Time filter

Source Type

Daegu, South Korea

Moon G.-H.,Daegu Science High School
Journal of Astronomy and Space Science

Polar cap potential has long been considered as an indicator for the amount of energy flowing in the magnetosphere-ionosphere system. Thus, the estimation of polar cap potential is important to understand the physical process of the magnetosphere. To estimate the polar cap potential in the Northern Hemisphere, merging electric field by Kan & Lee (1979) is adopted. Relationships between the PC index and calculated merging electric field (E*) are examined during full-time and storm-time periods separately. For this purpose Dst, AL, and PC indices and solar wind data are utilized during the period from 1996-2003. From this linear relationship, polar cap potential (Φ*) is estimated using the formula by Doyle & Burke (1983). The values are represented as 58.1 ± 26.9 kV for the full-time period and 123.7 ± 84.1 kV for a storm-time period separately. Considering that the average value of polar cap potential of Doyle & Burke (1983) is about 47 kV during moderately quiet intervals with the S3-2 measurements, these results are similar to such. The monthly averaged variation of Dst, AL, and PC indices are then compared. The Dst and AL indices show distinct characteristics with peaks during equinoctial season whereas the average PC index according to the month shows higher values in autumn than in spring. The monthly variations of the linear correlation coefficients between solar wind parameters and geomagnetic indices are also examined. The PC-AL linear correlation coefficient is highest, being 0.82 with peaks during the equinoctial season. As with the AL index, the PC index may also prove useful for predicting the intensity of an auroral substorm. Generally, the linear correlation coefficients are shown low in summer due to conductance differences and other factors. To assess the role of the PC index during the recovery phase of a storm, the relation between the cumulative PC index and the duration is examined. Although the correlation coefficient lowers with the storm size, it is clear that the average correlation coefficient is high. There is a tendency that duration of the recovery phase is longer as the PC index increases. © The Korean Space Science Society. Source

It is generally believed that the occurrence of a magnetic storm depends upon the solar wind conditions, particularly the southward interplanetary magnetic field (IMF) component. To understand the relationship between solar wind parameters and magnetic storms, variations in magnetic field polarity and solar wind parameters during magnetic storms are examined. A total of 156 storms during the period of 1997~2003 are used. According to the interplanetary driver, magnetic storms are divided into three types, which are coronal mass ejection (CME)-driven storms, co-rotating interaction region (CIR)-driven storms, and complicated type storms. Complicated types were not included in this study. For this purpose, the manner in which the direction change of IMF B y and B z components (in geocentric solar magnetospheric coordinate system coordinate) during the main phase is related with the development of the storm is examined. The time-integrated solar wind parameters are compared with the time-integrated disturbance storm time (Dst) index during the main phase of each magnetic storm. The time lag with the storm size is also investigated. Some results are worth noting: CME-driven storms, under steady conditions of B z < 0, represent more than half of the storms in number. That is, it is found that the average number of storms for negative sign of IMF B z (T1~T4) is high, at 56.4%, 53.0%, and 63.7% in each storm category, respectively. However, for the CIR-driven storms, the percentage of moderate storms is only 29.2%, while the number of intense storms is more than half (60.0%) under the B z < 0 condition. It is found that the correlation is highest between the time-integrated IMF B z and the time-integrated Dst index for the CME-driven storms. On the other hand, for the CIR-driven storms, a high correlation is found, with the correlation coefficient being 0.93, between time-integrated Dst index and time-integrated solar wind speed, while a low correlation, 0.51, is found between timeintegrated B z and time-integrated Dst index. The relationship between storm size and time lag in terms of hours from B z minimum to Dst minimum values is investigated. For the CME-driven storms, time lag of 26% of moderate storms is one hour, whereas time lag of 33% of moderate storms is two hours for the CIR-driven storms. The average values of solar wind parameters for the CME and CIR-driven storms are also examined. The average values of |Dst min| and |B zmin| for the CME-driven storms are higher than those of CIR-driven storms, while the average value of temperature is lower. © The Korean Space Science Society. Source

