• KSBB Journal
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• v.29 no.4
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• pp.278-284
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• 2014

We present microfluidic method to rapidly analyze the effect of temperature on the change of morphologies of Antarctic bacteria (Pseudoalteromonas sp., Shewanella vesiculosa, Shewanella sp., and Cellulophaga sp.). The microfluidic device is able to generate stable temperature gradient from 7 to$40^{\circ}C$ and dramatically reduce the number of experiments, experimental cost and labor, and amount of sample. Based on this approach, we found that specific bacteria transforming morphology into filament or elongated body strongly depends on cultivation temperature. Interestingly, we found that the morphologies of Pseudoalteromonas sp., Shewanella vesiculosa, Shewanella sp., and Cellulophaga sp. are elongated at below $25^{\circ}C$, above $20^{\circ}C$, above $15^{\circ}C$ and above $35^{\circ}C$, respectively. We envision the microfluidic device is a useful approach to analyze biological events with a high throughput manner.

• Journal of Microbiology and Biotechnology
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• v.19 no.11
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• pp.1408-1414
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• 2009

The obtention of high yields of purified plasmid DNA is viewed as an essential issue to be considered towards efficient production of DNA vaccines and therapeutic plasmids. In this work, Escherichia coli $DH5\alpha$. bearing the pVAXI-LacZ plasmid was grown in a developed semi-defined medium at different temperatures and tryptone concentrations. Analysis of pDNA yields and E. coli morphology revealed that at higher temperatures (37 and $40^{\circ}C$), higher specific yields and E. coli filamentation were obtained. However, the best results were achieved when a lower tryptone concentration was used. This approach was shown to be a powerful tool to promote plasmid amplification, keeping the desirable plasmid structure, and favoring the attainment of quality. Our results suggest that by using tryptone alone as an amino acid source, pDNA amplification was improved and a specific yield of 20.43 mg pDNA/g dcw was achieved, proving that this strategy can improve pDNA yield even at a small scale.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.5 s.182
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• pp.190-196
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• 2006

Transparent materials are widely used in the fields of optic parts and bio industry. We have experiment to find out the characteristics of the micromachining inside transparent materials using femtosecond laser pulses. With its non-linear effects by very high peak intensity, filament (plasma channel) was formed by the cause of the self-focusing and the self-defocusing. Physical damage could be found when the intensity is high enough to give rise to the thermal stress or evaporation. At the vicinity of the power which makes the visible damage or modification, the structural modification occurs with the slow scanning speed. According to the polarization direction to the scanning direction, the filament quality is quite different. There is a good quality when the polarization direction is parallel to the scanning direction. For fine filament, we could suggest the conditions of the high numerical aperture lens, the short shift of focusing point, the low scanning speed and the low power below 20 mW. As the examples of optics parts, we fabricated the fresnel zone plate with the $225{\mu}m$ diameter and Y-bend optical wave guide with the $5{\mu}m$ width.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.477-478
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• 2006

Characteristics of InAs/GaAs quantum dot (QD) ridge laser diodes (LDs) are investigated for high-power $1.3\;{\mu}m$ applications. For QD ridge LDs with a $5-{\mu}m$-wide stripe and a 1-mm-long cavity, the emission wavelength of 1284.1 nm, the single-uncoated-facet CW output power as high as 90 mW, the external efficiency of 0.31 W/A and the threshold current density of $800\;mA/cm^2$ are obtained. The linewidth enhancement factor ($\alpha$-factor) is successfully measured to be between 0.4 and 0.6, which are about four times as small values with respect to conventional quantum well structure. It is possible that this result significantly reduce the filamentation of far-field profiles resulting in better beam quality for high power operation.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.131-131
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• 2010

The power of semiconductor laser diodes has been limited primarily by the heating effects which occur at high optical intensities. The actual limiting event can take one of a number of forms such as. catastrophic optical damage or filamentation. A general approach to this problem is to design a heterostructure which creates a high powered output while maintaining low internal optical intensities. A graded index separate confinement heterostructure (GRIN-SCH) is one such structure that accomplishes the above task. Here, the active region is sandwiched between graded index layers where the index of refraction increases nearer to the active layer. This structure has been shown to yield a high efficiency due to the confinement of both the optical power and carriers, thereby reducing the optical intensity required to achieve higher powers. The optical confinement also reinforces the optical beam quality against high power effects. Quantum dots have long been a desirable option for laser diodes due to the enhanced optical properties associated with the zeroth dimensionality. In our work, we use PICS3D software created by Crosslight Software Inc. to simulate the performance of In0.67A10.33As/A10.2Ga0.8AsquantumdotsusedwithaGRIN-SCH. The simulation tools are used to optimize the GRIN-SCH structure for high efficiency and optical beam quality.

• Korean Journal of Microbiology
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• v.54 no.1
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• pp.1-8
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• 2018

A prokaryotic cell has various histone-like proteins also known as nucleoid-associated proteins (NAPs). These proteins bind AT-rich sequence at DNA, which induce DNA wrapping, bending, and bridging, and subsequently regulate the gene expression in bacteria. Because NAPs function in transcriptional silencing of virulence genes, it is important to study their roles in gene silencing and specific mechanisms of these proteins. In this review, we discussed two well-known NAPs, H-NS, and HU, and summarized their roles for gene expression in Escherichia coli and Salmonella Typhimurium. Through the oligomerization and filamentation of H-NS, it represses the expression of virulence genes in human pathogenic bacteria, such as Salmonella Typhimurium, and it works with other NAPs positively or negatively. Recently, H-NS also regulates typhoid toxin expression, which causes typhoid fever and systemic disease in human. Additionally, HU regulates the expression of genes related to both virulence and physiology of Salmonella. Therefore, we suggest that NAPs like H-NS and HU are crucial factors to reveal the molecular mechanisms of virulence gene expression in bacteria.