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The accuracy of laser diffraction size measurements of dry powder inhaler particles, which play an important role in guiding effective inhaler system design, is assessed. Additionally, data for lactose particle shape characteristics are presented. Comparisons made between microscopy and cohesion-minimized laser diffraction size measurements for pharmaceutical lactose particles indicate that non-sphericity causes a broadening of the size distribution while the median diameter is unchanged. This is corroborated by data in the literature. Poured particles and those dispensed from an inhaler shared a common characteristic agglomerate modal diameter that was absent in the cohesion-minimized wet suspension. It is concluded that the interpretation of integral measurements of the particle size distribution using laser diffraction, for cohesive particle systems, is reasonable. The method of dispensing particles from an inhaler and delivery through an artificial throat is critical and both decreased the proportion of agglomerates present.

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SUMMARYThin layer finite elements are employed to model the response of rock joints in finite element analyses of rock mechanics problems. The case of a circular opening embedded in a rock mass is investigated. Results are obtained for both solid and jointed rock masses, and the effects of the presence of joints on the stress and strain field are investigated. Results from the finite element analysis art verified with respect to measurements from physical modelling. It is shown that the comparison between measured and computed results is satisfactory and that the presence ofjoints has a pronounced effect on the stress and strain field as compared to that realized in the absence of any rock joints. This study provides valuable data which contribute to the verification of thin layer finite elements for modelling the response of rock joints.

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