
Physics/Fields Colloquium 20092010
Organizing Committee: Stephen Morris (Dept. of Physics,
University of Toronto) & Mary Pugh (Toronto)
The goal of the Physics/Fields Colloquium is to feature scientists
whose work is of interest to both the physics and the mathematical
science community. The series has been running since the Spring
of 2007.
Usually there is one speaker per semester. Each speaker gives a
primary, general talk in the regular physics colloquium venue and,
whenever possible, a second, more specialised talk at the Fields
Institute.
Previous speakers have been Phil Holmes (March 2007), Jun Zhang
(October 2007), Andrea Liu (Nov 2008), and Ehud Meron (March 2009).
200910
Schedule

Wednesday,
March 24
3:10 pm
Fields Institute,
Stewart Library 
Jane Wang,
Cornell University
Computing Insect Flight and Falling Paper
Our interest in computing the NavierStokes equations coupled
to moving boundaries is directed toward understanding the
unsteady aerodynamics of insect flight and fluttering and
tumbling objects. While many interesting fluid phenomena originate
near a moving sharp interface, computational schemes typically
encounter great difficulty in resolving them. We have been
designing efficient computational codes that are aimed at
resolving the moving sharp interfaces in flows at Reynolds
number relevant to insect flight. The first set of codes are
NavierStokes solvers for simulating a 2D rigid flapping wing,
which are based on highorder schemes in vorticitystream
function formulation. In these solvers we take advantage of
coordinate transformations and 2D conformal mapping to resolve
the sharp wing tips so as to avoid gridregeneration. These
methods were used to elucidate the unsteady aerodynamics of
forward and hovering flight. They were also used to examine
the aerodynamics of the fluttering and tumbling of plates
falling through fluids.
To go beyond 2D simulations of rigid objects, we recently
developed a more general purpose code for simulating 3D flexible
wing flight, based on immersed interface method. The main
improvement is to obtain the 2nd order accuracy along the
sharp moving surface. To avoid introducing adhoc boundary
conditions at the moving interface, we employ a systematic
method to derive from the 3D NavierStokes equation the jump
conditions on the fluid variables caused by the singular force.
In addition, the temporal jump conditions must be included
in order to have a correct scheme. To handle the spatial and
temporal jump conditions in the finite difference scheme,
we derive generalized Taylor expansions for functions with
discontinuities of arbitrary order. The code has been applied
to simulate 3D flows around a dragonfly wing.

Thursday
, March 25
4:10pm
Location
MP 102 
Jane Wang,
Cornell University
How Insects Fly and Turn.
Insects' aerial acrobatics result from the concerted efforts
of their brains, flight muscles, and flapping wings. To understand
insect flight, we started from the outer scale, analyzing
the unsteady aerodynamics of flapping flight, and are gradually
working toward the inner scale, deducing control algorithms.
In this approach, the physics of flight informs us about the
internal control scheme for a specific behavior.
I will first describe the aerodynamic tricks that dragonflies
employ to hover and fly efficiently. I will then describe
how fruit flies recover from aerial stumbles, and how they
make subtle wing movements to induce sharp turns in tens of
wing beats, or 4080ms.

Previous Seminars

Wednesday
December 2
3:10pm,
Location:
Fields Institute

Carson
Chow, National Institutes of Health
Kinetic theory of coupled oscillators
Coupled oscillators arise in contexts as diverse as the brain,
synchronized flashing of fireflies, coupled Josephson junctions,
or unstable modes of the Millennium bridge in London. Generally,
such systems are only analysed for a small number of oscillators
or in the infinite oscillator, meanfield limit. The dynamics
of a large but finite network of coupled oscillators are largely
unknown. Here, I will show how concepts from the kinetic theory
of gases and plasmas can be applied to a system of coupled
oscillators to infer the large scale collective behavior from
the small scale dynamics. Calculations are facilitated by
perturbative methods developed for quantum field theory.

Thursday
December 3
4:10pm
Location
MP 102

Carson
Chow, National Institutes of Health
The physics of obesity
The past few decades have seen a surge in the incidence of
obesity in the developed world. Changes in body weight that
can lead to obesity are known to result from imbalances between
the energy derived from food
and the energy expended to maintain life and perform physical
work. However, measuring and quantifying this relationship
has proved to be difficult. Here, I will show how simple ideas
from thermodynamics and nonlinear dynamics can be used to
provide a general theoretical description of how body weight
will change over time. The theory can then be used to answer
open questions (and dispel some myths) regarding weight loss
and gain.

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