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Engineering（科研） 2013年第9期5卷 756-763页

作者： Hyejin yoon Won Jong Chin Jeong-Rae Cho jae yoon kang Jongwon Kwark Structural Engineering Research Division Korea Institute of Construction Technology Goyang South Korea

Since high-speed railway bridges are subjected to cyclic loading by the continuous wheel loads traveling at high speed and regular spacing, their dynamic behavior is of extreme importance and has significant influence on the riding safety of the trains. To secure the riding safety of the trains, advanced railway countries have limited the vertical acceleration of the bridge slab below critical values at specific frequency domains. Since these limitations of the vertical acceleration constitute the most important factors in securing the dynamic safety of the bridges, these countries have opted for a conservative approach. However, the Korean specifications limit only the size of the peak acceleration without considering the frequency domain, which impede significantly rational evaluation of the high-speed railway bridges in Korea. In addition, the evaluation of the acceleration without consideration of the frequency domain is the cause of disagreement between the dynamic analysis and measurement results. This study conducts field monitoring and dynamic analysis on high-speed railway bridges to gather the acceleration signals and compare them. Significant difference in the size of the vertical acceleration was observed between the measured and dynamic analysis accelerations when discarding the frequency domain as done in the current specifications. The comparison of the accelerations considering only low frequencies below 30 Hz showed that the dynamic analysis reflected accurately the measured vertical acceleration.

关键词： High-Speed Railway Bridge Vertical Acceleration Dynamic Response

Modification strategies improving the electrochemical and structural stability of high-Ni cathode materials

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Journal of Energy Chemistry 2024年第9期96卷 185-205页

作者： yoon Bo Sim Hami Lee Junyoung Mun Ki jae Kim Department of Energy Science Sungkyunkwan UniversitySuwon 16419Republic of Korea School of Advanced Materials Science and Engineering Sungkyunkwan UniversitySuwon 16419Republic of Korea SKKU Institute of Energy Science and Technology(SIEST) Sungkyunkwan UniversitySuwon 16419Republic of Korea

With the increasing spotlight in electric vehicles,there is a growing demand for high-energy-density batteries to enhance driving ***,several studies have been conducted on high-energy-density LiNi_(x)Co_(y)Mn_(z)O_(2)***,there is a limit to permanent performance deterioration because of side reactions caused by moisture in the atmosphere and continuous microcracks during cycling as the Ni content to express high energy increases and the content of Mn and Co that maintain structural and electrochemical stabilization *** direct modification of the surface and bulk regions aims to enhance the capacity and long-term performance of high-Ni cathode ***,an efficient modification requires a study based on a thorough understanding of the degradation mechanisms in the surface and bulk *** this review,a comprehensive analysis of various modifications,including doping,coating,concentration gradient,and single crystals,is conducted to solve degradation issues along with an analysis of the overall degradation mechanism occurring in high-Ni cathode *** also summarizes recent research developments related to the following modifications,aims to provide notable points and directions for post-studies,and provides valuable references for the commercialization of stable high-energy-density cathode materials.

关键词： High energy density High-Ni cathode materials Degradation Structural stability Lithium-ion battery

Computation of Impact Factor of High-Speed Railway Bridge by KTX Train Riding Test

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Engineering（科研） 2013年第9期5卷 751-755页

作者： Hyejin yoon Won Jong Chin jae yoon kang Jongwon Kwark Eui-Seung Hwang Department of Civil Engineering Kyung Hee University Goyang South Korea Structural Engineering Research Division Korea Institute of Construction Technology Goyang South Korea

The design live load of railway is divided into common railway and high-speed railway separately inKorea. Accordingly, the Korean design specification of railway specifies the impact factor for common railway and high-speed railway respectively. The impact factor for high-speed railway is based on Eurocode. Since the impact factor criteria inKoreawere established by adopting those of the Eurocode and without dedicated investigation relying on research results reflecting the domestic circumstances, thorough examination should be implemented on these criteria. Therefore the evaluation of impact factor based on field tests is required. Both dynamic and static vertical displacements are necessary to compute the impact factor. The dynamic response can be obtained from the measurement of deflection of the bridge slab crossed by the firstKoreahigh-speed train (KTX, Korea Train eXpress) running at high-speed. The main difficulties encountered are in obtaining static response because static response corresponds to the response of the bridge when the train remains immobile on the bridge or crosses the bridge at speed slower than5 km/hr. This study introduces the static response derived by applying the moving average method on the dynamic response signal. To that goal, field measurements was conducted under train speeds of5 km/hr and ranging from100 km/hr to300 km/hr on Yeonjae Bridge located in the trial section of the Gyeonbu High-Speed Railway Line before its opening. The validity of the application of the moving average method is verified from comparison of measured static response and derived static response by moving average method. Moreover, evaluation is conducted on the impact factor computed for a bridge crossed by the KTX train running at operational speed.

