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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.
271

Etude phénoménologique des processus d‟allumage et de stabilisation dans les chambres de combustion turbulente swirlées. / Phenomenological study of ignition and stabilization processes for turbulent swirled flames

Frenillot, Jean-Philippe 08 April 2011 (has links)
Ce travail de recherche est consacré à l'étude des processus d'allumage et de stabilisation des flammes turbulentes en configuration aéronautique. Cette thèse, entièrement expérimentale, se base dans une première partie sur l'étude et la compréhension de l'effet des paramètres locaux (vitesse et concentration en combustible) et de l'historique du noyau de flamme au cours de sa propagation sur les statistiques d'allumage. Pour expliquer ces statistiques, des scénarios sont proposés et validés pour différentes configurations opératoires. La deuxième partie de la thèse est dédiée à l'amélioration de la stabilité des flammes kérosène/air par dopage en hydrogène. Nous avons montré qu'à même structure de flamme, l'amplitude des fluctuations de pression était abaissée par la présence d'hydrogène. / This research is dedicated to the study of turbulent flames ignition and stabilization processes in representatives' aircraft combustion chambers. This PHD thesis, fully experimental, is based on studying and understanding local parameters (velocity and fuel concentration) and historical effects of the flame kernel's environment during its propagation on ignition statistics. To explain this statistics, various scenarios arre proposed and discussed. In this way, we justify the existence of high and low efficiency areas thanks to a time development criterion of the flame kernel. The second part of this thesis is dedicated to flame stabilization improvment by using H2 enrichment. Turbulent kerosene/air flames have been doped in gaseous hydrogen. We demonstrate a reduction of pressure oscillations' amplitude for the same flame structure.
272

Untersuchung der Produktion reaktiver Sauerstoffspezies und der mitochondrialen Integrität bei Vorhofflimmern

