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Effects of the Ergonomic Lap Board for Computer Mouse Padding on Upper Limb Movements, Myoelectric Activities, Task Performance, and Subjective Discomfort (인체공학적 랩보드를 이용한 컴퓨터 마우스 사용이 상지의 움직임 및 근활성도, 작업수행도, 주관적 불편도에 미치는 영향)

  • Park, So-Yeon;Lee, Taek-Young;Yi, JinBock
    • The Journal of the Korea Contents Association
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    • v.13 no.2
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    • pp.348-358
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    • 2013
  • This study aimed to investigate the effect of a lap board that was developed to prevent musculoskeletal disorders caused by the use of a computer mouse. Study participants were 10 college students in their 20s who did not have any musculoskeletal symptoms. We analyzed the difference in upper limb movements, electromyographic activity, task performance, and subjective discomfort between 2 conditions: use of a mouse with the lap board and use of a mouse placed on a desk. Results of behavior analysis showed that there was a significant difference between the 2 conditions in terms of the average angle of shoulder flexion, shoulder internal rotation, and forearm pronation(p< 0.05). However, electromyographic activity, task performance, and subjective discomfort showed no significant differences between the 2 conditions. When subjects used the mouse with the lap board, their upper extremity was located much closer to the torso than when they used the mouse placed on the desk. Six of 10 participating students preferred the lap board. We expect that advanced research on prevention of musculoskeletal disorders due to the use of the computer mouse will be conducted in the near future.

Effect of Sc Addition on Microstructure, Electrical Conductivity, Thermal Conductivity and Mechanical Properties of Al-2Zn-1Cu-0.3Mg Based Alloy (Al-2Zn-1Cu-0.3Mg합금의 Sc첨가에 따른 미세조직, 전기전도도, 열전도도 및 기계적 특성 변화)

  • Na, Sang-Su;Kim, Yong-Ho;Son, Hyeon-Taek;Lee, Seong-Hee
    • Korean Journal of Materials Research
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    • v.30 no.10
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    • pp.542-549
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    • 2020
  • Effects of Sc addition on microstructure, electrical conductivity, thermal conductivity and mechanical properties of the as-cast and as-extruded Al-2Zn-1Cu-0.3Mg-xSc (x = 0, 0.25, 0.5 wt%) alloys are investigated. The average grain size of the as-cast Al-2Zn-1Cu-0.3Mg alloy is 2,334 ㎛; however, this value drops to 914 and 529 ㎛ with addition of Sc element at 0.25 wt% and 0.5 wt%, respectively. This grain refinement is due to primary Al3Sc phase forming during solidification. The as-extruded Al-2Zn-1Cu-0.3Mg alloy has a recrystallization structure consisting of almost equiaxed grains. However, the as-extruded Sc-containing alloys consist of grains that are extremely elongated in the extrusion direction. In addition, it is found that the proportion of low-angle grain boundaries below 15 degree is dominant. This is because the addition of Sc results in the formation of coherent and nano-scale Al3Sc phases during hot extrusion, inhibiting the process of recrystallization and improving the strength by pinning of dislocations and the formation of subgrain boundaries. The maximum values of the yield and tensile strength are 126 MPa and 215 MPa for the as-extruded Al-2Zn-1Cu-0.3Mg-0.25Sc alloy, respectively. The increase in strength is probably due to the existence of nano-scale Al3Sc precipitates and dense Al2Cu phases. Thermal conductivity of the as-cast Al-2Zn-1Cu-0.3Mg-xSc alloy is reduced to 204, 187 and 183 W/MK by additions of elemental Sc of 0, 0.25 and 0.5 wt%, respectively. On the other hand, the thermal conductivity of the as-extruded Al-2Zn-1Cu-0.3Mg-xSc alloy is about 200 W/Mk regardless of the content of Sc. This is because of the formation of coherent Al3Sc phase, which decreases Sc content and causes extremely high electrical resistivity.

