Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

This thesis presents the investigation of the liquid crystal (LC) - particle suspensions. Particles from nano- to micro-size, spherical to two-dimensional shapes, with different functionality are dispersed into nematic and smectic phases. The aim is to create ordered nanoparticle (NP) assemblies and thereby modify the common properties of the liquid crystal, such as dielectric anisotropy and electro-optical, revealing any interaction between particles and LC properties. It is found that for concentrations (>0.5vol%), the ferroelectric NPs have increased the sensitivity of the nematic liquid crystal to the electric field through electro-optical responses, which is seen by an enhancement in the dielectric anisotropy. This could be induced by the coupling of the electrical dipole moments in the spherical NPs with the LC director field. The electro-optical properties of the chiral smectic (SmC*) phase (tilt angle Θ, switching time τ_s and spontaneous polarisation P_s) are found to be independent of the concentration and sizes of the doped NPs. The relaxation frequency f_R of the Goldstone mode is faster in the ferroelectric NPs suspensions of 2.0vol% compared to the paraelectric NPs. In the graphene oxide (GO) - nematic LC (5CB) suspensions, the small GO sizes of mean size 560 nm are more easily dispersible than larger flakes of 2.8 micro metre mean size. As the GO concentration is increased, each of the threshold voltage and splay elastic constant dramatically increases, reaching saturation at ≈1.0wt%. The field driven switching-on time is practically not affected, while the purely elastically driven switching-off time is strongly sped-up. Interestingly, thermotropic and lyotropic LC phases are exhibited in the GO-5CB suspensions when heating the thermotropic liquid crystal into its isotropic phase. The isotropic phase of 5CB acts as a solvent for the GO particles, forming a lyotropic nematic phase with largely reduced birefringence. It is found that the nematic to isotropic phase transition is shifted toward higher temperature for the GO-5CB system compared to the BaTiO3-5CB system. Dispersions of different sizes of GO flakes are prepared in isotropic and nematic fluid media. The dielectric relaxation behaviour of GO-dispersions was examined for a wide temperature range (25-60 ℃) and frequency range (100 Hz-2 MHz). The mixtures containing GO flakes were found to exhibit varying dielectric relaxation processes, depending on the size of the flakes and the elastic properties of the dispersant fluid. The relaxation frequencies in the isotropic media were lower compared to the nematic medium. Relaxation frequencies (~10 kHz) are observed in the GO-isotropic media, which are reduced as the size of the GO flakes are decreased, are anticipated to be inherited from GO flakes. However, the fast relaxations (~100 kHz) that are observed in the nematic suspensions could imply strongly slowed down molecular relaxation modes of the nematogenic molecules. Finally, the phase diagram of lyotropic LC as a function of the lateral dimensions of the GO flakes, their concentration, geometrical confinement configuration and solvent polarity was investigated. Polarising optical microscopy was used to determine isotropic-biphasic-nematic phase evolution. The confinement volume and geometry of the sample relative to the GO size are shown to be vital to the observation of the lyotropic phase. GO LCs have the potential for a range of applications from display technologies to conductive fibres. The confinement related LC phase transition is critical toward their applications. It is also found that the stability of the LC phase is higher for the solvent of higher dielectric constant.

The wavelength-division multiplexing (WDM) is a well know technique capable of increasing the total capacity of a lightwave communication system; however, the system performance can be significantly limited by the dispersive and nonlinear effects, among others. This dissertation is mainly focused on the nonlinear effects upon the short-haul and long-haul lightwave systems.The short-haul lightwave system is mainly adopted in the access network. A passive optical access network is generally used to connect individual homes to a central office of a local area, and since there is no active component installed outside the central office of the passive optical access network, the system complexity and maintenance frequency can be significantly reduced. This dissertation provides a long-reach passive optical network (LR-PON) which can further reduce the system complexity and system cost. We found that four-wave mixing (FWM) and Rayleigh backscattering induced crosstalk were two main reasons to degrade the transmission performance in our proposed LR-PON. The long-haul lightwave system is mainly adopted in the transoceanic application. Although differential phase-shit keying (DPSK) modulation format has been confirmed to be suitable for long-haul WDM system, we found that a performance dip can be observed near the system zero dispersion avelength. In this dissertation, we designed various experiments to confirm the nonlinear effect to cause the performance dip being observed, and concluded that self-phase modulation (SPM) was the dominant reason to cause the performance dip rather than cross-phase modulation (XPM) or nonlinear phase noise.

