• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 468
  • 419
  • 176
  • 163
  • 75
  • 13
  • 9
  • 8
  • 4
  • 4
  • 3
  • 3
  • 3
  • 3
  • 3
  • Tagged with
  • 1749
  • 513
  • 260
  • 196
  • 193
  • 193
  • 184
  • 145
  • 134
  • 133
  • 125
  • 125
  • 113
  • 108
  • 105
  • 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.
1

Hybrid electric and thermal modelling of semiconductor devices using the transmission line matrix (TLM) methods

Aldabbagh, Ahmed January 2014 (has links)
Increasing the level of semiconductor devices' quality, reliability, and associated system safety is important as a fundamental contributor to overall technical advancement in the electronics sector. However, the growing requirements of optimizing device design for the broadest application areas need an enhanced level of understanding of thermal behaviour, and self-heating in particular, of semiconductor devices under harsh thermal operation conditions. The aim of the research presented in this thesis is to develop and verify a numerical tool to assist in the understanding and the prediction of phenomena that contribute to the ageing and stressing of semiconductor devices. An aged semiconductor device can substantially adversely affect a system's electromagnetic compatibility (EMC) performance and reduce the desired functionality. The chosen method is a co-simulation approach for a linked electrical and thermal model, using the Transmission Line Matrix (TLM) method. This selection is based on having a single method that can simulate both domains, that is intuitive and flexible. The method is enhanced by including electromigration and thermomigration mechanisms as an influential element in the calculation of material properties inside the hybrid solver. The proposed model was subjected to a customized Thermal Cycling Test (TCT) in order to observe device behaviour and comprehend the degradation phenomenon that Abstract appears after accelerated ageing test in RF LDMOS device. The research is a generic step forward, showing that a single TLM 'engine' can be used to model the linked factors in ageing and its effects, namely electrical, and thermal behaviour, that also allows for probabilistic events such as electro/thermo-migration. Further, the method developed in this thesis is applied to two problem areas: • Silicon nanowires, where the thermal radiation effects are addressed by adding an additional shunt conductance to a one-dimensional TLM node structure. The results demonstrate good agreement with previously published results and provide an appropriate tool to solve the internal heating problems and, hence, the degradation caused by thermal factors for future semiconductor devices. • Silicon Carbide Metal-Semiconductor Field Effect Transistor (MESFET) and RF Laterally Diffused Metal Oxide Semiconductor (LDMOS) devices, which are approached as 2D structures, where the probability of occurring electromigration and thermomigration phenomenon in MESFET devices is investigated and the MTTF is shown when the model is subjected to thermal stress. The TCT is applied as a thermal acceleration factor in a MOS device, where the impact on the device IV (current-voltage) characteristic is studied. The results demonstrated good agreement with previous published results.
2

Biodiversity-ecosystem service relationships in degraded and recovering ecosytems

