• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.5
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• pp.389-396
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• 2017

Peridynamics has been widely used in the dynamic fracture analysis of brittle materials. Recently, various crack patterns(compact region, floret, Hertz-type crack, etc.) of multilayered glass structures in experiments(Bless et al. 2010) were implemented with a bond-based peridynamic simulation(Bobaru et al.. 2012). The actual glass layers are bound with thin elastic interlayer material while the interlayer is missing from the peridynamic model used in the previous numerical study. In this study, the peridynamic interlayer modeling for the multilayered structures is proposed. It requires enormous computational time and memory to explicitly model very thin interlayer materials. Instead of explicit modeling, fictitious peridynamic particles are introduced for modeling interlayer materials. The computational efficiency and accuracy of the proposed peridynamic interlayer model are verified through numerical tests. Furthermore, preventing penetration scheme based on short-range interaction force is employed for the multilayered structure under compression and verified through parametric tests.

• Korean journal of communication and information
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• v.47
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• pp.5-22
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• 2009

This study analysed the complicated introduction process of IPTV in Korea, based on the rent seeking theory which is one of an useful economic theory for explaining the dynamic interaction between government and entrepreneurs. Rent seeking theory describes the possibility of lobbying for economic regulations or regulatory capture which refers to collusion between firms and the government agencies assigned to regulate them. The introduction of IPTV(Internet Protocol TV) in Korea was the most controversial policy issue since the beginning of new media business of cable TV in 1995. In addition to the ordinary conflict between the old and new entrepreneurs, IPTV caused the bureaucratic conflicts between the Ministry of Information and Communication and the Korean Broadcasting Commission (Two regulation agencies were merged into KCC(Korean Communications Commission) in 2008). Through the process all related policy players, including the government, pursued their own rent, and it caused vicious circle of continuous rent seeking and mutual distrust among players. Finally, all-directional lobby of pre-IPTV companies brought about the successful entrance to IPTV market and the enactment of IPTV special law which includes deregulation compared to the existing Broadcast Act. Considering the convergence trend of media related laws it means going against the times. Until now, the conflict phenomena occurring in broadcast industry were mostly explained based on the sociological conflict theory. However, the result of this study shows the usefulness and necessity of rent seeking theory because it gives an economic explanation of conflict behavior.

• The Journal of the Acoustical Society of Korea
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• v.35 no.6
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• pp.480-490
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• 2016

As wind turbines become larger and lighter, they are likely to respond sensitively by dynamic loads applied on them. Since the responses at resonances are particularly interested, it is required to be able to predict natural frequencies of wind turbines reliably at early design stage. To achieve this, the foundation-soil analysis is needed to be carried out and a finite element approach is adopted in general. However, the finite element approach would not be appropriate in early design stage because it demands heavy efforts in pile-soil modelling and computing facilities. On the contrary, theoretical approaches adopting linear approximations for soils are relatively simple and easy to handle. Therefore, they would be a useful tool in predicting a pile-soil interaction, particularly in early design stage. In this study an analysis for a pile inserted in soil is performed. The pile and soil are modelled as a beam and continuum medium, respectively, within an elastic range. In this analysis, influence factors at the pile head for lateral loads are predicted by means of this continuum approach for various length-diameter ratios of the pile. The influence factors predicted are validated with those reported in literature, proposed from a finite element analysis.

