Cosmic magnetism: The plasma physics of the recombining universe

This thesis presents an analytical and computational approach to modelling partially ionised, spatially-inhomogeneous and recombining plasmas. The specific context for this study is astrophysical plasmas, the early Universe in particular. Two models are investigated in detail: a magnetohydrodynamic (MHD) plasma model to simulate partially ionised plasmas; and a fully electromagnetic/kinetic model, used to study recombining plasmas. The first section further develops an existing computational model of a partially ionised plasma as a mixture of two cospatial fluids: an MHD plasma and a neutral gas. In order to model the interaction between the plasma and neutral gas populations ab initio, a collisional momentum exchange term was added to the momentum equation of each fluid. The model was used to investigate the combined response to different wave modes driven in the plasma or the neutral gas. The momentum coupling between the plasma and the neutral gas leads to complex interactions between the two populations. In particular, the propagation of plasma waves induces waves in the neutral gas by virtue of the collisional momentum exchange between the velocity fields of each fluid. This means that the normal wave modes of each independent fluid are modified to produce a combined, hybrid response, with the intriguing possibility that neutral gas can not only respond indirectly to magnetic fluctuations but also generate them via sound waves. This model is used to examine an existing observational method known as the ‘Chandrasekhar-Fermi method’ (CF53) for the diagnosis of magnetic fields in astrophysical plasmas. CF53 is commonly applied to objects such as nebulae and molecular clouds which are partially-ionised plasmas. It assumes that the gas motion can be used to infer the magnetic field strength, given coupling between Alfv´en waves in the plasma and the thermal motion of the neutral gas. Computational results show that this method may need to be refined, and that certain assumptions made should be re-evaluated. This is consistent with reports in the literature of CF53 under- or over-estimating the magnetic fields in objects such as molecular clouds. The second part of this thesis concentrates on the non-equilibrium evolution of magnetic field structures at the onset of the large-scale recombination of an inhomogeneouslyionised plasma, such as the Universe was during the epoch of recombination. The conduction currents sustaining the magnetic structure will be removed as the charges comprising them combine into neutrals. The effect that a decaying magnetic flux has on the acceleration of remaining charged particles via the transient induced electric field is considered. Since the residual charged-particle number density is small as a result of decoupling, the magnetic and electric fields can be considered essentially to be imposed, neglecting for now the feedback from any minority accelerated population. The electromagnetic treatment of this phase transition can produce energetic electrons scattered throughout the Universe. Such particles could have a significant effect on cosmic evolution in several ways: (i) their presence could influence the overall physics of the recombination era; and (ii) a population of energetic particles might lend a Coulomb contribution to localized gravitational collapse. This is confirmed by a numerical simulation in which a magnetic domain is modelled as a uniform field region produced by a thin surrounding current sheet. The imposed decay of the current sheet simulates the formation of neutrals characteristic of the decoupling era, and the induced electric field accompanying the magnetic collapse is able to accelerate ambient stationary electrons (that is, electrons not participating in the current sheet) to energies of up to order 10keV. This is consistent with theoretical predictions

The impact of the mandatory rest period in Fédération Equestre Internationale endurance events

Background: Endurance riding competitions are increasingly popular, with a corresponding awareness of the frequency of Failure to Qualify (FTQ) due to lameness or metabolic problems. Fédération Equestre Internationale (FEI) rules require a minimum number of days between competitions, known as a mandatory rest period (MRP). Objectives: To analyse the impact on FTQ outcomes of MRPs which applied between January 2014 and December 2016, and model potential changes to MRPs to establish which rule change could lead to the largest further reduction in the number of FTQ outcomes. Study design: Retrospective cohort study and predictive model using a subset of data collected by the FEI of every horse start worldwide in Concours de Raid d’Endurance Internationale (CEI) competitions between 2010 and 2017. Methods: Descriptive statistics followed by predictive/retrospective modelling of potential scenarios. Scenarios involved extended MRP for all horses and/or for only the fastest ridden horses. Results: There were clear direct benefits demonstrated from the introduction of MRPs. Among directly affected horses, current MRPs could have prevented 2.3% of FTQ outcomes. Further benefits could be gained by extending MRPs. The ‘best‐value’ impact could be found in a 1‐week extension for all horses plus a 1‐week extension for the fastest ridden horses – which could result in a reduction of up to 11.5% of FTQ outcomes among directly affected horses. Main limitations: The data set covers all FEI competitions but no National Federation events. The data set is geographically comprehensive but it does not include every competition started by every individual horse. Training data for each horse were not available. Conclusions: Mandatory rest periods for horses between endurance competitions have had the intended impact of reducing numbers of FTQ outcomes in CEI events. Further benefits could be gained by extending rest periods for all horses and/or for horses ridden at the highest average speeds

