Timing offsets result from the use of real clocks that are non-ideal in sampling intervals. These offsets also known as timing jitter were shown to degrade the performance of the two forms of UWB systems impulse radio and orthogonal frequency division multiplexing (OFDM)-based UWB. It was shown that for impulse radio, timing jitter distorts the correlation property of the transmitted signal and the resulting performance loss is proportional to the root-mean-square (RMS) value of the timing jitter. For the OFDM-based UWB, timing jitter introduced inter-channel interference (ICI) and the performance loss was dependent on the product of the bandwidth and the RMS of the timing jitter. A number of techniques were proposed for mitigating the performance degradation in each form of UWB. Specifically, for impulse radio, the methods of pulse shaping and sample averaging were provided, whereas for OFDM-based UWB, oversampling and adaptive modulation were given. Through analysis and simulation, it was shown that substantial gain in signal power-to-noise ratio can be achieved using these jitter-reduction methods.

The main objective of this research is to design, simulate, and evaluate telescope array-based receiver architectures for the inter-planetary optical communication links, which is able to provide broadband data support for future deep-space and universe exploration missions. The major aspects of this research are as follows: (1) evaluation and performance comparison of telescope arrays-based receiver with a large, monolithic telescope-based receiver, (2) mathematical modeling and analysis of the impact of various limiting factors (i.e., background noise, atmospheric turbulence, synchronization and tracking errors) on the performance of optical array receiver, (3) design and evaluation of subsystems and adaptive signal processing algorithms for the mitigation of the above-mentioned deleterious effects, and (4) development of an end-to-end simulation and analysis platform for an optical communication link between a transmitter in Mars orbit and an Earth-based array receiver after integration of the proposed sub-systems. In the second part of this research, I aim to extend the analysis to the free-space, short-range, terrestrial optical communication links. In this part, the objective is the development of the efficient simulation tools for the analysis of receiver performance and optical beam propagation through turbulent atmospheric channel. In the experimental part of the research, the investigation of the use of adaptive optics (AO) subsystems for turbulence and background noise compensation in the deep-space optical communication links will be carried out.

A novel approach to optical pulse shaping and arbitrary waveform generation (OAWG) using time-domain spectral shaping (TDSS) in negative and positive dispersion in commercial optical fibers has been proposed and evaluated. In order to study the pulse shaping capability of this OAWG system, mathematical analysis was used to determine expressions for the expected output waveform under certain assumptions. Then, Matlab code was developed to model the propagation of an optical signal through a fiber with arbitrary characteristics as well as optical modulation using an electro-optic modulator. The code was first benchmarked to several well-known theoretical systems to ensure that it produced accurate results, and then it was used to examine the ability of this novel OAWG approach to generate different waveforms under various conditions. The results of numerous simulations are presented and used to qualitatively examine the ability of this system to perform OAWG in a real-world setting. Based on the results of simulations, mathematical modeling, as well as previous research in this area, it was determined that higher-order fiber dispersion could be a limitation to the time-bandwidth product and pulse shaping fidelity of this pulse shaping method. Additional dispersion compensation techniques were devised to help overcome these limitations such as the use of multiple dispersion-compensating fibers and spectral phase modulation. An OAWG system employing these techniques was also simulated using the developed Matlab code. Using these results, the possibility and feasibility of employing this system in various pulse shaping applications such as optical communications, are discussed and analyzed. Limitations of the system are also investigated, and methods to improve the system for future applications are suggested.

