In this study the exposure of mining vehicle operators, on an opencast goldmine in Tanzania, to certain hazards specific to their occupation was assessed. The aim was to quantify these levels of exposure in order to estimate the risk of health effects but also to report levels of these hazards that exist on mining vehicles. Three different hazards with different physiological effects were assessed and it included exposure to whole-body vibration, A-weighted noise and low frequency noise. In each case correctly calibrated instrumentation was used and internationally accepted methods were followed. It was found that mining vehicles commonly exposed operators to levels of whole-body vibration within and above the ISO Health Guidance Caution Zone (HGCZ) and above the ropean action level, which indicates the need for intervention and control. These levels are a cause for concern and will likely lead to health effects. Noise that damages human hearing (A-weighted noise) was present in high levels on mining vehicles, in each case being higher than the permissible exposure limit of 85 dB(A). Thus operators of mining vehicles are exposed to noise levels that will damage their hearing in time. A potential hazard in the occupational world, low frequency noise, was also included in the assessment. Literature indicates that low frequency noise is capable of causing many human health effects and thus levels on mining vehicles were reported in order to give an indication of what levels may be expected in this department of mining. It was found that much of the sound energy measured on vehicles was located in the low frequency range. In the lowest frequency band measured, Leq levels of more than 100 dB(Z) were commonly found. Controls should be implemented as far as is reasonably practicable to ensure that operators are not exposed above recommended or permissible levels for each hazard. These controls can include good maintenance of vehicles and roads to reduce whole-body vibration, sound proofing of vehicle cabs along with hearing protection devices to protect hearing and further research regarding the exposure and health effects caused by low frequency noise. Following literature indicating the physiological effects of low frequency noise exposure and also the presence thereof in different occupations, it is concluded that A-weighted noise measurements alone can not be used when quantifying the risk involved in a given acoustical environment. / Thesis (M.Sc. (Occupational Hygiene))--North-West University, Potchefstroom Campus, 2009

Vibration energy harvesting devices have been widely used to power many electronic self-sustainable devices. The aim of this study is to introduce an alternative design to an existing electromagnetic energy harvesting devices to improve the power production of the unit. This thesis presents a multiple degree of freedom compared design and it has demonstrated higher power efficiency over a wider range of frequencies. The power outputs for both the previous single degree of freedom and the current designs are compared and the developed models are validated against their experimental values. Finally, the numerical model is used to find an optimal arrangement to produce the maximum power for the unit.

Η αναπαραγωγή χαμηλών συχνοτήτων γίνεται διαμέσου ηχείων μεγάλου όγκου και μεγαφώνων μεγάλης διαμέτρου κώνου και μεγάλης μαγνητικής επαγωγής. Είναι δυνατός ο διαχωρισμός του φάσματος χαμηλών συχνοτήτων σε τρεις περιοχές και η αναπαραγωγή της κάθε περιοχής από ξεχωριστό ηχείο. Λογω της χαμηλής ανάλυσης του ανθρωπίνου συστήματος ακοής στις χαμηλές συχνότητες, η ανακατασκευή του φάσματος χαμηλών συχνοτήτων από τα τρία ηχεία δεν είναι απαραίτητο να είναι επίπεδη. Έτσι το κάθε ηχείο περιλαμβάνει ειδικό μεγάφωνο το οποίο αναπαράγει σε υψηλή στάθμη κοντά στη συχνότητα συντονισμού του. Το μεγάφωνο αυτό μπορεί να έχει μικρή διάμετρο και μικρή μαγνητική επαγωγή που σημαίνει μικρών διαστάσεων μαγνήτη και μπορεί να εγκατασταθεί σε καμπίνα μικρού όγκου. Έτσι το φάσμα χαμηλών συχνοτήτων αναπαράγεται από σύστημα μειωμένων διαστάσεων σε σχέση με το συνηθισμένο και με υψηλότερη απόδοση. Η σχεδίαση και η κατασκευή ενός τέτοιου συστήματος αναπαραγωγής χαμηλών συχνοτήτων είναι το αντικείμενο της παρούσας εργασίας. / Low frequency reproduction can be done through large dimention loudspeakers and big magnetic force. Low frequency spectrum can be divided into three small regions and each one can be reproducted via independent loudspeakers. Because of the low resolution of the human auditory system in such frequencies, it's not necessary for the frequency response to be flat. Each speaker has a specially designed loudspeaker with high sensitivity at the resonance frequency. The resulted speaker will have small dimentions. The final system will have smaller overall dimentions compared to the usual basswoofers. The design and construction of such a system is the sybject of the thesis.

In this thesis I combine data from 29 volcanic earthquake swarms that follow the pattern predicted by the Generic Volcanic Earthquake Swarm Model (GVESM; Benoit and McNutt, 1996) to investigate whether the relative timing of various parameters of pre-eruptive volcanic earthquake swarms could be used to forecast the time of an impending eruption. Based on the analysis of seismic unrest preceding many eruptions, the GVESM suggests that it is common to see an increase first in high-frequency earthquakes, then low-frequency earthquakes, then the onset of volcanic tremor. While this pattern is useful to volcano-seismologists, the relative timing and durations of these three different types of volcanic seismicity, is explored here for the first time. The parameters investigated are the onset times of (i) low-frequency (LF) events and of (ii) tremor, and the time at which (iii) the peak rate (PR) of volcano-tectonic (VT) events and (iv) the maximum magnitude (MM) earthquake occur in relation to normalized time defined by swarm onset and end (i.e., eruption). The normalized time starts at the swarm onset (0%) and ends with the eruption (100%) allowing a comparison and joint consideration of parameter occurrences across swarms of different actual duration. We identify the normalized onset time of for each parameter (LF, tremor, PR, MM) with respect to the duration of each swarm. Each swarm has onset time uncertainties of the swarm itself and of its parameters. A swarm with large onset uncertainty could bias the normalized onset time of each parameter and we use weighted means to decrease the influence of swarms with large uncertainties on overall results. The weighted means of LF onset, tremor onset, MM and PR occurrence are 79% ± 23%, 96% ± 10%, 78% ± 29% and 75% ± 34%, respectively. Errors are the standard deviation of each parameter. The uncertainties for LF, MM and PR are large because their normalized onset times have the characteristics of a uniform distribution and therefore seem to have no predictive value. In contrast, tremor onset has a narrow distribution towards the end of swarms. A possible tremor mechanism consistent with this observation could be boiling of groundwater as magma nears the surface. LF onset always seems to precede tremor onset. LF and tremor start early (at less than 80% of normalized time) at five volcanoes with high SiO2 content possibly related to lower density and higher gas content of the resulting magma.

The standard electrical stimulation waveform used for electrical activation of nerve is a rectangular pulse or a charge balanced rectangular pulse, where the pulse width is typically in the range of ∼100 µsec through ∼1000 µsec. In this work, we explore the effects of a continuous sinusoidal waveform with a frequency ranging from 5 through 20 Hz, which was named the Low Frequency Alternating Current (LFAC) waveform. The LFAC waveform was explored in the Bioelectronics Laboratory as a novel means to evoke nerve block. However, in an attempt to evoke complete nerve block on a somatic motor nerve, increasing the amplitude of the LFAC waveform unexpectedly produced nerve activation, and elicited a strong non-fatiguing muscle contraction in the anesthetized rabbit model (unpublished observation). The present thesis aimed to further explore the phenomenon to measure the effect of LFAC waveform frequency and amplitude on nerve activation.<div><br></div><div>In freshly excised canine cervical vagus nerve (n=3), it was found that the LFAC waveform at 5, 10, and 20 Hz produced burst modulated activity. Compound action potentials (CAP) synchronous to the stimuli was absent from the electroneurogram (ENG) recordings. When applied <i>in-vivo</i>, LFAC was capable of activating the cervical vagus nerve fibers in anaesthetized swine (n=5) and induced the Hering-Breuer reflex. Additionally, when applied <i>in-vivo</i> to anesthetized Sprague Dawley rats (n=4), the LFAC waveform was able to activate the left sciatic nerve fibers and induced muscle contractions.</div><div><br></div><div>The results demonstrate that LFAC activation was stochastic, and asynchronous to the stimuli unlike conventional pulse stimulation where nerve and muscle response simultaneously and synchronously to stimulus. The activation thresholds were found to be frequency dependent. As the waveform frequency increases the required current amplitude decreases. These experiments also implied that the LFAC phenomenon was most likely to be fiber type-size dependent but that more sophisticated exploration should be addressed before reaching clinical applications. In all settings, the LFAC amplitude was within the water window preventing irreversible electrochemical reactions and damages to the cuff electrodes or nerve tissues. This thesis also reconfirms the preliminary LFAC activation discovery and explores multiple methods to evaluate the experimental observations, which suggest the feasibility of the LFAC waveform at 5, 10, and 20 Hz to activate autonomic and somatic nerve fibers. LFAC appears to be a promising new technique to activate peripheral nerve fibers.</div>

A long-standing controversy concerning the pros and cons of Vll selective amplification for the sensorineural hypacusic has been and is now being waged. There exists clinical evidence to the effect that some cases with high -frequency sensorineural hearing loss can receive benefit through selective amplification. The purpose of this study was to examine several aspects of the speech signal that could be affecting intelligibility when speech is presented at high -intensity levels.

Indiana University-Purdue University Indianapolis (IUPUI) / The standard electrical stimulation waveform used for electrical activation of nerve is a rectangular pulse or a charge balanced rectangular pulse, where the pulse width is typically in the range of ∼100 µsec through ∼1000 µsec. In this work, we explore the effects of a continuous sinusoidal waveform with a frequency ranging from 5 through 20 Hz, which was named the Low Frequency Alternating Current (LFAC) waveform. The LFAC waveform was explored in the Bioelectronics Laboratory as a novel means to evoke nerve block. However, in an attempt to evoke complete nerve block on a somatic motor nerve, increasing the amplitude of the LFAC waveform unexpectedly produced nerve activation, and elicited a strong non-fatiguing muscle contraction in the anesthetized rabbit model (unpublished observation). The present thesis aimed to further explore the phenomenon to measure the effect of LFAC waveform frequency and amplitude on nerve activation. In freshly excised canine cervical vagus nerve (n=3), it was found that the LFAC waveform at 5, 10, and 20 Hz produced burst modulated activity. Compound action potentials (CAP) synchronous to the stimuli was absent from the electroneurogram (ENG) recordings. When applied in-vivo, LFAC was capable of activating the cervical vagus nerve fibers in anaesthetized swine (n=5) and induced the Hering-Breuer reflex. Additionally, when applied in-vivo to anesthetized Sprague Dawley rats (n=4), the LFAC waveform was able to activate the left sciatic nerve fibers and induced muscle contractions. The results demonstrate that LFAC activation was stochastic, and asynchronous to the stimuli unlike conventional pulse stimulation where nerve and muscle response simultaneously and synchronously to stimulus. The activation thresholds were found to be frequency dependent. As the waveform frequency increases the required current amplitude decreases. These experiments also implied that the LFAC phenomenon was most likely to be fiber type-size dependent but that more sophisticated exploration should be addressed before reaching clinical applications. In all settings, the LFAC amplitude was within the water window preventing irreversible electrochemical reactions and damages to the cuff electrodes or nerve tissues. This thesis also reconfirms the preliminary LFAC activation discovery and explores multiple methods to evaluate the experimental observations, which suggest the feasibility of the LFAC waveform at 5, 10, and 20 Hz to activate autonomic and somatic nerve fibers. LFAC appears to be a promising new technique to activate peripheral nerve fibers.

Lightning strokes create powerful electromagnetic pulses that routinely cause very low frequency (VLF) waves to propagate across hemispheres along geomagnetic field lines. VLF antenna receivers can be used to detect these whistler waves generated by these lightning strokes. The particular time/frequency dependence of the received whistler wave enables the estimation of electron density in the plasmasphere region of the magnetosphere. Therefore the identification and characterisation of whistlers are important tasks to monitor the plasmasphere in real time and to build large databases of events to be used for statistical studies. The current state of the art in detecting whistler is the Automatic Whistler Detection (AWD) method developed by Lichtenberger (2009) [1]. This method is based on image correlation in 2 dimensions and requires significant computing hardware situated at the VLF receiver antennas (e.g. in Antarctica). The aim of this work is to develop a machine learning based model capable of automatically detecting whistlers in the data provided by the VLF receivers. The approach is to use a combination of image classification and localisation on the spectrogram data generated by the VLF receivers to identify and localise each whistler. The data at hand has around 2300 events identified by AWD at SANAE and Marion and will be used as training, validation, and testing data. Three detector designs have been proposed. The first one using a similar method to AWD, the second using image classification on regions of interest extracted from a spectrogram, and the last one using YOLO, the current state of the art in object detection. It has been shown that these detectors can achieve a misdetection and false alarm rate, respectively, of less than 15% on Marion's dataset. It is important to note that the ground truth (initial whistler label) for data used in this study was generated using AWD. Moreover, SANAE IV data was small and did not provide much content in the study.

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