arXiv subjects

Welles A. M. Morgado

Publications and source records attributed to Welles A. M. Morgado.

22 records · Page 2Linked to original sources

arXiv2006

The Ferromagnetic Potts model under an external magnetic field: an exact renormalization group approach

The q-state ferromagnetic Potts model under a non-zero magnetic field coupled with the 0^th Potts state was investigated by an exact real-space renormalization group approach. The model was defined on a family of diamond hierarchical lattices of several fractal dimensions d_F. On these lattices, the renormalization group transformations became exact for such a model when a correlation coupling that singles out the 0^th Potts state was included in the Hamiltonian. The rich criticality presented by the model with q=3 and d_F=2 was fully analyzed. Apart from the Potts criticality for the zero field, an Ising-like phase transition was found whenever the system was submitted to a strong reverse magnetic field. Unusual characteristics such as cusps and dimensional reduction were observed on the critical surface.

cond-mat.stat-mech↗

arXiv2005

Three-dimensional Ginzburg-Landau simulation of a vortex line displaced by a zigzag of pinning spheres

A vortex line is shaped by a zigzag of pinning centers and we study here how far the stretched vortex line is able to follow this path. The pinning center is described by an insulating sphere of coherence length size such that in its surface the de Gennes boundary condition applies. We calculate the free energy density of this system in the framework of the Ginzburg-Landau theory and study the critical displacement beyond which the vortex line is detached from the pinning center.

cond-mat.supr-con↗

arXiv2002

Numerical simulation of vibrated granular gases under realistic boundary conditions

A variant of the Direct Simulation Monte Carlo method is used to study the behavior of a granular gas, in two and three dimensions, under varying density, restitution coefficient, and inelasticity regimes, for realistic vibrating wall conditions. Our results agree quite well with recent experimental data. The role of the energy injection mechanism is discussed, as well as the behavior of state-functions, such as pressure, under realistic boundary conditions. Upon a density increase, we find signals of a clustering transition.

cond-mat.mes-hall↗

arXiv1999

Numerical Method for Zero-Temperature Vortex-Line Phase Diagrams

A numerical method to calculate equilibrium vortex-line configurations in bulk anisotropic type-II superconductors, at zero temperature, placed in an external magnetic field is introduced and applied to two physical problems. The method is designed to search for the minimum of the Gibbs free-energy in the London approximation and assumes only that the vortex lines are straight and arranged in a periodic lattice. Based on these assumptions a simulated annealing algorithm is developed to find the vortex-line-lattice unit cell shape, and vortex-line positions within it. This algorithm is made fast and accurate by the use of a rapidly converging series to calculate the lattice sums entering the vortex-vortex interaction energy. The method's accuracy is illustrated by calculating the magnetic induction versus applied field curve for an isotropic superconductor. The method is applied to a superconductor with a square lattice of columnar defects to study selected regions of the zero-temperature-phase diagram where vortex-line-lattices commensurate with the columnar defect lattice exist.

cond-mat.supr-con↗