Representative learning design in springboard diving: Is dry-land training representative of a pool dive?

Abstract

Two distinctly separate training facilities (dry-land and aquatic) are routinely used in springboard diving and pose an interesting problem for learning, given the inherent differences in landing (head first vs. feet first) imposed by the different task constraints. Although divers may practise the same preparation phase, take-off and initial aerial rotation in both environments, there is no evidence to suggest that the tasks completed in the dry-land training environment are representative of those performed in the aquatic competition environment. The aim of this study was to compare the kinematics of the preparation phase of reverse dives routinely practised in each environment. Despite their high skill level, it was predicted that individual analyses of elite springboard divers would reveal differences in the joint coordination and board-work between take-offs. The two-dimensional kinematic characteristics were recorded during normal training sessions and used for intra-individual analysis. Kinematic characteristics of the preparatory take-off phase revealed differences in board-work (step lengths, jump height, board depression angles) for all participants at key events. However, the presence of scaled global topological characteristics suggested that all participants adopted similar joint coordination patterns in both environments. These findings suggest that the task constraints of wet and dry training environments are not similar, and highlight the need for coaches to consider representative learning designs in high performance diving programmes.     

基于最优多属性约束的IPV6动态路由协议优化

提出一种基于最优多属性约束的IPV6动态路由协议优化方法。根据IPV6动态路由协议中数据属性的约束条件,建立最优多属性约束模型,用来描述不同属性约束条件需要符合的要求。详细描述了IPV6动态路由协议的设计方式,从而实现大范围网络通信。实验结果表明,利用这种方法进行网络通信,能够避免传统算法的缺陷,提高了通信效率,取得了令人满意的结果。     

Perceiving the affordance of string tension for power strokes in badminton: Expertise allows effective use of all string tensions

Abstract

Affordances mean opportunities for action. These affordances are important for sports performance and relevant to the abilities developed by skilled athletes. In racquet sports such as badminton, different players prefer widely different string tension because it is believed to provide opportunities for effective strokes. The current study examined whether badminton players can perceive the affordance of string tension for power strokes and whether the perception of affordance itself changed as a function of skill level. The results showed that string tension constrained the striking performance of both novice and recreational players, but not of expert players. When perceptual capability was assessed, perceptual mode did not affect perception of the optimal string tension. Skilled players successfully perceived the affordance of string tension, but only experts were concerned about saving energy. Our findings demonstrated that perception of the affordance of string tension in badminton was determined by action abilities. Furthermore, experts could adjust the action to maintain a superior level of performance based on the perception of affordance.     

Resource constraints as triggers of radical innovation: Longitudinal evidence from the manufacturing sector

Despite the significant role of radical innovation as a driver of firm growth and performance, the consequences of resource constraints for radical innovation outcomes remain unknown. Our paper addresses this gap. We combine arguments from entrepreneurship theory and the theory of recombinative innovation to construct an overarching theoretical framework that argues why resource constraints can promote, rather than impede, radical innovation. We then build hypotheses on two specific resource constraints, knowledge and financial, and test these by a lagged-variable random-effects Tobit model with longitudinal data from an exceptionally large and detailed innovation survey. Controlling for absorptive capacity, firm age, and firm growth, we find full support for the hypothesis that knowledge constraints spur radical innovation and partial support for the hypothesis that financial constraints spur radical innovation. We discuss the theoretical significance of these findings and point to managerial implications and paths for future research.     

企业家人口统计特征对中小企业融资约束的影响机制研究

基于高层梯队理论,以2010年我国530家中小上市企业为样本,采用层级回归方法,分析企业家人口统计特征对中小企业融资约束的影响及其作用机制。研究结果表明,企业家不同的人口统计特征对中小企业融资约束产生不同的影响,具体来说,企业家受教育程度和职称对缓解中小企业融资约束产生积极影响,企业家年龄和任期对中小企业融资约束产生显著的U型影响,而女性企业家对缓解中小企业融资约束产生消极影响。研究结果不仅丰富了企业家人口统计特征与中小企业融资约束之间的相关理论,并为缓解我国中小企业融资约束提供了实践支持。     

Multiplicative Measurements of a Trait Anxiety Scale as Predictors of Burnout

The purpose of the present study was to investigate whether combining the two dimensions of anxiety (i.e., intensity and direction) by using a multiplicative model would strengthen the prediction of burnout. Collegiate athletes (N = 157) completed the Athlete Burnout Questionnaire as well as a trait version of the Competitive State Anxiety Inventory-2D. Three separate hierarchical regression analyses with four blocks were conducted to predict each one of the burnout subscales from anxiety intensity and direction while controlling for gender. The multiplicative variable for cognitive anxiety was a significant predictor of reduced sense of accomplishment (p < .01). Self-confidence was the only directional scale that predicted reduced sense of accomplishment, emotional/physical exhaustion, and devaluation (p < .01). In addition, gender was found to predict overall burnout in all three subscales as a control variable (p < .05). Conclusions and applied implications are drawn based on the results.     

Is movement variability important for sports biomechanists?

This paper overviews the importance for sports biomechanics of movement variability, which has been studied for some time by cognitive and ecological motor skills specialists but, until quite recently, had somewhat been overlooked by sports biomechanists. The paper considers biomechanics research reporting inter- and intra-individual movement variability in javelin and discus throwing, basketball shooting, and locomotion. The overview does not claim to be comprehensive and we exclude such issues as the theoretical background to movement and coordination variability and their measurement. We overview evidence, both theoretical and empirical, of inter-individual movement variability in seeking to achieve the same task goal, in contrast to the concept of “optimal” movement patterns. Furthermore, even elite athletes cannot reproduce identical movement patterns after many years of training, contradicting the ideas of motor invariance and “representative” trials. We contend that movement variability, far from being solely due to neuromuscular system or measurement “noise” – as sports biomechanists may have previously supposed – is, or could be, functional. Such functionality could allow environmental adaptations, reduce injury risk, and facilitate changes in coordination patterns. We conclude by recommending that sports biomechanists should focus more of their research on movement variability and on important related topics, such as control and coordination of movement, and implications for practice and skill learning.     

Analyzing Mathematical Teaching-Learning Situations — the Interplay of Communicational and Epistemological Constraints

This is a commentary paper in the volume on “Teachings situations as object of research: empirical studies within theoretical perspectives”. An essential object of mathematics education research is the analysis of interactive teaching and learning processes in which mathematical knowledge is mediated and communicated. Such a research perspective on processes of mathematical interaction has to take care of the difficult relationship between mathematics education theory and everyday mathematics teaching practice. In this regard, the paper tries to relate the development in mathematics education research within the theory of didactical situations to developments in interaction theory and in the epistemological analysis of mathematical communication.     

线性不等式约束优化问题的强信赖域算法

对一类带有非负边界约束的线性不等式约束优化问题进行了研究，提出了一种新的信赖域算法．该算法在内点法的基础上，把非负边界约束从一般的不等式约束中分离出来，化为信赖域约束的一部分，得到一个简单易解的子问题．在一定的条件下证明了该算法具有强收敛性，并给出了数值结果．     

Multimedia learning environments: Issues of learner control and navigation

Using schema theory as a framework, we view learning as an active, constructive process. It is affected not only by learners' internal knowledge structures, but by the external constraints of the learning environment as well (Kozma, 1991). This article examines how different internal learner characteristics (e.g., prior knowledge, self efficacy and interest) and different external constraints (e.g., learner control, instructional design and level of control) influence the learning process. Specifically, we address learning from a variety of multimedia environments such as video, hypertexts, kiosks and other hypermedia within a schema theoretic approach that incorporates a constructivist view.