• Advances in nano research
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• v.5 no.3
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• pp.203-214
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• 2017

In this study we present the reaction mechanism of $Cu_2ZnSnSe_4$ (CZTSe) nanoparticles synthesized by microwave-assisted chemical synthesis. We performed reactions every 10 minutes in order to identify different phases during quaternary CZTSe formation. The powder samples were analyzed by x-ray diffraction (XRD), Raman spectroscopy, energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The results showed that in the first minutes copper phases are predominant, then copper and tin secondary phases react to form ternary phase. The quaternary phase is formed at 50 minutes while ternary and secondary phases are consumed. At 60 minutes pure quaternary CZTSe phase is present. After 60 minutes the quaternary phase decomposes in the previous ternary and secondary phases, which indicates that 60 minutes is ideal reaction time. The EDS analysis of pure quaternary nanocrystals (CZTSe) showed stoichiometric relations similar to the reported research in the literature, which falls in the range of Cu/(Zn+Sn): 0.8-1.0, Zn/Sn: 1.0-1.20. In conclusion, the evolution pathway of CZTSe synthesized by this novel method is similar to other synthesis methods reported before. Nanoparticles synthesized in this study present desirable properties in order to use them in solar cell and photoelectrochemical cell applications.

• Structural Engineering and Mechanics
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• v.62 no.6
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• pp.695-702
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• 2017

In this work, a nonlocal zeroth-order shear deformation theory is developed for the nonlinear postbuckling behavior of nanoscale beams. The beauty of this formulation is that, in addition to including the nonlocal effect according to the nonlocal elasticity theory of Eringen, the shear deformation effect is considered in the axial displacement within the use of shear forces instead of rotational displacement like in existing shear deformation theories. The principle of virtual work together of the nonlocal differential constitutive relations of Eringen, are considered to obtain the equations of equilibrium. Closed-form solutions for the critical buckling load and the amplitude of the static nonlinear response in the postbuckling state for simply supported and clamped clamped nanoscale beams are determined.

• Structural Engineering and Mechanics
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• v.67 no.6
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• pp.565-578
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• 2018

This research article reported the nonlinear finite solutions of the nonlinear flexural strength and stress behaviour of nano sandwich graded structural shell panel under the combined thermomechanical loading. The nanotube sandwich structural model is derived mathematically using the higher-order displacement polynomial including the full geometrical nonlinear strain-displacement equations via Green-Lagrange relations. The face sheets of the sandwich panel are assumed to be carbon nanotube-reinforced polymer composite with temperature dependent material properties. Additionally, the numerical model included different types of nanotube distribution patterns for the sandwich face sheets for the sake of variable strength. The required equilibrium equation of the graded carbon nanotube sandwich structural panel is derived by minimizing the total potential energy expression. The energy expression is further solved to obtain the deflection values (linear and nonlinear) via the direct iterative method in conjunction with finite element steps. A computer code is prepared (MATLAB environment) based on the current higher-order nonlinear model for the numerical analysis purpose. The stability of the numerical solution and the validity are verified by comparing the published deflection and stress values. Finally, the nonlinear model is utilized to explore the deflection and the stresses of the nanotube-reinforced (volume fraction and distribution patterns of carbon nanotube) sandwich structure (different core to face thickness ratios) for the variable type of structural parameter (thickness ratio, aspect ratio, geometrical configurations, constraints at the edges and curvature ratio) and unlike temperature loading.

• Korean Security Journal
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• no.8
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• pp.361-377
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• 2004

This study is to examine the relations between the big five critical crime that consist of homicide, robbery, rape, theft, violence and the private security services. To achieve this objective, this research selected the subject of study, specially, 2002 status of the private security such as the number of companies and employees classified by areas along with the big five crime mentioned above classified by area. The research data is secondary data that is from '2003 Crime Analysis' of the Supreme Public Prosecutors' Office and 'The private Security Related Data' of the National Police Agency. The selected data were analyzed according to the variables by using SPSS 10.0 statistics software program. Each hypothesis was verified around the level of significance ${\alpha}$=.05 by using the statistical techniques, such as Descriptive Statistics, Correlation, Regression, etc. The following was the result of the study, First, the total number of the big five crime affects the number of the companies at significant level. Second, the number of the security companies can be explained by the each total number of the big five crime in the order of theft, robbery, violence, rape and murder. Third, the total number of the big five crime affects the number of the security employees at significant level. Forth the number of the security employees can be explained by the each total number of the big five crime in the order of theft, robbery, violence, rape and murder.

• Korean Journal of Child Studies
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• v.8 no.1
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• pp.65-82
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• 1987

The purpose of the present research was to study mothers' perceptions about their children' cognitive abilities and the relations between such perceptions and the children's cognitive level. The subjects of this study were 60 children (mean age: 6 years 1 month: age range = 5;8 to 6;7) and their mothers. Each child responded to 18 tasks drawn from the Kodae-Binet IQ test. Subsequently, the mothers were asked 4 questions: an estimate of her child's success or failure on the tasks, a rating of the certainty of her judgment, an estimate of the age of mastery on each task both for her owr child and children in general. The data of the present study were analyzed with the 3-way ANOVA (sex x birth order x mother's education level), t-test, and Pearson correlation coefficient. Significant differences were found in (1) mothers' accuracy of their children's cognitive abilities according to children's birth order, (2) mothers' accuracy, overestimation, and certainty according to the level of difficulty of each task, and (3) mothers' estimate of age at mastery according to the level of each task. Furthermore, there were positive correlations between accurate predictions by the mother and correct answers by the child and between overestimations by the mother and correct answers by the child.

