• Nuclear Engineering and Technology
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• 제42권6호
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• pp.656-661
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• 2010

Lead-alloys are very attractive nuclear coolants due to their thermo-hydraulic, chemical, and neutronic properties. By utilizing the HELIOS (Heavy Eutectic liquid metal Loop for Integral test of Operability and Safety of PEACER$^2$) facility, a thermal hydraulic benchmarking study has been conducted for the prediction of pressure loss in lead-alloy cooled advanced nuclear energy systems (LACANES). The loop has several complex components that cannot be readily characterized with available pressure loss correlations. Among these components is the core, composed of a vessel, a barrel, heaters separated by complex spacers, and the plenum. Due to the complex shape of the core, its pressure loss is comparable to that of the rest of the loop. Detailed CFD simulations employing different CFD codes are used to determine the pressure loss, and it is found that the spacers contribute to nearly 90 percent of the total pressure loss. In the system codes, spacers are usually accounted for; however, due to the lack of correlations for the exact spacer geometry, the accuracy of models relies strongly on assumptions used for modeling spacers. CFD can be used to determine an appropriate correlation. However, application of CFD also requires careful choice of turbulence models and numerical meshes, which are selected based on extensive experience with liquid metal flow simulations for the KALLA lab. In this paper consistent results of CFX and Star-CD are obtained and compared to measured data. Measured data of the pressure loss of the core are obtained with a differential pressure transducer located between the core inlet and outlet at a flow rate of 13.57kg/s.

• Advances in nano research
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• 제7권3호
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• pp.209-221
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• 2019

Graphene, with impressive electronic properties, have high potential in the microelectronic field. However, graphene itself is a zero bandgap material which is not suitable for digital logic gates and its application. Thus, much focus is on graphene nanoribbons (GNRs) that are narrow strips of graphene. During GNRs fabrication process, the occurrence of defects that ultimately change electronic properties of graphene is difficult to avoid. The modelling of GNRs with defects is crucial to study the non-idealities effects. In this work, nearest-neighbor tight-binding (TB) model for GNRs is presented with three main simplifying assumptions. They are utilization of basis function, Hamiltonian operator discretization and plane wave approximation. Two major edges of GNRs, armchair-edged GNRs (AGNRs) and zigzag-edged GNRs (ZGNRs) are explored. With single vacancy (SV) defects, the components within the Hamiltonian operator are transformed due to the disappearance of tight-binding energies around the missing carbon atoms in GNRs. The size of the lattices namely width and length are varied and studied. Non-equilibrium Green's function (NEGF) formalism is employed to obtain the electronics structure namely band structure and density of states (DOS) and all simulation is implemented in MATLAB. The band structure and DOS plot are then compared between pristine and defected GNRs under varying length and width of GNRs. It is revealed that there are clear distinctions between band structure, numerical DOS and Green's function DOS of pristine and defective GNRs.

• Smart Structures and Systems
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• 제29권3호
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• pp.445-455
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• 2022

Steel anchor bolts are installed in concrete using a variety of methods. One of the most common methods of anchor bolt installation is using epoxy resin as an infill material injected into the drilled hole to act as a bonding material between the steel bolt and the surrounding concrete. Typical design standards assume uniform stress distribution along the length of the anchor bolt accompanied with single crack leading to pull-out failure. Experimental evidence has shown that the steel anchor bolts fail owing to the multiple failure patterns, hence these design assumptions are not realistic. In this regard, the presented research work details the analytical model that takes into consideration multiple micro cracks in the infill material induced via impact loading. The impact loading from the Schmidt hammer is used to evaluate the bond condition bond condition of anchor bolt and the epoxy material. The added advantage of the presented analytical model is that it is able to take into account the various type of end conditions of the anchor bolts such as bent or U-shaped anchors. Through sensitivity analysis the optimum stiffness and shear strength properties of the epoxy infill material is achieved, which have shown to achieve lower displacement coupled with reduced damage to the surrounding concrete. The accuracy of the presented model is confirmed by comparing the simulated deformational responses with the experimental evidence. From the comparison it was found that the model was successful in simulating the experimental results. The proposed model can be adopted by professionals interested in predicting and controlling the deformational response of anchor bolts.

