Band Gap Modification of Diamond Photonic Crystals by Changing the Volume Fraction of the Dielectric Lattice

Photonic crystals with a diamond structure of epoxy lattices in which TiO₂-based ceramic particles are dispersed were fabricated by stereolithography. The periodicity of the lattice was designed to reflect electromagnetic waves in the gigahertz range. The volume fraction (β) of the dielectric lattice medium was modified from 14% to 33% by changing the rod diameter of the lattice. The photonic band gap was observed along Γ-L 〈111〉, Γ-X 〈100〉, and Γ-K 〈110〉 directions and the complete photonic band gap was formed at over β= 20%. The width of the forbidden gap increased gradually when the β increased over 14%, and reached 2.4 GHz at β= 33%. These results agreed with the band calculation using the plane wave expansion method.     

Fabrication of TiO2–SiO2 Photonic Crystals with Diamond Structure

Ceramic photonic crystals with diamond structure were fabricated using stereolithography and successive sintering. The green body of an epoxy resin incorporating 10 vol% TiO₂–SiO₂ was formed by stereolithography and then heated in air at 1100°–1400°C for 2 h. The sintered products maintained the diamond structure with a linear shrinkage ratio of about 57% and a porosity of 38%. The ceramic photonic crystal with eight unit cells showed a photonic band gap at the center frequency of 23.5 GHz. This fabrication method of three-dimensional (3D) ceramic photonic crystals is applicable to other 3D structural ceramics and does not require any molding techniques.     

Creation of Titania Artificial Interfaces with Geometric Patterns by Using Microstereolithography and Aqueous Solution Techniques

Titania micropatterns with periodic arrangements were successfully formed on glass substrates for use with electromagnetic wave energy resonance and localizations in terahertz frequency ranges. Geometric arrangements of acrylic polygonal tablets with titania particle dispersions were fabricated by using micropatterning stereolithography. Moreover, periodically arranged full anatase‐phase titania tablets were created homogeneously through liquid‐phase crystal depositions of water solvent processes, using microtemplates fabricated by using the stereolithography system. The terahertz wave properties were measured and calculated by using a time‐domain spectroscopic system and finite‐difference time‐domain method.     

Fabrication of Three-Dimensional Micro Photonic Crystals of Resin-Incorporating TiO2 Particles and their Terahertz Wave Properties

Three-dimensional (3D) photonic crystals with a diamond structure made from 40 vol% TiO₂–acrylate dielectric composites were formed by means of a CAD/CAM micro-stereolithography system. The lattice constant of the diamond unit cell was 500 μm and the forming accuracy was 10 μm. The photonic band gap in the Γ–X 〈100〉 direction measured by terahertz-time-domain spectroscopy appeared at 280–360 GHz, which agreed fairly well with the band gap calculated by the plane wave expansion method.     

Titanium aluminide coating on titanium surface using three-dimensional microwelder

Feasibility of a new method of titanium aluminide coating on titanium surface based on a reaction between aluminum liquid beads and the surface of titanium substrate has been studied using a computer-aided three-dimensional microwelder (3DMW) designed by the present authors. A predetermined length of thin aluminum wire was fed onto the substrate surface, and a spark was stricken from a thin electrode of a W-Ce₂O₃ alloy to make a small aluminum liquid bead on the substrate surface and to simultaneously melt a small area of the substrate surface beneath the bead. All conditions including the length of the wire feeding, the position of the electrode, electric power, etc. had been programmed beforehand. The liquid bead containing aluminum and titanium rapidly solidified on the titanium substrate surface producing titanium aluminides on it. Repetition of the aluminum wire feeding, the electrode positioning and the spark striking produced a coating layer consisting of sub-layers of TiAl₃, TiAl and Ti₃Al from the surface side to the substrate side. Vickers hardness and wear resistance of the coated sample were remarkably improved.     

Electrical conductivity and thermoelectric power in irradiated UO2 + x

Two kinds of UO_{2 + x}, the O/U ratios of which were 2.002 and 2.004, respectively, were irradiated to a dose range between 1.14 × 10¹⁴ and 1.90 × 10¹⁸ fissions/cm³, and electrical conductivity changes were measured. A steep decrease in conductivity was observed with increasing dose up to 1 × 10¹⁵ fissions/cm³, a gradual increase followed between 1 × 10¹⁵ and 1 × 10¹⁸ fissions/cm³ and above this dose the conductivity abruptly increased. Thermoelectric power measurements were also carried out for the specimens irradiated in the dose range up to 1.90 × 10¹⁸ fissions/cm³. It might be suggested that p-type conduction contributes to the electrical conductivity in irradiated specimens up to 1.90 × 10¹⁸ fissions/cm³.     

