• 멤브레인
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• 제23권2호
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• pp.144-150
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• 2013

본 연구에서는 Poly (ether block amides)(PEBAX) 3533을 이용하여 $N_2$, $O_2$, $CH_4$, $CO_2$, $SO_2$에 대하여 투과도를 측정하였다. 투과선택도를 향상시키기 위하여 분자량 400의 Poly (ethylene glycol) (PEG)를 PEBAX 대비 20%, 40%, 50% 첨가하여 막을 제조한 후 $N_2$, $O_2$, $CH_4$, $CO_2$, $SO_2$ 순으로 투과도 및 순수 기체에 대하여 확산도 및 용해도를 각각의 막에 대하여 Time-lag법을 이용하여 측정하였다. 예상한 바와 같이 PEG 함량의 증가에 따라 순수 기체에 대한 투과도는 증가하였으며, 이상선택도의 경우 PEBAX 3533이 지니는 값과 큰 차이를 나타내지 않았으며 PEG 함량 증가에 따라 투과도의 증가는 각 기체의 PEG에 대한 용해도 증가때문인 것으로 밝혀졌으며 이에 대해서 본문에서 자세히 설명하고자 한다.

• 한국대기환경학회:학술대회논문집
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• 한국대기환경학회 1999년도 추계학술대회 논문집
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• pp.274-276
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• 1999

지구 기온상승에 영향을 주는 가스는 여러 부문에서 배출되지만, 환경기초시설에서는 소각시설에서 이산화탄소($CO_2$)와 아산화질소($N_2$O), 쓰레기매립지에서 메탄(CH$_4$), 하폐수처리장에서 메탄(CH$_4$)과 아산화질소($N_2$O)가 주로 배출된다. 그러나 우리나라에서는 이 부문의 배출량에 대하여 아직 체계적인 조사가 이루어지지 못하였다. 본 연구의 목적은 우리나라의 폐기물 소각시설에서 발생하는 온실가스 배출량을 산출하는 것이다.(중략)

• 한국재료학회지
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• 제12권6호
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• pp.427-430
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• 2002

Plasma nitrocarburizing treatment was performed for SCM 435 steel by using a plasma ion nitriding system. The effects of the variation of nitrogen and methan contents upon the hardened layer was investigated. Both the thickness of the compound layer and the amount of $\varepsilon$ phase in the compound layer increased with increasing nitrogen content. However, the thickness of the compound layer decreased due to unstable plasma for an atmosphere containing 90% $N_2$ gas content in the gas mixture. The amount of $\varepsilon$phase in the compound layer increased with increasing $CH_4$ gas content. For $CH_4$ gas content more than 2% in the gas mixture, the thickness of the compound layer decreased due to the formation of $\theta$ phase.

• Bulletin of the Korean Chemical Society
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• 제35권3호
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• pp.721-724
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• 2014

We have explored the potential energy surface for the dissociation of the pyridazine molecular ion using G3 model calculations. The pathways have been obtained for the formation of five possible $C_4H_4^{+{\bullet}}$ isomers by the loss of $N_2$ and the consecutive $H^{\bullet}$ loss. It is predicted that the methylenecyclopropene radical cation is the predominant product in the loss of $N_2$, which is formed via the allenylcarbene radical cation, and $CH_2=C-C{\equiv}CH^+$ is the predominant product in the consecutive $H^{\bullet}$ loss.

• 한국표면공학회지
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• 제52권6호
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• pp.293-297
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• 2019

Quasi-nano-hardness and corrosion behaviors of neutron-irradiated reactor pressure vessel (RPV) steels such as 15Ch2MFA (Ni<0.4, 2.520 n/㎠ (En>1.0 MeV) for 32 days. Quasi-nano-hardnesses of the 15Ch2MFA and 15Cr2NHFA steels were 183.8 and 179.8 Hv, respectively. Their corrosion rates and corrosion potentials were 2.4×10^-4Acm^-2, -515.9 mV_SHE and 6.8×10^-4 Acm^-2, -523.6 mV_SHE in NACE standard TM0284-96 solution at room temperature, respectively. 15Ch2MFA steel showed better quasi-nano-hardness and corrosion resistance than 15Cr2NHFA steel in this test condition.

