Fundamental research on the growth of porous anodic alumina (PAA) films has been undertaken for many years because of the complexity of the processes involved and the wide range of commercial applications. In this study, a tungsten tracer approach has been used to determine the influences of current density and electrolyte temperature on the incorporation of the tracer and its distribution and consequently, the growth mechanisms of PAA films. The efficiencies of growth of PAA films, formed during anodizing at 5 mA cm-2 in the three major forming acids at 25°C, are ~60%, due to loss of outwardly migrating Al3+ ions at the film/electrolyte interface. Thus, only the inwardly migrating O2- ions contribute to formation of the anodic oxide at the film/metal interface. The pores are developed due to flow of alumina from beneath the pore base regions toward the cell walls, which is indicated by distortion of the incorporated Al-W alloy layers and retention of the tungsten species within the anodic films. PAA films formed at a low range of current densities (<2 mA cm-2) develop by a field-assisted dissolution mode, with significant losses of aluminium and tungsten species to the electrolyte, and low expansion factors of less than 1.2. Conversely, films formed at current densities ≥2 mA cm-2 grow by a flow mechanism: flow of film material transports the alumina oxide, including the incorporated tungsten tracers, from the barrier layer regions to the cell walls, resulting in relatively thicker films at higher current densities and retention of the tungsten within the films. The tungsten remains mainly within the inner cell region of the films, with a tungsten-free region present next to the pore wall. The efficiency of film growth increases from ~0.29 to ~0.73 with increase of current density from 0.5 to 30 mA cm-2, and from ~0.26 to ~0.88 with increasing current density between 0.5 and 50 mA cm-2 for anodizing in sulphuric and oxalic acids respectively.Comparatively, for PAA films formed at 15 mA cm-2 in oxalic acid, reduction of electrolyte temperature from 20 to 1°C gives rise to a slight increase of the anodizing efficiency from ~0.67 to ~0.74; the film expansion factor also increases from ~1.32 to ~1.43. The previous arises from reduced field-assisted ejection of Al3+ ions at the decreased electrolyte temperature.Anodizing of the aluminium substrates in phosphoric acid or neutral phosphate solution generates barrier anodic alumina films and the barrier layers of porous films respectively, which comprise phosphorus-containing outer regions and a phosphorus-free inner regions. The phosphorus-containing outer region accounts for ~0.67 of the barrier films and the ~0.80 of the barrier layer of the porous films. Further, the distributions of phosphorus species are not significantly affected by the incorporation of the tungsten tracer nanolayer into the films; the influence of the phosphorus species on the outward migration of the tungsten species is also negligible.This tungsten tracer study suggests a significant influence of the flow of alumina oxide, under the high electric field, on the formation of PAA films at current densities ≥2 mA cm-2.

This thesis deals with the development and design of a mechanism used to change the geometry of impeller blades in radial fans. Firstly, a suitable design was selected and then constructed taking into account the forces and loads applied. The blade consists of two parts - fixed, and movable. The movable part extends or retracts behind the fixed part of the blade, changing its length and therefore the operating characteristics of the fan. The simulation part of the work deals with the effect of the changed blade geometry on the fan performance at one particular operating point. The results show a slight reduction in performance, but on the other hand the fan is operable under a wider range of operating conditions. The conclusion of the paper suggests the need for further research to gain a deeper understanding of the capabilities of radial control mechanism fans.

This dissertation addresses the heartbeat and the systems of natural philosophy that were used to explain it in the 17th century. Thus, I work in two domains of explanation. The first domain is physiology, in which William Harvey correctly ordered the heart’s systolic and diastolic motions, while René Descartes incorrectly reversed them. By looking at Harvey and Descartes’ more complete physiological models I reconsider the controversy that spun out of their divergent accounts. The second domain is the junction of physics and metaphysics, representing the frameworks of natural philosophy behind physiology. I argue that Harvey’s physiology was correct while his supporting principles were “wrong,” and Descartes’ physiology was incorrect while his supporting principles were “right.” Thus, my thesis is that Harvey was “right” but perhaps for the wrong reasons, while Descartes was “wrong” but perhaps for the right reasons. Of course, this judgement is made from a contemporary perspective. By using a contextualist approach to history, I aim to show how the controversy between Harvey and Descartes resolved in Nicolas Steno, when he discovered that the heart is a muscle.

