Gas flow around a planet embedded in a protoplanetary disc: the dependence on the planetary mass

The three-dimensional structure of the gas flow around a planet is thought to influence the accretion of both gas and solid materials. In particular, the outflow in the mid-plane region may prevent the accretion of the solid materials and delay the formation of super-Earths' cores. However, it is not yet understood how the nature of the flow field and outflow speed change as a function of the planetary mass. In this study, we investigate the dependence of gas flow around a planet embedded in a protoplanetary disc on the planetary mass. Assuming an isothermal, inviscid gas disc, we perform three-dimensional hydrodynamical simulations on the spherical polar grid, which has a planet located at its centre. We find that gas enters the Bondi or Hill sphere at high latitudes and exits through the mid-plane region of the disc regardless of the assumed dimensionless planetary mass $m=R_{\rm Bondi}/H$, where $R_{\rm Bondi}$ and $H$ are the Bondi radius of the planet and disc scale height, respectively. The altitude from where gas predominantly enters the envelope varies with the planetary mass. The outflow speed can be expressed as $|u_{\rm out}|=\sqrt{3/2}mc_{\rm s}$ $(R_{\rm Bondi}\leq R_{\rm Hill})$ or $|u_{\rm out}|=\sqrt{3/2}(m/3)^{1/3} c_{\rm s}$ ($R_{\rm Bondi}\geq R_{\rm Hill}$), where $c_{\rm s}$ is the isothermal sound speed and $R_{\rm Hill}$ is the Hill radius. The outflow around a planet may reduce the accretion of dust and pebbles onto the planet when $m\gtrsim\sqrt{\rm St}$, where St is the Stokes number. Our results suggest that the flow around proto-cores of super-Earths may delay their growth and, consequently, help them to avoid runaway gas accretion within the lifetime of the gas disc.Comment: 16 pages, 14 figures, Accepted for publication in Astronomy and Astrophysics (A&A

Dust ring and gap formation by gas flow induced by low-mass planets embedded in protoplanetary disks I\rm I. Steady-state model

Recent high-spatial-resolution observations have revealed dust substructures in protoplanetary disks such as rings and gaps, which do not always correlate with gas. Because radial gas flow induced by low-mass, non-gas-gap-opening planets could affect the radial drift of dust, it potentially forms these dust substructures in disks. We investigate the potential of gas flow induced by low-mass planets to sculpt the rings and gaps in the dust profiles. We first perform three-dimensional hydrodynamical simulations, which resolve the local gas flow past a planet. We then calculate the trajectories of dust influenced by the planet-induced gas flow. Finally, we compute the steady-state dust surface density by incorporating the influences of the planet-induced gas flow into a one-dimensional dust advection-diffusion model. The outflow of the gas toward the outside of the planetary orbit inhibits the radial drift of dust, leading to dust accumulation (the dust ring). The outflow toward the inside of the planetary orbit enhances the inward drift of dust, causing dust depletion around the planetary orbit (the dust gap). Under weak turbulence ($\alpha_{\rm diff}\lesssim10^{-4}$, where $\alpha_{\rm diff}$ is the turbulence strength parameter), the gas flow induced by the planet with $\gtrsim1\,M_{\oplus}$ (Earth mass) generates the dust ring and gap in the distribution of small dust grains ($\lesssim1$ cm) with the radial extent of $\sim1\text{--}10$ times gas scale height around the planetary orbit without creating a gas gap and pressure bump. The gas flow induced by low-mass, non-gas-gap-opening planets can be considered a possible origin of the observed dust substructures in disks. Our results may be helpful to explain the disks whose dust substructures were found not to correlate with those of the gas.Comment: 25 pages, 20 figures, Accepted for publication in Astronomy and Astrophysics (A&A

Spin of protoplanets generated by pebble accretion: Influences of protoplanet-induced gas flow

