Frequency Tuning of Nanowire Resonator Using Electrostatic Spring Effect

Jihan Kwon,Jungwook Choi,Kwanoh Kim,Jaesam Sim,Jinho Kim,Jongbaeg Kim IEEE 2009 IEEE transactions on magnetics Vol.45 No.5

<P>We have demonstrated resonant frequency tuning of nanowire resonator operated in both atmospheric circumstance and high vacuum environment using electrostatic spring-softening effect. The nanowire is synthesized at any desired position by focused ion beam-chemical vapor deposition (FIB-CVD) on the sidewall of batch-processed micro electrode. The resonant frequency in a vacuum chamber of 2.5 x 10(-4) Pa is 1.564 MHz under the driving voltage of 5 V-DC +/- 5 V-AC. When 30 VDC tuning bias is applied on tuning electrode, the resonant frequency is reduced to 1.529 MHz due to the electrostatic spring-softening effect while the driving bias is maintained. For the tuning bias of 60 V, the resonant frequency at atmospheric pressure has been tuned from 1.49 MHz to 1.41 MHz under the driving voltage of 30V(DC) +/- 10V(AC). The method demonstrated both in high vacuum and at atmospheric pressure is a simple and effective way to tune the deviated resonant frequency of nanowire resonator to the desired value without the alteration of the structure or post fabrication process.</P>

Time-to-failure of Compressively Loaded Composite Structures Exposed to Fire

Kim, Jihan,Lee, Sung W.,Kwon, Soonwook Sage Publications 2007 Journal of composite materials Vol.41 No.22

<P>A combined thermal-structural analysis methodology based on finite element modeling is developed for the analysis of composite structures exposed to high temperatures due to fire. A simplified heat transfer model proposed by Lattimer is adopted for the thermal response model to determine temperature distributions in composite structures with and without insulation while an assumed strain solid shell finite element formulation is adopted for the structural response model with a material model that takes into account the effects of temperature on modulus and charring. Numerical analyses are carried out to determine the time-to-failure via the global buckling of simply supported and clamped wide columns of an E-glass/ vinylester woven composite material with and without insulation subjected to heat flux and compression. Large deflection non-linear analyses are also conducted to determine the displacement of the columns as the temperature changes. The beneficial effect of insulation on time-to-failure is demonstrated via numerical calculations. Sensitivity analyses are carried out to examine the effect of variation in the glass transition temperature on the time-to-failure of the composite columns.</P>

아파트 리모델링 수직증축 허용에 대응한 서울시 정책방향

권영덕(YoungDuk Kwon),고준호(JunHo Ko),강지한(JiHan Kang) 서울연구원 2014 서울연구원 정책과제연구보고서 Vol.- No.-

The purpose of the study is to identify the major impacts on housing supply and transportation according to the alleviation of floor limitation in apartment remodeling and to present improvement of current policies. Apartment remodeling policy allowing to the alleviating height control(vertical extension) is to allow constructing two to three floors higher than the existing building, increase in the 15 percent of households, and selling out the increasing parts of the apartments. The method is to review impacts on possible infringement of the right of daylight sunshine amount and problems of FAR management according to floor number increase. And, it is to identify parking difficulties and transportation impacts according to the increase in the number of households and cars. It is, then, to identify securing feasibility according to parcel out of the extra apartments. Finally, it is to identify possible number of housing supply reviewing the physical condition of the apartment sites. Its impacts are identified on the first building with 90 percent and more, second and third buildings with 50 percent and more in terms of the infringement of day light amount from remodeling. Thus, it is difficult of the apartments with 3 buildings or less to do vertical extension remodeling. In order to do vertical extension remodeling for the apartments in a district plan with height control, there should be a rest of 15 percent more below legal FAR in the existing sites. Buildings needed structure reinforcement are apartment sites with earthquake-proof design standard, 16 percent and apartment sites falling short of current earthquake-proof design standard, 71 percent respectively. The possible numbers of housing supply, satisfying physical condition and project possibilities are currently 40,964 units and 55,625 units for the future in year 2024 standards. As a result of the transportation environment effect in Seoul due to the increase in the number of vehicles on the roads, it is shown that gross trip distance increases between 0.14 and 2.16% currently and gross trip time, 0.25~3-83% respectively while gross trip distance increases 0.17~3.83% and gross trip time, 0.30~6.31% in 2024. It becomes different in terms of transport effects on road by the increase in household sizes and choice of transport modes. However, the increase in the use of public transit can solve this kind of transport problems. Policy directions are focused on securing citizen safety, solution to the inconvenience of the life, sustainable development, and lengthening the longevity of housing. And policies are improved so as to shift from profitability, to manage considering a life cycle of apartments, to differentiate public supports about vertical extension and repair-type remodeling, and to maintain institutional amendments. Improvements related to the right of daylight sunshine amount are needed to readjust rationally the control of the right and to minimize unqualified buildings due to the applying of the new standard. Parking space is sufficiently secured toward increase in the number of the households, however problems related to the traffic volume in the sites can be solved by inducing public transit usage. Besides, these are recommended to pursue demonstration projects by the public in order for low-cost type remodeling to settle down, to encourage cost savings applying various public supports, to reinforce administrative organization.

