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11.
Sasakawa K Sakurai S 《Sports biomechanics / International Society of Biomechanics in Sports》2008,7(3):311-321
Joint angles of the throwing limb were examined from the acceleration phase up until release for the sidearm throwing motion when using a flying disc. 17 individuals (ten skilled, seven unskilled) threw a disc as far as possible ten times. Throwing motions were recorded using three-dimensional high-speed videography. The initial condition of disc release and joint angle kinematics of the upper limb during the throwing motion were obtained. Mean (+/- standard deviation) throwing distance and disc spin rate were significantly greater for skilled throwers (51.4 +/- 6.6 m, 12.9 +/- 1.3 rps) than for unskilled throwers (29.5 +/- 7.6 m, 9.4 +/- 1.3 rps), although there was no significant difference in initial velocity of the disc between the two groups (skilled: 21.7 +/- 1.7m/s; unskilled: 20.7 +/- 2.5m/s). A marked difference in motion of supination/pronation of the forearm before disc release was identified, with the forearm supinated in the final acceleration phase leading up to disc release for the unskilled participants, while the forearm was pronated in the same phase for the skilled participants. These differences in joint kinematics could be related to differences in disc spin rate, and thus led to the substantial differences in throwing distance. 相似文献
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Kei Sasakawa Shinji Sakurai 《Sports biomechanics / International Society of Biomechanics in Sports》2013,12(3):311-321
Joint angles of the throwing limb were examined from the acceleration phase up until release for the sidearm throwing motion when using a flying disc. 17 individuals (ten skilled, seven unskilled) threw a disc as far as possible ten times. Throwing motions were recorded using three-dimensional high-speed videography. The initial condition of disc release and joint angle kinematics of the upper limb during the throwing motion were obtained. Mean ( ± standard deviation) throwing distance and disc spin rate were significantly greater for skilled throwers (51.4 ± 6.6 m, 12.9 ± 1.3 rps) than for unskilled throwers (29.5 ± 7.6 m, 9.4 ± 1.3 rps), although there was no significant difference in initial velocity of the disc between the two groups (skilled: 21.7 ± 1.7 m/s; unskilled: 20.7 ± 2.5 m/s). A marked difference in motion of supination/pronation of the forearm before disc release was identified, with the forearm supinated in the final acceleration phase leading up to disc release for the unskilled participants, while the forearm was pronated in the same phase for the skilled participants. These differences in joint kinematics could be related to differences in disc spin rate, and thus led to the substantial differences in throwing distance. 相似文献
13.
Microorganisms can effectively generate propulsive force at the microscale where viscous forces overwhelmingly dominate inertia forces; bacteria achieve this task through flagellar motion. When swarming bacteria, cultured on agar plates, are blotted onto the surface of a microfabricated structure, a monolayer of bacteria forms what is termed a “bacterial carpet,” which generates strong flows due to the combined motion of their freely rotating flagella. Furthermore, when the bacterial carpet coated microstructure is released into a low Reynolds number fluidic environment, the propulsive force of the bacterial carpet is able to give the microstructure motility. In our previous investigations, we demonstrated motion control of these bacteria powered microbiorobots (MBRs). Without any external stimuli, MBRs display natural rotational and translational movements on their own; this MBR self-actuation is due to the coordination of flagella. Here, we investigate the flow fields generated by bacterial carpets, and compare this flow to the flow fields observed in the bulk fluid at a series of locations above the bacterial carpet. Using microscale particle image velocimetry, we characterize the flow fields generated from the bacterial carpets of MBRs in an effort to understand their propulsive flow, as well as the resulting pattern of flagella driven self-actuated motion. Comparing the velocities between the bacterial carpets on fixed and untethered MBRs, it was found that flow velocities near the surface of the microstructure were strongest, and at distances far above, the surface flow velocities were much smaller. 相似文献
14.
