In this dissertation we aim to perform a multi-wavelength analysis of galaxy clusters. We discuss various methods for clustering in order to determine physical parameters of galaxy clusters required for this type of study. A selection of galaxy clusters was chosen from 4 papers, (Popesso et al. 2007b, Yoon et al. 2008, Loubser et al. 2008, Brownstein & Mo at 2006) and restricted by redshift and galactic latitude to reveal a sample of 40 galaxy clusters with 0.0 < z < 0.15. Data mining using Virtual Observatory (VO) and a literature survey provided some background information about each of the galaxy clusters in our sample with respect to optical, radio and X-ray data. Using the Kayes Mixture Model (KMM) and the Gaussian Mixing Model (GMM), we determine the most likely cluster member candidates for each source in our sample. We compare the results obtained to SIMBADs method of hierarchy. We show that the GMM provides a very robust method to determine member candidates but in order to ensure that the right candidates are chosen we apply a select choice of outlier tests to our sources. We determine a method based on a combination of GMM, the QQ Plot and the Rosner test that provides a robust and consistent method for determining galaxy cluster members. Comparison between calculated physical parameters; velocity dispersion, radius, mass and temperature, and values obtained from literature show that for the majority of our galaxy clusters agree within 3 range. Inconsistencies are thought to be due to dynamically active clusters that have substructure or are undergoing mergers, making galaxy member identi cation di cult. Six correlations between di erent physical parameters in the optical and X-ray wavelength were consistent with published results. Comparing the velocity dispersion with the X-ray temperature, we found a relation of T0:43 as compared to T0:5 obtained from Bird et al. (1995). X-ray luminosity temperature and X-ray luminosity velocity dispersion relations gave the results LX T2:44 and LX 2:40 which lie within the uncertainty of results given by Rozgacheva & Kuvshinova (2010). These results all suggest that our method for determining galaxy cluster members is e cient and application to higher redshift sources can be considered. Further studies on galaxy clusters with substructure must be performed in order to improve this method. In future work, the physical parameters obtained here will be further compared to X-ray and radio properties in order to determine a link between bent radio sources and the galaxy cluster environment. / MSc (Space Physics), North-West University, Potchefstroom Campus, 2013

<p>The development of a deuterium-deuterium/ tritium-deuterium (D-D/ D-T) pulsed neutron generator based on the principle of the Plasma Immersion Ion Implantation (PI3) technique is presented, in terms of investigating development of a compact system to generate an ultra short burst of mono-energetic neutrons (of order 1010 per second) during a short period of time (&lt / 20&mu / s) at repetition rates up to 1 kHz. The system will facilitate neutron detection techniques, such as neutron back-scattering, neutron radiography and time-of-flight activation analysis.</p> <p><br /> Aspects addressed in developing the system includes (a) characterizing the neutron spectra generated as a function of the target configuration/ design to ensure a sustained intense neutron flux for long periods of time, (b) the system was also characterised as a function of power supply operating conditions such as voltage, current, gas pressure and plasma density.</p>

Neste trabalho a técnica de multiportadoras OFDM (Orthogonal Frequency Division Multiplexing), aplicada a sistemas ópticos, é estudada, com foco principal na geração e transmissão dos chamados supercanais ópticos modulados em altíssimas taxas (até Terabits/s). O OFDM prevê um melhor aproveitamento da largura de banda e, quando comparada à técnica FDM (Frequency Division Multiplexing), permite uma redução de aproximadamente 50% do espectro ocupado. Esta economia proporcionada pela técnica torna-a forte candidata para uso em redes ópticas reconfiguráveis, pois provê melhor eficiência espectral aos sinais com reconfiguração de tráfego remoto. Dois cenários serão abordados: o primeiro, em que o sinal com multiportadoras moduladas de forma híbrida (QAM - quadradure amplitude modulation) é gerado no domínio elétrico para, em seguida, modular uma portadora óptica; e o segundo, no qual as multiportadoras são geradas no domínio óptico e, posteriormente, moduladas individualmente também no domínio óptico - e neste caso o formato