Este trabalho teve por objetivo desenvolver uma metodologia para fabricação cerâmica de ítria (\'Y IND.2\'O IND.3\') transparente e, em paralelo, desenvolver um sistema de aquecimento que permitisse atingir temperaturas superiores a 1800ºC. Nos últimos 5 anos, cerâmicas transparentes ganharam grande destaque e foram incluídas entre os cinco supermateriais da atualidade. A ítria - \'Y IND.2\'O IND.3\' - apresenta algumas características ópticas promissoras para fabricação de cerâmicas transparentes, dentre as quais podemos destacar: isotropia óptica e ampla faixa de transparência. Além disso, possui elevada condutividade térmica, o que confere potencialidade para aplicações em sistemas lasers de alta potência. Neste trabalho são apresentados os resultados de estudos sistemáticos relacionados à síntese, compactação e sinterização do óxido de ítria. As amostras foram sintetizadas por reação do estado sólido, usando óxido de zircônio como aditivo para o processo de sinterização. As condições de compactação das pastilhas à verde foram investigadas e permitiu a obtenção de corpos cerâmicos com densidade relativa à verde de ~55%, com uso de prensagem uniaxial seguido de prensagem isostática. As cerâmicas foram sinterizadas utilizando-se programas de temperaturas específicos sob duas condições quanto ao aquecimento: em forno elétrico e em atmosfera aberta e em forno de indução, desenvolvido nesse trabalho, em condições de vácuo dinâmico. As caracterizações físicas das amostras foram feitas por difração de raios X, microscopia eletrônica de varredura e espectroscopia óptica. Os resultados mostraram que temperaturas superiores a 1800ºC combinado com o efeito do vácuo são indispensáveis para obtenção de ítria transparente pelo método de sinterização convencional; o sistema de aquecimento desenvolvido apresentou eficiência em atingir a temperatura desejada, porém apresentou algumas limitações que impossibilitou o controle e reprodutibilidade do processo. Por meio da metodologia desenvolvida foi possível a obtenção de cerâmica de ítria com transmissão na região do visível do espectro eletromagnético (400-700 nm) de até 42%, quando comparado a um monocristal. Avançou-se na fabricação de cerâmicas transparentes, porém, ainda será necessário otimizar o controle do sistema de aquecimento do forno desenvolvido, de modo a eliminar os poucos centros espalhadores de luz existentes. / The focus of this work was to develop a methodology for manufacture of transparent Yttria (\'Y IND.2\'O IND.3\') and in addition develop a heating system that operates in temperatures above 1800ºC. In the last 5 years, transparent ceramics featured among the five supermaterials of the present. Yttria - \'Y IND.2\'O IND.3\' - presents a few optical characteristics promising to manufacture transparent ceramics, such as: optical isotropy and wide range of transparency. Besides, it has high thermal conductivity, which gives potential for applications in high power laser systems. In the work presented here, the results of a systematic study of the synthesis, compaction and sintering of yttria oxide are presented. The samples were prepared by solid state reaction, using zircon oxide as an additive to the sintering process. The compaction conditions of the green tablets were investigated and allowed the obtainment of ceramic bodies with relative density around 55%, by using uniaxial pressing followed by isostatic pressing. The ceramics were sintered using specific temperature programs under two heating conditions: electric furnace and open atmosphere and under induction furnace, developed in this work, under dynamic vacuum conditions. The physical characterizations of the samples were made by X-ray diffraction, scanning electron microscopy and optical spectroscopy. The results showed that temperatures above 1800ºC combined with the effect of vacuum are necessary to obtain transparent Yttria by conventional sintering method; the heating system developed was efficient in reaching the desired temperature, however had some limitations that prevented the control and reproducibility of the process. By means of the methodology developed it was possible to obtain ceramic yttria with transmission in the visible region of the electromagnetic spectrum (400-700) up to 42% compared to single crystal yttria. Progress was made in manufacture of transparent ceramics, however, it is necessary to optimize the control of the heating system of the furnace developed, in order to eliminate the few existing light scattering centers.

