• Korean Journal of Optics and Photonics
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• v.16 no.5
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• pp.469-475
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• 2005

An integrated photonic microwave bandpass filter has been proposed and demonstrated incorporating a coherently coupled microring resonator in low-loss polymers. The proposed device may feature compact site, simple structure, tuning via the thermooptic and electrooptic effect, and flexible integration with other electrical and optical devices. The resonator was designed to have an extremely small bandwidth so that it could be used to selectively pass the optical signal carrying the microwave signal to attain efficient bandpass filtering. We made and tested two resonators with a single ring and double rings, and performed a theoretical fitting of their measured transfer curves to predict the performance of the microwave filters based on them precisely. It was found that as the number of the rings used for the resonator increases, the bandwidth gets smaller, the rolloff sharper, and the band rejection higher. Finally our filter exhibited the center frequency of 10GHz, the 3-dB bandwidth of 1.0GHz, the corresponding quality (Q) factor of 10, and the rejection outside of the passband of more than 25dB.

• Journal of Practical Engineering Education
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• v.13 no.2
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• pp.327-332
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• 2021

Materials used for education include SM20C, Al6061, and acrylic. SM20C materials are used a lot in certification tests and functional competitions as carbon steel, but they are also used in industrial sites. Al6061 is said to be a material that produces a lot of tools because it has lower hardness than carbon steel and is highly flexible. When practical guidance is given to students using acrylic materials, it is a material that causes vibration and tool damage due to excessive cutting. In this process, we examine how impact on the 5-axis equipment 2NC head can affect precision control. The weakest part of a five-axis equipment is the head that controls the AC axis. In the event of precision and cumulative tolerances in this area, the precision of all products is reduced. Thus, a key part of the 2NC head, the spindle housing was carried out using Al7075 T6 (U.S. Alcoasa) material and the entire body using FCD450 (spherical graphite cast iron). In the vibration and cutting process acting on these two materials, the analysis was carried out to determine the value of applying the force as a finite element analysis under extreme conditions. We hope that using these analytical data will help students see and understand the structure of 5-axis machining rather than 5-axis cutting.

• Korean Journal of Family Social Work
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• no.57
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• pp.217-253
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• 2017

This study examines the process of developing and managing parent participation education programs, its performance, and its factor of deriving performance targeted on multi-cultural parents with children in early elementary school. Particularly, opinions of multi-cultural parents were considered and every process of developing and managing the program in this study was reflected. The analysed results were largely divided into three upper categories, which were 'growing as parents', 'forming new multi-culturalism', 'creating support system', and eight sub-categories. In addition, the factors that led to the positive achievement of program were appeared as 'development of active education program', 'organization and operation of parent inclusive program', 'utilization of flexible group structure', 'implementation of close interaction and communication between the members of the development team and the management team'. Based on the following results, we propose development and management process for effective multi-cultural parent education program.

• Journal of the Korean GEO-environmental Society
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• v.12 no.7
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• pp.5-12
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• 2011

When choosing the support pattern of tunnel, the characteristics of rock are identified from the result of the surface geologic survey, boring, and geophysical prospecting and laboratory test. And a rock mass rating is classified and excavation method and standard support pattern are designed considering rock classification, domestic and international construction practices, numerical analysis. According to the revised design standard for tunnel, it was recommended to classify the rock mass rating for the design of tunnel into a rating based on RMR. If necessary, it proposed a flexible standard allowed applying more atomized the rock mass rating and Q-System. Also, the resonable verification of the support pattern must be accompanied because the factors affecting the structure and behavior of ground during the construction of tunnel are the main factors of uncertainty factors such as the nature of ground, ground water and the characteristics of structural materials. These days, such verification method is getting more specialized and diversified. In this study, the empirical method, numerical analysis and comparative analysis of in situ measurements were used to prove the reasonableness in the support pattern by RMR and Q-value on the Imha Dam emergency spillway.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.5
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• pp.61-68
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• 2020

