Le but de la radiothérapie est d’irradier les cellules cancéreuses tout en préservant au maximum les tissus sains environnants. Or, dans le cas du cancer du poumon, la respiration du patient engendre des mouvements de la tumeur pendant le traitement. Une solution possible est de repositionner continuellement le faisceau d’irradiation sur la cible tumorale en mouvement. L’e cacité et la sûreté de cette approche reposent sur la localisation précise en temps réel de la tumeur. Le suivi indirect consiste à inférer la position de la cible tumorale à partir de l’observation d’un signal substitut, visible en continu sans nécessiter de rayonnement ionisant. Un modèle de corrélation spatial doit donc être établi. Par ailleurs, pour compenser la latence du système, l’algorithme de suivi doit pouvoir également anticiper la position future de la cible. Parce que la respiration du patient varie dans le temps, les modèles de prédiction et de corrélation peuvent devenir imprécis. La prédiction de la position de la tumeur devrait alors idéalement être complétée par l’estimation des incertitudes associées aux prédictions. Dans la pratique clinique actuelle, ces incertitudes de positionnement en temps réel ne sont pas explicitement prédites. Cette thèse de doctorat s’intéresse au contrôle en temps réel de la précision du suivi indirect de tumeurs mobiles en radiothérapie. Dans un premier temps, une méthode bayésienne pour le suivi indirect en radiothérapie est développée. Cette approche, basée sur le filtre de Kalman, permet de prédire non seulement la position future de la tumeur à partir d’un signal substitut, mais aussi les incertitudes associées. Ce travail o re une première preuve de concept, et montre également le potentiel du foie comme substitut interne, qui apparait plus robuste et fiable que les marqueurs externes communément utilisés dans la pratique clinique. Dans un deuxième temps, une adaptation de la méthode est proposée afin d’améliorer sa robustesse face aux changements de respiration. Cette innovation permet de prédire des régions de confiance adaptatives, capables de détecter les erreurs de prédiction élevées, en se basant exclusivement sur l’observation du signal substitut. Les résultats révèlent qu’à sensibilité élevée (90%), une spécificité d’environ 50% est obtenue. Un processus de validation innovant basé sur ces régions de confiance adaptatives est ensuite évalué et comparé au processus conventionnel qui consiste en des mesures de la cible à intervalles de temps fixes et prédéterminés. Une version adaptative de la méthode bayésienne est donc développée afin d’intégrer des mesures occasionnelles de la position de la cible. Les résultats confirment que les incertitudes prédites par la méthode bayésienne permettent de détecter les erreurs de prédictions élevées, et démontrent que le processus de validation basé sur ces incertitudes a le potentiel d’être plus e cace que les validations régulières. Ces approches bayésiennes sont validées sur des séquences respiratoires de volontaires, acquises par imagerie par résonance magnétique (IRM) dynamique et interpolées à haute fréquence. Afin de compléter l’évaluation de la méthode bayésienne pour le suivi indirect, une validation expérimentale préliminaire est conduite sur des données cliniques de patients atteints de cancer du poumon. Les travaux de ce projet doctoral promettent une amélioration du contrôle en temps réel de la précision des prédictions lors des traitements de radiothérapie. Finalement, puisque l’imagerie ultrasonore pourrait être employée pour visualiser les substituts internes, une étude préliminaire sur l’évaluation automatique de la qualité des images ultrasonores est présentée. Ces résultats pourront être utilisés ultérieurement pour le suivi indirect en radiothérapie en vue d’optimiser les acquisitions ultrasonores pendant les traitements et faciliter l’extraction automatique du mouvement du substitut. / The goal of radiotherapy is to irradiate cancer cells while maintaining a low dose of radiation to the surrounding healthy tissue. In the case of lung cancer, the patient’s breathing causes the tumor to move during treatment. One possible solution is to continuously reposition the irradiation beam on the moving target. The e ectiveness and safety of this approach rely on accurate real-time localization of the tumor. Indirect strategies derive the target positions from a correlation model with a surrogate signal, which is continuously monitored without the need for radiation-based imaging. In addition, to compensate for system latency, the tracking algorithm must also be able to anticipate the future position of the target. Because the patient’s breathing varies over time, prediction and correlation models can become inaccurate. Ideally, the prediction of the tumor location would also include an estimation of the uncertainty associated with the