• Korean Chemical Engineering Research
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• 제51권6호
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• pp.774-779
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• 2013

We synthesized the solution processible monodispersed $TiO_2$ crystalline nano-sol with ~ 5 nm in size by sol-gel method. Through the spin-coating of crystalline $TiO_2$ nano-sol at low processing temperature, we could make even blocking interlayer on the rough FTO transparent electrode substrate. The rough FTO surface could be gradually smoothed by the spin-coating of nano-crystalline $TiO_2$ sol based blocking interlayer. The 1, 2.5, 5, and 10 wt% of nanocrystalline $TiO_2$ sol formed 29, 38, 62, and 226 nm-thick of blocking interlayer in present experimental condition, respectively. The 5 and 10 wt% of $TiO_2$ nano-sol could effectively fill up the valley part of bare FTO with 48.7 nm of rms (root mean square) roughness and consequently enabled the ZnO to be grown to vertically aligned one dimensional nanorods on the flattened blocking interlayer/FTO substrate.

• Journal of Life Science
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• 제30권2호
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• pp.162-168
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• 2020

Because of a continual reduction in its domestic market share, the quality of the Makgeolli, a Korean traditional liquor, needs to be upgraded. Among the several options for quality improvement, sufficient organoleptic expression of flavor is very important. We analyzed production changes of isoamyl acetate, which has a banana smell, based on fermentation temperature and sugar content through the cultivation of S. cerevisiae 98-5 KCCM 11396P using generally polished rice. The banana flavor of that fermentation mash was organoleptically high at 20℃, but a larger amount of isoamyl acetate was obtained with a higher sugar content at 10℃, based on analysis by GC-MS. Consequently, sufficient production of banana flavor from isoamyl acetate was based on the concentration of isoamyl alcohol as a substrate compound of isoamyl acetate, and the production depended highly on the maintenance of heat stability, since it is unstable in temperature and the minimized inhibition of alcohol acetyl transferase by unsaturated fatty acids. We also found that production of the flavor component required the addition of sugar and a slightly higher temperature of 20~25℃ at the beginning stage of fermentation, with additional mash fermentation and a gradual decrease in temperature to 10~15℃.

• Korean Journal of Ecology and Environment
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• 제50권4호
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• pp.363-373
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• 2017

This study was conducted to evaluate the characteristics of geosmin production of Anabaena circinalis under different environmental condition. The test cyanobacterium was isolated from Lake Paldang. The growth rate and geosmin production of A. circinalis were examined with different variables including temperature (10, 15, 20, $25^{\circ}C$), light intensity (60, 120, $240{\mu}mol\;photons\;m^{-2}\;s^{-1}$), and phosphorus concentration (0.01, 0.05, 0.25, 0.50, $1.00mg\;L^{-1}$). The highest growth rate and chlorophyll-a (Chl-a) concentration appeared at $25^{\circ}C$, $60{\mu}mol\;photons\;m^{-2}\;s^{-1}$ and $1.00mgP\;L^{-1}$ for temperature, light intensity, and P concentration, respectively. Total geosmin production was highest at the optimal growth condition of each variable, while chlorophyll-specific geosmin production (the ratio of geosmin to Chl-a) was higher at the less favorable growth condition, indicating high potential of the off-flavor problem during low temperature period, e.g., late fall and early winter. Our results demonstrated that geosmin production of A. circinalis was directly related to chlorophyll synthesis and varied with cellular growth condition.

• Applied Chemistry for Engineering
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• 제9권4호
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• pp.491-496
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• 1998

The composition of isocyanates and polyols influence prepolymeric properties of adhesive and calking sealant based on polyurethanes (PU). One component moisture curing prepolymers, which reacted with surface humidity of substrate, were synthesized in several kinds of composition. Reactivity, structural change and properties of the prepolymers were studied as a preliminary step to manufacture PU based adhesive and sealant. To study the effects of mole ratio ([NCO]/[OH]), we used toluene diisocyanate (TDI), 4, 4'-diphenylmethane diisocyanate (MDI), and ether-polyols such as PTMG and PPG which have good resistance to hydrolysis and excellent low-temperature properties. The each prepolymers could be prepared in different molecular weight without any significant structural change. The mole ratio 1.78 of [NCO] to [OH] showed the fastest reactivity. It was confirmed that effect of polyols was larger than that of isocyanates on the prepolymer in reactivity. Several kinds of compounds were manufactured with each prepolymer, and tensile and properties were tested. And the optimum quantity of curing accelerator for the PU was 0.05~0.1%. In the tensile test, TDI based PU was superior to MDI based PU, and also PTMG based PU was superior PPG based PU.

