Temperature Dependences in the Tomlinson/Prandtl Model for Atomic Sliding Friction

The temperature dependence of the Tomlinson/Prandtl model for nanoscale sliding friction is analyzed by considering the properties of the initial and final states between which the tip can move, as well as the energy barrier between them, for various sliding regimes defined by the value of the corrugation factor γ. When γ < 1, the friction force tends to zero, defining a so-called superlubricious regime. The most commonly observed behavior is found for γ > 4.603, where the friction force increases monotonically with increasing sliding velocity up to a critical value equal to the value of F ^* (lateral force at T = 0) and monotonically decreases with temperature from F ^* at T = 0. However, completely different behavior is found when 1 < γ < 4.603. The temperature dependence of the lateral force in this regime is investigated using Monte Carlo simulations. The friction force still tends to F ^* as T approaches 0 K, but in contrast to the behavior found when γ > 4.603, the friction force increases with increasing temperature from F ^* , reaches a maximum value, and then decreases monotonically as the temperature rises further. Such behavior has been observed in atomic force microscopy friction measurements.     

低能电子光刻的蒙特卡罗模拟

Electron beam lithography(EBL)has been playing an important role in the fabrication of large-scale integrated semiconductor devices because of its high resolution.Although high-energy electrons are widely employed in the present EBL system,high-energy electrons can penetrate through the resist layer,lose most of their energies in the substrate and,thus,cause damage to the underlying substrate.     

基于视觉特征的移动机器人Monte Carlo定位方法

提出了一种通过引入基于三角定位的重采样阶段对基于视觉特征的常规Monte Carlo定位加以改进的方法，以提高原有方法的实现效率，既能提高计算效率，又能避免过收敛现象。重采样的实现根据感知更新前后采样分布信息熵的变化和有效采样数目来判断，并且基于感知组织的贝叶斯网络识别视觉特征的方法为三角定位提供了准确的特征来源，有效减少了假阳性特征，大大简化了与环境模型的匹配。实验结果验证了方法的有效性。     

Monte Carlo calculations for specimens with microstructures

The calculation of secondary and backscattered signals from a heterogeneous sample has been done by modifying the calculation procedures that are used in the Monte Carlo calculations for homogeneous specimens.     

A general purpose code for Monte Carlo simulations

A general-purpose computer code MONTHY has been written to perform Monte Carlo simulations of physical systems. To achieve a high degree of flexibility the code is organized like a general purpose computer, operating on a vector describing the time dependent state of the system under simulation. The instruction set of the “computer” is defined by the user and is therefore adaptable in the particular problem studied. The organization of MONTHY allows iterative and conditional execution of operations.     

猝死轴承试验的蒙特卡洛模拟(续前)

3结果与讨论 试验永远不会被淘汰。在合理性和经济性方面，物理试验也是一种可选择的方法。猝死试验被认为是一种有潜力减少试验时间和经费的试验方法。与将全部轴承试验至失效的方法相比，猝死试验最大的争议是试验较大的样本且只让一小部分的试样失效是否具有优势。用物理试验无法验证这一点，因为物理试验和／或是经济条件受限制。以已知Weibull分布为基础，蒙特卡洛模拟法作为一种能得到的合理设计极限的方法进行说明。综合这些方法有潜力得到更进一步的试验数据，这些数据通过其他试验方法来得到是不太切合实际的或者是不太可能的。     

移动机器人的蒙特卡罗自主定位算法研究

在分析基于贝叶斯估计的定位过程基础上,针对Markov定位算法需要大量存贮空间和计算量导致无法在较高频率下有效利用传感器信息的问题,利用基于采样的Monte Carlo方法解决移动机器人的自主定位问题。理论分析和仿真试验表明,Monte Carlo自主定位算法很大程度上提高了定位效率,能够更有效的利用传感信息且降低了传感信息不确定性的影响,在“绑架”后以及在中心对称环境中都表现出良好的全局定位性能。     

