Computational burden is a major concern when an iterative algorithm is used to reconstruct a three-dimensional (3-D) image with attenuation, detector response, and scatter corrections. Most of the computation time is ...
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Computational burden is a major concern when an iterative algorithm is used to reconstruct a three-dimensional (3-D) image with attenuation, detector response, and scatter corrections. Most of the computation time is spent executing the projector and backprojector of an iterative algorithm. Usually, the projector and the backprojector are transposed operators of each other. The projector should model the imaging geometry and physics as accurately as possible. Some researchers have used backprojectors that are computationally less expensive than the projectors to reduce computation time. This paper points out that valid backprojectors should satisfy a condition that the projector/backprojector matrix must not contain negative eigenvalues. This paper also investigates the effects when unmatched projector/backprojector pairs are used.
In this paper, a dynamic user equilibrium traffic assignment model with simultaneous departure time/ route choices and elastic demands is formulated as an arc-based nonlinear complementarity problem on congested traff...
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In this paper, a dynamic user equilibrium traffic assignment model with simultaneous departure time/ route choices and elastic demands is formulated as an arc-based nonlinear complementarity problem on congested traffic networks. The four objectives of this paper are (1) to develop an arc-based formulation which obviates the use of path-specific variables, (2) to establish existence of a dynamic user equilibrium solution to the model using Brouwer's fixed-point theorem, (3) to show that the vectors of total arc inflows and associated minimum unit travel costs are unique by imposing strict monotonicity conditions on the arc travel cost and demand functions along with a smoothness condition on the equilibria, and (4) to develop a heuristic algorithm that requires neither a path enumeration nor a storage of path-specific flow and cost information. Computational results are presented for a simple test network with 4 arcs, 3 nodes, and 2 origin-destination pairs over the time interval of 120 periods. (C) 2002 Elsevier Science Ltd. All rights reserved.
In this paper, we introduce and study a new class of generalized nonlinear implicit quasivariational inclusions with fuzzy mappings. An existence theorem of solutions is proved without compactness assumptions. A new i...
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In this paper, we introduce and study a new class of generalized nonlinear implicit quasivariational inclusions with fuzzy mappings. An existence theorem of solutions is proved without compactness assumptions. A new iterative algorithm is suggested and analysed. The convergence of iterative sequences generated by the new algorithm are also given. As special cases, some known results are also discussed. (C) 2002 Elsevier Science B.V. All rights reserved.
Two new iterative algorithms to be used to reconstruct a tested wavefront from its cyclic radial shearing (CRS) fringe pattern are proposed. First, the phase difference (PHD) in the common area of the contracted and e...
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Two new iterative algorithms to be used to reconstruct a tested wavefront from its cyclic radial shearing (CRS) fringe pattern are proposed. First, the phase difference (PHD) in the common area of the contracted and expanded tested wavefront are determined directly from the CRS fringe pattern of the tested wavefront by the Fourier transform method. Then, according to the PHD, the tested wavefront is reconstructed precisely by the two iterative algorithms. The numerical simulation of the reconstruction of a tested wavefront with distortion is implemented, showing that the wavefront reconstruction can be performed precisely by these algorithms with root mean square (rms) less than or equal to lambda/20. A CRS interferometer is constructed with a radial shearing ratio of s = 1 : 1.4 and is used to test a distorted wavefront with a one-step phase jump successfully. The results of numerical simulation and optical testing show that with these algorithms, the CRS interferometric technique can be easily used to make the evaluation of the optical component quality as well as testing of the wavefront distortion of a high-power laser. Finally, the convergence of two algorithms is also analyzed. (C) 2002 Society of Photo-Optical Instrumentation Engineers.
Methods for selecting sites to be included in reserve networks generally neglect the spatial location of sites, often resulting in highly fragmented networks. This restricts the possibility of dispersal between sites,...
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Methods for selecting sites to be included in reserve networks generally neglect the spatial location of sites, often resulting in highly fragmented networks. This restricts the possibility of dispersal between sites, which for many species may be essential for long-term persistence. Here I describe iterative reserve selection algorithms which incorporate considerations of reserve connectivity and evaluate their performance using a data set for macroinvertebrates in ponds. Methods where spatial criteria were only invoked when ties between sites occurred did not perform significantly better than a simple greedy algorithm in terms of reserve connectivity. An algorithm based on a composite measure of species added and changes in reserve connectivity produced a reserve network with higher connectivity, but needed more sites to represent all species. A trade-off between connectivity and efficiency may be inevitable. but the costs in terms of efficiency may be justified if long-term persistence of species is more likely. (C) 2001 Elsevier Science Ltd. All rights reserved.
