Silicones are industrially important polymers characterized by a wide spectrum of chemical and physical properties with a number of important applications including automotive components, construction materials, isolating parts in electronic devices, flexible electronics, and medical products. Development of additive manufacturing methods for silicones enable production of complex and custom designed shapes and structures at both the micro- and macro-scale, economically feasible. In general, such materials can be fabricated using stereolithographic, extrusion-based, or inkjet printing techniques, in which silicones are polymerized using either photo- or heat-initiators. Silicones can also be crosslinked based on chemical reactions. Although this approach is supposedly the simplest, it has not been widely applied in additive manufacturing, as suitable technology for mixing and curing reactive inks without clogging nozzles has not be developed yet. To address this issue, a new 3D printer, that enables the fabrication of highly reactive and low viscous materials, has been developed and tested experimentally. The proposed fabrication method involves the ejection of two reactive droplets simultaneously from individual dispensers, merging and mixing them in free space outside the nozzle followed by deposition of the merged drop in a patterned format on a substrate. It was shown that the printing process is robust and stable more than 4 hours and it can be used on demand. By incorporating an XYZ positioner, it was possible to deposit droplets in an overlapping fashion to print any programmable shape featuring homogeneous structure, with a small number of pores. Moreover, due to the almost instantaneous reaction between two components (< 10s), the fabrication of very high aspect ratio (AR > 50) objects is possible. Lastly, the presented method can be easily adapted to print in free space without the use of support materials. / Thesis / Master of Applied Science (MASc)

The increasing demand on user rates in the fifth generation (5G) requires network architectures that can support high data rates with acceptable reliability. In order to increase the data rates in the presence of the current spectrum crisis, shrinking cells and reusing the spectrum is a proposed solution. Conventional implementation of dense cells requires a large number of expensive BSs to locally process and decode users’ signals. Another limiting factor that degrades the performance in a dense network is the inter-cell interference. A cloud radio access network (CRAN) is a promising solution to those cost, complexity, and interference challenges. A typical CRAN architecture consists of simplified low-cost base stations (BSs), termed radio units (RUs), that collect the radio frequency (RF) user equipments’ (UEs) signals and forward them over the fronthaul links to the central office (CO) where signal processing is done over shared resources. Besides the reduced cost and complexity of a CRAN, the joint processing at the CO enables joint interference mitigation techniques. However, the performance of CRANs depends critically on the availability of reliable fronthaul links with large bandwidth that may be expensive. Analog optical fronthaul links provide high data rates at lower cost and complexity since UEs’ signals are optically analog-modulated without digitalization, however, they suffer from other channel impairments and nonlinearities. In this thesis, analog optical fronthaul topologies are considered in which radio signals are forwarded over free-space optical (FSO) links, termed radio-over-free-space optical (RoFSO) links, and optical fiber (OF) links, termed radio-over-fiber (RoF) links. Firstly, a CRAN with mixed RF/RoFSO fronthaul is considered to investigate the performance improvement when RF fronthaul links are replaced one-by-one by RoFSO links. A novel joint optimization problem is introduced for the given architecture in which the weighted sum of UEs’ rates is maximized by jointly designing RF and RoFSO links. The optimization problem is solved over different numbers of RF and RoFSO links and under various weather conditions. Under favorable weather conditions, the replacement of 1 RF link by a RoFSO link is shown to increase the 50th percentile of UEs’ rates by 7 times. Secondly, the reliability of a CRAN with two-hop RoFSO/RoF fronthaul links is derived along with other performance metrics such as the average bit-error rate and the cumulative distribution function of UEs’ rates. For the given architecture, the Gaussian noise model of fiber nonlinearity is applied and an optimal OF average optical power is derived to minimize the outage probability. Using the optimal power, and under favorable weather conditions, the 50th percentile of user rate exceeds 1:5 Gbps. Finally, a CRAN with passive all-optical two-hop fronthaul links is considered where optical signals from the first RoFSO fronthaul hop are passively coupled into the RoF fronthaul link. The fronthaul outage probability is derived in the context of network planning to provide guidance on designing a set of system parameters. Those parameters include coverage area radius, density of RUs, RoFSO gain, RoFSO optical power and RoF length. / Thesis / Doctor of Philosophy (PhD) / The upcoming generation of wireless communications, termed fifth generation (5G), promises faster data rates and lower latency. In order to achieve this, more base stations (BSs) have to be deployed which increases the cost and complexity of the network. A solution to this challenge is to install simple BSs, i.e. radio units (RUs), that collect signals from users and forward them to a central office (CO) for joint processing which is referred to as a cloud radio access network (CRAN). The fronthaul network in a CRAN connects the RUs to the CO and it can be implemented using different kinds of links. While there are several fronthaul media (e.g., radio frequency (RF), free-space optical (FSO) links, copper lines, satellite communications, and optical fiber (OF)), optical links provide high data rates that are promising to achieve the 5G requirements. In this thesis, a novel architecture of a CRAN is considered in which analog optical links, namely FSO links and OF links, are used for fronthauling. Performance improvement in terms of rate and reliability is investigated and optimized through different design tools. In response to the challenges introduced by the proposed architecture, such as the nonlinearities of analog FSO and OF links, various design parameters are proposed in the optimization problems to tackle those challenges. Furthermore, a network planning framework is introduced to provide guidance and insights on designing the network.

