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Izumi Tsutsui, Tamás Fülöp, Taksu Cheon
Article type: General Physics
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3473-3476
Published: 2000
Released on J-STAGE: January 31, 2001
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We study systems with parity invariant contact interactions in one dimension. The model analyzed is the simplest nontrivial one -a quantum wire with a point defect- and yet is shown to exhibit exotic phenomena, such as strong vs weak coupling duality and spiral anholonomy in the spectral flow. The structure underlying these phenomena is SU(2), which arises as accidental symmetry for a particular class of interactions.
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Sachiko Kitajima
Article type: General Physics
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3477-3480
Published: 2000
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Relaxation and decoherence properties of the exactly solvable Coleman-Hepp model are studied by determining the time evolution of the entropy. With the aid of our previous results, we can calculate the entropy by solving an eigenvalue problem for the reduced density matrices. Detailed numerical studies are performed to clarify the decoherence processes.
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Hideki Okamoto, Akito Igarashi, Toyonori Munakata
Article type: General Physics
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3481-3484
Published: 2000
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Dynamical properties of a low-dimensional chaotic heat reservoir are investigated both numerically and theoretically. As long as the coupling between a harmonic oscillator (a system) and a highly chaotic Nelson system (a reservoir) is not strong, the projection operator method is found to give a reliable description of the reservoir.
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Kazuko Inoue, Kazuyuki Enami, Yasuo Yamaguchi, Kenji Ohoyama, Yukio Mo ...
Article type: Condensed Matter: Structure, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3485-3488
Published: 2000
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The magnetic controllability of the thermoelastic martensitic transformation, which is the origin of the shape-memory effect, has been investigated. We have carried out neutron diffraction measurements of a Heusler-type off-stoichiometric Ni
2.19Mn
0.81Ga alloy under the magnetic field of up to 5 T using the HERMES and the TAS-2 diffractometers both installed at the JRR-3M reactor of Japan Atomic Energy Research Institute (JAERI). This alloy has the martensitic transformation temperature (M
S point) of about 350 K, which coincides with the magnetic Curie temperature (T
C). It is ferromagnetic in the martensitic phase and paramagnetic in the cubic Heusler phase. By Rietveld analysis of the diffraction patterns we have confirmed that the martensitic phase and the cubic phase coexist at 350 K. We have also discovered that half of the cubic phase changes to martensitic phase under the magnetic field of 5 T at this temperature. This finding indicates the possibility of controlling the martensitic transformation by means of the external magnetic field.
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Katsunori Kubo, Dai S. Hirashima
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3489-3493
Published: 2000
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We calculate the magnetic penetration depth λ(T) in quasi-two-dimensional superconductors with line nodes. We find that λ(T)-λ(0) ∝ T
α with α=1 in many cases, but for a class of the order parameter it is possible that α=3 in special field directions; this may help the identification of the symmetry of the order parameter. A recent measurement of the penetration depth in Sr
2RuO
4 is discussed in light of the present results.
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Jun'ichiro Hara, Masami Ashida, Seiji Higashitani, Katsuhiko Nagai
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3493-3496
Published: 2000
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A quasi-classical theory of diamagnetic response of normal-superconducting proximity contact double layers with a finite reflection at the interface is developed for arbitrary concentrations of impurities. It is found that the reflection at the interface has strong influence on the screening fraction of a system with a finite concentration of impurities, as is the case in the clean limit. Taking into account the finite reflection at the interface, we calculate the temperature dependence of the screening fraction and find good agreement with the recent experimental results obtained for Cu/Ta and Ag/Nb samples.
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Masaru Onoda, Ikuo Ichinose, Tetsuo Matsui
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3497-3500
Published: 2000
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We calculate the spin-gap effect on dc resistivity in the t-J model of high-T
c cuprates by using the Ginzburg-Landau theory coupled with a gauge field as its effective field theory to obtain ρ(T) ∝ T {1-c(T
* -T)
d}, where T
* is the spin-gap onset temperature. By taking the compactness of the massive gauge field into account, the exponent d deviates from its mean-field value 1/2 and becomes a nonuniversal T-dependent quantity, which improves the correspondence with the experiments.
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Jun Goryo
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3501-3504
Published: 2000
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We analyze the chiral p-wave superconductor in the low temperature region. The superconductor has a ε
x p
x+i ε
y p
y-wave gap in two-dimensional space (2D). Near the second superconducting transition point, the system could be described by a quasi-1D chiral p-wave model in 2D. The axial anomaly occurs in such a model and causes an accumulation of the quasiparticle in an inhomogeneous magnetic field. The effect is related to the winding number of the gap.
