• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권4호
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• pp.1529-1547
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• 2015

Establishment of trust is important in wireless sensor networks for security enhancement and successful collaboration. Basically, a node establishes trust with other nodes by estimating a trust value based on monitored behavior of the other nodes. Since a malicious/misbehaving node might launch different attack strategies and might demonstrate random misbehavior, a trust estimation method should be robust against such attacks and misbehavior. Otherwise, the operation of trust establishment will be meaningless, and performance of an application that runs on top of trust establishment will degrade. In this paper, we propose a robust and novel trust estimation method. Unlike traditional trust estimation methods, we consider not only the weight of misbehavior but also the frequency of misbehavior. The frequency-of-misbehavior component explicitly demonstrates how frequently a node misbehaves during a certain observed time period, and it tracks the behavior of nodes more efficiently, which is a main factor in deriving an accurate trust value. In addition, the weight of misbehavior is comprehensively measured to mitigate the effect of an on-off attack. Frequency and weight of misbehavior are comprehensively combined to obtain the trust value. Evaluation results show that the proposed method outperforms other trust estimation methods under different attacks and types of misbehavior.

• 한국가시화정보학회지
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• 제2권2호
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• pp.52-57
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• 2004

The development and interaction of vortices over a delta wing with leading edge extension (LEX) was investigated through off-surface flow visualization using micro water droplets and a laser beam sheet. Angles of attack of $20^{\circ}$ and 24$^{\circ}$ were tested at sideslip angles of $0^{\circ}$, $-5^{\circ}$, and $-10^{\circ}$ The flow Reynolds number based on the main-wing root chord was $1.82{\times}10^{5}$. The wing vortex and the LEX vortex coiled around each other while maintaining comparable strength and identity at a zero sideslip. The increase of angle of attack intensified the coiling and shifted the cores of the wing and LEX vortices inboard and upward. By sideslip, the coiling, the merging and the diffusion of the wing and LEX vortices were increased on the windward side, whereas they were delayed significantly on the leeward side. The present study confirmed that the sideslip angle had a profound effect on the vortex structure and interaction of a delta wing with LEX, which characterized the vortex-induced aerodynamic load.

• Journal of Mechanical Science and Technology
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• 제16권3호
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• pp.327-337
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• 2002

This paper applies a recently developed on-line parameter identification (PID) technique to sets of real flight data and compares the results with those of a state-of-the-art off-line PID technique. The on-line PID technique takes Linear Regression from Fourier Transformed equations and the off-line PID is based on the traditional Maximum Likelihood method. Sets of flight data from the NASA F/A-18 High Alpha research Vehicle (HARV) circraft, which has been recorded from specifically designed maneuvers and used for our line parameter estimation, are used for this study. The emphasis is given on the accuracy and on-line measure of reliability of the estimates. The comparison is performed for both longitudinal and lateral-directional dynamics for maneuvers at angles of attack ranging u=20°through $\alpha$=40°. Results of the two estimation processes are also compared with baseline wind tunnel estimates whenever possible.

• International Journal of Aeronautical and Space Sciences
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• 제8권1호
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• pp.32-45
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• 2007

The T-50 advanced supersonic jet trainer employs the Relaxed Static Stability (RSS) concept to improve the aerodynamic performance while the flight control system stabilizes the unstable aircraft and provides adequate handling qualities. The T-50 flight control laws employ a proportional-plus-integral type controller based on a dynamic inversion method in longitudinal axis and a proportional type controller based on a blended roll system with simple roll rate feedback and beta-betadot feedback system. These control laws are verified by flight tests with various maneuver set flight envelopes and the control laws are updated to resolve flight test issues. This paper describes several concepts of flight control laws used in T-50 to resolve those flight test issues. Control laws for solving the roll-off problem during pitch maneuver in asymmetric loading configurations, improving the departure resistance in negative angle of attack conditions and enhancing the fine tracking performance in air-to-air tracking maneuvers are described with flight test data.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권2호
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• pp.978-1002
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• 2019

With the rapid development of the Internet of Things, the problem of privacy protection has been paid great attention. Recently, Nikooghadam et al. pointed out that Kumari et al.'s protocol can neither resist off-line guessing attack nor preserve user anonymity. Moreover, the authors also proposed an authentication supportive session initial protocol, claiming to resist various vulnerability attacks. Unfortunately, this paper proves that the authentication protocols of Kumari et al. and Nikooghadam et al. have neither the ability to preserve perfect forward secrecy nor the ability to resist key-compromise impersonation attack. In order to remedy such flaws in their protocols, we design a lightweight authentication protocol using elliptic curve cryptography. By way of informal security analysis, it is shown that the proposed protocol can both resist a variety of attacks and provide more security. Afterward, it is also proved that the protocol is resistant against active and passive attacks under Dolev-Yao model by means of Burrows-Abadi-Needham logic (BAN-Logic), and fulfills mutual authentication using Automated Validation of Internet Security Protocols and Applications (AVISPA) software. Subsequently, we compare the protocol with the related scheme in terms of computational complexity and security. The comparative analytics witness that the proposed protocol is more suitable for practical application scenarios.

