• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 220
  • 61
  • 30
  • 22
  • 7
  • 7
  • 7
  • 3
  • 2
  • 2
  • 2
  • 2
  • 2
  • 2
  • 1
  • Tagged with
  • 433
  • 433
  • 61
  • 59
  • 49
  • 42
  • 41
  • 39
  • 38
  • 36
  • 34
  • 32
  • 30
  • 27
  • 25
  • 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.
351

Synthese metallorganischer Gerüstverbindungen und poröser Polymere für den Einsatz in der Katalyse, Sensorik und Stofftrennung

Nickerl, Georg 17 September 2014 (has links) (PDF)
Poröse Materialien zeichnen sich durch hohe spezifische Oberflächen bzw. hohe spezifische Porenvolumina aus. Dies macht sie zu geeigneten Kandidaten für die Gasspeicherung, Stofftrennung und die heterogene Katalyse, die Hauptanwendungsgebiete poröser Materialien. Um poröse Materialien hinsichtlich der eben genannten Anwendungsfelder zu optimieren ist es von entscheidender Bedeutung, sie hinsichtlich ihrer jeweiligen Anwendung maßzuschneidern. Eine Klasse hochporöser Materialien, bei der das Maßschneidern der Poren möglich ist, ist die der metallorganischen Gerüstverbindungen [engl. Metal-Organic Frameworks (MOFs)]. MOFs zeichnen sich durch einen modularen Aufbau aus, der ein systematisches Design der Poren erlaubt. Auch poröse Polymere können durch Funktionalisierung der entsprechenden Monomere hinsichtlich verschiedener Anwendungsgebiete gezielt synthetisiert werden. Ein Ziel dieser Arbeit war die Integration des Metalls Rhodium als knotenbildendes Element in ein MOF. Dazu wurde Rhodium(II)-acetat, welches bereits das Schaufelradmotiv enthält, mit den trifunktionellen Carbonsäuren Trimesinsäure und 4,4´,4´´ Benzen-1,3,5-triyl-tribenzoesäure zu den MOFs DUT 82 und DUT 83 umgesetzt. Das Schaufelradmotiv als sekundäre Baueinheit in DUT-82 konnte durch röntgenabsorptionspektroskopische Untersuchungen nachgewiesen werden. Nach überkritischem Trocknen gefolgt von thermischer Aktivierung zeigten DUT-82 und DUT-83 eine permanente Porosität mit spezifischen BET-Oberflächen von bis zu 1150 m2g-1. Weiterhin konnte für DUT-82 eine sehr hohe Affinität zu Kohlenmonoxid, die selten für MOFs beobachtet wird, nachgewiesen werden. Berechnungen der Adsorptionsenthalpie ergaben bei niedrigen Beladungen einen Wert von ungefähr 50 kJmol-1, was für eine Chemisorption von Kohlenmonoxid an DUT-82 bei niedrigen Drücken spricht. Weiterhin zeigten katalytische Untersuchungen, dass sich DUT-82 als heterogener Hydrierkatalysator eignet. In einer Modellreaktion konnte Styrol erfolgreich zu Ethylbenzen umgesetzt werden. In einem weiteren Teil der Arbeit sollte ein MOF synthetisiert werden, das Stabilität und eine hohe Kapazität für Schwefelwasserstoff miteinander vereint. Eine Klasse bereits bekannter MOFs mit hoher Stabilität basiert auf dem [Zr6O4(OH)4]12+-Cluster. Durch Kombination des [Zr6O4(OH)4]12+-Clusters mit Bipyridindicarboxylat konnte das MOF UiO-67(bipy) hergestellt werden, welches isostrukturell zu UiO 67 ist. Untersuchungen an UiO 67(bipy) zeigten, dass das unbeladene Netzwerk keinen Schwefelwasserstoff adsorbiert. Die Bipyridinfunktionalität wurde anschließend für die permanente Integration weiterer Metallzentren (Metall = Cu, Ni, Co) genutzt. Dazu wurde UiO-67(bipy) zu wässrigen oder ethanolischen Metallsalzlösungen gegeben und es kam zur Adsorption der Metallsalze aus der Flüssigphase. Durch die postsynthetische Integration der Metallsalze konnte die Adsorptionskapazität der resultierenden Metallsalz@UiO-67(bipy)-Materialien für Schwefelwasserstoff bis auf 8 Gew.