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Very Good Accuracy (very + good_accuracy)
Selected AbstractsAn efficient hourglass control implementation for the uniform strain hexahedron using the Total Lagrangian formulationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 11 2008Grand Roman Joldes Abstract The under-integrated hexahedron is one of the best candidates for use in real-time surgical simulations, because of its computational efficiency. This element requires a very efficient method of controlling the zero energy (hourglass) modes that arise from one-point integration. An efficient implementation of the perturbation hourglass control method proposed by Flanagan and Belytschko for the uniform strain hexahedron is presented. The implementation uses the Total Lagrangian formulation and takes into consideration large deformations and rigid body motions. By using the Total Lagrangian formulation most of the necessary components for calculating the hourglass forces can be pre-computed, leading to a significant reduction of the additional computation time required for hourglass control. The performance evaluation results show the very good accuracy and computational efficiency of the presented algorithm. Copyright © 2007 John Wiley & Sons, Ltd. [source] A Cartesian-grid collocation technique with integrated radial basis functions for mixed boundary value problemsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 4 2010Phong B. H. Le Abstract In this paper, high-order systems are reformulated as first-order systems, which are then numerically solved by a collocation method. The collocation method is based on Cartesian discretization with 1D-integrated radial basis function networks (1D-IRBFN) (Numer. Meth. Partial Differential Equations 2007; 23:1192,1210). The present method is enhanced by a new boundary interpolation technique based on 1D-IRBFN, which is introduced to obtain variable approximation at irregular points in irregular domains. The proposed method is well suited to problems with mixed boundary conditions on both regular and irregular domains. The main results obtained are (a) the boundary conditions for the reformulated problem are of Dirichlet type only; (b) the integrated RBFN approximation avoids the well-known reduction of convergence rate associated with differential formulations; (c) the primary variable (e.g. displacement, temperature) and the dual variable (e.g. stress, temperature gradient) have similar convergence order; (d) the volumetric locking effects associated with incompressible materials in solid mechanics are alleviated. Numerical experiments show that the proposed method achieves very good accuracy and high convergence rates. Copyright © 2009 John Wiley & Sons, Ltd. [source] Input mapping algorithm for parallel transistor structuresINTERNATIONAL JOURNAL OF CIRCUIT THEORY AND APPLICATIONS, Issue 7 2009Spiridon NikolaidisArticle first published online: 17 JUL 200 Abstract A new algorithm for mapping every possible input pattern of a parallel transistor structure to an equivalent set of normalized inputs (having the same starting and ending point) is introduced. This algorithm is based on the analysis of the operation of the transistor structure and can be used for the development of analytical timing models for CMOS circuits. Simulation results show a very good accuracy of the algorithm. Copyright © 2008 John Wiley & Sons, Ltd. [source] Modelling and design considerations on CML gates under high-current effectsINTERNATIONAL JOURNAL OF CIRCUIT THEORY AND APPLICATIONS, Issue 6 2005M. Alioto Abstract In this paper, the effect of the transit time degradation of bipolar transistors on the power-delay trade-off in CML gates and their design is dealt with. A delay model which accounts for the transit time increase due to the high bias current values used in high-speed applications is derived by generalizing an approach previously proposed by the same authors (IEEE Trans. CAD 1999; 18(9):1369,1375; Model and Design of Bipolar and MOS Current,Mode Logic (CML, ECL and SCL Digital Circuits), Kluwer Academic Publisher: Dordrecht, 2005). The resulting closed-form delay expression is achieved by properly simplifying the SPICE model, and has an explicit dependence on the bias current which determines the power consumption of CML gates. Accordingly, the delay model is used to gain insight into the power-delay trade-off by considering the effect of the transit time degradation in high-speed designs. In particular, the cases where such effects can be neglected are identified, to better understand how the transit time degradation affects the performance of CML gates for current bipolar technologies. The proposed model has a simple and compact expression, thus it turns out to be suitable for pencil-and-paper evaluations, as well as fast timing analysis. Simulations of CML circuits with a 20-GHz bipolar process show that the model has a very good accuracy in a wide range of current and loading conditions. Copyright © 2005 John Wiley & Sons, Ltd. [source] An analytical model for the performance evaluation of stack-based Web cache replacement algorithmsINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 1 2010S. Messaoud Abstract Web caching has been the solution of choice to web latency problems. The efficiency of a Web cache is strongly affected by the replacement algorithm used to decide which objects to evict once the cache is saturated. Numerous web cache replacement algorithms have appeared in the literature. Despite their diversity, a large number of them belong to a class known as stack-based algorithms. These algorithms are evaluated mainly via trace-driven simulation. The very few analytical models reported in the literature were targeted at one particular replacement algorithm, namely least recently used (LRU) or least frequently used (LFU). Further they provide a formula for the evaluation of the Hit Ratio only. The main contribution of this paper is an analytical model for the performance evaluation of any stack-based web cache replacement algorithm. The model provides formulae for the prediction of the object Hit Ratio, the byte Hit Ratio, and the delay saving ratio. The model is validated against extensive discrete event trace-driven simulations of the three popular stack-based algorithms, LRU, LFU, and SIZE, using NLANR and DEC traces. Results show that the analytical model achieves very good accuracy. The mean error deviation between analytical and simulation results is at most 6% for LRU, 6% for the LFU, and 10% for the SIZE stack-based algorithms. Copyright © 2009 John Wiley & Sons, Ltd. [source] Rapid and accurate quantitative phase analysis using a fast detectorJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2004A. F. Gualtieri The accuracy of the weight fractions calculated with the Rietveld method for various polycrystalline systems using data collected for very short times (5,45,min) with an RTMS (real-time multiple strip) detector was verified. The weight estimates were compared with those obtained using the same conventional Bragg,Brentano geometry, a gas proportional detector and a 13,h data acquisition. The analysed samples were monophasic and polyphasic mixtures with different degrees of complexity: the standard corundum NIST 676; a sample (labelled 1g) provided as a standard sample for the IUCr CPD Quantitative Phase Analysis Round Robin; a natural pyroclastic rock from Riano (Rome, Italy) containing zeolitic minerals and a glass phase; and a hydraulic lime. The results of the refinements show estimated weights consistent with both those obtained with a gas proportional detector and with the nominal values, indicating a very good accuracy. Only when variable slits are used, the accuracy of the estimated weights slightly decreases. The outcome of this work is a very important step forward towards fast and accurate QPA for production control and quality management, obtained by combining the use of a rapid detector and existing user-friendly software. [source] Characterization of differential ebulliometers for measuring activity coefficientsAICHE JOURNAL, Issue 1 2000J. David Raal Differential ebulliometry is a powerful and rapid procedure for obtaining infinitely dilute activity coefficients with potentially very good accuracy. Tedious degassing procedures are not necessary, as in a static method, and from only a few measurements full system phase behavior can be evaluated. The principal problem, precise evaluation of the equilibrium liquid composition from the known composition of a prepared solution charged to the apparatus, is well known but has so far defied adequate resolution. A system of exact self-consistent equations was developed for the characterization of an ebulliometer through a dimensionless ebulliometer constant. Evaluation of this constant from typical data and its subsequent use are illustrated for a system of known phase equilibrium behavior. Remarkably, the equations permit evaluation of the effective "static" holdups in various parts of the equipment without any volume measurements. Since one equation is redundant to the main purpose, it can be used for a consistency check of measured and calculated data. The equations also furnish a guide for the operation of ebulliometers. [source] | |||||||||||||