Yes / Computer simulation is a powerful and convenient tool for the design and performance evaluation of free-space optical (FSO) communication systems. In this article, we present two simulation frameworks that incorporate not only the effects of atmospheric turbulence but also the impact of the angular fluctuations of the transmitter and receiver in FSO systems. In the first framework, the waveform of the optical signal is calculated sequentially from the transmitter to the receiver. Thus, it takes very long to run the simulation numerous times to obtain the statistical performance of the system. This is because the vast majority of simulation time is spent on the split-step beam propagation. In the second framework, we propose to isolate the beam propagation through atmospheric channel from the other effects. We compare the two frameworks in terms of accuracy and simulation time. We show that the second framework reduces the simulation time by more than a factor of 10 without sacrificing the accuracy under various conditions. / 10.13039/501100003725-National Research Foundation of Korea HR&D Center Funded by the Ministry of Science and ICT (Grant Number: 2022M1A3C2069728)

The physical-layer security of a line-of-sight (LOS) free-space optical (FSO) link using orbital angular momentum (OAM) multiplexing is studied. We discuss the effect of atmospheric turbulence to OAM-multiplexed FSO channels. We numerically simulate the propagation of OAM-multiplexed beam and study the secrecy capacity. We show that, under certain conditions, the OAM multiplexing technique provides higher security over a single-mode transmission channel in terms of the total secrecy capacity and the probability of achieving a secure communication. We also study the power cost effect at the transmitter side for both fixed system power and equal channel power scenarios.

Approximately, two-thirds of earth's surface is covered by water. There is a growing interest from the military and commercial communities in having, an efficient, secure and high bandwidth underwater wireless communication (UWC) system for tactical underwater applications such as oceanography studies and offshore oil exploration. The existing acoustic and radio frequency (RF) technologies are severely limited in bandwidth because of the strong frequency dependent attenuation of sound in seawater and the high conductivity of seawater at radio frequencies, respectively. Recently, underwater wireless optical communication (UWOC) has been proposed as the best alternative or complementary solution to meet this challenge. Taking advantage of the low absorption window of seawater in blue-green (400-550 nm) regime of the electromagnetic spectrum, UWOC is expected to establish secure, efficient and high data rate communication links over short and moderate distances (< 100 m) for versatile applications such as underwater oil pipe inspection, remotely operated vehicle (ROV) and sensor networks. UWOC uses the latest gallium nitrite (GaN) visible light-emitting diode (LED) and laser diode (LD) transmitters. Although some research on LED lased UWOC is being conducted, both the military and academic 5 research communities are favoring the use of laser beams, which potentially could enhance the available bandwidth by up to three orders of magnitude. However, the underwater wireless channel is optically very challenging and difficult to predict. The propagation of laser beams in seawater is significantly affected by the harsh marine environments and suffers from severe attenuation which is a combined effect of absorption and scattering, optical turbulence, and multipath effects at high transmission rates. These limitations distort the intensity and phase structure of the optical beam leading to a decrease in signal-to-noise ratio (SNR) which ultimately degrades the performance of UWOC links by increasing the probability of error. In this dissertation, we seek to experimentally demonstrate the feasibility of short range (≤ 20 m) UWOC systems over various underwater channel water types using different modulation schemes as well as to model and describe the statistical properties of turbulence-induced fading in underwater wireless optical channels using laser beam intensity fluctuations measurements.

