A variety of approaches have been used to solve a variety of combinatorial optimisation problems. Many of those approaches are tailored to the particular problem being addressed. Recently, there has been a growing number of studies towards providing more general search methodologies than currently exist which are applicable to different problem domains without requiring any algorithmic modification. Hyper-heuristics represent a class of such general methodologies which are capable of automating the design of search process via generating new heuristics and/or mixing existing heuristics to solve hard computational problems. This study focuses on the design of selection hyper-heuristics which attempt to improve an initially created solution iteratively through heuristic selection and move acceptance processes and their application to the real-world healthcare scheduling problems, particularly, nurse rostering and surgery admission planning. One of the top previously proposed general hyper-heuristic methodology was an adaptive hyper-heuristic consisting of many parameters, although their values were either fixed or set during the search process, with a complicated design. This approach ranked the first at an international cross-domain heuristic search challenge among twenty other competitors for solving instances from six different problem domains, including maximum satisfiability, one dimensional bin packing, permutation flow shop, personnel scheduling, travelling salesman, vehicle routing problems. The hyper-heuristics submitted to the competition along with the problem domain implementations can now be considered as the benchmark for hyper-heuristics. This thesis describes two new easy-to-implement selection hyper-heuristics and their variants based on iterated and greedy search strategies. A crucial feature of the proposed hyper-heuristics is that they necessitate setting of less number of parameters when compared to many of the existing approaches. This entails an easier and more efficient implementation, since less time and effort is required for parameter tuning. The empirical results show that our most efficient and effective hyper-heuristic which contains only a single parameter outperforms the top ranking algorithm from the challenge when evaluated across all six problem domains. Moreover, experiments using additional nurse rostering problems which are different than the ones used in the challenge and surgery scheduling problems show that the results found by the proposed hyper-heuristics are very competitive, yielding with the best known solutions in some cases.

In this thesis, GaAs heterostructure MOSFETs are investigated as a potential technology for digital circuit design. The devices under investigation are 0.6 μm gate length, enhancement mode, heterostructure MOSFETs, with a high-κ dielectric (Ga2O3), and an InGaAs channel. Historically silicon CMOS technology has been the natural choice for digital circuits, however the realisation of GaAs MOSFET digital circuits could allow full integration of RF, optoelectronic and digital circuits on a single system-on-chip. Additionally, there are potential performance advantages in using GaAs due to it's high electron mobility. For the first time compact models of complimentary GaAs/Ga2O3 MOS are developed to enable an investigation into establishing a digital design methodology for GaAs MOS. Drift-diffusion models are developed and calibrated to measured device data. These models then provide information on the necessary device parameters to build compact models of these devices. BSIM3v3.2 compact models are developed based on this to enable GaAs MOS technology to be investigated using standard circuit design tools. The compact models have been adapted to ensure that they are physically relevant for GaAs devices. This includes some necessary approximations using effective medium theory. Further adjustments, or ratio corrections, are introduced to ensure that the internal physical parameters of BSIM will be correct. The models are compared to similarly-sized silicon devices to investigate the difference in performance between GaAs and silicon MOSFETs. As expected, the GaAs NMOS devices demonstrate improvements in drive current over silicon. However, the GaAs PMOS devices do not offer this advantage due to low hole mobility. Therefore, as a consequence of the high mobility ratio in GaAs, it is important to consider alternative digital design methodologies to CMOS to optimise performance. The performance of benchmark circuits is investigated for this technology in various digital design styles including CMOS, NMOS saturated enhancement load, and NMOS precharge. GaAs digital circuits gain a signifcant advantage in using alternative design styles to CMOS due to the relatively poor performance of the PMOS devices. In using the alternative styles the number of PMOS devices used can be minimised, and it is shown that NMOS precharge offers both speed and power advantages for this technology. The particular GaAs technology investigated does not outperform silicon in terms of speed and power. However, it has allowed a methodology to be established for future device generations, where performance is anticipated to improve signifcantly.

The separation of gas-liquid flows is a necessary part of many industrial processes. Thus, it has received much attention over the years with the ultimate aim of reducing equipment costs whilst maintaining or improving efficiency. Traditionally, the Petroleum Industry has relied heavily on conventional vessel separators which are bulky, expensive and have a high inventory. Research has indicated that a cheap alternative may be a simple pipe junction. It has been shown that gas-liquid flows can be divided at pipe junctions in such a manner that there is a partial separation of the phases. The result is two streams - one richer in gas than the initial feed and the other richer in liquid. If the phases can be separated, albeit partially, at a simple pipe junction then the need for a large separator is diminished. Within this thesis the use of a simple T-junction is considered as a continuous, compact, economical partial phase separator with a minimal inventory for use within the oil industry. The main objective was to gain a better understanding of how a gas-liquid flow is divided at a large diameter T-junction and how the flow split is affected by T-junction geometry. Firstly, the orientation of the side arm from the horizontal was considered with both a regular (inlet arm diameter == branch arm diameter = 0.127m) T-junction and a reduced (branch arm to inlet diameter ratio = 0.6) T-junction. The side arm was placed horizontally (0'), vertically upwards (+90') and vertically downwards (-90') and the phase split of air water annular and stratified flows were investigated. To improve the phase separation characteristics of the regular T-junction, inserts protruding from the side arm into the main pipe were considered and for the junction with a vertically downwards side arm a U-bend was used to reduce the fraction of gas pulled through. The experimental investigation was expanded to incorporate the effect of placing two regular T-junctions in series. With the branch arm of the first placed vertically upwards (+90'). and the second vertically downwards (-90') a pure gas stream and a liquid rich stream were created from the multi-phase inlet. Reducing the sidearm diameter of the second junction lowered the fraction of gas drawn off in the liquid rich stream. The physical separation distance the T-junctions was found to have little effect on phase split. The interaction of the two junctions are interdependent and the phase split results from the two junction system was found to be more complex than simply considering the results of two individual T-junctions. Being able to predict the phase split at a junction is vital if they are to be considered seriously within industrial settings. The case of a regular T-junction with a vertically downwards (-90') side arm has received little specific attention. From the linear nature of the phase split results it was determined that if two key points could be accurately predicted then the phase split results can be determined. The "onset of gas take off', the fraction of liquid diverted down the branch arm when the first fraction of gas is pulled through, was successfully related to the bubble rise velocity of the gas entrained in the liquid column trapped in the branch arm. The "critical gas take off”, the fraction of gas diverted when all the liquid is drawn down the branch arm, was determined by relating the fluid flow to the motion of a failing particle.