Ab-initio HRTEM simulations of ionic crystals: a case study of sapphire

Solving the atomistic structure of crystal defects by HRTEM often requires comparison of experimental images with simulated images of trial structures. Although many materials of interest exhibit a strong component of ionic bonding, HRTEM image simulations conventionally rely on the scattering factors of neutral atoms. In the present case study of sapphire we thus examine the influence of ionicity on dynamical electron scattering in the specimen and on the HRTEM image. For this purpose, we compare simulated images obtained with ion electron scattering factors with conventional simulated images, obtained with the scattering factors of neutral atoms. We introduce several approaches to include ionicity in image simulations. The most reliable results were obtained by means of self-consistent ab-initio electron bandstructure calculations. After converting the charge density distribution obtained by these calculations into electron scattering factors of the corresponding ions we have implemented the data in our HRTEM image simulation software and used it for simulating HRTEM images. It turned out that these 'realistic' simulated images do not differ significantly from simulated images of neutral atoms. At least for sapphire, this result justifies the usage of 'conventional' image simulations.     

Computer-simulated high-resolution transmission electron microscopy (HRTEM) in tourmaline

The contrast distributions observed in high-resolution transmission electron microscopy (HRTEM) images of tourmaline depend on the types and magnitudes of the exchange components present and on the degree of atom overlap along the direction of observation. Furthermore, the fractional atomic coordinates in tourmalines are valid only for the specific specimen refined. These properties make the interpretation of experimental HRTEM images of tourmaline using image simulation if not impossible at least extremely difficult. A correct interpretation of experimental HRTEM images of tourmaline is possible provided the structural refinement data on the same crystal are available. Nevertheless, it is possible to interpret the experimental HRTEM images of tourmaline if the composition of the structural model chosen during image simulations approximates the composition of the specimen studied by electron microscopy. A good control of the composition of the specimen studied and an appropriate choice of a structural model for image simulation are therefore as important as properly controlling specimen thickness, specimen tilt, beam tilt and objective lens defocus.     

星敏感器星象模拟软件的研究

星敏感器是高精度姿态测量部件,广泛应用于各种航天器中,作用对象是空间恒星,成像过程涉及光学系统、CCD探测器及前端信号处理系统,最后输出惯性坐标系或地心坐标系下的姿态角.本文完成了对星敏感器成像过程的模拟,研制了星敏感器星像模拟软件,为星敏感器及其他类似航天器的性能评价提供了有效手段.     

The S-state model: a work horse for HRTEM

The S-state model describes the dynamical scattering of electrons in a specimen foil, consisting of atom columns parallel to the beam direction, such as a crystal or a particular crystal defect. In this model the electrons are considered to be trapped in the electrostatic potential of an atom column, in which it scatters dynamically. This picture allows physical insight, and it explains why a one-to-one correspondence is maintained between the exit wave and the projected structure, even in case of strong dynamical scattering. Furthermore the model can be parameterised in a simple closed analytical form. Apart from the computational advantages, the S-state model proves to be very useful to deduce the projected structure directly from the exit wave, so as to "invert" the dynamical scattering. In this paper the validity of the S-state model, is evaluated in much depth by a proper quantum mechanical treatment. The analytical parameterisation of the 1S eigenfunction and eigenenergy is discussed. It is shown that the method, even in case of small tilts, is valid for most thicknesses, currently used in HRTEM studies. Even for closely spaced atom columns, such as the dumbbells in Si [1 1 0], Sn [1 1 0] and GaN [1 1 0], the positions of the atom columns can be deduced with an accuracy of a few pm.     

COMSOL Multiphysics validation as simulation software for heat transfer calculation in buildings: Building simulation software validation

The main purpose of this article is a presentation of software validation for a calculation of heat transfer in buildings. The heat transfer calculation in the COMSOL Multiphysics is validated by using the analytical models, by the comparative verification provided by the International Energy Agency in the Task 34, and by the comparison with measured data in real building segment. The last model represents transient heat transfer process in an environment with complicated bindings. The similarity between the COMSOL Multiphysics results and other software tools for building simulations was investigated using the Task 34 results with minor dissimilarities. The comparison of simulation results with measured data is described in the paper with sufficient accuracy. The main deviation between the simulation and measured temperature data was caused by the precise calculation of the convective heat transfer coefficient value.     

