Viscous effects in the inception of cavitation

The inception of cavitation in the steady flow of liquids around bodies is seen to depend upon the real fluid flow around the bodies as well as the supply of nucleating cavitation sources—or nuclei—within the fluid. A primary distinction is made between bodies having a laminar separation or not having a laminar separation. The former group is relatively insensitive to the nuclei concentration whereas the latter is much more sensitive. Except for the case of fully separated wake flows and for gaseous cavitation by diffusion the cavitation inception index tends always to be less than the magnitude of the minimum pressure coefficient and only approaches that value for high Reynolds numbers in flows well supplied with nuclei.

BLOC-2 targets recycling endosomal tubules to melanosomes for cargo delivery

Hermansky-Pudlak syndrome (HPS) is a group of disorders characterized by the malformation of lysosome-related organelles, such as pigment cell melanosomes. Three of nine characterized HPS subtypes result from mutations in subunits of BLOC-2, a protein complex with no known molecular function. In this paper, we exploit melanocytes from mouse HPS models to place BLOC-2 within a cargo transport pathway from recycling endosomal domains to maturing melanosomes. In BLOC-2-deficient melanocytes, the melanosomal protein TYRP1 was largely depleted from pigment granules and underwent accelerated recycling from endosomes to the plasma membrane and to the Golgi. By live-cell imaging, recycling endosomal tubules of wild-type melanocytes made frequent and prolonged contacts with maturing melanosomes; in contrast, tubules from BLOC-2-deficient cells were shorter in length and made fewer, more transient contacts with melanosomes. These results support a model in which BLOC-2 functions to direct recycling endosomal tubular transport intermediates to maturing melanosomes and thereby promote cargo delivery and optimal pigmentation.