Journal of the Physical Society of Japan
Online ISSN : 1347-4073
Print ISSN : 0031-9015
ISSN-L : 0031-9015
Volume 70, Issue 3
Displaying 1-50 of 52 articles from this issue
  • Franklin Lambert, Ignace Loris, Johan Springael, Ralph Willox
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 605-608
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    Alternative Hirota representations in terms of a single tau-function are derived for a variety of soliton equations, including the sine-Gordon and the Tzitzeica equations. The relevance of these representations with respect to known bilinear representations of integrable hierarchies is briefly discussed. The essentials of the derivation method are presented.
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  • Haruhiko Takase
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 609-612
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    A divertor magnetic configuration is proposed that significantly reduces heat load on the divertor plates in tokamak devices. The proposed configuration utilizes an additional cusp-like magnetic field generated by four poloidal coils for expanding the divertor channels. This not only allows a significant reduction of the heat load due to expansion of the divertor channels but also hardly affects the original magnetic configuration of the core plasma. These special features are useful for fusion reactor designs.
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  • Sheikh Dastgeer, Jae Koo Lee
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 613-616
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    It is demonstrated using numerical simulation that spectral anisotropy in two-dimensional decaying electron magneto-hydrodynamic turbulence varies linearly with the ratio of fluctuating to mean magnetic field. Turbulent excitation scales larger (kλ e<1) as well as smaller (kλ e>1) than the electron skin depth scale length (λ e) are shown to exhibit such linear scaling behavior.
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  • Kazunobu Nagasaki, Michael G. Shats, Helen Smith, Horst Punzmann
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 617-620
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    Power absorption is calculated for electron cyclotron resonance heating (ECRH) in the H-1 heliac device by using a ray tracing numerical code. The three-dimensional magnetic field structure and the bean shape of flux surfaces are considered. The calculation results show that the second harmonic extraordinary mode heating is effective even at low density if the launching direction is properly adjusted. The localized power absorption profile can be shifted from on-axis to off-axis by controlling the magnetic field strength or the launching angle, making the heat transport experiment possible.
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  • Masako Shindo, Yoshinobu Kawai
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 621-623
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    An attempt to measure the negative ion density in an O2/Ar electron cyclotron resonance (ECR) plasma is made by means of the propagation of ion acoustic waves (IAWs) (fast mode). IAWs are launched along magnetic fields using a wire antenna to which positive pulse voltages are applied. The IAWs are detected as a fluctuation of the ion saturation current flowing into a plane Langmuir probe. The change of the phase velocity of IAWs is observed when the gas mixture ratio is varied. It is found that the density ratio of negative ions to positive ions, α, is less than 0.3, and has an optimum value at the gas mixture ratio of 15%.
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  • Jun-ichi Sakai, Takayuki Haruki
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 624-627
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    It is shown by using a 2-dimensional fully relativistic electromagnetic particle-in-cell (PIC) code that a force-free collisionless pair plasma which is stable against collisionless tearing instability becomes unstable when driven by relativistic plasma flows and the magnetic field energy can be strongly dissipated and converted to heat plasmas as well as high-energy particle production. The force-free current sheet becomes unstable against the firehose instability and eventually breaks up into current filaments which are associated with the magnetic reconnection. The energy spectrum in the high-energy region shows an exponential-type law. The interaction process between the force-free collisionless plasmas and the relativistic plasma flows is an important mechanism for understanding the effective magnetic energy conversion, filament structures and high-energy particle production in astrophysical plasmas.
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  • Hiroyuki Fujishiro, Tetsuo Fukase, Manabu Ikebe
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 628-631
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    The longitudinal sound velocity vs(T) has been measured for La1-XCaXMnO3 crystals, and anomalous softenings of vs(T) have been observed at the peculiar Ca concentrations of X=0.19 and X=0.82. For the X=0.19 sample, in which the ferromagnetic (FM) metallic phase competes with the FM insulating phase with a polaron ordering, the anomalous vs(T) softening occurs immediately below the FM transition temperature Tc. For the X=0.82 sample, in which the charge-ordered (CO) phase competes with the canted antiferromagnetic (CAF) phase, the deep local minimum of vs(T) occurs around the CO transition temperature TCO. These anomalous vs(T) softenings result from the giant lattice fluctuations which originate from phase competitions and suggest strong charge-lattice and spin-lattice coupling in this system.
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  • Shigeki Onoda, Masatoshi Imada
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 632-635
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    A new non-perturbative framework for many-body correlated systems is formulated by extending the operator projection method (OPM). This method offers a systematic expansion which enables us to project into the low-energy structure after extracting the higher-energy hierarchy. This method also opens a way to systematically take into account the effects of collective excitations. The Mott-Hubbard metal-insulator transition in the Hubbard model is studied by means of this projection beyond the second order by taking into account magnetic and charge fluctuations in the presence of the high-energy Mott-Hubbard structure. At half filling, the Mott-Hubbard gap is correctly reproduced between the separated two bands. Near half filling, strongly renormalized low-energy single-particle excitations coexisting with the Mott-Hubbard bands are shown to appear. The significance of the momentum-dependent self-energy in the results is stressed.
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  • Kiyomi Okamoto, Nobuhisa Okazaki, Toru Sakai
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 636-639
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    We study the magnetization plateau at 1/4 of the saturation magnetization of the S=1 antiferromagnetic spin ladder both analytically and numerically, with the aim of explaining recent experimental results on 3,3,5,5-tetrakis(N-tert-butylaminoxyl)biphenyl. We propose two mechanisms for the plateau formation and clarify the plateau phase diagram on the plane of the coupling constants between spins.
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  • Hirokazu Tsunetsugu
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 640-643
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    The ground state of the S=½ Heisenberg antiferromagnet on the pyrochlore lattice is theoretically investigated. Starting from the limit of isolated tetrahedra, I include interactions between the tetrahedra and obtain an effective model for the spin-singlet ground state multiplet by third-order perturbation. I determine its ground state using the mean-field approximation and find a dimerized state with a four-sublattice structure, which agrees with the proposal by Harris et al. I also discuss chirality correlations and spin correlations for this state.
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  • Yutaka Itoh, Takato Machi, Nobuaki Watanabe, Naoki Koshizuka
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 644-647
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    The difference in the lightly doped impurity effects on the local magnetic correlation between magnetic Ni and nonmagnetic Zn impurities has been studied by the planar 63Cu nuclear spin-lattice relaxation for high-Tc superconductor YBa2(Cu1-xMx)4O8 (M=Ni, Zn) with the Cu nuclear quadrupole resonance (NQR) spin-echo technique. In the light of an impurity-induced nuclear spin-lattice relaxation theory, we conclude that the wipeout region around impurities at T=4.2 K is more extended for Zn than for Ni. It was found that the magnetically enhanced region is wider around Zn than around Ni in the superconducting state.
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  • Masaru Kasahara, Hiroki Hasebe, Ruiping Wang, Mitsuru Itoh, Yoshirou Y ...
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 648-651
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    Antiferrodistortive and ferroelectric soft modes of isotoped ferroelectric SrTi18O3x16O3(1-x) were observed for a single crystal of x=0.87 with Raman scattering. The frequency of one of the antiferrodistortive modes exhibits a gradual change near the ferroelectric transition point at 24 K (Tc) induced as the isotope effect. The spectral forms characteristic of the ferroelectric microscopic regions were also observed in both phases. The ferroelectric soft mode does not exhibit any softening behavior even just at Tc. The transition mechanism of the isotopically induced ferroelectric phase is discussed.
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  • Yu Shun Wang, Meng Zhao Qin
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 653-661
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    The multisymplectic structure of the Nonlinear Klein Gordon equation is presented directly from the variational principle. In the numerical aspect, we give a multisymplectic nine points scheme which is equivalent to the multisymplectic Preissmann scheme. A series of numerical results are reported to show the effectiveness of the scheme.
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  • Ignace Loris
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 662-665
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    A class of solutions in determinant form to a set of coupled KdV equations is derived. The bilinear (Hirota) form of the coupled equations and links with the CKP system serve as guide.
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  • Derek W. C. Lai, Kwok W. Chow
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 666-677
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    New solutions of several nonlinear evolution equations (NEEs) are obtained by a special limit corresponding to a coalescence or merger of wavenumbers. This technique will yield the multiple pole solutions of NEEs if ordinary solitons are involved. This limiting process will now be applied through the Hirota bilinear transform to other novel solutions of NEEs. For ripplons (self similar explode-decay solutions) such merger yields interacting self similar solitary waves. For breathers (pulsating waves) this coalescence gives rise to a pair of counterpropagating breathers. For dromions (exponentially decaying solutions in all spatial directions) this merger might generate additional localized structures. For dark solitons such coalescence can lead to a pair of anti-dark (localized elevation solitary waves on a continuous wave background) and dark solitons.
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  • Akihide Takeda, Nobuaki Ikuta
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 678-688
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    Spatially resolved electron transport properties in steady state (SST) under the uniform electric field are investigated. It is found that the balance of local energy gain and loss always holds by taking into account the divergence of the energy flow, that is, the energy conservation law and the continuity equation of the energy flow for an electron swarm are affirmed to hold with the numerical data. Further, the features of the electron flux and the energy flow, the effects of ionization, excitation and attachment on the formation of the energy distribution, the condition forming the equilibrium and non-equilibrium regions in conservative and non-conservative cases for the electron number due to ionization and attachment etc. are discussed in detail.
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  • Oleg A. Yuminov, Sergei Yu. Platonov, Dmitri O. Eremenko, Olga V. Foti ...
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 689-695
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    The crystal blocking technique has been used to measure delay times in the fission channel for excited nuclei produced in the 28Si+natPt reaction. Experimental results range from 10-17 to 10-18 s at bombarding energies from 140 to 170 MeV. It is shown that fission barriers keep their double-humped structure for nuclear temperature up to 1.7-1.8 MeV, and that the lifetimes of excited states in the second potential well contribute essentially to the observed delay times in the fission channel.
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  • Radostin Danev, Kuniaki Nagayama
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 696-702
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    We report microscopic observation of complex waves emitted from objects. Two images sequentially detected at the image plane with two transmission electron microscopic (TEM) methods, the conventional and the phase-contrasted, are numerically combined to reproduce complex wave functions, which are holding complete optical information. The long lasting issue in conventional TEM that the contrast and the resolution of images are difficult to be simultaneously optimized was settled with the complex wave functions. The aberration-corrected phase images of ferritin (at 400 kV) and TMV (at 100 kV) did show an extraordinary high contrast free from image distortion without sacrificing the resolution compared with that obtained by conventional TEM.
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  • Tomoaki Itano, Sadayoshi Toh
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 703-716
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    We have examined bursting processes observed in turbulent channel flow by direct numerical simulation of the incompressible Navier-Stokes equations in a minimal flow unit. A traveling wave solution (TWS) is obtained by a shooting method. The TWS corresponds to a saddle point in a two-dimensional phase space. A low-dimensional dynamics confined to the near-wall region is proposed in terms of the TWS and its manifolds. The characteristics of the coherent structures constituting the TWS are investigated dynamically and statistically in detail. The dynamics well describes an elementary process of intermittent turbulent regeneration in wall turbulence.
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  • Hee Tae Jeong, Yong Chan Cho, Chae Ryong Cho, Se-Young Jeong
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 717-722
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    By the crystallographic consideration, all permissible domain walls were obtained for CsPbCl3, a crystal that undergoes very complicated phase transition sequences. We constructed the possible domain structures and classified the domain walls into various types according to the domain structures. In particular, those by a fourfold wall, Wƒ, which was found by considering the wall symmetry were constructed. The results also showed that the W' walls, which were defined in a continuous model of the mechanical properties, are the crystallographic planes with fixed indices.
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  • Kripa Shankar Upadhyaya, Gopal Krishna Upadhyaya, Mahendra Yadav
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 723-728
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    The basic equations of three-body force shell model have been corrected for the ionic charge parameter Z. This correction also modifies the expressions for the shell and core charge parameters. Our model has been applied to study the phonon dispersion curves, Debye temperatures variation, combined density of states and two-phonon Raman scattering spectra of wustite. This approach has been found successful in interpreting the complete lattice dynamics of FeO only when both the ions are considered to be polarizable. There is good scope for the fresh determination of positive ion polarizability and Debye temperatures variation. It is concluded that the presence of magnetic and anharmonic interactions have no effect on the lattice dynamics of FeO in its paramagnetic phase.
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  • Miho Motoyama, Yoshihiro Yamazaki, Takao Ohta
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 729-732
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    We introduce a quite simple model for a phase-separating binary mixture where one of the components is cross-linked. It is shown by computer simulations that target patterns are generated. We use a Cahn-Hilliard equation with a bulk free energy density which varies as a molecular weight changes with time. Target patterns are obtained in the following way. We first quench the system, having an off-critical composition, into a spinodal region, and find that disconnected droplets emerge in the system. With cross-linking one of the components, the phase diagram of the system shifts to a location where a bicontinuous structure is formed. As a result, target patterns grow from the droplets without any additional nuclei.
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  • Shijin Zhao, Dayong Cheng, Shaoqing Wang, Hengqiang Ye
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 733-737
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    The melting transition in three high-energy and two low-energy fcc Cu symmetrical tilt grain boundaries (STGBs) has been investigated by molecular-dynamics (MD) simulations. Low-energy STGBs are found to be crystalline from room temperature all the way up to T0 (T0 is the thermodynamic equilibrium melting point). In contrast, all high-energy STGBs undergo premelting which is initiated at a transition temperature Tc (Tc<T0). Moreover, the higher the zero-temperature GB energy, the lower the Tc.
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  • Jiunn-Ren Roan, Toshihiro Kawakatsu
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 738-742
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    A quasi two-dimensional (2D) model for the solid phases (CS, S, and LS) of Langmuir monolayers is proposed. The model can reproduce the CS-S and S-LS transitions and many other experimental results observed in the monolayers of fatty acids using parameters that can be estimated from experiments. It is demonstrated that, although being ignored in many theories, electrostatic interactions indeed play a crucial role in the polymorphism of the monolayer.
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  • Hideaki Uemura, Yukio Saito, Makio Uwaha
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 743-752
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    We introduce a two-dimensional lattice model with elastic deformations and calculate numerically the interaction energy between force distributions localized on a surface. In particular, the interaction between adatoms and that between steps are evaluated by the use of corresponding force distributions, and the result is compared with the continuum elasticity theory where surface defects are replaced by force dipoles placed on a flat surface. The continuum theory agrees with the simulation result asymptotically when the surface is flat, but it does not when there are steps on the surface. Steps with the same sign interact with the power law r-2 in agreement with the continuum theory, but its strength is about ten times larger than the theoretical one. The interaction between steps with the opposite signs shows an apparent discrepancy: the power-law interaction with noninteger exponents in the simulation whereas no interaction in the continuum elasticity theory.
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  • Shigeru Takayanagi, Shingo Araki, Rikio Settai, Yoshichika Onuki, Nobu ...
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 753-755
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    We have studied the pressure dependence of the specific heat in a CeNi single crystal using a clamp-type pressure-cell up to 0.8 GPa. The pressure dependence of the electronic specific heat coefficient is found to exhibit a sharp drop at 0.3-0.4 GPa. The present result indicates the instability of a mixed valence state of 4f electrons.
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  • Tomofumi Susaki, Atsushi Fujimori, Yukiharu Takeda, Masaki Taniguchi M ...
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 756-761
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    We have studied the substitution and temperature dependences of the B sp-Yb d-derived conduction-band states in Yb1-xLuxB12 (x = 0.25, 0.50, 0.75, and 1.00) by high-resolution photoemission spectroscopy. As the Yb content increases, the density of states (DOS) between the Fermi level (EF) and ∼ - 20 meV is reduced while a broad peak grows at ∼-80 meV. The DOS reduction is considerably weakened at high temperatures (> ∼100 K), consistent with the gap formation in YbB12 only at low temperatures. The temperature dependence of the DOS near EF gradually becomes stronger with decreasing x but is abruptly enhanced below x = 0.25-0.50, showing the crucial contribution of Yb-Yb intersite interaction to the gap formation in YbB12. The ∼-80 meV peak survives up to large x, indicating that it is caused by a single-impurity effect.
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  • Hideo Yoshioka, Masahisa Tsuchiizu, Yoshikatsu Suzumura
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 762-773
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    We examine effects of the next-nearest-neighbor repulsion on electronic states of a one-dimensional interacting electron system which consists of quarter-filled band and interactions of on-site and nearest-neighbor repulsion. We derive the effective Hamiltonian for the electrons around wave number ± kF (kF: Fermi wave number) and apply the renormalization group method to the bosonized Hamiltonian. It is shown that the next-nearest-neighbor repulsion makes 4kF-charge ordering unstable and suppresses the spin fluctuation. Further the excitation gaps and spin susceptibility are also evaluated.
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  • Haruyoshi Aoki, Masahiro Takashita, Noriaki Kimura, Taichi Terashima, ...
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 774-783
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    We have studied the Fermi surface properties of CeRu2Si2 below and above the metamagnetic transition (MT) under high pressures. The frequencies of the dHvA oscillations change considerably with pressure both below and above the MT. The pressure coefficient of the frequencies are larger than those of normal metals by more than ten times. The sign and value of the pressure coefficient depend on the dHvA frequency or the orbit. Below the MT the effective masses decrease with increasing pressure, while that above the MT is found to slightly increase. The dHvA oscillations can be traced through the MT at high pressures and it is found that the Fermi surface changes from that of the itinerant f electron to another Fermi surface which is similar to that of the localized f electron in a field range much narrower than that of the MT width in the magnetization. An analysis based on the pressure effect of the Fermi surface indicates that the Fermi surface remains unchanged when the filed approaches the MT field (Hm), if the volume is constant. If we extrapolate the experimental Hm vs. pressure relation to the negative pressure side, the volume at Hm=0 coincides with the volume at the quantum critical point suggested by the studies of CeRu2Ge2 system under high pressure or CeRu2(Ge1-xSix)2 system. The experimental observations are discussed to suggest that the MT of CeRu2Si2 is a phenomenon closely related with the quantum critical point.
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  • Keita Kishigi
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 784-788
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    The coexistent state of the spin density wave (SDW) and the charge density wave (CDW) in the one-dimensional systems is studied by the mean field approximation at T=0 in various electron-filling cases. We find that the coexistent state of SDW and CDW is stabilized at all fillings except for the half-filling when the on-site and the inter-site Coulomb interactions have the values estimated for organic conductors. The ground state energies have cusp-like minima at n/4m-filling, where n and m are integers.
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  • Nam Kim, Jinhee Kim, Jeong-O Lee, Kicheon Kang, Kyung-Hwa Yoo, Jong Wa ...
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 789-792
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    Non-local electric transport phenomena were observed for a multi-wall carbon nanotube. The magnetic field dependence of non-local resistance was out of phase with respect to the conventional four-probe resistance, which could be explained in terms of the Landauer-Büttiker formula. Our observations indicate that the phase coherence length of multi-wall carbon nanotube exceeds the voltage probe length of about 1.1 μm at the measured temperatures.
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  • Yoshitada Murata, Kazuo Nagata, Hiroshi Fujimoto, Takeaki Sakurai, Mic ...
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 793-796
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    High-quality single-crystal films of α-Al2O3 with various thicknesses below 35Å have been fabricated on the Ru(0001) surface. The phase transtion from γ- to α-Al2O3 has been used for fabrication. The thickness dependence of the band gap for the oxide layer has been measured by the interband transition using electron energy loss spectroscopy. The band gap has been found to decrease with decreasing oxide thickness. The same tendency of this extraordinary result has been observed in scanning tunneling spectroscopy. These results can be interpreted by the many-body effect.
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  • Zhenji Li, Kosaku Yamada
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 797-807
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    The crossover between the Cooper-pair condensation and the Bose-Einstein condensation of di-electronic molecules in quasi-two dimensional superconductors is investigated on the basis of the Nozières and Schmitt-Rink theory from a general point of view. By using this formalism we calculate directly thermodynamic quantities and develop further the theory by Tokumitu et al. Through the study we find that the T-linear coefficient of the electronic specific heat γ(T) decreases with decreasing temperature above Tc for sufficiently strong coupling interaction. This pseudo-gap behavior in the electronic specific heat coefficient is confirmed by using the t-matrix approximation in Luttinger's theory.
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  • Jun Kondo
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 808-812
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    Superconductivity of the two-dimensional Hubbard model with t=0 has been examined in the small U limit, where the matrix element of pair scattering is expressed as Vkk=U+U2χ (k+k). The susceptibility χ (k) of the unperturbed band has been evaluated accurately and the gap equation, which reduces to a seqular equation, has been solved precisely. The gap is found to be of the form ∝exp (-2t2/xU2), where x is the eigenvalue of the seqular equation. We have found the largest eigenvalue x is always positive (superconductive). The symmetry of the gap function is b1g for the electron density ne>0.6 and b2g for ne<0.6, depending on the peak position of χ (k). It is roughly (π , π ) for the former case and (π, 0) for the latter. The superconductivity seems to prevail even for ne→ 0. These results can be explained with a simple criterion.
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  • Tatsuo C. Kobayashi, Hiroshi Tatewaki, Akihiro Koda, Kiichi Amaya, Yas ...
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 813-817
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    Field-induced long-range ordering is investigated by heat capacity and high-field magnetization measurements in Haldane gap system Ni(C5H14N2)2N3(ClO4) (NDMAZ). In the high-field magnetization measurement along the crystal c-axis, the differential magnetization is found to reveal the characteristic peak corresponding to the phase transition to the ordered state. The magnetization increases as (H-HC)0.6 at the lowest temperature. The phase boundary determined down to 44 mK by the peak of the differential magnetization obeys TN∼ (H-HC)0.45. Anisotropic phase diagram is similar to that of Ni(C5H14N2)2N3(PF6) (NDMAP).
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  • Masanori Ichioka, Eiji Kaneshita, Kazushige Machida
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 818-828
    Published: 2001
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    Dynamical spin and charge susceptibility and collective modes are studied in the framework of the random phase approximation. They are calculated from the wave function of the selfconsistently obtained ground state, including all possible higher harmonics components of the ordering vector Q. We investigate a spin wave excitation in the spin transverse mode, and phason excitation related to the domain-wall motion in the spin longitudinal and charge modes. We consider the dispersion curve of the collective mode, and discuss the dependence on the on-site U interaction and the period of the incommensurate structure.
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  • Osiel F. de Alcantara Bonfim, Beatriz Boechat, Claudette Cordeiro, Fra ...
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 829-833
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    We study the time dependent behavior of the four-spin interactions Ising chain in the presence of a disordered transverse magnetic field. In order to analyze the effects of field randomness in the dynamical behavior of the system we calculate the time-dependent correlation function and the longitudinal relaxation function of the infinite chain. We consider a bi-modal distribution for the field energy strength, where one of its values equals the exchange coupling energy while the other value can be lower or higher than the coupling energy. We find that an increasing concentration of weaker fields produces an enhancement of the central mode behavior. However, when the concentration of stronger fields increases, the system undergoes a crossover from central mode to collective-type dynamics.
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  • Ichiro Tsukada, Tsuyoshi Yamamoto, Mikio Takagi, Takashi Tsubone, Susu ...
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 834-840
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    Ferromagnetism and accompanying large negative magnetoresistance in Pb-substituted Bi-Sr-Co-O misfit-layer compound are investigated in detail. Recent structural analysis of (Bi,Pb)2Sr3Co2O9, which has been believed to be a Co analogue of Bi2Sr2CaCu2O8+δ, revealed that it has a more complex structure including a CoO2 hexagonal layer [T. Yamamoto et al., Jpn. J. Appl. Phys. 39 (2000) L747]. Pb substitution for Bi not only introduces holes into the conducting CoO2 layers but also creates a certain amount of localized spins. Ferromagnetic transition appears at T = 3.2 K with small spontaneous magnetization along the c axis, and around the transition temperature large and anisotropic negative magnetoresistance was observed. This compound is the first example which shows ferromagnetic long-range order in a two-dimensional metallic hexagnonal CoO2 layer.
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  • Kunitomo Hirai
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 841-852
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    A first-principles electronic structure calculation for Fe/Cr superlattices with layered structures is performed by means of the Korringa-Kohn-Rostoker Green function method within the framework of the local spin density functional formalism. The calculation is carried out for periodic superlattices which consist of ferromagnetic Fe layers and antiferromagnetic or spin-density-wave Cr layers, with magnetizations of two successive Fe layers being aligned parallel or antiparallel, and interlayer magnetic coupling is evaluated by the total energy difference between the parallel and antiparallel couplings. It is shown that the interlayer magnetic coupling oscillates between parallel and antiparallel with a two-monolayer period of the spacer thickness of the Cr layer but the oscillation involves a phase slip around a critical thickness of 16 monolayers, at which the magnetic order in the Cr layer changes from the antiferromagnetic one to the spin-density-wave one. Characteristics of the spin-density-wave order are investigated in detail and are found to be different from those in bulk Cr, due to the proximity Fe layers.
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  • Haruhiro Hiraka, Yasuo Endoh, Masaki Fujita, Young S. Lee, Jiri Kulda, ...
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 853-858
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    We performed magnetic inelastic neutron-scattering experiments on La1.93Sr0.07CuO4 over a wide range of ω and T; 2 ≤ ω ≤ 44 meV and 1.5 ≤ T < 300 K. The dynamic susceptibility χ′′(q,ω) of this underdoped high-Tc superconductor (Tc=17 K) is characterized by broad, incommensurate peaks. Here, the incommensurate wavevector δω is approximately 0.07 reciprocal lattice units at low T and ω. The superconducting phase does not possess an observable gap in the spin excitation spectrum down to at least 2 meV. Scaling behavior is demonstrated for the Q-integrated energy spectrum χ′′(ω)T with respect to (ω/kBT). This scaling establishes a connnection between the magnetic excitations of the compositions on either side of the insulator-superconductor boundary in the La2-xSrxCuO4 phase diagram. We note a possible cross-over from an incommensurate to a commensurate response for ω > 20 meV or T > 300 K.
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  • Syuji Maruyama, Hidekazu Tanaka, Yasuo Narumi, Koichi Kindo, Hiroyuki ...
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 859-865
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    The static and dynamic magnetic properties of an S=1/2 stacked triangular antiferromagnet RbCuCl3 with a helical spin structure due to lattice distortion were investigated by magnetic susceptibility, high-field magnetization process and ESR measurements. The magnetic susceptibilities were analyzed by high-temperature expansion approximation in terms of ferromagnetic intrachain coupling and the antiferromagnetic interchain coupling. The magnetization saturates at Hs≈ 66.8 T at 1.5 K, the value of which is twice that of CsCuCl3. A small magnetization jump indicative of a phase transition was observed at Hc=21.2 T ≈ (1/3)Hs for H ⊥ c. ESR modes observed for H || c are well described by the calculation based on the helical spin structure. From the present measurements, the ferromagnetic intrachain and two kinds of antiferromagnetic interchain exchange interactions, and the planar anisotropy energy were determined as J0/kB=25.7 K, J1/kB=-10.6 K, J1'/kB=-17.4 K, and ΔJ0/kB=-0.45 K, respectively.
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  • Eiji Kaneshita, Masanori Ichioka, Kazushige Machida
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 866-876
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    Dynamical longitudinal spin susceptibility χzz(q,ω) and charge density susceptibility χnn(q,ω) are evaluated within random phase approximation for incommensurate spin density waves, or stripes, in two dimensional Hubbard model. Taking into account all possible higher harmonics of the fundamental component of the order parameter,we calculate these quantities for the full ranges of the momentum and energy, and analyze collective modes related to the motion of the stripe line. The anisotropy of the dispersion cone comes from the moving pattern of the stripes, i.e., the compression mode or the meandering mode. In the metallic stripe, there are also nesting excitations of the parallel sheet of the Fermi surfaces. We also discuss the excitation of the silent position in the insulating stripe.
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  • Tetsuya Takeuchi, Tetsutaro Inoue, Kiyohiro Sugiyama, Dai Aoki, Yoshih ...
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 877-883
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    We studied the magnetic properties in a non-magnetic heavy-fermion compound CeIrIn5 and an antiferromagnetic compound CeRhIn5 with the tetragonal structure. High-field magnetization of CeIrIn5 shows a weak metamagnetic transition around 420 kOe for the field along the [001] direction, while the magnetization gradually increases up to 500 kOe for [110]. On the other hand, we observed a two-step metamagnetic transition for the field perpendicular to [001] at 20 and 500 kOe in CeRhIn5. The magnetization is of the x-y type. The former transition indicates a 1/cosθ dependence, where the θ means a tilted angle of the field direction from the (001) plane. From the magnetic susceptibility and high-field magnetization measurements, we formed a magnetic phase diagram in CeRhIn5. The temperature dependences of the magnetic susceptibility and thermal expansion coefficient of both compounds were analyzed on the basis of the crystalline electric field model.
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  • Takahito Kaneyoshi
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 884-888
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    The phase diagram and magnetization curve of the decorated ferrimagnetic square lattice composed of three magnetic atoms are studied on the basis of the differential operator technique. The results indicate that there may exist some interesting phenomena in the system, such as the possibility of two compensation points and the new type of magnetization curve not predicted in the Néel theory of ferrimagnetism.
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  • Chiaki Uyeda, Kouichi Ohtawa, Kazuyuki Okita, Natsu Uyeda
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 889-892
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    The diamagnetic anisotropy (Δ χ )DIA derived from the individual bonding orbitals of the silicate [TO4] networks is estimated from the observed results on α-quartz [SiO2], orthoclase [KAlSi3O8] and apophyllite [Ca4KF(Si4O10)2, 8H2O]. The (Δ χ )DIA value of individual chemical bond was estimated to be -3.5× 10-30 emu/mol, the uniaxial principal axis being parallel to the bond direction. The calculated results indicate that the bond direction is the magnetically unstable axis. This result is compatible with the observed and calculated distributions of electron density for the T-O orbitals, which are preferentially spread in the direction off the bond direction.
