ANNUAL REPORT - MTA SzFKI

Fig. 1. ns-EC to s-EC transition induced (a) by increase of the temperature T (polarizing microscopy); (b) by
increase of the voltage U (light diffraction fringes). n denotes the initial director.
Interactions at liquid crystal surfaces. — Experiments on director gliding have been
carried out on Arabic gum and glucose layers. On Arabic gum flow alignment has been
detected with permanent director orientation, while on glucose layers gliding has been
found, which has speeded up above the glass-transition temperature of the glucose (32 o C).
According to the first measurements, the distribution of relaxation times of the gliding
process is much narrower for glucose than on corresponding polymer layers.
Granular flow. — The flow properties of a granular layer of thickness h on an inclined
plane (inclination angle θ) can be characterized by the so called flow rule, which describes
the thickness dependence of the surface velocity u. The flow rule of granular flows on a
rough inclined plane has been measured for various materials, including sand and glass
beads of various sizes and four types of copper particles with different shapes. The
materials have been characterized by measuring h s , the thickness at which the flow stops,
as a function of the plane inclination on various surfaces. Measuring the surface velocity u
of the gravity induced flow as a function of the flow thickness h, deviations from the
Pouliquen flow rule u/(gh) 0.5 ~h/h s have been detected for sand and glass beads. An
improved collapse of the experimental data has been obtained by using a recently proposed
scaling of the form u/(gh) 0.5 =β htan 2 θ/h s tan 2 θ 1 where θ 1 is the angle at which the h s curves
diverge. Measuring the slope β for ten different sizes of sand and glass beads, we find a
systematic, strong increase of β with the divergence angle θ 1 . Copper materials with
different shapes could not well be described by either flow rule.
E-Mail:
Tamás Börzsönyi btamas@szfki.hu
Ágnes Buka ab@szfki.hu
Nándor Éber eber@szfki.hu
Katalin Fodor-Csorba fodor@szfki.hu
István Jánossy janossy@szfki.hu
Tibor Tóth-Katona katona@szfki.hu
Anikó Vajda vajda@szfki.hu
30