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Kim, Yunsung,Kim, Youngsuk,Kim, Daewhan,Kim, Sungsoo,Nam, Wonjong,Choe, Heeman The Japan Institute of Metals 2011 Materials transactions Vol.52 No.3
<P>This study examined how the strain rate affects the room-temperature tensile behavior of hydrogen-charged 316L stainless steels. A high-temperature homogenization treatment was applied to the specimens after hydrogen charging and copper electroplating to remove the hydrogen concentration gradient. A softening phenomenon was observed in the hardening behavior of the H-charged and homogenized specimen at a strain rate of 2×10<SUP>−3</SUP>/s. The observation was further confirmed by an inspection of the fracture surface of the tensile test specimen.</P>
촉매제 요소함량에 따른 Urea-SCR의 배출가스 현황 조사
임윤성(Yunsung Lim),이종태(Jongtae Lee),김선문(Sunmoon Kim),박장민(Jangmin Park),문선희(Sunhee Moon),김동민(Dongmin Kim),김형준(Hyungjun Kim),김정수(Jeongsoo Kim) 한국자동차공학회 2012 한국자동차공학회 부문종합 학술대회 Vol.2012 No.5
Ministry of Environment prescribes urea water by Clean Air Conservation Act. Urea water manufaturer used urea(high purity) and distilled water. Urea contents must be 31.8 ~ 33.2% (m / m) by Clean Air Conservation Act. But urea water manufacturer should be prepared with a urea content exceeded or under. so this research is evalustion of exhaust emission according the concentration urea rate and urea water usage.
Flow and Learning satisfaction for Smart Learning Based of Mobile Augmented Reality
YunSung Cho,ByungTaek Kim,Sung-Soo Park,SeokHun Kim 보안공학연구지원센터 2015 International Journal of Software Engineering and Vol.9 No.4
While in the past, the paradigm of digital smart-learning contents was simply focused on efficiency of processing and delivery of information, today the focus has shifted toward more immediate, intuitive, real, and natural flow learning contents such as virtual reality and augmented reality. In other words, effort is being made to provide more realistic digital contents to learners with improved flow and interest. Augmented reality is next-generation media that can induce improved flow from learners by integrating real world and virtual world in a natural way, and has shown possibility as a new smart learning media with increased flow and satisfaction of learners. Therefore, in this study, the positive effect of characteristics of augmented reality on improvement of flow and satisfaction of smart learning in developing smart learning content was examined. The result showed that augmented reality has a significant effect on the learning flow and satisfaction of smart learners. In the future, more media research for various smart learning environments will be needed, and this study can help develop smart-learning contents.
A Dual Power-Mode Multi-Band Power Amplifier With Envelope Tracking for Handset Applications
Yunsung Cho,Daehyun Kang,Jooseung Kim,Dongsu Kim,Byungjoon Park,Bumman Kim IEEE 2013 IEEE transactions on microwave theory and techniqu Vol.61 No.4
<P>This paper presents a dual power-mode and multi-band power amplifier (PA) for handset applications that improves the efficiency in low-power regions. This PA operates in two modes through path control by a shunt switched capacitor. The proposed control method provides efficient mode control without any efficiency degrading and bandwidth (BW) limiting. The proposed PA, in conjunction with a boosted supply modulator for envelope tracking (ET) operation not only in the high-power mode, but also in the low-power mode, delivers good performance at all average output power levels. The linearity is improved by ET through a proper envelope-shaping method. For demonstrative purposes, the PA and supply modulator are implemented using an InGaP/GaAs heterojunction bipolar transistor and AIGaAs/InGaAs enhancement/depletion-mode pseudomorphic high electron-mobility transistor process and a 0.18-μ m CMOS process, respectively. The ET PA is tested across the range of 1.7-2.0 GHz using a long-term evolution signal with 16 quadrature amplitude modulation, a 7.5-dB peak-to-average power ratio, and 10-MHz BW. The proposed dual power-mode multi-band ET PA delivers good performance for high- and low-power modes, indicating that the architecture is promising for handset PA applications.</P>
Flexible and multi-directional piezoelectric energy harvester for self-powered human motion sensor
Kim, Min-Ook,Pyo, Soonjae,Oh, Yongkeun,Kang, Yunsung,Cho, Kyung-Ho,Choi, Jungwook,Kim, Jongbaeg Institute of Physics Publishing 2018 Smart materials & structures Vol.27 No.3
