• Journal of Hydrogen and New Energy
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• v.26 no.1
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• pp.79-87
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• 2015

In a gas engine, the exhaust and the engine cooling water are generated. The engine cooling water temperature is $100^{\circ}C$ and the exhaust temperature is $500^{\circ}C$. The amount of heat of engine cooling water is 43 kW and the amount of heat of exhaust is 21 kW. Eight different hybrid organic Rankine cycle (ORC) system configurations which considering different amount and temperature of waste heat are proposed for two gas engine tri-generation system and are thermodynamically analyzed. Simple system which concentrating two different waste heat on relatively low temperature engine cooling water shows highest thermal efficiency of 7.84% with pressure ratio of 3.67 and shaft power of 5.17 kW.

• Journal of Hydrogen and New Energy
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• v.29 no.1
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• pp.41-55
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• 2018

General polymer electrolyte fuel cell (PEMFC) operates at less than $80^{\circ}C$. Therefore liquid phase water resulting from electrochemical reaction accumulates and floods the cell which in turn increases the mass transfer loss. To prevent the flooding, it is common to employ serpentine flow channel, which can efficiently export liquid phase water to the outlet. The major drawback of utilizing serpentine flow channel is the large pressure drop that happens between the inlet and outlet. On the other hand, in the high temperature polymer electrolyte fuel cell (HT-PEMFC), since the operating temperature is 130 to $180^{\circ}C$, the generated water is in the state of gas, so the flooding phenomenon is not taken into consideration. In HT-PEMFCs parallel flow channel with lower pressure drop between the inlet and outlet is employed therefore, in order to circulate hydrogen and air in the cell less pumping power is required. In this study we analyzed HT-PEMFC's different flow channels by parallel computation using previously developed 3-D isothermal model. All the flow channels had an active area of $25cm^2$. Also, we numerically compared the performance of HT-PEMFC parallel flow channel with different manifold area and Rib interval against the original serpentine flow channel. Results of the analysis are shown in the form of three-dimensional contour polarization curves, flow characteristics in the channel, current density distribution in the Membrane, overpotential distribution in the catalyst layer, and hydrogen and oxygen concentration distribution. As a result, the performance of a real area fuel cell was predicted.

• Convergence Security Journal
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• v.19 no.5
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• pp.107-118
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• 2019

Based on the Internet of Things technology, one of the core technologies of the fourth industrial revolution, our Ministry of Defense is also pushing to establish M-IoT in defense area to improve management efficiency, innovate military culture and strengthen military power. However, devices connected to the Military Internet of Things can be easily exposed to various of cyber threats as most of them are developed and with a focus on improving sensing and communication skills that collect and transmit data. And it is not easy to uniquely identify the numerous heterogeneous devices, and to establish a secure communication channel between devices or between devices and management servers. In this paper, based on PUF technology, we propose a novel key management scheme that can uniquely identify the various devices, and generate the secret keys needed for the establishment of a secure communication channel using non-replicable information generated by the PUF. We also analyze the efficiency of our proposed scheme through comparison with existing key management scheme and verify the logic and security using BAN Logic.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.1
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• pp.55-61
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• 2011

In this paper, the outage probability of device-to-device (D2D) uplink communication underlaying cellular networks is analyzed over Rayleigh fading. We assume that a D2D pair and M cellular user equipments share the same frequency resources. To prevent any harmful interference from a D2D transmitter to the BS, the maximum transmit power of the D2D transmitter is strictly limited. Under these assumptions, the outage probability is represented as a function of the interference-to-signal ratio from M cellular user equipments to a D2D receiver and the number of cellular user equipments, M. In addition, the interference-to-signal ratio is represented as a function of distances among D2D equipments, cellular user equipments and the BS. Simulation results validate these analytical results.

• 전자공학회논문지 IE
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• v.46 no.1
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• pp.16-22
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• 2009

Integrated circuit of a pulse-type neuron for Hodgkin-Huxley model is implemented in a $0.5{\mu}m$ 1 poly 2 metal CMOS technology. Proposed pulse-type neuron model consist of input stage with summing function and pulse generating block which make neuron pulse above threshold value. Pulse generating circuit consist of several transistors, capacitors and negative resistor with a charge supply function. SPICE simulation results show that neuron pulse is generated above threshold current of 70 nA. Measurements of the fabricated pulse type neuron chip in condition of 5 V power supply are shown and compared with the simulated results.

