• Korean Chemical Engineering Research
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• v.61 no.1
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• pp.80-88
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• 2023

Ensuring safety in the designing of manufacturing and handling facilities for low-density polyethylene (LDPE) is difficult because there are no standards for the dust explosion characteristics of LDPE. In this study, a dust explosion test was performed on two dust samples collected from a bag filter (LDPE 1) during the LDPE manufacturing process and sedimentary dust (LDPE 2) leaked outside a facility such as a silo, and the LDPE 2 explosion test results were summarized. Particle size analysis showed that the volume-based particle diameter (median) was 95.04 ㎛ and the number density was 0-1 ㎛. The maximum explosion pressure (P_max) was 6.6 bar, and the maximum rate of explosion pressure rise was 366 [bar/s] at 1500 g/m³. Accordingly, the dust explosion index (K_st) was 99.4 bar·m/s, which was confirmed as ST-1 grade. Moreover, the minimum ignition energy and minimum ignition temperature was 10 mJ and 450 ℃, respectively. Currently, manufacturing and handling design is based on the characteristic values of high-density polyethylene (HDPE). However, as the test results show that LDPE 2 dust has a higher risk than HDPE (particle diameter 61.6 ㎛), caution is required when using the HDPE design criteria in the LDPE manufacturing process.

• Korean Journal of Radiology
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• v.20 no.5
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• pp.791-800
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• 2019

Objective: To compare various models of diffusion-weighted imaging including monoexponential apparent diffusion coefficient (ADC), biexponential (fast diffusion coefficient [D_f], slow diffusion coefficient [D_s], and fraction of fast diffusion), stretched-exponential (distributed diffusion coefficient and anomalous exponent term [α]), and kurtosis (mean diffusivity and mean kurtosis [MK]) models in the differentiation of renal solid masses. Materials and Methods: A total of 81 patients (56 men and 25 women; mean age, 57 years; age range, 30-69 years) with 18 benign and 63 malignant lesions were imaged using 3T diffusion-weighted MRI. Diffusion model selection was investigated in each lesion using the Akaike information criteria. Mann-Whitney U test and receiver operating characteristic (ROC) analysis were used for statistical evaluations. Results: Goodness-of-fit analysis showed that the stretched-exponential model had the highest voxel percentages in benign and malignant lesions (90.7% and 51.4%, respectively). ADC, D_s, and MK showed significant differences between benign and malignant lesions (p < 0.05) and between low- and high-grade clear cell renal cell carcinoma (ccRCC) (p < 0.05). α was significantly lower in the benign group than in the malignant group (p < 0.05). All diffusion measures showed significant differences between ccRCC and non-ccRCC (p < 0.05) except D_f and α (p = 0.143 and 0.112, respectively). α showed the highest diagnostic accuracy in differentiating benign and malignant lesions with an area under the ROC curve of 0.923, but none of the parameters from these advanced models revealed significantly better performance over ADC in discriminating subtypes or grades of renal cell carcinoma (RCC) (p > 0.05). Conclusion: Compared with conventional diffusion parameters, α may provide additional information for differentiating benign and malignant renal masses, while ADC remains the most valuable parameter for differentiation of RCC subtypes and for ccRCC grading.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.37 no.3
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• pp.585-592
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• 2017

Most sewer lines buried in the city are likely to be collapsed due to serious aging. Also, due to the high concentration of development and high population density and traffic, the collapse of the sewer will cause enormous social and economic damage. Therefore, proactive maintenance is required to prevent accidents caused by deteriorated sewer pipe. In order to utilize limited budget effectively, risk-based prioritization methods should be proposed that simultaneously consider the consequence of failure and the probability of failure. In this study, the method of risk-based prioritization of sewer was examined by reviewing various cases of overseas studies and applied to the urban sub-catchment. First, the impact factors that can be secured through the sewer GIS DB in Seoul were derived, and the weight, sub-criteria, and impact score of each impact factor were determined and the consequence of failure was calculated by weight sum method. In addition, the probability of failure was calculated by dividing the service life by the estimated useful life, and the consequence of failure and the probability of failure were classified into five grades by the Jenks natural breaks classification method. The prioritization method was applied to sub-catchment in the Seoul to derive a risk matrix and a risk grade. As a result, 26% of all subjects were selected as the inspection priority subjects with 4-5 risk grade. Therefore, using the risk-based CCTV prioritization methodology, it will be possible to systematically determine the objects that need investigation first.

