Events Archive

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.
Feb
24
2012
Diffusion and weak ergodicity breaking within living cells
Diffusion of single molecules and organelles in living cells has attracted considerable interest. The motion so essential for intra- and intercellular transport, regulation, and signaling, and hence for the life within cells exhibits surprising deviations from normal Brownian motion. Using optical tweezers combined with single particle tracking inside living cellular organisms we study intracellular diffusion of nano-sized organelles inside living cells. The temperature increase caused by absorption by the laser light as well as the potential physiological damage are important also to consider and will be addressed [1,2]. Lipid granules inside living...
Feb
24
2012
"Shocks in fragile matter"
In ordinary solids, acoustic shocks are extreme mechanical phenomena: they occur when rigid materials are subjected to violent impacts. But in soft materials things are different. Granular media, foams and polymer networks can all be prepared in a state of vanishing rigidity in which even the tiniest perturbation elicits an extreme mechanical response. When that happens these materials are not just soft, they have become fragile. In this talk, we present simulations in which two-dimensional jammed granular packings are dynamically compressed, and demonstrate that the elementary excitations are strongly nonlinear shocks, rather than ordinary...
Feb
23
2012
Angular momentum, stability and fragmentation in 3D attractive Bose-Einstein condensates
Trapped attractive atomic Bose-Einstein condensates (BECs) in three spatial dimensions are known to exist for some finite time only. This is because the gas is prone to self-collapse, due to the attractive nature of the interaction. The 'mainstream' way to describe the state of the condensate is a mean-field (MF) theory, that assumes total condensation of the system.  In this talk I will introduce the notion of fragmentation, in contrast to coherence, and show that the states of definite angular momentum of the 3D many-body system cannot be condensed MF states. With this at hand, I examine the impact of the angular momentum to the stability of the attractive gas and show that there...
Feb
22
2012
Stochasticity in gene expression and its regulation by non-coding RNAs
One of the fundamental problems in biology is understanding how phenotypic variations arise in individuals. Phenotypic variation is generally attributed to genetic or environmental factors. However, in several important cases, phenotypic variations are observed even among genetically identical cells in homogeneous environments. Recent research indicates that such `non-genetic individuality' can arise due to intrinsic stochasticity in the process of gene expression. Correspondingly there is a need to develop a framework for quantitative modeling of stochastic gene expression and its regulation. Of particular interest is modeling of regulation by non-coding...
Feb
21
2012
Fish robotics: understanding the diversity of fish locomotion using mechanical devices
There are over 28,000 species of fishes, and a key feature of this remarkable evolutionary diversity is a great variety of propulsive systems used by fishes for maneuvering in the aquatic environment.  Fishes have numerous control surfaces (fins) which act to transfer momentum to the surrounding fluid.  In this presentation I will discuss the results of recent experimental kinematic and hydrodynamic studies of fish fin function, and their implications for the construction of robotic models of fishes.  Recent high-resolution video...

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