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891.
Fatos Xhafa Leonard Barolli Santi Caballé Raul Fernández 《The Journal of supercomputing》2010,53(1):45-65
With the fast development of IT technologies, virtual organizations are more and more present in the current collaborative
work and learning activity. For instance, many subjects in virtual distance learning are organized as online groups of students,
who use groupware tools to complete their learning tasks. In this paper, we address the efficient management of peer groups
in JXTA-based P2P systems as a key issue in many P2P applications that use peer group as a unit such as for remote execution
of tasks in parallel and distributed applications. From this perspective, we consider peer grouping as the basis in the development
of groupware tools in P2P systems. 相似文献
892.
Jun Liu Haiyang Huang Zhongdan Huan Haili Zhang 《International Journal of Computer Vision》2010,90(2):131-149
In this paper, a new variational framework of restoring color images with impulse noise is presented. The novelty of this
work is the introduction of an adaptively weighting data-fidelity term in the cost functional. The fidelity term is derived
from statistical methods and contains two weighting functions as well as some statistical control parameters of noise. This
method is based on the fact that impulse noise can be approximated as an additive noise with probability density function
(PDF) being the finite mixture model. A Bayesian framework is then formulated in which likelihood functions are given by the
mixture model. Inspired by the expectation-maximization (EM) algorithm, we present two models with variational framework in
this study. The superiority of the proposed models is that: the weighting functions can effectively detect the noise in the
image; with the noise information, the proposed algorithm can automatically balance the regularity of the restored image and
the fidelity term by updating the weighting functions and the control parameters. These two steps ensure that one can obtain
a good restoration even though the degraded color image is contaminated by impulse noise with large ration (90% or more).
In addition, the numerical implementation of this algorithm is very fast by using a split algorithm. Some numerical experimental
results and comparisons with other methods are provided to show the significant effectiveness of our approach. 相似文献
893.
Extracting reliable image edge information is crucial for active contour models as well as vascular segmentation in magnetic
resonance angiography (MRA). However, conventional edge detection techniques, such as gradient-based methods and wavelet-based
methods, are incapable of returning reliable detection responses from low contrast edges in the images. In this paper, we
propose a novel edge detection method by combining B-spline wavelet magnitude with standard deviation inside local region.
It is proved theoretically and demonstrated experimentally in this paper that the new edge detection method, namely BWLSD,
is able to give consistent and reliable strengths for edges with different image contrasts. Moreover, the relationship between
the size of local region with non-zero wavelet magnitudes and the scale of wavelet function is established. This relationship
indicates that if the scale of the adopted wavelet function is s, then the size of a local region, from which the standard deviation is estimated, should be 2s−1. The proposed edge detection technique is embedded in FLUX, namely, BWLSD-FLUX, for vascular segmentation in MRA image
volumes. Experimental results on clinical images show that, as compared with the conventional FLUX, BWLSD-FLUX can achieve
better segmentations of vasculatures in MRA images under same initial conditions. 相似文献
894.
From Images to Shape Models for Object Detection 总被引:2,自引:0,他引:2
Vittorio Ferrari Frederic Jurie Cordelia Schmid 《International Journal of Computer Vision》2010,87(3):284-303
We present an object class detection approach which fully integrates the complementary strengths offered by shape matchers.
Like an object detector, it can learn class models directly from images, and can localize novel instances in the presence
of intra-class variations, clutter, and scale changes. Like a shape matcher, it finds the boundaries of objects, rather than
just their bounding-boxes. This is achieved by a novel technique for learning a shape model of an object class given images of example instances. Furthermore, we also integrate Hough-style voting with a non-rigid point matching algorithm to localize
the model in cluttered images. As demonstrated by an extensive evaluation, our method can localize object boundaries accurately
and does not need segmented examples for training (only bounding-boxes). 相似文献
895.
In this paper, we prove that the Legendre tau method has the optimal rate of convergence in L
2-norm, H
1-norm and H
2-norm for one-dimensional second-order steady differential equations with three kinds of boundary conditions and in C([0,T];L
2(I))-norm for the corresponding evolution equation with the Dirichlet boundary condition. For the generalized Burgers equation,
we develop a Legendre tau-Chebyshev collocation method, which can also be optimally convergent in C([0,T];L
2(I))-norm. Finally, we give some numerical examples. 相似文献
896.
