New plastic joining method using indentation of cold bar to hot forged part

A new plastic joining method for fixing bars with a hot forged plate is proposed in which bars kept at room temperature are directly indented into a high-temperature plate. The optimum conditions for the proposed plastic joining method are examined using a low-alloyed steel bar and a carbon steel plate. It is possible to indent the bar to the plate without buckling or plastic deformation by keeping the plate above 850 °C. The attained shear bonding stress of bar-plate is approximately 40% of the shear strength of the plate material. The bonding mechanism of the proposed plastic joining method is discussed from the viewpoints of seizure of the plate and mechanical clamping associated with the process. Furthermore, some applications of the proposed method are suggested.     

High temperature flexural strength and fracture toughness of AlN with Y<Subscript>2</Subscript>O<Subscript>3</Subscript> ceramic

The effects of temperature on the fast fracture behavior of aluminum nitride with 5 wt% Y₂O₃ ceramic were investigated. Four-point flexural strength and fracture toughness were measured in air at several temperatures (30–1,300 °C). The flexural strength gradually decreased with the increase of temperature up to 1,000 °C due to the change in the fracture mode from transgranular to intergranular, and then became almost constant up to 1,300 °C. Two main flaw types as fracture origin were identified: small surface flaw and large pores. The volume fraction of the large pores was only 0.01%; however, they limited the strength on about 50% of the specimens. The fracture toughness decreased slightly up to 800 °C controlled by the elastic modulus change, and then decreased significantly at 1,000 °C due to the decrease in the grain-boundary toughness. Above 1,000 °C, the fracture toughness increased significantly, and at 1,300 °C, its value was close to that measured at room temperature.     

Supersonic two-phase flow of CO2 through converging–diverging nozzles for the ejector refrigeration cycle

CO₂ is environmentally friendly, safe and more suitable to ejector refrigeration cycle than to vapor compression cycle. Supersonic two-phase flow of CO₂ in the diverging sections of rectangular converging–diverging nozzles was investigated. The divergence angles with significant variation of decompression were 0.076°, 0.153°, 0.306° and 0.612°. This paper presents experimental decompression phenomena which can be used in designing nozzles and an assessment of Isentropic Homogeneous Equilibrium (IHE). Inlet conditions around 6–9 MPa, 20–37 °C were used to resemble ejector nozzles of coolers and heat pumps. For inlet temperature around 37 °C, throat decompression boiling from the saturated liquid line, supersonic decompression and IHE solution were obtained for the two large divergence angles. For divergence angles larger than 0.306°, decompression curves for inlet temperature above 35 °C approached IHE curves. For divergence angles smaller than 0.306° or for nozzles with inlet temperature below 35 °C, IHE had no solution.     

Analyses of the Mode of Action of an Alpha-Adrenoceptor Blocker in Substantia Gelatinosa Neurons in Rats

To elucidate why naftopidil increases the frequency of spontaneous synaptic currents in only some substantia gelatinosa (SG) neurons, post-hoc analyses were performed. Blind patch-clamp recording was performed using slice preparations of SG neurons from the spinal cords of adult rats. Spontaneous inhibitory and excitatory postsynaptic currents (sIPSCs and sEPSCs, respectively) were recorded. The ratios of the frequency and amplitude of the sIPSCs and sEPSCs following the introduction of naftopidil compared with baseline, and after the application of naftopidil, serotonin (5-HT), and prazosin, compared with noradrenaline (NA) were evaluated. First, the sIPSC analysis indicated that SG neurons reached their full response ratio for NA at 50 μM. Second, they responded to 5-HT (50 μM) with a response ratio similar to that for NA, but prazosin (10 μM) did not change the sEPSCs and sIPSCs. Third, the highest concentration of naftopidil (100 μM) led to two types of response in the SG neurons, which corresponded with the reactions to 5-HT and prazosin. These results indicate that not all neurons were necessarily activated by naftopidil, and that the micturition reflex may be regulated in a sophisticated manner by inhibitory mechanisms in these interneurons.     

Effect of 20°–200oC Fabrication Temperature on Microstructure of Hydrothermally Prepared LiCoO2 Films

Films of LiCoO₂ were directly fabricated by hydrothermal treatment of a cobalt metal plate in a 4 M LiOH aqueous solution at 20°–200°C, with no subsequent annealing, and the effect of fabrication temperature on the film microstructure was investigated for the films. Micro-Raman studies have indicated that increasing the fabrication temperature produces a phase change in LiCoO₂ from spinel to hexagonal. This change is revealed by a variation in the film thickness and the film surface morphology, as seen in the micrographs. The present scanning electron microscopy results showed a growth of spinel LiCoO₂ particles up to 125°C and the formation of hexagonal particles at >125°C, in good agreement with the Raman and X-ray photoemission spectroscopy results. A film-formation mechanism based on the dissolution of cobalt metal, followed by precipitation, as LiCoO₂, onto the cobalt substrate, is proposed. The mechanism is supported by experimental data, such as the one-step potential evolution (0 → 0.6 V, with respect to the Ag/AgCl reference electrode) of the cobalt electrode during hydrothermal treatment and the detection of dissolved cobalt species by atomic absorption and ultraviolet–visible-light absorption spectroscopic analyses. Apparently, the evolution of the film structure arises from different nucleation and growth rates of LiCoO₂ particles on the film, caused by the dissolution–precipitation mechanism, and a phase selection of spinel or hexagonal as the fabrication temperature increases.     

