Electromagnetic wave absorbing properties of SiC-based and alumina ceramic woven fabrics have been investigated. Electrical conductivities of SiC-based ceramic woven fabrics were modified by heat treatment in air resulting in their oxidation. Surface properties of alumina woven fabrics were altered by gold-sputtering resulting in a high conductivity layer on the surface of the wovens. Electromagnetic wave interactions of single layer and double layered combinations of these ceramic woven fabrics were determined in 17-40 GHz frequency range using &ldquo / free-space&rdquo / method. Electromagnetic wave absorption potential of ceramic woven fabrics with different chemical compositions and woven types were correlated with their material properties by X-ray diffraction, scanning electron microscopy and electrical conductivity measurements. Effects of modifications and varying woven fabric arrangements in combinations on the electromagnetic wave absorption potential of the ceramic woven fabrics have been discussed. Various double layer combinations of SiC-based and alumina woven fabrics revealed a promising potential in terms of both reduced reflection and transmission resulting in more than ~95% absorption in millimeter wavelength range, which makes them powerful candidate materials for electromagnetic wave absorption applications.

Rewritable photochrome-based 3D optical data storage requires photochromic molecules with high two-photon absorption (2PA) cross sections. Currently, the low value of two-photon absorption cross sections of existing photochromes makes them unsuitable for practical application in 3D data storage. Worldwide attempts to increase the cross section of photochromic molecules by altering the chemical structure have yielded poor results. In this work, two ways to increase the two-photon absorption cross sections of photochromes were investigated. In the first method, partial success demonstrated by extending the conjugation of a photochromic molecule, a high two-photon absorption cross section of the closed form isomer and high photoconversion to the closed form were realized. At the same time, a decrease in photoswitching quantum yield and low photoconversion to open form was observed. A discussion is provided to explain the results, suggesting that the proposed method of extending the conjugation may not solve the problem. For this reason a new method for effective two-photon absorption cross section enhancement of photochromes was proposed. As a proof of principle, a new two-photon absorbing dye with a hydrogen bonding moiety was synthesized and used for the formation of supramolecular structures with a photochromic compound. Theoretical reasoning and experimental demonstration of energy transfer from the dye to the photochrome under one and two-photon excitation confirmed the practical value of the method. The effects of a 2PA dye on the photochromic properties of a diarylethene were investigated using a model compound to simplify data analysis. Formation of supramolecular structures was revealed using ¹H NMR spectroscopic methods. The model compound, having the same hydrogen bonding moiety as 2PA dye, has been demonstrated to bind with photochrome molecules at very low concentrations. Photochromic properties of 2,3-bis(2,4,5-trimethyl-3-thienyl)maleimide, including conversions at the photostationary state, extinction coefficients, photoisomerization reaction rates and quantum yields, were shown to be affected by hydrogen bonding with the model compound - 2,6-bis-(acetamido)pyridine. The extent of this change was determined and discussed, demonstrating a balanced supramolecular strategy to modulate photochemical and photophysical properties of this important class of photochromic material.

