Effect of dispersed oxides of rare earths and other reactive elements on the high temperature oxidation resistance of Fe-20Cr alloy

The isothermal oxidation resistance in air at 1273, 1323, and 1373 K of Fe-20Cr alloys with 1 wt pct dispersoid of Y₂0₃, La₂O₃, A1₂O₃, TiO₂, SiO₂, Cr₂O₃ and without dispersoid prepared by a conventional sintering and rolling procedures was examined. It was found that SiO₂ dispersoid reduced, while A1₂O₃ dispersoid slightly increased the oxidation resistance. The dispersoids of TiO₂ and Cr₂O₃ showed no beneficial effect on the oxidation resistance except for the oxidation after 10 h at 1373 K. The oxidation behavior after 10 h at 1373 K was rather complex including accelerated oxidation. The beneficial effect of La₂O₃ and Y₂O₃ dispersoids was excellent at all temperatures. The oxidation rates during the early stage of oxidation for the alloys with dispersoid were apparently dependent on the type of the dispersoid. There was no evidence that dispersoid accumulated at the scale-alloy interface. Comparison of results obtained for the oxidation of the alloys prepared by a powder metallurgical procedure with results for the alloys by arc-melting procedure indicated that the grain size of the alloy is an important factor for reduction of oxidation rate but does not seem to be critical, because the grain size of the alloys with dispersoid was not dependent on the type of the dispersoid. Ion Microanalyses of the Cr₂O₃ scale formed after 1 h oxidation at 1373 K showed an interesting feature in that all the dispersed elements were incorporated in the scale and the iron content of the scale was lower on the alloys which exhibited better oxidation resistance.     

Noncompetitive inhibition by L-cysteine and activation by L-glutamate of the iron-oxidizing activity of a mixotrophic iron-oxidizing bacterium strain OKM-9

A mesophilic, mixotrophic iron-oxidizing bacterium strain OKM-9 uses ferrous iron as a sole source of energy and L-glutamate as a sole source of cellular carbon. Uptake of L-glutamate into OKM-9 cells is absolutely dependent on ferrous iron oxidation. Thus, the Fe(2+)-dependent L-glutamate uptake system of strain OKM-9 is crucial for the bacterium to grow mixotrophically in iron medium with L-glutamate. The relationship between iron oxidation and L-glutamate transport activities was studied. Iron oxidase containing cytochrome a was purified 9-fold from the plasma membrane of OKM-9. A purified iron oxidase showed one rust-colored band following disc gel electrophoresis after incubation with Fe(2+). The Fe(2+)-dependent L-glutamate transport system was also purified 14.5-fold from the plasma membrane using the same purification steps as for iron oxidase. Fe(2+)-dependent L-glutamate and L-cysteine uptake activities of OKM-9 were 0.36 and 0.24 nmol/mg/min, respectively, when a concentration of 18 mM of these amino acids was used as a substrate. Both uptake activities were completely inhibited by potassium cyanide (KCN), suggesting that cytochrome a in the iron oxidase is involved in the transport process. The iron-oxidizing activity of strain OKM-9 was activated 1.7-fold by 80 mM L-glutamate. In contrast, the activity was noncompetitively inhibited by L-cysteine. The Michaelis constant of iron oxidase for Fe(2+) was 12.6 mM and the inhibition constant for L-cysteine was 41.6 mM. A marked inhibition of iron oxidase by 50 mM L-cysteine was completely reversed by the addition of 60 mM L-glutamate. The results suggest the possibility that iron oxidase has a binding site for L-cysteine and the cysteine first bound to the iron oxidase was replaced by the added L-glutamate.     

Measured resonance characteristics of a 2-ghz-fundamental quartz resonator

I fabricated an inverted-mesa AT-cut quartz resonator in which the thickness of the vibrating area was adjusted to 0.6 /spl mu/m by wet etching, and I demonstrated the excitation of a fundamental thickness vibration of 2.074 GHz. This main mode was inductive, and Q was 1037. However, all inharmonic modes were capacitive.     

Reconstruction of a high-resolution image on a compound-eye image-capturing system

The authors have proposed an architecture for a compact image-capturing system called TOMBO (thin observation module by bound optics), which uses compound-eye imaging for a compact hardware configuration [Appl. Opt. 40, 1806 (2001)]. The captured compound image is decomposed into a set of unit images, then the pixels in the unit images are processed with digital processing to retrieve the target image. A new method for high-resolution image reconstruction, called a pixel rearrange method, is proposed. The relation between the target object and the captured signals is estimated and utilized to rearrange the original pixel information. Experimental results show the effectiveness of the proposed method. In the experimental TOMBO system, the resolution obtained is four times higher than that of the unit image that did not undergo reconstruction processing.     

