• Corrosion Science and Technology
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• 제18권5호
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• pp.196-205
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• 2019

Surface modification techniques are known to improve SCC by adding large compressive residual stresses to metal surfaces. This surface modification technology is attracting attention because it is an economical and practical technology compared to the maintenance method of existing nuclear power plants. Surface modification techniques include laser, water jet and ultrasonic peening, pinning and ultrasonic Nano-crystal surface modification (UNSM). The focus of this study was on the effect of ultrasonic amplitude in UNSM treatment on the corrosion properties of Alloy 600. A microstructure analysis was conducted using an optical microscope (OM), scanning electron microscope (SEM) and electron backscattering diffraction (EBSD). A cyclic polarization test and AC-impedance measurement were both used to analyze the corrosion properties. UNSM treatment influences the corrosion resistance of Alloy 600 depending on its amplitude. Below the critical amplitude value, the pitting corrosion properties are improved by grain refinement and compressive residual stress, but above the critical amplitude value, crevices are formed by the formation of overlapped waves. These crevices act as corrosion initiators, reducing pitting corrosion resistance.

• Progress in Superconductivity
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• 제9권1호
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• pp.62-67
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• 2007

The effects of the heat-treatment temperature on the carbon (C) substitution amount, full width at half maximum (FWHM) value, critical temperature ($T_c$), critical current density ($J_c$) have been investigated for 10 wt % malic acid ($C_4H_6O_5$)-doped $MgB_2/Fe$ wires. All the samples were fabricated by the in-situ powder-in-tube (PIT) method and heat-treated within a temperature range of $650^{\circ}C$ to $1000^{\circ}C$. As the heat-treatment temperature increased, it seemed that the lattice distortion was increased by a more active C substitution into the boron sites from the malic acid addition. These increased electron scattering defects seemed to enhance the $J_c-H$ properties in spite of an improvement in the crystallinity, such as a decrease of the FWHM value and an increase of the $T_c$. Compared to the un-doped wire heat-treated at $650^{\circ}C$ for 30 min, the $J_c$ was enhanced by the C doping in a high-field regime. The wire heat-treated at $900^{\circ}C$ resulted in a higher magnetic $J_c$ of approximately $10^4\;A/cm^2$ at 5 K and 8 T.

• 한국세라믹학회지
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• 제34권10호
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• pp.1083-1091
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• 1997

반응성이 좋은 미분말의 고온 초전도상을 얻고자 액상 합성법 중의 하나인 옥살산염법을 이용하였다. 본 방법을 사용하여 합성 분체의 초기 형상과 입도를 제어하였고, 개선된 균일성을 가진 Bi(Pb)-Sr-Ca-Cu-O 초전도 분말을 제조할 수 있었다. 합성된 산화물 초전도체 분말의 특성 및 pellct으로 성형후 열처리한 시편의 미세구조와 전기적특성을 조사하였다. 또한, Tape casting법에 의해 후막을 제작하여 미세구조와 전기적 특성을 관찰하였다. 합성된 분말의 입자 크기는 100~300nm 이하의 구형이었으나 대부분이 1~3 ${\mu}{\textrm}{m}$ 크기로 응집되어 있었다. 84$0^{\circ}C$로 72시간 동안 열처리한 괴상 시편의 임계저항온도는 110K였으며, 열처리한 후막의 임계전류는 각각 0.6A, 1.9A였다.

• 한국축산식품학회지
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• 제35권1호
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• pp.35-40
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• 2015

Super- and sub-critical water treatments have been of interest as novel methods for protein hydrolysis. In the present study, we studied the effect of sub-critical water (Sub-$H_2O$, $300^{\circ}C$, 80 bar) treatment as well as super-critical water (Super-$H_2O$, $400^{\circ}C$, 280 bar) treatment on the physicochemical properties of porcine skin (PS), which has abundant collagen. Porcine skin was subjected to pre-thermal treatment by immersion in water at $70^{\circ}C$, and then treated with sub- or super-critical water. Physicochemical properties of the hydrolysates, such as molecular weight distribution, free amino acid content, amino acid profile, pH, color, and water content were determined. For the molecular weight distribution analysis, 1 kDa hydrolyzed porcine skin (H-PS) was produced by Super-$H_2O$ or Sub-$H_2O$ treatment. The free amino acid content was 57.18 mM and 30.13 mM after Sub-$H_2O$ and Super-$H_2O$ treatment, respectively. Determination of amino acid profile revealed that the content of Glu (22.5%) and Pro (30%) was higher after Super-$H_2O$ treatment than after Sub-$H_2O$ treatment, whereas the content of Gly (28%) and Ala (13.1%) was higher after Sub-$H_2O$ treatment. Super-$H_2O$ or Sub-$H_2O$ treatment affected the pH of PS, which changed from 7.29 (Raw) to 9.22 (after Sub-$H_2O$ treatment) and 9.49 (after Super-$H_2O$ treatment). Taken together, these results showed that Sub-$H_2O$ treatment was slightly more effective for hydrolysis than Super-$H_2O$ was. However, both Sub-$H_2O$ and Super-$H_2O$ treatments were effective processing methods for hydrolysis of PS collagen in a short time and can be regarded as a green chemistry technology.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 제35회 춘계학술대회
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• pp.248-254
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• 2002

