Supported metal nanoparticles present unique chemical and physical properties compared to their bulk counterparts. Their high surface energy provides outstanding catalytic activities, opening the door not only to improved catalytic systems but also to new catalytic routes. However, their high surface energy and liquid-like properties are responsible for their instability, usually leading to agglomeration under reaction conditions. This thesis seeks to investigate a novel nanoparticle stabilisation approach by physical confinement on curved supports. Specifically, the project focusses on the stabilisation of cobalt and gold nanoparticles on nanostructured -Al2O3 supports, motivated by the industrial interest of Sasol UK. The research hypothesis is validated by detailed characterisation and catalytic testing of a range of catalysts using different metal loadings and support morphologies. To enable this study, the mechanism of the hydrothermal synthesis of a series of nanostructured -Al2O3 supports with either flat or curved surfaces and differing degrees of curvature has been elucidated, leading to the development of a semi-continuous manufacturing process. Varying the method for loading cobalt onto -Al2O3 supports highlights the implications of method selection on the particle size, reducibility, composition and the tendency to form irreducible cobalt oxides, all of which affect the catalytic activity. The ability to obtain and stabilise small nanoparticles with low loading (1 wt% Co) without the formation of irreducible cobalt oxides exposes the beneficial effect of the support curvature. Specifically, the stabilisation effect is theorised to be effective under the condition where the ratio of the diameter of the nanoparticle (P) and the nanorod (R) is less than one, P:R < 1. In several cases, after cobalt or gold reduction, elongation of the nanoparticles, as opposed to agglomeration, is observed by electron microscopy confirming that the particles are physical confined by the curved surface in all directions except along the nanorod axis. In these cases, highly active Co/-Al2O3 and Au/-Al2O3 catalysts are reported for NH3 decomposition and CO oxidation respectively. For higher metal loadings (> 5 wt% Co), where the particles are the same size or larger than the diameter of the nanorod cross-section, no noticeable stabilisation effect is reported. The results of this thesis are scientifically and industrially important. If applied correctly, this novel nanoparticle stabilisation strategy could be used to design catalysts with improved activity and stability, resulting in lower operational costs and improved resource efficiency.

A visãao é o sentido humano mais complexo e importante para os processos de cognição e de interação de um indivíduo com o mundo. Neurofiisiologistas buscam identificar e compreender como funcionam os mecanismos celulares envolvidos neste processo. O sistema visual recebe os sinais de imagens captadas pelos olhos e, por meio de transformações e processamento diversos, integra esses sinais em representações de objetos internos perceptuais. O projeto Olho Virtual consegue reconstruir, em três dimensões, modelos de olhos utilizando córneas reais ou simuladas em computador, reproduzindo suas propriedades ópticas captando imagens de maneira satisfatória. Este trabalho introduz, no projeto Olho Virtual, um modelo computacional de retina baseado no modelo biológico, capaz de reproduzir as propriedades das células cones e bastonetes em suas distribuições radiais e também em suas funcionalidades em particular. Além dessa, é apresentado uma modelagem para reprodução dos campos receptivos das células ganglionares presentes na retina, gerando sinais de saída nos sistemas parvo e magno. Por fim são feitas simulações de experimentos psicofísicos com propósito de verificar a validade da modelagem proposta / The vision is the human sense more complex and important in cognitive processes and the interaction of an individual with the world. Neurophysiologists seek to identify and understand how the cellular mechanisms involved in this process work. The visual system receives the image signals captured by the eyes