• Journal of Adhesion and Interface
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• v.20 no.1
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• pp.1-8
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• 2019

Fabrication of monolayer is important method for enhancing physical and chemical characteristics such as light shielding and antireflection while maintaining thin film properties. In previous studies, monolayers were fabricated by various methods on small substrates, but processes were complicated and difficult to form monolayers with large area. We used rod coating equipment with a small amount of coating liquid to form a HCP (hexagonal closed packing) coating of PMMA beads on PET(poly(ethylene terephthalate)) substrate with $20cm{\times}20cm$ size. We observed that changes in morphologies of monolayers by using the solvents with different boiling points and vapor pressures, by adapting surfactants on particles and by applying plasma treatment on substrates. The coverage was increased by 20% by optimizing the coating conditions including meniscus of beads, control of the attraction - repulsion forces and surface energy. This result can potentially be applied to optical films and sensors because it is possible to make a uniform and large-scale monolayer in a simple and rapid manner when it is compared to the methods in previous studies.

• Korean Journal of Optics and Photonics
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• v.30 no.2
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• pp.37-47
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• 2019

A reflecting omnidirectional optical system with four spherical and aspherical mirrors, for use with long-wavelength infrared light (LWIR) for night surveillance, is proposed. It is designed to include a collecting pseudo-Cassegrain reflector and an imaging inverse pseudo-Cassegrain reflector, and the design process and performance analysis is reported in detail. The half-field of view (HFOV) and F-number of this optical system are $40-110^{\circ}$ and 1.56, respectively. To use the LWIR imaging, the size of the image must be similar to that of the microbolometer sensor for LWIR. As a result, the size of the image must be $5.9mm{\times}5.9mm$ if possible. The image size ratio for an HFOV range of $40^{\circ}$ to $110^{\circ}$ after optimizing the design is 48.86%. At a spatial frequency of 20 lp/mm when the HFOV is $110^{\circ}$, the modulation transfer function (MTF) for LWIR is 0.381. Additionally, the cumulative probability of tolerance for the LWIR at a spatial frequency of 20 lp/mm is 99.75%. As a result of athermalization analysis in the temperature range of $-32^{\circ}C$ to $+55^{\circ}C$, we find that the secondary mirror of the inverse pseudo-Cassegrain reflector can function as a compensator, to alleviate MTF degradation with rising temperature.

• Journal of Adhesion and Interface
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• v.22 no.2
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• pp.57-62
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• 2021

Recently, the atomically thin two-dimensional transition-metal dichalcogenides (TMDs) have received considerable attention for the application to next-generation semiconducting devices, owing to their remarkable properties including high carrier mobility. However, while a technique for growing graphene is well matured enough to achieve a wafer-scale single crystalline monolayer film, the large-area growth of high quality TMD monolayer is still a challenging issue for industrial application. In order to enlarge the size of single crystalline MoS₂ monolayer, here, we systematically investigated the effect of process parameters in molten-salt-assisted chemical vapor deposition method. As a result, with optimized process parameters, we found that single crystalline monolayer MoS₂ can be grown as large as 420 ㎛.

• Korean Chemical Engineering Research
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• v.59 no.4
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• pp.542-547
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• 2021

Glass lined impellers are corrosion resistant to most chemicals, including strong acids, and also have a smooth, non-stick surface, easy to clean and free from impurities in the process. Glass lined home base impeller is a multi-purpose impeller designed to stir a wide viscosity range of liquids from low viscosity fluids to high viscosity fluids, among others, cell culture, yeast culture, and beer fermentation pots, especially used for air-water system breathable stirring. The glass lining for HB impellers, which are simple in structure and competitive in performance, is essential to have upper and lower division in order to make the joint area between the impeller and shaft as small as possible. The upper and lower division of the impeller hardly affects the mixing performance, but the aeration performance. In this study, in order to optimize the shape of the Glass Lining HB impeller, a study was conducted on the effect of the angle between the upper and lower impellers, the clearance between the impellers, and the number of baffles on the aeration power. The optimal shape and baffle plate conditions for the Glass lined HB impeller were derived through the study results that the angle and the clearance between the upper and lower impellers decreased the ration of the power consumption with aeration P_g and that without aeration P₀, P_g/P₀.

• Economic and Environmental Geology
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• v.53 no.6
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• pp.703-713
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• 2020

In many geological fields, including hydrogeology, it is of great importance to determine the heterogeneity of the subsurface media. This study briefly introduces the concept and theory of the method that can estimate the hydraulic properties of the media constituting the aquifer, which was recently introduced by Park (2020). After the introduction, the method was applied to the synthetic aquifer to demonstrate the practicality, from which various implications were drawn. The introduced technique uses a global optimization technique called the covariance matrix adaptation evolution strategy (CMA-ES). Conceptually, it is a methodology to characterize the aquifer heterogeneity by assimilating the groundwater level time-series data due to the imposed hydraulic stress. As a result of applying the developed technique to estimate the hydraulic conductivity of a hypothetical aquifer, it was confirmed that a total of 40000 unknown values were estimated in an affordable computational time. In addition, the results of the estimates showed a close numerical and structural similarity to the reference hydraulic conductivity field, confirming that the quality of the estimation by the proposed method is high. In this study, the developed method was applied to a limited case, but it is expected that it can be applied to a wider variety of cases through additional development of the method. The development technique has the potential to be applied not only to the field of hydrogeology, but also to various fields of geology and geophysics. Further development of the method is currently underway.

