January 27, 2004
For simple systems you can use models, but complexity requires narrative.
Tim Allen, UW Department of Botany
Robert Rosen says that complexity cannot be modeled. Therefore it is all-or-nothing. When we speak of degrees of complexity, in fact we speak of what we had to do to make it simple, so we could model it. More complex is actually less simple. We can still deal with complexity, but not with models, only with narratives. This is neither soft nor hand-waving, but rather invokes a precision of definitions beyond the crass literalism of normal science. Science appears as a four-dimensional narrative. The narratives deal with several levels of analysis: n-1 is where formal identity harbors a plan for the complex system; n+1 gives semantic to the context; n itself is complex because the plan at n-1 is updated by experience at n+1. Complexity invokes several levels of time in the observer/observation complex.
February 3, 2004
Chaos in low-dimensional Lotka-Volterra models of competition
Clint Sprott, UW Department of Physics
An example of chaos in a Lotka-Volterra model with four competing species is described. The chaos occurs in a narrow region of parameter space but is robust to perturbations. The solution shows features of self-organized criticality (scale-invariance). Suggestions will be given for interesting extensions of the model that would be suitable for publishable student research projects.
J. A. Vano, J. C. Wildenberg, M. B. Anderson, J. K. Noel, and J. C. Sprott, Chaos in low-dimensional Lotka-Volterra models of competition (submitted to Physics Letters A)
February 10, 2004
Intraday stock price data and measures of adverse selection
Mark Ready, UW Business School
Mark Ready is an Associate Professor of Finance who served as Chief Economist of the US Securities and Exchange Commission and as member of the Nasdaq's Economic Advisory Board. Much of his research focuses on trade-by-trade equity data. Mark will give an overview of how Finance researchers view the trading process, with emphasis on the adverse selection problem faced by market makers (the problem that some traders have valuable information about the stock). Mark will discuss and compare three different techniques that have been developed to measure the degree of adverse selection. These three measures are discussed in the attached working paper, joint with Elizabeth Odders-White, which was presented at the annual meetings of the American Finance Association in early January.
February 17, 2004
Winds of chaos
John Young, UW Department of Atmospheric and Oceanic Sciences
Modern weather prediction centers chase the chaos of weather systems on time scales of days to months. Their business is to analyze, predict, and verify these systems using the most advanced data sources and numerical models. Two categories are most familiar to the public: - "medium range" atmospheric forecasts for 0-10 days covering the globe, and - "seasonal" forecasts of the atmosphere and ocean system for a few months.
In this talk, I will attempt to show a scrapbook of some of the many products that illustrate the chaotic patterns of weather. Some animations of ensemble forecasts will show the growth of errors over days and for different parts of the globe.The statistical skill shows the decline of the predictability of various features, and its trends over the past 20 years show the progress from huge efforts. The growth of uncertainty is seen to depend on location, the configuration of jet streams, and especially the physical property (wind, temperature, rain) being forecast. Forecasts for a particular city show the practical uncertainties of forecasts a few days in advance. Patterns of probability will be shown for seasonal forecasts of El Nino.
February 24, 2004
Ecological hysteresis: You can't go home again (at least simply)
Don Waller, UW Department of Botany
Many ecological interactions involve non-linear dynamics and dependencies on spatial and historical patterns. Such characteristics can produce 'alternative stable states' and add 'ecological hysteresis' making it difficult or impossible to simply reverse ecological change. We are investigating the historical dynamics of ecological change in Wisconsin forest herb communities where deer act as a 'keystone' herbivore to radically alter community composition. The impacts that deer have on these communities appear to depend on both deer and plant abundances. Once populations of sensitive plant species are depleted, even low deer populations may suffice to suppress recovery, producing hysteresis and impeding ecological restoration. Interactions between deer and their predators (wolves and humans) and deer and introduced species may also produce hysteresis, further complicating ecological interactions as well as practical management of these ecosystems.
March 2, 2004
Chaos and irregularity in vocal fold vibration
Jack Jiang, UW Medical School
Chaos has been observed in turbulence, chemical reactions, nonlinear circuits, the solar system, and biological populations, and seems to be an essential aspect of most physical systems. Chaos may be also central to the interpretation of irregularity in voice disorders. Studies have demonstrated the presence of chaos in computer models, experiments with excised larynges and human voices. Methods based on nonlinear dynamics can be used to quantify chaos and irregularity in vocal fold vibration. Studies have suggested that disordered voices from laryngeal pathologies such as laryngeal paralysis, vocal polyps and vocal nodules exhibit chaotic behaviors. Conventional parameters, such as jitter and shimmer, may be unreliable for analysis of aperiodic and chaotic voice signals. However, nonlinear dynamic methods have differentiated between normal and pathological phonations and can describe the aperiodic or chaotic voice. Chaos theory and nonlinear dynamics can enhance our understanding and assessment of laryngeal pathologies, as well as our ability to recommend appropriate treatment.
March 9, 2004
The basal ganglia - thalamic - cortical network as nested reentrant non-linear oscillators: new brain dynamics
Erwin Montgomery, UW Department of Neurology
Using newly developed methods for identifying periodic activity in neuronal spike trains and by using resonance effects resulting from paired-pulse stimulation, multiple and high frequency oscillations have been demonstrated in neurons of the basal ganglia-thalamic-cortical system in non-human primates. The evidence suggests that neurons in these systems participate in multiple reentrant non-linear oscillating circuits. Further, neurons are multi-stable in that they can display periodic activity at multiple frequencies simultaneously. Each stable state is manifest as a set of oscillatory frequencies and that neurons made abrupt transitions between these states. Further, changes in these states are correlated with behavior in an arm reaching task. These observations are remarkably similar to the mathematical properties of non-linear oscillators embedded in loosely-coupled networks. Combined, these observations provide a new context and opportunity to theorize the neurophysiology of reentrant systems including the limbic, cerebellar, and thalamic-cortical systems in addition to the basal ganglia-thalamic-cortical system. Already, these new concepts challenge the current hierarchical and sequential notions of basal ganglia physiology.
