1. Abramowitz, M., Stegun, I.A.: Handbook of Mathematical Functions with Formulas, Graphs, and Mathematical Tables. Dover, New York (1972)
2. Akhtar, N.: A multiscale harmonic spline interpolation method for the inverse spheroidal gravimetric problem. Ph.D. thesis, University of Siegen, Department of Mathematics, Geomathematics Group. Shaker, Aachen (2009)
3. Akhtar, N., Michel, V.: Reproducing Kernel based splines for the regularization of the inverse ellipsoidal gravimetric problem. Appl. Anal. (2011). Accepted for publication, pre-published online via doi:10.1080/00036811.2011.590479
4. Akram, M.: Constructive approximation on the 3-dimensional ball with focus on locally supported kernels and the Helmholtz decomposition. Ph.D. thesis, University of Kaiserslautern, Department of Mathematics, Geomathematics Group. Shaker, Aachen (2009)
5. Akram, M., Amina, I., Michel, V.: A study of differential operators for particular complete orthonormal systems on a 3D ball. Int. J. Pure Appl. Math. 73, 489–506 (2011)