Journal of the Physical Society of Japan
Online ISSN : 1347-4073
Print ISSN : 0031-9015
ISSN-L : 0031-9015
Volume 77, Issue 6
Displaying 1-47 of 47 articles from this issue
  • Kiyofumi Nitta, Yusuke Omori, Daisuke Kikuchi, Takafumi Miyanaga, Kats ...
    2008 Volume 77 Issue 6 Pages 063601
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    Extended X-ray absorption fine structure (EXAFS) measurements have been carried out on ROs4Sb12 (R = La, Ce, Pr, Nd, Sm) to study the motion of rare earth ions accommodated in the Sb icosahedron cage. The temperature dependences of the thermal (Debye–Waller) factors were analyzed from 15 to 300 K. The Einstein temperature obtained from EXAFS analysis of SmOs4Sb12 is the lowest of the compounds, while there are no significant differences among the other compounds. The local static disorder obtained from the temperature dependence of EXAFS shows good correlation with the space inside the Sb icosahedron cage. Effective static distortion is expected to occur when the cage space is larger than about 0.5 Å.
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  • Atsurou Sakurai, Masahiro Matsumura, Harukazu Kato, Takashi Nishioka, ...
    2008 Volume 77 Issue 6 Pages 063701
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    121Sb Knight shift K measurement has been carried out by applying a perturbing field to the nuclear quadrupole resonance (NQR) spectrum in alkaline-earth filled skutterudites AFe4Sb12 (A = Ca and Sr), which are close to ferromagnetic instability. The hyperfine coupling constant was determined for the first time as −14.9 kOe/μB f.u. from the K–χ plot. This relatively large value suggests a strong Fe–Sb covalent bonding. The intrinsic spin susceptibility χspin derived from K markedly decreases at low temperatures after Curie–Weiss-like increase at high temperatures, which seems to be responsible for the absence of ferromagnetic order. Using the T-dependence of χspin, the unusual gap-like suppression of nuclear spin–lattice relaxation rate divided by temperature 1⁄T1T in our previous report is reasonably explained by assuming the spin dependent-term to be proportional to χspin and the gap-like suppression of the spin-independent term.
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  • Ryusuke Kondo, Jun Otsuji, Seiichi Kagoshima, Yoshio Nogami
    2008 Volume 77 Issue 6 Pages 063702
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    We investigate the low-temperature electronic phase of a two-dimensional organic conductor, β″-(BEDT-TTF)2CsCd(SCN)4 [where BEDT-TTF denotes bis(ethylenedithio)tetrathiafulvalene], which has a large hump between 32 and around 5 K in the temperature dependence of the interlayer resistance. We present experimental results for the temperature dependence of the resistance under magnetic fields and its Kohler plots, and an x-ray diffraction study. We find that I) Kohler’s rule is strongly violated below 32 K, although the rule is valid above 32 K, and II) weak superlattice spots appear at 15.6 K in the x-ray study. On the basis of the experimental results, we suggest that the origin of the resistance hump is the formation of a possible charge density wave transition at about 32 K by the nesting of a pair of large one-dimensional Fermi surfaces obtained in the electronic structure calculation based on the crystal structure at room temperature.
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  • Yoshiaki Kobayashi, Taketo Moyoshi, Mai Yokoi, Masatoshi Sato
    2008 Volume 77 Issue 6 Pages 063703
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    In the temperature (T)–νQ3 phase diagram of NaxCoO2·yH2O, there exist two superconducting regions of νQ3 separated by the nonsuperconducting region, where νQ3 is usually estimated from the peak position of the 59Co-NQR spectra of the ±5⁄2↔±7⁄2 transition and well-approximated here as νQ3≅3νQ, νQ being the interaction energy between the nuclear quadrupole moment and the electric field gradient. We have carried out measurements of the 59Co-NMR Knight shift (K) for a single crystal in the higher-νQ3 superconducting phase and found that K begins to decrease with decreasing T at Tc for both magnetic field directions parallel and perpendicular to CoO2-planes. The result indicates together with the previous ones that the superconducting pairs are in the spin-singlet state in both phases, excluding the possibility of the spin-triplet superconductivity in this phase diagram. The superconductivity of this system spreads over the wide νQ3 regions, but is suppressed in the narrow region located at the middle point of the region possibly due to charge instability.
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  • Hiroyuki Kimura, Keisuke Nishihata, Yukio Noda, Naofumi Aso, Kazuyuki ...
    2008 Volume 77 Issue 6 Pages 063704
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    The pressure–temperature (pT) phase diagram for microscopic magnetism in the multiferroic compound HoMn2O5 was established using neutron diffraction measurements under a hydrostatic pressure up to 1.25 GPa. At ambient pressure, incommensurate–commensurate–incommensurate magnetic phase transitions occur successively with decreasing temperature. Upon applying pressure, the incommensurate phase at the lowest temperature almost decreases and the commensurate phase appears. The pT phase diagram established shows excellent agreement with the recently reported pT dielectric phase diagram, where ferroelectricity is induced by applying pressure. We also found that the pT magnetic phase diagram is quite similar to the previously obtained magnetic field–temperature phase diagram.
