379 research outputs found
Density matrix renormalization group for the Berezinskii-Kosterlitz-Thouless transition of the 19-vertex model
We embody the density matrix renormalization group (DMRG) method for the
19-vertex model on a square lattice in order to investigate the
Berezinskii-Kosterlitz-Thouless transition. Elements of the transfer matrix of
the 19-vertex model are classified in terms of the total value of arrows in one
layer of the square lattice. By using this classification, we succeed to reduce
enormously the dimension of the matrix which has to be diagonalized in the DMRG
method. We apply our method to the 19-vertex model with the interaction
and obtain for the conformal anomaly. PACS. 05.90.+m,
02.70.-cComment: RevTeX style, 20 pages, 12 figure
Roughening Induced Deconstruction in (100) Facets of CsCl Type Crystals
The staggered 6-vertex model describes the competition between surface
roughening and reconstruction in (100) facets of CsCl type crystals. Its phase
diagram does not have the expected generic structure, due to the presence of a
fully-packed loop-gas line. We prove that the reconstruction and roughening
transitions cannot cross nor merge with this loop-gas line if these degrees of
freedom interact weakly. However, our numerical finite size scaling analysis
shows that the two critical lines merge along the loop-gas line, with strong
coupling scaling properties. The central charge is much larger than 1.5 and
roughening takes place at a surface roughness much larger than the conventional
universal value. It seems that additional fluctuations become critical
simultaneously.Comment: 31 pages, 9 figure
Correlated percolation and the correlated resistor network
We present some exact results on percolation properties of the Ising model,
when the range of the percolating bonds is larger than nearest-neighbors. We
show that for a percolation range to next-nearest neighbors the percolation
threshold Tp is still equal to the Ising critical temperature Tc, and present
the phase diagram for this type of percolation. In addition, we present Monte
Carlo calculations of the finite size behavior of the correlated resistor
network defined on the Ising model. The thermal exponent t of the conductivity
that follows from it is found to be t = 0.2000 +- 0.0007. We observe no
corrections to scaling in its finite size behavior.Comment: 16 pages, REVTeX, 6 figures include
Loop condensation in the triangular lattice quantum dimer model
We study the mechanism of loop condensation in the quantum dimer model on the
triangular lattice. The triangular lattice quantum dimer model displays a
topologically ordered quantum liquid phase in addition to conventionally
ordered phases with broken symmetry. In the context of systems with extended
loop-like degrees of freedom, the formation of such topological order can be
described in terms of loop condensation. Using Monte Carlo calculations with
local and directed-loop updates, we compute geometric properties of the
transition graph loop distributions of several triangular lattice quantum dimer
wavefunctions that display dimer-liquid to dimer-crystal transitions and
characterize these in terms of loop condensation.Comment: 22 pages, 12 figures, fixed references and minor typo
Two phase transitions in the fully frustrated model
The fully frustrated model on a square lattice is studied by means of
Monte Carlo simulations. A Kosterlitz-Thouless transition is found at , followed by an ordinary Ising transition at a slightly
higher temperature, . The non-Ising exponents reported by
others, are explained as a failure of finite size scaling due to the screening
length associated with the nearby Kosterlitz-Thouless transition.Comment: REVTEX file, 8 pages, 5 figures in uuencoded postscrip
Finite-size scaling and conformal anomaly of the Ising model in curved space
We study the finite-size scaling of the free energy of the Ising model on
lattices with the topology of the tetrahedron and the octahedron. Our
construction allows to perform changes in the length scale of the model without
altering the distribution of the curvature in the space. We show that the
subleading contribution to the free energy follows a logarithmic dependence, in
agreement with the conformal field theory prediction. The conformal anomaly is
given by the sum of the contributions computed at each of the conical
singularities of the space, except when perfect order of the spins is precluded
by frustration in the model.Comment: 4 pages, 4 Postscript figure
Sine-Gordon mean field theory of a Coulomb Gas
