Documents found
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112101.More information
The aim of this study is to examine the impact of two university programs—one inadministration, offering less self-determination than the other, psychology—on theperception of classroom climate and motivation of students. A questionnairemeasuring these two variables was administered to 744 students in an undergraduateprogram in psychology and in administration. The results were analyzed in relationto the cognitive evaluation theory and as to the influence of university programs onstudents' motivation.
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112102.More information
This work describes a new approach to prediction of spatio-temporal evolution of mineral phosphorus in water bodies, particularly in Tiagba Lagoon Bay. Originality of this study lie on the use of artificial neural networks, principally multilayer perceptron, as modelling tool. Two approaches of spatio-temporal evolution of this nutrient were done: static evolution and dynamic evolutions. Data bases, formed by 3 966 and 4 627 data, served for static and dynamic modelling of this nutrient respectively. Weights of network connection are determined using Levenberg-Marquardt algorithm during execution of Multilayer Perceptron. Results obtained show that models 5-14-1 and 6-14-2 can predict to 70.30% and approximately 70% respectively for static and dynamic evolution of mineral phosphorus in this bay. These models, judged satisfactory, could be used for other studies led to rehabilitation and protection of this aquatic ecosystem for its long development.
Keywords: Phosphore, réseau de neurones artificiels, baie lagunaire de Tiagba, système Ébrié, Côte d'Ivoire, Phosphorus, artificial neural networks, multilayer perceptron, Tiagba Lagoon Bay, Ebrié system, Côte d'Ivoire
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112103.More information
AbstractThe Nahr Ibrahim catchment area is classified as an international heritage site. Along the Nahr Ibrahim River, solid and liquid effluents have an important impact on bacterial contamination. Physico-chemical and bacteriological parameters were studied at nine sampling sites located along the Nahr Ibrahim River from its source to its estuary. Total bacteria, total coliforms, fecal coliforms and fecal streptococci were studied during dry and wet weather periods. During these periods, the studied parameters revealed an important influence of the type of soil and leaching on the bacteriological composition of the river. Furthermore, the origin and the degree of temporary bacteriological contamination were identified. A multivariate statistical approach demonstrated that the effect of site location masked the effect of sampling date on the degree of bacteriological contamination. Downstream river sites were characterized by nitrate and bacterial pollution whereas upstream sites showed only by bacterial contamination.
Keywords: bactériologie, eaux de surface, coliformes totaux, coliformes fécaux, streptocoques fécaux, nitrates, Bacteriology, surface water, total coliforms, fecal coliforms, fecal streptococci, nitrates
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112104.More information
Molluscs are well known for their capacity to bioaccumulate heavy metals from water or sediments. This study involves an evaluation of the contamination level of the undergroud and surface waters from a specific irrigation system known as a « khetarra », located near the town of Marrakech (Morocco). Khettaras represent a traditional systern by means ofwhich the ground water is drained to the surface and then can be used as drinking water or for irrigation in some arid and semi-arid areas. The bioindicator chosen was the gasteropod Melanopsispraemorca L. Two stations (Kl and K2) were investigated in a khettara located in spreading Marrakech waste water. The contamination of soils and water by heavy metals, eipecially Zn, Cu and Cd was first described by EL MEZD1 (1985) and SEDKI(1990).The studied khettara (1500 m. in length) is contaminated in two different ways: first by infiltration of waste water from the Seguia system and secondly directly by over-flow and escape of a main common sewer which crosses over the khetarra between the Kl andK2 stations.At each station, sediment peripbyton, Spirogyra and M. praemorsa were sampled in different seasons. Each sample was prepared for analysis (S.A.A. varian 475.AA) according to the method described by COSSON (1987). Flame atomization was chosen for Zn and Cu, the grafite furnace for Cd.The main results concern the level of contamination, with a comparison between Kl and K2 stations, the variation in contamination according to the seasons, the dilferent routes of contamination, namely through water or by the trophic chaîn (periphfion and Spirogyra).The degree of contamination in M. praemona is signifïcatively higher at the Kl station, with