A novel alkylation procedure using MW irradiation for the synthesis of 1,2,3-trisubstituted 1,4,5,6,7,8-hexahydro-1,3-diazocinium salts from their corresponding 1,2-diaryldiazocines

In this work, we describe the synthesis of a series of 1,2,3-trisubstituted-1,4,5,6,7,8-hexahydro-1,3-diazocinium salts (1) by alkylation of the corresponding 1,2-diaryl-1,4,5,6,7,8-hexahydro-1,3-diazocines (2). Compounds 2 were obtained by ethyl polyphosphate-promoted cyclocondensation of N-aroyl-N′-arylpentamethylenediamines (3). Reaction of compounds 2 with alkyl iodides led to 1,2,3-trisubstituted 1,4,5,6,7,8-hexahydro-1,3-diazocinium iodides (1), a new family of cyclic amidinium salts. The best yields for the alkylation were achieved using a mixture of DCM–DMSO (10:1) as solvent. The reaction times of both, the cyclocondensation of compounds 3 and the reaction of 2 with alkyl halides, are dramatically decreased when using microwave irradiation.     

Influence of Ca2+ on tetracycline adsorption on montmorillonite

The adsorption of tetracycline (TC) on montmorillonite was studied as a function of pH and Ca(2+) concentration using a batch technique complemented with X-ray diffraction and transmission electron microscopy. In the absence of Ca(2+), TC adsorption was high at low pH and decreased as the pH increased. In the presence of Ca(2+), at least two different adsorption processes took place in the studied systems, i.e., cation exchange and Ca-bridging. Cation exchange was the prevailing process at pH<5, and thus, TC adsorption decreased by increasing total Ca(2+) concentration. On the contrary, Ca-bridging was the prevailing process at pH>5, and thus, TC adsorption increased by increasing Ca(2+) concentration. The pH 5 represents an isoadsorption pH where both adsorption processes compensate each other. TC adsorption became independent of Ca(2+) concentration at this pH. For TC adsorption on Ca(2+)-montmorillonite in 0.01 M NaCl experiments, the ratio adsorbed TC/retained Ca(2+) was close to 1 in the pH range of 5-9, indicating an important participation of Ca(2+) in the binding of TC to montmorillonite. X-ray diffraction and transmission electron microscopy showed that TC adsorption induced intercalation between montmorillonite layers forming a multiphase system with stacking of layers with and without intercalated TC.     

A cascadic multigrid algorithm for semilinear elliptic problems

Summary. We propose a cascadic multigrid algorithm for a semilinear elliptic problem. The nonlinear equations arising from linear finite element discretizations are solved by Newton's method. Given an approximate solution on the coarsest grid on each finer grid we perform exactly one Newton step taking the approximate solution from the previous grid as initial guess. The Newton systems are solved iteratively by an appropriate smoothing method. We prove that the algorithm yields an approximate solution within the discretization error on the finest grid provided that the start approximation is sufficiently accurate and that the initial grid size is sufficiently small. Moreover, we show that the method has multigrid complexity. Received February 12, 1998 / Revised version received July 22, 1999 / Published online June 8, 2000     

Sensitivity improvement in laser ablation inductively coupled plasma mass spectrometry achieved using a methane/argon and methanol/water/argon mixed gas plasma

The influence of the addition of carbon using methane or methanol/water to an inductively coupled plasma (ICP) via the carrier gas flow on the sensitivity in laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was studied. During the ablation of SRM NIST 610 with simultaneous addition of CH(4) (0.6-1.4 ml min(-1)), a sensitivity enhancement of more than one order of magnitude for selected analytes (e.g. (75)As(+)) was observed. In addition to the sensitivity enhancement for As, Te, I and Se, also all other measured elements showed a significantly enhanced sensitivity (minimum by a factor of 2). Potential mechanisms for the observed intensity enhancement include charge transfer reactions, a change in the ICP shape and a temperature increase in the plasma. Furthermore, the aspiration of a methanol-water mixture into a cooled spray chamber and the simultaneous addition to the laser ablated aerosol was investigated. This type of mixing leads to a sensitivity enhancement up to a factor of 20. To prevent clogging of the sampler cone and skimmer cone by carbon deposition, a fast cleaning procedure for the interface is tested during running ICP, which allows the application of such a set-up for specific applications.     

Mathematics in engineering programs: what teachers with different academic and professional backgrounds bring to the table. An institutional analysis

ABSTRACT

In this paper, we examine how differences in the academic and professional backgrounds of engineering teachers shape their personal relationship to the use of mathematics in engineering practices, and whether these differences affect some of their practices. The analyses herein are based on an institutional perspective and employ Chevallard's anthropological theory of the didactic (ATD). We interviewed two teachers in an engineering programme to identify specific elements of their practice that could be attributable to the mobilisation of knowledge and skills derived from their distinct academic backgrounds and experience. The results indicate that the teachers mobilise different tasks, techniques, and technologies in many of their practices, and that they take different approaches to using mathematics and applying rigour.     

Sorption of galactose by zeolite Y

The sorption of galactose by Na-Y, K-Y and Ba-Y zeolites has been investigated by isopiestic equilibration at 25°C. The equilibrium galactose and water contents of the zeolites were determined for water activitiesa _w in the range 0.111 <a _w < 0.98. It was found that the maximum uptake of galactose U ₀ ^G (observed fora _W 0) was highest for Na-Y and least for Ba-Y. In contrast at high water activities the galactose uptake was highest for Ba-Y and least for Na-Y.