1,145 research outputs found
SynthÚse d'un sulfatoferrate de potassium et son efficacité dans le traitement des eaux
Depuis le milieu du siĂšcle dernier, nous savons que le fer existe Ă son degrĂ© d'oxydation supĂ©rieur VI dans l'ion tĂ©traoxoferrate(VI) FeO42-, isostructural de SO42-, CrO42-, MnO42-. Cette espĂšce mise en solution aqueuse oxyde l'eau en O2, et ce quelque soit le pH de cette solution. La vitesse de cette rĂ©action est trĂšs grande en milieu acide, plus lente en milieu alcalin oĂč elle conduit Ă la prĂ©cipitation de Fe(OH)3. On peut donc envisager son emploi comme rĂ©actif polyfonctionnel : oxydant et floculant, dans le traitement de certaines eaux. La premiĂšre partie de ce travail dĂ©crit une voie originale de synthĂšse Ă l'Ă©tat solide, Ă la tempĂ©rature ambiante, du sel de formule K2(Fe,S)O4, appelĂ© sulfatoferrate de potassium, qui contient l'entitĂ© FeO42-. En effet, jusqu'Ă ce jour seules des synthĂšses par voie aqueuse, Ă rendements trĂšs faibles, chimiques ou Ă©lectrochimiques, ont Ă©tĂ© utilisĂ©es pour obtenir FeO42-.Dans une seconde partie, nous avons mesurĂ© les propriĂ©tĂ©s oxydantes et floculantes du sulfatoferrate de potassium agissant sur deux types d'eaux usĂ©es urbaines, chargĂ©es (MEST=258 mg.L-1, DCO=549 mg.L-1) et peu chargĂ©es (MEST=9 mg.L-1, DCO=37 mg.L- 1). Cette Ă©tude effectuĂ©e en collaboration avec le Centre International de l'Eau de Nancy (NANC.I.E.) nous a permis de prĂ©ciser les conditions optimales d'emploi de K2(Fe,S)O4 et de comparer ses performances Ă celles de FeCl3.6H2O et Al2(SO4)3.18H2O.Sur une eau chargĂ©e, l'abattement de la MEST est meilleur avec FeCl3.6H2O et Al2(SO4)3.18H2O, tandis que K2(Fe,S)O4 est plus efficace vis Ă vis de l'abattement de la DCO.Sur une eau peu chargĂ©e, c'est l'effet bactĂ©ricide de K2(Fe,S)O4 qui est le plus remarquable; une dose de 10 mg.L-1 en fer (VI) anĂ©antit 99,70% des coliformes totaux et 99,90% des coliformes fĂ©caux.Tetraoxoferrate(VI), FeO42-, possesses properties which make it potentially useful in certain areas of water purification: it is an excellent oxidizing agent, it has a powerful bactericidal action and it spontaneously decomposes over a short period of time. When reduced, the FeO42- ion generates base in solution and a Fe(OH)3 type gel which precipitates and carries down with it other ions (precipitation of hydroxide metal salts). These properties make ferrate(VI) useful in water disinfection and in wastewater treatment because it acts by an oxidation-coagulation-precipitation process. Iron, in its familiar form exists in the (II) and (III) oxidation states; ferrate(VI) ion has long been known, but, due to its instability and difficulty of preparation, it has not been studied extensively and has not been industrially produced. In this paper, we recommend a method of synthesis of alkali ferrate(VI) salts by a dry powder process, which occurs at room temperature and can be easily used for industrial production of Fe(VI). To minimize ferrate(VI) decomposition, we proceed in a strong alkaline medium (presence of a strong base like potash or caustic soda) where oxidation of an iron (bivalent or trivalent) containing salt becomes easier. By such a synthesis process, we produce stabilized ferrate(VI) which enters a solid solution with the formula:M2(Fe,X)O4where M designates Na or K, X is an element whose cation has the electronic structure of a rare gas, e.g. X=S. M2XO4 is an isomorph of K2FeO4 with closed unit cell parameters. The M2(Fe,X)O4 formula has been established by chemical means and by X-ray diffraction; [sup]57Fe Mössbauer spectrometry has been used to monitor the hexavalent iron oxidation state. This paper deals with sulfatoferrate K2(Fe,S)O4 properties for compounds having Fe/S ratios between 1 and 1.5. in aqueous solution, K2(Fe,S)O4 dissolves and gives rise to FeO42- and SO42- anions.In collaboration with NANC.I.E. (Centre International de l'Eau de Nancy), the effectiveness of K2(Fe,S)O4 in wastewater treatment has been studied. The product exhibits a real bactericidal effect on both coliforms and total bacteria. This bactericidal efficiency is reached in a short period of time with iron starting levels as low as 5-10 mg.L-Âč. Comparative coagulation jar-tests were carried out on raw wastewater and on secondary effluent using FeCl3·6 H2O, Al2(SO4)3·18 H2O and K2(Fe[inf]0.54,S[inf]0.46)O4. Total suspended solids (TSS) removal on the raw wastewater was better with Al(III) and Fe(III) than with sulfatoferrate. On the secondary effluent, 40% removal was achieved with sulfatoferrate as well as with Fe(III). For removal of chemical oxygen demand (COD), better results were reached with Fe(VI) than with either Fe(III) or Al(III). The effectiveness of FeO42- after 30 minutes of contact with the bacterial medium (secondary effluent) has also been studied. At pH=8.5, a dose of 10 mg.L-Âč iron(VI) removes 99.70% of the total coliforms and 99.90% of the fecal coliforms
