• Tribology and Lubricants
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• 제8권1호
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• pp.48-55
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• 1992

The friction characteristic of plastics (PTFE, Nylon, Acetal and phenolic) was studied on the lubricated condition with a pin on disk machine. Mineral oil without additive (base oil) and water were used as liquid lubricants at the controlled temperature. From the experimental work, it was found out that the coefficient of friction of plastics was controlled by the mechanical properities of plastic more than that of liquid for various load and temperature. Viscosity of liquid has affected on the friction only at low temperature under lighb load. Among the tested plastics, the coefficient of friction of PTFE was the lowest under light load and at low temperature while Nylon at medium load and temperature, and Acetal at heavy load and high temperature. The coefficient of friction of soft plastics like PTFE and Nylon were increased as the load and temperature were increased, while that of hard plastic (Acetal) was decreased and that of thermo setting plastic (phenolic) was mixed. Also for soft plastics, the coefficient of friction under heavy load was always higher than that under light load, while hard plastic was vice versa.

• 멤브레인
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• 제6권4호
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• pp.236-241
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• 1996

본 연구를 통해서 온도감응성 polyurethane을 제조하여 수분의 투과거동을 검토하고 약물방출조절용 제제로의 적용가능성을 검토하였다. Polyurethane의 기계적 물성 및 Tg는 사용한 polyol의 분자량과 hard segment의 양을 이용하여 조절하였으며 온도증가에 따라 수분의 투과도가 증가함을 알 수 있었다. 따라서 온도변화에 따라 약물의 투과도가 변화하는 온도감응성 약물방충용 재료로 사용 가능성을 확인하였다.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.1296-1297
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• 2006

Both plastic and elastic properties change dramatically from the beginning to the end of the compaction phase. Previous investigations have shown that powder transfer and high powder flow during initial compaction at low density affects the strength of the final component significantly. Investigated here are shear failure and elastic shear modulus in the low density range for hard metal powder and for pre-alloyed water atomized iron powder. Direct shear test equipment for sand and clay has been modified to measure the shearing properties of powder for an axial loading between 1 kPa and 500 kPa.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1998년도 춘계학술대회 논문집
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• pp.49-52
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• 1998

Preparation of hexagonal strontium-ferrite by modified spray co-roasting(MSC:H) which is expected to shorkn the length of the process and to elevate the magnetic properties of hard ferrite was studied. We prapared $Fe_2O_3/SrCO_3$ mixture powders by MSCR after stirring ionized $FeCI_2$ in distilled water with solid state $SrCO_3$. And then calcined the mixture powders up to $1150^{\circ}C$ for Sr-ferrite powders It is possible to prepare hexaferrite powders with high saturation magnetization (Ms > 69 emu/g) , coercivity (Hc > 4000 Oe) The nlagnetic values of saturation magnetization iire higher than those achieved by the conventional technique.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2001년도 추계학술발표회 초록집
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• pp.63-63
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• 2001

As a new approach to substitute for a hard alloy of stellite 6B containing Co which is radioactive in nuclear system, a hard-phase coating of CrN will be applicable to protect 12Cr steel from erosion at leading edge on steam turbine blade. The CrN coating was prepared by arc ion plating on 12 Cr steel and was undertaken in liquid impact test at the velocity of 35Om/sec, which simulate the environment in the last stage of blade. The erosion resistance of coating was evaluated by optical observation on damaged surface. The threshold number of impact was closely related with surface hardness. And thus, it was confirmed that surface hardening improves the life time of steam turbine blade.

• 한국학교보건학회지
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• 제8권2호
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• pp.305-314
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• 1995

A comparative study on the effects of the water fluoridation program and fluoride mouth rinsing program in the elementary school children. This study was performed to compare the oral health status of permanent teeth for children of the caries prevention effects by using methods of fluoride 309 children for water fluoridated program, 240 for fluoride mouth rinsing program and 248 for control group. The DMFS rate, DMFT index, soft and hard deposite rate were analysed from the oral examination. And 300 questionares from the parents who lived in Cheong ju city were evaluated to see the situations of using the tap water. The results were as follows; 1. Caries experience rate in permanent dentition was the lowest in fluoride mouth rinsing group. 2. It was estimated that soft deposite rate was comparatively low in the fluoride mouth rinsing group but calculus deposite rate was no significant difference in each other groups. 3. The 72.0 percentage of parents who lived in non fluoridated water area were misunderstood that they lived in water fluoridated area. 4. The 66.8 percentage of residents used the piped water as drinking water. 5. It was recommended that fluoride mouth rinsing program was suggested in rural area, on the other hands, toothbrusing program in urban area with water fluoridation to prevent the dental caries for school children.

