49,869 research outputs found
New family of potentials with analytical twiston-like solutions
In this letter we present a new approach to find analytical twiston models.
The effective two-field model was constructed by a non-trivial combination of
two one field systems. In such an approach we successfully build analytical
models which are satisfied by a combination of two defect-like solutions, where
one is responsible to twist the molecular chain by , while the other
implies in a longitudinal movement. Such a longitudinal movement can be fitted
to have the size of the distance between adjacent molecular groups. The
procedure works nicely and can be used to describe the dynamics of several
other molecular chains.Comment: 7 pages, 3 figure
Gaussian quantum Monte Carlo methods for fermions
We introduce a new class of quantum Monte Carlo methods, based on a Gaussian
quantum operator representation of fermionic states. The methods enable
first-principles dynamical or equilibrium calculations in many-body Fermi
systems, and, combined with the existing Gaussian representation for bosons,
provide a unified method of simulating Bose-Fermi systems. As an application,
we calculate finite-temperature properties of the two dimensional Hubbard
model.Comment: 4 pages, 3 figures, Revised version has expanded discussion,
simplified mathematical presentation, and application to 2D Hubbard mode
Elodie metallicity-biased search for transiting Hot Jupiters I. Two Hot Jupiters orbiting the slightly evolved stars HD118203 and HD149143
We report the discovery of a new planet candidate orbiting the subgiant star
HD118203 with a period of P=6.1335 days. The best Keplerian solution yields an
eccentricity e=0.31 and a minimum mass m2sin(i)=2.1MJup for the planet. This
star has been observed with the ELODIE fiber-fed spectrograph as one of the
targets in our planet-search programme biased toward high-metallicity stars,
on-going since March 2004 at the Haute-Provence Observatory. An analysis of the
spectroscopic line profiles using line bisectors revealed no correlation
between the radial velocities and the line-bisector orientations, indicating
that the periodic radial-velocity signal is best explained by the presence of a
planet-mass companion. A linear trend is observed in the residuals around the
orbital solution that could be explained by the presence of a second companion
in a longer-period orbit. We also present here our orbital solution for another
slightly evolved star in our metal-rich sample, HD149143, recently proposed to
host a 4-d period Hot Jupiter by the N2K consortium. Our solution yields a
period P=4.09 days, a marginally significant eccentricity e=0.08 and a
planetary minimum mass of 1.36MJup. We checked that the shape of the spectral
lines does not vary for this star as well.Comment: Accepted in A&A (6 pages, 6 figures
Building analytical three-field cosmological models
A difficult task to deal with is the analytical treatment of models composed
by three real scalar fields, once their equations of motion are in general
coupled and hard to be integrated. In order to overcome this problem we
introduce a methodology to construct three-field models based on the so-called
"extension method". The fundamental idea of the procedure is to combine three
one-field systems in a non-trivial way, to construct an effective three scalar
field model. An interesting scenario where the method can be implemented is
within inflationary models, where the Einstein-Hilbert Lagrangian is coupled
with the scalar field Lagrangian. We exemplify how a new model constructed from
our method can lead to non-trivial behaviors for cosmological parameters.Comment: 11 pages, and 3 figures, updated version published in EPJ
Diffraction and an infrared finite gluon propagator
We discuss some phenomenological applications of an infrared finite gluon
propagator characterized by a dynamically generated gluon mass. In particular
we compute the effect of the dynamical gluon mass on and
diffractive scattering. We also show how the data on photoproduction
and hadronic reactions can be derived from the and
forward scattering amplitudes by assuming vector meson dominance and
the additive quark model.Comment: 4 pages, 7 figures, added references and figures, changed structure.
Contribution to Proceedings of XVIIIth Reuniao de Trabalho sobre Interacoes
Hadronicas, Sao Paulo, Brazil, 22-24 May, 200
Density Dependent Parametrization Models: Formalism and Applications
In this work we derive a formalism to incorporate asymmetry and temperature
effects in the Brown-Rho (BR) scaled lagrangian model in a mean field theory.
The lagrangian density discussed in this work requires less parameters than the
usual models with density dependent couplings. We also present the formalism
with the inclusion of the eight lightest baryons, two lightest leptons, beta
equilibrium and charge neutrality in order to apply the BR scaled model to the
study of neutron stars. The results are again compared with the ones obtained
from another density dependent parametrization model. The role played by the
rearrangement term at T=0 for nuclear or neutron star matter and at finite
temperature is investigated. The BR scaled model is shown to be a good tool in
studies involving density dependent effective masses and in astrophysics
applications.Comment: 23 pages, 10 figure
Inductive learning spatial attention
This paper investigates the automatic induction of spatial attention
from the visual observation of objects manipulated
on a table top. In this work, space is represented in terms of
a novel observer-object relative reference system, named Local
Cardinal System, defined upon the local neighbourhood
of objects on the table. We present results of applying the
proposed methodology on five distinct scenarios involving
the construction of spatial patterns of coloured blocks
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