The numerical hydrodynamic modelling of beat Cepheid behavior has been a long standing quest in which purely radiative models had failed consistently. We find that beat pulsations occur naturally when turbulent convection is accounted for in our hydrodynamics code. The development of a relaxation code and of a Floquet stability analysis greatly facilitates the search for and the analysis of bea...

We have obtained ultra-high quality spectra (R = 180, 000; S/N > 300) with unprecedented wavelength coverage (4400 to 7400 Å) for a number of stars covering most of the HR diagram in order to test the predictions of models of stellar surface convection. Line bisectors and core wavelength shifts are both measured and modeled, allowing us to validate and/or reveal the limitations of state-of-the-...

The linear hydrodynamic stability of proto–neutron stars (PNSs) is considered taking into account dissipative processes such as neutrino transport and viscosity. We obtain the general instability criteria which differ essentially from the well-known Ledoux criterion used in previous studies. We apply the criteria to evolutive models of PNSs that, in general, can be subject to the various known ...

Magnetic fields can be created in stably stratified (non-convective) layers in a differentially rotating star. A magnetic instability in the toroidal field (wound up by differential rotation) replaces the role of convection in closing the field amplification loop. Tayler instability is likely to be the most relevant magnetic instability. A dynamo model is developed from these ingredients, and a...

This research focuses on entropy generation rate per unit volume in magneto-hydrodynamic (MHD) mixed convection boundary layer flow of a viscous fluid over an inclined stretching sheet. Analysis has been performed in the presence of viscous dissipation and non-isothermal boundary conditions. The governing boundary layer equations are transformed into ordinary differential equations by an approp...

Assuming that the neutrino luminosity from the neutron star core is sufficiently high to drive supernova explosions by the neutrino-heating mechanism, we show that low-mode (l=1,2) convection can develop from random seed perturbations behind the shock. A slow onset of the explosion is crucial, requiring the core luminosity to vary slowly with time, in contrast to the burstlike exponential decay...

Considerable efforts have recently been made to understand and identify various spatio-temporal transitions from an unstable state to a coherently oscillating or chaotic state in numerous hydrodynamic flows. Oscillatory convection in binary mixtures as well as a variety of open-flow systems show a transition to spatially developing traveling waves (TW). For these systems a generalized Ginzburg-...

We present three-dimensional numerical simulations of the dynamic evolution of uniformly buoyant, twisted horizontal magnetic flux tubes in a three-dimensional stratified convective velocity field. Our calculations are relevant to understanding how stratified convection in the deep solar convection zone may affect the rise and the structure of buoyant flux tubes that are responsible for the eme...

Two-dimensional hydrodynamic simulations of stellar core collapse are presented which for the first time were performed by solving the Boltzmann equation for the neutrino transport including a state-of-the-art description of neutrino interactions. Stellar rotation is also taken into account. Although convection develops below the neutrinosphere and in the neutrino-heated region behind the super...

This paper deals with the existence and stability of multiple equilibrium profiles in tubular bioreactors. We prove here that a tubular biological reactor can posses one or several equilibrium profiles according to the dispersion and convection terms as long as the kinetic function belongs to a general class of non-monotonic functions. Such systems allow the characterization of the hydrodynamic...