Karl Ludwig von Bertalanffy was an Austrian biologist known as one of the founders of general systems theory (GST), the "conceptual part" of which was first introduced by Alexander Bogdanov. This is an interdisciplinary practice that describes systems with interacting components, applicable to biology, cybernetics and other fields. Bertalanffy proposed that the classical laws of thermodynamics applied to closed systems, but not necessarily to "open systems" such as living things. His mathematical model of an organism's growth over time, published in 1934, is still in use today.