• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.506-508
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• 2005

In general, organic TFTs are comprised of four components: gate electrode, gate dielectric, organic active semiconductor layer, and source and drain contacts. The TFT current, in turn, is typically determined by channel length and width, carrier field effect mobility, gate dielectric thickness and permittivity, contact resistance, and biasing conditions. More recently, a number of techniques and processes have been introduced to the fabrication of OTFT circuits and displays that aim specifically at reduced fabrication cost. These include microcontact printing for the patterning of metals and dielectrics, the use of photochemically patterned insulating and conducting films, and inkjet printing for the selective deposition of contacts and interconnect pattern. In the fabrication of organic TFTs, microcontact printing has been used to pattern gate electrodes, gate dielectrics, and source and drain contacts with sufficient yield to allow the fabrication of transistors. We were fabricated a pentacene OTFTs on flexible PEN film. Au/Cr was used for the gate electrode, parylene-c was deposited as the gate dielectric, and Au/Cr was chosen for the source and drain contacts; were all deposited by ion-beam sputtering and patterned by microcontact printing and lift-off process. Prior to the deposition of the organic active layer, the gate dielectric surface was treated with octadecyltrichlorosilane(OTS) from the vapor phase. To complete the device, pentacene was deposited by thermal evaporation and patterned using a parylene-c layer. The device was shown that the carrier field effect mobility, the threshold voltage, the subthreshold slope, and the on/off current ratio were improved.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.6
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• pp.2023-2035
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• 1996

In the present study, the characteristics of the electrical deformation of a bubble and a drop under a uniform electric field have been investigated to understand EHD heat transfer enhancement by an electric field. The deformation of the bubble and the drop have been studied theoretically using an electric normal stress acting on their interfaces and assured by the numerical analysis and the experiment. From the variation of bubble volume and free energy, it is found that a bubble is compressed in an electric field and free energy had larger value with increasing W and the permittivity of a dielectric fluid. The electric normal stress induced on the interface of the bubble and the drop is different. Because of the surface charge induced at the drop interface, the electric normal stress acting on the drop is much larger than that of the bubble. The drop is, therefore, deformed much more than the bubble. In addition, the experimental and numerical results show that the aspect ratio and the contact angle of the bubble increase with increasing W.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.12
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• pp.1503-1512
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• 2013

In this study, we proposed an indentation evaluation method for fracture toughness using cohesive finite element simulations. First, we examined the effect of material properties (yield strain, Poisson's ratio, and elastic modulus) on crack size during Vickers indentation and then generated a regression formula that explains the relations among fracture toughness, indentation load, and crack size. We also proposed another indentation formula for fracture toughness evaluation using the contact size a and E/H (H: hardness). Finally, we examined the relation between the crack size and the indenter shapes. Based on this, we can generate from the formula obtained using the Vickers indenter a formula for an indenter of different shapes. Using the proposed method, fracture toughness is directly estimated from indentation data.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.12
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• pp.1465-1471
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• 2013

The electrical and mechanical properties of room temperature vulcanized (RTV) silicone rubber composites are investigated as functions of multi-walled carbon nanotube (CNT), carbon black (CB), and thinner content. The thinner is used to improve the CNT and CB dispersion in the matrix. The electrical and mechanical properties of the composite with CNT are improved when compared to the composite with CB at the same content. As the thinner content is 80 phr, the electric resistance of the composite decreases significantly with the CNT content and shows contact point saturation of CNT at 2.5 phr. As the thinner content increases, the dispersion of conductive particles improves; however, the critical CB content increases because of the reduction in the CB weight ratio. It is believed that an electrode that needs good flexibility and excellent electrical properties can be manufactured when the amount of CNT and CB are increased with the thinner content.

