• 한국분말재료학회지
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• 제14권1호
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• pp.26-31
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• 2007

Manufacturing bulk nanostructured materials with least grain growth from initial powders is challenging because of the bottle neck of bottom-up methods using the conventional powder metallurgy of compaction and sintering. In this study, bottom-up type powder metallurgy processing and top-down type SPD (Severe Plastic Deformation) approaches were combined in order to achieve both real density and grain refinement of metallic powders. ECAP (Equal Channel Angular Pressing), one of the most promising processes in SPD, was used for the powder consolidation method. For understanding the ECAP process, investigating the powder density as well as internal stress, strain distribution is crucial. We investigated the consolidation and plastic deformation of the metallic powders during ECAP using the finite element simulations. Almost independent behavior of powder densification in the entry channel and shear deformation in the main deformation zone was found by the finite element method. Effects of processing parameters on densification and density distributions were investigated.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1997년도 춘계학술대회논문집; 경주코오롱호텔; 22-23 May 1997
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• pp.627-635
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• 1997

In general, the booming noise intensity at tunnel exit is strongly related to the gradient of the compression wave front created by high speed train entering the tunnel. This paper presents some results in relation with the compression wave front produced when the high speed train enters a tunnel. Four kinds of tunnel entrance shape with real dimensions were studied to investigate the formation of compression wave front inside tunnel by train entering tunnel. Computations were carried out using three-dimensional compressible Euler equation with vanishing viscosity and conductivity of fluid. According to the reslts, the flow disturbance occured at tunnel entrance were eliminated by tunnel hood with same cross sectional area. The compression wave front is formed completely at 30-40m from tunnel entrance. The maximum pressure gradient of compression wave front is reduced by 29.8% for the inclined tunnel hood and reduced by 21.5% for the tunnel hood with holes at the top face with tunnel without hood. The length of the inclined hood is 15m and the length of the hood with holes is 20m.

• 한국방송∙미디어공학회:학술대회논문집
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• 한국방송공학회 2015년도 추계학술대회
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• pp.31-34
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• 2015

The U.S. music market is a lucrative market for many foreign musicians due to its sheer size and it continues to play a leading role in the world music industry. However, it is a challenge to gain entry into that market and an even greater challenge to achieve success and fame within it. In fact, changes in the media paradigm have allowed for musicians to be able to independently produce their own songs and promote them globally. Some scholars address that the media paradigm shifting from traditional outlets to new outlets gives a chance to bypass traditional gatekeepers when entering the U.S. music market. Based on this scenario, this article examined two songs from Korean singer, Psy: Gangnam Style and Gentleman as a single case study. Utilizing Google Trends as a source of information, this study examined how each song's recognition among American music fans was different based on radio spins on Top 40 commercial radio stations. This article sheds new light on radio, which has been neglected due to the media paradigm shift, and presents how radio programmers are part of a complicated gatekeeping process which ultimately decides which songs are to gain popularity.

• Journal of Advanced Research in Ocean Engineering
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• 제4권4호
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• pp.146-162
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• 2018

The unsteady problem of a rigid body impact onto a floating plate is studied. Both the plate and the water are at rest before impact. The plate motion is caused by the impact force transmitted to the plate through an elastic layer with viscous damping on the top of the plate. The hydrodynamic force is calculated by using the second-order model of plate impact by Iafrati and Korobkin (2011). The present study is concerned with the deceleration experienced by a rigid body during its collision with a floating object. The problem is studied also by a fully-nonlinear computational-fluid-dynamics method. The elastic layer is treated with a moving body-fitted grid, the impacting body with an immersed boundary method, and a discrete-element method is used for the contact-force model. The presence of the elastic layer between the impacting bod- ies may lead to multiple bouncing of them, if the bodies are relatively light, before their interaction is settled and they continue to penetrate together into the water. The present study is motivated by ship slamming in icy waters, and by the effect of ice conditions on conventional free-fall lifeboats.

