3,311 research outputs found
Ultracold heteronuclear molecules and ferroelectric superfluids
We analyze the possibility of a ferroelectric transition in heteronuclear
molecules consisting of Bose-Bose, Bose-Fermi or Fermi-Fermi atom pairs. This
transition is characterized by the appearance of a spontaneous electric
polarization below a critical temperature. We discuss the existence of a
ferroelectric Fermi liquid phase for Fermi molecules and the existence of a
ferroelectric superfluid phase for Bose molecules characterized by the
coexistence of ferroelectric and superfluid orders. Lastly, we propose an
experiment to detect ferroelectric correlations through the observation of
coherent dipole radiation pulses during time of flight.Comment: 4 pages and 3 figure
Entrada de nutrientes no solo pela água da chuva, e contribuição no processo da fitomassa aérea de capoeiras de diferente idades.
A entrada de nutrientes pela água da chuva em capoeiras com cinco e onze anos de idade. no nordeste paraense, foi avaliada em duas épocas do ano. A entrada dos nutrientes foi decomposta em: quantidades carreadas pela água da chuva (lNC), interceptação pela vegetação secundária. "throughfall"(THF), "stemflow''(Sf') e a lixiviação {(THF+SF)-( 1.25xINC)} As análises químicas foram obtidas pelos métodos usuais do Institut Iür Bodenkunde und Waldcmãrung. A chuva interna bruta mostrou um acréscimo nas quantidades de K, Na, Ca, Mg, e Si nas duas áreas estudadas, mesmo levando em consideração a concentração relativa causada pela interceptação da fitomassa. O incremento foi atribuído à liberação de nutrientes pelas folhas. às deposições de poeiras e excrementos da fauna entomológica. Da mesma forma, o incremento de S-So.4" e de nitrogênio orgânico, responsável pelo teor deste elemento no sistema, foi atribuído às perdas da vegetação. Com exceção do potássio em uma das épocas de coleta e do sódio. os demais elementos analisados evidenciam maior incremento na chuva interna da capoeira com onze anos mostrando a importância da fitomassa no sistema. A maior quantidade de sódio lixiviado na capoeira com cinco anos foi atribuída a algumas espécies encontradas na área.Editado por J. E. Péfaur
Thermodynamically stable noncomposite vortices in mesoscopic two-gap superconductors
In mesoscopic two-gap superconductors with sizes of the order of the
coherence length noncomposite vortices are found to be thermodynamically stable
in a large domain of the phase diagram. In these phases the vortex
cores of one condensate are spatially separated from the other condensate ones,
and their respective distributions can adopt distinct symmetries. The
appearance of these vortex phases is caused by a non-negligible effect of the
boundary of the sample on the superconducting order parameter and represents
therefore a genuine mesoscopic effect. For low values of interband Josephson
coupling vortex patterns with can arise in addition to the
phases with , where and are total vorticities in the two
condensates. The calculations show that noncomposite vortices could be observed
in thin mesoscopic samples of MgB.Comment: 5 pages, 3 figures, to be published in Europhysics Letter
Correlation equalities and upper bounds for the transverse Ising model
Starting from an exact formal identity for the two-state transverse Ising
model and using correlation inequalities rigorous upper bounds for the critical
temperature and the critical transverse field are obtained which improve
effective results.Comment: 8 pages, 1 figur
Nonzero orbital angular momentum superfluidity in ultracold Fermi gases
We analyze the evolution of superfluidity for nonzero orbital angular
momentum channels from the Bardeen-Cooper-Schrieffer (BCS) to the Bose-Einstein
condensation (BEC) limit in three dimensions. First, we analyze the low energy
scattering properties of finite range interactions for all possible angular
momentum channels. Second, we discuss ground state () superfluid
properties including the order parameter, chemical potential, quasiparticle
excitation spectrum, momentum distribution, atomic compressibility, ground
state energy and low energy collective excitations. We show that a quantum
phase transition occurs for nonzero angular momentum pairing, unlike the s-wave
case where the BCS to BEC evolution is just a crossover. Third, we present a
gaussian fluctuation theory near the critical temperature (),
and we analyze the number of bound, scattering and unbound fermions as well as
the chemical potential. Finally, we derive the time-dependent Ginzburg-Landau
functional near , and compare the Ginzburg-Landau coherence length
with the zero temperature average Cooper pair size.Comment: 28 pages and 24 figure
Nanostructured natural-based polyelectrolyte multilayers to agglomerate chitosan particles into scaffolds for tissue engineering
The Layer-by-Layer (LbL) deposition technique is a self-assembly process that allows the coating of material's surface with nanostructured layers of polyelectrolytes, allowing to control several surface properties. This technique presents some advantages when compared with other thin film assembly techniques like having the possibility to coat surfaces with complex geometries in mild conditions or to incorporate active compounds. Tissue engineering involves typically the use of porous biodegradable scaffolds for the temporary support of cells. Such structures can be produced by agglomeration of micro-spheres that needs to be fixed into a three dimensional structure. In this work we suggest the use of LbL to promote such mechanical fixation in free-formed micro-spheres assemblies and simultaneously to control the properties of its surface. For the proof of concept the biological performance of chitosan/alginate multilayers is first investigated in two-dimensional models in which the attachment and proliferation of L929 and ATDC5 cells are studied in function of the number of layers and the nature of the final layer. Scaffolds prepared by agglomeration of chitosan particles using the same multilayered system were processed and characterized; it was found that they could support the attachment and proliferation of ATDC5 cells. This study suggests that LbL can be used as a versatile methodology to prepare scaffolds by particle agglomeration that could be suitable for tissue engineering applications.Fundo Europeu de Desenvolvimento Regional (FEDER) através do Programa Operacional de Cooperação Transfronteiriça Espanha Portugal 2007-2013 (POCTEP)Fundação para a Ciência e a Tecnologia (FCT
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