• Earthquakes and Structures
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• 제16권4호
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• pp.415-423
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• 2019

Near-fault ground motions can impose particularly high seismic demands on structures due to the pulses that are typically observed in the velocity time-histories. In this study it is empirically found that the critical response can be estimated from the directions corresponding to the maximum (max) or minimum (min) pulse-energy. Determination of the pulse-energy requires removing of the high-frequency content. For achieving this, the wavelet analysis and the least-square-fitting (LSF) algorithm are adopted. Results obtained by the two strategies are compared and differences between them are analyzed. Finally, the relationship between the critical response and the response derived from directions having the max or min pulse-energy confirms that using the pulse-energy for deriving the critical response of the building structures is reasonable.

• 한국초전도ㆍ저온공학회논문지
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• 제23권1호
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• pp.1-6
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• 2021

Thermoacoustic oscillations (TAOs) could be often observed in liquid helium cryogenic system especially in half-open tubes. These tubes have closed warm end (300K) and open cold end (usually 4.4K). This phenomenon significantly induces additional heat load to cryogenic system and other undesirable effects. This work focuses on using computational fluid dynamics (CFD) method to study TAOs in liquid helium. The calculated physical model, numerical scheme and algorithm, and wall boundary conditions were introduced. The simulation results of onset process of thermoacoustic oscillations were presented and analyzed. In addition, other important characteristics including phase relation and frequency were studied. Moreover, comparisons between experiments and the CFD simulations were made, which demonstrated thevalidity of CFD simulation. CFD simulation can give us a better understanding of onset mechanism of TAOs and nonlinear characteristics in liquid helium cryogenic system.

• 한국정보처리학회:학술대회논문집
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• 한국정보처리학회 2013년도 추계학술발표대회
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• pp.277-279
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• 2013

스크램블링(Scrambling)은 네트워크에서 영상을 전송할 때 보안을 위해 데이터를 특정한 키에 의해 암호화 하여 전송함으로써, 수신자만이 원본 영상으로 복원할 수 있도록 하는 기술이다. 스크램블링은 전송에서 TDES, AES 뿐만아닌 SEED, AIRA의 암호화 알고리즘을 사용한다. 이 경우 암복호화에 많은 시간이 소요되어 실시간 전송환경에서는 전송속도 저하에 따른 QoS 문제가 발생한다. 이와 같은 문제를 해결하기 위해 기존 연구에서는 속도가 빠른 해쉬 함수를 이용하여 스크램블링 암호화 하는 기법을 제안하였다. 하지만 원본 이미지의 일부가 노출될 경우 이후 원본프레임이 노출될 수 있는 문제점을 가지고 있다. 본 논문에서는 이러한 문제점을 방지하기 위해 다중 해쉬 키 프레임을 이용한 Multi Hash key Frame based Scrambling Encryption 알고리즘을 제안한다. 성능평가에서는 제안하는 스크램블링 기법에 대한 암복호화 비용과 성능을 측정하였으며, 기존기법과 비교하였을 때 원본 노출로 인한 대입공격 취약성 부분을 기존 해쉬 함수의 보안 안전성만큼 향상시켰다.

• Journal of Information Processing Systems
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• 제17권1호
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• pp.89-106
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• 2021

Different samples can have different effects on learning support vector machine (SVM) classifiers. To rebalance an imbalanced dataset, it is reasonable to reduce non-informative samples and add informative samples for learning classifiers. Safe sample screening can identify a part of non-informative samples and retain informative samples. This study developed a resampling algorithm for Rebalancing imbalanced data using Safe Sample Screening (Re-SSS), which is composed of selecting Informative Samples (Re-SSS-IS) and rebalancing via a Weighted SMOTE (Re-SSS-WSMOTE). The Re-SSS-IS selects informative samples from the majority class, and determines a suitable regularization parameter for SVM, while the Re-SSS-WSMOTE generates informative minority samples. Both Re-SSS-IS and Re-SSS-WSMOTE are based on safe sampling screening. The experimental results show that Re-SSS can effectively improve the classification performance of imbalanced classification problems.

• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.680-690
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• 2020

In ocean environment, the sound speed gradient of seawater has an important influence on far field sound propagation. The FEM/BEM is used to decouple the vibroacoustic radiation of the spherical shell, and the Green function of the virtual source chain is adopted for decoupling. For far field radiated Sound Pressure Level (SPL), the Beam Displacement Ray normal Mode (BDRM) is employed. The vibration and near-/far-field radiated SPL of spherical shell is analyzed in shallow sea uniform layer, negative/positive gradient, negative thermocline environment, and deep-sea sound channel. Results show that the vibroacoustic radiation of spherical shell acted at 300Hz can be analogous to dipole. When the radiated field of the spherical shell is dominated by large-grazing-angle waves, it can be analogous to vertically distributed dipole, and the far field radiated SPL is lower; while similar to horizontally distributed dipole if dominated by small-grazing-angle waves, and the far field SPL is high.

• 대한수학회보
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• 제59권1호
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• pp.167-177
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• 2022

A vertex v of a graph G = (V, E) is said to ve-dominate every edge incident to v, as well as every edge adjacent to these incident edges. A set S ⊆ V is called a double vertex-edge dominating set if every edge of E is ve-dominated by at least two vertices of S. The minimum cardinality of a double vertex-edge dominating set of G is the double vertex-edge domination number γ_dve(G). In this paper, we provide an upper bound on the double vertex-edge domination number of trees in terms of the order n, the number of leaves and support vertices, and we characterize the trees attaining the upper bound. Finally, we design a polynomial time algorithm for computing the value of γ_dve(T) for any trees. This gives an answer of an open problem posed in [4].

• International Journal of Computer Science & Network Security
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• 제22권1호
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• pp.55-60
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• 2022

Churn prediction is a critical long-term problem for many business like music, games, magazines etc. The churn probability can be used to study many aspects of a business including proactive customer marketing, sales prediction, and churn-sensitive pricing models. It is quite challenging to design machine learning model to predict the customer churn accurately due to the large volume of the time-series data and the temporal issues of the data. In this paper, a parallel artificial neural network is proposed to create a highly-accurate customer churn model on a large customer dataset. The proposed model has achieved significant improvement in the accuracy of churn prediction. The scalability and effectiveness of the proposed algorithm is also studied.

• 국제학술발표논문집
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• The 3th International Conference on Construction Engineering and Project Management
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• pp.224-229
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• 2009

Digital image recognition has been used for steel bridge surface assessment since late 1990s. However, the non-uniform illumination problems such as shades, shadows, and highlights are still challenges in image processing to date. Therefore, this paper develops a new approach to tackle the non-uniform illumination problem for rust image adjustment. The inhomogeneous illumination problem is divided into shades/shadows and highlights in this paper. The proposed BEMD-morphology approach (BMA) utilizes the bidimensional empirical mode decomposition to mitigate the shade/shadow effect, and the morphological processing to detect and replace the highlight area. Finally, the rust image processed with the BMA will be segmented by the K-Means algorithm, one of the most popular and effective methods, to show the effectiveness of illumination adjustment.

• 국제학술발표논문집
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• The 3th International Conference on Construction Engineering and Project Management
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• pp.449-456
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• 2009

Image processing has been applied to steel bridge defect recognition since 1990s. Compare to human visual inspection, image processing provides a more objective and accurate way of assessment. Since shade and shadow may sometimes occur when taking bridge coating images, non-uniform illumination problems should be considered. By means of color image processing, this paper aims to mitigate the illumination effect for bridge coating assessment. Furthermore, the adaptable ellipse method (AEM) is proposed to recognize mild rust colors. Finally, AEM will be compared to the K-Means algorithm, a popular recognition method, to show its advantage.

• 한국정보처리학회:학술대회논문집
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• 한국정보처리학회 2011년도 춘계학술발표대회
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• pp.384-385
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• 2011

본 논문은 중요도 맵과 Mean Shift 알고리즘을 이용하여 모바일 폰 영상 내의 와인 라벨 검출 방법을 제안한다. Mean Shift 알고리즘은 비모수적 클러스터링 기술로 클러스터의 수에 대한 사전 지식이 없이도 클러스터링이 가능한 알고리즘인데 실행 시간이 많이 필요한 단점이 있다. 이러한 문제를 해결하기 위해서 입력 칼라 와인 영상에 Saliency Map을 먼저 적용하고 영상의 두드러진 영역을 찾는다. 다음으로 Mean Shift 알고리즘을 이용한 분할 결과에서 얻은 칼라 마스크를 따라 빈도가 가장 높은 칼라 영역을 찾고 와인 라벨 영역을 검출한다. 실험결과를 통하여 제안된 방법을 모바일 폰을 이용하여 획득된 다양한 와인 영상의 라벨 영역을 효율적으로 검출할 수 있음을 볼 수 있다.