• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 715
  • 595
  • 104
  • 84
  • 59
  • 14
  • 13
  • 10
  • 9
  • 9
  • 7
  • 6
  • 6
  • 6
  • 5
  • Tagged with
  • 2023
  • 450
  • 443
  • 379
  • 239
  • 234
  • 173
  • 153
  • 139
  • 139
  • 130
  • 127
  • 126
  • 121
  • 121
  • 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.
111

An integrated approach to combine computer-based training (CBT) and immersive training (ImT) for mechanical assembly

Kim, Young Jun, January 2007 (has links) (PDF)
Thesis (Ph. D.)--Washington State University, May 2007. / Includes bibliographical references (p. 106-109).
112

Minimisation of energy consumption variance in manufacturing through production schedule manipulation

Duerden, Christopher James January 2016 (has links)
In the manufacturing sector, despite the vital role it plays, the consumption of energy is rarely considered as a manufacturing process variable during the scheduling of production jobs. Due to both physical and contractual limits, the local power infrastructure can only deliver a finite amount of electrical energy at any one time. As a consequence of not considering the energy usage during the scheduling process, this limited capacity can be inefficiently utilised or exceeded, potentially resulting in damage to the infrastructure. To address this, this thesis presents a novel schedule optimisation system. Here, a Genetic Algorithm is used to optimise the start times of manufacturing jobs such that the variance in production line energy consumption is minimised, while ensuring that typical hard and soft schedule constraints are maintained. Prediction accuracy is assured through the use of a novel library-based system which is able to provide historical energy data at a high temporal granularity, while accounting for the influence of machine conditions on the energy consumption. In cases where there is insufficient historical data for a particular manufacturing job, the library-based system is able to analyse the available energy data and utilise machine learning to generate temporary synthetic profiles compensated for probable machine conditions. The performance of the entire proposed system is optimised through significant experimentation and analysis, which allows for an optimised schedule to be produced within an acceptable amount of time. Testing in a lab-based production line demonstrates that the optimised schedule is able to significantly reduce the energy consumption variance produced by a production schedule, while providing a highly accurate prediction as to the energy consumption during the schedules execution. The proposed system is also demonstrated to be easily expandable, allowing it to consider local renewable energy generation and energy storage, along with objectives such as the minimisation of peak energy consumption, and energy drawn from the National Grid.
113

Interferometric Methods for Seismic Monitoring in Industrial Environments

Dales, Philippe 19 October 2018 (has links)
As the global demand for energy and natural resources continues to increase so does our interaction with Earth's near surface through resource extraction and waste injection. In monitoring these interaction, seismology plays a central role. The focus of this work is on improving the detection and localization of seismic sources, a fundamental problem in seismology. After discussing the strengths and limitations of existing methods for source detection and localization, I develop a solution based on a beamforming approach that uses cross-correlation functions in a maximum likelihood search for sources of seismic energy. I call this method InterLoc, short for `interferometric locator', and apply it to data recorded at two active underground mines to demonstrate its effectiveness in monitoring both impulsive sources and persistent sources. Next, I demonstrate how persistent seismic sources, typically seen as contaminants, can be used directly to measure small changes in the medium between a source and either source-station pairs. This method relies on the ability to locate and monitor source activity and then use this information to identify and select cross-correlation functions to isolate each source of interest. From the resulting cross-correlations, it is possible to measure small temporal changes in the waveforms. To demonstrate this method, I show how ore-crushers can be used to track the growth of a block cave by measuring changes in traveltimes due to ray paths having to circumvent the growing cave. In the final chapter I focus on the development of a processing framework for the detection and location of microseismic events recorded on dense (or large-N) surface arrays. The proposed framework involves: (1) data reduction; (2) dividing the array into smaller sub-arrays; (3) waveform processing within fixed time windows; (4) stacking of time windows selected based on each potential origin time and source location; and (6) combining the output from all sub-arrays to infer detections and locations of sources. This methodology is validated with synthetic data built to emulate a real dataset from a 10,050 node survey to evaluate the suitability of land for carbon sequestration. Based on the presence of very strong coherent contaminating sources and low rock quality, I am only able to detect sources with moment magnitude greater than -0.5. In the five hours of data processed there is no positive detections suggesting this could be a good site for carbon storage. More work is needed to improve the detection threshold and quantify risk based on event location and magnitude. In summary, my work demonstrates how the interference (via cross-correlation) and stacking of seismic waveforms can be combined in different ways to create effective solutions for problems faced by today's industries.
114