• Journal of the Korean Chemical Society
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• v.54 no.5
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• pp.594-602
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• 2010

Since the requirement of the high density integration and thin package technique of semiconductor have been increasing, the main package type of semiconductor will be a chip scale package (CSP). The changes of diffusion coefficient and moisture content ratio of epoxy resin systems according to the change of liquid type epoxy resin and fillers for CSP applications were investigated. The epoxy resins used in this study are RE-304S, RE310S, and HP-4032D, and Kayahard MCD as hardener and 2-methylimidazole as catalyst were used in these epoxy resin systems. The micro-sized and nano-sized spherical type fused silica as filler were used in order to study the moisture absorption properties of these epoxy molding compound (EMC) according to the change of filler size. The temperature of glass transition (Tg) of these EMC was measured using Dynamic Scanning Calorimeter (DSC), and the moisture absorption properties of these EMC according to the change of time were observed at $85^{\circ}C$ and 85% relative humidity condition using a thermo-hygrostat. The diffusion coefficients in these EMC were calculated in terms of modified Crank equation based on Ficks' law. An increase of diffusion coefficient and maximum moisture absorption ratio with Tg in these systems without filler can be observed, which are attributed to the increase of free volume with Tg. In the EMC with filler, the changes of Tg and maximum moisture absorption ratio with the filler content can be hardly observed, however, the diffusion coefficients of these systems with filler content show the outstanding changes according to the filler size. The diffusion via free volume is dominant in the EMC with micro-sized filler; however, the diffusion with the interaction of absorption according the increase of the filler surface area is dominant in the EMC with nano-sized filler.

• Journal of the Korean Society of Marine Environment & Safety
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• v.21 no.5
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• pp.515-523
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• 2015

This study reviewed 612 DP LOP(Loss of Position) incident reports which submitted to IMCA from 2001~2010 and identified 103 human error caused incidents and classified it through HFACS. And, this study analysis of conditional probability of human error on DP LOP incidents through application of bayesian network. As a result, all 103 human error related DP LOP incidents were caused by unsafe acts, and among unsafe acts 70 incidents(68.0 %) were related to skill based error which are the largest proportion of human error causes. Among skill based error, 60(58.3%) incidents were involved inadvertent use of controls and 8(7.8%) incidents were involved omitted step in procedure. Also, 21(20.8%) incidents were involved improper maneuver because of decision error. Also this study identified that unsafe supervision(68%) is effected as the largest latent causes of unsafe acts through application to bayesian network. As a results, it is identified that combined analysis of HFACS and bayesian network are useful tool for human error analysis. Based on these results, this study suggest 9 recommendations such as polices, interpersonal interaction, training etc. to prevent and mitigate human errors during DP operations.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.4
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• pp.489-494
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• 2015

This research focused on minimizing the response of fixed cylindrical offshore structures to a ship impact considering the seawater fluid part. A collision between a ship and offshore structure is generally a complex problem and it is often impractical to perform rigorous finite element analyses to include all the effects and sequences during the collision. The structural behavior of a fixed cylindrical type offshore substructure with a seawater fluid part has a simpler response and small deformation due to the dissipation of impact energy. Upon applying the impact force of a ship to the cylindrical structure, the maximum acceleration, internal energy, and plastic strain are calculated for each load cases using Ls-dyna finite element software. In the maximum cases 2.0 m/s velocity, the response result for the structure was carried out to compare between having a fluid region and no fluid region. Fluid-structure interaction analysis was performed using the ALE method, which make it possible to apply a fluid region on the impact problem. The case of a fixed cylindrical type offshore structure without a seawater fluid part can be a more conservative design.

• Korean journal of communication and information
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• v.36
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• pp.78-108
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• 2006

This study examines the digital divide, one of the main issues in digital media environment, in relation with the digital literacy on the perspective of audience welfare. The study explores the current state of audience welfare policy with regard to the issue of digital divide which can be seen as the dark side of this flourishing digital technology society. The barriers and enablers of the digital divide are discussed with the question of how these factors are related with the digital literacy competence of audience. It has been criticized that both the research efforts and the policy implementations on the digital divide had been set within the limitation of physical access to the digital equipment and technology. Recent studies suggested that the digital divide should be viewed in dynamic interaction of a variety of factors such as psychological dispositions, inner attitudes toward digital media, competence and ability of audiences as well as socio-economic status of individuals. Despite the recent inclusive discussion, however, the role of digital literacy in the digital divide remains unexplored. It should be noted that the question of access is not just to do with equipment, but with skills and knowledge that are required to use equipment. This notion suggests an important implication for the digital divide policy establishment. This study proposes a two-stage solution for reducing the digital divide, in which the first stage focuses on physical access and technology education and the second stage on the digital literacy education.

