25,165 research outputs found
Chaos and a Resonance Mechanism for Structure Formation in Inflationary Models
We exhibit a resonance mechanism of amplification of density perturbations in
inflationary mo-dels, using a minimal set of ingredients (an effective
cosmological constant, a scalar field minimally coupled to the gravitational
field and matter), common to most models in the literature of inflation. This
mechanism is based on the structure of homoclinic cylinders, emanating from an
unstable periodic orbit in the neighborhood of a saddle-center critical point,
present in the phase space of the model. The cylindrical structure induces
oscillatory motions of the scales of the universe whenever the orbit visits the
neighborhood of the saddle-center, before the universe enters a period of
exponential expansion. The oscillations of the scale functions produce, by a
resonance mechanism, the amplification of a selected wave number spectrum of
density perturbations, and can explain the hierarchy of scales observed in the
actual universe. The transversal crossings of the homoclinic cylinders induce
chaos in the dynamics of the model, a fact intimately connected to the
resonance mechanism occuring immediately before the exit to inflation.Comment: 4 pages. This essay received an Honorable Mention from the Gravity
Research Foundation, 1998-Ed. To appear in Mod. Phys. Lett.
Fourier Eigenfunctions, Uncertainty Gabor Principle and Isoresolution Wavelets
Shape-invariant signals under Fourier transform are investigated leading to a
class of eigenfunctions for the Fourier operator. The classical uncertainty
Gabor-Heisenberg principle is revisited and the concept of isoresolution in
joint time-frequency analysis is introduced. It is shown that any Fourier
eigenfunction achieve isoresolution. It is shown that an isoresolution wavelet
can be derived from each known wavelet family by a suitable scaling.Comment: 6 pages, XX Simp\'osio Bras. de Telecomunica\c{c}\~oes, Rio de
Janeiro, Brazil, 2003. Fixed typo
Glassy behaviour in short range lattice models without quenched disorder
We investigate the quenching process in lattice systems with short range
interaction and several crystalline states as ground states. We consider in
particular the following systems on square lattice:
- hard particle (exclusion) model;
- q states planar Potts model.
The system is initially in a homogeneous disordered phase and relaxes toward
a new equilibrium state as soon as the temperature is rapidly lowered. The time
evolution can be described numerically by a stochastic process such as the
Metropolis algorithm. The number of pure, equivalent, ground states is q for
the Potts model and r for the hard particle model, and it is known that for r
or q larger or equal to d+1, the final equilibrium state may be
polycrystalline, i.e. not made of a uniform phase. We find that in addition n_g
and q_g exist such that for r > r_g, or q > q_g the system evolves toward a
glassy state, i.e. a state in which the ratio of the interaction energy among
the different crystalline phases to the total energy of the system never
vanishes; moreover we find indications that r_g=q_g. We infer that q=q_g (and
r=r_g) corresponds to the crossing from second order to discontinuous
transition in the phase diagram of the system.Comment: 10 pages, 3 figure
Operational Classification and Quantification of Multipartite Entangled States
We formalize and extend an operational multipartite entanglement measure
introduced by T. R. Oliveira, G. Rigolin, and M. C. de Oliveira, Phys. Rev. A
73, 010305(R) (2006), through the generalization of global entanglement (GE)
[D. A. Meyer and N. R. Wallach, J. Math. Phys. 43, 4273 (2002)]. Contrarily to
GE the main feature of this measure lies in the fact that we study the mean
linear entropy of all possible partitions of a multipartite system. This allows
the construction of an operational multipartite entanglement measure which is
able to distinguish among different multipartite entangled states that GE
failed to discriminate. Furthermore, it is also maximum at the critical point
of the Ising chain in a transverse magnetic field, being thus able to detect a
quantum phase transition.Comment: 14 pages, RevTex4, published versio
Enfezamentos em milho: expressão de sintomas foliares, detecção dos molicutes e interações com genótipos.
Com o objetivo de verificar a multiplicacao, expressao de sintomas foliares e efeito dos molicutes na producao de diferentes genotipos de milho, fitoplasma e Spiroplasma kunkelii foram inoculados, isolada ou simultaneamente, em cinco cultivares, mantidas em vasos ate a producao. Plantas sadias de todas as cultivares foram utilizadas como controle. Em cada vaso, foram cultivadas duas plantas, sendo uma utilizada para a deteccao dos molicutes na ultima folha completamente expandida, aos 30, 60 e 100 dias apos a inoculacao. A outra planta foi utilizada para deteccao dos molicutes nas folhas inferiores, medianas e apicais, aos 100 dias apos a inoculacao. O percentual de reducao causado pelos molicutes na altura e na producao de graos foi determinado nas duas plantas, em relacao as plantas sadias. A expressao de sintomas foliares e os resultados positivos obtidos na deteccao dos molicutes foram mais evidentes aos 100 dias apos a inoculacao. O periodo de enchimento de graos foi considerado a fase mais adequada para a deteccao desses patogenos. Os molicutes foram detectados nas folhas inferiores, medianas e apicais, observando-se maior frequencia nas folhas apicais. Verificou-se predominancia de infeccao por espiroplasma e maior efeito detrimental desse patogeno no crescimento e producao das plantas em relacao ao fitoplasma. Nao foi detectado efeito sinergistico significativo dos dois molicutes sobre o crescimento e producao das plantas. Observou-se que o efeito prejudicial desses patogenos sobre o crescimento e producao das cultivares foi determinado pela frequencia de plantas infectadas
Biossíntese e degradação de Lipídios, Carboidratos e Proteínas em oleaginosas.
Fisiologia vegetal; Metabolismo vegetal;bitstream/CNPA/21023/1/DOC178.pd
Oleaginosas e seus óleos: vantagens e desvantagens para produção de biodiesel.
bitstream/CNPA-2009-09/22146/1/DOC201.pd
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