• Journal of Preventive Medicine and Public Health
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• 제54권1호
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• pp.1-7
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• 2021

The Korean government's strategy to combat coronavirus disease 2019 (COVID-19) has focused on non-pharmaceutical interventions, such as social distancing and wearing masks, along with testing, tracing, and treatment; overall, its performance has been relatively good compared to that of many other countries heavily affected by COVID-19. However, little attention has been paid to health equity in measures to control the COVID-19 pandemic. The study aimed to examine the unequal impacts of COVID-19 across socioeconomic groups and to suggest potential solutions to tackle these inequalities. The pathways linking social determinants and health could be entry points to tackle the unequal consequences of this public health emergency. It is crucial for infectious disease policy to consider social determinants of health including poor housing, precarious working conditions, disrupted healthcare services, and suspension of social services. Moreover, the high levels of uncertainty and complexity inherent in this public health emergency, as well as the health and socioeconomic inequalities caused by the pandemic, underscore the need for good governance other than top-down measures by the government. We emphasize that a people-centered perspective is a key approach during the pandemic era. Mutual trust between the state and civil society, strong accountability of the government, and civic participation are essential components of cooperative disaster governance.

• 한국정보시스템학회지:정보시스템연구
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• 제29권4호
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• pp.193-208
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• 2020

Purpose Due to COVID19, the over-the-top media service (OTT) market is growing faster than expected at an annual average of 26.4%. In Korea, WAVVE, which integrated SKT's Oksusu and POOQ in September 2019, outperformed Netflix in the number of users immediately after its launch, but the number of users gradually decreased. Research on OTT investigated the spread of new media due to changes in regulations or policy, mostly in broadcasting media. On the other hand, OTT research in information systems began after the success of Netflix. It investigated consumers' satisfaction with information technology using the Information Technology Acceptance Model (TAM). This study investigates changes in consumer perceptions in the OTT market, which has grown after the Netflix's entry into Korea, the emergence of WAVVE and new OTT service providers, and the spread of COVID19. Design/methodology/approach This study selects contents, fees, service quality, and additional services as factors to evaluate consumer perception using AHP. Findings According to the 101 respondents, the content was the most important factor, followed by service quality, fees, and additional services. Contrary to previous findings that price is the determining factor in service adoption, this study reveals that consumers are willing to pay a reasonable amount for rich content and excellent service quality. Future research will use demographic analysis to reveal differences in consumer's perceptions of service selection.

• Journal of Periodontal and Implant Science
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• 제45권6호
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• pp.229-237
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• 2015

Purpose: The aim of this study was to determine the clinical feasibility of using dehydrothermally cross-linked collagen membrane (DCM) for bone regeneration around peri-implant dehiscence defects, and compare it with non-cross-linked native collagen membrane (NCM). Methods: Dehiscence defects were investigated in twenty-eight patients. Defect width and height were measured by periodontal probe immediately following implant placement (baseline) and 16 weeks afterward. Membrane manipulation and maintenance were clinically assessed by means of the visual analogue scale score at baseline. Changes in horizontal thickness at 1 mm, 2 mm, and 3 mm below the top of the implant platform and the average bone density were assessed by cone-beam computed tomography at 16 weeks. Degradation of membrane was histologically observed in the soft tissue around the implant prior to re-entry surgery. Results: Five defect sites (two sites in the NCM group and three sites in the DCM group) showed soft-tissue dehiscence defects and membrane exposure during the early healing period, but there were no symptoms or signs of severe complications during the experimental postoperative period. Significant clinical and radiological improvements were found in all parameters with both types of collagen membrane. Partially resorbed membrane leaflets were only observed histologically in the DCM group. Conclusions: These findings suggest that, compared with NCM, DCM has a similar clinical expediency and possesses more stable maintenance properties. Therefore, it could be used effectively in guided bone regeneration around dehiscence-type defects.

