Journal of Mathematical Sciences: Advances and Applications[1] J. Berndt, F. Tricerri and L. Vanhecke, Generalized Heisenberg
Groups and Damek-Ricci Harmonic Spaces, Springer-Verlag, Berlin,
Heidelberg, 1995.
[2] R. Caddeo, S. Montaldo and C. Oniciuc, Biharmonic submanifolds of
spheres, Israel J. Math. 130 (2002), 109-123.
[3] R. Caddeo, C. Oniciuc and P. Piu, Explicit formulas for
non-geodesic biharmonic curves of the Heisenberg Group,
arXiv:math.DG/0311221v1 13 Nov 2003.
[4] B. Y. Chen and S. Ishiara, Biharmonic pseudo-Riemannian
submanifolds in pseudo-euclidean spaces, Kyushu J. Math. 52 (1998),
167-185.
[5] J. Eells and J. H. Sampson, Harmonic mappings of Riemannian
manifolds, Amer. J. Math. 86 (1964), 109-160.
[6] G. Y. Jiang, Two-harmonic maps and their first and second
variational formulas, Chinese Ann. Math. Ser. A 7(4) (1986), 389-402.
