• Journal of the Korean Ceramic Society
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• v.21 no.2
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• pp.149-155
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• 1984

The effect of $ZrO_2$ dispersed phase on the mechanical properties in $Al_2O_3$-$ZrO_2$system has been studied. There are both metastable tetragonal phase and stable monoclinic phase of $ZrO_2$particles diespersed in Al2O3 matrix at room temperature. Metastable tetragonal $ZrO_2$ changes to the stable monoclinic structure within the stress field of the crack. And microcracks are formed by the expansion of $ZrO_2$during the tetragonal-monoclinic transformation on cooling. Therefore stress-induced phase transformation and inclusion-induced microcracking contribute to the mec-hanical properties of $Al_2O_3$-$ZrO_2$system. Sintered composites containing 10m/o $ZrO_2$ yield KiC values of 6.5MN/$m^{3/2}$ much greater than that of pure $Al_2O_3$ This increase results from microcrack extension and stress-induced phase transformation absor-bing energy by crack propagation. Flexural strength of composites is decreased considerably in comparison with pure $Al_2O_3$ This decrease results from microcrack as a crack former and higher porosity than pure $Al_2O_3$.

• Annual Conference of KIPS
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• 2004.11a
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• pp.805-808
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• 2004

본 논문에서는 두 단백질의 구조적 유사성을 기반으로 한 단백질 비교를 위해서 전처리 기법으로서의 주성분분석기법을 소개한다. 기존의 백본 및 알파탄소 간의 거리행렬(distance matrix), 2차 구조 비교기법, 구역(segment)단위의 비교 기법과 같은 단백질 비교 기법들은 위치이동(translation)와 회전(rotation)에 불변한(invariant) 차이를 구하기 위하여 거리행렬을 이용하였다. 그리고, 난 다음 이들의 최적화 과정을 거쳤다. 그러나, 본 논문에서 제시하는 전처리 기법으로서의 주성분분석기법은 단백질 구조를 전체적인 구조 관점에서 위치를 정렬시킨 후에 단백질 간의 구조를 비교하는 방식이다. 단백질의 구조의 방향성(Orientation)을 맞춘 다음에는 다양한 단백질 표현으로 구를 비교할 수 있다. 본 논문에서는 두 단백질의 구조의 유사성을 측정하기 위한 간결한 단백질 표현(representation)으로 3 차원 에지 히스토그램을 사용하였다. 이 기법은 방향성을 정렬하기 위하여 기존의 방법에서 사용되었던 반복적인 거리계산을 통한 최적화하는 과정을 없앰으로써 단백질 구조 비교 시간을 단축할 수 있는 새로운 단백질 구조 비교 패러다임을 가능하게 한다. 따라서, 이 패러다임을 통하여 적절한 단백질 구조 방향성 정렬과 단백질 구조 표현을 이용한 단백질 구조 비교 검색 시스템은 많은 양의 단백질 구조 정보로부터 원하는 형태의 단백질 구조를 빠른 시간에 검색할 수 있는 장점을 가질 수 있다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.9
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• pp.775-780
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• 2016

In this paper, a computational algorithm of an improved and versatile structural analysis applicable for large-size flexible nonlinear structures is developed. In more detail, nonlinear finite element based on the co-rotational (CR) framework is developed. Then, a finite element tearing and interconnecting method using local Lagrange multipliers (FETI-local) is combined with the nonlinear CR finite element. The resulting computational algorithm is presented and applied for nonlinear static analyses, i.e., cantilevered beam and multibody structure. Finally, the proposed analysis is evaluated with regard to its parallel computation performance, and it is compared with those obtained by serial computation using the sparse matrix linear solver, PARDISO.

• Journal of Korea Foundry Society
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• v.40 no.4
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• pp.118-127
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• 2020

Microstructural evolution during a heat treatment and high-temperature tensile properties have been investigated in conventionally cast CM247LC. In as-cast specimens, MC carbides with high amounts of Ta, Ti, Hf, and W were found to exist in the interdendritic regions, and γ' was observed in the form of cubes and octocubes prior to decomposition into cubes. In the heat-treated condition, some portion of eutectic γ-γ' remained, and uniform cubic γ' was observed in both interdendritic regions and dendrite core. Three types of carbides with different stoichiometries and compositions were found at the grain boundaries. MC carbides with high Hf contents were observed in the vicinity of eutectic γ-γ'. The highest tensile strength value was found at 750℃, whereas the greatest ductility appeared at 649℃. The effect of the temperature on the tensile properties was closely related to the dislocation structure. With increase in the test temperature, the density of dislocations inside γ' decreased, whereas that in the γ matrix increased. Stacking faults generated in γ' at 750℃ had a strengthening effect, whereas thermally activated dislocation motion at a high temperature was considered to have the opposite effect.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.6
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• pp.4131-4136
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• 2015

This paper compares and calculates more precisely the averaged reflectance of antireflection coating with different structure of single and 6 layer assuming the incident angle of light changing from $8^{\circ}$ to $60^{\circ}$ not like normal incidence as usual case. The reflectivity of AR coating of 6 layers with 180 nm thickness having index profile suggested as linear and quintic function and single layer with same thickness having even index are calculated and compared, when the wavelength of incident light ranges from 400 nm to 1200 nm. As the results the AR coating with 6 layers having quintic(linear) function index profile shows the lower reflectance about 11.6 %(14.6 %) than other index profiles, which is approximately 8 % lower reflectance compared with single layer case(about 19.6 %). This results could be applied for the better antireflection coating design applying to optical devices and filters.

