A series of zwitterionic materials of general formula R-D*-CH=C(CN)- CÖH4-C(CN)2', where D* is a pyridirium or quinolinium acceptor and R is a hydrophobic alkyl chain or an aryl group, were deposited using the Langmuir- Blodgett (LB) technique and their photochromic and nonlinear optical properties characterised. The materials are highly solvatochromic, exhibiting a broad photochromic charge transfer band in the visible region which bleaches when irradiated. LB films of the zwitterions, Z-ß-(1-hexadecyl-4-pyridinium)-a-cyano-4- styryldicyanomethanide (CMH33-P3CNQ) and the quinolinium analogue, Z-ß-(1- hexadecyl-4-quinolinium)-a-cyano-4-styryldicyanomethanide (CIÖH33-Q3CNQ), are non-centrosymmetric (Z-type). They exhibit sharp charge transfer bands at 495 n ana ses n respecivey with haf widths ai half maximum of 27 and zz mi. Unusually, mixed LB films of CIGH33-P3CNQ and C161-133-Q3CNQ exhibit a single sharp charge transfer band whose position is dependent upon the mole fraction and is finely tunable in the range 495 to 565 nm. These films are photobleached when irradiated at wavelengths which overlap the absorption bands, and may find potential applications a components of a multifrequency optical memory. Also, the unique peak wavelength tuning of the heteromolecular films enabled the effect of the position of the absorption band on second harmonic generation to be investigated for the first time. The zwitterionic materials have exciting norlinear optical properties and the strongest second harmonic intensity from any LB film has been obtained. LB films of the quinolinium zwitterion (CMH33-Q3CNQ) are non-centrosymmetric and the second harmonic intensity increases quadratically with the number of layers deposited to thicknesses of ca. 1 m. It is one of only five known materials to show such behaviour and the second-order susceptibility (xa) = 180 pm V* at 1064 nm) is the highest value obtained for a multilayer structure.

Orientador: Valdeci Pereira Mariano de Souza / Banca: Ricardo Paupitz B. dos Santos / Banca: Lúcio Campos Costa / Resumo: O fenômeno da supercondutividade atualmente um dos mais relevantes tópicos na Física da Matéria Condensada, tornando os sistemas fortemente correlacionados um tópico de grande interesse devido à possibilidade de estudar os aspectos fundamentas da interação elétron-elétron, que são o âmago da supercondutividade. Desta forma, a classe de condutores moleculares (TMTTF)2X (onde TMTTF é tetrametiltetratiafuvaleno e X é um contra-ânion) desempenha um papel sistemático e fundamental no estudo de tais aspectos de correlação. Nesta tese de mestrado, os materiais de interesse foram o (TMTTF)2PF6-H12 e o (TMTTF)2PF6-D12, onde uma anomalia na constante dielétrica diferente para os dois sais foi observada na transição ferroelétrica de Mott-Hubbard através de medidas de constante dielétrica quasi-estática no eixo c* (contribuição iônica) e o comportamento tipo relaxor da variante hidrogenada foi analisado com base na teoria de campo médio. Uma revisão de transições de fase clássicas e quânticas também foi realizada com o objetivo de estudar o chamado efeito magneto-calórico para o modelo do paramagneto de Brillouin (o parâmetro de Grüneisen magnético), que é uma grandeza Física única e poderosa para detectar experimentalmente uma transição de fase quântica induzida por campo magnético em um sistema real. Ainda, um estudo comparativo entre as fases delta (hexagonal) e delta' (tetragonal) da liga binária FeSe1-x foi realizado e monocristais foram sintetizados utilizando o método de síntese d... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The phenomenon of superconductivity is currently one of the most relevant topics in Solid State Physics, making strongly correlated systems a very highattractive topic due to the possibility of studying the fundamental aspects of the electron-electron interaction that are the core of superconductivity. Thus, the class of molecular conductors (TMTTF)2X (where TMTTF is tetramethyltetrathiafuvalene and X is a counter-anion) plays a systematic and fundamental role to study such correlation aspects. In this Master Thesis, the materials of interest were the (TMTTF)2PF6-H12 and (TMTTF)2PF6-D12, where a different dielectric anomaly at the Mott-Hubbard ferroelectric transition was observed for the two salts and the relaxor behavior of the hydrogenated variant was analysed based on the mean-field theory. A review of classical and quantum phase transitions was performed aiming to study the so-called magneto-caloric effect (the magnetic Grüneisen parameter) for the Brillouin paramagnet model, which is a powerful and unique physical quantity to experimentally detect a quantum phase transition induced by magnetic field in a real system. Also, a comparative study between the (hexagonal) and (tetragonal) phases of the binary alloy FeSe1-x was performed and single-crystals were synthesized employing the solid-state reaction method in order to achieve the phase / Mestre

