The thesis describes an optimal selective harmonic elimination strategy suitable for singlephase AC-DC converter-fed traction drives. The objective is to eliminate low-order supply current harmonics, including those injected into the supply due to load-side current ripple. Other advantages that the switching strategy has to offer over phase-control include improved supply power factor, reduced VA consumption for a given demand speed and load, reduced torque and speed ripple and smaller armature circuit smoothing inductance. The effect of field current boost on the dynamic response of the drive is also described. It is shown that field boost helps to reduce the speed rise-time by increasing the electromagnetic torque available during acceleration periods. Closed-loop control of a 4-quadrant DC drive is described and a comparison made between the performance of PID-control and pseudo-derivative feedback control. It is shown that pseudo-derivative feedback control has several advantages to offer, amongst which are ease of tuning of the controller gains and a superior performance following load torque disturbances. A laboratory size drive system was designed and built, and used to validate simulation predictions for both the switching strategy and pseudo-derivative feedback control. A microcontroller based hardware implementation of both the switching strategy and a digital pseudo-derivative feedback controller was adopted, with the switching strategy being implemented using an off-line approach of precalculating the switching angles and storing these in look-up tables. The armature voltage controller comprises a dual-converter employing IGBTs as switching devices. The use of IGBTs allows higher switching frequencies at significant power levels than would be possible if GTOs were used. It also simplifies the gate drive circuit design and minimises the need to use snubber circuits.

Thesis (MScIng)--University of Stellenbosch, 2007. / Bibliography. Also available via the Internet.

M.Tech. (Chiropractic) / Introduction: The most common chronic pain condition in modern society is neck pain (Jensen and Harms-Ringdahl, 2007). Chronic neck pain is a common complaint for many, from young patients to older patients with stressful work situations. According to Graham, Gross and Goldsmith (2006) neck disorders are common, disabling to various degrees and costly. Various structures in the cervical spine capable of transmitting pain include facet joints, intervertebral discs, nerve root dura, ligaments, and muscles (Manchikanti, Singh, Rivera and Pampati, 2002). According to Rochester (2009) chiropractors treat patients with chronic neck pain by using spinal manipulative therapy (SMT) to address a segmental joint hypomobility within the cervical spine as determined by joint motion palpation and endplay assessment. Traction is commonly used for the treatment of the spine by various physical therapists. It may be included as part of a chiropractic treatment protocol. According to Hooper (1996) traction involves the application of both manual and mechanical forces to draw adjacent body parts away from each other resulting in decompressed irritated tissues, realign parts, and relaxing tight structures. There are several types of cervical traction. The short and medium term improvement for chronic neck pain as well as the comparative effect of manual cervical traction versus mechanical cervical traction in combination with spinal manipulative therapy has not yet been established. Aim: This particular research study aimed to compare the short to medium term efficacy of manual cervical traction with mechanical cervical traction combined with spinal manipulative therapy with regards to decreased pain and improvement of cervical spine ranges of motion in patients with chronic neck pain. Methodology: Participants who met the inclusion and exclusion criteria were eligible to participate in this study. Advertisements were placed on notice boards around the campus of the University of Johannesburg and participants were recruited from the use of advertisements as well as word of mouth to partake in this research study. Thirty participants who suffered from chronic neck pain, volunteered for this comparative research study. This study was a randomized comparative study, where participants were randomly selected to be either in Group 1 or in Group 2. Group 1 received manual cervical traction whereas Group 2 received mechanical cervical traction. Both groups received spinal manipulative therapy to the restricted motion segments found in the cervical spine. Participants received seven trial sessions, with six treatments, over a period of two weeks. At the final 7th visit, one month after the sixth visit, no treatment was performed. Subjective and objective measurements were recorded at each visit. The subjective measurements of this particular study consisted of the Numerical Pain Rating Scale (NPRS) and the Vernon-Mior Neck Disability Index to evaluate the participants’ sensitivity to pain and disability. The objective measurements of this study included the Cervical Spine Range of Motion instrument to assess the participants’ cervical spine movement. Results: Both groups demonstrated a statistically significant improvement over time with regards to pain and disability, as well as increased range of motion to the cervical spine. The greatest percentage improvement with regards to range of motion was in lateral flexion and rotation of the cervical spine. Conclusion: According to the results of this study, it could be concluded that either manual cervical traction or mechanical cervical traction in combination with spinal manipulative therapy can be used effectively in the treatment of chronic neck pain as part of a chiropractic treatment protocol. Both groups proved to have a statistically significant improvement with regards to pain and disability as well as increased cervical spine range of motion...