This thesis proposes a novel technique using a phase-lock loop (PLL) style phase control loop to achieve retrodirective phased array antenna steering. This novel approach introduces the concept of phase scaling and frequency translation. It releases the retrodirective transmit-receive frequency ratio from integer constraints and avoids steering approximation errors. The concept was developed to achieve automatic and precise beam steering for the solar power satellite (SPS). The testing was performed using a transceiver converting a pair of received 2.9 GHz signals down to 10 MHz, and up converting two 10 MHz signals to 5.8 GHz. Phase scaling and conjugation was performed at the 10 MHz IF using linear XOR phase detectors and a PLL loop to synthesize a 10 MHz signal with conjugate phase. A phase control loop design is presented using PLL design theory achieving a full 2π steering range. The concept of retrodirective beam steering is also presented in detail. Operational theory and techniques of the proposed method are presented. The prototype circuit is built and the fabrication details are presented. Measured performance is presented along with measurement techniques. Pilot phase detectors and PCL achieve good linearity as required. The achieved performance is benchmarked with standards derived from likely performance requirements of the SPS and beam steering of small versus large arrays are considered.

This investigation looks on how Setswana short story writers depict female characters in short stories as compared to their male counterparts. Four methods are employed in this study, namely: definition, interpretation, comparison and classification, to cast light on the problems of depiction of female characters. An adapted narratological model was considered most suitable for this study. In this model, when content is discussed, topic is emphasized, when plot structure is analysed, theme is highlighted and when style is examined, atmosphere is of paramount importance. Vital concepts related to the portrayal of female characters are (a) author, (b) text structure, (c) character, (d) womanism and (e) feminism. Discussions of the concept of the author tend to fall into two groups, namely: the real author and the author of the text. This second group, is also subdivided into three classes, which are biolographical, implied and abstract authors. The author as a person is the originator of the events, which are obviously related to the depiction of female characters. A biographical author is connected to real events, which are then used to describe female characters. An abstract author in this study is taken to mean the same as an implied author, because both types of voice disclose the information of the real author in the depiction of female characters. This information is the events through which female characters are portrayed in Setswana short stories. The structure of the text is examined as divided into three strata, namely: content, plot structure and style. Content is discussed as the events which will make up the plot have not been arranged by the author yet, that is are there before the text is written. This content layer has four elements, namely: events, characters, time and space, which are united into one unit by the topic. This topic controls all these elements. Plot structure is then the way in which the author as originator of the events arranges them. In the plot structure the four elements of the content are allocated different functions which revolve around one theme only. Analysis of plot structure is very important because it is where events related to female characters are arranged. Style is defined as a way in which an author uses language to expose his female characters when writing his short stories. The short story is divided in this study into two major types, namely: stories that simply inform and stories that entertain. Description of both types of short stories is given equal attention because the portrayal of female characters in many Setswana short stories is the aim of this examination. Character is the next concept examined in this study. Characters can be any of four types, namely: (a) content characters, (b) plot structure characters, (c) flat characters and (d) round characters. Content and plot structure characters differ in function in the plot. The distinction between flat and round characters lies in the manner in which they are described. These distinctions are important because this research focuses on female characters in the presentation selected Setswana short stories. Female characters can be portrayed by the author himself/herself, the narrator, the character himself/herself and/or by other characters. In these Setswana short stories female characters are usually portrayed as having no rights, which reflect all the mistakes made by people though not admitted by society in general. The portrayal of female characters can be approached using several categories, namely: womanism, experimental phase and feminism. Thus, analysis of selected Setswana short stories unravels how Setswana short story writers depict female characters, whether as womanists, women of the experimental phase or as feminists. Thus, this study divides the selected Setswana short stories into three groups, namely: stories of phase of womanism, stories of experimental phase and stories of phase of feminism, to find out whether depiction of female characters belong to only one of these three themes or to more than one. Stories of phase of womanism The study gives an investigation of womanism: Distinguishing characteristics related to womanism are: -- oppression and ill-treatment of female characters; -- discrimination and segregation of female characters; -- ignorance of female characters; -- the fact that female character should be beaten when they have done something wrong; and -- restriction of the role of female characters to taking care of their own families and the extended family. Setswana short story writers who write about womanism include Chikane ('Mafaratlhatlha a botshelo'and 'Sego sa metsi'), Magoleng and Ntsime ('Khutsana and 'Lerato le eseng lona'), Shole ('Seteropo ke sa gago' and 'Tlogela ngwanake'), Malope ('Le fa o ka e buela lengopeng…' and 'O nkutlwe') and Sikwane ('MmaModiegi'). These short story writers portray female characters living traditional lives even through events which address the issues of feminism. This vividly indicates that although life changes, women`s lives remain static, according to these Setswana short story writers. Stories of phase of feminism Feminism is the next concept explored by this study. The outstanding features which have been discovered in feminism attempts to: -- eradicate oppression of female characters; -- fight for equality amongst women and men in all spheres of life; -- remove segregation of and discrimination against female characters; and -- change the whole society. Setswana short story writers whose work explores the above aspects include Sikwane ('MmaModiegi'), Shole ('Seteropo ke sa gago' and 'Tlogela ngwanake’), Chikane ('Sego sa metsi') and Malope ('Bodiba jo bo jeleng ngwana `a mmaago…' and 'O nkutlwe'). These short story writers emphasize a change in the lives of female characters, describing the fight for equality for all so that each person becomes liberated. Stories of experimental phase Finally, this study examines the experimental phase which shares with both womanism and feminism. Setswana short story writers of the experimental phase intertwine these two approaches when they write their short stories. Features that are identified in both womanism and feminism are: -- the freedom of female characters; -- the liberation of the whole society; -- agreement on marriage and -- working together as a team to solve the problems of society. Malope is shown to be a Setswana short story writer who mixes womanism and feminism. What Malope stresses is that often female characters do not know where they stand, whether they belong to womanism or feminism, and so they end up living a double life. / Thesis (DLitt (African Languages))--University of Pretoria, 2007. / African Languages / unrestricted