Electronic platforms that are able to re-shape and assume different geometries are attractive for the advancing biomedical technologies, where the re-shaping feature increases the adaptability and compliance of the electronic platform to the human body. In this thesis, we present a serpentine-honeycomb reconfigurable electronic platform that has the ability to reconfigure into five different geometries: quatrefoil, ellipse, diamond, star and one irregular geometry. We show the fabrication processes of the serpentine-honeycomb reconfigurable platform in a micro-scale, using amorphous silicon, and in a macro-scale using polydimethylsiloxane (PDMS). The chosen materials are biocompatible, where the silicon was selected due to its superior electrical properties while the PDMS was selected due to its unique mechanical properties. We study the tensile strain for both fabricated-versions of the design and we demonstrate their reconfiguring capabilities. The resulting reconfiguring capabilities of the serpentine-honeycomb reconfigurable platform broaden the innovation opportunity for wearable electronics, implantable electronics and soft robotics.

A thesis submitted to the Faculty of Engineering. University of the Witwatersrand. Johannesburg in fulfilment of the requirements for the degree of Doctor of Philosophy. / The general argument of the thesis is that the design of broadband antennas demands a thorough understanding of the factors influencing the current distribution on antenna wires. Specifically. current distribution concepts are used to improve the evaluation and design of small broadband antennas for the high frequency (HF) 2 to 30 MHz range. The current distribution on an antenna governs its input impedance, radiation efficiency and radiation patterns. (Abbreviation abstract) / Andrew Chakane 2018

In this thesis a thorough investigation of 4-reactor shunt compensated systems under unbalanced fault-transient conditions has been carried out. Mathematical models for incorporating 4-reactor compensators into single and multi-section feeder systems, together with the technique used to simulate reactor saturation, are developed. The techniques are very general, are applicable to transposed and untransposed multi-conductor lines of any configuration, and can take into account the frequency dependence of system parameters. Using these techniques computer programs are developed to study : a - Effect of shunt-compensation on primary system response. b - System and reactor overvoltages. c - The probability of reactor saturation and its effect on primary system wave forms and hence on the performance of distance protection. d - Effect of shunt-compensation on the performance of distance protection.

This dissertation is concerned with the improvement of the transient response of turbo-generator sets following a severe system disturbance. The improvement in response is obtained by the application of a single additional system state into the relevant controllers. The system state used is that of rotor acceleration. Theoretical studies are carried out to obtain the feedback gains required for single machine co-ordinate control of excitation and governing. The study is then extended to a multi-machine system. The control laws obtained from the theoretical studies are applied in the laboratory to micromachine systems. A method of obtaining a rotor acceleration feedback control signal is developed and applied to these laboratory micromachine systems. The acceleration transducer forms an essential part of a dedicated microprocessor data acquisition system, which, apart from the functions of data collection and processing, performs a real time simulation of the governor turbine model. The output of this simulation is then used to control the micro-machine prime mover torque. An essential feature of the microprocessor system is the determination of control laws for both the governing and excitations systems during transient conditions.