% gesteigert werden. Neben Adsorption und Katalyse ist die Sensorik ein weiteres Anwendungsfeld von MOFs. Eine organische Einheit, die sich als sensitive Komponente für eine Integration in ein MOF anbietet, ist Dihydro-1,2,4,5-tetrazin, das zu 1,2,4,5-Tetrazin oxidiert werden kann. Das bemerkenswerte Merkmal dieser Reaktion ist der radikale Farbwechsel von Gelb nach Pink. Nach erfolgreicher Synthese der Dihydro-1,2,4,5-tetrazindicarbonsäure sollte sie durch Kombination mit dem [Zr6O4(OH)4]12+-Cluster zu einem UiO-66 analogen Netzwerk in ein stabiles Netzwerk integriert werden. Da die direkte Syntheseroute eines UiO-66 analogen Netzwerks nicht zum Erfolg führte, wurde die mildere Variante des Linkeraustauschs gewählt. Über diese Route konnte das Dihydro-1,2,4,5-tetrazindicarboxylat erfolgreich partiell in das UiO-66 Netzwerk integriert werden. Anschließende Untersuchungen zeigten, dass die in das Netzwerk eingebaute Dihydro-1,2,4,5-tetrazin-Einheit sowohl in der Flüssig- als auch in der Gasphase erfolgreich oxidiert werden kann, was durch UV/vis-Messungen belegt werden konnte. Eine weitere Klasse poröser Materialien, die hervorragende chemische Stabilität aufweist, ist die der konjugierten Triazin-Netzwerke. Sie entstehen durch Cyclotrimerisierung multifunktioneller Nitrile. Durch geschickte Wahl der Monomere ist eine Funktionalisierung der Triazin-Netzwerke möglich. Um ein chirales Triazin-Netzwerk zu synthetisieren, wurde Spirobiindan erfolgreich mit Nitrilgruppen funktionalisiert. Die Umsetzung des Monomers in einer Zinkchlorid-Schmelze führte zu porösen Polymeren mit spezifischen BET-Oberflächen von bis zu 1180 m2g 1. Dabei konnte die Porengrößenverteilung des Triazin-Netzwerkes durch Variation des Verhältnisses von Zinkchlorid zu Monomer gezielt eingestellt werden. Die Polymersynthese erfolgte mit einer racemischen Mischung des Monomers und führte somit zu einem achiralen Polymer. Erste Untersuchungen zeigten, dass eine Trennung des racemisch vorliegenden Monomers mittels Hochleistungsflüssigchromatographie möglich ist. Die Imidazoliumgruppe ist eine weitere Baueinheit, die in Triazin-Polymere integriert werden sollte, da sie leicht in ein N-Heterocyclisches Carben überführt werden kann. N-Neterocyclische Carbene können direkt als Katalysator bzw. als Ligand für eine Vielzahl von Metallen zur Generierung eines Katalysators genutzt werden. Über mehrstufige Synthesen konnten zwei nitrilfunktionalisierte Imidazoliumsalze hergestellt werden. Die anschließende Cyclotrimerisierung führte zu porösen Polymeren mit spezifischen BET-Oberflächen von bis zu 680 m2g-1. Erste katalytische Untersuchungen zum Einsatz dieser Triazin-Netzwerke in Umpolungsreaktionen von Zimtaldehyd mit 2,2,2 Trifluoracetophenon zeigten jedoch lediglich einen geringen Umsatz zum gewünschten Produkt.
352

