英文阅读：咳嗽也能拍到胶卷上？
如果你看过《友好的巨人》，你一定记得巨人会在大家都睡着的时候出现在街道上，手上拿着长长的吹管，他会为小孩子吹入美梦，为做恶梦的小孩把恶梦吹出来，梦都装在玻璃瓶中，放在巨人背着的包包里。既然无形的梦可以装进包里，咳嗽为什么不能拍到胶卷上呢?At Pennsylvania State University, a professor of engineering has captured
something less whimsical but no less ephemeral — a cough — on film.
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.
“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.
A healthy student provided the cough. The expelled air, traveling at 18
miles per hour, mixed with cooler surrounding air and produced “temperature
differences that bend light rays by different amounts,” Dr. Settles said.
He went on: “The next thing is, you get a couple of people in front of the
mirror talking, or one coughs on another, and you see how the air flow moves,
how people infect one another. Or you look at how coughing can spread airborne
infection in a hospital. This is really a suggestion for how we might study all
that. The techniques used in wind tunnels can be used to study human
diseases.”
The final photograph, in a full-scale mock-up of an aircraft cabin,
captures in microseconds the flash of an explosion under a mannequin in an
airplane seat and the propagation of shock waves into the cabin. The blast was a
re-creation of a terrorist’s attempt in 1994 to bring down a Philippine Airlines
flight with a nitroglycerin bomb. The plane did not crash, but the explosion did
kill the passenger seated over the bomb. The simulation used a less intense
explosion than the actual bombing.
“The simulation helps to understand how the energy of an onboard blast
reverberates around the cabin,” Dr. Settles said, “and it is also useful to
check the results of computer blast simulations.”
This shadowgram captures an instant during the firing of a Smith&Wesson
44 Magnum revolver. Blast waves and propellant gases are observed to originate
first from the cylinder and later from the muzzle of the gun. Propellant gas
envelopes the hand of the shooter, leaving gunpowder residue. The bullet itself
travels at transonic speed, i.e. close to the speed of sound. This is a
colorized version of a monochrome original image.
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