• 대한수학회논문집
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• 제33권2호
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• pp.515-525
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• 2018

In this paper, we investigate a modified $G^2$ transform on a class of Boehmians. We prove the axioms which are necessary for establishing the $G^2$ class of Boehmians. Addition, scalar multiplication, convolution, differentiation and convergence in the derived spaces have been defined. The extended $G^2$ transform of a Boehmian is given as a one-to-one onto mapping that is continuous with respect to certain convergence in the defined spaces. The inverse problem is also discussed.

• 한국음향학회지
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• 제37권2호
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• pp.110-117
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• 2018

본 논문에서는 음성/오디오 부호화기를 위한 저지연 윈도우 스위칭 MDCT(Modified Discrete Cosine Transform) 방법을 제안한다. 윈도우 스위칭 알고리즘을 사용하여 신호의 특성이 빨리 변하는 전이 구간에서 음질 저하를 개선하고, 저지연 TDAC(Time Domain Aliasing Cancellation)를 사용하여 알고리즘 지연을 1/2로 줄일 수 있는 MDCT 방법을 제안한다. 제안된 윈도우 스위칭 방법은 기존 윈도우 스위칭 알고리즘이 다른 길이의 중첩합(overlap-add)을 사용하는 것과 달리, 일정한 길이의 중첩합을 사용하여 알고리즘 지연을 1/2로 줄일 수 있었고, 신호의 특성에 따라 윈도우의 종류를 2개로 줄여 프레임 상태를 표현하는 정보 비트를 1 bit 감소시킬 수 있었다. 제안한 알고리즘을 MDCT 기반의 음성/오디오 부호화기인 ITU-T(International Telecommunication Union - Telecommunication) G.729.1 부호화기에 적용하여 성능을 확인하였으며, 알고리즘 지연을 절반으로 감소시키면서 동일한 음질을 유지할 수 있었다.

• Elastomers and Composites
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• 제57권2호
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• pp.40-47
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• 2022

The effects of maleic-anhydride-grafted polypropylene (PP-g-MAH) and montmorillonite (MMT) on the wear resistance of polypropylene (PP) were investigated. The surface of MMT was modified with 3-aminopropyltriethoxysilane, and the interfacial interaction between PP and MMT was improved using PP-g-MAH. Fourier-transform infrared spectroscopy was used to confirm that silane was grafted on the surface of MMT. The Taber abrasion test and scanning electron microscopy were used to determine the wear resistance and observe the surface morphology of PP, respectively, after wear testing. Energy-dispersive X-ray spectroscopy was used to compare the effects of PP-g-MAH and silane modification of MMT on the dispersion of MMT. The results indicated that silane was successfully grafted onto the surface of MMT. Moreover, the wear resistance of PP was improved by the addition of MMT. The wear resistance of PP composites comprising silane-modified MMT and PP-g-MAH was higher than those of other PP composites. This was attributed to silane improving the interfacial interaction between MMT and PP.

• Elastomers and Composites
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• 제53권2호
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• pp.57-66
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• 2018

Styrene-butadiene rubber (SBR), reinforced with different contents of silica (with or without modification using silane coupling agents), was prepared by a modified sol-gel method involving hydrolyzation of tetraethoxysilane over an acid catalyst. The structures of the as-prepared samples were characterized using various techniques, such as scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and thermogravimetric analysis. The mechanical properties of the as-prepared samples were discussed in detail. The results revealed an increasing of the storage modulus (G') with increase in the silica content without modification. In contrast, G' decreased after modification using silane coupling agents, indicating a reduction in the silica-silica interaction and improved dispersion of silica in the SBR matrix. Both tensile stress and hardness increased with increase in the silica content (with modification) in the SBR matrix, albeit with low values compared to the samples with un-modified silica, except for the case of silica modified using (3-glycidyloxypropyl) trimethoxysilane (GPTS). The latter observation can be attributed to the special structure of GPTS and the effort of oxygen atom lone-pair.

