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Multi-scale UDCT dictionary learning based highly undersampled MR image reconstruction using patch-based

Min YUAN,Bing-xin YANG,Yi-de MA,Jiu-wen ZHANG,Fu-xiang LU,Tong-feng ZHANG

《信息与电子工程前沿（英文）》 2015年第16卷第12期页码 1069-1087 doi: 10.1631/FITEE.1400423

摘要： Recently, dictionary learning (DL) based methods have been introduced to compressed sensing magnetic resonance imaging (CS-MRI), which outperforms pre-defined analytic sparse priors. However, single-scale trained dictionary directly from image patches is incapable of representing image features from multi-scale, multi-directional perspective, which influences the reconstruction performance. In this paper, incorporating the superior multi-scale properties of uniform discrete curvelet transform (UDCT) with the data matching adaptability of trained dictionaries, we propose a flexible sparsity framework to allow sparser representation and prominent hierarchical essential features capture for magnetic resonance (MR) images. Multi-scale decomposition is implemented by using UDCT due to its prominent properties of lower redundancy ratio, hierarchical data structure, and ease of implementation. Each sub-dictionary of different sub-bands is trained independently to form the multi-scale dictionaries. Corresponding to this brand-new sparsity model, we modify the constraint splitting augmented Lagrangian shrinkage algorithm (C-SALSA) as patch-based C-SALSA (PB C-SALSA) to solve the constraint optimization problem of regularized image reconstruction. Experimental results demonstrate that the trained sub-dictionaries at different scales, enforcing sparsity at multiple scales, can then be efficiently used for MRI reconstruction to obtain satisfactory results with further reduced undersampling rate. Multi-scale UDCT dictionaries potentially outperform both single-scale trained dictionaries and multi-scale analytic transforms. Our proposed sparsity model achieves sparser representation for reconstructed data, which results in fast convergence of reconstruction exploiting PB C-SALSA. Simulation results demonstrate that the proposed method outperforms conventional CS-MRI methods in maintaining intrinsic properties, eliminating aliasing, reducing unexpected artifacts, and removing noise. It can achieve comparable performance of reconstruction with the state-of-the-art methods even under substantially high undersampling factors.

关键词： Compressed sensing (CS) Magnetic resonance imaging (MRI) Uniform discrete curvelet transform (UDCT) Multi-scale dictionary learning (MSDL) Patch-based constraint splitting augmented Lagrangian shrinkage algorithm (PB C-SALSA)

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On the added value of multi-scale modeling of concrete

《结构与土木工程前沿（英文）》 2022年第16卷第1期页码 1-23 doi: 10.1007/s11709-021-0790-0

摘要： This review of the added value of multi-scale modeling of concrete is based on three representative examples. The first one is concerned with the analysis of experimental data, taken from four high-dynamic tests. The structural nature of the high-dynamic strength increase can be explained by using a multi-scale model. It accounts for the microstructure of the specimens. The second example refers to multi-scale thermoelastic analysis of concrete pavements, subjected to solar heating. A sensitivity analysis with respect to the internal relative humidity (RH) of concrete has underlined the great importance of the RH for an assessment of the risk of microcracking of concrete. The third example deals with multi-scale structural analysis of a real-scale test of a segmental tunnel ring. It has turned out that multi-scale modeling of concrete enables more reliable predictions of crack opening displacements in tunnel segments than macroscopic models taken from codes of practice. Overall, it is concluded that multi-scale models have indeed a significant added value. However, its degree varies with these examples. In any case, it can be assessed by means of a comparison of the results from three sources, namely, multi-scale structural analysis, conventional structural analysis, and experiments.

关键词： experiments multi-scale analysis conventional structural analysis concrete reinforced concrete

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Environmental dispersivity in free-water-surface-effect dominated wetland: multi-scale analysis

Zi WU, Zhi LI, Li ZENG, Ling SHAO, Hansong TANG, Qing YANG, Guoqian CHEN

《环境科学与工程前沿（英文）》 2011年第5卷第4期页码 597-603 doi: 10.1007/s11783-011-0311-9

摘要： Distinct from the case with width-dominated shallow wetland flows, the longitudinal evolution of contaminant concentration in the most-typical pattern of wetland as dominated by free-water-surface-effect is characterized by a multi-scale analysis in the present study. An environmental dispersion model for the evolution of the mean concentration is deduced as an extension of Taylor's classical formulation by Mei’s multi-scale analysis. Corresponding environmental dispersivity is found identical to that determined by the method of concentration moments.

