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Hoon Lee,Sang-Rim Lee,Kyoung-Jae Lee,Han-Bae Kong,Inkyu Lee IEEE 2015 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.14 No.9
<P>This paper investigates the optimal transmit beamforming designs for simultaneous wireless information and power transfer (SWIPT) in multiple-input single-output interference channels (IFC). Based on cooperation level among transmitters and receivsers, we classify the SWIPT IFC systems into two categories. First, we consider the IFC with partial cooperation, where only channel state information (CSI) is available at transmitters and receivers, but not the signal waveform. Second, we examine the IFC with signal cooperation, where both the CSI and the signal waveforms are known to transmitters and receivers. Then, for the both scenarios, we identify the Pareto boundary of the achievable rate-energy (R-E) region which characterizes the optimal tradeoff between the information rate and the harvested energy. To this end, the problems for maximizing the information rate are formulated with minimum required harvested energy constraint. To solve these non-convex problems, we introduce parameterization techniques for characterizing the R-E region. As a result, the original problem is separated into two subproblems, for which closed-form solutions are obtained by addressing the line search method. Finally, we provide numerical examples for the Pareto boundary of the R-E region through simulations.</P>
Downlink Vertical Beamforming Designs for Active Antenna Systems
Wookbong Lee,Sang-Rim Lee,Han-Bae Kong,Sunho Lee,Inkyu Lee IEEE 2014 IEEE TRANSACTIONS ON COMMUNICATIONS Vol.62 No.6
<P>In this paper, we study a vertical beamforming technique for multiple-input multiple-output downlink multi-user systems. In general, the transmit antenna gain is controlled by adjusting the boresight of antennas in directional antennas, and thus the cell average rate varies according to the angle of the boresight. First, we compute the tilting angles for directional antenna systems which maximize the cell average rate. To this end, the probability density function of a three-dimensional user distribution is derived. Based on the result, we analyze the average rate gain of active antenna systems over passive antenna systems for a single user case. Furthermore, for a multi-user active antenna system, beamforming designs to maximize the weighted sum rate are proposed by optimizing the transmit antenna gain and power allocation. Since finding joint optimal parameters requires prohibitively high computational complexity, we separate the optimization problem into two sub-problems of the vertical beamforming and the power allocation. Then a simple vertical beamforming algorithm based on a high signal-to-noise ratio assumption is presented. Also, for a multi-user passive antenna system, we provide a beamforming scheme based on a multi-sector concept. Simulation results show that the proposed beamforming schemes outperform the conventional beamforming schemes.</P>
IoT 센서 연동 운전 보조 음성 AI Agent Device 및 App
이하은(Haeun Lee),이시윤(Siyoon Lee),오인규(Inkyu OH),박경만(Kyeongman Park),신승연(Seungyun Shin),이수민(Sumin Lee),정서우(Seowoo Jeong),이민구(Mingu Lee) 한국HCI학회 2022 한국HCI학회 학술대회 Vol.2022 No.2
‘캐리’는 운전에 어려움을 느끼는 초보 운전자와 장롱면허자의 안전운전을 위해 고안된 어플리케이션이다. ‘캐리’ 어플과 차량용 인공지능 스피커를 통해서 보다 안전하고, 심리적으로 안정된 상황에서 운전을 할 수 있도록 돕는다. 또한, 본 기능을 공유-렌터카 업체와 연동함으로써, 교통사고 발생 빈도가 상대적으로 높은 초보 운전자들에게 합리적인 가격으로 운전 교습을 제공하고, 심리적 안정감을 증진시키는 것을 목표로 한다. 본 논문에서는 ‘캐리" 어플리케이션의 프로토타입을 디자인 하는 과정을 담았으며, 그 과정에서 이루어진 설문조사와 사용성 평가의 결과를 중심으로 기술하였다. 각 평가는 "캐리"가 사용자들의 니즈를 정화하게 충족시키고 있는지, 어플의 디자인이 사용자에게 직관적으로 이용되고 있는지에 대해서 알아보기 위해 진행되었다. 평가는 실제 주행 환경이 아닌 테이블 테스트로 진행되었으며, 현재는 모듈 완성 이후 테스트 차량을 통한 사용자 평가와 AI Agent Device 베타 버전 평가를 진행중이다.
롤투롤 나노임프린팅 및 금속 경사증착 기반 대면적 유연 기판 상 3D LSPR 구조의 연속적 제작 및 투명센서 소자 응용
위정섭(Jung-Sub Wi),오동교(Dong Kyo Oh),이성호(Sung Ho Lee),이승조(Seungjo Lee),이규태(Kyu-Tae Lee),김정대(Jeong Dae Kim),이재혁(Jae Hyuk Lee),안주현(Ju Hyun Ahn),이원석(Won Seok Lee),지강민(Kang Min Jee),박인규(Inkyu Park),곽문규(Moon 한국기계가공학회 2017 한국기계가공학회 춘추계학술대회 논문집 Vol.2017 No.4
Optical and structural properties of Ag:Ta2O5 nanocomposites.
