On the Complexity of Stable Fractional Hypergraph Matching

In this paper, we consider the complexity of the problem of finding a stable fractional matching in a hypergraphic preference system. Aharoni and Fleiner proved that there exists a stable fractional matching in every hypergraphic preference system. Furthermore, Kintali, Poplawski, Rajaraman, Sundaram, and Teng proved that the problem of finding a stable fractional matching in a hypergraphic preference system is PPAD-complete. In this paper, we consider the complexity of the problem of finding a stable fractional matching in a hypergraphic preference system whose maximum degree is bounded by some constant. The proof by Kintali, Poplawski, Rajaraman, Sundaram, and Teng implies the PPAD-completeness of the problem of finding a stable fractional matching in a hypergraphic preference system whose maximum degree is 5. In this paper, we prove that (i) this problem is PPAD-complete even if the maximum degree is 3, and (ii) if the maximum degree is 2, then this problem can be solved in polynomial time. Furthermore, we prove that the problem of finding an approximate stable fractional matching in a hypergraphic preference system is PPAD-complete

Investigating the Chemical Ordering in Quaternary Clathrate Ba8AlxGa16- xGe30

Recently, there has been an increased interest in quaternary clathrate systems as promising thermoelectric materials. Because of their increased complexity, however, the chemical ordering in the host framework of quaternary clathrates has not yet been comprehensively analyzed. Here, we have synthesized a prototypical quaternary type-I clathrate Ba8AlxGa16-xGe30 by Czochralski and flux methods, and we employed a combination of X-ray and neutron diffraction along with atomic scale simulations to investigate chemical ordering in this material. We show that the site occupancy factors of trivalent elements at the 6c site differ, depending on the synthesis method, which can be attributed to the level of equilibration. The flux-grown samples are consistent with the simulated high-temperature disordered configuration, while the degree of ordering for the Czochralski sample lies between the ground state and the high-temperature state. Moreover, we demonstrate that the atomic displacement parameters of the Ba atoms in the larger tetrakaidecahedral cages are related to chemical ordering. Specifically, Ba atoms are either displaced toward the periphery or localized at the cage centers. Consequently, this study reveals key relationships between the chemical ordering in the quaternary clathrates Ba8AlxGa16-xGe30 and the structural properties, thereby offering new perspectives on designing these materials and optimizing their thermoelectric properties

Activity of Hokkaido University Neutron Source, HUNS

AbstractHokkaido University neutron source, HUNS was completed in 1973, and has been used actively for developments of moderators, neutron instruments, neutron devices and new methods for 40 years although its power is not so high. Recently, a pulsed neutron imaging method has been developed and a new type of small angle neutron scattering method has been also developed. The pulsed neutron imaging is a unique method that can give the physical quantities such as crystallographic quantities of materials over wide area of the real space. So far, the small angle neutron scattering (SANS) is considered to be impossible at a neutron source with a power of HUNS. However, mini focusing SANS (mfSANS) was developed and proved to be useful. Here, we present the present activities on the pulsed neutron imaging and mfSANS at HUNS

Anion ordering enables fast H¯ conduction at low temperatures

H¯イオンの低温高速伝導を実現. 京都大学プレスリリース. 2021-06-03.Bringing order to hydrogen energy devices. 京都大学プレスリリース. 2021-06-03.The introduction of chemical disorder by substitutional chemistry into ionic conductors is the most commonly used strategy to stabilize high-symmetric phases while maintaining ionic conductivity at lower temperatures. In recent years, hydride materials have received much attention owing to their potential for new energy applications, but there remains room for development in ionic conductivity below 300°C. Here, we show that layered anion-ordered Ba2−δH3−2δX (X = Cl, Br, and I) exhibit a remarkable conductivity, reaching 1 mS cm⁻¹ at 200°C, with low activation barriers allowing H⁻ conduction even at room temperature. In contrast to structurally related BaH2 (i.e., Ba2H4), the layered anion order in Ba2−δH3−2δX, along with Schottky defects, likely suppresses a structural transition, rather than the traditional chemical disorder, while retaining a highly symmetric hexagonal lattice. This discovery could open a new direction in electrochemical use of hydrogen in synthetic processes and energy devices

First Imaging Experiment of a Lithium Ion Battery by a Pulsed Neutron Beam at J-PARC/MLF/BL09

