Optimisation du dimensionnement des systèmes photovoltaïques, amélioration de leur rendement énergétique à travers des nouvelles techniques d’installation

Le sujet que nous traitons dans cet article est une comparaison de l’énergie reçue par des photovoltaïques (PV) sur deux installations différentes. Nous réalisons deux installations de supports de panneau solaire ; l’un est mobile et capable de se tourner dans deux directions différentes ; et l’autre est fixé et orienté selon une seule direction. A Antsiranana, le soleil passe au Nord environ huit (08) mois sur douze (12). C’est la raison pour laquelle l’installation du support fixe de panneau solaire est orientée vers le Nord. Toutefois, cette technique présente un faible rendement lorsque le soleil passe au Sud. Ainsi, l’idée de rendre mobile le support est envisagé pour palier à cet inconvénient. Le nouveau support peut s’orienter suivant l’Est-ouest et Nord-sud ou vis-versa. Ces orientations sont gérées par un module électronique programmable. En relevant les résultats des mesures obtenus sur les deux installations, nous remarquons une nette amélioration du rendement pour le support mobile. Ce dernier présent de rendement minimum de plus de 5% au mauvais temps et de 18% au temps ensoleillé par rapport à celle du support fixe.Mots-clés: capteur de lumière, support Mobile, microcontrôleur Atmega8, énergie 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

Contribution à l’étude de dose due à la radioactivité gamma du sol sur la rive de la baie des Français, Antsiranana, Madagascar

Le but de ce travail est d’étudier la radioactivité gamma des sols sur la rive de la baie des français et de déterminer l’impact dosimétrique sur la population locale dans les localités d’Ankorikihely, de betahitry et de Lazaret-Nord. Des échantillons du sol ont été prélevés et analysés pour identifier les activités spécifiques du potassium-40, des familles de l’Uranium-238 et du Thorium-232. Ces échantillons ont été analysés sur une chaine de spectrométrie gamma, muni d’un détecteur NaI(Tl) et du logiciel Scinti-vision. Le traitement des spectres a été réalisé en utilisant la méthode de Rybach. Après mesures, les résultats suivants ont été obtenus : les activités spécifiques du potassium-40 varient de 112 ± 34 Bq.kg-1 à 565 ± 50Bq.kg-1, avec une moyenne de 313 Bq.kg-1. Cette dernière est inferieure à la valeur moyenne mondiale, qui est 400 Bq.kg-1.Les activités spécifiques de la famille de l’uranium-238 varient de 87 ± 32 Bq.kg-1 à 190 ± 46Bq.kg-1, avec une moyenne de 139 Bq.kg-1. Cette valeur moyenne est quatre fois supérieure à la valeur moyenne mondiale, qui est de 35 Bq.kg-1. Les activités spécifiques de la famille du thorium-232 varient de 81 ± 20 Bq.kg-1 à 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 débits de dose absorbée à 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-clés: radioactivite, spectrométrie gamma, dose absorbée, dose efficace annuelle. Study of the dosimetric impact due to the gamma radioactivity of the soil in the border of the “baie des français”, Antsiranana, MadagascarThe aim of this work is to study gamma radioactivity of the soil in the border of the “baie des français” 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 à l’étude de la radioactivité gamma du sable des plages de Ramena et d’Orangea, Antsiranana, Madagascar

Les familles de l’Uranium -238, de l’Uranium -235, du Thorium -232 et du Potassium -40 sont d’origines telluriques et contribuent de manière générale aux expositions internes et externes d’un individu. Ce travail a pour objectif de mesurer la radioactivité du sable de deux plages de la baie de Diego-Suarez, à savoir celles de ramena et d’orangea. Différents échantillons ont été collectés pour avoir une représentation fidèle de ces sites. Les analyses par spectrométrie gamma de ces échantillons nous permettent de déterminer les activités des familles de l’Uranium -238, du Thorium -232 et du Potassium -40. Les analyses effectuées avec le détecteur NaI (Tl) de marque ORTEC et de modèle 905-4 série ont donné des résultats fiables. En effet, les activités varient de (66 ± 22) Bq.kg-1 à (180 ± 32) Bq.kg-1 pour la famille de l’Uranium-238, de (54 ± 14) Bq.kg-1 à (95 ± 16) Bq.kg-1 pour celle du Thorium-232 et de (107 ± 22) Bq.kg-1 à (321 ± 49) Bq.kg-1 pour le Potassium -40. Ainsi le radium équivalent varie de (174 ± 26) Bq.kg-1 à (319±37) Bq.kg-1 avec une moyenne de (235 32) Bq.kg-1.Mots-clés: radioactivité, spectrométrie gamma, radium équivalent.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 Zbylutów 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 Young’s modulus, bulk modulus, shear modulus, and Lame’s constant of Zbylutów sandstone have a positive correlation with good coefficient correlation with the increased stress, while the Poisson’s 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

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)

Topography of the Moho under central region of Madagascar

Consiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7 , Rome / CNR - Consiglio Nazionale delle RichercheSIGLEITItal

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

Consiglio Nazionale delle Ricerche (CNR). Biblioteca Centrale / CNR - Consiglio Nazionale delle RichercheSIGLEITItal