• 대한기계학회논문집
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• 제14권2호
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• pp.269-275
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• 1990

Nonaxisymmetric bifurcation behaviours of composite tubes two different materials subjected to uniform radial shrinkage at the external surface have been investigated and compared with those of single tube. The effect of material parameters normalized with respect to those of outer tube upon the bifurcation point and corresponding mode has been clarified. The parameters substantially affect the bifurcation mode with long-wavelength so that the composite tube with low hardening exponent or with high yield stress of inner tube destabilizes the overall deformation of the tube. However surface type bifurcation, short-wavelength mode, shown on the traction-free inner surface is hardly affected by the material parameters. The surface type bifurcation completely depends on the material characteristics of inner tube and the bifurcation point of composite tube almost coincides with the of single tube.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 추계학술대회 논문집
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• pp.316-319
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• 2002

Injection mold is a manufacturing process used to produce parts of complicated shape at a low cost. Many factors affect the quality of injection molded part during injection molding process. A study on the optimization of injection mold is progressed by using a simulation software like Moldflow. Filling, packing and cooling phases of injection molding processes are analyzed according to the mold design considering the shrinkage of molded part, the degree of filling rate and the wearing of a mold. Taguchi method is applied to analyze the significance of processing parameters and the dynamic characteristics according to the variation of processing parameters. From the results, the mold temperature and packing pressure influenced strongly the shrinkage of injection molded part.

• ETRI Journal
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• 제37권6호
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• pp.1251-1258
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• 2015

We investigate an image recovery method for sparse-view computed tomography (CT) using an iterative shrinkage algorithm based on a second-order approach. The two-step iterative shrinkage-thresholding (TwIST) algorithm including a total variation regularization technique is elucidated to be more robust than other first-order methods; it enables a perfect restoration of an original image even if given only a few projection views of a parallel-beam geometry. We find that the incoherency of a projection system matrix in CT geometry sufficiently satisfies the exact reconstruction principle even when the matrix itself has a large condition number. Image reconstruction from fan-beam CT can be well carried out, but the retrieval performance is very low when compared to a parallel-beam geometry. This is considered to be due to the matrix complexity of the projection geometry. We also evaluate the image retrieval performance of the TwIST algorithm -sing measured projection data.

• Journal of Ginseng Research
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• 제18권1호
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• pp.60-65
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• 1994

Fresh ginseng of same grade was stored under the 4$\pm$1$^{\circ}C$ and 87~92% RH for 10 weeks. During the storage, an aliquot amount of the ginseng was drawn, freeze dried and chemical constituents and physicochemical parameters were measured. After 10 weeks of storage drying rate and shrinkage of ginseng were 1520% and 9.04%, respectively, mold growth was seen at week 5 and observed for 51.2% of the ginseng week 10. Amylase activity level was elevated at the early stage of storage and decreased to 5% of initial value at week 5. At week 5, the elevated amylase activity was inconcomitant with the appearance of the mold growth. Crude protein contents were increased and decreased, respectively 5 week post storage. No significant changes in crude fat, crude fiber, ash, total sugar, n-butanol extract and ginsenoside were observed. The content of water-extractable substance showed maximum at week 7 to 8. The value of pH was slightly elevated and reducing sugar was increased during the storage. Key words Ginseng storage, physicochemical properties, drying rate, shrinkage, amylase activity.

• 응용통계연구
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• 제19권2호
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• pp.331-338
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• 2006

수량화 제3방법은 일본의 하야시(Hayashi)에 의해 창안된 교차표 분석 기법으로 사회조사 및 마케팅 조사 자료의 분석에서 매우 유용하다. 그러나 반응빈도가 작은 일부 범주들이 특이하게 큰 수량화 값을 갖는 경우가 있어 불안정한 과잉 해석으로 이어지기도 한다. 본 교신은 이 문제를 해결하고자 한 연구로서 수량화 제3방법을 새로 정식화하고 축소 해 (shrinkage solution)를 제안할 것이다. 그리고 실제 조사 자료에 새 방법론을 적용해 보고자 한다.

• 한국기계가공학회지
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• 제9권2호
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• pp.60-65
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• 2010

Injection molding process is one of the popular manufacturing methods to produce plastic parts with high efficiency and low cost. The tub-drum for drum type washer is made by an insert injection molding process with aluminum alloy insert of windmill type and has a big and complex structure consisted of many ribs to sustain the strength. In this paper, the volumetric shrinkages of rib part and bottom part surrounded by a windmill type insert are analyzed according to the vertical and circumferential direction of tub-drum. Volumetric shrinkage and its difference according to the height or radius of tub drum inform the designer to reduce the warpage of tub drum, and the optimal design of tub drum can be done from the those results. The change of volumetric shrinkage according to packing pressure is also analyzed. It is very important to analyze the volumetric shrinkage of tub drum because it generates the wearing phenomena at the rotating part connected to an aluminum alloy insert due to the warpage of tub drum.

