Recently, I have gotten involved with geometric methods for the boundary control of hyperbolic PDE's.

See the web pages for the 1999 Colorado conference and the IMA Summer 2001 program on related topics.

[40]. Chord Uniqueness and Controllability: the View from the Boundary, I (with Walter Littman), Contemporary Mathematics 268, 145-176 (2000). Postscript version or PDF version
[43]. Boundary Control of PDEs via Curvature Flows: the View from the Boundary II (with Santiago Betelu and Walter Littman), Applied Math. & Optimization 46, 167-178 (2002). Postscript version or the PDF version.
[46]. The Case for Differential Geometry in the Control of Single and Coupled PDEs: The Structural Acoustic Chamber (with Irena Lasiecka, Walter Littman and Roberto Triggiani). IMA Volumes in Mathematics and its Applications 137, 73-182 (2003) Postscript version or the PDF version.
[52]. The Use of Geometric Tools in the Boundary Control of Partial Differential Equations (with Walter Littman). Proceedings 3rd ISAAC Conference (Berlin, 2001). Postscript version or the PDF version. 88 pages. The figure is missing from these versions.
[58]. Boundary Control of Wave Equations in high dimensions via Harmonic Mean-Curvature Flow (with Walter Littman), in preparation.