• Elastomers and Composites
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• 제42권4호
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• pp.238-248
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• 2007

A series of polyhydroxyamides(PHAs) having ether linkages in the polymer backbone were prepared via solution polycondensation at low temperature. These polymers were studied by FT-IR, $^1H-NMR$, DSC, TGA and PCFC. The PHAs exhibited inherent viscosities in the range of $0.5{\sim}1.1dL/g\;at\;35^{\circ}C$ in DMAc solution. Most of PHAs except PHA 3 were soluble in polar organic solvents such as N,N-dimethylacetamide(DMAc), N-methyl-2-pyrrolidone(NMP), and N,N-dimethylform-amide(DMF). Subsequent thermal treatment of PHAs afforded polybenzoxazols(PBOs). However, the PBOs were insoluble in a variety of solvents. Most of the PBOs except PBO 3 showed glass-transition temperature($T_g$) in the range of $200{\sim}246^{\circ}C$ by DSC and maximum weight loss temperature in the range of $597{\sim}697^{\circ}C$ in nitrogen by TGA. PBOs showed high char yields in the range of $51{\sim}64%$. PCFC results of the PBOs showed the heat release(HR) capacity, $8{\sim}65J/gK$ and total heat release(total HR), $2.4{\sim}4.7kJ/g$.

• Journal of Life Science
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• 제23권4호
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• pp.487-494
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• 2013

An AlaAT knock-out mutant (alaat) of rice (Oryza sativa L.) was isolated from T-DNA tagging lines and the genotypes of its progeny were determined with AlaAT1-specific primers. The alaat phenotypes showed decreased growth and grain yield when compared with control plants. The activity of AlaAT1 in the mutant plants was practically undetectable. The responses of alaat plants to growth under salt stress were compared with those of control plants by measuring chlorophyll fluorescence and the activities and mRNA expression of antioxidant enzymes. All abiotic stresses tested (salt, drought, and chilling) caused a similar decrease in chlorophyll fluorescence in both alaat and wild type plants. The activity of peroxidase (POX), an antioxidant enzyme, decreased following salt treatment of alaat plants, while control plant showed an increased activity. The mRNA levels for cAPX (cytosolic ascorbate peroxidase), POX2, and AlaAT were determined by RT-PCR following salt stress. No AlaAT1 mRNA was detected in alaat plants. The POX2 mRNA showed a slightly increased level in the wild type but was not detected in alaat plants, in agreement with the activity assays. The levels of cAPX mRNA were greatly increased in both the wild type and alaat plants. The salt stress effects on rice plant growth are therefore proposed to reflect a loss of function of AlaAT, which alters the activity and synthesis of antioxidant enzymes (especially peroxidases), rather than a direct effect on photosynthesis.

• Journal of the Korean Society of Food Science and Nutrition
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• 제35권10호
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• pp.1399-1404
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• 2006

Structured lipid (SL) containing conjugated linoleic and caproic acid was produced from soybean oil through lipase-catalyzed reaction, and its oxidative stability was compared. When heated at $60^{\circ}C\;or\;150^{\circ}C$, soybean oil as control was more susceptible to oxidation than SL. When the antioxidants, such as ascorbyl palmitate, tea polyphenol, alpha-tocopherol, and rosemary extract, were added in SL, the induction periods of each antioxidant treats in SL were increased. The tea polyphenol showed the most effective antioxidant activity among them. When the emulsion form with SL was heated from oxidation, its oxidation stability was reduced compared to SL. The oxidation stability were also observed in photooxidation of SL.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 한국결정성장학회 1996년도 제11차 KACG 학술발표회 Crystalline Particle Symposium (CPS)
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• pp.55-85
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• 1996

