Colloquia
Department of Physics Colloquia Schedule
SPRING
2005
>
> FALL 2005
Thursday, February 3, 2005
DANIEL
KLEPPNER, Lester Wolfe Professor of Physics, Emeritus; Director,
MIT-Harvard Center for Ultracold Atoms
MIT
"Boost-Phase Intercept and the National Missile
Defense"
The United States is deploying an untested missile
defense system based on intercepting intercontinental-range ballistic
missiles in mid-flight. An alternative approach is also being
pursued in which missiles are intercepted in their boost phase
while their rocket engines are still burning, before they could
deploy multiple warheads or decoys. The American Physical Society
has carried out a study of such a boost-phase intercept system.
I will describe the technical issues involved in the proposed
system and go on to provide some personal observations on missile
defense.
Time: 4:15 pm
Place: Room 10-250 / MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room)
Thursday, February 10, 2005
VICTORIA
M. KASPI, Associate Professor of Physics
McGill University
"Magnetars"
The nature of an unusual class of cosmic X-ray source,
dubbed "Anomalous X-ray Pulsars," was a mystery since
1982 when the first example was discovered. In this talk, I will
show the recent observational evidence that unambiguously links
them with another equally exotic class of object, the explosive
"Soft Gamma Repeaters." The evidence to date strongly
supports the picture that both are "magnetars"—
isolated young neutron stars having surface magnetic fields ~1000
times greater than those in conventional neutron stars.
Time: 4:15 pm
Place: Room 10-250 / MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room).
Thursday, February 17, 2005
ANDREA J. LIU, Professor, Department of Physics
& Astronomy
University of Pennsylvania
"Jamming"
Many different systems jam. Even before breakfast,
coffee grounds and cereal jam as they refuse to flow into our
coffee filters or bowls. We have proposed that these examples
belong to a broader class of jamming transitions, where systems
can develop extremely long stress relaxation times in disordered
states as temperature is lowered, an applied shear stress is lowered,
or particle density is raised. We suggested that the state of
the system might be represented by a “jamming phase diagram”
as a function of temperature, shear stress and density. However,
such a diagram is unconventional because the glass transition
and other jamming transitions are not sharp; for example, the
glass transition temperature depends on how long one is willing
to wait in order to measure the stress relaxation time. We have
shown that at zero temperature and shear stress, the onset of
jamming is sharp with increasing particle density—it does
not depend on the measurement time. This point may control jamming
transitions at nonzero temperatures and shear stresses—including
the glass transition—and it has special properties: It is
a mixed first-order/second-order transition with a discontinuity
in the order parameter and a diverging length scale.
Time: 4:15 pm
Place: Room 10-250 / MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room).
Thursday, February 24, 2005
DAVID
E. PRITCHARD, Cecil & Ida Green Professor of Physics;
Associate Director, Research Laboratory of Electronics
MIT
We have developed a single ion balance that has
improved atomic and molecular mass measurement accuracy to ~10–11.
It compares the cyclotron frequency of two individual molecular
or atomic ions trapped in a uniform magnetic field to find the
mass ratio. Besides improving the mass of fundamental particles,
this has led to a correction to the cyclotron resonance formula,
a new route to determining the fine structure constant using simple
physics, the best measurement of the dipole moment of any charged
molecule, recalibration of the X-ray wavelength standard, a possible
route to replace the artifact kilogram with an atomic mass standard,
and a precise test of E=mc2.
Time: 4:15 pm
Place: Room 10-250
/ MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room).
Thursday, March 3, 2005
MARTIN
BAZANT, Associate Professor of Applied Mathematics
MIT
"Dynamics of Random Packings in Granular Flow"
The geometry of static sphere packings is an age-old
problem, but how do random packings flow? This question is at
the heart of condensed matter physics for liquids, glasses, and
granular materials, and yet it remains poorly understood at the
microscopic level. Here, we consider the case of granular drainage
(e.g. sand in an hourglass) and test the hypothesis that particles
rearrange cooperatively, in response to diffusing "spots''
of free volume. We find that spot-based simulations with only
five fitting parameters can accurately reproduce packing dynamics
in discrete-element simulations with 200,000 spherical, frictional,
visco-elastic grains. The spot simulations run over 100 times
faster and demonstrate the possibility of multiscale modeling
for amorphous materials.
