• Title/Summary/Keyword: dispersion degree

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A Communication Structure of Science Gifted Students Based on the Social Network Analysis (사회연결망법을 이용한 과학영재들의 의사소통 구조 분석)

  • Chung, Duk-Ho;Yoo, Dae Young
    • Journal of the Korean earth science society
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    • v.34 no.1
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    • pp.81-92
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    • 2013
  • The purpose of this study was to investigate the communication structures that science gifted students used in small group activities, and to examine the relationship between communication styles and their achievement level. Eight small groups,5 members in each, participated in small group activities, in which they discussed how to calculate the average density of the earth. The communication structures and the achievement level presented in the group activities were analyzed using Pajek, Ucinet 6.0. As a result, we classified the communication styles of science gifted students into monopolistic type and co-ownership type according to the degree of dispersion of the interaction. We also classified it into $D_H{\cdot}N_H$ type, $D_H{\cdot}N_L$ type, $D_L{\cdot}N_H$ type, and $D_L{\cdot}N_L$ type based on the density and network centralization of interaction. The achievement levels of gifted students in their group work were affected by the density of interaction and the network centralization in small group activities, not by the dispersion of interaction among the members of the groups. Therefore, we recommend that teachers make the communication relevant to solving problem when they utilize a small group activity in science teaching.

Spatial Distribution Pattern of Ascotis selenaria (Lepidoptera: Geometridae) larvae in a Small-Scale of Citrus Orchard (소규모 감귤원에서 네눈쑥가지나방 유충의 공간분포 특성에 대한 이해)

  • Choi, Kyung San;Kim, Dong-Soon
    • Korean journal of applied entomology
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    • v.52 no.3
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    • pp.243-248
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    • 2013
  • This study was conducted to understand the settlement process of Ascotis selenaria larvae into citrus orchards with respect to oviposition site and analysis of the spatial distribution pattern of the larvae. A. selenaria eggs were not found on citrus trees in field and green house, but not on citrus trees in the field. A. selenaria larvae showed a significant clump distribution in the greenhouse. In the open citrus field, the index of dispersion was around 1.0 in most cases, with a weak clumping degree. However, the d-statistic was between -1.96 and 1.96, indicating a statistically significant random distribution. In addition, the Green's index (a clumping index) was very low in all cases, even though the clump distribution was accepted. for most samples, the probability distribution of larval frequency in the field satisfied the probability distribution functions of Poisson (random pattern) and the negative binomial (clump pattern) distribution. In addition, the temporal distribution of the larvae in the open field showed a pattern which was formed by colonizers from outside oviposition sites. Further, the difference in larval spatial distribution between field and greenhouse orchards was discussed.

Preparation of Hydroxypropyl Methyl Cellulose with Controlled Solubility Rate by Surface Treatment Reaction (표면처리반응에 의한 용해속도조절용 Hydroxypropyl Methyl Cellulose의 제조)

  • Lee, Moo-Jin;Shin, Young-Jo
    • Applied Chemistry for Engineering
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    • v.10 no.4
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    • pp.581-585
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    • 1999
  • The surface treated hydroxypropyl methylcellulose(HPMC) which could adjust the soluble time was synthesized when 40 wt % glyoxal solution and $KH_2PO_4$ were sprayed and reacted. And also, the solution dynamic at different ratios of two adding agents were identified If the surface of HPMC was treated with only glyoxal, the dispersion characteristics at different ratios of two adding agents were identified If the surface of HPMC was treated with only glyoxal, the dispersion was observed in the neutral solution and the viscosity was increased after directly dissolved as the solution become alkali condition. But the fine-powder type of HPMC which reacted with glyoxal and $KH_2PO_4$ was dispersed regardless of pH of solution and observed that it was dissolved and its viscosity increased after elapsing some time. With increasing amount of glyoxal and $KH_2PO_4$, the soluble time was delayed. The reaction condition was about 60 min at $75{\sim}85^{\circ}C$. Especially, the removal process of organic solvent after reaction was not required due to reaction under water solution without organic during glyoxal and $KH_2PO_4$ treatment. And also, the HPMC which could adjust the soluble rate in water or organic solvent by changing the degree of substitution of HPMC was synthesized.

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A Change of Surface Properties of Carbon Black by Surface Treatment (표면처리에 의한 Carbon Black의 표면물성변화)

  • Lee, Chang-Woo;Lee, Chang-Il;Hong, Young-Ho;Hong, In-Kwon;Jang, Yun-Ho;Hahm, Yeong-Min
    • Applied Chemistry for Engineering
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    • v.7 no.4
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    • pp.768-776
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    • 1996
  • Carbon Black has various advantageous properties such as reinforcement, tinting, weathering, chemical resistance, electrical resistance, etc., but it has poor affinity in the solution. The purpose of this study is to enhance dispersion in the aqueous solution by altering the surface characteristics. Two different treatments were applied for both channel black and furnace black respectively. Channel black was treated in alkaline solution to replace hydrogen of the carboxyl group with alkaline metal, Li, Na, K. Furnace black has few functional groups, and it was treated with $HNO_3$ to increase the number of functional group on carbon black. It was seen that the substitution of alkaline metal on the surface of channel black enhances the degree of dispersion. Also the higher the acid concentration and reaction temperature, the more the number of some functional groups on the furnace black. Reaction time was not seen to be effective.