and, through several transformations and processing, integrate those signals into internal representations of perceptual objects. The project Virtual Eye can reconstruct three-dimensional models of eye corneas using real or simulated on the computer, playing their optical properties capturing images satisfactorily. This work introduces the Virtual Eye project, a computational model of retina-based biological model, able to reproduce the properties of rod and cone cells in their radial distributions and also in its functionality in particular. Besides this, a model is presented for reproduction of the receptive fields of ganglion cells present in the retina, generating output signals in the parvo and magno systems. Finally, simulations are made with psychophysical experiments in order to verify the accuracy of the proposed model

This report investigates the sensitivity of the control rod depletion coefficients, Sg, to different input parameters and how this affects the accumulated 10B depletion, β. Currently the coefficients are generated with PHOENIX4, but the geometries can be more accurately simulated in McScram. McScram is used to calculate Control Rod Worth, which in turn is used to calculate Nuclear End Of Life, and Sg cannot be generated in the current version of McScram. Therefore, it is also analyzed whether the coefficients can be related to CRW and thus be studied indirectly through it. Simulations of the coefficients were done in PHOENIX4, simulations of CRW were done in both PHOENIX4 and McScram and simulations of β were done in POLCA7. All simulations were performed for a CR99 in a BWR reactor. The control rod coefficients were found to be sensitive to the enrichment of the fuel, void fraction of the water and the width of the gap, and these effects were also seen in the results of β. As a result, one of three steps could be taken. First, the parameter values should not be set arbitrarily, instead default values could be chosen such that Sg is calculated more accurately. Second, a set of tables of Sg could be generated for different parameter values so that β can be calculated with Sg from the current conditions, although this would mean that PHOENIX4 needs to be updated. Third, McScram can be updated to be able to calculate Sg directly. It has been concluded that Sg cannot be studied indirectly through CRW since the trends and the sensitivity to the different parameters were not consistent between Sg, CRW calculated with PHOENIX4 and CRW calculated with McScram, where PHOENIX4 was more sensitive than McScram. The results can instead be used to bench-mark the PHOENIX4 results.

Nowadays, colloidal rods can be synthesized in large amounts. The rods are typically cylindrically and their length ranges from several nanometers to a few micrometers. In solution, systems of colloidal rodlike molecules or aggregates can form liquid-crystalline phases with long-range orientational and spatial order. In the present work, we investigate structure formation and fractionation in systems of rodlike colloids with the help of Monte Carlo simulations in the NPT ensemble. Repulsive interactions can successfully be mimicked by the hard rod model, which has been studied extensively in the past. In many cases, attractive interactions like van der Waals or depletion forces cannot be neglected, however. In the first part of this work, the phase behavior of monodisperse attractive rods is characterized for different interaction strengths. Phase diagrams as a function of rod length and pressure are presented. Most systems of synthesized mesoscopic rods have a polydisperse length distribution as a consequence of the longitudinal growth process of the rods. For many technical and research applications, a rather small polydispersity is desired in order to have well defined material properties. The polydispersity can be reduced by a spatial demixing (fractionation) of long and short rods. Fractionation and structure formation is studied in a tridisperse and a polydisperse bulk suspension of rods. We observe that the resulting structures depend distinctly on the interaction strength. The fractionation in the system is strongly enhanced with