• Title, Summary, Keyword: Chemical Change

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An Analysis of Concepts related to Physical and Chemical Change on Middle and High School Science Textbooks (물리변화와 화학변화에 대한 중등학교 과학 교과서의 개념 분석)

  • Seoung-Hey Paik;Sun Kyoung Kim
    • Journal of the Korean Chemical Society
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    • v.47 no.2
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    • pp.155-164
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    • 2003
  • This study examined the types of explanations related to physical change and chemical change in the science textbooks of middle and high school based on the prior study of science teachers' understanding. For this research, the researchers analyzed 44 textbooks of middle school science and high school chemistry. As a result, there were no explanation or property type explanation represented in most of the textbooks related to physical and chemical change concepts. Also, there are few relationship represented between physical change and chemical change, and the examples related to physical change and chemical change were confused. These representations of textbooks can give rise to confusion of understanding of teachers and learners. So, it needs to re-design the explanation types correctly and constantly in science textbooks related to physical change and chemical change.

A Survey of Secondary School Science Teachers’ Thinking on Classifying Phenomena Related to Dissolution of Ionic Compound and Acid into Physical and Chemical Change (이온결합 화합물과 산의 용해 현상을 물리변화와 화학변화로 구분하는 문제에 대한 중·고등학교 과학교사들의 인식 조사)

  • Baek, Seong Hye;Kim, Seon Gyeong
    • Journal of the Korean Chemical Society
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    • v.46 no.6
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    • pp.561-568
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    • 2002
  • This study examined secondary school science teachers' thinking on physical and chemical change. For this research, we analysed the answers of 80 secondary school science teachers. According to the result of the analysis,teachers had various opinions when they classified phenomena of dissolving ionic compound or diluting acid into phys-ical change and chemical change. Many teachers tended to classify similar phenomena into different change when those were represented with different focus. It means that teachers' opinions were not consistent.

Applicability Analysis of Chemical Fate Model Considering Climate Change Impact in Municipal and Industrial Areas in Korea (기후변화를 고려한 화학물질거동모형의 도시·산단지역 적용성 연구)

  • Ryu, Sun-Nyeo;Lee, Woo-Kyun
    • Journal of Climate Change Research
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    • v.6 no.2
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    • pp.121-131
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    • 2015
  • As the temperature has changed by climate change, changes in its own characteristic values of the chemical substance or the movement and distribution of chemicals take place in accordance with the changes of hydrological and meteorological phenomena. Depending on the impact of climate change on the chemical behavior, it is necessary to understand and predict quantitative changes in the dynamics of the environment of pollutants due to climate change in order to predict in advance the occurrence of environmental disasters, and minimize the impact on the life and the environment after the incident. In this study, we have analysed and compared chemical fate models validated by previous studies in terms of model configuration, application size and input/output factors. The potential models applicable to municipal and industrial areas were selected on the basis of characteristic of each model, availability of input parameters and consideration for climate change, identified the problems, and then presented an approach to improve applicability.

Analysis of Resonance Based Micromechanical Bio-Chemical Sensing Structures (공진 기반 마이크로기계 생화학 센싱 구조물의 해석)

  • Yeo, Min-Ku;Shin, Yoon-Hyuck;Yim, Hong-Jae;Lim, Si-Hyung
    • Proceedings of the KSME Conference
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    • pp.1767-1772
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    • 2008
  • A microcantilever is a well-known MEMS structure for sensing bio-chemical molecules. When bio-chemical molecules are adsorbed on the microcantilever's surface, resonance frequency shift is generated. There are two issues in this phenomena. The first one is which one between mass change and surface stress change effects is more dominant on the resonance frequency shift. The second one is what will be the performance change when the boundary condition is changed from cantilevers to double clamped beams. We have studied the effect of surface stress change and compared it with that of mass change by using FEM analysis. Furthermore, for microstructures having different boundary conditions, we have studied Q-factor, which determines the detection limit of micro/nano mechanical sensors.

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Modeling of Grade Change Operations in Paper Mills

  • Ko, Jun-Seok;Yeo, Yeong-Koo;Ha, Seong-Mun;Lim, Jung-Woo;Ko, Du-Seok;Hong Kang
    • Journal of Korea Technical Association of The Pulp and Paper Industry
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    • v.35 no.5
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    • pp.46-52
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    • 2003
  • In this work we developed the closed-loop model of a paper machine during grade change with the intention to provide a reliable dynamic model to be used in the model-based grade change control scheme. During the grade change, chemical and physical characteristics of paper process change with time. It is very difficult to represent these characteristics on-line by using physical process models. In this work, the wet circulation part and the drying section were considered as a single process and closed-loop identification technique was used to develop the grade change model. Comparison of the results of numerical simulations with mill operation data demonstrates the effectiveness of the model identified.

