• Korean Journal of Optics and Photonics
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• v.4 no.4
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• pp.420-427
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• 1993

Dielectric thin film mirrors are embedded in multimode and single-mode fibers by a fusion splicing technique. The fibers with $45{\circ}$ angled embedded mirrors serve as ultra-compact directional couplers with low excess optical loss of 0.2 dB for multimode and 0.5 dB for single mode at 1.3 ${\mu}m$ and excellent mechanical properties. The reflectance is wavelength dependent and strongly polarization depencient. Far-field scans of the reflected output power measured with a white-light source show a pattern which is almost circularly symmetric with aspect ratio of 1.09 at 5% of the peak power. The splitting ratio in a multimode coupler measured with a diode laser source is much less dependent on input coupling conditions than in conventional fused biconical-taper couplers, indicating that these couplers are less susceptible to modal noise occuring in optical fiber communication systems. Spectral properties of multilayer internal mirrors normal to the fiber axis have been investigated experimentally, and a matrix analysis has been used to explain the results.

• Korean Journal of Optics and Photonics
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• v.11 no.4
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• pp.271-278
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• 2000

We have fabricated and analyzed the lasing characteristics of 1.3$\mu\textrm{m}$ Spot-Size-Converter (SSC) integrated Fabry-Perot (FP) laser diodes, which are very promising light sources for optical subscriber networks. SSC-LDs has been developed by BIB (buttjoint-built-in) coupling and selective MOVPE growth. High-performances were achieved such as the slope efficiency from the SSC facet of 0.23-0.32 mW/mA, the full-width at the half maximum of the far-field pattern (FFP) of 9.5$^{\circ}$~12.3$^{\circ}$, the alignment tolerances of $\pm$2.3$\mu\textrm{m}$ and $\pm$2.5$\mu\textrm{m}$ within the extra-coupling loss of 1 dB for the vertical and parallel directions, respectively. These experimental results were compared to theoretical ones in order to clarify the operational problems and give a good design direction of the fabricated SSC-LDs. It was revealed that an asymmetric output power from the facets, an irrelevancy of FFP and the waveguide structure around SSC facet region, and a poor temperature characteristics were originated from the scattering in the BIB and SSC sections and SHB effect in the active section for the first time.t time.

• Journal of Mechanical Science and Technology
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• v.16 no.7
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• pp.986-998
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• 2002

Flow and spray characteristics are critical factors that affect the performance and exhaust emissions of a direct injection diesel engine. It is well known that the swirl control system is one of the useful ways to improve the fuel consumption and emission reduction rate in a diesel engine. However, until now there have only been a few studies on the effect of flow on spray. Because of this, the relationship between the flow pattern in the cylinder and its influence on the behavior of the spray is in need of investigation. First, in-cylinder flow distributions for 4-valve cylinder head of DI (Direct Injection) Diesel engine were investigated under steady-state conditions for different SCV (Swirl Control Valve) opening angles using a steady flow rig and 2-D LDV (Laser Doppler Velocimetry). It was found that swirl flow was more dominant than that of tumble in the experimented engine. In addition, the in-cylinder flow was quantified in terms of swirl/tumble ratio and mean flow coefficient. As the SCV opening angle was increased, high swirl ratios more than 3.0 were obtained in the case of SCV -70° and 90°. Second, spray characteristics of the intermittent injection were investigated by a PDA (Phase Doppler Anemometer) system. A Time Dividing Method (TDM) was used to analyze the microscopic spray characteristics. It was found that the atomization characteristics such as velocity and SMD (Sauter Mean Diameter) of the spray were affected by the in-cylinder swirl ratio. As a result, it was concluded that the swirl ratio improves atomization characteristics uniformly.

• Restorative Dentistry and Endodontics
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• v.43 no.2
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• pp.22.1-22.9
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• 2018

Objectives: To evaluate and compare light-transmittance in dental tissues and dental composite restorations using the incremental double-layer technique with varying layer thickness. Materials and Methods: B1-colored natural teeth slabs were compared to dental restoration build-ups with A2D and B1E-colored nanofilled, supra-nanofilled, microfilled, and microhybrid composites. The enamel layer varied from 0.3, 0.5, or 1.2 mm thick, and the dentin layer was varied to provide a standardized 3.7 mm overall sample thickness (n = 10). All increments were light-cured to $16J/cm^2$ with a multi-wave LED (Valo, Ultradent). Using a spectrophotometer, the samples were irradiated by an RGB laser beam. A voltmeter recorded the light output signal to calculate the light-transmittance through the specimens. The data were analyzed using 1-way analysis of variance followed by the post hoc Tukey's test (p = 0.05). Results: Mean light-transmittance observed at thicker final layers of enamel were significantly lower than those observed at thinner final layers. Within 1.2 mm final enamel resin layer (FERL) thickness, all composites were similar to the dental tissues, with exception of the nanofilled composite. However, within 0.5 mm FERL thickness, only the suprananofilled composite showed no difference from the dental tissues. Within 0.3 mm FERL thickness, none of the composites were similar to the dental tissues. Conclusions: The supra-nanofilled composite had the most similar light-transmittance pattern when compared to the natural teeth. However, for other composites, thicker FERL have a greater chance to match the light-transmittance of natural dental tissues.