prediction. However, in current clinical practice, these real-time positioning uncertainties are not explicitly predicted. This doctoral thesis focuses on real-time control of the accuracy of indirect tracking of mobile tumors in radiotherapy. First, a Bayesian method is developed. This approach, based on Kalman filter theory, allows predicting both future target motion in real-time from a surrogate signal and associated uncertainty. This work o ers a first proof of concept, and also shows the potential of the liver as an internal substitute as it appears more robust and reliable than the external markers commonly used in clinical practice. Second, an adaptation of the method is proposed to improve its robustness against changes in breathing. This innovation enables the prediction of adaptive confidence regions that can be used to detect significant prediction errors, based exclusively on the observation of the surrogate signal. The results show that at high sensitivity (90%), a specificity of about 50% is obtained. A new validation process based on these adaptive confidence regions is then evaluated and compared to the conventional validation process (i.e., target measurements at fixed and predetermined time intervals). An adaptive version of the Bayesian method is therefore developed to valuably incorporate occasional measurements of the target position. The results confirm that the uncertainties predicted by the Bayesian method can detect high prediction errors, and demonstrate that the validation process based on these uncertainties has the potential to be more e cient and e ective than regular validations. For these studies, the proposed Bayesian methods are validated on respiratory sequences of volunteers, acquired by dynamic MRI and interpolated at high frequency. In order to complete the evaluation of the Bayesian method for indirect tracking, experimental validation is conducted on clinical data of patients with lung cancer. The work of this doctoral project promises to improve the real-time control of the accuracy of predictions during radiotherapy treatments. Finally, since ultrasound imaging could be used to visualize internal surrogates, a preliminary study on automatic ultrasound image quality assessment is presented. These results can later be used for indirect tracking in radiotherapy to optimize ultrasound acquisitions during treatments and facilitate the automatic estimation of surrogate motion.

Doctor of Philosophy / Department of Chemistry / Stefan Bossmann / Estrogen-derived DNA adducts in human could be the initiating step of breast and prostate cancer, as the scientific literature suggests. Previous studies demonstrated that 4-hydroxy-estrone (estradiol)-1-N3Adenine and 4-hydroxy-estrone (estradiol)-1-N7Guanine were the most abundant adducts found in urine of human subjects. Sensitive detection of these adducts in urine samples could lead to better breast and prostate cancer risk assessment. The standard adducts were synthesized and characterized by NMR and mass spectrometry. Since these adducts are not fluorescent at room temperature an aminomethyl (-CH2NH2) linker was introduced at the C-17 position for derivatization with fluorescence label. This linker allowed to attach highly fluorescent water soluble quantum dots (QDs) for indirect adduct detection. A direct gram-scale synthesis of highly fluorescent, photostable water soluble QDs was executed by developing a new class of 4,4’-bipyridinium salt based twin ligands with 85% and 15% of carboxylic acid and maleimide termini, respectively. These ligands not only stabilized the QDs in water but also provided versatile linkers for two labeling strategies. The twin ligands were afforded by a facile synthesis through SN2 nucleophilic substitution reaction. Labeling of adducts was achieved via a covalent coupling between the (-CH2NH2) linker and the carboxyl (-COOH) terminal ligand on the QDs. However, ELISA experiments utilizing an IgM antibody didn’t reveal any measurable signal from adduct-QD complexes suggesting that one QD is bound to a large number of adducts through –COOH terminal ligands present on QD surface. To explore the binding capabilities of QDs in more detail, a maleimide terminal ligand (a twin partner on the QDs) was synthesized to explore the thiol (-SH) functionality of thiopyrene. Preliminary ELISA showed that these QDs gave detectable fluorescent signal originating from the [pyrene-S-QD] ̶ 8E11 monoclonal antibody (mAb) complex when QD was selectively excited at 470 nm. This clearly indicates that it is necessary to develop a strategy for a distinct 1:1 labeling procedure between QD and the adduct of interest. In addition, IgG (instead of IgM) antibodies should be developed for biosensor application. The latter could afford binding of mAb in upright position, leading to an increase in surface density of mAb and better detection limit.

