Hydrostatic equilibrium

About: Hydrostatic equilibrium is a research topic. Over the lifetime, 2451 publications have been published within this topic receiving 62172 citations.

Notes on hydrostatic pressure

Abstract: Hydrostatic pressure is one of the most elementary notions encountered in the fields of naval architecture and marine engineering. Its presentation in textbooks is not always clear, however, especially for floating bodies in the presence of waves. This brief article aims to clarify potential elements of confusion about hydrostatic pressure. Atmospheric pressure is duly considered at the air–water interface, and in the presence of waves, a consistent definition is possible that reconciles the points of view of naval architects performing hydrostatic calculations and of hydrodynamicists using, for example, potential theory.

Modelling the gas kinematics in disk galaxies

Abstract: Over the last few years, evidence that nearby spiral galaxies are surrounded by massive halos of cold gas has been accumulating. This extra-planar cold gas, rotating more slowly than the disk gas, is observed in galaxies with a range of different properties (such as mass and star formation rate, SFR) and it appears analogous to the Intermediate and High Velocity Clouds of the Milky Way. Models for the origin of extra-planar gas have been proposed taking into account the effects of supernova feedback (galactic fountain), cooling flow accretion and hydrostatic equilibrium. Several techniques have been used from analytical treatments and ballistic orbit integration to hydrodynamical simulations. I present a new model where a galactic fountain sweeps up ambient medium as it travels through the halo. This seems to give the best results in reproducing the kinematics of the extra-planar gas and it implies a gas accretion rate of the order of the SFR of the host galaxy.

Does space-time torsion determine the minimum mass of gravitating particles?

Abstract: We derive upper and lower limits for the mass-radius ratio of spin-fluid spheres in Einstein-Cartan theory, with matter satisfying a linear barotropic equation of state, and in the presence of a cosmological constant. Adopting a spherically symmetric interior geometry, we obtain the generalized continuity and Tolman-Oppenheimer-Volkoff equations for a Weyssenhoff spin-fluid in hydrostatic equilibrium, expressed in terms of the effective mass, density and pressure, all of which contain additional contributions from the spin. The generalized Buchdahl inequality, which remains valid at any point in the interior, is obtained, and general theoretical limits for the maximum and minimum mass-radius ratios are derived. As an application of our results we obtain gravitational red shift bounds for compact spin-fluid objects, which may (in principle) be used for observational tests of Einstein-Cartan theory in an astrophysical context. We also briefly consider applications of the torsion-induced minimum mass to the spin-generalized strong gravity model for baryons/mesons, and show that the existence of quantum spin imposes a lower bound for spinning particles, which almost exactly reproduces the electron mass.