Shocks, Superbubbles, and Filaments: Investigations into Large Scale Gas Motions in Giant Molecular Clouds

Pon, Andrew Richard 25 April 2013 (has links)
Giant molecular clouds (GMCs), out of which stars form, are complex, dynamic systems, which both influence and are shaped by the process of star formation. In this dissertation, I examine three different facets of the dynamical motions within GMCs. Collapse modes in different dimensional objects. Molecular clouds contain lower dimensional substructures, such as filaments and sheets. The collapse properties of finite filaments and sheets differ from those of spherical objects as well as infinite sheets and filaments. I examine the importance of local collapse modes of small central perturbations, relative to global collapse modes, in different dimensional objects to elucidate whether strong perturbations are required for molecular clouds to fragment to form stars. I also calculate the dependence of the global collapse timescale upon the aspect ratio of sheets and filaments. I find that lower dimensional objects are more readily fragmented, and that for a constant density, lower dimensional objects and clouds with larger aspect ratios collapse more slowly. An edge-driven collapse mode also exists in sheets and filaments and is most important in elongated filaments. The failure to consider the geometry of a gas cloud is shown to lead to an overestimation of the star formation rate by up to an order of magnitude. Molecular tracers of turbulent energy dissipation. Molecular clouds contain supersonic turbulence that simulations predict will decay rapidly via shocks. I use shock models to predict which species emit the majority of the turbulent energy dissipated in shocks and find that carbon monoxide, CO, is primarily responsible for radiating away this energy. By combining these shock models with estimates for the turbulent energy dissipation rate of molecular clouds, I predict the expected shock spectra of CO from molecular clouds. I compare the results of these shock models to predictions for the emission from the unshocked gas in GMCs and show that mid-to-high rotational transitions of CO (e.g., J = 8 to 7), should be dominated by shocked gas emission and should trace the turbulent energy being dissipated in molecular clouds. Orion-Eridanus superbubble. The nearby Orion star forming region has created a large bubble of hot plasma in the local interstellar medium referred to as the Orion-Eridanus superbubble. This bubble is unusual in that it is highly elongated, is believed to be oriented roughly parallel to the galactic plane, and contains bright filamentary features on the Eridanus side. I fit models for a wind driven bubble in an exponential atmosphere to the Orion-Eridanus superbubble and show that the elongation of the bubble cannot be explained by such a model in which the scale height of the galactic disk is the typical value of 150 pc. Either a much smaller scale height must be adopted or some additional physics must be added to the model. I also show that the Eridanus filaments cannot be equilibrium objects ionized by the Orion star forming region. / Graduate / 0606 / andyrpon@gmail.com
353

Vertical structure Of atmospheric trace gases over Southeast Australia

Pak, Bernard Ching-Yuen Unknown Date (has links) (PDF)
Trace gas (CO2 and its carbon and oxygen isotopes, CH4, CO, H2 and N2O) vertical profile data above Cape Grim, Tasmania for the period April 1992 to February 1997 are investigated. A climatology of the distribution of each trace gas has been compiled from statistical treatment of the raw data. These climatologies are useful for verification of transport model outputs. Here, the CO2 climatology is compared to simulation results from two transport models (Melbourne University Transport Model and TM2Z) using three different sets of CO2 fluxes separately (compiled with different methods by different authors). Large discrepancies are found between simulations and observations, especially in the free troposphere (4-6 km). By considering emission ratios, trajectories, satellite fire counts and simulation with biomass burning fluxes, the influence of tropical biomass burning plumes on the southeastern Australian region in the austral winter/spring is studied and quantified. This identification process requires a multiple-species approach where the large CO anomalies and the unexpected behaviour of H2 are most revealing. The frequent presence of burning plumes in the mid troposphere complicates one of the original motivations for the Cape Grim Overflight Program, which is to estimate the air-sea exchange of CO2 in this region. A suggestion arising from analysis of pre-1992 aircraft sampling in this region was that the regional CO2 air-sea flux south of Australia is exceptionally large.
354

Pollution de type urbaine au monoxyde de carbone et sensibilité du myocarde au syndrome d’ischémie-reperfusion : rôle cardioprotecteur de l’exercice / Simulated urban carbon monoxide air pollution and rat heart ischemia-reperfusion injury : cardioprotective effects of exercise

