New slow wave structures for travelling wave tubes

This thesis covers the design of slow wave structures for travelling wave tubes, with a specific focus on those that could be used for operation at millimetre or shorter wavelengths. Serpentine and a coupled cavity photonic crystal structure are covered in detail, together with the interaction between the electromagnetic waves they support and the electron gun and magnetic beam focusing systems needed for a travelling wave interaction. In Chapter 2, the existing small-signal theory of the travelling wave interaction is introduced and applied to a serpentine travelling wave tube. A set of synthesis equations for the serpentine structure are then derived from the analysis and verified with simulation. In Chapter 3, possible improvements to the serpentine structure for high frequency operation, and operation on harmonics other than the fundamental (for both the phase and the interaction impedance) are considered. From the investigation it can be concluded that higher harmonics allow a larger beam current than the fundamental. In Chapter 4, slow wave structures based on photonic crystals are proposed for use in travelling wave tubes. A specific photonic crystal arrangement – the coupled resonator optical waveguide (CROW) - that does not appear to have been studied previously in this application is then investigated. The conclusion is that a CROW is suitable for use in a travelling wave tube and is significantly more manufacturable than existing approaches. In Chapter 5, the design of a full electron beam system for use with both the original and the improved slow wave structures is presented. The design of an electron gun, cathode and collimating magnet using an immersed flow insertion are all covered in detail. In Chapter 6, conclusions are drawn and avenues for possible future work are presented.Open Acces

The Staff Views About Assessing Voices Questionnaire: Piloting a Novel Socratic Method of Evaluating and Training Multidisciplinary Staff's Cognitive Assessment of Patients' Distressing Voices.

Cognitive features of auditory hallucinations (voices) have important clinical significance and their assessment is vital for cognitive behavior therapy to be more widely deployed by multidisciplinary staff. Using a new Socratic instrument-The Staff Views About Assessing Voices Questionnaire (SVAVQ)-we surveyed a community inpatient rehabilitation multidisciplinary workforce's ( = 50) assessment and attitude toward asking cognitive questions about patients' voices. We found that there were many clinically important gaps in what staff asked about in relation to cognitive features of voices. We identified a range of beliefs the staff hold that may prevent assessment of voice cognitive features. However, after attending the Socratic SVAVQ interview, 84% of staff said they planned to ask patients more questions about cognitive features of patients' voices. Research could now test if other psychosis services neglect the assessment of important cognitive features of patients' voices and if staff Socratic questioning improves their cognitive assessments. [Abstract copyright: © Copyright 2021 Springer Publishing Company, LLC.

On differences in the equation-of-state for a selection of seven representative mammalian tissue analogue materials

Tissue analogues employed for ballistic purposes are often monolithic in nature, e.g. ballistic gelatin and soap, etc. However, such constructs are not representative of real-world biological systems. Further, ethical considerations limit the ability to test with real-world tissues. This means that availability and understanding of accurate tissue simulants is of key importance. Here, the shock response of a wide range of ballistic simulants (ranging from dermal (protective / bulk) through to skeletal simulant materials) determined via plate-impact experiments are discussed, with a particular focus on the classification of the behaviour of differing simulants into groups that exhibit a similar response under high strain-rate loading. Resultant Hugoniot equation-of-state data (Us-up; P-v) provides appropriate feedstock materials data for future hydrocode simulations of ballistic impact events

Mapping evidence on integrated conservation and health projects worldwide: an appeal for help in identifying past and ongoing interventions

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Visual stress, its treatment with spectral filters, and its relationship to visually induced motion sickness

We review the concept of visual stress and its relation to neurological disease. Visual stress can occur from the observation of images with unnatural spatial structure and an excess of contrast energy at spatial frequencies to which the visual system is generally most sensitive. Visual stress can often be reduced using spectral filters, provided the colour is selected with precision to suit each individual. The use of such filters and their effects on reading speed are reviewed. The filters have been shown to benefit patients with a variety of neurological conditions other than reading difficulty, all associated with an increased risk of seizures. © 2009 Elsevier Ltd

A supervised adverse drug reaction signalling framework imitating Bradford Hill’s causality considerations

