A STUDY ON IMPACT CHARACTERISTICS OF THE STACKING SEQUENCES IN CFRP COMPOSITES SUBJECTED TO FALLING-WEIGHT IMPACT LOADING

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.

Control of Threshold Voltage for Top-Gated Ambipolar Field-Effect Transistor by Gate Buffer Layer

Khim, Dongyoon,Shin, Eul-Yong,Xu, Yong,Park, Won-Tae,Jin, Sung-Ho,Noh, Yong-Young American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.27

<P>The threshold voltage and onset voltage for p-channel and n-channel regimes of solution-processed ambipolar organic transistors with top-gate/bottom-contact (TG/BC) geometry were effectively tuned by gate buffer layers in between the gate electrode and the dielectric. The work function of a pristine Al gate electrode (-4.1 eV) was modified by cesium carbonate and vanadium oxide to 2.1 and 5.1 eV, respectively, which could control the flat -band voltage, leading to a remarkable shift of transfer curves in both negative and positive gate voltage directions without any side effects. One important feature is that the mobility of transistors is not very sensitive to the gate buffer layer. This method is simple but useful for electronic devices where the threshold voltage should be precisely controlled, such as ambipolar circuits, memory devices, and light -emitting device applications.</P>

Stable Isotope Profiles of the Fossil Mollusks from Marginal Marine Environment: Is Carbon from the Seasonal Methanogenesis?

Khim, Boo-Keun,Bock, Kathy-W.,Krantz, David-E. The Korean Society of Oceanography 1997 Journal of the Korean Society of Oceanography Vol.32 No.2

Stable isotope profiles with fine-scale resolution were constructed from the fossil mollusk shells, Mercernaria mercernaria, obtained from the late Pleistocene transgressive deposits of Gomez Pit, Virginia, USA. Incremental sampling were made along the axis of maximum growth to provide high-resolution ${\delta}^{18}$O and ${\delta}^{13}$C records. The ${\delta}^{18}$O shell profiles exhibit a series of pronounced cycles in the overall amplitude, corresponding to strong seasonal variations in temperature, which is apparently positive environmental variable. Contrasts between the patterns of ${\delta}^{18}$O and ${\delta}^{13}$C profiles reflect the relationship influencing the seasonal carbon cycling in the shallow marine environment. Positive anomalies of the ${\delta}^{13}$C values during the summer were observed to be out of phase with the ${\delta}^{18}$O profile. Such relatively heavier carbon source may be alternated due to seasonal methanogenesis during the summer. A hypothesized methane-based system may be operated in the shallow and marginal marine environment, resulting in a ${\delta}^{13}$C enriched bicarbonate pool, in which the heavier isotope seems to be incorporated to the shell carbonate.

Observation of second spin reorientation transition within ultrathin region in Fe films on Ag(001) surface

Khim, T.-Y.,Shin, M.,Park, B.-G.,Lee, H.,Park, J.-H. American Institute of Physics 2014 JOURNAL OF APPLIED PHYSICS - Vol.115 No.23

We acquired direct measurements for in-plane and perpendicular-to-plane magnetic moments of Fe films using an x-ray magnetic circular dichroism technique with increase of the Fe thickness (up to 40 angstrom) on the Ag(001) surface. Epitaxial Fe/Ag(001) films were grown in situ with the thickness varying from 2 angstrom to 40 angstrom, and the magnetic anisotropy was carefully investigated as a function of the film thickness. We found re-entrance of the in-plane magnetic anisotropy of the Fe film in ultrathin region. The results manifest that the epitaxial Fe/Ag(001) film undergoes two distinct spin reorientation transitions from in-plane to out-of-plane at the film thickness t approximate to 9 angstrom and back to in-plane at t approximate to 18 angstrom as t increases. (C) 2014 AIP Publishing LLC.

On the Structure of the AGN Torus through the Fraction of Optically Selected Type 1 AGNs

Khim, Honggeun,Yi, Sukyoung K. American Astronomical Society 2017 The Astrophysical journal Vol.846 No.2

<P>The ratio in number between unobscured (type 1) and obscured (type 2) active galactic nuclei (AGNs) is often used to explore the structure of the torus in the unified scheme for AGNs. Oh et al. (2015) investigated the type 1 AGN fraction on two-dimensional space in terms of black hole mass (M-BH) and bolometric luminosity (L-bol) and found that the fraction changes depending on both M-BH and L-bol, forming a ridge-shaped distribution. In this study, based on the up-to-date type 1 AGN catalog of Oh et al. (2015), we examine how the trend of the type 1 AGN fraction in the M-BH-L-bol plane is affected by the different methods used to derive M-BH and L-bol, and suggest an analytic model to explain the observations. We use galaxies from the Sloan Digital Sky Survey Data Release 7 in the redshift range 0.01 <= z <= 0.2. In estimating L-bol, we employ two different methods using [O III] and/or [O I] emission lines, and find that the L-bol values obtained from the two methods agree well. We consider the M-BH-s* relation, the M-BH-L-bulge relation, and the single-epoch H alpha-based M-BH estimate in calculating M-BH. We find that the trends of the type 1 AGN fraction with respect to M-BH and L-bol are similar for the different methods of deriving L-bol but different when using different methods to derive M-BH. We present a model based on the clumpy-torus scheme that reproduces the ridge-shaped distribution of the fraction parallel to the iso-Eddington ratio lines.</P>

