arXiv subjects

Hiroto Kuninaka

Publications and source records attributed to Hiroto Kuninaka.

18 recordsLinked to original sources

arXiv2016

Home-run probability as a function of the coefficient of restitution of baseballs

In baseball games, the coefficient of restitution of baseballs strongly affects the flying distance of batted balls, which determines the home-run probability. In Japan, the range of the coefficient of restitution of official baseballs has changed frequently over the past five years, causing the the number of home runs to vary drastically. We analyzed data from Japanese baseball games played in 2014 to investigate the statistical properties of pitched balls. In addition, we used the analysis results to develop a baseball-batting simulator for determining the home-run probability as a function of the coefficient of restitution. Our simulation results are explained by a simple theoretical argument.

physics.soc-ph↗

arXiv2015

Power-like Tail Observed in Weight Distributions of Schoolchildren

We investigated the statistical properties of the weight distributions of Japanese children who were born in 1996, from recent data. The weights of 16- and 17-year-old male children have a lognormal distribution with a power-like tail, which is best modeled by the double Pareto distribution. The emergence of the power-like tail may be attributed to the low probability that an obese person will attain a normal weight.

physics.soc-ph↗

arXiv2014

Multiplicative Modeling of Children's Growth and Its Statistical Properties

We develop a numerical growth model which can predict the statistical properties of the height distribution of Japanese children. Our previous studies have clarified that the height distribution of schoolchildren shows a transition from the lognormal to the normal distribution during puberty period. In this paper, we demonstrate by our simulations that the transition occurs owing to the variability of the onset of the puberty period.

physics.data-an↗

arXiv2012

Origin of rebounds with a restitution coefficient larger than unity in nanocluster collisions

We numerically investigate the mechanism of super rebounds for head-on collisions between nanoclusters in which the restitution coefficient is larger than unity. It is confirmed that the temperature and the entropy of the nanocluters decrease after the super rebounds by our molecular dynamics simulations. It is also found that the initial metastable structure plays a key role for the emergence of the super rebounds.

cond-mat.mes-hall↗

arXiv2011

Fractal Structure of Isothermal Lines and Loops on the Cosmic Microwave Background

The statistics of isothermal lines and loops of the Cosmic Microwave Background (CMB) radiation on the sky map is studied and the fractal structure is confirmed in the radiation temperature fluctuation. We estimate the fractal exponents, such as the fractal dimension $D_{\mathrm{e}}$ of the entire pattern of isothermal lines, the fractal dimension $D_{\mathrm{c}}$ of a single isothermal line, the exponent $ζ$ in Korčak's law for the size distribution of isothermal loops, the two kind of Hurst exponents, $H_{\mathrm{e}}$ for the profile of the CMB radiation temperature, and $H_{\mathrm{c}}$ for a single isothermal line. We also perform fractal analysis of two artificial sky maps simulated by a standard model in physical cosmology, the WMAP best-fit $Λ$ Cold Dark Matter ($Λ$CDM) model, and by the Gaussian free model of rough surfaces. The temperature fluctuations of the real CMB radiation and in the simulation using the $Λ$CDM model are non-Gaussian, in the sense that the displacement of isothermal lines and loops has an antipersistent property indicated by $H_{\mathrm{e}} \simeq 0.23 < 1/2$.

astro-ph.CO↗

arXiv2009

Statistical Properties of Height of Japanese Schoolchildren

We study height distributions of Japanese schoolchildren based on the statictical data which are obtained from the school health survey by the ministry of education, culture, sports, science and technology, Japan . From our analysis, it has been clarified that the distribution of height changes from the lognormal distribution to the normal distribution in the periods of puberty.

physics.soc-ph↗

arXiv2009

Simulation of cohesive head-on collisions of thermally activated nanoclusters

Impact phenomena of nanoclusters subject to thermal fluctuations are numerically investigated. From the molecular dynamics simulation for colliding two identical clusters, it is found that the restitution coefficient for head-on collisions has a peak at a colliding speed due to the competition between the cohesive interaction and the repulsive interaction of colliding clusters. Some aspects of the collisions can be understood by the theory by Brilliantov {\it et al.} (Phys. Rev. E {\bf 76}, 051302 (2007)), but many new aspects are found from the simulation. In particular, we find that there are some anomalous rebounds in which the restitution coefficient is larger than unity. The phase diagrams of rebound processes against impact speed and the cohesive parameter can be understood by a simple phenomenology.

cond-mat.stat-mech↗

arXiv2008

Why Does Zipf's Law Break Down in Rank-Size Distribution of Cities?

