All seminars are Tuesday at 12:05 pm in 4274 Chamberlin except as noted.
January 18, 2005
Self-organization - Nature's intelligent design
Clint Sprott, UW Department of Physics
Complex patterns are common throughout
nature, from the distribution of the galaxies in the Universe to
organization of neurons in the human brain. It is generally
that such complex structure must have a complex cause, but it may
that simple mathematical and computer models can produce such
This talk will provide examples of self-organization in nature and
will describe six simple models that can replicate the features of
these patterns. The models typically produce fractal spatial
and chaotic temporal dynamics characterized by power laws and
unpredictability, even when the models are simple and purely
deterministic. The work has application to fields as diverse as
physics, ecology, political science, economics, sociology, and
This talk is available as a PowerPoint
Presentation and in HTML
January 25, 2005
Magnetic self-organization in laboratory and astrophysical
Jim Reardon, UW Department of Physics
A plasma is an ionized gas that contains a very large number of charged particles. The law that governs the movement of an individual charged particle is easy to write down, and has been known for more than 100 years. However, experiments have consistently shown that plasma behavior on all length and time scales is dominated by collective effects, few of which were predicted in advance. Recently, it has become clear that the behaviors of certain plasmas in the laboratory and in space are dominated by magnetic self-organization, a type of collective behavior in which the movements of particles are influenced by the fluctuations in magnetic fields, and vice-versa. Examples include astrophysical jets and the MST device in Chamberlin Hall.
February 1, 2005
Climate Variability in the Upper Atmosphere
Susan Nossal, UW Department of Physics
Understanding the influence of sources of natural variability is necessary for characterizing properties of the Earth's atmosphere and for isolating signatures of natural variability from those due to human caused change. Scientists are investigating the Earth's climate by studying patterns of variation both geographically and vertically in the atmosphere. This talk will focus on studies of higher altitude regions of the atmosphere. For example, there is predicted to be major greenhouse cooling in the stratosphere and higher altitudes, accompanying warming in the troposphere as a result of increased atmospheric concentrations of carbon dioxide. There are also expected to be changes in the chemical composition of the atmosphere at higher altitudes. This talk will address in more detail ongoing research of sources of natural variability in upper atmospheric hydrogen and predictions for change in its composition. Upper atmospheric hydrogen is a byproduct of chemistry in the middle and lower regions of the atmosphere involving hydrogen-containing species such as methane and water vapor, two of the most influential greenhouse gases.
February 8, 2005
A dynamics-based approach to sound source identification
Robert Lutfi, UW Department of Communicative Disorders
Everyday experience suggests that the ear is rather good at inferring basic attributes of objects and events from sound. The 'clunk' of the table struck with your knuckle indicates that the table is hollow and made of wood; the 'woosh' of the passing vehicle suggests a high speed chase. Such simple examples represent in principle how we use sound to gain information about our surroundings, but even in regard to these simple examples we understand very little of the process. In this talk I'll describe a method for measuring precisely how listeners judge the physical attributes objects and events from sound. The method involves estimating partial correlations of the listener's judgments with small, experimentally-introduced perturbations in acoustic parameters. Importantly, the perturbations are introduced in such a way so as not to violate the dynamic relations governing sound emission. One notable conclusion of these studies is that basic limits in auditory sensitivity exert a far greater influence on listener judgments than does knowledge of the intrinsic acoustic relations that would serve to disambiguate sources.
February 15, 2005
Ann Althouse, UW Law School
UW law professor (and prolific blogger) Ann Althouse will discuss the burgeoning phenomenon of time-stamped, frequently updated, on-line journals.
See a report
on this talk in the Madison Capitol Times, and visit the speaker's blog.
February 22, 2005
Numerical simulations of the Madison Dynamo Experiment
Adam Bayliss, UW Department of Physics
Saturation of a mean field magnetic dynamo via backreaction with
flow is described for increasing fluid turbulence. Our
dynamically and inductively self-consistent incompressible
code utilizes a propellor model for a mechanically driven flow
qualitatively compares well to LDV measurements in a purely
hydrodynamic analogue of the liquid sodium experiment in Madison.
find that for a laminar flow the exponentially growing magnetic
is saturated when the Lorentz force alters the shape and strength
the flow until a steady state is reached where the growth rate of
large scale saturated magnetic field is zero or producing
mild oscillations about a steady state magnetic energy; both
and character of the nonlinear saturation vary with magnetic
number. As the fluid Reynolds number, thus the mean flow, is
via more power into the simulated propellors, inertial terms
create increasingly nonlinear flows leading to strong magnetic
which re-laminarize the fluid flow. Recent simulations examine the
of turbulence in the anisotropic, inhomogeneous spherical system.
observe a small-scale dynamo which may inhibit the growth of the
large-scale magnetic field, despite being kinematically predicted
(using a fixed flow averaged over temporally correlated
Results of the simulations will numerically investigate the
saturation, and turbulent evolution of the liquid sodium dynamo
experiment in Madison.
March 1, 2005
Continuous measurements of crustal deformation through the earthquake cycle, western Mexico: Evidence for non-linear crustal response following megathrusting subduction earthquakes
Chuck DeMets, UW Department of Geology and Geophysics
The classical notion of faults as features that exhibit simple stick-slip behavior, represented by earthquakes and intervening aseismic periods of strain accumulation, is discussed in view of mounting evidence that other non-seismic phenomena exert important influences on the seismic cycle of active faults. Evidence for such phenomena will be presented from continuous GPS measurements in western Mexico and other places.
March 8, 2005
Effects of biodiversity on the functioning of ecosystems ...
why, and who cares?
