Kink side

Resistance to axial compressive deformation is another interesting property of the silk fibers. Based on microscopic evaluations of knotted single fibers, no evidence of kink-band failure on the compressive side of a knot curve has been observed (33,35). Synthetic high performance fibers fail by this mode even at relatively low strain levels. This is a principal limitation of synthetic fibers in some stmctural appHcations. 

FIGURE 2.1 A side view of the structure of the prototype G-protein-coupled, 7TM receptor rhodopsin. The x-ray structure of bovine rhodopsin is shown with horizontal gray lines, indicating the limits of the cellular lipid membrane. The retinal ligand is shown in a space-filling model as the cloud in the middle of the structure. The seven transmembrane (7TM) helices are shown in solid ribbon form. Note that TM-III is rather tilted (see TM-III at the extracellular and intracellular end of the helix) and that kinks are present in several of the other helices, such as TM-V (to the left), TM-VI (in front of the retinal), and TM-VII. In all of these cases, these kinks are due to the presence of a well-conserved proline residue, which creates a weak point in the helical structure. These kinks are believed to be of functional importance in the activation mechanism for 7TM receptors in general. Also note the amphipathic helix-VIII which is located parallel to the membrane at the membrane interface. 

Figure 5.9 Plan view of the (111) plane of the diamond structure. A—Normal structure with open circles in the plane of the paper, and crossed circles in the plane above. Each pair is connected by a covalent bond. B—Partial shear of the upper plane over the lower one on the right-hand side creating a screw dislocation line with a kink in it (dashed line). C—Upper plane sheared down-ward by the displacement, b.

Figure 8. Intercalative covalent binding to N2(G). Trans BPDE-adducts are bound to the 5 side of G in the +G C,C G,BPT,C G,C G+ complex in DNA kinked to site KMa.

A discontinuity in a function may or may not cause difficulty in optimization. In case A in Figure 4.1, the maximum occurs reasonably far from the discontinuity which may or may not be encountered in the search for the optimum. In case B, if a method of optimization that does not use derivatives is employed, then the kink in /(x) is probably unimportant, but methods employing derivatives might fail, because the derivative becomes undefined at the discontinuity and has different signs on each side of it. Hence a search technique approaches the optimum, but then oscillates about it rather than converges to it. 

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