• Pediatric Gastroenterology, Hepatology & Nutrition
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• v.6 no.2
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• pp.192-196
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• 2003

Angiodysplasia is the most common vascular abnormality of the gastrointestinal tract and probably the most frequent cause of recurrent lower intestinal bleeding in otherwise healthy elderly patients. Also, it is an important cause of hemorrhage in chronic renal failure observed in up to 19~32% of patients. Bleeding due to gastric angiodysplasia is treated by various endoscopic approaches, including argon and Nd : YAG laser photocoagulation, monopolar or bipolar electrocoagulation, heater probe, injection sclerotherapy, band ligation or hemoclipping. A 15-year-old boy, who had undergone hemodialysis for chronic renal failure for about 10 years, was admitted due to melena and progressive anemia. A gastroduodenoscopy revealed a cherry red and fern-like lesion with oozing on the posterior wall at junction of gastric body and fundus. Endoscopic hemoclipping therapy was performed. However, melena recurred four days later. Argon plasma coagulation and hemoclipping therapy were performed again. Since then, no recurrence of bleeding has been observed.

• Proceedings of the KWS Conference
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• 2010.05a
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• pp.42-42
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• 2010

알루미늄 합금은 질량 대비 강도가 우수하고 내식성 및 저온 특성이 양호하여 구조재로서 널리 사용되고 있다. 또한 그 사용 추세가 점점 증가 하고 있으며 알루미늄 합금의 용접을 위해 현재까지 다양한 용접 공정이 적용되었다. 일반적으로 GMAW, GTAW 등의 아크 용접과 박판의 경우 저항 점용접, 그 외의 $CO_2$ laser, Nd:YAG laser와 같은 고밀도 에너지 용접 공정에 의한 연구 결과들이 많이 발표 되었다. 하지만 알루미늄 합금의 특성 상 용접부에 기공과 균열과 같은 결함들이 각 공정에서 많이 발생하며 이러한 결함을 감소시키기 위한 용접기술에 관해 많은 연구가 진행되고 있다. 본 연구에서는 GMAW, Plasma-GMAW 공정을 적용하여 알루미늄 합금의 용접특성을 비교하였다. 알루미늄 합금 Al 5052, Al 6061 4mm 두께 모재에 대해 BOP(Bead On Plate) 용접실험을 실시하였으며 생산성 측면에서 각 공정에 따라 완전 용입 시 최대 용접 속도를 측정하여 비교하였다. 용접 품질 측면에서는 비드 표면 및 단면을 검사하고 인장시험을 수행하였으며, 용접 기공과 균열을 X-ray 촬영을 통해 비교하였다. 또한 고속카메라 촬영을 통해 용접 중 플라즈마로 인한 산화막 제거 효과를 확인하고 각 공정별 용접 시작부의 아크 안정성을 평가하였다. 인장시험 결과 모든 모드에서 모재에서 파단됨을 확인 하였고, Plasma-GMAW 공정의 경우 플라즈마의 예열효과로 인하여 GMAW 보다 완전용입 기준 용접속도가 빨랐으며, 청정작용도 우수한 것으로 확인되었다.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2004.10a
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• pp.263-268
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• 2004

In the present study, a Nd;YAG Laser (pulse type) was used to emit ultrasonic signals to a test material. In addition, a total ultrasonic investigation system was designed by adopting a Fabry-Perot interferometer, which receives ultrasonic signals without any contact. For non-destructive test SM45C, which contains some flaws was used as a test material. Because it is easy to align light beam in receiver, and the length of the light beam does not change much even if convex mirror leans towards one side, confocal Fabry-Perot interferometer, which has stable frequency, and PI control are used to correct interfered and unstable signals from temperature, fluctuation and time shift of laser frequency. Stable signals are always obtained by the feedback of PI circuit signals in the confocal Fabry-Perot interferometer. The type, size and position of flaws inside the test material were examined by achieving the stabilization of an interferometer. This study presented a useful method, which could quantitatively investigate the fault of objects by using a Fabry-Perot interferometer.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.15 no.2
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• pp.51-58
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• 2006

Laser welding of dissimilar metals has been widely used to improve a wear resistance and a corrosion resistance of the industrial parts. The objective of this research works is to investigate the influence of the process parameters, such as the welding for SM45C and STS304 with CW Nd:YAG lasers. The bead-on-plate welding tests are carried out for several combinations of the experimental conditions. In order to quantitatively examine the characteristics of the dissimilar welding, the welding quality of the cut section, stain-stress behavior and the hardness of the welded part are investigated. From the results of the investigation, it has been shown that the optimal welding condition without defects in the vicinity of the welded area and with a good welding qualify is 1600W of the laser power, 0.85m/min of welding speed and $4{\ell}/min$ of pressure for shielding gas.

• Journal of Advanced Marine Engineering and Technology
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• v.31 no.8
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• pp.961-969
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• 2007

The laser material processing has replaced a conventional material processing such as a welding, cutting, drilling and surface modification and so on. LTH(Laser Transformation Hardening) is one branch of the laser surface modification process. A lot of energy is needed for the LTH process to elevate workpiece surface to temperature of the austenite transformation($A_3$), which results from utilizing a beam with a larger size and lower power intensity comparatively. The absorptivity of the laser energy with respect to material depends on the wave length of a beam. This study is related to the surface hardening for the rod-shaped carbon steel by the high power diode laser(HPDL) whose beam absorptivity is better than conventional types of lasers such as $CO_2$ or Nd:YAG laser. Because a beam proceeds on the rotating specimen the pretreated hardened-phase can be tempered and softened by the overlapping between hardened tracks. Accordingly, the longitudinal hardness measurement and observation of the micro structure was carried out for an assessment of the hardening characteristics. In addition, a hardening characteristics as a hardenability of materials was compared in the point of view of the hardness distribution and hardening depth and width.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.736-742
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• 2000

