A simple procedure for the enzymic digestion of edible tissues prior to detection of drug residues.

A simple procedure for the enzymic digestion of edible tissues is described and compared with other procedures. The samples are digested overnight in an enzyme suspension containing subtilisin A at 60 degrees C and pH 9. The resulting digest contains only a few small tissue fragments. This method is suitable for routine analysis, since the manipulation of the samples is very limited.     

Polymer-modified glass fibre reinforced gypsum

Glass fibre reinforced gypsum, modified by addition of specially selected and developed thermosetting polymers, is the basis of a new composite material, called PGRG. An investigation has been performed into its mechanical properties such as bending strength, tensile strength and long-term performance under constant load and fatigue load. The influence of moisture and temperature on mechanical properties has been determined. The equilibrium moisture content at various relative humidities, the moisture content under natural weathering conditions, the coefficient of linear expansion and the microstructure have been studied. Furthermore, the durability has been investigated under accelerated ageing conditions and outdoor exposure. The results have shown that the polymer-modified glass fibre reinforced gypsum has good mechanical properties under tension and, unlike unmodified gypsum, is resistant to the Western European climate. A variety of new outdoor applications for gypsum are likely to be possible now: The material has already been used successfully for outdoor applications in the UK, the Middle East and The Netherlands.

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Resume Le platre renforcé de fibres de verre, modifié par l'addition de polymère thermodurcissable spécialement sélectionné et fabriqué, forme la base d'un nouveau matériau composite appelé PGRG, dont on a examiné certaines propriétés mécaniques: résistance à la flexion, à la traction et performance à long terme sous charge constante et charge de fatigue. On a déterminé l'influence de l'humidité et de la température sur les propriétés mécaniques. On a également étudié l'équilibre de la teneur en eau à différentes humidités relatives, la teneur en eau en exposition naturelle, le coefficient d'expansion linéaire et la microstructure. On a aussi examiné la durabilité dans des conditions de vieillissement accéléré et l'exposition à l'atmosphère. Les résultats ont montré que les propriétés mécaniques du composite sont bonnes et que, à la différence du platre non traité, il peut résister au climat d'Europe Occidentale. Ceci permet d'envisager maintenant pour le platre diverses applications en ouvrages extérieurs. Le matériau a déjà été utilisé avec succès pour ce type d'applications en Grande-Bretagne, aux Pays-Bas et au Moyen-Orient.

     

Photoluminescence characterization of AlGaN-GaN pseudomorphic quantum wells and calculation of strain induced bandgap shifts

The low temperature (77 K) photoluminescence characteristics of Al _x Ga_1-x N-GaN strained layer quantum wells with differentx values grown by metalorganic chemical vapor deposition (MOCVD) were investigated. The photoluminescence spectra were useful in analyzing both quantum confinement effects and strain induced energy shifts. The strain induced shifts were found to be a strong function of aluminum compositionx. A model was developed to calculate the strain induced bandgap shifts atk = 0. The values predicted by this model which took into account the wurtzite crystal structure of the material system, were in good agreement with (i.e. within 2 meV of) the experimentally measured shifts.     

Mechanism of shear modification of low density polyethylene

In this paper we address the aspects associated with shear modification of low density polyethylene by extrusion. By successive passes of the polymer through an extruder it can be shown that both the melt viscosity and melt elasticity are reduced by shear modification. These reversible variations are not accompanied by significant changes in molecular weight distribution. The major effects of extrusion are to decrease the amount of elastically effecitve material. Study of proton relaxation times at 150°C shows that the melt comprises regions of relatively ordered, entangled, and unentangled polymer. Shearing reduces the proportion of more ordered material. The elastically effective anchors that are reduced by shearing are regions with restricted segmental mobility rather than conventional entanglements or intermolecular knots. Successive extrusions produce a relatively small decrease in the number of such constraints to molecular motion. Repeated shearing has a diminishing effect on the proportion of more ordered material in the polyethlene melt. This parallels observations of the effects of repeated shear modification on the properties of polyethylene films and other extrudates.     

Pulsed corona for breaking up air bubbles in water

The injection of gas into water, through a hollow needle, gives a stream of bubbles. These bubbles can be effectively broken up by application of HV pulses. Our experimental work shows that this mechanism works in demineralized water and even in conducting tap water if the pulses have a short rise time. Bubble diameters are as low as 50 μm. Our pulse source uses either a HV tetrode or a spark gap as switching element. Extremely small bubbles are produced at a high rate and a low power input. Applications for this method can be found in chemical process technology     

Nonlinear state affine identification methods: Applications to electrical power plants

A nonlinear identification method by simple state-space models is proposed in the discrete-time case. This approach is suggested by theoretical results similar to the approximation property known for a long time for Volterra series. The proposed technique uses extensions with polynomial inputs of bilinear systems called state-affine systems. This modelling requires a small computing time and enables us to obtain nonlinear models which can be easily implemented on microprocessors and remain valid over a wide range of operating conditions. Several physical examples concerning electric power plants are also reported.     

U73122 and U73343 inhibit receptor-mediated phospholipase D activation downstream of phospholipase C in CHO cells

We investigated the effects of nitric oxide (NO) donors, S-nitroso-N-acetylpenicillamine and sodium nitroprusside on basal and K+-evoked release of [3H]noradrenaline from superfused synaptosomes from the rat cerebral cortex. Both substances produced concentration-dependent increases in the release of the labeled transmitter under basal and depolarized conditions. The effects of the donors on basal release were Ca2+-independent but were not inhibited by the carrier-uptake blocker, desipramine; the effects were abolished by hemoglobin (an NO scavenger). Thirty-five minutes after stimulation with sodium nitroprusside, the synaptosomes were still responsive to KCl stimulation, indicating that the donor's effects were not caused by damage to the synaptosome membrane. The cGMP analogue, 8-bromo-cGMP, had no effect on basal release, and the enhanced release produced by sodium nitroprusside was not inhibited by the specific inhibitor of soluble guanylate cyclase, 1H-[1,2,4]oxadiazolo[4,3-alpha]quinoxalin-1-one, indicating that NO's effects on basal release of the neurotransmitter are guanylate cyclase-independent. Both of the NO donors had more marked effects on release of [3H]noradrenaline during K+-stimulated depolarization. The NO-mediated increase in this case was partially antagonized by 10 microM LH-[1,2,4]oxadiazolo[4,3-alpha]quinoxalin-1-one, and 8-Br-cGMP was also capable of producing concentration-dependent increases in the K+-stimulated release of the transmitter. These findings indicate that the effects of the NO donors on [3H]noradrenaline release during depolarization are partially mediated by the activation of guanylate cyclase.     

High-speed gel-spinning of ultra-high molecular weight polyethylene

Summary This communication is concerned with the gel-spinning of ultrahigh molecular weight polyethylene (UHMWPE) at speeds up to 1500 m/min. It was found that 5 wt% solutions of UHMWPE in paraffin oil could be extruded through a conical die at a rate of 100 m/min. without the appearance of filament irregularities due to elastic solution fracture. These elastic turbulences occur at extrusion speeds of about 5 m/min. Without the addition of 1 wt% of Aluminium-stearate the spinline could be stretched at most to 60 m/min at 170°C but at 210°C it did not break at a speed of 1500 m/min.These high-speed gel-spinning experiments at temperatures around 200°C yielded polyethylene fibers with a tensile strength of 3.5 GPa. It was observed that drying of the as-spun fiber containing n-hexane at constant length led to excessive crazing.