Running summarizing tools on a new article

Abstract: Chapter 2 discusses the structure of gaseous protoplanetary disks. It begins by explaining how observations can be used to infer disk mass, disk structure, and stellar accretion rate. The vertical structure of a gas disk in hydrostatic equilibrium is derived, and the considerations that determine the surface density and temperature profile of a passive disk are described. The concept of the condensation sequence is outlined, along with the ionization and recombination processes that determine the ionization state. Physical processes that can produce large-scale structure in disks - zonal flows, vortices, and ice lines - are discussed.