가시적 격자점 문제를 이용한 안드로이드 잠금 패턴 가짓수의 상계와 하계 범위 개선

김현호,정성재,송상헌 한국과학영재교육학회 2019 과학영재교육 Vol.11 No.3

In larger than grid, the number of Android locking pattern to solve using full search is hard. In this study, the Visible Grid point Problem is applied to obtain a possible number of patterns. This problem will be expanded. In original, Visible Grid Point Problem have been studied with infinite grid, while in this study, it extends to finite grid. With reference to the process of solving ratio of visible points of arbitrary point in infinite grid, , we solved the ratio of visible points to arbitrary point in the finite plane. However, it is difficult to obtain the accurate ratio of visible points to arbitrary point in the finite plane. Thus, by calculating the upper bound and lower bound of this ratio, we obtained the upper bound and lower bound of the numbers of the Android locking patterns’ possible parameters to see the approximate range of the possible parameters. So, all of upper bounds are improved. 격자 평면 위 임의의 점에서 다른 점을 볼 수 있는 비율은 이라는 가시적 격자점 문제는 무한 격자 평면에 기반을 둔 것이다. 하지만 이상 의 유한 격자 평면에서는 경우의 수(전체탐색법)만으로 그 가짓수를 모두 구하는 것은 어렵다. 본 연구는 선행연구들을 바탕으로 유한 격자 평면으로 국한할 때의 안드로이드 잠금 패턴의 가짓수 범위(상계와 하계)를 구하는 알고리즘을 개발하였다. 특히 좌표평면 위 점의 위치에 따른 가시적 격자점 비율의 상계와 하계를 미지수화하여 경우의 수에 따라 세분화하면서 공식화하였다. 이 공식을 바탕으로 Python Coding으로는 오버플로가 발생하지 않는 범위(13×13 격자판) 내에서 일부의 하계 값과 대부분의 상계 값을 개선시켰다. 이 연구는 Lee(2017)가 제시하였던 가시성에 기반하지 않은 연구에서의 알고리즘을 발전시켰고 최승훈 (2017)이 제안한 가시성에 기반한 연구와 Goodrich, et, al. (2018)과는 Visible Grid Point Problem에 공통점이 있다. 그러나 이들의 연구 결과값을 일부 개선했던 정성재, 김현호, 송상헌(2018)과도 상계와 하계를 구하려는 목적은 같으나 이를 구하는 과정과 방법에 차이가 있다.

북한주민 탈북사태의 원인과 대책

김현호 한국전략문제연구소 1996 전략연구 Vol.3 No.2

Since the 1990's, North Korean refugees have been under great international interest due to their growing number. Also the escape movement is seen as closely related to the overall crisis that North Korea is currently facing. Some even compare it to that of the East Germans shortly before the downfall of the Berlin Wall. The escape of North Koreans should be observed with Korean Government's reunification policy. It is clearly not the simple matter of human rights. About 1,500 North Korean refugees are wandering in China and Russia. The Korean goverment sees that about 700 of them wish to move to South Korea. However, the exact number is unknown. The size has been suddenly increased during 1990~1993. The North Korean government has strengthened the boarder line watch since. The number has been decreased because the refugees were unsure about their safety. Currently, the annual number of refugees is not over some hundreds. The refugees are not active in anti-North Korean movement since it is impossible for them to act out in the open. The reform of Russia and China was in its height in the late 80's and early 90's. Naturally, it worked as an incentive to the massive escape. At the same time, as Korea expanded its diplomatical realtionship with China as well as Russia, Many North Koreans became aware of the South and they began to consider Korea as a place of refuge. North Korean economy has suffered a great deal in the 90's. Ecomomic difficulty is the main fundamantal factor of the refuge. The growing number of refugees especially in the 3rd countries has begun to act as a great burden in North Korean foreign policies. Therefore, the government become coersive which resulted in the increase of the refugees. North Korea may turn to economical reform. However, with the current size of refugees, it is yet hardly a threat to the regime. The size as well as the character of North Korean escapees are quite different from that of East German. From 1949 to the early half of the 90's about 5.2 million East Germans moved to the West. It was not difficult for East Germans to move out Some even moved out legally. The present North Korean refugees are risking their lives to cross the border. Korean Government's policy toward the refugees has always been impromtu. Or it has been just a talk without any principle. There has been a total of 80 submissions to the South since 1993 which takes up 10% of the overall number. Now is clearly the time for the government to come up with fundamental and comprehensive measures.

