A research electrohydraulic generator (Prieto, Loske, &
Yarger, 1991) with an ellipsoidal stainless steel reflector
(major axis=27.8 cm, minor axis=15.6 cm, depth=12.4 cm)
was used (Fig. 1). Each shock wave was generated due to an
underwater high voltage electric discharge at the focus (F1)
closest to the reflector. Shock waves reflected off the
ellipsoidal reflector were focused on the test vial placed at
the second focus (F2). The capacitance was set to 80 nF and
the spark gap between the electrodes at F1 (not shown)
adjusted to 1 mm. Truncated cone-shaped electrodes (Loske
& Prieto, 1993) were allowed to burn-in for 50 discharges at
18F0.1 kV DC before treatments. Samples were positioned
at F2 using a computer-controlled XYZ positioner. The error
in positioning was estimated to be F1 mm.