• Journal of the Korea Institute of Building Construction
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• v.23 no.5
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• pp.519-526
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• 2023

This research endeavors to explore the nuances in apparent resistivity readings in concrete specimens due to the proximity of embedded reinforcement. To systematically gauge this, concrete samples incorporating singular and paired rebars were meticulously crafted. These rebars were strategically positioned at intervals of 0.03m, 0.04m, and 0.05m from each specimen's midpoint. Subsequent resistivity assessments were conducted at 0.01m increments up to the predetermined rebar location for each sample. A consistent observation was the nadir in apparent resistivity manifesting at the rebar's epicenter. Notably, dual-rebar configurations registered lower resistivity values at this central juncture compared to their single-rebar counterparts. This metric underscores the palpable impact of surrounding reinforcement on resistivity readings. Further, as the spatial separation between rebars increased, the distinctness in their locational identification via resistivity became increasingly pronounced.

• Journal of the Earthquake Engineering Society of Korea
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• v.3 no.2
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• pp.87-96
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• 1999

To analyze the dynamic behavior of structure, direct integration and mode superposition may be utilized in time domain analysis. As finite number of frequencies can give relatively exact solutions, mode superposition is preferable in analyzing structural behavior. In non-linear analysis, however, mode superposition is seldom used since time-varying element stiffness changes stiffness matrix, and the change of stiffness matrix leads to the change of essential constants - natural frequencies and mode shapes. In spite of these difficulties, there are some attempts to adopt mode superposition because of low cost compared to direct integration, but the result is not satisfactory. In this paper, a method using mode superposition in non-linear analysis is presented by separating local element stiffness from global stiffness matrix with the difference between linear and non-linear restoring forces to the external force vectors included. Moreover, the hysteresis model changing with the relative deformation in each floor makes it possible to analyze non-linear behavior of structure. The proposed algorithm is applied to shear beam model and the maximum displacement is compared with the result using direct integration method.

• Journal of the Korean Geotechnical Society
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• v.29 no.2
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• pp.35-45
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• 2013

The void ratio is an important parameter for reflecting the soil behavior including physical property, compressibility, and relative density. The void ratio can be obtained by laboratory test with extracted soil samples. However, the specimen has a possibility to be easily disturbed due to the stress relief when extracting, vibration during transportation, and error in experimental process. Thus, the theoretical equations have been suggested for obtaing the void ratio based on the elastic wave velocities. The objective of this paper is to verify the accuracy of the proposed analytical solution through the error norm. The paper covers the theoretical methods of Wood, Gassmann and Foti. The elastic wave velocity is determined by the Field Velocity Probe in the southern part of Korean Peninsular. And the rest parameters are assumed based on the reference values. The Gassmann method shows the high reliability on determining the void ratio. The error norm is also analyzed as substitution of every parameter. The results show every equation has various characteristics. Thus, this paper may be widely applied for obtaining the void ratio according to the field condition.

• Journal of the Korean Applied Science and Technology
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• v.36 no.1
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• pp.142-152
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• 2019

This study aimed to explore the association between obesity index and heart rate variability (HRV) in college-aged male smokers. A total of 85 male college students (> 10 cigarettes per day for at least 3 years) were participated in this study. According to a standardized protocol, body mass index (BMI), percent body fat (%BF), waist circumference (WC), and waist-to-hip ratio (WHR) were taken as obesity indices. Resting r-r interval was monitored for HRV analysis as an indicator of cardiac autonomic regulation. Compared with low WHR subjects, high WHR subjects had significantly lower values of rMSSD, pNN50, HF, and SD1, suggesting decreased parasympathetic activity. No such differences in LF/HF ratio were found between the WHR-based subgroups. Bivariate correlation analysis showed that obesity indices of WC, WHR, and %BF were significantly associated with rMSSD, pNN50, HF, and SD1, with a tendency for correlation coefficient to be higher with WHR than with WC or %BF. No significant association was found between BMI and HRV parameters indicative of parasympathetic activity. This study suggest that central obesity is significantly associated with decrease in parasympathetic activation, independent of BMI as an indicator of obesity, in male college smokers.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2009.11a
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• pp.53-56
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• 2009

