The flow of concentrated suspensions of solid particles can be suddenly blocked by the formation of a percolated network of frictional contacts above a critical value of the applied stress. Suspensions of magnetic particles coated with a superplastifier molecule were shown to produce a strong jamming transition. We find that, for these suspensions with an abrupt discontinuous shear thickening, a model using the divergence of the viscosity at a volume fraction that depends on the applied stress does not well describe the observed behaviour both below and above the critical stress. At a constant applied stress above the critical one, we have a stick–slip behaviour of the shear rate whose period can be predicted and scaled as the square root of the relaxation time of the frictional contacts. The application of a small magnetic field allows us to continuously decrease the critical shear rate, and it appears that the yield stress induced by the magnetic field does not contribute to the jamming transition. Finally, it is shown that this jamming transition also appears in the extrusion of a suspension through a die, but with a much slower dynamics than in the case of stress imposed on a rotational geometry. This article is part of the theme issue ‘Heterogeneous materials: metastable and non-ergodic internal structures’.

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A new initialization method for the transportation problem is presented. It assigns value only if necessary. It gives good results and often the optimal solution. Résumé. Dans cet article nous proposons une nouvelle méthode d'initialisation du problème de transport classique. Cette méthode est basée sur le principe d'une affectation seulement si nécessaire. Elle donne de bons résultats et souvent la solution optimale. Mots Clés. Problème de transport, problème de Hitchcock, méthode du simplexe, initialisation.

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Synthetic pesticides used to protect stored smoked and dried fish often cause enormous damageto human health and the environment. To limit the harms due to the use of these chemicals, it is necessary to find alternative methods. For this purpose, natural substances may constitute a beneficial way. The objective of this work is to study the effect of crushed fresh leaves and essential oil of Eucalyptus camaldulensis on the mortality of the larvae of an insect pest of smoked and dried fish, Sardinella aurita "Kétiakh", Dermestes maculatus (De Geer, 1774). Essential Oil was obtained by steam distillation from Eucalyptus leaves (0.8% w/w) and analyses carried out by GC/FID and GC/MS. For the biological test, fresh crushed leaves and essential oil were tested at different doses at varying treatment times again larvae Dermestes maculates. The results showed that D. maculatus was sensitive for both fresh crushed leaves and the essential oil, the efficacy of which depended on the dose and duration of treatment. The doses of 2 g and 2.5 g of freshly ground leaves showed a high efficiency of 27 to 40%, of mortality respectively. However, for the essential oil, with the increase in the duration of exposure, the highest mortality (33.3%) was recorded after 72 hours of treatment with the 40µl dose and at 120 hours with the 60µl dose. This study showed that fresh crushed leaves and essential oil of Eucalyptus camaldulensis can be considered as an alternative to the use of chemical insecticides in the conservation of smoked and dried Sardinella aurita "Kétiakh" stored in Senegal.