• Journal of Korean Society on Water Environment
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• v.24 no.6
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• pp.718-724
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• 2008

The ion selective microelectrode (ISME) has been used for measuring the ion profile of DO, $NH_4{^+}-N$, $NO_2{^-}-N$ and $NO_3{^-}-N$ in biofilm. In this study we evaluated the detection limit and validity of ISME and applied ISME for the continuous measurement of $NH_4{^+}-N$ and $NO_3{^-}-N$ concentration in the modified Ludzack-Ettinger (MLE) process. Average detection limits of $NH_4{^+}-N$ and $NO_3{^-}-N$ ISME were $10^{-4.44}M$ and $10^{-4.62}M$, respectively. Since the ISME with $5{\sim}10{\mu}m$ of tip diameter showed a faster response time than that of $1{\sim}5{\mu}m$, the ISME with a tip diameter of $5{\sim}10{\mu}m$ was fabricated and used to make real-time ion detections. Direct monitoring of $NH_4{^+}-N$ and $NO_3{^-}-N$ concentrations in the aerobic (2) tank causes the instability of the electromotive force (EMF) for the initial 5~8 hours and also causes remarkable error values of $NH_4{^+}-N$ and $NO_3{^-}-N$ concentration. This phenomenon is caused by aeration and mixing in the reactor. Thus, the measuring chamber was newly designed for the aerobic (2) tank and then the EMF of the ISME were stabilized in less than 1 hour. Errors of $NH_4{^+}-N$ and $NO_3{^-}-N$ concentration were decreased after stabilization of the EMF. The ISME analysis were well corresponded to the results of auto analyzer and ion chromatography. Consequently, the concentration of $NH_4{^+}-N$ and $NO_3{^-}-N$ could be continuously measured for 178 hours by the ISME.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.15 no.1
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• pp.253-259
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• 2015

In this paper, we propose a transformer of alternating voltage source utilizing a semiconductor, operating in bidirectional fashion. Transformer is a device transferring energy by inductive coupling between its winding circuits. Conventional transformer is a device, composed of a primary coil and a secondary coil, transforming an alternating voltage. The system we propose is designed with a single circuit transforming the level of voltage signal in two ways; from the source to the load, and vice versa. For semiconductor switches, the NPN transistor is connected to the alternating voltage source terminal, and emitter terminal is connected to the inductor in the system as an energy storage element. The control signal is applied to the base terminal of the semiconductors. We have shown that the system we propose, by adopting only one circuit, drives an alternating voltage transformer that changes the amplitudes of voltage signal in reciprocal way.

• Applied Chemistry for Engineering
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• v.19 no.6
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• pp.583-591
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• 2008

Recently, as a demand for the portable device is surged, there are needs to develop a new fuel cell system for replacing the conventionally used secondary battery. For this purpose, it becomes important to develop direct formic acid fuel cell (DFAFC) that uses formic acid as a fuel. The formic acid can offer typical advantages such as excellent non-toxicity of the level to be used as food additive, smaller crossover flux through electrolyte, and high reaction capability caused by high theoretical electromotive force (EMF). With the typical merits of formic acid, the efforts for optimizing reaction catalyst and cell design are being made to enhance performance and long term stability of DFAFC. As a result, to date, the DFAFC having the power density of more than $300mW/cm^2$ was developed. In this paper, basic performing theory and configuration of DFAFC are initially introduced and future opportunities of DFAFC including the development of catalyst for the anode electrode and electrolyte, and design for the optimization of cell structure are discussed.

• KSBB Journal
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• v.25 no.1
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• pp.85-90
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• 2010

An ion selective microelectrode (ISME) was fabricated to measure concentrations of ammonium (${NH_4}^+$-N) and nitrate (${NO_3}^-$-N) according to the depth of nitrifying biofilm. The limits of detectability and validity of results were investigated to evaluate the ISME. The electromotive force (EMF) was directly proportional to the ion concentration, and average detection limits of ${NH_4}^+$ and ${NO_3}^-$ ISME were $10^{-5.14}$ and $10^{-5.18}$ M, respectively. The concentrations of ${NH_4}^+ $-N and ${NO_3}^-$-N in various depths on the nitrifying biofilm were measured by the ISME. When a modified Ludzack-Ettinger (MLE) process was operated at an HRT of 6 h, concentration gradients of ${NH_4}^+$-N in the bulk solution and biofilm at depths of $100\;{\mu}m$ decreased by $70\;{\mu}M$, while ${NO_3}^-$-N increased by $101\;{\mu}M$ and remained constant thereafter. At an HRT of 4 h, concentration gradients of ${NH_4}^+$-N at depths of $500\;{\mu}m$ decreased by $160\;{\mu}M$ and ${NO_3}^-$-N increased by $162;{\mu}M$ and remained constant thereafter. As HRT decreased, the concentration gradients of ${NH_4}^+$-N and ${NO_3}^-$-N between bulk solution and biofilm was higher due to the increase of nitrogen load. Also, the concentration gradients of the ${NH_4}^+$-N and ${NO_3}^-$-N of biofilm in the second aerobic tank were lower than those of the first aerobic tank, suggesting differences of nitrogen load and concentrations of DO between the first and second aerobic tank.

• Journal of Power Electronics
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• v.11 no.3
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• pp.294-303
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• 2011

In this paper an effective five-phase induction motor (IM) and its drive methods are proposed. Due to the additional degrees of freedom, the five-phase IM drive presents unique characteristics for enhancing the torque producing capability of the motor. Also the five-phase motor drives possess many other advantages when compared to traditional three-phase motor drives. Some of these advantages include, reducing the amplitude and increasing the frequency of the torque pulsation, reducing the amplitude of the current without increasing the voltage per phase and increasing the reliability. In order to maximize the torque per ampere, the proposed motor has concentrated winding, the produced back electromotive force (EMF) is almost trapezoidal, and the motor is supplied with the combined sinusoidal plus the third harmonic of the currents. For demonstrating the superior performance of the proposed five-phase IM, the motors are also analyzed on the synchronously rotating reference frame. To supply trapezoidal current waveform and to exclude the effect of the $3^{rd}$ harmonic current, a new control stratagem is proposed. The proposed control method is based on direct torque control (DTC) and rotor flux oriented control (RFOC) of the five-phase IM drives. It is able to reduce the acoustical noise, the torque, the flux, the current, and the speed pulsations during the steady state. The DTC transient merits are preserved, while a better quality steady-state performance is produced in the five phase motor drive for a wide speed range. Experimental results clearly demonstrated a more dynamic steady state performance with the proposed control system.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.8
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• pp.977-983
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• 2007

Recently, the number of systems which utilize wireless power transmission to a receiving module in a short distance is increasing. For efficient use of receiving space, coils are wound around the ferrite core to produce electromotive force(emf) in suppling power by wireless transmission. This paper analyzed the magnetic flux density distribution in the ferrite core in magnetic field environment which is uniformly oriented along to a single axis at 125kHz. For numerical analysis, Ansoft Maxwell which is applying the FEM(Finite Element Method) method was used. We studied the variations of the gathered magnetic fluxes to the changes of the relative permeabilities of the ferrite cores. Also we calculated the magnetic flux variation by shaving the ferrite core off for the groove of coil winding. Results showed that using a small ferrite core in magnetic field at 100kHz band can increase the amount of magnetic flux $3{\sim}4 times$ than without the core. The magnetic flux decreased 23% by shaving the core 0.5 mm on the periphery of 4.75 mm radius core with the relative permeability 800.