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김국세,이정기,박찬모,조애리,류천열 조선대학교 전자정보통신연구소 2003 電子情報通信硏究所論文誌 Vol.6 No.1
정보통신의 비약적인 발전에 힘입어 멀티미디어 데이터는 언제 어디서든 전송 받거나 공유할 수 있게 되었다. 아날로그 형태에서 디지털의 아날로그를 형태로 빠르게 대체되고 있으며, 디지털로 신호를 표현하는 방법은 기존 사용하여 표현하는 방법에 비해 많은 장점을 가지고 있다. 하지만 디지털로 된 데이터는 언제 어디서든 대단위 복제가 가능하다. 디지털 영상 정보의 보호를 위해 디지털 워터마크(Digital Watermark)가 있다. 디지털 워터마크는 공개키 알고리즘이나 방화벽 등으로 해독된 영상에 대하여 부가적인 보호를 제공한다. 디지털 영상에 대한 저작권 정보, 배포자 정보 그리고 사용자 정보를 영상에 삽입함으로써 훗날 법적인 문제가 발생하였을 때 해결책을 제시할 수 있다. 본 논문에서는 디지털 영상 데이터의 정보 보호를 위해 주파수 영역에서의 웨이브릿 변환(Wavelet Transform)을 이용한 이미지 적용 디지털 워터마킹(Image-Adaptive Digital Watermarking) 방법을 제안한다. 이미지 적응 웨이브릿(Image-Adaptive Wavelet)은 영상을 주파수적으로 분해하면서 각 대역들의 공간 영역에서의 정보를 함께 지닌고 JND긯(Just noticeable difference)을 포함한다. 이미지 적응 웨이브릿의 이러한 특성을 이용하여 다해상도 분해하고, 손실 압축(Loss Compression)이나 필터링(Fitering), 잡음(Noise)등에 크게 영향받는 저주파 성분과 인간의 시각적으로 큰 의미를 갖는 고주파 성분의 특성을 이용하여 워터마크를 삽입한다.
이정기,노정희,홍성표,조애리,이준 조선대학교 전자정보통신연구소 2002 電子情報通信硏究所論文誌 Vol.5 No.2
인터넷이 인류사에 등장한 것은 지금으로부터 30년에 불과 하다. 인터넷은 개방성과 공개성 그리고 수평성을 지향한다. 이러한 특성을 기반으로 해서 인터넷은 디지털 경제를 구체화시키고 실현시키는 중요한 수단이 되고 있다. 현재 주목받고 있는 P2P(Peer-to-Peer)는 인터넷의 이러한 이상을 실현해 가는데 중요한 위치를 차지하고 있다. 개인과 개인간의 정보공유 모델인 P2P는 인터넷을 통해서 다른 사용자들과 정보를 주고받을 수 있는 기술을 말한다. 또한 컴퓨터 네트워크를 통해서 교환되는 정보의 양의 증가와 함께 네트워크의 보안성이 새로운 문제점으로 부각되고 있다. 네트웍에 있는 어떤 사용자가 제한하기 위해서공개된 환경에 있다고 가정하면, 각 사용자간에 허가받은 사용자에게만 접속을 는 서비스에 대한 요구를 인증 해야한다. 본 논문에서는 이를 해결하기 위해 P2P 환경에서 보안을 유지하는 방법을 제안하고, P2P 환경에서 안전하게 정보를 공유할 수 있는 메커니즘으로 Kerberos 인증 메커니즘을 인용하여 인증 메커니즘을 설계하였다. It is not more in 30 years from now that internet appears to history of man.Internet intends patency and patency and horizontal. According as progress by information society, computer network use and enlargement of scale are accelerated more. Also, with good physician increase of information that is exchanged through computer network, security of network is embossed to controversial point that is new. Because P2P as that remove or weakens center server function is open network that can participate between each user, problem about authentication between each users is risen. If certain user in network is in open environment, this user must authenticate request about service to user who is admitted between each user to limit connection. This treatise proposed method to keep security in P2P environment to solve this and designed certification mechanism that quote Kerberos certification mechanism to mechanism that can share information safety in P2P environment.
