Thesis (Ph. D.)--University of Pennsylvania, 1984. / Includes bibliographical references (p. [196]-206) and index.

Thesis (Ph. D.)--University of Pennsylvania, 1984. / Includes bibliographical references (p. [196]-206) and index.

Η παρούσα εργασία περιλαμβάνει την μελέτη και τον χαρακτηρισμό του καναλιού ενός δορυφορικού καναλιού καθώς και την επίγεια διάδοση Αρχικά γίνεται μια εισαγωγή στα ασύρματα συστήματα τηλεπικοινωνιών . Ειδικά παρουσιάζεται το δορυφορικό σύστημα και αναλύονται τα μέρη αυτού. Γίνεται παρουσίαση των δορυφορικών ζεύξεων και μελετάται το περιβάλλον μέσα στο οποίο λαμβάνει χώρα μια σύνδεση. Αρχικά αναλύονται οι μέθοδοι διάδοσης της ηλεκτρομαγνητικής ακτινοβολίας και οι διάφορες εξασθενήσεις που υφίσταται το σήμα λόγω φαινομένων της ατμόσφαιρας καθώς και άλλων επιδράσεων. Γίνεται έπειτα μια εκτενής αναφορά στις διαλείψεις και στην ταξινόμησή τους. Στη συνέχεια γίνεται μια κατηγοριοποίηση των διαλείψεων αυτών με βάση τα χαρακτηριστικά τους. Ακολουθεί η στατιστική αναπαράσταση των καναλιών με διαλείψεις χρησιμοποιώντας τις βασικότερες κατανομές που συναντώνται στα τηλεπικοινωνιακά συστήματα. / This work includes the study and channel characterization for a satellite signal and also its terrestrial propagation. First we introduce the wireless telecommunications systems. We focus on the satellite system and its components are analyzed. A presentation of the satellite links follows and the propagation environment is studied. We analyze the propagation methods of electromagnetic radiation and the various losses that the signal endures due to atmospheric phenomena and other effects. There is then a reference to the fading channel and and its analysis. Then there is categorization of the fading according to its characteristics. The statistical representation of the fading channel follows, with the use of the key distributions found in telecommunication systems. Lastly, the satellite transmission is simulated for various orbit heights and conditions

Orientador: Ana Silvia Lopes Davi Médola / Banca: Mauro de Souza Ventura / Banca: Francisco Rolfsen Belda / Resumo: O presente trabalho tem o objetivo de refletir sobre o papel do jornalista contemporâneo diante do advento da internet e responder questões acerca de como os meios de comunicação devem se estruturar numa realidade em que o domínio das tecnologias digitais pode transformar qualquer um em 'repórter de ocasião' ou fonte exclusiva de informação. Propõe ainda ampliar o debate sobre as possibilidades de se aproveitar essa participação externa, como, por exemplo, fazer dos internautas colaboradores e não concorrentes. Até que ponto, essas participações são benéficas? De qualquer forma elas são efetivamente úteis ao jornalismo? Pode-se inferir que as ferramentas tecnológicas trazidas pela Web 2.0 que os usuários têm a seu favor são úteis, benéficas para os jornalistas quando colaboram com o processo de confecção da notícia como fonte de informação. No entanto, a colaboração não pode ser o produto final, apenas a fonte primária. A confecção deve ficar a cargo do profissional de jornalismo concluímos neste estudo. Dentro deste contexto de colaboração e compartilhamento online, temos as redes sociais como potenciais 'auxiliares', especialmente para os jornalistas que trabalham com entretenimento e mundo das celebridades. Por fim, foram selecionados casos extraídos da rede social Twitter para exemplificar como a colaboração dos usuários funciona para traçar desta forma considerações sobre o encadeamento midiático do sistema de microblog com a mídia convencional, a partir da identificação e análise de casos específicos do jornalismo de entretenimento e celebridade servindo como pauta de matérias publicadas em diversos veículos de comunicação ou mesmo como espaço para reverberação de conteúdos publicados / Abstract: The present project aims to reflect the contemporary role of the journalist in face of the advent of the impact the internet and answer questions about how the media trade should structured themselves, since the power of digital technologies can transform anyone into 'occasional reporter' or exclusive source of information. The project also suggests the increseament of the increseament of the debate about the possibility to take advantage of these participators, transforming them into partners, not competitors. To what extent these participations are beneficial? How they are actually useful to journalism? The technologies of the Web 2.0 are useful when they collaborate with the process of the notice confection as information source. However, the contribution cannot be the end, only the primary source. Inside of this context of contribution and sharing online, we have the social networks especially as potential help, for the journalists who work with entertainnment and world of the celebrities. Finally, the project draws consideration abouto the link between twitter and conventional media, from the identification and analysis of specific cases extracted from microblog, materials published in several media or even space for reverberation of published contents / Mestre

