**Thursday, September 12, 2002 **
(12.15 pm; Room 1207 Energy Research Building)

**Michael Efroimsky, Univ of Minnesota**

Inelastic Dissipation in a Freely Precessing Rotator.Applications to Interstellar-Dust Astrophysics, TumblingAsteroids, Comets, Rotating Spacecraft, etc...

Abstract:Neutron stars, asteroids, comets, cosmic-dust granules, spacecraft, as well as whatever other freely spinnig body dissipate energy when they rotate about any axis different from principal. We study the internal-dissipation-caused relaxation of a freely precessing rotator to its minimal-energy mode (which corresponds to the spin about the maximal-inertia axis). We show that the internal dissipation takes place not so much at the frequency of body's precession but rather at the second and higher harmonics. In other words, this simple mechanical system provides an example of extreme non-linerity. Most surprisingly, lower frequencies also do come into play. The earlier estimates, that ignored this non-linearity, considerably underestimated the efficiency of the internal relaxation of wobbling asteroids and comets. At the same time, owing to the non-linearlity of inelastic relaxation, small-angle nutations can persist for very long time spans. The developed formalism has been applied, by me and by my colleagues, to description of cosmic-dust alignment and to analysis of asteroidal and cometary wobble These results are applicable also to the studies of damping of rotating spacecraft.

**Atsushi Uchida, UMD**

Dual synchronization of chaos in optical and electronic systems

**Thursday, September 19, 2002 **
(12.15 pm; Room 1207 Energy Research Building)

**Daniel Wojcik, IPST, UMD**

Diffusive-ballistic crossover in 1D quantum multibaker walks

**Aleksey Zimin, UMD**

Efficient Local Ensemble Data Assimilation Technique

**Thursday, September 26, 2002 **
(12.15 pm; Room 1207 Energy Research Building)

**Eugenia Kalnay, UMD**

Are Bred Vectors and Lyapunov Vectors the same?

**Doug Armstead, UMD**

Long Time Algebraic Relaxation in Chaotic Billiards

**Thursday, October 3, 2002 **
(12.15 pm; Room 1207 Energy Research Building)

**Jonathan Ozik, UMD**

"Simulating Granular Coral Snake Patterns in Long Rotating Cylinders"

**Sang-Yoon Kim,UMD**

"Strange Nonchaotic Attractors in Quasiperiodically Forced Period-Doubling Systems."

**Thursday, October 10, 2002 **
(12.15 pm; Room 1207 Energy Research Building)

**Joerg Schumacher, Philipps-Universitaet, Germany**

Clustering of Lagrangian tracers on free-surface flows.

**Wayne Hayes, Univ. of Toronto**

Shadowing the softened N-body problem

**Thursday, October 17, 2002 **
(12.15 pm; Room 1207 Energy Research Building)

**Richard Prange, UMD**

Exotic quantum states in transiently integrable systems

no second speaker

**Thursday, October 24, 2002 **
(12.15 pm; Room 1207 Energy Research Building)

**Lou Pecora, NRL **

Synchronization of oscillators in smallworld networks

**Katepalli Sreenivasan, IPST, UMD**

Asymmetry in the presence of intermittency

**Thursday, October 31, 2002 **
(12.15 pm; Room 1207 Energy Research Building)

**Victor Yakhot, Boston University **

hydro-kinetic equation for description and simulation of strongly nonlinear fluids

(one talk only)

**Thursday, November 7, 2002
**
(12.15 pm; Room 1207 Energy Research Building)

**Tom Carroll, NRL**

Regions of Period Doubling in the Diode Resonator

**Moustafa Fofana, Department of Mechanical Engineering, Worcester
Polytechnic Institute**

Hopf Interactions in Machining Operations with Nonlinear Regenerative Chatter

**Thursday, November 14, 2002
**
(12.15 pm; Room 1207 Energy Research Building)

**Linda Moniz, NRL**

Damage AssessmentAbstract: Analysis of data from experiments on dynamical systems often centers on the embedding of time series data to reconstruct an attractor. In our system, we consider output from (chaotic excitation of) a circuit designed to simulate a spring-mass system in both a damaged and an undamaged state. We employ a new version of the continuity statistic, first introduced by Pecora, Carroll and Heagy[1]. Here we use the statistic in the new setting of multiple time series embedding. We show the continuity statistic is an appropriate and sensitive tool for showing differences in the reconstructed attractors in the damaged and undamaged states.

[1] Pecora, L.M., Carroll, T.L. and Heagy, J.F. [1995] Statistics for mathematical properties between time-series embeddings,

Physical Review E 52(4),3420.

**Thursday, November 21, 2002
**
(12.15 pm; Room 1207 Energy Research Building)

**Cristel Chandre, Georgia Tech**

Time-frequency analysis of chaotic systemsABSTRACT: We describe a method for analyzing the phase space structures of Hamiltonian systems. This method is based on a time-frequency decomposition of a trajectory using wavelets. This method detects resonance trappings and transitions and allows a characterization of the notion of weak and strong chaos. It provides dynamical properties of the system. We illustrate this method using examples from atomic physics, celestial mechanics and chemical physics.

**Guocheng Yuan, Brown University**

Cross-jet transport and mixing in a meandering jet

ABSTRACT: An f-plane, quasi-geostrophic, 2 1/2 layer model is used to examine whether cross-jet transport can be enhanced at depth in a surface-intensified ocean jet, similar to the Gulf Stream. By using dynamical systems techniques, we find that cross-jet transport can be enhanced in the lower layer, but only when the vertical shear is sufficiently strong. Some preliminary results for understanding the role of transport barriers in controlling potential vorticity mixing will also be presented.

