DR GARY SETTLES / SCIENCE PHOTO LIBRARY DR GARY SETTLES / SCIENCE PHOTO LIBRARY
Human coughing, schlieren image. Schlieren photography is an imaging technique that is used to show changes in the density of fluids and gases such as air, caused here by the turbulence produced by the coughing action. The jet of air expelled by coughing projects infectious pathogens deep into the surrounding air. The man's thermal boundary layer is also seen. The colour fringes in the background are due to an optical phenomenon known as Newton's rings. Photographed at Pennsylvania State University, USA.
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