12 research outputs found

    Electrical discharge reproduction in rod-barrier-plane system

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    The present paper deals with new modeling to reproduce the electric discharge in the rod-plane air gap system with rubber insulating barrier under AC and impulse voltage. This model considers the randomness character of discharge evolution which is governed by the electric field. The discharges shape obtained by this model are compared with ones given by experimental tests. The established model reproduces correctly the forms of discharges obtained by experimental tests under AC voltage. It is found that the behavior of the electrical discharge depends not only on the dimension (thickness and width) of the insulating barriers but on its positions in the air gap as well. It is to highlight that the mode of applied voltage is of key importance barrier. Experimental investigation shows that the developed arc can evolve on 1 to 4 channels. The generated discharges in AC voltage distinguish by the formation of a multiple-channel arc. Whereas, the discharge under lightning impulse voltage found to progress in a single channel whatever the barrier position and dimensions. The model confirms that electric field is the most important factor in the behavior of the rod-insulating barrier-plane system submitted to high voltage

    Salt response in pepper (Capsicum annuum L.): components of photosynthesis inhibition, proline accumulation and K+/Na+ selectivity

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    Three salinity of irrigation water (control, 70, 120 and 170 mM NaCl) were applied to five cultivars of hot pepper (Capsicum annuum L.) collected from the South of Tunisia. After three weeks, relative water content, photosynthetic pigment levels, gas exchange, proline, soluble sugars and ions K+ and Na+ concentrations were measured. The results showed that the inhibition of photosynthesis was not mainly stomatal, but probably biochemical manifesting by a stability of stomatal conductance up to 120 mM NaCl and accompanied by a continuous increase in intercellular CO2 concentration under the three concentrations of salt. Proline content increased considerably as a result of stress and reaches almost double those of controls in cultivars Alaya, Shkira and Sgay and even triple in cultivars Maghraoua and Farch. Solubles sugars do not contribute effectively to the osmotic adjustment. Mineral analysis showed that until 120 mM NaCl, the highest concentration of Na+ was obtained in stems, probably reflecting the existence of a re-circulation mechanism of Na+. Meanwhile, salinity reduced the foliar K+ content. At stems level, K+ concentration does not show significantly disruptions compared to control. However, at the roots, there is a continuous increase in potassium content. For K+/Na+ shoot ratio and at 70 mM NaCl, all cultivars showed a decrease of selectivity except cv. Maghraoua. At 120 and 170 mM, the same cultivar showed the lowest reduction. In root system, at 70 mM NaCl, cv. Maghraoua showed the greater improvement of selectivity.Â

    A mixed formulation for the Signorini problem in nearly incompressible elasticity

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    International audienceWe present a free-locking finite element approximation of the displacement-pressure formulation for the Signorini problem, in nearly incompressible elasticity. Studying the nonlinear variational problem requires an appropriate saddle point theory. An abstract framework is laid down and applied to the system of the variational inequalities we are involved in. Existence and uniqueness results for the continuous problem are proven and optimal convergence rates of the mixed Taylor-Hood finite element discretisation are proved. Some numerical experiences are reported to underline the reliability of this approach

    Salt response in pepper (Capsicum annuum L.): components of photosynthesis inhibition, proline accumulation and K+/Na+ selectivity

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    Three salinity of irrigation water (control, 70, 120 and 170 mM NaCl) were applied to five cultivars of hot pepper (Capsicum annuum L.) collected from the South of Tunisia. After three weeks, relative water content, photosynthetic pigment levels, gas exchange, proline, soluble sugars and ions K+ and Na+ concentrations were measured. The results showed that the inhibition of photosynthesis was not mainly stomatal, but probably biochemical manifesting by a stability of stomatal conductance up to 120 mM NaCl and accompanied by a continuous increase in intercellular CO2 concentration under the three concentrations of salt. Proline content increased considerably as a result of stress and reaches almost double those of controls in cultivars Alaya, Shkira and Sgay and even triple in cultivars Maghraoua and Farch. Solubles sugars do not contribute effectively to the osmotic adjustment. Mineral analysis showed that until 120 mM NaCl, the highest concentration of Na+ was obtained in stems, probably reflecting the existence of a re-circulation mechanism of Na+. Meanwhile, salinity reduced the foliar K+ content. At stems level, K+ concentration does not show significantly disruptions compared to control. However, at the roots, there is a continuous increase in potassium content. For K+/Na+ shoot ratio and at 70 mM NaCl, all cultivars showed a decrease of selectivity except cv. Maghraoua. At 120 and 170 mM, the same cultivar showed the lowest reduction. In root system, at 70 mM NaCl, cv. Maghraoua showed the greater improvement of selectivity.