• Journal of the Korean Society for Precision Engineering
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• v.24 no.8 s.197
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• pp.138-143
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• 2007

Microstereolithography technology is similar to the conventional stereolithography process and enables to fabricate a complex 3D microstructure. This is divided into scanning and projection type according to aiming at precision and fabrication speed. The scanning MSL fabricates each layer using position control of laser spot on the resin surface, whereas the projection MSL fabricates one layer with one exposure using a mask. In the projection MSL, DMD used to generate dynamic pattern consists of $1024{\times}768$ micromirrors which have $13.68{\mu}m$ per side. The fabrication range and resolution are determined by the field of view of the DMD and the magnification of the projection lens. If using the projection lens with high power, very fine microstructures can be fabricated. In this paper, the projection MSL system adapted to a large surface for array-type fabrication is presented. This system covers the meso range, which is defined as the intermediate range between micro and macro, with a resolution of a few ${\mu}m$. The fabrication of array-type microstructures has been demonstrated to verify the performance of implemented system.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.277.2-277.2
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• 2013

Petri dishes and glass slides have been widely used as general substrates for in vitro mammalian cell cultures due to their culture viability, optical transparency, experimental convenience, and relatively low cost. Despite the aforementioned benefit, however, the flat two-dimensional substrates exhibit limited capability in terms of realistically mimicking cellular polarization, intercellular interaction, and differentiation in the non-physiological culture environment. Here, we report a protocol of culturing embryonic rat hippocampal neurons on the electro-spun polymeric network and the results from examination of neuronal cell behavior and network formation on this culture platform. A combinatorial method of laser-scanning confocal fluorescence microscopy and live-cell imaging technique was employed to track axonal outgrowth and synaptic connectivity of the neuronal cells deposited on this model culture environment. The present microfiber-based scaffold supports the prolonged viability of three-dimensionally-formed neuronal networks and their microscopic geometric parameters (i.e., microfiber diameter) strongly influence the axonal outgrowth and synaptic connection pattern. These results implies that electro-spun fiber scaffolds with fine control over surface chemistry and nano/microscopic geometry may be used as an economic and general platform for three-dimensional mammalian culture systems, particularly, neuronal lineage and other network forming cell lines.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.185-185
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• 2011

Mapping of artificial levee lines, one of major tasks in river zone mapping, is critical to prevention of river flood, protection of environments and eco systems in river zones. Thus, mapping of artificial levee lines is essential for management and development of river zones. Coastal mapping including river zone mapping has been historically carried out using surveying technologies. Photogrammetry, one of the surveying technologies, is recently used technology for national river zone mapping in Korea. Airborne laser scanning has been used in most advanced countries for coastal mapping due to its ability to penetrate shallow water and its high vertical accuracy. Due to these advantages, use of LiDAR data in coastal mapping is efficient for monitoring and predicting significant topographic change in river zones. This paper introduces a method for construction of a 3D artificial levee line using a set of LiDAR points that uses normal vectors. Multiple steps are involved in this method. First, a 2.5-dimensional Delaunay triangle mesh is generated based on three nearest-neighbor points in the LiDAR data. Second, a median filtering is applied to minimize noise. Third, edge selection algorithms are applied to extract break edges from a Delaunay triangle mesh using two normal vectors. In this research, two methods for edge selection algorithms using hypothesis testing are used to extract break edges. Fourth, intersection edges which are extracted using both methods at the same range are selected as the intersection edge group. Fifth, among intersection edge group, some linear feature edges which are not suitable to compose a levee line are removed as much as possible considering vertical distance, slope and connectivity of an edge. Sixth, with all line segments which are suitable to constitute a levee line, one river levee line segment is connected to another river levee line segment with the end points of both river levee line segments located nearest horizontally and vertically to each other. After linkage of all the river levee line segments, the initial river levee line is generated. Since the initial river levee line consists of the LiDAR points, the pattern of the initial river levee line is being zigzag along the river levee. Thus, for the last step, a algorithm for smoothing the initial river levee line is applied to fit the initial river levee line into the reference line, and the final 3D river levee line is constructed. After the algorithm is completed, the proposed algorithm is applied to construct the 3D river levee line in Zng-San levee nearby Ham-Ahn Bo in Nak-Dong river. Statistical results show that the constructed river levee line generated using a proposed method has high accuracy in comparison to the ground truth. This paper shows that use of LiDAR data for construction of the 3D river levee line for river zone mapping is useful and efficient; and, as a result, it can be replaced with ground surveying method for construction of the 3D river levee line.

