• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 57
  • 13
  • 10
  • 6
  • 5
  • 4
  • 3
  • 2
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 129
  • 129
  • 55
  • 36
  • 20
  • 17
  • 17
  • 15
  • 14
  • 13
  • 13
  • 13
  • 13
  • 12
  • 12
  • 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.
121

Influência da poluição do ar na inflamação das vias aéreas e na atividade de doença de pacientes com lúpus eritematoso sistêmico juvenil / Influence of air pollution on airway inflammation and disease activity in childhood-systemic lupus erythematosus

Andressa Guariento Ferreira Alves 28 August 2018 (has links)
Lúpus eritematoso sistêmico juvenil é uma doença inflamatória autoimune multifatorial com elevação de citocinas inflamatórias e com gravidade variável. Estudos observaram associação entre exposição a poluição do ar e aumento do número de internações hospitalares devido à exacerbação das doenças reumáticas pediátricas e aumento no risco de crianças portadoras de lúpus eritematoso sistêmico juvenil apresentarem atividade de doença moderada /grave após exposição a material particulado e dióxido de nitrogênio. Exposição à poluição do ar pode acarretar agravo agudo em doenças reumatológicas pediátricas, incluindo lúpus eritematoso sistêmico juvenil. Objetivos: Avaliar o efeito da exposição real a poluentes atmosféricos sobre biomarcadores inflamatórios em condensado do ar exalado e sobre a fração de monóxido de nitrogênio em ar exalado em pacientes com lúpus eritematoso sistêmico juvenil. Avaliar ainda, a correlação entre os biomarcadores inflamatórios no ar exalado e atividade da doença. Métodos: Estudo longitudinal de painel de medidas repetidas realizado em 108 visitas consecutivas de pacientes com diagnóstico de lúpus eritematoso sistêmico juvenil sem doenças respiratórias. Por 4 semanas consecutivas, medidas diárias individuais de dióxido de nitrogênio, material particulado fino, temperatura ambiental e humidade relativa do ar foram obtidos. Este ciclo foi repetido a cada 2,5 meses ao longo de um ano, além disso, citocinas do condensado do ar exalado (interleucinas 6, 8, 17 e fator de necrose tumoral-alfa), fração exalada de monóxido de nitrogênio e parâmetros de atividade de doença foram coletados semanalmente. Modelos específicos de equação estimada generalizada foram usadas para avaliar o impacto destes poluentes no risco de Systemic Lupus Erythematosus Disease Activity Index 2000 >= 8, citocinas no condensado do ar exalado e fração exalada de monóxido de nitrogênio, considerando o efeito fixo para medidas repetidas. Os modelos foram ajustados para provas de fase aguda, índice de massa corpórea, infecções, medicações e variáveis meteorológicas. Resultados: Efeito positivo nas medidas de desfechos foi observado para um aumento do intervalo interquartil do material particulado fino (18.12 ?g/m3). Um aumento do intervalo interquartil na média móvel de 7 dias no material particulado fino (lag0 to lag6) foi associado a um aumento de 0.1pg/ml (95%IC:0.01;0.19) e 0.9pg/ml (95%IC:0.05;0,12) nos níveis de interleucina 17 e fator de necrose tumoral-? do condensado do ar exalado, respectivamente. Também foi observado um aumento no risco de Systemic Lupus Erythematosus Disease Activity Index 2000 >= 8 de 1.47(95%CI:1.10;1.84) associado ao aumento da média móvel de material particulado fino. Em adição, um efeito a curto prazo na fração exalada de monóxido de nitrogênio foi evidenciado, medida móvel de 3 dias do material particulado fino foi associada com um aumento de 0.75ppb (95%IC:0.38;1.29) na fração exalada de monóxido de nitrogênio. Conclusão: Exposição a partículas finas inaláveis pode aumentar a inflamação das vias aéreas e posterior inflamação sistêmica nos pacientes com lúpus eritematoso sistêmico juvenil / Systemic lupus erythematosus is an inflammatory multisystem, autoimmune disease with elevated inflammatory interleukins levels. Exposure to air pollution may trigger pulmonary inflammation/systemic inflammation. Objective: The objective of this study was to investigate the association between daily individual exposure to air pollutants and airway inflammation and disease activity in childhood-onset systemic lupus erythematosus patients. A longitudinal panel study was carried out in 108 consecutive appointments with childhood-onset systemic lupus erythematosus patients without respiratory diseases. Methods: Over four consecutive weeks, daily individual measures of nitrogen dioxide, fine particulate matter, ambient temperature, and humidity were obtained. This cycle was repeated every 2.5 months along 1 year, and cytokines of exhaled breath condensate (interleukins 6, 8, 17 and tumoral necrose factor-alpha), fractional exhaled nitrogen monoxide, and disease activity parameters were collected weekly. Specific generalized estimation equation models were used to assess the impact of these pollutants on the risk of Systemic Lupus Erythematous Disease Activity Index 2000 >= 8, exhaled breath condensate cytokines, and fractional exhaled nitrogen monoxide, considering the fixed effects for repetitive measurements. The models were adjusted for inflammatory indicators, body mass index, infections, medication, and weather variables. Results: An interquartile range increase in fine particulate matter 4-day moving average (18.12ug/m3) was associated with an increase of 0.05 pg/ml (95% CI 0.01; 0.09, p = 0.03) and 0.04 pg/ml (95% CI 0.02; 0.06, p = 0.01) in interleukin 17 and tumoral necrosis factor-alpha exhaled breath condensate levels, respectively. Additionally, a short-term effect on fractional exhaled nitrogen monoxide was observed: the fine particulate matter 3-day moving average was associated with a 0.75 ppb increase (95% CI 0.38; 1.29, p = 0.03) in fractional exhaled nitrogen monoxide. Also, an increase of 1.47 (95% CI 1.10; 1.84) in the risk of Systemic Lupus Erythematous Disease Activity Index 2000 >= 8 was associated with fine particulate matter 7-day moving average. Conclusion: Exposure to inhalable fine particles increases airway inflammation/pulmonary and then systemic inflammation in childhood-onset systemic lupus erythematosus patients
122

