• Journal of Hydrogen and New Energy
• /
• v.13 no.3
• /
• pp.233-241
• /
• 2002

To achieve hydrogen power system with high performance and stable operation, the COVimep of hydrogen fueled engine with direct injection was evaluated with the change of engine speed, injection timing, air-fuel equivalence ratio and spark timing. And the cause of cycle variation was analyzed by using coefficient of variation in combustion period defined in this study. the results showed that the cycle variation of hydrogen fueled engine is mainly dependent on the early combustion period.

• Journal of Astronomy and Space Sciences
• /
• v.28 no.1
• /
• pp.9-12
• /
• 2011

Results of an analysis of 11 nights of R-filter CCD photometry data of an intermediate polar MU Camelopardalis (MU Cam) obtained at the Korean 1.0 m telescope at Mt. Lemmon are reported. After checking the spin period with our data, $P_{spin}=0.^d01373801(59)$, we compiled the reported data of maxima timing and an O-C diagram analysis has been carried out to understand the spin period variation. A significant spin period variation was detected, and fitting the O-C points to a cubic parabola led to an ephemeris of $BJD_{max}=2453682.4178(94)+0.0137380(13)E-2.07(55){\times}10^{-11}E^2+2.28(52){\times}10^{-15}E^3$. The torque experienced by the magnetic compact star accreting in a disk is estimated as ${\tau}{\approx}1.815{\times}10^{35}gcm^2/s^2$ in a simple approximation in order to show how important monitoring the period variation is. Thus we conclude that monitoring the long-term spin period variation will help to understand the physical condition of magnetic compact stars.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2022.05a
• /
• pp.140-140
• /
• 2022

Recently an accurate quantification of streamflow under various climatological and anthropogenic factors and separation of their relative contribution remains challenging, because variation in streamflow may result in hydrological disasters. In this study, we evaluated the factors responsible for variation in streamflow in Korean watersheds, quantified separately their contribution using different Budyko-based functions, and identified hydrological breakpoint points. After detecting that the hydrological break point in 1995 and time series were divided into natural period (1966-1995), and disturbed period (1996-2014). During the natural period variation in climate tended to increase change in streamflow. However, in the disturbed period both climate variation and anthropogenic activities tended to increase streamflow variation in the watershed. Subsequently, the findings acquired from different Budyko-based functions were observed sensitive to selection of function. The variation in streamflow was observed in the response of change in climatic parameters ranging 46 to 75% (average 60%). The effects of anthropogenic activities were observed less compared to climate variation accounts 25 to 54% (average 40%). Furthermore, the relative contribution was observed to be sensitive corresponding to Budyko-based functions utilized. Moreover, relative impacts of both factors have capability to enhance uncertainty in the management of water resources. Thus, this knowledge would be essential for the implementation of water management spatial and temporal scale to reduce the risk of hydrological disasters in the watershed.

• Journal of The Korean Astronomical Society
• /
• v.47 no.3
• /
• pp.99-104
• /
• 2014

We present the rst period variation study for the Algol eclipsing binary V346 Cyg by constructing the (O-C) residual diagram using all the available precise minima times. We conclude that the period variation can be explained by a sine-like variation due to the presence of a third body orbiting the binary in about $68.89{\pm}4.69$ years, together with a long-term orbital period decrease ($dP/dt=-1.23{\times}10^{-7}day/yr$) that can be interpreted to be due to slow mass loss from the ${\delta}$-Scuti primary component. The sinusoidal variation may also be explained by using the the Applegate (1992) mechanism involving cyclic magnetic activity due to star-spots on the secondary component. The present preliminary solution needs more precise photometric observations to be confirmed.

• Journal of Astronomy and Space Sciences
• /
• v.14 no.2
• /
• pp.242-250
• /
• 1997

The CCD photometric observations of W UMa-type eclipsing binary AB And were made from September 1994 to October 1996. New four primary minimum times were obtained from these observations. The analysis of times of minimum light for AB And confirms other previous studies that the orbital period of AB And have been changing as a form of sinusoidal variation. In this paper, we calculated the new orbital elements with linear and nonlinear quadratic term, and the best fit equation is derived with the assumption that the period variation of AB And changes sinusoidal pattern. From the sinusoidal term of this orbital element, we calculate period variation as 92 years with amplitude of $0.^{d}059$. However this result considering only sinusoidal term, was not satisfied with our recent observations. Thus, by assuming another parabolic period variation with the sinusoidal pattern, we derived the best fit orbital elements. From the quadratic coefficient of this orbital elements, we calculated the secular variation of 0.73 seconds, and from the sinusoidal term, the period variation turned out to be 62.9 years with amplitude of $0.^{d}024$. If we assume only the sinusoidal period variation of AB And, the period has to be decreased within 10 years. However if we consider quadratic term with the sinusoidal period variation of the light elements, the period is expected to be increased. Therefore long-term observations of this binary system are required to confirm this issue.

