• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.7
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• pp.435-440
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• 2016

Effects of the increase rate of Reynold number on near-wall turbulent structures are investigated by performing direct numerical simulations of transient turbulent channel flows. The simulations were started with the fully-developed turbulent channel flow at $Re_{\tau}=180$, then temporal accelerations were applied. During the acceleration, the Reynolds number, based on the channel width and the bulk mean velocity, increased almost linearly from 5600 to 13600. To elucidate the effects of flow acceleration rates on near-wall turbulence, a wide range of durations for acceleration were selected. Various turbulent statistics and instantaneous flow fields revealed that the rapid increase of flow rate invoked bypass-transition like phenomena in the transient flow. By contrast, the flow evolved progressively and the bypass transition did not clearly occur during mild flow acceleration. The present study suggests that the transition to the new turbulent regime in transient channel flow is mainly affected by the flow acceleration rate, not by the ratio of the final and initial Reynolds numbers.

• The KIPS Transactions:PartA
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• v.12A no.2 s.92
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• pp.87-94
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• 2005

Pattern matching is one of critical parts of Network Intrusion Prevention Systems (NIPS) and computationally intensive. To handle a large number of attack signature fattens increasing everyday, a network intrusion prevention system requires a multi pattern matching method that can meet the line speed of packet transfer. In this paper, we analyze Snort, a widely used open source network intrusion prevention/detection system, and its pattern matching characteristics. A multi pattern matching method for NIPS should efficiently handle a large number of patterns with a wide range of pattern lengths and case insensitive patterns matches. It should also be able to process multiple input characters in parallel. We propose a multi pattern matching hardware accelerator based on Shift-OR pattern matching algorithm. We evaluate the performance of the pattern matching accelerator under various assumptions. The performance evaluation shows that the pattern matching accelerator can be more than 80 times faster than the fastest software multi-pattern matching method used in Snort.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.5
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• pp.49-56
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• 2022

In this study, numerical simulations for reducing noise between floors in an apartment building was carried out using Active Noise Control (ANC) technology. In order to examine the feasibility of using ANC to reduce noise between floors, accelerometers and microphones for noise collection were installed in the inter-floor noise test facility to measure noise and vibration caused by the impact ball drop test. By using the measured data, Filtered-x Least Mean Square (Fx-LMS) algorithm-based ANC simulations were carried out. In the simulations, after deriving optimal simulation conditions including the adaptive control convergence coefficient, the noise reduction effect was analyzed through numerical simulations using the number of installed accelerometers and speakers as variables. Finally, it was confirmed that the noise between floors could be reduced using ANC technology under limited conditions.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.33 no.6
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• pp.919-928
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• 2023

Deep learning technology is used in various fields such as self-driving cars, image creation, and virtual voice implementation, and deep learning accelerators have been developed for high-speed operation in hardware devices. However, several side channel attacks that recover secret information inside the accelerator using side-channel information generated when the deep learning accelerator operates have been recently researched. In this paper, we implemented a DNN(Deep Neural Network)-based MNIST digit classifier on a microprocessor and attempted a correlation power analysis attack to confirm that the weights of deep learning accelerator could be sufficiently recovered. In addition, to counter these power analysis attacks, we proposed a Node-CUT shuffling method that applies the principle of misalignment at the time of power measurement. It was confirmed through experiments that the proposed countermeasure can effectively defend against side-channel attacks, and that the additional calculation amount is reduced by more than 1/3 compared to using the Fisher-Yates shuffling method.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.7
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• pp.228-235
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• 2019