• International Journal of Naval Architecture and Ocean Engineering
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• 제6권2호
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• pp.219-235
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• 2014

With the development of the technology of underwater moving bodies, the need for developing the knowledge of surface effect interaction of free surface and underwater moving bodies is increased. Hence, the two-phase flow is a subject which is interesting for many researchers all around the world. In this paper, the non-linear free surface deformations which occur during the water-exit of a circular cylinder due to its buoyancy are solved using finite volume discretization based code, and using Volume of Fluid (VOF) scheme for solving two phase flow. Dynamic mesh model is used to simulate dynamic motion of the cylinder. In addition, the effect of cylinder mass in presence of an external force is studied. Moreover, the oblique exit and entry of a circular cylinder with two exit angles is simulated. At last, water-exit of a circular cylinder in six degrees of freedom is simulated in 3D using parallel processing. The simulation errors of present work (using VOF method) for maximum velocity and height of a circular cylinder are less than the corresponding errors of level set method reported by previous researchers. Oblique exit shows interesting results; formation of waves caused by exit of the cylinder, wave motion in horizontal direction and the air trapped between the waves are observable. In 3D simulation the visualization of water motion on the top surface of the cylinder and the free surface breaking on the front and back faces of the 3D cylinder at the exit phase are observed which cannot be seen in 2D simulation. Comparing the results, 3D simulation shows better agreement with experimental data, specially in the maximum height position of the cylinder.

• 한국건설관리학회논문집
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• 제8권4호
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• pp.90-98
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• 2007

국내 건설산업이 우리나라 경제성장을 견인해 오면서 매출규모와 건설기술측면에서 비약적인 발전을 거듭하여 왔으나, 건설공사를 실제적으로 수행하는 건설회사들은 건설업에 내재된 위험요인들에 대해 큰 관심을 기울이지 않아 왔다. IMF위기와 WTO가입을 계기로 건설업에 내재된 불확실성과 위험요인으로 초래되는 경영악화와 사업의 불안정성을 심각하게 경험하면서, 건설위험을 체계적으로 관리하기 위한 시도가 계속되고 있으며, 해외건설공사의 경우 수주영업단계에 적용할 수 있는 위험관리모델이 개발되어 실무에 적극적으로 활용되고 있는 실정이다. 그러나 국내 건설공사의 시공단계에서 위험관리를 체계적으로 수행할 수 있는 절차와 시스템 개발은 이루어지지 않고 있어, 본 연구는 건설현장의 실무자가 쉽게 이해하고 활용할 수 있는 건설현장 실무자들을 위한 건설공사 위험관리시스템 모델을 제안하고자 한다.

• 기술혁신학회지
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• 제12권1호
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• pp.237-264
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• 2009

선도적으로 기술창출단계의 기술혁신에 성공하여 최초경로로 기술리더가 된 국내기업에 대한 혁신 연구는 새롭게 도전하려는 국내기업과 개발도상국기업에게 시행착오를 줄일 수 있는 시사점을 제공할 수 있다. 그러나 개발도상국기업의 기술창출단계 혁신에 대한 연구가 부족하며, 특히 프로세스혁신에 대한 연구는 제품혁신연구에 비해 더욱 부족한 상황이다. 본 연구는 기술창출단계의 프로세스 기술혁신 프로젝트를 대상으로 하는 탐색적 연구이다. 최초경로로 기술리더가 된 POSCO의 FINEX(파이넥스) 사례에서는 기술창출단계 혁신은 기술내재화단계 고도화의 연장선이라기보다는 높은 위험을 감수하는 최고경영층의 결단에 의해 시도되는 불연속적인 특성이 있으며, 기술창출단계 혁신을 시작하는 개발도상국기업이 일반적으로 초기에 직면하는 원천기술을 개발을 위한 기술역량의 부족은 원천기술을 개발 중인 선발자와의 보완적 기술협력을 통해 극복하였다. 그리고 선진국 경쟁자보다 뒤늦게 기술 개발을 시작하였지만 가장 먼저 상용화단계에 도달할 수 있었던 것은 기술개발 가속화(Speed-up)로 기술개발속도에 영향을 주는 세부요인을 파악하였다.