• Journal of The Korean Astronomical Society
• /
• v.46 no.4
• /
• pp.151-159
• /
• 2013

We discuss the orbital period changes of the Algol semi-detached eclipsing binary DI Peg by constructing the (O-C) residual diagram via using all the available precise minima times. We conclude that the period variation can be explained by a sine-like variation due to the presence of a third body orbiting the binary, together with a long-term orbital period increase (dP/dt=0.17 sec/century) that can be interpreted to be due to mass transfer from the evolved secondary component (of rate $1.52{\times}10^{-8}M_{\odot}/yr$) to the primary one. The detected low-mass third body ($M_{3min.}=0.22{\pm}0.0006M_{\odot}$) is responsible for a periodic variation of about 55 years light time effect. We have determined the orbital parameters of the third component which show a considerable eccentricity $e_3=0.77{\pm}0.07$ together with a longitude of periastron ${\omega}_3=300^{\circ}{\pm}10^{\circ}$.

• Publications of The Korean Astronomical Society
• /
• v.30 no.2
• /
• pp.211-214
• /
• 2015

We investigated the period variation for 79 eclipsing binary systems using 20 years (1990-2009) of EROS, Macho, and OGLE survey observations. We discovered 9 apsidal motions, 8 mass transfers, 5 period increasing and decreasing systems, 12 light-travel-time effects, 5 eccentric systems and 40 other systems showing no period variations. We select 3 representative eclipsing binary systems; EROS 1052 for apsidal motion, EROS 1056 for mass transfer, and EROS 1037 for the light-travel-time effect. We determine the period variation rate (dP/dt), orbital parameters of the 3rd body (e3, ${\omega}_3$, $f(m_3)$, $P_3$, $T_3$), apsidal motion parameters ($d{\omega}/dt$, U, Ps, Pa, e) and apsidal motion period by analyzing the light curves and O-C diagrams.

• Journal of The Korean Astronomical Society
• /
• v.38 no.1
• /
• pp.13-16
• /
• 2005

We present a period analysis of the well known $\beta$ Lyrae type eclipsing binary GO Cyg $(P= 0^d .7177)$. Several new times of minimum light, recorded photoelectrically, have been gathered. Analysis of all available eclipse timings of GO Cyg has confirmed a significant period increase with rate of $2.52 {\times} 10^{-10}$ day / cycle, also new period has been estimated. New linear and quadratic ephemerides have been calculated for the system.

• Ocean and Polar Research
• /
• v.32 no.1
• /
• pp.15-22
• /
• 2010

Calcium carbonate ($CaCO_3$) content was measured from 3 box core (BC060301, BC060303, BC070301) sediments, in addition to pilot core (PC313) sediments, from deep waters within the Western Pacific Ocean. At the two collection sites (BC060301, PC313) located close to the equator, downcore variation exhibited low $CaCO_3$ content during the interglacial period and high $CaCO_3$ content during the glacial period. Variation of coarse fraction (>$63\;{\mu}m$) content also followed changes in $CaCO_3$ content, indicating that dissolution effect of bottom water decreased during the glacial period. Such variation pattern is typical of the Pacific Ocean. However, downcore variation at the two collection sites (BC060303, BC070301) in the Philippine Sea contrasted the trend of the previous two cores (i.e., high $CaCO_3$ content during the interglacial period and low during the glacial period). This pattern is typical of the Atlantic Ocean. Such results may be attributed to the increasing dilution effect, initiated possibly by the increased transportation of terrigenous materials from nearby continent and archipelago during the glacial period when sea level was low. Alternatively, it is possible that the non-carbonate biogenic particles may have been responsible for dilution. Because of these uncertainties, the record of $CaCO_3$ variation in the deep Western Pacific Ocean is not regionally consistent.

• Journal of the Korean earth science society
• /
• v.26 no.5
• /
• pp.417-428
• /
• 2005

The seasonal variation and frequency of precipitation phenomenon of the Korean Peninsula in summer show strong local weather phenomena because of its topographical and geographical factors in the northeastern area of Asia. The characteristics of the prevailing weather patterns in summer precipitation in Korea have great influences on the variation patterns and the appearances over a ten-day period during the summer precipitation. The purpose of this paper is to induce variation patterns over a period 10 days during the summer precipitation, clarify the variations of their space scales, and study the subdivision of precipitation regions in Korea according to the combinations of precipitation amounts and variation pattern during the period, using the mean values during the years $1991\~2003$ at 78 stations in Korea. The classified precipitation of a period of 10 days of summer precipitation, and the principal component vector and the amplitude coefficient by the principal component analysis were used for this study. The characteristics of variation pattern over the ten-day period can be chiefly divided into two categories and the accumulated contributory rate of these is $64.3\%$. The variation patterns of summer precipitation during period of 10 days in Korea are classified into 9 types from A to K. In addition, regional divisions of summer precipitation in Korea can be classified into 17 types.