• 한국분무공학회지
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• 제15권4호
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• pp.202-207
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• 2010

Mist cooling is widely employed as a cooling technique of high temperature surfaces, and it has heat transfer characteristics similar to boiling heat transfer which has the convection, nucleate and film boiling regions. In the present study, mist cooling heat transfer was experimentally investigated for the mist flow impacting on the heated surfaces of mico-fins. The mist flow was generated by supersonic vibration. Experiments were conducted under the test conditions of droplet flow rate, $Q=6.02{\times}10^{-9}{\sim}3.47{\times}10^{-8}\;m^3/s$ and liquid temperature, $T_f=30{\sim}35^{\circ}C$. From the experimental results, it is found that an increase in the droplet flow rate improves mist cooling heat transfer in the both case of smooth surface and surfaces of micro-fins. Micro-fins surfaces enhance the mist cooling heat transfer. Besides, the experimental results show that an increase in the droplet flow rate decrease the heat transfer efficiency of mist cooling.

• 한국분무공학회지
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• 제14권4호
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• pp.178-183
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• 2009

Spray cooling heat transfer was experimentally investigated for water sprays impacting on mico-fins structured surfaces in the single phase and nucleate boiling regions. The heat transfer surfaces consist of cubic fins and triangular grooved fins. The spray produced using full cone spray nozzles, and experiments were made under the test condition of $Q=4.92{\times}10^{-6}{\sim}15.83{\times}10^{-6}\;m^3/s$, $T_f=35{\sim}55^{\circ}C$. From the experimental results, it was found that cubic fins surface had the largest heat flux enhancement relative to the smooth surface.

• 한국시뮬레이션학회논문지
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• 제11권2호
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• pp.17-29
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• 2002

There is an increasing interest in high-performance A/D(Analog-to-Digital) converters for use in integrated analog and digital mixed processing systems. Pipeline A/D converter architectures coupled with BiCMOS process technology have the potential for realizing monolithic high-speed and high-accuracy A/D converters. In this paper, the design of 12bit pipeline BiCMOS A/D converter presented. A BiCMOS operational amplifier and comparator suitable for use in the pipeline A/D converter. Test/simulation results of the circuit blocks and the converter system are presented. The main features is low distortion track-and-hold with 0-300MHz input bandwidth, and a proprietary 12bit multi-stage quantizer. Measured value is DNL=${\pm}$0.30LSB, INL=${\pm}$0.52LSB, SNR=66dBFS and SFDR=74dBc at Fin=24.5MHz. Also Fabricated on 0.8um BiCMOS process.

• Animal cells and systems
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• 제3권1호
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• pp.17-21
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• 1999

A new species of gudgeon, Microphysogobio rapidus is described from 25 specimens collected from the Naktong River system, Korea. The new species is similar to Microphysogobio yaluensis but is distinguished from the latter and congeners by the combination of the following characteristics: number of papilla on the upper lip, 4.5 scales above the lateral line, short distance from the anus to the origin of the anal fin, wide scaleless area of the abdomen, nuptial colour consisting of a longitudinal green stripe on the lateral side of the body and bright blue colour of the suborbital region and operculum. A key to the species of Microphysogobio from Korea is also included.

• 한국산업융합학회 논문집
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• 제25권4_2호
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• pp.645-653
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• 2022

Recently, deep reinforcement learning has been applied to a variety of industries, such as games, robotics, autonomous vehicles, and data cooling systems. An algorithm called reinforcement learning allows for automated asset allocation without the requirement for ongoing monitoring. It is free to choose its own policies. The purpose of this paper is to carry out an empirical analysis of the performance of asset allocation strategies. Among the strategies considered were the conventional Mean- Variance Optimization (MVO) and the Proximal Policy Optimization (PPO). According to the findings, the PPO outperformed both its benchmark index and the MVO. This paper demonstrates how dynamic asset allocation can benefit from the development of a reinforcement learning algorithm.

• 전자통신동향분석
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• 제38권1호
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• pp.36-45
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• 2023

The increasing demand for ultra-high efficiency of compact power conversion systems for electric vehicle applications has brought GaN power semiconductors to the fore due to their low conduction losses and fast switching speed. In particular, the development of materials and core device processes contributed to remarkable results regarding the publication of vertical GaN power devices with high breakdown voltage. This paper reviews recent advances on GaN material technology and vertical GaN power device technology. The GaN material technology covers the latest technological trends and GaN epitaxial growth technology, while the vertical GaN power device technology examines diodes, Trench FETs, JFETs, and FinFETs and reviews the vertical GaN PiN diode technology developed by ETRI.

