• Journal of the Mineralogical Society of Korea
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• v.29 no.4
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• pp.209-220
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• 2016

Clay minerals are a major player to determine geochemical cycles of trace metals and carbon in the critical zone which covers the atmosphere down to groundwater aquifers. Molecular dynamics (MD) simulations can examine the Earth materials at an atomic level and, therefore, provide detailed fundamental-level insights related to physicochemical properties of clay minerals. In the current study, we have applied classical MD simulations with clayFF force field to dioctahedral clay minerals (i.e., gibbsite, kaolinite, and pyrophyllite) to analyze and compare structural parameters (lattice parameter, atomic pair distance) with experiments. We further calculated vibrational power spectra for the hydroxyls of the minerals by using the MD simulations results. The MD simulations predicted lattice parameters and interatomic distances respectively deviated less than 0.1~3.7% and 5% from the experimental results. The stretching vibrational wavenumber of the hydroxyl groups were calculated $200-300cm^{-1}$ higher than experiment. However, the trends in the frequencies among different surface hydroxyl groups of each mineral was consistent with experimental results. The angle formed by the surface hydroxyl group with the (001) plane and hydrogen bond distances of the surface hydroxyls were consistent with experimental result trends. The inner hydroxyls, however, showed results somewhat deviated from reported data in the literature. These results indicate that molecular dynamics simulations with clayFF can be a useful method in elucidating the roles of surface hydroxyl groups in the adsorption of metal ions to clay minerals.

• The Journal of the Korea Contents Association
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• v.6 no.11
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• pp.225-234
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• 2006

In this paper, we design a combined security processor, ECC, MD-5, and AES, as a SIP for cryptography of securing contents. Each SIP is modeled and designed in VHDL and implemented as a reusable macro through logic synthesis, simulation and FPGA verification. To communicate with an ARM9 core, we design a BFM(Bus Functional Model) according to AMBA AHB specification. The combined security SIP for a platform-based SoC is implemented by integrating ECC, AES and MD-5 using the design kit including the ARM9 RISC core, one million-gate FPGA. Finally, it is fabricated into a MPW chip using Magna chip $0.25{\mu}m(4.7mm{\times}4.7mm$) CMOS technology.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.18 no.6
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• pp.113-119
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• 2018

This paper relates the AM-NM-MMA algorithm which possible to adaptive equalization performance improvement using the adaptive modulus instead of fixed modulus in the NM-MMA algorithm. The NM-MMA emerged for the tradeoff the MMA and SE-MMA algorithm characteristics, the MMA provides the less residual values in the steady state and have a slow convergence rate, the SE-MMA provides the fast convergence rate and increae the risidual values in the steady state. But the fixed modulus can not give the zero residual values in the perfect equalization state and eqaulization performance were degrade, the adaptive modulus was applied in order to reducing the residual values, and its improved performance were confirmed by simulation. For this, the equalizer output constellation, residual isi, MD, MSE, SER were used for performance index. As a result of computer simulation, the AM-NM-MMA has more good performance in equalizer output signal constellation, residual isi, MD, MSE than the NM-MMA, but not in SER performance.

• Journal of the Mineralogical Society of Korea
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• v.32 no.3
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• pp.151-162
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• 2019

Todorokite, a tunnel-structured manganese oxide, can contain cations within the relatively large nanopores created by the $3{\times}3$ Mn octahedra. Because todorokite is poorly crystalline and found as aggregates mixed with other phases of Mn oxides in nature, the coordination structure of cations in the nanopores is challenging to fully characterize in experiment. In the current article, we report the atomistic coordination structures of $Mg^{2+}$ ions in todorokite tunnel nanopores using the classical molecular dynamics (MD) simulations. In experiment, $Mg^{2+}$ is known to occupy the center of the nanopores. In our MD simulations, 60 % of $Mg^{2+}$ ions were located at the center of the nanopores; 40 % of the ions were found at the corners. All $Mg^{2+}$ located at the center formed the six-fold coordination with water molecules, just as the ion in bulk aqueous solution. $Mg^{2+}$ ions at the corners also formed the six-fold coordination with not only water molecules but also Mn octahedral surface oxygens. The mean squared displacements were calculated to examine the dynamic features of $Mg^{2+}$ ions in the one-dimensional (1D) nanopores. Our MD simulations indicate that the dynamic features of water molecules and the cations observed in bulk aqueous solution are lost in the 1D nanopores of todorokite.

