• Journal of the Korea Institute of Information and Communication Engineering
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• v.5 no.2
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• pp.279-287
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• 2001

In this paper, we discuss the scale of subjective speech quality measurement over VoIP(Voice over IP) network which is a component of broadband networks. Objective parameters of multimedia services like PSNR or jitter can easily measured and defined, but these factors are not easily meet the user's perceptual recognition. We suggest the speech quality measurement scale through the subjective measurement for end-to-end speech quality composed of sender-side quality, transmission quality, receiver-side quality, which provide the degree of correctness of representation of speaker, the degree of impairment caused by various factors, the degree of recognition of processed speech, respectively. Also, we examined the proposed method and verify it's availability.

• Journal of the Korean Society of Safety
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• v.17 no.4
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• pp.71-79
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• 2002

It was attempted to evaluate the degree of degradation of thermally aged 2.25-1Mo steek by ultrasonic monlinear parameter(UNP) measurement and X-ray diffraction analysis of extracted carbide. Artificial aging was performed to simulate the microstructural degradation in 2.25Cr-1Mo steel arising from long time exposure at $540{\circ}C$. Microstructural analysis (number of carbides per unit area) and measurements of mechanical properties(Vickers hardness, DBTT) and degradation evaluation parameters(UNP and intensity ration of X-ray diffraction peak of electrolytically extracted carbide) were performed. Both of UNP and intensity ratio of X-ray diffraction peak for M6C carbide to that of M23C6 carbide(IR) increased abruptly in the initial 1000 hour of aging and then changed little. UNP and IR were proposed as potential parameters to evaluate the degree of aging degradation of 2.25Cr-1Mo steel.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.5
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• pp.3511-3517
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• 2015

It is necessary to maximize the durability of Concrete for the underground structure because its maintenance and reinforcement are difficult. For cracks due to drying shrinkage of the concrete on the characteristics of the material, there is a need for an alternative in the deterioration phenomenon that occurs. In this study, fundamental properties including drying shrinkage of mortar and concrete were investigated to replace fine aggregate from cooling slag for reducing drying shrinkage of mortar and concrete. In the case of rapid cooling slag fine aggregate, it was effective to reduce and restrain initial shrinkage of mortar and concrete, and compressive strength was increased through the all specimen in proportion to its replacement ratio.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.78-78
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• 2010

그래핀(Graphene)은 탄소원자가 육각형 벌집(honeycomb)구조로 빼곡히 채워진 2차원의 단원자 층으로 역학적 강도와 우수한 화학적/열적 안정성 및 흥미로운 전기 전도 특성을 가지고 있다. 이러한 그래핀의 우수한 특성으로 인하여 현재 기초연구뿐만 아니라 응용연구 등 많은 연구들이 진행되고 있다. 일반적으로 그래핀의 우수한 물리적 특성들은 그래핀의 층수, 모서리(edge)구조, 결함(defect), 불순물 등에 의해 크게 좌우되는 것으로 알려져 있다. 따라서 그래핀의 구조 및 결함정도를 자유로이 제어하고 그에 따르는 특성 변화를 관찰하는 것은 기초연구의 측면에서 뿐만 아니라 향후 그래핀 응용에 있어서도 매우 중요하다고 할 수 있다. 본 연구에서는 그래핀의 내산화 특성을 연구하기 위하여, 그래핀을 열 및 플라즈마 산화 분위기에 노출시킨 후, Raman 분광법을 이용하여 광학적, 구조적 변화를 분석함으로써 그래핀의 내산화 특성에 대하여 조사하였다. 그래핀은 실리콘 웨이퍼에 전자빔증착법으로 니켈박막을 증착한 후 열화학증기증착법으로 합성하였으며, 메탄가스를 원료가스로 $900^{\circ}C$ 전후에서 합성하였다. 합성한 그래핀은 산화반응 시 기판의 영향을 제거하기 위하여 트렌치 구조의 기판 위에 전사(transfer)함으로써 공중에 떠있는 구조를 구현하였다. 열 산화의 경우, 합성한 그래핀을 대기분위기의 고온($500^{\circ}C$) 챔버에 넣고 처리시간에 따른 특성변화를 살펴보았다. 플라즈마 산화의 경우는 공기를 이용하여 직류플라즈마를 발생시킨 후 0.4 W의 낮은 플라즈마 파워를 이용하여 플라즈마 산화처리와 특성평가를 매회 반복하였다. 그래핀의 특성분석은 Raman분광기와 광학현미경, 원자힘현미경(AFM) 등을 이용하여 분석하였으며, 상기 결과들은 향후 산화환경에서의 그래핀 응용소자 개발에 유용할 것으로 예상된다.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.190.1-190.1
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• 2013

