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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.
21

Performance modelling and evaluation of virtual channels in multicomputer networks with bursty traffic

Min, Geyong, Ould-Khaoua, M. January 2004 (has links)
No
22

Structural Analysis Of A Jet Trainer Cockpit

Altug, Muhittin Nami 01 February 2012 (has links) (PDF)
This thesis presents structural analysis of a cockpit of a jet trainer type aircraft and the correlation studies performed by using ground pressurisation test results. For this purpose, first the response of the complex integrated fuselage structure is investigated under the complex type cabin pressure load. Then, cockpit part of the fuselage structure is modelled using commercial finite element software MSC/PATRAN&reg / and MSC/NASTRAN&reg / . The finite element model (FEM) of the cockpit structure is improved by the examination of the ground pressurisation test data and is finalised after achieving a good correlation between the finite element analysis (FEA) and the test results. This final form of the FEM of the cockpit structure serving as a benchmark is proved to be reliable for any future modifications.
23

Economic analysis of the causes and consequences of social and emotional well-being in childhood

Turner, Alexander James January 2017 (has links)
The upward trend in the prevalence of childhood mental disorders observed in the UK over the previous two decades, together with UK’s poor performance in recent international comparisons of child well-being, has brought childhood social and emotional well-being (SEW) to the forefront of policy. Key to tackling this issue is to understand what causes SEW in childhood, what interventions are successful in improving it, and what are its late-life consequences. This thesis furthers the literature in each of these areas. Firstly, we examine whether foetal (or in-utero) exposure to influenza hampers the development of childhood SEW. To do so, we examine the use of an instrumental variables approach, whereby the severity of the 1957 Asian Flu epidemic in the local authority of birth is used as an instrument for whether mothers self-report contracting influenza during pregnancy. We establish that exposure has little effect on childhood SEW, but that it results in a 60% increase in the risk of being stillborn, suggesting an increasing focus on influenza vaccination during pregnancy is needed. Secondly, we investigate the long-term effectiveness of school-based interventions to improve SEW. In order to overcome the absence of long follow-up in trial datasets, we develop a new modelling approach which involves the matching of trial participants to individuals in birth cohort datasets. An application of this method found that a Promoting Alternative Thinking Strategies (PATHS) intervention implemented in Greater Manchester schools led to a statistically significant improvement in childhood SEW, and had a positive, although statistically insignificant, effect on health across the life-course. Finally, we address the paucity of studies examining the effects of childhood SEW on late-life health and labour market outcomes. To do so, we develop a method for generating predictions of the effects of childhood characteristics beyond the currently available follow-up periods in birth cohort datasets, adapting an existing mediation analysis framework. Applying this method, we establish that a one-standard deviation improvement in childhood SEW leads to an increase of up to 0.18 accumulated quality-adjusted-life-years in late-life, and an increase in pre-tax labour income in late-life of up to £23,850. Both of these effects are primarily driven by large positive effects of childhood SEW on educational attainment, employment, income and health in mid-life. Childhood SEW is a predictor of important outcomes throughout the lifecourse. More research is needed to identify its causes and interventions to successfully improve it.
24

Revisiting patterns and processes of forest cover change in the tropics : a case study from southeast Mexico

Gueye, Kinne January 2018 (has links)
Vast progress has been made in detecting rates of tropical deforestation, yet the relationship between visible patterns of forest change, multi-scalar human processes and the underlying drivers associated with them is poorly understood. Building on satellite imagery, a household livelihood survey and semi-structured interviews, this research scrutinised changes of forest cover from the mid-1990s to 2015 in a municipality located in southeastern Mexico and investigated the proximate causes and underlying drivers of change at the household and community levels. Emerging evidence indicated that, contrary to the persistent narrative of deforestation for the region, forest cover change is highly dynamic including periods of deforestation and forest recovery. Moreover, a close examination of 24 communities showed forest cover gained terrain, while the agricultural frontier retracted. Drawing on a comparison between the household survey and previous analyses, it could be inferred that forest resurgence was produced by the decrease in the farming area and the increase in the abandonment of farming activities by some communities. Associated with the adaptation of households was the development of formal and informal institutions at the community level in response to macro-global forces linked to the implementation of forest conservation strategies, environmental degradation, market liberalization and increased urbanization. Overall, this research adds not only to our understanding of the complexity of land-use and cover change in emerging globalized economies but also exemplifies the spatial and temporal heterogeneity of tropical forest systems, which challenges partial models of deforestation and policies designed to reduce it. The research may be focused on a narrow region of the globe, nevertheless, the insights and recommendation provided may be useful to further forest conservation schemes in other tropical regions.
25

