• Korean Journal of Optics and Photonics
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• v.16 no.2
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• pp.168-173
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• 2005

Ag-doped $TiO_2$ thin films were prepared by RF magnetron co-sputtering method, and their physical and chemical properties were examined as a function of calcination temperature. XRD results showed that the crystallite size of Ag-doped films was smaller than that of the $TiO_2$ thin films. SEM results showed that the particle size of $Ag/TiO_2$ film was smaller and more uniform than pure $TiO_2$ film. The films had high transparency in the visible range. The films calcined at $600^{\circ}C$ were the anatase phase, and the films calcined at $900^{\circ}C$ were a mixture of anatase and rutile phases. The absorption edge of films calcined at $900^{\circ}C$ was red-shifted. This is due to the augmented absorption resulting from the phase transformation from anatase to rutile phase. And the transmittance of films decreased by the light scattering and absorption in the films. Photocatalytic activity of $Ag/TiO_2$ thin films was higher than that of the pure $TiO_2$ thin films.

• Korean Journal of Materials Research
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• v.3 no.2
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• pp.175-184
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• 1993

Abstract Co-and/or AI-added Nd-Fe-B-based magnetic alloys were fabricated by using vacuum induction melting frunace, and melt-spun ribbons were made of the magnetic alloys with single roll rapid quenching method. The variation of magnetic properties of the melt-spun ribbons as a function of Cuwheel velocity (Vs) were investigated. Bonded magnets were made of the optimally quenched ribbon fragments, and the magnetic properties of the melt-spun ribbons and the bonded magnets were studied, relating to the microstructure and crystalline structure. Cu-wheel surface velocity had a strong effect on the magnetic properties of the melt-spun ribbons, and the maximum properties were obtained around Vs =20m/sec. The optimally quenched ribbon had a cellura-type microstructure, in which fine N$d_2$F$e_14$B grains were surrounded by thin Nd-rich phase. In case of a 2.1at% AI-added melt-spun ribbon, the magnetic properties were as follows: iHc, Br, and (BH)max were 15.5KOe, 7.8KG and 8.5MGOe respectively. And resin bonded magnets were fabricated by mixing optimally quenched ribbon fragments with 2.5wt % polyamide resin, compacting and binding at room temperature. The iHc, Br and (BH)max of bonded magnet were lO.2KOe, 4.4KG and 3.3MGOe respectively. And hot-pressed magnets were made by pressing the overquenched ribbons at high temperature. The magnetic properties of hot-pressed magnets were better than those of bonded magnets, and when the holding time was 8 minutes, the iHc, Br, and (BH)max of the hot-pressed magnet were 1O.8KOe, 7.3KG and 8.0MGOe respectively. Domain structure was mainly maze pattern, which means that the easy magnetization axis could be aligned, and the domain width of the hot-pressed magnets was smaller than that of bonded magnets.

• The Journal of the Korea Contents Association
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• v.13 no.9
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• pp.270-280
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• 2013

The Purpose of this study was to investigate the relationship between congenital muscular torticollis and maternal work activity. This study was conducted with a total of 89 outpatient pregnant women whose child presented congenital muscular torticollis at the Department of Rehabilitation of "C" Hospital in Suwon within the period from 2006 to April 30, 2011. The results were as followings: (1) The mean age at the time of giving birth was 30.09years; the proportion of pregnant women with college education or higher was high; the proportion of first delivery was 82.0%; the most common way of delivery was natural childbirth, followed by Cesarean section and vacuum extraction; the proportion of breech delivery was 20.2%; and in 82.0% of the women, the first child had congenital muscular torticollis. (2) 59.6% of the women had a career; 45.3% had engaged in professional practice or had a related job; 75.5% had worked until the third trimester of their pregnancy; 54.7% had worked for seven hours or more in a seated position; and the mean number of working hours was 8.75 (3) The level of work-related stress was a low 25% or less, and in the subdivisions of work-related stress, only the level of strained relations belonged to the upper 50% or higher. (4) For the correlation between the survey respondents' job stress and job features, stress (full score: 100 points) showed a strong positive correlation with job demand, strained relations, inadequate reward, and workplace culture. Workplace also showed a strong positive correlation with inadequate reward. Mean daily working hours showed a strong positive correlation with mean weekly working hours.

