INVITED AND CONTRIBUTED TALKS
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| Title: | How Vertical Flapping Induces Horizontal Flight |
| Name: | Silas Alben |
| Affiliation: | Harvard University, Division of Engineering and Applied Sciences |
| Abstract: | We present a computational study of a
prototype problem in biolocomotion--a 2-D rigid wing is flapped in the
vertical direction and is free to move horizontally. We find that the
flow and body can organize their horizontal motion together to produce
a very stable and robust state of unidirectional motion. The key to our
result is body inertia; with sufficient inertia, depending on body
shape, the body can take advantage of an initial instability to
organize the flow and move into locomotion. |
| Title: | Energy Cascades in Granular Matter Energy dissipation is a distinctive feature of granular matter. |
| Name: | Eli Ben-Naim
|
| Affiliation: | Los Alamos National Laboratory |
| Abstract: | Typically,
in driven granular gases, energy input balances the dissipation and the
system reaches a nonequilibrium steady state. A novel class of steady
states where energy is transferred from large velocity scales to small
velocity scales is reported. These steady-states exist for arbitrary
collision rules and arbitrary spatial dimension. Their signature is a
velocity distribution with an algebraic high-energy tail. The
characteristic exponent is obtained analytically and it varies
continuously with the spatial dimension, the homogeneity index
characterizing the collision rate, and the restitution coefficient.
These stationary states are realized in numerical simulations in which
energy is injected by infrequently boosting particles to high
velocities. It is proposed that these stationary states may be observed experimentally in driven granular systems.
|
| Title: | Biological and artificial swarms |
| Name: | Andrea Bertozzi |
| Affiliation: | UCLA |
| Abstract: | We
consider the problem of collective motion of a group based on local
interaction rules. We present several new continuum models for swarming
in biology that give rise to coherent swarm patches with sharp
boundaries and constant density in the interior. We discuss models
for artificial swarms for performing tasks with multiple robots based
on discrete particle models. Several of these algorithms are
demonstrated on the CalTech multi-vehicle wireless testbed (video
clips). |
| Title: | Dynamics and near-critical behavior of viscous drops in creeping flows |
| Name: | Jerzy Blawzdziewicz |
| Affiliation: | Yale University |
| Abstract: | Macroscopic emulsion properties are strongly influenced by the
deformation and breakup of drops in applied flow. This talk will focus
on the dynamics of an isolated drop under creeping-flow
conditions. The implications of the drop behavior for the rheology of
dilute emulsions will also be examined. We will explore a universal
slow drop evolution near the critical flow strengths for drop breakup,
nontrivial critical exponents characterizing drop behavior in this
regime, and a self-similar evolution of the neck region when a drop
pinches off. Below the critical flow strengths two stationary drop
shapes may exist in flows with a nonzero rotational component, and a
drop may undergo a sudden excitation when the flow direction is
reversed. All these phenomena can be explained in terms of an
interplay between several characteristic time scales, such as the
inverse strain rate, drop relaxation time, and the time scale for drop
rotation. The symmetry of Stokes equations with respect to flow
reversal is also essential. |
| Title: | Drying mediated self assembly |
| Name: | Michael Brenner |
| Affiliation: | Division of Engineering and Applied Sciences, Harvard University |
| Abstract: |
Developing reliable strategies for controlling the assembly of small
objects into functional structures is of great current interest.
