When using narrow correlator spacing in a GPS receiver, the CIA-code tracking errors are on the order of a decimeter. In the presences of multipath signals, tracking errors can be on the order of a few meters. In many differential GPS applications, multipath is the most significant source of error. In a previous paper, the authors demonstrated that it is possible to reduce multipath errors greatly by using the Multipath Estimating Delay Lock Loop (MEDLL). Since then, MEDLL has been implemented into a multichannel receiver that calculates the pseudorange multipath errors in real time.This paper reviews the multipath problem in the GPS receiver and the theory of the MEDLL. Two experiments carried out to evaluate the MEDLL are described. First, measurements were collected simultaneously with the MEDLL receiver and a standard NovAtel narrow-correlator receiver over a short baseline. Second, the same receivers were connected to a GPS signal simulator so a multipath signal could be introduced in a controlled enviroment.
Trials at a wastewater treatment works indicate that cross-flow microfiltration, using flexible woven fibre tubes, could significantly enhance the performance of anaerobic digesters. The cross-flow microfiltration unit decouples the solids residence time from the liquid residence time and thus enables the volumetric throughput of the digester to be significantly increased while maintaining a constant solids residence time and volatile solids destruction. In trials on a pilot-plant digester, the volumetric throughput was almost doubled, from 70 to 130 1 d−1, while the solids residence time was maintained at 26 days. The economic feasibility of the coupled system was evaluated, using permeate flux data obtained from a cross-flow microfiltration unit coupled to a full-scale digester. The evaluation indicates that the coupled process is economically favourable when compared to conventional digester systems. The coupled system is currently being developed into a full-scale process. A full-scale CFMF unit is being constructed and will be coupled to a full-scale digester. Over a three year project the long-term reliability and operability of the process will be investigated, together with its effect on digester fluid dynamics and biomass viability.
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