현장용 시멘트페이스트 레올로지 측정기구 개발

현철 대한건축학회 2007 大韓建築學會論文集 : 構造系 Vol.23 No.6

Rheological tests on cement paste were necessary for evaluation of workability on field. The slump, mini cone, and marsh cone test are common methods for assessing the flow properties of fresh cement paste and concrete. Although these methods provide quantitative measures of workability, the relationship between these methods and more quantitative rheological parameters is not fully understood. Some appliances for more accurate measurement are recently proposed. However, these are too expensive to use in field. Therefore, the goal is to propose the simple, cheap and useful rheometer for measuring the rheological properties of cement paste and concrete. In this study, C-P Rheometer consisting of a cylinder and a pipe is proposed. Yield stress of cement paste is calculated by measuring the height of cement paste in cylinder when it finishes dropping. Plastic viscosity is also done by measuring the time for cement paste to drop and pass through the range between two fixed heights of cylinder. The new rheometer is in excellent agreement with the experimental yield stress and plastic viscosity data obtained using the authorized rheometer(Brookfield RVDVⅢ+). The conclusion is that this new simple rheometer is reliable for measuring the rheological properties of cement paste.

고유동시멘트페이스트의 유동해석에 관한 연구

현철 경성대학교 공학기술연구소 2003 공학기술연구지 Vol.S1 No.2

In this paper the parameters of high-flowability cement paste affecting rheological behaviour were investigated. The evolution of the rheological properties of cement pastes up to setting has been the subject of numerous studies but most of them were made in shear mode, giving information related to practically interesting problems such as workability. However, such studies do not allow to obtain information concerning more fundamental phenomena. Rheology has also been used to study the mechanical properties of cement pastes from mixing up to setting. Factorial experimental design was adopted in this investigation to assess the combined effects of the following factors on fluidity, rheological properties : water/cement ratio (W/C), dosage of superplasticiser (SP). Flow test and rotating viscometer were used to evaluate the rheology of the cement paste. Superplasticiser (SP) is used to enhance flowability of cement-based systems. The use of SP decreases plastic viscosity of cement paste. Several researchers have related the improvement in rheological properties and the performance of cement paste to the addition of superplasticiser (SP). A general mixer was used to study rheology during the very first minutes following the end of mixing. The aim of this study is to evaluate the effect of the W/C and the dosages of SP on the rheological properties of cement paste. The flow test and viscometer were used for testing the behaviour of fresh cement pastes.

무인 수중 운동체의 제어기 설계 및 강인성 평가

현철,이동준 대한전기학회 2012 대한전기학회 학술대회 논문집 Vol.2012 No.7

반구형 공진 자이로스코프 재평형 제어기 설계

현철,강태삼,이동준 대한전기학회 2011 정보 및 제어 심포지엄 논문집 Vol.2011 No.10

집적형 하이브리드 구동장치의 성능시험

현철봉(Zhefeng Xuan),김태렬(Tailie Jin),구남서(Nam Seo Goo),배병운(Byung-Woon Bae),김태흔(Tae-Heun Kim),고한서(Han Seo Ko),윤기원(Ki-Won Yoon) 한국항공우주학회 2013 韓國航空宇宙學會誌 Vol.41 No.1

집적형 하이브리드 구동장치는 적층형 압전재료(압전스택)를 이용한 마이크로 펌프에서 토출되는 유체로 피스톤을 구동시키는데 크기는 작으면서도 큰 구동력과 높은 속도를 동시에 출력할 수 있는 새로운 개념의 통합 구동장치로서 현재 소형화 및 고출력을 요구하는 항공 우주, 유도무기 등 다양한 분야에서 광범위하게 연구되고 있다. 본 연구에서는 이러한 하이브리드 구동장치의 구동원리 및 성능 시험에 대해 소개하였다. 우선 구동장치의 주 동력인 압전 스택의 성능 시험을 수행함으로써 압전 스택의 구동전력과 구동시간에 따른 성능 변화를 관찰하였고 다음 구동장치의 성능 시험을 통해 구동장치의 최대 이송속도와 최대 구동력을 측정하였다. 구동장치의 최대 이송속도는 53.3 ㎜/s로, 최대 구동력은 240.7 N으로, 최대 일률은 3.2 W로 측정되었다. The piezoelectric-based hydraulic actuator is a hybrid device consisting of a hydraulic pump driven by piezoelectric stacks that is coupled to a conventional hydraulic cylinder via a set of fast-acting valves. Nowadays, such hybrid actuators are being researched and developed actively in many developed countries by requirement of high performance and compact flight system. In this research, operation principle and performance testing of the hybrid actuator were introduced. Output velocities have been measured in both loaded case and not loaded case and the blocking force also has been measured in external loaded case. The maximum velocity of the actuator is 53.3 ㎜/s, blocking force is 240.7 N and corresponding power output is 3.2 W.

