Events Archive

Mar
15
2012
Probing the Missing Baryons
Most of the baryons in the present universe are missing. This talk gives a historical review of the issue, followed by some highlights of current theoretical and observational effort to understand it.
Mar
14
2012
Synthetic Biology: Clocks, Queues, and Crowds
Engineered biological circuits expressed in living cells are becoming increasingly attractive as a technology, with applications...
Mar
13
2012
Physics of colloids in action
This talk will describe new results on the properties of colloidal crystals, both on their solidification and on their melting.  It will describe how hard-sphere like colloids crystallize, and will explore the huge discrepancy between the nucleation rates predicted by theory and measured in simulation and those measured experimentally.  The discrepancy can be as large as 150 orders of magnitude!  A simple modification to the theory, suggested by experiment, is able to account for this behavior and to rectify the discrepancy....
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...

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