Ce travail porte sur la conception de réseaux large bande à double polarisation basées sur des antennes spirales d'Archimède. Ces antennes sont connues pour avoir une bande passante très large. Mais, dans un réseau, la bande passante est diminuée du fait de l'apparition de lobes de réseaux. Pour que le réseau fonctionne à double polarisation, il est nécessaire d'utiliser des éléments de polarisations opposées, ce qui accroit encore la distance entre les éléments possédant la même polarisation. Ceci fait ainsi apparaître les lobes de réseaux à des fréquences inférieures par rapport au cas à mono polarisation. Dans ce travail, une méthode analytique a été développée pour estimer la bande passante des réseaux d'antennes spirales. Cette méthode a montré que la bande passante maximale d'un réseau à distribution spatiale uniforme est d'environ une octave pour le cas à mono polarisation et inexistant pour le cas à double polarisation. Pendant la validation de la méthode d'estimation quelques résonances ont été observées. Des explications de ce phénomène sont présentées, ainsi que des possibles solutions. Pour élargir la bande passante du réseau, nous montrons qu'il est possible d'utiliser en même temps les deux tendances actuelles de conception de réseaux d'antennes large bande. En utilisant deux techniques issues de ces deux tendances, nous avons pu réaliser un réseau présentant une bande passante de 6:1. Des perspectives sont aussi présentées. / This work focuses on the design of wideband dual polarized arrays using spiral antennas. These antennas are known for having wideband properties. But, due to the presence of the grating lobes, the bandwidth is decreased when using an array instead of a single antenna. In order to obtain a dual polarized array, it is needed to use elements of opposite polarization, which creates great distances between same polarization elements, meaning an earlier presence of the grating lobes. In this work, an analytic method was developed to estimate the bandwidth of the spiral arrays. This method showed that the maximum bandwidth of uniform spiral arrays is about an octave, for the mono-polarized case, and nonexistent for the dual polarized case. Working on the validation of the method, some resonances were observed. Explanations are presented, as well as possible solutions. Trying to expand the bandwidth of the array, it was found that it is possible and suitable to use at the same time the two current design paradigms for wideband arrays. Using this idea, a 6:1 bandwidth concentric rings array using connected spirals was achieved. Perspectives are also presented.

Submitted by (edna.saturno@ufrpe.br) on 2017-02-14T16:45:41Z No. of bitstreams: 1 Jose Carlos Pacheco dos Santos.pdf: 638792 bytes, checksum: 6f28321f4c3fd95cd1db01843c010e88 (MD5) / Made available in DSpace on 2017-02-14T16:45:41Z (GMT). No. of bitstreams: 1 Jose Carlos Pacheco dos Santos.pdf: 638792 bytes, checksum: 6f28321f4c3fd95cd1db01843c010e88 (MD5) Previous issue date: 2007-09-03 / Aiming compare the indices of catch per unit of effort, hook location, and the condition of the fishes caught in two different types of hook, the “circle” (18/0) and “J” (9/0), 81 pelagic longline sets in a equatorial area were observed. The indices of catches for the albacore (Thunnus alalunga), yellowfin tuna (Thunnus albacares) and swordfish (Xiphias gladius) had not presented a significant differences between the two the types of hook, whereas the bigeye tuna (Thunnus obesus) target specie in these fisheries, were significantly more caught in the circle hooks than in “J” hooks. The “circle” hooks also showed a mortality rate lesser than the “J” hooks, thus increasing the indices of non target species discarded alive, as for example the blue and white marlin, which in Brazil are being caught beyond the quotas stipulated by the ICCAT (International Commission for the Conservation of Atlantic Tunas). This fact brings a substantial quality improvement results during the disembark, resulting a high final products qualifying to export and consequently a best sale price. / No intuito de comparar o desempenho dos anzóis, o índice de captura por unidade de esforço, o posicionamento do anzol no corpo do animal capturado, e a condição do peixe no recolhimento, foram observados 81 lances de uma pescaria comercial com espinhel, operando no Atlântico sul equatorial, na qual os anzóis “circulares” (tamanho 18/0) e os anzóis do tipo “J” (tamanho 9/0) foram utilizados de forma alternada. As taxas de captura para albacora branca (Thunnus alalunga), albacora laje (Thunnus albacares) e o espadarte (Xiphias gladius) não apresentaram diferenças significativas entre os dois tipos de anzol, enquanto que a albacora bandolim (Thunnus obesus) principal alvo da pesca, foi significativamente mais capturada nos anzóis “circulares”, os quais apresentaram, também, uma taxa de mortalidade no momento do recolhimento muito menor, podendo assim aumentar a taxa de descarte vivo de animais que compõem a fauna acompanhante, como por exemplo os agulhões negro e branco, que no Brasil estão sendo capturados além das cotas estipuladas pela International Commission for the Conservation of Atlantic Tunas - ICCAT. Tal fato resulta em uma melhora substancial da qualidade do pescado na hora do desembarque, resultando, assim, em uma melhor qualificação do produto final para exportação e consequentemente um melhor preço de venda.