원격강의 학습 태도 모니터링 및 효과 분석

현철상(Chul-Sang Hyun),최병도(Byung-Do Choi),김종근(Chong-gun Kim) 한국멀티미디어학회 2004 한국멀티미디어학회 학술발표논문집 Vol.2004 No.2

한국 프로시론 형성 배경 고찰

현철종 ( Chol Jong Hyun ) 영주어문학회 2006 영주어문 Vol.11 No.-

모르터의 자기수축예측에 관한 연구

현철 경성대학교 공학기술연구소 2003 공학기술연구지 Vol.S2 No.2

Autogenous shrinkage of concrete has been defined as decrease in volume due to hydration. For ordinary concretes, autogenous shrinkage is so little that it has been dignored. It has recently been reported, however, that cracking can be caused by autogenous shrinkage, when high-strength concretes were used. In this study, we propose an analytical system to represent autogenous shrinkage in cement paste and mortar in order to control crack due to autogenous shrinkage. The system composed of the hydration model and pore structure model. The hydration model which refined Tomosawa's represents the situation that inner and outer products are made in cement paste. The pore structure model is based upon the physical phenomenon of ion diffusion in cement paste. The proposed model can predict the hydration ratio and the cumulative pore volume in cement paste satisfactorily. Autogenous shrinkage was predicted by elastic modulus calculated from experiment data and former study. The model for predicting autogenous shrinkage of cement paste and mortar shows a reasonable agreement with the experimental data in case of different mix-proportions.

고중성지방혈증 환자에서 단기간의 Fenofibrate 투여가 혈중 크레아티닌 농도에 미치는 영향

현철원 ( Cheol Won Hyeon ),최영환 ( Young Hwan Choi ),현성협 ( Seonghyup Hyun ),권지은 ( Jee Eun Kwon ),김은영 ( Eun Young Kim ),신승용 ( Seung Yong Shin ),이왕수 ( Wang Soo Lee ),이광제 ( Kwang Je Lee ),김상욱 ( Sang Wook Kim 대한내과학회 2014 대한내과학회지 Vol.86 No.6

