Electric and magnetic fields in the vicinity of strong sources of radiation (e.g. radar and broadcasting) can exceed the limits mentioned in the national standards for the exposition of persons. Field probes are needed to warn personnel if they are going too close to the RF-sources. For acceptance reasons the field probes should be universal in such a way that no user adjustment of frequency is required. The limits for power density, electric and magnetic field strength depend on the frequency. In contrast, field probes covering a large frequency range, e.g. 1 MHz to 18 GHz or even larger, normally have a flat frequency response. Therefore, the person using the field probe has to know the frequency of the electromagnetic field and to evaluate fieldstrength with respect to the frequency dependent limit value defined by law. Human mistakes while making that evaluation can lead to expositions above the limit value. On the other hand, the evaluation of the power density in the presence of multiple strong sources of radiation at different frequencies with different limit values also leads to measurement problems. A new approach has been undertaken to overcome these difficulties in the development of a rectifying field probe. It consists in shaping the antenna factor of the probe inversely proportional to the limit value. The isotropic response of field probes can be achieved, if three dipole antennas are arranged perpendicular to each other. The presence of dielectric supporting material leads to degradation of the isotropic response of such a field probe. The effect will be investigated. For typical substrates the isotropic response is degraded by up to 3.8 dB. An compensation for this effect will be proposed that leads to a residual unisotropic response of less than 0.2 dB.

La récupération optimale des amplitudes articulaires (AAs) et de la force musculaire est un objectif crucial de la réadaptation fonctionnelle intensive (RFI) à la suite d’une lésion médullaire (LM). Le but de la présente étude était de documenter les changements d’AAs des membres supérieurs durant la RFI chez des individus (n = 197) ayant subi une LM et d’établir le lien avec l’autonomie fonctionnelle. Les données (AA, force musculaire, spasticité, déficiences secondaires, autonomie fonctionnelle) ont été collectées à l’admission et au congé de la RFI. Des analyses descriptives, des tests d’association entre les changements d’AAs et des variables indépendantes (douleur, spasticité, déficiences secondaires, force) et des analyses multivariées ont été utilisées. Les individus ayant une paraplégie présentent peu de déficit d’AAs à l’épaule comparés à ceux ayant une tétraplégie. Parmi ces derniers, une majorité présente des AAs sous les valeurs de normalité en fin de RFI. Le groupe D, établi selon l’évaluation de l’American Spinal Injury Association (ASIA D) présente des pertes d’AAs plus importante qu’attendue. La douleur au niveau articulaire est un facteur influençant les changements d’AAs, particulièrement dans ce groupe. La force musculaire chez les personnes ayant une tétraplégie sévère (ASIA ABC) est plus faible que celle du groupe ayant une lésion moins sévère (ASIA D). Généralement, le gain de force corrèle avec le gain d’AA. La force musculaire, les AAs et le nombre de déficiences secondaires sont les principaux éléments influençant l’autonomie fonctionnelle. En conclusion, la perte d’AA est plus importante à l’articulation de l’épaule et, pour plusieurs individus, malgré un gain significatif, les AAs n’atteignent pas les valeurs de référence au congé de la RFI. La force musculaire et certaines déficiences secondaires sont des éléments à considérer pour expliquer les pertes d’AAs et d’autonomie fonctionnelle. Les études futures devront clarifier certains aspects dont l’atteinte de la rotation médiale qui semble montrer un patron différent de récupération en comparaison des autres mouvements de l’épaule. De plus, les études devront montrer si ces changements et résultats sont maintenus après le congé de la RFI. / Optimal recovery of range of motion (ROM) and strength are critical objectives of intensive rehabilitation following spinal cord injury (SCI). The aim of this study was to characterize the evolution of ROM and strength at the upper limb and analyze their relationship with functional independence during intensive rehabilitation. Data ROM, strength, spasticity, secondary impairments, functional independence) from 197 participants with SCI were collected at admission and discharge from intensive rehabilitation and were analyzed with descriptive statistics and multivariate analyses (regressions, ANOVA). Specific association analyses were used to determine the level of association between ROM, strength and independent variables such as pain, spasticity and secondary impairments. Lesser deficit in ROM was observed in participants with paraplegia compared to those with tetraplegia. The deficit in individuals with tetraplegia was larger to an extent that most of them did not reach normality in ROM at shoulder joint. Surprisingly, individuals with less severe injury according to the American Spinal Injury Association classification (ASIA D) showed larger deficit of ROM than expected. Joint pain was related to reduce ROM, particularly in participants with ASIA D lesion. Values of muscle strength in individuals with more severe tetraplegia (ASIA ABC) are lower than the ones observed in individuals with less severe injury (ASIA D). Overall, strength and ROM were correlated, except for medial rotation movement. ROM, strength, and secondary impairments are the major determinants of functional independence. In conclusion, shoulder joint was the most affected joint of the upper limb, and, despite of significant gains of ROM, abnormalities were greater than expected. Strength and some secondary impairment were related in loss of ROM and functional independence throughout rehabilitation. More study will be needed to understand the medial rotation movement at the shoulder that seems to evolve differently from other movements, and to determine whether or not changes observed during rehabilitation are maintained over time.

