Presence Of WC Research Articles

What the galaxies of the Local Group tell us about massive star evolution

We consider what we've learned about massive star evolution from observations of the resolved stellar content of Local Group galaxies. Studies of mixed-age (galaxy-wide) and coeval (single associations) populations reveal much about massive star evolution, and how it is controlled by metallicity, demonstrating the ‘Conti scenario’ in action! The number of WC stars to WN stars increases with increasing metallicity, as expected: in regions of higher metallicity stars of somewhat lower luminosity can evolve all the way to the WC stage. The exception is the starburst galaxy IC 10, for which I speculate that the IMF may be weighted towards high mass stars. The highest luminosity red supergiants are lacking in galaxies of higher metallicity, suggesting that the stars that would have become these RSGs are spending more of their time as WRs. The presence of luminous RSGs is highly correlated with the presence of WC and WN stars in OB associations, suggesting that many massive stars evolve through both a RSG and WR stage. The relative number of RSGs and WRs does decrease strongly with increasing metallicity, again consistent with higher metallicity systems leading to increased time in the WR phase. The various WC subclasses appear to be the result of the influence of metallicity on stellar wind structure in these stars, and are not due to to differences in mass or luminosity. Data on the field population in the Magellanic Clouds suggest that stars more massive than 30 become WRs in the LMC, while the limit may be more like 50 in the SMC, again as expected. Studies of the turn-off masses in clusters and associations in the MCs and Milky Way are nearing completion, while investigations in the more distant galaxies of the Local Group are just getting underway. For the LMC we find the following: WNE stars come from a large mass range of progenitor (30–100 ), and have very large (negative) bolometric corrections (−6 to −8 mag). The Ofpe/WN9 stars seem to come from lower mass progenitor (20–30 ), and have more modest BCs (−1 to −3 mag). WC stars come from stars with masses > 60–70 , and have BCs of −3 to −4 mag. Both ‘B2I+WN3’ systems and LBV stars like S Doradus are found only in clusters containing very high turn off masses (>70–90 ).

Study of the mechanism responsible for the elective toxicity of tungsten carbide-cobalt powder toward macrophages

We have previously demonstrated that tungsten carbide-cobalt powder (WC-Co) is more toxic toward murine macrophages in vitro than pure cobalt metal particles and that the cellular uptake of cobalt is enhanced when the metal is present in the form of WC-Co mixture. The present study was undertaken to assess the possible mechanism(s) of this interaction. We found that solubilization of cobalt in the extracellular milieu was increased in the presence of WC. This phenomenon, however, is not the critical factor explaining the greater toxicity of the WC-Co mixture since increasing the amount of solubilized cobalt in the extracellular medium in the absence of WC did not result in increased toxicity. Moreover, the amount of cobalt solubilized from a toxic dose of WC-Co was insufficient to affect by itself macrophage viability. A toxic effect was only observed when the WC-Co mixture came directly in contact with the cells. The elective toxicity of WC-Co can also not be explained by stimulation of phagocytosis of cobalt metal particles due to the simultaneous presence of other particles (WC) in the extracellular fluid since stimulation of phagocytosis by latex beads or zymosan particles did not amplify the toxicity of cobalt metal particles. These results indicate that the toxicity of the WC-Co mixture does not simply result from an enhanced bioavailability of its cobalt component. This suggests that hard metal dust behaves as a specific toxic entity.

超硬合金の電解加工に関する基礎的研究 (第2報)

The electrochemical removal amount of cemented carbide alloy and WC is treated in this paper, which is the second in a sequence of several papers, the first dealing with characteristic features under potentiostatic condition. It has frequently been observed that the electrochemical removal amount of cemented carbide varies from experiment to experiment. It was thought that this could be accounted for by the observation of ash grey residue at the anode surface in all experiments. On the basis of cathodic stripping studies, a method is developed to ensure to measure correctly the removal amount. It is found that the removal amount W is evaluated by W= Wα+ Wc, where Wα is anodic removal and Wc is anodic product which is residual on machined samples of cemented carbide and removed by cathodic stripping. In those experiments the value of Wc is 0.2 mg/min for P 20 alloy, and is 1 mg/min for K 40 alloy, which indicates a tendency to increase Wc as WC component in cemented carbide increases. A dissolution mechanism of WC is discussed and it is concluded that WC is dissolved with a valency of.9. The presence of WC in the dissolving product when machined with alternating current in NaNO3 electrolyte is identified by X-ray diffraction technique.