The effect of microwave radiation on soil bacteria in situ has been studied in both lab and field conditions. Radiation and thermal profiles show that heterotrophic bacteria, spores, fungi, and actinomycetes were not affected by total microwave radiations over the range 0 to 80 seconds of exposure at a net input of 1 KW of intensity. Nitrogen-fixing bacteria and nitrifying bacteria were also resistant to these doses. The soil microorganisms were inactivated as a function of microwave radiation in the range of 80 to 480 seconds of exposure to 1 KW of continuous radiation. By studying the relationship between temperature generated in dry and wet organisms and the pattern of destruction of inoculated bacteria by microwave radiation, it was found that inactivation was a function of cell hydration. It also revealed that bacterial cells do not absorb microwave energy and that the lethal effect of microwaves is due to direct energy transfer to cell water and the temperature increase of the suspending medium.

One potential alternative to chemical weed control is the use of microwave radiation, a particular form of indirect thermal weeding. Absorption of microwave radiation causes water molecules within the tissue to oscillate, thereby converting electromagnetic energy into heat. This technique is rapid, versatile and effective, as the electromagnetic waves heat the plant tissue and destroy cellular integrity. The objective of this research was to evaluate the potential use of dielectric heating for weed management. Ten weed species representing monocots and dicots were selected for this study: southern crabgrass, dallisgrass, yellow nutsedge, fragrant flatsedge, false green kyllinga, common ragweed, field bindweed, henbit, white clover, and pitted morningglory. There was a lag or warm up period between energizing the magnetron and actual microwave radiation production. To eliminate the gap between electric power supplied to magnetron and actual microwave radiation produced, a conveyer was used. Overall injury to grasses, sedges and broadleaf weeds was higher at each dose when weeds were treated by microwave radiation while moving on a conveyer in comparison to being stationary. Grasses showed slightly more tolerance to microwave treatments in comparison to broadleaf weeds. Older weeds (8 to 10 weeks old) showed more tolerance to microwave treatments in comparison to younger weed plants (4 to 6 weeks old). Microwave radiation was able to control a range of weed species, although larger weeds were more likely to regrow after treatment. Ambient temperature had a significant effect on injuries caused by microwave radiation to target weeds, with control increasing as the air temperature increased. Weed control using microwave radiation required more energy when weeds were treated at 13 C compared to 35 C. More energy was needed at lower air temperatures to raise the plant canopy temperature from ambient levels to beyond the biological limit. Microwave radiation at lower doses caused greater injury to common chickweed and yellow woodsorrel than bermudagrass, suggesting the potential for selective weed control in certain situations. A custom built microwave applicator provided similar control of emerged weeds as the contact herbicides diquat and acetic acid. / Ph. D.

This dissertation summarizes three research projects related to microwave radiation induced electron transport properties in the GaAs/AlGaAs two dimensional electron systems. In chronological order, the projects are: a microwave reflection and electron magneto-transport correlation study, the combined microwave power and polarization dependence on microwave radiation induced magneto-resistance oscillations study, and a comparative study about the effect of circularly polarized and linearly polarized microwaves radiation on magneto-resistance oscillations induced due to the microwave. These three research projects experimentally address many interesting issues in the non-equilibrium low dimensional electron transport under microwave irradiation and provide potential applications of utilizing microwave radiation induced magneto-resistance oscillations in two dimensional electron systems as a method to detect different qualities of microwaves or terahertz waves.

Entre as diferentes formas empregadas para o preparo de amostras orgânicas visando a determinação de elementos inorgânicos, uma alternativa que foi avaliada neste trabalho foi a digestão assistida por radiação microondas empregando ácidos diluídos. Estudos recentes demonstram ser essa uma alternativa eficiente no tocante à solubilização de elementos minerais para determinação por técnicas espectroscópicas. No entanto, a eficiência deste procedimento depende das características originais da amostra. Neste enfoque, a eficiência da decomposição foi avaliada, considerando-se as características originais das amostras e a caracterização dos produtos finais presentes na solução após a decomposição. Amostras de tecido vegetal (soja em gãos e Paspalum) e de tecido animal (sangue e vísceras de bovino), utilizando misturas oxidantes em diferentes concentrações ácidas foram digeridas em forno por radiação microondas com cavidade. A eficiência das decomposições, avaliada a partir da determinação dos teores de carbono orgânico residual e da recuperação de minerais. A caracterização original das amostras, realizada a partir da determinação dos teores de proteína bruta (PB), gordura (EE), carbono original (CHN-S), efetuada com o intuito de correlacionar essas características com os compostos remanescentes após as digestões. As soluções residuais foram caracterizadas inicialmente por técnica espectroscópica (RMN de 1H) para identificar os principais compostos orgânicos remanescentes. Após os primeiros resultados, estudos para separação FORAM realizados por cromatografia líquida de alta eficiência com detecção por ultravioleta. Em seguida os produtos de reação foram, correlacionados com a composição química inicial das amostras. / Microwave-assisted with diluted acids is an alternative to sample preparation of organic samples owing inorganic elements solubilization for spectroscopic techniques determination. The efficiency of this procedure depends on the sample?s original characteristics. In this way, the decomposition efficiency was evaluated considering the sample?s original characteristics and the final products presents in the solution after decomposition. Grains of soybean and samples of forage, bovine blood, and bovine viscera were digested in cavity-microwave oven using oxidants mixtures in different acid concentrations. The decomposition efficiency was evaluated from residual organic carbon determination and mineral recovery by inductively coupled plasma optical emission spectrometry. The original sample characterization was performed from crude protein amount, fatty, and original carbon. In order to identify the main remaining organic compounds, the residual solutions were firstly characterized by spectroscopy technique (1H NMR), with the identification of typical nitro-, aliphatic- and aromatic- compounds. Studies concerning separation of nitrobenzoic acids isomers were performed by HPLC-UV, by using reversal phase chromatography with C18 as stationary phase and H2O:acetonitrile:methanol (75:20:5) + 0.05% TFA as mobile phase. The use of diluted acids proved to be useful and recommended alternative, reducing the reagents volume and consequently the variability of the residues provided by the decomposition process. Comparing the digested solutions with the original sample composition, biological matrix with structural amino acids, proteins and lipids produced nitrobenzoic acid isomers and other organic compounds provided from the cleavage in chemical bonds.

