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Experimental Investigation of Flexible hawkmoth-like Wings on the Wing-wake Interaction in Hovering Flight

Journal of Bionic Engineering 2018年第1期15卷 139-153页

作者： YeongGyun Ryu Jo Won Chang Joon Chung dong-ha kim Department of Aerospace Engineering Ryerson University Toronto Ontario M5B 2K3 Canada Department of Aeronautical Science and Flight Operation Korea Aerospace University 76 Hanggongdaehak-ro Deogyang-gu Goyang-si Gyeonggi-do 10540 Republic of Korea Aerodynamics Group Korean Air R&D Center Daejeon Metropolitan City 34054 Republic of Korea

To study wing-wake interaction for various wing flexibilities, force measurements and digital particle image velocimetry were carried out on flapping hawkmoth-like wings in a water tank. Wing thickness was employed as a design variable for the wing flexi- bility distributions. Abrupt flap-down and phase delay in flexible wings influenced the behaviors of the Leading-Edge Vortex （LEV） and Trailing-Edge Vortex （TEV）, generated by the previous stroke. While the rigid wing exhibited a detached LEV at the end of the stroke, wing with specific flexibilities obtained attached LEVs. The attached LEVs induced a relatively rapid flow toward the wing surface as a result of encountering the TEV, and the flow caused a higher lift peak. On the other hand, the wings with larger wing deformations generated distinctive changes in LEV and TEV behaviors. The flap-down helped the TEV form closer to the wing surface, and it thus caused a downwash rather than wing-wake interaction. Furthermore, the most flexible wing had a newly-formed pair of LEVs above the wing during the wing reversal, thereby being not able to generate the wing-wake interaction. These results help to understand the different vortex structures generated by flexible wings during the wing reversal and the corresponding effects of wing-wake interaction.

关键词： hovering flight flexible hawkmoth wings wing-wake interaction Digital Particle Image Velocimetry (DPIV)

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Investigation into charge carrier dynamics in organic light-emitting diodes

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Nano Research Energy 2024年第2期3卷 39-46页

作者： dong-Guang Zheng Hyeon-dong Lee Gyeong Won Lee dong-Soo Shin Jeongwon kim Jong-In Shim Zhiqun Lin Tae-Woo Lee dong ha kim Information Engineering College Hangzhou Dianzi UniversityHangzhou 311305China Department of Materials Science and Engineering Seoul National University1 Gwanak-roGwanak-guSeoul 08826Republic of Korea Department of Photonics and Nanoelectronics Hanyang University ERICA55 Hanyangdeahak-roSangnok-guAnsanGyeonggi 15588Republic of Korea Department of Chemistry and Nanoscience Ewha Womans University52Ewhayeodae-gilSeodaemun-guSeoul 03760Republic of Korea Department of Chemical and Biomolecular Engineering National University of Singapore4 Engineering Drive 4Singapore 117585Singapore School of Chemical and Biological Engineering Institute of Engineering ResearchResearch Institute of Advanced MaterialsSoft FoundrySeoul National University1 Gwanak-roGwanak-guSeoul 08826Republic of Korea Basic Sciences Research Institute(Priority Research Institute) Ewha Womans UniversitySeoul 03760Republic of Korea Nanobio∙Energy Materials Center(National Research Facilities and Equipment Center) Ewha Womans UniversitySeoul 03760Republic of Korea

Organic light-emitting diodes(OLEDs)have demonstrated remarkable advancements in both device lifetime and luminous ***,insufficient operation lifetime due to device degradation remains a major hurdle,especially for brighter *** the degradation mechanisms of OLEDs due to the degradation of functional materials and the formation of defects in device architectures continues to be a significant ***,we evaluate the degradation characteristics by scrutinizing the electrical and optical properties,as well as analyzing the charge carrier dynamics in pristine and aged states of phosphorescent OLEDs(PhOLEDs).We show that degradation mechanisms in PhOLEDs can be elucidated in terms of the ideality factors of current and luminance in pristine and aged device *** consistent shifts in distinct ideality factors across various states points out that the device degradation is attributed to the deterioration of the guest material,***-light-emitting phosphorescent ***,the incongruity in ideality factor changes between the two states indicates that the degradation results from the deterioration of non-light-emitting *** characterization experiments provide further evidence that this degradation is primarily attributed to the deterioration of CBP-host *** thorough understanding of degradation mechanisms established in this study can contribute to realizing the highly reliable PhOLEDs with a long lifetime.