I will describe some current experimental efforts in this area, and focus
on a particularly beautiful example of V. Manahoran and D. Pine in which
small spheres assembled into precise configurations through the drying of
interstitial fluid (Science, 301, pg 483). For a given number of spheres,
the structures that formed uniquely corresponded to the sphere packing
that minimized the moment of inertia. I will describe our recent efforts
at understanding these results, focusing on the important role that
geometrical constraints play in determining the final packing. |
| Title: | Noise Robust Chaotic Synchronization |
| Name: | Thomas Carroll |
| Affiliation: | US Naval Research Lab |
| Abstract: | In many cases,
synchronized chaotic systems are very sensitive to added noise, but it
has been shown that some chaotic systems which have motion on 2 time
scales are not sensitive to noise, and synchronization can be
maintained when added noise is larger than the driving signal. In this
work, I use the quasi-steady-state approximation to separate fast and
slow time scales, which allows me to show that for some parameter
values, the slow part of the system acts much like a linear resonant
system. I find this by studying the eigenvalue spectrum of the unstable
periodic orbits of the slow part of the system. Finally, I show that
similar effects are present in a 4 dimensional neuron model. |
| Title: | Information transfer, decision-making and leadership in animal groups |
| Name: | Iain Couzin |
| Affiliation: | Princeton University and University of Oxford |
| Abstract: | For
animals that forage or travel in groups, making movement decisions
often depends on social interactions among group members. However, in
many cases, relatively few individuals have pertinent information, such
as knowledge about the location of a food source, or of a migration
route. Using a simple model we show how information can be transferred
within groups both without signalling and when group members do not
know which individuals, if any, have information. We reveal that the
larger the group the smaller the proportion of informed individuals
needed to guide the group and that only a very small proportion of
informed individuals is required to achieve great accuracy. We also
demonstrate how groups can make consensus decisions, even though
informed individuals do not know whether they are in a majority or
minority, how the quality of their information compares with that of
others, or even whether there are any other informed individuals. Our
model provides new insights into the mechanisms of effective leadership
and decision-making in biological systems. |
| Title: | Collective and stochastic effects in arrays of submicron oscillators |
| Name: | Michael Cross |
| Affiliation: | California Institute of Technology |
| Abstract: | Lithographically
prepared arrays of submicron oscillators combine collective behavior
and stochastic effects (thermal and ultimately quantum) in a
non-equilibrium, driven, dissipative system that is accessible
experimentally and important technologically. In this talk I will
describe our recent work in this area, which includes the study of
pattern formation in parametrically driven arrays, synchronization, and
activation between driven states. *Work done in collaboration with Y.
Bromberg, O. Kogan, R. Lifshitz, J. L. Rogers, and A.Zumdieck. |
| Title: | Impact craters in loose granular media |
| Name: | Douglas Durian |
| Affiliation: | UCLA Physics |
| Abstract: | We
report data for how the penetration of a projectile into a granular
medium scales with characteristics of the projectile and the medium.
Curiously, it is not a simple function of either the kinetic energy or
momentum of hte projectile at impact. We hope to report, too, on the
time dependence of the impact. |
| Title: | 2D turbulence: Experiments, cascades, and mechanisms |
| Name: | Robert Ecke |
| Affiliation: | Los Alamos National Lab |
| Abstract: | Two dimensional
turbulence is a fascinating problem that has features of turbulence in
atmospheres and oceans and that has some unique properties owing to its
reduced dimensionality. One such property is the dual cascades where
mean-squared vorticity is transferred to smaller scales while energy
cascades cascades towards larger scales. We study these turbulent
cascades using two physical systems: soap films and stratified layers.
n addition to traditional tools of statistical turbulence
characterization such as spectra and structure functions, we use a
filter approach to directly determine the flux of inertial quantities
in the turbulent range of scales. This method provides a way to
quantitatively understand the mechanisms of fluid turbulence and how
they are related to physical features of the flow. Results are shown
for ensemble-averaged Eulerian measurements and for fully Lagrangian
dynamical measurements. |
| Title: | Dynamical Analysis of Spatiotemporal Chaos in Physics and Biology |
| Name: | David Egolf |
| Affiliation: | Georgetown University |
| Abstract: |
|
| Title: | Large Scale Circulation in Rayleigh-Benard convection cells |
| Name: | Denis Funfschilling |
| Affiliation: | University of California, Santa Brabara |
| Abstract: | A Rayleigh-Benard
convection (RBC) cell consists of a hot bottom plate, a cold top plate,
and sidewalls. RBC is a closed, extremely well controlled system driven
by the temperature difference. It is an excellent system for the study
of the physical mechanism of heat transfer by natural convection. We
present new results about the Large-Scale Circulation (LSC) for
Rayleigh numbers > 4x10^7. The shadowgraph method was used to
visualize the hot and cold plumes ejected from the hot and cold
boundary layers respectively. Plumes follow the LSC. We observed that
the direction of travel of the plumes oscillates in time. The frequency
of these oscillations is proportional to the inverse turn-over time of
the LSC that had been measured previously by several groups. The
influence of the geometry of the cell and of the fluid properties (i.e.