    Flambement d'un pipeline en composite endommagé

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    le comportement mécanique d'un pipe muni d’entailles est différent selon l’orientation des fibres, la taille de l’entaille ainsi que la position de cette dernière. Dans notre étude, l’analyse du flambage a été effectuée sur des pipes en composite stratifiés avec une et deux entailles carrée, en ayant recours a la simulation numérique a l’aide du code Abaqus. le pipe stratifié comporte plusieurs couches alternées de la manière suivante (θ/-θ)5. La résistance au flambage des pipes est mise en évidence. Les résultats montrent que la charge de flambage est presque identique pour les cas étudiés, elle atteint les valeurs maximales pour les orientations (20°/-20°). Et pour la distribution des contraintes de Von mises, la concentration la plus importante est pour le pipe muni de deux entailles dont l’une est du coté de l’encastrement

    Evaluation of fruit quality traits of traditional varieties of tomato (Solanum lycopersicum) grown in Tunisia

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    Physicochemical, nutritional, agronomic and sensorial parameters, which define fruit quality of tomato (Solanum lycopersicum), were evaluated in 13 traditional varieties collected from several localities in Tunisia, using three commercial varieties as controls. Several varieties were identified as better score for total solid, soluble solid, sugars/acid ratio and vitamin C concentration than the commercial varieties. These varieties could be a resource of good quality in breeding programmes. The correlation between specific parameter seen in this study showed that the local varieties can be differentiated, not just as a function of their morphological attributes but also as a function of their organoleptic, nutritional and sensorial quality

    New p-type Al-substituted SrSnO 3 perovskites for TCO applications?

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    International audienceNovel p-type SrSn 1-x Al x O 3 (x=0, 0.2, 0.5) perovskites are presented as potential candidates for electro-optical applications. A combined experimental and theoretical study reveals that chemical substitutions can be used as a lever to stabilize oxygen holes in the valence band. Transparent conductive oxides (TCO) are an original class of materials combining two contrasting properties in one single compound that is, electrical conductivity and optical transparency in visible spectrum. TCOs are widely used in electro-optical devices such as flat-panels, organic light emitting diodes, photovoltaic devices, and plasma displays. 1-6 However, standard commercial TCOs are limited to post-transition metal oxides, e.g. ZnO, In 2 O 3 and SnO and derivatives. 7 These oxides are characterized by a band gap larger than 3eV between the O(2p) valence band maximum (VBM) and the metal (s,p) conduction band minimum (CBM). They display excellent n-type electronic conductivity when the donor, i.e. metal, is doped. In contrast, the development of high performant p-type TCOs is more challenging, 8-11 due to the strongly localized states of the acceptor, i.e. oxygen, which are at the origin of large hole effective mass (poor electronic conductivity). As a consequence, the probability is high that the newly created shallow acceptors are counterbalanced by the formation of native defects such as anion vacancies or cation interstice. 12 Up to now, n-type tin-doped indium oxide (ITO) shows the best performance. 1,13 Nevertheless and despite the remarkable properties of ITO, the relative high cost of In and its increasing scarcity appeals for alternative elements or materials. 14 ABO 3 perovskites are of great interest thanks to the use of mixed A and B cations capable of generating versatile structures and properties with high chemical stability. SrSnO 3 (SSO) is one of the most promising candidate due to its high visible light transmittance, high thermal stability and reasonable cost. 15 Pure SSO is a charge transfer insulator crystallizing in the orthorhombic GdFeO 3-type structure with lattice parameters a = 5.7113 Ã…, b = 8.0647 Ã… and c = 5.7042 Ã…. In this tri-dimensional structure, SnO 6 octahedra are corner-shared and Sr lies in the available vacant interstices. 16,17 To meet the industrial specifications of efficient TCOs, SSO must display high carrier concentration and mobility 18-21 which requires its doping. Attempts to develop n-type SSO candidates that could rival the electro-optical properties of ITO were intensively described and interesting performance were reported. 22-26 In contrast, p-type doping is still lacking for this class of materials. 27-29 Recently, Hautier et al. showed that the large difference in mobility between n-type and p-type materials is not inevitable and could be overcome by the investigation of alternative chemistries. Based on this statement and considering the high industrial stakes associated with the discovery of new p-type TCOs, we used chemical substitution to check the ability of SSO to behave as a performant p-type TCO. This concept was introduced for the first time by Hosono and coworkers 2 and is known as the "chemical modulation of the valence band" (CMVB). Based on the hypothesis that partial substitution of Sn(IV) for the smaller trivalent cation Al(III) can enhance electron delocalization (through a significant volume contraction of the perovskite structure) while concomitantly generate stable holes in the valence band, various Sn/Al-substituted SSO phases were synthesized. Using X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) equipped with Energy Dispersive X-ray Spectroscopy (EDX), we here demonstrate the solubility of the Al element in the SSO perovskite structure for SrSn 1-x Al x O 3 (SSAO) compositions x = 0 to 0.5. UV-Vis-NIR spectroscopy is then used to show that the absorption profile of SSO is not altered by the chemical Sn/Al substitution while the low-energy absorption band (intra-band transitions) is enhanced. A thermodynamic study based on first-principles DFT (Density Functional Theory) calculations is then performed to determine the type of charge carriers in SSO and SSAOs (p-type) and combined with chemical bond analyses to rationalize the impact of Sn/Al substitution on the p-type performance of SSAOs. SrSn 1-x Al x O 3 (x= 0, 0.2, 0.5) perovskites were successfully obtained through solid state reaction. Details of the synthesis steps are given in ESI part. The impact of the Sn(IV)/Al(III) substitution ratio on the macroscopic properties of SrSn 1-x Al x O 3 was investigated through complementary XRD and SEM-EDX. The structural and morphological analyses of the synthesized samples are presented in Fig.1 and S1. From the XRD patterns of SSO and SrSn 1-x Al x O 3 (SSAO) the orthorhombic Pnma structure (JCPDS 10-6354) is confirmed. A slight shift towards higher angles is observed in agreement with the smaller Shannon ionic radius of Al 3+ (0.54 Ã…) compared to Sn 4+ (0.69 Ã…)
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