arXiv subjects

Atsushi Ito

Publications and source records attributed to Atsushi Ito.

48 records · Page 3Linked to original sources

arXiv2014

Gauss maps of toric varieties

We investigate Gauss maps of (not necessarily normal) projective toric varieties over an algebraically closed field of arbitrary characteristic. The main results are as follows: (1) The structure of the Gauss map of a toric variety is described in terms of combinatorics in any characteristic. (2) We give a developability criterion in the toric case. In particular, we show that any toric variety whose Gauss map is degenerate must be the join of some toric varieties in characteristic zero. (3) As applications, we provide two constructions of toric varieties whose Gauss maps have some given data (e.g., fibers, images) in positive characteristic.

math.AG↗

arXiv2013

Okounkov bodies and Seshadri constants

Okounkov bodies, which are closed convex sets defined for big line bundles, have rich information on the line bundles. On the other hand, Seshadri constants are invariants which measure the positivity of line bundles. In this paper, we prove that Okounkov bodies give lower bounds of Seshadri constants.

math.AG↗

arXiv2013

Seshadri constants via toric degenerations

We give a method to estimate Seshadri constants on toric varieties at any point. By using the estimations and toric degenerations, we can obtain some new computations or estimations of Seshadri constants on non-toric varieties. In particular, we investigate Seshadri constants on hypersurfaces in projective spaces and Fano 3-folds with Picard number one in detail.

math.AG↗

arXiv2013

Seshadri constants and degrees of defining polynomials

In this paper, we study a relation between Seshadri constants and degrees of defining polynomials. In particular, we compute the Seshadri constants on Fano varieties obtained as complete intersections in rational homogeneous spaces of Picard number one.

math.AG↗

arXiv2009

Incident angle dependence of reactions between graphene and hydrogen atom by molecular dynamics simulation

Incident angle dependence of reactions between graphene and hydrogen atoms are obtained qualitatively by classical molecular dynamics simulation under the NVE condition with modified Brenner reactive empirical bond order (REBO) potential. Chemical reaction depends on two parameters, i.e., polar angle $θ$ and azimuthal angle $ϕ$ of the incident hydrogen. From the simulation results, it is found that the reaction rates strongly depend on polar angle $θ$. Reflection rate becomes larger with increasing $θ$, and the $θ$ dependence of adsorption rate is also found. The $θ$ dependence is caused by three dimensional structure of the small potential barrier which covers adsorption sites. $ϕ$ dependence of penetration rate is also found for large $θ$.

physics.plasm-ph↗

arXiv2008

Energy Current with Multi--body Interaction using Dirac Delta Function

Energy density and energy flux was introduced along Takesue's method. Particle energies were localized at particle positions using Dirac delta function. The energy density was connected with the energy flux by continuity equation. New method was proposed to deal with multi--body interaction. Consequently, the energy current between particles could be calculated even if the multi--body interaction appeared. Moreover, An application to the molecular dynamics simulation of hydrogen adsorption on a graphene with modified Brenner reactive empirical bond order potential was demonstrated.

cond-mat.stat-mech↗

arXiv2007

Molecular Dynamics Simulation of Plasma Surface Interaction

New interlayer intermolecular potential model was proposed and it represented ``ABAB'' staking of graphite. Hydrogen atom sputtering on graphite surface was investigated using molecular dynamics simulation. In the initial short time period, maintaining the flat structure of graphenes, hydrogen atoms brought about the difference interaction process in each incident energy. The first graphene often adsorbed 5 eV hydrogen atoms and reflected almost all of 15 eV hydrogen atoms. The hydrogen atoms which were injected at 30 eV penetrated into the inside of the graphite surface and were adsorbed between interlayer. The desorption of C2H2 on the clear graphite surface was observed in only the case incident at 5 eV. The animation of the MD simulation and radial distribution function indicated that the graphenes were peeled off one by one at regular interval. In common to the incident energy, the yielded molecules often had chain structures terminated by hydrogen atoms. The erosion yield increased compared with the case of no interlayer intermolecular force.

