• Smart Media Journal
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• v.4 no.4
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• pp.24-32
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• 2015

Recently, SDN is actively used as datacenter networks and gradually increase its applied areas. Along with this change of networking environment, research of deploying network security systems on SDN becomes highlighted. Especially, systems for detecting network flooding attacks by monitoring every packets through ports of OpenFlow switches have been proposed. However, because of the centralized management of a SDN controller which manage multiple switches, it may be substantial overhead that the attack detection system continuously monitors all the flows. In this paper, a sampling based network flooding attack detection and prevention system is proposed to reduce the overhead of monitoring packets and to achieve reasonable functionality of attack detection and prevention. The proposed system periodically takes sample packets of network flows with the given sampling conditions, analyzes the sampled packets to detect network flooding attacks, and block the attack flows actively by managing the flow entries in OpenFlow switches. As network traffic sampler, sFlow agent is used, and snort, an opensource IDS, is used to detect network flooding attack from the sampled packets. For active prevention of the detected attacks, an OpenDaylight application is developed and applied. The proposed system is evaluated on the local testbed composed with multiple OVSes (Open Virtual Switch), and the performance and overhead of the proposed system under various sampling condition is analyzed.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.34 no.6
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• pp.63-69
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• 2018

The machine learning model can capture the dynamics of building systems with less inputs than the first principle based simulation model. The training data for developing a machine learning model are usually selected in a heuristic manner. In this study, the authors developed a machine learning model which can describe supply air temperature from an AHU in a real office building. For rational reduction of the training data, the progressive sampling method was used. It is found that even though the progressive sampling requires far less training data (n=60) than the offline regular sampling (n=1,799), the MBEs of both models are similar (2.6% vs. 5.4%). In addition, for the update of the machine learning model, the normalized mutual information (NMI) was applied. If the NMI between the simulation output and the measured data is less than 0.2, the model has to be updated. By the use of the NMI, the model can perform better prediction ($5.4%{\rightarrow}1.3%$).

• Journal of KIISE:Computer Systems and Theory
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• v.27 no.8
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• pp.691-700
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• 2000

The standard volume ray-tracing, optimized with octree, needs to repeatedly traverse hierarchical structures for each ray that often leads to redundant computations. It also employs the expensive 3D interpolation for producing high quality images. In this paper, we present a new ray-casting method that efficiently computes shaded colors and opacities at resampling points by traversing octree only once. This method traverses volume data in object-order, finds resampling points on slices incrementally, and performs resampling based on 2D interpolation. While the early ray-termination, which is one of the most effective optimization techniques, is not easily combined with object-order methods, we solved this problem using a dynamic data structure in image space. Considering that our new method is easy to implement, and need little additional memory, it will be used as very effective volume method that fills the performance gap between ray-casting and shear-warping.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2005.05a
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• pp.922-926
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• 2005

Progressively censored variables sampling plans are proposed for the lot acceptance of parts whose life follows Weibull distribution with known shape parameter. Progressive type-II censoring gives us not only time to failure but also degradation information. So, one can construct more flexible and more cost effective sampling plans. Design parameters of our sampling plan are determined by using the usual two-point approach.

• Journal of the Korean GEO-environmental Society
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• v.14 no.10
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• pp.5-9
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• 2013

Electrokinetics technology is proposed for improving the recovery metals ion and oil from clay-sandy soil. In order to restore or extract them from clay-sandy soil, the gas produced by anode chamber is re-injected to the clay-sandy soil(sample). Samples produced in this study were completed to verify the proposed performance for 7 days by gradually increasing the pressure to the final pressure of 30psi($2.11kgf/cm^2$) through the compression process. Before compression, the copper rings were inserted into the sample, allowing us to observe the changes in appearance of copper ring after the end of the experiment. In this study, pressurized module and non-pressurized module were tested, respectively. The condition of test is a continuous process and the voltage gradient is 2V/cm during 24 hours. As a result, the efficiency of pressurized module is better than non-pressurized module.

• Journal of the Korea Computer Graphics Society
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• v.11 no.1
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• pp.31-39
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• 2005

음함수 표면을 이용한 모델링 방법은 부드러운 곡면을 나타내기에 적합하며 날카로운 부분을 표현하기 위해서는 CSG 연산을 적용한다. 기존의 방식을 이용해서 얻은 매쉬에서는 흔히 음함수의 표면과 상당한 오차를 가지는 매쉬 첨점(vertex)을 얻거나 겹쳐지는 삼각형 또는 날카로운 부분의 표현이 안 되는 점 등의 문제가 나타난다. 본 논문에서는 타원체의 특성을 이용해서 타원체 기반 음함수 표면을 정확하게 샘플링하고 동시에 날카로운 부분을 효과적으로 표현할 수 있는 매쉬를 얻기 위한 폴리곤화 방법을 제안한다. 이러한 목표를 위해 타원체의 투사 특성과 표면 법선 벡터의 연속 특성을 이용해서 음함수 표면 위에 정확하게 위치하는 첨점(vertex)의 위치를 찾고 날카로운 부분을 효과적으로 표현하기 위해 점진적인 방법으로 정확한 첨점(vertex) 위치를 찾는 방법을 제안한다. 지금까지 약점으로 지적되어 왔던 음함수 표면 모델링의 시각화 절차를 이 방법을 통해 개선함으로써 음함수 표면 모델링 기법이 제공하는 다른 장점들을 적극 활용할 수 있을 것으로 기대한다.

• Journal of Convergence for Information Technology
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• v.9 no.12
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• pp.141-146
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• 2019

Economic analysis predicts that the drone market will grow, and the growth of the toy and hobby drone market is expected to gradually expand. Drone expectations are rising due to the net economic function of drone market growth, but accidents due to improper management and operations are also increasing. The difference in toy drone performance is incomparably small compared to industrial drone performance, but the ordinary buyer can not know whether the difference can cause an accident during use. The toy drones used in this study were obtained from KC and CE certification, and 20 kinds of drones were used. The flight time ranged from a minimum of 3 minutes to a maximum of 12 minutes, and the control distance ranged from a minimum of 20m to a maximum of 380m. Therefore, it is necessary to secure product safety through sampling inspection of the radio wave output of toy drones, and it is also necessary to mount an algorithm that automatically lowers the altitude or hover when exceeding the limit flight distance. For future research, we will build data to establish toy drone safety standards through a altitude testing and impact testing of toy drone.

• Journal of the Korean Society for Marine Environment & Energy
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• v.11 no.1
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• pp.1-12
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• 2008

The prohibition of usage of tributyltin (TBT) compounds and the legal usage of new antifouling agents have changed the Korean costal environments in recent. 39 sampling sites of southwestern tidal flats were chosen in order to investigate the concentration of antifouling agents, and results in 2006 were compared with previous results in 1998. The concentrations of TBT compounds in most of sites except Incheon (It1) have been drastically decreased. Interestingly, In Jebudo (Jt2), Mokpo(MOt4) and Suncheon(SUt3) sites were detected as below the limit of detection and it is because of the legal restriction of TBT compounds. However, in most of the sampling sites in Korea, new antifouling agents, viz. Irgarol 1051, Dichlofluanid and Chlorothalonil, were detected. In particular, Irgarol 1051 was detected with high concentrations. In Jebudo (Jt4), a high concentration of Irgarol 1051 of 159.45 ng $g^{-1}$(dry wt) was detected. We were able to observe that the concentration of TBT compounds are has gradually been reduced whereas the new major antifouling agents are easily detected in most Korean tidal flats.