• Computers and Concrete
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• 제29권 6호
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• pp.393-405
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• 2022

Lightweight concrete is a superior material due to its light weight and high strength. There however remain significant lacunae in engineering knowledge with regards to shear failure of lightweight fiber reinforced concrete beams. The main aim of the present study is to investigate the optimum usage of steel fibers in lightweight fiber reinforced concrete (LWFRC). Multi-scale finite element model calibrated with experimental results is developed to study the effect of steel fibers on the mechanical properties of LWFRC beams. To decrease the amount of steel fibers, it is preferred to reinforce only the middle section of the LWFRC beams, where the flexural stresses are higher. For numerical simulation, a multi-scale finite element model was developed. The cement matrix was modeled as homogeneous and uniform material and both steel fibers and lightweight coarse aggregates were randomly distributed within the matrix. Considering more realistic assumptions, the bonding between fibers and cement matrix was considered with the Cohesive Zone Model (CZM) and its parameters were determined using the model update method. Furthermore, conformity of Load-Crack Mouth Opening Displacement (CMOD) curves obtained from numerical modeling and experimental test results of notched beams under center-point loading tests were investigated. Validating the finite element model results with experimental tests, the effects of fibers' volume fraction, and the length of the reinforced middle section, on flexural and residual strengths of LWFRC, were studied. Results indicate that using steel fibers in a specified length of the concrete beam with high flexural stresses, and considerable savings can be achieved in using steel fibers. Reducing the length of the reinforced middle section from 50 to 30 cm in specimens containing 10 kg/m3 of steel fibers, resulting in a considerable decrease of the used steel fibers by four times, whereas only a 7% reduction in bearing capacity was observed. Therefore, determining an appropriate length of the reinforced middle section is an essential parameter in reducing fibers, usage leading to more affordable construction costs.

• Journal of Hospice and Palliative Care
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• 제25권2호
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• pp.76-84
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• 2022

Purpose: We compared cost-effectiveness parameters between inpatient and home-based hospice-palliative care services for terminal cancer patients in Korea. Methods: A decision-analytic Markov model was used to compare the cost-effectiveness of hospice-palliative care in an inpatient unit (inpatient-start group) and at home (home-start group). The model adopted a healthcare system perspective, with a 9-week horizon and a 1-week cycle length. The transition probabilities were calculated based on the reports from the Korean National Cancer Center in 2017 and Health Insurance Review & Assessment Service in 2020. Quality of life (QOL) was converted to the quality-adjusted life week (QALW). Modeling and cost-effectiveness analysis were performed with TreeAge software. The weekly medical cost was estimated to be 2,481,479 Korean won (KRW) for inpatient hospice-palliative care and 225,688 KRW for home-based hospice-palliative care. One-way sensitivity analysis was used to assess the impact of different scenarios and assumptions on the model results. Results: Compared with the inpatient-start group, the incremental cost of the home-start group was 697,657 KRW, and the incremental effectiveness based on QOL was 0.88 QALW. The incremental cost-effectiveness ratio (ICER) of the home-start group was 796,476 KRW/QALW. Based on one-way sensitivity analyses, the ICER was predicted to increase to 1,626,988 KRW/QALW if the weekly cost of home-based hospice doubled, but it was estimated to decrease to -2,898,361 KRW/QALW if death rates at home doubled. Conclusion: Home-based hospice-palliative care may be more cost-effective than inpatient hospice-palliative care. Home-based hospice appears to be affordable even if the associated medical expenditures double.

• 한국건설순환자원학회논문집
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• 제11권4호
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• pp.467-475
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• 2023

본 논문에서는 내리기 시 파이프라인의 단면력 해석을 위한 합리적인 해석 모델을 제안했다. 본 해석 모델은 기하학적 특성과 경계조건을 고려하여 파이프라인을 분할한 후 two parameters Beam On Elastic Foundation과 Euler-Bernoulli 빔으로 모델링했다. 또한 파이프라인과 지반의 상호 작용 뿐만 아니라 파이프라인에 작용하는 축력을 했다. 기존 모델은 정형화된 하중 조건만 적용이 용이했으나 Segmented Pipeline Model로 정의된 제안 모델은 내리기 시 발생되는 대부분의 시공 조건에 대해 고려할 수 있다. 또한 가정을 최소화하고 요소를 세분화하여 모델링의 편의성과 적용성을 향상시켰다. 그럼에도 불구하고 이 모델은 FE 모델에 대비 높은 정확도를 갖고 있으므로 내리기 시 파이프라인의 안전성 평가는 물론 형상관리에도 효율적으로 활용될 수 있을 것으로 기대된다. 또한 시공 단계에서 파이프라인의 안전성을 확보함에 따라 운용 중 내구성 향상에 큰 도움이 될 것으로 판단된다.

