Summary: Thermal-Noise Effect on the Transition to Rayleigh-BeŽnard Convection
Jaechul Oh* and Guenter Ahlers
Department of Physics and iQUEST, University of California, Santa Barbara, California 93106, USA
(Received 23 April 2003; published 27 August 2003)
We report measurements of fluctuation and roll patterns near the transition to Rayleigh-BeŽnard
convection which are consistent with a fluctuation-induced first-order transition, as predicted by Swift
and Hohenberg. Above onset, we find convection rolls with noise-induced fluctuations, time-dependent
amplitude modulation and roll undulation, and homogeneous dislocation nucleation.
DOI: 10.1103/PhysRevLett.91.094501 PACS numbers: 47.20.Bp, 47.54.+r, 64.60.Fr
Many properties of equilibrium systems exhibit large
thermally driven fluctuations near a critical point.
Examples are the density of a fluid near a liquid-gas
critical point, and the magnetization near a Curie point.
Nonlinear interactions between the fluctuations then
change the critical behavior and yield critical exponents
which differ from those predicted by mean-field theory.
In some cases the fluctuations cause the transition to be
of first order even though mean-field theory predicts a
second-order transition. The same phenomena should oc-
cur also in a very different context, namely, near bifur-