In this study, 2-minute and 5-minute free operant preference assessments were conducted. Preference hierarchies and the order of item selection were both identified and compared. The preference assessments were administered in alternating order and the resulting differentially preferred items were utilized in subsequent reinforcer assessments to determine if the items selected were reinforcing. The reinforcer assessments were conducted using an initial baseline and an alternating treatment design. Social validity was assessed with both the families and the participants. Treatment fidelity and inter-observer agreement data were also collected. The 2-minute free operant preference assessment was shown to be effective at identifying effective reinforcers for two out of the three participants. The third participant did not respond consistently to the free operant preference assessment at any length and responded aversively to the presentation of the free operant preference assessment, one which is known for yielding few problem behaviors. For the two participants that responded to the preference assessment, items that were identified functioned effectively as reinforcers. There was also a strong correlation using the Spearman’s Rank-Order Correlation Coefficient between the preference hierarchies and the order of selection list. This study supports the usage of the shortened free operant preference assessment but requires expansion and repetition. The author discussed the limitations of the current study and directions for future research. / Applied Behavioral Analysis

This dissertation addresses several key issues related to high-frequency soft-switching PWM three-phase power converters. These are: 1. Analysis, synthesis, and design of three-phase soft-switching PWM power converter topologies 2. Design of input EMI filters for three-phase converters 3. Design of microprocessor controllers for three-phase converters. An analysis of existing soft-switching PWM techniques is performed, and two generalized soft-switching PWM converter circuit representations are derived. Based on these representations and common topological properties of three-phase and dc-dc PWM converters, two new procedures for synthesis of three-phase soft-switching PWM converters are derived. The two procedures are used to synthesize five new three-phase soft-switching PWM converter topologies suitable for wide range of applications. A digital signal processor-based controller implementation example is presented. It demonstrates the feasibility of producing versatile, high performance, reliable, low-cost digital controllers for soft-switching PWM three-phase power converters operating at high switching frequencies. A new approach to the design of input filters for ac power electronic circuits is presented here. This approach is based on the application of a vast body of knowledge about passive L-C filters that has existed for many years, but has not been used in power electronics. New passive and active filter pole damping schemes are applied to high-order elliptic filters, resulting in significant filter size reduction compared to the standard filter designs. / Ph. D.

Achieving autonomous in complex natural environments has the potential to transform society by bringing the benefits of automation from the confines of the factory floor to the outdoors. There, it could benefit areas such as environmental monitoring and clean-up, precision agriculture, delivery of goods. A fundamental requirement for achieving these goals are sensors that can provide reliable support for navigation, e.g., a drone, in natural environments. In this thesis, sonar-based navigation has been investigated as an approach to parsimonious autonomous sensing for drones. Bats living in dense vegetation have demonstrated that autonomous navigation in a complex, natural environment based on two one-dimensional ultrasonic echo streams is feasible. Here, a biomimetic sonar head has been used to collect echo data from recreations of natural foliage in the lab under controlled conditions. This data was used to address the research question whether the grazing angle at which the sonar is looking at a surface can be estimated from the echoes -- despite the random three-dimensional nature of the scatter from the foliage. To investigate this, the echoes have been subjected to statistical analysis such as spectral coherence and cross-correlation. Most importantly, the foliage data was compared against predictions made by the Endura method (energy, duration, and range method) that has been devices for two-dimension random scatterers. The results of this analysis shows that -- despite their profoundly random nature -- echoes can be used to estimate the sonar grazing angle directly, i.e., without the need to resort to reconstructions of the foliage geometry. This opens the possibility of developing simple devices for navigation control in natural environments that can control the direction of motion at a very little computational cost. / Master of Science / Autonomously flying drones is a potential technology that could bring benefits to the society and improve the quality of life for humans[22]. Therefore, a study of autonomously flying in a natural environment is necessary, and this thesis will focus on drone that could recognize objects with different grazing angle and acoustic signal by collecting data from near foliage surface. For example, when a bush wall is in front of the drone, a on board computer could inform drone whether the drone airline will collide with the bush wall or the bush wall is safely out of drone’s path[5]. If on board computer reads that there will be a collision with bush wall, then drone needs to make decision (change direction or stop immediately) to avoid crush on to bush wall. A sonar based navigation system has been investigated as an approach to achieve autonomous sensing for drones, which is inspired by bats. Bats use their natural sonar system to navigate in cave or forest, hence, it is hardly to see bats slam into any obstacles while flying. Bats navigation behaviours could be reconstructed as a sonar based autonomy. Hence, this thesis is inspired by bats to determine if there is a computational way to illustrate that sonar based sensor could be a solution to achieve reactive autonomy by using different grazing angle of the surface’s acoustic signals.

