Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2015-08-07T14:08:44Z No. of bitstreams: 0 / Made available in DSpace on 2015-08-07T14:08:44Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Entre os produtos confeccionados com polímeros reforçados com fibras, as hastes pultrudadas têm sido utilizadas em um número crescente de aplicações devido a características como baixa massa, elevada resistência mecânica, baixo custo de manutenção e alta resistência à corrosão, em particular quando comparadas com hastes confeccionadas em materiais convencionais equivalentes. Porém, os mecanismos de envelhecimento e de degradação dos compósitos poliméricos reforçados com fibras precisam ser mais bem compreendidos, particularmente os mecanismos de dano em condições de serviço, em aplicações de engenharia civil ou em águas profundas. Neste trabalho, foi avaliada a exposição de hastes pultrudadas produzidas a partir de fibras de carbono e vidro e resinas epóxi e éster-vinílica após 3000 horas em diferentes ambientes, como exposição à radiação UV, exposição à água do mar e exposição à água a 60 °C. Os principais aspectos microestruturais, físicos, térmicos, químicos, mecânicos e de vida útil das hastes foram avaliados antes e após as exposições. As hastes com fibras de carbono apresentaram maior resistência residual de forma geral quando comparadas às hastes de fibra de vidro, as quais perderam mais de 50% da sua resistência original após exposições de curta duração (744 h). Quando expostas à radiação UV, as hastes com fibras de carbono apresentaram maior resistência residual à tração, assim como quando submetidas a esforços combinados nos ensaios de SBS. O ambiente mais agressivo entre os estudados definitivamente foi a imersão em água destilada. Os resultados dos ensaios de short-beam apresentaram melhor relação com os efeitos de degradação do que os ensaios de resistência à tração. Através das análises microestruturais (MO e MEV) foi possível identificar alguns tipos de mecanismos de degradação atuantes em cada condição de envelhecimento acelerado. Após analisar uma combinação de fatores envolvidos, a resina epóxi, dentre as resinas estudas, foi a que apresentou melhores propriedades de interface quando utilizada com fibras de carbono. / Among products made with fiber-reinforced polymers, pultruded rods have been used in an increasing number of applications, due to such features as low weight, high strength, low maintenance costs, and high corrosion resistance, particularly when compared with rods manufactured with equivalent conventional materials. However, the ageing and degradation mechanisms of these polymer composite materials still need to be better understood, particularly the damage mechanisms under various service conditions, such as civil engineering or in deep water applications. This thesis presents an experimental study that evaluates the ageing of pultruded rods produced from reinforced carbon and glass fibers and epoxy and vinyl ester resin matrices when exposed to UV radiation, seawater and distilled water at 60 °C for 3000 hours. The degradation assessment in the different environments was made by analyzing and comparing the microstructural, physical, chemical, thermal and mechanical aspects and the lifespan of the pultruded composite rods before and after accelerated ageing. The carbon fiber rods presented a higher residual resistance considering all the aforementioned aspects when compared to the glass fibers rods, which lost more than 50% of their original resistance after short exposure (744 h) to weathering. When exposed to UV radiation, the carbon fiber rods showed higher residual resistance as compared with other types of degrading conditions. Distilled water was undoubtedly the most aggressive ageing factor in respect to all the evaluated properties and characteristics of the tested rods. The short-beam test results showed higher correlation with the degradation effects than the results of the tensile test. By means of microstructural analysis (SEM and OM), it was possible to identify some types of degradation mechanisms for each kind of applied accelerated ageing. After analyzing a combination of factors involved, it was possible to reach the conclusion that the epoxy resin incorporated with carbon fibers displayed the best overall performance among all possible resin/fiber couples

