In the late 1970s, a method was developed to estimate acoustic intensity in one dimension by taking the cross-spectral density of two closely-spaced microphone signals. Since then, multimicrophone probes have been developed to measure three-dimensional intensity as well as energy density. Their usefulness has led to the design of various types of multimicrophone probes, the most common being the four-microphone orthogonal, the four-microphone regular tetrahedron, and the six-microphone designs. These designs generally either consist of microphones suspended in space near each other or mounted on the surface of a sphere. This work analytically compares the relative merits of each probe design in measuring acoustic intensity and investigates the various finite-sum and finite-difference processing methods used with each. The analysis is limited to probes consisting of perfect point sensors in plane wave fields. The comparison is given in terms of average and maximum errors for intensity magnitude and direction as a function of angle of incidence as well as the spread between maximum and minimum errors for intensity magnitude. After existent probe geometries are reviewed, optimization techniques are introduced to predict what the optimal probe geometry would be for any given scenario. The probe is optimized to give the lowest intensity error averaged over angle of incidence of plane waves. This is done for full-space and half-space scenarios.

Os métodos geofísicos têm sido utilizados para definir a extensão em área e em profundidade de contaminações causadas por compostos orgânicos ou inorgânicos, uma vez que tais contaminações alteram as propriedades físicas do meio. Este trabalho abrangeu o desenvolvimento de ensaios realizados em laboratório e em campo para verificar a aplicabilidade de minissonda de resistividade, que utiliza quatro eletrodos dispostos segundo o arranjo Wenner em conjunto com uma fonte de corrente e dois multímetros, o que torna possível a execução de uma medida convencional de resistividade em diferentes profundidades à medida que a sonda é cravada no solo. Uma eventual aplicação desta minissonda seria sua utilização na avaliação de salinização secundária de solos. A agroindústria, principalmente no estado de São Paulo, vem utilizando cada vez mais estufas para a produção de frutos e flores, principalmente. Os processos de irrigação, e o microclima criados dentro das estufas, têm causado o incremento da quantidade de sais no solo, uma vez que o solo não é naturalmente lixiviado pela água da chuva. Isto pode comprometer a utilização dessas estufas para fins ligados à agricultura. A salinidade refere-se à presença de sais dissolvidos no solo, na água superficial e subterrânea. A salinização do solo pode estar ligada a processos naturais como a pedogênese do solo ou ao clima local por exemplo, ou pode ter origem secundária, podendo estar relacionada às atividades antrópicas capazes de alterar esta propriedade do meio. O presente trabalho visou testar a aplicabilidade da minissonda de resistividade para a avaliação da salinização secundária de solos. O trabalho foi inicialmente desenvolvido em laboratório, onde foram efetuados experimentos em amostras de solo saturadas com soluções de NaCl em diferentes concentrações. Os resultados obtidos nestes ensaios utilizando um meio arenoso totalmente saturado mostraram que a condutividade elétrica aumenta em função da concentração de NaCl utilizado na solução. Observou-se ainda a relação inversa entre a resistividade aparente calculada e a concentração da solução utilizada. Os ensaios de campo foram executados em duas estufas distintas, que utilizam diferentes técnicas de cultivo, localizadas nos municípios de Holambra e Elias Fausto, e não indicaram correlação entre a condutividade elétrica calculada a partir das resistividades obtidas e a condutividade elétricas medidas em laboratório, nas amostras de solo encaminhadas para análise. Foram analisados também os íons Al, Ba, Ca, Cr, Co, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, Zn, e cloretos. Nas duas estufas observa-se correlação entre as condutividades obtidas e alguns dos íons analisados. As diferenças observadas entre as condutividades elétricas calculada e medida, podem estar relacionadas às condições de campo, uma vez que nas duas estufas observou-se porções porosas no solo, a presença de solo argiloso nas estufas, principalmente em Holambra, e à presença dos metais presentes no solo local, conforme mostram os resultados analíticos obtidos. Adicionalmente, durante a realização dos ensaios em laboratório o meio encontrase totalmente saturado, o que não ocorreu nos ensaios realizados em campo, uma vez que na estufa em Holambra o solo estava úmido e na estufa em Elias Fausto apresentava-se bastante seco. As diferenças de umidade também podem ter interferido nos resultados obtidos. Os trabalhos realizados evidenciaram que a minissonda pode ser aplicada para medida de resistividade in situ, porém, seu uso deve se limitar à avaliação de áreas onde o solo é mais arenoso e pouco compactado. / Geophysical methods have been used to define the extension and depth of contaminations caused by organic and inorganic compounds spills. This is because those contaminations change the physical properties of the underground materials. This study presents the tests results performed both in laboratory