Future Projections of Urban Waste Flows aand their Impacts in African Metropolises Cities

This paper presents future trends of urban wastes and their impacts on the environment of African cities using plausible mitigation scenarios. To accomplish this, an integrated dynamic model for urban waste flows was developed, tested, calibrated and validated. Its parameter sensitivity was analyzed. Using population projection up to 2052 with different levels of technological implementation, policy enforcement and awareness raising, four runs were executed. The “business as usual” run showed that with no additional mitigation measures, the environmental quality in Kampala and Dar es salaam Cities deteriorates. The “more enforcement” and “more collection” scenarios showed good reduction in environmental loads but they perform less well in resource recovery. The “proper management” scenario that combines enhanced technological implementation, awareness raising and policy enforcement, produced the smallest environmental loads, and recovered the largest amount of resources. Thus, the city authorities, general public, community based organisations and Non-governmental organizations would have to increase their efforts in finances and commitment to improve the urban environmental quality and increase resource recovery

On closed queueing networks with mixed preemptive resume priority servers.

This paper discusses a typical closed queueing network model in which multiple preemptive resume servers are present with different priority structures at each priority node. An algorithm is developed that is applicable for the three-node two-class model and results are compared to point estimates obtained from simulation. The algorithm is partly based on the Delay/MVA algorithm developed by Bondi and Chuang, because of the accuracy with which instant arrival queue lengths at fcfs servers are calculated. Results are also compared with results obtained from the Shadow Approximation.Networks;

Queue lengths and waiting times in the two-class two-server queue with nonpreemptive heterogeneous priority structures.

Our aim is to analyze a multiserver queue with nonpreemptive heterogeneous priority structures, which arises in the performance evaluation of batch initiator settings n MVS. We use matrix-geometric methods and derive the stationary distribution of queue lenghts and waitng times for the Markovian two-class two-server case.Structure; Performance; Performance evaluation; Evaluation; Methods; Distribution;

Grosch's law: a statistical illusion?.

In this paper a central law on economies of scale in computer hardware pricing, Grosch's law is discussed. The history and various validation efforts are examined in detail. It is shown how the last set of validations during the eighties may be interpreted as a statistical misinterpretation, although this effect may have been present in all validation attempts, including the earliest ones. Simulation experiments reveal that constant returns to scale in combination with decreasing computer prices may give the illusion of Grosch's law when performing regression models against computer prices over many years. The paper also shows how the appropriate definition of computer capacity, and in particular Kleinrock's power definition, plays a central role in economies of scale for computer prices.Law;

LCA of the timber sector in Ghana: preliminary life cycle impact assessment (LCIA)

Purpose - Most life cycle impact assessment (LCIA) approaches in life cycle assessment (LCA) are developed for western countries. Their LCIA approaches and characterization methodologies for different impact categories may not be necessarily relevant to African environmental conditions and particularly not for the timber sector in Ghana. This study reviews the relevance of existing impact categories and LCIA approaches, and uses the most relevant for the timber sector of Ghana. Materials and methods - The study reviewed 23 life cycle inventories (LCIs) and LCAs on forestry, timber, and wood products for relevant impact categories and LCIA approaches for their relevance to the specific conditions in Ghana. This study uses an earlier LCI study of the timber industry as a starting point for an additional LCIA. We next performed a correlation and regression analysis to learn whether wood wastes may function as a reasonable single indicator for land use as proxy for biodiversity loss and the other impact categories. Results and discussion - The literature review shows that no LCI or LCA studies were developed for Africa or the tropics. The LCIA approaches in the reviewed LCAs are indeed shown to take their basis in the environmental problems in western countries and characterization methodologies relating to how these problems manifest themselves in the western world. Characterization methodologies for different impact categories in CML-2000 and other LCIA approaches may not be necessarily relevant to African tropical environmental conditions and particularly not for the timber sector in Ghana. This situation hampers the reliability of our LCIA and points to a serious research gap in LCIA development in general. We applied the scientifically well-recognized CML 2000 to the earlier LCI results and characterized the preliminary selected impact categories of global warming, acidification, eutrophication, photochemical oxidant formation, and human toxicity. The correlation analysis indicated that wood waste is indeed strongly correlated with land use as proxy for biodiversity loss and also positively correlated with the other five potential impact results. It can be concluded that wood waste production is a major driving force for biodiversity loss and a sufficiently good single indicator for all other environmental performance indicators in the timber sector of Ghana. Conclusions - This study and the previous LCI paper are pioneering a field not yet explored, since the correct environmental performance indicators are not yet developed or adapted to tropical conditions. The development of LCIA approaches in the tropics may be the start of a never-ending journey in LCA research in Africa, particularly Ghana