• 상하수도학회지
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• 제21권6호
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• pp.745-753
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• 2007

By struvite and hydroxyapatite crystallization, was high concentration of nitrogen and phosphorus in wastewater simultaneously. Particularly, removal of nitrogen and phosphate for crystallization have been applied to landfill leachates and animal wastewater. The purpose of this study is to decide the optimum struvite crystallization factors, sequence of $Mg^{2+}$ addition, pH control and the molar ratio of $Mg^{2+}$ over $PO_4^{3-}$. In conclusion, dosage of the magnesium followed by pH control formed magnesium hydroxide, so pH was decreased. Therefore, pH adjustment should followed by after magnesium dosage and then pH should be adjusted to 11. Over pH 10, it was not good for struvite crystallization efficiency by side reaction. Following of the $Mg^{2+}$ and the $PO_4^{3-}$ are dosed excessively, the removal efficiency of the $NH_4^+$ increased. A molar ratio of $Mg^{2+}:NH_4^+:PO_4^{3-}$, 1.3:1:1.3 was the most on effective for $NH_4^+$ removal at pH 9.5. But for the perfect removal $NH_4^+$, it is thought to be that molar ratio should be 2:1:2.

• 대한기계학회논문집B
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• 제27권7호
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• pp.893-900
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• 2003

Numerical simulations of freely propagating flames burning stoichiometric C $H_4$/CHC1$_3$/ $O_2$/$N_2$ mixtures are performed at atmospheric pressure in order to understand the effect of the $O_2$ enrichment level and the CHC1$_3$/C $H_4$ molar ratio. A chemical kinetic mechanism is developed, which involves 69 gas-phase species and 379 forward and 364 backward reactions. The calculated flame speeds are compared with the experiments for the flames established at several CHC1$_3$/C $H_4$ molar ratio (R<1), the results of which is in excellent agreement. As a results of the increased $O_2$ enrichment level from 0.21 to 1, the flame speed and the temperature in the burned gas are increased. At high CHC1$_3$/C $H_4$ molar ratio two peak values appear on the $O_2$ consumption rate, which are affected by CC1$_2$＋ $O_2$$_{-}$>C1O+CC1O and H＋ $O_2$$_{-}$>O＋OH.＋OH.

• Journal of the Korean Wood Science and Technology
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• 제49권2호
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• pp.169-180
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• 2021

Inherent crystalline domains present in low formaldehyde to urea (F/U) molar ratio urea-formaldehyde (UF) resins are responsible for their poor adhesion in wood-based composite panels. To modify the crystallinity of low molar ratio (LMR) UF resins, this study investigates the additional effect of cellulose nanomaterials (CNMs), such as cellulose microfibrils (CMFs), cellulose nanofibrils (CNFs), and TEMPO-oxidized CNFs (TEMPO-CNFs) on the crystallinity of modified LMR UF resins. First, two modification methods (post-mixing and in situ) were compared for modified LMR UF resins with TEMPO-CNFs. The modified UF resins with TEMPO-CNFs decreased the nonvolatile solid contents, while increasing the viscosity and gel time. However, the in situ modification of UF resins with TEMPO-CNFs showed lower crystallinity than that of post-mixing. Then, the in situ method was compared for all CNMs to modify LMR UF resins. The modified UF resins with CMFs using the in situ method increased nonvolatile solid contents and viscosity but decreased the gel time. The crystallinity of UF resins modified with TEMPO-CNFs was the lowest even though the crystalline domains were not significantly changed for all modified UF resins. These results suggest that these CNMs should be modified to prevent the formation of crystalline domains in LMR UF resins.

