Madison Chaos and Complex Systems Seminar

Spring 1997 Seminars

Dates, speakers, titles and abstracts will be listed as they become available. Meetings will be noon Tuesdays in 4274 Chamberlin Hall unless otherwise noted.

Short List

21 January. Steering Committee Meeting

28 January. Fred Brauer, UW Math: ``A Simple Model for Increasing Returns in a Competitive Economic Market.''

Abstract: The possibility of multiple equilibria in competitive markets with increasing returns has long been troublesome to economists. A dynamical stochastic model proposed by Brian Arthur to explain this possibility was one of the early successes in the study of complex systems, leading to much discussion of the economy as an evolving adaptive system. In fact, the crucial breakthrough was the willingness to consider a dynamic model rather than an equilibrium model, not the introduction of complexity.

Uninhibited by knowledge of either ecomomics or complex adaptive systems, we formulate a simple deterministic dynamic model (i.e., a two-dimensional autonomous system of differential equations) which may be analyzed by an easy geometric argument to show similar possibilities.

4 February. Clint Sprott, UW Physics: ``A Fractal View of the World.''

Abstract: Since the time of the ancient Greek philosophers, we have been taught that the geometry of lines and surfaces and solids is the proper description of the world. Recently, a new type of geometry has emerged in which the fundamental objects are "fractals." Fractals have non-integer dimension and self-similar structure on all scales. Natural objects such as rivers, mountains, clouds, and plants are best described by fractal geometry. Examples of fractals will be shown, and methods will be described whereby you can generate fractal patterns on your computer.

11 February. Paul Milewski, UW Math: ``Waves Generated by Water Flowing over a Bump.''

Abstract: When a fluid flows over a bump, the surface of the fluid will be affected (we have all watched a stream flowing over rocks). In this talk we will discuss models that have been derived to study this problem, and show some simple solutions that can be obtained from them. As the models become more involved (and presumably describe the problem more accurately), numerical solutions show a wealth of behavior: steady waves, periodic solitary wave generation, and more complex flows. This will be an introductory talk, assuming no prior knowledge of fluid flows.

18 February. David Newman, Fusion Energy Division, Oak Ridge National Lab: ``Self-organization in Nature: from Sandpiles to Plasmas.''

Abstract: In nature there are many systems which exhibit some form of self-organization. Among these are forest fires, earthquakes, sandpiles and even life itself. Investigations into the similarity of the dynamics of such systems have been undertaken by using simple cellular automata models. These models have produced a remarkable amount of insight into the dynamics of such systems. Recently a Self-Organized Criticality (SOC) model for turbulent transport in magnetically confined plasmas has been proposed in order to explain some of the observed features of the transport dynamics in these plasmas. The features of SOC systems, from forest fires to earthquakes, the extension to a sandpile model for turbulent transport and potential methods for control of SOC systems will be discussed.

25 February. Ray Kent, UW Communicative Disorders: ``Sounding Off in the First Year of Life: The Complex System of Infant Vocalization.''

CANCELLED due to an unfortunate illness; Dr. Kent's talk will be re-scheduled later in the semester.

Abstract: Beginning with the birth cry and proceeding through grunts, babbles, and maybe first words, the typical infant accomplishes a number of vocal milestones in this so-called ``prespeech'' period from birth to one year of age. This talk reviews some recent perspectives from complex systems theory as they relate to vocal development.

4 March. Jon Foley, UW Atmospheric and Oceanic Sciences: ``Exploring Dynamic Interactions Between Ecosystems and the Atmosphere.''

No abstract yet.

11 March. David Griffeath, UW Math: ``Digital Growth Models.''

Abstract: A colorful slide show will survey the theory of discrete growth dynamics. For the simplest cellular automaton crystal growth models one can identify a linear speed of spread and anisotropic convex asymptotic shape. Only slightly more complex local rules give rise to nonconvex chapes, dendritic crystals, fractal patterns, and other complex phenomena. We will also briefly discuss recent work on the ``reverse shape'' attained by basic automata just before they fill huge holes.

18 March. Grace Wahba, UW Statistics: ``How to Smooth Curves and Surfaces, or, Statistical Model Building with Applications in Demographic Risk Factor Estimation, Climate, and Numerical Weather Prediction.''