Schwach, Dorina 31 August 2022 (has links)
Sowohl in der Human- als auch in der Veterinärmedizin ist das Vorhofflimmern (VF) eine der am häufigsten vorkommenden, klinisch signifikanten Arrhythmien. Die Folgen und Auswirkungen der Erkrankung sind vielfältig und für die Behandlung entscheidend. Die auf molekularbiologischer Ebene ablaufenden Mechanismen sind trotz jahrelanger Forschung noch weitgehend unbekannt. Studien an menschlichem Gewebe sind selten. Vergleichende Aspekte zwischen Tier und Mensch sind in der Literatur nicht beschrieben. Ziel der Arbeit war es, die Produktion von reaktiven Sauerstoffspezies (ROS) sowie ROS-induzierte und –assoziierte zelluläre Mechanismen bei Patienten mit VF zu analysieren. ROS werden sowohl während des physiologischen oxidativen Metabolismus der Mitochondrien als auch in zellulärer Reaktion auf pathogene Agenzien gebildet. Zusätzlich sollte untersucht werden, ob das Thioredoxin-System (TRX-System), das als ROS-Scavenger fungiert, ein neuer Ansatzpunkt für eine medikamentöse Therapie sein könnte. Bereits vorhandene tierexperimentelle und humane Studien zum atrialen Remodeling (AR) und VF wurden besonders berücksichtigt und hinsichtlich ihrer Übertragbarkeit, sowie Vergleichbarkeit zwischen Tier und Mensch diskutiert. Im Rahmen der Arbeit wurden 30 linke Herzohrgewebeproben von humanen Patienten mit VF (n = 15) und von Patienten mit Sinusrhythmus (SR) (n = 15) untersucht. Die Enzymaktivitäten der NADPH-Oxidase (NOX), Xanthin-Oxidase (XO), Superoxiddismutase (SOD) und Katalase wurden mithilfe von photometrischen Absorptionsmessungen und die mitochondriale Schädigung anhand des Auftretens einer 4977 Basenpaardeletion (bp-Deletion) untersucht. Die Freisetzung des Apoptose-induzierenden Faktors (AIF) und von Cytochrom C ins Zytosol sowie die Veränderungen des TRX-Systems wurden mittels Enzyme-linked Immunosorbent Assay (ELISA) und Western Blot analysiert. Die Signifikanz von Unterschieden zwischen den Versuchsgruppen wurde mithilfe des T-Tests bei unabhängigen Stichproben analysiert. Als Signifikanzniveau wurde ein p-Wert von ≤ 0,05 definiert. Der Levene-Test wurde angewandt, um Varianzgleichheiten zu prüfen. Der Anteil der männlichen Patienten in der VF-Gruppe war größer als der Anteil der weiblichen Patienten (11 von 15 Patienten). Das durchschnittliche Alter der VF- und SR-Patienten war vergleichbar (65,9 Jahre). Weder die Aktivität der ROS-produzierenden Enzyme NOX und XO, noch die antioxidativ wirkenden Enzyme SOD und Katalase unterschieden sich signifikant zwischen Patienten mit und ohne VF. Die Literaturrecherche ergab insbesondere in von VF geschädigten Herzohren vom Schwein erhöhte Enzymaktivitäten der NOX und XO. Die zytosolische Freisetzung von AIF und Cytochrom C bei VF- und SR-Patienten waren ebenso wie das TRX-System vergleichbar. Ein statistisch signifikanter Unterschied zwischen den VF- und SR-Patienten konnte nicht nachgewiesen werden. Die in dieser Studie untersuchte 4977 bp-Deletion war seltener bei VF-Patienten als bei SR-Patienten nachweisbar (p = 0,028). Das statistisch signifikante, häufigere Auftreten der 4977 bp-Deletion in der SR-Gruppe könnte dem Umstand der im Allgemeinen in die Studie inkludierten kranken Patienten geschuldet sein. Die Ergebnisse dieser Arbeit leisten einen wichtigen Beitrag auf der Suche nach einer adäquaten Therapie der Erkrankung des VF sowohl in der Veterinärmedizin als auch in der Humanmedizin, denn es konnte gezeigt werden, dass ROS-induzierte und -assoziierte zelluläre Mechanismen vermutlich keine große Rolle in der Pathophysiologie dieser Erkrankung spielen. Nichtsdestotrotz sind sowohl in der Human- als auch in der Veterinärmedizin weitere Studien nötig, um eine adäquate Behandlung des VF zu gewährleisten und die Lebensqualität Betroffener zu verbessern.:1 Einführung 1.1 VF in der Humanmedizin 1.2 VF in der Veterinärmedizin 1.3 Pathophysiologie des VF 1.4 Oxidativer Stress und dessen Rolle in der Pathogenese des VF 1.5 Biomarker des oxidativen Stress 1.6 Apoptose und Hypoxie im Rahmen des VF 1.7 ROS- und DNA-Schäden 1.8 Einfluss des Thioredoxin-Systems bei oxidativem Stress 2 Zielsetzung 3 Material und Methoden 3.1 Geräte 3.2 Hilfsmittel und Verbrauchsmaterialien 3.3 Chemikalien und Reagenzien 3.4 Herzohrproben 3.4.1 Proteinextraktion Herzohrproben 3.4.2 Proteinkonzentrationsbestimmung der Herzohrgewebelysate 3.5 Bestimmung der Enzymaktivitäten 3.5.1 NOX-Aktivität 3.5.2 XO-Aktivität 3.5.3 SOD-Aktivität 3.5.4 Katalase-Aktivität 3.6 ELISA 3.6.1 AIF 3.6.2 Cytochrom C 3.6.3 HIF-1α 3.7 PCR 3.7.1 Isolierung der mtDNA 3.7.2 Bestimmung von Reinheit und Konzentration der mtDNA 3.7.3 Durchführung der PCR 3.7.4 Agarose-Gelelektrophorese 3.7.5 Isolierung der nucDNA 3.8. RT-PCR 3.9 SDS-PAGE und Western Blot 3.9.1 SDS-PAGE 3.9.2 Western Blot 3.10 Statistische Auswertung 4 Ergebnisse 4.1 Gruppencharakteristika 4.2 Enzymkinetik 4.2.1 NOX-Aktivität 4.2.2 XO-Aktivität 4.2.3 SOD-Aktivität 4.2.4 Katalase-Aktivität 4.3 Quantifizierung der AIF-, Cytochrom C- und HIF-1α-Konzentrationen mittels ELISA 4.3.1 AIF 4.3.2 Cytochrom C 4.3.3 HIF-1α 4.4 Nachweis der 4977 bp-Deletion in der humanen mtDNA mittels PCR 4.5 Quantifizierung des realtiven mtDNA-Gehaltes mittels RT-PCR 4.6 Proteinexpressionsmessungen von TRX 1, TXNIP und ITCH mittels Western Blot 4.6.1 TRX1 4.6.2 TXNIP 4.6.3 ITCH 5 Diskussion 6 Zusammenfassung 7 Summary 8 Literaturverzeichnis
273