• Korean Journal of Social Welfare
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• v.63 no.1
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• pp.29-55
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• 2011

This study aims to understand the experiences of rights-based social work practice in a residential facility for people with intellectual disabilities. A representative residential facility practicing a human rights perspective was selected by recommendation of professional groups. Using a qualitative case study method, data was collected and analysed. In detail, it explores the experiences of rights-based social work practice at both organizational and individual levels respectively, and then discusses ethical dilemmas that arise from workers in the process of rights-based social work practice. According to results at the organizational level, rights-based social work practice of the residential facility began from workers' interests in needs of users with intellectual disabilities. Some trials to apply human rights in social work practice resulted in regulations for people with intellectual disabilities and stepped up organizational culture on human rights perspectives. And, at the individual level, self determination and choice of users with intellectual disabilities were stressed among various forms of human rights. As the results of rights-based social work practice, it appeared to be improved for the participation of the users, workers' human rights sensitivity, and qualities of rights-based activities. However, ethical dilemmas still existed. Hence, rights-based social work practice should understand a process of dynamic interaction between users and workers, which require workers to endeavor continuously. This study is significant in that it explored rights-based social work practice, focusing on field experiences for the first time in Korea, and suggested practical tasks to settle it down in the future.

• Journal of Korea Water Resources Association
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• v.45 no.1
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• pp.39-52
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• 2012

Surface-subsurface interactions are an intrinsic component of the hydrologic response within a watershed. In general, these interactions are considered to be one of the most difficult areas of the discipline, particularly for the modeler who intends simulate the dynamic relations between these two major domains of the hydrological cycle. In essence, one major complexity is the spatial and temporal variations in the dynamically interacting system behavior. The proper simulation of these variations requires the need for providing an appropriate coupling mechanism between the surface and subsurface components of the system. In this study, an approach for modelling surface-subsurface flow and transport in a fully intergrated way is presented. The model uses the 2-dimensional diffusion wave equation for sheet surface water flow, and the Boussinesq equation with the Darcy's law and Dupuit-Forchheimer's assumption for variably saturated subsurface water flow. The coupled system of equations governing surface and subsurface flows is discretized using the finite volume method with central differencing in space and the Crank-Nicolson method in time. The interactions between surface and subsurface flows are considered mass balance based on the continuity conditions of pressure head and exchange flux. The major module consists of four sub-module (SUBFA, SFA, IA and NS module) is developed.

• Journal of Biomedical Engineering Research
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• v.24 no.4
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• pp.363-367
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• 2003

Contact area and pressure are important factors which directly influence a life of knee implants. Since implant's mechanical functions should be experimentally evaluated for clinical use, many studies using a knee simulator and a pressure sensor system have been conducted. However it has not been reported that the contact pressure's distribution of a knee implant motion was estimated in real-time during a gate cycle. Therefore. the objective of this study was to analyze the contact pressure distribution for the motion of a joint using the knee simulator and I-scan sensor system. For this purpose, we developed a force-controlled dynamic knee simulator to evaluate the mechanical performance of artificial knee joint. This simulator includes a function of a soft tissue and has a 4-degree-of-freedom to represent an axial compressive load and a flexion angle. As axial compressive force and a flexion angle of the femoral component can be controlled by PC program. The pressure is also measured from I-scan system and simulator to visualize the pressure distribution on the joint contact surfaces under loading condition during walking cycle. The compressive loading curve was the major cause for the contact pressure distribution and its center move in a cycle as to a flexion angie. In conclusion, this system can be used to evaluate to the geometric interaction of femoral and tibial design due to a measured mechanical function such as a contact pressure, contact area and a motion of a loading center.