Notre étude porte sur la caractérisation expérimentale et numérique de la dynamique des ondes de détonation dans des prémélanges gazeux non-uniformément distribués dont les gradients de composition sont orientés selon la direction de propagation de la détonation. Elle vise à améliorer la compréhension des phénomènes complexes présents dans une chambre de combustion de moteur à détonations pulsées (PDE) ou rotatives (RDE) et dans des situations de fuites accidentelles de combustibles. Nous rappelons d’abord le contexte de notre étude, la phénoménologie de la détonation dans les gaz et les travaux antérieurs sur la propagation de la détonation dans des compositions non-uniformes. Nous décrivons ensuite le banc expérimental que nous avons conçu pour satisfaire à la contrainte de génération contrôlée de gradients de composition dans une chambre d’étude de section carrée 50⇥50 mm2 et de longueur 665 mm, et les diagnostics que nous avons mis en œuvre : sondes à oxygène, capteurs de pression dynamique, enregistrements sur plaques recouvertes d’un dépôt de carbone, strioscopie et spectroscopie par chimiluminescence ultra-rapides. Nous présentons alors les résultats de nos expériences dans des compositions de propane ou d’éthane et d’oxygène à la pression et à la température initiales 200 mbar et 290 K. Nous avons considéré des distributions monotones, de richesse décroissante, et des distributions non-monotones, de richesse décroissante puis croissante. Dans les distributions monotones, nous avons identifié deux types d’extinction de la détonation, l’un brusque, par découplage choc-flamme, pour des gradients suffisamment forts, l’autre progressif, par transition vers des modes marginaux de propagation, pour des gradients plus faibles. Nous avons proposé et validé des critères d’existence de la détonation fondés sur les échelles caractéristiques du problème. Nous avons démontré, pour ces distributions, la capacité de simulations numériques avec cinétique chimique détaillée à représenter nos expériences, dans le cadre d’une collaboration avec l’Université Keio. Dans les distributions non-monotones, nous avons identifié des comportements super-critique, critique et sous-critique, selon que la détonation est transmise ou non de la zone où la richesse diminue vers celle où elle augmente. Nous avons en particulier identifié les conditions de réamorçage d’une détonation éteinte dans la zone de richesse décroissante. Notre étude souligne l’intérêt de travaux futurs sur des non-uniformités de compositions initiales constitués de gaz brûlés et de gaz frais et donc, également, des non-uniformités de température initiale. Elle souligne aussi la nécessité de diagnostics optiques et d’outils numériques performants, et de schémas détaillés de cinétique chimique adaptés aux hautes pressions et températures caractérisant la dynamique des détonations. / Our study is an experimental and numerical work on the dynamical behaviours of detonation waves in non-uniformly distributed premixed gases with composition gradients parallel to the direction of the detonation propagation. The study aims at improving the understanding of the complex phenomena involved in the combustion chambers of pulsed or rotating detonation engine (PDE, RDE) and after accidental leaks of fuels. We first remind the context of our study, the phenomenology of gaseous detonation and the previous works on detonation propagation in non-uniform compositions. We then describe the experimental set-up that we have designed in order to meet the constraint of a controlled generation of composition gradients in a 50⇥50 mm2 square-section, 665-mm length test chamber, and the diagnoses that we have implemented : oxygen probes, fast pressure transducers, carbon-sooted plates and ultrafast Schlieren and chemiluminescence spectroscopy. Next, we present the results of our experiments in mixtures of propane or ethane and oxygen with initial pressure and temperature 200 mbar and 290 K, respectively. We have considered monotonic distributions, with decreasing equivalence ratio, and non- monotonic distributions, with decreasing then increasing equivalence ratio. In the monotonic distributions, we have identified two types of detonation quenching, one sudden, with a shock-flame decoupling, for the steeper gradients, the other progressive, with a transition through marginal modes of detonation propagation, for the weaker gradients. We have proposed and validated criteria for detonation, based on the characteristic scales of the problem. We have demonstrated, for these monotonic distributions, the ability of numerical simulations with detailed schemes of chemical kinetics to represent our experimental observations, through a collaboration with Keio University. In the non-monotonic distributions, we have identified super-critical, critical and sub-critical behaviours, depending on whether the detonation is transmitted or not from the domain where the equivalence ratio decreases to that where it increases. In particular, we have identified the re-initiation conditions for a detonation that was quenched in the domain of decreasing equivalence ratio. Our study stresses the interest for future works to consider non-uniform distributions of mixtures comprising burnt gases and fresh reactants, and, consequently, non-uniform distributions of temperature. It also stresses the need for performing optical diagnoses and numerical capacities and for detailed schemes of chemical kinetics adapted to the high pressures and temperatures characterizing detonation dynamics.

