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Sökning: WFRF:(Imai Y.) > Chalmers tekniska högskola

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1.
  • Amada, K., et al. (författare)
  • Discovery of SiO Masers in the "Water Fountain" Source IRAS 16552-3050
  • 2022
  • Ingår i: Astronomical Journal. - : American Astronomical Society. - 1538-3881 .- 0004-6256. ; 163:2
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, we report new detections of SiO v = 1 and v = 2 J = 1 -> 0 masers in the "water fountain" source IRAS 16552-3050, which was observed with the Nobeyama 45 m telescope during 2021 March-April. Water fountains are evolved stars whose H2O maser spectra trace high-velocity outflows of >100 km s(-1). This is the second known case of SiO masers in a water fountain, after their prototypical source, W 43A. These SiO masers should shed light on the evolutionary status of this category of evolved stars, which are likely to be at the end of the asymptotic giant branch phase, when the star exhibits the most copious stellar mass loss, followed by development of the complicated morphologies of planetary nebulae. The origin of a large (up to 25 km s(-1)) velocity offset of the SiO masers with respect to the systemic velocity derived from the spectrum of CO J = 2 -> 1 line is discussed here.
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3.
  • Tamagawa, T., et al. (författare)
  • Correlation between musculoskeletal structure of the hand and primate locomotion: Morphometric and mechanical analysis in prehension using the cross- and triple-ratios
  • 2020
  • Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 15:5
  • Tidskriftsartikel (refereegranskat)abstract
    • Biometric ratios of the relative length of the rays in the hand have been analyzed between primate species in the light of their hand function or phylogeny. However, how relative lengths among phalanges are mechanically linked to the grasping function of primates with different locomotor behaviors remains unclear. To clarify this, we calculated cross and triple-ratios, which are related to the torque distribution, and the torque generation mode at different joint angles using the lengths of the phalanges and metacarpal bones in 52 primates belonging to 25 species. The torque exerted on the finger joint and traction force of the flexor tendons necessary for a cylindrical grip and a suspensory hand posture were calculated using the moment arm of flexor tendons measured on magnetic resonance images, and were compared among Hylobates spp., Ateles sp., and Papio hamadryas. Finally, the torques calculated from the model were validated by a mechanical study detecting the force exerted on the phalanx by pulling the digital flexor muscles during suspension in these three species. Canonical discriminant analysis of cross and triple-ratios classified primates almost in accordance with their current classification based on locomotor behavior. The traction force was markedly reduced with flexion of the MCP joint parallel to the torque in brachiating primates; this was notably lower in the terrestrial quadrupedal primates than in the arboreal primates at mild flexion. Our mechanical study supported these features in the torque and traction force generation efficiencies. Our results suggest that suspensory or terrestrial quadrupedal primates have hand structures that can exert more torque at a suspensory posture, or palmigrade and digitigrade locomotion, respectively. Furthermore, our study suggests availability of the cross and triple-ratios as one of the indicators to estimate the hand function from the skeletal structure.
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4.
  • Amada, Kei, et al. (författare)
  • Discovery of SiO masers in the Water Fountain source, IRAS 16552-3050
  • 2022
  • Ingår i: Proceedings of the International Astronomical Union. - 1743-9213 .- 1743-9221. ; 18, s. 359-361
  • Konferensbidrag (refereegranskat)abstract
    • We report new detections of SiO ν = 1 and ν = 2 J = 1 → 0 masers in the water fountain source IRAS 16552-3050, which was observed with the Nobeyama 45 m telescope from March 2021 to April 2023. Water fountains are evolved stars whose H2O maser spectra trace high-velocity outflows of >100 Km s-. This is the second known case of SiO masers in a water fountain, after their prototypical source, W 43A. The line-of-sight velocity of the SiO masers are blue-shifted by ∼25 km s-1 from the systemic velocity. This velocity offset imply that the SiO masers are associated with nozzle structure formed by a jet penetrating the circumstellar envelope, and that new gas blobs of the jet erupted recently. Thus, the SiO masers imply this star to be in a new evolutionary stage.
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5.
  • Imai, H., et al. (författare)
  • Water and silicon-monoxide masers monitored towards the water fountain sources
  • 2021
  • Ingår i: Proceedings of the International Astronomical Union. - 1743-9213 .- 1743-9221. ; 17, s. 91-93
  • Konferensbidrag (refereegranskat)abstract
    • We have investigated the evolution of 12 water fountain sources in real time in the accompanying H2O 2o and SiO masers through our FLASHING (Finest Legacy Acquisitions of SiO-/ H2O 2o-maser Ignitions by Nobeyama Generation) project. It has been confirmed that these masers are excellent probes of new jet blob ejections, acceleration of the material supplied from the parental circumstellar envelope and entrained by the stellar jets yielding its deceleration. Possible periodic variations of the maser emission, reflecting properties of the central dying stars or binary systems, will be further investigated.
