• Journal of Powder Materials
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• v.23 no.5
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• pp.384-390
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• 2016

Tri-isotropic (TRISO) coatings on zirconia surrogate beads are deposited using a fluidized-bed vapor deposition (FB-CVD) method. The silicon carbide layer is particularly important among the coated layers because it acts as a miniature pressure vessel and a diffusion barrier to gaseous and metallic fission products in the TRISO-coated particles. In this study, we obtain a nearly stoichiometric composition in the SiC layer coated at $1400^{\circ}C$, $1500^{\circ}C$, and $1400^{\circ}C$ with 20 vol.% methyltrichlorosilane (MTS), However, the composition of the SiC layer coated at $1300-1350^{\circ}C$ shows a difference from the stoichiometric ratio (1:1). The density decreases remarkably with decreasing SiC deposition temperature because of the nanosized pores. The high density of the SiC layer (${\geq}3.19g/cm^2$) easily obtained at $1500^{\circ}C$ and $1400^{\circ}C$ with 20 vol.% MTS did not change at an annealing temperature of $1900^{\circ}C$, simulating the reactor operating temperature. The evaluation of the mechanical properties is limited because of the inaccurate values of hardness and Young's modulus measured by the nano-indentation method.

• The Mathematical Education
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• v.59 no.3
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• pp.217-235
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• 2020

This study examined Korean fourth-grade students' performance by gender on the Trends in International Mathematics and Science Study(TIMSS) 2011 and 2015 mathematics assessment. We first identified items which had significantly higher mean scores by gender to decide which gender did better on a certain domain(domain-level analysis). Then, we examined the content of items(item-level analysis) to understand which items lead to gender differences in mathematics achievement. Our findings showed that about 80% of the items on both assessments did not show statistically significant differences between males and females. However, there were meaningful gender differences in the other 20% items. On both assessments, females had more items with significantly higher mean scores than males on the Shapes domain, and males had more those items on the Numbers and Measurement domains and all cognitive domains(Knowing, Applying, and Reasoning). In particular, females outperformed males on items related to identifying two- and three-dimensional shapes and drawing lines and angles and identifying them. Conversely, males had higher performance than females on items related to the pre-algebraic thinking, fractions and decimals, estimation of number differences, unit of length, and measuring time, height, and volume. The effect sizes for each item ranged from .12 to .33 and the mean effect size of all items across both assessments was .20, which indicated significant gender differences but small.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.4
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• pp.565-572
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• 2010

It is difficult to predict the accurate fatigue life of the ship structure because of load uncertainty and load redistribution at the ship structure members. As one of studies for accurate evaluation and prediction of fatigue life, it is a promising way to detect the crack previously by attaching the Fatigue Indicator Sensor (FIS) at the crack prediction region. In order to predict the fatigue life of the ship structure by using FIS, it is required to know previously the crack propagation characteristics according to pre-notch shapes. In this study, we obtained the stress distribution phase, stress concentration factors and stress intensity factor of various pre-notch shapes through FEA. Additionally, we conducted the fatigue test and obtained the characteristics of crack propagation according to the pre-notch shapes through comparison between the fatigue test and the FEA. Consequently, we classified the pre-notch shape into 3 categories: Long, Medium, and Short life type. On the basis of the numerical and experimental results, the FIS can be developed.

• IMMUNE NETWORK
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• v.6 no.3
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• pp.138-144
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• 2006

Background: There are at least two different subsets of B cells, B-1 and B-2. The characteristic features and function of B-2 cells in addition to the effect of steroids on B-2 cells are well-known. Although B-1 cells have different features and functions from B-2 cells, the effect of steroids on B-1 cells is not completely understood. Therefore, this study examined the effects of dexamethasone on peritoneal (or B-1 cells) and splenic B cells (or B-2 cells). Methods: Purified B cells were obtained from the peritoneal fluid and the spleens of mice. The isolated B cells were cultured in a medium and after adding different concentrations of dexamaethasone. The cell survival rate was measured by flow cytometry using propidium iodide. The expression level of the B cell surface marker was analyzed by flow cytometry. During the culture of these cells, immunoglobulin secreted into the culture supernatants was evaluated by an enzyme-linked immunosorbent assay. Results: The survival rate of peritoneal and splenic B cells decreased with increasing dexamethasone concentration. However, the rate of peritofieal B cell apoptosis was lower than that of splenic B cells. CDS and B7.1 expression in peritoneal B cells and CD23 and sIgM expression in splenic B cells after the dexamethasone treatment were reduced. When B cells were treated with dexamethasone, the spontaneous IgM secretion decreased with increasing dexamethasone concentration. Conclusion: Dexamethasone induces apoptosis in peritoneal and splenic B cells. However, peritoneal B cells are less sensitive to dexamethasone. The dexamethasone suppressed expression of the surface markers in peritoneal B cells is different from those in splenic B cells.