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  • Youichi Yanase
    2008 Volume 77 Issue 6 Pages 063705
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    The Fulde–Ferrel–Larkin–Ovchinnikov (FFLO) state near the antiferromagnetic quantum critical point (AFQCP) is investigated by analyzing the two dimensional Hubbard model on the basis of the fluctuation exchange (FLEX) approximation. The phase diagram against the magnetic field and temperature is compared with that obtained in the BCS theory. We discuss the influences of the antiferromagnetic spin fluctuation through the quasiparticle scattering, retardation effect, parity mixing and internal magnetic field. It is shown that the FFLO state is stable in the vicinity of AFQCP even though the quasiparticle scattering due to the spin fluctuation is destructive to the FFLO state. The large positive slope dHFFLOdT and the convex curvature (d2HFFLOdT2>0) are obtained, where HFFLO is the critical magnetic field for the second order phase transition from the uniform BCS state to the FFLO state. These results are consistent with the experimental results in CeCoIn5. The possible magnetic transition in the FFLO state is examined.
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  • Kazuaki Iwasa, Lijie Hao, Tomoo Hasegawa, Kenji Horiuchi, Youichi Mura ...
    2008 Volume 77 Issue 6 Pages 063706
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    PrFe4P12 exhibits clear heavy electron behaviors as well as the phase transition to an antiferro-type ordering of 4f electron state. In this paper, we report on inelastic neutron scattering results for powdered samples of PrxLa1−xFe4P12 (x=1.00 and 0.85). A clear quasielastic magnetic response is observed, and no distinct signal is seen for crystal-field (CF) excitations in the heavy electron state. A model with strong hybridization between conduction electrons and Pr3+ 4f2 electrons [J. Otsuki et al.: J. Phys. Soc. Jpn. 74 (2005) 200 and 2082] is consistent with the observed magnetic response. This result shows that the heavy electron behavior of PrxLa1−xFe4P12 (x=1.00 and 0.85) originates from the Kondo effect associated with low-lying singlet–triplet CF states.
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  • Hijiri Kito, Hiroshi Eisaki, Akira Iyo
    2008 Volume 77 Issue 6 Pages 063707
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    We have synthesized a series of oxygen-deficient, fluorine-free polycrystalline samples with nominal chemical formula NdFeAsO1−y using high-pressure technique. The ZrCuSiAs type crystal structure, as expected for NdFeAsO, is formed as the main phase for the composition 0≤y≤0.6. Sharp superconducting (SC) transition with their transition temperature (Tc) as high as 54 K is observed for 0.3≤y≤0.8 samples, which is higher than that of F-doped NdFeAsO. While Tc does not depend on y, SC volume fraction shows maximum at y=0.4. Around the same y, the lattice parameters show discontinuous shrinkage. These experimental results suggest the existence of a stable superconducting phase with a fixed atomic ratio close to Nd:Fe:As:O=1:1:1:0.6, presumably associated with a regular array of oxygen deficiency.
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  • Takafumi Sato, Seigo Souma, Kosuke Nakayama, Kensei Terashima, Katsuak ...
    2008 Volume 77 Issue 6 Pages 063708
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    We report high-resolution photoemission spectroscopy of newly-discovered iron-based layered superconductor La(O0.93F0.07)FeAs (Tc=24 K). We found that the superconducting gap shows a marked deviation from the isotropic s-wave symmetry. The estimated gap size at 5 K is 3.6 meV in the s- or axial p-wave case, while it is 4.1 meV in the polar p- or d-wave case. We also found a pseudogap of 15–20 meV above Tc, which is gradually filled-in with increasing temperature and closes at temperature far above Tc similarly to copper-oxide high-temperature superconductors.
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  • Miyabi Hiyama, Tomoyuki Kinjo, Shi-aki Hyodo
    2008 Volume 77 Issue 6 Pages 064001
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    A new simple algorithm is presented for solving the equations of motion for rigid molecules. These equations are integrated using a Verlet framework in the angular momentum form. This simple algorithm is named “the angular momentum Verlet algorithm”. For obtaining a high accuracy in molecular dynamics (MD) simulations, we introduce the scaling method with the constraint by Lagrange’s method of undetermined multipliers. The results of MD simulations for carbon tetrachloride using the angular momentum Verlet algorithm are reported. The relative total energy fluctuations for carbon tetrachloride using the angular momentum Verlet algorithm are compared with those using the standard leap-frog and Gear predictor–corrector algorithms. The energy drift using the angular momentum Verlet algorithm is smaller than that using the leap-frog or Gear predictor–corrector algorithm, particularly for large time intervals. The MD simulations for AXnY4−n-type models having different moments of inertia are also carried out to investigate the effects of the angular momentum Verlet algorithm for molecules with different symmetries. We found that the time integrations for the model with the largest moment of inertia are stable. The scaling method with the constraint by Lagrange’s method of undetermined multipliers in the angular momentum Verlet algorithm is effective in obtaining a smaller energy drift, particularly for large time intervals.
