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이용기,이정규 漢陽大學校 工學技術硏究所 1998 工學技術論文集 Vol.7 No.1
본 논문에서는 차세대 공개키 암호알고리즘으로 평가받고 있는 타원곡선 암호시스템(ECC, Elliptic Curve Cryptosystem)에 대해 전반적인 소개와 수학적 배경 및 구현 알고리즘에 대해 알아보도록 한다. ECC는 1985년 N. Koblitz와 V. Miller에 의해 제안되었으며, 현재 세계적으로 널리 쓰이고 있는 RSA(Rivest Shamir Adleman)나 DSA(Digital Signature Algorithm)에 비해 매우 뛰어난 안전성과 효율성을 가진 것으로 알려져 있다. 예를 들면 현재 안전하게 쓰일 수 있는 RSA와 DSA의 키 크기는 1024 비트인데 비해 ECC는 단지 160 비트의 크기만을 요구할 뿐 아니라 10 배 이상의 빠른 수행 속도를 보이고 있다. 이러한 ECC로 인해 공개키 암호 알고리즘의 가장 큰 결점이었던 수행 속도와 메모리 요구량의 문제점을 해결할 수 있게 되었으며, 스마트 카드와 같이 컴퓨팅 파워나 메모리의 양이 제한적인 어플리케이션에 효율적으로 적용할 수 있게 되었다. This paper introduces overall view of ECC(Elliptic Curve Cryptosystem) which is considered as the next generation's public key cryptosystem. ECC has proposed by N. Koblitz and V. Miller in 1985, and it is known to have better security and performance than RSA(Rivest Shamir Adleman) or DSA(Digital Signature Algorithm) which is recent commonly used cryptosystem. In case of RSA or DSA, 1024 bits key size is required for practical secure channel but ECC only uses 160 bits for the same secure level and this has contributed to reduce operating time more than 10 times than that of RSA or DSA. Therefore ECC has overcame the long operating time and lack of space problem and it will be applied to most cryptosystems especially smart card and the others which are restricted by space of memory or computing power.
Development of numerical analysis model for resistance spot welding of automotive steel
이용기,정훈철,박경배,김영준,조정호 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.7
Resistance spot welding (RSW) is a process in which contacting metal surfaces are joined by the pressure and heat obtained from resistance to electric current flow. It is widely accepted in the industry due to its advantages in high speed and suitability for automation. The RSW process is extremely important to quality in automotive industry because approximately 6000 spot welds were used in automotive body. In addition, the RSW process is a complicated process that includes electrical, thermal and mechanical phenomena. For this reason, it is necessary that researchers should perform electric field, heat transfer and thermo-elastic-plastic analysis, and consider phase change, contact conditions and temperature dependence of material properties in order to simulate a realistic RSW process. There were lots of previous studies for RSW simulation by using Finite element method (FEM), but most of studies have performed qualitative analysis which predicts the shape of weld nugget fatigue life and residual stress. Therefore, this study defines the contents which mentioned above based on the theoretical background and reproduces a 3D DC RSW process through using ABAQUS, commercial FEM program. It also obtains the reliability in terms of simulation results through quantitative approach by comparing between the nugget shape and the actual experimental results. The error percentage of nugget width between simulation and experiment shows outstanding results that from 0.44 % to 3.80 %. Based on the simulation results through these theoretical backgrounds, it is possible to effectively trace the weld nugget shape of all steels, provided the temperature dependent material properties are available. An illustration of such a simulation to predict the nugget shape and size of resistance spot welded SPRC 340 steel is presented in the paper.
이용기,김보련,한은영,이소영,서민지 대한근전도전기진단의학회 2016 대한근전도 전기진단의학회지 Vol.18 No.2
The anterior interosseous nerve syndrome is a rare focal neuropathy with typical clinical and electromyographic features. A number of etiologies have been implicated in this disorder and most commonly reported etiologies include spontaneous (idiopathic), fracture of the forearm and arm, trauma, or prolonged pressure on the forearm. However, we experienced one case of anterior interoeesous nerve syndrome in the postpartum period, which was not related to trauma. To the best of our knowledge, there are a few case reports in Korea.