Effective action in DSR1 quantum field theory

We present the one-loop effective action of a quantum scalar field with DSR1 space-time symmetry as a sum over field modes. The effective action has real and imaginary parts and manifest charge conjugation asymmetry, which provides an alternative theoretical setting to the study of the particle-antiparticle asymmetry in nature.Comment: 8 page

Effective field theory for models defined over small-world networks. First and second order phase transitions

We present an effective field theory method to analyze, in a very general way, models defined over small-world networks. Even if the exactness of the method is limited to the paramagnetic regions and to some special limits, it provides, yielding a clear and immediate (also in terms of calculation) physical insight, the exact critical behavior and the exact critical surfaces and percolation thresholds. The underlying structure of the non random part of the model, i.e., the set of spins filling up a given lattice L_0 of dimension d_0 and interacting through a fixed coupling J_0, is exactly taken into account. When J_0\geq 0, the small-world effect gives rise, as is known, to a second-order phase transition that takes place independently of the dimension d_0 and of the added random connectivity c. When J_0<0, a different and novel scenario emerges in which, besides a spin glass transition, multiple first- and second-order phase transitions may take place. As immediate analytical applications we analyze the Viana-Bray model (d_0=0), the one dimensional chain (d_0=1), and the spherical model for arbitrary d_0.Comment: 28 pages, 18 figures; merged version of the manuscripts arXiv:0801.3454 and arXiv:0801.3563 conform to the published versio

Fenologia da floração e frutificação da bracatinga.

Edição dos Anais do Congresso Florestal Brasileiro, 6., 1990, Campos do Jordão

k-core (bootstrap) percolation on complex networks: Critical phenomena and nonlocal effects

We develop the theory of the k-core (bootstrap) percolation on uncorrelated random networks with arbitrary degree distributions. We show that the k-core percolation is an unusual, hybrid phase transition with a jump emergence of the k-core as at a first order phase transition but also with a critical singularity as at a continuous transition. We describe the properties of the k-core, explain the meaning of the order parameter for the k-core percolation, and reveal the origin of the specific critical phenomena. We demonstrate that a so-called ``corona'' of the k-core plays a crucial role (corona is a subset of vertices in the k-core which have exactly k neighbors in the k-core). It turns out that the k-core percolation threshold is at the same time the percolation threshold of finite corona clusters. The mean separation of vertices in corona clusters plays the role of the correlation length and diverges at the critical point. We show that a random removal of even one vertex from the k-core may result in the collapse of a vast region of the k-core around the removed vertex. The mean size of this region diverges at the critical point. We find an exact mapping of the k-core percolation to a model of cooperative relaxation. This model undergoes critical relaxation with a divergent rate at some critical moment.Comment: 11 pages, 8 figure

Conhecimento, inovação e emprego

"Numa região pequena, geograficamente dispersa e ultra-periférica, onde quase tudo é limitado, o desempenho intelectual e a capacidade de adquirir conhecimento dos seus cidadãos, e portanto inovar, não deve ser restringida. Assim, uma reflexão, mesmo que superficial, sobre a constante turbulência verificada na Ciência e na Tecnologia, permite concluir que uma revisão da oferta de formação e emprego é imperativa. […]"

Conhecimento, inovação e emprego

"Numa região pequena, geograficamente dispersa e ultra-periférica, onde quase tudo é limitado, o desempenho intelectual e a capacidade de adquirir conhecimento dos seus cidadãos, e portanto inovar, não deve ser restringida. Assim, uma reflexão, mesmo que superficial, sobre a constante turbulência verificada na Ciência e na Tecnologia, permite concluir que uma revisão da oferta de formação e emprego é imperativa. […]"