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Young Sil Lee,Kwan Han Yoon 한국탄소학회 2015 Carbon Letters Vol.16 No.2
Multi-walled carbon nanotube (MWCNT)/polycarbonate (PC) nanocomposite was prepared by direct melt mixing to investigate the effect of the shear rate on the surface resistivity of the nanocomposites. In this study, an experiment was carried out to observe the shear induced orientation of the MWCNT in the polymer matrix using a very simple melt flow indexer with various loads. The compression-molded, should be eliminated. MWCNT/PC nanocomposite sample exhibited lower percolation thresholds (at 0.8 vol%) and higher electrical conductivity values than those of samples extruded by capillary and injection molding. Shear induced orientation of MWCNT was observed via scanning electron microscopy, in the direction of flow in a PC matrix during the extrusion process. The surface resistivity rose with increasing shear rate, because of the breakdown of the network junctions between MWCNTs. For real applications such as injection molding and the extrusion process, the amount of the MWCNT in the composite should be carefully selected to adjust the electrical conductivity.
지도자의 코칭행동이 중·고교 검도선수들의 팀 침묵현상 및 대처효율성에 미치는 영향
이실관(Lee Sil Kwan),이기경(Lee Ki Kyung),남인수(Nam In Soo) 학습자중심교과교육학회 2018 학습자중심교과교육연구 Vol.18 No.3
이 연구는 지도자의 코칭행동이 중 고교 검도선수들의 팀 침묵현상 및 대처효율성에 미치는 영향을 규명하는 데에 그 목적을 두었다. 이를 위해 자료 수집은 2016년 6월 3일부터 6월 5일까지 제25회 회장기 전국 중 고교 검도대회에 참여한 중 고교검도선수들을 대상으로 하였으며, 표본추출방법은 집락표집방법을 이용하였다. 수집된 설문 자료 중에서 507명의 자료를 최종적으로 분석에 이용하였다. 분석한 결과는 다음과 같다. 첫째, 지도자의 코칭행동과 팀 침묵현상의 관계에서 자율적 코칭행동은 방어적 침묵과 체념적 침묵에 부적 영향을 주는 반면에, 통제적 코칭행동은 방어적 침묵과 체념적 침묵에 정적 영향을 주는 것으로 나타났다. 둘째, 지도자의 코칭행동과 대처효율성의 관계에서 자율적 코칭행동은 문제중심적 대처, 초연 대처, 정서중심적 대처에 정적 영향을 주는 것으로 나타났다. 자율적 코칭행동은 회피 대처에 부적 영향을 주는 반면에, 통제적 코칭행동은 회피 대처에 정적 영향을 주는 것으로 나타났다. 셋째, 팀 침묵현상과 대처효율성의 관계에서 방어적 침묵과 체념적 침묵은 문제중심적 대처와 초연 대처에 부적 영향을 주는 반면에, 회피 대처에 정적 영향을 주는 것으로 나타났다. 이 연구의 결론에 미루어 볼 때, 지도자의 코칭행동은 검도선수들의 팀 침묵현상과 대처효율성 간에 밀접한 관련성이 있음을 확인하였다. The purpose of this study is to identify the effect of leaders coaching behavior on team silence and copy effectiveness of a middle and high school kumdo players. The subjects of this study consisted of 507 middle and high school kumdo players. The used instruments were the Park & Kim(2013) for measuring coaching behaviors scales, the Ko(2014) for measuring team silence scales, and the Kang(2012) for measuring copy effectiveness scales. The data were analyzed by descriptive statistics, frequency analysis, correlation analysis, reliability analysis, factor analysis, and multiple regression analysis as a statistical method. The result of this study were as follows. First, in the relationship between coaching behavior and team silence, autonomy coaching behaviors negatively influenced to defensive silence and acquiescent silence. But, controlled coaching behaviors positively influenced to defensive silence and acquiescent silence. Second, in the relationship between coaching behavior and copy effectiveness, autonomy coaching behaviors positively influenced to problem focused coping, detached coping, emotional focused coping. And autonomy coaching behaviors negatively influenced to avoidance coping but, controlled coaching behaviors positively influenced to avoidance coping. Third, in the relationship between team silence and copy effectiveness, defensive silence and acquiescent silence negatively influenced to problem focused coping and detached coping. defensive silence and acquiescent silence positively influenced to avoidance coping. In conclusions of this study, it demonstrated that leaders coaching behavior was closely related to team silence and copy effectiveness of kumdo players.