다방향 진동에 대응 가능한 정전용량형 2 축 에너지 포집기의 개발

정봉원(Bongwon Jeong),권지한(Jihan Kwon),이재익(Jae-Ik Lee),백대현(Dae-Hyun Baek),김종백(Jongbaeg Kim) 한국정밀공학회 2008 한국정밀공학회 학술발표대회 논문집 Vol.2008 No.11월

Influence of graphene thickness and grain boundaries on MoS₂ wrinkle nanostructures

Kim, Seon Joon,Kwon, Ohmin,Kim, Dae Woo,Kim, Jihan,Jung, Hee-Tae The Royal Society of Chemistry 2018 Physical chemistry chemical physics Vol.20 No.25

<P>Controlling wrinkle nanostructures of two-dimensional materials is critical for optimizing the material properties and device performance. In this study, we demonstrated the <I>in situ</I> synthesis of large-area MoS2 wrinkles on graphene by chemical-vapor-deposition-assisted sulfurization, and investigated the influence of graphene thickness and grain structures on the feature dimensions of MoS2 wrinkle nanostructures. The height, width, and overall surface roughness of the MoS2 wrinkles diminish as the number of graphene layers increases, which was further verified by determining the binding energy of graphene layers by density functional theory calculations. Furthermore, the feature dimensions of MoS2 wrinkle nanostructures were also influenced by graphene domain boundaries because of the difference in graphene nucleation density. This may be attributed to the influence of the mechanical properties of graphene substrates on the overall feature dimensions of MoS2 wrinkles, which are directly correlated with the interfacial adhesion energy. We believe that our findings may contribute toward the controllable synthesis of MoS2 wrinkle nanostructures and other two-dimensional materials used for high-performance devices.</P>

오픈소스를 활용한 한국어 퀄리티 개선 평가 지표 정의, AI 모델 개발 및 적용

최지원(Ji-Won Choi),권희정(Heejeong Kwon),백도희(Paik Dohee),신지한(Shin JiHan),최영락(Yeongrak Choi) 한국정보기술학회 2023 Proceedings of KIIT Conference Vol.2023 No.6

Molybdenum carbide chemical sensors with ultrahigh signal-to-noise ratios and ambient stability

Cho, Soo-Yeon,Kim, Ju Ye,Kwon, Ohmin,Kim, Jihan,Jung, Hee-Tae The Royal Society of Chemistry 2018 Journal of Materials Chemistry A Vol.6 No.46

<P>Herein, we present a demonstration of the usability of the chemical sensing properties of transition metal carbides (TMCs) as gas sensing channels. Two phases of nanostructured molybdenum carbide (α-MoC1−x and β-Mo2C) with high porosities were perfectly synthesized by a temperature-programmed reduction (TPR) method, and they showed distinct metallic characteristics due to different density of states (DOS) localization status. The molybdenum carbide sensors showed novel gas sensing characteristics which have not been shown by previous typical sensing materials: predominantly, an unprecedentedly high signal-to-noise ratio (SNR) with the ability to detect the ppb levels of NH3 and NO2 was achieved, which is attributed to a combination of high electrical conductivity and superior catalytic properties. In addition to high sensitivity, unlike previous channel materials, the molybdenum carbide sensors showed very high ambient stability. The electrical conductivity and sensing performance are well preserved for half-year ambient exposure without any oxidation or degradation of channel materials, due to the good corrosion resistance and low chemical reactivity of molybdenum carbides. In addition, a versatile gas sensing response is observed according to the crystal phase of molybdenum carbides due to the distinct DOS of α-MoC1−x and β-Mo2C. We believe that this observation of new chemical sensing materials can shed light on the superior potential of TMCs for highly sensitive and stable low-power operating internet-of-things (IoT) sensors. In addition, owing to their ultra-high chemical stability and high melting temperature, TMCs can be utilized as channel materials for sensors in harsh operating conditions.</P>

