High-temperature strength and thermal stability of a unidirectionally solidified Al2O3/YAG eutectic composite

A unidirectional solidification method was investigated to manufacture Al2O3/YAG eutectic composites with high-temperature resistance that would make them usable at very high temperatures. We were successful in manufacturing a single-crystal Al2O3/single-crystal YAG eutectic composite with a dimension of 40 mm in diameter and 70 mm in length containing no colonies or pores. This composite also displayed excellent high-temperature strength characteristics. The flexural strength was in the range 350400 MPa from room temperature up to 2073 K (just below its melting point of about 2100 K) with no apparent temperature dependence. During tensile tests above 1923 K, the eutectic composite showed evidence of plastic deformation occurring by dislocation motion, and a yield phenomenon similar to many metals was observed. In addition, the microstructure of the composite was extremely stable: after 1000 h of heat treatment at 1973 K in an air atmosphere there was no growth. The above superior high-temperature characteristics are caused by such factors as the eutectic composite having a single-crystal Al2O3/single-crystal YAG structure, the formation of a compatible interface with no amorphous phase and thermal stability, and the combined effect of a YAG phase with superior high-temperature characteristics. © 1998 Chapman & Hall     

Determination of the amounts of free arachidonic acid in resident and activated rabbit alveolar macrophages by fluorometric high performance liquid chromatography

An improved method of high performance liquid chromatography (HPLC) has been developed for the separation and quantitation of low levels of free fatty acids as they occur in mammalian tissues. The fatty acid analysis is based on the esterification of the carboxylic group with 9-anthryldiazomethane (ADAM). HPLC separation and fluorescence measurement of fatty acid ADAM esters allow the determination of pmole amounts of fatty acids. The amounts of free fatty acids of resident and activated alveolar macrophages were determined by the fluorometric HPLC method. There were approximately 2 μg/10⁶ cells of free fatty acids. In resident macrophages, free 20∶4 was a minor component (0.8% of total free fatty acids), while significant amounts of 20∶4 were found in the total glycerophospholipids, representing 16.6% of the total fatty acids. A marked increase in amounts of 20∶4 (8 times) occurred in activated macrophages stimulated for 1 hr with opsonized zymosan. Small but significant increases (1.5 times) also occurred in other fatty acids. These results show that the release reaction of fatty acids was not selective for 20∶4 in alveolar macrophages after the challenge with opsonized zymosan.     

The Creep and Thermal Stability Characteristics of a Unidirectionally Solidified Al2O3/YAG Eutectic Composite

Compressive creep characteristics at 1773, 1873, and 1973 K, oxidation resistance over 1000 h at a temperature of 1973 K in ambient air, and the thermal stability characteristics at 1973 K in ambient air of a unidirectionally solidified Al2O3/YAG eutectic composite were evaluated. At a test temperature of 1873 K and a strain rate of 10–4/s, the compressive creep strength of a eutectic composite manufactured by the unidirectional solidification method is approximately 13 times higher than that of a sintered composite with the same chemical composition. The insite eutectic composite also showed greater thermal stability, with no change in mass after an exposure of 1000 hours at 1973 K in ambient air. The superior high-temperature characteristics are closely related to such factors as (1) the in-situ eutectic composite having a microstructure, in which single crystal Al2O3 and single crystal YAG are three-dimensionally and continuously connected and finely entangled without grain boundaries and (2) no amorphous phase is formed at the interface between the Al2O3 and the YAG phases.     

Cadmium suppresses delta 9 desaturase activity in rat hepatocytes

This paper challenges contemporary portrayals in the nursing literature of the spaces within which care of patients in hospital settings is conducted. Within the wider discourse of fiscal restraint on health care spending, professional nursing has cast its disciplined eyes on details of the nurse-patient relationship for the ostensible purpose of repairing that which is treated as individual failings of nurses to practice in ways prescribed by nursing theories. Set aside in this approach to the so-called 'problems' of nursing practice has been an examination of the conditions within which nurses come in contact with patients, and a critical recognition that such contacts represent skilled accomplishments of social action. In this paper, these conditions are treated as resources available to both nurses and patients to generate accounts for the nurse's presence as well as the nurse's absence. Examples from an ethnographic study of nursing practice are used to illustrate how the spaces operating between nurses and patients are not empty voids but are social spaces through which particular meanings about nursing care can be conveyed.     

Production of flexible metal matrix composites reinforced with continuous Si-Ti-C-O fibers by atmospheric plasma spraying

An investigation of the production of aluminum matrix composite sheet reinforced with continuous Si-Ti-C-O fibers was performed by a plasma spraying method. The unidirectionally reinforced Si-Ti-C-O fiber/Al prepreg sheet (300 by 3000 mm, 0.1 to 0.15 mm thick, with 40 vol. % Fiber) was fabricated by plasma spraying under atmospheric conditions. The depth of the oxidation layer formed on the surface of the metal matrix composite (MMC) prepreg sheet was found to be about 200 Å, and this value is almost independent of the atmosphere during plasma spraying. The fibers homogeneously disperse and do not contact each other in the matrix of the MMC prepreg. No damage on the surface of the extracted fibers from the MMC prepreg sheet can be observed. The MMC prepreg sheet was used to produce MMC plate by hot pressing at 640 to 680 °C under 9.8 MPa. The flexural strengths in the longitudinal and transverse directions of the MMC plate pressed at 660 °C were 1.0 and 0.25 GPa, respectively.     

