• 한국산업융합학회 논문집
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• 제4권1호
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• pp.35-40
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• 2001

A spectral measurement system for reflection and transmission properties by using an optical fiber and an ellipsoidal mirror was newly developed. The hemispherical reflectance and transmittance spectra of several heating resisting ceramics materials were measured from visible to middle infrared region. The directional characteristics of reflection and transmission were also investigated in consideration of the absorptance. The measured data were analyzed by using a four flux model of radiation transfer, The radiation properties could be estimated by the obtained scattering and absorption coefficient spectra.

• East Asian mathematical journal
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• 제17권2호
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• pp.217-224
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• 2001

In this paper, we introduce the notion of some modification of given convergence structure and product convergence. Also, we find some properties which hold between the modification associated with a product of convergence structures and the product of modifications associated with the factor convergence structures.

• 한국전기전자재료학회논문지
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• 제35권2호
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• pp.178-183
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• 2022

For enhancing the flame-retardant properties of wallpapers, we developed an organic-inorganic hybrid solution with ZrSiO₄ as a functional ceramic powder, coated on non-woven fabric using dip coating, spray coating, and slot-die coating methods. Their flame retardant properties were characterized by a 45° combustion tester, which is manufactured according to the flame-retardant performance standard (KOFEIS 1001 and KS F 2819). In organic-inorganic hybrid solution, with increasing the concentration of acid-catalyst (acetic acid), the precipitation of ZrSiO₄ powders increased, and the flame retardant properties decreased. The highest flame retardant result was obtained for the solution adding 5 wt% acetic acid. The optimization of the coating method and coating number resulted in the most excellent flame-retardant properties being obtained for the non-woven fabric coated for 5 or 7 times by dip coating method, and their flame-retardant properties corresponded to class 2 flame-retardant performance of wallpapers.

• Composites Research
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• 제31권5호
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• pp.186-191
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• 2018

복합재료 기지재의 화학적 조성을 다르게 했을 때 염수처리 후 복합재료의 상태 및 물성을 파악하였다. 기지재는 2가지 종류의 에폭시 기지재와 3가지 종류의 경화제(아민계, 산 무수물계, 그리고 아마이드계) 이용하여 기지재의 유연성을 조절하였다. 각 복합재료에 염수 가속화 실험을 위해 염화나트륨 6 wt% 조건에 $60^{\circ}C$ 가하여 0, 15, 30일 처리하였다. 처리 후에 복합재료의 단면적을 관찰하였고, 기계 및 계면 평가를 실시하였다. 아민계를 이용한 복합재료의 가교밀도, 기계 및 계면 물성이 가장 좋은데 반해, 수분흡수율은 가장 작은 것을 확인하였다. 이는 물분자가 유리섬유와 다른 가교밀도의 에폭시 기지재간의 계면으로 침투가 어렵기 때문이다. 이는 복합재료가 염수에 잘 견딜 수 있는 요인으로 작용할 수 있다.

• 한국전기전자재료학회논문지
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• 제35권3호
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• pp.292-296
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• 2022

(La_0.5Nd_0.2Sr_0.3)MnO₃ specimens were prepared by a solid-state reaction. In all specimens, X-ray diffraction patterns of an orthorhombic structure were shown. The fracture surfaces of (La_0.5Nd_0.2Sr_0.3)MnO₃ specimens showed a transgranular fracture pattern be possibly due to La ions (0.122 nm) as a perovskite A-site dopant substituting for Nd ions (0.115 nm) having a small ionic radius. The full-width at half maximum (FWHM) of the Mn 2p XPS spectra showed a value greater than that [8] of the single valence state, which is believed to be due to the overlapping of Mn²⁺, Mn³⁺, and Mn⁴⁺ ions. The dependence of Mn 2p spectra on the Mn³⁺/Mn⁴⁺ ratio according to sintering time was not observed. Electrical resistivity resulted in the minimum value of 100.7 Ω-cm for the specimen sintered for 9 hours. All specimens show a typical negative temperature coefficient of resistance (NTCR) characteristics. In the 9-hour sintered specimen, TCR, activation energy, and B25/65-value were -1.24%/℃, 0.19 eV, and 2,445 K, respectively.

