• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.11
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• pp.1499-1508
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• 1998

A numerical study is performed to investigate pressure drops, particle trajectories and erosion around orifice plates in pulverized coal pipe lines. Particle impaction rates change significantly with orifice shapes and Stokes numbers. At Reynolds number of $5{\times}10^5$, the pulverized coal flows well with streamlines and do not collide at the orifice plates at small sizes (${\sim}20{\mu}m$). However, the large particles (over $70{\mu}m$) impact on the front face of the orifice and erode the orifice surface. The pressure loss coefficients around the erode orifice are largely different from the designed original orifice.

• Proceedings of the Korea Contents Association Conference
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• 2017.05a
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• pp.375-376
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• 2017

본 연구는 은퇴 후 신체적 건강이 시간이 지남에 따라 어떤 변화양상을 나타내는지, 은퇴 후 신체적 건강에 영향을 주는 것으로 알려진 은퇴 특성(은퇴시점, 은퇴자발성 여부) 변인이 은퇴 후 신체적 건강의 궤적에 어떠한 영향을 미치는지를 분석하고자 하는 목적으로 실시되었다. 분석 자료는 국민노후보장패널 3차시(2009년), 4차시(2011년), 5차시(2013년) 종단자료이며, 2,857명을 대상으로 잠재성장모형 분석을 실시하였다. 연구결과, 첫째, 중 고령은퇴자의 신체적 건강은 시간의 흐름의 변화를 알아보기 위해 무조건부 모형을 통해 확인한 결과, 중 고령은퇴자들은 시간이 지남에 따라 더 높은 수준의 ADL 값을 갖는 것으로 나타났다. 둘째, 중 고령은퇴자의 신체적 건강변화와 관련이 있는 은퇴특성은 무엇인지 조건부 모형을 통해 알아본 결과, 은퇴 특성 변수로는 조기은퇴자일 때, 은퇴가 비자발적일 때, 건강상 이유로 은퇴했을 때 더 높은 ADL 초기값을 보였다. 또한 변화궤적 영향요인을 살펴본 결과, 은퇴특성에서는 어떤 변수도 유의성을 보이지 않았고, 인구사회학적 변수 중에서는 연령이 높을수록, 소득이 높을수록 ADL의 증가속도가 더욱 가파른 것으로 나타났다.

• KDI Journal of Economic Policy
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• v.40 no.3
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• pp.45-68
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• 2018

We uncover a nexus between actual inflation, inflation perceptions and expectations in Korea through analyzing micro as well as aggregate data from the Consumer Survey. We document two novel findings. First, households' subjective perceptions of inflation exert more impact on expectation formation than actual inflation. Second, inflation perceptions are broadly in line with the trajectory of the inflation trend. This is attributable to the fact that changes in actual inflation have been generated mainly by the consumption items whose price changes are perceived more sensitively as those items are frequently bought or have a larger share in household expenditures. Conducting a cross-country comparison, we find that information rigidity in expectation formation process and the nexus between perceptions and expectations of inflation prove to be stronger in Korea. Additionally, we reconfirm the existing finding that the scope of information utilized for forming inflation expectations is fairly circumscribed.

• Advances in Energy Research
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• v.3 no.1
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• pp.1-10
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• 2015

In the past sidetracking was the means to bypass a damaged zone or to correct the direction of a wellbore. Nowadays, this method is very common and useful in relocating the bottom of a wellbore in a more productive zone and consequently enhancing the production of a reservoir by saving a significant amount of time and money. In this paper, the stability of the bend area is assessed considering varied conditions of stress regime and sidetrack orientation. In general, the stress regime and the orientation of the principal stresses have negligible effect on the stability of the sidetrack compared to sidetrack inclination. On the other hand, the sidetrack deviation angle from the vertical main well plays the major role in the stability of the bend area.

• Bulletin of the Korean Chemical Society
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• v.18 no.9
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• pp.985-994
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• 1997

The reaction of gas-phase atomic hydrogen with hydrogen atoms chemisorbed on Fe(110) surface is studied by use of classical trajectory procedures. Flow of energy between the reaction zone and bulk solid phase has been treated in the generalized Langevin equation approach. A London-Eyring-Polanyi-Sato energy surface is used for the reaction zone interaction. Most reactive events are found to occur in strong single-impact collisions on a subpicosecond scale via the Eley-Rideal mechanism. The extent of reaction is large and a major fraction of the available energy goes into the vibrational excitation of H2, exhibiting a vibrational population inversion. Dissipation of reaction energy to the heat bath can be adequately described using a seven-atom chain with the chain end bound to the rest of solid. The extent of reaction is not sensitive to the variation of surface temperature in the range of Ts=0-300 K in the fixed gas temperature, but it shows a minimum near 1000 K over the Tg=300-2500 K.

