We present a geometric construction of almost Poisson brackets for nonholonomic mechanical systems whose configuration space is a Lie group G. We study the so-called LL and LR systems where the kinetic energy defines a left invariant metric on G and the constraints are invariant with respect to left (respectively right) translation on G.For LL systems, the equations on the momentum phase space, T*G, can be left translated onto g*, the dual space of the Lie algebra g. We show that the reduced equations on g* can be cast in Poisson form with respect to an almost Poisson bracket that is obtained by projecting the standard Lie-Poisson bracket onto the constraint space.For LR systems, we use ideas of semidirect product reduction to transfer the equations on T*G into the dual Lie algebra, s*, of a semidirect product. This provides a natural Lie algebraic setting for the equations of motion commonly found in the literature. We show that these equations can also be cast in Poisson form with respect to an almost Poisson bracket that is obtained by projecting the Lie-Poisson structure on s* onto a constraint submanifold.In both cases the constraint functions are Casimirs of the bracket and are satisfied automatically. Our construction is a natural generalization of the classical ideas of Lie-Poisson and semidirect product reduction to the nonholonomic case. It also sets a convenient stage for the study of Hamiltonization of certain nonholonomic systems.Our examples include the Suslov and the Veselova problems of constrained motion of a rigid body, and the Chaplygin sleigh.In addition we study the almost Poisson reduction of the Chaplygin sphere. We show that the bracket given byBorisov and Mamaev is obtained by reducing a nonstandard almost Poisson bracket that is obtained by projecting a non-canonical bivector onto the constraint submanifold using the Lagrange-D'Alembert principle.The examples that we treat show that it is possible to cast the reduced equations of motion of certain nonholonomic systems in Hamiltonian form (in the Poisson formulation) either by multiplication by a conformal factor, by the use of nonstandard brackets or simply by reduction methods.

Orientador: Ary dos Santos Pinto / Resumo: Neste estudo investigou-se in vivo a eficácia da técnica de colagem direta comparada a colagem indireta em relação ao número de falhas na colagem que ocorreram durante o tratamento ortodôntico. Foram selecionados cento e vinte pacientes com idades de 13 e 57 anos, de ambos gêneros tratados consecutivamente numa clínica privada nos anos de 2011 a 2017 com aparelho ortodôntico fixo metálico e divididos em dois grupos: grupo A, com 54 indivíduos no qual se realizou a colagem de bráquetes pela técnica direta e o grupo B com 66 indivíduos, no qual se realizou a colagem de bráquetes pela técnica indireta. A comparação estatística entre as duas técnicas de colagem de bráquetes foi baseada no número total de descolagens e no tempo para a primeira descolagem, tendo sido cada paciente observado por 25 meses. Utilizou-se, respectivamente, os testes de Qui-quadrado e de sobrevida de Kaplan-Meier, com a comparação entre as curvas realizada pelo teste de Log-rank. Foi empregado o modelo de regressão de Cox para avaliar a ação conjunta dos fatores de interesse sobre o tempo da primeira descolagem. Adotou-se sempre o nível de significância de 5% para a tomada de decisão. No período de avaliação de 25 meses após a colagem dos bráquetes nos arcos superior e inferior, ocorreu diferença significativa de 1,6% na porcentagem de quedas de bráquetes pela técnica de colagem indireta em relação à direta, porém, a baixa porcentagem destas quedas indicou a eficácia da técnica de colagem direta de 97,3% ... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: In this in vivo study it was investigated the effectiveness of the direct bonding technique compared to indirect one to evaluate the number of bond failures that occurred during orthodontic treatment. One hundred and twenty patients aged 13 to 57 years, of both genders consecutively treated in a private practice in the years 2011 to 2017 with fixed metallic orthodontic appliance were selected and divided into two groups: group A, with 54 individuals in which the brackets were bonded by the direct technique and group B with 66 individuals, in which the brackets were bonded by the indirect technique. The statistical comparison between the two techniques of bracket bonding were based on the total number of bond failures and the time to first bond failure, with each patient being observed for 25 months. The chi-square test was used to compare the survival rates of the brackets bonded with direct and indirect bonding. The log-rank test was used to compare the Kaplan-Meier survival curves of both bonding methods. The Cox regression model was used to evaluate the joint association of the factors of interest on the time to first bond failure. The level of significance of 5% was adopted for decision-making. In the evaluation period of 25 months after the bonding of the brackets in the upper and lower arches, there was a significant difference of 1.6% in the percentage of bracket failure in the indirect bonding technique in relation to the direct one. The low percentages of these failu... (Complete abstract click electronic access below) / Doutor