• Journal of Elementary Mathematics Education in Korea
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• v.15 no.1
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• pp.57-75
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• 2011

This research aimed to explore the effects of collaborative writing activities in a mathematical context, specifically pertaining to areas such as numbers and operation, geometrical figure, and measurement in Mathematics: Level 5-b, on their mathematical achievement gain and disposition among Grade 5 students. To do this, out of a total of 62 students selected from two Grade 5 classes of J Elementary School in Dalseo-gu, Daegu City, who were found to be homogenic from the tests of math performance and dispositions, an experimental group(n=31) was designed and compared to a control group (n=31). Over a six week period from October to November in 2009, the experimental group was given collaborative writing lessons in math classes while the control group was given teacher-oriented regular lessons. The results were as follows. First, there was more or less considerable, though not significant, difference in overall mathematical achievement in the students experiencing collaborative writing activities when compared with the students in the control group. However, in terms of numbers and operation, a sub-category of mathematics, there was significant difference between the two groups. Second, the students experiencing collaborative writing activities were more positively affected in all sub-categories of mathematical disposition: confidence, flexibility, determination, curiosity, reflection, and value, than those in the control group. In summing up, the exposure of collaborative writing activities to mathematics learning was found to help students not only to have a concrete and proper grasp of the relevant problem solving process, which was observed from their mathematical achievement gain especially in the sphere of numbers and operation, but also to have their mathematical disposition set towards more positive direction, which was seen in all sub-categories of mathematical disposition measurement.

• Fibers and Polymers
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• v.2 no.3
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• pp.135-140
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• 2001

Organic-inorganic hybrid composites consisting of poly(vinylidene fluoride) (PVDF) and SiO$_2$ were prepared through a sol-gel process and the crystallization behavior of PVDF in the presence of $SiO_2$ networks was investigated by spectroscopic, thermal and x-ray diffraction measurements. The hybrid composites obtained were relatively transparent, and brittleness increased with increasing content of tetraethoxysilane (TEOS). It was regarded from FT-lR and DSC thermal analyses that at least a certain interaction existed between PVDF molecules and the $SiO_2$ networks. X-ray diffraction measurements showed that all of the hybrid samples had a crystal structure of PVDF ${\gamma}$-phase. Fresh gel prepared from the sol-gel reaction showed a very weak x-ray diffraction peak near 2$\theta$=$21^{\circ}$ due to PVDF crystallization, and Intensity increased grade-ally with time after gelation. The crystallization behavior of PVDF was strongly affected by the amount of $SiO_2$ networks. That is, $SiO_2$ content directly influenced preference and disturbance fur crystallization. In polymer-rich hybrids, $SiO_2$ networks had a favorable effect on the extent of PVDF crystallization. In particular, the maximum portent crystallinity of PVDF occurred at the content of 3.7 wt% $SiO_2$ and was higher than that of pure PVDF. However. beyond about 10 wt% $SiO_2$, the crystallization of PVDF was strongly confined.

• International Journal of Human Ecology
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• v.6 no.2
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• pp.25-35
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• 2005

The purpose of this study was to examine the effects of family-school relations on children's school adjustment with divorced mothers. Subcategories of the family-school relations were family participation in decision making, family help for schools, learning activities at home, school help for families, and school-home communication adopted from Epstein's parent involvement theory. Sub categories of children's school adjustment were delinquent behavior and academic achievement. The sample of this study included 3,367 children from first to fifth grade who lived either in a two-parent or one-parent home. Among them, 411 children with divorced mothers were analyzed. Independent t-test, Pearson's correlations, stepwise regression analysis were all conducted. Findings suggested that children with divorced mothers showed higher delinquency and lower academic achievement than children in intact families. Sub categories of family involvement and school involvement were correlated in divorced families. Children's delinquency was predicted by three of the family-school relation factors, which were school-home communication, family help for schools, and school help for families. Children's academic achievement was predicted by ail factors.