• IMMUNE NETWORK
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• v.7 no.2
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• pp.75-79
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• 2007

Background: Defective or immature antibody responses to pathogens in children may explain the increased susceptibility to acute otitis media. However, there is no study in Korea patients whether a correlation exists between otitis media with effusion and the levels of serum immunoglobulins, IgG subclasses, IgA, IgM and IgE. Methods: 45 children with otitis media with effusion more than 4 episodes in 12 months or 3 episodes in 6 months, 62 children with otitis media with effusion less than 3 episodes in 12 months and 102 children for control group took part in the study at the Department of Otorhinolaryngology of the KyungHee University from May 2004 to Feburary 2007. Serum immunoglobulin levels were determined by nephelometry. And then the relationship between otitis media with effusion and serum immunoglobulin level was evaluated. Results: In otitis media prone group, serum IgG1, IgG2, IgG4, and IgA level was lower than those level of control group, it was significantly decreased (p<0.05). In otitis media group, serum IgA, IgE, and IgG4 level was lower than those level of control. But it was not statistically significant (p>0.05). Conclusion: Lower immunoglobulins in children with otitis media with effusion suggest a generalized decreased antibody responses. Lower levels of serum IgG1, IgG2, IgG4, and IgA may be related with chronicity or intractability of otitis media with effusion.

• IMMUNE NETWORK
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• v.7 no.2
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• pp.87-94
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• 2007

Background: Chronic rhino-sinusitis and persistent allergic rhinitis is often cited as risk factor for developing adenoid hypertrophy or adenoiditis, but this relationship has not been studied extensively. In this study, we evaluated the mucosal barrier, squamous changes of ciliated epithelium, IgA secretion and BCL-6 expression in adenoids, and adenoid size. Methods: Six children with allergic rhinitis and sinusitis, nine children with only allergic rhinitis, nine children with only sinusitis and six children without any history of allergic rhinitis and sinusitis were enrolled. H-E stain of adenoid for squamous metaplasia, immunohistochemical study of adenoid for IgA and BCL-6, cytokeratin stain for evaluation of mucosal barrier and lateral view X-ray for adenoid size were performed. ANOVA test was used in the analysis and data showing p value of less than 0.05 were considered significant. Results: The number of ciliated cells had tendency to be decreased and squamous metaplasia had tendency to be increased in three experimental groups (p>0.05). Deterioration of mucosal barrier had tendency to be detected in three experimental groups than control group (p>0.05). BCL-6 had tendency to be increased and IgA secretion had tendency to be decreased in three experimental groups (p>0.05). There is no difference in adenoid size between three experimental groups and control group. Conclusion: Despite the expectation that adenoid would be affectecd by allergic rhinitis and rhino-sinusitis, we found no evidence for influence of adenoid immunity.

• Journal of the Korean Society of Costume
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• v.54 no.4
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• pp.75-84
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• 2004

Stage costumes perform not only the instrumental but also the expressive functions. The major goal of this study is to develop the functional and aesthetic costume designs for musical players considering the characteristics of instruments. players’ postures. The scope of this study is restricted to the musical costumes for female adult soloists playing the wind and string instruments. This study is composed of theory research, empiricalresearch and manufacturing a real costume. First, theory research contains theory of musical costumes and that of pure musical areas. Concept, characteristics and wearing effects are analysed in theory of musical costumes. Second, designs of instruments and playing postures are analysed in the theory of pure musical areas. Proper and improper designs are compared based on the survey asking the favorite designs of 56 wind and string players. Third, I manufacture a stage costume for a harpist. The conclusions of this study are as follows. First, wind and string players think the functionality of costumes more importantly than the esthetic sense. And there are differences in design preferences for different playing postures. Second, string Players basically use arms, fingers and the upper body. Wind players use fingers more than string players and do abdominal breathing. Third, string players think the design of arms and sleeves because of frequent usage of bow and prefer the design without sleeves. On the contrary, wind players think the silhouette importantly because of standing playing posture. Fourth, players don't think that the accessory is not important and want it so long as it doesn't hinder playing. Fifth, shoes plays more important role than costume in case of playing posture with using pedals and moving legs frequently. Lastly, both wind and string players prefer the design with simplicity and comfort most.