EFFECTS OF USING VIDEO, AUDIO, OR MIXED CHANNELS FOR VICARIOUS LEARNER INTERACTIONS IN A SYNCHRONOUS E-LEARNING ENVIRONMENT

Sarmiento, Roman Eduardo 01 August 2014 (has links)
Technology changes often force teachers, trainers, instructional designers, and administrators to make instructional design and delivery decisions that ideally should be based upon pedagogy research. In many circumstances, however, a foundational pedagogy question is only recognized when a technology decision reveals it. Such is the case when deciding what mode (video or audio) to use for learner interaction in a synchronous online learning event. While some research has focused on the learning and the satisfaction of learners when they were interacting, almost no research has addressed the learning value of observing the interactions of other learners. The purpose of this research study was to investigate whether the mode in which direct learner interactions were made affected non-interacting learners' recall of content in a synchronous virtual learning environment. The participants in this study viewed one of three versions of a webinar on Multimedia Games for Learning: a) all learners interacted in video mode; b) all learners interacted in audio mode; or all learners interacted in both video and audio in a mixed mode. No statistically significant difference was found between the video, audio, and mixed treatment conditions in terms of the recall of content from the questions or comments made by directly interacting learners. However, a statically significant difference was found in non-interacting learners' recall of the contributions of direct interactors based on the mode of interaction within the mixed-mode group. Study participants recalled more of the contributions made in the audio mode of interaction than in the video mode when the modes were mixed. These findings suggest that designers of synchronous online learning may choose either video or audio mode without affecting those learners who are not directly interacting but should take care in mixing interaction modes within a single synchronous online learning event. The contributions of the study reach beyond the findings. The study supports vicarious interaction as a process worthy of research and e-Learning design consideration. It provides a model for experimental manipulation of "simulated" synchronous sessions, and it introduces recall of others' verbal contributions as an approach to measurement of the attention granted vicarious interactions by those not interacting directly with others.
115

Using semantics to enhance query reformulation in dynamic distributed environments

Fernandes, Damires Yluska de Souza 31 January 2009 (has links)
Made available in DSpace on 2014-06-12T15:49:34Z (GMT). No. of bitstreams: 1 license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2009 / O processamento de consultas tem sido abordado como um problema central em ambientes dinâmicos e distribuídos. O ponto crítico do processamento, no entanto, é a reformulação da consulta submetida em um ponto origem em termos de um ponto destino, considerando as correspondências existentes entre eles. Abordagens tradicionais, em geral, realizam a reformulação utilizando correspondências de equivalência. Entretanto, nem sempre conceitos de um ponto origem têm correspondentes equivalentes no ponto destino, o que pode gerar uma reformulação vazia e, possivelmente, nenhuma resposta para o usuário. Neste caso, se o usuário considera interessante receber respostas relacionadas, mesmo que não precisas, é melhor gerar uma reformulação adaptada ou enriquecida e, por consequência, respostas aproximadas, do que nenhuma. Dentro deste escopo, o presente trabalho propõe um enfoque baseado em semântica, denominado SemRef, que visa integrar técnicas de enriquecimento e reformulação de consultas de forma a prover usuários com um conjunto de respostas expandidas. Reformulações exatas e enriquecidas são produzidas para permitir alcançar esse conjunto. Para tal, usamos semântica obtida principalmente de um conjunto de correspondências semânticas que estendem as normalmente encontradas na literatura. Exemplos de correspondências não usuais são closeness e disjointness. Além disso, usamos o contexto do usuário, da consulta e do ambiente como meio de favorecer o processo de reformulação e lidar com informações que somente são obtidas dinamicamente. Formalizamos as definições propostas através da Lógica Descritiva ALC e apresentamos o algoritmo que compõe o enfoque proposto, garantindo, através de propriedades aferidas, sua corretude e completude. Desenvolvemos o algoritmo SemRef através de um módulo de submissão e execução de consultas em um Sistema de gerenciamento de dados em ambiente P2P (PDMS). Mostramos exemplos que illustram o funcionamento e as vantagens do trabalho desenvolvido. Por fim, apresentamos a experimentação realizada com os resultados que foram obtidos
116

