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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

The application of interactive computer techniques and graph-theoretic methods to printed wiring board design

Hope, A. K. January 1973 (has links)
No description available.

Geometric reasoning for process planning

Salmon, Jonathan Charles January 1997 (has links)
A Feature Oriented Detail Design System (FODDS2) is described that allows design of 2½ D components. The geometric reasoning required to generate anteriority constraints for subsequent process planning is described with accompanying problems, experiments and proposed solutions. The geometric algorithms currently unavailable in commercial solid modellers, but required for the system are described along with their implementations. All features in the system are described in a consistent manner in terms of a 'tool profile' and 'cutter path' allowing new features to be added simply and easily and ensuring that geometric reasoning can still be carried out. Novel work in the area of anteriority checking and of proximity checking of feature-based designs is covered.

Image based finite element modelling for the mechanical characterisation of complex material systems

Notarberardino, Bruno January 2010 (has links)
There is been increasing interest in understanding the physical properties of cellular solid for designing function specific architectures. A new approach has been adopted for modelling those complex micro-systems using image based techniques. The image based meshing is a novel method capable of generating the required volume discretisation (finite element and finite volume meshes) directly and robustly from the image data obtained from a range of imaging modalities such as magnetic resonance imaging and computed tomography. The purpose of the present work is combining image based meshing with finite element method (FEM) for mechanically characterise complex micro-structures. Cellular solid, previously investigated using conventional analytical and experimental approaches and their limitations, will be now explored with the accuracy and the precision of the image based finite element approach. Analytical models of the mechanics of open cell foams are reviewed and extended into a new parametric model which includes axial compression as deformation mechanism during compression. The parametric model, supported by the novel method, is used to predict the mechanical behaviour of two regular open cell micro-structures and a topology obtained from tomographic imaging of an open celled foam. The new approach is then extended to the dynamic analysis of a Polyurethane open cell foam under large strain deformation and different boundary conditions. Bone scaffolds, having the architecture of cellular solids, are mechanically characterised and parametrically investigated. Finally the novel method is applied on two phases composite systems on which a wide range of parametric and sensitivity analysis are carried out. The potentialities of combining image based techniques with FEM are then enlighten. keywords: cellular solid, image processing, Finite Element Method, image based meshing, large strain deformation, dynamic analysis, bone scaffold, synthetic structures, Alumina-Aluminium composite, parametric model, Polyurethane open cell foam, reverse engineering, material characterisation, lattice factory.

Simplified sewer flow modelling

Austin, Rebecca Jane January 2013 (has links)
Sewer networks are designed to collect and transport stormwater runoff. The capacity of these systems can be exceeded during extreme rainfall events, which can lead to flooding. Computational modelling is used to understand the behaviour and capacity of these networks, and to determine possible flood locations. Traditional sewer models, thatwhich can be coupled with water quality or catchment hydrological models, are typically computationally expensive,. This which limits their use for real-time modelling during an event. Conceptual models that solve less complex numerical algorithms can be used for faster modelling. However, the conceptual models developed so far have often been less accurate. In this study, two conceptual sewer simulators have been developed based upon Cellular Automata (CA) principles, which have low computation times in comparison to recognised benchmark models. CA models represent the region being simulated by a grid of cells, and simple rules are used to change the cell states. These models have been tested using three case studies (one hypothetical and two real world cases). The accuracy was determined in the case studies by performing a visual and statistical analysis of the results. The statistical analysis included measures such as the Root Mean Square Error, the Nash-Sutcliffe Efficiency, and the Index of Agreement. From this and looking at the computation times of the modelsIt it has been demonstrated that these new simulators are both fast and accurate.

