Papers by Alejandro Garcia
The Journal of chemical physics, Jan 14, 2015
We formulate and study computationally the fluctuating compressible Navier-Stokes equations for r... more We formulate and study computationally the fluctuating compressible Navier-Stokes equations for reactive multi-species fluid mixtures. We contrast two different expressions for the covariance of the stochastic chemical production rate in the Langevin formulation of stochastic chemistry, and compare both of them to predictions of the chemical master equation for homogeneous well-mixed systems close to and far from thermodynamic equilibrium. We develop a numerical scheme for inhomogeneous reactive flows, based on our previous methods for non-reactive mixtures [Balakrishnan , Phys. Rev. E 89, 013017 (2014)]. We study the suppression of non-equilibrium long-ranged correlations of concentration fluctuations by chemical reactions, as well as the enhancement of pattern formation by spontaneous fluctuations. Good agreement with available theory demonstrates that the formulation is robust and a useful tool in the study of fluctuations in reactive multi-species fluids. At the same time, sever...
Multiscale Modeling & Simulation, 2010
A previously-developed hybrid particle-continuum method [J. B. Bell, A. Garcia and S. A. Williams... more A previously-developed hybrid particle-continuum method [J. B. Bell, A. Garcia and S. A. Williams, SIAM Multiscale Modeling and Simulation, 6:1256-1280, 2008] is generalized to dense fluids and two and three dimensional flows. The scheme couples an explicit fluctuating compressible Navier-Stokes solver with the Isotropic Direct Simulation Monte Carlo (DSMC) particle method [A. Donev and A. L. Garcia and B. J.
Solar Physics, 2000
Studying the appearance of active regions during periods of solar activity minima, we observed th... more Studying the appearance of active regions during periods of solar activity minima, we observed that the magnetic fields of active regions belonging to the old and new cycle were mutually related. This was the reason we decided to investigate the relation of the old and new cycle activity during the two last minima in more detail. We examined the distribution
Lecture Notes in Computer Science, 2009
In this work we extend the communication abilities of agents in multi-agent systems by enabling t... more In this work we extend the communication abilities of agents in multi-agent systems by enabling them to reason about the credibility of information to be shared with other agents. We propose a framework in which agents exchange sentences of a logical language enriched by meta-information. We discuss several possible approaches and present an advanced approach overcoming previously shown problems. For
Journal of Physics G-nuclear and Particle Physics, 2006
The goal of the present analysis is to find, in the free neutron beta decay, the expressions for ... more The goal of the present analysis is to find, in the free neutron beta decay, the expressions for the decay rate and the electron asymmetry that contain all the theoretical effects at the 10-4 level. This accuracy is better than the current experimental precision that modern experiments allow. For this aim it is necessary to study the strong interaction effects,
Journal of Magnetism and Magnetic Materials, 1998
Studies of the frequency dependence of the temperature of the AC susceptibility peak, of the ther... more Studies of the frequency dependence of the temperature of the AC susceptibility peak, of the thermal variation of the nonlinear DC susceptibility, and of ageing effects on the magnetization relaxation in γ-Fe2O3 4.7nm nanoparticle assemblies with interparticle interactions of varying strength, give evidence of three magnetic regimes: pure superparamagnetic, superparamagnetic modified by the interactions, and collective. The properties of the
Physica Status Solidi (c), 2007
SiO 2 films by atmospheric pressure chemical vapor deposition (APCVD) process, using tetraethoxys... more SiO 2 films by atmospheric pressure chemical vapor deposition (APCVD) process, using tetraethoxysilane (TEOS) and ozone (O 3 ) as reactant were obtained. The films were deposited on silicon substrates at various temperatures 125, 150, 175, 200, 225 and 250 °C Fourier transforms infrared (FTIR) spectroscopy was used to characterize the SiO 2 films. Absorbance spectrums show the vibration modes corresponding to SiO 2 films. Additional absorption bands due to residual groups were also observed, but they were found to be dependent on the deposition temperature. The observed current flowing through the oxide could be related to these residual groups, mainly to hydroxyl groups.
