• Korean Journal of Ecology and Environment
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• v.53 no.1
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• pp.91-101
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• 2020

Stormwater runoff is known as a major non-point water pollution source that transports heavy metals, which have accumulated in road surface, to stream and coastal area. Dissolved and particulate metals in stormwater runoffs have been investigated to understand the outflow characteristics of heavy metals during rainfall events and to identify their pollution sources. The concentration of dissolved Co and Ni decreased after the outflow with high concentrations at the beginning of the rainfall, and other metals showed different characteristics depending on the rainfall and rate of discharge. Particulate metals showed a similar trend with the temporal variation of suspended solids concentration in stormwater runoffs. The results of geo-accumulation index (I_geo) indicated that the stormwater runoffs from industrial region were very highly polluted with Cu, Zn and Cd. As a result of comparing the metal concentrations of <125 ㎛ for road dust near the study area, Cu, Zn and Cd were originated from inside of metal manufacturing facilities rather than traffic activities at road surface and these metals accumulated on the surface area of facilities were transported to the water environments during stormwater event. The average discharged amounts of heavy metals for one rainfall event were Cr 128 g, Co 12.35 g, Ni 98.5 g, Cu 607.5 g, Zn 8,429.5 g, As 6.95 g, Cd 3.7 g, Pb 251.75 g, indicating that metal runoff loads in the stormwater runoffs are closely related to surrounding industry types.

• Korean Chemical Engineering Research
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• v.50 no.2
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• pp.310-316
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• 2012

The chromaticity of polyethylene glycol (PEG) generated from the recyling of a silicone slurry waste was improved by using activated carbon powder and a carbon filter. The color change of the PEG waste was investigated by changing the amount of adsorbent, adsorption time and temperature. The surface area of activated carbon did not have a significant impact on improving the color of the PEG waste. According to the results for the APHA color variation of the PEG waste changing the amount of the carbon adsorbent, the optimal usage to achieve the low APHA value was 100~150 mg-C/g-PEG. From the investigatnion on the effect of the adsorption temperature range from $25^{\circ}C$ to $100^{\circ}C$, it was found that the optimal temperatures were $40{\sim}50^{\circ}C$ in terms of achieving the lowest APHA value. The variation of the APHA color was investigated by changing the operation condition of the activated carbon filters. The use of ACF was a good way to enhance the chromaticity of the PEG waste. As a result, the APHA value of the PEG waste (APHA=53 at the initial waste) was reduced to be 10 through the ACF purification. It was also confirmed that the performance of the used carbon adsorbent can be recovered by the washing with purified water.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.4
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• pp.653-659
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• 2017

In this study, the complex forging process of an outer support ring was developed and the prototype was manufactured. The current process, hot forging and MCT machining, has a disadvantage of excessive material removal rates and longer machining hours. To overcome this disadvantage, a general shape is given through hot forging and the precision is achieved through cold forging. The complex forging process was developed with the minimal machining process. Forging analysis was carried out to design a forging process using the commercial program, Deform-3D. The hot and cold forging processes were set up based on the analyzed result. The mold and prototype were manufactured. Hardness, surface roughness, internal defect, the grain low line of the prototype were evaluated. The results showed no particular problems, and there were no problems in mass production. Using complex forging, the material was reduced by approximately 27 % compared to the process using hot forging and MCT machining. In addition, the production speed was improved 2.15 fold compared to that of hot forging and MCT machining. Through this study, a cost-effective process and mold design technology were established, which is expected to have positive effects on other related automotive parts production.

• Journal of Dental Rehabilitation and Applied Science
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• v.37 no.1
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• pp.1-15
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• 2021

Additive manufacturing (AM) for dental materials can produce more complex forms than conventional manufacturing methods. Compared to milling processing, AM consumes less equipment and materials, making sustainability an advantage. AM can be categorized into 7 types. Polymers made by vat polymerization are the most suitable material for AM due to superior mechanical properties and internal fit compared to conventional self-polymerizing methods. However, polymers are mainly used as provisional restoration due to their relatively low mechanical strength. Metal AM uses powder bed fusion methods and has higher fracture toughness and density than castings, but has higher residual stress, which requires research on post-processing methods to remove them. AM for ceramic use vat polymerization of materials mixed with ceramic powder and resin polymer. The ceramic materials for AM needs complex post-processing such as debinding of polymer and sintering. The low mechanical strength and volumetric accuracy of the products made by AM must be improved to be commercialized. AM requires more research to find the most suitable fabrication process conditions, as the mechanical properties and surface of any material will vary depending on the processing condition.

