Velocity Selective Polarization Spectroscopy for Modulation-Free Dispersion Signals at Detuned Frequencies

Yu, Hoon,Kim, Seung Jin,Kim, Jung Bog Hindawi Limited 2014 Journal of spectroscopy Vol.2014 No.-

<P>We present a simple technique to obtain modulation-free locking signals at the detuned frequency from an atom transition between hyperfine structures. Polarization spectroscopy allows us to obtain the dispersion signals that are suitable for frequency locking. Velocity selective optical pumping using another laser beam also allows us to obtain signals at the detuned frequency and to shift crossover signal away. By combining these two techniques, we were able to obtain the velocity selective birefringence signal only at the principle transition in an Rb vapor cell and compare the birefringence signal with the theoretical spectrum predicted by using Nakayama’s model.</P>

Toward atom interferometer gyroscope built on an atom chip

Yu Hoon,Kim Seung Jin,Kim Jung Bog 한국물리학회 2023 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.82 No.9

This is a review about the progress of an atom interferometer in a confned trap as a gyroscope at Korea National University of Education. Our atom interferometer is based on the wave nature of matter. We cooled down neutral 87Rb gas below the critical temperature where the atomic ensemble follows Bose–Einstein distribution instead of Boltzman one, called BEC (Bose Einstein Condensation). At this temperature, atoms behave like wave and the amplitude of it is high enough to detect since most atoms occupy the same quantum state and phase. We produce BEC in a magnetic harmonic trap which is generated by an atom chip and bias magnetic feld. We also develop the process of splitting and recombining BEC in a circular waveguide. By combining splitting and recombination, we suggested a way to build matter wave Sagnac interferometer in a spatially confned trap. Our atomic Sagnac interferometer is aimed at miniaturizing and fast generating of BEC systems. In this article we introduce an experimental process and how to adopt an optimal control algorithm to build a Sagnac interferometer for an atomic matter wave gyroscope.

FACULTY ARTICLES ; Performance Budgeting in Korea

Yu Hoon 서울대학교 한국행정연구소 1970 行政論叢 Vol.8 No.2

Effects on nano zero-valent iron reactivity of interactions between hardness, alkalinity, and natural organic matter in reverse osmosis concentrate

Hwang, Yuhoon,Shin, Hang-Sik Elsevier 2013 Journal of environmental sciences Vol.25 No.11

<P>Nanoscale zero-valent iron (NZVI) is considered to have potential to reduce nitrate in the concentrate generated by high pressure membrane processes aimed at water reuse. However, it is necessary to verify the effect of the matrix components in the concentrates on NZVI reactivity. In this study, the influence of hardness, alkalinity, and organic matter on NZVI reactivity was evaluated by the response surface method (RSM). Hardness (Ca2+) had a positive effect on NZVI reactivity by accelerating iron corrosion. In contrast, alkalinity (bicarbonate; HCO-3) and organic matter (humic acid; HA) had negative effects on NZVI reactivity due to morphological change to carbonate green rust, and to competitive adsorption of HA, respectively. The validity of the statistical prediction model derived from RSM was confirmed by an additional confirmation experiment, and the experimental result was within the 95% confidential interval. Therefore, it can be indicated that the RSM model produced results that were statistically significant.</P>

나노 영가철 환원 반응성의 정량 분석을 위한 수정된 인도페놀법 적용

황유훈(Yuhoon Hwang),이원태(Wontae Lee),Henrik R. Andersen 대한환경공학회 2016 대한환경공학회지 Vol.38 No.12

나노 기술에 대한 관심이 증가함에 따라 다양한 종류의 나노 물질이 환경 정화 분야에서 활발히 연구되고 있다. 이에 따라 새롭게 개발된 나노 물질의 성능을 쉽고 신속하게 측정할 수 있는 분석법에 대한 요구가 증가하고 있다. 본 연구에서는 토양/지하수 정화 분야에서 활발히 사용되는 나노 영가철의 환원 반응성을 쉽고 신속하게 측정할 수 있는 방법으로써 수정된 인도페놀법을 제시하였다. 인도페놀법에서 한계반응물로 작용하던 암모늄과 과량으로 존재하던 페놀을 치환하여 사용함으로써 페놀류에 대한 정량 분석이 가능하도록 수정하였다. 대상으로 한 나노 영가철에 의한 환원 반응은 4-클로로페놀의 페놀로의 환원과 나이트로벤젠의 아닐린으로의 환원이었으며, 수정된 인도페놀법은 반응생성물인 페놀과 아닐린에 대하여 선택성을 나타내 분석 방법으로 사용이 가능함을 확인하였다. 민감도 향상을 위하여 발색 시약의 농도 및 반응 시간, 시료의 전처리 등의 영향에 대하여 평가하였다. 실제 시료를 대상으로 시험하였을 때, 용존 철 이온에 의한 저해 영향을 확인하여 탄산나트륨 용액 주입의 전처리를 이용하여 해결하였다. 최종적으로 개발된 분석 방법을 이용하여 나노 영가철 및 이중금속 나노영가철의 환원 반응성을 측정하였으며, 결과적으로 환원 반응 속도의 차이뿐 아니라 환원 기작의 차이도 구분할 수 있는 가능성을 보여 주어 나노 영가철의 환원과 관련된 연구 분야에서 유용하게 사용될 수 있을 것으로 사료된다. Nanoscale zero-valent iron (nZVI) has been effectively applied for environmental remediation due to its ability to reduce various toxic compounds. However, quantification of nZVI reactivity has not yet been standardized. Here, we adapted colorimetric assays for determining reductive activity of nZVIs. A modified indophenol method was suggested to determine reducing activity of nZVI. The method was originally developed to determine aqueous ammonia concentration, but it was further modified to quantify phenol and aniline. The assay focused on analysis of reduction products rather than its mother compounds, which gave more accurate quantification of reductive activity. The suggested color assay showed superior selectivity toward reduction products, phenol or aniline, in the presence of mother compounds, 4-chlorophenol or nitrobenzene. Reaction conditions, such as reagent concentration and reaction time, were optimized to maximize sensitivity. Additionally, pretreatment step using Na₂CO₃ was suggested to eliminate the interference of residual iron ions. Monometallic nZVI and bimetallic Ni/Fe were investigated with the reaction. The substrates showed graduated reactivity, and thus, reduction potency and kinetics of different materials and reaction mechanism was distinguished. The colorimetric assay based on modified indophenol reaction can be promises to be a useful and simple tool in various nZVI related research topics.

