• The Bulletin of The Korean Astronomical Society
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• v.42 no.1
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• pp.45.1-45.1
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• 2017

Optical variability is one way to probe the nature of the central engine of AGN at smaller linear scales, and previous studies have shown that optical variability of AGN is more prevalent at longer timescales and at shorter wavelengths. To understand the properties and physical mechanism of variability, we are performing the KMTNet Active Nuclei Variability Survey (KANVaS). Especially, we investigated intra-night variability of AGN with KMTNet data which observed COSMOS field during 3 separate nights from 2015 to 2016 in B, V, R, and I bands. Each night was composed of 5, 9, and 11 epochs with 20-30 min cadence. To find AGN in the COSMOS field, we applied multi-wavelength selection methods. Using X-ray, mid-infrared, and radio selection methods, 50-60, 130-220, 20-40 number of AGN are detected, respectively. Achieving photometric uncertainty ~0.01mag by differential photometry, we employed a standard time-series analysis tool to identify variable AGN, chi-square test. Preliminary results indicate that there is no evidence of intra-night optical variability of AGN. It is possible that previous studies discovered intra-night variability used inappropriate photometric error. However, main reason seems that our targets have fainter magnitude (higher photometric error) than that of previous studies. To discover variability of AGN, we will investigate longer timescale variability of AGN.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.1
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• pp.57.2-57.2
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• 2021

Variability in Young Stellar Objects (YSOs) can be caused by time-dependent accretion rates, geometric changes in the circumstellar disks, the stochastic hydromagnetic interactions between stellar surfaces and inner disk edges, reconnections within the stellar magnetosphere, and hot/cold spots on stellar surfaces. We uncover ~1400 variables from a sample of ~5300 YSOs in nearby low-mass star-forming regions using mid-IR light curves obtained from the 5.5-years NEOWISE All Sky Survey. The mid-IR variability traces a wide range of dynamical, physical, and geometrical phenomenon. We classify six types of YSO variability based on their light curves: secular variability (Linear, Curved, Periodic) and stochastic variability (Burst, Drop, Irregular). YSOs in earlier evolutionary stages have higher fractions of variables at all types and higher amplitudes for the variability. Along with brightness variability, we also find a diverse range of secular color variations, which can be attributed to a competitive interplay between the variable accretion luminosity of the central source and the variable extinction by material associated with the accretion process. We compare the variability of known FUors/EXors and VeLLOs/LLSs, which represent two extreme ends (burst versus quiescent) of the episodic accretion process; FUors/EXors have a higher fraction of variables (65%) than VeLLOs/LLSs (41%). Short-term (few day) and long-term (decades) variability, as well as possible AGB contamination in the YSO catalogues, are also discussed.molecules become more complex by surface chemistry induced directly by high energy photons or by the thermal energy diffused over heated grain surface. Therefore, the ice composition is an

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.1260-1264
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• 2009

Precipitation time series is a mixture of complicate fluctuation and changes. The monthly precipitation data of 61 stations during 36 years (1973-2008) in Korea are comprehensively analyzed using the EOFs technique and CSEOFs technique respectively. The main motivation for employing this technique in the present study is to investigate the physical processes associated with the evolution of the precipitation from observation data. The twenty-five leading EOF modes account for 98.05% of the total monthly variance, and the first two modes account for 83.68% of total variation. The first mode exhibits traditional spatial pattern with annual cycle of corresponding PC time series and second mode shows strong North South gradient. In CSEOF analysis, the twenty-five leading CSEOF modes account for 98.58% of the total monthly variance, and the first two modes account for 78.69% of total variation, these first two patterns' spatial distribution show monthly spatial variation. The corresponding mode's PC time series reveals the annual cycle on a monthly time scale and long-term fluctuation and first mode's PC time series shows increasing linear trend which represents that spatial and temporal variability of first mode pattern has strengthened. Compared with the EOFs analysis, the CSEOFs analysis preferably exhibits the spatial distribution and temporal evolution characteristics and variability of Korean historical precipitation.

