全科型小学教师培养教材建设之研究

为了实现全科型小学教师的培养目标,编写整套适应新时期小学教师培养的教材十分必要。在教材建设中,应编制科学的教学大纲,正确处理好几种关系,组织落实教材建设的具体实施,使编定的教材既能满足教师的自身需求,又能提升教师素质。     

Iron and phosphorus co-limit nitrogen fixation in the eastern tropical North Atlantic

The role of iron in enhancing phytoplankton productivity in high nutrient, low chlorophyll oceanic regions was demonstrated first through iron-addition bioassay experiments and subsequently confirmed by large-scale iron fertilization experiments. Iron supply has been hypothesized to limit nitrogen fixation and hence oceanic primary productivity on geological timescales, providing an alternative to phosphorus as the ultimate limiting nutrient. Oceanographic observations have been interpreted both to confirm and refute this hypothesis, but direct experimental evidence is lacking. We conducted experiments to test this hypothesis during the Meteor 55 cruise to the tropical North Atlantic. This region is rich in diazotrophs and strongly impacted by Saharan dust input. Here we show that community primary productivity was nitrogen-limited, and that nitrogen fixation was co-limited by iron and phosphorus. Saharan dust addition stimulated nitrogen fixation, presumably by supplying both iron and phosphorus. Our results support the hypothesis that aeolian mineral dust deposition promotes nitrogen fixation in the eastern tropical North Atlantic.     

Retrograde spins of near-Earth asteroids from the Yarkovsky effect

Dynamical resonances in the asteroid belt are the gateway for the production of near-Earth asteroids (NEAs). To generate the observed number of NEAs, however, requires the injection of many asteroids into those resonant regions. Collisional processes have long been claimed as a possible source, but difficulties with that idea have led to the suggestion that orbital drift arising from the Yarkovsky effect dominates the injection process. (The Yarkovsky effect is a force arising from differential heating-the 'afternoon' side of an asteroid is warmer than the 'morning' side.) The two models predict different rotational properties of NEAs: the usual collisional theories are consistent with a nearly isotropic distribution of rotation vectors, whereas the 'Yarkovsky model' predicts an excess of retrograde rotations. Here we report that the spin vectors of NEAs show a strong and statistically significant excess of retrograde rotations, quantitatively consistent with the theoretical expectations of the Yarkovsky model.     

光阑与透镜间距对聚焦高斯光束的影响

讨论高斯光束经过光阑,被一透镜聚焦后的轴上点光场分布,以及光阑和透镜的间距对最佳聚焦点的影响.理论计算结果表明,聚焦光场的光强分布与光阑和透镜之间的间距密切相关.     

长直导体辐射场仿真数学模型的研究

讨论了在时域范围内,面向长直导体的辐射场的仿真数学模型建立问题。通过对原有的数学模型的改进,扩大了其适用范围,并有效地解决了“低频近场”问题。