• Nuclear Engineering and Technology
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• v.49 no.4
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• pp.865-872
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• 2017

For more than 10 years, the laser process has been studied for dismantling work; however, relatively few research works have addressed the effect of high-power fiber laser cutting for thick sections. Since in the nuclear sector, a significant quantity of thick material is required to be cut, this study aims to improve the reliability of laser cutting for such work and indicates guidelines to optimize the cutting procedure, in particular, nozzle combinations (standoff distance and focus position), to minimize waste material. The results obtained show the performance levels that can be reached with 10 kW fiber lasers, using which it is possible to obtain narrower kerfs than those found in published results obtained with other lasers. Nonetheless, fiber lasers appear to show the same effects as those of $CO_2$ and ND:YAG lasers. Thus, the main factor that affects the kerf width is the focal position, which means that minimum laser spot diameters are advised for smaller kerf widths.

• Korean Journal of Bronchoesophagology
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• v.14 no.2
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• pp.10-16
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• 2008

Surgical resection and reanastomosis has been the treatment of choice in patients with tracheobronchial stenosis. Recent development of bronchoscopic intervention has been replacing the role of surgery in these patients. After summarizing the upto date data of bronchoscopic intervention, the proper management of tracheobronchial stenosis will be presented. Bronchoscopic intervention would be much effective when performed under rigid bron- choscopy, due to the stable patients' condition and endoscopic view. The usual method of intervention includes ballooning, Nd-YAG laser resection, bougienation, mechanical airway dilatation, stenting and photodynamic therapy. Silicone stents are very effective in patients with tracheobronchial stenosis to maintain airway patency. Bronchoscopic intervention provided immediate symptomatic relief and improved lung function in most of patients. After airway stabilization, stents were removed successfully in 2/3 of the patients at a 12-18 months post-insertion. Less than 5% of patients eventually needs surgical management. Acute complications, including excessive bleeding, pneumothorax, and pneumomediastinum develops in less than 5% of patients but managed without mortality. Stent-related late complications, such as, migration, granuloma formation, mucostasis, and restenosis are relatively high but usually controlled by follow-up bronchoscopy. In conclusion, bronchoscopic intervention, including silicone stenting could be a useful and safe method for treating tracheobronchial stenosis.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.05a
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• pp.168-171
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• 2002

In this study. a solid-state laser system adopting a sequential discharge method in which three flashlamps are turned on sequently was designed and fabricated to examine the pulse width and the pulse shape of the laser beams depending upon the changes in the lamp turn-on time. That is, this study shows a technology that makes it possible to make various pulse shapes by turning on three flashlamps sequently with the aid of a PIC one-chip microprocessor. With this technique, the lamp turn-on delay time can be varied more diversely from a to lamp and the real-time control is possible with an external keyboard, enabling various pulse shapes. In addition, longer pulses can be more widely used for industrial processing and lots of medical purposes.

• Proceedings of the KIEE Conference
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• 2007.11a
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• pp.88-89
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• 2007

ZnO thin films were deposited on $Al_2O_3$ (alumina) substrates by pulsed laser deposition (PLD) using Nd:YAG laser with a wavelength of 355nm, at room temperature and oxygen partial pressure of 1, 10, 30, 50, 100, and 200m Torr. Furthermore, deposited ZnO thin films were post-annealed at 400, 550, $600^{\circ}C$. The effects of oxygen partial pressure and post-annealing temperature on structural properties of the deposited films have been investigated by means of X-ray diffraction (XRD), and atomic force microscope (AFM), respectively. It has been found that ZnO thin films exhibit c-axis orientation, exhibiting an increased foil width at half maximum (FWHM) value of (002) diffraction peak at 30m Torr oxygen partial pressure and higher post-annealing temperature ($700^{\circ}C$).

• Proceedings of the KIEE Conference
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• 2007.11a
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• pp.94-95
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• 2007

We have observed electrical properties of ZnO thin films for the fabrication of transparent thin film transistor. ZnO thin films were deposited on $Al_2O_3$(0001) substrate at various temperatures by pulsed laser deposition(PLD). The third of harmonic(355nm) Nd:YAG laser was used for pulsed laser deposition. X-ray diffraction(XRD), field emission-scanning electron microscope(FE-SEM), and photoluminescence were used to characterize physical and optical properties of ZnO thin film.. The results indicated the ZnO film showed good optical properties as increasing temperatures, with low FWHM of exciton-related peak and XRD(0002) peak.

