Two persons at the department were awarded the degree of 'oavlönad docent' during 94/95.
Nicholas Apazidis
The title of the Docent lecture, given on October 28, was:
Geometrical approach to shock wave focusing in liquids
Abstract:
Analytical and numerical work describing propagation, reflection and
focusing of shock waves in confined chambers filled with liquid is
presented. The problem of shock wave focusing occupies an important place
within the area of shock wave research. Applications of the shock wave
focusing are closely related to such engineering problems as cavitation and
erosion. The spectacular effect of sonoluminescence - production of light
from sound - during the process of cavitation of gas bubbles is a topic of
extensive experimental and theoretical research. In the medical field the
gall, kidney and bladder stone disintegration by means of shock wave
focusing has been practiced during the last decade in world-wide range.
The problem of shock wave focusing is approached from the geometrical
point of view. This means that instead of attempting to solve the boundary
value problem in the total flow domain one searches for the solution in the
vicinity of the propagating wavefront. This approach of shock wave tracking
turns out to be a powerful tool in the analysis of shock wave propagation
in various complex geometries. Both linear and non-linear theories of
geometrical acoustics and geometrical shock dynamics by Whitham are applied
to various flow situations. The results of the calculations describe
elliptic and parabolic shock reflectors that are able to produce
cylindrical or plane shock waves with a desirable pressure distribution
along the shockfront. Also shock reflectors producing shocks of arbitrary
polygonal shapes are investigated.
Per Dahlqvist
The title of the Docent lecture, given on May 5, was:
Three trends in quantum chaos
Abstract:
We review three main lines in the area of research called
quantum chaos. The first focus on the correspondance principle and try
to explain how classical chaos is revealed in a quantum system when
Planck's constant tends to zero. It turns out, however, that this
question cannot be answered without taking the systems interaction with
the environment into account. The second, more modest line of research
studies behaviour of quantum spectra and eigenfunctions if the
corresponding classical system is chaotic. There are striking numerical
evidence for universal signals of chaos but poor theoretical
understanding. The third 'trend' involves modern semiclassical methods
for calculating spectra. The methods deals with classical periodic
orbits. Their multitude disables one to pursue the computations into
the semiclassical regime. We briefly discuss the need for periodic
orbit asymptotics and the possibility to derive level statistics from
the classical behaviour of the system. The talk is intended for
non-experts in the field.