Meyer, Grégory 21 October 2010 (has links)
Diverses études épidémiologiques ont mis en évidence une relation étroite entre pollution urbaine au monoxyde de carbone (CO) et mortalité cardiovasculaire. Récemment il a été mis en évidence, chez le rat, qu'une exposition prolongée à ce polluant urbain avait pour conséquence le développement d'un phénotype cellulaire pathologique, pouvant influencer la vulnérabilité du coeur à un stress aigu. L'objectif de nos travaux était donc i) d'évaluer l'impact de la pollution au CO, sur la sensibilité du myocarde de rats au syndrome d'ischémie-reperfusion (IR) ; et ii) d'évaluer les effets potentiellement cardioprotecteurs d'un exercice pratiqué régulièrement à intensité modérée, sur le remodelage phénotypique cellulaire myocardique. Pour cela, 187 rats Wistar ont été séparés en 3 groupes : des rats contrôles, des rats exposés pendant 4 semaines au CO (30-100 ppm), et des rats entraînés en endurance avant d'être exposés au CO. La sensibilité à l'IR était évaluée par ischémie régionale réalisée sur modèle de coeur isolé perfusé de Langendorff. La fonction et les mouvements calciques de cardiomyocytes isolés était évalués en condition basale et consécutivement à un protocole d'anoxie-réoxygénation. Les résultats de ce travail confirment l'apparition d’un phénotype pathologique chez les rats exposés de façon prolongée au CO. Ce phénotype pathologique caractérisé dans notre travail par une altération de l’homéostasie calcique et du statut redox cellulaire ainsi qu'une expression tissulaire de iNOS apparait comme à l'origine de la plus grande vulnérabilité du coeur à un stress d’IR. Un autre résultat majeur de ce travail est qu’une stratégie de cardioprotection par un exercice d'intensité modérée pratiqué de manière régulière, permet de prévenir le remodelage pathologique cardiomyocytaire et ainsi l'augmentation de la sensibilité du myocarde à l'IR / Epidemiological studies suggested that carbon monoxide (CO) urban air pollution is mainly related to cardiovascular mortality. In addition, recent experimental studies have highlighted that CO exposure was responsible for the development of cardiomyocytes’ pathological remodeling, which can render the heart more vulnerable to acute stresses. Therefore, the aim of this experimental work was to i) evaluate the impact of prolonged exposure to simulated CO urban pollution on the sensitivity of the myocardium to IR ; and ii) evaluate potential cardioprotective effects of regular bouts of endurance training in this model. 187 Wistar rats were separated into 3 groups : control rats, CO rats exposed during 4 weeks to CO (30-100 ppm), and CO exercised rats. Myocardial sensibility to IR was evaluated with a regional ischemia performed on a Langendorff model of isolated heart. Moreover, the cardiomyocytes’ function and calcium handling were evaluated at basal conditions, following a protocol of cellular anoxia and reoxygenation. The results of this study confirm that chronic exposure to CO is responsible for cardiac phenotypic changes, which are characterized in this work by an imbalance in the cardiomyocytes’ oxidative status, an impairment of calcium handling and iNOS expression. These phenotypic changes were associated in this work with higher heart vulnerability to IR. Another major result of this study is that regular bouts of endurance training conducted prior to CO exposure prevented the pathological cardiac remodeling, consequently leading to higher heart vulnerability due to IR
355

Utilização de dados fornecidos por satélites para determinação de riscos ambientais / Use of satellite data to determine environmental risks