The aim of this thesis was to investigate what the relation is between as-quench hardness and final surface hardness for steel beams is, depending on what tempering temperature is used. Also explain how chemistry, dimension and microstructure effects the final mechanical properties of the front axle beam. For this a review of literature concerning the effects was completed.Hardness measurement on the surface was performed on the ends of the beam (bottom and top). This hardness measurement was performed on 6 different front axle articles of the same material (41CrS4) and 2 different front axle articles of another material (40CrMo4). The relation diagram gives an estimation of what type of tempering temperature is needed to achieve the final hardness that is desired. Because the relation was done with some inconsistences it can’t be said to give a perfect answer. The relation diagrams only work for material 41CrS4 and 40CrMo4. For the core hardness test, 2 articles of 41CrS4 and one article of 40CrMo4 was measured on 5 different position on the cross-section, the beams for the respective articles were taken from quenched state and quenched+tempered. The beam dimensions have a significant effect when it comes to cooling down the part and achieve as close to uniform hardness as possible. Even though the Middle point of the I-section sample is one of the closest cores to the surface, it has a softer core compared with the other cores. While there exists hardness difference after quenching between different points in the core they even out after tempering. When comparing the core hardness with the surface hardness it can be said that the surface hardness is not as hard as the core because of decarburization. The microstructure analysis was done on 2 articles of 41CrS4 and one article of 40CrMo4. Samples from the 3 articles is taken from both the as-quenched state and quenched+tempered state. From the optical microscope it could be seen, that the surface of the beams decarbonizes leading to a higher amount of ferrite at the structure and softer surface. Because of this 15 mm into the material is harder than at-surface. Decarburization of the 41CrS4 steels made it so that what should have been a martensite and bainite dominated surface became a ferrite and bainite dominated.To decide the actual amount of retained austenite in the sample an XRD-analysis was performed. The XRD-analysis is done only for one article type of 41CrS4. From the front axle beam three samples of three different locations (bottom, middle, top) was taken for the analysis. For the theoretical calculation of the retained austenite vs the actual amount it can be said that is a very good representation of the total amount of retained austenite in the product. But the theoretical calculation deviates a bit from the actual amount at the top part of the beam. / Syftet med denna avhandling var att undersöka vad relationen är mellan härdat ythårdhet och slut ythårdhet för stålbalkar är, beroende på vilken anlöpnings temperatur som används. Tar också upp hur kemi, dimension och mikrostruktur påverkar de sista mekaniska egenskaperna hos framaxel balken. För detta genomfördes en genomgång av litteraturen om effekterna.Hårdhetsmätning på ytan utfördes på balkens ändar (botten och toppen). Denna hårdhetsmätning utfördes på 6 olika främre axelartiklar av samma material (41CrS4) och 2 olika främre axelartiklar av annat material (40CrMo4). Relationsdiagrammet ger en uppskattning av vilken typ av anlöpningstemperatur som behövs för att uppnå den slutliga hårdheten som önskas. Eftersom förhållandet gjordes med vissa inkonsekvenser kan det inte sägas ge ett perfekt svar. Relationsdiagrammen fungerar endast för material 41CrS4 och 40CrMo4.För kärnhårdhetstestet mättes 2 artiklar av 41CrS4 och en artikel av 40CrMo4 i 5 olika positioner på tvärsnittet, stålen för respektive artiklar togs från härdat tillstånd och härdat + anlöpt. Dimensionerna har en signifikant effekt när det gäller att kyla ner delen och uppnå så nära enhetlig hårdhet som möjligt. Även om mittpunkten i I-sektionsprovet är en av de närmaste kärnorna till ytan, så har det en mjukare kärna jämfört med de andra kärnorna. Det finns hårdhetsskillnad efter härdning mellan de olika punkter men de jämnar ut sig efter anlöpningen. När man jämför kärnhårdheten med ythårdheten kan man säga att ythårdheten inte är så hård på grund av avkolning.Mikrostrukturanalysen gjordes på 2 artiklar av 41CrS4 och en artikel av 40CrMo4. Prover från de 3 artiklarna tas från både härdat tillstånd och härdat + anlöpt tillstånd. Från det optiska mikroskopet kunde man se att stålbalkens yta har blivit utsatt för avkolning vilket leder till en högre mängd ferrit vid strukturen och en mjukare yta. På grund av detta, så är 15 mm in i materialet hårare än vid ytan. Avkolning av 41CrS4 stål gjorde så att det som borde ha varit ett martensit och bainit dominerat yta blev istället ferrit och bainit dominerat.XRD-analysen görs endast för en artikelart av 41CrS4. Från fram axelbalken togs tre prov från tre olika platser (botten, mitten, toppen) för analysen. För att bestämma den verkliga mängden restaustenit i provet utfördes en XRD-analys. För den teoretiska beräkningen av den rest austeniten jämfört med det faktiska beloppet kan man säga det är en mycket bra representation av den totala mängden kvarhållen austenit i produkten. Men den teoretiska beräkningen avviker lite från den faktiska mängden vid stålens övre del.