关键词： free-surface wetland environmental dispersion multi-scale analysis

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Hydromechanical model for hydraulic fractures using XFEM

Bo HE

《结构与土木工程前沿（英文）》 2019年第13卷第1期页码 240-249 doi: 10.1007/s11709-018-0490-6

摘要： In this study, a hydromechanical model for fluid flow in fractured porous media is presented. We assume viscous fluids and the coupling equations are derived from the mass and momentum balance equations for saturated porous media. The fluid flow through discrete cracks will be modelled by the extended finite element method and an implicit time integration scheme. We also present a consistent linearization of the underlying non-linear discrete equations. They are solved by the Newton-Raphson iteration procedure in combination with a line search. Furthermore, the model is extended to includes crack propagation. Finally, examples are presented to demonstrate the versatility and efficiency of this two-scale hydromechanical model. The results suggest that the presence of the fracture in a deforming, porous media has great impact on the fluid flow and deformation patterns.

关键词： multi-phase medium porous fracture multi-scale method

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A multi-scale model for CO

G. X. WANG, X. R. WEI, V. RUDOLPH, C. T. WEI, Y. QIN

《化学科学与工程前沿（英文）》 2009年第3卷第1期页码 20-25 doi: 10.1007/s11705-009-0138-0

摘要： This paper presents a multi-scale model to simulate the multicomponent gas diffusion and flow in bulk coals for CO sequestration enhanced coalbed methane recovery. The model is developed based on a bi-dispersed structure model by assuming that coal consists of microporous micro-particles, meso/macro-pores and open microfractures. The bi-disperse diffusion theory and the Maxwell-Stefan approach were incorporated in the model, providing an improved simulation of the CH —CO /CH —N counter diffusion dynamics. In the model, the counter diffusion process is numerically coupled with the flow of the mixture gases occurring within macro-pores or fractures in coal so as to account for the interaction between diffusion and flow in gas transport through coals. The model was validated by both experimental data from literature and our CO flush tests, and shows an excellent agreement with the experiments. The results reveal that the gas diffusivities, in particular the micro-pore diffusivities are strongly concentration-dependent.

关键词： multi-scale model gas transport coal coalbed methane CO₂ sequestration

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Characterization of random stress fields obtained from polycrystalline aggregate calculations using multi-scale

Bruno SUDRET,Hung Xuan DANG,Marc BERVEILLER,Asmahana ZEGHADI,Thierry YALAMAS

《结构与土木工程前沿（英文）》 2015年第9卷第2期页码 121-140 doi: 10.1007/s11709-015-0290-1

摘要： The spatial variability of stress fields resulting from polycrystalline aggregate calculations involving random grain geometry and crystal orientations is investigated. A periodogram-based method is proposed to identify the properties of homogeneous Gaussian random fields (power spectral density and related covariance structure). Based on a set of finite element polycrystalline aggregate calculations the properties of the maximal principal stress field are identified. Two cases are considered, using either a fixed or random grain geometry. The stability of the method w.r.t the number of samples and the load level (up to 3.5% macroscopic deformation) is investigated.

关键词： polycrystalline aggregates crystal plasticity random fields spatial variability correlation structure

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Multi-scale investigation of active failure for various modes of wall movement

《结构与土木工程前沿（英文）》 2021年第15卷第4期页码 961-979 doi: 10.1007/s11709-021-0738-4

摘要： Retained backfill response to wall movement depends on factors that range from boundary conditions to the geometrical characteristic of individual particles. Hence, mechanical understanding of the problem warrants multi-scale analyses that investigate reciprocal relationships between macro and micro effects. Accordingly, this study attempts a multi-scale examination of failure evolution in cohesionless backfills. Therefore, the transition of retained backfills from at-rest condition to the active state is modeled using the discrete element method (DEM). DEM allows conducting virtual experiments, with which the variation of particle and boundary properties is straightforward. Hence, various modes of wall movement (translation and rotation) toward the active state are modeled using two different backfills with distinct particle shapes (spherical and nonspherical) under varying surcharge. For each model, cumulative rotations of single particles are tracked, and the results are used to analyze the evolution of shear bands and their geometric characteristics. Moreover, dependencies of lateral pressure coefficients and coordination numbers, as respective macro and micro behavior indicators, on particle shape, boundary conditions, and surcharge levels are investigated. Additionally, contact force networks are visually determined, and their influences on pressure distribution and deformation mechanisms are discussed with reference to the associated modes of wall movement and particle shapes.

