Journal of the Physical Society of Japan
Online ISSN : 1347-4073
Print ISSN : 0031-9015
ISSN-L : 0031-9015
Volume 73, Issue 12
Displaying 1-50 of 50 articles from this issue
  • Naoki Kawashima
    2004 Volume 73 Issue 12 Pages 3219-3222
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    The quantum critical point of the three-dimensional XY model in a symmetry-preserving field is investigated. The results of Monte Carlo simulations with the directed-loop algorithm show that the quantum critical behavior is characterized by the mean-field values of critical exponents. The system-size dependence of various quantities is compared to a simple field-theoretical argument that supports the mean-field scaling.
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  • Eiji Kaneshita, Ivar Martin, Alan R. Bishop
    2004 Volume 73 Issue 12 Pages 3223-3226
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    We study a periodic polaronic system, which exhibits a nanoscale superlattice structure, as a model for hole-doped cuprates with checkerboard-like heterogeneity, as has been observed recently by scanning tunneling microscopy (STM). Within this model, the electronic and phononic excitations are investigated by applying an unrestricted Hartree–Fock and a random phase approximation (RPA) to a multiband Peierls–Hubbard Hamiltonian in two dimensions.
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  • Hironari Okada, Keiichi Koyama, Kazuo Watanabe
    2004 Volume 73 Issue 12 Pages 3227-3230
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    We have studied the magnetic, transport and structural properties of chalcogenide spinel compound CuV2S4 using a high-quality polycrystalline sample, in order to clarify the intrinsic physical properties of CuV2S4. The magnetic susceptibility and the electrical resistivity exhibit two sharp anomalies. One is reversible for temperature Tt1=91.5 K and the other shows a thermal hysteresis of about 4 K at Tt2=56 K. We clearly observed for the first time that both anomalies are accompanied with two-step structural modulations. The crystal structure changes the symmetry form cubic to tetragonal at Tt1, and then the lattice constant is modulated discontinuously at Tt2 without changing the symmetry. In addition, the paramagnetic susceptibility is very large, and the electrical resistivity at low temperatures shows a quadratic temperature dependence with the coefficient A=0.05 μΩ cm/K2, which is larger than that of conventional metals. These results indicate that CuV2S4 exhibits a Fermi-liquid-like behavior with strongly correlated electrons at lower temperatures.
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  • Shuichi Murakami, Ken-ichi Sasaki, Riichiro Saito
    2004 Volume 73 Issue 12 Pages 3231-3234
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    We analyze a common feature of a nontrivial fractional flux periodicity in two-dimensional systems. We demonstrate that an addition of fractional flux can be absorbed into re-parameterization of quantum numbers. For an exact fractional periodicity, all the electronic states undergo the re-parameterization, whereas for an approximate periodicity valid in a large system, only the states near the Fermi level are involved in the re-parameterization.
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  • Hisashi Aikawa, Kensuke Kobayashi, Akira Sano, Shingo Katsumoto, Yasuh ...
    2004 Volume 73 Issue 12 Pages 3235-3238
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    We present experimental results and a model to solve the problem of “in-phase Coulomb peaks” observed in transport through a quantum dot. In the marginal region between the Coulomb-blockade and open-dot, we have observed Fano-type interference through two energy levels inside the dot, which manifest themselves in two overlapped Coulomb-diamond-like structures in the excitation spectrum. One of the two levels is strongly coupled to the leads and the phase of traversing electrons is locked to it. We have detected the phase change at the vertices and the centers of the larger diamonds through the sign of Fano’s asymmetric parameters supporting the above deduction.
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  • Isao Maruyama, Naokazu Shibata, Kazuo Ueda
    2004 Volume 73 Issue 12 Pages 3239-3242
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    The Fano–Kondo effect in zero-bias conductance is investigated based on a theoretical model of a T-shaped quantum dot. The conductance as a function of gate voltage is generally characterized by the Fano asymmetric parameter q. With varying temperature the conductance shows a crossover between the high- and low-temperature regions compared with the Kondo temperature TK. It is characterized by two Fano asymmetric peaks at high temperatures and by the Fano–Kondo plateau inside a Fano peak at low temperatures. Temperature dependence of conductance is calculated numerically by the finite temperature density matrix renormalization group method (FT-DMRG).
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  • Mikito Koshino, Tsuneya Ando
    2004 Volume 73 Issue 12 Pages 3243-3246
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    Motivated by recent experimental attempts to detect the Hofstadter butterfly, we numerically calculate the Hall conductivity in a modulated two-dimensional electron system with disorder in the quantum Hall regime. We identify the critical energies where the states are extended for each of butterfly subbands, and obtain the trajectory as a function of the disorder. Remarkably, we find that, when the modulation becomes anisotropic, the critical energy branches accompanying a change of the Hall conductivity.
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  • Hitoshi Nishimori, Kazuharu Uchiyama, Shin-ichi Kaneko, Akio Tokura, H ...
    2004 Volume 73 Issue 12 Pages 3247-3250
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    The local quasi-particle density of states, Ns(E,r), in the isolated vortex of YNi2B2C has been measured at 0.46 K by low-temperature scanning tunneling microscopy and spectroscopy. The vortex core is found to be fourfold-symmetric star-shaped in real space: Near E=0 meV, Ns(E,r) extends toward ⟨100⟩ (the a-axis) and has a peak at the center of the vortex core. With increasing energy, Ns(E,r) comes to extend toward ⟨110⟩ and the peak of Ns(E,r) splits into four peaks toward ⟨110⟩. Ns(E,r) in the vortex core exhibits electron–hole asymmetry with the intensity, indicating the first observation of the vortex core in a quantum regime.
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  • Takanori Kida, Mikio Koyano
    2004 Volume 73 Issue 12 Pages 3251-3253
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    In a system of MnO–MoO2+δ composite thin films, an asymmetric magnetization curve is observed under a field-cooled (FC) condition. This shows that exchange-bias effects occurred because of a magnetic interaction between uncompensated magnetic moments at the surface of the MnO nanocrystallites and the antiferromagnetic (AF) moments of the core. This fact indicates that the AF domain wall is formed in the core of MnO nanocrystallites and that uncompensated magnetic moments at the surface are pinned by the AF domain wall.
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  • Kenji Goto, Masashi Fujisawa, Toshio Ono, Hidekazu Tanaka, Yoshiya Uwa ...
    2004 Volume 73 Issue 12 Pages 3254-3257
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    Magnetization measurements under hydrostatic pressure were performed on an S=1⁄2 coupled spin dimer system TlCuCl3 with a gapped ground state under magnetic field H parallel to the [201] direction. With increasing applied pressure P, the gap decreases and closes completely at Pc=0.42±0.05 kbar. For P>Pc, TlCuCl3 undergoes antiferromagnetic ordering. A spin-flop transition was observed at Hsf\\simeq0.7 T. The spin-flop field is approximately independent of pressure, although the sublattice magnetization increases with pressure. The gap and Néel temperature are presented as functions of pressure. The occurrence of the pressure-induced quantum phase transition is attributed to the relative enhancement of the interdimer exchange interactions compared with the intradimer exchange interaction.
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  • Takashi Tayama, Jeroen Custers, Hidekazu Sato, Toshiro Sakakibara, Hit ...
    2004 Volume 73 Issue 12 Pages 3258-3261
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    Dc magnetization and specific heat measurements on the filled skutterudite PrFe4P12 reveal the presence of a new ordered state (B phase) in high magnetic fields applied along the [111] direction. The present data suggest that the B phase exists in a limited angular range around the [111] direction. A possible origin of the B phase is discussed within the framework of the Γ1–Γ4 model.
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  • Hiroki Taniguchi, Masaki Takesada, Mitsuru Itoh, Toshirou Yagi
    2004 Volume 73 Issue 12 Pages 3262-3265
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    The ferroelectric microregion (FMR) in quantum paraelectric SrTiO3 is studied by Raman scattering using an optical cryostat with a 3He refrigerator. By the partial exchange of the oxygen atom for its isotope 18O, broad FMR spectra change drastically to underdamped Lorentzian-type spectra with decreasing temperature below 10 K. The peak is assigned to the ferroelectric soft Eu mode. The intense and sharp spectra of the Eu mode, which are nominally Raman inactive, indicate that the symmetry is lowered to a non-centrosymmetric symmetry in FMR. Furthermore, the softening characteristic of the soft Eu mode in a low-temperature region implies that the symmetry is not necessarily ferroelectric. The local symmetry breaking is enhanced by the substitution of the isotope 18O.
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  • Toshifumi Itakura
    2004 Volume 73 Issue 12 Pages 3266-3269
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    It has been proposed that a quantum computer can be constructed based on electron spins in quantum dots or based on a superconducting nanocircuit. During two-qubit operations, the fluctuation of coupling parameters is a critical factor. One source of such fluctuation is the stirring of background charges. We focused on the influence of this fluctuation on a coupled spin qubit system. The induced fluctuation in exchange coupling changes the amount of entanglement, fidelity, and purity. In our previous study, background charge fluctuations were found to be an important channel of dephasing for a single Josephson qubit.
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  • An Pang Tsai, Satoshi Kameoka, Yasushi Ishii
    2004 Volume 73 Issue 12 Pages 3270-3273
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    An intermetallic compound, PdZn, exhibits a similar valence electron density of states as pure Cu, which has been confirmed by energy band calculation and X-ray photoelectron spectroscopy. The catalytic function was verified to be identical for PdZn and Cu. This explains the origin of the high selectivity of PdZn for the steam reforming of methanol (SRM), CH3OH+H2O→3H2+CO2, a chemical reaction for which Cu is known to be one of the best catalyst; namely, PdZn is catalytically equivalent to Cu. Compared with PdZn, PtZn and NiZn, which have the same crystal structure but different valence band structures, exhibit a poorer selectivity of CO2. This suggests that the catalytic function, at least for SRM, is solely governed by the valence band structure of the catalyst. A simple but very important principle has been derived that an intermetallic compound may be logically designed by band structure calculation, aiming at replacing a selected metallic element without changing the catalytic function. Using this principle, we designed a compound, PdCd, which exhibits a similar valence electron density of state and selectivity for SRM with Cu.
