• 한국전산유체공학회:학술대회논문집
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• 2003.10a
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• pp.253-254
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• 2003

Computations of the mean and turbulence flows over three-dimensional hill of conical shape have implemented. Beside the standard ${\kappa}-{\varepsilon}$ , two other modifications proposed by Detering & Etling and Duynkerke for atmospheric applications were also considered. These predictions were compared with the data of a wind tunnel experiment. From the comparison, it was concluded that all three models predict the mean flow velocities equally well while only the Duynkerke's model accurately predicts the turbulence data statistics. It also concluded that there are large discrepancies between model predictions and the measurements near the ground surface. The flow field, which was obtained by using the Duynkerke's modification, was used to simulate gas dispersion from an upwind source. The calculation results are verified based on the measurement data. Modifications of the turbulent Schmidt number were carried out in order to match the measured results. The code was used to investigate the influence of the recirculation zone behind a building of cubical shape on the transport and dispersion of pollutant. For a stack behind and near the obstacle, some conclusions about the effect of the stack height and stack location were derived.

• 한국전산유체공학회:학술대회논문집
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• 2003.08a
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• pp.144-151
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• 2003

Computations of the mean and turbulence flows over three-dimensional hill of conical shape have implemented. Beside the standard $\kappa-\epsilon$, two other modifications proposed by Detering & Etling and Duynkerke for atmospheric applications were also considered. These predictions were compared with the data of a wind tunnel experiment. From the comparison, it was concluded that all three models predict the mean flow velocities equally well while only the Duynkerke's model accurately predicts the turbulence data statistics. It also concluded that there are large discrepancies between model predictions and the measurements near the ground surface. The flow field, which was obtained by using the Duynkerke's modification, was used to simulate gas dispersion from an upwind source. The calculation results are verified based on the measurement data. Modifications of the turbulent Schmidt number were carried out in order to match the measured results. The code was used to investigate the influence of the recirculation zone behind a building of cubical shape on the transport and dispersion of pollutant. For a stack behind and near the obstacle, some conclusions about the effect of the stack height and stack location were derive

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.10
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• pp.1979-1989
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• 1992

An experimental study has been performed to investigate the horseshoe vortex system formed around cylindrical obstacles mounted vertically on the surface over which a boundary layer is formed. To measure the mean velocity of the flow field, a five-hole Pitot tube has been used. In addition, surface static pressure measurements and surface flow visualization were also performed. From the five-hole probe measurements, vorticity distribution was deduced numerically and the streamwise velocity distribution was also examined. To consider the effect of the leading-edge shape on the formation of the horseshoe vortex, a qualitative comparison was made between the three-dimensional flows around a circular cylinder and a wedge-type cylinder. The five-hole probe measurements showed a single primary vortex which exists immediately upstream of the obstacles, and endwall flow visualization showed the existence of a corner vortex. As the vortex passes around the obstacle, the vortex strength is reduced and the vortex core moves radially outward. Due to this horseshoe vortex, the fluid momentum is found to decrease along the streamwise direction. Since the horseshoe vortex formed around a wedge-type cylinder has weaker strength and is confined to a narrower region than that around a circular, the possibility that the secondary flow loss due to the horseshoe vortex can be reduced through a change of the leading- edge shape is proposed.

• Proceedings of the Korean Society of Computer Information Conference
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• 2023.01a
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• pp.443-445
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• 2023

Following the global financial crisis, the global value chain contracted, and characteristics of "reverse globalization" of the economy and trade gradually emerged. This is due to the term "reverse globalization" referring to a shift away from globalization. Within a short period of time, the phenomenon known as "reverse globalization" developed as an inescapable obstacle, coinciding with the development and dissemination of the COVID-19 virus. At some time in the distant future, the "reverse globalization" of economic trade and the "globalization" of the digital economy will co-dominate the shifting trend of the global economic landscape. This will happen gradually over time. The goal of this research is to look at the minor changes that happened in the methods and techniques used by the economic mechanism known as "globalization against the flow." It employs Chinese smart manufacturing companies as a model and proposes a digital drive model to investigate the prospects and constraints of smart manufacturing technology enterprise innovation development under "reverse globalization," with the goal of establishing a digital innovation development path. The theoretical insights given in this study have the potential to serve as a reference for China as it attempts to build a new growth pattern based on a double-cycle and promote a new type of globalization.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.115-116
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• 2012

