Search

International audience; Highlights: • We investigated multifunctionality and ecosystem services in agroecosystems. • 18 research questions, obstacles and solutions were identified. • Future research must integrate knowledge from different sectors and communities. • Biodiversity is a key factor to explore and incorporate into modelling approaches. • Promoting dialogue, standardization and data-sharing would enhance progress.Abstract:Agroecosystems are facing new challenges in the context of a growing and increasingly interconnected human population, and a paradigm shift is needed to successfully address the many complex questions that these challenges will generate. The transition to providing multiple services within an agroecosystem is a starting point for heightened multifunctionality, however, there is still hesitation among stakeholders about moving towards multi-service systems, largely because of the lack of knowledge linking productivity and multifunctionality. We reason that much of this reticence could be overcome through a better understanding of stakeholder requirements and innovative transdisciplinary research extended in the dimensions of time and space. We assembled experts in France to identify priority research questions for co-constructing projects with stakeholders. We identified 18 key questions, as well as the obstacles that hinder their resolution and propose potential solutions for tackling these obstacles. We illustrate that research into agroecosystem multifunctionality and service production must be a hugely collaborative effort and needs to integrate knowledge from different sectors and communities. Promoting dialogue, standardization and data-sharing would enhance transdisciplinary progress. Biodiversity is highlighted as a key factor to explore and incorporate into modelling approaches, but major advances must be made in the understanding of dynamic changes in the biodiversity-function-service nexus across landscapes. Resolving these research questions will allow us to translate knowledge into decision objectives, identify adaptation and tipping points in agroecosystems and develop social-ecological economic pathways that are adaptive over time.

The design of electrode material for energy production and storage devices is becoming more and more timely in a world where energy is an essential pillar for development. This context urges us to develop and study the capacitive properties of polyaniline composite films – mixed oxide of Ni0.6 Co2.4O4 which can be used as electrode material.In the present study, the mixed oxides of Ni0.6Co2.4O4 were synthesized by the sol gel method via propionic acid. Polyaniline – Ni0.6Co2.4O4 composite films deposited on a platinum substrate (Pt/PANI - Ni0.6Co2.4O4) were prepared by incorporating mixed nickel and cobalt oxide particles into the matrix of polyaniline. This process was realized by chronoamperometry by electropolymerization of the aniline monomer dissolved in a 0.5M HCl electrolytewithdifferent contents of Ni0.6 Co2.4 O4 oxides (0.5 g/L, 1 g/L).Physical and electrochemical characterizations were made with scanning electron microscopy (SEM) coupled with Energy Dispersive Spectroscopy (EDS), UV-visible spectroscopy,X-ray diffraction (XRD) and cyclic voltammetry.SEM, EDS, XRD and UV-visible analyzes confirmed the nature of the synthesized products and the incorporation of Ni0.6Co2.4O4 in the composite films. The electrochemical performance measurements of the Pt/PANI-Ni0.6Co2.4O4 film (1 g/L) give a specific capacity about 386.108 F.g -1, which is much higher than that of the Pt/ PANI, 164.340 F.g -1 at 5 mV/s. &nbsp

Gravity, magnetic and electrostatic separation methods allowed to obtain different titanium oxide concentrates (ilmenite, leucoxene, rutile) and different varieties of zircon concentrates (premium zircon, standard zircon, medium grade zircon standard) from Senegal’s heavy mineral sands. During mining separation, monazite, which is a paramagnetic mineral, was found in a non-negligible concentration of 0.57 wt% on average in the medium grade zircon standard which also contains 37.96 wt% zircon and 44.46 wt% titanium oxides. Magnetic and gravity separation tests were carried out on the Medium grade zircon standard (MGZS) to produce a monazite concentrate at Eramet Ideas laboratory. Magnetic separation at 1.5 teslas intensity resulted in the recovery of 94.8% of the monazite from the MGZS. Gravity separation also recovered 76.6% of the monazite from the MGZS. The combination of these two treatment methods can thus produce three concentrates from MGZS (a monazite concentrate, a zircon concentrate, and a titanium oxide concentrate).

The Sabodala gold mine is located in the Kedegou region in eastern Senegal near the border with Mali in a tropical Savannah climate zone with distinct wet and dry seasons. The mine has been operating since 2009 with active tailings deposition giving an ideal opportunity to study the weathering characteristics of carbonate rich tailings materials under real world conditions. The mine is operated in accordance with international best practice with regular monitoring of water quality and tailings chemistry in accordance with the international cyanide management code (ICMC) and also in order to monitor and control any potential impacts from Acid Rock Drainage and Metal Leaching (ARDML) that may be generated from the tailings materials and waste rock. In 2015 as part of a project looking at the potential for re-use of generated tailings as construction materials, a number of additional geochemical tests including whole rock assays, mineralogy, Acid Base Accounting in accordance with modified Sobek method with siderite correction, together with paste pH and electrical conductivity (Ec) measurements were undertaken. The purpose of the study was to update the predictions of the potential for ARDML generation and drainage pH in leachates forming from the Sabodala tailings. The tests were run on one composite weathered and 3 selective fresh samples collected by auger drilling on three holes over the tailing. Results have enabled a better understanding of the chemical weathering characteristics of finely ground tailings materials under tropical weathering conditions and the nature of secondary minerals precipitated.

