• Korean Chemical Engineering Research
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• 제45권2호
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• pp.124-132
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• 2007

본 논문에서는 Ti 모재에 대한 Pt 도금 특성 연구를 통하여 안정한 platinized Ti 전극의 제조 방법이 제시되었으며, Sn이 흡착된 platinized Ti 전극의 질산염 이온에 대한 전기화학적 특성이 연구되었다. 에칭된 Ti 모재 표면에 전착된 Pt 도금 층 내에 적당하게 공간적 틈을 갖도록 도금하는 것은 도금 후 표면에 잔존하는 도금 용액 오염원을 제거하는데 효과적이며, 또 용액과 접하게 되는 전극의 실제 표면적을 최대화할 수 있었다. 제작된 platinized Ti 전극을 끓이는 과정과 전해 세정 과정을 통해 안정적이며 재현성 있게 만드는 것은 Sn-modified platinized Ti 전극에서 표면의 Sn 덮힘율을 정량화하는데 있어 매우 중요하였다. 전해 세정 과정은 전극 표면에 형성된 솜털과 같은 미세한 돌기들이 없어지면서 전극 표면을 안정화된 구조로 변화시켰다. 본 연구의 경우 질산염 이온의 환원을 목적으로 하는 Sn-modified platinized Ti 전극은 약 30분 도금 시간을 통해 제조한 경우가 가장 좋았다.

• 한국정밀공학회지
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• 제29권1호
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• pp.48-55
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• 2012

Pressure vessels in vehicle industries, power plants, and chemical industries are often affected by flaw and defect generated inside the pressure vessels due to production processes or being used. It is very important to detect such internal defects of pressure vessel because they sometimes bring out serious problems. In this paper, an optical defect detection method using digital shearography is used. This method has advantages that the inspection can be performed at a real time measurement and is less sensitive to environmental noise. Shearography is a laser-based technique for full-field, non-contacting measurement of surface deformation (displacement or strain). The ultimate goal of this paper is to detect flaws in pressure vessels and to measure the lengths of the flaws by using unwrapping, phase images which are only obtained by Phase map. Through this method, we could decrease post-processing (next processing). Real length of a pixel can be calculated by comparing minimum and maximum unwrapping images with shearing angle. Through measuring several specimen defects which have different lengths and depths of defect, it can be possible to interpret quantitatively by calculating gray level.

• Clinical and Experimental Pediatrics
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• 제60권1호
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• pp.17-23
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• 2017

Purpose: To examine the correlation of depression with Internet use and body image perception, and to analyze the risk factors of depression in a total of 920 students in Seoul, Korea. Methods: Students were recruited by contacting school principals and teachers and were encouraged to fill out a self-report questionnaire designed specifically for this study in July of 2008. Results: Female participants had an increased risk for depression than did male participants (adjusted odds ratio [aOR], 1.790; 95% confidence interval [CI], 1.330-2.410, P<0.001). Older students were more susceptible to depression (aOR, 1.246; 95% CI, 1.115-1.392, P<0.001). Longer daily Internet use and more frequent Internet use were analyzed as risk factors for depression. No physical activity was a risk factor for depression (aOR, 0.392; 95% CI, 1.264-4.526, P=0.014). Dissatisfaction with one's body image increased the risk for depression (aOR, 1.373; 95% CI, 1.169-1.613; P<0.001). Obesity and perception of body image showed no significant relationship with increased risk for depression. Conclusion: Prevalence of depression was 13.8% in adolescents in Seoul, Korea, in July 2008. Female sex, age, daily Internet use duration, weekly Internet use frequency, physical activity, and dissatisfaction with one's body image independently increased risk of depression.

• 한국항공우주학회지
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• 제35권12호
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• pp.1089-1094
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• 2007

연구에서는 코일 스프링 및 작동유체가 없는 새로운 감쇠기의 개념을 소개한다. 이 감쇠기는 영구자석과 전도체 실린더로 구성된다. 극성이 반대인 자석은 반발력을 발생시키고, 이는 코일 스프링과 같은 역할을 한다. 영구자석과 전도체 실린더 사이의 상대운동은 기전력을 발생시키는 와전류를 생성하고, 이로 인해 감쇠 유체를 대신할 수 있는 감쇠력을 만든다. 이러한 감쇠를 와전류 감쇠기라고 한다. 본 연구에서 제안된 와전류 감쇠기의 중요한 장점은 감쇠 유체 및 어떠한 외부의 전력도 필요로 하지 않고, 비접촉식이며, 온도에도 민감하지 않다. 본 연구에서는 제안된 와전류 감쇠기를 제작하고 실험을 통하여 감쇠기의 동적 특성을 조사하였다. 본 연구의 결과는 제안된 와전류 감쇠기가 우수한 감쇠 성능을 가짐을 보였다.

