Department of Physics and Astronomy Colloquia
Fall 2003
(1997/98,
1998/99,
1999/00,
2000/01,
2001/02,
2002/03)
Fall Colloquia are Wednesdays 4:00pm in David Rittenhouse
Laboratory (209 South 33d Street), in room A4, unless otherwise noted. Spring Colloquia are in
room A8 unless otherwise noted. Colloquia are preceded by a department tea at
3:30 in room 2E17.
September 10:
Tom Duke
Cambridge University
The Ising model as a paradigm for ultra-sensitive signal transduction
in living cells
Many of the sensory systems found in living organisms share a common
property: they can respond with exquisite sensitivity to minute changes in a
stimulus, and can do so over a vast range of ambient stimulus levels. How is
this remarkable performance achieved? Might very different systems operate
according to similar basic principles? I propose that they do. Sensory
systems employ adaptation and feedback mechanisms to poise themselves at a
critical point, where they are particularly susceptible to perturbation, and
consequently respond with heightened sensitivity. To illustrate this
concept, I will present an Ising model of the chemical signaling network
which permits bacteria to sense and react to their environment.
Host: Nelson
Tuesday, October 21
Fabiola Gianotti
CERN, Geneva
Physics at the Large Hadron Collider
I will discuss the motivations for building the CERN Large Hadron
Collider (LHC), a proton-proton accelerator of unprecedented
energy. I will also report about the construction status of the machine
and the experiments. Finally, I will present the huge physics potential
of the LHC and the possible impact on our understanding of
fundamental physics.
Host: Williams
November 12:
Boris Kayser
Fermi National Accelerator Laboratory
Title The Neutrino World: Present and Future
Neutrinos are among the most abundant particles in the universe. In the
past few years, we have found compelling evidence that the neutrinos made
in the earth's atmosphere by cosmic rays, and those made in the sun, can
morph from one "flavor" to another. This flavor change implies that
neutrinos have nonzero masses, and opens a whole new world for us to
explore. In this talk, we will explain what has been learned about the
neutrinos so far, identify some of the major open questions, and discuss
future experiments that can help us to answer them. (For background
see this
article.)
Host: Kroll
December 10:
Sara Seager
Carnegie Institution of Washington
Characterizing Extrasolar Planets
We have entered a new era in
planetary astrophysics with over 100
giant planets recently
discovered to orbit nearby sun-like
stars. Recent advances in
astronomical observations, theory, and
instrumentation have given us
new constraints on the formation and
evolution of planetary systems
as well as on the characteristics of
extrasolar planets. I will
discuss what is known about extrasolar
giant planets and the
potential to detect and study Earth-like planets
for signatures of
habitable conditions.
Host: Jain
Room change: Spring Colloquia are Wednesdays 4:00pm in David
Rittenhouse Laboratory, room A8, unless otherwise posted.
Friday, January 16 at 2:00pm
Bhuvnesh Jain
University of Pennsylvania
Gravitational Lensing and Cosmology
Gravitational lensing refers to the distortions
of the images of
distant
galaxies due to the bending of light by massive structures
along the line
of sight. I will first show how lensing has been used
to measure
the dark matter content of galaxy halos and
(statistically) of large scale
cosmological structures, and then move
on to describe "lensing tomography".
Lensing tomography is a way of
extracting information
on the evolution of clustering in the
universe. I will outline the prospects
for using this technique to
measure the equation of state of the dark
energy with future lensing
surveys.
Tuesday, February 3 in DRL room A4
Cumrun Vafa
Harvard University
Quantum Calabi-Yau Manifolds as Classical Melting Crystals
Host: Ovrut
February 11:
Neil Gehrels
NASA/Goddard Space Flight Center/University of Maryland
Gamma Ray Burst Discoveries and the Upcoming Swift Mission
Gamma-ray bursts (GRBs) are now known to be cosmological in origin
and produced by tremendous explosions. Although the physics of the
event is not fully understood, it is thought that the only viable
mechanism to release the necessary energy is the
stellar collapse
to a black hole. A new NASA mission to study GRBs
is in the final
stages of testing for launch in September 2004. It
is called SWIFT
and has the optimum instrument complement for burst
observations.
The talk will highlight recent discoveries in GRB
astronomy and
discuss the growing excitement leading up to the Swift
launch.
Host: Jain
March 3:
Tom Lubensky
University of Pennsylvania
On the occasion of his winning the Buckley Prize:
Liquid Crystals: What They are and Why You Should Know about Them
April 14:
The 21st annual Henry Primakoff Lecture:
Harry L. Swinney
University of Texas at Austin
Emergence of Spatial Patterns in Nonequilibrium Systems
We consider macroscopic systems driven away from thermodynamic
equilibrium by an imposed gradient in temperature, velocity, or
concentration. For a sufficiently small imposed gradient, the system
will exist in a base state, which has the symmetry of the boundary
conditions. However, when the imposed gradient is increased, a
critical value is reached at which the base state becomes unstable --
the system spontaneously breaks the symmetry of the boundary
conditions and forms an ordered spatial pattern. With larger imposed
gradients, the patterns can become chaotic or turbulent, but often
some order persists. The general principles of pattern formation in
systems driven away from equilibrium will be discussed and illustrated
with examples from physics, chemistry, and biology.
Host: Nelson