• 한국세라믹학회지
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• 제27권1호
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• pp.55-61
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• 1990

Effect of Al2O3 addition on the mechanical properties and microstructure of Ce-TZP were studied. 12, 14, 16Ce-TZP containing 0-40wt% Al2O3 were prepared by sintering at 155$0^{\circ}C$ for 2h. in air. Density, linear shrinkage, bending strength, Vickers hardness, microstructuer and the amount of stress induced phase transformation were examined. Vickers hardness increased linearly with increasing amounts of Al2O3. The amount of transformation and fracture toughness decreased linearly with increasing amount of Al2O3. Linear shrinkage and relative density decreased with increasing Al2O3 content in all composition of Ce-TZP. Grain growth of Ce-TZP was inhibited by Al2O3 dispersion and fracture mode of Ce-TZP/Al2O3 composites transformed from intergranular to transgranular fracture as the amount of Al2O3 increased. TEM observation revealed that Al2O3 particles were located mainly at grain boundaries of ZrO2.

• 한국세라믹학회지
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• 제13권2호
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• pp.31-38
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• 1976

Korean tremoitic talc, wollastonite and clay have been used to develop a wall tile body to appropriate to the fast firing process. Some of ceramic properties of the raw materials were investigated by X-ray diffraction, thermal analysis and chemical analysis. The body compositions were formulated from the range of 35~75% tremolitic talc, 0~30% wollastonite and 25~35% plastic clay. Thermal gravity analysis and thermal expansion were tested for each of unfired bodies to study the correlation between thermal dehydration and linear shrinkage during the firing procedure. Linear shrinkage and water absorption of the fired bodies at the various temperature were taken as a measures for determining the proper firing range of the bodies. Increasing the content of wollastonite and firing temperature, the thermal expansion of the fired body showed the gradual decrease, and the thermal expansion curves showed a tendency to straighten. These observations may be resulted from the fact that the amounts of diopside and anorthite formed were gradually increased and those of quartz relatively decreased. The optimum compositions of the wall tile bodies for fast firing are 30% clay, 10~20% wollastonite and 50~60% tremolitic talc.

• 한국항공우주학회지
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• 제43권1호
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• pp.1-7
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• 2015

본 연구에서는 탄소섬유강화 복합재를 적층각과 적층순서에 따라 C-channel 형상에서 발생하는 스프링-인을 유한요소해석(ABAQUS)을 통해 예측하였다. 복합재 제작공정에서 냉각시의 큰 온도차 및 적층각에 따른 열팽창계수 및 화학적 수축계수의 차이로 인해 변형(스프링-인)이 발생한다. 이러한 변형은 제품의 품질과 직결되는 문제이며, 반드시 고려되어야 할 사항이다. 유한요소해석 시 CHILE모델과 화학적 수축을 고려한 서브루틴을 제작하여 적용하였으며, [0/X/Y/90]s case에 대해 X,Y를 $0{\sim}90^{\circ}$까지 변화시키며 각 case에 대한 스프링-인 발생량을 예측, 분석하였다.

• Communications for Statistical Applications and Methods
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• 제31권4호
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• pp.393-408
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• 2024

The sparse linear discriminant analysis can be incorporated into the penalized linear regression framework, but most studies have been limited to specific convex penalties, including the least absolute selection and shrinkage operator and its variants. Within this framework, concave penalties can serve as natural counterparts of the convex penalties. Implementing the concave penalized direction vector of discrimination appears to be straightforward, but developing its theoretical properties remains challenging. In this paper, we explore a class of concave penalties that covers the smoothly clipped absolute deviation and minimax concave penalties as examples. We prove that employing concave penalties guarantees an oracle property uniformly within this penalty class, even for high-dimensional samples. Here, the oracle property implies that an ideal direction vector of discrimination can be exactly recovered through concave penalized least squares estimation. Numerical studies confirm that the theoretical results hold with finite samples.

• 대한토목학회논문집
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• 제32권5A호
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• pp.317-325
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• 2012

본 연구에서는 초고성능 섬유보강 콘크리트(Ultra High Performance Fiber Reinforced Concrete, UHPFRC)의 구속 상태에서의 수축 거동을 평가하고자 국내 외에서 가장 보편적으로 사용되는 링-테스트(ring-test)를 이용하여 구속 수축 실험을 수행하였다. 특히, 다양한 구속도에서의 수축 거동을 평가하기 위하여 내부 강재 링의 두께와 내부 반경을 달리하여 실험을 수행하였으며, 자유 수축과 인장강도 실험을 수반하여 구속도 및 응력 이완, 수축 균열 가능성 등을 복합적으로 평가하였다. 실험 결과 내부 링의 두께가 증가할수록 내부 링의 평균 변형률과 잔류 인장응력은 감소하였으며, 반면에 구속도는 증가하는 경향을 보였다. 내부 링의 반경에 따라서는 변형률 및 잔류 인장응력, 구속도의 차이가 거의 없는 것으로 나타났다. 모든 시험체에서 잔류 인장응력이 인장강도에 비해 작은 것으로 나타났으며, 수축 균열은 발생하지 않았다. 지속적으로 작용하는 계면 구속 하중에 의해 탄성 수축 응력의 약 39~65%가 이완되는 것으로 나타났으며, 최대 이완 응력은 내부 링의 두께가 두꺼울수록 증가하는 것으로 나타났다. 마지막으로 본 연구에서는 비선형 회귀분석을 수행하여 재령에 따라 변하는 구속도를 예측하였으며, 실험 결과와 잘 일치하는 것으로 나타났다.