South Africans are engaged in daily battles with work-related and non-work related issues. Although an organisation is not capable of addressing or changing all the issues experienced by the South African population, it can intervene in order to improve the quality of its employees’ working lives. A suggested starting point is person-environment fit (PE fit), due to its effect on job satisfaction and intentions to leave. Consequently, when an individual experiences low PE fit, it will contribute to job dissatisfaction, and intentions to leave as international research has shown. To possibly decrease the impact of these relationships, it is important for leader empowering behaviour to be evident throughout the organisation. The objectives of this study were to determine possible relationships, indirect effects, and moderating effects between PE fit, job satisfaction, intentions to leave, and leader empowering behaviour. A convenience sample of employees working under the guidance of a leader/manager/supervisor was taken from a retail company in Gauteng. Participation in the study was voluntary. A measuring battery measuring PE fit (i.e. person-organisation fit, needs-supplies fit, and demands-abilities fit), job satisfaction, intentions to leave, and leader empowering behaviour (i.e. delegation of authority, accountability, self-directed decision making, information sharing, skills development, and coaching for innovative performance) was used. Descriptive and inferential statistics, Raykov’s rho coefficients, Pearson product-moment correlations, measurement models, structural models, and goodness-of-fit statistics were used to analyse the data. The results indicate that PE fit has a positive relationship with job satisfaction. Job satisfaction has a negative relationship with intentions to leave. PE fit has an indirect effect on intentions to leave via job satisfaction. Leader empowering behaviour moderates the relationship between job satisfaction and intentions to leave. Various recommendations were made for the selected retail company as well as for future research. The retail company and employees should comprehend the impact of PE fit on outcomes such as job satisfaction and intentions to leave, as both parties are equally affected by its implications. Therefore, both pro-active and re-active measures should be institutionalised to address PE fit. Additionally, the retail company should understand the importance of leader empowering behaviour and the impact it can have on their business unit and the organisation as a whole. Recommendations for future research include longitudinal research designs, as well as the expansion of research beyond the selected company in the retail industry. / MCom (Industrial Psychology)--North-West University, Vaal Triangle Campus, 2015

The measurement of cardiorespiratory fitness has been extensively researched among adult populations, but very few researchers have focused their attention on the cardiorespiratory fitness of children and adolescents. Due to various constraints of direct 2max VO testing, various indirect testing methods have been developed of which the 20-m Shuttle Run Test is the most widely used testing method. The influence of various anthropometric, physical and motor performance components as well as certain demographic factors such as gender, race, living area, and sport participation as well as physical activity level on the 2max VO value of participants seems to suggest that 2max VO can be predicted by including these components in prediction models. It is against this background that the objectives of this study are provided. The following four objectives of the study were achieved through a literature review: Firstly, to name and describe the various direct and indirect methods for determining 2max VO ; secondly, to provide a review on the findings with regard to the aerobic performances or 2max VO values of children and adolescents; thirdly, to discuss the possible influence of various anthropometric, physical and motor-performance components on the aerobic performances or 2max VO values of the last-mentioned groups of subjects. As part of this objective, other literature-identified factors such as certain demographic factors (living area, race and gender), sport and physical activity participation level which may also influence the aerobic performances or 2max VO values of the participants, were also discussed; fourthly, all literature identified models for the prediction of aerobic performances or 2max VO values in children, and in adolescents were mentioned and discussed. The next few objectives were achieved through a selected group, cross-sectional experimental research design; fifthly, to develop a valid 2max VO prediction function from several anthropometric measurements and demographic factors such