关键词： High-Speed Railway Dynamic Response Impact Factor Moving Average Method

Shear Behavior in Indented Concrete Layers with Different Strengths

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Engineering（科研） 2016年第7期8卷 423-431页

作者： jae-yoon kang Jong-Sup Park Woo-Tai Jung Moon-Seoung Keum Structural Engineering Research Institute Korea Institute of Civil Engineering and Building Technology Goyang Republic of Korea

This paper investigates the design formula for the shear strength at the concrete-to-concrete interface proposed in Eurocode with regard to concrete layers with different strengths. Based upon the results of the study on the applicability of the design formula, push-off test is conducted on specimens with various indented interfaces to evaluate the actual behavior with respect to the surface roughness. The experimental results reveal that the interfacial shear strength increases with higher compressive strength of the concrete layers presenting different strengths and that the shear strength at the indented interface differs by 20% to 50% compared to the value predicted by the design formula. Especially, the shear strength developed between the concrete layers with different strengths appears to be different from the prediction of the design formula as much as the layers present larger difference in their compressive strengths.

关键词： Shear Strength Interface of Concrete Layers Surface Roughness Indented Surface Push-Off Test

Advances in Wireless,Batteryless,Implantable Electronics for Real‑Time,Continuous Physiological Monitoring

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Nano-Micro Letters 2024年第3期16卷 254-302页

作者： Hyeonseok Kim Bruno Rigo Gabriella Wong yoon jae Lee Woon‑Hong Yeo IEN Center for Wearable Intelligent Systems and Healthcare Georgia Institute of TechnologyAtlantaGA 30332USA George W.Woodruff School of Mechanical Engineering Georgia Institute of TechnologyAtlantaGA 30332USA School of Electrical and Computer Engineering Georgia Institute of TechnologyAtlantaGA 30332USA Wallace H.Coulter Department of Biomedical Engineering Georgia Tech and Emory University School of MedicineAtlantaGA 30332USA Parker H.Petit Institute for Bioengineering and Biosciences Institute for MaterialsInstitute for Robotics and Intelligent MachinesGeorgia Institute of TechnologyAtlantaGA 30332USA

This review summarizes recent progress in developing wireless,batteryless,fully implantable biomedical devices for real-time continuous physiological signal monitoring,focusing on advancing human health *** considerations,such as biological constraints,energy sourcing,and wireless communication,are discussed in achieving the desired performance of the devices and enhanced interface with human *** addition,we review the recent achievements in materials used for developing implantable systems,emphasizing their importance in achieving multi-functionalities,biocompatibility,and *** wireless,batteryless devices offer minimally invasive device insertion to the body,enabling portable health monitoring and advanced disease ***,we summarize the most recent practical applications of advanced implantable devices for human health care,highlighting their potential for immediate commercialization and clinical uses.

关键词： Implantable electronics Biomedical systems Batteryless devices Wireless electronics Physiological signal monitoring

Evaluation of the Shear Strength of Perfobond Rib Connectors in Ultra High Performance Concrete

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Engineering（科研） 2014年第13期6卷 989-999页

作者： jae yoon kang Jong Sup Park Woo Tai Jung Moon Seoung Keum Structural Engineering Research Division Korea Institute of Civil Engineering and Building Technology Goyang Korea

Since the previous strength prediction models for the perfobond rib connector were proposed based upon the results of push-out tests conducted on concretes with compressive strength below 50 MPa, push-out test is performed on perfobond shear connectors applying ultra high performance concretes with compressive strength higher than 80 MPa to evaluate their shear resistance. The test variables are chosen to be the diameter and number of dowel holes and, the change in the shear strength of the perfobond rib connector is examined with respect to the strength of two types of UHPC: steel fiber-reinforced concrete with compressive strength of 180 MPa and concrete without steel fiber with compressive strength of 80 MPa. The test results reveal that higher concrete strength and larger number of holes increased the shear strength, and that higher increase rate in the shear strength was achieved by the dowel action. The comparison with the predictions obtained by the previous models shows that the experimental results are close to the values given by the model proposed by Oguejiofor and Hosain [1].

关键词： Perfobond Rib Connector Ultra High Performance Concrete Push-Out Test Shear Strength

Connection between Concrete Layers with Different Strengths

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Engineering（科研） 2015年第7期7卷 365-372页

作者： jae yoon kang Jong Sup Park Woo Tai Jung Moon Seoung Keum Structural Engineering Research Institute Korea Institute of Civil Engineering and Building Technology Goyang Republic of Korea

As part of a research intending to develop steel-concrete hybrid girder using ultra high performance concrete with compressive strength of 80 MPa, this study conducts loading test on this girder to investigate the methods for its composition with a slab using 30 MPa-concrete and the corresponding interfacial behavior. Prior to the loading test, the design formula of the Eurocode for the shear resistance developed in concrete-to-concrete interface is examined for the interface between concrete layers of different strengths. The effect of the surface roughness on the shear resistance is examined using this formula and finite element analysis to verify the applicability of the formula. Based upon the results, loading test is conducted on girder specimens to evaluate the actual behavior with respect to the interfacial surface condition. The test results reveal that the specimen with rough interface could not develop perfectly composite behavior and experienced adhesive failure. In case of simultaneous action of flexure and shear, it appears that conservative design should be applied without consideration of the interfacial condition when determining the arrangement of shear reinforcement.

