61,666 research outputs found
Symplectic Quantization for Reducible Systems
We study an extension of the symplectic formalism in order to quantize
reducible systems. We show that a procedure like {\it ghost-of-ghost} of the
BFV method can be applied in terms of Lagrange multipliers. We use the
developed formalism to quantize the antisymmetric Abelian gauge fields.Comment: 12 pages, IF-UFRJ-22/9
Strong evidences for a nonextensive behavior of the rotation period in Open Clusters
Time-dependent nonextensivity in a stellar astrophysical scenario combines
nonextensive entropic indices derived from the modified Kawaler's
parametrization, and , obtained from rotational velocity distribution. These
's are related through a heuristic single relation given by , where is the cluster age. In a nonextensive
scenario, these indices are quantities that measure the degree of
nonextensivity present in the system. Recent studies reveal that the index
is correlated to the formation rate of high-energy tails present in the
distribution of rotation velocity. On the other hand, the index is
determined by the stellar rotation-age relationship. This depends on the
magnetic field configuration through the expression , where
and denote the saturation level of the star magnetic field and its
topology, respectively. In the present study, we show that the connection
is also consistent with 548 rotation period data for single
main-sequence stars in 11 Open Clusters aged less than 1 Gyr. The value of
2.5 from our unsaturated model shows that the mean magnetic field
topology of these stars is slightly more complex than a purely radial field.
Our results also suggest that stellar rotational braking behavior affects the
degree of anti-correlation between and cluster age . Finally, we suggest
that stellar magnetic braking can be scaled by the entropic index .Comment: 6 pages and 2 figures, accepted to EPL on October 17, 201
Theory of Magnetodynamics Induced by Spin Torque in Perpendicularly Magnetized Thin Films
A nonlinear model of spin wave excitation using a point contact in a thin
ferromagnetic film is introduced. Large-amplitude magnetic solitary waves are
computed, which help explain recent spin-torque experiments. Numerical
simulations of the fully nonlinear model predict excitation frequencies in
excess of 0.2 THz for contact diameters smaller than 6 nm. Simulations also
predict a saturation and red shift of the frequency at currents large enough to
invert the magnetization under the point contact. The theory is approximated by
a cubic complex Ginzburg-Landau type equation. The mode's nonlinear frequency
shift is found by use of perturbation techniques, whose results agree with
those of direct numerical simulations.Comment: 5 pages, 4 figures, submitted to PR
Application of the method of multiple scales to unravel energy exchange in nonlinear locally resonant metamaterials
In this paper, the effect of weak nonlinearities in 1D locally resonant
metamaterials is investigated via the method of multiple scales. Commonly
employed to the investigate the effect of weakly nonlinear interactions on the
free wave propagation through a phononic structure or on the dynamic response
of a Duffing oscillator, the method of multiple scales is here used to
investigate the forced wave propagation through locally resonant metamaterials.
The perturbation approach reveals that energy exchange may occur between
propagative and evanescent waves induced by quadratic nonlinear local
interaction
Bulgac-Kusnezov-Nos\'e-Hoover thermostats
In this paper we formulate Bulgac-Kusnezov constant temperature dynamics in
phase space by means of non-Hamiltonian brackets. Two generalized versions of
the dynamics are similarly defined: one where the Bulgac-Kusnezov demons are
globally controlled by means of a single additional Nos\'e variable, and
another where each demon is coupled to an independent Nos\'e-Hoover thermostat.
Numerically stable and efficient measure-preserving time-reversible algorithms
are derived in a systematic way for each case. The chaotic properties of the
different phase space flows are numerically illustrated through the
paradigmatic example of the one-dimensional harmonic oscillator. It is found
that, while the simple Bulgac-Kusnezov thermostat is apparently not ergodic,
both of the Nos\'e-Hoover controlled dynamics sample the canonical distribution
correctly
Correlation length scalings in fusion edge plasma turbulence computations
The effect of changes in plasma parameters, that are characteristic near or
at an L-H transition in fusion edge plasmas, on fluctuation correlation lengths
are analysed by means of drift-Alfven turbulence computations. Scalings by
density gradient length, collisionality, plasma beta, and by an imposed shear
flow are considered. It is found that strongly sheared flows lead to the
appearence of long-range correlations in electrostatic potential fluctuations
parallel and perpendicular to the magnetic field.Comment: Submitted to "Plasma Physics and Controlled Fusion
Eficiência agronômica de duas formulações da mistura de terbutilazina + metolachlor no controle em pré e pós-emergência inicial de plantas daninhas na cultura do milho.
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