Dynamic Compressive Strain Research Articles

Dynamic Mechanical Compression Influences Nitric Oxide Production by Articular Chondrocytes Seeded in Agarose

Nitric oxide (NO) has been implicated in the inhibition of cell proliferation in cytokine and lipopolysaccharide (LPS)-stimulated chondrocytes and is known to be influenced by physical forces in several tissues. In this study, a well-characterized model system utilizing bovine chondrocytes embedded in 3% agarose constructs has been used to investigate the effect of dynamic strain at 0.3, 1, or 3 Hz on NO production. LPS induced a significant increase in nitrite levels, which was reversed by bothl-NAME and dexamethasone. Dynamic compressive strain produced a significant reduction in nitrite production. The effect was partially blocked byl-NAME but unaffected by dexamethasone.l-NAME also reversed dynamic compression-induced stimulation of [3H]-thymidine incorporation. NO appears to be a constituent of mechanotransduction pathways which influence proliferation of bovine chondrocytes seeded within agarose constructs. The inhibitor experiments also infer that alterations in cNOS activity primarily determine the response.

Vapour phase deposition of cubic boron nitride

This paper reviews the “state-of-the-art” of the vapour phase deposition of cubic boron nitride (cBN) in terms of the nucleation and growth processes on ion bombardment, and provides an insight into the solution of the inherent disadvantages of ion-assisted processing for cBN deposition. To this end, current experimental and theoretical topics related to the vapour phase deposition of cBN are examined, and the initial growth stage is discussed in conjunction with recent findings derived from novel sputtering and plasma chemical vapour deposition. Finally, a qualitative growth scheme of cBN is proposed based on the concept of dynamic compressive strain, and research needs for the future development of cBN thin films are identified.

Stiffening of the Femoral Head Due to Intertrabecular Fluid and Intraosseous Pressure

The mechanical properties of cancellous bone, as measured from bone plug samples have been widely documented. However, few tests have been attempted to explore the effects the intertrabecular contents may have on the load bearing capabilities. In this study, canine femoral heads were subjected to dynamic compressive strain cycles. The femoral heads were tested intact, as well as with disrupted boundary conditions of the continuous, intraosseous fluid space. A significant reduction in mechanical stiffness was observed when the fluid compartment boundary was disrupted by drilling a hole part way into the femoral neck. A finite element model of a typical femoral head showed that the stiffness change was not due to removal of material from the neck, hydraulic effects notwithstanding. Refilling the hole in the neck with saline solution and sealing the boundary restored the stiffness to the intact baseline level. However, an increase in the fluid pressure did not cause a statistically significant increase in the stiffness of the femoral head.

Lower blasthole pressures: a means of reducing costs when blasting rocks of low to moderate strength

From a purely mechanical viewpoint, each explosive charge should produce a peak blasthole pressure (Pb) that just fails to crush (i.e. pulverise or plastically deform) the rock which surrounds it. WherePb exceeds a critical value, some explosion energy is wasted in crushing an annular section of rock immediately around each charge. As a rock's dynamic compressive breaking strain decreases, so shouldPb (Hagan, 1977b).

The influence of cyclic plastic deformation on electrode reactions on mild steel in aqueous chloride solutions of varying pH

AbstractAn attempt has been made to study the operative mechanisms which cause the corrosion-fatigue failure of mild steel in marine environments. To achieve this the influence of dynamic cyclic plastic strain on the electrode reactions on mild steel in 0.6 M (3.5% NaCl) at various pH levels has been investigated. Dynamic tensile and compressive strains were observed to enhance significantly both anodic and cathodic reactions. At open-circuit potentials in solutions of pH 1–11 where corrosion-fatigue failure is known to occur, the anodic reaction is stimulated significantly more than the cathodic reaction. At pH 1, where the corrosion-fatigue life is a minimum, the observed dissolution effects are greatest; at other pH values an inverse relationship exists between dissolution effects and corrosion-fatigue endurance. At pH 12, where the material exhibits its dry fatigue properties, enhanced dissolution effects were found to decrease rapidly with progressive strain cycling. It would appear therefore that a ...

Strain dependence of the piezoelectric polarization of z-cut lithium niobate

Measurements of the piezoelectric polarization of z-cut lithium niobate are accomplished for dynamic compressive strains of from 8.9 × 10 −4 to 6 × 10 −3. Values for the linear piezoelectric constant, e 33 and its strain derivative are determined. The logarithmic strain derivatives of the longitudinal piezoelectric constants of x-cut quartz and z-cut lithium niobate are found to be approximately equal.