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Masatoshi Sato, Mahito Kohmoto
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3505-3508
Published: 2000
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The unique Fermi surfaces and their nesting properties of Sr
2RuO
4 are considered. The existence of unconventional superconductivity is demonstrated for the first time, by magnetic interactions (due to nesting) and phonon-mediated interactions. Two possible mechanisms of spin-triplet superconductivity are pointed out: one is due to the quasi-1D nature of the α and β sheets of the Fermi surface and other is due to the anisotropy of antiferromagnetic (AF) fluctuations. The odd-parity superconductivity is favored in the α and β sheets of the Fermi surface, and various superconductivities are possible in the γ sheet. There are a number of possible odd-parity gaps, which include the gaps with nodes, the breaking of time-reversal symmetry and d ¶ z.
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Akihisa Koga
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3509-3512
Published: 2000
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We investigate quantum phase transitions in the three-dimensional orthogonal-dimer system of the compound SrCu
2(BO
3)
2 by means of the series expansion technique. We then discuss the phase diagram where the dimer phase, the Haldane phase, the frustration-induced disordered phase and the magnetically ordered phase compete with each other. It is found that the compound SrCu
2(BO
3)
2 is located in the dimer phase close to the phase boundary.
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Setsuo Mitsuda, Motoshi Mase, K. Prokes, Hideaki Kitazawa, H. Aruga Ka ...
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3513-3516
Published: 2000
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Neutron diffraction studies on a frustrated triangular lattice antiferromagnet (TLA) CuFeO
2 have been performed under an applied magnetic field up to 14.5 T. The first-field-induced state was found to be not the commensurate 5-sublattice (↑ ↑ ↑ ↓ ↓ ) magnetic state but rather an incommensurate complex helical state reflecting the Heisenberg spin character of orbital singlet Fe
3+ magnetic ions. In contrast, the second-field-induced state was found to be the 5-sublattice (↑ ↑ ↑ ↓ ↓ ) magnetic state predicted by the two-dimensional (2D) Ising spin TLA model with competing exchange interactions up to the 3rd neighbors.
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Kiyotaka Miyoshi, Yoshinori Nishimura, Kenji Honda, Kenji Fujiwara, Ju ...
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3517-3520
Published: 2000
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Magnetic ordering of a geometrically frustrated pyrochlore antiferromagnet Y
2Mo
2O
7 has been investigated by AC and DC magnetic measurements. A spin freezing transition at ∼23K is indicated by AC susceptibility and low-field DC magnetization data. Under magnetic field above 700 Oe, a two-step increase of the irreversible magnetization M
irr (=M
FC-M
ZFC) is observed, corresponding to the freezing of the transverse and longitudinal spin components. The field dependence of the freezing temperatures is consistent with the H-T relations of a Heisenberg mean field spin-glass. The coefficients of the H-T relations for the longitudinal freezing are, however, fairly large compared with those of conventional disordered spin-glasses studied so far.
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Tôru Sakai, Olivier Cépas, Timothy Ziman
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3521-3524
Published: 2000
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The direct electron spin resonance (ESR) absorption between a singlet ground state and the triplet excited states of spin gap systems is investigated. Such an absorption, which is forbidden by the conservation of the total spin quantum number in isotropic Hamiltonians, is allowed by the Dzyaloshinskii-Moriya interaction. We show a selection rule in the presence of this interaction, using the exact numerical diagonalization of the finite cluster of the quasi-one-dimensional bond-alternating spin system. The selection rule is also modified into a suitable form in order to interpret recent experimental results on CuGeO
3 and NaV
2O
5.
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Takafumi Saito, Taka-hisa Arima, Yoichi Okimoto, Yoshinori Tokura
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3525-3528
Published: 2000
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The optical reflectivity spectrum and its temperature dependence were measured on a cleaved (001) surface of SmBaCo
2O
5.6. With an increase in temperature, the reflectivity below 1eV increases up to the metal-insulator transition temperature, T
MI=360K, and saturates above T
MI. The spectrum of optical conductivity σ(ω) shows large variation in temperature which accompanies the transfer of spectral weight between a broad peak around 3eV, which can be assigned to the O
2p–Co
3d charge-transfer excitation, and the incoherent excitation of carriers below 1eV. The transferred spectral weight is as large as 0.17 per Co ion, which implies that the effective mass of an electron, m
*, can be estimated to be 6m
0. The optical gap of 0.2eV at 20K is consistent with the resistivity measurement.
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Ming-Fa Lin, Feng-Lin Shyu
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3529-3532
Published: 2000
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The optical properties of nanographite ribbons are studied within the gradient approximation. The spectral function exhibits rich peak structures due to the divergencies in its density of states. Whether there are prominent peak structures is mainly determined by the geometric structure, the edge structure and the width. The spectral function also depends on the chemical potential and the temperature (except in the case of narrow armchair ribbons). Important differences between zigzag ribbons and armchair ribbons include the validity of the Δ J=0 selection rule, the frequency range of the absorption peaks, the very special absorption peak at γ
0 or 2γ
0, and the temperature dependence.
