41 documentos corresponden a la consulta.
Palabras contadas: mathematical: 93, models: 269
Braberman, V. - López Pombo, C. - Olivero, A.
Electron. Notes Theor. Comput. Sci. 2002;65(6):60-67
2002
Temas: Algorithms - Chaos theory - Formal logic - Iterative methods - Mathematical models - Mathematical operators - Semantics - Set theory - Backwards verification - Chaotic iteration
Descripción: Fil:Braberman, V. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.
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Marshall, G. - Mocskos, P. - Swinney, H.L. - Huth, J.M.
Phys Rev E. 1999;59(2):2157-2167
1999
Temas: Buoyancy - Density (specific gravity) - Electric field effects - Electric potential - Electric space charge - Electrodes - Fluids - Heat convection - Ions - Mathematical models
Tipo de documento: info:ar-repo/semantics/artículo
Eguia, M.C. - Rabinovich, M.I. - Abarbanel, H.D.I.
Phys Rev E. 2000;62(5):7111-7122
2000
Temas: Chaos theory - Lyapunov methods - Mathematical models - Neurophysiology - Statistical mechanics - Biological neural communications channels - Neural networks - action potential - biological model - information science
Descripción: Fil:Eguia, M.C. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.
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Feuerstein, E.
Theor Comput Sci 1997;181(1):75-90
1997
Descripción: In this paper we extend the Paging Problem to the case in which each request specifies a set of pages that must be present in fast memory to serve it. The interest on this extension is motivated by many applications in which the execution of each task may require the presence of more than one page in fast memory. We introduce three different cost models that can be applied in this framework, namely the Full, Uniform and Constant cost models, and study lower and upper bounds for each one of them, using competitive analysis techniques.
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Sainz-Trapága, M. - Masoller, C. - Braun, H.A. - Huber, M.T.
Phys Rev E. 2004;70(3):11
2004
Temas: Cardiology - Computer simulation - Feedback - Mathematical models - Ordinary differential equations - Photoreactivity - Physiology - Sensitivity analysis - Delay differential equations (DDE) - Firing pattern
Tipo de documento: info:ar-repo/semantics/artículo
Aliaga, J. - Busca, N. - Minces, V. - Mindlin, G.B. - Pando, B. - Salles, A. - Sczcupak, L.
Phys. Rev. E Stat. Nonlinear Soft Matter Phys. 2003;67(6 1):061915-1-061915-8
2003
Temas: Bifurcation (mathematics) - Cells - Electronic equipment - Graph theory - Mathematical models - Numerical analysis - Perturbation techniques - Andronov-Hopf bifurcation - Leech - Neuron
Descripción: Fil:Aliaga, J. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.
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Méndez-Díaz, I. - Zabala, P.
Discrete Appl Math 2006;154(5 SPEC ISS):826-847
2006
Temas: Branch-and-Cut algorithms - Graph coloring - Integer programming - Graph theory - Integer programming - Mathematical models - Branch-and-cut algorithms - Graph coloring - Algorithms
Descripción: Fil:Méndez-Díaz, I. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.
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Costa, A. - González, R.
Astron. Astrophys. 2006;458(3):953-963
2006
Temas: Standards - Sun: corona - Waves - Continuous spectrum - Corona - Solar coronal loops - Thermodynamic irreversible energy principles - Magnetic fields - Mathematical models - Mathematical operators
Descripción: Aims. We study the modes and stability of non-isothermal coronal loop models with different intensity values of the equilibrium magnetic field. Methods. We use an energy principle obtained via non-equilibrium thermodynamic arguments. The principle is expressed in terms of Hermitian operators and allow to consider together the coupled system of equations: the balance of energy equation and the equation of motion. Results. We determine modes characterized as long - wavelength disturbances that are present in inhomogeneous media. This character of the system introduces additional difficulties for the stability analysis because the inhomogeneous nature of the medium determines the structure of the disturbance, which is no longer sinusoidal. Moreover, another complication is that we obtain a continuous spectrum of stable modes in addition to the discrete one. Conclusions. We obtain a unique unstable mode with a characteristic time that is comparable with the characteristic life-time observed for loops. The feasibility of wave-based and flow-based models is examined. © ESO 2006.
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Fernández Slezak, D. - Suárez, C. - Cecchi, G.A. - Marshall, G. - Stolovitzky, G.
