Quadrotor vehicle control via sliding mode controller driven by sliding mode disturbance observer

Over the last decade, considerable interest has been shown from industry, government and academia to the design of Vertical Take-Off and Landing (VTOL) autonomous aerial vehicles. This paper uses the recently developed sliding mode control driven by sliding mode disturbance observer (SMC-SMDO) approach to design a robust flight controller for a small quadrotor vehicle. This technique allows for a continuous control robust to external disturbance and model uncertainties to be computed without the use of high control gain or extensive computational power. The robustness of the control to unknown external disturbances also leads to a reduction of the design cost as less pre-flight analyses are required. The multiple-loop, multiple time-scale SMC-SMDO flight controller is designed to provide robust position and attitude control of the vehicle while relying only on knowledge of the limits of the disturbances. Extensive simulations of a 6 DOF computer model demonstrate the robustness of the control when faced with external disturbances (including wind, collision and actuator failure) as well as model uncertainties.     

Effects of physical activities that induce moderate external loading on bone metabolism in male athletes

Sports characterized by little or moderate weight bearing or impact have a low osteogenic effect. However, the action of such sports on bone turnover remains unclear. The objective of this study was to determine the effect on bone remodelling of physical activities that induce moderate external loading on the skeleton. Thirty-eight male athletes aged 18-39 years (cyclists, n = 11; swimmers, n = 13; triathletes, n = 14) and 10 age-matched sedentary controls aged 22-35 years participated in the study. The study combined measurement of bone mineral density by dual-energy X-ray absorptiometry and bone turnover assessment from specific biochemical markers: serum bone-specific alkaline phosphatase, osteocalcin, urinary type I collagen C-telopeptide and calcium. Compared with the controls and swimmers, adjusted bone mineral density was higher (P < 0.05) in triathletes at the total proximal femur and lower limbs. No differences in bone mineral density were found between cyclists, swimmers and controls. Compared with controls, osteocalcin was higher (P < 0.05) in triathletes and swimmers and urinary type I collagen C-telopeptide was higher in swimmers only. Serum bone-specific alkaline phosphatase was lower (P < 0.05) in cyclists than in all other groups. In conclusion, an osteogenic effect was found only in triathletes, mainly at bone sites under high mechanical stress. Bone turnover differed in athletes compared with controls, suggesting that bone turnover may be sport-practice dependent. Despite some encouraging observations, it was not possible to show that changes in the bone remodelling process were sport-discipline dependent.     

充分发挥县级图书馆社会教育职能为建设社会主义新农村服务

从公共图书馆的社会教育职能入手，阐述县级图书馆为建设社会主义新农村服务的意义、机遇，并从服务工作现状出发，有针对性地从服务理念、服务定位、服务方式、服务体系等方面提出具体对策。     

Preschool work against bullying and degrading treatment: experiences from an action learning project

This article deals with experiences from an action learning project against bullying and degrading treatment among nine Swedish preschools. Even though definitions of bullying and degrading treatment tend to lead to thoughts of school-age children rather than preschoolers, previous research shows that bullying occurs in preschool as well. Our data consist of documentation of improvement work carried out in the preschools that were analysed from both a peer culture perspective and a school improvement perspective. Our main results show that the preschools, by identifying challenges and actions anchored in the local context, ‘hit the target’ in their work against bullying and degrading treatment in the preschools. However, the children and their perspectives were rarely taken into account in the improvement work, which we consider as ‘missing the point’. Didactic implications for further preschool action learning projects are discussed.     

Predictors of Handwriting in Adolescents and Adults with Down Syndrome

Handwriting is a skill that is constantly used in schools and in the workplace – two environments that are targeted in French legislation passed in 2005 on the integration of people with disabilities. The aim of the present study was to determine the predictive factors for handwriting speed and quality in adolescents and adults with Down syndrome (DS), looking at chronological and developmental age, pen grasp and perceptual-motor processing, which are known to contribute to both the speed and quality of handwriting. Results yielded by simple linear and curvilinear analyses revealed that handwriting speed and quality are related to chronological age, developmental age and perceptual-motor processing. Moreover, multiple linear regressions showed that handwriting quality can be predicted by fine motor coordination. We discuss the influence of different factors on handwriting acquisition in individuals with DS, and the implications in terms of intervention programmes.     

Test-enhanced learning in third-grade children

Several recent studies have shown that retrieval is more efficient than restudy in enhancing the long-term retention of memories. However, studies investigating this effect in children are still rare. Here, we report an experiment in which third-grade children initially read a brief encyclopaedic text twice and then either performed a cued recall test on selected target contents of the text or reread the same text twice. A final four-choice memory test about the text’s contents was administered to all children after seven days as well as tests measuring their IQ and reading skills. In the final four-choice memory test, children who took the initial cued recall test showed significantly greater performance in comparison with children who restudied the text twice (their responses were 87 and 53% correct, respectively). The results suggest that cued recall tests can elicit very robust testing effects in young children, even when complex, educationally relevant materials are used as stimuli.     

Brain drain and the disenchantment of being a higher education student in Portugal

The efforts made by most countries to accelerate economic development have included a significant investment in education. It has been argued that investment in education, particularly higher education, was itself a potential factor in economic development. Education has become a relatively easy means of improving access to the labour market. However, in Portugal, the recent trend has been reversed, and the country now faces a growing number of university graduates in several fields of education and training that do not have a job based on their formal qualifications. Despite the differences of unemployment by area of education and training, unemployment of the young skilled has been a problem in recent years. Therefore, following this unemployment trend, there has been growing the exodus of highly skilled professionals from the Portuguese economy, leaving it with a reduced supply of skilled people. This article discusses the employability of graduates from several academic areas and discusses the educational and economic policies that generate a real brain drain.     

Organising primary grade literacy environments in Mozambique

Learning Environments Research - Print-rich environments are critical to early literacy development. This study profiled how teachers organise literacy environments in 21 early-primary classrooms...     

Peer acceptance and rejection during secondary school: Do associations with subsequent educational outcomes vary by socioeconomic background?

Research shows that peer relationships are associated with students' school adjustment. However, the importance of advantageous and disadvantageous factors for students' educational outcomes may vary by socioeconomic positioning. Drawing on sociometric and register data from a nationally representative sample of Swedish youth (n = 4996, girls 50%; migration background 19%), this study asks if family socioeconomic status moderates associations between youth's peer relationships and their subsequent educational outcomes. Based on preregistered analyses, associations that peer acceptance and rejection at age 14–15 years share with school grades at ~16 years and completion of upper secondary school at ~20 years were tested. The findings showed that positive and adverse peer relationships are most consequential for the educational outcomes of socioeconomically disadvantaged youth.     

The effects of player grip on the dynamic behaviour of a tennis racket

The aim of this article is to characterise the extent to which the dynamic behaviour of a tennis racket is dependent on its mechanical characteristics and the modulation of the player’s grip force. This problem is addressed through steps involving both experiment and modelling. The first step was a free boundary condition modal analysis on five commercial rackets. Operational modal analyses were carried out under “slight”, “medium” and “strong” grip force conditions. Modal frequencies and damping factors were then obtained using a high-resolution method. Results indicated that the dynamic behaviour of a racket is not only determined by its mechanical characteristics, but is also highly dependent on the player’s grip force. Depending on the grip force intensity, the first two bending modes and the first torsional mode frequencies respectively decreased and increased while damping factors increased. The second step considered the design of a phenomenological hand-gripped racket model. This model is fruitful in that it easily predicts the potential variations in a racket’s dynamic behaviour according to the player’s grip force. These results provide a new perspective on the player/racket interaction optimisation by revealing how grip force can drive racket dynamic behaviour, and hence underlining the necessity of taking the player into account in the racket design process.