Intrinsic strain

On the contrary, if a highly strained cyclic olefm such as the cyclopropene 16 [20] or the norbornene derivative 17 [21] is employed, the titanacycle is cleaved to form the corresponding titanocene-alkylidene 18 or 19. This reaction is clearly enhanced by the concomitant release of intrinsic strain energy (Scheme 14.10). 

In the case of filled systems, the two latter effects provide a substantial contribution to C2 compared with the influence of trapped entanglements [80]. For filled systems, the estimated or apparent crosslinking density can be analyzed with the help of the Mooney-Rivlin equation using the assumption that the hard filler particles do not undergo deformation. This means that the macroscopic strain is lower than the intrinsic strain (local elongation of the polymer matrix). Thus, in the presence of hard particles, the macroscopic strain is usually replaced by a true intrinsic strain ... 

It should be considered that in the case of plotting 1 = a/ X — X 2) against inverse extension ratio (X 1), the nominal stress a is defined as the force divided by the undeformed cross-sectional area of the sample and X is the extension ratio, defined as the ratio of deformed to the undeformed length of the sample stretched in the uniaxial direction (as shown in Fig. 3). For PTFE powder, the intrinsic strain is deduced from (2) by defining X - 1 ... 

Chain length may inter alia leave a potential ligand site dangling ,191 where the stability of the chelate is determined by its intrinsic strain (equation 48). Chelating ligands properties may also be described in terms of torsion angles. 

The electric field induced intrinsic strain for different crystallographic directions could be calculated from the shift in peak positions (see Figure 7.9). Figure 7.11 shows the result of the measurements for a rhombohedral pzt in [111] and [100] direction. Only one half of each cycle is shown for the sake of a clarity of the plot. The curve for the [100] direction reveals the typical shape of a butterfly loop for the electric field induced strain in ferroelectrics. However in [111] direction, which is parallel to the spontaneous polarization, strain is significantly smaller. From both curves, the so-called unipolar strain can be evaluated as the strain induced at the maximum electric field Emax with a reference to the remanent state (E = 0). The calculation gives strain values in [111] direction of 0.02% and for the [100] direction 0.15%. The observations are in good agreement with theoretical calculations made by Du et al. [22],... 

Figure 7.11 Electrical field dependence of the intrinsic strain measured along [111] and [100] direction in PZT with a rhombohedral structure.

Fig. 9. Critical current as a function of intrinsic strain eo in the NbaSn reaction layer. Ic values have been normalized to the maximum critical current, /cm Data are the same as those plotted in Fig. 8.

For this group of specimens, representing a wide range of prestress, it appears the large disparity of results is removed if the degradation is expressed as a function of the NbsSn s intrinsic strain. Only the starting points on the curve are different, depending on the initial state of prestress in each specimen. 

To summarize, there is no well-defined total strain at which multifilamentary NbaSn wire electrically degrades—it varies from specimen to specimen, depending on the amount of prestress present in each. The wire can be fabricated and heat treated to optimize /c, as in curves 1, 2, 3, and 4 in Fig. 8, or to optimize strain tolerance, as in curve 7. The difference is that in the first case the compressive stress on the NbaSn was minimized, while in the second case it was maximized. These results indicate, however, that there is a well-defined intrinsic strain at which the NbsSn itself degrades. Critical current degradation becomes significant (exceeds 5 % ) at about 0.2% intrinsic strain. For the remainder of this paper, only the intrinsic strain experienced by the NbsSn reaction layer will be considered. 

Fig. 10. Critical current density, /c, as a function of intrinsic strain for the NbaSn specimen containing 3553 filaments (curves 1, 2, and 3 in Fig. 8). The O s represent Jc under load the x s represent Jc measured at the recovery strain after load removal.

This reaction was first reported by Nenitzescu in 1931. It is the formation of an a,p-unsaturated ketone directly by aluminum chloride-promoted acylation of alkenes with acyl halides. Therefore, it is known as the Darzens-Nenitzescu reaction (or Nenitzescu reductive acylation), or Nenitzescu acylation. Under such reaction conditions, Nenitzescu prepared 2-butenyl methyl ketone from acetyl chloride and 1-butene and dimethylacetylcyclohex-ene from acetyl chloride and cyclooctene. However, in the presence of benzene or hexane, the saturated ketones are often resolved, as supported by the preparation of 4-phenyl cyclohexyl methyl ketone from the reaction of cyclohexene and acetyl chloride in benzene, and the synthesis of 3- or 4-methylcyclohexyl methyl ketone by refluxing the mixture of cycloheptene and acetyl chloride in cyclohexane or isopentane. This is probably caused by the intermolecular hydrogen transfer from the solvent. In addition, owing to its intrinsic strain, cyclopropyl group reacts in a manner similar to an oleflnic functionality so that it can be readily acylated. It should be pointed out that under various reaction conditions, the Darzens-Nenitzescu reaction is often complicated by the formation of -halo ketones, 3,)/-enones, or /3-acyloxy ketones. This complication can be overcome by an aluminum chloride-promoted acylation with vinyl mercuric chloride, resulting in a high purity of stereochemistry. ... 

The reduction in stress occurring beyond Sy is called intrinsic strain softening. It engenders a strain instability which, under tensile stress, is manifested as a neck of reduced sample thickness, as shown in Fig. 7.25a. The structure stabilises when local deformation reaches a certain value, called the natural stretching level. This depends on the polymer and load conditions (i.e., temperature T and deformation rate). 

The growth of 0. oeni strains isolated from wine and cultivated in the laboratory is activated at around 5-6% volume of ethanol it is inhibited in environments richer in ethanol and difficult at or above 13-14% volume. The ethanol tolerance of laboratory strains is much less than for the same strains cultivated in wine. Bacteria that multiply in wine adapt to the presence of ethanol but also probably to the wine environment as a whole. In addition to the intrinsic strain tolerance of ethanol, their adaptation capacity varies. It is therefore difficult to set a limit above which lactic acid bacteria no longer multiply. 

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