Made available in DSpace on 2017-07-21T18:15:37Z (GMT). No. of bitstreams: 1 Zingara Rocio Eurich.pdf: 7116862 bytes, checksum: 3aec67d482562b1faa0f2a199b297843 (MD5) Previous issue date: 2014-02-03 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / According to the importance of public spaces, especially parks, both for city population and the urban environment, this research aims to analyze the conditions of the squares of the city of Ponta Grossa-PR. For that there were used methodologies which were capable of evaluate qualitative and quantitative the afforestation and infrastructure of squares and to analyze the spatial aspects, checking the morphology, typology, distribution and functionality of these spaces, in order to promote and enhance the public open spaces of the city. Regarding the spatial distribution of the squares it was found that the concentration of them are presented in the central area of the city, and the downtown area has the highest Index for Quarter Square (IAPB), with 4.25%. While verified the morphology of the squares, it was observed that most of them 30.1% has the rectangular shape. Some areas considered as squares by the City Hall of Ponta Grossa are shown as an area without direct social function, and 83.1% could be considered effectively as squares. The most common function in the squares is the passive leisure (92.6%). In the survey of afforestation there were accounted 2,369 individuals, which 55.56% are from exotic origin. Regarding the infrastructure, the roads (85.71%), lighting (79.76%) and banks (69.05%) were the most frequent structures in squares. From the results, it is observed that there is a heterogeneous scenario in all analyzed items, since there are squares that have an extensive infrastructure and some areas have no equipment available to the population. / Em função da importância dos espaços públicos, sobretudo de praças, tanto para a população citadina como para o ambiente urbano, a presente pesquisa busca analisar as condições em que se encontram as praças da cidade de Ponta Grossa-PR. Para tanto se utilizou metodologias capazes de avaliar qualiquantitativamente a arborização e infraestrutura das praças e analisar os aspectos espaciais, verificando a morfologia, tipologia, distribuição e funcionalidade desses espaços, com o intuito de promover e valorizar os espaços livres públicos da cidade. Quanto à distribuição espacial das praças verificou-se que a concentração das mesmas apresenta-se na área central da cidade, sendo o Centro a região com maior Índice de Praças por Bairro (IAPB), com 4,25%. Quando verificado a morfologia das praças observou-se que a maioria das praças 30,1% possui o formato retangular. Algumas áreas consideradas pela Prefeitura Municipal de Ponta Grossa como praças se comportam como espaço sem função social direta, sendo que 83,1% podem ser consideradas efetivamente como praças. A função mais frequente nas praças é o lazer passivo (92,6%). No levantamento da arborização contabilizou-se 2.369 indivíduos os quais 55,56% são de origem exótica. E quanto ao levantamento da infraestrutura os caminhos (85,71%), iluminação (79,76%) e bancos (69,05%) foram as estruturas mais frequentes nas praças levantadas. A partir dos resultados observa-se um cenário heterogêneo em todos os itens analisados, visto que há praças que contam com ampla infraestrutura e algumas áreas não possuem nenhum equipamento disponível para a população.

Electroabsorption is the physical phenomenon by which the absorption of light in a medium can be controlled by applying an electric field. The Quantum–Confined Stark Effect, which makes the absorption band–edge in quantum wells very field–dependent, together with the strong absorption peak provided by excitons, are the physical foundations for the success of electroabsorption modulators based on quantum well structures in telecommunication networks. This thesis describes the design and fabrication of surface–normal electroabsorption modulation devices. The techniques needed to understand the design and fabrication of surface–normal multiple quantum well optical modulators are introduced, as are the various characterisation techniques used during and after the fabrication. Devices for several types of applications have been designed, fabricated, characterised and in some cases integrated into optical systems: – Two–dimensional arrays of 128´128 pixel amplitude modulators grown on GaAs substrates have been fabricated and characterised. Speeds of up to 11700 frames per second were demonstrated, limited by the output electronics of the computer interface. – Large–area modulators grown on GaAs substrates for free–space optical communication were developed, with an active area of 2cm2 and a modulation speed of several megahertz. Contrast ratios up to 5:1 on full modulator areas were measured. Problems limiting the yield and modulation speed of such devices have been studied, and solutions to overcome them have been demonstrated. – Large–area devices grown on InP substrates for free–space optical communication have been developed. Contrast ratios of up to 2:1 for transmissive types have been demonstrated. – Devices consisting of two rows of pixels, grown on GaAs substrates, with an active area of 22mm´5mm, divided into 64 or 128 pixels per row have been developed. These amplitude modulation devices were designed for optical signal processing applications. – One variant of these optical signal processing devices was also characterised as a ternary, binary amplitude and binary phase modulator array. – The use of GaAs multiple quantum well optical modulators in a free–space optical retro–communication system has been studied. An opto–mechanical design for a modulating retro–reflector is described, allowing a large field of view in one direction using reflecting, resonant–cavity modulators for high contrast ratios. / QC 20100802

