During the recession period of 2008/2009, global tourism declined by 8%. This was also evident is South Africa with the domestic travel market shrinking by 8% as well. However, this did not apply to the Kruger National Park (KNP) which experienced a sustained Accommodation Unit Occupancy growth of 1.6% during the same period. Visitors to the KNP thus see it as an attractive holiday destination irrespective of tough economic conditions characterised by less disposable income. To sustain this growth, it is important to be aware of the reasons visitors still visit the KNP during a recession. The aim of this study was to determine the reasons why visitors still travelled to the KNP during the 2008/2009 recession. This can be done by analysing the visitors’ behaviour and the motivational factors (internal feelings of the visitors) and determinants of the demand (income and exchange rates for instance) that influenced visitors’ choice to visit the KNP. To achieve this aim, a survey was conducted at the KNP between 15 and 20 December 2009 (high season). A total of 355 questionnaires were completed, after which a number of analyses were done to determine the effects of the recession on travel behaviour. For the purpose of this study, two articles were written. Article 1 is titled: “Motivations of visitors to the Kruger National Park during the 2008/2009 recession period”. The aim of this article was to determine the motivations of visitors to the KNP during the recession. A factor analysis on the motivations to visit the park was conducted, of which the following factors obtained the highest mean values: Escape, Wildlife experience and Family benefits. Push factors to the KNP were important to such an extent that visitors regarded visiting the park as a primary need or lifestyle. The results furthermore showed that visitors might have adapted their spending behaviour at the park to still afford to visit the park during the recession. This article provides a better understanding of visitors’ feelings towards the KNP, especially amidst recessions which, in turn, will improve niche marketing and a competitive advantage. Article 2 is titled: “Factors that influenced demand to the Kruger National Park during the 2008/2009 economic recession”. The aim of this article was to identify the determinants that influence the demand for visits to the KNP. Due to the homogeneous nature of the park’s market, the results of the stepwise logistic regression analysis revealed a few socio-demographic and behavioural determinants that influenced visitors’ demand to the park. The motives Escape and Souvenirs were the only two behavioural determinants while the provinces Gauteng and Mpumalanga were the only socio-demographic determinants. These two provinces are the two main markets for the KNP. Visitors indicated that visiting the KNP is a great way of escaping their busy metropolitan areas, especially in the Gauteng province. Mpumalanga residents have many tourism attractions in their province thus lowering the chances that they will visit the KNP. The determinant Souvenirs indicates that visitors adapted their spending at the park to still be able to afford visits. It was also found that demand to visit the park was not greatly influenced by the recession, because visitors could adapt their spending at the park. This is the first time the determinants of demand to a national park during a recession period have been conducted. The study indicated that visiting natural areas may have become a primary need or part of a lifestyle, especially during the 2008/2009 recession period. This article gives park management guidelines that will ensure the sustainability of the KNP because this information now allows for well-planned, thorough marketing and management of the park. In the case of KNP, which has a homogeneous market, the number of determinants identified influencing demand for visiting the park is fewer than has been found in other studies done on heterogeneous markets. This study therefore also makes a valuable methodological contribution in relation to analysing demand of homogeneous and heterogeneous markets. / Thesis (M.Com. (Tourism))--North-West University, Potchefstroom Campus, 2011.

