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이지형,홍성걸,Lee, Ji-Hyung,Hong, Sung-Gul 한국공간구조학회 2015 한국공간구조학회지 Vol.15 No.2
Ultra High Performance Fiber Reinforced Concrete (UHPFRC) has a outstanding tensile hardening behaviour after a crack develops, which gives ductility to structures. Existing shear strength model for fiber reinforced concrete is entirely based on crack opening behavior(mode I) which comes from flexural-shear failure, not considering shear-slip behavior(mode II). To find out the mode I and mode II behavior on a crack in UHPFRC simultaneously, maximum shear strength of cracked UHPFRC is investigated from twenty-four push-off test results. The shear stress on a crack is derived as variable of initial crack width and fiber volume ratio. Test results show that shear slippage is proportional to crack opening, which leads to relationship between shear transfer strength and crack width. Based on the test results a hypothesis is proposed for the physical mechanics of shear transfer in UHPFRC by tensile hardening behavior in stead of aggregate interlocking in reinforced concrete. Shear transfer strength based on tensile hardening behavior in UHPFRC is suggested and this suggestion was verified by comparing direct tensile test results and push-off test results.
이지형,오종윤,박익수,Lee Ji-Hyung,Oh Jong-Yun,Park Ik-Soo 한국군사과학기술학회 2004 한국군사과학기술학회지 Vol.7 No.4
A simplified test rig to simulate high-altitude environments was designed by analyzing the AEDC (Arnolds Engineering Development Center) report regarding simulated altitude testing. The test rig consists of a vacuum chamber, a supersonic nozzle connected to a cold-gas supplier and a diffuser. The preliminary tests were conducted to validate the AEDC design concepts. The test results showed that sub-atmospheric pressure(1.0psia) environments were realized inside the vacuum chamber and the design concepts were confirmed.
이지형,Seong Jin Lee,정대영,Ha-Young Kim,이두현,이태호,황종연,박우규,공재양,조희영,공영대 대한화학회 2014 Bulletin of the Korean Chemical Society Vol.35 No.8
Novel 2,6-difuctionalized 2H-benzopyrans were synthesized and evaluated for a sphingosylphosphorylcholine (SPC) inhibitor. The synthetic 2H-benzopyrans 1c and 3a showed high potency in SPC-induced cell proliferation assay (IC50 < 20 nM). Neither hERG K+ channel binding (> 10 μM) nor CYP inhibitions (> 10 μM) were observed. Also, the simple structure-activity relationship (SAR) results were obtained from analysis of 2H-benzopyran derivatives 1-3 and the anti-SPC effect of 2H-benzopyran 1c was confirmed by a HUVEC tube formation assay.
소형 초음속 디퓨저를 이용한 고고도환경 모사에 대한 시험적 연구
이지형,오종윤,변종렬,Lee Ji-Hyung,Oh Jong-Yun,Byun Jong-Ryul 한국군사과학기술학회 2004 한국군사과학기술학회지 Vol.7 No.4
Experimental study was conducted on cylindrical supersonic diffuser in order to investigate the effects of the ratios of diffuser area to nozzle throat area (Ad/At), diffuser area to nozzle exit area (Ad/Ae), nozzle exit area to its throat area (Ae/At), and diffuser length to its diameter (L/D), the free volume of vacuum chamber, and the relative distance between nozzle exit and diffuser inlet on the diffuser performance. The study showed that the minimum diffuser starting pressure (Po/Pa)st increased monotonically with increase in (Ad/At) as predicted by the normal shock and momentum theory models and the volume of vacuum chamber affected vacuum pressure level during diffuser operation at lower value of (Ad/Ae). The results of this investigation will be utilized in the design of real-scale high-altitude simulation test facility.
입사각에 따른 반원형 입구형상 S-Shaped Intake에 대한 유동특성 연구
이지형,조진수,Lee, Jihyeong,Cho, Jinsoo 한국교통대학교 융복합기술연구소 2015 융ㆍ복합기술연구소 논문집 Vol.5 No.2
Air intakes are an essential component of aircraft engines. They are mainly used to offer uniform airflows to engine faces. Fighter aircraft have to mask the engine face inside the fuselage in order to reduce the Radar Cross Section(RCS). Therefore, offset intakes like a S-Duct are one of promising components for this purpose. During a fight, it is unavoidable that the flow will enter the intakes at some face angles other than zero. In this case, the performance of the aircraft engine will be influenced to the angle of incidence. In this study, the CFD analysis of the semi-circular S-Duct with AR(0.5,0) is performed to investigate the influence of the angle of incidence on the performance of the S-Duct using a distortion coefficient. To consider the adverse pressure gradient, a $k-{\omega}$ SST turbulence model is employed. The secondary flow and flow separation are observed for all computational cases. It is found that the positive incidence angle produces the best performances.
PC기반 시야검사를 통한 효과적인 시선고정 유도방법 연구
이지형,이백희,박현지,최정한,유희천,강자헌,Ji Hyoung Lee,Baek Hee Lee,Hyun Ji Park,Jeong Han Choi,Hee Cheon You,Ja Heon Kang 대한안과학회 2013 대한안과학회지 Vol.54 No.9
Purpose: The present study explored novel methods in visual field tests that actively induce the gaze of the examinee to the fixation target in the center vision and compared their effectiveness. Methods: Four gaze induction methods (dot-on, dot-off, number-on, and number-off) were prepared by combining 2 types of fixation targets (dot and number) and 2 conditions of sound presence (on and off). The gaze induction methods were implemented to a PC-based visual field testing system and the 24-2 visual field testing protocol was administered to 14 participants without glaucoma. The performance of the gaze induction method was evaluated in terms of fixation error rate, target detection rate, and subjective satisfaction (7-point scale, 1 for least satisfied and 7 for most satisfied). Results: The fixation error rates of dot-on (5.7%) and number-on (6.4%) were relatively lower than the other methods; the target detection rates of the induction methods were very high (95-96%) without significant differences, and the subjective satisfaction levels of dot-on (5.7) and number-on (5.4) were significantly higher than the other methods. Conclusions: In the present study we determined number-on as the preferred effective gaze induction method compared to the conventional dot-off method when fixation error rates and subjective satisfaction were considered.