Analysis for Linear Type Classification Scheme on Holstein Cows in Korea (국내 홀스타인종 젖소의 선형형질의 점수제 분석)

  • Choi, Te-Jeong;Cho, Kwang-Hyun;Lee, Ki-Hwan;Sang, Byeong-Chan
    • Journal of Animal Science and Technology
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    • v.51 no.2
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    • pp.97-104
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    • 2009
  • Complement of test standard, evaluation methods and models are needed to improve national competitiveness and to exchange superior genetic resources through the comparison of genetic evaluation score among nations in dairy cattle. Therefore, this study was conducted for the application of international standard to Korea considering domestic circumstance by changing linear-classification test score system of 50 classes which is currently used in Korea to system of 9 classes which is used in advanced nations of dairy. 15,230 of holstein cow linear type records with first parity records for the fifteen linear type and one total score from 2001 to 2006 and pedigree data which were collected by the Korean Animal Improvement Association were used in this study. Population classified by 9 levels was more normal distributed than 50 levels. Correlation coefficients between 50 and 9 score system showed over 0.98 by each classification scheme. Therefore, the 50 point system can be substituted with 9 point system due to their highly positive correlation. However, scores in all traits were still very contingent on classifier under the 9 point system (p<0.001), and F values between foot angle and front teat attachment showed high fluctuation depending on classifier. It means that subjective opinions of classifier would influence on linear type score as ever even if class scheme transformed to system of 9 class. Therefore, the relevance of transformation to the 9 point system should be assessed after analyses about various environmental factors.

A Study on Mechanical Interfacial Properties of Copper-plated Carbon Fibers/Epoxy Resin Composites (구리도금된 탄소섬유/에폭시 수지 복합재료의 기계적 계면 특성에 관한 연구)

  • Hong, Myung-Sun;Bae, Kyong-Min;Choi, Woong-Ki;Lee, Hae-Seong;Park, Soo-Jin;An, Kay-Hyeok;Kim, Byung-Joo
    • Applied Chemistry for Engineering
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    • v.23 no.3
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    • pp.313-319
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    • 2012
  • In this work, the electroplating of copper was introduced on PAN-based carbon fibers for the enhancement of mechanical interfacial strength of carbon fibers-reinforced composites. The surface properties of carbon fibers were determined by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and contact angle measurements. Its mechanical interfacial properties of the composites were studied by interlaminar shear strength (ILSS) and critical stress intensity factor ($K_{IC}$). From the results, it was found that the mechanical interfacial properties of Cu-plated carbon fibers-reinforced composites (Cu-CFRPs) enhanced with increasing the Cu plating time, Cu content and COOH group up to Cu-CFRP-30. However, the mechanical interfacial properties of the Cu-CFRPs decreased dramatically in the excessively Cu-plated CFRPs sample. In conclusion, the presence of Cu particles on carbon fiber surfaces can be a key factor to determine the mechanical interfacial properties of the Cu-CFRPs, but the excessive Cu content can lead the failure due to the interfacial separation between fibers and matrices in this system.

Generation of Longitudinal Twin of GaAs Single Crystal by LEC Method (LEC법 GaAs 단결정의 종단쌍정 발생)

  • Gang, Jin-Gi;Yu, Hak-Do;Park, Jong-Mok
    • Korean Journal of Crystallography
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    • v.2 no.1
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    • pp.1-11
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    • 1991
  • When GaAs single crystals are grown by LEC method, a serious problem is that longitudinal twins are often generated. the growth axis is changed from (100) to (221) direction by logitudinal twin. In this experiment, 3 inch GaAs single crystals, slaving (100) uonh axis, were von by LEC method. Striations and edge facets generated during crystal growth, were observed by SPW photo-etching. Relationship between striations and edge facets was studied. Instability of their generation was the cause of goneration of longitudinal twins. The shape of striations was changed with the growth conditions such as crystal diameter and melt volume. In the region of crystal edge: there was the microscopic fluctuation by the instability of melt convection. Edge facets consisting of {111} plane developed well in the region which striation were convex to the melt. Because the angle between striation and {111} edge facet decreased in that region. Longitudinal twins were generated on the crystal surface at the <111> direction which is perpendicular to the growth axis. These were generated by unstable melt convection and propagated in the crystal as crystal grew. Longitudinal twins were generated when regrowth rate was very fast after {111} edge facets were remelted. So, in order to supress the generation of longitudinal twin, abrupt change of melt convection must be prohibited.

