244 research outputs found
Ăvaluation du niveau de pollution par les mĂ©taux lourds des lacs Bini et Dang, RĂ©gion de lâAdamaoua, Cameroun
La prĂ©sente Ă©tude a pour objectif principal dâĂ©valuer le niveau de pollution mĂ©tallique des lacs Bini et Dang (NgaoundĂ©rĂ©, Cameroun) Ă travers lâanalyse des eaux et des sĂ©diments de surface. La concentration des mĂ©taux lourds (Ni, Cr, Fe, Pb, Cd, Zn) a Ă©tĂ© mesurĂ©e par spectrophotomĂ©trie dâabsorption atomique. Des rĂ©sultats obtenus, il ressort que les Ă©lĂ©ments Ni, Fe, Cr, Pb et Cd ont des teneurs Ă©levĂ©es dans les eaux des deux lacs comparĂ©s aux normes OMS sur les eaux de boisson et aux normes canadiennes sur la protection de la vie aquatique. Afin dâĂ©valuer le niveau de contamination des sĂ©diments des deux lacs, le facteur dâenrichissement (FE) et lâindice de gĂ©oaccumulation (I-gĂ©o) ont Ă©tĂ© calculĂ©s.Ainsi, le cadmium prĂ©sente des FE forts Ă trĂšs forts alors que le plomb affiche des FE modĂ©rĂ©s Ă forts. LâIgĂ©o varie dâune forte contamination Ă une contamination extrĂȘme pour le cadmium. Cet index est modĂ©rĂ© Ă fort pour le plomb et modĂ©rĂ© pour le fer. Les sĂ©diments du lac de Dang sont dans lâensemble les plus contaminĂ©s en mĂ©taux lourds par rapport Ă ceux du lac Bini. Les activitĂ©s agricoles, les rejets des eaux usĂ©es domestiques et les dĂ©charges incontrĂŽlĂ©es sont considĂ©rĂ©s comme principales sources de pollution des deux lacs.Mots-clĂ©s : bini, dang, mĂ©taux lourds, lac, sĂ©diment
Analyse du fonctionnement biologique du sol par l'étude de la nématofaune : semis direct versus labour sur les hautes terres prÚs d'Antsirabé (Madagascar)
International audienceLes nématodes du sol possÚdent des qualités multiples (abondance, diversité taxonomique et fonctionnelle, existence d'indices liés à l'état du sol) qui en font des indicateurs pertinents du fonctionnement du sol. Ils intÚgrent un grand nombre d'informations sur l'état de la micro-chaßne trophique du sol (compartiment microbien, microfaune et mésofaune) qui est responsable de la décomposition et de la minéralisation des nutriments. La nématofaune a été analysée dans un essai comparant le semis direct avec restitution des résidus de récolte, au labour avec exportation des résidus de récolte dans une rotation soja/riz sur les hautes terres de Madagascar. Les résultats obtenus durant les deux années d'étude (année en soja & année en riz) ne sont pas significativement différents pour une grande majorité de paramÚtres nématologiques ce qui signifie qu'à moyen terme de cette expérience (essai mis en place depuis 10 ans), les différences interannuelles liées à la culture sont trÚs inférieures aux différences liées au travail du sol et à la fertilisation. L'absence de travail du sol simultané à la restitution des résidus de récolte, ainsi que la fertilisation minérale et organique, induit une augmentation de l'abondance de la nématofaune tellurique. L'analyse de la composition de la nématofaune indique que les densités de nématodes phytophages d'une part et de nématodes omnivores et prédateurs d'autre part, sont significativement augmentées dans les systÚmes en semis direct, alors que les fertilisations organiques et minérales induisent une augmentation de la plupart des groupes trophiques incluant également les microbivores (bactérivores et fongivores). L'analyse des indices nématofauniques montre que le travail du sol ainsi que l'absence de fertilisation sont aussi responsables de la simplification qualitative de la micro-chaßne trophique du sol. Les systÚmes en semis direct présentent une nématofaune plus complexe et moins opportuniste incluant des taxons sensibles aux perturbations contrairement au systÚme labouré
Investigation of the Mechanism of Apatite/Carbonates Separation in Acidic Flotation Process Using In Situ Raman Spectroscopy
