Finite element analysis of the magnetomechanical behavior of a toroidal coil with magnetic mirrors

A toroidal simulator is used to study the magnetomechanical behavior of a superconducting D-shaped coil set at the center between sectored ferromagnetic plates. Since the magnetic field distribution between the two plates is expected to be almost the same as that created by toroidal field coils arrayed in a torus, the toroidal simulator may be expected to show almost the same magnetomechanical behavior as that of the full torus coils. To verify its validity experimentally, buckling and vibration tests were carried out in a liquid helium cryostat. In addition numerical analyses were performed for the magnetic field distribution to reveal its similarity and for the experimental results from the toroidal simulator to confirm its validity. Its validity is fully demonstrated in the present study.     

Interactive Optimization of System Reliability Under Multiple Objectives

This paper considers a multiobjective reliability allocation problem for a series system with time-dependent reliability. The method determines the most preferable reliability allocation and preventive maintenance schedule. The problem is multiobjective nonlinear mixed-integer. The decision making procedure is based on interactive optimization and a nonlinear programming algorithm. The method is illustrated by a numerical example.     

Superplasticity of Fe-Ni alloys

In the two phase alloys which exhibit superplasticity, strain rate sensitivitym, in the relationship σ =Kε ^m, has been known to be strongly dependent on the volume fraction of the second phase. It, however, has not been necessarily confirmed experimentally on various two phase alloys. In this paper we present an experimental evidence showing that the largestm is obtained when the volume fraction of the second phase is around 0.5.     

Dibenzothiophene desulfurizing enzymes from moderately thermophilic bacterium Bacillus subtilis WU-S2B: purification, characterization and overexpression

The moderately thermophilic bacterium Bacillus subtilis WU-S2B desulfurized dibenzothiophene (DBT) at 50 degrees C through the selective cleavage of carbon-sulfur bonds. In this study, three enzymes involved in the microbial DBT desulfurization were purified and characterized. The first two enzymes, DBT monooxygenase (BdsC) and DBT sulfone monooxygenase (BdsA), were purified from the wild-type strain, and the last one, 2'-hydroxybiphenyl 2-sulfinic acid desulfinase (BdsB), was purified from the recombinant Escherichia coli overexpressing the gene, bdsB, with chaperonin genes, groEL/ES. The genes of BdsC and BdsA were also overexpressed. The molecular weights of BdsC and BdsA were determined to be 200 and 174 kDa, respectively, by gel filtration chromatography, suggesting that both enzymes had four identical subunits. BdsB had a monomeric structure of 40 kDa. The three enzymes were characterized and compared with the corresponding enzymes (DszC, DszA, and DszB) of mesophilic desulfurization bacteria. The specific activities of BdsC, BdsA, and BdsB were 84.2, 855, and 280 units/mg, respectively, and the latter two activities were higher than those of DszA and DszB. The heat stability and optimum temperature of BdsC, BdsA, and BdsB were higher than those of DszC, DszA, and DszB. Other enzymatic properties were investigated in detail.     

Properties of reverse osmosis membranes prepared from poly(4-vinyl pyridine)-acrylonitrile copolymer and the partially quaternized copolymer

Reverse osmosis membranes were prepared from 4-vinyl pyridine(4VP)-acrylonitrile (AN) copolymers and those partially quaternized. Their salt rejection (S) and hydraulic water permeability (K₁) were investigated with regard, to co-polymer composition, the membrane profile by SEM observation, cross-linking quaternization with diiodobutane (DIB) and the method of membrane preparation. S decreased with increasing AN content, but K₁ was closely dependent on water content which had a minimum at about 65% 4VP. The increase in K₁ and water content in a high AN range was caused by the change in the membrane structure from dense to porous one.Quaternization with DIB to a small extent notably improved K₁, up to ten times without significant change in S, and most effectively improved both of the membrane structure and the performance of AN rich copolymer membranes which were the highest in tensile strength among the copolymers. It was found by IR and elemental analysis that DIB charged was nearly completely reacted. The DIB modified membranes were anion exchangeable and more than two-thirds of iodide were exchanged for chloride. The modification reduced the membrane strength, to the least extent in the AN rich copolymers, with increasing DIB due to an increase in water content. The quaternized membranes prepared by surface-treating with DIB gave an essentially similar performance and had a composite structure which held unreacted layer.Monofunctional quaternizing agents merely brought about a poor membrane performance.Water transport through the membranes followed solution-diffusion mechanism for the membranes of volume fraction of water smaller than 0.41. The membranes modified with DIB to a small degree were regarded as tight ionic membranes and able to be treated as a nonionic ones, although they behaved ionically showing a decrease in S with the increasing feed concentration.     

Effects of periphery encapsulation material on the characteristics of micro vacuum dielectric capacitor

The effects of the periphery sealant on the electrical characteristics of vacuum dielectric capacitors (VDCs) are modeled. For the square shape VDCs, their characteristics are predominantly determined by the ratio of capacitor side length versus the width of boundary sealant layer, r. The smaller of the r value, the smaller of the dissipation factor, and the better frequency response of the VDCs are found. To achieve a dissipation factor of less than 10⁻⁵ at 1 GHz, the dimension parameter, r, should be smaller than 0.05 which has been achieved based on the present technology for a capacitor with size larger than 4 mm × 4 mm. The leakage current can also be reduced significantly in the VDCs. We found that the leakage current is mainly governed by the Poole-Frenkel emission of electrons over the periphery region. The present results have demonstrated that the VDC structure is a promising technology option for making high-frequency micro capacitors.     

Production of Carbon Nanotube by Ethylene Decomposition over Silica-Coated Metal Catalysts

Formation of carbon nanofibers (CNFs) and carbon nanotubes (CNTs) through the decomposition of ethylene at 973 K was achieved using various metal catalysts covered with silica layers. CNFs of various diameters were formed by ethylene decomposition over a Co metal catalyst supported on the outer surface of the silica. In contrast, silica-coated Co catalysts formed CNTs with uniform diameters by ethylene decomposition. Silica-coated Ni/SiO₂ and Pt/carbon black also formed CNTs with uniform diameters, while CNFs and CNTs with various diameters were formed over Ni/SiO₂ and Pt/carbon black without a silica coating. These results indicate that silica layers that envelop metal particles prevent sintering of the metal particles during ethylene decomposition. This results in the preferential formation of CNTs with a uniform diameter.     

Formation of carbon nanotubes through ethylene decomposition over supported Pt catalysts and silica-coated Pt catalysts

Ethylene decomposition was performed over supported Pt catalysts to fabricate composites of Pt metal nanoparticles and carbon nanotubes (CNTs). All supported Pt catalysts (Pt/carbon black, Pt/CNT, Pt/MgO, Pt/Al₂O₃ and Pt/SiO₂) showed catalytic activity for ethylene decomposition at 973 K to form CNTs. Pt metal particles were found at tips of CNTs. These results indicate that Pt metal particles have catalytic activity for growth of CNTs through hydrocarbon decomposition. A broad range (5-50 nm) of CNT diameters were formed from the use of supported Pt metal catalysts although Pt metal particles in the catalysts before ethylene decomposition were relatively uniform in size (2-5 nm). These results imply that Pt metal particles in the catalysts aggregated during ethylene decomposition at 973 K. Aggregation of Pt metal particles in catalysts during ethylene decomposition could be suppressed by covering catalysts with silica layers that were a few nanometers thick. Silica-coated Pt catalysts showed high activity for ethylene decomposition to form CNTs with uniform diameters (8-10 nm) despite the uniform coverage of Pt metal particles with silica layers.