• Journal of The Korean Astronomical Society
• /
• v.37 no.4
• /
• pp.143-149
• /
• 2004

We present photometric results for four new variable stars discovered in the vicinity of the ZZ Ceti-type pulsating white dwarf BR Cam. Observations were performed on 5 nights in November 2003 using the 1.8m telescope at Bohyunsan Optical Astronomy Observatory with no filter, on 3 nights in December 2003 using the 0.61m telescope at Sobaeksan Optical Astronomy Observatory with V, I filters, and on 3 nights in October 2004 using the 1.0m telescope at Mt. Lemmon Optical Astronomy Observatory with V, I filters. We estimated their periods from the phase-match technique for one eclipsing binary and the multiple frequency analysis for three pulsating stars. By considering the light curve shape, period and amplitude difference between two passbands, we classified the objects by their variability types as follows: V1 (USNO-A2.0 1425-05691757) is a W UMa-type eclipsing binary with an orbital period of $0^d.4641$; V2 (USNO-A2.0 1425-05703335) is a multi-periodic $\delta$ Set-type pulsating star with a dominant period of $0^d.0649$; V3 (USNO-A2.0 1425-05699659) is also a $\delta$ Set-type pulsating star with a period of $0^d.1408$; and V 4 (USNO-A2.0 1425-05707705) is a RR Lyr-type pulsating star with a period of $0^d.2643$.

• Korean Journal of Optics and Photonics
• /
• v.27 no.6
• /
• pp.212-217
• /
• 2016

In connection-oriented data-transport services, data loss can occur when the service experiences a problem on its end-to-end path. To promptly resolve this problem, the data-switching systems providing the service should quickly modify their internal configurations distributed among different places in each system. This is performed through a sequence of problem (event) recognition, sharing, and handling procedures among multiple control processors in the system. This paper proposes a method for event sharing and messaging between control processors, to improve the time determinacy of event processing. This method simplifies runtime event sharing and minimizes the time variability caused by the event data, resulting in a decrease in the latency time in processing global events. The proposed method lessens the latency time of global event processing by about 40%, compared to general methods, for 738 internal path changes.

• Korean Journal of Remote Sensing
• /
• v.39 no.5_1
• /
• pp.507-519
• /
• 2023

Multi-temporal optical images have been utilized for time-series monitoring of croplands. However, the presence of clouds imposes limitations on image availability, often requiring a cloud removal procedure. This study assesses the applicability of various machine learning algorithms for effective cloud removal in optical imagery. We conducted comparative experiments by focusing on two key variables that significantly influence the predictive performance of machine learning algorithms: (1) land-cover types of training data and (2) temporal variability of land-cover types. Three machine learning algorithms, including Gaussian process regression (GPR), support vector machine (SVM), and random forest (RF), were employed for the experiments using simulated cloudy images in paddy fields of Gunsan. GPR and SVM exhibited superior prediction accuracy when the training data had the same land-cover types as the cloud region, and GPR showed the best stability with respect to sampling fluctuations. In addition, RF was the least affected by the land-cover types and temporal variations of training data. These results indicate that GPR is recommended when the land-cover type and spectral characteristics of the training data are the same as those of the cloud region. On the other hand, RF should be applied when it is difficult to obtain training data with the same land-cover types as the cloud region. Therefore, the land-cover types in cloud areas should be taken into account for extracting informative training data along with selecting the optimal machine learning algorithm.

• Proceedings of the Korean Society of Agricultural Engineers Conference
• /
• 2002.10a
• /
• pp.25-28
• /
• 2002

The aim of the present study was the evaluation of methods for estimating the vegetation information in the field on the basis of spectral reflectance measured farm field, in particular the estimation of Leaf Area Index(LAI). Variability in tissue optical properties was wavelength-dependent. For rice and bean, the lowest variation was in the visible spectral region and the highest in the near-infrared. The structural attributes of ecosystems determine the relative contribution of tissue and canopy factors that drive variation in a reflectance signal.

