Publications

The paper describes the specific quasi-optical phenomena involved in the generation of the high coherent celestial and biological radiation. It examines the generation mechanism of the high coherent radiation in the living systems in the presence of the ambient celestial primordial isotropic background. Josephson and Kerr mechanisms provide an explanation of the concept of bio-coherence as a novel possibility of electromagnetic communication.

The paper describes the investigations of (Zr0.8Sn0.2)TiO4 compounds prepared by solid-state reaction techniques. The effect of La2O3, ZnO and NiO addition on microwave dielectric properties was investigated. The samples were sintered at temperatures T-s = 1280 divided by 1400 degrees C The inaterials exhibit a dielectric constant epsilon(r) similar to 36 and high values of the Q f productfroin 30,000 to 55,000 at microwave frequencies. The measured temperature coefficient of the resonance frequency tau(f) takes values in the range (-2 divided by+4) ppm/degrees C.

This paper reports an investigation of the gas-sensitive properties of thick film sensors based on mixed nanosized oxides (1-x)alpha Fe2O3-XSnO2 (x = 0.1 - 1.0), towards different reducing gases (CH4, CO, H2O). The samples were tested in the range of temperatures (200-400 degrees C). The mixed oxides proved a real sensitivity to CH4, being practically insensitive to detection limit of CO. The maximum response to CH4 takes place at 330 degrees, where the water interference was also studied.

Molecular dynamics of water confined to some molecular sieves is Studied by broadband dielectric spectroscopy (10(-2) to 10(9) Liz). Faujasite as well as molecular sieves with hexagonal cylindrical pores or cellular structure were used as confining matrix. It was found that the mean relaxation time of confined water has unusual non-monotonic saddle-like temperature dependence. Such temperature dependence was interpreted using a model recently developed by Ryabov et al. [J. Phys. Chem. B 2001, 105, 1845] to analyze the dynamics of water in nanoporous glasses. The unusual behavior is the result Of two competing processes: orientational fluctuations the water molecules following all Arrhenius-like temperature dependence and the formation of the defects necessary for this reorientation. The number of defects decreases with increasing the temperature. The temperature dependence of the relaxation time has been proven to be a quite fundamental phenomenon characteristic for water in confining geometries. The defects involved in the dynamics of confined water might be related to the presence of OH groups as defects of the confining framework.

We report an electron paramagnetic resonance (EPR) investigation of the spin dynamics in the paramagnetic regime of nanosized La0.67Ca0.33MnO3-delta manganites. The temperature dependences of the EPR line width and integral intensity have been analyzed in terms of the bottlenecked spin relaxation and small polaron hopping scenarios. The exchange coupling integral between Mn3+ and Mn4+ ions and the polaron activation energy decrease with the reduction of grain size. A discussion is given concerning the factors which could explain the observed changes.

Photoluminescence (PL) spectra of C-60 solutions in N-methyl-2-pyrrolidinone (NMP) show a drastic increase of the PL intensity if the solutions are stored longer periods of time. Two distinct spectral components, one in the red (1.92-2.00 eV) and another in the green (2.18-2.3 eV) were identified in the whole PL emission. Their weights depend on C-60 concentration and on storage time. The two emissions come from two successive processes running with different kinetics. Charge transfer, leading to (C-60, NMP) loose molecular complexes and a slow aggregation process of these entities seems to originate the red and green emission, respectively. Similar PL properties are found when pyrrolidine (P) is used as solvent.

Lead chalcogenides (PbS, PbSe, PbTe) are narrow band gap semiconductors which have been studied in the field of IR detection and thermoelectric devices. The template method is a general approach for synthesizing nanomaterials within the pores of membranes. The membranes employed contain cylindrical pores with monodisperse diameters, and corresponding cylindrical nanostructures are obtained. The aim of the present study was to prepare PbSe1-xTex nanorod arrays using electrodeposition. The process was investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The resulted PbSe1-xTex nanostructures were characterized using scanning electron microscopy (SEM) as well as energy dispersive X-ray analysis (EDAX).