• Korean Journal of Optics and Photonics
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• v.28 no.4
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• pp.153-157
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• 2017

An infrared camera and laser common-path optical system is applied to DIRCM (directional infrared countermeasures), to increase boresighting accuracy and decrease weight. Thermal effects of a laser beam in a common-path optical system are analyzed and evaluated, to predict any degradation in image quality. A laser beam with high energy density is absorbed by and heats the optical components, and then the surface temperature of the optical components increases. The heated optical components of the common-path optical system decrease system transmittance, which can degrade image quality. For analysis, the assumed simulation condition is that the laser is incident for 10 seconds on the mirror (aluminum, silica glass, silicon) and lens (sapphire, zinc selenide, silicon, germanium) materials, and the surface temperature distribution of each material is calculated. The wavelength of the laser beam is $4{\mu}m$ and its output power is 3 W. According to the results of the calculations, the surface temperature of silica glass for the mirror material and sapphire for the lens material is higher than for other materials; the main reason for the temperature increase is the absorption coefficient and thermal conductivity of the material. Consequently, materials for the optical components with high thermal conductivity and low absorption coefficient can reduce the image-quality degradation due to laser-beam thermal effects in an infrared camera and laser common-path optical system.

• Proceedings of the Korean Fiber Society Conference
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• 2003.10a
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• pp.77-78
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• 2003

The surface evenness and texture of textile products are closely related with the irregularity of yarn thickness which has an important role to influence the quality and the process efficiency. For measuring yam thickness the capacitive method is known to dominate the market, delivering results that are in a close relation with the mechanical properties of yarn, while the optical method offers information that seems related rather with the apparent quality of yarn. If a thin light beam is applied for the optoelectrical measurement, it is very possible that this method can provide us with important information which is not obtainable from the capacitive type measurement. This paper reports the results of a study about the yarn thickness and its variation on the basis of a new measurement system using a laser slit beam. Analysis of the new system confirms that we can extract new information on the yarn irregularity ranging into much short wavelengths. Even the visual shade created by the yam doubling and twisting can be measured and represented well. Depending on the yam types, the thickness measurements show their own characteristics.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.99-99
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• 2003

The growth of GaN on Si is of great interest due to the several advantages : low cost, large size and high-quality wafer availability as well as its matured technology. The crystal quality of GaN is known to be much influenced by the surface pretreatment of Si substrate[1]. In this work, the properties of GaN overlayer grown on ion beam modified Si(111) have been investigated. Si(111) surface was treated RIB with 1KeV-N$_2$$\^$+/(at 1.9 ${\times}$ 10$\^$-5/) to dose ranging from 5${\times}$10$\^$15/ to 1${\times}$10$\^$17/ prior to film growth. GaN epilayers were grown at 1100$^{\circ}C$ for 1 hour after growing AlN buffer layers for 5∼30 minutes at 1100$^{\circ}C$ in Metal Organic Chemical Vapor Deposition (MOCVD). The properties of GaN epilayers were evaluated by X-Ray Diffraction(XRD), Raman spectroscopy, Photoluminescence(PL) and Hall measurement. The results showed that the ion modified treatment markedly affected to the structural, optical and electrical characteristic of GaN layers.

• Journal of Korean Society of Steel Construction
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• v.27 no.4
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• pp.387-397
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• 2015

The domestic fire resistance performance test is conducted as a prescriptive design method such as quality test. In quality test there are 2 methods, unloaded fire resistance test and fire resistance test under load. In realistic, these tests, however, have problems with expense, time and diversity of structure. This study reviewed fire resistance performance of H-beam flexural member by thermal stress analysis using finite element ABAQUS program. This research is for the performance-based design reviewing applicability of domestic standard. As a result of this study, limit temperatures per each load ratio provied for proper performance of fire resistancy.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.402-407
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• 2002

Laminate tooling process is a fast and simple method to make metal tools directly for various molding processes such as injection molding in rapid prototyping field. Metal sheets are usually cut, stacked, aligned and joined with brazing or soldering. Through the joining process, all of the metal sheet layers should be rigidly joined. When joining process parameters are not appropriate, there would be defects in the layers. Among various types of defects, non-bonded gaps of the tool surface are of great importance, because they directly affect the surface quality and dimensional accuracy of the final products. If a laminate tool with defects has to be abandoned, it could lead to great loss of time and cost. Therefore a repair method for non-bonded gaps of the surface is essential and has important meaning for rapid prototyping. In this study, a rapid laminate tooling system composed of a CO2 laser, a furnace, and a milling machine was developed. Metal sheets were joined by furnace brazing, dip soldering and adhesive bonding. Joined laminate tools were machined by a high-speed milling machine to improve surface quality. Also, repair brazing and soldering methods of the laminates using the $CO_2$ laser system have been investigated. ill laser repair process, the beam duration, beam power and beam profile were of great importance, and their effects were simulated by [mite element methods. The simulation results were compared with the experimental ones, and optimal parameters for laser repair process were investigated.

