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Fast Calculation (fast + calculation)
Selected AbstractsExtraction of media and plaque boundaries in intravascular ultrasound images by level sets and min/max flowEXPERT SYSTEMS, Issue 2 2010Ali Iskurt Abstract: Estimation of the plaque area in intravascular ultrasound images after extraction of the media and plaque,lumen interfaces is an important application of computer-aided diagnosis in medical imaging. This paper presents a novel system for fully automatic and fast calculation of plaque quantity by capturing the surrounding ring called media. The system utilizes an algorithm that consists of an enhanced technique for noise removal and a method of detecting different iso levels by sinking the image gradually under zero level. Moreover, an important novelty with this technique is the simultaneous extraction of media and lumen,plaque interfaces at satisfactory levels. There are no higher dimensional surfaces and evolution of contours, stopping at high image gradients. Thus, the system runs really fast with curvature velocity only and has no complexity. Experiments also show that this shape-recovering curvature term not only removes the noisy behaviour of ultrasound images but also strengthens very weak boundaries and even completes the missing walls of the media. In addition, the lumen,plaque interface can be detected simultaneously. For validation, a new and very useful algorithm is developed for labelling of intravascular ultrasound images, taken from video sequences of 15 patients, and a comparison-based verification is done between manual contours by experts and the contours extracted by our system. [source] Fast and accurate calculation of transmission coefficients for an EBG microstrip structureMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 4 2010Shao Ying Huang Abstract In this article, an approach is proposed to provide an accurate and fast calculation on the transmission coefficients of an electromagnetic band-gap (EBG) structures where patches are periodically inserted into the microstrip line (capacitive loaded EBG microstrip structure). The stopband performance, such as the center frequency, bandwidth, and attenuation, of these EBG structures can be predicted at a high degree of accuracy through the calculation of the transmission coefficient. The dispersion relation of electromagnetic waves in the structure is derived, plotted, and analyzed. The grating nature of the structure is demonstrated. This approach can be applied to periodic microstrip structures of a similar nature to simplify the analysis and design procedures. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:793,797, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25046 [source] Semi-infinite reflection model of a multilayered dielectric through equivalent permittivity calculationMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 2 2009S. Mostarshedi Abstract This article proposes a semi-infinite model for a multilayered dielectric. It is based on an equivalent permittivity which is valid only for reflection. Here the model is applied to building windows. Inserting the new permittivity into Green's functions associated with a semi-infinite medium allows the fast calculation of reflected EM fields in the vicinity of building facades. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 290,294, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24032 [source] On a fast calculation of structure factors at a subatomic resolutionACTA CRYSTALLOGRAPHICA SECTION A, Issue 1 2004P. V. Afonine In the last decade, the progress of protein crystallography allowed several protein structures to be solved at a resolution higher than 0.9,Å. Such studies provide researchers with important new information reflecting very fine structural details. The signal from these details is very weak with respect to that corresponding to the whole structure. Its analysis requires high-quality data, which previously were available only for crystals of small molecules, and a high accuracy of calculations. The calculation of structure factors using direct formulae, traditional for `small-molecule' crystallography, allows a relatively simple accuracy control. For macromolecular crystals, diffraction data sets at a subatomic resolution contain hundreds of thousands of reflections, and the number of parameters used to describe the corresponding models may reach the same order. Therefore, the direct way of calculating structure factors becomes very time expensive when applied to large molecules. These problems of high accuracy and computational efficiency require a re-examination of computer tools and algorithms. The calculation of model structure factors through an intermediate generation of an electron density [Sayre (1951). Acta Cryst.4, 362,367; Ten Eyck (1977). Acta Cryst. A33, 486,492] may be much more computationally efficient, but contains some parameters (grid step, `effective' atom radii etc.) whose influence on the accuracy of the calculation is not straightforward. At the same time, the choice of parameters within safety margins that largely ensure a sufficient accuracy may result in a significant loss of the CPU time, making it close to the time for the direct-formulae calculations. The impact of the different parameters on the computer efficiency of structure-factor calculation is studied. It is shown that an appropriate choice of these parameters allows the structure factors to be obtained with a high accuracy and in a significantly shorter time than that required when using the direct formulae. Practical algorithms for the optimal choice of the parameters are suggested. [source] Novel computer program for fast exact calculation of accessible and molecular surface areas and average surface curvatureJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 6 2002Oleg V. Tsodikov Abstract New computer programs, SurfRace and FastSurf, perform fast calculations of the solvent accessible and molecular (solvent excluded) surface areas of macromolecules. Program SurfRace also calculates the areas of cavities inaccessible from the outside. We introduce the definition of average curvature of molecular surface and calculate average molecular surface curvatures for each atom in a structure. All surface area and curvature calculations are analytic and therefore yield exact values of these quantities. High calculation speed of this software is achieved primarily by avoiding computationally expensive mathematical procedures wherever possible and by efficient handling of surface data structures. The programs are written initially in the language C for PCs running Windows 2000/98/NT, but their code is portable to other platforms with only minor changes in input-output procedures. The algorithm is robust and does not ignore either multiplicity or degeneracy of atomic overlaps. Fast, memory-efficient and robust execution make this software attractive for applications both in computationally expensive energy minimization algorithms, such as docking or molecular dynamics simulations, and in stand-alone surface area and curvature calculations. © 2002 Wiley Periodicals, Inc. J Comput Chem 23: 600,609, 2002 [source] Analytical analysis of a rectangular shielded multilayer coupled coplanar waveguideMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 5 2004Zhiyong Shan Abstract The closed-form expressions for calculating the quasi-static parameters of a rectangular shielded multilayer coupled coplanar waveguide (RSMCCPW) are presented. Expressions of the odd- and even-mode characteristic impedances, which can provide accurate and fast calculations, are derived by using conformal-mapping techniques. The numerical results are obtained and compared with those available in the literature for similar unshielded structures. Good agreement between the results is observed. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 41: 392,395, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20149 [source] | |||||||||||||