• Journal of the Korean Chemical Society
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• v.62 no.3
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• pp.191-202
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• 2018

The aim of this work is to study Monte Carlo simulation of ethylene (co)polymerization over Ziegler-Natta catalyst as investigated by Chen et al. The results revealed that the Monte Carlo simulation was similar to sum square error (SSE) model to prediction of stage II and III of polymerization. In the case of activation stage (stage I) both model had slightly deviation from experimental results. The modeling results demonstrated that in homopolymerization, SSE was superior to predict polymerization rate in current stage while for copolymerization, Monte Carlo had preferable prediction. The Monte Carlo simulation approved the SSE results to determine role of each site in total polymerization rate and revealed that homopolymerization rate changed from site to site and order of center was different compared to copolymerization. The polymer yield was reduced by addition of hydrogen amount however there was no specific effect on uptake curve which was predicted by Monte Carlo simulation with good accuracy. In the case of copolymerization it was evolved that monomer chain length and monomer concentration influenced the rate of polymerization as rate of polymerization reduced from 1-hexene to 1-octene and increased when monomer concentration proliferate.

• Journal of Pharmaceutical Investigation
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• v.27 no.3
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• pp.219-223
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• 1997

Terfenadine, antihistaminic drug, is poorly soluble in water. The purpose of this study is to investigate the possibility of using $terfenadine-{\beta}-cyclodextrin$ inclusion compound, instead of terfenadine, as the active substance of solid dosage form by improving the solubility, dissolution and anti-histaminic activity of terfenadine. The solubility and binding characteristics of $terfenadine-{\beta}-cyclodextrin$ complex in pH $1.2{\sim}6.8$ were investigated. Furthermore, the preparing method of $terfenadine-{\beta}-\;cyclodextrin$ inclusion compound was setting up and its physico-chemical characteristics such as DSC curve, solubility, dissolution and anti-histaminic activity were investigated. In conclusion, the solubility of terfenadine was increasing ${\beta}-cyclodextrin$ and with the decreasing pH. $Terfenadine-{\beta}-cyclodextrin$ inclusion compound, whose yield is almost 100%, was prepared by neutralization method. This inclusion compound was 200-times as soluble as terfenadine in pH 1.2-6.8. In addition, it had the faster dissolution and anti-histaminic activity than terfenadine. Therefore, it is used to the active substance of solid dosage form such as tablet and capsule in stead of terfenadine.

• International Journal of Aeronautical and Space Sciences
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• v.3 no.1
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• pp.9-18
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• 2002

Thermal humidity characteristics were considered theoretically and experimentally. A Simply well-fitted correlation of a saturated vapor pressure-temperature curve of water was introduced based on Antoine equation to make theoretical prediction of relative humidity according to temperature variation. Characteristics of dew point were also examined theoretically and its relation with temperature and humidity was evaluated. The exact mass of water vapor in a specified humidity and temperature condition was estimated to provide useful insight into the idea about how much amount of water corresponds to a specified humidity and temperature condition in a confined system. A simple but well-fitting model of dehumidification process was introduced to anticipate the trend of relative humidity level during GN2(gaseous nitrogen) purge process in a humidity chamber. Well-suitedness of this model was also verified by comparison with experimental data. The overall appearance and specification of two thermal humidity chambers were introduced which were used to perform various thermal humidity tests in order to yield useful data necessary to support validity of theoretical models.

• Journal of Mechanical Science and Technology
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• v.20 no.6
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• pp.819-827
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• 2006

The stress-strain relation of aluminum (Al) alloy foam cell wall was evaluated by the instrumented sharp indentation method. The indentation in a few micron ranges was performed on the cell wall of Al-alloy foam having a composition or Al-3wt.%Si-2wt.%Cu-2wt.%Mg as well as its precursor (material prior to foaming). To extract the stress-stram relation in terms of yield stress ${\sigma}_y$, strain hardening exponent n and elastic modulus E, the closed-form dimensionless relationships between load-indentation depth curve and elasto-plastic property were used. The tensile properties of precursor material of Al-alloy foam were also measured independently by uni-axial tensile test. In order to verify the validity of the extracted stress-strain relation, it was compared with the results of tensile test and finite element (FE) analysis. A modified cubic-spherical lattice model was proposed to analyze the compressive behavior of the Al-alloy foam. The material parameters extracted by the instrumented nanoindentation method allowed the model to predict the compressive behavior of the Al-alloy foam accurately.

• Journal of the Korean Society of Industry Convergence
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• v.24 no.5
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• pp.525-530
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• 2021

The purpose of this study was to investigate the effect of spherodizing heat treatment holding time on the microstructure and mechanical properties of the accelerated cooling-treated API X70 steel, which is mainly used as a structural material for line pipe steel for natural gas pipes. The accelerated cooling-treated API X70 steel was spherodizing treated at 700℃ for 12~48 h. The microstructure was observed using an OM and a FEG-SEM, and mechanical properties were obtained by tensile test. The microstructure of the API X70 steel was banded in the hot rolling direction, and the polygonal ferrite(PF) adjacent to pearlite(P) has mainly a fine size, and coarse PF and fine acicular ferrite were formed in the middle of P and P. As the spherodizing treatment time increased, the number of carbide particles decreased and its distribution interval increased, and the ferrite grain size was coarsened. The tensile strength decreased and the ductility increased with spherodizing treatment time, and the yield point elongation was disappeared in a stress-strain curve after the spherodizing treatment.