• Journal of Powder Materials
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• v.21 no.6
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• pp.434-440
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• 2014

Silicon carbide(SiC) layer is particularly important tri-isotropic (TRISO) coating layers because it acts as a miniature pressure vessel and a diffusion barrier to gaseous and metallic fission products in the TRISO coated particle. The high temperature deposition of SiC layer normally performed at $1500-1650^{\circ}C$ has a negative effect on the property of IPyC layer by increasing its anisotropy. To investigate the feasibility of lower temperature SiC deposition, the influence of deposition temperature on the property of SiC layer are examined in this study. While the SiC layer coated at $1500^{\circ}C$ obtains nearly stoichiometric composition, the composition of the SiC layer coated at $1300-1400^{\circ}C$ shows discrepancy from stoichiometric ratio(1:1). $3-7{\mu}m$ grain size of SiC layer coated at $1500^{\circ}C$ is decreased to sub-micrometer (< $1{\mu}m$) $-2{\mu}m$ grain size when coated at $1400^{\circ}C$, and further decreased to nano grain size when coated at $1300-1350^{\circ}C$. Moreover, the high density of SiC layer (${\geq}3.19g/cm^3$) which is easily obtained at $1500^{\circ}C$ coating is difficult to achieve at lower temperature owing to nano size pores. the density is remarkably decreased with decreasing SiC deposition temperature.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.281-281
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• 2012

연꽃잎 효과(Lotus effect)라 불리는 자가 세정 효과(self cleaning effect)는 연꽃이 항상 깨끗한 상태를 유지하는 것이 관찰되면서 꾸준히 관심에 대상이 되어 왔었다. 자가 세정 효과는 접촉각 $150^{\circ}$ 이상의 초소수성 표면에서 구현이 가능하며 이런 표면을 일상생활부터 산업분야까지 응용하고자 하는 많은 노력들이 있었다. 물질의 친수성 또는 소수성은 표면의 거칠기(roughness)와 표면에너지(surface energy)의 두 가지 특성에 의해 결정된다. 하지만 낮은 표면에너지 물질을 사용해도 접촉각 $150^{\circ}$ 이상의 초소수성 표면을 얻긴 힘들며, 표면의 거칠기를 증가시켜야 한다. PTFE (polytetrafluoroethylene)는 낮은 표면에너지를 가진 소수성 물질로 bulk일 경우 접촉각이 약 $108^{\circ}$이지만 거친 표면을 가진 박막으로 만들 경우 접촉각이 $150^{\circ}$ 이상의 값을 가지는 초수수성 표면이 가능한 물질이다. 특히, 초소수성 표면 이외에 우수한 내열성 및 내화학성 특성을 가지고 있어 디스플레이 및 태양전지 등의 자가세정(self cleaning) 보호막으로써 응용이 기대되고 있다. 본 연구에서는 HFPO (hexafluoropropylene)를 원료 가스로 이용하여, Si(100)과 유리 기판위에 Cat-CVD (Catalytic Chemical Vapor Deposition)법으로 PTFE 박막을 증착하였다. 텅스텐(W)을 촉매로 사용하였으며, 촉매온도가 $850^{\circ}C$이상인 조건에서 접촉각이 $150^{\circ}$ 이상인 초소수성 PTFE 표면을 쉽게 얻을 수 있었다. 특히 본 연구에서는 제막압력을 300 mTorr에서 700 mTorr까지 변화시켜 가며 유리와 Si 기판위에 증착하였다. Cat-CVD 제막압력을 변화시켜가며 증착된 PTFE 박막의 접촉각을 측정한 결과, 제막압력이 300 mTorr일 때 glass와 Si 기판위에 증착된 PTFE박막 표면에서의 접촉각은 각각 133, $117^{\circ}$였지만, 제막압력이 400 mTorr이상일 땐 $150^{\circ}$ 이상의 높은 접촉각을 갖는 초소수성 표면을 얻을 수 있었다.

• Applied Chemistry for Engineering
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• v.17 no.3
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• pp.260-266
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• 2006

For the synthesis of polyurethane memory foam stabilizer with fine cells, hydrosilylation reaction with various polyalkyleneoxides and hydrogen functional group of polymethylhydrogensiloxane (D = 75, D' = 15) was conducted. Polyalkyleneoxides (PAO) used in this research were ethylene oxides or ethylene-co-propylene oxides with terminal groups of hydroxides or methyl groups. To analyze the molecular structures and molecular weights as well as the reaction yields (98%), NMR and GPC analysis were executed. Synthesized siloxane surfactants modified with polyalkylene (EO = 12 units) were applied to producing flexible polyurethane fine memory foams from 0.6 pphp to 2.0 pphp. By controlling the amount of the surfactant, physical characteristics, the polyurethane memory foam with cell size (minimum $0.868{\mu}m$), air flows (-78 KPa), and recovery times (8 sec) were achieved.