Investigation on the Interactions between Self-Assembled β-Sheet Peptide Nanofibers and Model Cell Membranes

Self-assembled peptide nanofibers (NFs) obtained from β-sheet peptides conjugated with drugs, including antigenic peptides, have recently attracted significant attention. However, extensive studies on the interactions of β-sheet peptide NFs with model cell membranes have not been reported. In this study, we investigated the interactions between three types of NFs, composed of PEG-peptide conjugates with different ethylene glycol (EG) lengths (6-, 12- and 24-mer), and dipalmitoylphosphatidylcholine (DPPC) Langmuir membranes. When increasing the EG chain length, those interactions significantly decreased considering measurements in the presence of the NFs of: (i) changes in surface pressure of the DPPC Langmuir monolayers and (ii) surface pressure–area (π–A) compression isotherms of DPPC. Because the observed trend was similar to the EG length dependency with regard to cellular association and cytotoxicity of the NFs that was reported previously, the interaction of NFs with phospholipid membranes represented a crucial factor to determine the cellular association and toxicity of the NFs. In contrast to NFs, no changes were observed with varying EG chain length on the interaction of the building block peptide with the DPPC membrane. The results obtained herein can provide a design guideline on the formulation of β-sheet peptide NFs, which may broaden its potential.     

Evidence that the cannabinoid CB1 receptor is a 2-arachidonoylglycerol receptor. Structure-activity relationship of 2-arachidonoylglycerol, ether-linked analogues, and related compounds

An endogenous cannabimimetic molecule, 2-arachidonoylglycerol, induces a rapid, transient increase in intracellular free Ca2+ concentrations in NG108-15 cells through a cannabinoid CB1 receptor-dependent mechanism. We examined the activities of 24 relevant compounds (2-arachidonoylglycerol, its structural analogues, and several synthetic cannabinoids). We found that 2-arachidonoylglycerol is the most potent compound examined so far: its activity was detectable from as low as 0.3 nM, and the maximal response induced by 2-arachidonoylglycerol exceeded the responses induced by others. Activities of HU-210 and CP55940, potent cannabinoid receptor agonists, were also detectable from as low as 0.3 nM, whereas the maximal responses induced by these compounds were low compared with 2-arachidonoylglycerol. Anandamide was also found to act as a partial agonist in this assay system. We confirmed that free arachidonic acid failed to elicit a response. Furthermore, we found that a metabolically stable ether-linked analogue of 2-arachidonoylglycerol possesses appreciable agonistic activity, although its activity was apparently lower than that of 2-arachidonoylglycerol. We also confirmed that pretreating cells with various cannabinoid receptor agonists nullified the response induced by 2-arachidonoylglycerol, whereas pretreating cells with other neurotransmitters or neuromodulators did not affect the response. These results strongly suggested that the cannabinoid CB1 receptor is originally a 2-arachidonoylglycerol receptor, and 2-arachidonoylglycerol is the intrinsic physiological ligand for the cannabinoid CB1 receptor.     

Effect of Moisture on the High-Temperature Stability of Unidirectionally Solidified Al2O3/YAG Eutectic Composites

The corrosion resistance of a unidirectionally solidified alumina/yttrium aluminum garnet (Al₂O₃/YAG) eutectic mixture was investigated at high temperature. Samples were exposed to high temperature (1200°–1800°C) in different atmospheres, which included argon, argon/water vapor, air, and air/water vapor. The most important microstructural changes occurred at the interface between the YAG and the Al₂O₃. Those changes consisted of localized thermal grooving, especially when the corrosive atmosphere contained water vapor. The samples exhibited significant weight loss at high temperature (1800°C) after 20 h of exposure. The calculated volume gain that was induced by the increased surface relief was low and limited, except when the corrosive atmosphere contained air, which indicated that the presence of air (particularly oxygen) induced a more-active corrosion process. On the other hand, no change in the flexural strength was observed, even after 100 h at 1800°C in a humid atmosphere, because of the cross-linked structure of the composite, which limited propagation of the groove.     

Sapphire matrix composites reinforced with single crystal YAG phases

An investigation of fabrication technology on eutectic composites consisting of Al₂O₃ phases and YAG (Y₃Al₅O₁₂) phases was carried out by applying the unidirectional solidification process. Unidirectionally solidified eutectic composites consisting of 110 sapphire phases and 420 single crystal YAG phases could be fabricated successfully by lowering a Mo crucible at a speed of 5 mm h^–1 under a pressure of 10^–5 mmHg of argon. These eutectic composites have excellent high-temperature properties up to 1973 K. For example, the flexural strength is 360–500 MPa independent of testing temperature from room temperature to 1973 K. Oxidation resistance at 1973 K in an air atmosphere is superior to SiC and Si₃N₄ and the microstructure of these eutectic composites is stable even after heat treatment at 1773 K for 50 h in an air atmosphere.     

The preparation of high transition temperature superconducting Pb-Bi-Ge alloy filaments using the method of glass-coated melt spinning

The melt spinning of Pb-Bi-Ge alloys with Pyrex glass was investigated as a means of producing a superconducting long filament with highT _c. Continuous filaments with maximumT _c of more than 10 K of Pb_100-x-y Bi _x Ge _y (15x37 and 725) were obtained from the molten state at 1500 K with a winding speed of 0.95 m sec^–1. The Pb₄₉Bi₃₃Ge₁₈ filament, which was 34×10^–6 m diameter and a ductile material with a tensile strength of 20 MPa and elongation of 2.7%, exhibited superconductivity at the highestT _c of 14.3 K. These filaments were found to be polycrystalline with a grain size of more than 5000×10^–10 m and had a mixed structure of germanium (diamond) (h c p) and bismuth phases. The germanium element distributed homogeneously in the filament.