Dopamine agonist therapy and deep brain stimulation (DBS) are both linked to increased impulsivity in Parkinson’s disease (PD), but the underlying mechanisms remain unclear. We trained intact and PD-like rats on a rat gambling task (rGT) measuring impulsive choice and premature responding. Animals were then retested with/without treatment, pramipexole (PPX) or DBS, administered chronically prior to rGT testing. Early PD-like rats did not exhibit major differences in rGT performance or treatment response. Our work suggests that DBS and PPX are not intrinsically linked with increases in impulsivity. Neither DBS nor PPX disrupted gambling-like behaviour in our paradigm, while differential effects on premature and perseverant responding in the task were observed with treatment. Based on our findings, the previously reported ability of PPX to increase impulsive choice might not be mediated by the dopamine D3 receptor. Interestingly, our work suggests that the effects of STN-DBS on impulse control might be amplitude-dependent.

Dopamine agonist therapy and deep brain stimulation (DBS) are both linked to increased impulsivity in Parkinson’s disease (PD), but the underlying mechanisms remain unclear. We trained intact and PD-like rats on a rat gambling task (rGT) measuring impulsive choice and premature responding. Animals were then retested with/without treatment, pramipexole (PPX) or DBS, administered chronically prior to rGT testing. Early PD-like rats did not exhibit major differences in rGT performance or treatment response. Our work suggests that DBS and PPX are not intrinsically linked with increases in impulsivity. Neither DBS nor PPX disrupted gambling-like behaviour in our paradigm, while differential effects on premature and perseverant responding in the task were observed with treatment. Based on our findings, the previously reported ability of PPX to increase impulsive choice might not be mediated by the dopamine D3 receptor. Interestingly, our work suggests that the effects of STN-DBS on impulse control might be amplitude-dependent.

This thesis addresses two fundamental topics in Engineering Seismology; the application of Probabilistic Seismic Hazard Analysis (PSHA) methodology, and the estimation of measures of Strong Ground Motion. These two topics, while being related, are presented as separate sections. In the first section, state-of-the-art PSHA methodologies are applied to various sites in the Buller Region, South Island, New Zealand. These sites are deemed critical to the maintenance of economic stability in the region. A fault-source based seismicity model is developed for the region that is consistent with the governing tectonic loading, and seismic moment release of the region. In attempting to ensure this consistency the apparent anomaly between the rates of activity dictated by deformation throughout the Quaternary, and rates of activity dictated by observed seismicity is addressed. Individual fault source activity is determined following the application of a Bayesian Inference procedure in which observed earthquake events are attributed to causative faults in the study region. The activity of fault sources, in general, is assumed to be governed by bounded power law behaviour. An exception is made for the Alpine Fault which is modelled as a purely characteristic source. The calculation of rates of exceedance of various ground motion indices is made using a combination of Poissonian and time-dependent earthquake occurrence models. The various ground motion indices for which rates of exceedance are determined include peak ground acceleration, ordinates of 5% damped Spectral Acceleration, and Arias Intensity. The total hazard determined for each of these ground motion measures is decomposed using a four dimensional disaggregation procedure. From this disaggregation procedure, design earthquake scenarios are specified for the sites that are considered. The second part of the thesis is concerned with the estimation of ground motion measures that are more informative than the existing scalar measures that are available for use in New Zealand. Models are developed for the prediction of Fourier Amplitude Spectra (FAS) as well as Arias Intensity for use in the New Zealand environment. The FAS model can be used to generate ground motion time histories for use in structural and geotechnical analyses. Arias Intensity has been shown to be an important strong motion measure due to its positive correlation with damage in short period structures as well as its utility in predicting the onset of liquefaction and landslides. The models are based upon the analysis of a dataset of New Zealand Strong Motion records as well as supplementary near field records from major overseas events. While the two measures of ground motion intensity are strongly related, different methods have been adopted in order to develop the models. As part of the methodology used for the FAS model, Monte Carlo simulation coupled with a simple ray tracing procedure is employed to estimate source spectra from various New Zealand earthquakes and, consequently, a magnitude - corner-frequency relationship is obtained. In general, the parameters of the predictive equations are determined using the most state-of-the-art mixed effects regression procedures.

