Thrassos Panidis

Estimation of hydrodynamic shear stresses developed on human osteoblasts cultured on Ti–6Al–4V and strained by four point bending. Effects of mechanical loading to specific gene expression

The aim of the present investigation was to study the effects of mechanical strain on the orthopedic biomaterial Ti–6Al–4V-osteoblast interface, using an in vitro model. Homogeneous strain was applied to Human Bone Marrow derived Osteoblasts (HBMDOs) cultured on Ti–6Al–4V, at levels which are considered physiological, by a four-point bending mechanostimulatory system. A simple model for the estimation of maximum hydrodynamic shear stresses developed on cell culture layer and induced by nutrient medium flow during mechanical loading, as a function of the geometry of the culture plate and the load characteristics, is proposed. Shear stresses were lower than those which can elicit cell response. Mechanical loading was found that contributes to the regulation of osteoblast differentiation by influencing the expression of the osteoblast-specific transcription factor Cbfa1, both at the mRNA and protein level, and also the osteocalcin expression, whereas osteopontin gene expression was unaffected by mechanical loading at all experimental conditions.

Performance of an Infrared Heating System in a Production Greenhouse

Abstract The performance of an Infra-Red heating system using gas fired IR radiators is demonstrated in a full scale production greenhouse for vegetable seedlings. Outside meteorological data and the greenhouse thermal conditions have been monitored for a heating period of 60 days, to assess the quality of the canopy climate and the potential in energy savings. Results indicate that the seedlings are kept at optimum thermal conditions while the greenhouse air is maintained at lower temperature, by 2-3 °C, indicating a significant reduction in energy requirements. During operation, plant growth seemed to be positively affected by the IR radiation, whereas no plant infections by pests and / or diseases were observed.

Water Air Bubble Grid Turbulence

The interaction of a swarm of bubbles with the isotropic grid turbulence generated in a vertical water channel has been studied experimentally. Measurements of local void fraction, mean velocity and all three turbulence intensity components are presented at a distance from the grid where isotropic turbulence prevails in single-phase flow. At low gas flow rate the interaction is rather mild with minor redistribution of the void but significant increase of the turbulence intensity. High gas flow rates result in significant modifications of the flow structure. Void distribution presents maxima at locations between the center of the channel and the wall reminiscing of the Segre-Sielberberg effect. Similar maxima are observed in mean velocity measurements at values much higher than the corresponding single-phase flow. Turbulence intensity components increase is following different trends in longitudinal and transverse direction and the isotropy of the flow is destroyed.

Co-rotating vortex interaction

Purpose The purpose of this paper is to study the structure and dynamic development of a pair of co-rotating trailing vortices, during their formation, interaction and merging, using detailed experimental measurements of the velocity and vorticity fields. Design/methodology/approach The vortices were generated using two half wings (NACA0030) positioned at equal and opposite angles of attack at the entrance of the test section of an open-circuit, subsonic, wind tunnel. Velocity vector measurements were obtained at Rec = 133,000, on cross-plane grids at several distances from the trailing edges of the wings, using an in-house developed four-sensor hot wire anemometer probe. Findings The results include cross-plane contour plots of the mean and fluctuating velocity as well as mean vorticity fields. Each of these variables is affected in a different way, providing complementary information on the development of the flow field. After shedding, the two vortices are swept along the stream-wise direction and spiral around each other, thereby developing a braid of two vortices, which then deforms the external flow field. Gradually, the interaction with the external flow field links both vortices together until the final merging and the formation of a new stable linear vortex emerges. Practical implications Trailing vortices have been rendered particularly important during the past decades, because of increasing traffic density of very heavy aircrafts and several plane “incidents”, which were attributed to the action of the vortex wake. Originality/value The presented results provide information on the evolution and merging of a pair of vortices formed by a closely spaced differential wing configuration. The vortices interact almost immediately after shedding as expected in flap–flap or flap–wing vortices interaction.

Considerations on reaction to fire tests of polyethylene foam with a cone calorimeter apparatus

This work describes efforts to improve the repeatability of cone calorimeter tests of polyethylene flexible foam, used for pipe insulation. This material presented significant random deformation during burning, such as warping and rolling, which led to drainage of the tar formed during material degradation and altered randomly the heating and burning processes. These effects severely undermined the repeatability of the tests and the accurate assessment of the reaction to fire characteristics of the material. Standard techniques to alleviate the problem, such as use of a retainer frame or a grid, were proven either inadequate to secure the specimen in place or undermined the accurate estimation of the material properties. The selected solution was to incorporate thin metallic pins in the sample holder, which along with the use of a retainer frame was able to eliminate the problems, producing results with good repeatability and small standard deviation.