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  • Hongming Weng, Taisuke Ozaki, Kiyoyuki Terakura
    2008 Volume 77 Issue 6 Pages 064301
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    Transition metal–benzene (TMnBzn+1, with TM=Sc, Ti, and V, n=1 and 2) multiple-decker sandwich clusters have been studied by first-principles calculations. It was shown in our previous paper that in V2Bz3, the antiferromagnetic (AFM) and ferromagnetic (FM) states are nearly degenerate since the energy gain in FM state due to Kanamori–Terakura mechanism is compensated by the energy gain in AFM state due to polarization of edge Bzs. To design new clusters having much more stable FM state, two approaches are suggested. One is reducing the number of d electrons and the other is to weaken the hybridization strength between transition metals and edge Bz. In order to demonstrate the latter aspect, we take a thought experiment of replacing edge Bz with cyclopentadienyl ring C5H5. Either of these two methods or combinations of both has been demonstrated to be effective. Thus, magnetic properties of transition metal–aromatic molecule sandwich clusters can be tailored.
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  • Mi-Young Song, Takako Kato, Daiji Kato, Izumi Murakami, Y. Ralchenko
    2008 Volume 77 Issue 6 Pages 064302
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    In this paper we study dielectronic and radiative recombination processes of Xe ions. We have calculated the energy levels, radiative transition probabilities, autoionization rates, and radiative recombination cross section for Xe10+ ions using the flexible atomic code (FAC). New dielectronic recombination rate coefficients to excited states of Xe9+ as well as total rate coefficients from the Xe10+ ions are presented. We also calculated the related dielectronic satellite lines. We studied the n- and l-dependence for the dielectronic recombination rate coefficient and the radiative recombination rate coefficient. The dielectronic satellite lines through the 4d8+e→4d7 4f1 nl→4d8 nl+hν and the 4d8+e→4d7 5p1 nl→4d8 nl+hν are calculated and found to be important at low electron temperature for line intensities comparing to the lines produced by excitation. The radiative recombination rate coefficients are always smaller than the values of the dielectronic recombination rate coefficient in the interesting temperature region of Te=1–1000 eV. The contribution of highly excited states to the total dielectronic recombination is important. We estimated the density effect on the dielectronic recombination rate coefficient. It is found that the dielectronic recombination rate coefficients are larger than radiative recombination rate coefficients in the density region ne<1019 cm−3.
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  • Yukio Kaneda, Junya Yoshino, Takashi Ishihara
    2008 Volume 77 Issue 6 Pages 064401
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    Kolmogorov’s 4/5 law is examined quantitatively by using the data of direct numerical simulations of incompressible turbulence in a periodic box with the number of grid points and the Taylor micro-scale Reynolds number 20483 and Rλ≈732, respectively. The examination is based on a generalization of the Kármán–Howarth–Kolmogorov (KHK) equation for isotropic turbulence to anitropic turbulence. An emphasis is put on the influence of the finite Reynolds number, length-scale and the weak but finite anisotropy. The analysis of the DNS data gives a quantitative idea on the role of the viscous and forcing terms in the KHK equation. It also suggests that the anisotropy has substantial influence on the 4/5 law for a wide scale-range.
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  • Benlong Wang, Jin E. Zhang, Hua Liu
    2008 Volume 77 Issue 6 Pages 064402
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    The effects of the depth parameter on the velocity-amplitude relation, wave profile of a single soliton and the interaction of two solitons are studied for the integrable Boussinesq model proposed by Zhang et al. (2004). By comparing with the numerical solutions of the full water wave problem governed by the Euler equations, it is found that the Boussinesq model with depth parameter b=0.207 gives a good prediction on the property of a single soliton and the interaction of solitons of small amplitude up to intermediate amplitude, such as 0.4, for both head-on and overtaking collisions.
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  • Yuko Ito, Yuki Kato, Kaoru Fujimura
    2008 Volume 77 Issue 6 Pages 064403
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    Steadily progressive solutions of the generalized Kuramoto–Sivashinsky equation are studied by means of a numerical simulation and a stability analysis under the periodic boundary conditions. Multiple solutions are obtained by the numerical simulation, including pulse trains with an extraordinary long flat tail. A flat solution of the generalized Kuramoto–Sivashinsky equation is known to be unstable. The stability analysis however reveals that the solution with the long flat tail can be stable in a certain range of parameters.
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  • Masato Makino, Leo Arai, Masao Doi
    2008 Volume 77 Issue 6 Pages 064404
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    The migration of chiral particles in shear flow is studied by parallel disk rotational rheometer. The chiral particles, made of silicon rubber with its two edges cut, are placed between the disks. When the disk rotates, the chiral particles move not only along the flow direction, but also migrate along the direction perpendicular to the flow (i.e., the radial direction). The migration direction, inner or outer, is determined by the handedness of the particle. This is the first experiment to show that the chiral particles can be separated by the velocity gradient field. The migration velocity is measured as a function of the shear rate, and compared with the result of simulation.
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  • Hideshi Fujishita, Akira Ogawaguchi, Susumu Katano
    2008 Volume 77 Issue 6 Pages 064601
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    We performed structural analysis of PbHfO3 between 10 and 500 K in the room-temperature antiferroelectric phase and the cubic phase using powder neutron diffraction. Disordered arrangements of Pb atoms were not detected in the cubic phase in contrast to the results of X-ray diffraction. This indicates that Pb atoms have an electron-density distribution that spreads out more widely than the expected distribution in isolated Pb ions. The simple concept of order parameters in soft-mode condensation, that is, all atomic shifts show proportional temperature dependences, was not observed in the antiferroelectric phase of PbHfO3. However, physical properties, such as lattice distortion, show the temperature dependences predicted on the basis of a phenomenological theory as if the simple concept were applicable over the entire temperature range.
