金属Al表面熔化各向异性的分子动力学模拟

采用嵌入原子势,使用分子动力学方法对金属Al不同低指数晶面的表面熔化现象分别进行了模拟.分析了熔化过程中样品结构组态的变化.模拟结果表明对于不同的自由表面,表面熔化呈现出明显的各向异性行为.Al（110）面在低于熔点的温度之下发生预熔化;（111）与（001）面都出现过热现象.与（111）面不同,（001）面发生过热现象时表面原子层为类液层,而（111）面仍然保持很好的晶格结构,即预熔化的Al（001）面在高于熔点的温度下,仍可以在很长的时间内处于相对稳定的亚稳态.由模拟得到Al的热力学熔点为950 K左右,与实验值基本符合. 关键词： 分子动力学 表面熔化 过热     

Carnot-Caratheodory空间中的变换论

Klein发表著名的埃尔兰根纲领,由群论角度研究了空间变换群的不变量,从而引进了各种不同的几何学．本文利用Felix Klein的观念,研究Carnot-Caratheodory空间{M,Q,g}(又称为次黎曼流形)上的类似问题,给出了次黎曼流形中的共形不变量和射影不变量．本文给出的共形和射影不变量可视为黎曼情形的一种自然推广．由于次黎曼流形与黎曼流形之间有着本质的差异,故此,本文通过次黎曼流形上存在的唯一非完整联络(Nonholonomic connections)来刻画所提的问题．     

枸橼酸铋制剂中铋元素的溶出量分析

微波消解溶样，ICP—AES法测定了枸橼酸铋制剂中铋元素的含量及其在人工胃液和人工肠液中的溶出量。结果表明，枸橼酸铋制剂中的铋元素在人工肠液中的溶出量明显高于人工胃液。方法的检出限为12ng／mL，相对标准偏差(n=7)为3．84％。     

逆向思维巧应用--匀变速直线运动实例

匀变速直线运动是一种常见而又重要的运动,它分为匀加速和匀减速运动两类,而这两类运动又存在互为可逆的规律,对其逆向思维,在处理某些问题时十分方便. 例如 正过程:坡顶上以10m/s的初速度匀加速行驶的汽车,下坡时获得0.2m/s2加速度,经10s钟汽车正好行至坡底,求汽车到达坡底速度和坡路长.     

数值模拟辐射驱动2维内爆压缩过程

采用2维三温非平衡辐射流体力学程序LARED-H数值模拟辐射驱动内爆过程。针对2维三温能量方程九点差分格式离散后的线性方程组,采用了高效的Krysolv子空间迭代解法,改进了代数解法器。将1维间接驱动内爆总体程序CFJ与LARED-H程序的计算结果进行比对,验证了LARED-H程序数值模拟1维内爆问题的正确性。并数值模拟了不同腔长辐射温度源驱动下的2维靶球运动,数值结果显示：随着腔长的增加,高压缩内爆燃料区分别被压缩成香肠形、球形和铁饼形,数值模拟结果与神光Ⅱ的实验结果定性上相同。     

Improvement of photoluminescence mechanism of CTA-treated Si-implanted SiO2 films by using RTA

In this paper, a shift in the photoluminescence (PL) peak from blue to near-infrared region was observed in the Si⁺-implanted 400-nm-thick SiO₂ films with the rapid thermal annealing (RTA) method only. As the Si⁺-fluence was 1×10¹⁶ ions/cm², a blue band was observed in the films after RTA at 1050 °C for 5 s in dry-N₂ atmosphere; then, the band shifted from blue to orange upon increasing the holding temperature of RTA to 1250 °C in the films after the isochronal RTA in dry N₂. Furthermore, while the fluence was increased to 3×110¹⁶ ions/cm² and the holding temperature was at the same range between 1050 and 1250 °C, the PL peak occurred between red and near-infrared regions. Although the RTA and conventional thermal annealing (CTA) methods produce a similar mechanism, the CTA method needs a much longer annealing-time and a higher Si⁺-implanted dose than the RTA method for producing the same shift and intensity of PL peak from the as-implanted sample. Therefore, the RTA method can produce the mechanism in the Si⁺-implanted sample with the PL energy between blue and near-infrared band in place of the CTA method.     

Simulation of current spreading for GaN-based light-emitting diodes

Uniform current spreading is crucial for the performance of light-emitting diodes (LEDs). It has been reported that the reliability and light distribution are affected by non-uniform current spreading. In this paper, the impact of different electrode patterns on the performance of LED chips is investigated. A hybrid modeling method is employed to analyze the electrical and thermal characteristics of LEDs with two different electrode mesa structures. Corresponding experiments are also carried out to validate the calculation results. It is found that increasing amount of p-electrodes in interdigitated electrode patterns is effective in improving the performance of LEDs.     

Optical design of high performance con-focal microscopy with digital micro-mirror and stray light filters

This research proposes a newly developed stray light filter in order to eliminate stray light, which otherwise might severely reduce the performance of the con-focal microscopy presented in this research. First, an optical design for con-focal microscopy with a digital micro-mirror device (DMD) is illustrated; second, a newly developed stray light filter is presented, which functions to eliminate possible stray light and ghost images without any sacrifice of luminance. It indicates that not only can the optical system be much simplified but also that its resolution could be one step higher, because the system employs neither a pinhole nor a CCD camera lens. Experimental results are shown in the paper, demonstrating an increase in contrast of up to 60%.     

The particular solutions for thin plates resting on Pasternak foundations under arbitrary loadings

Analytical particular solutions of splines and monomials are obtained for problems of thin plate resting on Pasternak foundation under arbitrary loadings, which are governed by a fourth‐order partial differential equation (PDEs). These analytical particular solutions are valuable when the arbitrary loadings are approximated by augmented polyharmonic splines (APS) constructed by splines and monomials. In our derivations, the real coefficient operator in the governing equation is decomposed into two complex coefficient operators whose particular solutions are known in literature. Then, we use the difference trick to recover the analytical particular solutions of the original operator. In addition, we show that the derived particular solution of spline with its first few directional derivatives are bounded as r → 0. This solution procedure may have the potential in obtaining analytical particular solutions of higher order PDEs constructed by products of Helmholtz‐type operators. Furthermore, we demonstrate the usages of these analytical particular solutions by few numerical cases in which the homogeneous solutions are complementarily solved by the method of fundamental solutions (MFS). © 2009 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2010     

Harvesting of a phytoplankton–zooplankton model

Considering that some phytoplankton and zooplankton are harvested for food, a phytoplankton–zooplankton model with harvesting is proposed and investigated. First, stability conditions of equilibria and existence conditions of a Hopf-bifurcation are established. Our results indicate that over exploitation would result in the extinction of the population and an appropriate harvesting strategy should ensure the sustainability of the population which is in line with reality. Furthermore, the existence of bionomic equilibria and the optimal harvesting policy are discussed. The present value of revenues is maximized by using Pontryagin’s maximum principle subject to the state equations and the control constraints. We discussed the case of optimal equilibrium solution. It is found that the shadow prices remain constant over time in optimal equilibrium when they satisfy the transversality condition. It is established that the zero discounting leads to the maximization of economic revenue and that an infinite discount rate leads to complete dissipation of economic rent. Finally, some numerical simulations are given to illustrate our results.