Journal of the Physical Society of Japan
Online ISSN : 1347-4073
Print ISSN : 0031-9015
ISSN-L : 0031-9015
Volume 77, Issue 8
Displaying 1-39 of 39 articles from this issue
  • Tetsuya Ohnishi, Toshiyuki Kubo, Kensuke Kusaka, Atsushi Yoshida, Koic ...
    2008 Volume 77 Issue 8 Pages 083201
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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    A search for new isotopes using in-flight fission of a 345 MeV/nucleon 238U beam has been carried out in the commissioning experiment of the next-generation in-flight radioactive isotope beam separator BigRIPS at the RI Beam Factory at the RIKEN Nishina Center. Two neutron-rich palladium isotopes 125Pd and 126Pd were observed for the first time, which demonstrates the great potential of the RIKEN RI beam factory.
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  • Jong-Hoon Huh, Shoichi Kai
    2008 Volume 77 Issue 8 Pages 083601
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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    New experimental aspects of multiplicative noise effects on the onset of ac-driven electroconvection in nematic liquid crystals are presented. In the superposition of a stochastic field with a deterministic one, the variation in the threshold voltage Vc (of the deterministic one) was investigated as a function of the intensity (VN), cutoff frequency (fc), and correlation time (τN) of the stochastic noise. In particular, it is observed that the noise effects vanish for certain stochastic and deterministic conditions.
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  • Christian Iniotakis, Satoshi Fujimoto, Manfred Sigrist
    2008 Volume 77 Issue 8 Pages 083701
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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    We examine intrinsic interfaces separating crystalline twin domains of opposite spin–orbit coupling in a noncentrosymmetric superconductor such as CePt3Si. At these interfaces, low-energy Andreev bound states occur as a consequence of parity-mixed Cooper pairing, and a superconducting phase which violates time reversal symmetry can be realized. This provides an environment allowing flux lines with fractional flux quanta to be formed at the interface. Their presence could have strong implications on the flux creep behavior in such superconductors.
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  • Hiroyuki Chudo, Hironori Sakai, Yo Tokunaga, Shinsaku Kambe, Dai Aoki, ...
    2008 Volume 77 Issue 8 Pages 083702
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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    We present 27Al NMR studies for a single crystal of the newly developed superconductor NpPd5Al2 (Tc=4.9 K). In the superconducting state, the 27Al NMR spectrum shifts to lower frequencies owing to a decrease of the spin part of the Knight shift, and exhibits broadening characteristic of the local field distribution associated with a vortex lattice. We have also found that the 27Al nuclear spin–lattice relaxation rate (1⁄T1) decreases just below Tc with no coherence peak and shows T3 behavior at low temperatures. The observed temperature dependences of the Knight shift and 1⁄T1 in general accord with those assuming a line-node superconducting gap with the gap value of 2Δ⁄kBTc\\simeq6.4. Therefore, the present NMR data provides evidence for strong-coupling d-wave superconductivity in NpPd5Al2.
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  • Takatsugu Masuda, Satoshi Takamizawa, Kazuma Hirota, Masaaki Ohba, Sus ...
    2008 Volume 77 Issue 8 Pages 083703
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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    We performed an inelastic neutron scattering experiment to study the magnetic excitation of O2 molecules adsorbed in a microporous compound. A dispersionless excitation with characteristic intensity modulation is observed at hω=7.8 meV at low temperature. The neutron cross section is explained by using a spin dimer model with an intradimer distance of 3.1 Å. Anomalous behaviour in the temperature dependence is discussed in the context of enhanced magnetoelasticity in the soft framework of the O2 molecule.
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  • Chul-Ho Lee, Akira Iyo, Hiroshi Eisaki, Hijiri Kito, Maria Teresa Fern ...
