• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.1 s.118
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• pp.41-47
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• 2007

Scattering fields of two dimensional acoustic waves by a circular cylinder are investigated. The present numerical approach for the acoustic scattering problem has difficulties of numerical robustness, long-time stability and suitability of far-field boundary treatments. The time-dependent periodic acoustic source is used to analyze Interference patterns between incident waves and waves reflected by the cylinder. Characteristic boundary algorithms coupled with 4th order Modified-Flux-Approach ENO(essentially non-oscillatory) schemes are employed in generalized coordinates to examine the effect of the wane frequency on the interference patterns. Non-reflecting boundary conditions, which is crustal for accurate computations of aeroacoustic problems, are used not to contaminate scattering fields by reflected waves at the outer boundary. Computed scattering fields show the circumferential acoustic modes generated by interacting between acoustic sources and scattered waves. At a lower frequency, the wave passes almost straight through the cylinder without Interacting with circular cylinder. Simulation results are presented and compared with the analytic solution. Computed RMS-pressure distribution on the cylinder wall is good agreement with exact solution.

• International Journal of Aeronautical and Space Sciences
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• v.16 no.1
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• pp.50-63
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• 2015

Explosive bolts are one of pyrotechnic release devices, which are highly reliable and efficient for a built-in release. Among them, ridge-cut explosive bolts which utilize shock wave generated by detonation to separate bolt body produce minimal fragments, little swelling and clean breaks. In this study, separation phenomena of ridge-cut explosive bolts or ridge-cut mechanism are computationally analyzed using Hydrocodes. To analyze separation mechanism of ridge-cut explosive bolts, fluid-structure interactions with complex material modeling are essential. For modeling of high explosives (RDX and PETN), Euler elements with Jones-Wilkins-Lee E.O.S. are utilized. For Lagrange elements of bolt body structures, shock E.O.S., Johnson-Cook strength model, and principal stress failure criteria are used. From the computational analysis of the author's explosive bolt model, computational analysis framework is verified and perfected with tuned failure criteria. Practical design improvements are also suggested based on a parametric study. Some design parameters, such as explosive weights, ridge angle, and ridge position, are chosen that might affect the separation reliability; and analysis is carried out for several designs. The results of this study provide useful information to avoid unnecessary separation experiments related with design parameters.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.8 no.4
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• pp.382-389
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• 1997

We present the results on the applicability of the polycrystalline AIN thin films for a surface acoustic wave filter operating at 800 MHz frequency. The films show the FWHM of 3 .deg. from th X-ray rocking curve, which indicates that the c-axis of the films is pre- ferentially oriented along the growth direction. The fabricated band pass filters exhibit the center frequency of 865 MHz with 3dB band-width of 45 MHz. From the measured frequency response, the electro-mechanical coupling constant of 0.8% and the SAW velocity of 5,709 m/s are obtained. Thus, we conclude that the sputtered AIN films are feasible for the fabrication of uper UHF band SAW filters.

• Korean Journal of Child Studies
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• v.37 no.1
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• pp.95-108
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• 2016

Objective: The purpose of this study was to examine the mediating effect of internet use type on the relationship between parental attachment and school life adjustment. Methods: For this study, data were drawn from 4th wave panel data of Korea Children and Youth Panel Survey. 1,537 1st graders of middle school were used for analysis. Results: The results of this study were summarized as follows. First, adolescents' parental attachment positively influenced school life adjustment. Second, study oriented internet use positively influenced school life adjustment. However, entertainment oriented internet use negatively influenced school life adjustment, and relation oriented internet use did not influence school life adjustment. Third, study and entertainment oriented internet use mediated parental attachment and school life adjustment. However, relation oriented internet use did not mediate parental attachment and school life adjustment. Conclusion: The discovery that study oriented internet is a factor that can improve school life adjustment carries a significant meaning. Based on the results, some implications are discussed to improve school life adjustment in early adolescence.

• Human Ecology Research
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• v.56 no.1
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• pp.55-69
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• 2018

This study examined how the resources from work, family and community lowered family-to-work conflict (FWC) and enhanced family-to-work facilitation (FWF) of employed women with a child younger than 18 years old in order to provide empirical support for the Korean government's effort to create a family-friendly community as a way to help employed mothers balance work and family life. Information from 608 employed mothers living in 45 different communities were extracted from the 4th-wave of the Korean Longitudinal Survey of Women and Families in 2012, while community resources indicators were selected from the 2012 database of the Korean Statistical Information Service. Findings from the HLM analysis were as follows. First, there were significant variation in FWC and FWF among employed mothers depending on the communities they resided in. Second, work satisfaction, representative of work resource, relieved FWC and enhanced FWF, but spousal support, which represents family resource, affected neither FWC nor FWF. Third, community resources, as represented by family-friendly environment and frequent volunteering by community residents, lowered FWC but failed to enhance FWF. Lastly, family-friendly community resources served to mitigate the negative relationship between work satisfaction and FWC. This study is meaningful in that it provided empirical evidence for the contribution of community resources to work-family balance of employed mothers.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.6 no.3
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• pp.216-225
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• 1994

