率高和稳定性好等优点而成为最早被研究的一类无机受体. 本文介绍了有机-无机杂化太阳能电池的结构及原理, 分析了影响有机-无机杂化太阳能电池效率的三个主要因素, 分别是开路电压(V_oc)、短路电流(J_sc)和填充因子(FF). 从改善Cd基化合物纳米晶的合成方法, 增加Cd基化合物纳米晶和有机聚合物间的界面接触, 以及优化Cd基化合物纳米晶和有机聚合物所用溶剂和所占比例等方面阐述了近年来Cd基化合物纳米晶-有机聚合物杂化太阳能电池的研究进展. 并展望了Cd基化合物纳米晶-有机聚合物杂化太阳能电池的发展方向.     

原子力显微技术研究ZnO纳米棒的压电放电特性

在原子力显微镜的接触扫描模式下,研究了半导体ZnO纳米棒的压电放电特性.采用两步湿化学法制备沿c轴择优生长的ZnO纳米棒阵列;利用镀Pt探针接触扫描ZnO纳米棒获得峰值达120 pA电流脉冲,脉冲持续时间可达30 ms,电流脉冲与纳米棒的形貌存在对应关系.镀Pt探针与ZnO纳米棒接触形成肖特基二极管,I-V特性研究表明放电的ZnO纳米棒压电电势必须大于03 V,以驱动肖特基二极管并输出电流;放电时肖特基二极管的结电阻达吉欧(GΩ)量级,是影响压电电势输出的主要因 关键词： ZnO 纳米棒 压电放电 肖特基接触     

熔石英亚表面三维Hertz锥形划痕附近光强分布的数值模拟

熔石英亚表面划痕对入射激光的调制是导致光学材料损伤的主要因素.本文建立了熔石英后表面上三维Hertz锥形划痕模型,采用三维时域有限差分方法对划痕周围的电场强度进行了计算模拟,并分别讨论了划痕的深度、半径以及倾斜角度对入射光场调制作用的影响.结果表明：Hertz锥形划痕中心区域的电场增强效果最明显,最容易被辐照损伤;划痕的深度从λ变化到9.5λ的过程中,熔石英内的最大电场强度逐渐增大;半径小于15λ的Hertz锥形划痕较容易引起熔石英的损伤,当半径大于175λ时,熔石英内的最大电场强度都维持在2.5 V/m,不再受半径大小影响;当入射激光在划痕的内侧界面和熔石英后表面之间发生内全反射时,光场增强效果愈加明显. 关键词： 三维时域有限差分 Hertz锥形划痕 电场分布 数值模拟     

组合材料方法研究膜厚对Ni/SiC电极接触性质的影响

采用组合材料方法研究了金属Ni膜厚对Ni/SiC接触性质的影响.16个膜厚均为18 nm的Ni/SiC电极具有较为一致的肖特基接触性质;膜厚从10 nm增加到160 nm,肖特基接触的电流-电压（I-V）曲线随膜厚发生显著变化.分析表明这种变化源于膜厚对理想因子n和有效势垒高度Ф_B的影响.1000℃快速退火后,这些肖特基接触都转变为欧姆接触,Ni₂Si是主要的生成物.I-V曲线测 关键词： 碳化硅 肖特基接触 欧姆接触 组合材料方法