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The present Thesis investigates the quasi-static and cyclic-fatigue properties of nano-modified epoxy polymers. A diglycidyl ether of bisphenol-A was used as the base epoxy and polymer-based materials, block copolymers and core-shell rubber particles were used as the toughening agents. The morphologies formed by the tougheners were determined and the associated fracture and fatigue properties, including the toughening mechanisms, were investigated. The modified epoxy polymers with some of the best properties are described below. The unmodified epoxy polymer had a fracture energy, GIc, of 494 J/m2 and this was increased to 2380 J/m2, when 10 wt.% of a polyurethane toughener was employed. This modified epoxy polymer possessed a second-phase morphology, which was a nano-sized 'worm-like' structure. This nano-phase debonded from the epoxy, which enabled plastic void growth to occur in the epoxy polymer. This mechanism also led to an increase in the cyclic-fatigue threshold fracture energy, Gth, from 153 J/m2 of the unmodified epoxy to 444 J/m2. Nano-sized core-shell rubber particles (either 100 nm or 200 nm nominal diameters) were employed and they formed a well dispersed rubbery particulate phase. A maximum fracture energy of 2540 J/m2 was observed and the particles were found to undergo internal cavitation that induced plastic void growth. However, only the relatively large particles were able to cavitate under the cyclic-fatigue loading. Hence only these type of particles led to a meaningful increase in the fatigue threshold, Gth. 'Hybrid' epoxy polymers contained a polymer based toughener and core-shell rubber particles. Several of these hybrid formulations gave very significant improvements in both values of GIc and Gth. For example, one based upon a polyurethane and styrenebutadiene-core/functionalised polymethylmethacrylate-shell particles gave a value of 2570 J/m2 and 438 J/m2 for GIc and Gth, respectively.

Multiple input multiple output (MIMO) techniques are the most promising technologies for next-generation wireless systems to achieve improved channel reliability as well as high spectral efficiencies. In real MIMO downlink scenarios, the numbers of users are usually greater than that of transmit antennas at a base station and the base station is likely to provide a variety of services to different quality-of-service (QoS) users. Therefore, a multiuser scheduling algorithm for the real MIMO BC scenarios has to support a mixture of QoS users simultaneously by exploiting the performance gains of multiple antennas whilst maximizing the sum-rate capacity by selecting a user set for transmission according to performance criteria. The main topic of this thesis is the design of QoS-guaranteed multiuser schedulers for MIMO systems. This should provide different QoS services to different users whilst satisfying the system-level requirements such as fairness among users, minimum data rate and delay constraints as well as trying to maximize the sum-rate capacity of MIMO channels. For this, this thesis first investigates the performance of MIMO transceiver techniques in terms of error rates and the sum-rate capacity with practical considerations to select a practically appropriate MIMO precoding technique. Then a QoS-aware sequential multiuser selection algorithm is proposed, which selects a user set sequentially from each QoS group in order to satisfy QoS requirements by trading off the transmit antennas between different QoS groups. Using a temporally-correlated MIMO channel model validated by channel measurements, a statistical channel state information (SCSI)-assisted multiuser scheduling algorithm is also proposed, which can minimize the effect of the temporal correlation on the sum-rate capacity. Finally, new metrics are proposed to support fairness among users in terms of throughput or delay whilst maximising the sum-rate capacity. With these proposed algorithms, the objective of this thesis, to support a mixture of different QoS users simultaneously with fairness considerations whilst maximising the sum-rate capacity by exploiting the advantages of MIMO techniques with practical implementation in mind, can be achieved.