Structure, strength and defect characterisation of cement based materials

Choudhury, Ajmol H. January 2014 (has links)
In cement based systems, the residual stresses are created by internal expansion. This provides toughening by the release of the residual stresses as the macro-crack propagates. While circumstantial evidence of the residual stresses exist (e.g. micro-crack formation leading to permanent deformation in flexural tests), it is very difficult to observe the mechanism in action. The quantitative estimate of the changes occurring in such cement-based systems is challenging due to the anisotropy and complexity of the material. Non-Destructive Testing (NDT) techniques were used in this research to observe the mechanism in action. An ultrasound technique is used to examine strength development and an acoustic emission (AE) technique is used to examine micro-structural changes, micro-cracks, crack initiation, crack propagation, crack arrests and crack bridging in plain concrete samples including samples containing admixtures and waste materials. The NDT techniques were found to be accurate in being able to measure compressive strength, with good correlation between both standard mechanical testing and NDT techniques. It was shown that admixtures could be effectively used to alter the properties of a curing cement mortar. This work has also demonstrated that ultrasound can be successfully used to determine the compressive strength of concrete from an early age. The ability to pre-determine the strength of concrete through correlation with NDT test parameters may reduce the time spent waiting on concrete to set and to obtain results using standard mechanical testing methods. The findings in this research present the effect admixtures had on the curing process of the cement based material. The introduction of certain additives into mortars have demonstrated an increase in both the rate of initial hardening and the magnitude of the compressive strength attained over the curing period depending on the mixture specification. The additives considered have been shown to actively alter and enhance the chemical process of curing from the start of hydration. Some additives that accelerate the curing process (accelerators) were found to lower the compressive strength of concrete using the ultrasound technique. Additives that caused an increase in the final strength of mortar also increased its toughness. The significant contributions in this research enabled observation of micro-structural changes and failure behaviour under compressive and flexural loading conditions on an on-line basis. The results obtained are encouraging and lead to increased understanding of cracking mechanisms in concrete containing various types of additives and aggregates. The application of the AE technique allowed the failure of interfacial bonding to be observed. The variation of the aggregate size and its effect on the monitored waveforms was established and the parameters in the AE signals are directly related to crack propagation (grain bridging/micro-mechanism) and strength of interfacial bonding. These findings have greatly contributed to the understanding of the concrete behaviour under complex conditions where no other technique could provide such valuable information on an online basis.

Indigenous capability building as an intervention strategy for sustainable energy implementation in vulnerable societies

Garniati, Leuserina January 2014 (has links)
Geospatial regions have different requirements for energy development due to variations in environmental, economic, social, and political constraints which influence their energy demand profiles and generation capacities. These constraints determine the policy, strategy, and implementation priorities for sustainable energy consumption, generation, and distribution. This PhD research project focuses on the role of interfaces between sustainable energy policy and appropriate technology; and its iterative feedback loop mechanism to encourage the implementation of sustainable energy systems in a vulnerable society. As a novel contribution to knowledge and practice, this PhD work concludes that: 1. Establishing a local business case for indigenous, appropriate technology, utilising a solid network which receives committed, political support, is an effective intervention strategy to fast track the deployment of sustainable energy systems, which breaks the cycle of vulnerability through social transformation and community empowerment. 2. Being aware of their own Western-Educated-Industrialised-Rich-Democratic (WEIRD) mindsets is a first step for knowledge exchange practitioners to overcome cultural differences and to introduce the intervention strategy. This was synthesised from the following new understandings which were obtained as the outputs of this PhD research: 1. Re-interpretation of the theory of vulnerable societies in relation to sustainable energy; 2. Re-interpretation of the theory of sustainable energy in relation to the proposed fourth dimension of sustainability; 3. Re-interpretation on the theory of appropriate technology in relation to technological independence and indigenous wisdom; 4. Novel conceptual model of a vulnerable society’s problem system; 5. Novel conceptual model of the interfaces between sustainable energy policy and appropriate technology in vulnerable societies. It is expected that the outcome of this PhD research can bridge the gaps identified in theoretical sustainable energy policies whilst in practice provide sound advice and confidence for policy makers and initiative implementers in grounding equal access to energy as a fundamental agent of change towards sustainable societal development.

