Basic Study on Islanding Detection Method for PV Systems by Harmonic Impedance Detection in Case of Including Induction Motor in Load System

It is important that photovoltaic (PV) systems detect islanding caused by power system faults to ensure electrical safety. Thus we propose a novel islanding detection method which detects the harmonic impedance by injecting harmonic currents synchronized with the exciting current harmonics of the pole transformer. For the case in which an induction motor load is included in the load system, basic experiments on islanding detection and simulation analysis are conducted to verify the effectiveness of the proposed method.     

Crystalline Phase Change in Yttria-Partially-Stabilized Zirconia by Low-Temperature Annealing

Changes in the phase composition and microstructure of yttria-partially-stabilized zirconia by low-temperature annealing were investigated at 100° to 500°C using bodies sintered from coprecipitated fine ZrO₂-Y₂O₃ powders at varied temperatures. Tetragonal zirconia on the surfaces of bodies sintered at <1500°C transformed to the monoclinic phase at 100° to 400°C. Transformation behavior was strongly affected by grain size.     

Investigation of Water Tree Degradation in Dry‐Cured and Extruded Three‐Layer (E‐E Type) 6.6‐kV Removed XLPE Cables

Dry‐cured and extruded three‐layer (E‐E type) 6.6‐kV cross‐linked polyethylene (XLPE) cables were introduced into electric power systems more than 30 years ago, but they do not experience failures because of water tree degradation. Also, the degradation index of water treeing for these cables has not been established. Therefore, investigating results of residual breakdown voltage and water tree degradation of these cables will help us plan for cable replacement and determine water tree degradation diagnosis scheduling, and will be fundamental data for cable lifetime evaluation. In this study, the authors measured the ac breakdown voltages of dry‐cured and E‐E type 6.6‐kV XLPE cables removed after 18 to 25 years of operation and observed the water trees in their XLPE insulation. As a result, it was observed that breakdown voltages were larger than the maximum operating voltage (6.9 kV) and the ac voltage for the dielectric withstanding test (10.3 kV). Water trees were mainly bow‐tie water trees and their maximum length was approximately 1 mm. Although the number of measured cables was limited, the lifetime of this type of cable was estimated to be approximately 40 years, even experiencing water immersion.     

Computationally Efficient Large-Eddy Simulation of Periodic Unsteady Flow using Harmonic Balance Method

To improve the efficiency and fidelity of the numerical analysis for cascade flutter, we propose an efficient scale-resolving simulation method dedicated to time-periodic flows by incorporating the harmonic balance approach into the large-eddy simulation. This method combined convergence calculations of the steady-state problem based on the harmonic balance method for periodic components, and the nonlinear time-marching method for turbulent fluctuations. Using the proposed method, deterministic periodic components and stochastic turbulent fluctuations were calculated simultaneously, and the effect of turbulent fluctuations on deterministic periodic components was directly calculated without using turbulence models. In this paper, we explain the algorithm and feature of this simulation technique and present the results of the computation for channel flow excited in the streamwise direction as an analysis example using the proposed method. In order to validate the proposed method, an analysis of sinusoidally pulsating channel flow at the central friction-velocity Reynolds numbers Rer = 180 was conducted, confirming that the amplitude and phase of the mean velocity oscillation computed by the proposed method were in good agreement with those of the conventional LES. The present calculation achieved an order of magnitude improvement in computational efficiency compared to conventional LES.     

OCCURRENCE OF RUPTURES ON THE SURFACE OF FOODS DURING FRYING

An attempt was made to clarify the mechanism of ruptures on the surface of foods occurring during frying. Two different products were fried in a corn oil bath at a temperature of 160C or 180C. One of the products was ellipsoidal croquettes coated by the crust with different thicknesses ranging from 1 mm to 4 mm, while the other was ring doughnuts consisting of the three different compositions of a fixed size. The type of ruptures on the crust of croquette samples could roughly be divided into two categories according to the results obtained by the precise observations during the process of frying, i.e., a small hole and a crack. The small hole, like a pinhole, occurred in the crust of the croquette with 1 mm thickness early in the procedure, while the cracks could be observed with the crusts of croquettes more than 2 mm thicknesses after 120 s or more of frying time. The cracks also occurred on the curved surface of all the doughnut samples tested, although the location of cracks on the three surfaces, i.e., upper, outer and inner, was much influenced by the composition of the samples. A variety of measurements were made to obtain information on the changes in mechanical properties of the core region and crusted surfaces of the samples in the frying process so as to confirm generalized simple considerations assumed for the occurrence of ruptures.     

Abalone (Hariltis discus): Seasonal Variations in Chemical Composition and Textural Properties

Seasonal changes in adenosine 5′-triphosphate, total free amino acids, and total oligopeptides in abalone meat were analyzed. Levels were higher in summer and lower in winter. In both seasons, the most abundant free amino acid was taurine followed by arginine, glycine, glutamine, and glutamic acid. The largest peptide-bond amino acid was glutamic acid + glutamine. The collagen content decreased in summer and increased in winter. The breaking stress values of the meat were low in summer and high in winter, indicating that summer abalone would be more tender. Scanning electron microscopy revealed the collagen network was more compact in winter.     

Reversible Molecular Rearrangement of Slightly Acid-treated Starches

The reersible association and dissociation of starch chain populations obtained from acid-treated starches (ATSs) was investigated. Potato starch, both nonglutinous and glutinous rice starches and sago starch were suspended in 15% sulfuric acid until 1% hydroysis occured. These ATSs had relative molecular weight ranges of 25,00–29,000 daltons. In water, about half the molecules were reconstituted into large aggregates of a few million daltons. This change in molecular size depended on presence of potassium chloride. It was not observed in debranched samples. The aggregates showed a clear endothermic peak on a DSC curve. Thus, the reversibly rearranging starch chain populations were not linear, but were branched and had some type of ordered structure.     

猫与四季流转的生活诗

春的樱花,夏的萤火,秋的落叶,冬的飘雪。四季的景致在平凡琐碎的生活中悄然划过。时间流转之中的细微美感也在快速厚重的现代化包裹之中渐渐磨失不见。或许大多数的我们选择接受这种方式、调整自己适合如此的生活,但也有人最终还是逆势去找寻内心最渴望的回归。     

超薄钛酸铅纳米管铁电性和力电耦合特性的第一性原理研究

利用基于密度泛函理论的第一性原理的方法研究了超薄钛酸铅(PbTiO₃)纳米管的铁电性及力电耦合特性。研究发现对于钛酸铅铁电纳米管结构, 即使在其特征尺寸小于铁电薄膜的铁电临界尺寸时, 依然存在自发极化。钛酸铅铁电纳米管结构不存在铁电临界尺寸。对纳米管力电耦合效应的研究发现, 轴向应变作用会引起包括极化沿轴向方向的铁电相、顺电相和极化沿周向方向的铁电相在内的丰富的相转变。这种相的转变是由于轴向应力所导致的Pb-O共价键的变化所引起的。另一方面, 研究了钛酸铅纳米管结构的机械强度, 明确了在轴向拉伸和压缩作用下纳米管的临界载荷。