This research focuses on developing sensors for properties of aerodynamic interest (i.e., flow and pressure) based on low-cost polymeric materials and simple fabrication processes. Such sensors can be fabricated in large arrays, covering the surface of airfoils typically used in unmanned vehicles, allowing for the detection of flow separation. This in turn potentially enables, through the use of closed-loop control, an expansion of the flight envelope of these vehicles. A key advance is compensation for the typically inferior performance of these low cost materials through both careful design as well as new readout methods that reduce drift, namely a readout methodology based on aeroelastic flutter. An all-polymer micromachined piezoresistive flow sensor is fabricated, based on a flexible polyimide substrate and an elastomeric piezoresistive composite material. The flow sensor comprises a cantilever that is extended into the embedding flow; flow-induced stress on the cantilever is sensed through the piezoresistive composite material. Increasing the sensitivity of the sensor is achieved by either utilizing a long single-cantilever beam or using a dual-cantilever beam supporting a flap extending into the flow. In the latter case, the sensor demonstrates increased sensitivity with a reduced cantilever length. The increase in sensitivity helps to reduce sensor drift, which in turn is further reduced by a new measurement method, the vibration amplitude measurement method. In this drift reduction measurement method, the flow-induced vibration amplitude of the sensor structure (i.e., the amplitude of the aeroelastic flutter induced by the flow), instead of the absolute value of cantilever deflection, is measured in order to find the flow rate. Measurement of this relative resistance change instead of the absolute resistance in the piezoresistor rejects common-mode drift and greatly reduces overall drift. Experimental results verify the expected drift reduction. Sensor drift is also reduced when the elastomeric piezoresistive material is replaced by a Pt thin film piezoresistor. Development of pressure sensors based on polymers proceeds by encapsulating a reference cavity within a multilayer polymer structure and forming capacitor plates on the polymeric membranes encapsulating the cavity. Measuring the capacitance change induced by changes in the embedding pressure (which cause changes in the positions of the bounding polymeric membranes) enables calculation of the pressure. The use of polymeric membranes requires understanding the leakage rate of gas into the reference cavity, which is a source of pressure drift. Developing a polymer-based pressure sensor that solves the problem of sensor drift as a result of gas permeation entails the fabrication of a silicon pressure reference cavity embedded in the polymer substrate, which results in a more hermetic and lower drift sensor while preserving the flexibility of the embedding polymer. Both wired and wireless versions of pressure and flow sensors of these types were developed and characterized. Further, the sensors were characterized on airfoils and their performance in a wind tunnel was determined.

Le futur système de transmission multicanaux (WDM) pourrait mettre à profit l'utilisation d'amplificateurs optiques à semi-conducteurs (SOA), pour bénéficier notamment de leur grande bande passante optique pour l'amplification du signal. Dans ce travail, nous étudions l'influence des SOA sur la transmission cohérente de signaux OFDM optiques (CO OFDM). Cette technique, récemment proposée, permet à la fois d'augmenter l'efficacité spectrale de la transmission et de compenser les imperfections linéaires du canal optique. Nous avons développé, dans ce travail, une chaîne expérimentale de transmission de signaux à formats de modulation complexes tout-optiques et une plateforme de simulation au niveau système. Les résultats obtenus par simulation, au niveau composant et au niveau système, sont en très bon accord avec ceux obtenus par les mesures expérimentales à la fois pour des formats de modulation QPSK et QPSK CO-OFDM. À travers différentes mesures et simulations, l'étude a permis de cerner clairement l'influence des paramètres du SOA sur la qualité de transmission des données. Les non-linéarités induites par le SOA, telles que le couplage phase amplitude, l'auto modulation du gain et de la phase (SGM et SPM), la modulation croisée du gain et de la phase (XGM et XPM) et le mélange à quatre ondes (FWM), jouent de façon importante sur les performances de ce format de modulation multi-porteuses ; leur influence a donc été analysée avec précision. Les connaissances acquises permettront à l'avenir d'une part de mieux définir les conditions d'utilisation des SOA dans les réseaux de transmission et d'autre part aideront à l'optimisation de nouvelles structures de SOA conçues pour la transmission de données à très haut débit utilisant des formats de modulation complexes.

