Showing papers by "Aoyama Gakuin University published in 1998"

Pressure-induced dimensional crossover and superconductivity in the hole-doped two-leg ladder compound Sr14-xCaxCu24O41

Abstract: Anisotropic electrical resistivity under high pressure was measured for a single crystal of ${\mathrm{Sr}}_{2.5}{\mathrm{Ca}}_{11.5}\ensuremath{-}{\mathrm{Cu}}_{24}{\mathrm{O}}_{41}$, a hole-doped two-leg ladder compound. Superconductivity was observed between 3.5 and 8 GPa, accompanied by metallic resistivity between the ladders, which indicates semiconducting behavior at ambient pressure. This in turn strongly suggests that the application of pressure brings about a dimensional crossover from one to two, and that superconductivity in this system is a consequence of an insulator to superconductor transition in the anisotropic two-dimensional system.

Spin dynamics of the spin-ladder dimer-chain material Sr 14 Cu 24 O 41

Abstract: We have performed inelastic neutron scattering on a single crystal sample of Sr14Cu24O41 to study the spin dynamics of the Cu2O3 spin ladder layers, and CuO2 chains. Data collected with incident energies of 50 meV, 200 meV, 350 meV and 500 meV are best fitted with a dispersion with a spin gap of 32.5+/-0.1 meV and a maximum of 193.52.4 meV, consistent with a coupling along the ladders, J|| = 130 meV and a rung coupling J^=72 meV. We find that excitations with an energy transfer of approximately 11.5 meV can be described solely in terms of a dimer chain with an antiferromagnetic intra-dimer coupling, J1 = 11.2 meV, between next-nearest-neighbour Cu ions and a ferromagnetic inter-dimer coupling, J2 = -1.1 meV. The dimers are separated by two Cu ions providing a periodicity for the dimer chain of five units.

Study on Crystallinity of Tin-Doped Indium Oxide Films Deposited by DC Magnetron Sputtering

Abstract: Tin-doped indium oxide (ITO) films were deposited by dc magnetron sputtering using oxide (ITO) or alloy (IT) targets. The ITO films sputter-deposited using Ar at total pressure (Ptot) lower than 1.2 Pa showed polycrystalline structure, whereas entirely amorphous films were deposited at Ptot higher than 1.4 Pa, indicating that the crystallinity of the ITO films were heavily affected by Ptot. This was quantitatively explained in terms of the kinetic energy of sputtered particles reaching to the substrate surface, which decreased due to an increase in collision frequency between the sputtered particles and sputtering gas molecules. ITO films were also deposited using Xe or He as sputtering gases, where amorphous films were deposited at Ptot higher than 0.7 Pa (Xe) and 12 Pa (He), respectively. Based on a hard sphere collision model, the energy loss rates of the sputtered particles due to collision with sputtering gas molecules were estimated to be consistent with the experimental results for the case of using He, Ar or Xe gases.

Spin gap and dynamics in Sr 14 − x Ca x Cu 24 O 41 comprising hole-doped two-leg spin ladders: Cu NMR study on single crystals