Abstract:We begin by describing the popular cubic smoothing spline as a tool for fitting smooth curves to noisy data, and go on to describe generalizations of the variational problem it solves. These generalizations can be used to build flexible models for discrete, noisy observational data in such diverse fields as analysis of demographic studies of risk factors for heart attacks and diabetic retinopathy, extracting patterns from global historical surface temperature records that may be relevant to global warming, tuning of imperfect dynamical systems models of the atmosphere and ocean, and other applications.

1 April. Ann Palmenberg, UW Animal Health and Biomedical Sciences: ``Structural Chaos vs Thermodynamics in the Evolution of Viral RNA Genomes. Part 1: Optimal RNA Folding: Thermodynamics of Genomic vs Randomized Sequences.''

Abstract: Did you ever wonder why most complex genomes are encoded by DNA? As an informational context, RNA surely predates DNA by any evolutionary measure. Yet today, only certain genomically simple, highly pathogenic viruses still use RNA as their genetic format. We have found the informational complexity of single-stranded viral RNA genomes is forged by a delicate balance between biological selective pressures and the thermodynamics of RNA folding. Energetically plausible alternative configurations punctuate and dominate these genomes, creating extensive regions topological disorder. The observed pattern of permissible chaos in the thermodynamics of RNA folding suggests that information conversion to DNA (topologically linear) was an evolutionary necessity for larger genome organization.

8 April. Ann Palmenberg, UW Animal Health and Biomedical Sciences: ``Structural Chaos vs Thermodynamics in the Evolution of Viral RNA Genomes. Part 2: Suboptimal RNA Folding: Thermodynamics and the Evolution of RNA Genomes.''

See abstract for 1 April above.

15 April. Bob Wilson, UW Math: ``A Closer Look at Fractals and the Mandelbrot Set.''

Abstract: It is one thing to say that the ``dimension'' of a fractal such as the Sierpinski Gasket should be more than 1 but less than 2, but why should it be 1.58496...? Magazines and coffee-table books have pretty pictures of the Mandelbrot Set, and we can even ``dive'' into it using computer software, but what is it and how is it produced? This talk will attempt to answers questions like these, with no attempt at mathematical rigor: No mathematics will be used beyond high school algebra.

18 April. Seminar of Possible Interest: Scott Camazine, Dept. of Entomology, Penn State: ``House-hunting by Honey Bee Swarms: from Individual Behaviors to Collective Decisions.

Unusual time and place: Entomology seminar, Friday, 3:30 pm in room 150 Russell Labs.

Bob Jeanne writes: ``Camazine has done some of the best work on modeling self-organizing systems, especially insect group behavior. Much of his work has been with honey bees, but he has investigated non-social insect systems as well. ... Scott will be available most of Friday and Saturday to chat with anyone interested in meeting with him. Please let me know if you would like some time with him (2-0899;''

22 April. Robert Jeanne, UW Entomology and Zoology: ``Social Insects are Self-Organized Biological Systems.''

No abstract yet.

29 April. Cosma Shalizi, UW Physics: ``Watching (Digital) Pots Boil, and Other Exciting Things.''

Abstract: Digital boiling is one of a large class of celluar automata which model excitable media, such as cardiac tissue, neurons, fires, aggregating cellular slime molds, and chemical oscillators. After the customary three-sentence explanation of what a cellular automaton is, I'll talk about the history and use of CA in studying excitable media in general. Finally, I will discuss some recent findings about digital boiling in particular, trying to make them both understandable and interesting to non-mathematicians. Technology permitting, the talk will be accompanied by animations of the CA and of physical excitable media.

6 May. John Cameron, UW Medical Physics: ``A Proposed Model for Imagination and Creativity.''

Abstract: In this talk I will propose a model for imagination and creativity based on known physical and chemical principles. The model does not depend on a detailed understanding of the memory or reasoning powers of the brain. I will suggest the use of pulsed magnetic fields to improve the imagination. I will describe a simple type of computer imagination. I will describe an analogy between imagination and mutations in plants and animals. I will suggest a possible inverse relation between memory and imagination. Finally, I will discuss some possible experiments.

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Last change worth mentioning Mon Apr 28 16:35:04 1997