The heavy mineral sands of Senegal are exploited to extract titanium oxides and zircon. Mining is carried out first by means of a floating dredge and concentration plant which produces a heavy mineral concentrate (HMC) containing on average 78% titanium oxides, 11% zircon and a set of silicate and alumino-silicate minerals. This heavy mineral concentrate is then treated by gravity, magnetic and electrostatic separation to produce titanium oxide concentrates (ilmenite, leucoxene, rutile) and three varieties of zircon concentrates (Premium zircon, standard zircon and medium grade zircon standard). In this study, we describe the various mineral concentrates in terms of mineralogical assemblages, and textural variability within grains, using Qemscan and Scanning Electron Microscopy. The titanium oxide concentrates are differentiated by their TiO2 content and vary from ilmenite to rutile. The zircon concentrates are characterized by the presence of impurities in the zircons, which consist in numerous inclusions of titanium oxides and silicate minerals. The mineralogical characteristics determined by scanning electron microscopy and by Qemscan showed great variability within the grains themselves. Heavy minerals contain many mineral inclusions and show strong chemical zoning.

This study assesses methodologies used during the selection of pilot products for the support to development of sustainable geographical indication projects by using the FAO/EBRD project as a case study. Relevant pilot products are essential to provide stakeholders with concrete experience, demonstrative effects and lessons learned in order to disseminate bets practices and facilitate scaling-out of sustainable GI processes. Qualitative data were transformed to quantitative data for product selection because data for local products were insufficient, and standard data were unavailable for each product. Analytic hierarchy process (AHP), simple scoring and geographical indication assessment form were used together as product selection methods. Gemlik Olives, the first registered geographical indication product in the Bursa province, was included during assessment as a control group. Six local products with a potential for GI registration were considered for pilot product selection to serve as demonstrative process. Results suggest that the most important selection criteria were “reputation of the product” and “power of the organisation” and first two ranked products selected for the project were Bursa Black Figs and Bursa Peaches.

International audience; In this paper, we use a laboratory experiment to analyze the effect of social preferences in a coordination game with Pareto-ranked equilibria. Inequality is increased by increasing the coordination payoffs of some subjects while the coordination payoffs of others remain unchanged. Theoretically, in this setting, inequality aversion may lead to a negative relationship between inequality and coordination success, while total payoff motivations lead to a positive relationship. Using a within-subject experimental design, we find that more inequality unambiguously yields a higher level of coordination success. Furthermore, this result holds even for subjects whose payoffs remain unchanged. Our results suggest that total payoff motivations drive the positive relationship between inequality and coordination success found in this experiment. Moreover, our data highlight that the order of treatment matters. Groups facing over time a reduction in inequalities reach the efficient outcome more often, over the entire experiment, compared to groups facing over time an increase in inequalities. This study thus contributes to understanding whether social preferences and variations in inequality affect the outcome of coordination problems.

Onion is an important vegetable in Senegal horticulture, where it occupies the first place. However in the greatest areas production like the Gandiolais, in the North of Senegal, Pink root disease caused by a soil born fungus Pyrenochaeta terrestris (Hansen) Gorentz, Walker and Larson affects its productivity especially in nursery. On soil sterilized and inoculated by the fungus, we tested 5 natural fungicides and 2 synthetic fungicides, to measure their effectiveness on the Pink root disease on onion, in nursery. The device used is a split plot with 4 repetitions and 8 treatments. The measured variables are the emergence rates, the survival rates and the infestation rates. Our experimentations have shown that, for the emergence rates, there is no significant difference between thiophanate-methyl (Pelt 44), Carbendazim (Bavistine), Azadirachta indica A. Juss and Carica papaya L. It is the same between C. papaya and Moringa oleifera Lam, between M. oleifera and Cassia alata L. It is also the same between C. alata and Crotolaria retusa L. Regarding the survival rates, there is no significant difference between thiophanate-methyl, Azadirachta indica, Carbendazim, C. papaya and M. oleifera. The same is true between M. oleifera and Cassia alata, and between C. alata and C. retusa. Concerning the infestation rates, apart from the control check, all other treatments show no difference.

