Physics

2004-2005 Colloquia

Submitted by Ellen F. Feld
Colloquia during the 2004-2005 academic year
16 September 2004: Prof. Gene Golowich (UMass Amherst)
About C, P and T
We introduce the concepts of charge conjugation (C), parity (P) and time-reversal (T) and explain how it is that measurment of the violation of CP is a hot topic in fundamental experimental physics these days.

23 September 2004: Prof. Courtney Lannert (Wellesley College)
Monte Carlo Simulations of Spin Systems

No abstract

7 October 2004: Prof. Seth Major (Hamilton College)
Quantum gravity and physics: how the former may become the latter

Quantum gravity is purported to be the theory which underlies both quantum theory and general relativity. I will introduce the subject, emphasizing recent results which suggest that space is discrete. Discrete geometry may have an observational signature and I will describe limits on such weird geometry by astrophysical observations. I will also argue that, in the not too distant future, quantum gravity may become physics and enjoy contact with observation and, perhaps, experiment.

14 October 2004: Dr. Mustafa Bal (Amherst College)
Photon-induced magnetization reversal in single-molecule magnets

Single-molecule magnets (SMM) have been subject to intensive research for more than a decade now because of their unique properties such as macroscopic quantum tunneling. Recent work in this area is focused on whether SMM are suitable candidates to realize quantum computation, as proposed theoretically. We use millimeer wave radiation to manipulate the populations of the energy levels of a single crystal molecular magnet Fe8. When a continuous wave radiation is in resonance with the magnetic dipole transitions (ms=1) between the energy levels, the equilibrium magnetization exhibits a dip. The position of this dip varies linearly with the radiation frequency. We will describe our experimental results, which provide a lower bound of 0.17 ns for \the relaxation time.

18 October 2004: Prof. Mark Beck (Whitman College)
Interference, Complementarity, Entanglement and all that Jazz

Technology has advanced to the point where it is possible for undergraduates to perform experiments exploring fundamental aspects of quantum mechanics, such as wave-particle duality, entanglement, and tests of Bell inequalities. At Whitman College we are developing a series of undergraduate laboratories and I will describe some of these. In one we perform an interference experiment with single photons where we clearly show that the individual photons behave both as waves and particles. This experiment is consistent with Bohr's principle of complementarity, but challenges some oft-held beliefs surrounding it. In another experiment, involving entangled photon pairs, we can demonstrate the operation of a "quantum eraser". We show that measurements performed on one beam can change the visibility of a fringe pattern in another, spatially separated beam.

28 October 2004: Prof. Stephane Willocq (UMass Amherst)
B-factories: powerful tools to probe the matter-antimatter asymmetry of the universe

No abstract

4 November 2004: Prof. Adam Monahan (University of Victoria)
Atmospheric Physics in the Kitchen

In this talk, I will use examples drawn from everyday experience in the kitchen, along with basic dynamics and thermodynamics, to illustrate processes of fundamental importance to the structure and variability of the atmosphere. Three topics will be addressed: (1) how can you build an altimeter from a gas stove and a thermometer? (2) why do boiling kettles steam? and (3) why do leaves in a stirred cup of tea pile up in the centre of the cup, and what does this have to do with wintertime storms?

11 November 2004: Prof. John Stachel (Boston University)
Einstein's Miraculous Year

Einstein's miraculous year was the culmination of his earlier efforts to master classical physics and criticize and supercede certain of its features. After a brief review of classical mechanics and 19th century optics and electrodynamics of moving bodies, Einstein's work in
  • further developing classical mechanics
  • resolving the apparent conflict between classical mechanics and Maxwell's electrodynamics, and
  • going beyond classical theory to develop a quantum theory of radiation and matter will be discussed.

John Stachel is Professor Emeritus of Physics and Director of the Center for Einstein Studies at Boston University. He was the founding editor of The Collected Papers of Albert Einstein, editor of "Einstein's Miraculous Year" (Princeton University Press), author of "Einstein from 'B' to 'Z' " (Birkauser Boston) and of the forhtcoming two-volume collection of his papers NOT about Einstein: "Going Critical" (Kluwer).