• Journal of the Korea Institute of Military Science and Technology
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• v.10 no.3
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• pp.5-15
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• 2007

A welding structures is generally composed of dissimilar steel materials in order to reduce weight cost, and has a gap to fill the welding agent. Also, heat flow analysis should be fulfilled for structure existing of gap to figure out residual stress which is generated after welding. Since mechanical properties of welding structure composed of dissimilar steel is more fragile than mechanical properties of welding structure consisted of same material, heat flow analysis verifying this should be fulfilled as well. Therefore, on this research, heat flow analysis about dissimilar steel weldment consisted of gap existing AISI304 and AISI630 is practiced so that it could be a basic data of research about mechanical properties of gap existing dissimilar steel welding part which is going to be studied later on. During heat flow analysis, heat input model which based on Gaussian profile and using volume heat flux was newly consisted and applied. In addition, for verifying of analysis on this research, gap existing dissimilar steel weldment which had gap of 0.25mm and was welded using Nd-YAG. The welding profile and temperature distribution for weldment during welding was compared to the result which was gotten through heat flow analysis. Both of those results corresponded each other.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.266-267
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• 2007

$Ba_{0.5}Sr_{0.5}TiO_3$(BST) films with different deposition temperatures were deposited on $Al_2O_3$ substrate by Nd:YAG Pulsed Laser Deposition(PLD). The deposition conditions to achieve high crystal structures and dielectric properties were optimized for both techniques. The structural characterization on the BST thin films was performed by X-Ray Diffraction(XRD) and Atomic Force Microscopy (AFM). Effects of post-deposition annealing of BST films were investigated. The best dielectric properties were obtained on $800^{\circ}C$ deposited BST film with post-deposition annealing at $1100^{\circ}C$ in flowing $O_2$ atmosphere for 2hours.

• Journal of Welding and Joining
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• v.23 no.6
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• pp.43-48
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• 2005

This work was carried out to obtain sound welds and to select a most suitable binary metal joint among three different dissimilar binary metal combinations such as Zr-4/Ta, Mo/Ta and Ti/Ta(seal tube/sensor sheath) joints fur the instrumented nuclear fuel irradiation test. To do this, Taguchi experimental method was employed to optimize the experimental data. In addition, metallography, micro-focus x-ray radiography and hardness test were conducted to examine the welds. From the weld bead appearance, penetration depth and bead width as well as weld defects standpoint, Zr-4/Ta joint is suggested for the circumferential joining between a seal tube and a sensor sheath. The optimized welding parameters based on Zr-4/Ta joint are suggested as well.

• 한국가시화정보학회:학술대회논문집
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• 2006.12a
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• pp.7-10
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• 2006

An experimental study has been conducted to quantitatively characterize the motion of neutrally buoyant particles in 2-dimensional Poiseuille flow through the micron-sized circular capillaries in the range of Re (Reynolds number) $\approx0.1\sim100$. $A{\mu}-PTV$ (Particle Tracking Velocimetry) system is adopted, which consists of a double-headed Nd:YAG laser, an epi-fluorescence microscope and a cooled CCD camera. Since high shear rate can be induced due to the scale effect even at low Re, it is shown that in micro scale neutrally buoyant particles in Poiseuille flow drift away from the wall and away from the center of the capillary. Consequently, particles accumulate at the equilibrium position of $0.52\sim0.64R$ with R being the radius of the capillary, which is analogous to that of tube flow in macro scale. There is a plateau in equilibrium position at small Re, while equilibrium position starts increasing at $Re\approx30$. The outermost edge of particle cluster is closer to the center of the capillary than that in previous studies due to low Re effect. The present study quantitatively presents characteristics of particle motion in circular capillaries. Furthermore, it is expected to give optimum factors for designing microfluidic systems that are to be used fur plasma separation from the blood.

• 한국가시화정보학회:학술대회논문집
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• 2006.12a
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• pp.111-112
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• 2006

In order to investigate flow characteristics of blood flow in a micro tube ($100{\mu}m$ in diameter) according to hematocrit, in-vitro experiments were carried out using a micro-PIV technique. The micro-PIV system consists of a microscope, a 2 head Nd:YAG laser, a 12 bit cooled CCD camera and a delay generator. Blood was supplied into the micro tube using a syringe pump. Hematocrit of blood was controlled to be 20%, 30% and 40%. The blood flow has a cell free layer near the tube wall and its thickness was changed with increasing the flow rate and hematocrit. The hemorheological characteristics such as shear rate and viscosity were evaluated using the velocity field data measured. As the flow rate increased, the blunt velocity profile in the tube center was sharpened. The viscosity of blood was rapidly increased with decreasing shear rate, especially in the region of low shear rate, changing RBC rheological properties. The variation of velocity profile and blood viscosity shows typical characteristics of Non-Newtonian fluids. On the basis of inflection points, the cell free layer and two-phase flow consisting of plasma and suspensions including RBCs were clearly discriminated.