Neste trabalho dois métodos de preparo de amostras para decomposição de bio-diesel foram avaliados para a posterior determinação de Cu e Ni por espectrometria de absorção atômica com forno de grafite (GF AAS). O primeiro método consistiu na de-composição ácida assistida por radiação micro-ondas em sistema fechado (MW-AD), que foi realizada com adição de HNO3 7 mol L-1 e 2 mL de H2O2 30% (m/m). O segun-do método de pré-tratamento avaliado foi a decomposição por via seca em forno mufla com programa de aquecimento até a temperatura máxima de 450 °C. O sólido resultante foi dissolvido em HNO3 1% (v/v). As temperaturas de pirólise e atomização para a téc-nica de GF AAS foram, respectivamente, 1000 ºC e 2000 ºC para Cu, e 1100 °C e 2300 °C para Ni. Os limites de detecção (LD) para Cu e Ni foram de 12,4 e 3,8 ng g-1 empre-gando o método de decomposição MW-AD. Enquanto que, para o método de decompo-sição por via seca os LD foram de 2,8 e 8,3 ng g-1 para Cu e Ni, respectivamente. A avaliação da exatidão foi efetuada a partir do ensaio de recuperação após adição de ana-lito ao biodiesel. As recuperações foram de 91 e 86% para o método MW-AD para Cu e Ni, respectivamente. Foram observadas perdas por volatilização com o emprego do mé-todo de via seca para Cu, com isso, a recuperação foi no máximo de 73%. / In this work, two methods for biodiesel digestion for determination of Cu and Ni by graphite furnace atomic absorption spectrometry (GF AAS) were evaluated. The microwave-assisted acid digestion (MW-AD) with the addition of 7 mol L-1 of HNO3 and 2 mL of H2O2 30% (m/m) was applied to biodiesel digestion. In addition, a dry ash method was applied to biodiesel digestion using a maximum temperature of 450 ºC. The inorganic residues were dissolved by addition of 1% (v/v) nitric acid. The optimiza-tion of temperature program was performed in the GF AAS for Cu and Ni using a sam-ple with standard addition. The pyrolysis and atomization temperatures were, respec-tively, 1000 ° C and 2000 ° C for Cu and 1100 ° C and 2300 °C for Ni. The limits of detection for Cu and Ni were 12,4 and 3,8 ng g-1, respectively, using a MW-AD meth-od. Using a dry ash method the limits of detection were 2,8 and 8,3 for Cu and Ni, re-spectively. The recoveries for Cu and Ni after MW-AD method were 91 and 86%, re-spectively. Using the dry ash method the recovery was 73% for Cu due to sample vo-latilization losses.

This thesis deals with RFID tags. In the first part of the thesis, the general overviews of the present-day RFID systems are presented. This part of the thesis is focused on the passive back-scatter UHF tags and the advantages of their application in supply chain usage. Subsequently, the electromagnetic simulators CST Microwave Studio and IE3D Zeland are described. These simulators were used to design loaded meander antennas. The antennas were designed for different materials and frequency bands of 867 MHz and 2.4 GHz. The designed antennas were made without as well as with the reflector which allows using the antennas in the vicinity of metals. Produced antennas were experimentally tested in the company METRA Blansko Inc, where one of the most significant characteristics of passive RFID tags – the read range was observed.

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The Sarbanes-Oxley Act mandates public companies to establish internal control systems and assess their effectiveness. Quarterly reports by all companies and annual reports by companies with less than $75 million public float (non-accelerated filers) do not require auditor’s attestation while annual reports by companies with $75 million or more public float (accelerated filers) do require such auditor attestations. Quarterly reports should provide early warning of any impending material weakness (MW) to be disclosed in subsequent annual filings. This dissertation explores three types of “surprise” MW disclosures—positive, negative and no surprise—and consequences of such surprise disclosures. In part one, I document the frequency of surprise MW disclosures and internal control factors that are associated with each surprise type by filer status. Results show that 78 (77) percent of accelerated (non-accelerated) MW disclosures are negative surprise MW disclosures during 2004-2016. Entity level MWs are more associated with no-surprise rather than negative or positive surprise MW disclosures. In part two, I examine some consequences of surprise MW disclosures. The results show that companies with MW disclosures are more likely to dismiss their auditors and CFOs, and experience more shareholder voting against auditor ratification, compared to companies that issue clean reports. Auditor dismissal and CFO turnover are equally likely at negative and no-surprise MW disclosure companies. However, negative surprise accelerated filer companies’ shareholders are more likely to vote against auditor ratification than no-surprise accelerated filer companies. The third essay investigates the association between MW disclosures and audit fees. The results indicate that there is a significant positive association between audit fees and MW disclosures. Further, the results show that audit fees are higher at no-surprise companies than at negative surprise companies. The fourth essay focuses on audit report lag. The results indicate that MWs are associated with increased audit report lags, for both accelerated and non-accelerated filers. Further, surprise MW firms are more likely to experience increased audit report lag than no-surprise MW firms. Overall the results suggest that adverse internal control reports have consequences, and that the consequences vary between surprise and no-surprise MW firms. The results provide relevant empirical evidence to the ongoing debate on the necessity and efficacy of SOX Section 404 requirements.

