Showing papers by "Samo Kralj published in 1991"

Nematic-isotropic phase transition in a liquid-crystal droplet

Abstract: Possible phases in a nematic liquid crystal confined to a spherical submicrometer droplet embedded in a solid polymer are analyzed in terms of a Landau--de Gennes theory. For a droplet with a radial structure we show that the strength of the nematic-polymer interfacial interaction affects the nematic-paranematic (partially ordered isotropic phase) phase transition and may in addition induce a boundary-layer nematic phase. This boundary layer phase exists only in a narrow (\ensuremath{\sim}0.1 K) temperature interval above the nematic phase for a restricted range of interfacial interactions. Also in the radial structure the degree of ordering is suppressed close to the center of the droplet where a defect is located. As the size of the droplet decreases, the relative size of this region of suppressed ordering increases. Below a critical radius ${\mathit{R}}_{\mathit{c}}$ (0.22 \ensuremath{\mu}m for 4-n-pentyl-4'-cyanobiphenyl), if the surface interaction is above a critical value (${\mathit{q}}_{\mathrm{max}}$=1.85\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$), the transition between the nematic phase and the paranematic phase no longer occurs. A three-dimensional phase diagram is presented to demonstrate the effect of the surface interaction strength, droplet radius, and sample temperature on the stability of phases within a droplet.

Variability of essential oils of hops, humulus lupulus l.

Abstract: A standard method for distinguishing the essential oils in hops has been developed. Factor, rotation-factor analyses have been used as well as correlation between gas chromatography and organoleptic estimation of aroma. A model for distinguishing 14 groups of oils using 31 descriptors has been developed utilising the variability of components in essential oils. The results are valid for the oils from older established plants, picked at full maturity in Slovenia.