Highly active new α-diimine nickel catalyst for the polymerization of α-olefins

A new silylated α-diimine ligand, bis[N,N′-(4-tert-butyl-diphenylsilyl-2,6-diisopropylphenyl)imino]acenaphthene 3, and its corresponding Ni(II) complex, {bis[N,N′-(4-tert-butyl-diphenylsilyl-2,6-diisopropylphenyl)imino]acenaphthene}dibromonickel 4, have been synthesized and characterized. The crystal structures of 3 and 4 were determined by X-ray crystallography. In the solid state, complex 4 is a dimer with two bridging Br ligands linking the two nickel centers, which have square pyramidal geometries. Complex 4, activated either by diethylaluminum chloride (DEAC) or methylaluminoxane (MAO) produces very active catalyst systems for the polymerization of ethylene and moderately active for the polymerization of propylene. The activity values are in the order of magnitude of 10⁷ g PE (mol Ni [E] h)⁻¹ for the polymerization of ethylene and of 10⁵ g PP (mol Ni [P] h)⁻¹ for the polymerization of propylene. NMR analysis shows that branched polyethylenes (PE) are obtained at room or higher temperatures and almost linear PE is obtained at 0 °C with 4/DEAC.     

Stimulated Brillouin scattering as the referencing mechanism of an optical fibre intensity sensor

An optical fibre intensity sensor referenced by stimulated Brillouin scattering is presented. The optical sensor uses Fresnel reflection signal at the sensor fibre end and employs an adequate relationship between Brillouin and Rayleigh scattering and Fresnel reflection to have a referenced optical fibre intensity sensor addressed in reflection.     

Diiso­propyl­phosphitocobalamin–acetone–water (1/3.48/7.56)

The di­iso­propyl­phosphite ligand in the title diiso­propyl­phosphitocobalamin compound, [Co(C₆₈H₁₀₂N₁₃O₁₇P₂)]·3.48C₃H₆O·7.56H₂O, coordinates to the Co^III atom via its P atom. The crystal structure is isomorphous with that of other cobalamins that adopt packing type II [Gruber, Jogl, Klintschar & Kratky (1998). Vitamin B₁₂ and B₁₂ Proteins, edited by Kräutler, Arigoni & Golding, pp. 335–347. New York: Wiley–VCH], with a Co—P bond length [2.227 (1) Å] similar to that found in other phosphitocobalamins. The structural trans influence in cobalamins is discussed.     

The finite-temperature photoluminescence correlation function in semiconductor heterostructures

We report the inclusion of temperature effects on the Mahan-Nozières-De Dominicis framework to study both many-body and temperature effects in photoluminescence spectra of doped semiconductors. The electronic part of the correlation function characterizes the photoluminescence spectra. We have treated the optical valence hole as a localized scattering potential center and studied effects of the electron-hole interaction enhancement on the photoluminescence spectra leading to the appearance of shake-up structures. We also have identified a term in the correlation function which represents the finite-temperature contribution to the intensities of the shake-up structures. The method is used to study the magnetophotoluminescence of modulation-doped quantum wells with a weak periodic lateral potential. Received 20 November 1998 and Received in final form 5 March 1999     

Colorimetric methodology for monitoring the cellulose insulating paper degradation in electrical equipments filled with mineral oil

During the operation of electrical equipments the compound 2-furfuraldehyde (2-FAL) and other related furanic substances are produced from the insulating paper degradation and can be detected in the mineral oil by high performance liquid chromatography (HPLC). Their concentration increase can be used to estimate the quality of the paper insulation inside the equipments. In this work colorimetric methodologies for quantification of these furanic degradation products in oil filled electrical equipment were evaluated. Two analytical methods were studied using aniline and modified Winkler’s reactions. For this purpose used oil samples and 2-FAL standard oil solutions were analyzed and the results for both methods were compared with HPLC analysis. The obtained results for 2-FAL standard oil solutions were in accordance with both methodologies. The results obtained for used mineral oil showed that the analysis of furanic compounds by the colorimetric methods may induce to false positive results due to the interference of oil oxidation by-products in the quantitative analysis.