• Structural Engineering and Mechanics
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• 제74권3호
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• pp.313-323
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• 2020

Non-destructive tests are commonly used in construction industry to access the quality and strength of concrete. However, till date there is no non-destructive testing method that can be adopted to evaluate the bond condition of reinforced concrete beams. In this regard, the presented research work details the use of ultra-sonic pulse velocity test method to evaluate the bond condition of reinforced concrete beam. A detailed experimental research was conducted by testing four identical reinforced concrete beam samples. The samples were loaded in equal increments till failure and ultra-sonic pulse velocity readings were recorded along the length of the beam element. It was observed from experimentation that as the cracks developed in the sample, the ultra-sonic wave velocity reduced for the same path length. This reduction in wave velocity was used to identify the initiation, development and propagation of internal micro-cracks along the length of reinforcement. Using the developed experimental methodology, researchers were able to identify weak spots in bond along the length of the specimen. The proposed method can be adopted by engineers to access the quality of bond for steel reinforcement in beam members. This allows engineers to carryout localized repairs thereby resulting in reduction of time, cost and labor needed for strengthening. Furthermore, the methodology to apply the proposed technique in real-world along with various challenges associated with its application have also been highlighted.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 춘계학술대회논문집
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• pp.494-497
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• 2005

Direct velocity feedback (DVFB) control with a collocated distributed actuator and point sensor pair is known that it offers a good stability with high performance when the control strategy is applied at the suppression of structural vibration. Also decentralized control method introduced to offer to reduce implementaion effort and malfunction due to failure in sensors and actuators of control system has become an important position in DVFB. In this paper, the decentralized control is compared with centralized control in terms of vibrational velocity reduction in a clamped-clamped beam.

• Structural Engineering and Mechanics
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• 제84권3호
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• pp.323-335
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• 2022

The main idea of the framework is to seamlessly combine a reasonably accurate and fast surrogate model with the importance sampling strategy. Developing a surrogate model for predicting structures' dynamic responses is challenging because it involves high-dimensional inputs and outputs. For this purpose, a novel surrogate model based on cutting-edge deep learning architectures specialized for capturing temporal relationships within time-series data, namely Long-Short term memory layer and Transformer layer, is designed. After being properly trained, the surrogate model could be utilized in place of the finite element method to evaluate structures' responses without requiring any specialized software. On the other hand, the importance sampling is adopted to reduce the number of calculations required when computing the failure probability by drawing more relevant samples near critical areas. Thanks to the portability of the trained surrogate model, one can integrate the latter with the Importance sampling in a straightforward fashion, forming an efficient framework called TTIS, which represents double advantages: less number of calculations is needed, and the computational time of each calculation is significantly reduced. The proposed approach's applicability and efficiency are demonstrated through three examples with increasing complexity, involving a 1D beam, a 2D frame, and a 3D building structure. The results show that compared to the conventional Monte Carlo simulation, the proposed method can provide highly similar reliability results with a reduction of up to four orders of magnitudes in time complexity.

• Journal of Information Technology Applications and Management
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• 제14권3호
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• pp.95-113
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• 2007

To minimize IT operational risks and the opportunity cost for lost business hours. it is necessary to have preparedness in advance and mitigation activities for minimization of a loss due to the business discontinuity. There are few cases that banks have a policy on systematic management, system recovery and protection activities against system failure. and most developers and system administrators response based on their experience and the instinct. This article focuses on the mitigation model development for minimizing the incidents of disk unit in IT operational risks. The model will be represented by a network model which is composed of the three items as following: (1) the risk factors(causes, attributes and indicators) of IT operational risk. (2) a periodic time interval through an analysis of historical data. (3) an index or an operational regulations related to the examination of causes of an operational risk. This article will be helpful when enterprise needs to hierarchically analyze risk factors from various fields of IT(information security, information telecommunication, web application servers and so on) and develop a mitigation model. and it will also contribute to the reduction of operational risks on information systems.