Κατά την διάδοση του σήματος στα οπτικά δίκτυα η ποιότητα του λαμβανόμενου σήματος εξασθενεί λόγω των διαφόρων ειδών απωλειών που υπεισέρχονται κατά τη μετάδοση. Οι κυριότερες εξ’ αυτών είναι: ο θόρυβος λόγω των οπτικών ενισχυτών, η διαφωνία, η χρωματική διασπορά, η διασπορά τρόπων πόλωσης, η μείξη τεσσάρων κυμάτων, η αυτοδιαμόρφωση φάσης κτλ. Προκειμένου να επιτευχθεί αποδεκτή ποιότητα λαμβανόμενου σήματος στον δέκτη είναι απαραίτητη, ιδιαίτερα για μεγάλα μονοπάτια, η χρήση οπτικών 3R αναγεννητών σε κάποιους ενδιάμεσους κόμβους για την περιοδική αναμετάδοση του σήματος. Στην παρούσα διπλωματική εργασία σχεδιάζονται και υλοποιούνται στατικοί αλγόριθμοι δρομολόγησης και ανάθεσης μηκών κύματος για ημιδιαφανή οπτικά δίκτυα. Συγκεκριμένα, θεωρώντας μια δικτυακή τοπολογία, έναν αριθμό διαθέσιμων μηκών κύματος, μια μήτρα κίνησης και μια (αραιή) τοπολογία 3R αναγεννητών για το εξεταζόμενο δίκτυο (ή εκφράζοντάς το διαφορετικά έναν αριθμό ελεύθερων πομποδεκτών για κάθε κόμβο του δικτύου) επιχειρείται η μεγιστοποίηση του αριθμού των συνδέσεων που μπορούν να επιτευχθούν, διατηρώντας παράλληλα την επιθυμητή ποιότητα μετάδοσης. Έτσι, το πρόβλημα της επιλογής της ακολουθίας των αναγεννητών μέσα από τους οποίους θα δρομολογηθεί η κάθε αδιαφανής αίτηση σύνδεσης, μοντελοποιείται σαν ένα πρόβλημα εικονικής τοπολογίας (virtual topology problem). Στην συνέχεια το πρόβλημα αυτό επιλύεται με τη βοήθεια μιας σειράς αλγορίθμων από πολύπλοκους που βασίζονται σε σχηματισμούς ακέραιου γραμμικού προγραμματισμού (Integer Linear Programming – ILP) έως απλούστερους αλλά πάντα πρακτικούς ως προς την εύρεση λύσης, ευριστικούς αλγόριθμους. Ύστερα από την επιλογή της ακολουθίας των χρησιμοποιούμενων αναγεννητών για κάθε αδιαφανή αίτηση σύνδεσης, η μήτρα κίνησης μετασχηματίζεται σε μια ισοδύναμη διαφανή, όπου κάθε αδιαφανής αίτηση έχει αντικατασταθεί από μια σειρά διαφανών συνδέσεων που τερματίζουν και ξεκινούν από τους συγκεκριμένους 3R κόμβους αναγέννησης. Ακολούθως, εφαρμόζεται ένας διαφανής IA-RWA αλγόριθμος για τη μετασχηματισμένη μήτρα κίνησης, ενώ τυχόν συνδέσεις που μποκάρονται ύστερα από την εφαρμογή του διαφανή αλγορίθμου επαναδρομολογούνται χρησιμοποιώντας τους υπολοιπόμενους αναγεννητές. Η Ποιότητα Μετάδοσης (Quality of Transmission QoT) των δημιουργουμένων lightpaths υπολογίζεται με τη βοήθεια ενός εκτιμητή της παραμέτρου Q του κάθε lightpath. Για την μοντελοποίηση των φυσικών περιορισμών του δικτύου χρησιμοποιούνται αναλυτικές φόρμουλες. Η απόδοση του προτεινόμενου αλγορίθμου υπολογίστηκε διεξάγοντας εξομοιώσεις για μια παραλλαγή του DTnet δικτύου εισάγοντας τη μοναδιαία μήτρα κίνησης. Η απόδοση του αλγορίθμου κρίνεται ικανοποιητική όχι μόνο για μεσαία, αλλά και για μεγάλης κλίμακας δίκτυα παρέχοντας βέλτιστες λύσεις. Το μεγαλύτερο μέρος του χρόνου εκτέλεσης του αλγορίθμου, οφείλεται στον υπολογισμό του διαφανούς IA-RWA αλγόριθμου της δεύτερης φάσης. Σχετικά με την απόδοση των εξεταζόμενων αλγορίθμων της πρώτης φάσης, φαίνεται ότι ο αλγόριθμος που παρουσιάζει τα καλύτερα αποτελέσματα είναι αυτός που ελαχιστοποιεί τον μέγιστο αριθμό των χρησιμοποιούμενων αναγεννητών μεταξύ των διαφορετικών κόμβων αναγέννησης του σήματος. / Physical impairments in optical fiber transmission necessitate the use of regeneration at certain intermediate nodes, at least for certain lengthy lightpaths. We design and implement impairment-aware algorithms for routing and wavelength assignment (IA-RWA) in translucent optical networks. We focus on the offline version of the problem, where we are given a network topology, the available wavelengths, a traffic matrix and a (sparse) placement of 3R regenerators in the network (or, in a slightly different setting, the number of available transceivers at each network switch), and we aim at maximizing the number of connections served with adequate quality of transmission. We formulate the problem of choosing the sequence of regenerators to be used by non-transparent connections as a virtual topology design problem, and address it using various algorithms, ranging from an integer linear program (ILP) to simple heuristic algorithms. Once the sequence of regenerators to be used has been determined, we transform the traffic matrix by replacing non-transparent connections with a sequence of transparent connections that terminate and begin at the specified 3R intermediate nodes. Using the transformed matrix we then apply an IA-RWA algorithm designed for transparent (as opposed to translucent) networks to route the traffic. Connections that are blocked are re-routed using any remaining regenerator(s).

