• Journal of The Korean Astronomical Society
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• v.36 no.3
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• pp.81-87
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• 2003

It is suggested that a flying-by star in a hot accretion disk may cool the hot accretion disk by the Comptonization of the stellar emission. Such a stellar cooling can be observed in the radio frequency regime since synchrotron luminosity depends strongly on the electron temperature of the accretion flow. If a bright star orbiting around the supermassive black hole cools the hot disk, one should expect a quasi-periodic modulation in radio, or even possible an anti-correlation of luminosities in radio and X-rays. Recently, the unprecedentedly accurate infrared imaging of the Sagittarius A$\ast$ for about ten years enables us to resolve stars around it and thus determine orbital parameters of the currently closest star S2. We explore the possibility of using such kind of observation to distinguish two quite different physical models for the central engine of the Sagittarius A$\ast$, that is, a hot accretion disk model and a jet model. We have attempted to estimate the observables using the observed parameters of the star S2. The relative difference in the electron temperature is a few parts of a thousand at the epoch when the star S2 is near at the pericenter. The relative radio luminosity difference with and without the stellar cooling is also small of order $10^{-4}$, particularly even when the star S2 is near at the pericenter. On the basis of our findings we tentatively conclude that even the currently closest pass of the star S2 is insufficiently close enough to meaningfully constrain the nature of the Sagittarius A$\ast$ and distinguish two competing models. This implies that even though Bower et al. (2002)have found no periodic radio flux variations in their data set from 1981 to 1998, which is naturally expected from the presence of a hot disk, a hot disk model cannot be conclusively ruled out. This is simply because the energy bands they have studied are too high to observe the effect of the star S2 even if it indeed interacts with the hot disk. In other words, even if there is a hot accretion disk the star like S2 has imprints in the frequency range at v $\le$ 100 MHz.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.559-563
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• 2015

Monitor of All-sky X-ray Image (MAXI) is a Japanese X-ray all-sky surveyer mounted on the International Space Station (ISS). It has been scanning the whole sky since 2009 during every 92-minute ISS rotation. X-ray transients are quickly found by the real-time nova-search program. As a result, MAXI has issued 133 Astronomer's Telegrams and 44 Gamma-ray burst Coordinated Networks so far. MAXI has discovered six new black holes (BH) in 4.5 years. Long-term behaviors of the MAXI BHs can be classified into two types by their outbursts; a fast-rise exponential-decay type and a fast-rise flat-top one. The slit camera is suitable for accumulating data over a long time. MAXI issued a 37-month catalog containing 500 sources above a ~0.6 mCrab detection limit at 4-10 keV in the region ${\mid}{b}{\mid}$ > $10^{\circ}$. The SSC instrument utilizing an X-ray CCD has detected diffuse soft X-rays extending over a large solid angle, such as the Cygnus super bubble. MAXI/SSC has also detcted a Ne emission line from the rapid soft X-ray nova MAXI J0158-744. The overall shapes of outbursts in Be X-ray binaries (BeXRB) are precisely observed with MAXI/GSC. BeXRB have two kinds of outbursts, a normal outburst and a giant one. The peak dates of the subsequent giant outbursts of A0535+26 repeated with a different period than the orbital one. The Be stellar disk is considered to either have a precession motion or a distorted shape. The long-term behaviors of low-mass X-ray binaries (LMXB) containing weakly magnetized neutron stars are investigated. Transient LMXBs (Aql X-1 and 4U 1608-52) repeated outbursts every 200-1000 days, which is understood by the limit-cycle of hydrogen ionization states in the outer accretion disk. A third state (very dim state) in Aql X-1 and 4U 1608-52 was interpreted as the propeller effect in the unified picture of LMXB. Cir X-1 is a peculiar source in the sense that its long-term behavior is not like typical LMXBs. The luminosity sometimes decreases suddenly at periastron. It might be explained by the stripping of the outer accretion disk by a clumpy stellar wind. MAXI observed 64 large flares from 22 active stars (RS CVns, dMe stars, Argol types, young stellar objects) over 4 years. The total energies are $10^{34}-10^{36}$ erg $s^{-1}$. Since MAXI can measure the spectrum (temperature and emission measure), we can estimate the size of the plasma and the magnetic fields. The size sometimes exceeds the size of the star. The magnetic field is in the range of 10-100 gauss, which is a typical value for solar flares.

• Journal of The Korean Association For Science Education
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• v.35 no.1
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• pp.143-157
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• 2015

The purpose of this study is to examine the possibility of science education using Korean TSK(Traditional scientific knowledge). In this study, we have developed five Korean TSK units including science concepts, historical knowledge and cultural experience and applied them to 10th graders. The five units are as follows: (1) Calendars(western and eastern), (2) Our traditional sundial, Angbuilgu, (3) A great scientist in the King Sejong Era, (4) Data interpretation of ancient record of natural phenomenon in Korea, and (5) Gyeongbokgung Palace. The analyses included a pre- and post test of students' perception, classroom observation, students' activity sheets, and interview. The results show that the students' perception of Korean TSK has changed toward recognizing the value of Korean TSK as a kind of natural science. They expressed their expectation of Korean TSK in scientific, practical, and emotional perspectives, wherein some students thought the practical and emotional perspectives of Korean TSK as non-scientific characteristics. Students showed five types of worldview about the relationship between Korean TSK and WMS(western modern science). Most students favored and cherished the Korean TSK but at the same time, they were confused about its scientific value. The results support the rethinking of the meaning of science and what students learn in school. We should consider how we teach the Korean TSK to students. It is important that a profound research of the Korean TSK should be continued to make our science education varied.

