Techno-economic analysis of stand-alone solar desalination at variable load conditions

The operation of large-scale reverse osmosis units in combination with different solar power plants, both, Concentrating Solar Power (CSP) and Photovoltaics (PV) has been evaluated under variable load conditions. In the case of the Reverse Osmosis (RO) unit, configurations with and without an energy recovery device have been considered. In the case of the CSP plant, a thermal storage system with several capacities (8-14 h) covers the periods with low solar radiation and no storage has been taken into account for the PV plant due to the prohibitively high cost of batteries at large scale. The analysis has been done for a specific location in Algeria, considering different scenarios to adapt the operation of the RO unit at partial load in order to assure a stable operation. The dynamic performance of the RO unit is presented for each scenario, together with an economic analysis

Prediction of direct normal irradiation using a new empirical sunshine duration-based model

In this work, we are interested in presenting a new approach allowing us to express the Direct Normal solar Irradiation (DNI) according to the sunshine duration essentially. This choice is justified by the fact that in addition to the sunshine, duration has a strong correlation with solar irradiation, it is measured in many radiometric stations. Some clear sky models with modifications developed exclusively here are made valid for all types of sky. The proposed model is compared with one of the intelligent models such as the Support Vector Regression (SVR) for daily data from Ghardaïa

Not Only Toxic but Repellent: What Can Organisms’ Responses Tell Us about Contamination and What Are the Ecological Consequences When They Flee from an Environment?

The ability of aquatic organisms to sense the surrounding environment chemically and interpret such signals correctly is crucial for their ecological niche and survival. Although it is an oversimplification of the ecological interactions, we could consider that a significant part of the decisions taken by organisms are, to some extent, chemically driven. Accordingly, chemical contamination might interfere in the way organisms behave and interact with the environment. Just as any environmental factor, contamination can make a habitat less attractive or even unsuitable to accommodate life, conditioning to some degree the decision of organisms to stay in, or move from, an ecosystem. If we consider that contamination is not always spatially homogeneous and that many organisms can avoid it, the ability of contaminants to repel organisms should also be of concern. Thus, in this critical review, we have discussed the dual role of contamination: toxicity (disruption of the physiological and behavioral homeostasis) vs. repellency (contamination-driven changes in spatial distribution/habitat selection). The discussion is centered on methodologies (forced exposure against non-forced multi-compartmented exposure systems) and conceptual improvements (individual stress due to the toxic effects caused by a continuous exposure against contamination-driven spatial distribution). Finally, we propose an approach in which Stress and Landscape Ecology could be integrated with each other to improve our understanding of the threat contaminants represent to aquatic ecosystems.Versión del edito

Amélioration des performances d’une installation de turbine à gaz par refroidissement de l’air d’admission

72 p. ; ill. ; 30 cmLes turbines à gaz ont connues une grande importance dans le domaine industriel notamment dans celui des hydrocarbures. Une installation de turbine à gaz est conçue pour fonctionner dans des conditions thermodynamiques de température et de pression précisées par les standards ISO. Malheureusement ces conditions ne sont pas toujours obtenues car elles varient d’un jour à un autre, d’une région à une autre (sud, nord), et d’un climat à un autre (climat humide, aride, sec, chaud, etc…). Les performances de l’installation d’une turbine à gaz sont inversement proportionnelles à la température ambiante puisque plus la température ambiante diminue plus la masse d’air admise dans le compresseur augmente ce qui influe directement sur les performances. A cet effet notre travail consiste à étudier l’amélioration des performances d’une installation de turbine à gaz par refroidissement de l’air de l’admission à l’entrée du compresseur. Plusieurs techniques existent pour assurer le refroidissement de l’air à la prise du compresseur mais chaqu’une a ses contraintes d’utilisation. Ainsi, l’exposé aborde l’étude d’un système de refroidissement d’air par évaporation d’eau (refroidisseur par ruissellent d’eau) qui est adaptable avec les zones sec et chaude comme celle du sud d’Algérie (zone saharienne). On a relevé les données réelles d’une turbine à gaz installée à la zone gazière de HassiR’Mel (250 Km au sud d’Alger) grâce à un stage pratique à SONATRACH. Pour la modélisation on à travailler à l’aide d’un logiciel appelé Engeneering equation Solver (EES). Les résultats obtenus montrent que les performances de la turbine à gaz étudiée sont améliorées grâce à l’utilisation d’un refroidisseur où l’augmentation de la puissance nette produite varie entre 1.5 à 5 MW avec augmentation du rendement thermique de l’installation. Un autre facteur qui n’est pas négligeable est le facteur environnemental. Le refroidisseur permet de diminuer les émissions des NOx de 1 jusqu’à 7 % par rapport au cas classique (sans refroidissement

Early Middle Stone Age personal ornaments from Bizmoune Cave, Essaouira, Morocco

International audienceOrnaments such as beads are among the earliest signs of symbolic behavior among human ancestors. Their appearance signals important developments in both cognition and social relations. This paper describes and presents contextual information for 33 shell beads from Bizmoune Cave (southwest Morocco). Many of the beads come as deposits dating to ≥142 thousand years, making them the oldest shell beads yet recovered. They extend the dates for the first appearance of this behavior into the late Middle Pleistocene. The ages and ubiquity of beads in Middle Stone Age (MSA) sites in North Africa provide further evidence of the potential importance of these artifacts as signals of identity. The early and continued use of Tritia gibbosula and other material culture traits also suggest a remarkable degree of cultural continuity among early MSA Homo sapiens groups across North Africa