Fall 2004 Tuesdays, 4:00  5:00 pm in JWB 335 Math 6960010 (credit hours available!) The goal of this Colloquium is to encourage interaction among graduate students, specifically between graduate students who are actively researching a problem and those who have not yet started their research. Speakers will discuss their research or a related introductory topic on a level which should be accessible to nonspecialists. The discussions will be geared toward graduate students in the beginning of their program, but all are invited to attend. This invitation explicitly includes undergraduate students. Talks will be held on Tuesdays at 4:00pm in JWB 335, unless otherwise
noted.
Speaker: Tom Robbins Title: A mechanistic model for seed dispersal Abstract: In this talk, I will present a mechanistic model to describe wind dispersed plant seeds. I will discuss the general modeling approach and the assumptions that go into the model. In addition, I will talk about external constraints on the model, simplicity verses realism, and how the model compares with real data. Speaker: Dan Margalit Title: Braids Abstract: While simple to define, braid groups display a surprising number of interesting features. After getting a feel for the basic structure of the group, we will explore connections to mapping class groups, geometric group theory, and representation theory. Speaker: Bori Mazzag Title: A Mathematical Model of Pattern Formation by Aerotactic Bacteria Abstract: Conventional bacterial chemotaxis depends critically on the fast decrease and slow adaptation of the cell's turning frequency in a favorable environment. This mechanism is relatively ineffective: the aggregation of the bacterial colony toward chemoattractant is slow and incomplete. Aerotaxis is a particular form of chemotaxis in which oxygen plays the role of both attractant (at moderate concentrations) and repellent (at high concentrations). It has been experimentally demonstrated that this taxis does not require slow adaptation, making aerotaxis a very effective mechanism for complete aggregation toward the most favorable oxygen concentration. Our model consists of a system of hyperbolic differential equations, each describing a group of bacteria moving in the same direction, coupled to a diffusion equation describing the dynamics of oxygen. Simulations allow comparisons of theoretical and experimental results and help in making a judgment on the validity of various biochemical mechanisms. Analytical results give estimates for parameters that are otherwise difficult to obtain experimentally. Speaker: Ken Chu Title: The First Things about ``Moduli'' Abstract: The idea of ``moduli'' is to express a given family of geometric objects belonging to a certain category as an object of the same category (or at least a related, slightly generalized category). For example, the socalled ``elliptic curves'' are complex manifolds. Then we ask: Does the set of all elliptic curves itself admit a natural structure of a complex manifold? In complex algebraic and analytic geometry, there are plenty of nontrivial moduli problems. The main examples of this talk will be the elliptic curves. I will show that the moduli space (in the category of analytic spaces) of elliptic curves is a nontrivial quotient (analytic orbifold), whose underlying space is in fact simply the complex plane. I will discuss the delicacy of constructing reasonable ``moduli spaces'' via forming quotients. Time permitting, I will also discuss deformation, singularities, and compactification of moduli spaces. Speaker: Robert Bell Title: Algorithms and Undecidability Abstract: We will formalize the intuitive notion of an algorithm. In particular, we will prove the MarkovPost Theorem which states that there is a finitely presented semigroup (strings of letters on a finite alphabet together with a finite number of substitution rules) for which there does not exist an algorithm which decides whether or not two given strings are equivalent. Speaker: Jason Preszler Title: pAdic Numbers Abstract: The padic numbers will be constructed using the methods of 1) padic expansion, 2) completion, and 3) inverse limits. The result of Ostrowski concerning absolute values on the rationals will be discussed as well as the localglobal principal and HasseMinkowski theorem. If time allows, the structure of the multiplicative group of $\mathbb{Q}_{p}$ will be explored. Speaker: YoungSeon Lee Title: From Heart Failure to Intracellular Ca2+ cycling Abstract: Heart failure is a serious condition which causes about 300,000 deaths each year in the United States. Mechanical alternans,a phenomenon of alternating strong and weak beats at a constant heart rate,is the hallmark of heart failure. Recent