Showing papers by "Aoyama Gakuin University published in 1994"
463 citations
TL;DR: In this article, the inelastic-neutron-scattering intensity in the inorganic spin-Peierls compound (CuGeO) was experimentally shown to exponentially decrease below (0, 1, 0.5) due to the formation of the spin Peierls gap.
Abstract: We experimentally show that in the inorganic spin-Peierls compound ${\mathrm{CuGeO}}_{3}$ the inelastic-neutron-scattering intensity with \ensuremath{\Delta}E=1 meV at (0,1,0.5) exponentially decreases below ${\mathit{T}}_{\mathrm{SP}}$(=14 K) due to the formation of the spin-Peierls gap. We also found that the magnetic excitation spectrum exhibits a pronounced energy dispersion, the intrachain and interchain exchange parameters ${\mathit{J}}_{\mathit{c}}$\ensuremath{\approxeq}10.4 meV, ${\mathit{J}}_{\mathit{b}}$\ensuremath{\approxeq}0.1${\mathit{J}}_{\mathit{c}}$, and ${\mathit{J}}_{\mathit{a}}$\ensuremath{\approxeq}-0.01${\mathit{J}}_{\mathit{c}}$, and the gap energy at T=0 K is 2.1 meV, suggesting that ${\mathit{J}}_{\mathit{b}}$/${\mathit{J}}_{\mathit{c}}$\ensuremath{\approxeq}0.1 is rather large compared to the organic spin-Peierls system.
188 citations
02 Oct 1994
TL;DR: In this article, the effect of PWM voltage waveform as dB/dt was taken into account by considering the PWM amplitude waveform of the stator and rotor yokes.
Abstract: In the switched reluctance motor, the flux waveforms are nonsinusoidal and different parts of the magnetic circuit have different waveforms. This paper presents a new approach to taking into account these flux waveforms in the calculation of core losses. Relations between the fluxes of different parts of the magnetic circuits are given in the form of matrix equations, where the fluxes are expressed in terms of normalized flux pulses. Rewriting the eddy-current loss term in the Steinmetz equation in terms of the square of dB/dt and combining it with the matrix equations, eddy-current losses for the complicated flux waveforms of the stator and rotor yokes are calculated. The effect of PWM is taken into account by considering the PWM voltage waveform as dB/dt. From the matrices, it is easy to count how many times the full and minor hysteresis loops occur at each pole and yoke segment. The effect of the minor loop is taken into account based on experimental results. The proposed approach gives a systematic procedure for the core loss calculation. The derived equations are simple and useful for the design of the SRM. >
106 citations
TL;DR: Subunit autolysis of mammalian m‐calpain upon activation was examined in kinetic terms using a set of antibodies recognizing different portions of the protease to identify the mode and role of autolytic activity among calpain isozymes.
69 citations
TL;DR: The observed oligomeric organization of T‐PPase allows a possible mechanism for the allosteric regulation of hexameric PPases to be suggested, which is discussed on the basis of the present crystal structure and with respect to site‐directed mutagenesis studies on the Escherichia coli enzyme.
Abstract: The 3-dimensional structure of inorganic pyrophosphatase from Thermus thermophilus (T-PPase) has been determined by X-ray diffraction at 2.0 A resolution and refined to R = 15.3%. The structure consists of an antiparallel closed beta-sheet and 2 alpha-helices and resembles that of the yeast enzyme in spite of the large difference in size (174 and 286 residues, respectively), little sequence similarity beyond the active center (about 20%), and different oligomeric organization (hexameric and dimeric, respectively). The similarity of the polypeptide folding in the 2 PPases provides a very strong argument in favor of an evolutionary relationship between the yeast and bacterial enzymes. The same Greek-key topology of the 5-stranded beta-barrel was found in the OB-fold proteins, the bacteriophage gene-5 DNA-binding protein, toxic-shock syndrome toxin-1, and the major cold-shock protein of Bacillus subtilis. Moreover, all known nucleotide-binding sites in these proteins are located on the same side of the beta-barrel as the active center in T-PPase. Analysis of the active center of T-PPase revealed 17 residues of potential functional importance, 16 of which are strictly conserved in all sequences of soluble PPases. Their possible role in the catalytic mechanism is discussed on the basis of the present crystal structure and with respect to site-directed mutagenesis studies on the Escherichia coli enzyme. The observed oligomeric organization of T-PPase allows us to suggest a possible mechanism for the allosteric regulation of hexameric PPases.
