Le contrôle de la qualité des fruits est un objectif de recherche agronomique, génétique mais également de production. La notion de qualité est cruciale pour les fruits destinés au commerce du fruit frais. Chez les agrumes, fruitier non climactérique, elle est définie sur l'arbre et utilisée pour déclencher la récolte qui doit précéder l'abscission des fruits. Néanmoins cette chute de fruit est parfois très proche du stade de maturité et occasionne donc des pertes du fait de délais trop courts pour assurer la récolte. Ceci est généralement observé chez les orangers cultivés en Espagne et en Tunisie. Par ailleurs, la qualité d'un agrume est souvent définie par la couleur de peau, la taille du fruit, l'absence de pépin, l'arôme et les teneurs en jus, en sucres et en acidité. Si l'absence de pépin peut être obtenue par la mutation induite ou par la triploïdie, le contrôle de la variation des autres caractères repose sur de nombreux facteurs: la variété, l'interaction avec le porte-greffe, les effets de l'environnement et les techniques culturales. Parmi eux le génotype variétal, c'est-à-dire sa structure génétique héritée de ses parents est un facteur prépondérant pour atteindre le niveau d'amélioration attendu. L'obtention d'une structure génétique adaptée aux objectifs de production n'est pas aisée car les caractéristiques liées à la reproduction telles que la polyembryonie, la phase juvénile ou l'auto-incompatibilité gamétique, sont contraignantes chez les agrumes. Dans le cadre de ce travail, nous avons eu pour objectif de développer des connaissances sur la variation des caractères de la qualité du fruit, en y incluant l'abscission, mais également sur leur héritabilité et leur hérédité afin de faciliter les programmes de sélection et de création variétale. Nous avons tout d'abord étudié la variation de l'abscission chez plusieurs variétés d'orangers sur 3 sites, en Tunisie en Espagne et en Corse. Cette étude démontre que pour des variétés identiques, le processus d'abscission mesurée via la diminution de la force de détachement du fruit du pédoncule (FDF), est très dépendante de l'environnement et non des caractères de qualité du fruit. De façon originale la Corse ne semble pas être favorable à l'expression de ce caractère. Parmi les facteurs environnementaux décrits sur les trois sites, celui de l'augmentation du nombre de jours favorable à la croissance (température moyenne ≥ 13°C) en fin d'hiver semble être à l'origine de la chute massive et soudaine des fruits. Néanmoins, en Corse, la FDF peut aussi diminuer au cours de la maturation sur d'autres agrumes que les oranges. L'analyse de l'hérédité des caractères de la qualité des fruits et de leur abscission a été réalisée par une approche de la ségrégation de QTLs dans une population de 116 hybrides issus d'un croisement de type backcross (clémentinier × mandarinier), le clémentinier étant déjà un hybride (mandarinier x oranger). Les analyses ont été reproduites sur deux campagnes de production à plusieurs dates de maturité et bornées par celles des deux parents. La plupart des caractères ont une variation importante et une hérédité transgressive découlant de l'hétérozygotie élevée des génomes parentaux. Trois cartes génétiques ont été développées (les parentales et la consensus) à l'aide de marqueurs SNP et SSR couvrant environ 75% du génome de référence. Après estimation de l'effet aléatoire sur la variance des caractères (BLUP), des QTLs de chacun des caractères ont été détectés (1 QTL pour l'acidité, le citrate, la teneur en jus, la TSS, la FDF à 5 QTLs pour l'indice a* de coloration). La plupart d'entre eux ne sont détectés qu'à une seule date de maturation. La stabilité interannuelle et inter-population de ces QTLs devra être vérifiée avant une possible utilisation des marqueurs liés dans les programmes d'amélioration. / Fruit quality control is an agronomic, genetics and production research objective. The concept of quality is crucial for fruit produced for the fresh fruit market. In citrus, which are non-climacteric fruit, fruit quality traits in the tree is set to trigger the harvest time that must precede fruit abscission. However, this fruit drop is sometimes very close to the stage of maturity and therefore causes losses because of shorter time to ensure the harvest. This is usually observed in orange grown in Spain and Tunisia. Furthermore, the quality of a citrus fruit is often defined by the skin color, fruit size, lack of seeds, aroma and juice content, sugar and acidity. If seedlessness can be obtained by induced mutations or triploidy, the control of the change in other characters is based on many factors: variety, interaction with the rootstock, environmental impact and cultivation techniques. Among