• Applied Chemistry for Engineering
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• v.24 no.2
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• pp.121-125
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• 2013

In this work, we prepared the carbon paper from chopped carbon fibers using a gas diffusion matrix in polymer electrolyte membrane fuel cells by wet processing. The process of making carbon paper using wet processing is consisted of the three steps involving the dispersion of chopped carbon fibers, the preparation of the carbon fiber web, the impregnating of phenol resin. This work was focused on finding the optimal surfactant to make the carbon paper with 2D orientation of carbon fibers by investigating the dispersion state of carbon fibers in different dispersion solutions. Furthermore, the effect of phenol resin and carbon black contents on properties of electric conductivity was analyzed. As a result, it is confirmed that the carbon fiber was well dispersed when using sodium dodecyl sulfate as a surfactant, and the carbon paper with 8 wt% of phenol and 5 wt% of carbon black contents showed the most excellent electrical property.

• Journal of the Korea institute for structural maintenance and inspection
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• v.8 no.2
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• pp.247-258
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• 2004

The composite shell element is developed for the solution of undamped forced vibration problem of composite curved panels. The finite element used in the current study is an 4-node enhanced assumed shell element with six degrees of freedom per node. The composite shell element is free of both shear and membrane locking phenomenon by using the enhanced assumed strain(EAS) method. A modification to the first-order shear deformation shell theory is proposed, which results in parabolic thorough-thickness distribution of the transverse shear strains and stresses. It eliminates the need for shear correction factors in the first order theory. Newmark's direct integration technique is used for carrying out the integration of the equation motion, to obtain the repones history. Parametric studies of curved composite panels are carried out for forced vibration analysis by geometrical shapes and by laminated composite; such as fiber orientation, stacking sequence.

• Composites Research
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• v.37 no.1
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• pp.40-45
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• 2024

In this research, we introduce a novel approach that employs a 3D convolutional neural network (CNN) model to predict the permeability of Gas Diffusion Layers (GDLs). For training the model, we create an artificial dataset of GDL representative volume elements (RVEs) by extracting morphological characteristics from actual GDL images obtained through X-ray tomography. These morphological attributes involve statistical distributions of porosity, fiber orientation, and diameter. Subsequently, a permeability analysis using the Lattice Boltzmann Method (LBM) is conducted on a collection of 10,800 RVEs. The 3D CNN model, trained on this artificial dataset, well predicts the permeability of actual GDLs.

• Journal of Korean Tunnelling and Underground Space Association
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• v.22 no.1
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• pp.91-105
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• 2020

This study is the basic study for improving the range of influence and potency of mixing bars in the chamber of Shield TBM. Currently, there are many studies on disk cutters, cutter bits and segments in the study of the domestic Shield TBM. However, studies that mix soil and rocks that come from the membrane during the Shield TBM excavation and scatter them with screw conveyors are not as good as those abroad. In this study, the existing Shield TBM Chamber was manufactured as a miniature and the experiment. Inside the chamber, different sizes (4 mm, 6 mm, 8 mm, 10 mm) and colors (black, white, red, and blue) were used to form layers. This experiment was carried out by different shapes and sizes of RPM and mixing bars. In addition, the difference between a miniature model and a reclining one was checked to determine the effect of the direction of gravity on the mixing efficiency. This was done in the same way for all other conditions other than differences in the direction of gravity. Through this experiment, we identified the orientation of the chamber model, the size and shape of the mixing bar inside, and the mixing effect and torque depending on RPM. A comparative review of the mixing effect and torque confirmed that the shape and size of the mixing bar affect the mixing of samples, and that the direction of gravity affects torque.

• Restorative Dentistry and Endodontics
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• v.13 no.2
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• pp.283-294
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• 1988

The purpose of this study was to investigate the characteristic features of the cells and tissues of the chronic periapical lesions using light microscope and electron microscope. Fifteen dental periapical lesions were obtained from the patients undergoing periapical surgery. Each specimen was divided into two parts along the tooth axis. One part was routinely processed for histopathologic examinations. 12 periapical lesions were diagnosed as granuloma and 3 periapical specimens as periapical cyst. The other part was fixed in 2.5% glutaraldehyde in 0.1M sodium cacodylate buffer at pH 7.4 and 1% osmic acid in same buffer. They were embedded in Epon 812. The semithin sections were used for the orientation of the lesions and the ultrathin sections were stained conventionally and examined with AEI Corynth 500 electron microscope. The results were as follows. 1. PMN and macrophages, which were dominant cell type, were scattered in small or large numbers throughout the central destructive area of granuloma. In the granulomatous area, plasma cells and lymphoytes were found in significant number and a lot of new capillary formation were revealed. Clefts caused by cholesterol were often seen in the connective tissue. Occasionally foam cells became collected in groups and epithelial proliferation were present. 2. In both granuloma and cyst, some plasma cells contained narrow cisternae of granular endoplasmic reticulum of which was tightly packed with electron dense materials, and other cells exhibited dilated profiles of granular endoplasmic reticulum. 3. In the area where plasma cells and lymphocytes were collected in groups, lymphocytes with well developed nucleolus and profuse cytoplasm were found and differentiating plasma cells were also present. 4. In the epithelial strands of the granulomatous area, epithelial cells contained enlarged endoplasmic reticulum, tonofilaments and ribosoms. Toward the intercellular space epithelial cells protruded a few microvilli. In the intercellular space, exudate-like electron dense materials, most of which was attached to the plasma membrane, appeared. 5. Some foam cells filled with numerous lipid droplets and others had lipid droplets and crystal-like structures. 6. Cyst epithelium consisted of bright cells and dark cells. The former had bright cytoplasm and small amounts of ribosoms, and the latter dark cytoplasm, many ribosoms, mitochondria and elongated microvilli. 7. Epithelial cells near the cyst lumen protruded a lot of long microvilli toward intercellular space and cyst lumen.