Microwave limiting amplifiers are the key components of Instantaneous Frequency Measurement (IFM) systems. Limiting amplifiers provide constant output power level in a wide input dynamic range and over a broad frequency band. Moreover, limiting amplifiers are high gain devices that are used to bring very low input power levels to a constant output power level. Besides, limiting amplifiers are required to provide minimum small signal gain ripple in order not to reduce the sensitivity of the IFM system over the operating frequency band. In this thesis work, a high gain, medium power, 2-18 GHz limiting amplifier module is designed, simulated, fabricated and measured. First, a 3-stage cascaded amplifier with 27 dB small signal gain is designed and fabricated. The 3-stage amplifier is composed of a novel cascaded combination of negative feedback and distributed amplifiers that provides the minimum small signal gain ripple and satisfactory input and output return losses inside 2-18 GHz frequency band. Then, the designed two 3-stage amplifiers and one 4-stage amplifier are cascaded to constitute a limiting amplifier module with minimum 80 dB small signal gain. The designed 10-stage limiting amplifier module also includes an analog voltage controllable attenuator to be used for compensating the gain variations resulting from temperature changes. The fabricated 10-stage limiting amplifier module provides 20 +/- 1.2 dBm output power level and excellent small signal gain flatness, +/- 2.2 dB, over 2-18 GHz frequency range.

This thesis is concerned with the material processing, photophysical and third-order nonlinear optical responses, and applications of a set of conjugated polymers in the telecommunication regions. Polyacetylene-based third-order nonlinear optical materials were chosen as candidates for all-optical signal and image processing. Substituted polyacetylenes were obtained using ring-opening metathesis polymerization of mono-substituted cyclooctatetraenes. Polymerization and processing conditions have been developed to generate thick, large-area films possessing large third-order nonlinearities in the telecommunication bands. The good optical quality of a 200 μm thick substituted polyacetylene film allowed for image correlation via off-resonant degenerated four-wave mixing with improved diffraction efficiency. Poly(2-methoxy-5-(2-ethyl-hexyloxy)-(phenylene vinylene)) (MEH-PPV) and (6,6)-phenyl-C61-butyric acid methyl ester (PCBM) composites showed strong nonlinear absorption and potential as optical limiters in the region of 700-900 nm. High optical quality, thick film of MEH-PPV:PCBM with the plasticizer dioctylphthalate (DOP) were made. Optical limiting of femtosecond and nanosecond pulses in the near infrared on these composites showed strong power suppression over a broad temporal regime. Femtosecond and nanosecond transient studies on the same thick MEH-PPV:PCBM:DOP composite films and the experimental results showed evidence for the photogeneration of radical ions as being responsible for the enhanced nonlinear absorption and strong optical suppression in the near infrared. Dithienopyrrole-based donor-acceptor copolymers with narrow bandgap showed strong nonlinear absorption and potential as optical limiters in the telecommunication wavelengths. Molecular engineering was applied to manipulate the spectral overlap of two-photon absorption and subsequent nonlinear absorptions. Femtosecond transient spectroscopy showed near infrared transient absorption and 22 - 61% yields of photogenerated charge-transfer species depending on donor-acceptor coupling strength. Torsional fluctuations of the backbone structure potentially affected the excited state behavior. Evidence suggests that ultrafast relaxation occurs to ground state and to long-lived charge-transfer state from the initially excited state. The dispersion of nonlinear absorption measured using the Z-scan method revealed large two-photon absorption cross sections of these polymers in the telecommunication region. Large suppression of nanosecond pulses at 1064 nm was achieved.

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.

<p>We investigate a certain epidemics model, with and without noise. Some parameter analysis is performed together with computer simulations. The model was presented in Iacus (2008).</p>

High temperature proton conducting perovskite oxides are very attractive materials for applications in electrochemical devices, such as solid oxide fuel cells (SOFCs) and hydrogen permeation membranes. A better understanding of the hydrogen oxidation mechanism over the metal/proton conductor interface, is critical for rational design to further enhance the performances of the applications. However, kinetic studies focused on the metal/proton system are limited, compared with the intensively studied metal/oxygen ion conductor system, e.g., Ni/YSZ (yttrium stabilized zirconia, Zr₁-ₓYₓO₂-δ). This work presents an elementary kinetic model developed to assess reaction pathway of hydrogen oxidation/reduction on metal/proton conductor interface. Individual rate expressions and overall hydrogen partial pressure dependencies of current density and polarization resistance were derived in different rate limiting cases. The model is testified by tailored experiments on Pt/BaZr₀.₁Ce₀.₇Y₀.₁Yb₀.₁O₃-δ (BZCYYb) interface using pattern electrodes. Comparison of electrochemical testing and the theoretical predictions indicates the dissociation of hydrogen is the rate-limiting step (RLS), instead of charge transfer, displaying behavior different from metal/oxygen ion conductor interfaces. The kinetic model presented in this thesis is validated by high quantitative agreement with experiments under various conditions. The discovery not only contributes to the fundamental understanding of the hydrogen oxidation kinetics over metal/proton conductors, but provides insights for rational design of hydrogen oxidation catalysts in a variety of electrochemical systems.