Submitted by Cleide Dantas (cleidedantas@ufpa.br) on 2014-04-22T11:59:03Z No. of bitstreams: 2 license_rdf: 23898 bytes, checksum: e363e809996cf46ada20da1accfcd9c7 (MD5) Dissertacao_EspectrometriaRamanUV.pdf: 2381148 bytes, checksum: 8b683a780d3a45cc6d3327997b3f30d9 (MD5) / Approved for entry into archive by Ana Rosa Silva (arosa@ufpa.br) on 2014-06-10T13:11:00Z (GMT) No. of bitstreams: 2 license_rdf: 23898 bytes, checksum: e363e809996cf46ada20da1accfcd9c7 (MD5) Dissertacao_EspectrometriaRamanUV.pdf: 2381148 bytes, checksum: 8b683a780d3a45cc6d3327997b3f30d9 (MD5) / Made available in DSpace on 2014-06-10T13:11:00Z (GMT). No. of bitstreams: 2 license_rdf: 23898 bytes, checksum: e363e809996cf46ada20da1accfcd9c7 (MD5) Dissertacao_EspectrometriaRamanUV.pdf: 2381148 bytes, checksum: 8b683a780d3a45cc6d3327997b3f30d9 (MD5) Previous issue date: 2011 / Esta dissertação aborda a análise espectroscópica de algumas estruturas moleculares presentes no tabaco (Nicotiana glauca), matéria-prima do cigarro, e suas interações com a molécula de DNA. De acordo com sua importância, dentre a grande variedade presentes no cigarro, às moléculas estudadas foram as derivadas do ácido nicotínico: ácido nicotínico (niacina/vitamina B3), nicotinamida, trigonelina, nicotina, nornicotina e anabasina. As otimizações dessas estruturas foram inicialmente obtidas no software computacional Hyperchem 8.0, baseadas na teoria da mecânica molecular. Em seguida, elas foram otimizadas, utilizando-se o método de Teoria do Funcional da Densidade, na base B3LYP/ 6-311++G(d,p), simulado no software Gaussian 03. Uma vez as estruturas otimizadas, obtivemos os espectros de absorção UV, Raman, Infravermelho, Dicroísmo Circular e Densidade de Estados para caracterizar as mesmas utilizando método de Teoria do Funcional da Densidade Dependente do Tempo, também simulados no mesmo software. Ao final desse processo, foi também simulado via mecânica molecular, as interações dessas estruturas com a molécula de DNA com o intuito de verificar a potencialidade cancerígena, ou não, dessas substâncias. / This work is about spectroscopic analysis of some molecular structures present in tobacco (Nicotiana glauca), the base for cigarette, and their interactions with the DNA molecule. According to its importance, among the variety present in the cigarette, the molecules studied were derived from nicotinic acid, nicotinic acid (niacin / vitamin B3), nicotinamide, trigonelline, nicotine, nornicotine and anabasine. The optimizations of these structures were initially obtained in the Hyperchem 7.5 computational software based on the theory of molecular mechanics. Then, they were optimized using the method Density Functional Theory, on the basis B3LYP/ 6-311 + + G (d, p), simulated in software Gaussian 03. Once the optimized structures, we obtained the UV absorption, Raman, Infrared, Circular Dichroism and Density of States spectra using Time-Dependent Density Functional Theory also simulated the in the same software. At the end of this process was also simulated, via molecular mechanics, the interactions of these structures with the DNA molecule in order to verify the potential carcinogenic or not these substances.