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Masahide Tona, Masahiro Kimura
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3533-3535
Published: 2000
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Novel modes of laser emission from levitated microdroplets have been observed. A single dye-doped glycerol droplet of micrometer size was confined in an ion trap and irradiated by a pulsed or a cw green laser. Photographic images of the emitting droplet and emission spectra were simultaneously recorded and compared each other for various intensities of the exciting laser. Both the images and the spectra obtained from the strongly excited droplet have no resemblance to those from the weakly excited one. With stronger excitation, lasing action was found to occur in the droplet in specific surface azimuthal modes. Relations between lasing modes and spectra are discussed.
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Akihiko Machida, Yutaka Moritomo, Eiji Nishibori, Masaki Takata, Makot ...
Article type: Cross-Disciplinary Physics
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3536-3539
Published: 2000
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Crystal and magnetic structures of Cr-doped manganites, Nd
1/2Ca
1/2Mn
1-yCr
yO
3 (y=0.00 and 0.03), have been investigated by synchrotron radiation (SR) x-ray powder diffraction as well as neutron powder diffraction measurements. A detailed analysis of the high-resolution x-ray profile has revealed that the Cr-doped compound exhibits broad extra reflections, suggesting the formation of microdomains below the charge-ordering temperature T
CO. The origin of the microdomain structure is discussed in terms of the charge separation.
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Shiro Kawabata
Article type: Cross-Disciplinary Physics
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3540-3543
Published: 2000
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The concept of a quantum interleaver and a simple method of quantum burst-error correction are proposed. By using the quantum interleaver, any quantum burst-errors that have occurred are spread over the interleaved code word, so that we can construct good quantum burst-error correcting codes without increasing the redundancy of the code. We also discuss the general method of constructing the quantum circuit for the quantum interleaver and the quantum network.
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Hidetsugu Sakaguchi, Kazutaka Watanabe
Article type: General Physics
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3545-3551
Published: 2000
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The circuit equations for Josephson junction arrays with random critical currents are numerically investigated. Dynamical order appears in the Josephson junction arrays via mutual entrainment. We discuss some kinds of multi-stability for the mutually entrained states.
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Hitoshi Mahara, Takahiro Saito, Yoshimitsu Amagishi, Hiroyuki Nagashim ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3552-3554
Published: 2000
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This paper presents a new model of a pacemaker in the oscillatory reaction-diffusion system called ``the ring-shaped model''. The present model has a frequency higher than that of the bulk oscillations in a ring-shaped region. Theoretical and experimental studies have revealed that the ``ring-shaped model'' explains the experiments with a piece of disk-shaped filter paper as a pacemaker, indicating that the wavelength is a function of the radius of the pacemaker and has a minimum value.
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Akihide Takeda, Nobuaki Ikuta
Article type: Atoms and Molecules
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3555-3562
Published: 2000
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Temporal relaxation properties of the velocity distribution of small amount gas A of mass m
A injected into ambient gas B of mass m
B in thermal equilibrium at temperature T
B are investigated with the Boltzmann equation rewritten in a linear form. Even if started from an equilibrium state at T
A, the velocity distribution of A gas can not be in the Maxwellian form in transient stage but finally settles in the Maxwell distribution at T
B. Temporal variations of the fractional changes of the mean energy and the H function show the relaxation behavior quite frankly. The relaxation properties are discussed in various aspects.
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Norito Ishikawa, Akihiro Iwase, Yasuhiro Chimi, Osamu Michikami, Hiron ...