Magister Scientiae Dentium - MSc(Dent) / Background: A close marginal adaptation between the tooth and the bracket base is important since it provides the space for the adhesive. In order to withstand and resist the orthodontic forces exerted as well as everyday forces like mastication and oral hygiene practices, the adhesive material to the bracket must have sufficient sheer bond strength. This means that no deformations, cracks, or fractures should occur within the bracket material and adhesive (Keizer et al., 1976). Aim: The aim of this study was to determine the accuracy of the marginal adaptation of the bracket bases of seven different brands of orthodontic brackets to the tooth surface of a right upper first premolar (ie. Abzil, Forestadent, GAC, Gemini, IMD, Ormco and Victory LP). Method: This research was an in vitro, descriptive comparison study. Fifteen caries and crack free intact human first premolars were used. The teeth were obtained from patients requiring extractions for orthodontic purposes and collected from Tygerberg Oral Health Centre. A convenience sample method was used, where whenever an upper caries free premolar was extracted, the parent was asked if the tooth could be used for this study and consent was obtained. The crowns of the 15 teeth were cleaned and polished with pumice and rubber cups for 10 seconds (as the clinician would do prior to bracket cementation). The same 15 teeth were used with the seven different brands of brackets in order to establish a comparison of the adaptability of the brackets. The brackets were placed at a set orthodontic prescription of 4mm (measured from the slot area of the bracket to the tip of the buccal cusp of the tooth) on the upper first premolars. After bracket placement, the dontrix gauge was applied to the bracket to engage the slot area. The brackets were held in place with a constant force of 0.70 Newton (N) by the dontrix gauge. This allowed for reproducibility for the seven brackets with all fifteen teeth. In order to assess the space between the brackets and the teeth no adhesive was used. The space between the margins of the bracket and tooth interface was viewed under the Stereomicroscope (Carl Zeiss microscope, Zeiss Stemi508) at 50 times magnification. A two way mixed measures ANOVA was run to determine whether there were differences between the seven brackets placed at six points on the tooth surface. Results: GAC had the smallest overall mean measurement between bracket base and tooth surface followed by Ormco and Gemini respectively. Abzil had the largest overall mean measurement for the six points around the bracket

OBJECTIVES: To compare the amount of fluoride, calcium and phosphate release and recharge of a fluoride containing bioactive glass composite to a conventional resin composite and a resin modified glass ionomer cement at different time points. Furthermore, bond strength of a fluoride containing bioactive glass composite, a conventional flowable composite, and a resin modified glass ionomer cement to metal orthodontic brackets was evaluated. METHODS: A fluoride containing bioactive glass (BG) was synthesized using a sol-gel method and mixed homogeneously with an unfilled resin. For ion release and recharge, resin modified glass ionomer (RMGIC), Photac Fil Quick Aplicap (3M/ESPE) and flowable composite (Control), Filtek Supreme Ultra (Kerr), were used for comparison. Disc shape samples were fabricated using custom aluminum mold (1 mm in thickness and 9 mm in diameter, (n=5 for each material) and stored in 15 mL deionized water at 37°C until the testing time. The amounts of fluoride, calcium, and phosphate ions released were evaluated at different time points: 1 hour, 24 hours, 2 days, 3 days, 4 days, 5 days 6 days and 7 days. At each time point, all of the storage solution was extracted, and 7.5 mL was used for fluoride release measurement and the remaining 7.5 mL for calcium and phosphate ion release measurements. After solution extraction, the samples were replaced in 15 mL fresh deionized water at 37°C until the next sampling time point. Ionic recharge was performed with 5% sodium fluoride varnish (FluoroDose, Centrix) and MI paste plus (GC) following the ion release-testing period. An ion meter with a Fluoride ionic selective electrode were used to determine fluoride concentration. A Microwave-Plasma Atomic Emission Spectrometer (MP-AES) was used to test the concentration of the calcium and phosphate. For the shear bond strength test, rectangular shaped ceramic samples with the dimensions of 2 mm x 12 mm x 14 mm (Vita Mark II, Vita) were fabricated. Standard edgewise-metal brackets (American Orthodontics) were bonded to the center of the ceramic samples using tested material (n=10 for each material). Excess material was removed, and the cementing materials were polymerized from each side for 20 seconds. Specimens were either stored in water for 24 hours at 37o C or went under thermocycling for 5000 cycles. After the storage period, the specimens were subjected to shear bond strength test using an Instron universal machine at a crosshead speed of 0.5mm/min. Loads to failure were recorded to calculate shear bond strength. Comparison of released/recharged ions and shear bond strength were done by ANOVA and Tukey-Kramer HSD (α = 0.05) using JMP Pro 13. RESULTS: RMGIC showed significantly higher fluoride release and recharge than BG composite and the control. BG showed significantly higher Ca and P ion release compared to RMGIC followed by composite. RMGIC and BG showed significant ion recharge capability compared to composite. For the shear bond strength, the control composite showed significantly higher shear bond strength than BG composite followed by RMGIC. Thermocycling significantly increase bond strength for RMGIC and control but not for BG composite. CONCLUSIONS: 1. A fluoride containing bioactive glass composite was fabricated that showed the ability of ion release and recharge. 2. There was a significant difference in the amount of ion release and recharge among tested materials at different time points. 3. Favorable fluoride, calcium and phosphate ion release and recharge of BG composite were maintained over the testing period. 4. BG composite showed favorable bond strength to orthodontic metal brackets. 5. Thermocycling had a significant influence in bond strength for the materials tested except for BG composite. / 2020-07-18T00:00:00Z