Os nervos periféricos são extensões do sistema nervoso central e responsável pela interação das atividades entre as extremidades, em suas funções sensitivas e motoras. São vulneráveis aos mesmos tipos de traumas que afetam outros tecidos: contusão, compressão, esmagamento, estiramento, avulsão e laceração. As lesões de nervos periféricos situam-se entre as mais incapacitantes que acometem indivíduos em idade produtiva, em face dos múltiplos aspectos concernentes às sequelas deste tipo de afecção. Desta forma, a interrupção de continuidade da estrutura do nervo, como no caso da neurotmese, por algum tipo de trauma, resulta na interrupção de transmissão dos impulsos nervosos e na desorganização de suas atividades funcionais. Por meio da utilização da microcirurgia foi possível desenvolver técnicas reparadoras que vão desde simples neurorrafia término-terminal até sofisticados procedimentos cirúrgicos com a utilização de enxertos de nervos, veias e artérias invertidas, tubos sintéticos de materiais variados, tais como silicone e polietileno. Outro aspecto que intriga pesquisadores de todo mundo é a utilização de fatores neurogênicos capazes de acelerar ou melhorar a regeneração de nervos periféricos. A gordura autóloga tem sido continuamente referenciada pela sua abundante oferta, no próprio sitio cirúrgico, apresentando resultados promissores, visto que a adventícia dos vasos é constituída por tecido conjuntivo frouxo, rico em adipócitos. Assim, em um trauma, os neuritos oriundos do coto proximal do nervo lesado, ficam diretamente em contato com esses adipócitos. Seguindo este raciocínio, e com base em trabalhos anteriores onde foi usada veia preenchida com músculo esquelético a fresco como enxerto, decidiu-se testar a possibilidade de crescimento axonal por meio de enxerto com tubo de polietileno preenchido por tecido adiposo autólogo associado a protocolo de imersão em câmara hiperbárica, por meio de um estudo Randomizado Controlado. Para tanto utilizou-se um tubo com 12 mm de comprimento por 0,25 mm de diâmetro, com poros de 80 μm de diâmetro, preenchido com tecido adiposo in natura retirado das adjacências do referido nervo, na tentativa de se recuperar o nervo isquiático. Os resultados morfométricos demonstraram que, os grupos experimentais com e sem preenchimento de gordura tiveram resultados, do ponto de vista morfométrico e funcional sem diferenças estatisticamente significantes, contudo, quando estes foram confrontados ao grupo controle final, apresentaram diferenças estatisticamente significantes. Já relevando a avaliação funcional, por meio do Catwalk, constatou-se que não houve diferença estatisticamente significante entre os grupos experimentais, mas teve diferença ao comparar com o grupo controle final, Diante das evidências encontradas e apoiados na literatura pode-se concluir que a câmara hiperbárica trouxe resultados positivos verificados pela aproximação dos resultados dos grupos experimentais tanto morfométrica como funcionalmente. / The peripheral nerves are extensions of the central nervous system and are responsible for the sensory and motor functions of the limbs. These nerves are vulnerable to the same types of traumas that affect other tissues: contusion, compression, crushing, stretching, avulsion, and laceration. Amongst the most disabling kinds of injuries that affect working-age individuals are those of the peripheral nerves; due to the multifaceted characteristics of the aftereffects of the injury. The break in continuity of the nerve structure due to trauma, as in the case of neurotmesis, results in the disruption of the transmission of nerve impulses and the disorganization of their functions. Through the use of microsurgery, it was possible to develop reconstructive techniques that range from a simple end-to-end neurorrhaphy to sophisticated surgical procedures that utilize nerve grafts, inverted veins and arteries, and synthetic rods of varied materials such as silicone or porous polyethylene. Another aspect that intrigues researchers around the world is the utilization of neurogenic factors capable of accelerating or improving the regeneration of peripheral nerves. Autologous fat has been a constant reference in this field of surgery due to its abundant supply at the surgical site itself. The results are promising, as the adventitia of vessels consists of loose connective tissue rich in adipocytes. Thus in a trauma, the neurites derived from the proximal stump of the damaged nerve are in direct contact with these adipocytes. Following this reasoning, and based on previous studies where veins grafted with fresh skeletal muscle were used, we decided to conduct a randomized controlled study to test the possibility of axonal growth by means of grating with a polyethylene rod filled with autologous adipocytes associated with immersion in a hyperbaric chamber. In an attempt to recover the sciatic nerve, a rod 12 mm in length, with a diameter of 0.25 mm, and with pores of 80 μm in diameter, filled with adipose tissue in natura removed from the surroundings of said nerve, was used. The morphometric results showed that the experimental groups with and without fat fillings had results that, from the morphometric and functional point of view, were of no statistically significant difference. However, when these results were compared with the final control group, statistically significant differences were noted. Highlighting the functional evaluation through the use of Catwalk, it was found that there were no statistically significant differences between the experimental groups, but there was indeed a difference in comparison to the final control group. In light of the evidence found and supported by literature, one can conclude that the use of the hyperbaric chamber brought positive results verified by the proximity of both the morphometric and functional results of the experimental groups.

