Contraction mismatch

Figure 2. Coronary microembolization causes a progressive perfusion-contraction mismatch, i. e. contractile function is progressively reduced, whereas regional myocardial blood flow remains unaltered (by permission from Dorge39).

As detailed above, this experimental model of coronary microembolization is not only characterized by a perfusion-contraction mismatch pattern, but also by reduced coronary reserve. Also, the inotropic response to intracoronary infusion of dobutaminc is diminished in microembolized myocardium.1 ... 

H. Drprge, T. Neumann, M. Behrends, A. Skyschally, R. Schulz, C. Kasper, R. Erbel and G. Heusch, Perfusion-contraction mismatch with coronary microvascular obstruction role of inflammation, Am J Physiol Heart Circ Physiol 279, H2587-H2592 (2000). 

Initially (at tQ), the aluminum plate is cooled and contracts, compressing the warmer foam, as shown in Fig. 3b. As time progresses (tj, t2, and t3), the insulation cools and the foam tends to contract in accordance with the local temperature and its coefficient of thermal expansion. However, near the tank surface, the insulation is constrained from contracting by the much stiffer aluminum plate, which, because of a lower coefficient of expansion, experiences less contraction than the foam. Ultimately, at t3 (as shown in Fig. 3c), the combination of the thermal contraction mismatch between the insulation and the aluminum tank and temperature distribution through the insulation lead to an in-plane stress pattern with large tensile stresses in the insulation near the tank and smaller compressive stresses at the free surface. 

The magnitude of the tensile stresses is determined primarily by the thermal contraction mismatch between the aluminum and the foam however, the length, width, and thickness of the insulation influences the level of the compressive stresses. For 15.2 cm (6 in) thick insulation, as shown in Fig. 4, edge effects significantly reduce compressive stresses for smaller pieces of insulation. [The stresses in Figs. 4 and 5 are based on polymethacryli-mide insulation bonded on an aluminum tank at 20 K (-424°F) with a maximum insulation exterior temperature of 317 K (110°F)]. For example, a 0.3 m (1 ft) square insulation sample experiences a maximum compressive stress that is approximately 1/3 the stress in a 1.83 m (6 ft) square piece of insulation. The latter approaches the stress level for an infinite slab of insulation. 

Because of the thermal contraction mismatch of a silicon chip, metal lead-frame and silica-filled epoxy molding compound integrated circuit (IC) packages bow or warp when cooled to room temperature after manufacture. The magnitude of the bow in an IC package can be determined quantitatively by... 

Oxide films of different thicknesses were thermally grown at a temperature of 1200 °C on a relatively thick metal alloy substrate. Upon cooling to room temperature (20 °C), the oxide films were found to develop a large equi-biaxial residual compressive stress, primarily as a consequence of its thermal contraction mismatch with the substrate. The elastic modulus and Poisson ratio for the film are Ef = 400 GPa and = 0.25, respectively, at room temperature, and the coefficients of thermal expansion for the film and the substrate are af = 8 X 10 °C and (Us = 14 X 10 respectively. 

A more recent study has examined the SH response from a Au(lll) electrode during UPD of a variety of metals, Ag, Cu, Pb, T1 and Sb [155]. In situ x-ray diffraction techniques have examined Ag, Cu and Pb on this substrate [159-161]. Silver is shown to form an epitaxial overlayer with Ag atoms sitting in 3-fold hollow sites forming a (1X1) commensurate overlayer. The lattice mismatch between lead and the substrate is shown to prevent formation of a commensurate overlayer but forms a hexagonal close-packed overlayer contracted by 0.7% from bulk lead. Although T1 and Sb on Au (111) have not been examined by x-ray diffraction, a close packed structure would necessitate an incommensurate overlayer due to the lattice mismatch. 

The authors have the pleasure to thank Prof. H. Amano for good collaboration and fruitful discussion. C. Wetzel thanks Prof E.E. Haller and Dr. J.W. Ager for previous collaborations. This work was partly supported by the Ministry of Education, Science, Sports and Culture of Japan (contract nos. 09450133 and 09875083, and High-Tech Research Center Project) and JSPS Research for the Future Program in the Area of Atomic Scale Surface and Interface Dynamics under the project of Dynamic Process and Control of Buffer Layer at the Interface in Highly-Mismatched Systems. 

In layered misfit structures of the type we are discussing, bonds at the layer surfaces (within and between the layers) will be strained periodically along a non-commensurate lattice direction parallel to the layers after a certain number of subcells there is a near match of the layers. Clapp has pointed out that, for a simple case, layer mismatch will cause tension in one layer type and compression in the other. The resulting strain energy may be relieved by the introduction of periodic antiphase boundary (apb) planes so that alternate contraction and extension occurs in all layers (Fig. 22) and hence cancels out (at the price of a small deformation of coordination polyhedra). 

Below the critical conversion the polymer forms a solid solution in the monomer phase. In this state the mismatch is exceptionally large and the polymer chains are contracted by 8 percent. After the transition the situation is reversed and the residual monomer occupies lattice sites within the polymer structure. Here, the packing is much more favourable for the polymerization, which proceeds with large speed. 

There are four principle causes for membrane failure under normal operating conditions (in other words, reduced membrane durability). These reasons are (a) hydrogen-induced embrittlement of the membrane, (b) fatigue fracture due to repetitive swelling and contraction of the membrane, (c) mismatch in the CTE of the membrane and underlying support layer, and (d) defects in the underlying support layer that cause a hole or tear to develop in the membrane. 

The lower theta temperature corresponds to the minimum solution temperature extrapolated to infinite chain length. Polymer precipitation at low temperatures comes about because of a poor heat of mixing between polymer and solvent. In a sealed tube at high temperatures, solvent volume expands much more than that of the polymer. Entropic factors make mixing more difficult when there is a large free volume mismatch between solute and solvent. One believes that the polymer dimensions contract as the LCST is approached. Phase separation occurs when it is exceeded. 

Recently, a coating of perhydropolysilazane on stainless steel has attracted attention. The perhydropolysilazane is converted into silicon nitride in an NH3 atmosphere at 600°C or to a transparent siliconoxynitride in humid air beyond 150°C. This material is making progress in overcoming some weakness in the expansion mismatch to the coated metal and in contraction during pyrolysis. 

Fatigue (defined as a decline in force following repeated contractions) can occur as a result of a failure to activate motoneurons (commonly referred to as central fatigue) or from failiire in neuromuscular transmission, excitation-contraction coupling, or from the mismatching of energy... 

---