• Polymer(Korea)
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• v.33 no.1
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• pp.39-44
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• 2009

Polymer substrates were fabricated by using poly (phenylene ether) as a base resin, N,N'-m-phenylenedimaleimide (PDMI) as a crosslinking agent and decabromodiphenylethane as a flame retardant. The effects of crosslinking agent and flame retardant on physical properties such as dielectric property of the substrate were investigated. Thermal curing feature of PDMI with or without an initiator was analyzed by DSC, and then, PPE-PDMI test compositions were designed based on this result. Composite sheets were cast by film coater, laminated under vacuum and pressure, and then, the changes of dielectric constant, dielectric loss, peel strength, solder heat resistance and inflammability according to increasing amount of PDMI and flame retardant were evaluated, Dielectric constant and dielectric loss showed increasing trend with increasing amount of PDMI and flame retardant, but solder heat resistance and inflammability were improved. Peel strength was obtained higher than 1 kN/m when PDMI above 10 wt% was added, but slightly decreased as the amount of flame retardant increased. From the measured gel contents, the reaction mechanism of PPE-PDMI system was deduced to the formation of network structure by crosslinking PDMI with PPE rather than the formation of semi-IPN structure. In conclusion, the polymer composite substrate materials with dielectric constant of 2.52$\sim$2.65 and dielectric loss below 0.002 at 1 GHz were obtained and they will be proper for high frequency applications.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.12
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• pp.1573-1579
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• 2013

To test the performance of nuclear fuels, coolant needs to be circulated through the test rig installed in the test loop. Because the pressure and temperature of the coolant is 15.5 MPa and $300^{\circ}C$ respectively, coolant sealing is one of the most important processes in fabricating a nuclear fuel test rig. In particular, 15 instrumentation cables installed in a test rig pass through the pressure boundary, and brazing is generally applied as a sealing method. In this study, an induction brazing system has been developed using a high frequency induction heater including a vacuum chamber. For application in the nuclear field, BNi2 should be used as a paste, and optimal process variables for Ni brazing have been found by several case studies. The performance and soundness of the brazed components has been verified by a tensile test, cross section test, and sealing performance test.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.10
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• pp.738-746
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• 2019

Instead of hydraulic actuation systems, an electromechanical actuation system is more efficient in terms of weight, cost, and test evaluation in the thrust vector control of the 7-ton gimbal engine used in the Korea Space Launch Vehicle-II(KSLV-II) $3^{rd}$ stage. The electromechanical actuator is a kind of servo actuator with position feedback and uses a BLDC motor that can operate at high vacuum. In the case of the gimballed rocket engine, a synthetic resonance phenomenon may occur due to a combination of a vibration mode of the actuator itself, a bending mode of the launcher structure, and an inertial load of the gimbals engine. When the synthetic resonance occurs, the control of the rocket attitude becomes unstable. Therefore, the requirements for the stiffness have been applied in consideration of the gimbal engine characteristics, the support structure, and the actuating system. For the 7-ton gimbal engine of the KSLV-II $3^{rd}$ stage, the stiffness requirement of the actuation system is $3.94{\times}10^7N/m$, and the direct drive type electromechanical actuator is designed to satisfy this requirement. In this paper, an equivalent stiffness analysis model of a direct drive electromechanical actuator designed based on the stiffness requirements is proposed and verified by experimental results.

• Journal of Sericultural and Entomological Science
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• v.53 no.2
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• pp.87-91
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• 2015

There is no specific data on Entomogenous fungus (DongChungHaCho) in accordance with the silkworm varieties, despite of very high value industrial use as functional materials at domestic and abroad. In this study, we investigated culture condition and characteristics of Paecilomyces tenuipes in 3 silkworm cultivars and 2 specific silkworm breeds. Infection rate of P. tenuipes for silkworm varieties was the highest Kumokjam, followed by Baegokjam, Daeseongjam, Golden silk, Yeonnokjam in that order. The optimum culture conditions were as follows: dark condition, $22^{\circ}C{\pm}1$, and about $4cm^2$ in planting density per pupa. Also, we have developed annual production technologies of P. tenuipes. First, in order that the moisture content of the infection pupa became 3% or less in the natural condition. Second, the dried pupa must be vacuum-packed and was kept under $4^{\circ}C$. Finally, by restoring the moisture content of the dried pupa and culture in optimal condition, the technique for annual production of the P. tenuipes was achieved. Therefore, we expect that the use of Kumokjam and annual production technique will contribute significantly to farm income.

