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(2011)ThesisA comprehensive literature review on the AWJ cutting technology and associated sciences has been carried out and reported. It has been found that little research effort has been made to the AWJ cutting process for AMM laminations. As a result, the first comprehensive study on AWJ cutting of AMM laminations using various cutting techniques is presented in this thesis, with a view to understanding and improving the cutting performance, i.e. the depth of cut, the top kerf width and the kerf taper angle. An experimental study in the traditional way of AWJ operation (i.e. placing the nozzle perpendicularly to the work surface without nozzle oscillation) was carried out first to gain the basic understanding of the cutting process and cutting performance. Studies with cutting performance enhancement techniques, i.e. the nozzle oscillation and kerf taper compensation techniques, were then undertaken. The experimental studies included about 200 test runs to provide sufficient data for statistical analysis. Plausible trends of the cutting performance measures with respect to the process parameters have been found from the statistical analyses of the experimental data. In general, an increase in the water pressure and a decrease in the nozzle traverse speed and abrasive mass flow rate within the tested ranges increase the depth of cut. An increase in the kerf taper compensation angle decreases the kerf taper angle almost linearly. Nozzle oscillation cutting can reduce the kerf taper angle to less than 1o, and the kerf taper compensation cutting technique can eliminate the kerf taper if the process parameters are properly selected. Recommendations have been made on the selection of the most appropriate process parameters to be used in practice for each cutting technique. Predictive models for the various cutting performance measures have finally been developed. The depth of cut models were developed using the energy conservation approach, while those for the top kerf width and kerf taper angle were developed empirically. The models were then assessed both qualitatively and quantitatively. It has been found that the model predictions are in good agreement with the experimental data and can give adequate predictions of the cutting performance measures.
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(2013)ThesisA large portion of the high temperature critical components, used in the power, petroleum, and chemical plants etc. of the world have been in operation for long time like 30 to 40 years, are welded. In comparison to the parent metal, the mechanical and structure characteristics and properties of as-welded and weld metal are different, i.e. Hardness values of weld metal are significantly larger. Moreover, the heat affected zone causes structural differences in the comparison to the unaffected parent metal. Therefore, it is very important to determine possible degradation processes occurring in the weld joint inducing the properties changes during long term service and study the behaviour of each zone of the weld joints in the service conditions, as if critical welded components can be replaced before their failure during in the long term operation of those plants. In this thesis, a new model has been introduced and implemented to predict the remaining life of weld joints subjected to creep failure at high temperature and compared with other existing models. This proposed model contains two independent methods, stress analysis approach and strain analysis approach, to predict the remaining life of welded joints. To calculate the creep life, at first finite element analysis of the experimental cases has been done on the basis of Norton s creep law and then numerical results have been used for further calculation according to the proposed model theory. Finite element analysis showed that strain energy density has its maximum value in the heat affected zone, so creep failure occurs there, which is similar to the experimental observations. A new creep parameter has been found during the implementation of the proposed model which is the function of temperature and material properties for both the approaches, independently. This parameter plays a significant role to control the margin of error of the proposed model. Furthermore, stress analysis approach of the proposed creep life model has more good accuracy than the strain analysis approach. The whole study showed that proposed model goes with excellent accuracy with the experimental cases than the other existing creep life prediction models.
