Journal of the Physical Society of Japan
Online ISSN : 1347-4073
Print ISSN : 0031-9015
ISSN-L : 0031-9015
Volume 69, Issue 3
Displaying 1-50 of 52 articles from this issue
  • Ryogo Hirota, Kinji Kimura
    2000 Volume 69 Issue 3 Pages 627-630
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    The Euler top described by the equations I1 frac d ω1 d t =(I2-I32 ω3, I2 frac d ω2 d t =(I3-I13 ω1, I3 frac d ω3 d t =(I1-I21 ω2, is discretized in the following form I11(t+δ)-ω1(t)] = frac12 δ (I2-I3)[ω2(t+δ)ω3(t)+ω2(t) ω3(t+ δ)], I22(t+δ)-ω2(t)] = frac12 δ (I3-I1)[ω3(t+δ) ω1(t)+ω3(t) ω1(t+ δ)], I33(t+δ)-ω3(t)] = frac12 δ (I1-I2)[ω1(t+δ) ω2(t)+ω1(t) ω2(t+δ)], which exhibits conserved quantities and exact solutions.
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  • Koji Hukushima
    2000 Volume 69 Issue 3 Pages 631-634
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    The fixed-point structure of three-dimensional bond-disordered Ising models is investigated using the numerical domain-wall renormalization-group method. It is found that, in the ± J Ising model, there exists a non-trivial fixed point along the phase boundary between the paramagnetic and ferromagnetic phases. The fixed-point Hamiltonian of the ± J model numerically coincides with that of the unfrustrated random Ising models, strongly suggesting that both belong to the same universality class. Another fixed point corresponding to the multicritical point is also found in the ± J model. Critical properties associated with the fixed point are qualitatively consistent with theoretical predictions.
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  • Hajime Sakakita, Yasuyuki Yagi, Yoichi Hirano, Shigeyuki Sekine, Takes ...
    2000 Volume 69 Issue 3 Pages 635-638
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    The plasma rotation velocities in both toroidal and poloidal directions are measured by the Doppler shift of the impurity spectral line in a new large reversed-field pinch device, TPE-RX. It is found that the magnitude of the toroidal rotation velocities varies with the plasma current. The poloidal rotation velocities are almost zero in the plasma current region studied here. The radial electric field around the plasma edge region varies with the plasma current under some assumptions. This behavior is discussed in relation to both the finite Larmor radius effect and the magnetic field line stochasticity.
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  • Kenji Ohwada, Hironori Nakao, Hirondo Nakatogawa, Naohisa Takesue, Yas ...
    2000 Volume 69 Issue 3 Pages 639-642
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    Pressure effect on phase transition in NaV2O5 has been studied at low temperature by x-ray scattering. In addition to two well-known phases at ambient pressure such as P-phase (a × b × c orthorhombic unit cell at T>Tc_ 0 = 35 K) and C¼-phase (2a × 2b × 4c supercell at Tc_ 0 ), we discovered a new high-pressure phase C0-phase, which has a 2a × 2b × 1c supercell and is considered to be a new ground state above 0.92 GPa at T<20 K. By measuring temperature dependence of superlattice intensity from the single crystal up to 1.24 GPa for the C¼- and C0-phases, we obtain the temperature-pressure phase diagram. The P-to-C¼ phase transition is significantly suppressed as (dTc_ 0 /dP)-- -11(1) (K/GPa) at 0.1 MPa (1 atm.) while the C¼-to-C0 phase transition takes place at Pc= 0.92 GPa nearly independent of temperature below 20 K.
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  • Masaki Takesada, Masaru Kasahara, Toshirou Yagi
    2000 Volume 69 Issue 3 Pages 643-646
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    A new mode related to melting is found by Brillouin scattering of the hydrogen-bonded ferroelectric LiH3(SeO3)2 crystal. The spectra of the mode show drastic precursor effects of the melting process. The anomalous increase of the spectral intensity and width has been observed in addition to the softening of the mode with temperature approaching the melting point. The new mode is assigned to be a longitudinal acoustic-type mode in the pre-melting layer.
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  • Shin–ichi Kimura, Hideaki Kitazawa, Giyu Kido, Takashi Suzuki
    2000 Volume 69 Issue 3 Pages 647-650
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    In order to investigate the electronic structures in the magnetically ordered states of CeSb, we measured the optical reflectivity and the magnetic circular dichroism in the infrared region at low temperatures under a magnetic field. The optical conductivity spectrum, as well as the reflectivity spectrum, varies with the changing of temperature and magnetic field due to the magnetic phase transition. The optical spectrum originates from the absorption from the top of the Sb 5 p band to the bottom of the Ce 5 d band. The spectra in the ordered states cannot be explained only by the energy band folding due to the appearance of the periodic magnetic structure. It was found that the Sb 5 p band is strongly modified by the appearance of the Ce 4 f Γ 8 state in the ordered state. The Sb 5 p-Ce 4 f mixing effect is considered to play an important role in the magnetic phase transition.