Thesis (MSc (Mathematics))--Stellenbosch University, 2008. / LULU smoothers is a class of nonlinear smoothers and they are compositions of the maximum and minimum operators. By analogy to the discrete Fourier transform and the discrete wavelet transform, one can use LULU smoothers to create a nonlinear multiresolution analysis of a sequence with pulses. This tool is known as the Discrete Pulse Transform (DPT). Some research have been done into the distributional properties of the LULU smoothers. There exist results on the distribution transfers of the basic LULU smoothers, which are the building blocks of the discrete pulse transform. The output distributions of further smoothers used in the DPT, in terms of input distributions, has been a challenging problem. We motivate the use of these smoothers by first considering linear filters as well as the median smoother, which has been very popular in signal and image processing. We give an overview of the attractive properties of the LULU smoothers after which we tackle their output distributions. The main result is the proof of a recursive formula for the output distribution of compositions of LULU smoothers in terms of a given input distribution.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Peltophorum dubium (Sprengel) Taubert is a native forest species that shows fast development with environmental and economic importance. However, studies related to the production of quality seedlings by vegetative propagation are still incipient. As a result, this study investigated methods for multiplication and in vitro root formation of Peltophorum dubium. For multiplication was evaluated the use, alone or combined, of the cytokinins 6-Benzylaminopurine (BAP), Kinetin (KIN), isopentenyladenine (2iP) and Thidiazuron (TDZ) in different concentrations and its association with the auxin alpha-naphthalene acetic acid (ANA) or activated charcoal. In the formation of roots were evaluated the auxins NAA, indole-3-butyric acid (IBA)and 2,4-dichlorophenoxyacetic acid (2,4-D) at different concentrations and the exposure time of shoots to these growth regulators and their cultivation in nutrient media MS and WPM. We evaluated also alternative substrates (vermiculite, Plantmax ® or fine sand) associated with different volumes of MS nutrient medium containing agar or not, in the in vitro root formation, with the aim of providing a more porous medium to the development of root system. There wasn t emission of adventitious shoots in the absence of cytokinins in epicotyls of Peltophorum dubium. TDZ and 2iP, at 5 or 10 μM, associated with 0.015 μM NAA in MS medium promoted the highest percentage of buds. However, the shoots showed little development, intensive formation of callus at the base and leaf chlorosis, which didn t permit its use. In the absence of cytokinin was not observed leaf chlorosis. The inclusion of 1 g L-1 of activated charcoal to the nutrient medium MS provided more vigorous shoots and the use of epicotyl containing cotyledonary nodes allowed the formation of new shoots in all treatments. When BAP was used alone was not observed the emission of adventitious buds on epicotyl; these only started to occur when we used combinations of BAP with KIN or 2iP. In MS nutrient medium, the highest callus formation was observed in the presence of 10 μM IBA, after 30 days. In nutrient medium WPM, the highest callus formation occurred in the absence of IBA. Reduced percentage of root formation in Peltophorum dubium shoots were both obtained in MS medium as in WPM, regardless of the absence or presence of IBA. In MS nutrient medium, regardless of the presence or absence of auxin and independent of the concentration of this class of growth regulators, callus formation occurred at the base of the shoots of Peltophorum dubium to 30 days in vitro culture. Both the nutrient media MS and WPM possibilite the formation of roots on shoots of Peltophorum dubium with the use of "pulse" treatments of IBA at concentrations between 0 and 20 μM for six days in nutrient medium. However, the root formation was not satisfactory. There was intense callus formation at the base of the shoots at 60 days of culture, when the vermiculite was used as substrate in the process of inducing rooting. At 60 days it was possible to obtain root formation on all substrates. The combination of MS medium supplemented with 10 μM IBA, vermiculite and agar provided 36.8% of root formation in shoots, as well as improved the quality of roots of Peltophorum dubium. The use of epicotyl containing cotyledonary nodes on MS nutrient medium, supplemented with activated charcoal reduces the callus at the base of the explants and raises the emission of adventitious shoots for 75% and provides the obtaining of more vigorous shoots and leaves without chlorosis. The auxins NAA, IBA and 2,4-D in concentrations