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(2012)ThesisThis thesis is concerned with the development of metallisation and interconnection schemes for e-beam evaporated polycrystalline silicon thin-film solar cells on glass substrates. Of particular interest is a method for series connection of individual cells to primarily minimise light leakage to the glass substrate and thus to reduce associated current loss. In this thesis, two new metallisation schemes have been developed and investigated. The first scheme is called the “aligned bifacial interconnected metallisation”. The diode is divided into individual cells by laser scribing an isolation groove, which is then filled with photoresist to act as an isolating dielectric. Aluminium is deposited over the whole device and patterned to form interconnected bifacial mini-modules. The open-circuit voltage of the mini-module was the sum of individual cells' voltages, indicating a successful interconnection. The mini-module short-circuit was slightly higher than the individual cell current due to lower light leakage in the glass substrate when a diffuse back surface reflector is used for light trapping. Current gain of about 2.6 % of a mini-module was achieved through the interconnection of individual cells. The second scheme investigated is the "self-aligned bifacial interconnected metallisation". In this scheme the emitter grooves are etched down to the glass substrates rather than to the emitter layer as in aligned bifacial scheme. Emitter electrodes are formed by filling the grooves with evaporated aluminium, which does not need alignment. The resulting emitter electrodes were wider, which was expected to reduce series resistance. However, the series resistance of both the individual cells and interconnected mini-modules were found to be higher due to reduced area of contact between the emitter electrodes and the emitter sidewalls. Devices metallised using this self-aligned scheme also recorded low shunt resistances due to Schottky contacts between emitter electrodes and the cell absorber. E-beam evaporated thin-film cells were successfully interconnected using the aligned bifacial scheme. Additional short-circuit current of the mini-module was reported, due to less current loss from light leakage through the glass substrate. Cells metallised with the self-aligned scheme suffered from series and shunt resistance.
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(2012)ThesisThe join query is a fundamental tool in many modern application areas including location-based services, geographic information system (GIS), finance and capital markets analysis, etc. Given two sets of objects U and V, a top-k similarity join returns k pairs of most similar objects from U x V. The top-k similarity joins have been extensively studied and used in a wide spectrum of applications such as information retrieval, decision making, spatial data analysis and data mining. In the conventional model of top-k similarity join processing, an object is usually regarded as a point in a multi-dimensional space and the similarity between two objects is usually measured by distance metrics such as Euclidean distance. However, in many applications such as decision making and e-business, an object may be described by multiple values (instances) and the conventional model is not applicable since it does not address the distributions of object instances. In this thesis, we study top-k similarity join queries over multi-valued objects. We formalize the problem of top-k similarity join over multi-valued objects, regarding quantile-based distance metrics which is applied to explore the relative instance distribution among the multiple instances of objects. Efficient and effective techniques to process top-k similarity joins over multi-valued objects are developed following a filtering-refinement framework. Novel distance, statistic and weight based pruning techniques are proposed. Comprehensive experiments on both real and synthetic datasets demonstrate the efficiency and effectiveness of our techniques.
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(2012)ThesisThis thesis has proposed and demonstrated a new 3D map which is realistic image-based, thus enabling geometry measurements and geo-location services. First and most important work of this study is the implementation of positioning and spatial measurements with image-based 3D maps, while current image-based 3D maps like Google Street View only provide virtual experience in terms of photos in which a number of details representing the topographic and terrain attributes are all lost, such as shapes and heights. Another contribution relates to quality analysis for a MRI 3D map. The research has deeply analyzed outlier impacts and introduced Dilution of Precision (DOP) values which are used to evaluate geometry quality for geo-referenced images either or measured vision points. In addition, the thesis has conducted a loose integration of mapping sensors like camera and GPS, and investigated image matching and stitching. The thesis has also proposed image-based 3D maps cooperated with Street View, in that panoramic viewing could make 3D maps more interactive with users, also bring an interesting immersive circumstance. This study has mainly focused on vision point positioning and implementation of spatial measurements on the MRI 3D map, analysis of data quality, outlier detection, and image processing. Users could obtain their orientation, position and object distance over basic functions of the MRI 3D map. A prototype geo-referencing system has been designed for the implementation of the MRI 3D mapping.