• Journal of the Economic Geographical Society of Korea
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• v.20 no.2
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• pp.158-172
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• 2017

This study analyzes the time-space variability for the weekly passenger flow of the Seoul Subway system based on the dynamic visualization methods. For the purpose, we utilize one-week T-card transaction databases. By applying data mining algorithms, we extract passenger data for edge flows, on/off passengers at each subway station per minute interval time. It is practically intractable to analyze such spatio-temporal passenger flows by general statistical techniques. We employ dynamic visualization methods to analyze intuitively and to grasp effectively characteristics of the diurnal passenger flows on the Seoul Metropolitan Subway system during one week. As the result, we found that substantial differences exist on the spatio-temporal distribution patterns among days as well as between weekdays and weekend. We also investigates the time-space variability among eight major centers, and we found wide differences in their spatio-temporal distribution patterns.

• Journal of Korea Association of Health Promotion
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• v.4 no.1
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• pp.28-38
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• 2006

Background : Phentermine classified by "sympathomimmetic amie", is a stimulant of sympatheic tone But there has been no concrete study which presents the influence of phentermine on autonomic nervous system. Analysis of Heart rate variability is reliable, non-invasive and very useful for evaluating function of autonomic nervous system. We tried to elucidate the influence of phentermine on autonomic nervovs system by heart rate variability. MethodsAmong the 70 candidates who participated in the double-blind case control study whichwas designed in purpose of approving whether- Adipekⓓ is effective for treatment of obesity, 45persons were folled up. From April, 2005 to May 2005, HRV of the candidates who takes phentermine or placebo for 1month, was recorded using BFM-5000ⓓ(medi-core) for 5 minutes in resting state. HRV measures were assessed by time-domain and by frequency- domain analysis. Time domain parameters contain SDNN(Standard Deviation of NN intervals) and RMSSD(Root-Mean-Square of Successive Differences), etc and frequency domain Parameters contain Total Power(TP), Low frequency(LF'0.04-0.15Hz) power. High Frequency(HF:0.15-0.4Hz) power and LF/HF ratio etc. Results: Intakes of phentermine reduce HRV significant1y. SDNN & RMSSD, the main tine domain parameters of HRV, were decreased significantly(P=0.007. 0.016). PSI(Physical Stress Index of Pressure Index) was increase significantly(P=0.002)The main frequency domain parameters(TP, LF & VLF), also decreased significantly. (P=0.024,0.033, 0.015)Conclusion: The result showed that intakes of phentermine reduce heart rate variability and influence on most parameters of HRV. So phentermine not only accelerates sympathetic tone, but also inhibit the balance and function of autonomic nervous system.

• Journal of KIISE:Software and Applications
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• v.30 no.3_4
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• pp.185-201
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• 2003

The business component for satisfying a variety of domain requirements should be developed to provide a variety. But, although components are developed by analyzing the variety of requirements when they are developed, developing components that satisfy all requirements is not easy since unexpected requirements occur as it is used components. For this reason, components are not provided as black boxes but as white boxes, and there by components are not modified in the interface only but the source codes are directly modified. Accordingly, a Time-To-Market by the use of components is not easy and a reusability of the components also decreases. This study proposes a customization technique that can be satisfied requirements of many different kinds of domains by analyzing variable spots of components. The initial variability of components is designed in the component development phase. and a customization technique is used to apply the variability. The variability can be redesigned during the development of application by using the components to which the variability is applied. Through this process, a variability of components evolves and a generality of the components can be improved. The proposing customization technique in this study can change the component to extend without changing the existing component when it is redesigned.

• Child Health Nursing Research
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• v.21 no.3
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• pp.195-203
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• 2015

Purpose: This study was done to investigate quality of sleep and heart rate variability by the physical activity in high school students. Methods: A survey that measures physical activity and quality of sleep was distributed to 118 students at Y High School. Heart rate variability was obtained using the LXC3203 heart rate monitor. The data of 105 students were analyzed using descriptive statistics, t-test, x2-test, and ANOVA with $Scheff{\acute{e}}$ test. Results: Boys and students with part-time jobs had significantly higher physical activity. The quality of sleep was significantly high when the students were non-smokers, felt healthy, happy, less stressed, and satisfied with their school lives. Mean heart rate was significantly higher among girls, and standard deviation from normal to normal R-R intervals were high in boys. Physical activity had no significant relationships with quality of sleep and heart rate variability. Conclusions: Physical activity should be encouraged for high school students, especially for girls. An experimental study with different intensity and time of physical activity is recommended to examine the relationships with quality of sleep and heart rate variability in the future.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.64.2-64.2
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• 2016

