Regularization techniques in realistic Laplacian computation

This paper explores regularization options for the ill-posed spline coefficient equations in the realistic Laplacian computation. We investigate the use of the Tikhonov regularization, truncated singular value decomposition, and the so-called lambda-correction with the regularization parameter chosen by the L-curve, generalized cross-validation, quasi-optimality, and the discrepancy principle criteria. The provided range of regularization techniques is much wider than in the previous works. The improvement of the realistic Laplacian is investigated by simulations on the three-shell spherical head model. The conclusion is that the best performance is provided by the combination of the Tikhonov regularization and the generalized cross-validation criterion-a combination that has never been suggested for this task before.     

Improved surface laplacian estimates of cortical potential using realistic models of head geometry

Surface Laplacian of scalp EEG can be used to estimate the potential distribution on the cortical surface as an alternative to invasive approaches. However, the accuracy of surface Laplacian estimation depends critically on the geometric shape of the head model. This paper presents a new method for computing the surface Laplacian of scalp potential directly on realistic scalp surfaces in the form of a triangular mesh reconstructed from MRI scans. Unlike previous methods, this algorithm does not resort to any surface fitting proxy and can improve the surface Laplacian estimation of cortical potential patterns by as much as 34% on realistically shaped head models. Simulations and experimental data are presented to demonstrate the advantage of the proposed method over the conventional spherical approximation and the utility of a more accurate surface Laplacian method for estimating cortical potentials from scalp electrodes.     

Improved method for computation of potentials in a realistic headshape model

The lead field analysis (LFA) algorithm, a new computational technique for the calculation of potentials on the surface of a realistic head shaped volume conductor model based on the boundary element method and the reciprocity theorem, is presented. The new algorithm, in comparison to the standard boundary element method, offers improved computational efficiency and lower storage requirements. It also yields more accurate surface potential results in the face of varying dipole source locations for a head shape boundary element model with a given number of nodes. Additionally, the algorithm results in quasi-analytic expressions of the derivatives of the surface potential with respect to the location of the sources, allowing the use of optimization techniques with better convergence properties. A set of simulations demonstrating the increased robustness of the LFA algorithm in the face of varying dipole source parameters is also described     

A computer model of human atria with reasonable computation loadand realistic anatomical properties

Atrial fibrillation is the most frequent arrhythmia, provoking discomfort, heart failure and arterial embolisms. The aim of this work is to develop a simplified anatomical computer model of human atria for the study of atrial arrhythmias and the understanding of electrical propagation mechanisms. With the model we propose, up to 40 s of real-time propagation have been simulated on a single-processor computer. The size and the electrophysiological properties of the simulated atria are within realistic values and information about anatomy has been taken into account in a three-dimensional structure. Besides normal sinus beat, pathological phenomena such as flutter and fibrillation have been induced using a programmed stimulation protocol. One important observation in our model is that atrial arrhythmias are a combination of functional and anatomical reentries and that the geometry plays an important role. This virtual atrium can reproduce electrophysiological observations made in humans but with the advantage of showing in great detail how arrhythmias are initiated and sustained. Such details are difficult or impossible to study in humans. This model will serve us as a tool to evaluate the impact of new therapeutic strategies and to improve them.     

Reduced computational redundancy implementation of DSP algorithms using computation sharing vector scaling

In this paper, we present a general approach which specifically targets reduction of redundant computation in common digital-signal processing (DSP) tasks such as filtering and matrix multiplication. We show that such tasks can be expressed as multiplication of vectors by scalars and this allows fast multiplication by sharing computation. Vector scaling operation is decomposed to find the most effective precomputations which yield a fast multiplier implementation. Two decomposition approaches are presented, one based on a greedy decomposition and the other based on fixed-size lookup and this leads to two multiplier architectures for vector-scalar products. Analog simulation of an example multiplier shows a speed advantage by a factor of about 1.85 over a conventional carry save array multiplier. Further simulations using 0.18 /spl mu/ technology show up to 20% speed advantage over Booth encoded Wallace tree multipliers.     

