Knowledge of flammability limits is essential in the prevention of fire and explosion. There are two limits of flammability, upper flammability limit (UFL) and lower flammability limit (LFL), which define the flammable region of a combustible gas/vapor. This research focuses on the flammability limits of hydrogen and its binary mixtures with light hydrocarbons (methane, ethane, n-butane, and ethylene) at sub-atmospheric pressures. The flammability limits of hydrogen, light hydrocarbons, and binary mixtures of hydrogen and each hydrocarbon were determined experimentally at room temperature (20ºC) and initial pressures ranging from 1.0 atm to 0.1 atm. The experiments were conducted in a closed cylindrical stainless steel vessel with upward flame propagation. It was found that the flammable region of hydrogen initially widens when the pressure decreases from 1.0 atm to 0.3 atm, then narrows with the further decrease of pressure. In contrast, the flammable regions of the hydrocarbons narrow when the pressure decreases. For hydrogen and the hydrocarbons, pressure has a much greater impact on the UFLs than on the LFLs. For binary mixtures of hydrogen and the hydrocarbons, the flammable regions of all mixtures widen when the fraction of hydrogen in the mixture increases. When the pressure decreases, the flammable regions of all mixtures narrow. The applications of Le Chatelier’s rule and the Calculated Adiabatic Flame Temperature (CAFT) model to the flammability limits of the mixtures were verified. It was found that Le Chatelier’s rule could predict the flammability limits much better than the CAFT model. The adiabatic flame temperatures (AFTs), an important parameter in the risk assessment of fire and explosion, of hydrogen and the hydrocarbons were also calculated. The influence of sub-atmospheric pressures on the AFTs was investigated. A linear relationship between the AFT and the corresponding flammability limit is derived. Furthermore, the consequence of fire relating to hydrogen and the hydrocarbons is discussed based on the AFTs of the chemicals.

Magnetic refrigeration is an alternative cooling technology to vapour compression. Due to the large operating space of magnetic refrigeration devices, modelling is critical to predict results, optimize device parameters and regenerator design, and understand the physics of the system. Modeling requires accurate material data including specific heat, magnetization and adiabatic temperature change, . For a reversible material can be attained directly from measurement or indirectly through calculation from specific heat and magnetization data. Data sets of nine MnFeP1-xAsx alloys are used to compare calculated against measured . MnFeP1-xAsx is a promising first order material because of a tunable transition temperature, low material cost and large magnetocaloric properties. Because MnFeP1-xAsx alloys exhibit thermal hysteresis there are four possible calculation protocols for adiabatic temperature change; , , and . deviates the most from measured data and therefore it is assumed that this case is not representative of the material behavior. Results show and align with measured data as well as . The three protocols that align best with measured data have two consistent errors including a colder peak and a larger . With more data sets and analysis a preferred calculation protocol may be found. / Graduate

Thesis (M.Sc.)--Memorial University of Newfoundland, 1995. / Typescript. Bibliography: leaves 69-73. Also available online.

The specialized pigment-protein complexes involved in the first process of photosynthesis are light-harvesting structures that are composed of networks of chromophores in protein scaffolds. Though light-harvesting complexes vary in chromophore composition and protein structure, they are capable of transferring the absorbed energy as molecular excitation energy from chromophore to chromophore with maximal efficiency. Thus, numerous interdisciplinary studies focus on elucidating energy transfer mechanisms in these biological complexes and how the same principles can be applied to artificial photosynthetic and photovoltaic machines. From advanced spectroscopic measurements and theoretical models, the interaction between the excited electronic states and the nuclear vibrational degrees of freedom is now established to be crucial for efficient energy transfer. In light-harvesting complexes of plants and bacteria, it is now understood that the classical-like vibrational modes of the protein and solvent environment drive energy transfer between the energetically close electronic states of the chromophores. On the other hand, recent spectroscopic measurements on algae light-harvesting complexes discovered signatures of quantized, high frequency vibrational modes of the chromophore. Unfortunately, a deterministic interpretation of the data and the underlying Hamiltonian is hindered due to significant inhomogeneous spectral line-broadening. Though numerous model Hamiltonians have been proposed from theoretical work, various computational approximations employed in these studies necessitate empirical parameter tuning in order to obtain agreement with benchmark linear optical spectra. Thus in this work, we present a simple, but improved, computational prescription to compute the ensemble of Hamiltonians for four closely-related algae light-harvesting complexes. We verify the reliability of our proposed models by comparing simulated optical spectra with experimental measurements. We show that static disorder and inhomogeneous broadening are significant for phycobiliproteins due to large site energy fluctuations. We also show that the nuclear environment plays an important role in defining the trapping state, or the final energy acceptor. Finally, our work for the first time suggests that EET dynamics can be tuned by varying the titration states of the chromophores.