Oxidation of terpenes in indoor environments : A study of influencing factors

Pommer, Linda January 2003 (has links)
<p>In this thesis the oxidation of monoterpenes by O3 and NO2 and factors that influenced the oxidation were studied. In the environment both ozone (O3) and nitrogen dioxide (NO2) are present as oxidising gases, which causes sampling artefacts when using Tenax TA as an adsorbent to sample organic compounds in the air. A scrubber was developed to remove O3 and NO2 prior to the sampling tube, and artefacts during sampling were minimised when using the scrubber. The main organic compounds sampled in this thesis were two monoterpenes, alfa-pinene and delta-3-carene, due to their presence in both indoor and outdoor air. The recovery of the monoterpenes through the scrubber varied between 75-97% at relative humidities of 15-75%.</p><p>The reactions of alfa-pinene and delta-3-carene with O 3, NO2 and nitric oxide (NO) at different relative humidities (RHs) and reaction times were studied in a dark reaction chamber. The experiments were planned and performed according to an experimental design were the factors influencing the reaction (O3, NO2, NO, RH and reaction times) were varied between high and low levels. In the experiments up to 13% of the monoterpenes reacted when O3, NO2, and reaction time were at high levels, and NO, and RH were at low levels. In the evaluation eight and seven factors (including both single and interaction factors) were found to influence the amount of alfa-pinene and delta-3-carene reacted, respectively. The three most influencing factors for both of the monoterpenes were the O 3 level, the reaction time, and the RH. Increased O3 level and reaction time increased the amount of monoterpene reacted, and increased RH decreased the amount reacted.</p><p>A theoretical model of the reactions occurring in the reaction chamber was created. The amount of monoterpene reacted at different initial settings of O3, NO2, and NO were calculated, as well as the influence of different reaction pathways, and the concentrations of O3 and NO2, and NO at specific reaction times. The results of the theoretical model were that the reactivity of the gas mixture towards alfa-pinene and delta-3-carene was underestimated. But, the calculated concentrations of O3, NO2, and NO in the theoretical model were found to correspond to a high degree with experimental results performed under similar conditions. The possible associations between organic compounds in indoor air, building variables and the presence of sick building syndrome were studied using principal component analysis. The most complex model was able to separate 71% of the “sick” buildings from the “healthy” buildings. The most important variables that separated the “sick” buildings from the “healthy” buildings were a more frequent occurrence or a higher concentration of compounds with shorter retention times in the “sick” buildings.</p><p>The outcome of this thesis could be summarised as follows;</p><p>-</p><p>-</p><p>-</p><p>-</p>
123

