• 공업화학
• /
• 제30권2호
• /
• pp.254-259
• /
• 2019

본 연구에서는 마그네슘-층상규산염(MgP) 층간에 솔잎 추출물(PLE)이 삽입되어 겹겹이 쌓여있는 샌드위치 구조의 나노입자(PLE/MgP)를 one-pot으로 합성하였다. XRD 분석을 통해 팔면체와 사면체 구조로 MgP가 성공적으로 합성되었으며, PLE가 층간에 삽입되어 MgP 간의 층간거리(d-spacing)가 벌어진 것을 확인하였다. HR-TEM을 통해 모폴로지 변화를 관찰하였으며, 열중량분석법을 통해 PLE가 MgP 대비 10%까지 함유된 것을 확인하였다. 최소저해농도(MIC) 및 최소 사멸농도(MBC) 분석을 통해 피부 상재균에 대한 항균 활성을 검토한 결과 MgP 또는 PLE보다 PLE/MgP의 항균 활성이 더욱 향상된 것을 확인하였다. 이러한 결과는 본 연구에서 개발한 PLE/MgP 유/무기 복합 소재가 화장품 소재, 의료용 소재 등의 다양한 분야에 적용 가능함을 확인하였다.

• 한국컴퓨터정보학회논문지
• /
• 제26권1호
• /
• pp.283-291
• /
• 2021

본 연구에서는 초등학교 3학년 분수 관련 내용을 학습 주제로 하여 재구성한 학습 부진 개선을 위한 소프트웨어 교육 프로그램을 개발하고 적용하였다. 학습 부진 개선을 위한 소프트웨어 교육프로그램은 프로젝트 학습 모형을 바탕으로 소프트웨어 교육의 성격과 학습 부진 학습자의 특성을 고려하여 그 구조를 설계하였고, 학습내용을 학습 과정에서 자연스럽게 체득할 수 있도록 의도적으로 배치하였으며, 반복적으로 경험하여 충분히 학습할 수 있도록 매 차시 구축하였다. 프로그램 적용 결과 실험군과 대조군 모두 학업 성취도, 메타인지, 자아존중감, 자기효능감의 유의미한 변화가 있었으나 실험군이 대조군에 비해 모든 영역에서 향상 정도가 큰 것으로 나타났다. 본 교육 프로그램은 학습 부진 개선이라는 측면과, 소프트웨어 교육이 가지고 있는 다양한 교육적 효과를 바탕으로 학습 부진 학생이 프로그램에 재구성된 과목의 학습 내용을 효과적으로 학습할 수 있다는 점에서 그 의미가 있다.

• Journal of Electrochemical Science and Technology
• /
• 제12권4호
• /
• pp.406-414
• /
• 2021

Electrochemical devices are constructed for continuous syngas (CO + H₂) production with controlled selectivity between CO₂ and proton reduction reactions. The ratio of CO to H₂, or the faradaic efficiency toward CO generation, was mechanically manipulated by adjusting the space volume between the cathode and the polymer gas separator in the device. In particular, the area added between the cathode and the ion-conducting polymer using 0.5 M KHCO₃ catholyte regulated the solution acidity and proton reduction kinetics in the flow cell. The faradaic efficiency of CO production was controlled as a function of the distance between the polymer separator and cathode in addition to that manipulated by the electrode potential. Further, the electrochemical CO₂ reduction device using Au NPs presented a stable operation for more than 23 h at different H₂:CO production levels, demonstrating the functional stability of the flow cell utilizing the mechanical variable as an important operational factor.

• 반도체디스플레이기술학회지
• /
• 제21권2호
• /
• pp.25-31
• /
• 2022

By an aid of needle coating, we have fabricated a spherical microlens array using poly(methyl methacrylate) for potential applications in light extraction of organic light-emitting diodes. With an attempt to achieve high-density and high-aspect-ratio microlens arrays, we have investigated the coating behaviors by varying the material parameters such as the solute concentration and wettability of the poly(methyl methacrylate) solution and process parameters such as the dwell time of needle near the substrate, retract distance of needle from the substrate, and coating gap between the needle and substrate. Under the optimized coating conditions, it is demonstrated that high-aspect-ratio microlens arrays can be obtained using a coating solution with high solute concentration and a small amount of a hydrophobic solvent. It is found that the diameter and height of microlens array are decreased with increasing poly(methyl methacrylate) concentration, yet the overall aspect ratio is rather enhanced. By the addition of 5 wt% hexylamine in 35 wt% poly(methyl methacrylate) solution, we have achieved a spherical microlens with the height of 7.7 ㎛ and the width of 94.24 ㎛ (the aspect ratio of 0.082). To estimate the capability of light extraction by the microlens array, we have performed ray tracing simulations and demonstrated that the light extraction efficiency of organic light-emitting diode is expected to be enhanced up to 24%.