• Steel and Composite Structures
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• v.32 no.2
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• pp.199-212
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• 2019

This paper presents an investigation on seismic behavior of out-of-code Q690 circular high-strength concrete-filled thin-walled steel tubular (HCFTST) columns made up of high-strength (HS) steel tubes (yield strength $f_y{\geq}690MPa$). Eight Q690 circular HCFTST columns with various diameter-to-thickness (D/t) ratios, concrete cylinder compressive strengths ($f_c$) and axial compression ratios (n) were tested under the constant axial loading and reversed cyclic lateral loading. The obtained lateral load-displacement hysteretic curves, energy dissipation, skeleton curves and ductility, and stiffness degradation were analyzed in detail to reflect the influences of tested parameters. Subsequently, a simplified shear strength model was derived and validated by the test results. Finally, a finite element analysis (FEA) model incorporating a stress triaxiality dependent fracture criterion was established to simulate the seismic behavior. The systematic investigation indicates the following: compared to the D/t ratio and axial compression ratio, improving the concrete compressive strength (e.g., the HS thin-walled steel tube filled with HS concrete) had a slight influence on the ductility but an obvious enhancement of energy dissipation and peak load; the simplified shear strength model based on truss mechanism accurately predicted the shear-resisting capacity; and the established FEA model incorporating steel fracture criterion simulated well the seismic behavior (e.g., hysteretic curve, local buckling and fracture), which can be applied to the seismic analysis and design of Q690 circular HCFTST columns.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.6
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• pp.9-18
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• 2019

This study derives load characteristics and analyzes the safety of plowshares operating in dry fields. We mounted a three-blade, reversible plow on a 23.7 kW tractor and measured the plow's tractive force as well as the torque from the engine output shaft on the rear axle under various working speeds (L4, M1, M2, M3). We chose a Korean test site of Seomyeon, Chuncheon with sandy soil texture, as determined using the USDA method. We constructed the load spectrum for torque and tractive force using measured data and derived the fatigue life of the plowshare from a stress-cycle (S-N) curve of the plow material. Our results show that the M3 gear maximizes the driving shaft torque loads and, applying the tractive force load spectrum, creates a cumulative damage sum of $4.14{\times}10^{-5}$. Considering sampling time, we estimate a fatigue life of 805 hours while using the M3 gear. When using the other working speeds, however, all of the stress levels fell within the endurance limits and, therefore, our model predicts infinite plowshare lifetimes. For this analysis, we used a yield strength of 1,079 MPa for the plowshare and static safety factors, analyzed using the maximum stress, between 6.83 and 8.63 under each working speed.

• Geomechanics and Engineering
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• v.23 no.6
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• pp.575-585
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• 2020

In this numerical study, the 2D dynamic behavior of a clayey basin and its effect on damage pattern over basin edge are investigated. To attain this goal, a fully nonlinear time domain analysis method has been applied. Then, the fragility curves of the considered two typical industrial structures for that certain point are estimated using the acceleration time histories recorded at each surface point. The results show that the use of the damage related parameters in site effect analyses, instead of amplification curves, can yield more realistic estimation of the basin dynamic response. In a distance about 150 m from outcrop at the basin edge, the differences between fragility curves increase when increasing the distance from outcrop with respect to the reference rock site. Outside this region and towards the basin center, they tend to occur in rather single curves. Furthermore, to connect the structural damage to the basin edge effect, the earthquake demand value at different points for two typical structures was evaluated. It was seen that the probability of occurrence of damage increases over 250 m from outcrop, while the effect of the basin edge was limited to 150 m in case of the basin edge evaluation by using fragility curves.

• Advances in concrete construction
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• v.11 no.3
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• pp.193-206
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• 2021

Extensive research has been conducted on the basic mechanical property and structural applications of engineered cementitious composites (ECC). Despite the high tensile ductility and high toughness of ECC, transverse steel reinforcement is still necessary to confine ECC for high performance. However, limited research has examined performance of ECC confined with practical amount of transverse reinforcement. This paper presents the results of axial compression tests on 14 square ECC columns and 4 conventional concrete columns (used as control specimens) with transverse reinforcement. The test variables were spacing, configuration (square ties or square and diamond shape ties), and yield strength of stirrups. The test showed that ECC columns confined with steel stirrup had good compressive ductility, and the stirrup spacing had the greatest effect on the compressive performance. The self-confinement effect of ECC results in a more uniform but slower expansion of the whole column compared with CC ones. The test results are then compared against the predictions from a number of existing models for conventional confined concrete. It is indicated that these models fail to predict the axial strains at peak axial stress and the trend of the stress-strain curve of steel stirrups-confined ECC with sufficient accuracy. Several new equations are then proposed for the compressive properties of steel-confined ECC based on test results and potential approaches for future studies are proposed.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.1
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• pp.73-80
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• 2022

Sensors are applied to small aviation platforms for various purposes. Radio frequency (RF) antennas, which are representative sensors, are available in many forms but require the application of slot array RF antennas to ensure high performance and designation. Slot RF array antennas are applied to dip brazing techniques, but the yield and production time are determined by the proficiency of production personnel in a labor-intensive form. Unmanned aerial vehicles or drones, which are representative small aviation platforms, are continuously exposed to various random vibrations because propellers and multiple power sources are used in them. In this study, the fatigue life of slot array RF antennas applied with additive manufacturing was evaluated through the cumulative damage method (Miner's rule) in a vibration environment with a small aviation platform. For the evaluation, an S N curve obtained from a fatigue strength test was used.