• Textile Coloration and Finishing
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• v.30 no.3
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• pp.180-189
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• 2018

To study the effect of stereoisomeric structures of curing agents on curing behaviors, thermal and mechanical properties of epoxy resins, DGEBA(diglycidyl ether of bisphenol A) epoxy resin and 3,3'- and 4,4'-DDS(diaminodiphenyl sulfone) curing agents were selected. The curing initiation temperature and activation energy of DGEBA/3,3'-DDS was lower than DGEBA/4,4'-DDS. DGEBA/3,3'-DDS has a faster curing rate and higher degree of cure than DGEBA/4,4'-DDS, suggesting that 3,3'-DDS has higher reactivity than 4,4'-DDS. Tensile strength and fracture toughness of DGEBA/3,3'-DDS was lower than those of DGEBA/4,4'-DDS, indicating that mechanical properties of the epoxy resin can be different only by the stereoisomeric difference in chemical structure of the curing agent.

• Journal of the Korean Society for Precision Engineering
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• v.30 no.8
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• pp.870-877
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• 2013

There has been much recent research interest in developing numerous kinds of human-machine interface. This field currently requires more accurate and reliable sensing systems to detect the intended human motion. Most conventional human-machine interface use electromyography (EMG) sensors to detect the intended motion. However, EMG sensors have a number of disadvantages and, as a consequence, the human-machine interface is difficult to use. This study describes a muscle volume sensor (MVS) that has been developed to measure variation in the outline of a muscle, for use as a human-machine interface. We developed an algorithm to calibrate the system, and the feasibility of using MVS for detecting muscular activity was demonstrated experimentally. We evaluated the performance of the MVS via isotonic contraction using the KIN-COM$^{(R)}$ equipment at torques of 5, 10, and 15 Nm.

• Journal of the Korean Society of Visualization
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• v.20 no.2
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• pp.70-77
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• 2022

Skeletal muscle tissues feature cellular heterogeneity, including differentiated myofibers, myoblasts, and satellite cells. Thanks to the presence of undifferentiated myoblasts and satellite cells, skeletal muscle tissues can self-regenerate after injury. In skeletal muscle regeneration, the collective motions among these cell types must play a significant role, but little is known about the dynamic collective behavior during the regeneration. In this study, we constructed in vitro platform to visualize the migration behavior of skeletal muscle cells in specific conditions that mimic the biochemical environment of injured skeletal muscles. We then visualized the spatiotemporal distribution of stresses arising from the differential collectiveness in the cellular clusters under different conditions. From these analyses, we identified that the heterogeneous population of muscle cells exhibited distinct collective migration patterns in the injury-mimicking condition, suggesting selective activation of a specific cell type by the biochemical cues from the injured skeletal muscles.

• Composites Research
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• v.35 no.1
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• pp.1-7
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• 2022

The activated carbon is a very good choice for using as supercapacitor electrode materials. Herein, the flower of Shorea robusta, a bio-waste material was successfully used to synthesize the activated carbons for application as supercapacitor electrode materials. The activated carbon was synthesized through chemical activation process followed by thermal treatment at 700℃ in presence of N₂ atmosphere using KOH, ZnCl₂ and H₃PO₄ as the activating agents. The physicochemical analyses demonstrate that the obtained activated carbons are graphitic in nature and the degree of disorder of the graphitic carbons is changed with the activating agents. The activated carbon obtained from Shorea robusta flower (ACSF-K) electrode shows the specific capacitance of ~610 F g^-1 at 2 A g^-1 current density, which is higher than ACSF-Z (560 F g^-1) and ACSF-H (470 F g^-1) electrode material under the identical current density. The synthesized graphitic carbons also demonstrated good rate capability and high electrochemical stability as supercapacitor electrode.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.753-756
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• 2005

Recently, the alkali activation of Fly-ash has become a significant field of research because it is possible to use these materials having highly chemical reaction property. Also, the product does not generate CO2 gas, unlike ordinary Portland cement(O.P.C). Therefore, the purpose of this paper is to design for improving mechanical and chemical properties using Fly-ash and Meta-kaolin. And additive(CaO) affected to control the strength behaviors and shrinkage rate.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10a
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• pp.173-178
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• 2000

New prediction model is investigated estimating splitting tensile strength and modulus of elasticity with curing temperature and aging. New prediction model is based on the model which was proposed to predict compressive strength, and splitting tensile strength and modulus of elasticity calculated by this model are compared with experimental values. New prediction model well estimated splittinge tensile strength and elastic modulus as well as compressive strength.

