X-Message-Number: 4741
From: Ralph Merkle <>
Subject: SCI.CRYONICS Re: Cold Start
Date: Tue, 8 Aug 1995 11:58:51 PDT

I've received several e-mail messages pointing out various
deficiencies in the "Cold Start" scenario (originally published
in Cryonics in 1990).

These may be summarized as:

1)  HF is highly reactive.  One issue, the appropriate design of
    a containing vessel, is merely technical.  One need merely
    look up in an appropriate reference manual the recommended
    material(s) for a container which holds HF.  One reference suggests
    the use of steel cylinders.  I would expect that
    the fluorinated diamond (111) surface would also be suitably
    unreactive (similar to Teflon, a polymer of C2F4 monomeric units).

    The second issue, of much greater concern, is the aesthetics (or
    lack thereof...) of HF.  These were excellently expressed by
    Charles Platt.  The best solution to this problem is to adopt a
    reaction which is generally accepted to be benign, such as the
    burning of hydrogen and oxygen to produce water.

    I did not propose this reaction as it requires either high temperature
    or a suitable catalyst.  I did not have a ready reference available for
    a catalyst that would work reliably at the required temperature, nor
    had I verified that a pellet on the order of 0.1 microns in diameter
    surrounded by tissue at ~140 Kelvins could be heated to the ignition
    temperature of the 2H2 + O2 reaction and maintained at that temperature
    despite the flow of heat out of the pellet.  Perhaps someone would be
    kind enough to propose an ignition mechanism and perform the necessary
    thermal calculations.  H2 + F2 is a reaction that proceeds spontaneously
    at any temperature down to (if memory serves) 20 Kelvins.

2)  The temperature immediately surrounding the heating pellets might
    cook the surrounding tissue.  This can be addressed by controlling
    the rate at which the reaction occurs. The simplest method would be
    to limit the rate at which the reactants are mixed together.  This can
    also be addressed by noting that the target temperature could be (say)
    40 degrees fahrenheit, so excursions up to ~100 degrees fahrenheit
    during the heating process would be harmless.  Finally, it would be
    possible to surround the heating pellet with a sphere that was free
    of tissue that might be damaged (e.g., surround the pellet with a
    sphere of ice containing salts).

3)  Tissue stability (cracking, etc) during the heating process might be
    of concern.  This can be addressed by insuring that the thermal
    coefficient of expansion of the material is small (by, for example,
    varying the structure of the water between amorphous and crystalline
    on a sub-micron scale, or otherwise controlling the details of the
    molecular structure);  increasing the strength of the material (by,
    for example, embedding long protein polymers to increase strength);
    and by insuring that heating is so rapid that there is insufficient
    time for any serious damage to occur.  This latter forestalls
    concerns of recrystallization damage which might occur during heating.

4)  Leaving heating pellets in place is unaesthetic.  Various methods
    of removing the pellets are feasible.  At the cost of increasing the
    heating time, pellets could be confined to the circulatory system
    (the distance from any cell to a capillary is ~40 microns).  They
    would then be washed away when circulation resumed.  If pellets
    are designed to be suitably benign, they could dissolve
    and be washed away (2H2 + O2 is particularly attractive here).
    For hard pellets,  exit tubes could be left in place
    which would permit the pellets to be ejected.  The tubes would
    themselves be degradable, and would dissolve harmlessly.

As the basic physics of the situation are well understood, others might
wish to make proposals.  Finding a technically simple, aesthetically
appealing proposal for rapid heating would seem to be useful, as this
question has arisen before and will no doubt arise again.  The best
proposal could be put on the web, and in the future when this question
arises we could simply point to this web page.


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