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Ab initio LCAO-MO-SCF calculations for several typical molecules containing phosphorus have been undertaken to study the role of phosphorus 3d orbitals in the bonding. It is emphasized that the discussion about the 3d orbital participation in bonding should be based on a reasonable choice of basis sets and it seems suitable to choose the atomic orbitals in proper molecular environment as the basis set. As an approximation, the optimized minimal STO-NG basis sets have been adopted in the present paper. The results obtained well exhibit the model of 3d orbital participation in bonding. It is shown that under the influence of highly electronegative ligands the phosphorus 3d orbitals contract greatly, their energy levels drop considerably, and thus they can effectively participate in bonding. The presence of highly electronegative ligands seems necessary. The contribution of 3d orbitals to bonding is achieved mainly through the concerted formation of σ bonds and p-d backbonds, though the contribution to σ bonding is minor. The three-center, four-electron bond model is only approximately correct. The results of the present paper demonstrate that the model of 3d orbital participation in bonding favoured by experimental chemists is reasonable and possesses sound ground.

In this work, the case of cracks located in a weld with mismatched creep properties from that of the surrounding base material is addressed. A weighted-average method for both over- and undermatched creep performance of the weld and base materials is presented, and an equivalent isochronous stress-strain curve (EISSC) is then defined. Accordingly, a time-dependent failure assessment curve is constructed using the method of R6 Option 2. This curve now depends not only on the mechanical properties of both weld and base materials but also on the weld geometry and crack size. The application of such an approach to an internal, circumferentially defected welded cylinder under axial tension has been studied. Results indicate that the dependence of the modified time-dependent failure assessment curves (TDFACs) on the geometry, crack size and service time is not significant and nearly collapses into one curve. The general failure assessment curve from isochronous data of austenitic steel, proposed by Ainsworth, is non-conservative for some cases and thus may not be applicable for Cr-Mo steel.

We studied the relation of radon exposure and tobacco use to lung cancer among tin miners in Yunnan Province in the People's Republic of China. Interviews were conducted in 1985 with 107 living tin miners with lung cancer and an equal number of age-matched controls from among tin miners without lung cancer to obtain information on lung cancer risk factors including a detailed history of employment and tobacco use. Occupational history was combined with extensive industrial hygiene data to estimate cumulative working level months (WLM) of radon daughter exposure. Similar data were also used to estimate arsenic exposure for control in the analysis. Results indicate an increased risk of lung cancer for water pipe smoking, a traditional form of tobacco use practiced in 91% of cases and 85% of controls. Ever use of water pipes was associated with a twofold elevation in risk when compared with tobacco abstainers, and a dose-response relation was observed with increasing categories of pipe-year (dose times duration) usage. Estimated WLM of radon exposure varied from 0 to 1,761 among subjects but averaged 515 in cases versus only 244 in controls. Analyses indicated that the persons in the highest quarter of the radon exposure distribution had an odds ratio (OR) = 9.5 (95% confidence interval = 2.7-33.1) compared to persons without radon exposure after controlling for arsenic exposure and other potential confounders. Examination of duration and rate of radon exposure indicated higher risk associated with long duration as opposed to high rate of exposure. Cross-categorizations of radon exposure and tobacco use suggest greater risk associated with radon exposure than tobacco in these workers.