• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.75-75
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• 2011

본 논문에서는 진동중인 교량 거더에 작용하는 풍하중을 산정하고 그에 따른 플러터 발생풍속을 예측하기 위하여 분산형 전산환경을 활용한 수치해석 연구를 수행하였다. 분산형 전산환경은 웹 포탈을 기반으로 수치해석 환경을 제공하는 수치풍동 시스템으로서, 전산유체역학(CFD : Computational Fluid Dynamics)에 대한 전문지식이 부족한 사용자들도 격자생성, 수치해석자를 이용한 계산, 가시화 등의 전 과정을 편리하게 수행할 수 있는 차세대 토목분야 연구 환경이다. 본 시스템은 그리드스피어(GfidSphere)를 기반으로 구성되었으며, 기본적으로 사용자 관리, 세션 관리, 그룹 관리, 레이아웃 관리 등을 제공하여 사용자가 포탈을 통해서 다양한 서비스를 쉽게 사용할 수 있는 환경을 구축하도록 도와준다. 수치해석을 위한 유체 지배방정식은 2차원 비정상 비압축성 RANS(Reynolds-Averaged Navier-Stokes) 방정식이며, pseudo compressibility 방법을 적용하였다. 비정상 유동장을 해석하기 위하여 이중시간 전진법(dual time stepping)을 사용하였으며, 수렴가속화를 위해 Multi-grid 기법을 적용하였다. 또한 난류 유동장 해석을 위해서 $k-{\omega}$ SST 난류 모델을 사용하였으며, 난류 천이 과정에서의 유동을 모사하기 위하여 Total stress limitation 방법을 적용하였다. 교량 거더의 연직과 회전방향의 2자유도 움직임을 모사하기 위하여 동적격자 기법을 도입하였다. 교량 거더 주변의 비정상 유동해석 결과를 통해, 거더 표면에서 떨어져나가는 크고 작은 와류의 영향으로 양력 및 모멘트 계수 그래프가 중첩된 진폭과 주기를 갖고 주기적으로 나타나는 것을 확인할 수 있었다. 또한 계산된 비정상 공기력을 적용한 2자유도 플러터 방정식을 통하여 플러터 발생풍속을 산정하였다. 최종적으로 본 연구에서 계산된 결과의 타당성을 검증하기 위하여 수치적으로 구한 플러터 발생풍속과 기존의 실험 및 수치해석 결과를 비교하였으며, 결과는 잘 일치하였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.7
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• pp.29-36
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• 2004

In this work, the effect of composite couplings on hub loads of a hingeless rotor in forward flight is investigated. The hingeless composite rotor blade is idealized as a laminated thin-walled box-beam. The nonclassical effects such as transverse shear, torsional warping are considered in the structural formulation. The nonlinear differential equations of motion are obtained by applying Hamilton's principle. The blade response and hub loads are calculated using a finite element formulation in space and time. The aerodynamic forces acting on the blade are calculated by quasi-steady strip theory. The theory includes the effects of reversed flow and compressibility. The magnitude of elastic couplings obtained by MSC/NASTRAN is compared with the classical pitch-flap $({\delta}3)$ or $pitch-lag({\alpha}1)$ coupling. It is found that the elastic couplings have a substantial effect on the behavior of $N_b/rev$ hub loads. Nearly 10 to 40% of hub loads is reduced by appropriately tailoring the fiber orientation angles in the laminae of the composite blade.

• Tunnel and Underground Space
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• v.21 no.1
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• pp.66-81
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• 2011

In this study, it was aimed to develop a thermal-hydraulic-mechanical coupled fracture mechanics code that models a fracture initiation, propagation and failure of underground rock mass due to thermal and hydraulic loadings. The development was based on a 2D FRACOD (Shen & Stephasson, 1993), and newly developed T-M and H-M coupled analysis modules were implemented into it. T-M coupling in FRACOD employed a fictitious heat source and time-marching method, and explicit iteration method was used in H-M coupling. The validity of developed coupled modules was verified by the comparison with the analytical result, and its applicability to the fracture initiation and propagation behavior due to temperature changes and hydraulic fracturing was confirmed by test simulations.

• Journal of Radiation Protection and Research
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• v.41 no.1
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• pp.31-39
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• 2016

Background: It is necessary to consider the overall countermeasure for analysis of nuclear activities according to the increase of the nuclear facilities like nuclear power and reprocessing plants in the neighboring countries including China, Taiwan, North Korea, Japan and South Korea. South Korea and comprehensive nuclear-test-ban treaty organization (CTBTO) are now operating the monitoring instruments to detect radionuclides released into the air. It is important to estimate the origin of radionuclides measured using the detection technology as well as the monitoring analysis in aspects of investigation and security of the nuclear activities in neighboring countries. Materials and methods: A three-dimensional forward/backward trajectory model has been developed to estimate the origin of radionuclides for a covert nuclear activity. The developed trajectory model was composed of forward and backward modules to track the particle positions using finite difference method. Results and discussion: A three-dimensional trajectory model was validated using the measured data at Chernobyl accident. The calculated results showed a good agreement by using the high concentration measurements and the locations where was near a release point. The three-dimensional trajectory model had some uncertainty according to the release time, release height and time interval of the trajectory at each release points. An atmospheric dispersion model called long-range accident dose assessment system (LADAS), based on the fields of regards (FOR) technique, was applied to reduce the uncertainties of the trajectory model and to improve the detective technology for estimating the radioisotopes emission area. Conclusion: The detective technology developed in this study can evaluate in release area and origin for covert nuclear activities based on measured radioisotopes at monitoring stations, and it might play critical tool to improve the ability of the nuclear safety field.