O objetivo deste estudo consiste em interpretar o uso dos links nas postagens dos blogs de pesquisadores brasileiros. A investigação tem início através da análise dos links dos blogs inclusos no Anel de Blogs Científicos. Sua efetivação ocorre a partir da composição dos aglomerados das redes de links oriundas dos blogrolls, dos blogs de ciência circunscritos ao Anel de Blogs Científicos. Em momento posterior, foram categorizados os 640 links inclusos no conteúdo das postagens de acordo com as categorias de funções e motivações obtidas de estudos precedentes, e de categorias que emergiram do fenômeno estudado. Por fim, a compreensão das motivações para a inserção de links na composição das postagens dos blogs e as funções que esses links cumprem foi inferida através da Análise de Conteúdo dos contextos aos quais os links estavam inseridos, considerando os espaços aos quais o leitor é remetido a partir de sua ativação. Resultados indicam que o conceito de diários pessoais, em que as mensagens têm um número reduzido de caracteres e são apresentadas em ordem cronológica inversa, só se confirmam em relação a essa última característica, decorrente dos softwares de composição que assim a condicionam. A pouca incidência de links em relação aos blogs de pesquisadores permite afirmar que há uma baixa conectividade por parte dos blogs compostos por diferentes atores que compõem a amostra relativa ao Anel e às áreas as quais pertencem, reforçada pela baixa existência de links entre as postagens e os comentários. Reforça essa questão a ausência de links trackbaks entre os comentários das postagens selecionadas. A primeira das hipóteses que guia o estudo foi refutada, na medida em que as postagens não indicam rearticulações através de seus links de interlocuções entre pesquisadores, leigos e jornalistas científicos, não permitindo reordenações e maior amplitude dessas interlocuções junto à sociedade. A segunda das hipóteses foi confirmada por se basear no fato de que os links colocam em evidência que os documentos e fontes de informação relacionados a partir desses dispositivos (links) são um híbrido de uso e socialização de informações, estas tanto circunscritas às fontes e documentos científicos quanto a fontes e documentos que não se caracterizem tradicionalmente como parte do ciclo de produção científica. A terceira hipótese que guia este estudo foi refutada, pois os dados analisados indicam que o uso dos links por pesquisadores brasileiros não se baseia em funções e motivações que objetivam agilizar processos de produção e comunicação dos resultados de pesquisa através de blogs. / The aim of this study is to interpret the use of links on the blog postings by Brazilian researchers. The investigation begins by examining the links of blogs included in the Anel de Blogs Científicos (Ring of Science Blogs). Its effectiveness is based on the combination of clusters of link networks coming from the blogrolls restricted to the Anel de Blogs Científicos. Afterwards the 640 links included in the content of the posts were classified according to categories of functions and motivations obtained from previous studies and from categories that emerged from the phenomenon studied. Finally, understanding of motivations for the insertion of links on the composition of the blog posts and the functions that such links fulfill were inferred by Content Analysis of the contexts to which the links were inserted, considering the locations to which the reader is referred from its activation. Results indicate that the concept of personal journals, in which the messages have a limited number of characters and are presented in reverse chronological order, is only confirmed through this latter feature, as a result of the software used for composing the posts. The low incidence of links in relation to blogs of researchers allows us to state that there is low connectivity by blogs composed by different authors who form the sample relative to the Anel and the areas which they belong to, reinforced by the low availability of links between posts and comments. What reinforces this point is the absence of trackbak links among comments of the selected posts. The first hypothesis guiding the study was refuted, in that the posts do not indicate rearticulations through its links of dialogues among researchers, lay people and science journalists, not allowing rearrangements and higher amplitude of these dialogues with society. The second hypothesis was confirmed by relying on the fact that the links give evidence that the documents and related sources of information from those devices (links) are a hybrid of using and sharing of information – this information being limited to the sources and scientific documents as much as to sources and documents that are not traditionally characterized as part of the cycle of scientific production. The third hypothesis that guides this study was refuted because the data analyzed indicate that the use of links by Brazilian researchers is not based on functions and motivations that aim at streamlining production processes and communication of research results through blogs.

