37 documentos corresponden a la consulta.
Palabras contadas: numerical: 149, results: 650
Cuadros-Melgar, B. - De Oliveira, J. - Pellicer, C.E.
J. Phys. Conf. Ser. 2013;453(1)
2013
Temas: Gravitation - Analytical results - Black holes - Numerical results - Quasinormal modes - Thermodynamical - Stars
Descripción: We consider scalar and spinorial perturbations on a background described by a z = 3 three-dimensional Lifshitz black hole. We obtained the corresponding quasinormal modes which perfectly agree with the analytical result for the quasinormal frequency in the scalar case. The numerical results for the spinorial perturbations reinforce our conclusion on the stability of the model under these perturbations. We also calculate the area spectrum, which prove to be equally spaced, as an application of our results.
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Umazano, J.P. - Bertolotto, J.A.
J Chem Phys 2013;138(9)
2013
Temas: Analytic solution - Electric field strength - Hydrodynamic coupling - Molecular orientational - Numerical approaches - Numerical procedures - Numerical results - Orientational distribution functions - Dichroism - Electric fields
Descripción: We study the effect of translational-rotational hydrodynamic coupling on the transient electric linear dichroism of DNA fragments in aqueous solution. As opposed to previous theoretical works, where analytic solutions valid in the limit of low electric field were reported, we present here a numerical approach which allows to obtain numerical results valid independently from the applied electric field strength. Numerical procedures here used are an extension to the transient-state of those developed in a previous work for the study of the problem in the steady-state. The molecular orientational processes induced by an electric field is characterized with statistical arguments solving the Fokker-Planck equation by means of the finite difference method to know the orientational distribution function of molecules. © 2013 American Institute of Physics.
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Pouquet, A. - Baerenzung, J. - Mininni, P.D. - Rosenberg, D. - Thalabard, S.
J. Phys. Conf. Ser. 2011;318(SECTION 4)
2011
Temas: Large eddy simulation - Numerical models - Conformal invariance - Dimensionalization - Helical turbulence - Laboratory experiments - Numerical evidence - Rotating turbulence - Scaling properties - Self-similarities
Descripción: We present numerical evidence on how three-dimensionalization is recovered at small scale in rotating turbulence with helical forcing provided by a Beltrami flow. The relevant ranges (large-scale inverse cascade of energy, anisotropic and isotropic direct cascades of energy and helicity, dissipative) are each moderately resolved. These results stem from large direct numerical simulations on grids of either 15363 or 30723 points. In the latter case, the scale at which the inertial wave time and the eddy turn-over time are equal is found to be more than one order of magnitude larger than the dissipation scale. We also examine how the presence of such an intermediate scale could affect truncation due to the use of a helical spectral Large Eddy Simulation procedure which can allow for extending the analysis to a wider range of parameters. Finally, the self-similarity of the direct cascade of energy to small scales for rotating flows, observed recently in numerical simulations as well as in several laboratory experiments, will be discussed briefly for its scaling properties and its conformal invariance.
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Prario, B.E. - Dragani, W. - Mediavilla, D.G. - D'Onofrio, E.
Appl. Math. Model. 2011;35(11):5265-5275
2011
Temas: Boundary conditions - Currents - Hydrodynamic modeling - Paraná river - Río de la Plata - Uruguay river - Astronomical tides - Colonia - Constant discharge - Currents
Descripción: A hydrodynamic numerical study at the mouths of the Paraná and Uruguay rivers and the upper Río de la Plata is presented in this paper. Water Quality Mapping numerical model was implemented and realistic and very simple boundary conditions were specially developed for this complex estuarial system. A set of numerical experiments were carried out using different constant discharges for the Paraná and Uruguay rivers but unrealistic currents were generated. In order to obtain more realistic results, a set of numerical simulations were carried out imposing water level timeseries at the open boundaries. M2, S2, K1 and O1 harmonic constants were used to generate water levels at Zárate (Paraná river), Nueva Palmira (Uruguay river) and the eastern boundary of the domain (La Plata-Colonia). A mean water level equal to zero was set between La Plata and Colonia. Positive mean water levels (0.3-0.4m) were imposed at Zárate and Nueva Palmira to simulate the hydraulic slope of both rivers and, consequently, to generate realistic and unsteady discharges. These boundary conditions, built by means of the addition of a mean water level and the astronomical tide, significantly improve the simulated currents at the northernmost region of the RDP estuary. © 2011 Elsevier Inc.
