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The gas-solid compatibility between environmentally friendly insulating gas and copper contacts is worth studying. In this paper, based on density functional theory, the adsorption calculation of CF3I, c-C4F8, five typical decomposition gases, and Cu (1 1 1) surface was carried out. The adsorption energies, transferred charges, charge densities, and densities of states were calculated for different adsorption configurations. Research indicates that there is no obvious charge transfer between the I atom and the Cu atom in the four adsorption sites of Cu (1 1 1) for the CF3I molecule. There is a charge transfer between the F atoms and the Cu top surface. The electrons lost by Cu are transferred to F atoms. In the configurations of different adsorption positions on CF3I and Cu (1 1 1) planes, the top and bridge adsorption energies are −0.835 eV and −0.993 eV, respectively, which are chemical adsorption. Therefore, CF3I is most likely to form adsorption at the top or bridge site of the Cu (1 1 1) surface. The adsorption energy of c-C4F8 gas on Cu (1 1 1) surface is similar to that of CF3I at fcc and hcp sites. The absolute values are all less than 0.8 eV, and the van der Waals force is the main force. The adsorption energies of C2F4 and C3F6 in the five decomposed gases are −1.315 eV and −1.204 eV, respectively. The charge transfer is −0.32 eV and −0.45 eV, respectively. Their values are larger than those of the other gases studied, which belong to chemical adsorption. The smaller values of the remaining three gases belong to physical adsorption. All molecular structures and Cu (1 1 1) planes were not significantly deformed. From a microscopic point of view, the gas can better exist on the copper surface.

The contact is the core element of the vacuum interrupter of the mechanical DC circuit breaker. The electrical conductivity and welding resistance of the material directly affect its stability and reliability. AgSnO2 contact material has low resistivity, welding resistance, and so on. This material occupies an important position of the circuit breaker contact material. This research is based on the first-principles analysis method of density functional theory. The article calculated the lattice constant, enthalpy change, energy band, electronic density of state, charge density distribution, population, and conductivity of Ce, C single-doped, and Ce-C codoped SnO2 systems. The results show that Ce, C single doping, and Ce-C codoping all increase the cell volume and lattice constant. When the elements are codoped, the enthalpy change is the largest, and the thermal stability is the best. It has the smallest bandgap, the most impurity energy levels, and the least energy required for electronic transitions. The 4f orbital electrons of the Ce atom and the 2p orbital electrons of C are the sources of impurity energy near the Fermi level. When the elements are codoped, more impurity energy levels are generated at the bottom of the conduction band and the top of the valence band. Its bandgap is reduced so conductivity is improved. From the charge density and population analysis, the number of free electrons of Ce atoms and C atoms is redistributed after codoping. It forms a Ce-C covalent bond to further increase the degree of commonality of electrons and enhance the metallicity. The conductivity analysis shows that both single-doped and codoped conductivity have been improved. When the elements are codoped, the conductivity is the largest, and the conductivity is the best.

Background. Antidiabetic medications (ADMs) can alter the risk of different types of cancer, but the relationship between lung cancer incidence and metformin remains controversial. Our aim was to quantitatively estimate the relationship between incidences of lung cancer and metformin in patients with diabetes in this meta-analysis. Methods. We performed a search in PubMed, Embase, ISI Web of Science, and Cochrane Library until September 20, 2017. The odds ratio (OR), relative risk (RR) or hazard ratio (HR), and 95% confidence interval (95% CI) were estimated using the random-effect model. The Newcastle-Ottawa Scale (NOS) was used to assess the study quality. Results. A total of 13 studies (10 cohort studies and 3 case-control studies) were included in the meta-analysis. Compared to nonmetformin users, metformin probably decreased lung cancer incidence in diabetic patients (RR=0.89; 95% CI, 0.83-0.96; P=0.002) with significant heterogeneity (Q=35.47, I2=66%, P=0.0004). Subgroup analysis showed that cohort studies (RR=0.91; 95% CI, 0.85-0.98; P=0.008), location in Europe (RR=0.90; 95% CI, 0.86-0.94; P<0.0001), the control drug of the sulfonylurea group (RR=0.91; 95% CI, 0.86-0.96; P=0.001), and adjusting for smoking (RR=0.86; 95% CI, 0.75-1.00; P=0.05) may be related to lower lung cancer risk. No significant publication bias was detected using a funnel plot. Conclusion. Metformin use was related to a lower lung cancer risk in diabetic patients compared to nonusers, but this result was retrieved from observational studies and our findings need more well-designed RCTs to confirm the association.

Summary In this paper, the electromagnetic efficiency factor is defined to describe the utilization rate of metal conductors in air-core coils. The geometry-electromagnetic character and the thermal condition of the coil are coupled to describe the electromagnetic efficiency of the air-core coils. The geometry-electromagnetic character is deduced form the inductance computation formula, while the thermal functions are given according to the “Uniformed electrical current density condition” and the “uniformed temperature rise” condition. Curves that reflect the electromagnetic efficiency factor are given while the thermal condition is considered as the mentioned two conditions. The former thermal condition is simpler and is proved to be suitable for midget air-core coils without complex heat transfer structure or coils with pulse current. While, the latter is proved to be with higher accuracy and can be wildly used in the optimization design of air-core power reactors. Copyright © 2014 John Wiley & Sons, Ltd.