Graphene and Fe3O4 were bound by electrostatic attraction and prepared by effective reduction through microwave treatments. As a result of fabricating graphene with Fe3O4 as a composite material, it has been confirmed that it contributes to the structural improvement in graphene stabilization and at the same time, it shows improved electrochemical performance through improved charge transfer. It was also confirmed that the crystalline Fe3O4 was uniformly dispersed in the rGO sheet, effectively blocking the reaggregation due to the van der Waals interaction between the neighboring rGO sheets. The structural analysis of prepared composites was confirmed by transmission electron microscopy, and X-ray diffractometer. Electrochemical properties of composites were studied by cyclic voltammetry, galvanostatic charge–discharge curves, and electrochemical impedance spectroscopy. The Fe3O4 (0.4 M)/rGO composite showed a high specific capacitance of 972 F g−1 at the current density of 1 A g−1 in 6 M KOH electrolyte, which is higher than that of the pristine materials rGO (251 F g−1) and Fe3O4 (183 F g−1). Also, the prepared composites showed a very stable cyclic behavior at high current density, as well as an improvement in comparison with pristine materials in terms of resistance.

Electrochemical properties and performance of composites performed by incorporating metal oxide or metal hydroxide on carbon materials based on graphene and carbon nanotube (CNT) were analyzed. From the surface analysis by field emission scanning electron microscopy and field emission transmission electron microscopy, it was confirmed that graphene, CNT and metal materials are well dispersed in the ternary composites. In addition, structural and elemental analyses of the composite were conducted. The electrochemical characteristics of the ternary composites were analyzed by cyclic voltammetry, galvanostatic charge-discharge tests, and electrochemical impedance spectroscopy in 6 M KOH, or 1 M Na2SO4 electrolyte solution. The highest specific capacitance was 1622 F g–1 obtained for NiCo-containing graphene with NiCo ratio of 2 to 1 (GNiCo 2:1) and the GNS/single-walled carbon nanotubes/Ni(OH)2 (20 wt%) composite had the maximum specific capacitance of 1149 F g–1. The specific capacitance and rate-capability of the CNT/MnO2/reduced graphene oxide (RGO) composites were improved as compared to the MnO2/RGO composites without CNTs. The MnO2/RGO composite containing 20 wt% CNT with reference to RGO exhibited the best specific capacitance of 208.9 F g–1 at a current density of 0.5 A g–1 and 77.2% capacitance retention at a current density of 10 A g–1.

대규모 사용자에 대한 멀티캐스트 콘텐츠 서비스는 핵심적인 요소로써 효율적인 그룹키 관리 방법을 필요로 한다. 그룹키 관리 방법의 목적은 브로드캐스트나 멀티캐스트를 이용하여 그룹내 멤버들 사이에 메시지를 주고받을 때 메시지 보호를 위해 사용하는 암호화 키를 안전하게 공유할 수 있는 방법을 제공하는 것이다. 본 논문에서는 IPTV와 같이 대규모 사용자를 대상으로 하는 멀티캐스트 서비스에서의 콘텐츠 보호 시스템을 제안하고 구현한다. 구현된 보호 시스템은 대규모 사용자 대상의 멀티캐스트 서비스에 적합한 효율적인 그룹키 관리 방법인 HCRGK(Hierarchical Chinese Remaindering Group Key)을 포함한다. 또한 그룹키를 기반으로 채널키，프로그램키，미디어키를 사용하는 계층적인 키 구조로 다양한 서비스를 지원하는 동시에 높은 보안성을 제공할 수 있도록 하였다.