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The
Metastability of the Biased Majority Vote Process.
Abstract:
The reduction method provides an algorithm to compute large deviation
estimates of (possibly non reversible) Markov processes with exponential
transition rates. It replaces the original graph minimisation equations
of Freidlin and Wentzell by more tractable path minimisation problems.
We apply this technique to the study of a biased majority vote process
generalising the one studied in Chen. We show that this non reversible
dynamics has a two well potential with a unique metastable state, and
give an upper bound for its relaxation time. |
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Heat
Kernel Estimate for Stable-like Processes on -Sets
Abstract:
-sets can be regarded as generalizations of fractals. In this
talk, we will study stable-like processes on -sets, which include
reflected stable processes in Euclidean domains as a special case. More
precisely, we will establish parabolic Harnack principle and derive sharp
two-sided heat kernel estimate for such stable-like processes. Results
on the exact Hausdorff dimensions for the graphs of stable-like processes
will also be presented. This talk is based on a joint work with Takashi
Kumagai. |
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Tangent Processes
and its Applications
Abstract: The
Camerm-Martin's quasi-invariance result for translations plays a fundmental
role in the theory of stochastic calculus of variations on the Wiener
space. When we deal with a non linear situation, the available Camerm-Martin
direction are needed to be enlarged: This gives rise the notion of tangent
processes. In this talk, we shall show by examples the role of tangent
processes to establish the quasi-invariance results in non linear situations. |
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Fleming-Viot
Process: Large Deviation and Quasi-Potential
Abstract:
Fleming-Viot process with neutral mutation is a measure-valued process
describing the evolution of genotype frequency in a population under the
influence of mutation and resampling. In this talk results will be presented
on large deviations and quasi-potential of the Fleming-Viot process. The
main difficulty is dealing with the degeneracy of the diffusion coefficient
at the boundary. These are joint work with D.A. Dawson, and with Jie Xiong. |
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Exponential
Integrability of Functions on Loop Spaces
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Gelation
of a Reversible Markov Process of Polymerization
Abstract: A
reversible Markov process as a chemical polymerization model which permits
the coagulation and fragmentation reactions is considered. We present
a necessary and sufficient condition for the occurrence of a gelation
in the process. We show that a gelation transition may or may not occur,
depending on the value of the fragmentation strength, and, in case the
gelation takes place, a critical value for the occurrence of the gelation
and the mass of the gel can be determined by close forms. (PDF
file) |
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Brownian
Motion and Dirichlet Problem at Infinity
Abstract: We
show how to solve the Dirichlet problem at infinity on a Cartan-Hadamard
manifold satisfying very generous curvature conditions by estimating the
angular oscillation of Brownian motion on such a manifold. (PDF
file) |
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Construction
of Measure-valued Diffusions Carried by Stochastic Flows
Abstract: Let
be a two parameter Brownian motion
(a time-space white noise). For a smooth and square-integrable function
$h(\cdot)$ on $\IR$ and any $r\ge0$ and $a\in\IR$, given $x(r,a,r) = a$
the equation $$ x(r,a,t) = a + \int_r^t\int_{\IR} h(y-x(r,a,s))W(ds,dy),
\quad t\ge r,$$ has a unique solution $\{x(r,a,t): t\ge r\}$, which defines
a isotropic stochastic flow. We consider a stochastic equation for measure-valued
process carried by the flow. The equation is driven by a Poisson point
process on the space of one-dimensional excursions. A pathwise unique
solution of the equation is proved, which gives a measure-valued diffusion
process. (PDF file) |
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Quantum
Markovian Approximation
Abstract: Markovian
approximation are used both in physics and mathematics. The basic idea
is to replace a rather complicate evolution of a physical system by a
simpler one which is determined by a semigroup. We shall give some useful
Markovian approximations and present their intuitive idea, discuss the
rigorous mathematical treatment. |
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Deviation
Kernels for One-Dimensional Diffusion Processes
Abstract: It
is proven that for the non-explosive and ergodic diffusion on the half
line with the ransition probability kernel $p(t,x,y)$, the deviation kernel
$d(x,y)=\int_0^\ift (p(t,x,y)-1)dt$ exists and is finite if and only if
$\int_0^\ift\E^x H_0 \mu(dx)<\ift$, where $H_0$ is the hitting time
of $0$ and $\mu$ is the speed measure. The explicit formulas are also
obtained. (PDF file) |
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Rate
of Mixing for Gibbs States of Dynamical Systems
Abstract: The
g measures are discrete stationary processes continuously depending
on their past, they extend in a natural way the Markov processes. If we
assume regularity of the weight g than the process is strongly
mixing and the rate of mixing exponential. We produce a new approach based
upon inequalities of Poincare's type for giving constructive estimates
of the mixing rate. |
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A
Cocycle Proof that Reversible Fleming-Viot Processes have Uniform Mutation
Abstract: Why
is the mutation operator associated with a reversible Fleming-Viot process
uniform? Our explanation is based on Handa's recent result that reversible
distributions must be quasi-invariant under a certain flow, forcing the
mutation operator to satisfy a cocycle identity. (PDF
file) |
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Gradient
Estimates of Dirichlet Heat Semigroups and Application to Isopermetric
Inequalities
Abstract: By
using probabilistic approaches, some uniform gradient estimates are obtained
for Dirichlet heat semigroups on a Riemannian manifold with boundary.
