A alelopatia, na qual uma espécie causa efeitos negativos sobre outra através da liberação de substâncias químicas, é um fenômeno que pode afetar comunidades vegetais. Em alguns casos, o estabelecimento de arbustos aromáticos em formações densas, com apenas poucas espécies ocorrendo em suas proximidades, é um padrão que tem sido relacionado aos efeitos fitotóxicos dos voláteis que os mesmos liberam. Em campos dos sul do Brasil, esse padrão de estabelecimento frequentemente ocorre para as espécies arbustivas aromáticas Heterothalamus psiadioides Less e Baccharis patens Baker, indicando a possibilidade de alelopatia. Dessa forma, o presente estudo teve como objetivo determinar se H. psiadioides e B. patens são fitotóxicas e se isso implica em efeitos negativos sobre a comunidade vegetal na qual os arbustos ocorrem. Em ensaios em laboratório, os efeitos dos voláteis liberados diretamente das folhas frescas e secas de H. psiadioides e B. patens foram testados sobre a germinação e o crescimento das plantas-alvo alface e cebola nas quatro estações do ano. Em um estudo em campo, foram avaliadas cobertura e biomassa vegetal, número de mudas, diversidade, riqueza, e variáveis de estrutura da vegetação no entorno de ambas as espécies arbustivas e onde não havia arbustos. Nos bioensaios, os voláteis de H. psiadioides e B. patens causaram inibição na porcentagem e velocidade de germinação e redução no tamanho da raiz e da parte aérea das plantas-alvo, sendo que folhas frescas apresentaram maior fitotoxidez. Esses parâmetros foram mais afetados por H. psiadioides que por B. patens em todas as estações, e os efeitos de ambas foram menores no verão. Em relação à investigação em campo, que objetivou avaliar os efeitos da espécie muito fitotóxica H. psiadioides sobre a comunidade vegetal, não foram observadas evidências de alelopatia. Houve maior riqueza e diversidade próximo a H. psiadioides, devido à menor cobertura de gramíneas dominantes. Variáveis de estrutura da vegetação e intensidade de luz explicaram os padrões observados de forma mais conclusiva que alelopatia. Esse estudo sugere que o potencial alelopático de plantas pode ser superestimado em bioensaios e que estudos em campo são necessários para demonstrar se efeitos alelopáticos são realmente relevantes em comunidades vegetais. Ainda, o trabalho ressalta a importância de conduzir estudos mais realistas em laboratório e de utilizar controles em estudos em campo. / Allelopathy, in which a species causes negative effects on another through the release of chemical substances, is a phenomenon that may affect plant communities. In some cases, the establishment of aromatic shrubs in dense stands, with few other species occurring in their surroundings, has been related to the phytotoxic effects of volatiles released by these shrubs. In South Brazilian grasslands, this pattern of establishment often occurs for the aromatic shrub species Heterothalamus psiadioides Less and Baccharis patens Baker, indicating the possibility of allelopathy. Thus, this study aimed to determine if H. psiadioides and B. patens are phytotoxic and if this implicates in negative effects on the plant community in which the shrubs occur. In laboratory assays, the effects of the volatiles released directly from fresh and dry leaves of H. psiadioides and B. patens on germination and growth of the target plants lettuce and onion were evaluated in four seasons. A field study was carried out, in which vegetation cover and biomass, number of seedlings, diversity, richness, and variables of vegetation structure were evaluated in the surroundings of both species and where there were not shrubs. In the bioassays, H. psiadioides and B. patens volatiles inhibited the germination rate and speed of germination and reduced the root and shoot length of the target plants, with fresh leaves showing higher phytotoxicity. These parameters were more strongly affected by H. psiadioides than by B. patens in all seasons, and effects of the both shrubs were lower in summer. In relation to the field investigation that aimed to quantify the effects of the highly phytotoxic H. psiadioides on the plant community, no evidences of allelopathy were found. Richness and diversity were higher near H. psiadioides, due to lower cover of dominant grasses. Variables of vegetation structure and light intensity explained vegetation patterns more conclusively than allelopathy. This study emphasizes that the allelopathic potential of plants can be overestimated in bioassays, and that field studies are necessary to elucidate if allelopathic effects are in fact significant in plant communities. Still, the relevance of conducting more realistic laboratory studies and of using controls in field studies is highlighted.