increasing interaction strength. Suspensions are typically confined in a container. We also examine the influence of adjacent substrates in systems of tridisperse and polydisperse rod suspensions. Three different substrate types are studied in detail: a planar wall, a corrugated substrate, and a substrate with rectangular cavities. We analyze the fluid structure close to the substrate and substrate controlled fractionation. The spatial arrangement of long and short rods in front of the substrate depends sensitively on the substrate structure and the pressure. Rods with a predefined length are segregated at substrates with rectangular cavities. / Kolloidale Stäbchen können mittlerweile in großen Mengen hergestellt werden. Die Form der Stäbchen ist in der Regel zylinderförmig und ihre Länge reicht von einigen Nanometern bis hin zu wenigen Mikrometern. Systeme aus kolloidalen stäbchenförmigen Molekülen oder Aggregaten können in Lösung flüssigkristalline Phasen mit langreichweitiger Orientierungs- und Raumordnung ausbilden. Im Rahmen dieser Arbeit werden Strukturbildung und Fraktionierung in Systemen aus stäbchenförmigen Kolloiden mittels Monte Carlo Simulationen im NPT Ensemble untersucht. Replusive Wechselwirkungen können erfolgreich durch harte Stäbchen modelliert werden. Dieses Modell wurde in der Vergangenheit bereits ausgiebig untersucht. Oft jedoch können attraktive Wechselwirkungen, wie z.~B. van der Waals- oder Depletionskräfte, nicht vernachlässigt werden. Im ersten Teil dieser Arbeit wird das Phasenverhalten von monodispersen attraktiven Stäbchen bei unterschiedlichen Wechselwirkungsstärken charakterisiert. Es werden Phasendiagramme bezüglich der Parameter Druck und Stäbchenlänge präsentiert. Die überwiegende Mehrzahl von Systemen aus synthetisierten mesoskopischen Stäbchen weist eine polydisperse Längenverteilung aufgrund des Längswachstums auf. Für eine Reihe technischer und wissenschaftlicher Anwendungen sind hingegen schmale Längenverteilungen wünschenswert, um wohl definierte Materialeigenschaften zu haben. Die Polydispersität kann durch räumliche Trennung (Fraktionierung) langer und kurzer Stäbchen reduziert werden. Fraktionierung und Strukturbildung werden in einer tridispersen und einer polydispersen Suspension untersucht. Wir beobachten, dass die entstehenden Strukturen ganz wesentlich von der Wechselwirkungsstärke abhängen. Der Grad der Fraktionierung wird durch Attraktivität stark erhöht. Suspensionen befinden sich typischerweise in Gefäsen. Wir untersuchen daher auch den Einfluss von begrenzenden Substraten auf Systeme aus tridispersen und polydispersen Stäbchensuspensionen. Drei verschiedene Substratstrukturen werden genauer betrachtet: Eine planare Wand, ein riefenförmiges Substrat und Substrate mit rechteckigen Aussparungen. Wir untersuchen die Flüssigkeitsstruktur in Substratnähe und substratinduzierte Fraktionierung. Die räumliche Anordnung von langen und kurzen Stäbchen hängt sehr sensibel von der Substratstruktur und dem Druck ab. Stäbchen mit einer festgelegten Länge werden an Substraten mit rechteckigen Aussparungen abgesondert.

Thesis (Ph. D.)--Ohio State University, 2008. / Title from first page of PDF file. Includes bibliographical references (p. 172-177).

Thesis (M.S.)--Mississippi State University. Department of Electrical and Computer Engineering. / Title from title screen. Includes bibliographical references.

Έχει περάσει περισσότερο από ένας αιώνας από τότε, που ο Χαρίλαος Τρικούπης, Πρωθυπουργός της Ελλάδας οραματίστηκε τη κατασκευή μιας γέφυρας, η οποία θα ένωνε την δυτική Πελοπόννησο με την ηπειρωτική Ελλάδα, το Ρίο με το Αντίρριο. Την εποχή εκείνη, τα τρία χιλιόμετρα θάλασσας, που μεσολαβούσαν μεταξύ των δυο πόλεων, φάνταζαν αδύνατο να γεφυρωθούν. Οι δυσκολίες ήταν πάρα πολλές και η τεχνογνωσία δεν είχε ακόμη φτάσει σε τέτοια επίπεδα, έτσι ώστε να δώσει πνοή σ’ αυτό το μεγαλόπνοο όραμα. Άλλωστε το σχέδιο φάνταζε πολύ ακριβό για τις οικονομικές δυνατότητες της χώρας μας εκείνης της εποχής. Παρ’ όλα αυτά το σχέδιο δεν εγκαταλήφθηκε ποτέ. Μελέτες γίνονταν συνέχεια με σκοπό να ληφθούν υπόψη όλες οι παράμετροι, όπως η σεισμικότητα της περιοχής, το εξαιρετικά μεγάλο βάθος του θαλάσσιου