Gravity modes as a way to distinguish between hydrogen- and helium-burning red giant stars

Red giants are evolved stars that have exhausted the supply of hydrogen in their cores and instead burn hydrogen in a surrounding shell. Once a red giant is sufficiently evolved, the helium in the core also undergoes fusion. Outstanding issues in our understanding of red giants include uncertainties in the amount of mass lost at the surface before helium ignition and the amount of internal mixing from rotation and other processes. Progress is hampered by our inability to distinguish between red giants burning helium in the core and those still only burning hydrogen in a shell. Asteroseismology offers a way forward, being a powerful tool for probing the internal structures of stars using their natural oscillation frequencies. Here we report observations of gravity-mode period spacings in red giants that permit a distinction between evolutionary stages to be made. We use high-precision photometry obtained by the Kepler spacecraft over more than a year to measure oscillations in several hundred red giants. We find many stars whose dipole modes show sequences with approximately regular period spacings. These stars fall into two clear groups, allowing us to distinguish unambiguously between hydrogen-shell-burning stars (period spacing mostly ～ 50 seconds) and those that are also burning helium (period spacing ～ 100 to 300 seconds).     

Fast core rotation in red-giant stars as revealed by gravity-dominated mixed modes

When the core hydrogen is exhausted during stellar evolution, the central region of a star contracts and the outer envelope expands and cools, giving rise to a red giant. Convection takes place over much of the star's radius. Conservation of angular momentum requires that the cores of these stars rotate faster than their envelopes; indirect evidence supports this. Information about the angular-momentum distribution is inaccessible to direct observations, but it can be extracted from the effect of rotation on oscillation modes that probe the stellar interior. Here we report an increasing rotation rate from the surface of the star to the stellar core in the interiors of red giants, obtained using the rotational frequency splitting of recently detected 'mixed modes'. By comparison with theoretical stellar models, we conclude that the core must rotate at least ten times faster than the surface. This observational result confirms the theoretical prediction of a steep gradient in the rotation profile towards the deep stellar interior.     

嵌入式系统实践教学研究与设计

为培养适应社会需求的嵌入式人才,本文提出符合计算机专业特点的嵌入式软件技术方向人才培养目标,对目前计算机嵌入式系统教学的现状展开分析与研究,结合嵌入式实验教学的特点,制定了一套切实可行的课程体系和教学模式,包括设计多层次嵌入式实验内容,实践开发平台,WinCE开发工具以及教学考核方式等多方面的内容。     

页岩支撑裂缝中渗透率变化规律实验研究

在页岩气藏的压裂开发中,支撑裂缝的渗透率是影响裂缝导流能力和压裂增产效果的重要因素。通过实验
手段,研究了吸附气体的溶胀作用和支撑剂的嵌入作用对Greenriver 页岩支撑裂缝渗透率的影响。采用Pulse test 实
验方法,测量并对比了非吸附气体和吸附气体的渗透率。以He 为代表性的非吸附性气体,实验测得其在花岗岩和页
岩中的渗透率曲线为线性,渗透率随着有效应力的减小而增加,且支撑剂的嵌入作用使页岩中的渗透率明显降低;以
CO2 为代表性的吸附性气体,实验测得其在页岩中的渗透率曲线呈典型的“U”型,这是由于CO2 溶胀作用和有效应力
共同作用的结果,从而说明在页岩支撑裂缝中,溶胀作用同样对渗透率有显著影响;与He 在页岩中的渗透率相比,相
同压力下的CO2 渗透率更低,且在Langmuir 压力值附近达到最小值。