• Korean Journal of Optics and Photonics
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• v.15 no.6
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• pp.575-582
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• 2004

We analyse the beam characteristics of the thermal-birefringence compensated symmetric resonator which consists of two laser rods with rod-end curvatures. The numerical results show that the stability and the beam quality can be improved in high power operation region when the rod-ends are made in the form of a negative lens. The thermal birefringence of the symmetric two-rods resonator is shown to be well compensated when the two rods closely contact each other.

• Progress in Medical Physics
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• v.28 no.1
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• pp.22-26
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• 2017

We have developed an analytic software that can easily analyze the spot position and width of proton beam therapy nozzles in a periodic quality assurance. The developed software consists of an image processing method that conducts an analysis using center-of-spot geometry and a Gaussian fitting method that conducts an analysis through Gaussian fitting. By using the software, an analysis of 210 proton spots with energies 150, 190, and 230 MeV showed a deviation of approximately 3% from the mean. The software we developed to analyze proton spot positions and widths provides an accurate analysis and reduces the time for analysis.

• Journal of the Optical Society of Korea
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• v.12 no.4
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• pp.298-302
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• 2008

We have developed a 270-W 15-kHz MOPA system based on side-pumped rod-type Nd:YAG gain modules. The master oscillator is a 3-W 15-kHz $TEM_{00}$ $Nd:YVO_4$ laser with a pulse duration of 30 ns. To preserve the high beam quality during the amplification, we use image relay and polarization rotation which can simultaneously compensate for thermal lensing and thermal birefringence generated in the rod-type gain modules. After the amplification to 270 W with six rod-type gain modules, the beam quality factor ($M^2$) of the amplified laser beam is 5-10, and the pulse duration is maintained at 30 ns.

• Applied Microscopy
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• v.50
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• pp.17.1-17.9
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• 2020

Recent advances in fabrication have enabled radial-junction architectures for cost-effective and high-performance optoelectronic devices. Unlike a planar PN junction, a radial-junction geometry maximizes the optical interaction in the three-dimensional (3D) structures, while effectively extracting the generated carriers via the conformal PN junction. In this paper, we report characterizations of radial PN junctions that consist of p-type Si micropillars created by deep reactive-ion etching (DRIE) and an n-type layer formed by phosphorus gas diffusion. We use electron-beam induced current (EBIC) microscopy to access the 3D junction profile from the sidewall of the pillars. Our EBIC images reveal uniform PN junctions conformally constructed on the 3D pillar array. Based on Monte-Carlo simulations and EBIC modeling, we estimate local carrier separation/collection efficiency that reflects the quality of the PN junction. We find the EBIC efficiency of the pillar array increases with the incident electron beam energy, consistent with the EBIC behaviors observed in a high-quality planar PN junction. The magnitude of the EBIC efficiency of our pillar array is about 70% at 10 kV, slightly lower than that of the planar device (≈ 81%). We suggest that this reduction could be attributed to the unpassivated pillar surface and the unintended recombination centers in the pillar cores introduced during the DRIE processes. Our results support that the depth-dependent EBIC approach is ideally suitable for evaluating PN junctions formed on micro/nanostructured semiconductors with various geometry.

• Korean Journal of Radiology
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• v.21 no.8
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• pp.1018-1023
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• 2020

The coronavirus disease (COVID-19) outbreak has reached global pandemic status as announced by the World Health Organization, which currently recommends reverse transcription polymerase chain reaction (RT-PCR) as the standard diagnostic tool. However, although the RT-PCR test results may be found negative, there are cases that are found positive for COVID-19 pneumonia on computed tomography (CT) scan. CT is also useful in assessing the severity of COVID-19 pneumonia. When clinicians desire a CT scan of a patient with COVID-19 to monitor treatment response, a safe method for patient transport is necessary. To address the engagement of medical resources necessary to transport a patient with COVID-19, our institution has implemented the use of mobile CT. Therefore, we report two cases of COVID-19 pneumonia evaluated by using mobile cone-beam CT. Although mobile cone-beam CT had some limitations regarding its image quality such as scatter noise, motion and streak artifacts, and limited field of view compared with conventional multi-detector CT, both cases had acceptable image quality to establish the diagnosis of COVID-19 pneumonia. We report the usefulness of mobile cone-beam CT in patients with COVID-19 pneumonia.