them, the varietal genotype, which means the genetic structure inherited from the parents, is a key factor to achieve the expected level of improvement in breeding. In citrus, obtaining a genetic structure adapted to production targets is not easy because the characteristics associated with reproduction such as polyembryony, juvenility or gamete self-incompatibility. In the present work, we aimed to develop knowledge on the variation of fruit quality traits by including abscission, heritability and traits inheritance to facilitate breeding programs and breeding.We first studied the variation of the abscission in several varieties of orange on 3 sites, Tunisia, Spain and Corsica. This study showed that for the same varieties, the process of abscission measured by investigating the decrease the fruit detachment force (FDF) required to separate the fruit from the calyx, was very dependent on the environment, but not on the fruit quality traits. Interestingly, Corsica does not seem favorable to the expression of this trait. Among the environmental factors described on the three locations, the increase of the number of days that favor growth (average temperature ≥ 13 °C) in late winter seems to be the cause of the sudden and massive fruit drop. Nevertheless, in Corsica, the FDF can also decrease during maturation in other citrus than oranges.The analysis of inheritance of fruit quality traits and abscission was achieved by investigating the segregation of QTLs in a population of 116 hybrids resulting from a backcross (clementine × mandarin), clementine being itself a hybrid (mandarin × orange). Analyzes were replicated two consecutive years at several maturity dates which were bounded by maturity dates of both parents. Most traits presented a significant variation and a transgressive inheritance arising from the high heterozygosity of parental genomes. Three genetic maps have been developed (parental and consensus) using SSR and SNP markers covering about 75% of the reference genome. After estimating the random effect on the variance of the traits (BLUP), QTLs of each trait were detected (1 QTL for acidity, citrate, juice content, TSS, FDF as well as 5 QTLs for the a* color index). Most of them were detected at a single date of maturation.Interannual and inter-population stability of these QTLs will be checked before any possible use of the linked markers in breeding programs.

Les systèmes de combustion à prémélange pauvre (PP) sont l’une des technologies les mieux adaptées pour la réduction des émissions de polluants, mais ils sont très sensibles aux phénomènes d’extinction, aux retours de flamme (flashback) dans l’injecteur et aux instabilités de combustion. La plupart des chambres de combustion des turbines à gaz utilisent de swirleurs pour stabiliser des flammes compactes et permettre une combustion efficace et propre avec des densités de puissance élevée. Une meilleure connaissance des mécanismes de la dynamique de la combustion d’écoulements swirlés PP présente un intérêt aussi bien pratique que fondamental. Ce travail est une contribution pour atteindre ce but. Le brûleur Noisedyn, avec une geometrie modifiable, a été spécialement conçu pour répondre à cet objectif. Une analyse expérimentale a etait conduite pour examiner les paramètres qui reduisent la sensibilité des systèmes PP aux phénomènes dynamiques. Mesures de fonction de transfert de flamme (FTF), diagnostiques laser (LDV et PIV) et imagerie des flammes sont les principaux techniques utilisé dans ce travail. Large eddy simulation sont aussi utilisé pour expliquer les mécanismes derrière les observations experimentaux. / Lean premixed (LPM) combustion systems achieve low pollutant emission levels, with compact flames and high power densities, but are highly sensitive to dynamic phenomena, e.g, flashback, blowout and thermoacoustic instabilities, that hinder their practical application. Most LPM gas turbine combustors use swirling flows to stabilize compact flames for efficient and clean combustion. A better knowledge of the mechanisms of steady and unsteady combustion of lean premixed swirled mixtures is then of practical, as well as fundamental interest. This thesis is a contribute towards the achievement of this goal. A burner, made of several components with variable geometry, was specifically designed for this scope. An experimental analysis was conducted to investigate the main parameters leading to a reduction of the sensitivity of LPM systems to dynamic phenomena. The diagnostics applied include flame transfer function (FTF) measurements, laser diagnostics (LDV and PIV) and flame imaging. Large eddy simulations were also exploited to elucidate the mechanisms behind the experimental observations.

