Atrial fibrillation (AF) is a common cardiac arrhythmia, but its mechanisms are incompletely understood. The identification of phase singularities (PSs) has been used to define spiral waves involved in maintaining the...
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Atrial fibrillation (AF) is a common cardiac arrhythmia, but its mechanisms are incompletely understood. The identification of phase singularities (PSs) has been used to define spiral waves involved in maintaining the arrhythmia, as well as daughter wavelets. In the past, PSs have often been identified manually. Automated PS detection algorithms have been described previously, but when we attempted to apply a previously developed algorithm we experienced problems with false positives that made the results difficult to use directly. We therefore developed a tool for PS identification that uses multiple strategies incorporating both image analysis and mathematical convolution for automated detection with optimized sensitivity and specificity, followed by manual verification. The tool was then applied to analyze PS behavior in simulations of AF maintained in the presence of spatially distributed acetylcholine effects in cell grids of varying size. These analyses indicated that in almost all cases, a single PS lasted throughout the simulation, corresponding to the central-core tip of a single spiral wave that maintained AF. The sustained PS always localized to an area of low acetylcholine concentration. When the grid became very small and no area of low acetylcholine concentration was surrounded by zones of higher concentration, AF could not be sustained. The behavior of PSs and the mechanisms of AF were qualitatively constant over an 11.1-fold range of atrial grid size, suggesting that the classical emphasis on tissue size as a primary determinant of fibrillatory behavior may be overstated. (C) 2002 American Institute of Physics.
The Apsara algorithm is an input-queued switch scheduler that uses limited parallelism to find a matching in a single iteration, as compared to the O(N-3) iterations of the more common maximum-weight matching algorith...
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The Apsara algorithm is an input-queued switch scheduler that uses limited parallelism to find a matching in a single iteration, as compared to the O(N-3) iterations of the more common maximum-weight matching algorithm. Apsara also achieves a throughput of up to 100 percent and has very good delay properties.
Link adaptation techniques, where the modulation, coding rate, and/or other signal transmission parameters are dynamically adapted to the changing channel conditions, have recently emerged as powerful tools for increa...
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Link adaptation techniques, where the modulation, coding rate, and/or other signal transmission parameters are dynamically adapted to the changing channel conditions, have recently emerged as powerful tools for increasing the data rate and spectral efficiency of wireless data-centric networks. While there has been significant progress on understanding the theoretical aspects of time adaptation in LA protocols, new challenges surface when dynamic transmission techniques are employed in broadband wireless networks with multiple signaling dimensions. Those additional dimensions are mainly frequency, especially in multicarrier systems, and space in multiple-antenna systems, particularly multiarray multiple-input multiple-output communication systems. In this article we give an overview of the challenges and promises of link adaptation in future broadband wireless networks. We suggest guidelines to help in the design of robust, complexity/cost-effective algorithms for these future wireless networks.
This article classifies a group of complicated relational calculus queries whose search algorithms run in time O(I Log(d) I + U) and space 0(1), where I and U are the sizes of the input and output, and d is a constant...
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This article classifies a group of complicated relational calculus queries whose search algorithms run in time O(I Log(d) I + U) and space 0(1), where I and U are the sizes of the input and output, and d is a constant depending on the query (which is usually, but not always, equal to zero or one). Our algorithm will not entail any preprocessing of the data. (C) 2002 Elsevier Science (USA).
We present an O(n(4))-time algorithm for the following problem: Given a set of items with known access frequencies, find the optimal binary search tree under the realistic assumption that each comparison can only resu...
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We present an O(n(4))-time algorithm for the following problem: Given a set of items with known access frequencies, find the optimal binary search tree under the realistic assumption that each comparison can only result in a two-way decision: either an equality comparison or a less-than comparisons. This improves the best known result of O(n(5)) time, which is based on split tree algorithms. Our algorithm relies on establishing thresholds on the frequency of an item that can occur as an equality comparison at the root of an optimal tree. (C) 2002 Elsevier Science (USA). All rights reserved.
Part II. Proposes the usage of symbolic learning methods based on multiple-valued logic and implemented in reconfigurable computer hardware. Aspects of realizing cube calculus operations in hardware; Types of cube ope...
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Part II. Proposes the usage of symbolic learning methods based on multiple-valued logic and implemented in reconfigurable computer hardware. Aspects of realizing cube calculus operations in hardware; Types of cube operations; Classes of computation patterns of cube operations.
It is of practical interest to identify which processes will benefit significantly from the use of constrained control algorithms such as model predictive control, and which will not. Explicit conditions are derived t...
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It is of practical interest to identify which processes will benefit significantly from the use of constrained control algorithms such as model predictive control, and which will not. Explicit conditions are derived that identify whether a particular process may benefit from constraint handling. These conditions are also useful for understanding the interactions between design and control for a particular system, especially for actuator placement and selection. The conditions are computable for a large-scale system directly from its transfer function model, a simulation model (e.g. defined by a set of ordinary/partial-differential equations and algebraic conditions), or experimental input-output data. The formulation considers the effects of measurement noise, process disturbances, model uncertainties, plant directionality and the quantity of experimental data. The conditions are illustrated by application to a paper-machine model constructed from industrial data.
Available register-transfer level (RTL) test generation techniques do not make a concerted effort to reduce the test application time associated with the derived tests. Chip tester memory limitations, increasing teste...
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Available register-transfer level (RTL) test generation techniques do not make a concerted effort to reduce the test application time associated with the derived tests. Chip tester memory limitations, increasing tester costs, etc., make it imperative that the issue of generating compact tests at the RTL be addressed and consolidated with the known gains of high-level testing. In this paper, the authors provide a comprehensive framework for generating compact tests for an RTL circuit. They develop a series of techniques that exploit the inherent parallelism available in symbolic test(s) derived for RTL module(s). These techniques enable them to schedule testing of multiple modules in parallel as well as perform test pipelining. In addition, the authors also present design for testability (DFT) techniques for lowering test application time. Using a maximum bipartite matching formulation, they choose a low-overhead set of test enhancements that can achieve compact tests. The authors' techniques can seamlessly plug into any, generic high-level test framework. Their experimental results in the context of one such framework indicate that the proposed methodology achieves an average reduction in test application time of 54.2% for the example circuits.
In this work, we describe and analyze algorithms for 2D wavelet packet (WP) decomposition for multicomputers and multiprocessors. In the case of multicomputers, the main goal is the generalization of former parallel W...
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In this work, we describe and analyze algorithms for 2D wavelet packet (WP) decomposition for multicomputers and multiprocessors. In the case of multicomputers, the main goal is the generalization of former parallel WP algorithms which are constrained to a number of processor elements equal to a power of 4. For multiprocessors, we discuss several optimizations of shared-memory algorithms and finally we compare the results obtained on multicomputers and multi-processors employing the message passing (MPI) and shared-memory programming (OpenMP) paradigm, respectively. (C) 2002 Elsevier Science Ltd. All rights reserved.
This paper presents and analyses an iterative process for the numerical realization of contact problems with Coulomb friction which is based on the method of successive approximations combined with a splitting type ap...
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This paper presents and analyses an iterative process for the numerical realization of contact problems with Coulomb friction which is based on the method of successive approximations combined with a splitting type approach. Numerical examples illustrate the efficiency of this method. (C) 2002 Elsevier Science B.V. All rights reserved.
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