339 research outputs found
AtomREM: Non-empirical seeker of the minimum energy escape paths on many-dimensional potential landscapes without coarse graining
No full textRecently a non-empirical stochastic walker algorithm has been developed to search for the minimum-energy escape paths from the minima of the potential surface (Akashi and Nagornov, 2018; Nagornov and Akashi, 2019). This method is based on the Master equation for the distribution function of the atomic configuration which has a nature to seek the reaction path up along the valley of the potential surface. This paper introduces AtomREM (Atomistic Rare Event Manager), which is an MPI parallelized solver program package for executing this method, which yields reaction pathways in terms of the microscopic evolution of atomic positions. It is open-source and released under the GNU General Public License (GPL). A feature AtomREM interfaces with the LAMMPS Molecular Dynamics Simulator as a library of versatile potential functions for application to various systems. Examples of the applications to molecular and solid systems are presented
Illuminating the Bragg intersections as roots of Dirac nodal lines and high-order van Hove singularities
No full textWe theoretically reexamine nearly uniform electron models with weak crystalline potentials. In particular, we theorize the modulation of the plane-wave branches at linear regions where multiple Bragg planes intersect. Any such linear intersections involve three or more plane-wave branches diffracted by the periodic potential. Small inter-branch interactions can yield various crossing and anticrossing singularities with promised breakdown of the quadratic approximation, extending alongside the intersection lines. Most of the intersections run in low-symmetric paths in the Brillouin zone and therefore we cannot completely characterize their electronic states with standard band structure plotting methods. The present theory reveals a general mechanism in nearly uniform systems to induce the Dirac nodal lines and van-Hove singularities with broken quadratic band approximation in three dimensions, which may host a variety of anomalous low-energy electronic properties. We apply the theory to a recently discovered high temperature superconductor HS to interpret the enigmatic density-of-state (DOS) peaking therein. The results show how and {\it why there} the continuous saddle points--the source of the peaked DOS--emerge, as well as reveal the companion Dirac nodal lines hidden in the conduction bands.8 pages, 7 figures: Submitted; Ver2: 12 pages, 8 figures, accepted versio
From the 'Rescue of the Nation State' to the Emergence of European Spaces. EUIJ-Kansai Workshop on "New Research Horizons of the History of European Integration", May 10, 2008, Toyonaka (Osaka)
No full textThe aim of this paper is to make some contribution to the discussion on the future direction of the historical research on the European integration processes. What I intend to do here is, broadly, to link the contemporary European studies to the Historical studies, and concretely, to emphasise the transnational dimension of European integration. This exercise should be read as presenting my "wish list" to the Integration Historians
Large intrinsic spin Hall conductivity in orthorhombic tungsten
No full textIn this paper, we explored metastable phases showing large intrinsic spin Hall conductivity (SHC) in bulk tungsten (W) using a crystal structure search scheme based on an evolutionary algorithm (EA) and first-principles calculations. W has been known to have the most stable phase with the body-centered cubic (bcc) structure (α-W) and the metastable phase with a cubic Pm￣3n structure (β-W) and show the enhancement of SHC in β-W. As the results of the EA search, we obtained 15 metastable structures in addition to α-W and β-W and found that orthorhombic Fddd and Cmcm structures show larger SHC at the Fermi level. The
Fddd structure is formed by adding a fourfold helical distortion along the [110] direction to bcc and the Cmcm structure is obtained by further distortion of Fddd. Although the energies are higher by about 300,meV/atom than that of bcc, the SHC values at the Fermi level show 1710,(?/e)(Ωcm)?1 for Fddd and 1573,(?/e)(Ωcm)?1 for Cmcm, which are almost twice as large as that of α-W and exceed 1455,(?/e)(Ωcm)?1 calculated for β-W.journal articl
Lattice dielectric properties of rutile TiO2: First-principles anharmonic self-consistent phonon study
No full textWe calculate the lattice dielectric function of strongly anharmonic rutile TiO2 from ab initio anharmonic lattice dynamics methods. Since an accurate calculation of the Γ point phonons is essential for determining optical properties, we employ the modified self-consistent approach, including third-order anharmonicity as well as fourth-order anharmonicity. The resulting optical phonon frequencies and linewidths at the Γ point much better agree with experimental measurements than those from a perturbative approach. We show that the four-phonon scattering process contributes as much as the third-order anharmonic term to phonon linewidths. Furthermore, incorporating the frequency dependence of phonon linewidth reveals that experimentally known but unidentified peaks of the dielectric function are due to two-phonon process. This work emphasizes the importance of a self-consistent approach in predicting the optical properties of highly anharmonic materials.journal articl
