1,208 research outputs found
Localization of gauge fields in a tachyonic de Sitter thick braneworld
In this work we show that universal gauge vector fields can be localized on
the recently proposed 5D thick tachyonic braneworld which involves a de Sitter
cosmological background induced on the 3-brane. Namely, by performing a
suitable decomposition of the vector field, the resulting 4D effective action
corresponds to a massive gauge field, while the profile along the extra
dimension obeys a Schroedinger-like equation with a Poeschl-Teller potential.
It turns out that the massless zero mode of the gauge field is bound to the
expanding 3-brane and allows us to recover the standard 4D electromagnetic
phenomena of our world. Moreover, this zero mode is separated from the
continuum of Kaluza-Klein (KK) modes by a mass gap determined by the scale of
the expansion parameter. We also were able to analytically solve the
corresponding Schroedinger-like equation for arbitrary mass, showing that KK
massive modes asymptotically behave like plane waves as expected.Comment: 7 pages in latex, no figure
Muonium spectrum beyond the nonrelativistic limit
A generalization of the Gell-Mann-Low theorem is applied to the
antimuon-electron system. The bound state spectrum is extracted numerically. As
a result, fine and hyperfine structure are reproduced correctly near the
nonrelativistic limit (and for arbitrary masses). We compare the spectrum for
the relativistic value alpha = 0.3 with corresponding calculations in
light-front quantization.Comment: 6 pages, LaTeX, 2 figures, uses aipxfm.sty. Talk delivered at the XI
Mexican Workshop on Particles and Fields, Tuxtla Gutierrez, Mexico, November
7-12, 2007; to be published in the proceeding
Neutrino Flavor States and the Quantum Theory of Neutrino Oscillations
The standard theory of neutrino oscillations is reviewed, highlighting the
main assumptions: the definition of the flavor states, the equal-momentum
assumption and the time = distance assumption. It is shown that the standard
flavor states are correct approximations of the states that describe neutrinos
in oscillation experiments. The equal-momentum assumption is shown to be
unnecessary for the derivation of the oscillation probability. The time =
distance assumption derives from the wave-packet character of the propagating
neutrinos. We present a simple quantum-mechanical wave-packet model which
allows us to describe the coherence and localization of neutrino oscillations.Comment: 16 pages; talk presented at the XI Mexican Workshop on Particles and
Fields, 7-12 November 2007, Tuxtla Gutierrez, Chiapas, Mexic
Coherent nu-N scattering and the search for physics beyond the standard model
We focus in future proposals to measure coherent neutrino-nuclei scattering
and we show that such kind of experiments are very sensitive to nonstandard
neutrino interactions with quarks. First in a model independent parametrization
and then we focused in particular models such as leptoquarks and models with
extra neutral gauge bosons and with R-parity breaking interactions. We show
that in all these three different types of new physics it is possible to obtain
competitive bounds to those of future collider experiments. For the particular
case of leptoquarks we found that the expected sensitivity to the coupling and
mass for most of the future experimental setups is quite better than the
current constraints.Comment: 6 pages, 1 Figure, Talk given at 11th Mexican Workshop on Particles
and Fields 2007, Tuxtla Gutierrez, Mexico, 7-12 Nov 200
Casinha de bonecas para as meninas e pista de carrinhos para os meninos.
