Disordering effects of colour in a system of coupled Brownian motors: phase diagram and anomalous-to-normal hysteresis transition

A system of periodically coupled nonlinear phase oscillators submitted to both additive and multiplicative white noises has been recently shown to exhibit ratchetlike transport, negative zero-bias conductance, and anomalous hysteresis. These features stem from the "asymmetry" of the stationary probability distribution function, arising through a noise-induced nonequilibrium phase transition which is "reentrant" as a function of the multiplicative noise intensity. Using an explicit mean-field approximation we analyze the effect of the multiplicative noises being coloured, finding a contraction of the ordered phase (and a reentrance as a function of the coupling) on one hand, and a shift of the transition from anomalous to normal hysteresis inside this phase on the other.Comment: Invited Talk LAWNP01, Proceedings to be published in Physica D, RevTex, 9 pgs, 5 figure

Nuclear Reaction Mechanism Study Over a Wide Target Mass Range for 6-Li and 12-C Ions

This work was supported by National Science Foundation Grants PHY 76-84033A01, PHY 78-22774, and Indiana Universit

The Particle-Vibration Coupling Form Factor

peer reviewe

Conservative bounds on Rayleigh-Bénard convection with mixed thermal boundary conditions

Using the background field variational method developed by Doering and Constantin, we obtain upper bounds on heat transport in Rayleigh-Bénard convection assuming mixed (Robin) thermal conditions of arbitrary Biot number η at the fluid boundaries, ranging from the fixed temperature (perfectly conducting, η = 0) to the fixed flux (perfectly insulating, η = ∞) extremes. Solving the associated Euler-Lagrange equations, we numerically find optimal bounds on the averaged convective heat transport, measured by the Nusselt number Nu, over a restricted one-parameter class of piecewise linear background temperature profiles, and compare these to conservative analytical bounds derived using elementary functional estimates. We find that analytical estimates fully capture the scaling behaviour of the semi-optimal numerical bounds, including a clear transition from fixed temperature to fixed flux behaviour observed for any small nonzero η as the usual Rayleigh number Ra increases, suggesting that in the strong driving limit, all imperfectly conducting boundaries effectively act as insulators. The overall bounds, optimized over piecewise linear backgrounds, are Nu ≤ 0.045 Ra1/2 in the fixed temperature case η = 0, and Nu ≤ 0.078 Ra1/2 in the large-Ra limit in all other cases, 0 < η ≤ ∞

Optimum fields and bounds on heat transport for nonlinear convection in rapidly rotating fluid layer

By means of the Howard-Busse method of the optimum theory of turbulence we investigate numerically the effect of strong rotation on the upper bound on the convective heat transport in a horizontal fluid layer of infinite Prandtl number Pr. We discuss the case of fields with one wave number for regions of Rayleigh and Taylor numbers R and Ta where no analytical asymptotic bounds on the Nusselt number Nu can be derived by the Howard-Busse method. Nevertheless we observe that when R > 108 and Ta is large enough the wave number of the optimum fields comes close to the analytical asymptotic result α1 = (R/5)1/4. We detect formation of a nonlinear structure similar to the nonlinear vortex discussed by Bassom and Chang [Geophys. Astrophys. Fluid Dyn. 76, 223 (1994)]. In addition we obtain evidence for a reshaping of the horizontal structure of the optimum fields for large values of Rayleigh and Taylor numbers