• Transactions of the Korean Society of Machine Tool Engineers
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• v.16 no.5
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• pp.24-32
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• 2007

Laser surface hardening is beneficially used for surface treatment of structural steel. Due to very rapid heating and cooling rates, structural low-alloy steel(SCM4) can be hardened as self quenching. The aim of this research project is to improve the influence of the process laser parameters: laser power, spot size, surface roughness, and traverse speed. The laser beam is allowed to scan on the surface of the workpiece at the constant power(1095W), varying the traverse speed at 0.3m/min, 0.5m/min and 0.8m/min. The optical lens with the elliptical profile is designed to obtain a wide surface hardening area with uniform hardness. From the results of the experiment, it has been shown that the stable hardness is about 600$\sim$700Hv, when the laser power, focal position and the traverse speed are P=1095W, z=0mm and v=0.3m/min.

• Journal of the Korean Society for Heat Treatment
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• v.23 no.5
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• pp.257-262
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• 2010

Recently, metal molding has become essential not only for automobile parts, but also mass production, and has greatly influenced production costs as well as the quality of products. Its surface has been treated by carburizing, nitriding and induction hardening, but these existing treatments cause considerable deformation and increase the expense of postprocessing after treatment; furthermore, these treatments cannot be easily applied to parts that requiring the hardening of only a certain section. This is because the treatment cannot heat the material homogeneously, nor can it heat all of it. Laser surface treatment was developed to overcome these disadvantages, and, when the laser beam is irradiated on the surface and laser speed is appropriate, the laser focal position is rapidly heated and the thermal energy of surface penetrates the material after irradiation, finally imbuing it with a new mechanical characteristic by the process of self-quenching. This research estimates the material characteristic after efficient and functional surface treatment using HPDL, which is more efficient than the existing CW Nd:YAG laser heat source.

• Journal of the Korean Society for Heat Treatment
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• v.22 no.6
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• pp.339-344
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• 2009

Recently, Laser surface treatment technologies have been used to improve wear charactenitics and fatigue resistance of metal molding. When the laser beam is irradiated on the surface and laser speed is appropriate, the laser focal position is rapidly heated and the thermal energy of surface penetrates the material after irradiation, finally imbuing it with a new mechanical characteristic by the process of self-quenching. This research estimates the material characteristic after efficient and functional surface treatment using HPDL, which is more efficient than the existing CW Nd:YAG laser heat source. To estimate this, microstructural changes and hardness characteristics of three parts (the surface treatment part, heat affect zone, and parental material) are observed with the change of laser beam speed and surface temperature. Moreover, the depth of the hardened area is observed with the change of the laser beam speed and temperature. From the results of the experiments, it has been shown that the maximum hardness is approximately 788Hv when the heat treatment temperature and the travel speed are $1150^{\circ}$ and 2 mm/sec, respectively.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2005.05a
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• pp.246-251
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• 2005

Laser surface hardening is an effective technique used to improve the tribological properties and also to increase the service life of automobile components such as camshafts, crankshatfs, lorry brake drums and gears. High power $CO_2$ lasers and Nd:YAG lasers are employed for localized hardening of materials and hence are of potential application in the automobile industries. The heat is conducted rapidly into the bulk of the specimen causing self-quenching to occur and the formation of martensitic structure. In this investigation, the microstructure features occurring in Nd:YAG laser hardening SM45C steel are discussed with the use of optical microscopic and scanning electron microscopic analysis. Moreover, This paper describes the optimism of the processing parameters for maximum hardened depth of SM45C steel specimens of 3mm thickness by using CW Nd:YAG laser. Travel speed was varied from 0.6m/min to 1.0m/min. The maximum hardness and case depth fo SM45C steel are 780Hv and 0.4mm by laser hardening.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.05a
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• pp.41.1-41.1
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• 2009

최근 금형은 자동차뿐만 아니라 여러 산업에서 필수적이며 제품의 품질은 물론 제조원가에 막대한 영향을 미친다. 이러한 금형은 침탄, 질화, 고주파담금질등에 의해 표면처리 되어져 왔으나, 이와 같이 기존의 처리 방법은 모두 처리물 전체를 가열하거나 균일한 가열을 하지 못하기 때문에 변형의 문제와 처리후의 후가공의 경비 문제, 그리고 극히 일부분만 경화가 필요한 부품에는 적용하기 어려운 문제점이 있다. 이러한 문제를 해결할 수 있는 표면처리로서 레이저 표면처리 방법이 대두되고 있으며, 레이저 표면처리는 레이저 빔을 피처리물의 표면에 조사하고 적당한 속도로 이동을 하게 되면 레이저조사부위가 급속하게 가열되고 레이저빔이 통과한 후에는 표면의 열이 내부로 열전도 되어 급속히 자기냉각(Self-quenching)됨으로서 표면에 새로운 기계적 성질을 갖게 하는 표면처리법이다. 이와 같이 레이저를 이용한 표면처리로 기존의 CW Nd:YAG 레이저 열원보다 효율이 좋은 HPDL(High Power Diode Laser)를 이용한 고효율, 고기능 금형 표면처리 후 재료적 물성을 평가하고자 한다. 평가방법은 레이저빔의 조사속도 및 온도변화에 따른 표면처리부, 열영향부 그리고 모재 부분에 대한 경도특성 및 미세조직 변화를 관찰하였다. 또한 조사속도 및 온도변화에 대해 경화깊이를 관찰하였다.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.1
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• pp.56.2-56.2
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• 2021

