12,300 research outputs found
Bent-Double Radio Sources as Probes of Intergalactic Gas
As the most common environment in the universe, groups of galaxies are likely
to contain a significant fraction of the missing baryons in the form of
intergalactic gas. The density of this gas is an important factor in whether
ram pressure stripping and strangulation affect the evolution of galaxies in
these systems. We present a method for measuring the density of intergalactic
gas using bent-double radio sources that is independent of temperature, making
it complementary to current absorption line measurements. We use this method to
probe intergalactic gas in two different environments: inside a small group of
galaxies as well as outside of a larger group at a 2 Mpc radius and measure
total gas densities of and per cubic centimeter (random and systematic
errors) respectively. We use X-ray data to place an upper limit of K on the temperature of the intragroup gas in the small group.Comment: 6 pages, 1 figure, accepted for publication in Ap
Electromagnetic waves around dilatonic stars and naked singularities
We study the propagation of classical electromagnetic waves on the simplest
four-dimensional spherically symmetric metric with a dilaton background field.
Solutions to the relevant equations are obtained perturbatively in a parameter
which measures the strength of the dilaton field (hence parameterizes the
departure from Schwarzschild geometry). The loss of energy from outgoing modes
is estimated as a back-scattering process against the dilaton background, which
would affect the luminosity of stars with a dilaton field. The radiation
emitted by a freely falling point-like source on such a background is also
studied by analytical and numerical methods.Comment: 9 pages, 1 figur
Localization properties of a tight-binding electronic model on the Apollonian network
An investigation on the properties of electronic states of a tight-binding
Hamiltonian on the Apollonian network is presented. This structure, which is
defined based on the Apollonian packing problem, has been explored both as a
complex network, and as a substrate, on the top of which physical models can
defined. The Schrodinger equation of the model, which includes only nearest
neighbor interactions, is written in a matrix formulation. In the uniform case,
the resulting Hamiltonian is proportional to the adjacency matrix of the
Apollonian network. The characterization of the electronic eigenstates is based
on the properties of the spectrum, which is characterized by a very large
degeneracy. The rotation symmetry of the network and large number of
equivalent sites are reflected in all eigenstates, which are classified
according to their parity. Extended and localized states are identified by
evaluating the participation rate. Results for other two non-uniform models on
the Apollonian network are also presented. In one case, interaction is
considered to be dependent of the node degree, while in the other one, random
on-site energies are considered.Comment: 7pages, 7 figure
The pros and cons of using SDL for creation of distributed services
In a competitive market for the creation of complex distributed services, time to market, development cost, maintenance and flexibility are key issues. Optimizing the development process is very much a matter of optimizing the technologies used during service creation. This paper reports on the experience gained in the Service Creation projects SCREEN and TOSCA on use of the language SDL for efficient service creation
Entropy Maximization in the Presence of Higher-Curvature Interactions
Within the context of the entropic principle, we consider the entropy of
supersymmetric black holes in N=2 supergravity theories in four dimensions with
higher-curvature interactions, and we discuss its maximization at points in
moduli space at which an excess of hypermultiplets becomes massless. We find
that the gravitational coupling function F^(1) enhances the maximization at
these points in moduli space. In principle, this enhancement may be modified by
the contribution from higher F^(g)-couplings. We show that this is indeed the
case for the resolved conifold by resorting to the non-perturbative expression
for the topological free energy.Comment: 22 pages, 8 figures, AMS-LaTe
On computing real logarithms for matrices in the Lie group of special Euclidean motions in Rn
We show that the diagonal Pade approximants methods, both for computing
the principal logarithm of matrices belonging to the Lie groupSE (n, IR) of special
Euclidean motions in IRn and to compute the matrix exponential of elements in
the corresponding Lie algebra se(n, IR), are structure preserving. Also, for the
particular cases when n == 2,3 we present an alternative closed form to compute
the principal logarithm. These low dimensional Lie groups play an important
role in the kinematic motion of many mechanical systems and, for that reason,
the results presented here have immediate applications in robotic
Nitrogen applied in okra under non-tightness grown and residual fertilization.
The aim of this study was to evaluate, in the Amazonian rainy season, the effect of nitrogen applied in okra under non-tightness grown and residual fertilization
Padé and Gregory error estimates for the logarithm of block triangular matrices
In this paper we give bounds for the error arising in the approximation of the logarithm of a block triangular matrix T by Padé approximants of the function f(x)=log[(1+x)/(1-x)] and partial sums of Gregory's series. These bounds show that if the norm of all diagonal blocks of the Cayley-transform B=(T-I)(T+I)-1 is sufficiently close to zero, then both approximation methods are accurate. This will contribute for reducing the number of successive square roots of T needed in the inverse scaling and squaring procedure for the matrix logarithm.http://www.sciencedirect.com/science/article/B6TYD-4G5BJ9P-2/1/398a212a906943d2474a2cd6166c1d3
Metodologia para estimação do mérito genético de animais com paternidade incerta sob inferência bayesiana.
Modelo animal reduzido com efeito materno; Modelo hierárquico bayesiano para paternidade incerta; Validação por simulação; Análise de dados de desempenho de um rebanho Hereford; Inferência Bayesiana; Análises do estudo de simulação; Análises de dados do rebanho Hereford; Critérios para escolha do melhor modelo; Inferência sobre dados simulados; Inferência nos dados do rebanho Hereford; Ganho de peso pós-desmama; Peso à desmama.bitstream/item/55802/1/BP32.pd
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