Stew art平台误差的蒙特卡洛模拟

建立了球铰的随机模型 ,在 Stewart平台误差模型的基础上 ,利用蒙特卡洛技术模拟分析了驱动杆杆长公差和球铰间隙对终端平台误差的影响 ,结果表明 :球铰间隙对终端平台误差影响比驱动杆杆长误差的影响要大许多。此研究为该类机构的误差估计和精度设计提供了一种方法     

猝死轴承试验的蒙特卡洛模拟

对猝死轴承试验蒙特卡洛模拟与序贯试验及修正序贯试验的轴承综合寿命、累积试验时间和日历时间等进行了比较。轴承寿命L10和Weibull斜率e是随失效轴承的数量而变化，与使用的试验方法及所试验轴承的总数量无关。与修正序贯试验相比。猝死试验在减少轴承试验时间或日历时间方面并不是更有效的方法。     

基于Monte Carlo模拟的系统矩阵解析算法

系统矩阵是单光子发射计算机断层成像系统(SPECT)中迭代重建算法的关键因素.蒙特卡洛(MC)模拟是计算系统矩阵最准确、最常用的方法,但是标准的MC算法最大的缺点就是耗时太长.为此,提出一种新的解析算法:利用MC模拟的投影数据,拟合准直器的点扩散函数,并以此作为计算系统矩阵的解析表达式.该新算法既缩短了计算耗时又包含了MC投影信息,使得解析计算的系统矩阵与MC模拟的结果相当.因此,该方法可用于修正准直器张角效应对系统矩阵计算的影响.本文采用解析计算得到的系统矩阵,重建了均匀泛源和Jaszczak模型的MC投影图像,重建图像能真实的反映原始图像.     

蒙特卡罗方法在软件可靠性测试中的应用

本文探索了运用蒙特卡罗(Monte-carlo)方法进行软件可靠性测试的基本技术,介绍了这一技术在软件可靠性测试中的基本过程。通过实例证明了这种技术的实用性和有效性,提高了软件测试的正确率,缩短了软件测试的周期。     

多次掩模湿法腐蚀硅微加工过程的蒙特卡罗仿真

探讨利用蒙特卡罗 (Monte Carlo, MC) 法模拟硅微加工各向异性湿法腐蚀的仿真,实现连续多次掩模,多步硅微加工工艺过程的仿真.介绍MC法的使用特点及其在湿法腐蚀硅微加工中的应用,仿真使用腐蚀概率方程确定表面原子适当的MC转移概率,模拟方法支持氧化硅和氮化硅掩模层作用下的各向异性腐蚀加工和多次掩模的传递过程.编制的仿真程序通过模拟一个原子力显微镜探针阵列多掩模连续6步工艺的硅微加工过程验证了MC法的正确性.     

A particle-in-cell Monte Carlo code for electron beam ion source simulation

FAR-TECH, Inc., has developed a particle-in-cell Monte Carlo code (EBIS-PIC) to model ion motions in an electron beam ion source (EBIS). First, a steady state electron beam is simulated by the PBGUNS code (see http://far-tech.com/pbguns/index.html). Then, the injected primary ions and the ions from the background neutral gas are tracked in the trapping region using Monte Carlo method. Atomic collisions and Coulomb collisions are included in the EBIS-PIC model. The space charge potential is updated by solving the Poisson equation each time step. The preliminary simulation results are presented and compared with BNL electron beam test stand (EBTS) fast trapping experiments.     