of up to 20 μM during the whole period of culture are not efficient in promoting the in vitro formation of roots on shoots of Peltophorum dubium. The use of pulse treatment with IBA for six days and the reduction the concentration of salts from the nutrient medium after this period allows the formation of roots, independent of IBA concentration and use of MS or WPM media. Most promising results are obtained using the combination of vermiculite, nutrient medium and agar, both in percentage of root formation, and the quality of root system formed. / Peltophorum dubium (Sprengel) Taubert é uma espécie florestal nativa de rápido crescimento e dotada de importância ambiental e econômica. No entanto, os estudos relacionados à produção de mudas de qualidade por meio da propagação vegetativa são, ainda, incipientes. Em virtude disso, este trabalho objetivou estudar metodologias para a multiplicação e para a formação de raízes in vitro de Peltophorum dubium. Para a multiplicação foram avaliados o emprego isolado ou combinado das citocininas 6-Benzilaminopurina (BAP), Cinetina (CIN), Isopenteniladenina (2iP) e Thidiazuron (TDZ) em diferentes concentrações, bem como sua associação com a auxina Ácido alfa-Naftaleno Acético (ANA) ou carvão ativado. Na formação de raízes foram avaliadas as auxinas ANA, Ácido 3-Indol Butírico (AIB) e Ácido 2,4-Diclorofenoxiacético (2,4-D) em diferentes concentrações, bem como o período de exposição das brotações a esses fitorreguladores e seu cultivo nos meios nutritivos MS e WPM. Foram avaliados, ainda, substratos alternativos (vermiculita, Plantmax® ou areia fina) associados a diferentes volumes de meio nutritivo MS, contendo ou não ágar, na formação in vitro de raízes, com o intuito de oferecer um meio mais poroso para o desenvolvimento do sistema radicular. Não ocorreu emissão de brotações adventícias na ausência de citocininas em epicótilos de Peltophorum dubium. TDZ e 2iP, a 5 ou 10 μM, associados a 0,015 μM de ANA, em meio MS, promoveram as maiores porcentagens de brotações adventícias. No entanto, as brotações apresentaram pequeno desenvolvimento, intensa formação de calos na base e clorose foliar, o que inviabilizou a sua utilização. Na ausência de citocininas não ocorreu clorose foliar. A inclusão de 1 g L- 1 de carvão ativado ao meio nutritivo MS proporcionou a obtenção de brotações mais vigorosas e a utilização de epicótilos contendo nós cotiledonares permitiu a formação de novas brotações em todos os tratamentos testados. Quando BAP foi utilizado isoladamente não foi observada a emissão de brotações adventícias em epicótilos; estas só passaram a ocorrer quando foram utilizadas combinações de BAP com CIN ou 2iP. Em meio nutritivo MS, a maior formação de calos foi observada na presença de 10 μM de AIB, aos 30 dias. Em meio nutritivo WPM, a maior formação de calos ocorreu na ausência de AIB. Reduzidas porcentagens de formação de raízes em brotações de Peltophorum dubium foram obtidas tanto em meio MS como em WPM, independentemente da ausência ou da presença de AIB. Em meio nutritivo MS, independente da presença ou não de auxinas e, independente da concentração utilizada, ocorreu calogênese na base das brotações de Peltophorum dubium aos 30 dias de cultivo in vitro.Tanto o meio nutritivo MS quanto o WPM possibilitaram a formação de raízes em brotações de Peltophorum dubium com a utilização de tratamentos pulse de AIB, em concentrações entre 0 e 20 μM, durante seis dias no meio nutritivo. No entanto, a formação de raízes não foi satisfatória. Ocorreu intensa formação de calos na base das brotações, aos 60 dias, quando a vermiculita foi utilizada como substrato no processo de indução ao enraizamento. Aos 60 dias foi possível obter formação de raízes em todos os substratos testados. A combinação de meio MS acrescido de 10 μM de AIB + vermiculita + ágar proporcionou 36,8% de formação de raízes nas brotações, bem como melhorou a qualidade do sistema radicular de Peltophorum dubium. A utilização de epicótilos contendo nós cotiledonares, em meio nutritivo MS, acrescido de carvão ativado, reduz a calogênese na base dos explantes e eleva a emissão de brotações adventícias para 75%, bem como proporciona a obtenção de brotações mais vigorosas e sem clorose foliar. As auxinas ANA, AIB e 2,4-D, em concentrações de até 20 μM durante todo o período de cultivo não são eficientes em promover a formação in vitro de raízes em brotações de Peltophorum dubium. O emprego de tratamento pulse com AIB por seis dias e a redução na concentração de sais do meio nutritivo após esse período permite a formação de raízes, independente da concentração de AIB e da utilização dos meios MS ou WPM. Resultados mais promissores são obtidos com a utilização da combinação de vermiculita, meio nutritivo e ágar, tanto na porcentagem de formação de raízes, como na qualidade do sistema radicular formado.

