• The korean journal of orthodontics
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• v.31 no.4 s.87
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• pp.467-477
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• 2001

This investigation was designed to determine the effects of wire size, bracket width and the number of bracket on bracket-wire dynamic frictional resistance during simulating arch wire-guided tooth movement in vitro. For simulation of an arch wire-guided tooth movement, we simulated tooth, periodontal ligament and cancellous bone. Maxillary premolar and 1st molar were simulated as real sized resin teeth, the simulated resin teeth which its root was coated by polyether impression material which its elastic modulus is similar to periodontal ligament were embedded in steel housing with inlay wax which its elastic modulus is similar to cancellous bone. Stainless steel wires in four wire size (0.016, 0.018, $0.016\;{\times}\;0.022,\;0.019\;{\times}\;0.025$ inch) were examined with respect to three (stainless steel) bracket widths (2.4, 3.0, 4.3mm) and the number of medium bracket(one, two, three) included in the experimental assembly under dry condition. The wires were ligated into the brackets with elastomeric module. The results were as follows : 1. In all the brackets, frictional resistance increased with increase in wire size. But, statistically similar levels of frictional resistance were observed between 0.018 inch and $0.016\;{\times}\;0.022$ inch wires in narrow bracket and also between 0.016 inch and 0.018 inch wire in wide backet. 2. The frictional forces produced by 0.016 inch wire were statistically similar levels in all the brackets. In 0.018 inch round wire, wide bracket was associated with lower amounts of friction than both narrow and medium brackets. In $0.016\;{\times}\;0.022,\;0.019\;{\times}\;0.025$ inch rectangular wire, wide bracket produced target friction than both narrow and medium brackets. In all the wirer, narrow and medium bracket demonstrated no statistical difference in levels of frictional resistance. 3. Frictional resistance increased with increase In number of medium bracket. 0.016 inch round wire demonstrated the greatest increment in frictional resistance, followed by $0.019\;{\times}\;0.025,\;0.016\;{\times}\;0.022$ inch rectangular wire which were similar level in increment of frictional resistance, 0.018 inch wire demonstrated the least increment. The increments of frictional resistance were not constantly direct proportion to number of bracket.

• Journal of Sericultural and Entomological Science
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• v.23 no.2
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• pp.37-49
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• 1982

Larvae of the silkworm (Bombyx mori L.) were reared during the 5th instar on the four kinds of artificial diets on the basis of the different amounts of soybean meal used as the protein source. In this experiment it was shown that the various levels of protein in the diet affected not only the growth and silk production but the digestibility of the diet. haemolymph protein and uric acid excretion. The results obtained are summarized as follows; 1. By an increase of the level of protein in the diet the apparant digestibility was increased. but the protein digestibility was comparatively decreased. 2. Larval body weight increment was not observed by the 3rd day of the 5th instar, but was increased from the 4th day as the level of protein was increased in the diet. 3. After the 3rd day of the 5th instar, protein content in the hemolymph was increased steeply by an increase of the protein content in the diet. However, the percentage of hemolymph protein to the ingested protein was decreased from the 2nd day of the 5th instar and increased more or less after the 4th day. 4. An increase of the uric acid excretion was observed as the content of protein in the diet was increased but the pattern of the uric acid excretion was different between high and low-protein diet. However, the percentage of the uric acid excretion to the ingested protein and to the hemolymph protein were both decreased steeply after the 2nd day of the 5th instar. 5. It was also evident that the high-protein diet increased the cocoon productivity. 6. It showed that the feed efficiency for body weight increment and silk formation was high by an increase of the level of protein in the diet, but the protein efficiency was not.

