Previously, we showed that ADAM10 is necessary for HIV-1 replication in primary human macrophages and immortalized cell lines. Silencing ADAM10 expression interrupted the HIV-1 life cycle prior to nuclear translocation of viral cDNA. Furthermore, our data indicated that HIV-1 replication depends on the expression of ADAM15 and γ-secretase, which proteolytically processes ADAM10. Silencing ADAM15 or γ-secretase expression inhibits HIV-1 replication between reverse transcription and nuclear entry. Here, we show that ADAM10 expression also supports replication in CD4+ T lymphocytes. The intracellular domain (ICD) of ADAM10 associates with the HIV-1 pre-integration complex (PIC) in the cytoplasm and immunoprecipitates and co-localizes with HIV-1 integrase, a key component of PIC. Taken together, our data support a model whereby ADAM15/γ-secretase processing of ADAM10 releases the ICD, which then incorporates into HIV-1 PIC to facilitate nuclear trafficking. Thus, these studies suggest ADAM10 as a novel therapeutic target for inhibiting HIV-1 prior to nuclear entry.

Beryllium-7 (Be-7) only decays by electron capture into lithium-7 (Li-7) with a half life of 53 days. We study the effect of ionization on this decay rate. We do so by trapping a Be-7 ion plasma in a cylindrical Malmberg-Penning trap and measuring Be-7 and Li-7 concentrations as functions of time by using Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). We have simulated these signals in a 2-dimensional electrostatic particle-in-cell (PIC) code. The two spectrum peaks merge at high ion densities whereas at low ion densities they can be resolved. The merged peak shifts linearly according to the relative abundances of these species. We have also simulated singly-ionized beryllium-7 hydride (BeH+) and Li-7 ion plasmas at high densities. These two separate peaks shift according to their relative abundances. We describe an analytical model that explains how these peaks shift.

No description available.

This dissertation focuses on quantifying the effects of multi-user co-channel interference for an avionic communication system operating in a heavy-traffic aeronautical mobile environment and proposes advanced interference cancellation techniques to mitigate the interference. The dissertation consists of two parts. The first part of the work investigates the use of a visualization method to quantify and characterize the multi-user co-channel interference (multiple access interference) effects impinging on an avionic communication system. The interference is caused by complex interactions of thousands of RF signals transmitted from thousands of aircraft; each attempts to access a common communication channel, which is governed by a specific channel contention access protocol. The visualization method transforms the co-channel interference, which is specified in terms of signal-overlaps (signal collisions), from a visual representation to a matrix representation for further statistical analysis. It is found that the statistical Poisson and its cumulative distribution provide the best estimates of multi-user co-channel interference. It is shown, using Monte Carlo simulation, that the co-channel interference of a victim aircraft operating in the heavy-traffic environment could result in as high as eight signal-overlaps. This constitutes to approximately 83.4% of success rate in signal detection for the entire three thousand aircraft environment using conventional FSK receiver. One key finding shows that high-quality communications, up to 98.5% success rate, is achievable if only three overlapping signals can be decoded successfully. The interference results found in the first part set the stage for interference cancellation research in the second part. The second part of the work proposes the use of advanced interference cancellation techniques, namely sequential interference cancellation (SIC) and parallel interference cancellation (PIC), as potential solutions to mitigating the interference effects. These techniques can be implemented in radio receivers to perform multi-signal decoding functionality to remove the required interferers (three overlapping signals) so that high-quality communication, as described in the first part, can be achieved. Various performance graphs are shown for B-FSK and B-PSK for both SIC and PIC techniques. One key finding is that the system performance can be improved substantially to an additional 15% in signal reception success rate by using SIC or PIC. This means that critical information transmitted from 450 aircraft (out of approximately three thousand aircraft in the environment) is preserved and successfully decoded. Multi-signal decoding using these interference cancellation receivers comes at a small penalty of 2 - 4.5 dBs in Eb/No when sufficient signal-to-interference (SIR) ratio (7-12 dB) is provided. / Ph. D.