현재 자동차 분야에서 차량 경량화를 통해 연비 향상 및 에너지 효율 향상을 기대하고 있으며, 차량 경량화의 한 수단으로 자동차용 유리를 고강도 투명 플라스틱 소재인 PC(Polycarbonate)로 대체하고자 하는 연구가 활발히 이루어지고 있다. 그러나, PC의 낮은 내마모 특성과 자외선에 의한 열화 및 변색 현상은 해결하여야 할 중요한 문제점으로 지적되고 있다. 본 연구에서는, PC의 내마모 특성을 향상시키기 위하여 transmittance가 확보되고, 고경도 특성을 갖는 Al-Si-N 박막 증착에 대한 연구를 하였고, 자외선 차단을 위하여 SiN:H 박막을 증착 하였다. 박막 증착을 위하여 ICP-assisted reactive magnetron sputtering 장비를 이용하였으며, 고경도 특성을 갖는 Al-Si-N 박막을 제조하였다. 그리고 300 nm 파장 이하의 자외선 차단을 위하여 SiN:H 박막을 증착하였다. 분석 장비로는 박막의 chemical state와 crystallinity를 확인하기 위하여 XPS(X-ray Photoelectron Spectroscopy), XRD(X-ray diffraction)를 이용하여 분석을 수행하였으며, Knoop ${\mu}$-hardness tester와 Pin-on-disk를 이용하여 경도 및 내마모 특성을 평가하였다. SiN:H 박막 위에 Al-Si-N 박막을 증착하였고 총 두께는 ~5000 $\AA$을 증착하였으며, 가시광 영역에서 평균 70% 이상의 transmittance를 나타내었다. 박막의 Si/(Al+Si) 비율에 따라 다른 경도 특성을 나타냈는데, Si/(Al+Si) 비율이 26~32% 부근에서 최대 31 GPa의 경도 값을 확인하였고 SiN:H 박막은 300nm 이하의 파장에서 2% 이하의 transmittance를 확인하였다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.6
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• pp.965-971
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• 2001

To estimate the reliability of 12Cr alloy steel, the material of turbine blade in the steam power plant, Its corrosion susceptibility and fatigue characteristics in NaCl and Na$_2$SO$_4$solution with the difference of concentration and temperature was investigated. The polarization tests recommended in ASTM G5 standard for corrosion susceptibility in the various corrosive solutions was estimated. It showed that the higher temperature, the faster corrosion rates and corrosion rates were the fastest in 3.5 wt.% NaCl and 1M Na$_2$SO$_4$solution. From these results, the degradation conditions were determined in distilled water, 3.5 wt.% NaCl and 1M Na$_2$SO$_4$solution at room temperature, 60$\^{C}$ and 90$\^{C}$ during 3, 6 and 9 months. Its surface had a few pits for long duration. But, it was not susceptible in sulfide and chloride condition of several temperatures. If the degraded 12Cr alloy steel and non-degraded one were compared with fatigue characteristics, Any differences were not found regardless of temperature and degradation period.

