On the proper understanding of the limiting behavior of generalizations of the h- and g-indices     

Nees Jan van Eck  Ludo Waltman   《Journal of Informetrics》2009,3(4):369-370

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The electron mechanics of induction acceleration     

Jan A. Rajchman  William H. Cherry 《Journal of The Franklin Institute》1947,243(4):261-285

The radial and axial motions of electrons in the betatron are described by means of a potential function of forces. Previously reported conditions of equilibrium, stability and damping of oscillations are derived for the region of parabolic variation of the potential. Extension of the analysis to, non-parabolic regions gives an account of the injection in conventional instruments in better agreement with experiment, particularly in regard to higher voltages of injection.Space charge limitations are discussed with the help of the Laplacian of the potential of forces.By means of an additional radial electric field electrons can be introduced as in the magnetron, without any asymmetry inherent in the conventional betatron circumferential injector. The analysis of the conditions of equilibrium and stability, greatly facilitated in this case by the notion of potential, shows that no substantial improvement in space charge limitations can be expected and that the required variations between the flux linking the electron orbits and the magnetic and electric fields at the orbits are difficult to realize on account of their complexity and narrow tolerances. The X-ray output of a small experimental double yoke instrument was measured by a phototube multiplier viewing an irradiated fluorescent screen and gave evidence of multiple group electron capture.  相似文献   

Indicators of sailing performance in youth dinghy sailing     

Margot Callewaert  Jan Boone  Bert Celie  Dirk De Clercq 《European Journal of Sport Science》2015,15(3):213-219

Abstract

This study aimed to determine indicators of sailing performance in 2 (age) groups of youth sailors by investigating the anthropometric, physical and motor coordination differences and factors discriminating between elite and non-elite male optimist sailors and young dynamic hikers. Anthropometric measurements from 23 optimist sailors (mean ± SD age = 12.3 ± 1.4 years) and 24 dynamic youth hikers (i.e. Laser 4.7, Laser radial and Europe sailors <18 years who have to sail the boat in a very dynamic manner, due to a high sailor to yacht weight ratio) (mean ± SD age = 16.5 ± 1.6 years) were conducted. They performed a physical fitness test battery (EUROFIT), motor coordination test battery (Körperkoordinationstest für Kinder) and the Bucket test. Both groups of sailors were divided into two subgroups (i.e. elites and non-elites) based on sailing expertise. The significant differences, taking biological maturation into account and factors discriminating between elite and non-elite optimist sailors and dynamic hikers were explored by means of multivariate analysis of covariance and discriminant analysis, respectively. The main results indicated that 100.0% of elite optimist sailors and 88.9% of elite dynamic hikers could be correctly classified by means of two motor coordination tests (i.e. side step and side jump) and Bucket test, respectively. As such, strength- and speed-oriented motor coordination and isometric knee-extension strength endurance can be identified as indicators of sailing performance in young optimist and dynamic youth sailors, respectively. Therefore, we emphasise the importance of motor coordination skill training in optimist sailors (<15 years) and maximum strength training later on (>15 years) in order to increase their isometric knee-extension strength endurance.  相似文献   

Validation of two accelerometers to determine mechanical loading of physical activities in children     

Ursina Meyer  Dominique Ernst  Silvia Schott  Claudia Riera  Jan Hattendorf  Jacqueline Romkes 《Journal of sports sciences》2015,33(16):1702-1709