Cette thèse propose une nouvelle méthode pour modéliser les fonctions non linéaires de modulation d'amplitude et de fréquence de signaux multicomposantes non stationnaires de durée longue. La méthode repose sur une décomposition du signal en segments courts pour une modélisation locale sur les segments. Pour initialiser la modélisation, nous avons conçu une première étape qui peut être considérée comme un estimateur indépendant et non paramétrique des fonctions de modulation. L'originalité de l'approche réside dans la définition d'une matrice de convergence totale intégrant simultanément les valeurs d'amplitude et de fréquence et utilisé pour l'association d'un pic à une composante selon un critère d'acceptation stochastique. Suite à cette initialisation, la méthode estime les fonctions de modulation par enchainement des étapes de segmentation, modélisation et fusion. Les fonctions de modulation estimées localement par maximum de vraisemblance sont connectées dans l'étape de fusion, qui supprime les discontinuités, et produit l'estimation globale sur la durée totale du signal. Les étapes sont conçues afin de pouvoir modéliser des signaux multicomposantes avec des morts et naissances, ce qui en fait une de ses originalités par rapport aux techniques existantes. Les résultats sur des signaux réels et simulés ont illustré les bonnes performances et l'adaptabilité de la méthode proposée.

The structure and dynamics of the smectic-A liquid crystal 8CB (4 cyano-4 octylbiphenyl) when sheared and confined to mesoscale gaps (with crossed cylindrical geometry and mica confining surfaces) were studied using a Surface Forces Apparatus (SFA). Triangular shear patterns with frequencies of 0.01, 0.1, 1.0 and 10 Hz, and amplitudes of 62.5 nm, 625 nm and 6.25 m were applied to samples at gap sizes of 0.5 and 5.0 m. The study was performed at room temperature (20.5C) and at two higher temperatures (22C and 27C). In order to minimize the thermal fluctuations within the test chamber and hence to allow for the rapid re-initialization of test runs, the SFA was modified to allow for quick, precise and remote control of the confining surfaces. The procedure maximized the number of tests that could be undertaken with a single pair of surfaces so that a single gap geometry could be maintained for the duration of the test run. In order to run the SFA remotely, scripts written with a commercial software package, LabVIEW, were used to control of the SFA components, its FECO-monitoring camera and all its peripheral electronic equipment as well. Samples were agitated to disrupt any shear-induced liquid crystal domain alignment from previous testing following each shear test, and methodologies were developed to ascertain the extent of confinement quickly and remotely following agitation. Separate methods were developed for gap sizes at each extreme of the mesoscale regime, where the transition from bulklike structure and dynamics to nano-confinement occurs (between 1 and 10 microns for smectic-A 8CB). The results revealed that the greater amplitude-gap aspect ratio and surface-to-domain contact associated with smaller gaps facilitated reorientation of the domains in the shear direction. Evidence was also presented of domains at the higher end or outside of the mesoscale regime that, while straining and accreting, were unable to reorient and thereby led to an overall increase of viscoelastic response. The effective viscosity was found to obey a simple power law with respect to shear rate, , and the flow behaviour indices, n, slightly in excess of unity indicate shear thickening occurs with large enough shear amplitude, and that the viscosity reached a plateau near unity over shear rates of 0.005 to 500 s-1 within the mesoscale regime. Different K and n values were observed depending on the shear amplitude used. Unlike bulk smectic 8CB, whose domains do not align well in the shear direction with large shear-strain amplitude, at mesoscale levels of confinement large amplitude shearing (up to 12.5 shear strain amplitude) was found to be very effective at aligning domains. In general domain reorientation is found to be much more rapid within the mesoscale regime than has been reported in bulk. Aggressive shearing was found to result in a complete drop in viscoelastic response within seconds, while gentler shearing is found to produce a very gradual increase that persists for more than six hours, with individual shear periods exhibiting frequent and significant deviations from the expected smooth shear path that may be a product of discrete domain reorientations. From these findings, certain traits of the smectic 8CB domain structures under mesoscale confinement were deduced, including how they respond to shear depending on the level of confinement, and how their reorientation due to shear varies not only with shear rate but also independently with shear amplitude. An equation describing the viscosity change as a function of both shear rate and shear amplitude is proposed. The shear amplitude dependence introduces the notion of shearing beyond the proposed smectic 8CB “viscoelastic limit”, which was shown to exhibit behaviour in accordance with Large Amplitude Oscillatory Shear (LAOS) techniques developed for Fourier Transform rheology. The findings provided an understanding of the behavioural changes that occur as one reduces the level of confinement of smectic materials from bulk to nanoconfinement.

