Dissertações em Física (Mestrado) - PPGF/ICEN
URI Permanente para esta coleçãohttps://repositorio.ufpa.br/handle/2011/2340
O Mestrado Acadêmico iniciou-se em 2003 e pertence ao Programa de Pós-Graduação em Física (PPGF) do Instituto de Ciências Exatas e Naturais (ICEN) da Universidade Federal do Pará (UFPA).
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Navegando Dissertações em Física (Mestrado) - PPGF/ICEN por Orientadores "ALVES, Danilo Teixeira"
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Item Acesso aberto (Open Access) Criação de fótons no efeito Casimir dinâmico em cavidade oscilante com condições de Neumann e Dirichlet(Universidade Federal do Pará, 2005-03) GRANHEN, Edney Ramos; ALVES, Danilo Teixeira; http://lattes.cnpq.br/6642002445572793We consider a massless scalar field in a two-dimensional space-time inside an oscillating cavity with mixed boundary conditions. In order to discuss particle creation phenomenum, we consider the situation of parametric resonance in which the oscillating frequency is twice the frequency of the first mode of the static cavity. For convenience, we suppose that one of the boundaries is at rest and imposes Neumann condition to the field, whereas the other is in non-relativistic motion and imposes a Dirichlet condition on the field. Following the procedure developed by Dodonov and Klimov (Phys. Rev. A, 56, 2664 (1996)), we compute the number of created particles, the generation rate and the energy in the cavity. We compare our results with those found in the literature for the Dirichlet-Dirichlet case.Item Acesso aberto (Open Access) Densidade de energia e força de radiação sobre fronteiras em movimento num espaço-tempo bidimensional(Universidade Federal do Pará, 2009-03) REGO, Andreson Luis Carvalho; ALVES, Danilo Teixeira; http://lattes.cnpq.br/6642002445572793In the present work, we investigate the energy density and the quantum radiation reaction force on one moving boundary which imposes on a massless scalar field a Dirichlet or a Neumann boundary condition. Though we assume a particular motion for the boundary, introduced by Walker and Davies many years ago (J. Phys. A, 15 L477, 1982), we consider new possibilities for the initial field state, namely, thermal state and coherent state. We also investigate the problem of a cavity with one of the boundaries in the particular motion proposed by Walker and Davies, taking into account the vacuum, thermal and coherent initial field states. Finnaly we investigate the case of a non-static boundary which imposes the Robin boundary condition to the field.Item Acesso aberto (Open Access) Densidade de energia e força de radiação sobre fronteiras em movimento para estados arbitrários do campo: aplicação ao estado coerente(Universidade Federal do Pará, 2008-08-29) LIMA, Mateus Gomes; ALVES, Danilo Teixeira; http://lattes.cnpq.br/6642002445572793In this work we consider a real massless scalar field in a two-dimensional spacetime, satisfying Dirichlet or Neumann boundary condition at the instantaneous position of a moving boundary. For a relativistic law of motion, we show that Dirichlet and Neumann boundary conditions yield the same radiation force on a moving mirror when the initial field state is invariant under time translations. We obtain the exact formulas for the energy density of the field and the radiation force on the boundary for vacuum, coherent and squeezed state. In the nonrelativistic limit, our results coincide with those found in the literature. We also investigate the field inside an oscillating cavity. Considering Neumann and Dirichlet boundary conditions, we write the exact formula for the energy density inside a non-static cavity for an arbitrary initial field state. Taking as basis the Moore equation, we calculate recursively the energy density and investigate its time evolution for the coherent state.Item Acesso aberto (Open Access) Fenômeno de interferência na densidade de energia em cavidades com duas fronteiras oscilantes(Universidade Federal do Pará, 2009) PIRES, Wagner Pinheiro; ALVES, Danilo Teixeira; http://lattes.cnpq.br/6642002445572793We consider a real massless scalar field inside a cavity with two moving mirrors in a two-dimensional spacetime, satisfying Dirichlet boundary condition at the instantaneous position of the boundaries, for arbitrary and relativistic laws of motion. Considering vacuum as the initial field state, we show that the exact value of the the energy density in the cavity can be obtained by tracing back a sequence of null lines, connecting the value of the energy density at the given spacetime point to a certain known value of the energy density at a point in the region where the initial field modes are not affected by the boundaries motion. We obtain formulas for the energy density of the field and the quantum force acting on the boundaries. We also show that for a large class of movements, including resonant cases found in the literature, the exact method proposed here enable us to find analytical solutions written as series in the parameter that controls the amplitudes of the movements. Using these analytical solutions, we investigate the interference phenomena in the energy density and total energy stored in the cavity.