Strain-induced

If these changes in length take place freely then we will have a thermally induced strain in the material (= 0.3 x 100/50 = 0.6% in the polypropylene) but no stress. However, if the polypropylene was constrained in some way so that the 0.3 mm expansion could not happen when it is heated by 60°C, then there would be a thermally induced stress in the material, i.e. 

While there is evidence in support of a lattice impurity or defect-induced, strain-field mechanism, this model has not enjoyed wide support. 

Zinc sulfide, ZnS, has been epitaxially deposited by the dual bath approach on Au(lll) surface and studied by STM and XPS [48]. The first complete ECALE cycle resulted in the formation of nanocrystallites of ZnS randomly distributed across Au(l 11) terraces, on account of lattice mismatch induced strain between ZnS and Au(lll) - although the mismatch is only 0.13% for ZnS/Au(lll). Atomically resolved STM images showed the ZnS/Au(lll) monolayer to be sixfold symmetric. The average diameter of the crystallites was 10 5 nm and the apparent coverage 0.38. 

Wong, H.C. and Ban, Y.S., Pigmentation and antibacterial activity of fast neutron-and x-ray-induced strains of Monascus purpureusWent, Plant Physiol, 60,578,1977. Blanc, P.J. et al.. Pigments of Monascus, J. Food Sci., 59, 862, 1995. 

Figure 2. Overproduction of PelZ. Lane 1 crude extract of the non-induced strain BL21/pTPZ. Lane 2 crude extract of Ae IPTG induced strain BL21/pTPZ. Lane 3 molecular weight marker. The arrow inAcates PelZ.

Lacey SF, McDanal CB, Horuk R, Greenberg ML. The CXC chemokine stromal cell-derived factor 1 is not responsible for CD8+ T cell suppression of syncytia-inducing strains of HIV-1. Proc Natl Acad Sci U S A 1997 94(18) 9842-9847. 

Figure 2.3 Schematic representation of the induced strain model of transition state stabilization. Source Redrawn from Copeland (2000).

The catalytic specificity of the cycloamyloses has led to their utilization as a model for understanding enzymatic catalysis. It is the authors expectation that the cycloamyloses will continue to serve as an enzyme model as well as a model for designing more efficient catalytic systems. Toward this end, it would seem profitable to pursue the idea that the cycloamyloses may lower the activation energy of a chemical reaction by inducing strain into the substrate. 

There are several reasons why the behaviour of the shorter chains deviate from the original formulation of the Jacobson and Stockmayer theory (Flory, 1969). First, if the ring size is small enough to induce strain, the enthalpy change for cyclisation (16) will differ from that for the intermolecu-lar process (17). In terms of the 0 operator (39), 0AH° will differ from zero and, presumably, be positive. Secondly, (57) is based on the implicit assumption that the relative orientation of the reacting bonds, when they come in close proximity in the cylisation reaction, is random. This independence of orientation and proximity, which leads to the absence of any factor referring to orientation in (57), must fail for short chains. Thirdly, short chains may not follow Gaussian statistics. When this occurs, an appropriate expression for the density of end-to-end vectors is required. 

M. D. Hollingsworth, U. Werber-Zwanziger, M. E. Brown, J. D. Chaney, J. C. Huffman, K. D. M. Harris, S. P. Smart, "Spring-loaded at the molecular level relaxation of guest-induced strain in channel inclusion compounds ,/. Am Chem Soc 1999,121, 9732-9733. 

Using solid-state physics and physical metallurgy concepts, advanced non-destructive electronic tools can be developed to rapidly characterize material properties. Non-destructive tools operate at the electronic level, therefore assessing the electronic structure of the material and any perturbations in the structure due to crystallinity, defects, microstructural phases and their features, manufacturing and processing, and service-induced strains.1 Electronic, magnetic, and elastic properties have all been correlated to fundamental properties of materials.2 5 An analysis of the relationship of physics to properties can be found in Olson et al.1... 

D. The binding of polysaccharide substrates that have six or more sugar groups to lysozyme, the enzyme in tears and saliva that cleaves such molecules, induces strain in the sugar nearest the active site making the nearby bond more susceptible to hydrolysis. 

Recall from Section 5.1.3.1 that thermal expansion is the change in dimensions of a solid due to heating or cooling. As a result, a thermaUy-induced strain can result when the material is heated, as dictated by Eq. (5.29). For small deformations at constant pressure, we can thus approximate the strain as... 

Lattice-induced strains clearly cause the bonds to violate the network equations and their presence may be indicated by a large value of the bond strain index (BSI) defined in eqn (12.1) (Preiser et al. 1999, <73 in table 1) ... 

Typically lattice-induced strain results in the bonds around one cation being stretched and the bonds around another cation being compressed as found in BaRuOs (10253) by Santoro et al. (1999, 2000). When this happens, the valence sum rule will be violated around the cations in question but the valence still distributes itself as uniformly as possible among the bonds, so that the experimental bond valences determined from the bond lengths remain as close as possible to the theoretical bond valences. For this reason the BSI is typically smaller than the GII for lattice-induced strains, though the opposite is true for compounds with electronically induced strain where the valence sum rule remains well obeyed. 

If possible, the lattice-induced strain will relax in such a way as to minimize both strain indices as illustrated in the following sections by the structure of... 

---