Les instabilités thermoacoustiques, également appelées instabilités de combustion, sont un problème majeur pour la production d’électricité ainsi que dans l’industrie aérospatiale. Ces instabilités sont dues à un transfert d’énergie entre une source chaude, le plus souvent une flamme stabilisée dans un brûleur, et le champ acoustique environnant. Les instabilités de combustion peuvent avoir de nombreuses conséquences délétères telles que l’extinction de la flamme, l’augmentation des flux de chaleur pariétaux, l’émission d’ondes sonores de grande amplitude à certaines fréquences, des vibrations importantes, des dégâts structurels et même l’explosion du moteur dans certains cas. Étant donné les conséquences potentielles de tels phénomènes, d’importants moyens de recherche ont été consacrés à la prédiction de l’apparition d’instabilités de combustion dans les chaudières, les moteurs de fusée et les turbines à gaz ces dernières décennies. Néanmoins, le cadre théorique associé à l’étude de ces instabilités est complexe et nécessite l’emploi de nombreuses disciplines de la physique. De plus, les brûleurs industriels sont constitués de nombreuses cavités tridimensionnelles interagissant entre elles d’un point de vue acoustique. Pour toutes ces raisons, la prédiction de la stabilité thermoacoustique d’un brûleur demeure une tâche ardue à ce jour... (Voir le texte de la thèse pour la suite du résumé) / Thermoacoustic instabilities, also known as combustion instabilities, are a major concern in the aerospace and energy production industries. They are due to an energy transfer that occurs between a heat source, usually a flame stabilized inside a combustor, and the surrounding acoustic field and may lead to undesirable phenomena such as flame extinction, increased heat fluxes, very large sound emissions at certain frequencies, vibration, structural damage and even catastrophic failure in some cases. Given the potential consequences of such phenomena, a large research effort has been devoted to predicting the onset of combustion instabilities in modern boilers, rocket engines and gas turbines during the past few decades. Unfortunately, the theoretical framework associated with the study of thermoacoustic instabilities is complex and multi-physics and the geometry of practical combustors is an intricate arrangement of 3D cavities. As a consequence, predicting the thermoacoustic stability of a combustor at an early design stage is a challenging task to date... (See inside the manuscript for the remainder of the abstract)

Magister Commercii - MCom / The research focuses on the acceptance of new technologies within the telecommunications industry. The study examines three models namely Innovation theory, Theory of Reason Action (TRA), and Technology Acceptance Model (TAM). This study explores the technology acceptance models in order to explain why certain monitoring officers at ICASA would prefer specific technologies over others. Models of interest could be the innovation theory, TRA and TAM. After reviewing both models, the author will examine the TAM in detail as a model of interest in this study. In turn, this model is expected to assist us to understand why monitoring officer's at ICASA would prefer a particular frequency monitoring technology over the other. / South Africa

Fixed Broadband Wireless Access (FBWA) is a technology aimed at providing high-speed wireless Internet access, over a wide area, from devices such as personal computers and laptops. FBWA channels are defined in the range of 1-20 MHz which makes the RF front end (RFE) design extremely challenging. In its pursuit to standardize the Broadband Wireless Access (BWA) technologies, IEEE working group 802.16 for Broadband Wireless Access has released the fixed BWA standard IEEE 802.16 – 2004 in 2004. This standard is further backed by a consortium, of leading wireless vendors, chip manufacturers and service providers, officially known as Wireless Interoperability for Microwave Access (WiMAX). In general, any wireless base station (BS), supporting a number of contiguous Frequency Division Multiplexed (FDM) channels has to incorporate an RF front end (RFE) for each RF channel. The precise job of the RFE is to filter the desired channel from a group of RF channels, digitize it and present it to the subsequent baseband system at the proper sampling rate. The system essentially has a bandpass filter (BPF) tuned to the channel of interest followed by a multiplier which brings the channel to a suitable intermediate frequency (IF). The IF output is digitized by an ADC and then brought to the baseband by an appropriate digital multiplier. The baseband samples, thus generated, are at the ADC sampling rate which is significantly higher than the target sampling rate, which is defined by the wireless protocol in use. As a result a sampling rate conversion (SRC) is performed on these baseband samples to bring the channel back to the target sampling rate. Since the input sampling rate need not be an integer multiple of the target sampling rate, Fractional SRC (FSRC) is required in most of the cases. Instead of using a separate ADC and IF section for each individual channels, most systems use a common IF section, followed