"A dissertation submitted in partial compliance with the requirements for the Master's Diploma in Technology: Chiropractic, Technikon Natal, 1995. / Mechanical lower back pain is a common clinical entity which encompasses a spectrum of disorders. studies show that spinal manipulative therapy is of value in the treatment of mechanical lower back pain, while some chiropractors are of the opinion that McManis traction offers an effective adjunct to spinal manipulative therapy in the treatment of such conditions / M

For an Electrical Vehicle, the power is delivered from the battery pack to the electric motor through the use of power converter. Many research projects have been conducted in improving the efficiency of traction inverters. Inverter topologies are categorized based on the number of voltage levels of the inverter output phase voltage. The conventional 2-level Voltage Source Inverter (VSI) is commonly used as a traction inverter due to its simple structure. Due to the recent trend in utilizing higher DClink voltage in traction motor drives to achieve a higher power rating, multi-level inverters are gaining attention to replace the conventional VSI in EV powertrain. Multi-level voltage source inverters (MLVSI) have been widely adopted in high-power converters and medium-voltage drives. There are four major categories of MLVSI: the Flying Capacitor (FC), Neutral Point Clamped (NPC), Cascaded and Hybrid. The power rating of the MLVSI increases with the increase of inverter levels, but the size, number of switching devices, cost and control difficulty also increases. Due to the above reasons, 3-level NPC can be a good solution for traction inverters. Due to the structure and control limitation, Diode Clamp NPC suffers from uneven loss distribution and neutral point voltage balancing issues. This issue can be resolved with Active Clamped NPC (ANPC). In this thesis, the design, simulation, prototyping and testing of a 70kw 3-level ANPC traction is introduced. / Thesis / Master of Science (MSc)

Dissertation in partial compliance with requirements for the Masters Degree in Technology: Chiropractic, Durban University of Technology, 2010. / The aim of this study was establish if Leander versus Static traction was useful for the treatment of facet syndrome, a common type of mechanical lower back pain seen by chiropractors. Two groups of fifteen participants were chosen on the basis of the inclusion and exclusion criteria. The first objective was to determine if Static linear traction was effective for the treatment of lumbar facet syndrome in terms of subjective and objective findings. The second objective was to determine if Leander traction was effective for the treatment of lumbar facet syndrome in terms of subjective and objective clinical findings. Lastly the third objective was to compare the subjective and objective clinical findings for both groups. Design: A randomised, two group parallel controlled clinical trial was carried out between the two sample groups. Participants had to have had chronic lower back pain (> 3months). Thirty symptomatic volunteer participants between 25 and 55 were randomly divided into two equal groups – group A (Leander traction) received 5 treatments over a 2 week period. Similarly, group B (Static linear traction) also received 5 treatments over a 2 week period. Algometer readings, Numerical Pain Rating Scale (NRS101), Pain Severity Scale (PSS) and Oswestery Disabilty Index (ODI) were used as v assessment tools. Subjective and objective clinical findings were taken on the first and second visits (i.e. 48 hours) prior to treatment and immediately after treatment. Another set of subjective and objective readings were taken one week after the fifth treatment in order to gauge the long term effects of both treatments. No treatment was given on the sixth visit. Pressure tolerance measurements using an algometer were taken at the end ranges of motion in Kemp’s test and spinal extension. Outcome measures: SPSS version 15 (SPSS Inc., Chicago, Illinois, USA) was used for statistical analysis of data. A p value of <0.05 was considered as statistically significant. The two groups were compared at baseline in terms of demographics variables and location using Pearson’s chi square tests and ttests as appropriate. Intra-group comparisons were made between all time points. A significant time effect indicated successful treatment intervention. Inter-group comparisons were achieved using repeated measures ANOVA tests for each outcome measured separately. A significant time group interaction effect indicated a significant treatment effect. Profile plots were used to assess the trend and direction of the treatment effect. Results: The results of the study showed that Leander traction and Static linear traction were both effective for treating chronic lumbar facet syndrome and no statistically significant difference was found between subjective and objective clinical findings between the two groups.

