High temperature limit in static backgrounds

We prove that the hard thermal loop contribution to static thermal amplitudes can be obtained by setting all the external four-momenta to zero before performing the Matsubara sums and loop integrals. At the one-loop order we do an iterative procedure for all the 1PI one-loop diagrams and at the two-loop order we consider the self-energy. Our approach is sufficiently general to the extent that it includes theories with any kind of interaction vertices, such as gravity in the weak field approximation, for $d$ space-time dimensions. This result is valid whenever the external fields are all bosonic.Comment: 15 pages, 11 figures. To be published in Physical Review

Thermal Effective Lagrangian of Static Gravitational Fields

We compute the effective Lagrangian of static gravitational fields interacting with thermal fields. Our approach employs the usual imaginary time formalism as well as the equivalence between the static and space-time independent external gravitational fields. This allows to obtain a closed form expression for the thermal effective Lagrangian in $d$ space-time dimensions.Comment: Accepted for publication in the Physical Review

Desenvolvimento profissional durante a implementação de inovações curriculares por professores do ensino secundário

Neste trabalho, apresentamos os primeiros resultados de uma pesquisa com cinco professores de física do ensino secundário que participaram de um projeto de inovação curricular na implementação de seqüências didáticas de ensino aprendizagem (Teaching and Learning Sequence) sobre Física Moderna. Por meio de questionário e entrevista semi-estruturada, buscou-se a partir da análise relacionar as fases de desenvolvimento profissional dos professores. Percebemos nos casos estudados, que alguns professores apresentaram uma discordância entre as fases deste desenvolvimento. Os resultados parecem indicar que a participação de professores em grupos de projetos inovadores no Ensino de Física, pode contribuir para consolidar seu desenvolvimento profissional na fase da experimentação ou diversificação

Spin-dependent beating patterns in thermoelectric properties: Filtering the carriers of the heat flux in a Kondo adatom system

We theoretically investigate the thermoelectric properties of a spin-polarized two-dimensional electron gas hosting a Kondo adatom hybridized with an STM tip. Such a setup is treated within the single-impurity Anderson model in combination with the atomic approach for the Green's functions. Due to the spin dependence of the Fermi wavenumbers the electrical and thermal conductances, together with thermopower and Lorenz number reveal beating patterns as function of the STM tip position in the Kondo regime. In particular, by tuning the lateral displacement of the tip with respect to the adatom vicinity, the temperature and the position of the adatom level, one can change the sign of the Seebeck coefficient through charge and spin. This opens a possibility of the microscopic control of the heat flux analogously to that established for the electrical current

The graphene sheet versus the 2DEG: a relativistic Fano spin-filter via STM and AFM tips

We explore theoretically the density of states (LDOS) probed by an STM tip of 2D systems hosting an adatom and a subsurface impurity,both capacitively coupled to AFM tips and traversed by antiparallel magnetic fields. Two kinds of setups are analyzed, a monolayer of graphene and a two-dimensional electron gas (2DEG). The AFM tips set the impurity levels at the Fermi energy, where two contrasting behaviors emerge: the Fano factor for the graphene diverges, while in the 2DEG it approaches zero. As result, the spin-degeneracy of the LDOS is lifted exclusively in the graphene system, in particular for the asymmetric regime of Fano interference. The aftermath of this limit is a counterintuitive phenomenon, which consists of a dominant Fano factor due to the subsurface impurity even with a stronger STM-adatom coupling. Thus we find a full polarized conductance, achievable just by displacing vertically the position of the STM tip. To the best knowledge, our work is the first to propose the Fano effect as the mechanism to filter spins in graphene. This feature arises from the massless Dirac electrons within the band structure and allows us to employ the graphene host as a relativistic Fano spin-filter

Efeito do volume e de diferentes concentrações de solução de cloreto de sódio nos resultados de análise de glúten.

Orientadora: Martha Zavariz de Miranda

Fano-Andreev effect in a T-shaped Double Quantum Dot in the Coulomb blockade regime

We studied the effects of superconducting quantum correlations in a system consisting of two quantum dots, two normal leads, and a superconductor. Using the non-equilibrium Green's functions method, we analyzed the transmission, density of states, and differential conductance of electrons between the normal leads. We found that the superconducting correlations resulted in Fano-Andreev interference, which is characterized by two anti-resonance line shapes in all of these quantities. This behavior was observed in both equilibrium and non-equilibrium regimes and persisted even when Coulomb correlations were taken into account using the Hubbard-I approximation. It is worth noting that the robustness of this behavior against these conditions has not been studied previously in the literature.Comment: 14 pages, 12 figure

As idéias dos alunos nas pesquisas de formação inicial de professores de ciências

Considerando as idéias dos alunos como uma componente essencial do ensino de ciências, apresenta-se uma revisão de 20 trabalhos sobre a formação inicial de professores selecionados de revistas em inglês no período de 1995 a 2005. Subdivididos em dois grupos, são comparados objetivos, contexto, amostra, metodologia e, especialmente, os obstáculos e avanços encontrados em direção a construção de uma concepção de aprendizagem centrada nas idéias dos alunos e na sua evolução. O primeiro grupo reúne apenas as pesquisas exploratórias e o segundo grupo contém aquelas em que alguma abordagem curricular inovadora foi implementada e analisada. Nessas últimas identificou-se as características dos processos implementados, os resultados e as barreiras encontradas na evolução dos futuros professores. Ao final são apresentadas implicações gerais desses resultados

Density and distribution of Xylocopa nests (Hymenoptera: Apidae) in Caatinga areas in the surroundings of Passion fruit crops.

Due to their importance as pollinators of many plant species, this study aimed to know the nest density, spatial distribution, and nesting substrates used by Xylocopa species in the Caatinga, a xerophilous vegetation f Northeastern Brazil. Three areas of Caatinga in the surroundings of passion fruit crops were sampled. The bee species found in these areas were Xylocopa grisescens Lepeletier and Xylocopa frontalis (Olivier). All nests were in Commiphora leptophloeos (Burseraceae) trees (n=113). Phytosociological analysis showed that this tree species presented the highest absolute density (212.5 individuals/ha) and index of importance value (52.7). The distribution pattern of the C. leptophloeos was aggregated. The nests were located in dead and dried branches with an average diameter of 5.3±2.0 cm (n=43). The mean number of nests/tree was 3.1± 2.8 (n=113). The less disturbed area showed 6.7 nests/ha and 4.2 nests/tree. In the disturbed areas, 0.9 nests/ha and 2.4 to 2.7 nests/tree were observed. The availability of substrate for nesting in the studied areas and its importance as a limiting factor for nesting are discusse

Protocolo para determinação de umidade de farinha de trigo em analisador halógeno de umidade Ohaus.

Orientadora: Martha Zavariz de Miranda