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6.
  • Imai, Hiroshi, et al. (författare)
  • Water Fountain Sources Monitored in FLASHING
  • 2022
  • Ingår i: Proceedings of the International Astronomical Union. - 1743-9213 .- 1743-9221. ; 18, s. 333-337
  • Konferensbidrag (refereegranskat)abstract
    • We have investigated the spectral evolutions of H2O and SiO masers associated with 12 water fountain sources in our FLASHING (Finest Legacy Acquisitions of SiO-/H2O-maser Ignitions by Nobeyama Generation) project. Our monitoring observations have been conducted using the Nobeyama 45 m telescope every 2 weeks-2 months since 2018 December except during summer seasons. We have found new extremely high velocity H2O maser components, breaking the records of jet speeds in this type of sources. Systematic line-of-sight velocity drifts of the H2O maser spectral peaks have also been found, indicating acceleration of the entrained material hosting the masers around the jet. Moreover, by comparing with previous spectral data, we can find decadal growths/decays of H2O maser emission. Possible periodic variations of the maser spectra are further being inspected in order to explore the periodicity of the central stellar system (a pulsating star or a binary). Thus we expect to see the real-time evolution/devolutions of the water fountains over decades.
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7.
  • Imai, N., et al. (författare)
  • Isobaric analog resonances of Mg-31 and the border of the island of inversion
  • 2014
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813 .- 2469-9985 .- 2469-9993. ; 90:1
  • Tidskriftsartikel (refereegranskat)abstract
    • The evolution of the nuclear shell structure in the region of the neutron-rich shell-breaking nucleus Mg-32 has been the subject of considerable interest. We present here the first determination of the overlap of the ground and two first excited states in Mg-31 with a neutron coupled to the ground state in Mg-30 based on studies of its isobaric analog resonances in Al-31. The excitation function for proton resonant elastic scattering on Mg-30 was measured close to 0 degrees in the laboratory frame by bombarding a thick polyethylene target with a Mg-30 beam at an energy of 2.92 MeV/nucleon at the REX-ISOLDE facility at CERN. Three resonances were successfully resolved, and angular momenta and total and proton resonance widths were determined by using R-matrix analysis. The deduced spectroscopic factor for the ground state in Mg-31 is consistent with the shell-model calculation, whereas those for the first and second excited states could not be reproduced. These results show that a drastic change in structure occurs between Mg-30 and Mg-31 and that the onset of structural change in this region therefore occurs between these two isotopes.
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9.
  • Törnqvist, Hans, 1985, et al. (författare)
  • Tilted foils polarization at REX-ISOLDE
  • 2013
  • Ingår i: Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms. - : Elsevier BV. - 0168-583X. ; 317:PART B, s. 685-688
  • Tidskriftsartikel (refereegranskat)abstract
    • The tilted-foils nuclear-spin polarization method has been evaluated using the REX-ISOLDE linear accelerator at the ISOLDE facility, CERN. A beam of 8Li delivered with an energy of 300 keV/u traversed through one Mylar foil to degrade the beam energy to 200 keV/u and consequently through 10 thin diamond-like carbon foils to polarize the nuclear spin. The attained nuclear spin polarization of 3.6±0.3% was measured with a β-NMR setup.
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10.
  • Uscanga, L., et al. (författare)
  • Evolution of the Outflow in the Water Fountain Source IRAS 18043-2116
  • 2023
  • Ingår i: Astrophysical Journal. - 1538-4357 .- 0004-637X. ; 948:1
  • Tidskriftsartikel (refereegranskat)abstract
    • We present the spectral and spatial evolution of H2O masers associated with the water fountain source IRAS 18043-2116, found in observations with the Nobeyama 45 m Telescope and the Australia Telescope Compact Array. We have found new highest-velocity components of the H2O masers (at the redshifted side V (LSR) similar or equal to 376 km s(-1) and at the blueshifted side V (LSR) similar or equal to -165 km s(-1)), and the resulting velocity spread of similar or equal to 540 km s(-1) breaks the speed record of fast jets/outflows in this type of sources. The locations of those components have offsets from the axis joining the two major maser clusters, indicating a large opening angle of the outflow (similar to 60 degrees). The evolution of the maser cluster separation of similar to 2.9 mas yr(-1) and the compact (similar to 0.'' 2) CO emission source mapped with the Atacama Large Millimeter-submillimeter Array suggest a very short (similar to 30 yr) timescale of the outflow. We also confirmed an increase in the flux density of the 22 GHz continuum source. The properties of the jet and the continuum sources and their possible evolution in the transition to the planetary nebula phase are further discussed.
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