Mellin transforms of closed curves and one-dimensional functions: Direct computation and scaling properties

The Mellin transform of a closed contour is examined, and a magnitude invariance property for affine homothetic shapes is derived. A direct computation of the Mellin transform is introduced, applicable to polygonal closed shapes and to arbitrary polygonal one-dimensional functions as well.     

Toward realistic soft-tissue modeling in medical simulation

Most of today's medical simulation systems are based on geometric representations of anatomical structures that take no account of their physical nature. Representing physical phenomena and, more specifically, the realistic modeling of soft tissue will not only improve current medical simulation systems but will considerably enlarge the set of applications and the credibility of medical simulation, from neurosurgery planning to laparoscopic-surgery simulation. To achieve realistic tissue deformation, it is necessary to combine deformation accuracy with computer efficiency. On the one hand, biomechanics has studied complex mathematical models and produced a large amount of experimental data for accurately representing the deformation of soft tissue. On the other hand, computer graphics has proposed many algorithms for the real-time computation of deformable bodies, often at the cost of ignoring the physics principles. The author surveys existing models of deformation in medical simulation and analyze the impediments to combining computer-graphics representations with biomechanical models. In particular, the different geometric representations of deformable tissue are compared in relation to the tasks of real-time deformation, tissue cutting, and force-feedback interaction. Last, the author inspects the potential of medical simulation under the development of this key technology     

Creating realistic scenes in future multimedia systems

Multimedia environments need systems with better performance to meet the growing demands for more realism. Ultra-large-scale integration will eventually make possible the advanced, real-time graphic rendering technology that such digital imagery requires. The hardware-only architecture prototype discussed in this article presents a possible solution     

Signal scaling in cascade digital filters

Scaling of filter variables is central to fixed-point implementation of digital filters. A simple method of scaling based on scaling constants of individual sections of a cascade digital filter is presented. The proposed method saves much computational labor in the implementation of higher-order digital filters. Maximal amplitude expressions of second-order filter transfer functions are also presented.This work was supported by the Department of Science and Technology, Government of India, under Grant No. D.O.No.III-5(17)/85-ET.     

Weighing in on logic scaling trends

In this paper, scaling trends and the associated challenges are discussed from the perspective of the 2001 International Technology Roadmap for Semiconductors (ITRS) for both high-performance and low-power logic technologies. Starting from the overall chip circuit requirements, MOSFET and front-end process integration technology requirements, scaling trends, and challenges are discussed, as well as some of the key potential solutions to the challenges, along with the long-term issues and possible solutions for mobility improvement and optimal scaling for very small transistors. Potential solutions include eventual use of high-k gate dielectrics, metal gate electrodes, and perhaps nonclassical MOSFET devices such as double-gate SOI     

Perception-centric force scaling in bilateral teleoperation

In this work we propose a control architecture that leads to an intrinsically stable bilateral teleoperation system, where the telepresence of the user is improved in terms of remote force discrimination. We identify, through a set of psychophysical experiments, a variable force scaling matrix that improves the operator’s feeling of the remote environment. We show that it is possible to build a passive control scheme that embeds this perception-centric scaling. Finally, an experiment is presented to validate the results proposed in the paper.     

Statistical constraints in nanocrystal memory scaling

This paper presents a detailed investigation of the statistical constraints that may limit nanocrystal memory scaling to the deca-nanometer scale-size. We adopted a Monte Carlo simulation approach to evaluate the probability distribution of the threshold voltage shift after program and of the retention time in presence of stress-induced leakage current. These distributions were used to extract a program and a retention fail probability. Both of them increase with cell dimensions scaling, strongly reducing the benefits offered by the nanocrystal technology in future microelectronics nodes.     

