Flaw Size Distribution in High-Quality Alumina

A difference in fracture strength was noted among commercial alumina ceramics. The origin of this difference was examined using optical microscopy in the transmission mode. Large defects measuring several tens of micrometers or more were clearly observed, and a direct correlation was found between the size of the large defects and the strength of the ceramics. The results indicated that a low concentration of large defects controlled the strength distribution of the ceramics studied.     

Small helical antenna made of high-temperature superconducting thick film

To realize a highly efficient small antenna, high-T _c superconducting thick films with zirconia cores are adopted in order to fabricate both a self-resonating small helical radiator and a quarter-wave matching circuit. The actual gain of a superconducting antenna measured at 478 MHz using a 1/70-wavelength radiator was 4.9 dB higher than that of a copper antenna.     

Process specification generation from communications service specifications

This paper proposes an algorithm for generating process specifications from communications service specifications described by a graph grammar. In this work, it is assumed that a communications system consists of homogeneous processes and that there is no global database. Processes that share a relationship form a global state, and a communications service defines global state transitions caused by inputs to the processes. A global state is represented by a labeled directed graph and a global state transition is described by a graph replacement rule. A process specification is regarded as a distributed algorithm whose purpose is to achieve the global state transitions described by the graph replacement rules. The communication time complexity of the generated distributed algorithm does not depend on the number of graph replacement rules.     

Effect of Moisture on the Structure and Fracture Strength of Ceramic Green Bodies

To study independently the effects of moisture on the structure and the mechanical strength of the binder in green bodies, specimens of the system alumina/PVA were formed with spray-dried granules of various moisture contents. The structure and fracture strength of these specimens then were examined after their moisture contents had been adjusted to specified values. As moisture content increased in the granules during compaction, the density and strength of the green body also increased. The accompanying change in the fracture mode, from intergranular to transgranular, showed that the strength of the green bodies was affected more significantly by bonding between granules than by bonding between powder particles.     

Direct Study of the Behavior of Flaw-Forming Defect in Sintering

The morphological change of natural pores with densification was examined in an alumina green body. The liquid-immersion technique was used for observing pores inside the body before and after sintering. In this technique the specimen is made transparent by an adequate immersion liquid and observed with a transmission optical microscope. Growth of large pores with densification was observed and is discussed along with past thermodynamic consideration of pore growth. Supplemental investigation of the results was conducted by SEM and mercury porosimetry.     

A novel bioaction of PAF: Induction of microbicidal activity in guinea pig bone marrow cells

When guinea pig bone marrow cells were incubated in the presence of 10⁻⁸ to 10⁻⁶ M platelet activating factor (PAF) for 24 to 72 hr, microbicidal activity againstCandida parapsilosis of cells was augmented. This augmentation was inhibited by PAF-specific antagonists, CV6209 or FR900452. PAF-specific binding sites with a high affinity were found on guinea pig bone marrow cells. Carrageenan or 2-chloroadenosine, reagents known to be preferentially cytotoxic to macrophages, abolished the microbicidal activity of PAF-treated bone marrow cells. Macrophages prepared from the peritoneal cavity, however, acquired no appreciable microbicidal action by treatment with PAF. These observations suggest that PAF may affect a class of guinea pig bone marrow cells through binding to receptors specific to PAF, resulting in activation and/or induction of differentiation of monocyte-macrophage lineage cells.