水分子团簇模拟及其在观测冷凝过程的应用

在气液相变过程中,水分子相互作用形成团簇,并产生分子间氢键,从而影响了羟基的振动频率。尺寸不同的团簇体系内氢键网络特性不同,红外吸收频率可反应OH所处的相邻氢键以及周围氢键的环境。本文采用密度泛函理论计算了不同尺寸水团簇的稳定结构和红外频率,分析了红外振动频率与团簇尺寸之间的演变关系。结果表明随着尺寸增大,内部水分子结构可能发生转变,(H2O)n团簇结构趋向于紧密的球形,并且伸缩振动频率向低频演化。研究结果可为通过红外光谱技术检测和确定团簇尺寸提供参考依据,并有可能用于水分子团簇在近壁区核化和生长过程的量化检测。     

建模法构建氧化硼笼状团簇结构

类似于C60的富勒烯笼状结构,理论计算表明化学计量关系的氧化硼团簇也倾向于形成笼状结构。对于小尺寸(B2O3)n团簇(n≤6),我们已经采用第一性原理全局优化方法预测了其结构。然而第一性原理结构预测非常耗时,目前的计算条件下很难做到更大尺寸。因此,我们研究了氧化硼笼状团簇的特点,提出了一种建模的方法用于构建大尺寸团簇的构型。以高对称(B2O3)n(n=2-5)团簇(四面体,三棱柱,正方体,五棱柱)为模板。用六元环(B3O3)取代顶点B原子可以增加一个B2O3单元,从而可以得到各种可能的大尺寸(B2O3)n团簇。最后采用密度泛函方法优化这些候选结构,从而预测了更大尺寸下(B2O3)n团簇(n=7-15)的几何构型。     

SO_4~(2-)微观水合结构DFT研究

运用密度泛函理论(DFT)计算方法系统研究硫酸根阴离子水合团簇,[SO_4(H_2O)_n]~(2-)(n=1-18),微观水合结构。理论计算采用ωB97XD泛函和6-311++G(d,p)基组。每个尺寸团簇结构,尽可能考虑所有合理初始结构,以此进行结构优化和频率分析等。结果表明,气相和液相条件下SO_4~(2-)与H_2O之间的相互作用能和溶剂稳定化能均与团簇尺寸n成线性关系,因此优化得到稳定结构均是合理构型。在[SO_4(H_2O)_n]~(2-)水合团簇稳定结构中,氢键的形式有两种,即溶质-溶剂(SO_4~(2-)…HOH)之间形成的对称双氢键,以及溶剂-溶剂(H_2O... HOH)之间形成的氢键。当SO_4(H_2O)_n]~(2-)水合团簇的尺寸为5个水分子时,由于水分子内氢键的形成,出现氢键环状结构,且团簇结构中出现水分子内氢键时,结构较为稳定。随着n增加,氢键结构逐渐变为网状直至稳定的笼状。通过能量参数和键参数分析可知,当团簇尺寸n≥18时,SO_4~(2-)第一水合层水分子数≥9,而第二水合层还有待进一步研究。同时随着浓度降低SO_4~(2-)与H_2O分子之间总相互作用能增加,溶液中溶剂-溶质相互作用增强。     

CPF-EDAS：无线传感器网络中一种基于簇势场的高效数据融合策略*

为了增强无线传感器网络中数据的融合效率,降低节点的能耗,延长网络的寿命,提出一种基于簇势场的高效数据融合策略（CPF-EDAS）。提出的策略是在簇内引入序列势场和在簇头与sink之间引入混合势场来进行数据融合,且簇头根据其局部信息快速构建路线。实验结果表明CPF-EDAS的性能明显优于DP。该方案不但适用于静态路由,且适合火灾监测等动态环境,具有更好的扩展性,可用于各种大规模的无线传感器网络。     

基于改进人工势场法的移动机器人导航控制

传统人工势场法在移动机器人导航过程中存在局部极小值,障碍物周围震荡等问题。针对采用传统人工势场法实现移动机器人导航过程中存在的问题,本文引入旋转力改进人工势场法,同时运用细菌觅食混合粒子群算法（BF-PSO）对移动机器人导航过程中的控制器参数及势场函数增益系数进行离线优化。运用优化参数进行基于改进人工势场法的移动机器人导航的仿真,仿真结果表明BF-PSO算法对移动机器人导航具有较好的优化效果。     

