Bibliography: pages 193-205. / In Part I theoretical aspects of hydrodynamic forces on immersed solids are considered. Part II contains a chronological review of research projects, laboratory as well as ocean experiments, which have been carried out since 1950. In Part III the recommended procedures, which emerge from Part. II, are applied to calculate wave forces acting on the proposed Green Point outfall sewer which is to serve the central city area of Cape Town. The results are discussed and compared. Part IV outlines the conclusions of this study and offers recommendations for future research in this field.

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This thesis examines the role of autogenic and allogenic forces in determining the timing and development of blanket peat initiation and how the occurrence and growth of blanket peat subsequently constrains human activities. A number of factors involved in the formation of blanket peat have been defined in the literature, in particular the roles of climate change, soil processes and anthropogenic effects, tested in this thesis from a typical peat-covered upland in south west Scotland. Tests are developed from a multi-proxy approach and by comparing peat-stratigraphic and palaeoecological records from a series of nine 14C dated peat profiles from a single hillside. A detailed examination of the sequence and timing of blanket peat initiation in the Holocene Epoch is presented from a case study from the head of the Glen App valley, Lagafater, south west Scotland. The evidence was taken from a total of nine peat transects at 215m OD, 300m OD and 400m OD where agricultural, hydrological and micro-climatic effects are expected to have differed and had different impacts on soils and vegetation. Samples were retrieved from the top, middle and bottom of a gently undulating slope at each altitude. This has allowed a localised picture of peat initiation to be obtained from each locality and with changes in altitude, allowed for an analysis of the factors responsible up and down slope and the identification of synchronous autogenic forces. A number of analytical techniques have been used. Pollen analysis was undertaken as the principal method of vegetation reconstruction at all sites, particularly through the initiation horizon. Variations in mire-surface wetness, determined through dry bulk density and humification analysis, were also employed to generate a record of probable changes in effective precipitation and the effect these may have had on the accumulation rate of the blanket peat. In order to attempt to answer the question of when blanket peat was initiated and to establish the synchroneity of changes, twenty nine AMS 14C dates were obtained. The evidence suggests that blanket peat developed during the Mesolithic period, through to the early Bronze Age. It substantiates an anthropogenic forcing factor for palaeohydrological changes, with early landscape management and cereal cultivation accelerating the process of blanket peat initiation. With progressive changes in precipitation interacting with factors such as weathering of bedrock and vegetation cover, the local landscape at Lagafater was covered by blanket peat by the early Bronze Age. The radiocarbon chronology obtained from the multi-proxy records allowed the synthesis of these data sets and the definition of Holocene vegetation change, climate change and the history of human impact throughout the early prehistoric era across this landscape.

The majority of offshore wind farms utilize monopile substructures. As these wind farms are typically located in water depths less than 30 meters, the effect of breaking waves on these structures is of great concern to design engineers. This research investigation examines many of the practical considerations and alternative ways of estimating breaking wave forces. A survey of existing European wind farms is used to establish a realistic range of basic design parameters. Based upon this information a parametric study was pursued and a series of realistic design scenarios were evaluated. Comparisons include the sensitivity to the wave force model as well as to analytical and numerical wave theories used to evaluate the wave kinematics. In addition, the effect of different kinematics stretching techniques for linear waves is addressed. Establishing whether the bathymetry will induce spilling or plunging wave breaking is critical. Spilling wave breaking can be addressed using existing wave and wave force theories; however for plunging wave breaking an additional impact force must be introduced. Dimensionless design curves are used to display pertinent trends across the full range of design cases considered. This research study provides insight into the evaluation of the maximum breaking wave forces and overturning moment for both spilling and plunging breaking waves as a function of bottom slope.