Vieira, Nilson Cesar Galvão [UNESP] 27 January 2016 (has links)
Submitted by NILSON CÉSAR GALVÃO VIEIRA null (nil_gv@yahoo.com.br) on 2016-03-10T01:50:31Z No. of bitstreams: 1 VIEIRA N.C.G..pdf: 2502695 bytes, checksum: 79c827f6494d3d8d91c8508084d0122b (MD5) / Approved for entry into archive by Juliano Benedito Ferreira (julianoferreira@reitoria.unesp.br) on 2016-03-10T20:11:35Z (GMT) No. of bitstreams: 1 vieira_ncg_me_guara.pdf: 2502695 bytes, checksum: 79c827f6494d3d8d91c8508084d0122b (MD5) / Made available in DSpace on 2016-03-10T20:11:35Z (GMT). No. of bitstreams: 1 vieira_ncg_me_guara.pdf: 2502695 bytes, checksum: 79c827f6494d3d8d91c8508084d0122b (MD5) Previous issue date: 2016-01-27 / Uma das principais causas de morbidade por problemas respiratórias em crianças e idosos é a poluição do ar. Os efeitos na saúde devido a exposição aos poluentes atmosféricos e a baixa qualidade do ar vem causando um aumento nas internações hospitalares. Esse estudo teve como objetivo desenvolver um modelo preditivo através do Modelo Linear Generalizado de Regressão de Poisson para analisar os efeitos da exposição de CO e PM2,5 sobre as internações hospitalares da rede pública no município de Rio Branco, AC, por problemas respiratórios em duas faixas etárias de ambos os sexos, de 0 a 14 anos e de iguais ou mais de 50 anos, durante o período de 01 de julho de 2012 a 30 de junho de 2013. A metodologia utilizada fundamenta-se na pesquisa de estudo ecológico de série temporal. A variável dependente considerada foi o número de internações hospitalares por doenças respiratórias CID 10 correspondentes aos códigos J 00 a J 99, cujos dados foram obtidos pelo DATASUS. As variáveis independentes consideradas foram a concentração diária de poluentes CO e PM2,5 (CCATT-BRAMS), número de queimadas (SISAM), umidade relativa do ar e temperatura mínima (INMET). Ajustes por tendência temporal e efeitos do calendário foram incluídos no modelo. Na análise unipoluente, devido a um incremento interquartil (25%-75%) para o CO (25 ppb) e PM2,5 (1,5 μg/m3 ), observou-se respectivamente, um aumento de 2,1% e 27,9% no aumento de internações para a faixa etária de iguais ou mais de 50 anos. E na análise multipoluente também com incremento interquartil, observou-se um aumento de 17,8% para a faixa etária de 0 a 14 anos e de 34,2% para a faixa etária de iguais ou mais de 50 anos. Os dados obtidos pelo aumento percentual forneceram uma variação de 1,13 % a 34,2 % no risco de internação, ou seja, aproximadamente 348 internações a mais, gerando para os cofres do município um custo de aproximadamente R$ 520 mil. / A major cause of morbidity due to respiratory problems in children and elderly is air pollution. Health effects due to exposure to air pollution and poor air quality is causing an increase in hospital admissions. This study aimed to develop a predictive model by Generalized Linear Model Poisson Regression to analyze the effects of CO exposure and PM2.5 on the hospitalization of the public network in Rio Branco, AC, for respiratory problems two age groups of both sexes, 0-14 years and of equal or more than 50 years during the period 1 July 2012 to 30 June 2013. The methodology used is based on the number of ecological research study temporal. The dependent variable was considered the number of hospital admissions for respiratory diseases ICD-10 codes corresponding to the J 00 and J 99, whose data were obtained by DATASUS. The independent variables considered were the daily concentration of pollutants CO and PM2.5 (CCATT-BRAMS), number of fires (SISAM), relative humidity and minimum temperature (INMET). Adjustments for time trend and calendar effects were included in the model. In unipoluente analysis, due to an increase interquartile (25% -75%) to CO (25 ppb) and PM2.5 (1.5 g / m3 ) was observed respectively, an increase of 2.1% and 27, 9% increase in hospitalizations for children aged equal or more than 50 years. And in multipoluente analysis also with interquartile increase, there was an increase of 17.8% for the age group 0-14 years and 34.2% for the age group of equal or more than 50 years. And in multipoluente analysis also with interquartile increase, there was an increase of 17.8% for the age group 0-14 years and 34.2 % for the age group of the same or more than 50 years. The data obtained by the percentage increase provided a range of 1.13 % to 34.2% in the risk of hospitalization, or approximately 348 hospitalizations more, generating for the municipal coffers a cost of approximately R$ 520 thousand.
356

AVALIAÇÃO DO USO DE ATMOSFERAS MODIFICADAS EM PORCIONADOS DE SUÍNOS / EVALUATION OF THE USE OF MODIFIED ATMOSPHERE IN PORK STEAKS

