Publications

Local and global scaling properties of the integrated density of states of the tight-binding Rudin-Shapiro model are numerically derived by investigating the dependence of the bandwidths of its periodic approximants on the size of the unit cells. Scaling relations intermediate between the power and exponential laws are found for various values of the energy and amplitude of the on-site potential V. An analysis of the global properties of the spectrum performed in the case when V is equal to the hopping integral t points out its multifractal structure. Multifractal arguments together with earlier results concerning the nature of the wave functions indicate a pure point spectrum for V greater t, while for smaller values of the amplitude V the spectrum reveals a mixed character.

A model for the interaction between CO and an SnO2 surface, which takes into account the role of water vapour, is presented. An assumption, supported by literature data, about the interaction of water vapour with the SnO2 surface as a generating process of chemisorption sites for oxygen is made. By means of the quasi-chemical reaction formalism and of an originally written rule of conservation of the number of electrons, we find an equation in agreement with experimental data. We conclude that in the conditions in which the model is valid (working temperature of about 600 K, etc.) the reacting chemisorbed species of oxygen is doubly ionized oxygen atoms and that their interaction with reducing gases is enhanced by the presence of water vapour.

Characterization of (Fe1-xNix)3C and (Fe1-xCOx)3C identified in metallic inclusions in synthetic diamond crystals grown in Fe-Ni-C and Fe-Co-C systems at a pressure of approximately 5.5 GPa and a temperature of approximately 1800 K was carried out using X-ray microprobe analysis, X-ray diffraction, hardness data, Mossbauer and magnetic measurements. The result suggests that in (Fe1-xCox)3C, metallic atoms have an electronic structure similar to that of Co.

The use of IR spectroscopic method to choose the best batches of ZSM-5 zeolites. is discussed. The crystallinity and the particle size were estimated from IR spectra and by XRD and electron microscopy measurements.

An analysis of the permitted structures for a cholesteric liquid crystal based on the continuum theory as a function of the anchoring conditions and the thickness of the liquid crystal layer is presented. A new type of bistability is found. The stability domains of various structure types are given.

In quasi-homeotropic oriented liquid crystal cells, obtained by oblique SiO deposition on glass and surfactant added to the nematic, a continuous tilt angle versus temperature change followed by an abrupt surface transition was observed. At room temperature, the sip of the tilt angle measured from the normal to the surface depends on the SiO deposition angle. A model for the temperature dependence of the tilt angle is proposed.

A new method for producing tilt angle in liquid crystal cells is proposed. The method requires a SiO vacuum deposition layer which is subsequently covered with a polyvinyl alcohol (PVA) layer, obtained by dipping in a solution. It was possible to obtain tilt angles between 7 and 30-degrees by changing the concentration of PVA in the solution.

We prepared superconducting Bi1.6Pb0.4-xBxSr2Ca2CU3Oy (x=0, 0.1, 0.2, 0.3 and 0.4) ceramics by the melt-quenching method and examined the effect of B addition on the formation of the high-Tc phase.The temperatures and sequence of formation of the superconducting phases within this composition were determined using simultaneous differential thermal analysis (DTA) and thermogravimetric analysis (TGA), X- ray powder diffraction (XRD). It was found that the bulk ceramics with x=0.1 and 0.2 exhibited superconductivity with a critical temperature range of 95-100 K. The lowering of the partial melting temperature caused by the coexistence of Pb and B elements is effective for the formation mechanism of the high-Tc phase.

The effect of thermal treatment and sweeping at different temperatures on the current peaks occurring during the heating-up phase of the electrodiffusion runs are studied. Arrhenius plots of swept synthetic quartz are discussed.