Semiconducting electronic structure of the ferromagnetic spinel HgCr2Se4 revealed by soft-x-ray angle-resolved photoemission spectroscopy
No full textWe study the electronic structure of the ferromagnetic spinel HgCr2Se4 by soft-x-ray angle-resolved photoemission spectroscopy (SX-ARPES) and first-principles calculations. While a theoretical study has predicted that this material is a magnetic Weyl semimetal, SX-ARPES measurements give direct evidence for a semiconducting state in the ferromagnetic phase. Band calculations based on the density functional theory with hybrid functionals reproduce the experimentally determined band gap value, and the calculated band dispersion matches well with ARPES experiments. We conclude that the theoretical prediction of a Weyl semimetal state in HgCr2Se4 underestimates the band gap, and this material is a ferromagnetic semiconductor.journal articl
POT1a deficiency in mesenchymal niches perturbs B-lymphopoiesis
No full textAbstract Protection of telomeres 1a (POT1a) is a telomere binding protein. A decrease of POT1a is related to myeloid-skewed haematopoiesis with ageing, suggesting that protection of telomeres is essential to sustain multi-potency. Since mesenchymal stem cells (MSCs) are a constituent of the hematopoietic niche in bone marrow, their dysfunction is associated with haematopoietic failure. However, the importance of telomere protection in MSCs has yet to be elucidated. Here, we show that genetic deletion of POT1a in MSCs leads to intracellular accumulation of fatty acids and excessive ROS and DNA damage, resulting in impaired osteogenic-differentiation. Furthermore, MSC-specific POT1a deficient mice exhibited skeletal retardation due to reduction of IL-7 producing bone lining osteoblasts. Single-cell gene expression profiling of bone marrow from POT1a deficient mice revealed that B-lymphopoiesis was selectively impaired. These results demonstrate that bone marrow microenvironments composed of POT1a deficient MSCs fail to support B-lymphopoiesis, which may underpin age-related myeloid-bias in haematopoiesis
SimpleBounce: A simple package for the false vacuum decay
No full textWe present SimpleBounce, a C++ package for finding the bounce solution for the false vacuum decay. This package is based on a flow equation which is proposed by the author R. Sato (2020) and solves Coleman–Glaser–Martin’s reduced problem (S. R. Coleman et al. 1978): the minimization problem of the kinetic energy while fixing the potential energy. The bounce configuration is obtained by a scale transformation of the solution of this problem. For models with 1–8 scalar field(s), the bounce action can be calculated with O(0.1) % accuracy in O(0.1) s. This package is available at http://github.com/rsato64/SimpleBounce
APPLICATION OF A MARKOV PROCESS TO A MECHANICAL MODEL OF GRANULAR MATERIALS (2)
No full textIn the previous paper the author proposed a mechanical model of particulate materials as aMarkov process and explained the concepts of the potential barrier and the potential slip planewhich are introduced in the proposed model. Furthermore, the strain of particulate materialswas defined by using the change of contact angles at the contact points of particles and the dis-continuous motion of particles.In this paper the results of shearing tests obtained by the modified triaxial apparatus whichis designed and constructed, and can generate three different principal stresses are presented.The results of numerical experiments which are carried out by using the proposed model arealso presented. From both results it is shown that the proposed model can versatilely follow themechanical behaviours of particulate materials such as sands with complicated stress paths include-ing the stress reverse and repeated loading.In the previous paper the author proposed a mechanical model of particulate materials as aMarkov process and explained the concepts of the potential barrier and the potential slip planewhich are introduced in the proposed model. Furthermore, the strain of particulate materialswas defined by using the change of contact angles at the contact points of particles and the dis-continuous motion of particles.In this paper the results of shearing tests obtained by the modified triaxial apparatus whichis designed and constructed, and can generate three different principal stresses are presented.The results of numerical experiments which are carried out by using the proposed model arealso presented. From both results it is shown that the proposed model can versatilely follow themechanical behaviours of particulate materials such as sands with complicated stress paths include-ing the stress reverse and repeated loading
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