Development of antimicrobial fabrics based on silver and copper nanoparticles

Mat-Zain, Norashikin January 2015 (has links)
With growing public unease surrounding the extent of microbial infections, there is a demand for antimicrobial materials including antimicrobial textiles. Nanotechnology has provided new solutions for the development of antimicrobial fabrics. In this study, nanoparticles of silver (Ag) and copper (Cu) and alloy nanoparticles of Ag and Cu (Ag/Cu) have been synthesized by reduction of their respective nitrates by ascorbic acid, using chitosan as a stabilising agent and microwave heating. UV-vis spectrophotometry indicated the presence of the alloy by a single peak (500 nm) for Ag/Cu nanoparticles, whereas mixtures of Ag and Cu nanoparticles (Ag+Cu) showed two peaks of 420 and 500 nm, corresponding to pure Ag and Cu nanoparticles respectively. Particle size is increased by increasing nitrate concentration and reducing the chitosan concentration. Surface zeta potentials were positive for all the nanoparticles and varied from +27.8 to +33.8 mV. Ag and Cu nanoparticles were shown to be spherical whilst the alloy nanoparticles had an irregular shape. Cu nanoparticles resulted in higher inactivation of bacteria such as Bacillus subtilis (B. subtilis), Escherichia coli (E. coli) and methicillin-resistant Staphylococcus aureus (MRSA) than did Ag nanoparticles at the same concentration. The effect was reversed when tested on nanoparticles of the same mean particle size with Ag nanoparticles emerging as more effective. Bacterial inactivation increased with concentration of chitosan and the metal concentration. The nanoparticles showed a more potent antibacterial effect than did ions of the same metal. B. subtilis was more susceptible than E. coli which may be due to the differences in their cell walls structure. MRSA proved harder to inactivate than both B. subtilis and E. coli under identical conditions. Antifungal activity was significantly affected by the types of nanoparticles employed. Ag nanoparticles displayed higher inactivation than Cu ones. Alloyed nanoparticles demonstrated the highest inactivation against both bacteria and fungi. This constitutes clear evidence of an antimicrobial synergy between the Ag and Cu. Bacteria and fungi in contact with nanoparticle-impregnated fabrics were revealed by FEGSEM to have taken on a shrunken appearance. Nanoparticle-impregnated fabrics reduced microbial viability by 80-90%, but this decreased in relation to the number of washes the fabric was subjected to and indicated a leached out of the nanoparticles. Pre-treatment of cotton fabrics with tannic acid and citric acid enhanced the durability of the antimicrobial effect when washed and this increased with concentration of the acid. Citric acid treated fabrics showed higher durability than tannic acid treated fabrics. Log reductions of Trichophyton interdigitale (T. interdigitale) were lower than those for B. subtilis, E. coli and MRSA at the same test conditions. The combination of nanoparticles with the antifungal drug fluconazole proved effective and reduced the time necessary to eliminate the T. interdigitale than either nanoparticles or fluconazole alone.

Investigating the performance characteristics of bromine quenched Geiger-Müller detectors with age and temperature

Abilama, Marc January 2015 (has links)
The halogen quench gas present within a Geiger-Müller detector will govern its operational lifetime. Such halogen gases are highly corrosive and are very likely to interact with their surroundings. This factor must be taken into account when designing GM detectors to extend their lifetimes. The quench gas depletion is thought to be linked to the current resulting from the gas ionisation from each detection event. As such, GM detector lifetimes are typically expressed in units of total counts accumulated. At elevated temperatures, the molecules will possess more thermal energy and become more likely to interact. To preserve the amount of halogen gas in each detector, three different corrosion-resistant techniques have been considered for investigation; the samples used are ZP1200 GM detectors that consist of 446 stainless steel components. The surface treatment techniques used to prepare each sample were labeled as “raw” for an oxygen plasma process, “passivated” for a combination of a nitric acid passivation and an oxygen plasma process and, finally, “plated” for a combination of a chromium plating process and an oxygen plasma process. The effectiveness of each process has been studied at temperatures of up to 175 oC. A Caesium-137 source was used to age all detector samples by irradiating them with dose rates of 1.3 mSv/hr. 32 samples were aged at room temperature and another 32 samples were aged in parallel at an elevated temperature of 125 oC. At room temperature, all detector types produced stable detectors with operational parameters that did not change significantly with age. The plated samples did show an initial rise in their starting voltage (Vs) measurements. At 125 oC, the plated detectors produced the most stable lifetime performance after an initial Vs conditioning period. The passivated and raw detector samples, however, showed a drop in their Vs values. Preliminary studies carried out at 175 oC confirm the superiority of the chromium plating process at resisting performance degradation at elevated temperatures. After investigating the surfaces of the detector components, no changes with age in the bromine content were observed. The plated cathodes showed no bromine deposits when investigated using Energy Dispersive X-Ray Spectroscopy. Bromine was detected on the passivated and raw cathode surfaces, but its quantity remained unchanged with age. The impact of contamination on the performance of gas-filled radiation detectors was also investigated in collaboration with the Institut Laue-Langevin in Grenoble, France.

