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Lee, Yongsu,Lee, Hyeonwoo,Jang, Jaeeun,Lee, Jihee,Kim, Minseo,Lee, Jaehyuk,Kim, Hyunki,Yoo, Seunghyup,Yoo, Hoi-Jun IEEE 2017 IEEE journal on emerging and selected topics in ci Vol.7 No.1
<P>A sticker-type system with hybrid integration of CMOS IC and organic optical sensors is proposed to monitor photoplethysmogram (PPG) signals. To solve problems with the previous solely organic sensor-based works, CMOS IC is implemented in 180 nm technology under 5 V/1.5 V dual power supply. The silver-wire printed planar-fashionable circuit board (P-FCB) is used to connect the CMOS IC with organic sensors. The proposed hybrid system has the five following key features: 1) Power-efficient structure of organic sensor; 2) Integrated analog front-end and digital processor; 3) Degradation compensation scheme; 4) Large parasitic elements optimized design; and 5) Motion artifact rejection scheme. The stickertype PPG monitoring system has mass of only 2g, including the batteries, and consumes only 233 mu W to operate. The PPG signal could be acquired from various body parts (finger, wrist, and neck). The peripheral oxygen saturation level (SpO(2)) extraction results are verified by comparison with a commercial sensor device.</P>
Highly Enhanced Performance of Network Channel Polysilicon Thin-Film Transistors
Lee, Hojoon,Lee, Junyoung,Baek, Sangwon,Jeong, Woong Hee,Lee, Yongsu,Yang, Taehoon,Lee, Jeong-Soo IEEE 2017 IEEE electron device letters Vol.38 No.2
<P>This letter presents the electrical characteristics of newly proposed network-channel low-temperature polysilicon channel (LTPS) thin-film transistors (TFTs). Due to effective reduction of grain boundary traps and enhanced gate controllability, the network-channel TFTs show better subthreshold slope, lower threshold voltage, and higher ON-OFF current ratio, compared with conventional planar devices. The extracted grain boundary trap density and the interface trap density are significantly reduced in the network-channel devices. In addition, the network-channel devices show higher immunity to hot-carrier stressing, which are confirmed from the low-frequency noise characteristics with various stressing time. These results suggest that the network-channel devices are very promising for next-generation LTPS TFT applications.</P>
데스크탑 규모의 간결한 롤투롤 나노임프린팅 기반 나노패턴 연속가공 시스템 개발
이정수(Jeongsoo Lee),이지훈(Jihun Lee),남승범(Seungbum Nam),조성일(Sungil Cho),조용수(Yongsu Jo),고민석(Minseok Go),이승조(Seungjo Lee),오동교(Dong Kyo Oh),김정대(Jeong Dae Kim),이재혁(Jae Hyuk Lee),옥종걸(Jong G. Ok) 한국기계가공학회 2017 한국기계가공학회지 Vol.16 No.1
We have developed a compact desktop-sized nanopatterning system driven by the Roll-to-Roll (R2R) nanoimprinting (NIL) principle. The system realizes the continuous and high-speed stamping of various nanoscale patterns on a large-area flexible substrate without resorting to ponderous and complicated instruments. We first lay out the process principle based on continuous NIL on a UV-curable resin layer using a flexible nanopatterned mold. We then create conceptual and specific designs for the system by focusing on two key processes, imprinting and UV curing, which are performed in a continuous R2R fashion. We build a system with essential components and optimized modules for imprinting, UV curing, and R2R conveying to enable simple but effective nanopatterning within the desktop volume. Finally, we demonstrate several nanopatterning results such as nanolines and nanodots, which are obtained by operating the built desktop R2R NIL system on transparent and flexible substrates. Our system may be further utilized in the scalable fabrication of diverse flexible nanopatterns for many functional applications in optics, photonics, sensors, and energy harvesters.