• Bulletin of the Korean Chemical Society
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• 제28권11호
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• pp.2056-2060
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• 2007

A successful combination of “oxygen-assisted chemical vapor deposition (CVD) process” and Co catalyst nanoparticles to grow highly pure single walled carbon nanotubes (SWNTs) was demonstrated. Recently, it was reported that addition of small amounts of oxygen during CVD process dramatically increased the purity and yield of carbon nanotubes. However, this strategy could not be applied for discrete Fe nanoparticle catalysts from which appropriate yields of SWNTs could be grown directly on solid substrates, and fabricated into field effect transistors (FETs) quite efficiently. The main reason for this failure is due to the carbothermal reduction which results in SiO2 nanotrench formation. We found that the oxygen-assisted CVD process could be successfully applied for the growth of highly pure SWNTs by switching the catalyst from Fe to Co nanoparticles. The topological morphologies and p-type transistor electrical transport properties of the grown SWNTs were examined by using atomic force microscope (AFM), Raman, and from FET devices fabricated by photolithography.

• 자원ㆍ환경경제연구
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• 제23권4호
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• pp.583-615
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• 2014

우리나라는 2011년 발생한 순환정전사태를 비롯하여 지난 5년간 급격한 전력소비 증가, 수요 예측 실패에 따른 전력 수급난을 겪고 있다. 또한 일본의 후쿠시마 원전사태와 국제 연료가격 상승, 기술 발전 및 적용 가능한 발전원 증가로 인해 발전 환경의 불확실성이 큰 폭으로 증가하였다. 이러한 대내외적 환경 변화로 인해 안정적 전력공급에 대한 정책적 검토가 필요하게 되었고 신규전원구성에 대한 다양한 논의가 이루어지게 되었다. 실제로 "민관 합동 워킹그룹" 에서는 에너지 기본계획 및 원전 비중 변화, 전원구성에 대한 시나리오 검토를 수행한 바 있다. 이러한 국내외 여건에 따라 본 연구에서는 제6차 전력수급기본계획과 정책 제안 그리고 우리나라의 전력 설비를 고려하여 포트폴리오 이론을 적용, 신규 전원구성 연구를 수행하였다. 본 연구의 전원 구성 결과에 따르면 향후 신재생 발전원의 비용하락과 화석 연료 발전원의 비용이 증가할 경우 신재생 발전원의 비중이 큰 폭으로 증가하며 발전믹스 내 발전원의 다양성이 증가 할 것이라는 결과가 도출되었다. 특히 위험수준(표준편차) 0.06~0.09 사이에서 가장 다양한 발전원을 보유한 효율적 전원구성이 나타남을 확인하였다. 이 밖에 기존 계획안은 효율적 곡선상에 위치하지 않기 때문에 비용-위험 기준에서 보다 개선될 수 있음을 확인하였으며 기존 방법론과 상호 보완적으로 본 연구의 방법론이 활용될 수 있음을 확인하였다. 마지막으로 본 연구 결과를 바탕으로 안정적이고 효율적인 전원믹스 운영을 위해서는 신재생 발전원의 확충과 더불어 전력저장시스템, 에너지관리시스템과 같은 전력 기술 개발 및 인프라 구축이 수반되어야 함을 확인하였다.

• Structural Engineering and Mechanics
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• 제34권6호
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• pp.779-799
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• 2010

In order to consider high-order effects on the actual limit state function, a new response surface method is proposed for structural reliability analysis by the use of high-order approximation concept in this study. Hermite polynomials are used to determine the highest orders of input random variables, and the sampling points for the determination of highest orders are located on Gaussian points of Gauss-Hermite integration. The cross terms between two random variables, only in case that their corresponding percent contributions to the total variation of limit state function are significant, will be added to the response surface function to improve the approximation accuracy. As a result, significant reduction in computational cost is achieved with this strategy. Due to the addition of cross terms, the additional sampling points, laid on two-dimensional Gaussian points off axis on the plane of two significant variables, are required to determine the coefficients of the approximated limit state function. All available sampling points are employed to construct the final response surface function. Then, Monte Carlo Simulation is carried out on the final approximation response surface function to estimate the failure probability. Due to the use of high order polynomial, the proposed method is more accurate than the traditional second-order or linear response surface method. It also provides much more efficient solutions than the available high-order response surface method with less loss in accuracy. The efficiency and the accuracy of the proposed method compared with those of various response surface methods available are illustrated by five numerical examples.

