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.

Produção e distribuição de biomassa de espécies arbóreas no Semi-Árido brasileiro.

Com o objetivo de avaliar a produção e distribuição de biomassa de algumas espécies arbóreas de múltiplo uso em condições de sequeiro do submédio do São Francisco, instalou-se um experimento no Campo Experimental da Caatinga da Embrapa Semi-Árido, Município de Petrolina, PE. Foram realizadas medições de altura e diâmetro à altura do peito (DAP) de 16 árvores centrais, em três parcelas de cada espécie: Leucaena diversifolia, Caesalpinia velutina, Caesalpinia coriaria, Mimosa tenuiflora e Ateleia herbert-smithii. A biomassa foi estimada com base na árvore de altura média de cada parcela, avaliando-se, separadamente, cada componente (folhas, galhos, cascas e lenho). A biomassa nos diferentes componentes arbóreos das espécies foi distribuída na seguinte ordem: folha<casca<galho<raiz<lenho, excetuando-se A. herbert-smithii, que produziu mais folha do que casca. A produção de biomassa total foi superior em C. velutina (51,6 kg ha-1), seguida por L. diversifolia (36,6 kg ha-1), A. herbert-smithii (26,4 kg ha-1), Caesalpinia coriaria (23,0 kg ha-1) e Mimosa tenuiflora (21,6 kg ha-1). Entretanto, a matéria seca foliar, que é o principal componente forrageiro das espécies, foi maior em C. velutina (3,7 kg ha-1), vindo em seguida A. herbert-smithii (2,8 kg ha-1) e C. coriaria (2,2 kg ha-1), L. diversifolia (2,0 kg ha-1) e M. tenuiflora (1,3 kg ha-1), representando, respectivamente, 7,2; 10,7; 9,5; 5,3; e 6,3% da biomassa total. C. velutina destacou-se por ser a mais produtiva, tanto como madeireira (lenho=30,8 t ha-1) quanto forrageira (folhas = 3,7 t ha-1), enquanto a M. tenuiflora foi a de menor potencial forrageiro

Integrated mango production in Brazil to enhancing production systems, quality, and safety of fruit.

The development and implementation of ecosystem-based technologies in plant protection have been important objectives of the International Organization for Biological Control (IOBC). Integrated Production/lntegrated Farming is a system that produces high quality and safe food and other products by using natural resources and regulating mechanisms to replace polluting inputs and to secure sustainable farming. The objectives and principles of Integrated Production (IP) are based in a holistic view of the system, combining strategies such as Integrated Pest Management (IPM), safety, fertilization, and agronomic measures to enhance their effectiveness

A comparative study for the pair-creation contact process using series expansions

A comparative study between two distinct perturbative series expansions for the pair-creation contact process is presented. In contrast to the ordinary contact process, whose supercritical series expansions provide accurate estimates for its critical behavior, the supercritical approach does not work properly when applied to the pair-creation process. To circumvent this problem a procedure is introduced in which one-site creation is added to the pair-creation. An alternative method is the generation of subcritical series expansions which works even for the case of the pure pair-creation process. Differently from the supercritical case, the subcritical series yields estimates that are compatible with numerical simulations

Potencial energético de área conservada de caatinga em Petrolina-PE.

O objetivo deste trabalho foi avaliar o potencial energético por meio do estoque de Carbono e biomassa de algumas espécies arbóreas de uma área conservada de caatinga em Petrolina ? PE