ZnO nanoparticles : synthesis of Ga-doped ZnO, oxygen gas sensing and quantum chemical investigation

Hagelin, Alexander January 2011 (has links)
Doped ZnO nanoparticles were synthesized by three different methods – electrochemical deposition under oxidizing conditions (EDOC) , combustion method and wet chemical synthesis – for investigating the oxygen gas sensing response. Ga-doped ZnO was mostly synthesized but also In-doped ZnO was made. The samples were analyzed by XRD, SEM, EDX and TEM. Gas response curves are given alongside with Langmuir fitted curves and data for pure ZnO and Ga-doped ZnO. DFT quantum chemical investigation of cluster models ZnO nanoparticles were performed to evaluate defect effects and oxygen and nitrogen dioxide reactions with the ZnO surface. Defects were investigated by DOS and HOMO-LUMO plots , and are oxygen vacancy, zinc vacancy, zinc interstitial and gallium doping by replacing zinc with gallium. Oxygen and nitrogen dioxide reactions were investigated by computing Mulliken charges, bond lengths, DOS spectra and HOMO-LUMO plots.
124

Spectroscopie EUV résolue temporellement à l'échelle femtoseconde par imagerie de vecteur vitesse et génération d'harmoniques d'ordres élevés

Handschin, Charles 01 July 2013 (has links)
Cette thèse fait l'étude expérimentale de dynamiques de relaxations ultrarapides au sein d'atomes et de molécules (Ar, NO2, C2H2). Les méthodes expérimentales qui sont utilisées sont basées sur l'interaction d'un rayonnement laser avec le système atomique ou moléculaire étudié et font intervenir le processus de génération d'harmoniques d'ordres élevés, ainsi que la spectrométrie d'imagerie de vecteur vitesse. Au cours de cette thèse, deux approchesexpérimentales de type pompe-sonde ont été mises en œuvre. Une première approche exploitela sensibilité du processus de génération d'harmoniques à la structure électronique dumilieu pour la sonder. Cette méthode a été utilisée sur la molécule de dioxyde d'azote pourobserver sa relaxation électronique à travers l'intersection conique des états X2A1-A2B2suite à une excitation autour de 400 nm. Une seconde approche utilise le rayonnementharmonique comme source de photons dans le domaine de l'extrême ultraviolet (EUV)pour exciter ou sonder les espèces d'intérêt. Cette approche a été couplée avec l'utilisationd'un spectromètre d'imagerie de vecteur vitesse (VMIS), qui a été développé durant lathèse. Des expériences menées sur un système modèle comme l'argon ont permis de validerle dispositif expérimental, qui a ensuite été mis en application pour étudier la photodissociationde la molécule d'acétylène, après excitation autour de 9,3 eV du complexe deRydberg 3d-4s. Les deux méthodes mises en œuvre permettent toutes-deux de réaliserdes études dynamiques résolues en temps à l'échelle femtoseconde. / Ultrafast atomic and molecular dynamics (Ar, NO2, C2H2) have been experimentally studied during this PhD. The employed techniques use the laser interaction with the atomic or molecular system produced in gas phase. High harmonic generation (HHG) pump-probe studies allow resolving dynamics on a femtosecond scale. Two applications of high harmonic generation have been implemented here. In the first one, the harmonic generation process is the probe of a vibronic relaxation induced by a pump pulse. This application is currently labeled high harmonic spectroscopy. The sensibility of the high harmonic process to the geometry of the atomic or molecular orbitals is exploited to obtain information about the electronic structure of the generating medium. This method have been used to reveal the electronic relaxation of the nitrogen dioxide molecule (NO2) through the X2A1-A2B2 conical intersection.A second way consists to use the harmonic radiation like a source of XUV photons. The produced XUV radiation permits thus to reach electronically excited energy levels of atoms or molecules, pumping only with a one photon transition. XUV photons can also be used like a probe to ionize products of a molecular reaction. Velocity map imaging spectrometer (VMIS) have been designed and built to complete this fs-VUV source. Above threshold ionization (ATI) experiments and pump-probe XUV-400 nm studies have been performed on reference system like Argon to characterize the built experimental setup. The last excitation scheme has been also applied to study the photodissociation of the Acetylene excited in the 3d-4s Rydberg complex.
125

