4,149 research outputs found
On-off intermittency over an extended range of control parameter
We propose a simple phenomenological model exhibiting on-off intermittency
over an extended range of control parameter. We find that the distribution of
the 'off' periods has as a power-law tail with an exponent varying continuously
between -1 and -2, at odds with standard on-off intermittency which occurs at a
specific value of the control parameter, and leads to the exponent -3/2. This
non-trivial behavior results from the competition between a strong slowing down
of the dynamics at small values of the observable, and a systematic drift
toward large values.Comment: 4 pages, 3 figure
Geometric origin of scaling in large traffic networks
Large scale traffic networks are an indispensable part of contemporary human
mobility and international trade. Networks of airport travel or cargo ships
movements are invaluable for the understanding of human mobility
patterns\cite{Guimera2005}, epidemic spreading\cite{Colizza2006}, global
trade\cite{Imo2006} and spread of invasive species\cite{Ruiz2000}. Universal
features of such networks are necessary ingredients of their description and
can point to important mechanisms of their formation. Different
studies\cite{Barthelemy2010} point to the universal character of some of the
exponents measured in such networks. Here we show that exponents which relate
i) the strength of nodes to their degree and ii) weights of links to degrees of
nodes that they connect have a geometric origin. We present a simple robust
model which exhibits the observed power laws and relates exponents to the
dimensionality of 2D space in which traffic networks are embedded. The model is
studied both analytically and in simulations and the conditions which result
with previously reported exponents are clearly explained. We show that the
relation between weight strength and degree is , the relation
between distance strength and degree is and the relation
between weight of link and degrees of linked nodes is
on the plane 2D surface. We further analyse the
influence of spherical geometry, relevant for the whole planet, on exact values
of these exponents. Our model predicts that these exponents should be found in
future studies of port networks and impose constraints on more refined models
of port networks.Comment: 17 pages, 5 figures, 1 tabl
Coal desulfurization by low temperature chlorinolysis, phase 2
An engineering scale reactor system was constructed and operated for the evaluation of five high sulfur bituminous coals obtained from Kentucky, Ohio, and Illinois. Forty-four test runs were conducted under conditions of 100 by 200 mesh coal,solvents - methlychloroform and water, 60 to 130 C, 0 to 60 psig, 45 to 90 minutes, and gaseous chlorine flow rate of up to 24 SCFH. Sulfur removals demonstrated for the five coals were: maximum total sulfur removal of 46 to 89% (4 of 5 coals with methylchloroform) and 0 to 24% with water. In addition, an integrated continuous flow mini-pilot plant was designed and constructed for a nominal coal rate of 2 kilograms/hour which will be operated as part of the follow-on program. Equipment flow sheets and design drawings are included for both the batch and continuous flow mini-pilot plants
Exact moments in a continuous time random walk with complete memory of its history
We present a continuous time generalization of a random walk with complete
memory of its history [Phys. Rev. E 70, 045101(R) (2004)] and derive exact
expressions for the first four moments of the distribution of displacement when
the number of steps is Poisson distributed. We analyze the asymptotic behavior
of the normalized third and fourth cumulants and identify new transitions in a
parameter regime where the random walk exhibits superdiffusion. These
transitions, which are also present in the discrete time case, arise from the
memory of the process and are not reproduced by Fokker-Planck approximations to
the evolution equation of this random walk.Comment: Revtex4, 10 pages, 2 figures. v2: applications discussed, clarity
improved, corrected scaling of third momen
The delayed uncoupled continuous-time random walks do not provide a model for the telegraph equation
It has been alleged in several papers that the so called delayed
continuous-time random walks (DCTRWs) provide a model for the one-dimensional
telegraph equation at microscopic level. This conclusion, being widespread now,
is strange, since the telegraph equation describes phenomena with finite
propagation speed, while the velocity of the motion of particles in the DCTRWs
is infinite. In this paper we investigate how accurate are the approximations
to the DCTRWs provided by the telegraph equation. We show that the diffusion
equation, being the correct limit of the DCTRWs, gives better approximations in
norm to the DCTRWs than the telegraph equation. We conclude therefore
that, first, the DCTRWs do not provide any correct microscopic interpretation
of the one-dimensional telegraph equation, and second, the kinetic (exact)
model of the telegraph equation is different from the model based on the
DCTRWs.Comment: 12 pages, 9 figure
Random matrices, non-backtracking walks, and orthogonal polynomials
Several well-known results from the random matrix theory, such as Wigner's
law and the Marchenko--Pastur law, can be interpreted (and proved) in terms of
non-backtracking walks on a certain graph. Orthogonal polynomials with respect
to the limiting spectral measure play a role in this approach.Comment: (more) minor change
Limit laws for distorted return time processes for infinite measure preserving transformations
We consider conservative ergodic measure preserving transformations on
infinite measure spaces and investigate the asymptotic behaviour of distorted
return time processes with respect to sets satisfying a type of Darling-Kac
condition. We identify two critical cases for which we prove uniform
distribution laws. For this we introduce the notion of uniformly returning sets
and discuss some of their properties.Comment: 18 pages, 2 figure
Exact numerical simulation of power-law noises
Many simulations of stochastic processes require colored noises: I describe
here an exact numerical method to simulate power-law noises: the method can be
extended to more general colored noises, and is exact for all time steps, even
when they are unevenly spaced (as may often happen for astronomical data, see
e.g. N. R. Lomb, Astrophys. Space Sci. {\bf 39}, 447 (1976)). The algorithm has
a well-behaved computational complexity, it produces a nearly perfect Gaussian
noise, and its computational efficiency depends on the required degree of noise
Gaussianity.Comment: 14 postscript figures, accepted for publication on Phys. Rev.
Brownian motion of a charged particle driven internally by correlated noise
We give an exact solution to the generalized Langevin equation of motion of a
charged Brownian particle in a uniform magnetic field that is driven internally
by an exponentially-correlated stochastic force. A strong dissipation regime is
described in which the ensemble-averaged fluctuations of the velocity exhibit
transient oscillations that arise from memory effects. Also, we calculate
generalized diffusion coefficients describing the transport of these particles
and briefly discuss how they are affected by the magnetic field strength and
correlation time. Our asymptotic results are extended to the general case of
internal driving by correlated Gaussian stochastic forces with finite
autocorrelation times.Comment: 10 pages, 4 figures with subfigures, RevTeX, v2: revise
ATP-dependent efflux of calcein by the multidrug resistance protein (MRP): no inhibition by intracellular glutahione depletion
AbstractIn this study we report that the multidrug resistance protein (MRP) transports calcein from the cytoplasmic compartment of tumor cells, in contrast to P-glycoprotein which transports calcein acetoxymethyl ester from the plasmamembrane. The transport of calcein by MRP is ATP-dependent and is inhibited by probenecid and vincristine. Intracellular glutathione (GSH) depletion which occurred when cells were exposed to buthionine sulfoximine had no effect on the efflux of calcein, whereas it reversed the daunorubicin accumulation deficit in MRP overexpressing tumor cells. In conclusion, ATP-dependent transport of calcein and possibly other organic anions by MRP is not inhibited by a large decrease of the intracellular GSH concentration, that inhibits daunorubicin efflux by MRP
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