CoMoS催化剂中活性位形成的分子模拟研究

运用分子模拟计算方法建立了较为合理的CoMoS相簇结构模型,讨论了助剂Co的优先取代位置,在此基础上对CoMoS相催化剂几种主要活性位的产生位置及结构性质进行了比较系统的量子化学计算,以探索Co助剂对加氢脱硫催化剂结构的影响。计算结果表明:在通常加氢脱硫条件下Co会优先取代在角位和S边,并且角位和S边引入Co之后S空位的形成过程从热力学和动力学上都更具优势,即S空位的数量和循环产生速度均有所提升。     

(OsB)_n(n=1-6)团簇结构与稳定性的第一性原理研究

基于第一性原理,采用密度泛函理论(DFT)中的广义梯度近似(GGA)对(OsB)_n(n=1-6)团簇各种可能的构型进行了几何结构优化,得出了各团簇的最稳定构型,并对最稳定构型的能量、结合能、二阶能量差分、能隙等性质进行了理论研究。研究结果表明:n=2、3时,体系的基态结构分别为棱形和锅盖形;n=4时,体系的基态结构是对称性为T_d的立方体形状,是本文对称性最高的构型;从n=4开始立方体构型主导着团簇基态结构的生长行为,表明团簇的稳定性不仅与团簇的尺寸大小有关,还与团簇的对称性有关。团簇(OsB)_4的能隙、结合能与能量的二阶差分比邻近的值都大,说明团簇(OsB)_4有较高的稳定性,n=4是团簇的幻数。     

基于多角度改进优化的无线视频传感器网络路由协议

无线视频传感器节点能量有限,为减小其能耗,延长网络生存时间,提出了一种多角度改进优化的视频传感器网络通信协议MSOWVRP.首先对传统技术的不足进行分析,结合相关性感知、虚拟势场等概念从簇首节点的选择、簇的形成、节点感知方向的调整、簇内通信以及簇间通信等几个方面进行改进和优化,最后在Matlab 2012平台上进行了仿真对比测试.仿真结果表明,MSOWVRP协议能够提高传感器网络生命周期和监测区域覆盖率.     

传统人工势场的改进

文中在分析足球机器人避碰的特点及传统人工势场法的不足的基础上,提出了引入障碍物和机器人自身的速度和加速度来改进人工势场法,并提前对规避动作做出预判来实现优化人工势场的方法。仿真试验表明,这种方法是可行的,可以有效地弥补传统人工势场的缺陷。     

反应概率置限二维DLCA模型分形模拟

本文采用有限扩散集团凝聚(Diffusion-Limited Cluster-Cluster Aggregation,DLCA)模型,编写反应概率置限二维DLCA模型程序,模拟絮凝体分形生长过程,计算其分形维数和空隙率等参数,探究在反应概率各向同性及各向异性条件下不同反应概率对絮凝体分形模拟结果的影响。在反应概率控制下的分形模拟更加符合实际絮凝体的生长过程,该模拟方法对探究絮凝体的生长机理及提高沉降分离效率有重要的理论指导价值。模拟结果表明:反应概率对絮凝体的形态及分形特征影响较大,反应概率越小,絮凝体团簇尺寸越小,团簇数目越多,团簇分布越稀疏,表现为空隙率增大,分形维数减小;反应概率越大,絮凝体团簇尺寸越大,团簇数目越少,团簇分布越密集,表现为空隙率减小,分形维数增大;反应概率各向异性直接影响絮凝体的形貌,絮凝体会偏向反应概率较大的方向聚集生长,絮凝体团簇形状十分细长,团簇数目较少,团簇分布较密集,但偏向不同方向生长絮凝体的分形维数相差不大,是同一性质的分形。     

原子动力学蒙特卡洛程序MISA-KMC在反应堆压力容器钢辐照损伤研究中的应用

材料科学领域的快速发展,使得核材料(反应堆压力容器钢)微观结构在受到强辐射时产生辐照损伤的问题成为了重点研究对象。采用动力学蒙特卡洛方法,可以模拟反应堆压力容器钢中溶质析出行为。为了给研究核材料在长期服役后微观结构演化及性能变化提供理论依据,文中介绍了自主开发的MISA-KMC程序的并行策略及大规模测试结果。在验证程序正确性的基础上,利用MISA-KMC程序研究了反应堆压力容器钢中多种溶质原子的析出过程。结果表明,经过长时间演化,溶质原子会发生聚集,形成富Cu团簇,富Cu团簇是引发反应堆压力容器钢脆化的主要微观结构之一。MISA-KMC程序模拟结果的准确性、可支持模拟规模大小以及模拟元素的多样化,为后续的材料性能变化研究提供了保障。     

