X-Message-Number: 4296
Date: 26 Apr 95 12:05:52 EDT
From: yvan Bozzonetti <>
Subject: SCI.CRYONICS: Angel's cooling part two

I don't live on the net, so I apologize for the long delay to answer. Some 
time ago Mike Darwin asked here some references about my message on 
astronomical mirror cooling. The information comes from a book in a public 
library, so I was unable to respond in a short time (I go there every three 
weeks).

The book is: Modern Technology and its Influence on Astronomy, edited by: 
J. V. WALL and A BOKSENBERG, Cambridge University Press, (1990). 
J.R.P.ANGEL's contribution is in part iv, chapter 13 p.143-156. See mostly: 
Mechanical thermal desing of glass mirror blanks, p. 147 - 149.

J.R.P. Angel is in the Department of Astronomy, University of Arizona, 
Tucson AZ 85721. I don't know if he is interested in cryonics ( I doubt 
this is the case).

Mike Darwin seems to think there is more common ground between glass mirror 
and glass/ice bodies in LN2. Angel gives a simple rule of the tumb to 
estimate the cooling time producing no harmful strains : It is 50 times the 
natural cooling time of an object. Assume for example you take a body at 
room temperature and put it in LN2, if it is fully cooled in ten hours, 
then the no strain cool down must be 10 x 50 = 500 hours or near 20 days. 

No cracking is not sufficient, cracks tell us internal strains are larger 
than the body mechanical stifness. As pointed out by M. Darwin, any 
handling add to the strain and can produce cracking in a stressed body. No 
stress cooling would be a first step in getting a better conservation.

		Yvan Bozzonetti.


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