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Abstract. The numerical hydrodynamic modelling of beat Cepheid behavior has been a long-standing quest in which purely radiative models have failed consistently. We find that beat pulsations occur quite naturally when turbulent convection is accounted for in our hydrodynamics code. The developments of a relaxation code and of a Floquet stability analysis greatly facilitate the search for and the analysis of beat Cepheid models. The conditions for the occurrence of beat behavior can be understood easily and at a fundamental level with the help of amplitude equations.

The energy-density formalism is applied to finite nuclei. The total energy of the many-nucleon system is expressed as a functional E{p) of the local density p (r), and the ground-state density distribution is found by minimization with respect to p(r). The functional of the potential energy is directly derived from a nuclear-matter calculation with variable neutron excess by Brueckner et al. The density-gradient correction which takes care of the density variation at the nuclear surface contains an exchange-and a correlationenergy part. In a first attempt, proton and neutron densities are assumed proportional; therefore the present calculation is limited to light nuclei. The density distributions are found to be of the so-called modified Gaussian type with a cubic polynomial. Binding energy, radius, and surface thickness are in good agreement with experiment.