by a wideband ADC, which operates over a wide frequency band containing a group of contiguous FDM channels. In this case a channelizer is employed to digitally extract the individual channels from the digital IF samples. We formally call this system a receiver channelizer. Such an implementation presents considerable challenge in terms of the computational requirement and of course the cost of the BS. The computational complexity further goes up for FBWA system where channel bandwidth is in the order of several MHz. Though such a system has been analyzed for narrow band wireless systems like GSM, to the best of our knowledge no analysis seems to have been carried out for a wideband system such as WiMAX. In this work, we focus on design of a receiver channelizer for WiMAX BS, which can simultaneously extract a group of contiguous FDM RF channels supported by the BS. The main goal is to obtain a simple, low cost channelizer architecture, which can be implemented in an FPGA. There are a number of techniques available in the literature, from Direct Digital Conversion to Polyphase FFT Filter Banks (PFFB), which can do the job of channelization. But each of them operates with certain constraints and, as a result, suits best to a particular application. Further all of these techniques are generic in nature, in the sense that their structure is independent of any particular standard. With regard to computational requirement of these techniques, PFFB is the best, with respect to the number of complex multiplications required for its implementation. But it needs two very stringent conditions to be satisfied, viz. the number of channels to be extracted is equal to the decimation factor and the sampling rate is a power of 2 times baseband bandwidth. Clearly these conditions may not be satisfied by different wireless communication standards, and in fact, this is not satisfied by the WiMAX standard. This gives us the motivation to analyze the receiver channelizer for WiMAX BS and to find an efficient and low cost architecture of the same. We demonstrate that even though the conditions required by PFFB are not satisfied by the WiMAX standard, we can modify the overall architecture to include the PFFB structure. This is achieved by dividing the receiver channelizer into two blocks. The first block uses the PFFB structure to separate the desired number of channels from the input samples. This process also achieves an integer SRC by a factor that is equal to the number of channels being extracted. This block generates baseband outputs whose sampling rates are related to their target sampling rate by a fractional multiplication factor. In order to bring the channels to their target sampling rate, each output from the PFFB block is fed to a FSRC block, whose job is to use an efficient FSRC algorithm to generate the samples at the target sampling rate. We show that the computational complexity, as compared to the direct implementation, is reduced by a factor, which is approximately equal to the square of the number of channels. After mathematically formulating the receiver channelizer for WiMAX BS, we perform the simulation of the system using a software tool. There are two basic motives behind the simulation of the system which has a mathematical model. Firstly, the software simulation will give an idea whether the designed system is physically realizable. Secondly, this will help in designing the logic for different blocks of the system. Once these individual blocks are simulated and tested, they can be smoothly ported onto an FPGA. For simulation purpose, we parameterize the receiver channelizer in such a way that it can be reconfigured for different ADC sampling rates and IF frequencies, by changing the input clock rate. The system is also reconfigurable in terms of the supported channel bandwidth. This is achieved by storing all the filter coefficients pertaining to each channel type, and loading the required coefficients into the computational engine. Using this methodology we simulate the system for three different IF frequencies (and the corresponding ADC sampling rates) and three different channel types, thus leading to nine different system configurations. The simulation results are in agreement with the mathematical model of the system. Further, we also discuss some important implementation issues for the reconfigurable receiver channelizer. We estimate the memory requirement for implementing the system in an FPGA. The implementation delay is estimated in terms of number of samples. The thesis is organized in five chapters. Chapter 1 gives a brief introduction about the WiMAX system and different existing channelization architecture followed by the outline of the proposed receiver channelizer. In chapter 2, we analyze the proposed receiver channelizer for WiMAX BS and evaluate its computational requirements. Chapter 3 outlines the procedure to generate the WiMAX test signal and specification of the all the filters used in the system. It also lists the simulation parameters and records the results of the simulation. Chapter 4 presents the details of a possible FPGA implementation. We present the concluding remarks and future research directions in the final chapter.