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\bibitem{Hajenius_etal2003} Hajenius, M., Baselmans, J. J. A., Gao, J. R., Klapwijk, T. M., de Korte, P. A. J., Voronov, B., et al. (2003). Improved NbN phonon cooled hot electron bolometer mixers. In \textit{Proc. 14$^{th}$ Int. Symp. Space Terahertz Technol.} (pp. 413--423). Tucson, USA.

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