• Journal of Astronomy and Space Sciences
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• v.34 no.1
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• pp.37-44
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• 2017

In this paper, analysis results of the photometric data of DO Dra will be presented. DO Dra had been observed with 1 m LOAO telescope and 0.6 m CBNUO telescope from 2005 through 2014. The data shows kind of periodic oscillation behavior in the orbital period and also in the spin period. It has been found that these QPOs are not observed always and that the periods vary from 30 min to 80 min. We also found that the period variation seems to repeat itself with the period of 13.5 days. It is essential to monitor this object in the future as well as to carry out model calculation in order to have better understanding of these QPO phenomena.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.4 no.4
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• pp.360-369
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• 1992

A heat pump system is constructed to evaluate its performance and heat transfer characteristics with mixtures of R22/R142b as working fluids. The heat transfer in the evaporator and the overall performance are measured and analyzed in terms of the compositions and relevant variables. Possibility of capacity modulation by changing composition is observed without degradation of heat transfer coefficients and coefficient of performance. The cooling capacity is varied continuously within 200 percent based on minimum capacity at constant compressor speed. For similar cooling capacity, COP is improved by mixing two refrigerants and shows maximum value at 60％ mass fraction of R22. Average heat transfer coefficients of mixtures decrease in comparison with pure refrigerants at similar cooling capacity and mass flow rate. However, the overall heat transfer coefficients decrease moderately. A cycle simulation is performed in order to manifest the advantages of using refrigerant mixtures, considering experimentally observed heat transfer characteristics.

• Journal of Korean Association for Spatial Structures
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• v.20 no.1
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• pp.95-102
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• 2020

The structural design of arch roofs or bridges requires the analysis of their unstable behaviors depending on certain parameters defined in the arch shape. Their maintenance should estimate the parameters from observed data. However, since the critical parameters exist in the equilibrium paths of the arch, and a small change in such the parameters causes a significant change in their behaviors. Thus, estimation to find the critical ones should be carried out using a global search algorithm. In this paper we study the parameter estimation for a shallow arch by a quantum-inspired evolution algorithm. A cost functional to estimate the system parameters included in the arch consists of the difference between the observed signal and the estimated signal of the arch system. The design variables are shape, external load and damping constant in the arch system. We provide theoretical and numerical examples for estimation of the parameters from both contaminated data and pure data.

• Journal of Forest and Environmental Science
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• v.28 no.2
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• pp.63-67
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• 2012

Crown ratio is the ratio of live crown length to tree height. It is often used as an important predictor variable for tree growth equation. It indicates tree vigor and is a useful parameter in forest health assessment. The objective of the study was to develop crown ratio prediction models for Tectona grandis. Based on the data set from the temporary sample plots, several non linear equations including logistics, Chapman Richard and exponential functions were tested. These functions were evaluated in terms of coefficient of determination ($R^2$) and standard error of the estimate (SEE). The significance of the estimated parameters was also verified. Plot of residuals against estimated crown ratios were observed. Although the logistic model had the highest $R^2$ and the least SEE, Chapman-Richard and Exponential functions were observed to be more consistent in their predictive ability; and were therefore recommended for predicting crown ratio in the stand.

• Publications of The Korean Astronomical Society
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• v.7 no.1
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• pp.155-166
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• 1992

We observed a total of 14 Mira variables as well as 4 late type variable stars for their SiO ${\nu}= 1$, J = 2 - 1 maser lines from April 1989 to November 1990 with the 13.7 m radio telescope at Daeduk Radio Astronomy Observatory. The maser intensity variations were the prime objective of the observations which well covered the periods of the variations. The origion of the variations were studied by comparing wi th those previousely measured in optical and infrared(IR) wavelengths and we confirmed that the intensity variations were in good correlation with those in V magnitude and IR intensity as previousely found in former investigators in general. However, for a few sources, we could find the missing maxima. The intensities themselves also were in good correlation with SiO ${\nu}\;=\;1$, J = 1 - 0 maser intensities observed in Yebes as expected. The good correlations indicate that the pumping source of the SiO maser is likely to be the IR emission in the masing regions and the "missing maxima" that are apparent in two particular sources are considered to relate wi th the strength of shocks arising from the eruptive mass-loss from central stars.