• Journal of The Korean Association For Science Education
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• v.32 no.10
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• pp.1489-1501
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• 2012

The purpose of this study was to search for effective strategies on teaching open-inquiry by comparing students' and teachers' recognition of its difficulties and helpful strategies. This study focused on the cases of science high school students and their teachers, who carried out open-inquiry to participate in KYPT. This research was conducted through participant observation, questionnaires, and interviews. The research findings were as follows: students stated that planning and doing experiments were the most difficult parts, whereas teachers viewed that their students had difficulties in analyzing data and making a conclusion. With respect to the effective strategy, students stated that they gained many ideas from peer discussions although they have had to carry out their individual tasks. On the contrary, teachers thought that reference materials and the discussions with teachers were most helpful. There were clear differences between students' and their teachers' recognition toward open-inquiry and the gap needs to be closed. Consequently, it would be useful to guide students to form teams and to spend more time in peer discussions especially when doing experiments and to encourage teachers to understand students' actual difficulties and needs.

• Journal of the Korean Chemical Society
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• v.39 no.4
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• pp.275-280
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• 1995

The electron transfer reactions between cis-[Co(en)2(NO2)2]+ and rac-[Co(Y)]2-(Y=EDTA, PDTA, CyDTA) have been investigated in the presence of hydrogen ion. From the kinetic data, it has been found that electron transfer reactions between cis-[Co(en)2(NO2)2]+ and rac-[Co(Y)]2- proceed via inner-sphere pathway by catalysis of hydogen ion. The stereoselectivity in the electron transfer reactions between optically active △-cis-[Co(en)2(NO2)2]+ and rac-[Co(Y)]2- produced 6.0, 2.9, 3.0% e.e.(e.e.=enantiomeric excess) of △-[Co(EDTA)]-, △-[Co(PDTA)]- and △-[Co(CyDTA)]-, respectively. Based upon this observation, it seems that △-cis-[Co(en)2(NO2)2]+ is associated with rac-[Co(Y)]2- at first, and followed by the electron transfer reaction. Therefore, it was suggested that stereoselective electron transfer reaction between △-cis-[Co(en)2(NO2)2]+ and rac-[Co(Y)]2- proceed through both inner-sphere by the proton catalysis and outer-sphere with ionic association.

• The Journal of Korean Medicine Ophthalmology and Otolaryngology and Dermatology
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• v.11 no.1
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• pp.23-39
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• 1998

The clinical data and thermographic imaging were analyzed on the 100 cases of Bell's palsy who were treated in the Kwang-Ju Oriental Medical Hospita! of Wonkwang University from February to October 1997. All the cases were taken Digital Infrared Thermograph Imaging(DITI) before treatment and 30 cases of them were taken follow up imaging again after recovery. And the following results were obtained. 1. Of 100 cases, under teenager occupied $1\%,\;teenager\;8\%,\;2nd\;decade\;14\%,\;3rd\;decade\;11\%,\;4th\;decade\;16\%,\;5th\;decade\;26\%,\;6th\;decade\;16\%,\;7th\;decade\;7\%\;and\;over\;80\;occupied\;1\%$. 2. Male occupied $48\%$ and female occupied $52\%$. 3. $42\%\;of\;male\;and\;23\%$ of female had the affected side at left side. And right facial nerve palsy occured at $29\%\;of\;male\;and\;29\%$ of female. 4. The most common cause of Bell's palsy was cold wind $18\%$, and the next were excessive labor $15\%,\;stress\;12\%,drinking\;2\%\;and\;cold\;food\;1\%$. 5. Thermal pattern were present as hyperthermal pattern in $44\%$ and hypothermal pattern in $22\%$. 6. The DITI showed hyperthermal pattern as close as to the onset day and changes to hypothermal pattern as times passed. 7. The DITI pattern and post-auricular pain, the most common prodomal syndrome, showed no significant relationship. 8. The relationship between the grade of paralysis and thermal patttern of DITI showed no significance. 9. Mean temperature of loci in affected side indicrtted $30.27^{\circ}C\;at\;Yang\;baek,\;30.02^{\circ}C\;at\;Taeyang,\;29.25^{\circ}C\;at\;Geoyo,\;29.62^{\circ}C\;at\;Jichang,\;29.78^{\circ}C\;at\;Hakwan,\;29.61^{\circ}C\;at\;Hyupgeo,\;and\;30.59^{\circ}C$at Yeopoong. 10. Mean temperature of loci in unaffected side showed $30.16^{\circ}C\;at\;Yang\;baek,\;30.02^{\circ}C\;at\;Taeyang,\;29.61^{\circ}C\;at\;Geoyo,\;29.68^{\circ}C\;at\;Jichang,\;29.70^{\circ}C\;at\;Hakwan,\;29.57^{\circ}C\;at\;Hyupgeo,\;and\;29.89^{\circ}C$at Yeopoong. 11. Of 30 cases who were taken follow up imaging again after recovery, the relationship between delta T at loci and symptoms showed no significance. It should be needed further investigation in order to apply them for clinical evaluation.