External costs of the Dieselgate – Peccadillo or substantial consequences?

Baumgärtner, Frank, Letmathe, Peter 15 August 2022 (has links)
The Dieselgate has changed the public view of diesel powertrains and local authorities have issued first driving bans on diesel cars in Germany. Nevertheless, a systematic calculation of the external costs of the Dieselgate considering different car models and a variety of emissions has not yet been conducted. We compare the results, which reflect emissions under test bench conditions, with those of diesel cars under the assumption that NOX emissions reflect realistic driving behavior. We find that diesel cars with idealized emissions are superior to petrol cars with regard to external costs and that electric cars have only partially lower external costs than diesel cars. However, when realistic driving behaviors are considered, diesel engines constitute the worst powertrain in all cases. Our results show that the Dieselgate has led to substantially higher external costs than cars which would comply with environmental regulations under realistic driving conditions.
274

A Study Of Central Florida Nonroad Voc And Nos Emissions And Potential Actions To Reduce Emissions

Radford, Michael 01 January 2009 (has links)
Ground-level ozone is harmful to the human respiratory system, as well as the environment. The national EPA 8-hour ozone standard for ground-level ozone was reduced from 85 parts per billion (ppb) to 75 ppb in 2008, and trends from previous years show that some of the counties in Central Florida could be in danger of violation. Violation means "non attainment" status; in which the county is ordered by EPA to develop specific implementation plans to reduce its emissions. The objective of this study was to compile an emissions inventory of volatile organic compounds (VOCs) and nitrogen oxides (NOx) from nonroad equipment in Osceola, Seminole, and Orange Counties (OSO) in Central Florida, and to develop possible action steps to reduce those emissions. This is important because VOC and NOx emissions are precursors to ground-level ozone. Thus, compiling emissions inventories is important to identify high VOC and NOx emitters. Mobile and point sources have long been the highest emitters of VOC and NOx and have therefore been targeted and monitored since the Clean Air Act of 1970, but the nonroad sources (such as construction and lawn equipment) have only been regulated since the 1990s. Using the NONROAD and NMIM modeling programs, the highest nonroad emitters of VOC for Central Florida were found to be lawn/garden equipment, and boating equipment, emitting a combined percentage of 77% of the total nonroad mobile source VOC. Construction equipment contributed 67% of the total nonroad mobile source emissions of NOx in Central Florida. The components of these categories were also analyzed to find the largest individual sources of VOC and NOx. Of the individual sources, lawn mowers and outboard boat engines were found to be the largest sources of VOCs. Of the NOx sources, all the construction equipment components had a relatively similar level of NOx emissions. Next, action steps were developed to reduce emissions, focusing on the high emitters, along with an estimated cost and feasibility for each measure. Of these steps, implementing a ban on leafblowers, and reducing use of lawn mowers, edgers, trimmers, etc. seemed to be the most effective for reducing VOCs. Although these are effective measures, the cost and feasibility of both pose challenges. The best action step for reducing NOx emissions in construction equipment seemed to be by simply reducing idling of equipment on job sites. This also poses challenges in feasibility and enforcement by management. Further, constant on/off cycles could result in decreasing the useful life of the older construction equipment. Finally, a survey was conducted with various construction managers and companies to find out the typical equipment and quantity needed for land clearing/grubbing, as well as the typical use, idling time, and total project time for each piece of equipment on a 10-acre site, under various conditions. The purpose of the study was to develop a rough estimate for the average amount of VOC and NOx emissions that will be produced per acre of land clearing activities, and to estimate the emissions reductions and cost savings if idling of the equipment was reduced.
275

