• Applied Chemistry for Engineering
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• v.5 no.4
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• pp.588-596
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• 1994

A decomposition reaction of bauxite ore with $(NH_4)_2SO_4$ was investigated to prepare Al component pregnant solution for the direct product of high purity $Al_2O_3$ from low grade bauxite ore. Al component in the bauxite was sulfatized to $NH_4Al(SO_4)_2$ or $Al_2(SO_4)_3$ in this decomposition. The optimum conditions of the decomposition for bauxite ore were reaction temperature of $425^{\circ}C$, reaction time of 40min, $(NH_4)_2SO_4$ weight ratio to bauxite of 7.0 and particle size of bauxite ore of -200mesh. The optimum leaching conditions of sulfated bauxite ore were leaching temperature of $100^{\circ}C$, leaching time of 1hr and pulp density of 200ml $H_2O$ to sulfated ore of 1.0g bauxite. Under the above mentioned decomposition and leaching conditions, 94% of Al component in the bauxite ore was extracted.

• Korean Journal of Radiology
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• v.20 no.5
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• pp.781-790
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• 2019

Objective: To assess the relationship between contrast-enhanced ultrasound (CEUS) parameters and perfusion CT (PCT) parameters of gastric cancers and their correlation with histologic features. Materials and Methods: This prospective study was approved by our Institutional Review Board. We included 43 patients with pathologically-proven gastric cancers undergoing CEUS using SonoVue^® (Bracco) and PCT on the same day. Correlation between the CEUS parameters (peak intensity [PI], area under the curve [AUC], rise time [RT] from 10% to 90% of PI, time to peak [TTP_US], and mean transit time [MTT_US]) and PCT parameters (blood flow, blood volume, TTP_CT, MTT_CT, and permeability surface product) of gastric cancers were analyzed using Spearman's rank correlation test. In cases of surgical resection, the CEUS and PCT parameters were compared according to histologic features using Mann-Whitney test. Results: CEUS studies were of diagnostic quality in 88.4% (38/43) of patients. Among the CEUS parameters of gastric cancers, RT and TTP_US showed significant positive correlations with TTP_CT (rho = 0.327 and 0.374, p = 0.045 and 0.021, respectively); PI and AUC were significantly higher in well-differentiated or moderately-differentiated tumors (n = 4) than poorly-differentiated tumors (n = 18) (p = 0.026 and 0.033, respectively), whereas MTT_CT showed significant differences according to histologic types (poorly cohesive carcinoma [PCC] vs. non-PCC), T-staging (≤ T2 vs. ≥ T3), N-staging (N0 vs. N-positive), and epidermal growth factor receptor expression (≤ faint vs. ≥ moderate staining) (p values < 0.05). Conclusion: In patients with gastric cancers, CEUS is technically feasible for the quantification of tumor perfusion and may provide correlative and complementary information to that of PCT, which may allow prediction of histologic features.

• The Journal of Korean Association of Computer Education
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• v.13 no.1
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• pp.9-18
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• 2010

The purpose of this study is to determine the differences in menu-layout preference for learners based on their demographics. The experiment was conducted in this manner: three class second grade and three class sixth grade elementary school students were separated by sex, grade, age and cognitive style such as field-dependent and field-independent. They were asked to choose which menu layouts they preferred or did not prefer out of 6 different types. The results of the research are as follows: First, there were no differences in sex, grade and cognitive style for preferences in the menu layout but there were meaningful differences with regard to age. Second grade students preferred map-type layout, but sixth grade students preferred the type having a main menu across the top with a sub menu in roll over. Second, there was a difference with regard to age as to what they do not prefer. Overall, the results of this study suggest that the menu layout for a learning web site on the internet needs to be different according to their age.

• The Korean Journal of Nuclear Medicine
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• v.26 no.2
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• pp.333-337
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• 1992

In order to establish the clinical significance of pubic bone uptake of radionuclide on $^{99m}Tc-MDP$ bone scintigraphs, we analyzed uptake patterns of normal adult pubic bone in 300 randomly sampled subjects. Bone scintigraphy was performed in each patient for the reasons other than pubic or pelvic problems. One-hundred-fifty-four were men and 146 women. The age ranged from 8 to 78 years. The pubic uptake was graded arbitrarily into 4 grades by comparing the pubic uptake density with that of L5 vertebra. Thus, grade I was defined as the L5 density greater than the pubic density, grade II as the L5 density equals to the pubic density, grade III as the L5 density less than the pubic cdensity, and grade IV as the L5 density much less than the pubic density. Statistical analysis revealed negative trend in the pubic uptake from grade IV to grade I with age. There was no sexual difference in the pubic uptake. The women in the 3rd and 4th decades disclosed higher pubic uptake (grades III, IV) probably due to pregnancy and labor.