Abstract: We report comprehensive Cu NMR studies on single crystals of ${\mathrm{Sr}}_{14\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{Cu}}_{24}{\mathrm{O}}_{41},$ which contain simple ${\mathrm{CuO}}_{2}$ chains and two-leg ${\mathrm{Cu}}_{2}{\mathrm{O}}_{3}$ ladders. From measurements of the ${}^{63}\mathrm{Cu}$ NMR shift, it is clear that the spin gap in the ladders decreases with isovalent Ca substitution from $\ensuremath{\Delta}=550\ifmmode\pm\else\textpm\fi{}30$ K for ${\mathrm{Sr}}_{14}{\mathrm{Cu}}_{24}{\mathrm{O}}_{41}$ (Sr14) to $350\ifmmode\pm\else\textpm\fi{}30$ K, $280\ifmmode\pm\else\textpm\fi{}30$ K, and $270\ifmmode\pm\else\textpm\fi{}30$ K for $x=6$ (Ca6), $x=9$ (Ca9), and $x=11.5$ (Ca11.5), respectively. The exponential decrease of the nuclear spin-lattice relaxation rate ${1/T}_{1}$ below \ensuremath{\sim}130 K is consistent with the presence of the spin gap in the spin excitation spectrum. In the $T$ range higher than $\ensuremath{\sim}200$ K, we observed the following dependences: ${1/T}_{1}=\mathrm{const}$ and the square of Gaussian spin-echo decay time, ${T}_{2G}^{2}\ensuremath{\propto}T$ which are consistent with the scaling theory for the $S=1/2$ one-dimensional (1D) Heisenberg model. The value of ${T}_{2G}{/T}_{1}\sqrt{T}$ is compatible with the theoretical prediction of an exchange constant along the leg ${J}_{\ensuremath{\parallel}}\ensuremath{\sim}1800$ K for Ca6 and ${J}_{\ensuremath{\parallel}}\ensuremath{\sim}1500$ K for Ca9 and Ca11.5. A notable finding is that the magnitude of the spin gap remains nearly constant and characteristics of novel 1D-like spin dynamics are maintained in the content varying from Ca9 to Ca11.5. On the other hand, the charge transport changes with increasing Ca content so that the more conductive Ca11.5 exhibits pressure-induced superconductivity exceeding 3.5 GPa. We have found that ${T}_{2G}^{2}$, which is proportional to the inverse spin correlation length ${\ensuremath{\xi}}^{\ensuremath{-}1}$, deviates from a linear $T$ dependence upon cooling and is described by $A+BT\mathrm{exp}(\ensuremath{-}\ensuremath{\Delta}/T)$, regardless of the Ca substitution. We point out that the value of ${T}_{2G}^{2}(T=0)=A$ is proportional to the finite value of ${\ensuremath{\xi}}_{0}^{\ensuremath{-}1}=\ensuremath{\Delta}{/c}_{1D},$ where ${c}_{1D}=(\ensuremath{\pi}{/2)J}_{\ensuremath{\parallel}}$ is the spin-wave velocity. From the result that the values of ${A}^{\ensuremath{-}1}\ensuremath{\sim}{\ensuremath{\xi}}_{\mathrm{eff}}$ for Ca6, Ca9, and Ca11.5 are significantly reduced compared to that for Sr14, it is suggested that ${\ensuremath{\xi}}_{\mathrm{eff}}$ is dominated at low $T$ by an average distance $d$ among mobile holes obeying the relation ${\ensuremath{\xi}}_{\mathrm{eff}}\ensuremath{\sim}d={\ensuremath{\xi}}_{h}.$ From an estimate of ${\ensuremath{\xi}}_{0}/a\ensuremath{\sim}$ 5.2 for Sr14, where $a$ is the Cu-Cu distance along the leg, ${\ensuremath{\xi}}_{h}/a$ is obtained as $\ensuremath{\sim}3.5$, 2.3, and 2.0, and hole content $x$ as $\ensuremath{\sim}0.14$, 0.22, and 0.25 per ${\mathrm{Cu}}_{2}{\mathrm{O}}_{3}$ ladder for Ca6, Ca9, and Ca11.5, respectively. These values were consistent with $x=$ 0.14, 0.2, and 0.22 for Ca6, Ca9, and Ca11 estimated from the optical conductivity experiment by Osafune et al. [Phys. Rev. Lett. 78, 1980 (1997)]. The ${\mathrm{Sr}}_{14\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{Cu}}_{24}{\mathrm{O}}_{41}$ compounds are thus hole-doped two-leg spin-ladder systems which reveal the metallic behavior dominated by the 1D-like spin dynamics at high $T$ and accompanied by the spin gap formation at low $T$. For Ca11.5, as the spin gap is formed upon cooling below $\ensuremath{\sim}180$ K, the resistivity increases in the direction perpendicular to the ladder, whereas the conductivity along the ladder remains metallic, followed by the localization of mobile holes in both directions below ${T}_{L}\ensuremath{\sim}60$ K. We point out that preformed pairs are confined in each ladder and localized below $\ensuremath{\sim}60$ K at an ambient pressure.

