Finite-temperature correlations in the trapped Bose-Einstein gasN. M. Bogoliubov, R. K. Bullough, V. S. Kapitonov, C. Malyshev and J. TimonenEurophys. Lett., 55 6 (2001) 755-761DOI: https://doi.org/10.1209/epl/i2001-00345-2