<p dir="ltr">This thesis presents novel methodologies to integrate AI-driven and physics-inspired methodologies into photonic inverse design, setting new benchmarks for high-performance photonic devices in different branches of photonics. By blending advanced computational techniques with the foundational principles of electromagnetism, this research tackles key challenges in optimizing device efficiency, robustness, and functionality. The aim is to propel photonic technology beyond its current capabilities, offering transformative solutions for a range of novel applications.</p><p dir="ltr">The first major contribution focuses on adjoint-based topology optimization for on-chip single-photon coupling. We developed an adjoint topology optimization scheme to design high-efficiency couplers between photonic waveguides and single-photon sources (SPSs) in hexagonal boron nitride (hBN). This algorithm addresses fabrication constraints and SPS location uncertainties, achieving a remarkable average coupling efficiency of 78%. A library of designs is generated for different positions of the hBN flake containing an SPS relative to a silicon nitride (SiN) waveguide. These designs are then analyzed using dimensionality reduction techniques to investigate the relationship between device geometry and performance, infusing the design process with deep physical intuition and insight.</p><p dir="ltr">The second key advancement is presented through a neural network-based inverse design framework specifically developed for optimizing single-material, variable-index multilayer films. This neural network-driven technique, supported by a differentiable analytical solver, enables the realistic design and fabrication of these multilayer films, achieving high performance under ideal conditions. The approach also addresses the challenge of bridging the gap between these ideal designs and practical devices, which are subject to growth-related imperfections. By incorporating simulated systematic and random errors—reflecting actual deposition challenges—into the optimization process, we demonstrate that the neural network, initially trained to produce the ideal device, can be reconfigured to create designs that compensate for systematic deposition errors. This method remains effective even when random fabrication inconsistencies are present. The results provide a practical and experimentally viable strategy for developing single-material multilayer film stacks, ensuring reliable performance across a wide range of real-world applications.</p><p dir="ltr">The final cornerstone of this research investigates the two-stage inverse design of superchiral dielectric metasurfaces. We propose a two-stage inverse design scheme for dielectric lossless metasurfaces with central superchiral hot spots. By leveraging the excitation of high-quality factor modes with low mode volumes, we achieve up to 19,000-fold enhancements of optical chirality. This method extends the local density of field enhancements for non-chiral fields into the chiral regime and significantly surpasses previous enhancements in superchiral field generation. Our results open new avenues in chiral spectroscopy and chiral quantum photonics, exemplifying the powerful synergy of AI techniques and physics-based design principles in creating highly innovative and functional photonic structures.</p><p dir="ltr">Collectively, the methodologies developed in this thesis signify a major advancement in the field of photonic inverse design. By merging AI-driven techniques with rigorous physics-based optimization frameworks, this research paves the way for the next generation of photonic devices.</p>

A oferta de novos serviços para os usuários finais, como o denominado triple play, que consiste no tráfego simultâneo de voz, vídeo e dados utilizando a mesma infra-estrutura de comunicação, vem exigindo que as estruturas de rede das operadoras ofereçam largura de banda adequada e qualidade de serviço. Nesse contexto, as redes ópticas passivas (PON) vêm se destacando em virtude de oferecerem maior largura de banda a custos relativamente baixos. Nas redes ópticas passivas, trechos de fibras ópticas podem ser compartilhados entre diversos assinantes, exigindo, para isso, a utilização de técnicas de controle de acesso múltiplo. Destaque maior é dado à técnica de acesso múltiplo por divisão de códigos ópticos (OCDMA), por apresentar características tais como maior segurança e capacidade flexível sob demanda. O desempenho dessa tecnologia é basicamente limitado pela interferência de acesso múltiplo, ou interferência multiusuário (MAI). No presente trabalho, cenários OCDMA-PON utilizando