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Two mechanisms have been suggested to explain stretching-induced maximum force depression: a mechanical alteration in the stretched muscle and an impairment of neural activation. Electrical stimulation allows standardization of the level of muscle activation without being limited by neural control. The aim of this study was to evaluate the stretching-induced changes in the electrical and mechanical properties of muscle during electrically elicited contractions. Twelve participants (age 22 +/- 1 years; body mass 75 +/- 2 kg; stature 1.79 +/- 0.02 m; mean +/- standard error) underwent six electrical stimulations of the medial gastrocnemius muscle before and after stretching. During the contractions, surface electromyogram (EMG) and mechanomyogram (MMG) were recorded simultaneously together with force. After stretching we found: (i) no differences in EMG parameters; (ii) MMG amplitude decreased by 4 +/- 1% (P < 0.05); and (iii) the peak force, the peak rate of force development, and the acceleration peak of force development decreased by 12 +/- 3%, 14 +/- 1%, and 24 +/- 5%, respectively (P < 0.05). In conclusion, acute passive stretching did not change EMG properties but altered the mechanical characteristics of the contracting muscle. Indeed, muscle force-generating capacity and stiffness of the muscle-tendon unit were significantly impaired. 相似文献
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Research in Science Education - The aim of this paper is to show how an innovative technique can be used to introduce a method for uncovering intrinsic mechanisms that motivate changes in... 相似文献
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The biological processes of photosynthesis and plant cellular respiration include multiple biochemical steps, occur simultaneously within plant cells, and share common molecular components. Yet, learners often compartmentalize functions and specialization of cell organelles relevant to these two processes, without considering the interconnections as well as the significance of the plant as an independent biological system functioning as a nested component within local and global ecosystems. Understanding connections among biological systems at macro and micro levels is important to biological literacy. This study examined preservice elementary teachers' conceptions of photosynthesis and plant cellular respiration, with attention to interconnections and systems. Participants were limited in their understanding of the processes impacting multiple ecological levels, and they held inadequate representations of interconnections between the processes. Participants' views were laden with sociological and egocentric components. They often compared plant functions with analogous human functions. Most participants viewed plants as dependent on humans while having societal use. Justifications for views included nominal knowledge of the processes; experiential authoritarian reasoning; and anthropomorphism. We discuss instructional implications in light of the findings. © 2009 Wiley Periodicals, Inc. J Res Sci Teach 46: 791–812, 2009 相似文献
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Raúl Bescós Marc Esteve Jordi Porta Mercè Mateu Alfredo Irurtia Martin Voracek 《Journal of sports sciences》2013,31(6):625-632
Abstract Associations of the second-to-fourth digit ratio (2D:4D), a putative marker for prenatal androgen action, and of absolute finger length, a putative marker for pubertal–adolescent androgen action, with sport performance were examined in a multinational sample of 87 world-class women épée fencers. Lower (masculinized) digit ratios correlated, although not significantly so, with better current and highest past world rankings. These correlations were significant for right-hand 2D:4D with controls for the most salient factors for 2D:4D (ethnicity) and world rankings (years of international experience, height, and weight). Longer (masculinized) fingers correlated strongly with better current and highest past world rankings; these correlations became insignificant with the same controls. Replicating previous evidence for fencers, left-handedness was much more prevalent in this sample (21%) than in the female general population, and left-handers had somewhat, but not significantly so, lower 2D:4D as well as better world rankings than right-handers. These findings extend related evidence suggestive of prenatal programming of aptitude across a variety of sports, especially running and soccer. Some known extragenital effects of prenatal testosterone that contribute to the development of efficient cardiovascular systems, good visuospatial abilities, physical endurance and speed, and to the propensity for rough-and-tumble play, apparently promote sporting success in adult life. 相似文献
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Mercè Viladrich 《Al-Masaq: Islam & the Medieval Mediterranean》2002,14(1):25-31
The last Arabic diplomatic document in Barcelona's Crown of Aragon Archive (ACA) that is still to be edited and studied is ACA Arabic doc. 164. The document is a preliminary draft of the commercial and peace treaty drawn up in 1430 by Alfons the Magnanimous, King of Aragon, Naples and Sicily (1396-1458), and the Mamluk Sultan al-Ashraf Sayf al-Din Barsbāy (825-841/1422-1437), signed in Rhodes (Ramadān 7 833/30 May 1430, ACA Arabic doc. 145), and published in 1939 by Ruíz Orsatti. Document 164 contained 111 folios, which were not in order, and for this reason specialists called it the "accursed riddle". The document was probably prepared for discussion during the summer of 1429, a few months before the definitive version was signed. It is longer than the final agreement, and contains an additional Chapter (33) which has not been published to date. Little documentary evidence of diplomatic negotiation between Muslim and Christian powers in Medieval times has survived, and this chapter provides us with a highly unusual example. In the first part of this study the document is described and its contents outlined. In sections 2 and 3 we edit and analyse the contents of the additional Chapter 33 and the Explicit that goes with it, which is absent from Ruíz Orsatti's version. We then present some historical data regarding the Catalan embassy to Rhodes, which will shed light on the diplomatic negotiations that concern us and the historical reasons for the censoring of Chapter 33. 相似文献