χώρου, η πιθανότητα δημιουργίας παλιρροϊκών κυμάτων μετά από ένα σεισμό, τα ασταθή υλικά που αποτελούσαν το πυθμένα της θάλασσας, η απομάκρυνση των τεκτονικών πλακών στον Κορινθιακό κόλπο, τα ισχυρά ρεύματα, οι άνεμοι και άλλα, που αποτελούσαν τροχοπέδη για τη δημιουργία της γέφυρας. Τελικά, στα μέσα της δεκαετίας του 90’, μια γαλλοελληνική σύμπραξη, αποτελούμενη από όμιλο εταιριών και από τις δυο χώρες, ανέλαβε τη σχεδίαση και κατασκευή της γέφυρας. Τα έργα ξεκίνησαν τον Ιούλιο του 1998 υπό την επίβλεψη και καθοδήγηση του αρχιτέκτονα Berdj Mikaelian. Η κατασκευή της γέφυρας αναμένετο να ολοκληρωθεί το χρονικό διάστημα μεταξύ Σεπτεμβρίου και Νοεμβρίου του 2004, άλλα οι εργασίες επισπεύθηκαν ένεκα των Ολυμπιακών Αγώνων, που θα λάβαιναν χώρα στην Αθήνα την ίδια χρονιά. Έτσι η γέφυρα παραδόθηκε στο κοινό στις 7 Αυγούστου του 2004, με την Ολυμπιακή φλόγα να την διασχίζει με κατεύθυνση την Αθήνα. Η γέφυρα θεωρήθηκε ως ένα θαύμα της σύγχρονης μηχανικής και όλα τα απαραίτητα μέτρα είχαν ληφθεί για την άρτια λειτουργία της. Παρ’ όλα αυτά στις 27 Ιανουαρίου του 2005, έξι μόλις μήνες μετά τα εγκαίνια, ένας κεραυνός έπληξε ένα από τα καλώδια στήριξης, τα οποία ενώνουν το κατάστρωμα της γέφυρας με τους πυλώνες. Ο κεραυνός έπληξε το ψηλότερο καλώδιο διαμέτρου 25cm, στη νοτιοδυτική πλευρά της γέφυρας, πάνω από το ii άνοιγμα των 286 μέτρων, κοντά στη περιοχή του Ρίου. Το υψηλής περιεκτικότητας σε πολυαιθυλένιο καλώδιο τυλίχτηκε στις φλόγες με αποτέλεσμα να καταστραφεί ολοσχερώς και να καταρρεύσει στο καταστρώμα. Όλες οι απαραίτητες ενέργειες έγιναν ταχύτατα, έτσι ώστε να αντικατασταθεί το καλώδιο και να παραδοθεί η γέφυρα και πάλι στη κυκλοφορία το συντομότερο δυνατό. Όμως πλέον ήταν φανερό ότι η αντικεραυνική προστασία της γέφυρας δεν ήταν αρκετή και αποτελεσματική. Στη συνέχεια του κειμένου θα γίνει ανάλυση του παραπάνω συμβάντος, αφού πρώτα γίνει αναφορά σε κάποιες βασικές αρχές γύρω από το φαινόμενο του κεραυνού και των συστημάτων αντικεραυνικής προστασίας. Συγκεκριμένα ακολουθούν πέντε κεφάλαια : I. Στο πρώτο κεφάλαιο γίνεται μια εισαγωγή στο φυσικό φαινόμενο του κεραυνού και τις διάφορες παραμέτρους του. II. Το κεφάλαιο 2 αναφέρεται στον ορισμό του συστήματος αντικεραυνικής προστασίας. III. Στο τρίτο κεφάλαιο γίνεται παρουσίαση της ακίδας του Franklin. IV. Το τέταρτο κεφάλαιο παρουσιάζει τα συστήματα αντικεραυνικής προστασίας πρώιμης εκπομπης (ESE) και γίνεται σύγκριση με την ακίδα του Franklin . V. Στο πέμπτο και τελευταίο κεφάλαιο αναλύεται το κεραυνικό πλήγμα στη γέφυρα. Γίνεται παρουσίαση της εφαρμογής ακίδων Franklin στο ΣΑΠ της γέφυρας και βελτίωσης αυτού. / More than a century has passed, since Charilaos Trikoupis, Prime Minister of Greece had contemplated the construction of a bridge that would connect western Peloponnese with the mainland of Greece, the city of Rion with Antirio. Back then, the three kilometers of sea water which separated the two cities, seemed impossible to be bridged. The difficulties were many and the know how had not reached that level, where it would make a great vision such as this, possible. Besides the project seemed extremely expensive for the country’s economic potential at that time. Despite all this, the project was never abandoned. Studies were made repeatedly, in order to take under consideration all the parameters, like the seismic activity of the area, the extraordinary depth of the sea, the possibility of a tsunami after an earthquake, the unstable materials that constituted the bottom of the sea, the movement of the tectonic plates in the Corinthian gulf away from one another, the strong currents, winds etc. All these factors acted as a brake for the construction of the bridge. Eventually, in the mid 90s, a greek-french collaboration, composed by a group of companies from both countries, took over the design and the building of the bridge. Construction works started in July of 1998 under the supervision and guidance of the architect Berdj Mikaelian. The construction of the bridge was expected to be completed during the period of September to November of 2004, but works were accelerated because of the Olympic games that would take place in Athens, that same year. Therefore the bridge was revealed to the public on the 7th of August 2004, with the Olympic Flame crossing it, on the way to Athens. The bridge was considered to be a miracle of modern mechanics and all the necessary measures were taken for its perfect operation. However, on January 27 of 2005, just six months after the opening of the bridge, a lightning stroke cut down one of the longest stay cables that connected the deck of the bridge to the pylons. The lightning struck the top 25cm diameter cable in the southwest fan of stays over the 286m span nearest Rion. The high density polyethylene cable was set on fire, and as a result of that the cable was completely iv destroyed and fell on the deck. All the necessary means were taken, in order to replace the cable and get traffic back on the bridge as soon as possible. It was obvious at that point that the lightning protection of the bridge was neither sufficient or effective enough. There are five chapters following: I. In the first chapter there is an introduction to the natural phenomenon of lightning and its characteristics II. The second chapter gives a definition of the lightning protection system of a structure III. In the third chapter, the Franklin rod is presented IV. The fourth chapters refers to the early streamer emission systems and compares them with the Franklin rod V. In the fifth and final chapter there is an analysis of the lightning incident on the bridge. The installation of Franklin rods on the lightning system of the bridge is presented, alongside with an enhancement of the protection.

Orientador: Douglas Domingues Bueno / Resumo: A redução de vibração estrutural tem sido um importante tópico para muitas aplicações de engenharia. Nos projetos tradicionais, diferentes técnicas de controle passivo envolvendo mate- riais visco-elásticos e absorvedores dinâmicos e, mais recentemente, metodologias de controle ativo incluindo atuadores e sensores têm sido empregado com sucesso. Diferentes pesquisas tem demostrado que redução de vibração pode ser obtida usando o conceito de periodicidade. As estruturas periódicas envolvem elementos idênticos ou partes conectadas repetidamente. O projeto de estruturas periódicas pode ser empregado para conseguir bandas de frequências em que não há propagação de ondas elásticas, denominadas de "stop bands", introduzindo um efeito similar ao de um filtro. Neste contexto, o presente trabalho apresenta uma abordagem alterna- tiva para o projeto de barras periódicas. Esta alternativa envolve a modelagem de uma barra periódica do tipo híbrida infinita na qual uma estrutura periódica finita é conectada entre duas barras semi-infinitas. Para isto, é utilizada uma metodologia que relaciona vetor de estados e amplitude de ondas. A principal proposta deste trabalho é desenvolver uma relação entre as amplitudes de ondas longitudinais transmitidas e incidentes em termos das propriedades físi- cas e geométricas de uma genérica estrutura periódica para simplificar o processo do projeto. Usando esta formulação mostra-se que uma barra periódica pode ser projetada para satisfazer os requisitos de um... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The reduction of structural vibration has been an important topic for many engineering applica- tions. In traditional projects different passive control techniques involving viscoelastic materials and dynamic absorbers and, more recently, active control methodologies including actuators and sensors have been successfully employed. Different researches have demonstrated that vibra- tion reduction can be obtained using the concept of periodicity. The periodic structures involve identical elements or parts connected repeatedly. The design of periodic structures can be em- ployed to get frequency band without elastic waves propagation, i.e., stop bands, introducing an effect similar to the filter. In this context, the present work introduces an alternative approach for designing periodic rods. This alternative involves the modeling of an infinite hybrid type periodic rod in which a finite periodic structure is connected between two semi-infinite rods. It is used a methodology that relates state vector and wave amplitudes. The main proposal of this work is to develop a relation between the transmitted and incident longitudinal waves amplitudes in terms of physical and geometrical properties of a generic candidate structure to simplify the process of designing. Based on this approach is shown that a periodic rod can be designed to satisfy requirements of a vibration suppression. A hypothetical problem is proposed and numerical and experimental results show the stop bands obtained to so... (Complete abstract click electronic access below) / Doutor

Essa dissertação aborda o tema de propagação de ondas de tensão em hastes metálicas retangulares. Este tipo de onda pode ser utilizada como base na verificação da integridade estrutural através de um ensaio não destrutivo (END). A propagação de ondas elásticas em sólidos apresenta muito potencial quando se deseja estimar a integridade de determinada estrutura. Porém para transformar esse fenômeno físico em uma técnica aplicável na detecção de danos, alguns passos devem ser seguidos, dentre eles: a compreensão das características de propagação da estrutura em estudo, in teração das ondas elásticas com defeitos, aten uação das ondas propagadoras devido a fontes de amortecimento e dispersão. Neste contexto o presente trabalho tem o principal foco no desenvolvimento de uma metodologia eficiente para a investigação da propagação de ondas de tensão em hastes retangulares metálicas, abordando o tema por diversos aspectos. No decorrer do mesmo são calcu ladas as curvas de dispersão de uma haste retangular com seção transversal de 15 x5 [rum], para uma faixa de frequência determinada [0,100 kHz], utilizando três metodologias distintas e realizando a comparação crítica entre elas. São realizadas investigações teóricas, de forma analítica e numérica (via análise explícita empregando elementos finitos) e uma inves tigação experimental das características de propagação da geometria referida. Também os efeitos da aten uação das ondas na geometria é estudado. Os resulta dos obtidos são discutidos procurando mostrar sua coerência e enfatizando a informação sobre o comportamento mecânico das ondas de tensão nesse tipo de estrutura, observando aspectos relevantes à concepção de técnicas de END que possi bilitem a avaliação da integridade dessas estruturas. / This dissertation addresses the issue of propagation of stress waves in metallic rectangular rods. This type of wave can be used as the integrity check structural integrity through a non-destructive test (NDT). The propagation of elastic waves in solids has a lot of potential when estimating the given structure integrity. But to turn this physical phenomenon in an applicable technique for the detection of damage, some steps should be taken, including: understanding of propagating characteristics of the structure under study, interaction of elastic waves with defects, attenuation of the propagating waves due to sources of damping and dispersion. In this context, the present work is the main focus in developing an effective methodology for investigating the propagation of stress waves in rectangular metal rods, addressing the issue by several aspects. During the same are calculated dispersion curves of a rod with rectangular cross section 15 x5 [mm], for a given frequency range [0,100 kHz], using three different methodologies and performing the critical comparison between them. Are performed theoretical investigations, in analytical and numerical form (via explicit analysis using finite element) and an experimental investigation of the propagation features said geometry. Also the effects of attenuation of the waves on geometry is studied. The results are discussed trying to show their consistency and emphasizing information about the mechanical behavior of stress waves in this type of structure, observing relevant aspects to the design of NDT techniques to enable the assessment of the integrity of these structures.

Made available in DSpace on 2014-10-09T12:42:53Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:08:38Z (GMT). No. of bitstreams: 1 04993.pdf: 7727472 bytes, checksum: 018707af67fb277f13c457a4276b421e (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP