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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Molecular and biochemical characterization of three lipoxygenases in maize

Nemchenko, Andriy 02 June 2009 (has links)
Most plant oxylipins, a large class of diverse oxygenated polyunsaturated fatty acids and their derivatives, are produced through the lipoxygenase (LOX) pathway. Recent progress in dicots has highlighted the biological roles of oxylipins in plant defense responses to pathogens and pests. In contrast, the physiological function of LOXs and their metabolites in monocots is poorly understood. We cloned and characterized three maize LOXs ZmLOX10 ZmLOX11 and ZmLOX12. Both ZmLOX10 and ZmLOX11 apeared to be 13-LOX, whereas ZmLOX12 is a unique 9-LOX. Whereas leaf was the preferential site of ZmLOX10 expression, ZmLOX11 was strongly expressed in silks. Induction of these ZmLOX10 and ZmLOX12 by wounding and defense-related compounds suggested their role in plant resistance mechanisms against pests and pathogens. Abscisic acid, however, was the only inducer of ZmLOX11 in leaves. Higher increase in ZmLOX10 transcripts in maize infected by fungus Cochliobolus carbonum implicated this gene in resistance responses to necrotrophic pathogens. In addition, ZmLOX10 was shown to be the first reported LOX to be regulated by a circadian clock. It was found that ZmLOX10 was also inducible by low temperatures. Phenotypical studies of wild type and mutant near isogenic lines showed that expression of ZmLOX12, specific to underground organs, was required for pathogenesis of F. verticillioides on maize mesocotyls.
22

An experimental study of liquid-phase separation in the systems Fe2SiO4-Fe3O4-KAlSi2O6-SiO2-H2O, Fe3O4-KAlSi2O6-SiO2-H2O and Fe3O4-Fe2O3-KAlSi2O6-SiO2-H2O with or without P, S, F, Cl or Ca0.5Na0.5Al1.5Si2.5O8: Implications for immiscibility in volatile-rich natural magmas

Lester, GREGORY W 11 April 2012 (has links)
Abstract Isobaric (200 MPa) experiments have been performed to investigate the effects of H2O alone or in combination with P, S, F or Cl on the phase relations and elemental and oxygen isotopic partitioning between immiscible silicate melts in the systems Fe2SiO4-Fe3O4-KAlSi2O6-SiO2, Fe3O4-KAlSi2O6-SiO2 and Fe3O4-Fe2O3-KAlSi2O6-SiO2 +/- plagioclase (An50). Experiments were heated in a newly-designed rapid-quench internally-heated pressure vessel at 1075, 1150 or 1200 oC for 2 hours. Water alone or in combination with P, S, or F significantly increases the temperature and composition range of two-liquid fields at fO2= NNO and MH buffers. Water-induced suppression of liquidus temperatures, considered with the effects of pressure on two-liquid fields stability in silicate melts, suggests that liquid phase separation may occur in some volatile-rich silicate magmas at pressures up to 2GPa. Two-liquid partition coefficients for Fe, Si, P and S correlate well with the degree of polymerization of the SiO2-rich conjugate melts and the data can be applied to assess the involvement of liquid-phase separation in the genesis of coexisting volatile-rich magmas. The partitioning of trace concentrations of selected HFSE, REE and transition elements between immiscible experimental volatile-rich melts at 1200 oC, 200 MPa has been determined at QFM, NNO and MH oxygen buffers. Water generally increases the partitioning of HFSE, REE and transition elements into the Fe-rich melt. Water alone, or combined with P or S, produces nearly parallel partitioning trends for HFSE and REE. Absolute partitioning values of transition elements are strongly dependent on the network-modifier composition of the melt. 18O in experimental immiscible melts with H2O or H2O and P or S partitions preferentially into the felsic conjugate melt (δ18O felsic melt- δ18O mafic melt values range from 0.4 to 0.8 permil) consistent with observations in anhydrous immiscible silicate melts. The expansion of the P-T-X-fO2 stability ranges of two- or three-liquid fields observed in the experimental melts demonstrates that liquid-immiscibility may be an important process in the evolution of some volatile-rich natural magmas. The results support an immiscible petrogenetic origin for some iron-oxide dominated, Kiruna-type, ore-deposits. / Thesis (Ph.D, Geological Sciences & Geological Engineering) -- Queen's University, 2012-04-10 15:06:35.797
23

