The image, published online Oct. 9 by The New England Journal of Medicine, was created by schlieren photography, which “takes an invisible phenomenon and turns it into a visible picture,” said the engineering professor, Gary Settles, who is the director of the university’s gas dynamics laboratory.
Schlieren is German for “streaks”; in this case it refers to regions of different densities in a gas or a liquid, which can be photographed as shadows using a special technique.
“In my lab we use this technique a lot,” Dr. Settles said. “Often it’s used for other things, like in supersonic wind tunnels, to show shock waves around high-speed aircraft.”
The process involves a small, bright light source, precisely placed lenses, a curved mirror, a razor blade that blocks part of the light beam and other tools that make it possible to see and photograph disturbances in the air. In the world of gas dynamics, a cough is merely “a turbulent jet of air with density changes.” Though coughs spread tuberculosis, SARS, influenza and other diseases, surprisingly little is known about them. “We don’t have a good understanding of the air flow,” Dr. Settles said.
