National Institute Of Materials Physics - Romania

Publications

5840 articles found

5301. SPECTROSCOPY OF MN-2+ IONS IN CDCL2

Authors: GHIORDANESCU, V; VODA, M; PEDRINI, C

Published: APR 16 1993, CHEMICAL PHYSICS LETTERS, 205, 414, DOI: 10.1016/0009-2614(93)87143-Q

An investigation of ultraviolet absorption and excitation spectra of Cd1-xMnCl2 Crystals is reported. At lower temperatures, T < 77 K, it is shown that a number of lines are associated with the manganese ions. No assignments are given for room temperature excitation spectra because the Mn2+ states are in the fundamental absorption edge.

5302. EXISTENCE OF EXPONENTIALLY LOCALIZED WANNIER FUNCTIONS FOR NONPERIODIC SYSTEMS

Authors: NENCIU, A; NENCIU, G

Published: APR 15 1993, PHYSICAL REVIEW B, 47, 10115, DOI: 10.1103/PhysRevB.47.10112

For a large class of nonperiodic systems, exponentially localized Wannier functions, associated with isolated parts of the energy spectrum, are proved to exist.

5303. UNUSUAL SCALING OF THE SPECTRUM IN A DETERMINISTIC APERIODIC TIGHT-BINDING MODEL

Authors: DULEA, M; JOHANSSON, M; RIKLUND, R

Published: APR 1 1993, PHYSICAL REVIEW B, 47, 8551, DOI: 10.1103/PhysRevB.47.8547

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.

5304. THE MECHANISM OF THE INTERACTION BETWEEN CO AND AN SNO2 SURFACE - THE ROLE OF WATER-VAPOR

Authors: BARSAN, N; IONESCU, R

Published: MAR 15 1993, SENSORS AND ACTUATORS B-CHEMICAL, 12, 75, DOI: 10.1016/0925-4005(93)85017-5

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.

5305. COMPLEX CARBIDES IN SYNTHETIC DIAMOND CRYSTALS PRODUCED AT SIMILAR-TO 5.5 GPA

Authors: PAVEL, E; BALUTA, G; BARB, D; LAZAR, DP; MORARIU, M; POPESCU, M; SORESCU, M

Published: MAR 15 1993, JOURNAL OF MATERIALS SCIENCE, 28, 1647, DOI: 10.1007/BF00363361

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.

5306. IR SPECTROSCOPIC MEASUREMENTS OF CRYSTALLINITY AND PHASE PURITY OF ZSM-5 SAMPLES

Authors: FRUNZA, L; DINCA, V; VAGAON, M; CRISAN, D; FLORESCU, I; MANOIU, D; CRISAN, M; RAGAN, N

Published: MAR 1993, REVUE ROUMAINE DE CHIMIE, 38, 246, DOI:

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.

5307. STABILITY OF SOME STRUCTURES IN A CHOLESTERIC LIQUID-CRYSTAL LAYER FOR TILTED ANCHORING

Authors: BEICA, T; FRUNZA, S; MOLDOVAN, R; GIURGEA, M; TINTARU, M

Published: JAN 1993, LIQUID CRYSTALS, 13, 138, DOI: 10.1080/02678299308029059

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.

5308. 8-POLE MONOLITHIC FILTERS USING LITHIUM TANTALATE

Authors: MATEESCU, I; KOSINSKI, J

Published: 1993, PROCEEDINGS OF THE 1993 IEEE INTERNATIONAL FREQUENCY CONTROL SYMPOSIUM, 625, DOI:

5309. INFLUENCE OF THE SURFACE-TOPOGRAPHY ON THE SURFACE TRANSITIONS IN NEMATICS

Authors: BARBERO, G; BEICA, T; ALEXEIONESCU, AL; MOLDOVAN, R

Published: 1993, LIQUID CRYSTALS, 14, 1134, DOI: 10.1080/02678299308027820

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.

5310. ORIENTATIONAL PROPERTIES OF PVA COATED SIO FILMS

Authors: FRUNZA, S; MOLDOVAN, R; BEICA, T; STOENESCU, D; TINTARU, M

Published: 1993, LIQUID CRYSTALS, 14, 296, DOI: 10.1080/02678299308027643

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.