    2008 Volume 77 Issue 8 Pages 083704
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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    The crystal structure of LnFeAsO1−y (Ln = La, Nd) has been studied by the powder neutron diffraction technique. The superconducting phase diagram of NdFeAsO1−y is established as a function of oxygen content which is determined by Rietveld refinement. The small As–Fe bond length suggests that As and Fe atoms are connected covalently. FeAs4-tetrahedrons transform toward a regular shape with increasing oxygen deficiency. Superconducting transition temperatures seem to attain maximum values for regular FeAs4-tetrahedrons.
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  • Ryousuke Shiina
    2008 Volume 77 Issue 8 Pages 083705
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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    A charge density wave transition and an associated metal–insulator transition in skutterudite PrRu4P12 are studied theoretically on the basis of an interaction between conduction and f electrons. It is found that the thermal fluctuation of f orbitals significantly reduces the magnitude of the gap in the quasi-particle spectrum even at low temperature. As a result, we show that resistivity exhibits a characteristic temperature dependence, which accounts well for a recent experimental observation.
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  • Fumitaka Sakamoto, Kenji Miyakawa
    2008 Volume 77 Issue 8 Pages 083801
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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    The Belousov–Zhabotinsky reaction system showing stationary patterns is realized on the basis of water-in-oil microemulsions with the surfactant sodium bis(2-ethylhexyl)sulfosuccinate. We experimentally demonstrate the formation of somitogenesis-like pattern in which chemical waves arising from spontaneous bulk oscillations are successively arrested and then stacked. The experimental results are qualitatively reproduced by numerical simulations using the two-variable oregonator model. These show that a somitogenesis can be accounted for by the genuine reaction–diffusion model.
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  • Makio Uwaha
    2008 Volume 77 Issue 8 Pages 083802
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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    By grinding crystals in a solution, the chirality conversion of the crystal structure and the resultant conversion of molecular chirality have been realized recently. Reaction-type models that enable the reproduction of these phenomena are studied. In the models, chiral clusters are assumed to be formed by grinding and that these clusters can be integrated into crystals of the same chirality. An initial chirality imbalance is amplified exponentially, and the rate is approximately proportional to the grinding strength and to the molecular racemization rate in a relevant parameter range.
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  • Norio Inui
    2008 Volume 77 Issue 8 Pages 084001
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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    Using the mode-by-mode summation technique, we study the contribution of the evanescent modes to the Casimir energy between semi-infinite dielectric slabs whose plasma frequencies change linearly near their surfaces. The vacuum energy is defined as the summation of the zero-point energy over all possible TM-polarized evanescent modes, and the dispersion relation is numerically obtained using multilayer approximation and the transfer matrix method. In contrast to homogeneous dielectric slabs, the number of allowed modes between inhomogeneous dielectric slabs diverges in the continuous limit; however, our computational method affords the convergent Casimir energy. Furthermore, the effect of inhomogeneity in dielectric permittivity on the Casimir energy is evaluated.
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  • Kiyoshi Sogo
    2008 Volume 77 Issue 8 Pages 084002
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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    Equations of motion for the Lagrange top in the inertial coordinates system are formulated in continuous-time variable, and they are solved explicitly in terms of the elliptic functions. Then it is shown that such equations of motion suggest time-discretized equations for the same model, which were given by Bobenko and Suris some years ago. And it is proved to be also a discrete integrable system. Exact solutions for such discrete equations are also constructed explicitly by using the elliptic functions.
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  • Khaled Hassaneen, Khalaf Gad
    2008 Volume 77 Issue 8 Pages 084201
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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    In this paper we have reported the study of symmetry energy within the self-consistent Green-function approach. For the sake of comparison, the same calculations are performed using Brueckner–Hartree–Fock approximation. The symmetry energy is calculated for different densities and discussed in comparison with other predictions. The self-consistent Green’s function leads to slightly larger energies as compared to the Brueckner–Hartree–Fock approach. This effect increases with density and thereby leads to smaller symmetry energies. The calculation of the symmetry energy in the Brueckner–Hartree–Fock approach shows a monotonic increase as a function of baryonic density. We extract the symmetry energy coefficient at density ρ=0.16 fm−3 to be about 28.3 MeV for self-consistent Green-function approach using CD-Bonn potential, which is in good agreement with the empirical value of 30±4 MeV. The dependence of the equation of state on the neutron excess parameter is clearly linear as function of α2 for self-consistent Green-function approach.