Power scaling in quantum-well laser amplifiers

The effects of increasing excitation on the performance of quantum-well semiconductor laser amplifiers were investigated. Amplified spontaneous emission (ASE) and gain roll over at high injected carrier densities are two limitations to the power scaling of these devices. A Rigrod analysis was used to study the effects of these limitations on the gain, ratio of signal to ASE power, and efficiency for different values of injection current, facet reflectivity, and input laser intensity. Comparisons are made with an equivalent amplifier operating with a bulk semiconductor gain medium. This analysis suggests that quantum-well semiconductor amplifier performance improves with a double-pass configuration     

Tailored versus realistic geometry in the inverse problem ofelectrocardiography

The stability and applicability of a previously developed inverse procedure for the noninvasive determination of the activation sequence of the human heart has been evaluated. In particular, the possibility of using a standard geometrical configuration representing the heart and the inhomogeneous volume conductor in this procedure has been tested. Results show that in order to obtain reliable inverse solutions, true "tailored" geometry should be used.     

Towards realistic connectivity restoration in partitioned mobile sensor networks

The connectivity of a disjoint mobile sensor network can be restored by moving a set of nodes to certain destinations. However, all of the existing works have assumed that the selected destinations can be reached via direct path movement, which may not be the case in real‐world applications because of obstacles or terrain elevation. In addition, even if direct path movement is successful, optimal energy efficiency cannot be attained by neglecting the elevation or friction of the terrain when determining the movement path of the nodes. Thus, in the recovery efforts, terrain type, elevation, obstacles, and possible localization errors should be considered in order to guarantee the connectivity restoration while minimizing the recovery cost in terms of energy. In this paper, we pick two sample distributed and centralized connectivity restoration approaches from the literature to show that these approaches fail to restore connectivity in many cases due to the lack of considering realistic issues. These approaches are re‐designed in order to determine movement trajectory based on a path planning algorithm, which considers the risk and elevation of the terrain sections. Experiment results reveal several issues regarding the performance in terms of energy consumption and recovery delay. Copyright © 2014 John Wiley & Sons, Ltd.     

Network design in realistic ?all-optical? backbone networks

Optical-bypass technology is finally being deployed in carrier backbone networks on a large scale. The reality, however, is that the resulting networks are not truly all-optical; all connections cannot be carried end-to-end solely in the optical domain. While a significant amount of regeneration can be eliminated through the deployment of new ultra-long-haul technology, a small amount is still required. We study the optical network design problem for realistic backbone networks, with a focus on the impact of regeneration     

Interactive computation in power system analysis

The analysis of power system performance has always been enhanced by close interaction between engineer and computation, and recent developments in high-speed displays, minicomputer capacity, and computational technology are encouraging major revisions of computing practices for power system analysis. A comprehensive power system analysis package, PSS/2, is described which has been developed specifically for use with dedicated computers. This dedicated computer approach allows load flow, short-circuit, and dynamic simulation work, data base maintenance, and printed report preparation to be handled in the interactive mode at lower cost than could be possible by alternative batch or time-shared computing methods. The subjects covered are data organization, computational techniques, user interface, and operational experience.     

电子指南针设计中的实时计算

电子指南针设计中会遇到反三角函数的计算问题,由于很多的微处理器不能直接计算,所以必须要考虑其他的处理方法。鉴于查表方法的各种局限性,本文提出一种实时计算方法,即数值逼近的方法来计算反三角函数。此方法在保证一定的计算复杂度的前提下,能够获得较小的误差,达到指南针设计的精度要求。     

Electrode processes in MHD generators

Electrode processes strongly influence the performance and durability of an MHD generator. In this paper a theoretical analysis of these processes is made based on a model suggested by experimental work. According to these observations current transfer at the cathode usually occurs by means of small arc spots, while at the anode the discharge covers the electrode. The basic relations resulting from an energy balance within these discharges, Poisson's equation for space charge, and the electrical and thermal boundary conditions are derived in terms of the properties of the ambient gas. The calculation of these properties for MHD duct gases is then described and special attention given to the perturbation of the ionization equilibrium resulting from charge transport within the discharge. Preliminary results of computer programs designed to carry out the calculation for open and closed cycle duct conditions are presented, and it is shown that under certain conditions the discharge part of the calculation can be presented as a unique set of curves, from which the running conditions and erosion can be calculated for any electrode material.     

Rotating Electrode in Electric-Field Sensor

Journal of Communications Technology and Electronics - It is shown that the application of rotating electrodes in an electrode sensor for measurement of the extremely-low-frequency electric field...