The Giant Impact Simulations with Density Independent Smoothed Particle Hydrodynamics

At present, the giant impact (GI) is the most widely accepted model for the origin of the Moon. Most of the numerical simulations of GI have been carried out with the smoothed particle hydrodynamics (SPH) method. Recently, however, it has been pointed out that standard formulation of SPH (SSPH) has difficulties in the treatment of a contact discontinuity such as a core-mantle boundary and a free surface such as a planetary surface. This difficulty comes from the assumption of differentiability of density in SSPH. We have developed an alternative formulation of SPH, density independent SPH (DISPH), which is based on differentiability of pressure instead of density to solve the problem of a contact discontinuity. In this paper, we report the results of the GI simulations with DISPH and compare them with those obtained with SSPH. We found that the disk properties, such as mass and angular momentum produced by DISPH is different from that of SSPH. In general, the disks formed by DISPH are more compact: while formation of a smaller mass moon for low-oblique impacts is expected with DISPH, inhibition of ejection would promote formation of a larger mass moon for high-oblique impacts. Since only the improvement of core-mantle boundary significantly affects the properties of circumplanetary disks generated by GI and DISPH has not been significantly improved from SSPH for a free surface, we should be very careful when some conclusions are drawn from the numerical simulations for GI. And it is necessary to develop the numerical hydrodynamical scheme for GI that can properly treat the free surface as well as the contact discontinuity.Comment: Accepted for publication in Icaru

On the Interaction between a Protoplanetary Disk and a Planet in an Eccentric Orbit: Application of Dynamical Friction

We present a new analytic approach to the disk-planet interaction that is especially useful for planets with eccentricity larger than the disk aspect ratio. We make use of the dynamical friction formula to calculate the force exerted on the planet by the disk, and the force is averaged over the period of the planet. The resulting migration and eccentricity damping timescale agrees very well with the previous works in which the planet eccentricity is moderately larger than the disk aspect ratio. The advantage of this approach is that it is possible to apply this formulation to arbitrary large eccentricity. We have found that the timescale of the orbital evolution depends largely on the adopted disk model in the case of highly eccentric planets. We discuss the possible implication of our results to the theory of planet formation.Comment: 27 pages, 11 figures, 2 tables, ApJ accepte

THE INFLUENCE OF WALKING SPEED ON SYMMETRY FOR TEMPORAL-SPATIAL AND GRF PARAMETERS IN BACKWARD WALKING

In general, changes in walking speed are known to influence many biomechanical characteristics of human locomotion. Backward walking (BW) is one of the unique strategies of human locomotion, but there is a little information in BW. The purpose of this study was to investigate whether or not walking speed influences on symmetry for temporal-spatial parameters and GRF in BW. Ten healthy subjects were asked to walk on a walk-way with force platform at three times on three speed conditions. The influence of walking speed on temporal-spatial parameters and GRF parameters were founded, and some gait parameters showed asymmetry. And also .the calculated SI were showing asymmetry, so the characteristics of backward walking would be influenced walking speed and have possibility of exist some asymmetrical movements in lower leg

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

A new and simple prescription for planet orbital migration and eccentricity damping by planet-disc interactions based on dynamical friction

During planet formation gravitational interaction between a planetary embryo and the protoplanetary gas disc causes orbital migration of the planetary embryo, which plays an important role in shaping the final planetary system. While migration sometimes occurs in the supersonic regime, wherein the relative velocity between the planetary embryo and the gas is higher than the sound speed, migration prescriptions proposed thus far describing the planet-disc interaction force and the timescales of orbital change in the supersonic regime are inconsistent with one another. Here we discuss the details of existing prescriptions in the literature and derive a new simple and intuitive formulation for planet-disc interactions based on dynamical friction that can be applied in both supersonic and subsonic cases. While the existing prescriptions assume particular disc models, ours include the explicit dependence on the disc parameters; hence it can be applied to discs with any radial surface density and temperature dependence (except for the local variations with radial scales less than the disc scale height). Our prescription will reduce the uncertainty originating from different literature formulations of planet migration and will be an important tool to study planet accretion processes, especially when studying the formation of close-in low-mass planets that are commonly found in exoplanetary systems.Comment: 10 pages, 1 figure, accepted for publication in MNRAS; typos corrected, the reference list was complete

