Ion tracks and microstructures in barium titanate irradiated with swift heavy ions: A combined experimental and computational study

Tetragonally structured barium titanate (BaTiO₃) single crystals were irradiated using 635 MeV ²³⁸U⁺ ions to fluences of 1 × 10⁷, 5 × 10¹⁰ and 1.4 × 10¹² ions cm^?2 at room temperature. Irradiated samples were characterized using ion channeling, X-ray diffraction, helium ion microscopy and transmission electron microscopy. The results show that the ion-entry spot on the surface has an amorphous core of up to ～10 nm in diameter, surrounded by a strained lattice structure. Satellite-like defects around smaller cores are also observed and are attributed to the imperfect epitaxial recrystallization of thermal-spike-induced amorphization. The critical value of the electronic stopping power for creating observable amorphous cores is determined to be ～22 keV nm^?1. Molecular dynamics simulations show an amorphous track of ～1.2 nm in radius under thermal energy deposition at 5 keV nm^?1; the radius increases to ～4.5 nm at 20 keV nm^?1. A linear fit of the core diameter as a function of the square root of the energy deposition rate suggests a reduction in the diameter by an average of ～8.4 nm due to thermal recrystallization if electron–phonon coupling efficiency of 100% is assumed. The simulation also reveals details of the bonding environments and shows different densities of the amorphous zones produced at different energy deposition rates.     

Advanced resonance self-shielding method for gray resonance treatment in lattice physics code GALAXY

A new resonance self-shielding method based on the equivalence theory is developed for general application to the lattice physics calculations. The present scope includes commercial light water reactor (LWR) design applications which require both calculation accuracy and calculation speed. In order to develop the new method, all the calculation processes from cross-section library preparation to effective cross-section generation are reviewed and reframed by adopting the current enhanced methodologies for lattice calculations. The new method is composed of the following four key methods: (1) cross-section library generation method with a polynomial hyperbolic tangent formulation, (2) resonance self-shielding method based on the multi-term rational approximation for general lattice geometry and gray resonance absorbers, (3) spatially dependent gray resonance self-shielding method for generation of intra-pellet power profile and (4) integrated reaction rate preservation method between the multi-group and the ultra-fine-group calculations. From the various verifications and validations, applicability of the present resonance treatment is totally confirmed. As a result, the new resonance self-shielding method is established, not only by extension of a past concentrated effort in the reactor physics research field, but also by unification of newly developed unique and challenging techniques for practical application to the lattice physics calculations.     

Leaching test of gamma-emitting Cs,Ru, Zr,and U from neutron-irradiated UO2/ZrO2 solid solutions in non-filtered surface seawater

The leaching behaviors of gamma-ray radionuclides, Cs-137, Ru-103, and Zr-95, produced by neutron irradiation of UO₂/ZrO₂ solid solutions, in real surface seawater were investigated under atmospheric conditions. The fraction of radionuclide inventory leached in the seawater was in the order of Cs > Ru (～U) ? Zr, indicating that the fraction was significantly affected by the chemical state of the radionuclides. However, the amount of soluble nuclides was proportional to that of uranium regardless of whether the solid solutions were prepared under an oxidative or reductive environment. A tiny fraction of Ru was filtered out by a 3 kDa nominal molecular weight cut-off filter after the 160 d leaching test, suggesting a different behavior from its ionic form, but Cs and U did not form a colloid-like species in seawater.     

Effects of electric field and poling on the mode I energy release rate in cracked piezoelectric ceramics at cryogenic temperatures

We discuss the mode I energy release rate of a rectangular piezoelectric material with a crack under electromechanical loading at cryogenic temperatures. A crack was created normal or parallel to the poling direction, and electric fields were applied parallel or normal to the poling. A plane strain finite element analysis was carried out, and the effects of electric field and localized polarization switching on the energy release rate were discussed for the piezoelectric ceramics at cryogenic temperatures.     

Selection of a pull production control system in multi-stage production processes

In this paper, we conduct an analytical comparison of three pull production control systems: Kanban, CONWIP and Base-stock in multi-stage production processes. First, we compare the three control systems in a multi-stage serial production process. Then, we compare them in multi-stage assembly production processes, and present guidelines that allow us to select the best system. As a result, we show which structural parameters decide the superiority of one control scheme to the others, and how they are related. A key for superiority is a configuration of parameters, such as processing times and number of cards employed in the system. We show that there is no general superiority amongst the analysed concepts. Finally, we verify the effect of variability on the system performance, and generalise the analytical results of deterministic cases by conducting numerical experiments.     

