Sophisticated Shapes

The shapes we have described have employed, in all but the last section, simple ligands that bind at one or two sites around a metal ion. However, most ligands are more complicated 

Some possible shapes for three-donor ligands, with examples. 

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The revolutionary solution was to think fundamentally about the best way to make the new shapes - simple rectangles at first, but later more sophisticated shapes. The alternatives were pressed steel die cast metal plastics. The pressed steel approach is the conventional one, and it is not as good, even at its best, as a moulding approach for accurate, complex shapes. 

The mathematical equations that govern the heterogeneous degradation are presented in Chapter 6. A key variable in the equations is the concenlration of the short chains. These short chains diffuse from where their concentration is high to where it is low. This principle can be combined with the requirement for matter conservation and written into a mathanatical equation. Before the computer age, such equations were very difficult to solve for real devices. It is almost impossible to find an analytical function to desalbe how the concentration varies with space and time in a device of sophisticated shape. The finite element method overcomes this difficulty by using two key ideas ... 

Plate I (a) in the colour section between pages 130 and 131 shows a finite element model for a single representative unit of a scaffold. It is very easy to use the irregular tetrahedral elements to model devices of sophisticated shapes. The vertexes of the elements are named as nodes . The tetrahedral elements share a common set of concentrations at the nodes. The distribution of concentration inside an element is less important if the elements are sufficiently small. This is like controlling the shape of a fishing net by holding all the knots. Instead of trying to find a mathematical function to describe the concentration in the entire device, the finite element method finds discrete values of the concentration at the nodes. 

Poly (ether-6-amide) products are known to have an excellent processability in injection molding, extrusion (cast films, blown films, sheets, tubes, etc.), as well as in assembly processes like overmolding and co-extrusion. This behavior allows the design of thin and sophisticated-shaped materials associating lightweight and good mechanical properties. In order to achieve the best processing... 

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