No description available.

The study of phase behavior is important for the oil and gas industry. Many approaches have been proposed and developed for phase behavior calculation. In this thesis, an alternative method is introduced to study the phase behavior by means of minimization of Helmholtz free energy. For a system at fixed volume, constant temperature and constant number of moles, the Helmholtz free energy reaches minimum at the equilibrium state. Based on this theory, a stochastic method called Particle Swarm Optimization (PSO) algorithm, is implemented to compute the phase diagrams for several pure component and mixture systems. After comparing with experimental and the classical PT-ash calculation, we found the phase diagrams obtained by minimization of the Helmholtz Free Energy approach match the experimental and theoretical diagrams very well. Capillary effect is also considered in this thesis because it has a significant influence on the phase behavior of reservoir fluids. In this part, we focus on computing the phase envelopes, which consists of bubble and dew point lines. Both fixed and calculated capillary pressure from the Young-Laplace equation cases are introduced to study their effects on phase envelopes. We found that the existence of capillary pressure will change the phase envelopes. Positive capillary pressure reduces the dew point and bubble point temperatures under the same pressure condition, while the negative capillary pressure increases the dew point and bubble point temperatures. In addition, the change of contact angle and pore radius will affect the phase envelope. The effect of the pore radius on the phase envelope is insignificant when the radius is very large. These results may become reference for future research and study. Keywords: Phase Behavior; Particle Swarm Optimization; Capillary Pressure; Reservoir Fluids; Phase Equilibrium; Phase Envelope.

No description available.