• Korean Journal of Metals and Materials
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• v.46 no.5
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• pp.276-282
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• 2008

Material degradation of Cr steels in boiler tubes was accompanied by the microstructural changes including carbide behavior and crack formation. The microstructural change and the mechanical behavior of hardness and creep properties in accelerated heat-treatments were studied in order to identify the material degradation of the X20 Cr steel. The degradation behavior was occurred in the hardness increasing followed by decreasing due to carbide dissolution and precipitation.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.4C
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• pp.147-154
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• 2011

Currently NATM tunnels are designed by applying the initial ground loads caused during construction to the primary supports, conisting of shotcrete, steel ribs and rock bolts. For long term considerations, it is assumed that the primary supports lose its functionality and therefore the secondary support, i.e. concrete lining, is design to resist against the entire ground loads. But the steel ribs, usually applied to bad ground conditions, are embedded in shotcrete causing very little corrosion and therefore the assumption that the primary support will lose all of its functionality is too conservative. Also even though shotcrete carbonates in long term, excluding it from design is also too conservative. In this study, we have, through analytical and numerical analysis, set a rational level of support pressure and allowable relaxed rock mass height sustainable by the primary support for long term design. Changes in sectional forces of the concrete lining considering the calculated support pressure of the primary supports was also carried out. Shallow subway tunnels were considered in the analysis with weathered rock and soft rock ground conditions. The analysis results showed that, by considering the support pressure of steel ribs, an economical design of the concrete lining is possible.

• Journal of Conservation Science
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• v.34 no.3
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• pp.157-166
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• 2018

In this study, gelatin binding ability was increased by adding cross linking agent to improve adhesive characteristic of animal glue. Animal glue added genipin measured gel strength and viscosity, the structural analysis, the color retention degree, elution degree, and rupture strength. And the water resistance and ultraviolet light resistance with the addition of genipin were compared. As a result of the study, the gel strength and viscosity increased with the amount of genipin. As a result of the structural analysis, in gelatin, the absorption peak of the triple structure of collagen structurally stabilized was observed. As a result of the color retention degree, the film was observed because of the lowered brightness. The amount of elution glue was increased with addition of genipin at $50^{\circ}C$ distilled water condition and rupture strength has increased with the amount of genipin. In the water resistance and light fastness, there was no appearance before and after deterioration due to the addition of genipin. Based on the results of this study, it confirmed the adhesive characteristics of animal glue added genipin and examined the experimental method applicable for animal glue. After the addition of genipin, flexibility, re-solving, adhesive force, and curing speed, which are unique characteristics of glue, can be improved without disappearing, so it is expected that it will be applicable to production of animal glue and conservation of cultural heritage when homogeneous glue is secured.

• Journal of the Korean Academy of Esthetic Dentistry
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• v.22 no.1
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• pp.30-46
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• 2013

Porcelain fused to metal crown has been used mostly over the last 50 years for restorations in dentistry. However, the patients' awareness of aesthetic aspect, biocompatibility and the problems such as an allergy to metals led to the growing interest in the 'metal free restoration'. In particular, the price of the precious metals that have been mainly used to date has risen drastically, which made them impossible to play their role as oral restorative materials anymore, and in addition, the PFM restoration has intrinsic problems of chipping and fracture. Therefore, the CAD/CAM has been drawing more attention than ever due to the popular needs for the material that is more aesthetic and stronger for restoration of the molar implant. Considerations in carrying out the full zirconia restoration are as follows: 1) strength, 2) combination work, 3) light penetrability, 4) treatment of cracks, 5) the color reproducibility of the block, 6) the abrasivity of antagonistic tooth, 7) low temperature degradation. In this presentation, the color reproducibility of the block will be discussed. One of the biggest reasons for avoiding the full zirconia restoration is that it is difficult to reproduce the natural color compared to the conventional PFM restoration. Thus, many clinicians show reluctance due to the exposure of the ugly block when the coloring on the surface is removed after occlusal adjustment. From the experience of using blocks by Zirkonzahn for more than 4 years, it is considered that these problems can be addressed to some degrees. Accordingly, how to make restorations that are well in harmony with surrounding prosthesis or natural teeth will be discussed.