Vibratory gyroscopes are inertial sensors, used to measure rotation rates in a number of applications. The performance of these sensors is limited by imperfections that occur during manufacture of the resonators. The effects of resonator imperfections, in piezoelectric vibratory gyroscopes, were studied. Hamilton's principle and the Rayleigh-Ritz method provided an effective approach for modeling the coupled electromechanical dynamics of piezoelectric resonators. This method produced accurate results when applied to an imperfect piezoelectric vibrating cylinder gyroscope. The effects of elastic boundary conditions, on the dynamics of rotating thin-walled cylinders, were analyzed by an exact solution of the Flügge shell theory equations of motion. A range of stiffnesses in which the cylinder dynamics was sensitive to boundary stiffness variations was established. The support structure, of a cylinder used in a vibratory gyroscope, should be designed to have stiffness outside of this range. Variations in the piezoelectric material properties were investigated. A figure-of- merit was proposed which could be used to select an existing piezoceramic material or to optimize a new composition for use in vibratory gyroscopes. The effects of displacement and velocity feedback on the resonator dynamics were analyzed. It was shown that displacement feedback could be used to eliminate the natural frequency errors, that occur during manufacture, of a typical piezoelectric vibrating cylinder gyroscope. The problem of designing the control system to reduce the effects of resonator imperfections was investigated. Averaged equations of motion, for a general resonator, were presented. These equations provided useful insight into the dynamics of the imperfect resonator and were used to motivate the control system functions. Two control schemes were investigated numerically and experimentally. It was shown that it is possible to completely suppress the first-order effects of resonator mass/stiffness imperfections. Damping imperfections, are not compensated by the control system and are believed to be the major source of residual error. Experiments performed on a piezoelectric vibrating cylinder gyroscope showed an order of magnitude improvement, in the zero-rate offset variation over a temperature range of 60°C, when the control systems were implemented. / Ph. D.

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The thesis contributes to the study of the relationship between competition and incentives, when asymmetric information is taken into account. Our main focus is the analysis of loan relationships. The first two chapters analyze the relationship between borrowers' financial constraints and endogenous fluctuations. We try to provide a potential departure from the traditional corporate finance theories by showing that the characteristics of firms' capital structure (i.e. their debt-to-equity ratio) can be affected by macroeconomic conditions. We construct a dynamic economy with asymmetric information in the credit market. The features of optimal securities issued at equilibrium are influenced by macroeconomic conditions. As a by-product, the debt-to-equity ratio in the overall economy will evolve according to the dynamics of aggregate variables. The remaining of the thesis develops a theoretical analysis of credit relationships where multiple financiers compete over the loan contracts they are offering to entrepreneurs-borrowers. To this extent, Chapter 3 proposes a unified framework to analyze the so-called literature on competing mechanisms and provides new results in terms of characterizing the equilibria of multi-principal multi-agent games. In the specific context of common agency games, we show that the introduction of a separability requirement on agent's preferences with respect to the contract offers she receives from principals is a sufficient condition to retrieve the Revelation Principle. Importantly, no restriction on principals' preferences is introduced. Chapter 4 investigates credit market relationships when competing lenders are explicitly considered. A reformulation of the traditional credit channel of Monetary Policy is then suggested. When lenders are strategically competing on their credit contract offers, positive-profit equilibria typically arise. Our analysis considers both the exclusive case and the non-exclusive one and it argues that monetary factors may affect the real sector mainly by modifying the structure of markets. The last chapter discusses the welfare implications of contractual externalities that arise in the presence of multiple financiers. We consider a scenario where a Social Planner is subject to the same informational constraints faced by principals in a simple model of the credit market. We identify conditions that sustain constrained-efficiency of market equilibria.

Curved panels constructed of laminated graphite-epoxy composite material are of potential interest in airframe fuselage applications. An understanding of structural response at elevated temperatures is required for anticipated future high speed aircraft applications. This study concentrates on the response of unstiffened, curved composite panels subjected to combinations of thermal and mechanical loading conditions. Mechanical loading is due to compressive end-shortening and thermal loading is due to a uniform temperature increase. Thermal stresses, which are induced by mechanical restraints against thermal expansions or contractions, cause buckling and postbuckling panel responses. Panels with three different lamination sequences are considered, including a quasi-isotropic laminate, an axially soft laminate, and an axially stiff laminate. These panels were chosen because they exhibit a range of stiffnesses and a wide variation in laminate coefficients of thermal expansion. The panels have dimensions of 10 in. by 10 in. with a base radius of 60 in. The base boundary conditions are clamped along the curved ends, and simply supported along the straight edges. Three methods are employed to study the panel response, including a geometrically nonlinear Rayleigh-Ritz solution, a finite element solution using the commercially available code STAGS, and an experimental program. The effects of inplane boundary conditions and radius of curvature are studied analytically, along with consideration of order of application in combined loading. A substantial difference is noted in the nonlinear load vs. axial strain responses of panels loaded in end-shortening and panels loaded with uniform temperature change, depending on the specific lamination sequence, boundary conditions, and radius of curvature. Experiments are conducted and results are presented for both room temperature end-shortening tests and elevated temperature tests with accompanying end-shortening. The base finite element model is modified to include measured panel thicknesses, boundary conditions representative of the experimental apparatus, measured initial geometric imperfections, and measured temperature gradients. With these modifications, and including an inherent end displacement of the panel present during thermal loading, good correlation is obtained between the experimental and numerically predicted load vs. axial strain responses from initial loading through postbuckling. / Ph. D.