• Proceedings of the Korean Information Science Society Conference
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• 2012.06d
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• pp.260-261
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• 2012

스마트 환경에 관심이 높아지면서 무선 센서 네트워크를 이용한 유비쿼터스 시스템을 실생활에 활용하려는 노력이 이어지고 있다. 무선 센서 네트워크는 무선 통신으로 정보를 수집하기 때문에 실생활에 적용할 경우 사생활 정보가 유출될 가능성을 가진다. 본 논문은 데이터 전송 과정에서 데이터가 유출되었을 때, 원본 데이터로의 해독을 어렵게 하는 해시 알고리즘을 제안한다. 제안하는 알고리즘은 단 방향 해시 함수인 MD5를 변형한 TinyMD5를 이용하여 데이터를 변환하고, MD5를 변형하면서 발생하는 해시 값 충돌 문제를 해결할 수 있는 기법을 추가하였다. 제안하는 알고리즘의 우수성을 보이기 위해 기존의 기법과 시뮬레이션을 통해 성능을 비교 평가하였다. 성능 평가 결과, 제안하는 알고리즘은 통신 에너지를 기존 알고리즘의 평균 29%만을 소모하였다.

• The Transactions of the Korea Information Processing Society
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• v.7 no.11
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• pp.3576-3583
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• 2000

Digital watermarks have recently been proposed for the purposes of copyright ptotechtion and autheutication for multimedia contents. A watermarking technique consists of an algorithm that incorporates a watermarking structure into an image in the spatial or frequency domains. In this paper we proposed a new watermarking method for authentication and integrity of digital images and the proposed algorithm uses the MD5 hash funiction and a symmetric key encryption algorithm. To decide the position of embedding watermark and the bit pasitionin the original image, the secret key is used as an input of the MD5 hash function. The simulation results show that the proposed algorithm has the advantage of difficulty to find positions of inserted watermarks, and keep the similar watermarked image quabty with Wong's method.

• Proceeding of EDISON Challenge
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• 2014.03a
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• pp.169-182
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• 2014

이 연구에서는 Lennard-Jones (LJ) particle을 이용하여 상분리 현상을 이해하기 위한 컴퓨터 시뮬레이션 연구를 수행하였다. 초기에 균일하게 분포되어 있는 LJ 입자들을 시뮬레이션 하면 상대적으로 dense phase와 dilute phase로 상분리 현상이 일어나게 된다. 상분리 현상의 첫 번째 단계를 핵 생성 (nucleation) 이라고 한다. 본 연구에서는 Brownian Dynamics (BD) Simulation과 Molecular Dynamics (MD) Simulation을 이용하여 상평형 그림을 구하고 초기에 일어나는 LJ 입자들의 nucleation rates를 구하였다.

• Journal of the Korea Society for Simulation
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• v.10 no.2
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• pp.25-32
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• 2001

The Multiple Recursive Generator(MRG) has been considered by many scholars as a very good random number generator. For the long period md excellent statistical properties, the method of the combination with random number generators is used. In this paper, we thought the two-combined MRGs. Using the frequency and serial test, and runs test, we studied the importance of the initial seeds likewise other random number generators.

• Proceedings of the Korea Institutes of Information Security and Cryptology Conference
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• 1995.11a
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• pp.341-364
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• 1995

본 고에서는 DAVIC 에서 권고 중인 VOD (video-on-demand) 시스템에 대한 액세스 제어 기법을 분석하고, 이를 바탕으로 국내 VOD 시스템에 적용 가능한 액세스 제어 기법을 제시한다. 이를 위하여 DAVIC 의 VOD 시스템에서의 보안 기법을 분석하고, 보안 시스템을 위한 참조 모델과 요구되는 서비스 및 보안 메카니즘을 분석한 후, 국내 VOD 시스템에 적용 가능한 액세스 제어 시스템 실현 방안과 정보보호 메카니즘을 제시한다. 그리고 방송용 서비스에 적용 가능한 ECM 채널을 DES, MD5, 그리고 RSA 알고리즘을 이용하여 C 언어로 구현하고 관련 동작을 시뮬레이션한다. 시뮬레이션 결과 ECM 채널이 정상 동작됨을 확인한다. 제시된 방안은 국내 VOD 시스템 실현시 유용하게 활용될 수 있다.

• Tribology and Lubricants
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• v.32 no.1
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• pp.9-17
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• 2016

Contact between solid surfaces is one of the most important factors that influence dynamic behavior in micro/nanoscale. Although numerous theories and experimental results on contact behavior have been proposed, a thorough investigation for nanomaterials is still not available owing to technical difficulties. Therefore, molecular dynamics simulation was performed to investigate the contact behavior of nanomaterials, and the application of conventional contact theories to nanoscale was assessed in this work. Particularly, the contact characteristics of cylindrical nanowires were examined via simulation and contact theories. For theoretical analysis, various contact models were utilized and work of adhesion, Hamaker constant and elastic modulus those are required for calculation of the models were obtained from both indentation simulation and tensile simulation. The contact area of the cylindrical nanowire was assessed directly through molecular dynamics simulation and compared with the results obtained from the theories. Determination of the contact area of the nanowires was carried out via simulation by counting each atom, which is within the equilibrium length. The results of the simulation and theoretical calculations were compared, and it was estimated that the discrepancy in the results calculated between the simulation and the theories was less than 10 except in the case of the smallest nanowires. As the result, it was revealed that contact models can be effectively utilized to assess the contact area of nanomaterials.