Fractional Oxidation State Control of Three-Way Catalyst with Stoichiometric Spark-Ignition Natural Gas Engines incorporating Cylinder Deactivation

Yunpeng Xu (14266550) 15 December 2022 (has links)
<p>A novel two-loop estimation and control strategy is proposed to reduce the natural gas (NG) spark-ignition (SI) engine tail pipe emissions, with focus on the outer loop development. In the outer loop, an fractional oxidation state (FOS) estimator consisting of a three-way catalyst (TWC) model and an extended Kalman-filter is used to estimate the real-time TWC's FOS, and a robust controller is used to control the first-half TWC's FOS by manipulating the desired engine lambda (i.e., air–fuel equivalence ratio; lambda=1 at stoichiometry). The outer loop estimator and controller are combined with an industry-production baseline inner loop controller, which controls the engine $\lambda$ based on the desired lambda value. This novel two-loop control strategy reduces more CH4 and NOx emissions over no-outer-loop control strategy and the conventional two-loop control strategies through simulation. </p> <p><br></p> <p>Engine with and without fuel cut-off are both investigated. Although fuel cut-off brings better fuel economy, it also over-oxidizes the TWC during fuel cut events, which makes the FOS-based controller's competence in NOx reduction over non-FOS-based controllers less significant. By comparing simulation results with and without fuel cut-off, it shows huge potential for much better emission result if fuel cut-off's side effect can be alleviated. Considering that fuel cut-off generally being cutting engine fueling during zero load periods and introducing unreacted oxygen into the after-treatment system, the best way of dealing with the issue is to cut off or reduce the oxygen input to the TWC during those events. Several advanced engine technologies such as cylinder deactivation and exhaust gas re-circulation are good candidates to approach this issue. </p> <p><br></p> <p>An industry-production Cummins B6.7N natural gas SI engine was installed in the Ray W. Herrick Laboratories for study of variable valve actuation (VVA) technology, for the purpose of evaluating/improving SI engine's fuel efficiency, emission reduction, and engine knock resistance. A one-dimensional, physics-based natural gas SI engine model was investigated and calibrated in GT-Power software. To calculate the burn rates in the cylinder, three different pressure analysis methods were investigated and implemented. It is observed that all six cylinders' pressure curves are different, which in turn render different burn rates cylinder-to-cylinder. Cylinder with a higher peak cylinder pressure has a faster burn rate. Each operating condition has its unique pressure curve, and their burn rates are different under different operating conditions. Considering that the burn rate profile can vary cylinder-to-cylinder and operation-to-operation, to make the GT combustion model work for a larger range of loads, a fixed burn rate model may help in the preliminary research phase, but a predictive combustion model is more preferable.</p> <p><br></p> <p>The GT-Power model's VVA capability is investigated, where intake valve closure (IVC) modulation and cylinder de-activation (CDA) are built and analyzed. To mitigate TWC's over-oxidation issue during engine's fuel cut-off events, the CDA is implemented and simulated to demonstrate its benefit on further emission and fuel consumption reductions.</p>
276

Multi-Physics Engine Simulation Framework for Drive Cycle Emissions Prediction. Development and Validation of a Framework for Transient Drive Cycle NOx Prediction Modelling based on Combining 1-D and 0-D Internal Combustion Engine Simulation and Statistical Meta-Modelling

Korsunovs, Aleksandrs January 2019 (has links)
The full text will be available at the end of the embargo period: 4th Aug 2025
277

Structure, Stability and Emissions of Lean Direct Injection Combustion, including a Novel Multi-Point LDI System for NOx Reduction

Villalva Gómez, Rodrigo January 2013 (has links)
No description available.
278

Design and Development of a Novel Injector (Micro-Mixer) with Porous Injection Technology (PIT) for Land-Based Gas Turbine Combustors

Ibrahim, Mahmoud I., Ph.D. 11 October 2018 (has links)
No description available.
279

A crank angle resolved CIDI engine combustion model with arbitrary fuel injection for control purpose