Sine-Gordon field theory is used to investigate the phase diagram of a
neutral Coulomb gas. A variational mean field free energy is constructed and
the corresponding phase diagrams in two (2d) and three dimensions (3d) are
obtained. When analyzed in terms of chemical potential, the Sine-Gordon theory
predicts the phase diagram topologically identical with the Monte Carlo
simulations and a recently developed Debye-H\"uckel-Bjerrum (DHBj) theory. In
2d we find that the infinite order Kosterlitz-Thouless line terminates in a
tricritical point, after which the metal-insulator transition becomes first
order. However, when the transformation from chemical potential to the density
is made the whole of the insulating phase is mapped onto zero density.Comment: 5 pages, Revtex with twocolumn style, 2 Postscript figures. Submitted
to PR
Electro-anatomical mapping of the left atrium before and after cryothermal balloon isolation of the pulmonary veins
Introduction: The 28 mm cryoballoon catheter is a device used for pulmonary vein isolation (PVI). The aim of this study was to evaluate the extent of the ablation in the antral regions of the left atrium. Methods and Results: Eighteen patients with drug refractory, symptomatic, paroxysmal AF were enrolled. A 3D electroanatomic reconstruction of the left atrium was made before and after successful PVI with the 28 mm cryoballoon. Markers were placed at the ostium. Sixteen patients were mapped. Fourteen patients had 4 veins each, and 2 patients had a common ostium of the left sided veins. All separate ostia were isolated in the antral region. The two common ostia showed ostial isolation. There was a significant difference in vein size between the common (29 and 31 mm) and the separate ostia (19∈±∈4 mm) (p∈<∈0.01). The performance of an additional segmental ablation if balloon PVI did not eliminate all electrical activity, did not influence the extent of the ablation. The earliest left atrial activation during sinus rhythm was located in the superior septal region before ablation in all patients. After ablation, two patients showed a substantial downward shift towards the middle and inferior septal region respectively (NS). Four patients demonstrated a slight downward shift of the first activation. Conclusions: In cryoballoon PVI, the majority of the veins undergo antral isolation. Veins with a diameter larger than the balloon, are isolated ostially. In individual cases, the left atrial activation sequence appears to be altered after ablation
Apparent phase transitions in finite one-dimensional sine-Gordon lattices
We study the one-dimensional sine-Gordon model as a prototype of roughening
phenomena. In spite of the fact that it has been recently proven that this
model can not have any phase transition [J. A. Cuesta and A. Sanchez, J. Phys.
A 35, 2373 (2002)], Langevin as well as Monte Carlo simulations strongly
suggest the existence of a finite temperature separating a flat from a rough
phase. We explain this result by means of the transfer operator formalism and
show as a consequence that sine-Gordon lattices of any practically achievable
size will exhibit this apparent phase transition at unexpectedly large
temperatures.Comment: 7 pages, 4 figure
Dynamics of Particles Deposition on a Disordered Substrate: II. Far-from Equilibrium Behavior. -
The deposition dynamics of particles (or the growth of a rigid crystal) on a
disordered substrate at a finite deposition rate is explored. We begin with an
equation of motion which includes, in addition to the disorder, the periodic
potential due to the discrete size of the particles (or to the lattice
structure of the crystal) as well as the term introduced by Kardar, Parisi, and
Zhang (KPZ) to account for the lateral growth at a finite growth rate. A
generating functional for the correlation and response functions of this
process is derived using the approach of Martin, Sigga, and Rose. A consistent
renormalized perturbation expansion to first order in the non-Gaussian
couplings requires the calculation of diagrams up to three loops. To this order
we show, for the first time for this class of models which violates the the
fluctuation-dissipation theorem, that the theory is renormalizable. We find
that the effects of the periodic potential and the disorder decay on very large
scales and asymptotically the KPZ term dominates the behavior. However, strong
non-trivial crossover effects are found for large intermediate scales.Comment: 52 pages & 17 Figs in uucompressed file. UR-CM 94-090
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