Ce travail nous a permis de proposer un cadre pour sonder la morphogenèse d'une micro-colonie bidimensionnelle. Plus particulièrement, nous avons exploré la manière dont les effets individuels de croissance et d'adhésion se combinaient au cours de la croissance de la micro-colonie. Nous avons montré (i) que l'adhésion de cellules isolées est asymétrique du fait d'un vieux pôle plus ancré et (ii) que l'allongement des bactéries peut induire des forces de poussée à l'intérieur des colonies. Dans la mesure où ces deux effets, combinés à l'échelle d'une micro-colonie, sont susceptibles de générer des contraintes mécaniques, nous avons développé une technique pour mesurer les forces d'adhésion résultantes à l'aide de substrats déformables. Nous avons ainsi démontré que des adhésions focales sont créées et rompues dynamiquement, avec un biais au vieux pôle des cellules. Nous avons aussi examiné le rôle de l'adhésion sur la forme des colonies. Nous avons montré que l'adhésion polaire était responsable de la transition d'un régime de croissance linéaire à un régime bidimensionnel qui est observée après la première division. Pour des colonies de taille plus importante, le niveau d'adhésion était aussi corrélé avec la forme globale des colonies. Enfin, l'adhésion est aussi impliquée dans la transition d'une colonie bidimensionnelle à une colonie tridimensionnelle. L'ensemble de ces résultats suggère que l'expression des adhésines ainsi que leur localisation à la surface des cellules pourraient permettre aux bactéries de moduler activement la forme du groupe dans lequel elles vivent. / In this work, we propose a framework to understand the morphogenesis of two-dimensional microcolonies. In particular, we have explored how growth and adhesion of individual cells compete during microcolony extension. We have shown (i) that isolated cells display an asymmetry in their adhesion, which is higher at the old pole, (ii) that bacterial elongation can result in pushing forces inside the colony. Since the combination of these two effects is expected to produce mechanical stress at the scale of the microcolony, we have developed a method to measure the resulting adhesion forces using deformable substrates. We have demonstrated that focal adhesions are dynamically established and ruptured, with a bias towards the old poles. We have also probed the role of adhesion in the shape of the colony. We have shown that polar adhesion drives the transition from a linear to a two-dimensional growth after the first division. At larger colony sizes, the level of adhesion continues to correlate with the global shape of the colony. Finally, adhesion is involved in the transition from a two-dimensional to a three-dimensional colony. Taken together, our results suggest that the expression of adhesins and their location at the surface of the cells could be levers by which bacteria actively modulate the shape of the group in which they reside.

