• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.9
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• pp.1606-1611
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• 2008

Recently, The diagnosis techniques of electric facilities are developed on live line. This paper describes the discharge characteristics of polymer insulator(EPDM A type). Keeping the facilities in good working order, the goal of this paper will provide the information to enable user to easily judge conditions of facilities on the spot. The performance of polymer insulator is assessed from the KS C IEC 60270 and CEA LWIWG-01(96)(Tracking Wheel Test). As the results, UV generation patterns of polymer insulator grow like a jellyfish shape follow the ramping voltage. Discharging UVs are detected at about 31.25% of breakdown voltage. Just then, dimension of UV image is about $0.84cm^{2}$. The dimension of max. UV image is about $297.4cm^{2}$ at $160kV(V_{bd})$. The position of UV generation due to surface discharge of polymer insulator is the center of insulator in the early, then moved the ground side and the last, UV image moved through the junction part of source side. Surface of aged polymer insulator is cracked and faded due to arc. UV absorption spectrum of polymer insulator are appeared the C-H bond of scissoring vib. at $1014cm^{-1}$ and C=O bond of recombination structure. Also, recombined UV absorption peak such as C-H, N-H, and O-H is detected at the $3321cm^{-1}$. Through the paper, there are inspection data which are the relations between surface discharge of polymer insulator and UV detecting image.

• Journal of the Korean Society for Nondestructive Testing
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• v.37 no.1
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• pp.29-36
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• 2017

Recently, KTX (Korean Train Express) train stoppage accidents were mainly caused by malfunctioning equipment, aging and cracking of railway vehicles, crack breakages of brake disks, and breakages of brake disks. Breakage of brake disk can cause large-scale casualties such as high-speed collision and concern about derailment by hitting lower axle and wheel. Therefore, in this study, a brake disk with solid and ventilation type, which is the brake disk of a KTX train was modeled, and a dynamometer system was constructed to operate the disk. A Rayleigh wave was used to inspect the surface of the brake disk. An ultrasonic inspection module was developed for the brake disk by using a local immersion method due to the difficulty involved in ultrasonic inspection using an existing immersion method. In addition, the surface defects of the brake disk were evaluated using a dynamometer mock-up system and an ultrasonic inspection module of the brake disk.

• Bulletin of the Korean Chemical Society
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• v.34 no.2
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• pp.447-452
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• 2013

In this study we report a new method for the synthesis of a silica monolithic column bed with bimodal pores (throughpores and mesopores). The template induced synthesis method was used to direct bimodal pores simultaneously instead of the usual post base-treating method. Block polymer Pluronic F127 was chosen as a dual-function template to form hierarchically porous silica monolith with both macropores and mesopores. This is a simplification of the method of monolithic column preparation. Poly(ethylene glycol) was used as a partial substitute for F127 can effectively prevent shrinkage during the monolith aging process without losing much surface area (944 $m^2/g$ to 807 $m^2/g$). More importantly, the resultant material showed a much narrower mesopore size (centered at 6 nm) distribution than that made using only F127 as the template reagent, which helps the mass transfer process. The solvent washing method was used to remove the remaining organic template, and it was proved to be effective enough. The new synthesis method makes the fabrication of the silica monolithic column (especially capillary column) much easier. All the structure parameters indicate that monolith PFA05 prepared by the above method is a good material for separation, with the merits of much higher surface area than usual commercial HPLC silica particles, suitable mesopore volume, narrow mesopore size distribution, low shrinkage and it is easily prepared.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.18 no.2
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• pp.104-113
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• 2019

The road management institute needs lots of cost to repair road surface damage. These damages are inevitable due to natural factors and aging, but maintenance technologies for efficient repair of the broken road are needed. Various technologies have been developed and applied to cope with such a demand. Recently, maintenance technology for road surface damage repair is being developed using image information collected in the form of a black box installed in a vehicle. There are various methods to extract the damaged region, however, we will discuss the image recognition technology of the deep neural network structure that is actively studied recently. In this paper, we introduce a new neural network which can estimate the road damage and its location in the image by region-based convolution neural network algorithm. In order to develop the algorithm, about 600 images were collected through actual driving. Then, learning was carried out and compared with the existing model, we developed a neural network with 10.67% accuracy.

• Tribology and Lubricants
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• v.37 no.5
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• pp.189-194
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• 2021

A straightforward, yet effective surface modification method of stainless steel mesh and its interesting anti-wetting characteristics are reported in this study. The stainless steel mesh is electrochemically etched, and the specimen has both micro and nano-scale structures on its surface. This process transforms the two types of mesh specimens known as the regular and dense specimens into hydrophobic specimens without applying any hydrophobic chemical coating process. The fundamental wettability of the modified mesh is analyzed through a dedicatedly designed experiment to investigate the waterproof characteristics, for instance, the penetration threshold. The waterproof characteristics are evaluated in a manner that the modified mesh resists as high as approximately 2.7 times the pressure compared with the bare mesh, i.e., the non-modified mesh. The results show that the penetration threshold depends primarily on the advancing contact angles, and the penetration stop behaviors are affected by the contact angle hysteresis on the surfaces. The findings further confirm that the inexpensive waterproof meshes created using the proposed straightforward electrochemical etching process are effective and can be adapted along with appropriate designs for various practical applications, such as underwater devices, passive valves, and transducers. In general, , additional chemical coatings are applied using hydrophobic materials on the surfaces for the applications that require water-repelling capabilities. Although these chemical coatings can often cause aging, the process proposed in this study is not only cost-effective, but also durable implying that it does not lose its waterproof properties over time.