GMIC++: Grouping method in C++: an efficient method to solve large number of Master equations

In typical nucleation, growth and coarsening problems in the study of defect/adatom accumulation in crystalline solids or surfaces, a large number of Master equations are involved to describe the evolution process. As examples, defect clusters nucleate and grow from point defects in solids when subjected to particle irradiation, and atoms depositing on a substrate form clusters leading to film growth. To efficiently solve the large number of master equations, the grouping method was used, which we have coded into a standard C++ program, taking full advantage of the object-oriented programming style supported in the C++ language. Because of the generic nature of this code, it may be of interest to the modeling nucleation and growth processes. As an example to demonstrate the application of this computer code, the Ostwald ripening process of vacancy clustering during aging in metal nickel is calculated.     

Vibration analysis of initially curved single walled carbon nanotube with vacancy defect for ultrahigh frequency nanoresonators

Single walled carbon nanotubes (SWCNTs) are ideal choices for resonators due to its ultrahigh natural frequency. Fundamental frequency of resonators significantly affects their functionality and performance; therefore, an accurate prediction of SWCNTs’ natural frequency is vital for designing and developing such devices. In reality, CNTs are not straight and perfect; indeed, they have some degree of vacancy defect and waviness, which occurs during growth and manipulation processes. This research investigates for the first time the combination effects of both initial curvature and vacancy defects on vibrational behaviour of SWCNTs in order to make the simulation closer to the “real world”. In this study, an efficient method based on the molecular dynamics model and the finite element method is used to simulate wavy SWCNTs with vacancy defects. Zigzag carbon nanotube with chirality indices (5, 0) is considered. Accuracy of our modelling method is verified by comparing our results with the results obtained from previous studies in simulating ideal SWCNT natural frequency. The effects of vacancy, vacancy location, curvature and aspect ratio on natural vibration of the defected wavy SWCNTs have been investigated, and a parameter of critical waviness ratio has been defined for the first time to emphasize the combination effect of vacancies and waviness on the natural frequency of SWCNTs. Our results show that critical waviness is sensitive to the aspect ratio and indicate that by increasing the length of SWCNTs, the critical waviness ratio increases.     

SearchFill: A stochastic optimization code for detecting atomic vacancies in crystalline and non-crystalline systems

We present an implementation of a stochastic optimization algorithm applied to location of atomic vacancies. Our method labels an empty point in space as a vacancy site, if the total spatial overlap of a “virtual sphere”, centered around the point, with the surrounding atoms (and other vacancies) falls below a tolerance parameter. A Metropolis-like algorithm displaces the vacancies randomly, using an “overlap temperature” parameter to allow for acceptance of moves into regions with higher overlap, thus avoiding local minima. Once the algorithm has targeted a point with low overlap, the overlap temperature is decreased, and the method works as a steepest descent optimization.Our method, with only two free parameters, is able to detect the correct number and coordinates of vacancies in a wide spectrum of condensed-matter systems, from crystals to amorphous solids, in fact in any given set of atomic coordinates, without any need of comparison with a reference initial structure.     

基于区间集的Cppcheck数组边界缺陷检测

针对开源软件Cppcheck误报率和漏报率过高,且不能检测出运行时程序缺陷等问题,基于Cppcheck程序,提出了抽象区间集算法,并将其应用于数组边界缺陷检测。在Cppcheck框架内,通过引入区间集概念,建立每个程序点变量和表达式的整型区间集和数组区间集,并由此定位出程序中的矛盾点,最终检测出程序缺陷。与Cppcheck相比较,所提算法的查准率提高18.5%,漏报率降低22.5%,误报率提高3.5%。实验结果表明,该方法能有效地检测出运行程序缺陷,并提高Cppcheck缺陷检测性能。     

基于通信优化的Infiniband集群MPI作业加载*

针对如何缓解Infiniband集群中因通信冲突引起的MPI程序性能下降问题进行了研究,从系统管理的角度出发,提出了通过改变进程映射来优化MPI作业加载方案从而优化应用程序通信性能的方法,设计了用于评价MPI作业加载方案的通信性能损失系数（CPLR）指标,基于模拟退火算法设计了优化加载方案的搜索算法,并对所提出的指标和算法进行了实现和测试。测试结果表明,经过优化加载后的MPI程序在通信性能上有一定程度的提高。     