Slowing Down Type II Migration of Gas Giants to Match Observational Data

The mass and semimajor axis distribution of gas giants in exoplanetary systems obtained by radial velocity surveys shows that super-jupiter-mass planets are piled up at > 1 au, while jupiter/sub-jupiter-mass planets are broadly distributed from ~0.03 au to beyond 1 au. This feature has not been explained by theoretical predictions. In order to reconcile this inconsistency, we investigate evolution of gas giants with a new type II migration formula by Kanagawa et al. (2018), by comparing the migration, growth timescales of gas giants, and disk lifetime and by population synthesis simulation. While the classical migration model assumes that a gas giant opens up a clear gap in the protoplanetary disk and the planet migration tied to the disk gas accretion, recent high-resolution simulations show that the migration of gap-opening planets is decoupled from the disk gas accretion and Kanagawa et al. (2018) proposed that type II migration speed is no other than type I migration speed with the reduced disk gas surface density in the gap. We show that with this new formula, type II migration is significantly reduced for super-jupiter-mass planets, if the disk accretion is driven by the disk wind as suggested by recent MHD simulations. Population synthesis simulations show that super-jupiter-mass planets remain at > 1 au without any additional ingredient such as disk photoevaporation. Therefore, the mystery of the pile-up of gas giants at > 1 au would be theoretically solved, if the new formula is confirmed and wind-driven disk accretion dominates.Comment: Accepted for publication in ApJ; the typos in Eq.(31) were correcte

Schwarzschild-De Sitter black holes in 4+1 dimensional bulk

We construct a static solution for 4+1 dimensional bulk such that the 3+1 dimensional world has a linear warp factor and describes the Schwarzschild-dS_{4} black hole. For m=0 this four dimensional universe and Friedmann Robertson Walker universe are related with an explicit coordinate transformation. We emphasize that for linear warp factors the effect of bulk on the brane world shows up as the dS_{4} background which is favored by the big bang cosmology.Comment: 6 page

BIOMECHANICAL CONSIDERATIONS OF CMJ AND SQJ ON THE SAFETY MAT

The purpose of this study was to detect whether differences exist concerning the kinematic parameters of jump (SQJ and CMJ) on two different surfaces (RS and SS). Nine healthy students performed two jumps on two surfaces. Two factor repeated measure (ANOVA) was used for statistical analysis (

Performance measures of alcohol-induced impairment: Towards a practical ignition-interlock system for motor vehicles

金沢大学大学院自然科学研究科Performance-based alcohol screening devices may help reduce road traffic accidents, but there is a shortage of easy-to-use performance tests available. To address this issue, four recently developed rapid, computerized, easily implementable performance tests, Spiral for iPhone and Spiral for Mac (psycho-motor tests), and the Modified Mental Rotation and Catch the Rabbit tests (cognitive tests), were assessed, testing participants at predrink baseline and then during three progressive amounts of alcohol intake. Analyses showed all tests were performed statistically significantly less accurately at 0.11% blood alcohol concentrations (BACs) than at 0.00% BAC, as were all tests except Spiral for iPhone at 0.06% BAC. These results indicate the suitability of all of these tests for measuring alcohol-induced impairment, and some potential for use as a practical performance-based alcohol screening device. © Perceptual and Motor Skills 2009

Accretion Rates of Planetesimals by Protoplanets Embedded in Nebular Gas

When protoplanets growing by accretion of planetesimals have atmospheres, small planetesimals approaching the protoplanets lose their energy by gas drag from the atmospheres, which leads them to be captured within the Hill sphere of the protoplanets. As a result, growth rates of the protoplanets are enhanced. In order to study the effect of an atmosphere on planetary growth rates, we performed numerical integration of orbits of planetesimals for a wide range of orbital elements and obtained the effective accretion rates of planetesimals onto planets that have atmospheres. Numerical results are obtained as a function of planetesimals' eccentricity, inclination, planet's radius, and non-dimensional gas-drag parameters which can be expressed by several physical quantities such as the radius of planetesimals and the mass of the protoplanet. Assuming that the radial distribution of the gas density near the surface can be approximated by a power-law, we performed analytic calculation for the loss of planetesimals' kinetic energy due to gas drag, and confirmed agreement with numerical results. We confirmed that the above approximation of the power-law density distribution is reasonable for accretion rate of protoplanets with one to ten Earth-masses, unless the size of planetesimals is too small. We also calculated the accretion rates of planetesimals averaged over a Rayleigh distribution of eccentricities and inclinations, and derived a semi-analytical formula of accretion rates, which reproduces the numerical results very well. Using the obtained expression of the accretion rate, we examined the growth of protoplanets in nebular gas. We found that the effect of atmospheric gas drag can enhance the growth rate significantly, depending on the size of planetesimals.Comment: 41 pages, 14 figures, accepted for publication in Icaru