códigos ópticos unidimensionais, baseados na codificação prima modificada (MPC), e bidimensionais, baseados na codificação óptica ortogonal de múltiplos comprimentos de onda (MWOOC), são descritos, e seus respectivos desempenhos investigados. Os desempenhos desses sistemas são verificados utilizando-se os seguintes esquemas de modulação: 1) On-off Keying (OOK), cujo formalismo para a codificação padded MPC (PMPC) e double padded MPC (DPMPC) foi aqui desenvolvido, 2) por posição de pulso (PPM), considerando os ruídos poissonianos de deteção, cujo formalismo foi também aqui desenvolvido, 3) por posição de pulso (PPM) considerando apenas a interferência de acesso múltiplo (MAI), 4) semelhante ao (3), porém, utilizando a técnica mitigadora de MAI via cancelamento paralelo de interferência (PIC), e 5) semelhante ao (4) porém utilizando modulação por chaveamento de frequência (FSK). Em seguida, a codificação bidimensional MWOOC, utilizando modulação OOK, é analisada com e sem a utilização de PIC. Além desses esquemas, são também incluídas, pela primeira vez nesses formalismos, técnicas de correção posterior de erro (FEC) baseadas no algoritmo Reed-Solomon (RS). A figura de mérito adotada nas simulações é baseada no cálculo da taxa de erro de bit (BER). Os resultados obtidos para os diversos casos investigados neste trabalho indicam que a combinação PIC/FEC deve ser considerada de modo a se obter níveis de BER compatíveis com a região livre de erros (BER < \'10 POT.-12\') para os cenários de redes de acesso atuais e futuros (visando atender a 32 ou 64 usuários simultâneos). / The advent of new services offered to end users, such as the so called triple play, which consists in the simultaneous traffic of voice, video, and data through the same communication infrastructure, has been pushing telecom operators towards providing adequate bandwidth as well as quality of service. This has brought the spotlight to passive optical networks (PONs) by virtue of their considerably higher bandwidth at relatively low cost. In PONs, certain fiber optic spans can be shared among different users as long as multiple access control techniques are used. One such technique is the optical code division multiple access (OCDMA) technique, which, in addition, presents improved data security and flexible capacity on demand. The performance of this technology is basically limited by multi access interference (MAI), which becomes more severe as the number of simultaneous users increases. In the present work, OCDMA-PON scenarios utilizing one- and two-dimensional optical codes separately such as modified prime codes (MPC) and multi-wavelength optical orthogonal codes (MWOOC), are described and thoroughly investigated. The performances of these systems are investigated based on the following modulation schemes: 1) On-off keying (OOK), where a new formalism for the double-padded MPC is proposed, 2) Pulse position modulation (PPM), and 3) Frequency shift keying (FSK) together with MAI mitigation technique based on parallel interference cancelation (PIC). Besides these schemes, it is also included for the first time in these formalisms forward error correction techniques (FEC) based on the Reed-Solomon (RS) algorithm. The figure of merit adopted in all simulations is the bit error rate (BER). The results obtained for the cases investigated in this work indicate that the combination PIC/FEC must be considered if one is interested in obtaining BER levels compatible with the error-free region (BER < \'10 POT.-12\') for the current and future access network scenarios (aiming at attending 32 or 64 simultaneous users).

Submitted by JOSIANE SANTOS DE OLIVEIRA (josianeso) on 2019-03-25T11:56:58Z No. of bitstreams: 1 Jeferson Cardoso do Rosario_.pdf: 3523684 bytes, checksum: 6d033c623e7ef74a93692efd6ca37e8e (MD5) / Made available in DSpace on 2019-03-25T11:56:58Z (GMT). No. of bitstreams: 1 Jeferson Cardoso do Rosario_.pdf: 3523684 bytes, checksum: 6d033c623e7ef74a93692efd6ca37e8e (MD5) Previous issue date: 2019-01-18 / Nenhuma / O traumatismo cranioencefálico (TCE) é atualmente a terceira maior causa de óbitos no âmbito mundial. Estudos recentes têm demonstrado que a monitorização de pressão intracraniana (PIC), como forma de cálculo da pressão de perfusão cerebral (PPC) é uma ferramenta importante para avaliação do fluxo sanguíneo cerebral (FSC), provocando sensível redução nas taxas de mortalidade. Além do TCE, outras patologias ou situações neurocirúrgicas tem utilizado a técnica de monitorização de PIC. A monitorização desse parâmetro foi proposta já na década de 50, onde um tubo com fluido em contato com o líquido cefalorraquidiano (LCR) era