Impact of photoevaporative mass loss on masses and radii of water-rich sub/super-Earths

Recent progress in transit photometry opened a new window to the interior of super-Earths. From measured radii and masses, we can infer planetary internal compositions. It has been recently revealed that super-Earths are diverse in composition. Such a diversity is thought to arise from diversity in volatile content. The stability of the volatile components is to be examined, because hot super-Earths undergo photo-evaporative mass loss. While several studies investigated the impact of photo-evaporative mass loss on hydrogen-helium envelopes, there are few studies as to the impact on water-vapor envelopes. To obtain theoretical prediction to future observations, we also investigate the relationships among masses, radii, and semimajor axes of water-rich sub/super-Earths that have undergone photo-evaporative mass loss. We simulate the interior structure and evolution of sub/super-Earths that consist of a rocky core surrounded by a water envelope, including mass loss due to the stellar XUV-driven energy-limited hydrodynamic escape. We find that the photo-evaporative mass loss has a significant impact on the evolution of hot sub/super-Earths. We then derive the threshold planetary mass and radius below which the planet loses its water envelope completely as a function of the initial water content, and find that there are minimums of the threshold mass and radius. We constrain the domain in the parameter space of planetary mass, radius, and semimajor axis in which sub/super-Earths never retain water envelopes in 1-10 Gyr. This would provide an essential piece of information for understanding the origin of close-in low-mass planets. The current uncertainties in stellar XUV flux and its heating efficiency, however, prevent us from deriving robust conclusions. Nevertheless, it seems to be a robust conclusion that Kepler planet candidates contain a significant number of rocky sub/super-Earths.Comment: 13 pages, 14 figures, accepted for publication in Astronomy & Astrophysic

Giant Impact Events for Protoplanets: Energetics of Atmospheric Erosion by Head-on Collision

Numerous exoplanets with masses ranging from Earth to Neptune and radii larger than Earth have been found through observations. These planets possess atmospheres that range in mass fractions from 1% to 30%, reflecting the diversity of atmospheric mass fractions. Such diversities are supposed to be caused by differences in the formation processes or evolution. Here we consider head-on giant impacts onto planets causing atmosphere losses in the later stage of their formation. We perform smoothed particle hydrodynamic simulations to study the impact-induced atmosphere loss of young super-Earths with 10%-30% initial atmospheric mass fractions. We find that the kinetic energy of the escaping atmosphere is almost proportional to the sum of the kinetic impact energy and self-gravitational energy released from the merged core. We derive the relationship between the kinetic impact energy and the escaping atmosphere mass. The giant impact events for planets of comparable masses are required in the final stage of the popular scenario of rocky planet formation. We show it results in a significant loss of the atmosphere, if the impact is a head-on collision with comparable masses. This latter fact provides a constraint on the formation scenario of rocky planets with substantial atmospheres.Comment: 29 pages, 27 figures, accepted for publication in Ap

太陽系および太陽系外における巨大氷惑星の進化

学位の種別: 課程博士審査委員会委員 : （主査）東京大学准教授 関根 康人, 北海道大学教授 倉本 圭, 東京大学教授 田近 英一, 東京工業大学教授 中本 泰史, 東京大学准教授 生駒 大洋University of Tokyo(東京大学

Digital transfer of the subgingival contour and emergence profile of the provisional restoration to the final bone-anchored fixed restoration

PURPOSE: This report was written to introduce an attempt at clinical application of our newly developed digital workflow to reproduce the morphology of the subgingival contour and the emergence profile of the provisional restoration within the final bone-anchored fixed restoration, using a bounded unilateral edentulous case. METHODS: This digital workflow involves superimposition of the composite images of two specific types of working casts onto the working cast for the provisional restoration namely, a split cast screwed with a titanium base and a split cast screwed with a provisional restoration and integrating these with the whole intraoral surface image, in which the provisional restoration was present. The final restoration fabricated using this technique could be installed without any clinical problems. The results of in silico analysis revealed that the cubic volume ratio of the total discrepancy between the provisional and the final restorations was only 2.4%. Further, sufficient oral hygiene was maintained and the patient was satisfied with the outcome of the treatment. CONCLUSIONS: This technical report suggests that our newly developed digital workflow provided clinical applicability and may enable accurate transfer of the morphology of the subgingival contour and emergence profile of the provisional to the final bone-anchored fixed restoration

Kaplan–Meier survival analysis and Cox regression analyses regarding right ventricular septal pacing: Data from Japanese pacemaker cohort

AbstractThe presented data were obtained from 982 consecutive patients receiving their first pacemaker implantation with right ventricular (RV) lead placement between January 2008 and December 2013 at two centers in Japan. Patients were divided into RV apical and septal pacing groups. Data of Kaplan–Meier survival analysis and Cox regression analysis are presented. Refer to the research article “Implications of right ventricular septal pacing for medium-term prognosis: propensity-matched analysis” (Mizukami et al., in press) [1] for further interpretation and discussion