목적: 고중성지방혈증 환자에서 단기간 fenofibrate를 투여하였을 때에 혈중 크레아티닌 농도의 변화와 이에 영향을 미치는 인자들을 관찰해 보고자 하였다. 방법: 혈중 중성지방 농도가 200 mg/dL 이상인 86명의 고중성지방혈증 환자를 대상으로 하였다. 이들을 micronized fenofibrate 160 mg을 투여한 Fenofibrate 투여군과 대조군으로 나누었다. 혈중 지질농도와 신기능을 나타내는 인자들을 치료 전과 치료 후 2개월에 측정하였다. 결과: 추정 사구체여과율은 Fenofibrate군에서 감소한 반면에(p < 0.001), 대조군에서는 변화가 없었다(p = 0.80). 이것의 백분율 변화는 각각 -18.6 ± 8.6%와 0.9 ± 9.6%로 두 군사이에 차이가 있었다(p < 0.001). 크레아티닌 농도는 Fenofibrate군에서 증가한 반면에(p < 0.001), 대조군은 변화가 없었다(p = 0.37). 크레아티닌 농도의 백분율 변화는 Fenofibrate 군에서 대조군에 비해 유의하게 더 많이 증가하였다(p < 0.001). 전체 환자(n = 86)에서 크레아티닌 농도의 백분율 증가는 fenofibrate 투여(r = 0.71, p < 0.001)와 고령(r = 0.27, p < 0.05) 과 독립적 연관이 있었다. Fenofibrate군에서 크레아티닌 농도의 백분율 증가는 고령(r = 0.51, p < 0.001), 비흡연(r = 0.42, p < 0.005)과 독립적 연관이 있었다. 전체 환자에서 크레아티닌 농도의 증가가 20% 이상인 군(n = 21)과 20% 미만인 군(n =65)으로 나누었을 때에, 20% 이상의 증가는 다변수 로지스틱 회귀분석에서 fenofibrate 투여(p < 0.001)와 고령(p < 0.005)과 연관이 있었다. Fenofibrate군에서는 단지 고령(p < 0.001)과 연관이 있었다. 결론: 고중성지방을 가진 한국인 환자에서 단기간의 fenofibrate의 투여는 크레아티닌 농도를 의미 있게 증가시키며 이러한 증가는 고령에서 더 뚜렷하였다. 따라서 fenofibrate를 투여할 때에는 신기능의 추적관찰이 특히 고령에서 투약 초기에 필요할 것으로 생각된다. Background/Aims: Previous studies have reported that fenofibrate therapy increases blood creatinine levels. The aim of this study was to evaluate the effect of fenofibrate therapy on the renal function in patients with hypertriglyceridemia and to determine the parameters associated with changes in renal functions. Methods: This prospective study enrolled 86 hypertriglyceridemic patients (triglycerides ≥ 200 mg/dL) who were divided into two groups: the fenofibrate group (n = 43), who received 160 mg of fenofibrate, and the control group (n = 43). Lipid profiles and renal function were measured at the beginning of the study and after 2 months. Results: The estimated glomerular filtration rate (eGFR) decreased in the fenofibrate group (p < 0.001), but did not change in the control group (p = 0.80). Accordingly, the decrease was more pronounced in the fenofibrate group than the control group (-18.6 ± 8.6 vs. 0.9 ± 9.6%, respectively; p < 0.001). Changes in serum creatinine (p < 0.001) and blood urea nitrogen (p < 0.005) levels were similar to those of eGFR. In a stepwise linear regression analysis, the percent change in creatinine was independently associated with fenofibrate therapy (r = 0.71; p < 0.001) and old age (r = 0.27; p < 0.05) in all patients. In the fenofibrate group, percent change in creatinine was associated with age (r = -0.51; p < 0.001) and smoking (r = 0.42; p < 0.005), while percent change was associated with body mass index (r = 0.31; p < 0.05) in the control group. Elevation of creatinine by 20% or more was associated with fenofibrate therapy (p < 0.001) and old age (p < 0.005) in all patients, and with old age (p < 0.001) in the fenofibrate group. Conclusions: Short-term fenofibrate therapy significantly impaired the renal function of hypertriglyceridemic patients, and this effect was more pronounced in elderly patients. This finding suggests that creatinine levels should be followed in patients receiving fenofibrate therapy. (Korean J Med 2014;86:702-709)

순환잔골재를 사용한 모르터의 물성에 관한 연구

현철 경성대학교 공학기술연구소 2010 공학기술연구지 Vol.16 No.-

Lately, Korea government recommends that concrete maker use more recycled sand in concrete production. Recycled sand needs consuming way because waste concrete cause environmental problems in case of burying in the ground. But the influence of recycled sand about concrete properties including strength and workability is not perfectly researched. Therefore, it is very necessary for recycled sand to be studied about cocrete properties. The aim of this study is to investigate the influence of recycled sand on the properties of mortars that included three different recycled sands. The properties of the mortars were tested with four kinds of sands including three recycled sands and natural sand. The mortars were prepared with the same content. A reference mix was prepared with 100% natural sand, and it was gradually replaced by each recycled sand. The compressive strength of mortars with mixed sands decreased as recycled sand replaced natural sand. In this paper the parameters of Bingham model about cement mortar with recycled were also investigated. According to mix ratio with three recycled sands, the rheological properties of cement mortar were changed. However, slump test or flow test do not allow to obtain information concerning more fundamental phenomena. Rheology has also been used to study the mechanical properties of cement mortar from mixing up to setting. Superplasticiser (SP) was not used. A general mixer was used to study rheology during the very first minutes following the end of mixing. This study evaluated the effect of water/cement ratio (W/C), types of recycled sands and replacement ratio of recycled sand in mortar. The rheometer was used for testing the behaviour of cement mortar.