Article type: Atoms and Molecules
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3563-3575
Published: 2000
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Resistivity as a function of ion-fluence has been measured
in situ in thin films of oxide superconductor EuBa
2Cu
3O
y irradiated with various heavy ions in a wide energy range of 90 MeV–3.84 GeV. From the resistivity measurements, the quantities characterizing the irradiation-induced columnar defects, such as the diameter of the columnar defect and the inside-resistivity (the resistivity inside the columnar defect), have been estimated. It is found that they are not scaled with the electronic stopping power, while they are strongly correlated with the primary ionization rate which is the number of atoms primarily ionized by an incident ion per unit path length. This result suggests that the defect production is triggered by Coulomb repulsion of ionized atoms. Based on the results of thermal annealing of irradiated samples, structure of the columnar defects has also been discussed.
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Shun Suzuki, Kenji Maruyama, Masakatsu Misawa
Article type: Condensed Matter: Structure, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3576-3580
Published: 2000
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RMC calculations with dimer molecules as a basic unit were performed for liquid selenium and tellurium at several temperatures, and the structure models reproducing the neutron diffraction patterns were obtained. For Se, in order to eliminate the artificial 3-membered rings, a restriction limiting the bond angles was introduced. From the obtained structure model, the covalent bonds were determined and the network structure was analyzed. The local structure parameters, such as bond length, bond angles and coordination number, were also analyzed at each temperature. The distribution of the obtained parameters were reasonable. The branches of chains shown increasing tendency with increasing temperature.
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Yasuo Nishijima, Hiroyuki Mashiyama
Article type: Condensed Matter: Structure, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3581-3588
Published: 2000
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The crystal structures of {P(CH
3)
4}
2CuCl
4 in phase I, II and III are determined by single crystal X-ray diffractometry. The phase I is isomorphous to the normal phase of {N(CH
3)
4}
2ZnCl
4-type crystal, though the CuCl
4 tetrahedron is fairly distorted from the regular tetrahedral shape. The incommensurate phase II is refined by the use of the 4-dimensional superspace group. The second harmonics of the modulation is comparably strong as the primary modulation at 360K. The incommensurate structure is compared with the room temperature phase III, where the cell dimension along the c axis is tripled. The structural transition sequence is discussed in connection to the size of tetrahedral monovalent cation.
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Yoshihide Itou, Kouichirou Narita, Seiichirou Inoue
Article type: Condensed Matter: Structure, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3589-3596
Published: 2000
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The ultrasonic attenuation is investigated for such quasi two dimensional systems with periodically undulating cylindrical Fermi surfaces as organic metals and superlattices. We obtained the most general forms of the ac-nonlocal magnetoconductivity, which becomes the dc-local magnetoconductivity obtained earlier in the limit of the high magnetic strength, where both the frequency and wave number can be assumed to become zero. The directional dependence of the magnetic field on the ultrasonic attenuation, one of what we call the Yamaji oscillations, appears in the high-field limits, only for longitudinal waves propagating parallel to the c-axis and for transverse waves polarized along the c-axis in the case of propagation in the plane perpendicular to the c-axis.
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Yu-qiang Ma
Article type: Condensed Matter: Structure, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3597-3601
Published: 2000
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The phase separation kinetics of three-component mixtures is investigated by cell dynamical system method. We emphasize the important of phase-ordering competition to the morphology and domain growth of the system, and discuss how to control the phase-separating speed and the final morphological changes in the late stage of spinodal decomposition under the critical quench condition, due to different interfacial tensions.
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Kazuya Saito, Akane Sato, Koichi Kikuchi, Hiroyuki Nishikawa, Isao Ike ...
Article type: Condensed Matter: Structure, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3602-3606
Published: 2000
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Heat capacity of a quasi-one-dimensional organic conductor (DIMET)
2I
3 has been measured by chopped-light ac calorimetry below room temperature. An anomaly due to a metal-insulator transition has been clearly detected around 40 K. The magnitude of the anomaly is analyzed through comparison with other Q1D conductors. A possible SDW mechanism is suggested.
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Yutaka Kaneko, Yasuaki Hiwatari, Katsuhiko Ohara, Tohru Murakami
Article type: Condensed Matter: Structure, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3607-3613
Published: 2000
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The structure of thin film deposited on a metal surface and formation of defects during the growth of the film have been studied with use of a kinetic Monte Carlo method. Simulations have been performed for a two-dimensional square lattice as a model of the growth from solution taking into account three events; adsorption, desorption and diffusion of surface atoms. The growth rate is controlled by the chemical potential μ which corresponds to the overpotential in electrodeposition. The solid-on-solid criterion, which is commonly used in modeling crystal growth, is not assumed in the present study. This extends to make lattice defects (vacancies) created in the film. It is shown that point defects (single vacancies) appear in the film when the surface has a layer structure for small μ and the density of defects increases as μ becomes large. For sufficiently large μ, the surface becomes rough and large voids are formed as well as point defects. The spatial distribution of defects in the film is closely related to the surface structure. The growth on a substrate which has a hill and a hole is also investigated to see the influence of the initial surface on the resulting film structure.
