Dynamics of Mushy Layers on a Finite Domain

p, li { white-space: pre-wrap; } Mushy layers are regions of intermixed liquid and solid which can arise during the solidification of binary alloys, generally consisting of dendritic solids with solute-rich liquid in the interstices. They occur due to an instability resulting from the buildup of rejected solute along the solidification front. Liquid ahead of the front becomes supercooled, so disturbances to the interface grow more rapidly than the interface itself. A simple experiment has a tank filled with a uniform solution at uniform temperature being placed upon a cold surface. Early on, a small solid layer forms at the bottom capped by a rapidly advancing mushy layer. Typical modeling efforts have made at least one of two assumptions, that the tank is of infinite depth or that the diffusion of solute is negligible. This dissertation investigates the finite-domain problem in the presence of solute diffusion, highlighting new interfacial dynamics and other behaviors that arise in this case

Search for intermediate-mass black hole binaries in the third observing run of Advanced LIGO and Advanced Virgo

International audienceIntermediate-mass black holes (IMBHs) span the approximate mass range 100−105 M⊙, between black holes (BHs) that formed by stellar collapse and the supermassive BHs at the centers of galaxies. Mergers of IMBH binaries are the most energetic gravitational-wave sources accessible by the terrestrial detector network. Searches of the first two observing runs of Advanced LIGO and Advanced Virgo did not yield any significant IMBH binary signals. In the third observing run (O3), the increased network sensitivity enabled the detection of GW190521, a signal consistent with a binary merger of mass ∼150 M⊙ providing direct evidence of IMBH formation. Here, we report on a dedicated search of O3 data for further IMBH binary mergers, combining both modeled (matched filter) and model-independent search methods. We find some marginal candidates, but none are sufficiently significant to indicate detection of further IMBH mergers. We quantify the sensitivity of the individual search methods and of the combined search using a suite of IMBH binary signals obtained via numerical relativity, including the effects of spins misaligned with the binary orbital axis, and present the resulting upper limits on astrophysical merger rates. Our most stringent limit is for equal mass and aligned spin BH binary of total mass 200 M⊙ and effective aligned spin 0.8 at 0.056 Gpc−3 yr−1 (90% confidence), a factor of 3.5 more constraining than previous LIGO-Virgo limits. We also update the estimated rate of mergers similar to GW190521 to 0.08 Gpc−3 yr−1.Key words: gravitational waves / stars: black holes / black hole physicsCorresponding author: W. Del Pozzo, e-mail: [email protected]† Deceased, August 2020