• 한국방재학회:학술대회논문집
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• 2008.02a
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• pp.233-236
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• 2008

To analyze the saline intrusion in the place, such as an estuary, the three-dimensional numerical model is developed. In this study, the advection terms of the governing equations are discretized by upwind scheme. By using an explicit scheme for the longitudinal direction and an implicit scheme for the vertical direction, the numerical model is free from the restriction of temporal step size caused by a relatively small grid ratio. The equation of state is used to consider the density, and the scalar transport equation for salinity is employed the third order TVD to scheme to prevent unphysical oscillation near discontinuity. In order to verify saline intrusion, the numerical model is conducted to compare the previous model in the lock exchange. The present model generally show a good agreement with the previous one.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.09a
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• pp.473-475
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• 2005

• Journal of Korea Water Resources Association
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• v.31 no.2
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• pp.209-219
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• 1998

Sea water volume intruded from the lock gated was compted by a one-dimensional numerical model and the extent of diffusion of sea water was evaluated for that. The volume of intruded sea water, in the exchange processes of salt and fresh waters, was computed by the conceptual model considering the tidal level, volume of chamber, volume of canal, and operation period only, It was divided into some cases according to whether ships enter or leave the canal and whether the level of tide is lower or higher than that of water level in canal. The model, developed in this work, assumed that intruded sea water is well mixed in the canal; and complete is the exchange of waters between sea and canal. The simulation case was divided into two categories according to whether the water was added from the Han River or not.

• Journal of the Korean Society for Marine Environment & Energy
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• v.3 no.2
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• pp.18-24
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• 2000

A two-dimensional numerical method for inviscid two-fluid flows with a significant entrainment into both directions is established, and the oil leakage from a non-pressurized underwater pipe is studied. The interface between two fluids is modeled at a vortex sheet. The flow field and the subsequent interface evolution are solved by using the vortex-in-cell method. For longer flow simulation with a realistic two fluids interaction, an efficient merging scheme is introduced. In the Boussinesq limit, the speed of the external fluid intrusion into the pipe is very close to the existing mathematical models, and the lock exchange is observed in spite of a significant roll-up of the interface and entrainments. It is believed that the developed method can be utilized effectively for further detailed studies on various two-fluid flows which are encountered in many different marine oil spill problems.

• Journal of Ocean Engineering and Technology
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• v.16 no.5
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• pp.15-20
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• 2002

In this research, the finite difference lattice Boltzmann method(FDLBM) is used to analyze gravity currents in the lock exchange configuration that occur in many natural and man-made situations. At a lock those are seen when a gate is suddenly opened, and, in the atmosphere, when the thunderstorm outflows make a cold front. At estuaries in the ocean, the phenomenon is found between fresh water from a river and salt water in the sea. Since such interesting phenomena were recognized, pioneers have challenged to make them clear by conducing both experiments and analysis. Most of them were about the currents of liquid or Boussinesq fluids, which are assumed as incompressible. Otherwise, the difference in density of two fluids is small. The finite difference lattice Boltzmann method has been a powerful tool to simulate the flow of compressible fluids. Also, numerical predictions using FDLBM to clarify the gravity currents of compressible fluids exhibit all features, but typically observed in experimental flows near the gravity current head, including the lobe-and-cleft structure at the leading edge.

• The Transactions of the Korea Information Processing Society
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• v.6 no.5
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• pp.1143-1152
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• 1999

A Mobile computing environment is a new paradigm which provides users with the access to information irrespective of users' location. A transaction scheduling method for the mobile computing environment must be designed so that database consistency is maintained with considering the limited performance of mobile hosts and the narrow bandwidth of a wireless network. The scheduling method using a lock has some problems: the high message overhead between a server and a mobile host for maintaining a lock and the high abort ratio of the mobile transactions owing to violating the serializability when a mobile host uses a cache. So, in this paper, we propose an efficient transaction management method using timestamp to resolve these problems. The proposed method is used in the environment under which a mobile host uses a cache having two versions for each cached data item and a server maintains several versions for each data item. So, even though a mobile transaction is executed during several broadcasting interval, can be committed. As a result, the proposed method can improve the commit ratio of the mobile transactions by maintaining multiversion for each data item and does not require the additional message exchange to schedule transactions by using timestamp.

