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Sökning: WFRF:(Koji Mizuno) > (2017)

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1.
  • Aharonian, Felix, et al. (författare)
  • Solar abundance ratios of the iron-peak elements in the Perseus cluster
  • 2017
  • Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 551:7681, s. 478-
  • Tidskriftsartikel (refereegranskat)abstract
    • The metal abundance of the hot plasma that permeates galaxy clusters represents the accumulation of heavy elements produced by billions of supernovae(1). Therefore, X-ray spectroscopy of the intracluster medium provides an opportunity to investigate the nature of supernova explosions integrated over cosmic time. In particular, the abundance of the iron-peak elements (chromium, manganese, iron and nickel) is key to understanding how the progenitors of typical type Ia supernovae evolve and explode(2-6). Recent X-ray studies of the intracluster medium found that the abundance ratios of these elements differ substantially from those seen in the Sun(7-11), suggesting differences between the nature of type Ia supernovae in the clusters and in the Milky Way. However, because the K-shell transition lines of chromium and manganese are weak and those of iron and nickel are very close in photon energy, highresolution spectroscopy is required for an accurate determination of the abundances of these elements. Here we report observations of the Perseus cluster, with statistically significant detections of the resonance emission from chromium, manganese and nickel. Our measurements, combined with the latest atomic models, reveal that these elements have near-solar abundance ratios with respect to iron, in contrast to previous claims. Comparison between our results and modern nucleosynthesis calculations(12-14) disfavours the hypothesis that type Ia supernova progenitors are exclusively white dwarfs with masses well below the Chandrasekhar limit (about 1.4 times the mass of the Sun). The observed abundance pattern of the iron-peak elements can be explained by taking into account a combination of near-and sub-Chandrasekhar-mass type Ia supernova systems, adding to the mounting evidence that both progenitor types make a substantial contribution to cosmic chemical enrichment(5,15,16).
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2.
  • Koji, Mizuno, et al. (författare)
  • Comparison of Real Accident and Near Miss Incident of Cyclist Collisions Based on Drive Recorder
  • 2017
  • Ingår i: Proceedings of the 2017 JSAE Annual Congress (Spring).
  • Konferensbidrag (refereegranskat)abstract
    • In order to examine factors that caused vehicle-cyclist collisions, vehicle-cyclist collisions at intersections that were recorded on a car driving recorder were compared to that of near-miss incidents. It was found that unless the cyclist took action to avoid the collision, collisions occur when the car needed a deceleration of 9.8m/s2 or more to avoid the collision. Two different types of collisions were observed: delays of drivers to start braking after a cyclist is present, and the sudden appearance of the cyclist. The percentage of incidents where the cyclist suddenly appeared was higher in collisions cases compared to near-miss incidents.
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