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Arbó, D.G. - Ishikawa, K.L. - Persson, E. - Burgdörfer, J.
J. Phys. Conf. Ser. 2012;388(PART 3)
2012
Temas: Atom lasers - Dinger equation - Doubly differential - Intracycle interferences - Long-range potential - Momentum distributions - Numerical solution - Semiclassical model - Time dependent - Atoms
Descripción: We analyze the doubly-differential momentum distributions of electrons ejected at the interaction of strong IR laser pulses with atoms. With the help of a semiclassical model we clarify the interplay between intracycle and intercycle interferences. The model results are compared with numerical solutions of the time-dependent Schrödinger equation for atoms with long-range potentials. Similarities and differences will be discussed. © Published under licence by IOP Publishing Ltd.
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Armentano, M.G. - Blasco, J.
J. Comput. Appl. Math. 2010;234(5):1404-1416
2010
Temas: Cross-grid - Macroelement technique - Mixed finite elements - Stability analysis - Stokes problem - A-stability - Finite Element - Macro element - Mixed finite element methods - Mixed finite elements
Descripción: In this paper we develop and analyze a family of mixed finite element methods for the numerical solution of the Stokes problem in two space dimensions. In these schemes, the pressure is interpolated on a mesh of rectangular elements, while the velocity is approximated on a triangular mesh obtained by dividing each rectangle into four triangles by its diagonals. Continuous interpolations of degrees k for the velocity and l for the pressure are considered, so the new finite elements are called cross-grid Pk Ql. A stability analysis of these approximations is provided, based on the macroelement technique of Stenberg. The lowest order P1 Q1 and P2 Q1 cases are analyzed in detail; in the first case, a global spurious pressure mode is shown to exist, so this element is unstable. In the second case, however, stability is rigorously proved. Numerical results obtained in these two cases are also presented, which confirm the existence of the spurious pressure mode for the P1 Q1 element and the stability of the P2 Q1 element. © 2010 Elsevier B.V. All rights reserved.
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Depine, R.A. - Skigin, D.C.
Phys Rev E. 2000;61(4):4479-4490
2000
Temas: Natural frequencies - Polarization - Efficiency distributions - Even- and odd-mode - Numerical results - P-polarization - Periodic gratings - Resonant behavior - Single cavity - Surface-shape resonances
Descripción: Fil:Depine, R.A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.
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Weissmann, M.
The Journal of Chemical Physics 1964;40(1):175-178
1964
Descripción: Free-volume integrals for hole theories of liquids were calculated for some special cases by Monte Carlo numerical integration. The dependence of the free volume on the number of nearest neighbors is thus obtained. Only molecules interacting with a Lennard-Jones potential and a temperature near the critical one have been considered. The results differ considerably from those of earlier theories, where spherical symmetry was assumed. However, the introduction of vacant cells (holes) does not improve the thermodynamic functions obtained with the cell theory of Lennard-Jones and Devonshire.
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Di Lorenzo, F. - Raspa, V. - Knoblauch, P. - Lazarte, A. - Moreno, C. - Clausse, A.
J Appl Phys 2007;102(3)
2007
Temas: Codes (symbols) - Image analysis - Numerical methods - Plasma devices - X ray analysis - Metallic pieces - Radiographic images - X ray emission - Radiography
Descripción: A compact tabletop plasma focus suitable for hard x-ray imaging applications is presented. The hard x-ray emission was characterized by means of an effective energy analysis, based on images obtained with a single shot. The effective energy of the radiation was estimated to be around 83 keV from radiographic images of metallic pieces. Numerical calculations, based on validated codes, are presented to give a quantitative interpretation of the experimental results. Experimental demonstration of the suitability of this device for introspective imaging of metallic pieces is also given. © 2007 American Institute of Physics.