Classifying and identifying negative Poisson's ratio : an examination of the auxeticity in zeolitic materials

Siddorn, Mark J. January 2014 (has links)
The aim of this thesis is to advance the understanding of auxeticity. This is achieved by developing a more accurate way to classify materials exhibiting the property, by carrying out high-throughput atomistic simulations of framework materials based on the SiO2 and GeO2 chemistries, and by exploring mechanistic models and possible correlations with directional density variations. At first this thesis outlines the development of a typographic system for negative Poisson's ratio. Materials are given classifications based on the degree to which auxetic behaviour is observed along specific axes of deformation and the frequency of occurrence of these axes. A systematic study is then performed on the elastic properties of zeolitic silicon dioxide and germanium dioxide structures. The typology is applied to these materials to better understand their auxetic behaviour. The JST framework is identified as isotropically auxetic, the first crystal to exhibit such general negative Poisson's ratios. An exploration into the effects of local density variations between parallel planes on Poisson's ratio is undertaken, but no clear correlation is found. Finally, software for systematically creating and evaluating two dimensional networks of triangles is produced. The geometrical analysis of these rotating structures predicts a high level of auxeticity and further work into three dimensional equivalents is recommended.

Sensory enhancement : a pilot perceptual study of subdermal magnetic implants

Harrison, Ian January 2015 (has links)
Subdermal magnetic implants originated as an art form in the world of body modification. To date an in depth scientific analysis of the benefits of this implant has yet to be established. This research explores the concept of sensory extension of the tactile sense utilising this form of implantation. This relatively simple procedure enables the tactile sense to respond to static and alternating magnetic fields. This is not to say that the underlying biology of the system has changed; i.e. the concept does not increase our tactile frequency response range or sensitivity to pressure, but now does invoke a perceptual response to a stimulus that is not innately available to humans. Within this research two social surveys have been conducted in order to ascertain one, the social acceptance of the general notion of human enhancement, and two the perceptual experiences of individuals with the magnetic implants themselves. In terms of acceptance to the notion of sensory improvement (via implantation) ~39% of the general population questioned responded positively with a further ~25% of the respondents answering with the indecisive response. Thus with careful dissemination a large proportion of individuals may adopt this technology much like this if it were to become available for consumers. Interestingly of the responses collected from the magnetic implants survey ~60% of the respondents actually underwent the implant for magnetic vision purposes. The main contribution of this research however comes from a series of psychophysical testing. In which 7 subjects with subdermal magnetic implants, were cross compared with 7 subjects that had similar magnets superficially attached to their dermis. The experimentation examined multiple psychometric thresholds of the candidates including intensity, frequency and temporal. Whilst relatively simple, the experimental setup for the perceptual experimentation conducted was novel in that custom hardware and protocols were created in order to determine the subjective thresholds of the individuals. Abstract iv The overall purpose of this research is to utilise this concept in high stress scenarios, such as driving or piloting; whereby alerts and warnings could be relayed to an operator without intruding upon their other (typically overloaded) exterior senses (i.e. the auditory and visual senses). Hence each of the thresholding experiments were designed with the intention of utilising the results in the design of signals for information transfer. The findings from the study show that the implanted group of subjects significantly outperformed the superficial group in the absolute intensity threshold experiment, i.e. the implanted group required significantly less force than the superficial group in order to perceive the stimulus. The results for the frequency difference threshold showed no significant difference in the two groups tested. Interestingly however at low frequencies, i.e. 20 and 50 Hz, the ability of the subjects tested to discriminate frequencies significantly increased with more complex waveforms i.e. square and sawtooth, when compared against the typically used sinewave. Furthermore a novel protocol for establishing the temporal gap detection threshold during a temporal numerosity study has been established in this thesis. This experiment measured the subjects’ capability to correctly determine the number of concatenated signals presented to them whilst the time between the signals, referred to as pulses, tended to zero. A significant finding was that when altering the length of, the frequency of, and the number of cycles of the pulses, the time between pulses for correct recognition altered. This finding will ultimately aid in the design of the tactile alerts for this method of information transfer. Preliminary development work for the use of this method of input to the body, in an automotive scenario, is also presented within this thesis in the form of a driving simulation. The overall goal of which is to present warning alerts to a driver, such as rear-to-end collision, or excessive speeds on roads, in order to prevent incidents and penalties from occurring. Discussion on the broader utility of this implant has been presented, reflecting on its potential use as a basis for vibrotactile, and sensory substitution, devices. This discussion furthers with postulations on its use as a human machine interface, as well as how a similar implant could be used within the ear as a hearing aid device.

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