Microgravité éthylène laminaires couche limite flammes de diffusion générés par un brûleur poreux plat et caractérisées par les vitesses d'injection de carburant de 3 et 4 mm / s et une vitesse d'oxydation de 250 mm / s ont été simulées en utilisant un modèle de rayonnement précis, un mécanisme cinétique complète et un modèle de suie constitué de lancement par suite de la collision de deux molécules de pyrène, l'évolution de la surface hétérogène et oxydation suivant l'abstraction d'un atome d'hydrogène addition d'acétylène (HACA) mécanisme, la coagulation à particules de suie, et la condensation de la surface de l'HTAP. La distance d'écartement et la production de suie sont améliorées lorsque la vitesse du carburant augmente. H et des radicaux OH, responsables de la de-hydrogénation des sites dans le processus HACA, et le pyrène, de l'espèce pour la création de la suie et des processus de condensation HAP, se trouvent à être situé dans une région qui suit la distance stand-off. La suie est ensuite produite dans cette région et est transporté à l'intérieur de la couche limite par convection et thermophorèse. Perte radiatif est sensiblement plus élevé dans ces flammes que dans flammes de diffusion de gravité normales dues à beaucoup plus longues durées de séjour. Calculs effectués par négliger le rayonnement de la suie et en utilisant l'approximation optiquement mince (OTA) a révélé que la suie domine le transfert de chaleur par rayonnement dans ces flammes et que l'utilisation de l'OTA donne lieu à des écarts significatifs dans la fraction du volume température et la suie. / Microgravity ethylene laminar boundary layer diffusion flames generated by a flat porous burner and characterized by the fuel injection velocities of 3 and 4 mm/s and an oxidizer velocity of 250 mm/s have been simulated by using an accurate radiation model, a comprehensive kinetic mechanism, and a soot model consisting of inception as a result of the collision of two pyrene molecules, heterogeneous surface growth and oxidation following the hydrogen abstraction acetylene addition (HACA) mechanism, soot particle coagulation, and PAH surface condensation. Model predictions are in reasonable agreement with the experimental data in terms of the stand-off distance and soot volume fraction. The stand-off distance and soot production are enhanced as the fuel velocity increases. H and OH radicals, responsible of the de-hydrogenation of sites in the HACA process, and pyrene, of the species for soot inception and PAH condensation processes, are found to be located in a region that follows the stand-off distance. Soot is then produced in this region and is transported inside the boundary layer by convection and thermophoresis. Radiative loss is substantially higher in these flames than in normal gravity diffusion flames owing to much longer residence times. Calculations carried out by neglecting soot radiation and by using the optically-thin approximation (OTA) revealed that soot dominates the radiative heat transfer in these flames and that the use of OTA gives rise to significant discrepancies in temperature and soot volume fraction.

Fluorescent proteins (FPs) are extremely valuable biochemical markers which have found a wide range of applications in cellular and molecular biology research. The monomeric variants of red fluorescent proteins (RFPs), known as mFruits, have been especially valuable for in vivo applications in mammalian cell imaging. Fluorescent proteins consist of a chromophore caged in the beta-barrel protein scaffold. The photophysical properties of an FP is determined by its chromophore structure and its interactions with the protein barrel. Application of hydrostatic pressure on FPs results in the modification of the chromophore environment which allows a systematic study of the role of the protein-chromophore interactions on photophysical properties of FPs. Using Molecular Dynamics (MD) computer simulations, I investigated the pressure induced structural changes in the monomeric variants mCherry, mStrawberry, and Citrine. The results explain the molecular basis for experimentally observed pressure responses among FP variants. It is found that the barrel flexibility, hydrogen bonding interactions and chromophore planarity of the FPs can be correlated to their contrasting photophysical properties at vaious pressures. I also investigated the oxygen diffusion pathways in mOrange and mOrange2 which exhibit marked differences in oxygen sensitivities as well as photostability. Such computational identifications of structural changes and oxygen diffusion pathways are important in guiding mutagenesis efforts to design fluorescent proteins with improved photophysical properties.

