Spring 2007

Date:   Thursday April 5, 2006

Speaker: Aaron Clauset, Santa Fee Institute
Title: Hierarchical decomposition of complex networks

Abstract: Hierarchical organization -- in which a system's elements
connect together into groups, and these groups into groups of groups,
etc. at all scales of organization -- is believed to characterize the
structure of many complex systems, including real-world networks such
as the Web, molecular networks, and food webs. In the past, efforts  to
extract information about hierarchy have been indirect and  heuristic,
which has led to ambiguous conclusions about its  significance. In this
talk, I will present recent work to resolve  this problem. First, I will
discuss a mathematically principled model  of hierarchical organization
in networks called the Hierarchical  Random Graph (HRG). Then, I will
describe a direct and objective  method, based on maximum likelihood and
Markov chain Monte Carlo  sampling, for inferring such hierarchical
structure from real data.  Finally, through concrete examples, I will
describe several distinct  advantages that this approach offers for
network analysis, including,  but not limited to, the generalization of
a single network into an  ensemble of statistically similar networks,
and the statistically  accurate prediction of missing or unobserved
structure. This latter  capability may be particularly valuable for
biological networks such  as protein interaction graphs and food webs,
where it is not yet  possible to automatically extract all true
interactions (edges).tba (Host Michelle Girvan)

Apr 12
Speaker1: Jim Yorke, UMD
Title: infinite horseshoes - better understand dynamical behavior

Speaker 2:  TBA

Apr 19
Speaker: Philippe Odier, Los Alamos National Lab
Title:  An experimental dynamo in a highly turbulent flow.

Abstract : The dynamo effect is a magnetohydrodynamics instability,
allowing the existence of a self-sustaining magnetic field in a flow of
an electrically conductive fluid. This effect is considered to be at the
origin of the magnetic field of the Earth and the stars. Until now, it
had only been evidenced experimentally in cases where internal
boundaries guide the flow. I will present the first observation of a
dynamo in a homogeneous flow of liquid sodium (VKS2 experiment), where
the turbulent fluctuations are of the same order of magnitude as the
mean flow. The behaviour of this instability close to the threshold will
be described, as well as scaling laws for its saturation. One striking
feature of such a dynamo, that makes it very different from the previous
constrained dynamos, is that it displays a large variety of dynamical
regimes, including chaotic reversals, strongly reminiscent of the
observed reversals of the Earth's magnetic field.
Apr 25
NOTE SPECIAL DAY/TIME (no pizza lunch!)- Wed 2.15pm

Speaker: Gene Tracy, College of William and Mary
Title:  mass spectroscopy for cancer diagnosis

May 3
Speaker: Ryan McAllister, Georgetown University
Title:   3D Imaging in Cells: a Physicist's Gateway into
              Biological Research

Processes in cellular biophysics and biology occur in 3D environments
at a range of time-scales from milliseconds to days. Studying such
processes poses three principal challenges: speed, sensitivity, and
spatial resolution in complex environments. These challenges also
simultaneously provide an entrée for physicists and engineers into
biological research. We describe the development of a high-speed,
high-sensitivity, 3D+time confocal system with the advantages of
relatively modest cost and complexity. We present results from
ongoing investigations into biological processes, including
biopolymer network formation, cytoskeletal dynamics, and
intracellular metabolism, that benefit from this system and that have
faciliated the speaker's transition from working in experimental
physics to collaborative biological and biophysical research.

May 11 - NOTE SPECIAL DAY FRIDAY, regular time 12.15pm
Speaker: Ed Ott, University of Maryland
Title: Nonlinear Dynamics of Novel Sensor Networks

May 17
Speaker1: Bora Sul, Univ of Maryland and NIH
Title:  Models for Fast Adaptation in Outer Hair Cells and its
            Frequency Limit for Amplification

Speaker 2:  TBA

May 23 - NOTE SPECIAL DAY WEDNESDAY, regular time 12.15pm
Speaker: Dan Gauthier, Duke University
Title:   TBA

June 7
Speaker:  Wally Manheimer
Title: TBA

Aug 9

Speaker1:  Viktor Nagy, UMD
Title:  Controlling Rare Intense Events in Spatiotemporally
          Chaotic Systems
Host: Ed Ott

Speaker 2:  Claire Christensen,  Penn State
Title:   Disease Dynamics on a Dynamic Social Network:
              Measles as a Case Study
Host:  Michelle Girvan

February 1
Speaker:  Yair Shokef, Univ of Pennsylvnia
Title: Minimal Modeling of Driven Dissipative Systems

By simple modeling of dissipative interactions we resolve
fundamental questions related to systems far from thermal
equilibrium, such as granular materials, foams and colloidal
 suspensions. We solve the non-Boltzmann energy distribution,
 demonstrate the violation of time-dependent fluctuation-
dissipation relations, show that different measures of effective
temperatures generally differ, and address further issues such
as ergodicity breaking and detailed balance violation.

Host:  Chris Jarzynski

Feb 8
Speaker 1: Arthur LaPorta, UMD
Title:  What makes RNA polymerase go?
Speaker 2: TBA

Feb 15
Speaker 1:  Jonathan Nichols, Naval Research Lab
Title:  TBA
Speaker 2:  TBA

Feb 22
Speaker 1:  Alexandra Landsman, Naval Research Lab
Speaker 2:  Eric Corwin, Univ. of Chicago (tentative)

Mar 1
Speaker:  Silvere Akamatsu, CNRS
Title:  TBA

Mar 8
No Seminar - APS March meeting

Mar 15
Systems Biology Workshop 12.15pm-5pm (tentative)

Mar 22

Mar 29
Speaker1: TBA
Speaker2: TBA

Apr 5
Speaker1: Chris Jarzynski (tentative)
Title:  TBA

Speaker2: TBA

Apr 12
Speaker1: TBA
Speaker2: TBA

Apr 19
Speaker1: TBA
Speaker2: TBA

Apr 26
Speaker1: TBA
Speaker2: TBA

May 3
Speaker1: TBA
Speaker2: TBA

May 10
Speaker1: TBA
Speaker2: TBA