24 research outputs found
Optimisation du dimensionnement des systĂšmes photovoltaĂŻques, amĂ©lioration de leur rendement Ă©nergĂ©tique Ă travers des nouvelles techniques dâinstallation
Le sujet que nous traitons dans cet article est une comparaison de lâĂ©nergie reçue par des photovoltaĂŻques (PV) sur deux installations diffĂ©rentes. Nous rĂ©alisons deux installations de supports de panneau solaire ; lâun est mobile et capable de se tourner dans deux directions diffĂ©rentes ; et lâautre est fixĂ© et orientĂ© selon une seule direction. A Antsiranana, le soleil passe au Nord environ huit (08) mois sur douze (12). Câest la raison pour laquelle lâinstallation du support fixe de panneau solaire est orientĂ©e vers le Nord. Toutefois, cette technique prĂ©sente un faible rendement lorsque le soleil passe au Sud. Ainsi, lâidĂ©e de rendre mobile le support est envisagĂ© pour palier Ă cet inconvĂ©nient. Le nouveau support peut sâorienter suivant lâEst-ouest et Nord-sud ou vis-versa. Ces orientations sont gĂ©rĂ©es par un module Ă©lectronique programmable. En relevant les rĂ©sultats des mesures obtenus sur les deux installations, nous remarquons une nette amĂ©lioration du rendement pour le support mobile. Ce dernier prĂ©sent de rendement minimum de plus de 5% au mauvais temps et de 18% au temps ensoleillĂ© par rapport Ă celle du support fixe.Mots-clĂ©s: capteur de lumiĂšre, support Mobile, microcontrĂŽleur Atmega8, Ă©nergie solaire. Optimization of the design of photovoltaic systems, improve their energy efficiency through new installationThis paper is treated a comparison of the energy received by solar panels using two different installations. We realize two stands for solar panel; the first one is able to turn following different directions; and the other is fixed and which is oriented at a single angle. In Antsiranana, the sun spends in the north about 08 months. That is the reason why the supports of photovoltaic panels are oriented to the north. However, this technique presents a low yield when the sun goes south. So the idea to make mobile the support have been realized to overcome this inconvenient. The new support can move along the East-West and North-South or vice-versa. These guidelines are managed by a programmable electronic module. Noting the results of measurements on the two facilities, we notice a significant improvement in performance for mobile support. Compared to the fixed support, the mobile panel provides minimum yield for about 5% high in bad weather and 18% more for the sunny.Keywords: light sensor, mobile support, microcontroller Atmega8, solar energy
Retour sur les travaux de la 14e Assemblée des Etats parties de la Cour pénale internationale : Qui sont les grands gagnants ?
Vendredi 12 janvier 2016, la Chambre dâappel de la Cour pĂ©nale internationale (la Cour) a portĂ© un coup dur Ă lâaccusation dans le procĂšs du vice-prĂ©sident kĂ©nyan William Ruto : les juges ont annulĂ© Ă lâunanimitĂ© la dĂ©cision autorisant lâutilisation rĂ©troactive de tĂ©moignages, fragilisant considĂ©rablement le dossier de la Procureure. Si le sens de cette dĂ©cision nâĂ©tonne pas en lui-mĂȘme, le contexte dans lequel elle sâinscrit mĂ©rite une attention particuliĂšre. Pour comprendre la dĂ©cision, il faut en effet se replonger dans les dĂ©bats qui ont marquĂ© la derniĂšre AssemblĂ©e des Etats parties (AEP ou AssemblĂ©e), trois mois plus tĂŽt. Le Kenya avait rĂ©ussi Ă placer le procĂšs de son vice-prĂ©sident au cĆur des discussions, cherchant Ă interfĂ©rer sur la procĂ©dure en cours devant la Chambre dâappel. Le prĂ©sent article se propose donc de revenir, plus gĂ©nĂ©ralement, sur les travaux de cette AssemblĂ©e, la plus mouvementĂ©e depuis la crĂ©ation de la Cour
Contribution Ă lâĂ©tude de dose due Ă la radioactivitĂ© gamma du sol sur la rive de la baie des Français, Antsiranana, Madagascar