de modulação pode variar. Para o segundo caso, três técnicas de geração de supercanais serão estudadas e avaliadas a fim de se realizar uma comparação entre elas. Neste trabalho também serão comparadas as técnicas de recepção óptica direta e coerente, aplicadas a sistemas OFDM. Os resultados para o estudo da geração de multiportadoras ópticas, obtidos através de simulações no software Optisystem v. 9.0, são validados por resultados experimentais obtidos no Laboratório de Comunicações Ópticas da Fundação CPqD. / This manuscript presents a study on the multicarrier modulation technique OFDM (Orthogonal frequency division multiplexing) applied to optical systems. The OFDM technique provides a better use of bandwidth and, compared with FDM (Frequency Division Multiplexing), provides a nearly 50% reduction of the occupied bandwidth. This feature makes the OFDM technique an ideal candidate for reconfigurable optical networks because it allows better spectral efficiency to the signals with remote traffic reconfiguration. The study focuses, mainly, on the theoretical investigation of OFDM applied to the transmission of the so-called optical superchannels, modulated at very high bit rates (above Terabits/s). Two scenarios are discussed: in the first, the multicarrier signal, modulated in a hybrid format (QAM - quadrature amplitude modulation), is generated in the electrical domain before modulating the optical carrier, and in the second the multicarrier beam is generated in the optical domain and subsequently each subcarrier is digitally modulated. In this second approach, three superchannel generation techniques are studied and evaluated for being compared. This work will also compare the direct and coherent detection techniques applied to OFDM systems. The results for the optical multicarrier generation study, obtained by numerical simulation (platform Optisystem v. 9.0), are validated by experimental results obtained at the Laboratory of Optical Communication CPqD Foundation.

<p>The development of a deuterium-deuterium/ tritium-deuterium (D-D/ D-T) pulsed neutron generator based on the principle of the Plasma Immersion Ion Implantation (PI3) technique is presented, in terms of investigating development of a compact system to generate an ultra short burst of mono-energetic neutrons (of order 1010 per second) during a short period of time (&lt / 20&mu / s) at repetition rates up to 1 kHz. The system will facilitate neutron detection techniques, such as neutron back-scattering, neutron radiography and time-of-flight activation analysis.</p> <p><br /> Aspects addressed in developing the system includes (a) characterizing the neutron spectra generated as a function of the target configuration/ design to ensure a sustained intense neutron flux for long periods of time, (b) the system was also characterised as a function of power supply operating conditions such as voltage, current, gas pressure and plasma density.</p>

Les chantiers de maintenance et d’assainissement dans les centrales nucléaires nécessitent la mise en place d’enceintes ventilées autour des zones contaminées afin de limiter la propagation de la contamination à l’environnement extérieur. L’air rentre dans l’enceinte aux travers d’ouvertures sous la forme d’un écoulement directionnel, orienté de l’extérieur vers l’intérieur, assurant ainsi le confinement dynamique. En raison des opérations qui se déroulent à l’intérieur de l’enceinte et des perturbations externes, il est possible que l’écoulement de confinement dynamique aux ouvertures soit perturbé et subisse des inversions locales et instationnaires, conduisant ainsi à transporter la contamination à l’extérieur de l’enceinte. La présente étude s’intéresse aux petites ouvertures de type fentes minces rectangulaires où l’écoulement au droit de celles-ci est généralement turbulent. Les principaux objectifs de la thèse sont d’une part d’identifier les conditions aérodynamiques susceptibles de produire le phénomène de rétrodiffusion aux ouvertures, d’autre part d’évaluer la capacité des approches de modélisation de la turbulence URANS et LES à reproduire les instabilités liées à ce type d’écoulement. Il a été montré que l’apparition du phénomène de rétrodiffusion est principalement liée à la présence d’une perturbation aéraulique additionnelle, de type jet turbulent ou sillage, en compétition avec l’écoulement initial de confinement dynamique. Des expériences de traçage gazeux ont été mises en place sur une maquette expérimentale dans le but de quantifier la rétrodiffusion en fonction des différentes conditions aérauliques à l’ouverture et des caractéristiques