La présente thèse s’intéresse à l’annotation multimodale d’images dans le contexte des médias sociaux. Notre objectif est de combiner les modalités visuelles et textuelles (tags) afin d’améliorer les performances d’annotation d’images. Cependant, ces tags sont généralement issus d’une indexation personnelle, fournissant une information imparfaite et partiellement pertinente pour un objectif de description du contenu sémantique de l’image. En outre, en combinant les scores de prédiction de différents classifieurs appris sur les différentes modalités, l’annotation multimodale d’image fait face à leurs imperfections: l’incertitude, l’imprécision et l’incomplétude. Dans cette thèse, nous considérons que l’annotation multimodale d’image est soumise à ces imperfections à deux niveaux : niveau représentation et niveau décision. Inspiré de la théorie de fusion de l’information, nous concentrons nos efforts dans cette thèse sur la définition, l’identification et la prise en compte de ces aspects d’imperfections afin d’améliorer l’annotation d’images. / This thesis deals with multimodal image annotation in the context of social media. We seek to take advantage of textual (tags) and visual information in order to enhance the image annotation performances. However, these tags are often noisy, overly personalized and only a few of them are related to the semantic visual content of the image. In addition, when combining prediction scores from different classifiers learned on different modalities, multimodal image annotation faces their imperfections (uncertainty, imprecision and incompleteness). Consequently, we consider that multimodal image annotation is subject to imperfections at two levels: the representation and the decision. Inspired from the information fusion theory, we focus in this thesis on defining, identifying and handling imperfection aspects in order to improve image annotation.

After the recent financial crisis of 2007, a connection between monetary policy and financial stability has started to be thoroughly investigated. One of the particular areas of this research field deals with the role of various financial variables in the monetary policy rules. The main purpose of this research is to find whether direct incorporation of the financial variables in the monetary policy rule can bring macroeconomic benefits in terms of lower volatility of inflation and output. So far, the main emphasis of the research has been placed on the investigation of the augmented Taylor rules in the context of a closed economy. This thesis sheds light on the performance of the augmented Taylor rules in a small open economy. For this purpose, a New Keynesian DSGE model with two types of financial frictions is constructed. The model is calibrated for the Czech Republic. The thesis provides four conclusions. First, incorporation of the financial variables (asset prices and the volume of credit) in the monetary policy rule is beneficial for macroeconomic stabilization in terms of lower implied volatilities of inflation and output. Second, the usefulness of the augmented monetary policy rule is the most apparent in case of the shock originating abroad. Third, there is a strong link between the financial and the...

The postbuckling load carrying capacity of composite plates offers immense potential to their applications for loads exceeding their primary buckling load. However, such an efficient and economical usage of these plates can be reliable only if the nonlinear postbuckling behavior of these plates, which includes a good understanding of secondary buckling, is understood thoroughly. The present investigation is an attempt to understand secondary buckling of almost square composite clamped-simply supported plates, both unstiffened as well as stiffened, in some detail. With the help of the finite element method, a large number of numerical studies have been conducted to understand the secondary buckling characteristics. The sensitivity of these characteristics to variations in boundary conditions, lamination sequence, imperfections, and stiffener geometry has been considered. It has been found that the occurrence of secondary buckling in clamped-simply supported plates under uniform end shortening critically depends on the intensity of restrictions imposed on the inplane normal displacements along the unloaded simply supported edges of the plate. These restrictions could be due to the actual boundary conditions at these edges, or due to the presence of stiffeners along these edges. It has also been found that the presence of imperfections significantly delays the event of secondary buckling. Finally, it has been found that changes in lamination sequence of the plate alter its secondary buckling characteristics in ways that are, in general, quantitative in nature. The numerical investigations were followed by a limited number of experiments involving the testing of unstiffened as well as stiffened composite plates with the intent of augmenting the confidence in the numerical predictions made. Three different lamination sequences were considered during the testing phase of this investigation. It was found that the agreement between experimental data and numerical predictions was quite good. The occurrence of secondary buckling followed the predictions closely. / Ph. D.

