A realistic, parametric compilation of optimised heliocentric solar sail trajectories

In this thesis, a selection of numerical optimisation methods were developed for application to realistic solar sail heliocentric trajectory optimisation problems. A Non-Linear Programming method based on Sequential Quadratic Programming was developed, with the sail controls parameterised in time. This method was hybridised with Genetic Algorithms or locally-optimal analytical control laws to generate an initial guess, where required. The goal of this thesis is to create a detailed catalogue of trajectories to a broad range of heliocentric targets, subject to realistic constraints on trip-time, sail performance, and thermal-limited solar approach. This thesis illustrates the wide range of targets in the solar system that can be reached with solar sailing. In addition, the trajectory problems for which solar sailing is not attractive are also identified. Trajectory analysis of sample return missions to the terrestrial planets, Mars, Venus and Mercury, has been conducted. Extensive depmiure date scans were perfOlmed, where it was found that there are minima and maxima in trip-time, separated by discontinuities, providing effective launch windows. Roundtrip optimal launch dates were identified, after combining outbound and return departure date scans. For Mercury rendezvous, the application of positive launch excess velocity and a Venus gravity assist was investigated, where a small trip-time saving can be made. Trajectories to rendezvous with the Short Period Comet Wirtanen have been optimised, where it was found that a significant reduction in trip time and launch mass could have been realised, relative to a conventional mission. An investigation of using higher performance sails to flyby Long Period Comets has also been conducted, to demonstrate that solar sailing could be used to reach newly discovered comets soon after first discovery, such as the previous Hale-Bopp apparition. It is also shown that solar sailing could be used, instead of solar electric propulsion, to rendezvous with two Main-Belt asteroids, with a reduction in launch mass. The open ended nature of solar sailing was used to show that rendezvous with two further asteroids is also possible. It is also shown that a three-phase trajectory concept, utilising an inclination cranking manoeuvre, could be used to return a sample from a high inclination Near-Earth Asteroid, that would be essentially impossible to reach using conventional propulsion. It is demonstrated that flyby missions to the outer planets, such as Pluto are feasible in reasonable timescales using a solar photonic assist concept. However, due to the faint solar radiation pressure at Jupiter, only flyby missions are practical to the Jovian system with solar sails. An extensive trade-off between launch hyperbolic excess energy, Jupiter arrival velocity, hip-time, and the number of photonic assist loops has been conducted. By contrast, solar sailing appears to be the only feasible option for missions to the Heliopause at 200 AD. Heliopause trajectory analysis included investigation of the number of loops, and the effect of thermallyconstrained closest solar approach on escape velocity and trip-time. It was found that, in order to reach the Heliopause in 25 years, a solar sail of characteristic acceleration of order 1.5 mm S-2 would be required, executing a thermally constrained solar photonic assist at 0.25 AD. Investigation of the effect of positive launch energy is also conducted for Heliopause trajectOlies. A key near-term mission application for solar sails is a Solar Polar Orbiter. Trajectory analysis has revealed that a solar sail transfer to a true solar polar orbit, Earth resonant at 0.48 AU, in 5 years would require a characteristic acceleration of 0.42 nun S-2. In the course of the parametric analysis, two-phase and three-phase scenarios were investigated, with an assessment of the effect of spiralling down to a close cranking orbit radius from positive launch excess energy. Finally, new transfers to exotic, displaced Non-Keplerian Orbits have been optimised for a range of final orbit dimensions among one family of these unique orbits. For lower performance sails, transfers to artificial Lagrange points have been optimised, in the context of the Geostorm and Polar Observer missions

