10:00 AM Friday, August 27, 1999 (my thesis defense!)
Jefferson Laboratory, Rm 456
Harvard University
ABSTRACT :We demonstrate experimentally the existence and significance of diffractive orbits in an open microwave billiard. Orbits that diffract off of a sharp edge strongly influence the conduction spectrum, especially in the regime where there are no stable classical orbits. On resonance, the wavefunctions are influenced by both classical and diffractive orbits. Off resonance, the wavefunctions are determined by the constructive interference of multiple transient orbits. The experimental results agree well with quantum computations and with a semiclassical theory that incorporates diffraction.
2:00 PM Wednesday, October 28, 1998
Lyman Laboratory, Rm. 330
Harvard University
ABSTRACT :Traditionally, the point scatterer model has only been applied to problems of low energy scattering. The reason for this is that the model has, up to now, only been capable of reproducing the s-wave scattering of a given potential. Here I will present a method for incorporating higher partial waves into the model. In principle, one can then solve for the multiple scattering of a particle on any number of finite range, non-overlapping potentials, at any incident energy. This solution involves simple algebraic matrix inversion techniques, instead of the coupled integral equations that one would normally be faced with in such a multiple scattering problem. I show how the boundary condition of psi = 0 on the surface of a hard disc can be reduced to an effective boundary condtion at the center, thus reducing a three dimensional problem to a zero dimensional problem.
4:00 PM Wednesday, September 30, 1998
Phillips Auditorium
Harvard-Smithsonian Center for Astrophysics
ABSTRACT :A system of two neighboring square wells in three dimensions is investigated for scattering resonances near threshold. The well parameters are chosen such that each well has a single bound state close to threshold. It is found that a narrow, low energy p-wave resonance appears suddenly in the scattering cross section as the distance between the wells is varied. A further surprising feature, namely, the disappearance of the low energy s-wave cross section of the combined system as the wells approach each other, is discussed. All results are in good agreement with the point scatterer model.
"Observation of proximity resonances in a parallel-plate waveguide"
2:30 PM Wednesday, June 24, 1998
Jefferson Laboratory Rm. 356
Harvard University
ABSTRACT :Experiments with dielectric scatterers in a parallel-plate waveguide have verified for the first time the existence of proximity resonances in two dimensions. A numerical solution to the scattering problem supports the analysis of the experimental data.
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