Design and control of parallel three phase voltage source Inverters in low voltage AC microgrid

Design and hierarchical control of three phase parallel Voltage Source Inverters are developed in this paper. The control scheme is based on synchronous reference frame and consists of primary and secondary control levels. The primary control consists of the droop control and the virtual output impedance loops. This control level is designed to share the active and reactive power correctly between the connected VSIs in order to avoid the undesired circulating current and overload of the connected VSIs. The secondary control is designed to clear the magnitude and the frequency deviations caused by the primary control. The control structure is validated through dynamics simulations.The obtained results demonstrate the effectiveness of the control structure

UC@MOOC's Effectiveness by Producing Open Educational Resources

Open education is one of the most important settings in every society. It grants everyone the right to learn freely. Today, technology is helping to make learning even more open by providing an environment of online education, which plays a remarkable role in shortening distances and encouraging students to learn. At Cadi Ayyad University (UCA) the new-enrolled students are facing linguistics barriers as well as overcrowding in classrooms, in particular for those in open access institutions. Subsequently, they cannot have an easy access to their face-to-face courses. To help students to overcome these problems, the university has decided to design an online environment for all courses and programmes. The most innovative project adopted at UCA to face massification was inspired from the massive open online courses and was designed as an open Educational platform entitled UC@MOOC. More than 120 scripted courses have been posted online so far. In this paper we will describe and discuss an analytics research on geometrical optics course designed for around 2000 students at UCA. Through out this research we will explain how this initiative has been considered as a source of producing open educational resources

Rétention des produits phytosanitaires dans les fossés de connexion parcelle-cours d'eau

Pour lutter contre les pollutions diffuses en milieu rural, de nombreux programmes d'action se mettent en place. Le développement de recherches sur les connexions parcelle - cours d'eau devrait permettre de mieux comprendre le transfert et la dissipation des polluants dans ce milieu. En particulier, les fossés, structures relativement fréquentes dans les territoires cultivés, peuvent, a priori, avoir une fonction de court-circuit et donc faciliter le transfert des produits phytosanitaires, ou au contraire constituer des éléments de pondération de la pollution. Afin d'éclaircir ce point, une première série d'expérimentations a été menée par le Cemagref (Institut français de recherche pour l'ingénierie de l'agriculture et de l'environnement) dans des fossés de drainage agricole. Une solution aqueuse contenant trois herbicides aux caractéristiques physico-chimiques différentes (isoproturon, diuron et diflufénicanil), et un traceur (chlorures) a été injectée pendant quelques minutes dans quatre fossés. Des échantillons d'eau ont été prélevés à pas de temps fins à deux emplacements en aval du point d'injection. Après dosage par chromatographie au laboratoire, les résultats indiquent une diminution du flux et de la concentration maximale du pic de polluants comparativement à un traceur. En outre, la variation observée est corrélée aux propriétés physico-chimiques des produits, en particulier au coefficient de partage Koc. L'étude présentée montre que la surface de contact (liée à la nature du substrat) et le temps de contact (dépendant essentiellement des conditions d'écoulement) entre les polluants et le substrat sont les paramètres qui influent majoritairement sur la dissipation des produits phytosanitaires.The use of pesticide may lead to the contamination of surface and groundwaters. Agricultural nonpoint source pollution originates from land areas which intermittently contribute to the compound transfer to water. Several studies report on the occurrence of pesticides in surface water resources, with concentrations over the limit set by the 80/778 EEC directive for drinking water (0.1 µg/L for each substance and 0.5 µg/L for all pesticides). Numerous herbicides of different chemical families are detected in surface waters, especially triazines and ureas. Their concentrations vary with time and space partly in relation with application patterns and pluviometry. Maximum concentrations are linked to runoff, originating from agricultural fields and primarily occur right after the application periods.Many methods and levels of actions can be used to reduce water pollution. First, better agricultural practices can be set up, such as choosing the best dose and application period, controlling toxic substance impacts, combining with non-chemical practices. However, pesticide losses from fields can't be totally cancelled because of the complexity of the involved parameters (agricultural practices, climatic conditions, soil physical, chemical and biological properties …). In fact drift during application, runoff or drainage systems may still occur and have an effect on water quality. It may be then pertinent to evaluate to which extent the non treated areas between the fields and the surface water bodies can dissipate pesticide concentrations before they reach them. Pesticides leaving a plot in surface runoff may pass through various landscape components before reaching rivers ; including another field, a ditch, a small brook, a vegetative buffer zone. Besides, pesticide leaving the plot through drainage straightly moves agricultural ditches or streams. However, the contribution of each of these elements in pesticide dissipation is not well known, except for buffer zones (grassed or forest strips) (PATTY (1997). Cemagref (a French research institute), CEH Wallingford and ITCF (Institut Technique des Cereales et des Fourrages) attempt to extend their study to the other elements as agricultural ditches.This paper deals with the role of farm ditches and small streams in the transport and retention of pesticides from fields to the main river network. Their presence seems to play a significant role in the transfer of nonpoint source pollution (especially in the West of France). Indeed they can either accelerate pesticide transport or reduce it, according to their characteristics (length, flow, bottom sediment or soil characteristics, plants and organic matter contents, etc.). Since 1998, Cemagref has been investigating the retention of pesticides by several natural ditches with varied flows and substratum. A water solution containing three herbicides with different physico chemical properties (diflufenican, diuron and isoproturon) and potassium chloride, a tracer, is introduced with a pump in each ditch for about five minutes with a constant concentration. Water samples are collected in the ditches every two or five minutes at two distances from the injection point. The samples are stored in amber polyethylene terephtalate bottles and frozen. Laboratory analysis is performed by liquid-liquid extraction with dichloromethane and then liquid or gas chromatography depending on the compounds.The analysis of the water samples highlights a reduction of the maximum concentration and of the accumulative mass of each pesticide with distance compared to the tracer. Indeed, even if all the chloride ions used as tracers are not recovered at each sampling point (due to infiltration or lateral losses), we notice more significant losses for all the studied herbicides. The reduction can reach 70 % of the applied mass for diflufenican compared to the tracer. The retention of pesticides is also linked to their own physical and chemical properties. Thus, diflufenican, which has the highest sorption coefficient value, Koc, is also the most retained pesticide, whereas the total injected mass of isoproturon is recovered in most cases. Diuron has an intermediate behaviour.In brief, this field experiment proves that the surface and time of contact between pollutants and substratum are likely to play a major role in pesticide retention. An estimated adsorption capacity of each ditch has been assessed, which is based on laboratory sorption experiments on different natural substratum. Despite the few data, a relationship between diflufenican retention in ditches and the estimated adsorption capacity of each ditch has been underscored.This study also highlighted major limits of field experiments. For example, accurate flow measurements are really difficult to carry out with simple methods for low values. The conventional techniques can't be used with small water height or in ditch where the bottom is filled with plants or grass. Chloride ion was chosen in this study because it is easy to analyze, but the results showed an initial presence of chloride ion in the natural ditch water which incites to replace it by another tracer such as bromide with is not found in the environment in future field experiments.For all these reasons, some pilot experiments with a physical model (an artificial ditch of 8 m long and 0.4 m wide) are now designed. This equipment allows to adjust and control hydrodynamic parameters such as water flow, water height, and the nature and structure of the substratum. Then, it is possible to quantify both the role played by the substratum, mainly the organic matter content, and the role of the contact time. These parameters could be then taken into account in order to optimize further experiments on adsorption. The primary tests without substratum already give references for hydrodynamic measurements, as the stability of the water flow and the homogeneity of the initial solution concentration

