Density measurement Terms Links

It is often convenient to express the change in linking number in terms of a quantity that is independent of the length of the DNA molecule. This quantity, called the specific linking difference (cr), or superhelical density, is a measure of the number of turns removed relative to the number present in relaxed DNA ... 

The formation of a polymer networks starts with an increase in molecular weight and formation of branched structures. At a typical extent of reaction, the gelation point is that point at which a network is first formed. The extent of reaction as well as the cross-linking density in radiation-induced cross-linking processes is determined by the radiation dose. The term dose means the quantity of radiation applied to or absorbed accidentally by a given volume or mass of sample. The absorbed dose is measured in Gray (Gy), 1 Gy = 1J kg-1. Therefore, the formation of a polymeric network needs a certain dose, the gelation dose Dg, which can be determined by sol-gel analysis. ... 

The dual site-bond description (DD) of disordered stmctures [3] allows a proper modeling of the porous structure. In the context of this treatment, two kinds of alternately intercormected void entities are thought to conform the porous network, i.e. the sites (cavities) and the bonds (capillaries, necks). C bonds meet into a site and each bond is the link between two sites. Thus a twofold distribution of sites and bonds is required to construct a porous network. For simplicity, the size of each entity can be measured in terms of a quantity, R, defined as follows for sites, considered as hollow spheres, R is the radius of the sphere while for bonds, idealized as hollow cylinders open at both ends, R is the radius of the cylinder. Under the DD scheme, FgfR) andFg(R)are the size distribution density functions, for sites and bonds respectively, on a number of elements basis and normalized so that the probabilities to find a site or a bond having a size R or smaller are ... 

So far, we have focused on the formal description of current generation in the catalyst layer and discussed major effects of structure and composition on exchange current density and catalyst utilization. In the remainder of this chapter, we will explore in detail, how electrocatalytic activity interferes with other processes at the catalyst surface (e.g. surface diffusion) and transport in the bulk phases. The key measure of catalyst layer performance is the current density that could be extracted from a cell for a given cell potential. This links the spatially varying concentrations and reaction rates with the global performance, rated in terms of power density and fuel cell efficiency. 

Due to manufacturing parameters, the resulting plates differed in terms of their area density. The measured area densities are given in Fig. 16.8 and are compared with their thicknesses. It is important to clarify that no matrix of the braided preforms is lost during the manufacturing process. Consequentiy, the fibre volume fraction of the samples is equivalent to the fibre volume content in the raw commingled yam 44%. The thickness is directiy linked with the area density due to the constant density of the global material. 

In this example, the first diagnosis to make is purely descriptive. There are 18 main actors or agents in the control room and outer office network connected by 70 communication links. In terms of network density, the figure achieved is 0.27. This represents a relatively loosely connected network and is in fact comparable to a number of other command-and-control types of situations that have been measured in this way previously (such as air-traffic control, for example see Walker et al., in press). In other words, the density of the network is such that it is some way short of maximum interconnectivity, or everyone speaking to everyone else. It is also indicative of being in some way short of full information sharing. 

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