The Sabodala gold mine tailings were stabilised using geopolymerization technics in order to improve their mechanical properties in general for a reuse as building materials for local communities. The effect of several preparation parameters on the compressive and tensile strength of the stabilised tailings has been studied to define their optimums. For each formulation, all parameters are kept constant and only one is variable. The prepared samples are then tested for compressive and tensile strength to see how the variable parameter impact on these properties. The same work was carried out for the fresh tailings and for the weathered one to see whether they behave differently and if they need different treatment. The results show that for most of parameters, there is an optimal value on either side of which compressive and tensile strength decrease. Except for few parameters, the fresh and the weathered tailings have a similar behaviour with regards to trends of their mechanical properties with changing preparation conditions. In addition to the similarity of weathered and fresh tailings mechanical characteristics following their stabilization by geopolymerization, this work has proved the considerable effects of the preparation’s parameters.

International audience; In this paper, we consider the controllability of a strongly degenerate parabolic equation with a degenerate one-order transport term. Despite the strong degeneracy, we prove a result of well-posedness and null controllability with a Dirichlet boundary control that acts on the degenerate part of the boundary. Then, we study the uniform controllability in the vanishing viscosity limit and prove that the cost of the control explodes exponentially fast in small time and converges exponentially fast in large time in some adapted weighted norm. The main tools used are a spectral decomposition involving Bessel functions and their zeros, some usual results on admissibility of scalar controls for diagonal semigroups, and the moment method of Fattorini and Russell. Keywords: degenerate parabolic equations, cost of the control, uniform controllability, degenerate transport equation.

The Sabodala gold deposit in the Mako volcanic Belt (SE-Senegal, West African Craton) occurs in mafic and ultramafic rocks overlain by clastic sedimentary rocks and felsic volcanic-volcaniclastic sequences. It is a structurally controlled mesothermal vein gold deposit developed in deformed rocks units near the Falombo pluton. The Sabodala Goldfield comprises several faults systems striking N-S to NE-SW. New structural evolution consisting of both thrusting and transcurrent events has been defined for the Sabodala Goldfield. The majority of the gold at Sabodala occurs on the western flank of a large, doubling plunging dome (the Sabodala Antiform) and is also associated with sinistral wrenching that overprints early structures within the Sabodala Mine. The gold bearing veins are hosted by flat lying and NW-trending shear zones. The NW-trending faults acted as transfers syn-gold mineralization, although only discrete segments of these faults were active during the main stage of gold mineralization. Late exhumation resulted in extension along fault zones was responsible for the juxtaposition of medium and low grade metamorphic rocks. The granitic suite of the Falombo pluton is linked to exhumation. Final dextral transpression postdating exhumation produced shearing and folding. Gold lodes developed during brittle deformation are associated with high fluid pressures in a northwest-southeast shortening regime. These are termed mainly the Sabodala deposit, and secondary the Niakafiri and Masato deposits.

In this paper we present a highly compact and low-cost antenna solution based on a dielectric lens and a waveguide horn array feed for operation in the 57–64 GHz frequency band. The antenna is targeted for applications in point-to-point backhaul systems for Small Cell mobile access networks and features a beamforming capability providing self-alignment for ease of installation and improved link stability.

In this paper, we deal with the existence of insensitizing controls for the Navier-Stokes equations in a bounded domain with Dirichlet boundary conditions. We prove that there exist controls insensitizing the $L^2$ -norm of the observation of the solution in an open subset $\mathcal{O}$ of the domain, under suitable assumptions on the data. This problem is equivalent to an exact controllability result for a cascade system. First we prove a global Carleman inequality for the linearized Navier-Stokes system with right-hand side, which leads to the null controllability at any time $T>0$. Then, we deduce a local null controllability result for the cascade system.

The use of computers in developing countries is quite novel. The aim of this article is to discuss problems related to the use of computers in developing countries and propose solutions. EFL teachers and students in these countries are encouraged to use computers in the educational systen7 because they are cost effective. It is hoped that once familiar with course authoring systems (CAS), EFL teachers will develop software programs adapted to their own social environment for the benefit of their students.

This paper shows geometric aspects of rock masses in the Senegalese side of Kedougou-Kenieba inlier. The studies are done in one part on sedimentary rocks (represented by sandstones) with stratification and on the other part in igneous rocks (represented by basalts). Geometric studies are the fractal configuration and the scale effect. Scale effect is stud- ied by comparing the results of mechanical tests done in the laboratory and on outcrops. For all samples, laboratory pa- rameters are higher than values of field. In this paper, scale effect is characterized by the decrease of mechanical pa- rameters from laboratory samples to field. The scale coefficient is defined and characterizes the relation between me- chanical properties. More importantly, the scale effect is more significant. This scale effect depends largely on the rock anisotropy. The anisotropy depends on the fracturation and the filling. The scale effect takes into account the fracturation, the filling minerals and their diversity which define the complexity of the rock. The anisotropy is complex; the impact of scale effect traduced by an increase of scale coefficient is the highest. Configuration of discontinuities also defines fractal geometry. This fractal aspect appears on the asperities, the spacing and the apertures of discontinuities. The fractal dimension is different from a parameter to another. All these two parameters estimate the stage of fracturation of the rock in a geological system and depend one on another if they are studied in the same element.