18 November 2004: Prof. Andy Kent (NYU)
Magnetic Quantum Tunneling in Single Molecule Magnets

Single molecule magnets (SMMs) are magnetic nanostructures that consist of a core of strongly exchange-coupled transition metal ions with a large collective magnetic moment per molecule, thus far upto 51 Bohr magnetons, and a predominantly uniaxial magnetic anisotropy. Their molecular nature enables experimental studies of nearly monodisperse ensembles of nanomagnets with well-defined size, shape, chemical composition, and magnetic anisotropy. This talk will present experiments that address the origin of magnetic quantum tunneling (MQT) in the prototype SMM Mn12-acetate and, in particular, the nature of the transverse interactions that produce quantum tunneling. Recent experiments that employ microwave fields to modulate MQT and characterize quantum superpositions states of "up" and "down" spin-projections will also be described.

2 December 2004: Kendall McConnel (Columbia)
My life in physics and in graduate school

Neutrinos are the smallest particles in the Standard Model, with a mass expected to be zero. However, many experiments have observed neutrino oscillation, which depends on a non zero neutrino mass. I will discuss neutrinos, neutrino oscillation, the past and future levels of students. In the second half of my talk, I will go over general tips about graduate school, how to get in, and what to do when you get there.

9 December 2004: Senior Honors Preliminary Thesis Talks

3 February 2005: Prof. Marilyn Gunner (CCNY)
The Role of Buried Charged Groups in Proteins

Proteins contain acidic and basic residues which would be ionized in aqueous solution. The Born solvation energy stabilizes charges in water. By having charged groups on their surface helps proteins remain soluable. A small, but significant number of ionizable residues are buried in the protein. I will describe how electrostatic analysis can be used to calculate the equilibrium ionization state of these residues by computing the interactions amongst charges and dipoles in the protein. In addition, I will describe how these buried acidic and basic groups function in pumping protons (H+) across cell membranes in proteins such as bacteriorhodopsin.

10 February 2005: Prof. Mark Goldman (Wellesley College)
How Neurons Do Integrals

Neurons that command the eyes to move generate action potentials, or "fire," at a rate that is proportional to eye velocity. To maintain the eyes at a fixed position, motor neurons that control the muscles of the eye fire at a rate that is proportional to eye position; in the absence of their firing, spring-like forces return the eyes to the center of the head. The transformation of velocity-coded eye movement commands to position-coded firing of motor neurons is accomplished by an area of the brain known as the oculomotor neural integrator. In this talk, I will describe the experimental characterization of the goldfish neural integrator, mathematical models of the neuronal mechanisms that enable the velocity-to-position integration to be performed, and connections between neural integration and the storage of short-term memories.

17 February 2005: Prof. Guy Blaylock (UMass Amherst)
Gamma Ray Astrophysics

Very high energy gamma ray science has progressed dramatically in the last 15 years. Several new telescope arrays currently being commissioned will push this field much farther in the next decade, combining many of the scientific interests of astrophysics and particle physics. On the astrophysics side, gamma ray studies drive the effort to understand some of the most powerful accelerators in the universe. On the particle physics side, very high energy gamma rays can be used to probe fundamental questions in physics. I will discuss two topics in the latter category, Lorentz breaking and dark matter, that have especialy captured the interest of the scientific community and that are currently being pursued in gamma ray experiments.

24 February 2005: Prof. Marianna Safronova (University of Delaware)
Parity Nonconservation in Atoms: The Evolving Story

Study of parity nonconservation (PNC) in heavy atoms provides atomic-physics test of the electroweak Standard Model and led to a first measurement of the nuclear anapole moment. The PNC interaction leads to a non-zero amplitude for transitions otherwize forbidden by the parity selection rule, such as the 6s-7s transition in cesium. Combining experimental measurements and theoretical calculations of the PNC amplitude permits one to infer the value of the weak charge and compare it with the value predicted by the Standard Model. In this talk, I will give an overview of the status of the parity nonconservation studies in heavy atoms. I will specifically focus on the calculation of the Cs PNC amplitude and the resulting analysis which yielded the value of the weak charge. The PNC experiment in Cs, combined with the calculation of the spin-depended PNC amplitude, also yielded the value of the nuclear anapole moment and allowed us to place constraints on PNC meson coupling constants which were found to be in disagreement with those obtained from other nuclear parity violating experiments. I will present preliminary results of the new calculation of spin-dependent amplitude in Cs conducted using a relativistic all-order method and discuss the issue of the accuracy of the atomic calculations needed to derive the value of the anapole moment.

