Professor Giorgos Tsironis

Department of Physics, University of Crete, Greece

Abstract: Wave propagation in complex media involves extreme phenomena such as branching and rogue-type waves as well as partial synchronization in the form of chimeras.    We present results from two distinct disordered media where singular wave events may appear.  The first involves wave propagation in optical metamaterial-type units with disorder and strong scattering.  We show both theoretically and experimentally that the coalescence of waves due to strong disorder leads to singular waves.  We present experimental work on silica layers where we use the intensity of the impinging laser light to tune from the linear to the nonlinear regimes.  The experiments show that nonlinearity is not essential in producing the extreme wave events.   The second related problem involves electric current patterns in doped graphene and the onset of branching.  We find theoretically and also numerically a scaling relationship that connects statistically the location of where the first branches occur to the disordered properties of the medium.  We show further that the patterns of the occurrence of branches in graphene may be detected through machine learning.  Specifically we use recurrent neural networks and show that after initial training and while using partial information on the electron flow, the network is able to predict quite accurately the location and properties of the branches.  We propose that machine learning may be used for experimental data reconstruction in graphene and related problems.   

Biography: Giorgos Tsironis got his Ph. D. degree in Physics form the University of Rochester in 1986.  He worked as postdoctoral associate in UC San Diego and Fermilab before becoming assistant professor of physics in North Texas University.  He joined the Department of Physics of the University of Crete in 1994 as associate professor and since 2000 has been professor in this institution. He has held various administrative positions including chairman of the department (2007-2011) and vice rector of the University of Crete (2016-17).  He is currently visiting scholar in the John Paulson School of Engineering and Applied Science of Harvard University.