Structural Evidence for a Reinforcing Response and Retention of Hydration During Confinement of Cartilage Lipids

Lipids have an important role in the complex lubrication of articulating joints, however changes in lipid phase behavior that occur owing to mechanical confinement are not well understood. Here, a surface force-type apparatus has been combined with neutron reflectometry to measure confinement-induced changes in the structure of lipids, the major surface-active component of the lubricant in articulating joints. The same incompressible state was accessed under low uniaxial stress (1 bar), irrespective of whether the lipids had started out unconfined above or below the Lα phase transition, and irrespective of whether they were fully or partially hydrated. In this incompressible state, the lipid component had thickened indicating extension and rearrangement of the lipid chains in response to the applied stress. The small amount of water remaining between each lipid bilayer was found to be similar for all chain lengths and starting phases. This represents the first structural evidence of the tightly bound water layer at the headgroups, which is required for hydration lubrication under load.

Numerical Evaluation of the Effect of a Surface-Active Component on the Convective Mass Transfer During the Metal Surface Melting by the Laser Impulse

Under consideration is a mathematical model of the alloying process of the metal surface by the pulsed laser radiation. The dependence of the surface tension on the surface-active impurities in the melt is analyzed. The numerical simulation enabled to determine the possibility of development of flows and distribution of the alloying material into the metal