63 citations
TL;DR: In this paper, the authors reported the frequency and temperature dependence of the dielectric constant of polycrystalline ErFe 2 O 4-δ with different degrees of oxygen deficiency δ and concluded that the elementary process of the dispersion is related to electron hopping between Fe 2 and Fe 3+ ions.
Abstract: We report the frequency and the temperature dependence of the dielectric constant of polycrystalline ErFe 2 O 4-δ with different degrees of oxygen deficiency δ. A large dielectric relaxation, with the order of magnitude of 10 4 and nearly of the Debye type, is observed in the magnetically ordered states within the temperature and frequency ranges of 150 K to 290 K and 1 kHz to 3 MHz, respectively. The dispersion is larger in the sample with more oxygen deficiency. From the temperature dependence of the characteristic frequency, we conclude that the elementary process of the dispersion is related to electron hopping between Fe 2+ and Fe 3+ ions. A large value of the dielectric constant is consistent with the existence of spontaneous polarization in the magnetic phases of this oxide. We propose that the motion of the polarization domain boundaries is a determining factor of low-frequency dielectric constant.
63 citations
TL;DR: In this article, an electron diffraction study of an inorganic spin-Peierls system CuGeO 3 was performed and strong diffuse streaks which run along the c * -direction through the fundamental reflections were observed at the same temperature.
Abstract: An electron diffraction study of an inorganic spin-Peierls system CuGeO 3 was performed Weak superlattice reflections indexed by ( h /2) k ( l /2)( h , k , l : o d d ) are observed in electron diffraction patterns taken at about 10 K with the [100] electron incidence The reflections are interpreted as characteristic of a superlattice structure of the space group B b c m or B b m m with cell dimensions a '≃2 a , b '≃ b and c '≃2 c and with dimerization of Cu atoms along the quasi-one-dimensional [001] or the [010] direction, which is strong evidence of the spin-Peierls transition Strong diffuse streaks which run along the c * -direction through the fundamental reflections are observed at the same temperature The streaks are attributed to low-frequency transverse acoustic waves of the oxygen octahedra and can be precursors to another phase transformation below the spin-Peierls transition
52 citations
TL;DR: In this paper, the synergistic effects of radio frequency discharge and catalysis of iron and molybdenum wires were investigated in nitrogen-h ydrogen radio-frequency and microwave plasmas.
Abstract: The synergistic effects o1 driving frequency of the discharge and catalysis of iron and molybdenum wires when then are placed in nitrogen-h ydrogen radio-frequency and microwave plasmas mere investigated. The ammonia Yield increased in the plasmas prepared using both driving frequencies. but the hydrazine yield increased only in fire radio-frequency discharge with the catalysts. The direct adsorption of NHx formed in the plasma on the catalyst surface followed by the formation of NH3 and N2H4 are considered as a reaction scheme in the radio-frequency discharge. On the other hand, the adsorption of N atoms and/or formation of the metal- N bond favors the formation of ammonia but does not affect the hydrazine formation in the microwave discharge.
51 citations
TL;DR: In this paper, the authors performed magnetization and submillimeter wave ESR measurements on single crystals of CuGeO 3 using a pulsed high magnetic field and found that magnetization jumps were observed at 12.8, 12.5 and 13.5 T for a -, b - and c -axes, respectively, at 4.2 K.
Abstract: Magnetization and submillimeter wave ESR measurements have been performed on single crystals of CuGeO 3 using a pulsed high magnetic field. Magnetization jumps are observed at 12.8, 12.5 and 13.5 T for a -, b - and c -axes, respectively, at 4.2 K. The temperature dependences of the linewidth and the integrated intensity of the ESR signal are discussed in connection with the conventional spin-Peierls systems, and the excitation gap against the magnetic field is estimated when the field is applied along the a -axis. ESR has been observed in the magnetic phase above the critical field H c and the g -values have different values from those in the spin-Peierls phase. The origin of this difference is discussed.
