Hydroelastic waves and their interaction with fixed structures

A selection of problems are presented which study the interaction of hydroelastic waves with fixed structures. A thin floating elastic plate model is considered which primarily represents a continuous floating ice sheet, but may also be applied to very large floating platforms. The incident hydroelastic waves are assumed to either propagate from long–distance towards the structures or be generated by a moving load. All aspects of the subsequent interaction are studied in detail. The elastic plate is clamped to the fixed vertical structures to model an ice sheet frozen to the structure boundary. Both linear and nonlinear formulations are admitted for a selection of two– and three–dimensional problems. For the linear problems, selection of appropriate integral transforms leads to explicit analytical solutions in terms of integral quadratures. For the nonlinear case, the numerical solution is found by application of Green’s second identity combined with a boundary element method. The resulting deflection fields are analysed as well as the strain in the ice sheet due to curvature from the hydroelastic waves. Particular attention is paid to the strain at the ice–structure boundary. The integral transforms also lead to concise expressions for the horizontal and vertical wave forces impacting on the structure. It is shown that these forces may reach a substantial magnitude and must be taken into account for the design of structures in ice–covered water. Several assumptions are utilised which allow the problems to be mathematically treatable while retaining accuracy. Realistic effects such as viscoelasticity and fluid stratification are studied. The solutions are investigated in detail under the variation of physical parameters of the fluid, the ice sheet and the incident/load–generated waves, based on realistic values from cold climate regions

Exploring the relationships between perfectionism, speech-monitoring and disfluency in the speech of people who do and do not stutter

This study investigates the hypothesis that domain-general perfectionism, as measured by the Frost Multidimensional Perfectionism Scale (FMPS: Frost, Marten, Lahart, & Rosenblate, 1990), is associated with hyper-vigilant speech monitoring, and with raised levels of disfluency in both normal and stuttered speech. It consists of two parts: (1) an online survey of perfectionism in people who stutter; and (2) a tongue-twister experiment conducted on people who do not stutter. The tongue-twister experiment included an auditory-masking condition which enabled an assessment of the impact of reduced speech-monitoring on participants’ disfluency rates. In the online survey both stuttering and stuttering participants’ self-ratings of difficulty speaking fluently were found to be associated with raised Concern over Mistakes and low Personal Standards FMPS subscale self-ratings. In the tongue-twister experiment, in which disfluency rates were measured directly, corresponding correlations were not found and, although participants’ disfluency rates overall were significantly reduced when auditory masking was applied, the size of the reduction was not modulated by their perfectionism ratings. It was concluded that (1) the perfectionism self-ratings provided by respondents who stutter in the online survey were likely to have reflected their attitudes and beliefs that related specifically to speaking and thus did not constitute evidence of a link between domain-general perfectionism and stuttering or disfluent speech; and (2) less vigilant monitoring improves the overall quality of speech irrespective of whether or not speakers are perfectionists. The potential clinical implications of these findings are discussed

Electro-mechanical dynamics of spiral waves in a discrete 2D model of human atrial tissue

We investigate the effect of mechano-electrical feedback and atrial fibrillation induced electrical remodelling (AFER) of cellular ion channel properties on the dynamics of spiral waves in a discrete 2D model of human atrial tissue. The tissue electro-mechanics are modelled using the discrete element method (DEM). Millions of bonded DEM particles form a network of coupled atrial cells representing 2D cardiac tissue, allowing simulations of the dynamic behaviour of electrical excitation waves and mechanical contraction in the tissue. In the tissue model, each cell is modelled by nine particles, accounting for the features of individual cellular geometry; and discrete inter-cellular spatial arrangement of cells is also considered. The electro-mechanical model of a human atrial single-cell was constructed by strongly coupling the electrophysiological model of Colman et al. to the mechanicalmyofilament model of Rice et al., with parameters modified based on experimental data. A stretch-activated channel was incorporated into the model to simulate the mechano-electrical feedback. In order to investigate the effect of mechano-electrical feedback on the dynamics of spiral waves, simulations of spiral waves were conducted in both the electromechanical model and the electrical-only model in normal and AFER conditions, to allow direct comparison of the results between the models. Dynamics of spiral waves were characterized by tracing their tip trajectories, stability, excitation frequencies and meandering range of tip trajectories. It was shown that the developed DEM method provides a stable and efficient model of human atrial tissue with considerations of the intrinsically discrete and anisotropic properties of the atrial tissue, which are challenges to handle in traditional continuum mechanics models. This study provides mechanistic insights into the complex behaviours of spiral waves and the genesis of atrial fibrillation by showing an important role of the mechano-electrical feedback in facilitating and promoting atrial fibrillation

Roles of speech errors, monitoring, and anticipation in the production of normal and stuttered disfluencies

