For decades, Penn State engineering professor Gary Settles has captured everyday images on film and made them extraordinary. And now the flu season's most common occurrence, the cough, has been published by The New England Journal of Medicine.

Settles specializes in schlieren photography, a technique that visualizes air flow patterns invisible to the naked eye. It produces images that are "interesting and colorful, sometimes even verging on artistic," Settles said.

"It's the type of scientific image that people like," he said, referring to his photo of the cough, adding that schlieren images are popular because they show familiar objects in a scientific context.

In the process, a beam of light is focused on a point, and a razor blade or color filters at that point are used to reveal disturbances around objects in the light beam. This makes it possible to photograph movements in gas and liquid.

The pictures have appeared around the world, including in Newsweek and the CBS science series, Universe. Settles said he gets "rediscovered by the press" every once in a while

"The press likes to think that what they're getting is brand new," he said.

However, the concept of schlieren photography dates back to the times of Robert Hooke and Sir Isaac Newton. It resurfaced in Germany in 1865, where it was dubbed with its current name, "schlieren," which translates to "streaks."

Today, Penn State's gas dynamics laboratory is home to the world's largest test facility for schlieren photography, and Settles, who is director of the laboratory, has written the only modern book on the subject, titled "Schlieren and Shadowgraph Techniques ¾ Visualizing Phenomena in Transparent Media."

This recent project was undertaken after he was approached by virologist Dr. Julian Tang from Singapore. By mapping the airflow of a cough, they hoped to better understand the way certain diseases spread, including influenza, SARS and tuberculosis.

"That understanding will suggest ways to interfere with airflow caused by a cough or a sneeze, and perhaps ways to contain it," Settles said.

2008 Penn State graduate Matthew Madalis -- the subject of the photograph -- worked with schlieren photography during his time studying mechanical engineering. He currently works for the Naval Surface Warfare Center in Maryland, and uses a process on the job similar to what he used while at Penn State.

"They do a lot of very modern work, which is what drew me to it in the first place," Madalis said. "It's very practical, all the projects that go on there."

The gas dynamics lab is currently working on issues that have applications in homeland security, such as detecting traces of explosives on aircraft passengers and studying the gas dynamics of explosions onboard airplanes.

As a result of such research, the lab has awarded over 15 doctorates and many more Master of Science degrees, according to the lab's Web site.

"Seeing the invisible is an important part of learning," Settles said.