Static fatigue in ceramic materials: influences of an intergranular glassy phase and fracture toughness

Static fatigue behaviour in various kinds of non-transforming ceramics has been investigated. It was found that static fatigue is closely related to the presence of a glassy phase between adjacent grains, as well as fracture toughness. Non-oxide ceramics, such as reaction-bonded silicon nitride which scarcely contains the glassy phase (group I), are insensitive to static fatigue, whereas non-transformation oxide ceramics, like alumina and non-oxide ceramics such as silicon nitride which contains the glassy phase (group II), are sensitive to static fatigue. However, static fatigue behaviour in the materials of group II also depends strongly on fracture toughness. K _IC. Namely, fatigue parameter n increases linearly as K _IC increases. From such a dependence the life time relation in the materials of group II is proposed as in terms of applied stress _S and K _IC.     

A knowledge assimilation method for logic databases

In this paper we consider a deductive question-answering system for relational databases as a logic database system, and propose a knowledge assimilation method suitable for such a system. The concept of knowledge assimilation for deductive logic is constructed in an implementable form based on the notion of amalgamating object language and metalanguage. This concept calls for checks to be conducted on four subconcepts, provability, contradiction, redundancy, independency, and their corresponding internal database updates. We have implemented this logic database knowledge assimilation program in PROLOG, a logic programming language, and have found PROLOG suitable for knowledge assimilation implementation.     

Application of functionally graded material for solid insulator in gaseous insulation system

Functionally graded materials (FGM) have spatial distribution of a material property in order to achieve efficient stress control. An application of the FGM to a solid insulator (spacer) for a gaseous insulation system, like gas insulated switchgear, is expected to improve electric field (E-field) distribution around the spacer. In this paper, we describe the applicability of the FGM spacer to gas insulated power equipment. In the FGM spacer, we gave spatial distribution of dielectric permittivity to control the E-field distribution inside and outside the spacer. This paper includes following key results for the applications of the FGM. Firstly, E-field simulation results when applying the FGM by a finite element method are presented, in which we show the effective reduction of the maximum field strength by applying the FGM. Next, a fabrication technique of the FGM spacer sample with not only step-by-step but also continuous changes of permittivity is presented by use of centrifugal force. Finally, dielectric breakdown tests using FGM samples which are accurately controlled the spatial distribution of permittivity are carried out under lightning impulse voltage applications. The test result indicates the increase of breakdown voltage (BDV). From these results, we verified the applicability and the fabrication technique of FGM spacer for improvement of the dielectric strength in the gaseous insulation system.     

Real-time and high-speed measurements of charging processes on dielectric surface in vacuum

In order to investigate the charging mechanisms of solid dielectrics in vacuum, we constructed real-time and high-speed measurement systems for charge density, current pulse, light emission and applied voltage. By applying a negative DC ramped voltage to an electrode with a cathode triple-junction (TJ), we measured the temporal variation of surface charge accumulation and current pulse waveforms expressing the electron emission from TJ, by electrostatic probes. From the measurement results, we explain the step like charging process and propose an electron emission model by taking the electric field and its relaxation by charging into account. In addition, we elucidate the relationship between the charging process and the location of electron emission.     

Charge behavior in flowing oil in oil/ pressboard insulation system by electro-optic field measurement

The electrical insulation structure of most power transformers is a combination of insulating oil and solid materials. One of the crucial problems we face in transformer operation is flow electrification, which occurs at a flowing oil/solid material interface. Thus, for the transformer insulation design, we need to clarify the now electrification phenomena. In this paper, we measured the electric field strength in an oil/pressboard composite insulation system using an electro-optic method of the Kerr effect. We obtained the time variation of electric field distribution in both flowing uncharged and charged oil. It is notable that we could quantitatively clarify the electric field distortion in flowing charged oil by flow electrification. Furthermore, we measured the leakage current from divided electrodes and derived a charge density distribution along the flow direction. Finally, we quantitatively discussed the electric field distribution and the charge behavior from the measurement results.     

Sound isolation by piezoelectric polymer films connected to negative capacitance circuits

Sound isolation has been achieved using a piezoelectric polymer film connected to a negative capacitance feedback circuit. A curved PVDF film was located in the middle of an acoustic tube and the transmission loss of sound through the film was determined in the audio frequency range. At any chosen frequency, the complete isolation of sound was achieved by adjusting the feedback, i.e. the complex capacitance of the circuit was matched precisely to that of the film.     

Development of Motor Model of Rotor Slot Harmonics for Speed Sensorless Control of Induction Motor

This paper proposes a novel mathematical dynamic model to represent the steady‐state and transient‐state characteristics of rotor slot harmonics of an induction motor for sensorless control. Although it is well known that the rotor slot harmonics originate from the mechanical structure of the induction motor, a mathematical model that describes the relationship between the stator/rotor currents of the induction motor and the slot harmonics has not yet been proposed. Therefore, in this paper, a three‐phase model of the induction motor that depicts the rotor slot harmonics is developed by taking into consideration the magnetomotive force harmonics and the change in the magnetic air gap caused by the rotor slots. The validity of the proposed model is verified by comparing the experimental results and the calculated values. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 186(3): 63–74, 2014; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.22478     

Design of Nonlinear Servo Systems by the Fuzzy Method

This paper presents the design of nonlinear servo systems using the fuzzy method. The idea behind this control method is to divide the operating region of a nonlinear system into a collection of local linear servo control systems and apply the fuzzy method for calculation of the control input. The control input of each local linear servo system is calculated using the Davison–Smith method and the Hikita pole assignment method. We can prove that all states of the fuzzy servo system are bounded and that the output errors converge to zero by the Lyapunov method. Simulations on a nonlinear mass‐spring‐damper system illustrate the effectiveness of the proposed method.     

Feasibility of zeolites in converting butyric acid into propylene for biorefineries

The biorefinery has been recognized as a new industry to produce both energy and chemical materials such as olefins and BTX from renewable resources. In this context the conversion of butyric acid over zeolites was investigated for establishing a new production route of propylene. Propylene was mainly generated by decarbonylation and dehydration of butyric acid. Our study proved that H-ZSM-5 (750) and silicalite were the best industrial catalyst among the tested ones. For H-ZSM-5 (750), the selectivity of propylene reached 64.2 C% and the ratio of the yield for propylene to theoretical yield (75 C%) became 85.6%.