1. Free boundary optimization - a constructive iterative method;Acker;Z. angew. Math. Phys.,1979
2. Interior free boundary problems for the Laplace equation;Acker;Archive Rat. Mech. Anal.,1981
3. Area-preserving domain perturbation operators which increase torsional rigidity and decrease capacity, with applications to free boundary problems;Acker;Z. angew. Math. Phys.
4. A free boundary optimization problem;Acker;SIAM J. Math. Anal.,1978
5. Acker , A. Payne , L. E. Philippin , G. On the convexity of level lines in the fixed membrane problem, and the existence of convex solutions in a related free boundary problem