experimental studies show that abnormal intracellular Ca2+ cycling is the key mechanism for mechanical alternans. In this talk, I will introduce mathematical models to understand the mechanism of mechanical alternans. Speaker:MunJu Kim Title: Low Reynolds Number Flow Abstract: Speaker: David Levin Title: Exact Sampling Abstract: Many probability distribution with large combinatorial state spaces, such as the Ising model, are hard to simulate directly. The idea of Markov chain Monte Carlo is to create a Markov chain whose equilibrium distribution is the desired distribution, and simulate the chain for "a long period of time" with the hope that after this time, the chain is close to stationarity. There are two potential difficulties with the method: in most cases, it will be impossible to obtain exactly the equilibrium distribution in finite time, and moreover it is in general a difficult problem to bound the time required before the chain is close to its equilibrium distribution. In 1996, Propp and Wilson introduced an algorithm, "coupling from the past", which allows sampling exactly from the equilibrium distribution and does not require computation of convergence rates. I will explain the ideas of Propp and Wilson, and give some examples from statistical mechanics. Speaker: Kazuma Shimomoto Title: Twin prime numbers Abstract: The study of prime numbers has a long history. Recently, it was announced that "Twin prime conjecture" was solved, but the proof, however, still contains a gap. While his proof is still incomplete, he found a nice approach to the conjecture. In this talk, I will present some basic ideas about this problem including historical aspects. Speaker: Amber Smith Title: Population Invasions: Models, Ro, and NGOs for Infectious Diseases Abstract: The basic reproductive number (Ro) and the next generation operator (NGO) give us some mathematical tools to analyze infectious disease dynamics. This includes finding out whether a disease population will survive, if it can invade another, and if two populations can coexist. We'll develop these tools as well as apply them to some models including the flu, foot and mouth disease, STDs, malaria, and Strep pneumoniae. Speaker: Renzo Cavalieri Title: Counting Bitangents With Stable Maps Abstract: Let's start from a pseudo high school problem: given a generic plane curve of degree d, count the number of lines that are tangent twice to this curve. If you try it at home, it's quite hard. A neat classical solution is a consequence of the Plucker formulas. However, the problem can be approached from a completely different angle, using moduli spaces and intersection theory. Goal of the talk is to sketch the strategy of this technique. Speaker: Dali Zhang Title: Twoscale electromagnetic imaging problems with a microstructured medium Abstract: Many engineering problems contain materials which are heterogeneous on a length scale that is small (microscopic) compared to the typical length scale (macroscopic) of the problem. Electromagnetic materials are particularly important to study in this regard. We will discuss largescale inverse problems based on Maxwell's equations in time or freqency domain. We will also discuss an inverse homogenization approach for microscale inversion to recover information about the fine structure of the random medium. We will show computational results regarding this approach and present the inverse problems related to this topic for future work. Speaker: Nessy Tania Title: Restitutionhow to study cardiac dynamics using one dimensional maps. Abstract: In this talk, we will learn how onedimensional maps can be used to study the dynamics of electrical activities in the cardiac system. The map, known as the restitution relation, specifies an action potential duration based on the previous diastolic interval. We will look at two models in particular  one derived from a biological experiment, and one obtained by taking asymptotics limit of a HodgkinHuxley like system. Bifurcation structures of the latter will be explored in some details. Speaker: Elijah Newren Title: Numerically Solving the Coupled Motion of a Fluid and an Elastic Material Abstract: There are a vast range of phenomena in biological fluid dynamics that involve the interaction of a viscous incompressible fluid with an elastic materialincluding the beating heart, insect flight, platelet aggregation, swimming, and many other applications. In this talk I will give a brief overview of a pair of methods used to solve such problems, namely the Immersed Boundary and Immersed Interface Methods.
Department of Mathematics University of Utah 155 South 1400 East, JWB 233 Salt Lake City, Utah 841120090 Tel: 801 581 6851, Fax: 801 581 4148 Webmaster 