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Rios, C.A. - Gravielle, M.S. - Mitnik, D.M. - Silkin, V.M.
J. Phys. Conf. Ser. 2012;388(PART 13)
2012
Temas: Condensed matter physics - Emission spectroscopy - Nonlinear equations - Photoelectron spectroscopy - Photoelectrons - Photons - Schrodinger equation - Ultrashort pulses - Band-structure-based models - Distorted waves
Descripción: Photoelectron emission spectra induced by grazing incidence of intense and ultrashort laser pulses on a metal surface are studied within a distorted-wave formalism. The proposed aproximation, named Band-Structure Based-Volkov (BSB-V) approach, includes a precise description of the surface potential, incorporating information of the band structure of the solid. Results are compared with the numerical solution of the time-dependent Schrodinger equation and with values derived from simpler theoretical models. © Published under licence by IOP Publishing Ltd.
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Mazzitelli, F.D. - Lombardo, F.C. - Villar, P.I.
J. Phys. Conf. Ser. 2009;161
2009
Descripción: We present an overview of the validity of the Proximity Force Approximation (PFA) in the calculation of Casimir forces between perfect conductors for different geometries, with particular emphasis for the configuration of a cylinder in front of a plane. In all cases we compare the exact numerical results with those of PFA, and with asymptotic expansions that include the next to leading order corrections. We also discuss the similarities and differences between the results for Casimir and electrostatic forces. © 2009 IOP Publishing Ltd.
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Bermudez, M.M. - Sosa, R. - Grondona, D. - Márquez, A. - Kelly, H. - Artana, G.
J. Phys. Conf. Ser. 2011;296(1)
2011
Temas: Actuators - Air - Boundary conditions - Boundary layers - Dielectric properties - Velocity - Velocity distribution - Flow behaviours - Flow Stabilization - Numerical experiments
Descripción: The use of plasma actuators is a recent technology that imposes a localized electric force that is used to control air flows. A suitable representation of actuation enables to undertake plasma actuators optimization, to design flow-control strategies, or to analyse the flow stabilization that can be attained by plasma forcing. The problem description may be clearly separated in two regions. An outer region, where the fluid is electrically neutral, in which the flow is described by the Navier-Stokes equation without any forcing term. An inner region, that forms a thin boundary layer, where the fluid is ionized and electric forces are predominant. The outer limit of the inner solution becomes the boundary condition for the outer problem. The outer problem can then be solved with a slip velocity that is issued from the inner solution. Although the solution for the inner problem is quite complex it can be contoured proposing pseudo-empirical models where the slip velocity of the outer problem is determined indirectly from experiments. This pseudo-empirical model approach has been recently tested in different cylinder flows and revealed quite adapted to describe actuated flow behaviour. In this work we determine experimentally the influence of the duty cycle on the slip velocity distribution. The velocity was measured by means of a pitot tube and flow visualizations of the starting vortex (i.e. the induced flow when actuation is activated in a quiescent air) have been done by means of the Schlieren technique. We also performed numerical experiments to simulate the outer region problem when actuation is activated in a quiescent air using a slip velocity distribution as a boundary condition. The experimental and numerical results are in good agreement showing the potential of this pseudo-empirical model approach to characterize the plasma actuation.
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Alexander, P.
Phys. Fluids 2003;15(10):3065-3077
2003
Temas: Atmospheric turbulence - Balloons - Body fluids - Drag - Perturbation techniques - Solutions - Thermodynamics - Balloon dynamics - Atmospherics - atmosphere
Descripción: The dynamics of open balloons in an atmosphere may be studied with a body-fluid coupled model. A numerical approach is required to solve the corresponding equation set. Solutions under different conditions are obtained here for the vertical and one horizontal direction. Relevant dynamical features during ascent, flotation, and descent depend on balloon thermodynamics, wind, air small-scale turbulence, and perturbations to the background atmosphere. After analysis of the results it is found that approximate analytical solutions may be found in certain cases. The effect of nonlinear drag on balloon oscillation period and damping near flotation is evaluated. © 2003 American Institute of Physics.
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Mazzaferri, J. - Ledesma, S.