Time: 4:15 pm
Place: Room 10-250 / MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room).
Thursday, March 10, 2005
HARRIS LECTURE
PETER GOLDREICH
The Institute of Advanced Study
"Progress and Problems in Understanding Planet
Formation"
I shall briefly review modern scenarios for planet
formation. The growth of the smallest gravitationally active bodies,
planetesimals, is mired in controversy. Orderly growth by the
merging of planetesimals is followed by runaway accretion in which
a small fraction of the bodies grow much larger than all the others.
When these big bodies are sparse enough, runaway growth gives
way to oligarchic growth during which the big bodies grow in lockstep,
maintaining similar masses and uniformly spaced orbits. As oligarchs
grow, their orbital spacing increases and their number decreases.
My focus will be on how oligarchy ends and what
happens after it does. I will address three major questions regarding
solar system planets:
1. What determined their number?
2. Why are their orbits nearly circular and coplanar?
3. How long did they take to form?
Answers to these questions will be given in terms
of stability against large scale chaos; dynamical friction by
small bodies; the accretion rate at the geometrical cross section
in the inner planet region, and the ejection rate at the gravitationally
enhanced cross section in the outer planet region.
Time: 4:15 pm
Place: Room 10-250 / MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room).
Thursday, March 17, 2005
DEBORAH
S. JIN, Fellow of JILA; Associate Professor Adjoint, Department
of Physics
JILA, University of Colorado, Boulder
Title TBA
Abstract forthcoming.
Time: 4:15 pm
Place: Room 10-250 / MIT
Refreshments @ 3:45 pm in
4-339 (Physics Common Room).
Thursday, March 31, 2005
WENDY
L. FREEDMAN, Director
The Observatories of the Carnegie Institution of Washington
"Measuring Cosmological Parameters"
Recent measurements have led to a concordance model
in cosmology, characterized by a geometrically flat and accelerating
universe, a current expansion rate (Hubble constant) of 72 kilometers/second/Megaparsec,
one third of the matter-energy density in matter, and the remaining
two thirds attributed to a dark energy component. I will discuss
the evidence for this current model, summarize the status of measurements
on the Hubble constant, and describe recent experiments to measure
the acceleration of the universe using Type Ia supernovae, including
the new Carnegie Supernova Project.
Time: 4:15 pm
Place: Room 10-250 / MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room).
Thursday, April 7, 2005
DAN
RUGAR
IBM Almaden Research Center
"Single Spin Detection by Magnetic Resonance
Force Microscopy"
Is it possible to build a microscope that can look
below surfaces and image molecules and materials with atomic resolution
in three dimensions? Such a microscope would revolutionize structural
molecular biology and be an important tool for nanoscale science
and technology. Magnetic resonance force microscopy (MRFM) is
an attempt to address this "holy grail" of microscopy.
In this talk, we describe the basic principles of
MRFM and discuss recent results that demonstrate the detection
of an individual electron spin buried within a silica sample.
We review various innovations that set the stage for single spin
detection, including ultrasensitive force detection and novel
spin manipulation techniques. We also discuss using MRFM for real-time
control of spin fluctuations. Finally, we consider some of the
challenges remaining before 3D atomic imaging and real-time quantum
state readout can be realized.
Time: 4:15 pm
Place: Room 10-250 / MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room).
Thursday, April 14, 2005
YOUNG
S. LEE, Assistant Professor of Physics
MIT
"The Physics of Frustration in Quantum Magnets"
In this talk, I will discuss our quest for the "holy
grail" of spin frustration here at MIT. One of the central
issues in condensed matter physics involves understanding the
exotic phases which emerge from collections of interacting electrons.
