841 research outputs found
The interaction of spatially modulated vortex pairs with free surfaces
Spatially modulated vortex pairs were generated below a free surface by two counter-rotating flaps whose edges approximate a sinusoid. The surface interactions of the vertically approaching vortex pairs were visualized by the shadowgraph technique. Two limiting cases were investigated in detail: the interaction with a surfactant-rich (contaminated) surface and with a surfactant-poor (âcleanâ) surface. In the latter case shadowgraph images showed that the underlying vortex core formed a line of circular surface depressions. Subsequent measurements of the temporally evolving velocity fields using digital particle image velocimetry (DPIV) of the vortex pair cross-sections and the subsurface plane confirmed the connection process of the main vortex core with the surface. As a result of the connection the initially modulated vortex tube was broken into a line of U-vortices. In the presence of surfactants this connection could not be observed; rather a Reynolds ridge (or stagnation line) was formed and a very weak connection of the secondary separation vortex could be seen in the shadowgraphs as well as measured with the time-resolved DPIV technique.
A prerequisite for connection of the vortex with the surface is that the flow's kinematics force the vortex core, that is, regions of concentrated vorticity, toward the surface. The ensuing locally concentrated viscous flux of surface-parallel vorticity through the surface is balanced by a local surface deceleration. Surface-normal vorticity appears on each side of the decelerated region whose gradually increasing circulation is directly balanced by the loss of circulation of the surface-parallel vortex. However, the shear forces caused by small amounts of surface contamination and its associated subsurface boundary layer inhibit the connection process by preventing the essential viscous flux of parallel vorticity through the surface. Instead, the subsurface boundary layer is associated with a flux of parallel vorticity into the surface which then concentrates into the observable secondary separation vortex
Assessing Consumer Preferences for Organically Grown Fresh Fruit and Vegetables in Eastern New Brunswick
consumer preferences, organic fresh produce, willingness-to-pay, Consumer/Household Economics, Crop Production/Industries, Demand and Price Analysis, Q1,
Effect of morphology on the large-amplitude flapping dynamics of an inverted flag in a uniform flow
The stability of a cantilevered elastic sheet in a uniform flow has been
studied extensively due to its importance in engineering and its prevalence in
natural structures. Varying the flow speed can give rise to a range of dynamics
including limit cycle behaviour and chaotic motion of the cantilevered sheet.
Recently, the "inverted flag" configuration - a cantilevered elastic sheet
aligned with the flow impinging on its free edge - has been observed to produce
large-amplitude flapping over a finite band of flow speeds. This flapping
phenomenon has been found to be a vortex-induced vibration, and only occurs at
sufficiently large Reynolds numbers. In all cases studied, the inverted flag
has been formed from a cantilevered sheet of rectangular morphology, i.e. the
planform of its elastic sheet is a rectangle. Here, we investigate the effect
of the inverted flag's morphology on its resulting stability and dynamics. We
choose a trapezoidal planform which is explored using experiment and an
analytical theory for the divergence instability of an inverted flag of
arbitrary morphology. Strikingly, for this planform we observe that the flow
speed range over which flapping occurs scales approximately with the flow speed
at which the divergence instability occurs. This provides a means by which to
predict and control flapping. In a biological setting, leaves in a wind can
also align themselves in an inverted flag configuration. Motivated by this
natural occurrence we also study the effect of adding an artificial "petiole"
(a thin elastic stalk that connects the sheet to the clamp) on the inverted
flag's dynamics. We find that the petiole serves to partially decouple fluid
forces from elastic forces and increases the freedom by which the flapping
dynamics can be tuned. These results highlight the intricacies of the flapping
instability and account for some of the varied dynamics of leaves in nature.Comment: 21 pages, 10 figures, 1 tabl
The Efficacy of Commercial Tooth Storage Media for Maintaining the Viability of Human Periodontal Ligament Fibroblasts
Aim
To evaluate SaveâAâTooth (SAT), EMT Toothsaver (EMT) and Hank\u27s Balanced Salt Solution (HBSS) for their influence on the viability and proliferative capacity of human periodontal ligament fibroblasts (HPDLFs). Methodology
Primary HPDLFs were seeded into 96âwell cell culture plates and exposed to SAT, EMT, HBSS and water (negative control) for 0.5, 1, 3, 6, 12 and 24 h at room temperature (22 °C). After each exposure time, cell viability was measured through quantifying adenosine triphosphate (ATP) using a luminescent dye. The proliferative capacity was also quantified using the PrestoBlue assay after 12 or 24 h storage in each medium. The data were analysed statistically by twoâway anova and post hoc Least Significant Difference (LSD) test (P \u3c 0.05). The morphology of the cells after 12 h storage was also investigated through live/dead viability/cytotoxicity kit together with fluorescence microscopy. Results
There was no significant difference in cell viability amongst HBSS, SAT and EMT groups up to 6 h. SAT was effective in maintaining cell viability only up to 12 h and then became detrimental to HPDLF; after 24 h, the effectiveness of SAT in maintaining cell viability was similar to that of water (P \u3e 0.05). Amongst all the media, only EMT could maintain the proliferative capacity of HPDLFs significantly higher than the negative control, that is water (P \u3c 0.05) after 24 h storage. Conclusion
EMT maintained the proliferative capacity of HPDLFs after 24 h storage
Effects of Phosphorus and Copper on Factors Influencing Nutrient Uptake, Photosynthesis, and Grain Yield of Wheat
Author Institution: Department of Agronomy, The Ohio State UniversityApplication of large amounts of phosphorus fertilizers is used to enhance early plant growth and yield of wheat (Triticum aestivum L.). This practice can lead to an accumulation of phosphorus in soil and a reduced copper uptake by plants which may result in a reduction of plastocyanin concentrations in chloroplasts. As a result, photosynthetic rates and crop yield can be adversely affected. While copper uptake is sometimes enhanced by vesicular-arbuscular mycorrhizal (VAM) fungi, large accumulations of soil phosphorus can reduce VAM-enhanced copper uptake
Recommended from our members
Shear design of HSC beams with combination of links and horizontal web steel
The existing recommendations in Eurocode 2 and the British Code of Practice for the shear design of beams are derived from research conducted essentially on normal-strength concrete (NSC) with cube strengths up to 50 MPa, and it was found that the shear strengths of high-strength concrete (HSC) members made with limestone aggregate are below the characteristic resistances of identical NSC members. Previous experimental tests have also shown that significant differences exist in the angle of crack of shear failure of NSC and HSC. This paper presents data from five beam tests, which demonstrate that HSC with limestone aggregate has a reduced shear strength compared with NSC made with gravel and thus shows a gap in knowledge in the design approach to shear resistance of HSC beams. Previous investigations have suggested that horizontal web steels can contribute to the overall shear resistance of a reinforced concrete member in conjunction with the other constituents, concrete, tension and shear steel. The paper also presents data from tests on 11 beam tests and shows that the shear resistance of HSC beams is highly dependent on dowel action resulting from horizontal web bars positioned at the centre of the depth of the beam. Past attempts to quantify this dowel action are investigated and an improved design rule is proposed
- âŚ