• Journal of Magnetics
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• v.2 no.4
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• pp.138-142
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• 1997

The magnetic and magneto-optical properties of Ni/Pt multilayers exhibiting square Kerr hysterisis loops at room temperature were studied. Squared polar Kerr hysterisis loops at room temperature in Ni/Pt multilayer thin films were obtained for the samples prepared by sequential dc magnetron sputter deposition of nickel and platinum with tNi=13-21$\AA$ and tPt=3.5-7.5$\AA$. The coercivity of these multilayers was in the range of 400-1100 Oe. The saturation magnetization was found to show an inverse dependence on nickel sublyaer thickness. About a monolayer of Ni at interface was observed to behave less magnetically than the interior Ni atoms. The polar Kerr rotation exhibited an increasing trend with decreasing wavelength in the spectral range of 7000-4000 $\AA$. The maximum of polar Kerr rotation was found to shift to higher wavelengths with increase in nickel sublayer thickness.

• Communications for Statistical Applications and Methods
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• v.20 no.5
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• pp.347-356
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• 2013

We propose a sequential method to construct approximate confidence limits for the ratio of two independent sequences of binomial variates with unequal sample sizes. Due to the nonexistence of an unbiased estimator for the ratio, we develop the procedure based on a modified maximum likelihood estimator (MLE). We generalize the results of Cho and Govindarajulu (2008) by defining the sample-ratio when sample sizes are not equal. In addition, we investigate the large-sample properties of the proposed estimator and its finite sample behavior through numerical studies, and we make comparisons from the sample information view points.

• Journal of the Korean Statistical Society
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• v.32 no.1
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• pp.33-46
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• 2003

The continual reassessment method (CRM) provides a Bayesian estimation of the maximum tolerated dose (MTD) in phase I clinical trials. The CRM has been proposed as an alternative design of the standard design. The CRM has been modified to improve practical feasibility and, recently, the likelihood approach CRM has been proposed. In this paper we investigate the consistency and asymptotic normality of the modified likelihood approach CRM in which the maximum likelihood estimate is used instead of the posterior mean. Small-sample properties of the consistency is examined using complete enumeration. Both the asymptotic results and their small-sample properties show that the modified CRML outperforms the standard design.

• Journal of the Korean Geotechnical Society
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• v.15 no.5
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• pp.217-228
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• 1999

The three methods of analysis (i) REV(representative elemental volume), (ii) non-REV and (iii) joint network analysis are introduced in this paper to analyze the groundwater flow in jointed rock mass and the inflow into underground excavations. The results from those methods are compared one another to reveal their characteristics by varying the number of joints and the diameter of the opening. The pre-processor, the so-called sequential analysis, is introduced to predict the equivalent hydraulic conductivity of a jointed rock mass having a number of intersecting joints. Using the finite element mesh, joint map and sequential analysis, the equivalent hydraulic conductivities are calculated for all 445 elements. The hydraulic inhomogeneity and the determination of the representative properties of jointed rock masses are discussed. In the REV analysis where the entire rock mass is homogenized through the representative properties, the inflow is increased regularly and consistently by increasing the joint density, the opening size and the conductivity contrast value. Though the non-REV analysis showed irregular variation of the inflow due to the local inhomogeneity allowed to individual elements, the inflow approached the REV results as the characteristic length increases. The joint network analysis showed the most sensitive reaction to the joint density, the opening size and the presence of the network crossing the opening. The reliability of the network analysis depends on the geometric data of individual joints. In view of the limited field data on joint geometry and possible uncertainty the REV and non-REV methods are considered more practical and rational than the joint network analysis.

• Geophysics and Geophysical Exploration
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• v.16 no.4
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• pp.257-267
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• 2013

3-D ore modeling was performed to understand the configuration of ore bodies by integrated analysis of borehole and geophysical data in iron-mine area. Five representative indices of rocks were designated, which were obtained from geological survey and borehole. The five indices of rocks were geostatistically simulated by Sequential Indicator Simulation method to delineate boundary of the ore bodies. And Ordinary Kriging and Sequential Gaussian Simulation was applied to make secondary information using resistivity data from magnetotellurics and DC resistivity survey, and this information was used for simple kriging with local varying means, one of integrated kriging techniques. From the correlation analysis between each properties, it was found that high grade of ore is characterized by increased density, whereas the electrical resistivity decreases. With the integrated results of geophysical and borehole data, it was also found that the real configuration of ore body was similar to the modeled result and information about ore grade in 3-D space was obtained.

• Journal of Korean Society for Atmospheric Environment
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• v.34 no.1
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• pp.177-186
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• 2018

It is a well-known fact that precipitation plays an important role in capturing ambient particles, however, the details of particle scavenging properties have not been fully proved. To clarify the particle scavenging properties, a complementary study was carried out with the bulk and semi-bulk rain samples collected in an urban city of Japan. pH showed a continued downturn for a little bit at the beginning rainfall and then a turn-up in the following rainfall. The recorded pH values of rainwater (ranged from 3.5-4.6) demonstrated that the strong acid rain was observed during our field measurements. Compared to the subsequent rainfall, electrical conductivity in the beginning rainfall had about 1.3 times higher level. Sulfur showed an overwhelmingly high concentration compared to other elements in both ambient total suspended particles (TSP) and rain samples. On the contrary to ambient TSP, every element including Ca and Zn in rain showed a continued rise in concentration accompanied by increasing of rainfall amount. During the first period of the rainfall there was no meaningful change in elemental carbon concentration, however, it was largely increased (up to $0.2mg\;L^{-1}$) in the sequential rainfall (4.0-4.5 mm rainfall amount). The theoretically calculated number concentration of particles scavenged by raindrops showed a strong decrease of with the increasing droplet diameter regardless of particle type.

