• The Journal of Engineering Geology
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• v.11 no.1
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• pp.81-99
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• 2001

In order to clarify an effect of the cutoff grouting, a series of field experiments were performed during construction of the waterway tunnel from the River Gilancheon(Andong) to the Youngcheon dam. The experiments were conducted in three different ways based on the grouting time in the construction sequence, i.e., the pre-grouting, after-grouting and consolidation grouting tests. And those were also planned to compare the efficiency of grouting in relation to the material types of grout, base rock types and other geologic factors such as discontinuities, depth and direction of grouting holes, and number of grouting stages. Among the materials of grout employed in the experiments, such as a common Portland cement, a micro-cement, a micro-cement with sodium silicate, and a urethane, the urethane was the most effective as the cutoff grouting. And for the same grout material, the pre-grouting was more effective to cutoff the water inflow comparing to the after-grouting and the consolidation grouting. For the rock types, the grouting efficiency in the sedimentary rocks as a base rock was less than the other rocks such as granite and volcanic rocks, which is believed due to the smaller separation of joints and the abundance of infilling materials in the joints developed in the sedimentary rocks. There was no direct relationship between the total RMR value of the rock mass and the grouting efficiency, however, the joint separation which is one of the RMR criteria is believed to have positive relation to the grouting efficiency. And the direction of the grouting holes might not so much affect on the grouting efficiency while increasing the number of grouting stage showed the better results.

• Journal of Radiation Protection and Research
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• v.30 no.2
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• pp.69-75
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• 2005

Gas avalanche microdetectors, such as micro-strip gas chamber (MSGC), micro-gap chamber (MGC), micro-dot chamber (MDOT), etc., are operated under high voltage to induce large electron avalanche signal around micro-size anodes. Therefore, the anodes are highly exposed to electrical damage, for example, sparking because of the interaction between high electric field strength and charge multiplication around the anodes. Gas electron multiplier (GEM) is a charge preamplifying device in which charge multiplication can be confined, so that it makes that the charge multiplication region can be separate from the readout micro-anodes in 9as avalanche microdetectors possible. Primary electron collection efficiency is an important measure for the GEM performance. We have defined that the primary electron collection efficiency is the fractional number of electron trajectories reaching to the collection plane from the drift plane through the GEM holes. The electron trajectories were estimated based on 3-dimensional (3D) finite element method (FEM). In this paper, we present the primary electron collection efficiency with respect to various GEM operation parameters. This simulation work will be very useful for the better design of the GEM.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.9
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• pp.623-629
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• 2017

Flow structure and mixing characteristics in a micro combustor with a multi-hole baffle were numerically studied using the Reynolds stress model. The multi-hole baffle has geometrical features to produce multiple three-dimensional vortices inside combustion chamber. When the thickness of the baffle's geometrical factors changes, variations of vortical structures occur variously. Among these vortices, the vortex generated from the fuel stream exerts a critical influence on the mixing enhancement. The three-dimensional vortical structure, in its development state, was strongly dependent on the baffle thickness. In particular, as the baffle thickness decreases to values less than the diameter of the fuel hole, the jet stream in baffle holes changes from the parabolic to saddleback profile type. The sizes of recirculation zones inside combustion chamber and the mixing state were closely affected by the structure of the jet streams.

• Science of Emotion and Sensibility
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• v.25 no.4
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• pp.45-52
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• 2022

Recently, interest in and demand for sensors that recognize physical activity and their products are increasing. In particular, the development of wearable materials that are flexible, stretchable, and able to detect the user's biological signals is drawing attention. In this study, an experiment was conducted to improve the dip-coating efficiency of a single-walled carbon nanotube dispersion solution after fine holes were made in a hydrophobic material with a micro needle. In this study, dip-coating was performed with a material that was not penetrated, and comparative analysis was performed. The electrical conductivity of the sensor was measured when the sensor was stretched using a strain universal testing machine (Dacell Co. Ltd., Seoul, Korea) and a multimeter (Keysight Technologies, Santa Rosa, CA, USA) was used to measure resistance. It was found that the electrical conductivity of a sensor that was subjected to needling was at least 16 times better than that of a sensor that was not. In addition, the gauge factor was excellent, relative to the initial resistance of the sensor, so good performance as a sensor could be confirmed. Here, the dip-coating efficiency of hydrophobic materials, which have superior physical properties to hydrophilic materials but are not suitable due to their high surface tension, can be adopted to more effectively detect body movements and manufacture sensors with excellent durability and usability.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.48 no.7
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• pp.521-524
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• 1999

Nb silicide was formed on the Si micro-tip arrays in order to improve field emission properties of Si-tip field emitter array. After silicidization of the tips, the etch-back process, by which gate insulator, gate electrode and photoresist were deposited sequentially and gate holes were defined by removing gradually the photoresist by $O_2$ plasma from the surface, was applied. Si nitride film was used as a protective layer in order to prevent oxygen from diffusion into Nb silicide layer and it was identified that the NbSi2 was formed through annealing in $N_2$ ambient at $1100^{\circ}C$ for 1 hour. By the Nb silicide coating on Si tips, the turn-on voltage was decreased from 52.1 V to 32.3 V and average current fluctuation for 1 hour was also reduced from 5% to 2%. Also, the fabricated Nb silicide-coated Si tip FEA emitted electrons toward the phosphor and light emission was obtained at the gate voltage of 40~50 V.