Experimental Investigation of Air Radiation from Behind a Strong Shock Wave

Abstract: Radiation phenomena behind a strong shock wave have been experimentally investigated using a freepiston double-diaphragm shock tube. The shock front is detected by pressure sensors, whose rise time is calibrated by a laser schlieren technique. Spatial distribution of emission spectra correlated with the shock front is obtained for a 270-520 nm wavelength range by means of one-dimensional imaging spectroscopy, in which a wavelength vs. position image is taken by an ICCD camera with the gate time of 100 ns. Molecular spectra of N2 second positive and N^~ first negative band are observed immediately after the shock front, while atomic line spectra from N become dominant shortly after it. The rotational and vibrational temperatures of molecules, and the electronic excitation temperature of atoms are evaluated, and their spatial profiles in the streamwise direction are obtained for a shock velocity of 11.9 km/s and an ambient pressure of 0.3 torr, using N2 as the test gas. The measured temperatures seem to be in significant nonequilibrium with the translational temperature. Also, the relaxation rates for Njj" seem to be much higher than those for Ng.

Identification of the major allergens in wheat flour responsible for baker's asthma

Abstract: Baker's asthma, a typical occupational allergic disease, is a serious problem in the food industries. In this study, purification and identification of major allergens recognized by IgEs in sera of allergic patients were performed. Major immunoreactive proteins were purified from the albumin fraction by gel filtration on a Toyopearl HW-50 column followed by reverse-phase HPLC. The N-terminal amino acid sequences and molecular masses measured by MS indicated that the major immunoreactive proteins are members of the alpha-amylase inhibitor family, 0.19 and 0.28. Significant leukotriene release by each purified protein was observed in cell-associated stimulation tests, suggesting in vivo activity of these antigens. Carbohydrate analyses of major allergens indicated that they are monoglycosylated but not N-glycosylated in spite of the presence of a potential N-glycosylation site. Recombinant 0.19 expressed in Escherichia coli showed the same reactivity with IgE as native wheat 0.19 in Western blotting and ELISA using methyl vinyl ether maleic anhydride co-polymer as an immobilizing reagent, suggesting that the allergenic epitopes are located in the peptide portions.

Resource Endowments and Agricultural Development: Africa versus Asia

Abstract: This chapter aims to examine the sources of agricultural stagnation/ deterioration in Sub-Saharan Africa by contrasting it with the agricultural growth experience in Asia, and East Asia in particular. An important and well-documented feature of the East Asian model of economic development is the considerable success of the countries concerned in expanding their agricultural sector. This success enabled them to provide more or less regular employment to a growing rural population before urban industrialization was advanced enough to absorb large numbers of workers (Fei, Ranis and Kuo, 1979; Morley, 1982, ch. 11). In the case of some countries (most notably, Japan and Taiwan), expansion of rural employment opportunities and incomes was greatly helped by a decentralized pattern of industrialization that resulted in the development of numerous rural industries (Smith, 1959; Ho, 1979). Moreover, since food supply increased rapidly, instead of being diverted to food imports, foreign exchange earnings could be reserved for importing capital and intermediate goods needed by modern industries.

Deposition of Heteroepitaxial In2O3 Thin Films by Molecular Beam Epitaxy

Abstract: Highly oriented thin film In2O3 was heteroepitaxially grown on an optically polished (001) plane of single crystalline yttria stabilized zirconia (YSZ) substrate using molecular beam epitaxy (MBE). The full-width at half maximum (FWHM) of the X-ray rocking curve was 0.08° for 200-nm-thick In2O3 layers indicating excellent uniformity of the crystallographic orientation compared with the heteroepitaxially-grown In2O3 deposited by a conventional method such as electron-beam (e-beam) evaporation. The minimum yield (χmin ) of the MBE grown In2O3 film obtained from Rutherford backscattering (RBS) spectra was also extremely small with a value of 3.1% implying high crystallinity with very low lattice defect density.

