THE PHYSICS GRADUATE PROGRAM invites everyone to the seminar:
Vignettes from the world of liquid crystals
Peter Palffy-Muhoray
Liquid Crystal Institute, Kent State University – USA
Abstract:
Liquid crystals, discovered some 125 years ago, are orientationally ordered soft materials. Although they have received considerable attention – much of it due to their potential for applications in display devices – they continue to astonish, puzzle and delight. In this talk, I will describe some unusual phenomena in liquid crystalline systems which originate in orientational order. I will discuss ideas about the underlying physics, and indicate some intriguing problems that remain unsolved.
Date: 15/July/2015 – (wednesday) – Place: Sala 212 – Auditório do Departamento de Física– Time: 10h15min
THE PHYSICS GRADUATE PROGRAM invites everyone to the seminar:
Gravitational lensing
Gena S. Bisnovatyi-Kogan
Space Research Institute, Russian Academy of Sciences,
Russia and National Research Nuclear University MEPhI, Moscow, Russia
Abstract:
After some historical remarks, we consider observational data on the gravitational lensing, different types of lensing: strong, weak, and microlensing, discovery of planets around distant stars by microlensing. We consider lensing with large deviation angles, when light passes close to the gravitational radius of the lens, and formation of weak relativistic rings. In the last part we consideran influence of plasma on the gravitational lensing. When a gravitating body is surrounded by a plasma, the lensing angle depends on the frequency of the electromagnetic wave, due to dispersion properties of plasma, in presence of a plasma inhomogeneity, and due to a gravity. The second effect leads, even in a uniform plasma, to a difference of the gravitational photon deflection angle from the vacuum case, and to its dependence on the photon frequency. Both effects are taken into account. Dependence of the lensing angle on the photon frequency in a homogeneous plasma resembles the properties of a refractive prism spectrometer, which strongest action is for longest radio waves. We have shown that the gravitational effect could be detected in the case of a hot gas in the gravitational field of a galaxy cluster.
Date: 26/July/2015 – (friday) – Place: Sala 212 – Auditório do Departamento de Física– Time: 10h15min
