Growth properties of eigensolutions of Laplacian in higher dimension

Speaker: 

Wencai Liu

Institution: 

UC Irvine

Time: 

Friday, January 13, 2017 - 1:00pm to 1:50pm

Location: 

510M

In this seminar, I will present  a classical result of Tosio Kato, which shows the growth properties of the eigen-solution of Laplacian in higher dimension if the potential decays fast. As an application, we can obtain some spectral properties of Laplacian, for example, the absence of eigenvalues and fractal dimension of spectral measure.

Professor Alice Silverberg invited to address the Joint Mathematics Meetings in Atlanta in January 2017

Professor Alice Silverberg gave an AMS-MAA Invited Address at the 2017 Joint Mathematics Meetings, which is the largest mathematics meeting in the world. She spoke on how mathematics can be useful in cryptography, how cryptography can motivate research of mathematical interest, and how mathematicians and cryptographers can learn to play well together. 

On Geometric Quantization of Poisson Manifolds

Speaker: 

Jonathan Weitsman

Institution: 

Northeastern University

Time: 

Thursday, March 2, 2017 - 4:00pm to 5:00pm

Host: 

Location: 

RH 306

Geometric Quantization is a program of assigning to
classical mechanical systems (symplectic manifolds and the associated
Poisson algebras of C-infinity functions) their quantizations ---
algebras of operators on Hilbert spaces.  Geometric Quantization has
had many applications in Mathematics and Physics.   Nevertheless the
main proposition at the heart of the theory, invariance of
polarization, though verified in many examples, is still not proved in
any generality.  This causes numerous conceptual difficulties:  For
example, it makes it very difficult to understand the functoriality of
theory.

Nevertheless, during the past 20 years, powerful topological and
geometric techniques have clarified at least some of the features of
the program.

In 1995 Kontsevich showed that formal deformation quantization can be
extended to Poisson manifolds.  This naturally raises the question as
to what one can say about Geometric Quantization in this context.  In
recent work with Victor Guillemin and Eva Miranda, we explored this
question in the context of Poisson manifolds which are "not too far"
from being symplectic - the so called b-symplectic or b-Poisson
manifolds - in the presence of an Abelian symmetry group.

In this talk we review Geometric Quantization in various contexts, and
discuss these developments, which end with a surprise.

 

Curve Shortening: An introduction to geometric flows

Speaker: 

Jeffrey Streets

Institution: 

UC Irvine

Time: 

Friday, January 20, 2017 - 4:00pm

Location: 

MSTB 124

What happens to an embedded curve in the plane if we decrease its length as fast as possible?  In this talk I will discuss the beautiful answer to this simple question, which involves techniques and ideas from multivariable calculus and plane geometry.  Generalizing this situation to higher dimensions leads to a number of interesting open questions in geometry, topology, and analysis.

Adelic points of elliptic curves

Speaker: 

Peter Stevenhagen

Institution: 

Universiteit Leiden

Time: 

Tuesday, January 17, 2017 - 2:00pm to 3:00pm

Location: 

RH 340P

We show how the Galois representation of an elliptic curve over a number field can be used to determine the structure of the (topological) group of adelic points  of that elliptic curve.

As a consequence, we find that for "almost all" elliptic curves over a number field K,  the adelic point group is a universal topological group depending only on the degree  of K. Still, we can construct infinitely many pairwise non-isomorphic elliptic curves  over K that have an adelic point group not isomorphic to this universal group.

This generalizes work of my student Athanasios Angelakis (PhD Leiden, 2015).

The spectral transitions of Laplacians with decaying potentials

Speaker: 

Wencai Liu

Institution: 

UC, Irvine

Time: 

Friday, January 6, 2017 - 1:00pm to 1:50pm

Location: 

510M

 Let us consider the Schrodinger operators $H$ with decaying potentials $V$ in $\R^d$. For the free Schrodinger operator(i.e.,potential $V=0$ ), there is no positive eigenvalue.   So  it is expected that  the Schrodinger operators keep such property for small potentials. In  this  Seminar, I will prove that $H$ does not have any positive eigenvalue  if $V(x)=\frac{o(1)}{|x|}$ for $d=1$. In the next Seminar, I will prove the result for higher dimension (i.e. $d>1$). This result is based on a classical paper of Kato[Growth Properties of Solutions of the Reduced Wave Equation With a Variable Cofficient]. 

