Multipath and receiver models for assessing the VOR bearing error: application to wind farms

L'implémentation des éoliennes à proximité des systèmes VOR (VHF Omnidirectional Range) est une préoccupation importante pour l'aviation civile. Les éoliennes constituent une source de multitrajets qui peuvent produire des erreurs sur l'information d'azimut estimée par le récepteur d'avion. Dans la littérature, l'erreur VOR est calculée à partir de paramètres multitrajets en utilisant l'expression analytique proposée par Odunaiya et Quinet. Dans cette thèse de doctorat, nous avons développé un modèle d'un récepteur IQ numérique qui peut reproduire la réponse d'un récepteur VOR lorsque les multitrajets varient dans le temps tout au long d'une trajectoire réaliste d'avion. Le Chapitre 1 présente les principes de base des systèmes : VOR conventionnel (VORC) et VOR Doppler (VORD). Le phénomène de multitrajets générés par les éoliennes à proximité des stations VOR est détaillé en présentant ses paramètres et certaines méthodes de modélisation associées qui existent dans la littérature. Un aperçu des récepteurs VOR est présenté en décrivant la structure classique d'un récepteur VOR et les étapes du traitement du signal appliquées afin d'extraire l'information d'azimut. Les expressions de l'erreur VOR proposées par Odunaiya et Quinet pour les systèmes VORC et VORD sont données et illustrées. Dans le Chapitre 2, nous présentons notre modèle de récepteur IQ numérique. Un générateur de séries temporelles au long d'une trajectoire réaliste d'avion est présenté. Un critère échantillonnage est également proposé pour être sûr de capturer toutes les variations de multitrajets dans l'espace. Le modèle de récepteur IQ numérique est détaillé en décrivant ses composantes. Afin d'analyser l'effet et dynamique de multitrajets sur le récepteur VOR, un test d'illustration est donné en comparant la réponse du modèle avec l'expression d'Odunaiya. Dans le Chapitre 3, le comportement de notre modèle de récepteur IQ numérique est analysé en le comparant avec un récepteur de calibration (R&S EVS300) à l'aide de deux mesures de laboratoire. La première mesure est effectuée dans la bande des fréquences VHF en traitant un multitrajet canonique. La seconde mesure est effectuée en utilisant des signaux en bande de base IQ générées à partir d'une simulation d'un scénario complexe. Les résultats des mesures montrent un bon accord entre les récepteurs. Une analyse critique de récepteur VOR est présentée dans le Chapitre 4. Pour le VORC, nous présentons une méthode permettant de déterminer le domaine de validité de l'expression statique d'Odunaiya afin de calculer l'erreur VOR. Pour le VORD, nous montrons que l'erreur VOR est sensible au type de démodulateur FM en développant et en validant une expression alternative de l'erreur Doppler analytique qui est cohérente avec notre démodulateur FM. Enfin, nous évaluons l'analyse de Bredemeyer qui indique que l'effet et des multitrajets sur le signal de référence doit être pris en compte dans le calcul de l'erreur VORD. Dans le Chapitre 5, nous proposons un modèle statistique d'erreur VOR dont les seuls paramètres sont les positions de l'avion et de l'éolienne et les autres paramètres suivent des distributions statistiques. Ce modèle permet de réduire le temps de simulation électromagnétique. Tout d'abord, nous déterminons les distributions statistiques associées aux paramètres multitrajets. Ensuite, la distribution statistique associée à l'erreur VOR est déduite. Enfin, nous effectuons des simulations de Monte Carlo pour évaluer les paramètres des distributions statistiques.The implementation of wind turbines close to VHF Omnidirectional Range (VOR) systems is an important concern for civil aviation. The wind turbines constitute a source of multipath that can yield bearing errors in the azimuth estimated by aircraft receivers. In the literature, the bearing error is computed from the multipath characteristics by means of the analytic expression proposed by Odunaiya and Quinet. In this PhD thesis, we have developed a digital IQ receiver model which can reproduce the response of a VOR receiver when the multipath change in time along a realistic aircraft trajectory. In Chapter 1, the basic principle of the Conventional VOR (CVOR) and Doppler VOR (DVOR) is pre-sented. The multipath phenomenon generated by the wind turbines in the vicinity of VOR stations is detailed by presenting its parameters and some associated modeling methods that exist in the literature. An overview of the VOR receivers is presented by describing the standard structure of a VOR receiver and the signal processing steps to extract the azimuth information. The analytical expressions proposed by Odunaiya and Quinet for the CVOR and DVOR systems are given and illustrated. In Chapter 2, we present our digital IQ receiver model. A time series generator along a realistic aircraft trajectory is presented. A sampling criterion is also proposed to be sure to capture all the multipath variations in space. The digital IQ receiver model is detailed by describing its components. In order to analyze the effect of multipath dynamics on the VOR receiver, an illustration test is given by comparing the receiver model response with the Odunaiya expression. In Chapter 3, the behavior of our digital IQ receiver model is analyzed by comparing with a calibration receiver (R&S EVS300) from two laboratory measurements. The first one is performed in the VHF frequency band for one canonical multipath. The second one is performed using baseband IQ signals in a complex scenario. The measurements results are shown a good agreement between receivers. A CVOR and DVOR analysis are given in Chapter 4. For CVOR, we present a method to determine the validity domain of the static Odunaiya expression for computing the bearing error. For DVOR, we show that the bearing error is sensitive to the type of FM demodulator by developing and validating an alternative expression of the analytic Doppler error which is consistent with our FM demodulator. Finally, we evaluate the analysis of Bredemeyer which indicates that the effect of multipath on the reference signal must be considered in the DVOR error computation. In Chapter 5, we propose a statistical model for the bearing error with which the only parameters are the aircraft and wind turbine positions and the other parameters follow statistical distributions. This model allows to reduce the electromagnetic simulation time. Firstly, we determine the statistical distributions associated with the multipath parameters. Secondly, the statistical distribution associated with the bearing error is deduced. Finally, we perform Monte Carlo simulations to assess the parameters of the statistical distributions

