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Function Used (function + used)
Selected AbstractsA Study on the Effects of Damage Models and Wavelet Bases for Damage Identification and Calibration in BeamsCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 8 2007Vikram Pakrashi A numerical study has been performed in this article addressing these issues for single and multispan beams with an open crack. The first natural modeshapes of single and multispan beams with an open crack have been simulated considering damage models of different levels of complexity and analyzed for different crack depth ratios and crack positions. Gaussian white noise has been synthetically introduced to the simulated modeshape and the effects of varying signal-to-noise ratio have been studied. A wavelet-based damage identification technique has been found to be simple, efficient, and independent of damage models and wavelet basis functions, once certain conditions regarding the modeshape and the wavelet bases are satisfied. The wavelet-based damage calibration is found to be dependent on a number of factors including damage models and the basis function used in the analysis. A curvature-based calibration is more sensitive than a modeshape-based calibration of the extent of damage. [source] 2D data modelling by electrical resistivity tomography for complex subsurface geologyGEOPHYSICAL PROSPECTING, Issue 2 2006E. Cardarelli ABSTRACT A new tool for two-dimensional apparent-resistivity data modelling and inversion is presented. The study is developed according to the idea that the best way to deal with ill-posedness of geoelectrical inverse problems lies in constructing algorithms which allow a flexible control of the physical and mathematical elements involved in the resolution. The forward problem is solved through a finite-difference algorithm, whose main features are a versatile user-defined discretization of the domain and a new approach to the solution of the inverse Fourier transform. The inversion procedure is based on an iterative smoothness-constrained least-squares algorithm. As mentioned, the code is constructed to ensure flexibility in resolution. This is first achieved by starting the inversion from an arbitrarily defined model. In our approach, a Jacobian matrix is calculated at each iteration, using a generalization of Cohn's network sensitivity theorem. Another versatile feature is the issue of introducing a priori information about the solution. Regions of the domain can be constrained to vary between two limits (the lower and upper bounds) by using inequality constraints. A second possibility is to include the starting model in the objective function used to determine an improved estimate of the unknown parameters and to constrain the solution to the above model. Furthermore, the possibility either of defining a discretization of the domain that exactly fits the underground structures or of refining the mesh of the grid certainly leads to more accurate solutions. Control on the mathematical elements in the inversion algorithm is also allowed. The smoothness matrix can be modified in order to penalize roughness in any one direction. An empirical way of assigning the regularization parameter (damping) is defined, but the user can also decide to assign it manually at each iteration. An appropriate tool was constructed with the purpose of handling the inversion results, for example to correct reconstructed models and to check the effects of such changes on the calculated apparent resistivity. Tests on synthetic and real data, in particular in handling indeterminate cases, show that the flexible approach is a good way to build a detailed picture of the prospected area. [source] Some remarks on the LSOWA approach for obtaining OWA operator weightsINTERNATIONAL JOURNAL OF INTELLIGENT SYSTEMS, Issue 12 2009Byeong Seok Ahn One of the key issues in the theory of ordered-weighted averaging (OWA) operators is the determination of their associated weights. To this end, numerous weighting methods have appeared in the literature, with their main difference occurring in the objective function used to determine the weights. A minimax disparity approach for obtaining OWA operator weights is one particular case, which involves the formulation and solution of a linear programming model subject to a given value of orness and the adjacent weight constraints. It is clearly easier for obtaining the OWA operator weights than from previously reported OWA weighting methods. However, this approach still requires solving linear programs by a conventional linear program package. Here, we revisit the least-squared OWA method, which intends to produce spread-out weights as much as possible while strictly satisfying a predefined value of orness, and we show that it is an equivalent of the minimax disparity approach. The proposed solution takes a closed form and thus can be easily used for simple calculations. © 2009 Wiley Periodicals, Inc. [source] domain averaged Fermi holes;JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 15 2003chemical bond; The recently proposed approach based on the analysis of domain-averaged Fermi holes was applied to the study of the nature of metalmetal bonding in transition metal complexes and clusters. The main emphasis was put on the scrutiny of the systems assumed to contain direct multiple metalmetal bonds. The studied systems involve: (1) systems of the type M2X6 (M = Mo, W, X = CH3) anticipated to contain metalmetal triple bonds; (2) the molecule of W2Cl8(4,) as the representative of the systems with quadruple metalmetal bonding; (3) diatomic molecules Mo2 and V2 considered as the potential candidates for higher than quadruple metalmetal bonding. Although the resulting picture of bonding has been usually shown to agree with the original expectations based on early simple MO models, some examples were also found in which the conclusions of the reported analysis display dramatic sensitivity to the quality of the wave function used for the generation of the Fermi holes. In addition to this we also report some examples where the original theoretical predictions of multiplicity of metalmetal bonds have to be corrected. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 1829,1838, 2003 [source] Trade costs in empirical New Economic GeographyPAPERS IN REGIONAL SCIENCE, Issue 3 2010Maarten Bosker Trade costs; New Economic Geography; market access Abstract Trade costs are a crucial element of New Economic Geography (NEG) models. Without trade costs there is no role for geography. In empirical NEG studies the unavailability of direct trade cost data calls for the need to approximate these trade costs by introducing a trade cost function. In doing so, hardly any attention is paid to the (implicit) assumptions and empirical consequences of the particular trade cost function used. Based on a meta-analysis of NEG market access studies as well as on the results of estimating the NEG wage equation for a uniform sample while using different trade costs functions, we show that the relevance of the key NEG variable, market access, depends nontrivially on the choice of trade cost function. Next, we propose an alternative way to approximate trade costs that does not require the specification of a trade cost function, the so called implied trade costs approach. Overall, our results stress that the specification of trade costs can matter a lot for the conclusions reached in any empirical NEG study. We therefore call for a much more careful treatment of trade costs in future empirical NEG studies. Resumen Los costos de comercio son un elemento crucial de los modelos de la Nueva Geografía Económica (NEG, siglas en inglés). Sin los costos de comercio no hay un rol para la geografía. En estudios empíricos de NEG, la falta de disponibilidad de datos de costos directos de comercio directo crea la necesidad de estimar estos costos de comercio mediante la introducción de una función de costos de comercio. Al hacer esto, apenas se presta atención a las suposiciones (implícitas) y consecuencias empíricas de la función de costo utilizada en particular. Basado en un meta análisis de estudios de acceso de mercado de NEG, así como en los resultados de estimar la ecuación salarial de NEG para una muestra uniforme al tiempo que utilizando diferentes funciones de costos de comercio, mostramos que la relevancia de la variable clave para la NEG, acceso a mercados, depende considerablemente de la elección de la función de costos de comercio. A continuación, proponemos una alternativa para estimar costos de comercio que no requiere especificar una función de costos de comercio, el llamado enfoque de costos de comercio implícitos. En resumen, nuestros resultados insisten en que el especificar los costos de comercio puede tener mucha importancia para las conclusiones alcanzadas en cualquier estudio empírico de NEG. Pedimos por tanto un tratamiento mucho más cuidadoso de los costos de comercio en futuros estudios empíricos de NEG. [source] An analysis of simplified muscle activation profile parameterizationPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2006Daniel Strobach This paper analyzes a simplified method for rough identification of muscle activation profiles of general motor tasks by means of dynamic optimization. Muscle activation profiles are parameterized with six parameters per muscle, using linear combinations of two smooth C, functions closely related to the GAUSSian distribution function used in stochastics and fuzzy control. The method is applied to a simplified subsystem of the human leg consisting of pelvis, thigh shank and foot, interconnected by planar joints at hip, knee and ankle. The system comprises one antagonistic muscle pair at the knee for knee flexion and extension (vastus intermedius and biceps femoris caput brevis). To simulate the swing phase of gait, rheonomic constraints are imposed on pelvis (translation and rotation), hip (rotation) and ankle (rotation). The optimization results show that, (1) the method is suitable to map typical muscle activation time histories that are recorded via EMG, (2) the method can reduce the number of design parameters and CPU-time consumption significantly in comparison to other parameterizations and (3) this reduction in CPU-time consumption additionally coinncides with an improved approximation quality to the target motion. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Delay-dependent H, control of parameter-varying delayed systems via parameter-dependent Lyapunov function approach,ASIAN JOURNAL OF CONTROL, Issue 2 2009Shaosheng Zhou Abstract The H, control problem of parameter-varying delayed systems is investigated in this paper. The state-space matrices of the systems are assumed to be dependent on a vector of time-varying real parameters which are assumed to be real-time measurable. The delays related to the parameter-varying systems are assumed to be unknown but with known upper bounds and to be in the states and control inputs. A delay-dependent H, performance condition of the system under consideration is derived by using a new parameter-dependent Lyapunov function. Based on the H, performance condition, a linear matrix inequality (LMI) based H, control strategy is proposed by using auxiliary variable technique. The combined parameter-dependent and delay-dependent results are less conservative due to the generality of the parameter-dependent and delay-dependent Lyapunov function used, which includes the parameter-independent one as a special case. It is shown that the underling H, control problem can be solved as LMI optimization problems that can be numerically computed very efficiently. A numerical example is also given to demonstrate the applicability of the proposed approach. Copyright © 2009 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society [source] Dividing Wall Distillation Columns: Optimization and Control PropertiesCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 