• Journal of the Korean Society of Propulsion Engineers
• /
• v.14 no.6
• /
• pp.31-37
• /
• 2010

This study was carried out to investigate the thermal decomposition and execute EIDS slow cook-off test for the propellant ingredients and 2 kinds of HTPE propellants. The thermal analysis of the propellant ingredients used in this study showed that the thermal stability of these materials decreases in the following order : AP > HTPE > AN > BuNENA. In addition, propellant HTPE 002 containing AN showed that an endothermic process at around $125^{\circ}C$ corresponding to the solid phase change(II$\rightarrow$I) of AN was followed by the exothermic process of BuNENA/AN mixture up to $200^{\circ}C$. In EIDS slow cook-off tests, HTPE 001 and HTPE 002 reacted at around $250^{\circ}C$ and $152^{\circ}C$ respectively, and both of them showed sudden temperature increase curves at $115^{\circ}C$. The critical temperatures, $T_c$, of thermal explosion for the propellants HTPE 001 and HTPE 002, were obtained from both the non-isothermal curves at various heating rates and Semenov's thermal explosion theory. Kissinger's method that was used to calculate $T_c$ was also employed to obtain the activation energies for thermal decompositions.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.22 no.1
• /
• pp.57-63
• /
• 2012

$Al_2TiO_5$ ceramics were sintered by a solid-state reaction. LAS (${\beta}$-spodumene) and $Fe_2O_3$ were added to the $Al_2TiO_5$ composition for enhancement of sintering behavior such as mechanical strength and thermal shock resistance. The sintered body was much densified by addition of LAS and $Fe_2O_3$ because LAS formed the liquid-phase and $Fe_2O_3$ suppressed the grain growth. We have systematically investigated the sintering characteristics, microstructures, mechanical properties, and thermal shock resistance according to the change of the amount of additive. When the additive of LAS (20 wt%)-$Fe_2O_3$ was added to $Al_2TiO_5$, it confirmed that superior mechanical properties of the fracture strength of over 120 MPa and the thermal shock resistance of over $1,200^{\circ}C$ were achieved.

• Journal of the Korean GEO-environmental Society
• /
• v.19 no.10
• /
• pp.21-26
• /
• 2018

Soil-water characteristic curve, which is called soil retention curve, is required to explore water flows in unsaturated soils, relative permeability of water in multi-phase fluids flow, and change to stiffness and volume of soils. Thus, the understanding of soil-water characteristic curves of soils help us explore the behavior of soils inclduing fluids. Biopolymers are environmental-friendly materials, which can be completely degraded by microbes and have been believed not to affect the nature. Thus, various biopolymers such as deacetylated power, polyethylene oxide, xanthan gum, alginic acid sodium salt, and polyacrylic acid have been studies for the application to soil remediation, soil improvement, and enhanced oil recovery. PAA (polyacrylic acid) is one of biopolymers, which have shown a great effect in enhanced oil recovery as well as soil remediation because of the improvement of water-flood performance by mobility control. The study on soil-water characteristic curves of sandy soils containing PAA (polyacrylic acid) has been conducted through experimentations and theoretical models. The results show that both capillary entry pressure and residual water saturation dramatically increase according to the increased concentration of PAA (polyacrylic acid). Also, soil-water characteristic curves by theoretical models are quite well consistent with the results by experimental studies. Thus, soil-water characteristic curves of sandy soils containing biopolymers such as PAA (polyacrylic acid) can be estimated using fitting parameters for the theoretical model.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.22 no.2
• /
• pp.155-169
• /
• 2002

The objective of this study was to investigate the effect of crack opening and closure in the AE activities during fatigue test. Laboratory experiment using various materials and test conditions were carried out to identify AE characteristics of fatigue crack propagation. Compact tension specimens of 2024-T4 and 6061-T6 aluminum alloy were prepared for fatigue test. AE activities were analyzed based on the phase of the loading cycle. Generally, most of AE were generated when the crack begins' opening and the crack closes fully, whereas a few in the pull opening of the crack. Also AE activity in the peak loading of cycle was different with each specimen. However, in the same material, AE activity was not affected by the change of cyclic frequency (0.1, 0.2, 1.0Hz). It was found that AE activities during crack opening and closure depend on material properties such as micro-structure, tensile strength and yield strength.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.14 no.6
• /
• pp.2596-2603
• /
• 2013

The precision and endurance of tire mold are very important factors to decide the quality of tire. However, the investigation on the thermal deformation of tire mold has a lot of trouble because the tire mold is produced in airtight permanent casting material. In this study, the thermal deformations such as temperature, displacement and stress distributions inside the AC7A tire mold casting material were analyzed by numerical analysis according to the preheating temperature of permanent casting device. In order to verify the results of numerical analysis, the experiments for temperature measurement of the AC7A casting material were carried out under the same condition with numerical analysis. For the numerical analysis, "COMSOL Multiphysics" was used. The preheating temperatures were set up $150^{\circ}C$, $200^{\circ}C$, $250^{\circ}C$ and $300^{\circ}C$, respectively. The thermal deformations were calculated in each case. When the preheating temperature is $300^{\circ}C$, displacement and stress are the lowest with 0.25mm and 0.351GPa, but the temperature is the highest with $374.27^{\circ}C$. When the experimental results were compared with the numerical results, there were some temperature differences because of the latent heat by phase change heat transfer. However, the cooling patterns were almost similar except for the latent heat section.

