Smooth surfaces typical profiles

Table 4 lists the operating conditions typically used in preliminary tests on the pultrusion line. In these tests, well defined U-shaped profiles with smooth surfaces (cross-section 24x4 mm, 2 mm thick) were produced. The towpregs used in the process were made from the GF/PP system (Table 1). 

The simulated free surface of liquid water is relatively stable for several nanoseconds [68-72] because of the strong hydrogen bonds formed by liquid water. The density decrease near the interface is smooth it is possible to describe it by a hyperbolic tangent function [70]. The width of the interface, measured by the distance between the positions where the density equals 90% and 10% of the bulk density, is about 5 A at room temperature [70,71]. The left side of Fig. 3 shows a typical density profile of the free interface for the TIP4P water model [73]. 

Two cavity probes were installed in the divertor of JET in the period from August f999 till November 2001. One was installed below the septum and the other in the inner module of the divertor. The analysis of these cavities was published by M. Mayer in 2003 [51]. Thick deposits of up to 14 and 45 pm were found on the outside of the inner module and septum cavity, respectively. The corresponding maximum thicknesses inside the cavity at the position opposite to the entrance slit are 15 and 10 pm. Ion-beam analysis of the layers showed that they consist mainly of D and C with a D/C ratio of about 1. Interestingly, the morphology and density of the two samples is very different. While the layer from the inner module is smooth with a density typical of a C H layers, the one from the septum is very porous and has about half the density only. The reason for this obvious difference remains unclear. A fit of the deposition profiles in the cavities leads to the conclusion that the layers are mainly deposited from species with a high surface loss probability (fH > 0.9) and a minor contribution of species with a low surface loss probability (f3 < 10-2). New cavity probes were installed inside the JET divertor in November 2001. They are planed to be removed in 2004. 

We now turn to the question of what we can say about the structure of the polymer surface at the microscopic level. As we have seen, in addition to predicting the surface tension, square gradient theories also predict the density profile at the surface of the polymer melt. Typically, the density goes smoothly from the melt density to zero (the density of the vapour phase being vanishingly small for high polymers) over a few angstroni imits, in very much the same way as it does at the surface of a small-molecule liquid. 

To examine the temperature dependence of the local properties of water, the fluid layers should be reasonably defined. The first surface layer may be defined in a natural way based on the first density oscillation, which is clearly visible at the density profiles even at high temperatures (see Figs. 44 and 45). Water molecules located in a shell bounded from one side by the van der Waals contact between water and surface ajl- 1.25 A from the surface, where Kz = 0) and by the first minimum in the liquid density distribution at low temperatures from another side (typically about 3.75 A) should be attributed to the surface layer. At low temperatures, the second density oscillation indicates the second layer of water, whose thickness is about 3 A. This oscillation practically disappears at high temperatures, where density changes gradually at the distances r > 5 A from the surface. In case of a smooth density variation, the layer thickness could be chosen to be arbitrarily small. It is convenient to set the thickness of third and subsequent water layers to 3 A. 

Figure 6 shows a cross sectional profile from the laser measurement of a typical embossed feature. It is seen that the edges appear sharp and there is no evidence of flash. This quality of the embossed feature is further seen in Figure 7, which is an SEM image. It is seen, that unlike previously reported results [9], the surface at the base of the feature is smooth and the edges are also relatively smooth. This suggests that the level of foaming was nearly ideal for this material (PP) and feature size. Most importantly, it is seen that there is no flash. 

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