• Korean Journal of Agricultural Science
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• v.13 no.1
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• pp.103-112
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• 1986

This study was carried out to prevent the entwining of rice straw on rotary shaft and blade where rice straw was spreaded on paddy field as an organic source before rotary tilling. The rotary tillage was conducted in the paddy field having the soil moisture contents of 30%, 39%, 59% in dry basis and spreaded rice straw (450kg/10a) of 30cm, 45cm, 90cm length with the edged curve angles of rotary blade of $30^{\circ}$, $40^{\circ}$, $50^{\circ}$, $55^{\circ}$ at Yuseung area. And the test were performed on the plot which has width of 30cm and 5cm length and the quantity of entwined rice straw was analized. The test results were summarized as the followings. 1. Entwining phenomenon of rice straw was decreased as the blade edged curve angle increased. The edged curve angle of rotary blade must be determind by considering the characteristics of soil cutting resistance, tilling torque and entwining phenomenon of rice straw. But according to the entwining phenomenon of rice straw only, the edged curve angle of rotary blade should be bigger than $55^{\circ}$ for design. 2. Amount of entwining rice straw was minimized when soil moisture contents was 30 percent (d. b.). It would be better that rotary tillage is performed when soil moisture contents is lower than 30 percent in dry basis. 3. Amount of entwining rice straw was minimized when the length of rice straw was 30cm with $55^{\circ}$ edged curve angle. Therefore, it would be better to chop rice straw as 30cm. 4. Entwining phenomenon of rice straw was decreased as the forward speed decreased. To decrease the entwining rice straw, rotary tillage should be done with forward fist gear (0.35m/s).

• Journal of Dental Rehabilitation and Applied Science
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• v.25 no.2
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• pp.109-123
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• 2009

The aim of the study was to assess the influence of insertion torque of bone quality and to compare axial force, moment and von Mises stress using finite element analysis of plastoelastic property for bone stress and strain by dividing bone quality to its thickness of cortical bone, density of trabecular bone and existence of lower cortical bone when implant inserted to mandibular premolar region. The $Br{\aa}nemark$ MKIII. RP implant and cylindrical bone finite model were designed as cortical bone at upper border and trabecular bone below the cortical bone. 7 models were made according to thickness of cortical bone, density of trabecular bone and bicortical anchorage and von Mises stress, axial force and moment were compared by running time. Dividing the insertion time, it seemed 300msec that inferior border of implant flange impinged the upper border of bone, 550msec that implant flange placed in middle of upper border and 800msec that superior border of implant flange was at the same level as bone surface. The maximum axial force peak was at about 500msec, and maximum moment peak was at about 800msec. The correlation of von Mises stress distribution was seen at both peak level. The following findings were appeared by the study which compared the axial force by its each area. The axial force was measured highest when $Br{\aa}nemark$ MKIII implant flange inserts the cortical bone. And maximal moment was measured highest after axial force suddenly decreased when the flange impinged at upper border and the concentration of von Mises stress distribution was at the same site. When implant was placed, the axial force and moment was measured high as the cortical bone got thicker and the force concentrated at the cortical bone site. The influence of density in trabecular bone to axial force was less when cortical bone was 1.5 mm thick but it might be more affected when the thickness was 0.5 mm. The total axial force with bicortical anchorage, was similar when upper border thickness was the same. But at the lower border the axial force of bicortical model was higher than that of monocortical model. Within the limitation of this FEA study, the insertion torque was most affected by the thickness of cortical bone when it was placed the $Br{\aa}nemark$ MKIII implant in premolar region of mandible.