The problem of the mutual exclusion of several independent processes from simultaneous access to a “critical section” is discussed for the case where there are two distinct classes of processes known as “readers” and “writers.” The “readers” may share the section with each other, but the “writers” must have exclusive access. Two solutions are presented: one for the case where we wish minimum delay for the readers; the other for the case where we wish writing to take place as early as possible.

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In many Sub-Saharan African countries, farmers typically have a choice between selling their products to traders who travel between villages and markets and transporting their products to the nearest market themselves. Because of communities' remoteness and poor communications with marketplaces, farmers' uncertainty about market prices is usually high. Traders may take advantage of farmers' ignorance of the market price and extract a rent from them by oering very low prices for their products. In this article, we model bargaining interactions between a farmer and a trader who incur dierent transportation costs, and we study how price information aects the bargain and the balance of power. We then estimate the causal eect of a Market Information System (MIS) working through mobile phone networks on Ghanaian farmers' marketing performances. We nd that farmers who have beneted from the MIS program received signicantly higher prices for maize and groundnuts: about 12.7% more for maize and 9.7% more for groundnuts than what they would have received had they not participated in the MIS program. These results suggest that the theoretical conditions for successful farmer use of MIS may be met in eld.

A step-by-step approach to model the dynamic behavior and evaluate the performance of computing systems is proposed. It is based on a technique of variable aggregation and the concept of nearly decomposable systems, both borrowed from Econometrics. This approach is taken in order to identify in multiprogramming paging systems (i) unstable regimes of operations and (ii) critical computing loads which bring the system into states of saturation. This analysis leads to a more complete definition of the circumstances in which "thrashing" can set in. Volume 18Number 7 is the Hrst large one using the RC 4000 multiprogramming system.

Biological invasions entail massive biodiversity losses and tremendous economic impacts that justify significant management efforts. Because the funds available to control biological invasions are limited, there is a need to identify priority species. This paper first review current invasive species prioritization methods and explicitly highlights their pitfalls. We then construct a cost-benefit optimization framework that incorporates species utility, ecological value, distinctiveness, and species interactions. This framework offers the theoretical foundations of a simple and operational method for the management of invasive species under a limited budget constraint. It takes the form of an algorithm for the prioritization of multiple biological invasions.