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  • Jun-Xiao Zhao, Xing-Biao Hu, Ryogo Hirota
    2004 Volume 73 Issue 12 Pages 3275-3284
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    Bilinear approach is applied to derive integrable multi-component generalizations of the so-called 1+1 dimensional special Toda lattice, the Volterra lattice, a simple differential-difference equation found by Adler, Moser, Weiss, Veselov and Shabat and another integrable lattice reduced from the discrete BKP equation. Their soliton solutions expressed by pfaffians and the corresponding bilinear Bäcklund transformations are obtained.
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  • Yoshimasa Matsuno
    2004 Volume 73 Issue 12 Pages 3285-3293
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    We present the new representations of the multiperiodic and multisoliton solutions of the Benjamin–Ono and nonlocal nonlinear Schrödinger equations. The key idea in the analysis is to explore the structure of the determinantal expressions of the solutions. After providing a direct verification of the multiperiodic solution by means of an elementary theory of determinants, we show that the solution admits a representation in terms of solutions for a system of nonlinear algebraic equations. This representation is found to be an analog of the multiperiodic solution of the Korteweg–de Vries equation. We also discuss the long-wave limit of the results associated with the multiperiodic solutions.
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  • Fumito Mori, Takashi Odagaki
    2004 Volume 73 Issue 12 Pages 3294-3298
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    Spectral properties of the Laplacian operator are studied numerically on the Watts–Strogatz-type small-world networks. The spectra on small-world networks are shown to have the characteristics that (i) the gap between the lowest frequency mode (Goldstone mode) and the second lowest frequency mode is small in contrast to that of random networks and (ii) the average participation ratio is as small as that of random networks. We also find that the highest frequency is essentially determined by the largest coordination degree.
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  • Masuo Suzuki, Hidenori Suzuki
    2004 Volume 73 Issue 12 Pages 3299-3303
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    The basic problem how spontaneous symmetry breaks is studied rigorously for local fields in a finite domain. Another basic problem is to investigate whether or not there exist lower dimensions (of the domain to which a field H is applied) below which no spontaneous symmetry breaking (SSB) occurs. This is studied using scaling, renormalization group and mean-field theory for partial fields in an infinite domain. Our main results are the following: (i) The total magnetization is proportional to the square of the spontaneous magnetization when a field is applied only to a finite region (an extension of Yang’s result [Phys. Rev. 85 (1952) 808], M=Nm2s for a fixed single spin). A general formulation is given to calculate the proportionality coefficient which is shown to vanish as the field goes to zero. This indicates no SSB in this situation. (ii) On the other hand, if we apply partial fields to a d′-dimensional region and make them vanish, we find that SSB occurs, at least, for d′>dc=β⁄ν. In the region 0<d′≤dc, the situation is subtle, as is exemplified by an exactly soluble model with such a field on one-side boundary as depends on the system-size.
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  • Hisashi Okumura, Yuko Okamoto
    2004 Volume 73 Issue 12 Pages 3304-3311
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    We investigate the liquid–gas phase transition of a Lennard-Jones 12-6 potential system by the multibaric–multithermal Monte Carlo algorithm. The advantage of this method is that one can sample configurational space both in the gas phase and in the liquid phase from only one simulation run. Our liquid–gas coexistence data agree well with those obtained previously by other methods. We also show that this method is efficient in investigation of the transition state, which is the saddle point of a free energy surface.
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  • J. Y. Moon, J. H. Lee, C. S. Lee
    2004 Volume 73 Issue 12 Pages 3312-3318
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    We performed pulse shape analysis to extract depth information for an interaction point of γ rays in a 25-fold segmented germanium detector. With a 90° Compton spectrometer with collimators on both incidence and exit sides, we measured pulse shapes for the two interaction points, (x,y,z)=(2.5cm,2.5cm,0.5cm) and (2.5cm,2.5cm,1.0cm). Experimental pulse shapes were compared with calculated ones by the three-dimensional Green’s function method. Analytical solutions for induced charges on each cathode and an anode were obtained for a hole and an electron as a function of time. It is suggested that a rise-time correlation between the anode and the central cathode signals, T90(anode)−T50(cathode), can be used as a useful means to determine the depth (z) of an interaction point given an in-plane position (x,y). It is shown that calculated rise-time correlations are in qualitative agreement with experimental ones obtained by uncollimated γ rays.
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  • Takeshi Watanabe, Takahiro Iwayama
    2004 Volume 73 Issue 12 Pages 3319-3330
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    The enstrophy inertial range of a family of two-dimensional turbulent flows, so-called α-turbulence, is investigated theoretically and numerically. Introducing the large-scale correction into Kraichnan–Leith–Batchelor theory, we derive a unified form of the enstrophy spectrum for the local and non-local transfers in the enstrophy inertial range of α-turbulence. An asymptotic scaling behavior of the derived enstrophy spectrum precisely explains the transition between the local and non-local transfers at α=2 observed in the recent numerical studies by Pierrehumbert et al. [Chaos, Solitons & Fractals 4 (1994) 1111] and Schorghofer [Phys. Rev. E 61 (2000) 6572]. This behavior is comprehensively tested by performing direct numerical simulations of α-turbulence. It is also numerically examined the validity of the phenomenological expression of the enstrophy transfer flux responsible for the derivation of the transition of scaling behavior. Furthermore, it is found that the physical space structure for the local transfer is dominated by the small scale vortical structure, while it for the non-local transfer is done by the smooth and thin striped structures caused by the random straining motions.
