714 research outputs found
Finite-Size Scaling Studies of Reaction-Diffusion Systems Part III: Numerical Methods
The scaling exponent and scaling function for the 1D single species
coagulation model are shown to be universal, i.e. they are
not influenced by the value of the coagulation rate. They are independent of
the initial conditions as well. Two different numerical methods are used to
compute the scaling properties: Monte Carlo simulations and extrapolations of
exact finite lattice data. These methods are tested in a case where analytical
results are available. It is shown that Monte Carlo simulations can be used to
compute even the correction terms. To obtain reliable results from finite-size
extrapolations exact numerical data for lattices up to ten sites are
sufficient.Comment: 19 pages, LaTeX, 5 figures uuencoded, BONN HE-94-0
Stochastic Ballistic Annihilation and Coalescence
We study a class of stochastic ballistic annihilation and coalescence models
with a binary velocity distribution in one dimension. We obtain an exact
solution for the density which reveals a universal phase diagram for the
asymptotic density decay. By universal we mean that all models in the class are
described by a single phase diagram spanned by two reduced parameters. The
phase diagram reveals four regimes, two of which contain the previously studied
cases of ballistic annihilation. The two new phases are a direct consequence of
the stochasticity. The solution is obtained through a matrix product approach
and builds on properties of a q-deformed harmonic oscillator algebra.Comment: 4 pages RevTeX, 3 figures; revised version with some corrections,
additional discussion and in RevTeX forma
Crossover from Rate-Equation to Diffusion-Controlled Kinetics in Two-Particle Coagulation
We develop an analytical diffusion-equation-type approximation scheme for the
one-dimensional coagulation reaction A+A->A with partial reaction probability
on particle encounters which are otherwise hard-core. The new approximation
describes the crossover from the mean-field rate-equation behavior at short
times to the universal, fluctuation-dominated behavior at large times. The
approximation becomes quantitatively accurate when the system is initially
close to the continuum behavior, i.e., for small initial density and fast
reaction. For large initial density and slow reaction, lattice effects are
nonnegligible for an extended initial time interval. In such cases our
approximation provides the correct description of the initial mean-field as
well as the asymptotic large-time, fluctuation-dominated behavior. However, the
intermediate-time crossover between the two regimes is described only
semiquantitatively.Comment: 21 pages, plain Te
Coupled Maps on Trees
We study coupled maps on a Cayley tree, with local (nearest-neighbor)
interactions, and with a variety of boundary conditions. The homogeneous state
(where every lattice site has the same value) and the node-synchronized state
(where sites of a given generation have the same value) are both shown to occur
for particular values of the parameters and coupling constants. We study the
stability of these states and their domains of attraction. As the number of
sites that become synchronized is much higher compared to that on a regular
lattice, control is easier to effect. A general procedure is given to deduce
the eigenvalue spectrum for these states. Perturbations of the synchronized
state lead to different spatio-temporal structures. We find that a mean-field
like treatment is valid on this (effectively infinite dimensional) lattice.Comment: latex file (25 pages), 4 figures included. To be published in Phys.
Rev.
Excitonic Funneling in Extended Dendrimers with Non-Linear and Random Potentials
The mean first passage time (MFPT) for photoexcitations diffusion in a
funneling potential of artificial tree-like light-harvesting antennae
(phenylacetylene dendrimers with generation-dependent segment lengths) is
computed. Effects of the non-linearity of the realistic funneling potential and
slow random solvent fluctuations considerably slow down the center-bound
diffusion beyond a temperature-dependent optimal size. Diffusion on a
disordered Cayley tree with a linear potential is investigated analytically. At
low temperatures we predict a phase in which the MFPT is dominated by a few
paths.Comment: 4 pages, 4 figures, To be published in Phys. Rev. Let
PCR array and protein array studies demonstrate that IL-1β (interleukin-1β) stimulates the expression and secretion of multiple cytokines and chemokines in human adipocytes
The role of IL-1β in regulating the expression and secretion of cytokines and chemokines by human adipocytes was examined. Adipocytes were incubated with human IL-1β for 4 or 24 h.
