Quel avenir pour la steppe à Alfa dans le Sud-Ouest algérien ?

Les résultats obtenus dans la lutte contre la désertification, malgré les moyens mobilisés, restent très mitigés et révèlent l’inefficacité des approches et méthodes adoptées. La steppe algérienne est confrontée depuis plusieurs décennies à un problème de dégradation induit par l’effet combiné de facteurs anthropiques et naturels. Toute action de préservation et de réhabilitation de la steppe doit reposer dans un premier temps sur un diagnostic permettant d’identifier et d’évaluer le poids de chaque facteur dégradant. Parmi les facteurs souvent soulignés on note le climat, le parcours, le défrichement et la pratique d’une agriculture pluviale sans une justification ni estimation de cet impact. Le diagnostic ciblant et classant les principaux facteurs de régression des formations steppique de Stipa tenacissima est l’objectif assigné à cette publication. La démarche retenue permettant de sauver la steppe doit d’abord reposer sur une identification des facteurs causaux de cette situation et une évaluation de leur impact et classification

Effect of MoO3 in the cathode buffer layer on the behaviour of layered organic solar cells

The behaviour of small-molecule organic solar cells based on coper-phthalocyanine/fullerene with different cathode buffer layer is investigated as a function of air exposure duration. We present the study of the effect of MoO3 on the properties of photovoltaic solar cells (OPVCs) when it is introduced in the cathode buffer layer (CBL). Photovoltaic performances were measured as a function of time of air exposure. During the first days of air exposure the efficiency of the OPVCs with MoO3 in their CBL increases significantly, while it decreases immediately after air exposure in the case of reference OPVCs, i.e. without MoO3 in the CBL. Nevertheless, the lifetime of the OPVCs with MoO3 in their CBL is around 60 days, while it is only 10 days in the case of reference OPVCs. The initial increase of the OPVC with MoO3 in their CBL is attributed to the slow decrease of the work function of MoO3 due to progressive contamination. Then, the progressive degradation of the OPVCs efficiency is due water vapour and oxygen contamination of the organic layers. The use of a double CBL, Alq3/MoO3, allows to interrupt the growth of pinholes, defects and increases the path of permeating gas. Also it can prevent the contamination of the organic layer by Al. All this results in significant increase of the lifetime of the OPVCs

Microstructural properties of ZnO :Sn thin films deposited by intermittent spry pyrolysis process

Zinc oxide films have been prepared via spray pyrolysis using a perfume atomizer. ZnCl2 has been used as precursor. The influence of the precursor solution and dopant concentration has been investigated. Homogeneous films are obtained with a precursor concentration ranging between 0.3 and 0.4 M and a SnCl2 dopant concentration of 1–2%. The films exhibit broad band gaps and small conductivity. The microstructural properties of these films have been compared with that of films deposited using a classical nozzle. Films deposited by perfume atomizer are rougher, with smaller grain size, compared to films deposited with a classical nozzle

Effect of a zinc oxide, at the cathode interface, on the efficiency of inverted organic photovoltaic cells based on the CuPc/C60 couple

The effect of ZnO buffer layer on the performances of inverted multilayers organic solar cells has been studied. ZnO:Al conductive films and insulating ZnO films deposited by spin coating have been probed. The ZnO buffer layer has been introduced between the ITO cathode and the Organic acceptor. The cells are based on the multilayer junctions bathocuproine/fullerene/copper phthalocyanine. The organic photovoltaic cells performances improvement depends of the ZnO layer introduced. ZnO:Al conductive layers decreases the potential barrier at the interface cathode/organic. This allows decreasing the series resistance which improves significantly the cell efficiency. Insulating ZnO increases only slightly the solar cells performance by increasing significantly the shunt resistance and therefore the open circuit voltage of the cells

Preparación y caracterización de cementos belíticos blancos activados con dopantes alcalinos

Activated white cement clinkers with a theoretical 60% (wt) belite (dicalcium silicate) content were prepared at a temperature 100 ºC lower than used to manufacture conventional white Portland cement clinkers. Activation was achieved by adding variable amounts of K2CO 3 or Na2CO 3 to the raw mixes. Rietveld quantitative analysis of X-ray diffraction findings showed that adding the alkalis stabilized the high temperature belite polymorphs. When 2.0% (wt) of Na2O was added, the composition (by wt) found was 16.4(4)% alpha-C2S, 16.7(8)% alpha’-H-C2S, 23.2(6)% beta-C2S, 32.7(7)% total C3S, 9.5(2)% orthorhombic C3A and 1.50(5)% free lime. Due to the high volatilization rate of K2O under the experimental conditions, it stabilized the alpha-type C2S less effectively than Na2O. A calorimetric study was likewise performed to correlate the phase composition with early age hydration (behaviour).Se han preparado clínkeres blancos activados con un porcentaje en peso teórico de belita (silicato dicálcico) del 60%, a una temperatura 100 ºC menor que los clínkeres Portland blancos convencionales. El proceso de activación se ha llevado a cabo añadiendo a las mezclas crudas cantidades variables de K2CO3 o Na2CO 3. Utilizando la difracción de rayos-X y la metodología de Rietveld se ha comprobado la estabilización a temperatura ambiente de porcentajes variables de los polimorfos de alta temperatura de la belita por la adición de alcalinos. De hecho, al añadir 2,0% en peso de Na2O se ha obtenido 16,4(4)% de alfa-C2S, 16,7(8)% de alfa’-H-C2S, 23,2(6)% de beta-C2S, 32,7(7)% de C3S total, 9,5(2)% de C3A ortorrómbico y 1,50(5)% de cal libre, porcentajes en peso. Se ha comprobado que el grado de volatilización de los alcalinos, en estas condiciones de preparación, ha sido muy acusado para el K2O, lo que ha provocado una menor estabilización de los polimorfos tipo-alfa-C2S. Además, se ha realizado un estudio calorimétrico para correlacionar el ensamblaje de fases con el comportamiento de hidratación a edades tempranas

