118 research outputs found
Collective Dynamics of Random Polyampholytes
We consider the Langevin dynamics of a semi-dilute system of chains which are
random polyampholytes of average monomer charge and with a fluctuations in
this charge of the size and with freely floating counter-ions in the
surrounding. We cast the dynamics into the functional integral formalism and
average over the quenched charge distribution in order to compute the dynamic
structure factor and the effective collective potential matrix. The results are
given for small charge fluctuations. In the limit of finite we then find
that the scattering approaches the limit of polyelectrolyte solutions.Comment: 13 pages including 6 figures, submitted J. Chem. Phy
Broad relaxation spectrum and the field theory of glassy dynamics for pinned elastic systems
We study thermally activated, low temperature equilibrium dynamics of elastic
systems pinned by disorder using one loop functional renormalization group
(FRG). Through a series of increasingly complete approximations, we investigate
how the field theory reveals the glassy nature of the dynamics, in particular
divergent barriers and barrier distributions controling the spectrum of
relaxation times. A naive single relaxation time approximation for each
wavevector is found to be unsatisfactory. A second approximation based on a
random friction model, yields a size (L) dependent log-normal distribution of
relaxation times (mean barriers ~L^\theta and variance ~ L^{\theta/2}) and a
procedure to estimate dynamical scaling functions. Finally, we study the full
structure of the running dynamical effective action within the field theory. We
find that relaxation time distributions are non-trivial (broad but not
log-normal) and encoded in a closed hierarchy of FRG equations. A thermal
boundary layer ansatz (TBLA) appears as a consistent solution. It extends the
one discovered in the statics which was shown to embody droplet thermal
fluctuations. Although perturbative control remains a challenge, the structure
of the dynamical TBLA which encodes barrier distributions opens the way for
deeper understanding of the field theory approach to glasses
Patterns of distribution of some freshwater molluscs of the Levant region
The evolutionary and dispersal history of the following freshwater mollusc species of the northern Levant has been reconstructed as an example by using new records and an analysis of the subspecific arrangement: Unio elongatulus, Unió terminális, Coibicula fluminalis, Leguminaia saulcyi, Leguminaia wheatleyi, Potomida littoralis, Maigaritifera homsensis (Bivalivia), Theodoxus joidani, Melanopsis piaemoisa (Gastropoda). The patterns of distribution confirm and complement the general geological and paleogeographical theories concerning the Levant region
Quantized Scaling of Growing Surfaces
The Kardar-Parisi-Zhang universality class of stochastic surface growth is
studied by exact field-theoretic methods. From previous numerical results, a
few qualitative assumptions are inferred. In particular, height correlations
should satisfy an operator product expansion and, unlike the correlations in a
turbulent fluid, exhibit no multiscaling. These properties impose a
quantization condition on the roughness exponent and the dynamic
exponent . Hence the exact values for two-dimensional
and for three-dimensional surfaces are derived.Comment: 4 pages, revtex, no figure
Phase transitions and noise crosscorrelations in a model of directed polymers in a disordered medium
We show that effective interactions mediated by disorder between two directed
polymers can be modelled as the crosscorrelation of noises in the
Kardar-Parisi-Zhang (KPZ) equations satisfied by the respective free energies
of these polymers. When there are two polymers, disorder introduces attractive
interactions between them. We analyze the phase diagram in details and show
that these interactions lead to new phases in the phase diagram. We show that,
even in dimension , the two directed polymers see the attraction only if
the strength of the disorder potential exceeds a threshold value. We extend our
calculations to show that if there are polymers in the system then -body
interactions are generated in the disorder averaged effective free energy.Comment: To appear in Phys. Rev. E(2000
Effect of a columnar defect on the shape of slow-combustion fronts
We report experimental results for the behavior of slow-combustion fronts in
the presence of a columnar defect with excess or reduced driving, and compare
them with those of mean-field theory. We also compare them with simulation
results for an analogous problem of driven flow of particles with hard-core
repulsion (ASEP) and a single defect bond with a different hopping probability.
The difference in the shape of the front profiles for excess vs. reduced
driving in the defect, clearly demonstrates the existence of a KPZ-type of
nonlinear term in the effective evolution equation for the slow-combustion
fronts. We also find that slow-combustion fronts display a faceted form for
large enough excess driving, and that there is a corresponding increase then in
the average front speed. This increase in the average front speed disappears at
a non-zero excess driving in agreement with the simulated behavior of the ASEP
model.Comment: 7 pages, 7 figure
Slow dynamics and aging in spin-glasses
Contribution presented by Eric Vincent in the Conference `Complex Behaviour
of Glassy Systems', Sitges, Barcelona, Spain, June, 1996. It contains a review
of the experimental results on Slow dynamics and aging in spin-glasses. It also
presents their comparison with recent theoretical developments in the
description of the out of equilibrium dynamics of disordered systems; namely,
the trap model and the mean-field theory.Comment: 35 pages, 12 figures, macro lmamult.sty (included
On Growth, Disorder, and Field Theory
This article reviews recent developments in statistical field theory far from
equilibrium. It focuses on the Kardar-Parisi-Zhang equation of stochastic
surface growth and its mathematical relatives, namely the stochastic Burgers
equation in fluid mechanics and directed polymers in a medium with quenched
disorder. At strong stochastic driving -- or at strong disorder, respectively
-- these systems develop nonperturbative scale-invariance. Presumably exact
values of the scaling exponents follow from a self-consistent asymptotic
theory. This theory is based on the concept of an operator product expansion
formed by the local scaling fields. The key difference to standard Lagrangian
field theory is the appearance of a dangerous irrelevant coupling constant
generating dynamical anomalies in the continuum limit.Comment: review article, 50 pages (latex), 10 figures (eps), minor
modification of original versio
9-Genes Reinforce the Phylogeny of Holometabola and Yield Alternate Views on the Phylogenetic Placement of Strepsiptera
Background: The extraordinary morphology, reproductive and developmental biology, and behavioral ecology of twisted wing parasites (order Strepsiptera) have puzzled biologists for centuries. Even today, the phylogenetic position of these enigmatic “insects from outer space” [1] remains uncertain and contentious. Recent authors have argued for the placement of Strepsiptera within or as a close relative of beetles (order Coleoptera), as sister group of flies (order Diptera), or even outside of Holometabola.Methodology/Principal Findings Here, we combine data from several recent studies with new data (for a total of 9 nuclear genes and ∼13 kb of aligned data for 34 taxa), to help clarify the phylogenetic placement of Strepsiptera. Our results unequivocally support the monophyly of Neuropteroidea ( = Neuropterida + Coleoptera) + Strepsiptera, but recover Strepsiptera either derived from within polyphagan beetles (order Coleoptera), or in a position sister to Neuropterida. All other supra-ordinal- and ordinal-level relationships recovered with strong nodal support were consistent with most other recent studies. Conclusions/Significance: These results, coupled with the recent proposed placement of Strepsiptera sister to Coleoptera, suggest that while the phylogenetic neighborhood of Strepsiptera has been identified, unequivocal placement to a specific branch within Neuropteroidea will require additional study.Organismic and Evolutionary Biolog
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