• Korean Journal of Remote Sensing
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• v.37 no.2
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• pp.245-256
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• 2021

This study was conducted to identify the applicability of a LiDAR sensor to forest resources inventories by comparing data on a tree's position, height, and DBH obtained by the sensor with those by existing forest inventory methods, for the tree species of Criptomeria japonica in Jeolmul forest in Jeju, South Korea. To this end, a backpack personal LiDAR (Greenvalley International, Model D50) was employed. To facilitate the process of the data collection, patterns of collecting the data by the sensor were divided into seven ones, considering the density of sample plots and the work efficiency. Then, the accuracy of estimating the variables of each tree was assessed. The amount of time spent on acquiring and processing the data by each method was compared to evaluate the efficiency. The findings showed that the rate of detecting standing trees by the LiDAR was 100%. Also, the high statistical accuracy was observed in both Pattern 5 (DBH: RMSE 1.07 cm, Bias -0.79 cm, Height: RMSE 0.95 m, Bias -3.2 m), and Pattern 7 (DBH: RMSE 1.18 cm, Bias -0.82 cm, Height: RMSE 1.13 m, Bias -2.62 m), compared to the results drawn in the typical inventory manner. Concerning the time issue, 115 to 135 minutes per 1ha were taken to process the data by utilizing the LiDAR, while 375 to 1,115 spent in the existing way, proving the higher efficiency of the device. It can thus be concluded that using a backpack personal LiDAR helps increase efficiency in conducting a forest resources inventory in an planted coniferous forest with understory vegetation, implying a need for further research in a variety of forests.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.103-103
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• 2014

Manufacturing of lens and mirror using Diamond Turning Machine (DTM) offers distinct advantages including short fabrication time and low cost as compared to grinding or polishing process. However, the DTM process can leave mid-frequency error in the optical surface which generates an undesirable diffraction effect and stray light. The mid-frequency error is expected to be eliminated by mechanical polishing after the DTM process, but polishing of soft surface of ductile aluminum is extremely difficult because the polishing process inevitably degrades the surface form accuracy. In order to increase its surface hardness, we performed electroless nickel plating on the surface of diamond-turned aluminum (Al-6061T6) off-axis mirrors, which was followed by the 6-hour-long baking process at $200^{\circ}C$ for improving its hardness. Then we polished the nickel plated off-axis mirrors to remove the mid-frequency error and measured polished mirror surfaces using the optical surface profilometer (NT 2000, Wyko Inc.). Finally, we ascertained that the mid-frequency error on the mirror surface was successfully removed. During the whole processes of nickel plating and polishing, we monitored the form accuracy using the ultra-high accurate 3-D profilometer (UA3P, Panasonic Corp.) to maintain it within the allowable tolerance range (< tens of nm). The polished off-axis mirror was optically tested using a visible laser source and a pinhole, and the airy pattern obtained from the polished mirror was compared with the unpolished case to check the influence of mid-frequency error on optical images.

• Korean Journal of Agricultural Science
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• v.45 no.4
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• pp.635-643
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• 2018

Bovine milk is widely consumed by humans and is a primary ingredient of dairy foods. Proteomic approaches have the potential to elucidate complex milk proteins and have been used to study milk of various species. Here, we performed a proteomic analysis using 2-dimensional electrophoresis (2-DE) and matrix assisted laser desorption ionization-time of flight mass spectrometer (MALDI-TOF MS) to identify whey proteins in bovine milk obtained soon after parturition (bovine early milk). The major casein proteins were removed, and the whey proteins were analyzed with 2-dimensional polyacrylamide gel electrophoresis (2-D PAGE). The whey proteins (2 mg) were separated by pI and molecular weight across pH ranges of 3.0 - 10.0 and 4.0 - 7.0. The 2-DE gels held about 300 to 700 detectable protein spots. We randomly picked 12 and nine spots that were consistently expressed in the pH 3.0 - 10.0 and pH 4.0 - 7.0 ranges, respectively. Following MALDI-TOF MS analysis, the 21 randomly selected proteins included proteins known to be present in bovine milk, such as albumin, lactoferrin, serum albumin precursor, T cell receptor, polymeric immunoglobulin receptor, pancreatic trypsin inhibitor, aldehyde oxidase and microglobulin. These proteins have major functions in immune responses, metabolism and protein binding. In summary, we herein identified both known and novel whey proteins present in bovine early milk, and our sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis revealed their expression pattern.