• Bulletin of the Korean Chemical Society
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• 제11권3호
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• pp.214-220
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• 1990

We have studied the Infrared Multiphoton Dissociation (IRMPD) of 1-bromo-3-chloropropane by using the pulsed $CO_2$ laser. The product yields and the HCl/HBr branching ratios in IRMPD of $BrCH_2CH_2CH_2Cl$ are studied under the focused beam geometry as a function of buffer gas (He) pressure, laser energy, and photolysing wavelength. It is observed that the total dissociation yield has a laser energy dependence of 1.8-2.0 power order and the branching ratio is very slightly dependent on the pulse energy for the laser lines employed. The dependences of total dissociation yield and branching ratio on the buffer gas pressures show that the dissociation yield monotonically decreases and the branching ratio slightly decreases with the increase of the buffer gas pressure. The Energy-Grained Master Equation (EGME) was applied to explain the laser pulse energy and the buffer gas pressure(He) dependence of the dissociation yield and the branching ratio.

• Journal of Welding and Joining
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• 제31권6호
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• pp.96-106
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• 2013

In this study, the effect of laser source($CO_2$ and Nd:YAG) on the microstructure and tensile properties of laser welded Al-Si coated boron steel(1.2mmt) was investigated with before and after hot-stamping. In case of as welds condition, fracture occurred in base metal unrelated to the laser source. It could be explained that tensile strength of fusion zone composed of martensite and bainite is higher than that of base metal that contains a lot of ferrite despite dilution of Al and Si from coating layer to fusion zone. In case of hot-stamping condition, the fracture occurred in fusion zone irrelevant to laser source and the tensile strength was lower than hot stamped base metal. In the $CO_2$ laser welds, $Fe_3$(Al,Si) formed near the bond line was transformed into ferrite during hot-stamping. Therefore tensile strength of bond line is lower than that of base metal and center of fusion zone and the fracture occurred in the bond line. On the other hand, in the Nd:YAG laser welds, the higher concentration of Al formed the ferrite in the fusion zone during hot-stamping treatment. Also, the thickness of centerline was thinner than that of base metal. Therefore, it is considered that fracture occurred in centerline of fusion zone due to effect of concentration stress, and it leaded to a lower tensile strength and elongation.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• 제26권5호
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• pp.437-445
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• 2000

Object This study is focused on the comparison between $CO_2$ laser and scalpel by examining the overal process of wound healing after partial glossectomy of rats so that the result from the research could be easily applied to actual clinical environment. Method and Material In this research, 2mm defect was formed on both lateral borders of the tongue of rats by using $CO_2$ laser and scalpel respectively. 4rats were sacrified each time on the 1st, 2nd, 4th, 7th, 14th and 21th day according to a general method. After fabricating $5{\mu}m$ paraffin specimen, H&E staining and MT staining were performed. Results Compared to scalpel, wound healing by $CO_2$ laser leads to a earlier initiation of vascular proliferation and re-epithelization. Therefore, some influence is exerted on the early stage of wound healing. However, the two methods seem to undergo the similar healing process.

• Journal of Periodontal and Implant Science
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• 제24권2호
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• pp.283-302
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• 1994

Gingivectomy has been utilized as a therapeutic method to remove diseased periodontal pocket wall in order to aid in root planing. Although chemical agents and electrosurgery has been used in addition to the conventional method of using surgical blades, difficulties in controling the depth of chemical penetration and effectively regenerating the gingival tissue as well as the slow wound healing has been pointed out as shortcomings of these methods. This study was designed to assess the effect of Aloe vera on wound healing of gingivectomy sites created by $CO_2$ laser on palatal gingiva of maxillary molar region of white rats. Those sites treated by surgical blades were designated as control, by $CO_2$ laser as Experimental group I, by surgical blades in addition to topical application of Aloe vera as Experimental group II, and by $CO_2$ laser and Aloe vera application as Experimental group III. Animals were sacrificed at 2 days, 3 days, 1 week, 2 weeks and 3 weeks postoperatively, and the specimens were histologically analyzed. The results were as follows : 1. Resorption of blood clots were observed in the control at 3rd day, followed by the rest of the experimental groups at 1 week postoperatively. 2. Persistent inflammation was observed up to 1 week in the control and Experimental group II and III, and until the 2nd week in Experimental group I. 3. Granulation tissue was observed up to 1 week in the control, and 2 weeks in the rest of the groups. 4. Epithelization started on the 2nd day. The control showed the most rapid epithelization, and the process was completed by the 2nd week in all groups. 5. Experimental group II and III, which were treated with Aloe vera, showed similar healing patterns to the control and Experimental group I.

