Mechanisms of Invasion Resistance of Aquatic Plant Communities.

Invasive plant species are among the major threats to freshwater biodiversity. Few experimental studies have investigated whether native plant diversity can provide biotic resistance to invaders in freshwater ecosystems. At small spatial scales, invasion resistance may increase with plant species richness due to a better use of available resources, leaving less available for a potential invader (Complementarity effect) and/or the greater probability to have a highly competitive (or productive) native species in the community (Selection effect).

The role of elastin in the mechanical properties of skin.

The elastin fibers of rat skin samples were degraded by the use of a purified preparation of elastase to which soybean inhibitor was added, preventing the collagenolytic activity of the elastase on collagen. Control experiments ascertained degradation of elastin and no effect on collagen. The mechanical properties of the skin samples were studied before and after the enzymatic treatment and differences ascribed to the degraded elastin fibers.

The measurement and modelling of the mechanical properties of human skin in vivo--II. The model.

The stress-strain relationship for human skin in vivo has a characteristic non linear shape even for low loads. Considerations are given on the basis of which a structural model has been selected, in which the mechanical properties of corrugated collagen fibrils are involved. It is found that such a model can describe the experimental stress-strain relationship surprisingly well with only three free parameters.

The measurement and modelling of the mechanical properties of human skin in vivo--I. The measurement.

The mechanical properties of human skin in vivo are studied by means of uniaxial strain measurements. In order to obtain a stress-strain relationship which is independent of the in vivo measuring configuration, values for the effective width and effective length of the loaded skin strip have to be known. By variation of tab width and tab distance in a few series of experiments on the same subject, these effective values are found.