We study rank-size distribution of cities in Japan on the basis of data analysis. From the census data after World War II, we find that the rank-size distribution of cities is composed of two parts, each of which has independent power exponent. In addition, the power exponent of the head part of the distribution changes in time and Zipf's law holds only in a restricted period. We show that Zipf's law broke down due to both of Showa and Heisei great mergers and recovered due to population growth in middle-sized cities after the great Showa merger.

physics.data-an↗

arXiv2008

Super-elastic collisions of thermal activated nanoclusters

Impact processes of nanoclusters subject to thermal fluctuations are investigated, theoretically. In the former half of the paper, we discuss the basis of quasi-static theory. In the latter part, we carry out the molecular dynamics simulation of collisions between two identical nanoclusters, and report some statistical properties of impacts of nanoclusters.

cond-mat.stat-mech↗

arXiv2008

Super-elastic collisions in a thermally activated system

Impact phenomena of small clusters subject to thermal fluctuations are numerically investigated. From the molecular dynamics simulation for colliding two identical clusters, it is found that the restitution coefficient for head-on collisions can exceed unity when the colliding speed is smaller than the thermal velocity of one ``atom'' of the clusters. The averaged behavior can be understood by the quasi-static theory of impact phenomena. It is also confirmed that our result is governed by the fluctuation theorem.

cond-mat.stat-mech↗

arXiv2005

Contact and Quasi-Static Impact of a Dissipationless Mechanical Model

Collisions and contacts of elastic materials are numerically and theoretically investigated. Using a two-dimensional spring-mass model with defect particles under the free boundary condition, we reproduce the Hertzian contact theory at equilibrium and the quasi-static theory for low speed impacts.

cond-mat.stat-mech↗

arXiv2004

The anomalous behavior of coefficient of normal restitution in the oblique impact

The coefficient of normal restitution in an oblique impact is theoretically studied. Using a two-dimensional lattice models for an elastic disk and an elastic wall, we demonstrate that the coefficient of normal restitution can exceed one and has a peak against the incident angle in our simulation. Finally, we explain these phenomena based upon the phenomenological theory of elasticity.

cond-mat.stat-mech↗

arXiv2003

Theory of the inelastic impact of elastic materials

We have reviewed recent developments of the theory of the impact for macroscopic elastic materials. This review includes (i) standard theories for the normal impact and the oblique impact, (ii) some typical approaches to simulate impact problems, (iii) and an example of our simulation to clarify the mechanism of anomalous restitution coefficient in an oblique impact in which the restitution coefficient exceeds unity.

cond-mat.stat-mech↗

arXiv2003

The Simulation of the Inelastic Impact

The coefficient of normal restitution (COR) in an oblique impact is theoretically studied. Using a two-dimensional lattice models for an elastic disk and an elastic wall, we investigate the dependency of COR on an incident angle and demonstrate that COR can exceed one and have a peak against an incident angle in our simulation. Finally, we explain these phenomena based upon the phenomenological theory of elasticity.

cond-mat.stat-mech↗

arXiv2003

Simulation for the oblique impact of a lattice system

The oblique collision between an elastic disk and an elastic wall is numerically studied. We investigate the dependency of the tangential coefficient of restitution on the incident angle of impact. From the results of simulation, our model reproduces experimental results and can be explained by a phenomenological theory of the oblique impact.

cond-mat.mtrl-sci↗

arXiv2001

Simulation and Theory of the Impact of Two-Dimensional Elastic Disks

The impact of a two-dimensional elastic disk with a wall is numerically studied. It is clarified that the coefficient of restitution (COR) decreases with the impact velocity. The result is not consistent with the recent quasi-static theory of inelastic collisions even for very slow impact. This suggests that the elastic model cannot be used in the quasi-static limit. A new quasi-static theory of impacts is proposed, in which the effect of thermal diffusion is dominant. The abrupt decrease of COR has been found due to the plastic deformation of the disk, which is assisted by the initial internal motion. (This paper is to be published in Chemical Engineering Science.)

cond-mat.stat-mech↗

arXiv2001

The impact of two-dimensional elastic disk

cond-mat.stat-mech↗

arXiv2000

Simulation of the Impact of Two-Dimensional Elastic Disks

The impact of a two-dimensional elastic disk with a wall is numerically studied. It is clarified that the coefficient of restitution (COR) decreases with the impact velocity. The result is not consistent with the recent quasi-static theory of inelastic collisions even for very slow impact. The abrupt drop of COR has been found due to the plastic deformation of the disk, which is assisted by the initial internal motion. (to be published in Proceedings of 9 th Nisshin Engineering Particle Technology International Symposium on 'Solids Flow Mechanics and Their Applications' held at Kyoto, 7th-9th January, 2001

cond-mat.stat-mech↗