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  • Hideo Yoshioka, Masahisa Tsuchiizu, Yoshikazu Suzumura
    2000 Volume 69 Issue 3 Pages 651-654
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    A one-dimensional electron system at quarter-filling has been examined by applying the renormalization group method to a bosonized model with on-site (U) and nearest-neighbor (V) repulsive interactions. By evaluating both normal scattering and Umklapp scattering perturbatively, we obtain a phase diagram in which a metallic state with a 2kF spin density wave (kF is the Fermi wave number) moves into an insulating state with charge disproportionation of a 4kF charge density wave with an increase in both U and V. The effect of the next-nearest-neighbor repulsion is also discussed.
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  • Yoshimasa Isawa, Hideto Horii
    2000 Volume 69 Issue 3 Pages 655-658
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    In the limit of strong interaction where a two-charge state approximation is applicable, the current through a metallic quantum dot is studied based on the Keldysh formalism. We performed diagrammatic analyses by describing the operators relevant to charge in terms of spin 1/2 operators and by describing the spin 1/2 operators in terms of the product of two Fermion operators. Two transport processes through a quantum dot are found: (i) The first one satisfies the current continuity independent of the configuration of the electrochemical potentials (ECPs) in the subsystems, and corresponds to the resonant tunneling process in double-barrier structures. Schoeller and Schön give an approximate expression for this process. (ii) The second one corresponding to the sequential process does not satisfy the current continuity regardless of the ECPs. It is also shown that, the currents through the left and the right junctions are continuous only in an appropriate configuration of the ECPs.
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  • Yoji Ohashi
    2000 Volume 69 Issue 3 Pages 659-662
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    We present a theoretical explanation for the correlation between the c-axis penetration depth and the c-axis conductivity (σc) in high-Tc cuprates which was experimentally discovered by Basov et al. [Phys. Rev. B 50 (1994) 3511]. Our model is based on the BCS theory for the quasi-two-dimensional d-wave superconductivity in which the strength of the incoherency in the c-axis charge dynamics is controlled by potential scatterings. We show that the Basov correlation is realized when the difference in the magnitude of σc among various high-Tc cuprate materials is dominated not by the damping of electrons but by the carrier density and/or the band mass along the c-axis. It is also shown that there exists a correlation between the c-axis Josephson plasma frequency and σc in high-Tc cuprates.
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  • Atsushi Tsuruta, Akito Kobayashi, Tamifusa Matsuura, Yoshihiro Kuroda
    2000 Volume 69 Issue 3 Pages 663-666
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    Possible orders in URu2Si2 are investigated using a two-channel degenerate Anderson model. The ground state of uranium ions is the non-Kramers quadrupolar doublet Γ 5 with (5f)2, and its relevalent excited state is the Kramers dipolar doublet Γ 7 with (5f)1. These states mix with each other via conduction electrons. At low temperatures, the system forms renormalized bands with both quadrupole and dipole degrees of freedom due to the quadrupolar Kondo effect which slightly mixes quadrupolar Γ 5, a primary state of uranium ions, with dipolar Γ 7. At a certain low temperature, conduction electrons in the renormalized bands undergo quadrupolar ordering with a large quadrupolar moment. At a further lower temperature, octupolar ordering occurs, accompanied by a tiny dipolar moment which is attributed to the property of the renormalized bands with primarily the Γ 5-character slightly mixed with the Γ 7-character. These phenomena are well described by the 1/N-expansion method with pseudo-fermions for the non-Kramers doublet Γ 5 and slave bosons for the Kramers doublet Γ 7.
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  • Tsuyoshi Hashiguchi, Naoya Takeda, Jiro Kitagawa, Nobuo Wada, Shigeru ...
    2000 Volume 69 Issue 3 Pages 667-670
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    We present the Hall constant, electrical resistivity, and low-temperature specific heat of the Kondo compound Ce3Pd20Si6 under high pressures. The temperature dependence of the Hall constant and the electrical resistivity shows very large pressure effects which are characteristic of Kondo compounds. On the other hand, the low-temperature specific heat shows little pressure effect. This contrasting result is discussed, taking into account two crystallographic Ce sites with much different Kondo temperatures.
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  • Yoshio Kuramoto, Hiroaki Kusunose
    2000 Volume 69 Issue 3 Pages 671-674
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    Possibility of a novel pseudoscalar (octupole) order is studied theoretically for orbitally degenerate systems with strong spin-orbit coupling such as CexLa1-xB6. We argue that coexistence of an octupole order parameter and antiferromagnetic fluctuation should lead to marked softening of the elastic constant by a mode-mixing effect. Nonlinear coupling between dipole, quadrupole and octupole fluctuations is taken into account in terms of a Ginzburg-Landau-type functional which is derived microscopically through a path integral.
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  • Hirotaka Manaka, Isao Yamada, N. V. Mushnikov, Tsuneaki Goto
    2000 Volume 69 Issue 3 Pages 675-678
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    We report measurements of the magnetization process of the gap system (CH3)2CHNH3CuCl3, in which ferromagnetic-dominant ferromagnetic and antiferromagnetic alternating Heisenberg chains are formed and then a pair of ferromagnetically coupled S = 1/2 spins behaves as a spin of S=1. The two critical fields Hc1 and Hc2, corresponding to the elimination of the energy gap and the alignment of all the spins along the direction of an external field H, are detected at 10.4 T and around 44 T, respectively, on a scale of the reduced magnetic field gH/2. These values are, in principle, consistent with those estimated from the analysis of the magnetic susceptibility. The critical exponents in the formula such as M(H)∝ (H-Hc1)1/δ1 and 1-M(H)∝ (Hc2-H)1/δ2 are found to be δ1>1 and δ2>1.
