• Bulletin of the Korean Chemical Society
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• v.23 no.2
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• pp.201-204
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• 2002

The rates of the aminolysis of S-phenyl substituted-acetate series $(RC(=O)SC_6H_4Z$, with R=Me, Et, i-Pr, t-Bu and Bn) with benzylamines $(XC_6H_4CH_2NH_2)$ are not correlated simply with the Taft's polar $({\sigma}^{\ast})$ and/or steric effect constants $(E_s)$ of the substituents due to abnormally enhanced rate of the substrate with R=Et. Furthermore, the cross-interaction constant, ${\rho}x_z$ , is the largest with R=Et. These anomalous behaviors can only be explained by invoking the vicinal bond $({\sigma})$-antibond $({\sigma}^{\ast})$ charge transfer interaction between C-$C{\alpha}$ and C-S bonds. In the tetrahedral zwitterionic intermediate, $T^{\pm}$ , formed with R=Et the vicinal ${\sigma}_{c-c}-{\sigma}^{\ast}_{c-s}$ delocalization is the strongest with an optimum antiperiplanar arrangement and a narrow energy gap, ${\Delta}{\varepsilon}={\varepsilon}_{{\sigma}^{\ast}}-{\varepsilon}_{\sigma}$. Due to this charge transfer interaction, the stability of the intermediate increases (with the concomitant increase in the equilibrium constant K (= $k_a/k_{-a}$)) and also the leaving ability of the thiophenolate leaving group increases (and hence $k_b$ increases) so that the overall rate, $k_n\;=\;Kk_b$, is strongly enhanced. Theoretical support is provided by the natural bond orbital (NBO) analyses at the B3LYP/6-31+$G^{\ast}$ level. The anomaly exhibited by R=Et attests to the stepwise reaction mechanism in which the leaving group departure is rate limiting.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.3
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• pp.157-161
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• 2017

$(1-x)Bi_{0.5}(Na_{0.78}K_{0.22})_{0.5}TiO_3-xLaFeO_3$ ceramics were fabricated using a solid state reaction method. The microstructural, ferroelectric and piezoelectric properties were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), and polarization hysteresis loops (P-E). XRD results indicated that BNKT ceramic crystal structure modified by $LaFeO_3$ was transformed from a ferroelectric tetragonal to a non-polar pesudo-cubic phase with increased $LaFeO_3$ content. The improved piezoelectric properties resulted from the addition of $LaFeO_3$ up to 3 mol%. The $LaFeO_3$ 3mol% sample showed markedly improved piezoelectric and strain behaviors in comparison with pure BNKT ceramic.

• Proceedings of the Korea Society of Environmental Toocicology Conference
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• 2003.05a
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• pp.195-195
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• 2003

It is well known that diesel exhaust particulate matter contains mutagenic PAHs, such as benzo[${\alpha}$]pyrene, benz[${\alpha}$]anthracene, chrysene, etc. Therefore it is suspected that these chemicals act on estrogen receptor and reveal endocrine-disrupting effects. Recent attention has focused on causative chemicals of endocrine-disrupting effects. We examined the estrogenic activity of respirable diesel exhaust particulate matter derived from diesel powered vehicle. PM2.5 diesel exhaust of vehicle was collected using a high volume sampler equipped with a cascade impactor. Diesel exhaust samples were fractionated according to EPA methods. The presence of estrogenic and antiestrogenic chemicals in PM 2.5 diesel exhaust was determined using E-screen assay. To quantitatively assess the estrogenic and antiestrogenic activities in diesel exhaust particulate matter, estradiol equivalent concentration (bio-EEQ) was calculated by comparing the concentration response curve of the sample with those of the estrogen calibration curve. Weak estrogenic activities and strong antiestrogenic activities were detected in the crude extract and moderately polar fractions. Higher antiestrogenic potency was observed with higher EROD activities in aliphatic and aromatic compounds fraction. In conclusion, estrogenic/antiestrogenic-like activities were present in diesel exhaust particulate matter. However, the health consequences of this observation was unknown, the presence of these activities may contribute to and exacerbate adverse health effect evoked by diesel exhaust particulate matter.