• Restorative Dentistry and Endodontics
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• v.29 no.3
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• pp.249-266
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• 2004

The purpose of this study was to determine whether pH and time has any influence on the degradation behavior of composite restoration by analyzing the leached monomers of dental composites qualitatively and quantitatively after storage in acetate buffer solution as a function of time using high performance liquid chromatography (HPLC) / mass spectrometer. Materials and Methods：Three commercial composite restorative resin materials (Z-250, Heliomolar and Aeliteflo) with different matrix structure and filler composition were studied. Thirty specimens (7mm $diameter{\times}2mm$ thick) of each material were prepared. The cured materials were stored in acetate buffer solution at different pH (4, 7) for 1, 7 and 45days. As a reference, samples of unpolymerized composite materials of each product were treated with methanol (10mg/ml). Identification of the various compounds was achieved by comparison of their mass spectra with those of reference compound, with literature data. and by their fragmentation patterns. Data were analysed statistically using ANOVA and Duncan's test. Results：1. Amounts of leached TEGDMA in Aeliteflo were significantly larger than those of UDMA in Z-250 and Heliomolar at experimental conditions of different storage time and pH variation (p<0.001). 2. As to comparison of the amounts of leached monomers per sorage time, amounts of leached TEGDMA in Aeliteflo and UDMA in Z-250 and Heliomolar were increased in the pH 4 solution more significantly than in the pH 7 solution after 1day, 7days and 45days, respectively (p<0.001). 3. In total amounts of all the leached monomers with storage times, the overall amounts of pH 4 extracts were larger than those of pH 7 extracts for all resin groups, but there was no significant difference (p>0.05).

• International Journal of Highway Engineering
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• v.11 no.4
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• pp.9-15
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• 2009

This research presents the structural performance and an improving technique for flexural capacity of road safety facilities based on the damage cases by wind pressure. Among road safety facilities, a support frame of soundproofing walls is considered as a prototype structure and its corresponding structural behaviors and section design are performed mainly by analytical and experimental studies. On the basis of analytical results, glass fiber reinforced polymer(GFRP) with an epoxy matrix which is high stiffness-to-weight ratio was used for applied one of strengthening techniques and their results shows that support frame strengthened by GFRP is the most effective compared to other cases proposed in this research for advancing its flexural improvement, Finally, optimum section design was performed analytically to evaluate wind-resistance capacity and its result would be very useful for developing a practical design guideline for Road safety facilities under strong wind.

• The Korean Journal of Applied Statistics
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• v.29 no.4
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• pp.581-594
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• 2016

We introduce innovations state space exponential smoothing models (ISS-ESM) that can analyze time series with multiple seasonal patterns. Especially, in order to control complex structure existing in the multiple patterns, the model equations use a matrix consisting of seasonal updating parameters. It enables us to group the seasonal parameters according to their similarity. Because of the grouped parameters, we can accomplish the principle of parsimony. Further, the ISS-ESM can potentially accommodate any number of multiple seasonal patterns. The models are applied to predict electricity demand in Korea that is observed on hourly basis, and we compare their performance with that of the traditional exponential smoothing methods. It is observed that the ISS-ESM are superior to the traditional methods in terms of the prediction and the interpretability of seasonal patterns.

• Journal of Korean Society of Steel Construction
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• v.18 no.2
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• pp.225-237
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• 2006

Based on the study conducted by Kim et al. (205a, b), an improved stability design method for evaluating the effective buckling lengths of beam-column members is proposed herein, using system elastic/inelastic buckling analysis and second-order elastic analysis. For this purpose, the stress-strain relationship of a column is inversely formulated from the reference load-carrying capacity proposed in design codes, so as to derive the tangent modulus of a column as a function of the slenderness ratio. The tangent stiffness matrix of a beam-column element is formulated using the so-called "stability functions," and elastic/inelastic buckling analysis Effective buckling lengths are then evaluated by extending the basic concept of a single simply-supported column to the individual members as one component of a whole frame structure. Through numerical examples of several structural systems and loading conditions, the possibilities of enhancement in stability design for frame structures are addressed by comparing their numerical results obtained when the present design method is used with those obtained when conventional stability design methods are used.

• Macromolecular Research
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• v.16 no.6
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• pp.517-523
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• 2008

A RGD (Arg-Gly-Asp) conjugated chitosan hydrogel was used as a cell-supporting scaffold for articular cartilage regeneration. Thermosensitive chitosan-Pluronic (CP) has potential biomedical applications on account of its biocompatibility and injectability. A RGD-conjugated CP (RGD-CP) copolymer was prepared by coupling the carboxyl group in the peptide with the residual amine group in the CP copolymer. The chemical structure of RGD-CP was characterized by $^1H$ NMR and FT IR. The concentration of conjugated RGD was quantified by amino acid analysis (AAA) and rheology of the RGD-CP hydrogel was investigated. The amount of bound RGD was $0.135{\mu}g$ per 1 mg of CP copolymer. The viscoelastic parameters of RGD-CP hydrogel showed thermo-sensitivity and suitable mechanical strength at body temperature for cell scaffolds (a> 100 kPa storage modulus). The viability of the bovine chondrocyte and the amount of synthesized glycosaminoglycans (GAGs) on the RGD-CP hydrogels were evaluated together with the alginate hydrogels as a control over a 14 day period. Both results showed that the RGD-CP hydrogel was superior to the alginate hydrogel. These results show that conjugating RGD to CP hydro gels improves cell viability and proliferation, including extra cellular matrix (ECM) expression. Therefore, RGD conjugated CP hydrogels are quite suitable for a chondrocyte culture and have potential applications to the tissue engineering of articular cartilage tissue.