121 research outputs found
A database for the industrial trawl fishery of Cote d'Ivoire
Fishery statistics for the industrial trawl fishery of Cote d'Ivoire have been well documented since 1968. However, data processing has changed significantly with time and some of the data files have been lost. In 1997, the Centre de Recherches Oceanologiques d'Abidjan decided to retrieve and process all trawl data available from different sources. This paper gives an overview of the database covering the period 1968 to 1997 and describes its coverage, format, structure and use. The database was developed using MS ACCESS and is a powerful tool for storing information about this fishery, and for analysis of its dynamics over a period of 30 years
Tectonic evolution of the Eastern Moroccan Meseta: from Late Devonian foreâarc sedimentation to Early Carboniferous collision of an Avalonian promontory
This study was founded by the Ministerio de Economia y Competitividad (MINECO) of Spain through the project PANGEATOR (CGL2015-71692-P) and the Doctoral scholarship BES-2016-078168. GeoHistory Facility instruments were funded via an Australian Geophysical Observing System grant provided to AuScope Pty Ltd. by the AQ44 Australian Education Investment Fund program. The NPII multicollector was obtained via funding from the Australian Research Council LIEF program (LE150100013). The authors want to express their gratitude to Dr. Manuel Francisco Pereira (University of Evora, Portugal) and Dr. Michel Villeneuve (Centre Europeen de Recherche et d'Enseignement des Geosciences de l'Environnement, France) for their constructive reviews that helped to improve the quality of the original manuscript. Special thanks to Brad McDonald (Curtin University, Australia) for technical assistance regarding LA-ICPMS and Hf analyses, Profs. Abdelfatah Tahiri (University Mohammed V of Rabat, Morocco) and Hassan El Hadi (University Hassan II of Casablanca, Morocco) for their support during field work, Prof. Yvette Kuiper (Colorado School of Mines, USA) for her precious hints about the interpretation of Hf data, and Dr. Lorenzo Valetti for proofreading the manuscript. Supporting information can be obtained in Mendeley Data: https://doi.org/10.17632/b8fdbykmbx.1 (https://data.mendeley.com/datasets/b8fdbykmbx/draft?a=eaae2da0-8e224056-861b-4824984f1c10).The deformed Paleozoic succession of the Eastern Moroccan Meseta crops out in relativelysmall and isolated inliers surrounded by Mesozoic and Cenozoic rocks. Two of the largest inliers(Mekkam and Debdou) are characterized by a monotonous succession of slates and greywackes affected bypolyphasic folding that occurred at lowâto very low grade metamorphic conditions. New UâPb ages ondetrital zircon grains from the DebdouâMekkam metasediments constrain the maximal depositional age asLate Devonian, interpreted to be close to the true sedimentation age. Furthermore, theΔHfvalues of theDevonian detrital zircons, together with the presence of a series of scattered zircon grains with ages betweenc. 0.9 and c. 1.9 Ga, suggest provenance from a subductionârelated magmatic arc located on the Avalonianmargin. The DebdouâMekkam massif is characterized by an Early Carboniferousfirst deformationalevent (D1), which gave way to a pervasive cleavage (S1) associated with plurikilometricâscale, tight toisoclinal, overturned to recumbent folds. Later events (Dc) occurred at Late Carboniferous time andgenerated variably developed crenulation cleavages (Sc) associated with variously oriented metricâtokilometricâscale folds, which complicate the pattern of both D1 intersection lineations (L1) and axial traces.The restoration of this pronounced curved pattern yields originally SWâNEâoriented D1 fold axes withregional SEâvergence. This important Early Carboniferous shortening and SEâdirected tectonic transport canbe explained by closure of the Rheic Ocean and thefirst phases of the collision between the northern passivemargin of Gondwana and an Avalonian promontory.Ministerio de Economia y Competitividad (MINECO) of Spain
CGL2015-71692-P
BES-2016-078168Australian Geophysical Observing SystemAustralian Education Investment Fund program
AQ44Australian Research Council
LE15010001
Understanding the destabilizing role for surface tension in planar shear flows in terms of wave interaction
Both surface tension and buoyancy force in stable stratification act to restore perturbed interfaces back to their initial positions. Hence, both are intuitively considered as stabilizing agents. Nevertheless, the Taylor-Caulfield instability is a counterexample in which the presence of buoyancy forces in stable stratification destabilize shear flows. An explanation for this instability lies in the fact that stable stratification supports the existence of gravity waves. When two vertically separated gravity waves propagate horizontally against the shear, they may become phase locked and amplify each other to form a resonance instability. Surface tension is similar to buoyancy but its restoring mechanism is more efficient at small wavelengths. Here, we show how a modification of the Taylor-Caulfield configuration, including two interfaces between three stably stratified immiscible fluids, supports interfacial capillary gravity whose interaction yields resonance instability. Furthermore, when the three fluids have the same density, an instability arises solely due to a pure counterpropagating capillary wave resonance. The linear stability analysis predicts a maximum growth rate of the pure capillary wave instability for an intermediate value of surface tension corresponding to We-1=5, where We denotes the Weber number. We perform direct numerical nonlinear simulation of this flow and find nonlinear destabilization when 2â€We-1â€10, in good agreement with the linear stability analysis. The instability is present also when viscosity is introduced, although it is gradually damped and eventually quenched. © 2017 American Physical Society