• The Korean Journal of Zoology
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• v.11 no.1
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• pp.5-12
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• 1968

The membrane structures were electron microscopically studied in the elongating lens fibers of the regenerating lens of adult Triturus pyrrhogaster. Observations were focused on the endoplasmic reticulum and mitochondria. The endoplasmic reticulum developed in the vicinity of the nucleus with active blebbing of the outer membrane. At the same time, the concentration of mitochondria around the rough-surfaced endoplasmic reticulum near by the nucleus was always observed. Both endoplasmic reticulum and mitochondrion undergo disintegration in the apical portion apart from the nucleus. Some considerations were discussed with reference to published data.

• Journal of Wetlands Research
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• v.17 no.4
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• pp.370-379
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• 2015

In recent, the natural disaster like localized heavy rainfall due to the climate change is increasing. Therefore, it is important issue that the precise observation of rainfall and accurate spatial distribution of the rainfall for fast recovery of damaged region. Thus, researches on the use of the radar rainfall data have been performed. But there is a limitation in the estimation of spatial distribution of rainfall using rain gauge. Accordingly, this study uses the Kriging method which is a spatial interpolation method, to measure the rainfall field in Namgang river dam basin. The purpose of this study is to apply KED(Kriging with External Drift) with OK(Ordinary Kriging) and CK(Co-Kriging), generally used in Korea, to estimate rainfall field and compare each method for evaluate the applicability of each method. As a result of the quantitative assessment, the OK method using the raingauge only has 0.978 of correlation coefficient, 0.915 of slope best-fit line, and 0.957 of $R^2$ and shows an excellent result that MAE, RMSE, MSSE, and MRE are the closest to zero. Then KED and CK are in order of their good results. But the quantitative assessment alone has limitations in the evaluation of the methods for the precise estimation of the spatial distribution of rainfall. Thus, it is considered that there is a need to application of more sophisticated methods which can quantify the spatial distribution and this can be used to compare the similarity of rainfall field.

• Journal of Korea Water Resources Association
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• v.44 no.5
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• pp.339-350
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• 2011

This study developed a climate informed Bayesian nonstationary frequency model which allows us to forecast seasonal summer rainfall at Nakdong River. We constructed a 37-year summer rainfall data set from 10 weather stations within Nakdong river basin, and two climate indices from sea surface temperature (SST) and outgoing longwave radiation (OLR) were derived through correlation analysis. The selected SST and OLR have been widely acknowledged as a climate driver for summer rainfall. The developed model was applied first to the 2010-year summer rainfall (888.1 mm) in order to assure ourself. We demonstrated model performance by comparing posterior distributions. It was confirmed that the proposed model is able to produce a reasonable forecast. The forecasted value is about 858.2 mm, and the difference between forecast and observation is about 30 mm. As the second case study, 2011-year summer rainfall forecast was made using an observed winter SSTs and an assumed 50% value of OLRs. The forecasted value is 967.7 mm and associated exceedance probability over average summer rainfall 680 mm is 92.9%. In addition, 50-year return period for summer rainfall was projected through the nonstationary frequency model. An exceedance probability over 1,400 mm corresponding to the 50-year return level is about 73.7%.

• Journal of Korea Water Resources Association
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• v.51 no.9
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• pp.803-812
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• 2018

The purpose of this study is to develop Particle Swarm Optimization (PSO) automatic calibration algorithm with multi-objective functions by Python, and to evaluate the applicability by applying the algorithm to the Soil and Water Assessment Tool (SWAT) watershed modeling. The study area is the upstream watershed of Gongdo observation station of Anseongcheon watershed ($364.8km^2$) and the daily observed streamflow data from 2000 to 2015 were used. The PSO automatic algorithm calibrated SWAT streamflow by coefficient of determination ($R^2$), root mean square error (RMSE), Nash-Sutcliffe efficiency ($NSE_Q$), and especially including $NSE_{INQ}$ (Inverse Q) for lateral, base flow calibration. The results between automatic and manual calibration showed $R^2$ of 0.64 and 0.55, RMSE of 0.59 and 0.58, $NSE_Q$ of 0.78 and 0.75, and $NSE_{INQ}$ of 0.45 and 0.09, respectively. The PSO automatic calibration algorithm showed an improvement especially the streamflow recession phase and remedied the limitation of manual calibration by including new parameter (RCHRG_DP) and considering parameters range.