Wood polymer composites (WPCs) were made with pine and polypropylene matrix (PP). Samples of WPCs were processed through melt compounding and hot-press moulding with different formulations of wood flour content and addition of coupling agent. This study focuses on the improvement of the mechanical properties of WPCs through the addition of compatibilizers. Generally fiber/matrix bonding or a strong interaction is required to ensure an appropriate transfer of stresses and satisfactorily physical properties. The effect of wood content and coupling agent like Maleic anhydride grafted polypropylene (MAPP) on the thermal behavior was monitored by DSC, water uptake and thickness of swelling during 2 months. The results exhibited increase of these two physical properties with wood flour content and coupling agent. In the thermal behavior, wood plays the role of nucleating agent. During the cooling step, the crystallization begins earlier than in pure PP and the percent of crystallization increase with wood amount. The effects of the reinforcements on the mechanical properties of the composites as well as the effect of compatibilization on the composite properties were highlighted. The mechanical study revealed the positive effect of coupling agent MAPP on interfacial bonding permitting better stress transfer from matrix to fiber.

This Note is devoted to some insensitizing control problems for the Stokes system with a reduced number of controls. We give some e -insensitization results with external unidirectional forces in different geometric configurations. We also provide a negative result of insensitization for the Stokes system in some 2-D manifold without boundary with one scalar control.

The western part of the Kedougou Kenieba Inlier is located in the West African Craton. It consists of paleoproterozoic NE-trending elongate belts (subprovinces) of metavolcanic and granitic rocks that alternate with metasedimentary belts. Major linear fault such as the MTZ which also approximate a north-easterly trend form the eastern boundaries. The field observations and geophysics analyses were completed by a microscopic study. Based on these data we define across this region four lithostructural domains from east to west. The western domain is structurally complex. The rocks of this domain have been subjected to a complex history of polyphase deformation and metamorphism. The structural analyse allow us to distinguished three deformation events. The deformation results in the formation of D1 thrust tectonic and D2 and D3 transcurrent tectonic. The structural evolution of the Mako Belt is characterized by deformation dominated by the intrusion of large TTG batholiths (D1) followed by basins formation and transpression accommodating oblique convergence and collision (D2 and D3). The change from thrusting (D1 deformation to transcurrent motion (D2 and D3) is recorded in the marginal basin of the central domain and in Tinkoto pull apart basin. The timing of these basins indicates a diachronous evolution. Deformation styles within the basin are compatible with a dextral transpression which terminated at ca 2090 Ma. Small extensional basins formed over the rocks of the Mako Belt are filled with continental detrital sedimentary rocks that show weak foliation and active felsic volcanism. We suggest that the sinistral transpressive tectonic associated with oblique subduction may have generated the pull-apart basin and subaqueous volcanism. In part these features are now related to terrain accretion, thrusting and strike slip movement during oblique convergence. The inversion of the large scale structural evolution from thrusting to strike slip is common to modern orogenies.

The Kedougou Kenieba Inlier (KKI) (Paleoproterozoic of Eastern Senegal) is a portion of the West African Craton (WAC) containing a granite-greenstone terrain that experienced three distinct periods of magmatic activity, peaking at 2200, 2160–2130 and 2100–2070 Ma. In the Inlier, Paleoproterozoic granitoids and large-scale transcurrent shear zones are spatially associated, suggesting a genetic link between magma bodies and shear zones. Granitic intrusions are associated with all the volcanic episodes and phases of deformation, and have been used to constrain the age of many of these events. Our structural data and deformation sequence indicate that the Mako Greenstone Belt and the adjacent granitoid complexes have undergone a multi-phase evolutionary history that is spread over a prolonged period. The available geochronological data and field studies allowed classification of the granitoids of the KKI into four generations GI, GII, GIII and GIV. The current data suggest that the oldest rocks in the KKI, the Badon granites (2198 ± 2 Ma) and the tonalitic gneisses from Tonkouto (2200–2198 Ma) (GI), could be correlated with an early Birimian magmatic event. The gneisses, crystallized at depth, record the earliest deformation and in contrast to other tonalites, do not appear to have intruded volcanic rocks. The second manifestation of magmatism was intrusion of mafic diorite – the Gabbro Sandikounda Layered Igneous Complex type (GII) and development of the Laminia Kaourou Plutonic Complex (LKPC) (2160–2130 Ma). These bodies pre-date or are sometimes synchronous with a major deformational episode, and may, therefore, have formed very early in convergent Birimian orogenesis. The third major peak of magmatic activity occurred after the above major episode with the development of the oval shaped Diombalou and Bouroumbourou plutons (GIII). The orientation of these plutons parallel to the regional strike of the schistosity indicates structural control on granite emplacement. Eburnean magmatism was terminated in the Mako Belt following compressional Eburnean deformation, with the emplacement of the Tinkoto, Mamakono plutons (GIV) in the east of the complex and continued in the Diale–Dalema supergroup with the syntectonic emplacement of the Saraya batholith. Garnitiferous granites of crustal derivation were emplaced in the final period of extensional activity around 2080 Ma. Field observations suggest the early plutons of the complex granitic (Kakadian) batholith intruded during convergent deformation whereas later igneous activity accompanied regional orogen-parallel extension, followed by exhumation. In the Mako Belt, thickening of the crust was proposed to have caused heating and the ‘apparent diapiric rise’ of the Diombalou and Bouroumbourou plutons.