the Prandtl number) are investigated. |
| Title: | Evolution of the glycolytic phenotype during carcinogenesis and its role in formation of invasive ca |
| Name: | Robert Gatenby |
| Affiliation: | University of Arizona |
| Abstract: | Carcinogenesis
is a multistep process in which progressively more malignant cellular
populations emerge over time coincident with accumulating genetic
mutations. This is often described as somatic evolution but the
dynamical interactions of genetic and epigenetic events in the evolving
cellular populations with changing microenvironmental selection forces
remain poorly understood. We apply mathematical models from
evolutionary game theory to define the cellular and extracellular
dynamics that govern somatic evolution of malignant phenotypes. We
demonstrate that common components of the cancer phenotype result from
active selection and must, therefore, confer a significant growth
advantage. We focus on a well-known and near-universal property of
primary and metastatic cancers - constitutive upregulation of aerobic
glycolysis. This component of the malignant phenotype was first
demonstrated by Warburg over 80 years ago. More recently, clinical
tumor imaging using FdG PET has demonstrated that nearly all human
cancers exhibit increased levels of aerobic glycolysis. By applying
evolutionary game theory and diffusion-reaction models, we demonstrate
persistent metabolism of glucose to lactic acid even in aerobic
conditions is an adaptation to intermittent hypoxia in premalignant
lesions. However, upregulation of glycolysis leads to
microenvironmental acidosis requiring further evolution to phenotypes
resistant to acid-induced cell toxicity. A cell population that emerges
from this evolutionary sequence has a powerful growth advantage
because, through upregulated glycolysis even in the presence of oxygen,
it produces an acidic microenvironment which is harmless to itself but
toxic to competing populations. We propose this promotes unconstrained
proliferation and invasion and is a critical evolutionary step in
formation of clinical human cancers. |
| Title: | Complex Networks: From Empirical Measurements to Mathematical Models |
| Name: | Michelle Girvan |
| Affiliation: | Santa Fe Institute |
| Abstract: | Many social,
biological, and technological systems take the form of complex
networks. Examples include friendship and collaboration networks,
neural networks, food webs, power grids, and the Internet. Recent
empirical evidence suggests that these networks share a number of
statistical features in common. I will focus particularly on the
appearance of mixing patterns, degree-correlations, and community
structure in these complex networks. I will also discuss how these
features can be incorporated into mathematical models which can lead to
new insights about the behavior of real-world networks. In particular,
I will focus on models of disease spread and information cascades. |
| Title: | Dynamics in Genetic Networks |
| Name: | Leon Glass |
| Affiliation: | McGill University |
| Abstract: | Genetic activity is partially regulated by a complicated network of
proteins called transcription factors. I will describe a mathematical
framework that can be used to relate the structure and dynamics of
these genetic networks. The networks are represented by differential
equations with switchlike nonlinearities. These equations are
represented schematically using a directed graph on an
hypercube. There are many advantages to these equations. Because of
the discrete representation of the continuous dynamics, the numbers of
different networks with N model genes can be counted and
classified. The methods are helpful in identifying networks that have
certain types of dynamic behaviors such as stable fixed points, stable
cycles, and chaotic dynamics. These methods can be used to help
design in vitro genetic networks that show oscillation and
multistability. They can also be used to determine gene network
structure based on the patterns of activation of genes (1). Finally, the
framework offers novel ways to study the evolution of rhythmic
patterns in model equations and also in electronic circuits that
simulate the differential equations (2).
(1) T. J. Perkins, M. T. Hallett, L. Glass. Inferring models
of gene expression dynamics. Journal of Theoretical
Biology. In Press, 2004.
(2) J. P. Mason, P. S. Linsay, J. J. Collins, L. Glass. Evolving
complex dynamics in electronic models of genetic networks.