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(2012)ThesisAs a well-established multilevel converter topology, the cascaded H-bridge (CHB) is suitable for large-scale PV grid-integration due to its high-voltage and high-power capability, high power quality, modular structure, and multiple DC-links which are able to incorporate a large number of PV generators. Since PV system grounding is required by most countries grid codes and the modulation process of the CHB introduces high potentials upon the DC-side of the converter, galvanic isolation between the PV and the grid is essential to avoid the potential induced degradation (PID) of the PV modules, and to prevent the leakage current, as a result of the PV panel-to-ground parasitic capacitance, from flowing through the converter and ground, posing serious safety concerns. PV isolation can be achieved by the implementation of isolated DC/DC converters. The DC/DC converters connect the PV sources to the CHB converter through DC-links, performing maximum power point tracking (MPPT) and necessary DC voltage amplification, while the imbedded high-frequency transformers isolate the PV from the AC-side. The thesis presents the system validation and documents the performance evaluation of the CHB converter with isolated DC/DC converters for large-scale PV grid-integration, featuring different power and voltage level configurations, tailored with two control approaches, and through specific case studies. Two isolated DC/DC converter topologies, namely the boost-half-bridge (BHB) and the flyback are implemented. The CHB converter provides good quality voltage and current waveforms and is capable of medium-voltage grid-connection of the PV system. The system can be well regulated with voltage-oriented control (VOC) schemes both in the synchronous frame using Proportional-Integral (PI) controllers, and in the stationary frame using Proportional-Resonant (PR) controllers. Both DC/DC converters are able to perform MPPT under Standard Test Conditions (STC) and track the varying input voltage reference signal in a wide range fast and accurately. Compared with the flyback, the BHB converter presents lower ripples on the control variables and offers better MPPT efficiency at a higher component count. As the building block of the multiphase DC/DC converters, which feature high-voltage and high-current capability with modular and interleaved structures, the BHB makes a competitive candidate for this application.
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(2012)ThesisNon-photorealistic arts have been an invaluable form of media for over tens of thousands of years, and are widely used in animation and games today, motivating research into this field. Recently, the novel 2.5D Model has emerged, targetting the limitations of both 2D and 3D forms of cartoons. The most recent development is the 2.5D Cartoon Model. The manual building process of such models is labour intensive, and no automatic building method for 2.5D models exists currently. This dissertation proposes a novel approach to the problem of automatic creation of 2.5D Cartoon Models, termed Auto-2CM in this thesis, which is the first attempt of a solution to the problem. The proposed approach aims to build 2.5D models from real world objects. Auto-2CM collects 3D information on the candidate object using 3D reconstruction methods from Computer Vision, then partitions it into meaningful parts using segmentation methods from Computer Graphics. A novel 3D-2.5D conversion method is introduced to create the final 2.5D model, which is the first method for 3D-2.5D conversion. The Auto-2CM framework does not mandate specific algorithms of reconstruction or segmentation, therefore different algorithms may be used for different kinds of objects. The effect of different algorithms on the final 2.5D model is currently unknown. A perceptual evaluation of Auto-2CM is performed, which shows that by using different combinations of algorithms within Auto-2CM for specific kinds of objects, the performance of the system maybe increased significantly. The approach can produce acceptable models for both manual sketches and direct use. It is also the first experimental study of the problem.
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(2012)ThesisIn this work the modeling and performance analysis are present for a proposed MIMO Free-Space system called "Phase-Fading" system, which is a single-user with multiple-antenna system, where the transmitters and receivers are randomly located in specific areas and the links are dominated by Line-of-Sight (LoS) components. Since Free-Space Phase-Fading MIMO system channel is stochastic, based on Telatar's research, its capacity is determined by singular eigenvalue distribution of the random correlation matrix corresponding to channel transmit matrix. Firstly, for proposed Free-Space MIMO system, the asymptotic analysis was performed for the ergodic capacity with respect to the infinite number of transmit and receive antennas while keeping the aspect ratio beta constant, for which the explicit expression of asymptotic capacity was uncovered. In addition, an unification property has been found for asymptotic capacity performances in Phase-fading and Rayleigh channel. Secondly, considering the finite order channel capacity, simulation plots were present and the Phase-Fading System has better capacity than the conventional Free-Space MIMO systems and Rayleigh channel. Moreover, the singular value distribution has been worked out for 2 by 2 Phase-fading channel as well the capacity formula. Besides, an essential part has been discovered in the joint probability density function of eigenvalues.