• 콘크리트학회논문집
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• 제16권6호
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• pp.841-850
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• 2004

전 세계적으로 많은 수의 크고 작은 댐이 사용되고 있으나, 콘크리트 댐의 안전성 평가에 있어서 댐 내에 필연적으로 존재하는 균열을 함께 고려한 실질적 해석은 아직 미진한 실정이다. 따라서 향후 건설될 댐에 대해서는 설계 단계에서부터 이러한 파괴역학적 해석이 뒷받침되어야 댐의 안전성 확보에 매우 유리하다고 볼 수 있다. 특히 댐 제체와 지반이 접하는 경계면은 많은 균열 발생이 예상되는 영역으로써 이 균열 사이에 작용하는 양압력의 모델링은 중력식 콘크리트 댐 해석시 매우 중요한 요소이다. 즉, 콘크리트 댐의 균열 안정성 평가는 정확한 양압력의 모델링이 선행되어야 올바른 예측이 가능하다. 댐에 있어서 양압력의 취급은 단지 댐 체제 안정성 평가를 위한 전형적인 수계산 방법으로 널리 사용되고 있으나, 양압력에 대한 유한요소 모델링 방법은 연구가 부족한 실정이다. 본 연구에서는 중력식 콘크리트 댐과 지반이 접하는 부분에 발생된 균열에 양압력이 작용할 경우, 선형탄성파괴역학의 관점에서 접근하여 양압력이 응력확대계수에 미치는 영향을 비교 분석하였다. 양압력의 분포형상은 현재 등분포로 가정한 간략해석법으로 수행되고 있으나 최근의 연구 결과에 의하면 양압력 분포형상이 균열면에 따라 변화함을 보이고 있어, 본 연구에서는 수압의 형태를 등분포 형상 외에 삼각형 분포, 제형분포 및 포물선 분포 형상에 대해서도 각각 고려하여 각 분포형상별 응력확대계수를 평가하였다. 응력확대계수의 계산은 일반 8절점 등매개변수요소를 사용한 표면적분법을 사용하였으며, 자중의 영향 및 월류 수압의 영향도 함께 고려하여 해석 결과를 나타내었다.

• 응용통계연구
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• 제28권5호
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• pp.921-932
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• 2015

본 연구에서는 증강된 보병대대의 과학화 전투훈련 데이터 중 공격작전에 관한 장병들의 생존분석을 실시하였다. 과학화 전투훈련은 KCTC(Korea Combat Training Center)로 불리는 전투훈련장에서 MILES(Multiple Integrated Lazer Engagement System)와 중앙통제장비체계 등 과학화된 훈련장비와 체계 운용하 훈련부대가 적 전술 및 무기체계를 사용하는 전문 대항군과 실시하는 쌍방 자유기동훈련이다. 이는 훈련기간 동안 훈련지역의 모든 데이터가 저장되어 훈련통제 뿐 아니라 분석 및 사후검토를 할 수 있는 첨단화된 군사 훈련으로 통계적 분석이 가능한 데이터를 제공한다. 분석방법은 모수적 분포 가정이 필요하지 않은 Cox의 비례위험모형을 적용하였으며, 보다 풍부하고 용이한 해석을 위해 의사결정나무모형(CART(Classification and Regression Trees), GUIDE(Generalized, Unbiased, Interaction Detection and Estimation), CTREE(Conditional Inference Trees))을 활용하였다. Cox 비례위험모형의 비례성 가정을 확인하여 이를 위배하는 변수에 대해서 층화하여 분석하고, Cox 비례위험모형 결과 복무기간에 관한 해석이 용이하지 않아 단변량으로 local 회귀분석을 통해 추가적인 해석을 시도하였다. CART, GUIDE, CTREE는 모형의 특성별로 나무모형을 형성하며 이를 통하여 다양한 해석이 가능하다.

• 한국수자원학회논문집
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• 제35권6호
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• pp.737-751
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• 2002

용담댐 건설 후 방류 유량 및 방류 수질의 변화에 따라 계산된 금강상류의 모의결과를 이용하여 대청호 수질 변화를 예측하였다. 용담댐의 방류수량, 수질 그리고 대청호의 유량 시나리오는 이 은형 등(2002)이 금강의 모의를 위해 사용한 것과 동일하게 보았으며, 각 경우의 결과를 연구기간중의 실측수질과 실측유량을 사용했을 경우의 결과와 비교하였다. 용담호 방류량의 변화는 대청호 입구 수질에 크게 영향을 미치는 것으로 나타났으나, 대청호댐 부근의 수질에는 영향이 상당 부분 완화되어 나타나는 경향을 나타냈다. 이는 BOD, TN 그리고 TP 성분들이 대청호 내부를 이동하면서 분해 또는 침강하여 제거되었기 때문에 나타나는 현상이다. 최대 갈수년을 기준으로 보았을 때, 용담댐의 방류량은 TP 농도 기준으로는 최소 8.9 ㎥/sec 이상을, TN 농도를 기준으로 볼 때는 8.9 $m^3$/sec 이하를 유지하는 것이 바람직할 것으로 예측되었다. 따라서 대청호의 수직에 영향을 미치지 않는 적정 수준의 용담댐 방류량은 8.9 $m^3$/sec 인 것으로 분석된다. 대청호의 수질에 미치는 영향은 갈수년에 특히 분명하게 나타나고 있으며 동시에 용담호의 수질에 따라 크게 다른 양상을 보이고 있다. 즉 용담댐 방류수의 수질이 일정 수준이하를 유지하는 경우에 한해서 용담호의 방류량이 증가함에 따라 대청호의 수질에 개선효과가 나타나는 것으로 분석되고 있다. 본 연구에서는 확보가 가능한 자료와 저자들의 경험에 의해 제작된 시나리오를 근거로 수질예측을 실시하였다. 향후 용담호 및 용담댐 방류수 그리고 금강 상류 및 대청호의 오염원 그리고 수문 및 수리학적 거동에 대한 자료가 보완될 경우 더욱 합리적인 예측이 가능할 것으로 판단된다.

• Journal of Korea Trade
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• 제24권8호
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• pp.153-170
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• 2020

Purpose - As the US-China trade war intensifies and lasts long time, there is growing concern about its potential effects on the global economy. In particular, for the countries like Korea that have a large economic dependence on the economy of the two countries, the US-China trade war may have a great repercussion in many ways. The aim of this paper is to investigate the global productivity and market structure implications of the US-China trade war for Korea, as well as for other surrounding countries and regions. Design/methodology - In this paper, we develop a full multi-country/region multi-sector computable general equilibrium (CGE) model of global trade incorporating heterogeneous workers and firms in individual skill levels and used technologies. We then calibrate the model using a global Social Accounting Matrix (SAM) dataset extracted from the recently released GTAP 10 Database, and assess the potential effects of the US-China trade war on the aggregate real productivity and the market structure for Korea, as well as for other surrounding countries and regions. Findings - We show that the US-China trade war may largely affect the aggregate productivity in each sector in each country/region, as well as the global market structure through entry and exit of firms, which results finally in considerable changes in the industrial comparative advantage of each country/region. Though the effects are diverse sector by sector, the results show that Korea may also be affected significantly: concerning the real productivity implications, it is shown that the machinery industry may be affected the most negatively; on the other hand, it is shown that the number of exporting firms may decrease the most in the other transports industry. Originality/value - As the US-China trade war intensifies, many studies have tried to estimate the possible implications, and for this usually the CGE models have largely been used as the standard tool for evaluating the impacts of changes in trade policies. Standard CGE models, however, cannot be used to assess the global productivity and market structure implications due to the symmetric and simplified base assumptions. This paper is the first to analyze and quantify the possible impacts of the US-China trade war on the aggregate productivity and global market structure using a CGE model incorporating endogenous skill-technology assignment of heterogeneous workers and firms.