Systematic study of epitaxy growth uniformity in a specific MOCVD reactor

Gallium nitride (GaN) is a direct bandgap semiconductor widely used in bright light‐emitting diodes (LEDs). Thin‐film GaN is grown by metal‐organic chemical vapour deposition (MOCVD) technique. Reliability, efficiency and durability of LEDs are influenced critically by the quality of GaN films. In this report, a systematic study has been performed to investigate and optimize the growth process. Fluid flow, heat transfer and chemical reactions are calculated for a specific close‐coupled showerhead (CCS) MOCVD reactor. Influences of reactor dimensions and growth parameters have been examined after introducing the new conceptions of growth uniformity and growth efficiency. It is found that GaN growth rate is mainly affected by the concentration of (CH3)3Ga:NH3 on the susceptor, while growth uniformity is mainly influenced by the recirculating flows above the susceptor caused by natural convection. Effect of gas inlet temperature and the susceptor temperature over the growth rate can be explained by two competing mechanisms. High growth efficiency can be achieved by optimizing the reactor design.     

锌卟啉对氨基酸甲酯手性分子识别的理论研究

用Tripos力场和分子力学方法研究了手笥锌卟啉的最低能量构象,并用分子动力学模拟了锌卟啉对氨基酸甲酯的识别过程,发现锌卟啉与D-氨基酸酯结合能力强于L-氨基酸,这与热力学实验结果一致.     

DTA中升温速率及样品热导率对T_g测量值影响的模拟研究

就不同升温速率和实际样品的不同热导率对差热分析 (DTA)中高分子材料的玻璃化转变曲线的影响进行了MonteCarlo模拟研究 ,发现当所有样品刚完成玻璃化转变时 ,在Tg 曲线中该特征点要低于Tg 的转变中点。转变中点所对应的样品温度肯定要高于实际的玻璃化转变温度。如果以玻璃化转变曲线的转变中点所对应的样品温度作为该材料的玻璃化转变温度 ,那么 ,升温速率越快、样品的热导率越小 ,所测得的玻璃化转变温度就越大 ,反之亦然。DTA测得的玻璃化转变温度与升温速率间有很好的线性依赖关系 ,但与样品热导率间的关系是非线性的     

裂隙岩体注浆模拟实验研究

通过单一裂隙岩体和裂隙网络岩体注浆渗流模拟实验,分析和总结了裂隙岩体注浆渗流中的一般规律,并讨论了影响注浆渗流工程的各种因素。     

磁聚焦问题中电子轨道的计算机模拟

不少普通物理教材对磁聚焦都有介绍,但只提供静态图片,本文建立了电子在匀强磁场中的轨道方程,并采用计算机动态模拟电子轨道,演示磁聚焦过程及图象,方便教师讲解,有利学生掌握。     

A simple atomistic model for the simulation of the gel phase of lipid bilayers

In this paper we present the results of a large-scale numerical investigation of structural properties of a model of cell membrane, simulated as a bilayer of flexible molecules in vacuum. The study was performed by carrying out extensive Molecular Dynamics simulations, in the (NVE) micro-canonical ensemble, of two systems of different sizes ( 2×32 and 2×256 molecules), over a fairly large set of temperatures and densities, using parallel platforms and more standard serial computers. Depending on the dimension of the system, the dynamics was followed for physical times that go from few hundred picoseconds for the largest system to 5-10 nanoseconds for the smallest one. We find that the bilayer remains stable even in the absence of water and neglecting Coulomb interactions in the whole range of temperatures and densities we have investigated. The extension of the region of physical parameters that we have explored has allowed us to study significant points in the phase diagram of the bilayer and to expose marked structural changes as density and temperature are varied, which are interpreted as the system passing from a crystal to a gel phase. Received 6 July 2000 and Received in final form 28 December 2000     

一种自由曲面光学视觉重构方法研究

通过对物体摄像来提取表面 3D信息正成为一种新兴的反求建模方法。传统的视觉算法是基于特征对应的 ,要求物体表面具有几何特征或色彩纹理 ,不适于无纹理自由曲面的重构。将计算机视觉方法与CAGD技术紧密结合 ,对无纹理自由曲面提出了一种新的视觉重构方法。首先将物体表面分割为N边域曲面片 ,经由边缘线提取、匹配 ,重构出曲面片的边界曲线 ;然后通过反射模型、图像光亮度分析求出曲面片的跨界切矢 ;最后综合上述信息 ,构造出光滑的曲面模型     

Laser-Induced Fluorescence Bronchoscopy for Detection and Localization of Early Lung Cancer

Experimenatal results on the development of a Laser-Induced Fluorescence Bronchoscopy(LIFB) for the detection and localization of early lung cancer are reported in this paper. The system utilizes fluorescence of photosensitizer drug to provide real time video imaging for the examined lung tissue. Color filters are used to differentiate signal from background and a computer image processing technique is also applied to subtract the background. Moreover, a pseudocolor contrast enhancement method was developed to enhance the fluorescence image displayed on the vidio monitor. Suspicious areas are identified by pseudocolor image to guide biopsy, and several clinical trials show that sensitivity and contrast capability of the system should permit the detection and localization of early lung cancer.     

银团簇结构与特性的分子动力学研究

用分子动力学方法模拟了银团簇的结构与力能学。计算模拟中使用了一种基于第一性原理的原子间互作用多体势函数。通过分子动力学模拟确定了银徽团簇（原子个数3－13）的稳态结构;模拟了原子个数为13－141的银FCC晶体结构理想球形团簇的力能学,发现球形银簇形成三维紧密结构;计算了平均结合能,给出了结合能随团簇原子数N的变化图,发现随N增大团簇结合能逐渐接近块材的数值。