Thermal boundary conditions for thermal lattice Boltzmann simulations

Consistent 2D and 3D thermal boundary conditions for thermal lattice Boltzmann simulations are proposed. The boundary unknown energy distribution functions are made functions of known energy distribution functions and correctors, where the correctors at the boundary nodes are obtained directly from the definition of internal energy density. This boundary condition can be easily implemented on the wall and corner boundary using the same formulation. The discrete macroscopic energy equation is also derived for a steady and fully developed channel flow to assess the effect of the boundary condition on the solutions, where the resulting second order accurate central difference equation predicts continuous energy distribution across the boundary, provided the boundary unknown energy distribution functions satisfy the macroscopic energy level. Four different local known energy distribution functions are experimented with to assess both this observation and the applicability of the present formulation, and are scrutinized by calculating the 2D thermal Poiseuille flow, thermal Couette flow, thermal Couette flow with wall injection, natural convection in a square cavity, and 3D thermal Poiseuille flow in a square duct. Numerical simulations indicate that the present formulation is second order accurate and the difference of adopting different local known energy distribution functions is, as expected, negligible, which are consistent with the results from the derived discrete macroscopic energy equation.     

模糊边缘检测无线传感器网络分簇算法

针对传统分簇算法簇头选举仅单一考虑节点位置或能量分布的问题,提出了一种基于模糊边缘检测的无线传感网络分簇算法,该算法综合考虑拓扑边缘信息和节点能量分布,根据网络能量分布情况调整带宽内边缘节点参与簇头选举的概率.仿真结果表明,该算法簇头选举相对于LEACH算法分布更加合理,有效延长网络生命周期.     

Electric potential in the earth’s ionosphere: a numerical model

Modeling the global distribution of the electric potential in the Earth’s ionosphere is based on the solution of a 2D continuity equation in the ionospheric-magnetospheric current circuit. The potential distribution is described by the boundary value problem for an elliptic system of partial differential equations on the spherical shell approximating the ionosphere, which is divided into three subregions with nonlocal boundary conditions. Implementation of the boundary conditions, which reflect the continuity of the common current circuit and potential equalization at the boundaries of the polar caps, is leading to the mutual dependence of the potential distribution within the northern and southern caps and their influence on the potential distribution in the midlatitude region. The problem is solved by an iterative method with a regularizing operator which is inverted using the separation of the variables and the fast Fourier transform with respect to the azimuthal variable and the sweep method with respect to the latitudinal one.     

噪声数据集上的边界点检测算法

为了有效检测聚类的边界点,提出了结合对象的密度及其Eps-邻域中数据的分布特点进行的边界点检测技术和边界点检测算法 ——BOUND。实验结果表明,BOUND能在含有不同形状、大小簇的噪声数据集上有效地检测出聚类的边界点,并且执行效率高。     

Temperature distribution in graphene doped with nitrogen and graphene with grain boundary

Graphene doped with nitrogen exhibits unique properties different than perfect graphene. The temperature distribution in nitrogen-doped graphene (N-graphene) and in the graphene with grain boundary is investigated using molecular dynamics simulations. The temperature distribution in nitrogen-doped graphene nanoribbon, containing two types of grain boundaries, was found to be sensitive to the number of dopants and grain boundary. We also found that there is a remarkable temperature gap in the temperature profile of N-graphene nanoribbon-containing a grain boundary. For any doping ratio N/C we found that the nitrogen atoms enhance roughness of N-graphene and decrease thermal conductivity.     

基于边界链码幅度谱的图像型火灾探测算法

在传统的图像型火灾探测中,对火焰颜色、边界等空间域特征进行识别的频率域方法研究较少。为此,提出一种基于边界链码有序数组幅度谱分析的图像型火灾探测算法。该算法将图像中目标轮廓的边界链码变换为有序数组,并对有序数组进行频域变换,获得其幅度谱分布。分析信号的频率域,得到图像空域特征与频域频谱分布之间的联系。将边界链码幅度谱分析理论应用于图像型火灾探测,并通过仿真实验验证了该算法的有效性。     

Approximation of Single Layer Distributions by Dirac Masses in Finite Element Computations

We are interested in the finite element solution of elliptic problems with a right-hand side of the single layer distribution type. Such problems arise when one aims at accounting for a physical hypersurface (or line, for bi-dimensional problem), but also in the context of fictitious domain methods, when one aims at accounting for the presence of an inclusion in a domain (in that case the support of the distribution is the boundary of the inclusion). The most popular way to handle numerically the single layer distribution in the finite element context is to spread it out by a regularization technique. An alternative approach consists in approximating the single layer distribution by a combination of Dirac masses. As the Dirac mass in the right hand side does not make sense at the continuous level, this approach raises particular issues. The object of the present paper is to give a theoretical background to this approach. We present a rigorous numerical analysis of this approximation, and we present two examples of application of the main result of this paper. The first one is a Poisson problem with a single layer distribution as a right-hand side and the second one is another Poisson problem where the single layer distribution is the Lagrange multiplier used to enforce a Dirichlet boundary condition on the boundary of an inclusion in the domain. Theoretical analysis is supplemented by numerical experiments in the last section.     