de celle-ci. Des visualisations des écoulements à l’ouverture ont également été réalisées à l’aide d’un dispositif de tomographie laser. Enfin, l’analyse des résultats des simulations CFD a démontré que les approches de type RANS ou URANS ne permettaient pas de reproduire les instabilités de l’écoulement conduisant au phénomène de rétrodiffusion, contrairement aux simulations des grandes échelles de la turbulence (LES) qui reproduisent fidèlement les structures locales et instantanées à l’origine du phénomène. / Operations of decommissioning and decontamination in nuclear facilities require setting up depressurized enclosures around contaminated areas in order to prevent leakage of radioactive materials, to the surrounding environment. Air passes through openings which generates a directional airflow ensuring the aerodynamic containment of hazardous material inside the enclosure. Due to operating activities inside or outside the enclosure, the directional flow might be disturbed. Consequently, local and unsteady backflows may occur at the opening leading to the outward transport of contamination. The current study is focused on airflow dynamics through small openings, such as rectangular slits where the initial inflow stream is turbulent. The main purposes of this work are to identify the required aerodynamic conditions likely to generate unsteady flow inversions at the studied opening and also to verify the ability of CFD simulations to predict this type of flow by using URANS and LES approaches. Results have shown that an additional flow, such as a turbulent jet or a wake in competition with inward flow, is the main cause leading to the leakage at the opening. Experiments, using gas tracer detection techniques, are conducted in order to quantify outflow leakage in the near field of the opening under different aerodynamic configurations and openings characteristics. A laser tomography technique is also implemented to visualize the external leakage airflow in the middle plane of the opening. CFD simulations have shown that a qualitative description of instantaneous leakage flow patterns at the opening can be achieved. This is characterized by the occurrence of local coherent structures transporting passive tracer outwards. Moreover, velocities obtained from CFD results (Large Eddy Simulations) are compared to those obtained from experimental measurements.

Neste trabalho a técnica de multiportadoras OFDM (Orthogonal Frequency Division Multiplexing), aplicada a sistemas ópticos, é estudada, com foco principal na geração e transmissão dos chamados supercanais ópticos modulados em altíssimas taxas (até Terabits/s). O OFDM prevê um melhor aproveitamento da largura de banda e, quando comparada à técnica FDM (Frequency Division Multiplexing), permite uma redução de aproximadamente 50% do espectro ocupado. Esta economia proporcionada pela técnica torna-a forte candidata para uso em redes ópticas reconfiguráveis, pois provê melhor eficiência espectral aos sinais com reconfiguração de tráfego remoto. Dois cenários serão abordados: o primeiro, em que o sinal com multiportadoras moduladas de forma híbrida (QAM - quadradure amplitude modulation) é gerado no domínio elétrico para, em seguida, modular uma portadora óptica; e o segundo, no qual as multiportadoras são geradas no domínio óptico e, posteriormente, moduladas individualmente também no domínio óptico - e neste caso o formato de modulação pode variar. Para o segundo caso, três técnicas de geração de supercanais serão estudadas e avaliadas a fim de se realizar uma comparação entre elas. Neste trabalho também serão comparadas as técnicas de recepção óptica direta e coerente, aplicadas a sistemas OFDM. Os resultados para o estudo da geração de multiportadoras ópticas, obtidos através de simulações no software Optisystem v. 9.0, são validados por resultados experimentais obtidos no Laboratório de Comunicações Ópticas da Fundação CPqD. / This manuscript presents a study on the multicarrier modulation technique OFDM (Orthogonal frequency division multiplexing) applied to optical systems. The OFDM technique provides a better use of bandwidth and, compared with FDM (Frequency Division Multiplexing), provides a nearly 50% reduction of the occupied bandwidth. This feature makes the OFDM technique an ideal candidate for reconfigurable optical networks because it allows better spectral efficiency to the signals with remote traffic reconfiguration. The study focuses, mainly, on the theoretical investigation of OFDM applied to the transmission of the so-called optical superchannels, modulated at very high bit rates (above