Self-organized pattern formation in laser-induced multiphoton ionization

We use finite-difference time-domain modelling to investigate plasma generation induced by multi-photon absorption of intense laser light in dielectrics with tiny inhomogenities. Plasma generation is found to be strongly amplified around nanometer-sized inhomogeneities as present in glasses. Each inhomogeneity acts as the seed of a plasma structure growing against the direction of light propagation. Plasma structures originating from randomly distributed inhomogeneities are found to interact strongly and to organize in regularly spaced planes oriented perpendicularly to the laser polarization. We discuss similarities between our results and nanogratings in fused silica written by laser beams with spatially homogeneous as well as radial and azimuthal polarization.Comment: 8 pages, 9 figure

Photonic potential for TM waves

We discuss the effective photonic potential for TM waves in inhomogeneous isotropic media. The model provides an easy and intuitive comprehension of form birefringence, paving the way for a new approach on the design of graded-index optical waveguides on nanometric scales. We investigate the application to nanophotonic devices, including integrated nanoscale wave plates and slot waveguides.Comment: 4 pages, 7 figure

The Development and Future of EU Agricultural Trade Preferences for North-African and Near-East Countries

The EU recently completed negotiating a series of Association Agreements with Mediterranean countries. Trade preferences for agricultural goods granted under these Agreements, as well as under former arrangements, are analyzed by calculating the value of preference margins at several stages in the evolution of preferences. The total value of preference margins for all countries covered was about 130 million under the agreements of the mid-1970s and increased by 48 per cent until 1995; by 2000 this value declined by about 14 per cent due to reduced EU MFN tariffs. The extended preferences under the new Agreements more than compensate for this decline and will result in a total value of preference margins of 226 million once all Agreements have entered into force.preferential trade, preference margin, Mediterranean countries, Euro-Mediterranean Agreements, preference erosion, International Relations/Trade,

Modeling sparse connectivity between underlying brain sources for EEG/MEG

We propose a novel technique to assess functional brain connectivity in EEG/MEG signals. Our method, called Sparsely-Connected Sources Analysis (SCSA), can overcome the problem of volume conduction by modeling neural data innovatively with the following ingredients: (a) the EEG is assumed to be a linear mixture of correlated sources following a multivariate autoregressive (MVAR) model, (b) the demixing is estimated jointly with the source MVAR parameters, (c) overfitting is avoided by using the Group Lasso penalty. This approach allows to extract the appropriate level cross-talk between the extracted sources and in this manner we obtain a sparse data-driven model of functional connectivity. We demonstrate the usefulness of SCSA with simulated data, and compare to a number of existing algorithms with excellent results.Comment: 9 pages, 6 figure

Interplay between multiple scattering and optical nonlinearity in liquid crystals

We discuss the role played by time-dependent scattering on light propagation in liquid crystals. In the linear regime, the effects of the molecular disorder accumulate in propagation, yielding a monotonic decrease in the beam spatial coherence. In the nonlinear case, despite the disorder-imposed Brownian-like motion to the self-guided waves, self-focusing increases the spatial coherence of the beam by inducing spatial localization. Eventually, a strong enhancement in the beam oscillations occurs when power is strong enough to induce self-steering, i.e. in the non-perturbative regime.SCOPUS: ar.jinfo:eu-repo/semantics/publishe