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The limit of current technology for mobile base station filters is the multimode filter, in which each cavity supports two (or possibly three) independent degenerate resonances. Shielded dielectric resonators with a rectangular cross-section are useful in this application. In the design of these filters, manufacturers are using software packages employing finite element or finite difference time domain techniques. However, for sufficient accuracy these procedures require large numbers of points or elements and can be very time consuming. Over the last decade research using the mode matching technique has been used to solve this kind of difficulty for various types of filter design and waveguide problems. In this thesis a mode matching method and computer program is developed to calculate the propagation coefficients and field patterns of the modes in a shielded rectangular dielectric rod waveguide. Propagating, complex, evanescent and backward wave modes are included and the work shows the presence of a dominant mode, and other fundamental modes, not previously identified. The effect of the shield proximity on the propagation characteristics and mode spectrum is investigated, together with the limitations on the accuracy of the mode matching method. In addition, the fields within the shielded rectangular dielectric rod waveguide, are used to calculate the attenuation coefficient of the dominant and fundamental modes. The influence on the attenuation coefficient of the proximity of the shield to the rod is also evaluated for these modes and limitations on accuracy are discussed. The calculated numerical results for the propagation and attenuation coefficient values are verified by measurement. The propagation coefficients results are typically within 2% of those measured. Verification of the attenuation coefficient results is achieved by comparing calculated and measured Q at the resonant frequencies of a number of shielded rectangular dielectric rod resonators. The

Excavation of the relict stratigraphy of a drained, agriculturally reclaimed mire in Lancashire, northwest England, has revealed evidence for prehistoric (i.e., c. 820–520 cal. bc) beaver activity in the form of gnawed timber stratified in the basal sediments. The lowest horizons of the peat deposits contained the intact root systems of a dense hazel wood, indicating that the mire probably owed its origins to the rapid flooding of a relatively dry landscape. The exact cause of this inundation remains uncertain, although beaver damming is a strong candidate. The possibility that beaver activity is implicated in the flooding of the site is potentially of great significance both palaeoecologically and archaeologically. The site may represent the first recorded example in British prehistory of a non-human animal playing a role in inducing mire development. It also adds weight to the possibility that some small-scale woodland clearances identified in British pollen diagrams (which have been attributed to anthropogenic activity) may be due to the effects of beaver.

Plant macrofossil analyses of five peat cores from undisturbed fens in the flood-plain of the Ant Valley of the Norfolk Broadland show the sequence of vegetation development during the last two millennia. Macrofossil assemblages have been grouped into five regional phases and are interpreted largely in terms of the response of the vegetation to changes in sea level, climate and management. Phase 1 represents pre-Roman fen woodland communities (>2000 cal. BP); phase 2 represents salt-marsh communities formed during an estuarine phase in Romano-British times (c. 2000–1600 cal. BP); phase 3 represents ‘tussock-fen’ and carr communities suggestive of drier conditions in the post-Roman to early Medieval period (c. 1600–800 cal. BP); phase 4 represents aquatic communities indicative of wetter conditions from the late Medieval period to c. 300 cal. BP; phase 5 represents communities comparable with present-day vegetation. The biostratigraphic development of the Ant Valley floodplain mires has analogues in climatically induced humification changes of some British ombrotrophic mires, suggesting a response to similar climatic controls. Widespread human interference and control of the fen vegetation may be a relatively recent phenomenon (beginning possibly,400 cal. BP). Peat-accumulation rates in the undisturbed mire sites suggest that the original Medieval turbaries which later flooded to form the Norfolk Broads may have been at least 0.5 m shallower when dug than their present depth. The wide range of environmental conditions experienced by the mires during the last two millennia is of relevance to the development of strategies for their conservation.

Mathematical models which describe the greenhouse environment, and the growth of a crop of cucumbers, in that environment, have be en developed and tested. The models have been used to predict: the response of the greenhouse to varying weather conditions, the growth of the crop leaf canopy, and the weight and number of fruit harvested The greenhouse environment has been modelled using a system of non-linear differential equations, derived from a consideration of the energy and mass balances of the glazing, internal structure, crop canopy, root media, fl oor, deep soil layers, and the greenhouse air space. The equations have been solved for five minute time steps, using measured values of outside weather conditions and control inputs as boundary values. Entry of solar radiation into the greenhouse, and absorption by various surfaces, has been determined using transmission tables generated using a "ray-tracing" light transmission model. The light transmission model has been calibrated in a separate experiment. The incoming solar radiation has been partitioned between diffuse, direct, photosynthetically active and near infra-red radiation, for use in the crop model. Validation experiments have been performed to test the greenhouse environment simulation model. The results of the validation exercise showed that the model was capable of predicting the temperatures in the greenhouse, within a few degrees. The mean errors were smaller for the crop canopy, root medium, and floor, than for the glazing or air temperature. Prediction errors for relative humidity and carbon dioxide concentration were more variable. An existing model of cucumber development rate, and leaf expansion, has been modified and validated. This gave good results when adequate account was taken of leaf senescense, and initiation of lateral growths. Sub-models for photosynthesis, respiration, and assimilate partitioning have been develope d , and c ombined with the greenhouse environment and leaf expansio