No description available.

A têmpera, que consiste no resfriamento rápido do aço, após austenitização, é um dos tratamentos térmicos mais utilizados. O objetivo desse tratamento é a obtenção da estrutura martensítica, que oferece ótimas propriedades de dureza e resistência. A água, as soluções de polímeros e os óleos minerais são os meios refrigerantes mais comuns, sendo os óleos responsáveis pelo resfriamento em 80% dos casos. Verificou-se, no Brasil, o desconhecimento, dos mercados produtor e consumidor, quanto ao universo dos óleos de têmpera comercialmente disponíveis e de suas respectivas características de resfriamento. Assim, atentou-se para a necessidade de apresentar aos mercados já descritos, uma classificação dos óleos de têmpera nacionais,relacionando-os como rápidos, intermediários e lentos, destacando ainda, aspectos importantes nos parâmetros de resfriamento. / Quenching of steels, which consist of very fast cooling from austenitizing temperatures, is the most used heat treatment. The aim of this treatment is the obtation of martensitic microstructure. This microstructure confer excellent hardness and strength properties. The most common quenchants are water, polymer solutions and mineral oils, and the oils themselves are responsible by the 80% of the quenchants used during quenching. In Brazil, it was verified consumer lack of knowledge of the oils available as quenchants and their characteristics. Therefore, in this work as attempt was made to present the quenchants available and their classification as fast, intermediary and slow quenchants.

The quenching of undesired flames by cold surfaces has been investigated for more than a century. The current quenching theory can predict simple configurations, this is not the case for real environments such as fuel management systems. Flames are sensitive to numerous parameters, such as fuel, mixture fraction, pressure, temperature, flow properties, acoustics, radiation, and surface interactions. The effects of some of these parameters are very well documented but there is a lack of information regarding the effects of acoustics and flow. This dissertation work will focus on improving the understanding of flow effect on the quenching of premixed gaseous flames. First, the effect of apparent velocity on flame quenching was investigated for different fuels and equivalence ratios. An experimental facility is designed such that the apparent flame velocity at which the flame enters and propagates through the channel can be varied without changing the initial mixture condition. High-speed (15,000 frames per second (FPS)) Schlieren and dynamic pressure measurement were used to measure the apparent flame velocity and to assess the flame quenching, respectively. This study showed that the high-speed laminar flames are harder to quench compared to self-propagating and turbulent flames. A similar trend was obtained for all the conditions investigated, lean and stoichiometric methane-air, lean propane-air, and lean ethylene-air mixtures. Further investigation was carried out to understand the quenching of high-speed laminar flames. The flame propagation through the channel was investigated using Hydroxyl (OH) planar laser induced fluorescence (PLIF). This study showed that the OH intensity fell below the detection threshold in the later part of the channel when quenching is observed. Then, the influence of heat transfer was investigated using spatial and temporal evolution of the temperature in the quenching channel. A high-speed (10 kHz) filtered Rayleigh scattering (FRS) technique was used to measure the one-dimensional time-resolved temperature profile. Three different channel heights (H = 1.3, 1.5, 2.0 mm) were investigated. Based on the evolution of the temperature profile in the quenching channel, a new parameter was identified and the importance of its evolution on the flame quenching was discussed.

This diploma thesis was focused on studying the interaction of humic substances with ionic organic xenobiotics and its structural aspects. The method was chosen from my bachelor thesis, steady-state fluorescence spectroscopy, which is suitable for substances with weak fluorescence. The results showed that the interaction between humic acids and representatives of ionic organic xenobiotics (Septonex) was reflected in fluorescence quenching of humic acids and the shift of emission maximum to lower wavelength, hypsochromic (blue) shift. From the measurement results, we can assume that the interaction that is formed between the aromatic structures in humic acids and Septonex could be -cation interaction.