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(2012)ThesisAnalysing cell motility is an important process in medical and biomedical studies since most active cellular functions involve change in shape and movements. Manual observation and analysis of cellular images and data sets is a tedious and error prone task. Therefore designing a reliable automatic cell tracking system could considerably ease the burden on biologists. Because of the limitations of microscopic imaging techniques, together with cell characteristics, analysing biological cells is a challenging task. This thesis proposes novel methods for cell segmentation and tracking as well as mitosis detection. It presents a Graph Cut-based cell segmentation algorithm that is fully automatic and exploits temporal information in video microscopy to achieve better segmentation results. It also presents a cell tracking method based on the network flow algorithm that does not rely on perfect cell segmentation, and uses the information of multiple frames for cell association. The tracking algorithm is able to cope with cells entering or exiting a frame any time. To detect mitosis events, the network flow cell tracking algorithm is extended in a novel way that can detect mitosis events and track their daughter cells afterwards. The proposed methods have been tested on the phase-contrast microscopic videos provided by Garvan Institute of Medical Research. Quantitative and qualitative analysis presented in this thesis show that employing temporal information for both cell segmentation and mitosis detection does improve the results considerably.
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(2012)ThesisThe aim of this thesis is to determine whether selecting usability testing participants on the basis of their personality, as measured by the Myers-Briggs Type Indicator (MBTI) extraversion/introversion scale, can enhance the results obtained in usability testing in a web context. This thesis assesses whether extraverted subjects can uncover a more significant subset of problems and, in particular, a larger number of more severe problems, than introverts during usability testing. If this were the case, then the process of usability testing can become more efficient by using participants who are able to provide the highest quality feedback and are able to find the greatest number of, and the most severe problems leading to a decrease in the number of necessary participants and a reduction in project costs and a higher return on investment. Forty-three randomly selected candidates were given the MBTI test. Of these, twenty qualified as either extraverts or introverts and were, therefore, selected to take part in the study. Two sample groups were constituted, one comprising ten extraverts and the other ten introverts. Each of these participants was then asked to take part in a formal laboratory-based usability testing with an e-commerce website. The participants were required to complete a total of five tasks. Performance metrics from these tasks were observed and recorded, with the main focus being on the number and severity of usability problems found by each of the participants. The severity rating was assigned based on an average severity score taken from four evaluators. This was then combined with the frequency of problem occurrence to give an overall severity rating to the usability problem ranging from two to eight, with two representing a low-level cosmetic problem and eight representing a major usability problem, which rendered the system unusable. The study established that extraverts found more usability problems than introverts (p<0.001), and also a larger number of more severe problems. Additionally, extraverts found on average 96% of all unique usability problems, whereas introverts found just 28% of all such problems. A strong positive correlation was found between the degree of extraversion and the overall number of usability problems found, using a Pearson correlation coefficient R=0.85 (p<0.01). Extraverted participants were more confident in their feedback and more comfortable voicing their opinions than introverted participants. Overall, extraverts talked more often, as measured by the words-per-second metric (p<0.001), and instigated more helpful commentary than introverts; through the feedback of extraverted subjects, 100% of all Category 6 high severity usability problems were uncovered. Based on the results of the usability testing carried out, this study has recommended a selection process for participants in usability testing, based on their levels of extraversion and their realistic use of the product. It is hoped that this approach to the selection of participants will ensure that the greatest number of, and the most severe, usability problems are found during usability testing. This will lead to a more efficient testing process and make it possible to decrease sample sizes in usability testing without reducing the quality of the results obtained, thereby providing a decrease in project costs and a higher return on investment.