Changes in soil invertebrate decomposer communities during regeneration of Scots pine within the Abernethy Forest Reserve, Scotland

Horwood, Jane January 2001 (has links)
Plans currently exist to extend the range of native woodland within the Scottish Highlands. The effects of such an expansion on birds, mammals and above ground invertebrates have been previously been investigated, but little consideration has been given to soil invertebrates. This research looks at effects of Scots pine (Pinus sylvestris) regeneration on the meso- and macro- soil invertebrate communities. Within the Abernethy Forest Reserve (the largest remaining tract of native Scots pine woodland within the UK) mature woodland (pine-dominated) and moorland (Calluna vulgaris-dominated) sites were chosen on the three soil types present; an iron podzol, humus-iron podzol and peat. Three intermediate regeneration sites, upon two of the soil types, were also selected based on tree density and diameter at breast height (dbh). Together these sites formed two transects representing succession from moorland to mature woodland on the two soil types. At each site soil invertebrates were collected to a depth of 0.1 in and pitfall traps set. Litter bags were placed at the woodland and moorland sites to examine invertebrate succession during Pinus and Calluna litter decomposition. All invertebrates were identified to order and oribatid mites identified further using the morphospecies technique. The influences of soil type, depth, season and tree age on invertebrate communities were analysed using TWINSPAN and CANOCO. Results suggested that differences were present in invertebrate abundance and community structure between the two soil types, with more variation occurring along the peat transect than podzol transect. A number of oribatid morphospecies showed differences in density between transect sites and indicator species were present which separated the younger regenerating sites form older woodland. CANOCO analysis demonstrated that this was primarily due to changes in soil pH and temperature. In litter bags, Calluna showed significantly greater colonisation compared with Pinus at all sites and woodland litter bags supported a greater diversity of invertebrates than comparable moorland bags. Calluna litter is more complex than Pinus and may therefore provide a greater number of niches for invertebrates and shelter from prey. Differences between sites may be due to the presence of species adapted to utilising both litter types at the woodland end of the transect. In general concentrations of N and P significantly influenced the community composition within litter bags (pc0.05), but there were no significant relationships with other macronutrients. This work has shown that there are differences in the invertebrate community composition during the regeneration of Scots pine and decomposition of litter, however it is currently unclear whether these changes are truly successional.
117

Farm waste management : the effects of fine bubble aeration on cattle slurry and the fate of ammonia during the treatment process

