• 한국소음진동공학회논문집
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• 제21권10호
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• pp.897-904
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• 2011

When whole-body is exposed to vertical vibration, asymmetry shape of human body affects the response on the translational(fore-aft, lateral, vertical) and rotational(roll, pitch, yaw) motion. While the translational motion has been studied with various titles, it has been rare to study the rotational motion of human body exposed to vertical excitation because of lack of experimental equipment. This study was performed by using a 6-axis force plate installing strain gage type sensors for the rotational response. Sixteen male subjects were exposed to vertical vibration on rigid seat in order to investigate apparent mass of three translational motion and apparent eccentric mass of three rotational motion. Random signal was generated to make excitation vibration which was on an effective frequency range of 3~40 Hz, and magnitude of 0.224 m/$s^2$ r.m.s. The frequency range and magnitude used was selected for the vibration of passenger vehicle on idling condition. As the result, cross-axis apparent masses of fore-and-aft and lateral direction were not significant showing 20 % and 3 % of vertical apparent mass relatively. And apparent eccentric mass of pitch motion was dominant when compared to that of roll and yaw motion, which is reasoned by asymmetry direction of human body sitting on a seat.

• 대한수학교육학회지:수학교육학연구
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• 제20권4호
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• pp.445-458
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• 2010

이 연구는 양 개념의 발달 과정을 알아보고 초등학교에서 양의 계산을 어떤 방식으로 다루는지를 분석함으로써 교육과정이나 교과서의 구성에 대한 시사점을 찾아보려는 것이다. 이산량과 연속량의 이원론에 근거한 유클리드의 수와 양의 구분은 이후 수학자에게 큰 영향을 미치다가 스테빈에 의해 극복되었다. 양의 덧셈과 뺄셈은 오래전부터 시행되어 왔지만, 양의 곱셈과 나눗셈은 수학계에서 될 수 있는 대로 피하려고 하였다. 그러나 자연과학계에서는 전부터 물리량의 계산을 허용하여왔고, 물리량 체계를 모델화한 대수 구조를 만들어 양의 곱셈이나 나눗셈을 이론적으로 정당화하였다. 교육과정과 교과서를 조사해 본 결과 우리나라 초등학교 수학과에서는 다른 나라와 비교하여 양의 계산 지도를 등한시하고 있음이 드러났다. 앞으로 이에 대해 충분한 논의를 하여 우리나라의 교육과정에서도 양에 대해 좀 더 적극적으로 지도할 수 있도록 명시하고, 현재 삭제된 내포량도 수학과에서 다룰 수 있도록 해야 할 것이다. 문장제도 실생활 관련 문제를 많이 제시하여 자연스럽게 양의 계산을 할 수 있도록 해야 하며, 문장제를 해결하는 과정에서 수로 된 식만 쓸 것이 아니라 단위를 붙인 식을 써서 양적인 추론에 도움을 줄 수 있도록 하는 문제에 대해서도 논의할 필요가 있다.

• 한국재료학회지
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• 제28권2호
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• pp.118-123
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• 2018

5 nm-thick $SiO_2$ layers formed by plasma-enhanced chemical vapor deposition (PECVD) are densified to improve the electrical and interface properties by using nitric acid oxidation of Si (NAOS) method at a low temperature of $121^{\circ}C$. The physical and electrical properties are clearly investigated according to NAOS times and post-metallization annealing (PMA) at $250^{\circ}C$ for 10 min in 5 vol% hydrogen atmosphere. The leakage current density is significantly decreased about three orders of magnitude from $3.110{\times}10^{-5}A/cm^2$ after NAOS 5 hours with PMA treatment, although the $SiO_2$ layers are not changed. These dramatically decreases of leakage current density are resulted from improvement of the interface properties. Concentration of suboxide species ($Si^{1+}$, $Si^{2+}$ and $Si^{3+}$) in $SiO_x$ transition layers as well as the interface state density ($D_{it}$) in $SiO_2/Si$ interface region are critically decreased about 1/3 and one order of magnitude, respectively. The decrease in leakage current density is attributed to improvement of interface properties though chemical method of NAOS with PMA treatment which can perform the oxidation and remove the OH species and dangling bond.