as gender, race and living area as well as sport participation level of a cohort of adolescents living in the Tlokwe Local Municipality (Potchefstroom area) of North West Province, South Africa; sixthly, to develop a 2max VO prediction function from the physical and motor-performance components as well as demographic variables such as gender, race and living area as well as sport participation level of a cohort of adolescents living in the Tlokwe Local Municipality (Potchefstroom area) of North West Province, South Africa; and finally, to determine the validity of the 20-m SRT to estimate the 2 VO and 2max VO of a cohort of adolescent boys in the Tlokwe Local Municipality (Potchefstroom area) of North West Province, South Africa. In order to fulfil the fifth and sixth objectives of the study, a total of 214 grade 8 adolescents (boys: 88 and girls: 126) (age: 15.82 ± 0.68 years) of high schools in the Tlokwe Local Municipality (Potchefstroom area) of the Dr Kenneth Kaunda District of the North West Province, South Africa were purposefully selected from pre-acquired class lists, from six secondary schools. Data was collected by means of various questionnaires, anthropometric measurements and physical and motor-performance tests, which also included the 20-metre SRT. For the fulfilment of the final objective of the study, 52 boys were purposefully selected from the above-mentioned group that completed various questionnaires as well as the 20-m SRT while they were fitted with a portable gas analyser apparatus. With regard to the anthropometric and demographic variable prediction model, the forward stepwise regression analysis results showed that muscle mass percentage, sport participation level, stature, hip circumference and ectomorphy act as significant predictors (p ≤ 0.05) of the indirect, 20-m SRT 2max VO values of a cohort of adolescents. Muscle mass percentage emerged as the strongest predictor (59%) of adolescents’ 2max VO values, followed by sport participation level (6%), ectomorphy (2%), stature (1%) and hip circumference (1%). The physical, motor-performance and demographic prediction model revealed that 10-metre speed, sit-up repetitions, sport participation level, handgrip strength, Vertical Jump Test (VJT) Tendo peak power, maximal heart rate (HRmax), living area, right shoulder external rotation flexibility (RPSERT), horizontal jump test distance (HJT) and right Modified Thomas iliopsoas flexibility (RMTIT) served as significant predictors (p ≤ 0.05) of the indirect, 20m-SRT-derived 2max VO values of a cohort of adolescents. However, only 10-metre speed served as a major contributor (53.5%) to the indirect 2max VO values of the adolescents. The rest of the variables contributed 17.4% to the overall variance in 2maxVO values. Overall, the last-mentioned anthropometric, physical, motor performance and demographic variables were responsible for 70.5% of the variance in the 2max VO values of the adolescents. Cross-validations also revealed that both models are valid for predicting the 20-m SRT-derived indirect 2max VO values of this cohort of adolescents. The 20-m SRT validity study showed that a significant difference (p ≤ 0.05) existed between the predicted indirect 2max VO results (42.06 ± 4.53 ml/kg/min) as obtained from the 20-m SRT booklet and the direct 2max VO results (50.62 ± 7.11 ml/kg/min) as obtained from the gas analysis. Furthermore, significant differences (p ≤ 0.05) were observed between the direct and indirectly predicted 2 VO values at levels 1-9 of the 20-m SRT compared to no significant differences at levels 10 and 11 of the 20-m SRT. In conclusion, to the researchers’ knowledge, this is the first study to develop valid 2max VO prediction functions from the use of several anthropometric measurements, physical and motorperformance test results and demographic information for a group of South African adolescents. Furthermore, this is also the first study to reveal that the 20-m SRT is not a valid test for the accurate prediction of 2 VO and 2max VO of a cohort of adolescent South African boys. The results of this study may possibly allow practitioners in the field of Human Movement Science to more accurately screen the indirect 2max VO values of adolescents by making use of easily obtainable measures and information, instead of the predicted 2max VO values of the 20-m SRT / PhD (Human Movement Science), North-West University, Potchefstroom Campus, 2014

