9,641 research outputs found
Decoherence of Semiclassical Wigner Functions
The Lindblad equation governs general markovian evolution of the density
operator in an open quantum system. An expression for the rate of change of the
Wigner function as a sum of integrals is one of the forms of the Weyl
representation for this equation. The semiclassical description of the Wigner
function in terms of chords, each with its classically defined amplitude and
phase, is thus inserted in the integrals, which leads to an explicit
differential equation for the Wigner function. All the Lindblad operators are
assumed to be represented by smooth phase space functions corresponding to
classical variables. In the case that these are real, representing hermitian
operators, the semiclassical Lindblad equation can be integrated. There results
a simple extension of the unitary evolution of the semiclassical Wigner
function, which does not affect the phase of each chord contribution, while
dampening its amplitude. This decreases exponentially, as governed by the time
integral of the square difference of the Lindblad functions along the classical
trajectories of both tips of each chord. The decay of the amplitudes is shown
to imply diffusion in energy for initial states that are nearly pure.
Projecting the Wigner function onto an orthogonal position or momentum basis,
the dampening of long chords emerges as the exponential decay of off-diagonal
elements of the density matrix.Comment: 23 pg, 2 fi
Replica analysis of the generalized p-spin interaction glass model
We investigate stability of replica symmetry breaking solutions in
generalized -spin models. It is shown that the kind of the transition to the
one-step replica symmetry breaking state depends not only on the presence or
absence of the reflection symmetry of the generalized "spin"-operators
but on the number of interacting operators and their individual
characteristics.Comment: 14 pages, 1 figur
Efeito da temperatura no crescimento de Xanthomonas axonopodis pv. passiflorae e Xanthomonas axonopodis pv. manihotis.
Bactérias do gênero Xanthomonas apresentam uma diversidade na gama de hospedeiros, causando sérios prejuízos em todas as regiões do Brasil. Xanthomonas axonopodis pv. passiflorae (Xap) e Xanthomonas axonopodis pv. manihotis (Xam) são responsáveis pelas bacterioses nas culturas do maracujá e da mandioca, respectivamente. O presente trabalho teve como objetivo avaliar o efeito de diferentes temperaturas sobre o crescimento de Xap e Xam. Foram avaliadas as temperaturas de 15ºC, 20ºC, 25ºC, 30ºC, 35°C e 40°C através da contagem de Unidades formadoras de colônia de patógeno após 48 horas de incubação. Para cada patógeno, o delineamento experimental foi inteiramente casualizado com 6 tratamentos e 10 repetições. Observou-se efeito da temperatura sobre o crescimento de ambas as bactérias fitopatogênicas, as quais cresceram no intervalo entre 25°C e 35°C. O crescimento bacteriano de ambos patógenos apresentou comportamento quadrático, sendo que os valores de temperatura ótima foram obtidos pela derivada da equação de regressão. O crescimento ótimo de Xap foi observado a 29,01°C, enquanto o de Xam foi observado a 28,38°C. Para os dois patógenos estudados não houve crescimento nas temperaturas de 15°C, 20°C e 40ºC
Sistemas de Integração lavoura-pecuária-floresta (iLPF)- Experiências no BRASIL.