the following ranking: Zn> Cu> Cd (fig. 2, 3 and 4). Compared with other literature data: FORSTNER et al., 1981; RADA, 1985; COSSON, 1987; PIP, 1992, the upper concentrations are the highest.The metal concentrations increase from winter to summer, with significant differences between winter and spring or summer values at Kl for Zn, Cu, Cd; the same distinction, but only for Zn and Cd at K2 station.The causes of variation in metal concentrations in the gasteropods from the two sites were investigated,by in situ cotransplantation experiences and by measuring metaflic concentrations in sediments, periphyton and Spirogyra. Results show that differences in gasteropod metal concentrations between sites appear to be related to differences in aqueous metal speciation. The data concerning the food chain show that metallic concentrations are higher for periphyton and, Spirogyra living at Kl station, this according to the data for M. praemorsa.In contrast, the level of contamination in sediments is higher at K2 station. The most probable hypothesis is that organic and suspended matter, present at a higher level in this station, bind the heary metals and reduce their bioavailability.The cotransplantation between Kl and K2 stations shows that the individuals transferred from Kl to K2 station for 15 days cease to bioaccumulate Zn and Cd. A detoxification process occurs for these two metals but not for Cu, which continues to increase; thus, bioavailability of different metals at the same station is not equivalent. On the other hand the individuals transferred from K2 to Kl station do not increase their Zn, Cu or Cd concentrations even after 30 days. Concerning this fact FRAZIER and GEORGE (1983) suggest the possibility of an adaptation to initial conditions.It seems that many other factors influence metal bioaccumulation and merit further study, e.g.: the size and the age of individuals, the biological cycle with the period of reproduction ; the interaction of abiotic factors: T°, salinity, dissolved orygen, turbidity, lighting.
Keywords: Eaux courantes souterraines, bioconcentration, Zn, Cu, Cd, Melanopsis praemorsa, Maroc, Ground water, bioconcentration, Zn, Cu, Cd, Melanopsis praemorsa, Morocco
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112105.More information
Modelling the hydrological behaviour of drainage basins is very important for solving problems related to the evaluation and optimal management of water resources. This is illustrated quantitatively in countries such as Algeria where water supply is a limiting factor. The principal aim of this paper was to explain the relationship between hydrological conditions and the availability of surface water. A model of rainfall-discharge was developed on a yearly scale, taking into account physical and climatic parameters. The application was carried out in northern Algeria where the total land surface is about 325 000 km2.The development of this model required a database, which was acquired during previous studies where maps of median rainfall and permeability as well as the digital elevation model were developed. In order to complete this database, the cartography of rainfall for the years for which we have discharge data was carried out using a methodology entitled "mapping standardized rainfall". To estimate and map annual rainfall, the kriging method was used. Two problems were encountered:- The presence of a drift highly altered the variogram and made it very difficult to infer a sub- structure function;- The variogram is significant only if the hypothesis of ergodicity is valid, which was not easy to assume for any given year.In order to resolve these difficulties, a homogeneous random and secondary stationary order function (same mean at all points and same covariance function) must be calculated. A previous study by ANRH (1993) allowed us to know the statistical parameters of the distribution at each point. These parameters were mapped, taking into consideration the topographical relief and distance to the sea. For every year and at each rainfall measure point, the standardized rainfall could be deduced. The correlogram gave information about the spatial variability of the phenomenon and its range, and subsequently the standardized rainfall was then interpolated. Annual rainfall was calculated by combining the grids of the means, the variances and the centered reduced rainfall (TOUAZI and LABORDE, 2000). Thus, the data of 467 rainfall gauges were used in order to create maps of the yearly isohyets.The rainfall-discharge relationship on an annual scale was based on 50 hydrometric stations distributed throughout the study area. The methodology used was derived from the production function of the S.C.S (Soil Conservation Service). This production function was part of modelling, which transformed total rainfall to net rainfall. This method was very representative of the natural hydrological processes. Indeed, it takes