cond-mat.mtrl-sci↗

arXiv2007

Hydrogen Adsorption of Back Side of Graphene

We studied the interaction between a single hydrogen atom and a single graphene using classical molecular dynamics simulation with modified Brenner REBO potential. Three interactions, which are adsorption, reflection, penetration, were observed. Overhang structure appears and creates an adsorption site on the backside of the graphene. It is considered that backside adsorption occurs under the two conditions that an incident hydrogen atom should have incident energy which is larger than the potential barrier of a hexagonal hole of the graphene and that after the hydrogen atom passes through the graphene, it does not keep its kinetic energy to be trapped by the adsorption site. The conditions explained that as the incident energy increased, the incident point of the backside adsorption shifted to the periphery of a hexagonal hole of the graphene in the simulation. Moreover, when a hexagonal hole of the graphene was expanded by the hydrogen atom incidence to the periphery of the hexagonal hole, its potential barrier was reduced.

cond-mat.mtrl-sci↗

arXiv2007

Molecular Dynamics Simulation of the Hydrogen Isotope Sputtering of Graphite

We used a molecular dynamics simulation with the modified Brenner reactive empirical bond order potential to investigate the erosion of a graphite surface due to the incidence of hydrogen, deuterium, and tritium atoms. Incident particles cause pressure on the graphite surface, and the chemical bond between graphene layers then generates heat to erode the graphite surface. We evaluated the speed of surface destruction by calculating the pseudo-radial distribution function. The speed of surface destruction due to incident hydrogen isotopes was higher than that due to hydrogen atoms. The surface destruction increased exponentially and its decay time constant was a power function of the incident energy. We measured the erosion yield, which indicated a steady state for the graphite erosion. The erosion yield flux in the steady state increased linearly with the incident energy. The erosion yield flux was almost independent of the type of incident particle, and the erosion yield start time was smaller for hydrogen isotopes than for hydrogen atoms.

cond-mat.mtrl-sci↗

arXiv2007

Chemical Reaction between Single Hydrogen Atom and Graphene

We study chemical reaction between a single hydrogen atom and a graphene, which is the elemental reaction between hydrogen and graphitic carbon materials. In the present work, classical molecular dynamics simulation is used with modified Brenner's empirical bond order potential. The three reactions, that is, absorption reaction, reflection reaction and penetration reaction, are observed in our simulation. Reaction rates depend on the incident energy of the hydrogen atom and the graphene temperature. The dependence can be explained by the following mechanisms: (1) The hydrogen atom receives repulsive force by pi-electrons in addition to nuclear repulsion. (2) Absorbing the hydrogen atom, the graphene transforms its structure to the ``overhang'' configuration such as sp-3 state. (3) The hexagonal hole of the graphene is expanded during the penetration of the hydrogen atom.

cond-mat.other↗

arXiv2006

Microscopic Energy Current Field with Multi--body Force in Hamiltonian System

Microscopic energy current can be derived from microscopic energy field localized only in particle positions. If the energy current is applied to classical molecular dynamics, it is expected to become a new information. However, multi-body force except two-body force causes obscurity when multi-body interaction energy is localized. In the present study, our new method enables to determine the localization of the multi--body interaction energy. We obtain the energy current between particles by the law of the multi--body force corresponding to Newton's third law on two--body force.

cond-mat.stat-mech↗

arXiv2006

Molecular Dynamics Simulation of Sputtering Process of Hydrogen and Graphene Sheets

To clarify the yielding mechanism of small hydrocarbon molecules in chemical sputtering between hydrogen and graphene sheets, we made classical molecular dynamics simulation with modified Brenner's REBO potential which we proposed to deal with chemical reaction. As the simulation model, we prepared more realistic physical system, which is composed of 160 incident hydrogen atoms and ten graphene multilayers, than our previous model. From the present work, we found the following fact: breaking the covalent bonds between carbon atoms by hydrogen does not play an important role during destruction process of graphene structure, but momentum transfer from incident hydrogen to graphene causes to destroy graphene structure. Moreover, it is found that almost all fragments of graphene sheets form chain-shaped molecules, and that yielded hydrocarbon molecules are composed of carbon chain and single hydrogen-atom.

cond-mat.mtrl-sci↗