New states of matter may be produced if quantum effects and frustration
conspire to prevent the ground state from achieving classical
order. After discussing the history of this problem and the motivation
for our work, I will describe our recent experimental progress.
In particular, I will explain some new physics we have learned
from neutron scattering measurements on a spin-frustrated material
based on the two-dimensional Kagome lattice. Our observations
reveal the presence of spin-textures related to chirality and
the existence of an unusual spin-wave mode with zero velocity.
Time: 4:15 pm
Place: Room 10-250 / MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room).
Thursday,
April 21, 2005
The Bruno Rossi
Lecture in Astrophysics*
JAMES
W. CRONIN, 1980
Nobel Laureate in Physics; University Professor Emeritus,
Department of Physics, Department of Astronomy and Astrophysics,
and The Enrico Fermi Institute, University of Chicago
"The Highest Energy Cosmic Rays"
From a series of nine lectures that I gave on the
history of cosmic rays from their discovery until the pivotal
conference in 1953 at Bagneres de Bigorres, I found that the contributions
of Bruno Rossi were the most extraordinary. It is a great honor
for me, a latecomer to the field, to be invited to present the
Rossi lecture. I will begin by relating some of Rossi's contributions
to the science of cosmic rays. This will be a natural introduction
to my present work, which concerns the study of the highest energy
cosmic rays, those with energy in excess of 1019 eV (1.6 joules).
An observatory in Argentina named for Pierre Auger,
the French physicist who first demonstrated the existence of extensive
air showers, is now half complete, and is producing beautiful
data. It is a natural extension of Rossi's array at the Agassi
Park in Cambridge and its successor at Volcano Ranch. The Auger
Observatory will be described, and examples of its operation will
be presented.
Time: 4:15 pm
Place: Room 10-250 / MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room).
*Co-sponsored by the MIT Astrophysics Colloquia
Series and the MIT Kavli Institute for Astrophysics and Space
Research.
Thursday, April 28, 2005
IAN
P. SHIPSEY, Professor of Physics
Purdue University
"Bringing Hearing to the Deaf—Cochlear
Implants: a Technical and Personal Account"
Cochlear implants are the first device to successfully
restore neural function. They have instigated a popular but controversial
revolution in the treatment of deafness, and they serve as a model
for research in neuroscience and biomedical engineering. In this
talk, the physiology of natural hearing will be reviewed from
the perspective of a physicist, and the function of cochlear implants
will be described in the context of historical treatments, electrical
engineering, psychophysics, clinical evaluation of efficacy, and
personal experience. The social implications of cochlear implantation
and the future outlook for auditory prostheses will also be discussed.
Time: 4:15 pm
Place: Room 10-250 / MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room).
Thursday, May 5, 2005
JEFFREY
D. RICHMAN, Professor of Physics
University of California at Santa Barbara
"Matter vs. Antimatter: What Have We Learned?"
How could you determine whether an alien being is
made of antimatter without shaking its hand and annhilating both
of you? To do answer this question, we would need to find ways
in which the behavior of antimatter differs from that of matter.
Such differences, also called CP (Charge-Parity) asymmetries,
are required to explain how the universe evolved from a presumed
initial state with equal amounts of matter and antimatter to its
present state in which there is only a tiny amount of antimatter.
In the BaBar experiment, we are probing CP asymmetries by studying
a large number of processes involving heavy quarks. Our method
compares quantum interference effects in particle decays to the
effects in the analogous antiparticle processes. While the Standard
Model of particle physics is able to explain the dominant pattern
of measured asymmetries, a vigorous search is underway to discover
effects of new physics that might disrupt the expected pattern.
I will present BaBar's latest results from these studies.
Time: 4:15 pm
Place: Room 10-250 / MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room).
The Department of Physics colloquia
series will resume in early September 2005.
Please visit this page in late
August for a listing of physics colloquia speakers for the 2005-06
academic year.