AIP Conf. Proc. 2008;992:1057-1060
2008
Descripción: In this work we introduce a new approach for corner extraction. The method that allows the corner extraction with rotation invariance is composed by a spiral phase function and a binary amplitude. The designed function can be easily implemented as a filter for a Vander Lugt-like optical correlator. A final image obtained with the detector presents intensity peaks in each corner location. Numerical simulation has been performed on a set of synthetic scenes, modulated either in amplitude or phase. Results that show the very good performance of the method are shown. © 2008 American Institute of Physics.
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Serrano, E.P.
Appl Comput Harmonic Anal 1996;3(1):57-64
1996
Descripción: In this paper we propose an extended family of almost orthogonal spline wavelets with compact support. These functions provide snug bases for L2 (ℛ), preserving semiorthogonal properties. As it is well known, orthogonality is a desirable quality while finite support has attractive features for numerical applications. This work represents an effort to combine these conditions in the spline case and to enhance previous results of Chui and Unser et al. We start by reviewing the concept of semiorthogonal wavelets and we discuss their performance. Next, we give a brief description of the general technique for computing compactly supported spline wavelets. Finally we expose these functions. We also develop several formulas in accord with our purposes. © 1996 Academic Press, Inc.
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Aucar, I.A. - Gómez, S.S. - Melo, J.I. - Giribet, C.C. - Ruiz De Azúa, M.C.
J Chem Phys 2013;138(13)
2013
Temas: Correlation effect - Nuclear magnetic shieldings - Numerical results - Quantitative result - Random phase approximations - Relativistic effects - Relativistic electron - Yield differences - Approximation algorithms - Chlorine compounds
Descripción: In the present work, numerical results of the nuclear spin-rotation (SR) tensor in the series of compounds HX (X=H,F,Cl,Br,I) within relativistic 4-component expressions obtained by Aucar [J. Chem. Phys. 136, 204119 (2012)10.1063/1.4721627] are presented. The SR tensors of both the H and X nuclei are discussed. Calculations were carried out within the relativistic Linear Response formalism at the Random Phase Approximation with the DIRAC program. For the halogen nucleus X, correlation effects on the non-relativistic values are shown to be of similar magnitude and opposite sign to relativistic effects. For the light H nucleus, by means of the linear response within the elimination of the small component approach it is shown that the whole relativistic effect is given by the spin-orbit operator combined with the Fermi contact operator. Comparison of "best estimate" calculated values with experimental results yield differences smaller than 2-3 in all cases. The validity of "Flygares relation" linking the SR tensor and the NMR nuclear magnetic shielding tensor in the present series of compounds is analyzed. © 2013 American Institute of Physics.
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Melita, M.D. - Licandro, J.
Astron. Astrophys. 2012;539
2012
Temas: asteroids: general - Kuiper belt: general - minor planets - Color distribution - Cometary activity - Dynamical evolution - Heliocentric distances - Kuiper belt: generals - Minor bodies - Minor planets
Descripción: The Centaurs are a transitional population of minor bodies of the solar system and the evolutionary link between the trans-Neptunian objects and the short period comets. The surface properties of these objects are very peculiar, because currently available data suggest that their visual surface colors divide the population into two distinctive groups, those with reddish slopes of the visual reflection spectra and those with neutral spectra. Moreover, some of them are known to posses comas produced by cometary activity. Aims. We aim to investigate possible links between the orbital dynamical history and the surface physical properties of the bodies of this population. Methods. By means of numerical integrations of the equations of motion we calculated the orbital evolution of three groups of Centaurs: the Red group, the Gray group, and the Active group. We looked for statistical differences in the timescales spent by the objects of each group at heliocentric distances below certain values that are associated with locations where certain particular physical processes occur at the surfaces. Results. We find remarkable differences when we compare the fraction of objects that penetrate below typical heliocentric distances for each group. Conclusions. Our results suggest that the observed bimodality in the distribution of surface colors of the Centaurs is caused by the different thermal reprocessing on the surface of bodies of the Red group on one side and the Active and Gray groups on the other. Centaurs of the Gray group likely had cometary activity, therefore their color distribution is similar to that of comet nuclei. © 2012 ESO.
