• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 추계학술대회 논문집
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• pp.247-250
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• 2005

The need for improved fuel efficiency, weight reduction has motivated the automotive industry to focus on aluminum alloys as a replacement for steel-based alloy. To cope with the needs for high structural rigidity with low weight, it is forecasted that substantial amount of cast components will be replaced by tubular parts which are mainly manufactured by the extruded aluminum tubes. The extrusion process is utilized to produce tubes and hollow sections. Because there is no weld seam, the circumferential mechanical properties may be uniform and advantageous for hydroforming. However the possibility of the occurrence of a surface defect is very high, especially due to the temperature increase from forming at high pressure when it comes out of the bearing and the roughness of the bearing, which cause the surface defects such as the dies line and pick-up. And when forming a extruded aluminum tube, the free surface of the tube becomes rough with increasing plastic strain. This is well known as orange peel phenomena and has a great effect not only on the surface quality of a product but also on the forming limit. In an attempt to increase the forming limit of the tubular specimen, in the present paper, surface asperities generated during the hydroforming process are polished to eliminate the weak positions of the tube which lead to a localized necking. It is shown that the forming limit of the tube can be considerably improved by simple method of polishing the surface roughness during hydroforming. And also the extent of the crack propagation caused by dies lines generated during the extrusion process is evaluated according to the deformed shape of the tube.

• 한국펄프종이공학회:학술대회논문집
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• 한국펄프종이공학회 2003년도 춘계학술발표논문집
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• pp.70-79
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• 2003

Paper coating can give smoothness surface and good printability to uncoated paper. Macro roughness of base paper would be decreasing its groove and grit in view of side. Nevertheless its improving effect for paper, some kind of problem is showing in the fine coated paper. Especially, back trap mottle is one of serious problems in printing with fine coated paper. Printers can not adjust conditions to overcome the problem. Also large amounts of paper can be rejected. There are many factors that influence back trap mottle. However it is not clear what the important parameters are in back trap mottle. Back trap mottle has some relationship with ink setting but good guidelines are not clear. Back trap mottle has been linked to non-uniform ink setting. We do not know how much variation in setting we can tolerate. Other mottle issues such as micro-picking and ink refusal are still common. This paper was prepared to identify correlation with ink setting and delta ink density obtained from experiment and then tried to find out some relationships with ink setting and back trap mottle. Basically fine calcium carbonate and ciay was used for main components and coarse calcium carbonate was mixed in two fine pigments to change its porosity and ink acceptance. Micro ink tack force at KRK printing tester was adapted to measure ink setting rate. KRK units were used for back trap mottle simulation and two printed samples were prepared to check delta ink density. Clay base coating has more fast ink setting time than calcium carbonate's though smoothness of clay was better than calcium carbonate. It could be explained by that clay has finer pore in its coating than calcium carbonate. DID(delta ink density) has shown a good correlation with ink setting time from micro ink tack. The total pore volume of coating layer did not match with ink setting and DID. From the results we might conclude coating that has fine pore size around 0.05 ${\mu}m$ can be exposed to high possibility of back trap mottle.

• 대한세포병리학회지
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• 제17권1호
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• pp.46-50
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• 2006

A micropapillary variant of urothelial carcinoma (MPC) is a distinct entity with an aggressive clinical course. It has a micropapillary configuration resembling that of ovarian papillary serous carcinoma. Its cytologic features have rarely been reported. We report a case of MPC detected by urine cytology. A woman aged 93 years presented with a chief complaint of macroscopic hematuria. Cytology of her voided urine showed clusters of malignant cells in a micropapillary configuration. Each tumor cell had a vacuolated cytoplasm, a high nuclear:cytoplasmic ratio, and irregular hyperchromatic nuclei. An ureteroscopic examination revealed exophytic sessile papillary masses extending from the left lateral wall to the anterolateral wall of the urinary bladder. A transurethral resection of the tumor was carried out. The tumor was characterized by delicate papillae with a thin, well-developed fibrovascular stromal core and numerous secondary micropapillae lined with small cuboidal cells containing uniform low- to intermediate-grade nuclei and occasional intracytoplasmic mucinous inclusions. These tumor cells infiltrated the muscle layers of the bladder, and lymphatic tumor emboli were frequently seen. Recognizing that the presence of MPC components in urinary cytology is important for distinguishing this lesion from low-grade papillary lesions and high-grade urothelial carcinomas can result in early detection and earlier treatment for an improved treatment outcome.