• 상하수도학회지
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• 제23권5호
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• pp.669-678
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• 2009

The reduction of excess activated sludge from petrochemical plant was investigated by the electro fenton (E-Fenton) process using electrogenerated hydroxyl radicals which lead to mineralization of activated sludge to $CO_2$, water and inorganic ions. Factors affecting the disintegration efficiency of excess activated sludge in E-Fenton process were examined in terms of five criteria: pH, $H_2O_2/Fe^{2+}$ molar ratio, current density, initial MLSS (mixed liquid suspended solids) concentration, $H_2O_2$ feeding mode. TSS total suspended solid and $TCOD_{cr}$ reduction rate increased with the increasing $H_2O_2/Fe^{2+}$ molar ratio and current density until 42 and $6.7 mA/cm^2$, respectively but further increase of $H_2O_2/Fe^{2+}$ molar ratio and current density would reduce the reduction rate. On the other hand, as expected, increasing pH and initial MLSS concentration of activated sludge decreas TSS and $TCOD_{cr}$ reduction rate. The E-Fenton process was gradually increased during first 30 minutes and then linearly proceed till 120 minutes. The optimal E-Fenton condition showed TSS reduction rate of 62~63% and $TCOD_{cr}$ (total chemical oxygen demand) reduction rate of 55~56%. Molar ratio $H_2O_2/Fe^{2+} = 42$ was determined as optimal E-Fenton condition with initial $Fe^{2+}$ dose of 5.4 mM and current density of $6.7{\sim}13.3 mA/cm^2$, initial MLSS of 7,600 mg/L and pH 2 were chosen as the most efficient E-Fenton condition.

• 한국세라믹학회지
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• 제33권11호
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• pp.1209-1216
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• 1996

MoSi2-Al2O3 composites were prepared by thermal explosion mode of self-propagating high temperature syn-thesis (SHS) using element powders of MoO3 Mo Si and Al. The combustion products of MoSi2 which have 10, 20, 30 and 40 wt% Al2O3 showed the molten state in the range of Mo to MoO3 6:1-9.5:1, 2:1-8:1, 1:1-5:1, and 1:1-3:1 (molar ratio) respectively. The combustion products which made least seperation the molten phase from the slag phase were in Mo/MoO3=9, 5:1, 8:1, 5:1 and 3:1 (molar ratio) respectively. Particles size of MoSi2 and Al2O3 in the combustion product were decreased as the molar ratio of Mo to MoO3 increase. By XRD analysis only MoSi2 and $\alpha$-Al2O3 peaks were identified in the combusion products, In case of MoSi2 containing 20wt% Al2O3 5.1wt% Al existed into MoSi2 grains and 30.7wt% Si and 7.7wt% Mo existed into Al2O3 grains. The relative density of MoSi2 containing 10, 20, 30 and 40 wt% Al2O3 were 82.7, 85.2, and 81.9% respectively. The fracture strength of MoSi2-Al2O3 composites increased with increasing Al2O3 and that of MoSi2-20wt% Al2O3 composite was 195 MPa.

• Imaging Science in Dentistry
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• 제37권4호
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• pp.197-203
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• 2007

Purpose: To provide diagnostic information by evaluation of the positional relationship between the mandibular third molar and the mandibular canal. Materials and Methods: Eighty-nine mandibular third molars were classified as mesioangular, horizontal, vertical, distoangular groups. The distances between the mandibular third molar and the mandibular canal were measured in cone-beam computed tomographs. The height and width ratios of distances from the mandibular third molar and the mandibular canal to the mandibular inferior border and to the lingual cortical plate were calculated. Results: The vertical and buccolingual distances between the mandibular third molar and the mandibular canal were 0.03 mm, 2.96 mm in the mesioangular, 0.37 mm, 3.38 mm in the horizontal, -1.50 mm, 1.38 mm in the vertical, -1.10 mm, 4.20 mm in the distoangular group. There were significant differences in vertical (P < 0.05), but not in buccolingual (P>0.05). The height and width ratios of distances on the mandibular third molar were 47.1 %, 36.1 % in the mesioangular, 47.4%, 34.4% in the horizontal, 37.0%, 46.7% in the vertical, 40.9%, 37.4% in the distoangular group. There were significant differences between the mesioangular and the vertical group, and the horizontal and the vertical group in height ratio (P < 0.05), and also between the mesioangular and the vertical group in width ratio (P < 0.05). The height and width ratios of distances on the mandibular canal showed no significant differences between groups (P > 0.05). Conclusion : The mesioangular group showed the nearest distance between the mandibular third molar and the mandibular canal vertically. The root apex of the mandibular third molar was positioned more buccally in the vertical group than in the mesioangular group.

