Résumé L’agriculture est l’activité dominante dans la vallée du moyen Cheliff occidental (Nord algérien). Les cultures principales sont l’arboriculture et le maraîchage, ce dernier est un grand consommateur de fertilisants minéraux de type azoté. La présente étude montre, dans une première étape, l’évolution spatiale des nitrates à travers une carte établie par krigeage ordinaire pour l’année 2004 en période de hautes eaux. Il apparaît, d’après cette carte, que les zones les plus affectées sont celles pour lesquelles le niveau d’intensification de la fertilisation azotée (zones de maraîchage) est le plus fort sous les sols les plus perméables situés sur les bordures de la vallée. Ces mêmes zones sont reconnues par des pratiques d’élevage importantes. Au contraire, les teneurs sont plus faibles sous les sols de texture fine couvrant la partie centrale de la vallée. L’infiltration assez faible, caractérisant en général les zones semi-arides, semble aussi jouer un rôle important dans ce sens. Dans une seconde étape, cette étude permet d’estimer, pour l’année 2004, l’apport total en azote sur les sols de la vallée. L’apport par l’agriculture constitue 86 % du total, dont 97 % est attribué aux fertilisants azotés utilisés d’une manière intensive dans les cultures maraîchères, la pomme de terre en particulier. Rapporté à la surface totale irriguée, cet apport est évalué à 238 kg•ha‑1 pour cette année. Les conditions pédoclimatiques semblent favoriser des pertes d’azote par volatilisation et par dénitrification en parallèle avec un apport faible d’azote naturel par minéralisation. Au contraire, les pertes par lessivage en profondeur sont très faibles.
The present work is a part of our scientific project about the valorisation of the common dates grown in southern Algeria. The principal aim was to study the drying ability of the fruit pulp with the view to produce food powders, which can easily take the place of many synthetics ingredients (white sugar, colorant like caramel) in many food preparations. The specific structure of the date pulp was also described: presence of two edible constitutive tissues (outside pigmented and inside white) that can influence the technological proprieties (as drying) of the whole fruit. The pigmented and white part weights were significantly different (p ≤ 0.05). Results reveal the preponderance of white part, which can favourably influence the heat processing such as drying since the coloured pulp is already pre-browned compared with the white part. Hot air (60°C) and microwave (MW) (350W) drying kinetics of date (Phoenix dactylifera L.) pulp pieces from Mech-Degla variety were investigated. Colour change (browning) was also analyzed during these drying processes using absorbance measurement at 420nm of the hydro alcoholic extract from pulp pigmented part. The latter has a heterogeneous initial colour in the same fruit. Three shades can be noticed: yellow, beige and brown related to the optic densities (at 420nm) of 0.92, 1.5 and 1.93 respectively. The minimal moisture contents reached by means of MW and hot air drying are about 8 (during 5 min) and 5 % dry basis (during 165 min) respectively. On the other hand, the MW drying could be considered instantaneous but it involves a few scorched spots on pulp pieces what may be due to the non uniformity of the initial date pulp colour or to the inadequacy of the chosen power. In addition, the applied model strongly fit the experimental data for convective air drying (R 2 = 0.995; MRE = 6.71%) compared to MW drying (R 2 = 0.94; MRE = 18.4%)
At the nanoscale system, the efficiency of carbon nanotube (CNT) reinforcement between the CNTs and polymer matrices in terms of interfacial load transferring is assessed for both nonfunctionalized and functionalized interfaces. The simulations of the mechanical properties (stress-strain) of polyethylene (PE)/CNT nanocomposites by the molecular dynamics are currently an area of discussion in the literature. In this work, PE considered as a thermoplastic material is studied, in which the characterization of its nanoscale load transfer has been carried out through the classification of representative nanoscale interface elements for nonfunctionalized CNTs for the diverse values of lengths and diameters. First, the main evaluations based on the density functional theory and the molecular dynamics method were used with the aim to examine the effect of PE monomers. Then, the effect of the diameter of CNTs with nonfunctionalization content on the electronic and mechanical properties of single-walled carbon nanotubes was examined. The findings reveal that the density of states highlights the absence of orbital hybridization between the PE monomers and nanotubes, whereas the Mulliken charge analysis depicts that the PE polymer produces a positive charge that is directly proportional to the number of monomers with many chains of PE and different diameters of CNTs. The decrease in diameters implies an increase in nanocomposites stress. In addition, the results show that the reinforcements in the longitudinal direction are more promising than those in the transverse direction.
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