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\bibitem{Xu_etal2006} {\textquotedblleft}\textit{Trial solution and critical frequency to the singly quantized vortex in big Bose-Einstein condensates}{\textquotedblright}. Xu Y, Jia DJ, Chen ZY, Modern physics letters B \textbf{20}, 995 (2006).   http://doi.org/10.1142/S0217984906011104

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