Investigation Of The Dynamic Properties Of Plate-like Structures

Kahraman, Engin 01 September 2011 (has links) (PDF)
This study presents the investigation and the verification of the modal parameters of a plate-like structure by using different modal analysis methods. A fin-like structure which is generally used in aircraft is selected as a subcategory of a plate-like test structure. In the first part of the thesis, the natural frequencies and the corresponding mode shapes of the fin are extracted by Finite Element Analysis method. Classical Modal Analysis and Testing methods comprising both impact hammer and modal shaker applications are then applied in order to obtain the modal parameters such as / resonance frequencies, mode shapes and damping ratios. In the second part, a recent modal analysis technique, Operational Modal Analysis, is also applied in the laboratory environment. Since Operational Modal Analysis method does not require any information of input forcing, the fin structure is tested under both mechanical and acoustical types of excitations without measuring the given input forces. Finally, Operational Modal Analysis and Testing is also performed under various flow conditions generated in the wind tunnel which may simulate the real operating environment for the fin structure. The modal parameters extracted under these flow conditions are then compared with the previously obtained Finite Element, Classical and Operational Modal Analyses results.
26

Supporting system deployment decisions in public clouds

Khajeh-Hosseini, Ali January 2013 (has links)
Decisions to deploy IT systems on public Infrastructure-as-a-Service clouds can be complicated as evaluating the benefits, risks and costs of using such clouds is not straightforward. The aim of this project was to investigate the challenges that enterprises face when making system deployment decisions in public clouds, and to develop vendor-neutral tools to inform decision makers during this process. Three tools were developed to support decision makers: 1. Cloud Suitability Checklist: a simple list of questions to provide a rapid assessment of the suitability of public IaaS clouds for a specific IT system. 2. Benefits and Risks Assessment tool: a spreadsheet that includes the general benefits and risks of using public clouds; this provides a starting point for risk assessment and helps organisations start discussions about cloud adoption. 3. Elastic Cost Modelling: a tool that enables decision makers to model their system deployment options in public clouds and forecast their costs. These three tools collectively enable decision makers to investigate the benefits, risks and costs of using public clouds, and effectively support them in making system deployment decisions. Data was collected from five case studies and hundreds of users to evaluate the effectiveness of the tools. This data showed that the cost effectiveness of using public clouds is situation dependent rather than universally less expensive than traditional forms of IT provisioning. Running systems on the cloud using a traditional 'always on' approach can be less cost effective than on-premise servers, and the elastic nature of the cloud has to be considered if costs are to be reduced. Decision makers have to model the variations in resource usage and their systems' deployment options to obtain accurate cost estimates. Performing upfront cost modelling is beneficial as there can be significant cost differences between different cloud providers, and different deployment options within a single cloud. During such modelling exercises, the variations in a system's load (over time) must be taken into account to produce more accurate cost estimates, and the notion of elasticity patterns that is presented in this thesis provides one simple way to do this.
27

Three-dimensional physical and numerical modelling of jack-up structures on sand

Bienen, Britta January 2007 (has links)
Mobile offshore jack-up drilling rigs are not custom-designed for a particular location but rated for typical operating characteristics, like water depths. They may be deployed at a number of different sites during their design life. Under the current guidelines, the jack-up is required to be assessed for its suitability for each new proposed location, assuming environmental loading conditions due to wind, waves and current corresponding to a 50-year return period storm applicable to the site. Traditionally, these assessments have been performed in two dimensions, simplifying the jack-up to a plane frame and the loading conditions to be in-plane with the rig's 'axis of symmetry'. This thesis introduces a computer program, named SOS_3D, for the fluid-structure-soil interaction analysis of jack-up response in three dimensions. Extensive experimental series have been performed to provide evidence for the generalisation of the foundationsoil interaction model to general six degree-of-freedom loading conditions and its applicability to load paths and stress levels relevant to jack-up spudcans. These experiments included (1) 1g single footing tests, (2) centrifuge single footing tests and (3) centrifuge model jack-up tests. The latter tests highlighted differences in response and mode of failure depending on the loading direction of the jack-up and re-iterated the importance of three-dimensional modelling. The numerical program SOS_3D introduced early in this thesis was shown to represent a useful tool for the prediction of jack-up behaviour under general combined loading in three dimensions. It provided reasonably good, conservative predictions of the experimentally measured jack-up behaviour.
28