Chaos, In Press, 2004. |
| Title: | Dynamics of a liquid drop in a flowing immiscible fluid |
| Name: | Stefano Guido |
| Affiliation: | Dynamics of a liquid drop in a flowing immiscible fluid |
| Abstract: | Liquid-liquid
systems, such as emulsions or polymer blends, are encountered in a
variety of applications, including, e.g., plastics technology, food
processing and cosmetics design. The morphology of such systems, which
plays a key role in determining product properties, is strongly
affected by the flow conditions experienced during processing. Some
insight into this complex problem can be gained by looking at the
idealized, but basic situation of a single drop in a well-controlled
flow field. Here, experimental results on the dynamics of a single drop
in an immiscible fluid, sheared in a parallel plate apparatus, are
presented. Drop deformation and break-up data both under steady and
transient flow conditions will be compared to theories and numerical
simulations from the literature. The effects of non-Newtonian fluid
components and of drop-drop interactions will be also considered.
|
| Title: | Iterated Conformal Maps: From DLA to DBM and SLE |
| Name: | Matthew Hastings |
| Affiliation: | Center for Nonlinear Studies and Theoretical Division, Los Alamos National Lab |
| Abstract: | Conformal mappings are extremely useful in solving problems with Laplace's
equation in two dimensions; however, to find the needed conformal mapping which
maps a simple shape, such as a circle, onto the boundary of a complicated
fractal object is a very difficult problem. By iterating elementary mappings,
this problem was solved for the problem of diffusion-limited aggregation (DLA)
in 1997. Since then, this technique has been extended to the
dielectric breakdown model (DBM), where it offers vastly improved simulation
speed compared to traditional techniques, and has lead to the possibity of
analytically understanding the branching process in this fractal growth problem.
An additional slight modification of the model leads to a discretization of
the stochastic Loewner equation (SLE), a model leading to powerful rigorous
results on two-dimensional critical problems. Finally, the technique of
iterated conformal mappings has been used to describe other problems such
as cracking. I will present some of these developments, and discuss the
possibility of further progress. |
| Title: | Combinatorial Control and Gain in Gene Regulation |
| Name: | Terence Hwa |
| Affiliation: | UC San Diego, Physics Department
|
| Abstract: |
|
| Title: | Ultra-low-level light-by-light switching using a collective instability |
| Name: | Lucas Illing |
| Affiliation: | Duke University |
| Abstract: | We demonstrate
light-by-light switching in a dissipative spatio-temporal system. The
experiment utilizes a collective instability that occurs through a
nonlinear interaction of two counterpropagating laser-beams with a
rubidium vapor. The stationary spatial pattern formed by the
instability-generated light is extremely sensitive to perturbation and
can thus be modified using a much weaker switching beam. In principle,
a single-photon switch can be realized using this novel approach, which
paves the way for quantum information networks and for improving
all-optical telecommunication networks. |
| Title: | Dynamics of Deformation in Glassy Materials (invited talk) |
| Name: | James Langer |
| Affiliation: | University of California, Santa Barbara |
| Abstract: |
|
| Title: | Sodium Experiments as Dynamical Models of the Earth's Outer Core |
| Name: | Daniel Lathrop |
| Affiliation: | University of Maryland |
| Abstract: |
|
| Title: | Waveform diversity and synchronization of semiconductor laser dynamics |
| Name: | Jia-ming Liu |
| Affiliation: | UCLA |
| Abstract: | In
this talk, the diversity of waveforms that can be generated from
nonlinear dynamics of semiconductor lasers under different
configurations will be discussed. Both unidirectional and bidirectional
synchronization of coupled semiconductor lasers will be addressed.
Besides the physics, some of the interesting applications using the
nonlinear dynamics of semiconductor lasers will be explored. |
| Title: | Impact: Void collapse and jet formation |
| Name: | Detlef Lohse |
| Affiliation: | University of Twente |
| Abstract: |
|
| Title: | Cell Motility: Dynamic Networks and Flexible Membranes |
| Name: | Wolfgang Losert |
| Affiliation: | University of Maryland |
| Abstract: | Motion
of cells in response to external signals is cruical for many biological
processes, from wound healing to the spread of cancer. I will discuss
two of the physical processes that can generate the forces needed for
cell motion: Dynamic changes in the scaffolding of filaments (actin,
tubulin, and intermediate filaments) that give a cell mechanical
strength, and deformations of cell membranes. I will introduce a toy
model of dynamic self-assembling filaments that recovers the key
properties of e.g. tubulin self assembly. Experimentally we use two
photon confocal microscopy for 3D imaging and a holographic laser
tweezer for multipoint mechanical measurements of both filament
networks and membranes. Recent experiments indicate that spatial
gradients in network properties can generate strong directional forces
on objects embedded in the network.
