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Re: how do you make WHITE?



At 22:51 3/6/99 -0500, John Denker wrote:
At 05:21 PM 3/6/99 -0500, Donald wrote:

Why can the transmission of light (intensity) be greater through
oil-soaked paper than through the same paper dry?
... If the
locations are exact, but the scattering parameters (e.g. size) is variable
from site to site, then we get Mott localization. If the sizes are uniform
but the locations are randomized, we get Anderson localization.
Note that you cannot make paper (or paint) that is really thin and really
white.


Oil permeates the pores of the paper and *index matches* to the cellulose.
We no longer have a random array of index-changes. We a thin sheet of
relatively uniform index, and the light just waltzes through.

You don't get perfect transparency for various reasons: (1) Typical oil
isn't a perfect match for cellulose. (2) Typical paper contains not just
cellulose but other junk. If you match to one, you can't match to the
other. (3) What's worse is that the cellulose fibers are *hollow* and
you'll never get oil into the cores. Therefore there will always be some
scattering off the cores. If we could lay hands on some paper made of
randomly-arranged solid fibers (such as rayon, which is solid cellulose), I
predict the oil-spot effect would be really spectacular.

One final remark: ... A large-gap semiconductor should be called
merely a semi-non-conductor, since it cannot be used as a practical
insulator. It will not immobilize any charge injected onto or into it. To
do that, you need localization of the electron wavefunction.

Cheers --- jsd


This was a truly splendid offering. It offered insight.
It offered experimentally verifiable prediction.
It was great!

That's what makes it such fun to nit-pick. :-)

The problem lies in the last sentence. It's a physicist's sentence.
John believes he is talking about a physical mechanism which can
provide a force field environment which holds charged particles in
place.
But what he actually SAYS, is a methematical construct.
"To immobilize a charge, you need localization of the electron
wavefunction."

John is certainly not alone in this way of writing.

Brian
brian whatcott <inet@intellisys.net>
Altus OK