20,179 research outputs found
Reflection matrices for the vertex model
The graded reflection equation is investigated for the
vertex model. We have found four classes of diagonal
solutions and twelve classes of non-diagonal ones. The number of free
parameters for some solutions depends on the number of bosonic and fermionic
degrees of freedom considered.Comment: 30 page
Majority-vote on directed Small-World networks
On directed Small-World networks the
Majority-vote model with noise is now studied through Monte Carlo
simulations. In this model, the order-disorder phase transition of the order
parameter is well defined in this system. We calculate the value of the
critical noise parameter q_c for several values of rewiring probability p of
the directed Small-World network. The critical exponentes beta/nu, gamma/nu and
1/nu were calculated for several values of p.Comment: 16 pages including 9 figures, for Int. J. Mod. Phys.
Ising model spin S=1 on directed Barabasi-Albert networks
On directed Barabasi-Albert networks with two and seven neighbours selected
by each added site, the Ising model with spin S=1/2 was seen not to show a
spontaneous magnetisation. Instead, the decay time for flipping of the
magnetisation followed an Arrhenius law for Metropolis and Glauber algorithms,
but for Wolff cluster flipping the magnetisation decayed exponentially with
time. On these networks the
Ising model spin S=1 is now studied through Monte Carlo simulations.
However, in this model, the order-disorder phase transition is well defined
in this system. We have obtained a first-order phase transition for values of
connectivity m=2 and m=7 of the directed Barabasi-Albert network.Comment: 8 pages for Int. J. Mod. Phys. C; e-mail: [email protected]
Simulation of majority rule disturbed by power-law noise on directed and undirected Barabasi-Albert networks
On directed and undirected Barabasi-Albert networks the Ising model with spin
S=1/2 in the presence of a kind of noise is now studied through Monte Carlo
simulations. The noise spectrum P(n) follows a power law, where P(n) is the
probability of flipping randomly select n spins at each time step. The noise
spectrum P(n) is introduced to mimic the self-organized criticality as a model
influence of a complex environment. In this model, different from the square
lattice, the order-disorder phase transition of the order parameter is not
observed. For directed Barabasi-Albert networks the magnetisation tends to zero
exponentially and for undirected Barabasi-Albert networks, it remains constant.Comment: 6 pages including many figures, for Int. J. Mod. Phys.
Critical behavior of the spin-3/2 Blume-Capel model on a random two-dimensional lattice
We investigate the critical properties of the spin-3/2 Blume-Capel model in
two dimensions on a random lattice with quenched connectivity disorder. The
disordered system is simulated by applying the cluster hybrid Monte Carlo
update algorithm and re-weighting techniques. We calculate the critical
temperature as well as the critical point exponents , ,
, and . We find that, contrary of what happens to the spin-1/2
case, this random system does not belong to the same universality class as the
regular two-dimensional ferromagnetic model.Comment: 5 pages and 5 figure
Kinematic Constraints to the Transition Redshift from SNe Ia Union Data
The kinematic approach to cosmological tests provides a direct evidence to
the present accelerating stage of the universe which does not depend on the
validity of general relativity, as well as on the matter-energy content of the
Universe. In this context, we consider here a linear two-parameter expansion
for the decelerating parameter, , where and are
arbitrary constants to be constrained by the Union supernovae data. By assuming
a flat Universe we find that the best fit to the pair of free parameters is
() = ( whereas the transition redshift is () (). This
kinematic result is in agreement with some independent analyzes and
accommodates more easily many dynamical flat models (like CDM).Comment: 10 pages, 4 figures, 1 tabl
Majority-vote on undirected Barabasi-Albert networks
On Barabasi-Albert networks with z neighbours selected by each added site,
the Ising model was seen to show a spontaneous magnetisation. This spontaneous
magnetisation was found below a critical temperature which increases
logarithmically with system size. On these networks the majority-vote model
with noise is now studied through Monte Carlo simulations. However, in this
model, the order-disorder phase transition of the order parameter is well
defined in this system and this wasn't found to increase logarithmically with
system size. We calculate the value of the critical noise parameter q_c for
several values of connectivity of the undirected Barabasi-Albert network.
The critical exponentes beta/nu, gamma/nu and 1/nu were calculated for several
values of z.Comment: 15 pages with numerous figure
Density-functionals not based on the electron gas: Local-density approximation for a Luttinger liquid
By shifting the reference system for the local-density approximation (LDA)
from the electron gas to other model systems one obtains a new class of density
functionals, which by design account for the correlations present in the chosen
reference system. This strategy is illustrated by constructing an explicit LDA
for the one-dimensional Hubbard model. While the traditional {\it ab initio}
LDA is based on a Fermi liquid (the electron gas), this one is based on a
Luttinger liquid. First applications to inhomogeneous Hubbard models, including
one containing a localized impurity, are reported.Comment: 4 pages, 4 figures (final version, contains additional applications
and discussion; accepted by Phys. Rev. Lett.
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