• 한국환경교육학회지:환경교육
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• 제24권4호
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• pp.62-77
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• 2011

The purpose of this study is to overcome the realistic pressure and the limit of school environmental education and to develop an environmental education program that can provide students, who live in an urban area, have difficulty in contacting with nature, with an opportunity to experience the nature in the school outdoor environment, which is their daily living space and is a ground of environmental education. First, I developed an analytical tool which can be used to determine the degree how the environmental education is related to the school outdoor environment with 8 categories(spaces). And I analyzed the 2007-79 curriculum of lower grade(1 and 2 grades) of the elementary school provided by the Ministry of Education and Human Resources Development by using the analytical tool and found out that this curriculum was suitable for the environmental education utilizing the school outdoor environment. According to this curriculum analysis, the studying subjects which could be suitable for the environmental education utilizing the school outdoor environment were extracted, and based on these subjects, an environmental education program was developed. The environmental education 'in' environment program were composed with 5 modules and 18 activity subjects suitable for students advancement phase, and these activities can be implemented with experiencing, understanding and expressing by using 5 senses. I also proposed a plan that can be used to apply this program continuously to the lower grades(1 and 2 grades) original experience activity class.

• 복식
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• 제60권6호
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• pp.23-36
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• 2010

This study set out to develop clothes made of electromagnetic wave shielding materials. Among the various worker groups exposed to electromagnetic waves for long hours, railroad workers were chosen for the study. After selecting the locations they worked, the investigator measured electromagnetic wave on the field. To examine the effects of electromagnetic wave shielding materials, I applied a lining made of electromagnetic wave shielding materials to the existing work clothes. The first experimental clothes had the silver fabric for the lining in the current working clothes, the second experimental clothes had the copper- and nickel-plate polyester placed between the outer and the lining to prevent the corrosive material from contacting the skin, and the third experimental clothes had the silver fabric for the lining and the copper- and nickel-plate polyester between the outer and the lining. The results indicate that even if a fabric is evaluated to shield electromagnetic waves after tests, it cannot completely shield electromagnetic waves emitting from everyday appliances of 60Hz. Therefore, there should be ongoing development and research efforts on fabrics that can shield electromagnetic waves to a certain degree in order to develop working clothes to alleviate fatigue for those who are constantly exposed to electromagnetic waves, relieve their anxiety, offer them psychological stability and thus help them increase job efficiency.

• Journal of Advanced Marine Engineering and Technology
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• 제22권1호
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• pp.67-76
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• 1998

Friction materials for brake linings and clutches have severe performance requirements. The principal function of such frictional elements is to convert kinetic energy to heat, and then either to absorb or to dissipate heat. In order to achieve these objectives, the coefficient of friction must be as high as possible, independent of variations in operating conditions, and the necessary energy conversion must be accomplished with a minimum of wear on the contacting parts. In this study, Al powder, Al bronze powder and Mo powder used in general for automobile brake was sprayed on automobile brake disc to restrain rust and to maintain friction performance. Dynamo and corrosion tests have been carried out. It is concluded that the sprayed disc with Al bronze powder has the most improved frictional performance and anti-corrosive characteristics. The main results obtained can be summarized as follows; 1. From the corrosion current density test for gray cast iron and sprayed disc with powders of Al, Al bronze and Mo, it was cleared that the spray treatment with Al bronze powder showed the most superior anti-corrosive characteristics than other powders. 2. By anode polarization toward the noble direction from corrosion potential, corrosion current density with sprayed brake disc by Al-bronze powder was the lowest. 3. Mean frictional coefficients obtained from dynamo test are as follows : the sprayed disc with Al(99.99%) powder was 0.190 ; the sprayed disc with Al-bronze powder was 0.312 ; the sprayed disc with Mo powder was 0.257 ; the non-sprayed disc of gray cast iron was 0.331. In the case of the sprayed disc Al-bronze powder showed the most excellent frictional characteristics . 4. Amount of burnish quantity obtained from burnish test by dynamometer is as follows : the sprayed disc with Al-powder was 1.079 mm : the sprayed disc with Al-bronze powder was 0.155 mm : the sprayed disc with Mo powder was 0.253 mm : the non-sprayed disc of gray cast iron was 0.241 mm. Al-bronze powder also showed the most excellent burnish characteristics.

