Effect of the coefficient of friction of a running surface on sprint time in a sled-towing exercise

This is an Author's Accepted Manuscript of an article published in Sports Biomechanics, 12(2), 175 - 185, 2013, copyright Taylor & Francis, available online at: http://www.tandfonline.com/10.1080/14763141.2012.726638,This study investigated the effect of the coefficient of friction of a running surface on an athlete's sprint time in a sled-towing exercise. The coefficients of friction of four common sports surfaces (a synthetic athletics track, a natural grass rugby pitch, a 3G football pitch, and an artificial grass hockey pitch) were determined from the force required to tow a weighted sled across the surface. Timing gates were then used to measure the 30-m sprint time for six rugby players when towing a sled of varied weight across the surfaces. There were substantial differences between the coefficients of friction for the four surfaces (μ = 0.21–0.58), and in the sled-towing exercise the athlete's 30-m sprint time increased linearly with increasing sled weight. The hockey pitch (which had the lowest coefficient of friction) produced a substantially lower rate of increase in 30-m sprint time, but there were no significant differences between the other surfaces. The results indicate that although an athlete's sprint time in a sled-towing exercise is affected by the coefficient of friction of the surface, the relationship relationship between the athlete's rate of increase in 30-m sprint time and the coefficient of friction is more complex than expected

Nonlinear control of a flexible aeroelastic system

Although it is a common practice in the field of Dynamics to treat a system as being linear, the assumption of linearity is only valid in situations where the effect of any nonlinearities is minimal. Significant nonlinear behaviour (such as Limit Cycle Oscillations) has been observed in many practical manifestations of aeroelastic systems, highlighting the need to account for system nonlinearities. A consequence of incorporating nonlinearity into the model is that the application of linear control methods becomes inadequate when the system operates in a substantially nonlinear regime. Thus, the present work addresses both these concerns by applying nonlinear control on an aeroelastic system consisting of a flexible wing with a structural nonlinearity. The Feedback Linearisation method is employed to render the system linear, such that linear control methods are applicable. The utility of the Small Gain Theorem and Adaptive Feedback Linearisation in situations where errors in the parameters describing the nonlinearities are present is demonstrated

Identification of systems containing nonlinear stiffnesses using backbone curves

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.This paper presents a method for the dynamic identification of structures containing discrete nonlinear stiffnesses. The approach requires the structure to be excited at a single resonant frequency, enabling measurements to be made in regimes of large displacements where nonlinearities are more likely to be significant. Measured resonant decay data is used to estimate the system backbone curves. Linear natural frequencies and nonlinear parameters are identified using these backbone curves assuming a form for the nonlinear behaviour. Numerical and experimental examples, inspired by an aerospace industry test case study, are considered to illustrate how the method can be applied. Results from these models demonstrate that the method can successfully deliver nonlinear models able to predict the response of the test structure nonlinear dynamics.This work was funded by the Engineering and Physical Sciences Research Council (EPSRC) in the UK as part of the Engineering Nonlinearity Programme Grant EP/K003836/1. Prof. S. A. Neild is supported by the EPSRC FellowshipEP/K005375/1 and Prof. J.E. Cooper is supported by the Royal Academy of Engineering in the UK through the RAEng Airbus Sir George White Chair in Aerospace Engineering. This financial support is gratefully acknowledged

Cognitive architectures as Lakatosian research programmes: two case studies

Cognitive architectures - task-general theories of the structure and function of the complete cognitive system - are sometimes argued to be more akin to frameworks or belief systems than scientific theories. The argument stems from the apparent non-falsifiability of existing cognitive architectures. Newell was aware of this criticism and argued that architectures should be viewed not as theories subject to Popperian falsification, but rather as Lakatosian research programs based on cumulative growth. Newell's argument is undermined because he failed to demonstrate that the development of Soar, his own candidate architecture, adhered to Lakatosian principles. This paper presents detailed case studies of the development of two cognitive architectures, Soar and ACT-R, from a Lakatosian perspective. It is demonstrated that both are broadly Lakatosian, but that in both cases there have been theoretical progressions that, according to Lakatosian criteria, are pseudo-scientific. Thus, Newell's defense of Soar as a scientific rather than pseudo-scientific theory is not supported in practice. The ACT series of architectures has fewer pseudo-scientific progressions than Soar, but it too is vulnerable to accusations of pseudo-science. From this analysis, it is argued that successive versions of theories of the human cognitive architecture must explicitly address five questions to maintain scientific credibility

Urbanisation and women's health in Khayelitsha Part I. Demographic and socio-economic profile

