A Typical Sublithospheric Mantle beneath the Tello Region, SE-Ngaoundéré (Cameroon Line)

Peridotite xenoliths,raised to the surface by alkaline basalts or kimberlites,provide us direct information on the processes and composition of the upper mantle.They are the major source of information on the state of stress,pressure and temperature in the deep mantle.They are thus a source of petrological and geochemical information that is generally not available on the Earth’s surface.Fresh spinel-lherzolite xenoliths exhibit a protogranular components of the Tello volcano.The Tello is the continental sector of the Cameroon Line,located in the South East of the town of Ngaoundéréat 75 km approximately between(N7°13’,N7°14’)and(E13°40’and E13°60’).Minerals’composition of the xenoliths is~64%olivine,~24%orthopyroxene,~11%clinopyroxene and~1%spinel.Significant variation in(Cr/Cr+Al)of the system shows the reciprocal nature of the spinel solution.The Tello spinel lherzolites show internal chemical homogeneity and represent a normal upper mantle.Their mineral chemistries suggest equilibrium condition of 830°-925°and 1.4 GPa-2.3 GPa.These data suggest that there is good correlation bracket between increasing activity of Al2O3 and decreasing of practionning of TiO2 into spinel.The AlIV and AlVI contents vary by 0.05-0.2 and 0.03-0.2 respectively.The majority of samples caracterise the lithospheric mantle.

The role of marine protected areas in sustaining fisheries: The case of the National Park of Banc d’Arguin, Mauritania

Mauritania is characterized by fast-growing fisheries that have developed over the past several decades from low levels of fishing to intense fishing and have led to severe decreases in biomass and severe signs of overexploitation.To ensure sustainable fisheries,a primary goal of science-based fisheries policy is to provide an adequate conservation status of marine habitats that are directly,or indirectly,fundamental for the lifecycle of fish populations of commercial interest.The National Park of Banc d’Arguin has been recognized for its nursery and fish biomass export functions.In this paper,we present the economic value of the fish provisioning service of marine coastal ecosystems of the protected area.We estimated the added value of artisanal fisheries,the spatial distribution of fishing activities,the contribution of the Park to the Mauritanian fisheries and the heritage value of artisanal fisheries.Overall,the average added value for artisanal fisheries is about 43 million MRU(1 million euros)over the period 2006–2017.It mainly benefits to the ship-owners,which generates inequalities and threatens the livelihoods of the Imraguen.The spatial distribution of fishing activities and associated revenues shows high variability throughout the years,the seasons and the geographic areas,and reveals the high adaptability of Imraguen fishers.Fishing grounds are mostly located close to the shore,associated with seagrass beds,confirming the service of fish provisioning rendered by this ecosystem.Furthermore,the high productivity of seagrass beds contributes to the spill-over of biomass.The contribution of the Park to fishing activities that occur within the Mauritanian Exclusive Economic Zone is estimated to 15%,representing an added value creation of 3.2 billion MRU(71 million euros).The heritage value of the fisheries is assessed,through fishers’willingness to accept to stop their fishing activities,at 17.5 million MRU(0.4 million euros).Thus,this paper highlights the necessity of incorporating an ecosystem-based approach along with fishers’knowledge and adaptability into future conservation plan of the National Park of Banc d’Arguin and fisheries management at the local,national and regional scale.

Photoexcitation dynamics in solution-processed formamidinium lead iodide perovskite thin films for solar cell applications

Formamidinium lead iodide(FAPbI3)is a newly developed hybrid perovskite that potentially can be used in high-efficiency solution-processed solar cells.Here,the temperature-dependent dynamic optical properties of three types of FAPbI3 perovskite films(fabricated using three different precursor systems)are comparatively studied.The time-resolved photoluminescence(PL)spectra reveal that FAPbI3 films made from the new precursor(a mixture of formamidinium iodide and hydrogen lead triiodide)exhibit the longest lifetime of 439 ns at room temperature,suggesting a lower number of defects and lower non-radiative recombination losses compared with FAPbI3 obtained from the other two precursors.From the temperature-dependent PL spectra,a phase transition in the films is clearly observed.Meanwhile,exciton-binding energies of 8.1 and 18 meV for the high-and lowtemperature phases are extracted,respectively.Importantly,the PL spectra for all of the samples show a single peak at room temperature,whereas at liquid-helium temperature the emission features two peaks:one in higher energy displaying a fast decay(0.5 ns)and a second red-shifted peak with a decay of up to several microseconds.These two emissions,separated by~18 meV,are attributed to free excitons and bound excitons with singlet and triplet characters,respectively.

On Lateral-Torsional Buckling of Non-Local Beams

Nonlocal continuum mechanics allows one to account for the small length scale effect that becomes significant when dealing with micro-or nanostructures.This paper deals with the lateral-torsional buckling of elastic nonlocal small-scale beams.Eringen’s model is chosen for the nonlocal constitutive bendingcurvature relationship.The effect of prebuckling deformation is taken into consideration on the basis of the Kirchhoff-Clebsch theory.It is shown that the application of Eringen’s model produces small-length scale terms in the nonlocal elastic lateraltorsional buckling moment of a hinged-hinged strip beam.Clearly,the non-local parameter has the effect of reducing the critical lateral-torsional buckling moment.This tendency is consistent with the one observed for the in-plane stability analysis,for the lateral buckling of a hinged-hinged axially loaded column.The lateral buckling solution can be derived from a physically motivated variational principle.