关键词： organic light-emitting diodes ideality factor carrier transport processes degradation mechanism

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Organic-inorganic hybrid Sn-based perovskite photodetectors with high external quantum efficiencies and wide spectral responses from 300 to 1000 nm

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Science China Materials 2019年第6期62卷 790-796页

作者： Yukun Wang Dezhi Yang dongge Ma dong ha kim Tansir Ahamad Saad M. Alshehri Agafbnv Vadim Institute of Polymer Optoelectronic Materials and Devices State Key Laboratory of Luminescent Materials and DevicesSouth China University of Technology Department of Chemistry and Nano Science Ewha Womans University Department of Chemistry College of ScienceKing Saud University Moscow Institute of Physics and Technology Dolgoprudny

Organic-inorganic hybrid perovskites are ideal materials for photodetection owing to their high charge carrier mobility, long charge carrier diffusion length, low dark current density and sharp absorption edge. However, a relatively small band gap(1.6 e V) limits their photonharvesting efficiency in the near-infrared region. In the present work, we demonstrate a hybrid methylamine iodide and Pb-Sn binary perovskite as the light absorption layer in photodetectors. Experimentally, the wavelength of photoresponse onset for the photodetectors can be extended to as great as 1,000 nm when the Sn content of the hybrid perovskite is increased to 30 mol%. In addition, the photodetectors exhibit a photoresponsivity of 0.39 A W^-1, a specific detectivity of 7×10^12 Jones, a fast photoresponse with rise and decay time constants and an external quantum efficiency greater than 50% in the wavelength range of350–900 nm, with a maximum value of about 80% at 550 nm.

关键词： organic-inorganic hybrid perovskite photodetector external quantum efficiency spectral response specific detectivity

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Aligned Ion Conduction Pathway of Polyrotaxane‑Based Electrolyte with Dispersed Hydrophobic Chains for Solid‑State Lithium–Oxygen Batteries

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Nano-Micro Letters 2025年第2期17卷 169-186页

作者： Bitgaram kim Myeong‑Chang Sung Gwang‑Hee Lee Byoungjoon Hwang Sojung Seo Ji‑Hun Seo dong‑Wan kim Department of Materials Science and Engineering Korea University145 Anam‑RoSeongbuk‑GuSeoul 02841Republic of Korea School of Civil Environmental and Architectural EngineeringKorea University145 Anam‑RoSeongbuk‑GuSeoul 02841Republic of Korea Materials Science and Chemical Engineering Center Institute for Advanced Engineering(IAE)Yongin 17180Republic of Korea

A critical challenge hindering the practical application of lithium–oxygen batteries(LOBs)is the inevitable problems associated with liquid electrolytes,such as evaporation and safety *** study addresses these problems by proposing a modified polyrotaxane(mPR)-based solid polymer electrolyte(SPE)design that simultaneously mitigates solvent-related problems and improves ***-SPE exhibits high ion conductivity(2.8×10^(−3)S cm^(−1)at 25℃)through aligned ion conduction pathways and provides electrode protection ability through hydrophobic chain *** this mPR-SPE into solid-state LOBs resulted in stable potentials over 300 *** situ Raman spectroscopy reveals the presence of an LiO_(2)intermediate alongside Li_(2)O_(2)during oxygen *** situ X-ray diffraction confirm the ability of the SPE to hinder the permeation of oxygen and moisture,as demonstrated by the air permeability *** present study suggests that maintaining a low residual solvent while achieving high ionic conductivity is crucial for restricting the sub-reactions of solid-state LOBs.

