标题： 分层凝聚中尘埃聚集体的结构 显示英文标题

标题： The structure of dust aggregates in hierarchical coagulation

摘要： 星际空间和原行星盘中的尘埃凝聚通常被视为两种极端情况之一：粒子-团聚体凝聚和团聚体-团聚体凝聚。 在本文中，我们研究了分层增长的过程，其中团聚体是由明显更小的团聚体（而非单体）构建而成的。 我们表明，这个过程可以被理解为一种修改后的、类似PCA的过程，该过程生成多孔但非分形的颗粒，其填充因子主要由构建块的孔隙率决定。 我们还表明，在相对速度由湍流驱动的凝聚环境中，对数平坦的质量分布（每十年质量相等）通常在碎片化不断补充小颗粒的环境中出现，这会导致小颗粒和团聚体主导大颗粒的增长。 因此，在这种环境中，分层增长应被视为常态。 因此，我们预测在这种环境中形成的团聚体不是分形结构且密度极低，因为它们会从将分形定律外推到大尺寸所得到的结果。 团聚体的致密化不仅来自于足以重新构造团聚体的碰撞——它更早开始，通过用较小的颗粒填充颗粒中的空隙来促进增长。 显示英文摘要

摘要： Dust coagulation in interstellar space and protoplanetary disks is usually treated as one of 2 extreme cases: Particle-Cluster Aggregation and Cluster-Cluster Aggregation. In this paper we study the process of hierarchical growth, where aggregates are built from significantly smaller aggregates (but not monomers). We show that this process can be understood as a modified, PCA-like process that produces porous, but non-fractal particles whose filling factor is chiefly determined by the porosity of the building blocks. We also show that in a coagulation environment where relative velocities are driven by turbulence, a logarithmically flat mass distribution (equal mass per mass decade) as it is typically found in environments where fragmentation replenishes small grains, leads to a situation where small particles and aggregates dominate the growth of large ones. Therefore, in such environments, hierarchical growth should be seen as the norm. Consequently, we predict that the aggregates in such environments are not fractals with extremely low densities as they would result from extrapolation fractal laws to large sizes. The compactification of aggregates does not only result from collisions with enough energy to restructure aggregates - it starts already earlier by filling voids in particles with smaller grains that contribute to the growth.