Ferroelectric-Paraelectric Phase Transition in Lead Titanate Containing Lattice Defects

A series of lead titanates containing lattice defects was prepared and characterized in terms of inhomogeneously distributed vacancies, □_Pb and □_O•. The tetragonal lattice strain and the Curie temperature varied as functions of the Pb or O deficiency in the crystals. The tetragonal strain for these crystals decreased slowly with increasing temperature as the Curie temperature was approached. The phase transition, which extends over a temperature interval, is interpreted according to a model in which microregions in the crystal differ in composition and therefore have different Curie temperatures.     

ON THE PARAMETER-SPACE CLASSIFICATION OF THE DYNAMIC BEHAVIOR OF A CONTINUOUS MICROBIAL FLOW REACTOR

Recently Agrawal et al.¹ classified the dynamic behavior of continuous stirred tank fermentor for the Monod's model and the two parameter hump function model with variable yield coefficient in the parameter space. We employed the more general three parameter substrate inhibition model which includes the Monod's model as a limiting case, derived the boundary equations which rigorously divide the parameter space of different dynamic behavior, and showed the interesting phenomenon that a limit cycle suddenly vanished for the slight change in the Damköhler number by computer simulation.     

Ferroelectric-Gate Field Effect Transistors Using (Y,Yb)MnO3/Y2O3/Si(111) Structures for 1T-Type FeRAMs

Fabrication and characterization of metal-ferroelectric-insulator-semiconductor field-effect-transistors (MFIS FETs) using (Y,Yb)MnO₃/Y₂O₃/Si structures were introduced for the first time. P-channel MFIS FETs were fabricated on n-type Si(111) substrates, in which an Y_0.5Yb_0.5MnO₃(200 nm)/Y₂O₃(25 nm) structure was used as gate insulator. The Y_0.5Yb_0.5MnO₃ and Y₂O₃ films were prepared by chemical solution deposition. A fabricated MFIS FETs showed the hysteresis loop due to spontaneous polarization in the I_D-V_GS characteristic, in which the memory window was about 0.9V when the applied gate voltage was swept between 8 V and ?8 V. Especially, the alternative drain current was retained after applying a single voltage pulse with a magnitude of +9 V or ?9 V.     

Molecular Dynamic Simulation of Eu3+ -Doped Sodium Borate Glasses and Their Fluorescence Spectra

A molecular dynamic simulation was performed for sodium borate glasses containing a small amount of Eu₂O₃ to investigate the local structures of cations in glass. A new potential V_B-B in the form -A exp[-C(r - 0.239)²] was added to the regular modified Born-Mayer-Huggins-type potentials, Φ_B-B, Φ^B-O, and ΦO-O, to account for the directional tendency of the borate network structure. With this potential added, both the radial distribution of sodium borate glasses observed by small-angle X-ray diffraction and the change in coordination number of boron with sodium content obtained by NMR agreed well with the simulation. The average coordination number of Ed³⁺ ions in the simulated glasses varied from 7.5 to 8.6, depending on the composition of the host sodium borate glasses. The inhomogeneous line width of the ⁵D₀-⁷F_z emission peak also changed, depending on the sodium content, with a maximum at 18 mol% Na_zO content; this result agrees well with experimental data obtained from laser-induced fluorescence spectra.     

Critical Generation Evaluation Using Hybrid Energy Function Method

It is well known that the transient energy function (TEF) method is useful for an efficient transient stability assessment as represented by the estimation of the critical clearing time (CCT). However, there still remains an issue for practical use: most of the TEF methods adopt the classical model of a synchronous machine in which the internally generated voltage is assumed to be constant. Moreover, critical generated output can be a more practical stability index instead of the CCT used in the conventional TEF methods. In this paper, a conventional hybrid TEF method is developed in order to estimate the transient stable critical generated power by using an improved hybrid simulation. The proposed method can handle the detailed model for a synchronous machine and can estimate the critical generated power with higher accuracy. Experimental results for a large network model are given in order to verify the practicability of the proposed method.     