Martin, Philip Anthony January 2014 (has links)
Biodiversity loss is occurring at an unprecedented rate and most of this loss is due to human induced pressure. This loss in biodiversity had led to concerns that the provision of ecosystem services that humans depend upon might be negatively affected. As such much modern conservation science focusses on preserving biodiversity whilst protecting priority ecosystem services. However, there may be spatial and temporal trade-offs between these services and the biodiversity that is considered important. Characterisation of such the relationships between biodiversity and ecosystem services is vital in order to improve management and policies which aim to protect and restore both biodiversity and ecosystem services. The broad aims of the thesis were to explore biodiversity-ecosystem service relationships in (1) ecosystems invaded by non-native plant species and (2) tropical forests affected by human exploitation and disturbance. Specifically this thesis aimed to answer the questions: 1. What effect do non-native plant invasions have on aboveground carbon storage, belowground carbon storage, carbon sequestration, water quality and water provision? 2. How do changes in species richness affect this ecosystem service provision? 3. How do these changes relate to the woodiness and traits of invasive and native dominant species, and the type of ecosystem invaded? 4. What factors drive differences in residual stand damage, biomass loss and species richness change following selective logging? 5. After deforestation how long do carbon stocks and plant biodiversity take to recover in tropical forests? 6. Do carbon and plant biodiversity differ in their recovery rates? 7. Which areas are priorities for restoration of tropical carbon? All chapters in this thesis make use of large datasets that I collated from the literature and other authors in order to draw broad conclusions about trade-offs and relationships between services and biodiversity In the section concentrating on invasive species my results suggest that non-native invasive plants generally increase the storage of carbon, whilst reducing water quality and availability. This may indicate a fundamental trade-off between services where increased biomass of plants results in higher evapotranspiration and thus water loss, while also enhancing the carbon cycle and nitrogen production of microorganisms. In addition my results suggest that aboveground carbon storage increases as species richness is reduced, showing the opposite relationship to that shown in many biodiversity ecosystem functioning experiments. This is the first time any such relationship has been found between community change and ecosystem level impacts in the context of species invasions. However, it seems likely that this relationship depends on the identity and traits of the species, with invasions in open habitats by woody species likely to drive a negative relationship between richness change and biomass change with the opposite true when grassy species invade woodlands. This result presents a trade-off between conservation priorities that managers will need to consider. In Chapter 3 I investigated the possibility of predicting the impact of non-native invasive plant impacts on ecosystem services by using characteristics and functional traits of both invasive and native species. This work suggested that aboveground carbon storage is most easily predicted by traits and characteristics of native and non-native species, with few other ecosystem services well explained by models. Results suggested that transition from woody to non-woody dominant species resulted in most dramatic changes in aboveground carbon storage. However, interestingly aboveground carbon storage also tended to increase where native species were replaced by species of similar woodiness. Similarly, given that woodiness and size of species are related, there was a positive relationship between the invasive species height and increases in aboveground carbon storage. However, all other ecosystem services were poorly predicted by species traits and characteristics. This work suggests that the most dramatic changes in carbon storage may result from shifts in ecosystems that resemble regime shifts. Future work addressing invasive species from this perspective is warranted as many invasions resemble such shifts. In Chapter 4 I investigated the relationships between logging intensity and methods and residual stem damage, biomass loss and species richness change in tropical logged forests. Many syntheses of the logging literature have made little distinction between logged sites, and only one has explored any of the mechanisms that may drive heterogeneity in logging impacts. This is particularly surprising given that Reduced Impact Logging (RIL) has been implemented relatively widely principally to reduce carbon loss from logged forests. My results from this chapter suggest that the principal driver of logging impacts is the intensity at which logging is carried out, showing broadly negative relationships with biomass and tree species richness change and a positive relationship with residual stem damage. Interestingly, RIL appeared to reduce residual stem damage slightly but evidence for this effect was weaker in other analyses. These analyses also suggest a slight increase in tree species richness at low logging intensities, showing some similarities to intermediate disturbance hypothesis type relationships. This is suggestive of a complex relationship between tree species richness and biomass changes during logging that deviated substantially from that suggested in grassland biodiversity-ecosystem function experiments. This is as far as I know the first time this relationship has been suggested in the context of logged forests. The result from this chapter also suggest that there is weak support that RIL reduces logging damage at low intensities but little evidence that this is reflected by changes in biomass. Further studies are needed to discern the effect of RIL over a wide range of logging intensities. Chapter 5 investigates tropical forest recovery following agricultural clearance. In this chapter I aimed to identify the recovery times of different above and belowground carbon pools and tree and epiphyte species richness as well as tree species composition using studies that had paired mature forest sites as comparators. Surprisingly this chapter represents the first attempt to generalise about this recovery rate. The results suggest that following clearance carbon and species richness of plants recovers relatively quickly (<100 years), but species indicative of old forests are rarely present in recovering forests and show few signs of recovery. Thus, while carbon recovery goals may be achievable full recovery of plant biodiversity may require centuries. This slow recovery may be aided by active restoration. Finally in Chapter 6 I investigated which areas should be considered as priorities when restoring tropical forests for carbon storage and bird biodiversity. In this chapter I found evidence of spatial trade-offs between carbon storage and bird species recovery. Empirical models suggested that carbon is accumulated most rapidly in forests with long growing seasons, while probability of bird species presence was primarily driven by habitat specificity, range size and forest cover. Model projections suggested that areas that should be considered a priority for restoration targeting carbon storage are found in the wet tropics while priorities for restoration of bird biodiversity are found in mountainous areas. These analyses indicated that there was no relationship between the two goals, but that by using model projections it was possible to identify areas that maximised both. In summary work in this thesis provides the best synthesis of the relationships between biodiversity and ecosystem services in the context of non-native invasive plants, and selective logging and recovery from tropical forest clearance to date. This is of particular value because such relationships have rarely been explored in these contexts despite widespread and of global importance for conservation.
3