March 23, 2004
Control without control: From complexity to the management of innovation
M. Mitchell Waldrop, Science writer and NSF public affairs officer
Dr. Waldrop looks back on his book Complexity a decade after it first appeared in 1992, and discusses why the book seemed to strike such a chord. He explores a recurrent theme he calls "Control Without Control": the challenge of creating an environment in which individual choice, individual initiative, and individual interests have free reign-and yet converge on a desirable result. As an illustration of this phenomenon, he draws from his new book, The Dream Machine, and finishes with a discussion of the ARPA computer community of the 1960s and 1970s-arguably the most fabulously successful program of federally funded research in history.
March 30, 2004
Food-web interactions govern the resistance of communities following non-random extinctions
Anthony R. Ives & Bradley J. Cardinale, UW Department of Zoology
Rates of species extinction are accelerating world-wide, causing growing concern about how loss of biodiversity will affect ecosystems. Whereas most previous studies have explored the consequences of losing biodiversity when species go extinct at random, here we compare random extinction to the more likely scenario of species going extinct in of order their sensitivity to a stress that intensifies through time (e.g., climate change). For both random and ordered extinction, strong food-web interactions in a community allow for compensatory responses among species that buffer the community against further environmental stress, and as species go extinct, the potential for compensation declines. For ordered extinction, however, this decline in compensation potential is offset, because the surviving species are those that are relatively tolerant to environmental stress. Furthermore, with each successive extinction, the relative sensitivities of the surviving species are reshuffled by altered indirect effects of food-web interactions, making it difficult to predict the potential of species to compensate for future extinctions. This unpredictability argues for "whole-ecosystem" approaches to biodiversity conservation, as seemingly insignificant species may become important as other species go extinct.
April 6, 2004
Synaptic tagging in neuronal function and dysfunction
Jerry Yin, UW Departments of Genetics and Psychiatry
The requirement for gene expression around the time of behavioral training is a molecular characteristic of long-term memory. This requirement begs the question of synaptic specificity. How does a neuron only strengthen one or a few synapses when cell-wide processes like transcription occur? The proposed molecular/cellular solution to this problem reveals aspects of neuronal function and dysfunction that will be discussed.
April 13, 2004
Modelling predator killing rates: History, current thought, and future directions
Damien O. Joly, UW Department of Wildlife Ecology
The way in which the killing rate of a predator responds to changes in prey density is an important determinant of the stability of predator-prey systems. There are currently greater than 40 mathematical models describing the relationship between killing rate and prey density (i.e., the functional response), all generally derived from simple equations developed by C.S. Holling in the 1950s. These models have clear analogy to enzyme kinetics, in particular the Michaelis-Menten equation. In this talk, I illustrate how the functional response affects the stability of predator-prey systems and provide examples from my own research on grey wolf predation of moose and caribou as well as human predation of Late Pleistocene woolly mammoths.
April 20, 2004
Transport of contaminated sediment in a river-estuary system
Jon B. Manchester, UW Environmental Chemistry and Technology Program
The chemical revolution of the 20th century created a new world of useful, and now perhaps irreplaceable, products that continue to improve the lives of people around the world. Unfortunately, a byproduct of this revolution is world-wide contamination of the environment by a variety of chemicals. This talk will provide an overview of environmental contamination by organic compounds, with an emphasis on the “complex systems” that are affected by the presence of chemical contaminants.
In some areas, progress has been made with implementation of “Green Chemistry” technologies that minimize environmental contamination while maintaining a robust chemical industry. Also, much effort is now being directed toward the goal of remediating past contamination. A major focus of this work is sediments at the bottom of many bodies of water that are contaminated with a variety of chemicals. A case study centered on the Fox River—Green Bay system will be presented. This work provides an opportunity to examine how non-linear flow dynamics in a river may transport, and so render unrecoverable, large amounts of contaminated sediment.
April 27, 2004
Self-organization in bankruptcy legal systems
Bernie Trujillo, UW Law School
Conventionally, lawyers explain patterns in legal systems’
reference to exogenous ordering (e.g. the directives of
appellate courts). U.S. bankruptcy law lacks meaningful
ordering, and yet patterns emerge
among local practice communities. I will present some empirical evidence of bankruptcy’s self-organization. I will also explore the possibility of modeling the adaptive behavior of bankruptcy legal systems, predicated on the notion that the
forms comprising a legal system’s content (e.g. particular expressions of public doctrine or of private ordering) compete against each other for finite institutional resources. More generally, I wish to explore whether the concepts of chaos,
complexity, and self-organizing criticality help explain the behavior of data generated by legal systems.
May 4, 2004
Biopsychosocial pathways to health and illness: Strategies for managing multidisciplinary complexity
Carol Ryff, UW Department of Psychology
I will describe a program of research that blends multiple
influence (i.e., sociodemographic factors, psychosocial factors,
health behaviors, neurobiological mechanisms) to understand
in health and well-being as individuals age. This kind
can translate to a quagmire of higher-order interaction terms if
with the usual analytic tools. As an alternative, we have
"person-centered" analytic strategies that use the person, rather
the variable, as the unit of analysis. The approach will be
with two investigations -- one involving life course pathways to
(operationalized as recovery from major depression) among midlife
and the other involving economic and social relational pathways to
load (a summary index of wear and tear on multiple physiological
I will also briefly sketch our ongoing plans to investigate
in a national sample of American adults.