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Large-amplitude flapping of an inverted flag in a uniform steady flow – a vortex-induced vibration
Sader, John E.,Cossé,, Julia,Kim, Daegyoum,Fan, Boyu,Gharib, Morteza Cambridge University Press 2016 Journal of fluid mechanics Vol.793 No.-
<P>The dynamics of a cantilevered elastic sheet, with a uniform steady flow impinging on its clamped end, have been studied widely and provide insight into the stability of flags and biological phenomena. Recent measurements by Kim<I>et al.</I>(<I>J. Fluid Mech.</I>, vol. 736, 2013, R1) show that reversing the sheet’s orientation, with the flow impinging on its free edge, dramatically alters its dynamics. In contrast to the conventional flag, which exhibits (small-amplitude) flutter above a critical flow speed, the inverted flag displays large-amplitude flapping over a finite band of flow speeds. The physical mechanisms giving rise to this flapping phenomenon are currently unknown. In this article, we use a combination of mathematical theory, scaling analysis and measurement to establish that this large-amplitude flapping motion is a vortex-induced vibration. Onset of flapping is shown mathematically to be due to divergence instability, verifying previous speculation based on a two-point measurement. Reducing the sheet’s aspect ratio (height/length) increases the critical flow speed for divergence and ultimately eliminates flapping. The flapping motion is associated with a separated flow – detailed measurements and scaling analysis show that it exhibits the required features of a vortex-induced vibration. Flapping is found to be periodic predominantly, with a transition to chaos as flow speed increases. Cessation of flapping occurs at higher speeds – increased damping reduces the flow speed range where flapping is observed, as required. These findings have implications for leaf motion and other biological processes, such as the dynamics of hair follicles, because they also can present an inverted-flag configuration.</P>
동기전동기의 안정된 운전을 위한 퍼지 부하각 제어 시스템에 관한 연구
이관태,김경엽,이준탁 동아대학교 정보기술연구소 2007 情報技術硏究所論文誌 Vol.14 No.2
The basic construction of a synchronous motor is four components ; a stator, a rotor, bearings, and either a generator(brushless) or a static exciter(brush-type). In case of driving in motor mode, full-out characteristics of synchronous motor occur as a result of instantaneous overload to stable synchronous motor performance. A synchronous motor has performance like a induction motor in first starting period, but does a constant slip afterward. If a DC current applies to a field coil near the synchronous velocity, a synchronizing torque appears to the field coil. However, the lack of synchronizing torque often leads to a load angle instability in full-in. The failure of full-in or the full-out take a fatal influence to a power ratio, and a stability of system. As a load angle of a synchronous motor is controlled with the DC current, it is possible to prevent from the hazardous situation which is referred to previously and drive a synchronous motor stably. In this paper, load angle is extracted with proposed method and as applying fuzzy control technology for u-processor PIC16F874 stable driving of Synchronous Motor is intended.
아세톤-물혼합용매에서 trans-[Co(en)_2Cl_2]^+ 및 trans-[Co(1,3-pn)_2Cl_2]^+ 이온의 가용매 분해 반응에 미치는 압력과 용매조성의 영향
朴裕哲,卞鍾轍,金京美,趙靈濟 慶北大學校 1984 論文集 Vol.38 No.-
The rates of solvolysis of trans-[Co(en)_2CL_2]^+ and trans- [Co(1,3-pn)_2CL_2]^+, in which en and 1,3-pn are ethylenediamine and 1,3-propylenediamine resepectively, have been investigated using conductometric and spectrophotometric methods at various pressures up to 2,000 bar in aceton-water mixture. The activation volumes obtained from the pressure effect on rate constants were small and positive values in both complexes of trans- [Co(en)_2Cl_2]^+ and trans- [Co(1,3-pn)_2CL_2]^+. These results are discussed in terms of dissociative mechanism (S_NI) for the solvolysis of both complexes. The importance of solvent composition on the reaction is further confirmed by application of a free energy cycle. It is concluded from the free energy cycle that the effect of solvation of transition state in the solvolysis of both complexes is more dominant than that of initial state. In addition to that, it is shown that the character of S_NI is further increased with increasing the content of acetone.
아세톤-물혼합용매에서 trans-[Co(en)_2Cl_2]^+ 및 trans-[Co(1,3-pn)_2Cl_2]^+ 이온의 가용매 분해 반응에 미치는 압력과 용매조성의 영향
朴裕哲,卞鍾轍,金京美,趙靈濟 慶北大學校 物理化學硏究所 1985 硏究論文集 Vol.6 No.-
The rates of solvolysis of trans-[Co(en)_2Cl_2]^+ and trans-[Co(1,3-pn)_2Cl_2]^+, in which en and 1,3-pn are ethylenediamine and 1,3-propylenediamine resepectively, have been investigated using conductometric and spectrophotometric methods at various pressures up to 2,000 bar in acetone-water mixture. The activation volumes obtained from the pressure effect on rate constants were small and positive values in both complexes of trans-[Co(en)_2Cl_2]^+ and trans-[Co(1,3-pn)_2Cl_2]^+. These results are discussed in terms of dissociative mechanism (S_NI) for the solvolysis of both complexes. The importance of solvent composition on the reaction is further confirmed by application of a free energy cycle. It is concluded from the free energy cycle that the effect of solvation of transition state in the solvolysis of both complexes is more dominant than that of initial state. In addition to that, it is shown that the character of S_NI is further increased with increasing the content of acetone.