Woodcock, David January 2003 (has links)
The aim of this investigation was to study the effect of fine bubble aeration on the relative amounts of N species, specifically NH 3 and NI-I4 within cattle slurry. Research into farm waste treatment systems has mainly concentrated on pig waste, yet cattle slurry treatment presents a challenging and relatively neglected research area. Farrell (1996) developed a fine bubble aeration treatment system and studied the effects of aeration on physical, chemical and fertiliser quality of slurry. He noted substantial loses of total Kjeldahl N from aerated slurry. This is a major concern as stripped NH3 can present a significant atmospheric pollutant. Here aeration treatment was studied at laboratory-scale (1 litre) and pilot-scale (100 litres). Air was externally supplied to tubular fine bubble diffusers. Initially a settleable floculative microbial culture was developed using batch-to-batch aeration that was continuously aerated for a maximum of 5 days. Treatment conditions were varied to study effects of aeration rate, temperature, pH and the addition of an adapted microbial culture upon N species within the slurry. The exhaust gases from the aeration bioreactors passed through a chemical capture system. Slurry samples were obtained during treatment to establish the chemical and biological changes. Finally, the effect of aeration on the fertiliser value of the treated slurry was studied. Experiments at laboratory-scale showed that N was released as NH 3 within the exhaust gases and that there were major changes in the amount and type of N species within the slurry. Increasing the pH of the slurry increased the quantity of NH3 released. Similar increases in rates of NH 3 release were shown for aeration rates up to 0.2 vvm and temperature up to 60 °C. The optimum conditions for NH3 stripping were found to be alkaline pH, high aeration rate and high temperature. At low aeration rates and low temperatures, there was a 96.59 % conservation of NH3 . The addition of an adapted microbial culture minimises the loss of N from the system, through the conversion of volatile N into organic microbial N fraction. In conserving N it was found that problems with sedimentation occurred. To improve rates of pollutant reduction it was necessary to increase temperature and aeration rates. Increasing temperature from 50 °C to 60 °C was found to have a negligible additional effect upon the biological degradation of the organic material within the slurry. This treatment strategy requires a capture system to trap the released NH3 . The aerobic treatment of cattle slurry was not found to have a significant effect upon the growth of maize in comparison to that of unaerated cattle slurry. Recommendations are made for operating conditions of an aerobic treatment system that will enable N to be either stripped from, or conserved within the slurry.
118

Studies on the excretion of pesticides in human milk as a means of investigating exposure and assessing the risk to infants in Indonesia

Barnes, Emma January 2004 (has links)
Humans bioaccumulate organochlorine pesticides throughout their lifetime due to the global environmental presence and physiochemical properties of these compounds, however, monitoring the current and lifetime exposure of the population to these compounds is complex. The collection and analysis of questionnaire data from Indonesia, human milk samples from Indonesian and UK born mothers living in Indonesia and milk samples during a 9-month lactation period as described in this thesis significantly contributes to the knowledge of human exposure to organochlorine pesticides and residue levels in human milk. Residue levels in milk samples from Indonesian mothers were positively correlated with the mother's age and parity, were higher in samples from urban than rural areas and did not show consistent correlations with diet. Correlations between pesticide levels and duration of lactation were not identified in a series of samples from the same mother or in samples from Indonesia. On a global scale residue levels from Indonesian samples were low, but p,p'-DDT was detectable in all samples and levels of y-HCH and p,p'-DDD were amongst the highest reported. The results from Indonesia including UK born women living in Indonesia coupled with existing data confirmed that the environment of Indonesia is contaminated with organochlorine pesticides and individuals had higher exposures in Indonesia than the UK. However, residue levels in milk samples from Indonesian women did not reflect the very high levels previously reported in local foods. An investigation into trends of organochiorine residue levels in human milk, foods and diets revealed that the consumption of animal fat significantly influenced human exposure and corresponding levels in human milk. Due to the extremely low consumption of animal fats by Indonesian people, the organochlorine levels detected in human milk did not reflect the environmental levels of these compounds. An exposure assessment model for residential Propoxur use in Indonesia was developed. It revealed that despite daily exposures, only low levels of Propoxur were likely to be absorbed and Propoxur exposure was unlikely to have toxicological effects. Despite more than 50 years of research, the detrimental effects of organochiorine pesticides in human milk have not been identified. The results indicated that 28% of Indonesian infants exceeded the acceptable daily intake (ADI) for Dieldrin, 90% exceeded the acute reference dose for total DDT and 24% for Endosulfan.
119

Monitoring and measuring the impacts and environmental implications of flood events on contaminated sediment dispersal in the River Swale catchment, North Yorkshire