Made available in DSpace on 2014-12-17T15:42:08Z (GMT). No. of bitstreams: 1 RegiaCP_TESE.pdf: 5580865 bytes, checksum: b0d574167afcc48aece0c780848733c2 (MD5) Previous issue date: 2009-12-22 / Universidade Estadual de Roraima / Were synthesized systems Ni0,5Zn0,5Fe2O4, i0,2Zn0,5Mn0,3Fe2O4, Mn0,5Zn0,5Fe2O4, Ni0,5Mg0,5Fe2O4, Ni0,2Cu0,3Zn0,5Fe2O4 and Ni0,2Cu0,3Zn0,5Mg0,08Fe2O4, the precursors citrate method. The decomposition of the precursors was studied by thermogravimetric analysis and spectroscopy in the infrared region, the temperature of 350?C/3h. The evolution of the phases formed after calcinations at 350, 500, 900 and 1100?C/3h was accompanied by X-ray diffraction using the Rietveld refinement to better identify the structures formed. The materials were also analyzed by scanning electron microscopy, magnetic measurements and analysis of the reflectivity of the material. The samples calcined at different temperatures showed an increase of crystallinity with increasing calcination temperature, verifying that for some compositions at temperatures above 500?C precipitates of second phase such as hematite and CuO. The compositions of manganese present in the structure diffusion processes slower due to the ionic radius of manganese is greater than for other ions substitutes, a fact that delays the stabilization of spinel structure and promotes the precipitation of second phase. The compositions presented with copper precipitation CuO phase at a temperature of 900 and 1100?C/3h This occurs according to the literature because the concentration of copper in the structure is greater than 0.25 mol%. The magnetic measurements revealed features of a soft ferrimagnetic material, resulting in better magnetic properties for the NiZn ferrite and NiCuZnMg at high temperatures. The reflectivity measurements showed greater absorption of electromagnetic radiation in the microwave band for the samples calcined at 1100?C/3h, which has higher crystallite size and consequently the formation of multi-domain, increasing the magnetization of the material. The results of absorption agreed with the magnetic measurements, indicating among the ferrites studied, those of NiZn and NiCuZnMg as better absorbing the incident radiation. / Foram sintetizados os sistemas Ni0,5Zn0,5Fe2O4, Ni0,2Zn0,5Mn0,3Fe2O4, Mn0,5Zn0,5Fe2O4, Ni0,5Mg0,5Fe2O4, Ni0,2Cu0,3Zn0,5Fe2O4 e Ni0,2Cu0,3Zn0,5Mg0,08Fe2O4, pelo m?todo dos citratos precursores. A decomposi??o dos precursores foi estudada por an?lise termogravim?trica e espectroscopia na regi?o do infravermelho, na temperatura de 350?C/3h. A evolu??o das fases formadas ap?s as calcina??es a 350, 500, 900 e 1100?C/3h foi acompanhada por difra??o de raios X utilizando o refinamento de Rietveld, para melhor identifica??o das estruturas formadas. Os materiais foram tamb?m analisados por microscopia eletr?nica de varredura, medidas magn?ticas e an?lise da refletividade do material. As amostras calcinadas em diferentes temperaturas indicaram um aumento da cristalinidade com o aumento da temperatura de calcina??o, verificando-se que, para algumas composi??es, em temperaturas acima de 500?C ocorre a precipita??o de segunda fase, como hematita e CuO. As composi??es com mangan?s na estrutura apresentaram processos de difus?o mais lentos devido ao raio i?nico do mangan?s ser maior em rela??o aos outros ?ons substituintes, fato que retarda a estabiliza??o da estrutura espin?lio e favorece a precipita??o de segunda fase. As composi??es com cobre apresentaram precipita??o da fase CuO na temperatura de 900 e 1100?C/3h, fato que ocorre segundo a literatura porque a concentra??o de cobre na estrutura ? maior que 0,25 mol%. As medidas magn?ticas revelaram racter?sticas de um material ferrimagn?tico macio, obtendo-se melhores ar?metros magn?ticos para as ferritas de NiZn e NiCuZnMg em altas temperaturas. As medidas de refletividade mostraram maior absor??o da radia??o eletromagn?tica na faixa de microondas para as amostras calcinadas a 1100?C/3h, que tem maior tamanho do cristalito e em conseq??ncia forma??o de multidom?nios, aumentando a magnetiza??o do material. Os resultados de absor??o concordaram com as medidas magn?ticas, indicando dentre as ferritas estudadas, as de NiZn e NiCuZnMg como melhores absorvedoras da radia??o incidente.