Conformational analysis of ethylene oxide and ethylene imine oligomers by quantum chemical calculations: solvent effects

Summary  Conformational analyses using quantum chemical calculations were carried out for 1- to 4-mers of ethylene oxide (EO) and ethylene imine (EI) oligomer models (EO-x and EI-x, x = 1 - 4) in the liquid phase using four solvents (permittivity: ε = 2.0 ~80.1). The results were compared against those obtained in the gaseous phase. The calculations involved either RHF/6-31+G(d,p) or B3LYP/6-31G(d) // SCRF/IPCM, based on the observed and calculated results for the energy difference between trans- and cis-dichloroethane. The conformations repeated for a unit of X-C, C-C and C-X bonds (X: O or N) were examined. For both oligomers, the energies of every conformer decreased with increasing ε values, and were linear against the Kirkwood function (K_f = (ε-1)/(2ε+1)). For the EO oligomers, the (ttt)_x conformer was most stable in the gaseous phase. In liquid phases, however, the preference for the gauche-conformation (gauche preference) of the C-C bonds increased with higher values of ε. In the case of EO-3, the (tg⁺t)_x conformer was most stable above an ε value of 8.9, which were in good agreement with those observed for triglyme solutions using NMR analysis. For the EI oligomers, the (tg⁺t)_x conformer was most stable in either gaseous or liquid phase, and the gauche preference of the C-C bonds in both phases were comparable. These results were in good agreement with those observed for di-MEDA solutions using NMR analysis. It was estimated that such small solvent effects on gauche preferences of the EI oligomers result in weakening for hydrogen bonds (NH-N) of neighboring imino groups by solvents.     

Preparation of 1 1 1-textured BaTiO3 ceramics by templated grain growth method using novel template particles

Dense BaTiO₃ ceramics with 1 1 1-texture were prepared by the TGG process. Platelike BaTiO₃ particles with their 1 1 1 direction perpendicular to the plate face were prepared by the reaction of platelike Ba₆Ti₁₇O₄₀ particles with BaCO₃ particles in molten NaCl. A green compact was composed of the aligned, platelike BaTiO₃ template particles dispersed in the matrix of small, equiaxed BaTiO₃ particles. Sintering caused densification and also the growth of template particles at the expense of matrix particles, resulting in texture development. Densification prior to grain growth was found to be necessary to obtain highly textured ceramics, and the effect of pre-sintering conditions on texture development was examined.     

EXAFS Study on Structural Change of Charcoal-supported Ruthenium Catalysts during Lignin Gasification in Supercritical Water

Lignin gasification in supercritical water over charcoal supported ruthenium trivalent salts was studied using a batch reactor at 673 K. Ruthenium (III) nitrosyl nitrate on charcoal (Ru(NO)(NO₃)₃/C) was more active than ruthenium (III) chloride on charcoal (RuCl₃/C) for the gasification reaction. EXAFS analysis revealed that ruthenium metal particles were formed in both RuCl₃/C and Ru(NO)(NO₃)₃/C catalysts during the lignin gasification and that the size of ruthenium metal in Ru(NO)(NO₃)₃/C was smaller than that in RuCl₃/C. It was concluded that well-dispersed ruthenium metal particles were active for the lignin gasification in supercritical water.     

Development of a novel microstructure fabrication method with co-axial dual capillary solution flow type droplet cells and electrochemical deposition

A new method for maskless fabrication of metallic patterns or structures on metals is described. A solution flow type droplet cell, with co-axial dual capillaries was applied to form fine metal structures such as strips and rods. This type of droplet cell enables movement of the cell during formation. Nickel fine patterns with a width of about 200 μm were formed on a Cu substrate. The width of the formed pattern does not change with the scanning speed of the cell, but the thickness of the formed pattern changes with the speed. Two different deposition modes were examined to form metal rods, one is a mold free deposition mode and the other is a mold assisted deposition mode. Both modes enable the formation of Ni rods, however, reproducibility of mold free deposition mode was not good. The mold assisted deposition mode has far better the reproducibility, because of the use of the inside wall of the 100 μm diameter inner tube as the mold. It is possible to form nickel micro-rods, about 100 μm in diameter and 12 mm long with relatively smooth surfaces by the mold assisted deposition mode.