National Institute Of Materials Physics - Romania

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5974 articles found

5441. 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.

5442. 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:

5443. 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.

5444. 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.

5445. PROMOTION OF HIGH-TC PHASE IN B-DOPED (BI,PB)2SR2CA2CU3OY SUPERCONDUCTORS PREPARED BY THE MELT-QUENCHING METHOD

Authors: FRUTH, V; ZAHARESCU, M; ALDICA, G

Published: MAR-JUN 1993, APPLIED SUPERCONDUCTIVITY, 1, 707, DOI: 10.1016/0964-1807(93)90280-F

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.

5446. EFFECT OF THERMAL-TREATMENT AND SWEEPING ON THE ELECTRICAL-CONDUCTIVITY OF QUARTZ CRYSTALS

Authors: ILIESCU, B; TOPA, V; TANASE, AT

Published: 1993, CRYSTAL RESEARCH AND TECHNOLOGY, 28, 1168, DOI: 10.1002/crat.2170280822

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.

5447. MEYER-NELDEL CORRELATION IN SEMICONDUCTORS AND MOTT MINIMUM METALLIC CONDUCTIVITY

Authors: POPESCU, C; STOICA, T

Published: DEC 15 1992, PHYSICAL REVIEW B, 46, 15071, DOI: 10.1103/PhysRevB.46.15063

The paper outlines conditions under which the statistical shift of the Fermi level within the density-of-states (DOS) distribution may result in the Meyer-Neldel correlation. Sufficient conditions have been found: (i) The DOS should have, around the Fermi level, two competing exponential slopes; (ii) The temperature range for the statistical shift should correspond to kT values higher than at least one of these two characteristic energies associated with the slopes. Under such conditions, the Fermi level is no longer the dominant energy for carrier-concentration changes. Relating the Mayer-Neldel correlation to DOS parameters is an essential step in a correct deduction of Mott's minimum-metallic-conductivity value from experiment.

5448. MAGNETIC-PROPERTIES OF XCEO2-(1-X)(3B2O3.PBO) GLASSES

Authors: BURZO, E; ARDELEAN, I; MATULESCU, D

Published: NOV 15 1992, JOURNAL OF MATERIALS SCIENCE LETTERS, 11, 1497, DOI: 10.1007/BF00729270

5449. RADIOACTIVE-WASTE TREATMENT PRODUCTS STUDIED BY MOSSBAUER-SPECTROSCOPY

Authors: SPANU, V; TURCANU, CN; FILOTI, G

Published: NOV 2 1992, JOURNAL OF RADIOANALYTICAL AND NUCLEAR CHEMISTRY-LETTERS, 166, 320, DOI: 10.1007/BF02163837

Mossbauer effect was used for the characterization of the radioactive waste treatment products, e.g. precipitate formed during the treatment of LLAW (Low Level Active Waste) using iron compounds and their conditioned matrix obtained by cementation.

5450. PERIODIC STRUCTURES IN A TWISTED NEMATIC LIQUID-CRYSTAL CELL UNDER DC EXCITATION

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

Published: NOV 1 1992, EUROPHYSICS LETTERS, 20, 411, DOI: 10.1209/0295-5075/20/5/005

Some new results concerning the appearance of a periodic structure in a pi/2-twist cell filled with MBBA under d.c. excitation are reported. This structure consists of rectilinear domains whose orientation varies with the applied voltage around the normal to the molecular orientation in the middle of the cell and this variation covers a large range of angles even for fixed polarity of the excitation. When the polarity is changed, the sense of the domain orientation is also changed.