• Journal of Magnetics
• /
• 제3권4호
• /
• pp.120-122
• /
• 1998

The higher order harmonic components of magnetostriction during ac magnetization in 3% SiFe are measured as a function of the magnetizing angle respect to [001] axis using a constructed laser interferometry. The magnetostriction with magnetizing angle from [001] axis agrees ith the calculation based on domain reorientation. The relative amplitudes of odd and even harmonics respectively for magnetic induction and magnetostriction decrease with the order of harmonics, accompanying the contraction of the amplitudes. The contraction of harmonics order of magnetostriction harmonics is shown to be the even number times of that of magnetic induction.

• Journal of Magnetics
• /
• 제16권2호
• /
• pp.140-144
• /
• 2011

We report on a numerical calculation study of two new functional properties in magnetic tunnel junctions (MTJs), negative dynamic resistance and RF amplification. The magnetic dynamics in a conventional CoFeB/MgO/CoFeB MTJ with in-plane magnetization was investigated using a macro-spin model simulation. To examine the influence of thermal fluctuations, random external magnetic fields were also included. Using a voltage controlled bias circuit, the negative dynamic resistance was obtained from time averaged I-V characteristics at both 0 K and 300 K under appropriate external magnetic fields and bias voltages. Using this negative dynamic resistance property, we demonstrated RF amplification with a 100 MHz high frequency signal. Sizable RF amplification gain was observed without thermal fluctuation. However, at 300 K, the RF signal was not amplified because low frequency magnetization dynamics were dominant.

• International Journal of Naval Architecture and Ocean Engineering
• /
• 제7권1호
• /
• pp.157-173
• /
• 2015

In the present study, the existing equivalent stain method is improved to make up for its weaknesses. The improved inherent strain model is built considering more sophisticated three dimensional constraints which are embodied by six cubic elements attached on three sides of a core cubic element. From a few case studies, it is found that the inherent strain is mainly affected by the changes in restraints induced by changes of temperature-dependent material properties of the restraining elements. On the other hand, the degree of restraints is identified to be little influential to the inherent strain. Thus, the effect of temperature gradients over plate thickness and plate transverse direction normal to welding is reflected in the calculation of the inherent strain chart. The welding deformation can be calculated by an elastic FE analysis using the inherent strain values taken from the inherent strain chart.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
• /
• 제49권7호
• /
• pp.457-461
• /
• 2000

The finite element method (FEM) is suitable for the analysis of a complicated region that includes nonlinear materials, whereas the boundary element method (BEM) is naturally effective for analyzing a very large region with linear characteristics. Therefore, considering the advantages in both methods, a novel algorithm for the alternate application of the FEM and BEM to magnetic field problems with the open boundary is presented. This approach avoids the disadvantages of the typical numerical methods with the open boundary problem such as a great number of unknown values for the FEM and non-symmetric matrix for the Hybrid FE-BE method. The solution of the overall problems is obtained by iterative calculations accompanied with the new acceleration method.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 1999년도 춘계학술대회 논문집
• /
• pp.399-402
• /
• 1999

In this paper, a new method for calculating capacitance in arbitrarily shape structure is Presented. This new approach based on divergence theorem of Gauss\`s law is acheive by Surface-Contacted Element(SCE) for Gaussian surface. To evaluate accurate capacitance value in nonuniform electric field. in two dimensional analysis the interpolation using the elements which contact one nod (PE: Point-Element) or two nod (FE: Face-Element) is employed. Because the elements contacted with surface are very small compared with total elements in analytic model, SCE method has shorter computing time to calculate capacitance. This proposed method is verified by comparing the simulated results with value obtained by analytic method.

• Bulletin of the Korean Chemical Society
• /
• 제11권4호
• /
• pp.303-306
• /
• 1990

Kinetic studies were carried out for the redox reaction of $[Co(NH_3)_4(C_2O_4)]^+$ with aqueous $[Fe(H_2O)_6]^{2+}$ solution in the present of $H^+$ by UV/VIS-spectrophotometric method. It was found that the order of $H^+$ for the reaction is first one in the higher $H^+$ concentration range of $1.67×10^{-1} M{\sim}1.00 M,$ while second order in the lower range of $6.30×10^{-2} M{\sim}1.67{\times}10^{-1} M.$ Reaction order of the substrates was found to be first order with respect to each of them. Accordingly overall reactions are third or fourth order. The results of calculation for the Extended Huckel Molecular Orbital theory contribute to estimate the preferred intermediates, bridging form of binuclear complex. On the basis of these results, we propose that this redox reaction proceed via inner-sphere reaction mechanism.

• 한국광물학회:학술대회논문집
• /
• 한국광물학회.한국암석학회 2001년도 공동학술발표회 논문집
• /
• pp.38-39
• /
• 2001

The seasonal changes in pH, Fe, Al and SO$_4$$\^$2-/ contents of acid drainage released from coal mine dumps play a major role in precipitation of metal hydroxides in the Taebaek coal field area, southeastern Korea. Precipitates in the creeks underwent a cycle of the color change showing white, reddish brown and brownish yellow, which depends on geochemical factors of the creek waters. White precipitates consist of Al-sulfate (basaluminite and hydrobasaluminite) and reddish brown ones are composed of ferrihydrite and brownish yellow ones are of schwertmannite. Goethite coprecipitates with ferrihydrite and schwertmannite. Ferrihydrite formed at higher values than pH 5.3 and schwertmannite precipitated below pH 4.3, and goethite formed at the intermediate pH range between the two minerals. With the pH being increased from acid to intermediate regions, Fe is present both as schwertmannite and goethite. From the present observation, the most favorable pH that basauluminte can precipitate is in the range of pH 4.45-5.95. SEM examination of precipitates at stream bottom shows that they basically consist of agglomerates of spheroid and rod-shape bacteria. Bacteria species are remarkably different among bottom precipitates and, to a less extent, there are slightly different chemical compositions even within the same bacteria. The speciation and calculation of the mineral saturation index were made using MINTEQA2. In waters associated with yellowish brown precipitates mainly composed of schwertmannite, So$_4$ species is mostly free So$_4$$\^$2-/ ion with less AlSo$_4$$\^$+/, CaSo$\sub$(aq)/, and MgSo$\sub$4(aq)/. Ferrous iron is present mostly as free Fe$\^$2+/, and FeSo$\sub$4(aq)/ and ferric iron exists predominantly as Fe(OH)$_2$$\^$+/, with less FeSo$\sub$4(aq)/, Fe(OH)$_2$$\^$-/, FeSo$_4$$\^$-/ and Fe$\^$3+/, respectively Al exists as free Al$\^$3+/, AlOH$_2$$\^$-/, (AlSo$_4$)$\^$+/, and Al(So$_4$)$\^$2-/. Fe is generally saturated with respect to hematite, magnetite, and goethite, with nearly saturation with lepidocrocite. Aluminum and sulfate are supersaturated with respect to predominant alunite and less jubanite, and they approach a saturation state with respect to diaspore, gibbsite, boehmite and gypsum. In the case of waters associated with whitish precipitates mainly composed of basaluminite, Al is present as predominant Al$\^$3+/ and Al(SO$_4$)$\^$+/, with less Al(OH)$\^$2+/, Al(OH)$_2$$\^$+/ and Al(SO$_4$)$\^$2-/. According to calculation for the mineral saturation, aluminum and sulfate are greatly supersaturated with respect to basaluminite and alunite. Diaspore is flirty well supersaturated while jubanite, gibbsite, and boehmite are already supersaturated, and gypsum approaches its saturation state. The observation that the only mineral phase we can easily detect in the whitish precipitate is basaluminite suggests that growth rate of alunite is much slower than that of basaluminite. Neutralization of acid mine drainage due to the dilution caused by the dilution effect due to mixing of unpolluted waters prevails over the buffering effect by the dissolution of carbonate or aluminosilicates. The main factors to affect color change are variations in aqueous geochemistry, which are controlled by dilution effect due to rainfall, water mixng from adjacent creeks, and the extent to which water-rock interaction takes place with seasons. pH, Fe, Al and SO$_4$ contents of the creek water are the most important factors leading to color changes in the precipitates. A geochemical cycle showing color variations in the precipitates provides the potential control on acid mine drainage and can be applied as a reclamation tool in a temperate region with four seasons.

