127 research outputs found
Interface disorder and layer transitions in Ising thin films
The disorder and layer transitions in the interface between an Ising spin-1/2
film denoted , and an Ising spin-1 film denoted , are studied using
Monte Carlo simulations. The effects of both an external magnetic field, acting
only on the spin-1/2 film, and a crystal magnetic field acting only on the
spin-1 film, are studied for a fixed temperature and selected values of the
coupling constant between the two films. It is found that for large
values of the constant , the layers of the film , as well as those of
the film , undergo a first order layering transition. On the other hand,
the only disordered layer of the film is that one belonging to the
interface films , for any values of the crystal field . We
show the existence of a critical value of the crystal field , above
which this particular layer of the film is disordered. We found that
depends on the values of the constant coupling between the
two films.Comment: 6 pages Latex, 13 figures Postscript forma
Driven Diffusive Systems with Disorder
We discuss recent work on the static and dynamical properties of the
asymmetric exclusion process, generalized to include the effect of disorder. We
study in turn: random disorder in the properties of particles; disorder in the
spatial distribution of transition rates, both with a single easy direction and
with random reversals of the easy direction; dynamical disorder, where
particles move in a disordered landscape which itself evolves in time. In every
case, the system exhibits phase separation; in some cases, it is of an unusual
sort. The time-dependent properties of density fluctuations are in accord with
the kinematic wave criterion that the dynamical universality class is
unaffected by disorder if the kinematic wave velocity is nonzero.Comment: To appear in Physica A, Proc. of International Workshop on Common
Trends in Traffic Systems (IIT, Kanpur,2006
Numerical study of rice-pile model
A one-dimensional model of a rice-pile is numerically studied for different driving mechanisms. We found that for a sufficiently large system, there is a sharp transition between the trivial behaviour of a 1D BTW model and self-organized critical (SOC) behaviour. Depending on the driving mechanism, the self-organized critical rice-pile model belongs to two different universality classes.A one-dimensional model of a rice-pile is numerically studied for different driving mechanisms. We found that for a sufficiently large system, there is a sharp transition between the trivial behaviour of a 1D BTW model and self-organized critical (SOC) behaviour. Depending on the driving mechanism, the self-organized critical rice-pile model belongs to two different universality classes
Phase diagrams and magnetic behavior of films with amorphization and anisotropy in surfaces
The phase diagrams and magnetic behavior of thin films with two amorphous surfaces are investigated by the use of the effective field theory with correlations. The transition temperature dependence of the exchange integral at surfaces, coupling between surface and nearest-layers, film thickness, and structural fluctuations are studied. Some interesting phenomena can occur as wetting phenomena and compensation point.The phase diagrams and magnetic behavior of thin films with two amorphous surfaces are investigated by the use of the effective field theory with correlations. The transition temperature dependence of the exchange integral at surfaces, coupling between surface and nearest-layers, film thickness, and structural fluctuations are studied. Some interesting phenomena can occur as wetting phenomena and compensation point
A simulation study of an asymmetric exclusion model with disorder
On the one hand, using numerical simulations, we study the asymmetric exclusion model with open boundaries, particlewise disorder. The phase diagram in the (α , β) -plane displays high density, low density and maximum current phases, with the first order transition line between high and low density phases shifted away from the line α =β. Within the low density phase a platoon phase transition occurs, many features of which can be explained using exact results for asymmetric exclusion with particlewise disorder on the ring. In a certain region of parameter space the disorder induces a cusp in the current-density relation at maximum flow. Our simulations indicate that this does not affect the topology of the phase diagram, nor the familiar 1/Öx -decay of the density profile in the maximum current phase. On the other hand, we study the effects of defects in the road and of jumping rate ∆t on the phase diagram J−ρ, using asymmetric exclusion model with periodic boundaries. For different level of disorder, the space-time evolution of particles displays «waves» for both phases low density and high density. Besides, there exist two critical values of density, a lower critical value ρc1 and a upper critical value ρc2, in between the current is constant and reaches its maximal value Jmax which increases with increasing the jumping rate ∆t and/or the degree of disorder c. Increasing ∆t and/or c, ρc1 increases and ρc2 decreases.On the one hand, using numerical simulations, we study the asymmetric exclusion model with open boundaries, particlewise disorder. The phase diagram in the (α , β) -plane displays high density, low density and maximum current phases, with the first order transition line between high and low density phases shifted away from the line α =β. Within the low density phase a platoon phase transition occurs, many features of which can be explained using exact results for asymmetric exclusion with particlewise disorder on the ring. In a certain region of parameter space the disorder induces a cusp in the current-density relation at maximum flow. Our simulations indicate that this does not affect the topology of the phase diagram, nor the familiar 1/Öx -decay of the density profile in the maximum current phase. On the other hand, we study the effects of defects in the road and of jumping rate ∆t on the phase diagram J−ρ, using asymmetric exclusion model with periodic boundaries. For different level of disorder, the space-time evolution of particles displays «waves» for both phases low density and high density. Besides, there exist two critical values of density, a lower critical value ρc1 and a upper critical value ρc2, in between the current is constant and reaches its maximal value Jmax which increases with increasing the jumping rate ∆t and/or the degree of disorder c. Increasing ∆t and/or c, ρc1 increases and ρc2 decreases
