Finite-size, magnetic and chemical-potential effects on first-order phase transitions

We perform a study about effects of an applied magnetic field and a finite chemical potential on the size-dependent phase structure of a first-order transition. These effects are introduced by using methods of quantum fields defined on toroidal spaces, and we study in particular the case of two compactified dimensions, imaginary time and a spatial one (a heated film). It is found that for any value of the applied field, there is a minimal size of the system, independent of the chemical potential, below which the transition disappears.Comment: 19 pages, 3 figures, version accepted for publication in Phys. Lett.

Tunable asymmetric magnetoimpedance effect in ferromagnetic NiFe/Cu/Co films

We investigate the magnetization dynamics through the magnetoimpedance effect in ferromagnetic NiFe/Cu/Co films. We observe that the magnetoimpedance response is dependent on the thickness of the non-magnetic Cu spacer material, a fact associated to the kind of the magnetic interaction between the ferromagnetic layers. Thus, we present an experimental study on asymmetric magnetoimpedance in ferromagnetic films with biphase magnetic behavior and explore the possibility of tuning the linear region of the magnetoimpedance curves around zero magnetic field by varying the thickness of the non-magnetic spacer material, and probe current frequency. We discuss the experimental magnetoimpedance results in terms of the different mechanisms governing the magnetization dynamics at distinct frequency ranges, quasi-static magnetic properties, thickness of the non-magnetic spacer material, and the kind of the magnetic interaction between the ferromagnetic layers. The results place ferromagnetic films with biphase magnetic behavior exhibiting asymmetric magnetoimpedance effect as a very attractive candidate for application as probe element in the development of auto-biased linear magnetic field sensors.Comment: 5 figure

Canonical transformation for stiff matter models in quantum cosmology

In the present work we consider Friedmann-Robertson-Walker models in the presence of a stiff matter perfect fluid and a cosmological constant. We write the superhamiltonian of these models using the Schutz's variational formalism. We notice that the resulting superhamiltonians have terms that will lead to factor ordering ambiguities when they are written as operators. In order to remove these ambiguities, we introduce appropriate coordinate transformations and prove that these transformations are canonical using the symplectic method.Comment: Revtex4 Class, 3 pages, No Figure

Uma ferramenta para cadastro e visualização de metadados em Agricultura de Precisão utilizando GeoNetwork.

A Rede Agricultura de Precisão (RedeAP) consiste em um sistema que pode ser descrito como uma estratégia de gestão dos dados produzidos nas Unidades Piloto, e é fundamentalmente constituído de três componentes inter-relacionados entre si, sendo eles: Bancos de Dados, Política de Acesso e uso dos Dados, e Aplicação. O componente de Aplicação se trata de um Sistema de Informações Geográficas para a Web baseado no software livre i3Geo com o aplicativo de catalogação de dados geoespaciais GeoNetwork (QUEIROS et al., 2011). A adição de novos registros no catálogo do GeoNetwork pode ser feita utilizando o próprio editor de metadados ou pela ferramenta de importação dos dados no formato XML. Em ambos os casos, o usuário deve ser, no mínimo, registrado como editor no grupo correspondente. Contudo, o controle de usuários, perfis e níveis de acesso deve ser feito pelo próprio sistema RedeAP, utilizando, assim, o GeoNetwork somente para a visualização dos metadados catalogados. Baseado nesse contexto, surgiu a necessidade da criação de uma ferramenta que fizesse a catalogação dos metadados com o objetivo de mantê-los armazenados no banco de dados do sistema e também possibilitar sua visualização nos padrões de exibição do GeoNetwork

Reply to "Comment on 'Quantization of FRW spacetimes in the presence of a cosmological constant and radiation'"

The Comment by Amore {\it et al.} [gr-qc/0611029] contains a valid criticism of the numerical precision of the results reported in a recent paper of ours [Phys. Rev. D {\bf 73}, 044022 (2006)], as well as fresh ideas on how to characterize a quantum cosmological singularity. However, we argue that, contrary to what is suggested in the Comment, the quantum cosmological models we studied show hardly any sign of singular behavior.Comment: 4 pages, accepted by Physical Review

Field-theoretical renormalization group for a flat two-dimensional Fermi surface

We implement an explicit two-loop calculation of the coupling functions and the self-energy of interacting fermions with a two-dimensional flat Fermi surface in the framework of the field theoretical renormalization group (RG) approach. Throughout the calculation both the Fermi surface and the Fermi velocity are assumed to be fixed and unaffected by interactions. We show that in two dimensions, in a weak coupling regime, there is no significant change in the RG flow compared to the well-known one-loop results available in the literature. However, if we extrapolate the flow to a moderate coupling regime there are interesting new features associated with an anisotropic suppression of the quasiparticle weight Z along the Fermi surface, and the vanishing of the renormalized coupling functions for several choices of the external momenta.Comment: 16 pages and 22 figure