484 research outputs found
Deconfinement transition dynamics and early thermalization in QGP
We perform SU(3) Lattice Gauge Theory simulations of the deconfinement
transition attempting to mimic conditions encountered in heavy ion collisions.
Specifically, we perform a sudden temperature quench across the deconfinement
temperature, and follow the response of the system in successive simulation
sweeps under spatial lattice expansion and temperature fall-off. In
measurements of the Polyakov loop and structure functions a robust strong
signal of global instability response is observed through the exponential
growth of low momentum modes. Development of these long range modes isotropizes
the system which reaches thermalization shortly afterwards, and enters a stage
of quasi-equilibrium expansion and cooling till its return to the confinement
phase. The time scale characterizing full growth of the long range modes is
largely unaffected by the conditions of spatial expansion and temperature
variation in the system, and is much shorter than the scale set by the interval
to return to the confinement phase. The wide separation of these two scales is
such that it naturally results in isotropization times well inside 1 fm/c.Comment: 11 pages, 8 eps figures, added references, typos correcte
Influence of Disorder Strength on Phase Field Models of Interfacial Growth
We study the influence of disorder strength on the interface roughening
process in a phase-field model with locally conserved dynamics. We consider two
cases where the mobility coefficient multiplying the locally conserved current
is either constant throughout the system (the two-sided model) or becomes zero
in the phase into which the interface advances (one-sided model). In the limit
of weak disorder, both models are completely equivalent and can reproduce the
physical process of a fluid diffusively invading a porous media, where
super-rough scaling of the interface fluctuations occurs. On the other hand,
increasing disorder causes the scaling properties to change to intrinsic
anomalous scaling. In the limit of strong disorder this behavior prevails for
the one-sided model, whereas for the two-sided case, nucleation of domains in
front of the invading front are observed.Comment: Accepted for publication in PR
Conservation laws for the voter model in complex networks
We consider the voter model dynamics in random networks with an arbitrary
distribution of the degree of the nodes. We find that for the usual node-update
dynamics the average magnetization is not conserved, while an average
magnetization weighted by the degree of the node is conserved. However, for a
link-update dynamics the average magnetization is still conserved. For the
particular case of a Barabasi-Albert scale-free network the voter model
dynamics leads to a partially ordered metastable state with a finite size
survival time. This characteristic time scales linearly with system size only
when the updating rule respects the conservation law of the average
magnetization. This scaling identifies a universal or generic property of the
voter model dynamics associated with the conservation law of the magnetization.Comment: 5 pages, 4 figures; for related material please visit
http://www.imedea.uib.e
Phase Separation Driven by External Fluctuations
The influence of external fluctuations in phase separation processes is
analysed. These fluctuations arise from random variations of an external
control parameter. A linear stability analysis of the homogeneous state shows
that phase separation dynamics can be induced by external noise. The spatial
structure of the noise is found to have a relevant role in this phenomenon.
Numerical simulations confirm these results. A comparison with order-disorder
noise induced phase transitions is also made.Comment: 4 pages, 4 Postscript figures included in text. LaTeX (with Revtex
macros
Decelerating microdynamics can accelerate macrodynamics in the voter model
For the voter model, we study the effect of a memory-dependent transition
rate. We assume that the transition of a spin into the opposite state decreases
with the time it has been in its current state. Counter-intuitively, we find
that the time to reach a macroscopically ordered state can be accelerated by
slowing-down the microscopic dynamics in this way. This holds for different
network topologies, including fully-connected ones. We find that the ordering
dynamics is governed by two competing processes which either stabilize the
majority or the minority state. If the first one dominates, it accelerates the
ordering of the system. The conclusions of this Letter are not restricted to
the voter model, but remain valid to many other spin systems as well.Comment: See http://www.sg.ethz.ch for related publication
Universality in the merging dynamics of parametric active contours: a study in MRI-based lung segmentation
Measurement of lung ventilation is one of the most reliable techniques of
diagnosing pulmonary diseases. The time consuming and bias prone traditional
methods using hyperpolarized HHe and H magnetic resonance
imageries have recently been improved by an automated technique based on
multiple active contour evolution. Mapping results from an equivalent
thermodynamic model, here we analyse the fundamental dynamics orchestrating the
active contour (AC) method. We show that the numerical method is inherently
connected to the universal scaling behavior of a classical nucleation-like
dynamics. The favorable comparison of the exponent values with the theoretical
model render further credentials to our claim.Comment: 4 pages, 4 figure
Majority Rule Dynamics in Finite Dimensions
We investigate the long-time behavior of a majority rule opinion dynamics
model in finite spatial dimensions. Each site of the system is endowed with a
two-state spin variable that evolves by majority rule. In a single update
event, a group of spins with a fixed (odd) size is specified and all members of
the group adopt the local majority state. Repeated application of this update
step leads to a coarsening mosaic of spin domains and ultimate consensus in a
finite system. The approach to consensus is governed by two disparate time
scales, with the longer time scale arising from realizations in which spins
organize into coherent single-opinion bands. The consequences of this
geometrical organization on the long-time kinetics are explored.Comment: 8 pages, 2-column revtex format, 11 figures. Version 2: minor changes
in response to referee comments and typos corrected; final version for PR
False Vacuum Decay after Inflation
Inflation is terminated by a non-equilibrium process which finally leads to a
thermal state. We study the onset of this transition in a class of hybrid
inflation models. The exponential growth of tachyonic modes leads to
decoherence and spinodal decomposition. We compute the decoherence time, the
spinodal time, the size of the formed domains and the homogeneous classical
fields within a single domain.Comment: Latex2e, 11 pages, 4 figure
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