Numerical simulation and verification of gas transport during an atomic layer deposition process

Atomic Layer Deposition (ALD) is a process used to deposit nanometer scale films for use in semiconductor electronics. The reactor consists of a warm wall horizontal flow tube, a substrate mounted on a disk downstream from the inlet, and cyclic flow between a reactant gas, a purging gas and a gas that preps the surface of the substrate. The objective is to achieve a uniform coating on the substrate layer by layer in minimal time. It is possible to use in situ monitoring of the gas phase and deposition to modify layer formation. Process improvement is currently accomplished experimentally by monitoring the precursor delivery and the growth of the film and adjusting the parameters: flow rates, temperature, pressure, concentrations, etc. Accurate simulation and optimization can decrease processing time and cost and increase control during product development. In addition, increased accuracy of gas transport simulation can be used to analyze reaction and diffusion rates, reaction mechanisms and other physical properties. In this paper we introduce the first comprehensive numerical solution of the Dusty-Gas Model including the complete binary diffusion term. We derive a concentration dependent Damkohler number relevant to the purge step of the process. The simulation matched the experimental data at a specific Damkohler number and further variation of the parameter confirmed existing experimentally observed phenomena.     

Origin and Prediction of Highly Specific Bond Cleavage Sites in the Thermal Activation of Intact Protein Ions

Predicting the fragmentation patterns of proteins would be beneficial for the reliable identification of intact proteins by mass spectrometry. However, the ability to accurately make such predictions remains elusive. An approach to predict the specific cleavage sites in whole proteins resulting from collision-induced dissociation by use of an improved electrostatic model for calculating the proton configurations of highly-charged protein ions is reported. Using ubiquitin, cytochrome c, lysozyme and β-lactoglobulin as prototypical proteins, this approach can be used to predict the fragmentation patterns of intact proteins. For sufficiently highly charged proteins, specific cleavages occur near the first low-basicity amino acid residues that are protonated with increasing charge state. Hybrid QM/QM′ (QM=quantum mechanics) and molecular dynamics (MD) simulations and energy-resolved collision-induced dissociation measurements indicated that the barrier to the specific dissociation of the protonated amide backbone bond is significantly lower than competitive charge remote fragmentation. Unlike highly charged peptides, the protons at low-basicity sites in highly charged protein ions can be confined to a limited sequence of low-basicity amino acid residues by electrostatic repulsion, which results in highly specific fragmentation near the site of protonation. This research suggests that the optimal charge states to form specific sequence ions of intact proteins in higher abundances than the use of less specific ion dissociation methods can be predicted a priori.     

Ideal Free Distribution in Two Patches

In this paper, the formats of Julia sets for a class of nonlinear complex dynamic systems with variable coefficients were studied under certain conditions. For the complex dynamic systems in piecewise cases, we proposed some methods to control the forms of their Julia sets and stable domains analytically. What’s more, we illustrated that our methods worked well by computational simulations. Our work provides a better understanding about how to control the Julia sets of certain complex dynamic systems.     

Newton trajectories for the tilted Frenkel–Kontorova model

ABSTRACT

Newton trajectories are used for the Frenkel–Kontorova model of a finite chain with free-end boundary conditions. We optimise stationary structures, as well as barrier breakdown points for a critical tilting force were depinning of the chain happens. These special points can be obtained straight forwardly by the tool of Newton trajectories. We explain the theory and add examples for a finite-length chain of a fixed number of 2,?3,?4,?5 and 23 particles.     

一种激光眼组织切割系统设计及实验

针对医生手工进行白内障手术,病人术后视力恢复效果取决于医生手术熟练度的问题,提出了一种激光眼组织切割光路运动系统。系统采用直线电机带动平面镜运动的形式改变光路,利用聚焦透镜实现激光对样品单点切割。建立了白内障手术中碎核、撕囊扫描轨迹的数学模型,通过MATLAB仿真验证扫描轨迹数学模型的正确性。最后以透明塑料为样品模拟眼球实验,结果表明此系统可以实现给定轨迹切割,为激光眼组织切割设备研发提供了一种新方案。     

带有媒体影响上限的传染病模型研究

媒体报道对传染病的传播有着一定的影响,但它并不是影响其传播的本质因素.通过建立一个具有分段感染率的传染病模型来刻画媒体报道对传染病传播影响的饱和性.分析了系统各平衡态的局部稳定性,同时利用排除极限环的存在性证明了各平衡态的全局稳定性.最后,通过模拟来验证我们的理论分析.     

A class of finite difference schemes for interface problems with an HOC approach

In this paper, we propose a new methodology for numerically solving elliptic and parabolic equations with discontinuous coefficients and singular source terms. This new scheme is obtained by clubbing a recently developed higher‐order compact methodology with special interface treatment for the points just next to the points of discontinuity. The overall order of accuracy of the scheme is at least second. We first formulate the scheme for one‐dimensional (1D) problems, and then extend it directly to two‐dimensional (2D) problems in polar coordinates. In the process, we also perform convergence and related analysis for both the cases. Finally, we show a new direction of implementing the methodology to 2D problems in cartesian coordinates. We then conduct numerous numerical studies on a number of problems, both for 1D and 2D cases, including the flow past circular cylinder governed by the incompressible Navier–Stokes equations. We compare our results with existing numerical and experimental results. In all the cases, our formulation is found to produce better results on coarser grids. For the circular cylinder problem, the scheme used is seen to capture all the flow characteristics including the famous von Kármán vortex street. Copyright © 2016 John Wiley & Sons, Ltd.