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Numerical modelling of optical micro-cavity ring resonators for WDM networks
Get PDFAugmenting the level of integration for a lower cost and enhancing the performance of the
optical devices have turned out to be the focus of many research studies in the last few
decades. Many distinct approaches have been proposed in a significant number of researches
in order to meet these demands. Optical planar waveguides stand as one of vital employed
approach in many studies. Although, their low propagation loss, and low dispersion, they
suffers from high power losses at sharp bends. For this reason, large radius of curvature is
required in order to achieve high efficiency and compromise the high level of integration. For
the purpose of this research, in this thesis different ways to improve the performance of
optical microcavity ring resonators (MRRs) have been thoroughly investigated and new
configurations have been proposed.
The Multiresolution Time Domain (MRTD) technique was further developed and employed throughout this thesis as the main numerical modelling technique. The MRTD algorithm is
used as a computer code. This code is developed and enhanced using self built Compaq
Visual Fortran code. Creating the structure and Post-processing the obtained data is carried
out using self built MATLAB code. The truncating layers used to surround the computational
domain were Uniaxial Perfectly Matched Layers (UPML). The accuracy of this approach is
demonstrated via the excellent agreement between the results obtained in literature using
FDTD method and the results of MRTD.
This thesis has focused on showing numerical efficiency of MRTD where the mesh size
allowed or the total number of computed points is about half that used with FDTD.
Furthermore, the MRR geometry parameters such as coupling gap size, microring radius of curvature, and waveguide width have been thoroughly studied in order to predict and
optimise the device performance.
This thesis also presents the model analysis results of a parallel-cascaded double-microcavity
ring resonator (PDMRR). The analysis is mainly focus on the extraction of the resonant
modes where the effect of different parameters of the structure on transmitted and coupled
power is investigated.
Also, accurate analysis of 2D coupled microcavity ring resonator based on slotted
waveguides (SMRR) has been thoroughly carried out for the purpose of designing optical
waveguide delay lines based on slotted ring resonator (SCROW).
The SCROW presented in this thesis are newly designed to function according to the
variation of the resonance coupling efficiency of a slotted ring resonators embedded between two parallel waveguides.
The slot of the structures is filled with SiO2 and Air that cause the coupling efficiency to vary
which in turn control both the group velocity and delay time of SCROW structures results
from the changing the properties of the bent slotted waveguide modes which strongly
depends on the slot’s position.
Significant improvements on the quality factor and greater delay time have been achieved by
introducing sub-wavelength-low-index slot into conventional waveguide
Colorectal cancer: a comparative study of models of health care delivery in two adjacent trusts in South Wales
Get PDFIntroduction
Survival in colorectal cancer patients is dependant on the stage of the cancer at diagnosis. Referral via an appropriate pathway to a specialist service is vital to the early detection of colorectal cancer but there is neither a standard referral system nor a nationally agreed referral pathway in the UK. Though studies have compared individual components of different models of health care in colorectal cancer, this is the first study comparing two models in their entirety.
Hypothesis
The distinct model of service delivery in Trust A picks up a higher percentage of early colorectal cancers than the model of service delivery in Trust B.
Method
The study compares colorectal cancers diagnosed from two adjacent Trusts in Wales during a three year period. The samples obtained after rigid exclusions correlate the two models of health care with the stage of cancer at diagnosis.
Results
Trust A has a higher emergency and urgent workload. The overall pick up of early cancers is similar in both Trusts. However, there is a higher pick up rate of early colorectal cancer in Trust A, when GPs accessed the specialist service using an urgent referral through the elective route. Trust A had lower overall waiting times for the first clinic appointment but there was no difference for urgent cases between the two Trusts. Specialists in Trust B had a higher rate of re-prioritisation of urgent GP referrals to the non urgent category.
Conclusion
There appears to be no significant difference in the overall pick-up rate of modified Dukes’ A colorectal cancers between the two models of health care delivery. The higher pick up rate of early colorectal cancer in Trust A was achieved only where GPs sent patients into the specialist service using an urgent referral through the elective route
A new unity power factor quasi-resonant induction heater
Get PDFThis thesis reports an investigation into the design of converters for induction heating
systems based upon resonant switch mode power converter techniques.
The proposed three phase unity power factor induction heating system consists of two
stages of power conversions. The important requirements for each stage of the power
conversion of a typical induction heating system working from a three-phase supply are
identified. A wide range of power converters which fulfil these requirements are
compared and evaluated. From the evaluation, the most applicable converter topologies
are selected. Each selected converter class is investigated in great detail to outline their
advantages and disadvantages.
The first stage consists of a push-pull buck converter connected to a unity power factor
rectifier stage. This stage converts the three phase AC mains supply to a required DC
value. The second stage, which converters the DC into AC is a single ended resonant
inverter system.
Analysis of the converters has been made and the design procedure has been
formulated. The design procedure allows a strenuous design of each resonant converter
for particular converter applications.
The final converter design has been simulated using the circuit simulation software
packages Design Architect and Accusim to verify the results of analysis. The most
important design and construction achievements can be summarised as follows:
I
A novel push-pull buck quasi-resonant converter with a three-phase rectifier stage has
been built and tested. At its maximum operating frequency of 40kHz, the prototype
converter delivers an output power of 500W. The converter draws nearly sinusoidal
currents from the three-phase mains supply and has an input power factor approaching
unity.
