22 research outputs found
Monte Carlo simulation of size-effects on thermal conductivity in a 2-dimensional Ising system
A model based on microcanonical Monte Carlo method is used to study the
application of the temperature gradient along a two-dimensional (2D) Ising
system. We estimate the system size effects on thermal conductivity, , for a
nano-scale Ising layer with variable size. It is shown that scales with
size as where varies with temperature. Both the
Metropolis and Cruetz algorithms have been used to establish the temperature
gradient. Further results show that the average demon energy in the presence of
an external magnetic field is zero for low temperatures.Comment: 10 pages, 7 figures, to appear in Physica
A method for solving systems of non-linear differential equations with moving singularities
We present a method for solving a class of initial valued, coupled,
non-linear differential equations with `moving singularities' subject to some
subsidiary conditions. We show that this type of singularities can be
adequately treated by establishing certain `moving' jump conditions across
them. We show how a first integral of the differential equations, if available,
can also be used for checking the accuracy of the numerical solution.Comment: 9 pages, 7 eps figures, to appear in Comput. Phys. Co
Worldline deviations of charged spinning particles
The geodesic deviation equation is generalized to worldline deviation
equations describing the relative accelerations of charged spinning particles
in the framework of Dixon-Souriau equations of motion
Accelerating universe in brane gravity with a confining potential
We construct the Einstein field equations on a 4-dimensional brane embedded
in an -dimensional bulk where the matter fields are confined to the brane by
means of a confining potential. As a result, an extra term in the Friedmann
equation in a -dimensional bulk appears that may be interpreted as the
X-matter, providing a possible phenomenological explanation for the
acceleration of the universe. The study of the relevant observational data
suggests good agreement with the predictions of this model.Comment: 10 pages, 2 figures, to appear in Phys. Lett.
Brans-Dicke DGP Brane Cosmology
We consider a five dimensional DGP-brane scenario endowed with a
non-minimally coupled scalar field within the context of Brans-Dicke theory.
This theory predicts that the mass appearing in the gravitational potential is
modified by the addition of the mass of the effective intrinsic curvature on
the brane. We also derive the effective four dimensional field equations on a
3+1 dimensional brane where the fifth dimension is assumed to have an orbifold
symmetry. Finally, we discuss the cosmological implications of this setup,
predicting an accelerated expanding universe with a value of the Brans-Dicke
parameter consistent with values resulting from the solar system
observations.Comment: 12 pages, 1 figure, to appear in JCA
Time reparameterization in Bianchi type I spinor cosmology
The problem of time reparameterization is addressed at both the classical and
quantum levels in a Bianchi-I universe in which the matter source is a massive
Dirac spinor field. We take the scale factors of the metric as the intrinsic
time and their conjugate momenta as the extrinsic time. A scalar character of
the spinor field is identified as a representation of the extrinsic time. The
construction of the field equations and quantization of the model is achieved
by solving the Hamiltonian constraint after time identification has been dealt
with. This procedure leads to a true Hamiltonian whose exact solutions for the
above choices of time are presentedComment: 16 pages, no figures, to appear in Annals of Physic
Numerical simulation of the stochastic dynamics of inclusions in biomembranes in presence of surface tension
The stochastic dynamics of inclusions in a randomly fluctuating biomembrane
is simulated. These inclusions can represent the embedded proteins and the
external particles arriving at a cell membrane. The energetics of the
biomembrane is modelled via the Canham-Helfrich Hamiltonian. The contributions
of both the bending elastic-curvature energy and the surface tension of the
biomembrane are taken into account. The biomembrane is treated as a
two-dimensional sheet whose height variations from a reference frame is treated
as a stochastic Wiener process. The lateral diffusion parameter associated with
this Wiener process coupled with the longitudinal diffusion parameter obtained
from the standard Einsteinian diffusion theory completely determine the
stochastic motion of the inclusions. It is shown that the presence of surface
tension significantly affects the overall dynamics of the inclusions,
particularly the rate of capture of the external inclusions, such as drug
particles, at the site of the embedded inclusions, such as the embedded
proteins.Comment: 17 pages, 4 figures, to appear in physica
Lorentz violation and the speed of gravitational waves in brane-worlds
Lorentz violation in a brane-world scenario is presented and used to obtain a
relationship between the speed of gravitational waves in the bulk and that on
the brane. Lorentz violating effects would manifest themselves in gravitational
waves travelling with a greater speed in the bulk than on the brane and this
effect is independent of the signature of the extra dimension.Comment: 8 pages, to appear in PL
Compactification and signature transition in Kaluza-Klein spinor cosmology
We study the classical and quantum cosmology of a 4+1-dimensional space-time
with a non-zero cosmological constant coupled to a self interacting massive
spinor field. We consider a spatially flat Robertson-Walker universe with the
usual scale factor and an internal scale factor associated with
the extra dimension. For a free spinor field the resulting equations admit
exact solutions, whereas for a self interacting spinor field one should resort
to a numerical method for exhibiting their behavior. These solutions give rise
to a degenerate metric and exhibit signature transition from a Euclidean to a
Lorentzian domain. Such transitions suggest a compactification mechanism for
the internal and external scale factors such that in the
Lorentzian region. The corresponding quantum cosmology and the ensuing
Wheeler-DeWitt equation have exact solutions in the mini-superspace when the
spinor field is free, leading to wavepackets undergoing signature change. The
question of stabilization of the extra dimension is also discussed.Comment: 12 pages, 1 figure, to appear in Annals of Physic
Brane-world black hole entropy from modified dispersion relations
The entropy of the Reissner-N\"{o}rdstrom black hole is studied within the
context of a brane-world scenario. Such a black hole is a solution of the
Einstein field equations on the brane, possessing a tidal charge which is a
reflection of the extra dimension. We use the modified dispersion relation to
obtain the entropy of such brane-world black holes. The resulting entropy
differs from that of the standard Bekenstein-Hawking's and contains information
on the extra dimension.Comment: 9 pages, 4 figures, to appear in PL