9 2008F. I. Gómez-Castro Abstract The optimal design of dividing wall columns is a non-linear and multivariable problem, and the objective function used as optimization criterion is generally non-convex with several local optimums. Considering this fact, in this paper, we studied the design of dividing wall columns using as a design tool, a multi-objective genetic algorithm with restrictions, written in MatlabTM and using the process simulator Aspen PlusTM for the evaluation of the objective function. Numerical performance of this method has been tested in the design of columns with one or two dividing walls and with several mixtures to test the effect of the relative volatilities of the feed mixtures on energy consumption, second law efficiency, total annual cost, and theoretical control properties. In general, the numerical performance shows that this method appears to be robust and suitable for the design of sequences with dividing walls. [source] Error estimation in a stochastic finite element method in electrokineticsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 11 2010S. Clénet Abstract Input data to a numerical model are not necessarily well known. Uncertainties may exist both in material properties and in the geometry of the device. They can be due, for instance, to ageing or imperfections in the manufacturing process. Input data can be modelled as random variables leading to a stochastic model. In electromagnetism, this leads to solution of a stochastic partial differential equation system. The solution can be approximated by a linear combination of basis functions rising from the tensorial product of the basis functions used to discretize the space (nodal shape function for example) and basis functions used to discretize the random dimension (a polynomial chaos expansion for example). Some methods (SSFEM, collocation) have been proposed in the literature to calculate such approximation. The issue is then how to compare the different approaches in an objective way. One solution is to use an appropriate a posteriori numerical error estimator. In this paper, we present an error estimator based on the constitutive relation error in electrokinetics, which allows the calculation of the distance between an average solution and the unknown exact solution. The method of calculation of the error is detailed in this paper from two solutions that satisfy the two equilibrium equations. In an example, we compare two different approximations (Legendre and Hermite polynomial chaos expansions) for the random dimension using the proposed error estimator. In addition, we show how to choose the appropriate order for the polynomial chaos expansion for the proposed error estimator. Copyright © 2009 John Wiley & Sons, Ltd. [source] Gaussian approximation of exponential type orbitals based on B functionsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 2 2009Didier Pinchon Abstract This work gives new, highly accurate optimized gaussian series expansions for the B functions used in molecular quantum mechanics. These functions are generally chosen because of their compact Fourier transform, following Shavitt. The inverse Laplace transform in the square root of the variable is used for Gauss quadrature in this work. Two procedures for obtaining accurate gaussian expansions have been compared for the required extended precision arithmetic. The first is based on Gaussian quadratures and the second on direct optimization. Both use the Maple computer algebra system. Numerical results are tabulated and compared with previous work. Special cases are found to agree before pushing the optimization technique further. The optimal gaussian expansions of B functions obtained in this work are available for reference. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] MODY: a program for calculation of symmetry-adapted functions for ordered structures in crystalsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2004awa Sikora This paper describes a computer program, based on the theory of groups and representations, which calculates symmetry-adapted functions used for the description of various ordered structures in crystals. It is assumed that the ordered structure, which is formed by a configuration of occupational probabilities, ion displacements, magnetic moments, quadrupolar moments or other local physical quantities, is obtained from a high-symmetry crystal structure with a given space group G, as a result of a symmetry-lowering phase transition. The detailed characteristics of the phase transition are given by the specification of the irreducible representations of group G, active in the transition. The symmetry-adapted functions obtained from the calculation are perfect tools for the construction of model structures, which can be used for comparison with experimental (e.g. neutron diffraction) data, and can be a great help in numerical data elaboration by reducing the number of adjustable parameters describing the structure of a given symmetry. [source] Light,matter interaction in finite-size plasma systemsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2007W. Hoyer Abstract It is well known that electromagnetic waves with frequencies below the plasma frequency cannot propagate inside an electron plasma. For plasmas with infinite extensions, this property can be mathematically described by a Bogoliubov transformation of the photonic operators. More generally, the presence of finite-size electron plasmas such as laser-induced atmospheric light strings or metallic nano structures including metamaterials leads to a modification of the light,matter interaction. It is shown how this geometric property can be fully accounted for with the help of adapted mode functions used for the quantization of the electromagnetic field. In addition to the analytical derivations, numerical results for luminescence spectra out of quasi-two-dimensional, planar plasma sheets are presented. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||