This work was primarily motivated by the industrial need for control of problems associated with the Gas Tungsten Arc Welding (GTAW) of small bore titanium and austenitic stainless steel tubes. These include: pore creation and entrapment in the weld zone, and variability of the fusion zone geometry. The primary aim of this study was the development of a low current orbital plasma welding capability using a structured approach which could lead to defect minimisation. The methodology should also have the potential to be used in a number of different conditions, extending the use of plasma welding in both melt-in and keyhole modes for the orbital welding of small bore tubes. The project originally involved the modification of a totally enclosed orbital GTAW welding head for low current welding operations. It was established that for the current range required for small bore and small to medium thickness tubes, the use of a solid copper torch was sufficient to provide the required heat absorption. A stable arc was produced even for very low current values (down to 7A) while arc voltages were within the operating range of a standard GTA welding power source. Procedural (i.e. off line) control was adopted for identification and optimisation of welding parameters. Since no procedure was available for the proposed welds it was necessary to generate the parameters required for the production of consistent weld profiles. Simultaneously, an expert system has been developed for the determination of optimum process parameters based on empirical models, developed using statistical techniques. Parameter combinations were selected based on physical as well as statistical relevance, providing a measure of confidence when predicting the required weld bead output characteristics. The approach also indicates the influence of the major input parameters on weld bead geometry and defect formation, such as undercut. Two quality acceptance criteria were employed during this investigation, weld bead dimensional accuracy, and the type and seriousness of defects present (penetration / burn-through, porosity and undercut). Off line programming was utilised to control heat build up and to ensure welds were obtained with the desired geometry and minimal defect levels. The end result was the development of a prototype system for low current orbital plasma welding (in both melt-in and keyhole mode) of small bore tubes in a totally enclosed head. Tolerant procedures for low current orbital melt-in and particularly keyhole welding have been generated and a systematic methodology for the prediction and optimisation of welding procedures based on predetermined criteria has been developed.

Thesis advisor: Richard Tresch / The Appalachia region has long been plagued by economic depression. Poverty is prevalent in this region, along with low income, and high unemployment. The Appalachian Regional Commission (ARC) was established in 1965 to promote economic development and alleviate poverty the historically lagging region. Until 1983 the ARC functioned under a growth center strategy that channeled funds to Appalachian areas that were more economically stable and appeared promising. In 1983 the ARC undertook a major change in policy with the introduction of the Distressed Counties Program, which shifted the focus and funds to counties in severe economic duress. My thesis uses regression analysis to test the effect of the Distressed Counties Program on poverty rates, unemployment rates, and real per capita income of the distressed counties in Appalachia. / Thesis (BS) — Boston College, 2007. / Submitted to: Boston College. College of Arts and Sciences. / Discipline: Economics Honors Program.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. August 2014. / The Central African Copperbelt is located in the Lufilian Arc which straddles the border between Zambia and the Democratic Republic of Congo (DRC). Mineralisation of the cupriferous Arc is found in basal Neoproterozoic Katangan Supergroup sedimentary rocks, which in DRC are termed the Mines Series Subgroup. The Mines Series is divided into the dolomitic and carbonaceous GRAT, DStrat RSF, RSC, SD and CMN units. The composition of the units is homogeneous across the Lubumbashi district and potentially across the Katangan basin. This study focussed on the Kinsevere and Ruashi deposits in the Lubumbashi district, which are approximately 50 km apart. The study confirmed that relative eustatic sea level changes resulted in the non-deposition of the RSF and RSC stratigraphic units at Kinsevere. Sedimentation was followed by early pervasive potassic alteration and silicification at the diagenetic stage whilst a magnesian dolomitisation event resulted in alteration of potassic feldspars and recrystallisation of carbonates. Albitisation was veincontrolled and late-stage scapolitisation altered evaporitic nodules. Finally, haematisation by late iron-rich fluids circulating through the Roan