2,081 research outputs found
Perturbative approach to the nonlinear saturation of the tearing mode for any current gradient
Within the traditional frame of reduced MHD, a new rigorous perturbation
expansion provides the equation ruling the nonlinear growth and saturation of
the tearing mode for any current gradient. The small parameter is the magnetic
island width w. For the first time, the final equation displays at once terms
of order w ln(1/w) and w which have the same magnitude for practical purposes;
two new O(w) terms involve the current gradient. The technique is applicable to
the case of an external forcing. The solution for a static forcing is computed
explicitly and it exhibits three physical regimes.Comment: 4 pages, submitted to Physical Review Letter
Cross phase modulation in a five--level atomic medium: Semiclassical theory
The interaction of a five-level atomic system involving electromagnetically
induced transparency with four light fields is investigated. Two different
light-atom configurations are considered, and their efficiency in generating
large nonlinear cross-phase shifts compared. The dispersive properties of those
schemes are analyzed in detail, and the conditions leading to group velocity
matching for two of the light fields identified. An analytical treatment based
on amplitude equations is used in order to obtain approximate solutions for the
susceptibilities, ehich are shown to fit well with the numerical simulations of
the full Bloch equations in a large parameter region.Comment: New version: section on pulse propagation added, reference list
expanded; 17 pages, 15 figure
Low Rank Vector Bundles on the Grassmannian G(1,4)
Here we define the concept of -regularity for coherent sheaves on the
Grassmannian G(1,4) as a generalization of Castelnuovo-Mumford regularity on
. In this setting we prove analogs of some classical properties. We
use our notion of -regularity in order to prove a splitting criterion for
rank 2 vector bundles with only a finite number of vanishing conditions. In the
second part we give the classification of rank 2 and rank 3 vector bundles
without "inner" cohomology (i.e. H^i_*(E)=H^i(E\otimes\Q)=0 for any
) on G(1,4) by studying the associated monads.Comment: 11 pages, no figure
Quantum theory of a polarization phase-gate in an atomic tripod configuration
We present the quantum theory of a polarization phase-gate that can be
realized in a sample of ultracold rubidium atoms driven into a tripod
configuration. The main advantages of this scheme are in its relative
simplicity and inherent symmetry. It is shown that the conditional phase shifts
of order can be attained.Comment: X International Conference on Quantum Optics, Minsk, Belaru
Vocalization-related stapedius muscle activity in different age chickens (Gallus gallus), and its role in vocal development
The stapedius muscle activity associated with vocalization was analyzed in young and adult roosters. Our results show that remarkable differences in the behavior of vocalization-related stapedius muscle activity exist between these two ages. Unlike young roosters, electrical stimulation in the midbrain of adult cocks yields vocalizations associated with stapedius muscle EMG responses that always show a higher threshold and a longer latency than those of the vocalization induced. Moreover, the maximal amplitude of the stapedius muscleEMG response is consistently lower than that detected in young roosters, despite the fact that the maximal vocalization amplitude of the adult birds is much higher. Onthewholeourresultsdemonstrate thatvocalization-relatedstapediusmuscleactivityisstronglyreducedinadulthood.Thepossibility that stapedius muscle may play a role during the vocal development was verified by comparing the crow of normal roosters with that of cocks from which the stapedius muscle had been removed shortly after hatching. Strong differences exist in the amplitude/frequency distribution of the crowing of normal and stapedectomized roosters, suggesting that the stapedius muscle exerts an important role in auditory feedback modulation, and that this feedback is used for normal vocal development
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