and field of a small probe that allows the in situ measurement of the resistivity, avoiding the need of installation of monitoring wells and allowing low cost and fast measurements. It consists in a probe with four electrodes according a Wenner array, a current source and two multimeters. It makes possible to take in situ resistivity measurements in different depths while the probe is inserted in the soil. An eventual application for that mini probe would be for evaluation of secondary salinity of the soil. The agro industry, mainly in the São Paulo state, has been using greenhouses to increase the production mainly of fruits and flowers. The irrigation processes used and the microclimate generated in the greenhouse have been causing an increasing salt quantity in the soil. This happens because the natural lixiviation (by the rain) does not occur. That increasing salinization may prejudice the use of such greenhouses for agricultural purposes. Salinization refers to a build up of salts in soil, in the superficial water and groundwater. It may be due to natural process, like e.g. the pedogenesis or the local climate, or it may have a secondary origin, normally related to antropic activities that are capable to modify such property. This study aimed at testing the applicability of the resistivity mini probe to evaluate the secondary salinization of the soil. It was performed firstly in laboratory, using soil samples saturated with NaCl solutions of different concentrations. The results of those experiments showed that the electrical conductivity increases as function of the NaCl concentration and, naturally, the inverse relation with the apparent and calculated resistivity. Field tests were performed in two different greenhouses where distinct techniques are used. They are located in the Holambra and Elias Fausto municipalities. These tests did not indicate correlation between the electrical conductivity calculated from the measures resistivities and the electrical conductivities measured in the soil samples sent to the laboratory. In those samples the ions Al, Ba, Ca, Cr, Co, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, Zn, and chloride were also analyzed. For both greenhouses, some ions presented correlation with the electrical conductivities. The observed differences between the electrical conductivity calculated and measured may be related to the field conditions, since that in both greenhouses the soil was porous (avoiding the perfect coupling of the probe), the presence of clay that sticks in the probe between the electrodes, or the presence of metals in the soil, shown by the chemical analysis. In addition, during the laboratory tests, the soil was completely saturated, what was not the case in the field. In Holambra the soil was wet and Elias Fausto it was completely dry. So, the humidity differences may have interfered in the results. Finally, the tests results showed that the mini probe may be applied to measure the resistivity in situ but, its use may be limited to the evaluation of areas where the soil is more sandy and relatively loose.

Electric propulsion for spacecraft has become increasingly commonplace in recent decades as designers take advantage of the significant propellant savings it can provide over traditional chemical propulsion. As electric propulsion systems are designed for very low thrust, the operational time required over the course of an entire mission is often quite long. The two most common types of electric thrusters both use hollow cathodes as electron emitters in the process of ionizing the propellant gas. These cathodes are one of the main life-limiting components of both ion and Hall thrusters designed to operate for tens of thousands of hours. Failure often occurs as a result of erosion by sputtering from high-energy ions generated in the plasma. The mechanism that is responsible for creating these high-energy ions is not well understood, and significant efforts have gone into characterizing the plasma produced by hollow cathodes. This work uses both a Langmuir probe and an emissive probe to characterize the variation of the plasma potential and density, the electron temperature, and the electron energy distribution function in the near plume region of a hollow cathode. The cathode used in this experiment is typical of one used in a 200-W class Hall thruster. Measurements were made to determine the variation of these parameters with radial position from the cathode orifice. Changes associated with varying the propellant and flow rate were also investigated. Results obtained from the cathode while running on both argon and xenon are shown. Two different methods for calculating the plasma density and electron temperature were used and are compared. The density and temperature were not strongly affected by reductions in the propellant flow rate. The electron energy distribution functions showed distinct shifts toward higher energies when the cathode was operated at lower flow rates. The plasma potential also displayed an abrupt change in magnitude near the cathode centerline. Significant increases in the magnitude of plasma potential oscillations at lower propellant flow rates were observed. Ions formed at the highest instantaneous plasma potentials may be responsible for the life-limiting erosion that is observed during long-duration operation of hollow cathodes.

