Thesis. 1978. M.S.--Massachusetts Institute of Technology. Dept. of Aeronautics and Astronautics. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND AERONAUTICS. / Includes bibliographical references. / M.S.

Frequency selectivity is one of the most important functions of the mammalian hearing organ – the cochlea. The interaction of fluid mass and organ of Corti compliance sets a traveling wave along the basilar membrane (BM), which is longitudinally tuned to different frequencies. Beyond this passive tuning process, cochlear amplification locally enhances the vibration of the best frequency peak by factors of hundreds to boost the frequency selectivity and sensitivity of the cochlea. This amplification is achieved by a positive feedback loop between BM motion and outer hair cell (OHC) electrical-mechanical response. However, this active mechanism is vulnerable to damage and cannot be fully recovered in vivo. As the instruments of cochlear amplification, the frequency response of BM and OHCs are of great importance to understand cochlear tuning process. This thesis used animal models, aimed to understand cochlear tuning and investigate possibilities to manipulate the cochlear amplifier, by testing the cochlear amplifier’s sensitivity to operating conditions. The first project tested whether the cochlear amplification can adjust to a lower endocochlear potential (EP), which controls OHC electromechanical force by providing part of the voltage source to drive OHC transduction current. To investigate this possibility, we use intraperitoneal (IP) and intravenous (IV) injection of furosemide to reversibly reduce EP, while monitoring the EP and cochlear amplification simultaneously. Cochlear amplification was monitored by measuring the local cochlear microphonic (LCM) and distortion product emission (DPOAE). With IV injection, the cochlear amplification observed in LCM could attain nearly full or even full recovery with reduced EP. This showed the cochlea has an ability to adjust to diminished operating condition. Furthermore, the cochlear amplifier and EP recovered with different time courses: cochlear amplification just started to recover after the EP was nearly fully recovered and stabilized. Using a Boltzmann model and the 2nd harmonic of the LCM to estimate the mechanoelectric transducer channel operating point, we found that the recovery of cochlear amplification occurred with re-centering of the operating point. The second project studied the physiological and anatomical effects of perfusing the cochlea with a viscous fluid, for better understanding cochlear fluid mechanics. Perilymphatic perfusion was applied with artificial perilymph and viscous sodium hyaluronate (Healon, HA) in four different concentrations. Using compound action potential (CAP) thresholds as an indicator of cochlear condition, our results and analysis indicated that the cochlea can sustain, without a significant CAP threshold shift, up to a 1.5 Pa shear stress. Histology of the cochleae perfused with higher shear stress showed the Reissner's membrane was torn. These data also indicated that the cochlea mechanics remains normal within increased perilymphatic fluid viscosity up to an increase of a factor of 50. Beside these findings, a temporary CAP threshold shift was observed, perhaps due to the presence and then clearance of viscous fluid within the cochlea, or to a temporary position shift of the organ of Corti. The last project was to test the effect of OHC intracellular Cl- concentration on cochlear amplification. Chloride is known to enable the electromotility of the OHC by binding its motor protein, prestin. By locally perfusing high chloride perilymph and the chloride ionophore tributyltin, this study investigated whether increasing intracellular chloride concentration can restore cochlear sensitivity in a cochlea that was slightly damaged. This had been shown by others in guinea pig. However, we did not observe recovery in several attempts in gerbil.

Thesis (M.S. in Applied Science (Signal Processing))--Naval Postgraduate School, June 2004. / Thesis advisor(s): Lawrence J. Ziomek. Includes bibliographical references (p. 47). Also available online.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Civil Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Bibliography: leaves 125-127. / by Amir Massoud Kaynia. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING / Bibliography: leaves 94-97. / by Daniel Michael Chernoff. / M.S.

