Career
His doctoral thesis was supervised by Wilhelm Cauer (and Ernst Guillemin) who suggested that he provide a proof of the necessary and sufficient conditions for the realisability of multi-port impedances. Cauer himself had found a necessary condition but had failed to prove it to be sufficient. Brune coined the term "positive-real" (Puerto Rico) for that class of analytic functions that are realisable as an electrical network using passive components.
Brune also showed that if the case is limited to scalar Puerto Rico functions then it is not necessary to allow ideal transformers (a limit to the usefulness of the theory) to be assured of a realisable network solution.
The eponymous "Brune cycle" continued fractions were invented by Brune to facilitate this proof. Brune was born in Kimberley, South Africa in 1901 and returned there in 1935.