• The Journal of Society for e-Business Studies
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• v.26 no.2
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• pp.123-141
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• 2021

As the dependence of technology on the economic structure increases, the importance of National Core Technology is increasing. However, due to the nature of the technology itself, it is difficult to determine the scope of the technology to be protected because the scope of the relation is abstract and information disclosure is limited due to the nature of the National Core Technology. To solve this problem, we propose the most appropriate literature type and method of analysis to distinguish important technologies related to National Core Technology. We conducted a pilot test to apply TF-IDF, and LDA topic modeling, two techniques of text mining analysis for big data analysis, to four types of literature (news, papers, reports, patents) collected with National Core Technology keywords in the field of Display industry. As a result, applying LDA theme modeling to patent data are highly relevant to National Core Technology. Important technologies related to the front and rear industries of displays, including OLEDs and microLEDs, were identified, and the results were visualized as networks to clarify the scope of important technologies associated with National Core Technology. Throughout this study, we have clarified the ambiguity of the scope of association of technologies and overcome the limited information disclosure characteristics of national core technologies.

• Korean Journal of Optics and Photonics
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• v.32 no.3
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• pp.120-125
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• 2021

We have developed a linearly polarized high-power Yb-doped fiber laser in the master oscillator power amplifier (MOPA) scheme for efficient spectral beam combining. We modulated the phase of the seed laser by pseudo-random binary sequence (PRBS), with the bit length optimized to suppress stimulated Brillouin scattering (SBS), and subsequently amplified seed power in a 3-stage amplifier system. We have constructed by coiling the polarization-maintaining (PM) Yb-doped fiber, with core and cladding diameters of 20 ㎛ and 400 ㎛ respectively, to a diameter of 9-12 cm for suppression of the mode instability (MI). Finally, we obtained an output power of 1.004 kW with a slope efficiency of 83.7% in the main amplification stage. The beam quality factor M² and the polarization extinction ratio (PER) were measured to be 1.12 and 21.5 dB respectively. Furthermore, the peak-intensity difference between the Rayleigh signal and SBS signal was observed to be 2.36 dB in the backward spectra, indicating that SBS is successfully suppressed. In addition, it can be expected that the MI does not occur because not only there is no decrease in slope efficiency, but also the beam quality for each amplified output is maintained.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.2
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• pp.212-220
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• 2021

National R&D investment has steadily increased, reaching number 5 in the world as of 2018. However, for public technology commercialization, the level of discovery of policy models through various cooperation initiatives between government ministries is insufficient, and the performance system that can spread technology commercialization is also limited. In this respect, in order to create results in public technology commercialization, it is necessary to prepare alternatives to strengthen multi-ministerial policy cooperation and increase policy execution power. In this paper, we analyzed the current state of national R&D projects by major ministries and suggested an optimized technology commercialization plan through analysis of the structure, budget, and form of each project. In particular, an alternative in terms of policy efficiency was suggested by analyzing the problems of policy discovery that have not been studied previously. This study is of great significance in that it diagnosed problems of public technology commercialization in terms of the lack of systematic research on public technology commercialization and suggested policy advancement for the spread of technology use and the strategic direction in terms of commercialization.

• Journal of Korea Water Resources Association
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• v.54 no.2
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• pp.105-119
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• 2021

An increase in the frequency and intensity of both floods and droughts has been recently observed due to an increase in climate variability. Especially, land-use change associated with industrial structure and urbanization has led to an imbalance between water supply and demand, acting as a constraint in water resource management. Accurate rainfall-runoff analysis plays a critical role in evaluating water availability in the water budget analysis. This study aimed to explore various continuous rainfall-runoff models over the Soyanggang dam watershed. Moreover, the ensemble modeling framework combining multiple models was introduced to present scenarios on streamflow considering uncertainties. In the ensemble modeling framework, rainfall-runoff models with fewer parameters are generally preferred for effective regionalization. In this study, more than 40 continuous rainfall-runoff models were applied to the Soyanggang dam watershed, and nine rainfall-runoff models were primarily selected using different goodness-of-fit measures. This study confirmed that the ensemble model showed better performance than the individual model over different flow regimes.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.12
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• pp.320-330
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• 2020

Fire is difficult to achieve good performance in image detection using deep learning because of its high irregularity. In particular, there is little data on fire detection in underground utility facilities, which have poor light conditions and many objects similar to fire. These make fire detection challenging and cause low performance of deep learning models. Therefore, this study proposed a fire detection model using deep learning and estimated the performance of the model. The proposed model was designed using a combination of a basic convolutional neural network, Inception block of GoogleNet, and Skip connection of ResNet to optimize the deep learning model for fire detection under underground utility facilities. In addition, a training technique for the model was proposed. To examine the effectiveness of the method, the trained model was applied to fire images, which included fire and non-fire (which can be misunderstood as a fire) objects under the underground facilities or similar conditions, and results were analyzed. Metrics, such as precision and recall from deep learning models of other studies, were compared with those of the proposed model to estimate the model performance qualitatively. The results showed that the proposed model has high precision and recall for fire detection under low light intensity and both low erroneous and missing detection capabilities for things similar to fire.