• 한국세라믹학회지
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• 제54권1호
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• pp.55-60
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• 2017

An anorthite-based traditional ceramic was developed by adding secondary flux materials to a mixture of kaolin and $CaCO_3$ in order to minimize the deformation during the sintering process. Three flux materials, feldspar, talc, and frit, were evaluated by comparison with two commercial chinaware bodies. Anorthite body with glass frit exhibited poor firing shrinkage. Poor mechanical properties (modulus of rupture, MOR < 30 MPa) was observed for the bodies with feldspar. Another anorthite body was formulated with wollastonite as a Ca source. The fired body showed a MOR of 81 MPa and a shrinkage rate of 6% when wollastonite was added up to 50%. In the XRD analysis, the phase ratio between anorthite and quartz was the highest in the specimen with 50% wollastonite addition. Homogeneous and relatively small closed pores were observed in the microstructural analysis. These results suggest that a ceramic body formulated with 50% kaolin and 50% wollastonite can be fired at $1200^{\circ}C$ with a 6% firing shrinkage rate, giving rise to minimal sintering deformation.

• 폴리머
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• 제31권6호
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• pp.491-496
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• 2007

고분자계 치아 수복용 복합재에서 2,2-bis[4-(2-hydroxy-3-methacryloyloxy propoxy) phenyl] propane(Bis-GMA) 70 wt%와 희석제인 triethylene glycol dimethacrylate(TEGDMA)가 30 wt% 포함된 혼합물이 레진 기질로 사용되고 있다. Bis-GMA의 높은 점도로 인해 첨가되는 TEGDMA는 수복재의 높은 경화 수축과 물성 저하의 원인이 된다. 본 연구에서는 TEGDMA 첨가량을 감소시켜 우수한 특성을 나타내는 수복재를 제조하기 위해 저점도 Bis-GMA 유도체들을 이용하여 새로운 치과용 수복재를 제조하였다. 히드록실기를 포함하지 않는 Bis-GMA 유도체들의 경화 특성은 Bis-GMA와 비슷하였지만 이들의 흡습성과 점도는 Bis-GMA에 비해 크게 낮았다. Bis-GMA 유도체를 포함한 수복재를 제조하여 경화 수축률, 흡습성, 기계적 물성을 실험한 결과 기존 상업적으로 사용되는 수복재보다 낮은 흡습성과 탁월한 물성을 나타내었고, 경화 수축률도 약 25% 감소하였다.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2013년도 춘계 학술논문 발표대회
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• pp.318-320
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• 2013

The spherical bead manufactured by rapidly cooling process shows high density of 3.64g/㎤, high unit volume weight of 2.6kg/l, and high solid volume of 71%. When it applies to the grouter, it is possible to obtain even high fluidity with only a small amount. This study, focusing the grouter using a rapidly-cooled electric arc furnace oxidizing slag(RC-EAFS), deals with the properties of flow and setting time in fresh state, compressive strength and length variation at 1, 3, 7 and 28 curing day in hardened state. As the results, even though the grouter with RC-EAFS shows comparative low strength, it will be possible to development the competitive product due to the properties of increasing flow and low cost.

• 콘크리트학회논문집
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• 제23권5호
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• pp.581-590
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• 2011

초고성능 시멘트 복합체(ultra-high-performance cementitious conposites, UHPCC)는 우수한 압축강도와 연성을 나타내기 때문에 구조 부재 적용 시 단면을 상당히 감소시키고, 낮은 물-결합재비와 고분말 혼화 재료의 사용으로 높은 수축 변형률이 발생하게 되어 거푸집 및 보강근 등의 구속에 의한 수축 균열의 발생 가능성이 크다. 그러므로 이 연구에서는 UHPCC의 수축을 저감시키기 위한 방법으로 팽창재와 수축 저감제를 조합하여 혼입하고 자유수축과 구속 수축 거동을 평가하여 적합성 여부를 산정하였다. 실험 결과 팽창재와 수축 저감제를 조합하여 혼입한 경우에 약 40~44%의 자유수축 저감 효과를 보였으며, 잔류 인장응력은 약 35%와 47% 감소하였다. 지속적인 구속 하중에 의한 인장 크리프의 발생으로 탄성 수축 응력의 약 61%, 64%가 이완되는 것으로 나타났으며, 따라서 구속 수축 거동을 평가할 때에는 반드시 크리프 효과를 고려해야 한다고 판단되었다. 구속도는 0.78~0.85로 나타났으며 팽창재와 수축 저감제의 혼입에 의한 영향은 미미하였고 콘크리트 링의 두께가 클수록 감소하는 경향을 보였다. 또한, UHPCC의 인장 크리프 변형률을 측정하고 재령에 따라 변하는 구속 하중을 적용한 4-매개 변수 크리프 예측 모델과 비교하였다.