We study the setting up of relativistic ponderomotive non-linearity in an under-dense collisionless cold plasma. Using the fluid model, coupled system of equations of the laser beam and electron plasma oscillations has been derived. We present the numerical simulation for this coupled system of equations, when the coupling arises through relativistic ponderomotive non-linearity. The filamentation of the laser beam has been found to vary appreciably with perturbation wave number. The results show that with time, localized structures become more complex and the plasma oscillation frequency spectra have several harmonic peaks at terahertz frequencies when the electron plasma frequency is in terahertz range and laser frequency is around 2.35 × 1015 rad/s. We also present the semi-analytical model to capture the underlying physics.

Modern telecommunications are moving towards (massive) multi-input multi-output (MIMO) systems in 5th generation (5G) technology, increasing the dimensionality of the systems dramatically. In this paper, the impairments of radio frequency (RF) power amplifiers (PAs) in a 3 × 3 MIMO system are compensated in both the time and the frequency domains. A three-dimensional (3D) time-domain memory polynomial-type model is proposed as an extension of conventional 2D models. Furthermore, a 3D frequency-domain technique is formulated based on the proposed time-domain model to reduce the dimensionality of the model, while preserving the performance in terms of model errors. In the 3D frequency-domain technique, the bandwidth of the system is split into several narrow sub-bands, and the parameters of the model are estimated for each sub-band. This approach requires less computational complexity, and also the procedure of the parameters estimation for each sub-band can be implemented independently. The device-under-test consists of three RF PAs including input and output cross-talk channels. The proposed techniques are evaluated in both behavioral modeling and digital pre-distortion (DPD) perspectives. The experimental results show that the proposed DPD technique can compensate the errors of non-linearity and memory effects in the both time and frequency domains.

Non-paraxial approximation based study of transient self-focusing of an intense short-pulse laser in plasma has been investigated by considering the effect of a transverse magnetic field. The laser with non-uniform distribution of intensity exerts a ponderomotive force on electrons and sets in an ambi-polar diffusion of the plasma. The ambient magnetic field, however, strongly inhibits the process, when the electron Larmor radius is comparable to or shorter than the laser spot size. As the plasma density is depleted, the laser beam becomes more self-focused. This study addresses a significant enhancement in the laser self-focusing rate by including the correction terms due the off-axis approximation.

Catchability is crucial for the economic performance of fisheries and their management. However, in many bio-economic simulation models it is assumed to be either constant or it is largely ignored, despite the fact that it is known to vary due to technical, environmental and behavioral factors. Such variation can cause the relationship between effort and fishing mortality to be nonlinear. This paper provides evidence for the possibility of nonlinear optimizing behavior from the Dutch beam trawl fishery, provides a methodology for estimating the curvature of the resulting relation, and a simple way of implementing these processes within a bio-economic model. Moreover, it shows the influence of a nonlinear relationship between effort and fishing mortality in a model of effort management (EU long-term flatfish management plan).

Sur le plan expérimental, l'analyse modale des structures non-linéaires est encore en butte à de nombreuses difficultés. Nous voulons montrer que l'utilisation exclusive de la transformée de Fourier unidimensionnelle ne permet pas d'obtenir les vraies fonctions de transfert nécessaires pour atteindre les fonctionnelles non-linéaires de Volterra. L'analyse jusqu'ici se cantonne dans la majorité des cas à l'obtention des valeurs propres de divers modes non-linéaires. Il est nécessaire d'obtenir par un moyen ou par un autre, les noyaux (ou réponses impulsionnelles) des fonctionnelles permettant d'évaluer les vecteurs propres correspondants. Nous utilisons la technique de multi-excitation pour déterminer les fonctionnelles non-linéaires.