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physics-astronomy

Physics and Astronomy Colloquium, 2011-2012

Colloquia are held on Thursdays at 4pm in room 4327 (building 4) of the Stevenson Science Center unless otherwise noted. Click here for directions, or phone the department. A reception with the speaker is held at 3:30pm in Stevenson 6333.

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Spring 2012

Thursday, January 19

Heinrich Päs, Technische Universität Dortmund

Neutrinos at the Terascale - a Tale of 3.5 Frontiers   (show abstract)

Neutrinos are the only hint for physics beyond the Standard Model, while the hierarchy problem, gauge coupling unification and dark matter give rise to hope for a direct discovery of new physics at the LHC. Occam's razor suggests that there might be a relation. In this talk I discuss 3.5 frontiers, where neutino physics might directly be related to new physics to be discovered in the unkwon realm of the Terascale: *the Majorana frontier *the Unification frontier *the Flavor frontier *the Exotics frontier

Host: T. Weiler

Thursday, January 26

Reserved

Thursday, February 2

Zenghu Chang, University of Central Florida

The attosecond laser-A new solution seeking problems   (show abstract)

The field of ultrafast optics has experienced a revolution during the last decade. Coherent XUV and soft x-ray pulses as short as 80 attoseconds can now be generated, which is quickly approaching one atomic unit of time-the natural time scale of electron motion in atoms and molecules. However, physicists are struggling to identify problems that can be tackled by this new tool. I will give a few examples on our attempts to shed new light on fundamental issues in atomic physics such as Autoionization and the AC Stark shift.

Host: N. Tolk

Thursday, February 9

Natalie Batalha, San Jose State University

The Kepler Mission's Year Three Census of Transiting Exoplanets    (show abstract)

Humankind's speculation about the existence of other worlds like our own turned into a veritable quest with the launch of NASA's Kepler spacecraft in March 2009. The mission is designed to survey a slice of the Milky Way Galaxy to identify planets via transit photometry. The last year of science operations has been a year of milestones in terms of exoplanet characterization: rocky, Earth-size, circumbinary, Habitable Zone, and even invisible planets have made headlines. However, the real work lies in the large sample statistics of the catalogs of viable planet candidates -- statistics that will drive us toward a determination of eta-"rocky". In the coming weeks, the Kepler team will be releasing its third catalog, consisting of 2,324 viable candidates associated with 1,971 stars. Dr. Batalha will describe some of the milestone discoveries that have marked the last year, the make-up of the new catalog, and the strategies moving forward. Now completeing its third year of operation, Kepler is honing in on the answer to the question that drives the mission: are potentially habitable worlds abundant in our galaxy.

Host: K. Stassun

Thursday, February 16

Dave Piston, Vanderbilt University

Molecular Communication Underlying Hormone Secretion   (show abstract)

The islet of Langerhans is the functional unit responsible for glucose-modulated insulin and glucagon secretion, and thus plays a key role in blood glucose homeostasis. Over the last 20 years, we have been interested in understanding the molecular mechanisms of islet function, and their role in the regulation of blood glucose under normal and pathological conditions. In many ways, the islet appears to function as a syncytium, which exhibits synchronous behavior across all b-cells in the islet. In other ways, the islet works as individual cells. Using quantitative optical imaging of metabolism, membrane potential, free Ca2+, and enzymatic activation, the dynamics of these mechanisms can be measured in islets and even in living animals. Glucose-stimulated insulin secretion is controlled by the activity of glucokinase (GK), and we have shown that GK is regulated by association with other cellular constituents. To determine the preferred interaction partners for GK, we have utilized Förster resonance energy transfer (FRET), which is widely used to study biomolecular dynamics and protein interactions in live cells. Many issues complicate FRET measurements. We have developed two novel approaches approach for absolute and high precision measurements of FRET efficiency, one based on lock-in detection of an optical switch acceptor and a second based on snapshot hyperspectral imaging. These approaches will be described and their use for measuring intracellular protein interactions will be discussed. Glucose-stimulated insulin secretion also depends on electrical depolarization of cell membranes that causes vesicle exocytosis. We have shown that gap junction coupling between islet cells regulates their membrane polarization, although other work suggests possible roles for other coupling mechanisms as well. We have introduced precise experimental perturbations in both the gap junction coupling and the individual cell membrane potentials. We find that decreasing gap junction coupling can lead to sub-regions becoming electrically active, but that these active sub-regions do not lead to increased insulin secretion. Mathematical models of coupled β-cell electrophysiology describe the variation in electrical activity as a function of coupling, but do not accurately predict the changes in secretion.

