9,066 research outputs found
Critical dynamics of the Potts model: short-time Monte Carlo simulations
We calculate the new dinamic exponent of the 4-state Potts model,
using short-time simulations. Our estimates and obtained by following the behavior of the
magnetization or measuring the evolution of the time correlation function of
the magnetization corroborate the conjecture by Okano et. al. In addition,
these values agree with previous estimate of the same dynamic exponent for the
two-dimensional Ising model with three-spin interactions in one direction, that
is known to belong to the same universality class as the 4-state Potts model.
The anomalous dimension of initial magnetization
is calculated by an alternative way that mixes two different initial
conditions. We have also estimated the values of the static exponents
and . They are in complete agreement with the pertinent results of the
literature.Comment: 12 pages, 7 figure
The role of differential rotation in the evolution of the r-mode instability
We discuss the role of differential rotation in the evolution of the l=2
r-mode instability of a newly born, hot, rapidly-rotating neutron star. It is
shown that the amplitude of the r-mode saturates in a natural way at a value
that depends on the amount of differential rotation at the time the instability
becomes active. It is also shown that, independently of the saturation
amplitude of the mode, the star spins down to a rotation rate that is
comparable to the inferred initial rotation rates of the fastest pulsars
associated with supernova remnants.Comment: 4 pages, 2 figures, in Proceedings of the 5th International Workshop
"New Worlds in Astroparticle Physics", Faro, Portugal, 8-10 January 200
On the critical behavior of the Susceptible-Infected-Recovered (SIR) model on a square lattice
By means of numerical simulations and epidemic analysis, the transition point
of the stochastic, asynchronous Susceptible-Infected-Recovered (SIR) model on a
square lattice is found to be c_0=0.1765005(10), where c is the probability a
chosen infected site spontaneously recovers rather than tries to infect one
neighbor. This point corresponds to an infection/recovery rate of lambda_c =
(1-c_0)/c_0 = 4.66571(3) and a net transmissibility of (1-c_0)/(1 + 3 c_0) =
0.538410(2), which falls between the rigorous bounds of the site and bond
thresholds. The critical behavior of the model is consistent with the 2-d
percolation universality class, but local growth probabilities differ from
those of dynamic percolation cluster growth, as is demonstrated explicitly.Comment: 9 pages, 5 figures. Accepted for publication, Physical Review
A Geant4 based engineering tool for Fresnel lenses
Geant4 is a Monte Carlo radiation transport toolkit that is becoming a tool
of generalized application in areas such as high-energy physics, nuclear
physics, astroparticle physics, or medical physics. Geant4 provides an optical
physics process category, allowing the simulation of the production and
propagation of light. Its capabilities are well tailored for the simulation of
optics systems namely in cosmic-rays experiments based in the detection of
Cherenkov and fluorescence light. The use of Geant4 as an engineering tool for
the optics design and simulation of Fresnel lens systems is discussed through a
specific example.Comment: 4 pages, 6 figures, Proceedings of the 30th ICRC, International
Cosmic Ray Conference 2007, M\'erida, M\'exico, 3-11 July 200
Numerical solution of the eXtended Pom-Pom model for viscoelastic free surface flows
In this paper we present a finite difference method for solving two-dimensional viscoelastic unsteady free surface flows governed by the single equation version of the eXtended Pom-Pom (XPP) model. The momentum equations are solved by a projection method which uncouples the velocity and pressure fields. We are interested in low Reynolds number flows and, to enhance the stability of the numerical method, an implicit technique for computing the pressure condition on the free surface is employed. This strategy is invoked to solve the governing equations within a Marker-and-Cell type approach while simultaneously calculating the correct normal stress condition on the free surface. The numerical code is validated by performing mesh refinement on a two-dimensional channel flow. Numerical results include an investigation of the influence of the parameters of the XPP equation on the extrudate swelling ratio and the simulation of the Barus effect for XPP fluids
Cartography and iconography as diachronic analysis tools of the urban fabric ─ Évora and Setúbal
The evolution of cities can be interpreted through graphic elements, such as that recommended by Marcus Vitruvius Pollio (1st century bC.) (Maciel, 2006), whose forms of expression were plans, elevations and perspectives, which prove to be precious and reliable instruments for the reading of cities. It is important to establish these elements, which appear as representations of cities, in various stages of construction of their urban fabrics, in documents such as cartography or iconography. These are relevant testimonies in the analysis and allow a careful reading of the "reality" of cities at different times. In addition to understanding them as representations of a certain period, they allow the current reinterpretation of the urban fabric, and should be considered dynamic instruments in the understanding of the reading of the cities. Considering cartography and iconography from several epochs, we will make a comparative analysis of the historical urban fabric of two cities, using differentiated urban implantation and development (Évora and Setúbal). To reach these objectives, we will read and interpret morphological elements of the Medieval City (fortifications, squares, streets, blocks, markets, singular buildings among others) and these respective witness documents, to understand the diachronic evolution in their similarities and differences
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