L’objectif de cette thèse est l’élaboration de sondes organiques pour la microscopie optique non-linéaire par fluorescence excitée à deux photons (F2P) et génération de seconde harmonique (GSH). Dans une première partie, cette thèse décrit la synthèse de sondes pour l’imagerie de potentiels de membrane par GSH, comportant un ou plusieurs motifs sucres ainsi que leurs caractérisations spectroscopiques. Les premiers essais en imagerie biologique ont permis de démontrer une bonne affinité des sondes sucres pour la membrane cellulaire et un signal de GSH sur cellule neuronale a pu être observé sur une période de temps allant jusqu'à près de trois heures. La seconde approche a consisté à synthétiser et étudier des chromophores possédant des propriétés de fluorescence à l’état solide pour des applications dans la synthèse de nanoparticules fluorescentes pour l’imagerie biologique. 18 des 21 composés synthétisés ont pu être cristallisés et leur structure résolue par diffraction des rayons X et les propriétés spectroscopique en solution et à l’état solide ont été réalisées. Cette étude a permis de montrer que l’arrangement des molécules les unes par rapport aux autres avait une grande influence sur la fluorescence à l’état solide et donc que les substituants avaient une grande importance. Enfin, cette partie se termine sur les premiers essais effectués pour synthétiser des nanoparticules fluorescentes. / The objective of this thesis is the design of new organic probes for nonlinear optical microscopy by two-photon excited fluorescence (TPEF) and second harmonic generation (SHG). In the first part, we describe the synthesis of probes for voltage sensitive imaging by SHG, bearing one or more sugar units and their spectroscopic characterization. The first biological imaging tests have shown good affinity of the probes to the cell membrane and the SHG signal of neuronal cell was observed over a period of nearly three hours. The second part comprises the synthesis and the study of chromophores with solid state fluorescence properties for use in fluorescent nanoparticles for biological imaging. 18 of the 21 compounds synthesized have been crystallized, their crystal structures determined by X-ray diffraction and their spectroscopic properties studied in solution and in the solid state. These studies showed that the arrangement of molecules relative to each had a great influence on the solid state fluorescence and therefore that the substitution was very important. The chapter ends with the first tests of fluorescent nanoparticles synthesis.

Recentemente a utilização de estruturas mistas, aço concreto, vem ganhando espaço nas construções. Isso deve-se principalmente a economia de tempo em sua execução. Além disto, nesta solução a utilização do aço e do concreto otimiza as características estruturais de seus elementos: a resistência a tração do aço e a compressão do concreto. A transferência dos esforços entre os dois materiais possui grande influência no desempenho de uma estrutura mista, sendo comum a utilização de conectores de cisalhamento na região da interface entre estes dois materiais. O Eurocode 4 define um ensaio experimental denominado push-out de modo a determinar a resistência e ductilidade de conectores de cisalhamento. Seu desempenho é influenciado pelas resistências do concreto a compressão, as dimensões e taxa de armadura da laje de concreto, dimensões do perfil de aço, a disposição e a geometria dos conectores e pelas características dos aços utilizados no conector, no perfil e nas barras de reforço. Nota-se com isso uma grande quantidade de variáveis que influenciam o ensaio. Assim, o presente trabalho apresenta o desenvolvimento de um modelo em elementos finitos com base no programa ANSYS para simulação de ensaios push-out. Os resultados numéricos apresentados neste trabalho foram calibrados com resultados obtidos em ensaios experimentais existentes na literatura de ensaios push-out para conectores do tipo pino com cabeça (stud) e conectores tipo perfobond. Estes últimos apresentam elevada resistência sendo influenciados por inúmeros fatores como: número e diâmetro dos furos no conector e a inclusão ou não de barras de reforço extras nestes furos. / A continuous increase of the use of (steel & concrete) composite structures in constructions can be recently observed. This is mainly due to its faster execution time when compared to other construction alternatives. Additionally, these solutions optimize the structural characteristics of the involved materials: the steel tension capacity and the concrete compressive strength. The transfer of forces between these different materials greatly influences the composite structure performance, where typical solutions uses shear connectors at the concrete to steel interface. The Eurocode 4 defines an experimental test, denominated push-out, to determine the shear connectors strength and associated ductility capacity. Its performance is influenced by the concrete compressive strength, slab dimensions and adopted reinforcing bar area, steel profile dimensions, shear connectors geometry and disposition and by the mechanical characteristics of the connector, profile and reinforcing bars steels. All these aspects indicate that a great number of variables can influence the test. This study presents the development of a finite element model, based on the ANSYS program, to simulate push-out tests. The numerical results presented in this investigation were calibrated against experiments reported in the literature for stud and Perfobond shear connectors. The Perfobond connectors present a substantial shear capacity being influenced by several factors like: connectors hole number and diameter and by the adoption, or not, of extra reinforcing bars passing through the connector holes.