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  • Shigeo Kida, Takao Taya, Takeshi Watanabe
    2008 Volume 77 Issue 8 Pages 084401
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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    The mixing properties of the orientation of passive vectors in an unstable periodic flow of Couette system are investigated numerically. The flow domain is divided into many small cubic regions and the distribution of directions of many passive vectors in each cube is calculated at several temporal phases of the unstable periodic flow. It is found that in most of cubes the passive vectors align either in a single direction (linear region) or on a plane (planar region). The unstable periodic flow exhibits the characteristic features of Couette turbulence having the streamwise vortices and the low-speed streaks. The linear regions are observed in streamwise vortices and low-speed streaks (or the ejection region near the wall), the planar regions in the periphery of vortices and in the sweep region near the wall. The dispersion in direction of passive vectors (also fluid mixing) depends on their near-past history over the characteristic times of the unstable periodic flow.
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  • Xiao Chen, Yu-cheng Su, Yi-Quan Wang, Di Yang, Yu-ping Yang, Hong-bing ...
    2008 Volume 77 Issue 8 Pages 084402
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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    The propagation of ultrashort laser pulses in water has been investigated with the extended nonlinear Schrödinger equation and the electron density equation. With the model that incorporates the diffraction, normal group-velocity dispersion, multiphoton absorption, self-focusing and defocus of light by the generated free electrons, we examined numerically the spatio-temporal development of the on-axis light intensity along the propagation and the laser-induced electron plasma. Simulation of the underlying dynamics of the ultrashort laser propagation in water reveals that the self-focusing interplays competitively with the laser-induced optical breakdown. Moreover, the laser energy, its duration and focusing geometry determine in combination the structure of plasma filament and the reshaping of energy fluence. The results may provide a better understanding and application of the ultrashort laser pulses in medicine.
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  • Kuo-Ching Chen, Chia-Chieh Li, Chi-Hao Lin, Li-Min Ju, Chau-Shioung Ye ...
    2008 Volume 77 Issue 8 Pages 084403
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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    This study presents experimental evidence for an extended granular clock, called the “granular follower”, in a vertically vibrated three-compartmentalized system with a bi-disperse granular mixture. In every skip of the mixture, small spheres first move to one of the empty compartments, and large spheres then follow the small spheres to the same zone. We present the phase diagram of the container width and large-sphere number, which exhibits three different regions, namely, one-clustering, granular follower, and two-clustering states. The mechanisms of the three states are explained by an expeller-trapper model, in that there are two minimum number densities: first for small spheres to cluster in one of the two empty compartments and second for large spheres to effectively expel small spheres. Furthermore, in this study, we also observe a granular follower in a three-compartmentalized system with tri-disperse spheres, revealing that the granular follower is not only an extension of the granular clock but also the most general case of granular oscillation.
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  • Mieko Toida, Masayuki Ueno, Yukiharu Ohsawa
    2008 Volume 77 Issue 8 Pages 084501
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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    The effect of the curvature of a shock front on electron trapping is investigated by means of a two-dimensional, fully kinetic, relativistic, electromagnetic particle code. Electron trapping and acceleration are observed even in a cylindrical shock wave in an external magnetic field B0. Furthermore, unlike that in the case of planar shock waves in a uniform B0, a significant fraction of trapped electrons can escape from the wave maintaining their ultrarelativistic energies. Such detrapping is due to the curvature of the shock front, i.e., the angle between the wave normal and B0 varies along the trajectory of a trapped particle. The detrapping in a planar shock wave in a nonuniform magnetic field is also shown with one-dimensional simulations.
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  • Masatoshi Sato, Yukiharu Ohsawa
    2008 Volume 77 Issue 8 Pages 084502
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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    Electron acceleration in magnetohydrodynamic waves produced by a collision of two high-temperature plasmas in an external magnetic field B0 is studied with particle simulations. First, possible particle motions that traverse multiple layers with alternating magnetic polarity are illustrated. Then, it is shown with one-dimensional, fully kinetic, relativistic, electromagnetic particle simulations that as a result of plasma collision, a large-amplitude Alfvén wave packet can be formed behind a magnetosonic shock wave. In the wave packet with alternating magnetic polarity, some electrons exhibit orbits predicted by the physical considerations and are accelerated to high energies such that γ>100. It is thus found that the Alfvén wave packet as well as the magnetosonic shock wave can create ultrarelativistic particles with its strong wave fields.
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  • Mohammad Kemal Agusta, Melanie David, Hiroshi Nakanishi, Hideaki Kasai
    2008 Volume 77 Issue 8 Pages 084601
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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    SO3 structure and reaction on Cu(100) were investigated by using density functional theory-based calculation. SO3 was found to adsorbed on the surface through its three oxygen atoms having a trigonal pyramid structure with its C3v axis lying nearly perpendicular to the surface. The interaction of SO3 with the surface was found to occur at the dz2 surface orbital that led to the delocalization of SO3 molecular orbitals. This delocalization resulted in the elongation of one S–O bondlength. The barrier for the reaction SO2+O→SO3 was found to be 0.2 eV, smaller than the one for reaction SO2→SO+O which indicate that the SO2+O→SO3 should be more favorable to occur.
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  • Yu Matsuda, Yasuteru Fukawa, Yuji Ike, Masao Kodama, Seiji Kojima
    2008 Volume 77 Issue 8 Pages 084602
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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    The physical properties of lithium borate glasses, xLi2O·(100−x)B2O3, vary anomalously with the lithium oxide content, known as “borate anomaly”. In this study, the compositional variations of the dynamic glass transition temperature Tgω and the non-Debye nature (or stretched exponentiality βKWW) in the vicinity of Tg have been investigated over a wide composition range. Since Tgω depends on the frequency of the temperature modulation, a more precise composition dependence can be discussed. The trend of Tgω shows a single broad maximum at about x=26–28. Moreover, the composition dependence of the non-Debye behavior has been presented. It shows a broad maximum at about x=40 mol %. It is found that βKWW is systematically controlled using the fraction of each intermediate structural unit, particularly the tetrahedron composed of the 4-coordinated boron atom. Both the composition dependences of Tgω and βKWW can be explained using the structure-superposition model.
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  • Hiroyuki Fujishiro, Tomoyuki Naito, Yohei Kashiwada, Yosuke Fujine
    2008 Volume 77 Issue 8 Pages 084603
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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    The thermal conductivities κ(T) of Co- and La-site-substituted LaCoO3 were measured and the origin of the κ(T) peak was investigated. The sharp κ(T) peak at approximately 30 K is strongly suppressed by the introduction of a small amount of Jahn–Teller (JT)-active Co4+ ions because of Co-site substitution by divalent ions such as Ni2+ and Cu2+, similarly to the La-site substitution by Sr2+. In contrast, the κ(T) peak of samples with the Co-site substituted by tetravalent ions such as Sn4+ and Zr4+, which introduce Co2+ ions, moderately decreased. The temperature at which a small and broad κ(T) peak in the Pr-containing RECoO3 [rare-earth (RE) = La1−yPry and Pr1−zNdz] is also observable shifts from 110 K for RE = La0.5Pr0.5 to 180 K for RE = Pr and Pr0.5Nd0.5, which corresponds to the spin-state transition temperature of Co3+ ions.
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  • Yoshihiko Kobayashi, Masanori Shiozawa, Keisuke Sato, Kohji Abe, Kichi ...
    2008 Volume 77 Issue 8 Pages 084701
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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    We have synthesized the polycrystalline La1−xBixNi0.5Mn0.5O3 for x=0–0.9 by soft chemical synthesis, and investigated the crystal structure, and the magnetic and the dielectric properties. The crystal has a monoclinic P21c structure with centrosymmetry for 0≤x≤0.7, and has a monoclinic C2 structure with non-centrosymmetry for 0.8≤x≤0.9 at room temperature. The ferromagnetic Curie temperature (TCM) decreases monotonically from 300 K at x=0 to 150 K at x=0.9, while the Ni2+–Mn4+ configuration is kept independent of Bi-content. For x≥0.5, An anomalous increment of the dielectric constant with increasing temperature and the maximum in the dielectric loss accompanied with frequency dispersion were observed around 150 K, which is close to TCM. However, no evidence showing a ferroelectric ordering was observed below 400 K. For x=0.7, the increment of the dielectric constant induced by the magnetic field is 7% at TCM at 9 T. The temperature and the magnetic field dependence of the dielectric properties is discussed based on Maxwell–Wagner model assuming an inhomogeneity of samples and a negative magnetoresistance.
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  • Shinta Watanabe, Kazuyoshi Ogasawara
    2008 Volume 77 Issue 8 Pages 084702
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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    In this paper, we investigated the 4f–5d absorption spectrum of Ce3+ in LiYF4 based on first-principles calculations. In order to take into account the effect of lattice relaxation, the local structure around Ce3+ was optimized based on a pseudopotential plane wave method using the CASTEP code. The scalar relativistic effects were taken into account in this calculation. The results indicated that the position of Ce3+ was shifted to an off-center position along c-axis by 0.074 Å, resulting in a symmetry reduction of Ce3+ site from S4 to C2. In order to calculate the theoretical absorption spectra, the fully-relativistic four-component molecular orbital (MO) calculations were also performed using a cluster model constructed from the optimized structure. The theoretical 4f–5d absorption spectrum of Ce3+ in LiYF4 obtained for the optimized structure was in good agreement with the experimental one. Especially the five peaks in the experimental spectrum were reproduced without any empirical parameters for the first time.
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  • Kazuaki Kobayashi, Shojiro Komatsu
    2008 Volume 77 Issue 8 Pages 084703
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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    We calculated the electronic and lattice properties of BN, SiC, and AlN polytypes. The calculated polytypes are 2H, 3C (= 3H), 4H, 5H, and 6H. These polytypes are sp3-bonded compounds. The 6H polytype has two crystal structures as ABCACB and ABCBCB stacking sequences. The lattice properties were optimized automatically by the first-principles molecular dynamics (FPMD) method. Most calculated electronic band structures of these polytypes are non-metallic and their band gaps are indirect. The most stable BN, SiC and AlN polytypes are 3C-BN, 4H-SiC, and 2H-AlN, respectively. The calculated total energies of BN polytypes are in the order of 3C<6H(ABCACB)<5H<4H<6H(ABCBCB)<2H. The calculated total energies of SiC polytypes are in the order of 4H<6H(ABCACB)<3C<5H<6H(ABCBCB)<2H. The calculated total energies of AlN polytypes are in the order of 2H<6H(ABCBCB)<4H<5H<6H(ABCACB)<3C. The total energies and energetical stabilities of the BN and AlN polytypes are related to hexagonality which corresponds to the ratio of the number of third-neighbor cation–anion pairs and the number of cation–anion bilayers in the unit cell. 6H-BN(ABCACB) and 6H-SiC(ABCACB) are energetically more favorable than 6H-BN(ABCBCB) and 6H-SiC(ABCBCB), respectively. In contrast, 6H-AlN(ABCBCB) is more favorable than 6H-AlN(ABCACB).
