6,096 research outputs found
The U(1) phase transition on toroidal and spherical lattices
We have studied the properties of the phase transition in the U(1) compact
pure gauge model paying special atention to the influence of the topology of
the boundary conditions. From the behavior of the energy cumulants and the
observation of an effective \nu -> 1/d on toroidal and spherical lattices, we
conclude that the transition is first order.Comment: LATTICE98(gauge
Study of the Coulomb-Higgs transition in the Abelian Higgs Model
The order of the Coulomb-Higgs transition in the U(1)-Higgs model with
unfrozen modulus of the scalar field is studied. Large lattices (up to
in one case) and high statistics are used. We fix and explore
specially a region of -values where metastability is observed. We
study the thermodynamical limit of several observables, in particular, the
latent heat, the specific heat, the decrement of the free energy between the
maxima and the central minimum of the two-peaked histogram, the Binder cumulant
and the displacement of the critical coupling with the lattice size. The
results point towards a second order transition for ,
while for smaller values of the strong metastability growing with the
lattice size seems to derive from a first order character.Comment: 10 pages, Latex, epsfig, uuencoded gzipped tar file, 4 figures
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A multisite microcanonical updating method
We have made a study of several update algorithms using the XY model. We find
that sequential local overrelaxation is not ergodic at the scale of typical
Monte Carlo simulation time. We have introduced a new multisite microcanonical
update method, which yields results compatible with those of random
overrelaxation and the microcanonical demon algorithm, which are very much
slower, all being incompatible with the sequential overrelaxation results.Comment: 13 pages, 4 figure
El magmatismo (Ortoneises y volcanismo del Ordovícico Superior) del Paleozoico de los Catalánides.
En el presente trabajo se caracterizan petrológica y geoquímicamente las rocas metavolcánicas del Ordovícico Superior de los Catalánides (Gavarres y Guilleries) y los ortoneises de las Guilleries. Estos últimos se encuentran en disposición estratiforme en materiales metasedimentarios cuya edad supuesta es Proterozoico Superior o Cámbrico Inferior. Las rocas metavolcánicas están constituidas por metarriolitas masivas y tobas dacítico-riolíticas con abundante mezcla de material fragmentario. Corresponden a un volcanismo explosivo subaéreo y de carácter freatomagmático. Sus caracteres geoquímicos lo definen como los términos ácidos de una secuencia calcoalcalina de procedencia cortical emplazada postcolisionalmente dentro de un contexto extensivo. El modelo de REE indica que se trata de fundidos poco fraccionados procedentes de la fusión de una corteza reciclada. Los "Ortoneises de las Guilleries" corresponden a leuconeises biotíticos con granate. Sus caracteres geoquímicos los caracterizan como metagranilos alumínicos de procedencia cortical. Sus espectros geoquímicos (elementos incompatibles y REE) presentan pautas análogas a los de las rocas metavolcánicas e indican que se trata de fundidos de procedencia cortical de baja alcalinidad emplazados en un contexto anorogénico. La ausencia de correlación geoquímica y de pautas de fraccionación entre metavolcanitas y ortoneises descarta la idea de una fuente común para ambos
SU(1,1) Coherent States For Position-Dependent Mass Singular Oscillators
The Schroedinger equation for position-dependent mass singular oscillators is
solved by means of the factorization method and point transformations. These
systems share their spectrum with the conventional singular oscillator. Ladder
operators are constructed to close the su(1,1) Lie algebra and the involved
point transformations are shown to preserve the structure of the
Barut-Girardello and Perelomov coherent states.Comment: 11 pages, 5 figures. This shortened version (includes new references)
has been adapted for its publication in International Journal of Theoretical
Physic
Interacting holographic tachyon model of dark energy
We propose a holographic tachyon model of dark energy with interaction
between the components of the dark sector. The correspondence between the
tachyon field and the holographic dark energy densities allows the
reconstruction of the potential and the dynamics of the tachyon scalar field in
a flat Friedmann-Robertson-Walker universe. We show that this model can
describe the observed accelerated expansion of our universe with a parameter
space given by the most recent observational results.Comment: 7 pages, 8 figures, accepted for publication in IJMP
A Proposal for a Modified Moller-Plesset Perturbation Theory
A modified version of the Moller-Plesset approach for obtaining the
correlation energy associated to a Hartree-Fock ground state is proposed. The
method is tested in a model of interacting fermions that allows for an exact
solution. Using up to third order terms improved results are obtained, even
more accurate in the limit of loosely bound particles. This result suggests the
possible convenience of the scheme for the study of chemical bound problems.Comment: 10 pages, 1 figur
The Academic Resilience Approach in the promotion of young people’s mental health. Proposals for its use in schools
Els joves que gaudeixen de bona salut mental són més propensos a tenir un rendiment acadèmic més bo i un millor desenvolupament social. Davant l’increment de problemes de salut mental entre adolescents a Catalunya, es presenta l’Enfocament de Resiliència Acadèmica (ERA) com una pràctica estratègica per a centres d’educació secundària que involucra tota la comunitat educativa. La finalitat és ajudar que els joves, especialment els més vulnerables, aconsegueixin obtenir un rendiment acadèmic més òptim, malgrat les circumstàncies en les quals es troben. Les propostes per integrar l’ERA als centres de secundària es basen en la redefinició de les activitats que ja es desenvolupen i en el disseny de noves pràctiques educatives considerant els elements del Marc de Resiliència
La restauración de Sambucus palmensis en La Gomera: Conservación genética y modelización de nicho climático
La conservación de especies vegetales amenazadas a menudo conlleva la restauración de sus poblaciones naturales, ya sea mediante el refuerzo de las poblaciones existentes, la reintroducción de poblaciones extintas o la introducción de nuevos núcleos. Antes de comenzar acciones de restauración, es esencial conocer la biología de las especies con el fin de determinar los factores más importantes que limitan el crecimiento de la población fundadora (Heywood & Iriondo, 2003
Phase diagram of the (bosonic) Double-Exchange Model
The phase diagram of the simplest approximation to Double-Exchange systems,
the bosonic Double-Exchange model with antiferromagnetic super-exchange
coupling, is fully worked out by means of Monte Carlo simulations, large-N
expansions and Variational Mean-Field calculations. We find a rich phase
diagram, with no first-order phase transitions. The most surprising finding is
the existence of a segment like ordered phase at low temperature for
intermediate AFM coupling which cannot be detected in neutron-scattering
experiments. This is signaled by a maximum (a cusp) in the specific heat. Below
the phase-transition, only short-range ordering would be found in
neutron-scattering. Researchers looking for a Quantum Critical Point in
manganites should be wary of this possibility. Finite-Size Scaling estimates of
critical exponents are presented, although large scaling corrections are
present in the reachable lattice sizes.Comment: 17 pages, 14 figure
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