关键词： discrete-element modelling granular materials retaining walls particle shape arching

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Multi-scale evaluation of river health in Liao River Basin, China

Fei XU, Yanwei ZHAO, Zhifeng YANG, Yuan ZHANG

《环境科学与工程前沿（英文）》 2011年第5卷第2期页码 227-235 doi: 10.1007/s11783-010-0219-9

摘要： Previous studies on river health evaluation mainly focused on characterizations at a river-corridor scale and ignored the complex interactions between the river ecosystem and other components of the river basin. Based on the consideration of the interactions among rivers, associated river basin and habitats, an assessment framework with multi-scale indicators was developed. An index system divided among these three scales to characterize the health of river ecosystems in China’s Liao River Basin was established. Set pair analysis was applied to integrate the multi-scale indicators and determine the health classes. The evaluation results indicated that the rivers in the western and eastern zones of the Liao River were classified as sick, and rivers in the main stream of the Liao and Huntai rivers were classified as unhealthy. An excessive level of disturbances, such as large pollution loads and dense construction of water conservation projects within the river basin, were the main causes of the river health deterioration.

关键词： multi-scale characterization river health evaluation Liao River Basin set pair analysis

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Macro-architectured cellular materials: Properties, characteristic modes, and prediction methods

Zheng-Dong MA

《机械工程前沿（英文）》 2018年第13卷第3期页码 442-459 doi: 10.1007/s11465-018-0488-8

摘要：

Macro-architectured cellular (MAC) material is defined as a class of engineered materials having configurable cells of relatively large (i.e., visible) size that can be architecturally designed to achieve various desired material properties. Two types of novel MAC materials, negative Poisson’s ratio material and biomimetic tendon reinforced material, were introduced in this study. To estimate the effective material properties for structural analyses and to optimally design such materials, a set of suitable homogenization methods was developed that provided an effective means for the multiscale modeling of MAC materials. First, a strain-based homogenization method was developed using an approach that separated the strain field into a homogenized strain field and a strain variation field in the local cellular domain superposed on the homogenized strain field. The principle of virtual displacements for the relationship between the strain variation field and the homogenized strain field was then used to condense the strain variation field onto the homogenized strain field. The new method was then extended to a stress-based homogenization process based on the principle of virtual forces and further applied to address the discrete systems represented by the beam or frame structures of the aforementioned MAC materials. The characteristic modes and the stress recovery process used to predict the stress distribution inside the cellular domain and thus determine the material strengths and failures at the local level are also discussed.

关键词： architectured material cellular materials multi-scale modeling homogenization method effective material properties computational method

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一种用于工业过程监测的鲁棒迁移字典学习算法 Article

阳春华, 梁慧平, 黄科科, 李勇刚, 桂卫华

《工程（英文）》 2021年第7卷第9期页码 1262-1273 doi: 10.1016/j.eng.2020.08.028

摘要：

由于数据驱动的过程监测方法具有普遍性，且不依赖反应机理，其已经成为复杂工业系统过程监测的主流。然而，大多数数据驱动的过程监测方法均假设历史训练数据和在线测试数据遵循相同的分布。事实上，由于工业系统恶劣的环境，从实际工业过程中收集的数据总是受到许多因素的影响，如多变的操作环境、原材料的变化和生产指标的修改。这些因素通常会使在线监测数据和历史训练数据分布不同，从而导致过程监测任务中的模型失配。因此，当将从训练数据中学习的模型应用于实际的在线监测时，很难实现精确的过程监测。为了解决操作环境变化导致的历史训练数据和在线测试数据之间的分布差异问题，提出了一种鲁棒的迁移字典学习（RTDL）算法用于工业过程监测。RTDL是表示学习和域自适应迁移学习的协同方法。该方法将历史训练数据和在线测试数据分别作为迁移学习问题的源域和目标域。然后将最大均值差异正则化和线性判别分析正则化引入字典学习框架，可以减少源域和目标域之间的分布差异。这样，即使源域和目标域的特征在实际变化的操作环境的干扰下明显不同，仍可以学习鲁棒的字典。这样的字典可以有效地提高过程监测和模态识别的性能。通过数值仿真和两个工业系统的实验验证了该方法的有效性和优越性。

关键词：过程监测多模态过程字典学习迁移学习

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图像边缘检测二维小波算法研究与实现

张红岩,张登攀

《中国工程科学》 2003年第5卷第4期页码 61-64

摘要：

边沿作为图像视觉的最主要特征，成为图像信息获取的重要内容。小波变换具有检测局域突变的能力，而且可以结合多尺度信息进行检测，因此成为图像信息边缘检测的优良工具。根据二维小波变换的特点,分析了利用二维小波进行图像边缘检测的基本原理，并设计了利用二维小波变换进行多尺度边缘匹配的检测算法。基于研究结果，编写了计算机应用程序，进行实例分析。

