A multi-wavelenght study of cataclysmic variable stars.

This thesis investigates the properties of two cataclysmic variables which have previously been considered to be non-magnetic systems. The goal of this work is to constrain the component star masses and other physical parameters of these systems using multi-wavelength observations. I carry out spectroscopic studies on the eclipsing nova-like system RW Tri in the ultraviolet, far red, and near infrared. I produce a simple absorption model to show that one possible scenario for the origin of ultraviolet narrow absorption features, seen in Hubble Space Telescope observations, is a ring-like structure with height above the orbital plane, centred on the primary star. I re-analyse far red data from the Issac Newton Telescope, using the tomographic technique of 'skew-mapping' to obtain the radial velocity amplitude of the secondary star. I have made new observations of RW Tri in the near infrared using the United Kingdom, Infra-Red Telescope to determine the accuracy of the secondary star radial velocity amplitude. The measured secondary star radial velocity has been combined with ultraviolet absorption line analysis and existing optical emission line data, to calculate the mass ratio, and hence the mass of the component stars. The rotational velocity of the secondary star has also been obtained from the infrared observations, and combined with the radial velocity of the secondary star to calculate more reliable component star masses. OY Car, an eclipsing dwarf nova, was observed at X-ray wavelengths using XMM-Newton. I study the light curves, and measure the extent of the boundary layer in the system. I also observe significant quasi-sinusoidal variations with an underlying periodicity of 2233 seconds, which may be the spin period of the white dwarf primary star. These results imply that OY Car may be weakly magnetic, and could therefore belong to a new class of intermediate polars below the period gap. Investigations of the eclipse profile lead to an estimate of the component star masses

A multi-wavelength study of cataclysmic variable stars

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Characteristics of 698 patients with dissociative seizures: a UK multicenter study

Objective We aimed to characterize the demographics of adults with dissociative (nonepileptic) seizures, placing emphasis on distribution of age at onset, male:female ratio, levels of deprivation, and dissociative seizure semiology. Methods We collected demographic and clinical data from 698 adults with dissociative seizures recruited to the screening phase of the CODES (Cognitive Behavioural Therapy vs Standardised Medical Care for Adults With Dissociative Non‐Epileptic Seizures) trial from 27 neurology/specialist epilepsy clinics in the UK. We described the cohort in terms of age, age at onset of dissociative seizures, duration of seizure disorder, level of socioeconomic deprivation, and other social and clinical demographic characteristics and their associations. Results In what is, to date, the largest study of adults with dissociative seizures, the overall modal age at dissociative seizure onset was 19 years; median age at onset was 28 years. Although 74% of the sample was female, importantly the male:female ratio varied with age at onset, with 77% of female but only 59% of male participants developing dissociative seizures by the age of 40 years. The frequency of self‐reported previous epilepsy was 27%; nearly half of these epilepsy diagnoses were retrospectively considered erroneous by clinicians. Patients with predominantly hyperkinetic dissociative seizures had a shorter disorder duration prior to diagnosis in this study than patients with hypokinetic seizures (P < .001); dissociative seizure type was not associated with gender. Predominantly hyperkinetic seizures were most commonly seen in patients with symptom onset in their late teens. Thirty percent of the sample reported taking antiepileptic drugs; this was more common in men. More than 50% of the sample lived in areas characterized by the highest levels of deprivation, and more than two‐thirds were unemployed. Significance Females with dissociative seizures were more common at all ages, whereas the proportion of males increased with age at onset. This disorder was associated with socioeconomic deprivation. Those with hypokinetic dissociative seizures may be at risk for delayed diagnosis and treatment