Über Gruppen,insbesondere continuierliche Gruppen von Cremona-Transformationen der Ebene und des Raumes

Ohne ZusammenfassungVortrag, gehalten auf dem internationalen Mathematiker-Congress in Zürich den 10. August 1897.     

Sur les différentes espèces de complexes du 2e dégrè des droites qui coupent harmoniquement deux surfaces du second ordre

Sans résumé     

Cathodically deposited polypyridine films: A novel electroactive polyconjugated polymer

Poly-2,5- and poly-2,6-pyridine coatings have been produced on glassy-carbon electrodes by nickelcatalysed reduction of the corresponding dibromopyridine in acetonitrile. Poly-2,5-pyridine films display two reversible cathodic cycles, one of which is due to nickel ions coordinated to pyridine moieties and the other to the polymeric backbone. Both reductions lead to the polymer changing from the insulating to the conductive state. Conversely, Poly-2,6-pyridine films are not reversibly electroactive and the differences are discussed in terms of conjugation along the polymeric chain.     

First countable extensions of regular spaces

We investigate feebly compact extensions of first countable regular locally feebly compact spaces. Solutions of problems posed by R. M. Stephenson, Jr. and G. M. Reed are given.

     

Evaluation of chlorinated by-products in drinking waters of Central Friuli (Italy)

Drinkable water supplied by aqueducts undergoes preliminar potabilization which, in Italy, is mainly accomplished by chlorine addition. The bactericidal action involved in this process is always accompanied by chlorination and oxidation of organic species (mainly humic and fulvic acids) naturally present in treated waters, so that many disinfection by-products (DBPs) are formed, such as trihalomethanes (THMs) and halo-acetic acids (HAA), which can represent a chemical risk for public health. The aim of this study was the monitoring of DBPs in drinking water disinfected by chlorination, supplied by four different aqueducts of Central Friuli (Italy). DBP evaluations were performed in water samples consisting of both input and output of disinfection plants. The results of analytical determinations were worked out to provide the THM and HAA parameters for disinfected waters, while in feeding waters the following different conventional parameters were adopted: (i) trihalomethanes formation potential (THMFP), (ii) halo-acetic acids formation potential (HAAFP) and (iii) UV absorbance at 254 nm (UV254). The quite moderate content of chlorinated products found in all samples considered highlighted the excellent quality of potabilized waters available in Central Friuli. Moreover, our results confirmed that the majority of DBPs formed when chlorine is used for water disinfection consists of THMs, while chlorites and chlorates prevailed when potabilization is accomplished by using chlorine dioxide. Finally, simple UV254 monitoring turned out to be a profitable approach for the determination of chlorinated by-products only when THMs prevail among DBPs.     

Acid-base equilibria in organic solvents : Part 3. An Absolute pH Scale from Proton Basicity Evaluated by Cyclic Voltammetry

The relative basicity of some organic solvents of electroanalytical interest (propylene carbonate, sulfolane, 2-methyltetrahydrofuran, methyl formate and morpholine) is evaluated by cyclic voltammetry. Anhydrous perchloric acid is electrogenerated in these solvents and the half-wave potentials of the redox couple H⁺/H₂ are recorded by referring them to a reference system, here bis(biphenyl)chromium (I)/bis(biphenyl)chromium(0), which is independent of the nature of the solvent. The data obtained, together with those found previously for other solvents by following the same procedure, are used to draw an absolute pH scale covering a wide range of basicities from nitromethane to morpholine. The same approach is also utilized to evaluate and compare, on the basis of this absolute pH scale, the strength in the solvents studied of some nitrogen bases which are suitable as titrants in nonaqueous media. The proposed proton basicity scale is compared with other basicity series defined in the literature.