Thursday, February 09, 2012

04:30 pm - 06:00 pm

Physics Colloquium II, Phillip Gould, UCONN, Colliding and Binding Ultracold Atoms using Frequency-Chirped Light

Most laser sources are either pulsed, where the timing is well defined, or continuous, where the frequency of the light is precisely determined. We have developed a diode laser system that produces nanosecond time scale pulses during which the frequency of the light is varied in a controlled way. We use these frequency-chirped pulses to coherently control interactions between trapped ultracold Rb atoms. In one set of experiments, we excite atom pairs to a long-range attractive potential, causing the atoms to collide inelastically and be lost from the trap. Matching the time scale of the collisional dynamics to that of the frequency chirp allows control of these collisions. In another set of experiments, we use frequency-chirped light to photoassociate ultracold atoms, thus forming bound molecules, which are detected by laser ionization. Ultracold molecules have many applications, including quantum computing, precision spectroscopy, and utlracold chemistry. Optimizing their production using the techniques of coherent control is therefore of significant interest.

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Thursday, February 16, 2012

04:30 pm - 06:00 pm

Physics Colloquium- Remodeling Microtubule Networks Through Severing, Jennifer Ross, UMASS

Microtubules are cytoskeletal filaments that organize intracellular space structurally and through active transport along their lengths. They need to be organized and remodeled quickly during development of differentiated cells or in mitosis. Much work has focused on remodeling from the ends of these long polymers that can stochastically disassemble through dynamic instability or be actively disassembled. Microtubule-severing enzymes are a novel class of microtubule regulators that create new ends by cutting the filament. We are interested in the inherent biophysical activities of these proteins and their ability to remodel cellular microtubule networks. Interestingly, despite first appearances, severing has the ability to create new microtubule networks in cells. We use two-color single molecule total internal reflection fluorescence imaging to visualize purified severing enzymes and microtubules in vitro. We have examined two families of severing enzymes to find that their biophysical activities are distinct giving them different network-regulating abilities.

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Thursday, February 23, 2012

04:30 pm - 06:00 pm

Physics Colloquium II, Brian Stewart, Chair's Colloquium

Professor Stewart will give an overview of research activity in the physics department during the past year. This is a good opportunity for students and the interested public to learn about the research carried out by members of the department

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Thursday, March 01, 2012

04:30 pm - 06:00 pm

Physics Colloquium II- "Portable Stellar Intensity Interferometry" Elliot Horch, SCSU

A limitation of the current generation of long baseline optical interferometers is the need to make the light interfere prior to detection. This is unlike the radio regime where signals can be recorded fast enough to use electronics to accomplish the same result.This talk will describe a modern intensity interferometer based on electronics with picosecond timing resolution. The instrument will allow for portable optical interferometry with much larger baselines than currently possible by using existing large telescopes. With modern electronics, the limiting magnitude of the technique at a 4-m aperture size becomes competitive with amplitude-based interferometers. The instrumentation will permit a wireless mode of operation with GPS clocking technology, extending the work to extremely large baselines. We discuss the basic observing strategy, a planned observational program at the Lowell Observatory 1.8-m and 1.0-m telescopes, and the science that can realistically be done with this instrumentation.

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Thursday, March 08, 2012

04:30 pm - 06:00 pm

Physics Colloquium II, Vacek Miglus, Curator Physics Department

Come see Vacek present the best of Wesleyan Physics E&M and Optics.For those that wanted more demos at the NSM talk.For those that want to see their theory realized in demonstrations. For those that like arcs and sparks and cool optics.

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Thursday, March 29, 2012

04:30 pm - 06:00 pm

Physics Colloquium II, Why Should You Care About Nuclear Fusion?, David Crandall, DOE, Office of Science

Three quick answers to that question: fusion energy will be a topic of discussion for your entire life; the science and engineering challenges in obtaining sustained fusion on earth are interesting; fusion connects to nearly all science in part because it is the fuel for the universe. The talk will define fusion and discuss the current efforts to sustain inertial and magnetic fusion in the laboratory. The talk will describe in some detail the most interesting endeavor right now, the attempt to reach inertial fusion ignition at the National Ignition Facility in Livermore, California using the world's largest laser to drive a tiny fusion fuel target. The world's largest fusion endeavor, the International Thermonuclear Experimental Reactor (ITER) under construction in Cadarache, France, will be described along with the magnetic confinement of plasma that it is to use. Connections of these fusion concepts to astrophysics and materials science will be described. Why fusion energy is so attractive and so elusive will be discussed.