Este trabalho teve por objetivo desenvolver uma metodologia para fabricação cerâmica de ítria (\'Y IND.2\'O IND.3\') transparente e, em paralelo, desenvolver um sistema de aquecimento que permitisse atingir temperaturas superiores a 1800ºC. Nos últimos 5 anos, cerâmicas transparentes ganharam grande destaque e foram incluídas entre os cinco supermateriais da atualidade. A ítria - \'Y IND.2\'O IND.3\' - apresenta algumas características ópticas promissoras para fabricação de cerâmicas transparentes, dentre as quais podemos destacar: isotropia óptica e ampla faixa de transparência. Além disso, possui elevada condutividade térmica, o que confere potencialidade para aplicações em sistemas lasers de alta potência. Neste trabalho são apresentados os resultados de estudos sistemáticos relacionados à síntese, compactação e sinterização do óxido de ítria. As amostras foram sintetizadas por reação do estado sólido, usando óxido de zircônio como aditivo para o processo de sinterização. As condições de compactação das pastilhas à verde foram investigadas e permitiu a obtenção de corpos cerâmicos com densidade relativa à verde de ~55%, com uso de prensagem uniaxial seguido de prensagem isostática. As cerâmicas foram sinterizadas utilizando-se programas de temperaturas específicos sob duas condições quanto ao aquecimento: em forno elétrico e em atmosfera aberta e em forno de indução, desenvolvido nesse trabalho, em condições de vácuo dinâmico. As caracterizações físicas das amostras foram feitas por difração de raios X, microscopia eletrônica de varredura e espectroscopia óptica. Os resultados mostraram que temperaturas superiores a 1800ºC combinado com o efeito do vácuo são indispensáveis para obtenção de ítria transparente pelo método de sinterização convencional; o sistema de aquecimento desenvolvido apresentou eficiência em atingir a temperatura desejada, porém apresentou algumas limitações que impossibilitou o controle e reprodutibilidade do processo. Por meio da metodologia desenvolvida foi possível a obtenção de cerâmica de ítria com transmissão na região do visível do espectro eletromagnético (400-700 nm) de até 42%, quando comparado a um monocristal. Avançou-se na fabricação de cerâmicas transparentes, porém, ainda será necessário otimizar o controle do sistema de aquecimento do forno desenvolvido, de modo a eliminar os poucos centros espalhadores de luz existentes. / The focus of this work was to develop a methodology for manufacture of transparent Yttria (\'Y IND.2\'O IND.3\') and in addition develop a heating system that operates in temperatures above 1800ºC. In the last 5 years, transparent ceramics featured among the five supermaterials of the present. Yttria - \'Y IND.2\'O IND.3\' - presents a few optical characteristics promising to manufacture transparent ceramics, such as: optical isotropy and wide range of transparency. Besides, it has high thermal conductivity, which gives potential for applications in high power laser systems. In the work presented here, the results of a systematic study of the synthesis, compaction and sintering of yttria oxide are presented. The samples were prepared by solid state reaction, using zircon oxide as an additive to the sintering process. The compaction conditions of the green tablets were investigated and allowed the obtainment of ceramic bodies with relative density around 55%, by using uniaxial pressing followed by isostatic pressing. The ceramics were sintered using specific temperature programs under two heating conditions: electric furnace and open atmosphere and under induction furnace, developed in this work, under dynamic vacuum conditions. The physical characterizations of the samples were made by X-ray diffraction, scanning electron microscopy and optical spectroscopy. The results showed that temperatures above 1800ºC combined with the effect of vacuum are necessary to obtain transparent Yttria by conventional sintering method; the heating system developed was efficient in reaching the desired temperature, however had some limitations that prevented the control and reproducibility of the process. By means of the methodology developed it was possible to obtain ceramic yttria with transmission in the visible region of the electromagnetic spectrum (400-700) up to 42% compared to single crystal yttria. Progress was made in manufacture of transparent ceramics, however, it is necessary to optimize the control of the heating system of the furnace developed, in order to eliminate the few existing light scattering centers.

