The statistical properties of the city transport in Cuernavaca (Mexico) and Random matrix ensembles

We analyze statistical properties of the city bus transport in Cuernavaca (Mexico) and show that the bus arrivals display probability distributions conforming those given by the Unitary Ensemble of random matrices.Comment: 4 pages, 3 figure

Wave Scattering through Classically Chaotic Cavities in the Presence of Absorption: An Information-Theoretic Model

We propose an information-theoretic model for the transport of waves through a chaotic cavity in the presence of absorption. The entropy of the S-matrix statistical distribution is maximized, with the constraint $=\alpha n$: n is the dimensionality of S, and $0\leq \alpha \leq 1, \alpha =0(1)$ meaning complete (no) absorption. For strong absorption our result agrees with a number of analytical calculations already given in the literature. In that limit, the distribution of the individual (angular) transmission and reflection coefficients becomes exponential -Rayleigh statistics- even for n=1. For $n\gg 1$ Rayleigh statistics is attained even with no absorption; here we extend the study to $\alpha <1$. The model is compared with random-matrix-theory numerical simulations: it describes the problem very well for strong absorption, but fails for moderate and weak absorptions. Thus, in the latter regime, some important physical constraint is missing in the construction of the model.Comment: 4 pages, latex, 3 ps figure

Global monopole, dark matter and scalar tensor theory

In this article, we discuss the space-time of a global monopole field as a candidate for galactic dark matter in the context of scalar tensor theory.Comment: 8 pages, Accepted in Mod. Phys. Lett.

Desenvolvimento de metodologia para atualização do Cadastro Vitícola por meio da utilização de geotecnologias.

Esse trabalho apresenta o desenvolvimento de uma metodologia para otimizar o processo de atualização dos vinhedos georreferenciados que compõem a base de dados do CV por meio da utilização de geotecnologias

Casimir-Polder interaction between an atom and a conducting wall in cosmic string spacetime

The Casimir-Polder interaction potential is evaluated for a polarizable microparticle and a conducting wall in the geometry of a cosmic string perpendicular to the wall. The general case of the anisotropic polarizability tensor for the microparticle is considered. The corresponding force is a function of the wall-microparticle and cosmic string-microparticle distances. Depending on the orientation of the polarizability tensor principal axes the force can be either attractive or repulsive. The asymptotic behavior of the Casimir-Polder potential is investigated at large and small separations compared to the wavelength of the dominant atomic transitions. We show that the conical defect may be used to control the strength and the sign of the Casimir-Polder force.Comment: 17 pages, 3 figure

Fatores físicos e microbiológicos do solo, nutricionais e vegetais correlacionados com a produção de grãos de feijoeiro (Phaseolus vulgaris L.)

Foram realizados quatro experimentos, um para cada tipo de terra, com o intuito de encontrar o fator ou o grupo de fatores que melhor se correlacionam com a produção de feijoeiro em dois solos representativos

Path Integral Approach to the Scattering Theory of Quantum Transport

The scattering theory of quantum transport relates transport properties of disordered mesoscopic conductors to their transfer matrix \bbox{T}. We introduce a novel approach to the statistics of transport quantities which expresses the probability distribution of \bbox{T} as a path integral. The path integal is derived for a model of conductors with broken time reversal invariance in arbitrary dimensions. It is applied to the Dorokhov-Mello-Pereyra-Kumar (DMPK) equation which describes quasi-one-dimensional wires. We use the equivalent channel model whose probability distribution for the eigenvalues of \bbox{TT}^{\dagger} is equivalent to the DMPK equation independent of the values of the forward scattering mean free paths. We find that infinitely strong forward scattering corresponds to diffusion on the coset space of the transfer matrix group. It is shown that the saddle point of the path integral corresponds to ballistic conductors with large conductances. We solve the saddle point equation and recover random matrix theory from the saddle point approximation to the path integral.Comment: REVTEX, 9 pages, no figure

Equivalence of Fokker-Planck approach and non-linear σ\sigma-model for disordered wires in the unitary symmetry class

The exact solution of the Dorokhov-Mello-Pereyra-Kumar-equation for quasi one-dimensional disordered conductors in the unitary symmetry class is employed to calculate all $m$-point correlation functions by a generalization of the method of orthogonal polynomials. We obtain closed expressions for the first two conductance moments which are valid for the whole range of length scales from the metallic regime ($L\ll Nl$) to the insulating regime ($L\gg Nl$) and for arbitrary channel number. In the limit $N\to\infty$ (with $L/(Nl)=const.$) our expressions agree exactly with those of the non-linear $\sigma$-model derived from microscopic Hamiltonians.Comment: 9 pages, Revtex, one postscript figur

Observações preliminares sobre a presença de microrriza vesículo-arbuscular em solos sujeitos à compactação e cultivados com feijoeiro (Phaseolus vulgaris L.).

Presença natural de esporos de fungo MVA em solos de testuras diferentes e em função do nível de compactação a eles aplicado

The ideal gas as an urn model: derivation of the entropy formula

The approach of an ideal gas to equilibrium is simulated through a generalization of the Ehrenfest ball-and-box model. In the present model, the interior of each box is discretized, {\it i.e.}, balls/particles live in cells whose occupation can be either multiple or single. Moreover, particles occasionally undergo random, but elastic, collisions between each other and against the container walls. I show, both analitically and numerically, that the number and energy of particles in a given box eventually evolve to an equilibrium distribution $W$ which, depending on cell occupations, is binomial or hypergeometric in the particle number and beta-like in the energy. Furthermore, the long-run probability density of particle velocities is Maxwellian, whereas the Boltzmann entropy $\ln W$ exactly reproduces the ideal-gas entropy. Besides its own interest, this exercise is also relevant for pedagogical purposes since it provides, although in a simple case, an explicit probabilistic foundation for the ergodic hypothesis and for the maximum-entropy principle of thermodynamics. For this reason, its discussion can profitably be included in a graduate course on statistical mechanics.Comment: 17 pages, 3 figure