One objective of this study was to explore the intramolecular [2+2] cycloadditions of phenoxyketenes to carbonyl groups with isoflavones and benzofurans as target compounds. The other objective was to investigate the eyeloaddition reactions of rarely studied aminoketenes. The conversion of 2-(carboxyalkoxy)benzils to the corresponding phenoxyketenes leads to an intramolecular [2+2] cycloaddition to ultimately yield isoflavones and/or 3-aroylbenzofurans. The product distributions are dependent upon the substitution pattern in the original benzil acids. The initial cycloaddition products, β-lactones, are isolated in some instances while some β-lactones spontaneously underwent decarboxylation and could not be isolated. The ketene intermediate was demonstrated in the intramolecular reaction of benzil acids or ketoacids with sodium acetate and acetic anhydride. It is suggested that sodium acetate and acetic anhydride could serve as a source for the generation of ketenes directly from certain organic acids. The treatment of ketoacids with acetic anhydride and sodium acetate provides a simpler procedure to prepare benzofurans than going through the acid chloride with subsequent triethylamine dehydrochlorination to give the ketenes. N-Ary1-N-alkylaminoketenes were prepared for the first time from the corresponding glycine derivatives by using p-toluenesulfonyl chloride and triethylamine. These aminoketenes underwent in situ cycloadditions with cyclopentadiene, cycloheptene and cyclooctenes to yield only the endo -bicyclobutanones. The cycloheptene and cyclooctene cycloaddition products underwent dehydrogenation under the reaction conditions to yield bicycloenamines. A mechanism is proposed for this dehydrogenation involving a radical cation of the arylalkylamine. (N-Phenyl-N-methyl) aminomethylketene was also prepared and found to undergo an intramolecular Friedel-Crafts type acylation to yield an indole derivative when prepared by the acetic anhydride, sodium acetate method. The in situ cycloaddition of N-aryl-N-alkyl aminoketenes with various imines was found to form predominately cis-3-amino-2-azetidinones. A mechanism involving a dipolar intermediate is provided whereby the structure of the intermediate is determined by both electronic and steric effects. The stereochemistry of the resulting β-lactams is dependent upon the structure of the dipolar intermediate.

Les appareils orthodontiques appliquent une force prolongée sur les dents, conduisant au mouvement dentaire provoqué, à l'aide d'arcs insérés à l'intérieur d'attaches. Le déplacement dentaire résulte de la biomécanique mais également des réponses biologiques des tissus de soutien. Notre problématique porte sur les efforts mécaniques présents à l'intérieur des attaches orthodontiques, lors de l'insertion d'un fil à mémoire de forme. Nous souhaitons quantifier les forces et moments à l'échelle d'une arcade dentaire en trois dimensions. Notre travail présente un protocole alliant expérimentation et modélisation numérique. Cette méthodologie innovante permet de mettre en évidence les forces et moments appliqués lors de la première phase d'un traitement orthodontique à l'insertion d'un arc nickel-titane de diamètre 0,356 mm (0 .014 inch) dans des gorges de diamètre 0,457x0,635 mm (0.018x0.025) sur une arcade maxillaire, obtenue après segmentation d'une imagerie tridimensionnelle d'un patient. Cette première étape ouvre les portes vers une individualisation des traitements orthodontiques par l'application des efforts mécaniques nécessaires sans être délétères. / Prolonged forces are applied on the teeth by orthodontie deviees, using arch wires inserted into brackets, leading to the orthodontie teeth movements. This displacement is the result of biomechanics but also the biological responses of the surrounding periodontal tissues. Our aim is to quantify the forces and moments applied on the orthodontie brackets, during the insertion of a shape memory alloy, at the scale of a three-dimensional dental arch. Our work presents a protocol combining experimentation and numerical modelling. This innovative methodology enables measuring the forces and moments applied during the first stage of an orthodontie treatment, when a 0.014-inch nickel-titanium arch wire is inserted into a maxillary arch. This first step will help in the definition of individualized treatments, applying the necessarymechanical forces without being iatrogenic.