Trabalho de ConclusĂŁo do Curso de Especialização em Educação Infantil - 1ÂȘ Edição â Polo Joinville - SC, para a obtenção do Grau de Especialista em Educação Infantil.Diante dos anseios de construirmos uma sociedade e uma escola mais justa, solidĂĄria e mais universal, nasceu este artigo, e trĂĄs como escopo, a discussĂŁo genuĂna e atenta com a comunidade do Centro de Educação Infantil Aventuras de Criança sobre os espaços externos no processo de sua revitalização em suas interfaces, com as relaçÔes e representaçÔes de GĂȘnero na Educação Infantil. Pretende ainda, apresentar e desvendar as prĂĄticas pedagĂłgicas vivenciadas pelos seus profissionais nestes locais, e discuti criticamente nos contextos dos espaços (casinha de bonecas e pista de carrinhos), qual Ă© o seu lugar no espectro social, apontando alguns problemas e impasses que a temĂĄtica acende. Organizar os espaços de forma a oferecer as crianças um ambiente que, embora parecendo silencioso, Ă© tambĂ©m educador, estĂĄ posto como desafio. Nesse sentido, suscitar mudanças de posturas nos profissionais do segmento em questĂŁo, se faz urgente e necessĂĄrio, sendo a formação em serviço essencial ao propĂłsito, pois o conhecimento possibilita a constituição do professor como um docente intelectual, crĂtico e transformador, atravĂ©s de um exercĂcio sistematizado de reflexividade sobre a sua prĂłpria prĂĄtica
Constraining a bulk viscous matter-dominated cosmological model using SNe Ia, CMB and LSS
We present and constrain a cosmological model which component is a
pressureless fluid with bulk viscosity as an explanation for the present
accelerated expansion of the universe. We study the particular model of a
constant bulk viscosity coefficient \zeta_m. The possible values of \zeta_m are
constrained using the cosmological tests of SNe Ia Gold 2006 sample, the CMB
shift parameter R from the three-year WMAP observations, the Baryon Acoustic
Oscillation (BAO) peak A from the Sloan Digital Sky Survey (SDSS) and the
Second Law of Thermodynamics (SLT). It was found that this model is in
agreement with the SLT using only the SNe Ia test. However when the model is
submitted to the three cosmological tests together (SNe+CMB+BAO) the results
are: 1.- the model violates the SLT, 2.- predicts a value of H_0 \approx 53 km
sec^{-1} Mpc^{-1} for the Hubble constant, and 3.- we obtain a bad fit to data
with a \chi^2_{min} \approx 400 (\chi^2_{d.o.f.} \approx 2.2). These results
indicate that this model is ruled out by the observations.Comment: 4 pages, 1 figure. Work presented in the XI Mexican Workshop on
Particles and Fields, Tuxtla Gutierrez, Mexico, nov 7-12, 2007. Submitted to
AIP Conference Proceedings of this conferenc
Proton to pion ratio at RHIC from dynamical quark recombination
We propose an scenario to study, from a dynamical point of view, the thermal
recombination of quarks in the midsts of a relativistic heavy-ion collision. We
coin the term dynamical quark recombination to refer to the process of
quark-antiquark and three-quark clustering, to form mesons and baryons,
respectively, as a function of energy density. Using the string-flip model we
show that the probabilities to form such clusters differ. We apply these ideas
to the calculation of the proton and pion spectra in a Bjorken-like scenario
that incorporates the evolution of these probabilities with proper time and
compute the proton to pion ratio, comparing to recent RHIC data at the highest
energy. We show that for a standard choice of parameters, this ratio reaches
one, though the maximum is very sensitive to the initial evolution proper time.Comment: To appear in the proceedings of the XI Mexican Workshop on Particles
and Fields, Tuxtla Gutierrez Chiapas, Mexico, 7-12 Nov. 200
Controle preditivo nĂŁo-linear para sistemas de Hammerstein
Tese (doutorado) - Universidade Federal de Santa Catarina, Centro TecnolĂłgico. Programa de PĂłs-Graduação em Engenharia ElĂ©tricaAs pesquisas associadas Ă s estratĂ©gias de controle preditivo nĂŁo-linear tĂȘm apresentado grande crescimento ultimamente registrando, tambĂ©m, um nĂșmero considerĂĄvel de aplicaçÔes na indĂșstria. A representação de um processo complexo atravĂ©s de um modelo nĂŁo-linear, com o objetivo de melhorar seu desempenho dinĂąmico, tende a sacrificar a simplicidade de projeto do controlador preditivo. Visando aliar a capacidade de representação da nĂŁo-linearidade de um processo com a simplicidade de projeto, torna-se interessante a utilização de controladores preditivos baseados no modelo de Hammerstein o qual Ă© constituĂdo de um bloco estĂĄtico, nĂŁo-linear, seguido de um bloco linear dinĂąmico. Esta tese apresenta um estudo de modelagem, identificação e controle preditivo nĂŁo-linear baseado em modelos de Hammerstein. Algumas tĂ©cnicas de seleção de estrutura e identificação do modelo de Hammerstein sĂŁo apresentadas e algumas inovaçÔes sĂŁo propostas. EstratĂ©gias de controle preditivo baseado no modelo de Hammerstein sĂŁo discutidas e sĂŁo propostas modificaçÔes num controlador para a inclusĂŁo de perturbaçÔes mensurĂĄveis e uma tĂ©cnica analĂtica para solucionar a multiplicidade do sinal de controle. Para avaliar as tĂ©cnicas de identificação e controle estudadas, sĂŁo apresentados resultados de simulação e experimentais em uma planta solar de climatização
CritĂ©rios de desempenho e aspectos de robustez na sĂntese de controladores preditivos adaptativos /
Dissertação (Mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico
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