Big longitudinal observational medical data potentially hold a wealth of information and have been recognised as potential sources for gaining new drug safety knowledge. Unfortunately there are many complexities and underlying issues when analysing longitudinal observational data. Due to these complexities, existing methods for large-scale detection of negative side effects using observational data all tend to have issues distinguishing between association and causality. New methods that can better discriminate causal and non-causal relationships need to be developed to fully utilise the data. In this paper we propose using a set of causality considerations developed by the epidemiologist Bradford Hill as a basis for engineering features that enable the application of supervised learning for the problem of detecting negative side effects. The Bradford Hill considerations look at various perspectives of a drug and outcome relationship to determine whether it shows causal traits. We taught a classifier to find patterns within these perspectives and it learned to discriminate between association and causality. The novelty of this research is the combination of supervised learning and Bradford Hill’s causality considerations to automate the Bradford Hill’s causality assessment. We evaluated the framework on a drug safety gold standard known as the observational medical outcomes partnership’s non-specified association reference set. The methodology obtained excellent discrimination ability with area under the curves ranging between 0.792 and 0.940 (existing method optimal: 0.73) and a mean average precision of 0.640 (existing method optimal: 0.141). The proposed features can be calculated efficiently and be readily updated, making the framework suitable for big observational data

Tinnitus Perception and Distress Is Related to Abnormal Spontaneous Brain Activity as Measured by Magnetoencephalography

BACKGROUND: The neurophysiological mechanisms underlying tinnitus perception are not well understood. Surprisingly, there have been no group studies comparing abnormalities in ongoing, spontaneous neuronal activity in individuals with and without tinnitus perception. METHODS AND FINDINGS: Here, we show that the spontaneous neuronal activity of a group of individuals with tinnitus (n = 17) is characterised by a marked reduction in alpha (8–12 Hz) power together with an enhancement in delta (1.5–4 Hz) as compared to a normal hearing control group (n = 16). This pattern was especially pronounced for temporal regions. Moreover, correlations with tinnitus-related distress revealed strong associations with this abnormal spontaneous activity pattern, particularly in right temporal and left frontal areas. Overall, effects were stronger for the alpha than for the delta frequency band. A data stream of 5 min, recorded with a whole-head neuromagnetometer under a resting condition, was sufficient to extract the marked differences. CONCLUSIONS: Despite some limitations, there are arguments that the regional pattern of abnormal spontaneous activity we found could reflect a tinnitus-related cortical network. This finding, which suggests that a neurofeedback approach could reduce the adverse effects of this disturbing condition, could have important implications for the treatment of tinnitus

Integration of medical service provision and nature conservation worldwide 1980–2022: collaborative evidence mapping of 43 projects across 22 countries

Background Biodiversity protection is fundamental to human wellbeing, and, in turn, serving human health in medically underserved areas can sometimes strengthen conservation. We aimed to collaboratively map the evidence on projects worldwide that are, or have been, providing health services with the intention of producing conservation outcomes in addition to health improvements. Methods Scoping indicated many NGO projects are never published in the academic literature. To avoid missing such interventions we asked conservation staff worldwide to contribute data online or through zoom calls. Advertising to join the collaboration was through formal networks (International Union for Conservation of Nature, Planetary Health Alliance, etc.), professional contacts, funders, and a call in The Lancet Planetary Health. Additionally, data and literature were synthesised from libraries and datasets of collaborators at Population Reference Bureau, Sussex Sustainability Research Programme, and Ecological Levers for Health. Findings Forty-three projects from 22 countries fitted inclusion criteria. Around half had not been published in the collected literature, with data only available through direct submission. Tropical wet forest was by far the most common habitat, followed by tropical dry forest, coral reefs, and tropical grasslands. The most represented region was Sub-Saharan Africa with 27 projects, followed by South-East Asia (five), South Asia (five), Oceania (two), South America (two), Central America (one), Europe (one). Projects ranged from basic health interventions bolted on to pre-existing conservation programmes to generate goodwill (e.g., vaccination rounds bordering national parks) to complex schemes jointly acting on health and biodiversity driven (and funded) by concerns for human welfare as much as conservation. Interpretation Synergistic action on biodiversity conservation and health service provision is very often effective and the approach is more widespread than literature would indicate. However, funding was usually provided on a siloed basis for either health or conservation, and this remains a barrier to wider adoption