The separation of phosphate from carbonate gangue using ïŹotation is extremely complex due to the similarities in surface properties. The acidic flotation process of carbonates at pH 4.5-5.0 followed by a direct phosphate flotation uses phosphoric acid as depressor of apatite during carbonate flotation. The mechanism of apatite depression is rather hypothetical because of lack of data on the surface speciation in such a complex mineral suspension. A real-time method for in situ control of surface compounds on the minerals (carbonated hydroxylapatite and calcite) using a submerged Raman analyzer probe is proposed in this work to collect the data on the nature and kinetics of phase formed. The carbonated hydroxyfluorapatite (C-HFAp) and calcite reactivity in phosphoric acid at concentrations between 0 and 1 M) during 15 minutes was studied. The Raman spectra collected in situ and ex situ showed the peak at 1085 cm-1 of calcium carbonate at 10-3 and 10-1 M on the surface of hydroxyfluorapatite that disappears at high acid concentration. Kinetics studies performed at 4.6 (±0.1) pH range during 15 minutes showed calcium carbonate formation after 2 minutes of conditioning and that disappears after three minutes (Figure 1). The infrared spectra of C-HFAp in presence of phosphoric acid showed at 10-3 and 10-1 M new peak at 713 cm-1 that belongs to calcium carbonate vibrations which seems to be due to C-HFAp surface conversion as observed on XRD patterns.
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Etude de lâeffet dâune source dâinoculum externe sur la propagation du CABMV (Cowpea aphid â borne mosaic virus) selon la proximitĂ© des parcelles voisines et la variĂ©tĂ© de niĂ©bĂ©
Un champ ensemencĂ© avec des semences de qualitĂ© peut se retrouver voisin avec un autre ensemencĂ©Â avec des semences infectĂ©es par le virus de la mosaĂŻque du niĂ©bĂ©. Ce virus est transmis par les semences Ă des taux de 0 Ă 40% selon les variĂ©tĂ©s. Ces semences infectĂ©es donnent des jeunes plantes virosĂ©es Ă partir desquelles les pucerons vont propager la maladie. Ce travail a Ă©tĂ© effectuĂ© pour dĂ©terminer la distance minimale permettant dâĂ©viter des contaminations Ă partir dâinoculum externe suivant la sensibilitĂ© de la variĂ©tĂ©. Ainsi, deux parcelles centrales de 300 m2 ont Ă©tĂ© semĂ©es avec des graines de Gorom local contaminĂ©es Ă 0,5% par le virus. Autour de la premiĂšre parcelle centrale, 4 parcelles de 200 m2 chacune ont Ă©tĂ© semĂ©es avec des graines de Gorom local indemnes de virus aux distances respectives de 10 m, 15 m, 20 m et 25 m. Autour de la deuxiĂšme parcelle centrale, des semences indemnes de virus de Kvx61-1 ont Ă©tĂ© utilisĂ©es. Un dispositif similaire a Ă©tĂ© constituĂ© pour les parcelles tĂ©moins avec des semences indemnes de virus. La propagation de la maladie a montrĂ© quâelle est liĂ©e Ă la variĂ©tĂ©, aux pucerons et Ă la distance avec la source dâinoculum.© 2015 International Formulae Group. All rights reserved.Mots clĂ©s: Semences indemnes de virus, semences contaminĂ©es, distance minimale, puceronsEnglish Title: Study of the effect of external inoculum source on CABMV (Cowpea aphid â borne mosaic virus) spread in relation to the proximity of neighboring plots and the cowpea varietyEnglish AbstractA field sown with quality seeds can be closed to another one sown with seeds infected by cowpea mosaic virus which is seed transmitted at rates ranging from 0 to 40% depending on cowpea varieties. Infected seeds germinate and grow into virus-infected seedlings from which aphids will spread the disease. This  research was carried out in order to determine the minimum distance needed for avoiding contaminations from external virus inoculum sources, in relation with the susceptibility of cowpea varieties. Thus, two central plots of 300 mÂČ have been sown with contaminated seeds at 0.5% by CABMV of cowpea variety Gorom local. Around the first central plot, four plots of 200 mÂČ each were sown with virus-free seeds of Gorom local at respective distances of 10 m, 15 m, 20 m and 25 m. Around the second central plot, virus-free seeds of Kvx61- 1 have been used. A similar layout was done for the control plots with virus-free seeds. It was found that the spread of the disease was related to the cowpea variety, the aphids and the distance from the inoculum source.© 2015 International Formulae Group. All rights reserved.Keywords: Virus-free seeds, contaminated seeds, minimum distance, aphid
Treatment of asymptomatic carriers with artemether-lumefantrine: an opportunity to reduce the burden of malaria?