The expression of a panel of 84 cytokine/chemokine genes was probed using PCR arrays. IL-1β stimulated the expression of >30 cytokine/chemokine genes on the arrays; 15 showed >100-fold increases in mRNA at 4 or 24 h including CSF3, CXCL1, CXCL2, CXCL12 and IL8. CSF3 exhibited a 10,000-fold increase in mRNA at 4 h. ADIPOQ was among the genes whose expression was inhibited. Protein arrays were used to examine the secretion of cytokines/chemokines from adipocytes. IL-1β stimulated the secretion of multiple cytokines/chemokines including MCP-1, IL-8, IP-10, MIP-1α and MCP-4. The most responsive was IP-10, which exhibited a 5,000-fold increase in secretion with IL-1β. IL-1β is likely to play a substantial role in stimulating the inflammatory response in human adipocytes in obesity
Disorder and Funneling Effects on Exciton Migration in Tree-Like Dendrimers
The center-bound excitonic diffusion on dendrimers subjected to several types
of non-homogeneous funneling potentials, is considered. We first study the
mean-first passage time (MFPT) for diffusion in a linear potential with
different types of correlated and uncorrelated random perturbations. Increasing
the funneling force, there is a transition from a phase in which the MFPT grows
exponentially with the number of generations , to one in which it does so
linearly. Overall the disorder slows down the diffusion, but the effect is much
more pronounced in the exponential compared to the linear phase. When the
disorder gives rise to uncorrelated random forces there is, in addition, a
transition as the temperature is lowered. This is a transition from a
high- regime in which all paths contribute to the MFPT to a low- regime
in which only a few of them do. We further explore the funneling within a
realistic non-linear potential for extended dendrimers in which the dependence
of the lowest excitonic energy level on the segment length was derived using
the Time-Dependent Hatree-Fock approximation. Under this potential the MFPT
grows initially linearly with but crosses-over, beyond a molecular-specific
and -dependent optimal size, to an exponential increase. Finally we consider
geometrical disorder in the form of a small concentration of long connections
as in the {\it small world} model. Beyond a critical concentration of
connections the MFPT decreases significantly and it changes to a power-law or
to a logarithmic scaling with , depending on the strength of the funneling
force.Comment: 13 pages, 9 figure
Soluble two-species diffusion-limited Models in arbitrary dimensions
A class of two-species ({\it three-states}) bimolecular diffusion-limited
models of classical particles with hard-core reacting and diffusing in a
hypercubic lattice of arbitrary dimension is investigated. The manifolds on
which the equations of motion of the correlation functions close, are
determined explicitly. This property allows to solve for the density and the
two-point (two-time) correlation functions in arbitrary dimension for both, a
translation invariant class and another one where translation invariance is
broken. Systems with correlated as well as uncorrelated, yet random initial
states can also be treated exactly by this approach. We discuss the asymptotic
behavior of density and correlation functions in the various cases. The
dynamics studied is very rich.Comment: 28 pages, 0 figure. To appear in Physical Review E (February 2001
PCR arrays indicate that the expression of extracellular matrix and cell adhesion genes in human adipocytes is regulated by IL-1β (interleukin-1β)
The role of IL-1β in regulating the expression of extracellular matrix (ECM) and cell adhesion genes in human adipocytes has been examined. Adipocytes differentiated in culture were incubated with IL-1β for 4 or 24 h and RNA probed with PCR arrays for 84 ECM and cell adhesion genes. Treatment with IL-1β resulted in changes in the expression at one or both time points of ~50% of the genes probed by the arrays, the majority being down-regulated. Genes whose expression was down-regulated by IL-1β included those encoding several collagen chains and integrin subunits. In contrast, IL-1β induced substantial increases (>10-fold) in the expression of ICAM1, VCAM1, MMP1 and MMP3; the secretion of the encoded proteins was also markedly stimulated. IL-1β has a pervasive effect on the expression of ECM and cell adhesion genes in human adipocytes, consistent with the derangement of tissue structure during inflammation in white fat
Investigating A Dose Response Relationship between High Fat Diet Consumption and the Contractile Performance of Isolated Mouse Soleus, EDL and Diaphragm Muscles
- …