L'4He et l'3He sont des systèmes modèles pour comprendre les propriétés quantiques de la matière fortement corrélée. C'est pour cette raison que plusieurs études ont été consacrées à la compréhension de leur dynamique. A basses températures où les effets quantiques jouent un rôle essentiel, les excitations élémentaires dans l'4He sont décrites par un mode collectif d'excitations: phonon-roton. Par contre pour un système d'3He la description est plus complexe, le spectre d'excitation a deux composantes: un mode collectif (zéro-son) et un continuum d'excitations incohérentes de type particule-trou. Les deux sont bien décrites par la théorie de Landau des liquides de Fermi qui trouve sa validité pour des petits vecteurs d'onde. Jusqu'à présent, on supposait que la dynamique dans les liquides de Fermi à vecteurs d'onde élevés était essentiellement incohérente. Cette thèse porte sur l'exploration, par diffusion inélastique de neutrons, des excitations collectives dans l'3He liquide 2D adsorbé sur un substrat de graphite. Un tel travail expérimental requiert trois ingrédients essentiels : un réfrigérateur à dilution afin de travailler à basses températures, un spectromètre temps de vol afin de mesurer le facteur de structure dynamique du système et un substrat solide (graphite exfolié ZYX) pour la préparation de films d'3He-2D par physisorption. Nos expériences sur ces films d'3He déposés en deuxième couche sur de l'4He solide adsorbé sur le graphite nous ont permis de faire les observations suivantes : à petit vecteur d'onde, le zéro-son est plus proche de la bande particule-trou que celui observé dans le cas de l'3He massif, tandis qu'à fort vecteur d'onde le mode collectif entre dans le continuum et réapparait de l'autre côté. Cette nouvelle branche, observée pour la première fois, est aujourd'hui décrite par la théorie dynamique à N-corps développée par nos collaborateurs de l'université Johannes Kepler de Linz, Autriche. Au cours de ce travail de thèse plusieurs techniques expérimentales ont été développées, en particulier, un réfrigérateur à dilution sans fluide cryogénique robuste adapté à des expériences de diffusion neutronique. Son optimisation a permis de réduire le temps de refroidissement de ce type de réfrigérateurs. / 4He and 3He are model systems for understanding quantum properties of strongly interacting matter. For this reason many studies have been devoted for the understanding of their dynamics. At low temperatures at which quantum effects play an essential role, the elementary excitations in 4He are described by a phonon-roton collective mode. For 3He, the physical description is more complicated, the spectrum has two components: collective excitations (zero-sound) and incoherent particle-hole excitations. Both are described by Landau's theory of Fermi liquids which is valid at low wave vectors. So far, it was thus believed that the dynamics at high wave vectors is essentially incoherent. This thesis is mainly concerned by exploring the collective excitations of a two dimensional 3He film adsorbed on graphite, using inelastic neutron scattering. Such an experiment has three main requirements: a dilution refrigerator in order to work at low temperatures, a time of flight spectrometer for measuring the dynamical structure factor of 3He and a solid substrate (exfoliated graphite ZYX) to obtain a two dimensional film by physical adsorption. Our investigations of the dynamics in two-dimensional 3He adsorbed on graphite preplated with 4He films have revealed important features: At low wave-vectors, the zero-sound mode is considerably depressed compared to bulk 3He. At higher wave vectors, the collective excitations branch enters the particle-hole continuum, and reappears at the lower energy branch of the continuum. This new branch, observed for the first time, is described by the dynamic many-body theory developed by our collaborators from Johannes Kepler University, Linz, Austria. During this work several low temperature techniques have been developed, in particular a robust, cryogen-free dilution refrigerator adapted to the demanding conditions of a neutron scattering experiments. Due to its efficient design, the cooling time has been considerably reduced compared to that of refrigerators of the same type developed in the past.