Indiana University-Purdue University Indianapolis (IUPUI) / The objectives: 1. To compare the flexural strength, flexural modulus, and fracture toughness of specimens fabricated from recently marketed translucent full-contour zirconia, traditional zirconia, and lithium disilicate glass ceramic. 2. To compare the load-to-failure of crowns fabricated from recently marketed translucent full-contour zirconia, traditional zirconia, and lithium disilicate glass ceramic at their recommended tooth-reduction thickness. Methodology: Four groups of translucent zirconia (BruxZir, KDZ Bruxer, CAP FZ, Suntech zirconia), one group of traditional zirconia (CAP QZ) and IPS e.maxCAD) were tested. Twelve bars of each material were made and tested for flexural strength, and fracture toughness. Fracture patterns were imaged under SEM. Forty-eight crowns (8 from each group) were fabricated with CAD/CAM technique following manufacturers’ recommendations for the amount of tooth reduction. All the crowns were cemented to prepared epoxy resin dies with RelyX Unicem and tested for static load to failure in a universal machine. Result: In bar-shape samples, CAP QZ (traditional zirconia) showed the highest flexural strength (788.12 MPa), fracture toughness (6.85 MPa.m1/2), and fracture resistance (2489.8 N). All translucent zirconia groups show lower mechanical properties than QZ. However, there were no differences between translucent and traditional zirconia in the fracture resistance of the crown-shape samples. There was no significant difference in fracture resistance between IPS e.max crowns at recommended thickness and other zirconia crowns at recommended thickness. Conclusion: With less reduction of tooth structure, a high inherent strength and chip resistance make full-zirconia crowns a good alternative to porcelain-fused-to-metal crowns and all other ceramic crowns.

Syfte  Syftet med föreliggande studie var att undersöka hur böjhållfastheten på zirkonia påverkas av värmebehandling, ytbehandlingar vid re-cementering och långtidsförvaring i cirka två år. Material och metod I en tidigare studie av A.Cervenka och H. Ekdahl (7) designades 30 stycken zirkoniahättor, med måtten 6 mm i tjocklek och 14 mm i ⌀(Z-CAD, HTL, Metoxit), i ett CAD-program (3shape) och frästes (DATORN 5).  Zirkoniahättorna delades in i tre grupper med tio provkroppar i varje grupp, beroende på ytbehandling: kontrollgrupp (C), sandblästring med aluminiumoxid (A) och skrapning (S). Zirkoniahättorna cementerades på titandistanser. Grupp S och grupp A utsattes för värmebehandling, för att kunna lossa hättorna från titandistanserna. Överskottet av cement avlägsnades genom två olika ytbehandlingar innan recementering (A respektive S). Samtliga grupper termocyklades i 5000 cykler (5° till 55°) innan de utsattes för ett draghållfasthetstest. När föreliggande studie genomfördes hade zirkoniahättorna förvarats torrt i rumstemperatur i cirka två år. Zirkoniahättornas underdel slipades ner till 2,9 mm i tjocklek i en slipmaskin (Phoneix 4000) för att tillverka provkroppar lämpade för utförande av ett biaxialt böjhållfasthetstest. Resultaten analyserades med One-way ANOVA, Tukey’s test med en signifikansnivå på α =0,05.   Resultat Det biaxiala böjhållfasthetstestet påvisade att grupp C hade högst medelvärde och S hade lägst medelvärde. Det fanns inte någon signifikant skillnad mellan grupperna, p>0,05.  Slutsats Inom ramen för föreliggande studie kan följande slutsats dras:  Böjhållfastheten på zirkoniahättor som har långtidsförvarats i cirka två år påverkas inte av tidigare genomförd värmebehandling och olika ytbehandlingar vid recementering / Purpose The purpose of the present study was to investigate how the flexural strength of zirconia is affected by heat treatment, various surface treatments during re-cementation, and long term storage for about two years. Material and method In a previous study by A.Cervenka and H. Ekdahl (7), 30 zirconia copings, measuring 6 mm in thickness and 14 mm in ⌀ (Z-CAD, HTL, Metoxit), were designed in a CAD-program (3shape) and milled (DATORN 5). Zirconia copings were divided into three groups with ten specimens in each group, depending on different surface treatment: control group (C), aluminum oxide abrasion group (A) and scraping (S). Zirconia copings were cemented on titanium abutments. Group S