基于神经网络和D-S证据理论辨识两相流流型

提出一种基于电容层析成像(ECT)系统、神经网络和证据理论辨识两相流流型的方法。这种方法采用神经网络与D-S证据理论相结合的方法来辨识两相流流型,并对两相流的几种常见流型进行了辨识。仿真实验结果表明:此种方法在两相流流型辨识中具有较高的判别精度,为两相流流型辨识提供了一种有效的手段。     

A multi-scale template method for shape detection with bio-medical applications

In this paper we present a novel methodology based on non-parametric deformable prototype templates for reconstructing the outline of a shape from a degraded image. Our method is versatile and fast and has the potential to provide an automatic procedure for classifying pathologies. We test our approach on synthetic and real data from a variety of medical and biological applications. In these studies it is important to reconstruct accurately the shape of the object under investigation from very noisy data. Here we assume that we have some prior knowledge about the object outline represented by a prototype shape. Our procedure deforms this shape by means of non-affine transformations and the contour is reconstructed by minimizing a newly developed objective function that depends on the transformation parameters. We introduce an iterative template deformation procedure in which the scale of the deformation decreases as the algorithm proceeds. We compare our results with those from a Gaussian Mixture Model segmentation and two state-of-the-art Level Set methods. This comparison shows that the proposed procedure performs consistently well on both real and simulated data. As a by-product we develop a new filter that recovers the connectivity of a shape.

基于高密度子网格光线追迹的三维发射层析重建算法

三维(three- dimensional,3D) 发射层析技术(emission computerized tomography,ECT) 是一种简单、高效且准确的燃 烧场3D成像与检测技术,其中权重矩阵的计算 精度决定了层析重建的精度和质量。本文研究了一种基于高密度子网格光线追迹的权重矩阵 计算方法, 将被测区域划分为密度更高的子网格,并根据相机成像模型实现光线追迹,以确定离散网格 对投影像素 的权重因子。数值模拟和燃烧火焰重建实验表明该算法具有较高的精度和计算效率。该研究 对于3D发射层析技术的实用化具有重要的理论意义。     

Bragg Edge Neutron Transmission Strain Tomography in Granular Systems

The advent of pixelated detectors for time‐of‐flight neutron transmission experiments has raised significant interest in terms of the potential for tomographic reconstructions of triaxial strain distributions. A recent publication by Lionheart and Withers [WRB Lionheart and PJ Withers, “Diffraction tomography of strain”, Inverse Problems, v31:045005, 2015] has demonstrated that reconstruction is not possible in the general sense; however, various special cases may exist. In this paper, we outline a process by which it is possible to tomographically reconstruct average triaxial elastic strains within individual particles in a granular assembly from a series of Bragg edge strain measurements. This algorithm is tested on simulated data in two and three dimensions and is shown to be capable of rejecting Gaussian measurement noise. Sources of systematic error that may present problems in an experimental implementation are briefly discussed.     

Elemental partitioning,lattice misfit and creep behaviour of Cr containing γ′ strengthened Co base superalloys

Novel Cr containing Co-Al-W base superalloys were studied by atom probe tomography and neutron diffraction. Cr is found to predominantly partition to the γ matrix and decrease partitioning of W to γ′. Furthermore, Cr significantly enhances the γ′ volume fraction, decreases the γ/γ′ lattice misfit and deteriorates the creep resistance. Addition of Ni to the Cr containing alloys affects partitioning of W and Al, further decreases the lattice misfit and results in the formation of irregularly shaped precipitates. Al, W and Cr tend to occupy the ‘B'sublattice in the γ′-A₃B phase (L1₂ type), while Co and Ni reside in the ‘A' sublattice.     

Atom probe tomography of nanoscale architectures in functional materials for electronic and photonic applications

Microscopy has played a central role in the advancement of nanoscience and nanotechnology by enabling the direct visualization of nanoscale structure, leading to predictive models of novel physical behaviors. Electronic and photonic device technologies, whose features and performance are often improved through miniaturization, have particularly benefited from new capabilities in the characterization of material structure and composition. This paper reviews recent applications of atom probe tomography to semiconducting materials with nanoscale architectures that are designed to impart novel properties and device functionality by virtue of their shape and size. A review is necessary because rapid advances in atom probe instrumentation and analysis in the last decade have greatly expanded the utility of atom probe tomography to address scientific questions and technical questions in this area. The paper is organized in terms of the surface topologies of nanoscale architectures. We begin with nominally planar interfaces including thin film heterostructures and superlattices with open surfaces. Distinctive capabilities in the analysis of interfaces are introduced, as are challenges arising from measurement artifacts. We then discuss nanowires and nanowire heterostructures with surfaces that are closed along one dimension, for which atom probe tomography has provided unique and important understandings on the doping processes. Finally, we consider nanocrystals and quantum dots with completely closed surfaces. Along the way, current challenges and opportunities for atom probe tomography are highlighted, and the reader is directed to complementary reviews of more technical aspects of atom probe analysis.     

Comparison of approaches based on optimization and algebraic iteration for binary tomography

Binary tomography represents a special category of tomographic problems, in which only two values are possible for the sought image pixels. The binary nature of the problems can potentially lead to a significant reduction in the number of view angles required for a satisfactory reconstruction, thusly enabling many interesting applications. However, the limited view angles result in a severely underdetermined system of equations, which is challenging to solve. Various approaches have been proposed to address such a challenge, and two categories of approaches include those based on optimization and those based on algebraic iteration. However, the relative strengths, limitations, and applicable ranges of these approaches have not been clearly defined in the past. Therefore, it is the main objective of this work to conduct a systematic comparison of approaches from each category. This comparison suggested that the approaches based on algebraic iteration offered both superior reconstruction fidelity and computation efficiency at low (two or three) view angles, and these advantages diminished at high view angles. Meanwhile, this work also investigated the application of regularization techniques, the selection of optimal regularization parameter, and the use of a local search technique for binary problems. We expect the results and conclusions reported in this work to provide valuable guidance for the design and development of algorithms for binary tomography problems.