Ce travail de thèse, effectué dans le cadre du projet européen MClocks (http://www.inrim.it/mclocks), reporte le développement et la caractérisation métrologique d’une horloge atomique à cellule de césium de haute performance basée sur le phénomène de piégeage cohérent de population (CPT). Cette horloge exploite un schéma de pompage CPT optimisé nommé push-pull optical pumping (PPOP), permettant la détection de résonances CPT à fort contraste sur la transition d’horloge 0-0. Une caractérisation détaillée des différents éléments de l’horloge est reportée. L’horloge fut exploitée en mode continu (CW) et en mode impulsionnel de type Ramsey. Dans les deux modes de fonctionnement, l’horloge démontre une stabilité relative de fréquence de l’ordre de 2 10−13 τ−1/2 jusque 100 s d’intégration, principalement limitée par des effets de puissance laser. Cette horloge atomique, parmi les meilleures horloges à cellule développées à travers le monde, pourrait trouver des applications pour les systèmes de télécommunications, d’instrumentation, de défense ou navigation par satellite.Cette thèse reporte aussi une technique originale de stabilisation de fréquence laser par spectroscopie sub-Dopplerbi-fréquence en cellule. La plateforme constituée par l’horloge a été utilisée pour mener des tests de physique plus amont incluant la caractérisation par spectroscopie CPT d’une cellule de césium avec un revêtement anti-relaxant OTS (octadecyltrichlorosilane) ou la caractérisation de microcellules à vapeur de césium avec gaz tampon développées à FEMTO-ST pour des horloges atomiques miniatures. / This thesis work, performed in the frame of the MClocks European project (http://www.inrim.it/mclocks), reports the development and metrological characterization of a high-performance Cs vapor cell atomic clock based on coherent population trapping (CPT). The clock uses an optimized CPT pumping scheme, named push-pull optical pumping (PPOP), allowing the detection of high-contrast CPT resonances on the 0-0 magnetic-field insensitive clock transition. A detailed characterization of key components of the clock is reported. The clock was operated in the continuous-wave (CW) regime and in a Ramsey-like pulsed regime. In both regimes, the clock demonstrates a short-term fractional frequency stability at the level of 2 10−13 τ−1/2 up to 100 s averaging time, mainly limited by laser power effects. This CPT clock, ranking among the best microwave vapor cell atomic frequency standards, could find applications in telecommunication, instrumentation, defense or satellite-based navigation systems.This thesis reports also a novel laser frequency stabilization technique using dual-frequency sub-Doppler spectroscopy in a vapor cell. The clock ”platform” has also been used to perform using CPT spectroscopy the characterization of a Cs vapor cell coated with octadecyltrichlorosilane (OTS) or original buffer-gas filled Cs vapor micro-fabricated cells developed in FEMTO-ST for CPT-based miniature atomic clocks.

Recentemente a utilização de estruturas mistas, aço concreto, vem ganhando espaço nas construções. Isso deve-se principalmente a economia de tempo em sua execução. Além disto, nesta solução a utilização do aço e do concreto otimiza as características estruturais de seus elementos: a resistência a tração do aço e a compressão do concreto. A transferência dos esforços entre os dois materiais possui grande influência no desempenho de uma estrutura mista, sendo comum a utilização de conectores de cisalhamento na região da interface entre estes dois materiais. O Eurocode 4 define um ensaio experimental denominado push-out de modo a determinar a resistência e ductilidade de conectores de cisalhamento. Seu desempenho é influenciado pelas resistências do concreto a compressão, as dimensões e taxa de armadura da laje de concreto, dimensões do perfil de aço, a disposição e a geometria dos conectores e pelas características dos aços utilizados no conector, no perfil e nas barras de reforço. Nota-se com isso uma grande quantidade de variáveis que influenciam o ensaio. Assim, o presente trabalho apresenta o desenvolvimento de um modelo em elementos finitos com base no programa ANSYS para simulação de ensaios push-out. Os resultados numéricos apresentados neste trabalho foram calibrados com resultados obtidos em ensaios experimentais existentes na literatura de ensaios push-out para conectores do tipo pino com cabeça (stud) e conectores tipo perfobond. Estes últimos apresentam elevada resistência sendo influenciados por inúmeros fatores como: número e diâmetro dos furos no conector e a inclusão ou não de barras de reforço extras nestes furos. / A continuous increase of the use of (steel & concrete) composite structures in constructions can be recently observed. This is mainly due to its faster execution time when compared to other construction alternatives. Additionally, these solutions optimize the structural characteristics of the involved materials: the steel tension capacity and the concrete compressive strength. The transfer of forces between these different materials greatly influences the composite structure performance, where typical solutions uses shear connectors at the concrete to steel interface. The Eurocode 4 defines an experimental test, denominated push-out, to determine the shear connectors strength and associated ductility capacity. Its performance is influenced by the concrete compressive strength, slab dimensions and adopted reinforcing bar area, steel profile dimensions, shear connectors geometry and disposition and by the mechanical characteristics of the connector, profile and reinforcing bars steels. All these aspects indicate that a great number of variables can influence the test. This study presents the development of a finite element model, based on the ANSYS program, to simulate push-out tests. The numerical results presented in this investigation were calibrated against experiments reported in the literature for stud and Perfobond shear connectors. The Perfobond connectors present a substantial shear capacity being influenced by several factors like: connectors hole number and diameter and by the adoption, or not, of extra reinforcing bars passing through the connector holes.