• Journal of Periodontal and Implant Science
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• 제38권4호
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• pp.657-668
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• 2008

Purpose: In this study, we compared low-power $CO_2$ laser treatment to ultrasonic scaling, which is generally approved as a power-driven mechanical instrumentation, and evaluated both of these treatments regarding their clinical effectiveness and change in the volume of in GCF. Material and methods: 20 patients who had gingivitis were selected. all of patients has no systemic problems. Randomly selected, one quadrant received ultrasonic scaling only, another quadrant received ultrasonic scaling and $CO_2$ laser irradiation, the other quadrant received $CO_2$ laser irradiation only. Clinical parameters measured at baseline, 1 weeks, 2weeks, 4weeks and 8weeks. Result: Pocket probing depth and clinical attachment level were not changed during study period. Gingival index of all group were improved after treatment. At 1 weeks after treatment, Gingival index of ultrasonic scaling group was only significantly different compared to control group. At 2 weeks after treatment, gingival index of all experimental group were significantly different compared to control group. At 4 and 8 weeks after treatment, gingival index of all group were increased, but experimental group were lower than control group. Sulcus bleeding index was similar to the results of gingival index. At 1 weeks after treatment, all experimental group were significantly different compared to control group and it maintained during study. At 2 weeks after treatment, sulcus bleeding index of all group were lowest during study. Gingival crevicular fluid were measured with $Periotron^{(R)}$ 8000($Oraflow^{(R)}$, Inc. USA). At baseline, all group were showed moderately severe condition. At 1 week after treatment, laser treatment only group was reduced quantity of gingival crevicular fluid mostly, and all group were reduced quantity of gingival crevicular fluid. At 2 weeks after treatment, all group were health state. At 4 and 8 weeks after treatment, all group were showed recurrent of inflammation, and control group was the most significantly increased. Conclusion: This study showed that the effects of $CO_2$ laser treatment were similar to conventional ultrasonic scaling and this result remained longer than plaque control only. These results suggest possibility of $CO_2$ laser treatment for altered periodontal therapy.

• 한국레이저가공학회지
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• 제13권3호
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• pp.1-6
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• 2010

The in-process monitoring of $CO_2$ welding of Zn-coated steel plates has been studied and compared with that of conventional thin plates. Relationships between weld defects and plasma emission signals were evaluated in laser lap joint of thick Zn-coated steel. According to the study, weld defects were found to increase with Zn content. As a result, measured plasma emission signals also decreased. In case of plate with $15{\mu}m$-thick Zn-coated layer, defects caused by evaporation of Zn could, therfore, controled by gap of 0.1mm, resulting in a stable emission signals. However, the amplitude of signals fluctuated very widely. Variation of amplitude sould be limited in 3-8V by FFT smoothing.

• Journal of Welding and Joining
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• 제21권3호
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• pp.30-34
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• 2003

This paper describes the heat distribution characteristics of ASTM A131DH36 high tensile steel for ship structures in 5㎾ $CO_2$ laser welding. In general, high energy of laser beam concentrates on the small area of the weldment instantaneously; therefore, this heat transfer mechanism induces the rapid changes of temperature and mechanical characteristics in laser welds this mechanism. So temperature distribution analysis is important to understand mechanical characteristics of laser welds. Authors have conducted finite element simulation to analyze the heat distribution characteristics in laser welds. The result of simulation has been verified by comparing with the metallurgical experiment result. From the result of this study, we can accurately predict the heat distribution characteristics in laser welds by using numerical simulation.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 1996년도 특별강연 및 추계학술발표 개요집
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• pp.186-190
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• 1996

Laser cladding is a technique for modification on surface in materials. This study describes a laser cladding equipment design and the results of laser cladding nickel on rolled steel for general structure. The laser clsdding equipment designed to consider continuous supply, a fixed quantity. The material used MC plastic. Laser cladding condition is found out by processing parameters. The experiment advanced to suppy substrate with powder. The substrate is rolled steel for general structure(KS D 3503) and powder is using the nickel powder for the corrosion resitance, wear resistance and surface hardness of materials. When the substrate travel on X-Y table, laser beam irradiates to prevent from oxidize with shielding gas on it. The obtained specimens measure the victors hardness test. For the research laser cladding results make a comparative study the microstructure.

• 한국기계가공학회지
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• 제10권1호
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• pp.31-37
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• 2011

Recently, the technology of surface treatment is being more important which affects the material cost reduction and substitution to the expensive material. The material used for the mechanical processing should have not only high intensity, but also strength toughness, wear resistance and corrosion resistance. In order to increase the durability and have better quality of the parts using such kind of tooling material, various kinds of research of the surface hardening through many kinds of heat resources is being done and practically applied. In this study, the characteristics of hardening surface zone for high strength of the press die material through laser beam irradiation are researched. In this study, it is experimentally observed by the status of the surface morphology, tensile strength, the hardness distribution of the base metal and wear condition by the surface hardness pattern by the laser beam based on the process parameters of $CO_2$ laser by using SM45C and STD11 used for press tool. Through this research, the characteristics of surface hardened zone for high strength of the thin metal by laser beam irradiation is done.

• Journal of Welding and Joining
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• 제24권4호
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• pp.22-26
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• 2006

In lap welding of zinc-coated steel, porosity formation is one of most significant weld defects, which is caused by zinc vapor generated between the steel sheets. Various solutions have been proposed in the past years but development of more effective method is a worthwhile subject to be investigated. In this study, autogenous laser welding and laser-TIG hybrid welding was applied to the lap welding of zinc-coated steel without gap, and weld pool behaviors were observed by using high speed camera and the porosity generation mechanism was analyzed. The weld defects were successfully eliminated by laser-TIG hybrid welding. This is because the leading TIG arc partially melted the upper sheet and vaporized/oxidized the coated zinc on the lapped surfaces prior to the trailing laser illuminating the specimen.