A description of veterinary eliminations within British National Endurance rides in the competitive season of 2019

Veterinary eliminations within the equestrian sport of endurance have predominantly been evaluated based on data from international competitions. However, in order to take part in international competition, each horse and rider must qualify by completing rides under their national federation. The aim of this study was to analyse the competitive data and veterinary eliminations, specifically lameness, from competitions run by the British governing body of endurance: Endurance GB, during the 2019 competitive season. Competitive results for 765 ride starts from seven different ride venues were evaluated; 81.6% (n=624) horses successfully completed the rides, with the remaining 18.4% (n=141) failing to complete the ride. The majority of horses that were unsuccessful were eliminated for lameness at veterinary inspections (n=83; 58.9%). Horses competing in single loop rides (up to 55 km rides) had a success rate of 88.6% (n=624), in contrast, horses competing in rides of three loops or more (>80 km rides) reported a decreased success rate of 61.8% (n=81). Hindlimb lameness was identified more frequently (n=50; 60.2%) compared with forelimb lameness (n=33; 39.8%). Further consideration should be given to the differences between single loop rides, where a higher percentage are presented to the veterinary panel as lame prior to the start, and multi loop rides, where a higher percentage of horses are eliminated lame during the ride and potential risk factors for the increased prevalence of hindlimb lameness observed

Factors associated with safe completion of Fédération Equestre Internationale eventing cross‐country (2008–2018)

Background Equestrian eventing involves competing in three phases: dressage, jumping, and cross-country. Competitors are ranked by number of penalties accrued—with those who have fewer penalties ranked higher. Completing the cross-country phase with zero obstacle penalties is commonly referred to as ‘running clear’. Understanding factors associated with running clear can help athletes plan strategically for success, while also helping governing bodies to refine qualification criteria for elite levels. Objectives This study was carried out to identify factors associated with running clear in the cross-country phase of Fédération Equestre Internationale (FEI) eventing. Study design Retrospective cohort study of 107 348 horse starts worldwide in all FEI competitions between January 2008 and December 2018. Methods Multivariable logistic regression models constructed stepwise using a bi-directional process. Two study cohorts were assessed: a complete cohort that met all inclusion requirements and separately, a cohort that included only horses starting at the level above their previous start. Results Sixteen factors were associated with running clear. Factors associated with increased likelihood of doing so included lower event level, lower dressage score earlier in the event, fewer recent FEI event starts, and more clear runs in their previous three FEI events. For horses that had stepped up an event level, 14 of these factors were still associated with running clear. Main limitations Data available covered only FEI events, no national federation competitions were available for inclusion in horse histories. No prior veterinary information or data on training were available. Conclusions This study provides a framework that allows stakeholders to potentially better understand the appropriate level of competition for any particular horse/rider combination, given the combination's recent history. This could provide an additional direct benefit in terms of safety by reducing the likelihood of a combination falling during cross-country

Student Attainment in the First Year of a Master’s Degree in Veterinary Nursing: Do Entry Qualifications Matter?