Baseado em uma seqüência já conhecida de Multislice Spin Echo convencional, implementamos uma seqüência do tipo Modified Driven Equilibrium Fourier Transform (MDEFT) adiabática multislice em um sistema de 2T e um de microimagens (9.4T). Essa metodologia utiliza, como pulso de inversão, um pulso de RF com modulação em amplitude e freqüência, conhecido por pulso adiabático. Dessa forma, os tempos de inversão são iguais para todos os planos selecionados, resultando num contraste por T1 uniformemente distribuído ao longo dos mesmos. O uso de um único e longo pulso adiabático de inversão tem, ainda, a vantagem de utilizar uma potência de pico menor para operar da mesma forma que um grupo de m pulsos convencionais. Utilizamos pulsos cujas modulações correspondentes de fase e freqüência foram calculadas com base nas condições de “Offset Independent Adiabaticity” (OIA) e a real eficiência dos mesmos foi avaliada através de simulações e experimentalmente. Para realização dos testes da metodologia desenvolvemos e caracterizamos dois “phantoms”, cujas imagens demonstram a aplicabilidade da metodologia nos dois sistemas utilizados. / Based on the conventional Multislice Spin Echo pulse sequence, we implemented an adiabatic multislice Modified Driven Equilibrium Fourier Transform (MDEFT) pulse sequence on a 2T and a 9.4T microimaging system. This methodology uses, as inversion pulse, an amplitude and frequency modulated RF pulse, known as adiabatic pulse. In that way, the inversion times are the same for all slices, resulting in an evenly distributed T1 contrast. A single and long adiabatic inversion pulse has in addition the advantage of using a reduced peak power to perform in the same way as the group of m conventional pulses. We used pulses whose corresponding phase and frequency modulations were based on Offset Independent Adiabaticity and their real efficiency were evaluated both through simulations and experimentally. To test the methodology, we developed and characterized two phantoms, whose images demonstrate the applicability of the methodology in the two mentioned systems.

Diploma thesis deals in the first part with recent knowledge of cold spray, its mechanism and parameters of deposition, advanced coatings made by cold spray and their applications, knowledge of Ti-6Al-4V coatings and their heat treatment. Deposit of Ti- 6Al-4V powder was made by cold spray process. In experimental part, microstructure and mechanical properties of supplied and its heat treated material were observed and examined. Mechanical properties and microstructure remained unchanged by annealing at 600 °C as in the case of supplied material. Recrystallization occured in microstructure of and phases by annealing at 800 °C. Grains were emerged in microstructure and mechanical properties were decreased. Mechanical properties were improved by annealing at 900 °C due to quenching. Microstructure consists of and ’ phases. Mechanical properties were the worst for annealed material at 1000 °C because of coarsed grains. Material which was annealed at 800 °C, quenched and precipitation hardened had the best microstructure and mechanical properties.

By the everyday increasing enthusiasm for using renewable-sustainable sources in energy production area, focusing on one and optimizing it in the best possible way should be of much interest. Biogas production from anaerobic digestion of wastes is a well known energy source which could be applied more efficiently if the CO2portion of it would be upgraded to CH4as well. There is a methanation reaction which could convert carbon dioxide to methane with the use of hydrogenation. In this report, the effort is to simulate this methanation reactor which is a catalytic bed of ruthenium on alumina base. The temperature change and its’ effect on reaction kinetics and equilibrium, also deriving designing parameters for the catalyst bed are different tasks which was tried to be covered in this thesis work. Based on calculations, the reactor can operate isothermally or adiabatically. The point is that each method has its own cons and pros. For the isothermal case finally the optimum temperature to run the reaction is decided to be 600 K in 10 bar total pressure. In adiabatic case then it is understood to work on interstage cooling strategy which in given conditions came to the number of 6 for reactors and 5 for interstage cooling devices. Afterwards it is thought to apply some technical changes to conventional adiabatic method and recycle some part of the product to the entrance of the reactor and assist the conversion. In this method number of reactors would be reduced to 2 and one heat exchanger in the middle. Selecting the best process in large scale treatment, needs lots of economical analysis and detail design while in small scale condition the most preferred method to run the reaction is isothermal.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20546号 / 理博第4304号 / 新制||理||1618(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 早川 尚男, 教授 川上 則雄, 教授 佐々 真一 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

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