Rate Matching Puncturing Algorithm for Turbo Codes

Youngwoo Yun(윤영우),Kijun Kim(김기준),Youngjo Lee(이영조),Jongyoun Chun(전종연) 한국통신학회 2000 한국통신학회 학술대회 및 강연회 Vol.2000 No.5

Optical Gain in MoS₂ <i>via</i> Coupling with Nanostructured Substrate: Fabry–Perot Interference and Plasmonic Excitation

Jeong, Hye Yun,Kim, Un Jeong,Kim, Hyun,Han, Gang Hee,Lee, Hyangsook,Kim, Min Su,Jin, Youngjo,Ly, Thuc Hue,Lee, Si Young,Roh, Young-Geun,Joo, Won-Jae,Hwang, Sung Woo,Park, Yeonsang,Lee, Young Hee American Chemical Society 2016 ACS NANO Vol.10 No.9

<P>Despite the direct band gap of monolayer transition metal dichalcogenides (TMDs), their optical gain remains limited because of the poor light absorption in atomically thin, layered materials. Most approaches to improve the optical gain of TMDs mainly involve modulation of the active materials or multilayer stacking. Here, we report a method to enhance the optical absorption and emission in MoS2 simply through the design of a nanostructured substrate. The substrate consisted of a dielectric nanofilm spacer (TiO2) and metal film. The overall photoluminescence intensity from monolayer MoS2 on the nanostructured substrate was engineered based on the TiO2 thickness and amplified by Fabry-Perot interference. In addition, the neutral exciton emission was selectively amplified by plasmonic excitations from the local field originating from the surface roughness of the metal film with spacer thicknesses of less than 10 nm. We further demonstrate that the quality factor of the device can also be engineered by selecting a spacer material with a different refractive index.</P>

양파 줄기파쇄 시작기 설계 · 제작 (Ⅰ)

윤영태 ( Youngtae Yun ),김영근 ( Youngkeun Kim ),최일수 ( Ilsoo Choi ),최용 ( Yong Choi ),현창식 ( Changsik Hyun ),남영조 ( Youngjo Nam ),김문택 ( Moontaek Kim ) 한국농업기계학회 2017 한국농업기계학회 학술발표논문집 Vol.22 No.2

양파 재배의 기계화는 논농사용 기계를 공용으로 이용하는 경운·정지, 방제, 휴립피복 작업을 제외하고 기계화가 미흡한 실정으로 경운· 정지 99%, 정식 8%, 방제 98%, 휴립피복 72%, 수확 21%로 정식 및 수확작업에 농업기계가 요구되어지고 있다. 국내 양파 재배는 재배지역과 토성에 따라 밭양파와 논양파로 구분되며 재배양식 및 방법에 큰 차이가 있다. 논양파는 주로 경상도 지역에서 재배하며 수확 시 인력으로 줄기를 절단한 후 비닐을 걷어내고 굴취기를 이용하여 수집하고, 밭양파는 주로 전라도 지역에서 재배하며 굴취기로 양파를 굴취 후 노지건조한 후 인력으로 줄기를 자르면서 수집한다. 따라서 재배형태(논양파, 밭양파)에 따라 서로 다른 농기계가 요구되어지고 있으며, 특히 논양파의 경우 벼 2모작으로 수확시기가 짧아 건조기간 없이 수확(줄기절단·굴취·수집)작업이 단시간에 이루어져야하기 때문에 줄기절단 작업의 기계화가 필요한 실정이다. 본 연구는 양파 줄기절단 작업 기계화를 위하여 트랙터 부착형양파 줄기파쇄 시작기를 설계·제작하였다. 트랙터 부착형 양파 줄기파쇄기는 트랙터 PTO에서의 구동력 전달을 위한 연결 조인트, 동력 전달과 PTO 회전수 변환을 위한 기어박스, 구동축으로 구성된 동력 전달부, 2조의 회전형 절단날, 양파절단 높이 설정 조정부, 높이 제어를 위한 센서부 및 작업기의 원활한 동작과 자체무게 지지를 위한 프레임 등으로 구성하였다. 양파 줄기파쇄기는 기울어진 절단 날의 회전을 이용하여 흡입력을 발생시켜 쓰러진 양파줄기를 일으켜 세우고 이를 절단하며 잘게 파쇄 되도록 설계하였으며, 파쇄된 양파줄기를 회전에 의해 발생한 풍압을 이용하여 양파 두둑의 양쪽 이랑에 분쇄된 상태로 뿌려 부패하면서 자연스럽게 분해되도록 하였다. 또한 절단 높이 제어 센서를 부착하여 양파 두둑의 요철을 감지하고, 이를 이용하여 파쇄기의 바퀴 높이를 조절하도록 하여 두둑의 요철과 무관하게 양파줄기의 잔존길이를 설정한 값으로 절단할 수 있도록 제작하였다. 회전형 절단날은 양파줄기의 깨끗한 절단을 위하여 적정한 회전수 및 칼날 연마각의 관계를 최적화한 상태로 설계하였으며, 줄기절단 높이 조정범위는 20~150 mm 범위로 조절 가능하도록 하였다.

