• Journal of the Korean Institute of Gas
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• v.26 no.2
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• pp.49-55
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• 2022

According to reinforce environmental regulations, coal power plants have used selective catalytic reduction using ammonia as a reducing agent to reduce the amount of nitrogen oxide generation. The purpose of the present study was to derive a mixing device for effectively mixing dilute air and ammonia in the ammonia mixing pipe by performing computational fluid dynamic analysis. The mixing effect was compared by analysing the %RMS of ammonia concentration at the down stream cross section in the mixing pipe and the 16 outlets based on the case 1-1 shape, which is an existing mixing pipe without a mixing device. The mixing device was performed by changing the positions of a square plate on the downstream side of the ammonia supply pipe and an arc-shaped plate on the wall of the mixing pipe. In the case of the existing geometry(Case 1-1), the %RMS of ammonia concentration at the 16 outlets was 29.50%. The shape of the mixing device for Case 3-2 had a square plate on the downstream side of the ammonia supply pipe and an arc plate was installed adjacent to it. The %RMS of ammonia concentration for Case 3-2 was 2.08% at 16 outlets and it could be seen that the shape of Case 3-2 was the most effective mixing shape for ammonia mixing.

• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.2
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• pp.120-129
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• 2023

Marine structures are subject to damage not only from sea salt but also from the adhesion of marine microorganisms and suspended particles, which cause additional damages. In order to prevent this, periodic coating is employed in the case of vessels to maintain the necessary performance. However, it is true that periodic coating is difficult for concrete or steel support structures, and there is a risk of marine environmental pollution. In this study, authors developed an anti-fouling coating agent using eco-friendly materials that possess hydrophilic cellulose nanofibers and AKD(alkyl ketene dimer). To achieve a homogeneous mixture, the content of cellulose nanofibers was fixed at 1 %, and AKD, distilled water, and waste glass were mixed using a digital mixer and homogenizer. The contact angle of the prepared coated surface was observed to be over 130°, indicating sufficient performance even in a water droplet flow test with a 15° slope, suggesting self-cleaning capability. Furthermore, through the analysis of viscosity characteristics at different temperatures, it was confirmed that the application is feasible at room temperature. Microstructure analysis also verified that the coating agent is uniformly applied to the concrete surface.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.4A
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• pp.761-766
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• 2006

Polymer composite are increasingly considered as structural components for use in civil engineering, on account of their enhanced strength-to-weight ratios. Unsaturated polyester (UP) resin have been widely used for the matrix of composites such as FRP and polymer composite, due to its excellent adhesive. Polymer nanocomposites are new class of composites derived from the nano scale inorganic particles with dimensions typically in the range of 1 to 1000 nm that are dispersed in the polymer matrix homogeneously. Owing to the high aspect ratio of the fillers, mechanical, thermal, flame, retardant and barrier properties are enhanced without significant loss of clarity, toughness or impact strength. To prepare the MMT (Montmorillonite)-UP exfoliated nanocomposites, UP was mixed with MMT at $60^{\circ}C$ for 3 hours by using pan mixer. XRD (X-ray diffraction) pattern of the composites and TEM (Transmission Electron Micrographs) showed that the interlayer spacing of the modified MMT were exfoliated in polymer matrix. The mechanical properties also supported these findings, since in general, tensile strength, modulus with modified MMT were higher than those of the composites with unmodified MMT. The thermal stability of MMT-UP nanocomposite is better than that of pure UP, and its glass transition temperature is higher than that of pure UP. The polymer concrete made with MMT-UP nanocomposite has better mechanical properties than of pure UP. Therefore, it is suggested that strength and elastic modulus of polymer concrete was found to be positively tensile strength and tensile modulus of the MMT-UP nanocomposites.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.33 no.6
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• pp.226-233
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• 2023

In this study, the basic physical properties and microstructure of concrete interlocking blocks with amount of different CO₂ gas injection were analyzed according to determine the applicability of In-situ carbonation technology to construction secondary products. The amount of carbon dioxide gas injection was selected as 0, 0.1, 0.3, 0.5, 0.7 wt.% compared to cement amount. A lab-scale press equipment was designed to apply developed carbonation technology to real construction site. And mixer for stable CO₂ gas injection was designed. Using the designed devices, CO₂ gas injected samples were created and physical property of samples were performed. As a result of the physical property test, as the CO₂ injection amount increased to 0.3 %, it showed higher strength behavior compared to the original mix. And more than 0.5 % samples showed lower strength behavior than original sample, but they satisfied the standard of concrete interlocking block. This results were determined that CO₂ injection contributed to the creation of hydrates such as C-S-H. Therefore, the possibility of applying carbonation technology, which injects CO₂ during mixing, to various secondary construction products was confirmed.

