69,452 research outputs found
Meson decay in a corrected model
Extensively applied to both light and heavy meson decay and standing as one
of the most successful strong decay models is the model, in which
pair production is the dominant mechanism. The pair production can
be obtained from the non-relativistic limit of a microscopic interaction
Hamiltonian involving Dirac quark fields. The evaluation of the decay amplitude
can be performed by a diagrammatic technique for drawing quark lines. In this
paper we use an alternative approach which consists in a mapping technique, the
Fock-Tani formalism, in order to obtain an effective Hamiltonian starting from
same microscopic interaction. An additional effect is manifest in this
formalism associated to the extended nature of mesons: bound-state corrections.
A corrected is obtained and applied, as an example, to
and decays.Comment: 3 figures. To appear in Physical Review
Nonextensive Quantum H-Theorem
A proof of the quantum -theorem taking into account nonextensive effects
on the quantum entropy is shown. The positiveness of the time variation
of combined with a duality transformation implies that the nonextensive
parameter lies in the interval [0,2]. It is also shown that the equilibrium
states are described by quantum -power law extensions of the Fermi-Dirac and
Bose-Einstein distributions. Such results reduce to the standard ones in the
extensive limit, thereby showing that the nonextensive entropic framework can
be harmonized with the quantum distributions contained in the quantum
statistics theory.Comment: 5 pages, LaTe
Supporting GUI exploration through USS tool
Advances in usability and design techniques (e.g. user-centered design) try to facilitate the use of interactive systems. However, users still have to adapt to interactive systems, i.e. they have to learn the steps required to accomplish a task either by trial and error or by obtaining help. While advanced users are usually able to adapt without much effort this is far from being the case with beginners. Some interactive systems offer different interaction styles in an attempt to meet the needs of all types of user but this is not the case with all interactive systems. In this sense, we present an approach to support the use of any interactive system making use of enriched models and picture-driven computing to achieve tasks automation. The USS tool (User Support System) is the basis to the adaptation of interactive systems accordingly to the users' needs. The approach provides the foundation for the addition of help (based on demonstration) to any graphical user interfaces (GUI) facilitating learning and use. The work is illustrated by a case study and completed with a preliminary user evaluation which provides insights about the validity of the approach.info:eu-repo/semantics/publishedVersio
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
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