Magalhães, Alex Uzêda de 28 April 2006 (has links)
The quality of the pork meat is strongly influenced by the existent gaseous composition around it. With the objective of determining the effects of mixtures of gases on meat, steaks of 100g of loin (longuissimus dorsi) and rib of swine was conditioned in plastic packages with high barrier to gases, being injected different concentrations of CO2, N2, O2 and CO. The samples were stored at 4°C for 30 days, making possible the analysis of these atmospheres on parameters as color, odour, microbial flora, pH and lipid oxidation. For this essay, the following treatments were used: 15%O2, 5%CO2 and 80%N2 (T1); 20%CO2 and 80%N2 (T2); 70%CO2, 29,5%N2 and 0,5% CO (T3) and Vacuum (T4), with the packages being opened every 4 days so that the analyses were made. It was observed that the treatment T3 was the one that best conserved the steaks colour of swine. Referring to color, the treatment T3 was the one which presented the best results, differing significantly from the other treatments and maintaining the desirable brilliant red color in meat, demonstrating the influence of CO in this factor of quality. The pork rib, due to its bone structure, presented smaller shelf-life than the loin. This way, the modified atmosphere becomes one more option for the commercialization of red meat. / A qualidade da carne suína é fortemente influenciada pela composição gasosa existente em sua volta. Com o objetivo de determinar os efeitos de misturas de gases sobre a carne, porcionados de 100g de lombo (longuissimus dorsi) e costela de suínos foram acondicionados em embalagens plásticas com alta barreira a gases, sendo injetadas diferentes concentrações de CO2, N2, O2 e CO. As amostras foram estocadas a 4°C por 30 dias, possibilitando a análise da ação destas atmosferas sobre parâmetros como cor, odor, flora microbiana, pH e oxidação lipídica. Os porcionados foram divididos em quatro tratamentos: 15%O2, 5%CO2 e 80%N2 (T1); 20%CO2 e 80%N2 (T2); 70%CO2, 29,5%N2 e 0,5% CO (T3) e Vácuo (T4), sendo as embalagens abertas a cada 4 dias para que fossem efetuadas as análises. Foi observado que o tratamento T3 foi o que melhor influenciou a cor dos porcionados de suíno, conferindo uma vida de prateleira de 26 dias sob refrigeração. No que diz respeito à cor, o tratamento T3 foi o que apresentou os melhores resultados, diferindo significativamente dos demais tratamentos e mantendo a cor vermelha brilhante desejável em carnes, demonstrando a influência do CO neste fator da qualidade. A costela suína, em decorrência de sua matriz óssea, apresentou uma vida de prateleira menor do que o lombo. Desta forma, a atmosfera modificada passa a ser mais uma opção para a comercialização de carnes vermelhas.
357

Etude expérimentale et par modélisation de l'impact d'impuretés de l'hydrogène sur le fonctionnement des piles à combustible à membrane échangeuse de protons (PEMFC) / Impact of impurities in hydrogen on the operation of proton exchange membrane fuel cells (PEMFC)

Passot, Sylvain 09 October 2012 (has links)
Les piles à combustible à membrane échangeuse de protons (PEMFC) sont sensibles aux polluantsde l’hydrogène et de l’air. Cette étude s’est focalisée sur l’impact du monoxyde de carbone (CO) et dusulfure d’hydrogène (H2S), deux polluants majeurs dans l’hydrogène (H2), suivant une approchecombinant expériences et modélisation.Le volet expérimental a consisté à étudier l’effet de la concentration des polluants individuels et enmélange et des chargements en catalyseurs, pour différents modes de fonctionnement. Cette étude amis en lumière un impact sur les deux électrodes (anode et cathode) dû à la distribution hétérogènedes polluants à la surface de l’anode et à la désactivation de la partie de la cathode en regard. Deplus, dans le cas d’un empoisonnement par H2S, cette étude a montré que la tension de cellule atteintun état quasi-stationnaire, en mode galvanostatique, ce qui n’avait jamais été mis en évidence dans lalittérature.Dans l’approche de modélisation multi-échelles, le couplage de l’électrochimie et de la fluidique ainsique le développement de différentes « briques » du modèle ont permis de perfectionner la descriptiondes phénomènes physico-chimiques. Le modèle permet maintenant de simuler le fonctionnementd’une cellule de pile à combustible dans les conditions opératoires réelles, en intégrant les cinétiquesd’empoisonnement du platine par CO et H2S.Enfin, la comparaison des données expérimentales et des simulations a montré des résultats trèssatisfaisants appuyant certains arguments pour l’interprétation de l’impact des impuretés de H2. / Protons exchange membrane fuel cells (PEMFC) are sensitive to hydrogen and air pollutants. Thisstudy is focused on the impact of carbon monoxide (CO) and hydrogen sulfide (H2S) which are twomajor impurities of hydrogen. A combined experimental and modeling approach has been followed.The experimental part consisted in studying the effect of the concentration of individual pollutants andmixtures, and the effect of catalyst loading, for different operating modes. This work has highlighted animpact on both electrodes (anode and cathode) due to a heterogeneous distribution of the pollutantson the anodic surface area and to a deactivation of the opposite cathodic surface area. Furthermore,in the case of H2S poisoning, this study has shown that the cell voltage can reach a quasi-steadystate, in galvanostatic mode, which had never been highlighted in the literature.In the multi-scales modeling approach, a coupling of the electrochemistry and fluidics as well as thedevelopment of new modules of the model have allowed improving the description of the physicochemicalphenomena. As a consequence, the model simulates a fuel cell in real operating conditions,including the kinetics of platinum poisoning by CO and H2S.Finally, experimental data and simulated data were compared and they showed satisfactory anduseful results for the understanding of the impact of H2 impurities.
358