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Formation of $CoSi_2$ Film and Double Heteroepitaxial Growth of $Si/epi-CoSi_2/Si$(111) by Solid Phase Epitaxy (고상 에피택시에 의한 초박막 $CoSi_2$ 형성과 $Si/epi-CoSi_2/Si$(111)의 이중헤테로 에피택셜 성장)

  • Choi, Chi-Kyu;Kang, Min-Sung;Moon, Jong;Hyun, Dong-Geul;Kim, Kun-Ho;Lee, Jeong-Yong
    • Korean Journal of Materials Research
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    • v.8 no.2
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    • pp.165-172
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    • 1998
  • Epitaxial ultrathin films of $CoSi_2$ and double heteroepitaxial structure of Si/$CoSi_2$/Si(lll) were prepared on Si(111)-$7\times{7}$ substrate by in situ solid-phase epitaxy in a ultrahigh vacuum(LHV). The phase, chemical composition, crystallinity, and the microsructure of the Si/$CoSi_2$/Si(lll) interface were investigated by 2-MeV $^4He^{++}$ ion backscattering spectrometry, X-ray diffraction, and high-resolution transmission electron microscopy. The growth mode of the Co film was the Stransky-Krastanov type with texture when the substrate temperature was room temperature. A-type $CoSi_2$ ultrathin film was grown by deposition of about 50A Co on Si(ll1)-$7\times{7}$ substrate followed by in situ annealing at $700^{\circ}C$ for 10 min. The matching face relationships were $CoSi_2$[110]//Si[110] and $CoSi_2$(002)//Si(002) with no misorientation angle. The A-type $CoSi_2$/Si(lll) interface was abrupt and coherent. The best epi-Si/epi-$CoSi_2$2(A-type)/Si(lll) structure was obtained by deposition of Si film on the CoSii at $500^{\circ}C$ followed by in situ annealing at $700^{\circ}C$ for 10 min in UHV.

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A Case of Giant Gastric Schwannoma Accompanied with Bleeding (출혈을 동반한 거대 위 신경초종 1예)

  • Kim, Je-Yeon;An, Ji-Yeong;Choi, Min-Gew;Noh, Jae-Hyung;Sohn, Tae-Sung;Kim, Sung
    • Journal of Gastric Cancer
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    • v.6 no.1
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    • pp.47-51
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    • 2006
  • The origin of a submucosal tumor is difficult to determine by endoscopic biopsy. One type of submucosal tumor, which originates in Schwann cell, a schwannoma represents 0.2% of all gastric tumors. We experienced the case of a 57-year-old female patient with a gastric schwannoma presenting with melena and anemia. Computed tomography and upper gastrointestinal endoscopy showed a protruded huge mass from 3 cm below the cardia to angle. Seven endoscopic biopsies indicated only necrotic debri and granulation tissue, chronic gastritis. Because we suspected an advanced gastric cancer, or lymphoma with bleeding, It was performed an operation for an exact diagnosis and a treatment for bleeding. A-post-operative histopathological, immunohistochemical examination led to the final diagnosis of a gastric schwannoma.