최근 HD 방송의 실현과 함께 HDTV가 빠르게 상용화되면서 고화질 비디오를 더 효율적으로 압축하기 위한 기술 개발이 활발하게 진행되고 있다. 최신 표준 비디오 압축 방식인 H.264/AVC에서는 고정 6탭 필터를 사용하여 참조 영상을 보간하고 움직임 예측을 수행하는데, 이의 압축 효율을 향상시키기 위하여 고정 필터를 개선한 비분리 적응형 보간 필터가 개발되었다. 하지만 비분리 적응형 보간 필터는 압축률뿐만 아니라 계산량도 증가하는 단점이 있기 때문에 2차원 필터를 1차원 필터의 연결로 모델링 한 분리 적응형 보간 필터가 개발되었고, 그 결과 압축률은 비슷하게 유지하면서 계산량을 훨씬 줄일 수 있게 되었다. 분리 적응형 보간 필터는 1차원 필터 모델링을 할 때, 수평방향의 필터링 수행 후 수직방향 필터링을 하기 때문에 이를 통해 만들어진 보간 영상은 원 영상의 수평방향에 대한 특성을 더 많이 반영하게 된다. 따라서 수직방향으로 더 높은 주파수 특성을 갖는 영상의 경우에는 효율이 떨어지게 된다. 이를 고려하여 본 논문에서는 영상의 수직방향 주파수 특성을 더 많이 반영할 수 있는 보간 필터를 추가함으로써 영상의 주파수 특성에 따라 보간 필터를 적응적으로 선택하는 향상된 분리 적응형 보간 필터를 제안한다. 제안한 알고리즘을 이용할 경우 기존의 분리 적응형 보간 필터에 비해 움직임 예측 및 보상이 더 정확하게 이뤄질 수 있으며, 부호화 효율이 향상됨을 확인할 수 있다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.2
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• pp.265-271
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• 2016

DEA is a typical method that allows measurements and evaluations of the efficiency. This study examined the management efficiency of bean farm households to suggest factors that influence the management efficiency. The results showed that a larger cultivation area has more positive effects on the scale efficiency of beans farm households. When summing up farmer's family labor, lease fee, hired labor cost, which are strongly related to the workforce, it reached up to 54.6%. This means that they all occupy more than half of the production cost and they show an increasing trend. Moreover, although the hired labor rate is higher, it has more positive influences on the gross efficiency, technical efficiency and scale efficiency. In addition, the results showed that environmentally-friendly agriculture decreases the efficiency.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.11
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• pp.1049-1059
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• 2010

This paper treats the aerodynamic optimization of the blade planform for helicopters. The blade shapes, which should be determined during the threedimensional aerodynamic configuration design step, are defined and are parameterized using the B$\acute{e}$zier curves. This research focuses on the design approaches generally adopted by industries and or research institutes using their own experiences and know-hows for the parameterization and for the definition of design constraints. The hover figure of merit and the equivalent lift-to-drag ratio for the forward flight are used to define the objective function. The resultant nonlinear programming (NLP) problem is solved using the sequential quadratic programming (SQP) method. The applications show the present method can design the important planform shapes such as the airfoil distribution, twist and chord variations in the efficient manner.

• Journal of the Korea Society of Computer and Information
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• v.18 no.3
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• pp.69-77
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• 2013

This research validates the correlation between usability and functional attributes whilst comparing the degree of satisfaction of information framework used in museum mobile apps via usability evaluation in pre-visit setting. In cases of Bilbao Guggenheim and American Natural History Museum apps, the degree of satisfaction measured for information service, functional attributes, motivation for actual museum visit and during-visit usability of the apps were all highly evaluated. Such evaluation data indicates the increased usability of apps when mobile applications take user-friendly design that intuitively reflect users' interests and needs. After thorough analysis of correlation between usability and fictional attributes, data pointed to more meaning relationships existed in non-intrusiveness and personalization than other functional attributes. In conclusion, we were able to acknowledge the usability of museum mobile apps depends upon the interaction between content and functional attributes rather than entertainment factor and technology.

• The Korean Journal of Financial Management
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• v.26 no.3
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• pp.31-64
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• 2009

This article investigates the short-term cash flow exposures to Korea's major trading partners' currencies based on the kospi and kosdaq firm data from 2000 to 2008. The cash flow approach allows us to analyze the influence on operational performances of individual firm's hedging strategies. Taken all three foreign exchange rates together, more than 30% of the sample firms exhibit significant exposure. Given that the short-term cash flow is rather easy to hedge, the result proves a poor exchange rate risk management practices of Korean firms. Kosdaq firms are more exposed than Kospi firms. On the contrary to the previous researches using stock prices, the operational cash flows show a positive relationship with the value of foreign currencies. The exchange rate-firm sample further shows that the size and leverage affect the level of exposure.

• Journal of the Earthquake Engineering Society of Korea
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• v.12 no.3
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• pp.21-28
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• 2008

To evaluate the seismic performance of multi-degree of freedom(MDF) systems, repeated nonlinear response history analyses are often conducted, which require extensive computational efforts. To reduce the amount of computation required, equivalent single degree of freedom(SDF) systems representing complex multi-degree of freedom(MDF) systems have been developed. For the equivalent SDF systems, bilinear models and trilinear models have been most commonly used. In these models, the P-$\Delta$ effect due to gravity loads during earthquakes can be accounted for by assigning negative stiffness after elastic range. This study evaluates the adequacy of equivalent SDF systems having these hysteretic models to predict the actual response of steel moment resisting frames(SMRF). For this purpose, this study conducts cyclic pushover analysis, nonlinear time history analysis and incremental dynamic analysis(IDA) for SAC-Los Angeles 9-story buildings using nonlinear MDF models(exact) and equivalent SDF models(approximate). In addition, this study considers the strength limited model.