IR study of chlorination of alumina employing mixtures of gaseous chlorine and carbon monoxide

The chlorination of an alumina with BET surface area of 100 m²/g has been studied in situ by transmission IR measurements at about 670 K. The chlorinating gases consisting of Cl₂ and CO were employed individually and in equimolar proportion. The IR results do not reveal the presence of a phosgene surface species which could support the only mechanism proposed so far to explain the chlorination. A detailed alternative reaction mechanism is suggested for the high temperature chlorination reaction, taking into account the IR results, together with the known electron donor-acceptor properties of the activated alumina and the reaction gases: Cl₂ molecules accept electrons from oxide ions with a lower coordination number on the alumina surface, leading to the formation of Cl^?and O_ad. While Cl^? yields AlCl₃, O_ad reacts further with CO producing CO₂.     

Studies of the stereospecific polymerization mechanism of propylene by a modified Ziegler-Natta catalyst based on 125 MHz 13C n.m.r. spectra

The mechanism of stereospecific polymerization of propylene (catalysed by a modified Ziegler-Natta system, TiCl₄/MgCl₂/C₆H₅COOC₂H₅/Al(C₂H₅)₃), has been analysed using the values of triad and pentad tacticity determined using 125 MHz ¹³C n.m.r. spectroscopy. The well-known single active-site models, such as the Bernoullian, first- and second-Markovian, and enantiomorphic models, were found to be inadequate to describe the observed tacticity. A two-sites model, in which at one site the stereospecific polymerization proceeds in obedience to the Bernoullian model and at the other proceeds under the control of enantiomorphic-site model, is proposed. It was found that the pentad tacticities of both soluble and insoluble (in boiling heptane) fractions of polypropylene agreed well with the two-sites model.     

Chemical and gel electrophoretic characterization of acetylated faba bean protein isolates

The extent of modification of amino and hydroxyl groups in acetylated faba bean protein isolates was determined. Gel electrophoretic studies of unmodified and acetylated faba bean legumin and protein isolates were carried out in acidic and alkaline buffer systems as well as in a SDS-containing system. A remarkable increase of O-acetylation was found after the N-acetylation has reached a degree of about 60%. Structure changes of the proteins were indicated from the gel electrophoresis patterns in the same region of modification. The quantity of acetyl residues fixed on hydroxyl groups in exhaustively modified protein isolates corresponds to 40 % of the total amount of acetyl groups introduced into the proteins. The SDS electrophoresis of the acetylated legumin and protein isolates revealed a remarkable increase of the molecular mass of the acidic α-polypeptide chains only, which is an experimental proof of a preferential acetylation of the latter ones. This gives confirmation of the structural model in which the α-chains are proposed to be situated on the surface of the protein.     

Improvement of nitrogen removal at WWTP Zürich Werdh?elzli after connection of WWTP Zürich-Glatt.

Optimisation of nitrifying activated sludge plants towards nutrient removal (denitrification and enhanced P-removal) leads to a substantial reduction of operating costs and improves effluent and operating conditions. At WWTP Zürich-Werdh?elzli, initially designed for nitrification only, an anoxic zone of 28% of total activated sludge volume was installed and allowed 60% nitrogen elimination besides several other optimisations. In 2001 the operation of WWTP Zürich-Glatt was stopped and the wastewater was connected to WWTP Werdh?elzli. To improve nitrogen removal, WWTP Werdh?elzli co-financed two research projects; one for separate digester supernatant treatment with the anammox process operating two SBRs in series and the other applying NH4 sensors for aeration control in order to decrease energy consumption and raise effluent quality. The results of both projects and the consequences for WWTP Werdh?elzli are discussed in this paper.     

Enhancement of the Sensitivity of Neutrino-Telescope Optical Modules to Cerenkov Light

The results of studies of thin-film wavelength shifters developed for optical modules of large-scale neutrino telescopes are presented. The effect of such wavelength shifters is an increase in the sensitivity of an optical module of the AMANDA neutrino telescope to Cerenkov light of 48%.     

Effect of primaquine on the elimination of sexual forms of Plasmodium falciparum in vivo]

A study was made on 49 patients, carriers of sexual forms of Plasmodium falciparum, verified through thick smear tests, who received 45 and 90 mg of primaquine base in different schedules selected at random. None of the employed schedules proved better than the traditional one of 45 mg base in a unique dose, although the schedule of 45 mg on the first and third days showed a slight reduction of the time of elimination of the parasitemia. Thus, further studies are recommended. No other factors showed an influence on the time of elimination of the parasitemia.     

Limited tryptic hydrolysis of legumin from faba bean (Vicia faba L.): formation of an [unequal] subunit pattern

One-dimensional and two-dimensional SDS-PAGE and Hydrophobic Cluster Analysis (HCA) were used for investigating the course of limited tryptic hydrolysis of faba bean legumin. SDS-PAGE revealed the formation of an “unequal” subunit pattern, characterized by 30 and 50 kDa subunits, which could be related to the A- and B-type subunits of legumin. These subunits followed different pathways during the non-cooperative part of the tryptic hydrolysis. HCA revealed structural differences between the subunit types and gave arguments to predicted potential splitting sites. A- and B-subunits differ in extension and composition of the flexible segments as well as in the interior of the C-terminal side, as in the C-termini of the α-chains which confirmed the observed non-uniform hydrolysis pattern. The HCA plot demonstrated that the number and exposition of flexible surface elements was changed by limited hydrolysis. This result was discussed with regard to the influence of tryptic modification on the emulsifying properties of legumin.     

Dislocation nucleation mechanism and doping effect in p-type ZnSe/GaAs

Nitrogen doped ZnSe/GaAs heterostructures grown at 150 and 250°C were studied by transmission électron microscopy (TEM). The density of threading dislocations and the interfacial dislocation structure in ZnSe/GaAs heterostructures are related to the N-doping concentration. In addition, in-situ TEM heating studies show that Frank partial dislocations formed below critical thickness in N-doped ZnSe/GaAs are the sources for nucleation of a regular array of misfit dislocations at the ZnSe/GaAs interface. By the dissociation of the Frank partial dislocations and interaction reactions between the dislocations, the 60° misfit dislocations form. The Frank partial dislocations bound stacking faults which usually form in pairs at the film/substrate interface. The density of stacking faults increases with increasing N-doping concentration. Thus, at high N-doping levels, the dislocation nucleation sources are close together and not all of the Frank partial dislocations dissociate, so that a high density of threading dislocations results in samples with high N-doping concentrations. The high density of threading dislocations in the ZnSe film are found to be associated with a reduction or saturation of the net carrier density.     

Thermodynamics of heat storage in a PCM shell-and-tube heat exchanger in parallel or in series with a heat engine

This paper addresses the thermodynamics of heat storage in a PCM shell-and-tube heat exchanger, which in a solar power plant is provided to damp the pulsed behaviour of the heat source. Unequal duration of the active and passive phases of the heat source, and consequently of the heat storage and discharge, is allowed. Two alternative schemes of connection of the storage element to the heat engine, referred to as the series and the parallel set-ups, are considered. Using the general framework developed in our previous work, we reformulate the second-law efficiencies for each scheme in terms of a few dimensionless parameters, reflecting the operating conditions of the system and the relevant heat-transfer characteristics of the storage element. For the particular storage system studied in this paper, i.e. the PCM shell-and-tube heat exchanger executing periodic storage-removal cycles, the latter characteristics are determined numerically. A parametric study is conducted to compare the series and parallel schemes with regard to various design objectives.