Os métodos geofísicos têm sido utilizados para definir a extensão em área e em profundidade de contaminações causadas por compostos orgânicos ou inorgânicos, uma vez que tais contaminações alteram as propriedades físicas do meio. Este trabalho abrangeu o desenvolvimento de ensaios realizados em laboratório e em campo para verificar a aplicabilidade de minissonda de resistividade, que utiliza quatro eletrodos dispostos segundo o arranjo Wenner em conjunto com uma fonte de corrente e dois multímetros, o que torna possível a execução de uma medida convencional de resistividade em diferentes profundidades à medida que a sonda é cravada no solo. Uma eventual aplicação desta minissonda seria sua utilização na avaliação de salinização secundária de solos. A agroindústria, principalmente no estado de São Paulo, vem utilizando cada vez mais estufas para a produção de frutos e flores, principalmente. Os processos de irrigação, e o microclima criados dentro das estufas, têm causado o incremento da quantidade de sais no solo, uma vez que o solo não é naturalmente lixiviado pela água da chuva. Isto pode comprometer a utilização dessas estufas para fins ligados à agricultura. A salinidade refere-se à presença de sais dissolvidos no solo, na água superficial e subterrânea. A salinização do solo pode estar ligada a processos naturais como a pedogênese do solo ou ao clima local por exemplo, ou pode ter origem secundária, podendo estar relacionada às atividades antrópicas capazes de alterar esta propriedade do meio. O presente trabalho visou testar a aplicabilidade da minissonda de resistividade para a avaliação da salinização secundária de solos. O trabalho foi inicialmente desenvolvido em laboratório, onde foram efetuados experimentos em amostras de solo saturadas com soluções de NaCl em diferentes concentrações. Os resultados obtidos nestes ensaios utilizando um meio arenoso totalmente saturado mostraram que a condutividade elétrica aumenta em função da concentração de NaCl utilizado na solução. Observou-se ainda a relação inversa entre a resistividade aparente calculada e a concentração da solução utilizada. Os ensaios de campo foram executados em duas estufas distintas, que utilizam diferentes técnicas de cultivo, localizadas nos municípios de Holambra e Elias Fausto, e não indicaram correlação entre a condutividade elétrica calculada a partir das resistividades obtidas e a condutividade elétricas medidas em laboratório, nas amostras de solo encaminhadas para análise. Foram analisados também os íons Al, Ba, Ca, Cr, Co, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, Zn, e cloretos. Nas duas estufas observa-se correlação entre as condutividades obtidas e alguns dos íons analisados. As diferenças observadas entre as condutividades elétricas calculada e medida, podem estar relacionadas às condições de campo, uma vez que nas duas estufas observou-se porções porosas no solo, a presença de solo argiloso nas estufas, principalmente em Holambra, e à presença dos metais presentes no solo local, conforme mostram os resultados analíticos obtidos. Adicionalmente, durante a realização dos ensaios em laboratório o meio encontrase totalmente saturado, o que não ocorreu nos ensaios realizados em campo, uma vez que na estufa em Holambra o solo estava úmido e na estufa em Elias Fausto apresentava-se bastante seco. As diferenças de umidade também podem ter interferido nos resultados obtidos. Os trabalhos realizados evidenciaram que a minissonda pode ser aplicada para medida de resistividade in situ, porém, seu uso deve se limitar à avaliação de áreas onde o solo é mais arenoso e pouco compactado. / Geophysical methods have been used to define the extension and depth of contaminations caused by organic and inorganic compounds spills. This is because those contaminations change the physical properties of the underground materials. This study presents the tests results performed both in laboratory and field of a small probe that allows the in situ measurement of the resistivity, avoiding the need of installation of monitoring wells and allowing low cost and fast measurements. It consists in a probe with four electrodes according a Wenner array, a current source and two multimeters. It makes possible to take in situ resistivity measurements in different depths while the probe is inserted in the soil. An eventual application for that mini probe would be for evaluation of secondary salinity of the soil. The agro industry, mainly in the São Paulo state, has been using greenhouses to increase the production mainly of fruits and flowers. The irrigation processes used and the microclimate generated in the greenhouse have been causing an increasing salt quantity in the soil. This happens because the natural lixiviation (by the rain) does not occur. That increasing salinization may prejudice the use of such greenhouses for agricultural purposes. Salinization refers to a build up of salts in soil, in the superficial water and groundwater. It may be due to natural process, like e.g. the pedogenesis or the local climate, or it may have a secondary origin, normally related to antropic activities that are capable to modify such property. This study aimed at testing the applicability of the resistivity mini probe to evaluate the secondary salinization of the soil. It was performed firstly in laboratory, using soil samples saturated with NaCl solutions of different concentrations. The results of those experiments showed that the electrical conductivity increases as function of the NaCl concentration and, naturally, the inverse relation with the apparent and calculated resistivity. Field tests were performed in two different greenhouses where distinct techniques are used. They are located in the Holambra and Elias Fausto municipalities. These tests did not indicate correlation between the electrical conductivity calculated from the measures resistivities and the electrical conductivities measured in the soil samples sent to the laboratory. In those samples the ions Al, Ba, Ca, Cr, Co, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, Zn, and chloride were also analyzed. For both greenhouses, some ions presented correlation with the electrical conductivities. The observed differences between the electrical conductivity calculated and measured may be related to the field conditions, since that in both greenhouses the soil was porous (avoiding the perfect coupling of the probe), the presence of clay that sticks in the probe between the electrodes, or the presence of metals in the soil, shown by the chemical analysis. In addition, during the laboratory tests, the soil was completely saturated, what was not the case in the field. In Holambra the soil was wet and Elias Fausto it was completely dry. So, the humidity differences may have interfered in the results. Finally, the tests results showed that the mini probe may be applied to measure the resistivity in situ but, its use may be limited to the evaluation of areas where the soil is more sandy and relatively loose.