关键词： Solid polymer electrolyte Lithium-oxygen batteries Polyrotaxane ion conductivity Hydrophobic chain

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A Flexible Smart Healthcare Platform Conjugated with Artificial Epidermis Assembled by Three‑Dimensionally Conductive MOF Network for Gas and Pressure Sensing

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Nano-Micro Letters 2025年第2期17卷 601-620页

作者： Qingqing Zhou Qihang Ding Zixun Geng Chencheng Hu Long Yang Zitong Kan Biao dong Miae Won Hongwei Song Lin Xu Jong Seung kim State Key Laboratory of Integrated Optoelectronics College of Electronic Science and EngineeringJilin UniversityChangchun 130012People’s Republic of China Department of Chemistry Korea UniversitySeoul 02841Republic of Korea TheranoChem Incorporation Seoul 02856Republic of Korea

The rising flexible and intelligent electronics greatly facilitate the noninvasive and timely tracking of physiological information in telemedicine *** building bionic-sensitive moieties is vital for designing efficient electronic skin with advanced cognitive functionalities to pluralistically capture external ***,realistic mimesis,both in the skin’s three-dimensional interlocked hierarchical structures and synchronous encoding multistimuli information capacities,remains a challenging yet vital need for simplifying the design of flexible logic ***,we construct an artificial epidermal device by in situ growing Cu_(3)(HHTP)_(2) particles onto the hollow spherical Ti_(3)C_(2)T_(x) surface,aiming to concurrently emulate the spinous and granular layers of the skin’s *** bionic Ti_(3)C_(2)T_(x)@Cu_(3)(HHTP)_(2) exhibits independent NO_(2) and pressure response,as well as novel functionalities such as acoustic signature perception and Morse code-encrypted message ***,a wearable alarming system with a mobile application terminal is self-developed by integrating the bimodular senor into flexible printed *** system can assess risk factors related with asthmatic,such as stimulation of external NO_(2) gas,abnormal expiratory behavior and exertion degrees of fingers,achieving a recognition accuracy of 97.6%as assisted by a machine learning *** work provides a feasible routine to develop intelligent multifunctional healthcare equipment for burgeoning transformative telemedicine diagnosis.

关键词： Ti_(3)C_(2)T_(x)@Cu_(3)(HHTP)_(2)composites NO_(2)/pressure flexible sensors Health-monitoring Machine learning

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Analytical evaluation and experimental validation on dynamic rocking behavior for shallow foundation considering structural response

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Earthquake Engineering and Engineering Vibration 2022年第1期21卷 37-51页

作者： Kil-Wan Ko Jeong-Gon ha dong-Soo kim Department of Civil and Environmental Engineering UC BerkeleyCalifornia 94720USA Advanced Structures and Seismic Safety Research Division Daejeon 34057Korea Department of Civil and Environmental Engineering KAISTDaejeon 34141Korea

The challenge in the practical application of rocking foundations is the estimation of its performance,particularly the rotation angle,during a strong *** this study,the dynamic rocking behavior for a shallow foundation considering structural response was evaluated through two analytical approaches:the conventional soil-foundation-structure interaction(SFSI)governing equation of a single-degree-of-freedom(SDOF)structure on a rocking shallow foundation,and the Housner rocking model(i.e.,a rocking rigid block on a rigid base).Both approaches were validated with dynamic centrifuge *** test models consisted of a soft soil deposit,a shallow rectangular foundation,and an SDOF structure dominated by a bending behavior.A total of 11 foundation-structure systems and six seismic waves,including recorded earthquake signals and sinusoidal waves,were *** results showed that the conventional SFSI equation well predicted the maximum rotation during strong ***,this method was less accurate regarding the rotational phase information and maximum rotation of the foundation during weak *** the other hand,although the modified Housner′s rocking model required five parameters relevant to a soil-foundation-structure system,it overestimated the maximum rotation of the foundation when compared with the results from dynamic centrifuge tests.

