In order to detect weld defects in laser welding T-joint of Al–Li alloy, a real-time X-ray image system is set up for quality inspection. Experiments on real-time radiography procedure of the weldment are conducted by using this system. Twin fillet welding seam radiographic arrangement is designed according to the structural characteristics of the weldment. The critical parameters including magnification times, focal length, tube current and tube voltage are studied to acquire high quality weld images. Through the theoretical and data analysis, optimum parameters are settled and expected digital images are captured, which is conductive to automatic defect detection.

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A numerical model based on cellular automaton algorithm is developed to simulate dendrite growth at the edge of weld molten pool and the solute diffusion during grain growing process in weld solidification is analysed too. By means of two-dimensional square cells and von Neumann neighbourhood, the growing morphologies of the columnar dendritic grains with different cooling rates and different numbers of seeds are simulated. The growth of secondary dendrite arms, tertiary dendrite arms and their competitive growth are also presented. The results illustrate that the final primary dendrite spacing depends on the number of seeds that initially generated. With increasing cooling rate, the growing speed is increasing obviously. It is also indicated that competitive growth exists between different dendrite arms. The tendency of competitive growth in high cooling rate conditions is weaker than the one in relatively small cooling rate conditions.

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Abstract-Perfluorooctanoic acid (PFOA) is an important perfluorinated compound (PFC) with various applications and has been widely disseminated in the environment, wildlife, and humans. The present study investigated the effects of waterborne PFOA on the expression of hepatic estrogen-responsive genes, vitellogenin (VTG), and estrogen receptor ␤ (ER␤) and on the gonadal development in a freshwater rare minnow (Gobiocypris rarus). The mRNA levels of VTG and ER␤ were determined using reverse transcription polymerase chain reaction (RT-PCR) techniques, and VTG protein levels were identified using enzyme-linked immunosorbent assay. A significant increase of VTG expression in the livers of both mature males and females was observed after 14 and 28 d of exposure to 3, 10, and 30 mg/L PFOA, indicating that PFOA could induce VTG synthesis. The expression of ER␤ increased significantly in livers of both mature males and females after a 14-d exposure, although no difference was observed after a 28-d exposure. The development of oocytes in testes exposed to PFOA also provided evidence of estrogenic activity in males. The ovaries of PFOA-exposed females underwent degeneration, as reported in other fish species exposed to environmental estrogens. This preliminary study indicates that PFOA can disturb the activity of estrogen in mature male rare minnows by inducing hepatic estrogen-responsive genes, VTG and ER␤, and barrier female reproduction.

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