Neck formation profile

By using leukocytes from chemotherapy patients with squamous-cell carcinoma of the head and neck region, it was demonstrated that damage removal from DNA was related to cisplatin resistance [83], This type of study assumes the profile of adduct formation and repair to be the same in peripheral and tumor tissue. The hypothesis was supported by several early studies which employed either atomic absorption spectroscopy or immunochemical techniques to demonstrate a relationship between DNA adduct formation in blood cells and disease response [84-89]. Subsequent work revealed, however, that cisplatin-DNA adduct levels do not always correlate with survival [90] and can vary substantially between individuals [91]. 

In materials of nominal purity small holes and cracks are formed when necking starts. These holes and cracks are produced during deformation at inclusions and, possibly, by dislocation interactions. In cylindrical specimens the formation of the neck is accompanied by the setting up of a triaxial stress system in the neck the forces between adjacent transverse sections of the neck have trajectories that follow the profile of the neck and will, therefore, have components normal to the specimen axis. This triaxial stress system may be considered as a hydrostatic stress plus a longitudinal stress. The former does not produce plastic deformation and so the material is effectively hardened. Any holes that are formed in the neck are able to grow transversely more rapidly than they can axially and so are able to coalesce, leading to an internal fracture surface at the centre of the minimum cross-section. The formation of this internal surface is followed by shearing on a surface of maximum shear stress. This surface is conical and the result is the so-called cup and cone fracture, typical of the fracture of many metallic materials at room temperature. 

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