Pseudomonas aeruginosa is one of the most studied biofilm-forming organisms and has emerged as a model organism in the study of surface- and biofilm-induced gene expression. The transition from a planktonic to a biofilm mode of growth results in diverse changes in gene expression, which causes the attaching cells to become phenotypically and metabolically distinct from their planktonic counterparts. In this study, a proteomic approach was used to study differences in protein profiles obtained from 18-h old P. aeruginosa PAO1 (DSM 1707) planktonic, surface influenced planktonic (SIP) and biofilm populations grown in batch in the absence or presence of a glass wool substratum. Glass wool as an attachment substratum not only supported growth of biofilms, but it also allowed for the separation of the biofilm biomass from the surrounding surface influenced planktonic (SIP) cells for further characterisation. Comparative analysis of the respective proteomes indicated striking differences in the protein patterns of planktonic, biofilm and SIP cells and several uniquely expressed proteins were seen on the 2-DE protein maps of the respective populations. Whereas a general down-regulation of protein expression was seen in the biofilm cells, in SIP cells, expression of the proteins was generally up-regulated. The results confirmed that the biofilm population differs from the planktonic population and indicated that the SIP population is not merely a mixture of planktonic and biofilm cells but rather a unique phenotype. Several differentially expressed protein spots were selected and identified using a combination of N-terminal protein sequencing and peptide mass fingerprinting. The proteins comprised mostly of outer membrane or membrane-associated proteins. Based on these analyses, a mutant P. aeruginosa strain, deficient in outer membrane protein OprG, was generated and its ability to form biofilms on a glass wool substratum was compared with that of the wild-type P. aeruginosa strain. The mutant strain was attachment-proficient but biofilm-deficient, suggesting that OprG plays a role in P. aeruginosa biofilm development under the culturing conditions used in this study. / Thesis (PhD (Microbiology))--University of Pretoria, 2007. / Microbiology and Plant Pathology / unrestricted

The Caribbean steelpan is a pitched percussion instrument that originated in Trinidad and Tobago during the Second World War. Despite several research initiatives to improve the making of this relatively new instrument, several areas remain unaddressed. This thesis presents new approaches to help improve the making of the instrument. These approaches are situated in the production, vibration and material aspect of the steelpan. A novel sheet forming technology termed Incremental Sheet Forming (ISF) is applied to the production of miniature steelpan dishes. The thickness distribution in the wall of the ISF dishes is compared to the wall thickness distribution in a traditionally formed steelpan dish and a wheeled dish. Unlike traditional forming and wheeling, ISF produces stretching in only a portion of the walls of the formed dishes. Multi-pass ISF is used to extend the stretched zone but this extension is minimal. A break even analysis is also applied to investigate the fiscal viability of ISF application to the production of miniature and full size steelpan dishes. The application of ISF to steelpan making is found to be commercially profitable but could be jeopardised by the tuning stage of the steelpan making process. A preliminary study on the effect of impact on tone stability is conducted on a pair of notes on a fullsize steelpan and detuning is found more likely to occur by repeated impact of the note at its centre. Mode confinement in test-pans is also investigated. ISF is used to produce miniature test-pans with test-notes that are geometrically identical to notes on full size pans. It is possible to confine modes by varying the curvature of the bowl surrounding the test-note. The number of localised modes in the test-note increases as the radius of curvature of the surrounding bowl increases. The natural frequency of the first confined mode in the test-notes is sensitive to material springback in ISF and the mechanism of confinement appears to be due to the change in geometry that occurs between the flat test-note region and the bowl wall. This control of mode confinement may find use in future efforts to completely or partially automate the steelpan making process. Material damping and mechanical properties in low-carbon steel used to produce steelpans are researched. Damping and mechanical properties are extracted from low-carbon steel that is subjected to identical stages to the steelpan production process. Material damping trends suggest that an annealing temperature between 300°C and 400°C would be appropriate for the heat treatment of steelpans. Air-cooled and water-quenched low-carbon specimens exhibit comparable damping trends. Hardness increases in cold formed low-carbon specimens is attributed to strain hardening and not strain ageing. Investigation of damping trends and mechanical properties in ultra low bake-hardenable and interstitial-free steels reveals that a wider range of low-carbon steels may be suitable for steelpan making.

