No description available.

Many researchers have devoted their work to the development of modal analysis extraction techniques in order to obtain more reliable identification of the modal parameters. Also, as a consequence of all this work, there are some other works devoted to the evaluation and comparison of these methods in order to find which one is the most reliable method with respect to certain characteristics. In this thesis the Rational Fraction Polynomial (RFP) Method, the Prony or Complex Exponential Method (CEM), the Ibrahim Time Domain (ITD) Method, and Hilbert Envelope Method are used to evaluate how the accuracy of the damping ratio is affected with respect to various parameters and conditions. The investigation focuses in the estimation of damping ratio because among the modal parameters, it is the most difficult to model. Each method is evaluated individually in order to understand how the damping ratio estimation is affected with respect to each method when the characteristics of the FRF are changed. Also, they are compared to show that, in general, the Rational Fraction Polynomial Method is a more reliable method than the other methods. To investigate this, a simulated analytical data and an experimental data are processed to estimate the modal parameters, but focusing in the damping ratio. For the simulated analytical data the damping ratio's percent of error were calculated. The highest damping ratio's percent of error of the RFP was 0.0073501%. In the other hand, for the CEM, ITD, and Hilbert Envelope Method their highest damping ratio's percent of error were 83.02%, 99.82%, and 4.077%, respectively. / Master of Science

This study was motivated by the fact that many times intact specimens with a number of oversized particles are dynamically tested in the laboratory and the impact of the particles on the dynamic properties is unknown. The effects of oversized particles represented by gravel particles on the shear modulus (G) and material damping ratio (D) of a uniform sand were evaluated in the linear (γ ≤ 0.001%) and nonlinear (γ > 0.001%) ranges of shear strain with combined resonant column and torsional shear (RCTS) equipment. The sand used in this investigation is a uniform sand as a reference, well-characterized material on the dynamic properties. Sand-gravel specimens were constructed using the undercompaction method. A variety of rounded gravel particles was used in building the specimens. Dynamic tests on the sand-gravel specimens were performed, and the tests results are presented. Among the findings of this investigation are that, compared to uniform sand: (1) oversized gravel particles symmetrically located along the longitudinal axis in uniform sand generally decreased slightly the small-strain shear modulus (Gmax), (2) oversized gravel particles asymmetrically located away from the longitudinal axis of rotation resulted in slight increases in Gmax and the small-strain material damping ratio (Dmin), (3) the G – log γ relationships of sand-gravel specimens with asymmetrically located gravel particles are generally above those with gravel particles symmetrically located along the longitudinal axis, and (4) the G/Gmax – log γ relationships of all specimens were reasonably close for the nonlinear ranges covered in these tests (γ < 0.05 % and G/Gmax > 0.6). As long as the oversized particles were near the axis of rotation, the particles had little effect on the dynamic properties (Gmax, Dmin and G – log γ relationships) regardless of sizes and numbers of particles. However, once the oversized particles were located away from the axis of rotation and closer to the perimeter of the specimen, the oversized particles influenced the dynamic properties. Finally, the additions of oversized particles located both symmetrically and asymmetrically in the uniform sand specimens have little impact on the nonlinear dynamic properties (G/Gmax – log γ and D – log γ relationships) which compared well with uniform sand. / text

Part A of 2 parts. / <p> This report is a study of the dynamic properties of semiconductor laser diodes. The measurement of some important laser diode parameters necessary for dynamic behaviour prediction is described. The relaxation oscillation behaviour for laser diodes pumped with nanosecond time scale current pulses is predicted using both an approximate analytic solution and computer simulations. This predicted behaviour is compared with experimental results. Dynamic experiments with an external cavity for extra optical feedback and a regenerative loop for optoelectronic feedback are also described and discussed. Details of the experimental setups and techniques used are given. </p> / Thesis / Master of Engineering (MEngr)

<p> The equilibrium and kinetic properties of semicoherent interfaces between γ precipitates and β matrix in Cu-Zn-Sn are examined using a simple dislocation model. The predicted surface energies and mobilities are compared to those observed in experiments which also assess the validity of current theories of interfacial stability in diffusion-controlled growth.</p> / Thesis / Master of Science (MSc)

