• 소성∙가공
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• 제22권8호
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• pp.463-469
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• 2013

In the previous work, a new forging process design, which included incremental upsetting, diffusion bonding and cogging, was suggested as a method to manufacture 1.9wt%C ultrahigh carbon workrolls. The previous study showed that incremental upsetting and diffusion bonding are effective in closing voids and healing of the closed void. In addition, compression tests of the 1.9wt%C ultrahigh carbon steel revealed that new microvoids form within the blocky cementite at temperatures of less than $900^{\circ}C$ and that local melting can occur at temperatures over $1120^{\circ}C$. Thus, the forging temperature should be controlled between 900 and $1120^{\circ}C$. Based on these results, incremental upsetting and diffusion bonding were used to check whether they are effective in closing and healing voids in a 1.9wt%C ultrahigh carbon steel. The incremental upsetting and diffusion bonding were performed using sub-sized specimens of 1.9wt%C ultrahigh carbon steel. The specimen was deformed only in the radial direction during the incremental upsetting until the reduction ratio reached about 45~50%. After deformation the specimens were kept at $1100^{\circ}C$ for the 1 hour in order to obtain a high bonding strength for the closed void. Finally, microstructural observations and tensile tests were conducted to investigate void closure behavior and bonding strength.

• Korea-Australia Rheology Journal
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• 제19권3호
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• pp.125-131
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• 2007

Biodegradable polymeric blends are expected to be widely used by industry due to their environmental friendliness and comparable mechanical and thermal properties. Poly (lactic acid) (PLA) and poly (butylene succinate) (PBS) are such biodegradable polymers which aim to replace commodity polymers in future applications. Since cost and brittleness of PLA is quite high, it is not economically feasible to use it alone for day to day use as a packaging material without blending. In this study, blends of PLA and PBS with various compositions were prepared by using a laboratory-scale twin-screw extruder at $180^{\circ}C$. Morphological, thermal, rheological and mechanical properties were investigated on the samples obtained by compression molding to explore suitability of these compositions for packaging applications. Morphology of the blends was investigated by scanning electron microscopy (SEM). Morphology showed a clear phase difference trend depending on blend composition. Modulated differential scanning calorimetry (MDSC) thermograms of the blends indicated that the glass transition temperature ($T_g$) of PLA did not change much with the addition of PBS, but analysis showed that for PLA/PBS blend of up to 80/20 composition there is partial miscibility between the two polymers. The tensile strength and modulus were measured by the Instron Universal Testing Machine. Tensile strength, modulus and percentage (%) elongation at break of the blends decreased with PBS content. However, tensile strength and modulus values of PLA/PBS blend for up to 80/20 composition nearly follow the mixing rule. Rheological results also show miscibility between the two polymers for PBS composition less than 20% by weight. PBS reduced the brittleness of PLA, thus making it a contender to replace plastics for packaging applications. This work found a partial miscibility between PBS and PLA by investigating thermal, mechanical and morphological properties.

• 소성∙가공
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• 제16권4호
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• pp.293-298
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• 2007

Recently, there is a need to produce a large forged part for the flight, shipping, some energies, and military industries, etc. Therefore, an open die forging technique of cast ingots is required to obtain higher quality of large size forged parts. Cogging process is one of the primary stages in many open die forging processes. In the cogging process prior to some open die forging processes, internal cavities have to be eliminated for defect-free. The present work is concerned with the elimination of the internal cavities in large ingots so as to obtain sound products. In this study, hot compression tests were carried out to obtain the flow stress of cast microstructure at different temperature and strain rates. The FEM analysis is performed to investigate the overlap defect of cast ingots during cogging stage. The measured flow stress data were used to simulate the cogging process of cast ingot using the practical material properties. Also the analysis of cavity closure is performed by using the $DEFORM^{TM}-3D$. The calculated results of cavity closure behavior are compared with the measured results before and after cogging, which are scanned by the X-ray scanner. From this result, the criteria for deformation amounts effect on the cavity closure can be investigated by the comparison between practical experiment and numerical analysis.

