Abraham C. Brandenburg to James H. Meredith (2 October 1962)

https://egrove.olemiss.edu/mercorr_pro/1542/thumbnail.jp

A novel type of intermittency in a nonlinear dynamo in a compressible flow

The transition to intermittent mean--field dynamos is studied using numerical simulations of isotropic magnetohydrodynamic turbulence driven by a helical flow. The low-Prandtl number regime is investigated by keeping the kinematic viscosity fixed while the magnetic diffusivity is varied. Just below the critical parameter value for the onset of dynamo action, a transient mean--field with low magnetic energy is observed. After the transition to a sustained dynamo, the system is shown to evolve through different types of intermittency until a large--scale coherent field with small--scale turbulent fluctuations is formed. Prior to this coherent field stage, a new type of intermittency is detected, where the magnetic field randomly alternates between phases of coherent and incoherent large--scale spatial structures. The relevance of these findings to the understanding of the physics of mean--field dynamo and the physical mechanisms behind intermittent behavior observed in stellar magnetic field variability are discussed.Comment: 19 pages, 13 figure

Lagrangian chaos in an ABC--forced nonlinear dynamo

The Lagrangian properties of the velocity field in a magnetized fluid are studied using three-dimensional simulations of a helical magnetohydrodynamic dynamo. We compute the attracting and repelling Lagrangian coherent structures, which are dynamic lines and surfaces in the velocity field that delineate particle transport in flows with chaotic streamlines and act as transport barriers. Two dynamo regimes are explored, one with a robust coherent mean magnetic field and one with intermittent bursts of magnetic energy. The Lagrangian coherent structures and the statistics of finite--time Lyapunov exponents indicate that the stirring/mixing properties of the velocity field decay as a linear function of the magnetic energy. The relevance of this study for the solar dynamo problem is discussed

Supersymmetric effects in top quark decay into polarized W-boson

We investigate the one-loop supersymmetric QCD (SUSY-QCD) and electroweak (SUSY-EW) corrections to the top quark decay into a b-quark and a longitudinal or transverse W-boson. The corrections are presented in terms of the longitudinal ratio \Gamma(t-->W_L b)/\Gamma(t--> W b) and the transverse ratio \Gamma(t-->W_- b)/\Gamma(t--> W b). In most of the parameter space, both SUSY-QCD and SUSY-EW corrections to these ratios are found to be less than 1% in magnitude and they tend to have opposite signs. The corrections to the total width \Gamma(t-->W b) are also presented for comparison with the existing results in the literature. We find that our SUSY-EW corrections to the total width differ significantly from previous studies: the previous studies give a large correction of more than 10% in magnitude for a large part of the parameter space while our results reach only few percent at most.Comment: Version in PRD (explanation and refs added

Measuring factors influencing valuation of nonmotorized improvement measures

This paper presents the application of a new methodology for data collection based on multiple survey methods to study how drivers and transit users value nonmotorized improvements. This multi-method survey consisted on a combination of user’s willingness to change, stated tolerance and contingent valuation experiments. Random parameter probit models were used to analyze data on willingness to cycle. Willingness to change to cycling is related to travel purpose, transportation mode, travel time and education level. Policies for promoting the use of bicycles should target these profiles so as to be more effective. Random parameter ordered probit models were used to study how different cycling measures were valued by respondents. The protection and maintenance of cycle lanes are significantly more valued than other improvement measures. The design of future cycling facilities should consider increasing safety and travel time reduction. Senior citizen’s willingness to change to cycling value to a lesser extent cycling improvement measures than people traveling to work or study. Strategies to promote cycling in each case are discussed.Ruiz Sánchez, T.; Bernabé, JC. (2014). Measuring factors influencing valuation of nonmotorized improvement measures. Transportation Research Part A: Policy and Practice. 67:195-211. doi:10.1016/j.tra.2014.06.008S1952116

CP violation

The salient features of CP-violating interactions in the standard electroweak theory and in a few of its popular extensions are discussed. Moreover a brief overview is given on the status and prospects of searches for CP non-conservation effects in low and high energy experiments.Comment: 28 pages, Lectures given at the 37th Winter School on Particle Physics, Schladming, Austria, 199

Lagrangian chaos in an ABC-forced nonlinear dynamo.

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