A Monte Carlo study of random surface field effect on layering transitions
The effect of a random surface field, within the bimodal distribution, on the
layering transitions in a spin-1/2 Ising thin film is investigated, using Monte
Carlo simulations. It is found that the layering transitions depend strongly on
the concentration of the disorder of the surface magnetic field, for a
fixed temperature, surface and external magnetic fields. Indeed, the critical
concentration at which the magnetisation of each layer changes the
sign discontinuously, decreases for increasing the applied surface magnetic
field, for fixed values of the temperature and the external magnetic field
. Moreover, the behaviour of the layer magnetisations as well as the
distribution of positive and negative spins in each layer, are also established
for specific values of , , and the temperature . \\Comment: 5 pages latex, 6 figures postscrip
Disorder-induced phase transition in a one-dimensional model of rice pile
We propose a one-dimensional rice-pile model which connects the 1D BTW
sandpile model (Phys. Rev. A 38, 364 (1988)) and the Oslo rice-pile model
(Phys. Rev. lett. 77, 107 (1997)) in a continuous manner. We found that for a
sufficiently large system, there is a sharp transition between the trivial
critical behaviour of the 1D BTW model and the self-organized critical (SOC)
behaviour. When there is SOC, the model belongs to a known universality class
with the avalanche exponent .Comment: 10 pages, 7 eps figure
Analytical Approach to the One-Dimensional Disordered Exclusion Process with Open Boundaries and Random Sequential Dynamics
A one dimensional disordered particle hopping rate asymmetric exclusion
process (ASEP) with open boundaries and a random sequential dynamics is studied
analytically. Combining the exact results of the steady states in the pure case
with a perturbative mean field-like approach the broken particle-hole symmetry
is highlighted and the phase diagram is studied in the parameter space
, where and represent respectively the
injection rate and the extraction rate of particles. The model displays, as in
the pure case, high-density, low-density and maximum-current phases. All
critical lines are determined analytically showing that the high-density
low-density first order phase transition occurs at . We show
that the maximum-current phase extends its stability region as the disorder is
increased and the usual -decay of the density profile in this
phase is universal. Assuming that some exact results for the disordered model
on a ring hold for a system with open boundaries, we derive some analytical
results for platoon phase transition within the low-density phase and we give
an analytical expression of its corresponding critical injection rate
. As it was observed numerically, we show that the quenched
disorder induces a cusp in the current-density relation at maximum flow in a
certain region of parameter space and determine the analytical expression of
its slope. The results of numerical simulations we develop agree with the
analytical ones.Comment: 23 pages, 7 figures. to appear in J. Stat. Phy
fluctuations in a ricepile model
The temporal fluctuation of the average slope of a ricepile model is
investigated. It is found that the power spectrum scales as
with when grains of rice are added only to
one end of the pile. If grains are randomly added to the pile, the power
spectrum exhibits behaviour. The profile fluctuations of the pile under
different driving mechanisms are also discussed.Comment: 4 pages, 4 eps figures; Revtex format, published versio
Genetic biomarkers for intravenous immunoglobulin response in chronic inflammatory demyelinating polyradiculoneuropathy
Background and purpose Chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is a clinical and electrophysiological heterogeneous immune-mediated polyneuropathy. Intravenous immunoglobulin (IVIg), corticosteroids, and plasma exchange are proven effective treatments for CIDP. The clinical response to IVIg is variable between patients and currently unexplained. Finding biomarkers related to treatment response can help to understand the diversity of CIDP and personalise treatment choice.Methods We investigated whether genetic variation between patients may explain some of these differences in treatment response. Based on previous publications, we selected six candidate genes that might affect immune and axonal functions, IVIg metabolism, and treatment response in CIDP. Genetic variants were assessed in 172 CIDP patients treated with at least one course of IVIg (2 g/kg). A response to IVIg was defined by >= 1 grade improvement on the modified Rankin Scale. Blood samples were tested for variations in CNTN2, PRF1, FCGRT, FCGR2B, GJB1, and SH2D2A genes.Results In univariate analysis, patients with the FCGR2B promoter variant 2B.4/2B.1 responded more often to IVIg than patients with the 2B.1/2B.1 variant (odds ratio [OR] = 6.9, 95% confidence interval [CI] = 1.6-30; p = 0.003). Patients with the p.(Ala91Val) variant of PRF1 were less often IVIg responsive (OR = 0.34, 95% CI = 0.13-0.91; p = 0.038). In multivariate analysis, both PRF1 and FCGR2B showed discriminative ability to predict the chance of IVIg response (area under the curve = 0.67).Conclusions Variations in PRF1 and the promoter region of FCGR2B are associated with the response to IVIg in CIDP. These findings, which require validation, are a first step towards the understanding of the heterogeneity in the treatment response in CIDP.Genetics of disease, diagnosis and treatmen
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