O objetivo deste estudo é avaliar a influência da irradiação com laser de Er,Cr:YSGG no espaço protético de condutos radiculares preparados para a fixação de pinos em fibra de vidro reforçados (FRC Postec®), avaliando-se o comportamento de três diferentes técnicas adesivas (self-etching= Panavia F®; total-etching= Excite DSC® + Variolink II® e self-adhesive= RelyX Unicem Aplicap®). Observaram-se as orientações da norma ISO-TS 11405 para a preparação das raízes dentais unirradiculares humanas. As amostras foram separadas na altura da junção amelo-dentinaria, tratadas endodonticamente com instrumentação rotatória e seladas com técnica de condensação lateral. Foram utilizados dois tipos diferentes de pontas de safira para irradiação intracanal o axial (Z4, 400 m de diâmetro) e o radial ou side firing (RFT4, 415 m de diâmetro) com densidade de energia de 40 J/cm2. Esta densidade de energia foi obtida como parte deste experimento, analisando-se diversos parâmetros de energia com os resultados morfológicos e térmicos obtidos. Nesta densidade, obtive-se grande quantidade de túbulos dentinários abertos e variação de temperatura segura para uso clínico. Cada raiz foi irradiada em cinco movimentos circulares, de apical para cervical, com intervalo de 20 segundos, entre elas. Os FRC Postec foram cimentados imediatamente após a irradiação e divididos randomicamente em nove grupos (n=10). Cada raiz foi seccionada em 6 discos de 1 mm de espessura para ensaio do tipo push-out, para a obtenção da força máxima de ruptura, e posterior cálculo da resistência de união adesiva em função da área de superfície do núcleo deslocado, resultando na pressão em MPa. A resistência de união adesiva nos grupos irradiados foi estatisticamente superior do que os grupos controle. Foram avaliadas as diferenças na resistência de união adesiva em diferentes porções do núcleo (cervical, médio e apical), onde o sistema adesivo tipo self-adhesive (RelyX Unicem Aplicap) teve o melhor resultado para os grupos irradiados. Avaliou-se por técnica de FTIR as diferenças químicas ocorridas na dentina intrarradicular irradiada com laser de Er,Cr:YSGG, em diferentes porções (cervical, médio e apical) em função da orientação dos túbulos. Foram observadas nos espectros de FTIR alterações na intensidade das bandas de algumas moléculas, indicando variação na quantidade da parte orgânica (amida I e amida II) após a irradiação, nas diferentes regiões dentais em função do feixe laser sobre a orientação dos túbulos dentinários, sem causar alterações na sua composição. Essas diferenças podem interferir no resultado da resistência de união adesiva. A técnica de utilização de laser de Er,Cr: YSGG em dentina radicular pré-cimentação de núcleo protético aumenta a resistência de união adesiva, na dependência do cimento utilizado. / The aim of this study was to evaluate the influence of the Er,Cr:YSGG laser irradiation in the prosthetic post space before FRC Postec placement using three different adhesive systems (self-etching- Panavia F; total-etching- Excite DSC + Variolink II e self adhesive - RelyX Unicem Aplicap). According to ISO-TS 11405, sectioned at the CEJ, human dental single roots were endodontically treated with rotatory instruments and filled with gutta-percha points and sealer. Were used at 40 J/cm2 an axial Z4 laser tip (400 m diameter) and a radial (side firing) RFT4 laser tip (415 m diameter). This density of energy was experimentally determinated observing morphological changes in SEM images due to an increase range in the energy applied to dentinal root canal surface. At the length between 32 and 49 J/cm2 most of the intracanal dentinal tubules were open. The temperature increase was within the biological safe suggesting a feasible clinical use. Each root canal was irradiated five times with helicoidal movements from apical to cervical, with 20 seconds interval. FRC Postec were immediately cemented and randomly divided in nine groups (n=10). Each root canal was cut in six discs for push out test, were the maximum failure load was obtained and the bond strength was calculated as a function of post bonded area. The bond strength for the irradiated groups was superior among all control groups. The evaluation of bond strength among root