Excitation of spirals and chiral symmetry breaking in rayleigh-benard convection.

Spiral-defect populations in low-Prandtl number Rayleigh-Bénard convection with slow rotation about a vertical axis were measured in carbon dioxide at high pressure. The results indicate that spirals act like "thermally excited" defects and that the winding direction of a spiral is analogous to a magnetic spin. Rotation about a vertical axis, the spiral analog of the magnetic field, breaks the zero-rotation chiral symmetry between clockwise and counterclockwise spiral defects. Many properties of spiral-defect statistics are well described by an effective statistical-mechanical model.

Heat transport in turbulent rayleigh-Benard convection

We present measurements of the Nusselt number N as a function of the Rayleigh number R in cylindrical cells with aspect ratios 0. 510(7) they are consistent with N = asigma-1/12R1/4+bsigma-1/7R3/7 as proposed by Grossmann and Lohse for sigma greater, similar2.

Deviations from linear theory for fluctuations below the supercritical primary bifurcation to electroconvection

Over two decades ago it was predicted that nonlinear interactions between thermally driven fluctuations in dissipative nonlinear nonequilibrium systems lead to deviations from mean-field theory. Here we report experimental observations of such deviations as a supercritical primary bifurcation is approached. We measured the mean-square director-angle fluctuations below the bifurcation to electroconvection of two different nematic liquid crystals. For epsilon(mf) identical withV2/V(2)(c,mf)-1 less, similar-0.1 ( V is the applied voltage) we find approximately |epsilon(mf)|(-gamma) with gamma given by linear theory (LT). Closer to the bifurcation there are deviations from LT with a smaller gamma and with V(2)(c)>V(2)(c,mf).

Effect of sidewall conductance on heat-transport measurements for turbulent Rayleigh-Bénard convection.

For measurements of turbulent heat transport in Rayleigh-Bénard convection the correction for the sidewall conductance is usually neglected or based on measurements or estimates for the empty cell. It is argued that the lateral thermal coupling between the fluid and the wall can invalidate these approaches, and that corrections based on calculations of the two-dimensional temperature fields are required in some cases. These corrections can increase gamma obtained from fits of N=N(0)Rgamma (R is the Rayleigh number) to the Nusselt number N(R) by 0.02 or more, yielding values in the range 0.30 to 0.33, which are larger than most theoretical predictions.