3,629 research outputs found
Critical behavior at edge singularities in one dimensional spin models
In ferromagnetic spin models above the critical temperature ()
the partition function zeros accumulate at complex values of the magnetic field
() with a universal behavior for the density of zeros \rho (H) \sim | H -
H_E |^{\sg}. The critical exponent \sg is believed to be universal at each
space dimension and it is related to the magnetic scaling exponent via
\sg = (d-y_h)/y_h. In two dimensions we have y_h=12/5 (\sg = -1/6) while
y_h=2 (\sg=-1/2) in . For the one dimensional Blume-Capel and
Blume-Emery-Griffiths models we show here, for different temperatures, that a
new value y_h=3 (\sg =-2/3) can emerge if we have a triple degeneracy of the
transfer matrix eigenvalues.Comment: to appear in Phys. Rev. E, 16 pages, 3 figure
Superfluid and Mott Insulating shells of bosons in harmonically confined optical lattices
Weakly interacting atomic or molecular bosons in quantum degenerate regime
and trapped in harmonically confined optical lattices, exhibit a wedding cake
structure consisting of insulating (Mott) shells. It is shown that superfluid
regions emerge between Mott shells as a result of fluctuations due to finite
hopping. It is found that the order parameter equation in the superfluid
regions is not of the Gross-Pitaeviskii type except near the insulator to
superfluid boundaries. The excitation spectra in the Mott and superfluid
regions are obtained, and it is shown that the superfluid shells posses low
energy sound modes with spatially dependent sound velocity described by a local
index of refraction directly related to the local superfluid density. Lastly,
the Berezinskii-Kosterlitz-Thouless transition and vortex-antivortex pairs are
discussed in thin (wide) superfluid shells (rings) limited by three (two)
dimensional Mott regions.Comment: 11 pages, 9 figures
Dinâmica recente no espaço rural do município de Nossa Senhora da Glória/SE.
O objetivo desse artigo é analisar a dinâmica recente no espaço rural de um município do semi-árido sergipano, reconhecido pelo dinamismo da sua economia que gira em torno da produção e processamento do leite por agricultores familiares, a despeito da inexistência de políticas específicas e continuadas para esse fim. A área de pesquisa é o município de Nossa Senhora da Glória localizado no Alto Sertão sergipano. A metodologia privilegiou o contato com atores-chave através de entrevistas, observações de campo, caminhadas transversais para observação da paisagem, participação em reuniões e levantamento de dados secundários. Os principais resultados demonstram que o município de Glória contem na sua totalidade três unidades de desenvolvimento com dinâmicas particulares a depender das estratégias dos agricultores, acesso e qualidade dos recursos naturais e vinculação com os mercados (trabalho, produto e financeiro
Evolution from BCS to BKT superfluidity in one-dimensional optical lattices
We analyze the finite temperature phase diagram of fermion mixtures in
one-dimensional optical lattices as a function of interaction strength. At low
temperatures, the system evolves from an anisotropic three-dimensional
Bardeen-Cooper-Schrieffer (BCS) superfluid to an effectively two-dimensional
Berezinskii-Kosterlitz-Thouless (BKT) superfluid as the interaction strength
increases. We calculate the critical temperature as a function of interaction
strength, and identify the region where the dimensional crossover occurs for a
specified optical lattice potential. Finally, we show that the dominant vortex
excitations near the critical temperature evolve from multiplane elliptical
vortex loops in the three-dimensional regime to planar vortex-antivortex pairs
in the two-dimensional regime, and we propose a detection scheme for these
excitations.Comment: 4 pages with 2 figure
Vortex-Antivortex Lattice in Ultra-Cold Fermi Gases
We discuss ultra-cold Fermi gases in two dimensions, which could be realized
in a strongly confining one-dimensional optical lattice. We obtain the
temperature versus effective interaction phase diagram for an s-wave superfluid
and show that, below a certain critical temperature T_c, spontaneous
vortex-antivortex pairs appear for all coupling strengths. In addition, we show
that the evolution from weak to strong coupling is smooth, and that the system
forms a square vortex-antivortex lattice at a lower critical temperature T_M.Comment: Submitted to Physical Review Letter
Phase Fluctuations and Vortex Lattice Melting in Triplet Quasi-One-Dimensional Superconductors at High Magnetic Fields
Assuming that the order parameter corresponds to an equal spin triplet
pairing symmetry state, we calculate the effect of phase fluctuations in
quasi-one-dimensional superconductors at high magnetic fields applied along the
y (b') axis. We show that phase fluctuations can destroy the theoretically
predicted triplet reentrant superconducting state, and that they are
responsible for melting the magnetic field induced Josephson vortex lattice
above a magnetic field dependent melting temperature Tm.Comment: 4 pages (double column), 1 eps figur
Nova praga exótica no ecossistema florestal.
O país está convivendo desde de junho de 2003 com mais uma séria praga de florestas de eucalipto, o psilídeode- concha, Glycaspis brimblecombei (Hemiptera: Psyllidae). Este inseto, de tamanho reduzido, é semelhante a uma cigarrinha que suga a seiva das folhas novas das árvores. A praga tem provocado danos às florestas de eucaliptos, e atualmente se encontra distribuída em mais de 140 municípios do Estado de São Paulo, em pelo menos 20 municípios de Minas Gerais, um de Goiás, dois de Mato Grosso do Sul e seis do Paraná.bitstream/CNPMA/5837/1/comunicado_18.pd
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