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This paper details a diversity performance study undertaken by Mason Communications, on behalf of Omnitel Pronto Italia (OPI), to investigate the use of dual polarisation antennas for cellular base stations within a dual band GSM900/1800 network. Extensive radio measurements for both uplink and downlink were taken using horizontally separated vertically polarised antennas, horizontally/vertically (H/V) polarised diversity antennas and ±45° polarised diversity antennas, in urban and suburban environments and in both the 900 and 1800 MHz bands. An analysis of the measurements was undertaken to find the gross mean and local mean of the signals received, and hence the branch imbalances, the correlation between the voltage envelopes of the signals, and the diversity gains achieved through the use of maximal ratio combining (MRC). The results of this analysis suggest that, in both environments and at both 900 and 1800 MHz, horizontally separated spatial diversity outperforms both ±45° and H/V polarisation diversity. However, the results indicate that ±45° polarisation provides a better performance than H/V polarisation at both frequencies and within both environments considered.

The estuarine leech Myzobdella lugubris has been reported to parasitize a number of fish and invertebrate species (Sawyer et al., 1975). Infestations of striped bass reported in the literature are rare, are usually on fish two years or older, and typically number one leech per fish (Paperna and Zwerner, 1976). We noted heavy leech infestations (81 to 377 per fish) on two year old striped bass reared under intensive culture conditions at the Crane Aquaculture Facility.

Recent developments in Artificial Intelligence result in computer programs with a knowledge-base and intelligence characteristics similar to those exhibited by humans. One of the most promising advances in AI has been in the area of knowledge representation using ‘frames’. Their use in KBS (Knowledge Based Simulation) for discrete event simulation has already been reported. The application of frames in continuous system simulation is the focus of this paper.