Silicone rubber selection for passive sampling of pesticides in water.

The authors thank G. Raffin and M. Hangouet (ISA, UMR 5280) for TGA analysis and interpretation, and C. Guillemain (Irstea) for analytical support.International audienceSilicone rubber can extract organic compounds with a broad range of polarities (logKow>2-3) from aqueous samples. Such compounds include substances of major concern in the protection of aquatic ecosystems and human health, e.g. pesticides. Silicone rubbers (SRs) with various characteristics have been successfully used in sorptive methods for water sample extraction in the laboratory (SPME, SBSE), and for passive sampling in aquatic environments. However, only few studies have evaluated variability in organic compound sorption due to the origin of SRs, particularly for pesticides. The aim of this study was to select an SR for the extraction of pesticides from water samples by passive sampling. To this end we measured the impact of seven SR formulations on sorption capacity, defined by the partition coefficient (Ksw). Kinetic experiments and sorption isotherms were performed to determine extraction recovery as a selection criterion for SRs, and pesticide partition coefficients. Very large differences in affinity for pesticides were found between two kinds of SRs: "Polymerized SR kits" and "Manufactured SRs". One SR was chosen among the "Manufactured SRs", and the Ksw values of 21 pesticides were determined, filling a gap in the literature (1.50<logKow<5.51). In light of sorption properties, literature data and additional economic and technical factors, we suggest using SR from Goodfellow in future work to reduce the variability of Ksw literature values

Assessing pesticide concentrations and fluxes in the stream of a small vineyard catchment. Effect of sampling frequency

