Robustness of bipartite Gaussian entangled beams propagating in lossy channels

Subtle quantum properties offer exciting new prospects in optical communications. Quantum entanglement enables the secure exchange of cryptographic keys and the distribution of quantum information by teleportation. Entangled bright beams of light attract increasing interest for such tasks, since they enable the employment of well-established classical communications techniques. However, quantum resources are fragile and undergo decoherence by interaction with the environment. The unavoidable losses in the communication channel can lead to a complete destruction of useful quantum properties -- the so-called "entanglement sudden death". We investigate the precise conditions under which this phenomenon takes place for the simplest case of two light beams and demonstrate how to produce states which are robust against losses. Our study sheds new light on the intriguing properties of quantum entanglement and how they may be tamed for future applications.Comment: To be published - Nature Photonic

Pragas quarentenárias A1 e A2 da citricultura baiana.

As barreiras fitossanitárias impactam o setor produtivo e comercial de diversos países que pretendem exportar seus produtos agrícolas, em face das exigências que impõem a trânsito internacional de vegetais. Entretanto, essas normativas visam a proteger os importadores do ingresso e disseminação de pragas em seu território. A certificação fitossanitária de origem (CFO) e a permissão de trânsito de vegetais (PTV), documentos que atestam a sanidade e garantem a rastreabilidade das partidas, são exemplos das exigências fitossanitárias interestaduais. A Bahia, segundo lugar no ranking nacional de produção de citros, foi reconhecida pelo Ministério da Agricultura, Pecuária e Abastecimento (MAPA) como área de não ocorrência de várias pragas da citricultura, das quais muitas já foram introduzidas no Estado e estão restritas a microrregiões produtoras. Faz-se necessário avaliar o risco de disseminação e estabelecimento dessas pragas na Bahia, bem como estratégia de prevenção do ingresso daquelas que ainda não ocorrem no Estado.bitstream/item/103892/1/ComunicadoTecnico-156-cristiane-definitivo.pd

Disentanglement in Bipartite Continuous-Variable Systems

Entanglement in bipartite continuous-variable systems is investigated in the presence of partial losses, such as those introduced by a realistic quantum communication channel, e.g. by propagation in an optical fiber. We find that entanglement can vanish completely for partial losses, in a situa- tion reminiscent of so-called entanglement sudden death. Even states with extreme squeezing may become separable after propagation in lossy channels. Having in mind the potential applications of such entangled light beams to optical communications, we investigate the conditions under which entanglement can survive for all partial losses. Different loss scenarios are examined and we derive criteria to test the robustness of entangled states. These criteria are necessary and sufficient for Gaussian states. Our study provides a framework to investigate the robustness of continuous-variable entanglement in more complex multipartite systems.Comment: Phys. Rev. A (in press

Gravitation and Duality Symmetry

By generalizing the Hodge dual operator to the case of soldered bundles, and working in the context of the teleparallel equivalent of general relativity, an analysis of the duality symmetry in gravitation is performed. Although the basic conclusion is that, at least in the general case, gravitation is not dual symmetric, there is a particular theory in which this symmetry shows up. It is a self dual (or anti-self dual) teleparallel gravity in which, due to the fact that it does not contribute to the interaction of fermions with gravitation, the purely tensor part of torsion is assumed to vanish. The ensuing fermionic gravitational interaction is found to be chiral. Since duality is intimately related to renormalizability, this theory may eventually be more amenable to renormalization than teleparallel gravity or general relativity.Comment: 7 pages, no figures. Version 2: minor presentation changes, references added. Accepted for publication in Int. J. Mod. Phys.

Limitação do requerimento microbiano em energia metabolizável fermentável ou proteína degradável na suplementação do pasto de inverno de vacas Canchim.

Scanea

Optimization of supply diversity for the self-assembly of simple objects in two and three dimensions

The field of algorithmic self-assembly is concerned with the design and analysis of self-assembly systems from a computational perspective, that is, from the perspective of mathematical problems whose study may give insight into the natural processes through which elementary objects self-assemble into more complex ones. One of the main problems of algorithmic self-assembly is the minimum tile set problem (MTSP), which asks for a collection of types of elementary objects (called tiles) to be found for the self-assembly of an object having a pre-established shape. Such a collection is to be as concise as possible, thus minimizing supply diversity, while satisfying a set of stringent constraints having to do with the termination and other properties of the self-assembly process from its tile types. We present a study of what we think is the first practical approach to MTSP. Our study starts with the introduction of an evolutionary heuristic to tackle MTSP and includes results from extensive experimentation with the heuristic on the self-assembly of simple objects in two and three dimensions. The heuristic we introduce combines classic elements from the field of evolutionary computation with a problem-specific variant of Pareto dominance into a multi-objective approach to MTSP.Comment: Minor typos correcte

Sugestão de adubação fosfatada do algodoeiro para o Estado de Goiás

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Levantamento de Diaphorina citri (Hemiptera: psylidae), vetor do Huanglongbing (HLB), em três regiões produtoras de citros no estado da Bahia.

O psilídeo Diaphorina citri, Kuwayama, inseto-vetor da bactéria Candidatus Liberibacter causadora da devastadora doença dos citros: a Huanglongbing ? HLB - (ex-greening), ocorre praticamente em todas regiões produtoras de citros do país. A Bahia é considerada área livre desta doença. A transmissão do HLB ocorre por meio de enxertia com material contaminado ou por inoculação da bactéria no floema da planta pelo inseto vetor.PDF. 153_11

Teleparallel Equivalent of Non-Abelian Kaluza-Klein Theory

Based on the equivalence between a gauge theory for the translation group and general relativity, a teleparallel version of the non-abelian Kaluza-Klein theory is constructed. In this theory, only the fiber-space turns out to be higher-dimensional, spacetime being kept always four-dimensional. The resulting model is a gauge theory that unifies, in the Kaluza-Klein sense, gravitational and gauge fields. In contrast to the ordinary Kaluza-Klein models, this theory defines a natural length-scale for the compact sub-manifold of the fiber space, which is shown to be of the order of the Planck length.Comment: Revtex4, 7 pages, no figures, to appear in Phys. Rev.