Injectable citrate-modified Portland cement for use in vertebroplasty

Abstract: The injectability of Portland cement (PC) with several citrate additives was investigated for use in clinical applications such as vertebroplasty (stabilization of a fractured vertebra with bone cement) using a syringe. A 2-wt % addition of sodium or potassium citrate with PC significantly improved cement inject-ability, decreased cement setting times from over 2 h to below 25 min, while increasing the compressive strength to a maxi-mum of 125 MPa. Zeta-potential measurements indicated that the citrate anion was binding to one or more of the positively charged species causing charged repulsion between cement particles which dispersed aggregates and caused the liquefying effect of the anion. Analysis of the hydrating phases of PC indi-cated that the early strength producing PC phase (ettringite) developed within the first 2 h of setting following addition of the citrate anion, while this did not occur in the control cement (PC only). Within 24 h ettringite developed in PC as well as calcium– silicate–hydrate (C–S–H), the major setting phase of PC, whereas cements containing citrate did not develop this phase. The evi-dence suggested that in the presence of citrate the cements lim-ited water supply appeared to be utilized for ettringite formation, producing the early strength of the citrate cements. The present study has demonstrated that it is possible to modify PC with citrate to both improve the injectability and crucially reduce the setting times of PC while improving the strength of the cement

Long-term outcomes after ablation of persistent atrial fibrillation: an observational study over 6 years.

ObjectivesTo address the limited long-term outcome data for catheter ablation (CA) of persistent atrial fibrillation (PeAF), we analysed consecutive ablations performed at our centre from 1 January 2008 to 31 December 2010 and followed patients prospectively until January 2014.MethodsBoth arrhythmia recurrence and symptom relief were assessed. Follow-up data were collected from hospital records, supplemented by data from general practitioners and referring hospitals. At the end of the follow-up period, all patients were contacted by phone to determine their up-to-date clinical condition.Results188 consecutive patients with PeAF (157 male, mean age 57.3±9.7 years, 20% with long-standing PeAF) underwent a mean of 1.75 procedures (range 1-4). Telephone follow-up was achieved for 77% of surviving patients. Over a mean follow-up of 46±16 months (range 4-72), 139 (75%) patients experienced arrhythmia recurrence after a single procedure and 90 (48%) after their final procedure. Median time to first recurrence was 210 days (range 91-1850). 71% of recurrences were within the first year following ablation and 91% within 2 years. At final follow-up, 82% of patients reported symptomatic improvement. 7 (2.3%) major complications occurred, and there was no procedure-related death or stroke.ConclusionsCA for PeAF is safe with a low rate of complications. Over a follow-up period of up to 6 years, a large majority of patients experience significant symptomatic improvement but recurrence after the initial procedure is the norm rather than the exception. 2 years' follow-up is sufficient to observe 90% of AF recurrences, but recurrence can occur even after 5 years' remission

Categorizing and Defining Popular Psychological Terms Used Within the Youth Athlete Talent Development Literature: A Systematic Review

Inconsistencies in the use and definition of psychological terms within the talent development literature have been identified. To advance the scientific field, the creation of a shared language is recommended. This review aimed to systematically (i) identify terms used in empirical studies to describe psychological components purported to facilitate athletes' development; (ii) analyse definition and meanings of these terms; and (iii) group, label and define terms into meaning clusters. A systematic review using a narrative approach to synthesise information was conducted. A comprehensive literature search of SPORTDiscus, PsycINFO, PsycARTICLES, and ERIC was completed in May 2015. In total 21 empirical studies, published between 2002 and 2015, met the inclusion criteria and were included in the narrative synthesis. Thematic analysis was used to analyse the findings. Identified psychological terms were categorised as psychological skills or psychological characteristics. Psychological skills were defined as athletes’ ability to use learned psychological strategies (e.g., self-talk) to regulate and facilitate the enhancement of psychological characteristics. Psychological characteristics were defined as predispositions that impact upon athlete development (e.g., self-confidence). Despite being relatively enduring and consistent across a range of situations, psychological characteristics can be regulated and enhanced through the use of psychological skills

Improving ablation outcomes in atrial fibrillation: improving procedural efficacy, safety, and patient selection