This thesis is concerned with the photophysical and nonlinear optical responses, and applications of a set of conjugated polymers and small molecules in the visible and near-IR spectral regions. Poly(phenylene ethynylene) PPE polymers were substituted with conjugated side-arms in a cruciform fashion to determine the impacts of electronic coupling on the one-photon (1PA), two-photon (2PA), and excited state absorption (ESA) properties of the co-polymer system. The cruciform-like PPEs showed significant changes in their nonlinear and phophysical behavior relative to their linear models, including shifts and splittings of the 1PA bands due to moderate mixing of the lowest singlet excited states, an increase in the 2PA cross section (δ) values, and an increase in the yield of triplet excited-state species. The cruciform-like PPE polymers exhibited effective optical pulse suppression of femtosecond and nanosecond laser pulses over a broad spectral range of ~200 nm in the visible and near-IR. The suppression capability of the cruciform-like PPEs exceeded the best reported value for alkyl-substituted PPE polymers. The spectroscopic effects due to conjugation length, structural configuration, and intramolecular charge transfer (ICT) are discussed for a family of bent donor-acceptor-donor (D-A-D) -type conjugated oligomers, which incorporate electron-rich triarylamine donors and electron-deficient triarylborane acceptor units into its conjugated structure. These organoborane oligomers are highly fluorescent and exhibit strong 2PA in the visible region with δ values as large as 1410 GM, as well as overlapping ESA bands attributed to singlet-singlet and triplet-triplet absorption. Saturation of the molar absorptivity, ε, and δ was observed at less than two repeat monomer units due to conformational disorder in the oligomer with increasing length. Positive solvatochromism of fluorescence with solvent shifts as large as ~70 nm was observed as a result of ICT from the arylamine donors to boryl-centered acceptor sites. The excited-state dynamics also show sensitivity to the solvent environment. Experimental findings suggest that these organoborane oligomers may have potential use as nonlinear material for optical power limiting (OPL) and two-photon sensing applications. The spectral properties of two bis-donor chromophores, (bis(diarylamino)biphenyl (TPD) and distyrylthiophene (DST), were investigated with and without the presence of AgNPs in order to better understand the local-field enhancement and subsequent effects on the photophysics and nonlinear behavior of 2PA dyes. While little changes were observed in the excited-state dynamics, measurements of nanoparticle aggregate-dye composite solutions with TPD revealed a 1.6-enhancement in the two-photon excited fluorescence signal. OPL measurements of nanosecond laser pulses at 532 nm revealed a reduction in threshold energy by a factor of 2 in solutions containing TPD and AgNP aggregates, relative to solutions of TPD alone. DST shows exceptional solubility (>1 M) in several organic solvents and exhibits a 2PA spectrum that overlaps well with its singlet-singlet and triplet-triplet ESA bands. Consequently, DST exhibits effective optical limiting of nanosecond laser pulses through two-photon induced excited-state absorption over a broad spectral range of approximately 200 nm in the red and near-IR.

Competition between species is believed to lead to patterns of either competitive exclusion or limiting similarity within ecological communities; however, to date the amount of support for either as an outcome has been relatively weak. The two classes of null model commonly used to assess co-occurrence and limiting similarity have both been well studied for statistical performance; however, the methods used to evaluate their performance, particularly in terms of type II statistical errors, may have resulted in the underreporting of both patterns in the communities tested. The overall purpose of this study was to evaluate the efficacy of the negative co-occurrence and limiting similarity null models to detect patterns believed to result from competition between species and to develop an improved method for detecting said patterns. The null models were tested using synthetic but biologically realistic presence-absence matrices for both type I and type II error rate estimations. The effectiveness of the null models was evaluated with respect to community dimension (number of species × number of plots), and amount of pattern within the community. A novel method of subsetting species was developed to assess communities for patterns of co-occurrence and limiting similarity and four methods were assessed for their ability to isolate the species contributing signal to the pattern. Both classes of null model provided acceptable type I and type II error rates when matrices of more than 5 species and more than 5 plots were tested. When patterns of negative co-occurrence or limiting similarity were add to all species both null models were able to detect significant pattern (β > 0.95); however, when pattern was added to only a proportion of species the ability of the null models to detect pattern deteriorated rapidly with proportions of 80% or less. The use of species subsetting was able to detect significant pattern of both co-occurrence and limiting similarity when fewer than 80% of species were contributing signal but was dependent on the metric used for the limiting similarity null model. The ability of frequent pattern mining to isolate the species contributing signal shows promise; however, a more thorough evaluation is required in order to confirm or deny its utility.