The Paleoproterozoic rocks in the Kedougou Kenieba Inlier (KKI) consist of volcanic and volcanosedimentary rocks intruded by granitoids with a wide compositional spectrum. Geochronological data based on single-grain zircon Pb-Pb evaporation, U-Pb single grain, Ar-Ar and K-Ar dating of several plutons point to a long lasting emplacement history in the KKI. The zircon data presented here yielded Paleoproterozoic ages for the emplacement/crystallization of the Badon granodiorite (2213 ± 3 to 2198 ± 2 Ma), tonalitic gneiss from Sandikounda (2194 ± 4 Ma), the Tinkoto pluton (2074 ± 9 Ma) as well as for the felsic host rocks of the Mamakono pluton (2067 ± 12Ma). The Badon granodiorite, formerly regarded to be relatively young and post-tectonic, is substantially older than all other known KKI intrusions. As a consequence, this new age may constrain the ongoing discussion on the existence of an Early Birimian cycle in the West African Craton (WAC). Ar-Ar and K-Ar ages on hornblende (2112 ± 12 and 2118 ± 31 Ma, respectively, in the tonalitic gneiss from Sandikounda) and biotite (2098 ± 26 and 2090 ± 21 Ma, respectively, in the Badon granodiorite) define an age of ca 2090 Ma, which is interpreted to mark the major tectonomagmatic episode in this part of the WAC. This is confirmed by the Paleoproterozoic ages of the Saraya, Tinkoto and Mamakono granite. A hydrothermal event at 2020 Ma followed the emplacement of the granitoids and caused the alteration of the Saraya granite. The new zircon ages, reflecting the magmatic and tectonothermal events in the study area correlate well with various magmatic and metamorphic events elsewhere in West Africa.

In the north of Senegal, the average annual rainfall has fallen to 300–400 mm because of the occurrence of drought. In addition, the soils are impoverished, with particularly low nitrogen content—less than 0.20 g N kg−1. Stylosanthes (Stylosanthes hamata) is a forage legume cover crop with high nitrogen fixing potential when inoculated with elite Bradyrhizobium strains such as strains ISRA 97 and ISRA 674 already selected in West Africa MIRCEN rhizobial culture collection. This species was used as a test plant to study the effect of drought stress on nodulation and nitrogen fixation, aiming at the recommendation of its cultivation in the north of Senegal. Use of S. hamata could therefore reach the objective to increase and to sustain soil productivity. A pot experiment was carried under greenhouse conditions to estimate the fixed nitrogen in stylosanthes after induced drought stress using the 15N isotope dilution technique. Maximum of fixation occurred when stylosanthes was inoculated with Bradyrhizobium ...

The photo-oxidation behavior under natural and accelerated conditions of polypropylene/layered silicate nanocomposite is studied in this article. The nanocomposites are prepared via simple melt mixing (extrusion and injection molding). The structure obtained is very dependent on the preparation mode and the modified clay used; mostly, exfoliation structure is produced. The nanocomposites start their photo-degradation earlier than the control samples polypropylene and polypropylene-graft-maleic anhydride with a higher oxidation rate for specimen produced by injection molding. This is explained by the presence of organiphilic-modified montmorillonite layers that trap the oxygen, increasing the oxygen pressure in the bulk and leading to a decrease of the induction period. Contrary to the control samples that display auto acceleration in their oxidation kinetics, the nanocomposites show a slight tendency to a plateau indicating a slowing down of the photo-oxidation process. This is ascribed to oxygen starvation that occurs in the nanocomposite. The acceleration factor is found to be higher for the nanocomposite comparatively of the control samples. With the aid of SF4 and NO treatments, the mechanism of photo degradation was found to be similar in PPgMA and its nanocomposites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

