7,326 research outputs found
Oscillatons revisited
In this paper, we study some interesting properties of a spherically
symmetric oscillating soliton star made of a real time-dependent scalar field
which is called an oscillaton. The known final configuration of an oscillaton
consists of a stationary stage in which the scalar field and the metric
coefficients oscillate in time if the scalar potential is quadratic. The
differential equations that arise in the simplest approximation, that of
coherent scalar oscillations, are presented for a quadratic scalar potential.
This allows us to take a closer look at the interesting properties of these
oscillating objects. The leading terms of the solutions considering a quartic
and a cosh scalar potentials are worked in the so called stationary limit
procedure. This procedure reveals the form in which oscillatons and boson stars
may be related and useful information about oscillatons is obtained from the
known results of boson stars. Oscillatons could compete with boson stars as
interesting astrophysical objects, since they would be predicted by scalar
field dark matter models.Comment: 10 pages REVTeX, 10 eps figures. Updated files to match version
published in Classical and Quantum Gravit
Entropic Entanglement Criteria for Continuous Variables
We derive several entanglement criteria for bipartite continuous variable
quantum systems based on the Shannon entropy. These criteria are more sensitive
than those involving only second-order moments, and are equivalent to
well-known variance product tests in the case of Gaussian states. Furthermore,
they involve only a pair of quadrature measurements, and will thus should prove
extremely useful the experimental identification of entanglement.Comment: 4 pages, 2 figure
Ocorrência de murcha por Fusarium em meloeiros no Nordeste Paraense.
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Relações interpessoais dos agricultores parceiros do Projeto Tipitamba, da Embrapa Amazônia Oriental.
Neste trabalho aplicou-se a sociometria moreniana para identificar a rede de comunicação interpessoal dos agricultores parceiros do projeto Tipitamba, da Embrapa Amazônia Oriental, que trabalha a temática agricultura sem queima e estão localizados em comunidades rurais, nos municípios de Igarapé-Açu e Marapanim, no nordeste paraense. Foram coletados dados nas comunidades de São João, Novo Brasil, Nova Olinda, Aparecida e Nossa Senhora do Rosário. Utilizaram-se perguntas abertas por meio de um roteiro pré-estabelecido que oportunizasse a elaboração do sociograma dos agricultores entrevistados referente às interações política, afetiva e técnica, bem como, conhecer e identificar as razões que os levam a se comunicar na comunidade. Os resultados apontam que nas comunidades envolvidas no estudo, as pessoas mantêm baixo nível de interação/comunicação interpessoal o que certamente impede o surgimento de novas lideranças locais, à integração entre os grupos e o fortalecimento das atividades coletivas nas comunidades
Quantum metrology at the Heisenberg limit with ion traps
Sub-Planck phase-space structures in the Wigner function of the motional
degree of freedom of a trapped ion can be used to perform weak force
measurements with Heisenberg-limited sensitivity. We propose methods to
engineer the Hamiltonian of the trapped ion to generate states with such small
scale structures, and we show how to use them in quantum metrology
applications.Comment: 10 pages, 6 figure
Quantum signatures of chaos in the dynamics of a trapped ion
We show how a nonlinear chaotic system, the parametrically kicked nonlinear
oscillator, may be realised in the dynamics of a trapped, laser-cooled ion,
interacting with a sequence of standing wave pulses. Unlike the original
optical scheme [G.J.Milburn and C.A.Holmes, Phys. Rev A, 44, p4704, (1991)],
the trapped ion enables strongly quantum dynamics with minimal dissipation.
This should permit an experimental test of one of the quantum signatures of
chaos; irregular collapse and revival dynamics of the average vibrational
energy.Comment: 9 pages, 9 Postscript figures, Revtex, submitted to Phys. Rev.
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