Study on Lightning Protection Measures for Distribution Lines and Customer Equipment against Back Flow Lightning Current from Radio Communication Station

Recently, with the expansion of communication network areas, the number of radio communication stations built in the neighborhood of customer houses has increased. If lightning strikes a communication radio tower, part of the lightning current flows into the distribution line and into customer houses. This may cause the failure of distribution lines or customer equipment. To protect distribution lines and customer equipment from lightning faults, it is necessary to analyze the surge phenomena in distribution lines and customer equipment and take appropriate protection measures. In this study, we examined the effect of lightning protection measures for distribution lines and customer equipment against lightning strikes to a communication tower. First, using an actual‐scale test distribution line, we measured the lightning current flowing into distribution lines and customer equipment. Second, we quantitatively examined the effect of lightning protection measures by lighting surge analysis while changing each parameter. From the experimental and analytical results, we show that the proposed protection measures can reduce the lightning current flowing into distribution lines and customer equipment.     

Impact of Postfault Active Power Recovery of Photovoltaic Power Generation on Transient Stability

Currently, Japanese grid codes require photovoltaic (PV) power generation systems to continue supplying power to the grid as soon as possible even if the systems temporarily stop their operation. Although the fault ride‐through capability was originally proposed for preventing a cascading frequency drop in the power system, the capability has the impact on other instability phenomena such as transient stability. In this study, we focus on the postfault active power recovery of the PV systems. The impact of the recovery speed on the transient stability is investigated under different load conditions, in particular static/dynamic load condition. Numerical examples are carried out for the one‐machine one‐load infinite‐bus system, and the effects of the recovery speed are evaluated by equal area criterion and critical clearing time. As a result, we have found both desirable and undesirable effects on the transient stability depending on the load condition.     

Fabrication and Characterization of Ba(Ti,Zr)O3 Thin Films Through the Chemical Solution Deposition Process

Lead- and bismuth-free Ba(Ti_{1 ? x} Zr _x )O₃ (BTZ) thin films were fabricated on Pt(111)/Ti/SiO₂/Si(100) substrates by the chemical solution deposition (CSD) process. The single phase BTZ thin films were obtained at 650°C by conventional process and the control of lattice parameter a was possible by Zr substitution. As the D-E hysteresis loops and J-V characteristics depended on the precipitates on film surface, the fabrication process was reexamined by 2-step sintering process. Consequently the decreasing of first sintering time was able to prevent the precipitates, and the larger grain of about 40–50 nm were obtained by additional sintering for 2 hour.     

Integration of Incinerator Plants and Utilization of Forest Biomass on the Basis of FIT

Feed‐in tariff (FIT) has been enforced in order to promote the utilization of renewable energy since 2012 in Japan. In consideration of FIT, we propose an integration plan for incinerator plants (IPs) with highly efficient power generation for the whole area of a prefecture. The plan includes disposal of forest biomass using the reserve capacity of IPs. The model prefecture's population is set to 1,200,000 and the proportion of the forested area is set to 70% of the model area based on data for northeastern Japan. The present 16 IPs are integrated into three new IPs. A relay transportation (RT) facility for waste is located at a decommissioned IP, and the waste from the area is transported to the new IP. In order to calculate the RT costs, an approximation formula for the RT distance is estimated via the IPs integration study. The plan will realize about 37% cost reduction and 1.8‐fold CO₂ reduction including RT as compared to the plan to update the current IP situation. Forest biomass of 56,500 tons per year, which is about 43% of available forest biomass volume in the model prefecture, can be disposed of at new IPs. On the other hand, enough profit is not expected from the dedicated biomass power generation plant as a result of wood chip processing fees. The plan will help to develop local forestry.     

Study of Lightning Risk Evaluation of Distribution Systems

Recently, concept of the lightning risk management has been proposed for the minimization of damages caused by lightning. In distribution systems (power distribution lines, low‐voltage distribution lines, telecommunication lines, and customer appliances), lightning protection measures based on the lightning risk management are effective since the number of facilities is enormous. In this paper, for the establishment of lightning risk management method of distribution systems, we expressed the lightning risk assessment method of distribution systems and examined the influence of arrangement of customer house on the lightning risk values of power distribution lines and customer appliances.