Reproduire les fonctionnalités du cerveau représente un défi majeur dans le domaine des technologies de l’information et de la communication. Plus particulièrement, l’ingénierie neuromorphique, qui vise à implémenter au niveau matériel les propriétés de traitement de l’information du cerveau, apparait une direction de recherche prometteuse. Parmi les différentes stratégies poursuivies dans ce domaine, la proposition de composant memristif a permis d’envisager la réalisation des fonctionnalités des synapses et de répondre potentiellement aux problématiques d’intégration. Dans cette dissertation, nous présenterons comment les fonctionnalités synaptiques avancées peuvent être réalisées à partir de composants mémoires memristifs. Nous présentons une revue de l’état de l’art dans le domaine de l’ingénierie neuromorphique. En nous intéressant à la physique des composants mémoires filamentaires de type cellules électrochimiques, nous démontrons comment les processus de mémoire à court terme et de mémoire à long terme présents dans les synapses biologiques peuvent être réalisés en contrôlant la croissance de filaments de type dendritiques. Ensuite nous implémentons dans ces composants une fonctionnalité synaptique basée sur la corrélation temporelle entre les signaux provenant des neurones d’entrée et de sortie. Ces deux approches sont ensuite analysées à partir d’un modèle inspiré de la biologie permettant de mettre l’accent sur l’analogie entre synapses biologiques et composants mémoires filamentaires. Finalement, à partir de cette approche de modélisation, nous évaluons les potentialités de ces composants mémoires pour la réalisation de fonctions neuromorphiques concrètes. / Replicating the computational functionalities of the brain remains one of the biggest challenges for the future of information and communication technologies. In this context, neuromorphic engineering appears a very promising direction. In this context memristive devices have been recently proposed for the implementation of synaptic functions, offering the required features and integration potentiality in a single component. In this dissertation, we present how advanced synaptic features can be implemented in memristive nanodevices. By exploiting the physical properties of filamentary switching, we successfully implemented a non-Hebbian plasticity form corresponding to the synaptic adaptation. We demonstrate that complex filament shape, such as dendritic paths of variable density and width, can reproduce short- and long- term processes observed in biological synapses and can be conveniently controlled by achieving a flexible way to program the device memory state and the relative state volatility. Then, we show that filamentary switching can be additionally controlled to reproduce a Hebbian plasticity form that corresponds to an increase of the synaptic weight when time correlation between pre- and post-neuron firing is experienced at the synaptic connection. We interpreted our results in the framework of a phenomenological model developed for biological synapses. Finally, we exploit this model to investigate how spike-based systems can be realized for memory and computing applications. These results pave the way for future engineering of neuromorphic computing systems, where complex behaviors of memristive physics can be exploited.

The common tomato of our garden belongs to the natural order Solanaceae and the genus Lycopersicum. The name from lykos, a wolf, and persica a peach, is given to it because of the supposed aphrodisiacal qualities, and the beauty of the fruit. By culture and use it is a vegetable, botanically it is a fruit and among the fruits, it is a berry being indehiscent, pulpy, with one or more seeds that are not stones. Though the tomato was not recognized as a valuable food until about a century ago, its merit is now universally accepted. Often it is referred to as "the poor man's orange" for it is rich in vitamins and in malic and citric acids, possessing besides, a fine appetizing flavor. The popularity of the tomato in man's diet is due to the fact that it is a most rewarding crop for the home garden. It grows well practically everywhere, affording high nutritional values. The demand for and acceptance of fresh tomato fruit is based largely on its nutritional value, flavor, aroma, taste, and other characteristics, such as color and texture. These quality criteria are dependent primarily on the structure and chemical composition of the fruit. The importance of quality in tomatoes beyond that which can be expressed in calories per gram, or even in vitamin content, is generally accepted in the United States. In order to meet this increasing demand throughout the year tomatoes often have to be grown in the greenhouses. Therefore, in commercial greenhouses, the tomato has replaced lettuce as the principal crop and it is likely to remain as an important underglass crop. Flavor is a composite of taste and odor. Odor is produced by many aromatic substances which are present in fruit. Flavor itself is a very complex sensation. The physiological basis of flavor perception is extremely complex and not clearly understood. Flavor chemistry is a comparatively new field of research. Tomato fruit quality is determined mainly by the sugar acid ratio, pectins, color, and flavor. Among these color and flavor are probably the most useful criteria for estimating maturity of tomato fruit. Higher quality is associated with redness of color and prominence of flavor. The flavor of a fruit becomes pronounced when the sugar content is at its maximum and the color of the skin acquires the richest shade. Isolation of volatile components from natural products is often difficult. Typical flavor and aroma of tomato fruit is primarily due to its volatile components. Neither complete analysis for nor synthesis of tomato flavor has been accomplished due to the marathon of problems associated with the extraction, separation, and identification techniques. The primary aim of this investigation was to separate and identify some of the major flavor and aroma components in the developing tomato fruit and also to assess the influence of certain physiological and biochemical changes on the biosynthesis of these components during fruit growth.