• The Korean Journal of Mycology
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• v.27 no.1 s.88
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• pp.10-14
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• 1999

A single phase composter was constructed by modifying the conventional mixer of sawdust for the cultivation of oyster mushroom Pleurotus ostreatus. The machine was designed on the basis of 3-phase-1 system which was controlled in prewetting, pasteurization and fermentation processes. In composting 200 kg of straw and cotton waste in the machine, it took 20 minutes in prewetting step and also to hours at $65^{\circ}C$ in pasteurization process. Postfermentation by aerothermophiles was completed by treating the compost at $45^{\circ}C-50^{\circ}C$ for 48 hours which was shorten 24 hours from the conventional method. In the postfermentation at high temperature, forced aeration and/or vigorous mixing process(es) played a great role in the improvement of spawn quality. The growth of mycelium of oyster mushroom was excellent in the culture combinated with 3 parts of surface inoculation and 7 parts of mechanical mixing.

• Journal of Applied Biological Chemistry
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• v.57 no.1
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• pp.73-81
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• 2014

The present study was carried out to assess exposure and risk to thiophanate-methyl wettable powder for agricultural worker during mixing/loading and application with power sprayer in green pepper, cucumber and apple fields. Dermal exposure was measured with patches, gloves, socks and masks, while inhalation exposure was evaluated with personal air pump and solid sorbent. Those methods were full validated before experiment. During mixing/loading, dermal exposure amount in green pepper, cucumber and apple fields was $24.0{\pm}6.7$, $4.5{\pm}1.5$ and $18.5{\pm}0.6mg$, corresponding to mean 0.007, 0.001 and 0.005% of prepared active ingredient, respectively. The major exposed part for mixer/loader was hands (78-92%). Dermal exposure amount for applicator in green pepper, cucumber and apple fields was $84.9{\pm}14.0$, $34.0{\pm}20.8$ and $30.7{\pm}9.1mg$, corresponding to mean 0.024, 0.016 and 0.013% of applied active ingredient, respectively. The main body parts of exposure in apple field were hands, while thighs and shins in other fields. Inhalation exposure amount in green pepper, cucumber and apple fields was $1.5{\pm}2.2$, $52.7{\pm}48.9$ and $4.0{\pm}4.9{\mu}g$ during mixing/loading and $0.2{\pm}0.1$, $23.2{\pm}12.4$ and $0.4{\pm}0.6{\mu}g$ for applicator, respectively. These results were suggested that main factors affecting dermal exposure were contact frequency to the plants, foliage density, hygienic behavior, work type, and working environment, while inhalation exposure was affected mainly by working environment, especially wind. In risk assessment, margin of safety for thiophanate-methyl in all cases was over 1. However, during application in green pepper field, margin of safety was close to 1.

• Applied Biological Chemistry
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• v.19 no.1
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• pp.36-40
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• 1976

The mucilage of the root of Abelmoschus manihot, MEDIC is important for production of Korean traditional hand-made paper. This study was proceeded to detect the variation of the amount of free reducing sugars and of the viscosity in the mucilage. The results as follow. 1. The mucilage of the root of Abelmoschus manihot, MEDIC has contained some of free reducing sugars, 2. The viscosity of the mucilage isolated from the root decreases with time at the constant temperature, but the amount of reducing sugars show a little change. 3. The amount of the reducing sugars is not changed on the agitation. 4. When $1{\sim}2%$ ammonium sulfate solution is added, the viscosity of the mucilage decreases very gradually, and the amount of the free reducing sugars in the mucilage shows a little change.