气流组织中悬浮边界面的数值仿真技术的研究

气流组织是空调房间内空气的分布、流动形式,主要反映在气流的温度、湿度、气流速度和清洁度等指标,是否符合行业标准规定的空调房间的要求.气流组织可以通过数值计算理论、计算机仿真技术给予实现.论文以一个典型的变风量中央空调房间为研究基础,以该房间内的送、回风口边界面为研究实例,通过分析悬浮在房间立体内的送、回风口的数值仿真方法,运用实体造型技术,设计出在房间立体与悬浮边界面之间的拓扑关系,使两者成为一体.然后该处理技术经过数值仿真实例的验证证明是合理的、可行的.     

基于区间2-型模糊度量的粗糙K-means聚类算法*

现有粗糙K-means聚类算法及系列改进、衍生算法均是从不同角度描述交叉类簇边界区域中的不确定性数据对象,却忽视类簇间规模的不均衡对聚类迭代过程及结果的影响.文中引入区间2-型模糊集的概念度量类簇的边界区域数据对象,提出基于区间2-型模糊度量的粗糙K-means聚类算法.首先根据类簇的数据分布生成边界区域样本对交叉类簇的隶属度区间,体现数据样本的空间分布信息.然后进一步考虑类簇的数据样本规模,在隶属度区间的基础上自适应地调整边界区域的样本对交叉类簇的影响系数.文中算法削弱边界区域对较小规模类簇的中心均值迭代的不利影响,提高聚类精度.在人工数据集及UCI标准数据集的测试分析验证算法的有效性.     

On the stability of the finite element immersed boundary method

The immersed boundary (IB) method is a mathematical formulation for fluid–structure interaction problems, where immersed incompressible visco-elastic bodies or boundaries interact with an incompressible fluid.The original numerical scheme associated to the IB method requires a smoothed approximation of the Dirac delta distribution to link the moving Lagrangian domain with the fixed Eulerian one.We present a stability analysis of the finite element immersed boundary method, where the Dirac delta distribution is treated variationally, in a generalized visco-elastic framework and for two different time-stepping schemes.     

基于边界点词性特征统计的韵律短语切分

由于基于规则方法的文本处理系统在系统建立时需要总结大量的规则,而且很难保证它在处理大规模真实文本时的强壮性,因此本文在使用统计方法进行韵律短语切分方面做了一些有益的探索。先对文本进行自动分词和自动词性标注,然后利用从已经经过人工标注的语料库中得到的韵律短语切分点的边界模式以及概率信息,对文本中的韵律短语切分点进行自动预测,最后利用规则进行适当的纠错。通过对一千句的真实文本进行封闭和开放测试, 词性标注的正确率在95%左右,韵律短语切分的召回率在60%左右,正确率达到了80%。     

A random walk procedure for texture discrimination

We consider the problem of texture discrimination. Random walks are performed in a plain domain D bounded by an absorbing boundary ? and the absorption distribution is calculated. Measurements derived from such distributions are the features used for discrimination. Both problems of texture discrimination and edge segment detection can be solved using the same random walk approach. The border distributions and their differences with respect to a homogeneous image can classify two different images as having similar or dissimilar textures. The existence of an edge segment is concluded if the boundary distribution for a given window (subimage) differs significantly from the boundary distribution for a homogeneous (uniform grey level) window. The random walk procedure has been implemented and results of texture discrimination are shown. A comparison is made between results obtained using the random walk approach and the first-or second-order statistics, respectively. The random walk procedure is intended mainly for the texture discrimination problem, and its possible application to the edge detection problem (as shown in this paper) is just a by-product.     