Le but de ce travail est dâĂ©tudier la radioactivitĂ© gamma des sols sur la rive de la baie des français et de dĂ©terminer lâimpact dosimĂ©trique sur la population locale dans les localitĂ©s dâAnkorikihely, de betahitry et de Lazaret-Nord. Des Ă©chantillons du sol ont Ă©tĂ© prĂ©levĂ©s et analysĂ©s pour identifier les activitĂ©s spĂ©cifiques du potassium-40, des familles de lâUranium-238 et du Thorium-232. Ces Ă©chantillons ont Ă©tĂ© analysĂ©s sur une chaine de spectromĂ©trie gamma, muni dâun dĂ©tecteur NaI(Tl) et du logiciel Scinti-vision. Le traitement des spectres a Ă©tĂ© rĂ©alisĂ© en utilisant la mĂ©thode de Rybach. AprĂšs mesures, les rĂ©sultats suivants ont Ă©tĂ© obtenus : les activitĂ©s spĂ©cifiques du potassium-40 varient de 112 ± 34 Bq.kg-1 Ă 565 ± 50Bq.kg-1, avec une moyenne de 313 Bq.kg-1. Cette derniĂšre est inferieure Ă la valeur moyenne mondiale, qui est 400 Bq.kg-1.Les activitĂ©s spĂ©cifiques de la famille de lâuranium-238 varient de 87 ± 32 Bq.kg-1 Ă 190 ± 46Bq.kg-1, avec une moyenne de 139 Bq.kg-1. Cette valeur moyenne est quatre fois supĂ©rieure Ă la valeur moyenne mondiale, qui est de 35 Bq.kg-1. Les activitĂ©s spĂ©cifiques de la famille du thorium-232 varient de 81 ± 20 Bq.kg-1 Ă 161 ± 23 Bq.kg-1, avec une moyenne de 126 Bq.kg-1. Cette valeur moyenne est quatre fois plus que la valeur moyenne mondiale, qui est de 30 Bq.kg-1. Les dĂ©bits de dose absorbĂ©e Ă 1m au-dessus de la surface de sol varient entre 89 ± 14 nGy.h-1 et 209± 29 nGy.h-1 avec une moyenne de 153 nGy.h-1. Les doses efficaces annuelles sont comprises entre 0,14 ± 0,02 mSv.a-1 et 0,25 ± 0,03 mSv.a-1. Ces valeurs annuelles sont bien en-dessous de la valeur limite acceptable pour le public qui est de 1 mSv.a-1.Mots-clĂ©s: radioactivite, spectromĂ©trie gamma, dose absorbĂ©e, dose efficace annuelle. Study of the dosimetric impact due to the gamma radioactivity of the soil in the border of the âbaie des françaisâ, Antsiranana, MadagascarThe aim of this work is to study gamma radioactivity of the soil in the border of the âbaie des françaisâ and then to determine the dosimetric impact to the local population of Ankorikihely, betahitry and Lazaret-Nord. Samples have been collected to identify the specific activities of the potassium-40, Uranium-238 series and Thorium-232.series. These samples have been analyzed by gamma spectrometry system, with NaI(Tl) detector using ScintiVision software. The spectrum processing has been done by using the method developed by Rybach. The results show that:The potassium-40 activity ranges are from 112 ± 34 Bq.kg-1 to 565 ± 50 Bq.kg-1, with an average of 313Bq.kg-1. This latter is below the work average value of 400 Bq.kg-1. The uranium-238 activity varies between 87 ± 32 Bq.kg-1 and 190 ± 46Bq.kg-1, with an average of 139 Bq.kg-1. This average value is 4 times higher than the world average value of 35 Bq.kg-1. The thorium-232 activity varies from 81 ± 20 Bq.kg-1 to (161 ± 23) Bq.kg-1, with an average of 126 Bq.kg-1. This average value is 4 times higher than the world average value of 30 Bq.kg-1. The absorbed dose rate at 1m above soil surface varies between 89 ± 14nGy.h-1and 209± 29 nGy.h-1, with an average of 153nGy.h-1. The annual effective dose ranges from 0.14 ± 0.02mSv.y-1to 0.25 ± 0.03mSv.y-1. The estimated annual effective doses are below 1mSv.y-1, the limit value for the public.Keywords: radioactivity, gamma spectrometry, absorbed dose rate, annual effective dose
Contribution Ă lâĂ©tude de la radioactivitĂ© gamma du sable des plages de Ramena et dâOrangea, Antsiranana, Madagascar
Les familles de lâUranium -238, de lâUranium -235, du Thorium -232 et du Potassium -40 sont dâorigines telluriques et contribuent de maniĂšre gĂ©nĂ©rale aux expositions internes et externes dâun individu. Ce travail a pour objectif de mesurer la radioactivitĂ© du sable de deux plages de la baie de Diego-Suarez, Ă savoir celles de ramena et dâorangea. DiffĂ©rents Ă©chantillons ont Ă©tĂ© collectĂ©s pour avoir une reprĂ©sentation fidĂšle de ces sites. Les analyses par spectromĂ©trie gamma de ces Ă©chantillons nous permettent de dĂ©terminer les activitĂ©s des familles de lâUranium -238, du Thorium -232 et du Potassium -40. Les analyses effectuĂ©es avec le dĂ©tecteur NaI (Tl) de marque ORTEC et de modĂšle 905-4 sĂ©rie ont donnĂ© des rĂ©sultats fiables. En effet, les activitĂ©s varient de (66 ± 22) Bq.kg-1 Ă (180 ± 32) Bq.kg-1 pour la famille de lâUranium-238, de (54 ± 14) Bq.kg-1 Ă (95 ± 16) Bq.kg-1 pour celle