Genetic and environmental factors in asthma: a population based European study

Castro Giner, Francesc 20 November 2009 (has links)
L'asma és una malaltia d'etiologia complexa, formada per factors genètics i ambientals, on la interrelació de ambdós factors mitjançant interaccions gen-ambient juga un paper clau. L'objectiu d'aquesta tesi ha sigut aprofundir en el coneixement del paper dels polimorfismes genètics, i la seva interacció amb factors ambientals, en la ocurrència d'asma, atòpia i hiperreactivitat bronquial. Aquest objectiu ha estat desenvolupat a través de la replicació de variants genètiques prèviament identificades, l'avaluació d'interaccions gen-ambient i la identificació de nous gens de susceptibilitat mitjançant un disseny basat en el genotipatge de variants genètiques all llarg del genoma en pools d'ADN. La tesi ha estat majoritàriament duta a terme dins l'estudi European Community Respiratory Health Survey (ECRHS) que està comprès per 5.000 individus seguits durant 9 anys, pels quals es disposa d'un qüestionari complet sobre símptomes respiratoris, avaluacions clíniques, informació sobre exposicions ambientals i mostres de ADN. Aquesta tesi a replicat l'associació del polimorfismes dels gens TNFA i NPSR1 amb asma. A més s'han establert les interaccions entre TNFA i obesitat, NQO1 i contaminació atmosfèrica, i NPSR1 i edat d'inici d'asma. L'anàlisi de pools d' ADN ha permès associar la regió on es situa el gen SGK493 amb atòpia. Aquesta tesi contribueix al coneixement de l'etiologia d'asma amb la identificació i replicació d'associacions genètiques i interaccions gen-ambient. / Asthma is a disease with a complex etiology, involving multiple genetic and environmental factors, and with an important role of the interplay of these factors through gene-environment interactions. In this thesis I aimed to advance our knowledge on the importance of genetic polymorphisms and their interaction with environmental data for the occurrence of asthma and related phenotypes (atopy and bronchial hyperreactivity). This objective was developed through the replication of genetic associations previously reported, the assessment of gene-environment interactions and the identification of new susceptibility genes using genome-wide analysis based on a pooling DNA strategy. The thesis was, mostly, performed within the European Community Respiratory Health Survey (ECRHS). This cohort has information and DNA samples from approximately 5,000 adult subjects followed-up for 9 years, with extensive questionnaires on respiratory symptoms, clinical evaluations and information on environmental exposures. This thesis replicates previous effects on asthma of polymorphisms in TNFA and NPSR1 genes. In addition, interactions have been established between TNFA and obesity, NQO1 and air-pollution, and NPSR1 and age at onset of asthma. The approach based on genome-wide analysis of DNA pools identified the SGK493 region being associated with atopy. This thesis contributes to the understanding of the etiology of asthma through the identification and replication of genetic associations and gene-environment interactions.
126

