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Kim, Jihwan,Kim, Bum-Kyu,Kim, Hong-Seok,Hwang, Ahreum,Kim, Bongsoo,Doh, Yong-Joo American Chemical Society 2017 NANO LETTERS Vol.17 No.11
<P>We report on the fabrication and electrical transport properties of superconducting junctions made of beta-Ag2Se topological insulator (Tl) nanowires in contact with Al superconducting electrodes. The temperature dependence of the critical current indicates that the superconducting junction belongs to a short and diffusive junction regime. As a characteristic feature of the narrow junction, the critical current decreases monotonously with increasing magnetic field. The stochastic distribution of the switching current exhibits the macroscopic quantum tunneling behavior, which is robust up to T = 0.8 K. Our observations indicate that the Tl nanowire-based Josephson junctions can be a promising building block for the development of nanohybrid superconducting quantum bits.</P>
Kim, Tae-Don,Kim, Jong-So,Kim, Jong Heon,Myung, Jihwan,Chae, Hee-Don,Woo, Kyung-Chul,Jang, Sung Key,Koh, Duk-Su,Kim, Kyong-Tai American Society for Microbiology 2005 Molecular and cellular biology Vol.25 No.8
<B>ABSTRACT</B><P>Serotonin <I>N</I>-acetyltransferase (arylalkylamine N-acetyltransferase [AANAT]) is the key enzyme in melatonin synthesis regulated by circadian rhythm. To date, our understanding of the oscillatory mechanism of melatonin has been limited to autoregulatory transcriptional and posttranslational regulations of AANAT mRNA. In this study, we identify three proteins from pineal glands that associate with <I>cis</I>-acting elements within species-specific AANAT 3′ untranslated regions to mediate mRNA degradation. These proteins include heterogeneous nuclear ribonucleoprotein R (hnRNP R), hnRNP Q, and hnRNP L. Their RNA-destabilizing function was determined by RNA interference and overexpression approaches. Expression patterns of these factors in pineal glands display robust circadian rhythm. The enhanced levels detected after midnight correlate with an abrupt decline in AANAT mRNA level. A mathematical model for the AANAT mRNA profile and its experimental evidence with rat pinealocytes indicates that rhythmic AANAT mRNA degradation mediated by hnRNP R, hnRNP Q, and hnRNP L is a key process in the regulation of its circadian oscillation.</P>
Hollow Microtube Resonators via Silicon Self-Assembly toward Subattogram Mass Sensing Applications
Kim, Joohyun,Song, Jungki,Kim, Kwangseok,Kim, Seokbeom,Song, Jihwan,Kim, Namsu,Khan, M. Faheem,Zhang, Linan,Sader, John E.,Park, Keunhan,Kim, Dongchoul,Thundat, Thomas,Lee, Jungchul American Chemical Society 2016 Nano letters Vol.16 No.3
<P>Fluidic resonators with integrated microchannels (hollow resonators) are attractive for mass, density, and volume measurements of single micro/nanoparticles and cells, yet their widespread use is limited by the complexity of their fabrication. Here we report a simple and cost-effective approach for fabricating hollow microtube resonators. A prestructured silicon wafer is annealed at high temperature under a controlled atmosphere to form self-assembled buried cavities. The interiors of these cavities are oxidized to produce thin oxide tubes, following which the surrounding silicon material is selectively etched away to suspend the oxide tubes. This simple three-step process easily produces hollow microtube resonators. We report another innovation in the capping glass wafer where we integrate fluidic access channels and getter materials along with residual gas suction channels. Combined together, only five photolithographic steps and one bonding step are required to fabricate vacuum-packaged hollow microtube resonators that exhibit quality factors as high as similar to 13 000. We take one step further to explore additionally attractive features including the ability to tune the device responsivity, changing the resonator material, and scaling down the, resonator size. The resonator wall thickness of similar to 120 nm and the channel hydraulic diameter of similar to 60 nm are demonstrated solely by conventional microfabrication approaches. The unique characteristics of this new fabrication process facilitate the widespread use of hollow microtube resonators, their translation between diverse research fields, and the production of commercially viable devices.</P>
Jihwan Kim,Ethan Oh,Mincheol Kim,Eui-Sun Kim 제어로봇시스템학회 2021 제어로봇시스템학회 국제학술대회 논문집 Vol.2021 No.10
Cable-driven parallel robot (CDPR) has advantages including a reconfigurable workspace and lightweight actuators. The goal of this study is to develop a three-cable driven planar parallel robot that can be utilized for upper arm exercise toward routine practice. To make a repetitive practice motion on a patient’s desk, we designed and prototyped a robotic system based on the three-cable driven planar parallel robot that can minimize the number of cable and related parts. Forward kinematics is derived with a novel closet set searching method and a model reference adaptive controller is designed for the desired trajectory tracking. The experimental results show that the root mean square error (RMSE) was 2.17 and 2.09 mm for a circle trajectory and 1.33 mm and 3.29 mm for a line trajectory, along with the x- and y-axis. We could confirm that the prototyped three-cable planer CDPR has the possibility to adapt in routine exercise or rehabilitation requiring repetitive motions with easy installation.
