• Structural Engineering and Mechanics
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• v.87 no.5
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• pp.405-418
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• 2023

This study focused on the effectiveness of seismic isolation technique in case of a reinforced concrete structure with soft story defined as the stiffness irregularity between adjacent stories. In this context, a seismically isolated 3-story reinforced concrete structure was analyzed by gradually increasing the first story height (3.0, 4.5, and 6.0 m). The seismic isolation system of the structure is assumed to be composed of lead rubber bearings (LRB). In the analyses, isolators were modeled by both deteriorating (temperature-dependent analyses) and non-deteriorating (bounding analyses) hysteretic representations. The deterioration in strength of isolator is due to temperature rise in the lead core during cyclic motion. The ground motion pairs used in bi-directional nonlinear dynamic analyses were selected and scaled according to codified procedures. In the analyses, different isolation periods (Tiso) and characteristic strength to weight ratios (Q/W) were considered in order to determine the sensitivity of structural response to the isolator properties. Response quantities under consideration are floor accelerations, and interstory drift ratios. Analyses results are compared for both hysteretic representations of LRBs. Results are also used to assess the significance of the ratio between the horizontal stiffnesses of soft story and isolation system. It is revealed that seismic isolation is a viable method to reduce structural damage in structures with soft story.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.35 no.3
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• pp.57-66
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• 2023

In order to understand the economic feasibility of an offshore wind farm, this paper analyzed the differences in LCOE (levelized cost of energy) according to the support type and construction method of the substructure in terms of LCOE and sensitivity analysis was conducted according to the main components of LCOE. As for the site to be studied, the Southwest Offshore Wind Farm was selected, and the capital expenditures were calculated according to the size of the offshore wind farm and the installation unit. As a result of the sensitivity analysis, major components showed high sensitivity to availability, turbine related cost, weighted average cost of capital and balance of system related cost. Moreover, the post-piling jacket method, which was representatively applied to the substructure of the offshore wind farm in Korea, was selected as a basic plan to calculate the capital expenditures, and then the capital expenditures of the pre-piling jacket method and the tripod method were calculated and compared. As a result of analyzing the LCOE, it was confirmed that the pre-piling jacket method of the supporting structure lowers the LCOE and improves economic feasibility as the installation number of turbines increases.

• Korean Journal of Agricultural and Forest Meteorology
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• v.16 no.4
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• pp.259-266
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• 2014

Understanding the forest fire patterns is necessary to comprehend the stability of the forest ecosystems. Thus, researchers have suggested the simulation models to mimic the forest fire spread dynamics, which enables us to predict the forest damage in the scenarios that are difficult to be experimentally tested in laboratory scale. However, many of the models have the limitation that many of them did not consider the complicated environmental factors, such as fuel types, wind, and moisture. In this study, we suggested a simple model with the factors, especially, the geomorphological structure of the forest and two types of fuel. The two fuels correspond to susceptible tree and resistant tree with different probabilities of transferring fire. The trees were randomly distributed in simulation space at densities ranging from 0.5 (low) to 1.0 (high). The susceptible tree had higher value of the probability than the resistant tree. Based on the number of burnt trees, we then carried out the sensitivity analysis to quantify how the forest fire patterns are affected by the structure and tree density. We believe that our model can be a useful tool to explore forest fire spreading patterns.

• Journal of the Korean Society of Radiology
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• v.9 no.6
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• pp.363-367
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• 2015

Digital radiography is divided into the direct method using photoconductor and indirect method using phosphor based on the principles in acquiring the image information, but both have different advantages and disadvantages. Therefore, this study conducted a preliminary research on the structure of the hybrid detector that combined phosphor and photoconductor to improve the sensitivity of X-ray. As a result, when the tube voltage was adjusted at 30ms of exposure time, the direct structure displayed an overall excellent sensitivity, but at the exposure time of 50ms or more, the hybrid structure displayed a better outcome. This seems to have enough research value considering that various clinical examinations usually include 50ms or more exposure time.

• Journal of Korean Academy of Nursing
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• v.34 no.3
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• pp.504-514
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• 2004

Purpose: The purpose of this study is to identify the influencing factors of mother-infant attachment and construct a descriptive model that explains mother-infant attachment during the early postpartum period. Method: The hypothetical model of this study consisted of 8 variables with 23 constructed paths. The subjects of this study were 152 postpartum women. Data was analyzed to test the hypothetical model using covariance structure analysis. Result: The final model which is modified from the hypothetical model improved to Chi-Square 41.92, GFI .95, AGFI .89, RMSR .02, RMSEA .06, NFI .94, and NNFI .95. Mother-infant attachment during the early postpartum period was proven to be influenced directly by neonatal perception, maternal sensitivity, and maternal-fetal attachment and also indirectly by social support, maternal-fetal attachment and maternal identity. These variables accounted for 32% of the variance of the mother-infant attachment during the early postpartum period. Conclusion: It is necessary that the nurses provide postpartum women with an intervention using social support for improving maternal identity and alleviating maternal role strain. It can be helpful to improve maternal sensitivity and in the end it will facilitate the mother-infant attachment during postpartum period.