Tese de Mestrado Integrado. Engenharia Mecânica. Faculdade de Engenharia. Universidade do Porto. 2013

The vectorial nature (polarization) of light plays a significant role in light-matter interaction that leads to a variety of optical devices. The polarization property of light has been exploited in imaging, metrology, data storage, optical communication and also extended to biological studies. Most of the past studies fully explored and dealt with the conventional polarization state of light that has spatially symmetric electrical field geometry such as linear and circular polarization. Recently, researchers have been attracted to light whose electric field vector varies in space, the so-called optical vector vortex beam (VVB). Such light is expected to further enhance and improve the efficiency of optical systems. For instance, a radially polarized light under focusing condition is capable of a tighter focus more than the general optical beams with a uniform polarization structure, which improves the resolution of the imaging system [1]. Interaction of ultrafast laser pulses with matter leads to numerous applications in material processing and biology for imaging and generation of microfluidic systems. A femtosecond pulse, with very high intensities of (10^{12} - 10^{13} W/cm^2), has the potential to trigger a phenomenon of optical breakdown at the surface and therefore induce permanent material modification. With such high intensities and taking into account the fact that most materials possess large bandgap, the interaction is completely nonlinear in nature, and the target material can be modified locally upon the surface and even further in bulk. The phenomenon of optical breakdown can be further investigated by studying the nonlinear absorption. Properties like very short pulse duration and the high irradiance of ultrashort laser pulse lead to more precise results during the laser ablation process over the long pulsed laser. The duration of femtosecond laser pulse provides a high resolution for material processing because of the significant low heat-affected zone (HAZ) beyond the desired interaction spot generated upon irradiating the material. Under certain condition, the interaction of intense ultrashort light pulses with the material gives rise to the generation of periodic surface structures with a sub-micron periodicity, i.e., much smaller than the laser wavelength. The self-oriented periodic surface structures generated by irradiating the material with multiple femtosecond laser pulses results in improving the functionality of the material's surface such as controlling wettability, improving thin film adhesion, and minimizing friction losses in automobile engines, consequently, influences positively on many implementations. In this work, we introduced a new method to study complex polarization states of light by imprinting them on a solid surface in the form of periodic nano-structures. Micro/Nanostructuring of diamond by ultrafast pulses is of extreme importance because of its potential applications in photonics and other related fields. We investigated periodic surface structures usually known as laser-induced periodic surface structures (LIPSS) formed by Gaussian beam as well as with structured light carrying orbital angular momentum (OAM), generated by a birefringent optical device called a q-plate (QP). We generated conventional nano-structures on diamond surface using linearly and circularly polarized Gaussian lights at different number of pulses and variable pulse energies. In addition, imprinting the complex polarization state of different orders of optical vector vortex beams on a solid surface was fulfilled in the form of periodic structures oriented parallel to the local electric field of optical light. We also produced a variety of unconventional surface structures by superimposing a Gaussian beam with a vector vortex beam or by superposition of different order vector vortex beams. This thesis is divided into five chapters, giving a brief description about laser-matter interaction, underlying the unique characterization of femtosecond laser over the longer pulse laser and mechanisms of material ablation under the irradiation of fs laser pulse. This chapter also presents some earlier studies reported in formation of (LIPSS) fabricated on diamond with Gaussian. The second chapter explains the properties of twisted light possessing orbital angular momentum in its wavefront, a few techniques used for OAM generation including a full explanation of the q-plate from the fabrication to the function of the q-plate, and the tool utilized to represent the polarization state of light (SoP), a Poincar'e sphere. Finally, the experimental details and results are discussed in the third and fourth chapters, respectively, following with a conclusion chapter that briefly summarizes the thesis and some potential application of our findings.

