Controlled Local Composition

By controlling the size and area of the spot where electron beam is irradiated, the local composition of the metal elements of bimetallic nanoparticles can also be determined (63). 

Case 2 includes many of the example systems studied in this book. For example, reactors with temperature as the only controlled variable fall into this category. Also, the isothermal ternary scheme CS4 shown in Fig. 2.13a has a local composition controller on one of the dominant variables, the composition of component A. However, Case 2 is characterized by the fact that other dominant variables are not controlled at the reactor. Instead, the plantwide control structure plays a significant role in its ability to influence these uncontrolled variables. When the uncontrolled compositions become disturbances and the controlled dominant variables are too weak, we have difficulties. On the other hand, the plantwide control structure can be arranged to provide indirect control of the dominant composition variables, thereby augmenting the unit control loops. The HDA process provides a good illustration. The dominant variables are reactor inlet temperature and toluene composi-... 

Several conundrums remain to be resolved including 1) have we greatly underestimated marine N2 fixation, 2) what are the quantitative contributions of the newly identified diazotrophs, 3) what is the spatial distribution of N2 fixation and 4) to what extent does the nature of nutrient Hmitation control the composition of diazotrophic populations locally and over broader scales. 

The method of cathodic alkalization is undoubtedly promising for synthesizing perovskite compounds [400]. By this method, a distribution of components in the deposit-precursor can be obtained that allows the subsequent annealing to be carried out at lower temperatures and for shorter periods. The disadvantage of the method is the spatial variation of the pH and, consequently, the difficulty of controlling product composition (especially when simultaneously several hydroxides with different dissociation constants are deposited locally). 

Ethylene has a symmetrical monomer, so the concept of tacticity does not apply. Consequently, the crystallinity of polyethylene is controlled either by chain branching or by copolymerisation. Copolymers are classified into random and block copolymers (Fig. 2.7) depending on whether the monomer locations are random, or whether long blocks of each monomer exist. Polyethylene copolymers are random. The figure suggests that the local composition of a random copolymer is the same as that of the monomer mixture. However, in a batch copolymerisation, monomers tend to add to the end of a growing chain at different rates. The monomer ratio drifts as the polymerisation proceeds, so polymer formed at the end of the polymer-... 

In a study, dyes have been used as model drugs in a matrix of biocompatible polymers. The release rate and the release time of the dyes can be controlled by the position of the dye within the system, or by the local composition and the microstructure that is formed in the course of the printing process (65). 

Plants utilize their ability to control the local composition and the microfibril orientation within the cell walls to accommodate differential strains within their composite architecture. This is evidenced for example by changes in the microfibril orientation in trees depending on the specific function of the tissue,as well as in the graded change in elastic modulus... 

When a beam of primary X-rays with (microscopically) small cross-section irradiates the sample, it induces the emission of fluorescent X-rays from a micro-spot, which carries information on the local composition of the sample. If the sample is moved either manually or under computer control in the X-ray beam path, spot or line analysis will be possible. 

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