region (cervical, middle and apical) was performed and differences were observed. The self-adhesive (RelyX Unicem Aplicap) system was noted superior among all irradiated groups and all regions. Chemical changes were analyzed by FTIR due to dental root portion and dentinal tubules orientation to laser beam direction. The FTIR spectra obtained indicated changes due to tubules orientation and root canal portion irradiated such as the proportion among the compositional ratio without causing chemical changes. These compositional ratio alterations may affect the bond strength results. The irradiation with Er,Cr:YSGG laser on dentinal walls of a prosthetic post space preparation before the post cementation, as suggested in this study, may increase the bond strength between the post and root canal dentin depending upon the luting cement that is used.

Submitted by Luanna Matias (lua_matias@yahoo.com.br) on 2015-03-27T17:05:59Z No. of bitstreams: 2 Dissertação - Marcel Willian Reis Sales - 2014.pdf: 4208639 bytes, checksum: b181bf240488740db8489468fb605743 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Approved for entry into archive by Luanna Matias (lua_matias@yahoo.com.br) on 2015-03-27T18:54:00Z (GMT) No. of bitstreams: 2 Dissertação - Marcel Willian Reis Sales - 2014.pdf: 4208639 bytes, checksum: b181bf240488740db8489468fb605743 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Made available in DSpace on 2015-03-27T18:54:00Z (GMT). No. of bitstreams: 2 Dissertação - Marcel Willian Reis Sales - 2014.pdf: 4208639 bytes, checksum: b181bf240488740db8489468fb605743 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2014-08-27 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Composite beams of steel and concrete are studied for some time. The mechanism of transfer of longitudinal shear stresses on the interface between the beam and the slab usually occurs by means of shear connectors. In this case, the set of two materials behavior depends on the strength and rigidity of the connector on the interface, being well known for connectors with pin-type head associated with massive concrete slab. However, there is little information on shear connectors with pin-type head associated with hollowcore slab concrete. This study aims to determine, by means of direct shear tests, the resistance of connectors with pin-type head when associated with cellular slab and precast concrete presence of cover concrete. Hollow core slabs are analyzed with two different heights and concrete cover of 40 mm in thickness. Is also varied the strength of concrete fill and rate of shear reinforcement at the link. The results are compared with normative prescriptions and suggestions for other jobs. At the end, we propose the modification of an expression commonly used to evaluate the resistance of stud bolt and alveolar slab so as to adapt it to the situation of cellular concrete slab with hood. / As vigas mistas de aço e concreto são estudadas há bastante tempo. O mecanismo de transferência de tensões de cisalhamento longitudinais pela interface entre a viga e a laje normalmente se dá por meio de conectores de cisalhamento. Nesse caso, o comportamento conjunto dos dois materiais depende da resistência e da rigidez do conector na interface, sendo bem conhecido para os conectores do tipo pino com cabeça associados com laje maciça de concreto. Entretanto, há pouca informação sobre conectores de cisalhamento do tipo pino com cabeça associados com laje alveolar de concreto pré-moldado. Este trabalho tem por objetivo determinar, por meio de ensaios de cisalhamento direto, a resistência de conectores do tipo pino com cabeça quando associados com laje alveolar de concreto pré-moldado e presença de capa de concreto. São analisadas lajes alveolares com duas alturas diferentes e capa de concreto de 40 mm de espessura. Também é variada a resistência do concreto de preenchimento e a taxa de armadura transversal à ligação. Os resultados são comparados com prescrições normativas e sugestões de outros trabalhos. Ao final, é proposta a modificação de uma expressão normalmente utilizada para avaliar a resistência do conector tipo pino com cabeça e laje alveolar de modo a adequá-la à situação de laje alveolar com capa de concreto.