Host: R. Scherrer

Thursday, February 23

Alyssa Goodman, Harvard University

Watching Stars Form   (show abstract)

Star formation is the key process in our Universe that turns cold gas in galaxies into the hot stars whose light dominates the visible sky. In spite of this fundamental role, though, the details of how interstellar gas arranges itself into the small blobs called "cores" that collapse under their own weight to form stars are still murky. On the theoretical end, the lack of clarity is due mostly to our inability to include all the physics that might be relevant (gravity, magnetic fields, thermal effects, chemistry, and radiative transfer) in even the best modern simulations. New telescopes are clearing up our view on the observational end, but not yet to the point where we understand the images. In this talk, I will describe new statistical and visualization techniques that have allowed us to measure and understand: 1) the role of self-gravity as a function of scale in star-forming regions; 2) the contribution of bipolar outflows from young stars, as well as spherical winds from older stars in stirring star-forming gas; and 3) the confusion caused by observational biases associated with observing particular "tracers"(e.g. molecular lines) of interstellar matter. I will conclude with a discussion of how the high-dimensional visualization and statistical techniques used in our studies apply in the world of medical imaging, and beyond.

Host: K. Stassun

Thursday, March 1

Eric Agol, U. Washington

New approaches to finding and characterizing planets orbiting other stars   (show abstract)

The discovery and characterization of planets orbiting other stars is challenging due to their small size and mass. A solution to this problem is to search for planets orbiting smaller stars: either smaller in mass, or smaller in size. One of the smallest types of stars, white dwarfs, turn out to be good targets for searching for second-generation, short-period planets using the detection of transits or eclipses. I will discuss several coincidences that would favor detection of earth-sized and earth-temperature planets, should they exist around white dwarf stars. I will conclude by discussing some new ideas for for mapping the infrared emission of planets; for measuring the masses of small planets; and for finding dynamically interacting planets using the Kepler satellite. This work has involved undergraduate students through the Pre-Major in Astronomy Program.

Host: K. Stassun

Tuesday, March 6 at 3 PM (Note special date and time!)

Herbert Levine, Rice University

Statistical Mechanics of Darwinian Evolution   (show abstract)

Motivated by experiments on laboratory-scale evolution in both microorganisms and biomolecules, we introduce and study a class of multi-locus evolution models. For these models, the population advances via being dragged forward by its most fit members and can be quantitatively studied using ideas from the theory of non-equilibrium spatially-extended processes. A key finding is the anomalously large dependence on population size and the related anomalously large usefulness of genetic recombination. Using this approach, insight can be obtained regarding the indirect selection for mechanisms which speed up adaptation, including becoming mutator-like and going into a state competent for genetic exchange.

Host: E. Rericha

Thursday, March 15, Carl Seyfert Lecture
Special location: Community Room in the Central Library

Alan Boss, Carnegie Institute

Kepler, Microlensing, and Direct Imaging: New Constraints on Exoplanet Formation Theories   (show abstract)

Doppler and ground-based transit searches have discovered over 700 exoplanet candidates to date. These discoveries have generally supported the core accretion mechanism for giant planet formation. However, more recent discoveries have raised questions about the core accretion mechanism as the sole mechanism for exoplanet formation. NASA's Kepler space telescope has now detected 2326 exoplanet candidates, with many of these candidates occupying an oasis in discovery space that was predicted to be a desert on the basis of population synthesis models based solely on core accretion. Similarly, ground-based microlensing surveys, as well as direct imaging detections, have demonstrated the existence of significant numbers of giant planets on orbits wide enough to be difficult to explain purely by core accretion. These new constraints on planet formation theories suggest that future population synthesis models need to consider hybrid formation mechanisms, where at least some of the giant planets are formed by the disk instability mechanism, coupled with the formation of rocky planets, hot and cold super-Earths, and some giant planets by the traditional core accretion mechanism.