• 한국광물학회지
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• 제19권3호
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• pp.189-195
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• 2006

황철석에 대한 압축성 연구를 다이아몬드 앤빌 기기 및 방사광을 이용하고 에너지분산 X-선회절법을 적용하여 상온에서 시행하였다. 황철석의 체적탄성률은 실험조건과 실험기기에 따라 매우 큰 변이를 보이고 있는데 이는 압력전달매체의 특성에 따른 것으로 알려져 있다. $FeS_{2}#1$(황철석+NaCl)과 $FeS_{2}#2$(황철석+MgO)에 대해 압력전달 매체로 각각 NaCl과 유체를 이용하여 체적탄성률 138.9 GPa와 198.2 GPa를 각각 얻었다. 이러한 값은 시료방의 압력상태에 따른 예측 결과치에 대치되는 것으로 그 원인은 압력전달액체의 상변이에 따른 것으로 추정되며 이외에 고상검출기의 차이, E*d값의 차이 등도 영향을 미친 것으로 판단된다. 모든 실험은 포항가속기연구소 1B2 빔라인에서 시행되었다.

• Journal of Biosystems Engineering
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• 제27권6호
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• pp.565-572
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• 2002

In order to control the root-zone temperature of greenhouse crops in the hydroponics at hot and cold season, heat pump system for cooling and heating was built and tested in this work. The system was air-to-water type and vapour compression type. The heating and cooling mode was selected by the four way valve. Capacity of the compressor was 3.75㎾ and heat transfer area of the evaporator and the condenser were 3.05㎡ and 0.6㎡, respectively. According to the performance test, it could supply heat of 42,360 to 64,372kJ/h depending on the water circulation rate of 600 to 1,500ℓ/h, respectively, when indoor air temperature was 10∼20$\^{C}$. COP of heat pump system was 3.0 to 4.0 in the heating mode. But, COP of the cooling mode was 1.3 to 2.1 at indoor temperature of 20∼35$\^{C}$. The feasibility test in the greenhouse the developed heating and cooling system was installed, showed that the heating cost of the developed system was only about 13% of that of the conventional heating system. The heating cost of the developed system was 367won/day(electric consumption 9.7㎾h/day), while that of the conventional system was 2,803won/day(oil consumption 7.7ℓ/day) at the same heating mode.

• 공업화학
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• 제10권2호
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• pp.201-205
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• 1999

Hydroxypropylmethylcelluloses (HPMC)는 친수성 cellulose 계통의 중합체로서 독성이 적고 가격이 저렴하여 경구용 서방출성 제제에 널리 이용되고 있다. 본 연구에서는 매트릭스로서 HPMC를 이용하여 새로운 서방출성제제인 HPMC/염산슈도에페드린계를 설계하고, 직타법에 의하여 정제를 제조하였으며, 이 팽윤될 수 있는 친수성 약물전달계를 이용하여 약물의 방출에 영향을 주는 여러 인자들이 약물의 방출속도에 미치는 영향에 대하여 조사하였다. 결과로서, HPMC/염산슈도에페드린계에서 매트릭스인 HPMC의 분자량이 클수록, HPMC의 함량이 많을수록 약물의 방출속도가 더 느려짐을 알 수 있었으며, 정제의 경도나 용출시 pH 변화에는 무관한 것으로 나타났다. 특히, 음이온 계면활성제인 sodium laurylsulfate는 HPMC로부터 염산슈도에페드린의 방출속도를 지연시키는데 큰 영향을 미치는 것으로 나타났으며, 이러한 현상은 음이온 계면활성제인 sodium laurylsulfate가 반대의 이온성을 갖는 약물인 염산슈도에페드린과 착물을 형성함으로써 약물의 용해성이 떨어져서 약물방출이 지연되는 것으로 생각된다.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2004년도 춘계학술대회 논문집
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• pp.89-94
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• 2004