|
| Title: | TBN |
| Name: | John Lowengrub
|
| Affiliation: | University of California, Irvine
|
| Abstract: |
|
| Title: | A Dynamical Model of Molecular Monolayers: Why Tethers Don't Snap |
| Name: | Elizabeth Mann |
| Affiliation: | Department of Physics, Kent State University |
| Abstract: | A bola-shaped domain in a Langmuir monolayer at the air/water interface
relaxes towards a circular shape under the influence of line tension.
The tether thickens continuously in this process, in marked contrast to
the Hele-Shaw and the three-dimensional cases, where hydrodynamic
instabilities lead to the tether snapping. A simplified dynamical model
allows us use lubrication theory to explain this without incorporating
repulsive forces to stabilize the tether in 2D. The model also allows
us to give a better estimate of line tensions from the relaxation rate
of such monolayer domains. This material is based upon work supported
by the National Science Foundation under Grant No.9984304. |
| Title: | Generalized Drive-Response Synchronization in a Two-Mode Laser System |
| Name: | Linda Moniz |
| Affiliation: | Naval Research Laboratory |
| Abstract: | Uchida, McAllister, Meucci and Roy indirectly showed drive-response
generalized synchronization in a two-mode laser with "hidden" degrees
of freedom within a certain parameter regime (2003). However, there was
no direct evidence of drive-response synchronization; the method used a
measure of response-response synchronization . Here we show, using the
Continuity test on data from the same experiment, direct evidence of
generalized synchronization between drive and response in the same
parameter regime. We also test for local clustering of this generalized
synchronization on the embedded attractor. Finally, we show that
although the system displays generalized (drive-response)
synchronization, it does not exhibit differentiable drive-response
synchronization in the sense of Hunt, Ott and Yorke's 1997
characterization. |
| Title: | Measuring and modeling the growth of a plant shoot apical meristem |
| Name: | Eric Mjolsness |
| Affiliation: | Institute for Genomics and Bioinformatics, UC Irvine |
| Abstract: | We present preliminary results on measuring and modeling the growing
tip (shoot apical meristem) of the plant Arabidopsis thaliana, and
constructing mathematical models at different spatial scales for the
mechanical and regulatory networks that interact in this living pattern
formation system. |
| Title: | Rayleig-Benard convection with modulated acceleration |
| Name: | Werner Pesch |
| Affiliation: | University of Bayreuth, Theoretical Physics |
| Abstract: | \documentstyle[12pt]{article}
\begin{document}
\begin{center}
{\Large \bf
Rayleigh-B\'{e}nard
convection with modulated acceleration} \\[.5cm]
\end{center}
\begin{center}
{\large
{Werner Pesch $ ^{+} $ } \\[.3cm]
University of Bayreuth, 95440 Bayreuth,
Germany}\\
\end{center}
\noindent
The Rayleigh-B\'enard convection instability (RBC) of a horizontal fluid
layer driven by a temperature gradient, is one of the best studied paradigms
of pattern formation in nonequilibrium systems.
Time periodic modulation (amplitude $\delta$, frequency $\omega$) of the acceleration (gravity force)
by shaking the standard convection cell provides an interesting model system
to study parametrically driven instabilities in continuous systems. The underlying Boussinesq equations a
re well founded
and allow a rigorous theoretical analysis of various competing pattern forming mechanism.
\noindent
The case of vertical shaking compares very well with recent experiments. $[1]$
A rich variety of patterns is observed, for instance "superlattices" of stars on a square backbone. They
exist near a
codimension-2 point, where a harmonic response of the system switches to a
subharmonic one, and
are organized by a new
four-mode resonance mechanism.