Le formage incrémental consiste à utiliser un poinçon de forme simple dont le mouvement va progressivement mettre en forme une tôle. Il ouvre de nouvelles perspectives quant au potentiel des procédés de mise en forme des tôles métalliques. La mise en oeuvre du formage incrémental par des systèmes mécaniques ayant des capacités dynamiques accrues et des volumes accessibles importants tels que les robots manipulateurs sériels ou parallèles est un moyen efficace d’améliorer, d’une part la productivité mais aussi la complexité des pièces formées. L’objectif scientifique de ce travail est de contribuer au développement d’une approche globale du problème, en se plaçant à la fois à l’échelle « mésoscopique » du procédé et à l’échelle « macroscopique » du système de fabrication. C’est dans ce contexte qu’est proposée une approche couplée matériau/structure combinant d’une part l’analyse éléments finis du procédé et d’autre part un modèle élastique de la structure du robot.Tout d’abord, les efforts requis au niveau de l’outil pour former la pièce sont calculés sous l’hypothèse d’une structure de machine parfaitement rigide. Afin de minimiser l’erreur entre la prédiction et la mesure des efforts de formage, trois facteurs identifiés comme influents sur le niveau d’effort sont étudiés. Il est alors démontré, qu’à partir d’un choix de paramètres adapté, il est possible de s’affranchir de la mesure des efforts de formage, ce qui n’est actuellement pas le cas dans la littérature.Les efforts prédits sont ensuite définis comme une donnée d’entrée du modèle élastique de la structure robot afin de calculer les erreurs de poses du centre outil. Pour prendre en compte le comportement élastique de la structure, la modélisation des structures robotisées par des éléments de type poutre est retenue puis appliquée à un robot industriel Fanuc S420if. Elle permet de prédire ce comportement avec une précision maximale de ± 0,35 mm, quelque soit le chargement en bout d’outil supportable par le robot.Afin de valider l’approche, deux pièces sont formées par le robot : un cône tronqué et une pyramide vrillée. La géométrie de ces deux pièces permet de valider à la fois les hypothèses de la simulation ainsi que l’approche globale. Ces deux expérimentations entraînent une amélioration de 80 % de l’exactitude de pose du robot, rapprochant ainsi celui-ci des performances d’une machine à commande numérique à structure cartésienne.Finalement, dans la dernière partie, une boucle d’optimisation permet de prendre en compte, dès le calcul de la trajectoire, l’effet du retour élastique de la tôle avant le débridage de la pièce afin de minimiser l’écart entre le profil nominal et le profil formé. L’application de l’approche couplée à cette trajectoire se traduit par une précision géométrique de ± 0,15 mm du profil formé avant desserrage de la tôle, ouvrant ainsi des perspectives intéressantes quant à l’application de la méthodologie. / The incremental forming is an innovative process which consists in forming a sheet by the progressive movements of a punch. A solution to improve the productivity of the process and the complexity of the parts shapes is to use robots (serial or parallel). The scientific aim of this work is to define a global approach of the problem by studying the mesoscopic scale of the process and the macroscopic scale of the machine. In this context, a process/machine coupling approach which combines a Finite Element Analysis (FEA) of the process and an elastic modeling of the robot structure is presented.First, the punch forces necessary to form the part are computed assuming a machine structure perfectly stiff. To minimize the error between the predicted forming forces and the measured ones, the weight of three numerical and material parameters of the FEA is investigated. This study shows that an appropriate choice of parameters avoids the force measurement step, unlike the available approaches in the literature.Then, the predicted forces are defined as input data of the elastic model of the robot structure to compute the Tool Center Point (TCP) pose errors. To consider the behavior of the elastic structure, the modeling of robotized structures by beam elements is chosen and applied to an industrial robot Fanuc S420if. The identified elastic model permits to predict the TCP displacements induced by the elastic behavior of the robot structure over the workspace whatever the load applied on the tool. The prediction maximum error of ±0.35 mm remains compatible with the process requirements.To validate the approach, two parts are formed by the robot: a truncated cone and a twisted pyramid. The geometry of these two parts confirms the hypothesis of the simulation and the global approach. These two tests give very interesting results since an improvement of 80 % of the TCP poseaccuracy is identified.Finally, an optimization loop based on a parametric trajectory and on a FEA anticipates the springback effects before the unclamping of the sheet, and then minimizes the error between the nominal shape and the formed one. The application of the process/machine coupling approach for this trajectory leads to a geometric accuracy of the part before unclamping of ± 0.15 mm. These results open interesting perspectives for the methodology application.

