A pixel selection rule based on the number of different-phase neighbours for the simulated annealing reconstruction of sandstone microstructure

Sandstone reservoir is one of the main types of oil and gas reservoirs in China. It has porous microstructure, which directly affects the transport properties of a sandstone. Hence, the study of porous microstructure is important to the exploration and exploitation of oil and gas. Three-dimensional microstructure of a sandstone can be reconstructed using the simulated annealing method based on statistical properties of its two-dimensional micrograph. The aim of reconstruction is to minimize the discrepancy between the statistical properties of the reconstructed microstructure and those of the two-dimensional image. To accelerate the rate of convergence, we proposed a different-phase neighbours (DPNs)-based pixel selection rule to replace the random pixel selection rule of the simulated annealing reconstruction. In this rule, pixels with the largest number of DPNs have the largest selection probability. The selection probabilities of other pixels are proportional to their DPNs. Microstructure reconstructed with the DPNs-based rule is compared with those with the random selection rule and two other biased pixel selection rules. The DPNs-based rule is the most effective in enhancing convergence. Permeability of the microstructure reconstructed with the DPNs-based rule is estimated by the Kozeny–Carman formula and is in good agreement with the one reconstructed with the random pixel selection rule.     

金属增材制造负载均衡异构并行切片算法

增材制造模型的几何复杂程度和体积不断提高,模型切片所需时间大幅增加,极大影响了数据处理效率.提出了一种自适应负载均衡的异构并行切片算法,利用不断增长的GPU超强并行计算能力对传统切片算法进行了GPU并行化研究,利用模拟退火算法对切片任务进行负载均衡装箱,使各线程间的任务量一致.实验结果证明,该算法提高了模型的切片效率,...     

Vibration and reliability of a rotating beam with random properties under random excitation

In this paper, vibration and reliability of a rotating beam with random properties under random excitations are studied. The rotating beam is under a stochastic load modeled as a stationary white noise. The cross-sectional area, elasticity modulus, moment of inertia, shear modulus, damping coefficient, mass density and rotational speed are modeled as random variables. To develop the equations of motion, the finite element method and space state analysis are applied. In order to consider the randomness of properties, a second order perturbation method is used. The effects of rotational speed, setting angle, hub radius, variances of random properties, correlation of random variables and damping matrix forms on the vibration and reliability of rotating beams, are studied completely.     

Near-field measurement of short-range correlation in optical waves transmitted through random media

Two‐dimensional near‐field images of speckle patterns formed by optical waves transmitted through a disordered porous silica glass sample are measured. The corresponding 2D intensity correlation function, C, is extracted. The subwavelength spatial resolution of near‐field microscopy allows us to resolve in the spatial distribution of C the expected subwavelength oscillations and to follow their dependence on the excitation wavelength. Finally, we deduce the effective refractive index of the material by fitting the theoretical spatial dependence of C to our experimental results.     

Accurate stochastic reconstruction of heterogeneous microstructures by limited x‐ray tomographic projections

An accurate knowledge of the complex microstructure of a heterogeneous material is crucial for its performance prediction, prognosis and optimization. X‐ray tomography has provided a nondestructive means for microstructure characterization in 3D and 4D (i.e. structural evolution over time), in which a material is typically reconstructed from a large number of tomographic projections using filtered‐back‐projection (FBP) method or algebraic reconstruction techniques (ART). Here, we present in detail a stochastic optimization procedure that enables one to accurately reconstruct material microstructure from a small number of absorption contrast x‐ray tomographic projections. This discrete tomography reconstruction procedure is in contrast to the commonly used FBP and ART, which usually requires thousands of projections for accurate microstructure rendition. The utility of our stochastic procedure is first demonstrated by reconstructing a wide class of two‐phase heterogeneous materials including sandstone and hard‐particle packing from simulated limited‐angle projections in both cone‐beam and parallel beam projection geometry. It is then applied to reconstruct tailored Sn‐sphere‐clay‐matrix systems from limited‐angle cone‐beam data obtained via a lab‐scale tomography facility at Arizona State University and parallel‐beam synchrotron data obtained at Advanced Photon Source, Argonne National Laboratory. In addition, we examine the information content of tomography data by successively incorporating larger number of projections and quantifying the accuracy of the reconstructions. We show that only a small number of projections (e.g. 20–40, depending on the complexity of the microstructure of interest and desired resolution) are necessary for accurate material reconstructions via our stochastic procedure, which indicates its high efficiency in using limited structural information. The ramifications of the stochastic reconstruction procedure in 4D materials science are also discussed.     