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  • Ryoji Kiyanagi, Hiroyuki Kimura, Masashi Watanabe, Yukio Noda, Tomoyuk ...
    2008 Volume 77 Issue 6 Pages 064602
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    The dielectric material with an isolated hydrogen-bond, 5-bromo-9-hydroxyphenalenon, was studied by means of neutron and X-ray diffractions in the temperature range between 300 and 10 K. Analyses on nuclear and electron density distributions revealed a discrepancy between the two distributions of the hydrogen atom in the hydrogen-bond region, leading to a local electronic dipole moment. Both a least-square structure analysis and the density distribution analysis by the maximum entropy method confirmed that the hydrogen atom occupies two equivalent sites near the center of the hydrogen-bond through the whole temperature range, even at the lowest temperature measured, 10 K. This feature, together with previous results on calorimetric, incoherent neutron scattering and far-infrared spectrum measurements, concludes that the hydrogen atom in the hydrogen-bond is in a tunneling state over the two sites. Consequently, 5-bromo-9-hydroxyphenalenon was experimentally identified as a quantum paraelectric material.
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  • Aki Yamane, Fuyuki Shimojo, Kozo Hoshino
    2008 Volume 77 Issue 6 Pages 064603
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    We have carried out ab initio molecular-dynamics (MD) simulations of dense liquid/solid sodium for 3s- and 2p3s-valence-electron models, and for different valence electron–ion interactions at high pressures. We have found that the melting curve has a melting point maximum, which depends on the type of valence-electron models used at high pressures. We have shown that, if we consider inner-core 2p states, the repulsive interatomic force becomes stronger and the pressure and temperature of the maximum melting point increase. We have investigated the effect of inner-core 2p states on the structure of liquid sodium, and found that, though the differences in the structures obtained with different valence-electron models are negligible in a relatively low-pressure region, the differences are significant at extremely high pressures, since inner-core 2p states play important roles at high pressures. We have also shown that the ultrasoft pseudopotential method and projector augmented-wave method give almost the same results.
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  • Kunio Yubuta, Xiangyang Huang, Yuzuru Miyazaki, Tsuyoshi Kajitani
    2008 Volume 77 Issue 6 Pages 064604
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    The crystal structure of partly Sr-substituted Co-121, i.e., “Ca3Co4Co9”, single crystal is studied by means of the electron diffraction measurements and high-resolution transmission electron microscopy (HREM). The crystal structure consists of two interpenetrating subsystems of a CoO2 sheet and a distorted three-layered (Ca,Sr)2CoO3 rock-salt (RS)-type block layers, which belong to a triclinic system. Both subsystems have common a-, c-axes and α-, β-, γ-angle with a=4.8267(1) Å, c=10.9214(3) Å, α=90.916(2)°, β=98.291(5)°, and γ=89.957(3)°. On the other hand, the crystal structure is modulated parallel to the b-axis, along which the CoO2 sheet has b1=2.8346(1) Å and the (Ca,Sr)2CoO3 RS-type block layer has b2=4.6391(2) Å, respectively. On the basis of the b1b2 ratio and analyzed chemical compositions, the structure analogue is formulated as [(Ca0.90Sr0.10)2CoO3]0.61CoO2. In electron diffraction patterns, there are many new satellite reflections, namely 010\\bar1, 020\\bar2, 0\\bar204, and 0\\bar103, which are not present in the end member Co-121, i.e., (Ca2CoO3)0.620CoO2. Because of the new superlattice reflections, the crystal structure of the Sr-doped compound is different from the end member. HREM images were taken with the incident electron beam parallel to the [0010] and [1000] directions. The basic crystal structure of the present system consists of 5-CoO2 and 3-RS subcells with b=14 Å being connected discommensuratedly parallel to the a- and b-axes. Systematic introduction of stacking faults parallel to the ab plane is also noticed.
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  • Tomoaki Itano, Takeshi Akinaga, Masako Sugihara-Seki
    2008 Volume 77 Issue 6 Pages 064605
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    An ideal of osmotic equilibrium between an ideal solution and pure solvent separated by a semi-permeable membrane is studied numerically using the method of molecular dynamics. The osmotic flow is observed as the inflow of the solvent across the membrane from the dilute to the concentrated side. The validity of van’t Hoff’s law for osmotic pressure is confirmed over a wide range of concentrations. It is found that the law is established by a balance between non-uniform partial pressures of solute and solvent. Furthermore, the present model permits an understanding of the mechanism of the osmotic flow in the relaxation process as the liquids evolve from the initial state to the equilibrium state. We focus in particular on the interaction between solute and solvent.
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  • Takeshi Sugimori, Hiroyuki Hyuga, Yukio Saito
    2008 Volume 77 Issue 6 Pages 064606
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    We propose a new mechanism for the achievment of homochirality for a small closed system without any autocatalytic production process. Our model consists of a spontaneous production together with a recycling cross inhibition in a closed system. It is shown that although the rate equations for this system predict no chiral symmetry breaking, the stochastic master equation predicts complete homochirality. This is because the fluctuation induced by the discreteness of population numbers of participating molecules plays essential roles. This fluctuation conspires with the recyling cross inhibition to realize the homochirality.