• 산업경영시스템학회지
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• 제40권2호
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• pp.145-149
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• 2017

One of the challenges facing precision manufacturers is the increasing feature complexity of tight tolerance parts. All engineering drawings must account for the size, form, orientation, and location of all features to ensure manufacturability, measurability, and design intent. Geometric controls per ASME Y14.5 are typically applied to specify dimensional tolerances on engineering drawings and define size, form, orientation, and location of features. Many engineering drawings lack the necessary geometric dimensioning and tolerancing to allow for timely and accurate inspection and verification. Plus-minus tolerancing is typically ambiguous and requires extra time by engineering, programming, machining, and inspection functions to debate and agree on a single conclusion. Complex geometry can result in long inspection and verification times and put even the most sophisticated measurement equipment and processes to the test. In addition, design, manufacturing and quality engineers are often frustrated by communication errors over these features. However, an approach called profile tolerancing offers optimal definition of design intent by explicitly defining uniform boundaries around the physical geometry. It is an efficient and effective method for measurement and quality control. There are several advantages for product designers who use position and profile tolerancing instead of linear dimensioning. When design intent is conveyed unambiguously, manufacturers don't have to field multiple question from suppliers as they design and build a process for manufacturing and inspection. Profile tolerancing, when it is applied correctly, provides manufacturing and inspection functions with unambiguously defined tolerancing. Those data are manufacturable and measurable. Customers can see cost and lead time reductions with parts that consistently meet the design intent. Components can function properly-eliminating costly rework, redesign, and missed market opportunities. However a supplier that is poised to embrace profile tolerancing will no doubt run into resistance from those who would prefer the way things have always been done. It is not just internal naysayers, but also suppliers that might fight the change. In addition, the investment for suppliers can be steep in terms of training, equipment, and software.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2012년도 춘계학술발표대회
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• pp.99.1-99.1
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• 2012

The thin-film photovoltaic absorbers (CdTe and $Cu(In,Ga)Se_2$) can achieve solar conversion efficiencies of up to 20% and are now commercially available, but the presence of toxic (Cd,Se) and expensive elemental components (In, Te) is a real issue as the demand for photovoltaics rapidly increases. To overcome these limitations, there has been substantial interest in developing viable alternative materials, such as $Cu_2ZnSnS_4$ (CZTS) is an emerging solar absorber that is structurally similar to CIGS, but contains only earth abundant, non-toxic elements and has a near optimal direct band gap energy of 1.4 - 1.6 eV and a large absorption coefficient of ~104 $cm^{-1}$. The CZTS absorber layers are grown and investigated by various fabrication methods, such as thermal evaporation, e-beam evaporation with a post sulfurization, sputtering, non-vacuum sol-gel, pulsed laser, spray-pyrolysis method and electrodeposition technique. In the present work, we report an alternative aqueous chemical approach based on chemical bath deposition (CBD) method for large area deposition of CZTS thin films. Samples produced by our method were analyzed by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, absorbance and photoluminescence. The results show that this inexpensive and relatively benign process produces thin films of CZTS exhibiting uniform composition, kesterite crystal structure, and some factors like triethanolamine, ammonia, temperature which strongly affect on the morphology of CZTS film.

• 설비공학논문집
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• 제18권12호
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• pp.1007-1016
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• 2006

Although the advance in electronic technology enables a large number of circuity to be packed in a small volume, it is simultaneously required to remove the high heat load produced by them. In this study, the heat transfer and pressure drop characteristics of a mini-channel heat exchanger, which is designed for liquid cooling of electronic components, are investigated by varying operating conditions. Water and FC-72 were used as working fluids. The mini-channel heat exchanger was made with circular shape channels having din-meters of 2, 3, and 4 mm in regular intervals, and the channel length was 100 mm. The header and inlet guide pathway to provide uniform inflow were attached at the inlet of the test section. Copper block including the heaters was attached at the sidewall of the test section as a heat source, which provided the heat flux from 5 to $15W/cm^2$. The entrance effects enhanced the heat transfer coefficient in the mini-channel significantly. In addition, the single-phase pressure drop in the mini-channel was very similar to that predicted by the laminar flow correlation except that the transition Re decreased due to flow instability in the entrance region.