\noindent
The case of vertical shaking is more involved since already the basic state is
associated with a time-periodic shear flow. Depending on the modulation parameters ($\delta, \omega$),
pattern formation is then organized by the competition of buoyancy-driven and
shear-flow instabilities, which leads again to complex pattern formation scenarios. \\[0.1cm]
[1] See e.g. J. L. Rogers, M. F. Schatz, and W. Pesch, {\it Nonlinearity} {\bf 16}, C1 (2003)\\[0.1cm]
\noindent
{\bf $ ^{+}$ In collaboration with:}\\ {\it J.L. Rogers $^*$, M.F. Schatz},
Center for Nonlinear Science, School of Physics, Georgia Tech
({\small $^*$ currently at HRL Laboratories, LLC)}\\
{\it O. Brausch, D. Palanappian}, University of Bayreuth\\
|
| Title: | Synchronization of Mutually Coupled Fiber Ring Lasers; A Time -Delayed System |
| Name: | Elizabeth Rogers |
| Affiliation: | University of Maryland |
| Abstract: | Mutually coupled
chaotic systems provide a means with which to study how things
synchronize. In a mutually coupled system, one may not find a clear
leader or laggard, as one does in unidirectionally coupled systems.
Bidirectional coupling allows chaotic systems to be driven into states
where neither may have been operating before. Erbium-doped fiber ring
lasers (EDFRLs) exhibit complicated chaotic behavior when coupled
together. The large number of modes and individual fiber
characteristics make this system very difficult to synchronize using
unidirectional coupling. However, synchronization is much more easily
obtained when they are mutually coupled. The optical frequency dynamics
and synchronization threshold were characterized for this system.
Synchronization was studied as a function of coupling strength and time
delays, both short and long compared to the round trip times within the
fiber ring. These EDFRLs provide a means for studying leader/laggard
roles in mutually coupled chaotic time-delayed systems. |
| Title: | Integrate and fire dynamics in bubble formation |
| Name: | Jose Carlos Sartorelli |
| Affiliation: | Instituto de Fsica, Universidade de So Paulo |
| Abstract: | The development of the
studies of bubble formation controlled by an external signal is found
in some areas of physics and chemical engineering. One direct
application of the effects of sound wave in bubble formation is to
change the bubble shape in order to improve the heat or mass transfer
between the two phases. We can use the periodic sound wave to tame the
chaotic bubbling, or in order to obtain complete routes to chaos in a
bubble column. We explain the sequence of bubbles from a nozzle in a
bubble column as an integrate-and-fire dynamics, in which there is
storage of the energy represented by the forming bubble, followed by a
discharge of this energy represented by the release of this bubble when
a threshold is reached. This threshold can be understood using our
phenomenological model based on the force balance acting on the bubble,
in which when a gas is flowing through a submerged nozzle, the surface
tension between the two phases acts in order to prevent the gas
encroachment inside the liquid, forming an attached bubble. As the
bubble grows, the buoyancy and inertial forces overcome the surface
tension, and the bubble detaches from the nozzle. We use the sound wave
to change this threshold is applying a sound wave at the top of the
bubble column. The simplifications in reducing the actual physical
system to an integrate-and-fire dynamics allows to us to investigate
more deeply the main features of this system and to compare with the
experimental results. |
| Title: | Conical Nanotube Ion-Current Rectifiers and protein sensors. Abiotic analogues of voltage-gated chan |
| Name: | Zuzanna Siwy |
| Affiliation: | University of Florida |
| Abstract: | We have studied
transport properties of single tapered cone pores in polymer membranes.
The small opening of the conical pores is as small as several
nanometers while the big opening is of micrometer range. The nanopores
are cation selective and function as an ionic current rectifier with
the preferential direction of cation flow from the narrow entrance
towards the big opening of the pore. We will show how to tailor the
degree and direction of rectification by appropriate surface
modification. We will also present preparation of abiotic voltage-gated
channels, which exhibit voltage-dependent discrete conductivity levels.
Gating properties of nanopores have been used to construct a biosensor
targeted at detection of proteins. The sensor is also capable to study
binding affinities between proteins. Functioning of the sensor will be
shown on the example of protein G/IgGs system. |
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