Parabolic pulse generation with active or passive dispersion decreasing optical fibers

We experimentally demonstrate the possibility to generate parabolic pulses via a single dispersion decreasing optical fiber with normal dispersion. We numerically and experimentally investigate the influence of the dispersion profile, and we show that a hybrid configuration combining dispersion decrease and gain has several benefits on the parabolic generated pulses

Faiblesse de l’effort français pour la recherche dans le domaine de l’Agriculture Biologique : approche scientométrique

La France est la première puissance agricole européenne et le troisième marché pour l'alimentation biologique. Pourtant elle ne se situe qu'au 25ème rang mondial en terme de pourcentage de la surface agricole consacrée à l'agriculture biologique, et importe plus de la moitié de sa consommation. Un fort développement de la recherche en ce domaine est réclamé par les associations afin de répondre aux défis écologiques, économiques, énergétiques et sociaux posés à l'agriculture du XXIème siècle. Quelle est exactement la place consacrée à l’agriculture biologique dans la recherche agronomique des différents pays européens ? La reconnaissance de la pertinence de l’agriculture biologique comme domaine de recherche par l'INRA depuis 1999 a-t-elle conduit à une meilleure priorisation de la recherche en agriculture biologique ? Une analyse bibliométrique par mots-clés des publications scientifiques recensées dans la base de données ISI Web of Science de Thomson Scientific permet de construire des indicateurs suffisamment pertinents pour une comparaison des efforts de recherche nationaux sur la période 2000-2006, et ainsi de juger du niveau de priorisation réel de la recherche en agriculture biologique. Les résultats obtenus confirment le retard de la France, et sont à mettre en relation avec le manque de soutien institutionnel, de moyens humains et financiers consacrés à l’agriculture biologique au sein des organismes en charge de la recherche agronomique française, et ce, malgré les ambitions affichées

The mean circulation of the southwestern Mediterranean Sea: Algerian Gyres

This is a study about the general circulation of the southwestern Mediterranean Sea based on observations of currents carried out in the southwestern Mediterranean Sea in the framework of the Mass Transfer and Ecosystem Response (MATER) program (EEC/MAST3 program). From July 1997 to August 2002, profiling floats (MEDPROF experiment), isobaric floats (LIWEX experiment), and moored current meters (ELISA experiment) give evidence of two large-scale barotropic cyclonic circulations, the here-called Western and Eastern Algerian Gyres, centered around [3730′N, 230′E] and [3830′N, 600′E], respectively. These gyres have typical horizontal scales of 100–300 km and are characterized by orbital velocities of about 5 cm/s corresponding to rotational periods of about 4 months. They are strongly related to the bottom topography of the basin and to the planetary vorticity gradient: closed f/H isocontours (f is the planetary vorticity, H the water depth) correspond to the locations of the gyres and favor such circulations as free geostrophic modes. A linear and barotropic model is used to investigate the possibility of wind driving, but the results suggest that the wind stress is not responsible for establishing such circulations. The boundary currents flowing along the continental slope of Africa, Sardinia, and the Balearic Islands are proposed to be the main drivers of these gyres

The drift of Modified Atlantic Water from the Alboran Sea to the eastern Mediterranean

The Algerian basin is a region of the western Mediterranean with a highly variable circulation structure, including the eastward transport of Modified Atlantic Water (MAW) in its surface layer. An experiment with satellite tracked Lagrangian drifters was performed in 1996-97 to analyse the mesoscale circulation of the Algerian current. The complete trajectories of 18 drifters indicate that, at basin scale, all the surface flow occured along the coast from the Alboran Sea to the strait of Sicily. At that time, no portion of the inflowing MAW was driven to the central or northern regions.No disponibl

Analysis of ADCP data above a bottom observatory

A 300-kHz ADCP was set on GEOSTAR, a six-m3 deep-sea observatory. It was operated with cells of 80 cm during a three-week test experiment at 42-m water depth in the northern Adriatic sub-basin. Although it provided valuable data about the horizontal current field over most of the water column, it also allowed specifying the wake disturbances induced by the observatory. These disturbances are characterised by vertical velocities that are significant up to ~20 m above seafloor (echo intensity data suggest that the wake can even reach the surface), and by inclinations of the bottom nepheloïd layer (as deduced from differences in echo intensities from beam to beam). Our analysis is validated by consistent relationships between the horizontal current direction and speed on one side and the characteristics of both dynamical (vertical velocity) and non-dynamical (echo intensity) parameters on the other side. It is in good agreement with the simulations from a numerical model, and hence specifies the sensitivity (especially with respect to echo intensity) and accuracy of an instrument usually operated within fields of current and scatterers not disturbed by the device supporting it. In addition, the error velocity parameter displays specific characteristics that easily allow specifying the thickness of the layer disturbed by the observatory, thus providing a technique to validate the quality of data acquired in similar conditions

