1,863 research outputs found
Parabolic Anderson model with a finite number of moving catalysts
We consider the parabolic Anderson model (PAM) which is given by the equation
with , where is the diffusion constant,
is the discrete Laplacian, and
is a space-time random environment that drives the equation. The solution of
this equation describes the evolution of a "reactant" under the influence
of a "catalyst" . In the present paper we focus on the case where is
a system of independent simple random walks each with step rate
and starting from the origin. We study the \emph{annealed} Lyapunov exponents,
i.e., the exponential growth rates of the successive moments of w.r.t.\
and show that these exponents, as a function of the diffusion constant
and the rate constant , behave differently depending on the
dimension . In particular, we give a description of the intermittent
behavior of the system in terms of the annealed Lyapunov exponents, depicting
how the total mass of concentrates as . Our results are both a
generalization and an extension of the work of G\"artner and Heydenreich 2006,
where only the case was investigated.Comment: In honour of J\"urgen G\"artner on the occasion of his 60th birthday,
25 pages. Updated version following the referee's comment
Intermittency in a catalytic random medium
In this paper, we study intermittency for the parabolic Anderson equation
, where , is the diffusion constant, is the
discrete Laplacian and is a
space-time random medium. We focus on the case where is times
the random medium that is obtained by running independent simple random walks
with diffusion constant starting from a Poisson random field with
intensity . Throughout the paper, we assume that
. The solution of the equation describes
the evolution of a ``reactant'' under the influence of a ``catalyst''
. We consider the annealed Lyapunov exponents, that is, the exponential
growth rates of the successive moments of , and show that they display an
interesting dependence on the dimension and on the parameters
, with qualitatively different intermittency behavior
in , in and in . Special attention is given to the
asymptotics of these Lyapunov exponents for and .Comment: Published at http://dx.doi.org/10.1214/009117906000000467 in the
Annals of Probability (http://www.imstat.org/aop/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Micropatterned Electrostatic Traps for Indirect Excitons in Coupled GaAs Quantum Wells
We demonstrate an electrostatic trap for indirect excitons in a field-effect
structure based on coupled GaAs quantum wells. Within the plane of a double
quantum well indirect excitons are trapped at the perimeter of a SiO2 area
sandwiched between the surface of the GaAs heterostructure and a
semitransparent metallic top gate. The trapping mechanism is well explained by
a combination of the quantum confined Stark effect and local field enhancement.
We find the one-dimensional trapping potentials in the quantum well plane to be
nearly harmonic with high spring constants exceeding 10 keV/cm^2.Comment: 21 pages, 6 figures, submitted to Phys. Rev.
Intermittency on catalysts: Voter model
In this paper we study intermittency for the parabolic Anderson equation
with
, where is
the diffusion constant, is the discrete Laplacian,
is the coupling constant, and
is a space--time random medium.
The solution of this equation describes the evolution of a ``reactant''
under the influence of a ``catalyst'' . We focus on the case where
is the voter model with opinions 0 and 1 that are updated according to a random
walk transition kernel, starting from either the Bernoulli measure
or the equilibrium measure , where is the density of
1's. We consider the annealed Lyapunov exponents, that is, the exponential
growth rates of the successive moments of . We show that if the random walk
transition kernel has zero mean and finite variance, then these exponents are
trivial for , but display an interesting dependence on the
diffusion constant for , with qualitatively different
behavior in different dimensions. In earlier work we considered the case where
is a field of independent simple random walks in a Poisson equilibrium,
respectively, a symmetric exclusion process in a Bernoulli equilibrium, which
are both reversible dynamics. In the present work a main obstacle is the
nonreversibility of the voter model dynamics, since this precludes the
application of spectral techniques. The duality with coalescing random walks is
key to our analysis, and leads to a representation formula for the Lyapunov
exponents that allows for the application of large deviation estimates.Comment: Published in at http://dx.doi.org/10.1214/10-AOP535 the Annals of
Probability (http://www.imstat.org/aop/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Violator Spaces: Structure and Algorithms
Sharir and Welzl introduced an abstract framework for optimization problems,
called LP-type problems or also generalized linear programming problems, which
proved useful in algorithm design. We define a new, and as we believe, simpler
and more natural framework: violator spaces, which constitute a proper
generalization of LP-type problems. We show that Clarkson's randomized
algorithms for low-dimensional linear programming work in the context of
violator spaces. For example, in this way we obtain the fastest known algorithm
for the P-matrix generalized linear complementarity problem with a constant
number of blocks. We also give two new characterizations of LP-type problems:
they are equivalent to acyclic violator spaces, as well as to concrete LP-type
problems (informally, the constraints in a concrete LP-type problem are subsets
of a linearly ordered ground set, and the value of a set of constraints is the
minimum of its intersection).Comment: 28 pages, 5 figures, extended abstract was presented at ESA 2006;
author spelling fixe
Drift mobility of long-living excitons in coupled GaAs quantum wells
We observe high-mobility transport of indirect excitons in coupled GaAs
quantum wells. A voltage-tunable in-plane potential gradient is defined for
excitons by exploiting the quantum confined Stark effect in combination with a
lithographically designed resistive top gate. Excitonic photoluminescence
resolved in space, energy, and time provides insight into the in-plane drift
dynamics. Across several hundreds of microns an excitonic mobility of >10^5
cm2/eVs is observed for temperatures below 10 K. With increasing temperature
the excitonic mobility decreases due to exciton-phonon scattering.Comment: 3 pages, 3 figure
Intermittency in a catalytic random medium
Article / Letter to editorMathematisch Instituu
Regulation of cargo transfer between ESCRT-0 and ESCRT-I complexes by flotillin-1 during endosomal sorting of ubiquitinated cargo
Ubiquitin-dependent sorting of membrane proteins in endosomes directs them to lysosomal degradation. In the case of receptors such as the epidermal growth factor receptor (EGFR), lysosomal degradation is important for the regulation of downstream signalling. Ubiquitinated proteins are recognised in endosomes by the endosomal sorting complexes required for transport (ESCRT) complexes, which sequentially interact with the ubiquitinated cargo. Although the role of each ESCRT complex in sorting is well established, it is not clear how the cargo is passed on from one ESCRT to the next. We here show that flotillin-1 is required for EGFR degradation, and that it interacts with the subunits of ESCRT-0 and -I complexes (hepatocyte growth factor-regulated tyrosine kinase substrate (Hrs) and Tsg101). Flotillin-1 is required for cargo recognition and sorting by ESCRT-0/Hrs and for its interaction with Tsg101. In addition, flotillin-1 is also required for the sorting of human immunodeficiency virus 1 Gag polyprotein, which mimics ESCRT-0 complex during viral assembly. We propose that flotillin-1 functions in cargo transfer between ESCRT-0 and -I complexes
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