K-8：教练机中的super star

在同学们的印象中,一提到军用飞机,首先想到的大都是战斗机、轰炸机、侦察机等。教练机是什么？许多人就有点摸不着头脑了。别急,听我慢慢道来。     

Biodegradab le metals—the rising star

<正>Biodegradable metals-the rising starBiodegradable metals(BMs)are one of the hotspots in the field of biomaterials,and are regarded as the rising star in the family of metallic biomaterials.They are metals expected to corrode gradually in vivo,with an appropriate host response     

Direct Urca processes involving hyperons in neutron star matter

The presence of the isovector scalar interaction in neutron star matter is considered by exchangingδmeson;we study the effects ofδmesons on the direct Urca processes involving hyperons.The calculation is based on the framework of the relativistic mean field theory.By our analysis,the hyperon direct Urca processes under beta equilibrium are open at lower densities due toδmesons,which create a larger energy gap between two baryons in the reactions.Theδmeson leads to an obvious enhancement of the neutrino emissivity for the hyperon direct Urca processes.In particular,the relativistic neutrino emissivity is found to be substantially larger than predicted in the nonrelativistic approach whetherδmesons appear in an neutron star or not.In our results,δmesons not only change the baryons properties,but also result in more rapid cooling rate of neutron stars by hyperon direct Urca processes.     

让“star”原则在听说训练中处处闪光

所谓star，就是simadon／Task／Acdon／Result．通过在一节听说课中不同任务的递进，最终学生在口语与写作上都得到了知识的生成。重视训练语言的内容，培养学生的语用能力。     

The excitation of solar-like oscillations in a δSct star by efficient envelope convection

Delta Scuti (δSct) stars are opacity-driven pulsators with masses of 1.5-2.5 M⊙, their pulsations resulting from the varying ionization of helium. In less massive stars such as the Sun, convection transports mass and energy through the outer 30 per cent of the star and excites a rich spectrum of resonant acoustic modes. Based on the solar example, with no firm theoretical basis, models predict that the convective envelope in δSct stars extends only about 1 per cent of the radius, but with sufficient energy to excite solar-like oscillations. This was not observed before the Kepler mission, so the presence of a convective envelope in the models has been questioned. Here we report the detection of solar-like oscillations in the δSct star HD187547, implying that surface convection operates efficiently in stars about twice as massive as the Sun, as the ad hoc models predicted.