 

Actually $V(x)=\frac{o(1)}{|x|}$  is optimal by Wigner-von Neumann type potential. Thus $V(x)=\frac{o(1)}{|x|}$ is a spectral transition for eigenvalue.  We can also get a spectral transition for singular continuous spectrum in some sense, which has been done by Agmon. Similar  results hold  for Laplacian on Riemannian manifold (especially for asymptotic flat and hyperbolic cases) which is characterized  by radial curvature or metric sturcture.  In this quarter, I plan to choose some specific topics among them to present. 

Full-dispersion shallow water models and the Benjamin-Feir instability

Speaker: 

Vera Mikyoung Hur

Institution: 

UIUC

Time: 

Tuesday, June 6, 2017 - 3:00pm

Host: 

Location: 

RH306

 In the 1960s, Benjamin and Feir, and Whitham, discovered that a Stokes wave would be unstable to long wavelength perturbations, provided that (the carrier wave number) x (the undisturbed water depth) > 1.363.... In the 1990s, Bridges and Mielke studied the corresponding spectral instability in a rigorous manner. But it leaves some important issues open, such as the spectrum away from the origin. The governing equations of the water wave problem are complicated. One may resort to simpler approximate models to gain insights.

I will begin by Whitham's shallow water equation and the modulational instability index for small amplitude and periodic traveling waves, the effects of surface tension and vorticity. I will then discuss higher order corrections, extension to bidirectional propagation and two-dimensional surfaces. This is partly based on joint works with Jared Bronski (Illinois), Mat Johnson (Kansas), and Ashish Pandey (Illinois).

Stokes waves with constant vorticity: numerical computation

Speaker: 

Vera Mikyoung Hur

Institution: 

UIUC

Time: 

Monday, June 5, 2017 - 4:00pm

Host: 

Location: 

RH306

Stokes in his classical memoir made many contributions about periodic traveling waves at the free surface of a water flow. In particular, he conjectured that a wave of greatest possible height would exhibit stagnation with a 120 degree's corner. In the zero vorticity case, Amick, Fraenkel, and Toland answered the conjecture affirmatively. But interior stagnation is not allowed for all waves.

 

The situation becomes much more complicated with non-zero vorticity. Recently, Constantin, Strauss, and Varvaruca worked out global bifurcation in the constant vorticity case, and they conjectured about limiting waves. I will present the joint work with Sergey Dyachenko (Illinois), numerically computing Stokes waves with constant vorticity from zero close to the limiting wave, and discovering new limiting waves.

Three principles of data science: predictability, stability, and computability

Speaker: 

Bin Yu

Institution: 

UC Berkeley

Time: 

Friday, February 3, 2017 - 2:00pm to 3:00pm

Host: 

Location: 

NS2, 1201

In this talk, I'd like to discuss the intertwining importance and connections of three principles of data science in the title in data-driven decisions. The ultimate importance of prediction lies in the fact that future holds the unique and possibly the only purpose of all human activities, in business, education, research, and government alike.
Making prediction as its central task and embracing computation as its core, machine learning has enabled wide-ranging data-driven successes. Prediction is a useful way to check with reality. Good prediction implicitly assumes stability between past and future. Stability (relative to data and model perturbations) is also a minimum requirement for interpretability and reproducibility of data driven results. It is closely related to uncertainty assessment. Obviously, both prediction and stability principles can not be employed without feasible computational algorithms, hence the importance of computability. The three principles will be demonstrated through analytical connections, and in the context of two on-going neuroscience projects, for which "data wisdom" is also indispensable. Specifically, the first project interprets a predictive model used for reconstruction
of movies from fMRI brain signals; the second project employs deep learning networks (CNNs) to understand pattern selectivities of neurons in the difficult visual cortex V4.

Pages

Subscribe to UCI Mathematics RSS