Measurement and optimisation of beam quality from laser wakefield accelerators

This thesis concerns experimental work in the field of laser wakefield acceleration, with a focus on the diagnosis and optimisation of the electron beam quality. The density length parameter space of a 5TW, 0.25J laser driven wakefield accelerator was characterised. Measurements of the electron beams and x-ray pulses were reported, and optimal parameters for various metrics were found. Beam-driven acceleration was identified as the mechanism that produced energies above 211MeV, and the peak x-ray brilliance was 4.2+/-0.8E20 ph/s/mm^2/mrad^2/0.1%BW^-1. Both the electron energy and the x-ray brilliance are significantly higher than literature values using comparable laser powers. Separately, the parameter scans were used to measure an extended dephasing length of the laser-accelerated beam, attributable to semi-localised depletion of the driving laser pulse, and measure the pulse evolution rate and injection length as a function of plasma density, which was found to be slower than would be expected when only considering the longitudinal evolution. An emittance diagnostic was developed using a beam mask and electron spectrometer. This was used to measure the spectrally resolved normalised emittance of GeV beams, produced by ionisation injection in a gas jet using a 165TW, 7.4J laser. Average emittance values as low as 4um were measured, which are the lowest emittances recorded using a beam mask technique in the literature, at energies that are close to an order of magnitude higher than other beam mask methods. The effect of density ramps and plasma mirrors on electron beam divergence was measured in the context of staged wakefield acceleration, using a 242TW, 11J laser. Termination of an acceleration stage with a plasma mirror was found to increase total beam divergence from 3.38+/-0.07mrad to 6.13+/-0.13mrad, and the effect was observed to persist at high energies, up to 2.2GeV. Using simulations and numerical models, the presence of the density ramp was shown to have a divergence-reducing effect with a magnitude that matched the experiment. The 10^3 tesla magnetic fields generated in plasma mirrors were investigated using simulations, and the effect of these fields on the electron beam was quantified. Compared to normal incidence, a 45 degree angle of the plasma mirror to the beam axis was found to reduce the integrated magnetic fields inside the mirror, with beneficial effects on electron beam emittance.Open Acces

An ecological model to understand the variety in undergraduate students’ personal information systems

A first-year undergraduate course in Information Systems in a South African university includes an opportunity for students to reflect on their own use of information and personal information systems. Their reflections provide data about the technologies and tools that they use to find and manage everyday life information, as well as academic information, and about the sources of information they draw on. This paper analyses data collected over three years and reports on the dominant technologies and information sources that students use. We then adapt the ecological model of information seeking and use developed by Williamson (1998) to make sense of the diversity of information sources and students’ choices in engaging with them. The results show that students rely to a very small degree on traditional university information sources. The study offers insights into the information contexts and behaviour of students and argues for the importance of a flexible range of information sources to support students in the complex process of managing information for academic success. The results will be of interest to those involved in designing and delivering undergraduate programmes, as well as those providing information services and infrastructures

An example of goal-directed proof

We prove a non-trivial property of relations in a way that emphasises the creative process in its construction.Comment: 9 pages. Submitted for publicatio

Exploring what patients with musculoskeletal conditions want from first point of contact health practitioners

Objectives This research was conducted to support the development of the Musculoskeletal (MSK) Health Capabilities Framework to ensure the framework reflected patients’ priorities. The aim of this study was to explore what patients with MSK problems want from their initial consultation with a first contact health practitioner and from the patient perspective what characterises a good first contact health practitioner. Methods Focus groups were held in four locations across England. Sixteen participants with a self-declared MSK condition aged 19 to 75 took part (11 female, five male). Participants discussed the questions they want answered when first going to see a health professional about a MSK problem and how they would describe a good first contact health provider. Results Participants wanted answers to questions about: the nature of the problem, the management of the problem, where to get information and support to help themselves, what activities they can do and what the future holds. Values and behaviours they expect and value from first contact health practitioners include: good communication skills, appreciation of impact, a willingness to discuss alternative and complementary therapies, shared decision making and an awareness of own limitations and when to refer. Conclusion The MSK core capabilities framework for first contact health practitioners aims to ensure a person-centred approach in the first stages of managing any MSK problem a person may present with. The focus groups enabled the developers of the framework to achieve a greater understanding of patient priorities, expectations and needs and allowed the patient perspective to be included in this national framework