模拟退火算法在车间设备布局中应用

给出模拟退火算法在车间布局评价中的具体应用方法,提出了搬运矩阵的概念。然后,给出了一个具体的应用实例,并对优化结果进行了分析,得出优化设计结果符合生产实际要求。     

遗传模拟退火混合算法在钣金自动排样中的研究

在钣金制造中,如何进行钣金件的排样,使得钣金达到最大的使用效率是目前机械设计工程迫切需要解决的方法。将人工智能领域中的遗传算法和模拟退火算法相结合,在前人排放算法的基础上,提出改进,利用遗传算法产生排样序列,利用模拟退火算法抑制遗传算法的早熟现象,进行排样处理,取得了理想的结果,实例测试表明,算法性能稳定。能为钣金排样系统的开发提供实用的、较优的排料算法。     

模拟退火算法在诊断问题求解中的应用

首先对模拟退火算法作了改进——设置了比较器,然后将其引入概率因果诊断模型,从非线性组合优化的角度解决了该诊断模型中具有组合爆炸数的多故障同时性诊断问题,并对模拟退火算法的求解过程进行了研究。     

异构网络负载均衡算法

首先建立异构网络模型,确定了链路负载函数,在此基础上提出了异构网络负载均衡算法。利用该算法合理分配网络带宽并调节适当的参数,使异构网络的负载在较小范围内变化,通过选择负载最小的生成树映射,最终实现异构网络的负载均衡。仿真实验表明,让用户在不同网络间的切换可使网络带宽优化分配、网络负载达到均衡,证明了该算法在异构网络中的有效性。     

Boolean random functions

A Boolean function f in Rⁿ is the supremum of upper semi-continuous random functions f'i which are almost surely positive, bounded with compact support and centred at the Poisson points (i). They generalize to functions of classical Boolean model for sets. The Boolean function f may be studied via its subgraph, i.e. as a random set in Rⁿ x R. The key notion is then the functional Q(Bt), i.e. the probability that a compact set Bt centred at altitude t misses the subgraph of f. The general expression of Q(Bt) is given, and followed by a series of important derivations (volumes, gradients, numbers of summits, etc). Theorems of structure are given: they concern the properties of infinite divisibility for the sup, and domains of attraction for Boolean functions. The last sections are devoted to the study of two particular Boolean functions; emphasis is put on the stereological implications of the approach. A critical example illustrates the theory.     

应用自适应模拟退火和多分辨率搜索实现医学超声图像的拼接

为提高图像拼接的成功率,提出了一种基于自适应模拟退火和多分辨率搜索策略的图像自动拼接新方法。该新算法先自适应地选取配准区域,再以互信息为相似度评价标准,结合自适应模拟退火和多分辨率搜索策略的思想分别进行图像平移和旋转参数的全局优化和局部搜索,最后实现图像的拼接。通过对含噪声数字图像和医学超声图像进行的24次模拟拼接实验表明,该新算法较传统的多分辨率直接搜索法有精度高、速度快和抗噪声能力强的优点。由于结合了模拟退火算法的高精度和多分辨率搜索法的高效率,改进后的图像拼接算法将拼接成功率提高了12.5%,并将运算时间控制在可接受的范围内。     

Dynamic imaging of multiphase flow through porous media using 4D cumulative reconstruction