• Journal of Astronomy and Space Sciences
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• v.32 no.2
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• pp.127-136
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• 2015

We present a by-product of our long term photometric monitoring of cataclysmic variables. 2MASS J18024395 +4003309 = VSX J180243.9 +400331 was discovered in the field of the intermediate polar V1323 Her observed using the Korean 1-m telescope located at Mt. Lemmon, USA. An analysis of the two-color VR CCD observations of this variable covers all the phase intervals for the first time. The light curves show this object can be classified as an Algol-type variable with tidally distorted components, and an asymmetry of the maxima (the O'Connell effect). The periodogram analysis confirms the cycle numbering of Andronov et al. (2012) and for the initial approximation, the ephemeris is used as follows: Min I. BJD = 2456074.4904+0.3348837E. For phenomenological modeling, we used the trigonometric polynomial approximation of statistically optimal degree, and a recent method "NAV" ("New Algol Variable") using local specific shapes for the eclipse. Methodological aspects and estimates of the physical parameters based on analysis of phenomenological parameters are presented. As results of our phenomenological model, we obtained for the inclination $i=90^{\circ}$, $M_1=0.745M_{\odot}$, $M_2=0.854M_{\odot}$, $M=M_1+M_2=1.599M_{\odot}$, the orbital separation $a=1.65{\cdot}10^9m=2.37R_{\odot}$ and relative radii $r_1=R_1/a=0.314$ and $r_2=R_2/a=0.360$. These estimates may be used as preliminary starting values for further modeling using extended physical models based on the Wilson & Devinney (1971) code and it's extensions

• Ocean and Polar Research
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• v.30 no.3
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• pp.261-275
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• 2008

The profile of a fixed site at station M ($34.77^{\circ}N,\;129.13^{\circ}E$) in the Korea Strait was studied from March 2006 to February 2007. The aim was to understand the relationship between the annual thermal stratification pattern and seasonal variation in phytoplankton community structure. Physicochemical factors including temperature, salinity and nutrient concentrations, which strongly influence the proliferation and diversity of phytoplankton, were measured. The study period was divided into three due to the characteristic of thermohaline structures; mixed I (March-May 2006), stratified (June-November 2006) and mixed II(December 2006-Feburuary 2007). Diatoms dominated during the mixed I (89%) and II (48%) periods, while nanoplankton group occupied over 83% of total population during the stratified period. The dominant species during the mixed I and II was Chaetoceros socialis (47% and 29%, respectively), while during the stratified period Gyrodinium sp.(4%) was the most dominant. Averaged total chl a concentrations during the mixed I and II periods were 0.61 mg $m^{-3}$ and 0.72 mg $m^{-3}$, respectively, which were at least two-fold higher than that during the stratified period (0.30 mg $m^{-3}$). The vertical mixing and convection process of the water column induced nutrient supply from the bottom layer to the euphotic zone. It also led to the dominance of diatoms during the mixed periods, whereas small phytoplankton prevailed over large phytoplankton as stratification blocked the upward movement of nutrients to subsurface during the stratified period. During the mixed I and II periods, microplanktonic chl a dominated concentrations (50% and 48%, respectively), while picoplanktonic chl a occupied over 37% of total chl a during the stratified period.

