We investigated the inhibitory effects of hesperidin on melanogenesis. To find melanosome transport inhibitor from natural products, we collected the structural information of natural products from Korea Food and Drug Administration (KFDA) and performed pharmacophore-based in silico screening for Rab27A and melanophilin (MLPH). Hesperidin did not inhibit melanin production in B16F10 murine melanoma cells stimulated with α-melanocyte stimulating hormone (α-MSH), and also did not affect the catalytic activity of tyrosinase. But, hesperidin inhibited melanosome transport in melanocyte and showed skin lightening effect in pigmented reconstructed epidermis model. Therefore, we suggest that hesperidin is a useful inhibitor of melanosome transport and it might be applied to whitening agent.

This study investigates the effect of roll surface profile on the centerline segregation of the molten metal (bloom) being solidified in the soft reduction process, where the molten metal (bloom) thickness is reduced consecutively by a set of rolls. The roll surface profiles are convex and flat. Finite element analysis was performed to examine the variations in solidus line contour, the phase state across the bloom cross-section and stress state of the bloom in the mushy zone to the casting direction when high carbon bloom (400 mm in thickness and 500 mm in width) was solidified and plastically deformed at the same time. To verify the finite element analysis results, soft reduction test with an actual bloom caster was also carried out.Results reveal that a convex roll surface profile is much more effective than a flat roll surface profile in decreasing the centerline segregation and the internal cracks in the bloom. The convex roll surface profile compresses the mushy zone from both directions (bloom thickness and width) and subsequently compensates efficiently the solidification shrinkage of molten metal. In addition, the convex roll can save energy required in deforming the bloom in the soft reduction process.

The movements of the driven rolls were measured during the continuous casting of steel and their fluctuations were compared with other signals such as the casting speed and the mold level. From the observation of large fluctuations in the movements of the driven rolls and the unevenness in the thickness of the solid shell, it is proposed that the unevenness in the thickness of the solid shell is the main reason for unsteady bulging during the casting of medium carbon steel. A two-dimensional model over the successive rolls was used to calculate the bulging profile and its changes with time, during the fluctuations in the casting speed, with the finite element method. As a result, the calculations were in good agreement with the experimental results, and, it could be concluded that the period of unsteady bulging is greatly influenced by the roll pitch, therefore, depends on the locations where different roll pitches occur, and is somewhat affected by casting speed variations. Finally, based on the calculations and the experimental results, the effect of the unsteady bulging on the mold level was discussed.KEY WORDS: continuous casting; driven roll; unsteady bulging; bulging over successive rolls; liquid level fluctuation; unevenness of shell thickness; roll pitch.

In this study, the surface crack sensitivities in samples of a Nb-bearing steel and a high Ni grade steel from continuous casting slabs have been examined by simple compression tests at various temperatures between 700-1 100°C using a metallography method to evaluate the severity of surface cracks, and corresponding microstructure in the two grades of steel has been investigated. The results show that most specimen have cracks on the hoop surface after 50% compression in height in the temperature range of interest, and the critical hoop strain obtained from the metallography examination gives a clear cracking tendency for the two grades of steel. Microstructure observation revealed that the static precipitation of TiNb(CN) before deformation and thin ferrite film along grain boundaries are important for controlling surface crack sensitivity for the Nb-bearing steel, while coarse grains with flat boundaries, and grain-boundary precipitation of Cu 2 S and flake-like Ti(CN) at lower temperature, is responsible for the high crack sensitivity in high Ni steel between 700-1 100°C, which implies Cu, S, Ti and N content should be kept as low as possible in this grade of steel, and surface temperatures of continuous casting slabs at the straightening point should be above 970°C for Nb-bearing steel while 980°C for high Ni steel to avoid transverse cracking.

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