Materials Genome in Action: Identifying the Performance Limits of Physical Hydrogen Storage

Thornton, Aaron W.,Simon, Cory M.,Kim, Jihan,Kwon, Ohmin,Deeg, Kathryn S.,Konstas, Kristina,Pas, Steven J.,Hill, Matthew R.,Winkler, David A.,Haranczyk, Maciej,Smit, Berend American Chemical Society 2017 Chemistry of materials Vol.29 No.7

<P/><P>The Materials Genome is in action: the molecular codes for millions of materials have been sequenced, predictive models have been developed, and now the challenge of hydrogen storage is targeted. Renewably generated hydrogen is an attractive transportation fuel with zero carbon emissions, but its storage remains a significant challenge. Nanoporous adsorbents have shown promising physical adsorption of hydrogen approaching targeted capacities, but the scope of studies has remained limited. Here the Nanoporous Materials Genome, containing over 850 000 materials, is analyzed with a variety of computational tools to explore the limits of hydrogen storage. Optimal features that maximize net capacity at room temperature include pore sizes of around 6 Å and void fractions of 0.1, while at cryogenic temperatures pore sizes of 10 Å and void fractions of 0.5 are optimal. Our top candidates are found to be commercially attractive as “cryo-adsorbents”, with promising storage capacities at 77 K and 100 bar with 30% enhancement to 40 g/L, a promising alternative to liquefaction at 20 K and compression at 700 bar.</P>

Alterations of ATP-sensitive K+ channels in human umbilical arterial smooth muscle during gestational diabetes mellitus

Li, Hongliang,Shin, Sung Eun,Seo, Mi Seon,An, Jin Ryeol,Ha, Kwon-Soo,Han, Eun-Taek,Hong, Seok-Ho,Kim, Jeeyoung,Yim, Mi-Jin,Lee, Jeong Min,An, Tae Gyu,Jeon, Jihan,Lee, Se Jin,Na, Sung Hun,Park, Won Sun Springer-Verlag 2018 Pfl ugers Arch Vol.470 No.9

Metallic Ti₃C₂T_<i>x</i> MXene Gas Sensors with Ultrahigh Signal-to-Noise Ratio

Kim, Seon Joon,Koh, Hyeong-Jun,Ren, Chang E.,Kwon, Ohmin,Maleski, Kathleen,Cho, Soo-Yeon,Anasori, Babak,Kim, Choong-Ki,Choi, Yang-Kyu,Kim, Jihan,Gogotsi, Yury,Jung, Hee-Tae American Chemical Society 2018 ACS NANO Vol.12 No.2

<P>Achieving high sensitivity in solid-state gas sensors can allow the precise detection of chemical agents. In particular, detection of volatile organic compounds (VOCs) at the parts per billion (ppb) level is critical for the early diagnosis of diseases. To obtain high sensitivity, two requirements need to be simultaneously satisfied: (i) low electrical noise and (ii) strong signal, which existing sensor materials cannot meet. Here, we demonstrate that 2D metal carbide MXenes, which possess high metallic conductivity for low noise and a fully functionalized surface for a strong signal, greatly outperform the sensitivity of conventional semiconductor channel materials. Ti<SUB>3</SUB>C<SUB>2</SUB>T<SUB><I>x</I></SUB> MXene gas sensors exhibited a very low limit of detection of 50–100 ppb for VOC gases at room temperature. Also, the extremely low noise led to a signal-to-noise ratio 2 orders of magnitude higher than that of other 2D materials, surpassing the best sensors known. Our results provide insight in utilizing highly functionalized metallic sensing channels for developing highly sensitive sensors.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2018/ancac3.2018.12.issue-2/acsnano.7b07460/production/images/medium/nn-2017-07460z_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn7b07460'>ACS Electronic Supporting Info</A></P>