du Thorium-232 et de (107 ± 22) Bq.kg-1 Ă (321 ± 49) Bq.kg-1 pour le Potassium -40. Ainsi le radium Ă©quivalent varie de (174 ± 26) Bq.kg-1 Ă (319±37) Bq.kg-1 avec une moyenne de (235 32) Bq.kg-1.Mots-clĂ©s: radioactivitĂ©, spectromĂ©trie gamma, radium Ă©quivalent.Contribution of the Measurements of beach sand radioactivities of Ramena and Orangea in Antsiranana, Madagascar Uranium -238, uranium -235 and Thorium -232 series are from telluric elements and with Potassium -40, they contribute to the internal and external exposure of the public. This work is essentially based on the measurement of beach sand radioactivities of Ramena and Orangea in Antsiranana. Enough samples have been collected in such way to have a good image of the two areas of interest. The samples analyses by gamma spectrometry system using ORTEC NaI(Tl) detector, 905-4 serie, allow us to determine the activities of Uranium -238, Thorium -232 series and the Potasium -40. The results show that the uranium -238, the thorium-232 series and the potassium-40 activities ranges are respectively from (66±22) Bq.kg-1 to (180 ± 32) Bq.kg-1, from (54 ± 14) Bq.kg-1 to (95 ± 16) Bq.kg-1 and from (107 ± 22) Bq.kg-1 to (321 ± 49) Bq.kg-1. Thus, the estimated radium equivalent ranges are between (174 ± 26) Bq.kg-1 to (319 ± 37) Bq.kg-1, with an average for about (235 32) Bq.kg-1.Keywords: radioactivity, gamma spectrometry, radium equivalent
Mechanical Properties of Sandstone using non-Destructive Method
The understanding of physical and mechanical properties of rock is considered as critical in drilling, geo-engineering, and construction applications. As an example, the awareness of these rock parameters contributes to avoid or minimizing instability around the wellbore while drilling. The laboratory experiment of understanding of these parameters can be done in two-different ways: static, where the sample subjects to destruction after the test and dynamic, known as non-destruction method. The non-destructive method using ultrasonic waves under a series of different stress conditions, starting from 7 to 56 MPa with incrementation of 7MPa, has been used in this paper in order to characterize the mechanical properties of dry ZbylutĂłw sandstone at 20 and 80°C. The velocity of primary (P) and secondary (S) waves within these ranges has been recorded in order to understand the behavior of the mechanical properties. The results showed that the Youngâs modulus, bulk modulus, shear modulus, and Lameâs constant of ZbylutĂłw sandstone have a positive correlation with good coefficient correlation with the increased stress, while the Poissonâs ratio showed a negative correlation. Besides, the effect of temperature on the rock parameters is approved by the decrease of primary wave velocity in this two-different temperature range. Such results are necessary when preparing the appropriate mud weight for drilling process, which is related to wellbore instability
The significance of human induced and natural erosion features (lavakas) on the central highlands of Madagascar
Massive hill slope erosion in Madagascar is represented by the widespread gullies called âlavakaâ. Lavakas may be result of natural processes that involves a combination of continuous tectonic uplift that maintains a high angle of repose, ground water sapping at the soil - saprolite interface, and subsequent collapse of the soil surface due to low grade seismic activity in the central highlands. Forest cover ranges between 25-45% in the study area and is primarily restricted to riparian and lavaka habitats. Development of forest cover associated with riparian and lavaka habitats may be due to increased soil moisture, exposure of a less nutrient poor saprolite and/or soil compaction. In addition, riparian and lavaka habitats harbor a significantly higher diversity of plant species than the surrounding grasslands. Lavakas may be a result of natural processes and may play a role in the development of Madagascarâs landscape evolution.RĂSUMĂLes formes dâĂ©rosion connues sous le terme de lavakas peuvent ĂȘtre le rĂ©sultat dâun processus naturel impliquant Ă la fois un soulĂšvement tectonique