introduzido no espaço intracraniano e conectado a um transdutor de pressão externo. Com a evolução da indústria microeletrônica e dos sistemas microeletromecânicos, foi possível colocar os transdutores na ponta do cateter, permitindo uma monitorização menos invasiva, com menos riscos de infecções. Os cateteres atuais com micro transdutor na ponta podem ser divididos em três grupo: straingauge, fibra óptica e pneumático. Cada grupo possui suas características, entretanto o primeiro tem se demonstrado como solução mais robusta e confiável, com boa relação custo benefício. No presente trabalho foi proposto o desenvolvimento de um cateter implantável de monitorização de pressão intracraniana do tipo micro transdutor strain-gauge. Foram construídos protótipos funcionais e submetidos a ensaios de desempenho, especificados em norma técnica para monitorização de pressão sanguínea, a influência da temperatura na medição de pressão, bem como a exatidão das medições. Os processos empregados no trabalho são utilizados comumente na indústria de encapsulamento de semicondutores, porém foram levadas em consideração as especificidades da aplicação, adequando as técnicas disponíveis às geometrias e materiais empregados, considerando a necessidade de utilização de materiais biocompatíveis. / The traumatic brain injury (TBI) is nowadays the third cause of death in the world. Recent studies have shown the intracranial pressure (ICP) monitoring as an important tool for cerebral perfusion pressure (CPP) calculation and cerebral blood flow (CBF) assestment, reducing significantly the mortality statistics. Besides TBI, several others pathologies and neurosurgery conditions have been using the ICP monitoring technique. The proposal of ICP monitoring first appeared on the 50’s, where a tube fulfilled with fluid in contact with cerebrospinal fluid (CSF) was introduced into the intracranial space and connected to an external pressure transducer. With the waves of the microelectronics and microelectromechanical systems (MEMS) industry evolution, it was possible to put the transducer and all the electronics inside the catheter tip, allowing a less invasive monitoring, decreasing the risk of infection. The state of art catheters with micro transducer on the tip can be divided into three groups: strain-gauge, optical fiber and pneumatic. Each group has it’s own characteristics, however the first has been demonstrated as the rugged solution, being reliable, cost effective and with good accuracy. In the present work, it was proposed the development of an strain-gauge micro transducer implantable catheter for intracranial pressure monitoring. Functional prototypes were built and submitted to performance tests, according to the technical standards in the medical equipment area, the temperature influence over the pressure measurements was evaluated, as well as the accuracy. The adopted processes are commonly used in the semiconductor packaging industry, however it was considered the application special requirements, adapting the processes to the geometry and materials used, considering the needs of biocompatible materials.

Cette thèse se place dans le contexte de la fusion thermonucléaire pour la production d’énergie, dans le cadre de l’allumage rapide par faisceaux d’électrons chauds. Le travail présenté a pour but de caractériser la source de faisceaux d’électrons rapides, accélérés par lasers intenses (1019≠1020 W/cm2), et leur propagation dans des plasmas denses aussi bien à l’état solide quecomprimé.La première étude présentée avait pour but d’étudier la propagation d’électrons rapides, caractérisés par une densité de courant > 1011 A/cm2, dans des cibles d’aluminium chauffées à la température de Fermi par un choc plan contra-propagatif, qui les comprimait à deux fois la densité du solide. La géométrie de compression plane nous a permis de dissocier les pertesd’énergie dues aux effets résistifs et collisionnels, en comparant des cibles solides et comprimées de masses surfaciques identiques. Nous avons observé pour la première fois une augmentation des pertes d’énergie d’origine résistive dans les échantillons chauffés. La confrontation des données expérimentales avec les simulations, incluant une caractérisation complète de la source électronique, de l’état de compression des cibles et du transport d’électrons, a permis d’étudier l’évolution temporelle de la résistivité du matériau. Elle a notamment permis d’estimer que le pouvoir d’arrêt résistif dans les cibles tièdes et denses est d’amplitude comparable au pouvoir d’arrêt collisionnel.Dans la deuxième étude, nous avons analysé l’accélération et le transport d’électrons rapides