38,545 research outputs found
Density Dependent Parametrization Models: Formalism and Applications
In this work we derive a formalism to incorporate asymmetry and temperature
effects in the Brown-Rho (BR) scaled lagrangian model in a mean field theory.
The lagrangian density discussed in this work requires less parameters than the
usual models with density dependent couplings. We also present the formalism
with the inclusion of the eight lightest baryons, two lightest leptons, beta
equilibrium and charge neutrality in order to apply the BR scaled model to the
study of neutron stars. The results are again compared with the ones obtained
from another density dependent parametrization model. The role played by the
rearrangement term at T=0 for nuclear or neutron star matter and at finite
temperature is investigated. The BR scaled model is shown to be a good tool in
studies involving density dependent effective masses and in astrophysics
applications.Comment: 23 pages, 10 figure
Phase Fluctuations in Bose-Einstein Condensates
We demonstrate the existence of phase fluctuations in elongated Bose-Einstein
Condensates (BECs) and study the dependence of those fluctuations on the system
parameters. A strong dependence on temperature, atom number, and trapping
geometry is observed. Phase fluctuations directly affect the coherence
properties of BECs. In particular, we observe instances where the phase
coherence length is significantly smaller than the condensate size. Our method
of detecting phase fluctuations is based on their transformation into density
modulations after ballistic expansion. An analytic theory describing this
transformation is developed.Comment: 11 pages, 7 figure
Effect of interactions on vortices in a nonequilibrium polariton condensate
We demonstrate the creation of vortices in a macroscopically occupied polariton state formed in a semiconductor microcavity. A weak external laser beam carrying orbital angular momentum (OAM) is used to imprint a vortex on the condensate arising from the polariton optical parametric oscillator (OPO). The vortex core radius is found to decrease with increasing pump power, and is determined by polariton-polariton interactions. As a result of OAM conservation in the parametric scattering process, the excitation consists of a vortex in the signal and a corresponding antivortex in the idler of the OPO. The experimental results are in good agreement with a theoretical model of a vortex in the polariton OPO
Controlling two-species Mott-insulator phses in an optical lattice to form an array of dipolar molecules
We consider the transfer of a two-species Bose-Einstein condensate into an
optical lattice with a density such that that a Mott-insulator state with one
atom per species per lattice site is obtained in the deep lattice regime.
Depending on collision parameters the result could be either a `mixed' or a
`separated' Mott-insulator phase. Such a `mixed' two-species insulator could
then be photo-associated into an array of dipolar molecules suitable for
quantum computation or the formation of a dipolar molecular condensate. For the
case of a Rb-K two-species BEC, however, the large inter-species
scattering length makes obtaining the desired `mixed' Mott insulator phase
difficult. To overcome this difficulty we investigate the effect of varying the
lattice frequency on the mean-field interaction and find a favorable parameter
regime under which a lattice of dipolar molecules could be generated
"Supersolid" self-bound Bose condensates via laser-induced interatomic forces
We show that the dipole-dipole interatomic forces induced by a single
off-resonant running laser beam can lead to a self-bound pencil-shaped Bose
condensate, even if the laser beam is a plane-wave. For an appropriate laser
intensity the ground state has a quasi-one dimensional density modulation --- a
Bose "supersolid".Comment: 4 pages, 3 eps figure
Observation of Phase Fluctuations in Bose-Einstein Condensates
The occurrence of phase fluctuations due to thermal excitations in
Bose-Einstein condensates (BECs) is studied for a variety of temperatures and
trap geometries. We observe the statistical nature of the appearence of phase
fluctuations and characterize the dependence of their average value on
temperature, number of particles and the trapping potential. We find pronounced
phase fluctuations for condensates in very elongated traps in a broad
temperature range. The results are of great importance for the realization of
BEC in quasi 1D geometries, for matter wave interferometry with BECs, as well
as for coherence properties of guided atom laser beams.Comment: 4 pages, 4 figure
Análise comportamental de um acesso de mandioca (Manihot esculenta Crantz) em relação a dois tipos de meio de cultura e doses de um fertilizante solúvel comercial.
A mandioca é uma cultura de grande importância nos trópicos, porque é um alimento de base prontamente disponível e com alto teor protéico (NASSAR et al., 2009). Como a mandioca convencionalmente é propagada de forma vegetativa ou assexuada, mediante segmentos do caule denominados de manivas-sementes ou apenas manivas, torna-se imprescindível que o material de plantio sofra uma rigorosa seleção, de forma que possa refletir na obtenção de plantas sadias, mais vigorosas e produtivas. No entanto, a multiplicação via manivas pode acumular pragas e patógenos, que associados a fatores ambientais, como clima e solo, podem afetar características como vigor, altura, teor de amido e produção de raízes, entre outras. Diante disso a produção de manivas sadias, partindo de materiais gerados pela micropropagação, constitui um importante procedimento na produção de materiais de plantio de qualidade. Mediante a micropropagação procura-se maximização da multiplicação de gemas, o que está estreitamente relacionado com o meio de cultura e a manipulação de seus componentes. A escolha do meio de cultura adequado é um fator relevante para a micropropagação devido ao importante papel que os componentes minerais desempenham no processo de regeneração. Além disso, visando melhorar o desenvolvimento vegetativo e radicular das plantas in vitro, diversos produtos tem sido estudados na micropropagação vegetal, sejam de natureza orgânica, como polpa de banana e água de coco ou mineral. O objetivo deste trabalho foi avaliar as diferentes concentrações de um fertilizante solúvel comercial, adicionado a dois tipos de meio de cultura, em relação a diversas variáveis e ao desenvolvimento das plantas de um acesso do Banco Ativo de Germoplasma in vitro de mandioca, o BGM 1660 (Aipim Brasil)
Quantum phases of dipolar bosons in optical lattices
The ground state of dipolar bosons placed in an optical lattice is analyzed.
We show that the modification of experimentally accessible parameters can lead
to the realization and control of different quantum phases, including
superfluid, supersolid, Mott insulator, checkerboard, and collapse phases.Comment: 4 pages, 4 eps figures, final versio
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
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