• 한국자기학회지
• /
• 제24권3호
• /
• pp.71-75
• /
• 2014

정비조성으로 성장시킨 $LiTaO_3$ 단결정 및 비정비조성으로 성장시킨 $LiTaO_3$ 단결정 내에 불순물로 도핑된 $Fe^{3+}$ 상자성 불순물 이온의 바닥 상태에서의 에너지 준위를 계산하였다. $LiTaO_3$ 단결정 내에서 육방정계 대칭성을 갖는 $Fe^{3+}$ 이온의 전자 상자성 공명 상수인 분광학적 분리인자 g 및 영자기장 갈라지기 D 값을 이용하여 6개의 에너지 준위 사이의 에너지 준위를 계산하였다. 자기장을 결정학적 주축 ([100], [001], [111])과 나란하게 가하여 자기장을 증가시켜 감에 따라 얻은 에너지 준위 갈라지기는 자기장을 가한 방향에 따라서 서로 다른 값을 나타내었다. ${\mid}{\pm}5/2$ > ${\leftrightarrow}{\mid}{\pm}3/2$ >및 ${\mid}{\pm}3/2$ > ${\leftrightarrow}{\mid}{\pm}1/2$ > 사이의 전이에서 계산한 영자기장 갈라지기 값은 정비조성으로 성장시킨 $LiTaO_3$ 단결정과 비정비조성으로 성장시킨 단결정의 경우에 각각 12.300 GHz, 6.150 GHz와 59.358 GHz, 29.679 GHz이다. 결정성장 조건에 따라 에너지 준위가 상당히 다른 것으로 나타났다.

• Steel and Composite Structures
• /
• 제3권2호
• /
• pp.123-140
• /
• 2003

The importance of the research on moment-resistant properties of unstiffened tubular joints and the research background are introduced. The performed experimental research on the bending rigidity and capacity of the joints is reported. The emphasis is put on the discussion of the flexural behavior of the joints including sets of geometrical parameters of the joints and several loading combinations. Procedures and results of loading tests on four full size joints in planar KK and X configuration are described in details at first. Mechanical models are proposed to analyze the joint specimens. Three-dimensional nonlinear FE models are established and verified with the experimental results. By comparing the experimental data with the results of the analysis, it is reported reasonable to carry out the structural analysis under the assumption that the joint is fully rigidly connected, and their bending capacities can assure the strength of the members connected under certain limitation. Furthermore, a parametric formula for inplane bengding rigidity of T and Y type tubular joints is proposed on the basis of FE calculation and regression analysis. Compared with test results, it is shown that the parametric formula developed in this paper has good applicability.

• 자원환경지질
• /
• 제28권3호
• /
• pp.213-220
• /
• 1995

Geochemistry of stream water and sediment collected in the vicinity of the Donghae coal mine in the Samchuk coalfied were investigated in order to evaluate the environmental impacts of acid mine drainage. The pH of stream water ranges from 2.85(at 2 km away from the mine) to 7.92(at uncontaminated tributary). The main cation and anion species in the upper stream are $Ca^{2+}$ and $SO_{4}{^2-}$, respectively. The level of pH and the amount of $HCO^{3-}$ in stream water increase to the downstream and where uncontaminated small tributaries are joining, and in the area covered with limestone. From the results of thermodynamic calculation, the main forms of iron in stream water are estimated as $Fe^{2+}$ and $FeSO_{4}{^0}$, and most of them could be precipitated as FeO(OH) with increase of pH. The white precipitates in stream sediments particularly found around the coal mine are proved to be $Al(OH)_3$ by XRD and XRF analysis. As a result of investigation for seasonal variation of AMD, the level of pH decreased and conductivity increased in dry season.