and group A were subjected to heat treatment in order to be able to detach the zirconia copings from titanium abutments. The excess cement was removed by two various surface treatments before the recementation (A respective S). All groups were thermocycled for 5000 cycles (5 ° to 55 °) before being subjected to a tensile strength test. At the time of the present study zirconia copings had been stored dry at room temperature for about two years. The lower part of the zirconia copings was reduced to 2.9 mm in thickness using a grinding machine (Phoneix 4000)in order to produce specimens suitable to performe a biaxial flexural strength test. The results were analyzed with One-way ANOVA, Tukey's test with a significance level of α = 0.05.. Results The biaxial flexural strength test showed that group C had the highest mean and S had the lowest mean. There was no significant difference between the groups, p> 0.05.  Conclusion Within the limitations of this study, the following conclusion can be drawn: The flexural strength of zirconia copings that have been stored for about two years is not affected by previously heat treatment performed during recementation and various surface treatments during recementation.

This master’s thesis focuses on effect of outer building construction on thermal load of space. The effect of translucent and non-translucent construction is discussed. The project of air-conditioning system is prepared for the two alternatives of the translucent construction, including the purchase price of the airconditioning system and glazing and the savings on summer cooling. Afterwards the period of the recovery of investment is calculated. The plan of the airconditioning system is connected to my bachelor’s thesis “Airconditioning in the car showroom”, the subject of which was the plan of the airconditioning system of the car showroom.

Current strategies for designing biomaterials involve creating materials and interfaces that interact with biomolecules, cells and tissues.  This thesis aims to investigate several bioactive surfaces, such as nanocrystalline diamond (NCD), hydroxyapatite (HA) and single crystalline titanium dioxide, in terms of material synthesis, surface functionalization and characterization. Although cochlear implants (CIs) have been proven to be clinically successful, the efficiency of these implants still needs to be improved. A CI typically only has 12-20 electrodes while the ear has approximately 3400 inner hair cells. A type of micro-textured NCD surface that consists of micrometre-sized nail-head-shaped pillars was fabricated. Auditory neurons showed a strong affinity for the surface of the NCD pillars, and the technique could be used for neural guidance and to increase the number of stimulation points, leading to CIs with improved performance. Typical transparent ceramics are fabricated using pressure-assisted sintering techniques. However, the development of a simple energy-efficient production method remains a challenge. A simple approach to fabricating translucent nano-ceramics was developed by controlling the morphology of the starting ceramic particles. Translucent nano-ceramics, including HA and strontium substituted HA, could be produced via a simple filtration process followed by pressure-less sintering. Furthermore, the application of such materials as a window material was investigated. The results show that MC3T3 cells could be observed through the translucent HA ceramic for up to 7 days. The living fluorescent staining confirmed that the MC3T3 cells were visible throughout the culture period. Single crystalline rutile possesses in vitro bioactivity, and the crystalline direction affects HA formation. The HA growth on (001), (100) and (110) faces was investigated in a simulated body fluid in the presence of fibronectin (FN) via two different processes. The HA layers on each face were analysed using different characterization techniques, revealing that the interfacial energies could be altered by the pre-adsorbed FN, which influenced HA formation. In summary, micro textured NCD, and translucent HA and FN functionalized single crystalline rutile, and their interactions with cells and biomimetic HA were studied. The results showed that controlled surface properties are important for enhancing a material’s biological performance.

