Condensed Matter Physics Seminar: MSc Seminar

Nonlinear scattering of light from dislocations in quadratic nonlinear photonic crystals

Abstract:

The presence of dislocations in materials can affect on their physical properties, therefore it has a significant importance in the study of the properties of materials. 

We studied the effects of topological edge dislocations on the nonlinear scattering of monochromatic light in (2)  photonic crystals. A standard quadratic nonlinear photonic crystal is formed by a one-dimensional periodic modulation of the sign of the relevant component of the second-order susceptibility tensor for the purpose of quasi-phase-matching a nonlinear frequency conversion process. When these periodically modulated crystals contain a single or multiple defects, which their structural topology is characterized by an even, an odd, or a fractional topological charge, their effects are manifested in the nonlinear
conversion efficiency spectrum of a second harmonic generation process. We have found theoretically and demonstrated experimentally that the topological charge governs the energy transfer between an input wave at the fundamental frequency and the generated wave at the second harmonic frequency. In this seminar, I will present the results of the theoretical calculations and experimental measurements of dislocated nonlinear photonic crystals.

Macroscopic dynamics in brain activity of neurological disorders

Abstract:

Statistical physics inspires quantitative measures to study brain activity. Macroscopic observation gives us the ability to understand the behavior of the brain and to develop means for measuring the effects of disorders on normal brain activity. We studied two neurological disorders, epilepsy and fibromyalgia, both are characterized with a wide person to person variability. However, macroscopic variables reveal a universal behavior that can give a new understanding on the processes that lead to the dysfunctions in the brain.
In the study of epilepsy we examined electrocorticogram (ECoG) recordings and developed a method for visualization and analysis of the dynamics and the evolvement of brain states during an epileptic seizure. We also present a statistical clinical trial investigating the effects of hyperbaric oxygen therapy treatment on brain activity of fibromyalgia patients, as measured by single photon emission computed tomography (SPECT) brain imaging. Since the magnitude of normal fluctuations in brain activity related to inherent person-to-person and time variations are comparable to the magnitude of the dysfunctional shift caused by fibromyalgia, our challenge was to reveal the changes in brain activity responsible for the changes in pain sensation by statistical tools. 

Seminar Organizer: Prof. Sasha Gerber