The objective of this study was to determine whether improvements could be made to increase the capture distance of traditional local exhaust ventilation (LEV) hoods by designing a circular slotted-hood. The criterion of success for this study was to achieve increases in capture velocity at an upstream distance equal to the diameter of the hood (11 inches). By increasing capture velocity further from the face, contaminant capture could take place at distances more convenient to the circular slotted-hood operator while maintaining adequate suction. This was to be achieved by the addition of two slots and a flange to a traditional conical hood opening. Three plates were designed to change the geometry of a plain conical hood (slot area: 0.1334, 0.0963 and 0.0694 ft2). They were tested at different airflow rates (243, 347, 467, 647, 897 cubic feet per minute) for a set number of distances from the hood face using a thermal anemometer. Three-dimensional maps of performance were created for visual comparisons, and t-tests were conducted to analyze performance by comparison of velocity at any point upstream of the hood. Velocity contours illustrated that two of the three designs had greater capture velocities compared to the standalone conical hood, and paired t-tests confirmed the significance (p<0.05). Each of the new designs failed to significantly increase capture distance further than 11 inches from the hood. However, increased velocities occurred near the hood opening (within 5 inches). These modest improvements for the largest slot design increases operating pressures by approximately 0.1" wg @ 250 cfm but 1.1" wg @ 650 cfm. Implementing these new designs would increase capture velocities close to the hood, although this advantage is offset by the cost it would require to compensate for the pressure loss incurred.

Despite the fame the prolific impressionistic, confessional poet, novelist, literary iconoclast, and pioneer of the Beat Generation, Jack Kerouac, has acquired since the late 1950’s, his written letters are not recognized as works of literature.  The aim of this thesis is to examine the different ways in which Kerouac develops and employs the poetics he is most known for in the letters he wrote to friends and publishers before becoming a well-known literary figure.  In my analysis of Kerouac’s poetics, I analyze 20 letters from Selected Letters, 1940-1956.  These letters were written before the publication of his best-known literary work, On The Road. The thesis attempts to highlight the characteristics of Kerouac’s literary control in his letters and to demonstrate how the examination of these poetics: repetition, language, and narration merits the letters’ treatment as works of artistic literature. Likewise, through the scrutiny of my first novella, “Trails” it then illustrates how the in-depth analysis of Kerouac’s letters improved my personal poetics, which resemble the poetics featured in the letters.

The fashion industry has for several years been driven by fast cycles of cheap industrial mass production and unsustainable consumption. At the same time the burden on the environment has been significant. New business models to prevent the environmental impact have therefore been developed, and circular business models have gained interest. Remanufacturing as one of the central activities within circular business model is not a new concept for the fashion and apparel industry, but there is a lack of focus of how to prioritise and develop the concept. The focus of the study is to understand the relative importance of the challenges and the enabling conditions that influence the adoption of remanufacturing as transition towards a circular economy within the fashion and apparel industry. The purpose is also to show the practitioners’ perspective on a relatively new phenomenon within the fashion and apparel industry, which can clarify how to further prioritise and direct the development of the concept. Furthermore, it is also expected to identify and investigate what might be the main challenges and the enabling conditions within remanufacturing. This research is conducted through a mixed method with a deductive approach where knowledge about generic challenges and the enabling conditions within remanufacturing was collected from a systematic literature review, as a modification of a Delphi method. An utilisation of online questionnaires led to verify relative importance of challenges and the enabling conditions for an adoption of remanufacturing as a transition towards a circular economy within the fashion and apparel industry. The result from the online questionnaire was analysed through finding consensus among the collected data. The result shows that the most important perspective for an adoption of remanufacturing was related to business model-, costs- and consumer perspective. Specifically, the challenge with how to change the business model seemed to be essential, and the lack of financial benefits and influencing the consumer behaviour was received to be of great importance. Identified enablers were collaborations and communication. There was no agreement among the most important challenges and the enabling conditions. However, the operations- and core- perspective where considered important by many. Significant consensus was found between the practitioners and their opinion about what influences an adoption of remanufacturing as a transition towards a circular economy. The practitioners’ verification and opinions of challenges and the enabling conditions can serve as support for managers in an adoption of remanufacturing, and provide guidance regarding what is essential to consider for an transition towards a circular economy. This study highlights and identifies what motivates and makes the adoption of remanufacturing attractive, as a way to transition towards a circular economy, in particular it provides support and guidance regarding how strategies can be developed and where to focus further development.