Kim, Chung-Gong 18 June 2004 (has links)
No description available.
280

APLICACIÓN DE TÉCNICAS ESPECTROSCÓPICAS IN SITU AL ESTUDIO DE REACCIONES DE INTERÉS MEDIOAMBIENTAL: ELIMINACIÓN DE ÓXIDOS DE NITRÓGENO

Moreno González, Marta 02 July 2015 (has links)
[EN] The Selective Catalytic Reduction of nitrogen oxides (SCR-NOx) is nowadays a very relevant process for reducing NOx emissions in diesel vehicles, which must comply with increasingly restrictive European regulations. In this thesis the reaction mechanism and active centers in Cu-zeolite catalysts with different structures has been investigated. For his purpose two in situ spectroscopic techniques were mainly used, being Nuclear Magnetic Resonance NMR and Electron Paramagnetic Resonance EPR, which allowed the detection of reaction intermediates and identification of Cu active species. In particular we have studied the SCR-NOx reaction using NH3 as the reducing agent and Cu-zeolites catalysts with the chabazite structure. The preliminary study of the interaction of the catalysts with NH3 has shown the formation of several Cu-NH3 complexes with different stability. At SCR typical reaction temperatures (250 ° C), ammonia forms NH4+ ions in Brønsted acids centers of the zeolite and stable Cu+-(NH3) complexes, while Cu2+ remains isolated at the 6R plane, which is precisely the active site. However, when studying species formed on Cu-zeolites in the presence of the reaction mixture NH3/NO/O2, it appears that NH4+ ions are consumed during reaction and the formation of various intermediates including nitrite/nitrate species that decompose at T > 250 ° C to the reaction products (N2 and H2O). We also investigated the mechanism of the SCR-NOx reaction using C3H8 as the reducing agent and Cu-zeolites of different topology with medium and large pore systems. The results show the formation of a hydrocarbon activated species in the Cu2+ which is related to the catalytic activity. Furthermore, isolated Cu2+ is an active site that is reduced to Cu+ during reaction, and then re-oxidized to Cu2+ in the presence of O2. Finally, the hydrothermal stability of Cu-zeolites has been studied, since it is a prerequisite for its application as SCR catalysts, comparing the very hydrothermally stable Cu-SSZ-13 zeolite and the Cu-ZSM-5 which is completely disabled after hydrothermal treatment. The findings suggest the origin of the deactivation to be a change in the coordination of isolated Cu2+ in the Cu-ZSM-5 type to form CuAlOx species which are inactive in the SCR-NOx reaction. / [ES] La Reducción Catalítica Selectiva de óxidos de nitrógeno, SCR-NOx (acrónimo del inglés Selective Catalytic Reduction of NOx) es un proceso muy importante actualmente para la reducción de las emisiones de NOx en vehículos diésel, que deben ajustarse a nuevas normativas europeas más restrictivas. En la presente tesis doctoral se ha investigado el mecanismo de reacción y los centros activos en catalizadores de Cu en zeolitas (Cu-zeolitas) con distintas estructuras. Para ello se han utilizado fundamentalmente dos técnicas espectroscópicas in situ, la resonancia magnética nuclear RMN y la resonancia paramagnética electrónica EPR, que han permitido la detección de intermedios de reacción y la identificación de especies de Cu activas. En concreto se ha estudiado la reacción SCR-NOx utilizando NH3 como reductor y catalizadores Cu-zeolitas con estructura chabazita. Los resultados obtenidos en el estudio preliminar de la interacción del catalizador con el NH3 muestran la formación de distintos complejos de Cu-NH3 con diferente estabilidad. A la temperatura de reacción (250 °C), el amoniaco forma iones NH4+ en centros ácidos Brønsted de la zeolita y complejos Cu+(NH3) estables, y el Cu2+ permanece aislado en el plano de los anillos 6R, que es precisamente el centro activo. Sin embargo, cuando se estudian las especies formadas con la mezcla de reacción NH3/NO/O2 en las Cu-zeolitas, se