CODIFI (Concordance in Diabetic Foot Ulcer Infection) : a cross-sectional study of wound swab versus tissue sampling in infected diabetic foot ulcers in England

OBJECTIVE: To determine the extent of agreement and patterns of disagreement between wound swab and tissue samples in patients with an infected diabetic foot ulcer (DFU). DESIGN: Multicentre, prospective, cross-sectional study. SETTING: Primary and secondary care foot ulcer/diabetic outpatient clinics and hospital wards across England. PARTICIPANTS: Inclusion criteria: consenting patients aged ≥18 years; diabetes mellitus; suspected infected DFU. EXCLUSION CRITERIA: clinically inappropriate to take either sample. INTERVENTIONS: Wound swab obtained using Levine's technique; tissue samples collected using a sterile dermal curette or scalpel. OUTCOME MEASURES: Coprimary: reported presence, and number, of pathogens per sample; prevalence of resistance to antimicrobials among likely pathogens. Secondary: recommended change in antibiotic therapy based on blinded clinical review; adverse events; sampling costs. RESULTS: 400 consenting patients (79% male) from 25 centres.Most prevalent reported pathogens were Staphylococcus aureus (43.8%), Streptococcus (16.7%) and other aerobic Gram-positive cocci (70.6%). At least one potential pathogen was reported from 70.1% of wound swab and 86.1% of tissue samples. Pathogen results differed between sampling methods in 58% of patients, with more pathogens and fewer contaminants reported from tissue specimens.The majority of pathogens were reported significantly more frequently in tissue than wound swab samples (P<0.01), with equal disagreement for S. aureus and Pseudomonas aeruginosa. Blinded clinicians more often recommended a change in antibiotic regimen based on tissue compared with wound swab results (increase of 8.9%, 95% CI 2.65% to 15.3%). Ulcer pain and bleeding occurred more often after tissue collection versus wound swabs (pain: 9.3%, 1.3%; bleeding: 6.8%, 1.5%, respectively). CONCLUSION: Reports of tissue samples more frequently identified pathogens, and less frequently identified non-pathogens compared with wound swab samples. Blinded clinicians more often recommended changes in antibiotic therapy based on tissue compared with wound swab specimens. Further research is needed to determine the effect of the additional information provided by tissue samples. TRIAL REGISTRATION NUMBER: ISRCTN52608451

Sex Differences in Cerebral Small Vessel Disease: A Systematic Review and Meta-Analysis

Background: Cerebral small vessel disease (SVD) is a common cause of stroke, mild cognitive impairment, dementia and physical impairments. Differences in SVD incidence or severity between males and females are unknown. We assessed sex differences in SVD by assessing the male-to-female ratio (M:F) of recruited participants and incidence of SVD, risk factor presence, distribution, and severity of SVD features. Methods: We assessed four recent systematic reviews on SVD and performed a supplementary search of MEDLINE to identify studies reporting M:F ratio in covert, stroke, or cognitive SVD presentations (registered protocol: CRD42020193995). We meta-analyzed differences in sex ratios across time, countries, SVD severity and presentations, age and risk factors for SVD. Results: Amongst 123 relevant studies (n = 36,910 participants) including 53 community-based, 67 hospital-based and three mixed studies published between 1989 and 2020, more males were recruited in hospital-based than in community-based studies [M:F = 1.16 (0.70) vs. M:F = 0.79 (0.35), respectively; p &lt; 0.001]. More males had moderate to severe SVD [M:F = 1.08 (0.81) vs. M:F = 0.82 (0.47) in healthy to mild SVD; p &lt; 0.001], and stroke presentations where M:F was 1.67 (0.53). M:F did not differ for recent (2015–2020) vs. pre-2015 publications, by geographical region, or age. There were insufficient sex-stratified data to explore M:F and risk factors for SVD. Conclusions: Our results highlight differences in male-to-female ratios in SVD severity and amongst those presenting with stroke that have important clinical and translational implications. Future SVD research should report participant demographics, risk factors and outcomes separately for males and females. Systematic Review Registration: [PROSPERO], identifier [CRD42020193995]

A systematic review and meta-analysis of randomised controlled trials on surgical treatments for ingrown toenails part I : recurrence and relief of symptoms