基于边界检测的多流形学习算法*

已知流形学习算法都假设数据分布于一个单流形,而现实中大部分数据都分布在多流形上,因此限制算法的实际应用.基于此种情况,文中提出基于边界检测的多流形学习算法,通过检测流形的边界处理分布于多流形的数据,并且可以较好地保持流形内、流形间的测地距离.算法首先检测流形边界,再分别降维处理各流形,最后将各低维坐标重置于一个全局坐标系中.在人工数据集和真实数据集上的对比实验表明文中算法的可行性和有效性.     

基于聚类的镜头边界检测算法

镜头边界检测是基于内容视频检索的重要组成部分。为从不同类型的视频中有效地检测出视频镜头边界,提出一种视频镜头边界检测算法。通过视频帧图像的颜色特征,得到视频的相似性矩阵,根据突变镜头和渐变镜头在Affinity Propagation聚类结果中的不同特点,运用双阈值法检测镜头边界。实验结果表明,该算法从视频的本身信息分布出发,能自动快速地检测出镜头边界。     

Decision boundary feature extraction for neural networks

In this paper, we propose a new feature extraction method for feedforward neural networks. The method is based on the recently published decision boundary feature extraction algorithm which is based on the fact that all the necessary features for classification can be extracted from the decision boundary. The decision boundary feature extraction algorithm can take advantage of characteristics of neural networks which can solve complex problems with arbitrary decision boundaries without assuming underlying probability distribution functions of the data. To apply the decision boundary feature extraction method, we first give a specific definition for the decision boundary in a neural network. Then, we propose a procedure for extracting all the necessary features for classification from the decision boundary. Experiments show promising results.     

基于BP神经网络的ZigBee无线定位边界效应优化

针对基于ZigBee技术的井下定位区域内定位误差在边界处定位节点会从网络外部向网络内部发生一定偏移,致使定位误差相对较大,但正负方向固定不变的分布规律,定义了定位边界效应,并提出了针对边界效应的优化方法。利用最小二乘法对边界区域的平均误差做二次函数拟合,并通过改进的BP神经网络预测针对不同节点间距对应的网络模型的边界区域补偿函数。实验结果表明,由BP神经网络预测的补偿函数可大幅改善边界区域的定位精度,使边界区域定位误差达到1m以下。     

改进边界指示函数的CV模型构建及应用

无边缘活动轮廓CV模型对于边界模糊以及背景灰度分布不均匀的图像缺乏良好的分割效果。基于此，对该模型进行了如下改进。对边界指示函数进行修改，将改进后的边界指示函数融入CV模型的长度项中。引用双阱势的距离正则项来避免水平集重新初始化，从而得到了一个梯度与区域信息相结合的水平集演化方程，并应用变分法中的有限差分法对方程进行求解。对木材虫眼、活节和死节图像进行了数值仿真模拟，仿真结果表明该模型对背景分布不均匀的图像具有良好的分割效果。     

离散模拟的粒子-边界作用模型

粒子-边界作用模型是粒子模拟中非常重要的一类边界条件,主要包括镜面反射、回弹反射和热边界等.本文详细介绍了这几类边界条件,重点分析讨论了几种模型中涉及的Maxwell分布和偏Maxwell分布以及它们在计算机模拟中的实现方式,并用硬球对流体做了模拟测试.模拟结果表明,对于热平衡状态下的流体,壁面反射粒子速度用Maxwell分布模拟的流体温度比边界要低,二维情况下只有壁面温度的约0.70,三维情况下则约为0.77.并且流体温度不是处处相等,靠近壁面处比其他地方要显得更低,而用偏Maxwell分布模拟的流体状态则与实际情形吻合的很好.     

结合仿射不变特征的平面目标区域矩研究

平面目标闭合曲线的傅里叶描述子只描述了目标区域的边界形状,无法反映目标内在属性。若目标区域的灰度分布已知,可利用目标区域的灰度分布构造各阶矩来描述目标的灰度分布特性及边界形状,即用区域矩来表征目标,可以得到反映目标内在属性的一些仿射不变特征,更能全面地反映目标本原特征。     

基于节点状态一致的路网边界控制

针对路网车流分布不均衡的问题,本文提出基于一致性思想的路网边界流量控制策略.首先,基于车辆守恒宏观模型,描述了区域边界车流的动态演化;以区域内路段占有率一致作为控制目标,边界交叉口配时参数为控制输入,进行区域边界反馈控制设计,并推导出边界车流输入与内部路段放行比例的解析关系;最后,通过路网实测数据验证了边界控制策略的适用性.结果表明:边界控制策略不仅能够有效改善路网交通流分布不均衡的状况,还能够有效降低路网的平均延误、排队长度等指标,提高路网运行效率.