• Journal of Physiology & Pathology in Korean Medicine
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• v.20 no.5
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• pp.1321-1326
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• 2006

Total ginsenosides were purified and their antioxidant, antibacterial and anticancer activities were measured. The crude extracts of ginseng, which were extracted with 75% ethanol by ultrasonification method, were firstly purified on AB-8 macroporous adsorption column to remove water soluble impurities, and decolored on Amberlite IRA 900 Cl anion-exchange column. Then, they were purified on Amberlite XAD16 adsorption column to delete the non-polar impurities. Total ginsenosides contents of the purified extracts were 79.4%, 71.7% and 72.5% in cultured wild ginseng, red ginseng and white ginseng, which were significantly increased than those of crude extracts. All of the three extracts showed concentration-dependant scavenging activities against DPPH radicals, among which white ginseng showed the most powerful activity. Cultured wild ginseng roots showed strongest effect against both B. subtilis PM 125(Gram-positive) and E. coli D31 (Gram-negative) bacteria, while red ginseng and white ginseng only showed the activity against B. subtilis. According to the result of the MTT assay, ail of the three extracts inhibited the growth of U-937 human hohistiocytic lympma cell, which were significantly different (p < 0.05) when compared to the control.

• Clinical and Experimental Reproductive Medicine
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• v.23 no.1
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• pp.87-94
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• 1996

For evaluating the suitability of human follicular fluid(HFF) as protein supplement in ART, this preliminary study was performed to examine the maturation promoting activity of HFF on mouse follicular oocytes in vitro. Mouse follicular oocytes were collected from ovaries of 21-28 day old ICR mice by puncturing the antral follicles with fine needle at 48 hours after PMSG injection. The oocytes were rinsed and cultured in modified Whittingham's $T_6$ medium containing purines or dbcAMP to maintain meiotic arrest, and different concentrations of HFF were added into the culture medium to examine the effect of HFF on releasing the oocytes from the suppressive influence of the meiotic inhibitors. As a control for HFF, the maturation promoting activity of human fetal cord serum(HFCS) was investigated and compared with the activity of HFF. While HFF was separated, by molecular weight(M.W), into high M.W. fraction(M.W>30,000) and low M.W. fraction(M.W<30,000) and the effects of the fractions on meiotic resumption were investigated in the presence of the meiotic inhibitors. Also hormone analysis was performed to compare the content of hormones in HFF with that in HFCS. Same concentrations of HFF and HFCS induced similar germinal vesicle break down(GVBD) rates of the oocytes meiotic arrested by purines(4mM hypoxanthine+0.75mM adenosine), but the extrusion rate of 1st polar body(PB) of the oocytes cultured in HFF(65.0%, P<0.05) was significantly higher than that(51.6%) in HFCS. While, in the presence of 200 M dbcAMP, the maturation promoting activity of HFF (GVBD: 70.5%, $p<10^{-6}$; 1st PB extrusion: 67.1%, $p<10^{-3}$) was significantly greater than that of HFCS(GVBD: 35.2%; 1st PB extrusion: 41.1%). The oocytes cultured in the fraction of HFF containing high M.W. components showed higher meiotic maturation rates than the oocytes cultured in the low M.W. fraction of HFF. Gonadotropins and $E_2$ were known to improve the completion of maturation changes, and the levels of these hormones were higher in HFF than in HFCS. Therefore, HFF was more effective than HFCS to use for promoting meiotic resumption of mouse oocytes in vitro.

• Ocean and Polar Research
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• v.43 no.4
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• pp.279-293
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• 2021

To investigate the effect of seasonal marine environment conditions on the cyanobacteria abundance and diversity in the South Sea, four-seasonal surveys were conducted along the 127.5°E survey transect line in the central South Sea using flow cytometry and 16S-23S ITS on the Miseq platform from August 2016 to May 2017. The average abundance of Synechococcus varied from 3.3 × 10³ to 7.4 × 10⁴ cells ml^-1. The abundance was the highest in the summer and the lowest in the winter, and the abundance fluctuated according to water temperature. The abundance was high in the outer sea affected by TWC. However, in summer, the Coastal areas affected by the Yangtze River were more populated than the outer sea. Prochlorococcus was rare and could not penetrate into coastal areas due to the fronts, but showed its dominance in the waters influenced by the TWC. Synechococcus clades II, VII, IX, CRD1, and CRD2 were predominant in the outer sea area affected by the TWC. In the coastal area, clades I and IV showed higher dominance whereas clades V, VI, WPC1, and 5.3-MS3 with euryhaline characteristics, showed a high dominance rate in the water masses affected by the low-salinity water of the Yangtze River in the summer. Clade XVI, XVII, CB1, CB5, and 5.3-I/II showed high dominance in nutrient-rich waters in the summer with increased water temperature. The abundance and community composition of cyanobacteria changed in the South Sea due to the influence of the TWC and stratification. In the summer, the abundance and the community composition differed, and were mainly affected by the general influence of the TWC in addition to the influence of the Yangtze River low-salinity water.

