Reduction of impurities in fluoride glass fibers

In order to realize a low-loss fluoride Optical fiber, impurity reduction is indispensable. The methods of recrystallization, extraction, chemical vapor-phase deposition, distillation, and sublimation were tried to purify the starting materials for a fluoride fiber. These purification methods were evaluated by measuring transmission loss of the fibers prepared by using the purified materials. It was found that recrystallization was useful for reducing impurities in ZrF4to the level of below 1 ppm. The extraction technique could be also applicable to purification of BaF2and GdF3. It was concluded that the sublimation was the most probable purification in order to prepare fluoride materials with less than 0.1-ppm impurities. As a result, a low-loss fiber with 8.5 dB/km at 2.12 μm was obtained by using the starting materials purified by sublimation.     

Microprocessor-Controlled DC Motor for Load-Insensitive Position Servo System

The conventional proportional P controller has been often used as the position controller of the dc servo motor. When the unknown and inaccessible load torque, such as the coulomb friction, the gravity, and so on, is imposed on the dc servo motor, this control system has the steady-and/or transient-state error.     

The δ′/δ phase transition in hafnium hydride and deuteride

Bulk samples of hafnium (Hf) hydride and deuteride were prepared and the thermal properties, heat capacity (C_P) and thermal conductivity (κ) were measured. In the C_P–temperature curves for both samples, typical lambda-type peaks were observed at around 350 K, which was due to the second-order phase transition from the δ′-phase to the δ-phase. In Hf hydride, it is considered that the δ′-phase and the δ-phase consist of regularly arranged and randomly arranged hydrogen atoms, respectively. Therefore, it can be said that the δ′/δ phase transition observed in both Hf hydride and deuteride is an order–disorder phase transition. The values of κ as well as C_P changed significantly at around the phase transition temperature.     

Ab initio study of hydrogen diffusion in zirconium oxide

Hydrogen diffusion in monoclinic and tetragonal zirconium oxides has been studied by electronic state calculations. In both structures, the optimized hydrogen site lies near the center of a distorted fluorite structure. The activation energy was calculated to be 120–200 kJ/mol, which is similar to experimentally measured values. The effects of compressive stress, alloying elements, and oxygen defects are considered individually. Compressive stress reduces the hydrogen diffusion coefficient by 40%/GPa. Oxygen defects and substituted Fe and Cr are thought to act as trapping sites for hydrogen, which probably reduces hydrogen diffusion in zirconium oxide.     

Synthesis and thermal conductivity of Y6UO12

Y₆UO₁₂ was synthesized by solid-state reactions of Y₂O₃ and U₃O₈. The high-density pellet of Y₆UO₁₂ was prepared by the spark plasma sintering followed by heat treatment in air for oxygen supplementation. The thermal conductivity (κ) was evaluated using the laser flash method from room temperature to 1173 K. The κ of Y₆UO₁₂ decreased with increasing temperature in the whole temperature range, indicating that the phonon contribution was predominant. The room temperature κ value of Y₆UO₁₂ was 4.90 Wm^?1K^?1. The magnitude relationship of κ among Y₆UO₁₂, Y₆WO₁₂, and Yb₆WO₁₂, i.e. κ of Yb₆WO₁₂ < κ of Y₆UO₁₂ < κ of Y₆WO₁₂, was discussed based on the general lattice thermal conductivity theory.     

Thermal and mechanical properties of hydrides of Zr–Hf alloys

Polycrystalline bulk samples of δ-phase Hf hydrides with various Zr contents were prepared and their high-temperature stability and thermal and mechanical properties were investigated. The phase structure was examined between room temperature and 973 K using high-temperature X-ray diffraction and thermogravimetric–differential thermal analysis. From room temperature to 673 K, the coefficient of linear thermal expansion, specific heat capacity, and thermal conductivity were evaluated. The Vickers hardness and sound velocity were measured at room temperature, and the elastic modulus was evaluated. The effect of the Zr content on the high-temperature stability and the thermal and mechanical properties of Hf hydrides was studied.     

Structural characterization of femtosecond laser modified regions inside sapphire

We report on structural characterization of sapphire photomodified by voids of sub-wavelength diameter surrounded by amorphised regions formed after exposure by tightly-focused femtosecond laser pulses of 800 nm wavelength and 150 fs duration at the single and double-pulse irradiation inside crystalline sapphire. Regrowth of a crystalline phase near the edge between the amorphous and crystalline phases was observed by transmission electron microscopy (TEM) in the case of double-pulse-irradiated locations. Regions patterned by single-pulse-induced voids inside sapphire were characterized by synchrotron X-ray diffraction (XRD) technique. The XRD patterns indicate presence of an expanded phase of the host crystal. The origin of structural changes observed in TEM and XRD is discussed and is consistent with fast thermal quenching.     

Establishment of evaluation method to determine effects of veterinary medicinal products on manure fermentation using small-scale composting apparatus

To evaluate on a laboratory scale the influence of veterinary medicinal products (VMPs) excreted into feces on manure fermentation, we have developed an evaluation method that uses a small-scale composting apparatus. Each run is of approximately 3 kg scale and the operation can be conducted in an environmentally controlled laboratory. The main evaluation parameter is calorific value generated by aerobic fermentation. At the sulfadimethoxine (SDM) trial, the volume of CO(2) generated during fermentation and the disappearance of the inhibitory effect of immature manure on sprouting (using Komatsuna (Brassica rapa var. perviridis)) were measured. In addition, DNA of 16S rRNA was extracted from a manure sample and subjected to denaturing gradient gel electrophoresis (DGGE). The results suggest that the presence of such VMPs in feces affected the microbial community in manure fermentation, and indicate that the evaluation method may be used as a standard method to evaluate the effect of VMPs on the microbial community. Using the method, we obtained data of the influence of five VMPs approved for stockbreeding in Japan on swine manure fermentation. Erythromycin (EM) affected the calorific value even at a relatively low concentration (105 mg/3 kg manure). In contrast, oxytetracycline hydrochloride (OTC), norfloxacin (NFLX), and tylosin tartrate (TS) had no effect at that concentration. These VMPs also affected the increase of fermentation temperature when added at high concentrations.     

Influence of oxygen transfer in Hf-based high-k dielectrics on flatband voltage shift

We investigated flatband voltage (Vfb) behavior for several Hf-based high-k dielectrics, including HfO₂, Mg-, and La-incorporated HfO₂, HfSiO_x, and Mg-, La-, and N-incorporated HfSiO_x, during the reduction (forming gas annealing: FGA) and oxidation annealing (ODA) processes. A negative Vfb shift appeared in all high-k dielectrics as the FGA temperature increased. In contrast, a positive Vfb shift was observed after the introduction of additional oxygen into the high-k layer during ODA. The oxygen diffusion coefficient (D) values of all samples were estimated using Fick's law. The results showed that the D value of the HfO₂ dielectric was five times as large as that of the HfSiO_x dielectric in ODA at 400 °C. Furthermore, the Mg-, La-, and N- incorporated high-k dielectrics exhibited a larger D value compared with the pure high-k dielectrics. These results strongly suggest that the ionicity of high-k dielectrics, which we attribute to a large positive Vfb shift, enhances oxygen diffusion in the high-k layer.