**Special Seminar (NOTE DAY**: **FRIDAY,
November 22, 2002 **
(12.15 pm; Room 1207 Energy Research Building)

**Detlef Lohse, Univeristy of Twente**

Rayleigh-Benard convection

Informal Statistical Physics seminar (due to a scheduling mistake, this talk was originally also scheduled for Dec 5):

Tuesday, November 26, 2002(1.15 pm; Room 1116 IPST building)

Steven Schiff, Krasnow Institute, George Mason University

Relating Bad Brains, Rocks, and Gases -- Are Seizures Phase

Transitions?

Special seminar (NOTE DAY+TIME): WEDNESDAY, November 27, 2002(2 pm; Room 1207 Energy Research Building)

Tomas Bohr, Technical University of Denmark

Structure formation in laminar fluid flow: the creation of corners,cusps and needles

Thursday, December 5, 2002(12.15 pm; Room 1207 Energy Research Building)

Romulus Breban, UMCP

Scaling Properties of the Indeterminate Saddle-Node Bifurcation

Thursday, December 12, 2002(12.15 pm; Room 1207 Energy Research Building)

Bob Behringer, Duke University

Fluctuations, rate-dependence, and jamming in dense granular materials.ABSTRACT: Granular materials exist in states that are roughly equivalent to those of ordinary molecular materials. Models for granular gases are at least moderately successful. However, models for dense granular phases, the subject of this talk, are still very much an open subject. Dense systems are typically characterized by enduring contacts between particles. In addition, forces are carried preferentially along a filamentary network known as force chains.

Recent work has focused on the statistical properties of these phases, and in particular on the transition that occurs from solid-like to fluid-like behavior as the shear stress is increased or more random energy is provided to the system. In engineering parlance, this transition is associated with Reynolds dilatancy, and in newer physics parlance, it is associated with jamming. Particularly intriguing is the possibility that the jamming transition of granular materials is representative of behavior in a much broader class of materials that includes colloids, foams, glasses and other systems.

We have carried out a number of experiments to characterize the statistical properties of dense granular materials. I will briefly outline issues associated with force propagation. In the remainder of the talk, I will present results on sheared systems. We have shown experimentally that there is a well-defined transition where the force-chain structure disappears. In MD simulations (with Lou Kondic--NJIT) this transition is associated with a major change in the partitioning of energy between kinetic and elastic modes. We have also investigated a long-standing tenet of continuum models: that stresses for sheared granular materials are rate-independent. We find that this is not the case, but rather that there is a logarithmic strengthening of the force network with shear rate.

tba

Note the different day and time for theses talks. Lunch will NOT be served for summer seminars unless otherwise posted.

**
Bhaskar Khubchandani, UMCP
**

The Influence of Stochasticity on Four-Wave-Mixing in an Optical Fiber

Nature of Power Dropouts of Semiconductor Laser with Optical Feedback: Deterministic or Stochastic?

** Hinke Osinga,
University of Bristol
**

The geometry of optimal control

We study the value function and the existence and regularity of optimal trajectories to determine the structure of the solution set of a class of infinite-horizon optimal control problems. Optimal trajectories are always images of Hamiltonian trajectories on a global stable manifold. These ideas are illustrated with the example of an inverted pendulum on a cart. This is joint work with John Hauser (Colorado).

Unstable manifolds in lasers with delay

We show how a new method for computing unstable manifolds of periodic orbits in delay differential equations can be used to study transitions to chaos in lasers with delay. This is joint work with Kirk Green (Bristol).

**
Jordi Garcia-Ojalvo, Technical University of Catalonia, Spain
**

Entrainment and synchronization in delay-coupled lasers

Order out of noise

**Stephan Koehler, Harvard University**

Foams: Drainage through single plateau borders. Direct observation of rigid and mobil interfaces.

**Istvan Szunyosh, UMCP**

On the relationship between the quality of weather forecasts and the resolution of the forecast models

Adaptation to the Edge of Chaos via Low-Pass Filtered Feedback

Hydrodynamic Instabilities of Wormlike Micellar Fluids

Communicating with optical spatio-temporal chaos

**Arshad Kudrolli, Clark University**

Vortices in vibrated granular rods

(One 1 hour talk)

**Katepalli Sreenivasan, UMCP**

An informal discussion of atmospheric predictability

(One 1 hour talk)

**Horst Meyer, Duke University**

Heat Transfer and Convection Onset in a Compressible Fluid: 3He Near the Critical Point

**Peter Schiffer, Penn State**

***SECOND TALK POSTPONED***Jamming and drag in granular media

**Ron Skupsky, NIH**

Mathematical modelling of gradient sensing in eukaryotic cells

Effects of shell geometry on planetary dynamos

**Paulo Arratia, Rutgers University**

Spontaneous Chaos in non-Newtonian Fluids

Mixing in 3-D Dynamical Systems

**Wayne Hayes, University of Toronto TALK POSTPONED
-- seminar will proceed with 1 talk**

Shadowing the gravitational N-body problem

Sandstone injectites: a geological record of granular fluidization, dynamic crack propogation, and seismic shaking

**Crystal Cooper, UMCP**

A Reaction-Diffusion Model for Experimentally Altered Visual Function in Xenopus Frogs

Using Large Member Ensembles to Study Regions of Local Low Dimensionality in the Atmosphere

**Allen Hunt, CIRES, University of Colorado, Boulder**

Why percolation theory is necessary to understand water retention, unsaturated flow, and solute diffusion in porous media

Competition between two frequencies for phase synchronization of a chaotic laser

**Robert Leheny, Johns Hopkins University**

Memory in an Aging Structural Glass

(Cell-Dendrite transition)

No seminar

**David DeShazer, UMCP**

Noise Induced Burst Synchronization in Fiber Ring Lasers

Shadowing the gravitational N-body problem