Alternate islands of multiple isochronous chains in wave-particle interactions

We analyze the dynamics of a relativistic particle moving in a uniform magnetic field and perturbed by a standing electrostatic wave. We show that a pulsed wave produces an infinite number of perturbative terms with the same winding number, which may generate islands in the same region of phase space. As a consequence, the number of isochronous island chains varies as a function of the wave parameters. We observe that in all the resonances, the number of chains is related to the amplitude of the various resonant terms. We determine analytically the position of the periodic points and the number of island chains as a function of the wave number and wave period. Such information is very important when one is concerned with regular particle acceleration, since it is necessary to adjust the initial conditions of the particle to obtain the maximum acceleration.Comment: Submitte

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

Alimentação dos peixes detritívoros da Baía Tuiuiú, rio Paraguai, Pantanal de Mato Grosso do Sul, Brasil.

Foram analisadas as dietas dos peixes detritívoros da baía Tuiuiú, meandro abandonado do rio Paraguai, próximo a Corumbá, Mato Grosso do Sul. Os peixes detritívoros apresentam estratégias específicas para o consumo do detrito orgânico existente na baía, como o sairu-boi, Potamorhina squamoralevis, que possui os olhos voltados para baixo para consumo do detrito acumulado no fundo, e o cascudo, Liposarcus anisitsi, que se coloca de barriga para cima para raspar os detritos e algas acumuladas nas raízes das macrófitas aquáticas. Para L. anisitsi, que teve os conteúdos estomacais analisados em quase todos os períodos de amostragem, foi encontrada correlação entre índice alimentar e altura de inundação e transparência da água. Peixes detritívoros apresentam adaptações e estratégias específicas para alimentar-se desse tipo especial de alimento nos ambientes inundáveis do Pantanal. Detritus feeding fishes from Tuiuiú bay, an oxbow lake of Paraguay River, near Corumbá city, Mato Grosso do Sul State were evaluated. Detritus feeding fishes have specific strategies to take this kind of food in the environment. Potamorhina squamoralevis has its eyes directed to the bottom to feed on detritus accumulated in the bay bottom while Liposarcus anisitsi, stay with the belly to the surface in order to scrape detritus and algae from the macrophyte roots. Correlations were found to alimentary index of L. anistisi in relation to river height and water transparency. Detritus feeding fishes have specific adaptations and strategies to take this kind of food in floodable environments in the Pantanal.bitstream/item/68605/1/BP115.pd

Semiclassical Evolution of Dissipative Markovian Systems

A semiclassical approximation for an evolving density operator, driven by a "closed" hamiltonian operator and "open" markovian Lindblad operators, is obtained. The theory is based on the chord function, i.e. the Fourier transform of the Wigner function. It reduces to an exact solution of the Lindblad master equation if the hamiltonian operator is a quadratic function and the Lindblad operators are linear functions of positions and momenta. Initially, the semiclassical formulae for the case of hermitian Lindblad operators are reinterpreted in terms of a (real) double phase space, generated by an appropriate classical double Hamiltonian. An extra "open" term is added to the double Hamiltonian by the non-hermitian part of the Lindblad operators in the general case of dissipative markovian evolution. The particular case of generic hamiltonian operators, but linear dissipative Lindblad operators, is studied in more detail. A Liouville-type equivariance still holds for the corresponding classical evolution in double phase, but the centre subspace, which supports the Wigner function, is compressed, along with expansion of its conjugate subspace, which supports the chord function. Decoherence narrows the relevant region of double phase space to the neighborhood of a caustic for both the Wigner function and the chord function. This difficulty is avoided by a propagator in a mixed representation, so that a further "small-chord" approximation leads to a simple generalization of the quadratic theory for evolving Wigner functions.Comment: 33 pages - accepted to J. Phys.

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.

Quantization of multidimensional cat maps

In this work we study cat maps with many degrees of freedom. Classical cat maps are classified using the Cayley parametrization of symplectic matrices and the closely associated center and chord generating functions. Particular attention is dedicated to loxodromic behavior, which is a new feature of two-dimensional maps. The maps are then quantized using a recently developed Weyl representation on the torus and the general condition on the Floquet angles is derived for a particular map to be quantizable. The semiclassical approximation is exact, regardless of the dimensionality or of the nature of the fixed points.Comment: 33 pages, latex, 6 figures, Submitted to Nonlinearit

Hidrólise de diacetato de fluoresceína como bioindicador da qualidade de solo de várzea subtropical.

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Hyperbolic Scar Patterns in Phase Space

We develop a semiclassical approximation for the spectral Wigner and Husimi functions in the neighbourhood of a classically unstable periodic orbit of chaotic two dimensional maps. The prediction of hyperbolic fringes for the Wigner function, asymptotic to the stable and unstable manifolds, is verified computationally for a (linear) cat map, after the theory is adapted to a discrete phase space appropriate to a quantized torus. The characteristic fringe patterns can be distinguished even for quasi-energies where the fixed point is not Bohr-quantized. The corresponding Husimi function dampens these fringes with a Gaussian envelope centered on the periodic point. Even though the hyperbolic structure is then barely perceptible, more periodic points stand out due to the weakened interference.Comment: 12 pages, 10 figures, Submited to Phys. Rev.

Perceptions of future leaders towards business ethics and sustainability

This paper examines the perception of business students (BS) concerning business ethics (BE) and sustainable operations management (SOM), in cases reporting ethical dilemmas. The BS have not previously attended any specific course, either dealing with BE, SOM or providing training in ethics. A test administered to 60 BS enabled to picture perceptions regarding: (i) ethical maturity level based on general education/personal sensitivity; and (ii) ethical decision-making processes of BS. The study also determined that BS have a surprisingly high ethical maturity. However, they are not sensitive to BE/SOM scientific’ research importance. Findings point out to development of Business School curricula