Group strata resulted in oxidation of sulphides. The structural analysis of Kinsevere Central pit indicates E-W and N-S shortening whereas the Ruashi pit 1 deposit underwent NE-SW and N-S shortening. Initial shortening, associated with Kolwezian deformation (D1), resulted in the formation of NE-thrust folds and a primary set of joints. The Kolwezian deformation event (D2), reoriented the shortening direction from E-W to N-S, creating interference folds and possibly a second set of joints. The final phase in the structural evolution of the Kinsevere and Ruashi deposits was late-stage brittle deformation (faulting). Mineralisation was a multi-stage process. Disseminated chalcopyrite and carrollite were deposited from formation waters during diagenesis in a stable basin environment. Chalcopyrite, carrollite, chalcocite and bornite are predominantly located at the base of the DStrat, whereas chalcopyrite and pyrite dominate the stratigraphically higher portions of the deposits. Hypogene vein mineralisation began at the syn- to late- orogenic stage with carrollite and chalcopyrite in beddingparallel veins. Possible changes in the compression direction created the perpendicularly oriented veins that host chalcopyrite, carrollite, bornite, covellite, digenite and chalcocite. Finally a late stage of chalcopyrite and pyrite deposition occurred in and around the evaporites, indicating a strong correlation between mineralisation, evaporites and scapolitisation. iii Near-surface supergene alteration of hypogene sulphide ores, resulted in Cu-Co carbonates and oxides, such as malachite, azurite, cobaltiferous malachite, chrysocolla, kolwezite and sphaerocobaltite being deposited in vugs and pore spaces above the meteoric water line. Faulted and brecciated zones tend to have deeper supergene alteration. Between the sulphide facies at depth and the supergene oxide facies at surface is a transition zone which marks the depth to which oxidation has penetrated. Sulphur isotope analysis from the Kinsevere and Ruashi deposits suggests a sulphur contribution from a continental Red-Bed sedimentary source and from an evaporitic source.

Diversas pesquisas em processos de soldagem para construção naval concentram-se em reduzir peso, aumentar a eficiência de energia, melhorar a resistência à corrosão e à tenacidade, bem como reduzir custos e tempo na construção dos navios. O aço naval microligado, AH36, apresenta boa correlação entre estrutura, propriedades mecânicas e soldabilidade. Estas características se devem principalmente a redução dos teores de carbono em função do uso de elementos microligantes como V, Nb e Ti, e do tipo de processo de obtenção das chapas pelo processo termomecânico seguido de resfriamento acelerado (em inglês: Thermomechanical control process -TMCP). Assim, o objetivo deste trabalho é avaliar a soldagem do aço naval AH 36 pelo processo de arco submerso com um e dois arames. Para tanto foram empregados os ensaios mecânicos de tração, de dobramento e de dureza. A tenacidade foi determinada pelo ensaio de Charpy com entalhe em V. Para caracterização metalográfica foram aplicadas as seguintes técnicas: Microscopia óptica (MO) e Microscopia eletrônica de varredura (MEV) e difração de raios X. Os resultados mostraram que as juntas soldadas apresentaram limite de resistência máxima de 561 MPa, com rompimento localizado no metal de base. No ensaio de microdureza foi observado que a região de crescimento de grão da zona afetada pelo calor, no experimento com a técnica Tandem, apresentou-se a região mais rígida das juntas analisadas, também o valor de microdureza no metal de solda foi 10% maior que no metal de base. Os resultados dos ensaios de impacto Charpy V mostraram que a temperatura de transição dúctil frágil do metal de base é de -30ºC. Da mesma maneira, o menor valor de energia absorvida foi para região do metal de solda. Através da análise da micrografia foi possível identificar diferentes morfologias de ferrita, a presença de perlita e pequenas regiões de martensita, bem como a presença de agregados MA. / Several researches in welding processes for shipbuilding has been focusing on reducing weight, increasing energy efficiency, improving corrosion resistance and toughness as well as reducing costs and time in the construction of ships. The microalloyed steel AH36 shipbuilding presents a good correlation among structure, mechanical properties and weldability. These features are mainly because reduction in carbon content due to the use of microalloying elements such as V, Nb and Ti, together with the process of steel plates by thermomechanical control process (TMCP), Therefore, the objective of this study is to evaluate the welding of shipbuilding steel AH 36 by submerged arc process with one and two wires. It was utilized tests such as: tensile, bending and hardness tests. The toughness was determined by Charpy V-Notch test. The metallographic characterization was carried out by the following