• Anxiety and mood
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• v.6 no.1
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• pp.65-70
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• 2010

Objectives : Indirect contact with trauma may occur when a person empathically listens to detailed descriptions, exposing the person to intense emotional pain from trauma victims. Although less severe than direct trauma, indirectly traumatized persons may experience the same fear, rage, and despair as direct trauma victims. This phenomenon has been variously termed vicarious trauma, traumatic countertransference, burnout, compassion fatigue, and secondary traumatic stress. Using a psychiatric symptoms questionnaires, this study investigated the effects of indirect exposure to co-worker's trauma on the mental health of firefighters who had not directly experienced traumatic events in the previous year. Methods : We administered self-report questionnaires, such as the Impact of Event Scale-Revised (IESR) and Alcohol Use Disorder Identification Test (AUDIT), to firefighters working at two fire stations in a metropolitan city. We analyzed 188 of 232 collected surveys, after excluding falsely entered data (28 cases) and questionnaires by directly-traumatized victims (16 cases). Results : Alcohol consumption and posttraumatic stress disorder (PTSD) symptoms, as determined by the AUDIT and IES-R, were significantly higher in the indirectly-traumatized group. The ratio of high-risk members scoring higher than 23 in IES-R was larger in the indirectly traumatized group, although this was not statistically significant. Conclusion : Alcohol consumption was significantly higher in the indirectly traumatized group. This group also included more members at high risk for PTSD. Further research, with a larger group of indirectly traumatized firefighters and ongoing investigation of PTSD development and other psychiatric symptoms, is needed.

• Elastomers and Composites
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• v.39 no.3
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• pp.234-243
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• 2004

The elastomeric and conductive polyurethane (PU) films were prepared by poly(propylene glycol) (PPG), toluene 2,4-diisocyanate, 3-methylthiophene (3-MT) at various preparation conditions, such as the reaction time, the $FeCl_3$ concentration, the weight ratio of the 3-MT to PU and the reaction temperature for the diffusion-oxidative reaction. The conductive poly (3-methylthiophene) (PMT) layers via the diffusion-oxidative reaction of 3-MT and ferric chloride were formed by immersing the film in organic solution of $FeCl_3$/ethyl acetate. The preparation conditions greatly affected the electrical conductivity of the 3-MT/PU composite. The effects of the reaction time and temperature on morphology and surface free energy were investigated by scanning electron microscopy (SEM) analysis and contact angle measurement, respectively. The conductivity of the composite was as high as 42 S/cm.

• Membrane and Water Treatment
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• v.10 no.2
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• pp.113-120
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• 2019

To investigate surface properties and interception performances of the new modified PVDF membrane coated with Graphene Oxide (GO) and nano-$TiO_2$ (for short the modified membrane) via the interface polymerization method combined with the pumping suction filtration way, filtration experiments of the modified membrane on Humic Acid (HA) were conducted. Results showed that the contact angle (characterizing the hydrophilicity) of the modified membrane decreased from $80.6{\pm}1.8^{\circ}$ to $38.6{\pm}1.2^{\circ}$. The F element of PVDF membrane surface decreased from 60.91% to 17.79% after covered with GO and $TiO_2$. O/C element mass ratio has a fivefold increase, the percentage of O element on the modified membrane surface increased from 3.83 wt% to 20.87%. The modified membrane surface was packed with hydrophilic polar groups (like -COOH, -OH, C-O, C=O, N-H) and a functional hydrophilic GO-polyamide-$TiO_2$ composite configuration. This configuration provided a rigid network structure for the firm attachment of GO and $TiO_2$ on the surface of the membrane and for a higher flux as well. The total flux attenuation rate of the modified membrane decreased to 35.6% while 51.2% for the original one. The irreversible attenuation rate has dropped 71%. The static interception amount of HA on the modified membrane was $158.6mg/m^2$, a half of that of the original one ($295.0mg/m^2$). The flux recovery rate was increased by 50%. The interception rate of the modified membrane on HA increased by 12% approximately and its filtration cycle was 2-3 times of that of the original membrane.