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  • Takashi Teramoto, Akira Saeki, Fumiko Yonezawa
    2000 Volume 69 Issue 3 Pages 679-682
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    The purpose of this letter is to propose an efficient numerical scheme to obtain the equilibrium pattern in a block copolymer system. Using this scheme, one can obtain well-defined periodic patterns from numerical simulations with a small amount of computational effort. This method is extended to the control of the fluctuations around the equilibrium pattern by keeping the kinetic energy of the system at a constant value.
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  • Shinji Kitao, Takaya Mitsui, Makoto Seto
    2000 Volume 69 Issue 3 Pages 683-685
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    The first observation of the nuclear resonant scattering from the 37.1-keV level of 121Sb and the 22.5-keV level of 149Sm excited by synchrotron radiation is reported. Delayed emission of fluorescent K or L X-rays following the internal conversion process is mainly used to observe this resonance. The evaluated energy of each excited level was 37.147±0.023 keV for 121Sb and 22.496±0.022 keV for 149Sm. Each half-life of the excited level was evaluated to be 3.47±0.39 ns for 121Sb and 7.40±1.15 ns for 149Sm. These values agree well with the reported values for each level.
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  • Yoshinori Inoue, Yutaka Uneura, Andrea Bellettini
    2000 Volume 69 Issue 3 Pages 687-694
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    The weakly nonlinear propagation of waves, which are generated in a half-space filled with a perfect gas through the heat addition, is studied from the standpoint of nonlinear acoustics. The wall temperature varies sinusoidally only during a half cycle. The result of analysis shows that the weak flow is induced at the outer edge of the thin boundary layer adjacent to the wall and thereby an acoustic wave is radiated to the outer wave region. The wave behavior in a far field can exactly be settled by solving Burgers equation. At a high acoustic Reynolds number, with the aid of the so-called equal-areas rule, it is shown that the entire wave profile develops into an N-wave with a long tail. In the farther far field, the tail diminishes and so the wave is reduced to an ordinary N-wave.
  • Iwao Hosokawa
    2000 Volume 69 Issue 3 Pages 695-700
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    The refined similarity hypothesis for isotropic turbulence established by Kolmogorov in 1962 is generalized so that the statistics of similarity variable may have a slight scale-ratio dependence. A reasonable form of the dependence is given on the basis of a recent multifractal model of intermittent energy dissipation and on some theoretical and experimental knowledge. This modification leads us to predict reasonable values of all the Kolmogorov prefactors and the scalings of longitudinal as well as transverse velocity structure functions in isotropic turbulence.
  • Daigen Fukayama, Toshihiro Oyamada, Toru Nakano, Toshiyuki Gotoh, Kiyo ...
    2000 Volume 69 Issue 3 Pages 701-715
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    In order to reliably compute the longitudinal structure functions in decaying and forced turbulence, local isotropy is examined with the aid of the isotropic expression of the incompressible conditions for the second and third order structure functions. Furthermore, the Karman-Howarth-Kolmogorov relation is investigated to examine the effects of external forcing and temporally decreasing of the second order structure function. On the basis of these investigations, the scaling range and exponents ζn of the longitudinal structure functions are determined for decaying and forced turbulence with the aid of the extended-self-similarity (ESS) method. We find that ζn's are smaller, for n ≥q 4, in decaying turbulence than in forced turbulence. The reasons for this discrepancy are discussed. Analysis of the local slopes of the structure functions is used to justify the ESS method.
  • Nobuaki Ohno, Tomokazu Kato
    2000 Volume 69 Issue 3 Pages 716-721
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    We investigate fluctuations near the relaxed state of RFP using MHD equations in terms of the cylindrical coordinates. We consider the fluctuations as perturbations near the relaxed state of RFP which is specified by Taylor's Bessel function model. The wave length of the fluctuations are regarded as small comparing to the scale length of the magnetic field of unperturbed relaxed state. The fluctuations of magnetic flux density and mass density are expressed by the shear Alfvén mode, and fast and slow magnetosonic mode, respectively. The comparison of the calculated frequencies and the reported experimental results shows us some discrepancy.
  • Takuya Iwasaki, Sanae–I. Itoh, Masatoshi Yagi, Kimitaka Itoh
    2000 Volume 69 Issue 3 Pages 722-728
    Published: March 01, 2000
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    An equation which includes the non-local effect in the heat flux is introduced to study the transient transport phenomena. A non-local heat flux, which is expressed in terms of the integral equation, is superimposed on the conventional form of the heat flux. This model is applied to describe the fast responses in the transition from Low confinement mode (L-mode) to High confinement mode (H-mode) and in the heating power switching. Examples of diffusivity models are chosen, i.e., constant, Bohm and Rebut-Lallia-Watkins (RLW) model and the comparison study is done. A small fraction of non-local component in the heat flux is found to be very effective in reducing the response time. Independent of the diffusivity models, the fast transient transport in the heat pulse propagation is reproduced based on this non-local model.