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>
Kim, Johanna Inyang,Yun, Je-Yeon,Park, Heyeon,Park, Suk-Young,Ahn, Youngsheen,Lee, Hansol,Kim, Tae-Kwon,Yoon, Sooran,Lee, Young-Joon,Oh, Sohee,Denninger, John W,Kim, Bung-Nyun,Kim, Jeong-Hyun JMIR Publications 2018 Journal of medical Internet research Vol.20 No.10
<P><B>Background</B></P><P>Videoconferencing-based treatments have shown great potential in increasing engagement and compliance by decreasing the barriers of time and distance. In general, employees tend to experience a lot of stress, but find it difficult to visit a clinic during office hours.</P><P><B>Objective</B></P><P>The purpose of this study was to investigate the effectiveness of a mobile videoconference-based intervention for stress reduction and resilience enhancement in employees.</P><P><B>Methods</B></P><P>In total, 81 participants were randomly allocated to one of the three conditions: mobile videoconferencing, in-person, and self-care; of these, 72 completed the study. All participants underwent assessment via self-reported questionnaires before, immediately after, and 1 month after the intervention. Intervention lasted for 4 weeks and consisted of elements of cognitive behavioral therapy, positive psychology, and meditation. Changes in clinical variables regarding stress and resilience across time were compared between treatment conditions.</P><P><B>Results</B></P><P>There were significant condition × time effects on variables measuring perceived stress, resilience, emotional labor, and sleep, demonstrating significantly differential effects across time according to treatment condition. Moreover, there were significant effects of condition on perceived stress and occupational stress. There were no significant differences in any variable between the mobile videoconferencing and in-person conditions at 1 month after the intervention.</P><P><B>Conclusions</B></P><P>Results indicate that both mobile videoconferencing and in-person interventions were comparably effective in decreasing stress and enhancing resilience. Further studies with a larger sample size and a longer follow-up period are warranted to investigate the long-term effect of mobile videoconferencing interventions.</P><P><B>Trial Registration</B></P><P>ClinicalTrials.gov identifier NCT03256682; https://clinicaltrials.gov/ct2/show/NCT03256682 (Archived by WebCite at http://www.webcitation.org/71W77bwnR)</P>
Unconventional anomalous Hall effect from antiferromagnetic domain walls of Nd2Ir2O7 thin films
Kim, Woo Jin,Gruenewald, John H.,Oh, Taekoo,Cheon, Sangmo,Kim, Bongju,Korneta, Oleksandr B.,Cho, Hwanbeom,Lee, Daesu,Kim, Yoonkoo,Kim, Miyoung,Park, Je-Geun,Yang, Bohm-Jung,Seo, Ambrose,Noh, Tae Won American Physical Society 2018 Physical Review B Vol.98 No.12
AUTO-GUIDING SYSTEM FOR CQUEAN (CAMERA FOR QUASARS IN EARLY UNIVERSE)
Kim, Eun-Bin,Park, Won-Kee,Jeong, Hyeon-Ju,Kim, Jin-Young,Kuehne, John,Kim, Dong-Han,Kim, Han-Geun,Odoms, Peter S.,Chang, Seung-Hyuk,Im, Myung-Shin,Pak, Soo-Jong The Korean Astronomical Society 2011 Journal of The Korean Astronomical Society Vol.44 No.4
To perform imaging observations of optically red objects such as high redshift quasars and brown dwarfs, the Center for the Exploration of the Origin of the Universe (CEOU) recently developed an optical CCD camera, Camera for QUasars in EArly uNiverse (CQUEAN), which is sensitive at 0.7-1.1 ${\mu}m$. To enable observations with long exposures, we develop an auto-guiding system for CQUEAN. This system consists of an off-axis mirror, a baffle, a CCD camera, a motor and a differential decelerator. To increase the number of available guiding stars, we design a rotating mechanism for the off-axis guiding camera. The guiding field can be scanned along the 10 arcmin ring offset from the optical axis of the telescope. Combined with the auto-guiding software of the McDonald Observatory, we confirm that a stable image can be obtained with an exposure time as long as 1200 seconds.
John Kim,Chang-Ryul Jung,Sung-Keun Lee,Sung-Soo Kim,Jin-Gwang Koh,Jae-Hyun Seo,Soo-Lyul Oh,Joon-Seub Cha,Choung-Seok Kim,Pyung-kee Kim 한국멀티미디어학회 2008 한국멀티미디어학회 국제학술대회 Vol.2008 No.-
The purpose of this study is to develop a PML server by using RFID technology and to save and manage information on agro-foods effectively in the distribution environment of Agro-foods(as, agricultural products). In a PML server, static and dynamic information on agro-foods in EPC, which is transmitted from a RFID tag and reader, are recorded and managed in XML schema in real time. The server receives information from RFID middleware, SAVANT, and transfers data to a traceability management application system for agro-foods. The major developments for a PML server consist of an EPC data registry, query processor, data converter, instance data storage on agro-foods, system management tools, and application API, etc. By using the implemented RFID-based PML technology, this study aims to suggest a beneficiary model that can integrate Agro-foods-related information for providing advantages to farmers, distributors, and consumers altogether.