10 March 2005: Prof. Kim Vandiver (MIT)
High-Speed Schlieren Photography of Ice Cubes, Soap Bubbles, Candle Flames and Shock Waves

In conjunction with the Mead Art Museum exhibit Quicker Than A Wink: Photographs By Harold Edgerton J. Kim Vandiver will deliver a lecture "High-sped schlieren photography of ice cubes, soap bubbles, candle flames and shock waves." The lecture is sponsored by the Departments of Astronomy and Physics.

Vandiver, Dean for Undergraduate Research and Director of the Edgerton Center at MIT, was a colleague of Edgerton's and has continued his pioneering work on ultra-high speed photography. He will show his beautiful and spectuacular images of everyday events, revealing hitherto-unseen phenomena, as well as explaining techniques for making such photographs. The lecture will be at a non-technical level and the public is invited to attend.

24 March 2005: Dr. Solomon Gilbert-Diamond (Harvard/Mass General Hospital)
Functional Neuroimaging: The Meeting Place of Physics and the Human Mind

Advances in functional neuroimaging are driving a revolution in our understanding of the human mind. The goal of understanding the neurological mechanisms with which the human brain carries out mental tasks is fantastically challenging. Functional neuroimaging technologies measure brain function from electromagnetic, metabolic and neurovascular response perspectives. Interpreting the massive quantities of data from neuroimaging studies pushes the limits of available computational power. This presentation will provide an outline the current challenges in functional neuroimaging with a look towards the future of this exciting field.

31 March 2005: Prof. Sarah Keller (University of Washington)
Spheres that break out in spots: Immiscible phases in membranes of lipids and cholesterol

Prof. Keller's research group does interdisciplinary science, and this seminar should be accessible to physicists, chemists, and biologists alike. Mammalian cells are surrounded by an outer wall or "plasma membrane" of proteins and lipids arranged in opposing leaflets of a bilayer. There is growing evidence that this membrane is not uniform, but instead laterally phase separates into "raft" domains rich in particular lipids and proteins. We study a simpler physical model of cell membranes, giant unilamellar vesicles (GUVs). Liquid domains in vesicles exhibit interesting behavior: they collide and coalesce, can finger into stripes, and can bulge out of the vesicle. We use fluorescence microscopy to directly observe liquid domains in the vesicles. We cross miscibility phase transitions by changing temperature. Using results from both fluorescence microscopy and NMR studies, we quantitatively construct tie-lines on phase diagrams. These tie-lines allow us to estimate free energies to transfer lipids between phases. We also find that it is possible to capture domains in lipid layers on glass substrates.

Dr. Sarah L. Keller is an assistant professor in the Department of Chemistry at the University of Washington in Seattle. Her research group includes an interdisciplinary team of postdocs, graduate students, and undergraduates.

Dr. Keller's group studies liquid domains in lipid bilayers and monolayers. In recent work, her group has advanced our knowledge of the miscibility phase behavior of model mixtures of phospholipids and cholesterol, and established tie-lines.

7 April 2005: Dr. Marijke Haverkorn (Harvard-Smithsonian Center for Astrophysics)
Radiopolarization measurements as a probe of the magnetoionic interstellar medium

The interstellar medium is an extremely complex mixture of interacting gas, dust, cosmic rays and magnetic fields. A suite of observations across the whole electromagnetic spectrum is needed to understand the dynamics and composition of the interstellar medium (ISM). A unique method to explore the warm ionized gas and Galactic magnetic fields is radiopolarimetry and Faraday rotation.

I will discuss our current understanding of the interstellar medium and Galactic magnetic fields, and the way radio polarization, depolarization and Faraday rotation can give insight into the structure of the magnetoionic ISM. As an example, I will present the Southern Galactic Plane Survey (SGPS) at 1.4 GHz full-polarization continuum. SGPS results include estimates of the typical scale of turbulence in HII regions and the determination of an additional source of magnetoionic structure only present in the spiral arms.

26 April 2005: Senior Honors Final Thesis Talks

28 April 2005: Senior Honors Preliminary Thesis Talks

 

Physics and Astronomy Department

AC# 2244
Amherst College
Amherst, MA 01002-5000
413-542-2251
Larry Hunter, Chair

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