夜间有雾图像的光照模型构建及去雾

夜间有雾图像会出现严重退化,而且人工光源的存在也使得环境光呈现不均匀性。针对上述问题,本文提出了一种适用于夜间有雾图像的光照模型,并在此基础上实现了夜间图像去雾。模型中主要包含了环境光和透射率两个参数,这两个参数都会随着图像局部内容的变化而产生空间变化。首先基于信息损耗约束理论对上述参数进行初始估计,随后利用快速导向滤波对其进行细化,以抑制块效应和光晕效应,最后将细化后的参数代入光照模型中,通过求解模型即可获得最终待还原目标图像。实验结果表明,本文提出的算法能够有效实现夜间有雾图像的去雾处理,在抑制亮区发散的同时能重现暗区的细节,恢复的场景具有较好的亮度和对比度,恢复的图像颜色自然,总体性能优于同类型的其它算法。     

Comprehensive simulation software for teaching camera calibration by a constructivist methodology

This paper describes the Metrovisionlab computer application implemented as a toolbox for the Matlab program. It is designed to teach the most important camera calibration aspects in dimensional metrology applications such as laser triangulation sensors and photogrammetry or stereovision systems. This software is used in several industrial vision courses for senior undergraduate mechanical engineering students. The application: simulates a virtual camera, providing a simple and visual understanding of how various characteristics of a camera influence the image that it captures; generates the coordinates of synthetic calibration points, both in the world reference system and the image reference system; and can calibrate with the most important and widely-used methods in the area of vision cameras, using coplanar or non-coplanar calibration points. Thus, the main goal is to have a simulation tool that allows characterizing the accuracy, repeatability, error mechanisms and influences for different measurement conditions and camera calibration algorithms. In the realized tests, the software has demonstrated to be a very effective educational tool.     

Aberration measurement in HRTEM: implementation and diagnostic use of numerical procedures for the highly precise recognition of diffractogram patterns

The precise characterisation of the instrumental imaging properties in the form of aberration parameters constitutes an almost universal necessity in quantitative HRTEM, and is underlying most hardware and software techniques established in this field. We focus in this paper on the numerical analysis of individual diffractograms as a first preparatory step for further publications on HRTEM aberration measurement. The extraction of the defocus and the 2-fold astigmatism from a diffractogram is a classical pattern recognition problem, which we believe to have solved in a near-optimum way concerning precision, speed, and robustness. The newly gained measurement precision allows us to resolve fluctuations of the defocus and the 2-fold astigmatism and to assess thereby the optical stability of electron microscopes. Quantitative stability criteria are elaborated, which may serve as helpful guidelines for daily work as well as for microscope acceptance tests.     

REPRINT OF: Aberration measurement in HRTEM: Implementation and diagnostic use of numerical procedures for the highly precise recognition of diffractogram patterns

The precise characterisation of the instrumental imaging properties in the form of aberration parameters constitutes an almost universal necessity in quantitative HRTEM, and is underlying most hardware and software techniques established in this field. We focus in this paper on the numerical analysis of individual diffractograms as a first preparatory step for further publications on HRTEM aberration measurement. The extraction of the defocus and the 2-fold astigmatism from a diffractogram is a classical pattern recognition problem, which we believe to have solved in a near-optimum way concerning precision, speed, and robustness. The newly gained measurement precision allows us to resolve fluctuations of the defocus and the 2-fold astigmatism and to assess thereby the optical stability of electron microscopes. Quantitative stability criteria are elaborated, which may serve as helpful guidelines for daily work as well as for microscope acceptance tests.     

A model for calculating secondary and backscattered electron yields

Images in the scanning electron microscope (SEM) are formed from both low-energy secondary, and high-energy backscattered, electrons. The quantitative interpretation of SEM images therefore requires a model which can predict the magnitude of both of these signal components for a specimen whose geometry and chemistry is known. It is shown that the combination of a simple electron diffusion model with a Monte Carlo trajectory simulation allows both yields to be calculated, simultaneously, with good accuracy. Data, such as the magnitude and energy of the maximum secondary yield, the secondary variation with tilt, and the contribution of backscattered electrons to the secondary yield coefficient, computed from this model are in excellent agreement with experimental data.     

EHL simulation using the free-volume viscosity model

The free-volume viscosity model can accurately predict the temperature–pressure–viscosity relationship of lubricants. However, it is seldom used in elastohydrodynamic lubrication (EHL) simulation. This paper presents the application of the free-volume viscosity model in a Newtonian EHL simulation of a squalane-lubricated circular contact. Good agreement is observed between available experimental data and simulation results. The pressure–viscosity coefficients fit from viscometer data are also discussed. A recently developed definition of the coefficient is used to compare the coefficient value extracted from EHL film thickness interference measurements. Results indicate that the coefficient values from the curve fitting and EHL film thickness extraction agree well which has not been previously observed. Two factors help achieve this agreement: the new coefficient definition and smaller prediction error when using the Hamrock–Dowson formula in the cases studied. The effects of different pressure–viscosity relationships, including the exponential model, the Roelands model and the free-volume model, are investigated through an example with bright stock mineral oil. It is found that the real pressure–viscosity behavior predicted by the free-volume model yields a higher viscosity at the low-pressure area which results in a larger central film thickness. Therefore, due to use of the free-volume model, the present results are more consistent with experimental observations than previously reported numerical results.     