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Entre as diferentes formas empregadas para o preparo de amostras orgânicas visando a determinação de elementos inorgânicos, uma alternativa que foi avaliada neste trabalho foi a digestão assistida por radiação microondas empregando ácidos diluídos. Estudos recentes demonstram ser essa uma alternativa eficiente no tocante à solubilização de elementos minerais para determinação por técnicas espectroscópicas. No entanto, a eficiência deste procedimento depende das características originais da amostra. Neste enfoque, a eficiência da decomposição foi avaliada, considerando-se as características originais das amostras e a caracterização dos produtos finais presentes na solução após a decomposição. Amostras de tecido vegetal (soja em gãos e Paspalum) e de tecido animal (sangue e vísceras de bovino), utilizando misturas oxidantes em diferentes concentrações ácidas foram digeridas em forno por radiação microondas com cavidade. A eficiência das decomposições, avaliada a partir da determinação dos teores de carbono orgânico residual e da recuperação de minerais. A caracterização original das amostras, realizada a partir da determinação dos teores de proteína bruta (PB), gordura (EE), carbono original (CHN-S), efetuada com o intuito de correlacionar essas características com os compostos remanescentes após as digestões. As soluções residuais foram caracterizadas inicialmente por técnica espectroscópica (RMN de 1H) para identificar os principais compostos orgânicos remanescentes. Após os primeiros resultados, estudos para separação FORAM realizados por cromatografia líquida de alta eficiência com detecção por ultravioleta. Em seguida os produtos de reação foram, correlacionados com a composição química inicial das amostras. / Microwave-assisted with diluted acids is an alternative to sample preparation of organic samples owing inorganic elements solubilization for spectroscopic techniques determination. The efficiency of this procedure depends on the sample?s original characteristics. In this way, the decomposition efficiency was evaluated considering the sample?s original characteristics and the final products presents in the solution after decomposition. Grains of soybean and samples of forage, bovine blood, and bovine viscera were digested in cavity-microwave oven using oxidants mixtures in different acid concentrations. The decomposition efficiency was evaluated from residual organic carbon determination and mineral recovery by inductively coupled plasma optical emission spectrometry. The original sample characterization was performed from crude protein amount, fatty, and original carbon. In order to identify the main remaining organic compounds, the residual solutions were firstly characterized by spectroscopy technique (1H NMR), with the identification of typical nitro-, aliphatic- and aromatic- compounds. Studies concerning separation of nitrobenzoic acids isomers were performed by HPLC-UV, by using reversal phase chromatography with C18 as stationary phase and H2O:acetonitrile:methanol (75:20:5) + 0.05% TFA as mobile phase. The use of diluted acids proved to be useful and recommended alternative, reducing the reagents volume and consequently the variability of the residues provided by the decomposition process. Comparing the digested solutions with the original sample composition, biological matrix with structural amino acids, proteins and lipids produced nitrobenzoic acid isomers and other organic compounds provided from the cleavage in chemical bonds.

No / Vortices circulating in a ring made from a Josephson array in the insulating phase are studied. The ring contains a `dual Josephson junction' through which the vortices tunnel. External non-classical microwaves are coupled to the device. The time evolution of this two-mode fully quantum mechanical system is studied, taking into account the dissipation in the system. The effect of the quantum statistics of the photons on the quantum statistics of the vortices is discussed. Entropic calculations quantify the entanglement between the two systems. Quantum phenomena in the system are also studied through Wigner functions. After a certain time (which depends on the dissipation parameters) these quantum phenomena are destroyed due to dissipation.

