TOWARDS EFFECTIVE DISPLAYS FOR VIRTUAL AND AUGMENTED REALITY

Virtual and augmented reality (VR and AR) are becoming increasingly accessible and useful nowadays. This dissertation focuses on several aspects of designing effective displays for VR and AR. Compared to conventional desktop displays, VR and AR displays can better engage the human peripheral vision. This provides an opportunity for more information to be perceived. To fully leverage the human visual system, we need to take into account how the human visual system perceives things differently in the periphery than in the fovea. By investigating the relationship of the perception time and eccentricity, we deduce a scaling function which facilitates content in the far periphery to be perceived as efficiently as in the central vision. AR overlays additional information on the real environment. This is useful in a number of fields, including surgery, where time-critical information is key. We present our medical AR system that visualizes the occluded catheter in the external ventricular drainage (EVD) procedure. We develop an accurate and efficient catheter tracking method that requires minimal changes to the existing medical equipment. The AR display projects a virtual image of the catheter overlaid on the occluded real catheter to depict its real-time position. Our system can make the risky EVD procedure much safer. Existing VR and AR displays support a limited number of focal distances, leading to vergence-accommodation conflict. Holographic displays can address this issue. In this dissertation, we explore the design and development of nanophotonic phased array (NPA) as a special class of holographic displays. NPAs have the advantage of being compact and support very high refresh rates. However, the use of the thermo-optic effect for phase modulation renders them susceptible to the thermal proximity effect. We study how the proximity effect impacts the images formed on NPAs. We then propose several novel algorithms to compensate for the thermal proximity effect on NPAs and compare their effectiveness and computational efficiency. Computer-generated holography (CGH) has traditionally focused on 2D images and 3D images in the form of meshes and point clouds. However, volumetric data can also benefit from CGH. One of the challenges in the use of volumetric data sources in CGH is the computational complexity needed to calculate the holograms of volumetric data. We propose a new method that achieves a significant speedup compared to existing holographic volume rendering methods

Development of a new tridentate pincer phosphine N-heterocyclic carbene ligand & Development of a copper II catalyzed three component tandem synthesis of isoindolinone derivatives

Two types of research were carried out in this thesis; the first section is about the development of a new phosphine-based tridentate pincer N-heterocyclic carbene ligand and examination of the catalytic activities of its transition metal compexes including conjugated addition, alkyne-aldehyde addition and Alkyne-Aldehyde-Amine (A-3) coupling reaction. The second section of the thesis is about the methodology development of an A-3 based tandem synthesis of isoindoline derivatives and gold (I) catalyzed cyclization for the synthesis of isoindolo[2,1-a]quinolines derivatives. The aim of these studies is to develop novel catalysts and synthetic methodologies that can approach conventional chemical syntheses in a "greener" manner, therefore substantially gain atom-economy, step-economy and leads to a more sustainable life.Deux types de recherches ont été accompli dans cette thèse. La première section comporte sur le développement d'un nouveau ligand carbène hétérocyclique et l'analyse de ses complexes formés avec des métaux de transitions et leur efficacité lors des additions conjuguées, d'addition alcyne-alcène et des réactions de couplage entre un alcyne, une aldéhyde et une amine (A-3). La deuxième partie de cette thèse porte sur le développement d'une méthodologie de synthèse de dérivés d'isoindoline utilisant une réaction en tandem dérivés du couplage A-3 et la synthèse de dérivés d' isoindolo[2,1-1]quinolines par cyclisation catalysée par des sels d'or(I). Le but de ces études étant de développer des méthodologies de synthèse et des catalyseurs novateurs pouvant s'appliquer à des synthèses conventionnelles et de ce fait les rendre plus "vertes", en augmentant leur économie d'atomes, économie d'étapes dans une perspective de développement durable

Electrochemical Studies on CaP Electrodeposition on Three Dimensional Surfaces of Selective Laser Melted Titanium Scaffold

In this work, calcium phosphate (CaP) coating was electrodeposited on the three dimensional surface of SLM-Ti scaffolds. The in situ measurement showed that the potential variation within 5 mm thickness porous selective laser melting (SLM)-Ti samples was about 80 mV as a result of the low conductivity of CaP coatings. SEM observation results revealed that the coating morphology depended on the distance between the surface position of porous SLM-Ti electrode and the auxiliary electrode. Based on the compared electrochemical experiments, it was found that the top and the bottom surfaces of SLM-Ti scaffolds exhibited continuous nucleation and instantaneous nucleation behavior respectively. The Electrochemical impedance spectroscopy (EIS) results also revealed that the electrodeposition processes at different depth of SLM-Ti scaffolds were not synchronized. These differences were ultimately caused by the non-uniform distribution of the potential and the current inside porous SLM-Ti electrodes. The present work provides a basic research method for studying the mechanism of the electrochemical process on three dimensional surfaces of SLM-Ti scaffolds

