Application of controlled and electrical discharge assisted mechanical alloying for the synthesis of nanocrystalline MgB2 superconducting compound

In this paper we present the results of our efforts to synthesize the nanocrystalline MgB₂ superconducting compound from elemental Mg and B powders by combination of controlled mechanical pre-alloying in a magneto-mill Uni-Ball-Mill 5 under shearing mode followed by electrical discharge (ED) assisted mechanical alloying (MA). There is no conclusive evidence of MgB₂ formation in the Mg-2B mixture using crystalline boron after controlled mechanical alloying (CMA) under protective argon or helium atmosphere as well as subsequent ED assisted alloying. There seems to be some XRD evidence of the strongest (1 0 1) MgB₂ peak presence in the Mg-2B mixture processed using both crystalline and amorphous boron after CMA under hydrogen as well as subsequent ED assisted alloying but this evidence is rather ambiguous. We postulate here that it is highly likely that a certain critical Mg nanograin size must be achieved before a successful reaction to form nanocrystalline MgB₂ is going to be completed. Following recent report by Gümbel et al. [Appl. Phys. Lett. 80 (2002) 2725] this critical value can be roughly estimated at 15 nm or less. Calculations of the Mg nanograin size in the present work show that only three Mg-2B powders ball milled under hydrogen meet this critical nanograin size criterion for the Mg phase. However, a massive formation of the β-MgH₂ hydride in these powders consumes the available Mg in the reaction with hydrogen which may leave inadequate concentration of Mg to form MgB₂ even though the nanograin size of Mg is sufficiently refined, say below 15 nm.     

The finite element solution of laminar combined convection from a horizontal cylinder

The purpose of this investigation is to study the flow and heat-transfer characteristics of laminar combined convection from an isothermal cylinder. The full Navier-Stokes and energy equations are solved by a finite element method. The variations of surface shear stress, pressure and Nusselt number are obtained over the whole cylinder surface including the zone beyond the separation point. The predicted values of the average Nusselt number as well as the angle of separation, and the results of the pressure distribution and the local Nusselt number are compared with the available experimental correlations and previous numerical investigations. The agreement is satisfactory.     

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.     

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.     

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.     

CAMBIO: software for modelling and simulation of bioprocesses

CAMBIO, a software package devoted to bioprocess modelling, which runs on Apollo computers, is described. This software enables bioengineers to easily and interactively design appropriate mathematical models directly from their perception of the process. CAMBIO provides the user with a set of design symbols and mnemonic icons in order to interactively design a functional diagram. This diagram has to exhibit the most relevant components with their related interactions through biological and physico-chemical reactions. Then, CAMBIO automatically generates the dynamical material balance equations of the process in the form of an algebraic-differential system by taking advantage of the knowledge involved in the functional diagram. The model may be used for control design purpose or completed by kinetics expressions with a view to simulation. CAMBIO offers facilities to generate a simulation model (for coding of kinetics, introducing auxiliary variables, etc.). This model is automatically interfaced with a specialized simulation software which allows an immediate visualization of the process dynamical behaviour under various operational conditions (possibly involving feedback control strategies). An example of an application dealing with yeast fermentation is given.     

Order and metric in the stream semantics of elemental concurrency

Summary Two denotational semantics for a language with simple concurrency are presented. The language has parallel composition in the form of the shuffle operation, in addition to the usual sequential concepts including full recursion. Two linear time models, both involving sets of finite and infinite streams, are given. The first model is order-theoretic and based on the Smyth order. The second model employs complete metric spaces. Various technical results are obtained relating the order-theoretic and metric notions. The paper culminates in the proof that the two semantics for the language considered coincide. The paper completes previous investigations of the same language, establishing the equivalence of altogether four semantic models for it.