The purpose of this study was to assess the validity of accelerometers using force plates (i.e., ground reaction force (GRF)) during the performance of different tasks of daily physical activity in children. Thirteen children (10.1 (range 5.4–15.7) years, 3 girls) wore two accelerometers (ActiGraph GT3X+ (ACT), GENEA (GEN)) at the hip that provide raw acceleration signals at 100 Hz. Participants completed different tasks (walking, jogging, running, landings from boxes of different height, rope skipping, dancing) on a force plate. GRF was collected for one step per trial (10 trials) for ambulatory movements and for all landings (10 trials), rope skips and dance procedures. Accelerometer outputs as peak loading (g) per activity were averaged. ANOVA, correlation analyses and Bland–Altman plots were computed to determine validity of accelerometers using GRF. There was a main effect of task with increasing acceleration values in tasks with increasing locomotion speed and landing height (P < 0.001). Data from ACT and GEN correlated with GRF (r = 0.90 and 0.89, respectively) and between each other (r = 0.98), but both accelerometers consistently overestimated GRF. The new generation of accelerometer models that allow raw signal detection are reasonably accurate to measure impact loading of bone in children, although they systematically overestimate GRF.  相似文献   

Optimal search strategies for identifying moderators and predictors of treatment effects in PubMed     

Marcia Tummers  Ralph van Hoorn  Charlotte Levering  Andrew Booth  Gert Jan van der Wilt  Wietske Kievit 《Health information and libraries journal》2019,36(4):318-340

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The unacknowledged value of female academic labour power for male research careers     

Petra Angervall  Jan Gustafsson 《高等教育研究与发展》2015,34(5):815-827

Academic work in Sweden's higher education system is changing character. Distinctly different career pathways are emerging, as facilities for developing research careers and capital have become both more restricted and more dependent on external funding. These developments are in focus in the present article. Based on ethnographic research and a series of semi-structured interviews with new academics and senior academic mentors in education faculties, the research suggests that several factors intercede in how careers are developed and experienced. The unacknowledged exploitation of female academic labour is perhaps amongst the more significant of these.  相似文献   

Endorsing achievement goals exacerbates the big-fish-little-pond effect on academic self-concept     

Sofie Wouters  Hilde Colpin  Jan Van Damme  Karine Verschueren 《教育心理学》2015,35(2):252-270

The big-fish-little-pond effect (BFLPE) model predicts students’ academic self-concept to be negatively predicted by the achievement level of their reference group, controlling for individual achievement. Despite an abundance of empirical evidence supporting the BFLPE, there have been relatively few studies searching for possible moderators. Integrating the BFLPE model with Achievement Goal Theory, the present study aims to determine whether the negative effect of class-average achievement on academic self-concept is moderated by individual and class-average achievement goals. Our sample comprised of 2987 students (50% boys) from Grade 6 in 112 elementary schools in the Flemish region of Belgium (174 classes). Applying multilevel modelling, we found a stronger BFLPE when students’ individual achievement goals were higher, regardless of the specific nature of these goals. The BFLPE was not moderated by class-average levels of achievement goals. Overall, our findings demonstrate that the BFLPE is moderated by individual goal-related factors.  相似文献   

Comparing student and expert-based tagging of recorded lectures     

Pierre Gorissen  Jan van Bruggen  Wim Jochems 《Education and Information Technologies》2015,20(1):161-181

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Teachers making sense of result-oriented teams: A cognitive anthropological approach to educational change     

Sijko J. Wierenga  Frans H. Kamsteeg  P. Robert Jan Simons  Marcel Veenswijk 《Journal of Educational Change》2015,16(1):53-78

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Preschoolers rely on rich speech representations to process variable speech     

Margaret Cychosz  Tristan Mahr  Benjamin Munson  Rochelle Newman  Jan R. Edwards 《Child development》2023,94(4):e197-e214

To learn language, children must map variable input to categories such as phones and words. How do children process variation and distinguish between variable pronunciations (“shoup” for soup) versus new words? The unique sensory experience of children with cochlear implants, who learn speech through their device's degraded signal, lends new insight into this question. In a mispronunciation sensitivity eyetracking task, children with implants (N = 33), and typical hearing (N = 24; 36–66 months; 36F, 19M; all non-Hispanic white), with larger vocabularies processed known words faster. But children with implants were less sensitive to mispronunciations than typical hearing controls. Thus, children of all hearing experiences use lexical knowledge to process familiar words but require detailed speech representations to process variable speech in real time.  相似文献