Should continuous or pulsed conditions be used

Ultrasonic pulse methods are also useful for the activation of the chemical reaction itself (pp. 95, 103, and 151), as, for example, in the PTC reaction of 2,4-dichloronitrobenzene with potassium fluoride in DMSO. Here sonication with pulses of 0.25 s applied after each second is the most effective technique compared with continuous conditions for this system.59 The importance of the pulse length with respect to the off period has been especially pointed out in the chemical activation of homogeneous systems.  

56 Kardashev, G.A. Salosin, A.V. Manukyan, S.G. Primen. Fiz. Fiz.-Khim. Metodov Tekhnol. Protsessakh 1990,166-169 Chem. Abstr. 1991,114, 154171. 

---