Sources and export of particle-borne organic matter during a monsoon flood in a catchment of northern Laos
International audienceThe yields of the tropical rivers of Southeast Asia supply large quantities of carbon to the ocean. The origin and dynamics of particulate organic matter were studied in the Houay Xon River catchment located in northern Laos during the first erosive flood of the rainy season in May 2012. This cultivated catchment is equipped with three successive gauging stations draining areas ranging between 0.2 and 11.6 km2 on the main stem of the permanent stream, and two additional stations draining 0.6 ha hillslopes. In addition, the sequential monitoring of rainwater, overland flow and suspended organic matter compositions was conducted at the 1 m2 plot scale during a storm. The composition of particulate organic matter (total organic carbon and total nitrogen concentrations, ÎŽ13C and ÎŽ15N) was determined for suspended sediment, soil surface (top 2 cm) and soil subsurface (gullies and riverbanks) samples collected in the catchment (n = 57, 65 and 11, respectively). Hydrograph separation of event water was achieved using water electric conductivity and ÎŽ18O measurements for rainfall, overland flow and river water base flow (n = 9, 30 and 57, respectively). The composition of particulate organic matter indicates that upstream suspended sediments mainly originated from cultivated soils labelled by their C3 vegetation cover (upland rice, fallow vegetation and teak plantations). In contrast, channel banks characterized by C4 vegetation (Napier grass) supplied significant quantities of sediment to the river during the flood rising stage at the upstream station as well as in downstream river sections. The highest runoff coefficient (11.7%), sediment specific yield (433 kg haâ1), total organic carbon specific yield (8.3 kg C haâ1) and overland flow contribution (78â100%) were found downstream of reforested areas planted with teaks. Swamps located along the main stream acted as sediment filters and controlled the composition of suspended organic matter. Total organic carbon specific yields were particularly high because they occurred during the first erosive storm of the rainy season, just after the period of slash-and-burn operations in the catchment
The Cosmological Dependence of Cluster Density Profiles
We use N-body simulations to study the shape of mean cluster density and
velocity profiles formed via gravitational instability. The dependence of the
final structure on both cosmology and initial density field is examined, using
a grid of cosmologies and scale-free initial power spectra P\propto k^n. For
each model, we stack clusters to define an average density profile in the
non-linear regime. The profiles are well fit by a power law over 99% of the
cluster volume, with a clear trend toward steeper slopes with both increasing n
and decreasing Omega_o. For models with a Omega_o = 0.2, the profile slopes are
consistently higher than those for Omega-1.0. Cluster density profiles are thus
potentially useful cosmological diagnostics. We find no evidence for a constant
density core in any of the models, although the density profiles do tend to
flatten at small radii. Much of the flattening is due to the force softening
required by the simulations, and an attempt is made to recover the unsoftened
profiles assuming angular momentum invariance. The recovered profiles in the
Omega=1 cosmologies are consistent with a pure power law up to the highest
density contrasts (10^6) accessible with our resolution. The low density models
show significant deviations from a power law above density contrasts \sim 10^5.