• The Journal of Korean Academy of Prosthodontics
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• v.46 no.5
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• pp.500-510
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• 2008

Statement of problem: Recently researches about WC/C (Tungsten Carbide/Carbon) or TiN (Titanium Nitride) coating on abutment screws are going on. It decreases friction coefficient, resistance against corrosion and withdrawal of physical fragility when the coating is applied to the metal surfaces. It is reported that coated abutment screws improved abrasion, adaptability and detorque force. Purpose: This study is about the effects of coated abutment screws on loosening of screw and for the purpose of solving the loosening phenomenon of abutment screws which is clinical problem. Material and methods: Detorque force and surface changes are compared when 10 times of repeated closing and opening are applied to both uncoated titanium abutment screws (Group A) and coated abutment screws with WC/C (Group B) and TiN (Group C). Each group was made up of 10 abutment screws. Results: 1. Before repeated closing and opening, Somewhat rough surface with regular direction was observed in Group A. Coated granules were observed in group B and group C and overall coated layer appeared in regular and smooth form. 2. Before repeated closing and opening, The coated surface showed bigger and thicker size of coated granules in Group C than Group B. 3. After repeated closing and opening, abrasion and deformation of abutment screw surface was observed in Group A and Group B. Exfoliation phenomenon was observed in Group B. 4. Group A showed biggest range of decrease when the weight changes of abutment screws were measured before and after repeated closing and opening. Group C showed less weight changes than Group B but there was no statistical difference between two groups. 5. Group B and Group C showed higher average detorque force than Group A and there was statistical difference. 6. Group A showed more prominent decrease tendency of average detorque force than Group B and Group C. Conclusion: Coated abutment screws with WC/C or TiN did not show prominent surface changes than uncoated titanium abutment screws even though they were repeatedly used. And they showed excellent resistance against friction and high detorque force. Thus it is considered that adaptation of WC/C or TiN coating on abutment screws will improve the screw loosening problem.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.6
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• pp.98-105
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• 2017

In this study, the fiber blending ratio and strain rate effect on the tensile behavior of hybrid fiber reinforced cement composite was evaluated. Hooked steel fiber and polyvinyl alcohol fiber were used for reinforcing fiber. The fiber blending ratio of HSF+PVA were 1.5+0.5, 1.0+1.0 and 0.5+1.5vol.%. As a results, the tensile strength, strain capacity and fracture toughness of the hooked steel fiber reinforced cement composites were improved by the increase of the bond strength of the fiber and the matrix according to increase of strain rate. However, the tensile stress sharply decreased after the peak stress because of the decrease in the number of straightened pull-out fibers by micro cracks in the matrix around hooked steel fiber. On the other hand, PVA fiber showed cut-off fracture at strain rate $10^{-6}/s$ with multiple cracks. However, at the strain rate $10^1/s$, the multiple cracks and strain capacity were decreased because of the pull-out fracture of PVA fiber. The HSF1.5PVA0.5 shown the highest tensile strength because the PVA fiber suppressed the micro cracks in the matrix around the hooked steel fiber and improved the pull-out resistance of hooked steel fiber. Thus, DIF of strain capacity and fracture toughness of HSF1.5PVA were greatly improved. In addition, the synergistic response of fracture toughness was positive because the tensile stress was slowly decreased after the peak stress by improvement of the pull-out resistance of hooked steel fiber at strain rate $10^1/s$.

• The Korean Journal of Mycology
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• v.29 no.1
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• pp.15-21
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• 2001

This study was conducted to investigate the immunomodulatory activities of proteoglycan extracted from cultured mycelia of Ganoderma lucidum IY009. The proteoglycan contained two polymer peaks, one was the higher MW peak of 2,000 kD and the other was low peaks of 12kD. To understand the part of strong pharmaceutical activity between two peak, the proteoglycan was separated by ultrafiltration and column chromatography and then examined the various pharmaceutical effects. High molecular weight fraction possesing high content of ${\beta}-linked$ glucan was exhibited high antitumor activity, against sarcoma 180 bearing ICR mouse. And also, anticomplementary activity was highly observed in high molecule fraction than low it fraction. When the raw 264.7 and murine peritoneal macrophage treated with low fraction, high fraction and other stimuli. The activities inducing tumor necrosis factor of the high factions were $2.2{\sim}2.5$ times stronger than that of low fraction.