• Bulletin of the Korean Chemical Society
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• 제29권4호
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• pp.790-794
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• 2008

Nucleophilic addition reaction of benzenethiols (PhSH) to 1-(2-nitrovinyl) benzenes ($\beta$ NS) in the presence of triethylamine (TEA) has been studied in acetonitrile at 25 ${^{\circ}C}$. The rate is first order with respect to [PhSH], [TEA] and [$\beta$ NS]. The reaction is found to proceed with the formation of ion-pair between benzenethiol and TEA. A suitable mechanism with the formation of an adduct between ion-pair and substrate in a slow step followed by its rearrangement to 1,2-addition product in a fast step has been proposed and corresponding rate law derived. From the rate law, the rate constants for the interaction between ion-pair and $\beta$NS have been evaluated. Interestingly, in both para-substituted substrates and benzenethiols the rate increases with the electron-withdrawing power of the substituents. The positive sign of $\rho_x$ in benzenethiols has been explained. The magnitude of cross-interaction constant, $\rho_{xy}$ is small (0.08). The magnitude of the Hammett $\rho_x$ values is higher than that of the Bronsted, $\beta_x$ values for benzenethiols. The kinetic isotope effect, $k_H/k_D$, is found to be greater than unity. A suitable transition state with simultaneous formation of $C_\beta$ -H and $B_\alpha$ -S bonds involving the ion-pair and $\beta$NS in a single concerted step has been proposed to account for these observations.

• 한국전자통신학회논문지
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• 제16권2호
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• pp.261-270
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• 2021

본 연구에서는 계통 연계 3상 인버터를 위한 LCL 필터를 설계 방법론을 연구하였다. 먼저, 대표적인 필터 구조들에 대해서 3상 인버터의 계통 연계를 위한 필터로서의 적용 시 장단점을 분석하였다. 다음, 3상 인버터의 계통 연계를 위한 필터 설계 방법론들을 분석하여 그리드 연계 시 고조파 요구 조건을 만족할 수 있는 효과적인 필터 설계 방법론을 결정하였다. 그리고 설계 방법론의 유효성을 확인하기 위해서 EMTP-RV를 이용하여 3상 인버터, LCL 필터 그리고 필터의 성능을 평가하기 위한 성능 평가 시스템을 모델링 하였다. 끝으로, 하나의 3상 인버터에 대한 LCL 필터를 설계하였으며, EMTP-RV 시뮬레이션 작업을 통해 3상 인버터의 출력 전류 리플의 크기가 제한됨을 확인함으로서 설계 방법론의 유효성을 검증할 수 있었다.

• 한국구조물진단유지관리공학회 논문집
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• 제27권1호
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• pp.9-18
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• 2023

이 논문의 목적은 콘크리트 댐의 내진성능평가 시 현행 설계기준과 평가요령에서 제시하는 감쇠비 값 크기에 대한 적용방안의 적정성을 검토하고 개선안을 제시하는 것이다. 연구결과 동적탄성해석 시 감쇠비의 크기는 지진하중의 크기가 유사하고 감쇠비에 대한 재현성이 검증된 유사댐의 사례를 참조할 필요가 있으며, 동적소성해석 시에는 지진하중의 크기와 상관없이 초기 탄성거동을 고려하여 감쇠비를 낮은값으로 적용하고 비선형 거동 시 이력감쇠가 추가되도록 고려할 필요가 있다. 또한 암반상에 위치한 콘크리트 댐체는 방사감쇠 효과가 미미하므로 방사감쇠를 반영하기 위해 콘크리트 댐체의 감쇠비를 증가시키는 것은 합리적이지 않다. 따라서 콘크리트 댐의 현실적인 내진성능평가를 위해 현행 댐 설계기준과 평가요령에 수록된 감쇠비 관련내용에 대해 개정이 필요하다.