• International Journal of Precision Engineering and Manufacturing-Green Technology
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• v.5 no.5
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• pp.583-591
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• 2018

Tool-chip adhesion impacts on cutting performance significantly, especially in finish cutting process. To promote cutting tools' anti-adhesion property, the concave micro-grooves texture (MGT) and convex volcano-like texture (VLT) were fabricated separately on lathe tools' rake faces by laser surface texturing (LST). Various orientations of MGT and different area densities (9% and 48%) and regions (partial and full) of VLT were considered in textured patterns designing. The following orthogonal cutting experiments, machining of aluminum alloy 5038, analyzed tools' performances including cutting force, cutting stability, chip shape, rake face adhesion and abrasion. It indicated that under dry finish cutting conditions, MGT contributed to cutting stability and low cutting forces, meanwhile friction and normal force reduced by around 15% and 10%, respectively with a weak correlation to the grooves' orientation. High density VLT tools, on the other hand, presented an obvious anti-adhesion property. A $5{\mu}m$ reduction of crater wear's depth can be observed on textured rake faces after long length cutting and textured rake faces presented half size of BUE regions comparing to the flat tool, however, once the texture morphologies were filled or worn, the anti-adhesion effect could be invalid. The bearing ratio curve was employed to analysis tool-chip contact and durability of textured surfaces contributing to a better understanding of anti-adhesion and enhanced durability of the textured tools.

• Journal of the Korean Society of Safety
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• v.33 no.6
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• pp.15-21
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• 2018

Ships may collide with reefs or other objects during operation, when arriving or departing ports. The hull plate may be damaged due to the contact with other ships. The total number of domestic powered fishing vessels has decreased, but that of FRP fishing vessels has increased by 0.7% and the ratio of FRP fishing vessels to the total fishing vessels increased to 96%. Recently, fishing vessels has been used as fishing boats for income of non-fishermen as well as fishermen. Therefore, safety management for repair and maintenance is necessary. The penetration of moisture and moisture in the composite material such as FRP may deteriorate the mechanical properties and the salt (NaCl) component of the damaged portion may cause a relatively high deterioration in material strength. The gel coat painting is the final stage of repairs ans maintenance of FRP fishing vessels. The thickness criteria in the domestic and foreign gel coat is 0.3~0.762 mm. The joint specimens, which was immersed in seawater for 120 days, were compared with those without seawater immersion. As a result, the tensile strength was 83 ~ 121.8% and the flexural strength was 83 ~ 113% compared with the specimens without seawater immersion. According to the previous study the tensile strength decreased by more than 29% and the flexural strength decreased by more than 50% when the composite material was immersed in seawater for 1,083 hours without coating. As a result, it was found that the gel coat with 0.5 mm thickness is very effective in preventing the strength decrease of the composite material.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.35 no.2
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• pp.21-28
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• 2019

Handmade hydrated lime has been used for preservation and repair of architectural heritage in Korea. However, the effect of the amount of water used for slaking quicklime on the physical and chemical properties of the hydrated lime, which is the result of the slaking process, has not been clearly understood. In this study, particle size distribution, chemical composition and crystalline phases of the hydrated lime are investigated by varying the amount of water used for the slaking. In addition, temperature history during the slaking process is examined. For this, various experiments, such as laser diffraction analysis, X-ray fluorescence, X-ray diffraction, thermogravimetric analysis, and temperature recording using a thermocouple, were performed. When the quicklime came into contact with water, its temperature reached $100^{\circ}C$ within 10 min due to sudden exothermic reaction of calcium oxide, and this temperature was maintained for about 30 min. The water to lime ratio influenced the cooling rate during the slaking process; that is, the more water was used, the longer it took to reach an ambient temperature. The amount of water for the slaking did not have a noticeable effect on the contents of major components of the hydrated lime such as calcium hydroxide and calcium carbonate, but when slaked with more amount of water, average particle size of the lime tended to decrease. The experimental results in this study can be used as references for developing guidelines on the safety or appropriate amount of water in the lime slaking process.