Degradation mechanism of SiC/Super α 2 composite due to interfacial reaction

The degradation mechanism of SiC(SCS-6)/Super α ₂ composite due to the interfacial reaction was studied using single-fiber composite specimens fabricated by the sputtering method, heat treated at 1273 K for various times, and tensile tested at room temperature. The main results are summarized as follows. (1) The tensile strength was reduced with progress of interfacial reaction by the formed defects on the fiber surface, while the formation of the reaction layers in the matrix side was not the direct reason for the reduction. (2) From the fracture mechanical analysis of the experimentally observed relation of the size and shape of the surface defects to the fiber strength, the fracture toughness of the fiber employed in the present work was estimated to be 2 to 4 MPa ρm. (3) The change in distribution of strength of the reacted fiber with progressing reaction was simulated successfully by combining the Monte Carlo method with the Weibull distribution function for the strength of the unreacted fiber, the Gumbell distribution function for the maximum effective size of the surface defect of the reacted fiber, and the fracture mechanics.     

Fracture behavior and toughening mechanism in Zanchor reinforced composites under mode II loading

The mode II interlaminar fracture behavior and the toughening mechanism of Zanchor reinforced composite laminates were investigated by using the End Notched Flexure (ENF) and Interlaminar Shear (ILS) specimens. The ENF test results demonstrated that the Zanchor process was highly effective to improve the mode II fracture toughness of composite laminates, where the fracture toughness increased almost linearly with the Zanchor density. The R-curves of Zanchor composites were roughly divided into the transition and stable regions, where the width of the transition region became larger as the Zanchor density increased. The macroscopic fracture behavior of the Zanchor composites was still brittle under mode II loading like that of the base composite, where the crack tip process zone was estimated to be rather small regardless of the Zanchor density. The ILS test results demonstrated that the square of the normalized shear strength increased linearly with the Zanchor density and agreed quantitatively with the normalized fracture toughness. The wedge effect was supposed to be the dominant toughening mechanism against the mode II fracture, where the entangled fiber bundles partly sustained the shear stress in the vicinity of the crack tip. The entangled fiber bundles played an important role to form the mode II fracture surface, where the microscopic fracture pattern of the entangled fiber bundles was mainly the breakage of the fiber bundles rather than the pull-out or debonding of the fiber bundles.     

Atomic structure of a CeO2 grain boundary: the role of oxygen vacancies

Determining both cation and oxygen sublattices of grain boundaries is essential to understand the properties of oxides. Here, with scanning transmission electron microscopy, electron energy-loss spectroscopy, and first-principles calculations, both the Ce and oxygen sublattices of a (210)Σ5 CeO(2) grain boundary were determined. Oxygen vacancies are shown to play a crucial role in the stable grain boundary structure. This finding paves the way for a comprehensive understanding of grain boundaries through the atomic scale determination of atom and defect locations.     

Evaluation of lightning fault rate of EHV transmission line based on lightning parameters derived from electromagnetic observation

Cloud-to-ground lightning flashes in the Niigata area in Japan have been observed for a few years by a magnetic direction-finder network. Data obtained so far are analyzed carefully taking into account the operating characteristics of the system. As a result, frequency distributions of return-stroke current for each polarity are produced, and their seasonal variations and the occurrence probabilities of high current exceeding 200 kA are clarified. Based on the estimated current distributions, back-flashover rates of 500-kV 2 cct transmission lines are calculated. It is known that the back-flashover caused by downward flashes can account for most of the line outages in the summer for both single- and multiple-line faults. However, this mechanism cannot explain the high outage rate in the winter experienced in the winter thunderstorm area in the late 1970s. In spite of the low lightning flash density in the winter, the multiple-line fault rate in the winter caused by back-flashovers is predicted to be comparable to that in the summer, because of the seasonal variation of the frequency distributions of return-stroke current.     

Heterogeneous point mutations of the p53 gene in pulmonary fibrosis

Lung cancer is a frequent complication in pulmonary fibrosis. Overexpression of p53 proteins has been demonstrated by immunostaining in bronchoepithelial cells in patients with idiopathic pulmonary fibrosis. However, it is still unclear whether this overexpressed p53 protein is wild-type or mutant. It was hypothesized that pulmonary fibrosis may be a precancerous lesion with deoxyribonucleic acid point mutations in bronchoepithelial cells. Mutations of the p53 gene were tested for by fluorescence-based single-strand conformation polymorphism (FSSCP), cloning-sequencing and immunostaining techniques. Out of 10 tissue samples that demonstrated overexpression of p53 protein by immunostaining, nine (90%) exhibited point mutations and eight (80%) exhibited heterogeneous point mutations of the p53 gene. The mutations found in pulmonary fibrosis were scattered throughout the central part of the p53 gene, and both guanine (G):cytosine (C) to adenine (A):thymine (T) and A:T to G:C transitions were frequently observed. In conclusion, frequent heterogeneous point mutations of the p53 gene were detected in pulmonary fibrosis. These mutations may have resulted from several types of deoxyribonucleic acid damage that occurred in bronchoepithelial cells and this may explain previous findings of a very high incidence of lung cancer complicating pulmonary fibrosis.     

Some characteristics of a miniature neutron spectrometer

Some characteristics of an NE213 miniature spherical spectrometer for in-assembly fast-neutron spectrometry were measured. As the bubbling time changed, the pulse-height did not change appreciably, but the n?γ discrimination characteristics changed considerably. As the count rate changed, the pulse-height did not change appreciably, and the change of the n?γ discrimination characteristics was acceptable. The neutron response function was measured to be almost isotropic except for the backward direction.     

A 1/3-in 510(H)×492(V) CCD image sensor with mirror imagefunction

A 1/3-in optical format 510(H)×492(V) interline charge-coupled-device (CCD) image sensor with a mirror-image function has been developed. To realize both a normal image and a mirror image, the horizontal shift register (H-CCD) is transferred forward and backward by a four-electrode, quasi-two-phase clock drive. The unit cell size is 9.6(H)×7.5(V) μm². An on-chip microlens has been developed to achieve a sensitivity of 28 mV/lx, which is higher than that of the conventional 1/2-in device. The hole accumulation diode (HAD) sensor used has the advantage of low dark current, negligibly small lag, high blooming suppression, and a variable-speed electronic shutter. The smear reduction level is -83 dB. Horizontal resolution of 330 TV lines is obtained