Instability and dynamics of two nonlinearly coupled laser beams in a plasma

We investigate the nonlinear interaction between two laser beams in a plasma in the weakly nonlinear and relativistic regime. The evolution of the laser beams is governed by two nonlinear Schroedinger equations that are coupled with the slow plasma density response. We study the growth rates of the Raman forward and backward scattering instabilities as well of the Brillouin and self-focusing/modulational instabilities. The nonlinear evolution of the instabilities is investigated by means of direct simulations of the time-dependent system of nonlinear equations.Comment: 18 pages, 8 figure

Nonlinear propagation of light in Dirac matter

The nonlinear interaction between intense laser light and a quantum plasma is modeled by a collective Dirac equation coupled with the Maxwell equations. The model is used to study the nonlinear propagation of relativistically intense laser light in a quantum plasma including the electron spin-1/2 effect. The relativistic effects due to the high-intensity laser light lead, in general, to a downshift of the laser frequency, similar to a classical plasma where the relativistic mass increase leads to self-induced transparency of laser light and other associated effects. The electron spin-1/2 effects lead to a frequency up- or downshift of the electromagnetic (EM) wave, depending on the spin state of the plasma and the polarization of the EM wave. For laboratory solid density plasmas, the spin-1/2 effects on the propagation of light are small, but they may be significant in super-dense plasma in the core of white dwarf stars. We also discuss extensions of the model to include kinetic effects of a distribution of the electrons on the nonlinear propagation of EM waves in a quantum plasma.Comment: 9 pages, 2 figure

Diversities and similarities in PFGE profiles of Campylobacter jejuni isolated from migrating birds and humans

Aims: To genetically sub-type Campylobacter jejuni strains isolated from migratory birds, and to compare these with clinical strains collected in the same area and corresponding time period, with the aim to increase our knowledge on sub-types occurring among wild birds and their possible impact on human disease. Methods and Results: We sub-typed C. jejuni strains from migrating birds (n = 89) and humans (n = 47), using macrorestriction profiling by pulsed-field gel electrophoresis. Isolates from migrant birds often exhibited sub-types with higher levels of similarity to isolates from birds of the same species or feeding guild, than to isolates from other groups of birds. Likewise, could the vast majority of sub-types found among the migrant bird isolates not be identified among sub-types from human cases. Only two bird strains, one from a starling (Sturnus vulgaris) and one from a blackbird (Turdus merula), had sub-types that were similar to some of the human strain sub-types. Conclusions: Isolates from one bird species, or feeding guild, often exhibited high similarities, indicating a common transmission source for individuals, or an association between certain sub-types of C. jejuni and certain ecological guilds or phylogenetic groups of birds. Sub-types occurring among wild birds were in general distinctively different from those observed in patients. The two bird isolates that were similar to human strains were isolated from bird species that often live in close associations with human settlements. Significance and Impact of Study: Wild birds have often been mentioned as a potential route for transmission of C. jejuni to humans. Our study demonstrates that strains isolated from birds most often are different from clinical strains, but that some strain similarities occur, notably in birds strongly associated with human activities

Mask testing of 28 gbaud 16-QAM transmitters using time-resolved error vector magnitude

We propose time-resolved EVM for characterization of 16-QAM transmitters. By designing a mask test, different impairments can be separated and quantified. The impact from quadrature error and timing skew are investigated experimentally

Predicting delay factors when chipping wood at forest roadside landings

Chipping of bulky biomass assortments at roadside landings is a common and costly step in the biomass-to-energy supply chain. This operation normally involves one chipping unit and one or several transport trucks working together for simultaneous chipping and chip transport to a terminal or end user. Reducing the delay factors in these operations is a relevant ambition for lowering supply costs. A method to estimate organizational delay based on: (1) the capacity ratio between the transport and the chipper, (2) the use of buffer storage, and (3) the number of transport units involved is suggested here. Other delays will also be present, and some of these may relate to the working conditions at the landing. A method to set a landing functionality index based on characteristics of the forest landing is also suggested. A total of 14 roadside chipping operations were assessed and the operators were interviewed to address the impact of machinery configuration and landing characteristics on machine utilization. At most sites, the chipper was the more productive part, and the chipper utilization was to a large extent limited by organizational delay. Still the utilization of the transport units varied between 37 and 97%, of which some 36% of the variation was explained by the landing functionality index. Knowledge from the work presented here should be a good starting point for improving biomass supply planning and supply chain configuration.acceptedVersio