Kim, Minseo,Jang, Jaeeun,Kim, Hyunki,Lee, Jihee,Lee, Jaehyuck,Lee, Jiwon,Lee, Kyoung-Rog,Kim, Kwantae,Lee, Yongsu,Lee, Kyuho Jason,Yoo, Hoi-Jun IEEE 2017 IEEE journal of solid-state circuits Vol.52 No.11
<P>A wearable electrical impedance tomography (EIT) system is proposed for the portable real-time 3-D lung ventilation monitoring. It consists of two types of SoCs, active electrode (AE)-SoC and Hub-SoC, mounted on wearable belts. The 48-channel AE-SoCs are integrated on flexible printed circuit board belt, and Hub-SoC is integrated in the hub module which performs data gathering and wireless communication between an external imaging device. To get high accuracy under the variation of conductivity, the dual-mode current stimulator provides the optimal frequency for time difference-EIT and frequency difference-EIT with simultaneous 4 k-128 kHz impedance sensing. A wide dynamic range instruments amplifier is proposed to provide 94 dB of wide dynamic range impedance sensing. In addition, the 48-channel AE system with the dedicated communication and calibration is implemented to achieve 1.4-m Omega sensitivity of impedance difference in the in vivo environment. The AE-/Hub-SoCs occupy 3.2 and 1.3 mm2in 65-nm CMOS technology and consume 124 mu W and 1.1 mW with 1.2 V supply, respectively. As a result, EIT images are reconstructed with 90% of accuracy, and up to 10 frames/s real-time 3-D lung images are successfully displayed.</P>
Robustness of model averaging methods for the violation of standard linear regression assumptions
Lee, Yongsu,Song, Juwon The Korean Statistical Society 2021 Communications for statistical applications and me Vol.28 No.2
In a regression analysis, a single best model is usually selected among several candidate models. However, it is often useful to combine several candidate models to achieve better performance, especially, in the prediction viewpoint. Model combining methods such as stacking and Bayesian model averaging (BMA) have been suggested from the perspective of averaging candidate models. When the candidate models include a true model, it is expected that BMA generally gives better performance than stacking. On the other hand, when candidate models do not include the true model, it is known that stacking outperforms BMA. Since stacking and BMA approaches have different properties, it is difficult to determine which method is more appropriate under other situations. In particular, it is not easy to find research papers that compare stacking and BMA when regression model assumptions are violated. Therefore, in the paper, we compare the performance among model averaging methods as well as a single best model in the linear regression analysis when standard linear regression assumptions are violated. Simulations were conducted to compare model averaging methods with the linear regression when data include outliers and data do not include them. We also compared them when data include errors from a non-normal distribution. The model averaging methods were applied to the water pollution data, which have a strong multicollinearity among variables. Simulation studies showed that the stacking method tends to give better performance than BMA or standard linear regression analysis (including the stepwise selection method) in the sense of risks (see (3.1)) or prediction error (see (3.2)) when typical linear regression assumptions are violated.
The Reinforcement Learning based Local Routing Optimization for Ad-hoc Network
Yongsu Lee,Jongchan Woo,Hoi-Jun Yoo 대한전자공학회 2019 Journal of semiconductor technology and science Vol.19 No.1
A reinforcement learning based local routing optimization scheme with two different semiconductor chips – hub IC and node ICs is proposed for the ad-hoc network. The received signal strength indicator (RSSI) in IC generates voltage information for analyzing network quality between each node and collected RSSI data are used for input and reward function of the learning agent. The Qlearning method is utilized for reinforcement learning. The chip fabricated with a 0.18 μm CMOS process, which uses the standard supply voltage of 1.5 V, achieves the lowest power consumption of 274 μW at the supply voltage of 0.8 V. The proposed reinforcement learning based local routing optimization for the ad-hoc network reduce 64 % of total network power consumption compare to the conventional infrastructure based network.
Acoustic monitoring using multi-beam imaging sonar through a set net in the Southern Sea, Korea
Lee, Hyungbeen,Lee, Kyounghoon,Kim, Seonghun,Lee, Donggil,Yang, Yongsu Springer Japan KK 2016 Fisheries Science Vol.82 No.5
<P>This study investigated a method for monitoring fish flux though a set net in the coastal South Sea, Korea, using sideward-looking wide angle multi-beam imaging sonar (blueview). This data set was used to examine the impact of changes in diel variation and current speed from a set net. During nighttime, the influx of fish in the set net was significantly 22 times higher than in daytime. The time when high fish flux was observed corresponded to the time of low current speed during nighttime. In contrast, the fish flux was not affecting current speed during daytime. The study provides implications for understanding fish behavior through use of a set net.</P>