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K.-H. IM,N.-S. PARK,Y.-N. KIM,L.-Y. YANG 한국자동차공학회 2003 International journal of automotive technology Vol.4 No.4
This paper describes a method for a falling weight impact test to estimate the impact energy absorbing characteristics and impact strength of CFRP (Carbon-fiber reinforced plastics) laminate plates based on considerations of stress wave propagation theory, which were converted to measurements of load and displacement verses time. The delamination area of impacted specimens for the different ply orientations was measured with an ultrasonic C-scanner to determine the correlation between impact energy and delamination area. The energy absorbed by a quasi-isotropic specimen having four interfaces was higher than that of orthotropic laminates with two interfaces. The more interfaces, the greater the energy absorbed. The absorbed energy of a hybrid specimen embedding GFRP (Glass-fiber reinforced plastics) layer was higher than that of normal specimens. Also, a falling weight impact tester was built to evaluate the characteristics and impact strength of CFRPs.
Electrical conductivity enhancement of epitaxially grown TiN thin films
Khim Yeong Gwang,Park Beomjin,Heo Jin Eun,Khim Young Hun,Khim Young Rok,Gu Minseon,Rhee Tae Gyu,Chang Seo Hyoung,Han Moonsup,Chang Young Jun 한국물리학회 2023 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.82 No.5
Titanium nitride (TiN) presents superior electrical conductivity with mechanical and chemical stability and compatibility with the semiconductor fabrication process. Here, we fabricated epitaxial and polycrystalline TiN (111) thin flms on MgO (111), sapphire (001), and mica substrates at 640℃ and room temperature by using a DC sputtering, respectively. The epitaxial flms show less amount of surface oxidation than the polycrystalline ones grown at room temperature. The epitaxial flms show drastically reduced resistivity (~ 30 micro-ohm-cm), much smaller than the polycrystalline flms. Temperature-dependent resistivity measurements show a nearly monotonic temperature slope down to low temperature. These results demonstrate that high-temperature growth of TiN thin flms leads to signifcant enhancement of electrical conductivity, promising for durable and scalable electrode applications.
Khim, Boo-Keun,Yoon, Ho-Il,Kang, Cheon-Yun,Zhao, Junlin Korea Institute of Ocean ScienceTechnology 2004 Ocean and Polar Research Vol.26 No.3
A sediment core drilled from Lake langer on King George Island was analyzed for a variety of textural md geochemical properties along with $^{14}C$ age dates. These data were combined with published records of other cores to provide a detailed history of Holocene variation of total organic carbon (TOC) contents with respect to terrestrial paleoclimate change. The lithologic contrast of the lower diamicton and upper fine-grained sediments shows the glacier activity and subsequent lake formation. Low TOC contents fluctuated during the diamicton deposition whereas the increase of TOC began with the lake formation during the postglacial period that started about 5,000 yr B.p More notable are the distinct TOC peaks that may imply enhanced primary productivity during the warm period. The uniform and low TOC contents may reflect the limited productivity during the evolution of the lake. However, the recent TOC readvance clearly indicates gradual warming on King George Island. However, the paleoclimatic signature in the terrestrial lake environment during the Holocene seems to be subtle and less distinct, compared to the marine environment.
A Three-axis Translation Stage Using Opposing Wedges with Error Compensation
Khim, Gyung-Ho,Ro, Seung-Kook,Park, Jong-Kweon,Ehmann, Kornel 한국정밀공학회 2012 International Journal of Precision Engineering and Vol.13 No.3
We describe the development of a three-axis translation stage using wedges and its motion error compensation. The three-axis stage uses three wedges and is capable of translation in the vertical and longitudinal directions by controlling the horizontal separation of two opposing wedges. An independent linear translation stage is used to achieve displacement along the third axis. Compensation for straightness and positioning errors is achieved using the combined motion of the two opposing wedges and the motion of an independent linear stage. The straightness error in the vertical and horizontal directions through the longitudinal axis was 0.83 ${\mu}m$ and 1.65 ${\mu}m$, respectively, before compensation and 0.22 ${\mu}m$ and 0.29 ${\mu}m$ with error compensation. The positioning error through the longitudinal axis was reduced from 8.96 ${\mu}m$ to 0.85 ${\mu}m$.