<p>Despite worldwide interest in a number of applications involving cryogenic fluids that are crucial to future space exploration, there is presently a lack of a large, reliable cryogenic pool boiling critical heat flux (CHF) database that can be used for assessment of accuracy of available predictive tools - model and correlations – or development of new tools. This shortcoming is a primary motivation for the present study, prompting compilation of a new consolidated cryogenic pool boiling CHF database from world literature. The database is used to assess accuracy of previous models and correlations, which are segregated according to ability to predict key operating parameters, such as pressure, surface orientation, and subcooling. A new correlation is constructed which shows very good predictive accuracy, evidenced by a mean absolute error of 16.95%, based on Earth gravity data which comprise a large fraction of the consolidated database. Using a limited subset of datapoints for three cryogens and a reduced gravity range of 0 to 0.7466, the new correlation is further modified with a reduced gravity multiplier to tackle reduced gravity conditions. The modified correlation has a mean absolute error of 17.47%, slightly higher than for Earth gravity alone. Overall, the new correlations are proven far more accurate than all prior models and correlations and therefore constitute new powerful tools for design of cryogenic space systems. It is shown CHF is very sensitive to pressure, increasing with increasing pressure up to maximum before decreasing appreciably toward critical pressure. CHF is also shown to be strongly influenced by surface orientation, being highest for horizontal surfaces and decreasing monotonically with increasing orientation angle, and increasing fairly linearly with increased subcooling.</p><p>Additionally, CHF models and correlations are assessed using amassed quenching CHF data that showed overpredictions of data. A new correlation is formulated which includes the effects of surface material and heater thickness to achieve high predictive accuracy for complied quenching CHF database. The new correlation has a mean absolute error and root mean square error of 10.79% and 16.12%, respectively, based on a compiled database. Analysis of complied quenching data showed that CHF is sensitive to the surface material, increasing with increasing thermal conductivity but, the influence of surface material becomes weak with increasing thermal conductivity. CHF is also strongly influenced by heater thickness, increasing with increased heater thickness till it reaches the asymptotic thickness. </p>

Pluronics are triblock copolymers of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) available in different molecular weights and PPO/PEO ratios. Pluronic hydrogels are able to dissolve hydrophobic compounds and they have application in different areas including drug delivery systems and oil recovery. The structure of Pluronic polymers can be designed for specific application by changing the size and ratio of the PPO and PEO blocks. In aqueous environments, the PPO blocks of different unimers form aggregates as they are more hydrophobic compared to the PEO blocks, and in the aggregates the PPOs have less exposure to water. The PEO blocks that are still hydrophilic remain soluble in water and form a shell around the PPO aggregated core. Moreover, some of the Pluronic copolymer aqueous solutions can form hydrogels at elevated temperatures. The aim of this thesis is to study the microheterogeneity of two different Pluronic hydrogels using singlet excited state probes and also study the mobility of small molecules in Pluronic hydrogels using triplet excited state probes. In the first project, the properties of different microenvironments in Pluronic F127 (PEO99PPO65PEO99) were characterized. The quenching of singlet excited state probes was used to determine the number and characteristics of solubilization sites in F127 hydrogels. This method was used to gain information on the accessibility of different quenchers to singlet excited molecules bound to the micellar structures. Singlet excited states are short lived, and these excited states do not move within the gel before their decay to the ground state. The techniques used for these studies were steady-state fluorescence and time-resolved fluorescence spectroscopies. My results showed that there are different solubilization sites in F127 micelles and the accessibility of quenchers to the singlet excited molecules bound to the micellar structure depends on the nature of the quencher and the size of the excited molecules. In the second project, the different microenvironments in Pluronic P104 (PEO27PPO61PEO27) were characterized, and these results were compared with those obtained for the Pluronic F127. Pluronic P104 has similar units of PPO blocks as F127 but different units of PEO blocks which results in different properties between these two Pluronic copolymers. My results showed that the solubilization sites inside Pluronic micelles changes with the change in PEO/PPO ratio. In the third project, I studied the mobility of different small molecules between aqueous and micellar environments in the F127 hydrogel by quenching triplet excited state probes. Excited triplet states are suitable for such studies because their lifetimes are longer than the lifetimes for singlet excited states. The laser flash photolysis technique was used for this aim. The results showed that the exit from the micellar environment is slow and depend on the size and hydrophobicity of the probe molecules. / Graduate / 2022-05-11