Narrowband communications systems employing frequency-shift-keyed (FSK) carrier modulation demand careful consideration of system transient responses. Discontinuous waveforms or their derivatives, such as produced by frequency modulation, can result in the generation of large transient currents and voltages. These transient conditions produce distortion which interferes with demodulation processes, and may be in excess of the physical limitations on continuous operation of the transmitting terminal. It has been suggested that a phase-locked-loop (PlL), whose reference signal is instantaneously switched between two discrete frequency sources, be employed as the modulated source of an FSK carrier. The characteristics of the PLL provide signal coherence and a means of "shaping" the modulation waveform, both of which are required in certain FSK transmissions. The investigation undertaken here is primarily concerned with the characterization of such a PLL output signal (exhibiting a finite frequency transition interval). Expressions are obtained for the output signal and the resulting modulation waveform for the case of a single frequency shift. Graphical evidence of the dependence of the modulation waveform on the loop parameters, gain and bandwidth, is presented. In order to facilitate the analysis of linear networks excited by the FS-PLL, an infinite series of damped sinusoidal terms, representing the PLL output signal is developed. This series is also utilized to determine the coefficients of the Fourier series representation of a periodically keyed PLL. Using this result, the signal bandwidth is shown to vary directly as the loop bandwidth. Application of the FS-PLL as a voltage source is made in the case of the equivalent circuit (a high Q series tuned circuit) of a VLf transmitting antenna. Representative curves are provided which show that the series tuned circuit transient response is in general the superposition of a transient component, resulting from a change in frequency, and a quasi-stationary component. Finally, an experiment is devised which provides an additional investigative tool. A unique method for achieving demodulation of narrowband signals, while maintaining wideband demodulator response characteristics, is used to experimentally substantiate the predicted modulation waveforms. Experimental data is also obtained, and graphically compared with the theory, to verify the frequency domain analysis of the FS-PLL output as well as the tuned circuit time domain analysis. / Ph. D.

Thesis (Ph. D.)--University of Hong Kong, 2008. / Includes bibliographical references (leaf 127-140) Also available in print.

Thesis (Ph. D.)--University of Hong Kong, 2008. / Includes bibliographical references (leaf 127-140) Also available online.

Orientador: José Maria Campos dos Santos / Dissertação (mestrado profissional) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-19T06:05:00Z (GMT). No. of bitstreams: 1 Sica_MauricioRoselli_M.pdf: 6187406 bytes, checksum: eb76c3ee4e60cfc7e2fbff17dbb0b05b (MD5) Previous issue date: 2011 / Resumo: As simulações físicas em laboratórios da indústria automotiva são realizadas utilizando informações colhidas de veículos que são submetidos a ciclos de testes em rotas urbanas. Medir as respostas em pontos específicos durante uma rota de teste, não significa conhecer as excitações a que o veículo esta sendo submetido, visto que este normalmente é composto por sistemas mecânicos não lineares. O objetivo deste trabalho é desenvolver um algoritmo que possibilite através dos dados de resposta medidos em campo, conhecer as excitações de entrada, contribuindo para a reprodução da rota de teste. A metodologia utilizada está baseada na obtenção de funções de resposta em freqüência, de modelos lineares simples e no desenvolvimento de sinais de entrada, capazes de reproduzir as mesmas respostas medidas nas rotas nos sistemas não lineares. O algoritmo desenvolvido foi avaliado com simulações em sistemas lineares e não lineares de um, dois e quatro graus de liberdade. Através dos sinais de resposta medidos em um sistema e, utilizando sinal de identificação tipo Schroeder, foi possível estimar as forças de excitação, com um erro menor do que 1,0% para sistemas de dois graus de liberdade lineares e não lineares. No caso de sistemas com quatro graus de liberdade este valor foi menor do que 1,5%, utilizando sinais de identificação do tipo multisseno. Discute-se a metodologia utilizada para a obtenção das funções de resposta em freqüência comparando-a com outras empregadas em equipamentos comerciais, bem como a influência de fatores no processo de convergência do algoritmo, como o grau de não linearidade, a qualidade do sinal medido e a importância da escolha do sinal para a identificação dos sistemas / Abstract: Laboratory simulation testing in the automotive industry is carried out considering information acquired from vehicle urban routes testing. Due to the non-linearity of the vehicle mechanical systems, the output measuring collected from routes on specific points, does not mean the knowledge of the input signal excitation which it is submitted. The present study focuses on the development of an iterative algorithm that knowing the output signals measured, it is able to search for the input excitations, so given subsidies to reproduce events of the urban route, with its load amplitude and its frequencies. The methodology is based on the frequency response function of simple linear models and on the development of input signal, which is capable to reproduce the same measured responses of non-linear system. The developed algorithm was validated with simulations on linear and non linear system with one, two and four degrees of freedom. Making use of the Schroeder identification signal, it was possible to estimate input forces with an error lower than 1,0%, for linear and non-linear systems with two degrees of freedom. In the case of four degrees of freedom the algorithm converges to estimate input force with a tolerance of error lower than 1,5%, using multissine identification signal. A discussion about the methodology used to obtain the frequency function response is carried out, comparing it with others found in commercial test equipments, as well the influence of some factors on the algorithm process of convergence, as the level of the non-linearity of the system, the quality of the acquisition of signal response and the importance of the correct choice of the input signal for the system identification / Mestrado / Dinâmica / Mestre em Engenharia Automobilistica

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy