Measurement of Rising R-Curve Behavior in Toughened Silicon Nitride by Stable Crack Propagation in Bending

A simple procedure for measuring the R -curve properties of ceramics by a stable fracture test in three-point bending is described. As a typical case, data are displayed for a Si₃N₄ material toughened by the presence of acicular grains in situ grown during the sintering process. The fracture mechanics specimen was a single-edge double-notched beam (SEDNB), whose notch was sharpened to a radius of <10 μm in order to reduce the amount of elastic energy stored at its root prior to crack extension. Furthermore, a stabilizer, specially designed for the bending geometry, was used to control crack stability. During stable extension, the crack could be easily arrested at selected locations of the load-displacement curve, the load quickly released, and the stable crack extension directly measured by the die-penetration technique. The crack resistance, K _R, of the material was calculated from the measured crack extent and the onset load value before unloading. This method enabled us to precisely monitor the critical load value at which the load-displacement curve deviated from linear behavior, as well as crack extensions from a few tens of micrometers to about 1 mm. As an application of this method, the fracture resistance of a Si₃N₄ material with rising R -curve behavior was measured and found to increase from about 5.5 to 9.0 MPaμm^1/2 within a 0.8-mm extension.     

Empirical values for growth-induced anisotropy energy coefficient for designing garnet LPE films

Growth-induced anisotropy energy coefficients and their super-cooling temperature dependence, both attributed to rare-earth ion-pairs, Kⁱ_j, and αⁱ_j, are obtained by analyzing the relationship between growth temperature dependence of uniaxial anisotropy energy, K_u, and garnet compositions. Regression processes were used for analysis. Better agreements are obtained when the newly obtained Kⁱ_j and αⁱ_j values are applied to estimate growth-induced anisotropy energy for 24 garnet compositions. The ratio of calculated growth-induced anisotropy energy values to observed values is 0.98 ± 0.12, when newly obtained Kⁱ_j and αⁱ_j values are used in place of Eschenfelder's Kⁱ_j values (0.85 ± 0.24). Appropriate melt compositions, to obtain LPE garnet films with bubble properties which meet device requirements, are easily given by computer simulation using the newly obtained values.     

Enzymatic differentiation and biochemical and serological characteristics of the clinical isolates of Streptococcus angiosus, S. intermedius and S. constellatus

Of the 29 'Streptococcus milleri' strains tested, all thirteen Streptococcus intermedius (DNA homology group 2) strains but none of the thirteen Streptococcus anginosus (group 1) strains produced beta-N-acetylglucosaminidase, beta-N-acetylgalactosaminidase, alpha-N-acetylneuraminidase, beta-galactosidase, alpha-glucosidase, and hyaluronidase. The three Streptococcus constellatus (group 3) strains produced only the latter two. Glycosidase production divided 274 clinical isolates into 103 S. anginosus, 101 S. intermedius, and 70 S. constellatus strains. Generally, strains of S. anginosus and S. intermedius were non-beta-haemolytic. API II and biotype Ia (lactose positive), but the former contained almost all API III strains and belonged to Lancefield group A/serotype a (A/a), -/b, C/c, -/d, -/e, F/f or G/k, and the latter included most of biotype IId (lactose negative) and serovar -/g, -/h, -/i or -/j. S constellatus strains were beta-, alpha- or gamma-haemolytic, of API I or II but mostly biotype Ib (lactose negative), and of F/- or -/b. S. intermedius was a major member of the oral isolates. Non-oral isolates were virtually all S. anginosus (mainly urogenital isolates) or S. constellatus (the other systemic isolates).     

Highly Durable Spin Filter Switching Based on Self-Assembled Chiral Molecular Motor

Chiral molecules have recently received renewed interest as highly efficient sources of spin-selective charge emission known as chiral-induced spin selectivity (CISS), which potentially offers a fascinating utilization of organic chiral materials in novel solid-state spintronic devices. However, a practical use of CISS remains far from completion, and rather fundamental obstacles such as (i) external controllability of spin, (ii) function durability, and (iii) improvement of spin-polarization efficiency have not been surmounted to date. In this study, these issues are addressed by developing a self-assembled monolayer (SAM) of overcrowded alkene (OCA)-based molecular motor. With this system, it is successfully demonstrated that the direction of spin polarization can be externally and repeatedly manipulated in an extremely stable manner by switching the molecular chirality, which is achieved by a formation of the covalent bonds between the molecules and electrode. In addition, it is found that a higher stereo-ordering architecture of the SAM of OCAs tailored by mixing them with simple alkanethiols considerably enhances the efficiency of spin polarization per a single OCA molecule. All these findings provide the creditable feasibility study for strongly boosting development of CISS-based spintronic devices that can simultaneously fulfill the controllability, durability, and high spin-polarization efficiency.     

Self-discharge behavior of polyacenic semiconductor and graphite negative electrodes for lithium-ion batteries

Variations in open-circuit potential (OCP) of artificial graphite and polyacenic semiconductor (PAS) negative electrodes have been investigated as a function of the storage time in alkylcarbonate-based electrolyte solutions after their cathodic charging (electrochemical lithiation) to discuss self-discharge phenomena of these negative electrodes for lithium ion batteries. The OCP of the graphite showed a plateau at ca. 90 mV vs. Li/Li⁺ for a long period (>8 × 10⁵ s), which suggested the retention of a stage structure of lithiated graphite during the storage. The lithiated PAS electrode gave gradual changes in OCP during the storage in the carbonate-based electrolyte solutions, suggesting continuous loss of Li species in the electrode. Variations in the interfacial resistance determined by an ac method, corresponding to the changes in the structure and properties at the electrode/electrolyte interface, also showed different features for the lithiated graphite and PAS electrodes. The mechanisms of self-discharging for these carbonaceous electrodes are discussed from the results of the influences of temperature and additives on the OCP variations.     

Charge-discharge rate of spinel lithium manganese oxide and olivine lithium iron phosphate in ionic liquid-based electrolytes

Rate capability of Li/spinel LiMn₂O₄ or olivine LiFePO₄ positive electrode cells containing mixed imidazolium ionic liquids electrolytes has been investigated under comparison with conventional organic solvent electrolyte and piperidinium ionic liquid. The LiMn₂O₄ electrode provides variation of rate capabilities among the ionic liquid electrolytes, while ionic liquid electrolytes provide similar extent of capacity degradation under high rate compared with organic solvent electrolyte for LiFePO₄ electrode. Such differences in electrolyte dependences of the rate capabilities can be explained in relation to parameters in the high frequency resistances on AC impedance, assumed as interfacial resistances. The rate capability of LiMn₂O₄ is somewhat related to the activation energy of the high frequency resistance, while for LiFePO₄ the resistance value appears to contribute to the rate capability.     

Thermal conductivity of neptunium dioxide

The thermal diffusivity of neptunium dioxide was measured in the temperature range from 473 to 1473 K by using a laser flash method. The thermal diffusivity slightly decreased with increasing temperature in the temperature range investigated. The heat capacity of NpO₂ was measured in the temperature range from 334 to 1071 K by using a drop calorimetry method. The heat capacity of NpO₂ determined in this study was slightly larger than that of UO₂ and about 7% smaller than that of PuO₂. The thermal conductivity of NpO₂ was determined from the thermal diffusivity, the heat capacity and the bulk density. It was found that the thermal conductivity of NpO₂ from 873 to 1473 K lay between those of UO₂ and PuO₂.     

Fabrication of micro-patterned TiO2 thin films incorporating Ag nanoparticles

A photosensitive TiO₂ thin film embedded with Ag nanoparticles has been prepared from a Ti(OBu)₄–acetylacetone solution, containing dispersed Ag nanoparticles, by the sol–gel method. UV–visible absorption spectra showed that the thin film obtained has two absorption bands, characteristic of the acetylacetone chelate rings and plasmon resonance from Ag nanoparticles. After the irradiation of UV light, the absorption band from the chelate rings almost disappeared, ascribed to structural changes associated with dissociation of the chelate rings. The thin film after the UV irradiation exhibited a broad absorption band in the IR spectrum, indicating that a Ti–O–Ti network was formed in the thin film. HRTEM and EDX spectra revealed that Ag nanoparticles were present and dispersed in the TiO₂ thin film. Micro-patterns of 50 μm dots have been fabricated by UV irradiation through a corresponding photomask, followed by leaching.     

Book reviews

Reducing design defects by proactive actions requires comprehensive understanding of how and why they happen. To achieve this, it is necessary to know the causal relationships of inherent factors, by which design defects arise. This paper represents a causal mechanism of defective design occurrence by considering interactions of underlying factors in designing process. The mechanism draws on the system approach to human errors to describe defects in design caused by designers' active failuresand failures of design reviews as defences to catch defects. It portrays the causal process of the failures with workplace factors and organizational factors as influencing factors. Workplace factors arise from designers' working conditions and include internal and external factors to the actors. Organizational factors comprise elements due to client and designer company's conditions. Then, two failure pathways are discussed to show how the factors lead to design defects. Two case studies are presented in this paper to clarify and explain the mechanism.