Stabilization of Extra Dimensions and The Dimensionality of the Observed Space

We present a simple model for the late time stabilization of extra dimensions. The basic idea is that brane solutions wrapped around extra dimensions, which is allowed by string theory, will resist expansion due to their winding mode. The momentum modes in principle work in the opposite way. It is this interplay that leads to dynamical stabilization. We use the idea of democratic wrapping \cite{art5}-\cite{art6}, where in a given decimation of extra dimensions, all possible winding cases are considered. To simplify the study further we assumed a symmetric decimation in which the total number of extra dimensions is taken to be $Np$ where N can be called the order of the decimation. We also assumed that extra dimensions all have the topology of tori. We show that with these rather conservative assumptions, there exists solutions to the field equations in which the extra dimensions are stabilized and that the conditions do not depend on $p$. This fact means that there exists at least one solution to the asymmetric decimation case. If we denote the number of observed space dimensions (excluding time) by $m$, the condition for stabilization is $m\geq 3$ for pure Einstein gravity and $m\leq 3$ for dilaton gravity massaged by string theory parameters.Comment: Final versio

Muoniated radical states in the organic semiconductor phthalocyanine

Phthalocyanine samples of ZnPc, H2Pc and CuPc were investigated by the muon spin rotation amp; 956;SR technique. In ZnPc and H2Pc, three muoniated radical states of paramagnetic origin were identified, two of which having hyperfine interactions in the range 110 150 MHz and correspondign to muonium addition at the outer benzene rings. The third state presents a smaller hyperfine interaction about 25 MHz , and is tentatively assigned to addition at bridging nitrogen atoms. CuPc has an unpaired electron from the Cu atom, which originates a diamagnetic like signal upon muonium addition. The signal exhibits two components with very different relaxation rates, corresponding to two different spatial couplings of the Cu electron with the muonium s electro

Balanços energéticos agropecuários: uma importante ferramenta como indicativo de sustentabilidade de agroecossistemas.

No Brasil, pouca atenção se tem dado às formas e caminhos com que os fluxos energéticos se distribuem nos sistemas produtivos. Na agropecuária, a atenção tem sido voltada a novas fontes de energia (biomassa) ou em tecnologia alternativa, visando a racionalização do uso de energia fóssil ou elétrica. Entretanto, a agricultura tem se desenvolvido baseada fortemente na utilização intensiva de máquinas agrícolas, com conseqüente uso de combustíveis fósseis. Um fator de estrangulamento muito forte no consumo energético geral tem sido a utilização massiva de fertilizantes derivados do petróleo nos agroecossistemas. Estudos de Balanços Energéticos visam determinar os pontos de estrangulamento energético fundamentando a busca por tecnologias poupadoras de energia, especialmente aquelas de origem fóssil (combustível, fertilizante, agrotóxicos, energia despendida na fabricação das máquinas e implementos, etc.). No Brasil, a Região Sul, é onde se encontram vários trabalhos buscando uma agricultura mais auto-sustentável, do ponto de vista da utilização da energia. Em vista da possibilidade de eventuais futuras crises energéticas, o presente trabalho procura analisar o estado-da-arte dos estudos em Balanço Energético, no Brasil e no Mundo, como uma ferramenta de indicação da sustentabilidade dos sistemas agropecuários

On the thin-shell limit of branes in the presence of Gauss-Bonnet interactions

In this paper we study thick-shell braneworld models in the presence of a Gauss-Bonnet term. We discuss the peculiarities of the attainment of the thin-shell limit in this case and compare them with the same situation in Einstein gravity. We describe the two simplest families of thick-brane models (parametrized by the shell thickness) one can think of. In the thin-shell limit, one family is characterized by the constancy of its internal density profile (a simple structure for the matter sector) and the other by the constancy of its internal curvature scalar (a simple structure for the geometric sector). We find that these two families are actually equivalent in Einstein gravity and that the presence of the Gauss-Bonnet term breaks this equivalence. In the second case, a shell will always keep some non-trivial internal structure, either on the matter or on the geometric sectors, even in the thin-shell limit.Comment: 17 pages, 2 figures, RevTeX 4. Revised version accepted for publication in Physical Review

Azucares reductores y azucares totales en 10 genotipos de nopales productores de Xoconostle (Opuntia spp.)

En este estudio se determinó el contenido de azucares totales y azucares reductores de diferentes genotipos de nopales productores de xoconostle (Opuntia spp.) colectados en localidades de los estados de Hidalgo, Estado de México y Zacatecas, México. La variables evaluadas fueron; Sólidos solubles totales, azúcares reductores y azúcares totales. Los resultados mostraron diferencias estadísticas significativas (P< 0.05) en el contenido de azúcares totales en el mesocarpio (pulpa) de los frutos de Xoconostle frutos de ‘Manso’, ‘Cuerón’ y ‘Invierno’ con valores de 0.65, 0.61 y 0.60 mg·g-1 y entre los frutos de ‘Virgen’ y ‘’Cuaresmeño Zacatecano’’ con 0.30 y 0.26 mg·g-1. El mayor contenido de azúcares totales se observó en los frutos de Xoconostle ‘Ulapa’ y ‘Cambray’ con valores de 1.3 y 0.91 mg·g-1. En relación al contenido de azúcares reductores en el mesocarpio (pulpa) de xoconostles, no se observaron diferencias estadísticas significativas, con valores que van de 0.13 a 0.18 mg·g-1, excepto en el mesocarpio (pulpa) de frutos de Xoconostle Ulapa (O. Oligacantha C. F. Först) 1.3 mg·g-1. El valor más alto en el contenido de azúcares reductores se observó en el mesocarpio de frutos de Xoconostle ‘Ulapa’ con valor de 0.84 mg·g-1. El mayor contenido de sólidos solubles totales (°Brix) se observó en Xoconostle ‘’Manzano’’, El mayor contenido de azúcares totales y azúcares reductores se observó en los frutos de Xoconostle ‘’Ulapa’’