• Carbon letters
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• 제25권
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• pp.68-77
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• 2018

Soybean straw (SS)-based activated carbon was employed as a precursor to prepare carbon molecular sieves (CMSs) via chemical vapor deposition (CVD) technique using methane as carbon source. Prior to the CVD process, SS was activated by 0.5 wt% $ZnCl_2$, followed by a carbonization at $500^{\circ}C$ for 1 h in $N_2$ atmosphere. $N_2$ (77 K) adsorption-desorption and $CO_2$ (273 K) adsorption tests were carried out to analyze the pore structure of the prepared CMSs. The results show that increasing the deposition temperature, time or methane flow rate leads the decrease in $N_2$ adsorption capacity, micropore volume and average pore diameter of CMSs. The adsorption selectivity coefficient of $CO_2/CH_4$ achieves as high as 20.8 over CMSs obtained under the methane flow rate of $30mL\;min^{-1}$ at $800^{\circ}C$ for 70 min. The study demonstrates the prepared CMSs are a candidate adsorbent for $CO_2/CH_4$ separation.

• 대한화학회지
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• 제20권3호
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• pp.221-228
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• 1976

$60{\%}$ dioxane 수용액에서 hydrazonyl bromide의 여러 유도체$(p-H,\;p-CH_3,\;p-OCH_3,\;p-Br,\;p-Cl\;및\;p-NO_2)$의 pH에 따르는 가수분해 반응속도를 $25^{\circ}C$에서 자외선 분광광도법으로 측정하여 넓은 pH 범위에서 잘 맞는 반응속도식을 구하였다. 가수분해 반응속도에 미치는 치한기효과를 검토하기 위하여 Hammett plot한 결과 pH 2 이하에서는 ${\Phi}$ = -0. 94, pH 4 이상에서는 ${\rho}$ = 0.54을 얻었다. pH에 따르는 반응속도 상수의 변화에 미치는 용매효과 브롬음이온효과 및 치환기효과등으로 부터 hydrazonyl bromide의 가수분해는 pH 2 이하에서는 carbonium ion 중간체를 거쳐 반응이 진행되는 $S_N1$ pH 4 이상에서는 hydrazonyl bromide에 직접 hydroxide ion이 반응하는 이른바 $S_N2$반응이 그리고 pH 2와 pH 4 사이에서는 이 두반응이 경쟁적으로 일어남을 알 수 있었다.

• Journal of the Korean Wood Science and Technology
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• 제43권2호
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• pp.238-247
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• 2015

Katsura tree (Cercidiphyllum japonicum Sieb. Et Zucc) leaves were collected, air-dried and extracted with 70% aqueous acetone, then concentrated and sequentially fractionated using n-hexane, $CH_2Cl_2$, EtOAc, and $H_2O$ to be freeze dried for antioxidant and ${\alpha}$-glucosidase inhibition activity tests. The antioxidant activity of the extracts was evaluated using DPPH (1,1-diphenyl 2-picrylhydrazyl) free radical scavenging assay. The test concentrations were adjusted to 500, 250, 125, 62.5, 31.25, 15.62, 7.81, 3.9, 1.95 and 0.97 ppm. The $H_2O$ and EtOAc fractions showed higher activities compared with the control, ${\alpha}$-tocopherol, at all concentrations. The crude fraction also gave better activity at the concentrations lower than 62.5 ppm. However, the nonpolar n-hexane and $CH_2Cl_2$ fractions gave prominently lower activities compared with the control at all concentrations. The $IC_{50}$ values of the crude, EtOAc, and $H_2O$ fractions exhibited 11.78, 4.29 and $9.80{\mu}g/m{\ell}$, respectively, compared with $12.08{\mu}g/m{\ell}$ of the control. But the n-hexane and $CH_2Cl_2$ fractions indicated 300 and $91.85{\mu}g/m{\ell}$ of $IC_{50}$, respectively. ${\alpha}$-Glucosidase inhibition activity was evaluated at the concentrations of 50, 25, 12.5, 6.3, 3.1, 1.6 and 0.8 ppm. The inhibition activities were increased according to as the increase of sample concentrations. However, the nonpolar n-hexane and $CH_2Cl_2$ fractions indicated very low inhibition activities compared with acarbose, a positive control. The EtOAc fraction showed very good capability as almost 100% compared with the control at the higher concentrations than 12.5 ppm and the crude fraction also indicated good potential as 95% and 100% at 25 and 50 ppm, respectively. The $H_2O$ fraction gave good inhibition value as 90% at 50 ppm although the value was lower than the control. These results showed that the polar fractions had better ${\alpha}$-glucosidase inhibition activities. The $IC_{50}$ values of the nonpolar fractions, n-hexane and $CH_2Cl_2$, showed very lower values as 468 and $103.6{\mu}g/m{\ell}$, respectively, than the control. ${\alpha}$-Glucosidase Inhibition Activity of the Extracts of Katsura Tree (Cercidiphyllum japonicum Sieb. Et Zucc) Leaves However, the polar fractions, crude, EtOAc and $H_2O$, showed 7.1, 3.7 and $13{\mu}g/m{\ell}$, respectively, indicating that these fractions can be used as natural bioresources for treating diabetes mellitus. Also ${\alpha}$-glucosidase inhibition activity had a positive correlation with antioxidant activity of the extracts.

