Physics

2005 - 2006 Colloquia

Submitted by Ellen F. Feld

Colloquia during the 2005-2006 academic year

8 September 2005: Dr. Ashfia Huq (Argonne National Lab)
In-situ measurements of catalysts using TOF neutron powder diffraction
Three elements commonly found in metal oxide alkene oxidation catalysts are molybdenum, bismuth and iron. In the case of ammoxidation of propylene to acrylonitrile many catalysts have ferric molybdate and a mixture of bismuth molybdates present in the as-prepared formulations. It is generally recognized that during catalyst activation ferric molybdate is reduced to Fe+2 phases, freeing molybdenum oxide for the formation of other phases. It is suspected, but has never been demonstrated, that this excess MoO3 then reacts with the bismuth containing phase(s) to form the active catalyst phase. Although this reaction is generally believed to occur in a number of catalytic processes the mechanism of the reaction has never been extensively studied. Due to the ease of in-situ measurements and the sensitivity to oxygen in the presence of heavy metals neutron diffraction is an ideal probe to study this reaction mechanism. We have developed a reaction cell that can be used in the General Purpose Powder Diffractometer at Intense Pulsed Neutron Source (IPNS), Argonne National Laboratory (ANL) for time resolved in situ study. Recent upgrades to GPPD, which have increased data rates by a factor of 6, now make these measurements possible. After an introduction of the Time of Flight (TOF) Neutron Scattering technique, preliminary findings about the evolution of a model oxidation catalyst under reaction conditions will be presented in this talk.

22 September 2005: Prof. Daniel Aalberts (Williams College)
Splicing messenger RNA

Messenger RNA is severly edited by our cells; only about 10% of a pre-mRNA is translated into a protein, the other 90% gets tossed away. I will describe two methods for identifying the splice junctions, a thermodynamic theory and a statistics theory incorporating ideas from scaling.

29 September 2005: Prof. Moses H. W. Chan (Penn State University)
Einstein's Legacy in Low Temperature Physics: Superfluids and Supersolids

Einstein, building on the idea of Satyendra Bose, made the remarkable prediction that a collection of certain of particles, known as bosons, will at sufficiently low temperature lose their individual identities and behaves as one giant 'atom'. This transformation, known as Bose-Einstein condensation, was observed in liquid helium nearly 70 years ago and in the vapor phase 10 years ago. Liquid helium then becomes a frictionless superfluid with a multitude of amazing properties, not imagined even by Einstein. Even more extraordinarily, solid helium was recently found in the laboratory to show the same amazing properties- it becomes what is now known as a 'supersolid' i.e, a solid which can flow like a superfluid, without any resistance, through even atomic-size holes. This public lecture will explain in simple terms how such incredible behavior is possible.

6 October 2005: Prof. Timothy Newman (Arizona State University)
Using tools from theoretical physics to model embryonic processes

One of the main research directions of my group is the construction of computational models of multi-cellular dynamical processes - examples being gastrulation in the early embryo, and growth of avascular cancer tumors. Our algorithms are constructed using techniques from many-body theory, which were originally invented in nuclear and condensed matter physics. In this talk I will give a general overview of this work, and try to convince the student audience that physicists have unique methodologies which can be useful for the better understanding of complex systems in biology. As Director of Graduate Admissions for the Department of Physics at ASU, I will also give a brief overview of research in our department, and opportunities for graduate study.

13 October 2005: Dr. Michael Stage (Amherst College/UMass)
Lines, Ti, and Bremss., Oh My! X-Ray Mapping of Supernova Remnants

I will present an analysis of the 1 Megasecond "Very Large Project" Chandra X-ray Telescope observation of the Cassiopeia A Supernova Remnant. The brightest remnant observable from earth at several wavebands, at a well known distance and having a well known age, the Cas A SNR is a rosetta stone for understanding the processes at work in the final, explosive stage of life of stars. I will discuss both the general physical picture of the remnant as observed in X-rays, and discuss our measurements of how the remnant is interacting with the ambient interstellar medium to create and accelerate cosmic rays. I will also give an introduction to the Chandra Telescope and the new analysis techniques we develped to create "maps" of the remnant emission.