This dissertation describes the investigation of the synthesis and characterization of new squaraine-based photonic and electronic materials. In the first part of this thesis, squaraine dyes with large conjugation systems, including extended squaraines consisting of bis(donor)substituted vinylene-heterocycles and bis(indolinylenemethyl)squaraine-based oligomers linking through different π-bridges were designed, synthesized and characterized to exhibit strong two-photon absorption (2PA) for femotosecond and nanosecond optical-power limiting applications in the near-infrared (NIR). One of the dendronized squaraine forms smooth and high optical quality films with large NIR transparency window. In the second part, a series of squaraine- and phthalocyanine-based metal complexes were studied. Those dyes did not show large triplet quantum yield but significantly improved photovoltaic performance compared to the metal-free compounds. In the last part, an effective approach on optimizing bis(indolinylenemethyl)-based squaraine sensitizers with various surface anchor groups and π-linkers, achieved high power conversion efficiencies (PCEs) of 6.7% in liquid dye-sensitized solar cells (DSSCs) and 2.7% in solid-state DSSCs, which stand out all the previous reported squaraine-based sensitizers.

Spacecloth design and development is vital and crucial in Radar Absorbing Materials (RAM) for achieving Low Observability in an Aircraft or an Unmanned Air Vehicle(UAV). The RAM design translates into the spacecloth design. The spacecloths form the constituent layers in a broadband Jaumann absorber in which case they have to be designed for various values of surface resistivity. The design specifications of spacecloth(s) in RAMS is well understood and documented in literature. But the design of spacecloth hitherto, has been the domain of materials' scientists wherein the specified properties of the spacecloth are achieved by an iterative, trial and error process, by mixing various constituents in different proportions to get the design specified surface resistivity in the final end-product. In an effort to bridge this gap, a novel spacecloth for RAM applications is proposed in the thesis. It is proposed that a repetitive geometrical grid network of chip resistors simulates spacecloth. The sheet resistivity of the spacecloth is derived by analyzing various geometries like square, rectangle, triangle and hexagonal grids. The transmission and reflection loss for the chip resistor spacecloth is derived. The design of chip resistor spacecloths for operation at S and C bands is given followed by experimental verification using waveguide simulator experiments. Numerical study of multilayer RAM has been carried out with exponential taper variation of surface resistivities for constituent spacecloth layers and design curves are given for multilayer RAM both for normal and oblique incidence for TE and TM polarizations.

During the last years perovskite materials have taken the photovoltaic community by storm, bringing promises of solar cells with efficiencies comparable to conventional silicon devices but at a lower price. However perovskite solar cells so far are facing two main obstacles, they are unstable in the presence of air, moisture and heat and they are usually toxic due to being based on lead-halide materials. This has spurred investigations into alternative materials with similar properties but without the mentioned drawbacks. Just next to Pb in the periodic table is bismuth (Bi) with just one more electron in its outer-shell, Bi however is less toxic. In this work the perovskite derived compounds of Ag-Bi-I and Cu-Bi-I are characterized and their properties as light absorbing material in solar cell devices are investigated. Devices are prepared by preparing Ag-Bi-I and Cu-Bi-I solutions which are then spin-coated on top of a mesoporous TiO2. A conducting polymer, P3HT, was then deposited and serve as hole transport material. For Ag-Bi-I, the molar ratios of AgI:BiI3= 1:2 and 2:1 were observed with SEM to form homogeneous crystal films with one dominating crystal phase, which by XRD could be determined to most likely have formed a cubic AgBi2I7 crystal structure for the 1:2 ratio and a hexagonal Ag2BiI5 crystal structure for the 2:1 ratio. The Cu-Bi-I materials were not successfully synthesized to form homogeneous films with a dominating crystal phase, although several molar ratios were investigated. All investigated compositions of both Cu and Ag devices showed to in principle work as light absorbing materials, the best Ag-Bi-I device showing a PCE of 1.92%, for the 2:1 ratio, while the Cu-Bi-I devices at best reached 0.32% for a ratio of 1:1. XPS measurements were carried out with a classical