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Thursday, April 05, 2012

04:30 pm - 06:00 pm

Physics Colloquium II- Cold Atom Diffraction, Janine Shertzer, Holy Cross

Cold Atom DiffractionThe wave-particle duality is fundamental to atomic physics. Under special conditions, we can observe wave properties of matter. The wavelength is , where is Planck's constant. For very cold atoms, the wavelength is large enough that one can design diffraction gratings and observe an interference pattern. I will explain how to cool atoms using lasers, and how to create an atomic diffraction grating. Optical interference (like Young's double slit experiment) can be understood theoretically by solving the wave equation. To fully understand the interference of cold atoms, one must solve the Schrvdinger equation using the appropriate scattering boundary conditions. The interaction of the magnetic dipole moment of the atoms with the periodic magnetic surface of the grating gives rise to an effective potential. The differential scattering cross section contains information about the angular position and relative intensity of the interference peaks. Theoretical calculations can be used to predict the optimal experimental parameters for observing atomic diffraction.

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Thursday, April 12, 2012

04:30 pm - 06:00 pm

Physics Colloquium II, The Genesis Projects: Laboratory Studies in Molecular Astrophysics from the First Star to the Beginnings of Organic Chemistry, Daniel Savin, Columbia Astrophysics Laboratory

Interstellar chemistry plays an important role in the evolution of the universe from the dark ages to the formation of life. I will discuss twoparticularly important links in this chain of chemical reactions. The first is the formation of H2 in the early universe. Uncertainties inthis process limit our ability to reliably model the formation of the first stars. The other link we study is the start of the cosmic pathwayto life which begins in interstellar gas clouds where atomic carbon is "fixed" into molecules, thereby initiating the synthesis of the complexorganic molecules that are eventually sequestered on planets. These reactions initiate not only the formation of organic molecules in the cosmos, but also provide some of the first threads knitting together atoms and molecules into solid material. Such processes are critical for the eventual formation of planets and may determine a major component of the organic chemistry that is present on their young surfaces. I willbriefly review these motivations for our research and explain how we reproduce the relevant reactions through laboratory experiments.

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Thursday, April 19, 2012

04:30 pm - 06:00 pm

Physics Colloquium II, Prof. Brian Stewart's Annual Earth Day Rant

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Thursday, April 26, 2012

04:30 pm - 06:00 pm

Physics Colloquium II- Stabilization of Secondary Structure of Disordered Proteins by Confinement: A Molecular Dynamics Study Luis Cruz Cruz, Drexel

Stabilization of Secondary Structure of Disordered Proteins by Confinement: A Molecular Dynamics StudyA complete understanding of protein folding in cellular environments is still lacking even after decades of scientific scrutiny. In vivo,proteins perform their biological function by folding into their native state within confining environments that include lipid membranes and chaperons, and within cavities, among others. Of particular importance are proteins that do not have a native state,known as intrinsically disordered proteins (IDP), that exist mainly in random structures whose function is not well understood. Some ofthese IDP, known to misfold and aggregate, have been associated with neurological diseases, such as the amyloid beta-protein (Abeta) in Alzheimer's disease. In this talk, results derived from all-atom molecular dynamics simulations in explicit water will be presented ofthe dynamics of the central decapeptide fragment of the full-length Abeta, the Abeta(21-30) decapeptide, under confinement. Transient beta-hairpin structures found in this decapeptide in bulk will be shown to be stabilized by the solvent when confined in nanometer-sized pores.However, for progressively smaller pores, the stability of these beta-hairpin structures will be shown to depend on the nature of the confining surface rather than on the stabilizing effects of the confined water. Possible connections with amyloid formation and aggregation will be discussed.

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