Previous studies have demonstrated the sensitivity of the amplitude of the microwave radiation-induced magnetoresistance oscillations to the microwave polarization. These studies have also shown that there exists a phase shift in the linear polarization angle dependence. But the physical origin of this phase shift is still unclear. Therefore, the first part of this dissertation analyzes the phase shift by averaging over other small contributions, when those contributions are smaller than experimental uncertainties. The analysis indicates nontrivial frequency dependence of the phase shift. The second part of the dissertation continues the study of the phase shift and the results suggest that the specimen exhibits only one preferred radiation orientation for different Hall-bar sections. The third part of the dissertation summarizes our study of the Hall and longitudinal resistance oscillations induced by microwave frequency and dc bias at low filling factors. Here, the phase of these resistance oscillations depends on the contact pair on the device, and the period of oscillations appears to be inversely proportional to radiation frequency.

La nanotechnologie est un domaine en voie d'expansion qui a attiré l'attention de la recherche en raison de ses applications potentielles illimitées. La technologie des ondes millimétriques est un autre domaine intéressant qui joue un rôle de premier plan dans le développement des systèmes de communications sans fil. La combinaison de ces deux champs de recherche avancée, donne naissance à l'innovation du Dispositif Ratchet qui est une nouvelle application qui représente un vrai défi. Ce dispositif est de taille nanométrique et son concept d'opération consiste à générer une tension DC lorsque le dispositif, basé sur le gaz d'électron bidimensionnel, est rayonné par l'énergie des micro-ondes. L'objectif de cette thèse est d'essayer d'améliorer la réponse du dispositif, ce qui ouvre de nouvelles perspectives dans la fabrication des détecteurs de champ à haute fréquence et à l'échelle nanométrique. Malheureusement, les Dispositifs Ratchet actuels, basés sur des hétérostructures de semiconducteurs, réalisés jusqu'à présent fonctionnent à basse température pour assurer une grande mobilité électronique. Cette condition nécessite l'utilisation d'un setup expérimental complexe qui a un grand impact sur la tension induite et sur la reproductibilité du phénomène Ratchet observé. Dans ce contexte, le travail effectué dans le cadre de cette thèse a abordé ce problème en deux parties. La première partie concerne l'analyse électromagnétique du setup expérimental. Ceci a été réalisé par la mise en oeuvre des simulations électromagnétiques intenses. D'autre part, différentes solutions ont été proposées afin d'optimiser le setup et ainsi améliorer la tension Ratchet produite. Outre l'étude électromagnétique, certaines mesures de modulation ont été réalisées pour tester la faisabilité du Dispositif Ratchet comme un démodulateur d'amplitude. La deuxième partie de cette thèse traite l'étude de la matière qui compose le Dispositif Ratchet. Récemment, le graphène commence à envahir le monde scientifique et technologique avec ses fascinantes propriétés électroniques, tels que sa mobilité d'électrons élevée à température ambiante, où les matériaux conventionnels sont en train de confronter des obstacles. En conséquence, l'idée de fabriquer un Dispositif Ratchet à base de graphène au lieu des hétérojonctions de semiconducteurs, a été introduite. Plusieurs modèles de conception, caractérisation et mesures RF ont été accomplis en vue d'obtenir un Dispositif Ratchet fiable approprié pour de nombreuses applications pratiques à la température ambiante, dans la gamme de fréquences micro-ondes et pourraient s'étendre à la bande térahertz. / Nanotechnology is a growing field that has attracted significant research attention due to its unlimited potential applications. Millimeter wave technology is another interesting field that plays a leading role in the development of wireless communications systems. Combining these two advanced research fields together, has given rise to the innovation of the Ratchet Device which is now a new challenging application. This device has a nanoscale size and its concept of operation consists of generating a DC voltage when radiating a two-dimensional electron gas based device with microwave energy. The aim of this thesis is in trying to improve the device response and hence opening new perspectives in the fabrication of high frequency field detectors on the nanoscale level. Unfortunately, the current Ratchet Devices, based on semiconductor heterostructures, realized till now, operate at low temperatures to ensure high electron mobility. This condition necessitates the use of a complex experimental setup that has a great impact on the induced voltage and on the reproducibility of the observed Ratchet phenomenon. In this context, the work performed within the framework of this thesis has addressed this problem in two parts. The first part concerns the electromagnetic analysis of the experimental setup behavior. This has been achieved by implementing intensive full wave electromagnetic simulations. Different solutions have been proposed to optimize the setup and thus enhance the Ratchet voltage produced. In addition to the electromagnetic study, some modulation measurements have been performed to test the feasibility of the Ratchet Device as an amplitude demodulator. The second part of this thesis deals with the study of the material composing the Ratchet Device. Recently, graphene has started to invade the scientific and the technological world with its fascinating electronic properties, such as its high electron mobility at room temperature, which distinguishes it from conventional materials that typically collide with obstacles. As a result, the idea of fabricating a Ratchet Device based on graphene instead of semiconductor heterojunctions has been introduced. Several design models, characterizations and RF measurements have been performed in order to obtain a reliable Ratchet Device suitable for many practical applications at room temperature. This has been done in the microwave frequency range and can also extend to the terahertz band.