Variable training: effects on velocity and accuracy in the tennis serve

Abstract

Variable practice has been shown to be an effective strategy to improve open motor skills. However, the usefulness of this procedure in closed motor skills remains controversial. The following study has the objective of analysing the effects of variability practice in the improvement of a closed skill. The skill studied has been the tennis serve. Thirty young tennis players (13 ± 1.52 years), divided in two groups, took part in this study. One group practiced in variable conditions and the other group in consistency conditions. Both groups performed 12 training sessions (60 serves/session). The variable practice group improved their accuracy significantly compared with the consistency group (F_3.25 = 3.078; P = 0.035). The velocity of serve increased after training in both groups (F_3.25 = 15.890; P = 0.001). The practice in variable conditions seems to be effective in improving the performance of the tennis serve.     

Reformation of VET and demands on teachers’ subject knowledge – Swedish vocational teachers’ recurrent participation in a national CPD initiative

This study investigates continuing professional development (CPD) of vocational teachers, with a focus on recurrent participation. Vocational teachers need to be competent as teachers and in relation to their vocational teaching subject. Reformation of Swedish vocational education in order to strengthen the working-life connection imposes demands on teachers to have up-to-date knowledge about the vocations related to their vocational subjects. To support the reform, vocational teachers have been offered to participate in a new national CPD initiative targeting their vocational competence. The study concerns participation in this initiative. Drawing on a socio-cultural perspective, vocational teachers’ CPD implies boundary-crossing between school and working-life. Theory concerning adults’ participation in education is considered relevant to understand conditions for such boundary-crossing, and learning, among vocational teachers. The article specifically investigates patterns in vocational teachers’ recurrent participation, which is expected to clarify the factors influencing further participation in professional development. The strongest predictor of recurrent participation, when adjusting for the influence of other factors, is the type of municipality that the teacher comes from, with low populated municipalities having the lowest likelihood of participation. Furthermore, recurrent participation is more likely by participating teachers from adult education or from privately owned schools, and by male teachers.     

Constructivist Approaches in a Dual-Language Classroom

Dual-language programs are becoming increasingly popular among educators and the public in general. In these programs, students aim at attaining full proficiency in English and another language while reaching an academic achievement at or above grade level. This article describes a series of pedagogical practices in the context of dual-language classrooms. We set the discussion across three defining characteristics of our constructivist perspective: learning as collaboration, teachers as facilitators, and language and culture as intertwined elements in schools. In sum, we postulate that dual-language programs bring equity to schools.     

陆地卫星MSS影象目视解译在土地资源调查中局限性的讨论

简述陆地卫星多光谱扫描(MSS)影象的特点,着重介绍陆地卫星多光谱扫描影象适用于中、小比例尺的土地资源凋查     

Individual, family, and neighborhood factors distinguish resilient from non-resilient maltreated children: a cumulative stressors model

OBJECTIVE: Children who are physically maltreated are at risk of a range of adverse outcomes in childhood and adulthood, but some children who are maltreated manage to function well despite their history of adversity. Which individual, family, and neighborhood characteristics distinguish resilient from non-resilient maltreated children? Do children's individual strengths promote resilience even when children are exposed to multiple family and neighborhood stressors (cumulative stressors model)? METHODS: Data were from the Environmental Risk Longitudinal Study which describes a nationally representative sample of 1,116 twin pairs and their families. Families were home-visited when the twins were 5 and 7 years old, and teachers provided information about children's behavior at school. Interviewers rated the likelihood that children had been maltreated based on mothers' reports of harm to the child and child welfare involvement with the family. RESULTS: Resilient children were those who engaged in normative levels of antisocial behavior despite having been maltreated. Boys (but not girls) who had above-average intelligence and whose parents had relatively few symptoms of antisocial personality were more likely to be resilient versus non-resilient to maltreatment. Children whose parents had substance use problems and who lived in relatively high crime neighborhoods that were low on social cohesion and informal social control were less likely to be resilient versus non-resilient to maltreatment. Consistent with a cumulative stressors model of children's adaptation, individual strengths distinguished resilient from non-resilient children under conditions of low, but not high, family and neighborhood stress. CONCLUSION: These findings suggest that for children residing in multi-problem families, personal resources may not be sufficient to promote their adaptive functioning.     

