Search results for "Instability"
showing 10 items of 724 documents
Vector Modulational Instabilities and Soliton Experiments
1999
In optical fibers, the interaction between nonlinear and dispersive effects leads to phenomena such as modulational instability (MI)[1, 2, 3, 4, 5, 6], in which a continuous or quasi-continuous wave undergoes a modulation of its amplitude or phase in the presence of noise or any other small perturbation. The perturbation can originate from quantum noise (spontaneous-MI) or from a frequency shifted signal wave (induced-MI). MI has been observed for the first time for a single pump wave propagating in a standard non birefringe.nt fiber (scalar MI)[7]. It has been shown that scalar MI only occurs when the group velocity dispersion (GVD) is negative (anomalous dispersion regime).
Dark- and bright-rogue-wave solutions for media with long-wave–short-wave resonance
2014
5 pags.; 5 figs.; PACS number(s): 46.40.−f, 47.20.Ky, 47.35.−i, 47.52.+j
Wave Modulations in the Nonlinear Biinductance Transmission Line
2001
Adding dissipative elements to a discrete biinductance transmission line which admits both low frequency (LF) and high frequency (HF) modes, dynamics of a weakly nonlinear modulated wave is investi...
Breathing solitary waves in a Sine-Gordon two-dimensional lattice.
1995
We study theoretically and numerically the dynamical behavior of a two-dimensional sine-Gordon lattice. We show that, via modulational instability, an initial-low-amplitude plane wave can evolve spontaneously into moving localized modes with large amplitude. These nonlinear modes, with dimensions depending on the characteristic wavelengths of the instability, behave like breathing solitary waves and present particlelike properties.
LONG TIME DYNAMICS OF MODULATED WAVES IN A NONLINEAR DISCRETE LC TRANSMISSION LINE
2003
The long-time dynamics of modulated waves in a nonlinear LC transmission line is investigated. Considering the higher-order nonlinear Schrodinger equation, we define analytically the conditions leading to the instability of modulated waves. We show that two kinds of instabilities may develop in the network depending on the frequency range of the chosen carrier wave and on the magnitude of its initial amplitude, which is confirmed by our numerical simulations. The nonreproducibility of numerical experiments on modulated waves is also considered.
Chiral Instabilities and the Onset of Chiral Turbulence in QED Plasmas
2020
We present a first principles study of chiral plasma instabilities and the onset of chiral turbulence in QED plasmas far from equilibrium. By performing classical-statistical lattice simulations of the microscopic theory, we show that the generation of strong helical magnetic fields from a helicity imbalance in the fermion sector proceeds via three distinct phases. During the initial linear instability regime the helicity imbalance of the fermion sector causes an exponential growth(damping) of magnetic field modes with right(left) handed polarization, for which we extract the characteristic growth (damping) rates. Secondary growth of unstable modes accelerates the helicity transfer from fer…
Structure and dynamics of sawteeth crashes in ASDEX Upgrade
2010
The crash phase of the sawteeth in ASDEX Upgrade tokamak [Herrmann et al., Fusion Sci. Technol. 44(3), 569 (2003)] is investigated in detail in this paper by means of soft x-ray (SXR) and electron cyclotron emission (ECE) diagnostics. Analysis of precursor and postcursor (1,1) modes shows that the crash does not affect the position of the resonant surface q=1. Our experimental results suggest that sawtooth crash models should contain two ingredients to be consistent with experimental observations: (1) the (1,1) mode structure should survive the crash and (2) the flux changes should be small to preserve the position of the q=1 surface close to its original location. Detailed structure of the…
Modulational stability brought by cubic–quartic interactions of the nearest-neighbor in FK model subjected in a parametrized on-site potential
2022
Abstract This work extends to higher-order interactions the results of Ref. Nguetcho (2021), in which we discussed only on modulational instability in one-dimensional chain made of atoms, harmonically coupled to their nearest neighbors and subjected to an external on-site potential. Here we investigate the competition between cubic-quartic nonlinearities interactions of the nearest-neighbor and substrate’s deformability, and mainly discuss its impact on the modulational instability of the system. This makes it possible to adapt the theoretical model to a real physical system such as atomic chains or DNA lattices. The governing equation, derived from the modified Frenkel-Kontorova model, is …
Pulsating B and Be Stars in the Magellanic Clouds
2010
Stellar pulsations in main-sequence B-type stars are driven by the κ-mechanism due to the Fe-group opacity bump. The current models do not predict the presence of instability strips in the B spectral domain at very low metallicities. As the metallicity of the Magellanic Clouds (MC) has been measured to be around Z = 0. 002 for the Small Magellanic Cloud (SMC) and Z = 0. 007 for the Large Magellanic Cloud (LMC), they constitute a very suitable objects to test these predictions. The aim of this work is to investigate the existence of B-type pulsators at low metallicities, searching for short-term periodic variability in a large sample of B and Be stars from the MC with accurately determined f…
Generation of vector dark-soliton trains by induced modulational instability in a highly birefringent fiber
1999
International audience; We present a set of experimental observations that demonstrate the generation of vector trains of dark-soliton pulses in the orthogonal axes of a highly birefringent optical fiber. We generated dark-soliton trains with terahertz repetition rate in the normal group-velocity dispersion regime by inducing a polarization modulational instability by mixing two intense, orthogonal continuous laser beams. Numerical solutions of the propagation equations were used to optimize the emission of vector dark pulses at the fiber output.