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Kwak, Cheol Hwan,Kang, Sung-Min,Jung, Euiyoung,Haldorai, Yuvaraj,Han, Young-Kyu,Kim, Woo-Sik,Yu, Taekyung,Huh, Yun Suk THE KOREAN SOCIETY OF INDUSTRIAL AND ENGINEERING 2018 JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY -S Vol.63 No.-
<P><B>Abstract</B></P> <P>A customized droplet-based microfluidic reactor was fabricated for the synthesis of silver nanoparticles (Ag NPs) using silver nitrate (AgNO<SUB>3</SUB>) and branched polyethyleneimine (BPEI) as a precursor and a reducing agent, respectively. The effects of static mixing, temperature, and the volumetric flow rates of AgNO<SUB>3</SUB> and BPEI on the particle size were investigated. The use of a static mixer and the optimization of the reaction temperature enhanced the monodispersity of the Ag NPs. In addition, the size of the Ag NPs was manipulated by changing the flow rate ratio of AgNO<SUB>3</SUB> to BPEI at 60°C for 60min.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Lee, Taekyung,Kwak, Byung Je,Kong, Taein,Lee, Jeong Hun,Lee, Sang Won,Park, Sung Hyuk ELSEVIER SCIENCE 2019 JOURNAL OF ALLOYS AND COMPOUNDS Vol.803 No.-
<P><B>Abstract</B></P> <P>This study investigated a caliber-rolled Mg–6Zn-0.5Zr (ZK60) alloy as part of an effort to achieve enhanced mechanical properties and bulk dimension out of lab scale. The caliber-rolled ZK60 alloy presented a high fraction of dynamically recrystallized (DRXed) grains with submicron sizes. The alloy also exhibited simultaneous improvements in strength and ductility in comparison to commercially extruded ZK60 alloys. The ultrafine-grained (UFG) structure and enhanced mechanical properties were attained while maintaining bulk dimension, which was difficult with severe plastic deformation processes. Furthermore, caliber rolling gave rise to nearly symmetric behavior in terms of yielding. These mechanical improvements in the caliber-rolled ZK60 alloy were interpreted in light of its microstructural characteristics, such as UFG structure, DRX, precipitates, basal texture with tilting of <I>c</I>-axes, and activation of mechanical twinning.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A caliber-rolled ZK60 alloy was investigated for the first time. </LI> <LI> It showed a high frequency of dynamic recrystallization comprising ultrafine grains. </LI> <LI> It showed the enhanced strength-ductility balance and yield symmetry. </LI> <LI> Effective grain refinement and dynamic recrystallization led to the improvements. </LI> <LI> Suppressed activation of extension twinning also contributed to the improvements. </LI> </UL> </P>
Lim, Guh-Hwan,Kwak, Sung Soo,Kwon, Nayoung,Kim, Taekyung,Kim, Han,Kim, Seong Min,Kim, Sang-Woo,Lim, Byungkwon Elsevier 2017 Nano energy Vol.42 No.-
<P><B>Abstract</B></P> <P>A patchable triboelectric nanogenerator (TENG) is highly promising for self-powered human-motion detection, but it may undergo repeated stretching/releasing cycles during daily activities of a human, which may lead to mechanical fracture of each component and degradation in electrical output performance of the TENG device. Here, we report a fully stretchable and durable triboelectric nanogenerator (TENG) with gold (Au) nanosheets (NSs) embedded into both PDMS matrix and micropyramid-patterned PDMS. It was found that a new design of the Au NS electrodes dramatically improves the mechanical flexibility and stretchability, enabling to achieve the outstanding output stability of the Au NS electrode-based TENG (Au NS-TENG) during 10,000 cycles of repeated pushing and stretching tests. Our fully stretchable and durable Au NS-TENGs were successfully applied to the hand joints that can be used in the self-powered human-motion detection processes for wearable applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We report a fully stretchable and durable triboelectric nanogenerator (TENG). </LI> <LI> The TENG consisted of gold nanosheet (Au NS)-embedded elastomer electrodes. </LI> <LI> Au NS-TENG showed excellent output stability during pushing and stretching tests. </LI> <LI> Au NS-TENGs were successfully applied for self-powered human-motion detection. </LI> </UL> </P> <P><B>Graphic abstract</B></P> <P>Fully stretchable and durable triboelectric nanogenerator with gold nanosheet embedded into both PDMS matrix and micro pyramid patterned PDMS has been successfully demonstrated in both pushing and stretching modes, then the durability test with 10,000 cycles. As our device is applied to hand joints, the possibility of self-powered systems as power source for wearable applications has been shown.</P> <P>[DISPLAY OMISSION]</P>
Service Mobility Management System using XML Security in the OSGi Service Platform
Sangkyun Nam,Taehun Kim,Taekyung Sung,Kyungsup Kwak 대한전자공학회 2007 ITC-CSCC :International Technical Conference on Ci Vol.2007 No.7
In this paper, we propose a service mobility management system using XML security in the OSGi service platform. We design a method that includes service order information to XML signature to reduce processing, and propose a service bundle authentication mechanism, which is signed by XML signature. As a result, the mobility of services in OSGi-based residential gateways can be supported more safely and efficiently.
Seamless lamination of a concave-convex architecture with single-layer graphene.