From Cinder Cones to Subduction Zones: Volatile Recycling and Magma Formation beneath the Southern Cascade Arc

Walowski, Kristina 18 August 2015 (has links)
Volatiles (H2O, CO2, S, Cl) play a key role in magmatic processes at subduction zones. In this study, the dissolved volatile contents of olivine-hosted melt inclusions from cinder cones in the Lassen segment of the Cascade arc are used to investigate dehydration of subducted oceanic lithosphere, magma formation in the sub-arc mantle wedge, and mafic magma storage and evolution in the crust. Relatively young, hot oceanic lithosphere subducts beneath the Cascade arc. The hydrogen-isotope and trace-element compositions of melt inclusions, when integrated with thermo-petrologic modeling, demonstrate that fluids in Cascade magmas are sourced from hydrated peridotite in the deep slab interior and that the oceanic crustal part of the slab extensively dehydrates beneath the forearc. In contrast to their slab-derived H, the melt inclusions have B concentrations and isotope ratios that are similar to mid-ocean ridge basalt (MORB), requiring little to no slab contribution of B, which is also consistent with extensive dehydration of the downgoing plate before it reaches sub-arc depths. Correlations of volatile and trace element ratios in the melt inclusions (H2O/Ce, Cl/Nb, Sr/Nd) demonstrate that geochemical variability in the magmas is the result of variable amounts of addition of a hydrous subduction component to the mantle wedge. Radiogenic isotope ratios require that the subduction component has less radiogenic Sr and Pb and more radiogenic Nd than the Lassen sub-arc mantle and is therefore likely to be a partial melt of subducted Gorda MORB. These results provide evidence that chlorite-derived fluids from the deep slab interior flux-melt the oceanic crust, producing hydrous slab melts that migrate into the overlying mantle, where they react with peridotite to induce further melting. The basaltic magmas that erupted at Cinder Cone near Mt. Lassen trapped melt inclusions during olivine crystallization at ~7-15 km depth. The melt inclusion compositions require that two different mantle-derived magmas were involved in the eruption, and temporal changes show that arrival of the two batches correlates with two explosive phases of activity. Both magmas experienced rapid crustal contamination before erupting, illustrating the complexities of cinder cone eruptions. This dissertation includes previously published and unpublished co-authored material.
24

Ecologia quimica de Maxillariinae, Spathodea campanulata e Meliponiinae / Chemical ecology in Maxillariinae, Spathodea, campanulata and Meliponiinae

