• Carbon letters
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• v.6 no.2
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• pp.106-110
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• 2005

In this work, the effects of atmospheric oxygen plasma treatment of carbon fibers on mechanical interfacial properties of carbon fibers-reinforced epoxy matrix composites was studied. The surface properties of the carbon fibers were determined by acid/base values, Fourier-transform infrared spectrometer (FT-IR), and X-ray photoelectron spectroscopy (XPS) analyses. Also, the crack resistance properties of the composites were investigated in critical stress intensity factor ($K_{IC}$), and critical strain energy release rate mode II ($G_{IIC}$) measurements. As experimental results, FT-IR of the carbon fibers showed that the carboxyl/ester groups (C=O) at 1632 $cm^{-1}$ and hydroxyl group (O-H) at 3450 $cm^{-1}$ were observed for the plasma treated carbon fibers, and the treated carbon fibers had the higher O-H peak intensity than that of the untreated ones. The XPS results also indicated that the $O_{1S}/C_{1S}$ ratio of the carbon fiber surfaces treated by the oxygen plasma led to development of oxygen-containing functional groups. The mechanical interfacial properties of the composites, including $K_{IC}$ (critical stress intensity factor) and $G_{IIC}$ (critical strain energy release rate mode II), were also improved for the oxygen plasma-treated carbon fibersreinforced composites. These results could be explained that the oxygen plasma treatment played an important role to increase interfacial adhesions between carbon fibers and epoxy matrix resins in our composite system.

• Journal of the Korean Society of Propulsion Engineers
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• v.18 no.6
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• pp.19-26
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• 2014

A ground hot-firing test (HFT) was carried out to make a close examination into the pressure instability for the 70 N-class hydrazine thruster under development. Monopropellant grade hydrazine was adopted as a propellant for the HFT, and catalyst-bed was filled with $Ir/Al_2O_3$ catalyst. In order to investigate the effects of thrust-chamber diameter on combustion stability, evaluation tests for the development models were performed on three kinds of lower thrust chambers having the length-to-diameter ratio (L/D) of 1.03, 1.13, and 1.26. As results, it was found that low frequency instability (~ 50 Hz) was inherent in the models, and in addition, increase of the L/D and decrease of the operating pressure led to an amplification of pressure oscillation in the test condition specified.

• Journal of Adhesion and Interface
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• v.9 no.1
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• pp.9-15
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• 2008

EVA foam was treated by oxygen plasma under a various treatment time for surface modification. The effect of plasma treatment on surface properties of EVA foam was investigated in terms of FT-IR ATR, XPS, contact angle, and SEM analysis and the adhesion characteristic of the EVA foam was studied in peel strength. As a results, EVA foam treated by plasma led to an elimination of organic compound, an increase of oxygen content, and an increase of surface roughness, resulting in improving the adhesion properties of the EVA foam. As the plasma treatment time increased, the hydrophilicity and physical change of surface of the EVA foam were increased and showed maximum value at 180 s and 420 s, respectively. The maximum adhesion strength appeared at plasma treatment time of 420 s and therefore, in this study the physical change was thought to be a major factor for improving the adhesion of the EVA foam.

• Korean Chemical Engineering Research
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• v.44 no.6
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• pp.644-649
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• 2006

In this paper, the Cr(VI) adsorption behaviors of activated carbons (ACs) treated by various ozone treatment conditions were studied. The surface properties of the ACs studied were determined by pH, acid-base, and FT-IR measurements. $N_2$ adsorption isotherm characteristics at 77K were confirmed by BET equation, Boer's t-plot method, and Horvath-Kawazoe's slit pore model. Also, the total Cr adsorption amount onto the ACs was measured by ICP-AES. As a result, the ozone treatment led to an increase of oxygen-containing polar functional groups and total acidity as well. Meanwhile, the specific surface areas or micropore volumes were slightly decreased after the ozone treatment due to the micropore filling or blocking. Nevertheless, the total Cr adsorption of ACs was increased with increasing of the ozone treatment time, attributed to the good interaction between Cr ions and polar functional groups on the ACs.

