לוח שנה משולב

We study the displacement of immiscible fluids in deformable, non-cohesive granular media by experiments and simulations. Experimentally, we inject air into a thin bed of water-saturated glass beads and observe the invasion morphology. Numerically, we develop a pore-scale model that captures the dynamic pressure redistribution at the invasion front and the feedback between fluid invasion and microstructure rearrangement. We identify three invasion regimes: capillary fingering, viscous fingering, and ``capillary fracturing'', where capillary forces induce the opening of conduits. We derive two dimensionless numbers that govern the transition among the different regimes: a modified capillary number and a fracturing number. We predict the emergence of fracturing in fine-grained media under low confining stress, a phenomenon that likely plays a fundamental role in many natural processes such as primary oil migration, methane venting from lake sediments, and the formation of desiccation cracks.

Black hole thermodynamics was developed about 40 years ago in the wake of deepening understanding of the black hole phenomenon. I will review the neces-sary background on black holes, and then explain why black hole physics required a thermodynamics, how the latter was constructed, and how its predictions were confirmed--at least at the theoretical level. I will then discuss two or three of the ramifications of black hole thermodynamics which are unfinished areas of research today.