Calculamos a densidade espectral do modelo de Anderson de duas impurezas por meio de uma extensão do grupo de renormalização numérico (GRN) preservando a assimetria partícula-buraco do modelo. O estado fundamental deste modelo depende fortemente da competição entre a interação RKKY 1 e a temperatura de Kondo TK. Essa competição gera três regimes característicos: (i) 11\\ « k B TK, regime Kondo; (ii) - 1» kBTK, regime ferromagnético; and (iii) 1» kBTK, regime antiferromagnético. O Hamiltoniano é invariante sob inversão das coordenadas da impureza ± R/2. Seus auto-estados, portanto, podem ser classificados de acordo com a paridade. Calculamos as densidades espectrais par e ímpar para os parâmetros representativos do modelo em cada um dos três regimes mencionados acima. Várias características dos resultados numéricos, associadas com a formação de um tripleto ou singleto entre as impurezas e com o efeito Kondo, são discutidas. / We calculated the spectral density for the two-impurity Anderson model by means of an extension of the numerical renormalization-group (NRG) preserving the particle-hole asymmetry of the model. The ground state of this model depends strongly on the competition between the RKKY interaction I and the Kondo temperature TK. That competition generates three characteristic regimes: (i) 11\\« kBTK, Kondo regime; (ii) - I» kBTK, ferromagnetic regime; and (iii) I > > k B TK, antiferromagnetic regime. The Hamiltonian is invariant under inversion of the impurity coordinates ± R/2 . Its eigenstates can therefare be classified according to parity. We have calculated the even and odd spectral densities for model parameters representative of each of the three above mentioned regimes. Various features af the numerical results, associated with the formation of an impurity singlet ar triplet and with the Kondo effect, are discussed.

Calculamos a densidade espectral do modelo de Anderson de duas impurezas por meio de uma extensão do grupo de renormalização numérico (GRN) preservando a assimetria partícula-buraco do modelo. O estado fundamental deste modelo depende fortemente da competição entre a interação RKKY 1 e a temperatura de Kondo TK. Essa competição gera três regimes característicos: (i) 11\\ « k B TK, regime Kondo; (ii) - 1» kBTK, regime ferromagnético; and (iii) 1» kBTK, regime antiferromagnético. O Hamiltoniano é invariante sob inversão das coordenadas da impureza ± R/2. Seus auto-estados, portanto, podem ser classificados de acordo com a paridade. Calculamos as densidades espectrais par e ímpar para os parâmetros representativos do modelo em cada um dos três regimes mencionados acima. Várias características dos resultados numéricos, associadas com a formação de um tripleto ou singleto entre as impurezas e com o efeito Kondo, são discutidas. / We calculated the spectral density for the two-impurity Anderson model by means of an extension of the numerical renormalization-group (NRG) preserving the particle-hole asymmetry of the model. The ground state of this model depends strongly on the competition between the RKKY interaction I and the Kondo temperature TK. That competition generates three characteristic regimes: (i) 11\\« kBTK, Kondo regime; (ii) - I» kBTK, ferromagnetic regime; and (iii) I > > k B TK, antiferromagnetic regime. The Hamiltonian is invariant under inversion of the impurity coordinates ± R/2 . Its eigenstates can therefare be classified according to parity. We have calculated the even and odd spectral densities for model parameters representative of each of the three above mentioned regimes. Various features af the numerical results, associated with the formation of an impurity singlet ar triplet and with the Kondo effect, are discussed.

<p> The electron density approach in conjunction with the Hellmann-Feynman theorem is used for a systematic analysis of binding characteristics of the two isoelectronic molecular series: N₂, CO, BF, and LiF, BeO. Electron density distributions, forces and field gradients corresponding to static properties of electron densities, have been calculated from Hartree-Fock wavefunctions (obtained from the work of other authors) for these molecules. Correlation of these static properties with binding characteristics are presented. Covalent and ionic characteristics are made evident by an analysis of the density distributions, density difference maps obtained by subtracting atomic from molecular distributions, and the forces exerted on nuclei by these distributions. A discussion of the field gradients, as related to quadrupole polarizations of the electron densities, is presented and the relevance of these polarizations to the interpretation of nuclear quadrupole coupling constants is indicated. </p> <p> Dynamic properties, as reflected by the magnitude of force constants, are analyzed in terms of functionals of the one-electron density. Force constant expressions are derived from the Hellmann-Feynman theorem. Any relation of force constants to field gradients is shown to be not unique as a result of cancellation of static and dynamic electron contributions to the total force constant. The total electronic contribution is shown to arise from a relaxation of density after a displacement of a certain nucleus. Relaxation of density with respect to one nucleus but which remains localized on some other nucleus in a molecule is shown to be equivalent to a field gradient. Thus, such density is separated from other density and its contribution to the force constant is treated as a field gradient. All contributions are computed from polynomial fits of the corresponding forces calculated at a number of internuclear distances. Relaxation density maps for the remaining atomic and overlap densities centered on a specific nucleus are presented. These maps are calculated as the difference between densities of the extended and equilibrium configurations of a molecule. The relaxation densities are correlated to the magnitude of the corresponding electronic force constant components. Thus, for the first time, there is demonstrated the concrete relation between covalent and ionic characteristics of electron densities in molecules and their dynamic properties which result in the magnitude of force constants. </p> / Thesis / Doctor of Philosophy (PhD)

The dynamic properties of the elastic coupling are not readily known; therefore testing has to be performed in order to determine these properties. This is the primary objective for this thesis. The dynamic properties in question are the stiffness and damping. An attempt to determine the dynamic properties was also be carried out through the use of finite element analysis. There are two different configurations of couplings. One configuration forms the coupling from several elastic elements, referred to as HRC elements, which are manufactured in three sizes: A, B, and C. The second configuration, referred to as the HEMD coupling, has a single elastic member in the form of a hollow rubber/fabric ring connecting the input to the output. The couplings have cords made of either polyester or nylon. These cords will affect the dynamic properties of the coupling.

Human-structure interaction is a relatively new topic that is not fully understood. There have been several human whole-body models from the research in body biomechanics and structural dynamics, which have been used in the study of human-structure interaction. It is not clear which body model is the most appropriate one. An interactive human body model was derived from a human-structure interaction model where a continuous standing human body was placed on a single degree-of-freedom (SDOF) structure. However, the dynamic parameters of the human body model cannot be determined accurately. In this thesis, a series of human-structure interaction experiments are conducted, which also leads to the identification of the dynamic parameters of the interactive body model and the assessment of the commonly used human body models. Two groups of 18 and 38 individual subjects participated in human-structure interaction experiment on a SDOF test rig with two different configurations. Two sweeping harmonic forces (6.6 and 13.2 N) were applied to the bare and occupied rigs. The repeatability of the tests was checked and confirmed. These experiments showed clearly two resonance frequencies of the human-structure system. It was also demonstrated that the dynamic parameters of the standing human body were independent of the test rig setup and of the subjects' gender. On the other hand, the vibration magnitude and the body masses significantly influenced the natural frequencies but not the damping ratios of the standing subjects. The fundamental natural frequency and damping ratio of the standing human body were about 6.6 Hz and 22% respectively. The identified dynamic parameters of the standing body can then be used to predict the responses of an occupied structure and the human body. Another group of 74 subjects were tested twice, with and without wearing shoes, which examined the effect of footwear on the dynamic parameters of the standing human body and on the dynamic response of the occupied rig. Only one sweeping harmonic force (13.2 N) was applied to the test rig. This study demonstrated that footwear significantly affected the dynamic parameters of the standing human body. The natural frequency and damping ratio of the standing body with bare feet are higher than those with footwear. When the two genders have the same body mass index (BMI), the maximum responses of the occupied rig are almost identical. When they have the same weight, the response of the rig occupied by the males was higher at the first resonance peak. The accelerations throughout the heights of two subjects were measured, which allowed a comparison between the predicted human whole-body acceleration and the measurements at different positions of the standing human bodies. The predicted frequency response functions (FRFs) had the same pattern as the measured ones and were larger than the measured responses at the head, neck and shoulders. The effects of the mass ratio of a crowd to a SDOF structure and the natural frequency of the structure on the human-structure interaction were examined. It was demonstrated that, for a light crowd, such as seen on office floors, the occupied structure would respond less than the bare structure, where the human body acts like a tuned-mass-damper, while the body responses were higher than that of the bare structure. For a larger crowd, such as seen on grandstands, the responses of the occupied structure and the human body were both smaller than that of the bare structure although the body response was larger than that of the occupied structure. A comparison between the human-structure interaction model used in this study and three other models was conducted. The dynamic parameters of the models were identified from the above experiments, in which the natural frequencies of the body for the four models were similar. It showed that the predicted responses of the occupied structure were similar based on the four models. However, there were obvious differences in the predicted body responses. A detailed comparison between the proposed model, Griffin's models and the available measurements showed that the damping ratios used in Griffin's models were too high, which prevents the two resonance frequencies from being observed. In addition, the predicted human body response calculated by the proposed model is much higher than that from Griffin's models.