Orbital Evolution of a Circumbinary Planet in a Gaseous Disk

Sub-Jupiter classed circumbinary planets discovered in close-in binary systems have orbits just beyond the dynamically unstable region, which is determined by the eccentricity and mass ratio of the host binary stars. These planets are assumed to have formed beyond the snow line and migrated to the current orbits rather than forming in situ. We propose a scenario in which a planet formed beyond the snow line and migrated to the inner edge of the circumbinary disk, which was within the unstable area, and then moved to the current orbit through outward transportation. This outward transportation is driven by the balance of orbital excitation of the central stars inside the gravitationally unstable region and damping by the gas-drag force. We carried out N-body simulations with a dissipating circumbinary protoplanetary disk for binary systems with different eccentricities and mass ratios. Planets are more likely to achieve a stable orbit just beyond the unstable region in less eccentric binary systems. This result is not as sensitive to mass ratio as it is to eccentricity. These dependencies are consistent with the data from observed binary systems hosting circumbinary planets. We find CBPs' orbits close to the instability boundaries are explained by our orbital evolution scenario.Comment: 26 pages, 8 figures, accepted for publication in Earth, Planets and Spac

Orbital Evolution of Close-in Super-Earths Driven by Atmospheric Escape

The increasing number of super-Earths close to their host stars have revealed a scarcity of close-in small planets with 1.5–2.0 R⊕ in the radius distribution of Kepler planets. The atmospheric escape of super-Earths by photoevaporation can explain the origin of the observed “radius gap.” Many theoretical studies have considered the in situ mass loss of a close-in planet. Planets that undergo atmospheric escape, however, move outward due to the change in the orbital angular momentum of their star–planet systems. In this study, we calculate the orbital evolution of an evaporating super-Earth with a H₂/He atmosphere around FGKM-type stars under stellar X-ray and extreme-UV irradiation (XUV). The rate of increase in the orbital radius of an evaporating planet is approximately proportional to that of the atmospheric mass loss during a high stellar XUV phase. We show that super-Earths with a rocky core of ≲10 M⊕ and a H₂/He atmosphere at ≲0.03–0.1 au (≲0.01–0.03 au) around G-type stars (M-type stars) are prone to outward migration driven by photoevaporation. Although the changes in the orbits of the planets would be small, they would rearrange the orbital configurations of compact, multiplanet systems, such as the TRAPPIST-1 system. We also find that the radius gap and the so-called “Neptune desert” in the observed population of close-in planets around FGK-type stars still appear in our simulations. On the other hand, the observed planet population around M-type stars can be reproduced only by a high stellar XUV luminosity model

Fatigue Damage in Wood Under Pulsating Multiaxial-Combined Loading

A fatigue test was performed under axial-torsion combined loading, with the aim of investigating fatigue damage in wood under multiaxial stresses. This research particularly focused on the energy loss captured during fatigue tests and the fatigue limit for wood. Air-dried samples of Japanese cypress were used for the tests. An electrohydraulic servomachine that could apply axial and torsional loads simultaneously was used for the fatigue tests. An axial load was applied in the fiber direction (along L), and torque was applied around the axis in the same direction as L. A pulsating triangular axial load was applied in the longitudinal direction at 1 Hz while each specimen was also simultaneously subjected to a twisting moment at the same phase. On the basis of the experimental results of the fatigue tests, energy loss was obtained from the stress-strain curve at each loading cycle and examined precisely in relation to the number of loading cycles and combined stress states. The energy loss per cycle in the dominant stress was large and increased gradually toward fatigue failure. The stress level was so high that the energy loss per cycle was extremely large. In the relationship between cumulative energy loss and the number of loading cycles, the cumulative energy loss was so large that the fatigue life was extremely long. The cumulative energy loss for shear in the compression group was larger than that in the tension group. The mean energy loss per cycle for the fatigue limit was also presumed from the relationships between mean energy loss per cycle, stress amplitude, and fatigue life, and was estimated to be about 10 kJ/m3/cycle, as determined on the basis of the equivalent stress principle. That is, the fatigue life will be infinite when the energy loss per cycle is below 10 kJ/m3/cycle

Microenvironmental stresses induce HLA-E/Qa-1 surface expressionand thereby reduce CD8(+) T-cell recognition of stressed cells.

腫瘍微小環境ストレスがCD8+T細胞応答を介した免疫応答に与える影響に関しては知られていない. 我々は微小環境ストレス（低酸素, グルコース飢餓）により腫瘍細胞表面の非古典的MHC class Ib (Qa-1b, HLA-E)発現が上昇し, 特異的CD8+T細胞応答を低下させることを明らかにした