  • Koh–ichi Suzuki, Shin’ichi Ishimaru, Ryuichi Ikeda
    2000 Volume 69 Issue 3 Pages 729-733
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    133Cs NMR spectra and the spin-lattice relaxation times, T1, in Cs2HgCl4 crystals were measured in the ranges of 160--361 K and 160--371 K, respectively. The central lines of the spectra show small splittings characteristic of the incommensurate (IC) phase. The splitting increases with decreasing temperature. The critical exponent ζ of T1 at the phase transition from normal (N) to IC phase was determined to be 0.615±0.025 in the high-temperature side of the transition, which is in good agreement with the three-dimensional XY model predicting the one-dimensional modulation wave in the IC phase. The frequency dependence of T1 in the IC phase can be explained by the fluctuations of phason with a small gap, 0--5 MHz, and amplitudon.
  • Yukio Saito
    2000 Volume 69 Issue 3 Pages 734-743
    Published: March 01, 2000
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    To analyse the effect of lattice misfit in the heteroepitaxial growth, a harmonic solid-on-solid model is proposed where lattice sites are connected by harmonic springs to allow for the lattice deformation. The ground state study shows that with the chemical cohesion a monolayer island extends laterally but splits into two at the middle due to the elastic strain. Kinetic Monte Carlo simulations reveals that the overlayer forms ordered islands, if the surface diffusion process is included.
  • Manabu Usuda, Noriaki Hamada
    2000 Volume 69 Issue 3 Pages 744-748
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    Electronic-structure calculations have been carried out for hexagonal NiS with the use of the full-potential linearized augmented plane-wave (FLAPW) method in the local-spin-density approximation +U (LSDA+U) approach. The U parameter is treated as an empirical parameter to improve the band structure near the Fermi energy. It is found that this approach succeeds in obtaining the antiferromagnetic state which is the ground state of NiS, and the insulating state with an energy gap of --0.1 eV. The photoemission spectra obtained from the density of states of the LSDA+U, however, fail to explain experiment. We conclude that further advanced treatment of electron-electron interaction is needed for describing the single-electron excited state of hexagonal NiS.
  • D. S. Kleinberg, F. C. Chou, R. J. Birgeneau, Mark A. Kastner
    2000 Volume 69 Issue 3 Pages 749-753
    Published: March 01, 2000
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    The optical absorption spectrum from 0.1 to 1.5 eV photon energy is presented for extremely lightly oxygen doped crystals of La2CuO4. Crystals grown by two different methods have different low temperature spectra and different temperature dependencies. However, at room temperature the spectra are nearly identical, suggesting that they result from the optical absorption of free isolated holes in the two dimensional antiferromagnetic CuO2 square lattice.
  • Yoshiyuki Shibayama, Hirohiko Sato, Toshiaki Enoki, Xiang–Xin Bi ...
    2000 Volume 69 Issue 3 Pages 754-767
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    Activated carbon fibers (ACFs) are microporous carbons consisting of a three-dimensional disordered network of nano-graphites with a mean in-plane size of about 30 Å. We investigated the structure, electronic properties and iodine doping effects for ACF samples heat-treated up to 2800°C. The samples heat-treated below 1000°C exhibit Coulomb gap variable-range hopping conduction and the presence of localized spins, suggesting the importance of charging effects and the edge-inherited non-bonding states in nano-graphites, the latter being predicted theoretically. Iodine doping reduces the charging effect due to the dielectric constant enhanced by the iodine that is accommodated in the micropores. Heat treatment above 1300°C changes ACFs from an Anderson insulator to a disordered metal by the development of an infinite inter-nano-graphite percolation path network for electron transport, accompanied by a change from localized-spin magnetism to itinerant electron magnetism. In the metallic regime, carrier scattering is subjected to nano-graphite boundaries in terms of a short range random potential. Iodine-doping introduces ionized impurity scattering, which is caused by the I3- ions generated by the charge transfer from iodine to nano-graphite.
  • Shigeru Koikegami, Kosaku Yamada
    2000 Volume 69 Issue 3 Pages 768-776
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    We study superconducting fluctuation effects on the quasi-two-dimensional d-p model, which can describe significant features of high-Tc superconducting cuprates. We adopt the fluctuation exchange approximation in order to derive both normal and anomalous vertices of renormalized d-electron propagators, and then solve the Bethe-Salpeter equation for the anomalous vertex and derive t-matrix as a superconducting fluctuation propagator. We calculate the normal d-electron self-energy self-consistently, and get a self-consistent solution for the circumstance in which the system is close to both antiferromagnetic and superconducting instabilities. The solution exhibits the suppression of the density of states near (± π, 0) and (0, ± π), which reflects the experimental result on the normal state of underdoped cuprates.
  • Katsuya Kawade, Atsuko Suzuki, Kazuhide Tanaka
    2000 Volume 69 Issue 3 Pages 777-784
    Published: March 01, 2000
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    The electrical conductivity σ of amorphous Si100-xTix alloys prepared by ion-beam sputtering has been measured over a temperature range between 4.2 and 290 K. The temperature dependence of σ is well expressed by a formula derived by the variable-range hopping theory with an exponent n-- 0.40 for x≤ 11.5, whereas, for x≥q 12.8, it is better expressed by a formula describing the conduction by electrons liberated from weakly localized states through inelastic electron-electron scattering. Thus, the metal-insulator transition takes place at 11.5c<12.8 in this system. The electronic structure of these alloys has been studied by measuring XPS and UPS spectra. Furthermore, DV-Xα calculation has been carried out for certain Si--Ti alloy clusters of diamond structure to simulate the electronic structure of the amorphous alloys. The calculated total and partial density of states well reproduces the features of the photoemission spectra. The calculation also provides information on the localization of electronic states in the amorphous alloys.