in-house XPS using an Al K X-ray source of 1486.7 eV as well as at the Diamond Light Source (UK) synchrotron facility using photon energies of 758 eV and 2200 eV so that a depth resolution of the composition could be observed. Because of their inhomogeneous crystal formation, XPS couldn’t give much useful quantitative information regarding the Cu devices. For Ag devices it was observed that the stoichiometry at the extreme surface deviated from that predicted by XRD, but deeper into the surface the relative ratio of elements approach the predicted ones, hinting towards a different structure at the outermost surface or a lot of surface defects. For all samples, two types of bismuth atoms were observed, metallic (Bi0) as well as a cationic (Bi+x), the later corresponding to Bi atoms which are partaking in the crystal bond. The ratio of metallic to cationic Bi was observed to decrease notably just a few nm below the extreme surface. The effect of the high presence of metallic Bi on final device performance was not concluded with certainty but not believed to be positive. By varying the annealing temperature, after spin coating the light absorber solution on the TiO2, it was observed that lower temperature resulted in a lower ratio of metallic Bi. As final conclusions, it was said that the synthesis method of Cu-Bi-I needs to be improved before those materials can be studied further. The synthesis of Ag-Bi-I is showing much more promise and one can start looking into further optimizing their final device structure to boost efficiency. Both Cu-Bi-I and Ag-Bi-I devices are relatively simple, cheap and energy efficient (with annealing temperatures around 150C) to produce, great aspects for solar cells. UVVis measurements showed they have band gaps around 1.6-1.7 eV which makes them a great potential material for use in tandem solar cells together with a semiconductor of lower band gap such as silicon.

Nowadays vehicle design paradigm influences not only the effectiveness of the different means of transport, but also the environment and economy in a critical way. The assessment of the consequences that design choices have on society at large are necessary to understand the limits of the methods and techniques currently employed. One of the mechanisms set in motion is the planned obsolescence of products and services. This has affected vehicle design paradigm in such a way that the variety in the market has shadowed the primary function of vehicle systems: the transport of persons and goods. Amongst the consequences of the expansion of such market is the exponential rise on combustion emissions to the atmosphere, which has become a great hindrance for humans health and survival of ecosystems. The development of evaluation tools for such consequences and their piloting mechanisms is needed so as to implement an ECO2  (Ecological and Economical) vehicle design paradigm. Moreover, the multifunctional design paradigm that drives aeronautical and vehicle engineering is an ever-growing demand of smart materials and structures, able to fulfil multiple requirements in an effective way. The understanding of certain phenomena intrinsic to the introduction of novel materials has found certain limits due to the complexity of the models needed. This work presents as a first step an assessment of the causes and consequences of the vehicle exponential market growth based on the analysis of the planned obsolescence within. Furthermore, a method for the acoustic response analysis of multilayered structures including anisotropic poroelastic materials is introduced. The methodology consists in a plane wave approach as a base for introducing the complex mechanic and acoustic equations governing anisotropic homogeneous media, e.g. open-celled foams, into an alternative mathematical tool manipulating physical wave amplitudes propagation within the studied media. In addition, this method is coupled to a power partitioning and energetic assessment tool so as to understand the phenomena present in complex multilayered designs. / <p>QC 20150323</p>

