Microstructure and transport properties of [0 0 1]-tilt bicrystal grain boundaries in iron pnictide superconductor,cobalt-doped BaFe2As2

Relationships between microstructure and transport properties of bicrystal grain boundary (BGB) junctions were studied in cobalt-doped BaFe₂As₂ (BaFe₂As₂:Co) epitaxial films grown on [0 0 1]-tilt bicrystal substrates of MgO and (La, Sr)(Al, Ta)O₃ with misorientation angles θ_GB = 3–45°. The θ_GB of BaFe₂As₂:Co BGBs were exactly transferred from those of the bicrystal substrates. No segregation of impurities was detected at the BGB junction interfaces, and the chemical compositions of the BGBs were uniform and the same as those in the bulk film regions. A transition from a strongly-coupled GB behavior to a weak-link behavior was observed in current density–voltage characteristics under self-field around θ_GB ～ 9°. The critical current density decreased from (1.2–1.6) × 10⁶ A/cm² of the intragrain transport to (0.7–1.1) × 10⁵ A/cm² of θ_GB = 45° because supercurrent becomes more governed by Josephson current with increasing θ_GB.     

Effects of Some Light Alloying Elements on the Oxidation Behavior of Fe and Ni-Cr Based Alloys During Air Plasma Spraying

The oxidation behavior of iron binary powders with addition of Si (1, 4 wt.%) and B (1, 3 wt.%) and that of a Ni-Cr based alloy powder with Si (4.3 wt.%), B (3.0 wt.%), and C (0.8 wt.%) additions during atmosphere plasma spray (APS) have been investigated. Analysis of the chemical composition and phases of oxides in the captured in-flight particles and deposited coatings was carried out. The results show that the addition of Si and B to iron effectively reduced the oxygen contents in the coatings, especially during the in-flight period at higher particles temperature. Ni-Cr based alloy powder with Si, B, and C additions reduced the oxidation of the base alloys significantly. Preferential oxidation and subsequent vaporization of Si, B, and C from the surface of the sprayed particles are believed to play a major role in controlling oxidation in the APS process.     

Waves in a rotating elastic solid

Wave propagation in a uniformly rotating elastic solid is discussed based on displacement equations in a moving frame. The time-harmonic Green’s dyadic for a point body force is obtained in closed form. It is reconfirmed that two quasi dilatational and shear waves are coupled to each other, and the deformation decomposition into the dilatation and rotation is not possible for the rotating solid. Further, it is also confirmed that the velocity of the Rayleigh surface wave depends not only on the rotational velocity but also on its direction and that the Rayleigh wave vanishes when the rotational velocity approaches the Rayleigh wave velocity of the immovable solid.     

Development of a grout database for geological disposal of high-level radioactive waste

Japan Atomic Energy Agency (JAEA) has developed a grout database (GDB) comprising the latest technical data of grout materials relevant to the geological disposal of high-level radioactive waste (HLW). Currently, only newly developed grout materials of low pH cements, superfine spherical silica and colloidal silica, which are expected to provide a target pH ≤ 11 leachate, are included in the GDB. Case examples from on-site works and laboratory-based tests that have been published in the literature have been used to add construction and material details to the GDB. The GDB is available online (https://groutdb.jaea.go.jp/grout/ [in Japanese]) for registered users to obtain and provide data of grout technology. Furthermore, the GDB can be used to correlate requirements of mechanical, physical, and/or chemical properties of a grout material to specifically address concerns over safety assessment, material and injection method development, and/or prediction of grout penetration.     

Promotion Effect of FeOx Addition on the Catalytic Activity of Supported Cu Catalysts for the Water–gas Shift Reaction

Among the supported Cu–FeO_x catalysts, Al₂O₃-supported Cu–FeO_x catalyst exhibited the highest activity for WGS reaction. The enhancement of the catalytic activity by adding FeO_x to Cu/Al₂O₃ could be interpreted by the two possibilities; one is the formation of highly dispersed Cu⁰ and the other is the participation of reduced FeO_x in WGS reaction in the presence of Cu⁰.     