The aim of this diploma thesis is detailed characterization of new diol-based column, i.e. Torus DIOL designed for supercritical fluid chromatography, in hydrophilic interaction liquid chromatography. This stationary phase contains diol ligands bonded on BEH ("bridged ethylene hybrid") particles. The BEH sorbent is more stable at high pH, pressure and temperature than conventional silica sorbents. Five fluorinated pesticides were successfully separated on Torus DIOL column. Retention mechanism and effect of different parameters were tested by analysis of small polar compounds (nucleobases, uridine and its derivatives, acidic, neutral and basic compounds). Both partitioning of analytes between an aqueous layer deposited on the surface of the stationary phase and the mobile phase and adsorption of analytes on the stationary phase participate in the retention mechanism. Effect of the mobile phase aqueous part pH was investigated with the following buffering solutions: formic acid (pH = 2.1), 10mM ammonium acetate (pH = 4.7 and pH = 9.5). Obtained results showed that aqueous part pH significantly affects retention of acidic compounds according to their pKA values. Retention of all tested analytes on Torus DIOL column slightly increased with increasing ionic strength of mobile phase. The retention...

Bibliography: pages 136-144. / This thesis is an attempt to defend explanatory incompatibilism, the view that mechanistic and intentional explanations of behaviour are incompatible, against various sorts of objections which come in the form of rival compatibilist theories. In the first chapter the author outlines the prima facie case for explanatory incompatibilism. This prima facie case is then bolstered by a discussion of explanation in general, conditions of compatibility for different explanations of the same phenomenon, and then a more rigorous account of mechanistic and intentional explanations which allows for a formal presentation of an argument for their incompatibility. Chapters Two, Three and Four discuss some of the combatibilist theories which have been advanced. Chapter Two involves a discussion of the "Double-Language" version of compatibilism as advocated by Ryle and Melden. This version is rejected for two main reasons: (1) it fails to keep the two sorts of explanation sufficiently apart so as to render them compatible, and (2) it fails to show that intentional explanations are not a species of causal explanation. Chapter Three attempts to deal with the "Instrumentalist" version of compatibilism as advanced by Daniel Dennett. This is rejected because it fails to provide a rich enough account of rational action and it also leads to epiphenomenalism. In Chapter Four the author discusses the "Physicalist" approach to the question of compatibility as advocated by Alvin Goldman and Donald Davidson. But this version of compatibilism is found to be wanting because it also leads to the epiphenomenalism of the mental. Chapter Five, the conclusion, summarises the basic argument and attempts to develop the author's own account of what the necessary and sufficient conditions for intentional action are. This is found to involve· three main elements: physical indeterminism, intentional intelligibility, and then something like the concept of agent-causation. In the course of this account there is a brief discussion of the problem of other minds and an argument against the desire-belief model of action and its explanation based on its inability to cope with the problem of deviant causal chains. It is concluded that mechanistic and intentional explanations are indeed incompatible and something is said about the broad metaphysical view which is required to accommodate this fact.