The synchronous reactances of a salient-pole synchronous machine are functions of the load of the machine because of the non-linearity caused by magnetic saturation. In the d-axis the machine is more saturated than in the q-axis, and for exact analysis appropriate saturated reactances have to be used. A three dimensional numerical solution of the field problem, based on network method is developed to calculate the reactance. The non-linearity of the magnetic materials, the complicated contours of the cross section of the machine, and the currents in the various windings are fully considered. The analysis is applied to the predetermination of flux and flux density in a homopolar linear synchronous machine. The flux densities are used to predict the magnetising inductances, by the use of a flux linkage method. The normal forces acting between the rotor and stator are also calculated in a number of different ways including the use of Maxwell's stress. The field is described and the simplifying assumptions arid boundary conditions are discussed. The governing equations for scalar potential in terms of network properties are developed from Maxwell's equations. The numerical solution of the linear set of network equations is obtained by successive over-relaxation and the nonlinearity is considered by an alternating relaxation procedure. The difficulties associated with the use of scalar potential have been overcome by considering the permeable region to be current free. All the current-carrying conductors are placed in the surrounding air. Equations for a simple air-gap calculation of the inductances and normal forces in a homopolar linear synchronous machine are derived. The leakage inductances produced by air-gap flux which fails to reach the rotor have been considered as parts of the magnetising inductances. Inclusion of these leakage components enables close agreement to be obtained with the measured voltages. The leakage components have no influence on the forces produced by the homopolar LSM. The good agreement achieved in a comparison between the calculated and experimental results for the homopolar linear synchronous motor, confirms the validity and accuracy of the network field calculation method. The mechanical and electrical characteristics of the homopolar LSM are compared with those already found for a heteropolar machine. The advantages and disadvantages of both these machines for advanced transport system are discussed in details. Methods for improvement of power factor and for reducing pole losses are also mentioned.

This thesis investigates the current approach to decision making in the construction industry with its background of uncertainty in relation to such factors as workload, production methods, resource availability and profitability. Given this situation, and the less than deterministic environment that usually surrounds the construction project, effective planning and control procedures are seen as a prime necessity and not as a luxury. Within this context, the most significant decisions relate to the time and cost parameters and more specifically to their interrelationship and the need to provide optimal or near optimal solutions to this relationship. A preliminary feasibility study was conducted in conjunction with six building construction companies operating in the United Kingdom. This indicated that the potential for substantial benefits exist and was further substantiated by replies received to a questionnaire circulated to one hundred additional construction companies. The time and cost parameters are investigated and the related decision problem formulated in a quantitative manner. Existing models are examined and three alternative models are postulated, viz. an integer linear programming model - this model, like the existing models studied, is difficult to implement due to the large number of variables and constraints involved; an integer linear programming model based on breakthrough points on the cost curve (since the number of breakthrough points is less than the number of points of discontinuity, there are fewer integer variables) and a heuristic model capable of dealing with the problems associated with nonlinear time cost curves using a microcomputer. Appropriate programs are developed for use on a CBM 32K microcomputer with a dual drive floppy disk system and high speed printer. Both the integer linear programming models and the heuristic model are tested using simulated project data. Comparative tests indicate that the heuristic model, although adopting a simpler method of analysis, is capable of providing a solution comparable in accuracy with the more sophisticated integer linear programming model. The computer system is designed to permit the data to be structured in several different ways depending on the needs of the recipient, ie., the person who makes the decisions receives only that part of the output that is relevant to their action.

