12,550 research outputs found
The thermal conductivity of alternating spin chains
We study a class of integrable alternating (S1,S2) quantum spin chains with
critical ground state properties. Our main result is the description of the
thermal Drude weight of the one-dimensional alternating spin chain as a
function of temperature. We have identified the thermal current of the model
with alternating spins as one of the conserved currents underlying the
integrability. This allows for the derivation of a finite set of non-linear
integral equations for the thermal conductivity. Numerical solutions to the
integral equations are presented for specific cases of the spins S1 and S2. In
the low-temperature limit a universal picture evolves where the thermal Drude
weight is proportional to temperature T and central charge c.Comment: 15 pages, 1 figur
The Noncommutative Anandan's Quantum Phase
In this work we study the noncommutative nonrelativistic quantum dynamics of
a neutral particle, that possesses permanent magnetic and electric dipole
momenta, in the presence of an electric and magnetic fields. We use the
Foldy-Wouthuysen transformation of the Dirac spinor with a non-minimal coupling
to obtain the nonrelativistic limit. In this limit, we will study the
noncommutative quantum dynamics and obtain the noncommutative Anandan's
geometric phase. We analyze the situation where magnetic dipole moment of the
particle is zero and we obtain the noncommutative version of the
He-McKellar-Wilkens effect. We demonstrate that this phase in the
noncommutative case is a geometric dispersive phase. We also investigate this
geometric phase considering the noncommutativity in the phase space and the
Anandan's phase is obtained.Comment: 15 pages, revtex4, version to appear in Physical Review
Noncommutative fields in three dimensions and mass generation
We apply the noncommutative fields method for gauge theory in three
dimensions where the Chern-Simons term is generated in the three-dimensional
electrodynamics. Under the same procedure, the Chern-Simons term is shown to be
cancelled in the Maxwell-Chern-Simons theory for the appropriate value of the
noncommutativity parameter. Hence the mutual interchange between
Maxwell-Chern-Simons theory and pure Maxwell theory turns out to be generated
within this method.Comment: Comments 5 pages, epl, version accepted for publication in
Europhysics Letter
Banco de sementes de café em criopreservação: experiência inédita no Brasil.
A conservação de sementes de café por longos períodos é dificultada pelo comportamento intermediário no armazenamento. No entanto, estudos recentes relatam que a partir da combinação de um grau crítico de umidade das sementes para cada temperatura de armazenamento, pode-se prolongar o período de conservação. Com o objetivo de estabelecer um Banco de Germoplasma de Coffea spp, através de técnicas de criopreservação, estudos vêm sendo desenvolvidos na Embrapa Recursos Genéticos e Biotecnologia, em Brasília, DF. O protocolo de conservação consta da desidratação parcial das sementes, até cerca de 20% de água, embalagem em sacos trifoliados de papel-alumínio-polietileno, selados hermeticamente e imersão direta no nitrogênio líquido. Após a criopreservação as sementes são descongeladas rapidamente em banho de água a 40°C, sob agitação constante. Os resultados obtidos até o momento, com cerca de 30 acessos de diferentes cultivares de Coffea arabica são bastante promissores, indicando a sobrevivência das sementes mesmo após períodos de dois anos de congelamento no nitrogênio líquido. A partir desses resultados será implantada uma core collection, ou uma pequena coleção com os principais acessos da espécie, constituindo-se o Banco de Germoplasma de café em criopreservação, experiência inédita no Brasil
Universal patterns in sound amplitudes of songs and music genres
We report a statistical analysis over more than eight thousand songs.
Specifically, we investigate the probability distribution of the normalized
sound amplitudes. Our findings seems to suggest a universal form of
distribution which presents a good agreement with a one-parameter stretched
Gaussian. We also argue that this parameter can give information on music
complexity, and consequently it goes towards classifying songs as well as music
genres. Additionally, we present statistical evidences that correlation aspects
of the songs are directly related with the non-Gaussian nature of their sound
amplitude distributions.Comment: Accepted for publication as a Brief Report in Physical Review
Structural network heterogeneities and network dynamics: a possible dynamical mechanism for hippocampal memory reactivation
The hippocampus has the capacity for reactivating recently acquired memories
[1-3] and it is hypothesized that one of the functions of sleep reactivation is
the facilitation of consolidation of novel memory traces [4-11]. The dynamic
and network processes underlying such a reactivation remain, however, unknown.
We show that such a reactivation characterized by local, self-sustained
activity of a network region may be an inherent property of the recurrent
excitatory-inhibitory network with a heterogeneous structure. The entry into
the reactivation phase is mediated through a physiologically feasible
regulation of global excitability and external input sources, while the
reactivated component of the network is formed through induced network
heterogeneities during learning. We show that structural changes needed for
robust reactivation of a given network region are well within known
physiological parameters [12,13].Comment: 16 pages, 5 figure
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