History of childhood abuse in Portuguese parents

OBJECTIVE: The study examines the self-reported prevalence of childhood physical and sexual abuse in a large sample of Portuguese parents. METHOD: Nearly 1,000 parents (506 mothers and 426 fathers) were selected through public primary schools from the Northern area of Portugal. All completed the Portuguese version of the Childhood History Questionnaire (CHQ) [Journal of Family Violence 5 (1990) 15]. RESULTS: Results show that the prevalence of abuse was 73%, but more severe physical abuse involving sequelae/injury was reported by 9.5%. Most physical abuses began prior to age 13, with half continuing after age 13. No gender differences were found for rates of physical abuse. However, among the milder physical abuse without sequelae/injury, those women who experienced "whipping" or "slapping/kicking" were more likely to do so from their mothers than fathers. Among men who were "slapped/kicked" this was more likely to be from their fathers. Low rates of sexual abuse were found at 2.6% with no gender or age differences. Lack of a supportive adult in childhood related to the more severe abuses, but only in adolescence. Portuguese rates of abuse were consistently lower than those reported in USA and Spanish studies using the CHQ. CONCLUSIONS: This is the first retrospective, self-report study of childhood abuse in a large sample of Portuguese parents and, even with a participation rate of 69%, shows lower rates than in US and Spanish samples.     

Competitive State Anxiety Inventory-2 (CSAI-2): evaluating the Swedish version by confirmatory factor analyses

The Competitive State Anxiety Inventory-2 (CSAI-2) is one of the most frequently used instruments when assessing competitive state anxiety in sport psychology research. However, doubts have been expressed about the factorial validity of both the English and the Greek versions of the scale. Hence, a revised version of the inventory (CSAI-2R) has recently been suggested to be more psychometrically sound (Cox et al., 2003). In the present study, the aim was to evaluate the psychometric properties of the Swedish version of the CSAI-2 using confirmatory factor analyses. A total of 969 athletes (571 men and 398 women) competing in 26 different sports completed the Swedish version of the CSAI-2. Three different factor structures were evaluated: the original three-factor model (with cognitive anxiety, somatic anxiety and self-confidence), a two-factor model in which self-confidence was excluded, and a three-factor model containing 17 items (CSAI-2R). The results revealed that only the 17-item model displayed an acceptable fit to the data. Although some doubts remain about the amount of variance that can be attributed to error variance in the subscales, the results suggest that it is better to use the CSAI-2R rather than the original CSAI-2.     

Retrieving and classifying instances of source code plagiarism

Automatic detection of source code plagiarism is an important research field for both the commercial software industry and within the research community. Existing methods of plagiarism detection primarily involve exhaustive pairwise document comparison, which does not scale well for large software collections. To achieve scalability, we approach the problem from an information retrieval (IR) perspective. We retrieve a ranked list of candidate documents in response to a pseudo-query representation constructed from each source code document in the collection. The challenge in source code document retrieval is that the standard bag-of-words (BoW) representation model for such documents is likely to result in many false positives being retrieved, because of the use of identical programming language specific constructs and keywords. To address this problem, we make use of an abstract syntax tree (AST) representation of the source code documents. While the IR approach is efficient, it is essentially unsupervised in nature. To further improve its effectiveness, we apply a supervised classifier (pre-trained with features extracted from sample plagiarized source code pairs) on the top ranked retrieved documents. We report experiments on the SOCO-2014 dataset comprising 12K Java source files with almost 1M lines of code. Our experiments confirm that the AST based approach produces significantly better retrieval effectiveness than a standard BoW representation, i.e., the AST based approach is able to identify a higher number of plagiarized source code documents at top ranks in response to a query source code document. The supervised classifier, trained on features extracted from sample plagiarized source code pairs, is shown to effectively filter and thus further improve the ranked list of retrieved candidate plagiarized documents.