Made available in DSpace on 2014-07-29T15:01:48Z (GMT). No. of bitstreams: 1 Dissertacao Christiane R de P Cavalcante.pdf: 2530151 bytes, checksum: c8418cc369a22584f8884d3a586e48ae (MD5) Previous issue date: 2011-09-23 / The PET, tereftalato of ethylene, is the most known and appropriated material in the manufacture of several packings of nourishing products, specially the bottles of beverages. The correct management of the urban solid residues to the transformation into those which return to the use and the environment education are essential tasks to guarantee the exploitation of the complete useful life of this material and to prevent it on environmental focus. From the industrial point of view, the PET recycling in Brazil is still a recently activity. All around the country there are recycling industries, but they were created specially for environmental reasons. Although they became an important source of jobs and income. That s why, nowadays, recycling industries are considered an important social order factor. In Brazil, there are industries which transform the PET into roofing tiles for covering for drawing or injection. In this work, the main analyzed topic was the properties of the transparent roofing tiles of PET and other materials, the polycarbonate and the available fiberglass in the civil construction market through the main properties and relative parameters to the natural illumination, including its optic properties and the objective of the luminous and thermal comfort. Using the results of the spectrophotometer device, it was made a comparison among the studied materials in order to help the best choice of luminous and thermal comfort materials. PET, compared to the other studied materials, is not the best choice, even concerned to the price. However, for environmental solutions, the best way to use this solid waste recycling is the utilization of the PET as transparent roofing tiles, specially considering the amount of material all around rivers, scoots, attires, and so on. / O PET, tereftalato de etileno, é o material mais conhecido e apropriado na fabricação de várias embalagens de produtos alimentícios, entre as quais se destacam as garrafas de refrigerante. A correta gestão dos resíduos sólidos urbanos, com a transformação desses resíduos para o retorno ao uso, e a educação ambiental são tarefas essenciais para garantir o aproveitamento da totalidade da vida útil daquele material e evitar que seja ele o foco de contaminação ambiental. Do ponto de vista industrial, a reciclagem de PET no Brasil ainda é uma atividade recente. Há indústrias recicladoras em todo o território nacional criadas primordialmente para guarnecer uma questão ambiental, mas que culminou em uma questão de ordem social com geração de empregos e renda. No mercado existem no Brasil empresas que transformam o PET em telhas de cobertura por extrusão ou injeção. Neste trabalho foram analisadas as propriedades das telhas transparentes de PET e de outros materiais, o policarbonato e a fibra de vidro disponíveis no mercado da construção civil através das principais propriedades e parâmetros relativos à iluminação natural, incluindo suas propriedades óticas e com o objetivo do conforto lumínico e o térmico. Por meio dos resultados obtidos pelo uso do aparelho de espectrofotômetro, elaborou-se uma comparação entre os materiais estudados a fim de auxiliar na sua escolha, visando um melhor conforto lumínico e térmico. O PET não obteve o comportamento ansiado em comparação com os demais materiais estudados, também em relação ao custo pode-se observar que é mais onerosa a instalação do telhado de PET. Mas já em relação ao quesito de reaproveitamento de resíduos sólidos urbanos descartados no meio ambiente, o PET possui melhor desempenho uma vez que seu material se encontra em abundância e pode ser transformado e reaproveitado, amenizando o impacto ambiental.