In this paper we employ mixed finite elements and numerically study an integrated two-dimensional model of fluid flow and compaction in a sedimentary basin. This model describes a single phase incompressible flow in a...
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In this paper we employ mixed finite elements and numerically study an integrated two-dimensional model of fluid flow and compaction in a sedimentary basin. This model describes a single phase incompressible flow in a two-dimensional section of a sedimentary basin with vertical compaction. At each time step, an iterative algorithm is used to solve this model. The determination of the grid movement is based on the mass conservation and movement of sediments in the basin, while the mixed method is utilized to solve the fluid flow over the moving grid. Numerical experiments are presented to verify this iterative algorithm and show representative solutions for the model under consideration.
In this paper, we study panel count data with covariates. A semiparametric pseudolikelihood estimation method is proposed based on the assumption that, given a covariate vector Z, the underlying counting process is a ...
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In this paper, we study panel count data with covariates. A semiparametric pseudolikelihood estimation method is proposed based on the assumption that, given a covariate vector Z, the underlying counting process is a nonhomogeneous Poisson process with the conditional mean function given by E(N(t) \ Z) = Lambda(0)(t) exp(beta(0)'Z). The proposed estimation method is shown to be robust in the sense that the estimator converges to its true value regardless of whether or not N(t) is a conditional Poisson process, given Z. An iterative numerical algorithm is devised to compute the semiparametric maximum pseudolikelihood estimator of (beta(0), Lambda(0)). The algorithm appears to be attractive, especially when beta(0) is a high-dimensional regression parameter. Some simulation studies are conducted to validate the method. Finally, the method is applied to a real dataset from a bladder tumour study.
Neural stem cells (NSCs) in vitro are able to generate clonal structures, "neurospheres," that exhibit intra-clonal neural cell-lineage diversity;i.e., they contain, in addition to NSCs, neuronal and glial p...
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Neural stem cells (NSCs) in vitro are able to generate clonal structures, "neurospheres," that exhibit intra-clonal neural cell-lineage diversity;i.e., they contain, in addition to NSCs, neuronal and glial progenitors in different states of differentiation. The present study focuses on a subset of neurospheres derived from fresh clinical specimens of human brain by using an in vitro system that relies on particular growth factors, serum, and anchorage withdrawal. Thirty individual and exemplary cDNA libraries from these neurosphere clones were clustered and rearranged within a panel after characterization of differentially expressed transcripts. The molecular phenotypes that were obtained indicate that clonogenic NSCs in our in vitro system are heterogeneous, with subsets reflecting distinct neural developmental commitments. This approach is useful for the sorting and expansion of NSCs and facilitates the discovery of genes involved in cell proliferation, communication, fate control, and differentiation.
A new algorithm for the removal of blocking artifacts in block-DCT compressed images and video sequences is proposed in this paper. The algorithm uses deblocking frames of variable size (DFOVS). A deblocking frame is ...
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ISBN:
(纸本)0780374029
A new algorithm for the removal of blocking artifacts in block-DCT compressed images and video sequences is proposed in this paper. The algorithm uses deblocking frames of variable size (DFOVS). A deblocking frame is a square of pixels which overlaps image blocks. Deblocking is achieved by applying weighted summation on pixels quartets which reside in deblocking frames. The pixels in a quartet are symmetrically aligned with respect to block boundaries. The weights are determined according to a special 2-D function and a predefined factor, we refer to as a grade. A pixel's grade is determined according to the amount of details in its neighborhood. Deblocking of monotone areas is achieved by iteratively applying deblocking frames of decreasing sizes on such areas. This new algorithm produces very good subjective results and PSNR results which are competitive relative to available state-of-the-art methods.
In this paper, two novel iterative (orthogonal and non-orthogonal projection) schemes are proposed for noise reduction in electrocardiogram (ECG). These methods are first tried out on the well-known Lorenz system befo...
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ISBN:
(纸本)0780376129
In this paper, two novel iterative (orthogonal and non-orthogonal projection) schemes are proposed for noise reduction in electrocardiogram (ECG). These methods are first tried out on the well-known Lorenz system before extending to the recorded ECG signals. Results from the studies show that for the same signal-to-noise ratio (SNR) improvement, the non-orthogonal projection method (M2) requires less iterations than the orthogonal projection method (M1). More importantly, the iterative nature of the algorithms improve the performance of the schemes compared to the non-iterative schemes.
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