Seminars and Colloquiums
for the week of March 9, 2009
Speakers:
Dr. Shiqui Ruan, University of Miami, Monday
Mr. Nick Gewecke, Wednesday
Mr. Kirill Yakovlev, Thursday
Dr. Johannes Zimmer, University of Bath, UK, Thursday
Dr. Johannes Zimmer, University of Bath, UK, Friday
Monday, March 9
COLLOQUIUM – NIMBioS Job Candidate
TIME: 3:35 – 4:35 p.m.
ROOM: HBB 102
SPEAKER: Dr. Shiqui Ruan, University of Miami
TITLE: “Nonlinear Dynamics in Structured Epidemic Models ”
ABSTRACT: Mathematical models have been successfully used to study many infectious diseases and nonlinear and complex dynamics have been observed in those models. Structured epidemic models distinguish individuals from one another according to characteristics, such as age, location, status, and movement, to determine the interaction with each other and with environment, infectivity, etc. The goal of structured models is to understand how these characteristics affect the dynamics of these models and thus the outcomes and consequences of the epidemiological processes.
In this talk we focus on two infectious diseases, malaria and influenza. We first show that different types of structured models, such as delay differential equation models, metapopulation models and reaction-diffusion equation models, can be used to study the transmission dynamics of malaria. Then by considering an age-structured type evolutionary epidemiological model of influenza A drift, we demonstrate that new
theories need to be developed to understand the nonlinear dynamics of such models and the phenomenon of the seasonal/periodic reoccurrence of influenza.
Wednesday, March 11
GRADUATE STUDENT FORUM
TIME: 3:35 – 4:25 p.m.
ROOM: HBB 121
SPEAKER: Mr. Nick Gewecke
TITLE: "LaTeX – Beautifying Homework Assignments, Exams and Presentations”
ABSTRACT: we will be going over the basics of LaTeX and how to use LaTeX to write up homework assignments, research articles, exams, and slide and poster presentations.
Thursday, March 12
PROBABILITY Math 529 SEMINAR
TIME: 12:40 – 1:55 p.m.
ROOM: HBB 132
SPEAKER: Mr. Kirill Yakovlev
TITLE: “Numerical Simulations”
JUNIOR COLLOQUIUM
TIME: 3:35 – 4:35 p.m.
ROOM: HBB 102
SPEAKER: Johannes Zimmer, University of Bath, UK
TITLE: "How to find chemical reaction pathways with a rubber band”
ABSTRACT: One branch of computational chemistry aims at determining the pathway taken by a reaction, with Molecular Dynamics (MD) simulations. For example, how does one configuration of a molecule flip into another configuration? A difficulty is that the time scale on which these events occur can be too large to be computationally tractable. For example, thermally activated reactions have many deep wells separated by large energy barriers. Reactants will then spend most of the time jostling around in one well before a rare spontaneous fluctuation occurs that lifts the atoms of the reactant over the barrier into the next (product) valley. A major challenge in MD is that these hopping events take place so rarely that the computational limits of MD simulations can be easily exceeded.
We will describe the mathematical formulation of this problem, and show that there is an equivalent formulation of the governing equation which has a simple interpretation. Namely, one can reformulate the chemical problem in such a way that one has to find a shortest (extremal) path between two given points. The latter formulation can be interpreted as having a rubber band which connects the two points, and shrinks to find a minimal connection. We will explain the mathematics behind this idea, and show how it works for chemical reactions.
Friday, March 13
COLLOQUIUM
TIME: 3:35 – 4:35 p.m.
ROOM: HBB 102
SPEAKER: Johannes Zimmer
TITLE: “Moving interfaces in solids: from conservative lattice models to macroscopic dissipation”
ABSTRACT: Moving interfaces in solids can dissipate energy, but are commonly described by conservative (Hamiltonian) equations on the lattice scale. How can conservative lattice models generate dissipation on the continuum scale? To understand this, we consider a model problem, namely travelling waves in a one-dimensional chain of atoms with nearest neighbour interaction. The elastic potential is piecewise quadratic and the model is thus capable of describing phase transitions. (The talk will start with a short survey on phase transitions.) A solution which explores both wells of the energy will then have an interface, moving with the speed of the wave. We show that for suitable fixed subsonic velocities, there is a family of ``heteroclinic" travelling waves (heteroclinic means here that they connect both wells of the energy). Though the microscopic picture is Hamiltonian, we derive non-trivial so-called kinetic relations on the continuum scale; they can be related to the dissipation generated by a moving phase boundary. We then investigate the question of when the kinetic relation does not vanish (dissipation is generated). It turns out that a microscopic asymmety determines here the macroscopic dissipation.
This is joint work with Hartmut Schwetlick (Bath).
If you are interested in giving or arranging a talk for one of our seminars or colloquiums, please review our calendar.
If you have questions, or a date you would like to confirm, please contact Dr. Steve Wise.
Week of:
Past notices:
Seminars from 2007-2008 academic year
Seminars from 2006-2007 academic year