浅谈劳动技能教学

劳动技能是一种在一定劳动任务、劳动目标指示下的操作程序和动作系列.如用台钳夹持工作,应先旋动台钳手柄,使钳口放大,然后把工件放入钳口中适当位置,最后旋动手柄把工件夹紧,这一过程就包含了实观目标的程序和执行这一程序的动作方式.劳动技能教学是让学生将这种规则和程序系统移植、内化为智力操作程式和肌肉动作程式,使学生学会当面临一个具体劳动任务时,在目标的指示下,通过一系列操作完成这一任务,即学会“如何去做.”一、劳动技能形成的基本途径学生学习劳动技能的本质是建立动作的连锁,根据心理学的有关理论,建立动作连锁的条件包括顺序、偶合、连贯和强化等四个方面,而练习能有效地改善这些条件,因此学生劳动技能形成的主要形式是练习.所谓练习,就是动作序列的重复,重复是练习最显著的特征.值得注意的是并非一切都是练习,,一般来说,当重复具有改善学生动作的目的,如提高动作的准确性、协调性、稳定性及熟练程序等,并能给学生提供起强化作用的反馈信息,这样的重复才称之为练习.为了取得良好的练习效果,在组织和指导学生练习时,要着重抓住以下几点:

Does the Asian monsoon modulate tropical cyclone activity over the South China Sea?

To investigate whether the Asian monsoon influences tropical cyclone (TC) activity over the South China Sea (SCS), TCs (including tropical storms and typhoons) over the SCS are analyzed using the Joint Typhoon Warning Center dataset from 1945 to 2009. Results show an increasing trend in the frequencies of TC-all (all TCs over the SCS) and TY-all (all typhoons over the SCS), due mainly to an increase in the number of TCs moving into the SCS after development elsewhere. Little change is seen in the number of TCs that form in the SCS. The results of wavelet analysis indicate that the frequency of typhoons (TY) shows a similar oscillation as that of TCs, i.e., a dominant periodicity of 8-16 years around the 1970s for all TC activity, except for TC-mov (TCs that moved into the SCS from the western North Pacific). To examine the relationship between typhoon activity and the summer monsoon, a correlation analysis was performed that considered typhoons, TCs, and five monsoon indexes. The analysis reveals statistically significant negative correlation between the strength of the Southwest Asian summer monsoon and typhoon activity over the SCS, which likely reflects the effect of the monsoon on TC formation in the western North Pacific (WNP) and subsequent movement into the SCS. There is a statistically significant negative correlation between TY-loc (typhoons that developed from TCs formed over the SCS) and the South China Sea summer monsoon and Southeast Asian summer monsoon.

Reconfigurable parallel mechanisms with planar five-bar metamorphic linkages

This paper presents the idea of constructing reconfigurable limbs by integrating metamorphic linkages as subchains.The planar five-bar metamorphic linkages that have three phases resulting from locking of motors are considered.Under the assumption that the constraint exerted by the reconfigurable limb can switch between no constraint,a constraint force,and a constraint couple,the output motions of the metamorphic linkage in its two planar four-bar linkage phases are identified.By adding an appropriate joint to planar four-bar linkages with translational output,four planar five-bar linkages that can be employed in the construction of reconfigurable limbs are enumerated.Serial chains that can provide a constraint couple and a constraint force are synthesized based on screw theory.Reconfigurable limbs that have three configurations associated with the three distinct phases of the metamorphic linkages are assembled with planar five-bar metamorphic linkages and serial chains with four degrees of freedom.A class of reconfigurable parallel mechanisms are constructed by connecting a moving platform and a base with three identical reconfigurable limbs.The degrees of freedom of the reconfigurable parallel mechanism in different configurations with the metamorphic linkages in different phases are given.Finally,the actuation scheme for this kind of mechanisms is addressed.