Dependence of railgun operation on current rise time

Railguns are facilities to accelerate projectiles up to several kilometers per second by electromagnetic force generated by driving current. Worldwide, a variety of current waveforms are used in railgun systems. This paper describes the dependence of railgun operation on the rise rate of the driving current. The use of the exploding wire as an opening switch makes it possible to change the rise time of the driving current. A secondary arc is likely to appear and the erosion on a rail surface is more severe when current with a short rise time is used. According to the nondimensional railgun simulation, current with a short rise time heats up the plasma so fast that many particles ablated from the bore surface, which seem to be the cause of the secondary arc, increase rapidly in the early phase of acceleration. © 1999 Scripta Technica, Electr Eng Jpn, 129(3): 17–28, 1999     

Radiation‐initiated graft polymerization of methylmethacrylate onto poly(tetrafluoroethylene): Characterization by 1H‐NMR

A broad‐line ¹H‐NMR study was carried out to examine the local structure of poly(methylmethacrylate) (PMMA) grafted onto Poly(tetrafluoroethylene) (PTFE). The NMR spectra were observed for three different samples with 1.0, 5.4, and 7.0 wt % PMMA over the temperature range from 150 to 380 K. With the help of selectively deuterated PMMA (PMMA‐d₅ and PMMA‐d₈)‐grafted samples, the NMR spectra were analyzed in terms of two components—a Gaussian (G) component, and a Lorentzian (L) component. Based on the second moments (〈ΔH²〉) analysis, the L and G components were attributed to the ¹H–¹H dipolar interactions within one CH₃ group and the interactions of CH₃ groups that are closely located in aggregated PMMA chains. Combining the results with the temperature dependence of 〈ΔH²〉 and the angular resolved XPS, the location and rotational motion of PMMA grafted onto PTFE are discussed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1386–1394, 1999     

Computational Study of Nonadiabatic Wave Patterns in Smouldering Combustion under Microgravity

We numerically study a thermal-diffusive model for smouldering combustion under microgravity with convective heat losses. In accordance with previous experimental observations, it is well known that porous materials burning against a gaseous oxidiser under microgravity exhibit various finger-like char patterns due to the destabilising effect of oxidiser transport. There is a close resemblance between the pattern-forming dynamics observed in the experiments with the mechanism of thermal-diffusive instability, similar to that occurring in low Lewis number premixtures. At large values of the Lewis number, the finger-like pattern coalesces and propagates as a stable front reminiscent of the pattern behaviour at large Péclet numbers in diffusion-limited systems. The significance of the order of the chemical kinetics for the coexistence of both upstream and downstream smoulder waves is also considered.     

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.     

Fabrication of dielectric nanocubes in ordered structure by capillary force assisted self-assembly method and their piezoresponse properties

Ordered structures of barium titanate (BT) nanocubes, strontium titanate (ST) nanocubes and BT/ST nanocubes mixture were directly fabricated on Si and Pt-coated Si substrates using a capillary force assisted assembly method. The morphology of self-assembled structures was observed using field emission scanning electron microscopy (FE-SEM) and scanning probe microscopy (SPM). It was revealed that nanocubes were arranged with various degrees of ordering to develop multilayer and monolayer regions at the surface of substrates. The elemental mapping of the structure consisting of the nanocubes mixture was also investigated by transmission electron microscopy (TEM) with an energy dispersive X-ray spectroscopy (EDX). It was revealed that BT and ST nanocubes coexisted homogeneously in the structure and had possibility to be arranged in order to each other. The piezoresponse properties obtained by scanning probe microscopy (SPM) indicated that the hetero-interface between BT and ST nanocubes would introduce anomaly in piezoelectric properties.     

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.