• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.11a
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• pp.116-121
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• 2006

The pressurization system in a liquid rocket propulsion system provides a controlled gas pressure in the ullage space of the vehicle propellant tanks. It is advantage to employ a hot gas heat exchanger in the pressurization system to increase the specific volume of the pressurant and thereby reduce over-all system weight. Therefore a significant improvement in pressurization system performance can be achieved, particularly in a cryogenic system. For this study air and $CN_2$ are employed as external fluid and pressurant respectively Numerical analysis on the pressurant discharging characteristics have been compared with the experimental results performed at the PTF(Propellant-feeding Test Facility). It is shown that the discrepancy of analytic and experimental results is within about ${\pm}15%$. It is estimated that the temperature drop rate of cryogenic pressurant immersed liquid oxygen can be predicted using this analytic approach method.

• Journal of the Microelectronics and Packaging Society
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• v.8 no.2
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• pp.25-29
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• 2001

This study examined the effects of carbon surface modification by the epoxy resin coating on the electrochemical performance. The mesocarbon microbeads(MCMB) carbon was surface-modified by coating the epoxy resin and its electrochemical properties as an anode was examined. The surface coating of MCMB was carried out by refluxing the MCMB powders in a dilute H2SO4 solution, and mixing them with the epoxy resin-dissolved tetrahydrofuran(THF) solution. Under heat-treatment of the coated MCMB at the temperature over $1000^{\circ}C$, the epoxy-resin coating layer was converted into amorphous phase which was identified by a high resolution transmission electron microscope (HRTEM). The epoxy resin coated MCMB has higher Brunauer-Emmett-Teller (BET) surface area, higher charge/ discharge capacity and better cycleability than a raw MCMB without coating. The reason for the enhancement of cell performance by the epoxy resin coating were considered as the epoxy resin coating layer plays an important role to be a barrier for carbon reacting with electrolyte and to retard the formation of passivation layer.

• Journal of Environmental Science International
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• v.27 no.9
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• pp.763-770
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• 2018

Bioremediation in situ is heavily dependent on the oxygenic environment which would privide the dwelling microorganism with sufficient oxygen. The situation could be easily resolved with supply of an Oxygen Releasing Compound (ORC). In this paper we prepared that sort of material out of oyster shell powder (mostly calcium carbonate) that prevails every shore areas of the country. We used two different oxidizing methods in the first step of the whole manufacturing process-conventional heating in a furnace and an ultrasound generator to obtain calcium oxide. Then that calcium oxide was further oxidized into calcium peroxide which may release oxygen under a moisturized condition. The oxygen releasing experiments were run to test the performance of our products, and to determine the gas kinetics during the experiments. Interestingly, calcium peroxide derived from ultrasound treatment was much more energy-effective as ORC than that from furnace heating although the heat derived process was better than that of ultrasound in terms of oxygen content and its releasing rate. We also found that most of the data collected from the gas releasing experiments fairly supported an ordinary $1^{st}$ order kinetics to oxygen concentration, which shaped a sharp discharge of oxygen at the very early moment of each test.

• The Journal of Korean Academy of Prosthodontics
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• v.44 no.5
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• pp.617-627
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• 2006