Background: Entry to the VN profession is achieved through a parallel pathway of degree and diploma-level qualification. Post-registration, VNs are encouraged by the RCVS to participate in lifelong learning and gain higher levels of specialised skills, and since 2019 they have accredited a selection of postgraduate (PG) programmes. These programmes typically recruit students from varied academic backgrounds, however it is unclear if this impacts their attainment. Summary of work: This study aimed to describe student attainment and retention in the first year (PG certificate) of a three-year master’s degree in Advanced Practice in Veterinary Nursing. All 68 student admissions records were reviewed and anonymised demographic and academic data collected, including route of qualification and grade point average (GPA) following completion of 60-credits. The majority resided in the UK (63.2%), were female (95.6%), with a median age of 34 years. Most held a VN qualification that was below degree-level (73.5%), though 8.8% had also ‘topped-up’ to a degree. The median length of qualification was 7 years. Of the 41 students who had thus far completed 60-credits, all had achieved a passing GPA, with 51.2% classified as a merit, and 7.3% with a distinction. Students in the latter group all held VN qualifications below degree-level. The overall attrition rate was 14.7%, where 10.3% withdrew at the outset. Of the non-completers, 70% were below degree-level, 20% were degree-level, and 10% held both qualifications. No academic factors were associated with attainment at the 95% level of statistical significance. Take home message: Levels of student attainment on this PG programme were high and showed that VNs from all academic backgrounds can succeed at masters-level study. VNs who have qualified through non-degree routes should not be excluded from PG study but may require additional support at the start to prevent withdrawal

Comparison of loop-mediated isothermal amplification (LAMP) and PCR for the diagnosis of infection with Trypanosoma brucei ssp. in equids in The Gambia

Introduction: Infection of equids with Trypanosoma brucei (T. brucei) ssp. is of socioeconomic importance across sub-Saharan Africa as the disease often progresses to cause fatal meningoencephalitis. Loop-mediated isothermal amplification (LAMP) has been developed as a cost-effective molecular diagnostic test and is potentially applicable for use in field-based laboratories. Part I: Threshold levels for T. brucei ssp. detection by LAMP were determined using whole equine blood specimens spiked with known concentrations of parasites. Results were compared to OIE antemortem gold standard of T. brucei-PCR (TBR-PCR). Results I: Threshold for detection of T. brucei ssp. on extracted DNA from whole blood was 1 parasite/ml blood for LAMP and TBR-PCR, and there was excellent agreement (14/15) between tests at high (1 x 103/ml) concentrations of parasites. Detection threshold was 100 parasites/ml using LAMP on whole blood (LWB). Threshold for LWB improved to 10 parasites/ml with detergent included. Performance was excellent for LAMP at high (1 x 103/ml) concentrations of parasites (15/15, 100%) but was variable at lower concentrations. Agreement between tests was weak to moderate, with the highest for TBR-PCR and LAMP on DNA extracted from whole blood (Cohen’s kappa 0.95, 95% CI 0.64–1.00). Part II: A prospective cross-sectional study of working equids meeting clinical criteria for trypanosomiasis was undertaken in The Gambia. LAMP was evaluated against subsequent TBR-PCR. Results II: Whole blood samples from 321 equids in The Gambia were processed under field conditions. There was weak agreement between LWB and TBR-PCR (Cohen’s kappa 0.34, 95% CI 0.19–0.49) but excellent agreement when testing CSF (100% agreement on 6 samples). Conclusions: Findings support that LAMP is comparable to PCR when used on CSF samples in the field, an important tool for clinical decision making. Results suggest repeatability is low in animals with low parasitaemia. Negative samples should be interpreted in the context of clinical presentation

Fédération Equestre Internationale eventing: Fence‐level risk factors for falls during the cross‐country phase (2008–2018)

Abstract Background The equestrian discipline of eventing tests athletes' and horses' skill over three phases: dressage, jumping and cross-country. Falls during cross-country can be particularly serious and result in serious or fatal injury for both horse and athlete. Cross-country course and fence design are crucial contributory factors to safety. Objectives To provide descriptive statistics and identify fence-level risk factors for horses competing in Fédération Equestre Internationale (FEI) events worldwide. Study Design Retrospective cohort study. Methods Data were collected for every horse start worldwide in all international (CI), championship (CH), Olympics (OG) and World Equestrian Games (WEG) eventing competitions between January 2008 and December 2018 and univariable logistic regression, followed by multivariable logistic regression were applied. The final model was built in a stepwise bi-directional process, with each step assessed by the Akaike information criterion. Results Risk factors were identified at the fence level covering aspects of fence design and course design. Ten fence types were at increased odds of a fall occurring compared with square spread fences, and seven types were at reduced odds. Fences with an approach downhill (odds ratio [OR] 1.35, 95% confidence interval [CI] 1.19–1.52), with landing into water (OR 1.82, CI 1.62–2.01), frangible devices (OR 1.28, CI 1.15–1.41) and later elements of combined obstacles (OR 1.33 CI 1.25–1.42 for the second element, OR 1.21 CI 1.10–1.32 for later elements) were associated with increased risk of falls occurring. Main Limitations Although the dataset covers every international competition worldwide, it does not include national-level competitions. Conclusions It is recommended that the most challenging fences are placed near the beginning of the course, and not in downhill or water settings. The complexity of individual elements in combined fences should be reduced. Adopting evidence-based course design is a crucial intervention for reducing the incidence of horse falls and associated serious and fatal injuries to horse and human athletes