South Africans are engaged in daily battles with work-related and non-work related issues. Although an organisation is not capable of addressing or changing all the issues experienced by the South African population, it can intervene in order to improve the quality of its employees’ working lives. A suggested starting point is person-environment fit (PE fit), due to its effect on job satisfaction and intentions to leave. Consequently, when an individual experiences low PE fit, it will contribute to job dissatisfaction, and intentions to leave as international research has shown. To possibly decrease the impact of these relationships, it is important for leader empowering behaviour to be evident throughout the organisation. The objectives of this study were to determine possible relationships, indirect effects, and moderating effects between PE fit, job satisfaction, intentions to leave, and leader empowering behaviour. A convenience sample of employees working under the guidance of a leader/manager/supervisor was taken from a retail company in Gauteng. Participation in the study was voluntary. A measuring battery measuring PE fit (i.e. person-organisation fit, needs-supplies fit, and demands-abilities fit), job satisfaction, intentions to leave, and leader empowering behaviour (i.e. delegation of authority, accountability, self-directed decision making, information sharing, skills development, and coaching for innovative performance) was used. Descriptive and inferential statistics, Raykov’s rho coefficients, Pearson product-moment correlations, measurement models, structural models, and goodness-of-fit statistics were used to analyse the data. The results indicate that PE fit has a positive relationship with job satisfaction. Job satisfaction has a negative relationship with intentions to leave. PE fit has an indirect effect on intentions to leave via job satisfaction. Leader empowering behaviour moderates the relationship between job satisfaction and intentions to leave. Various recommendations were made for the selected retail company as well as for future research. The retail company and employees should comprehend the impact of PE fit on outcomes such as job satisfaction and intentions to leave, as both parties are equally affected by its implications. Therefore, both pro-active and re-active measures should be institutionalised to address PE fit. Additionally, the retail company should understand the importance of leader empowering behaviour and the impact it can have on their business unit and the organisation as a whole. Recommendations for future research include longitudinal research designs, as well as the expansion of research beyond the selected company in the retail industry. / MCom (Industrial Psychology)--North-West University, Vaal Triangle Campus, 2015

The measurement of cardiorespiratory fitness has been extensively researched among adult populations, but very few researchers have focused their attention on the cardiorespiratory fitness of children and adolescents. Due to various constraints of direct 2max VO testing, various indirect testing methods have been developed of which the 20-m Shuttle Run Test is the most widely used testing method. The influence of various anthropometric, physical and motor performance components as well as certain demographic factors such as gender, race, living area, and sport participation as well as physical activity level on the 2max VO value of participants seems to suggest that 2max VO can be predicted by including these components in prediction models. It is against this background that the objectives of this study are provided. The following four objectives of the study were achieved through a literature review: Firstly, to name and describe the various direct and indirect methods for determining 2max VO ; secondly, to provide a review on the findings with regard to the aerobic performances or 2max VO values of children and adolescents; thirdly, to discuss the possible influence of various anthropometric, physical and motor-performance components on the aerobic performances or 2max VO values of the last-mentioned groups of subjects. As part of this objective, other literature-identified factors such as certain demographic factors (living area, race and gender), sport and physical activity participation level which may also influence the aerobic performances or 2max VO values of the participants, were also discussed; fourthly, all literature identified models for the prediction of aerobic performances or 2max VO values in children, and in adolescents were mentioned and discussed. The next few objectives were achieved through a selected group, cross-sectional experimental research design; fifthly, to develop a valid 2max VO prediction function from several anthropometric measurements and demographic factors such as gender, race and living area as well as sport participation level of a cohort of adolescents living in the Tlokwe Local Municipality (Potchefstroom area) of North West Province, South Africa; sixthly, to develop a 2max VO prediction function from the physical and motor-performance components as well as demographic variables such as gender, race and living area as well as sport participation