43 citations
TL;DR: A new homologous series of oxycarbonate superconductors with tetragonal structures was found by resistivity and magnetization measurements in this paper, and the transition temperatures were 50, 105 and 115 K for n=1, 2 and 3, respectively.
Abstract: A new homologous series of oxycarbonate superconductors Sr2(Ca,Sr)n−1Cun(CO3)1−χ(BO3)χOy (n=1, 2 and 3) prepared under high pressure have been found by resistivity and magnetization measurements. X-ray powder diffraction and HRTEM studies show that these phases have tetragonal structures with a=3.86 A and c=7.40 A for n=1, a=3.86 A and c=10.62 A for n=2, and a=3.87 A and c=13.98 A for n=3. Resistivity and magnetization measurements revealed that superconducting transition temperatures were 50, 105 and 115 K for n=1–3, respectively. These Tc's are higher than those of the structurally related analogous TlBa2Can−1CunO2n+3 at 100 and 110 K (n=2 and 3).
41 citations
TL;DR: A new Hg based oxycarbonate superconductor HgBa 2 Sr 2 Cu 2 O 6+ δ (CO 3 ) has been found by resistivity and magnetization measurements as mentioned in this paper.
Abstract: A new Hg based oxycarbonate superconductor HgBa 2 Sr 2 Cu 2 O 6+ δ (CO 3 ) has been found by resistivity and magnetization measurements. The superconductivity has been observed at 66 K by magnetization measurement. The electron-diffraction and HRTEM studies show that the crystal structure basically consisted of [HgBa 2 O 2+ δ ] and [Sr 2 CO 3 ] block layers and has a tetragonal unit cell, with a=3.88 A , c=16.94 A , with an orthorhombic superstructure, with A≈4.5√2a=24.71 A ,B≈√2a=5.49 A , C=c=16.94 A , due to the three times periodic replacements of a CO 3 block for HgO δ in the same c -planes or to a c /2 shift approximately at intervals of three tetragonal cells along the (110) direction. The crystal structure of this compound is described by the following combination: [(Hg 0.5 C 0.5 )(Ba,Sr) 2 O 2.5+ δ ]+CuO 2 +[(Ba,Sr) 2 (C 0.5 Hg 0.5 )O 2.5+ δ ]+CuO 2 .
TL;DR: In this article, a new approach to prepare graded CIS-based absorber layers using Se-containing precursors in a Se-vapor selenization process was developed, and active area efficiency of 12.6% was achieved with a ZnO:Al/CdS/ graded-CIGS cell fabricated with this approach.
TL;DR: In this article, high energy cosmic-ray hadron flux is measured in homogeneous-type thick lead chambers (total thickness being 60 cm and 110 cm) exposed at the Pamirs (atmospheric depth 595 g/ cm 2 ).
TL;DR: In this article, a symmetry-forbidden phonon for the tetragonal T' structure is observed for the Gd-type superconductors, which shows that oxygen in the T' plane is locally distorted along the plane.
Abstract: For ${\mathrm{Gd}}_{2}$${\mathrm{CuO}}_{4}$, a symmetry-forbidden phonon for the tetragonal T' structure is observed. This shows that oxygen in the ${\mathrm{CuO}}_{2}$ plane is locally distorted along the plane. Such distortion has not been observed for other T'-type superconductors. The normal-mode calculation shows that the correlation between the ${\mathrm{CuO}}_{2}$ plane and R-O layers increases with decreasing ionic radius. The increased three-dimensional character and the appearance of the distortion of O in the ${\mathrm{CuO}}_{2}$ plane along the a axis are useful experimental results that help clarify the mechanism that causes the disappearance of superconductivity for Gd.
TL;DR: In this paper, the Dirichlet L -series at positive integers was evaluated by q-calculation, and it was shown that δ( s ) is a Riemann δ-function at positive even integers.