• Structural Engineering and Mechanics
• /
• 제83권2호
• /
• pp.153-166
• /
• 2022

Structural pounding due to strong seismic excitations can result in severe damage or even collapse of colliding structures. Many researchers focused on studying the mutual pounding between two adjacent structures while very few researches were concerned with the pounding of a series of structures. This paper aims to study the pounding effect on a series of four buildings having different natural frequencies. The paper also investigates the effect of different arrangements of the four buildings on their pounding response. For this, a mathematical model was constructed using Matlab code where, pounding was modeled using a contact force-based approach. A Non-Linear viscoelastic (Hertzdamp) contact element was used and activated only during the approach period of collision. The mathematical model was validated by comparing its prediction versus experimental results on three adjacent buildings. Then the model was used to study the pounding between four adjacent structures arranged in different sequences according to their natural frequencies. The results revealed that increasing the gap distance generally led to decrease the peak responses of the towers. Such response is somehow different from that predicted earlier by the authors for the case of three adjacent buildings. Moreover, the arrangement of towers has a significant effect on their pounding response. Significant difference between the natural frequencies of adjacent structures increases the pounding forces especially when the more flexible buildings are located at the outer edge of the series. The study points out the need for further researches on buildings in series to gain a better understanding of such complex phenomena.

• Earthquakes and Structures
• /
• 제22권6호
• /
• pp.625-635
• /
• 2022

High-rise buildings (HRBs) are considered one of the most common structures nowadays due to the population growth, especially in crowded towns. The lack of land in crowded cities has led to the convergence of the HRBs and the absence of any gaps between them, especially in lands with weak soil (e.g., liquefaction-prone soil), but then during earthquakes, these structures may be exposed to the risk of collision between them due to the large increase in the horizontal displacements, which may be destructive in some cases to the one or both of these adjacent buildings. To evaluate methods of reducing the risk of collision between adjacent twin HRBs, this research investigates three vibration control methods to reduce the risk of collision due to five different earthquakes for the case of two adjacent reinforced concrete (RC) twin high-rise buildings of 15 floors height without gap distance between them, founded on raft foundation supported on piles inside a liquefaction-prone soil. Contact pounding elements between the two buildings (distributed at all floor levels and at the raft foundation level) are used to make the impact strength between the two buildings realistic. The mitigation methods investigated are the base isolation, the tuned mass damper (TMD) method (using traditional TMDs), and the pounding tuned mass damper (PTMD) method (using PTMDs connected between the two buildings). The results show that the PTMD method between the two adjacent RC twin high-rise buildings is more efficient than the other two methods in mitigating the earthquake-induced pounding risk.

• Journal of Korea Trade
• /
• 제24권3호
• /
• pp.20-36
• /
• 2020

Purpose - As the global product network expands through both internationalization and diversification of the multimodal transportation system, corporate strategies have shifted to emphasize the importance of a high value-added international logistics system. To guide policies and strategies to attract relevant industries, this study aims to analyze the location competitiveness of regional logistics distribution center to serve Northeast Asia. Design/methodology - Multi-criteria techniques are considered to offer a promising framework for evaluating decision-making factors. This paper employed an analytic hierarchy process to analyze the hierarchal structure of determinants for selecting the location of a regional logistics distribution center. Adopting both qualitative and quantitative evaluations, this study suggest political implications for a regional logistics distribution center development, such as the direction of political support, service differentiation and infrastructure development. Findings - This study developed a location competitiveness evaluation model, based on the case study of the major port-cities in Northeast Asia. Evaluation model incorporates five factors underpinning 17 components extracted using factor analysis. The results revealed that the logistics factor is the most significant factor for evaluating the competitiveness of a regional logistics distribution center. The remaining factors were market, costs, and services environment. Comparing qualitative and quantitative evaluations, results provide useful insights for a regional logistics distribution center development in Northeast Asia. Originality/value - This study revealed differences between qualitative and quantitative evaluations. The finding implies that prior works on evaluation models of competitiveness has not successfully measured the gap between quantitative data and expert' evaluations. To overcome this limitation, this paper considered both actual data such as actual distance, cost, the number of companies located, and expert opinions.