Kim, Minjin,Kim, Jihwan,Lee, In-Ho,Han, Woo Hyun,Park, Yun Chang,Kim, Woo Youn,Kim, Bongsoo,Suh, Junho Royal Society of Chemistry 2019 Nanoscale Vol.11 No.12
<P>We report a ternary silver chalcogenide, Ag2Se0.5Te0.5, as a new topological material with improved quantum transport properties. Single-crystalline nanostructures of ternary silver chalcogenides Ag2SexTe1−x are synthesized with a tunable chemical composition <I>via</I> the chemical vapor transport method. Quantum transport studies reveal that Ag2Se0.5Te0.5 nanowires present topological surface states with higher electron mobility and longer mean free path compared to binary Ag-chalcogenides. First-principles calculations also indicate that Ag2Se0.5Te0.5 is a topological insulator, and the observed enhancement in transport properties could imply reduced bulk carrier contribution in the new ternary silver chalcogenide.</P>
안드로이드 단말에서의 상황별 위험도 분석 및 상황별 위험도 기반 지속인증 기법
김지환(Jihwan Kim),김승현(SeungHyun Kim),김수형(Soo-Hyung Kim),이윤호(Younho Lee) 한국정보과학회 2016 정보과학회논문지 Vol.43 No.10
타인의 접근제어를 위해 사용하는 스마트폰 인증은 스마트폰 사용 시 마다 다양한 방법으로 스마트폰 소유자의 여부를 확인한다. 그러나 이러한 빈번한 인증은 사용자들의 불편함을 야기하며, 때로는 인증방법을 사용하지 않게 하는, 궁극적으로 스마트폰 보안의 치명적인 문제로 작용한다. 본 논문에서는 이러한 문제들을 해결하고 사용자들의 보안인증 사용을 촉진하여 보안성을 증대시키기 위한 안드로이드 플랫폼 기반의 지속인증 모델을 제안한다. 제안 모델은 스마트폰의 현 상황위험도를 측정, 그에 맞추어 적절한 인증 수단을 결정, 적용하며, 낮은 위험도 수준일 경우 인증을 수행하지 않아 사용자의 가용성을 높여준다. 상황위험도를 정의하기 위해 설문조사를 이용하였으며, 설문결과를 연령, 위치, 장소, 행동 등으로 세분화하여 분석하였다. 본 연구 결과의 시연을 위해 정의된 상황위험도와 보안인증수단과의 관계를 시각화하여 보여줄 수 있도록 시연프로그램을 구현하였다. To prevent the use of one’s smartphone by another user, the authentication checks the owner in several ways. However, whenever the owner does use his/her smartphone, this authentication requires an unnecessary action, and sometimes he/she finally decides not to use an authentication method. This can cause a fatal problem in the smartphone’s security. We propose a sustainable android platform-based authentication mode to solve this security issue and to facilitate secure authentication. In the proposed model, a smartphone identifies the current situation and then performs the authentication. In order to define the risk of the situation, we conducted a survey and analyzed the survey results by age, location, behavior, etc. Finally, a demonstration program was implemented to show the relationship between risk and security authentication methods.
CFD를 이용한 화염묘사함수 모델링 결과와 1D 열음향 해석의 결합
김지환(Jihwan Kim),김진아(Jinah Kim),김대식(Daesik Kim) 한국추진공학회 2016 한국추진공학회 학술대회논문집 Vol.2016 No.5
희박 예혼합 가스터빈의 연소 불안정 현상을 이해하기 위해서는, 선형 과정에 의하여 얻어지는 고유 주파수 및 초기 성장률뿐만 아니라, 연소기 비선형 특성에 의존하는 한계진폭의 예측이 필요하다. 특히 현재의 연구에서는 비선형 거동에 의한 한계 진폭을 예측하기 위해서 유동 섭동과 열발생의 비율이 주파수와 속도 진폭을 정의할 수 있는 화염묘사함수를 적용하였다. 본 연구에서는 화염묘사함수를 얻기 위하여 CFD 기법이 적용되었으며, 이를 통하여 비선형 열음향 해석으로부터 불안정 한계 진폭을 예측하는데 성공하였다. It is required to predict a limit cycle amplitude controlled by system’s nonlinear behavior as well as an eigenfrequency and initial growth rate of instabilities, in order to fully understand combustion instabilities in a lean premixed gas turbine combustor. Special focus of the current work is placed on the limit cycle amplitude prediction using flame describing function(FDF) where the ratio of a heat release fluctuation to a given flow perturbation is expressed as a function of frequency and amplitude. CFD modeling work is carried out to obtain FDF. Nonlinear thermoacoustic model is successfully developed for predicting the limit cycle amplitude of the combustion instability.