arXiv subjects

Y. Takada

Publications and source records attributed to Y. Takada.

9 recordsLinked to original sources

arXiv2013

Performance of a Remotely Located Muon Radiography System to Identify the Inner Structure of a Nuclear Plant

The performance of a muon radiography system designed to image the inner structure of a nuclear plant located at a distance of 64 m was evaluated. We concluded absence of the fuel in the pressure vessel during the measurement period and succeeded in profiling the fuel material placed in the storage pool. The obtained data also demonstrated the sensitivity of the system to water level changes in the reactor well and the dryer-separator pool. It is expected that the system could reconstruct a 2 m cubic fuel object easily. By operating multiple systems, typically four identical systems, viewing the reactor from different directions simultaneously, detection of a 1 m cubic object should also be achievable within a few month period.

physics.ins-det↗

arXiv2008

Towards first-principles understanding of the metal-insulator transition in fluid alkali metals

By treating the electron-ion interaction as perturbation in the first-principles Hamiltonian, we have calculated the density response functions of a fluid alkali metal to find an interesting charge instability due to anomalous electronic density fluctuations occurring at some finite wave vector ${\bi Q}$ in a dilute fluid phase above the liquid-gas critical point. Since $|{\bi Q}|$ is smaller than the diameter of the Fermi surface, this instability necessarily impedes the electric conduction, implying its close relevance to the metal-insulator transition in fluid alkali metals.

cond-mat.str-el↗

arXiv2008

Time-dependent current-density functional theory for the friction of ions in an interacting electron gas

Due to the strongly nonlocal nature of $f_{xc}({\bf r},{\bf r}',ω)$ the {\em scalar} exchange and correlation (xc) kernel of the time-dependent density-functional theory (TDDFT), the formula for Q the friction coefficient of an interacting electron gas (EG) for ions tends to give a too large value of Q for heavy ions in the medium- and low-density EG, if we adopt the local-density approximation (LDA) to $f_{xc}({\bf r},{\bf r}',ω)$, even though the formula itself is formally exact. We have rectified this unfavorable feature by reformulating the formula for Q in terms of the {\em tensorial} xc kernel of the time dependent current-density functional theory, to which the LDA can be applied without intrinsic difficulty. Our numerical results find themselves in a considerably better agreement with the experimental stopping power of Al and Au for slow ions than those previously obtained within the LDA to the TDDFT.

cond-mat.mtrl-sci↗

arXiv2007

Including nonlocality in exchange-correlation kernel from time-dependent current density functional theory: Application to the stopping power of electron liquids

We develop a scheme for building the scalar exchange-correlation (xc) kernel of time-dependent density functional theory (TDDFT) from the tensorial kernel of time-dependent {\em current} density functional theory (TDCDFT) and the Kohn-Sham current density response function. Resorting to the local approximation to the kernel of TDCDFT results in a nonlocal approximation to the kernel of TDDFT, which is free of the contradictions that plague the standard local density approximation (LDA) to TDDFT. As an application of this general scheme, we calculate the dynamical xc contribution to the stopping power of electron liquids for slow ions to find that our results are in considerably better agreement with experiment than those obtained using TDDFT in the conventional LDA.

cond-mat.mtrl-sci↗

arXiv2005

Spin polarization of light atoms in jellium: Detailed electronic structures

We revisit the problem of the spontaneous magnetization of an {\em sp} impurity atom in a simple metal host. The main features of interest are: (i) Formation of the spherical spin density/charge density wave around the impurity; (ii) Considerable decrease in the size of the pseudoatom in the spin-polarized state as compared with the paramagnetic one, and (iii) Relevance of the electron affinity of the isolated atom to this spin polarization, which is clarified by tracing the transformation of the pseudoatom into an isolated negative ion in the low-density limit of the enveloping electron gas.

cond-mat.mtrl-sci↗

arXiv2005

Time-Dependent Density-Functional Theory for the Stopping Power of an Interacting Electron Gas for Slow Ions

Based on the time-dependent density-functional theory, we have derived a rigorous formula for the stopping power of an {\it interacting} electron gas for ions in the limit of low projectile velocities. If dynamical correlation between electrons is not taken into account, this formula recovers the corresponding stopping power of {\it noninteracting} electrons in an effective Kohn-Sham potential. The correlation effect, specifically the excitonic one in electron-hole pair excitations, however, is found to considerably enhance the stopping power for intermediately charged ions, bringing our theory into good agreement with experiment.

cond-mat.mtrl-sci↗

arXiv2004

Time-dependent density-functional theory approach to nonlinear particle-solid interactions in comparison with scattering theory

An explicit expression for the quadratic density-response function of a many-electron system is obtained in the framework of the time-dependent density-functional theory, in terms of the linear and quadratic density-response functions of noninteracting Kohn-Sham electrons and functional derivatives of the time-dependent exchange-correlation potential. This is used to evaluate the quadratic stopping power of a homogeneous electron gas for slow ions, which is demonstrated to be equivalent to that obtained up to second order in the ion charge in the framework of a fully nonlinear scattering approach. Numerical calculations are reported, thereby exploring the range of validity of quadratic-response theory.

cond-mat.mtrl-sci↗

arXiv2001

Structural Phase Transition at High Temperatures in Solid Molecular Hydrogen and Deuterium

We study the effect of temperature up to 1000K on the structure of dense molecular para-hydrogen and ortho-deuterium, using the path-integral Monte Carlo method. We find a structural phase transition from orientationally disordered hexagonal close packed (hcp) to an orthorhombic structure of Cmca symmetry before melting. The transition is basically induced by thermal fluctuations, but quantum fluctuations of protons (deuterons) are important in determining the transition temperature through effectively hardening the intermolecular interaction. We estimate the phase line between hcp and Cmca phases as well as the melting line of the Cmca solid.

cond-mat.mtrl-sci↗

arXiv1998

Bloch electrons in a Jahn-Teller crystal and an orbital-density-wave state due to the Berry phase

The effect of the Berry phase is included explicitly in the wavefunction describing conduction electrons in a crystal composed of periodically arrayed Jahn-Teller centers that have conically intersecting potential energy surfaces. The Berry phase can make a drastic change in the band structure, leading generally to the formation of an orbital-density-wave state. We discuss implications of our theory and possible relations to the orbital ordering observed in the manganese perovskites.

cond-mat↗