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  • Takafumi Sato, Kensei Terashima, Seigo Souma, Hiroaki Matsui, Takashi ...
    2004 Volume 73 Issue 12 Pages 3331-3334
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    We have performed high-resolution angle-resolved photoemission spectroscopy (ARPES) with synchrotron radiation on layered transition-metal dichalcogenide 1T-VSe2 to study the mechanism of the three-dimensional charge-density-wave (CDW) transition. We found that the Fermi surface around the M(L) and K(H) points shows considerable wiggling along the wave vector normal to the layer (kz) despite the apparently two-dimensional crystal structure. ARPES spectra below the CDW transition temperature show a signature of pseudogap opening at a specific kz-region on the Fermi surface, demonstrating that the CDW transition of 1T-VSe2 is driven by three-dimensional Fermi-surface nesting.
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  • Mao Katsuhara, Takehiko Mori
    2004 Volume 73 Issue 12 Pages 3335-3340
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    Magnetic interactions J in [Cr(isoq)2(NCS)4]-based charge-transfer salts, (BDH-TTP)[Cr(isoq)2(NCS)4], (TMTTF)[Cr(isoq)2(NCS)4], and (BO)[Cr(isoq)2(NCS)4], are estimated on the basis of the extended Hückel molecular orbital calculations (BDH-TTP = 2,5-bis(1,3-dithiolan-2-ylidene)-1,3,4,6-tetrathiapentalene, BO = bis(ethylenedioxy)-tetrathiafulvalene, TMTTF = tetramethyltetrathiafulvalene, and isoq = isoquinoline). From this, experimental magnetic properties are discussed, and the magnetic structures are determined. (BDH-TTP)[Cr(isoq)2(NCS)4] is composed of two-dimensional array of antiferromagnetically coupled ferrimagnetic chains. These two-dimensional arrays, however, have net magnetic moment perpendicular to the sheets and give rise to weak ferromagnetism. (TMTTF)[Cr(isoq)2(NCS)4] and (BO)[Cr(isoq)2(NCS)4] have similar “body-centered” molecular arrangement. The TMTTF salt has considerable πd-interaction in two directions, and this compound actually shows a magnetic transition. The BO salt has large πd-interaction only in one direction, but the frustrating dd- and ππ-interactions are considerably large. Consequently, this compound does not exhibit a magnetic transition.
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  • Shinji Watanabe, Masatoshi Imada
    2004 Volume 73 Issue 12 Pages 3341-3350
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    Several useful thermodynamic relations are derived for metal–insulator transitions, as generalizations of the Clausius–Clapeyron and Eherenfest theorems. These relations hold in any spatial dimensions and at any temperatures. First, they relate several thermodynamic quantities to the slope of the metal–insulator phase boundary drawn in the plane of the chemical potential and the Coulomb interaction in the phase diagram of the Hubbard model. The relations impose constraints on the critical properties of the Mott transition. These thermodynamic relations are indeed confirmed to be satisfied in the cases of the one- and two-dimensional Hubbard models. One of these relations yields that at the continuous Mott transition with a diverging charge compressibility, the doublon susceptibility also diverges. The constraints on the shapes of the phase boundary containing a first-order metal–insulator transition at finite temperatures are clarified based on the thermodynamic relations. For example, the first-order phase boundary is parallel to the temperature axis asymptotically in the zero temperature limit. The applicability of the thermodynamic relations are not restricted only to the metal–insulator transition of the Hubbard model, but also hold in correlated systems with any types of phases in general. We demonstrate such examples in an extended Hubbard model with intersite Coulomb repulsion containing the charge order phase.
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  • Tsuneya Ando
    2004 Volume 73 Issue 12 Pages 3351-3363
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    Optical spectra are calculated in semiconducting carbon nanotubes in the presence of magnetic flux and strain within a k·p scheme. The exciton absorption energies show an extra logarithmic dependence on the diameter after being scaled by the inverse diameter, coming from that of the enhancement of the band gaps. The exciton binding energy remains almost independent of the extra dependence. The ratio of the absorption energies of the first and second bands is ∼1.8 for the wide range of the effective interaction parameter. By the Coulomb interaction, the Aharonov–Bohm splitting in small magnetic flux is enhanced (5–10%) and the shift due to strain is also enhanced (10–20%).
