Mechanical tensions

A marine riser must be held in tension to prevent the riser from collapsing under its own weight. This can be accomplished by adding buoyant material to the riser pipe, or by mechanical tensioning devices (Figures 4-498, 4-499). Tensioning devices are usually required in water depths greater than 250 ft. 

Stress fibers are parallel bundles of actin filaments that develop in the cytoplasm of fibroblasts from the cortical actin network in response to mechanical tension. These often bind to the plasma membrane at focal contacts and, through transmembrane linker glycoproteins, to the extracellular matrix. Thus, actin filaments of stress fibers indirectly Join to the inner face of the plasma membrane through molecular assemblies of attachment proteins, which include an actin-capping protein, a-actinin, vinculin, and talin (Small, 1988). 

In our approach to membrane breakdown we have only taken preliminary steps. Among the phenomena still to be understood is the combined effect of electrical and mechanical stress. From the undulational point of view it is not clear how mechanical tension, which suppresses the undulations, can enhance the approach to membrane instability. Notice that pore formation models, where the release of mechanical and electrical energy is considered a driving force for the transition, provide a natural explanation for these effects [70]. The linear approach requires some modification to describe such phenomena. One suggestion is that membrane moduli should depend on both electrical and mechanical stress, which would cause an additional mode softening [111]. We hope that combining this effect with nonlocality will be illuminating. 

The different methods to produce mulitlayer shrink-joints are based on the thermal contrac tion of welding seams, as well as the mechanical tension and thermal contraction during strip-wire- or coil-winding after cooling down. Fig. 4.3-4 D shows the ideal distribution of residual... 

The films of organic polymers like polypropylene orpolyethyleneterephta-late, when subjected to mechanical tensions, develop systems of micro- and mesopores that make them transparent for the diffusion of solutions in solvents not dissolving the polymers itself. The counterflow diffusion of solutions ofM02(0C2H40Me)2 (M = Mo, W) in MeOC2H4OH (from one side) and water solutions (from the other side) permitted composites to be obtained where the metal (Mo, W) oxohydroxide particles were formed in situ inside such organic polymer films and remained there after the removal of the solvents [171],... 

Grinnell F, Zhu M, Carlson MA, Abrams JM. Release of mechanical tension triggers apoptosis of human fibroblasts in a model of regressing granulation tissue. Exp Cell Res. 1999 248 608-619. 

Titanium tubes with diameter 22 mm and thickness 2.6 mm were subjected to cyclic non uniform heating for a long time. The temperature difference on the tube length of 15 cm is about 200°C. The tube edges were fixed that led to creation of thermo-mechanical tensions. After about 15000 cycles of loading, fatigue cracks were formed at the point with minimum temperature. 

Abstract The formation of stable metal/polymer joints is an enormous challenge in material sciences. Good adhesion requires an interphase which is able to specifically interact with the metal substrate as well as with the second component. Furthermore, the interphase should compensate thermally generated mechanical tensions between the two adhering components. It will be shown that statistic copolymers of poly(vinyl formamide) and poly(vinyl amine) (PVFA-co-PVAm) are potential candidates for adhesion promoters. The polyelectrolyte character of the copolymers allows to apply them from its aqueous solutions. The primary amino groups exhibit the copolymers as highly reactive to metal surfaces as well as to the second joint partner. The... 

From this description it becomes obvious that a mechanical tension must develop in the surface film, because the atoms will tend to assume a closer packing. Hence any adsorbed molecule or atom which can improve the screening of the solid will decrease their state of tension and cause the surface film to expand and release some of the pressure which it exerted upon the subjacent layers. Adsorption of screeners, even of inert gas atoms such as argon, causes many porous solids to expand. 

Crabbing. Crabbing is a wet-processing procedure which employs hot and finally cold water, together with mechanical tensioning, and finally drying for the purpose of equalizing tensions in the fabric. 

A peculiarity of polystyrene in bulk is the fact that it has a negative optical anisotropy. The optical anisotropy is revealed, for instance, by birefringence when the material is strained. Let us consider a uniaxial strain produced by a mechanical tension 3. For small deformations, the difference Sn of the indices for directions parallel and perpendicular to the axis vary linearly with respect to F... 

Non-muscle cells transmit mechanical tension generated by the actin cytoskeleton to the extracellular matrix via focal adhesion sites (Ingber... 

Wang, N. and Ingber, D.E. Control of cytoskeletal mechanics by extracellular matrix, cell shape, and mechanical tension, Biophys. J., 66,2181,1994. 

Third, molecular branched architecture can be tuned to ensure maximum concentration of mechanical tension at a specific chemical bond. For example, star-like [134] and pom-pom structures [125] as well as short bottlebrushes [135] may be used to introduce site-specific activation at the branching center. Figure 10b displays the concentration of tension in the middle of the backbone resulting in its mid-chain scission. In a similar fashion (Fig. 10c), molecular stars with a spoke wheel core and bottlebrush arms exhibit preferential dissociation of the arms followed by the scission of covalent bonds in the bottlebrush backbones... 

Sodium sulfate, which possesses good electrolytic properties and a good chemical stability towards gases, appeared a good choice for such an application. Unfortunately, this material cannot be used under a ceramic shape because it does not withstand the temperature variations. Indeed, at about 300°C, there is an allotropic change, that is, in the useful field of the sensor the mechanical tensions this transformation implies favoring the crackling of the sintered material. 

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