Statement of problem: HA has been used as a coating material on Ti implants to improve osteoconductivity. However. it is difficult to form uniform HA coatings on implants with complex surface geometries using a plasma spraying technique. Purpose : To determine if Ti6Al4V sintered porous-surfaced implants coated with HA sol-gel coated and hydrothermal treated would accelerate osseointegration. Materials and Methods : Porous implants which were made by electric discharge were used in this study. Implants were anodized and hydrothermal treatment or HA sol-gel coating was performed. Hydrothermal treatment was conducted by high pressure steam at $300^{\circ}C$ for 2 hours using a autoclave. To make a HA sol, triethyl phosphite and calcium nitrate were diluted and dissolved in anhydrous ethanol and mixed. Then anodized implant were spin-coated with the prepared HA sols and heat treated. Samples were soaked in the Hanks solution with pH 7.4 at $37^{\circ}C$ for 6 weeks. The microstructure of the specimens was observed with a scanning electron microscope (SEM), and the composition of the surface layer was analyzed with an energy dispersive spectroscope (EDS). Results : The scanning electron micrographs of HA sol-gel coated and hydrothermal treated surface did not show any significant change in the size or shape of the pores. After immersion in Hanks' solution the precipitated HA crystals covered macro- and micro-pores The precipitated Ca and P increased in Hanks' solution that surface treatment caused increased activity. Conclusion : This study shows that sol-gel coated HA and hydrothermal treatment significantly enhance the rate of HA formation due to the altered surface chemistry.

• Journal of Electrochemical Science and Technology
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• v.11 no.4
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• pp.384-391
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• 2020

Due to its characteristics of light weight, high energy density, good safety, long service life, no memory effect, and environmental friendliness, lithium-ion batteries (LIBs) are widely used in various portable electronic products. The capacity and performance of LIBs largely depend on the performance of electrode materials. Therefore, the development of better positive and negative materials is the focus of current research. The application of metal organic framework materials (MOFs) derivatives in energy storage has attracted much attention and research. Using MOFs as precursors, porous metal oxides and porous carbon materials with controllable structure can be obtained. In this paper, rod-shaped Co-MOF-74 was grown on Ni Foam (NF) by hydrothermal method, and then Co-MOF-74/NF precursor was heat-treated to obtain rodshaped Co₃O₄/NF. Ni Foam was skeleton structured, which effectively relieved. The change of internal stress changes and destroys the structural volume of the electrode material and reduces the capacity attenuation. Co₃O₄/NF composite material has a specific discharge capacity of up to 1858 mA h/g for the first time, and a reversible capacity of up to 902.4 mA h/g at a current density of 200 mA/g, and has excellent rate and impedance performance. The synthesis strategy reported in this article opens the way to design high-performance electrodes for energy storage and electrochemical catalysis.

• Journal of Korean Ophthalmic Optics Society
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• v.1 no.2
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• pp.49-55
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• 1996

Hydrogenated amorphous carbon(a-C:H) films were fabricated by the low-frequency (60Hz) glow discharge of the mixture of methane and hydrogen, and their electrical properties were investigated. We observed that a-C:H films show the persistent photoconductivity(PPC) by illumination of heat-filtered while light for a few seconds. The PPC was about 10 times larger than the annealed dark conductivity. The samples clearly showed metastable characteristics. With increasing illumination times from 1 to 100 min, the annealing activation energy of the PPC was about 0.39eV. The annealing temperature at which the PPC disappeared increasing from $100^{\circ}C$ to $130^{\circ}C$. Illumination longer than 80 min leads to the formation of ${\pi}$ defects and to the decrease of PPC. From these results, we tentatively propose that the states in the ${\pi}$ band act as deep trap centers generating the metastabilities.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.1
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• pp.49-54
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• 2010

Rotor pole for AC(alternating current) generator is manufactured through transfer warm forging die. As soon as the material is heated at the warm manufacturing process, it is transferred to the first stage for upsetting work and then to the second stage for lateral extrusion work. The processes at the lateral extrusion work such as die block, die bushing, center punch, and side punch make severe condition and abrasion which leads to shorten the die life. This causes production decrease, long maintenance time, and low level of precision. Research on the die material selection, heat process cycle improvement, electric discharge machining trouble solution, and re-construction of main parts is expected to find a method to lengthen the die life up to 40 - 50%.

