From: Hal Finney (hal@rain.org)
Date: Wed Dec 04 1996 - 12:58:36 MST
From: James Rogers <jamesr@best.com>
> There is a type of "active" composite that has the properties you are
> describing. It is a laminate composite consisting of piezo-electric
> ceramics and shape-memory alloys from the nickel-titanium family.
>
> When vibrations hit the ceramic outer laminate, the ceramic acts as a
> transducer, converting the vibration into an electrical signal. The signal
> is inverted (It may be inverted via an anisotropic material property. I am
> not sure.) and fed into the shape-memory alloy. The alloy flexes and
> reproduces the inverted signal, similar to a speaker, through the ceramic.
This is an interesting discussion, which I unfortunately don't know enough
solid state physics to contribute to.
However my instincts are that some of these ideas are based on a macroscopic
model which won't work at the level we are talking about. These atomic
vibrations are themselves heat. The notion of going in and producing
counter vibrations which will cancel these smacks of violating the Third
Law.
Of course refrigerators do exist, and there is nothing wrong with heat
flowing from a cold to a hot object as long as entropy somehow balances
out. But when you are talking about heat flowing from a cold to a hot
molecule, it is hard to see how to do it.
I know that one way refrigerators work is by evaporation, which in effect
means that we filter molecules, allowing the high speed ones to go away
and keeping just the low speed ones. We don't actually slow any down in
this process but we do end up with low energy molecules. However it is
not clear how to apply this to the atom-in-a-box example.
Hal
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