Effects of the buffer layer inserted between the transparent conductive oxide anode and the organic electron donor

In optoelectronic devices, the work function of the transparent conductive oxide, which is used as anode, does not match well the highest occupied molecular orbital of the organic material, which induces the formation of a barrier opposed to hole exchange at this interface. Therefore a thin buffer layer is often used to achieve good matching of the band structure at the interface. From experimental results it can be deduced that the main effects of the buffer layer consist in a better matching of the band structure at the interface anode/organic material and in a more homogeneous organic layer growth. We show that, whatever the nature of the buffer layer-metal, oxide, organic material—the classical Schottky–Mott model allows to anticipate, at least roughly, the behaviour of the contact, even if some dipole effect are often present. A good correlation between the “metal/buffer layer” work function and the barrier Φb for hole exchange at anode/organic electron donor interfaces is obtained, as expected by the model

On the influence of the exciton-blocking layer on the organic multilayer cells properties

The performances of organic photovoltaic cells based on the layer couple electron donor/electron acceptor (ED/EA) are significantly improved when an exciton blocking layer (EBL) is inserted between the organic acceptor and the cathode. A new material, the (Z)-5-(4-chlorobenzylidene)-3-(2-ethoxyphenyl)-2-thioxothiazolidin-4-one, that we called (CBBTZ), has been synthesized, characterized and probed as EBL. The energy levels corresponding to the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the CBBTZ have been determined from the first oxidation and reduction potential respectively, using cyclic voltametric (CV) measurements. From CV curves, CBBTZ in dichloromethane showed a one electron reversible reduction and oxidation waves. The values of its HOMO and LUMO have been estimated to be 6.42 eV and 3.42 eV respectively. Such values show that CBBTZ could be probed as EBL in organic solar cells based on the ED/EA couple copper phthalocyanine(CuPc)/fullerene (C60). The photovoltaic solar cells have been obtained by sequential deposition under vacuum of the different films. The different thin film thicknesses were measured in situ by a quartz monitor. Multilayer solar cells ITO/Au/CuPc/C60/EBL/Al have been probed, where EBL is the aluminium tris(8-hydroxyquinoline) (Alq3), the CBBTZ, the 2-(4-byphenylyl)-5-(4-tert-buthylphenyl)-1,3,4-oxadiazole (butyl PBD) or the bathocuproine (BCP). The optimum film thickness is 8–9 nm whatever the EBL used. When obtained in the same run, the averaged efficiency of the cells using the CBBTZ is of the same order of magnitude than that obtained with BCP and higher than that achieved with Alq3 or butyl PBD. It is shown by XPS study that some aluminium of the cathode is present in the buffer layer. This aluminium could justify the ability of the electrons to cross the insulating exciton blocking layer thick of 9 nm

Influence of the exciton blocking layer on the stability of layered organic solar cells

The life-time of multi-layer organic solar cells based on the couple donor acceptor copper phthalocyanine/fullerene is studied as a function of the nature of the exciton blocking layer (EBL). It is shown that organic EBL are more efficient than are the inorganic In2S3 EBLs. Moreover among the organic EBL, Alq3 is the most efficient EBL protecting layer. An organic solar cell’s lifetime depends on oxygen- and water-contamination of the organic materials. The solar cell’s degradation may correspond to bulk or interface phenomena. Using equivalent electrical schemes of solar cell diodes, we show that the structure degradation is mainly related to bulk modification. It is proposed that oxygen- and water-diffusion into the C60 induce a large increase in its resistivity and, therefore an increase in the series resistance, which decreases the solar cell efficiency. In the case of In2S3 EBLs, the degradation law predicts that with time two different phenomena will be present. The classical oxygen- and water-diffusion into the organic material, during the first hour of air exposure, leads to a modification in the In2S3 EBL/organic interface properties

Mutation of Rubie, a Novel Long Non-Coding RNA Located Upstream of Bmp4, Causes Vestibular Malformation in Mice

Background: The vestibular apparatus of the vertebrate inner ear uses three fluid-filled semicircular canals to sense angular acceleration of the head. Malformation of these canals disrupts the sense of balance and frequently causes circling behavior in mice. The Epistatic circler (Ecl) is a complex mutant derived from wildtype SWR/J and C57L/J mice. Ecl circling has been shown to result from the epistatic interaction of an SWR-derived locus on chromosome 14 and a C57L-derived locus on chromosome 4, but the causative genes have not been previously identified. Methodology/Principal Findings: We developed a mouse chromosome substitution strain (CSS-14) that carries an SWR/J chromosome 14 on a C57BL/10J genetic background and, like Ecl, exhibits circling behavior due to lateral semicircular canal malformation. We utilized CSS-14 to identify the chromosome 14 Ecl gene by positional cloning. Our candidate interval is located upstream of bone morphogenetic protein 4 (Bmp4) and contains an inner ear-specific, long non-coding RNA that we have designated Rubie (RNA upstream of Bmp4 expressed in inner ear). Rubie is spliced and polyadenylated, and is expressed in developing semicircular canals. However, we discovered that the SWR/J allele of Rubie is disrupted by an intronic endogenous retrovirus that causes aberrant splicing and premature polyadenylation of the transcript. Rubie lies in the conserved gene desert upstream of Bmp4, within a region previously shown to be important for inner ear expression of Bmp4. We found that the expression patterns of Bmp4 and Rubie are nearly identical in developing inner ears