2,361 research outputs found
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
Aging and fluctuation-dissipation ratio in a nonequilibrium -state lattice model
A generalized version of the nonequilibrium linear Glauber model with
states in dimensions is introduced and analyzed. The model is fully
symmetric, its dynamics being invariant under all permutations of the
states. Exact expressions for the two-time autocorrelation and response
functions on a -dimensional lattice are obtained. In the stationary regime,
the fluctuation-dissipation theorem holds, while in the transient the aging is
observed with the fluctuation-dissipation ratio leading to the value predicted
for the linear Glauber model
Finite-size scaling of the stochastic susceptible-infected-recovered model
The critical behavior of the stochastic susceptible-infected-recovered model
on a square lattice is obtained by numerical simulations and finite-size
scaling. The order parameter as well as the distribution in the number of
recovered individuals is determined as a function of the infection rate for
several values of the system size. The analysis around criticality is obtained
by exploring the close relationship between the present model and standard
percolation theory. The quantity UP, equal to the ratio U between the second
moment and the squared first moment of the size distribution multiplied by the
order parameter P, is shown to have, for a square system, a universal value
1.0167(1) that is the same as for site and bond percolation, confirming further
that the SIR model is also in the percolation class
Nonlinear evolution of r-modes: the role of differential rotation
Recent work has shown that differential rotation, producing large scale
drifts of fluid elements along stellar latitudes, is an unavoidable feature of
r-modes in the nonlinear theory. We investigate the role of this 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 a few hundred seconds after the mode instability sets in. The
saturation amplitude depends on the amount of differential rotation at the time
the instability becomes active and can take values much smaller than unity. It
is also shown that, independently of the saturation amplitude of the mode, the
star spins down to rotation rates that are comparable to the inferred initial
rotation rates of the fastest pulsars associated with supernova remnants.
Finally, it is shown that, when the drift of fluid elements at the time the
instability sets in is significant, most of the initial angular momentum of the
star is transferred to the r-mode and, consequently, almost none is carried
away by gravitational radiation.Comment: 10 pages, 5 figure
Anomalous magnetic and weak magnetic dipole moments of the lepton in the simplest little Higgs model
We obtain analytical expressions, both in terms of parametric integrals and
Passarino-Veltman scalar functions, for the one-loop contributions to the
anomalous weak magnetic dipole moment (AWMDM) of a charged lepton in the
framework of the simplest little Higgs model (SLHM). Our results are general
and can be useful to compute the weak properties of a charged lepton in other
extensions of the standard model (SM). As a by-product we obtain generic
contributions to the anomalous magnetic dipole moment (AMDM), which agree with
previous results. We then study numerically the potential contributions from
this model to the lepton AMDM and AWMDM for values of the parameter
space consistent with current experimental data. It is found that they depend
mainly on the energy scale at which the global symmetry is broken and the
parameter, whereas there is little sensitivity to a mild change in
the values of other parameters of the model. While the AMDM is of the
order of , the real (imaginary) part of its AWMDM is of the order of
(). These values seem to be out of the reach of the
expected experimental sensitivity of future experiments.Comment: 23 pages, 11 figures, new analysis and References adde
Probióticos como estrategia terapéutica en el tratamiento de la obesidad y el sobrepeso: Una revisión sistemática de ensayos clÃnicos
The fluctuation-dissipation theorem and the linear Glauber model
We obtain exact expressions for the two-time autocorrelation and response
functions of the -dimensional linear Glauber model. Although this linear
model does not obey detailed balance in dimensions , we show that the
usual form of the fluctuation-dissipation ratio still holds in the stationary
regime. In the transient regime, we show the occurence of aging, with a special
limit of the fluctuation-dissipation ratio, , for a quench at
the critical point.Comment: Accepted for publication (Physical Review E
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