20 October 2005: Marilena LoVerde (Columbia University)
How I Learned to Stop Worrying and Love the Universe

In recent years remarkable advances have been made in comology, however, what we have learned is that we know very little about most of the contents of the universe. Perhaps the most surprising observation is that the expansion of the universe is speeding up. The question remains: what is responsible for this acceleration? I will discuss dark energy as the culprit, why we need to learn more, and possibilites for future measurements.

In the second half of my talk I will discuss graduate school, deciding to go, applications, getting there and being there.

27 October 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.

3 November 2005: Prof. Rob Schoelkopf (Yale University)
Circuit Quantum Electrodynamics: Doing Quantum Optics on a Chip

I will describe experiments in which the strong coupling limit of cavity quantum electrodynamics has been realized for the first time using superconducting circuits. In our approach, we use a Cooper-pair box as an artificial atom, which is coupled to a one-dimensional cavity formed by a transmission line resonator. When the Cooper-pair box qubit is detuned from the cavity resonance frequency, we perform high-fidelity dispersive quantum non-demolition read-out of the qubit state. Using this read-out technique, we have characterized the qubit properties spectroscopically, performed Rabi and Ramsey experiments with the qubit, and attained coherence times greater than 500 ns and a visibility of > 90%, indicating that this architecture is extremely attractive for quantum computing and control. In the case when the qubit is tuned into resonance with the cavity, we observe the vacuum Rabi splitting of the cavity mode, indicating that the strong coupling regime is attained, and coherent superpositions between the qubit and a single photon are generated.

10 November 2005: Dr. Arielle Phillips (Amherst College/UMass)
WHIMsical Tracings: Probing the Intergalactic Medium to Solve the Missing Baryon Problem

A solution for the missing baryon problem, the discrepant local and high redshift baryon budgets, may lie in the warm/hot intergalactic medium (WHIM) in the cosmic web. I will discuss the observational evidence for such a component, touching on recent X-ray absorption observations in the Local Group as well as numerous detections of WHIM far-ultraviolet absorption features in quasar spectra. These observations compel us to revisit earlier theoretical predictions for the WHIM, to move beyond a threshold-based definition of this component and take a first look at the topology and geometry of this potentially substantial baryon reservoir. I will present a new algorithm to define and extract structures in large scale hydrodynamical simulations. This method is used to cull a well-defined sample of filaments and groups from simulations in order to elucidate the physics of the WHIM and question its very definition.

17 November 2005: Prof. Chad Orzel (Union College)
Counting Atoms for Astrophysics: Atom Traps, Neutrino Detectors, and Radioactive Background Measurements

A new generation of neutrino and dark matter detectors is currently under development, using liquid neon or xenon as a detection medium. These detectors offer unprecedented sensitivity, but in order to reach their full potential, the liquid in the detector must be purified to an extraordinary degree to avoid contamination by radioactive krypton isotopes. I will describe a new method for measuring the krypton content of other rare gases, by trapping and detecting single atoms of krypton. This method allows us to detect krypton contamination of a few parts in 1014 in a fraction of the time required for more conventional methods.

29 November 2005: Senior Honors Preliminary Thesis Talks

1 December 2005: Prof. Anthony Leggett (UIUC)
Does the Everyday World Really Obey Quantum Mechanics?

No abstract

6 December 2005: Senior Honors Final Thesis Talks

8 December 2005: Senior Honors Preliminary Thesis Talks

16 February 2006: Prof. Melissa Eblen-Zayas (Carleton College)
Electrical modulation of colossal magnetoresistance materials

Manganites, which exhibit colossal magnetoresistance (CMR), have drawn much attention from the condensed matter physics community not only because of the orders of magnitude change in resistance in response to applied magnetic fields, but also because of the rich and complex phase diagrams these materials exhibit. The competition between these various phases makes the manganites susceptible to external perturbations. I will discuss our exploration of the transport and magnetization responses of ultrathin La0.8Ca0.2MnO3 films to applied electric and magnetic fields, and present our interpretation of gate effect, magnetoresistance, and magnetization measurements in the context of phase boundary motion in a mixed phase scenario. I will also discuss our search for evidence of phase inhomogeneity in CMR materials beyond the manganites.