Resumo: Os sistemas de integração lavoura-pecuária-floresta são sustentáveis e a escolha do sistema adequado à determinada localidade depende das condições edafo-climáticas e da existência de infraestrutura para suprimento de insumos, armazenagem e escoamento da produção. A produtividade e a rentabilidade são três vezes maiores para a pecuária de corte e de 10 a 30% para as lavouras de grãos em relação aos sistemas tradicionais de produção. Por outro lado, observa-se nos sistemas mais complexos (com uso de componente arbóreo) o aumento do bem-estar animal e a mitigação de gases de efeito estufa. [Systems integration crop-livestock-forest (ICLF) - Experiences in Brazil]. Abstract: The integrated crop-livestock-forest systems are sustainable and the choice of the appropriate system to a given locality depends on the soil and climatic conditions and the availability of infrastructure for input supply, storage and transportation of production. Productivity and profitability are three times higher for beef cattle and 10-30% for grain crops relative to traditional production systems. On the other hand it is observed in more complex systems (using the tree component) animal welfare increase and mitigation of greenhouse gases
Diluted antiferromagnet in a ferromagnetic enviroment
The question of robustness of a network under random ``attacks'' is treated
in the framework of critical phenomena. The persistence of spontaneous
magnetization of a ferromagnetic system to the random inclusion of
antiferromagnetic interactions is investigated. After examing the static
properties of the quenched version (in respect to the random antiferromagnetic
interactions) of the model, the persistence of the magnetization is analysed
also in the annealed approximation, and the difference in the results are
discussed
Acute and chronic stress differentially regulate cyclin-dependent kinase 5 in mouse brain: implications to glucocorticoid actions and major depression
Stress activates the hypothalamic–pituitary–adrenal axis, which in turn increases circulating glucocorticoid concentrations and stimulates the glucocorticoid receptor (GR). Chronically elevated glucocorticoids by repetitive exposure to stress are implicated in major depression and anxiety disorders. Cyclin-dependent kinase 5 (CDK5), a molecule essential for nervous system development, function and pathogenesis of neurodegenerative disorders, can modulate GR activity through phosphorylation. We examined potential contribution of CDK5 to stress response and pathophysiology of major depression. In mice, acute immobilized stress (AS) caused a biphasic effect on CDK5 activity, initially reducing but increasing afterwards in prefrontal cortex (PFC) and hippocampus (HIPPO), whereas chronic unpredictable stress (CS) strongly increased it in these brain areas, indicating that AS and CS differentially regulate this kinase activity in a brain region-specific fashion. GR phosphorylation contemporaneously followed the observed changes of CDK5 activity after AS, thus CDK5 may in part alter GR phosphorylation upon this stress. In the postmortem brains of subjects with major depression, CDK5 activity was elevated in Brodmann's area 25, but not in entire PFC and HIPPO. Messenger RNA expression of glucocorticoid-regulated/stress-related genes showed distinct expression profiles in several brain areas of these stressed mice or depressive subjects in which CDK5-mediated changes in GR phosphorylation may have some regulatory roles. Taken together, these results indicate that CDK5 is an integral component of stress response and major depression with regulatory means specific to different stressors, brain areas and diseases in part through changing phosphorylation of GR
A typical reconstruction limit of compressed sensing based on Lp-norm minimization
We consider the problem of reconstructing an -dimensional continuous
vector \bx from constraints which are generated by its linear
transformation under the assumption that the number of non-zero elements of
\bx is typically limited to (). Problems of this
type can be solved by minimizing a cost function with respect to the -norm
||\bx||_p=\lim_{\epsilon \to +0}\sum_{i=1}^N |x_i|^{p+\epsilon}, subject to
the constraints under an appropriate condition. For several , we assess a
typical case limit , which represents a critical relation
between and for successfully reconstructing the original
vector by minimization for typical situations in the limit
with keeping finite, utilizing the replica method. For ,
is considerably smaller than its worst case counterpart, which
has been rigorously derived by existing literature of information theory.Comment: 12 pages, 2 figure
Avaliacão e caracterizacão de exopolissacarideos por bactérias isoladas de esponjas marinhas do arquipélago São Pedro e São Paulo.
On FO2 quantifier alternation over words
We show that each level of the quantifier alternation hierarchy within
FO^2[<] -- the 2-variable fragment of the first order logic of order on words
-- is a variety of languages. We then use the notion of condensed rankers, a
refinement of the rankers defined by Weis and Immerman, to produce a decidable
hierarchy of varieties which is interwoven with the quantifier alternation
hierarchy -- and conjecturally equal to it. It follows that the latter
hierarchy is decidable within one unit: given a formula alpha in FO^2[<], one
can effectively compute an integer m such that alpha is equivalent to a formula
with at most m+1 alternating blocks of quantifiers, but not to a formula with
only m-1 blocks. This is a much more precise result than what is known about
the quantifier alternation hierarchy within FO[<], where no decidability result
is known beyond the very first levels
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