Analysis of Preload of Three-Stator Ultrasonic Motor

The pre-pressure device of the ultrasonic motor plays a vital role in the design of the entire motor structure, the contact state of the stator and rotor of the motor, dynamic properties of the stator, friction and wear characteristics of the rotor; even the mechanical behaviors of the entire electric machinery have a profound impact. Appropriate pre-pressure is conducive to the smooth operation of the ultrasonic motor, so that the output performance remains excellent, reducing wear and effectively extend the service life of the motor. Therefore, the research on pre-stress is of great significance, as it can better optimize the structure of the three-stator ultrasonic motor and lay the foundation for the stable operation of the motor. First, this paper introduces the construction of the motor as a whole and the pre-pressure device briefly described the working mechanism of the motor, and then introduces the influence of the pre-pressure on the stator and rotor contact models, the position of the constant velocity point, and the modal frequency. Finally, the motor output under different pre-pressures is discussed. The performance experiment has determined the optimal pre-pressure interval, which provides help for its subsequent optimization

Non-linear direct effects of acid rain on leaf photosynthetic rate of terrestrial plants

Anthropogenic emissions of acid precursors have enhanced global occurrence of acid rain, especially in East Asia. Acid rain directly suppresses leaf function by eroding surface waxes and cuticle and leaching base cations from mesophyll cells, while the simultaneous foliar uptake of nitrates in rainwater may directly benefit leaf photosynthesis and plant growth, suggesting a non-linear direct effect of acid rain. By synthesizing data from literature on acid rain exposure experiments, we assessed the direct effects of acid rain on leaf photosynthesis across 49 terrestrial plants in China. Our results show a non-linear direct effect of acid rain on leaf photosynthetic rate, including a neutral to positive effect above pH 5.0 and a negative effect below that pH level. The acid rain sensitivity of leaf photosynthesis showed no significant difference between herbs and woody species below pH 5.0, but the impacts above that pH level were strongly different, resulting in a significant increase in leaf photosynthetic rate of woody species and an insignificant effect on herbs. Our analysis also indicates a positive effect of the molar ratio of nitric versus sulfuric acid in the acid solution on leaf photosynthetic rate. These findings imply that rainwater acidity and the composition of acids both affect the response of leaf photosynthesis and therefore result in a non-linear direct effect

Non-linear direct effects of acid rain on leaf photosynthetic rate of terrestrial plants

Anthropogenic emissions of acid precursors have enhanced global occurrence of acid rain, especially in East Asia. Acid rain directly suppresses leaf function by eroding surface waxes and cuticle and leaching base cations from mesophyll cells, while the simultaneous foliar uptake of nitrates in rainwater may directly benefit leaf photosynthesis and plant growth, suggesting a non-linear direct effect of acid rain. By synthesizing data from literature on acid rain exposure experiments, we assessed the direct effects of acid rain on leaf photosynthesis across 49 terrestrial plants in China. Our results show a non-linear direct effect of acid rain on leaf photosynthetic rate, including a neutral to positive effect above pH 5.0 and a negative effect below that pH level. The acid rain sensitivity of leaf photosynthesis showed no significant difference between herbs and woody species below pH 5.0, but the impacts above that pH level were strongly different, resulting in a significant increase in leaf photosynthetic rate of woody species and an insignificant effect on herbs. Our analysis also indicates a positive effect of the molar ratio of nitric versus sulfuric acid in the acid solution on leaf photosynthetic rate. These findings imply that rainwater acidity and the composition of acids both affect the response of leaf photosynthesis and therefore result in a non-linear direct effect

ADRC Control System of PMLSM Based on Novel Non-Singular Terminal Sliding Mode Observer

In an attempt to solve the problem of the many parameters of the traditional active disturbance rejection controller (ADRC) and to accurately estimate the mover position and speed required by a permanent magnet synchronous linear motor (PMLSM) system, an improved ADRC and a novel nonsingular fast terminal sliding mode observer (NFTSMO) are proposed. Firstly, the traditional first-order ADRC is simplified, the tracking differentiator (TD) module is removed, and the direct error is used to replace the nonlinear function in the extended state observer (ESO) and nonlinear state error feedback (NLSEF) module. Based on the traditional NFTSMO, the smooth back electromotive force (EMF) is obtained by adding the TD to reduce the phase delay caused by the low-pass filter in the traditional sliding mode observer (SMO), and the actuator position and speed information are modulated from the observed back EMF based on the principle of a phase-locked loop (PLL). Simulation and experiments show that this method not only simplifies the system structure of PMLSM but also optimizes many parameters in ADRC while retaining the original excellent performance. Compared with the traditional NFTSMO, the improved NFTSMO enhances the observation accuracy, reduces the chattering phenomenon of the system, and improves the robustness of the system