Optimalizace procesů v obchodní společnosti / Process optimization in a trade company

Kašpar, Václav January 2015 (has links)
The diploma thesis focuses on application of a chosen BPM methodology in a real trade company with the aim of optimization of its processes, identification of the possible improvement areas and proposing measures leading to an increase of the efficiency of the company. One BPM methodology is chosen based on a methodology comparison in the introductory part of the work. A description of the trade company and a process analysis follows. Then an identification of the improvement potential is done and limits of the improvement potential are found followed by the projects proposed, which should lead to an increase of the efficiency of the company's processes. This thesis produces an overview of chosen BPM methodologies and approaches, brings up the results of the process analysis in a real trade company, and proposes a set of project for realization. Ultimately the work done demonstrates a procedure of BPM methodology implementation in a small trading company, which may be replicated in another similar firm.
29

Modelling and analysis of wireless MAC protocols with applications to vehicular networks

Jafarian, Javad January 2014 (has links)
The popularity of the wireless networks is so great that we will soon reach the point where most of the devices work based on that, but new challenges in wireless channel access will be created with these increasingly widespread wireless communications. Multi-channel CSMA protocols have been designed to enhance the throughput of the next generation wireless networks compared to single-channel protocols. However, their performance analysis still needs careful considerations. In this thesis, a set of techniques are proposed to model and analyse the CSMA protocols in terms of channel sensing and channel access. In that respect, the performance analysis of un-slotted multi-channel CSMA protocols is studied through considering the hidden terminals. In the modelling phase, important parameters such as shadowing and path loss impairments are being considered. Following that, due to the high importance of spectrum sensing in CSMA protocols, the Double-Threshold Energy Detector (DTED) is thoroughly investigated in this thesis. An iterative algorithm is also proposed to determine optimum values of detection parameters in a sensing-throughput problem formulation. Vehicle-to-Roadside (V2R) communication, as a part of Intelligent Transportation System (ITS), over multi-channel wireless networks is also modelled and analysed in this thesis. In this respect, through proposing a novel mathematical model, the connectivity level which an arbitrary vehicle experiences during its packet transmission with a RSU is also investigated.
30

Pravděpodobnostní přístup pro hodnocení zemnících soustav / Probabilistic Approach for Assessment of Earthing System Design

Vyčítal, Václav January 2020 (has links)
This dissertation thesis deals with application of probabilistic approach to assessment of earthing system safety in distribution networks, especially for cases with common earthing of high and low voltage side of distribution transformers HV/LV. In these cases, the increased potential during fault might be transferred from high voltage to low voltage network and thus the individuals from public can be exposed to increased risk. Thus, for these cases were in this thesis defined expectable touch scenarios together with the resulting risk imposed on individuals from the public. Based on the results it seems that adoption of probabilistic approach for these cases of earthing systems might be more suitable compared to the conventional deterministic worst case approach. In accordance to the aims of the thesis, a thorough analysis of currently adopted probabilistic approaches was carried out as well and it was pointed out to some new possible simplifications in the adopted probabilistic based methodologies. For example, it seems that appropriate modelling of human body resistance by the full lognormal distribution is not completely necessary and similar results can be obtained when only the resistance for 50 % of population together with c3 and c4 fibrillation curves are used. Much of the work was also devoted to the determination of possible uncertainty of calculated risk of evaluated earthing system, especially due to inappropriate modelling of earthing system. The appropriateness of different earthing system modelling methods together with other parameters on the value of calculated risk was investigated through conducting sensitivity analysis. Based on the analysis results it seems, that due to using more, or less simplified modelling method, a possible underrating in the resulting risk of about 40 % (about half an order/decade) is expectable. On the other hand, the change of parameters related directly to calculation of fibrillation probability seems to exhibit greater change in calculated risk by up to units of orders/decades.

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