observa que los iones NH4+ se consumen en el transcurso de la reacción y la formación de varios intermedios incluyendo nitritos/nitratos que descomponen a T > 250 °C a los productos de reacción (N2 y H2O). También se ha investigado el mecanismo de la reacción SCR-NOx utilizando C3H8 como reductor y Cu-zeolitas de distinta topología con tamaños de poros medio y grande. Los resultados obtenidos evidencian la formación de una especie activada del hidrocarburo en el Cu2+ que está relacionada con la actividad catalítica. Además el Cu2+ aislado es un centro activo que se reduce a Cu+ en el transcurso de la reacción, y se re-oxida posteriormente a Cu2+ en presencia de O2. Finalmente, se ha estudiado la estabilidad hidrotermal de las zeolitas con cobre, puesto que es una condición indispensable para su aplicación como catalizadores SCR, comparando la zeolita Cu-SSZ-13 muy estable hidrotermalmente, y la Cu-ZSM-5 que se desactiva por completo tras el tratamiento hidrotermal. Los resultados obtenidos apuntan que el origen de la desactivación es el cambio en la coordinación del Cu2+ en la Cu-ZSM-5 para formar especies tipo CuAlOx inactivas en la reacción. / [CA] La reducció catalítica selectiva d'òxids de nitrogen, SCR-NOx (acrònim del anglès Selective Catalytic Reduction of NOx) és un procés molt important actualment per a la disminució de les emissions de NOx en vehicles dièsel, que deuen ajustar-se a les normatives europees més restrictives. En la present tesi doctoral s'ha investigat el mecanisme de reacció i els centres actius en catalitzadors de Cu en zeolites (Cu-zeolites) amb diferents estructures. Per a dur a terme aquesta tasca s'han utilitzat fonamentalment dos tècniques espectroscòpiques in situ, la ressonància magnètica nuclear RMN i la ressonància paramagnètica electrònica EPR, les quals han permès la detecció d'intermedis de reacció i la identificació d'espècies de Cu actives. Concretament s'ha estudiat la reacció SCR-NOx emprant NH3 com a reductor i catalitzadors Cu-zeolita amb estructura chabacita. Els resultats obtinguts en l'estudi preliminar de la interacció del catalitzador amb NH3 mostren la formació de diversos complexes de Cu-NH3 amb diferent estabilitat. A la temperatura de reacció (250 °C), l'amoníac forma ions NH4+ en centres àcids Brønsted de la zeolita i complexes Cu+(NH3) estables, a més, el Cu2+ roman aïllat en el plànol dels anells 6R, que és precisament el centre actiu. No obstant, quan s'estudien les espècies formades amb la mescla de reacció, NH3/NO/O2 en les Cu-zeolites, s'observa que els ions NH4+ es consumeixen durant la reacció i la formació de diversos intermedis incloent nitrits/nitrats que descomponen, a T > 250 °C, als productes de la reacció (N2 y H2O). També s'ha estudiat el mecanisme de la reacció SCR-NOx utilitzant C3H8 com a reductor i Cu-zeolites amb diferent topologia amb mides de porus mitges i grans. Els resultats obtinguts evidencien la formació d'una espècie en forma activa del hidrocarbur al Cu2+ que està relacionada amb l'activitat catalítica. A més a més, el Cu2+ aïllat és un centre actiu que és redueix amb el transcurs de la reacció, i es re-oxida posteriorment a Cu2+ en presència de O2. Finalment, s'estudia l'estabilitat hidrotermal de les zeolites amb coure, puix que és una condició indispensable per a la seua aplicació com a catalitzadors SCR, comparant la zeolita Cu-SSZ-13 que és molt estable hidrotermalment, i Cu-ZSM-5 que es desactiva completament després del tractament hidrotermal. Els resultats obtinguts indiquen que la causa de la desactivació és el canvi en la coordinació del Cu2+ en Cu-ZSM-5 per a formar espècies tipus CuAlOx que són inactives a la reacció. / Moreno González, M. (2015). APLICACIÓN DE TÉCNICAS ESPECTROSCÓPICAS IN SITU AL ESTUDIO DE REACCIONES DE INTERÉS MEDIOAMBIENTAL: ELIMINACIÓN DE ÓXIDOS DE NITRÓGENO [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/52601

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