SIMON FRASER UNIVERSITY DEPT. OF PHYSICS STUDENT SEMINAR

Friday, Oct 5, 2001 @ 2:00 PM Room K 9500

Carl Kübler
Dept. of Physics, SFU

Title: When Physics goes nuts - Cracking the Brazil nut problem

The behavior of granular materials like sand, powder or grain is 
often surprising, illustrating our limited understanding of 
dissipative many particle systems. A classic problem from the field 
of granular matter physics which has recently attracted new interest 
is the Brazil nut problem (BNP).  If you open a bag of mixed nuts, 
the large nuts are typically found on top and the small ones at the 
bottom. However three years ago the inverse-effect  (reversed BNP) 
was discovered experimentally. In my talk I will discuss a very 
interesting model proposed by Hong, Quinn and Luding (PRL 86, 3423) 
in April of this year, which provides the first unified description 
of these two effects.

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SIMON FRASER UNIVERSITY DEPT. OF PHYSICS STUDENT SEMINAR

Friday, Oct 5, 2001 @ 2:30 PM Room K 9500

Geoff Archibald
Dept. of Physics, SFU

Title: Left-Handed Metamaterials and Their Electromagnetic Properties

In 1964 Victor Veselago performed a thought experiment in which he
imagined how electromagnetic radiation would behave in a material that has
both a negative permittivity and a negative permeability.  This medium, if
it existed, would be left handed; it would have a negative index of
refraction and would exhibit the inverse of the Doppler effect. Cerenkov
radiation would even be emitted backwards from this material.  At the time
it was believed that such a material could not exist.  Recently a group at
the University of California in San Diego have constructed a composite
material which is left-handed.  This left-handed metamaterial (LHM) uses a
periodic array of split ring resonators and thin wires to realize a
negative effective permeability and negative effective permittivity.  The
lattice spacing of the resonators and the wires is much smaller than the
wavelength of the incident radiation so that the radiation sees an average
permeability and permittivity over many unit cells.  In this talk I will
discuss how the left-handedness is achieved and some of the interesting
properties of left-handed media.

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SFU DEPT OF PHYSICS COLLOQUIUM

Friday, Oct 5, 2001 @ 3:30 PM Room K 9500

G.T. Seidler,
University of Washington, Seattle WA

Title: Sandpiles, Strings, and Curved Space

The granular bed, or colloquially the sandpile, has become one of the
favorite systems of condensed matter physics, exhibiting geometric
frustration, nonlinear response, and self-organization.  Any fundamental
understanding of the transport and mechanical properties of mesoscale
disordered materials (such as sandpiles) must follow from a thorough
understanding of their structure.  However, in the overwhelming majority
of cases, experimental characterization of mesoscale materials has been
limited to first- and second-order structural correlation functions,
i.e. the mean filling fraction and the structural autocorrelation
function.  I will discuss the combination of synchrotron x-ray
microtomography and 3-d image processing to perform 3-d virtual
reconstructions of real sandpiles.  This complete knowledge of structure
will be used to compare and contrast two very different theoretical
approaches to the statistical mechanics of the random dense packing of
spheres.  One of these theories intimately connects global structure and
local dynamics in a phase diagram for sphere packings, while the other
proposes that sandpiles may join nematic liquid crystals and superfluid
helium as tabletop systems exhibiting topological defects analogous to
cosmic strings.