into account rainfall and the maximum infiltration capacity (S), which depends on the nature of the soil (lithology), vegetation and soil moisture content. In the current study, the basin surface and a regional parameter (a) were introduced in order to calibrate the model. This production function was implemented by supplying different values for the parameter (S). The values (n+1) were obtained by increasing the previous value (n) by 10 %. We evaluated the different values of (S) in the same way to obtain the last value (i). We calculated for these different values of the parameter (S) the square of the difference between the measured and estimated discharges for each year by measuring the discharge at different stations. For each station, we calculated the sum of these values for all the years and we retained the value of (S) that gave the minimal value. The results demonstrated that the values of (S) obtained were not significant because they tend to the infinite. For this reason, (S) was considered as a constant. In order to improve the model, we repeated the same operation, but instead of (S), we used the parameter (a) and performed the same calculation. After calibration of the model the results gave a coefficient of determination of 0.75, which means that 75 % of the variance was explained by the mean rainfall, the surface and the parameter (a).To explain the parameter (a), we calculated the correlation between its value at each station with the corresponding geology. This latter variable was characterized by the average storage capacity, which corresponds to the weighted average of the surfaces of the basin assigned to each permeability category (TOUAZI, 2001). The results demonstrated a coefficient of determination of 0.1. The correlation with the topographical relief was not necessary because it was taken into account in the cartography of the rainfall. We then proceeded to the cartography of the parameter (a). The results demonstrated an east-west gradient that was constant and a north-south gradient that decreased from north to south. With the digital elevation model, we used a geographical information system to deduce the slopes. For each basin, the average slope was calculated by taking the average of the values of the slopes of all the pixels that constituted the individual basin. The correlation between slopes and corresponding values of the parameter (a) gave a coefficient of correlation of 0.6.The results obtained by this model after calibration gave a coefficient of determination of 0.75, which means that 75% of the variance was explained by the mean rainfall, the surface and a coefficient (a), which corresponds to the average slope of the drainage basins.
Keywords: Algérie du Nord, bassins versants, cartographie automatique, débits, krigeage, système d'information géographique, fonction de production du SCS, Northern Algeria, soil conservation service production function, discharge, drainage basin, automatic mapping, kriging, geographical information system
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112106.More information
The present study emphasizes the mineral raw materials of Madagascar and their uses for the satisfaction of important local needs. As most treatments of water in Madagascar (drinking water, wastewaters) call for aluminium sulphate, which is still imported, the present work offers new products based on alumina and on silica, which allow the water to be treated by coagulation-flocculation. The aim is to control the treatment of kaolin by ammonium sulphate and to promote the use of the products of this reaction in water treatment.The raw materials used include kaolin, which exists copiously in Madagascar, and ammonium sulphate, which is going to become a locally-available industrial by-product as a result of the installation of a large plant for the extraction of nickel and cobalt in the east of Madagascar. The current processes for the preparation of alumina or some aluminium salts from kaolinite consist generally of a high-temperature thermal activation (500 to 800°C) of relatively important duration, followed by an acid attack. In our process, the kaolin is attacked by the ammonium sulphate without need of preliminary activation, at low temperatures between 200 and 350°C, for two hours at most, to obtain products containing some aluminium sulphate and also silica. It is known that silica, added in small quantities, is a flocculation additive to some aluminium sulphate preparations, and the results of our research showed that the whole product resulting from the ammonium sulphate attack allows one, without separation, to treat drinking water as well as urban and industrial wastewater. Various coagulation-flocculation trials with the final products were performed on different types of water and the analyses of the treated waters confirmed that some of these new products can be used to treat waters by coagulation-flocculation.
