• Korean Chemical Engineering Research
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• v.58 no.1
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• pp.142-149
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• 2020

In this study, the electrochemical performance of Graphite/Silicon/Pitch composites as anode material was investigated to improve the low theoretical capacity of artificial graphite. Spherical artificial graphite surface was coated with polyvinylpyrrolidone (PVP) amphiphiles material to synthesize Graphite/Silica material by silica islands growth. The Graphite/Silicon/Pitch composites were prepared by petroleum pitch coating and magnesiothermic reduction. The Graphite/Silicon/Pitch composite electrodes manufactured using poly(vinylidene fluoride) (PVDF), carboxymethyl cellulose (CMC) and polyacrylic acid (PAA) binders. The coin type half cell was assembled using various electrolytes and additives. The Graphite/Silicon/Pitch composites were analysed by X-ray diffraction (XRD), scanning electron microscope (SEM) and a thermogravimetric analyzer (TGA). The electrochemical characteristics of Graphite/Silicon/Pitch composite were investigated by constant current charge/discharge, rate performance, cyclic voltammetry and electrochemical impedance spectroscopy. The Graphite/Silicon/Pitch composites showed high cycle stability at a graphite/silica/pitch ratio (1:4:8 wt%). When the electrode is prepared using PAA binder, the high capacity and stability is obtained. The coin type half cell assembled using EC: DMC: EMC electrolyte showed high initial capacity (719 mAh/g) and excellent cycle stability. The rate performance has an capacity retention (77%) at 2 C/0.1 C and an capacity recovery (88%) at 0.1 C / 0.1 C when the vinylene carbonate (VC) was added.

• Journal of Korea Water Resources Association
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• v.39 no.12 s.173
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• pp.1043-1056
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• 2006

Our ultimate purpose is to investigate the potential change in regional surface climate due to the global warming and to produce higher quality regional surface climate information over the Korean peninsula for comprehensive impact assessment. Toward this purpose, we carried out two 30-year long experiments, one for present day conditions (covering the period 1971-2000) and one for near future climate conditions (covering the period 2021-2050) with a regional climate model (RegCM3) using a one-way double-nested system. In order to obtain the confidence in a future climate projection, we first verify the model basic performance of how the reference simulation is realistic in comparison with a fairly dense observation network. We then examine the possible future changes in mean climate state as well as in the frequency and intensity of extreme climate events to be derived by difference between climate condition as a baseline and future simulated climate states with increased greenhouse gas. Emphasis in this study is placed on the high-resolution spatial/temporal aspects of the climate change scenarios under different climate settings over Korea generated by complex topography and coastlines that are relevant on a regional scale.

• Korean journal of applied entomology
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• v.60 no.3
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• pp.287-304
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• 2021

Since 1995, researches on natural enemies have been conducted extensively in Korea. Research papers on natural enemies published in the Korean Journal of Applied Entomology from 1990 to 2020 were 130, which is 8.4% of all published papers during the same period. In 1990s, most research papers study the searching and biological characteristics of natural enemies, whereas the proportion of research papers related to the field application using the developed natural enemies has been increasing since 2010s. A total of 37 excellent natural enemies have been developed including 24 indigenous and 13 introduced natural enemies. In addition, 28 kinds of booklets and/or manuals were developed for field application of natural enemies. Although successes in research and development have been achieved since that period, more researches on search for and/or introduction of excellent natural enemy suitable for the Korean cultivation environment, mass production technology that can reduce cost, and quality control program in producing and distributing natural enemy remain to be pursued in the future. Furthermore, there is a need to develop the technology that can be used in compatible way with natural enemies and other crop protection agents including synthetic insecticides.

• Korean Chemical Engineering Research
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• v.57 no.1
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• pp.118-123
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• 2019

In this study, the electrochemical characteristics of Graphite/Silicon/Pitch anode composites were analyzed to improve the low theoretical capacity of graphite as a lithium ion battery. The Graphite/Silica composites were synthesized by bonding silica onto polyvinylpyrrolidone coated graphite. The surface of used silica was treated with (3-Aminopropyl)triethoxysilane(APTES). Graphite/Silicon/Pitch composites were prepared by carbonization of petroleum pitch, the fabrication processes including the magnesiothermic reduction of nano silica to obtain silicon and varying the mass ratio of silica. The Graphite/Silicon/Pitch composites were analysed by XRD, SEM and XRD. Also the electrochemical performances of Graphite/Silicon/Pitch composite as the anode of lithium ion battery were investigated by constant current charge/discharge, rate performance, cyclic voltammetry and electrochemical impedance tests in the electrolyte of $LiPF_6$ dissolved in organic solvents (EC:DMC:EMC=1:1:1 vol%). The Graphite/Silicon/Pitch anode composite (silica 28.5 in weight) has better capacity (537 mAh/g). The cycle performance has an excellent capacity retention to 30th cycle of 95% and the retention rate capability of 98% in 0.1 C/0.2 C.

