• Environmental Engineering Research
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• 제23권4호
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• pp.383-389
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• 2018

Microbial fuel cell (MFC) is an innovative environmental and energy system that converts organic wastewater into electrical energy. For practical implementation of MFC as a wastewater treatment process, a number of limitations need to be overcome. Improving cathodic performance is one of major challenges, and introduction of a current collector can be an easy and practical solution. In this study, three types of current collectors made of stainless steel (SS) were tested in a single-chamber cubic MFC. The three current collectors had different contact areas to the cathode (P $1.0cm^2$; PC $4.3cm^2$; PM $6.5cm^2$) and increasing the contacting area enhanced the power and current generations and coulombic and energy recoveries by mainly decreasing cathodic charge transfer impedance. Application of the SS mesh to the cathode (PM) improved maximum power density, optimum current density and maximum current density by 8.8%, 3.6% and 6.7%, respectively, comparing with P of no SS mesh. The SS mesh decreased cathodic polarization resistance by up to 16%, and cathodic charge transfer impedance by up to 39%, possibly because the SS mesh enhanced electron transport and oxygen reduction reaction. However, application of the SS mesh had little effect on ohmic impedance.

• 전자공학회논문지D
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• 제35D권5호
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• pp.11-17
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• 1998

In this paper, the synthesis procedufe of impedance matching network is presented for broad-band microwave amplifier design, whereby amplifier operating in the octave bandwidth is designed and fabricated in detail. The transfer function of the matching netowrks is synthesized by chebyshev approximation and element values for the networks of specified topology are calculatd for various MILs and ripples. After the transistor is modeled by negative-image device model, the synthesis procedure for matching networks is applied to broad-band amplifier design which has electrical performance of about 12dB gain in 4 to 8GHz range. Experimental results obtained from the fabricated amplifier are shown to approach the electrical performance designed in the given frequency range. Construction of the impedance matching networks by transfer function synthesis is very useful method for the design of broad-band microwave amplifiers.

• 대한교통학회지
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• 제18권4호
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• pp.19-30
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• 2000

환승은 대중교통 이용시 불가피하게 발생하여 승객에게 불편을 초래하는 통행저항(travel impedance)으로 작용하지만, 대부분의 기존 연구에서는 이를 제대로 고려하지 못하였다. 따라서 본 연구는 환승이 경로선택에 어떠한 영향을 미치는지를 살펴보기 위해서 서울시 지하철 이용자를 대상으로 선호의식(Stated Preference: SP) 및 현시선호(Revealed Preference: RP) 자료를 구축하여 분석하였으며, 차내시간, 환승횟수, 환승시간 그리고 에스컬레이터 유무의 가치를 추정하기 위한 모형식을 구축하였다. 연구 결과, SP분석과 RP분석의 결과가 조금씩 차이가 나지만 대체적으로 서울시 지하철 이용객들은 차내시간을 기준으로 할 때 환승시간은 1∼2배, 환승 1회는 10∼15분, 에스컬레이터 유무는 2∼4분의 가치를 부여하는 것으로 나타났다. 시장분할을 통해 통행특성별로 살펴본 결과 여자가 남자에 비해서 그리고 나이가 들수록 환승에 더 많은 가치를 부여함으로써 환승을 더 불편하게 느끼고 있는 것으로 나타났다. 또한 분석자료별로 차이가 있지만 귀가·하교 통행이 환승에 대한 저항이 크고, 출근·등교·업무 통행이 비교적 낮았다. 또한 통행시간 및 환승시간이 길수록 환승에 대한 저항이 크게 나타났다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 추계학술대회 논문집
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• pp.351-354
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• 2000

AC impedance of LiM $n_2$ $O_4$ and LiM $g_{0.1}$M $n_{1.9}$ $O_4$ samples have been studied at various temperature with charge-discharge test. AC impedance of LiM $n_2$ $O_4$ measured at -2$0^{\circ}C$, room temperature and 5$0^{\circ}C$ revealed that initial impedance before charge-discharge test was gradually decreased and become small by becoming law temperature. It indicates that the Li ion diffusion and the transfer resistance of the cathode are related to the temperature of cycling. Impedance at high temperature was suddenly increased because Mn dissolution and decomposition of electrolyte had been increased during cycling, compared to impedance at low temperature. Therefore, charge-discharge capacity was suddenly decreased at high but was slowly at low. In LiM $g_{0.1}$M $n_{1.9}$ $O_4$, impedance and capacity were stability at room temperature than there at 5$0^{\circ}C$, too. Initial impedance at 5$0^{\circ}C$ before charge-discharge test was small and impedance was suddenly increased during cycling than that at room temperature.ure.ure.