Background: Increased investment and commitment to malaria prevention and treatment strategies across Africa has produced impressive reductions in the incidence of this disease. Nevertheless, it is clear that further interventions will be necessary to meet the international target of a reversal in the incidence of malaria by 2015. This article discusses the prospective role of an innovative malaria control strategy - the community-based treatment of asymptomatic carriers of Plasmodium falciparum, with artemisinin-based combination therapy (ACT). The potential of this intervention was considered by key scientists in the field at an Advisory Board meeting held in Basel, in April 2009. This article summarizes the discussions that took place among the participants.
Presentation of the hypothesis: Asymptomatic carriers do not seek treatment for their infection and, therefore, constitute a reservoir of parasites and thus a real public-health risk. The systematic identification and treatment of individuals with asymptomatic P. falciparum as part of a surveillance intervention strategy should reduce the parasite reservoir, and if this pool is greatly reduced, it will impact disease transmission.
Testing the hypothesis: This article considers the populations that could benefit from such a strategy and examines the ethical issues associated with the treatment of apparently healthy individuals, who represent a neglected public health risk. The potential for the treatment of asymptomatic carriers to impair the development of protective immunity, resulting in a \u27rebound\u27 and age escalation of malaria incidence, is also discussed. For policymakers to consider the treatment of asymptomatic carriers with ACT as a new tool in their malaria control programmes, it will be important to demonstrate that such a strategy can produce significant benefits, without having a negative impact on the efficacy of ACT and the health of the target population.
Implications of the hypothesis: The treatment of asymptomatic carriers with ACT is an innovative and essential tool for breaking the cycle of infection in some transmission settings. Safe and effective medicines can save the lives of children, but the reprieve is only temporary so long as the mosquitoes can become re-infected from the asymptomatic carriers. With improvements in rapid diagnostic tests that allow easier identification of asymptomatic carriers, the elimination of the pool of parasites is within reach. © 2010 Ogutu et al; licensee BioMed Central Ltd
Morphology Evaluation of ZrO2 Dip Coating on Mild Steel and its Corrosion Performance in NaOH Solution
In this work, the morphology of ZrO2 thin film from dip coating process on mild steel has been investigated. Mild steel was dip-coated on solution made of zirconium butoxide as a precursor, ethanol as solvent, acetylacetone as chelating agent and water for hydrolysis. Number of dipping was adjusted at 3, 5 and 7 times. The dipped sample then annealed at 350°C for two hours by adjusting the heating rate at 1°C/min respectively. The optical microscope showed that micro-cracks were observed on the surface of the coating with its concentration reduced as dipping sequence increased. The XRD result showed that annealing process can produce polycrystalline tetragonal-ZrO2. Meanwhile, SEM image showed that the thicknesses of the ZrO2 coatings were in between 400-600 nm. The corrosion resistance of uncoated and coated substrates was studied by polarization test through potentio-dynamic polarization curve at 1mV/s immersed in with 3.5% NaCl. The coating efficiency was improved as the number of layer dip coated increased, which showed improvement in corrosion protection
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