Grant Award no. ES/G01230X/1In their Covert Repair Hypothesis (CRH), Postma and Kolk (1993) proposed that stuttering-like disfluencies arise, in both normal and stuttered speech, as a consequence of speakers‟ attempts to repair phonological-encoding errors before they start to speak. They posited that stutterers are particularly disfluent because they make larger numbers of such errors compared to normally-fluent speakers. To date, however, experimental research has provided little reliable evidence to support or counter this hypothesis. This thesis constitutes a systematic attempt to provide such evidence. Using a tongue-twister paradigm in conjunction with manipulations of auditory masking, it first documents (a) the vigilance with which normally-fluent speakers monitor for such errors; (b) the relative accuracy with which they detect them; and (c) the frequency with which they occur – in both inner and overt speech. A second set of experiments then extends the same investigation to a group of stutterers and matched controls and explores the relationship between the occurrence of participants‟ errors in the experimental paradigm and the frequency of their stuttering-like disfluencies in everyday speaking situations. Together, these experiments reveal that, compared to controls, participants who stutter monitor their speech with similar levels of vigilance; identify phonemic errors with similar degrees of accuracy; and, as predicted by the CRH, produce significantly more errors – in both their inner and overt speech. However, contrary to the predictions of the CRH, no relationship was found between the frequency of such errors in inner speech and the severity of participants‟ disfluencies. In a final set of experiments, a speech-recognition paradigm is employed to explore an alternative hypothesis: that stuttering-like disfluencies can be precipitated, in a speaker, by the mere anticipation that his words will result in communication failure. Results revealed that, for stutterers, stuttering decreased on words that were consistently followed by feedback implying correct recognition, but not on words followed by feedback implying incorrect recognition. For normally-fluent speakers, equivalent correlations were not found. The thesis concludes that slow or impaired phonological encoding may play a role in the development of the disorder. But, once established, the anticipation of communication failure may be a more important factor in determining where and when stuttering-like disfluencies actually occur. It then discusses implications of the experimental findings for hypotheses that posit a connection between phonological encoding and stuttering

Managing an ageing population: challenging oral epidemiology

Global population projections indicate that the proportion of older people is increasing and will continue to do so for the foreseeable future. Many countries are already experiencing the challenges of managing an ageing population, including increased pension contributions from workers, rises to national retirement ages, and spiralling healthcare costs. In oral health terms, in addition to simply an ageing population, epidemiological studies have demonstrated significant changes in the oral health of older adults in recent years. As the numbers of edentulous older adults has declined, there has been a significant increase in the number of partially dentate elderly. Changing attitudes, improved access to dental care and more effective preventative programmes have meant that large numbers of patients are now retaining natural teeth into old age. However, as older patients retain natural teeth for longer, the dental profession is charged with controlling chronic dental diseases in an increasingly challenging oral environment

The Completeness of the Fossil Record of Mesozoic Birds: Implications for Early Avian Evolution

Many palaeobiological analyses have concluded that modern birds (Neornithes) radiated no earlier than the Maastrichtian, whereas molecular clock studies have argued for a much earlier origination. Here, we assess the quality of the fossil record of Mesozoic avian species, using a recently proposed character completeness metric which calculates the percentage of phylogenetic characters that can be scored for each taxon. Estimates of fossil record quality are plotted against geological time and compared to estimates of species level diversity, sea level, and depositional environment. Geographical controls on the avian fossil record are investigated by comparing the completeness scores of species in different continental regions and latitudinal bins. Avian fossil record quality varies greatly with peaks during the Tithonian-early Berriasian, Aptian, and Coniacian–Santonian, and troughs during the Albian-Turonian and the Maastrichtian. The completeness metric correlates more strongly with a ‘sampling corrected’ residual diversity curve of avian species than with the raw taxic diversity curve, suggesting that the abundance and diversity of birds might influence the probability of high quality specimens being preserved. There is no correlation between avian completeness and sea level, the number of fluviolacustrine localities or a recently constructed character completeness metric of sauropodomorph dinosaurs. Comparisons between the completeness of Mesozoic birds and sauropodomorphs suggest that small delicate vertebrate skeletons are more easily destroyed by taphonomic processes, but more easily preserved whole. Lagerstätten deposits might therefore have a stronger impact on reconstructions of diversity of smaller organisms relative to more robust forms. The relatively poor quality of the avian fossil record in the Late Cretaceous combined with very patchy regional sampling means that it is possible neornithine lineages were present throughout this interval but have not yet been sampled or are difficult to identify because of the fragmentary nature of the specimens

Socioeconomic disparities in orthodontic treatment outcomes and expenditure on orthodontics in England's state-funded National Health Service:A retrospective observational study

Percentage distribution/means of variables used in the adjusted treatment outcomes analyses, by socioeconomic status (SES). Additional file 1 contains information on the distribution of variables used to adjust for potential confounding: IOTN AC scores, gender, and age. This information is provided by IMD quintile. (DOCX 16 kb

Productive efficiency and its determinants in the Community Dental Service i nthe north-west of England

To assess the efficiency of service provision in the Community Dental Services and its determinants in the North-West of England.40 Community Dental Services sites operating across the North-West of England.A data envelopment analysis was undertaken of inputs (number of surgeries, hours worked by dental officers, therapists, hygienists and others) and outputs (treatments delivered, number of courses of treatment and patients seen) of the Community Dental Services to produce relative efficiency ratings by health authority. These were further analyzed in order to identify which inputs (determined within the Community Dental Services) or external factors outside the control of the Community Dental Services are associated with efficiency.Relative efficiency rankings in Community Dental Services production of dental healthcare.Using the quantity of treatments delivered as the measure of output, on average the Community Dental Services in England is operating at a relative efficiency of 85% (95% confidence interval 77%- 99%) compared to the best performing services. Average efficiency is lower when courses of treatment and unique patients seen are used as output measures, 82% and 68% respectively. Neither the input mix nor the patient case mix explained variations in the efficiency across Community Dental Services.Although large variations in performance exist across Community Dental Services, the data available was not able to explain these variations. A useful next step would be to undertake detailed case studies of several best and under-performing services to explore the factors that influence relative performance levels