Colloquium Schedule

Star Formation from the Radio to Gamma-Rays

Mon, 13 Sep 2010 12:15 -0400

Massive stars are an important driver of much of galaxy evolution. These stars live furiously, greatly affecting their surroundings with their winds and radiation, then die dramatically in giant explosions that enrich the interstellar medium in heavy elements. Their lives are relatively brief as well (“only” 10 million years or less) so their impact is not only profound but immediate. Certain galaxies known as starbursts create numerous clusters of these massive stars in their centers. Starburst galaxies may be studied across all the electromagnetic bands, probing different physical regions and processes, but they are traditionally identified by their radio and infrared emission or optical spectroscopy. I augment these studies by including data from a window only recently opened to us: gamma-rays. The gamma-ray emission effectively ties together nearly the entire spectrum of a galaxy while elucidating the impact of cosmic rays on galaxy evolution.

Critical phenomena and biological networks

Mon, 20 Sep 2010 12:15 -0400

Graphene Nanophotonics and Nanoelectronics

Mon, 18 Oct 2010 12:15 -0400

Graphene, a 2-dimensional carbon based material system, recently attracts world-wide attention from physicists and engineers due to its unique electronic and photonic properties. In this talk, I will first discuss the historical evolvement of electronics and photonics, followed by the potential of graphene in electronics and photonics. A few important developments in graphene photonics will then be presented, including photocurrent imaging, ultrafast (> 40 GHz) photoresponse, and the application of graphene photodetector in a realistic optical communication link. Next, two approaches to create a bandgap, using lateral confinement in single layer graphene and vertical E-field in bi-layer graphene, will be covered in detail. I will show that a transport bandgap of > 130 meV can be realized in biased bilayer graphene. The developments in graphene bandgap engineering may enable a few important applications, such as graphene digital electronics, electron Veselago lens and graphene spin qubit

Designed proteins and hybrid metamaterials for chemotherapy and solar biofuel production

Mon, 1 Nov 2010 12:15 -0400

Solar sail to test fundamental physics

Mon, 8 Nov 2010 12:15 -0500

The motion of the solar sail is determined by the solar radiation pressure as well as the spacetime geometry. The Pioneer anomaly, which is the unexplained acceleration of the Pioneer 10 and 11 spacecraft on escape trajectories from the outer solar system and the effects of general relativity on a solar sail propelled satellite will be discussed. We present deviations from Kepler’s third law for heliocentric orbits near the sun. In particular, we consider deviations in the period of circular orbits due to the spacetime curvature near the sun, frame dragging from the rotation of the sun, and the oblateness of the sun. The Poynting-Robertson effect on a nearly-circular heliocentric trajectory of a solar sail is discussed. In addition, for non-Keplerian orbits which are outside of the plane of the sun, we predict an analog of the Lense-Thirring effect for which the orbital plane precesses around the sun. This can be tested by a solar sail propelled satellite.

The history of probability theory: Predicting the unpredictable

Mon, 15 Nov 2010 12:15 -0500

This lecture traces the history of probability theory from the throwing of bones, sticks, and dice to modern times. Early 18^th century books, Jacob Bernouill's “The Art of Conjecture” and Abraham DeMoivre's “The Doctrine of Chances” were rich with new mathematics, insight and gambling odds. Progress was often made by confronting paradoxes. The first of these confused probabilities with expectations and was explained in the Pascal-Fermat letters of 1654. The St. Petersburg Paradox involved a distribution with an infinite first moment, and Levy discovered a whole class of probabilities with infinite moments that have found a surprising utility in physics. The Bertrand paradox involved measure theory for continuous probabilities, Poisson discovered that adding random variables need not always produce the Gaussian, and Daniel Bernoulli and D'Alembert argued over the probabilities for the safety of smallpox vaccinations. Using these and other anecdotes, this lecture discusses vignettes that have brought us to our modern understanding of probability theory.

Aperiodic lasers

Mon, 22 Nov 2010 12:15 -0500

Slow and Fast Light : penetrating the Fog

Mon, 6 Dec 2010 12:15 -0500

Crystal Roughening below the Roughening Temperature

Mon, 7 Feb 2011 12:15 -0500

Epitaxial films are often grown or annealed below their roughening temperature. The microscopic physics involves the attachment and detachment of atoms at steps, and the diffusion of atoms across terraces. The macroscopic consequences of these atomic-scale mechanisms are still poorly understood. My talk will discuss recent progress with Hala Al Hajj Shehadeh and Jonathan Weare, concerning the evolution of a one-dimensional step-train separating two facets in the "attachment-detachment-limited" regime. I'll explain why the evolution is asymptotically self-similar, and why its continuum limit is associated with a certain fourth-order nonlinear PDE's. The talk will be self-contained, requiring no prior background about crystal growth.