Effects of Experimental Drought on Soil CO2 Efflux in a Larix Kaempferi Stand

Beomjeong Kim,Youngjo Yun,Byoungkoo Choi 강원대학교 산림과학연구소 2018 Journal of Forest Science Vol.34 No.3

Climate models forecast more frequent and a longer period of drought events which may impact forest soil carbon dynamics, thereby altering the soil respiration (SR) rate. We examine the simulated drought effects on soil CO2 effluxes from soil surface partitioning heterotrophic and autotrophic soil respiration sources. Three replicates of drought plots (6 x 6 m) were constructed with the same size of three control plots. We examined the relation between CO2 and soil temperature and soil moisture, each being measured at a soil depth of 15 cm. We also compared which factor affected CO2 efflux more under drought conditions. Total SR, autotrophic respiration (AR) and heterotrophic respiration (HR) were positively correlated with soil temperature (p < 0.05), and the relationships were stronger in roof plots than in control plots. Total SR, AR, and HR were negatively correlated only in roof plots, and the only HR showed a significant correlation (p < 0.05, r = -0.59). Soil respiration rates were more influenced by soil temperature than by soil moisture, and this relationship was more evident under drought conditions.

Effects of Experimental Drought on Soil CO₂ Efflux in a Larix Kaempferi Stand

Kim, Beomjeong,Yun, Youngjo,Choi, Byoungkoo Institute of Forest Science 2018 Journal of Forest Science Vol.34 No.3

Climate models forecast more frequent and a longer period of drought events which may impact forest soil carbon dynamics, thereby altering the soil respiration (SR) rate. We examine the simulated drought effects on soil $CO_2$ effluxes from soil surface partitioning heterotrophic and autotrophic soil respiration sources. Three replicates of drought plots ($6{\times}6m$) were constructed with the same size of three control plots. We examined the relation between $CO_2$ and soil temperature and soil moisture, each being measured at a soil depth of 15 cm. We also compared which factor affected $CO_2$ efflux more under drought conditions. Total SR, autotrophic respiration (AR) and heterotrophic respiration (HR) were positively correlated with soil temperature (p < 0.05), and the relationships were stronger in roof plots than in control plots. Total SR, AR, and HR were negatively correlated only in roof plots, and the only HR showed a significant correlation (p < 0.05, r = -0.59). Soil respiration rates were more influenced by soil temperature than by soil moisture, and this relationship was more evident under drought conditions.