International audience; The Kédougou Kénieba Inlier (KKI) of eastern Senegal forms a typical Paleoproterozoic greenstone belt characterised by low-metamorphic sequences of volcanic rocks and volcano-sediments that have been intruded at various stages by gabbroic suites and calc-alkaline granitoids. The main structures of the KKI comprise two anastomosing structures about N–S trending shear belts that are distinguished into the western Main Transcurrent Zone (MTZ) and the eastern Senegalo-Malian shear zone system (SMSZ). These shear belts are taken to define the limits between the western Mako, the central Diale-Kéniebandi and the eastern Daléma-Kofi domains even though transitions exist between their characteristic deposition sequences.Remote sensing analysis of airborne geophysics and satellite data (Landsat, ENVI, SRTM) in combination with geological field mapping, structural analysis and geochronology suggests that the SMSZ represents a Birimian structure that records a main stage of deformation that could characterise the major transcurrent Eburnean tectonics (D2) dated from 2105 Ma (Feybesse et al., 2006a–e). This sinistral transpressive deformation marked by a major constraint oriented NNW–SSE, is accompanied by a NNE–SSW extension leading to the opening of dilational areas such as small pull-apart basins marked by local calk-alkaline volcanic sequences and several coeval intrusions of the Boboti Suite dated 2080 ± 0.9 Ma (Hirdes and Davis, 2002). A post-Birimian to pre-Neoproterozoic deformation post dates the transcurrent phase and is marked by regional N–S extension.Review of the existing Au-mineralisation models in combination with the spatial analysis of soil geochemical data suggest seven possible mineralisation styles that are related to the transpressional tectonics and coeval magmatism.

Nanocomposites of polypropylene-graft-maleic anhydride/clay were prepared by melt blending in an extruder mixer. The nanoscale dispersion of the clay in the polymer was analysed by wide-angle X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results of XRD and TEM showed that the nanocomposites obtained were a kind of intercalated-delaminated structures side by side with different dominant states, depending on the clay used and on the processing conditions. The consequences of photo-oxidation on the thermal stability and fire retardant properties of the nanocomposites were investigated using thermogravimetric analysis and cone calorimetry tests. It appeared that this degradation dramatically affected the important properties of the nanocomposites. A loss of thermal stability and fire retardant performance was observed. This was ascribed to scission reactions that occurred during the oxidative degradation prior to thermal and fire tests.

Birimian (Paleoproterozoic) granitoids and associated volcanic and sedimentary rocks from the Kedougou-Kenieba-Inlier (KKI) of Eastern Senegal have been analyzed for their major, trace, REE concentrations and their Sr-Nd isotopic compositions. The calc-alkaline I-type granitoids were previously divided into several structural groups. The new geochemical data, however, do not give evidence for this subdivision into pre-, syn- and post-deformational intrusions. The results demonstrate the juvenile character of the granitic igneous rock suite and its isotopic similarities to the adjacent volcanic Mako and sedimentary Diale-Dalema Supergroups. The Birimian rocks show uniform juvenile features such as low initial Sr isotopic composition (~0.700 to ~0.704), positive ∑Nd(t) values (2.1 to 4.3) and restricted Nd model ages (~2.0 to ~2.3 Ga). They preclude the contamination of the juvenile Birimian crust of the KKI by notable amounts of reworked Archean crustal material. Comparison with existing data helps to clarify the complex evolution of Birimian Supergroups of the WAC. It can be concluded that the Birimian rocks are the product of a large-scale crustal growth process with large amounts of juvenile crust formed from the depleted mantle in a geodynamic environment compared to modern volcanic arcs. These bimodal volcanic arcs were later accreted to the WAC.

Polypropylene-graft-maleic anhydride (PPgMA)/montmorillonite nanocomposites have been prepared using direct melt intercalation techniques (extrusion and injection molding). Characterization of the nanocomposites, performed with X-ray diffraction and transmission electronic microscope techniques, suggested an importance of the mode of preparation and the type of organic modification that was used in the montmorillonite on the dispersability of clay in the polymer matrix. Injected mold nanocomposites were generally exfoliated in opposite to extruded samples that presented different structures (exfoliated, immiscible). Thermal degradation and fire behaviour of the corresponding nanocomposites displayed an improvement in comparison to pure PPgMA; this improvement was more important for injected mold specimen than for the extruded ones. It was ascribed to the presence of clay layers which act as diffusion barriers and reduced the mass loss; results that got the support of Limiting Oxygen Index measurements. A deterioration of these properties was observed on UV-irradiated nanocomposites. This was ascribed to the generation of weak points issue from the photo-oxidation reactions that take place mainly on the sample surface as shown in the oxidation profile. The oxygen starvation and reduced radical mobility, due to the presence of clay platelets, are blamed to be responsible for this oxidation profile. On the other hand, pure PPgMA showed an outstanding improvement of the fire behaviour with ageing time. Improvement that was attributed to cross-linking reactions which create a compact structure that is less inclined to volatilize.