• 한국전산유체공학회:학술대회논문집
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• 2007.10a
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• pp.232-235
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• 2007

A comprehensive numerical study was carried out to identify the on-set condition of the cell structures of oblique detonation waves (ODWs). Mach 7 incoming flow was considered with all other flow variables were fixed except the flow turning angles varying from 35 to 38. For a given flow conditions theoretical maximum turning angle is $38.2^{\circ}$ where the oblique detonation wave may be stabilized. The effects of grid resolution were tested using grids from $255{\times}100$ to $4,005{\times}1,600$. The numerical smoked foil records exhibits the detonation cell structures with dual triple points running opposite directions for the 36 to 38 turning angles. As the turning angle get closer to the maximum angle the cell structures gets finer and the oscillatory behavior of the primary triple point was observed. The thermal occlusion behind the oblique detonation wave was observed for the $38^{\circ}$ turning angle.

• Publications of The Korean Astronomical Society
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• v.8 no.1
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• pp.83-104
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• 1993

In principle, both radiation and collision are capable of pumping the SiO masers. In order to check which pumping mechanism is more efficient, we calculated the rate equation for our model including the 3 vibrational slates with 7 rotational states of each vibrational slate. Through solving the radiative transfer equation with the Sovolev approximation, we estimated the line profiles from an expanding envelope for several transitions. It is found that the collision works more efficiently than the radiation for the inversion in excited vibrational stales. However in an expanding envelope model we could not get the strong line intensity as observed one because the population inversion is possible only in a small restricted region. For the enough population inversion to get type observed maser intensity. the number density of SiO and hydrogen molecules should be up to about $2{\times}10^5\;cm^{-3}$ and $1{\times}10^9\;cm^{-3}$, respectively, and the inversion should be occured in the region of no Jess than 11014cm.

• Atmosphere
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• v.18 no.4
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• pp.493-506
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• 2008

In order to examine the variational features of Asian dust outbreak in recent years, observed WMO synop data were employed for the period from 1996 to 2007. We first divided Asian dust source regions into four subregions; 1) Taklamakan, 2) Gobi, 3) Inner Mongolia-Manchuria and 4) Loess, and the meteorogical variables such as wind speed, precipitation and threshold wind speed observed during the Asian dust outbreak period were compared with those during non-Asian dust period. The results showed that temporal variation of occurrence frequency of dust outbreak had a strong positive correlation with the frequency of strong wind speed and low precipitation in each of the 4 source regions. Spatial distributions of frequency of dust occurrence after 2002 showed increasing trend in Gobi and Inner Mongolia-Manchuria but decreasing trend in Loess region. This is showing a shift in main source region toward Northwest, especially since 2003.

• Journal of Welding and Joining
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• v.11 no.1
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• pp.73-79
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• 1993

The phenomenon of metal transfer has been investigated for different transfer modes using a digital high speed motion analyzer and an arc shadow-graphing system based on a laser source and related optical system. It was observed that the pinch instability phenomenon did not occur for the globular transfer mode, since the liquid globule was then spherical rateher than a cylindrical liquid bar. On increasing the ratio of carbon dioxide to argon, the transition current from globular to spray transfer generally increased, but it is interesting that the transition was observed to occur at the lowest current in a 5% CO$_{2}$-95% argon gas mixture. For pure carbon dioxide and helium shielding gases, the drop frequency increased slowly with increasing current. At high currents or an argon based shielding gas, the length of liquid bar decreased as the carbon dioxide content increased. The acceleration of a droplet within the arc was determined using the gas drag force theory and was found to be greater than the experimental results.

• Transactions of Materials Processing
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• v.17 no.2
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• pp.117-123
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• 2008

In this study, optimum processing condition of rolled AZ31 Mg alloy was investigated by utilizing processing map and constitutive equation considering microstructure evolution(dynamic recrystallization) occurring during hot-working. A series of mechanical tests were conducted at various temperatures and strain rates to construct a processing map and to formulate the recrystallization kinetics in terms of grain size. Dynamic recrystallization(DRX) was observed to occur at a domain of $250^{\circ}C$ and 1/s(maximum dissipation-efficiency region). The effect of DRX kinetics on microstructure evolution was implemented in a commercial FEM code followed by remapping of the state variables. The volume fraction and grain size of deformed part were predicted using a modified FEM code and were compared with those of actual hot forged part. A good agreement was observed between the experimented results and predicted ones.