Young, Elizabeth Anne January 2006 (has links)
The extraction, processing and smelting of ores has long been responsible for the release of heavy metals into the fluvial environment. As a consequence numerous studies have reported enhanced metal concentrations found in association with the sediments of rivers and in their surrounding floodplains. This thesis investigates the mobilisation, transport and the overbank deposition of sediment-associated heavy metals during flood events on the River Swale, North Yorkshire. This catchment has a prolonged history of mining for lead and zinc which spans approximately 2,000 years. Contemporary overbank sediment deposits for the fbll length of the river system were examined following three flood events that occurred in 2002. The quantity of sediment deposited and concentrations of associated metals were determined as well as the metal deposition flux and speciation, by using various analytical procedures including a nitric acid digestion and the BCR sequential extraction method. Physical characteristics such as sediment grain size, pH, loss on ignition and carbonate content were also investigated. Floodplain sedimentation rates were relatively high during the floods and the patterns in metal concentrations were both spatially and temporally consistent. The locations of most concern were located within the headwaters of the catchment where lead concentrations exceeded 25,000 mg kg'. Investigations into the mobility of the sediment-associated metals revealed that up to 88% of cadmium was found within the exchangeable phase of the sediment, however the concentrations of exchangeable lead and zinc were much higher and surpassed UK Government guidelines for crop growth and grazing livestock. Concentrations of exchangeable lead and zinc reached 19,241 mg kg' and 1,457 mg kg' respectively. Locations of 'exchangeable metal hotspots' with high levels of bioavailable metals were repeatedly found within the upper 21 km of the catchnent, around the confluence of tributaries which drain once intensively mined areas. These very high concentrations potentially pose a risk to flora and fauna that grow or graze on the floodplain surrounding the River Swale if they are taken up or ingested. Remediation measures could be adopted to treat either the source of metals in order to prevent them entering the fluvial system, reduce the concentrations already in the contaminated floodplain, or minimise the area inundated by flood waters. Alternatively, land management strategies could be adopted in order to reduce the potential for metal uptake by plants and animals and subsequently entering into the foodchain.
120

Aluminium toxicity (with reference to copper) in the aqueous environment and the mechanisms of its glutathione-mediated detoxification in the brine shrimp (Artemia franciscana)

Cookson, Stephen January 2001 (has links)
Glutathione (y-glutamylcysteinylglycine) is a vital and ubiquitous component of biological systems that has been demonstrated to have a protective role against the toxicity of a wide array of xenobiotics and their metabolic by-products. It has been shown to detoxify many metals by direct and indirect mechanisms; but this is not the case with Al. Inputs of this metal into the environment have increased substantially since the industrial revolution, due to its use in industrial processes and the advent of acid rain. As such, it is crucial that the full implications of such exposure upon the environment is investigated thoroughly. Levels of Cu have also increased, but, on account of its greater acute toxicity, it has been the focus of a much larger amount of research. These two metals (but principally Al) are the focus of both the ecotoxicological and biochemical research herein. Work involving aspects of Al and Cu behaviour and toxicity has been carried out at both an ecosystem and organism level. Ecosystem studies, in the form of chemodynamics experiments, have been conducted in an attempt to understand and contrast their transport in the aqueous environment and the speciation that occurs as a result. These concentrations have then been put into the context of what happened to two test species (the brine shrimp Artemiafranciscana and the bacterium Vibrio fischerii), and, in the case of Al, a field study entailing chemical and biological monitoring. In addition, studies were undertaken which showed that Al bioaccumulates in A. franciscana (which is farmed for aquaculture and is increasingly utilised in toxicity studies as a substitute for higher animals). Further toxicity tests, involving the depletion of glutathione in A. franciscana, showed that the tripeptide has a protective effect against the toxicity of the metal to these creatures. An analytical method (utilising high performance liquid chromatography with electrochemical detection) was then developed for measuring reduced and oxidized glutathione in A. franciscana. This was then applied to investigate the relationship between glutathione redox status and Al exposure in aqueous systems. Reduced glutathione was shown to be depleted and subsequently induced by Al exposure, and to have a protective role against Al toxicity. Furthermore, its redox status indicated that free radical production was not the underlying mechanism responsible for the deleterious effects of Al in A. franciscana, as with many other metals studied. NMR studies were conducted which showed an interaction between Al and glutathione. These studies suggest a possible detoxification and excretion mechanism for Al involving glutathione.

Page generated in 0.0676 seconds