@article{10_1007_s10587_013_0030_4,
     author = {Du, Yongguang and Liu, Huaning},
     title = {On the mean value of the mixed exponential sums with {Dirichlet} characters and general {Gauss} sum},
     journal = {Czechoslovak Mathematical Journal},
     pages = {461--473},
     publisher = {mathdoc},
     volume = {63},
     number = {2},
     year = {2013},
     doi = {10.1007/s10587-013-0030-4},
     mrnumber = {3073971},
     zbl = {06236424},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.1007/s10587-013-0030-4/}
}