In this study, the international standard ISO TS 16774 Part 3 Test Method for Water (wash out) Resistance and KS F 4935 ｢Sealant Injection type for water leakage maintenance of adhesive flexible rubber asphalt series｣, which are standardized as a quality control method of injection type repair materials used for water leakage cracks in underground concrete structures, are currently used in Korea. As a result, considering the performance criteria of "mass change rate -0.1%" stipulated in KS F 4935, the remaining 13 types repair materials, excluding RG-2 of synthetic rubber and UG-1 of urethane, need to be reviewed for stabilization of the loss resistance due to the flow of ground water. The results of this study are determined to be available as a basic indicator for the selection of repair materials used for cracks in concrete structures. In addition, it is expected that the results of this study can be utilized as reference data that can be reflected in the improvement of the quality of repair materials that will be researched and developed later.

• International Journal of Naval Architecture and Ocean Engineering
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• v.13 no.1
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• pp.889-901
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• 2021

The tension of cables and motion response significantly affect safety of an immersed tunnel element in the immersion process. To investigate those, a hydrodynamic scale-model test was carried out and the model experiments was conducted under wind, current and wave loads simultaneously. The immersion standby (the process that the position of the immersed tunnel element should be located before the immersion process) and immersion process conditions have been conducted and illustrated. At the immersion standby conditions, the maximum force of the cables and motion is much larger at the side of incoming wind, wave and current, the maximum force of Element-6 (6 cables directly tie on the element) is larger than for Pontoon-8 (8 cables tie on pontoon of the element), and the flexible connection can reduce the maximum force of the mooring cables and motion of element (i.e. sway is expecting to decrease approximate 40%). The maximum force of the mooring cables increases with the increase of current speed, wave height, and water depth. The motion of immersed tunnel element increases with increase of wave height and water depth, and the current speed had little effect on it. At the immersion process condition, the maximum force of the cables decrease with the increase of immersion depth, and dramatically increase with the increase of wave height (i.e. the tension of cable F4 of pontoons at wave height of 1.5 m (83.3t) is approximately four times that at wave height of 0.8 m). The current speed has no much effect on the maximum force of the cables. The weight has little effect on the maximum force of the mooring cables, and the maximum force of hoisting cables increase with the increase of weight. The maximum value of six-freedom motion amplitude of the immersed tunnel element decreases with the increase of immersion depth, increase with the increase of current speed and wave height (i.e. the roll motion at wave height of 1.5 m is two times that at wave height of 0.8 m). The weight has little effect on the maximum motion amplitude of the immersed tunnel element. The results are significant for the immersion safety of element in engineering practical construction process.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.5
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• pp.310-316
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• 2021

Conventional satellites are generally large satellites that are multi-functional and have high performance. However, small satellites have been gradually drawing attention since the recent development of lightweight and integrated electric, electronic, and optical technologies. As the size and weight of a satellite decrease, the barrier to satellite development is becoming lower due to the cost of manufacture and cheaper launch. However, solar panels are essential for the power supply of satellites but have limitations in miniaturization and weight reduction because they require a large surface area to be efficiently exposed to sunlight. Space solar cells must be manufactured in consideration of various space environments such as spacecraft and environments with solar thermal temperatures. It is necessary to study structural materials for lightweight and high-efficiency solar cells by applying an unfolding mechanism that optimizes the surface-to-volume ratio. Currently, most products are developed and operated as solar cell panels for space applications with a triple-junction structure of InGaP/GaAs/Ge materials for high efficiency. Furthermore, multi-layered junctions have been studied for ultra-high-efficiency solar cells. Flexible thin-film solar cells and organic-inorganic hybrid solar cells are advantageous for material weight reduction and are attracting attention as next-generation solar cells for small satellites.