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Mercè Izquierdo-Aymerich 《Science & Education》2013,22(7):1633-1653
Since at least the eighteenth century scientific knowledge (then natural philosophy) was produced in groups of experts and specialists and was transmitted in schools, where, future experts and specialists were trained. The design of teaching has always been a complex process particularly in recent years when educational aims (for example, teaching scientific competence to everyone, not just to experts and specialists) present significant challenges. These challenges are much more than a simple reorganisation of the scientific knowledge pre-determined by the existing teaching tradition for different educational level. In the context of chemical education, the new teaching approaches should bring about not only the transmission of chemical knowledge but also a genuine chemical activity so as to ensure that students can acquire chemical thinking. Chemistry teaching should be revised according to contemporary demands of schooling. In order to move forward towards new teaching proposals, we must identify the genuine questions that generate ‘chemical criteria’ and we should focus on them for teaching. We think that a good strategy is to look for those criteria in the philosophy and history of chemistry, from the perspective of didactics of science. This paper will examine the following questions: (1) How can school science be designed as a world-modelling activity by drawing on the philosophy of science. (2) How can ‘stories’ about the emergence of chemical entities be identified by looking at the history of chemistry? (3) How can modelling strategies be structured in school chemistry activities? 相似文献
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ResumenEl sistema de numeración posicional de base 10 constituye un objeto cultural, resultado de un largo y dificultoso desarrollo histórico, que se convierte en un objeto de conocimiento a asimilar por el niño. En este artículo se estudia el proceso de reconstrucción individual de este instrumento intelectual, a través de las producciones gráficas espontáneas de 100 niños de edades comprendidas entre los 6 y 10 años, obtenidas en situación de invención de sistemas de notación de cantidades. Las producciones de los niños, cuyas estrategias recuerdan en muchos casos a las empleadas en los sistemas de numeración históricos, describen una génesis. Esta se extiende desde producciones que no contemplan la estabilidad de los grafismos ni la posibilidad de combinarlos, hasta las que recurren al principio del valor posicional, pasando por producciones de tipo aditivo y producciones que intentan, sin conseguirlo, la transposición del sistema de numeración convencional. 相似文献
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In order to prevent bullying, research has characterised the adolescents involved in terms of their social skills, maladjustment and popularity. However, there is a lack of knowledge concerning the relationships between these variables and how these relationships predict bullying involvement. Moreover, the literature has focused on pure bullies and victims, despite the fact that bully-victims are known to be the most troubled. The aim of this work is to study the relationships between these variables and their predictive value, focusing on the bully-victim role. The sample (N?=?641) is made up of adolescents aged between 12 and 17?years. The results mainly indicate that the level of maladjustment and social skills predicts sociometric popularity, which is a significant predictor of bullying involvement. Differences in the social roles were observed, suggesting that social skills and maladjustment serve a different purpose for bully-victims than for the other roles involved. 相似文献
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Kaylee Litson Carly Thornhill Christian Geiser G. Leonard Burns Mateu Servera 《Structural equation modeling》2013,20(6):931-947
Latent state-trait (LST) models are commonly applied to determine the extent to which observed variables reflect trait-like versus state-like constructs. Mixture distribution LST (M-LST) models relax the assumption of population homogeneity made in traditional LST models, allowing researchers to identify subpopulations (latent classes) with differing trait- and state-like attributes. Applications of M-LST models are scarce, presumably because of the analysis complexity. We present a step-by-step tutorial for evaluating M-LST models based on an application to mother, father, and teacher reports of children’s inattention (n = 811). In the application, we found three latent classes for mother and father reports and four classes for teacher reports. All reporter solutions contained classes with very low, low, and moderate levels of inattention. The teacher solution also contained a class with high inattention. Comparable mother and father (but not teacher) classes exhibited similar levels of trait and state variance. 相似文献