Flach, Adriana 28 July 2005 (has links)
Orientador: Anita Jocelyne Marsaioli / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-04T21:09:37Z (GMT). No. of bitstreams: 1 Flach_Adriana_D.pdf: 12925693 bytes, checksum: 5201c81faeca903146104615fff177a3 (MD5) Previous issue date: 2005 / Resumo: O presente trabalho foi dividido em três partes todas relacionadas a química das relações entre os seres vivos. Na primeira parte do trabalho estudou-se a química da polinização de orquídeas da subtribo Maxillariinae em termos da composição dos voláteis e recompensas florais coletadas pelos polinizadores. Discutiu-se também os compostos envolvidos na atração dos polinizadores de Mormolyca ringens e Trigonidium obtusum. Identificou-se, nesta etapa uma série de compostos: hidrocarbonetos, terpenos, álcoois, aldeídos, cetonas, ésteres, etc. Em um segundo momento determinou-se a composição química do néctar de Spathodea campanulata (Bignoniaceae), uma planta relatada como tóxica. Identificou-se, além de carboidratos, compostos secundários como terpenos, esteróides e carboidratos acetilados. Também foram identificados os constituintes voláteis: 1-octen-3-ol e 1-octen-3-ona. Na última parte do trabalho explorou-se a modificação química das ceras de duas espécies de abelhas que estabeleceram uma relação de convivência em um mesmo ninho. A composição química das ceras de operárias de colônias puras e de colônias mistas de M. scutellaris apresentaram perfis químicos diferentes produzindo nas colônias puras uma série de n-alcanos e n-alcenos enquanto que a colônia mista apresentou elevado percentual de acetato de triacontanila. As ceras das colônias de M. rufiventris apresentaram variações nas proporções de hidrocarbonetos. / Abstract: This work is presented in three distincts parts, ali of them concerning the chemistry involved in inter-specific relations. In the first part we discuss the pollination chemistry of orchids, subtribe Maxillariinae, in terms of floral volatiles and rewards collected by polinators. It is also discussed the compounds involved in polinattors attraction by Mormlyca rigens and Trigonidium obtusum. At this stage we have identified hydrocarbons, terpenes, alcohols, aldehydes, ketones, esters, etc. In the second chapter we analyzed the chemical composition of Spathodea campanulata (Bignoniaceae) nectar. Occurence wich has been considered toxic, due to the dead insects inside the flower. Morever, we identified some secondary metabolites as terpenes, steroids and acetylated sugars. Volatiles compounds as 1-octen-3-ol and 1-octen-3-one were also identified. The last part explores the chemical modification in waxes from two bees species that established coexistence in the same nest. We compare the chemical modification of waxes from worker bees in pure and mixed colonies of Meliponia rufiventris and Melipona scutellaris. Revealing that the ratio of alkanes, alkenes, were altered in M. rufiventris colonies. M. scutellaris pure colonie produce alkanes and alkanes and the chemistry of mixed colonies were altered producing high ratio of triacontanyl acetate. / Doutorado / Quimica Organica / Doutor em Ciências
25

Caracterização quimica da fração volatil e estudo do potencial antioxidante em pimentas do genero Capsicum / Chemical caracterization of volatiles compounds and study of antioxidant potential in Capsicum chili peppers