Instability and Evolution of Nonlinearly Interacting Water Waves

We consider the modulational instability of nonlinearly interacting two-dimensional waves in deep water, which are described by a pair of two-dimensional coupled nonlinear Schroedinger equations. We derive a nonlinear dispersion relation. The latter is numerically analyzed to obtain the regions and the associated growth rates of the modulational instability. Furthermore, we follow the long term evolution of the latter by means of computer simulations of the governing nonlinear equations and demonstrate the formation of localized coherent wave envelopes. Our results should be useful for understanding the formation and nonlinear propagation characteristics of large amplitude freak waves in deep water.Comment: 4 pages, 4 figures, to appear in Physical Review Letter

Nonlinear dynamics of large amplitude dust acoustic shocks and solitary pulses in dusty plasmas

We present a fully nonlinear theory for dust acoustic (DA) shocks and DA solitary pulses in a strongly coupled dusty plasma, which have been recently observed experimentally by Heinrich et al. [Phys. Rev. Lett. 103, 115002 (2009)], Teng et al. [Phys. Rev. Lett. 103, 245005 (2009)], and Bandyopadhyay et al. [Phys. Rev. Lett. 101, 065006 (2008)]. For this purpose, we use a generalized hydrodynamic model for the strongly coupled dust grains, accounting for arbitrary large amplitude dust number density compressions and potential distributions associated with fully nonlinear nonstationary DA waves. Time-dependent numerical solutions of our nonlinear model compare favorably well with the recent experimental works (mentioned above) that have reported the formation of large amplitude non-stationary DA shocks and DA solitary pulses in low-temperature dusty plasma discharges.Comment: 9 pages, 4 figures. To be published in Physical Review

Twistless KAM tori

A selfcontained proof of the KAM theorem in the Thirring model is discussed.Comment: 7 pages, 50 K, Plain Tex, generates one figure named gvnn.p

Bifurcation curves of subharmonic solutions

We revisit a problem considered by Chow and Hale on the existence of subharmonic solutions for perturbed systems. In the analytic setting, under more general (weaker) conditions, we prove their results on the existence of bifurcation curves from the nonexistence to the existence of subharmonic solutions. In particular our results apply also when one has degeneracy to first order -- i.e. when the subharmonic Melnikov function vanishes identically. Moreover we can deal as well with the case in which degeneracy persists to arbitrarily high orders, in the sense that suitable generalisations to higher orders of the subharmonic Melnikov function are also identically zero. In general the bifurcation curves are not analytic, and even when they are smooth they can form cusps at the origin: we say in this case that the curves are degenerate as the corresponding tangent lines coincide. The technique we use is completely different from that of Chow and Hale, and it is essentially based on rigorous perturbation theory.Comment: 29 pages, 2 figure

Breakdown of Lindstedt Expansion for Chaotic Maps

In a previous paper of one of us [Europhys. Lett. 59 (2002), 330--336] the validity of Greene's method for determining the critical constant of the standard map (SM) was questioned on the basis of some numerical findings. Here we come back to that analysis and we provide an interpretation of the numerical results by showing that no contradiction is found with respect to Greene's method. We show that the previous results based on the expansion in Lindstedt series do correspond to the transition value but for a different map: the semi-standard map (SSM). Moreover, we study the expansion obtained from the SM and SSM by suppressing the small divisors. The first case turns out to be related to Kepler's equation after a proper transformation of variables. In both cases we give an analytical solution for the radius of convergence, that represents the singularity in the complex plane closest to the origin. Also here, the radius of convergence of the SM's analogue turns out to be lower than the one of the SSM. However, despite the absence of small denominators these two radii are lower than the ones of the true maps for golden mean winding numbers. Finally, the analyticity domain and, in particular, the critical constant for the two maps without small divisors are studied analytically and numerically. The analyticity domain appears to be an perfect circle for the SSM analogue, while it is stretched along the real axis for the SM analogue yielding a critical constant that is larger than its radius of convergence.Comment: 12 pages, 3 figure