• Korean Journal of Remote Sensing
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• v.28 no.1
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• pp.11-19
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• 2012

Air-borne pollen, biogenically created aerosol particle, influences Earth's radiative balance, visibility impairment, and human health. The importance of pollens has resulted in numerous experimental studies aimed at characterizing their dispersion and transport, as well as health effects. There is, however, limited scientific information concerning the optical properties of airborne pollen particles contributing to total ambient aerosols. In this study, for the first time, optical characteristics of pollen such as aerosol backscattering coefficient, aerosol extinction coefficient, and depolarization ratio at 532 nm and their effect to the atmospheric aerosol were studied by lidar remotes sensing technique. Dual-Lidar observations were carried out at the Gwangju Institute of Science & Technology (GIST) located in Gwagnju, Korea ($35.15^{\circ}E$, $126.53^{\circ}N$) for a spring pollen event from 5 to 7 May 2009. The pollen concentration was measured at the rooftop of Gwangju Bohoon hospital where the building is located 1.0 km apart from lidar site by using Burkard trap sampler. During intensive observation period, high pollen concentration was detected as 1360, 2696, and $1952m^{-3}$ in 5, 6, and 7 May, and increased lidar return signal below 1.5km altitude. Pollen optical depth retrieved from depolarization ratio was 0.036, 0.021, and 0.019 in 5, 6, and 7 May, respectively. Pollen particles mainly detected in daytime resulting increased aerosol optical depth and decrease of Angstrom exponent.

• Korean Journal of Remote Sensing
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• v.34 no.6_2
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• pp.1165-1178
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• 2018

Collapse of an Antarctic ice shelf and its flow velocity changes has the potential to reduce the restraining stress to the seaward flow of the Antarctic Ice Sheet, which can cause sea level rising. In this study, variations in ice velocity from 2000 to 2017 for the Nansen Ice Shelf in East Antarctica that experienced a large-scale collapse in April 2016 were analyzed using Landsat-7 Enhanced Thematic Mapper Plus (ETM+) and Landsat-8 Operational Land Imager (OLI) images. To extract ice velocity, image matching based on orientation correlation was applied to the image pairs of blue, green, red, near-infrared, panchromatic, and the first principal component image of the Landsat multispectral data, from which the results were combined. The Landsat multispectral image matching produced reliable ice velocities for at least 14% wider area on the Nansen Ice Shelf than for the case of using single band (i.e., panchromatic) image matching. The ice velocities derived from the Landsat multispectral image matching have the error of $2.1m\;a^{-1}$ compared to the in situ Global Positioning System (GPS) observation data. The region adjacent to the Drygalski Ice Tongue showed the fastest increase in ice velocity between 2000 and 2017. The ice velocity along the central flow line of the Nansen Ice Shelf was stable before 2010 (${\sim}228m\;a^{-1}$). In 2011-2012, when a rift began to develop near the ice front, the ice flow was accelerated (${\sim}255m\;a^{-1}$) but the velocity was only about 11% faster than 2010. Since 2014, the massive rift had been fully developed, and the ice velocity of the upper region of the rift slightly decreased (${\sim}225m\;a^{-1}$) and stabilized. This means that the development of the rift and the resulting collapse of the ice front had little effect on the ice velocity of the Nansen Ice Shelf.