信道質量和服務質量（QoS）是無線體域網的兩個重要挑戰。本文旨在研究信道特性和在保證高吞吐率和低數據弛豫時間前提下探索低功耗WBAN系統策略。本論文的貢獻在於三個方面。首先研究人體信道（HBC）特性。作為IEEE標準802.15.6定義的三種PHY層之一，HBC已經作為體表傳感器通信媒介被廣泛研究。但是，HBC的詳細機理至今仍然不夠明朗，特別是對於那些采用了體內傳感器的應用更少人涉足。因此，我們為此專門預設四種應用場景，並在場景中測量實際信道特性。依據測量結果，我們觀測到數個影響信道質量的因素。其次，我們提出了一種專門針對WBAN的信道建模方法。該方法依賴於對人體組織的直接測量結果，並且此建模方法在建模過程中兼顧體表通信和體內通信。該建模方法包括兩個階段，第一階段是構建人體各部分的子模型，在第二階段調用先前構建之子模型並依賴信號衰減特性來構造上層模型。最終得到的模型包含兩個自變量：頻率和信道長度，從而可應用此模型同時預測不同頻率和不同長度條件下的信道特性。在設計的實驗中，結果表明該模型具有良好的精度，在10 kHz到60 MHz的頻率範圍內，最差的誤差為2.5 dB。除此之外，我們還在一個演示系統中對信道進行了測試，尤其是誤碼率（BER）和信號衰減情形。該測試結果也顯示出該模型所具有的良好預測性。第三，我們提出了一種關註QoS的WBAN系統優化方法。在IEEE標準中定義了數種不同存取模式（Access mode）和存取方式（Access method）。為了提高功率效率，我們著重研究了數據壓縮對系統總功率的影響，另外還對系統吞吐率建立了分析模型。仿真結果顯示，在一定條件下，數據壓縮對功耗降低具有良好功效，另外采用較高數據傳輸速率會對功耗存在改進作用。當數據壓縮模塊的壓縮率超過2倍，而功耗低於收發器的40%時，插入數據壓縮模塊可以確保整個系統消耗更低能源。 / Channel loss and maintaining the Quality of Service (QoS) are two of the major challenges in realizing an effective Wireless Body Area Network (WBAN). This thesis studies the body channel characteristics and proposes a methodology to improve energy efficiency for an entire WBAN system to achieve high throughput and low data latency. Three main contributions are made in this thesis. Firstly, we focus on human body channel (HBC). HBC, as a possible PHY layer for IEEE standards 802.15.6, has been found useful in networking on-body sensors. However, the HBC channel dynamics is not well understood and this is particularly the case when transceivers implanted inside a human body are involved. To this end, channel measurements were performed on real subjects under four different scenarios so that factors affecting channel quality could be identified. Secondly, a channel modelling methodology is proposed for body area network that takes into account the body structure and the dielectric properties of human tissues; this represents the first modelling effort to cover both in-body and on-body communications in vivo. The proposed modelling method composes of two phases: sub-model construction and top-level model construction. The constructed model is a function of two variables, frequency and channel length, enabling channel impedance prediction with respect to either frequency or channel length. Meanwhile, experimental results show that good model accuracy, a maximum error of 2.5 dB, can be achieved in frequencies range from 10 kHz to 60 MHz. In this endeavor, a modified HBC development system was used to measure bit error rate (BER) and signal attenuation during transmission. The measurements show a good match against simulation results and the channel model. Thirdly, a power optimization technique is proposed for the WBAN. The latest IEEE standard 802.15.6 defines several access modes and access methods together with new power management schemes and frame structures. To improve the power efficiency of a body area network, the merit of having data compression was investigated. For this purpose, an analytical model was developed to evaluate the power efficiency of a BAN system. Simulation results show that good power efficiency can be achieved by employing data compression. It is evident that higher data rate can also help improve energy efficiency. When the compression factor is larger than 2, better energy efficiency can be guaranteed by introducing a data processing unit in a sensor node as long as its power consumption is limited to 40% of that of the transceiver unit. / Detailed summary in vernacular field only. / Ai, Yanqing. / Thesis (Ph.D.) Chinese University of Hong Kong, 2014. / Includes bibliographical references (leaves 126-135). / Abstracts also in Chinese.

The effectiveness of single-pole autoreclosure in maintaining power system stability is largely determined by the speed with which secondary arc extinction and hence autoreclosure can be achieved. Realistic simulation techniques are of obvious importance in relation to the design of systems employing single pole autoreclosure and, in this thesis, digital methods are developed to enable the faulted response of e.h.v. feeders subjected to secondary arcing phenomena to be more realistically simulated than hitherto had been possible. The new techniques are also of importance in relation to programmable based protection test equipment. The realistic simulation of the secondary arcing phenomena is of obvious importance in relation to pre-determining the shunt reactor compensation necessary to achieve acceptable autoreclosure dead-times in long line applications. Based upon experimental data, methods of modelling the non-linear behaviour of the earth fault arc path in both conducting and extinction states are described, together with the techniques developed for incorporating such models into practical e.h.v. system interconnections. The thesis concludes by illustrating and discussing the results of computational studies relating to typical 500 kV feeders employing single-pole autoreclosure.