continu qui maintient un angle de repos important, un processus de sape des eaux souterraines Ă lâinterface solâsaprolite et un effondrement consĂ©cutif de la surface du sol du Ă la faible activitĂ© sismique des hautes terres du centre. Ce phĂ©nomĂšne est suivi dâune succession gĂ©omorphologique Ă long terme et dâune succession de vĂ©gĂ©tation liĂ©es aux lavakas, de sorte que les lavakas et la vĂ©gĂ©tation quâils abritent sont isolĂ©s du bassin versant principal. Les riviĂšres et les bassins versants en tant quâĂ©lĂ©ments sĂ©parateurs ont, semble-t-il, jouĂ© un rĂŽle dans la richesse de la biodiversitĂ© de Madagascar. La prĂ©sente Ă©tude montre que la vĂ©gĂ©tation associĂ©e aux forĂȘts riveraines et aux lavakas reprĂ©sente 25-45% de la couverture forestiĂšre des hautes terres du centre. Lâabsence de forĂȘts sur les zones herbeuses voisines ou la prĂ©sence dâune succession de vĂ©gĂ©tation liĂ©e aux zones herbeuses suggĂšre que le dĂ©veloppement de la vĂ©gĂ©tation arborĂ©e pourrait ĂȘtre liĂ© Ă des changements du degrĂ© dâhumiditĂ© du sol, de la disponibilitĂ© des Ă©lĂ©ments nutritifs ou du tassement du sol. Le taux dâhumiditĂ© sâest avĂ©rĂ© ĂȘtre constant dans tous les habitats Ă©chantillonnĂ©s. La disponibilitĂ© en Ă©lĂ©ments nutritifs peut jouer un rĂŽle dans la structure de la vĂ©gĂ©tation. Les lavakas se formant par lâeffondrement du sol superficiel par un processus de sape des eaux souterraines Ă lâinterface solâsaprolite, la zone racinaire de la vĂ©gĂ©tation se trouve alors Ă proximitĂ© des saprolites pauvres en Ă©lĂ©ments nutritifs. Le degrĂ© de tassement du sol diffĂšre de maniĂšre significative entre les forĂȘts ripicoles/lavakas et les zones herbeuses. Les zones herbeuses ont montrĂ© des mesures de rĂ©sistance du sol au pĂ©nĂ©tromĂštre Ă©levĂ©es (moyenne de 17,9) et un profil de tassement qui peut limiter le dĂ©veloppement racinaire dâun certain nombre dâespĂšces. Les mesures effectuĂ©es dans les forĂȘts riveraines et les lavakas Ă©taient respectivement de 14,0 et 9,7 qui sont des valeurs compatibles avec un dĂ©veloppement racinaire. De ce fait, les diffĂ©rences entre les structures de la vĂ©gĂ©tation et la diversitĂ© peuvent trouver leur origine dans la capacitĂ© des plantes Ă dĂ©velopper leur systĂšme racinaire. Il existe Ă©galement un rapport inverse entre la diversitĂ© spĂ©cifique et le degrĂ© de tassement du sol dans les trois habitats. La mobilitĂ© des sols dans les lavakas et les habitats ripicoles peut rĂ©duire le tassement en surface et juste en dessous en favorisant ainsi un labourage naturel. Les lavakas peuvent ainsi ĂȘtre le rĂ©sultat dâun processus naturel et jouer un rĂŽle important dans le dĂ©veloppement de lâĂ©volution des paysages de Madagascar et de la biodiversitĂ©
40Arâ39Ar ages and isotope geochemistry of Cretaceous basalts in northern Madagascar: Refining eruption ages, extent of crustal contamination and parental magmas in a flood basalt province
The Madagascar Cretaceous igneous province exposed in the Mahajanga basin is represented by basalt and basaltic andesite lavas. New 40Arâ39Ar plateau ages (92.3 ± 2.0 Ma and 91.5 ± 1.3 Ma) indicate that the magmatism in the Mahajanga basin started about 92 Ma ago. Four geochemically distinct magma types (Groups AâD) are present. Group A and C rocks have low to moderate TiO2 (1.2â2.6 wt%), Nb (3â9 ÎŒg gâ1) and Zr (82â200 ÎŒg gâ1), and show large variations in ÉNdi (+0.1 to â10.8), 206Pb/204Pb (15.28 to 16.33) and ÎłOs (+11.4 to +7378). The large isotopic variations, particularly in Os, Nd and Pb isotopic compositions, are likely due to crustal contamination. The low Pb isotope ratios observed in the Group A and C rocks suggest involvement of continental crust with low ÎŒ (238U/204Pb). Group B and D rocks have moderate to high TiO2 (2.2â4.9 wt%), Nb (8â24 ÎŒg gâ1) and Zr (120â327 ÎŒg gâ1). Age-corrected isotopes of Group B and D lavas show a small range in ÉNdi (+1.0 to +4.0) and a wide range in ÎłOs (+128 to +1182). Values of 207Pb/204Pb are within the range for Groups A and C, but the Group D 206Pb/204Pb (16.52â17.08) and 208Pb/204Pb (37.51â38.01) values are higher, indicating a different crustal contaminant. Pb isotopic values of the Group B rocks seem to reflect the isotopic features of their mantle source. The magma groups of Mahajanga display a wide range of trace element and isotopic compositions that cannot be explained only by open-system crystallization processes but, rather, by distinct mantle sources
