2,171 research outputs found
Inverse spectral theory for a class of non-compact Hankel operators
We characterize all bounded Hankel operators such that
has finite spectrum. We identify spectral data corresponding
to such operators and construct inverse spectral theory including the
characterization of these spectral data
Weighted model spaces and Schmidt subspaces of Hankel operators
For a bounded Hankel matrix , we describe the structure of the
Schmidt subspaces of , namely the eigenspaces of
corresponding to non zero eigenvalues. We prove that these subspaces are in
correspondence with weighted model spaces in the Hardy space on the unit
circle. Here we use the term "weighted model space" to describe the range of an
isometric multiplier acting on a model space. Further, we obtain similar
results for Hankel operators acting in the Hardy space on the real line.
Finally, we give a streamlined proof of the Adamyan-Arov-Krein theorem using
the language of weighted model spaces.Comment: Final version, to appear in Journal of the London Mathematical
Societ
Biased random walks on random graphs
These notes cover one of the topics programmed for the St Petersburg School
in Probability and Statistical Physics of June 2012.
The aim is to review recent mathematical developments in the field of random
walks in random environment. Our main focus will be on directionally transient
and reversible random walks on different types of underlying graph structures,
such as , trees and for .Comment: Survey based one of the topics programmed for the St Petersburg
School in Probability and Statistical Physics of June 2012. 64 pages, 16
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Response of MarineāTerminating Glaciers to Forcing: Time Scales, Sensitivities, Instabilities, and Stochastic Dynamics
Recent observations indicate that many marineāterminating glaciers in Greenland and Antarctica are currently retreating and thinning, potentially due to longāterm trends in climate forcing. In this study, we describe a simple twoāstage model that accurately emulates the response to external forcing of marineāterminating glaciers simulated in a spatially extended model. The simplicity of the model permits derivation of analytical expressions describing the marineāterminating glacier response to forcing. We find that there are two time scales that characterize the stable glacier response to external forcing, a fast time scale of decades to centuries, and a slow time scale of millennia. These two time scales become unstable at different thresholds of bed slope, indicating that there are distinct slow and fast forms of the marine ice sheet instability. We derive simple expressions for the approximate magnitude and transient evolution of the stable glacier response to external forcing, which depend on the equilibrium glacier state and the strength of nonlinearity in forcing processes. The slow response rate of marineāterminating glaciers indicates that current changes at some glaciers are set to continue and accelerate in coming centuries in response to past climate forcing and that the current extent of change at these glaciers is likely a small fraction of the future committed change caused by past climate forcing. Finally, we find that changing the amplitude of natural fluctuations in some nonlinear forcing processes, such as ice shelf calving, changes the equilibrium glacier state
The cubic Szego equation on the real line: explicit formula and well-posedness on the Hardy class
We establish an explicit formula for the solution of the cubic Szego equation on the real line. Using this formula, we prove that the evolution flow of this equation can be continuously extended to the whole Hardy class on the real line. <br/
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