Noise-induced hearing loss (NIHL) is one of the most common illnesses that is frequently reported in the occupational and military sectors. Hearing loss due to high noise exposure is a major health problem with economic consequences. Industrial and military noise exposures often contain high-level impulsive noise components. The presence of these impulsive noise components complicates the assessment of noise levels for hearing conservation purposes. The current noise guidelines use equal energy hypothesis (EEH) based metrics to evaluate the risk of hearing loss. A number of studies show that the current noise metrics often underestimates the risk of hearing loss in high-level complex noise environments. The overarching goal of this dissertation is to develop advance signal processing based methods for more accurate assessments of the risk of NIHL. For these assessments, various auditory filters that take into account the physiological characteristics of the ear are used. These filters will help to understand the complexity of the ear’s response to high-level complex noises.

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Indiana University-Purdue University Indianapolis (IUPUI) / Voltage-gated sodium channels (VGSCs) are dynamic membrane spanning proteins which mediate the rapid influx of Na+ during the upstroke of the action potential (AP). In addition to the large inward Na+ currents responsible for the upstroke of the AP, some VGSC isoforms produce smaller, subthreshold Na+ currents, which can influence the excitable properties of neurons. An example of such a subthreshold current is resurgent Na+ current (INaR). These unusual currents are active during repolarization of the membrane potential, where the channel is normally refractory to activity. INaR exhibit slow gating kinetics and unusual voltage-dependence derived from a novel mechanism of channel inactivation which allows the channel to recover through an open configuration resulting in membrane depolarization early in the falling phase of the AP, ultra-fast re-priming of channels, and multiple AP spikes. Although originally identified in fast spiking central nervous system (CNS) neurons, INaR has recently been observed in a subpopulation of peripheral dorsal root ganglion (DRG) neurons. Because INaR is believed to contribute to spontaneous and high frequency firing of APs, I have hypothesized that increased INaR may contribute to ectopic AP firing associated with inherited and acquired disorders of excitability. Specifically, this dissertation explores the mechanisms which underlie the electrogenesis of INaR in DRG neurons and determines whether the biophysical properties of these unique currents were altered by mutations that cause inherited muscle and neuronal channelopathies or in an experimental model of nerve injury. The results demonstrate that (1) multiple Na+ channel isoforms are capable of producing INaR in DRG neurons, including NaV1.3, NaV1.6, and NaV1.7, (2) inherited muscle and neuronal channelopathIy mutations that slow the rate of channel inactivation increase INaR amplitude, (3) temperature sensitive INaR produced by select skeletal muscle channelopthy mutations may contribute to the triggering of cold-induced myotonia, and (4) INaR amplitude and distribution is significantly increased two weeks post contusive spinal cord injury (SCI). Taken together, results from this dissertation provide foundational knowledge of the properties and mechanism of INaR in DRG neurons and indicates that increased INaR likely contributes to the enhanced membrane excitability associated with multiple inherited and acquired disorders of excitability.

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This research uses Bayesian analysis of fluorescence spectroscopy results to determine if wastewater from the Heber Valley Special Service District (HVSSD) lagoons in Midway, UT has seeped into the adjacent Provo River. This flow cannot be directly measured, but it is possible to use fluorescence spectroscopy to determine if there is seepage into the river.Fluorescence spectroscopy results of water samples obtained from HVSSD lagoons and from upstream and downstream in the Provo River were used to conduct this statistical analysis. The fluorescence 'fingerprints' for the upstream and lagoon samples were used to deconvolute the two sources in a downstream sample in a manner similar to the tools and methods discussed in the literature and used for source apportionment of air pollutants. The Bayesian statistical method employed presents a novel way of conducting source apportionment and identifying the existence of pollution.This research demonstrates that coupling fluorescence spectroscopy with Bayesian statistical methods allows researchers to determine the degree to which a water source has been contaminated by a pollution source. This research has applications in determining the affect sanitary wastewater lagoons and other lagoons have on an adjacent river due to groundwater seepage. The method used can be applied in scenarios where direct collection of hydrogeologic data is not possible. This research demonstrates that the Bayesian chemical mass balance model presented is a viable method of performing source apportionment.

We tackle the problem of suppressing high-amplitude vibrations of cantilever beams when subjected to either primary external or principal parametric resonances. Guided by results of previous investigations into the nonlinear dynamics of single- and multi-degree-of-freedom structures, we design mechatronic systems of sensors, actuators, and electronic devices and implement nonlinear active feedback control. In the case of external excitation, we devise two vibration absorbers based on either quadratic or cubic feedback. We conduct theoretical analyses and demonstrate that when a two-to-one (one-to-one) internal resonance condition is imposed between the plant and the quadratic (cubic) absorber, there exists a saturation phenomenon. When the plant is forced near its resonant frequency and the forcing amplitude exceeds a certain small threshold, the nonlinear coupling creates an energy-transfer mechanism that limits (saturates) the response of the plant. Our theoretical studies reveal that the cubic absorber creates regimes of high-amplitude quasiperiodic and chaotic responses, thereby limiting its utility. However, we show that superior results can be achieved when the natural frequency of the quadratic absorber is set equal to one-half the excitation frequency. Consequently, we apply the quadratic technique through a variety of linear and nonlinear actuators, sensors, and electronic devices. We design and build second-order analog circuits that emulate the quadratic absorber. Using a DC motor, piezoelectric ceramics, and Terfenol-D struts as actuators and potentiometers, strain gages, and accelerometers as sensors, we demonstrate successful single- and multi-mode vibration control. In order to realize a more versatile implementation of the control strategy, we resort to a digital signal processing (DSP) board. We compose a code in C and design a digital absorber by developing algorithms that, in addition to replacing the analog circuit, automatically detect the amplitude and frequency of oscillation of the plant and fine-tune the absorber parameters. We take advantage of the digital realization, implement a linear absorber, and compare the performance of the quadratic absorber with that of its linear counterpart. In the case of parametric excitation, we investigate two techniques. First, we explore application of the quadratic absorber. We prove theoretically and demonstrate experimentally that this control scheme is not reliable. Then, we propose an alternate approach. We devise a control law based on cubic velocity feedback. We conduct theoretical and experimental investigations and show that the latter strategy leads to effective vibration suppression and bifurcation control. / Ph. D.

No / Organic matter (OM) causes many problems in drinking water treatment. It is difficult to monitor OM concentrations and character during treatment processes due to its complexity. Fluorescence spectroscopy is a promising tool for online monitoring. In this study, a unique dataset of fluorescence excitation emission matrixes (EEMs) (n = 867) was collected from all treatment stages of five drinking water treatment plants (WTPs) situated in diverse locations from subtropical to temperate climate. The WTPs incorporated various water sources, treatment processes and OM removal efficiencies (DOC removal 0%–68%). Despite these differences, four common fluorescence PARAFAC components were identified for characterisation of OM concentration and treatability. Moreover, fluorescence component ratios showed site-specific statistically significant correlations with OM removal, which contrasted with correlations between specific UV absorbance at 254 nm (SUVA) and OM removal that were not statistically significant. This indicates that use of fluorescence spectroscopy may be a more robust alternative for predicting DOC removal than UV spectroscopy. Based on the identified fluorescence components, four optical locations were selected in order to move towards single wavelength online OM monitoring.

In this dissertation, we present analytical and experimental investigations of the electrically actuated micro resonators, when using multi-frequency and/or multi-mode excitation, combined with partial electrodes. We aim to understand their interesting frequency performance and use it to improve the sensing and actuation in microelectromechanical systems (MEMS) and explore their potential applications, such as amplification, gas sensing, magnetometer, multi-physical sensors, and digital-to-analog converters. In the first part, we propose a method of the multi-mode excitation (MME). The concept of the multi-mode excitation is demonstrated by utilizing the superposition principle of two vibration modes in the same phase. To fully understand the difference between the single source excitation (SSE) and multi-mode excitation, we derive the dynamic equations of motions of the electrically-actuated micro cantilever beam and clamped-clamped beam actuated by single/multi-mode excitation. Then, we analytically solve the equations based on the procedure of the Galerkin method with five modes. The simulated results indicate that the MME is clearly superior to that of the SSE, as it can amplify the amplitude performance and signal-to-noise ratio of micro resonators. In the second part, we aim to experimentally prove the concept of the multi-mode excitation and explore its use for gas sensing applications. First, we experimentally investigate the performance of MEMS resonators by single source excitation and multi-mode excitation. We prove the feasibility of the MME approach in enhancing the higher-order mode response for both cantilever and clamped-clamped beams, respectively. We prove that the multi-mode excitation approach provides a better way to activate the higher-order modes with an improved amplitude under a small actuation compared to using a single-source excitation. We then show an improved performance for gas detection. In the third and fourth parts, we propose a technique based on multi-mode excitation for simultaneous sensing for two physical parameters: magnetic field and gas concentration. We respectively investigate a single out-of-plane/in-plane device for in-plane/out-of-plane magnetic field and gas concentration sensing based on tracking the first two vibration modes of a heated buckled micro-beam. We found that operating the resonator at the post-buckling regime, the magnetometer is gas-independent since the first antisymmetric mode (f2) is unaffected by the thermal axial load. Based on it, we utilized the first resonance frequency f1 to detect the gas based on the cooling/heating effects while the second resonance frequency f2 to sense the in-plane/out-of-plane magnetic field. The obtained results demonstrated the sensor acts as a magnetometer and gas sensor, showing good sensitivity, linearity and repeatability. Thus, this technique provides a good candidate for multi-environment monitoring applications. In the last part, we aim to investigate the effects of partial electrodes actuation on the micro resonator and explore its application on the digital-to-analog converter. We analytically and experimentally present modeling, investigation, validation, and optimization of the MEMS resonator-based 3-bit digital to analog converter (DAC) consisting of an in-plane clamped-clamped beam actuated by partial electrodes with different air gaps. The results suggest that the proposed modeling, simulations, and optimization analysis could be successfully implemented in the design of the DAC under various digital combinations. The rich nonlinear behavior with low energy consumption could provide some high potential applications in IoT, such as logic, computation, sensing, and actuation.