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Eiji Saitoh, Atsushi Asamitsu, Youichi Okimoto, Yoshinori Tokura
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3614-3620
Published: 2000
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Optical spectra for the ferromagnetic ground states have been investigated for single crystals of perovskite-type manganese oxides La
1-xSr
xMnO
3 with finely varying hole-doping concentration (x) around the metal-insulator (MI) phase boundary (x
c∼ 0.16). For such a fully spin-polarized state, orbital degree of freedom may play an important role in the MI transition, which is anticipated to be figured out in terms of optical spectroscopy. In the ferromagnetic ground state, the low-energy optical conductivity spectra are observed to vary from Drude-like (typically for x=0.4) to incoherent broad feature (for x< 0.2) with decreasing x. The spectral-weight analysis shows that the kinetic energy of conduction electron scarcely changes with change of x when viewed on a large energy scale (about 1 eV) whereas the coherent response on a low energy scale (∼0.1 eV) is critically suppressed toward the insulating phase. Orbital correlation and its coupling with lattice dynamics are likely responsible for such an anomalous variation of charge dynamics. Far-infrared pseudo gap structure observed in the ferromagnetic metallic phase of x=0.16 on the verge of MI transition suggests the charge localization affected by randomness and non-local interaction in the course of orbital and charge ordering.
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Keita Kishigi, Yasumasa Hasegawa
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3621-3628
Published: 2000
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The coexistent state of the spin density wave (SDW) and the charge density wave (CDW) in the one-dimensional quarter-filled system with the Coulomb interaction up to the next-nearest sites under magnetic fields is studied. It is found that under high magnetic fields, in the coexistent state of 2k
F-SDW and 2k
F-CDW, the charge order is suppressed, whereas, in the coexistent state of 2k
F-SDW and 4k
F-CDW, 4k
F-CDW still remains and 2k
F-SDW is suppressed. The critical temperature of the charge order is higher than that of the spin order when the inter-site Coulomb interaction is strong. These will be observed in experiment such as the X-ray scattering measurement.
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Makoto Yoshida, Keiichi Koyama, Takuo Sakon, Akira Ochiai, Mitsuhiro M ...
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3629-3632
Published: 2000
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Cyclotron resonance measurements on a single crystal of LaSb have been performed in the temperature range from 1.7 to 40 K and at the frequency range from 50 to 110 GHz to obtain the cyclotron effective mass of the carriers at the Fermi level. From analyzing the angular dependence of m
CR*, the cyclotron resonance is originated from the electron Fermi surface with an ellipsoidal shape (α-branch), and m
CR* varies from 0.27±0.03 m
0 to 0.51±0.05 m
0. This obtained m
CR* is about two times larger than m
QO* estimated from acoustic dHvA and band calculation.
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Osamu Sakai, Masahumi Kohgi, Hiroyuki Shiba, Akira Ochiai, Hidekazu Ao ...
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3633-3641
Published: 2000
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Yb
4As
3 exhibits very anisotropic magnetic properties, while its dynamic form factor of the inelastic excitation spectra at very low temperatures are well described by an almost-isotropic one-dimensional Heisenberg model, which is supplemented by the Dzyaloshinsky-Moriya interaction. To clarify the origin of this feature, the crystalline field effects in the inelastic neutron scattering and the magnetic susceptibility data of Yb
4As
3 are analyzed to separate out the contribution of the lowest Kramers-doublet state from those of the crystalline field excited states. The isotropic excitation mode is ascribed to the former state. The excitation spectra specified by the magnetic polarization directions are also calculated to give additional information of the crystalline field states. It is also pointed out that the magnetization
parallel to the c-axis is induced for the magnetic field, which is applied
perpendicular to the c-axis in the c-plane. Its magnitude is proportional to the cube of the field strength. The internal field can have different values on the two Yb
3+ sites which are connected by the glide operation. It is shown that the magnetization can give us detailed information of the local C
3 symmetry around the Yb
3+ site.
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Edmond Orignac, Yoshikazu Suzumura, Thierry Giamarchi
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3642-3649
Published: 2000
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The effect of interchain hopping on localization has been investigated for two coupled chains of spinless fermions with nearest neighbor interaction. By use of the renormalization group method, it is found that interchain hopping plays a significant role when the correlation gap induced by interplay of interchain hopping and intrachain interaction becomes larger than the Anderson localization energy scale induced by impurities. The strong competition between localization and delocalization is examined for attractive interaction.