  • Ryotaro Arita, Shigeki Onoda, Kazuhiko Kuroki, Hideo Aoki
    2000 Volume 69 Issue 3 Pages 785-795
    Published: March 01, 2000
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    The relation between three-dimensional lattice structure and magnetism in correlated electron systems is explored for face centered cubic (FCC), body centered cubic (BCC), and simple cubic (SC) lattices. In particular, we question which lattice structure has the strongest tendency toward the ferromagnetism or antiferromagnetism. We employ the Hubbard model to calculate the spin susceptibility and the single-particle spectrum with the fluctuation-exchange (FLEX) and the two-particle self-consistent (TPSC) approximations in the weak coupling regime. We have shown that (i) ferromagnetic spin fluctuations become dominant when the Fermi level lies around a sharp peak (divergence) in the density of states (D(E)) near the bottom of the band, which occurs for FCC with/without next nearest neighbor hoppings (t') or BCC with an appropriate value of t'. Among the cases studied, the ferromagnetic fluctuation is found to be the strongest for FCC with a finite t'. (ii) When the peak in D(E) resides around the band center as in bipartite SC or BCC, antiferromagnetic fluctuations become dominant when the band is close to the half-filling, with the fluctuation being much stronger in BCC.
  • Yuh Tomio, Yoshikazu Suzumura
    2000 Volume 69 Issue 3 Pages 796-804
    Published: March 01, 2000
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    Several kinds of spin density wave (SDW) states with both quarter-filled band and dimerization are reexamined for a one-dimensional system with on-site, nearest-neighbor and next-nearest-neighbor repulsive interactions, which has been investigated by [Kobayashi et al.: J. Phys. Soc. Jpn. 67 (1998) 1098]. Within the mean-field theory, the ground state and the response to the density variation are calculated in terms of phase variables, θ and φ, where θ expresses the charge fluctuation of SDW and φ describes the relative motion between density wave with up spin and that with down spin respectively. It is shown that the exotic state of coexistence of 2kF-SDW and 2kF-charge density wave (CDW) is followed by 4kF-SDW but not by 4kF-CDW where kF denotes a Fermi wave vector. The harmonic potential with respect to the variation of θ and/or φ disappears for the interactions, which lead to the boundary between the pure 2kF-SDW state and the corresponding coexistent state.
  • Hitoshi Seo
    2000 Volume 69 Issue 3 Pages 805-820
    Published: March 01, 2000
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    The charge ordering phenomena in quasi two-dimensional 1/4-filled organic compounds (ET)2X (ET=BEDT-TTF) are investigated theoretically for the θ and α-type structures, based on the Hartree approximation for the extended Hubbard models with both on-site and intersite Coulomb interactions. It is found that charge ordered states of stripe-type are stabilized for the relevant values of Coulomb energies, while the spatial pattern of the stripes sensitively depends on the anisotropy of the models. By comparing the results of calculations with the experimental facts, where the effects of quantum fluctuation is incorporated by mapping the stripe-type charge ordered states to the S=1/2 Heisenberg Hamiltonians, the actual charge patterns in the insulating phases of θ-(ET)2MM'(SCN)4 and α-(ET)2I3 are deduced. Furthermore, to obtain a unified view among the θ, α and κ-(ET)2X families, the stability of the charge ordered state in competition with the dimeric antiferromagnetic state viewed as the Mott insulating state, which is typically realized in κ-type compounds, and with the paramagnetic metallic state, is also pursued by extracting essential parameters.
  • Keita Kishigi, Yasumasa Hasegawa, Mitake Miyazaki
    2000 Volume 69 Issue 3 Pages 821-827
    Published: March 01, 2000
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    We study the effects of the spin splitting due to the Zeeman term on the de Haas van Alphen (dHvA) oscillation in two-dimensional two-band systems. Both systems with and without the magnetic breakdown are investigated. We found that the Fourier transform amplitudes of the oscillations are not described by the spin reduction factor as in the Lifshitz-Kosevich formalism in two-dimensional systems. The anomalous dependence of the Fourier transform amplitudes on the effective g-factor can be observed by tilting-angle dependence of the dHvA oscillation in Sr2RuO4 and quasi-two-dimensional organic conductors.
  • Hiroshi Shimada, Youiti Ootuka, Shun–ichi Kobayashi, Shingo Kats ...
    2000 Volume 69 Issue 3 Pages 828-835
    Published: March 01, 2000
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    Influence of the quantum charge fluctuations in a quantum dot on its charging effect has been investigated by using a quantum-dot device having four quantum point contacts (QPC's) which connect the dot to the reservoirs. The charging effect was detectable at combined tunnel conductance of four QPC's up to near 8e2/h beyond the intuitive criterion e2/h. We observed anomalously nonlinear dependences of the conductances at the tops (Gtop) and bottoms (Gbot) of the Coulomb oscillation on the tunnel conductances of QPC's, cal G QPC's. The result on Gtop indicates that a transition from Coulombically regulated tunnelings to non-correlated tunnelings occurs by increasing cal G QPC's. The result on Gbot shows the existence of leakage conductance beyond the 2nd-order cotunneling contribution. The offset voltage in the current-voltage characteristics of the device showed significant decrease with the increase of cal G QPC's, indicating the shrinkage of the effective charging energy. The results on Gtop and Gbot can be explained in the light of the shrinkage of the effective charging energy.