关键词： Shear Resistance Interface between Concrete Layers Surface Roughness Steel-Concrete Hybrid Girder Ultra High Performance Concrete (UHPC)

Parametric Analysis on the Optimal Dimensions of Steel Sleeve in Swaging Type Anchorage for CFRP Tendon

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Engineering（科研） 2013年第11期5卷 902-908页

作者： jae yoon kang Jong Sup Park Woo Tai Jung Moon Seoung Kum Structural Engineering Research Division Korea Institute of Construction Technology Goyang Korea

This paper presents the parametric analysis conducted to derive the optimal dimensions of the steel sleeve necessary to secure the bond performance of the swaging type anchorage for CFRP tendon with diameter of 5 mm. To that goal, finite element analysis is performed on the parameters determining the dimensions of the sleeve like the thickness and inner diameters of the sleeve. The results show that a constant swaging pressure of about 450 MPa on the mean is distributed in the sleeve when the thickness ratio of the stress relief zone to the effective swaging zone of the sleeve is larger than 1.1 and that the swaging pressure tends to reduce linearly as much as this thickness ratio becomes smaller than 1.1. The pressure varies within a range of about 30% according to the change in the inner diameter of the sleeve whereas varies within a range less than 10% according to the change in the inner diameter when the thickness ratio is larger than 1.1. Finally, the optimal dimensions of the steel tube sleeve enabling to secure an anchor force larger than the rupture strength of the CFRP tendon with diameter of 5 mm are determined based upon the results of the parametric analysis.

关键词： CFRP Tendon Prestressing Swaging Type Anchorage Swaging Sleeve

Behavior Characteristics of Bonded Type Anchorage for CFRP Tendon

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Engineering（科研） 2013年第11期5卷 909-918页

作者： Jong Sup Park Woo Tai Jung jae yoon kang Moon Seoung Kum Structural Engineering Research Division Korea Institute of Construction Technology Goyang Korea

This paper examines the shear stress and displacement occurring in CFRP tendons through finite element analysis on the parameters influencing the anchoring performance to evaluate the behavioral characteristics of the bonded type anchorage for CFRP tendon. The selected parameters are the inner angle of the anchorage barrel, the friction between the barrel and filling material, and the elastic modulus of the filling material. The difference in the behavioral characteristics is examined for each parameter. In view of the analytic results, the shear stress developed in the CFRP tendon reduces with larger inner angle of the barrel and lower elastic modulus of the filling material. However, such combination provokes also the increase of the relative displacement of the CFRP tendon. Especially, slip failure may occur due to the lack of the confining force necessary for the anchorage due to the sudden loss of vertical force brought by the wedge force. The experimental results relative to barrel inner angles of 2° and 4° showed that the specimen with an angle of 2° preserved its anchoring performance up to tensile failure whereas the specimen with an angle of 4°?failed in developing its maximum anchoring performance due to slip failure.

关键词： CFRP Tendon Prestressing Anchorage Wedge

Laser‑Induced and MOF‑Derived Metal Oxide/Carbon Composite for Synergistically Improved Ethanol Sensing at Room temperature

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Nano-Micro Letters 2024年第6期16卷 210-220页

作者： Hyeongtae Lim Hyeokjin Kwon Hongki kang jae Eun Jang Hyuk‑Jun Kwon Department of Electrical Engineering and Computer Science DGISTDaegu 42988South Korea Convergence Research Advanced Centre for Olfaction DGISTDaegu 42988South Korea

Advancements in sensor technology have significantly enhanced atmospheric ***,metal oxide and carbon(MO_(x)/C)hybrids have gained attention for their exceptional sensitivity and room-temperature sensing ***,previous methods of synthesizing MO_(x)/C composites suffer from problems,including inhomogeneity,aggregation,and challenges in ***,we introduce a refined method that employs a metal–organic framework(MOF)as a precursor combined with direct laser *** inherent structure of MOFs ensures a uniform distribution of metal ions and organic linkers,yielding homogeneous MO_(x)/C *** laser processing facilitates precise micropatterning(<2μm,comparable to typical photolithography)of the MO_(x)/C *** optimized MOF-derived MO_(x)/C sensor rapidly detected ethanol gas even at room temperature(105 and 18 s for response and recovery,respectively),with a broad range of sensing performance from 170 to 3,400 ppm and a high response value of up to 3,500%.Additionally,this sensor exhibited enhanced stability and thermal resilience compared to previous MOF-based *** research opens up promising avenues for practical applications in MOF-derived sensing devices.

关键词： Metal-organic frameworks Metal oxide Carbon composite Laser Gas sensor