• 한국간담췌외과학회지
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• 제28권2호
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• pp.238-247
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• 2024

Backgrounds/Aims: Prolonged use of steroids after liver transplantation (LT) significantly increases the risk of diabetes or cardiovascular disease, which can adversely affect patient outcomes. Our study evaluated the effectiveness and safety of early steroid withdrawal within the first year following LT. Methods: This study was conducted as an open-label, multicenter, randomized controlled trial. Liver transplant recipients were randomly assigned to one of the following two groups: Group 1, in which steroids were withdrawn two weeks posttransplantation, and Group 2, in which steroids were withdrawn three months posttransplantation. This study included participants aged 20 to 70 years who were scheduled to undergo a single-organ liver transplant from a living or deceased donor at one of the four participating centers. Results: Between November 2012 and August 2020, 115 patients were selected and randomized into two groups, with 60 in Group 1 and 55 in Group 2. The incidence of new-onset diabetes after transplantation (NODAT) was notably higher in Group 1 (32.4%) than in Group 2 (10.0%) in the per-protocol set. Although biopsy-proven acute rejection, graft failure, and mortality did not occur, the median tacrolimus trough level/dose/weight in Group 1 exceeded that in Group 2. No significant differences in safety parameters, such as infection and recurrence of hepatocellular carcinoma, were observed between the two groups. Conclusions: The present study did not find a significant reduction in the incidence of NODAT in the early steroid withdrawal group. Our study suggests that steroid withdrawal three months posttransplantation is a standard and safe immunosuppressive strategy for LT patients.

• Corrosion Science and Technology
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• 제14권1호
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• pp.1-11
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• 2015

Local wall thinning and integrity degradation caused by several mechanisms, such as flow accelerated corrosion (FAC), cavitation, flashing and/or liquid drop impingements, are a main concern in carbon steel piping systems of nuclear power plant in terms of safety and operability. Thinned pipe management program (TPMP) had been developed and optimized to reduce the possibility of unplanned shutdown and/or power reduction due to pipe failure caused by wall thinning in the secondary side piping system. This program also consists of several technical elements such as prediction of wear rate for each component, prioritization of components for inspection, thickness measurement, calculation of actual wear and wear rate for each component. Decision making is associated with replacement or continuous service for thinned pipe components. Establishment of long-term strategy based on diagnosis of plant condition regarding overall wall thinning is also essential part of the program. Prediction models of wall thinning caused by FAC had been established for 24 operating nuclear plants. Long term strategies to manage the thinned pipe component were prepared and applied to each unit, which was reflecting plant specific design, operation, and inspection history, so that the structural integrity of piping system can be maintained. An alternative integrity assessment criterion and a computer program for thinned piping items were developed for the first time in the world, which was directly applicable to the secondary piping system of nuclear power plant. The thinned pipe management program is applied to all domestic nuclear power plants as a standard procedure form so that it contributes to preventing an accident caused by FAC.

• Korean Circulation Journal
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• 제53권6호
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• pp.351-366
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• 2023

Along with the development of immunosuppressive drugs, major advances on xenotransplantation were achieved by understanding the immunobiology of xenograft rejection. Most importantly, three predominant carbohydrate antigens on porcine endothelial cells were key elements provoking hyperacute rejection: α1,3-galactose, SDa blood group antigen, and N-glycolylneuraminic acid. Preformed antibodies binding to the porcine major xenoantigen causes complement activation and endothelial cell activation, leading to xenograft injury and intravascular thrombosis. Recent advances in genetic engineering enabled knock-outs of these major xenoantigens, thus producing xenografts with less hyperacute rejection rates. Another milestone in the history of xenotransplantation was the development of co-stimulation blockaded strategy. Unlike allotransplantation, xenotransplantation requires blockade of CD40-CD40L pathway to prevent T-cell dependent B-cell activation and antibody production. In 2010s, advanced genetic engineering of xenograft by inducing the expression of multiple human transgenes became available. So-called 'multi-gene' xenografts expressing human transgenes such as thrombomodulin and endothelial protein C receptor were introduced, which resulted in the reduction of thrombotic events and improvement of xenograft survival. Still, there are many limitations to clinical translation of cardiac xenotransplantation. Along with technical challenges, zoonotic infection and physiological discordances are major obstacles. Social barriers including healthcare costs also need to be addressed. Although there are several remaining obstacles to overcome, xenotransplantation would surely become the novel option for millions of patients with end-stage heart failure who have limited options to traditional therapeutics.