Fractal rotation isolates mechanisms for form-dependent motion in human vision

Here, we describe a motion stimulus in which the quality of rotation is fractal. This makes its motion unavailable to the translationbased motion analysis known to underlie much of our motion perception. In contrast, normal rotation can be extracted through the aggregation of the outputs of translational mechanisms. Neural adaptation of these translation-based motion mechanisms is thought to drive the motion after-effect, a phenomenon in which prolonged viewing of motion in one direction leads to a percept of motion in the opposite direction. We measured the motion after-effects induced in static and moving stimuli by fractal rotation. The after-effects found were an order of magnitude smaller than those elicited by normal rotation. Our findings suggest that the analysis of fractal rotation involves different neural processes than those for standard translational motion. Given that the percept of motion elicited by fractal rotation is a clear example of motion derived from form analysis, we propose that the extraction of fractal rotation may reflect the operation of a general mechanism for inferring motion from changes in form.

Ovariole number - a predictor of differential reproductive success among worker subfamilies in queenless honeybee (Apis mellifera L.) colonies

A honeybee queen normally mates with 10-20 drones, and reproductive conflicts may arise among a colony's different worker patrilines, especially after a colony has lost its single queen and the workers commence egg laying. In this study, we employed microsatellite markers to study aspects of worker reproductive competition in two queenless Africanized honeybee colonies. First, we determined whether there was a bias among worker patrilines in their maternity of drones and, second, we asked whether this bias could be attributed to differences in the degree of ovary activation of workers. Third, we relate these behavioral and physiological factors to ontogenetic differences between workers with respect to ovariole number. Workers from each of three (colony A) and one (colony B) patrilineal genotypes represented less than 6% of the worker population, yet each produced at least 13% of the drones in a colony, and collectively they produced 73% of the drones. Workers representing these genotypes also had more developed follicles and a greater number of ovarioles per ovary. Across all workers, ovariole development and number were closely correlated. This suggests a strong effect of worker genotype on the development of the ovary already in the postembryonic stages and sets a precedent to adult fertility, so that

CO multipulse TAP studies of 2% Pt/CeO2 catalyst: Influence of catalyst pretreatment and temperature on the number of active sites observed

CO multipulse temporal analysis of products (TAP) experiments were used to characterize a ceria-supported platinum catalyst after various oxidative and reductive pretreatments using O-2, H2O, CO2, and H-2. Based on the amount of CO consumed, using the final CO-saturated catalyst composition as the common state point, the oxidatively pretreated catalyst could be described using a general scale. From a kinetic analysis of the CO multipulse responses, two kinetic regimes corresponding to two types of active sites could be identified. As the temperature was raised, the number of the most active sites did not change while the amount of the less active site increased. Comparison of the number of active sites determined from the TAP data reported herein with that determined by a previous steady-state isotope transient kinetic analysis experiment showed excellent agreement. This correlation indicates that the (very fast response) TAP experiments can provide information regarding the number and type of active sites that are relevant to a catalyst under real reaction conditions. (c) 2007 Elsevier Inc. All rights reserved.

Drum granulation of NPK fertilizers

Nitrate-based NPK fertilizer was granulated in a bench scale drum granulation unit. The initial fertilizer possessed a particle size distribution similar to those in industrial granulation units. In this work, three factors are identified affecting the degree of fertilizer granulation, these are solution to solid phase ratio, the binder viscosity and the optimal rotation speed of the drum. Experimental results indicate that a critical solution to solid phase ratio is required for an increase in granulation in terms of mass median diameter. The saturated solution viscosity in this system was measured and correlated well to binder viscosity granulation theory with the critical Stokes number calculated at 700. The optimum rotation speed for flighted and unflighted drums correlated with the Froude number relationship for full scale granulation units. (C) 2000 Elsevier Science S.A. All rights reserved.

Finding the magic number

Paul Wilson and Colin Cooper investigate methods used to extract the number of factors in a factor analysis

Kinematic Design of a 6-DOF Parallel Manipulator with Decoupled Translation and Rotation

A new three-limb, six-degree-of-freedom (DOF) parallel manipulator (PM), termed a selectively actuated PM (SA-PM), is proposed. The end-effector of the manipulator can produce 3-DOF spherical motion, 3-DOF translation, 3-DOF hybrid motion, or complete 6-DOF spatial motion, depending on the types of the actuation (rotary or linear) chosen for the actuators. The manipulator architecture completely decouples translation and rotation of the end-effector for individual control. The structure synthesis of SA-PM is achieved using the line geometry. Singularity analysis shows that the SA-PM is an isotropic translation PM when all the actuators are in linear mode. Because of the decoupled motion structure, a decomposition method is applied for both the displacement analysis and dimension optimization. With the index of maximal workspace satisfying given global conditioning requirements, the geometrical parameters are optimized. As a result, the translational workspace is a cube, and the orientation workspace is nearly unlimited.

The main-sequence rotation-colour relation in the Coma Berenices open cluster

We present the results of a photometric survey of rotation rates in the Coma Berenices (Melotte 111) open cluster, using data obtained as part of the SuperWASP exoplanetary transit-search programme. The goal of the Coma survey was to measure precise rotation periods for main-sequence F, G and K dwarfs in this intermediate-age (~600 Myr) cluster, and to determine the extent to which magnetic braking has caused the stellar spin periods to converge. We find a tight, almost linear relationship between rotation period and J - K colour with an rms scatter of only 2 per cent. The relation is similar to that seen among F, G and K stars in the Hyades. Such strong convergence can only be explained if angular momentum is not at present being transferred from a reservoir in the deep stellar interiors to the surface layers. We conclude that the coupling time-scale for angular momentum transport from a rapidly spinning radiative core to the outer convective zone must be substantially shorter than the cluster age, and that from the age of Coma onwards stars rotate effectively as solid bodies. The existence of a tight relationship between stellar mass and rotation period at a given age supports the use of stellar rotation period as an age indicator in F, G and K stars of Hyades age and older. We demonstrate that individual stellar ages can be determined within the Coma population with an internal precision of the order of 9 per cent (rms), using a standard magnetic braking law in which rotation period increases with the square root of stellar age. We find that a slight modification to the magnetic-braking power law, P ~ t0.56, yields rotational and asteroseismological ages in good agreement for the Sun and other stars of solar age for which p-mode studies and photometric rotation periods have been published.

Electron number density measurements in magnesium laser produced plumes

Interferometry has been used to investigate the spatio-temporal evolution of electron number density following 248 nm laser ablation of a magnesium target. Fringe shifts were measured as a function of laser power density for a circular spot obtained using a random phase plate. Line averaged electron number densities were obtained at delay times up to ∼100 ns after the laser pulse. Density profiles normal to the target surface were recorded for power densities on target in the range 125–300 MW cm−2.

Three dimensional number density mapping in the plume of a low temperature laser ablated magnesium plasma

Simultaneous optical absorption and laser-induced fluorescence measurements have been used to map the three-dimensional number densities of ground-state ions and neutrals within a low-temperature KrF laser-produced magnesium plasma expanding into vacuum. Data is reported for the symmetry plane of the plasma, which includes the laser interaction point at a delay of 1 μs after the ∼30 ns KrF laser ablation pulse and for a laser fluence of 2 J cm−2 on target. The number density distributions of ion and neutral species within this plane indicate that two distinct regions exist within the plume; one is a fast component containing ions and neutrals at maximum densities of ∼3×1013 cm−3 and ∼4×1012 cm−3, respectively and the second is a high-density region containing slow neutral species, at densities up to ∼1×1015 cm−3.