Made available in DSpace on 2016-12-08T17:19:38Z (GMT). No. of bitstreams: 1 VIVIANE LILIAN SOETHE.pdf: 4187786 bytes, checksum: ad2945f377ee8ffa2972dbc25afd42a0 (MD5) Previous issue date: 2004-03-25 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The Triode Magnetron Sputtering (TMS) is a system of depositing film characterized by the introduction of a third electrode, which is made up of a grounded mobile screen, located between the cathode (target) and the anode (substrate). The purpose of this screen is to capture cold electrons (at a lower energy level) of discharge. Changing its relative position to the cathode, some of the characteristics of the plasma are changed such as the ignition tension. Based on this, a study was made investigating the relationship between the current and the target voltage by changing the positioning of the screen to the target. Through this study, we could verify that, it s possible to work independently with either of above parameters of deposition. As a result of controlling these parameters, we could verify that the deposition of quality metallic films is possible, by using a TMS equipment on polymeric substrates. By choosing the suitable conditions of deposition, based on a preliminary study, a deposition of Al film on a poly(ethylene terephthalate) substrate was made. It was observed through this study that these films prove to be structurally whole and with few faults. The maintenance of a constant current (0,5A) fir deposition of Al films on polymeric substrates indicates that the change in voltage alters mainly the deposition energy particles, not significantly the superficial property of films. We can still observe that the rate of deposition does not alter significantly with voltage increase, what is evidenced by the little temperature increase in the samples. The Al films deposited submitted to a constant voltage (-700V) displayed a distinct superficial topography due to the current used. The current variation influence was verified notably for the final structure of the deposited film. Besides this, this parameter is directly related to the deposition rate, this being responsible for a temperature increase of the sample caused by increase of condensation heat of deposited atoms. Thus we can say that the sample temperature is more influenced by target current than by target voltage. So, we can observe that depositions made under constant current cause less aggression to polymer and to deposited film than those made under constant voltage. Through TMS, it is possible to control deposition condition and consequently the deposition rate in an accurate way. This makes this method an efficient alternative to metallic film deposition. In view of above, an application of the study of deposited film on polymers was made, altering either the current or voltage of target. Films of Al an Inconel were deposited on Mylar® , a type of PET, with the purpose of investigating film behavior concerning its attenuation characteristics of 4 incident electromagnetic energy. This application range is very wide, including aerospace equipment, radars an so on. When the rate of deposition for the condition used is known, the thickness of film can be altered by varying the time of deposition. A study was conducted of the influence of layer thickness and film material (Al or Inconel) on the characteristics of attenuation of electromagnetic wave energy. According to studies, it was observed that deposited layer thickness and film material influenced attenuating characteristics, so that Al and Inconel deposited films showed a maximum 13% attenuation. This leads us into believing that metallic films can be used with electromagnetic radiation absorbing materials, as long as ideal work thickness and its intrinsic characteristics are known. / O Triodo Magnetron Sputtering (TMS) é um sistema de deposição de filmes caracterizado pela introdução de um terceiro eletrodo, que é constituído de uma tela móvel aterrada, situado entre o catodo (alvo) e o anodo (substrato). Esta tela tem o papel de capturar elétrons frios (menos energéticos) da descarga. Alterando-se a posição relativa desta tela ao catodo, alteram-se algumas das características do plasma como, por exemplo, a tensão de ignição. Baseado nisso, realizou-se um estudo investigando-se a relação entre a corrente e a voltagem do alvo alterando-se a posição relativa da tela ao alvo. Por meio deste estudo, pode-se verificar que é possível tornar independentes estes dois parâmetros de deposição para uma determinada faixa de trabalho. Devido ao controle destes parâmetros, verificou-se que é possível depositar filmes metálicos de qualidade, utilizando um equipamento de TMS sobre substratos poliméricos. Através da escolha adequada das condições de deposição, baseadas no estudo realizado anteriormente, realizou-se a deposição de filmes de Al sobre um substrato de poli(Tereftalato de Etileno). Pode-se observar por meio deste estudo que estes filmes apresentam-se estruturalmente íntegros e com pouca quantidade de defeitos. As deposições de filmes de Al sobre substratos poliméricos mantendo-se a corrente constante (0,5A) indica que a mudança na voltagem altera principalmente a energia das partículas que se depositam, não modificando de forma significativa as propriedades superficiais dos filmes. Pode-se observar ainda que a razão de deposição não sofre alterações