关键词： soil-foundation-structure interaction maximum rotation angle rocking foundation Housner rocking model dynamic centrifuge test

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Observation and Numerical Simulations with Radar and Surface Data Assimilation for Heavy Rainfall over Central Korea

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Advances in Atmospheric Sciences 2011年第3期28卷 573-590页

作者： Ji-Hyun ha Hyung-Woo kim dong-Kyou LEE Atmospheric Sciences Program School of Earth and Environmental SciencesSeoul National UniversitySeoul 151-747Korea

This study investigated the impact of multiple-Doppler radar data and surface data assimilation on forecasts of heavy rainfall over the central Korean Peninsula;the Weather Research and Forecasting(WRF) model and its three-dimensional variational data assimilation system(3DVAR) were used for this purpose. During data assimilation,the WRF 3DVAR cycling mode with incremental analysis updates(IAU) was used. A maximum rainfall of 335.0 mm occurred during a 12-h period from 2100 UTC 11 July 2006 to 0900 UTC 12 July *** radar data showed that the heavy rainfall was due to the back-building formation of mesoscale convective systems(MCSs).New convective cells were continuously formed in the upstream region,which was characterized by a strong southwesterly low-level jet(LLJ).The LLJ also facilitated strong convergence due to horizontal wind shear,which resulted in maintenance of the *** assimilation of both multiple-Doppler radar and surface data improved the accuracy of precipitation forecasts and had a more positive impact on quantitative forecasting(QPF) than the assimilation of either radar data or surface data *** back-building characteristic was successfully forecasted when the multiple-Doppler radar data and surface data were *** data assimilation experiments,the radar data helped forecast the development of convective storms responsible for heavy rainfall,and the surface data contributed to the occurrence of intensified low-level *** surface data played a significant role in enhancing the thermal gradient and modulating the planetary boundary layer of the model,which resulted in favorable conditions for convection.

关键词： radar and surface data data assimilation mesoscale convective system heavy rainfall

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Effect of Al addition on corrosion behavior of high-purity Mg in terms of processing history

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Journal of Magnesium and Alloys 2023年第3期11卷 851-868页

作者： Sang Kyu Woo Byeong-Chan Suh ha Sik kim Chang dong Yim Helmholtz Zentrum Hereon Max-Planck-Straße 1Geesthacht D-21502Germany Korea Institute of Materials Science 797 Changwondae-roSeongsan-guChangwonGyeongnam 51508Republic of Korea University of Science and Technology 217 Gajeong-roYuseong-guDaejeon 34113Republic of Korea

In this study,the effects of Al addition on the corrosion behavior of pure Mg with controlled impurity contents were systematically analyzed according to the processing *** results revealed that the corrosion behavior of high-purity Mg-Al alloys is strongly related to changes in the microstructure,including theβphase and Al-Mn or Al-Fe phases,and the protectiveness of the surface film according to the Al content and processing *** the as-cast alloys,the corrosion rate increased due to the increase ofβphase as the Al content increased,but in the as-extruded alloys,the corrosion rate,which was high due to intermetallic compounds caused by impurities in the low Al alloy,decreased as the Al content increased,and then increased *** is due to the combined effect of the increase of theβphase and decrease of the impurity effect,and the increase of the dissolved Al *** results suggest that it is necessary to analyze the effect of alloying elements on the corrosion behavior of pure Mg with information concerning the impurity content and processing history.