Constraining the structure and thus the fate of giant molecular clouds (GMCs), the primary sites of star formation in galaxies, is crucial to understand the evolution of galaxies themselves. Exploiting the unprecedented sensitivity and angular resolution of the Atacama Large Millimeter/sub-millimeter Array (ALMA), we have measured the spatially-resolved (~ 20 pc resolution) properties of the GMCs in two nearby late-type galaxies, NGC 5806 (SAB(s)b) and NGC 6753 ((R)SA(r)b), as part of the WISDOM project. Although these results are preliminary, we identified ~ 200 resolved GMCs in NGC 5806 within a radius of 500 pc, most within a nuclear ring structure, and ~ 400 resolved GMCs in NGC 6753 within a radius of 2 kpc, most within a flocculent spiral structure. The GMCs of NGC 5806 have similar sizes but slightly higher linewidths than clouds in the Milky Way disc. Because the GMCs also have higher surface densities, the calculated cloud Virial parameters are nevertheless about unity, suggesting that the GMCs of NGC 5806 are in gravitational equilibrium and thus long lived. This is contrary to other WISDOM results on earlier-type galaxies, where large cloud linewidths are likely due to shear associated with the local (circular) orbital motions (rather than the clouds' self-gravity), and the clouds are either marginally or not gravitationally bound. These results support the notion that spheroids alter the dynamical states of clouds (morphological quenching), that are otherwise (i.e. in galaxy discs) fairly homogenous and similar to those of the Milky Way.

• Korean Journal of Materials Research
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• v.19 no.9
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• pp.457-461
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• 2009

Recently, metal molding has become essential not only for automobile parts, but also mass production, and has greatly influenced production costs as well as the quality of products. Its surface has been treated by carburizing, nitriding and induction hardening, but these existing treatments cause considerable deformation and increase the expense of postprocessing after treatment; furthermore, these treatments cannot be easily applied to parts that requiring the hardening of only a certain section. This is because the treatment cannot heat the material homogeneously, nor can it heat all of it. Laser surface treatment was developed to overcome these disadvantages, and, when the laser beam is irradiated on the surface and laser speed is appropriate, the laser focal position is rapidly heated and the thermal energy of surface penetrates the material after irradiation, finally imbuing it with a new mechanical characteristic by the process of self-quenching. This research estimates the material characteristic after efficient and functional surface treatment using HPDL, which is more efficient than the existing CW Nd:YAG laser heat source. To estimate this, microstructural changes and hardness characteristics of three parts (the surface treatment part, heat affect zone, and parental material) are observed with the change of laser beam speed and surface temperature. Moreover, the depth of the hardened area is observed with the change of the laser beam speed and temperature.

• 한국생물공학회:학술대회논문집
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• 2003.04a
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• pp.74-78
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• 2003

Multi-channel images of 11-MUA and 11-MUOH self-assembled monolayers were obtained by using two-dimensional surface plasmon resonance (SPR) absorption. Patterning process was simplified by exploiting direct photo-oxidation of thiol bonding (photolysis) instead of conventional photolithography. Sharper images were resolved by using a white light source in combination with a narrow bandpass filter in the visible region, minimizing the diffraction patterns on the images. The line profile calibration of the image contrast caused by different resonance conditions at each points on the sensor surface (at a fixed incident angle) enables us to discriminate the monolayer thickness in sub-nanometer scale. Furthermore, there is no signal degradation such as photo bleaching or quenching which are common in the detection methods based on the fluorescence.

• Journal of Crop Science and Biotechnology
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• v.11 no.2
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• pp.91-100
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• 2008

Melting curve analysis of fluorescently labeled DNA fragments is used extensively for genotyping single nucleotide polymorphism(SNP). Here, we evaluated a SNP genotyping method by melting curve analysis with the two probe chemistries in a 384-well plate format on a Roche LightCycler 480. The HybProbe chemistry is based on the fluorescence resonance energy transfer(FRET) and the SimpleProbe chemistry uses a terminal self-quenching fluorophore. We evaluated FRET HybProbes and SimpleProbes for two SNP sites closely linked to two quantitative trait loci(QTL) for southern root-knot nematode resistance. These probes were used to genotype the two parents and 94 $F_2$ plants from the cross of PI 96354$\times$Bossier. The SNP genotypes of all samples determined by the LightCycler software agreed with previously determined SSR genotypes and the SNP genotypes determined on a Luminex 100 flow cytometry instrument. Multiplexed HybProbes for the two SNPs showed a 98.4% success rate and 100% concordance between repeats two of the same 96 DNA samples. Also, we developed a HybProbe assay for the Rcs3 gene conditioning broad resistance to the frogeye leaf spot(FLS) disease. The LightCycler 480 provides rapid PCR on 384-well plate and allows simultaneous amplification and analysis in approximately 2 hours without any additional steps after amplification. This allowed for a reduction of the potential contamination of PCR products, simplicity, and enablement of a streamlined workflow. The melting curve analysis on the LightCycler 480 provided high-throughput and rapid SNP genotyping and appears highly effective for marker-assisted selection in soybean.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.6
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• pp.502-507
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• 2010

In order to design nano structured materials with enhanced thermoelectric properties, the alloys in the pseudo-binary $Bi_2Te_3$-PbTe system are investigated for their micro structure properties. For this synthesis, the liquid alloys are cooled by the water quenching method. Micro structure images are obtained by using an electron probe micro analyzer(EPMA). Dendritic and lamellar structures are clearly observed with the variation in the composition ratio between $Bi_2Te_3$ and PbTe. The increase in the $Bi_2Te_3$ composition ratio causes to change of the structure from dendritic to lamellar. The Seebeck coefficient of sample 5, in which the mixture rate of $Bi_2Te_3$ is 83%, is measured as the highest value. In contrast, the others decrease with the increase of the $Bi_2Te_3$ composition ratio. Meanwhile, p-type characteristics are observed in sample 6, at 91%-$Bi_2Te_3$ mixture rate. The power factors of the all samples are calculated with the Seebeck coefficient and resistivity.