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  • Satoshi Akutagawa, Takeyoshi Ohashi, Haruhisa Kitano, Atsutaka Maeda, ...
    2008 Volume 77 Issue 6 Pages 064701
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    In this paper, we investigate the electronic structure of quasiparticle in the vortex state of Y2C3 by the measurements of the specific heat, C, and the flux-flow resistivity, ρf. In contrast to a conventional s-wave superconductor, CT and ρf showed nonlinear B dependences at low temperatures. The result is discussed in terms of the two gap superconductivity. We estimated the viscosity and the mean free path of the quasiparticles in the vortex core for Y2C3. While we found that Y2C3 is a clean superconductor in a previous study, the mean free path of the quasiparticles in the vortex core was limited to the coherence length because of the Andreev reflection at the vortex–core boundary in this study.
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  • Katsuyoshi Komatsu, Yuuki Mizuno, Hideyuki Maki, Tetsuya Sato
    2008 Volume 77 Issue 6 Pages 064702
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    The anomalous Hall resistivity ρxy and the magnetization M of a reentrant spin glass Ni(Pt)Mn thin film were simultaneously measured as a function of temperature in fields from 1000 to 9000 Oe. The value of ρxyM depends on the cooling condition at temperatures below the spin glass transition temperature Tg and the low-field value of ρxyM shows a cusp like peak around Tg in the zero field cooled (ZFC) condition. The anomaly in the ZFC data can be explained in terms of the contribution to the anomalous Hall effect from chirality mechanism.
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  • Takanobu Jujo
    2008 Volume 77 Issue 6 Pages 064703
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    We investigate the nonlinear optical susceptibilities of Mott insulators with the dynamical mean field approximation. The two-photon absorption (TPA) and the third-harmonic generation (THG) spectra are calculated, and the classification by the types of coupling to external fields shows different behavior from conventional semiconductors. The direct transition terms are predominant both in the TPA and THG spectra, and the importance of taking all types of interaction with the external field into account is illustrated in connection with the THG spectrum and dc Kerr effect. The dependences of the TPA and THG spectra on the Coulomb interaction indicate a scaling relation. We apply this relation to the quantitative evaluation and obtain results comparable to those of experiments.
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  • Yoshinao Takaesu, Takao Nakama, Masataka Takeda, Dai Nakamura, Masato ...
    2008 Volume 77 Issue 6 Pages 064704
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    The electrical resistivity ρ and thermopower S of the Laves phase Y1−xTbxCo2 alloy system have been measured in magnetic fields up to 10 T and under pressures up to 8 GPa in the temperature range from 1.5 to 300 K. The residual resistivity of the alloys peaks at the critical composition xc≈0.2 of the onset of 4f-moment long-range magnetic order in the Tb sublattice. In the magnetically ordered region of the phase diagram x>xc, an anomalous large positive magnetoresistivity and a pressure effect on resistivity are observed. The variation of the resistivity with alloy composition, magnetic field, and pressure are attributed to the scattering of conduction electrons due to magnetic static disorder within the partially ordered Co 3d itinerant subsystem. The evolution of the temperature dependence of thermopower with pressure are in agreement with this conduction mechanism.
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  • Hiroshi Shiraki, Takashi Saito, Masaki Azuma, Yuichi Shimakawa
    2008 Volume 77 Issue 6 Pages 064705
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    The A-site-ordered perovskites ACu3V4O12 (A = Na+, Ca2+, and Y3+) have been found to be Pauli paramagnetic metals. Bond valence sum calculations, magnetic susceptibility measurement, and electronic structure calculations reveal that both Cu and V orbitals contribute to the metallic conduction. Changing the A-site ions in ACu3V4O12 from monovalent to divalent to trivalent ions changes the physical properties in ways that in a rigid band picture can be attributed to the shift of the Fermi energy. The ACu3V4O12 compounds, unlike the isostructural metallic CaCu3Ru4O12, show no conclusive evidence of heavy-fermion-like behavior.
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  • Mamoru Fukunaga, Yukio Noda
    2008 Volume 77 Issue 6 Pages 064706
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    A new technique, the double-wave method (DWM), is developed to refine ferroelectric DE hysteresis loops. The method discriminates non-hysteresis components from ferroelectric DE hysteresis loops by applying identical unipolar waves twice. It extracts only the hysteresis component automatically without any assumptions. The DWM can compensate intricate non-hysteresis components in DE loops which traditional methods cannot. It can separate an antiferroelectric component from ferroelectric and other components by applying a bias electric field. As a typical example of a ferroelectric, DE loops of NaNO2 by the DWM are examined. To demonstrate the advantages of the DWM, DE loops of multiferroic ErMn2O5 are presented. Antiferroelectric-like components in DE loops are separated and fine ferroelectric loops of ErMn2O5 are observed by the DWM.
