231 research outputs found
Land Cover Land Use Change and Soil Organic Carbon Under Climate Variability in the Semi-Arid West African Sahel (1960-2050)
Land Cover Land Use (LCLU) change affects land surface processes recognized to influence climate change at local, national and global levels. Soil organic carbon is a key component for the functioning of agro-ecosystems and has a direct effect on the physical, chemical and biological characteristics of the soil. The capacity to model and project LCLU change is of considerable interest for mitigation and adaptation measures in response to climate change. A combination of remote sensing analyses, qualitative social survey techniques, and biogeochemical modeling was used to study the relationships between climate change, LCLU change and soil organic carbon in the semiarid rural zone of Senegal between 1960 and 2050. For this purpose, four research hypotheses were addressed. This research aims to contribute to an understanding of future land cover land use change in the semi-arid West African Sahel with respect to climate variability and human activities. Its findings may provide insights to enable policy makers at local to national levels to formulate environmentally and economically adapted policy decisions. This dissertation research has to date resulted in two published and one submitted paper
Toxic effects of neem products (Azadirachta indica A. Juss) on Aedes aegypti Linnaeus 1762 larvae
Treatment and comparative analysis of the properties of aqueous extracts of seed kernel of Azadirachta indica A. Juss (neem) was carried out on Aedes aegypti larvae. The aim of this work was to evaluate lethal effects of neem products (1% Suneem, formulated neem oil and neem powder) on A. aegypti larvae. Assays showed that A. indica was toxic to larvae of A. aegypti. For 1% Suneem, 1% formulatedneem oil and neem powder, the lethal concentrations and lethal time at 50% (LC50 and LT50) for A. aegypti were 2 and 8 mg/l after 24 h and 3 mg/l after 120 h, respectively. Assays showed that Suneemand Formulated neem oil were more toxic to A. aegypti than Neem powder. Both products of the neem (A. indica, A. juss) have a remarkable influence on the development of A. aegypti larvae, causing an inhibition of nymphs and adults emergency. The Histopathological results revealed a serious damage on the epithelial columnar cells, a perturbation of alimentary flow, slightly hypertrophied cells, abeginning of vacuolisation on apical level, and a bursting of some cells in posterior part of the gut. However, nuclei, adipose tissue and muscles seem to keep normal appearance
Historical and simulated ecosystem carbon dynamics in Ghana: land use, management, and climate
International audienceWe used the General Ensemble biogeochemical Modeling System (GEMS) to simulate responses of natural and managed ecosystems to changes in land use, management, and climate for a forest/savanna transitional zone in central Ghana. Model results show that deforestation for crop production during the last century resulted in a substantial reduction in ecosystem carbon (C) stock from 135.4 Mg C ha?1 in 1900 to 77.0 Mg C ha?1 in 2000, and in soil organic C stock within the top 20 cm of soil from 26.6 Mg C ha?1 to 21.2 Mg C ha?1. If no land use change takes place from 2000 through 2100, low and high climate change scenarios (increase in temperature and decrease in precipitation over time) will result in losses of soil organic C stock by 19% and 25%, respectively. A low nitrogen (N) fertilization rate is the principal constraint on current crop production. An increase in N fertilization under the low climate change scenario would increase crop yield by 14% with 30 kg N ha?1 and by 38% with 60 kg N ha?1, leading to an increase in the average soil C stock by 12% and 29%, respectively, in all cropland by 2100. The results suggest that the climate changes in the future from current climate conditions will not necessarily become a determinant control on ecosystem C fluxes and crop production, while a reasonable N fertilization rate is critical to achieve food security and agricultural sustainability in the study area through the 21st century, and current cropping systems could be optimized to make full use of the rainfall resource
Efficacite agronomique du compost a base de la biomasse du « neem » et de lâanacarde sur des cultures maraicheres dans la zone des Niayes au Senegal
