This article was orignally published online and in print with an incorrect journal title in Ref. 9: “J. Bacteriol.” should have been “J. Phys. A”. AIP apologizes for this error. All online versions of the article have been corrected. Reference 9 appears correctly below:

9.
R. J.
McDermott
and
A. I.
Solomon
,
J. Phys. A
27
,
L15
(
1994
).