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  • Hiroaki Ikeda, Shogo Shinkai, Kosaku Yamada
    2008 Volume 77 Issue 6 Pages 064707
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    We investigate the Hubbard model on a two-dimensional square lattice by the perturbation expansion to the fourth order in the on-site Coulomb repulsion U. Numerically calculating all diagrams up to the fourth order in self-energy, we examine the convergence of perturbation series in the lattice system. We indicate that the coefficient of each order term rapidly decreases as in the impurity Anderson model for T\\gtrsim0.1t in the half-filled case, but it holds in the doped case even at lower temperatures. Thus, we can expect that the convergence of perturbation expansion in U is very good in a wide parameter region also in the lattice system, except for T\\lesssim0.1t in the half-filled case. We next calculate the density of states in the fourth-order perturbation. In the half-filled case, the shape in a moderate correlation regime is quite different from the three peak structure in the second-order perturbation. Remarkable upper and lower Hubbard bands locate at ω\\simeq±U⁄2, and a pseudogap appears at the Fermi level ω=0. This is considered as the precursor of the Mott–Hubbard antiferromagnetic structure. In the doped case, quasiparticles with very heavy mass are formed at the Fermi level. Thus, we conclude that the fourth-order perturbation theory overall well explain the asymptotic behaviors in a strong correlation regime.
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  • Nguyen Duc Dung, Tatsuma D. Matsuda, Yoshinori Haga, Shugo Ikeda, Etsu ...
    2008 Volume 77 Issue 6 Pages 064708
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    We succeeded in growing a single crystal of a layered compound Lu2Rh3Ga9 with an Y2Co3Ga9-type orthorhombic crystal structure by the Ga-flux method. The lattice, positional, and thermal parameters were determined by single-crystal x-ray diffraction measurement. We also measured the electrical resistivity, specific heat, and de Haas–van Alphen (dHvA) effect. The detected dHvA branches were well explained by the results of full potential linear augmented plane-wave (LAPW) energy band calculations. The electronic state was found to be quasi-two-dimensional, indicating nearly cylindrical Fermi surfaces along the [001] direction.
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  • Toshio Naito, Yukari Yamada, Tamotsu Inabe, Yasunori Toda
    2008 Volume 77 Issue 6 Pages 064709
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    The κ-type organic superconductors have unique physical properties, many of which are yet to be understood. Most of their physical properties are closely related to carrier dynamics, which can be directly observed by ultrafast optical measurements in their nonequilibrium states. Time-resolved temperature-dependent reflectivity changes were measured on single crystals of an isostructural pair of organic charge transfer salts κ-(ET)2Cu[N(CN)2]X, which are ambient- (X=Br) or high-pressure (X=Cl) superconductors. The latter compound in its ground state is a Mott insulator under ambient pressure. The obtained temperature dependences of relaxation times for both salts indicated the existence of an intermediate electronic state between those of metals and insulators at all measurement temperatures. Such an unusual electronic state coexisted with the superconducting and Mott insulating states in X=Br and X=Cl, respectively. In addition, the results for X=Br revealed the formation of a temperature-dependent well-defined gap in the superconducting transition, while those for X=Cl suggested that the Mott transition in this salt does not depend on electron–phonon interactions, consistent with the theory that the Mott transition should originate from electron correlation.
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  • Hiroaki Kusunose
    2008 Volume 77 Issue 6 Pages 064710
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    A systematic description of multipole degrees of freedom is discussed on the basis of the Stevens’ operator-equivalent technique. The generalized Stevens’ multiplicative factors are derived for all of the electric and the magnetic multipoles relevant to f-electron systems. With extensive use of the Stevens’ factors, we express the spatial dependences of the electric and the magnetic fields, and the electric and the magnetic charge densities of localized f electrons. The latter is utilized to draw wave functions including their magnetic profile in addition to their shape with the charge density. The definite relation between the operators as quantum-mechanical variables in a multipole exchange model and the multipole moments in expansion of electromagnetic fields is given. The general treatments for the exchange model with the random-phase-approximation (RPA) susceptibility and the Ginzburg–Landau free-energy expansion are discussed, using CexLa1−xB6 as a typical example. The representative formula of the vector spherical harmonics are summarized, which are suitable basis for vector fields in the spherical expansion.
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  • Takehito Yokoyama, Seiichiro Onari, Yukio Tanaka
    2008 Volume 77 Issue 6 Pages 064711
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    We study Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) state of superconductors with and without inversion symmetry based on the Hubbard model on the square lattice near half-filling, using the random phase approximation. We show that center of mass momentum Q tends to be parallel to x- or y-axis in the presence of inversion symmetry, while Q vector is likely to be perpendicular to the magnetic field in the absence of inversion symmetry. We also clarify that d+f-wave pairing is favored and the hetero spin triplet f-wave state is present in the FFLO state unlike state in the superconductors only with the Rashba type spin–orbit coupling (RSOC) originating from the broken inversion symmetry. The triplet f-wave state is enhanced by magnetic field and the RSOC. This stems from the reduction of the spin susceptibilities by the magnetic field and the RSOC.
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  • Hideoki Hoshino, Yusuke Sannohe, Yushi Suzuki, Takashi Azuhata, Takafu ...