Colorimetric Determination of pH Values using Silver Nanoparticles Conjugated with Cytochrome c

  • Park, Jun-Su;Choi, In-Hee;Kim, Young-Hun;Yi, Jong-Heop
    • Bulletin of the Korean Chemical Society
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    • v.32 no.9
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    • pp.3433-3436
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    • 2011
  • Some of metal nanoparticles have the potential for use as colorimetric assays for estimating solution properties, such as pH and temperature due to localized surface plasmon (LSP) phenomena. This report describes the use of silver nanoparticles (AgNP) conjugated with cytochrome c (Cyt c) for the colorimetric determination of solution pHs. When the pH of a solution decreases, the Cyt c immobilized on the AgNP undergoes a conformational change, leading to a decrease in the interparticle distance between Cyt c-AgNP probes and consequent red-shift in LSP. As a result, the color of the Cyt c-AgNP probe solution changes from yellow to red and finally to a grayish blue in the pH range from 11 to 3. This gradual color change can be used to determine the pH of a solution over a wide pH range, compared to other colorimetric methods that use gold nanoparticles.

Change in Chemical Compositions of Leachate and Medium Density Fiberboard from a Laboratory-scale Simulated Landfill

  • Lee, Min;Prewitt, Lynn;Mun, Sung Phil
    • Journal of the Korean Wood Science and Technology
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    • v.44 no.2
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    • pp.231-240
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    • 2016
  • The change in chemical compositions of leachate and medium density fiberboard (MDF) from a laboratory-scale simulated landfill which constructed in a plastic container containing alternating layers of soil and MDF was investigated to evaluate decomposing of MDF in soil. Four treatments were conducted: 1) MDF in soil, 2) MDF only, 3) cured UF resin in soil, and 4) soil only. Molecular weight (MW) distribution of compounds in leachate from soil only treatment did not change over time. In UF resin in soil treatment, the MW distribution shifted to a lower MW distribution over time, while the peak shifted to the left indicated changing to higher MW distribution in leachate from treatment 1 and 2 contained MDF. Higher percent nitrogen in leachate was observed in MDF containing treatments due to the UF resin in the MDF. The percent carbon slightly increased in MDF only while that greatly decreased in MDF in soil treatment maybe due to bacterial activity. The percent of extractable materials from the MDF decreased greatly on day 35 compare to day 0, and subsequently did not change much on day 77. In contrast, percent holocellulose and lignin did not change much over time. No structural change of the wood fiber in MDF occurs during the study. Water-soluble materials from MDF in soil contributed the change in chemical composition of leachate.

Management of Change in the Chemical Industries Based on Risk Assessment (위험성 평가에 기반한 화학산업의 변경관리)

  • Yoo, Jin Hwan;Lee, Heon Seok;Choi, Jeong Woo;Seo, Jae Min;Ko, Jae Wook
    • Korean Chemical Engineering Research
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    • v.46 no.1
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    • pp.156-163
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    • 2008
  • Process change and modification, which are caused by process failure, equipment life cycle and economic environment, have been generated in the chemical plants. And the MOC (management of change) base on the reasonable process safety technology such as change judgment, hazard identification by accurate technical references and risk assessment. But it is difficult to carry out the MOC because of lack of experience, shortage of knowledge and none of process safety specialists. In this study, the MOC system which could make enhancement of safety by finding and complementing weakness of MOC in chemical facilities was developed. This developed MOC system based on QRA was recommended the obvious standard for decision-making process, MOC procedure based on risk assessment and risk estimation of the process modification. The study based on the above way sought the enhancement of safety by performing Risk Based MOC for chemical plants.

Effects of Polymerization and Spinning Conditions on Mechanical Properties of PAN Precursor Fibers

  • Qin, Qi-Feng;Dai, Yong-Qiang;Yi, Kai;Zhang, Li;Ryu, Seung-Kon;Jin, Ri-Guang
    • Carbon letters
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    • v.11 no.3
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    • pp.176-183
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    • 2010
  • PAN precursor fibers were produced via wet-spinning process, and effects of polymerization and spinning processes, especially the stretching process, were investigated on mechanical properties and micro-morphologies of precursor fibers. An increase in molecular weight, dope solid and densification and a decrease in surface defects were possible by controlling polymerization temperature, the number of heating rollers for densification and the jet stretch ratio, which improved the mechanical properties of precursor fibers. The curves for strength, modulus, tensile power and diameter as a function of stretch ratio can be divided into three stages: steady change area, little change area and sudden change area. With the increase of stretch ratio, the fiber diameter became smaller, the degree of crystallization increased and the structure of precursor fibers became compact and homogeneous, which resulted in the increase of strength, modulus and tensile power of precursor fibers. Empirical relationship between fiber strength and stretch ratio was studied by using the sub-cluster statistical theory. It was successfully predicted when the strengths were 0.8 GPa and 1.0 GPa under a certain technical condition, the corresponding stretch ratio of the fiber were 11.16 and 12.83 respectively.