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1.
渐开线少齿差齿轮副,由于是内啮合,齿轮副的齿对之间的间隙很小,在受力后轮齿变形而使得同时有多对齿啮合。本文用简明的几何推导,弹性力学的方法,推导出了轮齿受载弹性变形后同时啮合的确切齿对和承受载荷最大的齿对的载荷与总载荷的比例系数——承载能力系数。利用承载能力系数可算出更符合实际的各齿对分别承受的载荷。经样机的设计、制造和试验结果表明,本文提出的计算方法和公式是正确的,可以有效地提高齿轮副的承载能力。 相似文献
2.
Oxygen and glucose supply is one of the important factors for the growth and viability of the cells in cultivation of tissues, e.g., spheroid, multilayered cells, and three-dimensional tissue construct. In this study, we used finite element methods to simulate the flow profile as well as oxygen and glucose supply to the multilayered cells in a microwell array chip for static and perfusion cultures. The simulation results indicated that oxygen supply is more crucial than glucose supply in both static and perfusion cultures, and that the oxygen supply through the wall of the perfusion culture chip is important in perfusion cultures. Glucose concentrations decline with time in static cultures, whereas they can be maintained at a constant level over time in perfusion cultures. The simulation of perfusion cultures indicated that the important parameters for glucose supply are the flow rate of the perfusion medium and the length of the cell culture chamber. In a perfusion culture chip made of oxygen-permeable materials, e.g., polydimethylsiloxane, oxygen is hardly supplied via the perfusion medium, but mainly supplied through the walls of the perfusion culture chip. The simulation of perfusion cultures indicated that the important parameters for oxygen supply are the thickness of the flow channel and the oxygen permeability of the walls of the channel, i.e., the type of material and the thickness of the wall. 相似文献
3.
Extracellular matrix (ECM) proteins are required for cell culture. In this paper, we report the use of O(2) plasma bonding to fabricate a perfusion culture microchamber array chip with identical-size ECM spots in the isolated microchambers. The chip was fabricated by assembly of two poly(dimethylsiloxane) (PDMS) layers, a microfluidic network layer, and an ECM array layer, which were aligned and then bonded by O(2) plasma oxidation with protection of the ECM microarray with a physical mask made from PDMS. We successfully cultivated Chinese hamster ovary K1 cells in the microchambers with fibronectin. In the fibronectin microchambers, the cells adhered and extended after 12 h of static culture and then grew over the course of 1 d of perfusion culture. 相似文献
4.
Kristin Sue Farley Shayne Piasta Mine Dogucu Ann O’Connell 《Early education and development》2017,28(4):488-505
Research Findings: The present study assessed the extent to which early childhood educators utilized small-group literacy instruction and explored factors potentially associated with the use of this evidence-based practice. The classroom activities of 83 early childhood educators were observed in the fall and spring, and videos were coded to calculate time spent in small-group literacy instruction. Educators completed questionnaires indicating classroom adult:child ratios, literacy beliefs, and feelings of self-efficacy. Classroom Assessment Scoring System scores for classroom organization and instructional support measured the quality of classroom management and instructional interactions, respectively. On average, educators provided 11.4 min (SD = 10.6) of small-group literacy instruction a day. It is notable that many educators provided little or no small-group literacy instruction. Negative binomial regression analyses indicated that educators with better classroom management, higher quality instructional interactions, and lower adult:child ratios were more likely to use small-group literacy instruction. Educators’ beliefs and feelings of self-efficacy were not associated with the use of small-group literacy instruction. Practice or Policy: Educators may be better able to provide small-group literacy instruction in contexts affording low adult:child ratios and high levels of classroom management and instructional support, all of which are malleable factors that can be changed via policy or professional development. 相似文献
5.
The purpose of this study was to develop a peer helping training program for university students in Turkey and to examine
its effectiveness in improving the helping skills and self-growth of peer helpers. A pre-test, post-test, follow-up-test experimental
design, involving a treatment and control group, was carried out with a total sample of 31 undergraduate participants. Results
indicate that there was a significant difference between treatment and control groups in specific measures of empathic and
reflection skills, but not in communication skills as a general measure. Significant improvements also were found in the treatment
group participants` self-esteem and self-acceptance in regard to time. 相似文献
6.