SPE Asia Pacific Oil and Gas Conference and Exhibition, 2010
Copyright 2010, Society of Petroleum Engineers This paper was prepared for presentation at the 20... more Copyright 2010, Society of Petroleum Engineers This paper was prepared for presentation at the 2010 SPE Asia Pacific Oil & Gas Conference and Exhibition held in Brisbane, Australia, 18-20 October 2010. This paper was selected for presentation by an SPE program ...
Copyright 2010, Society of Petroleum Engineers This paper was prepared for presentation at the SP... more Copyright 2010, Society of Petroleum Engineers This paper was prepared for presentation at the SPE Intelligent Energy Conference and Exhibition held in Utrecht, The Netherlands, 2325 March 2010. This paper was selected for presentation by an SPE program committee ...
Copyright 2010, Society of Petroleum Engineers This paper was prepared for presentation at the SP... more Copyright 2010, Society of Petroleum Engineers This paper was prepared for presentation at the SPE Intelligent Energy Conference and Exhibition held in Utrecht, The Netherlands, 2325 March 2010. This paper was selected for presentation by an SPE program committee ...
Physical review. E, Statistical, nonlinear, and soft matter physics, 2003
The cylindrical Couette flow of a rarefied gas is investigated, under the diffuse-specular reflec... more The cylindrical Couette flow of a rarefied gas is investigated, under the diffuse-specular reflection condition of Maxwell's type on the cylinders, in the case where the inner cylinder is rotating whereas the outer cylinder is at rest. The inverted velocity profile for small accommodation coefficients, pointed out by Tibbs, Baras, and Garcia [Phys. Rev. E 56, 2282 (1997)] on the basis of a Monte Carlo simulation, is investigated extensively by means of a systematic asymptotic analysis for small Knudsen numbers as well as the direct numerical analysis of the Boltzmann equation, and the parameter range in which the phenomenon appears is clarified.
Physical review. E, Statistical, nonlinear, and soft matter physics, 2003
In this paper we describe a direct simulation Monte Carlo algorithm for the Uehling-Uhlenbeck-Bol... more In this paper we describe a direct simulation Monte Carlo algorithm for the Uehling-Uhlenbeck-Boltzmann equation in terms of Markov processes. This provides a unifying framework for both the classical Boltzmann case as well as the Fermi-Dirac and Bose-Einstein cases. We establish the foundation of the algorithm by demonstrating its link to the kinetic equation. By numerical experiments we study its sensitivity to the number of simulation particles and to the discretization of the velocity space, when approximating the steady-state distribution.
Physical review. E, Statistical, nonlinear, and soft matter physics, 2014
Fluctuating hydrodynamics provides a model for fluids at mesoscopic scales where thermal fluctuat... more Fluctuating hydrodynamics provides a model for fluids at mesoscopic scales where thermal fluctuations can have a significant impact on the behavior of the system. Here we investigate a model for fluctuating hydrodynamics of a single-component, multiphase flow in the neighborhood of the critical point. The system is modeled using a compressible flow formulation with a van der Waals equation of state, incorporating a Korteweg stress term to treat interfacial tension. We present a numerical algorithm for modeling this system based on an extension of algorithms developed for fluctuating hydrodynamics for ideal fluids. The scheme is validated by comparison of measured structure factors and capillary wave spectra with equilibrium theory. We also present several nonequilibrium examples to illustrate the capability of the algorithm to model multiphase fluid phenomena in a neighborhood of the critical point. These examples include a study of the impact of fluctuations on the spinodal decompo...
Computational Models of Argument, 2010
Argument Theory Change applies classic belief change concepts to the area of argumentation. This ... more Argument Theory Change applies classic belief change concepts to the area of argumentation. This intersection of fields takes advantage of the definition of a Dynamic Abstract Argumentation Framework, in which an argument is either active or inactive, and only in the former case it is taken into consideration in the reasoning process. An approach for an argument revision operator defined through deactivation of arguments can be found in the literature. The present article is inspired by that approach, and complements it by considering activation of arguments to define a revision operator.