The development of a novel integrated analytical system for the investigation of anthracene degradation by ultrasound in a controlled low temperature environment

Paterson, John January 2016 (has links)
No description available.
4

Does the inclusion of a problem-solving component to standard care improve concordance with the self-management programme for adolescents living with diabetes?

Lewis, A. January 2014 (has links)
To investigate if problem-solving activity, not used in the UK, could support UK adolescent’s living with diabetes to improve self-management of their condition leading to improvements in self-care and glycaemic control when delivered alongside usual care at paediatric and young adults’ diabetes clinics. Method: A pilot study incorporating 23 Adolescents (13-18 years) with a diagnosis of Type 1 Diabetes of at least a year and with English as a primary language were randomised into a two arm (intervention based on the International Treatment Effectiveness Protocol (ITEP) node-mapping approach that addressed common aspects of non-adherence to life style factors via scenarios and personal experience to encourage behavioural change + usual care vs. education control DVD + usual care) randomised control trial. Results: 23 participants completed a 3 month follow up within the required time scale. There was no change in the HbA1c levels for either group. The intervention group appeared to improve self-management on scores for the SCI following the intervention. Conclusion: The study did not recruit substantial participants for a full powered study and any changes has to be treated with caution. As a pilot study it has helped identify protocols and processes that could lead to the delivery of a powered study. It received a grant from the InDependant Diabetes Trust and generated a number of learning outcomes that will support further research on its outcomes.
5

The performance of pyrotechnic solid propellants rockets igniters and combustion transients of solid propellants

Assil, M. A. January 1978 (has links)
No description available.
6

"Ahead on points" : understanding the long-term impact of colorectal cancer with liver metastases on quality of life and survivorship experiences

Whale, Katie January 2016 (has links)
The aim of this study was to investigate the impact of colorectal cancer (CRC) with liver metastases on long-term quality of life (QOL) and survivorship experiences, and to explore the relevance of the EORTC QOL questionnaires to this population, using a qualitative approach. Overall 15 participants were interviewed, 5 women and 10 men. Interviews were analysed using inductive theoretical thematic analysis. Three main themes were identified: Cancer and me: establishing a relationship with cancer; Living with cancer; and Aligning the long-term impacts: the person I’ve become. The results illustrate that CRC survivors with liver metastases define QOL in different ways and have a broad and diverse range of experiences. As long-term cancer survivors, the focus on short-term physical symptoms is no longer relevant. Instead, the relationship with cancer, development of coping strategies, and coming to terms with a post-cancer self are of far more importance. As QOL is a subjective experience, there is no ‘one size fits all’ approach to definition and measurement. Health care professionals and policy makers need to understand the variety in meaning and be clear about the purpose of QOL measures. In attempts to promote long-term positive adjustment, cancer survivors may benefit from a wider range of support and expertise. Health Psychologists in particular could offer valuable insight and support in relation to adaptive coping strategies, mental framing, adjustment to physical changes, and the development and adjustment to the ‘post-cancer self’. Future work would benefit from holistic definition of QOL and from using a broad range of assessment techniques.
7

The development of enzyme electrode biosensors and other bio-analytical techniques using squalene epoxidase