We investigate the spin state of a protoplanet during the pebble accretion influenced by the gas flow in the gravitational potential of the protoplanet and how it depends on the planetary mass, the headwind speed, the distance from the host star, and the pebble size. We perform nonisothermal three-dimensional hydrodynamical simulations in a local frame to obtain the gas flow around the planet. We then numerically integrate three-dimensional orbits of pebbles under the obtained gas flow. Finally, assuming uniform spatial distribution of incoming pebbles, we calculate net spin by summing up specific angular momentum that individual pebbles transfer to the protoplanet at impacts. We find that a protoplanet with the envelope acquires prograde net spin rotation regardless of the planetary mass, the pebble size, and the headwind speed of the gas. This is because accreting pebbles are dragged by the envelope that commonly has prograde rotation. As the planetary mass or orbital radius increases, the envelope is thicker and the prograde rotation is faster, resulting in faster net prograde spin. When the dimensionless thermal mass of the planet, $m = R_{\mathrm{Bondi}} / H$, where $R_{\mathrm{Bondi}}$ and $H$ are the Bondi radius and the disk gas scale height, is larger than a certain critical mass ($m \gtrsim 0.3$ at $0.1 \, \mathrm{au}$ or $m \gtrsim 0.1$ at $1 \, \mathrm{au}$), the spin rotation exceeds the breakup one. The predicted spin frequency reaches the breakup one at the planetary mass $m_{\mathrm{iso,rot}} \sim 0.1 \, (a / 1 \, \mathrm{au})^{-1/2}$ (where $a$ is the orbital radius), suggesting that the protoplanet cannot grow beyond $m_{\mathrm{iso,rot}}$. It is consistent with the Earth's current mass and could help the formation of the Moon by a giant impact on fast-spinning proto-Earth.Comment: 14 pages, 10 figures, Accepted for publication in Astronomy and Astrophysics (A&A

Evaluation of Blood Glucose Level and Condition Measured by Emergency Life-Saving Persons before Hospital Arrival

We investigated the relationship between blood glucose level measured by emergency life-saving persons and patient’s condition.　The blood glucose measurement by emergency life-saving persons was carried out according to the prepared criteria.　Some patients, despite blood glucose levels were less than 50 mg/dl, it was recognized that disturbance of consciousness was mild.　On the contrary, patients with blood glucose levels above 50 mg/dl were sometimes admitted to moderate consciousness disturbances.　There are several problems with the current protocol, and it seems that it is necessary to instruct the emergency life-saving persons to comply with the protocol.本論文の要旨は日本麻酔科学会第65回学術集会（2018年，横浜）で発表した

Impact of Ambulation Status in Patients with End-stage Renal Disease on Hemodialysis due to Diabetic Nephropathy : The PREDICT Study

Article信州医学雑誌 68(3): 131-138(2020)journal articl

Correct Use of a Conventional Lap-and-Shoulder Seatbelt Is Safest for Pregnant Rear-Seat Passengers : Proposal for Additional Safety Measures

The objectives of this study were to assess the safety of various methods of seatbelt use and propose safety improvements to the lap-and-shoulder seatbelt for pregnant rear-seat passengers. The Maternal Anthropometric Measurement Apparatus dummy, version 2B, was used. Sled tests were performed to simulate frontal impact at a speed of 48 km/h in the right rear seat. Kinematics of the dummy were examined using high-speed video imaging, and time courses of the seatbelt loads and displacement and acceleration of the chest and pelvis were measured during impact. The kinematic parameters were compared under the following conditions: conventional lap-and-shoulder seatbelt used correctly, lap belt crossed over left and right femurs, and lap belt attached to both thighs using an extra restraint device. Then, by applying pretensioner and/or force limiter systems, the safest condition was investigated. Correct conventional seatbelt use was the most effective restraint method. When both pretensioner and force limiter were applied, the kinematic parameters were smallest, and the best restraint was achieved. The safety of rear-seat travel can be improved by using both pretensioner and force limiter systems, which would reduce the risk of chest and abdominal injuries to pregnant passengers and prevent negative fetal outcomes