• Advances in materials Research
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• v.13 no.3
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• pp.161-171
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• 2024

This study aimed to investigate the effect of physicochemical properties and mix ratios of iron ore (oxide feed): coke (reductant) on the carbothermic reductions of iron ore. Coke size was fixed at ≤63 ㎛ while iron ore size varied between 150-63 ㎛ and ≤63 ㎛ respectively. Mix ratios were changed from 100:0 (reference) to 80:20 and 60:40 while the temperature, heating rate and soaking duration in muffle furnace were fixed at 1100 ℃, 10 ℃/min and 1 hour. Particle size analyzer, XRF, CHNS and XRD analyses were used for determination of raw feed characteristics. The occurrence of phase transformations from various forms of iron oxides to iron during the carbothermal reductions were identified through XRD profiles and supported with weight loss (%). XRF analysis proved that iron ore is of high grade with 93.4% of Fe₂O₃ content. Other oxides present in minor amounts are 2% Al₂O₃ and 1.8% SiO₂ with negligible amounts of other compounds such as MnO, K₂O and CuO. Composite pellet with finer size iron particles (≤63 ㎛) and higher carbon content of 60:40 exhibited 45.13% weight lost compared to 32.30% and 3.88% respectively for 80:20 and 100:0 ratios. It is evident that reduction reactions can only occur with the presence of coke, the carbon supply. The small weight loss of 3.88% at 100:0 ratio occurs due to the removal of moisture and volatiles and oxidations of iron ore. Higher carbon supply at 60:40 leads into better heat and mass transfer and diffusivity during carbothermic reductions. Overall, finer particle size and higher carbon supply improves reactivity and gas-solid interactions resulting in increased reductions and phase transformations.

• Journal of Korea Game Society
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• v.9 no.1
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• pp.3-10
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• 2009

This paper presents the effects on logical thinking of the Korean LOGO programming used in teaching for the second grade of middle school with regard to cognitive styles and specific sub-classifications of logical thinking. In result, the LOGO programming teaching method significantly affected logical thinking and its sub-classifications.

• International Journal of Contents
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• v.11 no.3
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• pp.1-6
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• 2015

This study presents an examination of the effects of the sub-factors of both self-control and school adjustment on smartphone addiction among a sample of elementary school students. The study is comprised of 93 5^th-grade students from x elementary school located in Seoul, Korea. A descriptive analysis, Pearson's correlation, and multiple regression analysis were performed, and the following two study results are presented: 1) Among the sub-factors of self-control, instant gratification positively predicts smartphone addiction. 2) Among the sub-factors of school adjustment, a student's adherence to school rules negatively predicts smartphone addiction. Based on these results, the implications for preventing smartphone addiction among elementary-school students are discussed.

• Journal of The Korean Association For Science Education
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• v.10 no.1
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• pp.33-45
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• 1990

To achieve the aim of science education, it is known that warious teaching, and learning materials should have to be used. As a sub-textbook for primary science education, 'Sil Hum-Kwan Chal (Experiment and Observation), teaching and learing material are developed and using now in science. This material have following characteristics; (a) Soruce-book contains reading materials for additional information, various pictures to enririch the science concepts, and supplementary and enrichment activities. (b) Work-book consists of the detailed procedures of activities of experiments presented in the textbook, student can record the experimental procedures and results. (c) Operational manuals provide operation techniques for experimental equipments which are used in science class. In this study the using status are surveyed for the 3rd grade of primary school, and based on this survey the improvement plan are discussed in view of design, quantity and utility, of sub-textbook.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.9
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• pp.472-482
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• 2016

The purpose of this study was to determine if a geriatric injury would have a statistically significant relationship with the spatial safety within a specific region. To achieve the objectives of this study, an independent sample t-test and One-way ANOVA were performed to verify difference in mean value of regional safety grade, depending on the injury intentionality, injury location, activities at the time of injury, and injury mechanism, in 6,572 geriatric injury patients by combining the National Hospital Discharge Patients Injury Survey data and regional safety index data. The results of statistical validation suggested that there was no difference in the mean value of regional safety grade by sub-group with respect to the injury intentionality. However, a statistically significant difference was observed in terms of the mean value of regional safety grade in each sub-group with regard to the injury location, activities at the time of injury, and injury mechanism in connection with some areas of the regional safety index. Based on the results of such analysis, we derived and presented 3 implications related to policies and practice for the prevention of geriatric injury and a reduction of its occurrence rate in light of spatial safety after a discussion of the results through a comparison with previous studies that examined individual areas.