Quantitaton of rate of gastrointestinal and buccal absorption of acidic and basic drugs based on extraction theory

Equations have been derived which quantitatively describe the rate of gastrointestinal and buccal absorption of acidic and basic drugs as a function of pH of aqueous lumenal contents and time. The equations have been used to fit observed data in the literature, and the estimated parameters are reported. An equation which describes the renal clearance of an acidic or basic drug as a function of urinary pH is also derived. In essence, the equations quantitate the pH-partition hypothesis and explain most, if not all, related observed data in the literature. The results suggest that the aqueous diffusion layer may not rate-limit absorption of monomeric drug molecules but that absorption is rate-limited by transfer of drug out of the membrane in vivo.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45024/1/10928_2005_Article_BF01060026.pd

Hybrid continuous fibre cement composites

SIGLEAvailable from British Library Document Supply Centre-DSC:DXN015643 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Filament fracture within glass fibre strands in hybrid fibre cement composites

In the study of hybrid fibre cement composites containing continuous polypropylene fibres and glass fibres, it is important to know the fracture behaviour of the glass fibre strand in order to minimise the discrepancies between experiment and theory. A new technique of light transmission through the glass fibres has been developed in order to obtain independent information about the failure of individual glass filaments within a strand. The technique gave quantitative results showing that in the hybrid composite, about 80% of the glass filaments were broken somewhere in the strands before the maximum stress in the composite was reached. This was in contrast to the composite reinforced with glass fibres alone where only about 30% of the filaments were fractured before the ultimate stress. The fractures of the glass filaments in the hybrid composite were more evenly distributed than in the singly reinforced composite which enabled greater strains to be achieved in the hybrid composite at the maximum stress. (C) 1998 Kluwer Academic Publishers

Techniques for determining some microstructural parameters in glass reinforced cement

Two important parameters which control the fracture behaviour of glass fibres in cement composites, whether they contain one fibre type or are hybrids of two fibre types, are the perimeter of the glass strands in contact with hydrated cement and the way in which glass filaments fracture in multifilament strands. In scanning electron microscopy (SEM) observations, much improved images were obtained by detecting backscattered electrons rather than secondary electrons. This improvement gave good contrast between the fibre strands and the matrix, hence the perimeter of the glass strands could be determined using an image analyser. The progression of filament fracture within a strand was examined using two techniques, acid dissolution and light transmission through the filaments. These techniques showed that strands tend to fail progressively in hybrid composites containing glass and polypropylene fibres and that glass fracture continues to occur after the peak loan has been reached