Careers education was first established in Sweden at the beginning of the 1940s. At that time it was mainly the concern of the Swedish Labour Market Board. The Labour Market Board started to develop a model, partly influenced by the activities of other countries in the field, that over the years grew into something exceptional with for instance a lot of activities in schools. In the early stages the aim was the development and production of informational texts. The person behind most of the ideas was Einar Neymark. In 1971, responsibility for careers education was handed over to the school authorities except for the part concerning the production of occupational information texts. The aim of this study is to improve our understanding of careers education as it is represented in occupational information texts produced by the Swedish Labour Market Board, in the period from 1940 - 1970. The empirical research focuses on careers education and gaining an understanding through the texts within (not about) careers education. The research has a philosophical-hermeneutic orientation and falls into two parts. Starting from an assumption that the intentions behind careers education are met, three “careers education realities” are constructed for the sake of argument. These realities are then analysed using a theoretical framework grounded in educational sociology, or more precisely the thinking of Durkheim and Bernstein. The result shows that careers education plays an important role in making invisible the connection between school and society hierarchies and also in creating a collective conscience in a Durkheimian sense. The first constructed “reality” shows that a careers education based on labour market considerations is both normative and deterministic. In this careers education the labour market consists of a variety of working lives depending on who you are and where you come from. For that reason careers education is both limiting and subordinating according to sex and class background. A consciousness-raising careers education is moralizing and limiting. A “perfect” working life is presented to which individuals can relate their personal qualities. For that reason careers education also subordinates. A study-motivating careers education is principally motivating for those who have already had good experiences of schooling. It limits and subordinates primarely in terms of sex. Possible relations between education and working life are mostly discussed in general terms. For example, education will be a good thing to have in a future working life as an insurance against unemployment. The extended analysis, where the above mentioned results are put together, shows that careers education can be described as unjust, limiting and concealing. It is unfair in that it creates images about different and non-questionable working lives for young people to fit into, in that it perpetuates sex and class subordination, and in that it uses present individually related competencies as the grounds for future education and employment. It is limiting through being normative, moralizing and subordinating. It is concealing in that it is being selective concerning the information given in the texts prepared for pupils. Careers education is also adjustable. It fits easily into different situations by being pragmatic and flexible, as is shown by the impact of other scientific areas. This adjustability makes it possible to use careers education regardless of the conception you may have of career choices or wherever careers education is carried out. Being adjustable is not something to be avoided in careers education, on the contrary it is a condition for its existence.

