Ri-ichi Murakami

Synthesis of Co-, Co-Zn and Ni-Zn ferrite powders by the microwave-hydrothermal method

Co-,Ni-Zn, and Co-Zn ferrites were prepared with nanosize well-developed spinel phases by the coprecipitation and microwave-hydrothermal (M-H) methods. X-ray diffraction (XRD) and transmission electron microscope (TEM) techniques showed that the average particle size of ferrites obtained by the M-H process is about 10 nm. In the Co-ferrite system, single-phase ferrites with a spinel structure began to form at a relatively low temperature (100°C) in a short holding time (30 min). The lattice parameter of M1−xZnxFe2O4 systems (M = Ni or Co, 0 ≦ x ≦ 1) increased with an increase of Zn concentration. The crystallization of the spinel ferrites was promoted by the increase in reaction temperature and time.

Microwave-hydrothermal versus conventional hydrothermal preparation of Ni- and Zn-ferrite powders

Ni- and Zn-ferrite powders were prepared by a coprecipitation method in a microwave-hydrothermal (M-H) reaction. The formation conditions of the ferrite were determined in detail according to the reaction conditions (pH, temperature, and time) in this work. The phase identification, crystallinity, and morphology of the prepared samples were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The ferrite phase began to form at a relatively low temperature (120°C) in a short-holding time (30 min) under the M-H process. The crystallization of single-phase ferrite was promoted with an increase of annealing temperature and time. In this work, we also compared the ferrite powder prepared by the M-H method with one prepared by the conventional hydrothermal method. Under the same conditions, the sample prepared by the conventional hydrothermal method did not show the ferrite phase in XRD pattern.

Effect of an interface charge density wave on surface plasmon resonance in ZnO/Ag/ZnO thin films

The optical transmission spectra of ZnO/Ag/ZnO films showed a broad range of transmission enhancement due to a harmonic generated by surface plasmon resonance. This resonance was correlated with interface electrons between metallic Ag and dielectric ZnO layer. The interface charge density wave was calculated and compared with experimental results using Maxwell’sequations with a modified boundary condition. Finally, an observed redshift in the transmission enhancement is discussed using both the Ohmic contact model and the Drude free electron model.

Cyclooxygenase-2 inhibitor delays fracture healing in rats

Background Cyclooxigenase-2 (COX-2) inhibitors have been reported to delay fracture healing. To investigate the major inhibitory period of COX-2 inhibitors in fracture healing, we administrated etodolac, a COX-2-specific inhibitor, to a rat fracture model by altering the period of administration from early to late. Method After closed fractures had been created at the middle of the femoral shafts in 12-week-old Wister rats, a standardized dose of etodolac was administrated in three ways: group I received it for 3 weeks, group II for just the first week after operation, and group III for just the third (final) week. Group IV was the vehicle control group. Bone maturation was estimated by radiographic scoring system, and mechanically by a three-point bending test. Results and interpretation In both the radiographic and mechanical studies, groups I and II showed lower scores than group IV, indicating that even a short period of administration of a COX-2-specific inhibitor in the early phase of fracture healing creates a risk of delayed healing. ▪

Slippage mechanism of pediatric spondylolysis: biomechanical study using immature calf spines.

STUDY DESIGN This study analyzed the skeletal-age-dependent strength of the lumbar growth plate to resist anterior shearing forces using the MTS system in the immature calf spine with pars defects. OBJECTIVE To clarify the pathomechanism of the skeletal-age-dependent incidence of slippage in pediatric patients with pars defects by comparing the strength of the lumbar growth plate among three skeletal age groups. SUMMARY OF BACKGROUND DATA Isthmic spondylolisthesis occurs and progresses more frequently during the growth period, whereas it is rare afterward. However, little evidence has been demonstrated to elucidate the etiology. METHODS For this study, 15 lumbar functional spine units were divided into three groups according to their skeletal ages. Five were from neonates (Group 1), five from calves approximately 2 months old (Group 2), and five from calves about 24 months old (Group 3). An anterior shearing force was applied to each specimen until failure, after bilateral pars defects were created. Failure load (newtons) and displacement at failure (millimeters) were calculated from the load-displacement curve. The site of failure was confirmed by plain radiograph. RESULTS All 15 functional spine units failed at the growth plate. The failure load was 242.79 +/- 46.05 N in Group 1, 986.40 +/- 124.16 N in Group 2, and 2024.54 +/- 245.53 N in Group 3. Statistically significant differences were found among the three groups (P < 0.05). The displacement at failure was 7.52 +/- 1.84 mm in Group 1, 11.10 +/- 2.30 mm in Group 2, and 8.15 +/- 2.66 mm in Group 3. There were no significant differences among the groups. CONCLUSIONS The results indicate that the strength of the growth plate, the weakest link in this model, against anterior shearing forces depends on the skeletal maturity, and that the biomechanical weakness of the growth plate plays an important role in the slippage mechanism.