The suitability of using rain-flow reconstructions as an alternative to an original loading spectrum for component fatigue life testing is investigated. A modified helicopter maneuver history is used for the rain-flow cycle counting and history regenerations. Experimental testing on a notched test specimen over a wide range of loads produces similar lives for the original history and the reconstructions. The test lives also agree with a simplified local strain analysis performed on the specimen utilizing the rain-flow cycle count. The rain-flow reconstruction technique is shown to be a viable test spectrum alternative to storing the complete original load history, especially in saving computer storage space and processing time. A description of the regeneration method, the simplified life prediction analysis, and the experimental methods are included in the investigation. / Master of Science

The KiK-net ground motion database is used to develop ground motion prediction equations for Arias Intensity (I_a), 5-95% Significant Duration (Ds_5-95), and 5-75% Significant Duration (Ds_5-75). Relationships are developed both for shallow crustal earthquakes and subduction zone earthquakes (hypocentral depth less than 45 km). The models developed consider site amplification using V_S30 and the depth to a layer with V_S=800 m/s (h₈₀₀). We observe that the site effect for I_α is magnitude dependent. For Ds_5-95 and Ds_5-75, we also observe strong magnitude dependency in distance attenuation. We compare the results with previous GMPEs for Japanese earthquakes and observe that the relationships are similar. The results of this study also allow a comparison between earthquakes in shallow-crustal regions, and subduction regions. This comparison shows that Arias Intensity has similar magnitude and distance scaling between both regions and generally Arias Intensity of shallow crustal motions are higher than subduction motions. On the other hand, the duration of shallow crustal motions are longer than subduction earthquakes except for records with large distance and small magnitude causative earthquakes. Because small shallow crustal events saturate with distance, ground motions with large distances and small magnitudes have shorter duration for shallow crustal events than subduction earthquakes. / This thesis presents the development of new Ground Motion Prediction Equations (GMPEs) for the prediction of the duration and the Arias Intensity of earthquake strong motions. . Arias Intensity is an index for the energy in the ground motion. The GMPEs are based on the Japanese KiK-net database. Based on the causative earthquake source, source to site path, and site properties, GMPEs give estimation of the mean and standard deviation of the parameters. This information is necessary for conducting probabilistic seismic hazard analyses. The characteristics of the ground motions with the same magnitude and source to site distance vary amongst different tectonic regimes. For this reason, we develop different GMPEs for earthquakes from different tectonic regimes (subduction zone and shallow crustal earthquakes). The primary motivation for this research is that no existing GMPEs for duration are directly applicable to subduction-zone earthquakes. In addition, because the same stations recorded both types of events, we can directly compare the effect of tectonic environment on the selected ground motion parameters. The estimation of mean duration and mean Arias intensity made by this study show while magnitude and distance scaling of Arias Intensity is the same for shallow crustal and subduction earthquakes, the tectonic regime has a significant effect on duration of ground motion.

Yes / A key question for temporal processing research is how the nervous system extracts event duration, despite a notable lack of neural structures dedicated to duration encoding. This is in stark contrast with the orderly arrangement of neurons tasked with spatial processing. In this study, we examine the linkage between the spatial and temporal domains. We use sensory adaptation techniques to generate after-effects where perceived duration is either compressed or expanded in the opposite direction to the adapting stimulus’ duration. Our results indicate that these after-effects are broadly tuned, extending over an area approximately five times the size of the stimulus. This region is directly related to the size of the adapting stimulus—the larger the adapting stimulus the greater the spatial spread of the aftereffect. We construct a simple model to test predictions based on overlapping adapted versus non-adapted neuronal populations and show that our effects cannot be explained by any single, fixed-scale neural filtering. Rather, our effects are best explained by a self-scaled mechanism underpinned by duration selective neurons that also pool spatial information across earlier stages of visual processing. / J.H. is supported by the Vision Research Trust (43069). N.W.R. is supported by a Wellcome Trust Research Career Development Fellowship (WT097387).