• Clinical and Experimental Pediatrics
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• v.45 no.7
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• pp.862-874
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• 2002

Purpose : We tried to evaluate whether the detection rate of Helicobacter pylori in gastric biopsy specimens could be improved by using pre-embedding immunoelectron microscopy. Methods : A total of 119 children who complained of upper gastrointestinal symptoms were endoscoped at the Gyeongsang National University Hospital from July, 1996 to July, 1999. Five biopsy specimens(three for urease test, one for hematoxylin-eosin(H & E) staining, and one for preembedding immunoelectron microscopy) were obtained from each antrum and body. Immunoblotting analysis were also performed. Results : Among the 119 patients, H. pylori were found in 116 patients(97.5%) by the immunoelectron microscopy. Among three patients who were found H. pylori negative in immunoelectron microscopy, two patients showed H. pylori in H & E stained slides and one patient was urease test positive(color change within six hours). Urease tests were positive in 107 patients(89.9 %). The positive rate of immunoblotting tests was 81.5%. However, only 13 patients(10.9%) showed H. pylori on the H & E stained antrum or body tissue. Conclusion : In this study, we found H. pylori histopathologically in most of the pediatric patients who complained of upper gastrointestinal symptoms. This study showed that pre-embedding immunoelectron microscopic examinations can be used as a gold standard in the diagnosis of childhood H. pylori infection. However, this method also has limited capacity to detect widely scattered H. pylori compared to the other histopathologic diagnostic methods.

• Geophysics and Geophysical Exploration
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• v.11 no.1
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• pp.26-33
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• 2008

The analysis of wide-angle seismic reflection and refraction data plays an important role in lithospheric-scale crustal structure study. However, it is extremely difficult to develop an appropriate velocity structure model directly from the observed data, and we have to improve the structure model step by step, because the crustal structure analysis is an intrinsically non-linear problem. There are several subjective processes in wide-angle crustal structure modelling, such as phase identification and trial-and-error forward modelling. Because these subjective processes in wide-angle data analysis reduce the uniqueness and credibility of the resultant models, it is important to reduce subjectivity in the analysis procedure. From this point of view, we describe two software tools, PASTEUP and MODELING, to be used for developing crustal structure models. PASTEUP is an interactive application that facilitates the plotting of record sections, analysis of wide-angle seismic data, and picking of phases. PASTEUP is equipped with various filters and analysis functions to enhance signal-to-noise ratio and to help phase identification. MODELING is an interactive application for editing velocity models, and ray-tracing. Synthetic traveltimes computed by the MODELING application can be directly compared with the observed waveforms in the PASTEUP application. This reduces subjectivity in crustal structure modelling because traveltime picking, which is one of the most subjective process in the crustal structure analysis, is not required. MODELING can convert an editable layered structure model into two-way traveltimes which can be compared with time-sections of Multi Channel Seismic (MCS) reflection data. Direct comparison between the structure model of wide-angle data with the reflection data will give the model more credibility. In addition, both PASTEUP and MODELING are efficient tools for handling a large dataset. These software tools help us develop more plausible lithospheric-scale structure models using wide-angle seismic data.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.10
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• pp.490-497
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• 2018

This study is to identify factors influencing therapeutic diversification strategy for Korean pharmaceutical companies. So, it purposes to find deciding factors for companies to adopt strategy for diversification or specialization. In this paper, we set six factors that are expected to influence diversification. The factors are asset scale, sales, profitability, and growth potential. Also, we included number of employees and SG&A cost ratio as factors that reflect business characteristics. We analyzed the impacts of each factor on diversification and found a relationship amongst each other. In this paper, regression analysis is applied with forward selection method, considering that it takes 5 years for companies to decide on diversification strategy. As a result, asset scale, the number of employees and profitability have significantly influenced decisions of diversification at t-1 time, and growth potential was significantly influenced at t-2 time. Korean pharmaceutical companies generally tend to go with specialization model if they have larger asset scale, higher profitability and growth potential. However, they have tendency to decide on diversification strategy, if they have large number of employees. Overall, the result of this study is expected to provide useful information for Korean pharmaceutical companies to set the suitable strategy for their situation to become a competitive company in global pharmaceutical market.