The safety of pipelines distributed in the infrastructure of many industries has become very important since the industrial revolution. The guided ultrasonic wave technique can provide the possibility for rapid screening in long pipelines with corrosion. Especially the torsional mode T(0,1) of guided waves has been used in the cases of the pipe in the hidden region substantially. The ability of evaluating the inaccessible areas of the pipe makes the guided ultrasonic wave technique sit high on the roster of non-destructive testing tool for pipe inspection. However, the problem arises when attempting to detect the corrosions at the welded support bracket or under the bitumen coating on the pipe. The signal reflected from the corrosion will be covered by a large signal induced by the welded support or attenuated by the bitumen coating seriously. Therefore, the effects of welded support and bitumen coating on the T(0,1) mode are investigated by the experimental and the simulative methods. The continuous wavelet transform analysis is the signal processing method to extract the hidden signal of corrosion in this dissertation. There are five test pipes in the experiments. The response of the normal welded support is studied on the #1 test pipe. The #2 test pipe is used for attenuation investigation. The reflected signals of the features on the #3, #4, and #5 test pipes are measured and processed by continuous wavelet transform during defect detection process. In addition, the linear hexahedron elements are used to build the finite element models of the 6-inch steel pipe with support bracket and the pipe with bitumen coating. It is found that the effects of support bracket on the reflection comprise mode conversion, delayed appearance, trailing echoes, and frequency dependent behavior. When the T(0,1) mode impinges on to the support bracket, it will convert into the A0 mode inside the support due to the circumferential disturbance on the pipe surface. The reflection of the support bracket is identified as three parts formed by the direct echo, delayed echo and the trailing echo. The constructive interference of the A0 mode reflecting from the boundaries inside the support causes that the reflection spectrum shows two maxima peak at around 20-22 kHz (frequency regime of 0.0) and 32-34 kHz (frequency regime of 4.0) from both the experimental and simulated results. For the bitumen coating, the data collected from the welds and defects under the bitumen coating on the #2 test pipe show the attenuation effect on guided wave propagation and the difficulty of minor corrosion detection. In the finite element model of coated pipe, the results of predicted attenuation curves of T(0,1) mode indicate that the attenuation effect on guided wave propagation is aggravated with the increased value of the thickness, density or damping factor of the coated layer. Especially, in the case of 5-mm, the predicted attenuation curve shows a maximum point. Before this point, the attenuation increases with the operating frequency. For long range pipe inspection, it is the best way to avoid choosing the operating frequency around the corresponding frequency of the point. The measured data of corrosion affected by the welded support or the coated bitumen layer was processed by continuous wavelet transform to form a time-frequency analysis. The corrosion signals were identified in the contour map of the wavelet coefficient successfully. The understanding of the guided wave propagation on the pipe welded with support or pipe coated with bitumen is helpful to interpret the reflected signals. The use of continuous wavelet transform on signal processing techniques can improve the ability of defect detection on pipe with complex geometries.

