Performances hydrauliques et agronomiques des systèmes d'irrigation gravitaires sur l'élimination de l'excès d'eau hivernal dans la plaine du Gharb au Maroc

International audienceLa plaine du Gharb présente une double problématique, celle des excès d'eau en hiver qui mettent en péril les levées et les premières phases des cycles culturaux et, à partir du printemps, celle du déficit en eau qui nécessite le recours à l'irrigation pour garantir un niveau de rendement acceptable. La valorisation de l'eau d'irrigation est en conséquence étroitement dépendante des conditions de drainage hivernales, déterminantes vis-à-vis des potentialités des cultures d'hiver. Toute action à entreprendre pour améliorer l'usage et l'efficience de l'eau ne doit pas perdre de vue ces deux aspects complémentaires. Le travail conduit dans le cadre de la présente recherche vise à démontrer que les systèmes d'irrigation gravitaire à la raie longue présentent non seulement un intérêt en période estivale mais également vis-à-vis du drainage de surface en période hivernale. L'un des enjeux majeur de ce travail est d'évaluer le gain que génère le système gravitaire modernisé (raie longue). A cet effet, des travaux d'expérimentation sont conduits depuis 2003-2004 à la station de Souk Tl et sur la betterave à sucre qui reste l'une des principales cultures pratiquées au Gharb mais dont les potentialités de production sont affectées par les excès d'eau hivernaux. Le travail de recherche a trait à l'évaluation des performances des systèmes d'irrigation gravitaire (raie longue, et " robta ") et des systèmes en aspersion en conditions nivelées et non nivelées. Cette évaluation se basera sur la prise en compte conjointe des contraintes d'excès d'eau hivernaux et de déficit estival de la betterave à sucre. Une bonne - et nécessaire - intégration de ces processus et le transfert des résultats auprès des agriculteurs constitue un enjeu majeur pour la durabilité environnementale et économique du périmètre irrigué du Gharb. C'est dans ce sens que des essais ont été conduits chez des agriculteurs pour la même culture, après correction du nivellement et ce, pour les deux systèmes d'irrigation. Les premiers résultats de ce travail de recherche montrent que le système d'irrigation gravitaire à la raie longue permet d'irriguer et d'évacuer efficacement les excès d'eau hivernaux. Des valeurs de rendements proches des potentialités attestant de cette efficacité ont été obtenues. Des très bons niveaux de rendement ont été également obtenus pour le système en aspersion nivelé. Il est sans conteste montré que l'absence de nivellement, frein à l'évacuation des excès d'eau par ruissellement et générateur de stagnations locales, est responsable de pertes de rendement importantes

Optical study of the band structure of wurtzite GaP nanowires

We investigated the optical properties of wurtzite (WZ) GaP nanowires by performing photoluminescence (PL) and time-resolved PL measurements in the temperature range from 4 K to 300 K, together with atom probe tomography to identify residual impurities in the nanowires. At low temperature, the WZ GaP luminescence shows donor-acceptor pair emission at 2.115 eV and 2.088 eV, and Burstein-Moss band-filling continuum between 2.180 and 2.253 eV, resulting in a direct band gap above 2.170 eV. Sharp exciton α-β-γ lines are observed at 2.140-2.164-2.252 eV, respectively, showing clear differences in lifetime, presence of phonon replicas, and temperature- dependence. The excitonic nature of those peaks is critically discussed, leading to a direct band gap o

Stress transfer among en echelon and opposing thrusts and tear faults : triggering caused by the 2003 Mw = 6.9 Zemmouri, Algeria, earthquake

Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 116 (2011): B03305, doi:10.1029/2010JB007654.The essential features of stress interaction among earthquakes on en echelon thrusts and tear faults were investigated, first through idealized examples and then by study of thrust faulting in Algeria. We calculated coseismic stress changes caused by the 2003 Mw = 6.9 Zemmouri earthquake, finding that a large majority of the Zemmouri afterslip sites were brought several bars closer to Coulomb failure by the coseismic stresses, while the majority of aftershock nodal planes were brought closer to failure by an average of ∼2 bars. Further, we calculated that the shallow portions of the adjacent Thenia tear fault, which sustained ∼0.25 m slip, were brought >2 bars closer to failure. We calculated that the Coulomb stress increased by 1.5 bars on the deeper portions of the adjacent Boumerdes thrust, which lies just 10–20 km from the city of Algiers; both the Boumerdes and Thenia faults were illuminated by aftershocks. Over the next 6 years, the entire south dipping thrust system extending 80 km to the southwest experienced an increased rate of seismicity. The stress also increased by 0.4 bar on the east Sahel thrust fault west of the Zemmouri rupture. Algiers suffered large damaging earthquakes in A.D. 1365 and 1716 and is today home to 3 million people. If these shocks occurred on the east Sahel fault and if it has a ∼2 mm/yr tectonic loading rate, then enough loading has accumulated to produce a Mw = 6.6–6.9 shock today. Thus, these potentially lethal faults need better understanding of their slip rate and earthquake history.Funding by the U.S. Office of Foreign Disaster Assistance of the U.S. Agency for International Development is gratefully acknowledged. Additional funding was provided by the INSU research project ACI Cat‐Nat Risque Sismique de la Région d’Alger. S. Belabbes was supported by the Algerian Ministry of Higher Education and Research

