11,765 research outputs found
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. […]"
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