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  • Shunsuke Kirino, Tatsuya Fujii, Jize Zhao, Kazuo Ueda
    2008 Volume 77 Issue 8 Pages 084704
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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    Resonant tunneling through quantum dot under a finite bias voltage at zero temperature is investigated by using the adaptive time-dependent density matrix renormalization group (TdDMRG) method. Quantum dot is modeled by the Anderson Hamiltonian with the one-dimensional nearest-neighbor tight-binding leads. Initially the ground state wave function is calculated with the usual DMRG method. Then the time evolution of the wave function due to the slowly changing bias voltage between the two leads is calculated by using the TdDMRG technique. Even though the system size is finite, the expectation values of current operator show steady-like behavior for a finite time interval, in which the system is expected to resemble the real nonequilibrium steady state of the infinitely long system. We show that from the time intervals one can obtain quantitatively correct results for differential conductance in a wide range of bias voltage. Finally we observe an anomalous behavior in the expectation value of the double occupation operator at the dot ‹nn› as a function of bias voltage.
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  • Masashi Yamamoto, Mikito Koshino, Tsuneya Ando
    2008 Volume 77 Issue 8 Pages 084705
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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    The distribution of induced electric field around a carbon nanotube is calculated in an external field applied perpendicular to the axis. In multi-wall nanotubes, the field is screened out almost completely by a few outer walls. The field distribution is calculated also for a magnetic field, showing that NMR line is broadened roughly in proportion to the wall number in multi-wall nanotubes.
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  • Jun-ichi Igarashi, Tatsuya Nagao
    2008 Volume 77 Issue 8 Pages 084706
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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    We study noncentrosymmetric effects on resonant x-ray scattering (RXS) in magnetite. The noncentrosymmetry at A sites in spinel structure makes the 4p states strongly hybridize with the 3d states through neighboring oxygen 2p states, giving rise to the non-vanishing contribution of the dipole–quadrupole (E1–E2) process in the RXS spectra. We substantiate this observation by introducing a microscopic model of a FeO4 cluster with multiplets and the 4p band. We show that the hybridization changes its sign between two kinds of A sites and accordingly the local amplitude from the E1–E2 process changes its sign, resulting in non-vanishing RXS intensities at forbidden spots (002) and (006) in the pre-edge region in agreement with the experiment. A large dependence of the pre-edge intensity on the direction of the applied magnetic field is predicted as a consequence of breaking both centrosymmetry and time-reversal symmetry. Furthermore we analyze the intensity difference between two opposite directions of the applied magnetic field at the allowed spot (222) in connection with the experiment. We obtain the intensity difference of a “dispersion” form, which resembles the observed spectra at the Mn pre-K-edge in MnCr2O4 but is quite different from the observed one in magnetite. Although the observed spectra are claimed to arise from “magnetoelectric” amplitude, we argue that this claim has no ground.
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  • Takafumi Kashi, Yukio Yasui, Taketo Moyoshi, Masatoshi Sato, Kazuhisa ...
    2008 Volume 77 Issue 8 Pages 084707
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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    Crystal and magnetic structures as well as magnetic properties have been studied for a newly synthesized system CoZn(TeO3)Br2. Although the system is isomorphic to Co2(TeO3)Br2, as revealed by neutron diffraction study, magnetic characteristics of the two systems are different, because the Zn atoms in CoZn(TeO3)Br2 decouple the magnetic interaction among the chains of corner-sharing CoO4Br2 octahedra, inducing the one-dimensionality of Co spins. At temperature TN∼9.0 K, it exhibits a transition to an antiferromagnetic state accompanied by the weak ferromagnetic moment. The Weiss temperature θW is estimated to be −68.5 K from the magnetic susceptibility data. The small value of |TN⁄θW| (∼0.13) indicates the existence of the effect of magnetic fluctuation. The magnetic structure below TN has also been determined by a powder neutron diffraction study, where Co spins within a chain are found to order basically in an antiferromagnetic way with the spins along the c direction (chain direction), but they are canted from the c-axis toward the b-axis by an angle of 17 (±3)°. Because the weak ferromagnetic components of the chains created by this canting align antiferromagnetically, the spontaneous moments stated above is considered to be due to the additional canting toward the a-axis. The existence of a temperature-linear component in the specific heat at low temperatures suggests that a significant fraction of Co spins remains in the disordered or glassy state.
