<p dir="ltr">Sinusoidal low frequency alternating current (LFAC) stimulation is a novel mode of electrical modulation observed in the Bioelectroics Lab in 2017. LFAC is capable of blocking the single fiber action potentials (APs) of the earthworm with only a few 100's of µA. The goal of this dissertation was to further explore and characterize the LFAC waveform to determine it's feasibility as a method for block in the mammalian peripheral nervous system (PNS). To better understand the mechanisms of LFAC block (LFACb), a blend of \textit{in-silico} modeling work was explored and the predictions were validated with <i>ex-vivo</i> and <i>in-vivo</i> experiments. </p><p dir="ltr"> This dissertation is divided into five chapters. The first chapter will explore the history of bioelectricity, the current state of <i>in-silico</i> modeling and methods of nerve block used in the PNS. The second chapter explores a major modeling assumption, the conductivity and permittivity of the nerve laminae of a mammalian nerve bundle. Four point electrochemical impedance spectroscopy (EIS) was performed on excised canine vagus nerve to evaluate the electrical properties of the perineurium and epineurium. This study's result, found that the corner frequency of the perineurium (2.6kHz) and epineurium (370Hz) were much lower than previously assumed. This explain a major difference between LFACb and the more established kilohertz frequency alternating current (kHFAC) block. The third chapter revisits the initial earthworm experiments during the discovery of LFACb. The effect of conduction slowing was observed in these earthworm experiments and were also seen in a mammalian canine vagus nerve and in the Horn-Yoshida-Schild (HYS) autonomic unmyelinated axon mode. These experiments showed that LFACb occurs as a cathodic block in which the sodium channels are held inactive. Chapter 4 explored the window between LFACb and LFAC activation (LFACa). The window between the two states was describes by LFAC amplitude and LFAC frequency in an <i>in-vivo</i> rat sciatic nerve and an <i>in-silico</i> model of a myelinated motor neuron, the McIntyre-Richardson-Grill (MRG) axon model. Geometrical effects were also observed by varying the bipolar pair of contacts used to deliver the LFACb waveform from an asymmetrical tripolar cuff electrode. Plantar flexor force measurements and electromyography (EMG) of the lateral gastrocnemius (LG) and soleus (Sol) were used to quantify the effects of the LFAC waveform. Convergence between <i>in-silico</i> modeling and <i>in-vivo</i> results showed promise that modeling efforts could be used with confidence to explore the LFAC block-activation more completly. LFACa was found to be highly dependent on frequency with increasing frequency lowering the threshold of activation. LFACb was shown to be mostly invariant to frequency. The final chapter takes the information found in this dissertation and summarizes it. Future work on LFAC is also proposed and the hypothesized results presented with the findings from this dissertation and available literature. </p>

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Wind power is a fast-growing source of non-polluting, renewable energy with vast potential. However, current wind technology must be improved before the potential of wind power can be fully realized. One of the key components in improving wind turbines is their blades. Blade failure is very costly because blade failure can damage other blades, the wind turbine itself, and possibly other wind turbines. A successful structural health monitoring (SHM) system incorporated into wind turbines could extend blade life and allow for less conservative designs. Impedance-based SHM is a method which has shown promise on a wide variety of structures. The technique utilizes small piezoceramic (PZT) patches attached to a structure as self-sensing actuators to both excite the structure with high-frequency excitations, and monitor any changes in structural mechanical impedance. By monitoring the electrical impedance of the PZT, assessments can be made about the integrity of the mechanical structure. Recent advances in hardware systems with onboard computing, including actuation and sensing, computational algorithms, and wireless telemetry, have improved the accessibility of the impedance method for in-field measurements. The feasibility of implementing impedance-based SHM on wind turbine blades is investigated in this work. Experimentation was performed to determine the capability of the method to detect damage on blades. First, tests were run to detect both indirect and actual forms of damage on a section of an actual wind turbine blade provided by Sandia National Laboratories. Additional tests were run on the same blade section using a high-frequency response function method of SHM for comparison. Finally, based on the results of the initial testing, the impedance method was utilized in an attempt to detect damage during a fatigue test of an experimental wind turbine blade at the National Renewable Energy Laboratory's National Wind Technology Center. / Master of Science

