• Design & Manufacturing
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• 제12권1호
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• pp.1-6
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• 2018

In this study, we calculated the redistribution of vacancy concentration in metal specimens induced by stress-induced diffusion at a high temperature. To deduce the governing equation, we associated the unit volume change equation of strains with a differential equation of vacancy concentration as a function of stress using the stress-strain relationship. In this governing equation, we considered stress as the only chemical potential parameter to stay in the scope of this study, which provided the vacancy concentration equation as of stress gradient in metals. The equation was then mathematically delineated to derive a analytical solution for a transient, one-dimensional diffusion case. With the help of Korhonen's approximation and the boundary conditions, we successfully deduced a general solution from the governing equation. To visualize the feasibility of our solutions, we applied the solution to two different stress-induced cases - a rod with fixed concentrated stresses at both ends and a rod with varying concentrated stresses at both ends. Although it is necessary to legitimatized the model in the future for improvement, our results showed that the model can be used to interpret the location of structural defects, the formation of vacancy, and furthermore the high temperature behavior of metals.

• 한국지반공학회논문집
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• 제16권6호
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• pp.35-41
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• 2000

Residual stress is defined as a minimum stress with a large displacement of specimens and the residual stress after peak shear stress appears with displacement volume but there is no provision to select the residual stress. In the previous study, residual stress was recorded when the change of shear load is small in the condition of the strain more than 15%. But, in this study, hyperbolic function((No Abstract.see full/text), b=experimental constant) of soil test is adapted to joint of rock and the propriety is investigated. In a landslide and landsliding of artificial slope, wedge failure of tunnel with a large displacement, tests are simulated from peak stress to residual stress for safety analysis. But now. direct shear stress and triaxial compressive tests are usually performed to find out characteristics of shear stress about joint. Although these tests get a small displacement, that data of peak stress and residual stress are used for safety analysis. In this study, we tried to determine failure criteria for joints of rock using ring shear test machine. The residual stress following shear behavior was determined by the result of ring shear test and direct shear test. In conclusion, after comparing the results of the two test, we found that cohesion(c) and internal friction angle(ø) of ring shear test are 30% and 22% respectively of those of the direct shear test.

• 한국환경교육학회지:환경교육
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• 제11권2호
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• pp.14-25
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• 1998

The Quality of human living depends on the environmental quality of the region sustaining the life. The environmental deterioration of the modern society is due to mechanical environmentalism. For the better quality of the life, The changes of recognition and attitude on the environments are required. These changes of mind are also important in environmental education for teenagers. The 7th national curriculum, officially anounced December 1998, focuses on the change of attitude to environments and practical behavior in real life for “Environments”, the environmental education curriculum in middle school. Basic elements of the curriculum are cultivation of the pro-environmental thinking, multi-levelling of teaching materials and methods, and encouraging of student participating activity. Actually, the curriculum construction is composed of stepped-levelling of teaching and learning, reasonable contents volume, encouraging of student practice, and suggesting of evaluation standards of textbook writing. Three main subjects of environmental education for middle school consist of (1) man and environment, (2) recognition of environmental problem, and (3) protection activity for environment. Methodology of environmental education can include multi-disciplinary approaches, variable teaching methods, and continuing evaluation of student practice and participation attitude. Environmental education for teenagers relating to the 7th national curriculum focuses on recognition of the environmental problems and practice activity in daily life. The recognition includes considering relationship of human life to environment, solving environmental problems in regional context, and development of comprehensive understanding concept of the environments. For the practice education, variable teaching methods, such as field survey and application of multi-media, are needed.

• 대한화학회지
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• 제36권1호
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• pp.100-106
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• 1992

스티렌-말레산(PSMA), 스티렌말레산 무수물(PSMAn), 및 스티렌-말레산의 $Eu^{3+}$ 염(PSMA-Eu)의 형광특성을 tetrahydrofuran 용액에서 연구하였다. 스티렌의 몰%가 75%인 PSMA와 PSMA-Eu은 들뜬 이합체의 결합에너지가 50%나 67%에 비해 크게 나타났다. 들뜬이합체-단위체 형광세기의 비로부터 스티렌 단위체의 농도가 $8.0{\times}10^{-3}M$까지도 분자내 들뜬이합체의 특성을 보였다. 들뜬이합체의 형성메카니즘을 설명하는 기존의 세 가지 모형은 이들 중합체에 대해서는 잘 맞지 않는 듯하다. benzylacetate, mesitylene 및 염소가 치환된 용매들이 들뜬이합체의 형광에 주는 영향을 을 조사하여 그 결과를 몰부피로 해석해 보았다.

• Structural Engineering and Mechanics
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• 제36권5호
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• pp.545-560
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• 2010

Two or more distinct materials are combined into a single functionally graded material (FGM) where the microstructural composition and properties change gradually. Thermal post-buckling behavior of uniform slender FGM beams is investigated independently using the classical Rayleigh-Ritz (RR) formulation and the versatile Finite Element Analysis (FEA) formulation developed in this paper. The von-Karman strain-displacement relations are used to account for moderately large deflections of FGM beams. Bending-extension coupling arising due to heterogeneity of material through the thickness is included. Simply supported and clamped beams with axially immovable ends are considered in the present study. Post-buckling load versus deflection curves and buckled mode shapes obtained from both the RR and FEA formulations for different volume fraction exponents show an excellent agreement with the available literature results for simply supported ends. Response of the FGM beam with clamped ends is studied for the first time and the results from both the RR and FEA formulations show a very good agreement. Though the response of the FGM beam could have been studied more accurately by FEA formulation alone, the authors aim to apply the RR formulation is to find an approximate closed form post-buckling solutions for the FGM beams. Further, the use of the RR formulation clearly demonstrates the effect of bending-extension coupling on the post-buckling response of the FGM beams.