세라믹 여재를 활용한 상향류식 여과형 비점오염저감시설의 최적 운전 및 역세척 조건

황유훈(Yuhoon Hwang),서영교(Younggyo Seo),김효원(Hyowon Kim),노건완(Kunwan Roh),신현상(Hyunsang Shin),김도군(Dogun Kim) 대한환경공학회 2017 대한환경공학회지 Vol.39 No.8

도로변 등에 여과형 강우유출수 처리시설이 많이 이용되고 있으나, 유지관리의 최소화, 성능의 검증 및 최적 조건의 수립이 선행되어야 한다. 본 연구에서는 강도가 우수하고 성형이 용이한 세라믹 여재를 사용하고, 하단 지지부와 상단의 여과조로 이루어진 상향류식 여과 시스템을 구성하고, SS 제거능과 역세척 조건을 검토하여, 최적 운전 조건을 설정하였다. 여과 선속도 20-40 m/h 조건에서 운전하였을 때, 총 고형물 부하 30 kg/m² 에 이르는 조건에서도 최대 수두 손실 상승이 3 cm 내외이었으며, SS 처리 효율이 96% 이상으로, 안정적인 운전이 가능하였다. 운전 중의 손실수두와 여재층 공극률은 급수 모델에 의해 모사가 가능하였다. 특히, 하단 지지부에서 일정 입도 이상의 SS가 상당량 제거되어, 여과조에 부하를 감소시킬 수 있음을 확인하였다. 최적의 역세척 조건을 설정하기 위하여 공기 및 수세척의 시간과 유량, 그리고 정체수 배출 공정의 유무에 따른 영향을 확인하였으며, 실험한 모든 조건에서 만족할 만한 손실수두의 회복을 달성할 수 있었다. 다만, 역세척 직후 SS의 배출을 최소화하기 위해서는 공기세척과 수세척 공정 사이에 정체수 배출 공정의 도입이 효과적인 것으로 파악되었다. 본 연구에서 설정한 역세척 조건을 적용하였을 때, SS 부하 400-450 kg/m² 의 여재층이 성공적으로 세척될 수 있어, 장기운전이 충분히 가능할 것으로 판단된다. Stormwater filtration is widely used for the urban runoff treatment. However, intensive maintenance and lack of information about the performance have resulted in an increased need of proper evaluation. In this study, the performance of an upflow stormwater runoff filtration system, consisting of a supporting unit and a filtration unit filled with a ceramic media, was investigated. The maximum head loss increase was about 3 cm under the suspended solid (SS) load of 30 kg/m² and the SS removal was more than 96%, when the filtration velocity was 20-40 m/h. The head loss and the porosity of the media can successfully be described by a power model. It was confirmed that the a significant amount of SS can effectively be removed at supporting unit, minimizing SS load to the filter media bed. Several backwashing strategies have been tested to establish the optimum condition. It was found that the stagnant water discharge is important to minimize the SS release immediately after backwashing. Also, the filter bed loaded with 400-450 kg/m² SS can almost completely be washed to reduce the head loss to the that of empty bed. The results in this study indicate that the upflow ceramic media filter is an excellent alternative to stormwater treatment, with high SS removal and long lifespan.