Molecular weight dependence in a relaxation phenomenon at glassy state: Physical aging of polycarbonate

At the glassy state of polymers, the reptation-type molecular motion should be frozen-in and the relaxation should be only by local motions, such as rotation, vibration, and torsion. Such local motions would not depend on molecular weight. This may be current understanding of the polymer glass. By contrast, we found that the rate of enthalpy relaxation in polycarbonate at 100 °C (50 °C below T_g) clearly depends on molecular weight. Deterioration of impact strength was also found to depend on molecular weight. The surprising results are presented in this letter.     

Fabrication of ferromagnetic nanoconstriction using atomic force microscopy nanoscratching

Nanolithography used in conjunction with atomic force microscopy (AFM) has attracted considerable attention as a technique for fabricating nanoscale structures. To obtain nanostructures and devices, AFM nanoscratching was performed on a photoresist and on NiFe at various values of the applied force, scan speed, and number of scan cycles. The scratching process was carried out using a diamond-coated tip on NiFe and a Si tip on the photoresist. By conducting scratching processes on NiFe and on the photoresist, we investigated the dependence of the size of the scratched part on the scratching parameters. These results show that the width and depth of the scratched part increase as the applied force and number of scan cycles increase, but not as the scan speed increases. This means that it is possible to control the size of the scratched parts by adjusting the applied force and number of scan cycles. AFM nanoscratching was then used to directly fabricate a nanoconstricted area with a width of 139 nm and a cross-sectional area of less than 300 nm2 was fabricated.     

Thermal and electrical conduction properties of vertically aligned carbon nanotubes produced by water-assisted chemical vapor deposition

We present both thermal and electrical conduction properties of vertically aligned carbon nanotubes (VACNTs), synthesized by the water-assisted chemical vapor deposition method using Fe–Ti–O nanoparticles as catalyst. Thermal diffusivity and electrical resistance of VACNTs have been measured by the laser flash method and direct-current four-terminal method, respectively. The VACNTs are found to have thermal diffusivities of the same order as isotropic graphite and the electrical characteristics of semiconductors. The electrical resistance shows a T^−1/4 temperature dependence, which implies that the conduction of electrons is dominated by 3D Mott variable range hopping.     

Humido-sensitive conducting polymer films and applications to linear actuators

Free-standing films made of poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT/PSS) with various PSS contents were newly prepared by casting water dispersion of the PEDOT/PSS colloidal particles in the presence of an extra PSS. Electrical conductivity, morphology, water vapor sorption, and electro-active polymer actuating behavior of the resulting films were investigated by means of four-point method, atomic force microscope (AFM), sorption isotherm, and electromechanical analyses. The maximum contraction of the film by application of an electric field increased with increasing both PSS content and relative humidity (RH), where the value attained 7% at 70% RH for the film with 93% of PSS. Since the isothermal sorption curve of the film was less dependent on the PSS content, the significant increase of the film contraction was explained by two mechanisms: (i) the extra PSS prevented from hydrogen bonding between adjacent PEDOT/PSS particles that suppressed dimensional changes of the film; and (ii) the higher the RH, the larger the degree of water vapor sorption, which led to the large film contraction by desorption of water vapor via Joule heating. On the basis of this phenomenon linear actuators utilizing PEDOT/PSS films were successfully developed and applied to leverage actuator and Braille cell.     

Novel grounded and floating high order immittance simulators using OTAs and OAs

This paper proposes novel grounded and floating high order series and parallel immittance simulators using operational transconductance amplifiers (OTAs) and operational amplifiers (OAs) with a finite gain–bandwidth (GB) product. They are composed of active devices (OTAs and OAs) and resistances, and are suitable for monolithic implementation in either CMOS or bipolar technologies. They also realize both positive and negative high order immittances. The circuit characteristics can be electronically tuned by adjusting the transconductances of OTAs and the GB products of OAs. Any transfer functions are realizable using the proposed simulators. Two examples are shown, together with simulation results.