Demographic and socio-economic data and information on migration patterns and urban/rural links was collected from 722 households in the formal housing area and the serviced and the unserviced site areas of Khayelitsha; 659 women and 61 men were interviewed. Thirty-eight per cent of the population were aged under 15 years and 77% under 35 years. There was a predominance of females in the 5 - 35-year age group. There was a mean of 4,9 persons per household, and 93,5% of sites contained 1 dwelling. Of the 659 female respondents, 7% had received no formal education, 39% had primary school education, and 54% had secondary school education. unemployment among women was 45%. Domestic service accounted for 66,2% of formal employment. Of all women 86% were unskilled, 71,9% had been born in a 'homeland', and 69,7% had migrated to an urban area before 1985. Ties to the rural areas were strong, particularly in the 'shack' areas. 'New arrivals' to an urban area were young, mostly unemployed, and lived in the worst environmental conditions. In the unserviced 'shack' areas, 47,5% of women had migrated to an urban area in the last 5 years. These are important target areas for a study of the health effects of urbanisation and for possible interventions. This study tends to confirm the 'quadruple' oppression of women in Khayelitsha, on the basis of race, social class and gender and as new arrivals in an urban environment

Urbanisation and women's health in Khayelitsha Part 11. Health status and use of health services

A study was conducted among women in Khayelitsha to determine the relationship between urbanisation, health status and use of health services; 722 households were visited, and 659 female respondents provided information on acute and chronic illness for the 3229 individuals who were members of their households. In addition, they provided information concerning their reproductive health, AIDS awareness, knowledge of cervical smears and use and knowledge of health services. Acute illness was reported for .4,3% of the study population, the commonest complaints being diarrhoea, abdominal pain and upper respiratory infections; 4,4% reported chronic illness, the commonest complaints being hypertension and tuberculosis; 16,2% of women reported gynaecological illness; 86% had of heard of AIDS (although their knowledge of transmission and prevention was poor); and 45% had heard of cervical smears. Patterns of illness and knowledge and use of health services vary in the different areas of residence of Khayelitsha. This appears to be related to urbanisation, age, and environmental and socio-economic factors

Dietary patterns of university students in the UK: A cross-sectional study

© 2018 The Author(s). Background: University represents a key transition into adulthood for many adolescents but there are associated concerns about health and behaviours. One important aspect relates to diet and there is emerging evidence that university students may consume poor quality diets, with potential implications for body weight and long-term health. This research aimed to characterise dietary patterns of university students in the UK and their sociodemographic and lifestyle antecedents. Methods: An online, cross-sectional survey was undertaken with a convenience sample of 1448 university students from five UK universities (King's College London, Universities of St Andrews, Southampton and Sheffield, and Ulster University). The survey comprised a validated food frequency questionnaire alongside lifestyle and sociodemographic questions. Dietary patterns were generated from food frequency intake data using principal components analysis. Nutrient intakes were estimated to characterise the nutrient profile of each dietary pattern. Associations with sociodemographic variables were assessed through general linear modelling. Results: Dietary analyses revealed four major dietary patterns: 'vegetarian'; 'snacking'; 'health-conscious'; and 'convenience, red meat & alcohol'. The 'health-conscious' pattern had the most favourable micronutrient profile. Students' gender, age, year of study, geographical location and cooking ability were associated with differences in pattern behaviour. Female students favoured the 'vegetarian' pattern, whilst male students preferred the 'convenience, red meat & alcohol' pattern. Less healthful dietary patterns were positively associated with lifestyle risk factors such as smoking, low physical activity and take-away consumption. The health-conscious pattern had greatest nutrient density. The 'convenience, red meat & alcohol' pattern was associated with higher weekly food spending; this pattern was also identified most consistently across universities. Students reporting greater cooking ability tended towards the 'vegetarian' and 'health-conscious' patterns. Conclusions: Food intake varied amongst university students. A substantial proportion of students followed health-promoting diets, which had good nutrient profiles obviating a need for dietary intervention. However, some students consumed poor diets, incurred greater food costs and practised unfavourable lifestyle behaviours, which may have long-term health effects. University policy to improve students' diets should incorporate efforts to promote student engagement in cooking and food preparation, and increased availability of low cost healthier food items

Supersymmetric quantum mechanics with nonlocal potentials

We consider supersymmetric quantum mechanical models with both local and nonlocal potentials. We present a nonlocal deformation of exactly solvable local models. Its energy eigenfunctions and eigenvalues are determined exactly. We observe that both our model Hamiltonian and its supersymmetric partner may have normalizable zero-energy ground states, in contrast to local models with nonperiodic or periodic potentials.Comment: 4 pages, REVTeX, Minor revisions for clarificatio