Loop Variables for a Class of Conical Spacetimes

Loop variables are used to describe the presence of topological defects in spacetime. In particular we study the dependence of the holonomy transformation on angular momentum and torsion for a multi-chiral cone. We also compute the holonomies for multiple moving crossed cosmic strings and two plane topological defects-crossed by a cosmic string.Comment: 17 pages, LATE

Vacuum polarization induced by a cylindrical boundary in the cosmic string spacetime

In this paper we investigate the Wightman function, the renormalized vacuum expectation values of the field square, and the energy-momentum tensor for a massive scalar field with general curvature coupling inside and outside of a cylindrical shell in the generalized spacetime of straight cosmic string. For the general case of Robin boundary condition, by using the generalized Abel-Plana formula, the vacuum expectation values are presented in the form of the sum of boundary-free and boundary-induced parts. The asymptotic behavior of the vacuum expectation values of the field square, energy density and stresses are investigated in various limiting cases. The generalization of the results to the exterior region is given for a general cylindrically symmetric static model of the string core with finite support.Comment: 21 pages, 5 figure

Fermionic current densities induced by magnetic flux in a conical space with a circular boundary

We investigate the vacuum expectation value of the fermionic current induced by a magnetic flux in a (2+1)-dimensional conical spacetime in the presence of a circular boundary. On the boundary the fermionic field obeys MIT bag boundary condition. For irregular modes, a special case of boundary conditions at the cone apex is considered, when the MIT bag boundary condition is imposed at a finite radius, which is then taken to zero. We observe that the vacuum expectation values for both charge density and azimuthal current are periodic functions of the magnetic flux with the period equal to the flux quantum whereas the expectation value of the radial component vanishes. For both exterior and interior regions, the expectation values of the current are decomposed into boundary-free and boundary-induced parts. For a massless field the boundary-free part in the vacuum expectation value of the charge density vanishes, whereas the presence of the boundary induces nonzero charge density. Two integral representations are given for the boundary-free part in the case of a massive fermionic field for arbitrary values of the opening angle of the cone and magnetic flux. The behavior of the induced fermionic current is investigated in various asymptotic regions of the parameters. At distances from the boundary larger than the Compton wavelength of the fermion particle, the vacuum expectation values decay exponentially with the decay rate depending on the opening angle of the cone. We make a comparison with the results already known from the literature for some particular cases.Comment: 34 pages, 6 figure

Variação do pigmento antocianina em diferentes regiões do cacho de açaí.

O açaí processado nas amassadeiras ou em agroindústrias representa um dos alimentos mais populares da Região Amazônica, notadamente no Amapá, assim como abastecendo outros mercados nacionais e até internacionais. Além de representar fonte de nutriente, também é reconhecido pelas suas propriedades funcionais, através do pigmento antocianina, de efeito antioxidante. Um dos problemas observados no abastecimento do mercado de frutos de açaí é a restrição quanto à época de produção de frutos, definida em safras diferenciadas em áreas limítrofes dos estados do Amapá e Pará, levando consequentemente à escassez de frutos nas entressafras respectivas, com aumento de preço e diminuição da qualidade dos frutos. Um teste de progênies foi instalado pela Embrapa Amapá, em Mazagão, com materiais coletados no estuário amazônico, onde avaliou-se a qualidade do fruto, em relação ao teor de antocianina total em três regiões do cacho: início, meio e fim, para verificar a variabilidade de concentrações de antocianina durante a maturação dos frutos. A antocianina total foi extraída e determinada pelo método de Fuleki e Francis (1968), com modificações de Constant (2003), após um período de 24 horas de extração e os dados analisados pelo programa SAS 9.2 TS Level 2MO (STATISTICAL...2010). Somente os materiais que produzem na época de safra amapaense, apresentaram diferenciação significativa em relação ao teor de antocianina total no início do cacho (43,21 mg/100g fruto) em relação à região do meio (31,82 mg/100g fruto) e fim do cacho (27,50 mg/100g fruto), influenciado pelos índices de maturação variados. Frutos de açaizeiro oriundo de materiais que produzem na entressafra amapaense apresentaram índice de maturação homogêneo, com teores semelhantes em todo o cacho. Conclui-se que, em produção comercial objetivando a extração de maiores teores de antocianina total, e que produzem nas condições da safra amapaense, pode-se selecionar, preferencialmente, os frutos localizados na parte superior do cacho

Polarization of the fermionic vacuum by a global monopole with finite core

We study the vacuum polarization effects associated with a massive fermionic field in a spacetime produced by a global monopole considering a nontrivial inner structure for it. In the general case of the spherically symmetric static core with finite support we evaluate the vacuum expectation values of the energy-momentum tensor and the fermionic condensate in the region outside the core. These quantities are presented as the sum of point-like global monopole and core-induced contributions. The asymptotic behavior of the core-induced vacuum densities are investigated at large distances from the core, near the core and for small values of the solid angle corresponding to strong gravitational fields. As an application of general results the flower-pot model for the monopole's core is considered and the expectation values inside the core are evaluated.Comment: 22 pages, 4 figure