• 콘크리트학회논문집
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• 제20권2호
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• pp.131-138
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• 2008

물-결합재비가 낮은 고성능콘크리트의 자기건조에 의한 습도감소와 수축과의 연관성을 파악하기 위하여 물-결합재비 0.3, 0.4의 배합에 대하여 습도와 변형률을 측정하였다. 그 결과 물-결합재비 0.3의 콘크리트 내부 습도 감소는 약 10%, 수축변형률은 약 $320\times10^{-6}$을 나타내었고, 물-결합재비 0.4의 콘크리트의 경우 4%의 습도 감소와 $120\times10^{-6}$ 수축변형률을 나타내었으며 배합에 상관없이 습도와 변형률은 모두 강한 선형성을 보였다. 콘크리트 내부 습도 변화와 수축변형률의 관계를 보다 구체화하기 위하여 콘크리트 내부 공극을 단일 네트워크로 가정하고 확장 메니스커스 생성가정 하에 공극수에서 발생하는 모세관 압력과 수화조직체에서 발생하는 표면에너지 변화를 습도의 함수로 모델링하여 수축의 구동력으로 작용시킨 결과 실험값과 비교적 일치하는 값을 나타내었다. 이를 근거로 물-결합재비가 낮은 고성능 콘크리트에서 자기건조에 의한 습도감소는 20 nm 이하의 소형공극에서 발생함을 파악할 수 있었으며 따라서 자기수축에 대한 제어 방안은 이러한 소형공극에서의 공극수 표면장력과 포화도에 초점을 맞추어야 함을 확인할 수 있었다.

• Structural Engineering and Mechanics
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• 제62권6호
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• pp.725-737
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• 2017

An analytical method considering axial equilibrium is proposed for the short- and long-term analyses of shear lag effect in reinforced concrete (RC) box girders. The axial equilibrium of box girders is taken into account by using an additional generalized displacement, referred to as the longitudinal displacement of the web. Three independent shear lag functions are introduced to describe different shear lag intensities of the top, bottom, and cantilever plates. The time-dependent material properties of the concrete are simulated by the age-adjusted effective modulus method (AEMM), while the reinforcement is assumed to behave in a linear-elastic fashion. The differential equations are derived based on the longitudinal displacement of the web, the vertical displacement of the cross section, and the shear lag functions of the flanges. The time-dependent expressions of the generalized displacements are then deduced for box girders subjected to uniformly distributed loads. The accuracy of the proposed method is validated against the finite element results regarding the short- and long-term responses of a simply-supported RC box girder. Furthermore, creep analyses considering and neglecting shrinkage are performed to quantify the time effects on the long-term behavior of a continuous RC box girder. The results show that the proposed method can well evaluate both the short- and long-term behavior of box girders, and that concrete shrinkage has a considerable impact on the concrete stresses and internal forces, while concrete creep can remarkably affect the long-term deflections.

• 한국수산과학회지
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• 제45권6호
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• pp.730-733
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• 2012

We investigated body shrinkage, defined as change in standard length and body weight of juvenile chub mackerel Scomber japonicus after preservation in 70% ethyl alcohol for 1, 8, or 12 days. Standard length (SL) was decreased by 3.6% and body weight (BW) was reduced by 27.5% after 8 day of preservation. There were no significant decreases in SL and BW after 8 or 12 days preservation. Linear regression equations for estimation of original body size from the size after preservation in 70% ethyl alcohol for 12 days were expressed as: $SL_{original}=0.96SL_{preserved}+5.17$ and $BW_{original}=1.16BW_{preserved}+0.37$. These equations will be useful for improving accuracy the estimation accuracy for various size-related biological parameters in juvenile chub mackerel juvenile.

• 한국염색가공학회지
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• 제7권2호
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• pp.24-31
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• 1995

The properties of carbon fibers made from PAN are controlled by the heat treatment conditions. The length changes of high strength homo-PAN and co-PAN (acrylonitrile/acrylamide= 98/2wt% ) fibers under constant tensile stress during heat treatment in nitrogen gas were investigated by measuring the shrinkage behavior. In order to elucidate the relation between the length and fine structure change, the measurements of the crystalline orientation and birefringence index etc. were made for the fibers treated under linear heating up to 27$0^{\circ}C$. There are two regions in the length change with heat treatment temperature. The change in the initial period is mainaly due to the relaxation of amorphous molecular chain confined by the fiber-manufacture process. The length change in later period is considered to arise as cyclization reactions. The co-PAN fibers caused a larger shrinkage, while the onset of the shrinkage change in later period is, shifted to lower temperature. Significant morphological changes are shown to precede onset of the cyclization reactions and also during these reactions.

• Journal of the Korean Statistical Society
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• 제33권4호
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• pp.411-433
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• 2004

The shrinkage preliminary test ridge regression estimators (SPTRRE) based on Wald (W), Likelihood Ratio (LR) and Lagrangian Multiplier (LM) tests for estimating the regression parameters of the multiple linear regression model with multivariate Student's t error distribution are considered in this paper. The quadratic biases and risks of the proposed estimators are compared under both null and alternative hypotheses. It is observed that there is conflict among the three estimators with respect to their risks because of certain inequalities that exist among the test statistics. In the neighborhood of the restriction, the SPTRRE based on LM test has the smallest risk followed by the estimators based on LR and W tests. However, the SPTRRE based on W test performs the best followed by the LR and LM based estimators when the parameters move away from the subspace of the restrictions. Some tables for the maximum and minimum guaranteed efficiency of the proposed estimators have been given, which allow us to determine the optimum level of significance corresponding to the optimum estimator among proposed estimators. It is evident that in the choice of the smallest significance level to yield the best estimator the SPTRRE based on Wald test dominates the other two estimators.