Poluição do ar por veículos automotores e tipos de tempo em áreas metropolitanas: a elaboração de um roteiro metodológico

Heiber, Rafael Figueiredo Duarte [UNESP] 28 March 2006 (has links) (PDF)
Made available in DSpace on 2014-06-11T19:27:49Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-03-28Bitstream added on 2014-06-13T20:17:17Z : No. of bitstreams: 1 heiber_rfd_me_rcla.pdf: 4605397 bytes, checksum: 97ee1a58d04ac33f90353e7fe3d2efe4 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / A sociedade contemporânea sofre intensos efeitos negativos e degradantes causados pela emissão de substâncias diversas na atmosfera. Doenças, redução das aptidões físicas, desconforto térmico, transformação de paisagens e mudanças climáticas que envolvem escalas do nível local ao global são apenas alguns exemplos da ação dos poluentes atmosféricos. Na Região Metropolitana de São Paulo (RMSP), expoente maior das áreas metropolitanas na América do Sul, o uso intenso dos veículos, congestionamentos e grandes percursos no espaço intra-urbano induzem episódios de grande poluição do ar. Nesta pesquisa é desenvolvido e apresentado um roteiro metodológico, baseado no paradigma do ritmo climático, para o estudo da poluição do ar causada por veículos automotores em áreas metropolitanas, confrontando episódios de intensa poluição e os tipos de tempo reinantes com uso da técnica de análise rítmica. O roteiro metodológico, aplicado à Região Metropolitana de São Paulo, com dados da estação Ibirapuera (CETESB) nos invernos de 2001, 2002, 2003 e 2004, mostrou que os episódios representativos de intensa poluição por monóxido de carbono (CO), material particulado (MP10) e dióxido de nitrogênio (NO2) foram caracterizados por ação anticiclonal que impediu as invasões frontais, com dias de calmarias que não dispersaram a poluição produzida dentro da RMSP. Os processos de tropicalização da MPA e de continetalização MPV, que influenciaram o aumento das temperaturas e a queda da umidade, representaram os dias de aumento de poluição do ar. Já os episódios de intensa poluição por ozônio (O3) foram caracterizados principalmtente pela influência de massas tropicais atlânticas e massas tropicais continentalizadas, com dias bastante ensolarados e com ventos que tiveram grande influência no transporte do ozônio e de seus precursores, trazidos das... . / The cotemporary society suffers many negative effects caused by the emission of substances in the atmosphere. Illnesses, reduction of the physical aptitudes, thermal discomfort, climatic transformation of landscapes and changes that involve scales of the local level to the global one are only some examples of the atmospheric pollutants action. At São Paulo Metropolitan Region (RMSP), the most important exponent of South American metropolitan areas, the intense use of motor vehicles, traffic jam and long distances in the urban space induce air pollution episodes. In this research it is developed and presented a methodology, based on the climate rhythm paradigm, for the study of the air pollution caused vehicles in metropolitan areas, collating episodes of intense pollution and types of weather using rhythmic analysis technique. The methodology was applied to the RMSP with the Ibirapuera station data (CETESB) in the 2001, 2002, 2003 and 2004 winters, showing that the representative episodes of intense pollution for carbon monoxide (CO), particulate matter (MP10) and nitrogen dioxide (NO2) had been characterized by stagnating anticyclones action that hindered the frontal invasions, with days of calmnesses that had not exhausted the produced pollution of the RMSP. The processes of tropicalization of the Atlantic Polar Air Mass (MPA), that had influenced the increase of the temperatures and the decrease of the humidity, had represented the days with high level of pollutants in the air. Already the episodes of intense pollution for ozone (O3) had been characterized mainly by the influence of Atlantic Tropical Air Mass (MTA) and Continental Tropical Air Mass (MTC) masses, with sufficiently sunny and hot days, winds that had great influence in the transport of ozone and its precursors from the industrial areas of ABCD region and Cubatão into the central area of the RMSP.
359