level of a cohort of adolescents living in the Tlokwe Local Municipality (Potchefstroom area) of North West Province, South Africa; and finally, to determine the validity of the 20-m SRT to estimate the 2 VO and 2max VO of a cohort of adolescent boys in the Tlokwe Local Municipality (Potchefstroom area) of North West Province, South Africa. In order to fulfil the fifth and sixth objectives of the study, a total of 214 grade 8 adolescents (boys: 88 and girls: 126) (age: 15.82 ± 0.68 years) of high schools in the Tlokwe Local Municipality (Potchefstroom area) of the Dr Kenneth Kaunda District of the North West Province, South Africa were purposefully selected from pre-acquired class lists, from six secondary schools. Data was collected by means of various questionnaires, anthropometric measurements and physical and motor-performance tests, which also included the 20-metre SRT. For the fulfilment of the final objective of the study, 52 boys were purposefully selected from the above-mentioned group that completed various questionnaires as well as the 20-m SRT while they were fitted with a portable gas analyser apparatus. With regard to the anthropometric and demographic variable prediction model, the forward stepwise regression analysis results showed that muscle mass percentage, sport participation level, stature, hip circumference and ectomorphy act as significant predictors (p ≤ 0.05) of the indirect, 20-m SRT 2max VO values of a cohort of adolescents. Muscle mass percentage emerged as the strongest predictor (59%) of adolescents’ 2max VO values, followed by sport participation level (6%), ectomorphy (2%), stature (1%) and hip circumference (1%). The physical, motor-performance and demographic prediction model revealed that 10-metre speed, sit-up repetitions, sport participation level, handgrip strength, Vertical Jump Test (VJT) Tendo peak power, maximal heart rate (HRmax), living area, right shoulder external rotation flexibility (RPSERT), horizontal jump test distance (HJT) and right Modified Thomas iliopsoas flexibility (RMTIT) served as significant predictors (p ≤ 0.05) of the indirect, 20m-SRT-derived 2max VO values of a cohort of adolescents. However, only 10-metre speed served as a major contributor (53.5%) to the indirect 2max VO values of the adolescents. The rest of the variables contributed 17.4% to the overall variance in 2maxVO values. Overall, the last-mentioned anthropometric, physical, motor performance and demographic variables were responsible for 70.5% of the variance in the 2max VO values of the adolescents. Cross-validations also revealed that both models are valid for predicting the 20-m SRT-derived indirect 2max VO values of this cohort of adolescents. The 20-m SRT validity study showed that a significant difference (p ≤ 0.05) existed between the predicted indirect 2max VO results (42.06 ± 4.53 ml/kg/min) as obtained from the 20-m SRT booklet and the direct 2max VO results (50.62 ± 7.11 ml/kg/min) as obtained from the gas analysis. Furthermore, significant differences (p ≤ 0.05) were observed between the direct and indirectly predicted 2 VO values at levels 1-9 of the 20-m SRT compared to no significant differences at levels 10 and 11 of the 20-m SRT. In conclusion, to the researchers’ knowledge, this is the first study to develop valid 2max VO prediction functions from the use of several anthropometric measurements, physical and motorperformance test results and demographic information for a group of South African adolescents. Furthermore, this is also the first study to reveal that the 20-m SRT is not a valid test for the accurate prediction of 2 VO and 2max VO of a cohort of adolescent South African boys. The results of this study may possibly allow practitioners in the field of Human Movement Science to more accurately screen the indirect 2max VO values of adolescents by making use of easily obtainable measures and information, instead of the predicted 2max VO values of the 20-m SRT / PhD (Human Movement Science), North-West University, Potchefstroom Campus, 2014

Le succès reproducteur, défini comme l’aptitude d’un individu à se reproduire et ainsi transmettre son bagage génétique aux générations futures, constitue une des motivations fondamentales qui dictera plusieurs des comportements observés chez une espèce animale. L’étude de ces divers comportements est essentielle afin de comprendre les stratégies évolutives sous-jacentes qui permettent aux individus d’augmenter leurs chances de reproduction. La monogamie sociale avec polygamie génétique est un bel exemple de stratégie reproductive chez laquelle les individus peuvent potentiellement augmenter leur succès reproducteur en tentant d’acquérir des fertilisations d’individus autres que le mâle et la femelle constituant le couple social. Ces fertilisations dites hors-couples, qui