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J. D. Munoz

Publications and source records attributed to J. D. Munoz.

8 recordsLinked to original sources
arXiv2010

A statistical model of fracture for a 2D hexagonal mesh: the Cell Network Model of Fracture for the bamboo Guadua angustifolia

A 2D, hexagonal in geometry, statistical model of fracture is proposed. The model is based on the drying fracture process of the bamboo Guadua angustifolia. A network of flexible cells are joined by brittle junctures of different Young moduli that break at a fixed threshold in tensile force. The system is solved by means of the Finite Element Method (FEM). The distribution of avalanche breakings exhibits a power law with exponent -2.93(9), in agreement with the random fuse model.

cond-mat.soft↗
arXiv2006

3D Lattice-Boltzmann Model for Magnetic Reconnection

In this paper we develop a 3D Lattice-Boltzmann model that recovers in the continuous limit the two-fluids theory for plasmas, and consecuently includes the generalizated Ohm's law. The model reproduces the magnetic reconnection process just by given the right initial equlibrium conditions in the magnetotail, without any assumption on the resistivity in the diffusive region. In this model, the plasma is handled like two fluids with an interaction term, each one with distribution functions associated to a cubic lattice with 19 velocities (D3Q19). The electromagnetic fields are considered like a third fluid with an external force on a cubic lattice with 13 velocities (D3Q13). The model can simulate either viscous fluids in the incompressible limit or non-viscous compressible fluids, and sucessfully reproduces both the Hartmann flow and the magnetic reconnection in the magnetotail. The reconnection rate obtained with this model is R=0.109, which is in excellent agreement with the observations.

physics.comp-ph↗
arXiv2005

The Single Histogram Method and the Quantum Harmonic Oscillator: Accuracy Limits

In a recent work, M. Troyer, F. Alet and S. Wessel \cite{brazilean} proposed a way to extend histogram methods to quantum systems in the World Line Quantum Monte Carlo (WLQMC) formulation. The strategy, also proposed in \cite{josedaniel}, allows to compute quantum averages on a narrow temperature range from a single Monte Carlo run at fixed temperature. This is achieved by fixing $N$, the number of temporal divisions in the Trotter-Suzuki expansion of WLQMC, and by changing $ε$$=$$1/(N \kb T)$. In this work we apply this strategy to construct a single histogram Monte Carlo method for a canonical ensemble of one-dimensional quantum harmonic oscillators and we explore its accuracy limits. We obtain that fixing $N$ imposses a limit of minimal temperature to the properly performance of the method, which is $T_{min}$$=$$1.9(2)N^{-0.80(6)}$ in our example. This limit is a consequence of the fact that the Trotter-Suzuki expansion fails for large $ε$ values, and, therefore, should be taken into account in all applications of this histogram method for quantum systems.

cond-mat.stat-mech↗
arXiv2004

A Cellular Automaton Model for the Traffic Flow in Bogota

In this work we propose a car cellular automaton model that reproduces the experimental behavior of traffic flows in Bogotá. Our model includes three elements: hysteresis between the acceleration and brake gaps, a delay time in the acceleration, and an instantaneous brake. The parameters of our model were obtained from direct measurements inside a car on motorways in Bogotá. Next, we simulated with this model the flux-density fundamental diagram for a single-lane traffic road and compared it with experimental data. Our simulations are in very good agreement with the experimental measurements, not just in the shape of the fundamental diagram, but also in the numerical values for both the road capacity and the density of maximal flux. Our model reproduces, too, the qualitative behavior of shock waves. In addition, our work identifies the periodic boundary conditions as the source of false peaks in the fundamental diagram, when short roads are simulated, that have been also found in previous works. The phase transition between free and congested traffic is also investigated by computing both the relaxation time and the order parameter. Our work shows how different the traffic behavior from one city to another can be, and how important is to determine the model parameters for each city.

cond-mat.stat-mech↗
arXiv2004

Equilibrium Times for the Multicanonical Method

This work measures the time to equilibrium for the multicanonical method on the 2D-Ising system by using a new criterion, proposed here, to find the time to equilibrium, teq, of any sampling procedure based on a Markov process. Our new procedure gives the same results that the usual one, based on the magnetization, for the canonical Metropolis sampling on a 2D-Ising model at several temperatures. For the multicanonical method we found a power-law relationship with the system size, L, of teq=0.27(15) L^2.80(13), and with the number of energy levels to explore, kE, of teq=0.7(13) kE^1.40(11), in perfect agreement with the result just above. In addition, some kind of critical slowing down was observed around the critical energy. Our new procedure is completely general, and can be applied to any sampling method based on a Markov process.

cond-mat.stat-mech↗
arXiv2002

Rejection-free Monte Carlo Algorithms for Models with Continuous Degrees of Freedom

We construct a rejection-free Monte Carlo algorithm for a system with continuous degrees of freedom. We illustrate the algorithm by applying it to the classical three-dimensional Heisenberg model with canonical Metropolis dynamics. We obtain the lifetime of the metastable state following a reversal of the external magnetic field. Our rejection-free algorithm obtains results in agreement with a direct implementation of the Metropolis dynamic and requires orders of magnitude less computational time at low temperatures. The treatment is general and can be extended to other dynamics and other systems with continuous degrees of freedom.

cond-mat.stat-mech↗
arXiv2001

The XY-model with $Z_2$ Symmetry: Finite-size scaling analysis using the Broad Histogram Method

In this work we investigate the classical ferromagnetic XY-model in two dimensions subject to a symmetry breaking field which impose a $Z_2$ symmetry to the system. We used the broad histogram method combined with microcanonical simulations and finite-size scaling analysis to estimate the critical temperature and critical exponents of this system with little computational effort. In addition, we present a general procedure which makes possible to use the broad histogram method for continuous systems, also when the macroscopic quantities needed by the method cannot be obtained analytically. Our results are robust under the choice of four different pseudo-random number generators.

cond-mat.stat-mech↗