• Publications of The Korean Astronomical Society
• /
• v.30 no.2
• /
• pp.175-178
• /
• 2015

Due to the lack of an accretion disk in a polar (magnetic cataclysmic variable, MCV), the material transferred from the secondary is directly accreted onto the white dwarf, forming an accretion stream and a hot spot on the white-dwarf component. During the eclipses, different light components can be isolated. Therefore, the monitoring of eclipsing polars could provide valuable information on several modern astrophysical problems, e.g., CVs as planetary hosting stars, mass transfer and mass accretion in CVs, and the magnetic activity of the most rapidly rotating cool dwarfs. In the past five years, we have monitored about 10 eclipsing polars (e.g., DP Leo and HU Aqr) using several 2-m class telescopes and about 100 eclipse profiles were obtained. In this paper, we will introduce the progress of our research group at YNOs. The first direct evidence of variable mass transfer in a CV is obtained and we show that it is the dark-spot activity that causes the mass transfer in CVs. Magnetic activity cycles of the cool secondary were detected and we show that the variable mass transfer is not caused by magnetic activity cycles. These results will shed light on the structure and evolution of close binary stars (e.g., CVs and Algols).

• Journal of Astronomy and Space Sciences
• /
• v.21 no.1
• /
• pp.39-72
• /
• 2004

We present a more complete and accurate catalogue of astronomical records far meteor showers and meteor storms appeared in primary official Korean history books, such as Samguk-sagi, Koryo-sa, Seungjeongwon-ilgi, and Chosen-Wangjo-Sillok. So far the catalogue made by Imoto and Hasegawa in 1958 has been widely used in the international astryonomical society. The catalogue is based on a report by Sekiguchi in 1917 that is mainly based on secondary history books. We observed that the catalogue has a number of errors in either dates or sources of the records. We have thoroughly checked the primary official history books, instead of the secondary ones, in order to make a corrected and extended catalogue. The catalogue contains 25 records of meteor storms, four records of intense meteor-showers, and five records of usual showers in Korean history. We also find that some of those records seem to correspond to some presently active meteor showers such as the Leonids, the Perseids, and the n -Aquarids-Orionids pair. However, a large number of those records do not correspond to suck present showers. This catalogue we obtained can be useful for various astrophysical studies in the future.

• Nuclear Engineering and Technology
• /
• v.52 no.12
• /
• pp.2699-2708
• /
• 2020

Helical-coil steam generator (HCSG) technology is a major design candidate for small modular reactors due to its compactness and capability to produce superheated steam with high generation efficiency. In this paper, we investigate the feasibility of the passively autonomous power maneuvering by coupling the 3-D transient multi-physics of a soluble-boron-free (SBF) core with a time-dependent HCSG model. The predictor corrector quasi-static method was used to reduce the cost of the transient 3-D neutronic solution. In the numerical system simulations, the feedwater flow rate to the secondary of the HCSGs is adjusted to extract the demanded power from the primary loop. This varies the coolant temperature at the inlet of the SBF core, which governs the passively autonomous power maneuvering due to the strongly negative coolant reactivity feedback. Here, we simulate a 100-50-100 load-follow operation with a 5%/minute power ramping speed to investigate the feasibility of the passively autonomous load-follow in a 450 MW_th SBF PWR. In addition, the passively autonomous frequency control operation is investigated. The various system models are coupled, and they are solved by an in-house Fortran-95 code. The results of this work demonstrate constant steam temperature in the secondary side and limited variation of the primary coolant temperature. Meanwhile, the variations of the core axial shape index and the core power peaking are sufficiently small.

• Nuclear Engineering and Technology
• /
• v.51 no.6
• /
• pp.1540-1553
• /
• 2019

A nuclear power plant (NPP) is a highly complex system-of-systems as manifested through its internal systems interdependence. The negative impact of such interdependence was demonstrated through the 2011 Fukushima Daiichi nuclear disaster. As such, there is a critical need for new strategies to overcome the limitations of current risk assessment techniques (e.g. the use of static event and fault tree schemes), particularly through simulation of the nonlinear dynamic feedback mechanisms between the different NPP systems/components. As the first and key step towards developing an integrated NPP dynamic probabilistic risk assessment platform that can account for such feedback mechanisms, the current study adopts a system dynamics simulation approach to model the thermal dynamic processes in: the reactor core; the secondary coolant system; and the pressurized water reactor. The reactor core and secondary coolant system parameters used to develop system dynamics models are based on those of the Palo Verde Nuclear Generating Station. These three system dynamics models are subsequently validated, using results from published work, under different system perturbations including the change in reactivity, the steam valve coefficient, the primary coolant flow, and others. Moving forward, the developed system dynamics models can be integrated with other interacting processes within a NPP to form the basis of a dynamic system-level (systemic) risk assessment tool.

• Current Photovoltaic Research
• /
• v.7 no.1
• /
• pp.1-8
• /
• 2019

The $Cu(In,Ga)Se_2$ (CIGS) thin film obtained by two-step process (metal deposition and Se annealing) has a rough surface morphology and many voids at the CIGS/Mo interface. To solve the problem a precursor that contains Se was employer by depositing a (In,Se)/(Cu,Ga) stacked layer. We devised a two-step annealing (vacuum pre-annealing and Se annealing) for the precursor because direct annealing of the precursor in Se environment resulted in the small grains with unwanted demarcation between stacked layers. After vacuum pre-annealing up to $500^{\circ}C$ the CIGS film consisted of CIGS phase and secondary phases including $In_4Se_3$, InSe, and $Cu_9(In,Ga)_4$. The secondary phases were completely converted to CIGS phase by a subsequent Se annealing. A void-free CIGS/Mo interface was obtained by the two-step annealing process. Especially, the CIGS film prepared by vacuum annealing $450^{\circ}C$ and subsequent Se annealing $550^{\circ}C$ showed a densely-packed grains with smooth surface, well-aligned bamboo grains on the top of the film, little voids in the film, and also little voids at the CIGS/Mo interface. The smooth surface enhanced the cell performance due to the increase of shunt resistance.

• Progress in Medical Physics
• /
• v.26 no.3
• /
• pp.185-191
• /
• 2015

As radiation therapy is one of three major cancer treatment methods, many cancer patients get radiation therapy. Because of the invisible and scattering characteristics of radiation, it is impossible to identify the quality and the amount of radiation and secondary cancer could be induced by scattered radiation. Because of advanced technique of radiation therapy and the reasons mentioned above, quality assurance of radiotherapy machine should be performed completely. International organizations such as International Atomic Energy Agency (IAEA), American Association of Physicists in Medicine (AAPM) suggest report of quality assurance to recommend united method of radiotherapy machine quality assurance. Domestic society of medical physics, however, is too small to make such a report, domestic hospitals selectively choose some of contents in global suggestions. As there are no suggestions for domestic hospitals and global suggestions are being updated, we did a survey about quality assurance for radiotherapy machine. The questionnaire is composed of possession of radiotherapy machine, items performed for quality assurance and manpower, etc. 37 of 72 hospitals answered to survey. These results could be used for making domestic standard quality assurance procedure.

• Fire Science and Engineering
• /
• v.33 no.2
• /
• pp.30-38
• /
• 2019

Tracking, which is one of the main causes of electrical fires, is perceived as a physical phenomenon of electrical discharge. Hence tracking should be explained based on electric field analysis, conduction path by electron generation, and gas discharge physics. However, few papers have considered these details. This paper proposes a tracking mechanism including their effects on tracking progress. In order to prove this mechanism, a tracking experiment, an electric field analysis for the carbonization evolution model, and an explanation of the tracking process by gas discharge physics were conducted. From the tracking experiment, the current waveforms were measured at each stage of the tracking progress from corona discharge to tracking breakdown. The electric field analysis was carried out in order to determine the electric field on the surface of a dry-band and the high electric field region for electron generation during the generation and progress of carbonization. In this paper, the proposed tracking mechanism consisted of six stages including electron avalanche by corona discharge, accumulation of positive ions, expansion of electron avalanche, secondary electron emission avalanche, streamer, and tracking by conductive path. The pulse current waveforms measured in the tracking experiment can be explained by the proposed tracking mechanism. The results of this study will be used as the technical data to detect tracking phenomenon, which is the cause of electric fire, and to improve the proof tracking index.

• Journal of the Korean Academy of Child and Adolescent Psychiatry
• /
• v.2 no.1
• /
• pp.11-23
• /
• 1991

The main purpose of this study was to investigated the relationship between test anxiety and academic performance, additionally to examine the sexual and developmental differences in test anxiety. Test anxiety was assessed by the TAI-K(Kim Moonjoo, 1990) and was done to 388 3rd, 4th, 5th, 6th, grades and 104 9th grades. The level of TAI-K scores devided into a threeway split or five-way split. In the case of elementary school, four main cognitive subject-areas makes(the mean sum of semester) were used as academic performance indicator and with secondary school, all twelve subject-areas were included. The data were processed by correlational analysis and one-way ANOVA. The Results of this study are as follws : 1) Test anxiety correlated negatively and significantly with academic performance. While in the case of elementary school, in four cognitive subject-areas(Korean, Mathmatics, Society and Physics), two variables showed negative relationship, it was shown negatively in six subject-areas among twelve by secondary students. 2) In the area of sexual differences in test anxiety, female showed significantly higher level than male in elementary school however, there were no significant differences in secondary school. 3) In the area of developmental differences in test anxiety, in the case of elementary school. there were no significant differences between four grades.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.08a
• /
• pp.232-232
• /
• 2012

The doping of semiconducting elements is essential for the development of silicon quantum dot (QD) solar cells. Especially the doping elements should be activated by substitution at the crystalline sites in the crystalline silicon QDs. However, no analysis technique has been developed for the analysis of the activated dopants in silicon QDs in $SiO_2$ matrix. Secondary ion mass spectrometry (SIMS) is a powerful technique for the in-depth analysis of solid materials and the impurities analysis of boron and phosphorus in semiconductor materials. For the study of diffusion behaviour of B and P by SIMS, Si/$SiO_2$ multilayer films doped by B or P were fabricated and annealed at high temperatures for the activated doping of B and P. The distributions of doping elements were analyzed by SIMS. Boron found to be preferentially distributed in Si layer rather than the $SiO_2$ layer. Especially the B in the Si layers was separated to two components of an interfacial component and a central one. The central component was understood as the activated elements. On the other hand, phosphorus did not show any preferred diffusion.

• BMB Reports
• /
• v.44 no.10
• /
• pp.674-679
• /
• 2011

Bacillus sphaericus produces mosquito-larvicidal binary toxin composed of BinA and BinB. While BinB is expected to bind to a specific receptor on the cell membrane, BinA interacts to BinB or BinB receptor complex and translocates into the cytosol to exert its activity via unknown mechanism. To investigate functional roles of aromatic cluster in BinA, amino acids at positions Y213, Y214, Y215, W222 and W226 were substituted by leucine. All mutant proteins were highly produced and their secondary structures were not affected by these substitutions. All mutants are able to insert into lipid monolayers as observed by Langmuir-Blodgett trough and could permeabilize the liposomes in a similar manner as the wild type. However, mosquito-larvicidal activity was abolished for W222L and W226L mutants suggesting that tryptophan residues at both positions play an important role in the toxicity of BinA, possibly involved in the cytopathological process after toxin entry into the cells.