• Journal of IKEEE
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• v.22 no.2
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• pp.432-439
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• 2018

In this paper, an omnidirectional visible light detector was developed by making the detecting surface of a flexible solar cell in a cylindrical form, which has a uniform receiving pattern in the horizontal plane. This solar cell detector receives simultaneously multiple signal lights incident from different directions and provides electrical power to the ASK demodulator in the receiver. In experiments, time division transmission method was used to receive three signal lights incident from different directions to the solar cell detector. Each signal light was ASK modulated using a carrier of 40 kHz, and the synchronizing pulses required for time division transmission were generated by detecting the 120 Hz AC signal included in the indoor illumination lamp with Cds cells. This receiving structure is useful in constructing an $N{\times}1$ optical link in visible light communication.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.42 no.5
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• pp.21-30
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• 2005

Recently, a mobile IPv6 binding update protocol using Address Based Keys (BU-ABK) was proposed. This protocol applies Address Based Keys (ABK), generated through identity-based cryptosystem, to enable strong authentication and secure key exchange without any global security infrastructure. However, because it cannot detect that public cryptographic parameters for ABKs are altered or forged, it is vulnerable to man-in-the-middle attacks and denial of service attacks. Furthermore, it has heavy burden of managing the public cryptographic parameters. In this paper, we show the weaknesses of BU-ABK and then propose an enhanced BU-ABK (EBU-ABK). Furthermore, we provide an optimization for mobile devices with constraint computational power. The comparison of EBU-ABK with BU-ABK shows that the enhanced protocol achieves strong security while not resulting in heavy computation overhead on a mobile node.

• Composites Research
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• v.29 no.4
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• pp.179-185
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• 2016

A self-charging supercapacitor is constructed through simple integration of the energy storage and photo exited materials at the photo electrode. The large band gap of $NiO/Fe_3O_4$ heterostructure generates photo electron at the photo electrode and store the charges through redox mechanism at the counter electrode. Sulfanilic acid azocromotrop/reduced graphene oxide layer at the photo electrode trapped the photo generated hole and store the charge by forming double layer. The solar supercapacitor device is charged within 400 s up to 0.5 V and exhibited a high specific capacitance of ~908 F/g against 1.5 A/g load. The solar illuminated supercapacitor shows a high energy and power density of 33.4 Wh/kg and 385 W/kg along with a very low relaxation time of ~15 ms ensuring the utility of the self charging device in the various field of energy storage and optoelectronic application.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.2
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• pp.217-224
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• 2014

We have developed the novel device that can extract energy from ocean waves utilizing the heaving motion of a floating mass. The major components of the energy converter are: a floater, a counterweight, a cable, a driving pulley, two idler pulleys, a ratchet, and a generator. The device generates power through the tension force in the cable and the weight difference between the floater and the counterweight. When the system is at static free condition, the tension in the cable is equal to the weight of the counterweight which is minimum. Therefore it is desirable to keep the counterweight lighter than the floater. However, experiments show that during the rise of the water level, the torque generated by weight of the counterweight is insufficient to rotate the driving pulley which causes the cable on the floater side to slack. The proposed application of the tension pulley rectifies these problems by preventing the cable from becoming slack when the water level rises. In this paper, the dynamics model is modified to incorporate the dynamics of the tension pulley. This has been achieved by first writing the dynamical equations for the tension pulley and the energy converter separately and combining them later. This paper investigates numerically the effect of the tension pulley on various physical quantities such as the cable tension, the floater displacement, and the floater velocity. Results obtained indicate that this application is successful in suppressing large fluctuations of the cable tension.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.9
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• pp.1051-1056
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• 2014

Nitrous oxide ($N_2O$) is naturally generated from biological activity, such as bacteria's material exchange. However, recent $N_2O$ concentration in the atmosphere has being increased by the human activities such as industrial growth. One of factors to increase $N_2O$ concentration in the atmosphere is a $N_2O$ emission caused by the combustion of marine fuel oils. The marine transportation presently handles over 99 percent of the international freight cargoes and the number of ship is continuously increasing with increment of cargoes. In this study, author conducted a series of the experimental investigations on which combustion of fuels containing different element concentrations used in a 4-stroke marine diesel engine affect $N_2O$ emissions in the exhaust gas. Moreover, it is assessed on the extent to which fuel combustion patterns in the combustion chamber affect $N_2O$ emissions.