A Radio Frequency Quadrupole Instrument for use with Accelerator Mass Spectrometry: Application to Low Kinetic Energy Reactive Isobar Suppression and Gas–phase Anion Reaction Studies

Eliades, John Alexander 21 August 2012 (has links)
A radio frequency (rf) quadrupole instrument, currently known as an Isobar Separator for Anions (ISA), has been integrated into an Accelerator Mass Spectrometry (AMS) system to facilitate anion–gas reactions before the tandem accelerator. An AMS Cs+ sputter source provided > 15 keV ions that were decelerated in the prototype ISA to < 20 eV for reaction in a single collision cell and re-accelerated for AMS analysis. Reaction based isobar suppression capabilities were assessed for smaller AMS systems and a new technique for gas–phase reaction studies was developed. Isobar suppression of 36S– and 12C3– for 36Cl analysis, and YF3– and ZrF3– for 90Sr analysis were studied in NO2 with deceleration to < 12 eV. Observed attenuation cross sections, σ [x 10^–15 cm^2], were σ(S– + NO2) = 6.6, σ(C3– + NO2) = 4.2, σ(YF3– + NO2) = 7.6, σ(ZrF3– + NO2) = 19. With 8 mTorr NO2, relative attenuations of S–/Cl– ~ 10^–6, C3–/Cl– ~ 10^–7, YF3–/SrF3– ~ 5 x 10^–5 and ZrF3–/SrF3– ~ 4 x 10^–6 were observed with Cl– ~ 30% and SrF3– > 90% transmission. Current isobar attenuation limits with < 1.75 MV accelerator terminal voltage and ppm impurity levels were calculated to be 36S–/Cl– ~ 4 x 10^–16, 12C3–/Cl– ~ 1.2 x 10^–16, 90YF3–/SrF3– ~ 10^–15 and 90ZrF3–/SrF3– ~ 10^–16. Using 1.75 MV, four 36Cl reference standards in the range 4 x 10^–13 < 36Cl/Cl < 4 x 10^–11 were analyzed with 8 mTorr NO2. The measured 36Cl/Cl ratios plotted very well against the accepted values. A sample impurity content S/Cl < 6 x 10^–5 was measured and a background level of 36S–/Cl < 9 x 10^–15 was determined. Useful currents of a wide variety of anions are produced in AMS sputter sources and molecules can be identified relatively unambiguously by stripping fragments from tandem accelerators. Reactions involving YF3–, ZrF3–, S– and SO– + NO2 in the ISA analyzed by AMS are described, and some interesting reactants are identified.
127

A Radio Frequency Quadrupole Instrument for use with Accelerator Mass Spectrometry: Application to Low Kinetic Energy Reactive Isobar Suppression and Gas–phase Anion Reaction Studies