• 한국기계가공학회지
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• 제20권3호
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• pp.53-59
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• 2021

In vibration-free vehicles such as limousine buses, the vibration is minimized by installing an air spring instead of the leaf spring used in the existing freight cars to prevent the damage to the loaded cargo from shocks generated during movement. In the existing vehicles, steel structures support the air spring system. This study was aimed at replacing the steel structures used in the Z-spring by carbon fiber and glass fiber reinforced plastics. In addition, the mechanical properties (elastic modulus, tensile strength, and shear strength) of carbon fiber and glass fiber prepreg were derived using specimens molded with the corresponding prepreg. The final goal was to develop a material lighter than the conventional steel material but with enhanced mechanical properties. Although the CF prepreg exhibited excellent mechanical properties, the production cost was extremely high. To overcome this limitation, hybrid composites with GF prepreg were examined, which are expected to be promising future materials.

• International Journal of Industrial Entomology and Biomaterials
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• 제48권1호
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• pp.25-32
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• 2024

Soy protein isolate (SPI) has garnered researchers' attention due to its abundance, costeffectiveness, excellent biocompatibility, hemo-compatibility, and biodegradability. However, SPI faces limitations in application due to poor processability and weak mechanical strength. Substantial efforts have been made to address these challenges. In this preliminary study, glycerol and biofibers were added to SPI to improve the mechanical properties and film forming, and glyoxal was employed to crosslink SPI molecules. The microstructure and mechanical properties of the resulting SPI/composite films were evaluated. A 15% addition of glycerol proved sufficient for good film formation. Among the biofibers, short SF microfibers were the most effective in enhancing breaking strength, while TEMPO-oxidized CNF (cellulose nanofiber) excelled among CNFs. Crosslinking with glyoxal significantly enhanced the mechanical properties, with the type of biofiber minimally affecting the mechanical properties of the crosslinked SPI composite films.

• Composites Research
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• 제30권4호
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• pp.241-246
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• 2017

취성을 가진 섬유강화플라스틱은 충격을 받을 때 충격에너지를 흡수하면서 섬유와 기지재 간 계면에서 탈착 및 박리가 일어난다. 이는 복합재료의 에너지 충격흡수정도의 지표로 삼을 수 있다. 복합재료의 취성을 해결하기 위해 pine과 복합재료의 접착에 대한 연구가 되어 지고 있다. 이번 연구에서는 열처리 된 pine이 탄소섬유강화복합재료와 에폭시 접착제를 이용하여 접착되었다. 최적의 열처리 조건을 확인하기 위해, pine을 160도 및 200도 조건하에 열처리를 하였다. Pine 및 pine/탄소섬유복합재료의 기계적 및 계면물성을 파악하기 위해 인장, 인장중첩전단 및 아이조드 실험을 하였다. 또한, 열처리에 따른 나뭇결간의 결합력을 확인하기 위해 나뭇결 수직방향으로 인장시편 제조 후 파단될 때 탄성파를 음향방출시스템을 이용하여 분석하였다. 160도 조건으로 열처리 했을 때 나무강화 효과로 기계, 계면 및 나뭇결간의 결합력이 좋은 것을 확인하였다. 그러나 과한 열을 주게 되면 열에 약한 헤미셀룰로오스가 분해되면서 잡아주는 인자가 줄어들어 물성이 감소하였다.

• 대한수학회지
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• 제44권4호
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• pp.845-854
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• 2007

In this paper we investigate relationships between closure-type and convergence-type properties of hyperspaces over a space X and covering properties of X.

• 호남수학학술지
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• 제43권3호
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• pp.433-440
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• 2021

In this study, we defined the notions of invariant convergence and invariant Cauchy sequences in fuzzy normed spaces. Also, we investigated some properties of invariant convergence and relations between invariant convergence and invariant Cauchy sequences in fuzzy normed spaces.