젊은 성인 일스병 뇌졸중 환자에게 동반된 뇌혈관협착

김현호,이경미,허성혁 대한신경과학회 2021 대한신경과학회지 Vol.39 No.4

Eales’ disease is an idiopathic disorder induced by ischemic retinal vasculitis, usually affecting the peripheral retina. We encountered a young patient diagnosed as cerebral infarction with a history of Eales’ disease. The patient’s middle cerebral artery showed multifocal stenosis with contrast enhancement, suggesting vasculitis. These findings might give clues to a rare cause of cerebral artery stenosis.

위성통신용 적응형 전송기술 리턴링크 채널예측 알고리즘 최적화

김현호,김국현,유준규,홍성용 한국위성정보통신학회 2015 한국위성정보통신학회논문지 Vol.10 No.2

위성통신서비스의 가용율 및 시스템 throughput 향상을 위해 사용하는 리턴링크 ACM(Adaptive Coding & Modulation)의 원리를 기술하였고, LMS(Least Mean Square) 기반 적응형 필터를 이용한 채널 예측 및 단말의 전송 MODCOD(Modulation & Code rate) 결정 알고리즘의 최적화 과정을 서술하였다. 시뮬레이션 결과 LMS 알고리즘은 필터 계수가 2차이고, μ(step size) 값이 0.00026인 경우 MMSE(Minimum Mean Square Error)가 최소임을 알 수 있다. 이때 MODCOD 결정 알고리즘을 위한 SNR 마진이 0.3dB일 경우 MODCOD 결정 오차를 최소화 할 수 있음을 확인하였다. In this paper, we present the return link ACM method to improve the link availability and system throughput for satellite communication service. Also, we describe the optimization of an algorithm for channel prediction using the LMS (Least Mean Square) adaptive filter and the MODCOD (Modulation & Code rate) decision. The simulation results show that the optimized filter taps and step-size of adaptive filter are 2 and 0.00026, respectively. And also confirms the required SNR margin for minimization of MODCOD decision error is 0.3dB.

단조성 보장을 위한 국지 선형 앙상블 모델

김현호,한민석,이종석 대한산업공학회 2023 대한산업공학회 춘계학술대회논문집 Vol.2023 No.5

다종 장사정포 공격에 대한 강화학습 기반의 동적 무기할당

김현호,김정훈,공주회,경지훈 한국산업경영시스템학회 2022 한국산업경영시스템학회지 Vol.45 No.4

North Korea continues to upgrade and display its long-range rocket launchers to emphasize its military strength. Recently Republic of Korea kicked off the development of anti-artillery interception system similar to Israel’s “Iron Dome”, designed to protect against North Korea’s arsenal of long-range rockets. The system may not work smoothly without the function assigning interceptors to incoming various-caliber artillery rockets. We view the assignment task as a dynamic weapon target assignment (DWTA) problem. DWTA is a multistage decision process in which decision in a stage affects decision processes and its results in the subsequent stages. We represent the DWTA problem as a Markov decision process (MDP). Distance from Seoul to North Korea’s multiple rocket launchers positioned near the border, limits the processing time of the model solver within only a few second. It is impossible to compute the exact optimal solution within the allowed time interval due to the curse of dimensionality inherently in MDP model of practical DWTA problem. We apply two reinforcement-based algorithms to get the approximate solution of the MDP model within the time limit. To check the quality of the approximate solution, we adopt Shoot-Shoot-Look(SSL) policy as a baseline. Simulation results showed that both algorithms provide better solution than the solution from the baseline strategy.

MPEG-I의 6DoF를 위한 360 비디오 가상시점 합성 성능 분석

김현호,김재곤 한국방송∙미디어공학회 2019 방송공학회논문지 Vol.24 No.2

360 비디오는 VR 응용의 확산과 함께 몰입형 미디어로 주목받고 있으며, MPEG-I Visual 그룹은 6 자유도(6DoF)까지의 몰입형 미디어를 제공하기 위한 표준화를 진행하고 있다. 제한된 공간내에서 전방위 6DoF를 제공하는 Omnidirectional 6DoF는 제공되는 제한된 수의 360 비디오로부터 임의의 위치에서의 뷰(view)를 제공하기 위한 가상시점 합성이 필요하다. 본 논문에서는 MPEG-I Visual 그룹에서 진행된 전방위 6DoF를 위한 합성에 대한 탐색실험의 성능 및 분석 결과를 기술한다. 즉, 합성하려는 가상시점과 합성을 위한 360 비디오의 입력시점 사이의 거리 및 입력시점의 개수 등의 다양한 실험조건에 따른 합성 성능 결과 및 분석을 제시한다.