A field experiment was conducted at Bel Air station, in Dakar using 15N isotope dilution technique and the non nodulating soybean (Glycine max) variety m129 as reference plant to test the compatibility of Dichlorofenthion-thiram (DCT) fungicide to the inoculation of common bean (Phaseolus vulgaris) Paulista variety with both Rhizobium etli ISRA 353 and R. tropici strain ISRA 554. Nodulation was not induced with R. etli ISRA 353 and nitrogen fixation did not occur. With R. tropici ISRA 554, a decrease in nodulation was observed, but nitrogen fixation was not significantly different compared to that of the non DCT-treated common bean. (African Journal of Biotechnology: 2003 2(7): 198-201)

The purpose of this study is to report our experience on Pott's disease in Senegal, which belongs to the group of least-developed countries .In these countries, tuberculosis is still a public health issue. Regarding spine tuberculosis, we attempted to implement a diagnostic and therapeutic approach appropriate for our conditions of medical practice. The authors reported a retrospective epidemiological and clinical study of 255 patients suffering from tuberculosis of the spine. Theses patients were hospitalized at the University Hospital of Fann in Dakar from January 1986 to July 1998. Sixty percent came from the capital, the mean age was 34.9 years, there were 136 males for 119 females, and antituberculosis immunization were not done every time. Associated extra-spinal tuberculosis, predominantly tuberculosis of the lung, was observed in 28.2 patients (59%). Of 37 patients tested for human immunodeficiency virus (HIV) infection, only one was positive. Patients came late to the hospital, leading to a high percentage of neurological complications (79.2%). Our diagnostic strategy was based on epidemiological and clinical criteria already defined by Martini. Thoracic spine (53.8%) and lumbar sacral spine (21.7%) were the column vertebral segments most frequently involved. All patients received antituberculosis chemotherapy, and only 39 patients underwent surgery with laminectomy without posterior instrumentation. Functional outcome study was done for 89 paraplegic patients: 26 (29%) went to Frankel grade D or E and, among 27 operated patients, nine entered theses grades. Seventeen patients (11.5%) died. We developed the concept of "spinal-cord rescue," which focuses more on neurological rather than biomechanical issues.

The incorporation of various types of fillers into polymer matrices is an interesting route for producing polymer composites with different properties. Considerable research has focused extensively on the use of natural fibers as reinforcement materials in thermoplastic matrices. The utilization of vegetable fibers is driven by growing market trends in terms of environmental impact. The most common composites with natural fibers are made with polyolefin (polyethylene [PP] and polypropylene [PE]) and polyvinyl chloride (PVC) matrices and wood fibers as reinforcements. CONTENTS

International audience

Indigenous rhizobial population is among the factors which influence increased crop yield through inoculation with elite strains. In this study, we compared in greenhouse conditions the competitiveness of Rhizobium strain ISRA 355 for nodulation of the common bean (Phaseolus vulgaris) cultivated in different unsterile Senegal soils in terms of pH, N and C contents. The strain ISRA 355 produced a stable GUS+ transconjugant which was used for competition with indigenous soil rhizobia in six localities. At Bayakh, the transconjugant ISRA 355gusA was less competitive than the indigenous rhizobial strains, whereas in the other localities, it was more competitive since it occupied more than 90% of the nodules. Thus the Rhizobium strain ISRA 355 should be used for successfully inoculating the common bean in Senegal soils.

This paper focuses on the relationships between bilingualism, intelligence quotient (IQ) and errors made by learners in their attempt to master the rules of the target language(s). The first part of the paper explains the true nature of bilingualism contrarily to the controversial and stereotyped definitions found in the previous literature of the 1950’s: the author refers to Weinreich’s and Suzan Ervin Tripp’s definitions and explains that bilingualism is an asset instead of being something negative. The second part deals with the elusive, multifaceted and controversial nature of the concept of intelligence quotient and as a result, the author talks about the different trends in the literature related to intelligence quotient (IQ) and shows that the complex relationships between linguistic performance and intelligence quotient are co relational but not causal. The third part of the paper deals with the negative perceptions of mistakes and errors in second or foreign language learning. Actually, mistakes and errors are part and parcel of the learning process and must not be considered as signs of lack of intelligence on the part of the learners. Some interim constructions made by the learner are rather synonymous with linguistic creativity and the author alluded to the differences of perceptions between Anglophones and Francophones about the notions of mistakes and errors. In conclusion, the author urges learners and their parents not to have negative views about bilingualism, because he thinks that bilingualism is synonymous with linguistic creativity and open mindedness.