Atrial fibrillation (AF) is a major health problem, affecting 1-2% of the population. AF reduces quality of life (QoL) and increases morbidity and mortality. Catheter ablation (CA) is the most efficacious means of restoring sinus rhythm but is not always successful and is occasionally associated with serious complications. Several questions are currently unanswered. True procedural effectiveness, particularly long-term, remains uncertain, especially in more advanced disease. The best technique for achieving success remains an issue of considerable debate and as yet, few, if any, means exist to predict when acute electrical success will translate into sustained clinical benefit. CA is indicated for symptomatic relief but QoL, both as a treatment outcome and as a guide to patient selection, has generally been overlooked in the published literature. Finally, although the maxim, “First, do no harm” may often be ascribed erroneously to Hippocrates, it remains a central tenet of medical practice. However, little previous research has focussed on improving the safety of CA. I have attempted to tackle these issues from a number of angles. I have performed a comprehensive literature review and a retrospective analysis of ablation outcomes at Liverpool Heart and Chest Hospital, the largest and longest such data from the UK, to ascertain a comprehensive, up-to-date assessment of practice. In an effort to improve procedural success, I carried out a multicentre randomised controlled trial testing two ablation strategies. A sub-study tests the hypothesis that clinical outcomes can be predicted by a novel measure of effective ablation. Two further studies aim to improve safety, through use of ultrasound to guide venous access, and to better understand QoL in AF – a theme throughout the thesis – which may help improve selection of appropriate patients for CA. Together, I hope these studies will help physicians improve the outcomes of CA for their patients.Open Acces

The Antikythera Mechanism

Professor Gareth Wynn-Williams will lecture on the ancient Greek enigma, "The Antikythera Mechanism." Recent X-ray analysis of the encrusted piece of bronze from a 2000-year-old Greek shipwreck shows it to be an astronomical computing device of astonishing complexity. What did it do? What purpose did it serve

Surveying the skies: how astronomers map the universe

Since the time of Galileo, astronomy has been driven by technological innovation. With each major advance has come the opportunity and enthusiasm to survey the sky in a way that was not possible before. It is these surveys of discovery that are the subject of this book. In the first few chapters the author discusses what astronomers learned from visible-light surveys, first with the naked eye, then using telescopes in the seventeenth century, and photography in the nineteenth century. He then moves to the second half of the twentieth century when the skies started to be swept by radio, infrared, ultraviolet, x-ray and gamma ray telescopes, many of which had to be flown in satellites above the Earth’s atmosphere. These surveys led to the discovery of pulsars, quasars, molecular clouds, protostars, bursters, and black holes. He then returns to Earth to describe several currently active large-scale projects that methodically collect images, photometry and spectra that are then stored in vast publicly-accessible databases. Dr. Wynn-Williams also describes several recent “microsurveys” – detailed studies of small patches of sky that have led to major advances in our understanding of cosmology and exoplanets.

Development of a Portland cement based system for vertebroplasty

Portland cement (PC) is generally known for its various applications in the construction industry. However, since mineral trioxide aggregate (MTA), a PC based root filling material, obtained food and drug administration (FDA) approval in the late 1990’s there has been an increased interest in the use of the cement for other in vivo applications. PCs are durable, possess high compressive strengths, set in aqueous environments such as those found in vivo and have demonstrated desirable tissue responses as an endodontic sealant. The injectability of PC with various additives was investigated for use in clinical applications such as vertebroplasty (the stabilisation of a fractured vertebra with bone cement) using a syringe with a 2 mm aperture. Additives significantly improved cement injectability, decreased setting times from over 2 h to below 20 minutes while maintaining the compressive strength of the material. Cement characterisation methods including X-ray diffraction (XRD), helium pycnometry and zeta potential measurements were employed to elucidate the effect of the additives on the cement setting reaction. The biocompatibility of PC was investigated with fibroblast and bone marrow cells. The freshly mixed cement appeared cytotoxic while set cement upregulated genes associated with the osteogenic phenotype