• 적정기술학회지
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• 제6권2호
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• pp.226-237
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• 2020

As the number of reported COVID-19 cases rises around the world, regions affected by the virus are taking serious measures to contain its spread. Face shields are one of the highest-need personal protective equipment (PPE) during COVID-19 pandemic. Beyond traditional face masks, as known cases of the coronavirus soar, currently there is a significant shortage of face shields around the world. In response, the protective face shields were designed and fabricated with open-source 3D modelling software and 3D printing technology, respectively. Our face shield consisted of two parts only; a reusable 3D printed headband and a visor made of transparent plastic sheet, as barrier. The resulting 3D printed face shields are affordable, lightweight, one-size-fits-most and ready-to-wear with minimal assemblies, and go on easily over glass, goggle and face mask. To ensure being donated to the healthcare professionals without risk infected by any pathogens, the 3D printed face shields were successfully be disinfected with ultraviolet germicidal irradiation (UVGI dosage of 1000 mJ/cm²) and 70% alcohol. For routine disinfection a UVGI chamber was designed and optimized to provide uniform UV-C illumination with an appreciated fluence for complete decontamination. More than 1,000 face shields were produced already and donated to the special hospitals for COVID-19 patients, quarantines, government and medical agencies in Ethiopia as well as in East-African countries. With certainty, our intention goes beyond the hospitals and other first responders, but not limited for all those who have to stay in the service or be in contact with many other people in the time of COVID-19 pandemic.

• Structural Monitoring and Maintenance
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• 제8권4호
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• pp.345-360
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• 2021

This paper presents an analytical approach to calculate the buckling load of the cylindrical ring structures subjected to both hydrostatic and hydrodynamic pressures. Based on the conservative law of energy and Timoshenko beam theory, a theoretical formula, which can be used to evaluate the critical pressure of buckling, is first derived for the simplified cylindrical ring structures. It is assumed that the hydrodynamic pressure can be treated as an equivalent hydrostatic pressure as a cosine function along the perimeter while the thickness ratio is limited to 0.2. Note that this paper limits the deformed shape of the cylindrical ring structures to an elliptical shape. The proposed analytical solutions are then compared with the numerical simulations. The critical pressure is evaluated in this study considering two possible failure modes: ultimate failure and buckling failure. The results show that the proposed analytical solutions can correctly predict the critical pressure for both failure modes. However, it is not recommended to be used when the hydrostatic pressure is low or medium (less than 80% of the critical pressure) as the analytical solutions underestimate the critical pressure especially when the ultimate failure mode occurs. This implies that the proposed solutions can still be used properly when the subsea vehicles are located in the deep parts of the ocean where the hydrostatic pressure is high. The finding will further help improve the geometric design of subsea vehicles against both hydrostatic and hydrodynamic pressures to enhance its strength and stability when it moves underwater. It will also help to control the speed of the subsea vehicles especially they move close to the sea bottom to prevent a catastrophic failure.

• Design & Manufacturing
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• 제16권1호
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• pp.27-35
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• 2022

Thermoforming is a plastic manufacturing process that applies a force to stretch a film of heated thermoplastic material over an engineered mold to create a 3-dimensional shape. After forming, the shaped part can then be trimmed and finished to specification to meet an end-user's requirements. The process and thermoplastic materials are extremely versatile and can be utilized to manufacture parts for a very wide range of applications. In this study, based on K-BKZ nonlinear viscoelastic model, thermoforming process analysis was performed for an interior room-lamp. The predicted thickness was minimum at the corner of a molded film, and maximum at the center of the bottom. By using the Taguchi method of design of experiments, the effects of process conditions on residual stresses were investigated. The dominant factors were the liner thickness and the film heating time. As the thickness of the liner increased, the residual stress decreased. And it was found that the residual stress decreased significantly when the film heating temperature was higher than the glass transition temperature. A thermoforming mold and a trimming mold were manufactured, and the spring back was investigated through experiments. The dominant factors were film heating time, liner thickness, and lower mold temperature. As the film heating time and liner thickness increased, the spring back decreased. In addition, it was found that the spring back decreased as the lower mold temperature increased.