With the increased significance of information technology (IT) in today’s society the term ‘electronic democracy’ (e-democracy) has gained much importance within the democracy theory. Naturally, there are several competing views on how the technology should be used for democratic purpose. One aspect of this is the somewhat revitalized claim for direct democracy in accordance with the hypothetical opportunity to finally realize it as a democratic system. The ideal of direct democracy combined with the almost total credence in the potential of technology constitute the idea of a ‘push-button democracy’. The term has to a large extent been used by critics to the idea. However, it does also figure as a generic term describing this ‘new’ claim for direct democracy. This essay seeks in a qualitative normative and theoretical way, to assess the plausibility of the idea of the push-button democracy in relation to classical democracy theory. In excess of the debate of direct versus representative democracy, the analysis seeks to give a normative approach on how information technology should be applied. The result of the analysis consists of a number of predicted implications with the realization of the push-button democracy, especially concerning the democratic process in regard to decision making. Furthermore, it is reasoned whether this utopian system is desirable, even from a principal view. Finally, the discussion concludes with a stance of policy that information technology should be used as a mean for the existing representative democracy, rather than a goal, in order to create a different political system.

Entrepreneurial activity can promote economic development on a national level. Women are the most underdeveloped workforce globally. The amount of entrepreneurs is higher in developing countries, where lack of equality, education and resources most detain them from engaging economically. It is crucial to understand what motivates these entrepreneurs, more specifically women entrepreneurs, since they are so important for the development. Few studies have been done about women entrepreneurs’ motivation compared to those done about men and even more scarce are the studies done in developing countries.This study is conducted through interviews and a survey among women entrepreneurs within the PFME. The PFME is a program within the private organisation CCIT that aims to strengthen women entrepreneurs in Honduras through support and education.Push-factors are those motivation factors that come out of necessity and pull-factors are those that come out of opportunity. This study shows that the push-factors are more common among these Honduran women than among women in studies from other countries. Economic reasons and independence are among the highest ranked motivations. Further research need to be done in order to understand what affects these motivation factors on a country level and why there are differences between the motivation of women entrepreneurs in developed countries and developing countries.

L'objectif de cette thèse est de modéliser les changements en chaîne historiques dans les théories phonologiques modernes. Martinet (1952, 1955, 1970) distingue deux principales catégories de changements en chaîne: les chaînes de propulsion et les chaînes de traction. Les chaînes de propulsion seront traitées dans la première partie de cette thèse (chapitres 2 et 3). Afin de modéliser les chaînes de propulsion, un modèle existant est utilisé: La théorie de préservation du contraste de Łubowicz (2003, 2012). Concernant la modélisation des chaînes de traction, qui sera principalement traitée dans la seconde partie de le thèse (chapitres 4 et 5), une nouvelle théorie sera proposée, basée sur les travaux phonétiques de De Boer (2001). Cette proposition est basée sur la notion des domaines piliers. Le chapitre 1 s'ouvre sur l'observation que ni les théories dérivationnelles orientées vers l'input – type SPE – ni les théories orientées vers l'output, comme la théorie de l'optimalité de Prince & Smolensky (TO) sont en mesure de formaliser les changements en chaîne. Dans les théories dérivationnelles, il est possible d'obtenir une bonne description des changements en chaîne. Cependant, afin de faire cela, nous devons briser les liens unissant les différentes étapes des changements en chaîne. Par conséquent, nous perdons l'interdépendance systémique entre les stades, ce qui est au cœur des changements en chaîne. Concernant la théorie de l'optimalité, sa structure stricte sur deux niveaux se révèle problématique dans le cas des changements en chaîne. Dans un changement en chaîne schématique comme /a/ → [e] > /e/ → [i], il est impossible pour la TO, dans la même analyse, de faire en sorte que [e] soit un candidat optimal et /e/ un candidat bloqué. Dans le chapitre 2, nous analysons et comparons plusieurs amendements à la théorie de l'optimalité proposés pour rendre compte des changements en chaîne. Beaucoup d'entre eux ne sont pas satisfaisants dans le