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\bibitem{Das_etal2008} {\textquotedblleft}\textit{Direct observation of nanometer-scale pinning sites in (Nd$_{0.33}$Eu$_{0.20}$Gd$_{0.47}$)Ba$_{2}$Cu$_{3}$O$_{7-\delta}$ single crystals}{\textquotedblright}. Das P, Koblischka MR, Turner S, Van Tendeloo G, Wolf T, Jirsa M, Hartmann U, Europhysics letters \textbf{83}, 37005 (2008).   http://doi.org/10.1209/0295-5075/83/37005

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