RESUMEN
Contrary to previous results, a unique anti-correlation effect of the alkyl chain size on the photovoltaic performance of acceptors was observed. For a centrally-extended acceptor, replacing linear alkyl chains (n-undecyl for CH-BBQ) on the thienothiophene unit with branched ones (2-butyloctyl for CH-BO) leads to a plunge in the power conversion efficiency of organic solar cells (18.12% vs. 11.34% for binary devices), while the largely shortened ones (n-heptyl for CH-HP) bring a surge in performance (18.74%/19.44% for binary/ternary devices). Compared with CH-BO, the more compact intermolecular packing of CH-HP facilitates carrier transport. The characterization of organic field effect transistors and carrier dynamics also echoes the above results. Molecular dynamics simulations indicate that the encounter of the branched alkyl chains and the extended central core hinders the effective interfacial interaction of polymer donors and acceptors, thus deteriorating the device performance. This work suggests that the conventional strategy for alkyl chain engineering of Y-series acceptors might need to be reconsidered in other molecular systems.
RESUMEN
The welding of steel-aluminum dissimilar metals plays a vital role in promoting automobile lightweight. However, it is tricky to obtain good mechanical properties of steel-aluminum laser weldments. Based on the principle of preheating welding, the laser double-pass reciprocating welding method of steel-aluminum dissimilar metals was proposed. In the experiment, different weld spacing such as 0, 0.5, 1.0, 1.5, and 2.0 mm were set, and numerical calculations of the temperature field of the molten pool were carried out. The results show that the tensile strength of weldment depends on the mechanical properties of the second weld seam in the optimal welding parameters. Compared with other weld spacing, when the weld spacing is 1.5 mm, the preheating temperature, peak temperature, and pool width on the steel side of the second weld are lower. In contrast, the weld penetration's peak value and molten pool center's temperature reach the maximum on the aluminum side. The thickness of the steel/aluminum transition layer changed from 14 to 11 to 8 µm with increased weld spacing. Moreover, the fracture mode of the second weld is a ductile fracture. Furthermore, the average tensile strength can reach 76.84 MPa. The results show that appropriate weld spacing and preheating temperature can effectively improve the tensile strength of the welding joint.
RESUMEN
OBJECTIVE: To observe the effect of vitamin C and E on blood lead (Pb) levels and SOD, GSH-Px, NOS activity and NO, MDA content in hippocampus of rats with lead poisoning. METHODS: Rat lead poisoning model was established by oral administration of 0.615 mmol/L lead acetate in drinking water for 4 weeks; and animals were fed with vitamin C 100 mg/kg. bw and/or vitamin E 100 mg/kg. bw for 1 week. Then blood Pb levels and SOD, GSH-Px, NOS activity and MDA, NO contents in hippocampus of rats were determined by corresponding kits. RESULT: Compared with control group, blood Pb level was decreased significantly (P<0.05) after given vitamin C, vitamin E or combination of vitamin C and E. The concentrations of SOD, GSH-Px, NO and NOS were significantly higher in vitamin C and/or E groups than those in control group (P<0.05). The concentration of MDA in vitamin treatment groups was significantly lower than that in lead control group (P<0.05); furthermore concentration of MDA in combination of vitamin C and E group was significantly higher than that in vitamin C alone group (P<0.05). CONCLUSION: Administration of vitamin C and E can decrease blood lead level, alleviate damage of lipid peroxidation in hippocampus by lead toxicity and reverse NO, NOS levels in rats with lead poisoning.
