稠密颗粒气体中团簇的实验研究及其对原行星盘中粒子停止时间的影响
Experimental study of clusters in dense granular gas and implications for the particle stopping time in protoplanetary disks
摘要：
在原行星盘中，密集的粒子结构区域促进了行星形成。稠密云层中的固体粒子通过集体效应和对气体的反作用改变它们的运动。研究了颗粒-气体反馈与环境固气比$ε> 1$对颗粒停留时间的影响。在国际空间站上的实验中，我们研究了稠密颗粒气体与空气相互作用时的演化。我们观察到扩散的集群在实验开始时释放，但也形成新的动态集群。团簇外的固气质量比在约$ε_{\rm avg} \sim 2.5 - 60$的范围内变化。我们发现，在粘性介质中的气体阻力的概念仍然成立，即使该介质是强烈占主导地位的固体质量。然而，必须使用取决于$ε_{\rm avg} $的集体因子，即，在最高质量比下，阻力减小18倍。因此，原行星盘中的颗粒群移动得更快，碰撞得更快，比它们的成分可能暗示的要快。
英文摘要：
In protoplanetary disks, zones of dense particle configuration promote planet formation. Solid particles in dense clouds alter their motion through collective effects and back reaction to the gas. The effect of particle-gas feedback with ambient solid-to-gas ratios $ε> 1$ on the stopping time of particles is investigated. In experiments on board the International Space Station we studied the evolution of a dense granular gas while interacting with air. We observed diffusion of clusters released at the onset of an experiment but also the formation of new dynamical clusters. The solid-to-gas mass ratio outside the cluster varied in the range of about $ε_{\rm avg} \sim 2.5 - 60$. We find that the concept of gas drag in a viscous medium still holds, even if the medium is strongly dominated in mass by solids. However, a collective factor has to be used, depending on $ε_{\rm avg} $, i.e. the drag force is reduced by a factor 18 at the highest mass ratios. Therefore, flocks of grains in protoplanetary disks move faster and collide faster than their constituents might suggest.
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