As an application, lower bound estimates of isoperimetric constants are
presented in terms of functional inequalities. (PDF
file) |
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Algebraic
Convergence of Markov Chains
Abstract:
Algebraic convergence
in $L^2$-sense is studied for general time-continuous, reversible Markov
chains with countable state space, and especially for birth-death chains.
Some criteria forthe convergence are presented. The results are effective since the convergence region can be completely covered, as illustrated by two examples. |
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Essential
Spectral Radius for Markov Kernel
Abstract: Using
two new parameters $\beta_{\tau}(P)$ and $\beta_{wc}(P)$ of non-compactness
for a positive kernel $P$ on a Polish space $E$, we obtain a new formula
of Nussbaum-Gelfand type for the essential spectral radius $r_{ess}(P)$
on $b{\mathcal B}$. Using that formula we show that different known sufficient
conditions for geometric ergodicity such as Doeblin's condition, drift
condition by means of Lyapunov function, geometric recurrence etc lead
to variational formulas of the essential spectral radius. All those can
be easily transported on the weighted space $b_u{\mathcal B}$. Some related
results on $L^2(\mu)$ are also obtained, especially in the symmetric case.
Moreover we prove that for a strongly Feller and topologically transitive
Markov kernel, the large deviation principle of Donsker-Varadhan for occupation
measures of the associated Markov process holds if and only if the essential
spectral radius is zero. The knowledge of $r_{ess}(P)$ allows us to estimate
eigenvalues of $P$ in $L^2$ in the symmetric case, and to estimate the
geometric convergence rate by means of that in the metric of Wasserstein.
Some examples are presented. |
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Perturbed
Reflected Diffusion Processes
Abstract: In
this talk we will present some recent results on existence and uniqueness
of perturbed reflected diffusion processes, which were studied by M.Yor,
Le Gall and others before. |
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On
Stochastic Order for Diffusion Processes
Abstract: Let
$X(t)$ be a diffusion process in $R^d$, i.e., let $X(t)$ satisfy the following
stochastic differential equation: $$dX(t)=b(X(t))+\sigma(X(t))dW(t),$$
where $b(x):R^d:\to R^1$ $\sigma(x)$ is a $d\times d$ matrix, and $W(t)$
is a d-dimensional Browian motion. The usual stochastic order and convex
order for two diffusion processes will be discussed. Some sufficient and
necessary conditions in terms of $b(x)$ and $\sigma(x)$ for two diffusion
processes to have usual stochastic order or convex order will be presented. |
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Dual
Variational Formulas for the First Dirichlet Eigenvalue on Half-Line
Abstract: The
aim of the paper is to establish two dual variational formulas for the
first Dirichlet eigenvalue of second order elliptic operators on half-line.
Some explicit bounds of the eigenvalue depending only on the coefficients
of the operators are presented. Moreover, the corresponding problems in
the discrete case and the higher-order eigenvalues in the continuous case
are also studied. This talk is based on a joint work with Mu-Fa Chen and
Xiao-Liang Zhao.(PDF file) |
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Stochastic
Analysis on p-Adics
Abstract: Some
new results on the stochastic analysis on p-adics will be introduced.
(PDF file) |
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Coalescing
Brownian Motion, its Dualities and a Measure-Valued Process
Abstract: Coalescing
Brownian motion captures the interactions among a system of Brownian motions.
It plays a key role in analying certain measure-valued processes. Some
aspects of coalescing Brownian motion will be discussed in this talk.
We will first introduce a characterization theorem. Then we will present
two dual relationships involving coalescing Brownian motion. A sketch
of the proof will be given. Such a duality can be applied to construct
a measure-valued process. |