Se describe la aplicación de pulsos láser ultracortos (≤10fs) en espectroscopía y microscopía de dos fotones llevada a cabo en nuestro grupo de investigación, subrayando las ventajas y requerimientos de este enfoque. Además se presenta una breve descripción de la manipulación de pulsos, de las distorsiones de fase experimentadas por los pulsos láser de femtosegundo y de cómo corregir tales distorsiones utilizando manipuladores de pulsos. / Femtosecond laser pulses in two-photon spectroscopy and microscopy: The application of shaped ultrashort laser pulses (≤10fs) in two-photon spectroscopy and microscopy carried out in our group is  described, highlighting the advantages and requirements of this approach. In addition, a brief description of pulse shaping, phase distortions experienced by femtosecond laser  pulses and how to correct these distortions using a pulse shaper is also presented.

Orientador: Ernesto Ruppert Filho / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-21T00:56:13Z (GMT). No. of bitstreams: 1 Dias_AgnaldoVieira_M.pdf: 2229736 bytes, checksum: 725a7fa267bc30780c457689e4356336 (MD5) Previous issue date: 2012 / Resumo: O estudo da utilização de conversores CC/CC isolados e elevadores de tensão para a alimentação de moduladores de pulsos é apresentado neste trabalho. Foi selecionada a topologia em ponte completa, dando-se enfoque ao problema das capacitâncias parasitas envolvidas no circuito, que aparecem de forma acentuada em transformadores elevadores de tensão e filtros indutivos de saída e são altamente indesejáveis quando se opera em regime chaveado. Essas capacitâncias são tratadas através de uma forma de amortecimento, onde a energia armazenada nas mesmas é devolvida à fonte primária ao final de cada semiciclo de chaveamento, tentando obter-se menor volume, maior rendimento e menor dissipação de calor no conversor. Além disso, um circuito de regulação de carga é utilizado para garantir uma maior estabilidade de pulso e contornar problemas típicos de moduladores de pulsos utilizados em radares, como o efeito de backswing. O modulador de pulsos utilizado como carga para esse sistema opera com uma tensão de alimentação de 1kV, frequência de repetição de pulsos (PRF) de 585Hz e consome uma potência da ordem de 2,1kW. O conversor CC/CC é alimentado por um barramento CC não regulado de 280V / Abstract: The study of high-voltage isolated DC/DC converters used to supply pulse modulators is presented on this dissertation. The Full Bridge topology was selected, focusing in problems caused by parasitic capacitances in the circuit. This characteristic, which appears sharply in high voltage transformers and in inductors of output filter, is highly undesirable when the circuit is operated in switching mode. These capacitances are handled using a soft commutation technique, where their stored energy are returned to the primary source in the end of each switching cycle, trying to get a low size, high efficiency and low heat dissipation in the converter. Moreover, a charging regulator circuit is used to ensure good pulse stability and avoid typical problems in the pulse modulators use, such as the backswing effect. The pulse modulator used as load for this converter operates with a supply voltage of 1kV, pulse repetition frequency (PRF) of 585Hz and consumes 2.1 kW. The converter input is supplied by a 280V unregulated DC bus / Mestrado / Energia Eletrica / Mestre em Engenharia Elétrica

The ultrashort chirped pulse amplification (CPA) laser technology opens the path to high intensities of 10^21 W/cm² and above in the laser focus. Such intensities allow laser-matter interaction in the relativistic intensity regime. Direct diode-pumped ultrashort solid-state lasers combine high-energy, high-power and efficient amplification together, which are the main advantages compared to flashlamp-pumped high-energy laser systems based on titanium-doped sapphire. Development within recent years in the field of laser diodes makes them more and more attractive in terms of total costs, compactness and lifetime. This work is dedicated to the Petawatt, ENergy-Efficient Laser for Optical Plasma Experiments (PENELOPE) project, a fully and directly diode-pumped laser system under development at the Helmholtz–Zentrum Dresden – Rossendorf (HZDR), aiming at 150 fs long pulses with energies of up to 150 J at repetition rates of up to 1 Hz. The focus of this thesis lies on the spectral and width manipulation