By use of laboratory experiment data set for an elliptic shoal by Berkhoff et al. (1982), both accuracy and Performance tests of numerical results between PCGM (Preconditioned Conjugate Gradient Method) and PA(Parabolic Approximation) are compared. Although both results show good agreement with the experimental data the PA model gives better reproduction of the relatively high amplitudes in the section 4-5 downwave of the shoal, in comparison with the PCGM. The PA model has been proved to be a useful tool for predicting wave transformationsin large shallow water region, but it can be applied only to the case of negligible reflection. On the other hand, there is a need to improve the computational efficiency of the PCGM model which is a finite difference scheme directly derived from the mild slope equation and can handle reflection. By taking the results of th PA model as an input data of the PCGM, the CPU time can be reduced by about 40%.

• The Korean Journal of Emergency Medical Services
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• v.9 no.1
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• pp.95-99
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• 2005

Penetrating neck trauma by gunshot injury involving tracheobronchial tree is rare in Korea. Extensive tissue damage by cavitation, tissue fragmentation and shock wave transmission of high-velocity projectile along with associated organ injury renders high rate of mortality and morbidity. A 28 year old man in military service with gunshot wound in left cervical area presented initial symptoms of severe dyspnea and subcutaneous emphysema. Computed tomography of chest and cervical region as well as bronchoscopic evaluation was performed to confirm highly suspected injury to cervical trachea. Surgical exposure was established through a low collar incision; the damaged segment of 3.5 cm length including 2-4th tracheal rings was resected out and end-to-end anastomosis was performed. Bleeding from lacerated anterior jugular vein was controlled by ligation of both ends and a K2 bulllet was found upon inner border of body of first rib, medial to right carotid sheath and removed out. Cervical esophagus, carotid artery, internal jugular vein and recurrent laryngeal nerve were spared. Extubation was done on the first postoperative day and postoperative course until discharge on nineth postoperative day remained uneventful.

• Bulletin of the Society of Naval Architects of Korea
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• v.27 no.3
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• pp.107-116
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• 1990

The liquid sloshing in an elastic tank is a fluid-structure interaction problem. It requires nonlinear analysis to solve the complicated physics involved in the large interaction of fluid-structure, the variation of dynamic characteristics of structure due to hydrodynamic loading, and the distorsion of fluid flow due to structural vibration. In this paper a Lagrangian FEM is introduced to analyze the liquid sloshing in an elastic tank assuming that the elastic wall is one degree of freedom rigid wall. Numerical integration is performed using an implicit-explicit algorithm, which is formed by mixing the predictor-corrector method and the Runge-Kutta 4th order method. The influence of dynamic characteristics of the sloshing tank on the fluid flow is discussed. The numerical method is also applied for the simulation of the wall generated wave in the tank.

• Korean Journal of Childcare and Education
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• v.15 no.4
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• pp.37-57
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• 2019

Objective: The purpose of this study was to examine the sequential mediating effects of self-esteem and positive peer play interaction between warmth parenting and the social competence of preschoolers. Methods: The 7th wave of the Panel Study on Korean Children(2014) was used to analyze 1,113 preschoolers. Sequential mediation effects were analyzed using SPSS Process Macro(Hayes, 2013). Results: Warmth parenting indirectly affected preschooler's social competence (cooperation, assertion, self-control) by yielding sequential mediation effects on self-esteem and peer play interaction. Namely, warmth parenting does not directly affect social competence but does have a significant effect on preschooler self-esteem, which positively affected peer play interaction. This path increases the social competence(cooperation, assertion, self-control) of preschool children. Conclusion/Implications: In order to increase the social competence (cooperation, assertion, self-control) of preschool children, it is important for the preschooler to consider themselves a worthy person and to learn positive interaction techniques through warmth parenting.

• Korean Journal of Childcare and Education
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• v.18 no.4
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• pp.37-52
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• 2022

Objective: This study pays attention to types of parental depression and differences in happiness and self-esteem of children in each group of parents. Methods: This study employed the 10th wave of the Panel Study on Korean Children. Cluster analysis, covariance analysis, and Bonferroni verification were performed on the data of 1,282 parents with 9-year-old children. Results: A total of four parental depression groups were categorized: 'both depressed,' 'mother depressed,' 'father depressed,' and 'not depressed.' Children of the not depressed group showed the highest psychological well-being among the four groups. Children of the mother mildly depressed group had lower scores in happiness and self-esteem than those of the father mildly depressed group. Conclusion/Implications: This study was a new attempt to categorize parental depression together, breaking away from individual approaches such as mother's depression, father's depression, and mother's and father's depression and complementary approaches between couples. When examining the impact of parental depression on children's psychological well-being, it is necessary to consider depression of the father and mother as a unit.