《面积与面积单位》的教学设计与反思

一、教材分析面积属于空间与图形领域,本课是在学生学习了长方形、正方形的特征及其周长计算的基础上进行教学的。从学生的知识水平来看,这部分内容是从直线到平面,从长度到面积,由一维空间向二维空间转化的开始,知识跨度大、难度高。二、教学目标1.通过摸一摸、看一看、比一比等体验活动,使学生理解面积的含义。2.在解决问题的过程中,使学生感受建立面积单位的必要性,初步理解面积单位的建立规则。     

Wavy film flow along periodic wall under monochromatic-frequency flowrate perturbation

Surface wave dynamics of falling film on the surface of periodic rectangular wall under monochromatic-frequency flowrate forcing disturbances is studied via numerical simulation. Waveforms formed on the periodic rectangular wall are different from those on the flat plate. At low frequency, the perturbation introduced at the inlet first undergoes a steady flow region and then develops into solitary waves. When the frequency becomes higher, solitary waves disappear. Film deformations in the steady flow region and characteristics of solitary waves are studied as the film travels down. There are circulations at the depression of periodic wall which are dependent on the local film characteristics and geometry of the corrugation. Moreover, the flow rate and geometry of the corrugations can also affect the evolvement of the monochromatic perturbation.     

给月球佩戴太阳能腰带

充分利用太阳能是新能源领域最热门的话题,对太阳能的利用设想甚至从地球开始延伸至浩渺的太空。在日本因地震引发的核泄漏危机后,用太阳能等清洁能源取代核电的呼声日渐高涨。日     

从制造大国到制造强国:中国还要做些什么 关于第41届世界技能大赛暨英、德职业教育考察报告

由中国职业技术教育学会职业教育装备专业委员会组织的第41届世界技能大赛暨英国德国职业教育考察团于10月4日至13日访问了英国和德国,考察了在伦敦举行的第41届世界技能大赛,英国CAD/CAM软件设     

浅谈薄壁套类零件镗孔时产生废品的原因及预防教学策略

在车床上车削加工薄壁套类零件,由于刚性差,在镗孔时常因孔经尺寸不正确,内孔不圊,内孔有锥度和表面粗糙度述不到要求而造成废品。本人根据实际工作经验,对违成零件废品的几种原因进行综合分析,提出有效预防方法及工艺改进措施,以确保零件的加工质量,减少度品率。     

化学实验中的洗涤大有讲究

化学高考试题中,经常涉及对所得晶体或固体残渣进行洗涤的相关问题,洗涤大有讲究,要考虑几个方面,如:为什么要洗涤?用什么洗涤?怎样洗涤?怎样证明已经洗涤干净?等等。1关于洗涤的目的1.1除去杂质除去晶体表面的可溶性杂质。     

Performance of passive and reactive profiled median barriers in traffic noise reduction

Median noise barriers, like parallel noise barriers, can be employed to reduce the impact of traffic on roadside communities via the direct propagation path. The performance of different shapes of median barriers was compared using reactive and passive surfaces and a 2D boundary element method (BEM). In the case of reactive surfaces, quadratic residue diffusers (QRDs) and primitive root diffusers (PRDs) were used on the top and stem surfaces of median barriers. To introduce passive barriers, two different absorbent materials including fibrous material and a grass surface with flow resistivity of 20 000 and 2500 kg/(s·m²), respectively, were similarly applied. The effect of thin absorptive barriers was similar at lower frequencies and better at mid and high frequencies to that of their equivalent rigid barriers. More improvement was achieved by covering the top surface of thick barriers with grass rather than with fibrous material. The performance of QRD and PRD barriers where the diffuser was located on the top surface was more frequency dependent than that of barriers coated with fibrous material. A comparison of the average A-weighted insertion loss in the thick barriers showed that the greatest improvement (2.59 dB (A)) was achieved using a barrier of 30-cm thickness covered with grass.     

聚烯烃复合抗静电材料的研究进展

聚烯烃大多为绝缘体,在干燥的空气中容易产生静电荷,从而给加工和使用造成巨大的危害.针对聚烯烃加工和使用过程中的静电问题,大多采用加入抗静电剂和其他相应助剂或填料的方法来降低其所积累的静电量,使制品的综合性能达到比较理想的效果.本文通过分析高分子材料的抗静电机理,描述了抗静电聚烯烃的研究进展和前景.     

木屑缓释尿素制备及其担载释放的研究

化肥在农业生产的使用中,易产生化肥的利用率低的问题,这样不仅会造成超量施肥,使土壤的物理性质不断恶化,还会影响农作物的产量和质量的提高,同时对环境造成污染.以木屑为载体来制备缓释尿素,通过其担载和释放行为的研究,对提高化肥的使用效率和环境的保护起到了积极的作用.     

泉州德化戴云寺珍藏张瑞图墨宝

泉州德化县戴云寺内,管藏的明代大书法家张瑞图题刻的“毫余精舍”残匾,部分残缺的木刻楹联,虽因年代久远,木料表面腐蚀严重,油漆大部分斑驳脱落,但字迹和印章落款仍清晰可辨。