The paper deals with a numerical analysis of the incomplete interior penalty Galerkin (IIPG) method applied to one dimensional
Poisson problem. Based on a particular choice of the interior penalty parameter σ (order of O(h
−1)), we derive the optimal error estimate in the L
2-norm for odd degrees of polynomial approximation for locally quasi-uniform meshes. Moreover, we show that only the mentioned
choice of the penalty parameter leads to optimal orders of convergence. Finally, presented numerical experiments verify the
theoretical results. 相似文献
897.
In this paper, Radial Basis Function (RBF) method for interpolating two dimensional functions with localized features defined
on irregular domain is presented. RBF points located inside the domain and on its boundary are chosen such that they are the
image of conformally mapped points on concentric circles on a unit disk. On the disk, a fast RBF solver to compute RBF coefficients
developed by Karageorghis et al. (Appl. Numer. Math. 57(3):304–319, 2007) is used. Approximation values at desired points in the domain can be computed through the process of conformal transplantation.
Some numerical experiments are given in a style of a tutorial and MATLAB code that solves RBF coefficients using up to 100,000 RBF points is provided. 相似文献
898.
Alina Chertock Charles R. Doering Eugene Kashdan Alexander Kurganov 《Journal of scientific computing》2010,45(1-3):200-214
The dispersal and mixing of scalar quantities such as concentrations or thermal energy are often modeled by advection-diffusion equations. Such problems arise in a wide variety of engineering, ecological and geophysical applications. In these situations a quantity such as chemical or pollutant concentration or temperature variation diffuses while being transported by the governing flow. In the passive scalar case, this flow prescribed and unaffected by the scalar. Both steady laminar and complex (chaotic, turbulent or random) time-dependent flows are of interest and such systems naturally lead to questions about the effectiveness of the stirring to disperse and mix the scalar. The development of reliable numerical methods for advection-diffusion equations is crucial for understanding their properties, both physical and mathematical. In this paper, we extend a fast explicit operator splitting method, recently proposed in (A. Chertock, A. Kurganov, G. Petrova, Int. J. Numer. Methods Fluids 59:309–332, 2009), for solving deterministic convection-diffusion equations, to the problems with random velocity fields and singular source terms. A superb performance of the method is demonstrated on several two-dimensional examples. 相似文献
899.
Keqin Li 《The Journal of supercomputing》2010,54(3):271-297
We present fast and highly scalable parallel computations for a number of important and fundamental matrix problems on distributed
memory systems (DMS). These problems include matrix multiplication, matrix chain product, and computing the powers, the inverse,
the characteristic polynomial, the determinant, the rank, the Krylov matrix, and an LU- and a QR-factorization of a matrix,
and solving linear systems of equations. Our highly scalable parallel computations for these problems are based on a highly
scalable implementation of the fastest sequential matrix multiplication algorithm on DMS. We show that compared with the best
known parallel time complexities on parallel random access machines (PRAM), the most powerful but unrealistic shared memory
model of parallel computing, our parallel matrix computations achieve the same speeds on distributed memory parallel computers
(DMPC), and have an extra polylog factor in the time complexities on DMS with hypercubic networks. Furthermore, our parallel
matrix computations are fully scalable on DMPC and highly scalable over a wide range of system size on DMS with hypercubic
networks. Such fast (in terms of parallel time complexity) and highly scalable (in terms of our definition of scalability)
parallel matrix computations were rarely seen before on any distributed memory systems. 相似文献
900.
Soledad Escolar Díaz Florin Isaila Alejandro Calderón Mateos Luis Miguel Sanchez García David E. Singh 《The Journal of supercomputing》2010,51(1):76-93
In the last years the Wireless Sensor Networks’ (WSN) technology has been increasingly employed in various application domains.
The extensive use of WSN posed new challenges in terms of both scalability and reliability. This paper proposes Sensor Node
File System (SENFIS), a novel file system for sensor nodes, which addresses both scalability and reliability concerns. SENFIS
can be mainly used in two broad scenarios. First, it can transparently be employed as a permanent storage for distributed
TinyDB queries, in order to increase the reliability and scalability. Second, it can be directly used by a WSN application
for permanent storage of data on the WSN nodes. The experimental section shows that SENFIS implementation makes an efficient
use of resources in terms of energy consumption, memory footprint, flash wear levelling, while achieving execution times similarly
with existing WSN file systems. 相似文献