A number of methods for the analysis of free amino acids in melon fruit have been evaluated experimentally. Analysis of their tBDMS derivatives by GC (gas chromatography) was found to be the most suitable for the mix of free amino acid found in the melon matrix. It affords good yields of amino acid derivatives with excellent gas chromatographic properties and characteristic mass spectra. The single-step derivatization procedure is highly reproducible and allows simultaneous analysis of asparagine and glutamine together with their corresponding acids. Changes in amino acids, sugars, the principal acids, volatiles and minerals in the free form were studied in the fruit mesocarp during development, ripening and storage of the fruits. Sucrose was the principal sugar, absent in young fruit but showing a dramatic increase during ripening while the levels of fructose and glucose remained constant during the whole course of fruit growth or slightly decreased during ripening and storage. The quantitative determination of 22 free amino acids was achieved by GC analysis using the method developed. Total aroma volatiles were determined using a headspace-gas chromatographic technique. They increased and reached a maximum value just before fruit full slip. Most of the esters characteristic of melon aroma were absent in young fruit but developed at the ripening stage. Changes in the quantities of mineral nutrients present in the fruits were determined by ICP-AES analysis. The concentrations of most elements increased thoughout the fruit development except for Ca which decreased markedly and Cu which decreased during early growth then fluctuated around lower values later in the development stage. All of the above changes can be related to the metabolic activity during fruit growth and maturation. Statistical analysis showed changes in TV, TSS, TS, pH, some free amino acids and some minerals were strongly correlated. / Master of Science (Hons)

The extraction and quantitative analysis of low molar mass compounds in polymers is an analytical challenge. It is also important from a practical point of view because the low molar mass compounds in time will migrate from the polymers into the surrounding environment. It is especially important to gain knowledge about the migrating compounds in applications such as medical implants, packaging materials and car interiors. The main aim of this thesis was to develop headspace solid phase microextraction (HS-SPME) methods to meet this challenge. In addition, the work aimed to show the applicability of the methods developed in quality control of polymers, degradation studies and assessment of polymer durability. Factors influencing the extraction of low molar mass compounds from polyamide 6.6 were studied. Particular attention was paid to the matrix effects and to the establishment of headspace equilibrium of 2-cyclopentyl-cyclopentanone in solid polyamide. Hydrogen bonding and adsorption of analyte to the polar matrix was observed and found to cause exceedingly slow establishment of equilibrium. The adsorption could be eliminated by the addition of water, which replaced 2-cyclopentyl-cyclopentanone at the adsorption sites of the polyamide and made it possible to measure the 2-cyclopentyl-cyclopentanone content in polyamide 6.6 using multiple headspace solid-phase microextraction (MHS-SPME). A correlation between the emitted amount of 2-cyclopentyl-cyclopentanone and the amount 2-cyclopentyl-cyclopentanone in the material was found. The correlation was valid also under non-equilibrium conditions, which allows rapid assessment of the 2-cyclopentyl-cyclopentanone content in polyamide 6.6 using headspace sampling. 20 different low molar mass compounds were identified in virgin and recycled polyamide 6.6. The compounds could be classified into four groups: cyclic imides, pyridines, chain fragments and cyclopentanones. The structures of the degradation products imply that the thermo-oxidative degradation starts at the N-vicinal methyl group. Larger amounts of degradation products at lower degree of degradation were formed in recycled than in virgin polyamide 6.6. Thus, processing increases the susceptibility of polyamide 6.6 to thermal oxidation. The total amount of cyclopentanones was reduced upon processing and oxidation. Cyclopentanones are thus not thermo-oxidation products of polyamide 6.6. N-pentyl-succinimide showed the most significant increase due to oxidation and processing. The formation of N-pentyl-succinimide was in correlation with the simultaneous changes in tensile strength. The largest increase in N-pentyl-succinimide coincided with the largest drop in tensile strength.

