The frequency of nasopharyngeal carcinoma is nearly 100-fold higher in southern Chinese than in most European populations. Earlier studies have suggested that an increased risk of nasopharyngeal carcinoma is associated with specific haplotypes in the HLA region: relative risks slightly over twofold were found for haplotypes A2, Bw46 and the antigen B17. We now report a linkage study based on affected sib pairs which suggests that a gene closely linked to the HLA locus confers a greatly increased risk of nasopharyngeal carcinoma. The maximum likelihood estimate is of a relative risk of approximately 21. The relationship between this suspected disease susceptibility gene (or genes) and known viral and environmental aetiological factors remains to be elucidated.
In this study, the fabrication of the desired SPR joints was investigated as a function of the preheat temperature and strain rate. To determine the optimum preheat temperature, Gleeble thermal analogue testing of 2mm thick magnesium AZ31 was used to assess the combined influence of preheat temperature and strain rate on the strength and total elongation of magnesium AZ31. Magnesium alloy AZ31 with a thickness of 2mm was preheated with various temperatures prior to self-piercing riveting. The appearances, cross-sections and mechanical tests of the SPR magnesium AZ31 joints were investigated. It was found that a preheat temperature of 180 to 200oC largely eliminated the cracking in magnesium AZ31 joints. The joint strength increases with increasing preheat temperature from ambient to 200oC. The strength increase is attributed to the reduction in joint cracking and an increase in mechanical interlock between the rivet and work pieces.
The short-circuiting metal transfer during gas metal arc welding (GMAW) is simulated by a numerical model. To the best of our knowledge, for the first time the energy equation and the Marangoni convection are considered in analyzing the short-circuiting time. A front-tracking free surface method is applied to explicitly track the bridge profile. To benchmark this method, effects of the density and viscosity ratios between different phases are investigated by simulating a drop driven by surface tension. The temporal profile of the drop is compared to that computed by a Volume of Fluid (VOF) model, and very good agreement is found. The model is then applied to simulate GMAW short-circuiting transfer. The velocity, pressure, temperature and electromagnetic fields are calculated. Effects of welding current and Marangoni shear stress on short-circuiting time are examined. It is shown that the Marangoni effect plays an important role in GMAW short-circuiting transfer.
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