Jang S.-Y.,Kyungpook National University | Bae J.-S.,Daegu Science High School | Lee Y.H.,Daegu Science High School | Oh K.Y.,Gyeongsang National University | And 2 more authors.
Natural Product Research

A methanol extract of Houttuynia cordata showed an inhibitory effect on mammalian DNA topoisomerase I. Two topoisomerase I inhibitory compounds were purified and identified as caffeic acid and quercitrin. Caffeic acid and quercitrin inhibited the activity of topoisomerase I with IC50 values of about 0.15 and 0.05 mM, respectively. A concentration of 45μ M caffeic acid caused 50% growth inhibition in human leukaemia U937 cells, but not on those of normal fibroblast NIH3T3 cells. However, quercitrin mysteriously stimulated proliferation of U937 and NIH3T3 cells. Caffeic acid-induced cell death was characterised with the cleavage of poly (ADP-ribose) polymerase and procaspase-3, indicating that this inhibitor triggered apoptosis. The apoptotic induction by caffeic acid was also confirmed using flow cytometry analysis. Because DNA topoisomerase I is an important target for tumour chemotherapy, the present study suggests that caffeic acid, but not quercitrin, may function by suppressing oncogenic disease through the inhibition of cellular topoisomerase I activity. © 2011 Taylor & Francis. Source

Min K.S.,Kyungpook National University | Kim Y.J.,Daegu Science High School | Ko H.J.,Daegu Science High School | Kwak D.H.,Daegu Science High School | And 3 more authors.
Journal of Physical Organic Chemistry

We have isolated two isomeric solids 1 and 2 of N,N′-bis(3,5-dichlorosalicylidene)-2,2′-ethylenedianiline and characterized by IR, UV/Vis, X-ray powder diffraction, thermogravimetric analysis/differential thermal analysis, and X-ray crystallography. Although the solids are same formulas, each shows different colors and crystal structures. Orange solid (1) shows endo conformation while yellow solid (2) exhibits exo form depending on packing modes. UV/Vis spectra of 1 and 2 appear very similar patterns in the solid state; however, the bands of 1 are slightly red-shifted compared with those of 2. 1 displays a strong fluorescent emission band at ∼582nm while 2 shows an intense fluorescent signal at ∼563 nm. The charge density populations of 1 and 2 have been studied by computational simulations using density functional theory at pbe1pbe/6-311G∗∗ level. The calculated highest occupied molecular orbital and lowest unoccupied molecular orbital energies of 1 and 2 confirm that charge transfer occurs within the organic molecules. The energy difference of HOMO-LUMO in 1 is smaller slightly than that of 2 about 0.05 eV (∼17 nm). Copyright © 2014 John Wiley & Sons, Ltd. Source

Kim B.-G.,Kyungpook National University | Dho J.,Kyungpook National University | Jeong S.,Daegu Science High School | Shin H.B.,Daegu Science High School | And 2 more authors.
New Physics: Sae Mulli

Inverse spinel NiFe2O4 (NFO) films were prepared on (110) MgAl2O4 substrates by using pulsed laser deposition. The NFO films were deposited at a substrate temperature of 600 °C and an oxygen partial pressure of 1 mTorr, and their thicknesses were in the range of 20 nm - 240 nm. As the film's thickness increased, the positon of the (440) NFO peak moved to a higher angle, implying a relaxation of the lattice strain. For 240 nm, the lattice constant of the NFO film was about 8.39 Å, which corresponded to a lattice mismatch of about 0.6% with the lattice constant of the NFO bulk. The magnetic hysteresis measurement suggested an increasing tendency of the perpendicular magnetic anisotropy with increasing film thickness. For 160 nm, the ratio of the remanent magnetization to the saturation magnetization (Mrem./Msat.) was maximally ∼0.22. The magnetic domain structure was observed by using magnetic force microscopy. The image contrast was improved with increasing film thickness, and it was the best for a film with a thickness of 160 nm. Source

Discover hidden collaborations