Enhanced hydrogen fermentation by zero valent iron addition

Hwang, Yuhoon,Sivagurunathan, Periyasamy,Lee, Mo-Kwon,Yun, Yeo-Myeong,Song, Young-Chae,Kim, Dong-Hoon Elsevier 2019 International journal of hydrogen energy Vol.44 No.6

<P><B>Abstract</B></P> <P>In this study, zero valent iron (ZVI) was applied to enhance hydrogen fermentation (H<SUB>2</SUB>). Glucose was used as a substrate at various concentrations of 5–40 g COD/L, and ZVI concentration was adjusted at 0–10 g/L. Without ZVI addition, H<SUB>2</SUB> yield decreased as substrate concentration increased, due to organic acids accumulation as substrate concentration increased. At low substrate concentration of 5 g COD/L, there was a slight increase of H<SUB>2</SUB> yield from 1.4 to 1.5 mol H<SUB>2</SUB>/mol glucose added by ZVI addition. However, the increment was substantial at higher substrate range. For example, H<SUB>2</SUB> yield increased from 0.9 to 1.2–1.5 mol H<SUB>2</SUB>/mol hexoseadded by ZVI addition at 20 g COD/L. The results indicated that ZVI may create a more favorable environment for anaerobic microbial acidogenesis with providing buffering effect to prevent pH drop due to produced hydroxyl ions as it dissolved. These changes of environmental conditions also brought differences on organic acids profile and microbial community, and those may affect to overall H<SUB>2</SUB> fermentation performances.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Investigate the effect of ZVI on the dark fermentative hydrogen production. </LI> <LI> H<SUB>2</SUB> yield and production rate were increased up to 54% and 72%, respectively. </LI> <LI> pH decrease was well prevented by buffering effect of ZVI. </LI> <LI> Organic acid production was significantly enhanced with favorable composition. </LI> </UL> </P>

단일공 주입-추출 실험을 이용한 지하수 내 질산성질소의 생물학적 원위치 정화공법 적용가능성 평가

염여훈 ( Yuhoon Yeum ),한경진 ( Kyungjin Han ),윤종현 ( Jonghyeon Yoon ),박선화 ( Sunhwa Park ),김태승 ( Taeseung Kim ),권수열 ( Sooyoul Kwon ),김영 ( Young Kim ) 한국물환경학회(구 한국수질보전학회) 2016 한국물환경학회·대한상하수도학회 공동 춘계학술발표회 Vol.2016 No.-

영가철이 고정된 입상활성탄 제조를 위한 최적 합성조건 도출

황유훈(Yuhoon Hwang),Paul D. Mines,이원태(Wontae Lee),Henrik R. Andersen 대한환경공학회 2016 대한환경공학회지 Vol.38 No.9

나노 영가철은 산화환원기작을 통하여 염소계 유기화합물과 같은 물질을 효과적으로 처리할 수 있다고 알려져 있지만, 작은 사이즈로 인하여 회수가 어려운 단점으로 인하여 실제 수처리 공정에서는 유출 등의 우려로 널리 적용되지 못하였다. 이와 같은 한계를 극복하기 위하여 활성탄과 같은 담체에 고정화 하여 사용하는 연구가 활발히 진행되었다. 본 연구에서는 활성탄에 영가철의 고정화 시 대표적으로 사용되는 고온 및 상온의 두 가지 경로에 대해 평가하였으며, 결과를 바탕으로 최적의 합성 조건을 도출하였다. 효과적인 나노영가철/입상활성탄 복합체를 합성하기 위해서는 높은 철 함량과 더불어 영가철의 분율을 높이는 것이 중요하며, 이를 위해서는 합성 과정에서 형성되는 철 산화물 및 수산화물의 형성을 억제하는 것이 중요한 것으로 나타났다. 또한 영가철의 분율을 높이기 위한 환원 시간 및 중간 건조 과정의 유무 등 합성 조건의 영향을 살펴보았으며, 그 결과 중간 건조 과정 없이 바로 NaBH4를 이용한 환원 조건을 약 2시간 이상 유지하는 것이 최적 조건임을 확인하였다. 합성된 나노영가철/입상활성탄 복합체는 활성탄의 흡착 능력과 영가철의 환원 능력을 동시에 보유함으로써 나이트로벤젠과 같은 환원이 가능한 오염물질의 제거에 효과적으로 나타났다. Nanoscale zero valent iron (nZVI) has been intensively studied for the treatment of a plethora of pollutants through reductive reaction, however, the nano size should be of concern when nZVI is considered for water treatment, due to difficulties in recovery. The loss of nZVI causes not only economical loss, but also potential risk to human health and environment. Thus, the immobilization onto coarse or structured support is essential. In this study, two representative processes for nZVI immobilization on granular activated carbon (GAC) were evaluated, and optimized conditions for synthesizing Fe/GAC composite were suggested. Both total iron content and Fe<SUP>0</SUP> content can be significantly affected by preparation processes, therefore, it was important to avoid oxidation during preparation to achieve higher reduction capacity. Synthesis conditions such as reduction time and existence of intermediate drying step were investigated to improve Fe<SUP>0</SUP> content of Fe/GAC composites. The optimal condition was two hours of NaBH4 reduction without intermediate drying process. The prepared Fe/GAC composite showed synergistic effect of the adsorption capability of the GAC and the degradation capability of the nZVI, which make this composite a very effective material for environmental remediation.

Adsorption of Radioactive Cesium by Immobilizing Prussian Blue on Polypropylene Non-woven Filter

Narges Dehbashi,Yuhoon Hwang 대한환경공학회 2020 대한환경공학회 학술발표논문집 Vol.2020 No.11