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황재진(JaeJin Hwang),최명렬(Myung-Ryul Choi) 한국정보과학회 2004 한국정보과학회 학술발표논문집 Vol.31 No.2Ⅰ
인터넷 보안에 대한 중요성이 나날이 증가하고 있으며 이러한 인터넷 보안 문제의 해 결책으로 개발된 IPSec은 IP 계층에서 보안서비스를 제공하기 위하여 AH와 ESP를 사용하여 보안연계(Security Association) 서비스를 제공한다. 본 논문에서는 32-bit 데이터 버스를 이용하여 새로운 AES 로 채택된 Rijndael 암호 알고리즘과 HMAC-SHA-1 인증 알고리즘을 통합시킨 IPSec 암호 프로세서를 구현하였다. Xilinx ISE 5.2i를 사용하여 VHDL로 설계하였고, ModelSim으로 시뮬레이션 검증을 수행하였으며 Xilinx사의 Vertex XCV1000E로 구현하였다. 본 논문에서 구현한 IPSec 암호 프로세서는 WLAN이나 VPN, Firewall 등에 응용될 수 있을 것이다.
Evaluation of upper extremity swing motion reproducibility of exoskeleton gait training device
Jae Ho Kim(김재호),Jaejin Hwang(황재진),Myung-Chul Jung(정명철),Seung-Min Mo(모승민) 대한인간공학회 2021 대한인간공학회 학술대회논문집 Vol.2021 No.11
Objective: This study’s objective was to evaluate the kinematics variables of the upper extremities joints in response to changes in walking speed to identify movement characteristics and propose ergonomic guidelines for exoskeleton devices’ gait stability. In addition, a training device was developed by applying this guideline and mechanism that can reproduce the swing motion of the upper extremity during gait motion. And the reproducibility of the upper extremity swing motion of this training device was evaluated. Background: The natural swing motion of the upper extremity during walking helps to secure the stability of walking by improving the balance ability of the body. And the natural rhythm of human movements in the upper extremity while walking could be useful to determine the functional limit of the exoskeletal devices to enhance the limb dynamics. Method: Walking speed was set as four levels, including 3.6, 4.3, preferred walking speed (PWS), 5.4, and 7.2 ㎞/h as a within-subject variable. The subject walked according to the randomized walking speed for 90 seconds on the treadmill. Twenty gait cycles of motion capture data from each experimental condition of each subject were extracted. The shoulder joint’s kinematic data were analyzed in 2 DOF and the elbow joint data were analyzed in 1 DOF. Results: The kinematic variables of shoulder and elbow were associated with increasing proportionally to walking speed. A sufficient swing of the arm was required to maintain walking stability and reduce the walking energy cost as walking speed increases. The shoulder ROM was analyzed slightly lower at PWS than the slowest walking speed of 3.6㎞/h. The preferred walking speed will induce natural walking patterns of the limb and improve walking stability. The elbow and shoulder joints reflect dynamic covariation of the torque patterns according to the movement of the human body and generate linear synergy. And the reproducibility evaluation of the upper extremity swing motion of the developed training device, it was confirmed that there was no statistically significant difference for most of the independent variables compared to the walking movement without the training device. It means that the device developed through this study reflects the swing motion of the upper extremity well during walking. Conclusion: This study recommended designing a natural shoulder-elbow movement as a linked segment system for the exoskeleton devices’ gait stability. Application: This study"s findings would be used to design the features of the exoskeletal devices (wearable robot, upper limb swing equipment, etc.).
등축정계 페로브스카이트의 포논 분산에 대한 비조화 효과의 영향
박관홍(Kwanhong PARK),황재진(Jaejin HWANG),이재광(Jaekwang LEE) 한국물리학회 2024 새물리 Vol.74 No.5
페로브스카이트 (Perovskite)는 온도에 따라 정방정계, 사방정계, 등축정계 등 다양한 구조를 갖는 것으로 알려져 있다. 그러나 상온에서 실존하는 것으로 알려져 있는 등축정계 페로브스카이트 물질에 대한 조화 근사 기반 포논 분산에서 허수 주파수가 나타난다. 보다 정확히 포논 분산을 얻기 위해 비조화 효과를 고려할 필요가 있다. 본 연구에서는 그를 위해 자체 일관 포논 이론 (Self-Consistent Phonon Theory)을 사용하여 등축정계 SrTiO3, BaTiO3, RbCaF3, CsSrF3의 비조화 효과가 포함된 포논 분산을 계산하였다. 본 연구는 상온에서 존재하는 상의 포논 분산과 그 온도 의존성이 비조화 효과를 고려함으로써 잘 예측될 수 있음을 보여준다. Perovskites are known to exhibit a variety of phases, including tetragonal, orthorhombic, and cubic, depending on the temperature. However, in the cubic phase, which indeed exists at room temperature, imaginary frequencies appear in the phonon dispersion based on the harmonic approximation. That’s why we need to consider the anharmonic effect to accurately capture the phonon dispersion. In this work, self-consistent phonon theory was utilized to calculate the phonon dispersion, including anharmonic effects, for the cubic phases of SrTiO3, BaTiO3, RbCaF3, and CsSrF3. This study demonstrates that the phonon dispersion of the cubic phase, present at room temperature, and their temperature dependency can be accurately predicted by considering the anharmonic effect.