Events Archive

Mar
13
2012
The fluid mechanics of marine microbes: Phytoplankton gyrotaxis and bacterial rheotaxis
Mar
12
2012
The Physics of How Viruses Make New Viruses
The viruses that infect bacteria have a hallowed position in the development of modern biology, and once inspired Max Delbruck refer to them as "the atom of biology".  Recently, these viruses have become the subject of intensive physical investigation.  Using single-molecule techniques, it is actually possible to watch these viruses in the act of packing  and ejecting their DNA.    This talk will begin with a general introduction to viruses and their life cycles and will then focus on simple physical arguments about the forces that attend viral DNA packaging and ejection, predictions about the ejection process and single-molecule measurements...
Mar
10
2012
Squishy Physics: The Physics of Food and Cooking
In this exciting event, three lectures will be presented from world renown Chef Jose Andres and Harvard Physics Professors Michael P. Brenner and David A. Weitz.  Awards will also be presented to the top Dekalb County high school student...
Mar
09
2012
Membrane-protein insertion: One helix and one amino acid at a time
Membrane proteins are critical components of all cells, controlling, e.g., signaling, nutrient exchange, and energy production, and are the target of over half of all drugs currently in production.  At an early stage of their synthesis, nearly all membrane proteins are directed to a protein-conducting channel, the SecY/Sec61 complex, which permits access to the membrane via its lateral gate.  By combining molecular dynamics simulations with cryo-electron microscopy data, we recently resolved the first structure of a membrane-protein-insertion intermediate state of SecY bound to a translating ribosome, with a transmembrane (TM) segment...
Mar
08
2012
Effect of electron-electron interaction on transport in non-Galilean invariant Fermi systems: Application to the Bi_2Te_3 family of 3D Topological Insulators
We study the effect of electron-electron interaction on the resistivity of a metal where umklapp scattering is either not effective or suppressed. This can happen in cases such as in a metal near a Pomeranchuk quantum phase transition or in a system with low density of carriers, e.g., the surface states of three-dimensional (3D) topological insulators. In such cases, one must consider both interactions and disorder to obtain a finite and T dependent resistivity. The existence of the Fermi-liquid (T^2) term in resistivity of a two-dimensional (2D) metal, as we show, then depends on 1) dimension (2D vs 3D), 2) geometry (concave vs convex), and 3) topology (simply vs multiply...
Mar
08
2012
Topological Materials
Topological states of matter have quantum entangled ground states characterized by topological quantum numbers rather than symmetrybreaking. Inspired by the discovery of topological insulators, I describe recent progress in finding a variety of new classes of topological materialsin semiconductors and superconductors. Potential applications in electronics and quantum computation will be briefly discussed.
Mar
07
2012
Watching single ribosome translation in real time: a quantitative study of ribosome helicase activity
The ribosome translates the genetic information encoded in messenger RNA into protein. Folded structures in the coding region of an mRNA representa kinetic barrier that lowers the peptide elongation rate, as the ribosome must disrupt structures it encounters in the mRNA to allow translocation to the next codon. Such structures are exploited by the cell to create diverse strategies for translation regulation. Although strand separation activity is inherent to the ribosome, requiring no exogenous helicases, its mechanism is still unknown. By using a single-molecule optical tweezers assay to follow in real time the codon-by-codon translation of mRNA...
Mar
06
2012
Short peptides: versatile bricks for nanotechnology
Mar
06
2012
Low-order models for control of fluids
The ability to effectively control a fluid would enable many exciting technological advances, such as the design of quieter, more efficient aircraft.  Model-based feedback control is a particularly attractive approach, but the equations governing the fluid, although known, are typically too complex to apply standard tools for dynamical systems analysis or control synthesis.  This talk addresses model reduction techniques, which are used to simplify existing models, to obtain low-order models tractable enough to be used for analysis and control, while retaining the essential physics.
Mar
05
2012
Nobel Colloquium: Surveying the Accelerating Universe with Supernovae
In 1998 two rival teams of astronomers studying exploding white dwarf stars, called type Ia supernovae, came to the surprising conclusion that the expansion of the Universe is speeding up. This discovery of "the accelerating Universe" ushered in a revolution in our cosmological understanding. I will describe the steps leading to this discovery, and how observations of supernovae from telescopes on the ground and in space can be used to trace the history of cosmic expansion. The continued study of these stellar explosions will shed light on the mysterious "dark energy" that dominates and drives our accelerating Universe.

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