• Publications of The Korean Astronomical Society
• /
• v.24 no.1
• /
• pp.9-18
• /
• 2009

From the short-period variability survey (SPVS) in Bohyunsan Optical Astronomy Observatory, we obtained time-series BV CCD images in the region of an open cluster M38 (NGC 1912) for 23 nights from February 1, 2007 to December 7, 2008. We found 18 $\delta$ Scuti stars and 2 $\gamma$ Doradus stars. Among them, only 3 $\delta$ Scuti stars were known ones. From the color-magnitude diagram (CMD) of M38, most of them have been located in the instability strip. The two $\gamma$ Doradus stars have been located within $\gamma$ Doradus strip of M38. But, only four $\delta$ Scuti stars were located within radius 10' from the center of M38. To confirm of their membership for M38, we need more study, such as, proper motion by spectroscopic observation.

• International Journal of Reliability and Applications
• /
• v.9 no.1
• /
• pp.17-30
• /
• 2008

Analysis of measurement systems is important to determine if the measurement process is adequate to measure the part-to-part variability in the process. Control chart techniques provide an effective, and easy-to-use method for performing this analysis. However, application with the real data for the evaluation procedure for multiple measurement systems have not been demonstrated. This research will provide a methodology for the evaluation of part-to-part variation and variation of different measurement systems step by step followed by number of case studies for each methodologies provided.

• Publications of The Korean Astronomical Society
• /
• v.30 no.2
• /
• pp.599-601
• /
• 2015

The short time scale X-ray variability associated with the accretion disk around compact objects is complex and is vaguely understood. The study of the cross correlation function gives an insight into the energy dependent behavior of the variations and hence connected processes. Using high resolution RXTE data, we investigate the dynamical cross correlation function of an observation of a black hole source XTE J1550-564 in the steep power law state. The cross correlation between soft and hard X- ray energy bands revealed both correlated and anti-correlated delays (${\leq}{\pm}15s$) on a correlation time scale of 50 s. It was noticed that the observed delays were similar to the delays between X-ray and optical/IR bands in other black hole and neutron star sources. We discuss the possible mechanisms/processes to explain the observed delays in the dynamical CCF.

• The Bulletin of The Korean Astronomical Society
• /
• v.37 no.2
• /
• pp.140.1-140.1
• /
• 2012

We investigate properties of maser emission for 3373 O-rich AGB stars. We divide the sample stars into four different groups whether they were detected by OH, SiO and $H_2O$ maser emission or not. To understand the nature of the maser sources, we present various infrared two-color diagrams (2CDs) using IRAS, near infrared and AKARI data. For each group, we compare the positions on the various infrared 2CDs with theoretical models. We find that OH maser sources generally show higher color indices and larger dust optical depths than SiO or $H_2O$ maser sources. This could be due to differences of the mass-loss rates and/or variability which may influence the maser pumping mechanisms.

• Journal of Astronomy and Space Sciences
• /
• v.38 no.4
• /
• pp.193-202
• /
• 2021

We present analysis results of Korean VLBI Network (KVN) four-band data for the highly variable blazar 3C 279. We measured the 22, 43, 86, and 129 GHz flux densities and spectral indices of the source using contemporaneous data taken over 5.6 years. We used the discrete correlation function to investigate correlations between the radio emission properties and those measured in the optical (2 × 10¹⁴ - 1.5 × 10¹⁵ Hz), X-ray (0.3-10 keV), and gamma-ray (0.1-300 GeV) bands. We found a significant correlation between the radio spectral index and gamma-ray flux without a time delay and interpreted the correlation using an extended jet scenario for blazar emission.

• The Bulletin of The Korean Astronomical Society
• /
• v.42 no.2
• /
• pp.76.4-77
• /
• 2017

We have been performing a long term AGN Monitoring project, to measure the time lag of H beta line with respect to AGN optical continuum based on the reverberation mapping method. From October 2015, 69 AGNs have been monitored with BVR band photometry, using the MDM 1.3m & 2.4m and LOAO 1m telescopes, and long-slit spectroscopy, using the Lick 3m and MDM 2.4m telescopes. In this poster, we report the preliminary results of the variability study of a subsample of 9 AGNs, particularly with a few of tentative time rag measurements between B band magnitude and H beta luminosity based on the 1st year data set from February 2016 - January 2017.