• Structural Engineering and Mechanics
• /
• 제85권3호
• /
• pp.381-391
• /
• 2023

The seismic performance of the tall building equipped with a tuned mass damper (TMD) considering soil-structure interaction (SSI) effects is well studied in the literature. However, these studies are performed on the nominal model of the seismic-excited structural system with SSI. Hence, the outcomes of the studies may not valid for the actual structural system. To address the study gap, the reliability theory as a useful and powerful method is utilized in the paper. The present study aims to carry out reliability analyses on tall buildings equipped with TMD under near-field pulse-like (NFPL) ground motions considering SSI effects using a subset simulation (SS) method. In the presence of uncertainties of the structural model, TMD device, foundation, soil, and near-field pulse-like ground motions, the numerical studies are performed on a benchmark 40-story building and the failure probabilities of the structures with and without TMD are evaluated. Three types of soils (dense, medium, and soft soils), different earthquake magnitudes (M_w = 7,0. 7,25. 7,5 ), different nearest fault distances (r = 5. 10 and 15 km), and three seismic performance levels of immediate occupancy (IO), life safety (LS), and collapse prevention (CP) are considered in this study. The results show that tall buildings built near faults and on soft soils are more affected by uncertainties of the structural and ground motion models. Hence, ignoring these uncertainties may result in an inaccurate estimation of the maximum seismic responses. Also, it is found the TMD is not able to reduce the failure probabilities of the structure in the IO seismic performance level, especially for high earthquake magnitudes and structures built near the fault. However, TMD is significantly effective in the reduction of failure probability for the LS and CP performance levels. For weak earthquakes and long fault distances, the failure probabilities of both structures with and without TMD are near zero, and the efficiency of the TMD in the reduction of failure probabilities is reduced by increasing earthquake magnitudes and the reduction of fault distance. As soil softness increases, the failure probability of structures both with and without TMD often increases, especially for severe near-fault earthquake motion.

• Earthquakes and Structures
• /
• 제23권2호
• /
• pp.129-138
• /
• 2022

One of the objectives to prevent building pounding between two adjacentstructures is to considerseparation distance or decrease relative displacement during seismic excitation. Although the majority of building codes around the world have basically suggested some equations or approximately recommended various distances between structuresto avoid pounding hazard, but a lot of reportsin zone of pounding have obviously shown thatsafety situation or economic consideration are not always provided due to the collisions between buildings and the cost of land, respectively. For this purpose, a dynamic MDOF model by having base isolation system is numerically considered and using various earthquake records, relative displacements are mathematically investigated. Different equations to determine the value of damping ratio are collected and the results of evaluations are listed for comparison among them to present a new equation for determination of impact damping ratio. Presented equation is depends significantly on impact velocity before and after impact based on artificial neural network, which the accuracy of them is investigated and also confirmed. In order to select the optimum equation, hysteresisloop of impact between base of building and rubber bumper is considered and compared with the hysteresis loop of each impact, calculated by different equations. Finally, using representative equation, the effect of thickness, number and stiffness of rubber bumpers are numerically investigated. The results of analysis indicate that stiffness and number of bumpers have significantly affected in zone of impact force while the thickness of bumpers have not shown significant influence to calculate impact force during earthquake. For instance, increasing the number of bumpers, gap size between structures and also the value of stiffness is caused to decrease impact force between models. The final evaluation demonstrates that bumpers are able to decrease peak lateral displacement of top story during impact.

• 한국음향학회지
• /
• 제26권8호
• /
• pp.381-389
• /
• 2007

본 논문에서는 천해역에서 PN 신호열의 자기상관특성을 이용하여 수중 초음파통신 채널 특성을 측정하는 방법과 수신 신호 샘플 데이터로부터 수중통신 채널 특성 분석 결과에 대하여 기술한다. 수중음향통신 채널의 특성을 측정하기 위하여 두개의 PN 신호를 I-채널 및 Q-채널 데이터로 사용하여 QPSK 심볼을 생성하고, 5 kHz 심볼율과 25 kHz 반송파를 갖는 신호로 변조하여 전송한다. 수신부는 송신기에서 675 m와 1492 m 떨어진 위치에서 수신 신호를 샘플링하여 저장한다. 저장된 샘플 데이터를 이용하여 산란 함수, 상관 시간, 지연전력 프로파일, spaced-tone 자기상관함수, 지연 확산 및 상관 대역폭을 각각의 음파 전파 거리에 대하여 분석한다. 또한, 분석한 채널 특성을 토대로 수중 전송 시스템 설계 및 구현을 위한 설계 지침을 제안한다.