S-W Kim

The Microstructure of Direct Squeeze Cast and Gravity Die Cast 7050 (Al–6.2Zn–2.3Cu–2.3Mg) Wrought Al Alloy

A 7050 (Al–6.2 wt% Zn–2.3 wt% Cu–2.3 wt% Mg) Al alloy, conventionally used for wrought products, has been successfully cast to near-net shape using direct squeeze casting. Squeeze casting with an applied pressure of 50 MPa removes the defects observed in gravity die cast billets, in particular, (1) shrinkage pipe, (2) poor die replication and waisting, and (3) microporosity. Squeeze casting results in considerable refinement of the microstructure due to an increase in cooling rate from ∼0.5°C s−1 for gravity casting to ∼11°C s−1 for squeeze casting in a tool steel die lined with porous insulation, and from ∼2.5 to ∼10°C s−1, respectively, in an uninsulated die. A normal segregation pattern of increasing eutectic toward the center of the billet is found for squeeze casting, compared to an inverse segregation pattern of increasing eutectic toward the edge of the billet for gravity casting. This change in segregation pattern is due to a higher radial temperature gradient and reduced time in the semisolid state for squeeze casting.

Complex Capacitance Analysis of Ionic Resistance and Interfacial Capacitance within Cathode Layers of PEMFC and DMFC Electrodes

In PEMFCs (polymer electrolyte membrane fuel cells) and DMFCs (direct methanol fuel cells), the catalyst layers are prepared together with a Nafion ionomer to extend reaction sites throughout the bulk electrodes. In order to achieve high performances with the large TPB (three-phase boundary) area, the catalyst layers should have well-developed networks for electron conduction (catalyst particles), proton transport (Nafion ionomer particles), and reactant gas supply (pores). Therefore, characterization of the microstructures of catalyst layers, as well as performance measurements, is very important to optimize various preparation factors. Also, the microstructure characterization is required to elucidate degradation mechanisms for practical fuel cell operation. In this study, a complex capacitance analysis of impedance data was developed to evaluate the catalyst/ionomer interfacial capacitance and ionic resistance of ionomer networks, without non-linear data fitting. Firstly, assuming no Faradaic reactions, equivalent circuits for the catalyst layers were suggested, which are similar to EDLC systems with porous carbon electrodes. Then, with the simulated complex capacitances, it was confirmed that the plots of the real and imaginary parts as a function of ac frequency are determined by the catalyst/ionomer interfacial capacitances and RC time constants, which are important characteristics for high fuel cell performances. Experimentally, the condition of no Faradaic reactions was realized by supplying nitrogen or water to the cathodes instead of air and fixing the dc potential at 0.4 V during the impedance measurements. By analyzing the real and imaginary capacitance plots of experimental impedance data, the catalyst/ionomer interfacial area and proton conductivity were graphically estimated. Also, the interfacial capacitances and ionomer resistances could be quantitatively determined from the real capacitance at low frequency and peak frequency in the imaginary capacitance plots. Here, the experimental impedance and transformed complex capacitances could be well described by equivalent circuits that contain the transmission line model. From the complex capacitance analysis of impedance data measured at 0.4 V under a N2/H2 atmosphere for PEMFC MEAs, it was found that the ionic resistance within cathode layers was higher for the MEA with lower ionomer content (20 wt.%), especially at low relative humidity. In single cell testing, the MEA with 20 wt.% ionomer showed larger activation overpotential, probably due to the limited utilization of active sites with high ionic resistances. 0 1 2 3 0 1 2

Abstract P1-10-01: Curcumin suppresses MMP-9 expression via inhibition of PKCα/MAPKs and NF-κB/AP-1 activation in MCF-7 cells

Background: Curcumin is a polyphenol derived from the plant turmeric ( Curcuma longa ), which is commonly used as a spice. It was recently reported for its anticancer effect on several types of cancer cells in vitro, however the molecular mechanisms of this anticancer effect are not fully understood. In the present study, we investigated the effect of curcumin on 12- O -tetradecanoylphorbol-13-acetate(TPA)-induced matrix metalloproteinase-9(MMP-9) expression and cell invasion in MCF-7 breast cancer cells. Materials and Methods: The effect of curcumin on MCF-7 cell viability was determined using MTT assay. The cells invasion was demonstrated by the Matrigel-coated transwell assay. Western blot analysis was performed to detect the effect of curcumin on the expression of MMP-9. MMP-9 mRNA levels were analyzed by real-time PCR. NF-κB and AP-1 DNA binding was analyzed by EMSA. Results: Our results showed that curcumin inhibits TPA-induced MMP-9 expression and cell invasion through suppressing NF-κB and AP-1 activation. Curcumin strongly repressed the TPA-induced phosphorylation of p38 and JNK and also inhibited TPA-induced translocation of PKCa from the cytosol to the membrane, but did not affect the translocation of PKCδ. Conclusion: It is concluded that curcumin inhibits the TPA-induced MMP-9 expression and cell invasion through the suppression of the PKCα/MAPK/NF-kB/AP-1 pathway in MCF-7 breast cancer cells. Accordingly, curcumin may have the therapeutic potential in restricting breast cancer metastasis. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P1-10-01.