The objective of this PhD research program is to develop an accurate and efficient heterogeneous three-dimensional computational model for simulating the drying of wood at temperatures below the boiling point of water. The complex macroscopic drying equations comprise a coupled and highly nonlinear system of physical laws for liquid and energy conservation. Due to the heterogeneous nature of wood, the physical model parameters strongly depend upon the local pore structure, wood density variation within growth rings and variations in primary and secondary system variables. In order to provide a realistic representation of this behaviour, a set of previously determined parameters derived using sophisticated image analysis methods and homogenisation techniques is embedded within the model. From the literature it is noted that current three-dimensional computational models for wood drying do not take into consideration the heterogeneities of the medium. A significant advance made by the research conducted in this thesis is the development of a three - dimensional computational model that takes into account the heterogeneous board material properties which vary within the transverse plane with respect to the pith position that defines the radial and tangential directions. The development of an accurate and efficient computational model requires the consideration of a number of significant numerical issues, including the virtual board description, an effective mesh design based on triangular prismatic elements, the control volume finite element discretisation process for the cou- pled conservation laws, the derivation of an accurate dux expression based on gradient approximations together with flux limiting, and finally the solution of a large, coupled, nonlinear system using an inexact Newton method with a suitably preconditioned iterative linear solver for computing the Newton correction. This thesis addresses all of these issues for the case of low temperature drying of softwood. Specific case studies are presented that highlight the efficiency of the proposed numerical techniques and illustrate the complex heat and mass transport processes that evolve throughout drying.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Soil compaction is a process inherent in the no-tillage system and therefore, it will be always observed with varying intensity degrees. However, this system has features which can be maximized in order to reduce the compression process and its consequences. The objective of this study was evaluate soil hydro-physical properties as indicators of quality in an Oxisol, long time cultivated under no-tillage system. The specific objectives were determine the critical bulk density in which the soil resistance penetration and air porosity are restrictive to development of plants, using the methodology of least limiting water range (LLWR); evaluate the relationship between permeability air with macroporosity, total porosity and bulk density in different water tensions; determine the relationship between the saturated soil hydraulic conductivity and macroporosity, total porosity and bulk density. The soil was collected in a farmer located in Ibirubá (RS). The climate falls under the classification of Köppen in zones "Cfa" and "Cfb" (humid subtropical climate with hot summers or mild). The soil is classified as Oxisol. The area dedicated to collecting of samples has been cultivated under no-tillage since 1998 with soybeans, in the spring / summer, oats and rye or wheat in the fall / winter. Determinations of LLWR, texture, bulk density, total porosity, macroporosity, saturated hydraulic conductivity and air permeability of soil (under different soil water tensions: 1, 6 33 and 100 kPa) was carried out. Soil samples with preserved structure were collected with metal cylinders (0.03 m height and 0.055 m internal diameter) at depths of 0.02 to 0.07 m and 0.12 to 0.18 m, at various points of the area in order to obtain a large variation in bulk density. The results indicated that the increase of bulk density influence the reduction of LLWR which is associated with effects of soil penetration resistance and aeration porosity. The lower the matric potential, the higher was the observations of soil air conductivity, especially on the superficial soil layer, where the frequency of macropores is bigger and its decrease by the increase in soil depth. The soil air conductivity and saturated soil hydraulic conductivity were highly correlated with macroporosity and total porosity and negatively with the bulk density in different soil water tensions. / A compactação do solo é um processo inerente ao sistema de plantio direto e, portanto, sempre será observada com maior ou menor intensidade. Entretanto, esse sistema possui características que podem ser maximizadas com vistas a reduzir o processo de compactação e suas conseqüências. Com o intuito objetivou-se avaliar indicadores físico hídricos de qualidade de um Latossolo Vermelho cultivado por longo prazo sob o sistema de plantio direto. Os objetivos específicos foram determinar a densidade do solo crítica em que a resistência mecânica à penetração e a porosidade de aeração são restritivos ao desenvolvimento de plantas, através da metodologia do intervalo hídrico ótimo; avaliar a relação da permeabilidade ao ar com a macroporosidade, a porosidade total e a densidade do solo em diferentes tensões de água; determinar a relação entre a condutividade hidráulica do solo saturado e a macroporosidade, porosidade total e a densidade do solo. O solo foi coletado em uma lavoura comercial, no município de Ibirubá (RS). O clima da região enquadra-se na classificação de Köppen, zonas Cfa e Cfb (clima subtropical úmido com verões quentes ou amenos). O solo do local é classificado como Latossolo Vermelho Distrófico típico. A área destinada à coleta das amostras vinha sendo cultivada sob plantio direto desde 1998, com soja na primavera/verão, aveia + azevém e/ou trigo no outono/inverno. Foi realizado determinações de intervalo hídrico ótimo, granulometria, densidade, porosidade total, macro, condutividade hidráulica em solo saturado e permeabilidade ao ar do solo (submetidas a diferentes tensões de água no solo: 1, 6 33 e 100 kPa). As amostras de solo com estrutura preservada foram coletadas com o auxílio de anéis metálicos (0,03m de altura e 0,055m de diâmetro interno), nas camadas 0,02 a 0,07m e 0,12 a 0,18m e em vários pontos da lavoura com o intuito de se obter grande variação na densidade do solo. Os resultados indicaram que o aumento da densidade do solo influenciou na redução do IHO associada aos efeitos da resistência do solo à penetração e da porosidade de aeração. A maior condutividade do solo ao ar foi observada nos menores potenciais matriciais e na camada superficial do solo, onde há maior presença de macroporos. Também, houve redução em profundidade. A condutividade do solo ao ar e a condutividade hidráulica do solo saturado apresentaram correlação positiva com a macroporosidade e com a porosidade total e negativa com a densidade do solo nas tensões de água no solo.