Complex sentence: Prof. in't Veld developed for this purpose his' Steady State Model' (1975): a stable system, the behavior is repeatable in time and the goal of the system is constant based on a dynamic balance under varying circumstances.
Split into simpler sentences: Prof. in't Veld developed for this purpose his' Steady State Model' (1975). The model is usable if the system is a stable system, the behaviour is repeatable in time and the goal of the system is constant based on a dynamic balance under varying circumstances.