Optical variability is one way to probe the nature of the central engine of AGN at smaller linear scales and previous studies have shown that optical variability is more prevalent at longer timescales and at shorter wavelengths. Especially, intra-night variability can be explained through the damped random walk model but small samples and inhomogeneous data have made constraining this model hard. To understand the properties and physical mechanism of optical variability, we are performing the KMTNet Active Nuclei Variability Survey (KANVaS). Test data of KMTNet in the COSMOS field was obtained over 2 separate nights during 2015, in B, V, R, and I bands. Each night was composed of 5 and 9 epochs with ~30 min cadence. To find AGN in the COSMOS field, we applied multi-wavelength selection methods. Different selection methods means we are looking different region in unification model of AGN, and 100~120, 400~500, 50~100 number of AGN are detected in X-ray, mid-infrared, and radio selection of AGN, respectively. We performed image convolution to reflect seeing fluctuation, then differential photometry between the selected AGN and nearby stars to achieve photometric uncertainty ~0.01mag. We employed one of the standard time-series analysis tools to identify variable AGN, chi-square test. Preliminarily results indicate that intra-night variability is found for X-ray selected, Type1 AGN are 23.6%, 26.4%, 21.3% and 20.7% in the B, V, R, and I band, respectively. The majority of the identified variable AGN are classified as Type 1 AGN, with only a handful of Type 2 AGN showing evidence for variability. The work done so far confirms that there are type and wavelength dependence of intra-night optical variability of AGN.

• Journal of Astronomy and Space Sciences
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• v.33 no.3
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• pp.177-183
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• 2016

Active galactic nuclei (AGN) are too compact to be resolved by any existing optical telescope facility, making it difficult to understand their structure and the emission processes responsible for their huge energy output. However, variability, one of their characteristic properties, provides a tool to probe the inner regions of AGN. Blazars are the best candidates for such a study, and hence a considerable amount of effort is being made to investigate variability in these sources across the electromagnetic spectrum. Here, using the Mt. Abu infrared observatory (MIRO) blazar monitoring program, we present intra-night, inter-night, and long term aspects of the variability in S5 0716+71, 3C66A, and OJ 287. These stars show significant variability on short (a few tens of mins, to a few hours, to a few days) to long term (months to years) timescales. Based on the light travel time argument, the shortest variability timescales (micro-variability) provide upper limits to the size of the emission region. While S5 0716 shows a very high duty cycle of variability (> 80 %), 3C66A shows a much lower intra day variability (IDV) duty cycle (< 20 %). All three show rapid variations within 2.5 to 3.5 hr, which, perhaps, are generated near the vicinity of black holes. Assuming this, estimates of the masses of the black holes are made at ~10⁹, 8×10⁸, and 2.7×10⁹ M_⨀ for S5 0716+71, 3C66A, and OJ 287, respectively. Multi-wavelength light-curves for the blazar PKS 1510-089 are discussed to infer the emission processes responsible for the recent flaring episodes in this source.

• Journal of KIISE:Software and Applications
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• v.33 no.6
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• pp.539-549
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• 2006

Component-Based Development (CBD) has emerged as a new effective technology that reduces development cost and time-to-market by assembling reusable components in developing software. The degree of conformance to standards and common features in a domain largely determines the reusability of components. In addition, variability within commonality should also be modeled and customization mechanism for the variability should be designed into components. Enterprise JavaBeans (EJB) is considered a most suitable environment for implementing components. However. the reusability of EJB is limited because EJB does not have built-in variability design mechanisms. In this paper, we present efficient variability design techniques for implementing components in EJB. We propose a method to customize the variability of EJB-based components by applying three variability design mechanisms; selection, plug-in, and external profile. And we elaborate the suitable situations where each variability design mechanism can be applied, and conduct a technical comparison to other approaches available.