PLoS ONE 2010;5(10)
2010
Temas: article - bioinformatics - mathematical model - mathematical parameters - process optimization - tumor growth - Cell Division - Humans - Models, Biological - Neoplasms
Descripción: Background: The vast computational resources that became available during the past decade enabled the development and simulation of increasingly complex mathematical models of cancer growth. These models typically involve many free parameters whose determination is a substantial obstacle to model development. Direct measurement of biochemical parameters in vivo is often difficult and sometimes impracticable, while fitting them under data-poor onditions may result in biologically implausible values. Results: We discuss different methodological approaches to estimate parameters in complex biological models. We make use of the high computational power of the Blue Gene technology to perform an extensive study of the parameter space in a model of avascular tumor growth. We explicitly show that the landscape of the cost function used to optimize the model to the data has a very rugged surface in parameter space. This cost function has many local minima with unrealistic solutions, including the global minimum corresponding to the best fit. Conclusions: The case studied in this paper shows one example in which model parameters that optimally fit the data are not necessarily the best ones from a biological point of view. To avoid force-fitting a model to a dataset, we propose that the best model parameters should be found by choosing, among suboptimal parameters, those that match criteria other than the ones used to fit the model. We also conclude that the model, data and optimization approach form a new complex system and point to the need of a theory that addresses this problem more generally. © 2010 Fernandez Slezak et al.
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Milaszewicz, J.P.
Comput Math Appl 1995;30(1):79-90
1995
Temas: Discretized Newton method - Functional elimination - Nonlinear systems - Order convex functions - Approximation theory - Boundary value problems - Convergence of numerical methods - Differentiation (calculus) - Function evaluation - Iterative methods
Descripción: The improvement in convergence by means of accurate functional elimination in the context of the monotone Newton theorem is further analyzed and extended to discrete approximations of the Newton method. © 1995.
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Mindlin, G.B. - Gardner, T.J. - Goller, F. - Suthers, R.
Phys. Rev. E Stat. Nonlinear Soft Matter Phys. 2003;68(4 1):419081-419085
2003
Temas: Air - Biological organs - Data reduction - Elasticity - Electrodes - Electromyography - Mathematical models - Muscle - Oscillations - Pressure measurement
Descripción: An experimental validation of an model for the production of birdsongs was discussed. The derivation of the model with functions whose time dependence came from recordings of muscle activities and air sac pressure was studied. It was found that birds' songs were recorded and compared with the synthetic songs. Some predictions of the model concerning the relative levels of activity in the gating muscles at the beginning and end of a syllable were also tested.
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Durán, G. - Lin, M.C. - Mera, S. - Szwarcfiter, J.L.
Discrete Appl Math 2006;154(13 SPEC ISS):1783-1790
2006
Temas: Algorithms - Circular-arc graphs - Clique-independent sets - Helly circular-arc graphs - Algorithms - Computational complexity - Computational methods - Mathematical models - Set theory - Circular-arc graphs
Descripción: Fil:Durán, G. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.
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Kandus, A. - Calzetta, E.A. - Mazzitelli, F.D. - Wagner, C.E.M.
Phys Lett Sect B Nucl Elem Part High-Energy Phys 2000;472(3-4):287-294
2000
Temas: article - cosmos - elementary particle - gravity - magnetic field - mathematical analysis - mathematical model - quantum theory
Descripción: We study the generation of primordial magnetic fields, coherent over cosmologically interesting scales, by gravitational creation of charged scalar particles during the reheating period. We show that magnetic fields consistent with those detected by observation may be obtained if the particle mean life τ(s) is in the range 10-14 s ≤ τ(s) ≤ 10-7 s. We apply this mechanism to minimal gauge-mediated supersymmetry-breaking models, in the case in which the lightest stau τ(l) is the next-to-lightest supersymmetric particle. We show that, for a large range of phenomenologically acceptable values of the supersymmetry-breaking scale √F, the generated primordial magnetic field can be strong enough to seed the galactic dynamo. (C) 2000 Elsevier Science B.V.
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Graham, J.P. - Holm, D.D. - Mininni, P.D. - Pouquet, A.
Phys. Fluids 2008;20(3)
2008
Temas: Approximation theory - Direct numerical simulation - Mathematical models - Navier Stokes equations - Reynolds number - Energy spectrum - Subfilter-scale physics - Subgrid-scale (SGS) models - Flow of fluids - Approximation theory
Descripción: We determine how the differences in the treatment of the subfilter-scale physics affect the properties of the flow for three closely related regularizations of Navier-Stokes. The consequences on the applicability of the regularizations as subgrid-scale (SGS) models are also shown by examining their effects on superfilter-scale properties. Numerical solutions of the Clark-α model are compared to two previously employed regularizations, the Lagrangian-averaged Navier-Stokes α-model (LANS-α) and Leray-α, albeit at significantly higher Reynolds number than previous studies, namely, Re≈3300, Taylor Reynolds number of Re≈790, and to a direct numerical simulation (DNS) of the Navier-Stokes equations. We derive the de Kármán-Howarth equation for both the Clark-α and Leray-α models. We confirm one of two possible scalings resulting from this equation for Clark-α as well as its associated k-1 energy spectrum. At subfilter scales, Clark-α possesses similar total dissipation and characteristic time to reach a statistical turbulent steady state as Navier-Stokes, but exhibits greater intermittency. As a SGS model, Clark-α reproduces the large-scale energy spectrum and intermittency properties of the DNS. For the Leray-α model, increasing the filter width α decreases the nonlinearity and, hence, the effective Reynolds number is substantially decreased. Therefore, even for the smallest value of α studied Leray-α was inadequate as a SGS model. The LANS-α energy spectrum ∼k1, consistent with its so-called "rigid bodies," precludes a reproduction of the large-scale energy spectrum of the DNS at high Re while achieving a large reduction in numerical resolution. We find, however, that this same feature reduces its intermittency compared to Clark-α (which shares a similar de Kármán-Howarth equation). Clark-α is found to be the best approximation for reproducing the total dissipation rate and the energy spectrum at scales larger than α, whereas high-order intermittency properties for larger values of α are best reproduced by LANS-α. © 2008 American Institute of Physics.