La capacité des cellules à sentir les propriétés physiques de leur environnement est un facteur déterminant de l'homéostasie tissulaire. Ainsi, la rigidité de la matrice extracellulaire (forces exogènes) et les tensions du cytosquelette (forces endogènes) coopèrent de manière fonctionnelle modulant les transformations phénotypiques. Les cellules perçoivent et transmettent des forces en développant des structures d'adhérences appelées adhésions focales. Ces adhésions sont composées de protéines transmembranaires, les intégrines, qui font le lien entre le cytosquelette et la matrice extracellulaire.La partie centrale de mon projet de thèse aborde la question du couplage des intégrines b1 et b3 dans la mécanotransduction. Les données actuelles plaident fortement en faveur d'une relation bidirectionnelle entre l'adhésion intégrine-dépendante et les forces mécaniques générées dans ce processus. Les approches génétiques classiques ont souligné le rôle majeur des intégrines b1 et b3 dans mécanosensibilité cellulaire, sans préciser leur contribution relative. Par exemple, la manière dont la modulation de l'expression de l'intégrine b3 affecte la génération des forces de traction cellulaires et la distribution des adhésions intégrines-dépendantes reste à être explorées. Dans ce travail de thèse nous avons montré que les intégrines b1 ont un rôle essentiel dans la génération de forces cellulaires, que les intégrines b1 sont régulées négativement par les intégrines b3 en affectant la distribution spatiale des intégrines b1 à travers leur capacité à lier à la fois la taline et la kindline. Et enfin, nous avons montré que les intégrines b3 régulent temporellement l'activité contractile de la cellule.J'ai également participé à deux autres études dans le cadre de collaborations avec le Pr. Holmgren et le Dr. Debili, au cours desquelles j'ai utilisé la microscopie à traction de forces comme un outil diagnostique afin d'observer l'effet des forces contractiles dans la formation de la lumen aortique et de la formation des plaquettes sanguines. J'ai ainsi pu confirmer que la protéine amotL2, reliant les fibres contractiles aux VE-cadhérines, est impliquée dans la force intercellulaire nécessaire à la formation de la lumen aortique. Et lors d'une deuxième collaboration, j'ai pu montrer que la contractilité des mégacaryocytes, via leur système actomyosine, est nécessaire pour la formation des proplaquettes. / Cell ability to sense mechanical properties of their microenvironment is crucial for tissue homeostasis which means their capacity to maintain mechanical integrity as they are submitted to external forces.Integrins have been highlighted as mechanotransducers able to form micro-scale structures called focal adhesion sites which mechanically link cells to the extracellular matrix by recruiting various adaptors. Both b1 and b3 integrins have been identified as the principal actors of tensional homeostasis. However as the resulting mechanotransduction processes are intrinsically dynamic, the respective and cooperative roles b1 and b3 integrins need to be addressed over time and space.In the present work, coupling time-resolved traction force microscopy and genetics approaches, we investigated the respective role of b1 and b3 integrins in active force generation at the single cell level. Our findings show that b1 integrins has an essential role in generation of cellular traction forces, b1 integrin-generated force is negatively regulated by b3 integrins which impacts the redistribution of b1 integrin containing adhesion through its ability to bind to talin and kindlin, b3 integrin supports min-scale temporal regulation of cellular contractile activity generated by b1 integrin. Finally, cell mechanical equilibrium relies on the ability of cells to maintain a fixed contractile moment.I also participated in two others studies in the framework of collaborations in which I used the traction force microscopy as a diagnostic tool to observe the effect of contractile forces in the formation of the aortic lumen and the formation of proplatelets. I was able to confirm that the protein amotL2 connecting the contractile fibers to VE-cadherin, is involved in intercellular forces necessary for the formation of the aortic lumen. And in a second collaboration, where I found by using traction force microscopy that the contractility of megakaryocytes via its actomyosin system, is necessary for the formation proplatelets.