• 환경위생공학
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• 제21권3호
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• pp.27-36
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• 2006

For the last 20 years, China has transformed itself from a rural economy into an industrial giant, averaging over 8 % annual growth of GDP. Unfortunately, this rapid growth has taken a significant toll on its natural resource base as well, particularly water resources. These problems have been exacerbated by a low level of sewage treatment technology and by the operating and maintenance (O&M). In case of urban areas, most big cities in China have a well functioning sewage system comprised of sewers and sewage treatment plants (STPs). Nevertheless, the existing STPs are still not capable of properly treating the sewage, both quantitatively and qualitatively. The rural areas in China cover a large land, with two-third of the nation's population. The low educational and poor economic states make it hard to process self-protection and management. In the surveyed area in Henan, there was no STPs put into use as of 2004, and the sewer lines are not well organized. The big issue for the currently planned STPs is the collection system not included in the plans.

• Corrosion Science and Technology
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• 제9권5호
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• pp.216-222
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• 2010

Most of the thirteen substations in operation in the metropolitan area were installed around the year 2000, and since water cooling methods are used to directly withdraw heat from transformer oils, a stable supply of electric power is required through optimal maintenance of facilities. The water cooling tower installed outdoors, which uses the water supply as sprinkler water, experiences the most problems. Since more than 90% of the cooling water is reused, the dissolved composition in the water becomes concentrated due to long operating hours, and impurities dissolve in the water due to air flowing in from the outside, forming hard scales on the outer surface of the cooling tube, and in extreme cases, reacting with the tube material composition, leading to corrosion. As a result, not only is cooling efficiency lowered, but in extreme cases the cooling tube must be replaced. In this study, the characteristics and composition of the scales formed on the cooling tube were analyzed and corrosion characteristics of material types were identified in order to find an efficient maintenance method for cooling tubes. In addition, the degree of dissolution of various chemicals were investigated during the removal of scales that have been formed.

• 상하수도학회지
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• 제29권3호
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• pp.371-380
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• 2015

Particulate matters in a water distribution system are main causes of turbidity and discoloration of tap water. They could be removed by conventional or uni-directional flushing in a water distribution system. The behaviors and required flow velocity of particles are not well known for their flushing. A model water main and hydrant were made from transparent acrylic pipe of 30mm and 16mm in diameter, respectively. We analyzed the effect of flushing velocity, particle density, and particle diameter. We found that the existence of break-though velocities at which particles begin to be removed, and which are affected by their physical properties. The removal efficiencies seemed to be influenced by resuspension capabilities related to their upward movement from the bottom. Heavy particles like scale were hard to remove through upflow hydrant because the falling velocity, calculated using Stokes' law, was higher. Particle removal efficiencies of upward hydrant and downward drain showed minor differences. Additionally, the length between hydrant and control valve affected flushing efficiency because the particulate matters were trapped in this space by inertia and recirculating flow.

• 한국멀티미디어학회논문지
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• 제22권2호
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• pp.242-249
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• 2019

Old people and patients with cardiovascular disease could die of a heart attack in the bath with heated water for a long time. Various researches have been studied to prevent these accidents from happening such as measuring the ECG signal when taking bath. However, these devices are hard to use and the higher price is not easily accepted by the public. In this paper, a low-cost and use-friendly, real time high precision water temperature monitoring device to prevent heart attack in the bath was developed. The device with waterproof design that lets the device can float on the surface of the water, and an accurate way to make water temperature measurement method was proposed by this paper that is immerging the sensor into water with 4cm depth to measure the temperature of underwater. The manufactured device was conducted to two experiments; one was to verify the basic functions of the device, and another one was for compare the proposed device with commercial products for monitoring the water temperature in the bathtub. As the experimental results shown, the proposed device has stable performance for the water temperature measurement and communicating with laptop in wireless.