Transient induced creep for irradiated fuels

Creep of nuclear fuels under irradiation has generally been considered as an athermal process. A transient state of irradiation induced creep, however, was treated with kinetic equations based on thermodynamics. For this purpose, the kinetic equations for enhanced diffusion, annihilation of excess vacancies and migration probability under irradiation were derived. Effective works were introduced to the above processes as a result of the fission damage, and reduced activation energies for each process were defined. Based on the knowledge obtained in the transient state, the effective activation energies in the steady state were discussed. The above concepts were examined using the experiments of Clough.     

Covalency,semiconductor-like and thermoelectric properties of Al-based quasicrystals: icosahedral cluster solids

A unified picture of icosahedral cluster solids obtained by comparing Al-based icosahedral quasicrystals to boron-based cluster solids, which consist of icosahedral clusters of the same group III element, B, is discussed. Metallic-covalent bonding conversion in icosahedral clusters of Al and B was demonstrated by molecular orbital calculations. According to theelectron density distribution obtained using the maximum entropy method and the Rietveld method, the bonding conversion phenomenon occurs even in cluster solids such as some Al- and B-based icosahedral approximant phases (Al₁₂Re, α-AlMnSi, α-rhombohedral boron). The covalent bonds observed by the electron density analysis give rise to extremely low carrier density and small density of states at E_f in α-AlMnSi and perhaps in icosahedral quasicrystals. In β-rhombohedral boron, the electronic structure and properties depend on slight variation in atomic environment of the icosahedral multiple-shell structure of the crystals. As metallic atoms are doped into specific atomic sites of β-rhombohedral boron, the atomic structure, the electrical conductivity and its temperature dependence approach those of AlLiCu icosahedral quasicrystal and equal those of AlPdRe icosahedral quasicrystal. From the absolute densitymeasurement, it was revealed that the concept of rigid sphere packing, i.e. metallic bonding, is not applicable to AlPdReicosahedral quasicrystal. Various semiconductor-like behaviors of Al-based icosahedral quasicrystals were demonstrated by means of not only conventional conductivity and Hall coefficient measurements but also modulated photocurrent measurements.In addition, the thermoelectric properties of AlPdRe quasicrystal were estimated. The potential for application of the icosahedral quasicrystals as thermoelectric materials is also discussed.     

Antinociceptive effects of ONO-9902, an enkephalinase inhibitor, after visceral stress condition in rats

PURPOSE: The present study was designed to examine the antinociceptive effects of orally administered ONO-9902, an enkephalinase inhibitor, on both somatic and visceral pain after visceral stress conditions. METHODS: Twenty six male rats were examined. Tail-flick (TF) and colorectal distension (CD) tests were used to determine somatic and visceral antinociceptive effects, respectively. Measurements were performed in rats under immediate post-stress conditions (group ST; n = 14) and in rats nor under stress conditions (group NST; n = 12). In the stressed group, the same device, CD, for visceral antinociceptive effects was used for visceral stress and was applied with an intracolonic pressure of 60 mmHg for 20 min after drug administration. The TF latency and CD threshold were measured before and at 30, 40, 50, 60 and 90 min after administration of ONO-9902 300 mg.kg-1 or distilled water. RESULTS: Orally administered ONO-9902 did not produce any changes in the % maximum possible effect (%MPE) in either TF or CD tests in the unstressed group. In the stressed group, %MPE in the CD test increased 18% and 31% at 30 and 40 min, respectively, after oral administration of ONO-9902 compared with the control group (P < 0.05). However, %MPE to TF test did not alter even after the CD-induced stress condition. CONCLUSION: These results suggest that ONO-9902 may have analgesic effects on visceral pain but not on somatic pain under immediate post-stress conditions.     

Combustion synthesis of single-phase β-sialons (z = 2–4)

Single-phase β-sialon powders (z = 2–4) have been prepared with homogeneous compositions by the combustion synthesis. The raw materials (Si, Al and SiO₂) were combusted under N₂ pressure of 1 MPa. Without using a diluent, the reaction temperatures were very high (>2000 °C) and the combustion products contained Si and Al residues. With addition of commercial β-sialon (z = 1) as a diluent (up to 50 wt%), both the reaction temperatures and amount of residual Si and Al significantly decreased. The combustion reactions completed at 50 wt% dilution, and pure β-sialon phases were synthesized. When the combustion product itself is used instead of the commercial diluent, the phase content of desired z value increased with the repetition times until a single-phase powder is produced. The sinterability of the synthesized powders was then tested using 5 wt% Y₂O₃ as a sintering aid by the spark plasma sintering (SPS).