• Journal of Power Electronics
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• v.17 no.1
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• pp.262-271
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• 2017

This paper studies the performances of five typical Phase-locked Loops (PLLs) for distorted and unbalanced grid, which are the Decoupled Double Synchronous Reference Frame PLL (DDSRF-PLL), Double Second-Order Generalized Integrator PLL (DSOGI-PLL), Double Second-Order Generalized Integrator Frequency-Lock Loop (DSOGI-FLL), Double Inverse Park Transformation PLL (DIPT-PLL) and Complex Coefficient Filter based PLL (CCF-PLL). Firstly, the principles of each method are meticulously analyzed and their unified small-signal models are proposed to reveal their interior relations and design control parameters. Then the performances are compared by simulations and experiments to investigate their dynamic and steady-state performances under the conditions of a grid voltage with a negative sequence component, a voltage drop and a frequency step. Finally, the merits and drawbacks of each PLL are given. The compared results provide a guide for the application of current control, low voltage ride through (LVRT), and unintentional islanding detection.

• The Korean Journal of Community Living Science
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• v.12 no.2
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• pp.47-59
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• 2001

The purpose of this study was to examine the factors affecting financial satisfaction of rural housewives. Data for this study were collected from 202 households living in 8 provinces. The results were as follows; 1) The most frequent financial problems experienced from expenditures on clothes(82.1%), lack of expense for social intercourse (61.47), and difficulty in purchasing durable goods(60.1%) in the order. 2) 44.6% of the respondents said they were satisfied with their net worth, and 21.6% of them confessed they had difficulties in debt redemption while 52.5% of them said they felt pressure about monthly payments of installments, which reveals that farm households find it hard to pay back short-term debt. 3) The path analysis was adopted to see the causal relations among the variables influenced the financial satisfaction. The variables of experiences of economic problems, educational background(graduated from middle school), saving, income, and age appeared to be important in the order of effectiveness. Among them, the variables of saying and experiences of economic problems showed a direct effect, and those of age and saving displayed an indirect effect with the experiences of economic problems as the parameter. From this findings, it is suggested that rural extension workers and educators should emphasize the importance of the financial plan in their educational programs.

• The Journal of Korean Academic Society of Nursing Education
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• v.23 no.3
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• pp.241-251
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• 2017

Purpose: The purpose of this study is to examine how the acceptance of diversity of nursing college students affects creativity and to verify empirically the role of individual cooperative learning competency and unlearning competency in such influence relations. Methods: This study surveyed 209 nursing college students and analyzed the structured questionnaire data using SPSS WIN 21.0 and AMOS 18.0. Results: The results of this study were as follows. First, the creativity of the subjects showed significant correlations with all other variables. Second, diversity openness directly affected creativity. We also confirmed that diversity openness and cooperative learning competency have a positive effect on creativity through mediating unlearning competency. Conclusion: In order to enhance the creativity of nursing college students, diversity openness should be actively reflected in the curriculum. In addition, concrete teaching-learning strategies should be developed in order to increase and enhance the unlearning competency and cooperative learning competency of nursing students.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.2 no.2
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• pp.52-59
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• 2003

Cam mechanism is a machine part frequently used in machinery. Specially, conjugate cam mechanism is very suitable for the high speed working and the heavy power translation. Then a conjugate cam mechanism need high precision for the relations between cam profiles and follower rollers. So, its design and manufacturing are very difficult. Thus, this study is a branch of exclusive CAM systems for design and NC machining of conjugate earn mechanism based on a master plate earn profile in order to exchange an old plate cam mechanism to a new conjugate earn mechanism. For the design of the other cam profile by using a master cam profile, some calculation processes were used by vector summation methods, from master cam profile data to the center data of master follower, from the center data of master follower to the center data of the other follower considered in link mechanism, and offsetting in the center direction of base circle of the other cam from the center data of the other follower. Finally, a sample conjugate cam was selected and machined m order to prove the contents of this study.

• Advances in Computational Design
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• v.3 no.3
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• pp.213-232
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• 2018

First time, an exact solution for free vibration of the Levy-type rectangular laminated plate is developed considering the most efficient Zig-Zag theory (ZIGT) and third order theory (TOT). The plate is subjected to hard simply supported boundary condition (Levy-type) along x axis. Using the equilibrium equations and the plate constitutive relations, a set of 12 m first order differential homogenous equations are obtained, containing displacements and stress resultant as primary variables. The natural frequencies of a single-layer isotropic, multi-layer composites and sandwich plates are tabulated for three values of length-to-thickness ratio (S) and five set of boundary conditions and further assessed by comparing with existing literature and recently developed 3D EKM (extended Kantorovich method) solution. It is found that for the symmetric composite plate, TOT produces better results than ZIGT. For antisymmetric and sandwich plates, ZIGT predicts the frequency for different boundary conditions within 3% error with respect to 3D elasticity solution while TOT gives 10% error. But, ZIGT gives better predictions than the TOT concerning the displacement and stress variables.