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  • Yuki Ida, Rikio Settai, Yuuki Ota, Fuminori Honda, Yoshichika Onuki
    2008 Volume 77 Issue 8 Pages 084708
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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    An antiferromagnet CeRhIn5 is well known to be changed into a superconductor by applying pressure P. Its electronic state is also clarified to be changed at the critical pressure Pc\\simeq2.5 GPa under magnetic fields. We measured the low-temperature electrical resistivity of CeRhIn5 in magnetic fields up to 17 T and at pressures up to 2.45 GPa, and constructed phase diagrams. At P=2.45 GPa, which is close to Pc\\simeq2.5 GPa, there are four kinds of phases, namely, the paramagnetic, superconducting, superconducting and antiferromagnetic, and antiferromagnetic phases in the temperature vs magnetic field phase diagram. The antiferromagnetic phase is found to be induced in the superconducting phase under magnetic fields and expanded in magnetic fields higher than the upper critical field in superconductivity. Interestingly, the anisotropy of the upper critical field in CeRhIn5 is found to be different from that in a similar non-magnetic heavy-fermion superconductor CeCoIn5, revealing the anisotropic paramagnetic suppression of the upper critical field.
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  • Hiroyuki Mashiyama, Serges Eric Mkam Tchouobiap, Masami Ashida
    2008 Volume 77 Issue 8 Pages 084709
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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    A ferrodistortive phase transition is analyzed for a quantum particles in a simple quartic potential. The interactions are taken into account by the mean-field approximation. A quantum thermodynamic treatment gives analytic expressions for the static susceptibility, the specific heat and the soft mode frequency. The Rhodes–Wohlfarth ratio is a measure whether the system is order–disorder or displacive, however, the border is fuzzy depending on the interaction strength. The quantum effect is discussed when the transition takes place at low temperature. Whether the atomic density is a single or multiple peak distributions seems to be a definite criterion for the character of the structural phase transition.
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  • Tatsuya Nagao, Jun-ichi Igarashi
    2008 Volume 77 Issue 8 Pages 084710
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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    Developing an expression of resonant x-ray scattering (RXS) amplitude which is convenient for investigating the contributions from the higher rank tensor on the basis of a localized electron picture, we analyze the RXS spectra from the magnetic phases of Ho near the M4,5 absorption edges. At the M5 edge in the uniform helical phase, the calculated spectra of the absorption coefficient, the RXS intensities at the first and second satellite spots capture the properties the experimental data possess, such as the spectral shapes and the peak positions. This demonstrates the plausibility of the adoption of the localized picture in this material and the effectiveness of the spectral shape analysis. The latter point is markedly valuable since the azimuthal angle dependence, which is one of the most useful informations RXS can provides, is lacking in the experimental conditions. Then, by focusing on the temperature dependence of the spectral shape at the second satellite spot, we expect that the spectrum is the contribution of the pure rank two profile in the uniform helical and the conical phases while that is dominated by the rank one profile in the intermediate temperature phase, so-called spin slip phase. The change of the spectral shape as a function of temperature indicates a direct evidence of the change of magnetic structures undergoing. Furthermore, we predict that the intensity, which is the same order observed at the second satellite spot, is expected at the fourth satellite spot from the conical phase in the electric dipolar transition.
