Double-wedge technique

Cleavage of bulk crystals to expose clean, defined lattice planes is possible for brittle substances. Some materials, like mica or highly oriented pyrolytic graphite (HOPG) that exhibit a layered structure, are readily cleaved by just peeling off some layers or using a razor blade. For other materials the so-called double-wedge technique can be used (Fig. 8.8). 

Figure 8.8 Double-wedge technique for cleavage of brittle materials. To ensure proper cleavage, the crystal is pre-cut and positioned between the wedges according to its crystallographic orientation.

The double-cantilever-beam (DCB) test uses fracture mechanics techniques to evaluate the SSC resistance of tuhular steels [7]. It employs a 9.5 by 25 by 100 mm (0.375 by 1.0 by 4.0 in.) specimen with side grooves and loaded with a double taper wedge. In some cases, the specimen is precracked. Typical test duration is 14 days. 

For intubated infants, flexible flberoptic bronchoscopy may not always be feasible. Modifications of fiberoptic bronchoscopy techniques have been performed with moderate success. A styletted intracatheter wedged blindly by way of the endotracheal tube and blind wedging of a double catheter system through the endotracheal tube to obtain lower respiratory tract secretions have been described (68). 

Double- and triple-staining techniques enable visualization of two or more affinity reactions in the same preparation, using differently coloured fluoro-chromes for each reaction. Special filter combinations are available to facilitate simultaneous visualization of the different colours, and wedge-free filters allow sequential photography of images in each colour without image shift. 

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