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An application of the Udwadia-Kalaba dynamic formulation to flexible multibody systems 总被引：1，自引：0，他引：1
For the transient response analysis of a flexible slider-crank mechanism, the coordinate partitioning scheme and the Udwadia-Kalaba formulation are herein compared. The flexibility of the coupler has been modelled by means of a single Timoshenko beam element. The present analytical treatment can be viewed as an extension of the model discussed by Shabana in his textbook. 相似文献
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Dynamic squat is one of the most executed fitness exercise. Its use is widespread both for rehabilitation and training purposes. Several typologies of the squat exercise can be performed. The most important are the front squat and the back squat. In the front squat the barbell is held in front of the body across the clavicles and deltoids, while in the back squat exercise the bar is held on the back of the body at the base of the neck. In this paper we will refer to dynamic back squat. The squat exercise can be performed with or without the help of a machine that has the scope of guiding the person during the movement and ensuring his stability and safety. The use of this type of machine is often necessary when the workout is heavy and the risk of incorrect exercise and injuries is high. On the other hand, the rigid structure of this device often overconstrains the lifting movement. From all these observations, the purpose of the paper is to discuss an alternative design of a mechanism able to maintain the advantage to allow a free-body execution and to preserve the safety of the athletes as well. The proposed mechanism has been designed starting from an anthropometric study on the squat movement. This has been performed by using a motion capture system and applying computer-aided engineering techniques. The design activity started from the experimental investigation of the trajectory of the barbell during the natural execution of the unrestricted back squat exercise. The tests have been performed on several subjects with different mass, anthropometry and gender. In a second phase, the data have been processed and analyzed and a specific mechanism, able to reproduce the natural trajectories, has been synthetized. Finally, the design and optimization of the entire structure has been performed through the use of virtual prototyping techniques. 相似文献
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Nadia Cristina Valentini Licia Pierosan Mary E. Rudisill Peter A. Hastie 《Physical Education & Sport Pedagogy》2017,22(4):349-363
Background: Fundamental motor skill proficiency is essential for engagement in sports and physical play and in the development of a healthy lifestyle. Children with motor delays (with and without disabilities) lack the motor skills necessary to participate in games and physical activity, and tend to spend more time as onlookers than do their peers. As such, intervention programs are crucial in promoting motor skill development of children with motor delays. While mastery climate (MC) interventions have shown to positively impact children’s motor performance, what is unknown is the impact of cognitive strategies used by children within these climates. Furthermore, although vigorous play seems to be related to the development of gross motor skills, it is still unknown if children with and without disabilities would benefit from exercise play (EP) interventions.Purpose: This study examined the effects of MC and EP interventions on the motor skill development and verbal recall (VR) of children with motor delays. The sample included children with and without disabilities.Research designs: One hundred and thirty-eight children from 27 urban public schools were referred to the present study. Children were assessed using the Test of Gross Motor Development second edition (TGMD-2) and a VR checklist. Sixty-four children (18 with disabilities and 46 without) met the inclusion criteria, which was a score less than the fifth percentile on the TGMD-2. Participants were randomly assigned to the MC or EP 14-week interventions emphasizing gross motor skill practice.Data collection and analysis: Children were assessed at pre- and post-intervention. A 2 (groups)?×?2 (disability) × 2 (time) analyses of variance with repeated measures on the last factor was conducted. Change scores, t-test comparisons on the delta scores and Cohen’s D were also calculated.Results: The MC group demonstrated significant and positive changes over the intervention period. Further, the MC group showed superior locomotor and object control performance and higher recall of verbal cues (p?≤?.05) at post-intervention compared to the EP group. Children with and without disabilities within the MC showed similar patterns of improvement. The EP intervention did not demonstrate significant improvements.Conclusion: Children with and without disabilities showed improvements in motor skills and VR when exposed to an MC, incorporating the six TARGET structures. These structures included (a) providing feedback and encouragement, providing opportunities for decision-making and establishing personal goals, (b) including parents in the recognition of children’s achievements, (c) creating opportunities to experience leadership and self-pacing, (d) guiding children to use verbal cues and modeling when practicing gross motor skills, and (e) providing demonstrations and teaching children to self-monitor their performance. Instruction is therefore seen as critical to learning gross motor skills, as demonstrated from the findings. Although there were opportunities for vigorous play within the EP intervention, the children did not show improvements in motor performance or VR. These findings suggest that new trends in teacher education physical education to prioritize physical activity over good motor skill instruction may not be advantageous for children in the early years, and should be reconsidered. 相似文献
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Links with science have been argued to improve the (innovation) performance of firms. Yet we still know comparatively little about the project-level characteristics affecting the organization of such links. Our study, based on a sample of 52 projects carried out by a multinational company in the semiconductor industry, reveals that the knowledge attributes of a project help in predicting how the R&D activities will be organized. In particular, basic projects are likely to be developed through formal cooperative agreements with universities. Such projects also tend to be strategically less important. For strategically more important projects, in contrast, and for those where the knowledge to be developed is particularly novel to the firm, the firm is more likely to resort to formal contracting with a university for a specific component of the R&D project, usually early on in the project. 相似文献
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This paper reports both procedures for the kinematic design and the results of dynamic analyses of three models of sit-ski
in order to evaluate their vibrational comfort. The model described in the US Patent US 6,019,380 has been assumed as a reference
in the following kinematic and dynamic analyses of the new models proposed. The two main features to be considered while designing
a sit-ski are the manoeuvrability and the range of vision of the driver. These two features appear to be important considering
that the sit-ski is generally used by disabled people (e.g. paraplegic). Thus the kinematic design phase should account for
the fulfillment of these requirements. On the basis of these, three new models have been proposed and herein named: Flex,
modified Flex and eight-bar linkage (Smarrini 2003). Once the kinematic synthesis and analysis have been completed the dynamic
performance of each model is investigated. For this purpose two kinds of slope profiles are simulated in order to reproduce
the stresses which may likely occur during a downhill race. In particular the position and the acceleration of the seat have
been monitored during the simulations. This is important in order to test the range of vision and handling requirements. The
seat acceleration is also important to evaluate the vibrational comfort of the sit-ski according to the British standard BS
6841 (Griffin 1990). The dynamic simulation is first executed by means of the multibody dynamics code NumDyn3D, then the vibrational
comfort analysis is performed using in-house developed software (Vita 2001, Valentini and Vita 2003). 相似文献
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The information sector is a dynamic disciplinary and professional field, located in a fluid social and technological environment. The educational choices of students in library and information science (LIS) departments is an important aspect of the process through which they construct their ambitions, plans, and future capabilities, and so research on students' choices and their educational careers as social processes is also important. Through a detailed consideration of case study accounts of students from LIS departments in Greece, the argument for the importance of social and cultural factors in the formation of students' identity is advanced. Data were collected in two research phases using a questionnaire survey and semi-structured interviews. Analysis of data demonstrates the complexity of the process of making educational choices, revealing how individual, family, social, and institutional factors interrelate with the ways young people cope with contingencies, and with social and personal relations. How these complex influences facilitate or impede students' trajectories within higher education institutions is also shown, as well as how they act upon the construction of their pedagogic identities. Of considerable significance is the finding that students from lower social class backgrounds tend to form pedagogic identities that are fragile. By contrast, students from families with significant amounts of cultural and social capital are in a position to exploit the academic and social resources of institutions, and to construct embedded identities with a strong scientific basis. More research is needed to illuminate how LIS departments could develop mechanisms to reduce such discrepancies. 相似文献
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