7,891 research outputs found
Dynamics of CP^1 lumps on a cylinder
The slow dynamics of topological solitons in the CP^1 sigma-model, known as
lumps, can be approximated by the geodesic flow of the L^2 metric on certain
moduli spaces of holomorphic maps. In the present work, we consider the
dynamics of lumps on an infinite flat cylinder, and we show that in this case
the approximation can be formulated naturally in terms of regular Kaehler
metrics. We prove that these metrics are incomplete exactly in the multilump
(interacting) case. The metric for two-lumps can be computed in closed form on
certain totally geodesic submanifolds using elliptic integrals; particular
geodesics are determined and discussed in terms of the dynamics of interacting
lumps.Comment: 35 pages, 10 figure
The singularity problem and phase-space noncanonical noncommutativity
The Wheeler-DeWitt equation arising from a Kantowski-Sachs model is
considered for a Schwarzschild black hole under the assumption that the scale
factors and the associated momenta satisfy a noncanonical noncommutative
extension of the Heisenberg-Weyl algebra. An integral of motion is used to
factorize the wave function into an oscillatory part and a function of a
configuration space variable. The latter is shown to be normalizable using
asymptotic arguments. It is then shown that on the hypersufaces of constant
value of the argument of the wave function's oscillatory piece, the probability
vanishes in the vicinity of the black hole singularity.Comment: 4 pages, revtex
Laser-light scattering approach to peptide–membrane interaction
© International University Line, 2010Membrane-active peptides are becoming widely used, mainly due to their high therapeutic potential. Although the therapeutic action is characterized, the mechanisms of interaction are often unclear or controversial. In biophysical studies, non-invasive techniques are overlooked when studying the effect of peptides on membranes. Light scattering techniques, such as dynamic light scattering and static light scattering, can be used as tools to determine whether promotion of membrane aggregation in the presence of peptides and of self-peptide aggregation in solution occurs. More recently, light scattering has been used for evaluating the alteration on membrane surface charge (ζ-potential) promoted by membrane–peptide interactions. The data obtained by these techniques (either by themselves or combined with complementary experimental approaches) therefore yield valuable elucidations of membrane-active peptides’ mechanisms of action at the molecular level.This work was partially supported by the Fundação para a Ciência e Tecnologia (FCT) of the Portuguese Ministry of Science, Technology and Higher Education. M.M.D. acknowledges the grant SFRH/BD/41750/2007 from FCT
Stationary scalar and vector clouds around Kerr-Newman black holes
Massive bosons in the vicinity of Kerr-Newman black holes can form pure bound
states when their phase angular velocity fulills the synchronisation condition,
i.e. at the threshold of superradiance. The presence of these stationary clouds
at the linear level is intimately linked to the existence of Kerr black holes
with synchronised hair at the non-linear level. These configurations are very
similar to the atomic orbitals of the electron in a hydrogen atom. They can be
labeled by four quantum numbers: , the number of nodes in the radial
direction; , the orbital angular momentum; , the total angular
momentum; and , the azimuthal total angular momentum. These synchronised
configurations are solely allowed for particular values of the black hole's
mass, angular momentum and electric charge. Such quantization results in an
existence surface in the three-dimensional parameter space of Kerr-Newman black
holes. The phenomenology of stationary scalar clouds has been widely addressed
over the last years. However, there is a gap in the literature concerning their
vector cousins. Following the separability of the Proca equation in
Kerr(-Newman) spacetime, this work explores and compares scalar and vector
stationary clouds around Kerr and Kerr-Newman black holes, extending previous
research.Comment: 17 pages, 6 figures. Contribution to Selected Papers of the Fifth
Amazonian Symposium on Physics (accepted in IJMPD
Sources of gains from international portfolio diversification.
This paper looks at the determinants of country and industry specific factors in international portfolio returns using a sample of thirty-six countries and thirty-nine industries over the last three decades. Country factors have remained relatively stable over the sample period, while industry factors have significantly increased during the last decade. The importance of industry and country factors is correlated with measures of economic and financial international integration and development. Country factors are smaller for countries integrated in world financial markets and have declined as the degree of financial integration and the number of countries pursuing financial liberalizations has increased. Higher international financial integration within an industry increases the importance of industry factors in explaining returns. Economic integration of production also helps in explaining returns. Countries with a more specialized production activity have higher country factors.International diversification; Country/Industry effects; Financial integration;
Efficient algorithm to study interconnected networks
Interconnected networks have been shown to be much more vulnerable to random
and targeted failures than isolated ones, raising several interesting questions
regarding the identification and mitigation of their risk. The paradigm to
address these questions is the percolation model, where the resilience of the
system is quantified by the dependence of the size of the largest cluster on
the number of failures. Numerically, the major challenge is the identification
of this cluster and the calculation of its size. Here, we propose an efficient
algorithm to tackle this problem. We show that the algorithm scales as O(N log
N), where N is the number of nodes in the network, a significant improvement
compared to O(N^2) for a greedy algorithm, what permits studying much larger
networks. Our new strategy can be applied to any network topology and
distribution of interdependencies, as well as any sequence of failures.Comment: 5 pages, 6 figure
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