Regression towards the mode

We propose a semi-parametric mode regression estimator for the case in which the variate of interest is continuous and observable over its entire un- bounded support. The estimator is semi-parametric in that the conditional mode is specified as a parametric function, but only mild assumptions are made about the nature of the conditional density of interest. We show that the proposed estimator is consistent and has a tractable asymptotic distribution. Simulation results and an empirical illustration are provided to highlight the practicality and usefulness of the estimator.

Desigualdades sociais e acesso seletivo ao ensino superior no Brasil no período 1994-2001

O ensino superior no Brasil experimentou um significativo processo de expansão, iniciado em meados da década de 90. A retomada do crescimento do número de matrículas, após um período de estagnação na década anterior, ocorreu num contexto de aumento do número de concluintes do nível médio, e acentuou-se a partir de 1997, sob os efeitos das políticas governamentais para a ampliação da oferta de vagas. O setor privado foi o principal responsável pelo processo de expansão, em vista da redução das restrições legais para a criação de novos cursos e instituições. Este trabalho investiga as relações entre as chances de ingresso e o risco de evasão e algumas características sociais e familiares dos estudantes, no contexto da expansão recente deste nível de ensino no Brasil. A análise foi baseada nos dados da Pesquisa Mensal do Emprego do IBGE de 1994 a 2001. Os resultados indicam que tanto o ingresso quanto a evasão são fortemente condicionados pelas características sociais dos estudantes, que as chances de ingresso reduziram-se para o conjunto dos concluintes do ensino médio e que o risco de evasão manteve-se constante. Também não foram observadas alterações nas desigualdades de acesso entre estudantes de diferentes grupos sociais no período

On spin-1 massive particles coupled to a Chern-Simons field

We study spin one particles interacting through a Chern-Simons field. In the Born approximation, we calculate the two body scattering amplitude considering three possible ways to introduce the interaction: (a) a Proca like model minimally coupled to a Chern-Simons field, (b) the model obtained from (a) by replacing the Proca's mass by a Chern-Simons term and (c) a complex Maxwell-Chern-Simons model minimally coupled to a Chern-Simons field. In the low energy regime the results show similarities with the Aharonov-Bohm scattering for spin 1/2 particles. We discuss the one loop renormalization program for the Proca's model. In spite of the bad ultraviolet behavior of the matter field propagator, we show that, up to one loop the model is power counting renormalizable thanks to the Ward identities satisfied by the interaction vertices.Comment: 14 pages, 5 figures, revte

On Aharonov-Casher bound states

In this work bound states for the Aharonov-Casher problem are considered. According to Hagen's work on the exact equivalence between spin-1/2 Aharonov-Bohm and Aharonov-Casher effects, is known that the $\boldsymbol{\nabla}\cdot\mathbf{E}$ term cannot be neglected in the Hamiltonian if the spin of particle is considered. This term leads to the existence of a singular potential at the origin. By modeling the problem by boundary conditions at the origin which arises by the self-adjoint extension of the Hamiltonian, we derive for the first time an expression for the bound state energy of the Aharonov-Casher problem. As an application, we consider the Aharonov-Casher plus a two-dimensional harmonic oscillator. We derive the expression for the harmonic oscillator energies and compare it with the expression obtained in the case without singularity. At the end, an approach for determination of the self-adjoint extension parameter is given. In our approach, the parameter is obtained essentially in terms of physics of the problem.Comment: 11 pages, matches published versio

Genetic mapping and QTLs detection in a Theobroma grandiflora progeny : S04P01

The genus Theobroma covers 22 native species to the Amazon region. Two species are cultivated in Brazil:Theobroma cacao and T. grandiflorum (cupuaçu). T. grandiflora is economically important to the amazonian states of Brazil where it was developed in food and cosmetics with various products manufactured mainly from the pulp of the seed. Both species are susceptible to Moniliophthora perniciosa (Stahel) Singer, the causal agent of witches' brooms disease. 139 SSRs markers (Single Sequence Repeat) from T. grandiflora and 500 SSRs developed by CIRAD in T. cacao, were used to select polymorphic markers and carry out a genetic mapping of a Th. Grandiflora progeny from "174" x "1074" clones, respectively resistant and susceptible to witches' brooms. 145 plants were obtained by Embrapa-CPATU (Belém) today installed in the field at the CEPLAC (Belém) station. Inoculations with the M. perniciosa (from T. grandiflora) were carried out in the progenies and parents to evaluate the resistance. Other observations as vigor or number of ovules per ovary were observed also. We present the first results obtained with the selection of polymorphic specific markers of Th Grandiflora and Cocoa and the first genotying results from 44 SSRs of T. grandiflora including 14 SSRs from expression sequences. In conclusion this study including different teams is ongoing to have at the end of the project: i) the first genetic map of Theobroma grandiflora, ii) identification of QTLs of resistance to witches' broom, and other QTLs and iii) to compare genetic map and QTLs between both species. (Texte intégral

New bounds for Tsallis parameter in a noncommutative phase-space entropic gravity and nonextensive Friedmann equations

In this paper, we have analyzed the nonextensive Tsallis statistical mechanics in the light of Verlinde's formalism. We have obtained, with the aid of a noncommutative phase-space entropic gravity, a new bound for Tsallis nonextensive (NE) parameter (TNP) that is clearly different from the ones present in the current literature. We derived the Friedmann equations in a NE scenario. We also obtained here a relation between the gravitational constant and the TNP.Comment: 15 pages. Final version to appear in Physica

Effect of the Surface on the Electron Quantum Size Levels and Electron g-Factor in Spherical Semiconductor Nanocrystals

The structure of the electron quantum size levels in spherical nanocrystals is studied in the framework of an eight--band effective mass model at zero and weak magnetic fields. The effect of the nanocrystal surface is modeled through the boundary condition imposed on the envelope wave function at the surface. We show that the spin--orbit splitting of the valence band leads to the surface--induced spin--orbit splitting of the excited conduction band states and to the additional surface--induced magnetic moment for electrons in bare nanocrystals. This additional magnetic moment manifests itself in a nonzero surface contribution to the linear Zeeman splitting of all quantum size energy levels including the ground 1S electron state. The fitting of the size dependence of the ground state electron g factor in CdSe nanocrystals has allowed us to determine the appropriate surface parameter of the boundary conditions. The structure of the excited electron states is considered in the limits of weak and strong magnetic fields.Comment: 11 pages, 4 figures, submitted to Phys. Rev.

Convergence of the critical attractor of dissipative maps: Log-periodic oscillations, fractality and nonextensivity

For a family of logistic-like maps, we investigate the rate of convergence to the critical attractor when an ensemble of initial conditions is uniformly spread over the entire phase space. We found that the phase space volume occupied by the ensemble W(t) depicts a power-law decay with log-periodic oscillations reflecting the multifractal character of the critical attractor. We explore the parametric dependence of the power-law exponent and the amplitude of the log-periodic oscillations with the attractor's fractal dimension governed by the inflexion of the map near its extremal point. Further, we investigate the temporal evolution of W(t) for the circle map whose critical attractor is dense. In this case, we found W(t) to exhibit a rich pattern with a slow logarithmic decay of the lower bounds. These results are discussed in the context of nonextensive Tsallis entropies.Comment: 8 pages and 8 fig