Brad Cardinale, UW Department of Zoology
Abstract: Loss of biological complexity -- due to species
as homogenization by the spread of exotic taxa -- ranks among the
striking changes to the global environment. It has been
ecosystems characterized by lower biocomplexity may be less
performing fundamental biological processes - processes that may
prove important to society. Using 3 case studies as
address several conditions under which diversity does vs. does not
key fluxes of energy and matter. These will focus on the
freshwater invertebrates on fluid dynamics, (ii) marine benthic
invertebrates on sediment bioturbation, and (iii) terrestrial
predators on pest control.
March 15, 2005
The dynamics of host-parasite coevolution and the evolution of
Andy Peters, UW Department of Zoology
Antagonistic coevolution (also known as the "Red Queen process"), in which biological enemies such as hosts and parasites are under constant selection to evade each other's recent adaptations, has long been known to provide a potential advantage to the shuffling of genomes that results from genetic recombination. I present the results of computer simulations showing that the dynamics of this process make it qualitatively different from any other model of the evolution of recombination. I also consider the feedback between the increase in recombination and the process of coevolution, and show that the mechanisms by which host populations respond to parasite selection change fundamentally as recombination becomes more common.
March 29, 2005
Dynamics of protein molecules
George Phillips, UW Departments of Biochemistry and Computer Sciences
Proteins molecules comprise thousands of atoms that self assemble into working machines. The basic physical forces that drive them to a folded structure are generally understood, but the energy landscape of their possible configurations is rich and complex. Aspects of protein folding, such as metastable states and prions will be discussed as well as attempts to visualize these dynamic systems using simulations and experiments alike.
April 5, 2005
Sleep apnea: from obscurity to epidemic in just a few decades
Terry Young, UW Department of Population Health Sciences
Until the early 1990’s, little was known about sleep apnea, a condition of repeated breathing pauses during sleep. We initiated the early epidemiological studies of this disorder by recruiting a random population sample of men and women to undergo overnight sleep studies every four years: the Wisconsin Sleep Cohort (WSC). The studies based on the WSC, now in its 17th year, uncovered a rather shockingly high prevalence of undiagnosed sleep apnea across a wide severity spectrum in both men and women. Most importantly, there is a dose-response (but nonlinear!) association between sleep apnea and significant behavioral and cardiovascular morbidity. The dilemma lies in the lack of clinical resources to deal with diagnosis and treatment of the huge number of people with unrecognized sleep apnea. Where, on the severity spectrum should the “clinical significance” cut-point be? Current findings from the WSC relevant to this question will be presented.
April 12, 2005
Influence of habitat type and field shape on margin weed diversity
Ed Luschei, UW Department of Agronomy
Despite the tremendous economic costs associated with weeds,
little is known about their population dynamics. The primary
focus of applied weed scientists has been on fine tuning our
decrease weed seedling survivorship through cultural practices,
mechanical disturbance and chemical application. While this focus
sense as a means to minimize crop yield lost to resource
it clearly must be considered tending the proverbial symptom
than the disease. I will briefly discuss the traditional
stage-structured formulation of weed population dynamics and why
largely failed to helpful in an applied sense. In short, I argue
stochasticity and scale conspire to make most experiments
uninformative. As an alternative to the “bottom up” construction
dynamics, I will describe several experiments my lab has conducted
more explicitly address the stochastic nature of processes of
importance in weed dynamics.
April 19, 2005
Complex dynamics in spatially-dependent Lotka-Volterra ring systems
Joe Wildenberg, UW Department of Physics
Mathematical models often need to
incorporate spatial dependence to accurately model real-world
We consider competitive Lotka-Volterra models
modified to include this spatial dependence through organization
competing species into a one-dimensional ring by an appropriate
interaction matrix. We show that these
systems can exhibit complex dynamics, spatiotemporal chaos, and
symmetry breaking. A high-dimensional, spatially homogeneous,
example with interaction strengths decreasing with distance is
including an analysis of how the dynamics of the system vary with
dimension. We also show the existence of Lyapunov
functions that arise from this method of including spatial
they prohibit complex dynamics for certain regions of the
This talk is available as a PowerPoint
April 26, 2005
Entropy, symbolic dynamics, and dynamical systems
Jeff Noel, UW Department of Physics
We all know entropy as that mysterious physical necessity that hot objects always become cool and cool objects never spontaneously become hot. Increasing entropy, or more noticeably increasing disorder, is the Second Law of Thermodynamics. Boltzmann showed that the Second Law was really only a statistical likelihood, that manifested as a law for macroscopic systems. Claude Shannon used the same mathematical formulation as Boltzmann to define the entropy of information and communication. This formulation allows for a quantification of the disorder of information and gives several important results including the value of the maximum possible compression of data. This same technique when applied to dynamical systems and their associated symbolic dynamics allows for investigation of the disorder of the systems and gives alternative methods to calculate quantities such as the Lyapunov exponent and the predicability time. In this talk, entropy, information theory, and the symbolic dynamics of a low dimensional chaotic Lotka-Volterra system are discussed.
May 3, 2005
Physics of running
Jim Reardon, UW Department of Physics
I would like to demonstrate that running (the sort that humans
for example when they are late to the Chaos and Complex Systems
Seminar) is both very much more simple and very much more complex
is commonly thought. "Simple" in that it is possible to
anthropomorphic robots, with gaits quite like human gaits, that
almost no control systems but nonetheless have gross dynamic
and "complex" in that humans achieve fine dynamic stability by
a much more sophisticated control system which is almost always
"user-transparent". Possible implications of all this for
lowering your 5k time will be discussed.