Rôle des évaluations continues dans la prédiction des performances des élèves au secondaire collégial

La présente étude traite l’effet de l’évaluation continue (contrôle continu) sur les performances des élèves lors des examens de fin de semestres (examen local, examen régional et note globale d‘évaluation) en Mathématiques et en Sciences physique. Pour ce faire, un échantillon de plus de 2600 élèves de la troisième année du secondaire collégial des établissements scolaires de la direction provinciale d’El Jadida, Académie Régionale d’Education et de Formation de Casablanca-Settat (Maroc) a été choisit. Les données collectées sont analysées à l'aide du coefficient de corrélation de Pearson ainsi que le test t de student. Les résultats obtenus montrent des valeurs élévées des coefficients déterminés et qui sont statistiquement significatifs (p< 0,05). Cela implique que l’évaluation continue influe positivement les performances des élèves en examen local et en note globale d’évaluation pour les deux matières étudiées. Sur la base de ces résultats, il est plus judicieux que l'évaluation continue reçoive une attention plus sérieuse de la part des enseignants. This study examines the effect of continuous assessment on the performance of students in end-of-semester exams (local exam and regional exam), and the global assessment scores in Mathematics and Physical Sciences. To do this, a sample of more than 2,600 pupils of secondary school of the provincial direction of El Jadida, Regional Academy of education and training of Casablanca-Settat (Morocco) was chosen. The data collected is analyzed using the Pearson’s Product Moment Correlation Coefficient (r) as well as the student's t test. The results obtained show high values of the determined coefficients which are statically significant at 0.05. This implies that continuous assessment positively influences student performance in the local exam and the global assessment scores for the two subjects studied. However, this continuous assessment did not have a strong impact on the learning progress of the students in the regional exam. Based on these results, it is more appropriate for the continuous assessment of students to receive more serious attention from the teachers

Measurement of Natural Radioactivity and Radon Exhalation Rate in Coal Ash Samples from a Thermal Power Plant

International audienceCoal is the main energy source for electricity generation in the world. In Morocco, 37% of electricity generation comes from combustion coal in thermal power plants. This combustion process generates large amounts of fly and bottom ashes. In recent years, these ashes became a great topic of interest because of their different uses and especially in construction materials. In this work, we assess radiation risks due to natural radioactivity in samples of fly and bottom ashes collected from JLEC (Jorf Lasfar Energy Company) thermal power plant, and different analyses are performed through two nuclear techniques such as gamma spectrometry and alpha dosimetry based on the use of LR115 films detectors. Our analysis shows that 226 Ra activities and 232 Th in both ash samples are well above the permissible activity. The values of the external risk index (Hex) and internal one (Hin) for these ashes are below unity, with the exception of 1.28 in fly ash for Hin. The obtained values for the equivalent radium Raeq and annual effective doses Ė in fly and bottom ashes are 324 Bq/kg and 210 Bq/kg, and 0.18 mSv/y and 0.11 mSv/y, respectively. The surface radon exhalation rates for the samples of fly and bottom ashes are 276 mBq • m −2 • h −1 and 381 mBq • m −2 • h −1 , respectively. Based on these results, we have shown that fly ash and bottom one from thermal power plant JLEC didn't have, in any case, a health risk to the public so it can be effectively used in various construction activities

Enhancing Molten Sulfur Filtration during Sulfuric Acid Manufacturing for Phosphate Fertilizer Production in Morocco with Cellulose-Based Filter Aids

International audienceThe filtration of liquid sulfur is a key operation in the production of sulfuric acid that isused for phosphate fertilizer production in Morocco and elsewhere. The purpose of the filtrationprocess is to remove solid impurities from liquid sulfur, which could clog the sulfur burner spraynozzles, leading to the reduction of the lifetime of the sulfuric acid production unit. The standardlife cycle operation for sulfuric acid units is 24 months, while due to clogging, this lifetime can bereduced to less than 18 months, which is obviously a tremendous economic disadvantage. In theliquid sulfur filtration process, a precoat made of diatomaceous earth is usually used. In this work,the performance of a standard diatomaceous earth filter aid was compared to the performance of twocommercial, inexpensive, cellulose-based filter aids, namely, FILTER-900 and FILTER-1100, whichare distinguished by their respective Dalton numbers (900 Da and 1100 Da). The experiments wererealized using an industrial sulfur filtration device, and the results indicated that all three of the filteraids yielded similar performance in terms of the impurity content in the filtered liquid sulfur. Thecellulose-based filter aids did, however, show a lower specific filter-aid consumption, accompanied byan increase in operating cycle times from 24 to 72 h. In addition, the use of the cellulose-based filtersallowed for the relatively easy removal of the filter cake without damaging the filter cloths (which isoften an issue with the diatomaceous earth filter aids). It was further noticed that the filtered liquidsulfur obtained using the cellulose-based filter aids remained uncontaminated by silicate, which isone of the main elements that can result in clogging of the sulfur spray nozzles. The first experimentaldata presented here are therefore promising, and further industrial tests as well as economic analysisfor using cellulose-based filter aids in industrial sulfuric acid production are encouraged

Enhancing rare earth element transfer from phosphate rock to phosphoric acid using an inexpensive fly ash additive

International audienceAdding active silica (SiO2) to reduce the free fluoride content is a known method to improve the filterability of phosphogypsum (PG) during wet phosphoric acid (WPA) processing of phosphate rock (PR). Besides, this process can also promote the transfer of valuable rare earth elements (REE) from the PR into the liquid phosphoric acid (PA) stream rather than into the solid PG matrix from which later economic recovery is more challenging. Khouribga PR, that shows total REE concentrations of 577 ppm (328 ppm heavy REE and 249 ppm light REE) of which yttrium (Y) with 240 ppm constitutes the major fraction, is processed at the Jorf Lasfar El-Jadida chemical complex in Morocco that is also home to the country’s largest coal power plant. Fly ash produced during thermal power production, 70% of which is stacked in the immediate vicinity, presently remains mostly unused and consists largely (48%) of silica. In this work the use of fly ash (34 kg per t PR) and pure silica (8.5 kg per t PR) on the transfer of REE from Khouribga PR into the PA and PG stream during dihydrate WPA production was examined. The inexpensive fly ash/silica additive increases the transfer of various REE to the PA stream. For Y an increase of 37% was measured that resulted in a concentration of 48 ppm in the PA stream prior to further concentration by evaporation