• Journal of the Korean Geosynthetics Society
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• v.10 no.2
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• pp.73-79
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• 2011

Based on the results of Part 1 of our two-parts paper, the possibility on field applicability of CMDS(Coal Mine Drainage Sludge) mixed with bentonite and cement as a liner in landfill sites was investigated. The optimum moisture content that met the landfill liner condition was obtained when the ratio of CMDS: bentonite: cement was 1: 0.5: 0.3 in a lab-scale. The relative compaction was measured in 90.1%, which results for construction field have been generally acceptable. In this study, a large-scale Lysimeter($1.0m{\times}1.5m{\times}2.0m$) was used to simulate the effects of the layer on the freeze/thaw by -20 average temperature. The mixture after freezing/thawing showed compressive strength more than $5kg/cm^2$, which was satisfied with EPA standards. Initial permeability of CMDS was $7.10{\times}10^{-7}cm/s$ and permeability its mixture after freezing/thawing was increased to $9.80{\times}10^{-7}cm/s$. The change of temperature in the layers rises and falls with linear and temperature gradient keep maintain the present state. Moisture contents in the layers have not been radically changed. Through the leaching test determined by KSLT method, it was found that heavy metals excluding Zn and Ni were not leached out or leached out less than the standards during 7 cycles of freezing/thawing process. Since it shows the increased permeability about 1.5 times and slight change in moisture content, but it was satisfied with EPA standar through 7 cycles of freezing/thawing process, this mixture can be applied as a liner in landfill final cover system.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.3 no.3
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• pp.71-86
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• 1983

Current R.C. retaining wall design is bared on WSD, but the reliability based design method is more rational than the WSD. For this reason, this study proposes a reliability based design criteria for the cantilever retaining wall, which is most common type of retaining wall, and also proposes the theoretical bases of nominal safety factors of stability analysis by introducing the reliability theory. The limit state equations of stability analysis and design of each part of cantilever retaining wall are derived and the uncertainty measuring algorithms of each equation are also derived by MFOSM using Coulomb's coefficient of the active earth pressure and Hansen's bearing capacity formula. The levels of uncertainties corresponding to these algorithms are proposed appropriate values considering our actuality. The target reliability indices (overturning: ${\beta}_0$=4.0, sliding: ${\beta}_0$=3.5, bearing capacity: [${\beta}_0$=3.0, design for flexure: [${\beta}_0$=3.0, design for shear: ${\beta}_0$=3.2) are selected as optimal values considering our practice based on the calibration with the current R.C. retaining wall design safety provisions. Load and resistance factors are measured by using the proposed uncertainties and the selected target reliability indices. Furthermore, a set of nominal safety factors, allowable stresses, and allowable shear stresses are proposed for the current WSD design provisions. It may be asserted that the proposed LRFD reliability based design criteria for the R.C. retaining wall may have to be incorporated into the current R.C. design codes as a design provision corresponding to the USD provisions of the current R.C. design code.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2000.09a
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• pp.201-210
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• 2000

Rock bridge in rock masses can be considered as one of several types of opening-mode fractures, and also it has been known to have a great influence on the stability of structures in rock mats. In the beginning of researching a rock bridge it used to be studied only in characteristics of its behavior, as considering resistance of material itself. However the distribution pattern of rock bridges, which can affect the stability of rock structures, is currently researched with a fracture mechanical approach in numerical studies. For investigating the effect of rock bridges on the development pattern of hydraulic fractures, the author analyzed numerically the stress state transition in rock bridges and their phenomena with a different pattern of the rock bridge distributons. From the numerical studies, a two-crack configuration could be defined to be representative of the most critical conditions for rock bridges, only when cracks are systematic and same in their length and angle. Moreover, coalescence stresses and onset of propagation stresses could be known to increase with decreasing s/L ratio or increasing d/L ratio. The effect of pre-existing crack on hydraulic fracturing was studied also in numerical models. Different to the simple hydraulic fracturing modeling in which the fractures propagated exactly parallel to the maximum remote stress, the hydraulic fractures with pre-existing cracks dial not propagate parallel to the maximum remote stress direction. These are representative of the tendency to change the hydraulic fractures direction because of the existence of pre-existing crack. Therefore s/L, d/L ratios will be identical as a function effective on hydraulic fractures propagation, that is, the $K_{I}$ vague increase with decreasing s/L ratio or increasing d/L ratio and its magnification from onset to propagation increases with decreasing s/L ratio. The scanline is a commonly used method to estimate the fracture distribution on outcrops. The data obtained from the scanline method can be applied to the evaluation of stress field in rock mass.s.

