A symbolic representation of Anosov-Katok Diffeomorphisms III

Speaker: 

Matt Foreman

Institution: 

UC Irvine

Time: 

Tuesday, March 3, 2015 - 1:00pm to 2:00pm

Location: 

RH 440R

I present joint work with B. Weiss that describes a concrete operation on words that allows one to generate symbolic representations of Anosov-Katok diffeomorphisms. We show that each A-K diffeomorphism can be represented this way and that each symbolic system generated by this operation can be realized as an A-K diffeomorphism.

Global in time Gevrey regularity solution for a class of nonlinear gradient flows

Speaker: 

Cheng Wang

Institution: 

University of Massachusetts, Dartmouth

Time: 

Tuesday, March 17, 2015 - 3:00pm

Location: 

RH 306

The existence and uniqueness of Gevrey regularity solution for a class of nonlinear
bistable gradient flows, with the energy decomposed into purely convex and concave parts,
such as epitaxial thin film growth and square phase field crystal models, are discussed in this talk.
The polynomial pattern of the nonlinear terms in the chemical potential enables one to derive a
local in time solution with Gevrey regularity, with the existence time interval length dependent
on certain functional norms of the initial data. Moreover, a detailed Sobolev estimate for the gradient
equations results in a uniform in time bound, which in turn establishes a global in
time solution with Gevrey regularity. An extension to a system of gradient flows,
such as the three-component Cahn-Hilliard equations, is also addressed in this talk.

Unit root L-functions coming from families of exponential sums

Speaker: 

Douglass Haessig

Institution: 

University of Rochester

Time: 

Tuesday, March 10, 2015 - 2:00pm to 3:00pm

Host: 

Location: 

RH340P

Motivated from his p-adic study of the variation of the zeta function as
the variety moves through a family, Dwork conjectured that a new type of
L-function, the so-called unit root L-function, was always p-adic
meromorphic. In the late 1990s, Wan proved this using the theory of
sigma-modules, demonstrating that unit root L-functions have structure.
Little more is known.

This talk is concerned with unit root L-functions coming from families of
exponential sums. In this case, we demonstrate that Wan's theory may be
used to extend Dwork's theory -- including p-adic cohomology -- to these
L-functions. To illustrate the technique, the unit root L-function of the
Kloosterman family is studied in depth.

New characterizations of the catenoid and helicoid

Speaker: 

Jaigyoung Choe

Institution: 

KIAS

Time: 

Monday, February 23, 2015 - 4:00pm to 5:00pm

Host: 

Location: 

Rowland Hall 340N

Bernstein and Breiner found a characterization of the catenoid that the area of a minimal annulus in a slab is bigger than that of the maximally stable catenoid. We give a simpler proof of their theorem and extend the theorem to some minimal surfaces with genus (joint work with Benoit Daniel). New characterizations of the helicoid recently proved by Eunjoo Lee will be also presented.

Consistency strength of Stationary Catching Axioms

Speaker: 

Andres Forero Cuervo

Institution: 

University of California, Irvine, Department of Mathematics

Time: 

Tuesday, March 3, 2015 - 10:00am

Location: 

340N Rowland Hall

The purpose of this thesis is to use the tools of Inner Model Theory to the study of notions relative to generic embeddings induced by ideals. We seek to apply the Core Model Induction technique to obtain lower bounds in consistency strength for a specific stationary catching principle called StatCatch*(I), related to the saturation of an ideal I of omega_2. This principle involves the central notion of self-genericity in its formulation, introduced by Foreman, Magidor and Shelah. In particular, we show that assuming StatCatch*(I) (plus some additional hypothesis in the universe), we can obtain, for every finite n, an inner model with n Woodin Cardinals.

Arcs in the Projective Plane

Speaker: 

Nathan Kaplan

Institution: 

Yale University

Time: 

Tuesday, May 12, 2015 - 2:00pm to 3:00pm

Location: 

RH 340P

An arc in the projective plane over a finite field Fq is a collection of points, no three of which lie on a line.  Segre’s theorem tells us that the largest size of an arc is q+1 when q is odd and q+2 when q in even.  Moreover, it classifies these maximal arcs when q is odd, stating that every such arc is the set of rational points of a smooth conic.  

We will give an overview of problems about arcs in the plane and in higher dimensional projective spaces.  Our goal will be to use algebraic techniques to try to understand these extremal combinatorial configurations.  We will also see connections to special families of error-correcting codes and to modular forms.

 

Isotropic curve flows in R^{n+1, n}

Speaker: 

Zhiwei Wu

Institution: 

Ningbo University

Time: 

Tuesday, March 31, 2015 - 4:00pm

Location: 

RH 306

We will explain a systematic way to study a type of curve flows in R^{n+1, n}, whose geometric invariants are solutions of some integrable systems. In detail, we will construct a hierarchy of isotropic curve flows in R^{2, 1}, construct explicit solutions from Backlund transformation, and study its Hamiltonian formulation.

Blowup Dynamics in the Keller-Segel Model of Chemotaxis

Speaker: 

Israel Michael Sigal

Institution: 

University of Toronto

Time: 

Thursday, February 26, 2015 - 4:00pm to 5:00pm

Host: 

Location: 

RH 340P

The Keller-Segel equations model chemotaxis of bio-organisms. In a reduced form, considered in this talk, they are related to Vlasov equation for self-gravitating systems and are used in social sciences in description of crime patterns.  

It is relatively easy to show that in the critical dimension 2 and for mass of the initial condition greater than 8 \pi, the solutions 'blowup' (or 'collapse') in finite time. This blowup is supposed to describe the chemotactic aggregation of the organisms and understanding its mechanism, especially its universal features, would allow to compare theoretical results with experimental observations. Understanding this mechanism turned out to be a very subtle problem defying solution for a long time. 

In this talk I discuss recent results on dynamics of solutions of the (reduced) Keller-Segel equations in the critical dimension 2 which include a formal derivation and partial rigorous results on the blowup dynamics of solutions. The talk is based on the joint work with S. I. Dejak, D. Egli and  P.M. Lushnikov.

Galois groups of Mori polynomials, semistable curves and monodromy

Speaker: 

Yuri G. Zarhin

Institution: 

Pennsylvania State University

Time: 

Tuesday, May 5, 2015 - 2:00pm

Host: 

Location: 

RH 340P

We study the monodromy of a certain class of semistable hyperelliptic curves over the rationals that was introduced by Shigefumi Mori forty years ago (before his Minimal Model Program). Using ideas of Chris Hall, we prove that the corresponding $\ell$-adic monodromy groups are (almost) ``as large as possible". We also discuss an explicit construction of two-dimensional families of hyperelliptic curves over an arbitrary global field with big monodromy.

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