Mass removed from crystalline silicon samples during high power single-pulse laser ablation was studied by measuring the resulting crater morphology with a white light interferometric microscope. The volume and depth of the craters show a strong nonlinear change as the laser irradiance increases across a threshold value, that is, approximately $2.2{\times}10^{10}\;W/cm^2$. Time-resolved shadowgraph images of the ablation plume show the ejection of large particulates from the sample for laser irradiance above the threshold, with a time delay of about 300-400 nsec. The thickness of superheated liquid layer near the critical temperature was numerically estimated, considering the transformation of liquid metal into liquid dielectric near the critical state (i.e., induced transparency). The estimated thickness of the superheated layer at a delay time of 200 nsec agreed with the measured crater depths, suggesting that induced transparency promotes the formation of a deep superheated liquid layer which leads to an explosive boiling responsible for the sudden increase of crater volume and depth.

• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.57.1-57.1
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• 2010

레이저 색소 분자간의 회합을 막음으로써 높은 레이저 효율을 갖는 고체 색소 레이저를 제조하기 위해 레이저 색소인 DCM을 유-무기 하이브리드 재료에 화학적으로 결합시켰다. 수산화기를 기능기로 갖는 DCM을 합성하여 이를 솔-젤반응의 전구체로 활용하였다. 유기실란을 DCM과 함께 솔-젤반응을 시킴으로써 DCM이 결합된 유무기 하이브리드 재료를 제조하였다. DCM이 결합된 유-무기 하이브리드 재료는 유기물과 무기물의 특성을 각각 갖고 있기 때문에 용액공정을 통해 고체 색소 레이저를 단시간에 제작할 수가 있을 뿐만 아니라 열적 및 광학적으로 우수한 특성을 보여주었다. Nd:YAG 레이저를 여기광으로 이용하여 DCM이 결합된 유-무기 하이브리드 재료의 레이저 효율을 측정하여 DCM을 유기용매에 녹인 색소 레이저의 레이저 효율과 비교하였다. DCM이 결합된 유-무기 하이브리드 재료는 DCM의 농도가 높아질 수록 유기용매를 이용한 색소 레이저에 비해서 더 높은 레이저 효율을 가지는 것을 관찰하였다. 이는 DCM이 결합된 유-무기 하이브리드 재료에 각각의 DCM 분자가 실록산 망목구조와 화학적으로 결합이 되어있기 때문에 하이브리드 재료에 안정적으로 존재할 수 있게 되고 망목구조에 둘러쌓여 분자간의 회합이 방지되는 효과를 가지게 되기 때문이다.

• Journal of ILASS-Korea
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• v.11 no.3
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• pp.140-146
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• 2006

The objective of this work is to analyze the atomization and evaporation characteristics of dimethyl ether(DME) fuel for the application of HCCI diesel engine. In order to investigate the spray behavior of DME fuel, the macroscopic and microscopic characteristics were investigated in terms of spray development, spray tip penetration, impingement time, SMD, and axial mean velocity under the various injection timing and ambient conditions. For the illumination of spray, the spray visualization system was composed of a Nd:YAG laser and an ICCD camera and laser-sheet method was used. The atomization characteristics of DME fuel are analyzed by using phase Doppler particle analyzer (PDPA) system It was reveal that the spray development of DME is slower and rapidly disappeared as elapsed time after start of injection at the same injection duration. The impingement timing of diesel fuel was fester than that of DME fuel. The comparison of spray atomization characteristics in both fuels shows that diesel fuel has a large SMD value that DME.

• Proceedings of the KIEE Conference
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• 2002.07c
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• pp.1559-1561
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• 2002

적외선 확산반사형 결정화유리를 응용한 레이저 여기용 공진기를 제작하여 미세구조 분석 및 레이저 여기 효율특성을 조사하였다. 출발물질로는 Cordierite를 주결정상으로 하는 MAS(MgO, $Al_2O_3$, $SiO_2$) 3성분계 조성에 결정화 유도용 조핵제로 $TiO_2$를 첨가하였으며, 형성된 유리 용융물을 흑연제 몰드에 부어 공진기를 제조하였다. 용융물 중 일부를 2단계 열처리를 행하여 상분석을 실시한 결과 Cordierite($2MgO{\cdot}2Al_2O_3{\cdot}5SiO_2$)와 Rutile($TiO_2$)이 주결정상으로 관찰되었으며, 열처리 온도를 변화시켜 생성된 입자의 크기에 따른 확산반사율간의 관계를 조사한 결과, $1100{\sim}1200nm$에서 열처리된 시편의 경우 $500{\sim}2200nm$의 영역에서 95% 이상의 확산반사율을 나타내었다. 대표적인 고체레이저인 Nd:YAG의 경우, $700{\sim}900nm$ 파장이 주흡수대이며, 이를 결정화유리로 제조된 공진기의 레이저 효율특성실험에 이용하였다. 수냉 및 단일 펄스의 조건에서 $1.7{\sim}1.9%$의 효율을 나타내었다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.11a
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• pp.41-42
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• 2005

The characteristics of ZnO films are reported depending on different deposition conditions for film bulk acoustic resonators (FBARs). The ZnO films have been deposited on Al films evaporated on p-type (100) silicon substrate by pulsed laser deposition (PLD) technique using a Nd:YAG laser. These films exhibit an electrical resistivity higher than $10^7$ $\Omega$m. X-ray diffraction measurements have shown that ZnO films are highly c-axis oriented with full width at half maximum (FWHM) below $0.5^{\circ}$. These results show the possibility of FBAR devices using by PLD.