• Smart Structures and Systems
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• v.26 no.4
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• pp.419-433
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• 2020

Investigation of structural integrity has been a critical issue in the field of civil engineering for years. Visual inspection is one of the most available methods to explore deteriorative components in structures. Still, this method is not applicable to invisible damage of structures. Alternatively, system identification methods are capable of tracking modal properties of structures over time. The deviation of these dynamic properties can serve as indicators to access structural integrity. In this study, a modal tracking technique using frequency-domain system identification from seismic responses of structures is proposed. The method first segments the measured signals into overlapped sequential portions and then establishes multiple Hankel matrices. Each Hankel matrix is then converted to the frequency domain, and a temporal-average frequency-domain Hankel matrix can be calculated. This study also proposes the frequency band selection that can divide the frequency-domain Hankel matrix into several portions in accordance with referenced natural frequencies. Once these referenced natural frequencies are unavailable, the first few right singular vectors by the singular value decomposition can offer these references. Finally, the frequency-domain stochastic subspace identification tracks the natural frequencies and mode shapes of structures through quick stabilization diagrams. To evaluate performance of the proposed method, a numerical study is carried out. Moreover, the long-term monitoring strong motion records at a specific site are exploited to assess the tracking performance. As seen in results, the proposed method is capable of tracking modal properties through seismic responses of structures.

• Economic and Environmental Geology
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• v.35 no.3
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• pp.285-297
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• 2002

This study was carried out to prove the factor properties of the soil affected by a forest fire through the physical and chemical analysis and the data from the conclusion of those analysis are applied to the development of technics that reduces a forest fire-induced 2nd damage. The forest fire was in December 2000 at Gangreung city and Donghae city, Gangwon provinces, Korea. Soil samples were collected at upper layers (0-5 cm) and bottom layers (5-40 cm) in November 2001 from the burned and control sites. Values of pH in burned soils of the upper layers affected by forest fire are higher than those in control soils. Both the fragments of fire-burned plant and differences of geological properties are resulted in a class of soil. Contents of organic matters in burned soils are higher than those in control soils, exceptionally the contents of organic matters in burned soils that contain coaly shale are lower than those in control soils. Weathering indices in burned soils are higher than those in control soils and it concerned with loss of soil. Iron ions Fe(Fe$^{2+}$ or Fe$^{3+}$) are easily extracted from the burned soils by rainfall, but Mn ions are straightly exist in the burned soils by physiochemical adsorption of colloid. Through the sequential extraction in the burned soils and control soils, we are certificate the extraction of Fe ions and the disturbance of Mn ions from the burned soils. As a consequence of factor analysis in burned soil and control soil, we are certificate that the influence of forest fire results in a disturbance of positive correlation factors.

• Journal of Welding and Joining
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• v.27 no.5
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• pp.81-87
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• 2009

Recently, extruded aluminium-alloy panels have been used in the car bodies for the purpose of the light-weight of railway vehicles and FSW(Friction Stir Welding), which is superior to the arc weldings, has been applied in the railway vehicles. This paper presents the optimum design of the FSW process on A6005 extruded alloy for railway vehicles to improve its mechanical properties. Rotational speed, welding speed and tilting angle of the tool tip were chosen as design parameters. Three objective functions were determined; maximizing the tensile strength, minimizing the hardness and maximizing the difference between the normalized tensile strength and hardness. The tensile tests and the hardness tests for fifteen FSW experiments were carried out according to the central composite design table. Recursive model functions on three characteristic values, such as the tensile strength, the hardness difference(${\Delta}Hv$) and the difference of normalized tensile strength and ${\Delta}Hv$, were estimated according to the classical response surface analysis methodology. The reliability of each recursive function was verified by F-test using the analysis of variance table. Sensitivity analysis on each characteristic value was done. Finally, the optimum values of three design parameters were found using Sequential Quadratic Programming algorithm.

• Transactions of the Korean hydrogen and new energy society
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• v.2 no.1
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• pp.29-37
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• 1990

The effect of pressure cycling of $Zr_{0.9}Ti_{0.1}Cr_{0.7}Fe_{1.3}$ on the hydrogenation properties was investigated using the P-C-Isotherm curves and hydrogen absorption rate curves in the isotherm condition. The reversible hydrogen absorption capacity was decreased about 45 % after 3300 cycles. In the case of activated sample, the rate controlling steps of hydriding reaction changed from the surface reaction to the hydrogen diffusion process through hydride phase sequentially as reaction proceeded. After 3300 cycles, the sequential change of rate controlling step was same as activated one. However, the hydrogen absorption rate significantly decreased. It is suggested that the degradation of $Zr_{0.9}Ti_{0.1}Cr_{0.7}Fe_{1.3}$ can be interpreted with the formation of $ZrFe_3$ phase at the particle surface.