Quiet-List 1997

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Quiet Jackhammer-again



Oops! I inadvertently sent my work in progress when I checked for new mail.
I had just re-installed my e-mail software and had not yet changed the
default settings. Sorry about the mailbox clutter. Here's the complete
message:

The following article is from the November '97 issue of Discover magazine
(page 38). It has always been my opinion that technology will eventually
solve some noise problems. 

Annette Feige
Citizens' Coalition Against Noise

---------------------------------
Technology: A Quiet Jackhammer

Although Ronald Reagan's dream of an orbiting fleet of space weapons to
shield us from nuclear attack never materialized, several projects of the
former Star Wars program have inspired somewhat more mundane research. One
recent and rather humble spin-off had its origins as a sort of orbiting
pellet gun that would shred enemy missiles with a hail of high-speed
projectiles. While no weapons have come of this, some engineers at
Brookhaven National Laboratory on Long Island have managed to scale down
the technology to a more peaceful level: they've invented a quiet jackhammer.

The jackhammer consists of a ten-foot-long cylinder (the next prototype
should be half that length) that houses a freely sliding piston inside a
narrow tube. Pressurized air flows into the tube just behind the piston. In
front of the piston is helium gas. As the pressurized air drives the piston
into the helium, says Robert Hall, head of the engineering technolgy
division at Brookhaven, the piston sets up a pressure wave in the helium.
The wave blows down a muzzle and hits a bean-size steel projectile, which
shoots out the end of the jackhammer at 3,000 feet per second--almost three
times the speed of sound.

A single pellet from the gun can break up more than a square foot of
concrete. Unlike a regular jackhammer, the Brookhaven version doesn't raise
any dust--the pellets, which lose all their energy on impact, don't
pulverize concrete into a powder but break it up into pebble-size
fragments. And by attaching a set of baffles to the end of the
barrel--similar to a silencer on a rifle--Hall says his jackhammer is less
noisy than an idling car engine.

Hall and his team are now working on a more advanced model. With expected
projectile speeds of up to 10,000 feet per second, it will be able to cut
the thick steel rods found in reinforced highway concrete. Hall says the
jackhammer prototype will begin ripping up streets in New York City
sometime next year.
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