High Performance Varistor Discs Obtained from Chemically Synthesized Doped Zinc Oxide Powder

The ceramic microstructure, the chemical homogeneity of specific dopants and the mechanical integrity of a varistor disc are critical parameters in determining the transient voltage suppression features of these devices. The material properties and overall quality of the starting ceramic powders used to produce such components are essential in achieving the desired properties. The present work describes a novel chemical method developed to produce doped zinc oxide powders and an industrial scale manufacturing process for the production of final varistor blocks for surge arrester applications. The results are compared with those obtained when using standard varistor powder made by the mixed oxide route is used. All the fundamental electrical properties of the discs have been determined and correlated with the relevant manufacturing steps.     

Environmetric modeling of emission sources for dry and wet precipitation from an urban area

Monitoring data from chemical analysis of rainwater and aerosol samples collected in an urban area have been interpreted by the use of environmetric approaches. An attempt was done to compare the data set structures of both type of precipitation and to estimate the contribution of different anthropogenic and naturally occurring emission sources to the total mass of the wet and dry precipitation. It was found that three latent factors explaining over 80% of the total variance of the set are responsible for the rainwater set structure-'sea spray', 'soil dust', and 'anthropogenic'. Only two were the latent factors explaining the dominant part of the variance in the case of aerosol samples-'anthropogenic' and 'natural'. It is shown that the anthropogenic influence for aerosol samples is more complex that that of rainwater samples and represents interaction between typical anthropogenic sources and natural emitters. Additionally, a source apportioning using multiple regression on absolute principal component scores is performed in order to obtain qualitative information about the impact of the different identified emission sources on the urban environment.     

Stereoselective synthesis of erythro-β-hydroxy carboxylic acids via iron acyl complexes

β-Hydroxy acyl ligands bound to (η⁵-C₅H₅)Fe(CO)(PPh₃) are stereoselectively alkylated on the α-carbon to give after decomplexation erythro-β-hydroxy carboxylic acids.     

Propagation of melting cooperativity along the phosphodiester backbone of DNA

The role of the DNA phosphodiester backbone in the transfer of melting cooperativity between two helical domains was experimentally addressed with a helix-bulge-helix DNA model, in which the bulge consisted of a varying number of either conformationally flexible propanediol or conformationally constrained bicyclic anucleosidic phosphodiester backbone units. We found that structural communication between two double helical domains is transferred along the DNA backbone over the equivalent of ca. 12-20 backbone units, depending on whether there is a symmetric or asymmetric distribution of the anucleosidic units on both strands. We observed that extension of anucleosidic units on one strand only suffices to disrupt cooperativity transfer in a similar way as if extension occurs on both strands, indicating that the length of the longest anucleosidic inset determines cooperativity transfer. Furthermore, conformational rigidity of the sugar unit increases the distance of coopertivity transfer along the phosphodiester backbone. This is especially the case when the units are asymmetrically distributed in both strands.     

Laser-Induced fluorescence detection in conventional-size liquid chromatography with a frequency-doubled argon-ion laser

Laser-induced fluorescence (LIF) detection in conventional-size column liquid chromatography is achieved at 257 nm with a frequency-doubled argon-ion laser. Short-wavelength excitation offers two important advantages: firstly, a wide variety of analytes can be excited, and secondly, the Raman scatter of the eluent does not interfere with the fluorescence of the analytes. A standard mixture of polynuclear aromatic hydrocarbons was studied, both with LIF detection and with a commercially available sensitive conventional fluorescence detector. The improvement in the detection limits ranges from about a factory of 4 to 30; the LIF detection limits are typically at the 50 ng l^?1 level, which corresponds to an injected amount of 0.5 pg.     

Etude de la structure de l'iodatochromate de potassium par spectrographie d'absorption infrarouge entre 3 et 35μ

Résumé Dans le spectre d'absorption infrarouge de l'iodatochromate de potassium K[(CrO₃)(IO₃)], on peut identifier la présence de bandes de vibration de valence de ponts Cr-0-I à 508 et680 cm^–1.

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Summary The infrared absorption spectrum of potassium iodatochromate K(CrO₃)(IO₃) contains vibration bands of the valence bridges Cr-O-I at 508 and 680 cm^–1.

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Zusammenfassung Im Infrarot-Absorptionsspektrum des Kaliumjodatochromats lassen sich Banden der Valenzschwingungen der Atomgruppe Or-O-J bei 508 und 680 cm^–1 nachweisen.

     

Studies of trace element transport in plants using high resolution γ-ray spectroscopy and perturbed directional correlation measurements

Two examples are given to illustrate how modern experimental techniques may extend the scope of possibilities of radiotracer applications. The first example refers to the use of a Ge-detector -ray spectrometer to measure the transport in plants of 15 elements simultaneously. The second example presented is an in-vivo study of the binding of Cd-ions in plants using meansurements of perturbed --directional correlations.     

Amperometric detection of amino acids with a passivated copper electrode

The amperometric behaviour of a copper electrode towards amino acids is studied by means of a rotating disc electrode. A theoretical model describing the anodic background current in a buffer solution and the increase of the current caused by amino acids is checked experimentally. The influences of the amino acid concentration, the rotation speed of the electrode and the composition of the buffer solution are studied. It is proved that chemical dissolution of a passivating film on the electrode surface, which is enhanced by the complexation reaction between the amino acid and copper(II) ions, is the principle of the phenomena observed. The applicability to flow systems is demonstrated.     

Zinc(II) as a versatile template for the design of dipolar and octupolar NLO-phores

Thermally stable dipolar and octupolar (D2d, D3) NLO-phores are readily accessible by combining one, two, or three 4,4'-bis(dialkylaminostyryl)-[2,2']-bipyridyl ligands with zinc(II) salts. The off-resonant beta0 values point out the superiority of octupoles versus dipoles in terms of nonlinearity/transparency tradeoff. The octahedral tris(bipyridyl)zinc(II) complex exhibits a very large beta0 value (241 x 10-30 esu), which is the largest ever reported for octupolar molecules.     

Langmuir films of (alpha-amino) phosphorus amphiphiles on various ion-containing subphases

Monolayers of amphiphilic (alpha-amino)phosphonocarboxylic and (alpha-amino)phosphonic acids have been formed by adsorption at the air/water interface. The influence of both the ionic strength and the pH of the subphase on the stability and compactness of the monolayers have been studied. The stability and the compactness of the Langmuir films are enhanced by introduction of metallic ions such as Ca(2+) or Mg(2+) in the subphases. These effects are more pronounced with Ca(2+). These metal ions can form dimeric complexes with the phosphorus moieties of the surfactant polar heads and therefore bring the amphiphiles closer. For the less hydrophobic derivative, complexation with Ca(2+) or Mg(2+) is required to ensure the formation of a stable monomolecular film. For both phosphonocarboxylic and phosphonic compounds, models have been proposed to represent the complexation phenomenon at the air/water interface.