• Asian-Australasian Journal of Animal Sciences
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• 제20권11호
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• pp.1705-1712
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• 2007

The effect of different tropical feed sources on rumen ecology, cellulolytic bacteria, feed intake and digestibility of beef cattle was investigated. Four fistulated, castrated male crossbred cattle were randomly allocated to a $4{\times}4$ Latin square design. The treatments were: T1) urea-treated (5%) rice straw (UTS); T2) cassava hay (CH); T3) fresh cassava foliage (FCF); T4) UTS:FCF (1:1 dry matter basis). Animals were fed concentrates at 0.3% of body weight on a DM basis and their respective diets on an ad libitum basis. The experimental period was 21 days. The results revealed that the use of UTS, CH, FCF and UTS:FCF as roughage sources could provide effective fiber and maintain an optimal range of ruminal pH and $NH_3-N$. Total viable and cellulolytic bacterial populations were enhanced (p<0.05) with UTS as the roughage source. Animals fed FCF had a higher rumen propionate production (p<0.05) with a lower cellulolytic bacteria count. Moreover, three predominant cellulolytic bacteria species, namely Fibrobacter succinogenes, Ruminococcus albus and Ruminococcus flavefaciens, were found in all treatment groups. Roughage intake and total DM intake were highest with UTS (2.2 and 2.5% BW, respectively) as the roughage source (p<0.05). Nutrient intake in terms of organic matter intake (OMI) was similar in UTS, CH and UTS:FCF treatments (8.0, 6.8 and 8.7 kg/d, respectively), while crude protein intake (CPI) was enhanced in CH, FCF and UTS:FCF as compared to the UTS treatment (p<0.05). Digestion coefficients of DM and organic matter (OM) were similar among treatments, while the CP digestion coefficients were similar in CH, FCF and UTS:FCF treatments, but were higher (p<0.05) in CH than in UTS. CP and ADF digestible intakes (kg/d) were highest (p<0.05) on the CH and UTS treatments, respectively. It was also observed that feeding FCF as a full-feed resulted in ataxia as well as frequent urination; therefore, FCF should only be fed fresh as part of the feed or be fed wilted. Hence, combined use of FCF and UTS as well as CH and FCF were recommended.

• 한국주조공학회지
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• 제38권2호
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• pp.41-47
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• 2018

In a numerical study, equations relating the mechanical properties and cooling rate in a casting process have been applied to an AC4CH cast aluminum alloy. Good agreement was found between the measured and predicted material properties. Step-shaped steel blocks were made to comprise a casting mold with a Y-shaped cavity. Thermometers were inserted into each step of the mold to investigate temperature changes. The microstructure and mechanical properties, such as hardness and tensile stress were measured for each cut of piece. The correlation between the cooling rate and SDAS was found by curved fitting. Moreover, both the solidification time and the temperature were simulated using a commercial package, ZCast. The simulation results for yield strength, tensile strength, elongation, and hardness were compared with experimental results. Using the estimated K and n values, the hardness values of a ship propeller were simulated, and the results were similar to those obtained for actual castings.