Recent trends in mobile broadband indicates that the available radio frequency (RF) spectrum will not be enough to support the data requirements of the immediate future. Visible light communication, which uses visible spectrum to transmit wirelessly could be a potential solution to the RF ’Spectrum Crunch’. Thus there is growing interest all over the world in this domain with support from both academia and industry. Visible light communication( VLC) systems make use of light emitting diodes (LEDs), which are semiconductor light sources to transmit information. A number of demonstrators at different data capacity and link distances has been reported in this area. One of the key problems holding this technology from taking off is the unavailability of power efficient, miniature LED drive schemes. Reported demonstrators, mostly using either off the shelf components or arbitrary waveform generators (AWGs) to drive the LEDs have only started to address this problem by adopting integrated drivers designed for driving lighting installations for communications. The voltage regulator based drive schemes provide high power efficiency (> 90 %) but it is difficult to realise the fast switching required to achieve the Mbps or Gbps data rates needed for modern wireless communication devices. In this work, we are exploiting CMOS technology to realise an integrated LED driver for VLC. Instead of using conventional drive schemes (digital to analogue converter (DAC) + power amplifier or voltage regulators), we realised a current steering DAC based LED driver operating at high currents and sampling rates whilst maintaining power efficiency. Compared to a commercial AWG or discrete LED driver, circuit realised utilisng complementary metal oxide semiconductor (CMOS) technology has resulted in area reduction (29mm2). We realised for the first time a multi-channel CMOS LED driver capable of operating up to a 500 MHz sample rate at an output current of 255 mA per channel and > 70% power efficiency. We were able to demonstrate the flexibility of the driver by employing it to realise VLC links using micro LEDs and commercial LEDs. Data rates up to 1 Gbps were achieved using this system employing a multiple input, multiple output (MIMO) scheme. We also demonstrated the wavelength division multiplexing ability of the driver using a red/green/blue commercial LED. The first integrated digital to light converter (DLC), where depending on the input code, a proportional number of LEDs are turned ON, realising a data converter in the optical domain, is also an output from this research. In addition, we propose a differential optical drive scheme where two output branches of a current DAC are used to drive two LEDs achieving higher link performance and power efficiency compared to single LED drive.

abstract: Current treatment methods for cerebral aneurysms are providing life-saving measures for patients suffering from these blood vessel wall protrusions; however, the drawbacks present unfortunate circumstances in the invasive procedure or with efficient occlusion of the aneurysms. With the advancement of medical devices, liquid-to-solid gelling materials that could be delivered endovascularly have gained interest. The development of these systems stems from the need to circumvent surgical methods and the requirement for improved occlusion of aneurysms to prevent recanalization and potential complications. The work presented herein reports on a liquid-to-solid gelling material, which undergoes gelation via dual mechanisms. Using a temperature-responsive polymer, poly(N-isopropylacrylamide) (poly(NIPAAm), the gelling system can transition from a solution at low temperatures to a gel at body temperature (physical gelation). Additionally, by conjugating reactive functional groups onto the polymers, covalent cross-links can be formed via chemical reaction between the two moieties (chemical gelation). The advantage of this gelling system comprises of its water-based properties as well as the ability of the physical and chemical gelation to occur within physiological conditions. By developing the polymer gelling system in a ground-up approach via synthesis, its added benefit is the capability of modifying the properties of the system as needed for particular applications, in this case for embolization of cerebral aneurysms. The studies provided in this doctoral work highlight the synthesis, characterization and testing of these polymer gelling systems for occlusion of aneurysms. Conducted experiments include thermal, mechanical, structural and chemical characterization, as well as analysis of swelling, degradation, kinetics, cytotoxicity, in vitro glass models and in vivo swine study. Data on thermoresponsive poly(NIPAAm) indicated that the phase transition it undertakes comes as a result of the polymer chains associating as temperature is increased. Poly(NIPAAm) was functionalized with thiols and vinyls to provide for added chemical cross-linking. By combining both modes of gelation, physical and chemical, a gel with reduced creep flow and increased strength was developed. Being waterborne, the gels demonstrated excellent biocompatibility and were easily delivered via catheters and injected within aneurysms, without undergoing degradation. The dual gelling polymer systems demonstrated potential in use as embolic agents for cerebral aneurysm embolization. / Dissertation/Thesis / Ph.D. Bioengineering 2012

