Bondy, France
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Hieu N.T.,IRD UMI 209 UMMISCO | Hieu N.T.,University Pierre and Marie Curie | Hieu N.T.,Vietnam National University, Hanoi | Brochier T.,British Petroleum | And 4 more authors.
Acta Biotheoretica | Year: 2014

We consider a fishery model with two sites: (1) a marine protected area (MPA) where fishing is prohibited and (2) an area where the fish population is harvested. We assume that fish can migrate from MPA to fishing area at a very fast time scale and fish spatial organisation can change from small to large clusters of school at a fast time scale. The growth of the fish population and the catch are assumed to occur at a slow time scale. The complete model is a system of five ordinary differential equations with three time scales. We take advantage of the time scales using aggregation of variables methods to derive a reduced model governing the total fish density and fishing effort at the slow time scale. We analyze this aggregated model and show that under some conditions, there exists an equilibrium corresponding to a sustainable fishery. Our results suggest that in small pelagic fisheries the yield is maximum for a fish population distributed among both small and large clusters of school. © 2014 Springer Science+Business Media Dordrecht.


Yenke B.O.,Ngaoundere Institute of Technology | Mehaut J.-F.,French Institute for Research in Computer Science and Automation | Tchuente M.,IRD UMI 209 UMMISCO | Tchuente M.,University of Yaounde I
IEEE Transactions on Services Computing | Year: 2011

Nowadays, enterprises can provide computing services through their intranet networks by letting their available resources be used as virtual clusters for scientific computation during idle periods such as nights, weekends, and holidays. Generally, these idle periods do not permit to carry out the computations completely. It is therefore necessary to save the context of uncompleted applications for possible restart. This checkpointing mechanism is subject to resource constraints: the network bandwidth, the disk bandwidth, and the delay T imposed for releasing the workstations. We first introduce a function bw that gives the bandwidth bw(m,V) of a system during the checkpointing of m applications with aggregated memory requirement V. Assuming that this bandwidth is shared equitably among the applications, the scheduling problem becomes a sequence of knapsack problems with nonlinear constraints for which we propose approximate solutions. Experiments carried out on Grid5000 show that the running time of this algorithm is negligible compared to the delay T which is of the order of few minutes. This means that the proposed scheduling algorithm does not induce a significant overhead on the checkpointing process. As a consequence, our mechanism can be incorporated in a batch scheduler. © 2011 IEEE.

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