Cusp edge

Fig. 17.1 Electron micrograph of the cusp tip of a limpet tooth showing the alignment of acicu-lar goethite parallel to the tooth posterior edge and the changing orientation within the central region (courtesy S. Mann).

All faces can be grown dislocation-free, and the current below the critical overvoltage has been found to be zero. A pulse excitation can induce nucleation, preferably on the front (100) face, followed by a current flow. As expected, the current-time curve has a veiy specific form in this case (Fig 5.11b). Tlie four cusps of the curve indicate the moments where the growing monolayer reach consecutively the four edges of the rectangular front face. 

To determine the equilibrium shape from a y-plot, connect all of the y points in the polar diagram to the centre of the diagram, and construct perpendicular planes (Wulff planes) on the y points. Then, the minimum volume enveloped by the Wulff planes exhibits the equilibrium shape of the crystal. This is because the surface energy of a plane is proportional to the distance from the centre to the y point, and, therefore, the total surface energy is proportional to the volume enveloped by Wulff planes. When a minimum cusp is present in a y-plot, a facet plane appears. For a point and a line of energy maximum in a y-plot, a corner and an edge appear in the equilibrium shape. 

Finally, from a strictly qualitative point of view, the movement of the valve leaflets was studied using a video camera. Pictures were taken from the valve in closed and open positions (Fig. 16.16). In the closed position, it can be observed that the three cusps come together with good coaptation. In the open position, the flexibility of the cusps induces low flow resistance. As to the free-edge curvature, it inverts easily from closed to open position. 

Optical microscopy showed that the original fracture extended across the catheter where it joined the bag, and showed how the fracture extended between two shoulders from the bag extension, one above and the other below the crack surface (Fig. 9.19). The survey confirmed the lack of clear features on the fracture surface itself although a cusp was found at one edge... 

Figure 3.493. In situ mode II crack in CF/epoxy (a) very high magnification of the region ahead of the crack tip (b) crack with shear cusps as the edges (arrow) and a bridging fibre in the interior of the crack [1317],...

Fig. 9 The deviations in the exact atomic electrostatic potential and the one obtained from the multipole moments up to the octupole (/ = 3) for the Cq, atoms in alanine. The part of the picture in front of the plotting plane is deleted in order to show the interior of the object. The largest deviations occur near the cusp-like edges of the atom and the region of closest proximity. Color code (in kj/mol) white < O.K grey < 0.2 < blue < 0.3 < green < 0.4 < yellow < 0.5. (with permission from the American Chemical Society)...

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