904 research outputs found
Sublattice synchronization of chaotic networks with delayed couplings
Synchronization of chaotic units coupled by their time delayed variables are
investigated analytically. A new type of cooperative behavior is found:
sublattice synchronization. Although the units of one sublattice are not
directly coupled to each other, they completely synchronize without time delay.
The chaotic trajectories of different sublattices are only weakly correlated
but not related by generalized synchronization. Nevertheless, the trajectory of
one sublattice is predictable from the complete trajectory of the other one.
The spectra of Lyapunov exponents are calculated analytically in the limit of
infinite delay times, and phase diagrams are derived for different topologies
Stable isochronal synchronization of mutually coupled chaotic lasers
The dynamics of two mutually coupled chaotic diode lasers are investigated
experimentally and numerically. By adding self feedback to each laser, stable
isochronal synchronization is established. This stability, which can be
achieved for symmetric operation, is essential for constructing an optical
public-channel cryptographic system. The experimental results on diode lasers
are well described by rate equations of coupled single mode lasers
Precise calculation of the threshold of various directed percolation models on a square lattice
Using Monte Carlo simulations on different system sizes we determine with
high precision the critical thresholds of two families of directed percolation
models on a square lattice. The thresholds decrease exponentially with the
degree of connectivity. We conjecture that decays exactly as the
inverse of the coodination number.Comment: 2 pages, 2 figures and 1 tabl
Evaporation and Step Edge Diffusion in MBE
Using kinetic Monte-Carlo simulations of a Solid-on-Solid model we
investigate the influence of step edge diffusion (SED) and evaporation on
Molecular Beam Epitaxy (MBE). Based on these investigations we propose two
strategies to optimize MBE-growth. The strategies are applicable in different
growth regimes: during layer-by-layer growth one can reduce the desorption rate
using a pulsed flux. In three-dimensional (3D) growth the SED can help to grow
large, smooth structures. For this purpose the flux has to be reduced with time
according to a power law.Comment: 5 pages, 2 figures, latex2e (packages: elsevier,psfig,latexsym
Directed Polymer -- Directed Percolation Transition
We study the relation between the directed polymer and the directed
percolation models, for the case of a disordered energy landscape where the
energies are taken from bimodal distribution. We find that at the critical
concentration of the directed percolation, the directed polymer undergoes a
transition from the directed polymer universality class to the directed
percolation universality class. We also find that directed percolation clusters
affect the characterisrics of the directed polymer below the critical
concentration.Comment: LaTeX 2e; 12 pages, 5 figures; in press, will be published in
Europhys. Let
Cluster mean-field study of the parity conserving phase transition
The phase transition of the even offspringed branching and annihilating
random walk is studied by N-cluster mean-field approximations on
one-dimensional lattices. By allowing to reach zero branching rate a phase
transition can be seen for any N <= 12.The coherent anomaly extrapolations
applied for the series of approximations results in and
.Comment: 6 pages, 5 figures, 1 table included, Minor changes, scheduled for
pubication in PR
A simple model of epitaxial growth
A discrete solid-on-solid model of epitaxial growth is introduced which, in a
simple manner, takes into account the effect of an Ehrlich-Schwoebel barrier at
step edges as well as the local relaxation of incoming particles. Furthermore a
fast step edge diffusion is included in 2+1 dimensions. The model exhibits the
formation of pyramid-like structures with a well-defined constant inclination
angle. Two regimes can be distinguished clearly: in an initial phase (I) a
definite slope is selected while the number of pyramids remains unchanged. Then
a coarsening process (II) is observed which decreases the number of islands
according to a power law in time. Simulations support self-affine scaling of
the growing surface in both regimes. The roughness exponent is alpha =1 in all
cases. For growth in 1+1 dimensions we obtain dynamic exponents z = 2 (I) and z
= 3 (II). Simulations for d=2+1 seem to be consistent with z= 2 (I) and z= 2.3
(II) respectively.Comment: 8 pages Latex2e, 4 Postscript figures included, uses packages
a4wide,epsfig,psfig,amsfonts,latexsy
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Functional characterization of reappearing B cells after anti-CD20 treatment of CNS autoimmune disease.
The anti-CD20 antibody ocrelizumab, approved for treatment of multiple sclerosis, leads to rapid elimination of B cells from the blood. The extent of B cell depletion and kinetics of their recovery in different immune compartments is largely unknown. Here, we studied how anti-CD20 treatment influences B cells in bone marrow, blood, lymph nodes, and spleen in models of experimental autoimmune encephalomyelitis (EAE). Anti-CD20 reduced mature B cells in all compartments examined, although a subpopulation of antigen-experienced B cells persisted in splenic follicles. Upon treatment cessation, CD20+ B cells simultaneously repopulated in bone marrow and spleen before their reappearance in blood. In EAE induced by native myelin oligodendrocyte glycoprotein (MOG), a model in which B cells are activated, B cell recovery was characterized by expansion of mature, differentiated cells containing a high frequency of myelin-reactive B cells with restricted B cell receptor gene diversity. Those B cells served as efficient antigen-presenting cells (APCs) for activation of myelin-specific T cells. In MOG peptide-induced EAE, a purely T cell-mediated model that does not require B cells, in contrast, reconstituting B cells exhibited a naive phenotype without efficient APC capacity. Our results demonstrate that distinct subpopulations of B cells differ in their sensitivity to anti-CD20 treatment and suggest that differentiated B cells persisting in secondary lymphoid organs contribute to the recovering B cell pool
Directed Fixed Energy Sandpile Model
We numerically study the directed version of the fixed energy sandpile. On a
closed square lattice, the dynamical evolution of a fixed density of sand
grains is studied. The activity of the system shows a continuous phase
transition around a critical density. While the deterministic version has the
set of nontrivial exponents, the stochastic model is characterized by mean
field like exponents.Comment: 5 pages, 6 figures, to be published in Phys. Rev.
Active Width at a Slanted Active Boundary in Directed Percolation
The width W of the active region around an active moving wall in a directed
percolation process diverges at the percolation threshold p_c as W \simeq A
\epsilon^{-\nu_\parallel} \ln(\epsilon_0/\epsilon), with \epsilon=p_c-p,
\epsilon_0 a constant, and \nu_\parallel=1.734 the critical exponent of the
characteristic time needed to reach the stationary state \xi_\parallel \sim
\epsilon^{-\nu_\parallel}. The logarithmic factor arises from screening of
statistically independent needle shaped sub clusters in the active region.
Numerical data confirm this scaling behaviour.Comment: 5 pages, 5 figure
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