Audit Committees and Bank Governance: the Case of Tunisian Banks

This paper examines the impact of setting up new audit committees in Tunisian banks on their corporate governance. Specifically studied were the effects of the establishment of audit committees on boards of directors' effectiveness, internal auditor independence, external auditor effort, and internal control and financial reporting quality. The interview and survey methods were used to collect data from board members and the internal and external auditors of eight Tunisian banks shortly after they introduced audit committees on their boards. The main findings show that the establishment of new audit committees influences the breadth of the directors' discussions during board meetings. In some of the banks studied, the new audit committees improve the internal auditors' independence from top management, internal controls and financial reporting quality, and/or result in less effort by external auditors. Some of the interviewed external auditors view the new audit committees as a valuable governance mechanism, especially in cases of disagreement with management

LIDO: A universal language

LIDO is a Metamodeling language for developing IoT solutions. It is a set of concepts of high-level abstraction. LIDO makes it possible that people with different technical backgrounds and IoT culture to come together around the development of IoT solutions. LIDO allows people of different disciplines, having different viewpoints, to come together to discuss and reflect on the modeling and implementation of an IoT solution. This article presents the philosophy underlying LIDO that makes it a universal language allowing sustainable development

Thermal oxidation kinetics of additive free polyamide 6-6

Thermal aging of an additive free PA 6-6 has been elucidated at 90, 100, 120, 140, 150 and 160 C in airventiled ovens by Fourier transform infrared spectrophotometry, viscosimetry in molten state and uniaxial tensile testing. Oxidation of methylene groups starts after a considerably shorter induction period but reaches a lower maximal rate than in additive free PE. Cleavage of CeN bonds constitutes the main source of chain scissions. It leads to the formation of aldehyde chain-ends and a catastrophic decrease in molar mass. Embrittlement occurs at a very low conversion ratio of the oxidation process, in particular when the concentration of aldehyde chain-ends reaches a critical value of [PH¼O]F z 5.6 10 3 mol l 1, corresponding to a critical value of the number average molar mass ofMnFz17 kg mol 1. At this stage, the entanglement network in the amorphous phase is deeply damaged. A non-empirical kinetic model has been derived from the oxidation mechanistic scheme previously established for PE, but improved by adding elementary reactions specific to polyamides such as the rapid decomposition of unstable hydroxylated amide groups. This model describes satisfyingly the main features of the thermal oxidation kinetics of PA 6-6, but also of other types of aliphatic polyamides studied previously in the literature such as: PA 6, PA 12 and PA 4-6, as long as it is not controlled by oxygen diffusion. At the same time, it confirms the existence of an universal character for the thermal oxidation kinetics of aliphatic polyamides whatever their origin, i.e. their initial molar mass, crystallinity ratio, concentration of impurities, structural irregularities, etc