Phase field modeling and simulation is employed to study the underlying mechanism of enhancing electromechanical properties in single crystals and polycrystals of perovskite-type ferroelectrics around the morphotropic phase boundary (MPB). The findings include: (I) Coherent phase decomposition near MPB in PZT is investigated. It reveals characteristic multidomain microstructures, where nanoscale lamellar domains of tetragonal and rhombohedral phases coexist with well-defined crystallographic orientation relationships and produce coherent diffraction effects. (II) A bridging domain mechanism for explaining the phase coexistence observed around MPBs is presented. It shows that minor domains of metastable phase spontaneously coexist with and bridge major domains of stable phase to reduce total system free energy, which explains the enhanced piezoelectric response around MPBs. (III) We demonstrate a grain size- and composition-dependent behavior of phase coexistence around the MPBs in polycrystals of ferroelectric solid solutions. It shows that grain boundaries impose internal mechanical and electric boundary conditions, which give rise to the grain size effect of phase coexistence, that is, the width of phase coexistence composition range increases with decreasing grain sizes. (IV) The domain size effect is explained by the domain wall broadening mechanism. It shows that, under electric field applied along the nonpolar axis, without domain wall motion, the domain wall broadens and serves as embryo of field-induced new phase, producing large reversible strain free from hysteresis. (V) The control mechanisms of domain configurations and sizes in crystallographically engineered ferroelectric single crystals are investigated. It reveals that highest domain wall densities are obtained with intermediate magnitude of electric field applied along non-polar axis of ferroelectric crystals. (VI) The domain-dependent internal electric field associated with the short-range ordering of charged point defects is demonstrated to stabilize engineered domain microstructure. The internal electric field strength is estimated, which is in agreement with the magnitude evaluated from available experimental data. (VII) The poling-induced piezoelectric anisotropy in untextured ferroelectric ceramics is investigated. It is found that the maximum piezoelectric response in the poled ceramics is obtained along a macroscopic nonpolar direction; and extrinsic contributions from preferred domain wall motions play a dominant role in piezoelectric anisotropy and enhancement in macroscopic nonpolar direction. (VIII) Stress effects on domain microstructure are investigated for the MPB-based ferroelectric polycrystals. It shows that stress alone cannot pole the sample, but can be utilized to reduce the strength of poling electric field. (IX) The effects of compressions on hysteresis loops and domain microstructures of MPB-based ferroelectric polycrystals are investigated. It shows that longitudinal piezoelectric coefficient can be enhanced by compressions, with the best value found when compression is about to initiate the depolarization process. / Ph. D.

The increase in capacity demand along with the advancement in digital signal processing (DSP) have recently revived the interest in coherent optical communications and led to its commercialization. However, design and development of robust DSP algorithms for example for carrier phase recovery (CPR) becomes complex as we opt for high order modulation formats such as 16QAM and beyond. Further, electrical-domain dispersion compensation (EDC), while providing many advantages, makes the system more susceptible to laser frequency noise (FN). For instance, in coherent optical links with post-reception EDC, while the transmitter frequency noise causes only phase impairment, the local oscillator (LO) FN in these systems results in a noise enhancement in both amplitude and phase. This noise is commonly known as equalization enhanced phase noise (EEPN). It results in asymmetric requirements for transmitter laser and LO laser. Further, the system design in the presence of lasers with non-white frequency noise becomes increasingly challenging for increased capacity-distance product. The main contributions of this thesis are, firstly, an experimentally validated theory of coherent optical links with lasers having general non-white frequency noise spectrum and corresponding system/laser design criteria and mitigation technique. Secondly, low complexity and high phase noise tolerant CPR for high order modulation formats. The general theory propounded in this thesis elucidates the origin of the laser frequency noise induced noise enhancement in coherent optical links with different DSP configurations. The thesis establishes the existence of multiple frequency noise regimes and shows that each regime results in different set of impairments. The influence of the impairments due to some regimes can ideally be reduced by optimizing the corresponding mitigation algorithms, while other regimes cause irretrievable impairments. Experimentally validated theoretical boundaries of these regimes and corresponding criteria applicable to system/laser design are provided. Further, an EEPN mitigation method and its two possible implementations are proposed and discussed. The thesis also demonstrates an intrinsic limitation of the conventional Blind Phase Search (BPS) algorithm due to angular quantization and provides methods to overcome it. Finally, this thesis proposes and demonstrates single stage and multi-stage carrier phase recovery algorithms for compensation of phase impairments due to the two lasers for higher order circular and square modulations. The proposed methods outperform the state of art algorithms both in performance and in complexity. / <p>QC 20170516</p> / European project ICONE gr. #608099