• Elastomers and Composites
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• 제36권3호
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• pp.177-187
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• 2001

폴리프로필렌(PP)/폴리우레탄(PU) 블렌드를 compositional quenching으로 제조하여 모폴로지, 인장물성, 표면에너지 그리고 열안정성 등을 조사하였다. 블렌드 제조시, 말레인산 무수물이 그라프트된 PP(MPP)와 히드록시에틸 말레이미드가 그라프트된 PP(HPP)를 반응성 상용화제로 도입하였으며, 이들의 생성 및 PU 조성과의 반응을 FT-IR로 확인하였다. Compositional quenching으로 제조한 블렌드는 용융블렌드에 비해 높은 혼화성을 보였으며, 블렌드내의 상용화제의 함량이 증가함에 따라 모폴로지, 인장물성. 표면특성, 그리고 열안정성 등의 물성이 현저하게 향상되었다. 상용화제로 MPP를 도입한 블렌드는 HPP를 도입한 블렌드에 비해, 높은 표면 에너지를 가졌다.

• 한국진공학회지
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• 제5권4호
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• pp.377-386
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• 1996

오스테나이트 스테인리스강 304L을 고질소 저압 분위기에서 400~$600^{\circ}C$ 범위내의 온도변수 $50^{\circ}$간격차이에 따라 펄스 직류 플라즈마를 발생시켜 펄스작용 시간비에 따라 5시간씩 질화처리를 실시하였다. 처리온도 $500^{\circ}C$를 전후하여 질화처리층의 상과 조직이 현저히 다르게 형성되었다. $500^{\circ}C$미만 범위에서 저온일수록 펄스작용 시간비가 높을 때 질화층은 일종의 비화학량론적인 질화 스테인리스강으로 형성되었고 박피막을 이루며 균열이 많이 발생했다. 처리온도가 $500^{\circ}C$보다 높을 때는 온도가 높아지거나 펄스작용 시간비가 50s/100s로 높아짐에 따라 질화층은 CrN 및 Fe4N 위주로 구성되어 주상정 조직을 이루며 균일하게 성장하며 무균열층이 된다. $500^{\circ}C$에서는 저온 조직 및 상과 고온 조직 및 상이 혼합된 질화층이 형성되며 취성이 대단히 크다.

• 한국가스학회지
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• 제11권4호
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• pp.1-6
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• 2007

본 논문은 LPG 엔진에서 밸브스템의 표면거칠기가 오일 누설에 미치는 영향에 대한 실험적 결과를 제공하고자 한다. 밸브스템시일은 밸브스템과의 미세한 밀봉간극을 통해 유출하는 오일을 차단하기 위한 부품이다. 이들 두개의 부품사이에서 발생되는 밀봉성은 밸브스템과 밸브스템시일의 누유안전성과 수명연장에 관련된 중요한 요소이다. 본 실험결과에 의하면, 밸브스템의 표면거칠기를 중심선 표면거칠기, Ra로 나타낼 경우 $0.4{\sim}0.5{\mu}m$가 최적의 가공조건이고, 표면의 거칠기 단면형상은 균일하게 분포되도록 가공하는 것이 가장 이상적인 설계조건이 될 것이다. 기본적으로 매끄러운 밸브표면과 균일하게 분포된 거칠기 형상을 유지하는 것이 밸브스템과 밸브스템 시일장치의 간극을 통해 빠져나가는 누유량을 줄일 수 있다.

• 한국음향학회지
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• 제35권6호
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• pp.466-472
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• 2016

본 연구에서는 고분해능 초음파 영상 획득이 가능한 20 MHz 대역의 의료용 초음파 선형 배열 트랜스듀서를 개발하였다. 먼저 고주파 음파의 전파가 용이한 트랜스듀서의 구조를 고안한 후, 구성소자의 최적치수를 도출하였다. 이후 설계에 따라 트랜스듀서의 제작공정을 개발하고, 트랜스듀서 시편의 제작 및 평가를 수행하였다. 제작된 초음파 트랜스듀서는 중심주파수가 19 MHz이고, 비대역폭이 84.5 %, 감도의 표준편차가 0.74 dB로 측정되었다. 측정 결과는 설계 결과와 잘 일치하였으며, 이에 의해 본 연구에서 개발한 고주파 초음파 트랜스듀서 구조의 타당성을 검증하였다. 개발된 트랜스듀서는 새로운 구조에 의해 기존의 20 MHz 트랜스듀서에 비해 더 넓은 주파수 대역폭과 균일한 감도를 가지는 것으로 확인되었다.