• 대한기계학회논문집B
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• 제22권8호
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• pp.1073-1082
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• 1998

When thermal diffusivity is measured by laser flash method, the thermal diffusivity call be calculated front the assumption of the uniformly heated whole surface of the specimen. It has been known that the approximate 5% error is made by the non-uniform energy distribution on the specimen surface of laser pulse heat source. In this study, to obtain the highly-uniformed laser beam, which has both the low non-uniform heating error from non-uniform laser beam and the energy loss, research was carried out on no transmitting loss by optical fiber and high repetitions. In addition, heating error and thermal diffusivity were measured as the measuring positions were varied and compared with the results using the uniform and the non-uniform laser beams. In addition, dole to using the uniformalized laser beam, the whole surface of the specimen was heated uniformly and as a result, it was the thought that this was very effective to reduce the variations of the errors of the thermal diffusivity as the measuring positions were varied. It can be obtained that when the thermal diffusivity of POCO-AXM-5Q1 of SRM in NBS was measured with both the uniform and the non-uniform laser beams, the dispersion error of the former was from 2 to 2.5%, which was more improved than that of the latter.

• 공업화학
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• 제16권3호
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• pp.361-365
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• 2005

$O_2$, $H_2O$, acrylic acid, diaminocyclohexane 등의 저온 플라즈마를 이용하여 시멘트 보강용 탄소 섬유 표면을 친수성으로 개질한 다음, 이에 대한 효과를 살펴보았다. 물과의 접촉각이 $75{\sim}80^{\circ}$ 정도로 소수성이던 표면이 친수성으로 변하여 접촉각이 $10^{\circ}$ 이하로까지 낮아졌으며, 이에 따라 흡습성 및 수용액에서 분산성이 크게 향상되었다. 또한, 섬유표면의 제타 포텐셜이 변하여 시멘트와 정전기적 인력이 향상됨으로써 시멘트의 결착도 향상과 함께 시멘트와의 결합이 57~124%까지 향상되었다.

• 비파괴검사학회지
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• 제33권3호
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• pp.264-269
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• 2013

Since MFC(macro-fiber composite) transducer has been developed, many researchers have tried to apply this transducer on SHM(structural health monitoring), because it is so flexible and durable that it can be easily embedded to various kinds of structures. The objective of this paper is to figure out the benefits and feasibility of applying MFC transducers to guided wave technique. For this, we have experimentally tested the performance of MFC patches as transmitter and sensors for excitation and reception of guided waves on the thin aluminum alloy plate. In order to enhance the signal accuracy, we applied the FIR filter for noise reduction as well as used STFT(short-time Fourier transform) algorithm to image the guided wave characteristics clearly. From the results, the guided wave generated based on MFC showed good agreement with its theoretical dispersion curves. Moreover, the ultrasonic Lamb wave techniques based on MFC patches in pitch-catch manner was tested for detection of surface notch defects of which depths are 10%, 20%, 30% and 40% of the aluminum plate thickness. Results showed that the notch was detectable well when the notch depth was 10% of the thickness or greater.

• 한국광학회지
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• 제5권2호
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• pp.319-325
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• 1994

Stochastic 접근 방식을 사용한 Manchester 코드 파장분할다중 시스템의 성능이 산탄 잡음과 광섬유 비선형성에 기인한 four-wave mixing을 고려하여 평가되었다. DPSK 변조방식에 대하여 Manchester code 시스템의 결과는 기존의 non-return-to-zero 시스템과 비교된다. 더구나 최대 입력 전력(FWM에 의해 제한)과 최소 입력 전력(수신 감도에 의해 제한)의 비로서 정의된 dynamic range가 평가되었다. $1.55.{\mu}m$ 16채널 시스템에서 DPSK Manchester 코드 시스템의 dynamic range는 NRZ에 대한 관점에서 2.1dB의 개선을 보인다. 이 결과는 분산 천이 광섬유와 기존의 광섬유에 대해서 같은 결과를 얻어졌으며 10GHz의 채널 간격과 1Gbps/channel bit rate에서 이루어졌다.

• 전자공학회논문지D
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• 제36D권12호
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• pp.70-77
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• 1999

본 논문에서는 유니폼 위상마스크를 이용하여 긴 광섬유격자를 제작할 수 있는 새로운 방법을 제안한다. 제안하는 방법은 짧은 유니폼 위상마스크 한 개를 이용하여, 유효굴절률이 일정하거나 선형적으로 변하는 여러개의 부광섬유격자(subgrating)를 직렬로 연속적으로 제작함으로써 긴 광섬유격자를 제작하는 방법이다. 길이가 25mm인 한 개의 유니폼격자를 사용하여 200mm이고, 반사율 95% 이상인 유니폼 공섬유격자를 제작하였으며, 길이가 250mm이며 대역폭과 분산보상기울기의 평균값이 0.5nm와 4.965ps/nm인 선형처프된 광섬유격자를 제작할 수 있었다.