Park, Ji-Hoon,Lim, Taekyung,Baik, Jaeyoon,Seo, Keumyoung,Moon, Youngkwon,Park, Noejung,Shin, Hyun-Joon,Kyu Kwak, Sang,Ju, Sanghyun,Real Ahn, Joung RSC Pub 2015 Nanoscale Vol.7 No.43
<P>Graphene has been used as an electrode and channel material in electronic devices because of its superior physical properties. Recently, electronic devices have changed from a planar to a complicated three-dimensional (3D) geometry to overcome the limitations of planar devices. The evolution of electronic devices requires that graphene be adaptable to a 3D substrate. Here, we demonstrate that chemical-vapor-deposited single-layer graphene can be transferred onto a silicon dioxide substrate with a 3D geometry, such as a concave-convex architecture. A variety of silicon dioxide concave-convex architectures were uniformly and seamlessly laminated with graphene using a thermal treatment. The planar graphene was stretched to cover the concave-convex architecture, and the resulting strain on the curved graphene was spatially resolved by confocal Raman spectroscopy; molecular dynamic simulations were also conducted and supported the observations. Changes in electrical resistivity caused by the spatially varying strain induced as the graphene-silicon dioxide laminate varies dimensionally from 2D to 3D were measured by using a four-point probe. The resistivity measurements suggest that the electrical resistivity can be systematically controlled by the 3D geometry of the graphene-silicon dioxide laminate. This 3D graphene-insulator laminate will broaden the range of graphene applications beyond planar structures to 3D materials.</P>
Tang, Zengmin,Park, Ju Hyun,Kim, Su Hwan,Kim, Jaemin,Mun, Junyoung,Kwak, Sang Kyu,Kim, Woo-Sik,Yu, Taekyung Elsevier 2018 JOURNAL OF ALLOYS AND COMPOUNDS Vol.764 No.-
<P><B>Abstract</B></P> <P>Copper sulfide (Cu<SUB>7</SUB>S<SUB>4</SUB>) nanoparticles were synthesized by adding ethanolic elemental sulfur solution to an aqueous solution containing Cu(II) precursor, branched polyethyleneimine (BPEI), and ascorbic acid. By varying the Cu(II) precursor used, we could control the morphology of the nanoparticles produced to be either quasi spherical (CuF<SUB>2</SUB>, Cu(NO<SUB>3</SUB>)<SUB>2</SUB>, and CuSO<SUB>4</SUB>) or vine like nanofibers (CuCl<SUB>2</SUB> and CuBr<SUB>2</SUB>). By comparing experimental results and conducting calculations we found that selective adsorption of Br<SUP>−</SUP> and Cl<SUP>−</SUP> onto specific crystal facets and slowing of the reaction rate owing to formation of Cu(I)–anion–BPEI complexes explain the observed change in morphology from spherical particles to vine like nanofibers. We also found that the differences in morphology of Cu<SUB>7</SUB>S<SUB>4</SUB> nanoparticles affects the electrochemical performance of Li batteries including the nanoparticles as electrode materials.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A facile aqueous synthesis of Cu<SUB>7</SUB>S<SUB>4</SUB> nanofibers and spherical nanoparticles. </LI> <LI> Experiments and calculations reveal the importance of Cl<SUP>−</SUP> and Br<SUP>−</SUP> in the formation of nanofibers. </LI> <LI> Slow reaction rate also leads to the formation of nanofibers. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>By means of experiments and calculations, we found that selective adsorption of Br<SUP>−</SUP> and Cl<SUP>−</SUP> onto specific crystal facets and slowing of the reaction rate by formation of Cu(I)-anion-BPEI complex leads to morphology changes of Cu<SUB>7</SUB>S<SUB>4</SUB> nanoparticles, from spherical particles to vinelike nanofibers.</P> <P>[DISPLAY OMISSION]</P>
The Effect of Everyday Creativity and Communication Ability on Self-Leadership in Nursing Students
SiHyeon Park,MyungHoon Kim,GaRam Park,SeungWon Shin,SuIn Lee,SooJin Chae,TaeKyung Kwak,BonJin Koo 한국성인간호학회 2021 성인간호학회 학술대회 Vol.2021 No.8
Aim(s): Recently, as the importance of providing medical information to patients and guaranteeing their rights is emphasized, autonomous leadership development of medical staff is emphasized in providing quality medical services. In particular, daily creativity and appropriate and efficient communication skills, which are concepts that improve self-actualization and adaptability in new and unique ways, are identified as factors that can develop self-leadership. The purpose of this study was to investigate the effect of everyday creativity and communication ability to self-leadership of nursing students. Method(s): The study conducted 157 nursing students in the first and third grades who agree with study participation. Data were collected using a structured questionnaire from August to October 2020. SPSS/WIN 25.0 program was used to conduct statistical analyses, including descriptive statistics, an independent t-test, a one-way analysis of variance, and stepwise multiple linear regression. Result(s): Self-leadership based on general characteristics showed statistically significant differences in grade, economic level, and way of living. Also everyday creativity and communication skills showed statistically significant differences in gender. Self-leadership of nursing students showed that statistically significant positive correlations in the order of everyday creativity (r=.881, p<.01), communication ability (r=.829, p<.01). Stepwise multiple linear regression demonstrated that everyday creativity explained 59.0% of the variance in self-leadership. Conclusion(s): Through this study, positive correlation was confirmed between self-leadership, everyday creativity, and communication ability of nursing students, and it was found that everyday creativity has the greatest influence on self-leadership. Therefore, it suggests that further research is needed on the development and effectiveness of self-leadership programs that can improve everyday creativity and communication skills of nursing students.