kirlik@hms2 (Alex Kirlik) (04/11/89)
The following is taken from Stephen Jay Gould's _Hen's Teeth and
Horse's Toes_, W.W. Norton & Co., New York, 1984 (p. 161):
"After Berg had modified his microscope to track individual bacteria,
he noted that an E. coli moves in two ways. It may "run," swimming
steadily for a time in a straight or slightly curved path. Then it
stops abruptly and jiggles about--a "twiddle" in Berg's terminology.
After twiddling, it runs off again in another direction. Twiddles
last a tenth of a second and occur on an average of once a second.
The timing of twiddles and the directions of new runs seem to be
random unless a chemical attractant exists at high concentration at
one part of the medium. A bacterium will then move up-gradient toward
the attractant by decreasing the probability of twiddling when a
random run carries it in the right direction. When a random run
moves in the wrong direction, twiddling frequency remains at its
normal, higher level. The bacteria therefore drift toward an
attractant by increasing the lengths of runs in favored directions."
Not exactly simulated annealing, but close enough for patent
infringement? :-)
Alex Kirlik
UUCP: kirlik@chmsr.UUCP
{backbones}!gatech!chmsr!kirlik
INTERNET: kirlik@chmsr.gatech.edu