Atmospheric icing presents serious challenges to the development of wind power of the wind energy industry in cold regions. The potential detrimental impact on the safe operation of wind turbines and the energy harvest hasn't been fully understood and requires further investigation. This thesis presents the research on icing profiles under different weather conditions and their impact on natural frequency, fatigue life, and lift and drag of the wind turbine blade. The research aims to develop a further understanding of the effect of atmospheric ice accretion on the structural integrity and aerodynamic performance of wind turbine blades through numerical and aerodynamic investigations to address the challenges facing the industry. A 5-MW NREL (National Renewable Energy Laboratory) wind turbine blade was selected for this study, due to availability of required geometric design parameters and experimental data for verification. The turbine rotor and its three blades were modelled and numerically simulated with commercial finite element software ANSYS. Three icing scenarios were chosen according to the ISO Standard and the corresponding icing profiles were developed to investigate their influence on vibrational behaviours of the wind turbine blade and rotor under different weather conditions. Icing loads were applied on the leading edge of the blade and natural frequency results were compared between clean and iced blades. It was found that harsh icing weather drove the natural frequency down to the near resonance limit, which could lead to significant issue on structural integrity of the wind turbine. The effect of atmospheric ice accretion with additional load due to varying wind speeds on the fatigue life of the wind turbine blade has been investigated. Significant reduction of fatigue life was found due to the increase of the von Mises stresses. Finally, computational fluid dynamics (CFD) analysis was carried out to investigate the effect of atmospheric ice accretion on the aerodynamic performance of typical 1-MW and 5-MW wind turbine blades. Results of the drag and lift coefficients and power production under different icing scenarios were obtained for five angles of attack. Compared with the results of the clean aerofoil profile, remarkable reduction in the power generation was observed due to the accreted ice at various aerofoil sections in the spanwise direction of the blade, demonstrating the detrimental impact of atmospheric icing on energy harvest for the wind energy industry.

Lightweight aluminium-silicon alloy is an attractive material for making engine cylinders in automobiles. It imparts good power to weight ratio to the engine. High silicon containing aluminium alloys are used in current engine block castings where the bore surface is etched or honed to partially expose the silicon particles to provide the primary contact between the piston ring and certain regions of the piston and the cylinder. Piston reversal near the top dead centre however causes starvation of lubrication which leads to wear. To explore the wear behaviour of etched aluminium-silicon alloys under nominally dry conditions and extreme lubricated conditions, a host of mechanical and spectroscopic techniques are used here to characterize mechanical and chemical changes caused by wear. In the absence of complex chemical transformations on the wear surface in dry condition, allows a close examination of surface and subsurface microstructures. Given this understanding of the wear under dry condition, we explore the effect of boundary lubrication, where chemical transformations leading to surface modifications are involved. In dry sliding tribology of aluminium-silicon alloy slid against a steel ball four stages of wear are identified; ultra-mild wear, mild wear, severe wear and post severe oxidative wear. In the ultra-mild wear regime silicon particles bears the load. Transition to mild wear occurs when the protruded silicon particles disappear(by sinking and fracture) under higher pressure and sliding. The sinking of silicon particles under normal loading is further investigated using a naoindenter. It is found that the resistance to sinking of such particles into the matrix increases with the unexposed surface area to the buried volume of the particles. In that sense, small particles are seen to provide the stiffest resistance to sinking. While in ultra-mild wear regime the basic energy dissipation mechanism is sinking/tilting, in mild wear regime the subsurface is either in an elastic or an incipiently plastic state. Subsurface plasticity in mild wear regime leads to a grain refinement, fracture of silicon and nucleation of cracks at silicon-matrix interfaces but does not promote large scale flow of the matrix. Transition to severe wear occurs when the contact pressure exceeds the plastic shakedown limit. Under this condition gross plasticity leads to a severe fragmentation of silicon particles and the fragmented silicon are transported by the matrix as it undergoes incremental straining with each cyclic contact at the asperity level. A large reduction in the inter-particle distance com-pared to that in a milder stage of wear, gives rise to high strain gradients in the severe wear regime which contribute to the enhancement of dislocation density. The resulting regions of very high strains at the boundaries of the recrystallised grains as well as within the subgrains lead to the formation of microvoids/ cracks. This is accompanied by the formation of brittle oxides at these subsurface inter-faces due to enhanced diffusion of oxygen. We believe that the abundance of such microcracks in the near surface region, primed by severe plastic deformation, is what distinguishes a severe wear regime from that in the mild wear. The transition from severe wear to post severe oxidative wear is thermally induced and it transfers the metal to metal contact interaction to metal to ceramic interaction. A thick oxide layer is abraded and spalls while the metal underneath continues to flow and delaminate. A study of lubricated tribology of ultra-mild and mild wear regime of aluminium-silicon alloy shows that the initial stages of sliding friction is controlled by the abrasion of the steel pin by the protruding silicon particles of the aluminium-silicon disc. Thegeneration of nascent steel chips helps to breakdown the additive in the oil by a cationic exchange that yields chemical products of benefits to the tribology. The friction is initially controlled by abrasion, but the chemical products gain increasing importance in controlling friction with sliding time. After long times, depending on the contact pressure, the chemical products determine sliding friction exclusively. In the mild wear chemically induced low friction is achieved in short periods of time whereas in ultra-mild wear regime it takes very long time to reach this low friction state. While the basic dissipation mechanisms are the same in the ultra-mild wear and mild wear regimes ,the matrix remains practically unworn in the low pressure ultra-mild wear regime. In the higher pressure mild wear regime at long sliding times a small but finite wear rate prevails. Incipient plasticity in the subsurface controls the mechanism of wear.

This master´s thesis deals with an examination of different solution types a for the chemical passivation of a silicon surface. Various solutions are tested on silicon wafers for their consequent comparison. The main purpose of this work is to find optimal solution, which suits the requirements of a time stability and start-up velocity of passivation, reproducibility of the measurements and a possibility of a perfect cleaning of a passivating solution remainig from a silicon surface, so that the parameters of a measured silicon wafer will not worsen and there will not be any contamination of the other wafers series in the production after a repetitive return of the measured wafer into the production process. The cleaning process itself is also a subject of a development.

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