<P>A flexible piezoelectric strain energy harvester that is responsive to multi-directional input forces produced by various human motions is proposed. The structure of the harvester, which includes a polydimethylsiloxane (PDMS) bump, facilitates the effective conversion of strain energy, produced by input forces applied in random directions, into electrical energy. The structural design of the PDMS bump and frame as well as the slits in the piezoelectric polyvinylidene fluoride (PVDF) film provide mechanical flexibility and enhance the strain induced in the PVDF film under input forces applied at various angles. The amount and direction of the strain induced in PVDF can be changed by the direction of the applied force; thus, the generated output power can be varied. The measured maximum output peak voltage is 1.75, 1.29, and 0.98 V when an input force of 4 N (2 Hz) is applied at angles of 0°, 45°, and 90°, and the corresponding maximum output power is 0.064, 0.026, and 0.02 <I>μ</I>W, respectively. Moreover, the harvester stably generates output voltage over 1.4?×?10<SUP>4</SUP> cycles. Thus, the proposed harvester successfully identifies and converts strain energy produced by multi-directional input forces by various human motions into electrical energy. We demonstrate the potential utility of the proposed flexible energy harvester as a self-powered human motion sensor for wireless healthcare systems.</P>
Envelope-Tracking Two-Stage Power Amplifier With Dual-Mode Supply Modulator for LTE Applications
Jooseung Kim,Dongsu Kim,Yunsung Cho,Daehyun Kang,Byungjoon Park,Bumman Kim IEEE 2013 IEEE transactions on microwave theory and techniqu Vol.61 No.1
<P>This paper presents an envelope tracking power amplifier (ET PA) using a dual-mode supply modulator for handset application. The supply modulator has a combined structure with a linear amplifier and a switching amplifier. The dual-mode supply modulator operates in high-power mode and low-power mode by providing the supply voltage of the linear amplifier of 5 and 2.5 V, respectively. For 1.74-GHz long-term evolution signal with 10-MHz bandwidth, 6.44-dB peak-to-average power ratio, and 16-quadrature amplitude modulation, the ET PA delivers a power-added efficiency (PAE) of 39.8%, an evolved universal terrestrial radio access adjacent channel leakage ratio (E-UTRA<SUB>ACLR</SUB>) of - 35.7 dBc, and an error vector magnitude (EVM) of 3.81% at an average output power of 27 dBm. The ET PA also delivers a PAE of 22.6% at an average output power of 18 dBm, which is 6.6% higher than that of the conventional ET PA and 13.1% higher than that of the standalone PA. The supply modulator is connected to a drive stage and a power stage of the PA simultaneously for further enhanced efficiency at a power back-off region. The dual-mode two-stage ET PA delivers a PAE of 38.1%, an E-UTRA<SUB>ACLR</SUB> of - 32.9 dBc, and an EVM of 4.74% at an average output power of 27 dBm. The dual-mode two-stage ET PA also delivers a PAE of 26.3% at an average output power of 18 dBm, which is 7.8% higher than that of the conventional two-stage ET PA and 16.7% higher than that of the standalone PA.</P>
김효신(Kim, Hyoshin),이종호(Lee, Jongho),김호성(Kim, Ho-Sung),이윤성(Lee, Yunsung) 한국신재생에너지학회 2010 한국신재생에너지학회 학술대회논문집 Vol.2010 No.06
LSM is widely used as a cathode material in SOFC, because of its high electrochemical activity, good stability and compatibility with YSZ electrolyte at high temperature. However, LSM in traditional cathode materials will not generate a satisfactory performance at intermediate temperature. In order to reduce the polarization resistance of cell with the operating temperature of SOFC system, the cathode material of LSCF is one of the most suitable electrode materials because of its high mixed ionic and electronic conductivity. In this report, cathode material, La_{0.6}Sr_{0.4}Co_{0.2}Fe_{0.8}O₃ powder for intermediate temperature SOFC was synthesized by Pechini method using the starting materials such as nitrate of La, Sr, Co and Fe including ethylene glycol, etc. As a result, the synthesized powder that calcined above 700?C exhibits successfully perovskite structure, indicating phase-pure of LSCF. Moreover, the particle size, surface area, crystal structure and morphology of the synthesized oxide powders were characterized by SEM, XRD, and BET, etc. In order to evaluate the electrochemical performance for the synthesized powder, slury mixture using the synthesized cathode material was coated by screen-printing process on the anode-supported electrolyte which was prepared by a tape casting method and co-sintering. Finally, electrochemical studies of the SOFC unit cell, including measurements such as power density and impedance, were performed.