• Journal of the Korean Ceramic Society
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• v.25 no.6
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• pp.601-608
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• 1988

The effect of SiO2 addition on sintering characteristics of 8 mole percent yttria-stabilized zirconia ceramics is investigated. As the addition of SiO2 is increased, sinterbility, microstructure, and Vickers hardness of the zirconia ceramic increased but fracture toughness and electrical conductivity are decreased. It is considered that the electrical conductivity decrease with the increase of SiO2 is due to the decrease of defect concentration of ionized oxygen. From the complex impedance measurement, it is shown that the influence of SiO2 is more dominant at the resistivity of bulk region than of grain boundary region.

• Journal of the Korean Ceramic Society
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• v.28 no.12
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• pp.953-960
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• 1991

Effect of MgO doping was studied by measuring complex impedance of PZT[Pb(Zr0.52Ti0.48)O3] samples doped with 0.25~6 mol% MgO. Electrical conductivity of PZT samples increased within 1.5 mol% of MgO doping. However above 1.5 mol%, no noticeable changes were found. Activation energy and pre-exponential factor of electrical conductivity were found to decrease within 1.5 mol% of MgO doping, but increase above 1.5 mol%. Therefore it was concluded that the decrease of electrical conductivity with MgO doping was due to the decrease of activation energy.

• Journal of the Korean Ceramic Society
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• v.28 no.3
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• pp.179-188
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• 1991

The semiconducting BaTiO3 ceramics used in this study were sintered in the reducing atomosphere(hydrogen gas) and neutral atmosphere(nitrogen gas), then were heat-treated in air to vary defect concentrations. In this experiment, the correlations between the composition analysis and electrical characteristics of these samples were investigated. When the BaTiO3 ceramics were sintered in N2 atmosphere, it was observed that the Ba contents near the interface were lower than that of the grain center, and these samples showed superior PTCR effects. From analysis of the resistivities of grains and grain boundaries by CIRM(Complex Impedance Resonance Method), it was confirmed that the PTCR effects were caused by the resistivity of grain boundaries. And from measurement of the capacitance at each temperature, the samples sintered in N2 atmosphere show the increase of room temperature resistance and the decrease of capacitance as a result of the increase of the charge depletion layers. This phenomenon agrees well with the cation deficiencies in the analytical results.

• Proceedings of the KIPE Conference
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• 2013.07a
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• pp.275-276
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• 2013

In this paper, we proposed the Z-source four-switch three-phase rectifier. As we know, the conventional Four-Switch Three-Phase Rectifier(FSTPR) has advantages of the lower cost and less complex switching control. However, The conventional FSTPR can only either perform buck or boost operation, it can only attain the buck-boost operation by adding another DC-DC converter. In addition, besides its narrow output voltage region, distortion of the input current is serious either. Thus, we proposed the Z-source FSTPR which has buck-boost function and better input current waveform by applying the Z-impedance network to the conventional FSTPR. The validity of the proposed system was confirmed by experiments.

• International journal of advanced smart convergence
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• v.7 no.1
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• pp.7-14
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• 2018

In this paper, we derive a transfer function of cross-coupled microwave filter systems by using a characteristics of chain matrices. Depending on the lumped element of capacitor or inductor, the cross-coupled system is negatively- or positively system. We used a ladder network as a starting system composed of several subsystems connected in chain. Each subsystem is descrived by Laplace impedance. By solving the transmission zero characteristic equation derived from the cascaded subsystems, we can find the zeros of filter system with externally cross-coupled lumped elements. With the cross-coupled elements of capacitors, the numerator polynomial of system transfer function is used to locate the quadruplet zeros in complex plane. We show the polynomoials of numerator and denominator of cascaded transfer function, obtaining the zeros of the cross-coupled system.

• Wind and Structures
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• v.14 no.4
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• pp.359-381
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• 2011

This paper deals with the flutter instability problem of flexible bridge decks in the framework of bimodal-coupled aeroelastic bridge system analysis. Based on the analysis of coefficients of the polynomials deduced from the singularity conditions of an integral wind-structure impedance matrix, a set of simplified formulations for calculating the critical wind velocity and coupled frequency are presented. Several case studies are discussed and comparisons with available approximated approaches are made and presented, along with a conventional complex eigenvalue analysis and numerical results. From the results, it is found that the formulas that are presented in this study are applicable to a variety of bridge cross sections that are not only prone to coupled-mode but also to single-mode-dominated flutter.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.204-207
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• 2000

In this paper, we have studied the effect of doped with B-Bi-Zn on properties (microstructure, density, shrinkage, permeability as a function of frequency, etc.) of hexagonal-ferrite for high frequency chip-inductor material about several GHz. The permeability were analyzed by impedance analyzer(100 kHz~40 MHz) and network analyzer(30 MHz~3 GHZ). As a result of the characteristics, the B-Bi-Zn glass ceramic was used to lower the sintering temperature for additive as a function of frequency from 100 kHz to 1.8 GHz showed constant tends. The maximum imaginary value of complex permeability was observed near the resonance frequency of 2 GHz.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.12
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• pp.3782-3791
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• 1996

A great deal of effert has been invested in upgrading the performance and the efficiency of mechanical structures. Using experimental modal analysis(EMA) or finite element analysis(FEA) data of mechanical structures, this performance and efficiency can be effectively evaluated. In order to analyze complex structures such as automobiles and aircraft, for the sake of computing efficiency, the dynamic substructuring techniques that allow to predict the dynamic behavior of a structure based on that of the composing structures, are widely used. By llinking a modal model obtained from EMA and an analytical model obtained from FEA, the best conditioned structures can be desinged. In this paper, a new algorithm for structural dynamic modification-SRFSM (substructure response function sensitivity method) is proposed by linking frequency responce function synthesis and response function sensitivity. A mehtod to obtain response function sensitivity using direct derivative of mechanical impedance, is also used.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2006.03a
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• pp.613-619
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• 2006

This paper introduces a new structural health monitoring using a nano sensor. The sensor is made of nano smart composite material based on carbon nanotubes. The nano sensor is fabricated as a thin and narrow polymer film sensor that is bonded or deposited onto a structure. The electrochemical impedance and dynamic strain response of the neuron change due to deterioration of the structure where the sensor is located. A network of the long nano sensorcan form a structural neural system to provide large area coverage and an assurance of the operational health of a structure without the need for actuators and complex wave propagation analyses that are used with other methods.

• Bulletin of the Korean Chemical Society
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• v.10 no.6
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• pp.495-500
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• 1989

The ionic conductivity of polycrystalline, glass, and glass-ceramic silicates was measured using two-terminal AC method with blocking electrode over a frequency range of 100 Hz to 100 KHz in the temperature range of $200^{\circ}C$ to $320^{\circ}C$. Analysing the capacitance (C), susceptance (B), impedance (Z), and conductance (G) under the given conditions, an equivalent circuit containing temperature and frequency dependent component is proposed. Higher capacitance could be observed in the low frequency region and on the improved ionic migration conditions i.e., at higher temperature in a better ionic conductor. Also the electrode polarization built up at the electrode-specimen interface could be sorted out above 10 KHz. However, grain boundary contribution couldn't be extracted from the bulk resistance over the frequency range measured here.