Bogusz Junior, Stanislau 03 October 2010 (has links)
Orientador: Helena Teixeira Godoy / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-15T20:37:31Z (GMT). No. of bitstreams: 1 BoguszJunior_Stanislau_D.pdf: 3727338 bytes, checksum: 9a31fb487f5c969747c0dc90cbde0d73 (MD5) Previous issue date: 2010 / Resumo: Nos últimos anos, no Brasil, o volume das exportações de pimentas Capsicum aumentou significativamente, fato que fez com que este produto agrícola se posicionasse como a segunda principal hortaliça exportada pelo país. Acredita-se que o crescimento nas exportações de pimentas esteja relacionado à avidez do mercado por este condimento que é amplamente empregado em formulações alimentícias industrializadas ou caseiras em diversos países. Além disso, a indústria de alimentos as emprega largamente como agente colorante e flavorizante em molhos, sopas, carnes processadas, lanches, doces e bebidas alcoólicas. Dada esta ampla utilização, pode-se considerar os caracteres sensoriais, proporcionados pelas pimentas, como um fator importante na qualidade sensorial dos alimentos que as empregam em suas formulações. Neste trabalho, o objetivo foi analisar a fração volátil e a fixa de três variedades de pimentas Capsicum brasileiras: malagueta (Capsicum frutescens), dedo-de-moça (Capsicum baccatum var. pendulum) e murupi (Capsicum chinense) em dois estádios de maturação (tecnológica e comercial). Para a fração volátil foi empregada microextração em fase sólida do espaço de cabeça (HS-SPME, ¿Headspace-Solid Phase Microextraction¿). Foram testadas as fibras: carboxen/polidimetilsiloxano (CAR/PDMS-75µm), polidimetilsiloxano (PDMS-100µm), divinilbenzeno/polidimetilsiloxano (DVB/PDMS-65µm), carbowax/divinilbenzeno (CW/DVB-70µm), e divinilbenzeno/carboxen/polidimetilsiloxano (DVB/CAR/PDMS-50/30µm), sendo que, esta última foi a que apresentou melhor eficiência na captura dos voláteis. Para esta fibra foram otimizadas as condições de extração utilizando delineamento composto central rotacional (DCCR). Empregando-se as condições ótimas de extração por HS-SPME e cromatografia gasosa (GC, ¿Gas Chromatography¿) hifenada a detector de ionização em chama (FID, ¿Flame Ionization detector¿) e espectrometria de massas (MS, ¿Mass Spectrometry¿), um total de 83 voláteis foram identificados na pimenta malagueta, em sua maioria ésteres e alcoóis; enquanto que na pimenta dedo-de-moça foram identificados 50 voláteis, em sua maioria monoterpenos e sesquiterpenos e na pimenta murupi foram identificados 79 voláteis, em sua maioria ésteres e sesquiterpenos. Também foi verificada uma diminuição das áreas dos picos dos voláteis nas três amostras, com o processo de maturação, principalmente nas amostras de pimenta dedo-de-moça, na qual a maioria dos voláteis desapareceu com o amadurecimento. Para a análise das frações voláteis das pimentas, também foram desenvolvidas e otimizadas metodologias de cromatografia gasosa bidimensional abrangente (GCxGC, ¿Comprehensive Two-Dimensional Gás Chromatography¿) hifenada aos detectores FID e espectrometria de massas por tempo de voo (TOF/MS, ¿Time of Flight Mass Spectrometry¿). Através destas técnicas multidimensionais um total de 220 compostos voláteis foi identificado (125 em pimenta malagueta, 123 em murupi e 75 em dedo-de-moça), destes compostos, 24 apresentaram potencial para discriminação das amostras e foram utilizados na análise de componentes principais (PCA). Os resultados do PCA permitiram discriminar as amostras entre si e também segundo seus estádios de maturação. As amostras de pimenta malagueta foram discriminadas principalmente por compostos pertencentes ao grupo dos ésteres ramificados; a pimenta murupi, por sesquiterpenos e a pimenta dedo-de-moça pela presença de aldeídos e metoxipirazina. Além disso, foi avaliado o potencial antioxidante das frações fixas das três pimentas, também em diferentes estádios de maturação e em diferentes épocas do ano. Nas análises foram empregados os ensaios de compostos fenólicos totais (CFT) por Folin-Ciocalteau, e atividade antioxidante pelos métodos de redução do ferro (FRAP- ¿Ferric Reducing Antioxidant Power¿) e de seqüestro do radical livre DPPH. (2,2-difenil-1-picrilhidrazil). Os maiores valores de CFT foram observados para as amostras imaturas do primeiro ano sendo que