significativas com o aumento da voltagem, o que é evidenciado pela pequena elevação da temperatura sofrida pelas amostras. Os filmes de Al depositados sob voltagem constante (-700V) apresentaram topografia superficial distinta em função da corrente utilizada. Pode-se verificar que a variação da corrente influencia de forma significativa a estrutura final do filme depositado. Além disso, este parâmetro está diretamente relacionado com a razão de deposição, sendo este o fator responsável pelo aumento na temperatura da amostra devido a elevação no calor de condensação dos átomos que se depositam. Pode-se desta forma, dizer que a temperatura da amostra é mais influenciada pela corrente que pela voltagem do alvo. Assim, é possível observar que deposições realizadas sob corrente constante provocam menor agressão ao polímero e ao filme depositado que aquelas realizadas sob voltagem constante. Por meio do TMS, é possível controlar-se as condições de deposição e conseqüentemente a razão de deposição de maneira precisa, o que proporciona um controle da camada depositada. Isto faz deste 2 método uma alternativa eficiente para a deposição de filmes metálicos, passível de ser utilizado em muitos ramos de pesquisa. Atentando-se a este fato, realizou-se uma aplicação do estudo dos filmes depositados sobre polímero, alterando-se a corrente ou a voltagem do alvo independentemente. Para isso depositaram-se filmes de Al e Inconel (liga de níquel cromo) sobre Mylar®, um tipo de PET (poli (Tereftalato de etileno)), com a finalidade de investigar o comportamento deste filme quanto as suas características de atenuação de energia eletromagnética incidente. Esta aplicação é bastante vasta envolvendo equipamentos aeronáuticos, radares, e outros. Conhecida a razão de deposição da condição utilizada, pode-se alterar a espessura do filme obtido variando-se o tempo de deposição. Assim, fez-se um estudo da influência da espessura da camada e do material que constitui o filme (Al ou Inconel) nas características de atenuação de energia da onda eletromagnética. De acordo com os estudos, pode-se verificar que a espessura da camada depositada, e o material do filme influenciam nas características atenuadoras, sendo que os filmes de Al e Inconel depositados apresentaram uma atenuação de no máximo 13% . Isto nos leva a crer que filmes metálicos podem ser utilizados com materiais absorvedores de radiação eletromagnética, desde que se conheça a espessura ideal de trabalho e outras características intrínsecas do mesmo.

No description available.

Indiana University-Purdue University Indianapolis (IUPUI) / The sympathetic nervous system strongly modulates the contractile and electrical function of the heart. The anatomical underpinnings that enable a spatially and temporally coordinated dissemination of sympathetic signals within the cardiac tissue are only incompletely characterized. In this work we took the first step of unraveling the in situ 3D microarchitecture of the cardiac sympathetic nervous system. Using a combination of two-photon excitation fluorescence microscopy and computer-assisted image analyses, we reconstructed the sympathetic network in a portion of the left ventricular epicardium from adult transgenic mice expressing a fluorescent reporter protein in all peripheral sympathetic neurons. The reconstruction revealed several organizational principles of the local sympathetic tree that synergize to enable a coordinated and efficient signal transfer to the target tissue. First, synaptic boutons are aligned with high density along much of axon-cell contacts. Second, axon segments are oriented parallel to the main, i.e., longitudinal, axes of their apposed cardiomyocytes, optimizing the frequency of transmitter release sites per axon/per cardiomyocyte. Third, the local network was partitioned into branched and/or looped sub-trees which extended both radially and tangentially through the image volume. Fourth, sub-trees arrange to not much overlap, giving rise to multiple annexed innervation domains of variable complexity and configuration. The sympathetic network in the epicardial border zone of a chronic myocardial infarction was observed to undergo substantive remodeling, which included almost complete loss of fibers at depths >10 µm from the surface, spatially heterogeneous gain of axons, irregularly shaped synaptic boutons, and formation of axonal plexuses composed of nested loops of variable length. In conclusion, we provide, to the best of our knowledge, the first in situ 3D reconstruction of the local cardiac sympathetic network in normal and injured mammalian myocardium. Mapping the sympathetic network connectivity will aid in elucidating its role in sympathetic signal transmisson and processing.