Ibm Journal of Research and Development, 2008
In this article we introduce the basics for understanding the mechanisms of Argument Theory Chang... more In this article we introduce the basics for understanding the mechanisms of Argument Theory Change. In particular we reify it using Defeasible Logic Programming. In this formalism, knowledge bases are represented through defeasible logic programs. The main change operation we define over a defeasible logic program is a special kind of revision that inserts a new argument and then modifies the resulting program seeking for the argument's warrant. Since the notion of argument refers to a set of defeasible rules, we generalize this technique in order to handle extended arguments, i.e., arguments containing also strict rules. Hence, revision using extended arguments allows us to consider program-independent arguments, which brings about new issues. A single notion of minimal change is analyzed, which refers to keep the contents of the program as much as possible. Finally, a brief discussion about the relation between our approach and the basic theory of belief revision is exposed, along with a description of other possible (more complex) minimal change principles.
Logic Programming and Non-monotonic Reasoning, 2011
In this paper, we investigate the problem of contraction in Defeasible Logic Programming (DeLP), ... more In this paper, we investigate the problem of contraction in Defeasible Logic Programming (DeLP), a logic-based approach for defeasible argumentation. We develop different notions of contraction based on both, the different forms of entailment implicitly existent in argumentation-based formalisms and the influence literals exhibit in the reasoning process. We give translations of widely accepted rationality postulates for belief contraction to
Non-Monotonic Reasoning, 2004
The BDI model provides what it is possibly one of the most promising architectures for the develo... more The BDI model provides what it is possibly one of the most promising architectures for the development of intelligent agents, and has become one of the most studied and well known in the literature. The basic BDI model needs to be complemented with two mechanisms: one for reasoning about intentions, and one for revising beliefs upon percep- tion. In this
National Conference on Artificial Intelligence, 2008
In this article we work on certain aspects of the belief change theory in order to make them suit... more In this article we work on certain aspects of the belief change theory in order to make them suitable for argumentation sys- tems. This approach is based on Defeasible Logic Program- ming as the argumentation formalism from which we ground the definitions. The objective of our proposal is to define an argument revision operator that inserts a new argument into
Computational Models of Argument, 2008
We propose an abstract argumentation theory whose dynamics is cap- tured by the application of be... more We propose an abstract argumentation theory whose dynamics is cap- tured by the application of belief revision concepts. The theory is deemed as ab- stract because both the underlying logic for arguments and argumentative seman- tics remain unspecified. Regarding our approach to argument theory change, we de- fine some basic change operations along with their necessary theoretical elements towards the
ABSTRACT Thermodynamic fluctuations are significant at microscopic scales even when hydrodynamic ... more ABSTRACT Thermodynamic fluctuations are significant at microscopic scales even when hydrodynamic transport models (i.e., Navier-Stokes equations) are still accurate; a well-known example is Rayleigh scattering, which makes the sky blue. Interesting phenomena also appear in non-equilibrium systems, such as the enhancement of diffusion during mixing due to the correlation of velocity and concentration fluctuations. Direct Simulation Monte Carlo (DSMC) simulations are useful in the study of hydrodynamic fluctuations due to their computational efficiency and ability to model molecular detail, such as internal energy and chemical reactions. More recently, finite volume schemes based on the fluctuating hydrodynamic equations of Landau and Lifshitz have been formulated and validated by comparisons with DSMC simulations. This paper discusses some of the relevant numerical issues and physical effects investigated using DSMC and stochastic Navier-Stokes simulations. This paper also presents the multi-component fluctuating hydrodynamic equations, including chemical reactions, and illustrates their numerical solutions in the study of Turing patterns. We find that behind a propagating reaction front, labyrinth patterns are produced due to the coupling of reactions and species diffusion. In general, fluctuations accelerate the propagation speed of the leading front but differences are observed in the Turing patterns depending on the origin of the fluctuations (stochastic hydrodynamic fluxes versus Langevin chemistry).
Uploads
Papers by Alejandro Garcia