Eliades, John Alexander 21 August 2012 (has links)
A radio frequency (rf) quadrupole instrument, currently known as an Isobar Separator for Anions (ISA), has been integrated into an Accelerator Mass Spectrometry (AMS) system to facilitate anion–gas reactions before the tandem accelerator. An AMS Cs+ sputter source provided > 15 keV ions that were decelerated in the prototype ISA to < 20 eV for reaction in a single collision cell and re-accelerated for AMS analysis. Reaction based isobar suppression capabilities were assessed for smaller AMS systems and a new technique for gas–phase reaction studies was developed. Isobar suppression of 36S– and 12C3– for 36Cl analysis, and YF3– and ZrF3– for 90Sr analysis were studied in NO2 with deceleration to < 12 eV. Observed attenuation cross sections, σ [x 10^–15 cm^2], were σ(S– + NO2) = 6.6, σ(C3– + NO2) = 4.2, σ(YF3– + NO2) = 7.6, σ(ZrF3– + NO2) = 19. With 8 mTorr NO2, relative attenuations of S–/Cl– ~ 10^–6, C3–/Cl– ~ 10^–7, YF3–/SrF3– ~ 5 x 10^–5 and ZrF3–/SrF3– ~ 4 x 10^–6 were observed with Cl– ~ 30% and SrF3– > 90% transmission. Current isobar attenuation limits with < 1.75 MV accelerator terminal voltage and ppm impurity levels were calculated to be 36S–/Cl– ~ 4 x 10^–16, 12C3–/Cl– ~ 1.2 x 10^–16, 90YF3–/SrF3– ~ 10^–15 and 90ZrF3–/SrF3– ~ 10^–16. Using 1.75 MV, four 36Cl reference standards in the range 4 x 10^–13 < 36Cl/Cl < 4 x 10^–11 were analyzed with 8 mTorr NO2. The measured 36Cl/Cl ratios plotted very well against the accepted values. A sample impurity content S/Cl < 6 x 10^–5 was measured and a background level of 36S–/Cl < 9 x 10^–15 was determined. Useful currents of a wide variety of anions are produced in AMS sputter sources and molecules can be identified relatively unambiguously by stripping fragments from tandem accelerators. Reactions involving YF3–, ZrF3–, S– and SO– + NO2 in the ISA analyzed by AMS are described, and some interesting reactants are identified.
128

Electron Transfer and Other Reactions Using Atomic Metal Anions

Butson, Jeffery M. 04 February 2014 (has links)
The atomic metal anions Rb-, Cs-, Cu-, Ag- and Fe- have been generated in the gas phase and reacted with various neutral reactants in a triple quadrupole mass spectrometer. The metal anions were formed via electrospray ionization of the metal-oxalate solutions and form in gas phase between the capillary and the first quadrupole. Neutral gas phase reactants investigated include NO, NO2, SO2, C6F5OH, C6F5NH2, C6F6, E-octafluoro-butene and 1,2,3/1,2,4/1,3,5 trifluoro-benzene. When possible, CBS-4M methods were used to suggest the lowest energy products based on relative energy. Observed reactions of atomic metal anions with the aforementioned neutral species include electron transfer and dissociative electron transfer to the neutral gas phase reactants. In addition, hydrogen abstraction and fluorine abstraction forming a neutral metal hydride or fluoride as well as the formation of multiply substituted metal-oxide/fluoride anions was also observed. Metal-complex anions observed from the gas phase reactions include CuF-,CuF2-,CuO-,CuO2-, FeO-, FeO2-, FeO3-, FeF-, FeF2-, FeF3-, CsF- and CsF2-.
129

Electron Transfer and Other Reactions Using Atomic Metal Anions

Butson, Jeffery M. January 2014 (has links)
The atomic metal anions Rb-, Cs-, Cu-, Ag- and Fe- have been generated in the gas phase and reacted with various neutral reactants in a triple quadrupole mass spectrometer. The metal anions were formed via electrospray ionization of the metal-oxalate solutions and form in gas phase between the capillary and the first quadrupole. Neutral gas phase reactants investigated include NO, NO2, SO2, C6F5OH, C6F5NH2, C6F6, E-octafluoro-butene and 1,2,3/1,2,4/1,3,5 trifluoro-benzene. When possible, CBS-4M methods were used to suggest the lowest energy products based on relative energy. Observed reactions of atomic metal anions with the aforementioned neutral species include electron transfer and dissociative electron transfer to the neutral gas phase reactants. In addition, hydrogen abstraction and fluorine abstraction forming a neutral metal hydride or fluoride as well as the formation of multiply substituted metal-oxide/fluoride anions was also observed. Metal-complex anions observed from the gas phase reactions include CuF-,CuF2-,CuO-,CuO2-, FeO-, FeO2-, FeO3-, FeF-, FeF2-, FeF3-, CsF- and CsF2-.

Page generated in 0.0918 seconds