• Journal of the Korean Society of Industry Convergence
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• v.23 no.4_2
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• pp.669-674
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• 2020

Liquid-phase-sintered (LPS) SiC materials were briefly examined with their microstructure and mechanical property. Especially, effect of high-temperature exposure on the tendency of fracture toughness of LPS-SiC were introduced. The LPS-SiC was fabricated in hot-press by sintering powder mixture of sub-micron SiC and sintering additives of Al₂O₃-Y₂O₃. LPS-SiC represented dense morphology and SiC grain-growth with some amount of micro-pores and clustered additives as pore-filling. The strength of LPS-SiC might affected by distribution of micro-pores. LPS-SiC tended to decrease fracture toughness depending on increasing exposure temperature and time.

• Polymer(Korea)
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• v.36 no.6
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• pp.685-692
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• 2012

Injection molding operation consists of phases of filling, packing, and cooling. The highest cavity pressure is involved in the packing phase among the operation phases. Thus the cavity pressure largely depends upon velocity to pressure (v/p) switchover timing and magnitude of packing pressure. Developed cavity pressure is directly related to stress concentration in the cavity of mold and it may cause a crack in the mold. Consequently control of cavity pressure is considered very important. In this study, cavity pressure was analyzed in terms of v/p switchover timing and packing pressure through computer simulation and experiment. Cavity pressure was increased as the v/p switchover timing was delayed. Residual pressure after cooling phase was observed when the v/p switchover timing was late, which was due to increased pressurizing time for long filling phase. Cavity pressure was increased proportionally with the packing pressure. Residual pressure after cooling phase was also observed, and it was increased with increasing packing pressure. High cavity pressure and residual pressure have been observed at late v/p switchover and high packing pressure. Compared with simulation and experimental results, the profiles of pressures were very similar however simulation could not predict residual pressure. Packing condition was important for the control of cavity pressure and the optimum condition could be set up using CAE analysis.

• Proceedings of the National Institute of Ecology of the Republic of Korea
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• v.2 no.2
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• pp.129-138
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• 2021

Living modified organisms (LMOs) are managed by seven government agencies according to their use in South Korea. The Ministry of Environment is responsible for LMOs used for environmental remediation. This study aimed to develop guidelines for assessing potential risks posed by transgenic plants used for remediation to insect ecosystems by investigating arthropod communities in sunflower fields. A total of 2,350 insects and spiders belonging to 134 species of 10 orders and 71 families were collected from sunflower fields over four growth stages ranging from anthesis to seed maturity. At the R3 phase of flower-bud formation, Chironomidae sp. of a decomposer insect guild presented the highest density, while Apis mellifera of a pollinator guild was the most abundant in the R5.8 phase of flowering. During the R7 seed-filling phase and the R9 phase of seed maturity, herbivorous Pochazia shantungensis predominated. During the R9 phase, richness and diversity indices of arthropod communities were distinctly lower whereas their dominance indices were significantly higher than those at other phases. In addition, the composition of arthropod communities was strongly correlated not only with the sampling date, but also with the sampling method depending on the growth stage of sunflowers. Our results suggest that appropriate sampling timing and methods should be considered in advance and that long-term field trials that cover a variety of environmental conditions should be carried out to evaluate potential risks to insect ecosystems.

• Journal of the Mineralogical Society of Korea
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• v.16 no.1
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• pp.49-63
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• 2003