Resumo: O interesse em conhecer o comportamento supercondutor tem sido cada vez maior nas últimas décadas. Na busca de melhores características supercondutoras, descobriu-se que amostras volumétricas apresentam características muito diferentes de amostras mesoscópicas (amostras com dimensões próximas dos comprimentos de penetração de London e coerência). Como exemplo, podemos citar a não formação de rede de Abrikosov, como consequência do efeito de confinamento (efeito associado às dimensões reduzidas da amostra) e também uma mudança considerável nos valores dos campos críticos. Neste trabalho foram resolvidas as equações de Ginzburg-Landau dependentes do tempo (TDGL), para fazer uma análise detalhada da dinâmica de vórtices em filmes finos mesoscópicos. Para revolvê-las, utilizamos o método das variáveis de ligação com invariância de calibre, adaptado para o algoritmo de diferenças finitas, utilizado para obter a densidade dos pares de Cooper e também curvas de magnetização. O estudo dessa dinâmica de vórtices, foi feito em três amostras com superfícies geométricas diferentes (côncova, convexa e rugosa). Observamos que na comparação entre as duas primeiras, há uma diferença considerável nos valores dos campos críticos, bem como no comportamento da magnetização comparado com um filme plano. Já para a amostra de superfície rugosa, observamos que existe uma competição entre o efeito de confinamento e a rugosidade em relação à configuração dos vórtices. Apresentamos também, uma tabela que mostra resumidamente os estados estacionários dos vórtices nas três amostras. / Abstract: The interest to investigate the investigate the behavior of a superconductor has grown in the last few decades. Having in mind to search for better superconducting characteristics, it has been found that bulk samples present characteristics much more different than mesoscopic samples (samples with dimensions of the same order of the same order of the London penetration length and the coherence length). As an example, we can mention the non-formation of an Abrikosov vortex lattice as a consequence of the confinement effect (effect associated with the reduced dimensions of the sample) and also considerable change in the critical field values. In the present work we solved the time dependent Ginzburg-Landau equation (TDGL), in order to make a detailed analysis of the vortex dynamics in mesoscopic thin films. To solve these equations, we have used the link variables method which is gauge invariant. From this, we obtain the Cooper pair density and the magnetization curves. The vortex dynamics was investigated for three different surfaces of the film (concave, convex, and irregular). We have observed that, with respect to the parabolic geometries, there is a considerable difference for the critical fields, as well as for the behavior of the magnetization compared to a flat film. On the other hand, for a sample with an irregular surface, we have seen that there is a competition between the confinement effect and rugosity with respect to vortex configurations. We also present a table which summarizes the vortex stationary states for the three topologies mentioned above. / Orientador: Paulo Noronha Lisboa Filho / Coorientador: Edson Sardella / Banca: Wilson Aires Ortiz / Banca: Clelio Clemente de Souza Silva / Mestre

Millimeter wave technologies present an appealing solution for increasing data throughputs as they provide abundant contiguous channel bandwidths as compared to conventional microwave networks. However, millimeter wave technologies suffer from severe propagation limitations and channel impairments such as atmospheric attenuation and absorption, path and penetration losses, and blockage sensitivity. Therefore, phased arrays and beamforming technologies are necessary to compensate for the degraded signal levels due to the aforementioned factors. Namely, base stations and mobile stations utilize directional transmission in the control- and data- plane for an enhanced channel capacity, which results in initial access challenges due to the absence of omni-directional transmission. Here the base station and mobile station are compelled to exhaustively search the entire spatial domain, i.e., in order to determine the best beamforming and combining vectors that yield the highest received signal level. Overall, a wide range of studies have looked at the initial beam access challenges in millimeter wave networks, with most efforts focusing on iterative and exhaustive search procedures, as well as subarrays schemes and out-of-band beam access. However, these studies suffer from significant signaling overhead attributed to the prolonged beam scanning cycle. In particular, access times here are excessively high that exceed control plane latencies and coherence times. Furthermore, existing work suffer from high computational complexity, power consumption, energy inefficiency, as well as low directivities and high outage probabilities. In light of the above, the contributions in this dissertation propose fast initial beam access schemes based upon novel meta-heuristic search schemes and beamforming architectures. These contributions include modified search procedures inspired by Nelder Mead, Luss-Jaakola, divide-and-conquer with Tabu search, generalized pattern search, and Hooke Jeeves methods. Furthermore, efficient and highly-directive access schemes are also developed in this dissertation levering sidelobe emissions, grating lobes and Hamming codes. The overall performance of the proposed solutions here is extensively evaluated versus traditional access schemes and incorporating different channel and path loss models. Finally, this dissertation addresses the problem of link sensitivity and blockage effects in millimeter wave networks, a subsequent stage to beam access and link association. Nevertheless, a novel link recovery procedure is proposed here that features instantaneous link-recovery and high signal levels.

