Time‐frequency analysis of a pressure wave caused by impulse tree using wavelet transform

This paper describes results of time‐frequency analysis of a pressure wave caused by impulse tree extension using wavelet transform. Pressure waves were measured by a piezo sensor which was located on the back of the plane electrode when high‐voltage nanosecond pulses were applied to a point electrode in a low‐density polyethylene block. Frequency of the pressure wave from induced charges on the plane electrode was higher than that of the pressure wave from tree. In addition, the frequency of the pressure wave from tree tended to decrease with increasing gap length because of the dispersion of the pressure wave during its propagation. When a large tree extension occurred between a 5‐mm gap, pressure waves of about 10 MHz propagated from the tree tip and a pressure wave of 1 MHz propagated from the tree stem. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 142(1): 1–7, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10097     

Adsorption and desorption properties on the fluorine-doped tin oxide film surface on a glass substrate under UV light irradiation in vacuum

Various functional metal-oxide coatings on glass substrate have the possibility to be used for many applications in these days. For keeping the high performance of these applications, it is very important to understand the adsorption property on those coating surfaces. However, there are few reports about such properties of metal-oxide film surface in vacuum state, especially the carbon adsorption property on fluorine-doped tin oxide (SnO₂:F) film in vacuum.In this study, we have investigated the chemical state on SnO₂:F film in vacuum with XPS analysis. From the results of the SnO₂:F film surface analysis, the adsorbed carbon (C1s orbit) on the SnO₂:F film surface and the adsorbed carbon dependence of heat treatment in vacuum were observed. Also, it was found that the adsorbed carbon distribution on the SnO₂:F film existed after the heat treatment at low temperature in vacuum, uniformly spread in large area with UV light irradiation. Besides, the influence of UV light irradiation with respect to the carbon contents in the SnO₂:F film was observed by SIMS analysis. As the result, it was implied that the carbon state in the SnO₂:F film remained unchanged under UV light irradiation and the carbon adsorption and desorption occurred only on the surface of the SnO₂:F film.     

Effects of osteoprotegerin administration on osteoclast differentiation and trabecular bone structure in osteoprotegerin-deficient mice

Osteoprotegerin (OPG)-deficient mice exhibit severe bone loss including the destruction of growth plate cartilage. Using OPG-deficient mice, we attempted to clarify the differentiation and ultrastructure of osteoclasts located on the destroyed growth plate cartilage and trabecular bone matrix in long bones. In (-/-) homozygous OPG knockout mice, adjacent to the growth plate cartilage, the formation of bone trabeculae without a calcified cartilaginous core resulted in an irregular chondrocyte distribution in the growth plate cartilage. At the metaphyseal ossification center, TRAP-positive osteoclasts showed unusual localization on both type-II collagen-positive cartilage and type-I collagen-positive bone matrix. Osteoclasts located on cartilage matrix lacked a typical ruffled border structure, but formed resorption lacunae. During growth plate cartilage destruction, osteoclasts formed ruffled border structures on bone matrix deposited on the remaining cartilage surfaces. These findings suggest that, in OPG (-/-) mice, osteoclast structure differs, depending on the matrix of either cartilage or bone. Then, we examined the effects of OPG administration on the internal trabecular bone structure and osteoclast differentiation in OPG (-/-) mice. OPG administration to OPG (-/-) mice significantly inhibited trabecular bone loss and maintained the internal trabecular bone structure, but did not reduce the osteoclast number on bone trabeculae. For most osteoclasts, OPG administration caused disappearance or reduction of the ruffled border, but induced neither necrotic nor apoptotic damages. These results suggest that OPG administration is an effective means of maintaining the internal structure and volume of trabecular bone in metabolic bone diseases by inhibition of osteoclastic bone resorption.     

Production of Carbon Nanotube by Ethylene Decomposition over Silica-Coated Metal Catalysts

Formation of carbon nanofibers (CNFs) and carbon nanotubes (CNTs) through the decomposition of ethylene at 973 K was achieved using various metal catalysts covered with silica layers. CNFs of various diameters were formed by ethylene decomposition over a Co metal catalyst supported on the outer surface of the silica. In contrast, silica-coated Co catalysts formed CNTs with uniform diameters by ethylene decomposition. Silica-coated Ni/SiO₂ and Pt/carbon black also formed CNTs with uniform diameters, while CNFs and CNTs with various diameters were formed over Ni/SiO₂ and Pt/carbon black without a silica coating. These results indicate that silica layers that envelop metal particles prevent sintering of the metal particles during ethylene decomposition. This results in the preferential formation of CNTs with a uniform diameter.     

Formation of carbon nanotubes through ethylene decomposition over supported Pt catalysts and silica-coated Pt catalysts

Ethylene decomposition was performed over supported Pt catalysts to fabricate composites of Pt metal nanoparticles and carbon nanotubes (CNTs). All supported Pt catalysts (Pt/carbon black, Pt/CNT, Pt/MgO, Pt/Al₂O₃ and Pt/SiO₂) showed catalytic activity for ethylene decomposition at 973 K to form CNTs. Pt metal particles were found at tips of CNTs. These results indicate that Pt metal particles have catalytic activity for growth of CNTs through hydrocarbon decomposition. A broad range (5-50 nm) of CNT diameters were formed from the use of supported Pt metal catalysts although Pt metal particles in the catalysts before ethylene decomposition were relatively uniform in size (2-5 nm). These results imply that Pt metal particles in the catalysts aggregated during ethylene decomposition at 973 K. Aggregation of Pt metal particles in catalysts during ethylene decomposition could be suppressed by covering catalysts with silica layers that were a few nanometers thick. Silica-coated Pt catalysts showed high activity for ethylene decomposition to form CNTs with uniform diameters (8-10 nm) despite the uniform coverage of Pt metal particles with silica layers.     

Biomimetic Zirconia with Cactus-Inspired Meso-Scale Spikes and Nano-Trabeculae for Enhanced Bone Integration

Biomimetic design provides novel opportunities for enhancing and functionalizing biomaterials. Here we created a zirconia surface with cactus-inspired meso-scale spikes and bone-inspired nano-scale trabecular architecture and examined its biological activity in bone generation and integration. Crisscrossing laser etching successfully engraved 60 μm wide, cactus-inspired spikes on yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) with 200–300 nm trabecular bone-inspired interwoven structures on the entire surface. The height of the spikes was varied from 20 to 80 μm for optimization. Average roughness (Sa) increased from 0.10 μm (polished smooth surface) to 18.14 μm (80 μm-high spikes), while the surface area increased by up to 4.43 times. The measured dimensions of the spikes almost perfectly correlated with their estimated dimensions (R² = 0.998). The dimensional error of forming the architecture was 1% as a coefficient of variation. Bone marrow-derived osteoblasts were cultured on a polished surface and on meso- and nano-scale hybrid textured surfaces with different spike heights. The osteoblastic differentiation was significantly promoted on the hybrid-textured surfaces compared with the polished surface, and among them the hybrid-textured surface with 40 μm-high spikes showed unparalleled performance. In vivo bone-implant integration also peaked when the hybrid-textured surface had 40 μm-high spikes. The relationships between the spike height and measures of osteoblast differentiation and the strength of bone and implant integration were non-linear. The controllable creation of meso- and nano-scale hybrid biomimetic surfaces established in this study may provide a novel technological platform and design strategy for future development of biomaterial surfaces to improve bone integration and regeneration.