MMMRN test ~ 1 kyr (top), ~2 kyr (middle), and ~4 kyr (bottom) after the first core formation (t_core = 72.84 kyr). Mid-plane view of the total dust ratio (left) and the dust ratio of the least coupled species (right). The colorbar is the same for both figures. The dotted white lines represent the regions where the total (left) or 160 μm grain (right) dust-to-gas ratio is at its initial value, which can also be regarded as a dust enrichment line.