We interpret this curvature as reflecting the non scale-invariant nature of the
background cosmology in these models.Comment: uuencoded, 22 pages + 13 figs. Astrophysical Journal, in pres
Amphibians and Reptiles Captured in Drift Fences in Northwest Wisconsin Pine Barrens
Drift fence surveys were initiated by the Wisconsin Department of Natural Resources (WDNR) in the Crex Meadows Wildlife Area (CMWA) in 1993. Systematic drift fence trapping of amphibians and reptiles in the northwest pine barrens was conducted in a 1996- 97 cooperative effort by the WDNR, the U.S. Forest Service (USFS), and the Great Lakes Indian Fish and Wildlife Commission (GLIFWC). Drift fences were operated in four managed barrens properties, the CMWA, Namekagon Barrens Wildlife Area (NBWA), the Douglas County Wildlife Area (DCWA), and the Moquah Barrens Wildlife Area (MBWA). Eighteen amphibian and reptile species (four salamanders, eight anurans, one turtle, one lizard, four snakes) were captured in ten drift fences in the Northwest Wisconsin Pine Barrens. Fourteen species were captured in the CMWA. The most common species were chorus frogs (Pseudacris triseriata ssp.), wood frogs (Rana sylvatica), and northern spring peepers (P. c. crucifer). The relative abundance of the amphibians and reptiles captured, expressed as mean 1996-97 catch per effort, did not differ between the four managed properties, but species composition did. Only three species were common to all four properties, the blue-spotted salamander (Ambystoma laterale), the eastern American toad (Bufo a. americanus), and the spring peeper. The most likely reason that species composition differs is that the Northwest Wisconsin Pine Barrens is an ecotone for amphibian and reptile species of the western prairies (e.g. tiger salamanders, Ambystoma t. tigrinum) and species of the eastern forests (e.g. spotted salamanders, A. maculatum). All but three tiger salamanders were captured in the southwesternmost property (CMWA) whereas the spotted salamander was captured only in the northeastern-most property (MBWA). Annual variation in CMWA catch/effort rates occurred in total amphibians and reptiles and individual species captured. Total April-May precipitation did not appear to support the catch/effort variation from year to year. However, when broken down into five-day periods, increased catch/effort rates were significantly correlated to precipitation increases, but not to changes in temperature. Timing and amount of precipitation within the breeding season may have impacted herptile movements in the CMWA
Assessment of fine scale population genetic diversity and regeneration in Congo basin logged forests
In the Congo Basin most of the light-demanding timber tree species display a deficit of natural regeneration which is a major handicap for sustainable production and certification. Whilst the majority of scientists investigate abiotic and biotic factors explaining that pattern, we hypothesize that tree population density or individual spatial isolation may also affect the tree fitness through inbreeding. In this study, we integrate ecological and genetic approaches to characterize the regeneration potential of a set of priority timber species by (i) estimating pollen dispersal distances at various tree population densities, and (ii) evaluating the impact of increasing spatial isolation on mating characteristics and tree fitness. The ultimate goal is the proposal of minimum population density that prevents inbreeding consequences.
Method
This ongoing study focuses on 10 timber species (Pericopsis elata, Milicia excelsa, Baillonella toxisperma, Entandrophragma cylindricum, E. utile, E. angolense, E. candollei, Afzelia bipindensis, Erythrophleum suaveloens, Terminalia superba). The data collection was carried out in the logging concession granted to Pallisco in Cameroon.