This paper introduces an original application on reconstruction strategies for X‐ray computed microtomography, enabling the observation of time‐dependent changes that occur during multiphase flow. In general, by sparsely collecting radiographs, the reconstruction of the object is compromised. Optimizations can be achieved by combining specific characteristics of the dynamics with the acquisition. Herein, the proposed method relies on short random intervals in which no drastic changes occur in the sample to acquire as many radiographs as possible that constitute a reconstructible data set. As these intervals are unpredictable, the method tries to guarantee that the collected radiograph data during these specific intervals are enough to recover useful information about the dynamics. Simulations of a percolating fluid in a digital rock are used to replicate an X‐ray computed microtomography experiment to test the proposed method. The results demonstrate the potential of the proposed strategy for imaging multiphase flow in porous media and how data collected during distinct events can be combined to enhance the reconstruction of frames of the percolation process.     

Quantitative image analysis of finite porous media

Software for the reconstruction of branch-node charts from serial sections is tested with a simple cubic lattice, and is applied to determine the genus per unit volume (specific genus) of a Berea sandstone sample from seventy-eight serial sections. The genus is found analytically for the cubic lattice as a function of depth, cross-section and volume. These results enable us to draw conclusions about the relative importance of depth and cross-section and provide useful information on how to treat finite sample data to obtain the specific genus of an infinite homogeneous porous medium. It is shown that it is more important to have a deep sample (many serial sections) than a sample of large cross-section. For samples which are too small in the direction of sectioning, the genus and the rate of change of genus with volume are too low because some of the large loops are not completed within the sample boundaries. For the Berea sample, this ‘shallow-sample depth’ is about 2·2 grain diameters (forty-five serial sections). Only data points at depths in excess of this value are used in determining the genus per unit volume. The slope of the genus versus volume curve is the better predictor of the genus per unit volume of the unbounded medium, of which the sample is a small part, than the value of genus/volume of the sample. For samples of finite cross-section, the G_min and G_max versus volume curves are divergent and they only become essentially parallel when the dimensions in the plane of sectioning are large multiples of the grain size. It is shown that it is reasonable to assume that the arithmetic mean slope found for a small cross-sectional area is a good estimate of the common slope that would be attained at high cross-sectional areas. Therefore, samples of small cross-section can be used, resulting in a reduction in the amount of data to be processed and an enhancement of the resolution of small features. The Berea sample data, beyond the ‘shallow-sample’ region, show the same qualitative features as predicted analytically for the cubic lattice. The ratio of the slopes of the G_max and G_min curves is 1·22 and the genus per unit volume from the mean slope is 52·6 × 10^?8 μm^?3.     

Probabilistic data analysis: an introductory guide

Quantitative science requires the assessment of uncertainty, and this means that measurements and inferences should be described as probability distributions. This is done by building data into a probabilistic likelihood function which produces a posterior 'answer' by modulating a prior 'question'.
Probability calculus is the only way of doing this consistently, so that data can be included gradually or all at once while the answer remains the same. However, probability calculus is only a language; it does not restrict the questions one can ask by setting one's prior. We discuss how to set sensible priors, in particular for a large problem like image reconstruction.
We also introduce practical modern algorithms (Gibbs sampling, Metropolis algorithm, genetic algorithms, and simulated annealing) for computing probabilistic inference.     

基于Geomagic的曲面CAD模型重构

随着逆向工程的发展,越来越多的产品采用逆向制造。以冲压件为例,讲述了Geomagic、UG软件进行逆向参数化建模的设计思路和应用特点。使用Geomagic软件将获取的制件表面数据进行预处理,并基于NURBS曲面对制件进行自由曲面重构及误差分析,最后在UG中完成曲面局部重构及实体建模。表明,应用Geomagic、UG软件相互结合,可以进行曲面快速重构,大大缩短了设计周期,提高了研发效率。     

Testing mounting media to eliminate background noise in confocal microscope 3-D images of insect genitalia