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Bochicchio, R.C. - Torre, A. - Lain, L.
J Chem Phys 2005;122(8)
2005
Temas: Condensed matter - Cumulants - Molecular systems - Quantum fields - Computational methods - Correlation methods - Electrons - Functions - Mathematical models - Matrix algebra
Descripción: This paper describes a matrix formulation for the correlated hole theory within the framework of the domain-averaged model in many electron systems (atoms, molecules, condensed matter, etc.). General relationships between this quantity and one-particle reduced density matrices for any independent particle or correlated state functions are presented. This formulation turns out to be suitable for computational purposes due to the straightforward introduction of cumulants of two-particle reduced density matrices within the quantum field structure. Numerical calculations in selected simple molecular systems have been performed in order to determine preliminary correlated values for such a quantity.
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Boente, G. - He, X. - Zhou, J.
Ann. Stat. 2006;34(6):2856-2878
2006
Temas: Kernel weights - Partially linear models - Rate of convergence - Robust estimation - Smoothing
Descripción: In this paper, we introduce a family of robust estimates for the parametric and nonparametric components under a generalized partially linear model, where the data are modeled by y i |(x i , t i ) ∼ F (·, μ i ) with μ i = H(η(t i ) + x i T β), with for some known distribution function F and link function H. It is shown that the estimates of β are root-n consistent and asymptotically normal. Through a Monte Carlo study, the performance of these estimators is compared with that of the classical ones. © Institute of Mathematical Statistics, 2006.
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Curé, M. - Rial, D.F. - Cidale, L.
Astron. Astrophys. 2005;437(3):929-933
2005
Temas: Stars: early-type - Stars: mass-loss - Stars: rotation - Stars: winds, outflows - Bifurcation (mathematics) - Ionization - Mathematical models - Optical bistability - Parameter estimation - Radiation
Descripción: The effects of rapid rotation and bi-stability upon the density contrast between the equatorial and polar directions of a B[e] supergiant are re-investigated. Based on a new slow solution for different high rotational radiation-driven winds and the fact that bi-stability allows a change in the line-force parameters (α, k, and δ), the equatorial densities are about 102-104 times higher than the polar ones. These values are in qualitative agreement with the observations. © ESO 2005.
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Elola, M.D. - Laria, D.
J Chem Phys 2002;117(5):2238-2245
2002
Temas: Algorithms - Chemical relaxation - Diffusion - Electronic properties - Ground state - Mathematical models - Molecular structure - Photochemical reactions - Quantum theory - Solutions
Descripción: New insights into equilibrium and dynamical aspects of electron photodetachment reactions in small water clusters were given. It focuses on assessing the effects of thermal and polarization fluctuations provided by three cluster environments with different extents of spatial confinement, on the microscopic mechanisms that drive the reaction. These fluctuations, in turn, determine the characteristics of the electron localization and the subsequent detachment following photoexcitation of the probe.
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Yacomotti, A.M. - Mindlin, G.B. - Giudici, M. - Balle, S. - Barland, S. - Tredicce, J.
Phys Rev E. 2002;66(3)
2002
Temas: Adhesion - Bacteria - Dispersions - Mathematical models - Porous materials - Probability - Sorption - Fluid phases - Microbial transport - Microflow cells
Descripción: In this work we investigate experimentally the dynamics of two coupled optical excitable cells, namely, two semiconductor lasers with optical feedback. We analyze the dynamics observed in terms of the statistical properties of the time series and in terms of the phase space reconstruction from the data. We build a model based on a simple set of deterministic equations (on a two torus) plus noise in order to capture the essential features of the dynamics observed. We discuss the validity of our theoretical results in terms of families of excitable systems and coupling terms. © 2002 The American Physical Society.
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Mitnik, D.M. - Badnell, N.R.
Astron. Astrophys. 2004;425(3):1153-1159
2004
Temas: Atomic data - Atomic processes - Plasmas - Approximation theory - Database systems - Electrons - Ionization - Mathematical models - Nitrogen - Potential energy
Descripción: Dielectronic recombination data for nitrogen-like ions forming oxygen-like ions has been calculated as part of the assembly of a level-resolved dielectronic recombination database necessary for the modelling of dynamic finite-density plasmas (Badnell et al. 2003). Dielectronic recombination rate coefficients for a selection of ions from O+ to Xe47+ are presented and the results discussed.
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