• Journal of the Korean Institute of Landscape Architecture
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• v.27 no.4
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• pp.80-86
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• 1999

The purpose of this study was to suggest a case study and anlaysis of the visual impact in dam construction through visual impact assessment method in Dong-sang river. The results can be summarized as follows; 1) For the evaluation of the visual impact of dam construction, five steps such as field analysis of visual status, finding visual sensitivity area and visual control point, making visual simulation material and evaluation, and visual impact analysis and assessment were suggested as desirable. 2) In the case study, the visual impact of dam construction was evaluated to be simple, unique, modern, static, cool and unfamiliar. 3) There was a few difference between the pre-construction and post-construction in statistical test. Especially, The dam in Man-Jee area was evaluated to be artificial, unique and destroyed in statistical difference, and then we design dam structure with visual friendliness. 4) In conclusion, there was high correlation between pre-construction landscape and post-construction landscape through semantic differential scale method using eleven adjectives. Therefore, we state that there is no visual impact for the dam construction for the moment.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.12
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• pp.1772-1781
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• 2017

In this study, the design methodology for alleviating the overfitting problem of Polynomial Neural Networks(PNN) is realized with the aid of two kinds techniques such as L2 regularization and Sum of Squared Coefficients (SSC). The PNN is widely used as a kind of mathematical modeling methods such as the identification of linear system by input/output data and the regression analysis modeling method for prediction problem. PNN is an algorithm that obtains preferred network structure by generating consecutive layers as well as nodes by using a multivariate polynomial subexpression. It has much fewer nodes and more flexible adaptability than existing neural network algorithms. However, such algorithms lead to overfitting problems due to noise sensitivity as well as excessive trainning while generation of successive network layers. To alleviate such overfitting problem and also effectively design its ensuing deep network structure, two techniques are introduced. That is we use the two techniques of both SSC(Sum of Squared Coefficients) and $L_2$ regularization for consecutive generation of each layer's nodes as well as each layer in order to construct the deep PNN structure. The technique of $L_2$ regularization is used for the minimum coefficient estimation by adding penalty term to cost function. $L_2$ regularization is a kind of representative methods of reducing the influence of noise by flattening the solution space and also lessening coefficient size. The technique for the SSC is implemented for the minimization of Sum of Squared Coefficients of polynomial instead of using the square of errors. In the sequel, the overfitting problem of the deep PNN structure is stabilized by the proposed method. This study leads to the possibility of deep network structure design as well as big data processing and also the superiority of the network performance through experiments is shown.

• Earthquakes and Structures
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• v.10 no.2
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• pp.261-291
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• 2016

This paper deals with the seismic assessment of a real RC frame building located in Italy, designed according to the current Italian seismic code. The first part of the paper deals with the calibration of the structural model of the investigated building. The results of an in-situ dynamic identification test are employed in a sensitivity and parametric study in order to find the best fit model in terms of frequencies and modal shapes. In the second part, the safety of the structure is evaluated by means of nonlinear static analyses, taking into account the results of the previous dynamic study. In order to investigate the influence of the infills on the seismic response of the structure, the nonlinear static analyses are performed both neglecting and taking into account the infill panels. The infill panels differently change the behavior of the structure in terms of strength and stiffness at different seismic intensity levels. The assessment study also verifies the absence of brittle failures in structural elements, which could be caused by either the local interaction with infills or the failure of the strength hierarchy.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.5
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• pp.757-772
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• 2018

Recently, earthquakes have occurred in large cities such as Gyeongju and Pohang, and seismic analysis studies have been actively conducted in various fields. However, since most of the previous seismic analyses have dealt with ground structures and the ground separately, there is a lack of a study on the complete soil-structure dynamic interaction. Therefore, in this study, a sensitivity analysis is conducted with MIDAS GEN and MIDAS GTS NX to apply the underground structure fixed-end model considering only the building and the complete system model considering both the building and the ground, respectively and the validity of dynamic analysis considering SSI is examined. As a result of the study, in most conditions it is found that the maximum horizontal displacement of the tall building in case of the underground structure fixed-end model is estimated to be smaller, the bending stress is larger, and the range of the weak part is smaller than that of the complete system model. Therefore, it is expected to be more reasonable to use the complete system model considering soil-structure interaction in seismic analysis.

• Computational Structural Engineering
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• v.9 no.4
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• pp.117-126
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• 1996

Damage detection methods using structural tests can be divided into two methods, i.e., static and dynamic. The static methods which use the stiffness properties of the structure are simpler than the dynamic methods. However, static approaches are very sensitive to the displacement measurement noises and modeling errors. The dynamic methods also have limitations in acquiring the natural frequencies and mode shapes of the high frequencies. In this study, a method for the structural damage assessment using sensitivity matrices is developed, in which the drawbacks of the static and dynamic methods can be compensated. Based on the measurement data for the static displacements and dynamic modal properties, the damage locations and the degree of damage are determined using the presented sensitivity matrix method. The efficiency of the proposed method has been examined through numerical simulation studies on truss type structures.