• 한국항공우주학회지
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• 제47권3호
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• pp.195-203
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• 2019

극초음속 영역에서 운용되는 스크램제트엔진의 흡입구는 엔진 전체 성능에 직접적으로 연관되어 있으므로 개발에 앞서, 다양한 조건에서의 성능 특성 분석이 필수적이다. 본 연구에서는 축대칭 내부 압축형 흡입구인 Busemann과 외부 압축형 흡입구 형상을 설계하고, 설계점 및 탈설계점에서의 전산해석을 수행하였다. 해석결과를 토대로, 마하수와 받음각에 대한 극초음속 흡입구의 전반적인 성능 특성을 파악하였다. Busemann 흡입구는 $2^{\circ}$의 Truncation 각에 따라 흡입구의 길이를 단축하여도 성능 저하가 미미하였으며 탈설계 마하수에서는 흡입구 성능이 우수하였으나, 받음각이 있는 경우 시동 특성이 크게 저하되었다.

• 한국재난정보학회 논문집
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• 제6권1호
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• pp.122-137
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• 2010

The purpose of this study is to find the exact state of cyberbullying and the countermeasure for it. cyberbullying is characterized by having the wideness, the anonymity and the intellectualization unlike the harassment of off-line. The result of this study, the cyberbullying is increased through the e-mail, cellular phone, and website around the teenagers. In particular, the cyberbullying has appeared mainly among the same age friends, it is proved that injurers inflict the harassment mainly at their own place and the ratio of the harassment by one self is higher than many. In addition, it is quite probable that the injurer-student who inflicts the harassment in off-line also can do it in on-line and to attack the cyberbullying is easy to find by the student who is indulged himself in internet use. Therefore, it is presented that the countermeasure in educational side and systematic side on this study. First on the educational side, there are presented the practice of the preventive education against the cyberbullying, expansion of the preventive schools for the cyber ethics and cyber crime and strengthening of the guideline for students in cyberspace. Second on the systematic side, there are presented the appointment of various committee, to strengthen the protection of damaged students, preparation of laws for cyberbullying, expansion of information office for internet addiction, improvement of the system for the school custodian and to extend the operating for cyber clearness school.

• 대한토목학회논문집
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• 제40권5호
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• pp.521-526
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• 2020

활주로 및 유도로 등의 비행장 포장체는 고정익 항공기의 원활한 이착륙을 위해 반드시 필요한 시설물로 군에서도 전·평시 항공작전의 수행을 위해서 가장 중요한 시설물이라 할 수 있다. 따라서 전시에 이러한 시설의 피해를 줄이고 최단시간에 복구하는 것이 필요하다. 최근의 공격양상은 대형 폭발구를 조성하기 위한 고폭탄을 사용하기 보다는 적의 비행장을 효과적으로 공격하고자 정확도와 관계없는 다탄두 무기체계를 사용하는 것으로 변화되고 있다. 따라서 본 연구에서는 다탄두 무기체계에 적용된 탄두의 제원과 구성을 통해 현재 군에 설치된 활주로 및 유도로 등에 접촉하여 폭발이 이루어졌을 때 포장체의 방호성능 및 피해양상을 확인해 보았으며, 다탄두 무기체계는 광범위한 피해를 줄 수 있지만 각각의 탄두의 파괴력은 그리 크지 않으므로 이러한 공격 대한 최소한의 방호를 위해서 필요한 비행장 포장체의 설계 방안을 제시하고자 한다.

• Journal of Electrical Engineering and Technology
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• 제13권1호
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• pp.476-484
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• 2018

The high capacity audio watermarking algorithms are facing a main challenge in satisfying the robustness against attacks especially on de-synchronization attacks. In this paper, a robust and a high capacity algorithm is proposed using segment selection, Stationary Wavelet Transform (SWT) and the Quantization Index Modulation (QIM) techniques along with new synchronization mechanism. The proposed algorithm provides enhanced trade-off between robustness, imperceptibility, and capacity. The achieved watermarking improves the reliability of the available watermarking methods and shows high robustness towards signal processing (manipulating) attacks especially the de-synchronization attacks such as cropping, jittering, and zero inserting attacks. For imperceptibility evaluation, high signal to noise ratio values of above 22 dB has been achieved. Also subjective test with volunteer listeners shows that the proposed method has high imperceptibility with Subjective Difference Grade (SDG) of 4.76. Meanwhile, high rational capacity up to 176.4 bps is also achieved.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2006년도 추계학술대회
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• pp.494-497
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• 2006

For commercialization of polymer electrolytemembrane fuel cell (PEMFC), durability of membrane electrode assemblies (MEAs) has to be improved. Especially, long-term stability of MEA is one of the most important issues for frequent shut-down and start-up processes of PEMFC. The degradation of MEA could be attributed to chemical attack of hydrogen peroxide radicals that are formed at high cell voltages without any special treatment to remove residual hydrogen from anode gas channel after shut-down of the fuel cell. In this study, we investigated the long-term stability of MEA under different on/off operation conditions. Residential hydrogen gas was removed from the anode flow channel by purging air or nitrogen. Also, a dummy resistance was applied to the fuel cell to exhaust residential hydrogen at the anode. In these cases, MEA showed much more stable durability. Electrochemical characteristics of the fuel cell were measured byrepeating the on/off cycles with the hydrogen removal processes. Also, degradation of MEA components was examined by SEM, TEM and XRD analyses.