Investigating Compaction by Intergranular Pressure Solution Using the Discrete Element Method.

Intergranular pressure solution creep is an important deformation mechanism in the Earth's crust. The phenomenon has been frequently studied and several analytical models have been proposed that describe its constitutive behavior. These models require assumptions regarding the geometry of the aggregate and the grain size distribution in order to solve for the contact stresses and often neglect shear tractions. Furthermore, analytical models tend to overestimate experimental compaction rates at low porosities, an observation for which the underlying mechanisms remain to be elucidated. Here we present a conceptually simple, 3-D discrete element method (DEM) approach for simulating intergranular pressure solution creep that explicitly models individual grains, relaxing many of the assumptions that are required by analytical models. The DEM model is validated against experiments by direct comparison of macroscopic sample compaction rates. Furthermore, the sensitivity of the overall DEM compaction rate to the grain size and applied stress is tested. The effects of the interparticle friction and of a distributed grain size on macroscopic strain rates are subsequently investigated. Overall, we find that the DEM model is capable of reproducing realistic compaction behavior, and that the strain rates produced by the model are in good agreement with uniaxial compaction experiments. Characteristic features, such as the dependence of the strain rate on grain size and applied stress, as predicted by analytical models, are also observed in the simulations. DEM results show that interparticle friction and a distributed grain size affect the compaction rates by less than half an order of magnitude.

Once weekly administration of levamisole in rheumatoid arthritis.

The therapeutic as well as the unwanted effects, in rheumatoid arthritis patients, of once weekly administration of 150 mg levamisole were compared, under double-blind conditions, with 3 50-mg daily doses of levamisole for 3 consecutive days weekly and placebo. The applied minimization method was used to assign patients to treatment groups so that all groups were comparable at the start of the trial. All patients were evaluated monthly, for 26 weeks. Three patients on the levamisole 3-day-weekly dosage interrupted their treatment because of side-effects. Except for the unwanted effects, the differences in the therapeutic efficacy in the 2 levamisole groups were not statistically significant. Twenty-one patients (3 in the levamisole once weekly administration group and 18 in the placebo group) interrupted their treatment because of inefficacy. Placebo was statistically less effective than the active drug. It is concluded that once weekly is as effective as 3-day-weekly administration of levamisole, but has fewer side-effects.