  • Ken–ichi Hino
    2000 Volume 69 Issue 3 Pages 836-850
    Published: March 01, 2000
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    A spectral profile of a Fano resonance for a quasi-two-dimensional magnetoexciton in a quantum well is investigated based on the three-channel Landau-Zener model. It is found that both the Coulomb coupling and the hole-subband mixing have a lot of effects on the line-profile. The former coupling is responsible for a prominent asymmetric profile, having a peak-and-dip structure characteristic of the Fano resonance, whereas the latter one blurs the asymmetry and eventually smears the peak-and-dip structure. Such behavior is analyzed in terms of the multi-channel resonant scattering theory. The stronger either the Coulomb coupling or the hole-subband mixing is, the broader the spectral width becomes. Moreover, the asymmetric profile vanishes with increasing strength of an applied magnetic field, and it is restored, however, as the Coulomb coupling becomes stronger.
  • Hiroyuki Kimura, Kazuma Hirota, Chul–Ho Lee, Kazuyoshi Yamada, G ...
    2000 Volume 69 Issue 3 Pages 851-857
    Published: March 01, 2000
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    Comprehensive inelastic neutron-scattering measurements were performed to study the soft optical phonons in La2-xSrxCuO4 at x=0.10, 0.12 and 0.18. We found at x=0.18 that the softening of Z-point phonon, suggesting incipient structural transition from the low-temperature orthorhombic (LTO) to low-temperature tetragonal (LTT) phase, breaks at Tc, which is consistent with the previous report by Lee et al. for the optimally doped x=0.15 sample. As for x=0.10 and 0.12, on the other hand, the softening continues even below Tc. It is thus clarified that the breaking of soft phonon is characteristic of La2-xSrxCuO4 in the optimally and overdoped regions. In the course of studying the soft phonons, we discovered that a central peak remains above the LTO to high-temperature tetragonal (HTT) phase transition at Ts1 and splits into incommensurate components along the [1 1 0]HTT direction at higher temperatures. This is a common feature for both x=0.12 and 0.18 and their temperature dependences of the splitting 2δ can be scaled by using a renormalized temperature T/Ts1. In the high temperature limit, δ saturates around δ -- 0.12 r.l.u., which value is close to the splitting of incommensurate magnetic signals. This implies that the incipient lattice modulation starts appearing at very high temperature. Details of this modulation and its relations with other properties are, however, not yet clarified.
  • Yukihiro Okuno
    2000 Volume 69 Issue 3 Pages 858-867
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    We study the impurity effect in the time reversal symmetry ( cal T ) breaking superconductor based on the Bogoliubov-de Gennes (BdG) equations. In cal T -violating superconductors, spontaneous currents are induced around the impurity. The current patterns around the impurity reflect the structures of the Cooper pairs. We investigate impurity problem numerically for two kinds of cal T violating superconductors (px± ipy and d+is) and investigate the currents around the impurity. We also study the effects of the magnetic impurity in p-wave (px± ipy) superconductor, especially in view of the zero-energy crossing of energy levels related to the phase transition of the ground state.
  • Naoya Takeda, Masayasu Ishikawa
    2000 Volume 69 Issue 3 Pages 868-873
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    We have studied superconducting and magnetic properties of RERu4Sb12 prepared by an Sb-flux method and found that LaRu4Sb12 is superconducting below 3.58 K and PrRu4Sb12 is a Van Vleck paramagnet which becomes superconducting below 1.04 K. CeRu4Sb12 is a unique substance which shows intermediate-valence behavior with a characteristic broad peak around 100 K in the magnetic susceptibility and Kondo-like behavior in the electrical resistivity at high temperatures. Furthermore, non-Fermi liquid behavior is observed in the specific heat and electrical resistivity at low temperatures. NdRu4Sb12 and EuRu4Sb12 show a magnetic transition at 1.3 K and 3.3 K, respectively.
  • Pieter Kuiper
    2000 Volume 69 Issue 3 Pages 874-877
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    Magnetic circular dichroism in XAS, XPS, and XES at the 2p levels of magnetic 3d transition metals is analyzed using a pedagogical method. A back-of-the-envelope analysis of the dichroism in X-ray absorption is extended to circular dichroism in 2p photoemission. X-ray emission from the polarized 2p core holes is then analyzed using the same graphic single-particle model. The fact that spin is not a constant of motion at the spin-orbit split 2p levels is included. This gives MCD ratios of L_β emission that are much smaller and in much better agreement with experiment than those predicted by [Jo and Parlebas: J. Phys. Soc. Jpn. 68 (1999) 1392]. The same analysis is also applied to dichroism in X-ray emission on the L2 and L3 absorption resonances.