AbstractWe obtain the transmission image of a commercial lithium ion (Li-ion) battery using a pulsed neutron beam at the beamline 09 of the Materials and Life Science Experimental Facility at the Japan Proton Accelerator Research Complex. The purpose of this study is to improve the performance of the Li-ion battery by nondestructive observation of its charging and discharging. The transmission images for three charge states (3.2V, 3.7V, and 4.2V) reveal differences between these three states, which we attribute to electrolyte migration. The transmission spectra show Bragg edges originating from the electrodes, current collectors, and battery vessel. Although the battery as a whole has the expected relation between the charge accumulation and the quantity of lithium amounts in the positive and negative electrodes, a portion of the battery deviates from this relation, which may imply a position dependent charging in the battery

In-plane anisotropy of the single-qq and multiple-qq ordered phases in the antiferromagnetic metal CeRh2_2Si2_2 unveiled by the bulk measurements under uniaxial stress and neutron scattering

We performed magnetization, resistivity, and neutron diffraction measurements under uniaxial stress applied along [1-10] direction on the tetragonal magnet CeRh$_2$Si$_2$ with commensurate magnetic orders. CeRh$_2$Si$_2$ has two successive antiferromagnetic (AF) orders in zero magnetic field. The high temperature phase (AF1 phase) has the magnetic modulation wave vector of $q = (\frac{1}{2}, \frac{1}{2}, 0)$, and the low temperature phase (AF2 phase) is characterized by the four $q$-vectors of $q = (\frac{1}{2}, \frac{1}{2}, 0), (\frac{1}{2}, -\frac{1}{2}, 0), (\frac{1}{2}, \frac{1}{2}, \frac{1}{2})$, and $(\frac{1}{2}, -\frac{1}{2}, \frac{1}{2})$. By measuring the uniaxial stress dependence of the magnetization, resistivity and the intensities of magnetic Bragg reflections, we confirmed that the AF1 phase has the single-$q$ magnetic order with two-fold rotational symmetry and the AF2 phase has the multi-$q$ magnetic order with four-fold rotational symmetry. In order to understand the origin of multi-$q$ order of CeRh$_2$Si$_2$, we also performed inelastic neutron scattering measurement on the single crystal samples. We found a magnetic excitation at the transfer energy $\hbar \omega \sim$ 8 meV. By applying the linear spin-wave theory, we found that the nearest and the next-nearest neighbor exchange interactions on the $ab$-plane, $J_1$ and $J_2$, are dominant in the AF2 phase. However, the $J_1$-$J_2$ model cannot lift the degeneracy between the single-$q$ (AF1) and multi-$q$ (AF2) phases. We suggest that it can be lifted by taking into account the biquadratic interaction derived from the perturbative expansion for the Kondo lattice Hamiltonian. [S. Hayami et al., Phys. Rev. B 95, 224424 (2017).Comment: 7 pages, 7 figure

General tendencies of stable isotopes and major chemical constituents of the Dome Fuji deep ice core (scientific paper)

Stable isotope compositions of water and major chemical constituents of the Dome Fuji ice core are analyzed and the data sets over the entire depth of the 2503-m core are presented in appropriate time resolution as consecutive series of average value in definite terms. These results based on the first stage analyses allow a temporal climatic dividing of the three glacial-interglacial cycles present in the records. A Comparison of the climatic and environmental characteristics of these climate stages is presented

Doping Dependence of Spin-Lattice Coupling and Two-Dimensional Ordering in Multiferroic Hexagonal Y₁₋ₓLuₓMnO₃ (0 ≤ x ≤ 1)

We have examined a complete phase diagram of Y1-x Lu xMnO3 with 0≤x≤1 by using bulk measurements and neutron-diffraction studies. With increasing Lu concentration, Curie-Weiss temperature and Neel temperature are found to increase continuously while the two-dimensional nature of short-range magnetic correlation persists even in the paramagnetic phase throughout the entire doping range. At the same time, the lattice constants and the unit-cell volume get contracted with Lu doping, i.e., chemical pressure effect. This decrease in the lattice constants and the unit-cell volume then leads naturally to an increased magnetic exchange interaction as found in our local spin-density approximation band calculations. We also discover that there is strong correlation in the temperature dependence of a volume anomaly at TN and the magnetic moments