Recently, the confocal laser scanning microscope (CLSM) has been used to image and generate three-dimensional reconstructions of miniscule insect tissues and cuticular structures. These three-dimensional reconstructions provide the investigator with key information concerning the spatial relationship among structures and substructures. Unfortunately, there can be high levels of background "noise" which can obscure the specimen in these three-dimensional reconstructions. This background "noise" might be a result of the mounting media either autofluorescing or reflecting and scattering the imaged specimen's fluorescence. The standard nonpermanent mounting medium is glycerine jelly (a 1:17:17 ratio of porcine gelatin to glycerine to water). In this study, the organic molecule (lipid, protein, or carbohydrate) added to the glycerine water mixture was varied. The relative background to specimen signal (the mean voxel brightness reading in ImageJ freeware) was compared across mountants. The mounting media tested are ranked from best (least background noise) to worst (most background noise) as follows: agarose, agar, pectin, gelatin (the standard), petroleum jelly. A 1% agarose mountant (1:50:50 ratio of agarose to glycerine to water) is recommended because it causes little to no background noise, provides consistent high quality contrast between specimen and background with increasing depth, and is easy to handle.     

Estimates for the elastic moduli of random orthorhombic polycrystals

Our variational bounds are suggested to provide estimates on the possible scatter ranges for the macroscopic elastic moduli of random polycrystalline materials. Explicit expressions for the random aggregates of orthorhombic crystals are derived and calculated. The complicated general bounds are well approximated by the simple ones for specific spherical cell polycrystals, which are proposed also to represent practical equi-axed particulate aggregates. Hence the latter could be recommended for practical uses. The results for a number of polycrystals indicate that their macroscopic moduli may be determined with the accuracy from two to four significant digits.     

故障识别中并行组合模拟退火算法的应用

提出了一种基于并行组合模拟退火算法的故障识别方法，该混合算法综合了遗传算法和模拟退火算法的优点。详细讨论了并行组合模拟退火算法的原理及实现方法，并应用于两个设备诊断实例中，结果证实了该算法的有效性。     

遗传模拟退火算法在冲裁件优化排样中的应用

主要研究冲裁工件排样优化算法及实现问题。多边形顶点算法适于各种形状单件条料排样方式的优化 ,但随着优化精度提高 ,其搜索空间将急剧增大 ;将其与遗传模拟退火算法相结合 ,克服了顶点算法计算量大 ,耗时多的局限 ,可高效、准确地得出工件排样的最优解。该算法已在ObjectARX开发出的冲裁模优化排样系统中得到验证     

Optimal dispatching of multipriority jobs to two heterogeneous workstations

The general problem scenario of this paper is the following: Jobs of various priorities, stationed in a common storage area, are waiting to be dispatched to two non-identical workstations. Any of the waiting jobs can be accessed from the storage at any given time. Each job can be processed on either of the workstations, but once a job has been assigned it may not be preempted. By job priority it is meant that a higher priority job has disptach preference over a lower priority job. The processing time of a job on a given workstation is assumed to be random, the distribution being dependent on the job type and the configuration of the workstation.Specifically, the first problem studied considers only two classes of jobs: (1) hot jobs, whose processing is to be expedited and thus have the higher dispatch priority, and (2) routine jobs which may be assigned to an available workstation only if the workstation has been rejected by all hot jobs. The processing times are assumed to be exponentially distributed with means depending on the job class and workstation. We assume that, on the average, one workstation is faster than the other with regard to processing any job. The dispatching objective for each job class is to minimize its expected flowtime. It is shown that threshold dispatching policies are optimal for this problem. That is, the faster processor should be utilized whenever possible, and for each class there exists an explicit threshold such that when the number of jobs of that class in the buffer exceeds this threshold then a job of that class is dispatched to the slower processor, otherwise these jobs wait for the faster processor to become available. For the higher priority jobs, this threshold is shown to be a function only of the various processing rates of the two workstations. For the lower priority jobs, the threshold also depends on the number of higher priority jobs in the buffer.The results is extended to a system with n priority classes. Again, it is shown that when the processing times are exponentially distributed with different rates and the dispatching objective for each class is to minimize its expected flowtime, the optimal dispatching policies are of threshold type. Explicit thresholds are easily derived.