Bringing Together Gravity and the Quanta

Due to its underlying gauge structure, teleparallel gravity achieves a separation between inertial and gravitational effects. It can, in consequence, describe the isolated gravitational interaction without resorting to the equivalence principle, and is able to provide a tensorial definition for the energy-momentum density of the gravitational field. Considering the conceptual conflict between the local equivalence principle and the nonlocal uncertainty principle, the replacement of general relativity by its teleparallel equivalent can be considered an important step towards a prospective reconciliation between gravitation and quantum mechanics.Comment: 9 pages. Contribution to the proceedings of the Albert Einstein Century International Conference, Paris, 18-22 July, 200

Dynamical Evolution of a Cylindrical Shell with Rotational Pressure

We prepare a general framework for analyzing the dynamics of a cylindrical shell in the spacetime with cylindrical symmetry. Based on the framework, we investigate a particular model of a cylindrical shell-collapse with rotational pressure, accompanying the radiation of gravitational waves and massless particles. The model has been introduced previously but has been awaiting for proper analysis. Here the analysis is put forward: It is proved that, as far as the weak energy condition is satisfied outside the shell, the collapsing shell bounces back at some point irrespective of the initial conditions, and escapes from the singularity formation. The behavior after the bounce depends on the sign of the shell pressure in the z-direction. When the pressure is non-negative, the shell continues to expand without re-contraction. On the other hand, when the pressure is negative (i.e. it has a tension), the behavior after the bounce can be more complicated depending on the details of the model. However, even in this case, the shell never reaches the zero-radius configuration.Comment: To appear in Phys. Rev.

Magnetic states of linear defects in graphene monolayers: effects of strain and interaction

The combined effects of defect-defect interaction and of uniaxial or biaxial strains of up to 10\% on the development of magnetic states on the defect-core-localized quasi-one-dimensional electronic states generated by the so-called 558 linear extended defect in graphene monolayers are investigated by means of {\it ab initio} calculations. Results are analyzed on the basis of the heuristics of the Stoner criterion. We find that conditions for the emergence of magnetic states on the 558 defect can be tuned by uniaxial tensile parallel strains (along the defect direction) at both limits of isolated and interacting 558 defects. Parallel strains are shown to lead to two cooperative effects that favor the emergence of itinerant magnetism: enhancement of the DOS of the resonant defect states in the region of the Fermi level and tuning of the Fermi level to the maximum of the related DOS peak. A perpendicular strain is likewise shown to enhance the DOS of the defect states, but it also effects a detunig of the Fermi level that shifts away from the maximum of the DOS of the defect states, which inhibts the emergence of magnetic states. As a result, under biaxial strains the stabilization of a magnetic state depends on the relative magnitudes of the two components of strain.Comment: 9 pages 8 figure

Sinorhizobium Meliloti, A Bacterium Lacking The Autoinducer-2 (AI-2) Synthase, Responds To AI-2 Supplied By Other Bacteria

Many bacterial species respond to the quorum-sensing signal autoinducer-2 (AI-2) by regulating different niche-specific genes. Here, we show that Sinorhizobium meliloti, a plant symbiont lacking the gene for the AI-2 synthase, while not capable of producing AI-2 can nonetheless respond to AI-2 produced by other species. We demonstrate that S. meliloti has a periplasmic binding protein that binds AI-2. The crystal structure of this protein (here named SmlsrB) with its ligand reveals that it binds (2R,4S)-2-methyl-2,3,3,4-tetrahydroxytetrahydrofuran (R-THMF), the identical AI-2 isomer recognized by LsrB of Salmonella typhimurium. The gene encoding SmlsrB is in an operon with orthologues of the lsr genes required for AI-2 internalization in enteric bacteria. Accordingly, S. meliloti internalizes exogenous AI-2, and mutants in this operon are defective in AI-2 internalization. S. meliloti does not gain a metabolic benefit from internalizing AI-2, suggesting that AI-2 functions as a signal in S. meliloti. Furthermore, S. meliloti can completely eliminate the AI-2 secreted by Erwinia carotovora, a plant pathogen shown to use AI-2 to regulate virulence. Our findings suggest that S. meliloti is capable of \u27eavesdropping\u27 on the AI-2 signalling of other species and interfering with AI-2-regulated behaviours such as virulence

Metodologia para determinação de dieta alimentar de peixes detritívoros.

bitstream/CPAP/56116/1/CT71.pdfFolheto Formato Eletrônico

Alimentação de Gymnotus cf. carapo (Pisces: Gymnotidae) e suas relações com a fauna associada às macrófitas aquáticas no Pantanal, Brasil.

