• Journal of the Korea Computer Industry Society
• /
• v.3 no.2
• /
• pp.235-242
• /
• 2002

To minimize restructuring cost of a tree, experiments were conducted to collect quantitative information of searching efficiencies varying degrees of imbalance in a binary search tree. Degrees of tree imbalance were measured by a balance factor, an absolute value of height difference of left subtree and right subtree in a binary search tree. The average number of comparisons increased (p＜0.01), and searching efficiency of O(n) was more appropriate rather than O(logn), as degrees of imbalance in a binary search tree deteriorated. However, there were no significant differences of searching efficiencies in height balanced trees and trees with subtrees to have height 3 less than the other (p＞0.05). Therefore, the findings would be applicable to maintain searching efficiency of a software with a binary search tree.

• Journal of Internet Computing and Services
• /
• v.7 no.1
• /
• pp.39-47
• /
• 2006

The evaluation of MDx family hash functions such as MD5 is difficult because the design background or a generalized model is unknown. In this paper, an approximated model is proposed to generalize hash functions. The diffusion of a input difference is tested by an approximated model for MD5. The results show that MD5 does not provide perfect diffusion, so MD5 is weak against some attacks. We propose a multiple chaining pattern which provides perfect diffusion in approximated model of hash function without extra calculation or memory. And We show the probability of differential characteristics of our proposal.

• Journal of Digital Convergence
• /
• v.12 no.11
• /
• pp.349-355
• /
• 2014

In this paper, we propose the artificial vision system using human visual information processing and wavelet. Artificial vision system may be used for the visually impaired person and the machine recognition system. In this paper, we have constructed the information compression process to ganglion cells from the human retina. And we have reconstructed the primary visual information using recovery process to primary visual cortex from ganglion. Primary visual information is constructed by wavelet transformation using a high frequency and low frequency response. In the experiment, we used the faces database of AT&T. And the proposed method was able to improve the accuracy of face recognition considerably. And it was verified through experiments.

• The KIPS Transactions:PartA
• /
• v.15A no.6
• /
• pp.345-350
• /
• 2008

Recently, a HyperStar network HS(2n,n) has been introduced as a new interconnection network of new topology for parallel processing. HyperStar network has properties of hypercube and star graph, further improve the network cost of a hypercube with the same number of nodes. In this paper, we show a construction algorithm of edge-disjoint spanning trees in HyperStar network HS(2n,n). Also, we prove that edge-disjoint spanning tree by the algorithm is optimal.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.11 no.3
• /
• pp.540-548
• /
• 2007

The parer proposes a power factor correction high efficiency PWM single-phase rectifier. Its good characteristics such as simple PWM control, low switch stress, and low VAR rating of commutation circuits make the proposed rectifier very suitable for various unidirectional power applications. In addition, the proposed rectifier consists of three boost-converter-type IGBT modules with the switching devices located at the bottom leg of the rectifier scheme, which also enables the use of the same power supply in both control and gate driver, thus resulting in simple control and power circuit structure. The detailed principle of operation and experimental results are also included. In particular, the design guide line is also suggested to make the circuit design of the proposed rectifier easy and fast.

• Convergence Security Journal
• /
• v.18 no.2
• /
• pp.11-17
• /
• 2018

Lamport's one-time password (OTP) was originally proposed to address the weaknesses of a simple password system: fixed password, pre-shared password. However, a main weakness of Lamport's OTP is that a root hash value of a new hash chain should be re-registered after consuming all the hash values since OTP generation is based on the finite hash chain. Several studies have been conducted to solve these drawbacks, but new drawbacks such as increased burden of proof for verifiers and verifiers have been exposed. In this paper, we propose and compare a novel OTP that overlaps several short hash chains instead of one long hash chain, which is the core of existing Lamport OTP, to solve the drawbacks while maintaining the advantages of Lamport.

