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Population structure of north african honey bees is influenced by both biological and anthropogenic factors
No full textHoney bee diversity is under threat due to anthropogenic factors as the use of pesticides and the replacement of local colonies to recover from colony losses. To assess the effect of these activities on the genetic diversity and structure of North African honey bee colonies, we studied colonies from the north (Tellian) and the south (Saharan) regions in Algeria, by determining their mitochondrial haplotype and the variation of ten microsatellite loci. Particular haplotypes have been found with a high frequency in each region that may constitute subspecies-specific markers for Apis mellifera intermissa (haplotype A8 at the north) and A. m. sahariensis (haplotype A9 at the south). Moreover, the presence of the haplotype A8 in some Saharan colonies may reflect recent introductions of A. m. intermissa. Structure analysis suggests that a natural differentiation between honey bee populations from Saharan and Tellian regions still exists despite increased colony movements (migration, queen purchases, etc.) during the last decades. One apiary established for the conservation of A. m. sahariensis showed no indication of maternal introgression since all the colonies bear the same haplotype A9. Furthermore, Hardy–Weinberg equilibrium observed in this population indicates that this apiary is appropriate for conservation programs of A. m. sahariensi
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No full textMurissement des BHPF avec ajout de laitier dans les milieux sulfatés
Get PDFUne panoplie de sulfates en solution se trouve souvent dans les eaux souterraines, les eaux usées ou dans l’eau de mer. Au contact du béton ces sulfates réagissent chimiquement avec ses hydrates, cela peut entrainer la détérioration du béton dans un laps de temps très réduit, selon deux mécanismes physico-chimiques à savoir l’expansion et la perte des propriétés liantes des CSH. Les bétons de haute performance de fibres métalliques sont de plus en plus utilisés dans la construction. Dans le cadre de la politique de développement durable actuelle, ce sont des matériaux qui procurent des gains de masse conséquents, qui permettent d’augmenter la tenue dans le temps des ouvrages, ce qui contribue à la diminution de l’impact des matériaux cimentaires sur l’effet de serre. Dans ce travail, on présente les résultats d’une étude expérimentale portant sur la durabilité après 6 et 24 mois de murissement dans l’eau séléniteuse, d’un béton de haute performance fibré avec substitution de 15% du ciment par du laitier de hauts fourneaux et cela par des essais qui permettent de caractériser sa compacité, la microstructure de sa matrice cimentaire et l’altération éventuelle de ces fibres métallique
Tension fatigue behavior of the laminates jute/epoxy
No full textWork presented is interested in the characterization of the quasistatic mechanical properties and in fatigue of a composite laminated in jute/epoxy. The natural fibres offer promising prospects thanks to their interesting specific properties, because of their low density, but also with their bio deterioration. Several scientific studies highlighted the good mechanical resistance of the vegetable fibre composites reinforced, even after several recycling. Because of the environmental standards which become increasingly severe, one attends the emergence of eco-materials at the base of natural fibres such as flax, bamboo, hemp, sisal, jute. The fatigue tests on elementary vegetable fibres show an increase of about 60% of the rigidity of elementary fibres of hemp subjected to cyclic loadings. In this study, the test-tubes manufactured by the method infusion have sequences of stacking of 0/90° and ± 45° for the shearing and tensile tests. The quasistatic tests reveal a variability of the mechanical properties of about 8%. The tensile fatigue tests were carried out for levels of constraints equivalent to half of the ultimate values of the composite. Once the fatigue tests carried out for well defined values of cycles, a series of static tests of traction type highlights the influence of the number of cycles on the quasi static mechanical behavior of the laminate jute/epox
Design of compact low pass filter with large reject band using open circuit stubs and two cascaded DGS-Quasi-triangular resonators
No full textThis article investigates a quasitriangular of defected ground structure (DGS) for low-pass filters (LPFs) application. An equivalent RLC circuit model is presented and its corresponding designed and fabricated. The proposed LPF presents the advantages of small size, low insertion loss and ultrawide stopband with 20 dB attenuation from 4 GHz to > 20 GHz. The simulated results obtained by equivalent circuit model and full-wave electromagnet show good agreement with the measured ones. V C 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:122–127, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27260 parameters are as well extracted using the parametric relationships. The LPFs using the proposed DGS pattern combined with open stubs ar
A review of studies on central receiver solar thermal power plants
No full textThe use of central receiver system (CRS) for electricity production promises to be one of the most viable options to replace fossil fuel power plants. Indeed, research and development activities on its basic subsystems have been booming rapidly since 1980s. This paper reviews the most important studies on the major components of central receiver solar thermal power plants including the heliostat field, the solar receiver and the power conversion system. After an overview of Concentrating Solar Power (CSP) technology, current status and applications of the CRSs are highlighted. Next, a detailed literature survey of existing design comprising optical, thermal and thermodynamic analysis, and techniques used to assess components have been arranged. This is followed by experimental investigations in which design concepts are established. The last section contains recent subsequent improvement of such key components as heliostat, receiver and hybrid solar gas turbine that are boosting in many R&D activities merging international collaboration during the past 30 year