• 열처리공학회지
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• 제36권1호
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• pp.1-6
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• 2023

In order to process plastic with similar mechanical performance to metal materials, it is necessary to improve the strength and hardness of core parts of the injection equipment in extrusion system. The tempering process is a heat treatment performed to reduce brittleness and improve elongation along with improvement of dimensional defects of martensite formed after quenching. In this study, changes in microstructure and mechanical properties according to temperature were evaluated after quenching and tempering of SM30C material. As a result, the strength and hardness were gradually decreased by tempering at 250~400℃, and the decrease was greatly increased under the tempering condition at 450℃. Under the tempering condition of 200~400℃, the main structure was lath martensite, and the precipitation amount and size of needle-shaped cementite increased along the lath with the increase of the tempering temperature. Most of the shape of cementite has a needle-like structure, and the formation of some spherical cementite is observed. Under the tempering condition of 450℃, a mixed structure of ferrite and martensite was formed according to the decomposition of martensite.

• 대한토목학회논문집
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• 제26권5C호
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• pp.359-368
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• 2006

시공후 터널의 거동에 영향을 주는 대표적인 인자들로 시간에 따른 투수상태와 지반의 장기거동을 들 수 있다. 본 연구에서는 이러한 인자들과 관련된 터널거동을 분석하기 위한 수치해석모델을 개발하고 터널이 겪을 수 있는 다양한 시공 후 하중 조건에 대하여 수치해석을 수행하였다. 터널 변상에 대한 영향인자와 터널거동의 메카니즘을 파악하기 위해 가능한 모든 변상 발생 시나리오를 구성하였으며, 부직포의 투수계수, 수위상승, 장기적인 이완하중과 과발파로 인한 손상 등 터널의 시공 후 장기 변상에 관련된 인자들이 조사되었다. 시공 후 터널 변상 발생 시나리오는 터널형식과 그에 따른 하중 메카니즘에 따라 크게 두 가지로 구분할 수 있음을 알 수 있었다. 토사터널에 대해서는 투수상태와 관련된 거동이 주요 변상의 원인으로 분석되었으며 배수재의 투수계수 저하와 수위상승에 의한 영향에 대해 분석하였다. 암반 터널에서는 암반의 점소성 거동을 분석하였고 암반의 이완과 크립에 의한 장기적인 이완하중의 영향에 대해 연구하였다.

• 한국건축시공학회지
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• 제24권2호
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• pp.215-226
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• 2024

본 연구에서는 초고분말 플라이 애시가 다량 치환된 자기감지형 그라우트의 성능을 검토하기 위하여 실험적 연구를 진행하였다. 또한 기존의 대표적인 산업부산물인 고로슬래그 미분말과 플라이 애시를 동일한 양으로 치환하여 굳지 않은 그라우트의 유동특성, 경화 그라우트에서 압축강도, 길이변화율, 전기적 특성을 평가하였다. 실험결과 초고분말 플라이 애시 치환시 소성점도가 크게 낮아져 유동성이 향상되었으며, 압축강도도 플레인보다 초기재령에서부터 높게 나타났다. 또한 전기적 특성에서도 FCR-Stress, FCR-Strain의 관계가 유사하게 나타났다.

• 한국병원경영학회지
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• 제29권3호
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• pp.54-69
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• 2024