• Korean Journal of Child Studies
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• v.32 no.5
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• pp.121-134
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• 2011

The purposes of this study were to test the differences in communicative competence and conflict-resolving strategies between both popular and rejected children, and to thereby verify the discriminance of communicative competence and conflict-resolving strategies for both types of children. 52 popular children and 41 rejected children from among a pool of 202 6th grade elementary students were selected, and the data were analyzed by means of independent sample t-test and discriminant analysis. The research findings are as follows : First, listen up (sub-factors of perceiving), self-presentation, planning, and coding revealed statistically significant differences between the popular and the rejected children. Second, only negotiation and cooperation strategies revealed any statistically significant differences between the popular and the rejected children, while other sub-factors of conflict-resolving strategies indicated broad indifference between them. Third, it was only the factor of planning among 5 factors of communicative competence and 4 factors within conflict-resolving strategies which indicated that it was the most discriminant predictor between the popular and the rejected children. These results suggest that a comprehensive program is needed to improve the communicative competence and conflict-resolving strategies of rejected children.

• Journal of the Korean Society of Clothing and Textiles
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• v.25 no.1
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• pp.154-161
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• 2001

We have treated polyester fabric with $CF_4,\;C_2F_6,\;SF_6\;and\;C_3F_6$ glow discharge plasmas to develop functional fabrics which preserve moisture transportation and water proofing nature. Modified properties were evaluated by water vapor permeation rate and breakthrough water pressure. The change of surface morphology was observed by SEM. Fiber interstice of the plasma treated fabric was calculated as $0.32{\mu}{\textrm}{m}$, and this value was sufficiently ideal as water repellent material. The moisture transportation of ${CF_4}-treated$ fabric was good as much as untreated fabric, and those of $C_2$F(sub)6-treated, SF(sub)6-treated fabrics were reduced by 1~3%, and that of ${C_3F_6}-treated$ fabric was reduced by 15%. The best treatment condition were 0.06 torr 120 seconds in $CF_4$, 0.05 torr 30 seconds in $SF_6$, 0.08~0.15 torr 90 seconds in $SF_6$ and 0.1 torr 45 seconds in $C_3F_6$ respectively. The grade of moisture transportation effect was $CF_4>C_2F_6>SF_6>>C_3F_6$, and water proofing effect was $C_2F_6{\approx}CF_4>C_3F_6>SF_6$. It was observed by SEM that the thin film was formed on the surface of the treated substrate by the fluorocarbon plasma treatment.

• International Journal of Advanced Culture Technology
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• v.3 no.2
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• pp.25-33
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• 2015

This study aims to synthesis the self-cleaning fibers. The nano-titanium dioxide ($TiO_2$) were blend with the polypropylene (grade 561R) at 1wt%, 3wt%, 5wt%, 10wt%, 15wt% and 20wt%. The $TiO_2$-fibers were obtained from single screw extruder. The mechanical, thermal, rheology and self-cleaning properties were also investigated. The results showed that the tensile strength of the $nTiO_2$-PP fibers decreased with increasing of the amount of $TiO_2$. The presents of the $TiO_2$ in the PP fibers significantly showed the improving of the self-cleaning properties under sunlight and 20 watt of UV radiation. The $TiO_2$-PP fibers in presents of $TiO_2$ 20wt% showed the best results of self-cleaning under 5 hours of the sunlight which the similar results were found under 5 hours of 20 watts of UV radiation.

• Journal of the Korean Home Economics Association
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• v.50 no.8
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• pp.97-112
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• 2012

The purpose of this study is to develop the concept of manner leadership for adolescents based on the manner of the East and leadership of the West. Also, it is to investigate the influence of manner leadership on happiness of adolescents. For this, manner leadership was developed through literature review, focus group interview, empirical study, in-depth interview, exploratory factor analysis, and confirmatory factor analysis. The sub-dimensions of manner leadership consisted of time management, academic performance, goal attainment and citizenship behavior, communication, family relationship, social relationship, image management and conflict resolution. The data were obtained by administering a self-reported questionnaire to high school students residing in Seoul. Statistical analyses were carried out using SPSS and AMOS. The main results of the study can be summarized as follows. First, the level of the adolescents' manner leadership tended to be more than average. In addition, they were good at image management but time management was absolutely lacking among the sub-dimension of manner leadership. On the other hand, it appeared that the adolescents' happiness level was lower than the manner leadership. Second, the result of the study was that the manner leadership was positively correlated with happiness of adolescents. Finally, happiness of adolescents was affected on these variables, such as grade, self-efficacy, emotional intimacy between mother and adolescent, time management, goal attainment, communication, and family relationship. Based on this study, it is expected that the manner leadership programs for enhancing happiness for adolescents would be developed.