of the front-end amplifiers, trivalent ytterbium-doped calcium fluoride (Yb3+:CaF2) as gain material as well as the pump source for the final two main amplifiers of the PENELOPE laser system. Here, all crucial design parameters were investigated and a further successful scaling of the laser system to its target values was shown. Gain narrowing is the dominant process for spectral bandwidth reduction during the amplification at the high-gain front-end amplifiers. Active or passive spectral gain control filter can be used to counteract this effect. A pulse duration of 121 fs was achieved by using a passive spectral attenuation inside a regenerative amplifier, which corresponds to an improvement by a factor of almost 2 compared to the start of this work. A proof-of-concept experiment showed the capability of the pre-shaping approach. A spectral bandwidth of 20nm was transferred through the first multipass amplifier at a total gain of 300. Finally, the predicted output spectrum calculated by a numerical model of the final amplifier stages was in a good agreement with the experimental results. The spectroscopic properties of Yb3+:CaF2 matches the constraints for ultrashort laser pulse amplification and direct diode pumping. Pumping close to the zero phonon line at 976nm is preferable compared to 940nm as the pump intensity saturation is significantly lower. A broad gain cross section of up to 50nm is achievable for typical inversion levels. Furthermore, moderate cryogenic temperatures (above 200K) can be used to improve the amplification performance of Yb3+:CaF2. The optical quality of the doped crystals currently available on the market is sufficient to build amplifiers in the hundred joule range. The designed pump source for the last two amplifiers is based on two side pumping in a double pass configuration. However, this concept requires the necessity of brightness conservation for the installed laser diodes. Therefore, a fully relay imaging setup (4f optical system) along the optical path from the stacks to the gain material including the global beam homogenization was developed in a novel approach. Beside these major parts the amplifier architecture and relay imaging telescopes as well as temporal intensity contrast (TIC) was investigated. An all reflective concept for the relay imaging amplifiers and telescopes was selected, which results in several advantages especially an achromatic behavior and low B-Integral. The TIC of the front-end was improved, as the pre- and postpulses due to the plane-parallel active-mirror was eliminated by wedging the gain medium.

La mesure récente de l'angle de mélange theta-13, à laquelle l'expérience Double Chooz contribue, a ouvert la voie aux futures expériences de la physique des neutrinos. Dans ce manuscrit, la caractérisation de certains bruits de l'expérience sont décrits. Les muons cosmiques qui s'arrêtent et se désintègrent dans le détecteur sont mal reconstruits, résultant en distorsion de la distribution temporelle des signaux laquelle peut être utilisée pour identifier ce type de fond. Les neutrons rapides créés par spallation par les muons cosmiques produisent de nombreux protons de recul qui peuvent entraîner un décalage dans la distribution temporelle des signaux et ainsi être identifiés. Ces distributions temporelles ont aussi été utilisées pour identifier la formation de l'état d'orthopositronium en observant et en mesurant un délai entre l'ionisation du positron et l'annihilation de celui-ci, pouvant permettre une séparation positron-électron. / The measurement of the theta-13 mixing angle, to which the Double Chooz experiment contributed, paves the way to future findings in neutrino physics. In this manuscript, we describe the characterization of some Double Chooz backgrounds. Cosmic muons that stop and decay in the detector are characterized by anisotropic emission of the scintillation light, causing the vertex to be poorly reconstructed. The resulting pulse shape distortion can be used to tag and remove such background. Fast spallation neutrons producing multiple recoil protons may produce a similar distortion in the pulse shape and can also be tagged. Pulse shapes are also used to identify the formation of ortho-positronium. The tagging of such electron-positron bound state is made possible by the induced distortion in the pulse shape due to the delay in the positron annihilation, and can be used for an electron-positron separation.