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  • Shuichi Ban, Kazuo Kanematsu, Kenji Shimizu
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 893-896
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    We have carried out 141Pr and 143Nd NMR measurements on Ce1-xRxFe2 (R = Pr, Nd) at 1.4 K. The hyperfine fields of Pr and Nd remain nearly constant in the measured concentration ranges: 0.15 ≤ x ≤ 0.43 and 0.1 ≤ x ≤ 0.4 for Pr and Nd compounds, respectively. The hyperfine fields analysis combining with 57Fe Mössbauer effect results give the magnetic moments of Pr and Nd in the compounds to be about 2.6 μB and 2.8 μB, respectively. The magnetizations of Ce1-xRxFe2 are estimated and discussed.
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  • F. L. Shyu, Ming Fa Lin
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 897-901
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    The simple hexagonal graphite exhibits novel excitation properties. The low-frequency π-electronic excitations principally reflect the π-band characteristics, the strong wave-vector-dependence, the highly anisotropic behavior, and the special symmetry. The plasmon frequency increases with momentum, while the opposite is true for the intensity of plasmon peak. The low-frequency plasmon behaves as the optical plasmon in a 3D electron gas. The main differences between plasmons parallel and perpendicular to the graphite planes are very special. The former have higher plasmon frequencies. However, their plasmon peaks and critical momenta are much lower than those of the latter. Doping leads to significant changes in the π-electronic excitations, such as the great enhancement of plasmon frequency and plasmon peak. The electronic excitations of the simple hexagonal graphite quite differ from those in the Bernal graphite or the 2D graphite sheet.
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  • Akira Takazawa, Hiroyuki Nojiri, Keigo Nagasaka, Kazuma Hirota, Yasuo ...
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 902-910
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    Drastic changes have been observed in the temperature and doping dependence of the phonon spectra in La1-xSrxMnO3 with x=0.10-0.125. For the x=0.11 and 0.125 samples, some of the bending (Mn-O-Mn bond angle modulation) modes show broadening and softening in the ferromagnetic metallic phase, which appears in intermediate temperature range. In the low-temperature orbital-ordered phase, these bending modes become sharper and the temperature dependence of the oscillator strength coincides with that of the orbital ordering order-parameter directly determined by resonant X-ray scattering. These facts indicate a strong correlation between the bending-type lattice distortion and the orbital ordering in the low temperature phase. For x=0.10, the phonon spectrum shows similarity with that of the end material LaMnO3 and no clear temperature dependence is found. The x-dependence of the phonon spectra is consistent with the existence of vertical phase boundary around x=0.11 newly discovered by a recent X-ray powder diffraction study.
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  • Jun-ichi Wakita, Hirotoshi Shimada, Hiroto Itoh, Tohey Matsuyama, Mits ...
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 911-919
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    We have investigated the periodic colony growth of bacterial species Bacillus subtilis. A colony grows cyclically with the interface repeating an advance (migration phase) and a rest (consolidation phase) alternately on a surface of semi-solid agar plate under appropriate environmental conditions, resulting in a concentric ring-like colony. It was found from macroscopic observations that the characteristic quantities for the periodic growth such as the migration time, the consolidation time and the terrace spacing do not depend so much on nutrient concentration Cn, but do on agar concentration Ca. The consolidation time was a weakly increasing function of Ca, while the migration time and the terrace spacing were, respectively, weakly and strongly decreasing function of Ca. Overall, the cycle (migration-plus-consolidation) time seems to be constant, and does not depend so much on both Cn and Ca. Microscopically, bacterial cells inside the growing front of a colony keep increasing their population during both migration and consolidation phases. It was also confirmed that their secreting surfactant called surfactin does not affect their periodic growth qualitatively, i.e., mutant cells which cannot secrete surfactin produce a concentric ring-like colony. All these results suggest that the diffusion of the nutrient and the surfactin are irrelevant to their periodic growth.
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  • Atsushi Ogawa, Shinichiro Katsura, Hideo Uesaka, Yoshifumi Harada
    Article type: General Physics
    Subject area: Mathematical methods in physics.
    2001 Volume 70 Issue 3 Pages 920-923
    Published: 2001
    Released on J-STAGE: February 28, 2003
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    We have experimentally studied the electrohydrodynamic instability in a nematic liquid crystal under an oscillatory shear flow. In the vicinity of an instability threshold, we observed the very slow dynamics of convection under the oscillatory shear flow with fixed control parameters. We found the resonant behavior between a mode of the underlying convection rolls and the shear flow. Dynamical scaling law is successfully applied.
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