Supersonic Boundary Layer in Regions with Small Temperature Perturbations on the Wall
The problem of disturbed flow in the laminar boundary layer when heating elements are located on the surface is investigated. The flow is described by the theory of viscous-inviscid interaction with full Navier–Stokes equations. We apply the triple-deck model of the flow and describe asymptotic multiscale structure for the supersonic case. Using this structure as a base, we construct the solution to the flat stationary problem by means of Fourier transform and analysis in the complex plane. It is also shown that localization of a heating element may arrive at a singularity of the pressure downstream. Results of numerical and analytic analysis are presented. Using these elements gives us the opportunity to develop a novel method for the separation control of the boundary layer.
Boundary-Layer Flow Near the Trailing Edge of a Flat Plate
Goldstein [1] has given a solution to the boundary-layer equations for the flow just downstream from the trailing edge of a flat plate. It is shown here that this approximation is no longer valid if the nondimensional distance $\bar x/L$ from the edge is $O( R^{ - 3/8} )$. A second order correction to Goldstein’s stream function is obtained to take into account the pressure gradient induced locally in the external flow, and is found to overtake the first order term when $\bar x/L = O( R^{ - 3/ 8} )$. For an alternative derivation, a limit of the Navier-Stokes equations is taken for $R \to \infty $ with $x^ * = R^\alpha \bar x/ L$ fixed, and it is concluded that the choice $\alpha = 3/8$ corresponds to a distinguished limit in the sense that it leads to a special set of approximate equations. A solution analogous to Goldstein’s, including a second order term, is constructed for the boundary layer just upstream, from the trailing edge.The approximate equations derived in the limit for $R \to \infty $ with $...
Cross talk between redox signalling and metabolic activity of osteoblasts and fibroblasts in the presence of hydroxyapatite-based biomaterials influences bone regeneration
Regeneration of bone tissue defects that result from metabolic disorders, including periodontal diseases, can be supported by biomaterials based on hydroxyapatite. Despite of good biocompatibility of biomaterials they can cause oxidative stress and inflammatory processes as a result of mechanical interaction with surrounding tissues. Because osteoblasts are responsible for bone regeneration process in which gingival fibroblasts may also participate, the aim of the work was to investigate the influence of hydroxyapatite-based biomaterials (allogeneic and xenogeneic) and biomaterials combined with enamel matrix derivative (Emdogain) on osteoblast and fibroblast redox balance in the context of osteoblast proliferation and differentiation.
The results showed that examined substitutes were not cytotoxic in vitro, but affected redox balance of osteoblasts and fibroblasts (ROS level increase and GSH level decrease) which led to oxidative stress (MDA and protein carbonyl groups level increase) resulting in an increase of the Nrf2 and NFκB expression. The consequence of these changes was partial inhibition of proliferation and osteoblast differentiation. Emdogain alone and combined with biomaterials decreased ROS generation and increased GSH level in both osteoblasts and fibroblasts leading to reduction of transcription factors expression especially proinflammatory NFκB, which promoted osteoblast differentiation and mineralization process.