Fédération Equestre Internationale (FEI) eventing: risk factors for horse falls and unseated riders during the cross‐country phase (2008‐2018)

Background: Eventing is an equestrian sport that tests athletes’ and horses’ skill over three phases: dressage, jumping, and cross-country. Falls during the cross-country phase can have very serious outcomes up to and including death for both horse and athlete. Therefore, understanding risk factors associated with falls is essential for improving equine and human welfare. Objectives: To provide descriptive statistics and identify risk factors at the horse-, athlete-, and course-level affecting horses competing in Fédération Equestre Internationale (FEI) events worldwide. Study design: Retrospective cohort study. Methods: Data collected by the FEI of every horse start worldwide in all international (CI), championship (CH), Olympics (OG), and World Equestrian Games (WEG) competitions between January 2008 and December 2018 were analysed. Descriptive statistics followed by univariable logistic regression to identify risk factor candidates for inclusion in the final multivariable logistic regression model. Models were constructed stepwise using a bi-directional process and assessed using the Akaike information criterion. Results: Factors associated with increased risk of falls and or unseated rider included: higher event levels, longer course distances, more starters at cross-country phase, and less experienced horses and athletes. Main limitations The data set is geographically comprehensive but covers only FEI competitions, not National Federation events i.e. not every competition started by every individual horse. Nor does the data set include any prior veterinary information or data on training or schooling. Conclusions: This is the first large-scale epidemiological study of cross-country falls in FEI eventing. Results suggest that a potential risk profile can be constructed for each horse-athlete combination prior to entering a given competition, based on individual histories and course-level factors. This could lead to interventions that can reduce the number of falls, thus protecting equine and human welfare

Risk factors for lameness elimination in British endurance riding

Background: Horse welfare is a priority in the equine sport of endurance riding. Identification and reduction of risk factors associated with elimination and lameness have been the focus of research to date, however, this has centred on international competition. National federations recognise there is a need to consider risk factors for elimination at a more local level. Objectives: Determine current risk factors associated with horse eliminations, specifically lameness eliminations within British endurance. Study design: Retrospective cohort study. Methods: Data were extracted from the Endurance GB database, for open and advanced horses, competing in rides >64 km in the 2017 and 2018 competitive seasons. Variables were analysed via univariable models which informed subsequent multivariable binary logistic regression modelling. Two models were completed: (A) horse eliminated vs. not eliminated and (B) horse lame vs. not lame. Results: One thousand seven hundred and forty-seven competitive starts were analysed; 542 horses were eliminated. Lameness accounted for 56.1% (n = 304) of eliminations. Multivariable analysis identified decreased odds of lameness in graded rides compared with race rides (adjusted odds ratio, OR 0.6; 95% confidence interval, CI 0.4–0.8). There were increased odds of elimination (OR 4.7, CI 3.5–6.5) and increased odds of lameness (OR 1.9, CI 1.2–3.06) when competing in FEI competitions of 2* and above, compared to rides run under national rules. Horses and riders who had not competed as a combination previously had increased odds of elimination (OR 2.2, CI 1.5–3.02). Main limitations: Variables which can influence performance such as speed, environmental and topographical conditions were not recorded in the data set. Only two seasons of data were analysed. Conclusions: Competitive history of horses, including the number of previous starts, previous eliminations and the category of ride entered are significant in establishing the likelihood of elimination and more specifically lameness elimination in British national endurance