• Journal of the Korea Society of Computer and Information
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• v.28 no.3
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• pp.25-33
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• 2023

Noise generated during the acquisition and transmission of CT images acts as a factor that degrades image quality. Therefore, noise removal to solve this problem is an important preprocessing process in image processing. In this paper, we remove noise by using a deformable convolutional autoencoder (DeCAE) model in which deformable convolution operation is applied instead of the existing convolution operation in the convolutional autoencoder (CAE) model of deep learning. Here, the deformable convolution operation can extract features of an image in a more flexible area than the conventional convolution operation. The proposed DeCAE model has the same encoder-decoder structure as the existing CAE model, but the encoder is composed of deformable convolutional layers and the decoder is composed of conventional convolutional layers for efficient noise removal. To evaluate the performance of the DeCAE model proposed in this paper, experiments were conducted on CT images corrupted by various noises, that is, Gaussian noise, impulse noise, and Poisson noise. As a result of the performance experiment, the DeCAE model has more qualitative and quantitative measures than the traditional filters, that is, the Mean filter, Median filter, Bilateral filter and NL-means method, as well as the existing CAE models, that is, MAE (Mean Absolute Error), PSNR (Peak Signal-to-Noise Ratio) and SSIM. (Structural Similarity Index Measure) showed excellent results.

• Clean Technology
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• v.28 no.4
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• pp.278-284
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• 2022

This study presents an excellent planar heater based on low-dimensional composites. By optimizing the ratio of 1D carbon nanotubes (CNT) and 2D MXene (Ti₃C₂T_X), it is possible to create a planar heater that has superior electrical conductivity and high heat generation characteristics. Low-dimensional composites were prepared by mixing CNT paste and MXene solution with eco-friendly waterborne polyurethane (WPU). In order to find the optimal mixing ratio for the MXene-CNT-WPU composites, samples with MXene to CNT weight ratios of 3:1, 1:1, 1:3, 1:7, and 1:14 were investigated. In addition to these different weight ratios, 5 wt% WPU was equally applied to each sample. It was confirmed that the higher the weight ratio of CNT, the lower the sheet resistance and the higher the heating temperature. In particular, when the MXene-CNT-WPU planar heater was fabricated by mixing MXene and CNT at a weight ratio of 1:7 and 1:14, the heating temperature was higher than the heating temperature of a CNT-WPU planar heater. These characteristics are due to the optimized mixture of the 1D materials (CNT) and the 2D materials (MXene) causing the formation of a flat surface and a dense network structure. The low-dimensional composites manufactured with the optimized mixing ratios found in this study are expected to be applied in flexible electronic devices.

• Composites Research
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• v.34 no.6
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• pp.357-372
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• 2021

The energy harvesting device is known to be promising as an alternative to solve the resource shortage caused by the depletion of petroleum resources. In order to overcome the limitations (environmental pollution and low mechanical properties) of piezoelectric elements capable of converting mechanical motion into electrical energy, many studies have been conducted on a polymer matrix-based composite piezoelectric energy harvesting device. In this paper, the output performance and related applications of the reported piezoelectric composites are reviewed based on the applied materials and processes. As for the piezoelectric fillers, zinc oxide, which is advantageous in terms of eco-friendliness, biocompatibility, and flexibility, as well as ceramic fillers based on lead zirconate titanate and barium titanate, were reviewed. The polymer matrix was classified into piezoelectric polymers composed of polyvinylidene fluoride and copolymers, and flexible polymers based on epoxy and polydimethylsiloxane, to discuss piezoelectric synergy of composite materials and improvement of piezoelectric output by high external force application, respectively. In addition, the effect of improving the conductivity or the mechanical properties of composite material by the application of a metal or carbon-based secondary filler on the output performance of the piezoelectric harvesting device was explained in terms of the structure of the composite material. Composite material-based piezoelectric harvesting devices, which can be applied to small electronic devices, smart sensors, and medicine with improved performance, can provide potential insights as a power source for wireless electronic devices expected to be encountered in future daily life.