Multi-component phase-field simulation of microstructural evolution and elemental distribution in Fe–Cu–Mn–Ni–Al alloy

A quinary phase-field model coupled with CALPHAD thermodynamic data was developed to simulate diffusion-controlled phase decomposition in the Fe–Cu–Mn–Ni–Al alloy system during isothermal aging. The effects of Ni/Al concentrations and magnetic interactions on the kinetics of Cu-rich phase formation and component distribution features were systematically studied. Simulated atom maps indicate that the Cu-rich phase possessed a complex core−shell structure consisting of a BCC Cu-rich core and a B2 Ni/Al/Mn-rich shell. Ni/Al/Mn-rich shells could be regarded as a buffer layer hindering Cu cluster formation and also as a diffusion channel connecting neighboring small particles, thus influencing the precipitation of the Cu-rich phase. It was found from the analyses of volume fraction and particle size distribution that the deviation between the proposed coarsening law and the theoretical LSW theory occurred due to the inhibiting effect of Ni–Al–Mn shells and the mixed coarsening mechanism of coalescence and Ostwald ripening. High Ni/Al contents and magnetic interactions obstructed the phase separation, growth and coarsening of the Cu-rich phase, thus leading to particle refinement and the clustering of Ni–Al–Mn atoms. Therefore, the obtained results can provide useful information for the preparation of Fe–Cu–Mn–Ni–Al alloy.     

保特征的点云骨架提取算法

三维模型的骨架提取是计算机图形学中一个重要的研究方向。对于有噪声的点云模型,曲线骨 架提取的难点在于保持正确的拓扑结构以及良好的中心性;对于无噪声的点云模型,曲线骨架提取的难点在于 对模型细节特征的保留。目前主流的点云骨架提取方法往往无法同时解决这 2 个难点。算法在最优传输理论的 基础之上结合聚类的思想,将点云骨架提取的问题转化为一个最优化问题。首先使用最优传输得到原始点云与 采样点云之间的传输计划。然后使用聚类的思想将原始点云进行分割,采样点即成为了簇的中心。接着通过簇 与簇之间的调整与合并减少聚类个数,优化聚类结果。最后通过迭代的方式得到粗糙的骨架并使用插点操作进 行优化。大量实验结果表明,该算法在有噪声与无噪声的三维点云模型上均能提取出质量良好的曲线骨架并保 留模型的特征。     

Unsupervised learning of arbitrarily shaped clusters using ensembles of Gaussian models

We propose a new clustering algorithm, called SyMP, which is based on synchronization of pulse-coupled oscillators. SyMP represents each data point by an Integrate-and-Fire oscillator and uses the relative similarity between the points to model the interaction between the oscillators. SyMP is robust to noise and outliers, determines the number of clusters in an unsupervised manner, and identifies clusters of arbitrary shapes. The robustness of SyMP is an intrinsic property of the synchronization mechanism. To determine the optimum number of clusters, SyMP uses a dynamic and cluster dependent resolution parameter. To identify clusters of various shapes, SyMP models each cluster by an ensemble of Gaussian components. SyMP does not require the specification of the number of components for each cluster. This number is automatically determined using a dynamic intra-cluster resolution parameter. Clusters with simple shapes would be modeled by few components while clusters with more complex shapes would require a larger number of components. The proposed clustering approach is empirically evaluated with several synthetic data sets, and its performance is compared with GK and CURE. To illustrate the performance of SyMP on real and high-dimensional data sets, we use it to categorize two image databases.     

一种卫星温度自主管理的优化设计

温度自主管理是卫星主动式热控的主要表现形式,温度自主管理系统将接收到的被控设备的温度数据和固化在软件中的温度阈值进行比较后,发出相应的指令控制加热器的通或断,从而确保星上设备或部件的温度始终保持在一个合理的范围内,不会因为温度过高或过低影响卫星的可靠性和安全性,在一些卫星中,部分被控设备的接口发生了变化,传统的自主管理系统在新接口的温度控制上存在一定缺陷,导致地面测试中出现了热控回路报警,采用增加同一加热器回路通断指令的自主重试次数的方法对温度自主管理软件进行了优化,经过实验验证,优化后的温度自主管理系统能够很好地适应新的接口,该系统已经在多个卫星中成功应用,可为后续卫星提供参考。