• The Journal of Advanced Prosthodontics
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• v.16 no.2
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• pp.115-125
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• 2024

PURPOSE. The purpose of this in vitro study was to investigate the fracture resistance, surface hardness, and color stain of 3D printed, CAD-CAM milled, and conventional interim materials. MATERIALS AND METHODS. A total of 80 specimens were fabricated from auto polymerizing polymethyl methacrylate (PMMA), bis-acryl composite resin, CAD-CAM polymethyl methacrylate resin (milled), and 3D printed composite resin (printed) (n = 20). Forty of them were crown-shaped, on which fracture strength test was performed (n = 10). The others were disc-shaped specimens (10 mm × 2 mm) and divided into two groups for surface hardness and color stainability tests before and after thermal cycling in coffee solution (n = 10). Color parameters were measured with a spectrophotometer before and after each storage period, and color differences (CIEDE2000 [DE00]) were calculated. The distribution of variables was measured with the Kolmogorov Smirnov test, and one-way analysis of variance (ANOVA), Tukey HSD, Kruskal-Wallis, Mann-Whitney U tests were used in the analysis of quantitative independent data. Paired sample t-test was used in the analysis of dependent quantitative data (P < .05). RESULTS. The highest crown fracture resistance values were determined for the 3D printed composite resin (P < .05), and the lowest were observed in the bis-acryl composite resin (P < .05). Before and after thermal cycling, increase in mean hardness values were observed only in 3D printed composite resin (P < .05) and the highest ΔE₀₀ value were observed in PMMA resin for all materials (P < .05). CONCLUSION. 3D printing and CAD-CAM milled interim materials showed better fracture strength. After the coffee thermal cycle, the highest surface hardness value was again found in 3D printing and CAD-CAM milled interim samples and the color change of the bis-acryl resin-based samples and the additive production technique was higher than the PMMA resin and CAD-CAM milled resin samples.

• Polymer(Korea)
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• v.39 no.3
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• pp.403-411
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• 2015

A series of hydrophobically associating fluorinated amphiphilic polyacrylamide copolymers with remarkably high heat resistance and salt tolerance were synthesized by free radical micellar copolymerization, using acrylamide (AM) and sodium 2-acrylamido-tetradecane sulfonate ($AMC_{14}S$) as amphiphilic monomers, and 2-(perfluorooctyl) ethyl acrylate (PFHEA) as hydrophobic monomer. The structure of the terpolymer was characterized by FTIR, $^1H$ NMR and $^{19}F$ NMR. The solution properties of the terpolymers were investigated in details, and the results showed that the terpolymer solution had strong intermolecular hydrophobic association as the concentration exceeded the critical association concentration 1.5 g/L. The terpolymer solution possessed high surface activity, viscoelasticity, excellent heat resistance, salt tolerance and shearing resistance. The viscosity retention rate of copolymer solution was as high as 59.9% under the condition of fresh wastewater, $85^{\circ}C$ and a 60-days aging test.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.47 no.4
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• pp.127-135
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• 2015

Artists have been used animal glues for a long time as binding and sizing materials of paintings in many countries including Korea. Since animal glues as a binding material lose their own adhesive strength by aging, pigment particles or pigment layers are easily detached from painting surface. Restaurators prefer to use animal glues for consolidation of pigment particles or pigment layers because artists use animal glues as a binder for their painting works. It is widely known that animal glues have different characteristics such as viscosity, stability on water etc. But there are still a few requirements to consider their stabilities for the restoration of paintings. Therefore, this study was aimed to evaluate of stability and efficiency of animal glue applications. The efficiency of animal glue application was decreased with increasing the concentration of animal glue solution. This result means the simple tendency, but does not representative data for other animal glues made from same raw materials. In most cases, the surface and mechanical characteristics of animal glues are dependent on some factors, like viscosity and concentration of animal glue solution.

• Journal of the Korean Ceramic Society
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• v.44 no.3 s.298
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• pp.162-168
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• 2007

Silica wet gels were prepared ken water glass ($29\;wt%\;SiO_{2}$) by using Amberlite as a ion exchange resin. After washing in distilled water, the wet gels were further aged in a solution of TEOS/EtOH to strengthen of 3-dimensional network structure. As increase TEOS content in aging solution, BET surface area and porosity of the ambient dried silica aerogels were significantly decreased, and average pore diameter was also decreased 30 nm to -10 nm. Also, higher density and compressive strength were obtained in case of higher TEOS content. This is due to precipitation of $SiO_{2}$ nano particles by TEOS. Hence, TEOS addition plays an important role of both strengthening and stiffness of silica wet gel network. By adding over 30 vol% TEOS, a crack-free monolithic silica aerogel tiles were obtained and its density, compressive strength, and thermal conductivity were shown $0.232g/cm^{3}$, 7.3 MPa, and 0.029 W/mk, respectivly.

• Economic and Environmental Geology
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• v.45 no.2
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• pp.205-215
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• 2012

Metal ions, toxic or potentially toxic to biota and human beings, can be immobilized by sorption onto the mineral surfaces in soils and sediments. This article briefly explains theories regarding the chemical properties of mineral surfaces to sorb metal ions and processes of extended X-ray absorption fine structure (EXAFS) analysis for sorption study, and reviews atomic-scale findings on metal sorption on mineral surfaces. The theoretical understanding on the chemistry of mineral surfaces and metal sorption is fundamental to the proper analysis of the atomic-scale spectroscopy to determine the sorption phases. Atomic-scale findings on metal sorption phases discussed here include co-precipitation, ternary complexation, aging effects, and desorption possibilities, as well as outer-sphere complexation, inner-sphere complexation, and surface precipitation.