L'objectif principal de cette étude consiste à réduire les temps de calcul des simulations de procédés de mise en forme continus sous le logiciel Forge3®. Ces procédés, tel que le laminage et le tréfilage, sont caractérisés par des pièces dont la longueur est très importante en comparaison des dimensions de la section ainsi que de la zone de contact. Une approche incrémentale générale implique des temps de calcul conséquents allant de quelques heures à plusieurs jours. En se concentrant sur le régime quasi permanant de ces procédés, une formulation stationnaire est développée pour accélérer leur simulation. Le domaine de calcul correspond initialement à une estimation de la forme de l'écoulement solution au voisinage des outils. Une étape de correction du domaine est ajoutée en plus du calcul stationnaire de l'écoulement. Comme les conditions aux limites sont modifiées, ces deux étapes sont répétées jusqu'à convergence.L'étude s'est concentrée principalement sur l'étape de correction du domaine correspondant à la résolution d'un problème de surface libre par la méthode des éléments finis. Le caractère purement convectif du problème ainsi que la prise en compte du contact nécessite l'utilisation de formulations faibles faisant apparaître un décalage amont (SUPG). Deux nouvelles formulations basées sur la méthode des moindres carrés sont développées avec succès (MC_supg et MC_lc). Pour appliquer la méthode à des géométries complexes, différentes méthodes de généralisations sont développées où un 2ème degré de liberté est ajouté aux nœuds de surface. La méthode la plus performante (CSL_dif) consiste à utiliser ce 2ème degré de liberté pour le calcul de surface libre uniquement sur les nœuds appartenant à une arête géométrique, pour les autres une régularisation du maillage dans la direction tangente y est effectuée. Des résultats excellents ont été observés sur un grand nombre de cas tests analytiques. Le contact est appliqué par une méthode de pénalisation aux nœuds. Afin de renforcer le couplage entre cette étape et celle du calcul de l'écoulement, un contact bilatéral glissant est attribué aux nœuds en compression alors que pour les autres nœuds un contact unilatéral est employé. Un algorithme spécifique est développé pour déterminer avec précision la zone de contact.Cette formulation itérative pour la recherche de l'état stationnaire a été appliquée avec succès sur un grand nombre de cas tests de mise en forme. Des accélérations comprises entre 10 et 60 ont été obtenues par rapport à Forge3®. / The aim of this study is to reduce the computational time for the simulation of continuous material forming processes with Forge3® software. These processes, like rolling and wire drawing, are characterized by an important length of the pieces in comparison to their sectional's dimensions and to the local contact area. A general and incremental approach requires important computational times ranging from a few hours to several days. By focusing on the quasi permanent regime of these processes, a stationary approach is developed to speed up their simulation. The computational domain consists of an initial guess of the steady flow near the tools. A domain correction stage is added after the computation of the steady flow. As boundary conditions are changed, these two stages are repeated until the convergence is reached.Most of the works is concentrated on the domain correction which is a free surface problem solved by the finite elements method. As it is a case of a pure convection problem where the treatment of contact is necessary, weak formulations have to show up an upwind shift (SUPG). Two new formulations based on the least squares method have been successfully developed (MC_supg, MC_lc). To take into account complex geometries, severals new methods have been developed by adding a second degree of freedom for surface nodes. The most efficient method (CSL_dif) uses this second degree of freedom for free surface computation only for nodes belonging to geometric edges, whereas the other nodes have a mesh regularization in tangent direction of the surface. Excellent results are obtained for many analytical test cases. A penalization method is used to apply contact equations on nodes. In order to enforce the coupling between this stage and the one for the computation of the flow, a bilateral sliding contact is assigned to the nodes in compression, whereas for the others a unilateral contact is used. A specific algorithm has been developed to efficiently compute the contact area.This iterative formulation for the search of the steady state is successfully used on a large number of material forming test cases. Important accelerations are gained compared to Forge3®, ranging from 10 to 60.

