1,796 research outputs found
Measuring the Spins of Stellar Black Holes: A Progress Report
We use the Novikov-Thorne thin disk model to fit the thermal continuum X-ray
spectra of black hole X-ray binaries, and thereby extract the dimensionless
spin parameter a* = a/M of the black hole as a parameter of the fit. We
summarize the results obtained to date for six systems and describe work in
progress on additional systems. We also describe recent methodological
advances, our current efforts to make our analysis software fully available to
others, and our theoretical efforts to validate the Novikov-Thorne model.Comment: 6 pages, conference proceedings, X-ray Astronomy 2009: Present
Status, Multi-Wavelength Approach and Future Perspectives, AIP, eds. A.
Comastri et al.; list of authors revise
Rural-urban migration in d-dimensional lattices
The rural-urban migration phenomenon is analyzed by using an agent-based
computational model. Agents are placed on lattices which dimensions varying
from d=2 up to d=7. The localization of the agents in the lattice define their
social neighborhood (rural or urban) not being related to their spatial
distribution. The effect of the dimension of lattice is studied by analyzing
the variation of the main parameters that characterizes the migratory process.
The dynamics displays strong effects even for around one million of sites, in
higher dimensions (d=6, 7).Comment: 9 pages, 7 figures, to be published in International Journal of
Modern Physics C 1
A dynamic density functional theory for particles in a flowing solvent
We present a dynamic density functional theory (dDFT) which takes into accou
nt the advection of the particles by a flowing solvent. For potential flows we
can use the same closure as in the absence of solvent flow. The structure of
the resulting advected dDFT suggests that it could be used for non-potential
flows as well. We apply this dDFT to Brownian particles (e.g., polymer coils)
in a solvent flowing around a spherical obstacle (e.g., a colloid) and compare
the results with direct simulations of the underlying Brownian dynamics.
Although numerical limitations do not allow for an accurate quantitative
check of the advected dDFT both show the same qualitative features. In contrast
to previous works which neglected the deformation of the flow by the obstacle,
we find that the bow-wave in the density distribution of particles in front of
the obstacle as well as the wake behind it are reduced dramatically. As a
consequence the friction force exerted by the (polymer) particles on the
colloid can be reduced drastically.Comment: 7 pages, 5 figures, 2 tables, submitte
Seismic risk of critical facilities in the Dominican Republic: case study of school buildings
Abstract
The island of Hispaniola, shared by the Dominican Republic and Haiti, is located in a subduction zone between the North America plate and the Caribbean plate. In addition, there are 13 geological faults in the interior of the island, some of which have shown the potential to generate earthquakes of magnitude 7.5 and higher. Thus, the whole island is considered to be a high seismic risk region. In the past 100 years, several earthquakes have affected both parts of the island. In the case of the Dominican Republic, two earthquakes stand out: a magnitude 8.1 earthquake on August 4, 1946, north of the Samaná Province, which caused a tsunami, soil liquefaction, and the loss of about 100 lives, and a magnitude 6.5 earthquake on September 22, 2003, in the city of Puerto Plata, which caused significant damage for infrastructures. Among the observed effects, the partial and total collapse of several school buildings had a remarkable impact on local communities. In addition to the high seismic risk, a large part of the national infrastructure may exhibit high vulnerability to earthquakes because the seismic regulations had been the same for 32 years, namely from 1979 to 2011. During these three decades, thousands of structures were built nationwide, including essential facilities such as hospitals and schools. Considering that the current student population in public schools in the Dominican Republic is over 2 million, with the majority attending buildings that were designed with the 1979 seismic code and which proved to be highly vulnerable during the Puerto Plata earthquake, it is vital to take measures that reduce the risk and minimize potential earthquake damage to school buildings. In this context, the Technological Institute of Santo Domingo (INTEC) has undertaken recently a project with the main objective to assess the seismic vulnerability of 22 schools located in the San Cristóbal Province, in the south of the Dominican Republic. The latter schools were all built prior to the adoption of the current updated seismic code. This paper presents the results of the assessment of the Fernando Cabral Ortega School. Although only the results of a single RC building are presented, the response of such structure can be considered representative of a portfolio of existing schools in Dominican Republic
An agent-based model to rural-urban migration analysis
In this paper we analyze the rural-urban migration phenomena as it is usually
observed in economies which are in the early stages of industrialization. The
analysis is conducted by means of a statistical mechanics approach which builds
a computational agent-based model. Agents are placed on a lattice and the
connections among them are described via an Ising like model. Simulations on
this computational model show some emergent properties that are common in
developing economies, such as a transitional dynamics characterized by
continuous growth of urban population, followed by the equalization of expected
wages between rural and urban sectors (Harris-Todaro equilibrium condition),
urban concentration and increasing of per capita income.Comment: 16 pages, 9 figure
Love kills: Simulations in Penna Ageing Model
The standard Penna ageing model with sexual reproduction is enlarged by
adding additional bit-strings for love: Marriage happens only if the male love
strings are sufficiently different from the female ones. We simulate at what
level of required difference the population dies out.Comment: 14 pages, including numerous figure
Scalar QED -Corrections to the Coulomb Potential
The leading long-distance 1-loop quantum corrections to the Coulomb potential
are derived for scalar QED and their gauge-independence is explicitly checked.
The potential is obtained from the direct calculation of the 2-particle
scattering amplitude, taking into account all relevant 1-loop diagrams. Our
investigation should be regarded as a first step towards the same programme for
effective Quantum Gravity. In particular, with our calculation in the framework
of scalar QED, we are able to demonstrate the incompleteness of some previous
studies concerning the Quantum Gravity counterpart.Comment: LaTeX, 16 pages, 4 figures as one ps-fil
Excitation spectroscopy of vortex lattices in a rotating Bose-Einstein condensate
Excitation spectroscopy of vortex lattices in rotating Bose-Einstein
condensates is described. We numerically obtain the Bogoliubov-deGenne
quasiparticle excitations for a broad range of energies and analyze them in the
context of the complex dynamics of the system. Our work is carried out in a
regime in which standard hydrodynamic assumptions do not hold, and includes
features not readily contained within existing treatments.Comment: 4 pages, 4 figures. Submitted for publicatio
Catastrophic senescence and semelparity in the Penna aging model
The catastrophic senescence of the Pacific salmon is among the initial tests
used to validate the Penna aging model. Based on the mutation accumulation
theory, the sudden decrease in fitness following reproduction may be solely
attributed to the semelparity of the species. In this work, we report other
consequences of mutation accumulation. Contrary to earlier findings, such
dramatic manifestation of aging depends not only on the choice of breeding
strategy but also on the value of the reproduction age, R, and the mutation
threshold, T. Senescence is catastrophic when . As the organism's
tolerance for harmful genetic mutations increases, the aging process becomes
more gradual. We observe senescence that is threshold dependent whenever T>R.
That is, the sudden drop in survival rate occurs at age equal to the mutation
threshold value
Convergence of simulated annealing by the generalized transition probability
We prove weak ergodicity of the inhomogeneous Markov process generated by the
generalized transition probability of Tsallis and Stariolo under power-law
decay of the temperature. We thus have a mathematical foundation to conjecture
convergence of simulated annealing processes with the generalized transition
probability to the minimum of the cost function. An explicitly solvable example
in one dimension is analyzed in which the generalized transition probability
leads to a fast convergence of the cost function to the optimal value. We also
investigate how far our arguments depend upon the specific form of the
generalized transition probability proposed by Tsallis and Stariolo. It is
shown that a few requirements on analyticity of the transition probability are
sufficient to assure fast convergence in the case of the solvable model in one
dimension.Comment: 11 page
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