Magnetic ordering, spin waves, and Haldane-gap excitations in (Nd x Y 1-x ) 2 BaNiO 5 linear-chain mixed-spin antiferromagnets

Abstract: Linear-chain nickelates with the composition (Nd{sub x}Y{sub 1{minus}x}){sub 2}BaNiO{sub 5} (x=1, x=0.75, x=0.5, and x=0.25) are studied in a series of neutron-scattering experiments. Powder diffraction is used to determine the temperature dependence of the magnetic structure in all four systems. Single-crystal inelastic neutron scattering is employed to investigate the temperature dependence of the Haldane-gap excitations and low-energy spin waves in the x=1 compound Nd{sub 2}BaNiO{sub 5}. The results of these experiments are discussed in the context of the {open_quotes}Haldane chain in a staggered field{close_quotes} model for R{sub 2}BaNiO{sub 5} systems, and quantitative agreement with theory is obtained. {copyright} {ital 1998} {ital The American Physical Society}

Performance evaluation of popular distributed object technologies for Java

Abstract: System development using Java and distributed object technology (DOT) is becoming common, and can become the standard way of doing network computing in the near future. The performance of DOTs is crucial in high-performance network computing systems. In this paper, the performance of popular DOTs for Java is evaluated in a common environment employing the fastest available PCs and 100 Mbit/s Ethernet. We evaluate HORB, Java RMI, Voyager, two commercial CORBA IIOP implementations, and Distributed COM. For comparison a Java socket version and a C socket version are also evaluated. To represent the characteristics of the DOT, the performance of primitive object operations including remote object creation, remote method call, transferring arrays of objects and transferring large numerical data is measured and evaluated. No DOT won all benchmarks, but HORB showed very good performance for most benchmarks. © 1998 John Wiley & Sons, Ltd.

Experimental measurement of the staggered magnetization curve for a haldane spin chain

Abstract: Long-range magnetic ordering in ${R}_{2}{\mathrm{BaNiO}}_{5}$ ( $R\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\mathrm{magnetic}$ rare earth) quasi-one-dimensional mixed-spin antiferromagnets is described by a simple mean-field model that is based on the intrinsic staggered magnetization function of isolated Haldane spin chains for the Ni subsystem, and single-ion magnetization functions for the rare earth ions. The model is applied to new experimental results obtained in powder diffraction experiments on ${\mathrm{Nd}}_{2}{\mathrm{BaNiO}}_{5}$ and ${\mathrm{NdYBaNiO}}_{5}$, and to previously published diffraction data for ${\mathrm{Er}}_{2}{\mathrm{BaNiO}}_{5}$. From this analysis we extract the bare staggered magnetization curve for Haldane spin chains in these compounds.

A duality of the twisted group algebra of the symmetric group and a Lie superalgebra

Abstract: Let A_k denote the twisted group algebra of the symmetric group S_k, whose representations correspond to the nonlinear projective representations of S_k. We establish a duality relation between A_k and a Lie superalgebra q(n), sometimes called the ``queer'' Lie superalgebra. This duality clarifies Schur's formula, in the sense that the Schur-Weyl duality clarifies Frobenius' formula.

Toward an East Asian Model of Economic Development

Abstract: Exceptionally high growth performances of East Asian economies in the past several decades have been amply documented (eg, P Kuznets, 1988; Wade, 1990, chapter 2; World Bank, 1993) The task of this conference volume is to identify the institutional structure underlying those performances with respect to how unique or general it is in the world development context and to what aspects the East Asian model (if it is a coherent economic system distinguishable from others) will be applicable to development of the Third World

S = 1/2 Degrees of Freedom in Haldane System Y2BaNiO5 Observed by Submillimeter Wave ESR

Abstract: We have performed submillimeter wave ESR measurement of Haldane system Y 2 BaNiO 5 in the frequency region from 50 to 383 GHz using the pulsed magnetic field up to 16 T. Due to the excess oxygens, a few percent of Ni 2+ ions of Y 2 BaNiO 5 , which we used, are substituted by the Ni 3+ ion of which spin is S =1/2. The ESR signals coming from the S =1/2 degrees of freedom originated by the Ni 3+ ion at the end of the finite chain, are observed at 4.2 K. The frequency-field relations of these ESR signals are analyzed by the model based on the VBS model, which is used in the case of Cu 2+ doped NENP. The signs of the single ion anisotropies D and E are determined from the analysis.