The most controversial topics in plasma sprayed ceramic coating system are recently mechanical properties such as bond strength, cohesive strength, toughness and so on. Determination of bond strength of coatings is one of the most important problems. In the industry, the bond strength of coating system has been estimated by Pull-off test(ASTM standard C633-79). But, without a fixed jig and specimen, it is impossible to obtain the bond strength. Therefore, it is necessary to study the critical fracture load on interface of the coating by indentation test. Because the critical fracture load plays an important role in evaluating the bond strength for plasma sprayed ceramic coating system. So, we have estimated critical fracture load in plasma sprayed ceramic coating system, and it was shown that inverse relationship between the cross-section hardness of coating and the critical fracture load(Pc). In case of the high load(1kgf, 2kgf) in $Al_{2}O_{3}+13%TiO_{2}$, it was found that the critical point(Pco), which the coating was broken on.

• 천문학회보
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• 제46권1호
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• pp.47.2-47.2
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• 2021

Focusing on both small separations and baryonic acoustic oscillation scales, the cosmic evolution of the clustering properties of peak, void, wall, and filament-type critical points is measured using two-point correlation functions in ΛCDM dark matter simulations as a function of their relative rarity. A qualitative comparison to the corresponding theory for Gaussian random fields allows us to understand the following observed features: (i) the appearance of an exclusion zone at small separation, whose size depends both on rarity and signature (i.e. the number of negative eigenvalues) of the critical points involved; (ii) the amplification of the baryonic acoustic oscillation bump with rarity and its reversal for cross-correlations involving negatively biased critical points; (iii) the orientation-dependent small-separation divergence of the cross-correlations of peaks and filaments (respectively voids and walls) that reflects the relative loci of such points in the filament's (respectively wall's) eigenframe. The (cross-) correlations involving the most non-linear critical points (peaks, voids) display significant variation with redshift, while those involving less non-linear critical points seem mostly insensitive to redshift evolution, which should prove advantageous to model. The ratios of distances to the maxima of the peak-to-wall and peak-to-void over that of the peak-to-filament cross-correlation are ~2-√~2 and ~3-√~3WJ, respectively, which could be interpreted as the cosmic crystal being on average close to a cubic lattice. The insensitivity to redshift evolution suggests that the absolute and relative clustering of critical points could become a topologically robust alternative to standard clustering techniques when analysing upcoming surveys such as Euclid or Large Synoptic Survey Telescope (LSST).

• 폴리머
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• 제37권1호
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• pp.61-65
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• 2013

본 실험에서는, 양극산화 처리된 탄소섬유의 표면변화가 탄소섬유강화 복합재료의 기계적 계면특성을 통하여 살펴보았다. 양극산화 처리된 탄소섬유의 표면특성은 FTIR, XPS, 그리고 SEM을 통하여 알아보았다. 복합재료의 기계적 계면특성은 층간전단강도(interlarminar shear strength; ILSS)와 임계세기인자(critical stress intensity factor; $K_{IC}$) 그리고 임계변형속도에너지(critical strain energy release rate; $G_{IC}$)를 통하여 고찰하였다. 실험결과 양극산화에 의한 각각의 표면 처리된 탄소섬유는 표면특성의 변화를 가져오며, 복합재료의 ILSS, $K_{IC}$, 그리고 $G_{IC}$같은 기계적 계면특성은 탄소섬유의 양극산화를 통하여 향상되어진다. 전해질이 20% 황산/질산(3/1)일 때 다른 전해질보다 기계적 물성의 가장 큰 향상을 보였다. 이는 양극산화로 탄소섬유와 매트릭스 사이의 계면결합력의 향상때문이라 판단된다.

• 한국건설순환자원학회지
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• 제12권1호
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• pp.16-22
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• 2017

• 천문학회지
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• 제24권1호
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• pp.1-12
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• 1991

The mathematical properties of gravitational lens equations are examined in the frame work of gravitational micro-lensing effects. The caustics of the gravitational lens may be defined in terms of "cusp" and "folding" in general. In some cases for overfocussing, however, the critical curves (caustics) have no cusp and no folding. If the observer is in the overfocussed region, he may not see any lensed image.

• Advances in concrete construction
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• 제6권1호
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• pp.29-45
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• 2018

This paper investigates the effect of inclusion of glass fibers on mechanical and fracture properties of binary blend geopolymer concrete produced by using fly ash and ground granulated blast furnace slag. To study the effect of glass fibers, the mix design parameters like binder content, alkaline solution/binder ratio, sodium hydroxide concentration and aggregate grading were kept constant. Four different volume fractions (0.1%, 0.2%, 0.3% and 0.4%) and two different lengths (6 mm, 13 mm) of glass fibers were considered in the present study. Three different notch-depth ratios (0.1, 0.2, and 0.3) were considered for determining the fracture properties. The test results indicated that the addition of glass fibers improved the flexural strength, split tensile strength, fracture energy, critical stress intensity factor and critical crack mouth opening displacement of geopolymer concrete. 13 mm fibers are found to be more effective than 6 mm fibers and the optimum dosage of glass fibers was found to be 0.3% (by volume of concrete). The study shows the enormous potential of glass fiber reinforced geopolymer concrete in structural applications.