关键词： Mg High purity Mg-Al alloys Processing history Micro-galvanic Surface film

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In situ synthesis of chemically bonded NaTi2（PO4）3/rGO 2D nanocomposite for high-rate sodium-ion batteries

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Nano Research 2016年第6期9卷 1844-1855页

作者： ha-Kyung Roh Hyun-Kyung kim Myeong-Seong kim dong-Hyun kim Kyung Yoon Chung Kwang Chul Roh Kwang-Bum kim Department of Material Science & Engineering Yonsei University 50 Yonsei-ro Seodaemun-gu Seou103722 Republic of Korea Department of Materials Science and Metallurgy University of Cambridge 27 Charles Babbage Road Cambridge CB30FS UK Center for Energy Convergence Korea Institute of Science and Technology 5 Hwarang-ro 14-gil Seongbuk-gu Seou102792 Republic of Korea Energy & Environmental Division Korea Institute of Ceramic Engineering & Technology 101 Soho-ro Jinju-si Gyeongsangnam-do 52851 Republic of Korea

A phase-pure NaTi2（PO4）3/reduced graphene oxide （rGO） nanocomposite was prepared using a microwave-assisted one-pot method and subsequent heat treatment. The well-crystallized NaTi2（PO4）3 nanoparticles （30-40 nm） were uniformly precipitated on rGO templates through Ti-O-C bonds. The chemical interactions between the NaTi2（PO4）3 nanoparticles and rGO could immobilize the NaTi2（PO4）3 nanoparticles on the rGO sheets, which might be responsible for the excellent electrochemical performance of the nanocomposite. The NaTi2（PO4）B/rGO nanocomposite exhibited a specific capacity of 128.6 mA-h.g-1 approaching the theoretical value at a 0.1 C-rate with an excellent rate capability （72.9% capacity retention at 50 C-rate） and cycling performance （only 4.5% capacity loss after 1,000 cycles at a high rate of 10 C）. These properties were maintained even when the electrodes were prepared without the use of an additional conducting agent. The excellent sodium storage properties of the NaTi2（PO4）B/rGO nanocomposite could be attributed to the nano-sized NaTi2（PO4）3 particles, which significantly reduced the transport lengths for Na＋ ions, and an intimate contact between the NaTi2（PO4）3 particles and rGO due to chemical bonding.

关键词： NaTi2(PO4)dreducedgraphene oxide (rGO)nanocomposite chemical bonding energy-efficiency in situ synthesis high-rate sodium-ion batteries

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Effect of Length Scale Tuning of Background Error in WRF-3DVAR System on Assimilation of High-Resolution Surface Data for Heavy Rainfall Simulation

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Advances in Atmospheric Sciences 2012年第6期29卷 1142-1158页

作者： Ji-Hyun ha dong-Kyou LEE Atmospheric Sciences Program School of Earth and Environmental SciencesSeoul National UniversitySeoul 151-747Korea

We investigated the impact of tuning the length scale of the background error covariance in the Weather Research and Forecasting （WRF） three-dimensional variational assimilation （3DVAR） system. In particular, we studied the effect of this parameter on the assimilation of high-resolution surface data for heavy rainfall forecasts associated with mesoscale convective systems over the Korean Peninsula. In the assimilation of high-resolution surface data, the National Meteorological Center method tended to exaggerate the length scale that determined the shape and extent to which observed information spreads out. In this study, we used the difference between observation and background data to tune the length scale in the assimilation of high-resolution surface data. The resulting assimilation clearly showed that the analysis with the tuned length scale was able to reproduce the small-scale features of the ideal field effectively. We also investigated the effect of a double-iteration method with two different length scales, representing large and small-length scales in the WRF-3DVAR. This method reflected the large and small-scale features of observed information in the model fields. The quantitative accuracy of the precipitation forecast using this double iteration with two different length scales for heavy rainfall was high; results were in good agreement with observations in terms of the maximum rainfall amount and equitable threat scores. The improved forecast in the experiment resulted from the development of well-identified mesoscale convective systems by intensified low-level winds and their consequent convergence near the rainfall area.

关键词： WRF 3DVAR tuning surface data heavy rainfall

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