The two atom switching reactions referred to in the title were originally studied at temperatures greater than 2000°K in shock tubes by other investigators. For each reaction they proposed a direct four-center exchange mechanism in which one of the reactant molecules must be vibrationally excited, (the vibrational excitation mechanism or VEM). One of the predictions of the VEM is that molecules which are vibrationally hot but translationally cold should react through the four center transition state that leads to exchange. Using a mercury photosensitization technique, it is shown in the present work that excitation of CO to high vibrational levels is not sufficient to cause the CO self-exchange reaction. Similar attempts were also made to verify the VEM for the N2 reaction, but no exchange was observed. Kinetic modeling studies show that an atomic chain mechanism triggered by traces of oxygen impurity is responsible for all or much of the CO exchange observed in the shock tubes. Modeling studies show that many of the observed features of the N2 reaction are also correctly predicted by an atomic chain mechanism; however, the critical step in the mechanism, the N + N2 exchange reaction, has never been observed. Potential surface calculations show that at the restricted Hartree-Fock level of approximation the N3 potential surface has an energy barrier for exchange of over 80 kcal/mole, which is much too high if the atomic mechanism is to operate in the shock tubes. By comparison with similar calculations on N2o+, it is argued that the RHF calculations probably overestimate the true barrier height by about 80 kcal/mole, so the barrier to exchange on the N3 potential surface is probably no more than a few kcal/mole, and the N + N2 reaction is probably fast at high temperatures. Potential surface calculations on N4 show that the barrier to exchange through the four-center transition state is almost certainly much too high to account for the exchange observed in the shock tubes. Certain limitations on the rate law and energy barrier to exchange are derived for the VEM. It is concluded that both exchange reactions can be explained by atomic chain mechanisms and there is no need to invoke the VEM for either reaction.

Molybdenum compounds present a series of baffling chemical puzzles. By no means are all of these yet even clearly defined and many may never be. This complexity results from the ability of molybdenum to form six different oxidation states, which can possess three different coordination numbers. Furthermore, molybdenum compounds readily disproportionate to yield mixed valence compounds; and finally, molybdate ions readily aggregate in solution to form a variety of polyions by polymerization-condensation reactions which are controlled by pH and the concentration of the system. Molybdenum' s complexity can best be summed up in the words of the late Edgar Smith who described molybdenum to his classes as “ambidextrous, bi-sexual and polygamous.”

The phosphothreonine lyase class of enzymes represents a recently discovered set of enzymes that catalyze a dephosphorylation reaction. The catalysis is carried out using a unique elimination mechanism without any involvement of cofactors. Crystallographic studies of SpvC, a phosphothreonine lyase, and its mutant show that the mutation of the general catalytic acid does not result in any significant perturbations to the tertiary and the secondary structure of the protein. Using results from the structural studies and a deuterium isotope exchange experiment, we conclude that the reaction catalyzed by SpvC may not involve formation of a carbanion at the active site.

Seepage barriers have been used extensively to mitigate seepage problems in dams and levees. Although the design of many of these dams and levees has been based on intact barriers, seepage barriers have been shown to be susceptible to deformation and cracking when high differential hydraulic pressures act across the barrier. Under certain conditions, these cracks can lead to serious seepage problems, which could potentially lead to the development of a low-resistance seepage pathway. Three scenarios have been identified where there is the potential for erosion to occur adjacent to a crack in a barrier: 1) erosion at the interface between a fine-grained soil and a course-grained soil, 2) erosion of overlying soil due to flow along a joint in bedrock, and 3) erosion of the barrier material. The objective of this study is to investigate the first mode of erosion and identify the conditions at which more serious seepage problems can develop. The research has been performed using a laboratory model to simulate conditions near a seepage barrier crack under the scenarios described above. The results from the laboratory testing were compared to finite element seepage models for each scenario to estimate the flow velocities near the crack. The flow velocities were compared to estimated critical velocities of the soil to asses where erosion is likely to occur. A comparison was made between the observed behavior in the model and the behavior predicted with the computer model. The results of the research will be used to develop a method to assess the potential for erosion to occur and develop into a failure mode based on conditions near seepage barrier cracks.

Ultrasonic welding (UW), as a solid-state joining process, uses an ultrasonic energy source (usually with a frequency of 20 kHz or above) to induce oscillating shears between the faying surfaces to produce metallurgical bonds between a wide range of metal sheets [1, 2], thin foils [3], semiconductors [4], plastics [5], glass [6], and ceramics [7]. In contrast to traditional fusion welding processes, ultrasonic welding has several inherent advantages [3,8] derived from its solid-state process characteristics, and has been in use as a versatile joining method in the electronics, automotive, and aerospace industries since the 1950s