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  • Koichi Inagaki, Ichiro Terasaki, Hatsumi Mori, Takehiko Mori
    2004 Volume 73 Issue 12 Pages 3364-3369
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    The dielectric constant and ac conductivity have been measured for the layered organic conductor θ-(BEDT-TTF)2CsZn(SCN)4 along the out-of-plane direction, which show a relaxation behavior similar to those in the charge-density-wave conductor. Most unexpectedly, they exhibit a large bias dependence with a hysteresis, and changes in magnitude by 100–1000 times at a threshold. These findings are very similar to the collective excitation of the charge density wave. θ-(BEDT-TTF)2CsZn(SCN)4 has collective excitations associated with charge ordering, though it shows no clear indication of long range order.
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  • Yaushiro Iye, Masaaki Ueki, Akira Endo, Shingo Katsumoto
    2004 Volume 73 Issue 12 Pages 3370-3377
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    Three kinds of Aharonov–Bohm (AB)-type oscillation have been investigated in triangular antidot lattice fabricated from a GaAs/AlGaAs two-dimensional electron gas sample. The oscillation periods of Altshuler–Aronov–Spivak (AAS) effect and AB-type effect near zero magnetic field are determined by the unit cell area, whereas those of AB-type oscillations in the quantum Hall plateau transition regime are governed by the effective area of antidot. The evolution of the high-field AB-type oscillation as a function of gate voltage gives infomation on the profile of the self-consistent potential associated with compressible edge channels formed around antidot. The temperature dependences and decoherence mechanisms of the AAS and AB-type oscillations near zero magnetic field as well as the high-field AB-type oscillation are discussed.
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  • Hyunho Shin, Euijoon Yoon, Yo-Han Yoo, Woong Lee
    2004 Volume 73 Issue 12 Pages 3378-3383
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    The change in strain-modified band gap energies in truncated and untruncated InAs quantum dots (QDs) in the GaAs matrix has been comparatively investigated as a function of vertical inter-dot spacing, based on the strain-modified band lineups. The direct band gap energy is larger for truncated QDs at a given inter-dot spacing and shows more uniform band lineups in the truncated QD than in the untruncated counterpart, regardless of stacking distance. For both QD shapes, a narrower stacking increases the direct band gap energy. However, excessively close inter-dot spacing yields an indirect transition in which band gap decreases as dot spacing is narrowed further. From the viewpoint of band lineups, for both QD shapes, a blueshift of emission energy with a closer inter-dot spacing is anticipated in a large dot spacing regime and a redshift in a small spacing regime. The experimental results in the literature, reporting either blueshift or redshift as the QDs are stacked closer, have been compared with the current results and discussed.
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  • Dongmei Deng, Mitsunori Numata, Takanori Suzuki
    2004 Volume 73 Issue 12 Pages 3384-3388
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    Second-harmonic generation (SHG) has been demonstrated to facilitate studies of the kinetics of two-dimensional Ag adatom gas on Si(111)–\\sqrt3×\\sqrt3-Ag surfaces. At room temperature, the SH intensity at the excitation photon energy of 1.17 eV decreased for Ag deposition of small coverages up to 0.02 ML, and did not recover after ceasing the deposition; while for thicker Ag coverages where the decrease was more than 50%, the SH intensity recovered monotonically after ceasing the deposition. The change of the SH intensity for a series of excitation photon energies were found to be consistent with the SH response reflecting the resonance enhancement due to the one-photon transition between the surface states S2 (S3) and S1. At a sample temperature of 330°C, the SH intensity showed a “plateau” during recovery to the initial value after ceasing the deposition for thicker coverages.
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  • Yutaka Kishimoto, Yu Kawasaki, Takashi Ohno, Dexin Li, Yoshiya Homma, ...
    2004 Volume 73 Issue 12 Pages 3389-3393
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    To investigate the electronic state of La3Ir2Ge2, we have carried out 139La-NQR measurement. In the normal state, the spin–lattice relaxation rate 1⁄T1 is proportional to the temperature T. 1⁄T1 shows a small coherence peak just below the superconducting transition temperature Tc=4.7 K and decreases exponentially well below Tc. La3Ir2Ge2 is found to be a BCS superconductor with an energy gap 2Δ(0)=3.52kBTc.
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  • Kazunori Tanaka, Hiroaki Ikeda, Kosaku Yamada
    2004 Volume 73 Issue 12 Pages 3394-3403
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    The pressure dependence of the inverse square of the magnetic penetration depth λ−2 in κ-(ET)2Cu(NCS)2 was measured by Larkin et al. [Phys. Rev. B 64 (2001) 144514]. According to the paper, λ−2 behaves differently under low pressure and under high pressure. Under low pressure, the development of λ−2 just below T=Tc is rapid compared to the case under high pressure. Moreover, Tc in κ-(ET)2Cu(NCS)2 increases under c-axis pressure up to 1 kbar and decreases under higher pressure, while Tc decreases monotonically under the hydrostatic pressure, or under the uniaxial pressure parallel to other axes. In order to explain these behaviors, we calculate Tc and λ−2 for κ-(ET)2Cu(NCS)2 under pressure. In the calculation we mainly use an effective dimer Hubbard model. In conclusion, the behavior of λ−2 results from three effects: the variation of the bandwidth of quasiparticles, the change of the Fermi surfaces, and the effect of vertex correction. This is a different mechanism from that of λ−2 in cuprates which we observe when the doping varies. Moreover, we explain the increase in Tc under the c-axis pressure up to 1 kbar and the decrease in Tc over 1 kbar from our calculation. With the increase in the c-axis pressure, two competitive effects with respect to Tc appear. One is the approach of the Fermi surface to the antiferromagnetic Brillouin zone boundary, and the other is the suppression of the electron correlation. Under the low c-axis pressure, Tc increases since the former effect is dominant. On the other hand, Tc decreases since the latter effect is dominant under the high c-axis pressure.