produits lors de l’interaction d’un laser à haut contraste avec un cône de cuivre, enchâssé dans un bloc de carbone, et comprimé par un choc plan contra-propagatif. Un système d’imagerie X a permis de visualiser le couplage entre le faisceau laser intense et le cône à différents instants de la compression. Ce diagnostic, donnant accès à la distribution spatiale du faisceau d’électrons chauds, a montré une génération d’électrons dans tout le volume du cône pour des temps supérieurs au temps de débouché de choc au niveau de la pointe. Pour des temps antérieurs, l’interaction se produit à haut contraste, la source est restreinte au niveau de la pointe du cône, et la propagation collimatée des électrons vers l’intérieur de la cible est assurée par les champs magnétiques auto-générés. Ces conclusions ont été obtenues en confrontant les données expérimentales aux simulations.Une caractérisation hydrodynamique de la compression par choc de la cible a été effectuée à l’aide d’une technique de radiographie X, permettant de visualiser la propagation du front de choc dans la cible, sa collision avec la pointe du cône et son glissement le long des parois. Les mesures sont en accord avec des simulations hydrodynamiques. / The framework of this PhD thesis is the inertial confinement fusion for energy production, in the context of the electron fast ignition scheme. The work consists in a characterization of the transport mechanisms of fast electrons, driven by intense laser pulses (1019 ≠ 1020 W/cm2) inboth cold-solid and warm-dense matter.The first goal was to study the propagation of a fast electron beam, characterized by a current density > 1011 A/cm2, in aluminum targets initially heated close to the Fermi temperature by a counter-propagative planar shock. The planar compression geometry allowed us to discriminate the energy losses due to the resistive mechanisms from collisional ones by comparing solid and compressed targets of the same initial areal densities. We observed for the first time a significant increase of resistive energy losses in heated aluminum samples. The confrontation of the experimental data with the simulations, including a complete characterization of the electron source, of the target compression and of the fast electron transport, allowed us to study the time-evolution of the material resistivity. The estimated resistive electron stopping power in a warm-compressed target is of the same order as the collisional one.We studied the transport of the fast electrons generated in the interaction of a high-contrast laser pulse with a hollow copper cone, buried into a carbon layer, compressed by a counterpropagative planar shock. A X-ray imaging system allowed us to visualize the coupling of thelaser pulse with the cone at different moments of the compression. This diagnostic, giving access to the fast electron spatial distribution, showed a fast electron generation in the entire volume of the cone for late times of compression, after shock breakout from the inner cone tip. For earlier times, the interaction at a high-contrast ensured that the source was contained within the cone tip, and the fast electron beam was collimated into the target depth by self-generated magnetic fields. These conclusions were obtained by a confrontation of experimental data to simulation results.The hydrodynamic characterization of the shock-induced target compression was performed using a X-ray point projection radiography technique, allowing to visualize a propagation of the shock front into the target, its collision with the cone tip and its subsequent sliding along the cone walls. The measurements are in agreement with hydrodynamic simulations.

Entladungsbasierte Elektronenquellen mit Kaltkathode waren gegen Ende des 19. Jahr hunderts weithin genutzte Forschungswerkzeuge und ermöglichten die Entdeckung des Elektrons und der Röntgenstrahlung. In jüngster Zeit erfahren sie erneutes Interesse in Wissenschaft und Industrie, motiviert durch ihre Fähigkeit, Elektronenstrahlen hoher Leistung für Produktionsprozesse (wie das Schweißen, die Materialverdampfung in der Vakuum beschichtung oder die Vakuum-Schmelzveredlung in der Metallurgie) basierend auf einem robusten Design sowie einfachen Versorgungs- und Steuerungssystemen zu erzeugen. Entladungsbasierte Elektronenquellen könnten also eine wirtschaftlich attraktive Alternative zu den gegenwärtig noch etablierten Elektronenstrahlkanonen mit Glühkathoden bieten. Trotz der langen Geschichte und vieler empirischer Ansätze, Gasentladungen zur Elektronenstrahlerzeugung für diverse Anwendungen zu nutzen, sind die bestimmenden Mechanismen bei dieser Art von Elektronenquellen