No / This paper considers both the linear elastic and creep buckling of polymeric pipe linings used for the rehabilitation of gravity pipes, for which external groundwater pressure has been identified as the prime source of loading. Theoretically perfect and imperfect conditions are considered, with the imperfections taken to be in the form of a concentric or eccentric annulus between the rigid host pipe (cylindrical constraint) and polymeric lining. Under these conditions two recently obtained mathematical procedures for the prediction of linearly and non-linearly elastic buckling are compared with the results of complementary laboratory testing. Linear elastic conditions are shown to be well approximated by undertaking short-term (¿30 min) testing under increasing pressure to failure. Controlled imperfections are introduced into the laboratory tests and excellent correlation with the theoretical predictions is obtained. In particular, the dominant geometrical imperfections are shown to be major influences on the obtained buckling pressure. The mathematical models are then adapted to simulate the creep buckling process under long-term constant pressure. The results obtained are again compared with those provided by complementary physical testing, and appropriate conclusions are made.

No / This paper considers both the linear elastic and creep buckling of polymeric pipe linings used for the rehabilitation of gravity pipes, for which external groundwater pressure has been identified as the prime source of loading. Theoretically perfect and imperfect conditions are considered, with the imperfections taken to be in the form of a concentric or eccentric annulus between the rigid host pipe (cylindrical constraint) and polymeric lining. Under these conditions two recently obtained mathematical procedures for the prediction of linearly and non-linearly elastic buckling are compared with the results of complementary laboratory testing. Linear elastic conditions are shown to be well approximated by undertaking short-term (¿30 min) testing under increasing pressure to failure. Controlled imperfections are introduced into the laboratory tests and excellent correlation with the theoretical predictions is obtained. In particular, the dominant geometrical imperfections are shown to be major influences on the obtained buckling pressure. The mathematical models are then adapted to simulate the creep buckling process under long-term constant pressure. The results obtained are again compared with those provided by complementary physical testing, and appropriate conclusions are made.

Discussed is a numerical and experimental characterization of the response of small-scale fiber-reinforced composite cylinders constructed to represent a fuselage design whereby the crown and keel consist of one laminate stacking sequence and the two sides consist of another laminate stacking sequence. This construction is referred to as a segmented cylinder. The response to uniform axial endshortening is discussed. Numerical solutions for the nonlinear prebuckling, buckling, and postbuckling responses are compared to experimental results. Focus is directed at the investigation of two specific cylinder configurations, referred to as axially-stiff and circumferentially-stiff cylinders. Small-scale cylinders, each having a nominal radius of 5 in., were fabricated on a mandrel by splicing adjacent segments together to form 0.5 in. overlaps. Finite-element models of both cylinder configurations, including the overlap regions, are developed using the STAGS finite-element code. Perfectly circular cylinder models are considered, as are models which include the measured geometry of the specimens as an imperfection. Prebuckling predictions show that the segmented cylinder response is characterized by the existence of circumferential displacement, and an axial boundary layer accompanied by circumferential gradients in radial displacement. Experimental measurements, taken with strain gages and displacement transducers, confirm these numerical findings. As the endshortening approaches the critical, or buckling, values, the response of the cylinders is characterized by wrinkling in the axial direction. In the axially-stiff cylinder, the crown and keel segments wrinkle, while in the circumferentially-stiff cylinder the side segments wrinkle. Experimental images taken from Moire interferometry show this response in the circumferentially-stiff cylinder. Four methods are used to predict the buckling values of endshortening and load for both cylinders, and the four values are in good agreement. The experimentally-measured buckling conditions, however, show that the models overpredict buckling values. For the axially-stiff cylinder, the difference could be due to the fact material failure not included in the model plays a role in the cylinder response. For the circumferentially-stiff cylinder, the difference is definitely due to material failure characteristics not included in the model. The predicted postbuckling response of the segmented cylinders is shown to be dominated by the existence of inward dimples in some or all of the segments. For the axially-stiff cylinder, the as-predicted dimpled crown and keel configuration is observed in the experiment but at a load 12 percent below predicted values. For the circumferentially-stiff cylinder material failure in the linear prebuckling range of response triggered buckling that resembled the predicted circumferential rings of dimples, but at a load 31 percent below predictions. Finally, it is shown that the effect of including the measured imperfections in the model has little observable effect on the circumferentially-stiff cylinder. For the axially-stiff cylinder the inclusion of the imperfections is found to effect the transition from buckling to postbuckling, but ultimately has little effect on postbuckling deformations. / Ph. D.