• Korean Chemical Engineering Research
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• v.60 no.3
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• pp.446-451
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• 2022

In this study, to improve capacity and cycle stability, the pitch coated nano silicon sheets/CNT composites were prepared through electrostatic bonding of nano silicon sheets and CNT. Silica sheets were synthesized by hydrolyzing TEOS on the crystal planes of NaCl, and then nano silicon sheets were prepared by using magnesiothermic reduction method. To fabricate the nano silicon sheets/CNT composites, the negatively charged CNT after the acid treatment was used to assemble the positively charged nano silicon sheets modified with APTES. THF as a solvent was used in the coating process of PFO pitch. The physical properties of the prepared anode composites were analysed by FE-SEM, XRD and EDS. The electrochemical performances of the synthesized anode composites were performed by current charge/discharge, rate performances, differential capacity and EIS tests in the electrolyte LiPF₆ dissolve solvent (EC:DMC:EMC = 1:1:1 vol%). It was found that the anode material with high capacity and stability could be synthesized when high composition of silicon and conductivity of CNT were used. The pitch coated nano silicon sheets/CNT anode composites showed initial discharge capacity of 2344.9 mAh/g and the capacity retention ratio of 81% after 50 cycles. The electrochemical property of pitch coated anode material was more improved than that of the nano silicon sheets/CNT composites.

• Journal of the Korean Institute of Landscape Architecture
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• v.46 no.2
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• pp.27-36
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• 2018

This study suggests the necessity of behavior analysis as changes to a park environment to reflect user desires can be implemented only by grasping the needs of park users. Online data (blog) were defined as the basic data of the study. After collecting data by 5 - year units, data mining was used to derive the characteristics of the time series behavior while the significance of the online data was verified through social network analysis. The results of the text mining analysis are as follows. First, primary results included 'walking', 'photography', 'riding bicycles'(inline, kickboard, etc.), and 'eating'. Second, in the early days of the collected data, active physical activity such as exercise was the main factor, but recent passive behavior such as eating, using a mobile phone, games, food and drinking coffee also appeared as a new behavior characteristic in parks. Third, the factors affecting the behavior of park users are the changes of various conditions of society such as internet development and a culture of expressing unique personalities and styles. Fourth, the special behaviors appearing at Olympic Park were derived from educational activities such as cultural activities including watching performances and history lessons. In conclusion, it has been shown that people's lifestyle changes and the behavior of a park are influenced by the changes of the various times rather than the original purpose that was intended during park planning and design. Therefore, it is necessary to create an environment tailored to users by considering the main behaviors and influencing factors of Olympic Park. Text mining used as an analytical method has the merit that past data can be collected. Therefore, it is possible to form analysis from a long-term viewpoint of behavior analysis as well as to measure new behavior and value with derived keywords. In addition, the validity of online data was verified through social network analysis to increase the legitimacy of research results. Research on more comprehensive behavior analysis should be carried out by diversifying the types of data collected later, and various methods for verifying the accuracy and reliability of large-volume data will be needed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.7
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• pp.857-864
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• 2013

A laser machining process has been applied in many manufacturing fields and it provides an excellent energy control for treating materials. However, a heat effect during laser machining can deteriorate material properties. Specifically, a thermally induced stress can be a problem in laser-machined structures on a metal surface. In this study, temperature and stress on cold-rolled carbon steel sheet machined with laser hole drilling were explored in an experimental approach and a numerical method. Stresses by temperature gradients inside the materials were generated in fast cooling. The stresses were measured by using a hole-drilling method and the material properties of carbon steel (SCP1-S) were obtained in the experiment. It was found that the stress predicted from the numerical analysis was in agreement with the stresses measured by using the hole-drilling method. The analysis can be applied for evaluating structure characteristics machined with a laser.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.1
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• pp.81-87
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• 2020

Crack control is essential to increase the durability of concrete significantly. Healing of crack can be controlled by rehydration of unreacted clinkers at the crack surface. In this paper, by comparing the results of isothermal calorimetry test and regression analysis, the Parrot & Killoh's cement hydration model was verified and clink er hydration model was proposed. The composition and quantification of hydration products were simulated by combining kinematic hydration model and thermodynamic model. Hydration simulation was conducted using the verified and proposed hydration model, and the simulation was performed by the substitution rate of clink er. The type and quantity of the final hydration product and healing product were predicted and, in addition, the optimal cementitious material of self-healing concrete was selected using the proposed hydration model.

• Microbiology and Biotechnology Letters
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• v.17 no.2
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• pp.148-153
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• 1989

A strain of alkalophilic Bacillus sp. YC-335 has been isolated from soil. The strain was capable of producing large amount of cyclodextrin glycosyl transferase (CGTase) in the culture broth. The preferable medium composition has been determined to be as follows : 1.5% soluble starch, 5% corn steep liquor, 0.1% $K_2$HPO$_4$, 0.02%mgSO$_4$.7$H_2O$, 1% CaCO$_3$and 1% Na$_2$CO$_3$(pH 10.3). The highest enzyme production was observed after 48 hours of cultivation at 31$^{\circ}C$. The optimum pH and temperature for the activity of crude enzyme were 6.0 and 5$0^{\circ}C$, respectively. The enzyme was stable between pH 5 and 9, and upto 5$0^{\circ}C$. The enzyme converted starch into $\alpha$-, $\beta$- and ${\gamma}$-CD in the relative amounts of 1:10:1.5, respectively.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.509-512
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• 2008

The lining concrete of water tunnel is a much capability to occur crack due to drying shrinkage and vibrator compaction etc. Because of crack of concrete induce structural problem and decrease durability of concrete, it is need to reduce crack of concrete. In this an Analytical study to analyze the effect of curing of concrete and compaction on the lining concrete. As the results, it was found that control of construction condition into curing of concrete and compaction improve on construction efficiency of the lining concrete.