This study reports on the occurrence and behaviour of six pesticides and one metabolite in a small stream draining a vineyard catchment. Base flow and flood events were monitored in order to assess the variability of pesticide concentrations according to the season and to evaluate the role of sampling frequency on the evaluation of fluxes estimates. Results showed that dissolved pesticide concentrations displayed a strong temporal and spatial variability. A large mobilisation of pesticides was observed during floods, with total dissolved pesticide fluxes per event ranging from 5.7*10-3 g/Ha to 0.34 g/Ha. These results highlight the major role of floods in the transport of pesticides in this small stream which contributed to more than 89% of the total load of diuron during August 2007. The evaluation of pesticide loads using different sampling strategies and method calculation, showed that grab sampling largely underestimated pesticide concentrations and fluxes transiting through the stream

Les infrastructures à la lumière des théories du commerce : le rôle des coûts de transport

There is some conviction that the costs of logistics and transport were not integrated into the economic question until the late 19th century. Nevertheless, several studies have revealed that the importance of transport was evident, so it would be interesting to highlight the starting point for the consideration of transport in trade. The objective of this paper is to provide a critical review of the theoretical work governing the link between macroinfrastructure and trade. Our analysis of trade is informed by the limitations that have marked the neglect of space in the classical field of trade, looking at classical trade theories related to the notion of comparative advantage. This shortcoming has been the subject of much criticism by spatial economists. Subsequently, transport costs, which were somewhat neglected in classical trade theory, became the focus of new trade theories. This can be seen in the Samuelson model and in the advances of the new classical trade theory. The results of our critical analysis have shown that the inclusion of transport costs has followed a gradual sequence that has eventually made transport costs a cornerstone of economic analysis, and that its omission will lead to results that escape reality. &nbsp; Keywords: Transportation costs, Infrastructure, Trade JEL Classification: &nbsp;B17 Paper type: Theoretical Research&nbsp;Il existe une certaine conviction que les coûts de la logistique et du transport n'ont pas été intégrés dans la question économique avant la fin du 19ème siècle. Néanmoins, plusieurs études ont révélé que l'importance du transport était évidente, il serait donc intéressant de mettre en évidence le point de départ de la prise en compte du transport dans le commerce. L’objectif de cet article est de fournir une revue critique des travaux théoriques régissant le lien entre la macro-infrastructure et le commerce. Notre analyse du commerce est éclairée par les limites qui ont marqué la négligence de l'espace dans le champ classique du commerce, en se penchant sur les théories commerciales classiques liées à la notion d'avantage comparatif. Cette lacune a fait l'objet de nombreuses critiques de la part des économistes spatiaux. Par la suite, les coûts de transport, qui étaient quelque peu négligés dans la théorie classique du commerce, sont devenus le centre d'intérêt des nouvelles théories du commerce. Ceci se manifeste à travers le modèle de Samuelson et les avancées de la nouvelle théorie classique du commerce. Les résultats de notre analyse critique ont montré que la prise en compte des coûts de transport a suivi une séquence graduelle qui a fini par faire des coûts de transport, une pierre angulaire de l'analyse économique, et que son omission conduira à des résultats qui échappent à la réalité. &nbsp; Mots clés : Coûts de transport, Infrastructure, Commerce Classification JEL:&nbsp; B17 Type de l’article&nbsp;: Recherche théorique. &nbsp

Capital immatériel et logistique : examen de l’impact de l’innovation sur la performance logistique à travers un Modèle ARDL

Le passage de l'économie traditionnelle à une économie basée sur l'immatériel a montré que les actifs immatériels sont la clé du développement économique. C'est à la lumière de ce constat que la littérature s'est enrichie d'analyses sur l'importance du capital immatériel comme déterminant du progrès économique. Ainsi, le développement du commerce international est principalement mu par l'innovation technologique ayant un retentissement sur la compétitivité internationale d'un pays, à travers un impact remarquable sur les performances logistiques.L'objectif de cet article est de souligner l'importance du capital immatériel pour la performance logistique en examinant la relation entre le capital immatériel et la performance logistique et ses effets innovants sur le commerce transfrontalier. Notre analyse basée sur un modèle autorégressif à retards échelonnés ARDL utilisant les données sur l'innovation de l'indice global d'innovation et les données sur les coûts et les délais du commerce transfrontalier du Maroc sur la période 2007-2019 montre un effet positif significatif à long et à court terme de l'innovation sur la performance logistique marocaine

Infrastructures de transport et croissance économique : Une analyse économétrique à travers le modèle autorégressif à retards échelonnés ARDL