A greenhouse experiment was carried out in a sandy soil with a low available phosphorus to evaluate responsiveness of four Solanum aethiopicum cultivars to indigenous arbuscular mycorrhizal fungi. Results showed clear interaction between genetic variability of cultivars and fungal isolates on shoot biomass and on mineral status. Arbuscular mycorrhizal fungi can be ranked as Glomus aggregatum > Glomus mosseae > Glomus versiforme for improving yield as well as nitrogen, phosphorus, and potassium acquisition of Solanum cultivars. Key words : Arbuscular mycorrhizal fungi, Solanum aethiopicum, sterile soil, relative mycorrhizal dependency. African Journal of Biotechnology Vol.2(11) 2003: 429-433

Kyste Dermoide Extracranien Congenital de l\'Enfant - a Propos de 5 Cas Resume Description Le kyste dermoide extracrânien congenital est une tumeur benigne siegeant le plus frequemment sur la fontanelle anterieure. Il a ete decrit dans toutes les races. Objectif Le but de ce travail est de degager les caracteristiques epidemiologique, clinique, radiologique, chirurgicale et histologique avec une importante revue de la litterature. Methodes Il s\'agit d\'une etude retrospective concernant cinq jeunes patients admis de janvier 1968 a Decembre 2000 au service de Neurochirurgie du centre hospitalier universitaire de Fann a Dakar. Resultats Les auteurs rapportent 5 cas dont 4 etaient de sexe feminin. La lesion siegeait sur la fontanelle anterieure dans trois cas et sur la ligne mediane de l\'os frontal dans deux cas. La radiographie standard du crâne etait normale dans tous les cas. L\'echographie de la lesion a ete realisee dans deux cas et avait montre des zones hypo et hyperechogenes sans extension durale. Les suites operatoires ont ete tres simples. L\'examen anatomo-pathologique a diagnostique dans tous les cas un kyste dermoide. Conclusion Le kyste dermoide extracrânien congenital est une tumeur benigne. Son traitement reste chirurgical et seule une exerese complete evite la recidive. Background Congenital extracranial dermoid cyst is a benign tumour most frequently located on the anterior fontanel. It has been described in all races. Objective The purpose is to report the epidemiological, the clinical, the radiological and the surgical features. The pertinent litterature is also reviewed. Methods A retrospective study has been conducted from January 1968 to december 2000 about five young patients were admited at the neurosurgical unit at Fann university teaching hospital, Dakar. Results The s report 5 cases with a female-to-male ratio of 4 :1. The dermoid cyst over the anterior fontanel was found in 3 cases and 2 cases in the mid-forehead behind the anterior fontanel. The skull roentgenogram was normal in all cases. Sonography was perfomed in admission in 2 cases and showed the cyst with hypo and hyperechoic areas without any subdural extension. The post operative course was uneventful and the children were discharged without any neurological deficit. Pathology examination confirmed the diagnosis of dermoid cyst in all cases. Conclusion Congenital extracranial dermoid cyst is a benign tumour. The lesion should be treated surgically and radical removal is necessary to prevent recurrence. Keywords: Africa, Cranial dermoid cyst, Anterior fontanel, Afrique, Fontanelle anterieure, Kyste dermoide crânien Af J Neuro Sci: 2002 21(1)

A total of 62 bacterial strains (50 from Sahelian areas in Senegal, 3 from Mauritania, 8 from Mediterranean areas in Tunisia and 1 from Burundi) obtained from under Acacia raddiana trees, were compared with 51 reference strains of Rhizobium, Bradyrhizobium, Azorhizobium, Sinorhizobium and Agrobacterium. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDSPAGE) of proteins was used to determine the taxonomic positions of those mentioned and the relationships between strains obtained from the soil surface and those obtained from deep soil. Fiftyone strains could be placed in twelve protein electrophoretic clusters, seven of which were different from clusters containing various references or representative strains. The other 11 strains could not be placed in any group and are separated from one another. The possible relationships among electrophoretic groups, geographic origins and depths of isolation at a particular site are discussed. (Af. J. of Science and Technology: 2002 3(1): 34-44)

The influences of seasons, plant age, and physicochemical properties of the soil on surface and deep biological arbuscular mycorrhizal fungus parameters associated with Acacia albida were assessed in different areas of Senegal. More indigenous arbuscular mycorrhizal propagules were found in the localities of the Sudano-Guinean zone (Djinaki and Kabrousse) than in those of the Sahelian zone (Louga and Diokoul), and species belonging to the genera Glomus, Gigaspora, Acaulospora , and Sclerocystis prevailed. The numbers of total and viable spores increased more during the rainy season than during the dry season (about 108% more total spores and 262% more viable spores). Similarly, both total and viable spores were more prevalent around young Acacia trees than old trees. However, the intensities of root colonization did not differ in each ecoclimatic zone.