Terabits/s). Two scenarios are discussed: in the first, the multicarrier signal, modulated in a hybrid format (QAM - quadrature amplitude modulation), is generated in the electrical domain before modulating the optical carrier, and in the second the multicarrier beam is generated in the optical domain and subsequently each subcarrier is digitally modulated. In this second approach, three superchannel generation techniques are studied and evaluated for being compared. This work will also compare the direct and coherent detection techniques applied to OFDM systems. The results for the optical multicarrier generation study, obtained by numerical simulation (platform Optisystem v. 9.0), are validated by experimental results obtained at the Laboratory of Optical Communication CPqD Foundation.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-04-20T12:33:06Z No. of bitstreams: 1 analuizasiqueiraferreira.pdf: 2299159 bytes, checksum: 4a5563c4c2ee9592b3902e4440a2031b (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-04-20T12:45:20Z (GMT) No. of bitstreams: 1 analuizasiqueiraferreira.pdf: 2299159 bytes, checksum: 4a5563c4c2ee9592b3902e4440a2031b (MD5) / Made available in DSpace on 2017-04-20T12:45:20Z (GMT). No. of bitstreams: 1 analuizasiqueiraferreira.pdf: 2299159 bytes, checksum: 4a5563c4c2ee9592b3902e4440a2031b (MD5) Previous issue date: 2011-04-11 / O uso de banda ultra-larga (ultra wideband - UWB) vem sendo tema de pesquisa na área da comunicação sem fio há cerca de 20 anos e os bons resultados obtidos tem levado à introdução de novas tecnologias no mercado de transmissão de dados a curtas distâncias. No entanto, o uso de UWB para a transmissão de dados através da rede elétrica (power line communications - PLC) ainda é uma questão de investigação em aberto, interessante e promissora para um conjunto específico de aplicações que demandam elevada taxa de transmissão em curtas distâncias e baixo custo, tais como impressoras, monitores, etc. Neste contexto, a presente dissertação analisa diferentes aspectos da transmissão UWB através de cabos de distribuição de energia elétrica. Um sistema UWB impulsivo é analisado quando i) o canal PLC é outdoor, linear e variante no tempo; ii) o canal PLC é indoor, linear e invariante no tempo; iii) há ruído AWGN (additive white Gaussian noise) e iv) há ruído AIGN (additive impulsive Gaussian noise). Além disso, são respondidas questões referentes à adequação do pulso UWB ao canal de comunicação, considerando o espectro do mesmo quando o canal PLC é outdoor ou indoor. As modulações UWB investigadas são pela posição do pulso (pulse position modulation - PPM) e pela amplitude do pulso (pulse amplitude modulation - PAM). Além de apresentar diretrizes para o projeto de um sistema UWB para aplicações PLC, a presente dissertação analisa diversas estratégias e técnicas para recepção e redução da complexidade computacional do receptor UWB. Os resultados indicam que o uso de UWB é interessante para algumas aplicações específicas que envolvam elevada taxa de transmissão, através de curtas distâncias e baixo custo. / Ultra wideband modulation (UWB) has been a subject of research in the wireless field for nearly 20 years and the good results achieved have led to the introduction of new technologies in the market of short distances data communication. However, the employment of UWB for data transmission over power lines (PLC) is still an open, interesting and promising research theme for a specific set of applications which require high throughput over short distances and low cost, such as printers, computer monitors, etc. In this context, this dissertation examines several aspects of the UWB transmission through electricity distribution cables. An UWB impulsive system is analyzed when i) the PLC channel is outdoor, linear and time invariant; ii) the PLC channel is indoor, linear and time invariant; iii) there is AWGN (additive white gaussian noise) and iv) there is AIGN (additive impulsive gaussian noise) noise. Moreover, many questions regarding the adequacy of UWB pulse for the communication channel are answered, taking into account its spectrum when the PLC channel is outdoor or indoor. The UWB modulations investigated are pulse position modulation (PPM) and pulse amplitude modulation (PAM). Apart from presenting some guidelines to project a UWB system, this work analyzes different strategies and techniques for reception that reduce the computational complexity of the UWB receiver. The results point out that UWB is interesting for some specific applications which require high data transmission rate in short distances and low cost.