• Journal of Korean Ophthalmic Optics Society
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• v.20 no.3
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• pp.285-291
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• 2015

Purpose: The hydrogel lenses have been functionalized with HA(Hyaluronic Acid) using two different methods: construction of an IPN(Interpenetrating Polymer Networks) and formation of CCB(Chemical Covalent Bonding). The lysozyme adsorption and physical properties such as optical transmittance and water content of the hydrogel lenses have been investigated in order to determine whether method is suitable for the application potentials in contact lens industry. Methods: HA have been added to the hydrogel lenses prepared in the Lab using the two different method, e.g. IPN and CCB. The optical transmittance was measured in the wavelength range of 300~800 nm. The water content was measured by the gravimetric method using 0.9% NaCl saline solution. The amounts of adsorbed lysozyme on the contact lenses was analyzed by HPLC after incubation for 12h in artificial tears. Results: The water content of the HA added hydrogel contact lenses was increased, and the lens made by IPN method showed higher water content than the lens made by CCB method. The optical transmittance was over 90% both before and after addition of HA. Comparing the lysozyme adsorption reduction ratio, contact lens manufactured by IPN method was 60.0%, and the lens made by CCB method was 40.4%. Conclusions: CCB method is appropriate to distribute the functional material evenly throughout the lens, whereas IPN method is effective for the case of giving the functionality on the lens surface without phase separation.

• Journal of the Society of Naval Architects of Korea
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• v.30 no.1
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• pp.65-72
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• 1993

A numerical method for nonlinear free-surface-wave problem is developed in this paper. The final goal of this study is to simulate the towing tank experiment of a ship model and to partially replace the experiment by the numerical model. The exact problem in the scope of potential flow theory is formulated by a variational principle based on the classical Hamilton's principle. A localized finite element method is used in the present numerical computations which made use of the following two notable steps. The first step is an efficient treatment of the numerical radiation condition by using the intermediate nonlinear-to-linear transition buffer subdomain between the fully nonlinear and linear subdomains. The second is the use of a modal analysis in the final stage of the solution procedures, which enables us to reduce the computation time drastically. With these improvements the present method can treat a much larger computational domain than that was possible previously. A pressure patch on the free surface was chosen as an example. From the present computed results we could investigate the effect of nonlinearity on the down-stream wave pattern more clearly than others, because much larger computational domain was treated. We found, specifically, the widening of the Kelvin angle and the increase of the wave numbers and the magnitude of wave profiles.

• Korean Journal of Psychosomatic Medicine
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• v.27 no.1
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• pp.50-59
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• 2019

Objectives : Many of the patients with type 2 diabetes are associated with sleep problems, and the rate of insomnia is known to be higher in the general population. The aims of this study were to know the frequency and clnical characteristics of insomnia, and related variables to insomnia in patients diagnosed with type 2 diabetes. Methods : For 99 patients from 18 to 80 years of age (65 males and 34 females) with type 2 diabetes, interviews were performed. Total sleep time and sleep latency was evaluated. Insomnia was evaluated using the Korean Version of the Insomnia Severity Index (ISI-K). Severity of depressive symptoms were evaluted using the Korean version of the Hamilton Depression Scale (K-HDRM). According to the cutoff score of 15.5 on the ISI-K, subjects were divided into the group of type 2 diabetics with insomnia (N=34) and those without insomnia (N=65) at first, and then statistically analyzed. Results : TInsomnia could be found in 34.34% of type 2 diabetics. Type 2 diabetics with insomnia had significantly more single or divorced (respectively 11.8%, p<0.05), higher total scores of the K-HDRS ($11.76{\pm}5.52$, p<0.001), shorter total sleep time ($5.35{\pm}2.00hours$, p<0.001), and longer sleep latency ($50.29{\pm}33.80minutes$, p<0.001). The all item scores of the ISI-K in type 2 diabetics with insomnia were significantly higher than those in type 2 diabetics without insomnia, that is, total ($18.38{\pm}2.69$), A1 (Initial insomnia) ($2.97{\pm}0.76$), A2 (Middle insomnia) ($3.06{\pm}0.69$), A3 (Terminal insomnia) ($2.76{\pm}0.61$), B (Satisfaction) ($3.18{\pm}0.72$), C (Interference) ($2.09{\pm}0.97$), D (Noticeability) ($2.12{\pm}1.09$) and E (Distress) ($2.21{\pm}0.81$) (respectively p<0.001). Variables associated with insomnia in type 2 diabetics were as following. Age had significant negative correlation with A3 items of the ISI-K (${\beta}=-0.241$, p<0.05). Total scores of the K-HDRS had significant positive correlation, while total sleep time had significant negative correlation with all items of the ISI-K (respectively p<0.05). Sleep latency had significant positive correlation with total,, A1, B and E item scores of the ISI-K (respectively p<0.05). Conclusions : Insomnia was found in about 1/3 of type 2 diabetics. According to the presence of insomnia, clinical characteristics including sleep quality as well as quantity seemed to be different. Because depression seemed to be correlated with insomnia, clinicians should pay attention to early detection and intervention of depression among type 2 diabetics.