• Structural Engineering and Mechanics
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• v.65 no.4
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• pp.465-476
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• 2018

This article investigates buckling behavior of a multi-phase nanocrystalline nanobeam resting on Winkler-Pasternak foundation in the framework of nonlocal couple stress elasticity and a higher order refined beam model. In this model, the essential measures to describe the real material structure of nanocrystalline nanobeams and the size effects were incorporated. This non-classical nanobeam model contains couple stress effect to capture grains micro-rotations. Moreover, the nonlocal elasticity theory is employed to study the nonlocal and long-range interactions between the particles. The present model can degenerate into the classical model if the nonlocal parameter, and couple stress effects are omitted. Hamilton's principle is employed to derive the governing equations and the related boundary conditions which are solved applying an analytical approach. The buckling loads are compared with those of nonlocal couple stress-based beams. It is showed that buckling loads of a nanocrystalline nanobeam depend on the grain size, grain rotations, porosities, interface, elastic foundation, shear deformation, surface effect, nonlocality and boundary conditions.

• 한국해양학회지
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• v.28 no.1
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• pp.72-78
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• 1993

Sediment grain size was analysed and compared for standard solids and sediment samples using two different methods; SediGraph and MasterSizer. SediGraph results on sediment samples appeared as finer than those of MasterSizer, and the difference is great especially for biogenic siliceous ooze. The difference is maybe due to the following different points in two methods; pretreatment procedure, sample concentration, detachability on fine grains (about 1 um), and detection principle on nonspherical grains.

• Journal of the Korean Ceramic Society
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• v.42 no.11 s.282
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• pp.718-721
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• 2005

The high temperature tetragonal phase of zirconia containing $1.40{\~}1.60\;mol\%$ of yttria can be fully retained at room temperature by rapid cooling. The metastable tetragonal phase transforms into the monoclinic phase athermally upon subzero cooling. The transformation exhibited an athermal burst transformation. The effects of yttria content and grain size on the athermal martensitic transformation were studied in detail. The burst temperature linearly decreased with increasing yttria content or decreasing grain size. To consider the distribution of martensite nuclei, the Weibull modulus of the athermal martensitic transformation was evaluated from the distribution of the burst transformation temperature. From the Weibull analysis, the distribution of embryos appears to be more homogeneous than that of the defects responsible for the fracture of similar material.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1323-1324
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• 2006

Refractory materials, such as W and Mo, are very useful elements for use in high-temperature applications. But it is not easy to fabricat pure W and Mo with very high density and retaining very fine grain size because of their high melting point. In this paper, a newly developed method named as resistance sintering under ultra high pressure was use to fabricate pure fine-grained W and Mo. The microstructure was analysis by SEM. The sintering mechanism is primary analyzed. Basic physical property of these sintered pure W and Mo, such as hardness, bend strength, are tested.

• Journal of Korea Water Resources Association
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• v.56 no.9
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• pp.553-562
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• 2023

The Gobiobotia naktongensis is a species endemic to Korea, and it has recently been designated as a class I endangered species of freshwater fish. Naeseong Stream, one of the tributaries of the Nakdong River, where the Gobiobotia naktongensis was first discovered, provided an optimal habitat for the Gobiobotia naktongensis in the past with fine sand beds and riffle. Currently, due to the construction of Yeongju Dam and the excessive dredging of river channels by the local government, the riverbed armoring in the downstream area of the dam is undergoing rapid changes, and as a result, the habitat environment of the Gobiobotia naktongensis is deteriorating. In this study, the variations of the habitat suitability of the Gobiobotia naktongensis due to the change in the riverbed grain size of the Naeseong Stream were analyzed based on the WUA (weight usable area) using the physical habitat model, River2D. The study domain is the reach from Seoktap Bridge to Hoeryong Bridge downstream of Yeongju Dam. The change in riverbed grain size was analyzed using D50 acquired in 2010 and 2020, respectively. The substrate grain size of Naeseong Stream in 2020 was thicker than that in 2010, and the riverbed coarsening phenomenon was evident overall. As a result of the River2D analysis, the area in which the Gobiobotia naktongensis could inhabit was only about 0.75% in 2010 compared to the entire area of the flow, and even this decreased to 0.55% in 2020 due to riverbed armoring.

