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Bumjoon Shin,Eunji Lee,박상영 한국우주과학회 2019 Journal of Astronomy and Space Sciences Vol.36 No.3
In this study, a batch least square estimator that utilizes optical observation data is developed and utilized to determine geostationary orbits (GEO). Through numerical simulations, the effects of error sources, such as clock errors, measurement noise, and the a priori state error, are analyzed. The actual optical tracking data of a GEO satellite, the Communication, Ocean and Meteorological Satellite (COMS), provided by the optical wide-field patrol network (OWL-Net) is used with the developed batch filter for orbit determination. The accuracy of the determined orbit is evaluated by comparison with two-line elements (TLE) and confirmed as proper for the continuous monitoring of GEO objects. Also, the measurement residuals are converged to several arcseconds, corresponding to the OWL-Net performance. Based on these analyses, it is verified that the independent operation of electro-optic space surveillance systems is possible, and the ephemerides of space objects can be obtained.
Effective Blocking of Microbial Transcriptional Initiation by dCas9-NGMediated CRISPR Interference
( Bumjoon Kim ),( Hyun Ju Kim ),( Sang Jun Lee ) 한국미생물생명공학회(구 한국산업미생물학회) 2020 Journal of microbiology and biotechnology Vol.30 No.12
CRISPR interference (CRISPRi) has been developed as a transcriptional control tool by inactivating the DNA cleavage ability of Cas9 nucleases to produce dCas9 (deactivated Cas9), and leaving dCas9 the ability to specifically bind to the target DNA sequence. CRISPR/Cas9 technology has limitations in designing target-specific single-guide RNA (sgRNA) due to the dependence of protospacer adjacent motif (PAM) (5'-NGG) for binding target DNAs. Reportedly, Cas9-NG recognizing 5'-NG as the PAM sequence has been constructed by removing the dependence on the last base G of PAM through protein engineering of Cas9. In this study, a dCas9-NG protein was engineered by introducing two active site mutations in Cas9-NG, and its ability to regulate transcription was evaluated in the gal promoter in E. coli. Analysis of cell growth rate, D-galactose consumption rate, and gal transcripts confirmed that dCas9-NG can completely repress the promoter by recognizing DNA targets with PAM of 5'-NGG, NGA, NGC, NGT, and NAG. Our study showed possible PAM sequences for dCas9-NG and provided information on target-specific sgRNA design for regulation of both gene expression and cellular metabolism.
IO Workload Characterization Revisited: A Data-Mining Approach
Bumjoon Seo,Sooyong Kang,Jongmoo Choi,Jaehyuk Cha,Youjip Won,Sungroh Yoon IEEE 2014 IEEE Transactions on Computers Vol.63 No.12
<P>Over the past few decades, IO workload characterization has been a critical issue for operating system and storage community. Even so, the issue still deserves investigation because of the continued introduction of novel storage devices such as solid-state drives (SSDs), which have different characteristics from traditional hard disks. We propose novel IO workload characterization and classification schemes, aiming at addressing three major issues: (i) deciding right mining algorithms for IO traffic analysis, (ii) determining a feature set to properly characterize IO workloads, and (iii) defining essential IO traffic classes state-of-the-art storage devices can exploit in their internal management. The proposed characterization scheme extracts basic attributes that can effectively represent the characteristics of IO workloads and, based on the attributes, finds representative access patterns in general workloads using various clustering algorithms. The proposed classification scheme finds a small number of representative patterns of a given workload that can be exploited for optimization either in the storage stack of the operating system or inside the storage device.</P>
Bumjoon Kim,Jonghoon Lee,Jiwoo Im,김종범,김문기,김학준,송성진,임병수 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.10
In this work, we examined the influence of microstructural changes, such as an intermetallic sigma (σ) phase, on the fatigue behavior of high-temperature aged AISI 316L stainless steel. Nondestructive ultrasonic test and fatigue crack growth tests were performed to determine the threshold stress intensity factor of these artificially aged specimens. Ultrasonic test results characterizing the microstructural changes were compared with those of the fatigue tests to propose an empirical formula capable of predicting the threshold stress intensity factor by a nondestructive method. We observed a strong correlation between the increase in the volume fraction of the σ phase and the decrease of +Kth. Ultrasonic velocity increased in response to the coarsening behavior of the σ phase in the vicinity of the grain boundaries.