Keywords: coagulation-floculation, traitement eau potable, eaux usées, kaolin, sulfate d'ammonium, coagulation-flocculation, drinking water treatment, wastewaters, kaolin, ammonium sulphate
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112107.More information
Plotting position formulae (PPFs) maintain an important role in engineering practice. In the area of flood frequency analysis they are used to assign exceedance probabilities to observed floods. In the present study we review various principles for the choice of PPFs. These can be divided into three main categories : (1) formulae based on the observed sample frequencies, (2) formulae based on the distribution of sample frequencies, and (3) formulae based on the distribution of order statistics. PPFs in the first two categories are distribution-free, meaning that no assumption needs to be made regarding the form of the parent distribution of events. The Hazen PPF is an example of a formula belonging to the first category.The Weibull PPF, which is probably the most used formula in practice, belongs to the second category. It can be shown that the frequency corresponding to a particular order statistic is beta distributed regardless of the form of the parent distribution. Being equivalent to the expected value in the beta distribution the Weibull plotting position, pm = m/(n + 1), therefore corresponds to the mean value of sample frequencies. In his book on statistical extremes GUMBEL (1958) recommended the Weibull formula, because it fulfils a set of criteria which he found important. Some of these criteria have later been questioned, for instance by CUNNANE (1978). Various studies have demonstrated that the Weibull PPF is significantly biased in the event domain for most common distributions (an exception is the uniform distribution, where the Weibull PPF is the exact unbiased plotting position).In recent years most attention has been paid to PPFs of the third category. CUNNANE (1978) strongly recommended the use of unbiased PPFs, i.e. formulae for the exceedance probabilities of the expected values of order statistics. In the last decade much effort has been devoted to the development of unbiased plotting positions. As unbiased PPs in virtue of their definition are related to the parent distribution, they will differ for each individual distribution. In general, it is not possible to derive exact unbiased PPFs, but good approximations have been developed for most common distributions such as the normal, the Gumbel, the generalized extreme value, and the Pearson type III distributions (see table 1). If a distribution contains a shape parameter, this must be reflected in its unbiased PPF. Approximate formulae for such distributions are therefore in general of a more complex form. This fact along with the need for distribution-dependent formulae is probably the reason why the Weibull formula is still the most used PPF in practice.In the present study we emphasize the practical convenience of having a distribution-free PPF which at the same time has a statistical interpretation and is related to the distribution of order statistics. The median PP fulfils these points. It is easily seen to be distribution-free by observing that the median in the distribution of order statistics corresponds to the median in the distribution of frequencies (beta distribution). In general, one of two different principles is commonly adopted when developing estimators : either the choice of the modal value (maximum likelihood principle) or the choice of the mean value (principle of unbiasedness). Unfortunately these distinct principles usually lead to different estimators. For continuous distributions used in flood frequency, the median of order statistics is located in between the modal value and the mean value. In general, it is much less biased thon the Weibull PPF, which for the EV1 distribution is a reasonable approximation to the modal PP. Although no analytical expression exists for the median plotting position, an approximation has been deduced by BENARO and BOS-LEVENBACH (1953), namely pm = (m - 0.3)/(n + 0.4). This formula is also known as the Chegodayev PPF.Various PPFs are exemplified in the case of three different parent distributions, namely the normal, the log-normal, and the Gumbel distributions. The sample size n = 10 is considered. The results of applying different PPFs are presented in table 2 (for the largest order statistic in the sample). Several observations can be made : 1) The Benard and Bos-Levenbach-formula is a good approximation to the median PP; 2) The Weibull-formula is close to the modal value PP when the parent is EV1, but differs significantly in the case of other parents; 3) The unbiased PPs depend strongly on the underlying distribution, and an unbiased PPF suitable for all distributions can therefore not be found; 4) The median PP is a fair compromise between the mean and the modal values of the order statistics in all three cases, and it is therefore recommended as a good choice of a standard PPF.
Keywords: Formules de probabilité empirique, distribution des fréquences échantillonnales, médiane des statistiques d'ordre, formule de Benard et Bos-Levenbac, Plotting position formulae, unbiasedness, median, Beta distribution, Benard and Bos-Levenbach formula
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112108.More information
Keywords: Féminismes, Québec, intersectionnalité, queer, nationalisme, idées politiques
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112110.More information
It is often argued that development aid can and should compensate the restrictions on migration. Such compensation, Shachar has recently argued, should be levied as a tax on citizenship to further the global equality of opportunity. Since citizenship is essentially a ‘birthright lottery', that is, a way of legalizing privileges obtained by birth, it would be fair to compensate the resulting gap in opportunities available to children born in rich versus poor countries by a ‘birthright privilege levy'. This article sets out a defence of three theses. The first states that equality of opportunity is incompatible with, and cannot be achieved in, segregated territories. The second posits that to believe that material equality compensates the injustice of restrictions on movement is to commit a ‘sedentarist mistake'. The third affirms that any citizenship levy, including the egalitarian and non-sedentarist formula I'm proposing, would be better understood as a penalty rather than a tax.