We established two 400-ha plots, where all individuals (DBH > 10 cm) of the target species were inventoried and mapped. A sample of leave or cambium was collected for each of these individuals, as well as for seedlings to characterize patterns of gene flow using genetic tools (nuclear microsatellites). Dispersal agents were identified by direct observations and camera traps. Germination success was characterized in nursery for seeds collected on trees under an increasing isolation gradient.
Results
Main dispersal agents (wind, bat, rodent) and predators (rodent) were identified for all the species. The gene flow and germination data is still being analyzed and the main results will be presented in the poster.
Conclusion
Our data will allow characterizing the reproductive biology of a set of important timber species from the Congo basin. These information will strengthen sustainable forest management and the application of certification by adjusting harvesting norms through the use of scientifically-relevant data. In particular, we will tentatively define a maximum distance to be maintained between two adults to allow a qualitative reproduction
Influence of Projection in Cluster Cosmology Studies
Projection tends to skew the mass-observable relation of galaxy clusters by
creating a small fraction of severely blended systems, those for which the
measured observable property of a cluster is strongly boosted relative to the
value of its primary host halo. We examine the bias in cosmological parameter
estimates caused by incorrectly assuming a Gaussian (projection-free)
mass-observable relation when the true relation is non-Gaussian due to
projection. We introduce a mixture model for projection and explore Fisher
forecasts for a survey of 5000 sq. deg. to z=1.1 and an equivalent mass
threshold of 10^13.7 h^-1 solar masses. Using a blended fraction motivated by
optical cluster finding applied to the Millennium Simulation and applying
Planck and otherwise weak priors, we find that the biases in Omega_DE and w are
significant, being factors of 2.8 and 2.4, respectively, times previous
forecast uncertainties. Incorporating eight new degrees of freedom to describe
cluster selection with projection increases the forecast uncertainty in
Omega_DE and w by similar factors. Knowledge of these additional parameters at
the 5% level limits degradation in dark energy constraints to <10% relative to
projection-free forecasts. We discuss strategies for using simulations and
complementary observations to characterize the fraction of blended clusters and
their mass selection properties.Comment: 11 pages, 4 figures to be submitted to phys. rev.
Connaissances, attitudes et pratiques de la dépigmentation cosmétique volontaire dans les lycées, collÚges et universités du département des Collines au Bénin
Introduction : la pratique de la dĂ©pigmentation cosmĂ©tique volontaire est de plus en plus adoptĂ©e par les jeunes filles. Ce phĂ©nomĂšne de " mode " rĂ©vĂšle un certain aspect socio-anthropologique qui assimile la couleur noire de la peau Ă une vision nĂ©gative et infĂ©rieure de l'ĂȘtre humain.
Méthode : il s'agit d'une étude transversale réalisée entre avril et mai 2023 qui a concerné 1039 étudiantes des écoles et universités du département des Collines sélectionnées par sondage aléatoire simple à plusieurs degrés.
RĂ©sultats : la prĂ©valence de la dĂ©pigmentation chez les filles enquĂȘtĂ©es est de 78,2%. Les principaux produits utilisĂ©s sont les savons Ă base de dĂ©rivĂ© mercuriel et d'hydroquinone (21,55%) et les lotions Ă base d'hydroquinone et de corticoĂŻdes (75,65). 50% de ces filles savaient ce qu'Ă©tait la dĂ©pigmentation. Pour 82,9% d'entre elles, la couleur de la peau est une reprĂ©sentation d'un critĂšre de beautĂ© et 14,5% l'associent Ă un critĂšre de classe sociale. Les principales motivations sont entre autres : ĂȘtre plus belle (58,8%) ; unifier le teint (23,0%) ; plaire aux hommes (15,5%) ; Ă l'occasion d'Ă©vĂ©nements sociologiques tels que le mariage ou le baptĂȘme (1,7%) et la rivalitĂ© (0,8%). 49,8 % avaient pour complication principale une dyschromie, 24,1 % des vergetures, 14,9 % des dermatites allergiques, 3,3 % de l'acnĂ© et 3,0 % des mycoses.