Yes / We investigated whether changes in low-level image characteristics, in this case spatial frequency, were capable of generating a well-known expansion in the perceived duration of an infrequent “oddball” stimulus relative to a repeatedly-presented “standard” stimulus. Our standard and oddball stimuli were Gabor patches that differed from each other in spatial frequency by two octaves. All stimuli were equated for visibility. Rather than the expected “subjective time expansion” found in previous studies, we obtained an equal and opposite expansion or contraction of perceived time dependent upon the spatial frequency relationship of the standard and oddball stimulus. Subsequent experiments using equi-visible stimuli reveal that mid-range spatial frequencies (ca. 2 c/deg) are consistently perceived as having longer durations than low (0.5 c/deg) or high (8 c/deg) spatial frequencies, despite having the same physical duration. Rather than forming a fixed proportion of baseline duration, this bias is constant in additive terms and implicates systematic variations in visual persistence across spatial frequency. Our results have implications for the widely cited finding that auditory stimuli are judged to be longer in duration than visual stimuli. / Wellcome Trust, UK, the Federation of Ophthalmic and Dispensing Opticians, UK, and the College of Optometrists, UK.

Yes / In conflict with historically dominant models of time perception, recent evidence suggests that the encoding of our environment’s temporal properties may not require a separate class of neurons whose raison d'être is the dedicated processing of temporal information. If true, it follows that temporal processing should be imbued with the known selectivity found within non-temporal neurons. In the current study, we tested this hypothesis for the processing of a poorly understood stimulus parameter: visual event duration. We used sensory adaptation techniques to generate duration aftereffects: bidirectional distortions of perceived duration. Presenting adapting and test durations to the same vs different eyes utilises the visual system’s anatomical progression from monocular, pre-cortical neurons to their binocular, cortical counterparts. Duration aftereffects exhibited robust inter-ocular transfer alongside a small but significant contribution from monocular mechanisms. We then used novel stimuli which provided duration information that was invisible to monocular neurons. These stimuli generated robust duration aftereffects which showed partial selectivity for adapt-test changes in retinal disparity. Our findings reveal distinct duration encoding mechanisms at monocular, depth-selective and depthinvariant stages of the visual hierarchy. / The Wellcome Trust [WT097387].

The theory of operation of a controlled transformer is described. A PWM controlled transformer is proposed and implemented in a forward converter to provide post regulation. Experimental results are presented to verify the new control scheme. Overall efficiency of 82%-86% is achieved in a 200khz, 500-watt, 5V-output off-line regulator. A discussion of design issues of the controlled transformer is also presented. / Master of Science

Les recherches menées dans cette thèse se sont intéressées à l'étude des obligations convertibles (OC) sous différents angles : le premier essai analyse les motivations des dirigeants à émettre des OC. Nous avons proposé un questionnaire qui a été envoyé à des entreprises françaises et nous avons conclu que les émissions d'OC ont principalement pour objectif de réaliser une augmentation de capital différée, émettre un signal, payer un coupon moins élevé, éviter la dilution et diversifier les sources de financement. Ensuite, à travers une ACP, nous avons identifié trois groupes d'émetteurs: les entreprises motivées par les avantages que peut procurer une émission d'OC par rapport à une augmentation de capital ; les entreprises qui souhaitent s'endetter à moindre coût ; et les entreprises intéressées par la souplesse des OC pour effectuer un financement séquentiel. Dès lors que la décision d'émettre des convertibles est prise, le manager doit décider du design de son obligation. Dans le deuxième essai, nous avons cherché à identifier et analyser les facteurs qui influencent la structure de l'OC, mesurée par la proportion de fonds propres et de dette dans l'actif émis. Nous avons montré que le risque de sous-investissement, la performance opérationnelle future, le niveau de l'endettement et la concentration de l'actionnariat influencent la structure de l'OC. Dans le troisième essai, nous avons analysé l'effet du risque de défaut et de conversion sur la sensibilité de l'OC aux variations du taux d'intérêt, mesurée par sa duration. Nous avons montré que le risque de défaut et de conversion ont un effet négatif sur la duration pour la plupart des convertibles. / This thesis have focused on the study of convertible bonds (CB) from different angles: The first essay analyzes the motivations of firms to issue OC . We proposed a questionnaire that was sent to French companies and concluded that emissions of OC mainly aim to make a back-door equity increase, issue a signal, pay a lower coupon, avoid dilution and diversify financing sources. Then, through a principal component analysis, we identified three groups of issuers : companies motivated by the benefits of an OC issue compared to a capital increase; companies wishing to borrow at lower cost ; and companies interested in the flexibility of the OC to perform a sequential financing. Once the decision to issue convertible is taken, the manager have to decide the design of its bond. In the second study, we have identified and analyzed the factors that influence the structure of the OC, measured by the proportion of equity and debt. We have shown that the risk of underinvestment, future operating performance, the level of debt and the ownership concentration influence the structure of the OC. In the third essay, we analyzed the effect of default and conversion risks on the sensitivity of the OC to interest rates changes, as measured by its duration. We have shown that the risk of default and conversion have a negative effect on the duration for most convertible bonds.