immer noch unzulänglich verstanden. Es war deshalb das Ziel der für die vorliegende Dissertation durchgeführten experimentellen und theoretischen Arbeiten, nicht nur die technologischen Potentiale und Limitierungen entladungsbasierter Elektronenstrahlquellen zu untersuchen, sondern auch die Kenntnis grundlegender physikalischer Effekte zu verbessern. Analysiert wurden zunächst verschiedene, im Fraunhofer FEP vorhandene Kaltkathoden-Strahlquellen, die - ungeachtet der Tatsache, dass sie für unterschiedliche Anwendungen konstruiert wurden - sämtlich auf demselben Funktionsprinzip beruhen: Innerhalb des Gerätes wird eine Hochspannungs-Glimmentladung (HSGE) unterhalten. Ionen erfahren im Kathodenfall einen Energiezuwachs, treffen auf die Kathode und setzen dort Sekundärelektronen frei. Diese Elektronen werden in Richtung des Plasmas be schleu nigt und verlassen schließlich die Strahlquelle, um am Prozessort die beabsichtigte Wirkung zu erzielen. Zur Optimierung der Stabilität der die Ionen produzierenden Entladung, der Effizienz der Strahlerzeugung sowie der Strahlleistungsdichte und Kathodenlebensdauer wurden verschiedene Kombinationen von Kathodenmaterialien und Plasma-Arbeitsgasen experimentell untersucht. Die Abhängigkeit der Ausdehnung des Kathodenfalls von Strom und Spannung der Entladung wurde gemessen und konnte durch ein analytisches Modell erklärt werden. Emittanz und Richtstrahlwert sind wichtige Kenngrößen zur Charakterisierung der Qualität von Elektronenstrahlen. Beide wurden in dieser Arbeit für den Elektronenstrahl einer HSGE-basierten Kaltkathoden-Schweißstrahlquelle bestimmt, wobei zwei Ansätze verfolgt wurden: Zum einen konnte die Emittanz aus der Randstrahlgleichung gewonnen werden, die den experimentell beobachteten Verlauf des Strahldurchmessers entlang der Ausbreitungsachse analytisch beschreibt. Zum anderen wurde die Emittanz anhand des aus der numerischen Simulation berechneten Phasenraumprofils ermittelt. Eine Kernaufgabe dieser Arbeit war es, Software-Werkzeuge zur Simulation der Strahl erzeugung in verschiedenen geometrischen Konfigurationen zu entwickeln und zu validieren, mit denen künftig die Konstruktion und Optimierung neuer entladungsbasierter Strahlerzeuger unterstützt werden sollte. Da kommerziell verfügbare Programme zur Simulation der Erzeugung und Führung von Elektronenstrahlen grundlegende Effekte plasma basierter Quellen, wie z. B. die Raumladung der Ionen oder die ioneninduzierte Sekundär elektronen-Freisetzung, nicht berücksichtigen, wurde für diese Arbeit eine neue Herangehensweise favorisiert: „Particle-in-Cell“ (PIC)-Algorithmen werden in der Plasma forschung üblicherweise zur Modellierung von Entladungen sowie zum Studium nichtlinearer Probleme, wie z. B. Instabilitäten, verwendet. Deshalb wurde nun eine PIC-Simulations umgebung zur Modellierung der HSGE und der damit verbundenen Strahlerzeugung entwickelt. Die Simulation reproduziert experimentelle Ergebnisse, wie etwa die Charakteristik der Entladung, die Emittanz des Strahls oder die Ausdehnung des Kathodendunkelraums, in befriedigender Weise. Schließlich wurde im Rahmen dieser Arbeit eine entladungsbasierte Elektronenstrahlquelle neuen Typs entwickelt und charakterisiert, die die Einfachheit der bekannten Kaltkathoden-Strahler und vorteilhafte Leistungsparameter, z. B. eine hohe Strahlleistungsdichte und niedrige Arc-Rate, wie sie bisher nur mit traditionellen Glühkathodenstrahlern erreichbar waren, in sich vereinigt. Die Kathode bestand aus LaB6 - einem Material, das sowohl eine hohe Sekundärelektronen-Ausbeute als auch eine niedrige Austrittsarbeit aufweist - und wurde gegen die Halterung thermisch isolierend montiert. Dadurch kann sie von Ionen aus einer HSGE auf hohe Betriebstemperaturen geheizt werden und in erheblichem Maße thermisch freigesetzte Elektronen emittieren. Neben technisch nützlichen Gebrauchs eigenschaften weist diese so genannte „Hybrid-Kathode“ auch ein physikalisch interessantes Verhalten auf. Einige neuartige Effekte, die von Entladungen mit kalten Kathoden nicht bekannt waren, konnten beobachtet und erklärt werden, wie z.B. die auffällige „N-förmige“ Druck-Strom-Charakteristik, die bei plötzlicher Abschaltung der Entladung nur langsam und ungleichmäßig abklingende Elektronenemission, die Limitierung des erreichbaren Strahl stromes und eine Fülle von Kathodenverschleiß-Mechanismen. Physikalische Modelle zur Beschreibung verschiedener Aspekte der Hybridkathoden-Entladung wurden erarbeitet und mit den experimentellen Befunden verglichen. / Discharge-based, cold-cathode electron sources were routinely used as research tools at the end of the 19th century and facilitated then the