• Journal of the Korea Institute of Information Security & Cryptology
• /
• v.7 no.3
• /
• pp.65-78
• /
• 1997

Due to the cryptographic functional structure including the S-box, DES is not robust against differential cryptoanalysis (DC). Therefore, to increase the security against DC, we have to redesign the S-box or modify DES algorithm to decrease the probability for the N-1 round characteristics. However, it has been shown that a new design for the S-box is not secure enough. Rather, if will be more reliable to devise a modified cryptographic algorithm. In this paper, we propose a modified DES algorithm to decrease the probability of N-1 round characteristics to be robust against DC. According to our comparative study, the proposed algorithm is shown to be more robust against the DC than DES.

• The Journal of the Korea institute of electronic communication sciences
• /
• v.16 no.6
• /
• pp.1239-1248
• /
• 2021

In this paper, we present FDNN algorithm to perform prediction based on academic understanding. In order to apply prediction based on academic understanding rather than data-dependent prediction to deep learning, we constructed algorithm based on mathematical and hydrology. We construct a model that predicts flow rate of a river as an input of precipitation, and measure the model's performance through K-fold cross validation.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2021.06a
• /
• pp.256-256
• /
• 2021

Saint-Venant 방정식은 수평규모가 수심규모보다 큰 천수흐름을 기술하는 수리동역학 모형으로 지난 수십년간 공학적 분야에서 널리 이용되어 왔다. 최근에도 기후변화에 따른 도시 홍수의 위기 증대로 홍수위기관리의 관심이 높아짐에 따라 홍수파(flood wave), 도시침수(urban inundation), 돌발홍수(flash flood) 등의 신속한 예측을 위한 Saint-Venant 방정식의 연구가 활발히 진행되고 있다. 그러나 도시와 같은 인공구조물이 즐비한 상황에서 천수흐름을 해석하는 고전적인 수치해법들은 다양한 불연속 지형들의 존재로 인하여 불안정하며 지배방정식의 정해로 수치해가 잘 수렴하지 않는 문제가 있다. 지난 수년간 이를 해결하기 위해 불연속한 지형을 안정적으로 해결할 수 있는 수치기법의 연구가 진행되어 왔으나, 정해로의 수렴성, 정확성에 관하여 연구가 부족한 실정이다. 본 연구는 수치해법의 주요 구조를 구성하는 Saint-Venant 방정식의 불연속한 지형조건에 대한 리만 문제의 정해를 연구하였다. 쌍곡선형 시스템의 특징을 고려하여 요소파들(elementary waves)의 공식을 유도하였는데, 질량과 에너지의 보존법칙에 위배되지 않으며 운동량이송부의 비선형성과 지형의 불연속에 의한 비엄격성을 고려할 수 있는 조건을 제시하였다. 또한, 유도된 요소파들을 바탕으로 L-M & R-M 커브이론(Han et al. 2014)을 사용할 수 있는 조건과 당위성을 증명하였고, 이를 바탕으로 Saint-Venant 방정식의 정해법을 구성하였다. 리만문제의 다양한 초기조건들을 바탕으로 모든 경우의 정해 구조를 조사하였고, 이를 통해 불연속 지형에 대한 Saint-Venant 지배방정식의 정해가 다수해를 갖을 수 있음을 보였으며, 이를 근사할 수 있는 수치기법의 전략을 소개하였다.

• The Journal of the Acoustical Society of Korea
• /
• v.13 no.5
• /
• pp.40-50
• /
• 1994

In this paper, the sensitivity compensation method for three-dimensional acoustic intensity probe in the higher frequency range has been studied. The measurement error in the higher frequency range is generated from the phase mismatch between microphone's signals of the probe. If the wavelength of sound signal measured is less than those of the distance between microphones of the probe, that is, the higher frequency of the sound signal, the bigger measurement error is generated. In this study, we proposed the compensation methods for one-dimensional acoustic intensity probe with two-microphones, and the efficiency of those methods were investigated by numerical calculation of computer. It was most effective method to compensate the phase mismatch between microphone for the acoustic intensity probe was investigated for the sound estimated. and the efficiency of this method in a three-dimensional probe was investigated for the sound wave travelling in the arbitrary direction by numerical calculation of computer. In this result, the efficiency was proved that, for the measurement error of 1dB or less with the three-dimensional probe of 60mm space, the frequency should be less than 1.2kHz without the error compensation method, but the frequency increased up to 2.8kHz with the error compensation method.