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151.
Undersampling k-space is an effective way to decrease acquisition time for MRI. However, aliasing artifacts introduced by undersampling may blur the edges of magnetic resonance images, which often contain important information for clinical diagnosis. Moreover, k-space data is often contaminated by the noise signals of unknown intensity. To better preserve the edge features while suppressing the aliasing artifacts and noises, we present a new wavelet-based algorithm for undersampled MRI reconstruction. The algorithm solves the image reconstruction as a standard optimization problem including a ?2 data fidelity term and ?1 sparsity regularization term. Rather than manually setting the regularization parameter for the ?1 term, which is directly related to the threshold, an automatic estimated threshold adaptive to noise intensity is introduced in our proposed algorithm. In addition, a prior matrix based on edge correlation in wavelet domain is incorporated into the regularization term. Compared with nonlinear conjugate gradient descent algorithm, iterative shrinkage/thresholding algorithm, fast iterative soft-thresholding algorithm and the iterative thresholding algorithm using exponentially decreasing threshold, the proposed algorithm yields reconstructions with better edge recovery and noise suppression. 相似文献
152.
153.
This paper is divided into two parts. In the first part of the paper, the plant location model is adapted for the special case of siting wastewater treatment facilities when the wastewater sources and treatment facilities are arranged in a chain or linear configuration. In this problem, flows or shipments may be merged in common pipes that provide economies of scale in transport. In order to apply the plant location model, an appropriate definition of the additional cost incurred when a waste source joins a regional facility is required. In addition, sequential priority constraints are developed in the siting model in order to make possible proper accounting of transport costs. The new siting model can be conveniently solved by linear programming.In the second part of the paper, a dual of the plant location model is explored as a cost allocation method for the fixed charge facility siting problem. The constraint sets of the dual model can be shown to imply the core conditions of the related cost game; hence, a set of the dual variables from the dual problem can be regarded as rational cost allocations. The analysis places both facility siting and cost allocation in a common framework. 相似文献
154.
采用相对论和非相对论理论模型可描述奇异核的性质 .相对论平均场理论预言了2 6,2 7,2 8P存在一个质子晕 ,而27,28,29S存在两个质子晕 .最近 ,MSU的最新的实验发现了2 6,2 7,2 8P核存在一个质子晕.采用相对论 Hartree- Fock理论研究了 Fock项和矢量介子对奇异核性质的贡献,研究表明交换项和矢量介子对非常丰中子核性质的影响非常不同于对稳定线附近核性质的影响.同时,采用形变的Hartree- Fock- Bogoliubov理论研究了某些轻核同位素链的性质和形变. 相似文献
155.
非晶态Fe0.5Al0.5PO4表面上激光促进甲烷直接氧化合成甲醇的研究 总被引:1,自引:0,他引:1
用溶胶-凝胶法合成了非晶态Fe0.5Al0.5PO4。用XRD和TPR表征了其结构和晶格氧的活性;用IR和TPD表征了CH4在其表面上的吸附行为;用LSSR方法考察了CH4直接氧化合成CH3OH的反应规律。结果表明,Fe0.5Al0.5PO4具有非晶态的结构,FePO4和AlPO4的微区被均匀地相互隔离,导致固体本身不具有长程有序性。非晶态的Fe0.5Al0.5PO4与晶态的Fe0.5Al0.5P 相似文献
156.
157.
With the application of the topological upgrade, more and more experts are interested in the problems concerning the mathematical
structure’s upgrade to its power set. This paper is a further study on the structure and interrelationship of a power group.
By revealing the nature of relationship between the power group and a regular one, the present paper proves some theorems
of the structure of the power group and constructs some theorems on its homomorphism and isomorphism as well, proposing an
expression form and isomorphism replacement construct methods of the power group. 相似文献
158.
We investigate the relationship between the Gröbner-Shirshov bases in free associative algebras, free left modules and “double-free” left modules (that is, free modules over a free algebra). We first give Chibrikov’s Composition-Diamond lemma for modules and then we show that Kang-Lee’s Composition-Diamond lemma follows from it. We give the Gröbner-Shirshov bases for the following modules: the highest weight module over a Lie algebra sl 2, the Verma module over a Kac-Moody algebra, the Verma module over the Lie algebra of coefficients of a free conformal algebra, and a universal enveloping module for a Sabinin algebra. As applications, we also obtain linear bases for the above modules. 相似文献
159.
Tongde Zhong 《中国科学A辑(英文版)》1997,40(8):817-824
The homotopy formulas of (r, s) differential forms and the solution of $\bar \partial $ -equation of type (r, s) on localq-convex domains in Stein manifolds are obtained. The homotopy formulas on localq-convex domains have important applications in uniform estimates of $\bar \partial $ -equation and holomorphic extension of CR-manifolds. 相似文献
160.