Events

## SMARTech Video Archive

Mar

29

Topological insulators, a novel kind of three-dimensional insulators can have a bulk insulating gap but non-trivial topological surface states. The surface states of these topological insulators show Dirac-like behavior with the spin polarization locked perpendicular to the electron momentum by the effect of strong spin-orbit interaction. As the locking protects the surface electrons from back scattering, they are predicted to have high mobilities. The surface state of Bi_{2}Se_{3} and Bi_{2}Te_{3} topological insulators has been observed by angle-resolved...

Mar

27

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

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

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

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

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

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

Engineered biological circuits expressed in living cells are becoming increasingly attractive as a technology, with applications...

Mar

13

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

Mar

12

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

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

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

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...