Τα οπτικά δίκτυα αποτελούν την αποδοτικότερη επιλογή όσον αφορά την εγκατάσταση ευρυζωνικών δικτύων κορμού, καθώς παρουσιάζουν μοναδικά χαρακτηριστικά μετάδοσης. Διαθέτουν τεράστιο εύρος ζώνης, υψηλή αξιοπιστία, ενώ επίσης έχουν μειωμένο κόστος μετάδοσης ανά bit πληροφορίας σε σχέση με τα υπόλοιπα ενσύρματα δίκτυα. Τις τελευταίες δεκαετίες διατυπώθηκαν οι αρχές μίας τεχνολογίας μετάδοσης πολλαπλών φερουσών, γνωστής ως Ορθογώνια Πολυπλεξία Διαίρεσης Συχνότητας (Orthogonal Frequency Division Multiplexing - OFDM), η οποία στηρίζεται στην πολυπλεξία διαίρεσης συχνότητας, αλλά πετυχαίνει πολύ καλύτερη χρησιμοποίηση του διαθέσιμου εύρους ζώνης. Πρόσφατα και στις οπτικές επικοινωνίες άρχισε να μετατοπίζεται το ενδιαφέρον στην Οπτική Ορθογώνια Πολυπλεξία Διαίρεσης Συχνότητας (O-OFDM), λόγω της προόδου στην κωδικοποίηση και στην ηλεκτρονική ψηφιακή επεξεργασία σήματος (DSP). Οι εξελίξεις αυτές μπορούν να αλλάξουν ριζικά τα οπτικά δίκτυα. Μέσω της πολυπλεξίας υποφερουσών και της δέσμευση μεταβλητού φάσματος, που είναι χαρακτηριστικά της O-OFDM τεχνολογίας, ένα οπτικό μονοπάτι μπορεί να χρησιμοποιεί το απολύτως απαραίτητο φάσμα (αριθμό υποφερουσών) ανάλογα με το μεταδιδόμενο ρυθμό δεδομένων. Με τον τρόπο αυτό επιτυγχάνεται καλύτερη χρησιμοποίηση φάσματος αναιρόντας τον περιορισμό σταθερού πλέγματος των δικτύων πολυπλεξίας μήκους κύματος (WDM). Παράλληλα η αρχιτεκτονική αυτή υποστηρίζει τη δέσμευση χωρητικότητας μικρότερης ή μεγαλύτερης από αυτή ενός μήκους κύματος μέσω της δέσμευσης κατάλληλου αριθμού υποφερουσών από κατάλληλους transponders και μεταγωγείς WXCs. Στην παρούσα διπλωματική εργασία αντιμετωπίζεται το πρόβλημα της σχεδίασης ευέλικτων OFDM οπτικών δικτύων, όπου οι αιτήσεις εξυπηρετούνται από κατάλληλους transponders όσον αφορά την επιλογή του χρησιμοποιούμενου φάσματος και του επίπεδου διαμόρφωσης. Με δεδομένη την τοπολογίας του δικτύου, τον πίνακα αιτήσεων και των χαρακτηριστικών των transponders, παρουσιάζονται οι μοντελοποιήσεις γραμμικού ακέραιου προγραμματισμού (Integer Linear Programming) για την επίλυση του προβλήματος σχεδίασης διαφανών (transparent) και ημι-διαφανών (translucent) οπτικών OFDM δικτύων λαμβάμνοντας υπόψη τους υπαρκτούς περιορισμούς φυσικού επιπέδου. Σχεδιάζεται λοιπόν, ένα πρόβλημα βελτιστοποίησης που λαμβάνει υπόψη του τόσο το εύρος ζώνης που χρησιμοποιείται όσο και τον αριθμό των transponders. Από τη στιγμή που το πρόβλημα της δρομολόγησης και δέσμευσης φάσματος (Routing and Spectrum Allocation RSA) είναι ΝP πλήρες (NP-complete), η λύση του προβλήματος γραμμικού ακέραιου προγραμματισμού (ILP) δεν είναι αποδοτική για μεγάλα στιγμιότυπα του προβλήματος. Για το λόγο αυτό, παρουσιάζονται ευριστικοί αλγόριθμοι (heuristic algorithms) για την επίλυση του προβλήματος σχεδίασης διαφανών και ημι-διαφανών οπτικών δικτύων. / We consider the planning problem of a spectrum flexible optical network where traffic is served by flexible transponders that can be tuned in both the spectrum and the modulation format that they utilize. We assume that physical layer impairments are incorporated in the definition of the feasible transmission configurations for the transponders, described by capacity-reach-spectrum-guardband tuples. Given the feasible configurations (tuples) of the transponders and the traffic matrix, we formulate the planning problem of a spectrum flexible optical network considering both the use or not of regenerators in the network. Demands are served for their requested rates by choosing the route, breaking the transmission in more than one connection if needed, placing regenerators if needed, and allocating spectrum to the connections. The connections are separated by appropriate spectrum guardbands so that physical layer interference is kept at acceptable levels. The objective is to serve the traffic and find a solution that is Pareto optimal with respect to the total amount of spectrum utilized and the number of transponders used. We start by presenting algorithms that are based on integer linear programming (ILP) formulations for planning both transparent (without regenerators) and translucent (with regenerators) networks and then we continue by presenting heuristic algorithms. Our heuristic algorithms utilize simulated annealing to tradeoff performance with running time. We use transmission tuples based on studies on OFDM-based networks in our simulation experiments. We initially examine the optimality performance of the heuristic algorithms in small scale experiments. Then we use the heuristic algorithms to study realistic network planning problems and evaluate the spectrum and transponder cost savings that can be obtained by an OFDM-based network as compared to a mixed line rate (MLR) fixed-grid WDM optical network.