• Restorative Dentistry and Endodontics
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• v.22 no.1
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• pp.1-33
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• 1997

The objective of this study was to analyze the in vitro and in vivo corrosion products of low and high copper amalgams. The four different types of amalgam alloy used in this study were Fine cut, Caulk spherical, Dispersalloy, and Tytin. After each amalgam alloy and Hg were triturated according to the directions of the manufacturer by means of the mechanical amalgamator(Amalgam mixer. Shinhung Co. Korea), the triturated mass was inserted into a cylindrical metal mold which was 12mm in diameter and 10mm in height. The mass was condensed by 150Kg/cm compressive force. The specimen was removed from the mold and aged at room temperature for about seven days. The standard surface preparation was routinely carried out by emery paper polishing under running water. In vitro amalgam specimens were potentiostatically polarized ten times in a normal saline solution at $37^{\circ}C$(potentiostat : HA-301. Hukuto Denko Corp. Japan). Each specimen was subjected to anodic polarization scan within the potential range -1700mV to+400mV(SCE). After corrosion tests, anodic polarization curves and corrosion potentials were obtained. The amount of component elements dissolved from amalgams into solution was measured three times by ICP AES(Inductive Coupled Plasma Atomic Emission Spectrometry: Plasma 40. Perkim Elmer Co. U.S.A.). The four different types of amalgam were filled in occlusal and buccal class I cavities of four human 3rd molars. After about five years the restorations were carefully removed after tooth extraction to preserve the structural details including the deteriorated margins. The occlusal surface, amalgam-tooth interface and the fractured surface of in vivo amalgam corrosion products were analyzed. In vivo and in vitro amalgam specimens were examined and analyzed metallographically by SEM(Scanning Electron Microscope: JSM 840. Jeol Co. Japan) and EDAX(Energy Dispersive Micro X-ray Analyser: JSM 840. Jeol Co. Japan). 1. The following results are obtained from in vitro corrosion tests. 1) Corrosion potentials of all amalgams became more noble after ten times passing through the in vitro corrosion test compared to first time. 2) After times through the test, released Cu concentration in saline solution was almost equal but highest in Fine cut. Ag and Hg ion concentration was highest in Caulk spherical and Sn was highest in Dispersalloy. 3) Analyses of surface corrosion products in vitro reveal the following results. a)The corroded surface of Caulk spherical has Na-Sn-Cl containing clusters of $5{\mu}m$ needle-like crystals and oval shapes of Sn-Cl phase, polyhedral Sn oxide phase. b)In Fine cut, there appeared to be a large Sn containing phase, surrounded by many Cu-Sn phases of $1{\mu}m$ granular shapes. c)Dispersalloy was covered by a thick reticular layer which contained Zn-Cl phase. d)In Tytin, a very thin, corroded layer had formed with irregularly growing Sn-Cl phases that looked like a stack of plates. 2. The following results are obtained by an analysis of in vivo amalgam corrosion products. 1) Occlusal surfaces of all amalgams were covered by thick amorphous layers containing Ca-P elements which were abraded by occlusal force. 2) In tooth-amalgam interface, Ca-P containing products were examined in all amalgams but were most clearly seen in low copper amalgams. 3) Sn oxide appeared as a polyhedral shape in internal space in Caulk spherical and Fine cut. 4) Apical pyramidal shaped Sn oxide and curved plate-like Sn-Cl phases resulted in Dispersalloy. 5) In Tytin, Sn oxide and Sn hydroxide were not seen but polyhedral Ag-Hg phase crystal appeared in internal space which assumed a ${\beta}_l$ phase.

• Korean Journal of Food Science and Technology
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• v.40 no.2
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• pp.123-128
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• 2008

The MRLs (maximum residue limits) of DDT (DDD and DDE) in fresh ginseng, dried ginseng, and steamed red ginseng are set as low as 0.01 mg/kg, 0.05 mg/kg, and 0.05 mg/kg, respectively. Therefore, this study was undertaken to develop a simple and highly sensitive analysis method, as well as to reduce interfering ginseng matrix peaks, for the determination of DDT isomers (o,p'-DDE, p,p'-DDE, o,p'-DDD, p,p'-DDD, o,p'-DDT, and p,p'-DDT) in fresh ginseng, dried ginseng, and steamed red ginseng at the 0.01 mg/kg level. The method used acetonitrile extraction according to simultaneous analysis, followed by normal-phase Florisil solid-phase extraction column clean-up. The purification method entailed the following steps: (1) dissolve the concentrated sample extract in 7 mL hexane; (2) add 3 mL of $H_2SO_4$; (3) vigorously shake on avortex mixer; (4) cetrifuge at 2000 rpm for 5 min; (5) transfer 3.5 mL of the supernatant to the Florisil-SPE (500 mg/6 mL);and (6) elute the SPE column with 1.5 mL of hexane and 10 mL of ether/hexane (6:94). The determination of DDT isomers was carried out by a gas chromatography-electron capture detector (GC-${\mu}$ECD). The hexane and ether/hexane (6:94) eluate significantly removed chromatographic interferences, and the addition of 30% $H_2SO_4$ to the acetonitrile extract effectively reduced many interfering ginseng matrix peaks, to allow for the determination of the DDT isomers at the 0.01 mg/kg level. The recoveries of the 6 fortified (most at 0.01 mg/kg) DDT isomers from fresh ginseng, dried ginseng, and steamed red ginseng ranged from 87.9 to 99.6%. The MDLs (method detection limits) ranged from 0.003 to 0.009 mg/kg. Finally, the application of this method for the determination of DDT isomers is sensitive, rapid, simple, and inexpensive.

