ИСТИНА

We show that many important models of the natural sciences in their mathematical description can be reduced to a non-strictly hyperbolic systems of the same form. This allows to apply to them the same methods, so some important results concerning a particular model can be obtained as corollaries of general theorems. However, in each case, the models have specific features. The talk contain a review both of the methods that can be potentially applied to similar cases and of the known results just obtained for specific model. In addition, we obtain new models and results in this field.