• Investigative Magnetic Resonance Imaging
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• v.23 no.3
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• pp.202-209
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• 2019

Purpose: To investigate the temperature-based differences of cortical bone ultrashort echo time MRI (UTE-MRI) biomarkers between body and room temperatures. Investigations of ex vivo UTE-MRI techniques were performed mostly at room temperature however, it is noted that the MRI properties of cortical bone may differ in vivo due to the higher temperature which exists as a condition in the live body. Materials and Methods: Cortical bone specimens from fourteen donors ($63{\pm}21$ years old, 6 females and 8 males) were scanned on a 3T clinical scanner at body and room temperatures to perform T1, $T2^*$, inversion recovery UTE (IR-UTE) $T2^*$ measurements, and two-pool magnetization transfer (MT) modeling. Results: Single-component $T2^*$, $IR-T2^*$, short and long component $T2^*s$ from bi-component analysis, and T1 showed significantly higher values while the noted macromolecular fraction (MMF) from MT modeling showed significantly lower values at body temperature, as compared with room temperature. However, it is noted that the short component fraction (Frac1) showed higher values at body temperature. Conclusion: This study highlights the need for careful consideration of the temperature effects on MRI measurements, before extending a conclusion from ex vivo studies on cortical bone specimens to clinical in vivo studies. It is noted that the increased relaxation times at higher temperature was most likely due to an increased molecular motion. The T1 increase for the studied human bone specimens was noted as being significantly higher than the previously reported values for bovine cortical bone. The prevailing discipline notes that the increased relaxation times of the bound water likely resulted in a lower signal loss during data acquisition, which led to the incidence of a higher Frac1 at body temperature.

• Journal of the Korean Institute of Intelligent Systems
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• v.26 no.3
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• pp.176-181
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• 2016

In this paper, the autonomous mobile robot control system for detecting fire was proposed using the wearable device based on EMG(Electromyogram) signal. Myo armband is used for detecting the user's EMG signal. The gesture was classified after sending the data of EMG signal to a computer using Bluetooth communication. Then the robot named 'uBrain' was implemented to move by received data from Bluetooth communication in our experiment. 'Move front', 'Turn right', 'Turn left', and 'Stop' are controllable commands for the robot. And if the robot cannot receive the Bluetooth signal from a user or if a user wants to change manual mode to autonomous mode, the robot was implemented to be in the autonomous mode. The robot flashes the LED when IR sensor detects the fire during moving.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.58.1-58.1
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• 2010

In solar cell module manufacturing, single solar cells has to be joined electrically to strings. Copper stripes coated with tin-silver-copper alloy are joined on screen printed silver of solar cells which is called busbar. The bus bar collects the electrons generated in solar cell and it is connected to the next cell in the conventional module manufacturing by a metal stringer using conventional hot air or infrared lamp soldering systems. For thin solar cells, both soldering methods have disadvantages, which heats up the whole cell to high temperatures. Because of the different thermal expansion coefficient, mechanical stresses are induced in the solar cell. Recently, the trend of solar cell is toward thinner thickness below 180um and thus the risk of breakage of solar cells is increasing. This has led to the demand for new joining processes with high productivity and reduced error rates. In our project, we have developed a new method to solder solar cells with a laser heating source. The soldering process using diode laser with wavelength of 980nm was examined. The diode laser used has a maximum power of 60W and a scanner system is used to solder dimension of 6" solar cell and the beam travel speed is optimized. For clamping copper stripe to solar cell, zirconia(ZrO)coated iron pin-spring system is used to clamp both joining parts during a scanner system is traveled. The hot plate temperature that solar cell is positioned during lasersoldering process is optimized. Also, conventional solder joints after $180^{\circ}C$ peel tests are compared to the laser soldering methods. Microstructures in welded zone shows that the diffusion zone between solar cell and metal stripes is better formed than inIR soldering method. It is analyzed that the laser solder joints show no damages to the silicon wafer and no cracks beneath the contact. Peel strength between 4N and 5N are measured, with much shorter joining time than IR solder joints and it is shown that the use of laser soldering reduced the degree of bending of solar cell much less than IR soldering.