Pneumococcal lineages associated with serotype replacement and antibiotic resistance in childhood invasive pneumococcal disease in the post-PCV13 era: an international whole-genome sequencing study

Background: Invasive pneumococcal disease remains an important health priority owing to increasing disease incidence caused by pneumococci expressing non-vaccine serotypes. We previously defined 621 Global Pneumococcal Sequence Clusters (GPSCs) by analysing 20 027 pneumococcal isolates collected worldwide and from previously published genomic data. In this study, we aimed to investigate the pneumococcal lineages behind the predominant serotypes, the mechanism of serotype replacement in disease, as well as the major pneumococcal lineages contributing to invasive pneumococcal disease in the post-vaccine era and their antibiotic resistant traits. / Methods: We whole-genome sequenced 3233 invasive pneumococcal disease isolates from laboratory-based surveillance programmes in Hong Kong (n=78), Israel (n=701), Malawi (n=226), South Africa (n=1351), The Gambia (n=203), and the USA (n=674). The genomes represented pneumococci from before and after pneumococcal conjugate vaccine (PCV) introductions and were from children younger than 3 years. We identified predominant serotypes by prevalence and their major contributing lineages in each country, and assessed any serotype replacement by comparing the incidence rate between the pre-PCV and PCV periods for Israel, South Africa, and the USA. We defined the status of a lineage as vaccine-type GPSC (≥50% 13-valent PCV [PCV13] serotypes) or non-vaccine-type GPSC (>50% non-PCV13 serotypes) on the basis of its initial serotype composition detected in the earliest vaccine period to measure their individual contribution toward serotype replacement in each country. Major pneumococcal lineages in the PCV period were identified by pooled incidence rate using a random effects model. / Findings: The five most prevalent serotypes in the PCV13 period varied between countries, with only serotypes 5, 12F, 15B/C, 19A, 33F, and 35B/D common to two or more countries. The five most prevalent serotypes in the PCV13 period varied between countries, with only serotypes 5, 12F, 15B/C, 19A, 33F, and 35B/D common to two or more countries. These serotypes were associated with more than one lineage, except for serotype 5 (GPSC8). Serotype replacement was mainly mediated by expansion of non-vaccine serotypes within vaccine-type GPSCs and, to a lesser extent, by increases in non-vaccine-type GPSCs. A globally spreading lineage, GPSC3, expressing invasive serotypes 8 in South Africa and 33F in the USA and Israel, was the most common lineage causing non-vaccine serotype invasive pneumococcal disease in the PCV13 period. We observed that same prevalent non-vaccine serotypes could be associated with distinctive lineages in different countries, which exhibited dissimilar antibiotic resistance profiles. In non-vaccine serotype isolates, we detected significant increases in the prevalence of resistance to penicillin (52 [21%] of 249 vs 169 [29%] of 575, p=0·0016) and erythromycin (three [1%] of 249 vs 65 [11%] of 575, p=0·0031) in the PCV13 period compared with the pre-PCV period. / Interpretation: Globally spreading lineages expressing invasive serotypes have an important role in serotype replacement, and emerging non-vaccine serotypes associated with different pneumococcal lineages in different countries might be explained by local antibiotic-selective pressures. Continued genomic surveillance of the dynamics of the pneumococcal population with increased geographical representation in the post-vaccine period will generate further knowledge for optimising future vaccine design. / Funding: Bill & Melinda Gates Foundation, Wellcome Sanger Institute, and the US Centers for Disease Control

Hund’s Rule-Driven Dzyaloshinskii-Moriya Interaction at 3d − 5d Interfaces

Using relativistic first-principles calculations, we show that the chemical trend of the Dzyaloshinskii-Moriya interaction (DMI) in 3d−5d ultrathin films follows Hund’s first rule with a tendency similar to their magnetic moments in either the unsupported 3d monolayers or 3d−5d interfaces. We demonstrate that, besides the spin-orbit coupling (SOC) effect in inversion asymmetric noncollinear magnetic systems, the driving force is the 3d orbital occupations and their spin-flip mixing processes with the spin-orbit active 5d states control directly the sign and magnitude of the DMI. The magnetic chirality changes are discussed in the light of the interplay between SOC, Hund’s first rule, and the crystal-field splitting of d orbitals

Hund’s Rule-Driven Dzyaloshinskii-Moriya Interaction at 3

Using relativistic first-principles calculations, we show that the chemical trend of Dzyaloshinskii-Moriya interaction (DMI) in 3d-5d ultrathin films follows Hund's first rule with a tendency similar to their magnetic moments in either the unsupported 3d monolayers or 3d-5d interfaces. We demonstrate that, besides the spin-orbit coupling (SOC) effect in inversion asymmetric noncollinear magnetic systems, the driving force is the 3d orbital occupation and their spin flip/mixing processes with the spin-orbit active 5d states control directly the sign and magnitude of the DMI. The magnetic chirality changes are discussed in the light of the interplay between SOC, Hund's first rule, and the crystal field splitting of d orbitals

Preparation and characterization of a new Kieselguhr based gas chromatography support

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