  • Hai–Qing Lin, J. L. Shen
    2000 Volume 69 Issue 3 Pages 878-882
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    We study a set of exactly soluble net spin models. There exist two kinds of ground state, one is a complete dimerized state, and the other one is the ground state of corresponding spin-1 model. For the excitation gap, various phases were discovered and determined.
  • Jiro Kitagawa, Naoya Takeda, Masayasu Ishikawa, Masahiko Nakayama, Nor ...
    2000 Volume 69 Issue 3 Pages 883-887
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    We present a report on crystalline-electric-field effects observed in the electrical resistivity and the specific heat of Ce3Pd20Ge6, which are discussed within an energy level scheme of the Γ 8 ground state and the Γ 7 excited state at 50 K for both inequivalent crystallographic sites of Ce atom. The third-order magnetic susceptibility was deduced from the magnetization measurement in the paramagnetic phase of a single-crystalline sample in magnetic fields applied along [0~0~1] and [1~1~1]. In order to explain the temperature dependence of the third-order magnetic susceptibility along [0~0~1], a positive total quadrupolar pair interaction constant of 22 mK is required in addition to a small antiferromagnetic exchange interaction, thereby suggesting ferroquadrupolar ordering with the Γ 3 symmetry in this compound.
  • Masafumi Ito, Yukio Yasui, Masaki Kanada, Hiroshi Harashina, Shunsuke ...
    2000 Volume 69 Issue 3 Pages 888-894
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    Neutron Rietveld analyses have been carried out on Y2Ru2O7 and Nd2Ru2O7 to clarify the primary mechanism of the transition at TG to the spin-glass-like state which is accompanied by the specific heat jump. The results indicate that the lattice system does not seem to participate in the transition and changes of the neutron diffraction data with decreasing temperature through TG can consistently be understood by the ordering of magnetic moments at Ru sites to an almost long range ordered state, even though the low temperature phase is glassy in the macroscopic sense.
  • Takao Ebihara, Yoshihiko Inada, Masao Murakawa, Shinya Uji, Chieko Ter ...
    2000 Volume 69 Issue 3 Pages 895-899
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    We carried out the de Haas-van Alphen (dHvA) experiment in YbAl3 with the cubic crystal structure. One of the six dHvA branches, named β with a dHvA frequency of 4.5×107 Oe, is nearly spherical in topology and has a large cyclotron mass of 23.9 m0. The other branches were observed only in small angular regions centered at symmetrical directions. Their cyclotron masses are in the range from 13.5 to 17.4 m0. The topology of the Fermi surface cannot be explained by the conventional band model because the fully occupied 4f-levels in YbAl3 are below the Fermi level. A small alteration so as to shift upwards the 4f-levels is necessary to fit to the experimental dHvA data. These give a direct evidence that the 4f-electrons form heavy fermions at low temperatures, which is most likely related to the many-body Kondo effect.
  • Takashi Yamamoto, Yasuhiro Saiga, Mitsuhiro Arikawa, Yoshio Kuramoto
    2000 Volume 69 Issue 3 Pages 900-925
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    The dynamical structure factor S(q, ω) of the SU(K) (K=2, 3, 4) Haldane-Shastry model is derived exactly at zero temperature for arbitrary size of the system. The result is interpreted in terms of free quasi-particles which are generalization of spinons in the SU(2) case; the excited states relevant to S(q, ω) consist of K quasi-particles each of which is characterized by a set of K-1 quantum numbers. Near the boundaries of the region where S(q, ω) is nonzero, S(q, ω) shows the power-law singularity. It is found that the divergent singularity occurs only in the lowest edges starting from (q, ω) = (0, 0) toward positive and negative q. The analytic result is checked numerically for finite systems via exact diagonalization and recursion methods.
  • Shin–ichiro Kobayashi, Masafumi Sera, Masahiko Hiroi, Norio Koba ...
    2000 Volume 69 Issue 3 Pages 926-936
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    We have performed the detailed studies of the magnetoresistance of CexLa1-xB6 (x=0.75, 0.7, 0.65, 0.6, 0.5, 0.47, 0.38, 0.36, 0.25) in detail and obtained the magnetic phase diagram of CexLa1-xB6. The results show that recently discovered new phase IV exists between 0.3 ≤ x ≤ 0.8 and the Kondo singlet ground state is realized for x < 0.3. All the long-range orders seem to disappear at x -- 0.3. As for the nature of phase IV, judging from the results of the electrical resistivity, the specific heat, magnetic susceptibility, magnetic phase diagram and the similarities between the natures of two phases of PrB6 and ones of phase III and IV of Ce0.75La0.25B6, we conjecture that phase IV is the incommesurate AF magnetic oredred state.
  • Myung–Hwa Jung, Byung–Hoon Min, Yong–Seung Kwon, Isa ...
