Hydrostatic equilibrium

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

Physics of the Atmosphere and Climate

Abstract: 1. The Earth-atmosphere system 2. Thermodynamics of gases 3. The second law and its implications 4. Heterogeneous systems 5. Transformations of moist air 6. Hydrostatic equilibrium 7. Static stability 8. Radiative transfer 9. Aerosol and cloud 10. Atmospheric motion 11. Atmospheric equations of motion 12. Large-scale motion 13. The planetary boundary layer 14. Atmospheric waves 15. The general circulation 16. Dynamic stability 17. Influence of the ocean 18. Interaction with the stratosphere.

A New Static Failure Criterion for Isotropic Polymers

Abstract: A new static failure criterion for isotropic polymers with different strengths in tension and compression based on exponential dependence between the mean stress and the von Mises equivalent stress is proposed. The two material parameters introduced can be determined by two simple tests - the uniaxial tension and compression. The locus of the criterion is nearly conical for low hydrostatic pressures and tends to a cylindrical form if an increased hydrostatic pressure is applied. The validity of the criterion is demonstrated by experimental strength data taken from the literature for several polymers in the case of superimposed hydrostatic pressure.

Changes of solar luminosity and radius following secular perturbations in the convective envelope

Abstract: The effect on solar models of several types of slow, spherically symmetric perturbations, acting at various depths within the convective envelope, are calculated. Results are presented on perturbations of the efficiency of convective energy transport (alpha perturbations) and on changes in the nongas component of pressure (beta perturbations). The effects of magnetic fields concentrated near the interface between the radiative core and the convective envelope are explored. It is found that the response and relaxation diagnostics depend both on the type of perturbation and on the depth at which the perturbation is applied. In addition to the general depth dependence, model behavior is sensitive to the presence of major ionization zones near the perturbed layer. The time dependence of the solar model behavior is characterized by an initial hydrostatic reaction followed by a thermal readjustment on a time scale of about 100 years, and finally relaxation to a new thermal equilibrium on a Kelvin time scale.

Be star disk models in consistent vertical hydrostatic equilibrium

Abstract: A popular model for the circumstellar disks of Be stars is that of a geometrically thin disk with a density in the equatorial plane that drops as a power law of distance from the star. It is usually assumed that the vertical structure of such a disk (in the direction parallel to the stellar rotation axis) is governed by the hydrostatic equilibrium set by the vertical component of the star's gravitational acceleration. Previous radiative equilibrium models for such disks have usually been computed assuming a fixed density structure. This introduces an inconsistency as the gas density is not allowed to respond to temperature changes and the resultant disk model is not in vertical, hydrostatic equilibrium. In this work, we modify the BEDISK code of Sigut & Jones so that it enforces a hydrostatic equilibrium consistent with the temperature solution. We compare the disk densities, temperatures, Hα line profiles, and near-IR excesses predicted by such models with those computed from models with a fixed density structure. We find that the fixed models can differ substantially from the consistent hydrostatic models when the disk density is high enough that the circumstellar disk develops a cool (T 10, 000 K) equatorial region close to the parent star. Based on these new hydrostatic disks, we also predict an approximate relation between the (global) density-averaged disk temperature and the T eff of the central star, covering the full range of central Be star spectral types.

Radiation thermo-chemical models of protoplanetary discs – III. Impact of inner rims on spectral energy distributions

Abstract: We study the hydrostatic density structure of the inner disc rim around Herbig Ae stars using the thermo-chemical hydrostatic code prodimo. We compare the spectral energy distributions (SEDs) and images from our hydrostatic disc models to that from prescribed density structure discs. The 2D continuum radiative transfer in prodimo includes isotropic scattering. The dust temperature is set by the condition of radiative equilibrium. In the thermal-decoupled case, the gas temperature is governed by the balance between various heating and cooling processes. The gas and dust interact thermally via photoelectrons, radiatively, and via gas accommodation on grain surfaces. As a result, the gas is much hotter than in the thermo-coupled case, where the gas and dust temperatures are equal, reaching a few thousands K in the upper disc layers and making the inner rim higher. A physically motivated density drop at the inner radius ('soft-edge') results in rounded inner rims, which appear ring-like in near-infrared images. The combination of lower gravity pull and hot gas beyond similar to 1 au results in a disc atmosphere that reaches a height over radius ratio z/r of 0.2, while this ratio is 0.1 only in the thermo-coupled case. This puffed-up disc atmosphere intercepts larger amount of stellar radiation, which translates into enhanced continuum emission in the 3-30 mu m wavelength region from hotter grains at similar to 500 K. We also consider the effect of disc mass and grain size distribution on the SEDs self-consistently feeding those quantities back into the gas temperature, chemistry and hydrostatic equilibrium computation.