关键词：小波变换多尺度边缘检测

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基于稀疏表示的拉普拉斯稀疏字典图像分类 Article

Fang LI, Jia SHENG, San-yuan ZHANG

《信息与电子工程前沿（英文）》 2017年第18卷第11期页码 1795-1805 doi: 10.1631/FITEE.1600039

摘要：为取得更小且表现更好的字典，本文提出一种基于流形学习及双稀疏理论的拉普拉斯稀疏字典学习方法（Laplacian sparse dictionary, LSD）。

关键词：稀疏表示；拉普拉斯正则子；字典学习；双稀疏；流形

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具有深度阈值噪声消除的多尺度分析调制识别网络 Research Article

李响1,2,李一兵1,2,汤春瑞3,4,李迎松1,2

《信息与电子工程前沿（英文）》 2023年第24卷第5期页码 742-758 doi: 10.1631/FITEE.2200253

摘要：为了提高多变环境下调制信号识别的准确性、减少先验知识不足等因素对识别结果的影响，研究人员逐渐采用深度学习技术来替代传统的调制信号处理技术。为了解决低信噪比下调制信号识别精度低的问题，我们设计了一种具有深度阈值噪声消除的多尺度分析调制识别网络，在标签平滑的对称交叉熵函数作用下识别实际采集的调制信号。该网络由一个具有深度自适应阈值学习的消噪编码器和一个具有多尺度特征融合的解码器组成。将两个模块进行跳跃连接，共同作用以提高整体网络的鲁棒性。实验结果表明，该方法在低信噪比下比以前的方法具有更好的识别效果。该网络展示了对噪声阈值的灵活自学习能力以及所设计的特征融合模块对各种调制类型的多尺度特征获取的有效性。

关键词：信号消噪；深度自适应阈值学习网络；多尺度特征融合；调制识别

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Decreasing complexity of glucose time series derived from continuous glucose monitoring is correlated with deteriorating glucose regulation

《医学前沿（英文）》 2023年第17卷第1期页码 68-74 doi: 10.1007/s11684-022-0955-9

摘要： Most information used to evaluate diabetic statuses is collected at a special time-point, such as taking fasting plasma glucose test and providing a limited view of individual’s health and disease risk. As a new parameter for continuously evaluating personal clinical statuses, the newly developed technique “continuous glucose monitoring” (CGM) can characterize glucose dynamics. By calculating the complexity of glucose time series index (CGI) with refined composite multi-scale entropy analysis of the CGM data, the study showed for the first time that the complexity of glucose time series in subjects decreased gradually from normal glucose tolerance to impaired glucose regulation and then to type 2 diabetes (P for trend < 0.01). Furthermore, CGI was significantly associated with various parameters such as insulin sensitivity/secretion (all P < 0.01), and multiple linear stepwise regression showed that the disposition index, which reflects β-cell function after adjusting for insulin sensitivity, was the only independent factor correlated with CGI (P < 0.01). Our findings indicate that the CGI derived from the CGM data may serve as a novel marker to evaluate glucose homeostasis.

关键词： complexity of glucose time series continuous glucose monitoring impaired glucose regulation insulin secretion and sensitivity refined composite multi-scale entropy

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结合全变分最小化和稀疏字典学习后处理的低剂量CT重建 Article

Yong DING, Tuo HU

《信息与电子工程前沿（英文）》 2017年第18卷第12期页码 2001-2008 doi: 10.1631/FITEE.1700287

摘要：随着CT（computed tomography）中过量辐射剂量带来的健康风险日渐引发人们的担忧，低剂量CT得到了大量的关注。然而对于低剂量CT成像而言，在降低剂量的同时保证图像的高质量是一个很大的挑战。相比传统的滤波反投影算法，基于压缩感知的迭代重建法取得了良好的成像效果。但是迭代重建计算复杂度高，阻碍了其临床应用。本文提出一种结合全变分（total variation, TV）最小化和稀疏字典学习的重建方法，不仅提高了重建效果，而且通过自适应的停止策略提高了重建速度。实验结果表明，本文提出的方法相比其他类型的方法能获得更好的图像质量和更高的计算效率。

关键词：低剂量CT；CT成像；全变分；稀疏字典学习

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标题作者时间类型操作

Multi-scale UDCT dictionary learning based highly undersampled MR image reconstruction using patch-based

Min YUAN,Bing-xin YANG,Yi-de MA,Jiu-wen ZHANG,Fu-xiang LU,Tong-feng ZHANG

期刊论文

On the added value of multi-scale modeling of concrete

期刊论文

Environmental dispersivity in free-water-surface-effect dominated wetland: multi-scale analysis

Zi WU, Zhi LI, Li ZENG, Ling SHAO, Hansong TANG, Qing YANG, Guoqian CHEN

期刊论文

Hydromechanical model for hydraulic fractures using XFEM