Rare and unusual occurrence of hydrothermal minerals were found in Geode mine area. They are developed in the late stage of hydrothermal alteration of earlier skarns and later by the open-space filling crystallization. The alteration of earlier skarns of clinopyroxene, garnet, and plagioclase formed mainly chlorite or sometimes uncommon hydrothermal minerals of prehnite, illite, and pumpellyite. Open-space filling crystallization characterized by hydrothermal minerals developedin open sapce or good are prehnite, pumpellyite, clinozoisite, illite, and Ca-zeolites of stilbite annstellerite. Mineral phases and paragenesis are examined in detail by microscopy, XRD, SEM, and EPMA. Using the Schreinemaker's method, equibrium reactions among these minerals are establishedand isothemal-isobaric phase diagrams of $\mu$$H_2O$-$\mu$$CO_2$cot are plotted. Hydrothermal minerals such asprehnite, pumpellyite, clinozoisite, illite, and some chlorite were ffrmed under high partial pressure of $CO_2$with relatively low $H_2$O fugacity. Later, stilbite and calcite in association with illite crystallized under relatively both high partial Pressure of $CO_2$and high $H_2$O fugacity.

• Korean Journal of Agricultural Science
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• v.9 no.1
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• pp.269-274
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• 1982

These studies were conducted to evaluate the bulk pasteurization system in comparison with the conventional mushroom growing technique of and to establish the phase II fermentation method for the system. The results obtained were as follows. 1. From the mushroom compost peak-heated in the bulk pasteurization system higher mushroom yield was obtained than that of the conventional method. 2. The compost fermented in the bulk pasteurization system showed poor mycelial growth and low crop. It was caused by the imperfect blower and its operation, not by ununiform moisture content of the compost and ununiform filling. 3. A bulk pasteurization system which modified the mushroom house was not proper for the fermentation of the mushroom compost and the sporophore yields were lower than the standard pasteurization system. 4. In the bulk pasteurization system, peak-heating time, phase II period and quality of the compost were influenced by the air temperature but its effects were not more significant than those of the conventional method. 5. During phase II in the bulk pasteurization system moisture content of the compost at filling did not affect the fermentation of the compost.

• Restorative Dentistry and Endodontics
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• v.36 no.5
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• pp.377-384
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• 2011

Objectives: The purpose of this study was to observe the change in the viscoelastic properties of thermoplasticized injectable root canal filling materials as a function of temperature and to compare the handling characteristics of these materials. Materials and Methods: Three commercial gutta perchas and Resilon (Pentron Clinical Technologies) in a pellet form were heated in the Obtura-II system (Obtura Spartan) at $140^{\circ}C$ and $200^{\circ}C$, and the extrusion temperature of the thermoplasticized materials was measured. The viscoelastic properties of the materials as a function of temperature were evaluated using a rheometer. The elastic modulus G', viscous modulus G", loss tangent tan${\delta}$, and complex viscosity ${\eta}^*$ were determined. The phase transition temperature was determined by both the rheometer and a differential scanning calorimeter (DSC). The consistency of the materials was compared under compacting pressure at $60^{\circ}C$ and $40^{\circ}C$ by a squeeze test. Results: The three gutta perchas had dissimilar profiles in viscoelastic properties with varying temperature. The phase transition of softened materials into solidification occurred at $40^{\circ}C$ to $50^{\circ}C$, and the onset temperatures obtained by a rheometer and a DSC were similar to each other. The onset temperature of phase transition and the consistency upon compaction pressure were different among the materials (p < 0.05). Resilon had a rheologically similar pattern to the gutta perchas, and was featured between high and low-flow gutta perchas. Conclusions: The rheological characteristics of the thermoplasticized root canal filling materials changed under a cooling process. The dissimilar viscoelastic properties among the materials require different handling characteristics during an injecting and compacting procedure.

