30,724 research outputs found
A percolation system with extremely long range connections and node dilution
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
for a connection between two occupied sites at a distance
decays as a power law, i.e. when , and
when . Site dilution means that the occupancy probability of a site
is . 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 with is
well-known, being the exactly solvable mean-field model. The percolation order
parameter is investigated numerically for different values of
, and . We show that in the ranges
and the percolation order parameter depends only on
the average connectivity of sites, which can be explicitly computed in
terms of the three parameters , and
Neutral heavy lepton production at next high energy linear colliders
The discovery potential for detecting new heavy Majorana and Dirac neutrinos
at some recently proposed high energy 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 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
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 described by a covariance matrix \textbf{V}, the
Schur complement of a local covariance submatrix 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 -partite Gaussian state is given and it is demonstrated that the
system state conditioned to a partial parity projection is given by a
covariance matrix such as its 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
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
The ground-state phase diagram of an Ising spin-glass model on a random graph
with an arbitrary fraction 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
, correponding to an unbiased spin glass, is a singular point in the
phase diagram, separating a region with a spin-glass phase () from a
region with spin-glass, ferromagnetic, mixed, and paramagnetic phases
()
Structure of fish assemblages on coastal rocky shores of the Azores
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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