The demand for flexible electronic systems such as wearable computers, E-paper, and flexible displays has increased due to their advantages of excellent portability, conformal contact with curved surfaces, light weight, and human friendly interfaces over present rigid electronic systems. This seminar introduces three recent progresses that can extend the application of high performance flexible inorganic electronics. The first part of this seminar will introduce a RRAM with a one transistor-one memristor (1T-1M) arrays on flexible substrates. Flexible memory is an essential part of electronics for data processing, storage, and radio frequency (RF) communication and thus a key element to realize such flexible electronic systems. Although several emerging memory technologies, including resistive switching memory, have been proposed, the cell-to-cell interference issue has to be overcome for flexible and high performance nonvolatile memory applications. The cell-to-cell interference between neighbouring memory cells occurs due to leakage current paths through adjacent low resistance state cells and induces not only unnecessary power consumption but also a misreading problem, a fatal obstacle in memory operation. To fabricate a fully functional flexible memory and prevent these unwanted effects, we integrated high performance flexible single crystal silicon transistors with an amorphous titanium oxide (a-TiO2) based memristor to control the logic state of memory. The $8{\times}8$ NOR type 1T-1M RRAM demonstrated the first random access memory operation on flexible substrates by controlling each memory unit cell independently. The second part of the seminar will discuss the flexible GaN LED on LCP substrates for implantable biosensor. Inorganic III-V light emitting diodes (LEDs) have superior characteristics, such as long-term stability, high efficiency, and strong brightness compared to conventional incandescent lamps and OLED. However, due to the brittle property of bulk inorganic semiconductor materials, III-V LED limits its applications in the field of high performance flexible electronics. This seminar introduces the first flexible and implantable GaN LED on plastic substrates that is transferred from bulk GaN on Si substrates. The superb properties of the flexible GaN thin film in terms of its wide band gap and high efficiency enable the dramatic extension of not only consumer electronic applications but also the biosensing scale. The flexible white LEDs are demonstrated for the feasibility of using a white light source for future flexible BLU devices. Finally a water-resist and a biocompatible PTFE-coated flexible LED biosensor can detect PSA at a detection limit of 1 ng/mL. These results show that the nitride-based flexible LED can be used as the future flexible display technology and a type of implantable LED biosensor for a therapy tool. The final part of this seminar will introduce a highly efficient and printable BaTiO3 thin film nanogenerator on plastic substrates. Energy harvesting technologies converting external biomechanical energy sources (such as heart beat, blood flow, muscle stretching and animal movements) into electrical energy is recently a highly demanding issue in the materials science community. Herein, we describe procedure suitable for generating and printing a lead-free microstructured BaTiO3 thin film nanogenerator on plastic substrates to overcome limitations appeared in conventional flexible ferroelectric devices. Flexible BaTiO3 thin film nanogenerator was fabricated and the piezoelectric properties and mechanically stability of ferroelectric devices were characterized. From the results, we demonstrate the highly efficient and stable performance of BaTiO3 thin film nanogenerator.

• Journal of Science Education
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• v.47 no.1
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• pp.52-62
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• 2023

This study examines how prospective earth science teachers perceive the concept of "equilibrium" and "interaction between Earth's spheres" in understanding Earth's radiative equilibrium and tries to identify their misconceptions. For this purpose, a questionnaire was designed and put to them to look into their thought flow based on the items that appeared in the national level evaluation. As a result of analyzing their answers, even though all the prospective teachers correctly described the concept of radiative equilibrium, about 90% of them did not apply the concept of radiative equilibrium to the new environment of the Earth without atmosphere. They do not seem to be able to smoothly derive the concept of a new 'interaction' between the changed regions and a new 'equilibrium' that will be reached over a long period of time. In this respect, it is likely that the textbooks had some influence on the formation of their concepts. In particular, high school Earth Science textbooks describe the Earth's radiation equilibrium in a quantitative manner, focusing on the heat budget of the equilibrium state rather than the process of reaching radiation equilibrium. Such an approach of textbooks might be an obstacle to fostering students into creative convergence-type talents pursued in the 2015 revised curriculum. Meanwhile, in order to eliminate the misconceptions of students often found in the understanding of Earth's radiation equilibrium, this study suggests that the core concepts need to be dealt with more attention even in college courses for training prospective teachers.