30,724 research outputs found

    A percolation system with extremely long range connections and node dilution

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    We study the very long-range bond-percolation problem on a linear chain with both sites and bonds dilution. Very long range means that the probability pijp_{ij} for a connection between two occupied sites i,ji,j at a distance rijr_{ij} decays as a power law, i.e. pij=ρ/[rijαN1−α]p_{ij} = \rho/[r_{ij}^\alpha N^{1-\alpha}] when 0≀α<1 0 \le \alpha < 1, and pij=ρ/[rijln⁥(N)]p_{ij} = \rho/[r_{ij} \ln(N)] when α=1\alpha = 1. Site dilution means that the occupancy probability of a site is 0<ps≀10 < p_s \le 1. The behavior of this model results from the competition between long-range connectivity, which enhances the percolation, and site dilution, which weakens percolation. The case α=0\alpha=0 with ps=1p_s =1 is well-known, being the exactly solvable mean-field model. The percolation order parameter P∞P_\infty is investigated numerically for different values of α\alpha, psp_s and ρ\rho. We show that in the ranges 0≀α≀1 0 \le \alpha \le 1 and 0<ps≀10 < p_s \le 1 the percolation order parameter P∞P_\infty depends only on the average connectivity Îł\gamma of sites, which can be explicitly computed in terms of the three parameters α\alpha, psp_s and ρ\rho

    Neutral heavy lepton production at next high energy e+e−e^+e^- linear colliders

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    The discovery potential for detecting new heavy Majorana and Dirac neutrinos at some recently proposed high energy e+e−e^+e^- colliders is discussed. These new particles are suggested by grand unified theories and superstring-inspired models. For these models the production of a single heavy neutrino is shown to be more relevant than pair production when comparing cross sections and neutrino mass ranges. The process e+e−⟶Μe±W∓ e^+e^- \longrightarrow {\nu} e^{\pm} W^{\mp} is calculated including on-shell and off-shell heavy neutrino effects. We present a detailed study of cross sections and distributions that shows a clear separation between the signal and standard model contributions, even after including hadronization effects.Comment: 4 pages including 15 figures, 1 table. RevTex. Accepted in Physical Review

    Physical properties of the Schur complement of local covariance matrices

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    General properties of global covariance matrices representing bipartite Gaussian states can be decomposed into properties of local covariance matrices and their Schur complements. We demonstrate that given a bipartite Gaussian state ρ12\rho_{12} described by a 4×44\times 4 covariance matrix \textbf{V}, the Schur complement of a local covariance submatrix V1\textbf{V}_1 of it can be interpreted as a new covariance matrix representing a Gaussian operator of party 1 conditioned to local parity measurements on party 2. The connection with a partial parity measurement over a bipartite quantum state and the determination of the reduced Wigner function is given and an operational process of parity measurement is developed. Generalization of this procedure to a nn-partite Gaussian state is given and it is demonstrated that the n−1n-1 system state conditioned to a partial parity projection is given by a covariance matrix such as its 2×22 \times 2 block elements are Schur complements of special local matrices.Comment: 10 pages. Replaced with final published versio

    Generalized Euler-Lagrange equations for variational problems with scale derivatives

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    We obtain several Euler-Lagrange equations for variational functionals defined on a set of H\"older curves. The cases when the Lagrangian contains multiple scale derivatives, depends on a parameter, or contains higher-order scale derivatives are considered.Comment: Submitted on 03-Aug-2009; accepted for publication 16-March-2010; in "Letters in Mathematical Physics"

    Spin-glass behaviour on random lattices

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    The ground-state phase diagram of an Ising spin-glass model on a random graph with an arbitrary fraction ww of ferromagnetic interactions is analysed in the presence of an external field. Using the replica method, and performing an analysis of stability of the replica-symmetric solution, it is shown that w=1/2w=1/2, correponding to an unbiased spin glass, is a singular point in the phase diagram, separating a region with a spin-glass phase (w<1/2w<1/2) from a region with spin-glass, ferromagnetic, mixed, and paramagnetic phases (w>1/2w>1/2)

    Structure of fish assemblages on coastal rocky shores of the Azores

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    Bol. Mus. Mun. Funchal, Sup. N.Âș 6: 127-138, 2001The structure of fish assemblages was investigated from the surface down to 25 m depth on Azorean rocky shores. A total of 57 fish species was recorded by visual censuses, most species (66%) occurring in the whole depth range studied. Fish abundance was dominated by 11 species, mainly sparids, labrids, carangids and pomacentrids, which constituted over 88% of the total number of individuals recorded. The trophic structure of the fish assemblages studied in the Azores was characterized by the dominance of benthic mesocarnivores and high proportions of herbivores and pelagic macrocarnivores.A estrutura das comunidades ictiolĂłgicas dos fundos rochosos dos Açores foi estudada desde a superfĂ­cie atĂ© aos 25 m de profundidade. Um total de 57 espĂ©cies de peixes foi identificado com recurso a censos visuais. A maioria das espĂ©cies (66%) ocorreu em toda a gama de profundidades estudada. A fauna ictiolĂłgica era dominada, em termos de abundĂąncia, por 11 espĂ©cies, principalmente pertencentes Ă s famĂ­lias Sparidae, Labridae, Carangidae e Pomacentridae, os quais constituĂ­ram mais de 88% do nĂșmero total de indivĂ­duos observados. A estrutura trĂłfica das comunidades ictiolĂłgicas estudadas nos Açores apresentouse dominada por meso-carnĂ­voros bentĂłnicos e proporçÔes elevadas de herbĂ­voros e macro-carnĂ­voros pelĂĄgico
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