How a liquid drop forms is a question important for ink jet printers, paint sprayers, and other machines that emit fluids from nozzles. "Ink jet printing uses tiny drops of ink that are shot out of a nozzle using piezo action," says Osman Basaran, a professor of chemical engineering at Purdue University. He and others at Purdue did the math behind drop formation. "Another application where drop formation is critical is in DNA arraying, where ink jets spray solutions containing DNA fragments onto biochip surfaces," says Basaran. The mathematical model he helped develop computes the quickly changing pressures and velocities of fluid in evolving drops. Engineers found that the formation of droplets changes when the fluid flow is increased and decreased. They say that the findings are important for controlling the quality of sprayed materials, such as the adhesive sprayed on tapes. They also point out that fluctuations in the performance of pumps and other equipment used for spraying sometimes increases or decreases the flow rate of a system without warning, so knowing how drops form is important to improving those processes that are vulnerable. Additional applications for Basaran's work include extraction processes used in chemical, petrochemical, pharmaceutical, and metallurgic industries. More information about Basaran's work is available at http:// ChE.www.ecn.purdue.edu/ChE/Fac_.Staff/obasaran/.