Background Ingrown toenails are a common nail pathology. When conservative treatments are ineffective, a surgical approach is often utilised. Despite recent narrative reviews, there is a need for an up-to-date and rigorous systematic review of surgical methods for treating ingrown toenails. Methods Five databases (MEDLINE, Embase, CINAHL, Web of Science and CENTRAL) and two registers (Clinicaltrials.gov and ISRCTN) were searched to January 2022 for randomised trials evaluating the effects of a surgical intervention(s) for ingrown toenails with a follow-up of at least 1 month. Two independent reviewers screened records, extracted data, assessed risk of bias and certainty of evidence. Results Of 3,928 records identified, 36 (3,756 participants; 62.7% males) surgical interventions were included in the systematic review and 31 studies in the meta-analysis. There was very low quality evidence that using phenol with nail avulsion vs nail avulsion without phenol reduces the risk of recurrence (risk ratio [RR] 0.13 [95% CI 0.06 to 0.27], p < 0.001). No favourable effect was observed between chemical or surgical vs conservative management (0.55 [0.19 to 1.61], p = 0.280; 0.72 [0.33 to 1.56], p = 0.410), chemical or surgical vs other (e.g., CO2 laser, electrocautery) (1.61 [0.88 to 2.95], p = 0.120; 0.58 [0.25 to 1.37], p = 0.220), chemical vs surgical (0.75 [0.46 to 1.21], p = 0.230), surgical vs surgical (0.42 [0.21 to 0.85]), chemical vs chemical (0.19 [0.01 to 3.80], p = 0.280), surgical vs surgical + chemical (3.68 [0.20 to 67.35], p = 0.380), chemical vs surgical + chemical (1.92 [0.06 to 62.30], p = 0.710), local anaesthetic vs local anaesthetic + adrenaline (1.03 [0.22 to 4.86], p = 0.970), chemical timings 30 s vs 60 s (2.00 [0.19 to 21.41]) or antibiotics vs no antibiotics (0.54 [0.12 to 2.52], p = 0.430). Central toenail resection was the only procedure to significantly relieve symptoms (p = 0.001) but data were only available up to 8 weeks post-surgery. Conclusion Despite the high number of publications, the quality of research was poor and the conclusions that can be inferred from existing trials is limited. Phenolisation of the nail matrix appears to reduce the risk of recurrence following nail ablation, and with less certainty 1 min appears to be the optimum time for application. Despite this being a widely performed procedure there remains a lack of good quality evidence to guide practice

Preliminary concurrent validity of the Fitbit-Zip and ActiGraph activity monitors for measuring steps in people with polymyalgia rheumatica

Background Activity monitors provide objective measurements of physical activity, however, the accuracy of these devices in people with polymyalgia rheumatica (PMR) is unknown. Therefore, this study aimed to obtain preliminary evidence of the accuracy of two activity monitors and explore if clinical and gait-related factors altered device accuracy in people with PMR. Methods The ActiGraph with low frequency extension (+LFE) and standard (-LFE) algorithms, Fitbit-Zip (waist) and Fitbit-Zip (shirt) were concurrently tested using a two-minute walk test (2MWT) and stairs test in 27 people with PMR currently treated with prednisolone. To determine accuracy, activity monitor step-count was compared to a gold-standard step-count (GSSC; calculated from video recording) using Bland-Altman plots. Results The Fitbit-Zip (waist) achieved closest agreement to the GSSC for the 2MWT (mean bias (95%CI): 10 (-3, 23); 95%LOA: −55, 74). The ActiGraph (+LFE) achieved closest agreement to the GSSC for the stairs test (mean bias (95%CI): 0 (-1, 1); 95%LOA: −5, 5). The ActiGraph (-LFE) performed poorly in both tests. All devices demonstrated reduced accuracy in participants with lower gait velocity, reduced stride length, longer double-limb support phase and greater self-reported functional impairment. Conclusion Our preliminary results suggest that in controlled conditions, the Fitbit-Zip fairly accurately measures step-count during walking in people with PMR receiving treatment. However, device error was greater than data published in healthy people. The ActiGraph may not be recommended without activation of the LFE. We identified clinical and gait-related factors associated with higher levels of functional impairment that reduced device accuracy. Further work is required to evaluate the validity of the activity monitors in field conditions