Foi analisada a alimentação da tuvira, Gymnotus cf. carapo e as possíveis relações com a fauna associada às raízes das macrófitas aquáticas, os parâmetros físicos e químicos da água e o teor de matéria orgânica retido nas raízes das macrófitas, na planície de inundação do baixo rio Negro, Mato Grosso do Sul. As ordens Insecta, Cladocera, Rotifera e Gastropoda foram os recursos alimentares predominantes nas raízes das macrófitas. As tuviras do Pantanal do baixo rio Negro são carnívoras generalistas e alimentam-se seletivamente da fauna associada às raízes de macrófitas aquáticas. A alimentação é baseada em invertebrados, dentre os insetos, Ephemeroptera e Odonata foram os recursos alimentar preferidos, seguido de Cladocera. São encontradas freqüentemente nos estandes de macrófitas capazes de reter altos teores de matéria orgânica em suas raízes ou em baceiros, nos ambientes onde há conexão com o rio principal e em profundidades inferiores a 120cm. Pela sua história filogenética, é uma espécie encontrada em condições físico-química de águas bem diversificada.bitstream/CPAP/55941/1/BP68.pdfFormato eletrônic

Peixes detritivoros da planicie inundavel do Rio Miranda, Pantanal, Mato Grosso do Sul, Brasil.

Foi analisada a alimentacao de 17 especies de peixes detritivoros, pertencentes as familias Prochilodontidae, Curimatidae e Loricariidae, de quatro ambientes da planicie de inundacao (dois meandros abandonados, uma "vazante" e um pequeno lago) de rio Miranda. Duas metodologias foram utilizadas para a avaliacao da alimentacao dessas especies. O teor de materia organica do detrito foi determinado por diferenca entre o peso seco e o peso apos queima em mufla; amostras dos conteudos estomacais foram colocadas em lamina microscopica quadriculada para avaliacao do volume proporcional de detritos e outros organismos como algas, rotiferos e cladoceros, com metodologia desenvolvida para essa finalidade. O item dominante na alimentacao dessas especies e o detrito organico, cujo teor da materia organica e bastante variavel entre os periodos analisados e entre as especies. Em alguns ambientes e periodos do ano, as algas e microorganismos como rotiferos e cladoceros foram importantes na alimentacao de algumas especies.bitstream/item/37441/1/BP12.pd

Gravitation: Global Formulation and Quantum Effects

A nonintegrable phase-factor global approach to gravitation is developed by using the similarity of teleparallel gravity with electromagnetism. The phase shifts of both the COW and the gravitational Aharonov-Bohm effects are obtained. It is then shown, by considering a simple slit experiment, that in the classical limit the global approach yields the same result as the gravitational Lorentz force equation of teleparallel gravity. It represents, therefore, the quantum mechanical version of the classical description provided by the gravitational Lorentz force equation. As teleparallel gravity can be formulated independently of the equivalence principle, it will consequently require no generalization of this principle at the quantum level.Comment: Latex (IOP style), 14 pages, 3 figures. To appear in Classical and Quantum Gravit

Asymptotics of Spinfoam Amplitude on Simplicial Manifold: Euclidean Theory

We study the large-j asymptotics of the Euclidean EPRL/FK spin foam amplitude on a 4d simplicial complex with arbitrary number of simplices. We show that for a critical configuration (j_f, g_{ve}, n_{ef}) in general, there exists a partition of the simplicial complex into three regions: Non-degenerate region, Type-A degenerate region and Type-B degenerate region. On both the non-degenerate and Type-A degenerate regions, the critical configuration implies a non-degenerate Euclidean geometry, while on the Type-B degenerate region, the critical configuration implies a vector geometry. Furthermore we can split the Non-degenerate and Type-A regions into sub-complexes according to the sign of Euclidean oriented 4-simplex volume. On each sub-complex, the spin foam amplitude at critical configuration gives a Regge action that contains a sign factor sgn(V_4(v)) of the oriented 4-simplices volume. Therefore the Regge action reproduced here can be viewed as a discretized Palatini action with on-shell connection. The asymptotic formula of the spin foam amplitude is given by a sum of the amplitudes evaluated at all possible critical configurations, which are the products of the amplitudes associated to different type of geometries.Comment: 27 pages, 5 figures, references adde