Seminars at UCSB
Applied Mathematics and PDE Seminar
Graduate Student Hypatian Seminar
Mathematics Department Seminars
Kavli Institute for Theoretical Physics (KITP)
Institute for Theoretical Physics (ITP)
Materials Research Laboratory (MRL)
California Nanosystems Institute (CNSI)
Center for Control, Dynamical Systems, and Computation (CCDC)
Molecular Cellular and Developmental Biology (MCDB)
Institute for Polymers and Organic Solids (IPOS)
Center for Interdisciplinary Research in Fluids Physics (CIRF)
Neuroscience Institute Seminars
Chemistry Department Seminars
Chemical Engineering Seminars
Electrical Engineering Seminars
Materials Department Seminars
Applied Mathematics and PDE Seminar
Parameterization of Turbulent Transport by Mesoscale Eddies.
Monday, Oct. 5, 2009 from 11:00am - 12:00pm, South Hall 6617.
Peter Kramer, Rensselaer Polytechnic Institute.
Abstract: We employ homogenization theory to develop a systematic
parameterization strategy for quantifying the transport effects of
mesoscale coherent structures in the ocean which cannot be well
resolved by large-scale weather and climate simulations. We work from
the ground up with simple kinematic models and study in particular how
the effective diffusivity depends on the governing parameters, such as
Strouhal number and Peclet number, in a class of dynamical random
vortex flows. We will also briefly describe some connections between
the homogenized effective diffusivity and a recently introduced
alternative mixing efficiency measure. This is joint work with
Banu Baydil, Shane Keating, and Shafer Smith.
Solving Nonlinear Eigenvalue Problems in Electronic Structure Calculations.
Friday, May 15, 2009 4:00pm - 5:00pm, SH 4617.
Chao Yang, Lawrence Berkeley Laboratory.
Abstract: One of the fundamental problems in electronic structure
calculations is to determine the electron density associated with the
minimum total energy of molecules, solids or other types of nanoscale
materials. The total energy minimization problem is often formulated as a nonlinear
eigenvalue problem. It is also known as the Kohn-Sham problem. In this
talk, I will discuss several numerical methods for solving this type
of problem and examine their convergence properties.
Topological quantization of ensemble averages .
Friday, April 10, 2009 from 2 to 3 p.m., SH 4607.
Dr. Emil Prodan, Yeshiva University, New York, NY.
Abstract: Non-commutative geometry and calculus have been successfully
used in the past to unlock the secretes of several important observations in
condensed matter. In this talk I will discuss my own efforts to apply the
non-commutative geometry and calculus to a new class of materials called
topological insulators.
I will briefly review the non-commutative theory of the Integer Quantum Hall Effect, with emphasis on some relatively recent results concerning the edge physics. I will then discuss a result that underlines a general principle for the quantization of ensemble averages. I will use several examples to convey the implications of the result. These examples include quantization of conductance in metallic wires, quantization of edge conductance in 2D Chern insulators with random edges, robustness of the edge modes in 2D quantum spin-Hall systems against disorder. Notes on the 3D insulators will be also presented if time allows.
References:
1. E. Prodan, Topological quantization of ensemble averages, J. Phys. A:
Math. and Theor. 42, 065207 (2009)
2. E. Prodan, An edge index for the quantum spin-Hall effect, J. Phys. A:
Math. and Theor. 42, 082001 (2009)
3. E. Prodan, The edge spectrum of Chern insulators with rough boundaries,
arXiv:0809.2569v2 (2009)
Dynamics of a Stochastically Driven Neuronal Network Model.
Tuesday, February 17th, 2009; 4:00pm - 5:00pm, SH 4607.
Peter R. Kramer, Dept. Mathematical Sciences, Rensselaer Polytechnic Institute.
Abstract: We study an all-to-all coupled network of identical excitatory
integrate-and-fire (I\&F) neurons driven by an external spike train
modeled as a Poisson process. Numerical simulations demonstrate that
over a broad range of parameters, the network enters a synchronized
state in which the neurons all fire together at regular intervals. We
identify mechanisms leading to this synchronization for two regimes of
the external driving current: superthreshold and subthreshold. In the
former, a probabilistic argument similar to the proof of the Central
Limit Theorem yields the oscillation period, while in the latter, this
period is analyzed via an exit time calculation utilizing a diffusion
approximation of the Kolmogorov forward equation. In both cases,
stochastic fluctuations play a central role in determining the
oscillation period. We also develop a criterion for
synchrony in the network through a probabilistic argument. This work
is in collaboration with Katherine Newhall, Gregor Kovacic, David Cai,
and Aaditya Rangan.
Title Here.
Tuesday, February 17th, 4:00pm - 5:00pm, SH 4607.
Speaker Name, Dept., Affiliation.
Abstract: Description of talk.