Flow forming is a fairly new technique used for the production of dimensionally accurate near net shaped hollow components. The process has many advantages such as cost effectiveness and eliminating further operations like welding, machining, etc. This study focuses on the characterization of flow formed components to understand the process. Flow formed components are composed of different reductions and characterization techniques are applied to reveal the resulting microstructural differences. Effect of number of passes on the material is also investigated. Metallographic analysis was conducted by optical microscope, electron micro probe analyser (EPMA) and the electron back scatter diffraction technique (EBSD) in a scanning electron microscope (SEM). Texture evolution of the samples was examined either by laboratory X-ray diffraction or EBSD technique. Furthermore, residual stresses were measured by neutron diffraction (at StrainAnalyzer for Large and Small Scale Engineering Applications (SALSA) and PulseOverlap Diffractometer (POLDI) instruments), laboratory X-ray diffraction and hole drilling. Stress relief heat treatments were carried out at 500°C for either 4 or 16 hours to mitigate residual stresses without losing much of the strength. The experiments conducted show that flow forming is a process resulting in heterogeneous microstructure with grains elongated along the deformation direction. Texture evolution is different from the typical rolling of steels with body centred cubic crystal structure. Any significant effect of the number of passes was not observed. Due to the nature of the process, residual stresses in the axial and hoop directions are critical. Therefore, stress distributions through thickness of the samples are plotted. It is observed that in the thick section, the stresses are higher. Heat treatments applied at 500°C for 4 or 16 hours are effective in diminishing the stresses.

In this experiment, fluorescent N- (1-pyrenyl) iodoacetamide modified the two reactive thiols, SH1 (Cys 707) and SH2 (Cys 697) on myosin to detect SH1-SH2 a -helix melting. The excimer forming property of pyrene is well suited to monitor the dynamics of the SH1 and SH2 helix melting, since the excimer should only form during the melted state. Decreased anisotropy of the excimer relative to the monomeric pyrene fluorescence is consistent with the disordering of the melted SH1-SH2 region in the atomic model. Furthermore, nucleotide analogs induced changes in the anisotropy of the excimer, suggesting that the nucleotide site modulates the flexibility of SH1-SH2 region.

A unique, previously undescribed Gram-negative bacterium was isolated from several soils in Texas and extensively characterized in this study. The cells measured 1-2 by 4-6 μm. The distinguishing characteristic of the bacterium is the extraordinary capsular material which surrounds the cells. The new isolates are aerobic, mesophilic, non motile and have the ability to utilize a variety of organic compounds as the sole source of carbon and energy. The organism grows optimally at 30° C and the optimal pH lies between 7.0-8.0. The isolates produce catalase but oxidase is not produced. They do not produce indole or hydrogen sulfide. The organism can hydrolyze gelatin and Tween 80 but not starch, esculin and casein. The major cellular fatty acid is anteiso 15:0. The guanine and cytosine content is 58-62 mole%. The organism's taxonomic position was further established by specific gene probes, 16S rRNA homology, DNA homology and "ribotyping." These data showed that it was most closely related to members of the genus Paenibacillus, although somewhat divergent from other species classified in this genus. After careful evaluation of the results obtained during this study, it is proposed that this unique bacterium be named Paenibacillus velasolus sp. nov.

Machine tool coolant concentration and pH data.

An array of Bacillus licheniformis strains were isolated from a commercial powdered milk process. Bacteriophages exhibiting activity against B. licheniformis were isolated from cattle manure and effluent samples destined for a lagoon at a dairy farm. After sequencing, 8 of the 10 phages were found to be novel and genetically differentiated. Transmission electron scanning microscopy (TSEM) was performed. All bacteriophages were of the family Herelleviridae with contractile tail sheaths ranging from 80µm to 150µm and, surprisingly, survived a common fluid milk processing treatment used to inactivate vegetative cells. The survival of the phage after high temperature short time pasteurization of 73℃ for 20 s shows that the use of bacteriophages in milk to control B. licheniformis could be applied as a potential quality control, retarding the germination of spores and reduction of final spore counts in products with long run times such as dairy powders.

The thesis presents a manufacturing technology proposition for a terminal pin made of copper according to ČSN 42 3001.1 located in combution engine distributor in a series of 320 000 pcs. Based on a literature study, 3 versions of operation sequence were proposed, 2 of them with concern for lowest number of operations possible and the third, chosen one, was designed so the strain and therefore mechanical properties were equal in whole volume of final part. Forming force and work were calculated, utilizing the Johnson-Cook material model. Overall calculated forming force was 64,5 kN and total work for one part 189 J. Subsequently technical drawings of die and punch for the second operation of forward extrusion of shaft were processed along with workspace assembly drawing for the Šmeral TPM 5 machine, which was chosen for the fabrication. Economic evaluation set the costs for one part manufactured 0,09 Eur and equilibrium point, after which the production generates profit, located at 170 000 pcs produced.