• Journal of Korea Foundry Society
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• v.37 no.5
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• pp.148-156
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• 2017

The effects of minor additives on the casting properties of AC4A aluminum alloys were investigated. Measurements of the cooling curve and microstructure observations were conducted to analyze the effects of Ti-B and Sr minor elements during the solidification process. A fine grain size and an increase in the crystallization temperature for the ${\alpha}-Al$ solution were evident after the addition of 0.1wt% Al-5%Ti-1%B additive. The modification effect of the eutectic $Mg_2Si$ phase with the addition of 0.05% Al-10%Sr additive was prominent. A fine eutectic $Mg_2Si$ phase and a decrease in the growth temperature of the eutectic $Mg_2Si$ phase were evident. Fluidity, shrinkage and solidification-cracking tests were conducted to evaluate the castability of the alloy. The combined addition of Al-5%Ti-1%B and Al-10%Sr additives showed the maximum filling length owing to the effect of the fine ${\alpha}-Al$ grains. The macro-shrinkage ratio increased, while the micro-shrinkage ratio decreased with the combined addition of Al-5%Ti-1%B and Al-10%Sr additives. The macro-shrinkage ratio was nearly identical, while the micro-shrinkage ratio increased with the addition of the Al-10%Sr additive. The tendency of the occurrence of solidification cracking decreased owing to the effect of the fine ${\alpha}-Al$ grains and the modification of the $Mg_2Si$ phase with the combined addition of Al-5%Ti-1%B and Al-10%Sr additives.

• Geomechanics and Engineering
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• v.12 no.5
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• pp.863-870
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• 2017

With the increasing interest in using bacterial biofilms in geo-engineering practices, such as soil improvement, sealing leakage in earth structures, and hydraulic barrier installation, understanding of the contribution of bacterial biofilm formation to mechanical and hydraulic behavior of soils is important. While mechanical properties of soft gel-like biofilms need to be identified for appropriate modeling and prediction of behaviors of biofilm-associated soils, elastic properties of biofilms remain poorly understood. Therefore, this study investigated the microscale Young's modulus of biofilms produced by Shewanella oneidensis MR-1 in a liquid phase. The indentation test was performed on a biofilm sample using the atomic force microscopy (AFM) with a spherical indentor, and the force-indentation responses were obtained during approach and retraction traces. Young's modulus of biofilms was estimated to be ~33-38 kPa from these force-indentation curves and Hertzian contact theory. It appears that the AFM indentation result captures the microscale local characteristics of biofilms and its stiffness is relatively large compared to the other methods, including rheometer and hydrodynamic shear tests, which reflect the average macro-scale behaviors. While modeling of mechanical behaviors of biofilm-associated soils requires the properties of each component, the obtained results provide information on the mechanical properties of biofilms that can be considered as cementing, gluing, or filling materials in soils.

• 한국금형공학회:학술대회논문집
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• 2008.06a
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• pp.163-166
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• 2008

Injection molding operation consists of filling, packing, and cooling phase. The highest pressure is involved during the packing phase among the operation phases. Cavity pressure depends upon velocity to pressure switchover time and magnitude of packing pressure. The cavity pressure is directly related to stress concentration in the cavity of mold. Thus the observation and control of cavity pressure is very important to prevent mold cracking. In this study, cavity pressures were observed for operational conditions using the commercial CAE software,Moldflow. Operational conditions were velocity to pressure switchover time and packing pressure. Cavity pressures were also measured directly during injection molding. Simulation and experimental results showed good agreement.

• Journal of Drive and Control
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• v.17 no.3
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• pp.47-56
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• 2020

As a shift control of automatic transmission was managed with the electronic control unit (ECU), shift quality which is a measure of shift shock during gear change has markedly improved. However, the initial clutch pressure control of the clutch filling phase should continue to rely on the predetermined control input since the input and output speeds are unchanged until the shifting process attains the inertia phase. It is critical to minimize the clutch response time and control the clutch pressure accurately at the end of clutch fill to achieve quick shift response and smoothness. Advanced transmission companies have adopted an auto calibration method which establishes the databases for the clutch piston fill-up attributes and the frictional characteristics of the disks. In this study, a distinctive auto calibration algorithm for forklift transmission under development is proposed and verified with the real-vehicle test. The experimental calibration results showed consistent turbine dynamics at the initial stage of shifts with the properly calibrated clutch-fill control parameters. By using this technique, it is necessary to finalize the shift control for the various operation conditions.