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Surface-modified Nanoparticle Additives for Wear Resistant Water-based Coatings for Galvanized Steel Plates

  • Becker-Willinger, Carsten;Heppe, Gisela;Opsoelder, Michael;Veith, H.C. Michael;Cho, Jae-Dong;Lee, Jae-Ryung
    • Corrosion Science and Technology
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    • v.9 no.4
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    • pp.147-152
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    • 2010
  • Conventional paints for conversion coating applications in steel production derived mainly from water-based polymer dispersions containing several additives actually show good general performance, but suffer from poor scratch and abrasion resistance during use. The reason for this is because the relatively soft organic binder matrix dominates the mechanical surface properties. In order to maintain the high quality and decorative function of coated steel sheets, the mechanical performance of the surface needs to be improved significantly. In fact the wear resistance should be enhanced without affecting the optical appearance of the coatings by using appropriate nanoparticulate additives. In this direction, nanocomposite coating compositions (Nanomer$^{(R)}$) have been derived from water-based polymer dispersions with an increasing amount of surface-modified nanoparticles in aqueous dispersion in order to monitor the effect of degree of filling with rigid nanoparticles. The surface of nanoparticles has been modified for optimum compatibility with the polymer matrix in order to achieve homogeneous nanoparticle dispersion over the matrix. This approach has been extended in such a way that a more expanded hybrid network has been condensed on the nanoparticle surface by a hydrolytic condensation reaction in addition to the quasi-monolayer type small molecular surface modification. It was expected that this additional modification will lead to more intensive cross-linking in coating systems resulting in further improved scratch-resistance compared to simple addition of nanoparticles with quasi-monolayer surface modification. The resulting compositions have been coated on zinc-galvanized steel and cured. The wear resistance and the corrosion protection of the modified coating systems have been tested in dependence on the compositional change, the type of surface modification as well as the mixing conditions with different shear forces. It has been found out that for loading levels up to 50 wt.-% nanoparticles, the mechanical wear resistance remains almost unaffected compared to the unmodified resin. In addition, the corrosion resistance remained unaffected even after $180^{\circ}$ bending test showing that the flexibility of coating was not decreased by nanoparticle addition. Electron microscopy showed that the inorganic nanoparticles do not penetrate into the organic resin droplets during the mixing process but rather formed agglomerates outside the polymer droplet phase resulting in quite moderate cross linking while curing, because of viscosity. The proposed mechanisms of composite formation and cross linking could explain the poor effect regarding improvement of mechanical wear resistance and help to set up new synthesis strategies for improved nanocomposite morphologies, which should provide increased wear resistance.

Properties of Nanocomposites Based on Polymer Blend Containing PVDF, Carbon Fiber and Carbon Nanotube (PVDF를 포함한 고분자 블렌드와 탄소섬유/탄소나노튜브를 이용한 복합재료의 특성)

  • Kim, Jeong Ho;Son, Kwonsang;Lee, Minho
    • Applied Chemistry for Engineering
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    • v.25 no.1
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    • pp.14-19
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    • 2014
  • Nanocomposites based on poly(methyl methacrylate) (PMMA)/poly(vinylidene fluoride) (PVDF) and poly(ethylene terephthalate) (PET)/(PVDF) blended with carbon fibers (CF) and carbon nanotube (CNT) were prepared by melt mixing in the twin screw extruder. Morphologies of the PMMA/PVDF/CF/CNT and PET/PVDF/CF/CNT nanocomposites were investigated using SEM. The aggregation of CNT was observed in PMMA/PVDF/CF/CNT nanocomposites while the good dispersion of CNT was shown in PET/PVDF/CF/CNT nanocomposites. In SEM image of PET/PVDF/CF/CNT nanocomposite, the CNT were mainly located at the PET domain of phase-separated PET/PVDF blend due to the ${\pi}-{\pi}$ interaction between the phenyl ring of PET and graphite sheet of the CNT's surface. In addition, a fairly good compatibility between PET/PVDF matrix and CF was shown in the SEM image. In the case of PET/PVDF nanocomposites blended with the co-addition of CF and CNT, the volume electrical resistivity decreased while no change was observed in PMMA/PVDF/CF/CNT composites. The degree of CNT dispersion in morphology results was consistent with the electrical conductivity results. From the DSC results, the crystallization temperature (Tc) of PET/PVDF/CF/CNT nanocomposites increased due to the co-addition of CF and CNTs acting as a nucleating agent. Flexural modulus of PET/PVDF/CF/CNT were sharply enhanced due to increasing the interaction between PET and CF.