• 한국가스학회지
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• 제26권2호
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• pp.1-8
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• 2022

본 연구에서는 탄산염암 저류층에서 활용 가능한 GPTMS((3-Glycidoxypropyl)trimethoxysilane)-SiO₂ 나노유체를 제조하고 주입 효과를 분석하였다. 표면개질에 따른 나노입자의 구조적 변화를 확인하기 위해 푸리에변환적외선분광(Fourier transform infrared spectroscopy, FTIR) 분석을 수행했으며, 0.5 mmol/g 이상의 GPTMS 농도에서 실리카 입자의 표면개질을 의미하는 2,950 cm^-1의 C-H 신축 진동(C-H stretching vibration)을 확인하였다. 또한, 친유성 상태로 에이징된 석회석과 백운석을 대상으로 나노입자의 농도와 주입률에 따른 GPTMS-SiO₂ 나노유체의 코어유동 실험을 수행하였다. 나노유체 주입에 따라 최대 18.9%의 오일이 추가로 회수되었으며, 암석의 접촉각과 투과도 변화를 확인할 수 있었다. 이는 나노입자가 탄산염암 표면에 흡착됨에 따라 습윤도를 개선함과 동시에 공극에 영향을 준다는 것을 의미한다. 따라서, 제조된 나노유체는 탄산염암 저류층을 대상으로 한 석유회수증진의 주입유체로 사용될 수 있으며 습윤도, 투과도 변화와 같은 유체 유동물성 개선에 활용될 것으로 기대된다.

• Journal of Ceramic Processing Research
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• 제20권4호
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• pp.411-417
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• 2019

Graphene doped zinc oxide nanoparticles (G-ZnO) were prepared using modified hummer's technique together with the ultrasonic method and characterized by field emission scanning electron microscopy (FESEM), X-ray powder diffraction (XRD), fourier-transform infrared spectroscopy (FTIR) and high-resolution transmission electron microscopy (HRTEM). Different samples of epoxy resin nanocomposites reinforced with G-ZnO nanoparticles were prepared and were marked as F1 (without adding nanoparticles), F2 (1% w/w G-ZnO), and F3 (2% w/w G-ZnO) in combination of ≈ 56:18:18:8w/w% with epoxy resin/hardener, ammonium polyphosphate, boric acid, and Chitosan. The peak heat release rate (PHRR) of the epoxy nanocomposites was observed to decrease dramatically with the increasing G-ZnO nanoparticles. However, the LOI values increased significantly with the increase in wt % of G-ZnO nanoparticles. From the UL-94V data, it was confirmed that the F2 and F3 samples passed the flame test and were rated as V-0. The results obtained in the present work clearly revealed that the synthesized samples can be used as efficient materials in fire-retardant coating technology.

• 한국재료학회지
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• 제22권6호
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• pp.275-279
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• 2012

(3-mercaptopropyl)trimethoxysilane (MPTMS) was used as a silylation agent, and modified silica nanoparticles were prepared by solution polymerization. 2.0 g of silica nanoparticles, 150 ml of toluene, and 20 ml of MPTMS were put into a 300 ml flask, and these mixtures were dispersed with ultrasonic vibration for 60 min. 0.2 g of hydroquinone as an inhibitor and 1 to 2 drops of 2,6-dimethylpyridine as a catalyst were added into the mixture. The mixture was then stirred with a magnetic stirrer for 8 hrs. at room temperature. After the reaction, the mixture was centrifuged for 1 hr. at 6000rpm. After precipitation, 150 ml of ethanol was added, and ultrasonic vibration was applied for 30 min. After the ultrasonic vibration, centrifugation was carried out again for 1 hr. at 6000rpm. Organo-modification of silica nanoparticles with a ${\gamma}$-methacryloxypropyl functional group was successfully achieved by solution polymerization in the ethanol solution. The characteristics of the ${\gamma}$-mercaptopropyl modified silica nanoparticles (MPSN) were examined using X-ray photoelectron spectroscopy (XPS, THERMO VG SCIENTIFIC, MultiLab 2000), a laser scattering system (LSS, TOPCON Co., GLS-1000), Fourier transform infrared spectroscopy (FTIR, JASCO INTERNATIONL CO., FT/IR-4200), scanning electron microscopy (SEM, HITACHI, S-2400), an elemental analysis (EA, Elementar, Vario macro/micro) and a thermogravimetric analysis (TGA, Perkin Elmer, TGA 7, Pyris 1). From the analysis results, the content of the methacryloxypropyl group was 0.98 mmol/g and the conversion rate of acrylamide monomer was 93%. SEM analysis results showed that the organo-modification of ultra-fine particles effectively prevented their agglomeration and improved their dispensability.