os valores médios de fenólicos totais aumentaram com o amadurecimento de todas as pimentas investigadas. Verificou-se também a existência de correlações positivas entre os resultados de CFT e os métodos de ação antioxidantes, sendo que, esta correlação foi maior para o método de FRAP do que para o de DPPH, provavelmente em função das particularidades de estereoquímica destes ensaios antioxidantes / Abstract: In the last years, in Brazil, the exportations of chili peppers has increased significantly, therefore, this agricultural product became the second largest vegetable exported by the country. It is believed, that growth in exports of chili peppers is related to the greed of the market for this spice that is widely used in food formulations in many different countries. Moreover, the food industry employs the chili peppers as coloring and flavoring agent in sauces, soups, processed meats, snacks, sweets and beverages. Given this widespread use can be considered the characters provided by the sensory chili peppers as an important factor in the sensory quality of food. The aim of this study was to evaluate the volatile and fixed fractions of three varieties of Brazilian chili peppers: ¿malagueta¿ (Capsicum frutescens), ¿dedo-de-moça¿ (Capsicum baccatum var. Pendulum) and ¿murupi¿ (Capsicum chinense) in two stages of maturation (technological and commercial). For the volatile fraction was used headspace-solid phase microextraction (HS-SPME). For the extraction phase, five fibers were tested: carboxen/polydimethylsiloxane (CAR/PDMS-75µm), polydimethiylsiloxane (PDMS-100µm) divinylbenzene/polydimethylsiloxane (DVB/PDMS-65µm), carbowax/divinylbenzene (CW/DVB-70µm), and divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS-50/30µm) that showed be the more efficient fiber in trapping the volatiles compounds. The optimization of the extraction conditions was carried out using multivariate strategies such as factorial design and response surface methodology. Using the optimal extraction by HS-SPME and gas chromatography (GC) detector coupled with flame ionization (FID) and mass spectrometry (MS), a total of 83 compounds were identified in malagueta, mostly esters and alcohols, while in dedo-de-moça 50 compounds were identified, mostly monoterpenes and sesquiterpenes and in murupi 79 compounds were identified, mostly esters and sesquiterpenes. Moreover, a decrease of peak areas with the maturation process of compounds was observed in the three samples, especially in samples of dedo-de-moça, in which most of the compounds disappeared during ripening. In the present work, methods for comprehensive two-dimensional gas chromatography (GC × GC) coupled to FID detectors and mass spectrometry time of flight (TOF/MS) were developed and optimized for the analysis of volatile fractions of chili peppers. Through these multidimensional techniques a total of 220 volatile compounds were identified, these compounds, 24 showed potential to discriminate the samples and were used in principal component analysis (PCA). The results of PCA show variability among samples and also according to their maturation stages. Samples of malagueta were discriminated mainly by compounds belonging to the group of branched esters, the murupi, by sesquiterpenes and the dedo-de-moça by the presence of aldehydes and methoxypyrazine. Also, in this study the antioxidant potential of fixed fractions of three peppers was evaluated, also in different stages of maturation and in different seasons. For analysis, the tests of total phenolic compounds (CFT) by Folin-Ciocalteau and antioxidant activity by the methods of reduction of iron (FRAP, "Ferric Reducing Antioxidant Potential¿) and DPPH radical scavenging assay. (2,2-diphenyl-1-picrylhydrazyl) were used. The highest values of CFT were observed for the immature samples of the first year and the medium values of total fenólicos increased with the ripening of all of the investigated peppers. The existence of positive correlations between the results of CFT and the antioxidant action methods was also verified, and, this correlation went larger for the method of FRAP than for the one of DPPH, probably in function of the particularities of stereochemistryof these antioxidant assays / Doutorado / Doutor em Ciência de Alimentos
26

