A series of homogeneous halogen containing polymers have been studied whilst sliding against mild steel and oxides present on mild steel. The degradation characteristics of P. V. C. and C1d P. V. C. have been correlated in terms of current mechano-chemical comminution theory and the process causing the wear of P. V. C., C1d P. V. C., P. T. F. E. and P. C. T. F. E. described in relation to the chemical and physical conditions at the sliding interface. In addition the potential importance of the chemical role of oxide free iron surfaces in wear processes has been demonstrated by interacting an analogue compound of P. T. F. E. (n-C5F12) with clean iron under ultra high vacuum conditions. The resulting fragmentation of the perfluorinated compound is discussed and a simplified degradation mechanism suggested.

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第17522号 / 工博第3681号 / 新制||工||1560(附属図書館) / 30288 / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 辻 康之, 教授 大江 浩一, 教授 松原 誠二郎 / 学位規則第4条第1項該当

The work presented in this thesis is an investigation of the dynamics of unconfined hydrogen-air flames in the presence of buoyant effects and the determination of an ignition criterion for flame propagation between adjacent pockets of reactive gas separated by air. The experimental work was conducted using the soap bubble technique and visualized with high speed schlieren or large scale shadowgraph systems. A study was first conducted to determine the most suitable soap solution additive among glycerol, guar and polyethylene oxide for conducting the experiments, isolating guar as the best candidate. The soap solution was then used to study the dynamics of flames in single or multiple soap bubbles filled with reactive mixtures of different compositions. The soap bubble method was also further improved by designing a soap dispenser that can maintain a bubble indefinitely and a method to burst the soap solution prior to an experiment using timed heated wires. In the experiments with single bubbles, it was found that for sufficiently lean hydrogen-air mixtures, buoyancy effects become important at small scales. The critical radius of hemispherical flames that will rise due to buoyancy was measured and estimated using a model comparing the characteristic burning speed and the rise speed of the flame kernel. Excellent agreement was found between the model predictions and the measured critical flame radii. The experiments with multiple bubbles provided the scaling rules for flame transition between neighboring pockets of hemispherical or spherical shape separated by an inert gas. The test results demonstrated that the separation distance between the bubbles is mainly determined by the expansion ratio when the buoyancy effects are negligible, corresponding to near stoichiometric mixtures. For leaner mixtures with stronger buoyant effects, the critical separation distance was no longer governed by the expansion ratio alone, as buoyancy forces render the flame propagation across the inert gas more difficult. Visualization of the ignition dynamics confirmed that buoyancy forces tend to accelerate the first kernel up before ignition of the second kernel can be achieved.

Consider a semisimple linear algebraic group G over an arbitrary field F, and a projective homogeneous G-variety X. The geometry of such varieties has been a consistently active subject of research in algebraic geometry for decades, with significant contributions made by Grothendieck, Demazure, Tits, Panin, and Merkurjev, among others. An effective tool for the classification of these varieties is the notion of a cohomological (or alternatively, a motivic) invariant. Two such invariants are the set of Tits algebras of G defined by J. Tits, and the J-invariant of G defined by Petrov, Semenov, and Zainoulline. Quéguiner-Mathieu, Semenov and Zainoulline discovered a connection between these invariants, which they developed through use of the second Chern class map. The first goal of the present thesis is to extend this connection through the use of higher Chern class maps. Our main technical tool is the Steinberg basis, which provides explicit generators for the γ-filtration on the Grothendieck group K_0(X) in terms of characteristic classes of line bundles over X. As an application, we establish a connection between the J-invariant and the Tits algebras of a group G of inner type E6. The second goal of this thesis is to relate the indices of the Tits algebras of G to nontrivial torsion elements in the γ-filtration on K_0(X). While the Steinberg basis provides an explicit set of generators of the γ-filtration, the relations are not easily computed. A tool introduced by Zainoulline called the twisted γ-filtration acts as a surjective image of the γ-filtration, with explicit sets of both generators and relations. We use this tool to construct torsion elements in the degree 2 component of the γ-filtration for groups of inner type D2n. Such a group corresponds to an algebra A endowed with an orthogonal involution having trivial discriminant. In the trialitarian case (i.e. type D4), we construct a specific element in the γ-filtration which detects splitting of the associated Tits algebras. We then relate the non-triviality of this element to other properties of the trialitarian triple such as decomposability and hyperbolicity.