• Journal of the Korean institute of surface engineering
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• v.32 no.3
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• pp.331-335
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• 1999

Electroless plating nickel has superior mechanical property to electroplated nickel. Furthermore nickel can be coated on nonconducting substrate. In this research, electroless plating of nickel were conducted in different bath condition to find optimum conditions of electroless nickel plating for MEMS applications. The selectivity of activation method on several substrates was investigated. The effects of nickel concentration, reducing agent concentration and inhibitor on deposition rate were investigated. The effect of pH on deposition rate and content of phosphorous in deposited nickel was also investigated.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.4
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• pp.111-120
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• 2014

The aim of this study is to develop an integrated urea-SCR catalytic filter system for reducing soot and $NO_X$ emissions simultaneously in diesel engines. In this study, the characteristics of exhaust emissions relative to reactive activation temperature under four kinds of engine loads are experimentally investigated by using a four-cycle, four-cylinder, direct injection type, water-cooled turbo intercooler ECU common-rail diesel engine with the integrated urea-SCR $MnO_2-V_2O_5-WO_3/TiO_2/SiC$ catalytic filter system operating at three kinds of engine speeds. The urea-SCR reactor is used to reduce $NO_X$ emissions, and the catalytic filter system is used to reduce soot emissions. The reactive activation temperature is very important for reacting a reducing agent with exhaust emissions. The reactive activation temperatures in this experiment is applied to 523, 573 and 623 K. The fuel is sprayed by the pilot and main injections at the variable injection timing between BTDC $15^{\circ}$ and ATDC $1^{\circ}$ according to experimental conditions. It is found that the $NO_X$ conversion rate is the highest as 83.9% at the reactive activation temperature of 523 K in all experimental conditions of engine speed and load, and the soot emissions shown by the average reduction rate of approximately 93.3% are almost decreased below 0.6% in all experimental conditions regardless of reactive activation temperatures. Also, the THC and CO emissions by oxidation reaction of Mn, V and Ti are shown in the average reduction rates of 70.3% and 38% regardless of all experimental conditions.

• Journal of the Korean institute of surface engineering
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• v.49 no.3
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• pp.260-264
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• 2016

In this study, fractured surface morphology and mechanical properties of Ni-Cr-Mo alloys with various contents of Mo for dental material use have been evaluated by mechanical test. The alloys used were Ni-13Cr-xMo alloys with Mo contents of 4, 6, 8, and 10 wt.%, prepared by using a vacuum arc-melting furnace. Ni-13Cr-xMo alloys were used for mechanical test without heat treatment. The phase and microstructure of alloys using an X-ray diffraction (XRD) and optical microscopy (OM) were evaluated. To examine the mechanical properties of alloys according to microstructure changes, the tensile test and the hardness test were carried out using tensile tester. To understand the mechanism of Mo addition to Ni-Cr alloy on mechanical property, the morphology and fractured surfaces of alloys were investigated by field-emission scanning electron microscope (FE-SEM). As a result, 79Ni-13Cr-8Mo alloy was verified that the tensile strength and the hardness were better than others. Varying Mo content, the changes of microstructures of alloys were identified by OM and SEM and that of 79Ni-13Cr-8Mo alloy was proved fabricated well. Microstructures of alloys were changed depending on Mo content ratio. It has been observed that 8% alloy had the most suitable mechanical property for dental alloy.

• Journal of the Korean Chemical Society
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• v.19 no.5
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• pp.386-393
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• 1975

Polystyrene and polystyrene blended with SBR were subjected to the mechanical degradation by roll mastication. The results obtained are as follows. 1. For the polystyrene which is blended with SBR, the overall shape of the molecular weight distribution curve moves from the higher molecular weight portion to the lower molecular weight portion, becomes narrower in breadth, and its peak becomes higher as the degradation proceeds. The final molecular weight distribution exhibits a relative uniformity. This is due to the fact that only the polymer molecules with the high molecular weight consisted in original polystyrene are degraded mechanically and produced the polymer molecules with the low molecular weight. 2. The scission number of polystyrene chains increases with mastication time, and the number of degraded polymer chains produced when the polymer is masticated for 100 minutes at 140, 150 and $160^{\circ}C$ are $2.36{\times}10^{20},\;1.76{\times}10^{20}\;and\;1.52{\times}10^{20}$, respectively. 3. The rate of the degradation of polystyrene decreases with the mastication temperature. The activation energy is found to have the negative value, -8.7 kcal/mole. Therefore it is indicated that the mechanical degradation is a chemical process of which the activation energy is supplied mechanically.