• Food Engineering Progress
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• v.14 no.4
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• pp.359-366
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• 2010

Large-scale preparation steps of antithrombotic materials from wood ear mushroom (Auricularia auricular-judae) were established as follows. Grounded dry wood ear mushroom was extracted with 75% ethanol and its precipitate was extracted with $76^{\circ}C$ water for 2 hr followed by filter pressing. The filtrate was then concentrated by vacuum and extracted with 80% ethanol, and the resulting precipitate was then freeze-dried. The formula of the product was determined using consumer susceptibility tests as follows; mushroom extract 90.5%, high fructose corn syrup 2.0%, $\beta$-cyclodextrin 1.5%, fructo-oligosaccharide 2.0%, pear puree 4.0%. When the packed products were stored at 25, 37, or $45^{\circ}C$ for 8 weeks, there were no noticeable changes in water activity, moisture content, pH, and acidity. The viable cell number of total bacteria was slightly increased during the storage period at 25 and $37^{\circ}C$, The total bacteria were not detected in the product when stored at $45^{\circ}C$. When the product was injected intravenously into rat at the level of 1,000 mg/kg, antithrombotic activities such as activated partial thromboplastin time, thrombin time, prothrombin time, and FIB were increased when compared with the control group. When the product was administrated orally into rat at the level of 500 mg/kg, it showed the same antiplatelet activity to aspirin.

• Journal of the Korean Geosynthetics Society
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• v.17 no.4
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• pp.169-177
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• 2018

Glass fiber reinforced polyester (GFRP) composites are widely used as structural materials in harsh environment such as underground pipes, tanks and boat hulls, which requires long-term water resistance. Especially, these materials might be damaged due to delamination between gelcoat and composites through an osmotic process when they are immersed in water. In this study, GFRP laminates were prepared by surface treatment of UPE (unsaturated polyester) gelcoat by vacuum infusion process to improve the durability of composite materials used in underground pipes. The composite surface coated with gelcoat was examined for surface defects, cracking, and hardness change characteristics in water-immersion environments (different temperatures of $60^{\circ}C$, $75^{\circ}C$, and $85^{\circ}C$). The penetration depth of cracks was investigated by micro CT imaging according to water immersion temperature. It was confirmed that cracks developed into the composites material at $75^{\circ}C$ and $85^{\circ}C$ causing loss of durability of the materials. The point at which the initial crack initiated was defined as the failure time and the life expectancy at $23^{\circ}C$ was measured using the Arrhenius equation. The results from this study is expected to be applied to reliability evaluation of various industrial fields where gelcoat is applied such as civil engineering, construction, and marine industry.

• Asian-Australasian Journal of Animal Sciences
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• v.32 no.10
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• pp.1528-1539
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• 2019

Objective: To evaluate the effects on microbial diversity and biochemical parameters of gradually increasing temperatures, from $5^{\circ}C$ to $25^{\circ}C$ on corn silage which was previously fermented at ambient or low temperature. Methods: Whole-plant corn silage was fermented in vacuum bag mini-silos at either $10^{\circ}C$ or $20^{\circ}C$ for two months and stored at $5^{\circ}C$ for two months. The mini-silos were then subjected to additional incubation from $5^{\circ}C$ to $25^{\circ}C$ in $5^{\circ}C$ increments. Bacterial and fungal diversity was assessed by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) profiling and biochemical analysis from mini-silos collected at each temperature. Results: A temperature of $10^{\circ}C$ during fermentation restricted silage fermentation compared to fermentation temperature of $20^{\circ}C$. As storage temperature increased from $5^{\circ}C$ to $25^{\circ}C$, little changes occurred in silages fermented at $20^{\circ}C$, in terms of most biochemical parameters as well as bacterial and fungal populations. However, a high number of enterobacteria and yeasts (4 to $5\;log_{10}$ colony forming unit/g fresh materials) were detected at $15^{\circ}C$ and above. PCR-DGGE profile showed that Candida humilis predominated the fungi flora. For silage fermented at $10^{\circ}C$, no significant changes were observed in most silage characteristics when temperature was increased from $5^{\circ}C$ to $20^{\circ}C$. However, above $20^{\circ}C$, silage fermentation resumed as observed from the significantly increased number of lactic acid bacteria colonies, acetic acid content, and the rapid decline in pH and water-soluble carbohydrates concentration. DGGE results showed that Lactobacillus buchneri started to dominate the bacterial flora as temperature increased from $20^{\circ}C$ to $25^{\circ}C$. Conclusion: Temperature during fermentation as well as temperature during storage modulates microorganism population development and fermentation patterns. Silage fermented at $20^{\circ}C$ indicated that these silages should have lower aerobic stability at opening because of better survival of yeasts and enterobacteria.