• Tunnel and Underground Space
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• v.10 no.3
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• pp.447-456
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• 2000

Rock bridge in rock masses can be considered as one of several types of opening-mode fractures, and also it has been known to have a great influence on the stability of structures in rock mass. In the beginning of researching a rock bridge it used to be studied only in characteristics of its behavior, as considering resistance of material itself. However the distribution pattern of rock bridges, which can affect the stability of rock structures, is currently researched with a fracture mechanical approach in numerical studies. For investigating the effect of rock bridges on the development pattern of hydraulic fractures, the author analyzed numerically the stress state transition in rock bridges and their phenomena with a different pattern of the rock bridge distributions. From the numerical studies, a two-crack configuration could be defined to be representative of the most critical conditions for rock bridges, only when cracks are systematic and same in their length and angle. Moreover, coalescence stresses and onset of propagation stresses could be known to increase with decreasing s/L ratio or increasing d/L ratio. The effect of pre-existing crack on hydraulic fracturing was studied also in numerical models. Different to the simple hydraulic fracturing modeling in which the fractures propagated exactly parallel to the maximum remote stress, the hydraulic fractures with pre-existing cracks did not propagate parallel to the maximum remote stress direction. These are representative of the tendency to change the hydraulic fractures direction because of the existence of pre-existing crack. Therefore s/L, d/L ratios will be identical as a function effective on hydraulic fractures propagation, that is, the K$_1$ value increase with decreasing s/L ratio or increasing d/L ratio and its magnification from onset to propagation increases with decreasing s/L ratio. The scanline is a commonly used method to estimate the fracture distribution on outcrops. The data obtained from the scanline method can be applied to the evaluation of stress field in rock mass.

• The Journal of Engineering Geology
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• v.22 no.2
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• pp.145-155
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• 2012

The matric suction and volumetric water content of Jumunin standard sand with a relative density of 60% were measured using an Automated Soil-Water Characteristic Curve (SWCC) apparatus during both drying and wetting processes. The test time for the drying process was longer than that for the wetting process, because the flow of water is likely to be protected by air trapped in voids within the soils during the drying process. Based on the matric suction and volumetric water content, the SWCC was estimated using the model proposed by van Genuchten (1980). For the drying process, the unsaturated fitting parameters ${\alpha}$, n, and m were 0.399, 8.586, and 0.884, respectively; for the wetting process, the values were 0.548, 5.625, and 8.220, respectively. The hysteresis phenomenon occurred in the SWCCs, which means the SWCC of the drying process is not matched with the SWCC of the wetting process. Using these unsaturated parameters, we estimated the Suction Stress Characteristic Curve (SSCC), based on the relationship between suction stress and the effective degree of saturation. The suction stress showed a rapid decrease when the matric suction exceeds the Air Entry Value (AEV). Therefore, the effective stress of unsaturated soils is different from that of saturated soils when the matric suction exceeds the AEV. The suction stress of the drying process exceeds that of the wetting process for a given effective degree of saturation. The hysteresis phenomenon was also recognized in SSCCs. The hysteresis phenomenon of SSCCs arises from that of SWCCs, which is induced by the ink bottle effect and the contact angle effect. In the case of a sandy slope, the suction stress is positive and acts to enhance the slope stability as the water infiltrates the ground, but is negative when the suction stress exceeds the AEV. The results obtained for the wetting process should be applied in analyses of slope stability, because the process of water infiltration into ground is similar to the wetting process.