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다단계 수리체계의 성능평가를 위한 폐쇄형 대기행렬 네트워크 모형
박찬우,김창곤,이효성 한국경영과학회 2000 한국경영과학회지 Vol.25 No.4
In this study we consider a spares provisioning problem for repairable items in which a parts inventory system is incorporated. If a machine fails, a replacement part must be obtained at the parts inventory system before the failed machine enters the repair center. The inventory policy adopted at the parts inventory system is the (S,Q) policy. Operating times of the machine before failure, order in lead times and repair times are assumed to follow a two-stage Coxian distribution. For this system, we develop an approximation method to obtain the performance measures such as steady state probabilities of the number of machines at each station and they probability that a part will wait at the parts inventory system. For the analysis of the proposed system, we model the system as a closed queueing network and analyze it using a product-form approximation method. A recursive technique as well as an iterative procedure is used to analyze the sub-network. Numerical tests show that the approximation method provides fairly good estimation of the performance measure of interest.
Biochemical characterization of type I‑E anti‑CRISPR proteins, AcrIE2 and AcrIE4
Koo Jasung,Lee Gyujin,Ka Donghyun,Park Changkon,Suh Jeong-Yong,Bae Euiyoung 한국응용생명화학회 2023 Applied Biological Chemistry (Appl Biol Chem) Vol.66 No.-
In bacteria and archaea, CRISPRs and Cas proteins constitute an adaptive immune system against invading foreign genetic materials, such as bacteriophages and plasmids. To counteract CRISPR-mediated immunity, bacteriophages encode anti-CRISPR (Acr) proteins that neutralize the host CRISPR–Cas systems. Several Acr proteins that act against type I-E CRISPR–Cas systems have been identified. Here, we describe the biochemical characterization of two type I-E Acr proteins, AcrIE2 and AcrIE4. We determined the crystal structure of AcrIE2 using single-wavelength anomalous diffraction and performed a structural comparison with the previously reported AcrIE2 structures solved by different techniques. Binding assays with type I-E Cas proteins were carried out for the target identification of AcrIE2. We also analyzed the interaction between AcrIE4 and its target Cas component using biochemical methods. Our findings corroborate and expand the knowledge on type I-E Acr proteins, illuminating diverse molecular mechanisms of inhibiting CRISPR-mediated prokaryotic anti-phage defense.