Numerical Tests of Rotational Mixing in Massive Stars with the new Population Synthesis Code BONNFIRES

We use our new population synthesis code BONNFIRES to test how surface abundances predicted by rotating stellar models depend on the numerical treatment of rotational mixing, such as spatial resolution, temporal resolution and computation of mean molecular weight gradients. We find that even with identical numerical prescriptions for calculating the rotational mixing coefficients in the diffusion equation, different timesteps lead to a deviation of the coefficients and hence surface abundances. We find the surface abundances vary by 10-100% between the model sequences with short timestep of 0.001Myr to model sequences with longer timesteps. Model sequences with stronger surface nitrogen enrichment also have longer main-sequence lifetimes because more hydrogen is mixed to the burning cores. The deviations in main-sequence lifetimes can be as large as 20%. Mathematically speaking, no numerical scheme can give a perfect solution unless infinitesimally small timesteps are used. However, we find that the surface abundances eventually converge within 10% between modelling sequences with sufficiently small timesteps below 0.1Myr. The efficiency of rotational mixing depends on the implemented numerical scheme and critically on the computation of the mean molecular weight gradient. A smoothing function for the mean molecular weight gradient results in stronger rotational mixing. If the discretization scheme or the computational recipe for calculating the mean molecular weight gradient is altered, re-calibration of mixing parameters may be required to fit observations. If we are to properly understand the fundamental physics of rotation in stars, it is crucial that we minimize the uncertainty introduced into stellar evolution models when numerically approximating rotational mixing processes.Comment: 8 pages, 6 figures, accepted by A&

Gallium Arsenide preparation and QE Lifetime Studies using the ALICE Photocathode Preparation Facility

In recent years, Gallium Arsenide (GaAs) type photocathodes have become widely used as electron sources in modern Energy Recovery Linac based light sources such as the Accelerators and Lasers in Combined Experiments (ALICE) at Daresbury Laboratory and as polarised electron source for the proposed International Linear Collider (ILC). Once activated to a Low Electron Affinity (LEA) state and illuminated by a laser, these materials can be used as a high-brightness source of both polarised and un-polarised electrons. This paper presents an effective multi-stage preparation procedure including heat cleaning, atomic hydrogen cleaning and the activation process for a GaAs photocathode. The stability of quantum efficiency (QE) and lifetime of activated to LEA state GaAs photocathode have been studied in the ALICE load-lock photocathode preparation facility which has a base pressure in the order of 10^-11 mbar. These studies are supported by further experimental evidence from surface science techniques such as X-ray Photoelectron Spectroscopy (XPS) to demonstrate the processes at the atomic level.Comment: Presented at First International Particle Accelerator Conference, IPAC'10, Kyoto, Japan, from 23 to 28 May 201

A newly discovered population of the critically endangered false limpet Siphonaria compressa Allanson, 1958 (Pulmonata: Siphonariidae), with observations on its reproductive biology

The endangered false limpet, Siphonaria compressa, originally described by Allanson in 1958 from Langebaan Lagoon, Saldanha, has been found living in intertidal eelgrass meadows in the embayment of the Knysna River estuary at Bollard Bay, Leisure Isle, Knysna, South Africa. This represents only the second known site of occurrence of the species. Although classified by the IUCN as critically endangered, the Knysna population is viable.Acrobat Distiller 6.0 (Windows

BIOMECHANICAL GOLF SWING ANALYSIS

The Biomechanics Laboratory of the Australian Institute of Sport has spent eight years developing a comprehensive golf swing analysis system. The system is designed to assist the golfer and professional golf coach in identifying problems within the goWs swing and enable corrections to be made so that the golfer may reach full potential. Correct weight transference is a major component of the perfect swing. The Golf Analysis System measures changes in the centre of pressure of the golfer during the swing which provides a measure of the golfer's weight transference pattern. The path the club follows during the swing is directly related to the quality of the swing. An automatic digitising system is used in the Golf Analysis System to capture the location of the club shaft every one two-hundredths of the second during the swing. This path is then reconstructed by computer, plotted on paper and animated on video for review purposes. Views from the front, side and above the club path plane are reconstructed in relation to the movement of the leading shoulder for examination. The absolute velocity of the club's head is obtained and plotted out for 0.1 sec. before impact to 0.1 seconds after impact. The velocity components of the club head in the forward, crosswise and vertical direction are also plotted out which provides information as to the direction the club head is moving at the time of ball contact. A graph of the angle that the club is making to the desired ball path is also graphed out from 0.02 seconds before impact to 0.02 seconds after impact. A split vision video image of the golf swing is f h e d during the swing. This is captured by way of two shuttered S-VHS video cameras located directly above and to the open side of the golfer. The video provides a complete visual image of each entire golf swing analyzed. The position of the golf club head during ball contact phase has a direct relationship to the path the ball will follow after ball contact. In the Golf Analysis System the path of the golf club head is captured by a high speed video camera (400 frames per second) several frames before ball contact to several frames after contact. Sensors in the tee-off platform provide immediate feedback on the velocity of the club head immediately before impact and velocity of the ball immediately after impact. The direction and elevation of ball flight is also measured by sensors. A printout of this information together with where the ball would have landed as a d tof the swing is also provided in printouts. The Golf Analysis System provides valuable information about the golfefs swing which if used properly can produce drastic improvement in the goWs game. To be most effective a professional golf coach should be utilised to eliminate faults which are disclosed by Golf Analysis System. The swing analysis of 65 third year apprentices in the Australian P.G.A. professional coaching course has come up with some interesting information. This information will be presented at the ISBS 1995 Symposium