비선형 시스템 계통에서 신경망에 근거한 가변구조 제어

김현호,이천희,Kim, Hyeon-Ho,Lee, Cheon-Hui 한국정보처리학회 2001 정보처리학회논문지 A Vol.8 No.1

This paper presents a neural network based variable structure control scheme for nonlinear systems. In this scheme, a set of local variable structure control laws are designed on the basis of the linear models about preselected representative points which cover the range of the system operation of interest. From the combination of the set of local variable structure control laws, neural networks infer the approximate control input in between the operating points. The neural network based variable structure control alleviates the effects of model uncertainties, which cannot be compensated by the control techniques using feedback linearization. It also relaxes the discontinuity in the system’s behavior that appears when the control schemes based on the family of the linear models are applied to nonlinear systems. Simulation results of a ball and beam system, to which feedback linearization cannot be applied, demonstrate the feasibility of the proposed method.

Oblique Single-Cut Rotation Osteotomy for Correction of Femoral Varus-Torsional Deformities in 3D-Reconstructed Canine Bone Models

김현호,노윤호,이제훈,정재민,정성목,이해범 한국임상수의학회 2020 한국임상수의학회지 Vol.37 No.4

The purpose of this study was to report the reliability and validity of oblique single-cut rotation osteotomy (OSCRO) in 3D-reconstructed canine bone models with femoral varus and torsional deformities. A healthy adult male beagle was recruited to create a 3D bone model, and this bone model was modified by using a 3D program. Fifteen bone models were constructed for this study. OSCRO simulation was performed in accordance with the plan after printing using a 3D printing machine. The anatomical lateral distal femoral angle (aLDFA), anteversion angle (AA), anatomical caudo-distal femoral angle (aCdDFA), mechanical caudo-distal femoral angle (mCdDFA) and pre- and postoperative bone length were calculated. There were no significant differences between the target values and postoperative values. In addition, the difference between pre- and postoperative bone length was small (p = 0.001). Our findings suggest that OSCRO could be an effective surgical option for MPL with bone deformities in small-breed dogs that often undergo conventional distal femoral osteotomy.

용매추출-전해채취법에 의한 망간단괴 매트상 모의 침출용액으로부터 코발트 회수

김현호,남철우,박경호,윤호성,김민석,김철주,박상운,Kim, Hyun-Ho,Nam, Chul-Woo,Park, Kyung-Ho,Yoon, Ho-Sung,Kim, Min-Seuk,Kim, Chul-Joo,Park, Sang-Woon 한국자원리싸이클링학회 2016 資源 리싸이클링 Vol.25 No.2

망간단괴 매트상 모의 침출용액에서 구리 용매추출과 수산화 침전법에 의해 구리와 철이 제거 된 용액(Co 1.91 g/L, Ni 14.65 g/L)으로부터 용매추출-전해채취 연속공정을 통해 코발트를 분리, 회수를 위한 규모확대 실험(망간단괴 기준 380 kg/day)을 수행하였다. 용매추출의 경우 추출제로는 NaOH로 45% 비누화 된 0.22 M Cyanex 272, 세정용액은 코발트 2 g/L(pH : 3.0), 탈거용액은 코발트 전해폐액(Co 36.0 g/L, $Na_2SO_4\;70g/L$, pH : 1.5)을 사용하였으며, 탈거된 유기상은 산과 증류수의 세척 공정을 통해 재사용하였다. 추출단, 세정단 그리고 탈거단의 O/A 비는 각각 1/1.5, 10/1 그리고 1.5/1 이었으며, 산세척과 수세척단의 O/A 비는 각각 1/1, 6/1이었다. 용매추출공정의 코발트의 추출율과 탈거율은 각각 99.8%와 99.88%이었으며 탈거액의 코발트와 니켈의 농도는 각각 40.27 g/L, 4 ppm이었다. 전해액의 pH 조절을 위해 전해폐액 순환 방식을 도입한 전해채취공정은 $0.563A/dm^2$의 전류밀도에서 67.0%의 전류효율을 나타내었으며, 99.963% 순도의 금속 코발트를 얻었다. A scale up tests (380 kg/day) using a continuous solvent extraction and electro-winning system was carried out to separate and recover cobalt from a solution containing 1.91 g/L Co and 14.65 g/L Ni. The solution was obtained during a process including solvent extraction and precipitation stages for removal of Cu and Fe from a synthetic sulfuric acid solution of manganese nodule matte. The optimal condition for solvent extraction was : solvent concentration of 0.22M Na-Cyanex 272 (45% saponified with NaOH) and O:A phase ratios of 1:1.5, 10:1 and 1.5:1 used in extraction, scrubbing and stripping stages, respectively. The extraction and stripping efficiencies were found to be 99.8% and 99.88%, respectively. The stripped solution contained 40.27 g/L Co with 4 ppm Ni. Cobalt metal of 99.963% purity was yielded with current efficiency of 67% and current density of $0.563A/dm^2$ during the electro-winning process.