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Numerical analysis for heat transfer and pressure drop characteristics of (다양한 배플 인자에 따른 셀-튜브 열교환기의 열전달 및 압력강하 특성에 관한 수치해석)

  • Hou, Rong-Rong;Park, Hyeong-Seon;Yoon, Jun-Kyu;Lim, Jong-Han
    • Journal of Advanced Marine Engineering and Technology
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    • v.38 no.4
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    • pp.367-375
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    • 2014
  • In numbers of kinds of heat exchanger, the shell-tube heat exchanger is the most commonly used type of heat exchanger in the industry field. In order to improve the thermal performance of the heat exchanger, this study was analyzed heat transfer characteristics according to arrangement of baffle and direction of baffle and bump phase of baffle about shell-tube heat exchanger using appropriate SST (Shear Stress Transport) turbulence model for flow separation and boundary layer analysis. As the boundary condition for CFD (Computational Fluid Dynamics) analysis, the inlet temperature of shell side was constantly 344 K and the variation of the water flow rate was 6, 12, 18 and 24 l/min. As the result of analysis, zigzag baffle arrangement enhances heat transfer rate and pressure drop. Furthermore, in the direction of the baffle, heat transfer rate is more improved with vertical type and angle $45^{\circ}$ type than existing type, and pressure drop was little difference. Also, the bump shape of baffle surface contributes to heat transfer rate and pressure drop improvement due to the increased heat transfer area. Through analysis results, we knew that the increase of the heat transfer was influenced by flow separation, fluid residual time, contact area with the tube, flow rate, swirl and so on.

Optical Analysis for Designing a Planar Solar Concentrator Based on Light Guide System (광도파 원리의 평면형 태양광 집광기 설계를 위한 광학해석)

  • Han, Jong-Ho;Kim, Jong-Sun;Hwang, Chul-Jin;Yoon, Kyung-Hwan;Kang, Jeong-Jin
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.36 no.1
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    • pp.9-16
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    • 2012
  • Recently, an optics-based concentrator for solar concentration has been a key issue in development of photovoltaic systems. In the present study, a new, simple, easily producible planar concentrator based on a light guide system is proposed. In this device, solar light is concentrated by microprism optical patterns guiding the light, mainly through total reflection and refraction. The main design variables of the concentrator are the geometric concentration ratio ($R_c$) and the ${\Theta}_1$ and ${\Theta}_2$ of the microprism pattern. Ray tracing was simulated using commercial software, SPEOS, and the optical efficiencies of the light guide solar concentrator were predicted in each case. The predicted maximum optical efficiencies are 65.60%, 54.78%, and 46.78%, respectively, for $R_c$ values of 4, 5, and 6. The variation of the optical efficiencies according to ${\Theta}_1$, ${\Theta}_2$, and the incline angle of the incident light were predicted.

Plasma Surface Modification of Graphene and Combination with Bacteria Cellulose (Graphene의 플라즈마 표면 개질과 박테리아 셀룰로오스와의 결합성 검토)

  • Yim, Eun-Chae;Kim, Seong-Jun;Oh, Il-Kwon;Kee, Chang-Doo
    • Korean Chemical Engineering Research
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    • v.51 no.3
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    • pp.388-393
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    • 2013
  • The study was focused to evaluate the possibility for combination membrane of bacterial cellulose (BC) and graphene with high electrical properties. BC with natural polymer matrix was known to have strong physical strength. For the combination of graphene with BC, the surface of graphene was modified with oxygen plasma by changing strength and time of radio waves in room temperature. Water contact angle of modified graphene grew smaller from $130^{\circ}$ to $12^{\circ}$. XPS analysis showed that oxygen content after treatment increased from 2.99 to 10.98%. Damage degree of graphene was examined from $I_D/I_G$ ratio of Raman analysis. $I_D/I_G$ ratio of non-treated graphene (NTG) was 0.11, and 0.36 to 0.43 in plasma treated graphene (PTG), increasing structural defects of PTG. XRD analysis of PTG membrane with BC was $2{\theta}$ same to BC only, indicating chemically combined membrane. In FT-IR analysis, 1,000 to 1,300 $cm^{-1}$ (C=O) peak indicating oxygen radicals in PTG membrane had formed was larger than NTG membrane. The results suggest that BC as an alternation of plastic material for graphene combination has a possibility in some degree on the part like transparent conductive films.