TL;DR: In this article, the magnetoelectric effect of a polycrystalline sample of a triangular Ising antiferromagnet ErFe2O4-δ was inferred from the neutron and dielectric studies.
Abstract: We report the magnetoelectric effect of a polycrystalline sample of a triangular Ising antiferromagnet ErFe2O4-δ, in which the existence of short range charge ordering was inferred from the neutron and dielectric studies. The sign of the magnetoelectric signal was reversed at 77 K, when the electric or magnetic field was applied in the opposite directions during cooling the specimen down to 77 K. The sign of the signal was independent of the direction of the static bias magnetic field in the range above 150 K. The signal was maximum at 183 K. We suggest a relation between the origin of the magnetoelectric effect and the dielectric relaxation due to an electron hopping between Fe3- and Fe2+ sites.
TL;DR: In this paper, the authors examined the charge-density-wave (CDW) density of states in quasi-one-dimensional conductor NbSe3 using low temperature tunneling conductance.
Abstract: Charge-density-wave (CDW) density of states in quasi-one-dimensional conductor NbSe3 has been examined using low temperature tunneling conductance. Most of the CDW gap structures are expressed by the Gaussian distribution model of the BCS gaps. The two-dimensional anisotropic density of states predicted by Huang and Maki also fits to some of the data. Furthermore we observed the conductance having the perfect zero value at zero bias. These results suggest that the CDW gap in NbSe3 is spatially varied or being anisotropic.
TL;DR: It is proposed that the suppression of the DOS peak at ${\mathit{E}}_{\Mathit{F}}$ is caused by dynamical lattice distortion: The DOS peak predicted for the cubic structure presumably induces the lattice instability, leading to the dynamical clustering distortion.
Abstract: The electronic structure of ${\mathrm{Ba}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{K}}_{\mathit{x}}$${\mathrm{BiO}}_{3}$ has been studied by photoemission spectroscopy. With increasing x, the spectra are generally shifted towards the Fermi level (${\mathit{E}}_{\mathit{F}}$), indicating a downward shift of ${\mathit{E}}_{\mathit{F}}$ due to hole doping. The magnitudes of the shifts, however, are substantially smaller than those predicted by band-structure calculations. In the cubic metallic phase, although band-structure calculations on the cubic structure predict the density of states (DOS) to show a peak at or close to ${\mathit{E}}_{\mathit{F}}$, the photoemission intensity decreases towards ${\mathit{E}}_{\mathit{F}}$, suggesting that the splitting of the Bi 6s band persists and results in a pseudogap behavior. We propose that the suppression of the DOS peak at ${\mathit{E}}_{\mathit{F}}$ is caused by dynamical lattice distortion: The DOS peak predicted for the cubic structure presumably induces the lattice instability, leading to the dynamical lattice distortion.
TL;DR: In this paper, the authors measured the polarity and temperature dependence of Raman scattering spectra of CuGeO 3 from room temperature to 5 K and found that the energy of the five inter-chain phonons increases with decreasing temperature.
Abstract: Polarization and temperature dependence of Raman scattering spectra of CuGeO 3 has been measured from room temperature to 5 K. The observed phonons at room temperature are well assigned by the group theoretical estimation for Pbmm (D 5 2h ). The qualitative change for all possible Raman scattering spectra has not been found from room temperature to 14 K. The energy of the five inter-chain phonons increases with decreasing temperature. Below spin-Peierls transition temperature T sp (=14 K), five peaks at 27, 107, 230, 370, and 820 cm -1 have been observed for the ( c , c ) geometry while the peaks at 370 and 820 cm -1 appear for ( b , c ).
TL;DR: In this paper, a design chart and a manufacturing process for millimetre-wave absorbers consisting of two spacers and two resistive sheets are presented, and a multilayered type absorber was manufactured and it has a significant absorption level (≤ −20 dB) at a wide frequency range of 46-66 GHz.
Abstract: The authors present a design chart and a manufacturing process for millimetre-wave absorbers consisting of two spacers and two resistive sheets. The conventional design chart gives sufficient information to enable a desired absorber to be made. On the basis of the chart, a multilayered type absorber was manufactured and it has a significant absorption level (≤ –20 dB) at a wide-frequency range of 46–66 GHz.