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Jun-ichiro Ohe, Kousuke Yakubo
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3650-3655
Published: 2000
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Quantum transport in harmonically driven double-barrier systems has been studied quantitatively by using a transfer matrix method, especially focusing our attention on the conductance as a function of the strength of the time-varying potential. In the case that the frequency ω of the time-varying potential is different from Δ ε/h (Δ ε is the energy distance between adjacent resonant levels of the system), it is found that the sideband quenching predicted previously does not occur perfectly if static and time-varying potentials have continuous profiles as in a realistic system. Although previous theories have suggested that the spectral weight of sideband components is scaled by ω
-2 for inhomogeneous time-varying potentials, our results show that conductance dips corresponding to the quenching scale with ω
-1. In the case that hω =Δε, the Rabi-type splitting is observed. We clarified that the profile of the time-varying potential affects significantly how the resonant level splits. Furthermore, the quenching effect on the Rabi-type splitting is also discussed.
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Nobuyuki Ogawa, Michael E. Zhitomirsky
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3660-3663
Published: 2000
Released on J-STAGE: January 31, 2001
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In this study we calculate numerically the vortex structure for a two-component Ginzburg-Landau functional in the regime when time-reversal symmetry is not spontaneously broken. In a wide range of parameters a single-quantum vortex dissociates into a bound pair (molecule) of half-quantum vortices. We determine the phase diagram of different types of vortices in the space of parameters of the Ginzburg-Landau functional. A novel characteristic length which is related to the vortex molecule size is found. The characteristic length is longer than the coherence length and shorter than the magnetic penetration length.
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Youichi Yanase, Takanobu Jujo, Kosaku Yamada
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3664-3677
Published: 2000
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The anomalous properties of High-T
c cuprates are investigated both in the normal state and in the superconducting state. In particular, we pay attention to the pseudogap in the normal state and the phase transition from the pseudogap state to the superconducting state. The pseudogap phenomena observed in cuprates are naturally understood as a precursor of the strong coupling superconductivity. We have previously shown by using the self-consistent T-matrix calculation that the pseudogap is a result of the strong superconducting fluctuations which are accompanied by the strong coupling superconductivity in quasi-two dimensional systems [J. Phys. Soc. Jpn.
68 (1999) 2999]. We extend the scenario to the superconducting state. The close relation between the pseudogap state and the superconducting state is pointed out. Once the superconducting phase transition occurs, the superconducting order parameter rapidly grows rather than the result of BCS theory. With the rapid growth of the order parameter, the gap structure becomes sharp, while it is remarkably broad in the pseudogap state. The characteristic energy scale of the gap does not change. These results well explain the phase transition observed in the spectroscopic measurements. Further, we calculate the magnetic and transport properties which show the pseudogap phenomena. The comprehensive understanding of the NMR, the neutron scattering, the optical conductivity and the London penetration depth is obtained both in the pseudogap state and in the superconducting state.
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Takuji Nomura, Kosaku Yamada
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3678-3688
Published: 2000
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We discuss the possibility of spin-triplet superconductivity within the third order perturbation theory with respect to on-site Coulomb repulsion U. Critical temperature T
c for spin-triplet pairing state is calculated in a single-band two-dimensional Hubbard model and relatively high T
c is obtained for moderately large U. The present situation considered here is particularly intended for the main branch γ in Sr
2RuO
4. According to the calculation, third order vertex correction terms, which are not direct contribution from spin fluctuation, are important, while the bare susceptibility χ
0(q) need not always have a prominent peak at q=0 for the spin-triplet pairing state. The picture that strong ferromagnetic spin fluctuations mainly induce the spin-triplet superconductivity in Sr
2RuO
4 may not be appropriate, and such momentum dependence of renormalized effective interaction between quasi-particles as is not sufficiently taken into account in spin fluctuation mediated interaction is essential for realizing the spin-triplet pairing.
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Tomio Koyama
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3689-3695
Published: 2000
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We formulate a theory for the size effect for the longitudinal Josephson plasma oscillations in a 1D intrinsic Josephson-junction array (IJJA) with a finite in-plane area. The charging energy of the superconducting layers causes the size-dependence of the plasma frequency. The size effect can be described as a quantum correction for the superconducting phase differences in this system. The plasma oscillations become unstable as the in-plane area decreases. It is predicted that the resonant state in which the single-particle plasma excitation resonates with thermally-excited plasma oscillations appears in an IJJA with a small in-plane area.
