Advanced techniques to improve the design of tennis ball cores

Over the past century tennis balls have seen little development, despite issues with durability and recyclability. Over the same period rackets have seen several development iterations through the use of wood, aluminium and carbon fibre reinforced composites frames. Players physical capabilities have dramatically improved and even line-calling has been automated. In professional tennis, balls are used for as little as nine games before being discarded, whilst recreational players demand a long-lasting product at minimal cost. Balls are comprised of a vulcanised rubber core, which is pressurised, and woven felt covering. Similarities in materials, combined with strict performance limits defined by the International Tennis Federation (ITF) and consumer pressures culminates in a product with low profit margins and little market differentiation. The work presented in this thesis focussed on the elastomeric material used to manufacture the core of tennis balls, presenting a scientific means of assessing alternative ball core materials that could benefit players and brands alike. Ball tracking data collected during professional tournaments, spanning the major court surfaces used in professional tennis, was analysed and used to determine the impact frequency and conditions a ball is subjected to during play. The range of impact conditions determined were replicated in the laboratory and subjected to digital image correlation techniques (GOM Correlate Professional), which were applied to measure the surface strains and strain rates present during impact. The results of which enabled the transformation of typical ball impact conditions in professional tennis into mechanical testing conditions representative of what occurs during impact. Current pressurised and pressureless ball core rubber were subjected to tensile testing, matching as closely as was possible, the strains and strain rates measured during impact. Dynamic mechanical analysis (DMA) was also utilised to characterise the viscoelastic properties of current ball core rubber. The characterisation of current materials provided a benchmark against which alternatives could be compared and enabled the implementation finite element (FE) simulations of ball cores during impact. FE modelling utilised advanced viscoplasticity material models (Bergstrӧm-Boyce model) enabling the viscoelastic and strain rate dependent behaviour of rubber to be incorporated, eradicating the need to artificially tune model coefficients, as seen in previous examples of tennis ball modelling. Having quantified the conditions required for materials characterisation testing and developed a methodology for the simulation of pressurised ball core impacts, alternative materials were identified and assessed. Thermoplastic elastomers (TPEs) were identified as materials with potential for replacing vulcanised rubber. TPEs offered potential improvements to pressure retention properties, recyclability as well as the opportunity to utilise thermoplastic manufacturing processes. When subject to the same materials characterisation testing and FE modelling as ball core materials, TPEs exhibited, in part, comparable properties to ball core rubber, with simulations estimating similar ball core performance for melt processible rubber TPE. The work presented in this thesis implies TPE materials are worthy of further investigation for use as tennis ball cores

“Come you spirits unsex me!”: representations of the female executive in recent French film & fiction

This article analyses the representation of female executives in a corpus of French films and novels produced from 2000 on. The corpus includes a mixture of male and female directors and novelists, all of whom adopt broadly centre-left or left-wing positions that are highly critical of contemporary forms of globalised, neo-liberal capitalism. Yet each of these directors and novelists depicts powerful female executives in highly conservative terms, figuring them as ‘unsexed’ beings who have turned their backs on their ‘natural’ destinies as wives and mothers. Further, these films and novels all imply that neo-liberal capitalism could be defeated if women were just to return to their traditional roles as wives and mothers and if the patriarchal nuclear family could once again perform its proper role as the foundation of community and national integrity. The corpus thus offers depictions of a range of powerful women who are, alternately, punished, pitied, or tamed. This being the price that must apparently be paid, if French national integrity is to be preserved from what are figured as the inherently foreign forces of globalised capitalism. Having offered an inventory of these deeply conservative tropes, the article concludes by suggesting some possible reasons for their dispiriting recurrence

Experiments on the DCASE Challenge 2016: Acoustic Scene Classification and Sound Event Detection in Real Life Recording

In this paper we present our work on Task 1 Acoustic Scene Classi- fication and Task 3 Sound Event Detection in Real Life Recordings. Among our experiments we have low-level and high-level features, classifier optimization and other heuristics specific to each task. Our performance for both tasks improved the baseline from DCASE: for Task 1 we achieved an overall accuracy of 78.9% compared to the baseline of 72.6% and for Task 3 we achieved a Segment-Based Error Rate of 0.76 compared to the baseline of 0.91

Calibration of the Barnes-Evans relation using interferometric observations of Cepheid variables

Direct diameter measurements of Cepheid variables are used to calibrate the Barnes-Evans Cepheid surface brightness relation. More than 50 separate Cepheid diameter measurements from four different optical interferometers are used to calculate surface brightnesses as a function of magnitude and color. For two Cepheids, η Aquilae and ζ Geminorum, high precision diameter measurements as a function of pulsation phase are available from the Palomar Testbed Interferometer (PTI). Relations using only these diameters are found for each individual Cepheid in order to search for differences between Cepheids of different pulsation period. In all cases the best-fit relations are simple linear relations between surface brightness and color with the constraint that for a spectral type A0 star (where all colors equal zero) all relations must yield the same surface brightness (i.e., there must be a common zero-point). The derived relations found using interferometric Cepheid diameters are consistent with functions in the literature found using interferometric observations of non-variable giant and supergiant stars. In addition, while the separate relations for η Aquilae and ζ Geminorum are marginally consistent within the errors they do differ in the direction predicted for Cepheids of differing pulsation period. Using these new surface brightness relations the distance is calculated to the nearby Cepheid δ Cephei for which a new distance has been found using trigonometric parallax with the Hubble Space Telescope. These distances are well within the errors of the distance derived from trigonometric parallax