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\bibitem{Ryabchun_etal2009} Ryabchun, S. A., Tretyakov, I. V., Finkel, M. I., Maslennikov, S. N., Kaurova, N. S., Seleznev, V. A., et al. (2009). NbN phonon-cooled hot-electron bolometer mixer with additional diffusion cooling. In \textit{Proc. 20$^{th}$ Int. Symp. Space Terahertz Technol.} (pp. 151--154). Charlottesville, USA.

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