Monte Carlo simulation of CL and EBIC contrasts for isolated dislocations

Electron beam-induced current (EBIC) and cathodoluminescence (CL) are widely used to investigate semiconductor materials and devices, particularly to obtain information on the recombination properties and the geometry of defects. This report describes a simple formulation of CL and EBIC contrasts based on the Born approximation of excess carrier density in the presence of a pointlike defect. Quantitative interpretation of the CL and EBIC images is often difficult because of a lack of accurate theory treating simultaneously both the details of the electron beam penetration in the semiconductor and the generation of EBIC and CL signals. To overcome this difficulty, the Monte Carlo approach to the phenomenon of the electron beam penetration in solids has been developed to calculate the CL and EBIC signals during a simulation of the electron trajectory. Results for an inclined dislocation in GaAs are presented.     

基于Monte Carlo方法的战斗部部件质心偏移量仿真分析

针对导弹技术远程化、高命中率的发展趋势,为在设计阶段掌握质心偏移的情况,以尺寸误差为主要分析对象,探讨了质心偏移产生的原因。以某导弹战斗部部件为例,采用极值法与Monte Carlo方法计算了质心偏移量。结果表明,采用极值法计算得到的结果属于小概率事件,而Monte Carlo方法基于大多数机械化零件在公差范围内呈正态概率分布的事实,能够更真实地描述质心偏移的情况。     

Monte Carlo simulation of scanning electron microscope signals for lithographic metrology

Two computer codes for simulating the backscattered, transmitted, and secondary-electron signals from targets in a scanning electron microscope are described. The first code, MONSEL-II, has a model target consisting of three parallel lines on a three-layer substrate, while the second, MONSEL-III, has a model target consisting of a two-by-two array of finite lines on a three-layer substrate. Elastic electron scattering is determined by published fits to the Mott cross section. Both plasmon-generated electrons and ionized valence electrons are included in the secondary production. An adjustable quantity, called the residual energy loss rate, is added to the formula of Joy and Luo to obtain the measured secondary yield. The codes show the effects of signal enhancement due to edge transmission, known as blooming, as well as signal reduction due to neighboring lines, known as the “black-hole” effect.     

三参数威布尔分布的蒙特卡洛点估计方法

现阶段可靠性分析过程中,首发故障时间并非绝对从零开始,而三参数威布尔分布多使用相关系数法转换为极值问题从而使用极值法或右逼近法进行参数估计,然而此方法精度主要依赖初值和步长选择。结合某中走丝电火花线切割机床可靠性数据,分析了模型形状参数与位置参数对对数似然函数值的影响趋势,提出使用蒙特卡洛方法结合极大似然估计法对三参数威布尔分布模型进行参数点估计数值求解,同时使用D检验和NRMSE评估两种参数点估计方法的精度。结果显示此方法便于计算机自动求解,精度可控。     

The Monte Carlo study of techniques for determining bremsstrahlung focal spots

The Monte Carlo statistical modeling has been used to study the techniques for determining the size of bremsstrahlung focal spots in the approximation of a normal distribution of bremsstrahlung quanta over the target surface.     

机械传动系统可靠性Monte Carlo仿真算法

机械传动系统的可靠性分析具有元件间存在相关性，极限状态方程非线性等解析方法难以处理的特点，本文采用基于Ｍｏｎｔｅ Ｃａｒｌｏ法的计算机仿真技术进行机械传动的可靠性计算，讨论了机械传动系统可靠性仿真的一般原理与方法，并给出了计算实例。     

Monte Carlo方法模拟晶粒在气-液-固三相体系下的各向异性生长

基于Monte Carlo方法,建立了气-液-固三相体系下晶粒生长的传质路径;根据最小能量原理,确立了最优和非最优生长取向上能量值的选取准则;采用各向异性的液-固和固-气界面能,对陶瓷晶粒的生长进行了二维模拟,并探讨了各向异性界面能量差值对晶粒形貌的影响规律。结果表明,在状态点发生相变时,引入寻找能量最低状态的过程,不仅消除了液相分布不合理现象,且晶粒边界更平直,形状更规则,质点在晶粒最优生长方向上的生长几率明显高于非最优方向;随着各向异性界面能差值的增加,晶粒的长径比基本呈线性变化,各向异性生长更突出。