Vacuum fluctuations of a scalar field near a reflecting boundary and their effects on the motion of a test particle

The contribution from quantum vacuum fluctuations of a real massless scalar field to the motion of a test particle that interacts with the field in the presence of a perfectly reflecting flat boundary is here investigated. There is no quantum induced dispersions on the motion of the particle when it is alone in the empty space. However, when a reflecting wall is introduced, dispersions occur with magnitude dependent on how fast the system evolves between the two scenarios. A possible way of implementing this process would be by means of an idealized sudden switching, for which the transition occurs instantaneously. Although the sudden process is a simple and mathematically convenient idealization it brings some divergences to the results, particularly at a time corresponding to a round trip of a light signal between the particle and the wall. It is shown that the use of smooth switching functions, besides regularizing such divergences, enables us to better understand the behavior of the quantum dispersions induced on the motion of the particle. Furthermore, the action of modifying the vacuum state of the system leads to a change in the particle energy that depends on how fast the transition between these states is implemented. Possible implications of these results to the similar case of an electric charge near a perfectly conducting wall are discussed.Comment: 17 pages, 8 figure

Diagnóstico da agricultura familiar no município de Moju, Pará.

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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

Modelagem conceitual de banco de dados geográfico aplicado ao sistema de dados georreferenciados para os campos experimentais da Embrapa Tabuleiros Costeiros.

A Embrapa Tabuleiros Costeiros diante da necessidade de utilizar uma ferramenta que auxilie o planejamento espacial dos campos experimentais, e tendo em vista as diversas possibilidades de mapeamento, associações, conexões e visualização dinâmica proporcionadas pelos Sistemas de Informações Geográficas (SIGs), iniciou o desenvolvimento de um projeto de SIG a ser disponibilizado pela internet (WebGis). Dentre as etapas do projeto está a modelagem conceitual de Banco de Dados Geográficos (BDG), considerada entre as principais atividades que contribuem para o sucesso de um SIG. Essa técnica auxilia tanto os desenvolvedores quanto aos usuários na definição e entendimento do escopo, da estrutura e do comportamento desejado do sistema, garantindo assim que as funcionalidades e informações disponibilizadas atenderão as necessidades do público-alvo do projeto. Nessa perspectiva, esse trabalho apresenta o modelo conceitual inicial do Sistema de Dados Geográficos dos Campos Experimentais, elaborado em conformidade com o ML-Geo-Frame e implementado no ArgoCaseGeo