Hmj Snijders

Confined compression of canine annulus fibrosus under chemical and mechanical loading

Uniaxial confined compression and swelling experiments on cylindrical specimens taken either in an axial or in a radial direction from a canine lumbar annulus fibrosus are presented. The loading protocol consisted of a combination of stepwise mechanical and chemical loading. Swelling and consolidation curves of normalized displacement versus square root of normalized time did not show a dependence on site or orientation of the specimen. All stages in which height increases, namely, conditioning, swelling, and desolidation show only slight differences in these normalized curves. Consolidation is initially faster, and later slower. The transport coefficient for axial specimens is higher than for radial specimens, for consolidation e.g., 3.14 +/- 1.56 10(-10) m2s(-1) and 1.11 +/- 0.33 10(-10) m2s(-1) respectively, the biphasic aggregate moduli are 1.01 +/- 0.31 MPa and 0.66 +/- 0.30 MPa, respectively.

A high-speed gas chromatograph coupled to a Time-of-Flight mass analyzer

Abstract A high-speed gas chromatographic system that produces peak widths of about 0.1 s has been coupled to a time-of-flight mass analyzer that can record up to several thousand single-shot mass spectra per second. The effect of the improved scan rate on the chromatographic resolution is demonstrated. The detection limits are in the low picogram range. The mass spectra are in good agreement with library spectra.

A mixture approach to the mechanics of the human intervertebral disc

A finite deformation model for charged hydrated tissues, such as the intervertebral tissue, is developed. The model predicts not only the response to a mechanical load but also to a chemical load. This response is characterised by ion diffusion, fluid flow relative to the solid matrix and osmotic pressure. The reasonable agreement between experiment and prediction of the model supports its physical basis.

Porous Media Mechanics

A family of finite elements for two-dimensional, three-dimensional and axisymmetric finite deformation of porous media has been implemented into DIANA. This implementation includes two extensions of Biot’s theory: one for swelling media, the other for blood perfused soft tissue. Mineral, biological and synthetic porous media often exhibit swelling or shrinking when in contact with changing salt concentrations. This phenomenon, observed in clays, shales, cartilage and gels, is caused by electric charges fixed to the solid, counteracted by corresponding charges in the fluid. Three phases are involved in the swelling mechanics: a solid, a fluid and an ion phase. Blood perfusion involves a spectrum of intercommunicating fluid phases saturating the porous medium. The finite element modelling of blood perfusion is applied to a contracting skeletal muscle.