• The Bulletin of The Korean Astronomical Society
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• v.39 no.1
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• pp.56.1-56.1
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• 2014

With the advent of high-resolution high-sensitivity observations, spiral patterns have been revealed around several asymptotic giant branch (AGB) stars. Such patterns can provide possible evidence for the existence of central binary stars embedded in outflowing circumstellar envelopes. It is, however, not generally recognized that the binary induced pattern, vertically extended from the orbital plane, exhibits a ring-like pattern with an inclined viewing angle. I will first review the binary-induced spiral-shell patterns on the AGB circumstellar envelopes with the effect of inclination angle with respect to the orbital plane, of which large inclination cases reveal incomplete ring-like patterns. I will describe a method of extracting such spiral-shell from the gas kinematics of an incomplete ring-like pattern to place constraints on the characteristics of the (unknown) central binary stars. This first success may open the possibility of connecting the ring-like patterns commonly found in the AGB circumstellar envelopes and in the outer parts of (pre-)planetary nebulae and pointing to the conceivable presence of central binary systems, which may give a clue for the onset of asymmetrical planetary nebulae.

• Journal of Korean Society of Transportation
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• v.33 no.2
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• pp.214-222
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• 2015

Jeju International Airport has become the most delayed airport in Korea, due to increased demand in air passengers and unexpected local weather condition. Observing the demands continuously grow for a decade, the airport is expected to be saturated in the near future. As a part of effort to prepare effective and timely measure for this expected situation, airport planners seeks the annual runway capacity, i.e., the appropriate number of flight operations in a given year with tolerable delay. In practice, the FAA formula is frequently adopted for the capacity estimation. The method, however, has intrinsic issues: 1) the hourly capacity imbedded in the formula is not clearly defined and thus the estimated value is vulnerable to be subjective judgement, and 2) the formula doesn't consider aircraft delay resulted from runway congestion. In this paper, we explain a novel method for estimating the daily runway capacity and then converting to the annual capacity taking into account the aircraft delay. In this paper, average delay of aircraft was measured using microscopic air traffic simulation model. Daily capacity of the runways were analyzed based on the simulation outputs and the method to assess the yearly capacity is introduced. Using a microscopic simulation model named TAAM, we measure the average aircraft delay at various levels of flight demand, and then estimate the practical daily runway capacity. The estimated daily and annual runway capacities of Jeju airport are about 460 operations a day which is equal to 169,000 operations year. The paper discusses how to verify the simulation model, and also suggests potential enhancement of the method.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.457-459
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• 2015

Observations show that the accretion flows in low-luminosity active galactic nuclei (LLAGNs) probably have a two-component structure with an inner hot, optically thin, advection dominated accretion flow (ADAF) and an outer truncated cool, optically thick accretion disk. As shown by Taam et al. (2012), within the framework of the disk evaporation model, the truncation radius as a function of mass accretion rate is strongly affected by including the magnetic field. We define the parameter ${\beta}$ as $p_m=B^2/8{\pi}=(1-{\beta})p_{tot}$, (where $p_{tot}=p_{gas}+p_m$, $p_{gas}$ is gas pressure and $p_m$ is magnetic pressure) to describe the strength of the magnetic field in accretion flows. It is found that an increase of the magnetic field (decreasing the value of ${\beta}$) results in a smaller truncation radius for the accretion disk. We calculate the emergent spectrum of an inner ADAF + an outer truncated accretion disk around a supermassive black hole by considering the effects of the magnetic field on the truncation radius of the accretion disk. By comparing with observations, we found that a weaker magnetic field (corresponding to a bigger value of ${\beta}$) is required to match the observed correlation between $L_{2-10keV}/L_{Edd}$ and the bolometric correction $k_{2-10keV}$, which is consistent with the physics of the accretion flow with a low mass accretion rate around a black hole.