Influences of protoplanet-induced three-dimensional gas flow on pebble accretion

Context. The pebble accretion model has the potential to explain the formation of various types of planets. The main difference between this and the planetesimal accretion model is that pebbles not only experience the gravitational interaction with the growing planet but also a gas drag force from the surrounding protoplanetary disk gas. Aims. A growing planet embedded in a disk induces three-dimensional (3D) gas flow, which may influence pebble accretion. However, so far the conventional pebble accretion model has only been discussed in the unperturbed (sub-)Keplerian shear flow. In this study, we investigate the influence of 3D planet-induced gas flow on pebble accretion. Methods. Assuming a nonisothermal, inviscid gas disk, we perform 3D hydrodynamical simulations on the spherical polar grid, which has a planet located at its center. We then numerically integrate the equation of motion of pebbles in 3D using hydrodynamical simulation data. Results. We find that the trajectories of pebbles in the planet-induced gas flow differ significantly from those in the unperturbed shear flow for a wide range of investigated pebble sizes (St = 10−3–100, where St is the Stokes number). The horseshoe flow and outflow of the gas alter the motion of the pebbles, which leads to a reduction of the width of the accretion window, wacc, and the accretion cross section, Aacc. On the other hand, the changes in trajectories also cause an increase in the relative velocity of pebbles to the planet, which offsets the reduction of wacc and Aacc. As a consequence, in the Stokes regime, the accretion probability of pebbles, Pacc, in the planet-induced gas flow is comparable to that in the unperturbed shear flow except when the Stokes number is small, St ~ 10−3, in 2D accretion, or when the thermal mass of the planet is small, m = 0.03, in 3D accretion. In contrast, in the Epstein regime, Pacc in the planet-induced gas flow becomes smaller than that in the shear flow in the Stokes regime in both 2D and 3D accretion, regardless of assumed St and m. Conclusions. Our results combined with the spacial variety of turbulence strength and pebble size in a disk, suggest that the 3D planet-induced gas flow may be helpful to explain the distribution of exoplanets and the architecture of the Solar System

Comparison of the Injury Mechanism between Pregnant and Non-Pregnant Women Vehicle Passengers Using Car Crash Test Dummies

This paper analyzes the kinematics and applied forces of pregnant and non-pregnant women dummies sitting in the rear seat during a frontal vehicle collision to determine differences in the features of abdominal injuries. Sled tests were conducted at 29 and 48 km/h with pregnant and non-pregnant dummies (i.e., MAMA IIB and Hybrid III). The overall kinematics of the dummy, resultant acceleration at the chest, transrational acceleration along each axis at the pelvis, and loads of the lap belt and shoulder belt were examined. The belt loads were higher for the MAMA IIB than for the Hybrid III because the MAMA IIB had a higher body mass than the Hybrid III. The differences in the lap belt loads were 1119 N at 29 km/h and 1981–2365 N at 48 km/h. Therefore, for restrained pregnant women sitting in the rear seat, stronger forces may apply to the lower abdomen during a high-velocity frontal collision. Our results suggest that for restrained pregnant women sitting in the rear seat, the severity of abdominal injuries and the risk of a negative fetal outcome depend on the collision velocity

Correct Use of a Conventional Lap-and-Shoulder Seatbelt Is Safest for Pregnant Rear-Seat Passengers: Proposal for Additional Safety Measures

The objectives of this study were to assess the safety of various methods of seatbelt use and propose safety improvements to the lap-and-shoulder seatbelt for pregnant rear-seat passengers. The Maternal Anthropometric Measurement Apparatus dummy, version 2B, was used. Sled tests were performed to simulate frontal impact at a speed of 48 km/h in the right rear seat. Kinematics of the dummy were examined using high-speed video imaging, and time courses of the seatbelt loads and displacement and acceleration of the chest and pelvis were measured during impact. The kinematic parameters were compared under the following conditions: conventional lap-and-shoulder seatbelt used correctly, lap belt crossed over left and right femurs, and lap belt attached to both thighs using an extra restraint device. Then, by applying pretensioner and/or force limiter systems, the safest condition was investigated. Correct conventional seatbelt use was the most effective restraint method. When both pretensioner and force limiter were applied, the kinematic parameters were smallest, and the best restraint was achieved. The safety of rear-seat travel can be improved by using both pretensioner and force limiter systems, which would reduce the risk of chest and abdominal injuries to pregnant passengers and prevent negative fetal outcomes