Electromagnetic wave absorbing properties of SiC-based and alumina ceramic woven fabrics have been investigated. Electrical conductivities of SiC-based ceramic woven fabrics were modified by heat treatment in air resulting in their oxidation. Surface properties of alumina woven fabrics were altered by gold-sputtering resulting in a high conductivity layer on the surface of the wovens. Electromagnetic wave interactions of single layer and double layered combinations of these ceramic woven fabrics were determined in 17-40 GHz frequency range using &ldquo / free-space&rdquo / method. Electromagnetic wave absorption potential of ceramic woven fabrics with different chemical compositions and woven types were correlated with their material properties by X-ray diffraction, scanning electron microscopy and electrical conductivity measurements. Effects of modifications and varying woven fabric arrangements in combinations on the electromagnetic wave absorption potential of the ceramic woven fabrics have been discussed. Various double layer combinations of SiC-based and alumina woven fabrics revealed a promising potential in terms of both reduced reflection and transmission resulting in more than ~95% absorption in millimeter wavelength range, which makes them powerful candidate materials for electromagnetic wave absorption applications.

Den här uppsatsen baseras på en enkätundersökning bland lärare i en kommun i Östergötland, där lärarnas uppfattning, om det fanns plats för passion i vardagspraktiken och om det uppmuntrades och stöttades av skolledningen, undersöktes. Frågeställningarna, om lärarnas uppfattning om de har någon passion, om de får möjlighet att utöva den i sin vardagsprakrik, om de stimuleras eller hindras av styrdokumenten, samt om de upplever att skolledningen tillför inspirerande motivation i en passionerad vardagspraktik, ledde till enkätfrågorna. Detta är en kvantitativ studie i enkätform, inom det empirisk-induktiva fältet, med en kvalitativt inriktad analys då svaren i enkäten är lärares uppfattningar av bl.a. relationer till skolledning och kollegor. Den har sin grund i positivismen, med så objektiva frågeformulering som möjligt samt lärarnas uppfattningar av fenomen och företeelser som svar (Bryman, 2002). Goda exempel av lärares uppfattningar analyserades och sammanfattades utifrån den förståelse som tidigare forskning gett. Aktuell forskning undersöktes och sammanlänkades med de undersökningsresultat som erhållits. Lärarna uppfattar att de får utrymme för sina passioner i vardagspraktiken, att de uppmuntras och stöttas av skolledningen och att deras arbete med passioner är lönemeriterande. Skolledarna möter lärarna i pedagogiska diskussioner, men är mindre benägna att ge tid schemamässigt. Vad gäller styrdokumenten anser lärarna att de inte är något hinder för en passionerad vardagspraktik. Kärnan i undersökningen var ändå om lärarna ansåg att de hade någon passion och det fanns en samstämmighet runt den elevcentrerade passionen: Elevernas lärande och elevernas välmående var i fokus när de skulle ange sin passion i vardagspraktiken. / This essay is based on a survey among teachers in a municipality in Östergötland, where the teachers' opinion, if there was room for passion in everyday practice and if it was encouraged and supported by the school management, was investigated. The issues of teachers' perception if they have passion, if they are given the opportunity to exercise it in the everyday practice, if they are stimulated or hindered by the policies, and whether they interpret the school management adding inspiring motivation in a passionate everyday practice, led to the survey questions.   This is a quantitative survey in the form of a questionnaire, in the empirical-inductive field, with a qualitatively oriented analysis where the answers in the questionnaire are teachers' experiences of, inter alia, relationships with school management and colleagues. It is rooted in positivism, with objective questionnaires, as well as teachers' perceptions of phenomena and phenomena responses (Bryman, 2002).   Good examples of teachers impressions were analyzed and summarized based on the understanding that was given by previous research. Current research was studied and linked with the findings obtained. The teachers perceive they get space for their passions in everyday practice, they are encouraged and supported by the school management and that their work passions are wage meritorious. School leaders meet teachers in educational discussions, but are less likely to give time schedule-wise. As for the policy documents the teachers consider them not to be an obstacle to a passionate everyday practice.   The core of the investigation was still if the teachers perceived that they had any passion, and there was a consensus around the student-centered passion: Students' learning and students' well-being was the focus when their passion in everyday practice was to be mentioned.

This study uses the concepts of everyday politics and cultural resistance to explore how young people are experimenting with ‘free spaces’ in which to develop alternative ideas and practices within the food justice movement. Through a case study of the Spring Ridge Commons – a youth-generated free space – this research describes how youth are redefining relationships to place and to people by practicing alternative foodways like urban foraging; creating decommodified food sources; sharing skills and knowledge through peer-to-peer networks; building community through relationships of mutual support; and experimenting with non-hierarchical governance. Such practices have potential implications for child and youth care such as: reconnecting youth and adults through shared practice and meaningful work in “real life” politics and community building, reconceptualizing 'youth' and 'adult' such that both have greater access to acts of cultural production, and creating experiences of democracy in everyday life. / Graduate