Spaces such as the closed interval [0, 1] do not have the property of being homogeneous, strongly locally homogeneous (SLH) or countable dense homogeneous (CDH), but the Hilbert cube has all three properties. We investigate subsets X of real numbers to determine when their countable product is homogeneous, SLH, or CDH. We give necessary and sufficient conditions for the product to be homogeneous. We also prove that the product is SLH if and only if X is zero-dimensional or an interval. And finally we show that for a Borel subset X of real numbers the product is CDH iff X is a G-delta zero-dimensional set or an interval.

Formic acid (FA) has been considered as one of the most promising materials for hydrogen storage today. The catalytic decarboxylation of formic acid ideally leads to the formation of CO2 and H2, and such CO2/H2 mixtures can be successfully applied in fuel cells. A large number of transition-metal based homogeneous catalysts with high activity and selectivity have been reported for the formic acid decarboxylation. In this presentation, we report ruthenium and rhodium complexes containing an N, N′-diimine ligand for the selective decomposition of formic acid to H2 and CO2 in water in the absence of any organic additives. Among them, the Ru complex could provide a TOF (turnover frequency) of 12 000 h–1 and a TON (turnover number) of 350 000 at 90 °C in the HCOOH/HCOONa aqueous solution. In addition to that, efficient production of high-pressure H2 and CO2 (24.0 MPa (3480 psi)) was achieved through the decomposition of formic acid with no formation of CO by this Ru complex. Moreover, well-defined ruthenium (II) PN3P pincer complexes were also developed for the reversible reaction-hydrogenation of carbon dioxide. Excellent product selectivity and catalytic activity with TOF and TON up to 13,000 h-1 and 33,000, respectively, in a THF/H2O biphasic system were achieved. Notably, effective conversion of carbon dioxide from the air into formate was conducted in the presence of an amine, allowing easy product separation and catalyst recycling.

An investigation into the general and pitting corrosion rates of rolled homogeneous armor (RHA) steel in immersion and saltog environments is presented. The mechanical properties of RHA steel have been studied, but the effects of corrosion on RHA have not been analyzed. An immersion environment of 3.5% NaCl was used to induce corrosion for the total testing period of 1500 hours for four immersion samples. A Qog cyclic corrosion tester was used to simulate a saltog/humidity/drying environment for four saltog samples. The different mechanisms of corrosion (general and pitting) and their associated rates were quantified through evolved hydrogen gas measurements, profilometry, Scanning Electron Microscopy (SEM) and Optical Microscopy (OM). The primary corrosion mechanism in the immersion samples was general corrosion, while the primary corrosion mechanism in the saltog samples was pitting corrosion. The immersion samples showed no signs of pitting corrosion.

Yes / This study presents the experimental results of the flow characteristics, such as the flow adjustment, velocity profiles, mixing layer, and the momentum exchange, in the partially vegetated channel with homogeneous and heterogeneous layouts. Three cases are considered, including two homogeneous canopies with uniform sparse and dense vegetation patches respectively, and a heterogeneous canopy consisting of alternating patches of both densities. Results show that heterogeneous canopy requires a longer adjustment distance to reach the quasi-equilibrium region, compared with the homogenous canopy of the same density. In heterogeneous canopy flow, the mixing layer width and the momentum thickness fluctuates with the alternation of vegetation density. The increased values for these two parameters compared to those values for the homogeneous canopies indicate that the greater resistance and momentum loss occur for the heterogeneous layout. A wavy region of the enhanced in-plane turbulence kinetic energy (TKE) is observed in the heterogeneous canopy, suggesting a comparatively more chaotic flow condition, whereas the contours of in-plane TKE are smooth in homogeneous canopies. The presence of the coherent structures in heterogeneous canopy is identified by spectral analysis and the quasi-periodic fluctuations of velocities. The Reynolds stress associated with the coherent structures is found to be the dominator of the contribution to the total Reynolds stress. The comparison between the homogenous canopies of different density is also conducted. These results will be of practical importance for the design of vegetation layouts in water ecological restoration projects and for river management. / National Natural Science Foundation of China (grant numbers 52020105006 and 11872285) and the Open Funding of State Key Laboratory of Water Resources and Hydropower Engineering Science (WRHES), Wuhan University (Project number 2018HLG01)