Preparation of Ni-GDC Powders by the Solution Reduction Method Using Hydrazine and Its Electrical Properties (하이드라진을 이용한 용액환원법에 의한 Ni-GDC 미분말 합성과 전기적 특성)

  • Kim, Sun-Jung;Kim, Kang-Min;Cho, Pyeong-Seok;Cho, Yoon-Ho;Lee, Choong-Yong;Park, Seung-Young;Kang, Yun-Chan;Lee, Jong-Heun
    • Korean Journal of Materials Research
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    • v.18 no.12
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    • pp.660-663
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    • 2008
  • Ni-GDC (gadolinia-doped ceria) composite powders, the anode material for the application of solid oxide fuel cells, were prepared by a solution reduction method using hydrazine. The distribution of Ni particles in the composite powders was homogeneous. The Ni-GDC powders were sintered at $1400^{\circ}C$ for 2 h and then reduced at $800^{\circ}C$ for 24 h in 3% $H_2$. The percolation limit of Ni of the sintered composite was 20 vol%, which was significantly lower than these values in the literature (30-35 vol%). The marked decrease of percolation limit is attributed to the small size of the Ni particles and the high degree of dispersion. The hydrazine method suggests a facile chemical route to prepare well-dispersed Ni-GDC composite powders.

A study on the color controlled of painter's work (페인트 도장공사의 색관리에 관한 연구)

  • Shim, Myung-Sup;Lee, Hyun-Jeong
    • Journal of the Korea Institute of Building Construction
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    • v.3 no.1
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    • pp.107-114
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    • 2003
  • This study aims to find methods that prevents aging of buildings paint coating and that limits defects in construction. Defects in painting can occur in four stages: pure paint, during painting, after the paint coating has dried, and after some period of time has passed after coating. Paint may become bad due to precipitation of pigments, formation of membranes, and seeding during manufacturing. Therefore, it is important that the paint is well mixed and kept airtight at a cool, dark place. Indents, paint brush strokes, orange peel, separation of colors, and paint running and spreading during the paint work process can be prevented by using high quality materials and applying a high-level of construction method. After the paint coating has dried, boiling, yellowing, poor drying, poor bonding, and/or glen deficiency may occur. These are influenced by the levels of cleanness of the dried product, drying temperature and hydration. Then, when the coating has been left dried for some period of time, cracking, peeling, scaling, swelling, discoloring, and/or rusting may develop due to the ultraviolet and contaminants in the air. Since these defects occur due to inappropriate construction schedule and/or hot and humid condition, one must use weatherproof materials. Furthermore, poor paint color may be caused by contamination in the sample plate, discoloration, and/or discrepancies in colors which are due to material differences, level of glossiness, degree of dispersion, dual color property of metallic colors, precipitation of pigments, etc. One should achieve reduction in construction cost and effectiveness in paint work by limiting contaminations in the construction site and strictly observing to construction regulations.

Innovative Method to Expand a Degree of Freedom of Observation in the Depth Direction without Losses of the Horizontal Number of Views in Autostereoscopic Multi-Views 3D Display System (시차장벽식 무안경 다시점 입체디스플레이 시스템에서 수평방향의 시점 수 저하 없이 깊이방향의 자유도를 증가시키기 위한 혁신적 방법)

  • Lee, Kwang-Hoon;Park, Min-Chul
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.38C no.10
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    • pp.903-910
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    • 2013
  • An autostereoscopic multi-view 3D display system has the narrower degrees of freedom in the observational directions, such as the horizontal and perpendicular directions to the display plane, than the glasses-on type of 3D display. In this paper, we propose an innovative method to expand the width of the viewing zone formed in the depth direction while maintaining the number of views in the horizontal direction by using a triple segmented-slanted parallax barrier (TS-SPB) in the glasses-off type of 3D display. The validity of the proposal was verified by an optical simulation based on an environment similar to an actual case. The maximum number of views that can be displayed in the horizontal direction is 2n, and the width of the viewing zone with depth increased up to a factor of 3.36 compared to the existing one-layered parallax barrier system.

Basic Properties of Polymer Cement Mortar with EVA Emulsion and Admixtures (EVA 에멀젼과 혼화재를 사용한 폴리머 시멘트 모르타르의 기초적 성질)

  • Jo, Young-Kug
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.23 no.6
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    • pp.53-60
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    • 2019
  • The purpose of this study is to evaluate the degree of improvement in strengths by mixing blast-furnace slag and fly ash in polymer cement mortar(PCM). The test specimens are prepared with EVA polymer dispersion, two types of Admixtures (blast-furnace slag and fly ash), five kinds of polymer-cement ratios (0, 5, 10, 15 and 20%), and six kinds of admixtures (0, 3, 5, 10, 15 and 20%). Plain cement mortar is also made for comparison. From the test results, the flowing of PCM is greatly improved with the mixing of the admixtures, and strengths of PCM compared to ordinary cement mortar are also improved due to a decrease in water cement ratio. In addition, the strength characteristics of PCM by admixtures are greatly improved in flexural strength with fly ash compared to other strengths. It is apparent that the optimum mix proportions with polymer-cement ratio of 10% or more, admixture contents 5 to 10% of flay ash for flexural strength improvement of EVA-cement mortar are recommended in this study.