A simple model for the interplay of predators, rodents and food.

This paper presents a simple mathematical model for multiannual population cycles, in particular the periods, for the triple of small rodents and their predators and food. The parameters used are average birth rates of rodents and predators. The period lengths fit observations of lemmings and voles rather well and the model explains why the observed periods cluster around 4 years and around 10 years.

The mitral valve mechanism with normal and prolapsed leaflets in the light of a dynamic model.

A dynamic model was presented to explain some of the clinical and morphologic findings in primary mitral valve prolapse. In normal cases, the leaflets, chorda tendinae, the annular ring, and the papillary muscles represent a functional entity balanced by the pressure force acting upon the leaflets. When the leaflets are larger, as in primary mitral valve prolapse, a negative interference with this balance is achieved, causing an increased traction on the papillary muscles and a concomitant dilatation of the annular ring.