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\bibitem{Ekstrom_etal1993} Ekstrom, H., Karasik, B., Weikle, R., Yngvesson, K. S., Gol{\textquoteright}tsman, G., Kollberg, E., et al. (1993). Mixers using superconducting Nb films in the resistive state. In \textit{23rd European Microwave Conf.} (pp. 787--789).

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