sont communes chez les oiseaux, sont un moyen efficace pour les mâles d’augmenter leur succès reproducteur via leur nombre de jeunes produits dans diverses nichées pour une saison de reproduction donnée. Pour les femelles, les avantages que procure ce comportement restent encore obscurs malgré la panoplie d’études s’étant penchées sur la question. L’acquisition de bénéfices indirects, de nature génétique, est une hypothèse fréquemment mise de l’avant pour tenter d’expliquer les motivations des femelles à s’engager dans des copulations hors-couples. L’objectif de ma maîtrise consistait à évaluer si la femelle, via l’acquisition de paternités hors-couples au sein de sa nichée, tente d’acquérir des bénéfices de types indirects pour les oisillons issus de ce type de fertilisation chez une population sauvage d’Hirondelle bicolore (Tachycineta bicolor) dans le Sud du Québec. Ces bénéfices indirects peuvent se refléter au niveau des oisillons dits hors-couples en leur conférant des avantages génétiques et donc potentiellement une survie plus élevée, par rapport aux oisillons issus du couple social. En premier lieu, mes résultats indiquent une survie plus élevée pour les oisillons issus du couple social par rapport aux oisillons issus de paternités hors-couples contrairement aux prédictions initiales. Ensuite, en comparant une mesure intégratrice basée sur plusieurs mesures de capacité immunitaire, les résultats obtenus suggèrent une différence dans le patron d’allocation immunitaire des deux types d’oisillons. Les oisillons issus du couple social ayant une tendance à investir préférentiellement au niveau de l’immunité adaptative par opposition aux oisillons issus de paternités hors-couples ayant une tendance à investir dans les composantes de l’immunité constitutive. Cette différence d’investissement entre les composantes de l’immunité constitutive et adaptative pourrait représenter un développement asynchrone entre les oisillons en couple et hors-couple dû à un compromis d’allocation d’énergie entre les fonctions immunitaires et les paramètres de croissance. En conclusion, cette étude montre la complexité du phénomène des paternités hors-couples ainsi que les motivations qui poussent la femelle à rechercher de telles fertilisations. De plus, cette étude met l’emphase sur l’importance de considérer plus d’une mesure immunitaire lors de la comparaison entre individus.

La conception de turboréacteurs présente de plus en plus de défis. Le respect de l'environnement, naturel et sonore, est devenu un enjeu majeur pour les motoristes car il devient un argument de vente important et une condition sine qua non afin de valider les futures normes en aviation. Dans ce contexte, il est devenu nécessaire d'étudier et de prédire les différentes sources de bruit d'un turboréacteur pour les inclure dans sa conception. Parmi ces différentes sources de bruit, celle de la chambre de combustion est méconnue et devient une source de bruit aval de plus en plus importante dans les phases d'approche et de croisière où le bruit de jet a été significativement réduit. Nous pourrons aussi nous intéresser aux modes de conduit générés par les interactions rotor-stator des différents étages de compresseurs et de turbines en amont et aval de la chambre de combustion respectivement. L'effet de masquage étant réduit par la diminution du nombre d'étages de turbines, il est donc nécessaire d'évaluer la transmission et la réflexion des ondes acoustiques (responsables du bruit direct) mais aussi entropiques et de vorticité (responsables du bruit indirect) issues de la combustion ainsi que des modes de conduit à travers les étages de turbines d'un turboréacteur. L'objectif, dans le cadre de la Chaire de recherche en acoustique appliquée à l'aviation en collaboration avec Pratt & Whitney Canada, est de développer un modèle de pertes par transmission valide autant pour les basses fréquences (chambre de combustion) que pour des fréquences plus élevées (interactions rotor-stator). Différents niveaux de modélisation sont utilisés à partir de disques actifs ou semi-actifs. Ces théories sont utilisées pour les très basses fréquences en considérant que l'espace inter-aubes et la corde du profil sont faibles devant la longueur d'onde. Les théories plus complexes prennent en compte une corde non négligeable et donc des fréquences plus élevées. Parmi les modèles existants dans la littérature, nous avons choisi de sélectionner deux modèles en particulier. Tout d'abord un modèle de disque actif pour prendre en compte la déviation de l'écoulement par les aubes puis un modèle de grille d'aubes pour prendre en compte la corde et l'espace inter-aubes. L'objectif est de coupler ces deux modèles afin de prendre en compte tous les effets intervenant dans la transmission des ondes à travers les étages de turbines d'un turboréacteur.