Vortices catapult droplets in atomization
International audienceA droplet ejection mechanism in planar two-phase mixing layers is examined. Any disturbance on the gas-liquid interface grows into a Kelvin-Helmholtz wave, and the wave crest forms a thin liquid film that flaps as the wave grows downstream. Increasing the gas speed, it is observed that the film breaks up into droplets which are eventually thrown into the gas stream at large angles. In a flow where most of the momentum is in the horizontal direction, it is surprising to observe these large ejection angles. Our experiments and simulations show that a recirculation region grows downstream of the wave and leads to vortex shedding similar to the wake of a backward-facing step. The ejection mechanism results from the interaction between the liquid film and the vortex shedding sequence: a recirculation zone appears in the wake of the wave and a liquid film emerges from the wave crest; the recirculation region detaches into a vortex and the gas flow over the wave momentarily reattaches due to the departure of the vortex; this reattached flow pushes the liquid film down; by now, a new recirculation vortex is being created in the wake of the wave--just where the liquid film is now located; the liquid film is blown up from below by the newly formed recirculation vortex in a manner similar to a bag-breakup event; the resulting droplets are catapulted by the recirculation vortex
HAPEX-Sahel : a large-scale study of land-atmosphere interactions in the semi-arid tropics
The Hydrologic Atmospheric Pilot EXperiment
in the Sahel (HAPEX-Sahel) was carried out in Niger, West Africa, during 1991 -
1992, with an intensive observation period (IOP) in August - October 1992. It
aims at improving the parameterization of land surface atmosphere interactions
at the Global Circulation Model (GCM) gridbox scale. The experiment combines
remote sensing and ground based measurements with hydrological and
meteorological modelling to develop aggregation techniques for use in large
scale estimates of the hydrological and meteorological behaviour of large areas
in the Sahel. The experimental strategy consisted of a period of intensive
measurements during the transition period of the rainy to the dry season, backed
up by a series of long term measurements in a 1° by 1° square in Niger. Three
"supersites" were instrumented with a variety of hydrological and
(micro) meteorological equipment to provide detailed information on the surface
energy exchange at the local scale. Boundary layer measurements and aircraft
measurements were used to provide information at scales of 100 - 500 km2.
All relevant remote sensing images were obtained for this period. This programme
of measurements is now being analyzed and an extensive modelling programme is
under way to aggregate the information at all scales up to the GCM grid box
scale. The experimental strategy and some preliminary results of the IOP are
described
Evidence for surface uplift of the Atlas Mountains and the surrounding peripheral plateaux: Combining apatite fission-track results and geomorphic indicators in the Western Moroccan Meseta (coastal Variscan Paleozoic basement)
This work represents an initial attempt to link the evolution of the topography in relation to the general tectonic framework of western Morocco. For this purpose, in a section of the Western Moroccan Meseta different tools are combined in order to attain the general objective. Apatite fission-track (AFT) data of granitic rocks of the RabatâKhenifra area give ages around 200 Ma with track length distributions which are compatible with the thermal models already established for the area. An inverse correlation between AFT ages and elevation is observed which is compatible with previous models indicating northward tilting of the whole Western Moroccan Meseta which is younger than 20â25 Ma. In order to test this possibility a detailed analysis of the topography at different scales in the Western Moroccan Meseta has been performed. Results indicate that two open folds with different amplitudes are recognized and that the one with wider wavelength could correspond to a lithospheric fold as previously stated by other authors on the basis of independent geological arguments. The northward tilting proposed based on the AFT data agrees with the results obtained in the analysis of the topography which reinforces the presence of a very open fold with a wavelength of 200â300 km in the north-western limb of the Western Moroccan Meseta
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