1997年以来香港科技政策转向及其特征分析 总被引：2，自引：1，他引：2
以殖民时期港英政府科技政策的简要回顾为出发点,着重考察1997年以来香港科技政策新的发展趋向,并在此基础上分析香港科技政策演变的特征和面临的挑战. 相似文献
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Kei Tomita 《TechTrends》2018,62(1):103-112
While authors like Mayer (2009) suggest that designers should avoid using visuals for the purpose of attracting learners’ interests, some scholars suggest that visuals could influence learners’ emotions. In this study the author investigated whether the perception of the visual appeal of instructional handouts affects learners’ self-reported motivation to learn from the handouts. Two handouts were prepared for this study: a minimalist handout following Mayer’s (2009) Coherence Principle and an appealing handout complying with everyday visual trends. Participants were instructed to look at the handouts in different orders according to groups and were asked about their impressions of the handouts. The appealing handout was perceived as motivating when it was seen after the minimalist handout. However, the group that saw the minimalist handout first did not perceive the appealing handout as motivating. The result implies that not only the design but also the learning context influences learners’ self-reported motivation to engage with the handout. 相似文献
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Yue Yin Miki K. Tomita Richard J. Shavelson 《International Journal of Science Education》2013,35(4):531-552
This study examined the effect of learning progression-aligned formal embedded formative assessment on conceptual change and achievement in middle-school science. Fifty-two sixth graders were randomly assigned to either an experimental group or a control group. Both groups were taught about sinking and floating by the same teacher with identical curriculum materials and activities. The experimental group received, in addition, three sets of formal embedded formative assessments with qualitative feedback as to how to improve their understandings aligned with an expected learning progression during instruction. The control group spent the corresponding time between new curriculum activities conducting curriculum-specific extension activities. Overall, the experimental group experienced on average greater conceptual change than the control group. The experimental group also scored higher on average than the control group on general achievement tests, especially the performance assessment. This study supported the contention, then, that embedding formal formative assessments within a curricular sequence built around an expected learning progression is a useful way to promote conceptual change along that learning progression in science classrooms. 相似文献
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路跑者是一个峰值1．375Pflop／s的混合体系结构，由LANL和IBM共同开发。它包含12，240个IBMPowerXCell8核处理器和12，240个AMDOpeteron核心。路跑者是第一台运行Linpak时能持续超越1Pflops／s的超级计算机。这篇文章介绍了路跑者的设计细节，详细的性能评测，以及利用路跑者体系结构优化Sweep3D的一个实例。 相似文献
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We aimed to assess the relationship between throwing distance and kinematic release parameters of the flying disc in unskilled throwers, and to assess the relationship between kinetic variables acting on flying discs and the change in spin velocity during long forehand throws by skilled and unskilled throwers. Ten skilled and eleven unskilled throwers performed throws at maximum effort. Reflective marker positions on the disc and body were recorded with a 3D motion capture system during the throws to derive kinematic variables of a disc and kinetic variables acting on the disc. The analysis interval was from maximum external shoulder rotation to disc release. Significant correlations were observed between the throwing distance and spin velocity in skilled (r = 0.722, P < 0.05) and unskilled throwers (r = 0.794, P < 0.01), between the change in spin velocity and the angular impulse of moments of force, in unskilled throwers (r = 0.703, P < 0.05), and between the change in spin velocity and the angular impulse of torque among skilled throwers (r = 0.680, P < 0.01). Therefore, a strategy for increasing spin velocity in unskilled throwers could be used to generate a larger torque, similar to that observed in skilled throwers. 相似文献
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农业废弃物资源化生态补偿支付意愿的影响因素及其差异性分析——基于湖北省农户调查的实证研究 总被引：8，自引：2，他引：6
本文利用湖北省农村地区的调查数据,运用Binary Logistic回归模型分析了农户对农业废弃物资源化生态补偿支付意愿的影响因素及其差异性.研究表明:①73.4％的农户愿意为农业废弃物资源化所带来的生态效益付费;②影响农户支付意愿的关键因素按贡献度大小排序依次为性别、对环境的依赖程度、对农业废弃物资源化有益于人体健康的价值认同、农业收入所占比、对农业废弃物资源化有益于农村发展的价值认同、农业经济规模、对环境状况的评价和环境知识了解程度;③不同性别、不同农业收入所占比、不同环境知识、不同心理感知等限定条件下,影响农户对农业废弃物资源化生态补偿支付意愿的因素具有异质性:男性更加注重农业废弃物资源化对人体健康的影响;对于农业收入所占比“一般”的农户,文化程度是影响其支付意愿的关键因素,但这种影响受环境知识水平限制;对环境状况评价“较好”的农户更为重视对现有环境的维护. 相似文献