Interband polarized absorption in InP polytypic superlattices

Recent advances in growth techniques have allowed the fabrication of semiconductor nanostructures with mixed wurtzite/zinc-blende crystal phases. Although the optical characterization of these polytypic structures is well eported in the literature, a deeper theoretical understanding of how crystal phase mixing and quantum confinement change the output linear light polarization is still needed. In this paper, we theoretically investigate the mixing effects of wurtzite and zinc-blende phases on the interband absorption and in the degree of light polarization of an InP polytypic superlattice. We use a single 8$\times$8 k$\cdot$p Hamiltonian that describes both crystal phases. Quantum confinement is investigated by changing the size of the polytypic unit cell. We also include the optical confinement effect due to the dielectric mismatch between the superlattice and the vaccum and we show it to be necessary to match experimental results. Our calculations for large wurtzite concentrations and small quantum confinement explain the optical trends of recent photoluminescence excitation measurements. Furthermore, we find a high sensitivity to zinc-blende concentrations in the degree of linear polarization. This sensitivity can be reduced by increasing quantum confinement. In conclusion, our theoretical analysis provides an explanation for optical trends in InP polytypic superlattices, and shows that the interplay of crystal phase mixing and quantum confinement is an area worth exploring for light polarization engineering.Comment: 9 pages, 6 figures and 1 tabl

Spin Chains in an External Magnetic Field. Closure of the Haldane Gap and Effective Field Theories

We investigate both numerically and analytically the behaviour of a spin-1 antiferromagnetic (AFM) isotropic Heisenberg chain in an external magnetic field. Extensive DMRG studies of chains up to N=80 sites extend previous analyses and exhibit the well known phenomenon of the closure of the Haldane gap at a lower critical field H_c1. We obtain an estimate of the gap below H_c1. Above the lower critical field, when the correlation functions exhibit algebraic decay, we obtain the critical exponent as a function of the net magnetization as well as the magnetization curve up to the saturation (upper critical) field H_c2. We argue that, despite the fact that the SO(3) symmetry of the model is explicitly broken by the field, the Haldane phase of the model is still well described by an SO(3) nonlinear sigma-model. A mean-field theory is developed for the latter and its predictions are compared with those of the numerical analysis and with the existing literature.Comment: 11 pages, 4 eps figure

Large Scale Morphological Segregation in Optically Selected Galaxy Redshift Catalogs

We present the results of an exhaustive analysis of the morphological segregation of galaxies in the CfA and SSRS catalogs through the scaling formalism. Morphological segregation between ellipticals and spirals has been detected at scales up to 15-20 h$^{-1}$ Mpc in the CfA catalog, and up to 20-30 h$^{-1}$ Mpc in the SSRS catalog. Moreover, it is present not only in the densest areas of the galaxy distribution, but also in zones of moderate density.Comment: 9 pages, (1 figure included), uuencode compressed Postscript, (accepted for publication in ApJ Letters), FTUAM-93-2

D-branes, Orientifolds and K-theory

The complete D-brane spectrum in ZZ[squared] orientifolds is computed. Stable non-BPS D-branes with both integral and torsion charges are found. The relation to K-theory is discussed and a new K-theory relevant to orientifolds is suggested

Determining R-parity violating parameters from neutrino and LHC data

In supersymmetric models neutrino data can be explained by R-parity violating operators which violate lepton number by one unit. The so called bilinear model can account for the observed neutrino data and predicts at the same time several decay properties of the lightest supersymmetric particle. In this paper we discuss the expected precision to determine these parameters by combining neutrino and LHC data and discuss the most important observables. We show that one can expect a rather accurate determination of the underlying R-parity parameters assuming mSUGRA relations between the R-parity conserving ones and discuss briefly also the general MSSM as well as the expected accuracies in case of a prospective e+ e- linear collider. An important observation is that several parameters can only be determined up to relative signs or more generally relative phases.Comment: 13 pages, 13 figure

Os habitats do jacaré-paguá no entorno do Pantanal.

bitstream/CPAP/55904/1/ADM112.pdfDisponível também em: internel, jornal o Estado de Mato Grosso do Sul, portalbonito, agrolink, zoonews, campogrande.news, opantaneiro, riosvivos, navirai.news, boletimpecuario, famasul, bbcnews, perfilnews, agronoticias, midiamaxnews, agrosoft, douradosinforma, cassilandianews, matogrossoonline, corumbaonline, capitaldopantanal, criareplantar, clickpantanal, estadomsnews, bonitonoticias, agenciapantanal, folhadedourados, aquidauananews, portalms, agorams, douradosagora, baixadanews, unifolha, infobibos, agronline, folhadoms, msnoticias, diarioms, portaldoagronegocio, maracajunews, interiornews, corumbanet, reporterms, folhadedourados, ultimahora, douradosnews

Uso da radiotelemetria no estudo do movimento e termorregulação do jacaré-do-Pantanal.

A técnica de radiotelemetria é uma ferramenta usada para obter informações necessárias para conservar e manejar as espécies selvagens (Hansson, 1991). Para alguns animais a ferramenta pode elucidar e revelar segredos de suas histórias de vida. Por meio da rádio-transmissor o pesquisador pode saber onde o animal está, ou pode usar a informação de localização para extrapolar a atividade do animal, conhecer suas temperaturas corporais, e seus batimentos cardíacos. A Embrapa Pantanal ao longo de duas décadas vem realizando importantes avanços no programa de pesquiosa em Ecologia, Conservação e Manejo do jacaré-do-Pantanal, Caiman crocodilus yacare. Estudos de dispersão e movimento do jacaré vêm sendo desenvolvidos, ao longo de 18 anos, por marcação-recaptura, e ao longo de 10 anos por radiotelemetria (Campos et al., 2004). Nos últimos anos, a técnica de radioteletria foi utilizada também para determinar as temperaturas corporais dos jacarés e seu comportamento de termorregulação (Campos et al., 2003). Nesses quase 20 anos de pesquisa a Embrapa Pantanal tem avançado nas etapas do monitoramento e experimentação no campo, com populações de jacarés em vida livre (Mourão et al., 2000; Coutinho, 2000), com a obtenção de informações sobre a biologia e ecologia da espécie. O objetivo dessa circular técnica é descrever o uso da técnica de radiotelemetria no jacaré-do-Pantanal e os resultados alcançados ao longo dessa experiência.bitstream/item/37488/1/CT49.pd