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
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Speaker1: Jim Yorke, UMD
Title: infinite horseshoes - better understand dynamical behavior
Speaker 2: TBA
Apr 19
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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.
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Apr 25
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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
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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
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Speaker: Ed Ott, University of Maryland
Title: Nonlinear Dynamics of Novel Sensor Networks
May 17
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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
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Speaker: Dan Gauthier, Duke University
Title: TBA
June 7
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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
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February 1
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Speaker: Yair Shokef, Univ of Pennsylvnia
Title: Minimal Modeling of Driven Dissipative Systems
Abstract:
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
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Feb 8
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Speaker 1: Arthur LaPorta, UMD
Title: What makes RNA polymerase go?
Speaker 2: TBA
Feb 15
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Speaker 1: Jonathan Nichols, Naval Research Lab
Title: TBA
Speaker 2: TBA
Feb 22
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Speaker 1: Alexandra Landsman, Naval Research Lab
Speaker 2: Eric Corwin, Univ. of Chicago (tentative)
Mar 1
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Speaker: Silvere Akamatsu, CNRS
Title: TBA
Mar 8
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No Seminar - APS March meeting
Mar 15
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Systems Biology Workshop 12.15pm-5pm (tentative)
Mar 22
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SPRING BREAK
Mar 29
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Speaker1: TBA
Speaker2: TBA
Apr 5
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Speaker1: Chris Jarzynski (tentative)
Title: TBA
Speaker2: TBA
Apr 12
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Speaker1: TBA
Speaker2: TBA
Apr 19
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Speaker1: TBA
Speaker2: TBA
Apr 26
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Speaker1: TBA
Speaker2: TBA
May 3
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Speaker1: TBA
Speaker2: TBA
May 10
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Speaker1: TBA
Speaker2: TBA