• Fire Science and Engineering
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• v.32 no.4
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• pp.86-94
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• 2018

A sports center fire in Jecheon caused 29 deaths and 40 injuries. This study focused only on the structural factors of the building and equipment to investigate the causes of casualties based on the fire investigation results at the sports center. The structural factors of the building and equipment were a piloti-type parking lot, lack of a fire compartment between the piloti-type parking lot and lobby, lack of an installed sprinkler system, lack of an installed fire door in the main stairs on the $1^{st}$ floor, lack of an installed fire water tank on the rooftop, an installed pocket fire door in the main entrance on the $2^{nd}$ floor, poor fire compartments in an EPS space and a pipe pit and on each floor, a leak in the joint of a drain pipe, plywood installed in the hoistway of the freight elevator and interior wall, illegal remodeling of a closed rooftop structure, which cannot discharge smoke and heat, installed styrofoam insulation in the inside of the parking lot ceiling, an installed tempered glass window, which cannot be opened in the ladies bathroom on the $2^{nd}$ floor, and a finished dryvit exterior wall.

• Transactions of the Korean Society of Automotive Engineers
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• v.13 no.2
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• pp.72-82
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• 2005

The objective of this paper is to describe the optimization of design parameters in a large-sized commercial bus heater system by using CFD(computational fluid dynamics) analysis and Taguchi method. In order to obtain the best combination of each control factor which results in a desired performance of heater system, the parameter design of the Taguchi method is adopted for the robust design considering the dynamic characteristic. The research activity may be divided into four phases. The first one is analyzing the problem, i.e., ascertaining the influential factors. In the second phase the levels were set in such a way that their variation would significantly influence the response. In the third phase the experimental runs were designed. In the final phase the planned runs were carried out numerically to evaluate the optimal combination of factors which is able to provide the best response. In this study, eight factors were considered for the analysis: one with two level and seven with three level combinations comprising the $L_{18}(2^1{\times}3^7)$ orthogonal array. The results of this study can be summarized as follows ; (i)The optimum condition of control factor is a set of <$A_2\;B_1\;C_3\;D_3\;E_1\;F_2\;G_3\;H_2$> where A is shape of the outer fin, B is pitch of the outer fin, C is height of the outer fin, D is the inner fin number, E is the inner fin height, F is length of the flame guide, G is diameter of the heating element and H is clearance between air guide and heating element. (ii)The heat capacity of heated discharge air under the optimum condition satisfies the equation y=0.6M w here M is a signal factor. (iii)The warm-up rate improves about three times, more largely as com pared with the current condition, which results in about 9.2minutes reduction.

• The Journal of Korean Medicine
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• v.32 no.5
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• pp.25-40
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• 2011

Objectives: This study was performed to assess whether herbal medicine and acupuncture before in vitro fertilizationembryo transfer (IVF-ET) is effective on clinical pregnancy. Methods: From May 2010 to January 2011, a prospective analysis study was performed in 38 patients planning to undergo IVF-ET after taking herb medicine and acupuncture treatment. This study investigated the pregnancy rate and analyzed the change of dysmenorrhea by visual analog scale (VAS), body heat and condition of premenstrual syndrome (PMS), vaginal discharge and menstruation status. Results: 1. During herbal medicine and acupuncture treatment, five patients (13.16%) naturally became pregnant and six patients (15.79%) withdrew. After treatment, 15 patients (39.47%) received IVF-ET, 12 patients (31.58%) did not. 2. The biochemical pregnancy rate was 26.67%, the clinical pregnancy rate 26.67%, miscarriage rate 25% and ectopic pregnancy rate was 0%. 3. After treatment, PMS, dysmenorrhea and dysmenorrhea VAS was significantly decreased and the overall menstrual status improved. 4. After treatment, temperature difference of CV17-CV12 and CV4-CV12 increased, but it was not a statistically significant difference. 5. After treatment, decrease of hemoglobin and protein and increase of total bilirubin and creatinine were statistically significant. All the blood test results were within normal levels which proves safety of treatment. Conclusions: This study suggests that herbal medicine and acupuncture treatment before IVF-ET shows similar pregnancy rates with existing rates, but contributes to increasing the possibility of natural pregnancy.