28,269 research outputs found
Space-time Torsion and Neutrino Oscillations in Vacuum
The objective of this study is to verify the consistency of the prescription
of alternative minimum coupling (connection) proposed by the Teleparallel
Equivalent to General Relativity (TEGR) for the Dirac equation. With this aim,
we studied the problem of neutrino oscillations in Weitzenbock space-time in
the Schwarzschild metric. In particular, we calculate the phase dynamics of
neutrinos. The relation of spin of the neutrino with the space-time torsion is
clarified through the determination of the phase differences between spin
eigenstates of the neutrinos.Comment: 07 pages, no figure
Magnetic states of linear defects in graphene monolayers: effects of strain and interaction
The combined effects of defect-defect interaction and of uniaxial or biaxial
strains of up to 10\% on the development of magnetic states on the
defect-core-localized quasi-one-dimensional electronic states generated by the
so-called 558 linear extended defect in graphene monolayers are investigated by
means of {\it ab initio} calculations. Results are analyzed on the basis of the
heuristics of the Stoner criterion. We find that conditions for the emergence
of magnetic states on the 558 defect can be tuned by uniaxial tensile parallel
strains (along the defect direction) at both limits of isolated and interacting
558 defects. Parallel strains are shown to lead to two cooperative effects that
favor the emergence of itinerant magnetism: enhancement of the DOS of the
resonant defect states in the region of the Fermi level and tuning of the Fermi
level to the maximum of the related DOS peak. A perpendicular strain is
likewise shown to enhance the DOS of the defect states, but it also effects a
detunig of the Fermi level that shifts away from the maximum of the DOS of the
defect states, which inhibts the emergence of magnetic states. As a result,
under biaxial strains the stabilization of a magnetic state depends on the
relative magnitudes of the two components of strain.Comment: 9 pages 8 figure
The Stellar Parameters and Evolutionary State of the Primary in the d'-Symbiotic System StH\alpha190
We report on a high-resolution, spectroscopic stellar parameter and abundance
analysis of a d' symbiotic star: the yellow component of StH\alpha190. This
star has recently been discovered, and confirmed here, to be a rapidly rotating
(vsini=100 km/s) subgiant, or giant, that exhibits radial-velocity variations
of probably at least 40 km/s, indicating the presence of a companion (a white
dwarf star). It is found that the cool stellar component has Teff=5300K and log
g=3.0. The iron and calcium abundances are close to solar, however, barium is
overabundant, relative to Fe and Ca, by about +0.5 dex. The barium enhancement
reflects mass-transfer of s-process enriched material when the current white
dwarf was an asymptotic giant branch (AGB) star. The past and future evolution
of this binary system depends critically on its current orbital period, which
is not yet known. Concerted and frequent radial-velocity measurements are
needed to provide crucial physical constraints to this d' symbiotic system.Comment: 9 pages, 1 table, 3 figures. In press to Astrophysical Journal
Letter
Educação transformadora para uma comunicação cidadã.
O avanço tecnológico, a convergência e a integração das novas mídias impactaram profundamente as relações de produção e distribuição de informação. Os recursos de conectividade, mobilidade e portabilidade da internet ampliam as possibilidades de os sujeitos tornarem-se co-produtores de informação e conteúdo, democratizando a comunicação e favorecendo a produção colaborativa. No campo da educação, as novas tecnologias têm o potencial de promover inclusão digital de forma mais rápida e eficiente. Entretanto, não basta inserir a tecnologia no espaço escolar; é necessário o apoio de uma proposta pedagógica que favoreça a construção coletiva de conhecimento e estimule a visão crítica e a autonomia do sujeito. Neste sentido, a aproximação dos campos da educação e da comunicação busca incentivar a construção compartilhada de informações, conhecimento e experiências num contexto de trocas e interações sociais que pode estimular o exercício da cidadania. A proposta deste artigo é discutir, sob a ótica da educomunicação, como o uso das tecnologias de informação e comunicação podem contribuir para a construção de relações dialógicas no espaço escolar que estimulem a autoria e a produção compartilhada. Em um ambiente mediado pelas tecnologias, é preciso considerar a intencionalidade do processo educativo que efetivamente proporcione uma apropriação do conhecimento, alicerçada na autonomia do sujeito e no desenvolvimento da sua capacidade de apropriar-se do processo, para criar ecossistemas comunicativos que lhe permitam constituir-se como cidadão e promover transformações sociais
The quadratic spinor Lagrangian, axial torsion current, and generalizations
We show that the Einstein-Hilbert, the Einstein-Palatini, and the Holst
actions can be derived from the Quadratic Spinor Lagrangian (QSL), when the
three classes of Dirac spinor fields, under Lounesto spinor field
classification, are considered. To each one of these classes, there corresponds
a unique kind of action for a covariant gravity theory. In other words, it is
shown to exist a one-to-one correspondence between the three classes of
non-equivalent solutions of the Dirac equation, and Einstein-Hilbert,
Einstein-Palatini, and Holst actions. Furthermore, it arises naturally, from
Lounesto spinor field classification, that any other class of spinor field
(Weyl, Majorana, flagpole, or flag-dipole spinor fields) yields a trivial
(zero) QSL, up to a boundary term. To investigate this boundary term we do not
impose any constraint on the Dirac spinor field, and consequently we obtain new
terms in the boundary component of the QSL. In the particular case of a
teleparallel connection, an axial torsion 1-form current density is obtained.
New terms are also obtained in the corresponding Hamiltonian formalism. We then
discuss how these new terms could shed new light on more general
investigations.Comment: 9 pages, RevTeX, to be published in Int.J.Mod.Phys.D (2007
Ocorrencia do complexo da queima das folhas em diferentes fases de desenvolvimento da cenoura.
Com o objetivo de avaliar a frequência da ocorrência destes três patógenos em diferentes fases de desenvolvimento da cultura no campo, foram coletadas 50 folhas ao acaso com sintomas da doença.bitstream/item/57219/1/BPD-79.pd
Manejo da pinta preta: uma ameaça às lavouras de tomateiro a céu aberto.
bitstream/item/84910/1/cot-95.pd
Monitoramento para detecção de Ceratitis capitata (Diptera: Tephritidae) no Estado do Amapá.
bitstream/item/62612/1/AP-2012-Monitoramento-deteccao-Ceratitis-capitata.pd
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