旋转体系中湍流的LBM模拟

采用基于多松弛时间因子的格子Boltzmann方法对旋转体系中的湍流进行数值研究,考察Rossby数和Ekman数对湍流的影响,包括湍流能量及其耗散率、速度、涡结构及湍流的耗散尺度即Kolmorogov尺度和积分尺度等.研究表明,系统的旋转延缓了湍流能量的衰减速率,逐步破坏初始涡结构的均匀性,与旋转方向相反的涡逐步被抑制,并最终形成若干与旋转同向的涡柱.结果还表明,系统旋转越快,湍流的耗散尺度越小而积分尺度越大.     

A velocity-difference-separation model for car-following theory

We introduce a velocity-difference-separation model that modifies the previous models in the literature. The improvement of this new model over the previous ones lies in that it not only theoretically retains many strong points of the previous ones, but also performs more realistically than others in the dynamical evolution of congestion. Furthermore, the proposed model is investigated with analytic and numerical methods, with the finding that it can demonstrate some complex physical features observed in real traffic such as the existence of three phases: free flow, synchronized flow, and wide moving jam; sudden flow drop in flow-density plane; and traffic hysteresis in transition between the free and the synchronized flow.     

基于模拟退火算法的递归自动阈值分割方法

针对目标图像灰度对比度差的现象,以及对目标对象检测实时性的要求,并考虑到传统的Otsu分割方法在分割图像质量较差以及目标区域小时准确性差的缺点,提出了一种基于模拟退火算法的递归Otsu分割方法。在图像直方图呈双峰的情况下能够准确地找到分割阈值。在成像模糊、光照度较差的情况下此方法仍然可以获得较高的准确度。该方法在保证了检测质量的同时并没有导致运算时间的大幅度提升,有效地保证了处理的实时性。实际应用表明该方法切实可行。     

浅层目标亚波长声学成像新方法

正声学成像是一种用来检测物质结构和成分的重要方法,其分辨率受限于衍射极限(diffraction limit)。为了获取更高的分辨率,往往需要测量高空间频率的声倏逝波(acoustic evanescent wave)。倏逝波带有物体的细节特征信息,离开天然材料物体后的衰减特性满足指数关系。近年来,科学家利用结构声学超常材料(structured acoustic metamaterials,AMM)克服衍射极限,通过增强倏逝波     

Image reconstruction tomography with only a method for laminar optical single Monte-Carlo simulation

Laminar optical tomography （LOT） is a new mesoscopic functional optical imaging technique. Currently, the forward problem of LOT image reconstruction is generally solved on the basis of Monte-Carlo （MC） methods. However, considering the nonlinear nature of the image reconstruction in LOT with the increasing number of source positions, methods based on MC take too much computation time. This letter develops a fast image reconstruction algorithm based on perturbation MC （pMC） for reconstructing the absorption or scattering image of a slab medium, which is suitable for LOT or other functional optical tomography system with narrow source-detector separation and dense sampling. To calculate the pMC parameters, i.e., the path length passed by a photon and the collision numbers experienced in each voxel with only one baseline MC simulation, we propose a scheme named as the trajectory translation and target voxel regression （TT＆TVR） based on the reciprocity principle. To further speed up the image reconstruction procedure, the weighted average of the pMC parameters for all survival photons is adopted and the region of interest （ROI） is extracted from the raw data to save as the prior information of the image reconstruction. The method is applied to the absorption reconstruction of the layered inhomogeneous media. Results demonstrate that the reconstructing time is less than 20 s with the X - Y section of the sample subdivided into 50 × 50 voxels, and the target size quantitativeness ratio can be obtained in a satisfying accuracy in the source-detector separations of 0.4 and 1.25 mm, respectively.     

激光双棱镜干涉实验的改进方法

提出了一种新的光路进行激光双棱镜干涉实验,作为经典激光双棱镜干涉实验的改进实验.解决了经典激光双棱镜干涉实验存在的观测视场小(这里的视场指的是眼睛能看到干涉条纹的观察范围)、观测不方便、不易演示等问题.     

二氧化钒强关联固体的三相点

<正>在强关联材料中,电子—电子,电子—晶格的相互作用可导致各种电子相、磁相以及结构相之间的竞争。研究在这些竞争相之间的相变,往往可以揭示出用其他方法难以获得的有关基础量子态的信息。最近,来自美国华盛顿大学的Park等在Nature周刊上撰文,报道了他们使用微机械设备和纳米单晶束所完成的实验:在二氧化钒     

二维多介质欧拉自适应网格方法研究

要对聚能和流场的剧烈变化进行模拟，欧拉方法具有明显的优势。而在这些方面的研究中，所涉及的流场十分复杂，为达到所需的计算精度，必须采用很密的网格才能以较好的分辨率去模拟流场的剧烈变化部分和介质的界面，特别是大空间尺度流场局部细节的数值模拟，有些问题如果用统一网格计算，即使最快的计算机也不能提供足够的分辨率。所以目前计算机的内存和速度限制了整个计算区域的网格细分程度，对计算区域作局部的网格自适应细分、用大的动态空间分辨率划分流场是必要的和迫切的。     

非线性抛物型方程迭代加速计算方法

研究非线性抛物型方程隐式格式的迭代加速求解方法，包括三方面内容：一是构造具有二阶收敛性的非线性迭代方法，二是迭代初值的选取方法，三是证明迭代方法的保正性。