• 대기
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• 제29권4호
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• pp.381-390
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• 2019

This study investigates the impacts of urban land-use fraction and temperature advection on the urban heat island intensity over the Seoul metropolitan area using the UM (Unified Model) with the MORUSES (Met Office Reading Urban Surface Exchange Scheme) during the heat wave over the region from 2 to 8, August 2016. Two simulations are performed with two different land-use type, the urban (urban simulation) and the urban surfaces replaced with grass (rural simulation), in order to calculate the urban heat island intensity defined as the 1.5-m temperature difference between the urban and the rural simulations. The land-use type for the urban simulation is obtained from Korea Ministry of Environment (2007) land-use data after it is converted into the types used in the UM. It is found that the urban heat island intensity over high urban-fraction regions in the metropolitan area is as large as 1℃ in daytime and 3.2℃ in nighttime, i.e., the effects of urban heat island is much larger for night than day. It is also found that the magnitude of urban heat island intensity increases linearly with urban land-use fraction. Spatially, the estimated the urban heat island intensities are systematically larger in the downwind regions of the metropolitan area than in the upwind area due to the effects of temperature advection. Results of this study indicate that urban surface fraction in the city area and temperature advection play a key role in determining the spatial distribution and magnitude of urban heat island intensity.

• 수산해양기술연구
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• 제47권4호
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• pp.411-418
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• 2011

As a fish way is a structure for fish migrating well toward upper stream due to breaking river flow by a dam or dammed pool, the specific fish's swimming ability is one of the main factors in making a plan and managing it. In addition, it also needs to understand the current field in fish road to evaluate its performance. This study is aimed to analyze the swimming patterns with current velocity changes using a Particle Imaging Velocimetry (PIV) in order to understand the swimming ability of silver fish (Plecoglossus altivelis) that is one of the fishes migrating through the fish way of Nakdong River, and to analyze the 2 dimensional current field near to silver fish at swimming momentum. The results showed that average values of tail beat frequencies for continuous swimming with current velocity were 2.8 Hz at 0.3 m/s, 3.2 Hz at 0.4 m/s, 3.8 Hz at 0.5 m/s, respectively. The wake would be produced by direction turning of fish's tail fin and its magnitude would be verified by the difference of pressure. The pressure turbulent flow produced by its tail beat would be made in both sides, and then, the magnitude of wake should be the source of moving direction. The swimming momentum will help to support the primary factor in making a suitable design for specific fish species migrating toward the district river.

• 한국지반공학회논문집
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• 제34권6호
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• pp.25-36
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• 2018

지반의 액상화는 지진 피해의 대표적인 형태 중 하나이다. 이는 막대한 인적 경제적 피해를 줄 수 있는 현상으로, 지반구조물의 설계 전 필수적으로 검토해야 하는 대상이다. 본 연구에서는 하천 제방을 대상으로 임의의 지진 규모와 수위에서 액상화에 대한 실용적인 복합재해 취약도 곡면 작성법을 제시하였다. 지반의 파괴 정도를 나타내는 액상화 가능 지수(LPI)로 제방의 액상화에 대한 한계상태를 정의하였다. 지반 물성치의 불확실성을 고려하기 위해 Monte Carlo Simulation 기반의 확률론적 해석을 수행하였고, 해석 결과를 바탕으로 임의 수준의 수위와 지진 규모에 대하여 액상화에 의한 파괴확률을 나타내는 3차원의 취약도 곡면을 작성하였다. 작성된 복합재해 취약도 곡면은 홍수 및 지진에 대한 제방의 안전성 평가와 취약지역에 대한 위험도 평가에 사용될 수 있다.

• 한국운동역학회지
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• 제25권1호
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• pp.39-47
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• 2015

Objective : The purpose of this study was to investigate the velocity conversion coefficient and invariance for the optimal phase ratio on the performance of the women's triple jump. Methods : Three-dimensional kinematic data were obtained from the three finalists of the women's triple jumper competition at the 2011 Daegu IAAF World Championships. Computer simulations were performed using the biomechanical model of the triple jump to optimize the phase ratio for the longest actual distance for all athletes with altered velocity conversion coefficients. Results : Top elite triple jumpers showed better technical consistency at the phase ratio. Also, no consistent relationship was observed between the loss in horizontal velocity and the gain in vertical velocity across supporting the three phase. In addition, regardless of the magnitude A1, all athletes were optimized with jump-dominated technique. Finally, as the magnitude of A1 increased, the athletes showed better performance. The obtained overall distance jumped showed the longest actual distance when the optimal phase ratio was transferred from hop-dominated to jump-dominated(the step ratio was 30%~31%), and when the optimal phase ratio was transferred from balanced to jump-dominated(the step ratio was 27%~29%). Conclusion : Future studies need to be conducted in order to explore the active landing motion and the inclination angle of the body with the velocity conversion coefficient simultaneously at each supporting phase.