31 research outputs found
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