Overlapping patterns of morphometric and genetic differentiation in the Mediterranean goby Pomatoschistus tortonesei Miller, 1968 (Perciformes, Gobiidae) in Tunisian lagoons

Abstract. The genetic and morphological variations of Pomatoschistus tortonesei Miller, 1968 were studied in samples collected from three Tunisian lagoons. The morphological analysis included 18 morphometric measurements and was based on linear discriminant analysis (LDA), whereas the genetic analysis was based on the 16S-rRNA and COI mitochondrial genes. Both analyses differentiated the populations and demonstrated consistently a well-supported differentiation between the western Mediterranean samples (Bizerta and Tunis South lagoons) and the eastern Mediterranean sample (El Bibane lagoon). The observed differentiation could be explained in terms of the geographic isolation of the various populations and the influence of environmental factors, which differ greatly between the different sites. The molecular results revealed that the populations are characterised by unique haplotypes which are well defined in relation to limited gene flow and restricted dispersal abilities. Additionally, it seems that local selective pressures have modelled biometrical variation. Morphological results can reflect a differential habitat use revealed in the cephalic features and a different response to hydrodynamic constraints developed in dissimilar dorsal and pelvic fin lengths

Impact de la mise en places des comités d'audit dans les banques tunisiennes

Dans le cadre de la présente étude, nous proposons d'investiguer l'impact de la création du comité d'audit sur certains éléments du système de gouvernance des banques tunisiennes. Plus particulièrement, ces éléments concernent le fonctionnement du conseil d'administration, la qualité de l'information financière produite, l'indépendance de l'auditeur interne, la qualité du contrôle interne ainsi que l'étendue des travaux d'audit externe planifiés. A cet effet, l'étude de huit cas de banques tunisiennes dévoile la portée limitée du comité d'audit comme mécanisme de contrôle. Une situation pareille peut être essentiellement expliquée par la composition inappropriée du comité d'audit.Banque; comité d'audit; efficacité; étude de cas; gouvernance

Effect of Water Stress on Photosynthetic Assimilation and Biomass Accumulation in Olive Tree

The climate change that we are attending in recent years requires a revision of the water resources management in order to en sure a sustainable supply. For this reason, in order to test the plants ability to face water stress, three water stress intensities (100% (T0), 50 (T1) and 25% (T2) field capacity (fc)), for 42 days in a greenhouse under semi-controlled conditions, were applied on 18 olive plants (Olea europaea L. cv 'Meski') of one year old. An evaluation of the response of the olive tree at different water supplies was conducted by monitoring the photosynthetic assimilation, chlorophyll index measured by SPAD, plant growth and dry matter accumulation. The results showed that photosynthesis has increased after 42 days for T0 plants while it increased during the first two weeks before dropping to the 42th day of the application of water restriction (AWR) for T1 plants; a decrease of 26% compared to control treatment. The photosynthetic assimilation of T2 plants has increased at a rate slower until the 28th day AWR then it has dropped after 42 days a decrease of 46% from the witness thus increasing the irrigation dose results in improved photosynthesis. The chlorophyll index fell 2, and 7% compared to the control treatment for T1 and T2, respectively, after 42 days AWR showing that fluid restriction affects the integrity of chlorophylls. Plant growth was shown by the development of a longer root for T2 plants ex plained by the search for minimum quantities of water available. The results showed that the control plants have accumulated more dry matter than stressed plants in the roots and the stem while the underground part/aerial part report seems indifferent to water stress. Water restriction has affected thereby biomass of roots and stems in favor of the leaves, the first operator of the photosyn thetic activit