Intermittent hydrostatic pressure

The third and perhaps most important class of water repellents consists of materials appHed to the surface of concrete for above-grade stmctures or others where water pressure on the concrete is small. This iacludes damp-proofing ia which treatments cannot be subjected to continuous or even intermittent hydrostatic pressure (83). Repellents that may be used are oils, waxes, soaps, resias, and siUcon-based systems (84). 

The application of tensile stresses to osteoblasts appears to cause induction of the BMP-4 gene in preosteoblastic cells and adjacent spindle-shaped fibroblasts suggesting that BMP-4 may play a pivotal role by acting as an autocrine and a paracrine factor for recruiting osteoblasts in tensile stress-induced osteogenesis. Intermittent hydrostatic pressure (IHC) up-regulates osteopontin (OPN) mRNA expression in osteoblast cell cultures. In both... 

Smith RL, Lin J, Trindale MC, Shida J, Kajiyama G, Vu T, Hoffman AR, van der Meulen MC, Goodman SB, Schurman DJ, Carter DR. Time-dependent effects of intermittent hydrostatic pressure on articular chondrocyte type II collagen and aggrecan mRNA expression. J Rehabil Res Dev. 2000 2 153-161. 

Tanck, E., W. D. Van Driel, J. W. Hagen, E. H. Burger, L. Blankevoort, and R. Huiskes. 1999. Why does intermittent hydrostatic pressure enhance the mineralization process in fetal cartilage / Biomech 32 153-61. 

Hu, J. C. and K. A. Athanasiou 2006. The effects of intermittent hydrostatic pressure on self-assembled articular cartilage constructs. Tissue Eng 12(5) 1337-44. 

Ikenoue, T., M. C. Trindade et al. 2003. Mechanoregulation of human articular chondrocyte aggrecan and type 11 collagen expression by intermittent hydrostatic pressure in vitro. J Orthop Res 21(1) 110-16. 

In experiments with cultured cells it has been shown that osteocytes, but not periosteal fibroblasts, are extremely sensitive to fluid flow, resulting in increased prostaglandin as well as nitric oxide production [104, 105], Three different cell populations, namely osteocytes, osteoblasts, and periosteal fibroblasts, were subjected to two stress regimes, pulsatile fluid flow and intermittent hydrostatic compression [104], Intermittent hydrostatic compression was applied at 0.3 Hz with a 13-kPa peak pressure. The pulsatile fluid flow was a fluid flow with a mean shear stress of 0.5 Pa with cyclic variations of 0.02 Pa at 5 Hz. The maximal hydrostatic pressure rate was 130 kPa/sec and the maximal fluid shear stress rate was 12 Pa/sec. Under both stress regimes, osteocytes appeared more sensitive than osteoblasts, and osteoblasts more sensitive than periosteal fibroblasts. However, despite the large difference in peak stress and peak stress rate, pulsatile fluid flow was more effective than intermittent hydrostatic compression. Osteocytes, but not the other cell types, responded to 1 hour pulsatile fluid flow treatment with a sustained prostaglandin E2 upregula-... 

Now visualize the action of a submerged jet of air in liquid. At very low air flow velocities, the bubbles are large. They rise as independent bubbles at the orifice. When the velocity of air through the orifice increases, the air projects as a cone into the liquid and small bubbles shear off. The maximum velocity is reached when the ratio of absolute hydrostatic pressure outside the orifice divided by the absolute air pressure in the orifice is 0.528. This determines sonic velocity. Four regions of the air cone or jet are conceptually drawn in Fig. 11. Region I is called the potential core of air with a uniform velocity. The outermost annular cone, Region II, is an intermittency zone in... 

Suh, J. K., G. H. Back et al. 1999. Intermittent sub-ambient interstitial hydrostatic pressure as a potential mechanical stimulator for chondrocyte metabolism. Osteoarthritis Cartilage 7(1) 71-80. 

Occasional loads are those loads that act on the system on an intermittent basis. Examples of occasional loads are those placed on the systan from the hydrostatic leak test, seismic loads, and other dynamic loads. Dynamic loads are those from forces acting on the system, such as forces caused by water hammer, and the energy released by a pressure relief device. Another type of occasional load is caused by the expansion of the piping system material. An example of an expansion load is the thermal expansion of pipe against a restraint due to a change in temperature. 

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