Dense packing limit

Recent reports of dendrimers with a versatile C60 core [212] allowing an unusual core branching multiplicity of 12, and reaching dense-packing limits already in the first generation, continues to prove that there are many more unique dendrimers with varied architectures and associated interesting properties that need to be discovered. 

Aharoni and coworkers characterized 59 Denkewalter s cascade macromolecules 4 by employing classical polymer techniques viscosity determinations, photo correlation spectroscopy (PCS), and size exclusion chromatography (SEC). It was concluded that at each tier (2 through 10) these globular polymers were, in fact, monodisperse and behaved as nondraining spheres. The purity of these molecules was not ascertained and the dense packing limits were either not realized or simply not noted. 

A very high number of termini can be reached (see the theoretical numbers on the scheme) if these termini are small and can fold back towards the center of the dendrimer. The construction is then no longer limited by the periphery (de Gennes dense-packing limit), but by the volume. 

An alternative containment scheme is immobilization of active species on a surface" " or within a tethered polymer brush or network. ° Surface immobilization can achieve high surface utilization by locating mediators and biocatalysts within nanometers of conducting surfaces. Immobilization on polymer networks allows for dense packing of enzymes within electrode volumes at the expense of long-distance electron mediation between the enzyme active center and a conductive surface. Such mediation often represents the rate-limiting step in the overall electrode reaction. 

Cable tray fires have resulted from the accumulation of process leakage, residues or combustible dusts or debris on top of cable trays with densely packed wires and cables. Covering shields above cable trays have been used to minimize such accumulations however, such shields should be used with caution as they can limit air circulation and increase cable and wire temperatures in densely loaded trays particularly those carrying power cables. Covering shields may also block fixed fire protection water spray or manually applied firefighting water spray from reaching the cables. 

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