3,410 research outputs found
Competition of rotation and stratification in flux concentrations
In a strongly stratified turbulent layer, a uniform horizontal magnetic field
can become unstable to spontaneously form local flux concentrations due to a
negative contribution of turbulence to the large-scale (mean-field) magnetic
pressure. This mechanism, called the negative effective magnetic pressure
instability (NEMPI), is of interest in connection with dynamo scenarios where
most of the magnetic field resides in the bulk of the convection zone, and not
at the bottom. Recent work using the mean-field hydromagnetic equations has
shown that NEMPI becomes suppressed at rather low rotation rates with Coriolis
numbers as low as 0.1.}{Here we extend these earlier investigations by studying
the effects of rotation both on the development of NEMPI and on the effective
magnetic pressure. We also quantify the kinetic helicity from direct numerical
simulations (DNS) and compare with earlier work.}{To calculate the rotational
effect on the effective magnetic pressure we consider both DNS and analytical
studies using the approach. To study the effects of rotation on the
development of NEMPI we use both DNS and mean-field calculations of the 3D
hydromagnetic equations in a Cartesian domain.}{We find that the growth rates
of NEMPI from earlier mean-field calculations are well reproduced with DNS,
provided the Coriolis number is below about 0.06. In that case, kinetic and
magnetic helicities are found to be weak. For faster rotation, dynamo action
becomes possible. However, there is an intermediate range of rotation rates
where dynamo action on its own is not yet possible, but the rotational
suppression of NEMPI is being alleviated.}{Production of magnetic flux
concentrations through the suppression of turbulent pressure appears to be
possible only in the upper-most layers of the Sun, where the convective
turnover time is less than 2 hours.}Comment: 13 pages, 13 figures submitted to A&
Neutrinos in the simplest little Higgs scenario and TeV leptogenesis
The little Higgs scenario may provide an interesting framework to accommodate
TeV scale leptogenesis because a TeV Majorana mass of the right-handed neutrino
that we employ for the latter may find a natural place near the ultraviolet
cutoff of the former. In this work we study how a light neutrino spectrum,
generated radiatively, and TeV scale leptogenesis can be embedded in the
simplest little
Higgs framework. Alternatively, we highlight how the neutrino Yukawa textures
of the latter are constrained.Comment: 10 pages, latex, v2: refs and comments added, to appear in PR
Rational characteristic functions and markov chains
Abstract 1 We investigate in this paper how to estimate the density function of a random variable using a parametric ARMA model for its characteristic function. The choice of this model is motivated by the fact that this type of density characterizes the duration of staying at an N-states Markov chain, but the approach is general enough to be applied to many practical problems. Both ML and moment-based linear estimates are derived, the former being based on the optimization of a highly non-linear function. 1.Peer ReviewedPostprint (published version
Productivity of silvoarable systems established with Prunus avium L. in Galicia (NW Spain)
info:eu-repo/semantics/publishedVersio
Non-periodic driving of coupled oscillators:a spherical swing
Nonlinearly coupled, damped oscillators at 1:1 frequency ratio, one oscillator being driven coherently for efficient
excitation, are exemplified by a spherical swing with some phase-mismatch between drive and response. For certain
damping range, excitation is found to succeed if it lags behind, but to produce a chaotic attractor if it leads the response. Although a period-doubhng sequence, for damping increasing, leads to the attractor, this is actually born as a hard (as regards amplitude) bifurcation at a zero growth-rate parametric line; as damping decreases, an unstable fixed point crosses an invariant plane to enter as saddle-focus a phase-space domain of physical solutions. A second hard bifurcation occurs at the zero mismatch line, the saddle-focus leaving that domain. Times on the attractor diverge when approaching either fine,
leading to exactly one-dimensional and noninvertible limit maps, which are analytically determined
A POF model for short fiber segments in avionics applications
Plastic Optical Fibres (POF) have now been a well-established media for transporting high-speed at low cost in short distance communications systems, and avionics is the latest segment where these fibers are becoming an important factor. In fact, the POF''s flexibility and ease of installation make this fiber a great option for the replacement by fiber of some of the existing aircraft data links. We propose a new model for short fiber links that are suitable for plane''s systems that involve a lot of connectors; the model is built around two important properties, namely, power transfer among modes and attenuation. The model expands on our previous work on the subject and is based on detailed experimental measurements for various fiber types and lengths
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