Keele University

About: Keele University is a education organization based out in Newcastle-under-Lyme, United Kingdom. It is known for research contribution in the topics: Population & Stars. The organization has 11318 authors who have published 26323 publications receiving 894671 citations. The organization is also known as: Keele University.

The perception of apparent movement.

Abstract: When two similar pictures, overlapping but slightly displaced, were projected on a screen in alternation, apparent movement could be seen. How similar must successive pictures be to give apparent movement? This is the 'correspondence problem'. Manipulations of the local and global correspondences between pictures included motion phenomena such as reversed apparent movement; a four-stroke oscillatory cycle which gave an illusion of continuous motion in one direction; edges defined by texture, stereoscopic depth, or flicker, kinetic edges; and wave motion. It was concluded that human motion perception may comprise two separate mechanisms. Local point-by-point correlations between pictures are detected by a relatively peripheral system, probably based on directionally selective neural units. More subtle global correspondences are analysed by a more cognitive system which extracts edges before it processes motion.

Calcite Fabrics, Growth Mechanisms, and Environments of Formation in Speleothems from the Italian Alps and Southwestern Ireland

Abstract: Five fabrics were identified in Alpine and Irish caves on the basis of morphological and microstructural characteristics, and re- lated to growth mechanisms and growth environment. Columnar and fibrous fabrics grow when speleothems are continuously wet, and from fluids at near-equilibrium conditions (low supersaturation; SIcc , 0.35), through the screw dislocation mechanism. The highly defective microcrystalline fabrics form at the same supersaturation range as co- lumnar fabric but under variable discharge and the presence of growth inhibitors. Dendritic fabrics, which have the highest density of crystal defects, develop in disequilibrium conditions (high supersaturation) un- der periodic very low-flow-regime periods that result in prolonged out- gassing. Cave calcareous tufa forms in disequilibrium conditions. Only the calcite crystals of fabrics formed at low supersaturation seem to precipitate near-isotopic-equilibrium conditions.

An empirical formula for the mass-loss rates of dust-enshrouded red supergiants and oxygen-rich Asymptotic Giant Branch stars

Abstract: We present an empirical determination of the mass-loss rate as a function of stellar luminosity and effective temperature, for oxygen-rich dust-enshrouded Asymptotic Giant Branch stars and red supergiants. To this aim we obtained optical spectra of a sample of dust-enshrouded red giants in the Large Magellanic Cloud, which we complemented with spectroscopic and infrared photometric data from the literature. Two of these turned out to be hot emission-line stars, of which one is a definite B[e] star. The mass-loss rates were measured through modelling of the spectral energy distributions. We thus obtain the mass-loss rate formula log Mdot = -5.65 + 1.05 log(L / 10,000 Lsun) -6.3 log(Teff / 3500 K), valid for dust-enshrouded red supergiants and oxygen-rich AGB stars. Despite the low metallicity of the LMC, both AGB stars and red supergiants are found at late spectral types. A comparison with galactic AGB stars and red supergiants shows excellent agreement between the mass-loss rate as predicted by our formula and that derived from the 60 micron flux density for dust-enshrouded objects, but not for optically bright objects. We discuss the possible implications of this for the mass-loss mechanism.