[TML] Personal Armor Noise was Re: Current USAF fleet

[Jerry W Barrington]

On 5/4/08 11:06 PM, "Timothy Little" <tim at little-possums.net> wrote:

> On Sun, May 04, 2008 at 10:08:31PM -0400, Jerry W Barrington wrote:
>> But *anybody* can (in theory) make a highly accurate duplicate of
>> *the* standard kg reference object.
> 
> There are such copies, all with slightly different masses and
> different rates of change of their masses over time.  For very highly
> precise measurements, this is a truly horrible situation.

And we have no way to check the stability of the silicon sphere either.  And
whereas platinum & iridium have to be coaxed into oxidizing, the silicon
*will* acquire a layer of silicon mono- & dioxides.

<http://en.wikipedia.org/wiki/Kilogram#Avogadro_project>

>> A major problem with using a sphere is that atoms don't line up in
>> neat little spherical arrangements.  They do lattices.  Any lattice
>> cut to a sphere has "jaggies" like a pixelated curve.
> 
> Even a perfectly aligned crystal surface has "jaggies" in that sense.
> Even more so since silicon atoms aren't cubical pixels in a cubic
> arrangement.  No surface is truly flat, and they're not expecting to
> get subatomic precision anyway.
> 
> There are advantages to using spheres over cubes or other shapes.

Actually, on that page it mentions an effort to define the kg in reference
to a cube of 84,446,886^3 carbon-12 atoms...  :)