cas des changements en chaîne car ils ne parviennent pas à modéliser la force systémique des changements en chaîne. La seule théorie qui semble accomplir cet objectif est la théorie de préservation du contraste (CPT) de Łubowicz. Cette théorie est basée sur les notions de contraste, préservation du contraste et elle évalue des scénarios au lieu de candidats individuels. La préservation du contraste est accomplie à travers la transformation du contraste. La notion de transformation du contraste signifie que les niveaux de contraste du système pré-changement sont préservés dans le système post-changement mais leur nature change. Une observation sur la CPT est que Łubowicz l'avait originellement conçue pour les changements en chaîne synchroniques. Dans le chapitre 2, nous démontrons que la CPT est en mesure de modéliser la force systémique qui donne aux changements en chaîne diachroniques leur cohérence. Ainsi, dans le chapitre 3, nous décidons de tester la validité de la CPT sur de véritables changements en chaîne historiques. Nous avançons deux études de cas sur deux changements en chaîne. Le premier, bien connu, est le changement en chaîne vocalique du Grand Changement Vocalique Anglais (English Great Vowel Shift). L'autre changement en chaîne est la Seconde Mutation Consonantique allemande (High German Consonant Shift). Nous démontrons que la CPT est en mesure de rendre compte de ces deux changements en chaîne. Au terme du chapitre 3, la CPT est testée sur une autre catégorie de changements en chaîne : les changements en chaîne observés dans l'acquisition de la langue maternelle. Le changement en chaîne étudié est s → θ → f. Ce changement en chaîne est différent des deux autres car il n'y a pas de nouveau niveau de contraste créé. Le dernier stade du changement en chaîne se conclut par une fusion. Encore une fois, la CPT peut rendre compte de ce changement en chaîne de manière satisfaisante. / The aim of this thesis is to formalise historical chain shifts within modern phonological theories. Martinet (1952, 1955, 1970) distinguishes two main categories of chain shifts: push chains and pull chains. Push chains will be dealt with in the first main part of this thesis (chapters 2 and 3). For modelling of push chains, an existing model is used: Łubowicz's (2003, 2012) Contrast Preservation Theory. For modelling pull chains, which will be the focus of the second part of this thesis (chapters 4 and 5), a new theory will be proposed, based on the phonetic work by De Boer (2001). This proposition is based on the notion of the pillar domains (domaines piliers). Chapter 1 starts with the observation that neither the derivational, SPE-like, theories or output driven theories like Prince's & Smolensky's Optimality Theory (OT) are able to formalise chain shifts properly. Within the derivational theories, it is possible to get a correct description of a chain shift. However, in order to do that, we have to break the links between the different stages of the chain shift. Therefore, one loses the systemic interdependence of the different stages, which is the essence of the chain shift. As regards to Optimality Theory, it is the two-level structure of the theory which proves problematic for chain shifts. In a theoretical chain shift such as /a/ → [e] > /e/ → [i], it is impossible for OT to make, in the same analysis, [e] an optimal candidate and /e/ a non-optimal one. In chapter 2, we analyse and compare several output-driven propositions that have been made to account for chain shifts. Many of them are not satisfactory because they do not manage to model the systemic motivation of chain shifts. The only theory that seems able to complete this objective is Łubowicz's Contrast Preservation Theory (CPT). This theory is based on the notions of contrast, contrast preservation and it evaluates scenarios rather than individual candidates. Contrast preservation is achieved through contrast transformation. The term contrast transformation indicates that the contrast levels of the input system are preserved but that their nature is different in the output system. One observation about CPT is that Łubowicz designed it for synchronic chain shifts. In chapter 2, we prove that CPT is able to model the perceptible coherence in diachronic chain shifts. In chapter 3, thus we decide to test the validity of CPT on actual historical chain shifts. It is tested on two cases. One is the well-known vocalic chain shift the Great Vowel Shift in English. The other one is the Second German Sound Shift (or High German Consonant Shift). We demonstrate that CPT is able to account for both of these chain shifts. At the end of chapter 3, CPT is tested on another type of chain shifts, i.e. chain shifts in first-language acquisition. The studied chain shift is s → θ → f. This chain shift is different from the other two because there is no new contrast level created. The last stage of this chain shift ends with a merger . Once again, CPT can account for this chain shift in a coherent way.