浮子流量传感器仿真模型研究

针对DN100孔板浮子流量传感器,通过不同网格划分方案的比较,建立无支撑架三维仿真模型。并在此基础上建立二维轴对称模型,对该模型使用边界层网格划分方案,在不需要微观流场具体数据的情况下,计算精度更高,计算周期更短。     

含移动副四杆机构运动仿真设计的数学模型

综述了计算机仿真连杆机构运动的技术特点,建立了曲柄滑块机构和导杆机构二种含移动副四杆机构运动仿真设计的数学模型。     

一种可用于Footing效应模拟的ICP刻蚀模型

电感耦合等离子体（ICP）刻蚀在目前的硅微机械加工中应用十分广泛。在这一加工过程中,存在着影响结构拓扑特性、被加工结构性能的一些效应,SOI结构中的Footing效应就是其中之一。本文在利用一种改进的复合交替深刻蚀（TMDE）模型对ICP刻蚀表面进行建模及数值模拟的基础上,根据Footing效应的实验表现特征,设定类高斯分布的表面描述方程。同时借助实验数据确定了表面描述方程中的参数,添加了一种简单有效的Footing效应模拟模块。最后对Footing效应刻蚀表面进行模拟,并得到与实验较为一致的表面模拟结果。     

Hybrid neural network bushing model for vehicle dynamics simulation

Although the linear model was widely used for the bushing model in vehicle suspension systems, it could not express the nonlinear characteristics of bushing in terms of the amplitude and the frequency. An artificial neural network model was suggested to consider the hysteretic responses of bushings. This model, however, often diverges due to the uncertainties of the neural network under the unexpected excitation inputs. In this paper, a hybrid neural network bushing model combining linear and neural network is suggested. A linear model was employed to represent linear stiffness and damping effects, and the artificial neural network algorithm was adopted to take into account the hysteretic responses. A rubber test was performed to capture bushing characteristics, where sine excitation with different frequencies and amplitudes is applied. Random test results were used to update the weighting factors of the neural network model. It is proven that the proposed model has more robust characteristics than a simple neural network model under step excitation input. A full car simulation was carried out to verify the proposed bushing models. It was shown that the hybrid model results are almost identical to the linear model under several maneuvers. This paper was recommended for publication in revised form by Associate Editor Hong Hee Yoo Dr. Wan-Suk Yoo was born in 1954, and received B.S. degree from Seoul National University (1976), and got M.S. degree from KAIST (1978) and Ph.D. from the University of Iowa (1985). He is currently a full professor at the Pusan National University in Korea, where he joined since 1978. His major area is vehicle dynamics and flexible multibody dynamics. He became an ASME Fellow (2004), and currently serving as an associate editor for the ASME, J. of computational and nonlinear dynamics. He is also serving a contributing editor for the multibody system dynamics journal. He is serving as ISC chair for the ACMD2008, and a member at IFToMM TC for multibody dynamics. He is currently a vicepresident of the KSME (Korean Society of Mechanical Engineers).     

气体放电电源模型的建立及仿真

控制模型的建立对系统的设计有着重要作用,本文详细阐述了气体放电电源的模型建立过程,并通过仿真得到了控制器的参数。     

软件即服务流程模型的自动演化

针对信息技术的高速发展,研究了软件即服务个性化定制中的流程配置。引入可配置过程模型作为支持软件即服务应用流程配置的手段;针对业务流程变化引起的流程模型簇膨胀和预定义的基本流程模型过时的情况,提出了流程模型的演化方法,即根据上一个基本流程模型有效期内各个流程模型被执行的概率和流程模型簇中流程模型间的距离,产生新的基本流程模型并更新配置规则集,从而达到减少流程模型簇所需存储空间并提高流程模型实例化效率的效果。     

捷联式导引头系统模型与仿真分析

应用力学与空间飞行原理,针对捷联式光学导引头特点,建立了俯仰、方位双框架导引头系统模型,对空间视线的坐标描述与变换、载体扰动下导引头光轴稳定和导航解算原理进行了研究。针对气动弹性振动对捷联稳定式导引头工作的影响,进行了导弹系统飞行仿真分析,结果表明,在气动弹性振动的干扰下,跟踪图像出现了大幅抖动,视线角偏差峰值达0.5°,容易丢失目标而无法跟踪;在能够实时跟踪的条件下,通过对视线角速率的滤波处理,在有、无气弹振动干扰的情况下,输出的制导信号波动基本相同,使导弹具有相同的命中精度,误差约为1m。     

数控实验教学仿真软件的开发

利用Visual C 开发数控技术刀具轨迹仿真软件，用于本科生实验教学。该软件可以实现数控程序的编制、语法检测、插补放大、刀具轨迹仿真、基础知识学习等功能。     

基于着色解释Petri网的网络协议建模及协同仿真方法

为解决协议工程中协议形式化验证和仿真断裂的问题,结合着色Petri网和解释Petri网,构造出一种可建模复杂离散事件系统的着色解释Petri网.借助观察者模式,依据着色解释Petri网的特点,提出了一种具有通用性的与协议仿真工具协同工作的方法.作为对该方法的示例,采用着色解释Petri网对避免冲突的多路访问协议进行建模.在保证与OPNET仿真模型一致的基础上,通过着色解释Petri网与OPNET的协同仿真,改良了避免冲突的多路访问的功率控制算法.基于着色解释Petri网的协同仿真,第一次紧密连接了Petri网和通用协议仿真工具,对协议工程将起到重要作用.