Dans la zone des Niayes au SĂ©nĂ©gal, les sols sont pauvres en matiĂšres organiques et en Ă©lĂ©ments nutritifs nĂ©cessaires aux plantes. Les engrais chimiques utilisĂ©s pour amĂ©liorer les rendements ont engendrĂ© une forte pollution des sols et de la nappe phrĂ©atique. Lâobjectif de cette Ă©tude est dâĂ©valuer la valeur agronomique du compost fabriquĂ© Ă base des feuilles de neem et dâanacarde, de fiente de volaille et de la cendre de bois. Le compost obtenu prĂ©sente un rapport C/N de 15,49 et des teneurs en N - P - K de 9,1, 14,8 et 7,3 mg/kg, respectivement. Les diffĂ©rentes doses du compost testĂ©es sur des cultures maraichĂšres ont rĂ©vĂ©lĂ©Â des performances agronomiques meilleures par rapport aux tĂ©moins. La dose T3 (30 t/ha) a induit les meilleurs rendements pour la tomate (27,213 t/ha) et lâoignon (105,263 t/ha). Pour le chou et la pomme de terre, la dose T1 (10 t/ha) a permis dâobtenir les meilleurs rendements (144,533 t/ha et 55,163 t/ha, respectivement). Par contre pour le poivron, la dose T2 (20 t/ha) a favorisĂ© les meilleurs rendements (32,534 t/ha) avec un poids moyen (81,748g) et un nombre de fruits/rĂ©colte considĂ©rablement plus Ă©levĂ©. Ce compost pourrait constituer une alternative rĂ©elle Ă lâutilisation abusive de lâengrais minĂ©ral dans la zone agricole des Niayes.Mots clĂ©s : Compost, Neem, Feuilles dâanacarde, Maraichage, SĂ©nĂ©ga
Etude de lâactivitĂ© antifalcĂ©miante dâextraits de racines de Leptadenia hastata Decne. (Asclepiadacae)
Lâobjectif de cette Ă©tude est dâĂ©valuer lâactivitĂ© antifalcĂ©miante dâextraits de racines de Leptadenia hastata sur des hĂ©moglobines falciformes et dâidentifier les principes actifs Ă lâorigine de cette activitĂ©. La mĂ©thode employĂ©e Ă©tudie la rĂ©versibilitĂ© des drĂ©panocytes, en fonction du temps dâincubation des extraits par rapport aux tĂ©moins (eau physiologique, phĂ©nylalanine et arginine) sur des Ă©chantillons de sang de patients drĂ©panocytaires homozygotes. Des concentrations de 0,05; 0,5; 5 et 10 mg/ml de quatre extraits (mĂ©thanol, hexane, acĂ©tate dâĂ©thyle et mĂ©thanol rĂ©siduel) ont Ă©tĂ© mises en contact avec des drĂ©panocytes de type SS aprĂšs avoir provoquĂ© leur falciformation avec une solution Ă 2% de mĂ©tabisulfite de sodium. LâĂ©valuation a Ă©tĂ©Â effectuĂ©e toutes les 30 minutes pendant 120 minutes. Les diffĂ©rents extraits ont montrĂ© une activitĂ© dosedĂ©pendante sur la rĂ©versibilitĂ© de la falciformation des globules rouges avec plus de 80% dâinversion en 120 minutes pour lâextrait mĂ©thanolique, le plus actif. Un screening phytochimique a permis de faire une corrĂ©lation entre les flavonoĂŻdes et lâactivitĂ© antifalcĂ©miante des extraits de Leptadenia hastata.Mots clĂ©s : DrĂ©panocytose, hĂ©moglobine, activitĂ© antifalcĂ©miante, Leptadenia hastata, flavonoĂŻdes
Do drugs interact together in cardiovascular prevention? A meta-analysis of powerful or factorial randomized controlled trials.
To explore whether preventive cardiovascular drugs (antihypertensive, antiplatelet, lipid lowering and hypoglycemic agents) interact together in cardiovascular prevention.
We searched PubMedÂź, Web of scienceâą, Embase and Cochrane library for powerful randomized placebo-controlled trials (>1000 patients). We explored whether drug effect on major vascular events changed according to cross-exposure to other drug classes or to cardiovascular risk factors (hypertension or type 2 diabetes), through a meta-analysis of relative odds ratio computed by trial subgroups. A significant interaction was suggested from confidence intervals of the ratio of odds ratios, when they excluded neutral value of 1.
In total, 14 trials with 178,398 patients were included. No significant interaction was observed between co-prescribed drugs or between these medications and type 2 diabetes/hypertension status.
Our meta-analysis is the first one to evaluate drug-drug and drug-hypertension/type 2 diabetes status interactions in terms of cardiovascular risks: we did not observe any significant interaction. This indirectly reinforces the rationale of using several contrasted mechanisms to address cardiovascular prevention; and allows the combination effect prediction by a simple multiplication of their odds ratios. The limited availability of data reported or obtained from authors is a strong argument in favor of data sharing
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