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espanolEn este trabajo se estudia la posibilidad de preparar aleaciones de alta entropia del sistema Al-Sc-Ti-V-Cr. Para ello se han seleccionado los elementos y la composicion utilizando los criterios conocidos y disponibles en la literatura y se han preparado mediante fusion por arco tres aleaciones con contenidos que varian entre el 10 y 35 at.%. Las tres aleaciones tienen una microestructura dendritica bifasica similar, siendo las dendritas una solucion solida bcc enriquecida en Ti, V o Cr. El escandio aparece unicamente en el espacio interdendritico formando el intermetalico Al2Sc. La dureza de las dendritas crece con el contenido en Ti y se hace menor a medida que es mayor el contenido en Cr. Ademas, la tenacidad de las aleaciones depende de la dureza de las dendritas siendo esta mayor cuanto mas blandas son las dendritas. Los resultados obtenidos demuestran que ni los criterios empiricos utilizados ni los calculos mediante THERMOCALC permiten predecir la formacion de una unica solucion solida ni la naturaleza de las fases observadas experimentalmente. EnglishThe feasibility of preparing high entropy alloys in the Al-Sc-Ti-V-Cr system has been evaluated taking into account the different criteria reported in the literature. Based on such criteria, three Al-Sc-Ti-V-Cr alloys were chosen with contents of each element varying from 10 to 35 at. %, and prepared by arc melting. All alloys exhibit a two-phase dendritic microstructure, with the major dendritic phase being a bcc solid solution enriched in Ti, V, or Cr. Scandium is strongly rejected from the dendrites towards the interdendritic regions to form Al2Sc in the three alloys. The bcc solid solution dendrites become harder with high Ti content and lower with high Cr content. The toughness of the alloys depends on the hardness of the dendrites, with alloys with harder dendrites becoming more brittle. The results indicate that neither empirical criteria used nor THERMOCALC calculus tool can predict properly the formation of a single solid solution nor the nature of the existing phases respectively.

We describe a novel approach for simultaneously determining regional differences in action potential (AP) morphology and tissue electrophysiological properties in isolated atria. The epicardial surface of rat atrial preparations was placed in contact with a multi-electrode array (9 × 10 silver chloride electrodes, 0.1 mm diameter and 0.1 mm pitch). A glass microelectrode (100 MΩ) was simultaneously inserted into the endocardial surface to record intracellular AP from either of 2 regions (A, B) during pacing from 2 opposite corners of the tissue. AP duration at 80% of repolarisation and its restitution curve was significantly different only in region A (p < 0.01) when AP was initiated at different stimulation sites. Alternans in AP duration and AP amplitude, and in conduction velocity were observed during 2 separate arrhythmic episodes. This approach of combining microelectrode array and intracellular membrane potential recording may provide new insights into arrhythmogenic mechanisms in animal models of cardiovascular disease.

The large number of missions associated with ESA’s Copernicus program has necessitated several new image sensor designs for earth observation (or living planet) applications as each instrument needs to be highly optimized. Whilst the majority of these sensors have utilised CCD technology, the use of CMOS is starting to increase. New CCD designs and technology trends for hyperspectral applications such as Sentinel 4, Sentinel 5, Sentinel 5 precursor (TropOMI), Flex and 3MI are described. In these the sensor design has been optimized to provide highest possible signal levels with lowest possible noise in combination with higher frame rates and reduced image smear. CMOS sensors for MTG (Meteosat Third Generation) and METImage are then described. Both use extremely large pixels, up to 250μm square, at high line rates. Radiation test data and key performance measurements are shown for MTG and for a test device that has been made for METImage. Finally, newer developments including back-illumination and means for achieving a TDI function in standard-processed CMOS are briefly described.

Many important metallic alloys are characterised by the chemical ordering of their atomic component elements. Examples are beta brass (βCuZn - one of the components of common brass), many of the gold-base alloys used in dentistry, Nickel-Titanium shape memory alloys with superelastic properties (great stretchability, as used for orthodontic wires) and Nickel-Aluminium gamma-prime phase which strengthens superalloys for high-temperature turbines. The figure shown below (Fig. 1) represents such an ordered arrangement of two atomic species (could be copper and gold, or nickel and aluminium) on a face centred cubic lattice. The disordered lattice would have the yellow and blue atoms randomly distributed. While such important materials, the realisation that these crystals are chemically ordered (in contrast to chemically-disordered alloys, such as alpha brass (αCuZn), steels, aluminium alloys, and most other metallic alloys) is a relatively new understanding, being just now one century old. It had been understood for a long time before that crystals contained spatially-ordered atoms, but not that there was chemical order hidden inside. It was only with the development of methods of diffraction of x-rays by crystals that it became possible to recognise and quantify such chemical order.