Inner speech sustains predictable task switching: direct evidence in adults

It has been proposed that inner speech supports task selection in task-switching studies, especially when the need for endogenous control is increased. This has been established through the suppression of inner speech in cognitive-flexibility tasks that leads to poorer performance. The aim of this study is to quantify the role of inner speech in a flexibility task by using surface laryngeal electromyography, which, contrary to previous studies, enables participants to freely verbalise the tasks. We manipulated endogenous and exogenous flexibility in a mathematical switching task paradigm. Experiment 1 shows that inner speech acts as a support for switching and is recruited more often when the tasks are of an endogenous type. The main result of Experiment 2 that language is recruited more for the mixing cost than for the switch cost (regardless of the endogenous factor) extends past findings obtained through articulatory suppression

Spatiotemporal Characterization of Supercontinuum Extending from the Visible to the Mid-Infrared in Multimode Graded-Index Optical Fiber

We experimentally demonstrate that pumping a graded-index multimode fiber with sub-ns pulses from a microchip Nd:YAG laser leads to spectrally flat supercontinuum generation with a uniform bell-shaped spatial beam profile extending from the visible to the mid-infrared at 2500\,nm. We study the development of the supercontinuum along the multimode fiber by the cut-back method, which permits us to analyze the competition between the Kerr-induced geometric parametric instability and stimulated Raman scattering. We also performed a spectrally resolved temporal analysis of the supercontinuum emission.Comment: 5 pages 7 figure

Molecular dynamics simulations of elementary chemical processes in liquid water using combined density functional and molecular mechanics potentials. I. Proton transfer in strongly H-bonded complexes

The first molecular dynamics (MD) simulation of a chemical process in solution with an ab initio description of the reactant species and a classical representation of the solvent is presented. We study the dynamics of proton (deuterium) transfer in strongly hydrogen-bonded systems characterized by an energy surface presenting a double well separated by a low activation barrier. We have chosen the hydroxyl-water complex in liquid water to analyze the coupling between the reactive system and the environment. The proton is transferred from one well to the other with a frequency close to 1 ps−1 which is comparable to the low-frequency band associated to hindered translations, diffusional translation and reorientation of water molecules in water. The proton transfer takes place in 20–30 fs whereas the solvent response is delayed by about 50 fs. Therefore, the reaction occurs in an essentially frozen-solvent configuration. In principle, this would produce a barrier increase with respect to the equilibrium reaction path. However, solvent fluctuations play a substantial role by catalyzing the proton transfer. The solvent relaxation time after proton transfer has been evaluated. Since it falls in the same time scale than the reactive events (0.6 ps) it substantially influences the proton dynamics. The present study is intended to model charge transfer processes in polar media having a low activation barrier for which many reactive events may be predicted in a MD simulation. The case of reactions with large activation barriers would require the use of special techniques to simulate rare events. But still in that case, hybrid QM/MM simulations represent a suitable tool to analyze reaction dynamics and non-equilibrium solvent effects in solution [email protected]

The Benthic Boundary Layer: geochemical and oceanographic data from the GEOSTAR-2 observatory

Geochemical and oceanographic data, acquired throughout 6 months by the GEOSTAR-2 benthic observatory in southern Tyrrhenian Sea, evidenced ocean-lithosphere interactions in the 1900-m deep Benthic Boundary Layer (BBL), distinguishing two water masses with different origin and, possibly, benthic residence time. Gas concentration, helium isotopic ratios, radioactivity, temperature, salinity and vertical component of the current converged towards the indication of a BBL characterised by a colder and fresher western water (WW), which is episodically displaced by the cascading of the warmer and saltier Eastern Overflow Water (EOW). The benthic WW has higher concentration of geochemical tracers diffusing from the seafloor sediments. The data set shows the potential of long-term, continuous and multiparametric monitoring in providing unique information which cannot be acquired by traditional, short-term or single-sensor investigations