Effects of ICI 118.551, a selective beta-2 adrenergic blocking agent on the guinea pig cardic excitability and ventricular fibrillation threshold

In isolated guinea pig perfused hearts ICI 118.551, a selective beta 2 adrenoceptor antagonist, induced transient ventricular extrasystoles. Following the termination of the perfusion, a very significant increase of both the ventricular fibrillation threshold and the refractory periods were measured. In guanethidine pretreated hearts, ICI 118.551 failed to induce premature beats. At the same time the fibrillation threshold and refractory periods exhibited a very significant decrease. The perfusion of equimolecular concentration of metoprolol, a beta-1-adrenoceptor antagonist, and (+) propranolol, a quinidine-like compound, induced, in most experimental settings, similar results as ICI 118.551. Thus, besides its beta-2-adrenoceptor antagonist properties, ICI 118.551 presented other pharmacological actions

Electron beam processing of Al-2Sc alloy for enhanced precipitation hardening

Scandium is a light but highly potent hardening element for aluminium. However, the amount of Sc that can be precipitated for hardening is rather limited because of its limited solubility. Electron beam direct manufacturing (EBDM) is a novel metal fabrication technique. We show that electron beam processing substantially increases the solubility of Sc in α(Al) and the attendant hardening effect is about twice that attained from solid solution and ageing. These findings provide a basis for new alloy design for EBDM

Evolution of nanoscale porosity during equal-channel angular pressing of titanium

Small-angle neutron scattering (SANS) analysis and transmission electron microscopy evidence suggest the occurrence of nanoscale porosity in commercial-purity titanium processed by equal-channel angular pressing (ECAP). SANS data were produced at two different facilities (GKSS, Germany; and Los Alamos, USA) and were analysed using three different methods. The results are consistent and yield a conclusive picture of the distribution of the scattering centres, which are believed to be associated with nanoporosity. Back pressure applied during ECAP tends to reduce the average pore size, which also depends on the processing route used. The results of the study strongly suggest that ECAP leaves a footprint in titanium in the form of a population of polydispersed nanovoids, which may play an important role in subsequent processing of the material

Microstructural characteristics of electron beam processed Al-2Sc

Plate samples of Al-2Sc were processed with an electron beam (EB) gun in a vacuum of 10-3 Pa at 50kV and 30 µA. EB processing suppressed the formation of primary Al3Sc, altered the morphology of the eutectic a(Al)-Al3Sc, and increased the solubility of Sc in the eutectic a(Al). In addition, its cyclic heating effect induced the precipitation of Al3Sc. EB processing resulted in more profound hardening than conventional high temperature solid solution and ageing

Microstructural development of electron beam processed Al-3Ti-1Sc alloy under different electron beam scanning speeds

A systematic study has been made of the microstructural development in as-cast 30 mm thick Al-3Ti-1Sc (wt%) plate samples that were processed by electron beam (EB) melting at different scanning speeds of 3, 5, 8, 12, 15 and 20 mm/s. The composition of the alloy is designed to capitalize on the potential for significantly extended solubility values of both Sc and Ti in Al when cooled at high cooling rates. The resulting microstructures are characterised using transmission electron microscopy (TEM) and other analytical means, assisted with Thermo-Calc predictions and Vicker's microhardness measurements. EB scanning speed plays a key role in determining the phase formation and microstructural development in the Al-3Ti-1Sc alloy when the beam is applied an accelerating voltage of 50 kV and a current of 30 μA. The major microstructural features in the re-solidified zone include (i) the formation of the primary tetragonal Al(Ti,Sc) phases and their retention or subsequent transformation to stable cubic Al(Ti,Sc) phases; (ii) the complete suppression of the primary tetragonal Al(Ti,Sc) phases at the scanning speed of 20 mm/s; and (iii) the formation of cubic Al(Ti,Sc) precipitates in the α(Al) matrix supersaturated with both Sc and Ti. These experimental findings are informative for both EB processing of Al-Ti-Sc alloys and the design of new Al alloys for additive manufacturing processes