• Bulletin of the Korean Chemical Society
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• v.34 no.9
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• pp.2675-2679
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• 2013

Activity-directed isolation of the methylene chloride fraction from the stems of Parthenocissus tricuspidata have led to the identification of two new compounds (1-2): 1-(2',3',5'-trihydroxyphenyl)-2-(4"-hydroxyphenyl)-ethane-1,2-(E)-epoxide (1, tricuspidatin A) and erythro-1-(3',5'-dihydroxyphenyl)-2-(4"-hydroxyphenyl)-ethane-1,2-diol (2, tricuspidatin B), together with four known compounds (3-6): ${\beta}$-sitosterol (3), nonacosan-1-ol (4), 3-(4-hydroxy-3-methoxyphenyl)-2-propenoic acid hexacosyl ester (5) and betulinic acid (6). Their chemical structures were elucidated based on spectroscopic (IR, UV, MS, 1D and 2D NMR) and physicochemical analyses. Compounds 1 and 2 showed strong DNA topoisomerase II inhibitory activity at both concentrations of 20 and $100{\mu}M$. In addition, 3 exhibited strong cytotoxic activity against the HT-29 and HepG2 cancer cell lines, and 6 showed strong cytotoxicity against the HT-29 and MCF-7 ones.

• Membrane and Water Treatment
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• v.11 no.3
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• pp.231-235
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• 2020

Industrialization and modern developments have led to an influx of toxic heavy metals into the aquatic environment, and the accumulation of heavy metals has serious adverse effects on humans. Among the various heavy metal treatment methods, adsorption is very useful and frequently used. Plastic materials, such as polypropylene and polyethylene, have been widely used as filter media due to their mechanical and chemical stability. However, the surface of plastic material is inert and therefore the adsorption capability of heavy metals is very limited. In this study, granular media and fiber media composed of polypropylene and polyethylene are used, and the surface modification was conducted in order to increase adsorption capability toward heavy metals. Oxygen plasma generated hydroxyl groups on the surface of the media to activate the surface, and then acrylic acid was synthesized on the surface. The grafted carboxyl group was confirmed by FT-IR and SEM. Heavy metal adsorption capability of pristine and surface modified adsorbents was also evaluated. Overall, heavy metal adsorption capability was increased by surface modification due to electrostatic interaction between the carboxyl groups and heavy metal ions. Fibrous PP/PE showed lower improvement compared to granular PP media because pore blockage occurred by the surface modification step, thereby inhibiting mass transfer.

• Textile Coloration and Finishing
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• v.13 no.5
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• pp.18-18
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• 2001

Natural colorants have attracted much attention all over the world because of their non-hazardous nature. The world is becoming increasingly aware of environmental issues, such as ozone layer depletion, water pollution and waste disposal problems. The use of synthetic dyestuffs for their synthesis and application in the dyeing industries has been criticized due to introduction of contaminants into the environment. This has led to the desire to turn to the traditional, and more natural way of life. In this study, the colorants of extract of Ginkgo biloba bark were analysed and their dyeing properties on silk, wool and cotton were studied. It was found that uv-visible absorption spectra of extract of Ginkgo biloba bark showed two strong absorption peaks in the range of 240∼400 nm. From the result of IR spectra, the major ingredient of extract of Ginkgo biloba bark seems to be the flavon which is one of the flavonoid derivatives. Silk, wool, and cotton dyed with the extract of Ginkgo biloba bark showed a reddish yellow color. Their color differences were increased drastically with repetition of dyeing by three times.