Chemical-, site-, and taxa-dependent benthic community health in coastal areas of the Bohai Sea and northern Yellow Sea: A sediment quality triad approach

Khim, Jong Seong,Park, Jinsoon,Song, Sung Joon,Yoon, Seo Joon,Noh, Junsung,Hong, Seongjin,Kwon, Bong-Oh,Ryu, Jongseong,Zhang, Xiaowei,Wang, Tieyu,Lu, Yonglong,Giesy, John P. Elsevier 2018 The Science of the total environment Vol.645 No.-

<P><B>Abstract</B></P> <P>To investigate benthic ecological quality associated with coastal pollution in the Bohai Sea and northern Yellow Sea, a sediment quality triad (SQT) approach was applied. Chemical (six groups of persistent toxic substances (PTSs) and 8 metals and metalloids), toxicological (AhR-mediated potency), and ecological (bacterial and meiofaunal communities) elements were selected and used in an integrated sediment assessment. The benthic meiofaunal community was newly analyzed and used as an additional component of the infaunal community during the SQT. Concentrations of chemicals and potential toxicity in sediments both indicated moderate to severe pollution in the study area, characterized by site-specific and land-uses. In particular, As, DDTs, and bioassay-derived dioxin equivalents exceeded corresponding sediment quality guidelines at nearly all locations. Limited occurrences of meiofaunal taxa (mean = 5.2) and relatively low species diversity, mainly comprised of nematodes (75.3%) and copepods (14.6%), among locations was generally consistent with pollution. The benthic community was consistent with compound-specific responses to gradients of contamination, particularly for As. Densities of two taxa, Nematoda and Nemertea exhibited strong negative correlations with concentrations of As. Compound-, site-, and taxa-specific variability of pollution of sediments was further supported by results of cluster analysis (CA) and nonmetric multidimensional scaling (NMDS). Finally, assessment integrating five benthic quality elements, including: 1) PTSs; 2) metals and metalloids; 3) sediment toxicity; 4) sediment microbiome; and 5) benthic meiofaunal community, explained contamination of sediments associated with land-uses, locality, or habitat. Status of the benthic community could not be explained by single component and their associations were not quantitative. Results of the integrated assessment, considering multiple benthic quality elements were useful to address overall quality of sediment, and were consistent with chemical-, species-, or site-dependent pollution of sediments in the Bohai and Yellow Seas.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Extended-sediment quality triad was applied to enhance typical benthic assessment. </LI> <LI> Sediment toxicity might be over- or under-estimate chemical pollution and benthic health. </LI> <LI> Meiofaunal abundance would be a good ecological indicator of pollution by arsenic. </LI> <LI> Moderate to severe pollution evidenced in over half of the sampling locations. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

δ¹³C and δ¹⁵N Values of Sediment-trap Particles in the Japan and Yamato Basins and Comparison with the Core-top Values in the East/Japan Sea

Khim, Boo-Keun,Otosaka, Shigeyoshi,Park, Kyung-Ae,Noriki, Shinichiro Korean Ocean Research & Development Institute and 2018 OCEAN SCIENCE JOURNAL Vol.53 No.1

Investigation of sediment-trap deployments in the East/Japan Sea (EJS) showed that distinct seasonal variations in particulate organic carbon (POC) fluxes of intermediate-water sediment-traps clearly corresponded to changes in chlorophyll <TEX>${\alpha}$</TEX> concentrations estimated from SeaWiFS data. The prominent high POC flux periods (e.g., March) were strongly correlated with the enhanced surface-water phytoplankton blooms. Deep-water sediment-traps exhibited similar variation patterns to intermediate-water sediment-traps. However, their total flux and POC flux were higher than those of intermediate-water sediment-traps during some months (e.g., April and May), indicating the lateral delivery of some particles to the deep-water sediment-traps. Distinct seasonal <TEX>${\delta}^{13}C$</TEX> and <TEX>${\delta}^{15}N$</TEX> variations in settling particles of the intermediate-water sediment-traps were observed, strongly supporting the notion of seasonal primary production. Seasonal variations in <TEX>${\delta}^{13}C$</TEX> and <TEX>${\delta}^{15}N$</TEX> values from the deep-water sediment-traps were similar to those of the intermediate-water sediment-traps. However, the difference in <TEX>${\delta}^{13}C$</TEX> and <TEX>${\delta}^{15}N$</TEX> values between the intermediate-water and the dee-pwater sediment-traps may be attributed to degradation of organic matter as it sank through the water column. Comparison of flux-weighted <TEX>${\delta}^{13}C$</TEX> and <TEX>${\delta}^{15}N$</TEX> mean values between the deep-water sediment-traps and the core-top sediments showed that strong selective loss of organic matter components (lipids) depleted in <TEX>$^{13}C$</TEX> and <TEX>$^{15}N$</TEX> occurred during sediment burial. Nonetheless, the results of our study indicate that particles in the deep-water sediment-trap deposited as surface sediments on the seafloor preserve the record of surface-water conditions, highlighting the usefulness of sedimentary <TEX>${\delta}^{13}C$</TEX> and <TEX>${\delta}^{15}N$</TEX> values as a paleoceanographic application in the EJS.

Holocene Variations of Organic Carbon Contents in Lake Langer of King George Island, South Shetland Islands, West Antarctica

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.

Mahatma's Struggle for Human Rights - Spirit of Our Epoch -

Khim, Suk-jin 한인문화연구원 2000 한인문화논총 Vol.14 No.-