• 농업과학연구
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• 제46권4호
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• pp.941-953
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• 2019

Biodiesels are being explored as a clean energy alternative to regular diesel, which causes pollution. In this study, the optimum conditions for producing biodiesel (BD) by combining beef tallow, an animal waste resource with a high saturated fatty acid content, and corn oil, a vegetable oil with a high unsaturated fatty acid content, were investigated, and the fuel properties were analyzed. Furthermore, Multivariate Analysis of Variance (MANOVA) was used to verify the optimum conditions for producing biodiesel. The influences of control factors, such as the oil blend ratio and methanol to oil molar ratio, on the fatty acid methyl ester and biodiesel production yield were investigated. As a result, the optimum condition for producing blended biodiesel was verified to be tallow to corn oil blend ratio of 7 : 3 (TACO7) and a methanol to oil molar ratio of 14 : 1. Moreover, the interaction between the oil blend ratio and the methanol to oil molar ratio has the most crucial effects on the production of oil blended biodiesel. In conclusion, the analysis results of the fuel properties of TACO7 BD satisfied the BD quality standard, and thus, the viability of BD blended with waste tallow as fuel was verified.

• 한국응용과학기술학회지
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• 제23권4호
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• pp.300-306
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• 2006

The esterification of palmitic acid in rapeseed oil and methanol emulsified by propylene glycol with PTSA(p-toluene sulfonic acid) was followed by the transesterification of rapeseed oil into biodiesel with 1(w/v)% GMS(glycerol monostearate) as an emulsifier using TMAH(tetramethyl ammonium hydroxide) catalysts at $60^{\circ}C$. The former reaction was optimized at the 1:20 of molar ratio of oil to methanol and 5wt% PTSA, and the latter was optimized at the 1:8 of molar ratio of oil to methanol and 0.8wt% TMAH. The overall conversion into biodiesel was 98% after 60min of reaction time at the 1:8 of molar ratio, 0.8wt% TMAH and $60^{\circ}C$. TMAH was a good catalyst to control the viscosity of biodiesel mixture.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 춘계 학술발표회 논문집(II)
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• pp.77-80
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• 2006

Graft copolymerized polycarboxylate(PC)-type superplasticizers(PCs) which have carboxylic acid with $\pi$ bond among the molecular structure and polyethyleneglycol methyl ether methacrylate(PMEM) were synthesized by free radical reaction and investigated the chemical structure, polymerization condition, and physical and chemical properties. Also, the effects of PCs in the dispersion, adsorption and hydration of cement were evaluated. As the molecular weight of graft chain decreases, the adsorption amount on cement particles increased. It was advantageous for the flow to reduce molar ratio, the lower the side bone molecular weight, and increase the molar ratio, the larger the side bone molecular weight. The hydration reaction speed was highly delayed at day 1, due to increase in molar ratio and reduction in side bone molecular weight, but it was recovered in the days after.

• 한국세라믹학회지
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• 제32권9호
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• pp.1009-1018
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• 1995

(Ti.Si)C composite powders were synthesized by SHS method using microwave energy. Compositional and structural characterization of the powder were carried out by using scanning electron microscopy and X-ray diffraction. The average particle size of the synthesized (Ti.Si)C composite powders was smaller than that of the starting materials. From the results of the temperature profile, combustion temperature and velocity were decreased with increasing Si molar ratio. With increasing C molar ratio combustion temperature and velocity did not change. (Ti.Si)C composite was sintered at 185$0^{\circ}C$ for 60 min by using hot-pressing with 30 MPa. The best properties were obtained from the sintered specimen whose composition was 1 : 1 : 1.9 molar ratio of Ti : Si : C. The sintering density, flexural strength and vickers hardness of the sintered body were 4.71 g/㎤, 423 MPa and 21 GPa, respectively.