Analysis of Oversized Sliding Waveguide by Mode Matching and Multi-Mode Network Theory

Transmission and reflection coefficients of hybrid modes in the sliding waveguide are discussed on the basis of mode matching method and multi-mode network theory. It is confirmed that the decrease in power of < 0.2% at 84 GHz is obtained for 2 cm in gap of the sliding waveguide which is composed of the corrugated waveguide with 88.9 mm diam. and the smooth-wall waveguide with 110 mm diam. At the sliding length near multi-half-wavelength in vacuum, transmission and reflection powers in the sliding waveguide change slightly, because the very small amount of standing wave in high higher-mode is produced resonantly in the gap.     

Phase Diagram and Oxygen-Ion Conductivity in the Y2O3-Nb2O5 System

The phase equilibria in the Y₂O₃-Nb₂O₅ system have been studied at temperatures of 1500° and 1700°C in the compositional region of 0-50 mol% Nb₂O₅. The solubility limits of the C-type Y₂O₃ cubic phase and the YNbO₄ monoclinic phase are 2.5 (±1.0) mol% Nb₂O₅ and 0.2 (±0.4) mol% Y₂O₃, respectively, at 1700°C. The fluorite (F) single phase exists in the region of 20.1-27.7 mol% Nb₂O₅ at 1700°C, and in the region of 21.1-27.0 mol% Nb₂O₅ at 1500°C, respectively. Conductivity of the Y₂O₃- x mol% Nb₂O₅ system increases as the value of x increases, to a maximum at x = 20 in the compositional region of 0 ≤ x ≤ 20, as a result of the increase in the fraction of F phase. In the F single-phase region, the conductivity decreases in the region of 20-25 mol% Nb₂O₅, because of the decrease in the content of oxygen vacancies, whereas the conductivity at x = 27 is larger than that at x = 25. The conductivity decreases as the value of x increases in the region of 27.5 ≤ x ≤ 50, because of the decrease in the fraction of F. The 20 mol% Nb₂O₅ sample exhibits the highest conductivity and a very wide range of ionic domain, at least up to log p _O2=−20 (where p _O2 is given in units of atm), which indicates practical usefulness as an ionic conductor.     

A mutant D-amino acid aminotransferase with broad substrate specificity: construction by replacement of the interdomain loop Pro119- Arg120-Pro121 by Gly-Gly-Gly

D-amino acid aminotransferase (EC 2.6.1.21) catalyzes the interconversion of various D-amino acids and 2-oxo acids. Each homodimer subunit consists of two domains, which are connected by a single loop, Asn118-Pro119-Arg120-Pro121. The loop has no direct contact with the active site region or the cofactor, pyridoxal 5'- phosphate. We attempted to increase the conformational flexibility of this loop through a triple glycine substitution. The resultant mutant P119G-R120G-P121G has features clearly different from the wild-type enzyme under overall as well as half-reaction conditions. The pre- steady-state kinetic analyses of half reactions showed that the mutant enzyme has kmax values higher than the wild-type enzyme towards most D- amino acids examined. A concomitant decrease in substrate affinity (1/Kd), particularly for acidic amino acids, was also observed. A putative binding site for the distal carboxyl group of acidic amino acids in the wild-type enzyme was incidentally displaced by the loop mutation, indicating a functional linkage between the interdomain loop and the active site region. This study has exemplified the usefulness of engineering relatively distant loops as a means to modify substrate specificity of an enzyme.      

New thermosetting resin from poly(p‐vinylphenol) based benzoxazine and epoxy resin

Poly(p‐vinylphenol) (VP) based benzoxazine was prepared from VP, formaline, and aniline. The curing behavior of the benzoxazine with the epoxy resin and the properties of the cured resin were investigated. Consequently, the curing reaction did not proceed at low temperatures, but it proceeded rapidly at higher temperatures without a curing accelerator. The reaction induction time or cure time of the molten mixture from VP based benzoxazine and epoxy resin was found to decrease, compared with those from conventional bisphenol A based benzoxazine and epoxy resin. The curing reaction rate of VP based benzoxazine and epoxy resin increased more than that of conventional bisphenol A based benzoxazine and epoxy resin. The properties of the cured resin from neat resins and from reinforced resins with fused silica were evaluated. The cured resins from VP based benzoxazine and epoxy resin showed good heat resistance, mechanical properties, electrical insulation, and water resistance compared to the cured resin from VP and epoxy resin using imidazole as the catalyst. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 555–565, 2001