    2008 Volume 77 Issue 6 Pages 064712
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    The photoluminescence (PL) and extended X-ray absorption fine structure (EXAFS) measurements have been carried out for the dehydrated fully Ag+ exchanged zeolite A powders packed with controlled amounts of the adsorbed H2O molecules. The powders are designated as “air-packed 12Ag-A” and have been prepared by packing the dehydrated 12Ag-A in the glass cell under air at different temperatures between 120 and 30 °C in the cooling process after the dehydration at 500 °C for 24 h under air. The PL spectra obtained by radiation of 400 nm light have main peaks around 2.15 eV and subpeaks around 2.70 eV. The PL spectra were fitted by four Gaussians. The peak around 2.15 eV consists of the band I ∼1.94 eV and band II ∼2.10 eV, while the subpeak around 2.70 eV of the band III ∼2.50 eV and band IV ∼2.80 eV. The temperature variations of the integral intensities for the bands II and IV show maxima between 50 and 80 °C where the interaction between the zeolite framework and the adsorbed H2O molecules is found to become dominant by the infrared measurements. The integral intensities of the band I increase below 90 °C. The analyses of the Ag K-edge EXAFS spectra obtained for the air-packed 12Ag-A reveal that there appears a silver cluster, Ag5m+ (m≥3) which consists of two 6-ring Ag+ ions and one 4-ring Ag+ ion bonded to two 8-ring Ag atoms below 100 °C. We conclude that the PL of the air-packed 12Ag-A is attributed to the Ag5m+ clusters.
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  • Akira Endo, Yasuhiro Iye
    2008 Volume 77 Issue 6 Pages 064713
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    The line shape of the Shubnikov–de Haas (SdH) oscillation has been analyzed in detail for a GaAs/AlGaAs two-dimensional electron gas. The line shape, or equivalently the behavior of the Fourier components, of the experimentally observed SdH oscillation is well reproduced by the sinusoidal density of states at the Fermi energy that oscillates with a magnetic field in a saw-tooth shape to keep the electron density constant. This suggests that the broadening of each Landau level by disorder is better described by a Gaussian than by a Lorentzian.
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  • Keizo Yasukawa, Youtarou Takahashi, Susumu Kurita, Tohru Suemoto
    2008 Volume 77 Issue 6 Pages 064714
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    We report on the time-resolved luminescence spectroscopy of a quasi-one-dimensional halogen-bridged platinum complex, [Pt(en)2][Pt(en)2I2] (ClO4)4, at room temperature in the energy range between 1.2 and 0.9 eV. A strong first peak at the time origin and subsequent oscillating features were observed in the time evolution curves of luminescence intensity. As the frequency of the wavepacket oscillation in the self-trapped exciton, we obtained 2.92 THz (97 cm−1), which is 77% of the symmetric stretching mode frequency in the ground state. We analyzed the measured time evolution of the luminescence intensity by using the theory of resonant secondary radiation.
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  • Andrea Sacchetti
    2008 Volume 77 Issue 6 Pages 064715
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    In this work we discuss the effective-mass approximation with a rapidly varying exterior potential and non-parabolic bands, recently proposed by Gómez-Campos et al. In particular, we numerically test such an approximation confirming its validity on an explicitely solvable model.
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  • Tomoya Kawai, Hiroshi Muranaka, Marie-Aude Measson, Tetsuya Shimoda, Y ...
    2008 Volume 77 Issue 6 Pages 064716
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    We grew single crystals of non-centrosymmetric compounds CeTSi3 and CeTGe3 (T: transition metal), and studied the magnetic properties by measuring the electrical resistivity, magnetic susceptibility and magnetization. We also studied the effect of pressure on the electronic states in antiferromagnets CeTGe3 (T: Co, Rh, Ir) by measuring the resistivity under pressure. No noticeable change of the Néel temperature was observed up to 8 GPa in CeRhGe3 and CeIrGe3, which are far from the magnetic quantum critical point. On the other hand, the Néel temperature in CeCoGe3 was strongly decreased as a function of pressure, and pressure-induced superconductivity was observed in the pressure region from 5.4 GPa to about 7.5 GPa. The slope of upper critical field Hc2 at 6.5 GPa is found to be extremely large, with an upturn curvature of Hc2 with decreasing temperature: −dHc2dT=200 kOe/K at the superconducting transition temperature Tsc=0.69 K, revealing unconventional superconductivity.
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  • Tomoya Kawai, Hiroshi Muranaka, Toyoaki Endo, Nguyen Duc Dung, Yusuke ...
    2008 Volume 77 Issue 6 Pages 064717
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    We succeeded in growing single crystals of LaTGe3 (T: Fe, Co, Rh, Ir) and PrCoGe3 with the non-centrosymmetric tetragonal crystal structure, and studied the split Fermi surface properties and the magnitude of the antisymmetric spin–orbit interaction 2|αp|. The 2|αp| value is found to vary when LaTGe3 is changed from T=Co, Rh to Ir, but remains unchanged in LaIrX3 from X=Si to Ge. It is found that this 2|αp| value is large in LaIrSi3 and LaIrGe3: 2|αp|=460 K in LaCoGe3, 510 K in LaRhGe3, 1100 K in LaIrSi3, and 1090 K in LaIrGe3 for the main outer orbits named α of bands 69 and 70 electron Fermi surfaces, for example. This is due to the large effective atomic number of Ir and a large distribution of the radial wave function of Ir-5d electrons close to the nuclear center, compared with those of Co and Rh. In the case of a paramagnet PrCoGe3 and LaFeGe3 with the relatively large cyclotron mass, the corresponding 2|αp| value is found to become small: 2|αp|=280 and 460 K for main orbits α in PrCoGe3 and LaCoGe3, respectively, and 130 K for main orbits in LaFeGe3.