Purposes: This study aims to analyze the location patterns, concentration, and accessibility of clinics in Seoul with the grids of a geographic information system(GIS) and provide useful indicators for research on hospital and clinic management and policies based on the results. The study especially sets out to identify areas falling behind in the service of the essential medical care departments based on an analysis with 250m×250m grids and contribute to efficient medical business management and public healthcare policies based on the results. Methodology: The study analyzed clinics in Seoul in terms of concentration, distribution and clustering patterns, accessibility, and hot spots by dividing the entire city into 500m×500m cells and generating grids. The accessibility analysis for the essential medical care departments was especially in detail based on grids in a 250m×250m cell size. Findings: The Herfindahl results show that plastic surgery and rehabilitation medicine recorded the highest concentration level. General medicine and dermatology recorded the highest Moran's I value, and internal medicine was the highest in hot spots. Obstetrics and gynecology capable of child delivery showed considerably lower accessibility in the grids corresponding to Gangseo-gu, Yangcheon-gu, and Gwanak-gu. Surgery had low accessibility in the grids corresponding to the northern parts of Gangseo-gu for the total population. Practical Implication: Unlike previous studies whose analyses covered wide areas, the present study examined minute spatial patterns, concentration, and accessibility based on an analysis with 500m×500m or 250m×250m grids. Based on its findings, the study expects a more minute analysis for future research on medical business management and policies.

• 청정기술
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• 제17권2호
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• pp.124-133
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• 2011

2006년 시행되어 온 RoHS 규제에 유해물질을 추가하여 더 강화된 RoHS II의 공표에 대비하여 본 연구에서는 RoHS II의 최우선 규제 물질이면서 2010년 발표된 REACH SVHC 후보목록에도 포함된 물질인 Hexabromocyclododecane (HBCDD) 및 3종 프탈레이트, Dibutyl phthalate (DBP), Butyl benzyl phthalate (BBP), Diethylhexyl phthalate (DEHP)의 국내 전기 전자제품내의 함유 여부를 사전 검토해보려는 목적으로 사례 연구를 진행하였다. 이에 고분자 소재로 구성된 세탁기, 냉장고, 혹은 전자렌지의 부품 20개를 12개 전기전자 부품 생산회사로부터 수거하여 4종 규제 물질을 기체크로마토그래피 질량분석법으로 분석하여 그 함유량을 측정한 결과 Nitrile Butadine Rubber (NBR), Polypropylene (PP), Polybutylene Terephthalate (PBT), Ethylene Propylene Rubber (EPDM), Polyvinyl Chloride (PVC) 등의 소재로 된 부품 중 HBCDD는 NBR 소재로 된 3종 부품에서 42~381 mg/kg 범위로 검출되어 규제값 0.1 wt% (1,000 mg/kg)보다는 적지만 주의를 요한다. DBP 및 BBP는 20개 부품모두에서 검출되지 않고 있어 이 두 물질은 전지전자 제품용 플라스틱 소재에서 넓게 사용되지 않고 있을 가능성을 시사하고 있다. 그러나 DEHP는 40~59,400 mg/kg 범위로 NBR, PP, PBT, EPDM 및 PVC로 이루어진 부품에서 모두 검출되어 광범위하게 사용되고 있음을 알 수 있었고 특히 NBR 및 PVC로 이루어진 8개 부품에서 예상 규제치인 0.1 wt% (1,000 mg/kg)을 훨씬 능가한 0.45~5.94 w%로 검출되고 있어 이에 대한 대비가 필요함을 알 수 있었다. 추가로 REACH SVHC (고위험성 물질)에 속하는 Diarsenic pentaoxide, Diarsenic trioxide, Lead hydrogen arsenate, Triethyl arsenate의 4종 물질의 함유 여부를 ICP에 의한 비소(Arsenic) 분석으로 스크리닝해 본 결과 NBR, PBT 소재의 4개 부품에서 15~700 mg/kg으로 검출되었고 이 중 PBT소재의 부품인 Thermistor에서는 규제되는 비소화합물이 규제값(0.1 wt%, 1,000 mg/kg)을 초과할 가능성이 매우 높다.