Fractal Nature of Magnetic Colloidal Dispersion with Cobalt Iron Oxide and Metal Iron Particles
( Kwan Han Yoon ),( Young Sil Lee ) 한국화학공학회 2022 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.60 No.1
The microstructure of highly aggregated colloidal dispersions was investigated by probing the rheological behavior of magnetic suspensions. The dynamic moduli as functions of frequency and strain amplitude are shown to closely resemble that of colloidal gels indicating the formation of network structure. The two types of characteristic critical strain amplitudes, γ<sub>c</sub> and γ<sub>y</sub>, were characterized in terms of the changing microstructure. The amplitude of γ<sub>c</sub> indicates the transition from linear to nonlinear viscoelasticity and depends only on particle volume fraction not magnetic interactions. The study of scaling behavior suggests that it is related to the breakage of interfloc, i.e., floc-floc structure. However, yielding strain, γ<sub>y</sub>, was found to be independent of particle volume fraction as well as magnetic interaction. It relates to extensive deformation resulting in yielding behavior. The scaling of elastic constant, G<sub>e</sub>, implies that this yielding behavior and hence γ<sub>y</sub> is due to the breakage of long-range interfloc interactions. Also, the deformation of flocs due to increase strain was indicated from the investigation of the fractal nature.
Kwan Han Yoon,Young Sil Lee 한국탄소학회 2019 Carbon Letters Vol.29 No.1
Effects of multi-walled carbon nanotube (MWCNT) type and flow type (shear and elongational flow) on the electrical conductivity of polycarbonate (PC)/MWCNT nanocomposites were investigated. Two different MWCNTs produced a huge difference in electrical conductivity in an injection molded PC/MWCNT nanocomposite. It was observed that MWCNTs having a higher aspect ratio provide much lower electrical conductivity in injection molded PC/MWCNT nanocomposites while the conductivities of compression molded samples from two different MWCNTs were the same. We found that this is due to a difference in the deformability of the two MWCNTs. Nanocomposite samples prepared at a higher extensional rate and shear rate showed lower electrical conductivity. This is attributed to flow induced orientation of the MWCNTs. The experimental results were discussed in relation to variation in the tube–tube contact due to the change of the MWCNT orientation.
Effects of combined radiofrequency radiation exposure on the cell cycle and its regulatory proteins
Lee, Kwan‐,Yong,Kim, Bong Cho,Han, Na‐,Kyung,Lee, Yun‐,Sil,Kim, Taehong,Yun, Jae‐,Hoon,Kim, Nam,Pack, Jeong‐,Ki,Lee, Jae‐,Seon Wiley Subscription Services, Inc., A Wiley Company 2011 BioElectroMagnetics Vol.32 No.3
<P><B>Abstract</B></P><P>The aim of this study was to investigate whether single or combined radio frequency (RF) radiation exposure has effects on the cell cycle and its regulatory proteins. Exposure of MCF7 cells to either single (837 MHz) or combined (837 and 1950 MHz) RF radiation was conducted at specific absorption rate values of 4 W/kg for 1 h. During the exposure period, the chamber was made isothermal by circulating water through the cavity. After RF radiation exposure, DNA synthesis rate and cell cycle distribution were assessed. The levels of cell cycle regulatory proteins, p53, p21, cyclins, and cyclin‐dependent kinases were also examined. The positive control group was exposed to 0.5 and 4 Gy doses of ionizing radiation (IR) and showed changes in DNA synthesis and cell cycle distribution. The levels of p53, p21, cyclin A, cyclin B1, and cyclin D1 were also affected by IR exposure. In contrast to the IR‐exposed group, neither the single RF radiation‐ nor the combined RF radiation‐exposed group elicited alterations in DNA synthesis, cell cycle distribution, and levels of cell cycle regulatory proteins. These results indicate that neither single nor combined RF radiation affect cell cycle progression. Bioelectromagnetics 32:169–178, 2011. © 2010 Wiley‐Liss, Inc.</P>
Chae-Sil Kim(김재실),Hoon-Hyung Jung(정훈형),Bong-Kwan Park(박봉관) 한국기계가공학회 2013 한국기계가공학회지 Vol.12 No.6
High speed rotor systems with magnetic bearings have been the subject of much research in recent years due to the potential for active vibration control. In this thesis, optimal design was conducted for an 8-pole heteropolar magnetic bearing used in the flexible rotor of a turbo blower. In connection with bearing stiffness, this optimal design process was conducted using a genetic algorithm(GA), which is based on natural selection and genetics. The maximum stiffness of the magnetic bearing-rotor was found by considering the critical speeds of the flexible rotor. As a result, the magnetic bearings were optimized to have maximum stiffness.