• KEPCO Journal on Electric Power and Energy
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• 제7권2호
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• pp.255-261
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• 2021

This paper proposes impedance-based stability analysis of DC-DC boost converters, where a harmonic state space (HSS) modeling technique is used. At first, the HSS model of the boost converter is developed. Then, the closed-loop output impedance of the converter is derived in frequency domain using small signal modeling including frequency couplings, where harmonic transfer function (HTF) matrices of the open-loop output impedance, the duty-to-output, and the voltage controller are involved. The frequency response of the output impedance reveals a resonance frequency at low frequency region and frequency couplings at sidebands of switching frequency which agree with the simulation and experimental result.

• 소음진동
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• 제5권1호
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• pp.117-122
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• 1995

The transfer matrix method is proposed to compensate the attachment effect of a piezo-electric impedance head. To validate the proposed method, an experiment is carried out for axial vibration of a uniform rod for which an analytical solution is known. The impedance head is attached to the test rod by a stud and is connected to the exciter. The frequency response function is mesured by applying random excitation from the electro-magnetic exciter. The frequency response function compensated by the method proposed in this research shows good agreement with the analytical solution.

• 전기화학회지
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• 제8권3호
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• pp.117-124
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• 2005

Electrochemical oxidation of ethanol at nickel electrodes has been studied in 1 M KOH solution containing 0.20M ethanol using electrochemical impedance spectroscopy. Equivalent circuits have been worked out by simulating the impedance data, and the results were used to model the oxidation of ethanol as well as the passivation of the electrode. The maximum rate of oxidation of $Ni(OH)_2$ to NiOOH was observed at about 0.37V vs. Ag/AgCl reference electrode, while the maximum rate of ethanol oxidation at the Ni electrode was observed at about 0.42V, The charge-transfer resistance for oxidation of the electrode itself became smaller in the presence of ethanol than in its absence. These results suggest that the $\beta-Ni(OH)_2/\beta-NiOOH$ redox couple is acting as an effective electron transfer mediator far ethanol oxidation. The kinetic parameters also were obtained by the experimental and simulated results.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 추계학술대회논문집 II
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• pp.1341-1346
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• 2001

In this study, the acoustic properties of steel-wire sound absorbing materials with different thickness and bulk density were investigated in terms of characteristic impedance, propagation constant, and absorption coefficient. The well-known two-cavity method was used for evaluating those acoustic parameter values in experiments. Also, in order to validate the experimentally measured values, the results were compared with the results obtained from Chung and Blaser's transfer function method and SWR method. The experimentally measured values of normal absorption coefficients were generally agreed well with the corresponding values from the transfer function method and the SWR method. Based on the experimental results, the following conclusions could be made. The magnitude of the absorption coefficient and the frequency range of the maximum absorption coefficient were controllable by changing the thickness and bulk density of the sound absorbing materials. Also, the magnitude of the absorption coefficient depended on the characteristic impedance and the propagation constant. As large as the air cavity depth at the rear side of the steel-wire sound absorbing materials, the maximum magnitude of the absorption coefficient occurred at the lower frequency ranges.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문집
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• pp.896-901
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• 2002

The sound absorption coefficients for multiple layer perforated plate systems containing several compartments with airspaces and porous absorbing materials are estimated using the transfer matrix method developed in the previous paper. The absorption coefficients from transfer matrix method agree well with the values measured by the two-microphone impedance tube method for various combinations of perforated plates, airspaces or porous materials. Based on these results, a guidance for the design of multiple layer perforated plate systems combined with airspaces and porous absorbing materials is discussed in detail.

• 소음진동
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• 제6권5호
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• pp.635-644
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• 1996

In this paper, Allard's modelling method which employs the method of acoustic transfer matrix(ATM) is applied to yield more precise results in the analysis of porous sound absorbing material. The method of ATM, based on Biot's theory, is known to play an important role in the estimation of the sound absorption when a sound projects onto the material. In the case of a single layered porous sound absorbing material, the surface impedance and the absorption coefficient by using the method of ATM are estimated. With the variation of the material properties, sound absorption characteristics and analyzed. Transmission Loss in a combination of the porous sound absorbing material with a thin plate is predicted.