Dynamic behavior of bubble domains at low drive field

Dynamic properties of bubble domains at low drive pulse field are examined by the bubble transport method. Important findings are as follows. 1) The bubble does not move unless the pulse duration exceeds a critical value which depends on the pulse amplitude. 2) A minimum pulse amplitude is also required for the bubble translation which depends on the pulse duration. 3) As the pulse duration goes to infinity, the minimum drive field approaches a constant value which is different from the dynamic coercivity. 4) As soon as the pulse duration exceeds the critical value, the bubble is displaced discontinuously by a finite distance independent of the drive field. All of these properties are adequately explained by a simple phenomenological theory, in which the domain wall is assumed to be connected by springs to pinning sites until the wall is displaced by a finite distance.     

Purification and characterization of rice alpha-glucosidase, a key enzyme for alcohol fermentation of rice polish

Alpha-glucosidase, a key enzyme for nuka-sake brewing, was purified from Oryza sativa cv. Yamadanishiki, which is widely used for sake brewing. The molecular weight of the purified enzyme was 95 kDa. The optimum pH and temperature were 4.5 and 55 degrees C, respectively. The substrate specificity differed from that of Oryza sativa cv. Shinsetsu, which is a variety of rice consumed as a cereal. The extraction of alpha-glucosidase from the rice was stimulated by lactic acid, which suggests that lactic acid plays an important role not only in preventing bacterial contamination, but also in stimulating the parallel fermentation that occurs in nuka-sake brewing.     

Cathodoluminescence study of AlGaAs/GaAs multilayers grown on ridge-type triangles on GaAs (111)A substrates

We have studied the cathodoluminescence of AlxGa1-xAs/GaAs multilayers grown on ridge-type triangles by molecular beam epitaxy. The compositional variation of Al, as well as the distribution of impurity and/or defect, was revealed by variations in the cathodoluminescence spectra and images. The Al composition in an AlxGa1-xAs layer was highest in the (111)A facet and decreased in the order (100), (411)A, (111)-delta and (110) facets. On the other hand, the carbon concentration was highest in the (411)A facet and decreased in the order (111)A, (111)-delta, (100) and (110) facets. It should be noted that the (111)-delta facet has a significant effect on the redistribution of Al. Although our ridge-type triangles are rather large for the quantum structures, these data have elucidated the self-organization mechanism of the AlxGa1-xAs/GaAs system and have yielded information on the design of quantum structures. We conclude that cathodoluminescence observation is a powerful tool for studying the compositional variation or band structure of three-dimensional microscale or nanoscale construction.     

High-Speed X-Cut Thin-Sheet LiNbO3 Optical Modulator With Folded Structure

We propose a small-footprint X-cut thin-sheet lithium niobate optical modulator with high-speed and low-driving-voltage characteristics. Since an optical waveguide is folded by a mirror placed at one edge of the modulation chip, the chip can be shortened by about half. In addition, a wide modulation bandwidth can be achieved, because the path-length difference between the optical waveguide and the coplanar-waveguide (CPW) electrode is decreased to as short as possible by placing the CPW electrode as far as possible along the optical waveguide in the folded portion, and the microwave effective index is set to realize effective velocity matching between the lightwave and the microwave. A small footprint of 1.78 times 29 mm, a low half-wave voltage of 2.0 V at dc, and a 3-dBe modulation bandwidth of 20 GHz were obtained.     

ELECTROFORCED SEDIMENTATION OF THICK SLURRIES IN CONSOLIDATION REGION

It is shown that the settling rates of thickened slurries can be greatly enhanced by application of D.C. voltages. It is demonstrated that the settling rates increase remarkably with increasing electric field intensity. The basic differential equation for gravitational settling of thick slurries is derived and this is extended to electroforced sedimentation. The theoretical' settling rates and the porosity distributions in settling sediments of both gravitatinal and electroforced settling compare favorably with experimental observations. In addition, it is shown that the compression-permeability characteristics in the low compressive pressure region can be closely determined analytically by using batch sedimentation data.     

Hydrocracking of diphenylmethane and tetralin over bifunctional NiW sulfide catalysts supported on three kinds of zeolites

Hydrocracking reactions of diphenylmethane and tetralin were carried out over three kinds of zeolites with or without NiW sulfide to discuss the roles of catalytic bifunctionality in two types of hydrocracking reactions. It was found that strong acid sites were not needed for the hydrocracking of diphenylmethane, while the conversion of tetralin required relatively strong acid sites. Ultra-stable Y zeolite with strong acidity exhibited high hydrocracking activity for both reactions. In contrast, mordenite catalysts did not show high activity for either hydrocracking, though isomerization of tetralin and excess hydrocracking to gaseous products proceeded. The superior performances of ultra-stable Y zeolite in the tetralin hydrocracking were suggested to be related to the hydrogen transfer ability. In most cases, the loading of NiW sulfide enhanced catalytic activity. In the diphenylmethane hydrocracking, the role of NiW sulfide was found to supply active hydrogen to the hydrocracking active sites on zeolite and to prevent polymerization of benzyl cations. In the tetralin hydrocracking, the dehydrogenated products from tetralin were re-hydrogenated over NiW sulfide.