Recognizing the responsibility businesses has in sustainable development, a rising number of entrepreneurs are attempting to innovate business models together with digital technology to address environmental and societal needs. Circular business models is an example of how businesses can become more sustainable. However, there is a growing phenomenon of entrepreneurs suggesting digital platforms as a supportive element in an enterprise to enable circular features. This research aims to investigate the role of a single entrepreneur as a transition intermediary to sustainable development by using digital platforms. Additionally, this research aims to explore the success factors and challenges this entrepreneur can uncover. Contrary to most studies, this thesis adopts the entrepreneur's perspective as being a key actor in sustainable development but also as an innovative force in a socio-technical system. A case study was conducted on the Swedish online secondhand store Sellpy. The qualitative data were collected using semi-structured interviews. Given the thesis' exploratory research design, the finding can be used in further research as artifacts for more conclusive and generalizing research. The entrepreneur, as a transition intermediary, can establish valuable partnerships and networks to accelerate circulation and sustainability awareness. Additionally, the entrepreneur can influence others by spreading knowledge to engage other entrepreneurs to innovate businesses towards sustainability. The main success factors found in this case study is the approach to develop with the user community, digital ownership, skilled and diverse workforce, and partnerships with similar businesses. The challenges discovered was to maintain and find new users to enter the circular system and the external skepticism towards sustainability-oriented businesses.

The motion of neutral test particles, both massive and massless, in the space time of a charged source described by the Reissner-Nordström solution is studied. This solution is characterized by two parameters, mass and charge, which defines the horizons of the source. When the mass is larger than the charge, the solution describes a black hole, with two distinct horizons. When the mass and charge are equal there is an extremal black hole, and both horizons merge to one. Finally, when the charge is larger than the mass there is a naked singularity, with no horizon. The structure and properties of these different type of solution are presented and discussed. A general solution of the equations of motion is presented in function of the Weierstrass elliptic function &weierp;. In addition, the possible orbits for test particles are discussed, and the conditions for existence of closed, circular or escape orbits are presented. The classifications is made based on the particles energy, and the mass and charge of the source. We find that all mentioned orbits are allowed for the three different type of solutions. In particular, for extremal black holes and naked singularities, we find stable circular orbits located outside the event horizon and hence being visible for an external observer. / O movimento de partículas teste neutras, ambas massivas e sem massa, no espaço-tempo de uma fonte carregada descrita pela solução de Reissner-Nordström é estudada. Essa solução é caracterizada por dois parâmetros, massa e carga, que definem os horizontes da fonte. Quando a massa é maior que a carga tal solução descreve um buraco negro com dois horizontes distintos. Quando a massa e a carga são iguais há um buraco negro extremo, e ambos os horizontes se unem em um. Finalmente, quando a carga é maior que a massa, há uma singularidade nua, sem horizontes. A estrutura e as propriedades dessas diferentes soluções são apresentadas e discutidas. Uma solução geral da equação de movimento é apresentada em termos da função elíptica de Weierstrass, &weierp;. Além do mais as possiveis órbitas para uma partícula teste são discutidas, e as condições para existência de órbitas fechadas, circulares e de escape são apresentadas. A classificação é feita a partir da energia da partícula, e da massa e carga da fonte. Encontramos que todas as orbitas mencionadas são permitidas nos três diferentes tipos de soluções. Em partícular, para buracos negros extremos e singularidades nuas, encontramos órbitas circulares estáveis localizadas fora do horizonte de eventos e, consequentemente, sendo visível para observadores externos.