Chemistry, mineralogy, and grain properties at Namib and High dunes, Bagnold dune field, Gale crater, Mars: A synthesis of Curiosity rover observations

Ehlmann, B. L., Edgett, K. S., Sutter, B., Achilles, C. N., Litvak, M. L., Lapotre, M. G. A., Sullivan, R., Fraeman, A. A., Arvidson, R. E., Blake, D. F., Bridges, N. T., Conrad, P. G., Cousin, A., Downs, R. T., Gabriel, T. S. J., Gellert, R., Hamilton, V. E., Hardgrove, C., Johnson, J. R., Kuhn, S., Mahaffy, P. R., Maurice, S., McHenry, M., Meslin, P.-Y., Ming, D. W., Minitti, M. E., Morookian, J. M., Morris, R. V., O'Connell-Cooper, C. D., Pinet, P. C., Rowland, S. K., Schröder, S., Siebach, K. L., Stein, N. T., Thompson, L. M., Vaniman, D. T., Vasavada, A. R., Wellington, D. F., Wiens, R. C., Yen, A. S. 12 1900 (has links)
The Mars Science Laboratory Curiosity rover performed coordinated measurements to examine the textures and compositions of aeolian sands in the active Bagnold dune field. The Bagnold sands are rounded to subrounded, very fine to medium sized (similar to 45-500m) with 6 distinct grain colors. In contrast to sands examined by Curiosity in a dust-covered, inactive bedform called Rocknest and soils at other landing sites, Bagnold sands are darker, less red, better sorted, have fewer silt-sized or smaller grains, and show no evidence for cohesion. Nevertheless, Bagnold mineralogy and Rocknest mineralogy are similar with plagioclase, olivine, and pyroxenes in similar proportions comprising >90% of crystalline phases, along with a substantial amorphous component (35%15%). Yet Bagnold and Rocknest bulk chemistry differ. Bagnold sands are Si enriched relative to other soils at Gale crater, and H2O, S, and Cl are lower relative to all previously measured Martian soils and most Gale crater rocks. Mg, Ni, Fe, and Mn are enriched in the coarse-sieved fraction of Bagnold sands, corroborated by visible/near-infrared spectra that suggest enrichment of olivine. Collectively, patterns in major element chemistry and volatile release data indicate two distinctive volatile reservoirs in Martian soils: (1) amorphous components in the sand-sized fraction (represented by Bagnold) that are Si-enriched, hydroxylated alteration products and/or H2O- or OH-bearing impact or volcanic glasses and (2) amorphous components in the fine fraction (<40m; represented by Rocknest and other bright soils) that are Fe, S, and Cl enriched with low Si and adsorbed and structural H2O. Plain Language Summary The Bagnold dune field is an active sand field with moving dunes and sits between the landing site of the Curiosity rover and rocks of interest higher up on Mount Sharp. When passing through the dune field, we used all of Curiosity's instruments to measure the chemistry, mineralogy, and grain size of sands in the Bagnold dune field in order to figure out where they came from, how the sands are transported, and what volatile materials (like water) lie within Martian soils. We found that the Bagnold sand dunes are very well sorted; no dusty materials are found within them, in stark contrast to soils seen previously with Curiosity and with rovers at other landing sites. We found that the coarser sand grains are enriched in the volcanic minerals olivine and pyroxene, confirming a prediction from orbit that wind-related activity seems to concentrate these phases. We also found that the dunes were much lower in water and other volatile elements like sulfur and chlorine versus all previous Mars soils. Using a combination of the rover's sieving system and chemical measurement tools, we figured out that two types of materials host water. In the first type of material, common in these sands, water is low in abundance (similar to 1%), very tightly bound to the grains, and is not released until temperatures >200 degrees C. In the second type of material, water is higher in abundance (2%) and more easily released by heating. Sieved water-bearing fine materials may be a useful resource for human explorers.
27

Fast Detection and Chemical Characterization of Gunshot Residues by CMV-GC-MS and LIBS

Tarifa, Anamary 06 November 2015 (has links)
Gunshot residue (GSR) is the term used to describe the particles originating from different parts of the firearm and ammunition during the discharge. A fast and practical field tool to detect the presence of GSR can assist law enforcement in the accurate identification of subjects. A novel field sampling device is presented for the first time for the fast detection and quantitation of volatile organic compounds (VOCs). The capillary microextraction of volatiles (CMV) is a headspace sampling technique that provides fast results (< 2 min. sampling time) and is reported as a versatile and high-efficiency sampling tool. The CMV device can be coupled to a Gas Chromatography-Mass Spectrometry (GC-MS) instrument by installation of a thermal separation probe in the injection port of the GC. An analytical method using the CMV device was developed for the detection of 17 compounds commonly found in polluted environments. The acceptability of the CMV as a field sampling method for the detection of VOCs is demonstrated by following the criteria established by the Environmental Protection Agency (EPA) compendium method TO-17. The CMV device was used, for the first time, for the detection of VOCs on swabs from the hands of shooters, and non-shooters and spent cartridges from different types of ammunition (i.e., pistol, rifle, and shotgun). The proposed method consists in the headspace extraction of VOCs in smokeless powders present in the propellant of ammunition. The sensitivity of this method was demonstrated with method detection limits (MDLs) 4-26 ng for diphenylamine (DPA), nitroglycerine (NG), 2,4-dinitrotoluene (2,4-DNT), and ethyl centralite (EC). In addition, a fast method was developed for the detection of the inorganic components (i.e., Ba, Pb, and Sb) characteristic of GSR presence by Laser Induced Breakdown Spectroscopy (LIBS). Advantages of LIBS include fast analysis (~ 12 seconds per sample) and good sensitivity, with expected MDLs in the range of 0.1-20 ng for target elements. Statistical analysis of the results using both techniques was performed to determine any correlation between the variables analyzed. This work demonstrates that the information collected from the analysis of organic components has the potential to improve the detection of GSR.
28

