[Beowulf] Stroustrup regarding multicore

Lux, James P james.p.lux at jpl.nasa.gov
Wed Sep 3 09:44:44 EDT 2008




On 9/3/08 2:04 AM, "Greg Lindahl" <lindahl at pbm.com> wrote:

> On Thu, Aug 28, 2008 at 11:54:05AM -0400, Peter St. John wrote:
>
>> I think a physicist programming is like an astronomer grinding lenses (maybe
>> nobody does that anymore). Some astronomers (in the old days) ground their
>> own lenses and ended up contributing to optics; others never looked through
>> telescopes, they do math on the measurements taken by others.
>
> This is the 2nd funniest posting in this thread. Did you notice that
> ground-based telescopes recently started being much, much bigger?
> These new lenses were invented and made in Arizona by an astronomer,
> who figured out how to spin molten glass into roughly the right shape,
> instead of taking a huge, flat, thick piece of glass and grinding it
> into the shape of a mirror.
>
> http://www.npr.org/templates/story/story.php?storyId=4773461
>
>
>
>
> ----
Ahem.. Reflectors, not lenses

And, actually, the fact that a spinning body of liquid assumes a parabolic
shape has been known for centuries (Kepler?), and, in fact, as early as
1850, an
astronomer (Ernesto Capocci) proposed and built a telescope using liquid
metal (e.g. Mercury) for a reflector.  He probably wasn¹t unique, as there
are mentions of a Mr. Buchan in notes by Brewster (as in Brewster angle)
about the same time.  There¹s a fascinating thesis by Brad Gibson from Univ
of Vancouver that gives a dozen or so pages of all the problems faced with
liquid metal telescopes (ripples, etc.)
>
 What Dr Angel and the folks in Arizona have done is build an enormous
spinning oven and worked out the process controls (more of an engineering
task than a science, one, I might add.. Being an Engineer, I think these
distinctions are important, not that new science isn't being done here).
They also still have to do a conventional polishing step, but, at least the
general figure of the mirror¹s surface is already close to what it needs to
be.  (Interestingly, there¹s apparently an article about this in Science
News back in Feb 1985, which is when the latest work in LMTs got going at
Laval)

Jim Lux


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