• Advances in concrete construction
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• 제8권4호
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• pp.311-320
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• 2019

In this study, the effect of cellulose nanocrystals (CNCs) on the fire resistance properties of fiber-reinforced cement composites was investigated. The main variables were CNCs content (0.4, 0.8 and 1.2vol.% compared with cement), steel fiber ratio, and exposure temperature (100, 200, 400, 600 and 800℃). The fire resistance properties, i.e., residual compressive strength, flexural strength, and porosity, were evaluated in relation with the exposure temperature of the specimens. The CNCs suspensions were prepared to composited dispersion method of magnetic stirring and ultra-sonication. CNCs are effective for increasing the compressive strength at high temperatures but CNCs do not seem to have a significant effect on flexural reinforcement. Porosity test result showed CNCs reduce the non-hydration area inside the cement and promote hydration.

• Applied Biological Chemistry
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• 제34권4호
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• pp.353-359
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• 1991

대두단백 섬유의 texture 분석을 위한 도구로서, 그들의 미세구조를 관찰하였다. 미세구조와 texture profile analysis 결과, 대두단백 섬유의 구조를 유지 및 결정하는 인자중 disulfide 결합과 수소결합이 가장 중요한 인자중의 하나임을 확인하였다. 이와함께 대두단백 섬유의 원료물질인 대두단백질 수화물과 dope의 미세구조도 관찰하였다.

• Macromolecular Research
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• 제14권5호
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• pp.504-509
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• 2006

Poly(vinyl phosphate-b-styrene) (PVPP-b-PS) block copolymers were synthesized successfully from poly(vinyl alcohol-b-styrene) (PVA-b-PS) by reaction with phosphorus oxychloride and subsequent hydrolysis. The obtained block copolymers were slightly crosslinked, and were characterized by various analytical techniques. The total phosphorus content and the ratio of the differently bound phosphorus were obtained by both solid-state $^{31}P$ NMR and pH titration, but the results differed slightly. Characterization by energy dispersion X-ray analysis (EDS) or Rutherford back scattering (RBS), on the other hand, determined the total phosphorus contents, but the results were quite different from those by solid-state $^{31}P$ NMR.

• 한국통신학회논문지
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• 제25권9B호
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• pp.1518-1526
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• 2000

본 논문은 기존 표준 단일모드 광섬유 링크를 통하여 초고속 광신호의 장거리 전송이 가능하도록 분산보상 광섬유를 이용한 최적 분산보상 기법에 기반을 둔 전송링크 설계 방법을 제안하였다. 제안한 방법에서는 광섬유의 비선형성에서 비롯되는 자기위상변조(Self-Phase Modulation: SPM)와 광증폭기에서 발생하는 증폭자연방출(Amplified Spontaneous Emission : ASE) 잡음에 대하여 증폭기간 거리와 중계기간 거리를 최적화함으로써 전송신호 속도에 따른 최대 전송거리를 제시하였다. 또한 주어진 증폭기간 거리와 중계기간 거리에 대하여 ASE 잡음과 SPM의 효과의 균형적 관계로부터 최적의 입력 신호전력의 범위가 있음을 제시하였다.

• Steel and Composite Structures
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• 제31권5호
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• pp.517-527
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• 2019

To move forward in large steps rather than in small increments, the community would benefit from a systematic and comprehensive database of multi-scale composites and measured properties, driven by comprehensive studies with a full range of types of fiber-reinforced polymers. The multi-scale hierarchy is a promising chemical approach that provides superior performance in synergistically integrated microstructured fibers and nanostructured materials in composite applications. Achieving high-efficiency thermal conductivity and mechanical properties with a simple surface treatment on single-walled carbon nanotubes (SWCNTs) is important for multi-scale composites. The main purpose of the project is to introduce ozone-treated SWCNTs between an epoxy matrix and basalt fibers to improve mechanical properties and thermal conductivity by enhancing dispersion and interfacial adhesion. The obvious advantage of this approach is that it is much more effective than the conventional approach at improving the thermal conductivity and mechanical properties of materials under an equivalent load, and shows particularly significant improvement for high loads. Such an effort could accelerate the conversion of multi-scale composites into high performance materials and provide more rational guidance and fundamental understanding towards realizing the theoretical limits of thermal and mechanical properties.