Browsing by Author "Sakai, N."

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    Physical properties of accretion shocks toward the Class I protostellar system Oph-IRS 44
    (2022) de la Villarmois, E. Artur; Guzman, V. V.; Jorgensen, J. K.; Kristensen, L. E.; Bergin, E. A.; Harsono, D.; Sakai, N.; van Dishoeck, E. F.; Yamamoto, S.
    Context. The final outcome and chemical composition of a planetary system depend on its formation history: the physical processes that were involved and the molecular species available at different stages. Physical processes such as accretion shocks are thought to be common in the protostellar phase, where the envelope component is still present, and they can release molecules from the dust to the gas phase, altering the original chemical composition of the disk. Consequently, the study of accretion shocks is essential for a better understanding of the physical processes at disk scales and their chemical output.
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    Surpass Flow Diverter in the Treatment of Intracranial Aneurysms: A Prospective Multicenter Study
    (2015) Wakhloo, A. K.; Lylyk, P.; de Vries, J.; Taschner, C.; Lundquist, J.; Biondi, A.; Hartmann, M.; Szikora, I.; Pierot, L.; Sakai, N.; Imamura, H.; Sourour, N.; Rennie, I.; Skalej, M.; Beuing, O.; Bonafe, A.; Mery, F.; Turjman, F.; Brouwer, P.; Boccardi, E.; Valvassori, L.; Derakhshani, S.; Litzenberg, M. W.; Gounis, M. J.
    BACKGROUND AND PURPOSE: Incomplete occlusion and recanalization of large and wide-neck brain aneurysms treated by endovascular therapy remains a challenge. We present preliminary clinical and angiographic results of an experimentally optimized Surpass flow diverter for treatment of intracranial aneurysms in a prospective, multicenter, nonrandomized, single-arm study.
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    The Perseus ALMA Chemical Survey (PEACHES) III. Sulfur-bearing species tracing accretion and ejection processes in young protostars
    (EDP Sciences S A, 2023) Artur de la Villarmois, Elizabeth; Guzmán Veloso, Viviana; Yang, Y. -l.; Zhang, Y.; Sakai, N.
    Context. Sulfur chemistry is poorly understood in the process of low-mass star and planet formation, where the main carriers of sulfur in both the gas and the dust phase are still unknown. Furthermore, the chemical evolution of sulfur-bearing species is not fully understood given that simple S-bearing molecules, such as SO and SO2, are commonly seen in embedded Class 0/I sources but hardly detected in more evolved Class II disks. Despite the fact that simple S-bearing molecules are usually detected toward embedded sources, large surveys of S-bearing molecules with high angular resolution and sensitive observations are currently lacking., Aims. The goal of this work is to present an unbiased survey of simple sulfur-bearing species in protostars and provide new statistics on detection rates, emitting regions, and molecular column densities. In addition, we investigate the role of S-bearing molecules in accretion processes and the connection between (non-)detection of complex organic molecules (COMs) and S-related species., Methods. We present the observations of sulfur-bearing species (CS, SO,(SO)-S-34, and SO2) that are part of the Perseus ALMA Chemical Survey (PEACHES). We analyzed a total of 50 Class 0/I sources with observations that have an average angular resolution of about 0.'' 6 (similar to 180 au) in ALMA band 6., Results. Class 0 sources show detection rates of 97% for CS, 86% for SO, 31% for(34)SO, and 44% for SO2, while Class I sources present detection rates of 71% for CS, 57% for SO, 36% for (SO)-S-34, and 43% for SO2. When (SO)-S-34 is detected, the SO/(SO)-S-34 ratio is lower than the canonical value of 22, suggesting optically thick emission, and the lowest values are found for those sources that are rich in COMs. When SO2 is detected, those sources that show CS and SO emission parallel to the outflow direction are usually very rich in COMs, while for sources where the CS and SO emission is perpendicular to the outflow direction, only a few or no COMs are detected. When CH3OH and SO2 are detected, the comparison between CH3OH and SO2 abundances shows a positive trend and CH3OH is between 10 and 100 times more abundant than SO2. The SO2 abundances toward the PEACHES sample are, on average, two orders of magnitude lower than values from the Ophiuchus star-forming region and comparable with sources in Taurus., Conclusions. The SO/(SO)-S-34 ratio seems to be a good tracer of the inner high-density envelope and it could be used in the future to infer the presence of multiple COMs. The detection of multiple COMs seems to be related to the presence of collimated outflows (seen in CS and SO emission), where a high column density of warm material is expected close to the protostar, and SO2 emission seems to trace the warm gas in those sources where CH3OH is also detected. The difference in SO2 abundances between different star-forming regions might indicate that the sulfur depletion in the gas-phase could depend on the external UV radiation toward the molecular cloud. Finally, the SO2 emission detected in different evolutionary stages seems to arise from different physical mechanisms: high column density of warm material in Class 0 sources, shocks in Class I/II, and exposure to UV radiation from the protostar in more evolved Class II disks.