Knowledge of the provenance of crustal volatiles and the processes by which they are released is extremely important for the dynamics of magmatic systems. Presented here are the results of multiple investigations, which aim to understand magmatic volatile contamination from contrasting but complementary perspectives. The main methodologies used include He and C isotope values and CO2/3He ratios of volcanic gases and fluids; simulation of magma-carbonate interaction using high-pressure high-temperature experimental petrology; X-ray microtomography of vesiculated xenoliths and computer modeling. Findings show that the contribution from upper crustal volatiles can be substantial, and is dependant on the upper crustal lithology on which a volcano lies, as well as the composition of the magma supplied. Carbonate dissolution in particular is strongly controlled by the viscosity of the host magma. The details of the breakdown of vesiculated xenoliths is complex but has wide reaching implications, ranging from the dissemination of crustally derived materials through a magma body to highlighting that crustal volatiles are largely unaccounted for in both individual volcano and global volatile budgets. In synthesizing the conclusions from each of the individual perspectives presented, I propose the contribution of volatiles from crustal sources to play a significant role in many geological systems. This volatile component should be taken into consideration in future research efforts.

Lipoxygenase (LOX)-derived oxylipins are known to play critical roles in defense against herbivores and pathogens. The objective of this study was to determine the biochemical, molecular and physiological roles of a specific maize lipoxygenase gene, ZmLOX10, with special emphasis on LOX10-derived oxylipins in plant-insect and plant-pathogen interactions. To achieve this goal, independent mutant alleles were generated and genetically advanced to create near-isogenic mutant and wild-type lines suitable for functional analysis. Here we provide genetic evidence that LOX10 is the sole LOX isoform in maize required for the biosynthesis of green leafy volatiles (GLV) in leaves and show that LOX10- mediated GLVs play a significant role in direct and indirect defense responses to insects through their regulation of jasmonic acid and volatile organic compound production. Contrary to the defensive role of LOX10 in plant-insect interactions, tests for susceptibility to fungal pathogens suggest that LOX10-mediated GLVs may contribute to the development of disease symptoms to the economically important maize pathogens, Aspergillus flavus and Colletotrichum graminicola. Specifically, LOX10-derived GLVs may facilitate aflatoxin accumulation in response to A. flavus infection and may play a positive role in anthracnose leaf blight and stalk rot caused by C. graminicola. Collectively, our results suggest that metabolites derived from GLV-regulated pathways have a significant impact on molecular plant-herbivore and plant-pathogen interactions.

<p>The extraction and quantitative analysis of low molar mass compounds in polymers is an analytical challenge. It is also important from a practical point of view because the low molar mass compounds in time will migrate from the polymers into the surrounding environment. It is especially important to gain knowledge about the migrating compounds in applications such as medical implants, packaging materials and car interiors. The main aim of this thesis was to develop headspace solid phase microextraction (HS-SPME) methods to meet this challenge. In addition, the work aimed to show the applicability of the methods developed in quality control of polymers, degradation studies and assessment of polymer durability. </p><p>Factors influencing the extraction of low molar mass compounds from polyamide 6.6 were studied. Particular attention was paid to the matrix effects and to the establishment of headspace equilibrium of 2-cyclopentyl-cyclopentanone in solid polyamide. Hydrogen bonding and adsorption of analyte to the polar matrix was observed and found to cause exceedingly slow establishment of equilibrium. The adsorption could be eliminated by the addition of water, which replaced 2-cyclopentyl-cyclopentanone at the adsorption sites of the polyamide and made it possible to measure the 2-cyclopentyl-cyclopentanone content in polyamide 6.6 using multiple headspace solid-phase microextraction (MHS-SPME). </p><p>A correlation between the emitted amount of 2-cyclopentyl-cyclopentanone and the amount 2-cyclopentyl-cyclopentanone in the material was found. The correlation was valid also under non-equilibrium conditions, which allows rapid assessment of the 2-cyclopentyl-cyclopentanone content in polyamide 6.6 using headspace sampling. </p><p>20 different low molar mass compounds were identified in virgin and recycled polyamide 6.6. The compounds could be classified into four groups: cyclic imides, pyridines, chain fragments and cyclopentanones. The structures of the degradation products imply that the thermo-oxidative degradation starts at the N-vicinal methyl group. Larger amounts of degradation products at lower degree of degradation were formed in recycled than in virgin polyamide 6.6. Thus, processing increases the susceptibility of polyamide 6.6 to thermal oxidation. The total amount of cyclopentanones was reduced upon processing and oxidation. Cyclopentanones are thus not thermo-oxidation products of polyamide 6.6. N-pentyl-succinimide showed the most significant increase due to oxidation and processing. The formation of N-pentyl-succinimide was in correlation with the simultaneous changes in tensile strength. The largest increase in N-pentyl-succinimide coincided with the largest drop in tensile strength.</p>

