Events Archive

Oct
12
2012
Science and a Journey of Extremes
Physicist and adventurer Francis Slakey describes his decade long journey that led to his becoming the first person to both summit the highest mountain on every continent and surf every ocean.  The talk reviews some of the people he encounters and the challenges he endures – a Lama who gives him an amulet etched with “life’s meaning”, an ambush in the jungles of Indonesia, a life-or-death choice atop Everest – that culminate in a recognition that science is the most powerful tool we have to...
Oct
11
2012
GRB Studies in the GeV Band
Gamma-ray bursts (GRBs) have been shown by the Fermi LAT to be a source of gamma rays with energies as high as ~100 GeV in the rest frame. Detection at higher energies may be possible with next-generation ground-based instruments. I will present results from a new simulation of GRB detections with the upcoming Cherenkov Telescope Array (CTA), using models based on the combined observations of Fermi LAT and lower-energy satellite experiments. This simulation allows the prediction of the overall detection rate, how this rate might vary as a function of telescope performance and uncertain GRB statistical properties, and the likely properties of detected GRBs. I will also show a preliminary...
Oct
11
2012
Diatomic Molecules as Quantum Tools
Our group is applying the techniques of modern atomic physics to the system of diatomic molecules.  Molecules are more complex than atoms because of their vibrational and rotational degrees of freedom, and this makes them difficult to control.  However, we have identified a variety of simple principles that allow us to make use of these "new" properties to provide powerful types of leverage on a broad range of problems.  These span...
Oct
09
2012
Geometry-induced rigidity and functionality in thin elastic shells
I will present some recent results from our Lab on the mechanical response of complex-shaped shells subject to loading and in different mechanical environments (with or without an in-out pressure difference). A powerful aspect of our experimental approach is that the geometry and material properties of our shells can be accurately custom-controlled using digital rapid prototyping techniques. First, we focus on the linear response of non-spherical shells under indentation to explore the new concept of geometry-induced rigidity. Despite the complex geometries, we find a remarkable predictive description. Moreover, we investigate universal modes of localization...
Oct
08
2012
Topological Insulator Heterostructures: Searching for Exotic Particles on a Bench Top
A triumph of contemporary physics is the highly successful description of the most fundamental constituents of Nature and their excitations. Recent theories of “topological insulators” [1,2] have shown that in the complex and emergent world of condensed matter physics, one can engineer the interplay between fundamental symmetries, band structure and spin-orbit coupling to create novel energy-spin-momentum relationships for band electrons and to yield effective realizations of exotic particles predicted but yet unobserved in Nature.  This Colloquium will describe the experimental routes we are pursuing in this context to build "detectors" for such particles, by...
Oct
04
2012
IceCube Results from GRB Neutrino Searches
Cosmic rays have been observed on Earth with energies in excess of 10^20 eV. Because cosmic rays are charged particles and are bent by galactic magnetic fields, the origin of these particles has remained a mystery. Gamma-ray bursts are one of a few astronomical sources containing an environment capable of accelerating charged particles to the energies observed. In addition, gamma-ray bursts are the leading candidate due to the fact that the total aggregate power observed in gamma-ray bursts and ultra high energy cosmic rays are the same order of magnitude. Neutrinos can only be created by hadronic interactions, so an observation of neutrinos in coincidence with a gamma-ray burst would...
Oct
02
2012
Mechanical communication between cells and substrates
Cells are sensitive to mechanical signals produced either by application of exogenous force, or by the resistance to cell-generated forces caused by the viscoelastic properties of the materials to which they adhere. The range of stiffness over which different cell types respond can vary over a wide range and generally reflects the elastic modulus of the tissue from which these cells were isolated. Many cell types can alter their own stiffness to match that of the substrate to which they adhere. The maximal elastic modulus that cells can attain is similar to that of crosslinked actin networks at the concentrations in the cell cortex...
Oct
01
2012
Physics of the Piano
Why does a piano sound like a piano? A similar question can be asked of virtually all musical instruments. A particular note, such as middle C, can be produced by a piano, a violin, and a clarinet.  Yet, it is easy for even a musically untrained listener to distinguish between these instruments.  One would like to understand why the sound of the “same” note depends greatly on the instrument.  In particular, we would like to understand what aspects of the piano are most critical in...
Sep
27
2012
Exploring novel quantum few- and many-body physics by quantum simulation
Recent cold atom researches are reaching out far beyond the realm that was conventionally viewed as atomic physics. Many long standing issues in other...
Sep
24
2012
Packing & Assembling Polyhedra: New directions in colloidal matter
Entropy can order shapes into complex structures, even in the absence of explicit attractive forces. As such, shape is important in the self assembly and crystallization of colloids, nanoparticles, proteins and viruses, and in the packing of granular matter.  Using computer simulations of nearly 200 different hard polyhedra, including families of tetrahedra, we demonstrate the emergence of entropic bonds and show how simple measures of building block shape and local order in fluid phases can predict crystals and quasicrystals, liquid crystals, rotator crystals, and glasses.  From these findings, we propose design rules for entropically patchy particles.

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