TL;DR: In this article, a large lattice anomaly in the a-b plane, vertical to the one-dimensional antiferromagnetic spin chain, associated with additional diffraction peaks in the b * -axis at temperatures much higher than the spin-Peierls transition temperature was found.
Abstract: Crystal structure and phonon dynamics up to 150 meV of the spin-Peierls material CuGeO 3 have been investigated by neutron scattering experiments. We found a large lattice anomaly in the a-b plane, vertical to the one-dimensional antiferromagnetic spin chain, associated with additional diffraction peaks in the b * -axis at temperatures much higher than the spin-Peierls transition temperature. The phonon modes of the chain oxygens at 100 meV show consistent evolution with diffraction. Therefore, we conclude that the structural evolution of the chain oxygens in the a-b plane, which mediates the spin-spin interaction along the c -axis, drives the spin-Peierls transition.
TL;DR: In this paper, the Tl-1201 structure with 6 and 7 times periodicities along the b-axis was synthesized over a wide range of x (1.0≤ x ≤ 3.2) and examined by X-ray powder diffraction, electron diffraction and magnetometry methods.
Abstract: TlBa x Sr 4- x Cu 2 (CO 3 )O y oxycarbonates with the Tl-1201 structure were synthesized over a wide range of x (1.0≤ x ≤3.2) and examined by X-ray powder diffraction, electron diffraction, high-resolution electron microscopy and magnetometry methods. New phases with the Tl-1201 structure having 6 and 7 times periodicities along the b -axis were isolated. The former was stable for a wide Ba-rich range (1.8≤ x ≤3.2), and the latter was observed for a smaller Ba content range (1.2≤ x ≤1.6). The phase stability was found to depend on the synthesis condition. The maximum T c of the as-synthesized specimen in this series occurred at about 70 K around x =2.0. The Meissner volume fraction of the as-synthesized specimen ( x =2.4) was 30% at 5 K.
TL;DR: In this paper, tunneling measurements have been performed on high-quality Ba 1− x K x BiO 3 single crystals with T c's between 15 and 30 K. The average ratio of 2Δ/k B T c = 3.5±0.1 is obtained using more than 20 different junctions (different samples) with T C's determined from tunnel junctions.
Abstract: Tunneling measurements have been performed on high-quality Ba 1− x K x BiO 3 single crystals with T c 's between 15 and 30 K. The junctions are Ba 1− x K x BiO 3 /natural barrier/Au sandwich type, which exhibit very low leakage currents at zero bias and sharp conductance peaks at the gap-edges. The average ratio of 2Δ/ k B T c = 3.5±0.1 is obtained using more than 20 different junctions (different samples) with T C 's determined from tunnel junctions. Temperature dependence of the energy gap is consistent with the BCS prediction. Second derivative measurements of current-voltage characteristics have also been carried out. Observed strengths and peak positions of the superconducting phonon structures in d 2 I /d V 2 strongly support phonon-mediated superconductivity in Ba 1− x K x BiO 3 .
TL;DR: In this article, the effect of yttrium in the behavior of coatings produced by thermal spraying MCrAlY (M=Ni, Co) powders, CO2 laser processing was conducted.
Abstract: To improve the corrosion resistance and to study the effect of yttrium in the behavior of coatings produced by thermal spraying MCrAlY (M=Ni, Co) powders, CO2 laser processing was conducted. Three methods were used: (1) a combination of gas flame and plasma spraying in air followed by laser glazing in argon, (2) low-pressure plasma spraying (LPPS) and laser glazing in argon, and (3) LPPS and laser-gas (O2) alloying. Laser glazing in argon of the MCrAlY coatings sprayed in air promoted formation of weakly adherent agglomerates of Al−Y oxides and an alumina-chromia solid solution. Glazing in argon atmosphere of LPPS CoNiCrAlY and NiCrAlY coatings caused the formation of nickel aluminides besides the formation of Y−Al compounds. Gas (O2)-alloying of these coatings produces continuous and adherent (yttrium-containing) alumina and chromia layers. The effects of yttrium on the characteristics of the oxides formed in the coatings during laser glazing, laser-gas alloying, and high-temperature oxidation is discussed. This work also investigated the oxidation resistance of the laser-processed MCrAlY coatings in air and in the presence of 85 mol/o V2O5−Na2SO4 fused salt at 900°C.