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Donato, S. - Servidio, S. - Dmitruk, P. - Valentini, F. - Greco, A. - Veltri, P. - Wan, M. - Shay, M.A. - Cassak, P.A. - Matthaeus, W.H.
AIP Conf. Proc. 2013;1539:99-104
2013
Descripción: In this work, recent advances in numerical studies of local reconnection events in the turbulent plasmas are reviewed. Recently [1], the nonlinear dynamics of magnetic reconnection in turbulence has been investigated through high resolution numerical simulations. Both fluid (MHD and Hall MHD) and kinetic (HybridVlasov) 2D simulations reveal the presence of a large number of X-type neutral points, where magnetic reconnection locally occurs. The associated reconnection rates are distributed over a wide range of values and they depend on the local geometry of the diffusion region. This new approach to the study of magnetic reconnection has broad applications to the turbulent solar wind (SW). Strong magnetic SW discontinuities are in fact strongly related to these intermittent processes of reconnection [2, 3]. Methods employed to identify sets of possible reconnection events along a one-dimensional path through the turbulent field (emulating experimental sampling by a single detector in a highspeed flow) are here reviewed. These local reconnection/discontinuity events may be the main sites of heating and particle acceleration processes [4]. Results from hybrid-Vlasov kinetic simulations support these observations [5, 6]. In the turbulent regime, in fact, kinetic effects manifest through a deformation of the ion distribution function. These patterns of non-Maxwellian features are concentrated in space nearby regions of strong magnetic activity. These results open a new path on the study of kinetic processes such as heating, particle acceleration, and temperature anisotropy, commonly observed in astrophysics. © 2013 AIP Publishing LLC.
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Gibbons, F. - Chauwin, J.-F. - Despósito, M. - José, J.V.
Biophys. J. 2001;80(6):2515-2526
2001
Temas: kinesin - article - calculation - dynamics - mathematical analysis - microtubule - model - velocity - Goes
Descripción: A two-dimensional stochastic model for the dynamics of microtubules in gliding-assay experiments is presented here, which includes the viscous drag acting on the moving fiber and the interaction with the kinesins. For this purpose, we model kinesin as a spring, and explicitly use parameter values to characterize the model from experimental data. We numerically compute the mean attachment lifetimes of all motors, the total force exerted on the microtubules at all times, the effects of a distribution in the motor speeds, and also the mean velocity of a microtubule in a gliding assay. We find quantitative agreement with the results of J. Howard, A. J. Hudspeth, and R. D. Vale, Nature. 342:154-158. We perform additional numerical analysis of the individual motors, and show how cancellation of the forces exerted by the many motors creates a resultant longitudinal force much smaller than the maximum force that could be exerted by a single motor. We also examine the effects of inhomogeneities in the motor-speeds. Finally, we present a simple theoretical model for microtubules dynamics in gliding assays. We show that the model can be analytically solved in the limit of few motors attached to the microtubule and in the opposite limit of high motor density. We find that the speed of the microtubule goes like the mean speed of the motors in good quantitative agreement with the experimental and numerical results.
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Melo, J.I. - De Azúa, M.C.R. - Peralta, J.E. - Scuseria, G.E.
J Chem Phys 2005;123(20)
2005
Temas: Density functional theory - Douglas-Kroll-Hess approximation - Heavy elements - Quasirelativistic approach - Approximation theory - Hamiltonians - Perturbation techniques - Probability density function - Nuclear magnetic resonance
Descripción: We have employed the Douglas-Kroll-Hess approximation to derive the perturbative Hamiltonians involved in the calculation of NMR spin-spin couplings in molecules containing heavy elements. We have applied this two-component quasirelativistic approach using finite perturbation theory in combination with a generalized Kohn-Sham code that includes the spin-orbit interaction self-consistently and works with Hartree-Fock and both pure and hybrid density functionals. We present numerical results for one-bond spin-spin couplings in the series of tetrahydrides C H4, Si H4, Ge H4, and Sn H4. Our two-component Hartree-Fock results are in good agreement with four-component Dirac-Hartree-Fock calculations, although a density-functional treatment better reproduces the available experimental data. © 2005 American Institute of Physics.
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