Khim, B.K.,Park, Y.H.,Bahk, J.J.,Jin, J.H.,Lee, G.H. Pergamon Press 2008 Quaternary international Vol.176 No.-
Geochemical (opal, total organic carbon (TOC), and CaCO<SUB>3</SUB>) analyses of three sediment cores from the South Korea Plateau in the East Sea (Japan Sea) revealed that the late Quaternary (<190kyr BP to the present) paleoceanographic conditions are characterized by the orbital variations of geochemical properties that have recorded the changes of surface- and bottom-water conditions. Chronostratigraphy of the sediment cores was accomplished by the direct correlation of L<SUP>*</SUP> values to the well-dated core MD01-2407 in Oki Ridge, supplement to the AMS <SUP>14</SUP>C dates, well-known lithostratigraphic and tephrostratigraphic markers. Biogenic opal concentrations are high during Marine Isotope Stage (MIS) 1 and MIS 5.5, and low during the glacial period, suggesting that diatom production was enhanced during the warm period when the surface-water exchange between the East Sea and adjacent marginal seas was active. In contrast, glacial opal paleoproductivity appears to have been depressed, probably because of insufficient nutrient availability, resulting from limited vertical ventilation. Overall TOC contents follow the orbital variations; high during the interglacial and relatively low during the glacial time. However, high-resolution TOC fluctuations are independent of opal concentration, which may be attributed more to the preservation of organic matter rather than to the surface-water production. The high TOC contents in the thin dark mud (i.e., TL) layers may be due to the enhanced surface-water production as well as the intensified bottom-water anoxia. On the other hand, high CaCO<SUB>3</SUB> contents associated with the TL layers during the glacial and stadial period may be attributed to the reduced dissolution. The temporal variations of these geochemical properties are likely to follow the global orbital cycles, indicating the significant changes of surface- and bottom-water properties due to the eustatic sea-level fluctuations between the interglacial and glacial period. The comparable values of these geochemical properties among the sediment cores suggest that the spatial paleoceanographic conditions in the South Korea Plateau were consistent and uniform during the late Quaternary, in spite of a little local discrepancy in amounts of properties and timing of events.
Analysis of 5-DOF Motion Errors Influenced by the Guide Rails of an Aerostatic Linear Motion Stage
Khim, Gyungho,Oh, Jeong Seok,Park, Chun Hong 한국정밀공학회 2014 International Journal of Precision Engineering and Vol.15 No.2
This paper presents an estimation method for five-degrees-of-freedom (5-DOF) motion errors, which are influenced by the profiles of guide rails of an aerostatic linear motion stage. The transfer function, which is the relationship between the magnitude of the rail form error and the reaction force of a bearing pad, was introduced to simplify and systematize the estimation of the motion errors. The motion errors were calculated from the equilibrium conditions for the forces and moments of the stage using the geometrical relationships between the bearing pads, the transfer function, and rail form errors. Experimental verification of the rail form error was carried out using a porous aerostatic linear motion stage and the mixed sequential two-probe method. The aerostatic feed table of the experimental stage, on which sensors were mounted, was also used as the feed unit for measuring the rail profiles. The 5-DOF motion errors were estimated from the measured rail form errors using the transfer function method. The estimated results were in good agreement with the experiments.
A Vacuum-Compatible Air Bearing: Design Analysis and Optimization
Khim, G.H.,Park, Chun Hong,Lee, H.S.,Kim, S.W. Trans Tech Publications, Ltd. 2007 Key Engineering Materials Vol.339 No.-
<P>This paper describes the vacuum-compatible air bearing designed with a cascaded exhaust scheme to minimize the leakage of air in a vacuum environment. The design of the air bearing, including the differential exhaust system, required great care because several design parameters, such as the number of exhaust stages, diameter and length of the exhaust tube, pumping speed and ultimate pressure of the vacuum pump, and seal length and gap greatly influenced the leakage of air and thus the degree of vacuum. A leakage analysis was performed to estimate the chamber pressure and an optimization method based on the genetic algorithm was proposed under several constraint conditions. The results showed that the degree of vacuum improved dramatically compared to the initial design, and that the distribution of the spatial design parameters and technical limit of the pumping speed were well achieved.</P>