• Journal of ILASS-Korea
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• v.20 no.1
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• pp.43-52
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• 2015

Experimental study was conducted to investigate the effects of ultra-high injection pressure and nozzle hole diameter on diesel flow and spray characteristics. Electronically controlled ultra-high pressure fuel injection system was made to supply the fuel of ultra-high pressure consistently. Three injection pressures, 80, 160, and 250MPa were applied. Four type of injectors with identical eight nozzle holes were used. The four injectors have nozzle hole diameters of 115, 105, 95, and $85{\mu}m$ respectively. Injection quantity and rate were measured to investigate flow characteristics according to injection pressures and nozzle hole diameters. Mie-scattering and shadowgraph were performed to visualize liquid and vapor phases of diesel spray in a constant volume combustion chamber (CVCC). Ambient conditions of high pressure and high temperature in a diesel engine were simulated by using CVCC.

• Restorative Dentistry and Endodontics
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• v.11 no.1
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• pp.43-52
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• 1985

The purpose of this study was to measure the Micro-Knoop Hardness of three commercial visible light-cured composite resins (Plurafil-super, He1iosit and Durafi) according to the difference of depth and shade. Specimens of the resin were prepapared in plastic tubes 5mm in diameter with height of 5mm, and the tubes were put into the columned holes in stone molds. The molds were exposed to the visible light through the hole 5mm in diameter in metal plate. Specimens were sectioned (longitudinally) with disk. Knoop Hardness measurements were made at the depth of surface, 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0mm from the surface to the deep portion. Knoop Hardness numbers were taken on each depth under 20gm load for 10 seconds with Shimadzu Tester. The following results were: 1. The highest hardness value was measured at 0.5mm depth. Then the deeper the depth, the lesser the hardness was observed. 2. The value of hardness was directly propotional to the time of exposure to the light. 3. The hardness of light shade resin was higher than the that of the dark shade. 4. The pattern of hardness change at varying depth is similar to all the experimental materials with no relation to the shade nor exposure time.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.11a
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• pp.260-265
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• 2004

LTCC(Low temperature co-fired ceramic) is being recognized as a significant packaging material of electrical devices for the advantages such as relatively low temperature being needed for process, low conductor resistance and high printing resolution. In the process of LTCC electrical devices, the punched via-hole quality is one of the most important factors on the performance of the device. However, its mechanism is very complicated and optimization of the process seems difficult. In this paper, to clarify the process, via-hole punching experiments were carried out and the punched holes were examined in terms of their burr formation. The effects of thickness of PET sheet and ceramic sheet and punch-to-die clearance on via-hole quality were also discussed. Optimum process conditions are proposed and a factor k is introduced to express effect of the process variables.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.4
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• pp.717-725
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• 1989

An experimental investigation on the combustion behavior of pulverized coal particles was performed using the cross-section micrography techniques while sample coal particles were collected in-situ from the flow reactor. The coal particles were representative of pulverized bituminous coal undergoing a raped pyrolysis and combustion, however, quenched at the time when the particles were deposited onto a sample plate. The internal structure of coal was observed to change as deposited. Upon injection into a flow reactor, bituminous coal particles showed many holes which represented internal pore formation during the pyrolysis. The relative portion of the remaining matrix of coal was decreasing as the residence time progressed. This direct observation of cross-section of burning particles enabled better understanding of the coal combustion behavior.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.6
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• pp.591-597
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• 2001

Ti alloy is used for essential parts of aircraft for high temperature environment. Although Ti alloy has excellent performance in regard to mechanical properties, it is difficult ot find fatigue cracks by nondestructive ultrasonic inspection due to its two-phase microstructure, which consists of hard alpha and beta phases. Sound energy reflected from microstructural features in the component produces a background inspection noise which is seen even when no defects are present. This noise can inhibit the detection of critical internal defects such as pores cracks or inclusions. To obtain fundamental data on ultrasonic inspection of Ti alloy, ultrasonic testing was performed using a specimen with small drill holes and ultrasonic wave propagation velocites were measured.