The purpose of this study was to investigate the effect of 6 weeks' accelerated rehabilitation with anti-gravity treadmill exercise on VAS, ROM, isokinetic myofunction, and dynamic stability after surgery of modified brostrom operation in chronic ankle instability patients. The subjects of this study were 12 chronic ankle instability patients who underwent modified Brostrom operation(MBO) by the same doctor. 6 weeks' accelerated rehabilitation program is scheduled to perform for 60min, everyday, and also anti-gravity program performed for 15~30min, everyday. The visual analog scale(VSA) and significantly decreased(p<.001) and ROM in all of dorsal flexion, plantar flexion, inversion and eversion significantly increased(p<.05) after 6 weeks' accelerated rehabilitation with anti-gravity treadmill exercise. Both inversion and eversion peak torque at $60^{\circ}/sec$(p<.001, p<.01) and at $180^{\circ}/sec$(p<.001) significantly increased after 6 weeks' accelerated rehabilitation with anti-gravity treadmill exercise respectively. In muscle defect, although inversion(p<.01) and eversion(p<.001) at $60^{\circ}/sec$ and inversion(p<.01) at $180^{\circ}/sec$ significantly decreased, eversion at $180^{\circ}/sec$ tended to decrease but did not change significantly after 6 weeks' accelerated rehabilitation with anti-gravity treadmill exercise. The dynamic stability significantly increased after 6 weeks' accelerated rehabilitation with anti-gravity treadmill exercise(p<.001). These results suggest that 6 weeks' accelerated rehabilitation with anti-gravity treadmill exercise has positive effect of VAS, ROM, isokinetic myofunction, and dynamic stability after surgery of modified brostrom operation in chronic ankle instability patients. Therefore, we consider that the accelerated rehabilitation with anti-gravity treadmill exercise, which is safely and fast method, has effect on more faster recovery of ankle stability, play ground and normal daily activities.

• KDI Journal of Economic Policy
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• v.17 no.1
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• pp.3-49
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• 1995

한국경제의 선진권진입(先進圈進入)은 국민이 선진국의 생활수준을 향유할 수 있는 국가경쟁우위(國家競爭優位)의 확보를 의미한다. 국가경쟁우위를 확보하기 위해서는 (1)국내기업의 핵심역량(核心力量)이 배양되고 과학기술하부구조(科學技術下部構造)가 확충되는 등 지식집약산업의 중추기능(中樞機能)이 집적되어야 하고, (2)정보공유(情報共有)와 공동학습(共同學習)을 실현하는 혁신주체간의 네트워크도 형성되어야 한다. 세계기업(世界企業)을 지향하는 국내기업들이 90년대에 무형경영자산(無形經營資産)에 대한 장기투자를 확대하기 시작하여, 2000년대에는 핵심역량의 축적이 가속될 것이며, 2010년대에는 한국계 다국적기업 중에서 기업내(企業內) 세계분업(世界分業)을 전개하는 초우량기업(超優良企業)이 나타날 것이다. 2010년대에는 초우량기업을 중심으로 연구개발(硏究開發)네트워크와 생산분업(生産分業)네트워크가 구축되고 과학기술하부구조가 확충되는 등 세계기업이 고부가활동(高附價活動)(상품기획 연구개발 엔지니어링 등)을 배치하는 입지조건(立地條件)이 구비될 것이다. 특히 차세대(次世代) 원천특허기술(源泉特許技術)의 확보를 위한 기초 응용연구의 국내기반도 확충될 것이다. 중소기업분야에서도 지식집약화에 경영자원을 집중적으로 투입하면서 세계시장을 대상으로 입지를 선정하고 네트워크를 활용하는 것이 보편화될 것이다. 중소기업의 조직화(組織化) 공동화(共同化)를 통하여 지식집약화와 세계화에 요구되는 경영자원의 축적이 가속되고 기능적 상호보완으로 혁신활동(革新活動)의 상승효과(相乘效果)를 증폭시키는 네트워크의 형성도 촉진될 것이다. 중견 중소기업의 업종은 특정지역에 군락(群落)을 이루고 기능(機能)의 집적(集積)과 네트워크의 형성을 통하여 지역산업(地域産業)으로서 세계시장에서 경쟁우위를 확보하게 될 것이다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.7
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• pp.655-663
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• 2010

