Hydrodynamic stability theory has recently seen a great deal of development. After being dominated by modal (eigenvalue) analysis for many decades, a different perspective has emerged that allows the quantitative description of short-term disturbance behavior. A general formulation based on the linear initial-value problem, thus circumventing the normal-mode approach, yields an efficient framew...

In the present work we suggest a general covariant theory which can be used to study the stability of any physical system treated geometrically. Stability conditions are connected to the magnitude of the deviation vector. This theory is a modification of an earlier joint work, by the same authors, concerning stability. A comparison between the present work and the earlier one is given. The sugg...

We introduce a new device in the study of abstract elementary classes (AECs): Galois Morleyization, which consists in expanding the models of the class with a relation for every Galois (orbital) type of length less than a fixed cardinal κ. We show: Theorem 0.1 (The semantic-syntactic correspondence). An AEC K is fully (< κ)-tame and type short if and only if Galois types are syntactic in the Ga...