지르코니아 분말은 ZrO2 결정상이 온도변화에 따라 부피변화를 수반하는 상전이변태를 나타낸다. 단사정 ZrO2가 110$0^{\circ}C$에서는 정방정으로, 2$700^{\circ}C$ 내외에서는 입방정으로 결정구조가 가역적으로 변한다. 이 ZrO2에 금속산화물을 고용시키면 형석 (CaF2:Florite)형의 입방정 결정구조가 실온에서도 안정하게 존재하게 된다. 안정화제 산화물은 caO, MgO등 2가 산화물외에 3가 또는 4가의 금속산화물로서 Sc2O3, Y2O3, Sm2O3, Nd2O3, Gd2O3, Y2O3, CeO2 등이며 이들은 금속이온의 원자가가 변하기 쉬운 희토류 산화물이다. 안정화 지르코니아는 형석형 결정구조이며 결정화학적으로 보면 금속양이온이 산소이온에 대해서 정육면체형의 8배위를 하고 있다. 이때 이온반경비(양이온/음이온)에 따라 Zr+4자리와 O-2자리의 격자위치와 모양이 형성되므로 비틀어진 정육면체구조이건 이상적인 정육면체 형석구조를 이룬다. 이는 지르코니아의 결정상의 2상-3상인 부분안정화 지르코니아다결정체(PSZ : partially stabilized zirconia)이거나 단일상-2상인 정방정 지르코니아다결정체(TZP : tetragonal zirconia polycrystal)의 결정구조를 가지는데 기인한다. PSZ는 주로 MgO, CaO를 안정화제로 고용시켜 입방정 영역에서 소결하고 이를 다시 입방정과 정방정의 상 영역에서 열처리하여 입방정 입자내부에 정방정을 석출 형성시킨 것이며 TZP는 Y2O3 및 CeO2를 고용시켜 PSZ와 다르게 일반적인 상압소결한 정방정 결정상의 미립자이다. 산화지르코늄 분말은 지르콘사에서 열분해시킨 지르코늄소결.융해괴(caustic fusion clinker)를 산처리하여얻어진 지르코늄산용액(zirconyl acid solution : cloride, sulfide, nitride 등)으로부터 제조된다. 고순도 산화지르코늄은 용액 결정석출법에 의해 ZrOCl2.8H2O, 5ZrO2.3SO3.15H2O, ZrO(NO3)2.xH2O 등의 지르코늄 수화물만을 재결정화시킨 것으로부터 얻을 수 있으며 이 지르코늄염 수용액으로부터 입자미세구조를 효과적으로 제어하여 산화지르코늄 및 안정화 지르코니아 분말제조가 가능하다. 안정화 지르코니아 분말은 ZrO2와 안정화산화물의 고용을위하여 가열처리를 필요로 하며 일정온도에서 최적상태로 숙성하므로서 2가지 상(phase) 이상의 고용체를 가지게 된다. 안정화 지르코니아 분말은 고용처리온도를 낮추고 효과적으로 생성시키기 위해서는 지르코늄 및 안정화제염을 혼합하고 습식 직접합성하여 저온에서 고용체의 합해진상 영역을 생성시키는 것이다. 이는 지르코니아 원료분말의 미세구조를 제어하므로서 가능하며 이때 화학성분조성과 크기형태가 균일하게 분포된 입자분말을 얻을 수 있다.

• New Physics: Sae Mulli
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• 제68권12호
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• pp.1302-1307
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• 2018

The crystallographic, electrical and magnetic behaviors of magnetite powder in the vicinity of its Verwey transition were investigated in this study. Magnetite was prepared by synthesizing a nanoparticle precursor and then annealing it at $800^{\circ}C$ for 1 h under a dynamic vacuum. Crystallographic and morphology analyses were done by using scanning electron microscope (SEM) and X-ray diffraction (XRD). The electrical and the magnetic properties were examined by using $M{\ddot{o}}ssbauer$ spectroscopy, vibrating sample magnetometer (VSM) and resistivity measurement. Both the magnetic moment and the resistivity showed discontinuous changes at the Verwey transition temperature ($T_V$). The temperature dependence of magnetic anisotropy constant showed a monotonic decrease with increasing temperature, with slight dip near $T_V$. $M{\ddot{o}}ssbauer$ spectra showed the superposition of two sextets, one from the tetrahedral (A) and the other from the octahedral (B) sites. The results revealed that identical charge states existed in the B site at temperatures both above and below $T_V$. A coordination crossover resulted in a transition from an inverse to a normal spinel at or close to $T_V$.

• Applied Chemistry for Engineering
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• 제33권6호
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• pp.581-587
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• 2022

The leather industry generates a large amount of hazardous leather waste of various types every year. Among them, shaving scrap is difficult to recycle because it contains chromium ions. Many studies in recent years have shown that shaving scraps can be processed into various types of valuable products, such as adsorbent, filler, and poultry feed. In this study, collagen peptides were extracted from shaving scraps and structurally modified to be developed as new materials with improved physicochemical properties. First, the chromium ions contained in the shaving scraps were removed using a sodium hydroxide solution, and purified through concentration and low-temperature crystallization. The purified collagen peptide was used to prepare the powder using a spray dryer. The extracted collagen peptides were structurally modified by introducing double bonds by reacting with methacrylic anhydride (MAA), and the product was confirmed by ¹H NMR spectroscopy. Next, a copolymer was prepared by redox polymerization of the modified collagen peptide (MCP) and 2-ethylhexyl acrylate (2-EHA). The structure of the copolymer was qualitatively confirmed by FT-IR. In conclusion, this study confirmed that collagen peptides can be extracted from shaving scrap and converted into new eco-friendly materials through certain treatments.