Events Archive

Mar
27
2012
Wet Drop Impact
When a fast moving drop collides with a layer of fluid it a produces a splash, a spray of secondary droplets.  There is a bewildering variety of splash morphologies and droplet distributions which manifest as the system parameters (droplet size and speed, layer depth, fluid properties) are varied.  Despite this complexity, a splash begins with the formation of a sheet-like jet.  There are at least two varieties of jets: the large and slow lamella jet and the small and quick ejecta jet.  In this talk I will present our progress towards understanding the simplest of splashes, the so-called crown splash, which results from the disintegration...
Mar
26
2012
"Smectics!"
The homotopy theory of topological defects in ordered media fails to completely characterize systems with broken translational symmetry. We argue that the problem can be understood in terms of the lack of rotational Goldstone modes in such systems and provide an alternate approach that correctly accounts for the interaction between translations and rotations. Dislocations are associated, as usual, with branch points in a phase field, whereas disclinations arise as critical points and singularities in the phase field. We introduce a three-dimensional model for two-dimensional smectics that clarifies the topology of disclinations and geometrically captures...
Mar
26
2012
Got symmetry? Here is how you slice it
With recent advances in experimental imaging, computational methods, and dynamics insights it is now possible to start charting out the terra incognita explored by turbulence in strongly nonlinear classical field theories, such as fluid flows. In presence of continuous symmetries these solutions sweep out 2- and higher-dimensional manifolds (group orbits) of physically equivalent states, interconnected by a web of still higher-dimensional stable/unstable manifolds, all embedded in the PDE infinite-dimensional state spaces. In order to chart such invariant manifolds, one must first quotient the symmetries, i.e. replace the dynamics on M by an equivalent, symmetry reduced flow on M/G, in...
Mar
22
2012
Gamma-Ray Bursts as Tools for Extragalactic Astrophysics and Cosmology
Gamma-Ray Bursts (GRBs) are the brightest light sources in the Universe, as well as the most distant sources known. These characteristics, combined with their powerlaw spectra, make them ideal cosmological probes. In this talk I will discuss how GRBs are impacting several areas of extragalactic astrophysics and cosmology. In particular, I will show how they can be used to trace the evolution of the mean density and clumpiness of the interstellar medium with redshift, and the properties of dust in high-z galaxies. Detection of GRBs at very high redshifts can help set constraints on the small-scale power spectrum of density fluctuations. High-resolution observations of long GRBs...
Mar
19
2012
Complexity without all the complications: the fruit fly circadian clock as a gateway towards quantitative understanding of complex behavior
In the natural world, complex behaviors such as learning, aggression and sleep are regulated by interconnected networks of genes and their products. Owing to their nontrivial topology and large number of components, most of these networks are poorly understood and consequently, our knowledge of how diverse behaviors arise remains limited. In this talk, I will argue that the fruit fly circadian clock, a genetic circuit that signals to and modulates several key behavioral networks, is an ideal system with which to dissect the fundamental principles that govern organismal...
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...

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