Macro-heterogeneity

One of the major reasons for the development of nonequilibrium noise in electrochemical systems is the inhomogeneity (micro- or macro-heterogeneity) of electrode surfaces. For this reason, the analysis of electrochemical noise proved... 

Region—spatial distribution of phases dependent on boundary conditions (macro-heterogeneity) top and bottom core and wall. 

According to these approaches, one assumes a given chemistry and/or morphology of the solid surface. Yet, the same function cannot simultaneously describe a macro-heterogeneous surface solid such as talc, clay minerals or crystalline silicas, having basal and lateral surfaces and a micro-heterogeneous one like the surface of an amorphous silica. Therefore many authors tried to develop resolution methods without making any assumption for the shape of the distribution function. 

Partition effects are important in macro-heterogeneous biphasic systems (see section 1.6) where the enzyme is in one phase, while the substrates and/or products are in the other. In that case, effective substrate (and product) concentration is the one in the enzyme phase (usually the aqueous phase in the case of biphasic systems) so that partition coefficient of substrate (and product) between both phases can be a very relevant parameter that needs to be determined. 

Yu. S. Lipatov, Role of Interfacial Phenomena in the Formation of Micro and Macro-Heterogeneities in Multicomponent Polymer Systems, PureAppl. Chem. 43,273 (1975). Review of blends and filled IPNs. Physical properties, electron microscopy. 

Another important factor in macro-heterogeneous biphasic systems with the substrates/products in one phase and enzyme in another is partitioning, which produces discontinuity of the profiles at the medium-biocatalyst interface (Fig. 6.70)... 

Biomineralization. In biomineralization, inorganic elements are extracted from the environment and selectively precipitated by organisms. Usually, templates consisting of suitable macro-molecules serve as a substrate for the heterogeneous nu-cleation of bulk mineralized structures such as bone, teeth and shells. Biological control mechanisms are reflected not only in the type of the mineral phase formed but also in its morphology and crystallographic orientation (Mann et al., 1989 Lowenstamm and Weiner, 1989). Two examples (perhaps oversimplified) may illustrate the principle (Ochial, 1991) ... 

The characterization work has shown that, although the titanate ceramic appears to be homogeneous on a macro scale, it is actually quite heterogeneous on an atomic scale and contains at least l4 different phases and possibly more. Since interactions of the waste form with any environment surrounding it will also occur on an atomic scale, it is important that this type of information be available when speculating on the long term stability of any waste form. 

It is evident that composite or heterogeneous networks, which result from macro- and micro-syneresis respectively, are not suitable for the verification of basic rubber-elasticity theories. The interpretation of their behaviour in the light of existing network elasticity theories should be quite complicated. Especially for heterogeneous networks, additional... 

In aqueous food materials Tj and T2 relaxation behavior of water are related to different aspects of the interaction and motion of the water molecules. The relationship is not so simple, especially in heterogeneous food materials [63-65]. There are at least four types of protons to be considered, namely free (or bulk) water, bound (or hydrated) water, exchangeable macro-moleculc protons such as those found in hydroxyl and amino groups, and unexchangeable macromolecule protons. Under such circumstances measurement of Ti is more reliable than T2 measurement, but can be complicated by the spin diffusion, while T2 relaxation can be complicated by slow translational diffusion and proton exchanges. 

A large number of heterogeneous catalysts have been tested under screening conditions (reaction parameters 60 °C, linoleic acid ethyl ester at an LHSV of 30 L/h, and a fixed carbon dioxide and hydrogen flow) to identify a suitable fixed-bed catalyst. We investigated a number of catalyst parameters such as palladium and platinum as precious metal (both in the form of supported metal and as immobilized metal complex catalysts), precious-metal content, precious-metal distribution (egg shell vs. uniform distribution), catalyst particle size, and different supports (activated carbon, alumina, Deloxan , silica, and titania). We found that Deloxan-supported precious-metal catalysts are at least two times more active than traditional supported precious-metal fixed-bed catalysts at a comparable particle size and precious-metal content. Experimental results are shown in Table 14.1 for supported palladium catalysts. The Deloxan-supported catalysts also led to superior linoleate selectivity and a lower cis/trans isomerization rate was found. The explanation for the superior behavior of Deloxan-supported precious-metal catalysts can be found in their unique chemical and physical properties—for example, high pore volume and specific surface area in combination with a meso- and macro-pore-size distribution, which is especially attractive for catalytic reactions (Wieland and Panster, 1995). The majority of our work has therefore focused on Deloxan-supported precious-metal catalysts. 

On the basis of the observations in the macroscale, the flow of a fast fluidized bed can be represented by the core-annulus flow structure in the radial direction, and coexistence of a bottom dense region and a top dilute region in the axial direction. Particle clusters are an indication of the heterogeneity in the mesoscale. A complete characterization of the hydrodynamics of a CFB requires the determination of the voidage and velocity profiles. There are a number of mathematical models accounting for the macro- or mesoaspects of the flow pattern in a CFB that are available. In the following, basic features of several types of models are discussed. 

Study of enzyme structure often means elucidation of protein structure. In the early stage of enzyme studies, protein was considered to be the heterogeneous macromolecule that could be never determined by methods available in those days. In 1926, Svedberg developed an ultracentrifugation technique to determine molecular weight of macro-... 

Nontheless, such a reaction course occurs only very infrequently in chemical reaction engineering. Most chemical reactions take place in heterogeneous material systems (G/L, L/L, G/S, L/S, G/L/S) and generate considerable amounts of reaction heat. Consequently, the genuine chemical action is accompanied by mass and heat transfer processes ( macro-kinetics ) which are scale-dependent. The course of such chemical reactions will be similar on a small and large scale, if the mass and heat transfer processes are similar and the chemistry remains the same. 

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