• Nuclear Engineering and Technology
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• 제50권1호
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• pp.211-215
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• 2018

Chitosan was modified by gamma radiation-induced grafting with maleic acid and then used for the removal of cobalt ions from aqueous solutions. Chitosan-g-maleic acid was characterized by Fourier Transform infrared spectroscopy (FT-IR). The effect of the dose (1-5 kGy) and monomer concentration (0.3-1.3%, m/v) on the grafting ratio was examined. The adsorption kinetics and isotherms were also investigated. The results showed that the optimal dose for grafting was 2 kGy. When monomer concentration was within the range of 0.3-1.3% (m/v), the grafting ratio increased almost linearly. For the adsorption of cobalt ions by chitosan-g-maleic acid beads, the pseudo second-order kinetic model ($R^2=0.99$) and Temkin isotherm model ($R^2=0.96$) were able to fit the experimental data reasonably well. The equilibrium adsorption capacity of cobalt ions increased from 2.00 mg/g to 2.78 mg/g after chitosan modification.

• 한국식품영양학회지
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• 제12권3호
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• pp.233-239
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• 1999

To develop the potential use as new host strain for gene cloning the optimal conditions for transform-ation of alkali-tolerant Bacillus sp. were examined. The Bacillus sp. YA-14 was cultured to late logarith-mic growth phase at 37$^{\circ}C$ in modified SPI medium (pH8.0) containing 0.4% MgSO4 0.5mM CaCl2 1 ml of competent cell was mixed with 0.5$\mu$g of plasmid DNA and incubated with shaking at 37$^{\circ}C$ for 40min. The transformation frequency under the optimal condition was 4.53$\times$10-6 CFU/ml/g plasmid DNA. The electrophresis and stably maintained in the new host.

• 한국지하수토양환경학회지:지하수토양환경
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• 제20권2호
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• pp.22-31
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• 2015

In the present study, surface of laccase producing Ceriporia lacerata was modified using 4-bromobutyryl chloride and polyethylenimine. The modified biomass was freeze dried and utilized as a biosorbent for the removal of Ni(II) from aqueous solution. The physicochemical properties of the biosorbent were analyzed using scanning electron microscopy and Fourier transform infrared spectroscopy. Batch experiments were carried out as a function of contact time (0-60 min), pH (2 to 8), adsorbent dosage (25-150 mg), and initial Ni(II) concentration (25-125 mg/L). The results indicate that surface modified biosorbent effectively adsorbed (9.5 mg/0.1 g biomass) Ni(II) present in the solution. The equilibrium adsorption data were modeled with different kinetic and isotherm models. The Ni(II) adsorption followed pseudo-first-order kinetics (R² = 0.998) and Langmuir isotherm (R² = 0.994) model. Hydroxyl and carbonyl functional groups present in biomass play a major role in the adsorption of Ni(II). The adsorbed Ni(II) from the biosorbent was successfully desorbed (85%) by 1M HCl. The results of the study indicate that the surface modified C. lacerate biomass could be used for the treatment of Ni(II) contaminated ground waters.