Grieveson, Lynsey Anne January 1999 (has links)
No description available.
8

Electrokinetic manipulation of micro- and nano-structured materials in microfabricated devices

Bayati, Marzieh January 2009 (has links)
No description available.
9

Quantitative modelling of an industrial roll - blade gap former

Boxer, Tim January 1999 (has links)
No description available.
10

Quantification of performance analysis factors in front crawl using micro electronics : a data rich system for swimming

Callaway, Andrew January 2014 (has links)
The aim of this study is to increase the depth of data available to swimming coaches in order to allow them to make more informed coaching decisions for their athletes in front crawl swimming. A coach’s job is to assist with various factors of an individual athlete to allow them to perform at an optimum level. The demands of the swimming coach require objective data on the swim performance in order to offer efficient solutions (Burkett and Mellifont, 2008). The main tools available to a coach are their observation and perceptions, however it is known that these used alone can often result in poor judgment. Technological progress has allowed video cameras to become an established technology for swim coaching and more recently when combined with software, for quantitative measurement of changes in technique. This has allowed assessment of swimming technique to be included in the more general discipline of sports performance analysis. Within swimming, coaches tend to observe from the pool edge, limiting vision of technique, but some employ underwater cameras to combat this limitation. Video cameras are a reliable and established technology for the measurement of kinematic parameters in sport, however, accelerometers are increasingly being employed due to their ease of use, performance, and comparatively low cost. Previous accelerometer based studies in swimming have tended to focus on easily observable factors such as stroke count, stroke rate and lap times. To create a coaching focused system, a solution to the problem of synchronising multiple accelerometers was developed using a maxima detection method. Results demonstrated the effectiveness of the method with 52 of 54 recorded data sets showing no time lag error and two tests showing an error of 0.04s. Inter-instrument and instrument-video correlations are all greater than r = .90 (p < .01), with inter-instrument precision (Root Mean Square Error; RMSE) ≈ .1ms−2, demonstrating the efficacy of the technique. To ensure the design was in line with coaches' expectations and with the ASA coaching guidelines, interviews were conducted with four ASA swim coaches. Results from this process identified the factors deemed important: lap time, velocity, stroke count, stroke rate, distance per stroke, body roll angle and the temporal aspects of the phases of the stroke. These factors generally agreed with the swimming literature but extended upon the general accelerometer system literature. Methods to measure these factors were then designed and recorded from swimmers. The data recorded from the multi-channel system was processed using software to extract and calculate temporal maxima and minima from the signal to calculate the factors deemed important to the coach. These factors were compared to video derived data to determine the validity and reliability of the system, all results were valid and reliable. From these validated factors additional factors were calculated, including, distance per stroke and index of coordination and the symmetry of these factors. The system was used to generate individual profiles for 12 front crawl swimmers. The system produced eight full profiles with no issues. Four profiles required individualisation in the processing algorithm for the phases of the stroke. This was found to be due to the way in which these particular swimmers varied in the way they fatigued. The outputs from previous systems have tended to be either too complicated for a coach to understand and interpret e.g. raw data (Ohgi et al. 2000), or quite basic in terms of output e.g. stroke rate and counts (Le Sage et al. 2011). This study has added to the current literature by developing a system capable of calculating and displaying a breadth of factors to a coach. The creation of this system has also created a biomechanical research tool for swimming, but the process and principles can be applied to other sports. The use of accelerometers was also shown to be particularly useful at recording temporal activities within sports activities. Using PC based processing allows for quick turnaround times in the processing of detailed results of performance. There has been substantial development of scientific knowledge in swimming, however, the exchange of knowledge between sport science and coaches still requires development (Reade et al. 2008; Williams and Kendall 2007). This system has started to help bridge the gap between science and coaching, however there is still substantial work needed. This includes a better understanding of the types of data needed, how these can be displayed and level of detail required by the coach to allow them to enact meaningful coaching programmes for their athletes.

Page generated in 0.0195 seconds