This thesis is motivated by the need for noise control in aircraft engine with orifices and perforated liner. The presence of high-level acoustic excitation, different flow situations either bias flow, grazing flow or any combination in the aircraft engine, makes the acoustic behavior complex due to the interaction between sound and flow over the lined wall. Both systematic acoustic prediction of aircraft engines and liner optimization necessitate progress in impedance measurement methods by including the effect of the complex flow situations. The aim of the present thesis is to experimentally study the change in acoustic properties of orifices and perforated liners under bias or grazing flow. In order to study the effect of different combinations of bias flow and high-level acoustic excitation, an in-duct orifice has been investigated with finely controlled acoustic excitation levels and bias flow speeds. This provides a detailed study of the transition from cases when high-level acoustic excitation causes flow reversal in the orifice to cases when the bias flow maintains the flow direction. Nonlinear impedance is measured and compared, and a scattering matrix and its eigenvalues are investigated to study the potentiality of acoustic energy dissipation or production. A harmonic method is proposed for modelling the impedance, especially the resistance, which captures the change in impedance results at low frequencies compared with experimental results. The presence of grazing flow can increase the resistance of acoustic liners and shift their resonator frequency. So-called impedance eduction technology has been widely studied during the past decades, but with a limited confidence due to the interaction of grazing flow and acoustic waves. A comparison has been performed with different test rigs and methods from the German Aerospace Center (DLR). Numerical work has been performed to investigate the effect of shear flow and viscosity. Our study indicates that the impedance eduction process should be consistent with that of the code of wave propagation computation, for example with the same assumption regarding shear flow and viscosity. A systematic analysis for measurement uncertainties is proposed in order to understand the essentials for data quality assessment and model validation. The idea of using different Mach numbers for wave dispersion and in the Ingard-Myers boundary condition has been tested regarding their effect on impedance eduction. In conclusion, a local Mach number based on friction velocity is introduced and validated using both our own experimental results and those of previous studies. / <p>QC 20150522</p>

Title: Nutritional aspects and body composition in motocross Objectives: The goal of this work is monitoring nutritional habits and parameters for the assessment of body composition and somatotype for Czech junior national team in motocross and enduro. Methotds: There was used four day record of consumed food to map out nutritional habits, which was evaluted by software Nutirs. The input data of body composition were obtained by Bioimpendance InBody 230. Following were also measured selected anthropometric parameters. Results: The results of our study indicate quantitative variations in motocross riders nutrition, especially the negative energy balance and the low proportion of carbohydrates in the diet in pre-season and in the day of the race. These can be some way influenced by individual variability. The research somatotype and body composition suggests that in relation to physical abilities are motocross riders and riders Enduro the most versatile talent for sport. Keywords: Motocross, nutrition, supplements, body composition, somatotype, bioelectrical impedance

Les Surfaces à Haute Impédance (SHI) ont été largement étudiées pour améliorer toutes sortes de performances des antennes, comme le gain, le facteur de qualité, les formes et dimensions. L'objectif de cette thèse est de modéliser les structures de SHI et de caractériser leurs performances en vue de futures applications aux antennes.Après une brève introduction aux structures SHI et une étude de quelques modèles analytiques fréquemment traités dans la littérature, deux nouvelles méthodes numériques sont proposées pour calculer l'impédance de surface de structures SHI. Ces deux méthodes (dites « méthode du flux de Poynting » et « méthode <E>/<H> ») sont validées sur des structures symétriques, puis mises en service sur des structures de SHI asymétriques. Elles sont également validées par comparaison de résultats analytiques, numériques et expérimentaux.Nous présentons ensuite un modèle équivalent basé sur l'idée de remplacer les structures hétérogènes de SHI par une surface homogène, caractérisée par son impédance surfacique. Ce modèle nous permet d'avoir une prédiction avec un temps de calcul et une occupation de mémoire PC largement réduits. / High impedance surfaces (HIS) have proved good candidates for antenna miniaturization or antennas performance improvement. Within a certain frequency band, they can enhance the gain of an antenna while simultaneously suppressing the unwanted surface waves.In this thesis, the focus of our work is on numerical modeling of these structures by using the finite element method (FEM) based on edge elements.One of our contributions is that we propose two new numerical methods (the Poynting flux method and <E>/<H> method) to calculate the surface impedance not only for HIS structures with symmetric geometries, but also for those with asymmetric geometries. These two numerical methods have been validated by comparing analytical, numerical and experimental results.Another significant contribution of the thesis is that we introduce an equivalent model, based on the idea of replacing the heterogeneous HIS structures by a homogeneous surface, characterized by its surface impedance. Compared with the normal model, this equivalent model can save computing time and memory space.

Electrical Impedance Spectroscopy (EIS) is a relatively new method applied to food quality assessment. EIS allows relatively inexpensive assessment, is fast, easy to operate and non-invasive. It has been adopted for investigation of fundamental electrical properties of plant tissues. Although the applications of EIS for food quality determination have been reported previously, the analytical relationships between electrical impedance properties and quality criteria have not yet been fully developed. Further exploration is thus important in acquiring more data on electrical impedance characteristics of fruits and vegetables and researching new approaches for determination of their quality. This dissertation aims to investigate the electrical impedance properties of fruits and vegetables, and explore the relationship between impedance and quality criteria. In particular, the present dissertation outlines experimental research conducted on relationships between impedance properties and fruit tastes as well as the impedance changes observed during ripening process. Impedance measurement to monitor moisture content changes in the progress of drying is also included in this research. In summary, the impedance properties have merits in fruits and vegetables quality assessment. The current used subjective visual inspection and assessment could be replaced by the EIS based approach as it is a more precise measurement of food quality. Further study is required to give this method practical value.

