The effect of normal load force and roughness on the dynamic traction developed at the shoe–surface interface in tennis

During tennis-specific movements, such as accelerating and side stepping, the dynamic traction provided by the shoe–surface combination plays an important role in the injury risk and performance of the player. Acrylic hard court tennis surfaces have been reported to have increased injury occurrence, partly caused by increased traction that developed at the shoe–surface interface. Often mechanical test methods used for the testing and categorisation of playing surfaces do not tend to simulate loads occurring during participation on the surface, and thus are unlikely to predict the human response to the surface. A traction testing device, discussed in this paper, has been used to mechanically measure the dynamic traction force between the shoe and the surface under a range of normal loading conditions that are relevant to real-life play. Acrylic hard court tennis surfaces generally have a rough surface topography, due to their sand and acrylic paint mixed top coating. Surface micro-roughness will influence the friction mechanisms present during viscoelastic contacts, as found in footwear–surface interactions. This paper aims to further understand the influence micro-roughness and normal force has on the dynamic traction that develops at the shoe–surface interface on acrylic hard court tennis surfaces. The micro-roughness and traction of a controlled set of acrylic hard court tennis surfaces have been measured. The relationships between micro-roughness, normal force, and traction force are discussed.     

Testing method for objective evaluation of cross-country ski poles

The aim of the study was to develop an objective classification method for cross-country ski poles. A test device was designed to expose different pole models to maximal loading and impact tests. A load cell measured the axial forces in the pole shafts, and a laser distance meter measured shaft deflection when a load was applied via the wrist strap. In the loading tests, each shaft reached a plateau where no more force could be transferred. This maximal force transfer (MFT) value was a characteristic measure for flexural rigidity and thereby also strength. The developed test method enables a loading that is more similar to real-life skiing than a standard three-point bending test. Results show that the introduction of shaft indices for buckling strength is beneficial for comparison purposes. The MFT is a relevant parameter used in the characterization of poles.     

The effects of surface traction characteristics on frictional demand and kinematics in tennis

The interaction between footwear and surfaces influences the forces experienced by tennis players. The purpose of this study was to investigate traction demand and kinematic adaptation during tennis-specific movements with changes in traction characteristics of surfaces. We hypothesised that players would increase the utilised coefficient of friction (horizontal to vertical ground reaction force ratio) when the shoe surface combination had a high coefficient of friction and flex their knee after contact to facilitate braking. Eight participants performed two separate movements, side jump out of stance and running forehand. Ground reaction force was measured and three-dimensional kinematic data were recorded. Clay surface and cushioned acrylic hard court (low vs. high shoe–surface friction) were used. The peak utilised coefficient of friction was greater on clay than the hard court. The knee was less flexed at impact on clay ( ? 5.6 ± 10.2°) and at peak flexion ( ? 13.1 ± 12.0°) during the running forehand. Our results indicate that tennis players adapt the level of utilised friction according to the characteristics of the surface, and this adaptation favours sliding on the low friction surface. Less knee flexion facilitates sliding on clay, whereas greater knee flexion contributes to braking on the hard court.     

Attention interchanges at story-time: a case study from a deaf and hearing twin pair acquiring Swedish sign language in their deaf family

This case study longitudinally analyzes and describes the changes of attentional expressions in interchanges between a pair of fraternal twins, 1 deaf and 1 hearing, from the age of 10-40 months, and their Deaf family members. The video-observed attentional expressions of initiating and reestablishing interchange were grouped in 5 functional categories: "getting," "directing," "maintaining," "redirecting," and "checking" attention. Changes appear to be associated with development during the twins' ages of 10-13, 15-24, and 28-40 months, including the use of vision in communication. Although there are similarities in the changes of each twin's communicative initiations, there are also differences based on hearing status, personality, and use of modality. This is evident in the ways in which each twin's individual attention interchanges unfold over time; it is also connected with the parents' negotiating attention and arranging "seating positions" with them. Implications and findings for special educational purposes are discussed.     

A comparative analysis of the efficiency of national education systems

The present study assesses the performance of 54 participating countries in PISA 2006. It employs efficiency indicators that relate result variables with resource variables used in the production of educational services. Desirable outputs of educational achievement and undesirable outputs of educational inequality are considered jointly as result variables. A construct that captures the quality and quantity of educational resources consumed is used as resource variables. Similarly, environmental variables of each educational system are included in the efficiency evaluation model; while these resources are not controllable by the managers of the education systems, they do affect outcomes. We find that European countries are characterized by weak management, the Americans (mainly Latin Americans) by a weak endowment of resources, and the Asians by a high level of heterogeneity. In particular, Asia combines countries with optimal systems (South Korea and Macao-China); countries with managerial problems (Hong Kong, China-Taipei, Japan and Israel); others where the main challenge is the weak endowment of resources (Jordan and Kyrgyzstan), and, finally, others where the main problem is in the long run since it concerns structural conditions of a socioeconomic and cultural nature (Turkey, Thailand, and Indonesia).     

Measuring the effectiveness of online problem solving for improving academic performance in a probability course

Education and Information Technologies - Research on impact in student achievement of online homework systems compared to traditional methods is ambivalent. Methodological issues in the study...     

The educational e-portfolio: preliminary evidence of its relationship with student’s self-efficacy and engagement

Education and Information Technologies - The educational use of portfolios has been increasing in the last few years, especially as technology has also developed electronic versions of portfolios....     

Balancing competing demands: Enhancing the mathematical problem posing skills of prospective teachers through a mathematical letter writing initiative

Responding to mathematical problems is a core activity in classrooms. The problems that teachers select determine the mathematical content, processes and nature of mathematical inquiry occurring in classrooms and thereby contribute to the development of mathematical skills and dispositions. Selecting, designing or reformulating mathematical problems is a critical skill, then, for prospective and practising teachers. This study explores the influence of a mathematical letter writing initiative in developing the problem posing skills of 28 prospective primary teachers. We examine the characteristics of mathematical problems designed by prospective teachers, and their understandings of what constitutes a good mathematical problem, prior to and following completion of a 12-week letter writing initiative with 10–11-year-old children. Analysis of the data reveals the benefits of engaging in the initiative as evidenced in improvements in several problem characteristics. There was an increase in the number of multiple approach and multiple solution problems and in the level of cognitive demand of problems posed. The challenge of posing non-traditional problems, alongside the competing demands of building in opportunities for success, may have diminished participants’ ability to evaluate and attend to the cognitive demand of problems.