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Jang, Seung Yup,Shin, Jong-Hoon,Hwang, Eu Jin,Choi, Hyo-Seung,Jeong, Hun,Song, Sang-Hun,Kwon, Hyuck-In The Institute of Electronics and Information Engin 2014 Journal of semiconductor technology and science Vol.14 No.4
We propose a new method which can extract the information about the electronic traps in the semi-insulating GaN buffer of AlGaN/GaN heterostructure field-effect transistors (HFETs) using a simple test structure. The proposed method has a merit in the easiness of fabricating the test structure. Moreover, the electric fields inside the test structure are very similar to those inside the actual transistor, so that we can extract the information of bulk traps which directly affect the current collapse behaviors of AlGaN/GaN HEFTs. By applying the proposed method to the GaN buffer structures with various unintentionally doped GaN channel thicknesses, we conclude that the incorporated carbon into the GaN back barrier layer is the dominant origin of the bulk trap which affects the current collapse behaviors of AlGaN/GaN HEFTs.
Jang, Seung-Yup,Karthick, Subbiah,Kwon, Seung-Jun Hindawi Publishing Corporation 2017 Advances In Materials Science And Engineering Vol.2017 No.1
<P>The significance of concrete durability increases since RC (Reinforced Concrete) structures undergo degradation due to aggressive environmental conditions, which affects structural safety and serviceability. Steel corrosion is the major cause for the unexpected failure of RC structures. The main cause for the corrosion initiation is the ingress of chloride ions prevailing in the environment. Hence quantitative evaluation of chloride diffusion becomes very important to obtain a chloride diffusion coefficient and resistance to chloride ion intrusion. In the present investigation, 15 mix proportions with 3 water-to-binder ratios (0.37, 0.42, and 0.47) and 3 replacement ratios (0, 30, and 50%) were prepared for HPC (high-performance concrete) with fly-ash and ground granulated blast furnace slag. Chloride diffusion coefficient was measured under nonstationary condition. In order to evaluate the microstructure characteristics, porosity through MIP was also measured. The results of compressive strength, chloride diffusion, and porosity are compared with electrical charges. This paper deals with the results of the concrete samples exposed for only 2 months, but it is a part of the total test plan for 100 years. From the work, time-dependent diffusion coefficients in HPC and the key parameters for durability design are proposed.</P>
장승엽(Jang Seung Yup),양신추(Yang Sin-Chu),김정일(Kim Jeong Il),김태욱(Kim Tae Wook) 한국철도학회 2003 한국철도학회 학술발표대회논문집 Vol.- No.-
Precast concrete slab track has been already turned out to be more efficient than cast-in place concrete slab track in view of the easiness of construction and the quality control of concrete. Thus, there is a great need to bring in the precast slab track system. In order to develop the realistic precast slab track system that is well conformed to our circumstances, the performance criteria of slab track, and the state-of-the art of precast slab track systems that are used in other countries are briefly discussed here.
장승엽(Seung Yup Jang),조호현(Ho-Hyun Cho),양신추(Sin Chu Yang) 한국철도학회 2010 한국철도학회 학술발표대회논문집 Vol.2010 No.7
In the areas susceptible to vibration and noise induced by railway traffic such as downtown area and stations under railway lines, the vibration and the structure-borne noise can be solved by floating slab track system separating the entire track structure from its sub-structure using anti-vibration mat or springs. In other countries, the core technologies for vibration-proof design and vibration isolator - one of key components - have been developed and many installation experiences have been accumulated. However, in Korea, since the design technology of system and components are not yet developed, the foreign systems are being introduced without any adjustment. Thus, in this study, the vibration isolator has been developed and its performance are investigated by the dynamic analysis of a station structure under railways lines and the floating slab track system. For this purpose, the loads transferred from the vibration isolator of the floating slab track were evaluated by train running simulation considering vehicle-track interaction, and then the dynamic analysis of station structure subjected to these loads was performed. The dynamic analysis results show that the proposed floating slab track can reduce the vibration of structure by about 25dB compared with that in conventional ballast track without floating system.
연속 프리캐스트 콘크리트 슬래브궤도에서의 온도하강에 따른 슬래브 이음매 개구량 해석
장승엽(Seung Yup Jang),이정완(Jeong Wan Lee) 한국철도학회 2011 한국철도학회 학술발표대회논문집 Vol.2011 No.10
Precast concrete slab track is a track structure to be installed by transporting and assembling precast concrete slabs manufactured at the factory. This method can improve concrete quality provide easy maintenance and reduce construction time compared with in-situ concrete track. However the concrete slabs being continuously connected in longitudinal direction due to the temperature change between summer and winter the openings at slab joints have occurred. Thus in this study to identify the cause of this opening of slab joint the joint opening caused by temperature drop in the longitudinally continuous precast concrete slab track has been predicted using three-dimensional finite element analysis and compared with field measurements. Based on the proven model the slab joint opening and the stress pattern of concrete slab and steel reinforcement according to concrete slab-base friction properties concrete-reinforcement bond properties and prestressing were analyzed.