Effect of intrinsic properties of ceramic coatings on fatigue behavior of Cr–Mo–V steels

Abstract The effect of intrinsic properties of ceramic coatings such as TiN, TiCN and TiAlN films on fatigue behavior has been studied on the commonly used rotor steel, Cr–Mo–V steel, in which test samples were deposited with ceramic coating layers of 2.5–5 μm thick by a filtered arc ion plating. The coating layer micro-hardness, film characteristics and residual stresses of coating films by X-ray diffraction were investigated, and the high-cycle fatigue tests were conducted under rotary bending and axial constant amplitude loading. The hardness of coating layers increased approximately 5–10 times more than that of uncoated substrate dependent on the coatings, and large compressive residual stresses appeared on the coating layers. It is also shown that the fatigue strength of coated specimens is superior to those of uncoated substrate, in particular at long fatigue life. Based on detailed observation of crack initiation, growth and fracture surfaces, it has been concluded that the improved fatigue strength of ceramic-coated material is mainly attributed to the retardation of crack initiation of the substrate by hard coating layers, compared with the influence of crack growth resistance by ceramic coatings.

Organization of cubic CeO2 nanoparticles on the edges of self assembled tapered ZnO nanorods via a template free one-pot synthesis: significant cathodoluminescence and field emission properties

The present investigation explores the controlled architecture of a CeO2–ZnO nanocomposite via a template-free, low temperature, facile single step solvothermal approach. This complex architecture depicts cubic single crystalline CeO2 nanoparticles (size ∼15 nm) grown on the edges of tapered ZnO nanorods with definite orientations and alignments. The formation of wurtzite ZnO, cubic CeO2 and the coexistence of Ce3+ and Ce4+ on the surface of the CeO2–ZnO nanocomposites are confirmed using various characterization tools. The finding of such unique nanostructures by a facile method is exemplified by a plausible growth mechanism. Surprisingly, the aqueous mediated ultrasonication reaction conferred the formation of crystalline ZnO nanotubes of diameter ∼50 nm. Spatially resolved cathodoluminescence spectra are obtained by linearly scanning an individual CeO2–ZnO nanorod along its length, which reveals the size-dependent surface effects. Interestingly, such hybrid CeO2–ZnO nanoarchitecture is observed to exhibit enhanced field emission properties, demonstrating better current stability as compared to other ZnO nanostructures. This is attributed mainly to strong surface interactions between the Ce-ionic species and the ZnO nanorods. Herein, a soft-chemical approach is used for the first time to architect a binary oxide nanostructure, which is otherwise accomplished using high temperature techniques, as reported elsewhere. Also, the present work not only gives insight into understanding the hierarchical growth behaviour of the CeO2–ZnO nanocomposite in a solution phase synthetic system, but also provides an efficient route to enhance the field emission performance of ZnO nanostructures, which could be extended to other potential applications, such as chemical sensors, optoelectronic devices and photocatalysts.

Three dimensional finite element analysis of the pediatric lumbar spine. Part II: biomechanical change as the initiating factor for pediatric isthmic spondylolisthesis at the growth plate

A non-linear 3-dimensional finite element pediatric lumbar spine model with vertebral growth plate and apophyseal bony ring was developed. Lumbar spondylolysis was simulated in the model. The Von Mises stresses in the structures surrounding the vertebral growth plate, including apophyseal bony ring and osseous endplate were calculated in various loading modes. Instantaneous axis of rotation (IAR) path from flexion to extension was also analyzed. The results were compared with those of the intact model and the literature. The IAR path was at the posterior disc-endplate space of the lower vertebra in the intact spine, and moved cranially towards the upper-posterior disc space in the lytic spine. This was in agreement with in vivo radiological data by Sakamaki et al. [19]. During various loading modes, stresses in the spondylolytic pediatric model were higher than that of the intact model; ranging from 1.1 to 6.0 times, with the highest value in extension at the growth plate. In conclusion, FE models indicate that stress concentrations in the lytic model increase at the growth plate which may lead to physis stress fracture leading to spondylolisthesis.

Enhancement of light transmission by coupling to surface plasmon polaritons of a layer-plus-islands silver layer

Enhanced light transmission through coupling incident light with surface plasmon polaritons (SPPs) on a layer-plus-islands nanostructure Ag layer, surrounded by symmetric ZnO dielectrics (ZnO/Ag/ZnO), was investigated. The couple and decouple processes at ZnO/Ag and Ag/ZnO grating interfaces were considered to confine the incident light to SPPs (near field) and then to excite the SPPs to radiate light (far field), which enhanced light transmission. A broad range of light transmission enhancement showed a blueshift with increasing Ag midlayer mass thickness. The physical reasons for light transmission enhancement were theoretically discussed using both the metal/dielectric grating interface model and the Drude–Lorentz free electron model.

Evaluation of mechanical and wear properties of potassium acid titanate whisker-reinforced copper matrix composites formed by hot isostatic pressing

Abstract Copper matrix composites, in which copper powders are reinforced by potassium acid titanate whiskers, were formed by hot isostatic pressing. Two powder sizes (average diameters, 30 μm and 250 μm) were employed. The effects of the copper powder size, whisker content and strain rate on the tensile properties were studied. The wear properties were investigated by changing the normal load and sliding speed. Numerous whisker clusters were present in the copper matrix of the composites. For the 250 μm copper powder, the ultimate tensile strength of the composite was not increased significantly by blending with the whiskers. For the 30 μm copper powder, a uniform distribution of up to 5 wt.% whisker content enhanced the tensile strength. For pure copper and the composite containing 5 wt.% whiskers, the tensile strength increased with the strain rate. However, for composites with high whisker content, the tensile strength decreased at high strain rates. The wear volumes of the composites were nearly proportional to the sliding distance. Debonded whiskers promoted severe wear of the composites. It was confirmed that, if the abrasive wear is constrained under low applied and slow sliding speed, potassium acid titanate whiskers provide an effective reinforcement and improve the wear resistance of the composites.