discovery of the electron and of the x-rays. In recent time, they experience a renewed interest in science and industry due to their capability of generating high power electron beams for production processes (like welding, evaporation of materials for vapor deposition, and vacuum melt refining in metallurgy) relying on rugged mechanic designs as well as simple supply and control systems. Hence, discharge-based electron sources could provide an economically attractive alternative to the currently established electron beam guns with thermionic cathodes. Despite the long history and many empirical trials to utilize electron beam generation by gas discharges in several applications, the mechanisms governing this kind of electron sources are far from being well understood. Therefore, it was the purpose of the theoretical and experimental work performed for this thesis not only to investigate in the technological potentials and limitations of discharge-based electron beam guns but also to improve the knowledge of physical basic effects. At first, several cold-cathode beam sources existing at Fraunhofer FEP were analyzed. Regardless that they were designed for different applications, all were based on the same function principle: A high-voltage glow-discharge (HVGD) is sustained inside the device. Ions gain energy in the cathode fall, hit the cathode and release secondary electrons. These electrons will be accelerated towards the plasma then and can finally leave the beam source to perform the desired action at the process site. In order to optimize stability of the ions generating discharge, efficiency of the beam generation, beam power density and longevity of the cathode, different combinations of cathode materials and plasma forming gases have been investigated experimentally. The dependence of the cathode dark space width on current and discharge voltage was measured and could be explained by an analytic model. Emittance and brightness are important measures which quantify the quality of electron beams. In this work, both were determined for the beam originating from a HVGD based cold-cathode electron gun designed for welding following two approaches: First the emittance could be extracted from the envelope equation which analytically describes the evolution of the experimentally observed beam diameter along the propagation axis. Second the emittance was calculated from numerically simulated traces in the phase space. It was a core purpose of this work to develop and validate software tools capable of simulating the beam formation in various geometric configurations. This task was aimed at supporting the design and optimization of new discharge-based beam sources. Since commercially available software for modeling electron beam generation and transport do not consider the key mechanisms of plasma-based sources like the ion space charge or the ion-dependent production of free electrons, a new attempt was favored for this work: Particle-in-Cell (PIC) are being used in plasma research for studying nonlinear problems like instabilities. Therefore, a PIC simulation environment was utilized to numerically model the HVGD and the related beam generation. The simulation satisfactorily reproduces experimental findings, like the characteristics of the discharge, the emittance of the beam or the cathode dark space dimension. Finally, a discharge-based electron-beam sources of a new type was developed and characterized in the frame of this work. It merges the simplicity of known cold cathode devices with beneficial performance parameters, like high beam power density and low arcing rate, which have been reached so far with traditional thermionic electron sources only. The cathode of the new beam source consists of LaB6 - a material with a high secondary electron yield and a low thermionic work function - and was mounted thermally insulated against the holder. Then, an elevated operation temperature resulting in considerable thermionic emission was maintained by ions extracted from a HVGD. Besides to technically advantageous features, this so called “hybrid“ cathode mode of beam generation shows a physically interesting behaviour. Several new effects - not known from traditional cold-cathode discharges - could be observed, like a peculiar “N-shaped“ appearance of the pressure-current characteristic, the slowly and irregularly decreasing electron emission after a sudden discharge cutoff, a limitation of achievable beam current, and a multitude of possible cathode wear mechanisms. Physical models describing various features of the hybrid cathode discharge were elaborated and compared with the experimental findings.