Lee, Geon Joon,Kim, Hee Soo,Yoon, Chong Seung,Kim, Jihye,Park, Inkyu,Lee, Young Pak American Scientific Publishers 2013 Journal of Nanoscience and Nanotechnology Vol.13 No.5
<P>In this paper, we investigated the optical and structural properties of the Ag:Ta2O5 nanocomposites. The nanocomposite films were prepared by magnetron co-sputtering of Ta2O5 with Ag chips. The transmission electron microscopy images clearly revealed that Ag nanoparticles were successfully produced by post-thermal annealing of the deposited films. The reflection spectra exhibited the surface plasmon resonance behavior. The photoluminescence (PL) spectra indicated that the Ag:Ta2O5 nanocomposites exhibited larger PL intensity than pure Ag or pure Ta2O5. The PL enhancement is thought to be due to the surface plasmon resonance of Ag nanoparticles. From the spatial intensity distributions that were obtained by solving Maxwell equations using the three-dimensional, finite-difference time-domain method, we found that there was strong confinement of optical field near the Ag nanoparticle. This optical confinement effect makes it possible to exhibit the enhanced PL.</P>
Optical properties of Ag hemisphere-like nanoparticles.
Lee, Geon Joon,Kim, Jin Joo,Hwangbo, Chang Kwon,Kim, Jihye,Park, Inkyu,Lee, Young Pak American Scientific Publishers 2013 Journal of nanoscience and nanotechnology Vol.13 No.1
<P>We investigated the optical properties of Ag hemisphere-like nanoparticles. The nanoparticles were prepared by using magnetron sputtering and post-thermal annealing. The scanning-electron microscopy images reveal that hemisphere-like nanoparticles were successfully produced. The transmission spectra exhibit the surface plasmon resonance effect. From the spatial intensity distributions obtained by solving Maxwell equations using the three-dimensional, finite-difference time-domain method, we found that there is strong confinement of the optical field near the nanoparticle. This optical confinement makes it easy to exhibit the plasmon resonance effect.</P>
Design and Optimization of a Pure Refrigerant Cycle for Natural Gas Liquefaction with Subcooling
Lee, Inkyu,Tak, Kyungjae,Kwon, Hweeung,Kim, Junghwan,Ko, Daeho,Moon, Il American Chemical Society 2014 INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH - Vol.53 No.25
<P>Natural gas liquefaction is an energy-intensive process in which energy reduction is a main concern. This research focused on minimizing the energy of the pure refrigeration cycle in natural gas liquefaction by improving the subcooling system. To minimize energy consumption, a pure refrigeration cycle with a subcooling system was simulated, and the result was thermodynamically analyzed. The thermodynamic analysis identified an opportunity to reduce the energy consumption, and a new design was proposed for the subcooling system. In addition, the proposed design was deterministically optimized to find the optimal compressing ratio, temperature, pressure, and flow rate. As the result, the optimal operating conditions were determined, and the energy consumption was reduced by 17.74%.</P>
Dynamic Behaviors of Skewed Bridge with PSC Girders Wrapped by Steel Plate
Inkyu Rhee,Lee-Hyeon Kim,Hyun-Min Kim,Joo-Beom Lee 한국철도학회 2010 International Journal of Railway Vol.3 No.3
This paper attempts to extract the fundamental dynamic properties, i.e. natural frequencies, damping ratios of the 48 mlong, 20° skewed real bridge with PSC girders wrapped by a steel plate. The forced vibration test is achieved by mounting 12 ㎐-capacity of artificial oscillator on the top of bridge deck. The acceleration histories at the 9 different locations of deck surface are recorded using accelerometors. From this full-scaled vibration test, the two possible resonance frequencies are detected at 2.38 ㎐ and 9.86 ㎐ of the skewed bridge deck by sweeping a beating frequency up to 12 ㎐. The absolute acceleration/energy exhibits much higher in case of higher-order twist mode, 9.86 ㎐ due to the skewness of bridge deck which leads asymmetric situation of vibration. This implies the test bridge is under swinging vertically in fundamental flexure mode while the bridge is also flickered up and down laterally at 9.86 ㎐. This is probably by asymmetric geometry of skewed deck. A detailed 3D beam-shell bridge models using finite elements are performed under a series of train loads for modal dynamic analyses. Thereby, the effect of skewness is examined to clarify the lateral flickering caused by asymmetrical geometry of bridge deck.