General Electric (Netherlands)

In 2006 the desmid flora of Lake Nabugabo and some adjacent peat bogs was studied. All in total some 108 taxa were identified. Fourteen taxa, most of them being only known from the African continent, are discussed in detail. Six taxa are newly described: Euastrum gemmatum var. quadrituberosum, Micrasterias stuhlmannii var. nabugabonum, Cosmarium nabugabonum, Xanthidium thomassonii, Staurodesmus eckertii var. africanus and Staurastrum capitulum var. foersteri. The morphological variation found in Staurastrum longicolle is discussed in the light of possible speciation of desmids in a limnetic environment.

Redistribution of poly(2,6-dimethyl-1,4-phenylene ether) (PPE) with a phenolic compound yields a depolymerized polymer having the phenolic compound incorporated as the tail end. The molecular weight of the product is adjusted by use of the ratio of phenol over PPE repeating units. PPE oligomers and telechelics with a large variety of end groups, including reactive end groups, can be prepared in this way. Furthermore, block copolymers can be prepared by reacting a phenol terminated polymer in a redistribution with PPE. This is illustrated by the reaction of phenol terminated polystyrene with PPE, leading to polystyrene−PPE diblock copolymers. TMDPQ or copper/amine catalysts can be used as catalyst depending on the reacting phenolic compound, desired reaction time, and product purity. For a fast PPE redistribution with ortho-unsubstituted phenols, without any oxidation of the methyl substituents of the PPE chain, the use of TMDPQ is preferred. For the preparation of pure oligomers and block copolymers, a slow redistribution using copper catalysts in the absence of oxygen is preferred.

Abstract Retention gape deactivated with Silicone OV‐1701‐OH show good chromatographic performance and remarkable stability against water induced stationary phase degradrdation. In an attempt to better understand the findamentals off the deactivation process using silanol terminated polysiloxanes, a fumed silica was deactivated with Silicon OV‐1701‐OH. In contrast to fused silic capillaries, fumed silica (Aerosil A‐200) can be studied by 29Si cross‐polarization magic‐angle‐spinning (CPMAS) NMR, thus serving as a model substrate for fused silica. Retention data from inverse gas chromatography at infinite dilurion and 29Si CP MAS NMR data of five Aerosil phases, differing in residual silanol surface concentration, are correlated with the aim of validating this approach for stationary phase characterization. A comparatively detailed model of the deactivating polymer layer that explains the observed absorption activities is deduced.Surface silanols are shown to play a key role in the polymer layer, the structure of which is of primary importance for the absorption behavior after deactivation. Contrary to common belief, the absolute silanol surface concentration after deativation is only of secondary importance for the overall absorption activity. High silanol surface concentrations enhance degradation of the polysiloxane chains into small cyclic fragments as well as subsequent absorption and immobolization to the silica substrate surface. The mobility of linear polysiloxane chains in the kHz regime (as determined bby NMR cross‐polarization dynamics) appears to determine the extent which the residual silanols are accessible for analytes. It is therefore anticipated that there is an optimum silanol surface concentration of fused silica surfaces to be deactivated with silanol terminated polysiloxanes; it should be lazrge enough to adsord polymer fragments, but not large to avoid excessive residual silanol activity.

Abstract Companies must constantly improve their technologies to survive the competitive battle in the nineteen nineties and beyond. This now holds more than ever for producers of engineering thermoplastics, who traditionally have enjoyed significantly higher margins than the commodity plastic producers. In today's competitive environment it is vital to be the high quality, low cost producer. At the same time products and processes need to become “greener”. The drivers call for specific R&D approaches focused at cost and ecological improvements of processes and products. Examples are:(i) novel catalysis with fewer process steps, higher yields and selectivity for the production of monomers and polymers.(ii) solvent‐free polymerisation processes, resulting in lower investment cost, lower operating cost and the lack of solvent traces in the final product(iii) design of polymer modifications, e.g. higher flow and/or higher heat co‐polymers such that products can be produced in existing equipment resulting in acceptable Return‐on‐Investment (ROI).Higher flow products are specifically needed for thin‐wall designs to allow optimum use of the high mechanical properties of engineering thermoplastics, making shorter processing cycles possible during moulding and bringing less material in the environment.This paper reviews various routes to high flow technology, such as improving processing window, molecular engineering and blends. The pull for these technology developments come from optical data storage, thin wall bumper and super thin note bloc computer applications. The need for greener products is addressed through improved flame and fire retardant product design.

This paper describes results obtained in the optical control of a Dielectric Resonator Oscillator operated at X-band. A commercially available DRO device was modified to facilitate optical control of its output characteristics. The device was found to be optically tunable up to 15 MHz and FM rates up to 130 MHz were observed. Frequency stability with respct to temperature am bias voltage of the device was unaffected, however a 30% degradation of the Qex was noted. No attempt was made to optimize its performance.

Presentation d'une methode permettant d'obtenir une solution exacte pour le transfert de chaleur par conduction entre deux cylindres excentres avec conditions limites de troisieme espece. Obtention de cette solution sous forme d'une serie ou l'evaluation des coefficients necessite la resolution d'un systeme d'equations algebriques. Pour eliminer cette difficulte, presentation d'une formule approchee et facile a utiliser pour le facteur de forme, cette approximation etant bonne a 5% pres