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  • Tsutomu Watanabe, Hisatoshi Yokoyama, Yukio Tanaka, Jun-ichiro Inoue, ...
    2004 Volume 73 Issue 12 Pages 3404-3412
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    As a model of a novel superconductor NaxCoO2·yH2O, a single-band tJ model on a triangular lattice is studied, using a variational Monte Carlo method. We calculate the energies of various superconducting (SC) states, changing the doping rate δ and sign of t for small J⁄|t|. Symmetries of s, d, and d+id (p+ip and f) waves are taken up as candidates for singlet (triplet) pairing. In addition, the possibility of Nagaoka ferromagnetism and phase separation is considered. It is revealed that, among the SC states, the d+id wave always has the lowest energy, which result supports previous mean-field studies. There is no possibility of triplet pairing, although the f-wave state becomes stable relative to a normal state in a special case (δ=0.5 and t<0). For t<0, the complete ferromagnetic state is dominant in a wide range of δ and J⁄|t|, which covers the realistic parameter region of superconductivity.
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  • Shuichi Wakimoto, Seunghun Lee, Peter M. Gehring, Robert J. Birgeneau, ...
    2004 Volume 73 Issue 12 Pages 3413-3417
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    Soft phonons and diffuse scattering in insulating La2−xSrxCuO4 (x=0.05) have been studied by the neutron scattering technique. The X-point phonon softens from high temperature towards the structural transition temperature Ts=410 K, and the Z-point phonon softens again below 200 K. The Z-point phonon softening persists to low temperature, in contrast to the behavior observed in the superconducting x=0.15 compound, in which the Z-point phonon hardens below Tc. The diffuse scattering associated with the structural phase transition at 410 K appears at commensurate positions. These results highlight interesting differences between superconducting and insulating samples.
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  • Masugu Sato, Yoshihiro Koike, Susumu Katano, Naoto Metoki, Hiroaki Kad ...
    2004 Volume 73 Issue 12 Pages 3418-3421
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    Neutron inelastic scattering experiments have been performed on the paramagnetic heavy fermion compound CeRu2Si2 in magnetic field along the crystal c-axis. Around the metamagnetic crossover field Hm=7.7 T, the quasi-elastic excitation in the vicinity of the reciprocal lattice point (110) with an energy of 0.4 meV is significantly enhanced at T=0.4 K. The result indicates that the metamagnetic crossover in this compound is associated with a field-induced ferromagnetic correlation. The observation is consistent with the recent theoretical prediction by Satoh and Ohkawa based on quasi-particle band spectrum considerations.
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  • Masafumi Sera, Moo-Sung Kim, Hideki Tou, Satoru Kunii
    2004 Volume 73 Issue 12 Pages 3422-3428
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    We have studied the magnetization and the thermal expansion of PrB6 in both C and IC phases. In the IC phase, the crystal is found to be nearly cubic. This is because the magnitude of ⟨Oxyav is different from site to site in the IC phase. In the C phase, the crystal is easily deformed into the diamond shaped one by a small external field such as a magnetic field or a uniaxial stress along the two-fold axis. This indicates the small AFQ interaction in PrB6. The magnetization exhibits the anisotropy, M⟨001⟩>M⟨110⟩>M⟨111⟩ in the IC phase and M⟨001⟩>M⟨111⟩>M⟨110⟩ in the C phase. The former is explained by a difference of the domain distribution for three field directions, i.e., the larger the population of the χ configuration, the larger the magnitude of M. In the C phase, the planer type Kxy domain state and the χ configuration are realized for three magnetic field directions. For H||⟨110⟩ and ⟨111⟩, the 1-k collinear magnetic structure is realized and the moment is rotated in the xy plane, while for H||⟨001⟩, the moment is canted towards z axis from the xy plane. Altough in both cases, χ is associated with the Zeeman energy gain, χ in the former is smaller than that in the latter. This difference makes the anisotropy of M in the C phase as M⟨001⟩>M⟨111⟩>M⟨110⟩.
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  • Grégoire Misguich, Masaki Oshikawa
    2004 Volume 73 Issue 12 Pages 3429-3434
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    We extend the self-consistent Hartree–Fock–Popov calculations by Nikuni et al. [Phys. Rev. Lett. 84 (2000) 5868] concerning the Bose–Eistein condensation of magnons in TlCuCl3 to include a realistic dispersion of the excitations. The result for the critical field as a function of temperature behaves as Hc(T)−Hc(0)∼T3⁄2 below 2 K but deviates from this simple power-law at higher temperature and is in very good agreement with the experimental results. The specific heat is computed as a function of temperature for different values of the magnetic field. It shows a λ-like shape at the transition and is in good qualitative agreement with the results of Oosawa et al. [Phys. Rev. B 63 (2001) 134416].
