4,144 research outputs found
Confined magneto-optical waves in graphene
The electromagnetic mode spectrum of single-layer graphene subjected to a
quantizing magnetic field is computed taking into account intraband and
interband contributions to the magneto-optical conductivity. We find that a
sequence of weakly decaying quasi-transverse-electric modes, separated by
magnetoplasmon polariton modes, emerge due to the quantizing magnetic field.
The characteristics of these modes are tuneable, by changing the magnetic field
or the Fermi energy.Comment: 9 pages, 7 figures. published version: text and figures revised and
updated + new references and one figure adde
Dilatonic, Current-Carrying Cosmic String
We study the implications of a scalar-tensorial gravity for the metric of an
isolated self-gravitating superconducting cosmic string. These modifications
are induced by an arbitrary coupling of a massless scalar field to the usual
tensorial field in the gravitational Lagrangian. We derive the metric in the
weak-field approximation and we analyse the behaviour of light in this
spacetime. We end with some discussions.Comment: 12 pp, Latex, no figures, based on a talk given by M. E. X. Guimaraes
at the COSMO 99, 27/9 to 02/10/99, ICTP, Trieste, I
Electron-Electron Bound States in Maxwell-Chern-Simons-Proca QED3
We start from a parity-breaking MCS QED model with spontaneous breaking
of the gauge symmetry as a framework for evaluation of the electron-electron
interaction potential and for attainment of numerical values for the e-e bound
state. Three expressions are obtained for the potential according to the
polarization state of the scattered electrons. In an energy scale compatible
with Condensed Matter electronic excitations, these three potentials become
degenerated. The resulting potential is implemented in the Schrodinger equation
and the variational method is applied to carry out the electronic binding
energy. The resulting binding energies in the scale of 10-100 meV and a
correlation length in the scale of 10-30 Angs. are possible indications that
the MCS-QED model adopted may be suitable to address an eventual case of
e-e pairing in the presence of parity-symmetry breakdown. The data analyzed
here suggest an energy scale of 10-100 meV to fix the breaking of the
U(1)-symmetry.
PACS numbers: 11.10.Kk 11.15.Ex 74.20.-z 74.72.-h ICEN-PS-01/17Comment: 13 pages, style revtex, revised versio
Mathematical modeling of bovine brucellosis control by vaccination
As fêmeas bovinas, por sua importância na transmissão e na manutenção da brucelose, constituíram o alvo dos inquéritos do Programa Nacional de Controle e Erradicação da Brucelose e da Tuberculose Animal. Com base em informações obtidas em unidades federativas onde foram realizados inquéritos sorológicos e observadas prevalências de animais acima de 2%, elaborou-se um modelo para simular a dinâmica da brucelose em rebanhos bovinos formados exclusivamente por fêmeas, analisando o efeito de estratégias de vacinação. Para baixa cobertura vacinal, da ordem de 30%, o tempo para reduzir a prevalência a 2%, valor adotado como referência, pode ser longo, aproximando-se do dobro do tempo necessário para uma cobertura mais alta, de 90%. De acordo com o modelo, o tempo para reduzir a prevalência a 1% ou 2%, que permitam passar à fase de erradicação, pode chegar a uma década. Recomenda-se a intensificação do esforço para a vacinação de fêmeas, procurando atingir alta cobertura vacinal.Due to the important role played by female bovines in the transmission and maintenance of brucellosis, they were the target of the serological surveys of the Brazilian National Program for the Control and Eradication of Bovine Brucellosis and Tuberculosis. Based on the information obtained in Brazilian states, where the serological surveys were carried out and prevalences higher than 2% were observed, a model to simulate the dynamics of brucellosis in herds of female bovines was developed to analyze the effects of vaccination strategies. For low vaccination coverage (around 30%), the time to reduce the prevalence to 2%, adopted as a reference, may be long, approximately twice as long as the time observed for a higher coverage (90%). According to the model, the time to reduce the prevalence to levels of 1% or 2%, adequate to start the eradication phase, may reach a decade. It is recommended an intensification of the effort to vaccinate females, aiming at attaining high vaccination coverage.FAPESPCNPqMAPA Ministério da Agricultura, Pecuária e Abasteciment
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