Confinement of two-dimensional excitons in a non-homogeneous magnetic field

The effective Hamiltonian describing the motion of an exciton in an external non-homogeneous magnetic field is derived. The magnetic field plays the role of an effective potential for the exciton motion, results into an increment of the exciton mass and modifies the exciton kinetic energy operator. In contrast to the homogeneous field case, the exciton in a non-homogeneous magnetic field can also be trapped in the low field region and the field gradient increases the exciton confinement. The trapping energy and wave function of the exciton in a GaAs two-dimensional electron gas for specific circular magnetic field configurations are calculated. The results show than excitons can be trapped by non-homogeneous magnetic fields, and that the trapping energy is strongly correlated with the shape and strength of the non-homogeneous magnetic field profile.Comment: 9 pages, 12 figure

Hysteresis and re-entrant melting of a self-organized system of classical particles confined in a parabolic trap

A self-organized system composed of classical particles confined in a two-dimensional parabolic trap and interacting through a potential with a short-range attractive part and long-range repulsive part is studied as function of temperature. The influence of the competition between the short-range attractive part of the inter-particle potential and its long-range repulsive part on the melting temperature is studied. Different behaviors of the melting temperature are found depending on the screening length ($\kappa$) and the strength ($B$) of the attractive part of the inter-particle potential. A re-entrant behavior and a thermal induced phase transition is observed in a small region of ($\kappa,B$)-space. A structural hysteresis effect is observed as a function of temperature and physically understood as due to the presence of a potential barrier between different configurations of the system.Comment: 8 pages, 6 figure

Extension of the Nambu--Jona-Lasinio model at high densities and temperatures by using an implicit regularization scheme

Traditional cutoff regularization schemes of the Nambu--Jona-Lasinio model limit the applicability of the model to energy-momentum scales much below the value of the regularizing cutoff. In particular, the model cannot be used to study quark matter with Fermi momenta larger than the cutoff. In the present work an extension of the model to high temperatures and densities recently proposed by Casalbuoni, Gatto, Nardulli, and Ruggieri is used in connection with an implicit regularization scheme. This is done by making use of scaling relations of the divergent one-loop integrals that relate these integrals at different energy-momentum scales. Fixing the pion decay constant at the chiral symmetry breaking scale in the vacuum, the scaling relations predict a running coupling constant that decreases as the regularization scale increases, implementing in a schematic way the property of asymptotic freedom of quantum chromodynamics. If the regularization scale is allowed to increase with density and temperature, the coupling will decrease with density and temperature, extending in this way the applicability of the model to high densities and temperatures. These results are obtained without specifying an explicit regularization. As an illustration of the formalism, numerical results are obtained for the finite density and finite temperature quark condensate, and to the problem of color superconductivity at high quark densities and finite temperature.Comment: 7 pages, 5 eps figures - in version 3, substantial changes in text, results and conclusions unchanged. To be published in Phys. Rev.

Transition from single-file to two-dimensional diffusion of interacting particles in a quasi-one-dimensional channel

Diffusive properties of a monodisperse system of interacting particles confined to a \textit{quasi}-one-dimensional (Q1D) channel are studied using molecular dynamics (MD) simulations. We calculate numerically the mean-squared displacement (MSD) and investigate the influence of the width of the channel (or the strength of the confinement potential) on diffusion in finite-size channels of different shapes (i.e., straight and circular). The transition from single-file diffusion (SFD) to the two-dimensional diffusion regime is investigated. This transition (regarding the calculation of the scaling exponent ($\alpha$) of the MSD $$ $\propto t^{\alpha}$) as a function of the width of the channel, is shown to change depending on the channel's confinement profile. In particular the transition can be either smooth (i.e., for a parabolic confinement potential) or rather sharp/stepwise (i.e., for a hard-wall potential), as distinct from infinite channels where this transition is abrupt. This result can be explained by qualitatively different distributions of the particle density for the different confinement potentials.Comment: 13 pages, 11 figure

Coeficientes de repetibilidade e de correlação para caracteres dos frutos de mangabeiras.

Este trabalho visou estimar os coeficientes de repetibilidade e de correlação para os caracteres dos frutos coletados em 39 matrizes