    2000 Volume 69 Issue 3 Pages 937-944
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    Highly anisotropic properties of CeTe2-x with the layered Cu2Sb-type structure have been found by the measurements of electrical resistivity ρ(T), magnetic susceptibility χ(T) and magnetization M(B) on single crystals for x=0.15--0.18. Both M(B// c) and M(B⊥ c) at 2 K exhibit a metamagnetic transition at 0.04 T. M(B// c) saturates rapidly to a value of 1.06 μB/f.u. at around B=0.2 T, whereas M(B⊥ c) gradually increases to a value of 0.75 μB/f.u. at 5.5 T. The absence of hysteresis and remanence in M(B) indicates an antiferromagnetic ground state. The resistivity ratio ρ// c⊥ c increases from 3 to 150 on cooling from 300 K to 1.5 K. Both ρ// c and ρ⊥ c exhibit a sharp peak at 6 K before the onset of long-range magnetic order at TN=4.3 K, where χ(T) exhibits a sharp peak. Measurements of the Hall coefficient RH(T), specific heat C(T), magnetoresistance ρ(B) and electron tunneling have been done for polycrystals with x=0.13 and 0.18. Electron-tunneling spectra at 77 K revealed the presence of a charge density wave with a pseudogap of 0.35 eV. It is found that C(T) exhibits a peak at TN with a significant tail up to 10 K, whereas RH(T) continuously increases. The magnetic entropy at TN is only 0.7Rln2, being indicative of a short-range order above TN. At 1.5 K, ρ(B) shows a peak at 0.075 T and then decreases rapidly for B≤ 1 T, resulting in a negative magnetoresistance of 20%. These results are analogous to those found in EuTe0.9, GdAs0.95 and CeSb, where low-density carriers form a pseudo-localized state and align the 4f spins within a magnetic polaron.
  • Makoto Iwata, Ryosuke Iguchi, Hiroshi Orihara, Jiri Hlinka, Yoshihiro ...
    2000 Volume 69 Issue 3 Pages 945-947
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    DC field dependence of the dielectric dispersion in the 2/7 phase of betaine calcium chloride dihydrate was measured in the frequency region between 100 Hz and 10 MHz. It was found that there exists a dielectric dispersion, and both the relaxation frequency and the reciprocal strength are proportional to the DC field strength, therefore their ratio is independent of the DC field strength. We discussed these results on the basis of the phenomenological consideration taking the interaction between domain walls into account.
  • R. B. Chen, F. L. Shyu, Yan–Ten Lu
    2000 Volume 69 Issue 3 Pages 948-954
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    Using 4× 4 Luttinger Hamiltonian, we compute the opto-absorption spectra for a 200 Å quantum well. The mixing between heavy-hole and light-hole renders non-parabolic valence subbands, therefore deforms the stair-like spectra. The electric field modulation spectra exhibit oscillatory feature, but the oscillations is different in nature from the bulk Franz-Keldysh oscillation. Stark shift of confine levels brings about the oscillations. Imposing a 10 meV broadening, it is impractical to determine the confine energies from the modulation spectra. Instead, we find that the polarization-modulation spectra contain more clear information about the confine levels.
  • Koji Sakata, Hirotaka Iijima, Takao Sekiya, Susumu Kurita
    2000 Volume 69 Issue 3 Pages 955-957
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    Electron-phonon interaction is studied on the trans-[PtCl2(en)2](ClO4)2, where en denotes ethylenediamine. The electronic states of platinum in this system are directly modulated by the breathing mode of halogen ions and strong electron-phonon interaction occurs. Luminescence spectrum has a Gaussian-like lineshape which is superimposed by phonon side bands of more than 20 series. The shape of the spectrum is well interpreted by taking account of halogen breathing mode. The estimated coupling strength (Haung-Rhys factor) is 9.52.
  • Makoto Yasutomi, Mitsuaki Ginoza
    2000 Volume 69 Issue 3 Pages 958-962
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    Calculations are presented of the measurable structure factor of a binary-species polydisperse Percus-Yevick fluid of colloidal hard spheres with Schulz distributed diameters in order to discuss dependences of structural properties on the polydispersity and the multiplicity of species. On spatial density distributions of materials inside spheres, two cases are considered: homogeneous type spheres and Gaussian type spheres.
  • Silvina Dengra, Guillermo Marshall, Fernando Molina
    2000 Volume 69 Issue 3 Pages 963-971
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    We present an experimental and theoretical study of front interaction during the growth of patterns in thin-layer electrochemical deposition. Simultaneous schlieren and particle image velocimetry techniques are used to follow front development of concentration fields and convection rolls in gravitoconvection prevailing flows. A theoretical model describing full front nonlinear interaction taking into account diffusive, migratory and convective motion of ions in a viscous fluid subject to an electric field is presented. The equations are written in terms of a set of dimensionless numbers showing the significance of the gravity Grashof number in a gravitoconvection prevailing regime. Our experiments reveal that concentration and gravity driven convection fronts which develop near the electrodes coincide and that the two evolve together. Prior to the appearance of rough growth, cathodic and anodic concentration and convective fronts are parallel to the electrodes. After branching develops, the cathodic fronts become slaved to the deposit front, all three growing linearly in time. Our model predicts that, in the parallel flow regime, the convective and concentration fronts coincide, both scaling first as t4/5 and then slowing down to t1/2, as it is observed in our experiments. After branching develops, this behavior applies only to the anodic front.
  • Masahiro Nakagawa
    2000 Volume 69 Issue 3 Pages 972-980
    Published: March 01, 2000
    Released on J-STAGE: July 28, 2000
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    We find that a chaos neural network (CNN) model with a time-dependent skew-tent activation function shows --10--20 times larger memory capacity than CNN with the sigmoidal activation function. Our model exhibits complete association with a certain noise involved in an input key vector beyond the time-invariant tent model.
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