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  • T. Waki, Y. Morimoto, C. Michioka, M. Kato, H. Kageyama, K. Yoshimura, ...
    2004 Volume 73 Issue 12 Pages 3435-3438
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    We observed a field-induced magnetic ordering in the quasi one-dimensional antiferromagnetic alternating chain system Pb2V3O9 for the first time. The characteristic temperature dependence of the magnetic susceptibility below TN and the power law behavior of phase boundary between paramagnetic and ordered phases in the Pb2V3O9 system can be comprehended in terms of Bose–Einstein condensation of triplons, as in the case of TlCuCl3 [Phys. Rev. Lett. 84 (2000) 5868]. Our results indicate that BEC of triplons can be observed in the present strongly-coupled-dimer system, while TlCuCl3 is a weak inter dimer coupling system.
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  • Satoru Kobayashi, Toshihiro Osawa, Hiroyuki Kimura, Yukio Noda, Noriak ...
    2004 Volume 73 Issue 12 Pages 3439-3443
    Published: December 15, 2004
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    Neutron diffraction measurements have been performed on a single crystal of TbMn2O5 to elucidate the interplay between magnetic ordering and ferroelectricity. On cooling below TN1=42 K, the system enters a lock-in commensurate magnetic (CM) state with the magnetic propagation vector q=(1⁄2,0,1⁄4) from a two-dimensionally modulated (2D) incommensurate magnetic (ICM) one with the temperature-dependent q=(qx,0,qz). Unlike isomorphous YMn2O5 and ErMn2O5 where a 1D-ICM phase with q=(qx,0,1⁄4) appears and separates both 2D-ICM and CM phases, the CM phase coexists with the 2D-ICM one at temperatures between T=36.5 and 37.8 K, associated with a kink and a sharp peak in the dielectric constant along the b axis. On further cooling, the system reenters an ICM state at T=22.4 K whose q is pinned at (20⁄41,0,5⁄16) at low temperatures. The comparison between the temperatures of dielectric anomalies and magnetic phase transitions indicates that the formation of the CM ordering is related to the appearance of ferroelectricity in TbMn2O5, while that of the 1D-ICM ordering is so in YMn2O5 and ErMn2O5.
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  • Marcin Regulski, Radoslaw Przenioslo, Izabela Sosnowska, Jens-Uwe Hoff ...
    2004 Volume 73 Issue 12 Pages 3444-3447
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    The magnetic long range ordering (LRO) and short range ordering (SRO) in β-MnO2 has been studied by neutron powder diffraction. Below TN=92.5(1) K β-MnO2 has an incommensurate modulated magnetic LRO with temperature dependent propagation vector length kz. The values of kz show a maximum, corresponding to kz=(2⁄7)+0.0120(1), near 90 K. The c lattice constant has a minimum near TN. The temperature dependence of the ordered magnetic moment shows a critical behavior M(T)∝(TNT)β with β=0.18(2). β-MnO2 has also a magnetic SRO from 50 up to 300 K as conjectured by Sato et al. [Phys. Rev. B 61 (2000) 3563]. The SRO magnetic correlation length of about 9.5(1.0) Å do not change with temperature. The Q-position of the SRO contribution decrease by 20% on warming from 50 to 300 K.
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  • Daisuke Matsunaka, Hideaki Kasai, Wilson Agerico Diño, Hiroshi ...
    2004 Volume 73 Issue 12 Pages 3448-3452
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    We present a theoretical method to study diluted magnetic semiconductors, beyond the single-site approximation, extending the dynamical cluster approximation (DCA). By the method, we can consider the nonlocal correlations due to disorder and discuss effects of the direct exchange interaction between magnetic impurities on the properties of the itinerant carriers. We apply the method to a three-dimensional cubic lattice system with random localized spins. We show that the strong antiferromagnetic superexchange interaction between nearest-neighbor sites suppresses the polarization of the carrier spins.
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  • Ryousuke Shiina, Masashige Matsumoto, Mikito Koga
    2004 Volume 73 Issue 12 Pages 3453-3461
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    One possible origin of the field-induced ordered phase (FIOP) in PrOs4Sb12 is an interaction of quadrupolar moments of Pr 4f electrons in the singlet–triplet crystal-field (CF) levels. We study theoretically excitations and inelastic neutron-scattering (INS) spectra of this compound, based on the antiferro-quadrupolar (AFQ) interaction. It is pointed out that a unique feature of the AFQ model shows up in the momentum dependence of the INS spectra, which is in agreement with recent experiments. Then, it is shown that the spectral shape of INS is drastically changed with increasing magnetic field and changing field direction. The origin of this change is discussed in terms of a reconstruction of the CF states by the field and the FIOP. Finally, we report the properties of critical dynamics around the transition field to the FIOP. It is shown that the Th symmetry is relevant to the low-energy dynamics, giving anisotropic critical properties.