• Journal of the Korean Society of Food Science and Nutrition
• /
• v.34 no.9
• /
• pp.1471-1476
• /
• 2005

The optimization of ethanol treatment was carried out by response surface methodology (RSM) which was expressed through change of ${\Delta}$E value for improvement of color of dried large anchovy. The optimum condition was shown as treatment with 7 volumes (v/m) of ethanol at $50^{\circ}C$ for 9 hrs. At this condition, the removal rates of trimethylamine (TMA) and fat considered as fishy odor-causing materials were 81.1 and $77.4\%$, respectively, when analyzed by solid phase microextraction (SPME)/gas chromatography and soxhlet method, respectively The effect of citric acid on the removal rate of TMA was the highest one among organic acid treatments. The removal rate of TMA was affected greatly by the concentration of organic acid rather than the temperature and time of treatment. $73\%$ of TMA was removed by treatment of $1\%$ of citric acid at $20^{\circ}C$ for 20 min. Specially, above $90\%$ of TMA could be removed by the combination of alcohol and citric acid treatment. In vitro absorption rate of calcium was also increased to $12.3\%$ by the combination of alcohol and citric acid treatment compared with $2.9\%$ of control.

• Journal of the Society of Cosmetic Scientists of Korea
• /
• v.39 no.1
• /
• pp.65-73
• /
• 2013

Lip make-up products can be easily taken into body with food. For this reason, those products are requires to meet lots of qualifications compared with other cosmetic products. In addition, concerns about safety on synthesized tar pigments is constantly issued. Thus, demand of natural pigments is gradually increased and many kinds of natural pigments have been developed. However, there are some problems when natural pigments are applied to cometic products instead of synthetic ones. There is a reason that most of natural pigments consist of hydrophilic materials of sort of anthocyanin, but the existing lip make-up products is anhydrous oil dispersion type without water consisting oil and wax. Therefore, when watersoluble natural pigments are applied to anhydrous lip make-up products, color expression is lower and phase separation occurs due to the instability of the product. In addition, natural pigments have disadvantages that they can easily change by pH, heat and sunlight. There are troubles of stability because it is not easy to adjust for these factors in case of anhydrous forms. Aim of study is to develop lip make-up products which have not only safe to human but being high in expression of color by using natural pigments and securing stability of colorant as natural pigments are offered to polyol in oil emulsion. Then, lip make-up products which have heavy moisture while having not dryness that is created when the moisture evaporates are developed.

• Clinics in Shoulder and Elbow
• /
• v.10 no.2
• /
• pp.167-174
• /
• 2007

Purpose: We evaluated calcium resolution and clinical improvement of calcific tendinitis after conservative and arthroscopic treatment. Materials and Methods: We reviewed 126 patients of calcific tendinitis treated from January, 2002 to April, 2005. Average age was 53 and female dominant in 77% of the cases. Calcium deposits were involved in supraspinatus tendon in 84% of the cases. We compared clinical changes for 64 cases treated with injection, and 12 cases treated by arthroscopic decompression with 6 month follow-up. Results: 77%(49/64) of the cases with steroid injection showed symptom improvement. Even though complete resolution of calcific deposit occurred in 36%(23/64), incomplete resolution in 17%(11/64) and no change in 47%(30/64), Pain was relieved in 87%(20/23), 82%(9/11) and 67%(20/30), respectively. With arthroscopic treatment, calcium deposit completely resolved in 83%(10/12), and all cases showed pain free motion after 6 months. Conclusion: Conservative treatment with steroid injection was effective for acute pain in resorptive phase. In cases of arthroscopic treatment, there was no need for complete removal of calcium deposit during the procedure, but clinical symptoms improved with resolution of the deposit.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.31 no.5
• /
• pp.218-227
• /
• 2021

A thick film NTC thermistor for low temperature co-firing was manufactured by printing and sintering a paste prepared using NTC powder of Mn_1.5Ni_0.4Co_0.9Cu_0.4O₄ composition, lead free frit, and RuO₂ on a 96 % alumina substrate. The effect of frit and RuO₂ on the electrical properties of thick film NTC thermistor was studied. The resistance of the thick film NTC thermistor was higher than that of the bulk phase sintered at the same temperature, but it was found that the negative resistance temperature characteristic appeared more clearly and linearly in the resistance - temperature characteristic. On the other hand, the area resistance decreased as the sintering temperature increased, and the area resistance increased as the amount of frit added increased. The B constant of the thick film NTC thermistor was 3000 K or higher. Among them, it was found that the B constant of the thick film NTC thermistor made of paste with 5 wt% of frit added and sintered at 900℃ showed the highest B constant. Also, it can be seen that the area resistance decreased with the addition of RuO₂, and the change in the area resistance decrease of the thick film NTC thermistor obtained by sintering the paste containing 5 wt% of RuO₂ at 900℃ is the most obvious.

• Korean Journal of Construction Engineering and Management
• /
• v.20 no.1
• /
• pp.14-21
• /
• 2019

The construction phase of the construction project needs a large scale of manpower, materials and equipment. Among them, manpower is a core part for project construction. These manpower are divided into two groups. The first is the management group that manages the construction, and the second is the site technician manpower for construction work. Recently, construction company has suffering due to the insufficient supply of technician labor. Accordingly, this study will perform an empirical analysis about the construction technician. To do this, we surveyed related research trends and conducted surveys on the satisfaction of the construction technician. The result, satisfaction with pay and insurance was relatively low compared to other items. Therefore, this study were conducted in-depth interviews with technician managers in order to analyze the cause. In addition, case analysis was conducted to analyze actual working conditions. As a result, it was analyzed that the wage level and insurance system of construction technician were considerably stable compared to the manufacturing industry. The result of this study is expected to contribute to the activation of excellent technician cultivation through the change of recognition about construction technician.