Host: D. Weintraub

Thursday, March 22

Saul Teukolsky, Cornell University

Simulations of Black Holes, Neutron Stars and Gravitational Waves   (show abstract)

Gravitational wave detectors like LIGO are poised to begin detecting signals. One of the prime scientific goals is to detect waves from the coalescence and merger of black holes and neutron stars in binary systems. Confronting such signals with the predictions of Einstein's General Theory of Relativity will be the first real strong-field test of the theory. Until recently, theorists were unable to calculate what the theory actually predicts. I will describe recent breakthroughs that have occurred and that have set things up for an epic confrontation of theory and experiment.

Host: R. Scherrer

Thursday, March 29

Spring Faculty Assembly, no colloquium

3:00 pm, 4309SC, Monday, April 2 (Note SPECIAL DATE, TIME and PLACE)

Keith Olive,

The impact of the LHC and direct detection experiments on Supersymmetric Dark Matter   (show abstract)

The nature and identity of the dark matter of the Universe is one of the most challenging problems facing modern cosmology. Only ~5% of the energy density of the Universe can be associated with known forms of matter. Supersymmetry is an extension of the Standard Model of particle interactions and predicts the existence of dark matter. Searches for supersymmetry have begun in ernest at the LHC and these searches are intimately connected to the search for the Higgs boson. The effect of 2011 LHC data are discussed in connection to the potential for the direct detection of supersymmetric dark matter. The impact of the recent direct detection results are contrasted to these predictions. Expectations for indirect detection are also discussed.

Host: R. Scherrer

Thursday, April 5, Francis G. Slack Lecture

Deborah Jin, JILA, U. Colorado-Boulder

Ultracold Polar Molecules   (show abstract)

Gases of atoms can be cooled to temperatures close to absolute zero, where intriguing quantum behaviors such as Bose-Einstein condensation and superfluidity emerge. A new direction in experiments is to try to produce an ultracold gas of molecules, rather than atoms. In particular, polar molecules, which have strong dipole-dipole interactions, are interesting for applications ranging from quantum information to modeling condensed matter physics. I will describe experiments that produce and explore an ultracold gas of polar molecules.

Host: R. Scherrer

Tuesday, April 10 (Note SPECIAL DATE but usual room and time)

Christopher White, Illinois Institute of Technology

Observation of Electron Antineutrino Disappearance by the Daya Bay Reactor Neutrino Experiment.   (show abstract)

Many experiments have demonstrated the neutrino's ability to change flavor while traveling through space. One of the last remaining unknown parameters describing these oscillations, theta_13, is crucial in defining the magnitude of possible CP-violation in the lepton sector, and examining the neutrino's role in the universe's matter-antimatter asymmetry. The Daya Bay experiment has measured theta_13 with unprecedented precision by observing the disappearance of reactor antineutrinos with identical detectors at multiple locations. With roughly two months of data, the experiment has measured the value of sin^2(2theta13) to be 0.092 +/- 0.017, and excluded the theta13=0 hypothesis to five standard deviations. This talk will describe the Daya Bay experiment and current results.

Host: P. Sheldon

Thursday, April 12

Kate Jones, U. Tennessee

CANCELED, to be rescheduled in the fall

Host: J. Hamilton

Thursday, April 19

Konrad Gelbke, Michigan State University

From NSCL to FRIB at MSU   (show abstract)

NSCL (National Superconducting Cyclotron Facility) is currently funded by the U.S. National Science Foundation (NSF) under a cooperative agreement to operate NSCL’s Coupled Cyclotron Facility (CCF) as a national user facility and to support research and education in nuclear science, nuclear astrophysics, and accelerator and beam physics and engineering. In 2009, Michigan State University (MSU) and the U.S. Department of Energy (DOE) have signed a cooperative agreement to design and establish the Facility for Rare Isotope Beams (FRIB) on the MSU campus. FRIB will be a world-leading research facility to advance understanding of rare nuclear isotopes and the evolution of the cosmos. FRIB will be built adjoined to NSCL. CCF operations will cease and the NSCL infrastructure will merge into the FRIB laboratory when FRIB construction nears completion. FRIB was approved for CD-1 in September 2010 and is scheduled for its baseline review on April 24-26, 2012, hopefully clearing the path for approval of CD-2 and CD-3a. The FRIB project is technically ready to begin of civil construction in Spring 2012, but funding issues are likely to cause some delays. In this talk, I will provide a high-level summary of the NSCL’s current facility and research plans, the envisioned integration into FRIB, the FRIB project status, emerging new opportunities, and planned user interfaces.

Host: A. V. Ramayya

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