O objetivo deste estudo consiste em interpretar o uso dos links nas postagens dos blogs de pesquisadores brasileiros. A investigação tem início através da análise dos links dos blogs inclusos no Anel de Blogs Científicos. Sua efetivação ocorre a partir da composição dos aglomerados das redes de links oriundas dos blogrolls, dos blogs de ciência circunscritos ao Anel de Blogs Científicos. Em momento posterior, foram categorizados os 640 links inclusos no conteúdo das postagens de acordo com as categorias de funções e motivações obtidas de estudos precedentes, e de categorias que emergiram do fenômeno estudado. Por fim, a compreensão das motivações para a inserção de links na composição das postagens dos blogs e as funções que esses links cumprem foi inferida através da Análise de Conteúdo dos contextos aos quais os links estavam inseridos, considerando os espaços aos quais o leitor é remetido a partir de sua ativação. Resultados indicam que o conceito de diários pessoais, em que as mensagens têm um número reduzido de caracteres e são apresentadas em ordem cronológica inversa, só se confirmam em relação a essa última característica, decorrente dos softwares de composição que assim a condicionam. A pouca incidência de links em relação aos blogs de pesquisadores permite afirmar que há uma baixa conectividade por parte dos blogs compostos por diferentes atores que compõem a amostra relativa ao Anel e às áreas as quais pertencem, reforçada pela baixa existência de links entre as postagens e os comentários. Reforça essa questão a ausência de links trackbaks entre os comentários das postagens selecionadas. A primeira das hipóteses que guia o estudo foi refutada, na medida em que as postagens não indicam rearticulações através de seus links de interlocuções entre pesquisadores, leigos e jornalistas científicos, não permitindo reordenações e maior amplitude dessas interlocuções junto à sociedade. A segunda das hipóteses foi confirmada por se basear no fato de que os links colocam em evidência que os documentos e fontes de informação relacionados a partir desses dispositivos (links) são um híbrido de uso e socialização de informações, estas tanto circunscritas às fontes e documentos científicos quanto a fontes e documentos que não se caracterizem tradicionalmente como parte do ciclo de produção científica. A terceira hipótese que guia este estudo foi refutada, pois os dados analisados indicam que o uso dos links por pesquisadores brasileiros não se baseia em funções e motivações que objetivam agilizar processos de produção e comunicação dos resultados de pesquisa através de blogs. / The aim of this study is to interpret the use of links on the blog postings by Brazilian researchers. The investigation begins by examining the links of blogs included in the Anel de Blogs Científicos (Ring of Science Blogs). Its effectiveness is based on the combination of clusters of link networks coming from the blogrolls restricted to the Anel de Blogs Científicos. Afterwards the 640 links included in the content of the posts were classified according to categories of functions and motivations obtained from previous studies and from categories that emerged from the phenomenon studied. Finally, understanding of motivations for the insertion of links on the composition of the blog posts and the functions that such links fulfill were inferred by Content Analysis of the contexts to which the links were inserted, considering the locations to which the reader is referred from its activation. Results indicate that the concept of personal journals, in which the messages have a limited number of characters and are presented in reverse chronological order, is only confirmed through this latter feature, as a result of the software used for composing the posts. The low incidence of links in relation to blogs of researchers allows us to state that there is low connectivity by blogs composed by different authors who form the sample relative to the Anel and the areas which they belong to, reinforced by the low availability of links between posts and comments. What reinforces this point is the absence of trackbak links among comments of the selected posts. The first hypothesis guiding the study was refuted, in that the posts do not indicate rearticulations through its links of dialogues among researchers, lay people and science journalists, not allowing rearrangements and higher amplitude of these dialogues with society. The second hypothesis was confirmed by relying on the fact that the links give evidence that the documents and related sources of information from those devices (links) are a hybrid of using and sharing of information – this information being limited to the sources and scientific documents as much as to sources and documents that are not traditionally characterized as part of the cycle of scientific production. The third hypothesis that guides this study was refuted because the data analyzed indicate that the use of links by Brazilian researchers is not based on functions and motivations that aim at streamlining production processes and communication of research results through blogs.