• Resources Recycling
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• v.9 no.5
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• pp.11-15
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• 2000

The sample made of $Mn_3O_4$ indicated an excellent frequency dependency for intial permeability and core loss. Moreover the homogeneity of cation configuration in he spinel structure was confirmed by X-ray diffraction analysis. The result of homogeneity of the spinel structural coincided with the analytical results of temperature dependence of magnetization. Furthermore, the influence of manganese oxide as starting material, on homogeneity of spinel structure was examined by using thermogravimetry-differential thermal analysis. It may be concluded that the reaction between $Mn_3O_4$ and Fe-Zn oxide mixture proceeds at fist in all combination of manganese oxide and oxie mixture, and then Mn-Zn-Fe spinel was formed.

• Journal of Biomedical Engineering Research
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• v.29 no.4
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• pp.267-271
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• 2008

The RF shimming technique has been used to improve the transmit RF field homogeneity in highfield MRI. In the RF shimming technique, the amplitude and phase of the driving currents in each coil element are optimized to get homogenous flip angle or uniform image intensity. The inductive and capacitive coupling between the coil elements may degrade the RF field homogeneity if not taken into account in the optimization procedure. In this paper, we have analyzed the coupling effects on the RF shimming using a sixteen-element TEM RF coil model operating at 300 MHz. We have found that the coupling effects on the RF shimming can be reduced by putting high dielectric material between the active rung and the shield.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.931-932
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• 2006

The microstructures of Ni-containing P/M steels produced by admixed powders or diffusion alloyed powders are usually heterogeneous. To improve the microstructure homogeneity, the effects of Mo and Cr additions in the prealloyed powder form were examined. The results showed that the microstructural homogeneity was improved and superior mechanical properties were achieved with increases in the alloy content, particularly for the Cr. Such a beneficial effect was attained due to the reduction of the repelling effect between Ni and C, as was demonstrated through thermodynamic analysis using the Thermo-Calc software.

• Journal of Environmental Science International
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• v.27 no.12
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• pp.1271-1277
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• 2018

The National Environmental Specimen Bank (NESB) has been sampling and cryogenically preserving various wildlife specimens to monitor bio-accumulations of chemical pollutants since 2010. Recently, the NESB set up a plan to develop reference materials at their facility to assure the analytical quality of and validate the analytical methods for their monitoring samples. One of the crucial characteristics of reference materials is intra- and inter-bottle homogeneity. In this study, we used ANOVA for total mercury concentrations in some samples to validate their homogeneities after milling and homogenization. We examined the intra- and inter-bottle homogeneities of two cryogenically-milled samples (Korean mussel (Mytilus coruscus) and black-tailed gull's egg (Larus crassirostris). The variations in the total mercury concentrations were not significantly different intra- and inter-bottle (mussel: F=0.74, p=0.67; gull egg: F=1.96, p=0.10). Additionally, the relative standard deviations of the total mercury concentrations showed low values (mussel: 2.02%, gull egg: 1.78%). Therefore, the cryogenic-milling process statistically proves the homogeneity of the materials of mussels and sea gull eggs for chemical analysis for total mercury.

• Computers and Concrete
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• v.10 no.4
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• pp.409-417
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• 2012

The quality of high performance concrete largely depends on water cement ratio, porosity, material composition and mix methods. The uniformity of color, texture and compressive strengths are quality indicators commonly used to assess the overall characteristics of concrete mixes. The homogeneity and share of coarse aggregates play a key role in concrete quality and must be analyzed in a microscopic point of view. This research studies the quality of high performance concrete by taking drilled cores in both horizontal and vertical directions from a 1.0 $m^3$ specimen. The coarse aggregate, expressed in digitized $100{\times}116$ dpi resolution images are processed based on brightness in colors through commercial software converted into text files. With the image converting to text format, the share of coarse aggregate is quantified leading to a satisfactory assessment of homogeneity - a quality index of high performance concrete. The compressive strengths of concrete and the shares of coarse aggregate of the samples are also compared in this research study to illustrate its correlation in concrete quality. It is concluded that a higher homogeneity of aggregate exists in the vertical plane than that of the horizontal planes of the high performance concrete. In addition, the concrete specimen showing denser particle packing has relatively higher compressive strengths. The research methodology provides an easy-to-use, direct measurement of high performance concrete when conducting quality assessment in the construction site.

