Confined states and direction-dependent transmission in graphene quantum wells

We report the existence of confined massless fermion states in a graphene quantum well (QW) by means of analytical and numerical calculations. These states show an unusual quasi-linear dependence on the momentum parallel to the QW: their number depends on the wavevector and is constrained by electron-hole conversion in the barrier regions. An essential difference with non-relativistic electron states is a mixing between free and confined states at the edges of the free-particle continua, demonstrated by the direction-dependent resonant transmission across a potential well.Comment: Submitted to PR

Some addition formulae for Abelian functions for elliptic and hyperelliptic curves of cyclotomic type

We discuss a family of multi-term addition formulae for Weierstrass functions on specialized curves of genus one and two with many automorphisms. In the genus one case we find new addition formulae for the equianharmonic and lemniscate cases, and in genus two we find some new addition formulae for a number of curves, including the Burnside curve.Comment: 19 pages. We have extended the Introduction, corrected some typos and tidied up some proofs, and inserted extra material on genus 3 curve

A note on the cylindrical collapse of counter-rotating dust

We find analytical solutions describing the collapse of an infinitely long cylindrical shell of counter-rotating dust. We show that--for the classes of solutions discussed herein--from regular initial data a curvature singularity inevitably develops, and no apparent horizons form, thus in accord with the spirit of the hoop conjecture.Comment: 8 pages, LaTeX, ijmpd macros (included), 1 eps figure; accepted for publication in Int. J. Mod. Phys.

AE Aurigae: first detection of non-thermal X-ray emission from a bow shock produced by a runaway star

Runaway stars produce shocks when passing through interstellar medium at supersonic velocities. Bow shocks have been detected in the mid-infrared for several high-mass runaway stars and in radio waves for one star. Theoretical models predict the production of high-energy photons by non-thermal radiative processes in a number sufficiently large to be detected in X-rays. To date, no stellar bow shock has been detected at such energies. We present the first detection of X-ray emission from a bow shock produced by a runaway star. The star is AE Aur, which was likely expelled from its birthplace by the encounter of two massive binary systems and now is passing through the dense nebula IC 405. The X-ray emission from the bow shock is detected at 30" to the northeast of the star, coinciding with an enhancement in the density of the nebula. From the analysis of the observed X-ray spectrum of the source and our theoretical emission model, we confirm that the X-ray emission is produced mainly by inverse Compton upscattering of infrared photons from dust in the shock front.Comment: Accepted for publication in the Astrophysical Journal with number ApJ, 757, L6. Four figure

Identificação de variedades genéticas de laranja doce por meio de imagens de fluorescência.

bitstream/CNPDIA-2010/12622/1/BPD27-2009.pd

Climatização de Bananas 'Prata-Anã' e 'BRS Platina' com diferentes concetrações de etileno.

Bananas quando colhidas após sua completa maturação fisiológica, frequentemente amadurecem de forma desuniforme, por causa da diferença de idade fisiológica das pencas. O processo denominado de climatização visa à homogeneização no amadurecimento dos frutos, sem alterar a qualidade dos mesmos. O objetivo deste trabalho foi avaliar o efeito da climatização com diferentes concentrações de etileno sobre a qualidade física e química de bananas 'Prata-Anã' e 'BRS Platina'. Foram aplicadas três concentrações de etileno para as cultivares Prata-Anã e BRS Platina: 100 e 500 'L L-1 de etileno e o controle (sem etileno). Os tratamentos foram aplicados com gerador comercial de etileno (Banasil®) por 48 horas a 16°C. Após a climatização os frutos foram armazenados a 25°C até atingirem o estádio 6 de amadurecimento, quando foram avaliados. As variáveis analisadas foram: acidez titulável (AT), sólidos solúveis (SS), relação SS/AT e perda de massa. Observou-se que a aplicação de etileno, independente da concentração, não influi nos parâmetros de qualidade física e química estudados para ambas as cultivares, porém mais estudos deverão ser realizados