Xenoliths preserve evidence of magma-crust interactions in magmatic reservoirs and conduits. They reveal processes of partial melting of country rock, and disintegration into magma. Widespread evidence for frothy xenoliths in volcanic deposits exists, and these evidently indicate processes of gas liberation, bubble nucleation and bubble growth. This report focuses on textural analysis of frothy sandstone xenoliths from Krakatau in Indonesia, Cerro Negro in Nicaragua, Cerro Quemado in El Salvador and from Gran Canaria, Canary Islands, and involves attempts to experimentally reproduce xenolith textures. To achieve this, magmatic conditions acting upon country rock in volcanoes are simulated by subjecting sandstones to elevated temperature and pressure in closed system-autoclaves. Subsequent decompression imitates magma ascent following xenolith entrainment, and is largely responsible for the formation of frothy xenolith textures. The experiments show a range of successive features, such as partial melting, gas-pressure build up, bubble nucleation, growth and development of bubble networks. The experiments closely reproduced textures of natural xenoliths and help to assess the controlling P-T parameters that encourage efficient bubble growth. Conditions proved ideal between 850˚C and 870˚C and pressure release from 1 kbar. Such conditions limit bubble overprinting by secondary crystallization and melt infilling. Country rock lithology proved vital regarding gas pressure build-up and resulting bubble nucleation during decompression. In particular, increased water content and relict crystals in the melt produced appear to ease and promote gas liberation by enabling early and effective bubble nucleation. Moreover, experiments confirm a decisive role for bubble coalescence. These results attest to the great potential of country rock to develop interconnected bubble networks upon magma contact, exsolving large amounts of crustal volatiles into the magma. Volatile input involves a change in magma viscosity and thus an accompanied change in disruptive behaviour, and may hence be responsible for increased potential to cause explosive volcanic eruptions. Moreover, H2O and CO2 vapour are severe greenhouse gases, which seems to be added to the atmosphere from crustal rocks via recycling by volcanic activity, and may have yet underappreciated effects on Earth’s climate.

Les deux principales limitations des mémoires non-volatiles de type Flash à stockage de charges dans des nanocristaux en silicium sont la faible fenêtre mémoire et la dispersion des caractéristiques électriques due à la dispersion en taille des nanocristaux. Dans cette thèse, plusieurs solutions sont étudiées afin de remédier à ces deux défauts. Afin d'augmenter la fenêtre de programmation, une première approche consiste à augmenter la densité de stockage de charges grâce à l'utilisation d'une double couche de nanocristaux en silicium. Le fonctionnement et les performances électriques de ces dispositifs mémoires sont étudiés puis interprétés grâce à un modèle analytique. Une seconde approche, plus amont, consiste à utiliser des nanocristaux métalliques pour augmenter la quantité de charges piégées dans les nanocristaux. Le dépôt, la passivation et l'intégration de nanocristaux à caractère métallique (Pt, TiN, W) en tant que grille flottante dans un dispositif mémoire sont ainsi réalisés. Enfin, l'organisation " bottom-up " des nanocristaux est proposée comme une solution à la dispersion des caractéristiques électriques des dispositifs mémoires. Un procédé original de transfert et de gravure d'un masque auto-organisé à base de copolymères diblocs est développé.