• Journal of the Korean Ceramic Society
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• v.33 no.1
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• pp.17-24
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• 1996

Pb(Mg1/3Nb2/3)O3 powder with high purity chemical homogeniety and reactivity was prepared by solvent eva-poration of common solution. The common solution was fabricated using a Pb(NO3)2 Mg(NO)3 and NB solution which was prepared by dissolving NbC in H2O2 acquous solution. In precusor powder prepared by solvent evaporation method the synthetic temperature of Pb(Mg1/3 Nb2/3)O3 phase was lowered. And the formation of homogeneous Pb(Mg1/3Nb2/3)O3 phase was enhanced but the formation of pyrochlore phase was reduced. The dielectric constant of PMN ceramics from the synthesized powder was found to increase with both sintering temperature and excess MgO and subsequent analysis of the microstructures confirmed that this was due to an increase in grain size. The grain size dependence is explained as a consequence of low-permittivity grain boundaries.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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• pp.328-331
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• 2000

The effect of the constituent elements and their composition of the seed layer on the properties of the evaporated Zn thin films was investigated. It was carried out by the analysis of the preferred orientation and the grain size, and the corrosion characteristics. Seed layers were prepared by evaporation of Al and AlCu respectively, and here the Cu content as additives of the source materials of seed layers were designed 5 a/o to 20 a/o. The values of full width at half maximum (FWHM) of the (002) x-ray diffraction peaks of Zn decreased by increasing the amount of the additives on Al seed layer, as a results, the grain sizes also decreased. In order to characteristics of Zn thin films evaporated on the various seed layers, electrical resistivity changes with a function of time at the temperature of 40$^{\circ}C$ and the relative humidity of 80%, as a result, the relative resistivity changes were increased by decreasing the grain size and the FWHM values of (002) peaks of Zn.

• Korean Journal of Plant Resources
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• v.12 no.3
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• pp.186-191
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• 1999

This study was conducted to evaluate the growth characteristics and grain component of 10 collected colored rice cultivars to find out the possibilities of using the agronomically usefull characters to provide information for colored rice breeding and cultivation. The coefficients of variation of culm length, grains number, ripening rate, maturity time, and coat color of grain and seed were higher than those of other characters. The positive correlations were observed among heading dates, grain numbers per panicle, and 1000 grain weight, as well as between culm length and panicle length, panicle length and grain numbers per panicle, 1000 grain weight and darkness of seed coat color, while negative correlations were observed between heading dates and panicle numbers per hill, grain yield and seed coat color as well as among culm length, length, number per hill and seed coat color of brown rice, respectively. The first component of principal component analysis was consist of panicle numbers per hill, 1000 grain weight, and grain yield showing higher correlations among them which explained the variance of the sink size of respective cultivars. The second component of principal component analysis was consist of heading date, grain numbers per panicle and maturing date showing higher correlations among them which explained the variance of maturity of respective cultivars.

• International Journal of Precision Engineering and Manufacturing
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• v.4 no.2
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• pp.49-56
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• 2003

As semi-solid forging (SSF) is compared with conventional casting such as gravity die-casting and squeeze casting, the product without inner defects can be obtained from semi-solid forming and globular microstructure as well. Generally, SSF consists of reheating, forging, and ejecting processes. In the reheating process, the materials are heated up to the temperature between the solidus and liquidus line at which the materials exists in the form of liquid-solid mixture. The process variables such as reheating time, reheating temperature, reheating holding time, and induction heating power has large effect on the quality of the reheated billets. It is difficult to consider all the variables at the same time for predicting the quality. In this paper, Taguchi method, regression analysis and neural network were applied to analyze the relationship between processing conditions and solid fraction. A356 alloy was used for the present study, and the learning data were extracted from the reheating experiments. Results by neural network were in good agreement with those by experiment. Polynominal regression analysis was formulated using the test data from neural network. Optimum processing condition was calculated to minimize the grain size and solid fraction standard deviation or to maximize the specimen temperature average. Discussion is given about reheating process of row material and results are presented with regard to accurate process variables fur proper solid fraction, specimen temperature and grain size.

• Nuclear Engineering and Technology
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• v.53 no.5
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• pp.1619-1625
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• 2021

This paper demonstrates the possible nondestructive analysis of iron artifacts' metallurgical characteristics using neutron imaging. Ancient kingdoms of the Korean Peninsula used a direct smelting process for ore smelting and iron bloom production; however, the use of iron blooms was difficult because of their low strength and purity. For reinforcement, iron ingots were produced through refining and forge welding, which then underwent various processes to create different iron goods. To demonstrate the potential analysis using neutron imaging, while ensuring artifacts' safety, a sand iron ingot (SI-I) produced using ancient traditional iron making techniques and a sand iron knife (SI-K) made of SI-I were selected. SI-I was cut into 9 cm², whereas the entirety of SI-K was preserved for analysis. SI-I was found to have an average grain size of 3 ㎛, with observed α-Fe (ferrite) and pearlite with a body-centered cubic (BCC) lattice structure. SI-K had a grain size of 1-3 ㎛, α-Ferrite on its backside, and martensite with a body-centered tetragonal (BCT) structure on its blade. Results show that the sample's metallurgical characteristics can be identified through neutron imaging only, without losing any part of the valuable artifacts, indicating applicability to cultural artifacts requiring complete preservation.