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Kazuyoshi Takeda, Osamu Fujita, Masako Hitaka, Masaki Mito, Tatsuya Ka ...
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3696-3703
Published: 2000
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The site dilution problems on a square lattice antiferromagnet with spin S=5/2, Mn(HCOO)
22(NH
2)
2CO (T
N=3.77 K), have been studied for a wide range of magnetic concentration x, covering the percolation threshold x
p=0.59 for the square lattice, by the measurements of magnetic heat capacity and susceptibility. The Néel temperature T
N(x) has been found to decrease as d/dx{T
N(x)/T
N(1)}=R=2.7 just below x=1 for the three kinds of non-magnetic impurities, Mg
2+(2p
6), Zn
2+(3d
10) and Cd
2+(4d
10), at almost the same reduction rate as in the cases of the antiferromagnet K
2MnF
4 with S=5/2 and the ferromagnet K
2CuF
4 with S=1/2. The present value R=2.7, however, makes a contrast to R=3.1 for the diluted La
2CuO
4, an S=1/2 Heisenberg antiferromagnet. The extrapolation of T
N(x), with R=2.7(3.1) down to T
N(x)=0 gives a pseudo-critical concentration x=x
c=0.63(0.68) deviating from x
p=0.59. This indicates that T
N(x) must draw concavely near T
N(x
p)=0 at low temperatures, making a contrast to the convex curve of decreasing T
N(x) down to zero at x=x
p for Ising systems. As x decreases, dilution effects reflected on the reduction of lattice dimensionality, the Curie-Weiss temperature and the Curie constant are discussed on the base of the absolute values of the magnetic heat capacity and susceptibility. An anomalous enhancement of the heat capacities has been found in the external field of 50 kOe for the system with x=0.12, which was theoretically reproduced by the contribution from isolated ions and clusters computer-generated on the square lattice with the same magnetic concentration.
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Chong Der Hu
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3704-3710
Published: 2000
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We studied the double exchange interaction. Starting from [Kubo and Ohata's Hamiltonian: J. Phys. Soc. Jpn.
33 (1972) 21] we used a 1/(2S+1) expansion to calculate the thermodynamic potential, magnetization and T
C. It was found that including superexchange interaction results in realistic Curie temperature.
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Toshiaki Ohsaka, Tadanobu Shoji, Kazuya Tanaka
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3711-3714
Published: 2000
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The far-infrared absorption of three kinds of silica glasses with different OH concentrations has been measured at 11 K in the region 10–100 cm
-1 and compared with the absorption at 297 K. Below the so-called boson peak, the absorption was markedly dependent on temperature, but by contrast above the boson peak, it was almost independent of temperature, indicating the existence of two different types of low-frequency modes. It is suggested that the temperature-dependent absorption is due to structural relaxation modes, and the temperature-independent absorption reflects the density of states of collective motions of atoms related to clusters, though it is incomprehensible why the absorption is temperature independent.
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Osamu Arimoto, Shigeo Umemoto, Kaizo Nakamura
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3715-3719
Published: 2000
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Nonradiative relaxation processes of excitons have been investigated by means of photocalorimetric (PC) spectroscopy in the exciton resonance region of β-ZnP
2 by detecting temperature increase of the crystal under excitation with a Ti:sapphire laser at 4.5 K. For singlet excitons, power of the light absorbed by the crystal is converted to that of the thermal heating of the crystal almost at a constant rate as high as about 80% in the energy range from the 1s longitudinal exciton energy E
L to the band gap energy E
g. The heat generation, however, is largely suppressed in the 1s reflection band, where the exciton luminescence is also decreased in intensity, which suggests the presence of other optical process in this region such as resonant Rayleigh scattering. From comparison of the PC spectrum with excitation spectrum for the singlet exciton luminescence, it is found that a ratio of the PC signal to the luminescence intensity increases at the exciton resonances n=1, 2, 3 and 4. This fact indicates that the rate of the nonradiative decay of excitons relative to the emission of the luminescence is high at the exciton resonances. The PC spectrum for triplet excitons is also presented.