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  • Toshihito Osada
    2008 Volume 77 Issue 8 Pages 084711
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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    The interlayer magnetotransport has been considered in multilayer Dirac electron systems, in which two-dimensional electron layers with Dirac-cone dispersion stack with weak interlayer coupling. Under magnetic fields, one Landau level (zero-mode) always appears at the contact point of Dirac cones, and tunneling between the zero-modes on neighboring layers dominates interlayer transport in multilayer systems. The increase of zero-mode degeneracy causes strong negative magnetoresistance. Spin splitting of the zero-mode could change the negative magnetoresistance to the positive one in high magnetic fields and low temperatures. The magnetotransport features observed in an organic conductor α-(BEDT-TTF)2I3 are discussed based on the present model.
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  • Hidetsugu Sakaguchi, Toru Maruyama
    2008 Volume 77 Issue 8 Pages 084801
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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    The Luo–Rudy model is one of the standard models for the excitation of cardiac cells. Traveling pulses and spiral waves appear in one-dimensional or two-dimensional Luo–Rudy models. Spiral waves in two-dimensional systems are interpreted as a possible origin of ventricular fibrillation, which is the most serious type of cardiac arrhythmia. Defibrillation is a process to eliminate spiral waves and stop ventricular fibrillation. We perform numerical simulations to eliminate traveling pulses and spiral waves by applying direct current or alternating current to the Luo–Rudy model.
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  • Hisanao Takahashi, Naoto Horibe, Masakazu Shimada, Takashi Ikegami
    2008 Volume 77 Issue 8 Pages 084802
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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    This paper presents a detailed characterization of the trajectory of a single housefly with free range of a square cage. The trajectory of the fly was recorded and transformed into a time series, which was fully analyzed using an autoregressive model, which describes a stationary time series by a linear regression of prior state values with the white noise. The main discovery was that the fly switched styles of motion from a low dimensional regular pattern to a higher dimensional disordered pattern. This discovered exploratory behavior is, irrespective of the presence of food, characterized by anomalous diffusion.
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  • Chen-Yu Tsai, Mei-Chu Chang, Lin I
    2008 Volume 77 Issue 8 Pages 084803
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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    We experimentally demonstrate the observation of several pathways with a few tens of ms inter-cluster delay but negligible intra-cluster delay, in the spontaneous synchronous burstings (SSBs) of clusterized cortical neuronal networks in vitro through epifluorescence microscopy of Ca2+ indicator. Nearby clusters sharing the similar relative firing timings in different SSB events form a group. Switching among different SSB pathways initiated by different master groups is found. Under chemical tuning such as decreasing the mutual coupling by increasing [Mg2+] or lowering the effective firing threshold by increasing [K+], the firing sequence of each pathway remains robust, but the occurrence probability and the temporal persistence of each pathway, and the inter-cluster delay times in the firing sequences can be varied.
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  • Ryoichi Yamamoto, Kang Kim, Yasuya Nakayama, Kunimasa Miyazaki, David ...
    2008 Volume 77 Issue 8 Pages 084804
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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    In this letter, we investigate several aspects related to the effect of hydrodynamic interactions on phase separation-induced gelation of colloidal particles. We explain physically the observation of hydrodynamic stabilization of cellular network structures in two dimensions. We demonstrate that hydrodynamic interactions have only a minor quantitative influence on the structure of transient gels in three dimensions. We discuss some experimental implications of our results.
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  • Hitoshi Sugawara, Eiichi Kuramochi, Takahiro Namiki, Tatsuma D. Matsud ...
    2008 Volume 77 Issue 8 Pages 085001
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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  • Keisuke Matsuda, Shin Miyahara, Nobuo Furukawa
    2008 Volume 77 Issue 8 Pages 085002
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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  • Takehito Yokoyama, Seiichiro Onari, Yukio Tanaka
    2008 Volume 77 Issue 8 Pages 088001
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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  • Tetsuya Nakajima, Koji Hukushima
    2008 Volume 77 Issue 8 Pages 088002
    Published: August 15, 2008
    Released on J-STAGE: December 28, 2011
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