techniques: optical microscopy (OM) and scanning electron microscopy (SEM) and X-Rays diffraction. The results showed that the tensile test for welded joints presented maximum resistance limit of 561 MPa, and the rupture was located in the base metal. Microhardness test showed that the region of coarse grain of heat affected zone, in the tandem submerged arc welding (SAW), presented the hardest region of the welded joint, also the microhardness value in the weld metal was 10% greater than the metal base. Charpy V notch test tests depicted a ductile brittle transition temperature at about -30 ºC. In the same way, the lowest absorbed energy was identified in the weld metal region. Through microstructure characterization it was possible to identify different morphologies of ferrite, pearlite and the small presence of martensite, as well as, the presence of aggregates MA.

In recent years, due to a need to reduce emissions, the automotive industry has focused on increasing vehicle efficiency. One of the areas being examined for potential improvement is the automatic transmission; specifically, the torque converter clutch damper. The better the performance of the damper, the more time the torque converter can be kept in the optimum locked position, thus increasing vehicle efficiency. Currently a large number of vehicle manufacturers use transmission technology sourced from external OEMs; due to a lack of available performance data or validated simulations, sometimes vehicle manufacturers are not able to fully understand the behaviour of the damper. If damper performance (or interactions with other components) cannot be fully assessed during the design development phase, key issues may become known too late in the development process. Thus a deeper understanding of the processes of experimentally characterising and simulating torque converter dampers is required. This thesis describes the development of an arc spring torque converter damper simulation, including the gathering of the experimental data required to validate the simulation. The simulation is used to draw conclusions on the impact of excitation signal form on damper behaviour, leading to new knowledge on the signals required to experimentally characterise a damper. In this thesis a methodology for (and implementation of) the characterisation of torque converter dampers is detailed. It was found that existing available technologies (e.g. fired engines, electric dynamometers) were either too inflexible or prohibitively expensive; thus a novel high frequency mechanical pulsation generator was developed. This solution was developed from a 4 cylinder motored diesel engine; the cylinders are filled with compressed air and the crankshaft driven using an electric dynamometer. Simulation and experimental data has confirmed that mean torque can be controlled using the input dynamometer, with the compressed air producing fluctuations of up to 900Nm amplitude. However, it was found that the frequency of the output pulsations varied from a fired engine; this is due to reactions between the pulsation generator and the stiffness and inertias of other components on the rig. A review of the performance of the novel pulsation generation concept against other damper excitation methods was also conducted. It was determined that fired engines and electric motors are more suitable for durability testing; the flexibility of the electric motors and the low running costs of the pulsation generator suit damper performance tests. The second phase of this project was to develop a simulation of a two-stage arc spring turbine damper. This damper consists of three inertias, separated by two spring sets; the outer spring set has 3 individual arc springs, while the inner spring set has 5 nested pairs. The principle of conservation of angular momentum is applied to each of the three inertias in order to calculate their individual accelerations. This method is also applied when calculating the acceleration and movement of the springs; the arc springs are discretised into mass and (massless) spring segments. Two features not previously seen in literature are included in the simulation; hardstops and nested springs. The physical hardstops limit the movement of the spring sets (relative movements of the inertias). In this study, the nested springs were simulated as a pair of parallel springs, rather than as a single stiffer arc spring; this is due to the friction that occurs between the springs (the inner race of the larger spring forms the housing for the inner spring). These two features highlight the need for hardware examination before simulation development; disassembling the hardware also allows the location of hardstops (and other features) to be measured rather than relying on the test data. Once a damper simulation was designed, a methodology for simulation parameterisation was required; parameterisation is the process of improving simulation performance through