Photo-optical behaviour of a photosensitive chiral nematic copolymer and mixtures containing non-chiral photoactive azobenzene groups

For the first time, the phenomenon of the light-induced increase in helix pitch length is described for cholesteric polymer systems containing photosensitive non-chiral fragments. This phenomenon is observed for a copolymer and mixtures containing azobenzene fragments which are able to undergo E-Z photoisomerization. In all cases, upon UV irradiation, the selective light reflection maximum is shifted to the long wavelength spectral region. This shift appears to be quite appreciable and, in some cases for mixtures, it might be as high as 300 nm. This process is known to be thermally reversible: upon annealing, the selective light reflection maximum comes back to its initial position. The specific features of the kinetics of this photoprocess were studied, and the fatigue resistance of such systems investigated. The advantages of their application for reversible recording of optical information with a possible non-destructive data reading is outlined.     

Geodesics in Heisenberg Groups

We obtain equations of geodesic lines in Heisenberg groups H²ⁿ⁺¹and prove that the ideal boundary of the Heisenberg group H²ⁿ⁺¹is a sphere S^2n-1with a natural CR-structure and corresponding Carnot-Carathéodory metric, i.e. it is a one-point compactification of the Heisenberg group H^2n-1of the next dimension in a row.