Oxidation Effect in Octahedral Hafnium Disulfide Thin Film

Chae, Sang Hoon,Jin, Youngjo,Kim, Tae Soo,Chung, Dong Seob,Na, Hyunyeong,Nam, Honggi,Kim, Hyun,Perello, David J.,Jeong, Hye Yun,Ly, Thuc Hue,Lee, Young Hee American Chemical Society 2016 ACS NANO Vol.10 No.1

<P>Atomically smooth van der Waals materials are structurally stable in a monolayer and a few layers but are susceptible to oxygen-rich environments. In particular, recently emerging materials such as black phosphorus and perovskite have revealed stronger environmental sensitivity than other two-dimensional layered materials, often obscuring the interesting intrinsic electronic and optical properties. Unleashing the true potential of these materials requires oxidation-free sample preparation that protects thin flakes from air exposure. Here, we fabricated few-layer hafnium disulfide (HfS2) field effect transistors (FETs) using an integrated vacuum cluster system and study their electronic properties and stability under ambient conditions. By performing all the device fabrication and characterization procedure under an oxygen- and moisture-free environment, we found that few-layer AA-stacking HfS2-FETs display excellent field effect responses (I-on/I-off approximate to 10(7)) with reduced hysteresis compared to the FETs prepared under ambient conditions. Oxidation of HfS2 occurs uniformly over the entire area, increasing the film thickness by 250% at a prolonged oxidation time of >120 h, while defects on the surface are the preferential initial oxidation sites. We further demonstrated that the stability of the device in air is significantly improved by passivating FETs with BN in a vacuum cluster.</P>

Role of alkali metal promoter in enhancing lateral growth of monolayer transition metal dichalcogenides

Kim, Hyun,Han, Gang Hee,Yun, Seok Joon,Zhao, Jiong,Keum, Dong Hoon,Jeong, Hye Yun,Ly, Thuc Hue,Jin, Youngjo,Park, Ji-Hoon,Moon, Byoung Hee,Kim, Sung-Wng,Lee, Young Hee IOP 2017 Nanotechnology Vol.28 No.36

<P>Synthesis of monolayer transition metal dichalcogenides (TMDs) via chemical vapor deposition relies on several factors such as precursor, promoter, substrate, and surface treatment of substrate. Among them, the use of promoter is crucial for obtaining uniform and large-area monolayer TMDs. Although promoters have been speculated to enhance adhesion of precursors to the substrate, their precise role in the growth mechanism has rarely been discussed. Here, we report the role of alkali metal promoter in growing monolayer TMDs. The growth occurred via the formation of sodium metal oxides which prevent the evaporation of metal precursor. Furthermore, the silicon oxide substrate helped to decrease the Gibbs free energy by forming sodium silicon oxide compounds. The resulting sodium metal oxide was anchored within such concavities created by corrosion of silicon oxide. Consequently, the wettability of the precursors to silicon oxide was improved, leading to enhance lateral growth of monolayer TMDs.</P>

Junction-Structure-Dependent Schottky Barrier Inhomogeneity and Device Ideality of Monolayer MoS₂ Field-Effect Transistors

Moon, Byoung Hee,Han, Gang Hee,Kim, Hyun,Choi, Homin,Bae, Jung Jun,Kim, Jaesu,Jin, Youngjo,Jeong, Hye Yun,Joo, Min-Kyu,Lee, Young Hee,Lim, Seong Chu American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.12

<P>Although monolayer transition metal dichalcogenides (TMDs) exhibit superior optical and electrical characteristics, their use in digital switching devices is limited by incomplete understanding of the metal contact. Comparative studies of Au top and edge contacts with monolayer MoS2 reveal a temperature-dependent ideality factor and Schottky barrier height (SBH). The latter originates from inhomogeneities in MoS2 caused by defects, charge puddles, and grain boundaries, which cause local variation in the work function at Au MoS2 junctions and thus different activation temperatures for thermionic emission. However, the effect of inhomogeneities due to impurities on the SBH varies with the junction structure. The weak Au MoS2 interaction in the top contact, which yields a higher SBH and ideality factor, is more affected by inhomogeneities than the strong interaction in the edge contact. Observed differences in the SBH and ideality factor in different junction structures clarify how the SBH and inhomogeneities can be controlled in devices containing TMD materials.</P>