Text in Afrikaans / Tradisioneel is aanvaar dat die indirekte voorwerp nie in Afrikaanse stelsinne kan optree sander die voorkoms van 'n direkte voorwerp in dieselfde sin nie. Hierdie ondersoek het aan die lig gebring dat sekere voorwerpe wat voorheen as "direkte voorwerpe" geklassifiseer is, eerder die eienskappe van indirekte Hulle word dus nou geklassifiseer as en die parameters van die indirekte ooreenkomstig uitgebrei. Aangesien daar geen formele merkers vir die uitkenning en onderskeiding van direkte en indirecte voorwerpe bestaan nie, is parameters vir die doel vasgestel. Skoon indireckte voorwerpe (op enkele uisonderings na) verskyn altyd direk na die SPIL-posisie in 'n stelsin toon 'n groot affiniteit vir voorsetsels (versa vir, aan), en kan in die koers van adjunk afgegradeer word, deur me 'n voorsetsel te verbind, en kan sodoende ook na' 'n adjunk verskyn. Direkte voorwerpe kan daarenteen nie met voorset-: sels verbind nie en kan buitendien na enige adjunk verskyn. / Language Education, Arts and Culture / M.A. (Afrikaans)

BACKGROUND: The abnormal signal intensity in cardiac T₂-weighted images is associated with various pathologies including myocardial edema. However, the assessment of pathologies based on signal intensity is affected by the acquisition parameters and the sensitivities of the receiver coils. T₂ mapping has been proposed to overcome limitations of T₂-weighted imaging, but most methods are limited in spatial and/or temporal resolution. Here we present and evaluate a double inversion recovery radial fast spin-echo (DIR-RADFSE) technique that yields data with high spatiotemporal resolution for cardiac T₂ mapping. METHODS: DIR-RADFSE data were collected at 1.5 T on phantoms and subjects with echo train length (ETL) = 16, receiver bandwidth (BW) = +/-32 kHz, TR = 1RR, matrix size = 256 x 256. Since only 16 views per echo time (TE) are collected, two algorithms designed to reconstruct highly undersampled radial data were used to generate images for 16 time points: the Echo-Sharing (ES) and the CUrve Reconstruction via pca-based Linearization with Indirect Echo compensation (CURLIE) algorithm. T₂ maps were generated via least-squares fitting or the Slice-resolved Extended Phase Graph (SEPG) model fitting. The CURLIE-SEPG algorithm accounts for the effect of indirect echoes. The algorithms were compared based on reproducibility, using Bland-Altman analysis on data from 7 healthy volunteers, and T₂ accuracy (against a single-echo spin-echo technique) using phantoms. RESULTS: Both reconstruction algorithms generated in vivo images with high spatiotemporal resolution and showed good reproducibility. Mean T₂ difference between repeated measures and the coefficient of repeatability were 0.58 ms and 2.97 for ES and 0.09 ms and 4.85 for CURLIE-SEPG. In vivo T₂ estimates from ES were higher than those from CURLIE-SEPG. In phantoms, CURLIE-SEPG yielded more accurate T₂s compared to reference values (error was 7.5-13.9% for ES and 0.6-2.1% for CURLIE-SEPG), consistent with the fact that CURLIE-SEPG compensates for the effects of indirect echoes. The potential of T₂ mapping with CURLIE-SEPG is demonstrated in two subjects with known heart disease. Elevated T₂ values were observed in areas of suspected pathology. CONCLUSIONS: DIR-RADFSE yielded TE images with high spatiotemporal resolution. Two algorithms for generating T₂ maps from highly undersampled data were evaluated in terms of accuracy and reproducibility. Results showed that CURLIE-SEPG yields T₂ estimates that are reproducible and more accurate than ES.