Bio-activité des huiles essentielles de l’Armoise blanche Artemessia herba alba : effet sur la reproduction et la mortalité des adultes d’un ravageur des denrées stockées Ephestia kuehniella (Lepidoptera)

Notre travail révèle un effet insecticide de l’huile essentielle extraite de la plante aromatique Artemissia herba alba, sur la population d’insectes ravageurs des denrées stockées Ephestia kuehniella (Lepidoptera). Le bio-pesticide agit avec un double mécanisme d’action. Administré chez les adultes, l’huile essentielle provoque un taux de mortalité significatif par rapport aux témoins. Alors que son administration sur les chrysalides, prolonge leur développement nymphal et perturbe la reproduction des adultes, en prolongeant la période de préoviposition et en réduisant la période de dépôt des œufs puisque les femelles fécondées, ne pouvant vivre plus d’un ou deux jours, ce qui réduit le nombre d’œufs déposés.Bio-activity of essential oils of Artemisia herba alba : effects on reproduction and adult mortality of a pest of stored Ephestia kuehniella (Lepidoptera)Our work reveals an insecticidal effect of essential oils extracted from aromatic plant Artemissia herba alba on population of insect pests Ephestia kuehniella. The biopesticide is adual mechanism of action. Administered in adults, the essential oil causes significant mortality compared with controls. Whilehis administration on pupae, it extending their pupal development and disrupts reproductive adults by extending the preoviposition period and reducing the period for depositing eggs asfertilized females, who can’t live more than one or two days, which reduces the number of eggs deposited

Generalized (\kappa,\mu)-space forms

Generalized (\kappa ,\mu)-space forms are introduced and studied. We examine in depth the contact metric case and present examples for all possible dimensions. We also analyse the trans-Sasakian case.Comment: 20 pages, several changes have been done in this versio

Influence of the Filler Type on the Rupture Behavior of Filled Elastomers

International audienceThis work is devoted to the rupture behavior of elastomers filled with carbon black (CB) or silica. Two elastomers have been studied: one which crystallizes under strain, natural rubber (NR), and another one which does not crystallize, styrene butadiene rubber (SBR). The study of the crack propagation of Single Edge Notched specimen (SENT) during stretching at different speeds focuses on the crack initiation and crack deviation phenomenon. This deviation is of main importance in the materials crack resistance as it leads to a large increase in the energy needed for rupture. The deviation in filled or unfilled NR is controlled by crystallization, which is a slow process. In unfilled SBR, deviation is controlled by polymer chain orientation, which is hindered by relaxation mechanisms. The introduction of fillers promotes strain amplification, and strain anisotropy in the crack tip region of the notched samples, and therefore crack deviation. In term of energy density at break of the SBR composites, the SBR filled with silica treated with a covering agent is the most efficient. Thus, a weak interface between the silica and SBR promotes better rupture properties. When comparing Silica and CB filled NR, the highest strain energy to rupture is also obtained with silica. This might be due to the weaker filler-matrix interface for silica. Thus, these results evidence the kinetic aspect of the rupture, and of the mechanisms it involves: the polymer relaxation, the crystallization (for NR), and the filler-matrix interaction and decohesion, all of them being strongly interrelated

Non-isothermal crystallization kinetics of polyamide 66/glass fibers/carbon black composites

cited By 7International audienceThe non-isothermal crystallization of the polyamide 66 (PA66) reinforced with 15 mass% glass fibers and/or 0.4 mass% carbon black has been the object of a thermal analysis by differential scanning calorimetry with various cooling rates ranging from 2 to 25 °C min−1. The modified Avrami’s equation, Ozawa’s theory and Mo’s method were applied to study the non-isothermal crystallization kinetics of neat PA66 and the PA66 composites. The activation energies of non-isothermal crystallization were calculated by Kissinger method. The results showed that the Mo’s method can successfully account for the overall non-isothermal crystallization kinetics for neat PA66 and PA66 composites. The modified Avrami’s method and Ozawa’s approach as well did not apply satisfactorily. It was also revealed that GF and CB could accelerate the crystallization rates of PA66. The combined effect of GF and CB was shown to be stronger than that of GF only in spite of rather low CB content. © 2016, Akadémiai Kiadó, Budapest, Hungary

Optimization of the crystallinity of polypropylene/submicronic-talc composites: The role of filler ratio and cooling rate

cited By 4International audienceMicronic and submicronic mineral fillers recently appeared as efficient reinforcing agents for polyolefins in addition to the benefit of bypassing the exfoliation/dispersion problem encountered in the case of incorporation of nanoscopic fillers such as clay. Submicronic-talc, designated as μ-talc, belongs to this kind of new fillers. This work was aimed at searching to optimize the crystallinity ratio of isotactic polypropylene in the presence of μ-talc in relation to the filler ratio of the composites and the cooling rate from the melt. In order to highlight the efficiency of the μ-talc on the crystallization of polypropylene comparison has been made with PP composites containing conventional talc particles. The study has been carried out on samples having μ-talc weight fractions covering the range 3–30%. In the context of optimizing the crystallinity ratio of the polypropylene matrix in the composites, calorimetric experiments have been planned using a full factorial design. The results were statistically processed by analysis of the variance via mathematical models for predicting the crystallinity ratio in relation to the cooling rate and the filler ratio. Contour graphs have been plotted to determine the effect of each parameter on crystallinity. The cooling rate proved to have a significantly stronger influence on crystallinity than the type and content of filler. © BME-PT

Cracking behavior of carbon black filled elastomers

cited By 1International audienceThe study of crack propagation in rubber has a very high economic significance but is still not well understood. For this purpose the main objective of this work is to study the fracture behavior of two types of rubber: the NR, which crystallizes under stress and the noncrystallizing SBR. To study the cracking behavior of materials we have made tests of cracking follow-up. The mode of crack propagation has been studied in terms of fillers ratio and traction speed. The unfilled SBR and NR showed simple lateral propagation independently of the test speed, whereas the mode of cracking of filled materials was very influenced by the parameters mentioned previously. The filled SBR can present important deviations of the crack when the fillers ratio is sufficiently high; this deviation is even more pronounced when the speed increases. On the other hand, the natural rubber which crystallizes under stress showed particular mode of propagation characterized by the appearance of longitudinal cracks. This mode of cracking is much more important at low speeds than at the high speeds. It is proposed that the fillers increase the breaking strength of a noncrystallizing material and allows that the crack takes a deviated way if the fillers ratio is sufficiently high. But if it is a material which crystallize like the NR, crystallization and fillers will act simultaneously and the material will be much more resistant which gives rise to a particular mechanism which is the appearance of the longitudinal cracks before the catastrophic rupture. © 2010 World Scientific Publishing Company

Crystallization of glass-fiber-reinforced polyamide 66 composites: Influence of glass-fiber content and cooling rate

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HIV-1 Tat protein inhibits neurosecretion by binding to phosphatidylinositol 4,5-bisphosphate

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