Made available in DSpace on 2014-10-09T12:51:05Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:29Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2015-08-07T14:08:44Z No. of bitstreams: 0 / Made available in DSpace on 2015-08-07T14:08:44Z (GMT). No. of bitstreams: 0 / Os aços inoxidáveis têm um amplo campo de aplicação, por ter alta resistência mecânica e à corrosão quando trabalha em temperaturas elevadas. Uma aplicação recorrente é em reatores nucleares, podendo ser utilizado no vaso de pressão e nas estruturas de contenção do reator. O aço inoxidável austenítico foi muito utilizado no núcleo de reatores para revestimento do combustível nuclear. No entanto, foi substituído por uma liga de zircônio denominada zircaloy, em consequência da menor absorção de nêutrons térmicos desta liga. Após o acidente de Three Miles Island o aço inoxidável voltou a ser usado para esta aplicação. Para atenuar a corrosão intergranular, muito característica em aços inoxidáveis austeníticos, utiliza-se elementos estabilizantes como o nióbio. O aço inoxidável AISI 348 é estabilizado com nióbio. Neste trabalho, estudou a soldagem de tubos de AISI 348 e tampões de mesmo material soldados pelo processo GTAW (Gas Tungsten Arc Welding) sob diversas condições, procurando-se obter penetração de soldagem de 110 % da espessura do tubo e reforço do cordão de solda inferior a 0,15 mm. As amostras soldadas foram submetidas à caracterização microestrutural com microscopia ótica e microscopia eletrônica, utilizando também a técnica EDS (Espectroscopia de Energia Dispersiva). Foram realizados ensaios mecânicos de tração, fadiga, microdureza Vickers e arrebentamento, como também verificado a susceptibilidade à corrosão intergranular. O cordão de solda passou por ensaios não destrutivos de inspeção visual, dimensional, líquido penetrante, raios X e ensaio de estanqueidade por fuga de gás hélio. A microdureza não apresentou diferenças nas regiões da solda, não sendo possível identificar claramente a zona afetada pelo calor. O arrebentamento ocorreu a uma distância acima de 30 mm do cordão de solda, sendo o resultado considerado aprovado. No ensaio de tração, a ruptura ocorreu no cordão de solda e no metal de base tubo, o local da ruptura dependeu do afastamento lateral do eletrodo em relação à junta soldada. O ensaio de fadiga com corrente de 40 A obteve número de ciclos de 2,14 x 105. Este valor é 50% maior no tempo de vida comparado com amostra de 30 A. No ensaio de corrosão intergranular, as amostras que foram submetidas não apresentaram sensitização no contorno de grão. A análise por EDS identificou áreas com carbonetos oriundos do processo de fabricação do tubo. / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Semiconductor nanocrystals, also referred to as quantum dots (QDs), have been the focus of great scientific and technological efforts in solar cells, as a result of their advantages of low-cost, photostability, high molar extinction coefficients and size-dependent optical properties. Due to the multi-electron generation effect, the theoretically maximum efficiency of quantum dots-sensitized solar cells (QDSCs) is as high as 44%, which is much higher than that of dye-sensitized solar cells (DSCs). Thus QDSCs have a clear potential to overtake the efficiency of all other kinds of solar cells. In recent years, the efficiency of QDSCs has been improved very quickly to around 5%. It is however still much lower than that of DSCs. The low efficiency is mostly caused by the high electron loss between electrolyte and electrodes and the lack of an efficient electrolyte. In this thesis, we have been working to enhance the performance of QDSCs with II-VI group nanocrystals by increasing the electron injection efficiency from QDs to TiO2 and developing new redox couples in electrolyte. To increase the electron injection, firstly, colloidal ZnSe/CdS type-II QDs were synthesized and applied for QDSCs for the first time, whose photoelectron and photohole are located on CdS shell and ZnSe core, respectively. The spatial separation between photoelectron and photohole can effectively enhance the charge extraction efficiency, facilitating electron injection, and also effectively expand the absorption spectrum. All these characteristics contribute to the high photon to current conversion efficiency. Furthermore, a comparison between the performances of ZnSe/CdS and CdS/ZnSe QDs shows that the electron distribution is important for the electron injection of the QDs in QDSCs. Secondly, colloidal CdS/CdSe quantum rods (QRs) were applied to a quantum rod-sensitized solar cell (QRSCs) that showed a higher electron injection efficiency than analogous QDSCs. It is concluded that reducing the carrier confinement dimensions of nanocrystals can improve electron injection efficiency of nanocrystal sensitized solar cells. In this thesis, two types of organic electrolytes