Volatiles in Subglacially Erupted Basaltic Glasses and Their Use in Reconstructing Paleo-Ice Thicknesses

Lee, Carver 24 March 2017 (has links)
Volatile concentrations in basaltic tuyas, edifices that form during a subglacial eruption and remain once the ice sheet has retreated, have been used to calculate the thickness of the overlying ice sheet at the onset of the eruption (Tuffen, 2010). However, subglacial eruptions are complex events and this technique does not always provide a clear answer (Schopka et al., 2006; Edwards et al., 2009). The purpose of this research is to evaluate this technique and investigate constraints on the quality of data collected by attempting to calculate the minimum ice thickness under which Hlöðufell, a tuya in south-central Iceland, erupted. Hlöðufell is a Holocene tuya located in the Western Rift Zone of Iceland, 9 km south from the modern edge of Langjökull ice cap. Dissolved H2O concentrations were measured using Fourier transform infrared spectroscopy (FTIR) and quenching pressures were calculated using the VolatileCalc pressure-solubility model (Newman and Lowenstern, 2002). Overlying ice thickness was calculated by relating quenching pressures, the density of ice, and the elevation of the sample. Water concentrations range from 0.068 –to 0.478 wt. % H2O, representing pressures ranging from 0.66 to 24.72 bars. These pressures represent ice thicknesses between 0 and 268 m thick. The minimum ice thickness level is represented in the lithofacies of the tuya by the passage zone, the transition between subaerial and subaqueous flows. The minimum ice thickness for Hlöðufell is ~ 500 m, much thicker than this study calculated using water concentrations. This indicates that the volatile concentrations in the basaltic glasses at Hlöðufell do not record the accurate quenching pressure. We interpret the overall low water concentrations to mean that our samples must have degassed at or close to atmospheric pressures at higher elevations, and flowed downslope into areas of thicker ice or deeper melt-water before quenching. These results show that subglacial eruptions and degassing processes are complex and variable and require further investigation.
29

Correlation of SPME-GC-MS Volatile Compounds with Descriptive Sensory Odor Analysis of Whole Wheat and Quinoa Flours in Accelerated Storage

Turner, Sarah Snow 01 June 2017 (has links)
The acceptability of whole grain flours during storage varies widely, as does the estimated shelf life of such flours, in part because acceptability is typically determined using subjective human sensory testing. Research is needed to establish more objective measures of acceptability. This study correlated the quantitative results of a descriptive odor sensory panel with volatile compounds determined by solid-phase microextraction-gas chromatograph-mass spectrometry (SPME-GC-MS). Whole wheat flour and quinoa flour were held at 40°C for up to 24 weeks to accelerate changes occurring during storage. Samples were collected every 4 weeks and placed in frozen storage. Thawed samples were then evaluated using SPME-GC-MS and descriptive sensory odor analysis. Significant correlations were found between 1-hexanol, 2-pentylfuran, phenol, hexanoic acid, and hexanal volatiles of whole wheat flour and the odor descriptor cardboard/stale. This indicates that SPME-GC-MS can be used as a less expensive, less time-consuming, more precise method to determine the acceptability of whole wheat flour during storage. Significant correlations were not present in the quinoa flour data, suggesting that SPME-GC-MS may not be preferable to human sensory odor analysis in determining acceptability of stored quinoa flour.
30

Origine des éléments volatils terrestres : apport de la géochimie des gaz rares / Origin of terrestrial volatile elements : constraints from noble gases

Peron, Sandrine 04 December 2018 (has links)
L’origine des éléments volatils, éléments avec des températures de condensation très basses comme l’eau, l’azote, le carbone et les gaz rares, sur Terre et sur les autres planètes telluriques reste mal comprise. Comprendre comment ces éléments sont arrivés sur Terre permettra de mieux appréhender les mécanismes de formation du système solaire. De par leur caractère inerte, les gaz rares (He, Ne, Ar, Kr, Xe) constituent des traceurs uniques des sources d’éléments volatils. L’étude de la composition en gaz rares du manteau terrestre s’avère donc essentielle afin de déterminer l’origine de ces éléments. L’objectif de ces travaux était de mesurer précisément la composition des isotopes stables et non-radiogéniques des gaz rares dans le manteau à partir de verres basaltiques. Ces derniers étant très souvent contaminés par l’air, des techniques d’analyse des gaz rares ont été mises en place pour s’affranchir de cette contamination. Des échantillons du volcan Fernandina du point chaud des Galápagos ont été étudiés par ablation laser. Les résultats montrent que le rapport 20Ne/22Ne des bulles est en moyenne de 12,65 ± 0,04 (1σ), ce qui est proche de la valeur estimée pour le pôle d’implantation du vent solaire (~ 12,7). Cette étude suggère donc que l’implantation du vent solaire sur les grains précurseurs de la Terre serait à l’origine des éléments volatils légers du manteau.Des données d’échantillons de popping rocks, aussi analysés par cette technique, indiquent que le manteau supérieur est hétérogène à petite échelle et pourraient impliquer le recyclage de gaz rares dans le manteau, y compris He, Ne, lors de la subduction. Un nouveau protocole d’analyse du Kr et Xe a été développé. Les résultats montrent les plus forts excès en 124Xe, 126Xe et 128Xe mesurés pour le manteau et suggèrent une source chondritique. Les isotopes fissiogéniques du xénon ont permis de dater le début du recyclage des éléments volatils dans le manteau aux alentours de 3 Ga. / The origin of volatiles, elements with low condensation temperatures such as water, nitrogen, carbon and noble gases, on Earth and other terrestrial planets is still misunderstood. Determining how these elements were delivered to the Earth will allow a better understanding of the processes of solar system formation. Due to their inertness, noble gases (He, Ne, Ar, Kr, Xe) constitute unique tracers of volatiles sources. Studying the noble gas composition of the Earth’s mantle is hence critical to unravel volatile origin. The aim of this PhD was to measure precisely the composition of non-radiogenic, stable noble gas isotopes in the mantle from basaltic glasses. The latter being very often contaminated by air, analytical techniques were thus set up to overcome this contamination.Samples from Fernandina volcano from the Galápagos hotspot were studied with laser ablation. The results show that the mean 20Ne/22Ne ratio in the vesicles is 12.65 ± 0.04 (1σ), close to the estimated value of the solar wind implanted end-member (~ 12,7). This study suggests that light volatiles in the mantle would originate from implantation of solar wind on the Earth’s precursors grains. Data from popping rock samples, also analyzed with this technique, indicate that the upper mantle is heterogeneous at small scale and that noble gases, included He, Ne, could be recycled into the mantle in subduction zones. A new protocol to analyse Kr and Xe was set up. The results show the highest measured excess in 124Xe, 126Xe and 128Xe for the mantle and suggest a chondritic source. The xenon fissiogenic isotopes allowed us to constrain the onset of volatile recycling in the mantle to around 3 Ga.

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