When multiple cold cathode fluorescent lamps (CCFLs) are set up in a backlight module, parasitic capacitances are inevitably existent between the lamps and the aluminum back-plank. These parasitic capacitances are different from each other in introducing different leakage currents, and in turn cause current imbalance between lamps with undesired unequal brightness of the backlight module. In order to tackle this current imbalance problem, it relies critically upon a balance driving scheme. This thesis adopts the impedance-matching principle for a uniform light output. A detailed analysis and design of the balance circuit is implemented in a direct-type backlight module, which employs a series resonant parallel-loaded inverter with a transformer to generate a high AC voltage to drive multiple lamps. Adding appropriate capacitors on the load resonant circuits helps alleviate the discrepancy among lamp currents. Based on the experimental results, the maximum total current deviation is defined as an index of the current imbalance for multiple lamps system. Accordingly, the minimum impedance ratio can be provided for the designers to achieve balance driving. A prototype of the multi-lamp driving circuit with balance capacitors is designed and built for a backlight module with 16 lamps in a 32-inch liquid crystal display (LCD). Simulation and experimental results demonstrate the effectiveness and feasibility of the current balance scheme.

Les systèmes de combustion sont sujets aux instabilités de combustion (IC). Elles résultent d'un couplage constructif entre le taux de dégagement de chaleur instationnaire et des modes acoustiques du système. Les IC peuvent mettre en danger la performance et l'intégrité des systèmes de combustion. Même si ces phénomènes sont connus depuis plus d'un siècle, éviter quelles aient lieux dans les chambres de combustions industrielles reste difficile. Les objectifs de cette thèse sont les suivants : (1) étudier la dynamique des modes acoustiques, (2) analyser la réponse de flamme d'un moteur de fusée à propergol liquide H2/O2 (appelé "BKD"), sujet aux IC, à l'aide de la Simulation aux Grandes Echelles (SGE) et (3) dériver, utiliser et étudier des conditions limites permettant d'imposer des impédances acoustiques complexes en SGE. / Combustion devices are prone to combustion instabilities. They arise from a constructive coupling between the unsteady heat release rate of the flame and the resonant acoustic modes of the entire system. The occurence of such instabilities can pose a threat to both performance and integrity of combustion systems. Although these phenomena have been known for more than a century, avoiding their appearance in industrial engines is still challenging. The objective of this thesis is threefold: (1) study the dynamics of the resonant acoustic modes, (2) investigate the flame response of a liquid rocket engine under unstable conditions using Large Eddy Simulation(LES) and (3) derive, use and study Time Domain Impedance Boundary Conditions (TDIBCs), i.e. boundary conditions modeling complex acoustic impedances.

As linhas de transmissão são usadas para transmitir energia elétrica por longas distâncias e estão naturalmente expostas a condições climáticas severas e à ocorrência de faltas, especialmente as linhas aéreas. Estatísticas mostram que entre 70% - 90% das faltas em linhas de transmissão aéreas são momentâneas (ou transitórias) e apresentam formação de arco elétrico. O arco elétrico é a principal característica de uma falta de alta impedância e resulta do pobre contato entre um condutor energizado e a superfície envolvida. Esta tese aborda o problema de localização de faltas de alta impedância em linhas de transmissão curtas. Propõese uma nova técnica de localização de faltas de alta impedância baseada na impedância aparente, desenvolvida no domínio da frequência e que utiliza componentes de fase. A estimativa da distância da falta é obtida a partir da solução de um sistema sobredeterminado de equações lineares, obtida pela aplicação do método de mínimos quadrados. A abordagem proposta permite estimar a distância de faltas de alta impedância momentâneas e permanentes, em linhas de transmissão curtas simples e paralelas, transpostas ou não. O desempenho da técnica de localização de faltas proposta é avaliado mediante estudos de casos simulados no Alternative Transients Program (ATP) considerando análises de sensibilidade e comparativa, bem como casos reais de faltas. Os resultados obtidos, considerando faltas de alta impedância simuladas e reais, indicam claramente que a abordagem proposta possui validade como técnica de localização de faltas em linhas de transmissão curtas em decorrência do desempenho demonstrado e, também, por características tais como: formulação simplificada no domínio da frequência, simplicidade e facilidade de implementação em dispositivos reais e aplicabilidade a casos reais. / Transmission lines are used to transmit electric power over long distances and are naturally exposed to severe weather conditions, especially overhead lines. Such conditions are highly favorable to the occurrence of faults. Statistics show that between 70% - 90% of faults on overhead lines are nonpermanent (or transient), and present arcing. Arcing is the main characteristic of a nonlinear high impedance fault and is the result of poor contact between an energized conductor and the ground or a grounded object. This thesis approaches the high impedance fault location on short transmission lines problem. It is proposed an impedancebased nonlinear high impedance fault location formulation developed in frequency domain and phase components. The formulation uses the least square method and synchronized phasors, measured by, for example, digital fault recorders installed at both line terminals. The proposed approach allows to estimate the distance of high impedance momentary and permanent faults on short transposed or untransposed transmission lines. The performance of the proposed fault location approach is evaluated through analysis of simulated cases in the Alternative Transients Program (ATP) considering sensitivity and comparative analyzes, and actual cases of high impedance faults. The results, considering simulations of high impedance faults and actual cases, indicate clearly that the proposed approach is valid as fault location technique in short transmission lines due to the demonstrated performance.