based McMT-/BMT and TMTU/TMTU-TFO were used for QDSCs. By reducing the charge recombination between the electrolyte and counter electrode, fill factor (FF) of these QDSCs was significantly improved. At the same time, the photovoltages of the QDSCs were remarkably increased. As a result, the overall conversion efficiency of QDSCs based on the new electrolytes was much higher than that with a commonly used inorganic electrolyte. In addition, CdS QDSCs on NiO photoelectrode were studied which shows a n-type photovoltaic performance. This performance is attributed to the formation of a thin Cd metal film before CdS QDs formation on NiO. Since the CB edge of CdS sits between the Fermi level and the CB edge of Cd metal, a much strong electron transfer between Cd and CdS QD is obtained, resulting in the observed n-type photovoltaic performance of these CdS/NiO QDSCs. / QC 20120425

Lattice Density Functional Theory is a powerful method to treat equilibrium structural properties and non-equilibrium kinetics of condensed matter systems. In this thesis an approach based on Markov chains is followed to derive exact density functionals for interacting particles in one-dimension. First, hard rod mixtures on a lattice are considered. For the treatment of this system, certain sets of site occupation numbers are introduced. These sets reflect zero-dimensional or one-particle cavities in continuum treatments, which can hold at most one particle. The exact functional follows from rather simple probabilistic arguments. Thereby the derivation simplifies an earlier, more complicated treatment. A rearrangement of the functional casts it into a form according to lattice fundamental measure theory. This makes it possible to systematically setup approximate density functionals in higher dimensions, which become exact under dimensional reduction. In the next step, the theory is extended to hard rod mixtures with contact interactions. Finally, hard rods with arbitrary nearest-neighbor interactions extending over two rod lengths are studied. For those interactions, two types of zero-dimensional cavities need to be introduced. The first one is a one-particle cavity corresponding to a set of occupation numbers with at most one occupation number being nonzero. The second type is a two-particle cavity, which is a cavity that cannot hold more than two particles, that means at most two occupation numbers can be one in the corresponding set. In order to account for time-dependent kinetics, a lattice version of Time-Dependent Density Functional Theory is followed and applied to hard rods with contact interactions.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Includes bibliographical references. / by King-Wo Thomas Chiu. / M.S.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 1982 / Includes bibliographical references. / by Paul Douglas Symolon. / Ph. D. / Ph. D. Massachusetts Institute of Technology, Department of Mechanical Engineering

Ancillary structures are highway support structures such as traffic signals, sign structures, luminaires, and high-mast light towers which are typically fastened to a concrete foundation using embedded anchor rods and anchor nuts. The inventory of ancillary structures across the United States is huge, and these structures vary dramatically in type, age, size, and material. There have been reported cases of anchor nut loosening on ancillary structures in the past few decades, but the cause of loosening is still unknown. Ancillary structures are susceptible to vibrations due to different wind loadings like natural gusts, vortex shedding, galloping, and truck-induced gusts. Wind-induced vibrations are believed to be one of the potential causes of anchor nut loosening. Previous research also suggests that vibrations can lead to loosening of nuts in structural and mechanical connections. There is concern regarding the current tightening procedures specified in the various federal and state specifications. Improper tightening can potentially lead to anchor nut loosening under the effect of wind-induced vibrations. In ancillary structures, the anchor rods and nuts are first snug-tightened using a wrench before fully pretensioning them as per the current specifications. The snug-tight condition is vaguely defined at present and needs revisions to avoid any under-tightening or over-tightening. Galvanization and overtapping of the anchor nuts also pose a potential concern. Anchor nuts are tapped oversize after galvanization to ensure the nuts fit well on the galvanized rod. American Society for Testing and Materials (ASTM) standards provide specific allowable tolerances on the thread parameters of the anchor rod and nut after galvanization and overtapping. Any deviation from the allowable tolerances can lead to gaps between the mating threads, which can contribute to the loosening of nuts under vibrations. This study focuses on investigating the following potential causes of loosening: improper tightening, wind-induced vibrations, snug-tight condition, and thread fabrication tolerance. Current tightening procedures for double-nut and single-nut connections on ancillary structures were verified using a tightening study as part of the investigation. New revisions to the specified nut rotation values for double-nut connections and a draft for proposed new specifications on single-nut connections has been provided as a result of discrepancies and inconsistencies in the current specifications. Vibration testing of a full-scale traffic signal was conducted on the basis of results from a four-month field monitoring program in order to investigate the effects of wind-induced vibrations on anchor nut loosening. It was concluded from testing that improper tightening (pretension < 5ksi) can lead to loosening of anchor nuts under wind-induced vibrations. A small-scale testing was also conducted to verify the results from the large-scale vibration testing. Snug-tight pretension in grade 55, 1-inch and 2-inch anchor rods was found to be highly variable due to different wrench lengths and personnel strength. Thread parameters of galvanized anchor rods and nuts procured from 3 different regional suppliers were found to be within specified tolerances. Various recommendations were then made as a result of the above tightening, vibration, and thread tolerance studies in an effort to reduce the cases related to anchor nut loosening in the future. / Doctor of Philosophy / Ancillary structures like traffic signals, sign structures, and light poles are typically connected to the ground using anchor rods and anchor nuts. There is a very large number of ancillary structures throughout the United States and vary in type, age, size, and material. There have been reported cases of anchor nut loosening on ancillary structures in the past few decades, but the cause of loosening is still unknown. Different types of wind loadings like natural gusts, vortex shedding, galloping, and truck-induced gusts vibrate the ancillary structures. These vibrations due to the wind are believed to be one of the potential causes of anchor nut loosening. Vibrations in the past have been shown to cause loosening of nuts in other structural and mechanical connections. There is also concern that the anchor rods and anchor nuts are not tightened properly as per the specifications, which can lead to loosening of nuts when the ancillary structures vibrate due to wind loadings. In ancillary structures, the anchor nuts are first made tight using a wrench with the full effort of a worker, also known as the snug-tight condition. The snug-tight condition is not properly defined at present and needs to be changed to prevent any under-tightening or over-tightening of the anchor nuts. Also, the anchor rods and nuts are generally coated with a hot zinc layer to prevent their corrosion when exposed to environmental effects like ice, snow, humidity, and rain. This process is called galvanization. The American Society for Testing and Materials (ASTM) provides some guidelines on the amount of coating allowed on the threads of the anchor rods and nuts. Any deviation from the allowable tolerances can lead to gaps between the threads of the anchor rod and nut, which can contribute to the loosening of nuts during vibrations of ancillary structures due to wind. This study focuses on investigating the following potential causes of loosening: improper tightening, vibrations of ancillary structures due to wind, snug-tight condition, and allowable tolerances for the amount of galvanization. Current tightening procedures for anchor rods and nut on ancillary structures were verified using a tightening study as part of the investigation. New revisions to the current tightening procedures have been provided as a result of discrepancies and inconsistencies observed in the current specifications. A traffic signal and a light pole were instrumented with sensors for four months to measure wind-related forces acting on these structures. Further, a full-scale traffic signal was vibrated in the laboratory using an electric motor to simulate the vibrations due to the measured wind forces. It was determined from the testing that if the anchor nuts were not properly tightened, they could become loose during vibrations due to wind. A small-scale testing was also conducted to check the results from the full-scale vibration testing. The snug-tight force in the anchor rods was also found to be dependent on the length of the wrench and the worker tightening it. The amount of galvanization on the rods and nuts procured from 3 different suppliers were found to be within allowable tolerances. Various recommendations were then made as a result of the conclusions in an effort to reduce the cases related to anchor nut loosening in the future.