Optical frequency standards are necessary tools for accurate measurement of time and length. In practice these standards are stabilised laser systems locked to a known frequency reference. These references are typically the resonant frequencies of the atoms of an absorption medium that have been theoretically calculated to a high degree of accuracy. This thesis describes a combination of experimental and theoretical research performed on modulation transfer spectroscopy (MTS)--a technique used to frequency stabilise a laser in order to produce an accurate frequency reference--with emphasis placed on developing techniques and procedures to overcome the limitations found in existing MTS stabilised laser systems. The focus of the thesis is to generate a highly accurate frequency reference by researching the system parameters that will increase the signal to noise ratio and improve the accuracy of the reference through refinement of the signal structure. The early theoretical interpretation of MTS was effectively a low absorption approximation that occurs at low pressures. This approximation ignores the depletion of beam energy through absorption and is a distinct limitation of the theoretical model in its ability to accurately predict the influence of a range of system parameters on signal strength and structure. To overcome this limitation a 3-D (or volumetric) analysis was developed and is presented here for the first time. This volumetric model is a measure of two depleted beams interacting collinearly in an absorbing medium of iodine and is described to accurately predict the signal maximum as a function of pressure for all wavelengths. This model was found to be more accurate in predicting the influence of system parameters on the signal strength and structure, including that of pump beam intensity, pressure, saturation parameter, cell length and modulation parameters. The volumetric model is a novel approach to MTS theory but is more complex computationally than the traditional low pressure model and therefore more difficult to implement in many situations. To overcome this problem a hybrid model was developed as a combination of the low pressure and volumetric models. The comparison between the rigorous volume model and the hybrid model indicate that there is a deviation in the signal strength at high pressures. However, the agreement was very good in the pressure regimes that are commonly used to realise actual frequency references. Comparison of the hybrid model to experimental data was performed over a range of different wavelengths (532 nm, 543.5 nm, 612 nm and 633 nm) and found to be in close agreement. This gives confidence in the model to accurately predict signal strength and structure in any situation. Three mechanisms have been identified that limit the accuracy of frequency references due to the creation of residual amplitude modulation (RAM) where it shifts the frequency of the reference. The influence of RAM is included in the hybrid model as a ratio of the amplitude modulated and frequency modulated components of the saturating beam. These RAM production mechanisms result from the modulation of the saturating beam, the overlap of the beams in the medium, and the differential absorption of the sidebands in the medium. While the first mechanism has been previously reported the latter two are discussed here in detail for the first time. RAM generated by the modulators used (acousto-optic or electro-optic modulators) was typically of the order of 10% to 12%, depending on the excursion of the created sidebands. RAM generated by an asymmetric beam overlap with the modulators used was found to be as large as 30%. A combination of these two independent mechanisms can be used to provide a "RAM-free" state of the system by using one to cancel the effects of the other. The third RAM generation process--medium induced RAM--is difficult to remove but through a careful combination of absorption related parameters--namely, pump intensity, cell length, pressure and detector phase--the effects of RAM can be removed, leading to a distortion free MTS signal. Further investigation into the predictions provided by the hybrid model shows that there is a complex relationship between cell length and the optimum pressure required for maximum signal strength, such that longer cell lengths will not necessarily improve the signal strength. This is contrary to conventional thinking and is important in the MTS design process to reduce unnecessary costs and improve the signal to noise ratio and frequency accuracy. Optimisation of frequency stabilised laser systems using MTS are generally performed using trial and error. Comparison of these optimum parameter values to those predicted by the hybrid model show that for popular wavelengths such as 532 nm they are similar. In addition, the hybrid model is able to predict the frequency shifts that arise within the system parameters used and has shown that existing systems being used at 532 nm, 633 nm and 778 nm could improve their signal to noise ratio and accuracy through a variation in the parameters. A methodology based on the hybrid model is presented that can be used to calculate the optimum parameters for maximum signal strength and a "RAM-free" state for any wavelength. This systematic approach can therefore be used to guide the design of actual frequency stabilised laser systems prior to and during the design process.