Schedule

Except where noted, seminars begin at 12:30pm, with pizza and softdrinks available for purchase at 12:15pm. Seminars are typically held in the IREAP conference room (ERF 1207), which is located on the second floor of the Energy Research Building. Detailed directions and parking information is available on our directions page.

Upcoming Seminars

Modulation of complex collective behaviors in a network of theta neurons by synaptic diversity
March 12, 2015, 12:30 pm in IREAP Conference Room (ERF 1207)
Paul So
Dept. of Physics, George Mason University

Defining Chaos
March 26, 2015, 12:30 pm in IREAP Conference Room (ERF 1207)
Brian Hunt
University of Maryland

Dynamics of Langmuir films: theory and experiment
April 2, 2015, 12:30 pm in IREAP Conference Room (ERF 1207)
James Alexander
University of Maryland

A Langmuir film is a molecularly thin film on a surface. Here we consider the behavior of such films on a flat water surface. (Note: “we” consists of a team of mathematicians, a physicist, a chemical engineer, and several students/post-docs.) The equilibrium state of a finite domain (= “blob”) of such a film is a circular disk. We consider the dynamical behavior when such a domain is disturbed. The tension at the boundary of the domain is the restoring force (so-called line tension, analogous to surface tension of a fluid), which competes against the viscosity of the underlying fluid. A prominent problem is to measure the line tension. The system is modeled as two coupled Navier-Stokes systems, which, because the Reynolds numbers are small, reduces to two coupled Euler flows. Solutions are found which permit comparison with experiment. An advance we make is to model the system globally, not just asymptotically at the end of relaxation to equilibrium. This requires advances in numerical techniques to make the computation effective. In this lecture, we describe the project, from conceptual beginning through to the quantitative dovetailing of theory with experiment.

Colored Noise in Nucleation
April 9, 2015, 12:30 pm in IREAP Conference Room (ERF 1207)
Evelyn Sander
Dept. of Mathematics, George Mason University

Hierarchical transition chronometries in the human central nervous system
April 16, 2015, 12:30 pm in IREAP Conference Room (ERF 1207)
Paul Rapp
Uniform Services University of the Health Sciences (Bethesda, MD)

Using Group Theory to Find All Possible Synchronization Patterns in a Network of Oscillators
April 23, 2015, 12:30 pm in IREAP Conference Room (ERF 1207)
Louis Pecora
Naval Research Laboratory

Effect of heterogeneous dynamics and structured communication on collective motions of delay-coupled swarms
April 30, 2015, 12:30 pm in IREAP Conference Room (ERF 1207)
Klimka Szwaykowska
Naval Research Laboratory, Lab of Dr. Ira Schwartz

Finite time Lyapunov exponents and gradient statistics in fluid turbulence
May 14, 2015, 12:30 pm in IREAP Conference Room (ERF 1207)
Charles Meneveau
Johns Hopkins University
The presentation will briefly review a Lagrangian model for deforming droplets in turbulence, in which the cumulative deformation of fluid elements at small scales is crucial. In particular, we show how knowledge about the statistical distribution of finite-time Lyapunov exponents (FTLEs) can be used to find a critical Capillary number above which droplets will break up. Probability distribution functions of droplet sizes show power-law tails and diverging moments. Inspired by these connections between turbulent phenomena and Lyapunov exponents, we embark on a more systematic study of finite-time Lyapunov exponents in isotropic turbulence. A quantitative statistical characterization of FTLEs can be accomplished using the statistical theory of large deviations, based on the so-called Cramer function. To obtain the Cramer function from data, we use both the method based on measuring moments and measuring histograms, and introduce a finite-size correction to the histogram-based method. We generalize the existing univariate formalism to the joint distributions of the two independent FTLEs in 3D flows. The joint Cramer function of turbulence is measured from two direct numerical simulation datasets of isotropic turbulence. The results serve to characterize the fundamental statistical and geometric structure of turbulence at small scales including cumulative, time integrated effects. These are important for deformable particles such as droplets and polymers advected by turbulence (work done in collaboration with PhD student Perry Johnson, and Profs. L. Biferale and R. Verzicco).