5,732 research outputs found
Rate analysis for a hybrid quantum repeater
We present a detailed rate analysis for a hybrid quantum repeater assuming
perfect memories and using optimal probabilistic entanglement generation and
deterministic swapping routines. The hybrid quantum repeater protocol is based
on atomic qubit-entanglement distribution through optical coherent-state
communication. An exact, analytical formula for the rates of entanglement
generation in quantum repeaters is derived, including a study on the impacts of
entanglement purification and multiplexing strategies. More specifically, we
consider scenarios with as little purification as possible and we show that for
sufficiently low local losses, such purifications are still more powerful than
multiplexing. In a possible experimental scenario, our hybrid system can create
near-maximally entangled (F = 0.98) pairs over a distance of 1280 km at rates
of the order of 100 Hz
Effects of Mass Media and Cultural Drift in a Model for Social Influence
In the context of an extension of Axelrod's model for social influence, we
study the interplay and competition between the cultural drift, represented as
random perturbations, and mass media, introduced by means of an external
homogeneous field. Unlike previous studies [J. C. Gonz\'alez-Avella {\it et
al}, Phys. Rev. E {\bf 72}, 065102(R) (2005)], the mass media coupling proposed
here is capable of affecting the cultural traits of any individual in the
society, including those who do not share any features with the external
message. A noise-driven transition is found: for large noise rates, both the
ordered (culturally polarized) phase and the disordered (culturally fragmented)
phase are observed, while, for lower noise rates, the ordered phase prevails.
In the former case, the external field is found to induce cultural ordering, a
behavior opposite to that reported in previous studies using a different
prescription for the mass media interaction. We compare the predictions of this
model to statistical data measuring the impact of a mass media vasectomy
promotion campaign in Brazil.Comment: 10 pages, 3 figures; minor changes; added references. To appear in
IJMP
Immunization and Aging: a Learning Process in the Immune Network
The immune system can be thought as a complex network of different
interacting elements. A cellular automaton, defined in shape-space, was
recently shown to exhibit self-regulation and complex behavior and is,
therefore, a good candidate to model the immune system. Using this model to
simulate a real immune system we find good agreement with recent experiments on
mice. The model exhibits the experimentally observed refractory behavior of the
immune system under multiple antigen presentations as well as loss of its
plasticity caused by aging.Comment: 4 latex pages, 3 postscript figures attached. To be published in
Physical Review Letters (Tentatively scheduled for 5th Oct. issue
Evolution of Coordination in Social Networks: A Numerical Study
Coordination games are important to explain efficient and desirable social
behavior. Here we study these games by extensive numerical simulation on
networked social structures using an evolutionary approach. We show that local
network effects may promote selection of efficient equilibria in both pure and
general coordination games and may explain social polarization. These results
are put into perspective with respect to known theoretical results. The main
insight we obtain is that clustering, and especially community structure in
social networks has a positive role in promoting socially efficient outcomes.Comment: preprint submitted to IJMP
Status of the HIE-ISOLDE project at CERN
The HIE-ISOLDE project represents a major upgrade of the ISOLDE nuclear
facility with a mandate to significantly improve the quality and increase the
intensity and energy of radioactive nuclear beams produced at CERN. The project
will expand the experimental nuclear physics programme at ISOLDE by focusing on
an upgrade of the existing Radioactive ion beam EXperiment (REX) linac with a
40 MV superconducting linac comprising thirty-two niobium-on-copper
sputter-coated quarter-wave resonators housed in six cryomodules. The new linac
will raise the energy of post-accelerated beams from 3 MeV/u to over 10 MeV/u.
The upgrade will be staged to first deliver beam energies of 5.5 MeV/u using
two high- cryomodules placed downstream of REX, before the energy
variable section of the existing linac is replaced with two low-
cryomodules and two additional high- cryomodules are installed to attain
over 10 MeV/u with full energy variability above 0.45 MeV/u. An overview of the
project including a status summary of the different R&D activities and the
schedule will outlined.Comment: 7 pages, 12 figures, submitted to the Heavy Ion Accelerator
Technology conference (HIAT) 2012, in Chicag
Exatidão de classificações automáticas de uma imagem LANDSAT 5 TM para a região cafeeira de Machado, MG.
O presente trabalho avalia a acurácia de dois classificadores automáticos disponíveis no Sistema de Informação Geográfica SPRING para o mapeamento de uso e ocupação da terra da região cafeeira de Machado, MG. Foram utilizados os classificadores: Battacharya, ?por região?; e o Máxima Verossimilhança (Maxver), ?pixel a pixel? para a imagem Landsat 5 TM e como referência foi utilizada a imagem do satélite Spot 4 classificada visualmente e validada em campo. Ambos algoritmos demonstraram baixo rendimento para a região. Posteriormente às classificações, foram criadas matrizes de erro, comparando as classificações automáticas com a visual. O desempenho das classificações foi avaliado pelos índices de exatidão Global, Kappa e Tau. O baixo desempenho das classificações pode ser explicado pela região cafeeira de Machado possuir um relevo muito movimentado, proporcionando regiões sombreadas e lavouras cafeeiras contíguas a fragmentos de vegetação nativa, os quais apresentam resposta espectral semelhante
Forest fires and other examples of self-organized criticality
We review the properties of the self-organized critical (SOC) forest-fire
model. The paradigm of self-organized criticality refers to the tendency of
certain large dissipative systems to drive themselves into a critical state
independent of the initial conditions and without fine-tuning of the
parameters. After an introduction, we define the rules of the model and discuss
various large-scale structures which may appear in this system. The origin of
the critical behavior is explained, critical exponents are introduced, and
scaling relations between the exponents are derived. Results of computer
simulations and analytical calculations are summarized. The existence of an
upper critical dimension and the universality of the critical behavior under
changes of lattice symmetry or the introduction of immunity are discussed. A
survey of interesting modifications of the forest-fire model is given. Finally,
several other important SOC models are briefly described.Comment: 37 pages RevTeX, 13 PostScript figures (Figs 1, 4, 13 are of reduced
quality to keep download times small
Sensoriamento remoto para a caracterização do ambiente cafeeiro das cidades: Arceburgo, Monte Santo de Minas, Guaxupé e Guaranésia, MG.
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