Koji Murofushi Shinji Sakurai Koji Umegaki Junji Takamatsu 《Sports biomechanics / International Society of Biomechanics in Sports》2013,12(3):301-314
Ground reaction force and wire tensile force were measured during test throws by three hammer throwers: the Asian record holder, who had a personal best of 83.47 m at the time of the investigation, and two university athletes, with personal bests of 59.95 m and 46.30 m respectively. They were filmed using three high-speed video cameras (250 Hz). The displacements of the hammer head and the athletes' centres of mass were calculated using three-dimensional analysis procedures. The Asian record holder's centre of mass and the hammer head on the final two turns exhibited approximate conjunctions of the hammer high point and the thrower's low point and vice versa about the hammer's azimuth angle. It is conjectured that the reason why the thrower's movement is asynchronous with the hammer's movement by approximately half a turn is to accelerate the hammer head in a manner similar to the way that the amplitude of a pendulum increases when it is pulled upward by a string against the downward movement of the swinging weight. 相似文献
7.
Murofushi K Sakurai S Umegaki K Takamatsu J 《Sports biomechanics / International Society of Biomechanics in Sports》2007,6(3):301-314
Ground reaction force and wire tensile force were measured during test throws by three hammer throwers: the Asian record holder, who had a personal best of 83.47 m at the time of the investigation, and two university athletes, with personal bests of 59.95 m and 46.30 m respectively. They were filmed using three high-speed video cameras (250Hz). The displacements of the hammer head and the athletes' centres of mass were calculated using three-dimensional analysis procedures. The Asian record holder's centre of mass and the hammer head on the final two turns exhibited approximate conjunctions of the hammer high point and the thrower's low point and vice versa about the hammer's azimuth angle. It is conjectured that the reason why the thrower's movement is asynchronous with the hammer's movement by approximately half a turn is to accelerate the hammer head in a manner similar to the way that the amplitude of a pendulum increases when it is pulled upward by a string against the downward movement of the swinging weight. 相似文献
8.
Zeynep Mine Derince 《International Review of Education/Internationale Zeitschrift für Erziehungswissenschaft/Revue internationale l'éducation》2011,29(1):377-395
After passing their university entry exam, students who wish to study a subject at one of the Turkish universities offering
English-medium courses attend a one-year preparatory class. At the end of this, they need to pass an English language proficiency
exam in order to be admitted to their chosen course of study. The existing curriculum for such preparatory classes is designed
to be taught in English only and very much oriented towards passing the concluding standardised language proficiency exam
at the end. This approach does not teach the students any of the skills they will need for their further study, such as how
to think critically or to question their own conditioning and political attitudes. Using a different methodology, the author
of this paper conducted an in-class project with students learning English in a Turkish state university’s preparatory class.
The project was carried out within a framework of critical pedagogy and used both Turkish and English during the phases of
research and discussion. Evaluating the students’ own reflections on the experience as well as their final presentations which
were prepared in English, the author suggests that the critical pedagogy approach in combination with a maximum use of students’
means of expression and language resources led to a more meaningful learning experience – both for the students and for herself
– as well as a more efficient and lasting English language proficiency. 相似文献
9.
Direction of spin axis and spin rate of the pitched baseball 总被引：1，自引：0，他引：1
Jinji T Sakurai S 《Sports biomechanics / International Society of Biomechanics in Sports》2006,5(2):197-214
In this study, we aimed to determine the direction of the spin axis and the spin rate of pitched baseballs and to estimate the associated aerodynamic forces. In addition, the effects of the spin axis direction and spin rate on the trajectory of a pitched baseball were evaluated. The trajectories of baseballs pitched by both a pitcher and a pitching machine were recorded using four synchronized video cameras (60 Hz) and were analyzed using direct linear transform (DLT) procedures. A polynomial function using the least squares method was used to derive the time-displacement relationship of the ball coordinates during flight for each pitch. The baseball was filmed immediately after ball release using a high-speed video camera (250 Hz), and the direction of the spin axis and the spin rate (omega) were calculated based on the positional changes of the marks on the ball. The lift coefficient was correlated closely with omegasinalpha (r = 0.860), where alpha is the angle between the spin axis and the pitching direction. The term omegasinalpha represents the vertical component of the velocity vector. The lift force, which is a result of the Magnus effect occurring because of the rotation of the ball, acts perpendicularly to the axis of rotation. The Magnus effect was found to be greatest when the angular and translational velocity vectors were perpendicular to each other, and the break of the pitched baseball became smaller as the angle between these vectors approached 0 degrees. Balls delivered from a pitching machine broke more than actual pitcher's balls. It is necessary to consider the differences when we use pitching machines in batting practice. 相似文献
10.
煤炭职工高中等教育研究会课题组 《煤炭高等教育》2003,21(2):101-105
教学督导就是依据一定的评价标准对教学工作的过程和绩效进行调查研究、测量分析及评定，在此基础上对教学工作进行监督和指导；素质体系包括学习素质、创新素质、知识素质、成功素质；应建立全国职业技术教育师资培训中心，建立“双师型”人才资格认征体系，建立专兼职相结合的教师队伍；高职教育招生和毕业生就业指导工作要加大改革力度。 相似文献