The economic literature has clearly proven that infrastructure development is an essential lever for productivity and sustained economic growth. This hypothesis has been tested in depth in the literature using different approaches and methods. This research aims to study the dynamics of the short- and long-term impacts of transport infrastructure on Morocco's economic growth over the period 1984-2019 from an investment perspective. To accomplish this, we used the Auto-regressive distributed lags ARDL of (( Pesaran, Shin and Smith (2001)). Our results show that the positive effects of transport infrastructure on economic growth in Morocco occur in the short and long term. Economic theory has revealed that the beneficial effects of transport infrastructure will be felt in monetary terms and in other terms such as travel time, environmental effects, safety and so on, which implies the need for Morocco to take this constant into account in order to strengthen its accessibility and internal mobility and thus promote its integration into the world economy.La littérature économique a clairement démontré que le développement des infrastructures est un levier essentiel pour la productivité et la croissance économique soutenue. Cette conjecture a été vérifiée en profondeur dans la littérature à l'aide de différentes approches et méthodes. Cette recherche vise à étudier la dynamique de l'impact à court et long terme des infrastructures de transport sur la croissance économique du Maroc au cours de la période 1984-2019, considérée sous l'angle des investissements. Pour ce faire, nous avons utilisé le modèle autorégressif à retards échelonnés ARDL de (Pesaran, Shin et Smith (2001)). Nos résultats font ressortir que les effets positifs des infrastructures de transport sur la croissance économique au Maroc se concrétisent à court et à long terme. La théorie économique a révélé que les effets bénéfiques des infrastructures de transport se feront sentir en termes monétaires et en d'autres termes tels que le temps de trajet, les effets environnementaux, la sécurité, etc., ce qui implique la nécessité pour le Maroc de prendre en compte cette constante afin de renforcer son accessibilité et sa mobilité interne et ainsi promouvoir son insertion dans l'économie mondiale &nbsp

Corruption et Commerce : Une digue ou lubrifiant des exportations marocaines ? Une analyse dynamique.

En théorie normative, le commerce et la corruption sont incompatibles. Cependant, lespreuves empiriques illustrent une antilogie dans le débat qui s’articule sur les effets de la corruption sur le commerce. Ce papier a pour objectif d’examiner le lien entre la corruption et les exportations marocaines. Nous avons appliqué un modèle de gravité dynamique sur les exportations du Maroc vers un groupe de 80 principaux partenaires commerciaux durant 2008-2018, afin de déceler la nature de la relation entre la corruption et l’offre exportatrice marocaine. Nos résultats suggèrent un lien négatif entre la corruption et les exportations marocaines, en outre, une diminution des pratiques de corruption entrainera une expansion des flux à l’export, en somme, le Maroc en améliorant la qualité de ses institutions, moyennant une lutte efficace contre la corruption, renforcera sa compétitivité internationale

Interactive Effects of Pesticides and Nutrients on Microbial Communities Responsible of Litter Decomposition in Streams

Global contamination of streams by a large variety of compounds, such as nutrients and pesticides, may exert a high pressure on aquatic organisms, including microbial communities and their activity of organic matter decomposition. In this study, we assessed the potential interaction between nutrients and a fungicide and herbicide [tebuconazole (TBZ) and S-metolachlor (S-Met), respectively] at realistic environmental concentrations on the structure (biomass, diversity) and decomposition activity of fungal and bacterial communities (leaf decay rates, extracellular enzymatic activities) associated with Alnus glutinosa (Alnus) leaves. A 40-day microcosm experiment was used to combine two nutrient conditions (mesotrophic and eutrophic) with four pesticide treatments at a nominal concentrations of 15 μg L-1 (control, TBZ and S-Met, alone or mixed) following a 2 × 4 full factorial design. We also investigated resulting indirect effects on Gammarus fossarum feeding rates using leaves previously exposed to each of the treatments described above. Results showed interactive effects between nutrients and pesticides, only when nutrient (i.e., nitrogen and phosphorus) concentrations were the highest (eutrophic condition). Specifically, slight decreases in Alnus leaf decomposition rates were observed in channels exposed to TBZ (0.01119 days-1) and S-Met (0.01139 days-1) than in control ones (0.01334 days-1) that can partially be explained by changes in the structure of leaf-associated microbial communities. However, exposition to both TBZ and S-Met in mixture (MIX) led to comparable decay rates to those exposed to the pesticides alone (0.01048 days-1), suggesting no interaction between these two compounds on microbial decomposition. Moreover, stimulation in ligninolytic activities (laccase and phenol oxidase) was observed in presence of the fungicide, possibly highlighting detoxification mechanisms employed by microbes. Such stimulation was not observed for laccase activity exposed to the MIX, suggesting antagonistic interaction of these two compounds on the ability of microbial communities to cope with stress by xenobiotics. Besides, no effects of the treatments were observed on leaf palatability for macroinvertebrates. Overall, the present study highlights that complex interactions between nutrients and xenobiotics in streams and resulting from global change can negatively affect microbial communities associated with leaf litter, although effects on higher trophic-level organisms remains unclear