Dans les structures confinées, comme les silices mésoporeuses, la mobilité et l'interaction des cations avec les surfaces sont des phénomènes clés. Ils guident les propriétés d'adsorption dont découlent de nombreuses applications, en particulier pour l’extraction et la séparation. Ce travail de thèse en modélisation propose de s'intéresser aux propriétés d'interface, d'équilibre et de transport qui pilotent l'échange ou l'adsorption ionique. Il s’agit de décrire la physico-chimie du processus d’adsorption de cations alcalins à la surface de silices chargée par une approche multiéchelle ayant une base moléculaire. Pour cela une étude de la série des alcalins (Li+, Na+, K+ et Cs+) a été menée. Le cadre théorique est la théorie de Mc Millan Mayer. Celle-ci, fondamentale pour les solutions libres s’est révélée également être une méthode de choix pour les milieux confinés. Le potentiel de force moyenne de McMillan Mayer entre les ions et des sites de surface a pu être calculé par la méthode d'Umbrella Sampling associé à l’algorithme WHAM. Le phénomène qui s’est révélé le plus pertinent correspond à la présence de paires au contact (Contact Ion Pairs - CIP) entre les oxygènes de la surface et les cations, sans molécule d’eau qui les sépare. Ces CIP se traduisent dans les courbes de potentiel par un premier minimum d’intensité supérieure à l’agitation thermique. Pour les petits ions (lithium), ce complexe de surface est particulièrement stable, les constantes d’adsorption et les temps de résidence étant particulièrement élevés, ce qui rend délicat la simulation moléculaire directe de ces phénomènes. Il a été observé une inversion de sélectivité entre les sites silanolates et siloxanes. L'adsorption est différente pour un ion cosmotrope comme Li+ qui doit se déshydrater pour s'adsorber et un ion chaotrope comme Cs+ qui est moins lié au solvant. Les constantes d’adsorption de chaque site de même type ne sont pas toutes égales. L’étude des phénomènes électrocinétiques (électro-osmose et conductivité de surface) a également été menée en comparant les descriptions classiques (modèles de Poisson-Boltzmann, de Smoluchowski, et de Bikerman) aux résultats de dynamique moléculaire. Il est apparu que l'image traditionnelle en plusieurs couches des interfaces (couches de Helmholtz internes et externes, de Stern, de Gouy-Chapman, plan de cisaillement) devait être remplacée par un modèle beaucoup plus simple mais plus efficace. Du point de vue des ions, deux domaines apparaissent : les CIP, globalement fixés à la surface transmettant la force électrique au solide et pas au fluide, et les autres ions, globalement libres, transmettant la force électrique au fluide. Aucune viscosité ou constante diélectrique dépendant de la distance n’a été mise en évidence. Une diminution de la mobilité des ions à proximité de la surface a en revanche été observée. Ce phénomène peut être quantitativement compris comme un effet hydrodynamique du à la présence des surfaces qui gênent le flux en retour du solvant. Ce travail permet ainsi de mieux caractériser l'interface verre chargé-solution pour les applications en science de la séparation. Il a pu montrer comment les simulations moléculaires pouvaient non seulement prédire les paramètres des modèles macroscopiques (constantes d’adsorption, coefficients de transport, etc.) mais surtout modifier ceux-ci pour les rendre en accord avec la description moléculaire. Une telle stratégie pourra par la suite être mise en œuvre sur des systèmes plus complexes, comme des modèles de surfaces greffées. / In confined structures, such as mesoporous silica, the mobility of the cations and the surface/cations interactions are key phenomena. They drive adsorption properties, which control numerous applications, especially for extraction and separation. This modelling work describes equilibrium and transport interface properties that control ion exchange and ionic adsorption. The physical and chemical properties of adsorption processes of alkali cations at the surface of charged silica is studied thanks to a multiscale approach based on a molecular description. The systematic study of alkali serie (Li+, Na+, K+ and Cs+) has been studied to that goal. The theoretical framework is Mc Millan-Mayer theory. The latter, which is known to be of fundamental significance for bulk solutions is found to be also relevant for confined media. The mean force potential of Mc Millan-Mayer between ions and surface sites has been calculated by Umbrella Sampling associated to the WHAM algorithm. The most important phenomenon we identified corresponds to the existence of Contact Ion Pairs (CIP) between the surface oxygen and the cations, without separating solvent molecules. The CIP correspond to the first minima in the potential curves if the associated energy is more than the thermal agitation (kT). For small ions (lithium) this surface complex is especially stable, adsorption constant and residence time being particularly high so that the direct molecular simulations are very difficult. A selectivity inversion has been observed between silanolates and siloxanes. Adsorption is different for kosmotropic ions (as Li+) which has to be dehydrated to be adsorbed and chaotropic ions (as Cs+) for which the solvent bound is weaker. Adsorption constants for sites of the same nature are not equal. The study of the electrokinetic phenomena (electro-osmosis and surface conductivity) has also been performed by comparing the classical descriptions (Poisson-Boltzmann, Smoluchowski, and Bikerman models) to molecular simulations. The traditional picture of the interface with several layers (inner and outer Helmholtz, Stern and Gouy-Chapman layers, shear plane) is found to be replaced by a simpler but more efficient model. For the ions, two domains are obtained: (i) CIPs, firmly bound to the surface that transmit the electrical force to the solid (and not the fluid) (ii) other ions that are globally free that transmit the electric force to the fluid. No space dependent viscosity or dielectric constant have been obtained. On the other hand, a decrease of ion mobility in the vicinity of the surface has been observed. This phenomenon can be quantitatively understood as a hydrodynamic effect that comes from the solid surface, which hinders the backflow of the solvent. This work allows a better characterization of charged glass-solution interfaces for separation science. It shows how molecular simulations can not only predict the parameters of macroscopic models (adsorption constant, transport coefficients), but also modify the latters in order to make them in agreement with molecular descriptions. Such a strategy can be extended to more complex systems, such as models of grafted surfaces.

Thesis (M.A. (Human Resource Management))--North-West University, Potchefstroom Campus, 2007.

Dissertation--Universität Potsdam, 2003. / Bibliogr. p. 573-615.