( Ai Sheng Xiong ),( Quan Hong Yao ),( Ri He Peng ),( Xian Li ),( Hui Qin Fan ),( Mei Jin Guo ),( Si Liang Zhang ) 생화학분자생물학회 2004 BMB Reports Vol.37 No.3
Phytases catalyze the release of phosphate from phytic acid. Phytase-producing microorganisms were selected by culturing the soil extracts on agar plates containing phytic acid. Two hundred colonies that exhibited potential phytase activity were selected for further study. The colony showing the highest phytase activity was identified as Aspergillus niger and designated strain 113. The phytase gene from A. niger 113 (phyII) was isolated, cloned, and characterized. The nucleotide and deduced amino acid sequence identity between phyII and phyA from NRRL3135 were 90% and 98%, respectively. The identity between phyII and phyA from SK-57 was 89% and 96%. A synthetic phytase gene, phyIIs, was synthesized by successive PCR and transformed into the yeast expression vector carrying a signal peptide that was designed and synthesized using P. pustoris biased codon. For the phytase expression and secretion, the construct was integrated into the genome of I? pustoris by homologous recombination. Over-expressing strains were selected and fermented. It was discovered that -4.2 g phytase could be purified from one liter of culture fluid. The activity of the resulting phytase was 9.5 U/mg. Due to the heavy glycosylation, the expressed phytase varied in size (120, 95, 85, and 64 kDa), but could be deglycosylated to a homogeneous 64 kDa species. An enzymatic kinetics analysis showed that the phytase had two pH optima (pH 2.0 and pH 5.0) and anoptimum temperature of 60℃.
Xiong, Ai Sheng,Yao, Quan-Hong,Peng, Ri-He,Li, Xian,Fan, Hui-Qin,Guo, Mei-Jin,Zhang, Si-Liang Korean Society for Biochemistry and Molecular Biol 2004 Journal of biochemistry and molecular biology Vol.37 No.3
Phytases catalyze the release of phosphate from phytic acid. Phytase-producing microorganisms were selected by culturing the soil extracts on agar plates containing phytic acid. Two hundred colonies that exhibited potential phytase activity were selected for further study. The colony showing the highest phytase activity was identified as Aspergillus niger and designated strain 113. The phytase gene from A. niger 113 (phyI1) was isolated, cloned, and characterized. The nucleotide and deduced amino acid sequence identity between phyI1 and phyA from NRRL3135 were 90% and 98%, respectively. The identity between phyI1 and phyA from SK-57 was 89% and 96%. A synthetic phytase gene, phyI1s, was synthesized by successive PCR and transformed into the yeast expression vector carrying a signal peptide that was designed and synthesized using P. pastoris biased codon. For the phytase expression and secretion, the construct was integrated into the genome of P. pastoris by homologous recombination. Over-expressing strains were selected and fermented. It was discovered that ~4.2 g phytase could be purified from one liter of culture fluid. The activity of the resulting phytase was 9.5 U/mg. Due to the heavy glycosylation, the expressed phytase varied in size (120, 95, 85, and 64 kDa), but could be deglycosylated to a homogeneous 64 kDa species. An enzymatic kinetics analysis showed that the phytase had two pH optima (pH 2.0 and pH 5.0) and an optimum temperature of $60^{\circ}C$.
Directed Evolution of Beta-galactosidase from Escherichia coli into Beta-glucuronidase
Xiong, Ai-Sheng,Peng, Ri-He,Zhuang, Jing,Liu, Jin-Ge,Xu, Fang,Cai, Bin,Guo, Zhao-Kui,Qiao, Yu-Shan,Chen, Jian-Min,Zhang, Zhen,Yao, Quan-Hong Korean Society for Biochemistry and Molecular Biol 2007 Journal of biochemistry and molecular biology Vol.40 No.3
In vitro directed evolution through DNA shuffling is a powerful molecular tool for creation of new biological phenotypes. E. coli $\beta$-galactosidase and $\beta$-glucuronidase are widely used, and their biological function, catalytic mechanism, and molecular structures are well characterized. We applied an in vitro directed evolution strategy through DNA shuffling and obtained five mutants named YG6764, YG6768, YG6769, YG6770 and YG6771 after two rounds of DNA shuffling and screening, which exhibited more $\beta$-glucuronidase activity than wild-type $\beta$-galactosidase. These variants had mutations at fourteen nucleic acid sites, resulting in changes in ten amino acids: S193N, T266A, Q267R, V411A, D448G, G466A, L527I, M543I, Q626R and Q951R. We expressed and purified those mutant proteins. Compared to the wild-type protein, five mutant proteins exhibited high $\beta$-glucuronidase activity. The comparison of molecular models of the mutated and wildtype enzymes revealed the relationship between protein function and structural modification.