Conclusion : la prĂ©valence des dĂ©pigmentations enregistrĂ©es est trĂšs Ă©levĂ©e et les actions de sensibilisation ainsi que la rigueur dans le contrĂŽle des produits dĂ©pigmentants doivent ĂȘtre renforcĂ©es.
Introduction: the practice of voluntary cosmetic depigmentation is increasingly being adopted by young girls. This âfashionâ phenomenon reveals a certain socio-anthropological aspect, which equates the black color of the skin with a negative and inferior vision of the human being.
Method: this is a cross-sectional study carried out between April and May 2023 which involved 1039 female students from schools and universities in the Collines department selected by simple multistage random sampling.
Results: the prevalence of depigmentation among the girls surveyed was 78.2%. The main products used were soaps based on mercurial derivative and hydroquinone (21.55%) and lotions based on hydroquinone and corticosteroids (75.65). 50% of these girls knew what depigmentation was. For 82.9% of them, skin color is a representation of a beauty criterion and 14.5% relate it to a social class criterion. The main motivations are among others: to be more beautiful (58.8%); even out the complexion (23.0%); pleasing men (15.5%); on the occasion of sociological events such as marriage or baptisms (1.7%) and rivalry (0.8%). 49.8% had dyschromia as the main complication; 24.1% had stretch marks, 14.9% had allergic dermatitis, 3.3% had acne; and 3.0% had mycoses.
Conclusion: the prevalence of depigmentation recorded is very high and awareness-raising actions as well as rigor in the control of depigmenting products should be increased
Connaissances, Attitudes et Pratiques de la Dépigmentation Cosmétique Volontaire des Jeunes Filles en Milieu Scolaire et Universitaire du Département des Collines au Bénin
Introduction : La pratique de la dĂ©pigmentation cosmĂ©tique volontaire est de plus en plus adoptĂ©e par les jeunes filles. Ce phĂ©nomĂšne de " mode " rĂ©vĂšle un certain aspect socio-anthropologique qui assimile la couleur noire de la peau Ă une vision nĂ©gative et infĂ©rieure de l'ĂȘtre humain.
Objectif: lâobjectif est de comprendre ce qui motive les jeunes filles scolarisĂ©es Ă sâadonner Ă une telle pratique plus spĂ©cifquement dâĂ©valuer leurs connaissances, attitudes et pratiques face Ă la dĂ©pigmentation.
Méthode : Il s'agit d'une étude transversale réalisée entre Avril et Mai 2023 qui a concerné 1039 étudiantes des écoles et universités du département des Collines sélectionnées par sondage aléatoire simple à plusieurs degrés.
RĂ©sultats : La moitiĂ© des filles enquĂȘtĂ©es savaient que la dĂ©pigmentation est lâutilisation de produits chimiques dans le but dâĂ©claircir la peau. Pour la plupart (82,9%) dâentre elles, la couleur de la peau Ă©tait une reprĂ©sentation de critĂšre de beautĂ©. Une femme Ă peau claire avait plus de valeur quâune femme Ă peau noire selon 43,0% des enquĂȘtĂ©es. 78,2% avaient adoptĂ© la pratique de la dĂ©pigmentation volontaire et le rythme dâapplication Ă©tait biquotidien chez 70,6% dâentre elles. La principale motivation des filles Ă©tait dâuniformiser le teint.
Conclusion : La dĂ©pigmentations est un phĂ©nomene bien connu des Ă©lĂšves et Ă©tudiantes du dĂ©partement des collines. La plupart des enquĂȘtĂ©es pratique la dĂ©pigmentation et le critĂšre de beautĂ© est utilisĂ© pour justifier le phĂ©nomĂšne.
Introduction: the practice of voluntary cosmetic depigmentation is increasingly adopted by young girls. This "fashion" phenomenon reveals a certain socio-anthropological aspect that assimilates the black color of the skin to a negative and inferior vision of the human being.
Objective: was to understand what motivates young girls at school to engage in such a practice more specifically evaluate their knowledge, attitudes, and practices regarding depigmentation.
Method: This is a cross-sectional study carried out between April and May 2023 which involved 1039 female students from schools and universities in the Collines department selected by simple multistage random sampling.