• 대한영양사협회학술지
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• 제4권2호
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• pp.225-234
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• 1998

Nutrition during childhood is essential for growth and maintenance of health. Good food habits developed during the childhood will contribute both to the healthy growth and the prevention of the degenerative disease of later life. Both parents and the providers in child care centers play an important role for children's good eating behavior. Therefore all child care programs should achieve recommended standards for meeting children's nutritional and educational needs in a safe, sanitary, and supportive environment to promote the healthy growth and development of children. The purposes of this study were to evaluate the foodservice management practices and assess the needs for a Central Production Unit by contacting the child care center' providers. This approach was achieved using a variety of qualitative and quantitative information including the general foodservice management practices and the needs for a Central Production Unit. An indepth face-to-face interview with structured-questionnaires was undertaken at 32 representative child-care centers in Seoul. Statistical data analysis was done using the SAS program for descriptive analysis and ANOVA. The number of national/public and private sectors were 11 respectively, followed by 10 licensed home day-care centers. Total average number of children in child-care centers was 54.3 $\pm$48.5. The foodservice productivity index in child-care centers was 4.8 minutes per meal for public child care centers, 6.0 for private child-care centers, and 9.8 for home child care centers. Home child care centers were found to have the lowest productivity index which indicated inefficient foodservice practice. The important factors in group purchasing were menus(39.6%) or close distance(39.6%) > type of foodservice operation(32.8%) > total number of meals(19.9%) > food costs(16.2%) in order. Average score of the efficiency for central food production in child-care centers was 3.80 $\pm$0.84 out of 5.

• 한국세라믹학회지
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• 제35권2호
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• pp.163-171
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• 1998

Continuously contacting with camshaft the face of Valve Lifter made of cast iron brings about abnormal wear such as unfairwear or earlywear because it is heavily loaded in the valve train systems as the engine gets more powered. This abnormal wear becomes a defet namely over-clearance when the valve is lifting so that the fuel gas imperfectly combusted by unsuitable open or close aaction of the engine valve in the combustion chamber. The imperfect combustion in the end results in the major cause of air pollution and combustion chamber. The imperfectly combusted by unsuitable open or close action of the engine valve in the combustion chamber. The imperfect combustion in the end results in the major causes of air pollution and decrease of the engine output. Consequently to prevent this wear this study was to develop the valve lifter which is joined by brazing process with SCM435H and a tip by manufacturing the face as a superhardened which is joined by brazing process with SCM435H and a tip by manufacturing the face as a superhardened ceramics alloy which has high wear resistance. Having the excellent surface hardness with Hv1100-1200 the sintered body developed with superhardened alloy(WC) can endure the severe face loading in the valve train system. We experienced with various brazing alloys and obtained the excellent joining strength to the joint had 150MPa shear strength. Interface analysis and microstructure in a joint were examined through SEM & EDS Optical microscope. Also 2,500 hours high speed(3,000-4,000 rpm) and continuous (1step 12hr) engine dynamo testing was carried out to casting valve liter and ceramics-metal joint valve lifter so that the abnormal wears were compared and evaluated.

• 한국세라믹학회지
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• 제35권2호
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• pp.172-179
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• 1998

Valve lifter namely tappet is supported by lifter hole which is located upper side of camshaft in cylinder block transforms rotatic mvement of camshaft into linear movement and helps to open and shut the en-gine valve as an engine parts. The face of valve lifter which is continuously contacting with camshaft brings about abnormal wears such as unfair wear and early wear because it is severely loaded in the valve train system. These wears act as a defect like over-clearance and cause imperfect combustion of fuel during the valve lifting in the combustion chamber. Consequently this imperfect combustion makes the engine out-put decrease and has cause on air pollution. To prevent these wears therefore The valve lifter cast in me-tal developed into SiC ceramics valve lifter which has an excellence in wear and impact resistance As a results the optimum process conditions like injection condition mixture ratio and debonding process could be established. After sintering fine-sinered dual microstructure in which prior ${\alpha}$-SiC matches well with new SiC(${\beta}$-SiC) produced by reaction among the ${\alpha}$-SiC carbon and silicon was obtained. Based on the study it is verified that mechanical properties of SiC valve lifter are excellent in Vickers hardness 1100-1200 bending strength (300-350 Pa) fracture toughness(1.5-1.7 Mpa$.$m1/2) Through engine dynamo test-ing SiC valve lifter and metal valve lifter are examined and compared into abnormal phenomena such as early fracture unfair and early wear. It is hoped that this research will serve as an important springboard for the future study of heavy duty diesel engine parts developed by ceramics which has a good wear resis-tance relaibility and lightability.