일반적으로 강구조물을 복잡한 판넬로 구성되어 있다. 구조의 전체적인 붕괴는 각각의 구성요소들의 좌굴과 소성붕괴에 영향을 받는다. 최종한계상태설계법에서는 어떤 구조적인 구성요소들의 좌굴과 소성붕괴에 대한 정확한 계산은 중요하다. 구조물은 개별적 요소로 구성되어 있지 않으며 고차 부정정 자유도를 가진 복잡한 구조이다. 이러한 구조물을 해석하기 위해서 단순화나 이상화를 통하여서 가능하며 일반적으로 복잡한 부정정 구조의 해석에 사용되어지고 있다. 본연구의 목적은 일축압축하중이 작용할 경우에 보강재의 트리핑이 최종강도에 미치는 영향을 규명하는 것이며 또한 보강재 단면의 특성에 따른 트리핑거동을 탄소성대변형 유한요소법을 이용하여 해석하였다.

• 방송공학회논문지
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• 제18권6호
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• pp.816-822
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• 2013

최신 동영상 압축 표준화 기술인 HEVC(High Efficiency Video Coding)는 ITU-T(VCEG)와 ISO-IEC(MPEG)에서 JCT-VC(Joint Collaborative Team on Video Coding)라는 팀을 이루어 진행했으며 표준화의 막바지에 다다르고 있다. 기존 H.264/AVC에 약 50% 이상의 성능 향상을 가져왔으나, 다양한 압축 기술을 사용함에 따라 부호화 및 복호화의 복잡도가 매우 증가하는 문제가 있다. 제안하는 방법은 CPU 병렬처리와 GPU 가속처리를 통해 HEVC의 복잡도를 줄이고, 이를 UHD(Ultra High Definition) 초고해상도 영상에 적용하는 방법으로 UHD($3840{\times}2144$) 영상에서 15fps 이상 인코딩/디코딩의 속도를 가지며, CPU와 GPU간의 데이터 전송 방법의 발전으로 추가적인 속도 향상이 기대된다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권9호
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• pp.4467-4486
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• 2018

Trying to deal with the problem of low robustness of Copy-Move Forgery Detection (CMFD) under various transformation and degradation attacks, a novel CMFD method is proposed in this paper. The main advantages of proposed work include: (1) Discrete Analytical Fourier-Mellin Transform (DAFMT) and Locality Sensitive Hashing (LSH) are combined to extract the block features and detect the potential copy-move pairs; (2) The Euclidian distance is incorporated in the pixel variance to filter out the false potential copy-move pairs in the post-verification step. In addition to extracting the effective features of an image block, the DAMFT has the properties of rotation and scale invariance. Unlike the traditional lexicographic sorting method, LSH is robust to the degradations of Gaussian noise and JEPG compression. Because most of the false copy-move pairs locate closely to each other in the spatial domain or are in the homogeneous regions, the Euclidian distance and pixel variance are employed in the post-verification step. After evaluating the proposed method by the precision-recall-$F_1$ model quantitatively based on the Image Manipulation Dataset (IMD) and Copy-Move Hard Dataset (CMHD), our method outperforms Emam et al.'s and Li et al.'s works in the recall and $F_1$ aspects.

• 한국지반공학회지:지반
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• 제12권1호
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• pp.73-86
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• 1996

본 연구에서는 국내 8개 석탄화력발전소에서 발생하는 석탄회중 영월화력발전소에서 부산되는 석탄회를 주 대상으로 순수 비회(FA)와 저회(BA), 회사장에 투기되는 흔합회(FA:BA=8:2), 적정비로 혼합된 석탄회(FA:BA=5:5),그리고 일반도로성토재에 대하여 토질역학시험을 통해 공학적 특성이 비교, 분석되었으며 석탄회를 성토재 및 매립재로서 대규모로 이용할 경우의 변형해석을 위해 Hyperbolic Mode야 적용시 필요한 제반 변수를 산정하였다. 석탄회의 토공재로서의 활용 가능성을 검토한 결과 석탄회는 동일입도의 일반 홀에 비해 강도 정수 등 유리한 공학적 특성을 갖고 있으며,특히 연약지반상에 매립 또는 구조물 됫채움재로서 사용할 경우 자경성, 경량성 등 우수한 조건을 지니고 있다.