• Asian-Australasian Journal of Animal Sciences
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• 제8권3호
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• pp.281-287
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• 1995

A study was conducted to investigate the effect of different inclusion levels of urea treated whole-crop wheat silage (UWCWS) in grass silage based rations on the performance of growing beef cattle. The winter wheat (variety, Riband) was harvested (in the summer of 1991) at a dry matter proportion of 520 g/kg and treated with feed grade urea at the rate of 37 kg/tonne crop dry matter and preserved in a heavy duty plastic bag using a silo press. The urea treated whole crop wheat silage (UWCWS) was mixed with grass silage to replace 0.00 (S100), 0.33 (S33) and 0.67 (S67) parts of the forage dry matter and fed ad libitum in a cross over design to 18 Simmental X Holstein Friesian growing beef animals. Two energy sources {one high in starch, rolled barley (RB) and one high in digestible fibre, sugar beet pulp (SBP)} were fed to supply sufficient energy for the efficient use of nitrogen by the rumen micro-organisms. The data on DMIF (dry matter intake of forage), TDMI (total dry matter intake), DLWG (daily live weight gain), FCR (feed conversion ratio) were recorded and faecal samples were collected to determine the digestibility coefficients. Results revealed that with the inclusion of UWCW in the animals' diets the DMI of the forage was significantly increased (p < 0.05). The highest DMIF was found in the treatment "S33" ($6.28{\pm}0.25kg$) where 67% of the silage dry matter was replaced with the UWCW and the lowest value for DMIF was observed in the control treatment ($5.03{\pm}0.23kg$). The DLWG did not differ significantly between the treatments. However, treatment "S100" showed a trend towards a superior DLWG. Feed conversion ratio in the control treatment differed significantly from "S67" and "S33". The addition of the UWCW in the animals' diet resulted in the lower FCR There was no effect of type of energy supplement on any aspect of performance either overall or in interaction with grass silage: UWCWS ratio. The regression and correlation coefficients for DMIF (r = 5.22 + 0.0184x*), DLWG (r = $1.04-0.00086x^{NS}$) and FCR (r = 4.78 = 0.022x*) on the inclusion of UWCW in the diet were calculated. The effect of the inclusion of UWCW on the overall digestibility coefficients was significant (p < 0.05). The addition of the UWCWS in the diet decreased the digestibility of the DM, OM, ADF and NFE but effect on the protein digestibility was non significant. The results of present study suggests that a DLWG slightly over 1 kg can be achieved with UWCW during the store period (period in which animal performance targets are low especially during winter) and the prediction of ME was overestimated as the high intake of DM did not reflect in improved animal performance.

• 농촌의학ㆍ지역보건
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• 제13권1호
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• pp.19-25
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• 1988

It is very important to supply safe drinking water for rural area not only a prevention of entric diseases but also a promotion of health life. It is estimated that 6,981,000 rural inhabitants were covered by the simple piped water supply system at the end of 1987 in Korea. The programme for improvement of water supply system in rural villages was initiated by the government since 1967. But most of these systems have been operated carelessly by the hands of villagers who have no proper knowledge and experience. Since most of water sources were located nearby farmland, there might be a possibility that the sources could be contaminated by pesticides and fertilizers. For this reason, it is recommended to take underground water as a water source rather than surface water such as a pond or streamwater in rural areas. However, the system is supplied from the surface water, its water quality can be improved by using of simple sand filter and simple chlorinator inexpensively. On the basis of an on-site study, conducted during 1986-87, in San-Buk Village, Keum-Sa-Myon, Yeju-Gun, Kyong-Gi-Do, the new simple piped water supply system was designed by the Institute for Environmental Research, Yonsei University, and constructed by the villagers themselves in September 1987. This simple system which is protected by metal fences consists of three main parts, pump house, vertical sand filter and water tank. The pumped water from underground flows into the upper part of the sand filter, through the sand, and out the water tank which is connected to the bottom of vertical filter. And the simple plastic-bottle chlorinator was installed in the water tank for chlorination. The water quality was remarkably improved after completion of construction. The total bacterial count was not detected from the tap water in households distributed by this simple piped water supply system. The construction cost of this system which was connected 34 households in San-Buk Village, was 4,851,000 won (approximately 6,020 U.S. dollars : 1$=805.8 won) in 1987,77% of expenses was supported by the Community Development Foundation in Korea. This case study for simple piped water supply projects will be applicable to other programme for improvement of water supply system in rural areas of Korea, and other developing countries.