• Acta Via Serica
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• v.5 no.2
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• pp.91-110
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• 2020

This paper traces the trajectory of a variety of complicated economic and political developments between China and India - the world's most ancient civilizations connected by rich history. These recent developments, which are heavily acrimonious and include military clashes involving loss of lives, have greatly damaged bilateral relations. The paper examines the reasons behind the bilateral relations dipping to new lows. Aside from specific bilateral disputes like outstanding border problems, China-India relations have been affected by global and regional developments. The paper identifies rising tensions between the U.S. and China, the evolution of the Belt and Road Initiative, and the growth of the Indo-Pacific construct, as the reasons that have expanded distance and mistrust between the two countries. Both China and India are now part of country coalitions aiming to marginalize each other's strategic influences. The paper argues that such efforts by them are going to impact countries in their neighbourhood - such as in Central Asia - by forcing them to make complex choices in the areas of trade engagement and technological development.

• Advances in aircraft and spacecraft science
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• v.9 no.1
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• pp.1-15
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• 2022

This paper presents calibration of flush air data sensing systems during ascent period of a satellite launch vehicle. Aerodynamic results are numerically computed by solving three-dimensional time dependent compressible Euler equations over a payload shroud of a satellite launch vehicle. The flush air data system consists of four pressure ports flushed on a blunt-cone section of the payload shroud and connected to on board differential pressure transducers. The inverse algorithm uses calibration charts which are based on computed and measured data. A controlled random search method coupled with neural network technique is employed to estimate pitch and yaw angles from measured transient differential pressure history. The algorithm predicts the flow direction stepwise with the function of flight Mach numbers and can be termed as an online method. Flow direction of the launch vehicle is compared with the reconstructed trajectory data. The estimated values of the flow direction are in good agreement with them.

• Electronics and Telecommunications Trends
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• v.39 no.3
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• pp.36-47
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• 2024

Low Earth Orbit (LEO) satellite communications has become a crucial technology for next-generation communication networks owing to its hyperconnectivity capabilities. We examine the progress and application areas of LEO satellite communication services. The LEO satellite communication industry has transitioned from being predominantly driven by governments and institutions to being led by the private sector, following the trajectory of the NewSpace movement. Leading corporations such as SpaceX Starlink and Eutelsat OneWeb are deploying LEO satellite networks to offer internet services, while Telesat is preparing to establish its satellite communication network. LEO satellite communications is expected to have a major impact on various sectors of society, particularly for upcoming sixth-generation services. Therefore, the South Korean government must promptly formulate policy support strategies aimed at invigorating the LEO satellite communication industry. This can be achieved through initiatives such as bolstering research and development and extending corporate assistance.

• Journal of the Korean Institute of Intelligent Systems
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• v.19 no.3
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• pp.388-397
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• 2009

There are many tasks which require robotic manipulators interaction with environment. It consists of three control problems, i.e., position control, impact control and force control. The position control means the way of reaching to the environment. The moment of touching to the environment yields the impact control problem and the force control is to maintain the desired force trajectory after the impact with the environment. These three control problems occur in sequence, so each control algorithm can be developed independently. Especially for redundant manipulators, each of these three control problems has been important independent research topic. For example, joint torque minimization and impulse minimization are typical techniques for such control problems. The three control problems are considered as a single task in this paper. The position control strategy is developed to improve the performance of the task, i.e., minimization of the individual joint torques and impulse. Therefore, initial conditions of the impact control problem are optimized at the previous position control algorithm. Such a control strategy yields improved result of the impact control. Similarly, the initial conditions for the force control problem are indirectly optimized by the previous position control and impact control strategies. The force control algorithm uses the individual joint torque minimization concept. It also minimizes the force disturbances. The simulation results show the proposed control strategy works well.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.35 no.5
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• pp.405-414
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• 2017

Spatial data processing often poses challenges due to the unique characteristics of spatial data and this becomes more complex in spatial big data processing. Some tools have been developed and provided to users; however, they are not common for a regular user. This paper presents a benchmark test between two notable tools of spatial big data processing: GIS Tools for Hadoop and SpatialHadoop. At the same time, a MapReduce application is introduced to be used as a baseline to evaluate the effectiveness of two tools and to derive the impact of number of maps/reduces on the performance. By using these tools and New York taxi trajectory data, we perform a spatial data processing related to filtering the drop-off locations within Manhattan area. Thereby, the performance of these tools is observed with respect to increasing of data size and changing number of worker nodes. The results of this study are as follows 1) GIS Tools for Hadoop automatically creates a Quadtree index in each spatial processing. Therefore, the performance is improved significantly. However, users should be familiar with Java to handle this tool conveniently. 2) SpatialHadoop does not automatically create a spatial index for the data. As a result, its performance is much lower than GIS Tool for Hadoop on a same spatial processing. However, SpatialHadoop achieved the best result in terms of performing a range query. 3) The performance of our MapReduce application has increased four times after changing the number of reduces from 1 to 12.