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  • Akito Kobayashi, Yoshikazu Suzumura, Hidetoshi Fukuyama
    2008 Volume 77 Issue 6 Pages 064718
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    The apparent zerogap fermions in α-(BEDT-TTF)2I3 are recently proposed to obey the tilted Weyl equation which is very unusual. The Hall conductivity, the conductivity and the orbital susceptibility are investigated theoretically for electrons described by this tilted Weyl equation. It is found that these quantities are enhanced due to tilting but keeping the same dependence on chemical potential as in the absence of tilting. Based on these results and expected temperature dependence of the chemical potential in α-(BEDT-TTF)2I3, it is found that there will be the strong enhancement of the Hall coefficient toward low temperatures. Moreover, it is proposed that the sharp but continuous reversal of the sign of the Hall coefficient is possible at low temperatures if the extremely small amount of electron doping, about 1 ppm, exists. These results may explain very anomalous features of Hall coefficient observed in α-(BEDT-TTF)2I3 and can be an unambiguous indication of the existence of the zerogap fermions in α-(BEDT-TTF)2I3. In addition, it is shown that the orbital diamagnetism can have a peak at the temperatures where the Hall coefficient changes sign. All these strong temperature dependences of both the Hall coefficient and the orbital diamagnetism are due to the inter-band effects of magnetic field.
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  • Kenji Kamishima, Yoshitaka Nagashima, Koichi Kakizaki, Nobuyuki Hirats ...
    2008 Volume 77 Issue 6 Pages 064801
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    Ceramic composites (2Ni0.41Zn0.41Cu0.18Fe2O4–BaTiO3) were successfully prepared by a direct solid-state reaction of raw materials (BaCO3, CuO, α-Fe2O3, NiO, TiO2, and ZnO). X-ray diffraction (XRD) and electron probe micro analysis (EPMA) measurements were performed for these samples and it is confirmed that the composites consist of spinel ferrite and BaTiO3 phases. The composites are so homogeneous that the ferrite and BaTiO3 grains do not react with each other and have radii in the range of 1–5 μm. Hexagonal BaTiO3 (h-BaTiO3) can be made in this composite form with a sintering temperature of 1200 °C, although h-BaTiO3 can be usually synthesized above 1460 °C. The freezing-point depression of BaTiO3 takes place due to the mixing with the spinel ferrite, which may result in the formation of h-BaTiO3 at a low temperature of 1200 °C.
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  • Masafumi Oizumi, Yoichi Miyawaki, Masato Okada
    2008 Volume 77 Issue 6 Pages 064802
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    We proposed a systematic method for reducing Hodgkin–Huxley-type networks to networks of rate equations on the basis of Shriki et al.’s formulation. Our rate model predicts the results of numerical simulations of the Hodgkin–Huxley-type network model very precisely over a broad range of synaptic conductances. However, in the proposed framework, we ad hoc assumed that the firing threshold and the gain of the fI curve of the Hodgkin–Huxley-type conductance-based model have a second-order dependence on leak conductance. Here, we discuss optimal model selection with respect to the dependence of the threshold and the gain on the fI curve, using the Akaike information criterion. We then apply our rate reduction method to an associative memory model of Hodgkin–Huxley neurons. Most associative memory models have been studied using two-state neurons or graded-response neurons. We check the correspondence between an associative memory model of Hodgkin–Huxley neurons and that of graded-response neurons, particularly in terms of phase diagrams. We store correlated patterns in the network and investigate the phase transition between the memory state and the mixed state. We demonstrate that our rate model, which is obtained by the reduction method, explains the phase diagram of the Hodgkin–Huxley-type network very well.
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  • Kengo Oka, Masaki Azuma, Naoaki Hayashi, Shigetoshi Muranaka, Yasuo Na ...
    2008 Volume 77 Issue 6 Pages 064803
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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    The charge ordering and the magnetic ordering in InFe2O4 were investigated using samples free of impurity Fe3O4. X-ray diffraction, magnetic susceptibility, magnetization, Mössbauer spectroscopy, and dielectric constant measurements consistently showed that both these orderings occurred between 230 and 250 K. This temperature range is much smaller than the corresponding one in the cooling of electronic ferroelectric LuFe2O4, where charge ordering occurs at 320 K and magnetic ordering occurs at 250 K.
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  • Yoshiyuki Matsumoto
    2008 Volume 77 Issue 6 Pages 065001
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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  • Tohru Kawarabayashi, Yoshiyuki Ono, Chiduru Watanabe
    2008 Volume 77 Issue 6 Pages 065002
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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  • Makoto Iwata, Zdravko Kutnjak, Yoshihiro Ishibashi, Robert Blinc
    2008 Volume 77 Issue 6 Pages 065003
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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  • Masashi Watanabe, Kenichiro Yamamoto, Takayoshi Ito, Yusaku Nakashima, ...
    2008 Volume 77 Issue 6 Pages 065004
    Published: June 15, 2008
    Released on J-STAGE: December 28, 2011
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