• 제어로봇시스템학회논문지
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• 제6권8호
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• pp.727-731
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• 2000

This paper presents a new practical autopilot design approach to acceleration control for tail-controlled STT(Skid-to-Turn) missiles. The approach is novel in that the proposed parametric affine missile model adopts acceleration as th controlled output and considers the couplings between the forces as well as the moments and control fin deflections. The aerodynamic coefficients in the proposed model are expressed in a closed form with fittable parameters over the whole operating range. The parameters are fitted from aerodynamic coefficient look-up tables by the function approximation technique which is based on the combination of local parametric models through curve fitting using the corresponding influence functions. In this paper in order to employ the results of parametric affine modeling in the autopilot controller design we derived a parametric affine missile model and designed a feedback linearizing controller for the obtained model. Stability analysis for the overall closed loop sys-tem is provided considering the uncertainties arising from approximation errors. the validity of the proposed modeling and control approach is demonstrated through simulations for an STT missile.

• 제어로봇시스템학회논문지
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• 제16권8호
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• pp.799-803
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• 2010

Recently, there is a rising interest on studying bio-inspired robotic fish because of real fish's great maneuverability and high energy efficiency. However, the researches about the robotic fish have not been done so much and there are still lots of problems to use them in the real environment such as in the river. This paper describes a bio-inspired robotic fish 'Ichthus' which is developed in KITECH and has 3 DOF propulsive mechanism. We develop the dynamic motion equation of 'Ichthus' in the underwater environment and analyze response characteristics of 'Ichthus' according to the input parameters of tail fin's amplitude and oscillation frequency. Then we propose control parameters at the various velocities. These parameters are useful to increase energy efficiency and it can be used when the fish robot moves in the real environment, for example, we can propose proper amplitude and oscillation frequency when the fish robot passes through the narrow space between obstacles.

• International Journal of Fuzzy Logic and Intelligent Systems
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• 제5권4호
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• pp.316-321
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• 2005

We designed and implemented fish robots for various purposes such as autonomous navigation, maneuverability control, posture balancing and improvement of quick turns in a tank of 120 X 120 X 180cm size. Typically, fish robots have 30-50 X 15-25 X 10-20cm dimensions; length, width and height, respectively. It is essential to have the ability of quick and smooth turning to avoid collision with obstacles or walls of the water pool at a close distance. Infrared distance sensors are used to detect obstacles, magneto-resistive sensors are used to read direction information, and a two-axis accelerometer is mounted to compensate output of direction sensors. Because of the swing action of its head due to the tail fin movement, the outputs of an infrared distance sensor contain a huge amount of noise around true distances. With the information from accelerometers and e-compass, much improved distance data can be obtained by fuzzy logic based estimation. Successful swimming and smooth turns without collision demonstrated the effectiveness of the distance estimation.

• 한국정보시스템학회지:정보시스템연구
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• 제28권3호
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• pp.59-81
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• 2019

Purpose The purpose of this study is to investigate the resistance factors interfering the acceptance factors of the mobile easy remittance service focusing on the switching cost and the innovation resistance model. Design/methodology/approach This study focuses on revealing the resistance factors of the mobile easy remittance service acceptance. The resistance factor is designed consisting both consumer characteristics and service characteristics in the Innovation Resistance Model. Furthermore, the effect of resistance factors on the innovation resistance and acceptance intentions were detected by moderating the switching cost. Findings According to the empirical analysis result, this study investigated the effect of resistance factors on innovation resistance and acceptance intention for the mobile easy remittance service. The results of this study as follows; (1) The consumer's inherent innovativeness did not significantly affect the innovation resistance and acceptance intention. (2) The attitude toward existing services and complexity significantly affected innovation resistance in direct manner, thus affecting the acceptance intention in indirect manner. (3) The perceived usefulness significantly affected both the innovation resistance and the acceptance intention in direct manner. (4) The perceived risk only effected the acceptance intention. (5) The switching cost had a moderating effect on the innovation resistance and acceptance intention.