A oferta de novos serviços para os usuários finais, como o denominado triple play, que consiste no tráfego simultâneo de voz, vídeo e dados utilizando a mesma infra-estrutura de comunicação, vem exigindo que as estruturas de rede das operadoras ofereçam largura de banda adequada e qualidade de serviço. Nesse contexto, as redes ópticas passivas (PON) vêm se destacando em virtude de oferecerem maior largura de banda a custos relativamente baixos. Nas redes ópticas passivas, trechos de fibras ópticas podem ser compartilhados entre diversos assinantes, exigindo, para isso, a utilização de técnicas de controle de acesso múltiplo. Destaque maior é dado à técnica de acesso múltiplo por divisão de códigos ópticos (OCDMA), por apresentar características tais como maior segurança e capacidade flexível sob demanda. O desempenho dessa tecnologia é basicamente limitado pela interferência de acesso múltiplo, ou interferência multiusuário (MAI). No presente trabalho, cenários OCDMA-PON utilizando códigos ópticos unidimensionais, baseados na codificação prima modificada (MPC), e bidimensionais, baseados na codificação óptica ortogonal de múltiplos comprimentos de onda (MWOOC), são descritos, e seus respectivos desempenhos investigados. Os desempenhos desses sistemas são verificados utilizando-se os seguintes esquemas de modulação: 1) On-off Keying (OOK), cujo formalismo para a codificação padded MPC (PMPC) e double padded MPC (DPMPC) foi aqui desenvolvido, 2) por posição de pulso (PPM), considerando os ruídos poissonianos de deteção, cujo formalismo foi também aqui desenvolvido, 3) por posição de pulso (PPM) considerando apenas a interferência de acesso múltiplo (MAI), 4) semelhante ao (3), porém, utilizando a técnica mitigadora de MAI via cancelamento paralelo de interferência (PIC), e 5) semelhante ao (4) porém utilizando modulação por chaveamento de frequência (FSK). Em seguida, a codificação bidimensional MWOOC, utilizando modulação OOK, é analisada com e sem a utilização de PIC. Além desses esquemas, são também incluídas, pela primeira vez nesses formalismos, técnicas de correção posterior de erro (FEC) baseadas no algoritmo Reed-Solomon (RS). A figura de mérito adotada nas simulações é baseada no cálculo da taxa de erro de bit (BER). Os resultados obtidos para os diversos casos investigados neste trabalho indicam que a combinação PIC/FEC deve ser considerada de modo a se obter níveis de BER compatíveis com a região livre de erros (BER < \'10 POT.-12\') para os cenários de redes de acesso atuais e futuros (visando atender a 32 ou 64 usuários simultâneos). / The advent of new services offered to end users, such as the so called triple play, which consists in the simultaneous traffic of voice, video, and data through the same communication infrastructure, has been pushing telecom operators towards providing adequate bandwidth as well as quality of service. This has brought the spotlight to passive optical networks (PONs) by virtue of their considerably higher bandwidth at relatively low cost. In PONs, certain fiber optic spans can be shared among different users as long as multiple access control techniques are used. One such technique is the optical code division multiple access (OCDMA) technique, which, in addition, presents improved data security and flexible capacity on demand. The performance of this technology is basically limited by multi access interference (MAI), which becomes more severe as the number of simultaneous users increases. In the present work, OCDMA-PON scenarios utilizing one- and two-dimensional optical codes separately such as modified prime codes (MPC) and multi-wavelength optical orthogonal codes (MWOOC), are described and thoroughly investigated. The performances of these systems are investigated based on the following modulation schemes: 1) On-off keying (OOK), where a new formalism for the double-padded MPC is proposed, 2) Pulse position modulation (PPM), and 3) Frequency shift keying (FSK) together with MAI mitigation technique based on parallel interference cancelation (PIC). Besides these schemes, it is also included for the first time in these formalisms forward error correction techniques (FEC) based on the Reed-Solomon (RS) algorithm. The figure of merit adopted in all simulations is the bit error rate (BER). The results obtained for the cases investigated in this work indicate that the combination PIC/FEC must be considered if one is interested in obtaining BER levels compatible with the error-free region (BER < \'10 POT.-12\') for the current and future access network scenarios (aiming at attending 32 or 64 simultaneous users).