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What Are the Origins of V-Shaped (Chevron) Dunes in Madagascar? The Case for Their Deposition by a Holocene Megatsunami
Chevrons are elongated dunes with a V-shaped pattern in map view. In some exposures, smaller Vs are nested within the larger Vs. The term chevron was first used to describe desert dunes (Maxwell and Haynes, 1989) based on their similarity to the nested chevrons used on military uniforms or in heraldry. Chevrons later were identified in coastal regions and proposed to represent megastorm deposits (Hearty et al., 1998; Kindler and Strasser, 2000). Subsequently, other workers suggested that some coastal chevron dunes were tsunami deposits (Bryant and Nott, 2001; Scheffers and Kelletat, 2003; Scheffers et al., 2008).
The proposal that some coastal chevron dune complexes represent tsunami deposits is based on three sets of observations (Scheffers and Kelletat, 2003). The first is that the long axes of many coastal chevron complexes are not oriented parallel to the direction of the prevailing wind. The second is that some chevron complexes extend several kilometers (km) inland and rise to over 100 meters (m) above sea level. Some of these chevron complexes are located on shorelines that lack beaches. In these particular cases, it is difficult to understand how either megastorms or wind could have formed the chevrons. Megastorms cannot move subaerial rock and sediment over km-scale distances with elevation gains of hundreds of meters (Cox et al., 2012; Erdmann et al., 2015). Wind cannot move sediment inland if there are no subaerial, poorly consolidated sediments on the coast.
In this chapter, we describe three chevron complexes, V-shaped, elongated dune complexes on the southern coast of Madagascar. Their origin is disputed because individual dunes are elongated along an azimuth that is close to the direction of the prevailing winds (Abbott et al., 2008; Pinter and Ishman, 2008), although their low angle of deposition generally is inconsistent with aeolian dunes. However, other characteristics preclude their derivation from modern beach deposits, although we do not discount later aeolian reworking of some chevron deposits. In particular, the Madagascar chevrons contain significant proportions of early Holocene carbonate tests resembling shells of marine foraminifera, including some that are partially dolomitized, and some that are infilled with mud. These observations suggest that marine carbonate tests in the chevrons were eroded from the continental shelf, and not from modern beaches. Furthermore, despite having lateral extents of tens of km, characteristics of the chevrons (degree of sediment sorting, carbonate content, and marine microfossil concentrations) do not change significantly along strike, as might be expected for aeolian deposits
Simultaneous inversion of hypocentral parameters and structure velocity of the central region of Madagascar as a premise for the mitigation of seismic hazard in Antananarivo
A layered velocity is obtained using arrival-time data of P and S waves from local earthquakes for the Central Region of Madagascar. A damped least-squares method is applied in the inversion of the data. The data used are 770 P-wave arrival times for 154 events which have epicenters in the region inside the Malagasy network operated by the Institut et Observatoire de Ge \u301ophysique d\u2019Antananarivo (IOGA). These data are jointly used in the inversion for the earthquake hypocenters and P- and S-wave velocity models. S waves are not used in the first step of the inversion, since their use leads to large location errors. If the error on the phase reading for the P wave is about 0.1 s, for the S wave it is considerably bigger. The reference average model used here is a variant of the model given by RAKOTONDRAINIBE (1977)