Molecular Cloning, Expression, and Site-Directed Mutagenesis of Inorganic Pyrophosphatase from Thermus thermophilus HB8

Abstract: The genomic DNA encoding the inorganic pyrophosphatase from an extremely thermophilic bacterium, Thermus thermophilus HB8 (ATCC27634), was isolated by colony hybridization with a probe designed as a part of gene amplified by the PCR method, which was derived from the partial amino acid sequence of the enzyme. The DNA was cloned into a plasmid vector, pUC118, after digestion with BamHI. The inserted nucleotide fragment was about 1.8 kbp in length and the nucleotide sequence included a 525 bp open reading frame. The deduced amino acid sequence was completely identical with that of the enzyme determined by automated Edman analysis of peptide fragments isolated from digests obtained with Staphylococcus aureus V8 protease and Achromobacter protease I, and also from products obtained on chemical cleavage with cyanogen bromide and 70% formic acid. The subunit of this enzyme is composed of 174 amino acid residues with a calculated molecular weight of 19,084. Then, the gene was overexpressed in Escherichia coli BL21 (DE3) using a plasmid vector, pET15b, system. The recombinant enzyme was fully active, and exhibited higher thermostability than the E. coli enzyme. Amino acid residues located on the surface of the recombinant enzyme were determined by means of limited proteolysis, and the results revealed that the environment of Lys residues is almost the same as the crystal structure reported previously [Teplyakov, A. et al. (1994) Protein Sci. 3, 1098-1107]. Furthermore, the roles of two tryptophan residues were investigated by site-directed mutagenesis, which indicated that they may be responsible for the structural integrity and thermostability.

Tricolor photoviscoelastic technique and its application to moving contact

Abstract: A new technique for simultaneous determination of both fringe order and principal direction of birefringence in practical photoviscoelastic analysis using white incident light with a set of the primary colors, called tricolor photoviscoelasticity, is described. This method can determine both the fringe order and principal direction of birefringence from a single-color photoviscoelastic image under plane polarization. Then, the authors evaluate time dependent stresses and strains around a contact region in a viscoelastic strip plate under nonproportional loading condition. The variations of the principal stresses and strains are easily obtained over a wide time range by use of the optical constitutive equations of photoviscoelasticity and the characteristic material property functions.

Norms and Rationality in the Evolution of Economic Systems: A View from Asian Villages

Abstract: The evolution of economic systems is viewed as a process in which various informal arrangements are experimented with for improving efficiency under changed economic environments, some of which may survive and become established as new social norms. The process is illustrated by a micro case study of Philippine villages. It reveals the ability of peasants subsisting on small farms to resolve a major disequilibrium between labour's marginal productivity and the wage rate resulting from the intro duction of modern rice technology, by creating, on the basis of their traditional experience, an appropriate institution consistent with their cultural norm. Concurrently, large estate farms were seen to arrive at an inferior outcome because of their inability to utilize the peasant community's norm, thereby demonstrating the existence of multiple equilibria JEL Classification Numbers: D23, O17, P51

Coulomb blockade in nano-junction array fabricated by nonlithographic method

Abstract: The first observation of the Coulomb blockade (CB) is reported in a single nano-tunnel junction (Al/Al 2 O 3 /Ni-nanowire) array prepared in a self-organized porous alumina film without using any lithography. The linear temperature dependence of the zero-bias conductance anomaly observed suggests the presence of the CB. The high resistance Ni-nano wire directly and automatically attached to the single tunnel junction and the high uniformity of array parameters make the emergence of the CB possible in spite of the absent external high resistance block and the high packing density of the tunnel junctions, respectively. The G – V 1/2 curve observed outside the CB-voltage and -temperature regions indicates that the high resistance of Ni-wire originates from the electron–electron (e–e) interaction in a disordered conductor. Our report is, therefore, also the first observation of the CB co-operated by the e–e interaction and of the phase transition between these regimes on temperature and voltage. As one of some interesting problems, which geometry part of the Ni-wire is effective for the parasitic capacitance of the CB is discussed proposing an electric field propagation model.

Effect of Sn Doping on the Crystal Growth of Indium Oxide Films

Abstract: Heteroepitaxial growth of tin-doped indium oxide (ITO) and non-doped indium oxide (IO) thin films was carried out on single-crystal yttria-stabilized zirconia substrates by molecular beam epitaxy. The surface morphology of these epitaxial films was characterized by scanning electron microscopy. The doped ITO and non doped IO epitaxial films showed drastic changes in surface morphology, which suggested that Sn acted not only as a dopant but also as a growth modifier for IO films. The surface morphology analysis of IO and ITO films revealed a growth rate enhancement by Sn doping along the direction.