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Giuseppe Graziano
Article type: Cross-Disciplinary Physics
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3720-3725
Published: 2000
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Reliable values for the thermodynamic functions associated with the hydration of N-methylacetamide, NMA, in the temperature range 5–100ºC, are obtained using experimental data from different investigations. They are analyzed by means of a suitable theoretical approach. The large and negative hydration entropy values are determined by the excluded volume effect owing to cavity creation in water in order to host the NMA molecule. The large and negative hydration enthalpy values are determined by the NMA-water van der Waals interaction and H-bond energies. The latter are so large in magnitude to overwhelm the work of cavity creation, causing the good solubility of NMA in water. The analysis assumes that the reorganization of H-bonds among water molecules in the hydration shell of NMA is characterized by a nearly perfect enthalpy-entropy compensation, so that such process does not affect the hydration Gibbs energy change.
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Hideo Hasegawa
Article type: Cross-Disciplinary Physics
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3726-3735
Published: 2000
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Model calculations have been performed on the spike-train response of a pair of Hodgkin-Huxley (HH) neurons coupled by recurrent excitatory-excitatory couplings with time delay. The coupled, excitable HH neurons are assumed to receive the two kinds of spike-train inputs: the transient input consisting of M impulses for the finite duration (M: integer) and the sequential input with the constant interspike interval (ISI). The distribution of the output ISI T
o shows a rich of variety depending on the coupling strength and the time delay. The comparison is made between the dependence of the output ISI for the transient inputs and that for the sequential inputs.
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Fukuo Yoshida, Kihachiro Horiike, Huang ShiPing
Article type: Cross-Disciplinary Physics
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3736-3743
Published: 2000
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The concentration profile of secreted molecules is studied to understand characteristic properties of the intercellular signaling. Diffusion equations are solved for the concentration by assuming the rectangular, triangular and oscillatory time-dependence of the flux at the cell surface. The concentration is examined as a function of time and distance from a secreting cell by varying both the strength of an enhanced secretion rate and a secretion time. The time-dependence of the secretion rate is found to be inevitable for the concept of communication distance and characteristic time. Realistic estimations of these quantities are given for human cytokines.
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Yasushi Honda, Tsuyoshi Horiguchi
Article type: Cross-Disciplinary Physics
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3744-3751
Published: 2000
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We propose a four-direction traffic-flow model and its modified model with four types of cars on a two-dimensional network; cars of each type go straight toward one of four directions or turn to the left with the probability γ at each crossing. We use cellular automata to describe the models and investigate their properties by means of numerical simulations. It turns out that the models have a sort of continuous transition from a free-moving phase to a traffic-jam phase as the density of cars increases. The continuous transition is due to a self-organization by core configurations. The modified model is defined by imposing restriction rules for formation of some of core configurations to the original model. An average velocity of cars in the free-moving phase is analytically estimated within a one-body approximation for the modified model.
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Namiko Mitarai, Hiizu Nakanishi
Article type: Cross-Disciplinary Physics
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3752-3761
Published: 2000
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The effects of a localized perturbation in an initially uniform traffic flow are investigated with the optimal velocity model under an open boundary condition. The parameter region where the uniform solution is convectively unstable is determined by linear analysis. It is shown that the oscillatory flow, which is linearly unstable but convectively stabilized, is triggered out of a linearly unstable uniform flow by a localized perturbation, and in the upper stream it eventually breaks up into an alternating sequence of jams and free flows. This observation suggests that the real traffic flow pattern observed near an on-ramp [B. S. Kerner: Phys. Rev. Lett.
81 (1998) 3797] is a noise-sustained structure in an open flow system. We also find that, in a certain parameter region, the convectively stabilized uniform flow is destabilized by the non-linearly induced free flow.
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Akira Endo, Yasuhiro Iye
Article type: General Physics
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3656-3659
Published: 2000
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Unidirectional lateral lattice of a unit which in itself consists of small number of lateral-superlattice units has been fabricated from two-dimensional electron gas (2DEG) and its magnetoresistance has been measured. It shows commensurability oscillation similar to that of ordinary lateral superlattice (LSL), but with much altered amplitude distribution; the amplitude vanishes at some index n, then increases and decreases with n, in marked contrast to monotonic decrease for ordinary LSL. The amplitude distribution is well explained by the relative abundance of semi-classical trajectories responsible for the corresponding oscillation. The spacing between peaks or dips is determined by the lattice period within a unit, as is the case with commensurability oscillation of ordinary LSL. The phase, on the other hand, is shown to be controlled by the distance between adjacent units, allowing independent manipulation of the spacing and the phase of the magnetoresistance oscillation.
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Koji Kaneko, Kenji Ohoyama, Hideya Onodera, Yasuo Yamaguchi
Article type: Others
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3762-3763
Published: 2000
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Kwai-Kong Ng, Manfred Sigrist
Article type: Others
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 11 Pages
3764-3765
Published: 2000
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