Individual #thermionics__thermionic  the branch of electronics dealing with thermionic phenomena (especially thermionic vacuum tubes)
  >part of:  #electronics__electronic  the branch of physics that deals with the emission and effects of electrons and with the use of electronic devices
     >part of:  #physics__physic__physical_science__natural_philosophy__naturalphilosophy  the science of matter and energy and their interactions

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