Modeling of Nonlinear Magnetizing Characteristics of Pole Transformer for Analyzing Islanding Prevention of Photovoltaic System

With increasing penetration of distributed generators such as photovoltaic (PV) systems in distribution systems, it is very important to quickly detect islanding caused by power system faults in order to assure electrical safety. We have developed a nonlinear magnetizing characteristics model of pole transformers for use in analyzing islanding prevention in PV systems. Basic experiments on the islanding detection were performed for verification of the proposed model. Analytical results obtained by the proposed model agreed well with experimental results.     

Novel functional polymers: Poly(dimethylsiloxane)–polyamide multiblock copolymer. III. Synthesis and surface properties of disiloxane–aromatic polyamide multiblock copolymer

Disiloxane–aromatic polyamide(aramid) multiblock copolymers(2SiPASs) were synthesized using 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane(BATS) as an analog of aramidsilicone resin consisting of aromatic polyamide and poly(dimethylsiloxane) (PDMS). 2SiPASs afford a transparent and toughened plastic film. The surface properties of 2SiPAS were investigated by X-ray photoelectron spectroscopy (xps) and static contact angle measurement. The results of surface analysis suggested that BATS content of the 2SiPAS surface increased with increasing BATS content in bulk. The interaction between the platelets and the 2SiPAS surface was found to be very weak when the BATS content reached 26 wt % in bulk. © 1996 John Wiley & Sons, Inc.     

Crack-Healing Behavior of Si3N4/SiC Ceramics under Cyclic Stress and Resultant Fatigue Strength at the Healing Temperature

Si₃N₄/SiC composite ceramics were sintered and subjected to three-point bending. A semi-elliptical surface crack of 100 μm surface length was made on each specimen. The crack-healing behavior under cyclic stress of 5 Hz, and resultant cyclic fatigue strengths at healing temperatures of 1100° and 1200°C, were systematically investigated. The main conclusions are as follows: (1) Si₃N₄/SiC composite ceramics have an excellent ability to heal a crack at 1100° and 1200°C. (2) This sample could heal a crack even under cyclic stress at a frequency of 5 Hz. (3) The crack-healed sample exhibited quite high cyclic fatigue strength at each crack-healing temperature, 1100° and 1200°C.     

Mechano-electrochemistry of a passive surface using an in situ micro-indentation test

Depassivation–repassivation of iron surfaces in boric–borate solutions were investigated by using the micro-indentation test. A pair of current peaks due to repair of the passive film following rupture of the film were observed during a series of indenter drives, i.e., loading and unloading of the indenter. The shape of the current peak depended on environmental conditions (conductivity and pH of the solution) and substrate conditions (mechanical processing history, alloyed element) as well as indentation conditions (repetition, maximum depth, and maximum load). Plastic deformation of the surface was accompanied by surface depassivation, while no depassivation occurred during the elastic deformation, indicating that the passive film on iron has a ductile property. The solution conditions did not affect the scale of depassivation but affected the rate of repassivation. Dislocations in the substrate made surface depassivation difficult but enhanced reactivity during the repassivation. The test also revealed that type-312L stainless steel has high corrosion resistance in a concentrated NaCl solution.     

Leak detection in pipe using transient flow and genetic algorithm

An inverse transient method with genetic algorithm (GA) was applied to leak detection in pipeline. Transient flow caused by valve operation was calculated using the characteristics method. The location and discharge of leak were determined so that the difference of the calculated pressure may be minimized from the reference pressure calculated under a given leak condition. Calculations were done for the leak at one and two locations in pipeline. Furthermore, the effect of noise in pressure data was discussed, and the leak locations and leak discharges can be predicted precisely even in the case of noisy data. This paper was presented at the 9^th Asian International Conference on Fluid Machinery (AICFM9), Jeju Korea, October 16–19, 2007.     

The secondary buckling and post-secondary-buckling behaviours of rectangular plates

Secondary buckling and post-secondary-buckling behaviours are theoretically studied for simply-supported rectangular plates, whose primary buckling modes of deflection contain more than half-waves in the load acting direction. Modal coupling effects more complex than one two-term-coupling effects are incorporated into the secondary buckling and post-secondary-buckling analyses. Then, unstable or stable symmetric secondary branching points are found on the post-primary-buckling paths and “snap through” motions involving an abrupt change in wave-form are shown to be possible. Wave-form variations along post-secondary-buckling paths are also disclosed by means of a numerical analysis of equilibrium paths.     

Ozonization of amides

Ozonization of various amides was carried out as a model reaction for the degradation of polyamides with ozone. N-alkylamides and N,N-dialkylamides were found to be reactive compared with those amides which have no alkyl group on the nitrogen atom, and it was suggested that ozone attacks preferentially N-methylene or N-methyl group of amides in the first step of ozonization.     

The steric effect of exfoliation agent for fabrication of layer niobium oxide nanosheet

In this research, the steric effect of an exfoliation agent between n-ethylamine and triethylamine for the fabrication of Ca₂Nb₃O₁₀⁻ nanosheet was investigated. The experimental results revealed that the different structures of the exfoliation agent have affected to fabrication of Ca₂Nb₃O₁₀⁻ nanosheet. The use of n-ethylamine as an exfoliation agent gave a maximum exfoliation efficiency of 10 wt.% while the maximum exfoliation efficiency of triethylamine was 90 wt.%. The result showed that the difference in exfoliation efficiency was caused by the steric effect of exfoliation agents. The image of transmission electron microscopy exhibited Ca₂Nb₃O₁₀⁻ nanosheets which were formed by exfoliation of HCa₂Nb₃O₁₀. Furthermore, the reaction time for liquid exfoliation was studied in this work. The reaction time at 4 h gave a maximum of exfoliation efficiency. The Ca₂Nb₃O₁₀⁻ suspension was tested capability to remove hazardous ions. After the experiment, we found the white precipitate which was the formation of CsCa₂Nb₃O₁₀. The result showed that the Ca₂Nb₃O₁₀⁻ nanosheet was efficient for the removal of Cs⁺ ions in the wastewater.     

High-sensitivity determination of graft ratio of maleic anhydride-grafted polyolefin by anhydride methylation in supercritical methanol followed by H NMR spectroscopy

A wide range of graft ratios in Maleic anhydride (MA)-grafted polyolefin (PO), MA-g-PO, was determined by the combination of the methylation of grafted MA in supercritical methanol with quantification by ¹H NMR spectroscopy. The combination enabled the determination of a graft ratio as low as 0.01 wt% (100 ppm) in MA-g-PO.     

Preparation of novel silica/poly(butylene succinate-co-adipate) organic–inorganic hybrid biodegradable material via sol–gel method

Silica/poly(butylene succinate-co-adipate) organic–inorganic hybrid biodegradable materials were prepared by the sol–gel method. Fourier-transform infrared spectroscopy (FT-IR) and Thermogravimetry/differential thermal analysis (TG/DTA) indicated that the inorganic (SiO₂, C₆H₅SiO_3/2) and organic (PBSA) components were well dispersed in the hybrid material. Heat resistant test shows that the hybrid material was both heat resistant and flexible. The presence of phenyl groups and siloxane network was responsible for the flexibility and heat resistance.