A secondary stage resonant converter provides AC for the induction heater coil. This
AC current flowing in the induction coil creates an alternating electromagnetic field for
the workpiece. An induction heating coil has been designed and built by using electrical
equivalent coil design method.
A novel control strategy was developed to provide output power control. Both
converter and inverter stage of the system are operated in the zero-current switching
condition. The use of this technique allows higher switching frequencies and provides
low switching losses.
The full design details are presented along with simulation and practical results. The
simulation and practical performance results presented show good correlation with
theoretical predictions
Improving road ice prediction through the introduction of GIS gererated geographical parameters to an ice forecasting model
No full textImplementation and the effectiveness of quality management systems within the construction industry and organisational change management in this process
Get PDFWelsh-language provision on party web sites during the 2010 UK General Election
No full textThe internet is now an important element of most political parties' communication strategies during elections. While online communication might be claimed to enable smaller parties and marginal voices to compete more effectively with major parties, it might also enable minority languages to challenge the existing dominance of majority languages in traditional political communication. This paper explores Welsh-language provision on the websites of the 18 parties which fielded candidates in Wales during the 2010 UK General Election. Three websites making bilingual provision are examined in greater detail, considering the Welsh-language experience in terms of information seeking tasks, the use of web2.0 and resource generation. Overall the provision of regional information relating to Wales and of Welsh-language material has remained remarkably static since the last General Election in 2005. It appears that only parties which regularly contest seats in Wales make regional provision and that Welsh-language provision is limited to those parties who have websites specifically orientated to Wales. The Welsh language does not appear to have been a priority in terms of online political communication for most of the parties campaigning in Wales during the General Election. Even on those sites making a bilingual provision, the quality, timeliness and extent of the Welsh-language experience varied considerably
Presenting DEViSE: data exchange for visualizing security events
No full textThe Data Exchange for Visualizing Security Events (DEViSE) is an open-source architecture designed to enable data sharing between security visualization tools. The security visualization market currently lacks interoperability between different applications, which tend to be constrained to certain log formats. DEViSE is a middleware layer that manages these interactions so one visualization tool can transfer security-related information to another application. DEViSE uses XML for all communication purposes. This allows a much greater level of freedom for application integration. To demonstrate DEViSE, the authors have created several security visualization tools that adhere to different visualization paradigms
Connecting archaeological data sets and grey literature: semantic cross search
No full textThe advantages of making research data widely available have become widely recognised in recent years. In archaeology, this has been difficult to achieve at a detailed data level. Repositories of curated excavation datasets are emerging, such as the Archaeology Data Service in the UK, tDAR in the USA, Arachne in Germany but cross search across different organisational data structures remains difficult. Increasingly such digital libraries are including the ‘grey literature’ of excavation reports not formally published. However, these reports are not meaningfully connected with other online data. Significant problems impede achieving the full potential of exposing excavation datasets for wider reuse, even supposing that cross search is technically possible. Problems of semantic interoperability include differing terminology and database schema. Different archaeological teams may use different terms to mean the same thing and the same term may be used for different things. In addition, database structure varies and similar entities may have different names and field structure, making it difficult to search like with like. This paper discusses results from an AHRC funded research project that addressed the issue of semantic interoperability. STAR has demonstrated that semantic interoperability can be achieved by mapping and extracting different datasets and key concepts from OASIS reports to a core CRM-EH ontology via the central RDF based triple store
Novel radio link buffer management schemes for end-user multi-class traffic in high speed packet access networks
No full textThe requirement to provide multimedia services with QoS support in mobile networks has led to standardization and deployment of high speed data access technologies such as the High Speed Downlink Packet Access (HSDPA) system. HSDPA improves downlink packet data and multimedia services support in WCDMA-based cellular networks. As is the trend in emerging wireless access technologies, HSDPA supports end-user multi-class sessions comprising parallel flows with diverse Quality of Service (QoS) requirements, such as real-time (RT) voice or video streaming concurrent with non real-time (NRT) data service being transmitted to the same user, with differentiated queuing at the radio link interface. Hence, in this paper we present and evaluate novel radio link buffer management schemes for QoS control of multimedia traffic comprising concurrent RT and NRT flows in the same HSDPA end-user session. The new buffer management schemes—Enhanced Time Space Priority (E-TSP) and Dynamic Time Space Priority (D-TSP)—are designed to improve radio link and network resource utilization as well as optimize end-to-end QoS performance of both RT and NRT flows in the end-user session. Both schemes are based on a Time-Space Priority (TSP) queuing system, which provides joint delay and loss differentiation between the flows by queuing (partially) loss tolerant RT flow packets for higher transmission priority but with restricted access to the buffer space, whilst allowing unlimited access to the buffer space for delay-tolerant NRT flow but with queuing for lower transmission priority. Experiments by means of extensive system-level HSDPA simulations demonstrates that with the proposed TSP-based radio link buffer management schemes, significant end-to-end QoS performance gains accrue to end-user traffic with simultaneous RT and NRT flows, in addition to improved resource utilization in the radio access network