Oxidative coupling of methane (OCM) represents a potentially viable method to convert methane directly into more desirable products such as ethane, and ethylene. In this dissertation, a comprehensive kinetic study of oxidative coupling of methane was performed over La2O3-based catalysts. An accurate and reliable gas-phase model is critical for the entire mechanism. The gas-phase kinetics was first studied using a jet-stirred reactor without catalyst. Both experiments and simulations were conducted under various operating conditions using different gas-phase models. Quantities of interest and rate of production analyses on hydrocarbon products were also performed to evaluate the models. NUIGMech1.1 was selected as the most comprehensive model to describe the OCM gas-phase kinetics and used for the next study. Next, microkinetic analysis on La2O3-based catalysts with different dopants was performed. The Ce addition has the greatest boost over the performance. The kinetics at low conversion regimes were analyzed and correlated to the catalysts’ properties. The activation energy for methane hydrogen abstraction was estimated, with the formation rate of primary products, which suggested that the initiation reaction steps were similar for La2O3-based catalyst. A homogeneous-heterogeneous kinetic model for La2O3/CeO2 catalyst was then constructed. By applying in situ XRD, the doping of CeO2 not only enhanced catalytic performance but also improved catalyst stability from CO2 and H2O. A wide range of operating conditions was investigated experimentally and numerically, where a packed bed reactor model was constructed based on the dimensions of experimental setup and catalyst characterization. The rate of production (ROP) was also performed to identify the important reactions and prove the necessity of surface reactions for the OCM process. Laser-induced fluorescence was implemented to directly observe the presence of formaldehyde. The last section includes the implementation of in situ laser diagnosis techniques at the near-surface region to solve the existing challenges. Raman scattering was implemented to quantitate the concentration profiles of major stable species near the surface and measure the in situ local temperatures at different heights above the catalyst surface, to study the kinetics transiting from the surface edge to the near-surface gas phase and provide a new perspective in OCM kinetic studies.

<p> The homogeneous partial oxidation of ortho-xylene vapour by air in a 316 s.s. flow reactor was studied in this work, which was conducted in connection with, and preceding an investigation of the kinetics of catalytic vapour-phase partial oxidation of a-xylene. The main purpose of the present work was to make an exploratory study of the contribution of the homogeneous reaction, if any, in as much as it would affect the catalytic oxidation to be studied on the same experimental set-up. This would permit the correction for the rate of homogeneous reaction during the catalytic reaction under a range of experimental conditions, or, reveal conditions under which the catalytic reaction could be conducted with minimum contribution by the homogeneous reaction. </p> <p> The three variables studied and the range of conditions for each are as follows : 1. Air: o-xylene molar ratio: ,124 to J78 2. Residence time: 0.443 sec. to 0.539 sec. 3. Temperature: 430° C to 490° c </p> <p>The reaction product stream was analyzed mainly by Gas Chromatography, both qualitatively and quantitatively. Qualitative analyses of liquid samples of the reactor condensate were also conducted using a Nuclear Magnetic Resonance Spectrometer, Mass Spectrometer, Infrared Spectrophotometer and also by conventional chemical techniques. </p> <p> Product analysis indicated a-xylene oxide as the reaction product at the lmv conversions studied. An empirical correlation obtained by statistical analysis of the experimental data, relating the conversions obtained and the variables studied, has been proposed to calculate the extent of the homogeneous reaction under the conditions of a catalytic reaction study. The results obtained in this work are consistent with the suggested kinetics and mechanism for this reaction. </p> / Thesis / Master of Engineering (MEngr)