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  • Kentaro Indoh, Aya Tobo, Kenji Ohoyama, Hideya Onodera
    2004 Volume 73 Issue 12 Pages 3462-3465
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    In order to elucidate quadrupolar and magnetic interactions in the antiferroquadrupolar (AFQ) and antiferromagnetic (AFM) ordering compound DyB2C2, 161Dy Mössbauer spectroscopy was performed on the Y-diluted system Dy1−xYxB2C2. The results reveal that the AFQ and AFM interactions compete with each other. The magnetic hyperfine field that is proportional to the magnetic moment strongly depends on the number and site of Y substitution in the nearest neighbors. Some kinds of Y substitution in the neighbors cause larger hyperfine fields than that in DyB2C2.
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  • Hiroyuki Mashiyama
    2004 Volume 73 Issue 12 Pages 3466-3470
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    Dynamical susceptibility for a proton tunneling system is investigated by using the linear response theory and the mean field approximation. The double-minimum self-potential is constructed by a two-Morse potential, whose parameters are fixed to represent O–H stretching mode. Quantum mechanical calculations give a dynamic susceptibility showing a pronounced soft mode. The phase transitions for KDP and DKDP are described qualitatively, if an effective interaction between protons and a phenomenological damping factor are introduced. The temperature dependence of the dynamical susceptibility is discussed.
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  • Tohru Kawamoto, Yutaka Moritomo, Shuji Abe
    2004 Volume 73 Issue 12 Pages 3471-3478
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    We investigated theoretically the nonequilibrium steady state of a bistable molecular solid under continuous external excitation in terms of an Ising-like model. We performed Monte Carlo simulations and mean-field calculations, in both of which we found dynamical phase transitions with varying the intensity of external excitation. Depending on the intermolecular coupling, the population of excited states grows with increasing the excitation intensity in different ways: a monotonic increase and saturation for weak coupling; a sigmoidal increase for intermediate coupling; and the dynamical phase transition with a hysteresis for strong coupling. In increasing the coupling further, the hysteresis region expands, and finally the excited state survives even when the excitation is turned off, corresponding to the ordinary photoinduced phase transition in equilibrium. These results are consistent with experiments in spin-crossover complexes under photoexcitation, including temperature dependence.
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  • Masao Ichida, Yasushi Hamanaka, Hiromichi Kataura, Yoji Achiba, Arao N ...
    2004 Volume 73 Issue 12 Pages 3479-3483
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    We have investigated carrier relaxation dynamics in both metallic and semiconducting single-walled carbon nanotubes by means of femtosecond pump-probe experiments. The femtosecond excitation pulse bleaches the absorption bands of both metallic and semiconducting tubes. In the metallic tubes, the change in the absorption spectra vary from bleaching to broadening. The relaxation aspects of the spectral features change from internal thermalization to electron temperature cooling. In the semiconducting tubes, the nonradiative channel governes the recovery behavior via trapping at defects in the SWNTs.
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  • Motonari Shibakami, Masashi Sonoyama, Rie Goto, Michiko Mori, Hikokazu ...
    2004 Volume 73 Issue 12 Pages 3484-3488
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    High sensitivity differential scanning calorimetry is applied to the problem of interaction between phospholipids and cholesterol in bilayers, i.e., whether or not cholesterol shows a preferential interaction with sphingomyelins over glycerophospholipids. The simplest system yet used for exploring this problem is designed—one composed of 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC), chemically and stereochemically pure N-palmitoyl-sphingomyelin (pure-C16:0-SM), and cholesterol, based on a belief that chemically and stereochemically purity excludes chain length mismatch and chiral interaction that may affect the interaction from this system. Incremental addition of cholesterol to mixtures of DMPC and pure-C16:0-SM with a ratio of 6:4 or 4:6 leads to a continuous shift in endotherm due to DMPC toward a lower temperature. Such results indicate that cholesterol favors pure-C16:0-SM.
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  • Toshiaki Omori, Tsuyoshi Horiguchi
    2004 Volume 73 Issue 12 Pages 3489-3494
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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    We propose a two-layered neural network model for oscillatory phenomena in the thalamic system and investigate an effect of neuromodulation due to the acetylcholine on the oscillatory phenomena by numerical simulations. The proposed model consists of a layer of the thalamic reticular neurons and that of the cholinergic neurons. We introduce a dynamics of concentration of the acetylcholine which depends on a state of the cholinergic neurons, and assume that the conductance of the thalamic reticular neurons is dynamically regulated by the acetylcholine. From the results obtained by numerical simulations, we find that a dynamical transition between a bursting state and a resting state occurs successively in the layer of the thalamic reticular neurons due to the acetylcholine. Therefore it turns out that the neuromodulation due to the acetylcholine is important for the dynamical state transition in the thalamic system.
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  • Shonosuke Ohta
    2004 Volume 73 Issue 12 Pages 3495-3496
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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  • Kazutaka Kudo, Takashi Noji, Yoji Koike, Terukazu Nishizaki, Norio Kob ...
    2004 Volume 73 Issue 12 Pages 3497-3498
    Published: December 15, 2004
    Released on J-STAGE: July 25, 2007
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  • 2004 Volume 73 Issue 12 Pages 3499
    Published: December 15, 2004
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