9 March 2006: Prof. Larry Abbott (Columbia University)
Neural Network Dynamics: Slow processes from fast neurons

No abstract

16 March 2006: Prof. Peter Fisher (MIT)
Dark Matter

No abstract

30 March 2006: Dr. Paul Boureois (Amherst College)
OOPS! We stretched the proton! Virtual Compton Scattering and the Generalized Polarizabilities of the Proton

The process of Virtual Compton Scattering (VCS) has become a valuable tool in the study of nucleon structure. New observables of the proton are now accessible which set constraints on theoretical models of the proton. This talk will focus on using VCS to measure the Generalized Polarizabilities (GP's) of the proton. The GP's are fundamental properties of the proton and their precise measurement will help enhance our understanding nucleon structure.

6 April 2006: Prof. David Pimentel (Cornell University)
Ethanol: Biofuels, Biomass and the Environment

Currently the U.S. is producing 3.4 billion gallons of ethanol per year (DOE). This represents about 1% of total U.S. vehicle fuel use per year and is using 14% of U.S. corn production. The environmental impacts are significant and include: increased global warming; soil erosion; freshwater use; use of large quantities of pesticides and nitrogen fertilizer, which pollute the land and aquatic ecosystems. Additional information.

7 April 2006: Prof. Peter Garnavich (Notre Dame University)
Measuring Dark Energy in a Dusty, Lumpy, Evolving Universe

Type Ia supernovae are excellent distance indicators and observation of high-redshift explosions were used to establish the existence of the accelerating universe. But to select between competing theories of dark energy the luminosity distance measured with type Ia events must be reliable to 1% or better. This is hard! Properties of supernovae and dust extinction evolve over the age of the Universe and may introduce systematic errors in the derived cosmological parameters. I will discuss observations of nearby supernovae that may help reduce systematic uncertainties and outline the best design for a space mission which may one day study dark energy.

13 April 2006: Prof. Krishna Kumar (UMass Amherst)
Electrons and Mirror Symmetry

We report on a precision measurement of the neutral weak force between two electrons from the E158 experiment at the Stanford Linear Accelerator Center. The neutral weak interaction amplitude is isolated by measuring the fractional change, under a mirror reflection, of the scattering probability of highly energetic longitudinally polarized electrons off unpolarized target electrons. The short range of the weak force makes it a good testing ground to search for substructure of the fundamental constituents of matter and for new shorter range forces between them. While the weak force between an electron and positron has been extensively studied, that between two electrons has never directly been measured before. After a description of the experiment and the implications of the final results, the prospects for even more precise measurements at future facilities will be discussed.

20 April 2006: Prof. David Kawall (UMass Amherst)
Probing Mysteries in the Spin Structure of the Proton

The proton is a spin 1/2 particle composed of quarks and gluons. Experiments have shown that, quite surprisingly, quark spins only contribute about 25% of the total spin 1/2. The source of the remaining 75% is still undetermined - and constitutes a bold challenge to theorists and experimentalists.

New insight into this stubborn problem is on its way from new experiments based at RHIC, the world's first collider of high energy polarized protons. Within the next few years, our understanding of spin structure will take an enormous leap forward.

In this talk, some of the stunning successes and failures of our understanding will be presented, along with the new path forward using results from the PHENIX experiment at RHIC.

27 April 2006: Senior Honors Thesis Talks

Dan Guest (preliminary talk)
David Stein (final talk)

2 May 2006: Senior Honors Final Thesis Talks

4 May 2006: Senior Honors Final Thesis Talks

 

Physics and Astronomy Department

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

Particle Paths