• Magazine of the Korean Society of Agricultural Engineers
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• v.11 no.1
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• pp.1604-1615
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• 1969

This experiment was carried out as one of the basic studies to improve the acid resistance of concrete and it was conducted to investigate some relations among physical properties such as basorption, ratio of water to cement, compressive strength, density and ratio of mix to weight losses of mortar when exposed to 0.1 N solution of hydrochrolic acid. The results obtained from the limited data secured so far in this experiment are summarized as follows: 1. The specimens used in the experiment were made of 5 cubic centimeters of mortar having such various ratios of mix by weight as 1 : 1, 1 : 3, 1 : 5, 1 : 7, 1 : 10. 2. Physical tests included compressive strengths at 7 days, 28 days, 3 months, and 6 month, and 5 hour boiling absorption test. 3. In acid test, every specimen was immersed into 0.1 N solution of hydrochrolic acid. The specimens exposed to the acid solution were weighed to determine the weight losses of the acid-corroded at one week interval for 7 weeks exposure, and the old acid solutions were also changed to fresh one when weighed the weight losses by acid attack at one week interval. 4. The correlative relations were found among physical properties and they are expressed by certain formulas as follows; i) Relation between ratio of mix and absorption Y = 1.036x + 13.53 where Y: absorption(%) X: ratio of mix ii) Relation between ratio of mix and ratio of water-cement Y = 0.204x + 0.214 where Y: ratio of water-cement. X: ratio of mix iii) Relation between ratio of water-cement and absorption Y = 5.01x + 12.53 where Y: absorption(%). X: ratio of water-cement iv) Relation between density and absorption Y = 50.6 - 0.0176X where Y: absorption(%). X: density($kg/m^3$) v) Relation between density and ratio of water cement Y = 7.2183 - 0.0033X where Y: ratio of water-cement . X: density($kg/m^3$) 5. After completing the acid exposure test the specimens were corroded and , the per cent ranges of weight losses varies from a minimum of 20.4 per cent at a 1 : 1 mix to a maximum of 92.0 per cent at a 1:10 mix 6. The correlative relations of physical properties of mortar to weight losses by acid attak were found and they are also expressed by certain formulas as follows: i) Relation between weight losses and ratio of mix Y = 8.59X + 8.63 where Y: weight losses(%), X: ratio of mix ii) Relation between wieght losses and absorption Y = 0.121x + 12.43 where Y: absorption(%). X: weight losses(%) iii) Relation between weight losses and ratio of w/c Y = 0.0226X + 0.07 where Y: ratio of w/c X: weight losses(%) iv) Relation between weight losses and compressive strength LogY = 3.6097 - 0.05058X + 0.00022$X^2$ where Y: compressive strength ($kg/cm^3$) X: weight losses(%) v) Relation between weight losses and density Y = 2153.1 - 6.62X where Y: density($kg/m^3$) X: weigh losses(%) 7. In order to make better acid resistant mortar, it could be concluded that a 1 : 3 mix or richer mixes, adequate mixing water to minnimize the ratio of water-cement considering the workability, 16 per cent or less absorption by 5 hour boiling water, 1,800 kilogram per cubic meter or denser density by absolute weight base and 200 kilogram per square meter or compressive strength at 20 day, etc are required so as to obtain acid-resistant mortar. In addition to the above, it might be recommonded to select the fine aggregate and to use better equipments such as a mechanical vibrator, a mechanical mixer etc. in concrete manufacturing works.