• The Transactions of the Korean Institute of Power Electronics
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• v.13 no.1
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• pp.46-54
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• 2008

In this paper, a low-cost impedance spectroscopy system(LCISS) suitable for modeling the electrochemical power sources such as fuel cells, batteries and supercapacitors is designed and implemented. Since the developed LCISS is composed of simple sensor circuits, commercial data acquisition board and LabVIEW software, a graphic language with powerful HMI(Human-Machine Interface), it is expected ta be widely used in substitution of the expensive EIS instruments. In the proposed system, the digital lock-in amplifier is adopted to achieve the accurate measurements even in the presence of the high level of noises. The developed hardware and software is applied to measure the impedance spectrum of the Ballard Nexa 1.2kW proton exchange membrane fuel cell stack and an equivalent impedance model is proposed based on the measurement results. The validity of the proposed equivalent circuit and the developed system is proven by the measurement of the ac power losses of the PEM fuel celt stack by the ripple current.

• Asia-Pacific Journal of Business
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• v.10 no.4
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• pp.49-63
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• 2019

The export regulation of semiconductor core materials, which began with the recent revision of the export management regulations of Japan, raises the need for a new cooperation network. A hierarchical management network that was effective in the fast-follower system requires organic cooperation between the public sector and industry through a multilateral network that emphasizes horizontal co-operation among innovation actors. This study focused on the relational capital that exists among members of a business association such as an association that has been relatively marginalized from previous studies. In addition, this study aimed to analyze the effect of network activity characteristics such as industry-university linkage and informal exchange on technological innovation. Through this, I would like to draw implications for enhancing the effectiveness of the government's R & D support and innovation performance of R & D companies. Based on the results of the SMEs R & D survey, this study found that relational capital, informal exchange had a positive effect on technological innovation performance. However, if the relational capital exceeds a certain level, it is analyzed that there is a negative effect due to group think and lock-in effect. This means that informal exchange channels should be expanded for innovation and enhancement, and relational capital should be managed in consideration of the negative effects that may occur when certain levels are exceeded.

• Bulletin of the Korean Chemical Society
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• v.33 no.3
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• pp.848-854
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• 2012

We have studied the oligomerization of a fibril-forming segment of ${\alpha}$-Synulcein using a replica exchange molecular dynamics (REMD) simulation. The simulation was performed with trimers and tetramers of a 12 amino acid residue stretch (residues 71-82) of ${\alpha}$-Synulcein. From extensive REMD simulations, we observed the spontaneous formation of both trimer and tetramer, demonstrating the self-aggregating and fibril-forming properties of the peptides. Secondary structure profile and clustering analysis illustrated that antiparallel ${\beta}$-sheet structures are major species corresponding to the global free energy minimum. As the size of the oligomer increases from a dimer to a tetramer, conformational stability is increased. We examined the evolution of simple order parameters and their free energy profiles to identify the process of aggregation. It was found that the degree of aggregation increased as time passed. Tetramer formation was slower than trimer formation and a transition in order parameters was observed, indicating the full development of tetramer conformation which is more stable than that of the trimer. The shape of free energy surface and change of order parameter distributions indicate that the oligomer formation follows a dock-and-lock process.

• Journal of Yeungnam Medical Science
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• v.6 no.2
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• pp.63-70
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• 1989

This paper describes to design and to examine the mechanical characteristics of high frequency jet ventilator. The device consists of Phase lock loop(PLL) system, solenoid valve driving control part and Air regulating system. This study is carried out by changing several factors such as endotracheal tube(E.T. tube)diameter, injector cannula diameter, 1%, and frequency(breaths/mim.) having direct effects on the gas exchange as well as parameters of the entrained gas by venturi effects, so as to measure the tidal volume and minute volume. This system characteristics were as follows : 1) Frequency : 6-594bpm 2) Inspiration time : 1-99% 3) Variance of input air pressure : 1-30PSI.