01 Apr 1994
TL;DR: In this paper, Salicylaldehyde methylenediimine (salen) and its Cu(II) complexes have been measured in various media at various temperatures, and it is found that salen takes an enolimine-type structure in cyclohexane and exists as an equilibrium mixture of enol-imine and keto-amine type species in alcoholic media.
Abstract: Electronic absorption spectra of Salicylaldehydeethylenediimine (salen) and its Cu(II) complexes have been measured in various media at various temperatures. It is found that salen takes an enol-imine-type structure in cyclohexane and exists as an equilibrium mixture of enol-imine and keto-amine type species in alcoholic media. The polarization spectrum of salen-Cu(II) measured in the stretched PVA film shows that 282, ∼ 290, ∼ 250, and 230.4 nm bands are polarized along the longer-molecular-axis, and 354, 273.0, 242.4 and ∼ 220 nm bands along the shorter-molecular-axis. The 242.4 and ∼ 250 nm bands can be assigned to intramolecular charge transfer (CT) transitions between the metal ion and ligand and between the two π-electronic systems of the ligand, respectively. The complex of salen-Cu(II) forms a dimer in EPA (ether: isopentane: ethanol = 5:5:2 in volume) at low temperatures. The first two bands of the monomer at 380 and 362 nm are blue-shifted by the dimer formation, and appear at 370 and 351 nm, respectively, and the 278 nm monomer band splits into two bands at 275 and 267 nm. These spectral changes on the dimer formation are well reproduced by an extended PPP calculation.
05 Dec 1994
TL;DR: In this paper, chemically deposited CBD-CdS layers were used for window layers of superstrate-type CIS solar cells, and the best cell yielded an efficiency of 8.1% with Voc=440 mV.
Abstract: Chemically deposited CdS was used for window layers of superstrate-type CIS solar cells. The CBD-CdS layers had no pinholes and had higher optical transmission at short wavelengths than evaporated CdS layers, which led to the increase in Jsc. Relatively high substrate temperature of 450/spl deg/C was used for CIS deposition, resulting in high Voc due to improved crystallinity of CIS films. However, the interdiffusion and alloy formation at CIS/CdS deteriorated cell performance. The best cell yielded an efficiency of 8.1% with Voc=440 mV, Jsc=34 mA/cm/sup 2/ and FF=0.54 using near-stoichiometric (Cu/In=0.91-0.98) CIS films.
TL;DR: In this article, high-chromium (Cr) nickel (Ni)-Cr coatings were deposited by thermal spraying in air and in an argon (Ar) gas atmosphere.
Abstract: High-chromium (Cr) nickel (Ni)-Cr coatings were deposited by thermal spraying in air and in an argon (Ar) gas atmosphere. Coatings sprayed in Ar gas were free of pores and defects and of t...
TL;DR: In this article, the first tunneling measurements of the superconducting energy gap in YNi2B2C have been carried out, and the ratio 2Δ/kBTc = 3.5±0.1 is determined from the standard analysis using the BCS theory.
Abstract: The first tunneling measurements of the superconducting energy gap in YNi2B2C have been carried out. Observed energy gap value is typically 2Δp-p = 5.3±0.1 meV from the peak-to-peak amplitude in dI/dV, while 2Δ = 3.7±0.1 meV is determined from the standard analysis using the BCS theory. Since the Tc measured from the tunnel junction is 12 K, the ratio 2Δ/kBTc = 3.5±0.1 is obtained. This is in good agreement with the BCS prediction, indicating that the superconducting mechanism in this compound is a conventional type.
TL;DR: In this paper, muscle and shell samples from abalone (Haliotis) from a shallow water locality in a Japanese coastal region were analyzed to obtain information about the behavior of heavy metals in biological assimilation processes in a marine food chain.