Factors affecting inhomogeneity

Oxidative degradation of a crystalline polyolefin is a complex reaction involving a dissolved gas and a two-phase, impure, inhomogeneous solid. Factors affecting the reaction rate are antioxidant concentrations, crystallinity, UV illumination intensity, UV absorber concentration, and the samples previous oxidation history. Failure of a sample is often mechanical rather than chemical, and cannot be regarded as occurring at a particular degree of oxidation. 

Mechanically, the tissue is anisotropic and Inhomogenous, its moduli vary with direction and depth from the surface (10,11). Its principal mechanism for attaining stress relaxation, at strains above a critically small strain, is by exuding interstitial fluid (12). Its stress relaxation rates are therefore not only functions of the viscoelastic properties of its macromolecular network, but also the frictional resistances to fluid transport in and out of the tissue. Factors affecting fluid exudation and imbibition therefore necessarily affect the tissue s wear resistance. 

Crazing can be considered as a type of inhomogenous localized yielding. A major factor affecting ESC is yield strength CTj, and this can be expressed in terms of thermally activated shear flow, as described by Eyring s equation ... 

Wampler and Levy [1] have discussed factors affecting reproducibility in pyrolysis - gas chromatography (Py-GC) such as sample size, sample inhomogeneity, and pyrolyser design. There are two broad areas of application of Py-GC. The first is its use as a means of qualitatively identifying unknown polymers, for example, competitors products or in forensic investigations. This fingerprinting approach, useful as it is, is not pursued further in this book. 

Strain rate, test temperature and the thermal history of the specimen all affect the appearance of shear bands in a particular glassy polymer [119]. The differences in morphology of shear bands was proposed to be due to different rates of strain softening and the rate sensitivity of the yield stress. Microshear bands tend to develop in polymers with a small deformation rate sensitivity of Oy and when relatively large inhomogeneities exist in the specimen before loading. This is sometimes characterized by a factor e j, introduced by Bowden in the form [119] ... 

On the other hand arrhythmia due to uncoupling may be prevented. If coupling is enhanced selectively in the previously uncoupled area only within that area cellular uncoupling would be antagonized, which means that the surrounding tissue would not be affected in the way described above. There might be a similar effect in the close border zone between diseased and normal tissue, but the effect would be confined to that zone. Inhomogeneities within the diseased zone would be smoothened whereas the normal tissue behavior would probably be less affected. This could especially smooth differences in action potential duration and thereby prevent, in some situations, from reentrant arrhythmia, since this is often related to differences in action potential duration, to dispersion. Another important factor in the initiation of reentry... 

The surface of the silicon crystal, no matter how it is finished, will have a certain number of lattice defects, which tend to dissolve preferentially resulting in formation of etch pits and other features. Terraces and steps of various sizes are inevitable consequences of anisotropic dissolution of the surfaces misoriented from the (111) surface. Also, a silicon surface, whether initially smooth or not, in HF solutions, has an intrinsic tendency to roughen and form micropores governed by sensitivity of the electrochemical reactions on a semiconductor electrode to surface curvature. Furthermore, the two groups of factors shown in Fig. 7.57 may affect each other. For example, the initial lattice inhomogeneities may provide the sites for deposition whereas localized deposition may enhance the development of etch features such as pits or hillocks. 

When evaluating U the analyst has to include the Us component, which in fact consists in doing a sampling of the material and therefore includes potential heterogeneity or inhomogeneity factors. This often limits the determination of U. If the analyst works properly this should not affect too much the determination of U as the sub-sampling factor is mainly an uncertainty due to weighing. Various ways exist to... 

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