Results: Half the girls surveyed knew that depigmentation is the use of chemicals to lighten the skin. For the majority (82.9%) of them, skin color was a representation of beauty criteria. A light-skinned woman was more valuable than a dark-skinned woman, according to 43.0% of respondents. 78.2% have adopted the practice of voluntary depigmentation, and 70.6% of them apply their products twice a day. The girls' main motivation was to even out their skin color.
Conclusion: Depigmentation is well known among pupils and students in the hill district. Most of those surveyed practice depigmentation and the criterion of beauty is used to justify the phenomenon
Connaissances, attitudes et pratiques de la dépigmentation cosmétique volontaire dans les lycées, collÚges et universités du département des Collines au Bénin
Introduction : la pratique de la dĂ©pigmentation cosmĂ©tique volontaire est de plus en plus adoptĂ©e par les jeunes filles. Ce phĂ©nomĂšne de " mode " rĂ©vĂšle un certain aspect socio-anthropologique qui assimile la couleur noire de la peau Ă une vision nĂ©gative et infĂ©rieure de l'ĂȘtre humain.
Méthode : il s'agit d'une étude transversale réalisée entre avril et mai 2023 qui a concerné 1039 étudiantes des écoles et universités du département des Collines sélectionnées par sondage aléatoire simple à plusieurs degrés.
RĂ©sultats : la prĂ©valence de la dĂ©pigmentation chez les filles enquĂȘtĂ©es est de 78,2%. Les principaux produits utilisĂ©s sont les savons Ă base de dĂ©rivĂ© mercuriel et d'hydroquinone (21,55%) et les lotions Ă base d'hydroquinone et de corticoĂŻdes (75,65). 50% de ces filles savaient ce qu'Ă©tait la dĂ©pigmentation. Pour 82,9% d'entre elles, la couleur de la peau est une reprĂ©sentation d'un critĂšre de beautĂ© et 14,5% l'associent Ă un critĂšre de classe sociale. Les principales motivations sont entre autres : ĂȘtre plus belle (58,8%) ; unifier le teint (23,0%) ; plaire aux hommes (15,5%) ; Ă l'occasion d'Ă©vĂ©nements sociologiques tels que le mariage ou le baptĂȘme (1,7%) et la rivalitĂ© (0,8%). 49,8 % avaient pour complication principale une dyschromie, 24,1 % des vergetures, 14,9 % des dermatites allergiques, 3,3 % de l'acnĂ© et 3,0 % des mycoses.
Conclusion : la prĂ©valence des dĂ©pigmentations enregistrĂ©es est trĂšs Ă©levĂ©e et les actions de sensibilisation ainsi que la rigueur dans le contrĂŽle des produits dĂ©pigmentants doivent ĂȘtre renforcĂ©es.
Introduction: the practice of voluntary cosmetic depigmentation is increasingly being adopted by young girls. This âfashionâ phenomenon reveals a certain socio-anthropological aspect, which equates the black color of the skin with a negative and inferior vision of the human being.
Method: this is a cross-sectional study carried out between April and May 2023 which involved 1039 female students from schools and universities in the Collines department selected by simple multistage random sampling.
Results: the prevalence of depigmentation among the girls surveyed was 78.2%. The main products used were soaps based on mercurial derivative and hydroquinone (21.55%) and lotions based on hydroquinone and corticosteroids (75.65). 50% of these girls knew what depigmentation was. For 82.9% of them, skin color is a representation of a beauty criterion and 14.5% relate it to a social class criterion. The main motivations are among others: to be more beautiful (58.8%); even out the complexion (23.0%); pleasing men (15.5%); on the occasion of sociological events such as marriage or baptisms (1.7%) and rivalry (0.8%). 49.8% had dyschromia as the main complication; 24.1% had stretch marks, 14.9% had allergic dermatitis, 3.3% had acne; and 3.0% had mycoses.
Conclusion: the prevalence of depigmentation recorded is very high and awareness-raising actions as well as rigor in the control of depigmenting products should be increased
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