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oil
SESSION IT DISCUSSION
and water
emulsion that was essentially nonsedimenting. The
problem becomes more complicated in sedimenting systems because
another term is introduced into the Smoluchowski equation. We are
examiningthis now. The time it takes to reach an asymptotic self-
preserving form, as we call it, depends on the initial distribution.If
there is an initial distribution that is near the self-preserving form,
then within relatively short times this asymptotic limit is reached. If
one begins with a system that differs greatly from the self-preserving
form, it will take longer.
I think some answers will come out of calculations such as those
recently done by Dr. George Hidy of the National Center for Atmo-
spheric Research, who has put in various types of initial distributions
and followed coagulation in a computer experiment. An appropriate
characteristic time for an initially monodisperse system would be
3u/KTNyo, where is the viscosity of the fluid, k is the Boltzmann con-
stant, T is the temperature in °K, and N, is the total numberof particles in the system. Hidy found, as I recall, that about three of these
characteristic times were necessary for an initially monodisperse
system to reach the self-preserving form. He also tried very unusual
initial distributions and found that they took a longer characteristic
time. So these are reasonable questions to ask and they are the same
ones we are asking now, having worked out the initial formalism and
checked the method experimentally with hydrosols.
STEVENSON: Would the formation of compounds such as sulfates
from the oxidation of sulfur dioxide to sulfur trioxide add another term
to the Smoluchowski equation, and have you also investigated this ?
FRIEDLANDER: We have not investigated this. I think this effect
probably could be accounted for in the Smoluchowski equation by adding
a term for condensation. Again, one would have to look at the equations
and see whether or not the so-called “self-preserving forms”still
satisfy the modified equations.
FREUDENTHAL: I would like to ask Dr. Feely if he noticed seasonal differences in the horizontal stratospheric data?
FEELY: Yes, very much so. The movement of nuclear debris
through the tropical stratosphere especially seems to be seasonally
dependent. In both 1959 and 1963, we observed movementof debris
from the northern tropical stratosphere into the southern polar stratosphere during the winter and the spring seasons of the southern hemi-
sphere. I do not know what the cause is, but there does seem to be
a seasonal dependence.
BENSON: I
have a question for Dr. Feely. Generally, a half-
residence time of about five years for “Sr in the stratosphere has been