It is mentioned in page 166, of the book Experimental techniques in low-temperature physics by Guy Kendall White, Philip J. Meeson
"Most properties of materials are categorised in terms of the phonon system, the electron system and the spin system (i.e. the nuclear or electronic magnetic moments)."
Three subsystems that make up for most of the properties of materials, the physical and chemical properties, matter organised into the macroscopic system of the physical world, determine how the physical world behaves.
"These different subsystems, although intimately mixed together in any one material, can be separated in the imagination and analysed as independent systems."
Determine physical behaviour as the embedded sub-systems are intimately mixed, which brings into mind attractors and synchronization, attractors achieved by the ever so slight tweaking of relevant parameters, the electron-phonon interactions synchronized, by even the transient fluctuation enhancement referred to as peculiar to macroscopic systems, triggered by the exposure to additional parametres brought in, by the other embedded sub-systems.
These three subsystems separated and analysed independently? Their connections severed, each one imagined on itself? An approach which can be followed on all subsystems, lower-dimensional systems embedded in higher dimensional systems, the macroscopic systems? Understanding the relationships between embedded and embedding systems, all systems in all realms, portable via the self-similarity principle of chaos.
And all the while, each sub-system being dynamic, ever so 'touchy' to any changes introduced by either sub-system, via the electron-phonon interaction.
"Consider for example the separation of the phonon system from the electron system in a metal. This proceeds from the knowledge that the phonon system is 'heavy' arising from the motion of ions in the lattice whilst electrons are light. The mass difference (and differing statistics) influences the available energy levels in each system and ultimately limits the flow of momentum and energy between the two systems."
The phonon system 'heavy', the electron system 'light' a matter of size. The phonon system arises from the motion of ions, the electron system from electrons. This mass difference limits the flow of momentum and energy between the two systems, practically isolated from one another, each system with its own agent, phonon electron, interactions between their agents determine their behaviour.
Accordingly, it can be assumed that any introduction of extra agents, like nanoparticles upsets this balance, the flow of momentum and energy, between the two systems, as the mass of the nanoparticles being similar in size, could introduce novel interactions, leading to the emergence of properties, alien to the subsystems. The observation of novel chemical and physical properties in nanoparticles, when introduced into the nanoscales, indicative of this process.
"This 'adiabatic' or Born-Oppenheimer approximation regards the two subsystems as separate but interacting via an electron-phonon interaction."
Embedded sub-systems separate but interacting via an electron-phonon interaction? Interacting as sub-systems? Preserving their integrity, their independence of a sort. An adiabatic boundary, a barrier that prevents the direct flow of energy and momentum from an embedded system to another or even the embedding macroscopic system apart from the electron-phonon interaction, each sub-system the 'whole' by itself and as a whole interacts.
Embedded sub-systems adiabatic. Embedding systems, by virtue of being embedded themselves, sub-systems to higher dimensional systems, adiabatic too. All systems adiabatic. Biological, emotional, psychological, social systems adiabatic? Understanding systems by using the adiabatic system property?