This paper examines 878 mergers and acquisitions between 2003 and 2012 to investigate the impact of advisor choice on transaction performance. Differentiating between bulge bracket, boutique and mixed team advisors, this analysis uses cumulative abnormal announcement returns, purchase premiums, completion ratios, and deal durations as indicators of outcome. Using ordinary least squares and probit regressions an analysis of premium outcomes and target abnormal returns point to there being significant shareholder benefits to using boutique advisors. However, the use of boutiques significantly increases the length of the transaction, and appears to have no impact on the likelihood of a successful completion.

The invention of mass timber products, including cross laminated timber (CLT), over the past two decades has made tall wood building possible. In CLT structures, angle brackets are commonly used in wall-to-floor connections to transfer the shear in seismic and wind loads. In reality, these connections could experience loads in various directions, as well as multi-directional forces. This research consists of two parts: an experimental study carried out in Part 1, followed by a numerical program completed in Part 2. The research aims to investigate the performance of wall-to-floor CLT angle bracket connections under various loading situations. In Part 1 of the research, a two-phase experimental program consisting of 12 monotonic tests in the first phase, and 24 monotonic and 24 cyclic tests in the second phase was conducted to investigate the behaviour of wall-to-floor CLT angle bracket connections. Connections were assembled using two different sizes of steel angle brackets and four types of fasteners, under uplift, in-plane shear, and out-of-plane shear loads. The performance of the connections was evaluated in terms of strength, stiffness, ductility, energy dissipation capacity, and failure modes. Results show that small diameter fasteners are more desirable for wood-to-wood angle bracket connections in terms of failure modes, load-bearing capacity and stiffness. Specimens exhibited considerable ductile performance under both uplift and in-plane shear loads due to combinations of yielding of brackets and yielding or pull-out of screws. Connections loaded under out-of-plane tension may fail in the splitting of CLT panels. Fully-threaded screws led to higher strength, stiffness and energy dissipation capacity but less ductility compared to partially-threaded screws in angle bracket connections. In Part 2 of the research, a two-phase numerical program was carried out to assess the coupling effect of biaxial loading on the performance of CLT wall-to-floor angle bracket connections. In Phase I, a 3D finite element model of connections was developed using ABAQUS software and verified with the data from experimental tests carried out in Part 1 of the research. In Phase II of the numerical program, the verified model was used to simulate the performance of connections under three biaxial loads, i.e., shear and in-plane uplift, shear and out-of-plane tension, and shear and out-of-plane compression. The coupling effect on the performance of the connections was evaluated in terms of strength, stiffness, ductility, and failure modes under biaxial loads, and compared with the scenario where the connection was only loaded in shear. Results show that the application of biaxial loading may considerably decrease the shear performance of the connections. Additionally, the results confirm the analytical equation suggested by the European Technical Assessment to predict the resistance of angle bracket connections under biaxial loads. / Graduate / 2022-08-04

Magister Scientiae Dentium - MSc(Dent) / The purpose of this study was to compare the accuracy of direct versus indirect bracket placement in orthodontics in a controlled setting. The more accurate the initial bracket placement is the less time will be required in terms of treatment. Accurate bracket placement can reduce the envelope of error in the three dimensions of vertical (incisal height, height of tooth), horizontal (mesial-distal) and angular (degrees incisal to root apex causing rotational irregularities) based on Andrews’ six keys to normal occlusion (Andrews, 1979). In this comparative experimental study, 10 Class I molar relation study models were selected from the researcher’s practice archives. Only the MBT pre-adjusted or angulated orthodontic brackets were used on manikins, followed by the use of 3D CAD CAM technology to evaluate the results against a pre-determined golden standard.

In this Thesis we study two types of mechanical nonholonomic systems, namely systems with linear constraints and lagrangian with a linear term in the velocities, and nonholonomic systems with affine constraints and lagrangian without a linear term in the velocities. For the former type of systems we construct an almost-Poisson bracket using elements related to a riemannian metric induced by the kinetic energy, and we show that under certain conditions gauge momenta exist. For the latter type of systems, we focus on the ones possessing a \emph{Noether symmetry}. To everyone of these systems we associate an equivalent system of the former type, and we exhibit the procedure to relate them and their gauge momentum. As a test case for the theory, we analyze the system of a heavy ball rolling without slipping on a rotating surface of revolution: we elucidate that also in this framework the so-called Routh integrals are related to symmetries, we give conditions for boundedness of the motions. In the particular case the surface of revolution is an inverted cone we characterize the qualitative behavior of the motions.

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