Transfer RNAs (tRNAs) are known for their role as adaptors during translation of the genetic information and as regulators for gene expression; uncharged tRNAs regulate global gene expression in response to changes in amino acid pools in the cell. Aminoacylated tRNAs play a role in non-ribosomal peptide bond formation, post-translational protein labeling, modification of phospholipids in the cell membrane, and antibiotic biosynthesis. [1] tRNAs have a highly stable structure that can present a challenge for their detection using conventional techniques. [2] To enable signal amplification and lower detection limits, a split probe - split deoxyribozyme (sDz or BiDz) probe, which uses a double-labeled fluorogenic substrate as a reporter – has been introduced. In this project we developed an assay based on sDz probe to detect yeast tRNAPhe as a proof-of-principle highly structured target. An sDz probe was designed specific to tRNAphe that could efficiently unwind stable secondary and tertiary structure of the target RNA thereby providing an efficient tool for tRNA detection. [3]The efficiency of the developed sDz probe was compared with a currently used state-of-the-art hybridization probe – molecular beacon probe. The results obtained in the project further demonstrate the power of sDz probes for the detection of highly structured RNA analytes. The split probes show signal amplification capabilities in detection of structured analytes, which will benefit diagnostics, fundamental molecular biology research and therapeutic fields.

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This thesis presents an overview of the research activities undertaken during my PhD under the supervision of Dr. F. Iza from the School of Electronic, Electrical and Systems Engineering and Dr. B. Buckley from the Chemistry Department at Loughborough University. The thesis is divided as follows. The first chapter of the thesis presents an introduction to plasma and chemical probes as well as the motivation for developing fluorescent probes for plasma characterisation. Analytical techniques used during this work to analyse chemical substances are described in the second chapter. Results and discussions from the experiments are discussed in chapters 3 to 7. Conclusions and future work are presented in chapter 8. In chapter 9, experimental data is presented. In the last century, plasma has attracted the attention of numerous researchers. Due to the wide-range of applications of this ionised gas, people from different fields have focused their effort on studying plasma. Low-temperature plasmas have received growing attention in the last 50 years when the development in cold plasma devices made them more controllable. Plasma played (and continues to play) a critical role in the fabrication process of integrated circuits and recent advances in the generation of low-temperature atmospheric-pressure plasmas have resulted in the emergence of new applications including treatment of temperature sensitive surfaces and biological targets. During the first months at Loughborough I worked on the ozonolysis of various alkenes with air plasmas. This allowed me to familiarised myself with plasma as this was new to me and get a feeling of some of the challenges lying ahead. Nonetheless, the data I obtained was encouraging and I presented the results of batch and flow plasma-based ozonolysis of alkenes at the Technological Plasma Workshop held in Manchester in January 2012. Once I had familiarised myself with the plasma system, I worked on synthesising fluorescent probes to detect ozone, one of the many reactive species that are typically generated in oxygen containing plasmas. Details of the experiments conducted to date and most significant findings are discussed in this thesis.

The main task of this thesis is to find the ICT activator of a carotenoid spheroidenone in the pigment-protein complex LH1 of Rhodobacter sphaeroides. The ICT state is characterized by a red-shifted positive transient absorption signal around 750 - 800 nm. We hypothesize that the presence of the ICT state is associated with the pigment-protein interaction of a carotenoid keto group and specific amino acid in the protein. To perform the experiment, four mutant complexes with amino acids substitutions, which should result in decreased intensity of the ICT signal due to a weaker or missing pigment-protein interaction, were obtained and measured using femtosecond time resolved pump-probe spectroscopy.