• Structural Engineering and Mechanics
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• v.43 no.1
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• pp.89-103
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• 2012

In this study, the stability of laminated homogeneous and non-homogeneous orthotropic truncated conical shells with freely supported edges under a uniform hydrostatic pressure is investigated. It is assumed that the composite material is orthotropic and the material properties depend only on the thickness coordinate. The basic relations, the modified Donnell type stability and compatibility equations have been obtained for laminated non-homogeneous orthotropic truncated conical shells. Applying Galerkin method to the foregoing equations, the expression for the critical hydrostatic pressure is obtained. The appropriate formulas for the single-layer and laminated, cylindrical and complete conical shells made of homogeneous and non-homogeneous, orthotropic and isotropic materials are found as a special case. Finally, effects of non-homogeneity, number and ordering of layers and variations of shell characteristics on the critical hydrostatic pressure are investigated.

• Analytical Science and Technology
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• v.27 no.6
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• pp.339-346
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• 2014

The author assessed the availability of urine reference material for proficiency test provided for laboratories in occupational health. N-methylacetamide is the biomarker of exposure to N,N-dimethyl acetamide, which was used as the substitute for hepatotoxic N,N-dimethylformamide (DMF). N-methylacetamide (NMAC) urine samples of 3 different levels covering the 0.2~2 times of the exposure limit were tested. Stability test up to 180 days (0, 7, 30, 60, 180 days) at 4 different temperatures (-60, -20, 5, $25^{\circ}C$) and homogeneity test were performed for these samples. New analytical condition by GC/MSD using SIM mode (m/z 58, 59) and DB-624 column was investigated for better selectivity, sensitivity and resolution. Urinary NMAC samples showed good homogeneity for 3 levels. These samples also showed good stability up to 180 days. The data of stability and homogeneity of urinary DMAC confirmed the basis of including this item into Korean proficiency test for occupational health laboratories since 2008.

• Structural Engineering and Mechanics
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• v.56 no.1
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• pp.137-156
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• 2015

In this paper, an analytical solution of displacement, strain and stress field for rotating thick-walled cylinder made of functionally graded material subjected to the uniform external magnetic field and thermal field in plane strain state has been studied. Stress, strain and displacement field as a function of radial coordinates considering magneto-thermo-elasticity are derived analytically. According to the Maxwell electro-dynamic equations, Lorentz force in term of displacement is obtained in cylindrical coordinates. Also, symmetric temperature distribution along the thickness of hollow cylinder is obtained by solving Fourier heat transfer equation in cylindrical coordinates. Using equation of equilibrium and thermo-mechanical constitutive equations associated with Lorentz force, a second-order inhomogeneous differential equation in term of displacement is obtained and will be solved analytically. Except Poisson's ratio, other mechanical properties such as elasticity modulus, density, magnetic permeability coefficient, heat conduction coefficient and thermal expansion coefficient are assumed to vary through the thickness according to a power law. In results analysis, non-homogeneity parameter has been chosen arbitrary and inner and outer surface of cylinder are assumed to be rich metal and rich ceramic, respectively. The effect of rotation, thermal, magnetic field and non-homogeneity parameter of functionally graded material which indicates percentages of cylinder's constituents are studied on displacement, Von Mises equivalent stress and Von Mises equivalent strain fields.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1998.06a
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• pp.477-480
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• 1998

Sol-gel processing, which started some decades back as a laboratory curiosity, has proved to be a powerful and versatile technique for the synthesis of materials. The utility of the sol-gel method for producing glass and ceramic materials in the form of powders, fibers, thin films and bulk shapes with high purity, functional microstructures and potentially high chemical homogeneity at relatively low temperature (compared to conventional processing) has been discussed.

• Journal of Environmental Science International
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• v.28 no.11
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• pp.1041-1045
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• 2019

In this study, the KS A ISO Guide 35 was applied to develop analytical standards for heavy metal cadmium using the Korean mussel (Mytilus coruscus) and to evaluate the homogeneity and stability of the sample. Some of the crucial characteristics that reference materials must consist include homogeneity and stability of both intra- and inter-bottles. We tested homogeneity using ANOVA analysis and short-term stability using regression analysis. The variations of cadmium concentrations did not significantly differ between intra- and inter-bottles (F=0.41, p=0.90). For short-term stability verification, cadmium analysis results were not statistically significant as a result of the regression analysis (significance F=0.51, p=0.53). This suggests that we can not dismiss the null hypothesis that there is no significant variation in concentrations of cadmium over time. These results indicated that the cryogenic-milling process has statistically proven the short-term stability for materials from mussels in the chemical analysis of cadmium. Therefore, we propose that the Korean mussel's reference material developed for the proficiency test could be used as a tool to evaluate reliability and consistency in laboratories.