• Proceedings of the KIEE Conference
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• 2004.11a
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• pp.75-78
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• 2004

$Bi_{3.25}Eu_{0.75}Ti_3O_{12}$ (BET) thin films were deposited on the $LaNiO_3$ (LNO (100))/Si and Pt/Ti/$SiO_2$/Si substrates by the metal-organic decomposition method. Structural and dielectric properties of BLT thin films for the applications in nonvolatile ferroelectric random access memories were investigated. Both the structure and morphology of the films were analyzed by x-ray diffraction (XRD) and atomic force microscope (AFM). Even at low temperatures $650^{\circ}C$, the BET thinfilms were successfully deposited on LNO bottom electrode and exhibited (001) and (117) orientation. Compared with the Pt electrode films, the BET thin films on the LNO electrode annealed at $650^{\circ}C$ showed better dielectric constantsand remanent polarization. The BET thin films on the LNO electrode for the annealing temperature of $650^{\circ}C$, the remanent polarization Pr and coercive field were $45.6\;C/cm^2$ and 171 kV/cm, respectively.

• Journal of Powder Materials
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• v.15 no.2
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• pp.148-155
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• 2008

Nano magnetite particles have been prepared by two step reaction consisting of urea hydrolysis and ammonia addition at certain ranges of pH. Three different concentrations of aqueous solution of ferric ($Fe^{3+}$) and ferrous ($Fe^{2+}$) chloride (0.3 M-0.6 M, and 0.9 M) were mixed with 4 M urea solution and heated to induce the urea hydrolysis. Upon reaching at a certain pre-determined pH (around 4.7), 1 M ammonia solution were poured into the heated reaction vessels. In order to understand the relationship between the concentration of the starting solution and the final size of magnetite, in-situ pH measurements and quenching experiments were simultaneous conducted. The changes in the concentration of starting solution resulted in the difference of the threshold time for pH uprise, from I hour to 3 hours, during which the akaganeite (${\beta}$-FeOOH) particles nucleated and grew. Through the quenching experiment, it was confirmed that controlling the size of ${\beta}$-FeOOH and the attaining a proper driving force for the reaction of ${\beta}$-FeOOH and $Fe^{2+}$ ion to give $Fe_3O_4$ are important process variables for the synthesis of uniform magnetite nanoparticles.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.1162-1165
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• 2001

Operational Modal Analysis also known as Output Only Modal Analysis has in the recent years been used for extracting modal parameters of civil engineering structures and is now becoming popular for mechanical structures. The advantage of the method is that no artificial excitation need to be applied to the structure or force signals to be measured. All the parameter estimation is based upon the response signals, thereby minimising the work of preparation for the test. This test case is a controlled lab set-up enabling different parameter estimation methods techniques to be used and compared to the Operational Modal Analysis. For Operational Modal Analysis two different estimation techniques are used： a non-parametric technique based on Frequency Domain Decomposition (FDD), and a parametric technique working on the raw data in time domain, a data driven Stochastic Subspace Identification (SS!) algorithm. These are compared to other methods such as traditional Modal Analysis.

• Structural Engineering and Mechanics
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• v.68 no.5
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• pp.549-561
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• 2018

Sobol method is applied as a powerful variance decomposition technique in the field of global sensitivity analysis (GSA). The paper is devoted to increase convergence speed of the extracted Sobol indices using a new proposed sampling technique called genetic based Latine hypercube sampling (GBLHS). This technique is indeed an improved version of restricted Latine hypercube sampling (LHS) and the optimization algorithm is inspired from genetic algorithm in a new approach. The new approach is based on the optimization of minimax value of LHS arrays using manipulation of array indices as chromosomes in genetic algorithm. The improved Sobol method is implemented to perform factor prioritization and fixing of an uncertain comprehensive high speed rotor-bearing system. The finite element method is employed for rotor-bearing modeling by considering Eshleman-Eubanks assumption and interaction of axial force on the rotor whirling behavior. The performance of the GBLHS technique are compared with the Monte Carlo Simulation (MCS), LHS and Optimized LHS (Minimax. criteria). Comparison of the GBLHS with other techniques demonstrates its capability for increasing convergence speed of the sensitivity indices and improving computational time of the GSA.

• Nuclear Engineering and Technology
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• v.54 no.7
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• pp.2625-2634
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• 2022

Discretization errors are extremely challenging conundrums of discrete ordinates calculations for radiation transport problems with void regions. In previous work, we have presented a multi-collision source method (MCS) to overcome discretization errors, but the efficiency needs to be improved. This paper proposes a goal-oriented algorithm for the MCS method to adaptively determine the partitioning of the geometry and dynamically change the angular quadrature in remaining iterations. The importance factor based on the adjoint transport calculation obtains the response function to get a problem-dependent, goal-oriented spatial decomposition. The difference in the scalar fluxes from one high-order quadrature set to a lower one provides the error estimation as a driving force behind the dynamic quadrature. The goal-oriented algorithm allows optimizing by using ray-tracing technology or high-order quadrature sets in the first few iterations and arranging the integration order of the remaining iterations from high to low. The algorithm has been implemented in the 3D transport code ARES and was tested on the Kobayashi benchmarks. The numerical results show a reduction in computation time on these problems for the same desired level of accuracy as compared to the standard ARES code, and it has clear advantages over the traditional MCS method in solving radiation transport problems with reflective boundary conditions.

• Steel and Composite Structures
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• v.42 no.3
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• pp.299-313
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• 2022

Steel-concrete-steel composite structures with bidirectional webs (SCSBWs) are used in large-scale projects and exhibit good mechanical performances and constructional efficiency. The shear behaviors of SCSBW deep beam members in key joints or in locations subjected to concentrated forces are of concern in design. To address this issue, experimental program is investigated to examine the deep-beam shear behaviors of SCSBWs, in which the cracking process and force transfer mechanism are revealed. Compared with the previously proposed truss model, it is found that a strut-and-tie model is more suitable for describing the shear mechanism of SCSBW deep beams with a short span and sparse transverse webs. According to the experimental analyses, a new model is proposed to predict the shear capacities of SCSBW deep beams. This model uses strut-and-tie concept and introduces web shear and dowel action to consider the coupled multi mechanisms. A stress decomposition method is used to distinguish the contributions of different shear-transferring paths. Based on case studies, a simplified model is further developed, and the explicit solution is derived for design efficiency. The proposed models are verified using experimental data, which are proven to have good accuracy and efficiency and to be suitable for practical application.

• Polymer(Korea)
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• v.39 no.1
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• pp.88-98
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• 2015

4-Amino-N-hexadecylbenzamide-graphene sheets (AHB-GSs), used in the preparation of the polyimide (PI) nanocomposite films, were synthesized by mixing a dispersion of graphite oxide with a solution of the ammonium salt of AHB. The atomic force microscope image of functionalized-GS on mica and a profile plot revealed the average thickness of AHB-GS to be ~3.21 nm. PI films were synthesized by reacting 4,4'-biphthalic anhydride and bis(4-aminophenyl) sulfide. PI nanocomposite films containing various contents of AHB-GS over the range of 0-10 wt% were synthesized using the solution intercalation method. The PI nanocomposite films under different thermal imidization temperatures, 250 and $350^{\circ}C$, were examined. The graphenes, for the most part, were well dispersed in the polymer matrix despite some agglomeration. However, micrometer-scale particles were not detected. The average thickness of the particles was <10 nm, as revealed from the transmission electron microscope images. Only a small amount of AHB-GS was required to improve the gas barrier, and electrical conductivity. In contrast, the glass transition and initial decomposition temperatures of the PI hybrid films continued to decrease with increasing content of AHB-GS up to 10 wt%. In general, the properties of the PI hybrid films heat treated at $350^{\circ}C$ were better than those of films heat treated at $250^{\circ}C$.

• Journal of the Korean Magnetics Society
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• v.2 no.3
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• pp.244-250
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• 1992

Iron nitride $Fe_4N$ by partial substitution of nitrogen by carbon was prepared by nitriding the iron oxalate whose thermal decomposition gives a carburating atmosphere. Iron oxalates, the precursors, were prepared by precipitation and co-precipitation. The size and shape of the carbonitride particles could be controlled by modifying the conditions of preparation of the oxalate precursor. From the results of electron micrographs, it is clear that the $Fe_4N$ pigment particle maintains the original shape(needle shape) of the starting materials and that it consists of fine unit particles which link together to form a stereo-network structure. An investigation of the $Fe^{II}_3\;Fe^I_{1-x}\;Sn_xN_{1-y}C_y$ solid solution has shown that Sn plays the role of a growth inhibitor of the elementary microcrystallites of the iron carbonitride. The coercive force and saturation magnetization of iron carbonitride obtained from co-precipitated iron oxalate were 500 Oe and 120 emu/g, respectively.

• Structural Engineering and Mechanics
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• v.65 no.5
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• pp.547-556
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• 2018

Based on the shaking table tests of a 1:3.52 scale one-bay and one-story ancient wooden structure, a simplified structural mechanics model was established, and the structural state equation and observation equation were deduced. Under the action of seismic waves, the damage rule of initial stiffness and yield stiffness of the joint was obtained. The force hammer percussion test and finite element calculations were carried out, and the structural response was obtained. Considering the 5% noise disturbance in the laboratory environment, the stiffness parameters of the mortise-tenon joint were identified by the partial least squares of singular value decomposition (PLS-SVD) and the Extended Kalman filter (EKF) method. The results show that dynamic and static cohesion method, PLS-SVD, and EKF method can be used to identify the damage degree of structures, and the stiffness of the mortise-tenon joints under strong earthquakes is reduced step by step. Using the proposed model, the identified error of the initial stiffness is about 0.58%-1.28%, and the error of the yield stiffness is about 0.44%-1.21%. This method has high accuracy and good applicability for identifying the initial stiffness and yield stiffness of the joints. The identification method and research results can provide a reference for monitoring and evaluating actual engineering structures.

• Korean Journal of Social Welfare
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• v.64 no.2
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• pp.55-83
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• 2012

Self-employment rate is high in Korean labor market, while the income gap within self-employed is also high. Although, there are very few studies that addressed on the income inequality of self-employed. Thus, this study has measured the earnings inequality of self-employed by generalized entropy indices and decomposed inequality factor and trend. The empirical study is based on Korea Welfare Panel Study wave 1~4. The main result from this analysis is summarized in three points. Firstly, earnings inequality of self-employed is severely high and the earnings polarization within self-employed has become more serious in Korea. Secondly, this study provides the evidence that the main factor of earnings inequality of self-employed is the status of self-employment, education level, age group, workplace scale and industry. Thirdly, the contribution of relative changes in the incomes of the status of self-employment is the largest to the inequality trend. In terms of education level, age group and industry, the increase of inequality within group(pure effect) mainly attributes to the rise of earnings inequality of self-employed and the change effect of group composition contributes to deterioration of inequality.