• Nuclear Engineering and Technology
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• 제50권3호
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• pp.439-445
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• 2018

Experimental measurements of the response of $BF_3$ detector to a 3 Ci Am-Be neutron source for three different reflecting materials, i.e., aluminum, wood, and Perspex of varying thicknesses have been carried out. The varying contribution of wall effect to the response due to change in active volume of the detector has also been determined experimentally. Then, a Monte Carlo code has been developed for the calculation of the neutron response function of the $BF_3$ detector using source biasing and importance sampling. This code simulates the $BF_3$ detector response exposed to the neutron field in a three-dimensional source, detector, and reflecting medium configurations. The results of simulation have been compared with the corresponding experimental measurements and are found to be in good agreement. The experimental neutron albedo measurements for various values of Perspex thickness show saturating behavior, and results agree very well with the data obtained by Monte Carlo simulation.

• 대한금속재료학회지
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• 제50권9호
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• pp.619-627
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• 2012

One of the barriers limiting wide applications of magnesium alloys to various industries is their poor corrosion resistance. The corrosion properties of AZ91 magnesium alloy, which is the most popular magnesium casting alloy, are affected by microstructural and environmental factors. The corrosion properties of AZ91 magnesium alloy are affected by the corrosion properties of ${\alpha}-Mg$ and ${\beta}$ phases, the volume fraction and distribution of ${\beta}$ phase and area ratio of ${\alpha}-Mg/{\beta}$ phases. The corrosion properties of AZ91 magnesium alloy under various environments also change according to the passivity of films and types of corrosion products formed on its surface. The corrosion resistance of the magnesium alloys can be improved by microstructural control through the addition of alloying elements and optimization of the production process.

• Steel and Composite Structures
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• 제33권1호
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• pp.93-109
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• 2019

In the present study, vibration analysis of double bonded micro sandwich cylindrical shells with saturated porous core and carbon/boron nitride nanotubes (CNT/BNNT) reinforced composite face sheets under multi-physical loadings based on Cooper-Naghdi theory is investigated. The material properties of the micro structure are assumed to be temperature dependent, and each of the micro-tubes is placed on the Pasternak elastic foundations, and mechanical, moisture, thermal, electrical, and magnetic forces are effective on the structural behavior. The distributions of porous materials in three distributions such as non-linear non-symmetric, nonlinear-symmetric, and uniform are considered. The relationship including electro-magneto-hydro-thermo-mechanical loadings based on modified couple stress theory is obtained and moreover the governing equations of motion using the energy method and the Hamilton's principle are derived. Also, Navier's type solution is also used to solve the governing equations of motion. The effects of various parameters such as material length scale parameter, temperature change, various distributions of nanotube, volume fraction of nanotubes, porosity and Skempton coefficients, and geometric parameters on the natural frequency of double bonded micro sandwich cylindrical shells are investigated. Increasing the porosity and the Skempton coefficients of the core in micro sandwich cylindrical shell lead to increase the natural frequency of the structure. Cylindrical shells and porous materials in the industry of filters and separators, heat exchangers and coolers are widely used and are generally accepted today.

• Geomechanics and Engineering
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• 제6권2호
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• pp.139-151
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• 2014

Mudstone is a very common rock that, when in contact with water, can exhibit considerable volume change and breakdown. This behavior of mudstone is frequently encountered in geotechnical engineering and has a considerable influence on infrastructure stability. This is particularly important in the present work, which focuses on mitigating the harmful properties of mudstone. The samples studied are of Permian Age mudstone from Shandong Province, China. Modification tests using organic silicone additive material were carried out. The mechanisms of physical properties modification of mudstone were comparatively studied using corresponding test methods, and the modification mechanism of organic silicone additive material acting on mudstone was analyzed. The following conclusions were drawn. The surface texture and characters of mudstone changed dramatically, surface character turns from hydrophilic to hydrophobic after organic silicone additive material modification. The changes in the surface character indicate a reduction in the water sensitivity of mudstone. After modification, the shape of porosity and fracture of mudstone changed unremarkable, and the total and free expansion ratios decreased obviously, whereas the strength increased markedly.

• 산업융합연구
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• 제2권1호
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• pp.159-186
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• 2004

One of the biggest change in the distributive market recently is that the development of private brand is progress actively since consumers purchasing behavior is tend to shift to resonable and practical planned purchase from brand image or brand name. Once the development of private brands is done successfully, the independent merchandising distinguished from other distribution companies is established, store image through customer satisfaction is strengthen and volume of sales and profit are increased. However, the existing studies in this field have not dealt with this matter systematically. Therefore, the purpose of this study is to propose an integrated framework within which to view private brand proneness. Factors found to influence private brand proneness included perceived cost, with private brand, perceived value for money, store fame, perceived risk, perceived quality variation between national and private brand products. Foe empirical analysis, the data were collected from 211 consumers who purchased the private brands in discount store and department store. With the collected survey data, reliability test, factor analysis for validity test and regression analysis for hypotheses test were conducted. Most hypotheses were accepted but on hypotheses were rejected negative relation of perceived cost and private brand proneness. Research results indicate that private brand proneness is affected by perceived value, perceived fame and there are negative relation between private brand proneness and perceived quality variation.