iterations of estimated parameters. The simulated damper was excited using sampled experimental data; to maximise parameterisation process efficiency, each time a parameter change was made, a set of key test points were selected in order to assess simulation performance change. It is not recommended that single test points be examined individually; parameter changes may improve simulation performance at one test point but have an adverse reaction at another. A clear causal relationship between simulation timestep and accuracy (as well as simulation run time) was found; a link between the number of discretised segments and simulation accuracy (and run time) was also confirmed. It was determined that 8 segments was optimal for the inner springs and 18 outer segments offered the best balance between computing power and simulation time. A variety of methods for analysing damper (and simulation) performance are presented in this thesis; it was found that for the 2.5 bar torque curve experimental data set the simulation performs excellently, with on average less than 5% error. Overall torque error is less than 10% across the tested speed range (900 to 2800rpm), with mean torque differences between simulated and tested order magnitudes of less than 5Nm. It has been determined that hysteresis loops are not an accurate predictor of real-world damper performance; while they can approximate general trends, they do not cover the normal operating condition. In the final phase of this thesis, the validated simulation has been used to investigate excitation signal, areas of poor damper performance and the link between speed and damper stiffness. By subjecting the simulation to a variety of sinusoidal input signals, it was established that if a sinusoidal signal approximates the 3 most dominant frequencies in a real signal, the damper will behave in a representative manner. Additional orders that have lower frequencies than the dominant order will have a greater impact on the attenuation behaviour of the damper; the effect of additional orders on attenuation behaviour is also linked to their magnitude (relative to the dominant order). A methodology for efficient damper mapping is proposed; the key aim is to produce a dataset that will minimise the length of the parameterisation process while capturing key damper behaviours. It was found that the magnitude of the torque oscillations used to excite the damper is linked to parameter adjustment impact, though this relationship is not linear for all parameters; an approximate level of 300Nm should be used for excitation. Parameters such as spring stiffness and plate inertias are more likely to have a substantial impact on damper performance at frequencies below 70Hz; friction tuning factors are impacted more by magnitude changes at frequencies above 150Hz. It has been demonstrated that while speed can have an effect on magnification ratio, this effect is far less significant at mean torques above the knee point and when sinusoidal input magnitude is kept at or above 300Nm. It was concluded that neither engine speed nor precise excitation magnitude must be replicated in order to predict approximate performance. During the investigation into areas of poor damper performance, it was confirmed that the trend of increasing magnification ratio with lower frequencies ( < 30Hz) seen in experimental data continued. Simulation testing above 140Hz revealed that there is not a linear relationship between increased frequency and increased magnification ratio; these areas of magnification ratio spikes are likely due to system resonances. It has been confirmed that while fluctuation magnitude does impact magnification ratio, fluctuation frequency has the most significant (dominant) impact. Finally, the effect of speed on apparent damper stiffness was investigated for both hysteresis loop testing and across a range of outer spring vibration angles; it was confirmed that increasing speed does result in non-homogeneous compression of the springs. It was established that while speed can have an effect on spring stiffness, this effect will vary significantly depending on the movement range (vibration angle) of the spring. / The largest increase in spring stiffness with speed is seen when segments of the spring become inactive (cease to move), hence why the effect of speed is more substantial at vibration angle of < 10°. The simulation was used to confirm the theories linking speed and stiffness found in the literature; higher speeds increase frictional forces, slowing damper segments, resulting in reduced movement. The findings of this thesis are relevant to damper simulation and testing engineers; by expanding knowledge of damper behavioural responses to high frequency excitation signals, as well as demonstrating an effective method for producing validated damper simulations, it is hoped that the vehicle design process will be more efficient and damper modifications more effective.

