Electrides as a New Platform of Topological Materials

Recent discoveries of topological phases realized in electronic states in solids have revealed an important role of topology, which ubiquitously appears in various materials in nature. Many well-known materials have turned out to be topological materials, and this new viewpoint of topology has opened a new horizon in material science. In this paper we find that electrides are suitable for achieving various topological phases, including topological insulating and topological semimetal phases. In the electrides, in which electrons serve as anions, the bands occupied by the anionic electrons lie near the Fermi level, because the anionic electrons are weakly bound by the lattice. This property of the electrides is favorable for achieving band inversions needed for topological phases, and thus the electrides are prone to topological phases. From such a point of view, we find many topological electrides, Y$_2$C (nodal-line semimetal (NLS)), Sc$_2$C (insulator with $\pi$ Zak phase), Sr$_2$Bi (NLS), HfBr (quantum spin Hall system), and LaBr (quantum anomalous Hall insulator), by using ab initio calculation. The close relationship between the electrides and the topological materials is useful in material science in both fields.Comment: 12 pages, 9 figure

Monte Carlo Calculation of Neutrons Transmitted through Matter

The neutron Monte Carlo code, CYGNUS, which is written in Fortran IV has been shown. This code can easily be used for several limitted geometries and requires considerably less computing time than O5R. In this paper, two methods of calculation are described : one by weight method and the other by collision density method, and the two techniques for determination of the anisotropic scattering angle in the center-of-mass system, i.e., Legendre expansion and Coveyou technique, and the method for determination of the excited level in the inelastic scattering are also described. The results calculated with CYGNUS code are compared with the numerical solution by PALLAS code for the sealer flux in water and graphite spheres, and with experimental spectra for the angular neutron flux in water and iron shields. The agreement obtained between the CYGNUS calculations and numerical or experimental results is good

Spacial Distribution of Photoneutrons in an Iron Slab Produced by 20-MeV Electron Bombardment

Photoneutron distribution was measured with activation of aluminum and magnesium in an iron slab bombarded by a beam of 20-MeV electrons from a linear accelerator. In order to compare with the experimental results, the spacial neutron distribution was calculated as follows : the photoneutron source distribution originating from the photonuclear reaction was calculated by an approximate analytical method ; and the neutron distribution in the medium was calculated on the basis of this distributed source by Monte Carlo code, CYGNUS. The calculated neutron distribution was in good agreement with the measured distribution, using activities of aluminum detectors. From the comparison of both saturated activities of aluminum and magnesium, it is found that the photonuclear effects are remarkable when γ is equal to 10 cm and Z is between 2 and 5 cm. The spacial distribution of neutron flux above about 6.5 MeV in the iron slab is nearly spherical symmetric around the beam incident point ; and an exponential attenuation with the slope of effective removal cross section of iron, ∑ₑffᴿ＝0.172 cm⁻¹

Implementation of muon pair production in PHITS and verification by comparing with the muon shielding experiment at SLAC

We implemented a model of muon pair production through a real photon in PHITS and compared our calculations with data of the muon shielding experiment conducted at SLAC to verify the validity of the implemented model. Our predictions of the muon fluence induced by electrons are in good agreement with the experimental data. To understand the known differences between the calculations of the muon fluence, which have been determined using other Monte-Carlo codes, we quantitatively evaluate the fluctuations in the Monte-Carlo results due to systematic errors in multiple Coulomb scattering, differences in the approximation methods and energy loss models, and whether incoherent production is considered.Comment: 16 pages, 8 figure

MPP6 stimulates both RRP6 and DIS3 to degrade a specified subset of MTR4-sensitive substrates in the human nucleus

ヒト細胞内でRNA分解時に働く因子の役割を解明 --細胞内におけるRNA分解機構の全容解明に期待--. 京都大学プレスリリース. 2022-08-05.Recent in vitro reconstitution analyses have proven that the physical interaction between the exosome core and MTR4 helicase, which promotes the exosome activity, is maintained by either MPP6 or RRP6. However, knowledge regarding the function of MPP6 with respect to in vivo exosome activity remains scarce. Here, we demonstrate a facilitative function of MPP6 that composes a specific part of MTR4-dependent substrate decay by the human exosome. Using RNA polymerase II-transcribed poly(A)⁺ substrate accumulation as an indicator of a perturbed exosome, we found functional redundancy between RRP6 and MPP6 in the decay of these poly(A)⁺ transcripts. MTR4 binding to the exosome core via MPP6 was essential for MPP6 to exert its redundancy with RRP6. However, at least for the decay of our identified exosome substrates, MTR4 recruitment by MPP6 was not functionally equivalent to recruitment by RRP6. Genome-wide classification of substrates based on their sensitivity to each exosome component revealed that MPP6 deals with a specific range of substrates and highlights the importance of MTR4 for their decay. Considering recent findings of competitive binding to the exosome between auxiliary complexes, our results suggest that the MPP6-incorporated MTR4-exosome complex is one of the multiple alternative complexes rather than the prevailing one