DUP (direct underside pressurization) is a device that can considerably increase lift, reduce take-off speed and minimize hump drag when a WIG effect vehicle takes off on the water surface. A 3-dimensional numerical investigation of a WIG effect vehicle with DUP is performed to analyze aerodynamic characteristics and the static height stability. The model vehicle, named Aircat, consists of a propeller in the middle of a fuselage, an air chamber under the fuselage, Lippisch-type wings and a large horizontal T-tail. The lift is mainly increased by the stagnation of the accelerated air coming into the air chamber through the channel in the middle of the fuselage. However, the accelerated air increases drag as well as reduces static height stability.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.263-267
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• 2011

This paper presents a numerical investigation of the deflagration to detonation transition (DDT) of flame acceleration by a shock wave filled with an ethylene-air mixture in bent tube. A model consisting of the reactive compressible Navier-Stokes equations and the ghost fluid method (GFM) for complex boundary treatment is used. A various intensities of incident shock wave simulations show the generation of hot spots by shock-flame interaction and the accelerated flame propagation due to geometrical effect. Also the first detonation occurs nearly constant chemical heat release rate, 20 MJ/($g{\cdot}s$). Through our simulation's results, we concentrate the complex confinement effects in generating strong shock wave, shock-flame interaction, hot spot and DDT in pipe.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.100-100
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• 1999

가시광선 영역에서 높은 광학적 투과성과 함께 우수한 전기 전도성을 갖는 ITO 박막은 디스플레이 소자나 투명전극재료 등 다양한 분야에서 응용성이 더욱 증대되고 있다. 증착기판으로서 유리를 사용할 때 생기는 활용범위 제한을 극복하고자 최근 유기물 위에 증착이 가능한 저온 증착방법에 대한 연구가 활발히 이루어지고 있다. 그 가운데 이온빔과 같은 energetic한 beam을 이용한 박막의 제조는 기판을 플라즈마 발생지역으로부터 분리시켜 이온빔의 flux 및 에너지, 입사각 등의 자유로운 조절을 통해 상온에서도 우수한 성질의 박막 형성 가능성이 제시되어 왔다. 본 연구에서는 ion beam assisted evaporation방법을 이용하여 ITO 박막을 성장시켰으며, ion-surface interaction 효과가 박막 성장주에 미치는 영향을 이해하기 위하여 먼저 반응성 산소 이온빔에 비 반응성 아르곤 이온빔을 다양하게 변화시켜가며 증착하였으며, 이와 더불어 산소 분위기에서 아르곤 이온빔에 의한 ITO 박막의 특성 변화를 각각 관찰하였다. 증착전 후의 열처리 없이 상온에서 비저항이 ~10-4$\Omega$cm 이하로 낮고 80% 이상의 투과율을 갖는 ITO 박막을 성장시켰다. 실험에서 이용된 e-beam evaporation 물질은 In2O3-SnO2(1-wt%)였으며, 이온빔 source는 산소에 의한 filament의 산화를 막기 위해 filament cathodes type이 아닌 rf(radio-frequency)를 사용하였다. 중요 증착변수인 이온빔의 flux 변화는 산소와 Ar의 flow rate를 MFC로 조절하고 rf power를 변화시켜 얻었으며, 이온빔 에너지는 가속 grid의 가속전압 변화와 ion gun과 기판사이의 거리 조절을 통해 최적화하였다. 이온빔의 에너지와 flux는 Faraday cup으로 측정하였으며, 성박된 박막의 특성은 UV-spectrometer, 4-point probe, Hall measurement. $\alpha$-step, XRD, XPS 등을 이용하여 광학적, 전기적, 구조적 특성을 분석하였다.

• Journal of the Korean Institute of Intelligent Systems
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• v.19 no.4
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• pp.538-544
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• 2009

As the world game marcket has been recording weak growth, the development of new gane concept is required to attract the gamer's attention from those who were fed up with the previous game paradigm. Recently, the game which can recognize the player's motions and provide new interaction between the game and user is more popular than ever before. In the games with somesthesia based on Virtual Reality, the sense of the reality is considered the most important factor for drawing immersion from the gamers. In this work, a new type of 3-axis accelerometer based interactive game interface which can effectively recognize the gamer' motion is suggested. Furthermore, various experiments are carried out to verify the effectiveness of the proposed scheme.