2,342 research outputs found

    Discrete concavity and the half-plane property

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    Murota et al. have recently developed a theory of discrete convex analysis which concerns M-convex functions on jump systems. We introduce here a family of M-concave functions arising naturally from polynomials (over a field of generalized Puiseux series) with prescribed non-vanishing properties. This family contains several of the most studied M-concave functions in the literature. In the language of tropical geometry we study the tropicalization of the space of polynomials with the half-plane property, and show that it is strictly contained in the space of M-concave functions. We also provide a short proof of Speyer's hive theorem which he used to give a new proof of Horn's conjecture on eigenvalues of sums of Hermitian matrices.Comment: 14 pages. The proof of Theorem 4 is corrected

    Small Angle X-Ray Scattering Investigation of Taser Using Correlation Functions

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    Quantum cohomology via vicious and osculating walkers

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    We relate the counting of rational curves intersecting Schubert varieties of the Grassmannian to the counting of certain non-intersecting lattice paths on the cylinder, so-called vicious and osculating walkers. These lattice paths form exactly solvable statistical mechanics models and are obtained from solutions to the Yang–Baxter equation. The eigenvectors of the transfer matrices of these models yield the idempotents of the Verlinde algebra of the gauged u^(n)k -WZNW model. The latter is known to be closely related to the small quantum cohomology ring of the Grassmannian. We establish further that the partition functions of the vicious and osculating walker model are given in terms of Postnikov’s toric Schur functions and can be interpreted as generating functions for Gromov–Witten invariants. We reveal an underlying quantum group structure in terms of Yang–Baxter algebras and use it to give a generating formula for toric Schur functions in terms of divided difference operators which appear in known representations of the nil-Hecke algebra

    Fauna edáfica como indicadora de contaminação do solo.

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    Recentemente, o solo tem se tornado foco de preocupação devido à gradativa contaminação de ambientes terrestres e aquáticos, decorrente do progresso e avanços sócio-econômicos no país. Diante dessa realidade, a demanda por atividades antrópicas menos agressivas ao ambiente é cada vez maior. Os possíveis impactos ambientais, portanto, devem ser monitorados, controlados e remediados, a fim de evitar problemas irreversíveis ao meio ambiente e à sociedade. A ecotoxicologia estuda os efeitos dos poluentes sobre os organismos e a interação destes com o habitat. Para se avaliar o impacto de uma substância no solo, ensaios ecotoxicológicos com metodologia padronizada internacionalmente podem ser realizados com invertebrados edáficos, tais como as minhocas, enquitreídeos e colêmbolos, por serem importantes na decomposição da matéria orgânica do solo. Esses ensaios de laboratório, no entanto, precisam ser adaptados, pois a metodologia padrão se baseia em espécies e condições de clima temperado que não condizem com a realidade do Brasil. Adaptações aos ensaios de efeito agudo (mortalidade), efeito crônico (reprodução) e de fuga (comportamento) têm sido estudados por vários grupos e os resultados têm sido positivos com relação ao uso do substrato com o pó da fibra da casca do côco e utilização de temperaturas maiores que 20ºC. Algumas espécies encontradas no Brasil também têm sido testadas, algumas delas apresentando resultados promissores, outras, com limitações. De modo geral, os métodos para avaliação da contaminação do solo em laboratório têm apresentado avanços, entretanto, mais estudos se fazem necessários para o estabelecimento de espécies nativas recomendadas para cada tipo de ensaio.Resumo expandido

    Universality-Breaking Effects in Leptonic Z Decays

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    We analyze the possibility of universality violation in diagonal leptonic decays of the ZZ boson, in the context of interfamily "see-saw" models. In a minimal extension of the Standard Model with right-handed neutrino fields, we find that universality-breaking effects increase quadratically with the heavy Majorana neutrino mass and may be observed in the running LEPLEP experiments.Comment: MZ-TH/93-04 #, LaTeX, 14 p. (2 Figs

    Long-Term Preservation of Cones and Improvement in Visual Function Following Gene Therapy in a Mouse Model of Leber Congenital Amaurosis Caused by Guanylate Cyclase-1 Deficiency

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    Leber congenital amaurosis (LCA) is a severe retinal dystrophy manifesting from early infancy as poor vision or blindness. Loss-of-function mutations in GUCY2D cause LCA1 and are one of the most common causes of LCA, accounting for 20% of all cases. Human GUCY2D and mouse Gucy2e genes encode guanylate cyclase-1 (GC), which is responsible for restoring the dark state in photoreceptors after light exposure. The Glicy2e(-/-) mouse shows partially diminished rod function, but an absence of cone function before degeneration. Although the cones appear morphologically normal, they exhibit mislocalization of proteins involved in phototransduction. In this study we tested the efficacy of an rAAV2/8 vector containing the human rhodopsin kinase promoter and the human GUCY2D gene. Following subretinal delivery of the vector in Glicy2e(-/-) mice, GC1 protein was detected in the rod and cone outer segments, and in transduced areas of retina cone transducin was appropriately localized to cone outer segments. Moreover, we observed a dose-dependent restoration of rod and cone function and an improvement in visual behavior of the treated mice. Most importantly, cone preservation was observed in transduced areas up to 6 months post injection. To date, this is the most effective rescue of the Glicy2e(-/-) mouse model of LCA and we propose that a vector, similar to the one used in this study, could be suitable for use in a clinical trial of gene therapy for LCA1
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