例谈“体验式学习”在数学定理教学中的应用

体验式学习就是强调以学生为主体的参与与体验,让学生在经历活动中体验,在观察与反思中体验,在归纳与抽象中体验,让思维活动在体验中循环反复,发展数学核心素养.本文中以“三角形全等的判定5”一课的教学为例,实践了体验式学习在数学定理教学中的应用.     

平行平板间径向气流的 Navier-Stokes 方程的新的近似解

文献[1]得到了两平行平板间径向气流的 Navier-Stokes 方程的近似解——迭代近似解和级数解。用迭代法求得压力二级近似解,与实验十分符合。本文指出,用М.Е.Щвец法亦可得到与文献完全相同的结果.如果用本文新提出的改进了的М.Е.Щвец法,则可得到比[1]更加精确(这主要反映在流速分布的规律上)的结果。文中指出,按照原М.Е.Щвец法,求一级近似解时,忽略的是一阶微量;而按本文新提出的改进了的М.Е.Щвец法,略去的是二阶微量,这就是本文结果较文献[1]的结果更加准确的理论根据。     

叶片扩压器进口安装角对离心压缩机性能影响的数值与实验研究

对不同扩压器进口安装角下离心压缩机的性能进行了实验研究,并详细计算分析了相应的流场分布。分析表明, 不同的进口安装角对压缩机的流动有较大的影响,压缩机的性能曲线也有不同程度的左右偏移;进口处较大的正冲角和负冲角均会在扩压器叶片表面出现大尺度的分离涡团;在给定的流量工况下,应存在一个最佳的进口安装角,使得扩压器效率最高;设计工况下,最高效率所对应的冲角并非为零。     

基于上海激光电子γ源的天体核合成关键反应12C(α,γ)16O的反应率研究

正在研制的上海激光电子γ源是MeV量级的高品质γ光束线站，基于该装置可以开展一系列核天体物理实验, 从而更准确的确定各天体核合成反应的反应率. 本文研究了天体核合成中的关键反应¹²C(α,γ)¹⁶O的反应率. 根据多组实验和理论截面数据分别计算了反应率, 并给出了这些反应率计算结果的平均值和统计误差. 根据该结果拟合了理论反应率的解析形式, 确定了新的参数. 进而给出俘获反应¹²C(α,γ)¹⁶O在He燃烧环境下的反应率和误差, 并讨论了电子屏蔽效应对天体反应率的修正.     

Spectra and Spin Polarization of the Valence Band Auger Emission from Cr （100） Surface

Calculations have been carried out on spin-polarized Auger electron emission from a seven-layer chromium (lO0)-film. The core and valence states concerning the Auger transition are obtained from a self-consistent full-potential linearized augmented plane wave calculation by using a repeated slab geometry. The calculations refer to experiments on the L3M23 V- and L3 VV-transRions that have recently been carried out by Heinzmann et al. The Auger spectrum obtained for the L3VV transition agrees relatively well with our calculations, whereas the observed L3M23V-Auger structure is considerably wider than that predicted by our theory. Nevertheless, the spin-polarization in the latter case, which is about -13%, is in fair agreement with the experiment, different from the L3VV-transition where the experiment yields -10% as opposed to the theoretical value of -25%. We give possible reasons for the origin of these discrepancies.     

Role of chelating agent in chemical and fluorescent properties of SnO2 nanoparticles

A modified polyacrylamide gel route is applied to synthesize SnO2 nanoparticles. High-quality SnO2 nanoparticles with a uniform size are prepared using different chelating agents. The average particle size of the samples is found to depend on the choice of the chelating agent. The photoluminescence spectrum detected at λex = 230 nm shows a new peak located at 740 nm due to the surface defect level distributed at the nanoparticle boundaries.     

交叉分子束方法研究H+CH4和H+CD4反应:CH3/CD3的振动激发态产物通道

We study the H+CH₄/CD₄→H₂/HD+CH₃/CD₃ reactions using the time sliced velocity map ion imaging technique. Ion images of the CH₃/CD₃ products were measured by the (2+1) resonance enhanced multi-photon ionization (REMPI) detection method. Besides the CH₃/CD₃ products in the ground state, ion images of the vibrationally excited CH₃/CD₃ products were also observed at two collision energies of 0.72 and 1.06 eV. It is shown that the angular distribution of the products CH₃/CD₃ in vibrationally excited states gradually vary from backward scattering to sideways scattering as the collision energy increases. Compared to the CH₃/CD₃ products in the ground state, the CH₃/CD₃ products in vibrationally excited states tend to be more sideways scattered, indicating that larger impact parameters play a more important role in the vibrationally excited product channels.     

激光诱导Ti等离子体电子温度的实验研究

室温,常压下,利用Nd∶YAG脉冲激光器产生的波长为1 064 nm, 脉宽12 ns,能量分别180, 230和280 mJ的脉冲激光冲击Ti靶,使用中阶梯光栅光谱仪检测了三种激光能量下对应的光谱。调节延时器DG645的延迟时间,检测了延迟0～500 ns时间范围内Ti等离子体对应激光能量下的发射光谱,分析光谱,可以得到了九条不同的的TiⅠ 和TiⅡ等离子体谱线,证明在该实验条件下,Ti靶能够充分吸收能量电离且离子谱线具有不同的演化速率,利用Saha-Boltzmann法计算并分析Ti等离子体电子温度,实验结果表明：相同的延迟时间,激光能量越大,谱线相对强度越大,电子温度越高,谱线相对强度的变化量随激光能量的变化量增大而增大;在延时0～150 ns内,三种激光能量下的等离子体电子温度和谱线的相对强度都随延迟时间的增加而快速下降,其中280 mJ激光能量下的等离子体电子温度和谱线强度下降速率较快;在150～250 ns范围内,电子温度和谱线强度均随延迟时间的增加有一个缓慢的上升,180 mJ激光能量下的等离子体电子温度和谱线强度的上升速率较快。250～500 ns范围内,三种激光能量下的电子温度和谱线强度均随延迟时间的增加而缓慢下降。     

光参量啁啾脉冲放大增益特性研究

 通过对非线性三波耦合方程组进行数值求解，研究了光参量放大的增益特性及饱和放大特性。给出了泵浦光、信号光参数对参量增益的影响及其与晶体饱和长度的关系。且OPA具有传统CPA系统所不具有的优点，将有可能取代传统的CPA系统而作为超短超强激光系统的新型前端。