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.

Caracterização do meio físico da Bacia Hidrográfica do Rio da Prata, Mato Grosso do Sul.

Caracterização do meio físico; Localização; Altimetria; Solos; Recursos hídricos.bitstream/item/38332/1/DOC41.pd

Plantas daninhas associadas às cochonilhas-farinhentas (Hemiptera: Pseudococcidae) em áreas de videira no semiárido brasileiro.

O objetivo deste trabalho foi identificar as espécies de plantas daninhas associadas às cochonilhas-farinhentas em plantios de videira