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A flexible supercapacitor based on vertically oriented ‘Graphene Forest’ electrodes
Ma, Yifei,Wang, Mei,Kim, Namhun,Suhr, Jonghwan,Chae, Heeyeop The Royal Society of Chemistry 2015 Journal of Materials Chemistry A Vol.3 No.43
<▼1><P>A flexible supercapacitor was demonstrated with ‘graphene forest’ as electrodes. No capacitance loss was observed even with 100 000 times of bending.</P></▼1><▼2><P>Vertically-grown graphene electrodes are developed for flexible electric double-layer capacitors (EDLC). Solid-state electrolytes and large area flexible electrodes are essential parts for wearable applications. In this work, the vertically-grown graphene electrodes were fabricated by a plasma-enhanced chemical vapor deposition process and applied to flexible electrodes of EDLC. The areal capacitance of the capacitor based on vertical graphene is 2.45 mF cm<SUP>−2</SUP>, which is much better even with solid electrolytes when compared to other reported vertical graphene capacitors. The capacitance also shows good flexibility and it remains unaltered even after 100 000 times of bending or 180 degree folding. These unique features of the capacitor could be ascribed to a discrete ‘tree-like’ morphology of the vertical graphene, which has not been known before.</P></▼2>
Ma, Yifei,Kim, Daekyoung,Jang, Haegyu,Cho, Sung Min,Chae, Heeyeop American Scientific Publishers 2014 Journal of nanoscience and nanotechnology Vol.14 No.12
<P>Low-temperature graphene was synthesized at 400 degrees C with inductively coupled plasma chemical vapor deposition (PECVD) process. The effects of plasma power and flow rate of various carbon containing precursors and hydrogen on graphene properties were investigated with optical emission spectroscopy (OES). Various radicals monitored by OES were correlated with graphene film properties such as sheet resistance, I-D/I-G ratio of Raman spectra and transparency. C2H2 was used as a main precursor and the increase of plasma power enhanced intensity of carbon (C-2) radical OES intensity in plasma, reduced sheet resistance and increased transparency of graphene films. The reduced flow rate of C2H2 decreased sheet resistance and increased transparency of graphene films in the range of this study. H-2 addition was found to increase sheet resistance, transparency and attributed to reduction of graphene grain and etching graphene layers. OES analysis showed that C-2 radicals contribute to graphite networking and sheet resistance reduction. TEM and AFM were applied to provide credible information that graphene had been successfully grown at low temperature.</P>
Ma, Yifei,Jang, Haegyu,Kim, Sun Jung,Pang, Changhyun,Chae, Heeyeop Springer US 2015 NANOSCALE RESEARCH LETTERS Vol.10 No.1
<P>Vertical graphene (VG) nanosheets are directly grown below 500 °C on glass substrates by a one-step copper-assisted plasma-enhanced chemical vapour deposition (PECVD) process. A piece of copper foil is located around a glass substrate as a catalyst in the process. The effect of the copper catalyst on the vertical graphene is evaluated in terms of film morphology, growth rate, carbon density in the plasma and film resistance. The growth rate of the vertical graphene is enhanced by a factor of 5.6 with the copper catalyst with denser vertical graphene. The analysis of optical emission spectra suggests that the carbon radical density is increased with the copper catalyst. Highly conductive VG films having 800 Ω/□ are grown on glass substrates with Cu catalyst at a relatively low temperature.</P><P><B>Electronic supplementary material</B></P><P>The online version of this article (doi:10.1186/s11671-015-1019-8) contains supplementary material, which is available to authorized users.</P>
马宜菲 ( Ma-yifei ),金明华 ( Jin-minghua ) 경상대학교 교육연구원 2023 현대교육연구 Vol.35 No.1
School bullying is a widespread and seriously harmful social problem that needs to be of great concern to the whole society. According to a UNESCO report, school violence and bullying are major problems worldwide. Formally speaking, school bullying is characterized by the low age of the subjects, the diversity of the methods, the violence, the repetitiveness of the behaviors, and the long-term nature, and the subjective maliciousness of the bully, the serious consequences of the bullying, and the serious social harm of the bullying behavior, and some serious bullying behaviors have certain criminal illegality, which cause great harm to the physical and psychological aspects of the bully. To address the phenomenon of school bullying, we should not only focus on the causes of school bullying, and look for the sources of school bullying from the perspectives of individuals, families, schools and society, but also find a reasonable means of regulation from legislation and judicial practice to maintain the peace of campus and society and protect the rights and interests of the bully. Although China currently has laws to protect the legal rights of minors, there are no specific provisions to regulate bullying in schools. In judicial practice, because of the young age of the group in which school bullying occurs, the punishment for bullying behavior is too light to achieve educational and preventive effects. Bullying in schools is also an important issue globally. In view of the laws and regulations on school bullying in foreign countries, some countries have already introduced specific laws and regulations on school bullying. Therefore, we should further improve the law on the protection of minors and other related laws and introduce relevant laws on school bullying as soon as possible to make up for the current problems of school bullying, taking into account the legislation and judicial practice. And through the cooperation of family, school and society, the legal awareness of minors should be enhanced to curb the phenomenon of school bullying from the source.
Chao Ma,Xiaojun Jin,Song Luo,Yifei Wei,Xiao-jun Wang 한국인터넷정보학회 2023 KSII Transactions on Internet and Information Syst Vol.17 No.7
The arrival of the Internet of Things and 5G technology enables users to rely on edge computing platforms to process massive data. Data sharing based on edge computing refines the efficiency of data collection and analysis, saves the communication cost of data transmission back and forth, but also causes the privacy leakage of a lot of user data. Based on attribute-based encryption and blockchain technology, we design a fine-grained access control scheme for data in edge computing, which has the characteristics of verifiability, support for outsourcing decryption and user attribute revocation. User attributes are authorized by multi-attribute authorization, and the calculation of outsourcing decryption in attribute encryption is completed by edge server, which reduces the computing cost of end users. Meanwhile, We implemented the user's attribute revocation process through the dual encryption process of attribute authority and blockchain. Compared with other schemes, our scheme can manage users' attributes more flexibly. Blockchain technology also ensures the verifiability in the process of outsourcing decryption, which reduces the space occupied by ciphertext compared with other schemes. Meanwhile, the user attribute revocation scheme realizes the dynamic management of user attribute and protects the privacy of user attribute.