Les lésions traumatiques de l’intestin sont responsables d’une part importante de la morbidité et de la mortalité consécutives aux lésions traumatiques abdominales. Elles sont pourtant mal connues. Les mécanismes à l’origine de ces blessures sont mal compris alors qu’un rôle paradoxalement négatif de l’usage de la ceinture de sécurité automobile est suspecté. En pratique clinique, le diagnostic précoce reste difficile, alors qu’une relation directe entre le délai diagnostic et le pronostic a été établi. Les règles de prise en charge thérapeutique ne sont pas consensuelles. Concernant la recherche, les quelques données de la littérature sur le comportement mécanique de l’intestin n’ont été obtenues qu’en condition quasi-statique ne reflétant pas les conditions d’un traumatisme. Le présent travail fait le lien entre données cliniques et travaux de recherche. Il apporte des connaissances pratiques sur un certain nombre de questions: quelles sont les situations à risque de chirurgie ? Comment se crée une lésion traumatique intestinale par décélération? Quelles sont les propriétés mécaniques de l’intestin qui dépendent de la cinétique du traumatisme ? Quelles sont les données anthropométriques et issues de l’imagerie médicale qui expliquent la variabilité de l’anatomie de l’intestin et de son mésentère ? Ces travaux serviront de base pour l’élaboration de modèles numériques d’hommes virtuels personnalisés et bio-fidèles utilisables dans le cadre de la traumatologie virtuelle. Ces outils de simulation numérique permettront de valider nos hypothèses sur le processus traumatique et participeront à l’amélioration des moyens de prévention de ces lésions traumatiques. / Traumatic injuries of the intestine are responsible for a significant proportion of the morbidity and mortality in blunt abdominal trauma. Nevertheless they are known very badly. The mechanisms involved are poorly understood despite the fact that a negative effect in the use of car seat belts is suspected. In clinical everyday practice, early diagnosis is often difficult, whereas a direct relationship between diagnosis delay and prognosis has been established. No consensus from academic society is available to help the therapeutic management. Regarding biomechanical research, the few data on the mechanical behavior of the intestine were obtained only in quasi-static condition and so does not reflect the conditions of trauma. The present work creates the link between clinical and research work. It provides practical knowledge on a number of questions: what situations are at risk of surgery? How intestinal injury occurs during traumatic deceleration? What are the mechanical properties of the intestine that depend on the velocity of trauma? What are the anthropometric data from medical imaging that explain the variability of the intestinal and mesenteric anatomy? This work constitutes the basis for the further development of numerical bio-faithful models of humans that could be used in virtual trauma applications. These numerical simulation tools will validate our assumptions about the traumatic process and will participate in the improvement of prevention means.

Les cellules épithéliales forment des tissus cohésifs, sous forme de monocouches que l'on retrouve dans les poumons, les reins ou la peau. Travaillant à partir d'expériences in vitro, nous avons caractérisé le comportement mécanique de monocouches cellulaires. Nous avons étudié la fermeture de blessures circulaires sur un substrat non adhésif. En comparant différents modèles, nous avons montré comment la fermeture est possible grâce à un cable contractile d'acto-myosine et aux fluctuations de la tension du tissu. La Microscopie des Forces de Traction (TFM) permet de mesurer les forces que les cellules exercent sur leur substrat. A partir de cette mesure et en utilisant l'équilibre des forces, nous avons développé une méthode qui résout ce problème sous-déterminé par inversion bayésienne et permet d'obtenir le champ des contraintes internes au tissu. En appliquant cette méthode sur des images (BISM: Microscopie des contraintes par inversion bayésienne) et en l'adaptant à l'aide d'un filtre de Kalman sur des films (KISM: Microscopie des contraintes par inversion de Kalman), nous avons inféré le tenseur des contraintes de monocouches cellulaires sans faire aucune hypothèse sur la rhéologie du tissu. Enfin, nous avons estimé les contraintes directement depuis les déplacements du substrat, sans passer par les forces de tractions et donc en réduisant le nombre d'inversions de matrice (BISMu: Microscopie des contraintes par inversion bayésienne à partir des déplacements du substrat). / Epithelial cells are known to form cohesive monolayers, a form of tissue organization encountered in the lung, the kidney or the skin. From in vitro experiments, we have characterized the mechanical properties of cell monolayers. We have studied the closure of circular wounds over a nonadhesive substrate. Comparing different models, we have shown how closure is possible thanks to a contractile acto-myosin cable and to fluctuations of the tissue tension. Traction Force Microscopy (TFM) allows to measure the forces that cells exert on their substrate. Starting from this measurement and using the force balance equations, we have solved this underdetermined problem by Bayesian inversion and obtained the internal stress field of the tissue. Applying this method on single images (BISM: Bayesian Inversion Stress Microscopy), and adapting it with a Kalman filter for movies (KISM: Kalman Inversion Stress Microscopy) we have inferred the stress tensor of cell monolayers, without making any hypothesis on the tissue rheology. Finally, we have estimated the stresses directly from the substrate displacements, without computing the traction forces and thus reducing the number of matrix inversions (BISMu: Bayesian Inversion Stress Microscopy from substrate displacements).