Thesis. 1977. Sc.D. cn--Massachusetts Institute of Technology. Dept. of Chemical Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Bibliography: leaves 222-228. / Sc.D.cn

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING / Includes bibliographical references. / by Miriam Zacksenhouse. / M.S.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by José Converti. / Ph.D.

Major depressive disorder (MDD) is a growing health problem. Current treatment options are not always effective and take several weeks of regular administration before an improvement can be seen in symptoms. Sub-anaesthetic doses of ketamine have been found to have antidepressant effects in previously treatment-resistant MDD after just one dose. However, ketamine also produces short term psychosis-like side effects which are undesirable for MDD patients. Ketamine is known to be an NMDA receptor antagonist, binding within the channel pore to block ion flow, however the molecular mechanism(s) underlying its antidepressant and psychosis-like effects are still unclear. In this thesis several genetically modified mouse lines were used to probe the molecular events involved in ketamine's actions. Firstly, a mouse line in which the c-terminal domain (CTD) of the NMDAR subtype GluN2B had been replaced with that of GluN2A, and a second line in which the opposite replacement had taken place, were used to investigate the role of the CTD in the NMDAR response to ketamine. It was found that the GluN2B CTD is required for the short-term psychosis-like response to a sub-anaesthetic dose of ketamine. This is interesting as the channel pore region, containing the binding site for ketamine, is unaltered in these mutants. Therefore, this finding implicates GluN2B CTD specific intracellular signalling molecules in this action of ketamine and raises the question of whether the CTD itself is able to respond to ketamine binding within the pore to induce signalling changes, perhaps via a conformational change. Secondly, a mouse line, in which the activity-regulated synaptic protein Arc has been tagged with a fluorescent marker, was used to investigate the response of synapses to both anaesthetic and sub-anaesthetic doses of ketamine. In this experiment tagged Arc protein was visible as punctate accumulations at synapses. A novel method termed 'synaptome mapping' was used to image these accumulations across entire coronal sections and to quantify their number, size and intensity. Using this method alterations to the Arc synaptome map were detected 1h, 6h and 24h following ketamine administration. The two doses used produced different changes to this map, with the sub-anaesthetic antidepressant dose inducing increases in Arc puncta number across many brain regions, whereas the anaesthetic dose induced short term (1h) increases followed by longer term decreases in Arc puncta number. This finding links long-term increases in Arc at the synapse with an antidepressant response to ketamine.

This thesis investigates the application of plasma immersion ion implantation (PIII) to polymers. PIII requires that a high negative potential be applied to the surface of the material while it is immersed in a plasma. This presents a problem for insulating materials such as polymers, since the implanting ions carry charge to the surface, resulting in a charge accumulation that effectively neutralises the applied potential. This causes the plasma sheath at the surface to collapse a short time after the potential is applied. Measurements of the sheath dynamics, including the collapsing sheath, are performed using an electric probe. The results are compared to theoretical models of the plasma sheath based on the Child-Langmuir law for high voltage sheaths. The theoretical model predicts well the sheath dynamics for conductive substrates. For insulating substrates the model can account for the experimental observations if the secondary electron coefficient is modified, justified on the basis of the poly-energetic nature of the implanting ions. If a conductive film is applied to the insulator surface the problem of charge accumulation can be avoided without compromising the effectiveness of PIII. The requirement for the film is that it be conductive, yet transparent to the incident ions. Experimental results are presented which confirm the effectiveness of the method. Theoretical estimates of the surface potential show that a film of the order of 5nm thickness can effectively circumvent the charge accumulation problem. Efforts to produce and characterise such a film form the final two chapters of this thesis. The optimal thickness is determined to be near the percolation threshold, where a marked increase in conductivity occurs. Spectroscopic ellipsometry is shown to be an excellent method to determine the film thickness and percolation threshold non-invasively. Throughout this work cathodic vacuum arcs are used to deposit thin films and as a source of metal plasmas. The design and construction of a pulsed cathodic vacuum arc forms a significant part of this thesis. Investigations of the cathode spots and power supply requirements are presented.