Estudo da eletro-oxidação da mistura Hsub(2)Co utilizando eletrocatalisadores à base de Pt/C e céria dopada com ítria ou rutênio para aplicação em células a combustível de membrana polimérica condutora de prótons / Study of electro-oxidation the mix Hsub(2)/CO using Pt/C etek and yttria or ruthenium doped ceria electrocatalysts for proton exchange membrane fuel cell

LULIO, LIGIA C.D. 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:34:46Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:03:29Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
360

Poluentes atmosf?ricos: mon?xido e di?xido de carbono no nordeste do Brasil

Pereira, Cleuber Dias 15 July 2011 (has links)
Made available in DSpace on 2015-02-24T20:19:46Z (GMT). No. of bitstreams: 1 CleuberDP_DISSERT.pdf: 1822708 bytes, checksum: c7e3fa0c90fc3f249a77e1e4b40508c3 (MD5) Previous issue date: 2011-07-15 / The interference of man in the middle atmosphere can be evidenced by the presence of carbon monoxide, gas associated with burning fossil fuels and carbon dioxide content, essential for respiration of plants and thermal balance of the Earth. In this thesis we initially evaluated the intensity of the spatial distribution of carbon monoxide in the Northeast of Brazil, and subsequently the behavior of temporal variations of the pollutants carbon monoxide and carbon dioxide in the atmospheric boundary layer Maxaranguape / RN. Research has shown that, driven by speculation and promoting the occupation of land for agriculture, cattle ranching and tourism in the Northeast of Brazil, the changes established by the man in the middle geomorphological affect the lower troposphere on a large scale, with a predominance of concentrations in central Pernambuco, Paraiba's south-central and central-west of Alagoas. However, the study of Maxaranguape / RN results showed little variation in carbon monoxide and carbon dioxide, with the speed of the wind persisting with values greater than 7.8 m / s, showing dispersion and diffusion of pollutants which resulted in faster renewal of local atmospheric air / As interfer?ncias do ser humano no meio atmosf?rico podem ser evidenciadas mediante a presen?a do mon?xido de carbono, g?s associado a queima de combust?veis f?sseis e do di?xido de carbono, conte?do fundamental para respira??o dos vegetais e para balan?o t?rmico da Terra. Nesta disserta??o inicialmente avaliou-se a intensidade da espacializa??o do mon?xido de carbono no Nordeste do Brasil e, posteriormente o comportamento das varia??es temporais dos contaminantes mon?xido e di?xido de carbono na camada limite atmosf?rica de Maxaranguape/RN. As pesquisas mostraram que, motivadas pela especula??o imobili?ria e promovendo a ocupa??o da terra para a explora??o agropecu?ria e tur?stica no Nordeste do Brasil, as mudan?as estabelecidas pelo homem no meio geomorfol?gico afetam a baixa troposfera em grande escala, com predomin?ncia de concentra??es na ?rea central de Pernambuco, centro-sul da Para?ba e centro-oeste de Alagoas. Entretanto, no estudo realizado em Maxaranguape/RN os resultados apresentaram pouca varia??o do mon?xido e di?xido de carbono, com a velocidade do vento persistindo com valores superiores a 7,8 m/s, mostrando dispers?o e difus?o dos poluentes o que propiciou maior rapidez na renova??o do ar atmosf?rico local

Page generated in 0.4507 seconds